Rozprawy doktorskie na temat „Research Subject Categories – TECHNOLOGY – Engineering physics”

Lo scopo del lavoro sperimentale della presente tesi di Dottorato e' stato focalizzato allo studio della reazione di sintesi di un'innovativa classe di tecnopolimeri a base aromatica aventi una struttura parzialmente polare; i poli(arilen eteri-solfoni) (PES). Tale studio sperimentale avra' l'obiettivo, a partire dai dati di letteratura e dall'esperienza maturata dal gruppo di ricerca nel settore, di studiare la cinetica della reazione di policondensazione, e partendo dai risultati di tale studio riuscire a mettere a punto un metodo innovativo di sintesi per questa classe di macromolecole, in alternativa al metodo gia' utilizzato. Cio' sarebbe particolarmente utile per riuscire ad ottenere materiali idonei ad essere utilizzati in determinati campi applicativi, dato che con le tecniche tradizionali di sintesi i polimeri non garantiscono le proprieta' chimiche, termiche e meccaniche richieste.
The purpose of the experimental work of this PhD thesis was focused on the study of the synthesis reaction of an innovative class of polymers based on aromatic structure with a polar part, the poly (arylene ether-sulfone) (PES). This experimental study will aim, starting from literature data and experience gained by the research team in the field, to study the kinetics of polycondensation reaction, and from the results of this study fail to develop an innovative method synthesis for this class of macromolecules, as an alternative to the method already in use. This would be particularly useful to be able to obtain materials suitable for use in specific application fields, as with traditional techniques of synthetic polymers do not provide the chemical, thermal and mechanical requirements.

Implantación de la Norma NOM-011-STPS-2001 en el Taller de Diseño y Desarrollo de Prototipos del Centro Universitario UAEM Valle de México para Integrarlo al programa de Autogestión en Seguridad y salud en el trabajo de la Secretaría del Trabajo y Previsión Social
El presente trabajo escrito presenta la propuesta para la implantación de la Norma NOM-011-STPS-2001, condiciones de seguridad e higiene en los centros de trabajo donde se genere ruido en el Taller de Diseño y Desarrollo de Prototipos del Centro Universitario UAEM Valle de México para integrarlo al Programa de Autogestión en Seguridad y Salud en el Trabajo. Además de que con la implantación de esta norma se pretende generar una cultura de seguridad y salud en los espacios donde se generan actividades durante el desarrollo de Unidades de Aprendizaje del Programa Educativo de Ingeniería Industrial. Lo anterior se puede lograr con la aplicación de concomimientos de seguridad e higiene adquiridos en mencionadas unidades de aprendizaje, mismos que sin duda es un campo en el cual el estudiante de ingeniería industrial al terminar sus estudios puede incursionar de manera eficiente en el mundo laboral para la solución de problemas que mencionado campo conlleva. Con los conocimientos adquiridos y con la propuesta de implantación de la norma mencionada anteriormente se podrá ingresar al Programa de Autogestión en Seguridad y Salud en el Trabajo (PASST) para lograr en algún momento dado el reconocimiento de Empresa Segura para el Taller de Diseño y Desarrollo de Prototipos que emite la STPS. Adicionalmente con lo anterior se puede brindar condiciones de seguridad y salud específicamente cuando se desarrollen actividades donde pueda generarse ruido para todos los usuarios y así asegurar una integridad física y de salud colaborando en el desarrollo de conocimientos aplicados y adquiridos de la ingeniería industrial en el campo de la seguridad y salud en el trabajo.

MANUFACTURA Y PROCESAMIENTO DE MATERIALES AVANZADOS CERMETS BASE ALÚMINA REFORZADOS CON PARTICULAS DE PLATA
En esta investigación se realizó el estudio de un material cerámico avanzado, este material compuesto está formado por el sistema cerámico-metal también denominado CERMET. El sistema de estudio en particular está formado por alúmina-plata, el material cerámico y el material metálico utilizado en este sistema son alúmina (Al2O3) comercial en polvo de la marca Reasol con una pureza de 99.2% y plata (Ag) comercial en polvo de la marca Meyer con una pureza del 99.99%. La composición química del sistema consiste en la base cerámica con adiciones de plata al 5% y 10% en peso. La composición química en polvos del material compuesto (Al2O3-Ag) se sometió a un proceso de mezcla molienda en un molino de giro planetario de alta energía de la marca Fritsch durante un periodo de 2 horas a 200 rpm. Posteriormente los polvos fueron compactados uniaxialmente en frio mediante una prensa hidráulica a una presión de 200 MPa para obtener muestras cilíndricas de 20 mm de diámetro y un espesor de 5 mm. Las muestras compactadas fueron sometidas al proceso de sinterización a una velocidad de calentamiento de 25 °C/min a una temperatura de sinterización de 1500°C y 1600 °C expuestos a un tiempo de 1 y 2 horas, en una atmósfera controlada con gas nitrógeno y enfriamiento en horno. Posterior al proceso de sinterizado se determinó la densidad y porosidad a las muestras obtenidas a partir del principio de Arquímedes. Se realizó un análisis por microscopia óptica (MO) y microscopia electrónica de barrido (MEB/EDX) para observar las características microesctructurales de los materiales fabricados. El MEB está equipado con un detector de energía dispersiva de rayos-X (EDX) el cual se ocupó para realizar un análisis puntual en diferentes zonas de los materiales manufacturados e identificar los elementos químicos de las especies existentes en el sistema fabricado. Finalmente se determinó la propiedad mecánica de dureza Vickers con un indentador de punta de diamante, en un microdurómetro de la marca EMCOTEST que esta acondicionado con un software que determina la dureza a partir de la medición del tamaño de las diagonales de la huella del indentador Vickers y la carga aplicada.

PLANEACIÓN DE MATERIALES PARA LAS REVISTAS TV y NOVELAS Y VANIDADES DE EDITORIAL TELEVISA
El presente reporte desarrolla la planeación de materiales para imprimir dos revistas de Editorial TELEVISA, las cuales son líderes en ventas. TV y Novelas, revista dirigida al gran sector de público televidente, que quiere enterarse de lo que pasa en la vida de la farándula y el medio del espectáculo. VANIDADES, revista dirigida a las mujeres que quieren enterarse de la vida de las celebridades alrededor del mundo y que gustan de las últimas tendencias de la moda y belleza, es conservadora sin llegar a ser audaz. Editorial TELEVISA tiene más títulos, sin embargo, la planeación de materiales en ambos casos se presenta con mayor frecuencia comparado con otros títulos sobre todo a lo que se refiere al consumo de papel tanto de los interiores como de la portada, que aparte de ser los principales materiales para la elaboración de revistas representa el 74 % del costo de producción. Capitulo I. Definición y caracterización del problema y su relación con el plan de estudios cursado. Se hace una presentación de la empresa y de sus principales características, se define el problema a tratar y las consecuencias que tiene en su entorno, también se mencionan las materias de la carrera de ingeniería industrial con las que se tiene relación y como los conocimientos obtenidos al cursarlas son utilizados para presentar una propuesta de mejora en la planeación de materiales para hacer frente a la problemática que actualmente enfrentan la editorial. Al hablar del marco teórico se presenta de forma amplia todos los conceptos que se utilizan para poder realizar un adecuado tratamiento de la problemática presentada. Capitulo II. Análisis de alternativas previas de solución. Se hace una breve descripción de la industria gráfica y del proceso de producción gráfico, se plantea una propuesta de solución y se hace una delimitación del problema a solucionar. Capitulo III. Solución propuesta o implementada. Presenta el desarrollo metodológico de la solución a la problemática, así como también el impacto que se tiene en los resultados con el desarrollo del nuevo método de planeación de materiales. Capítulo IV. Conclusiones y sugerencias. Se exponen las conclusiones obtenidas en la solución del problema y las sugerencias de mejora al sistema. Fuentes bibliográficas. Describen los libros utilizados, las páginas de internet consultadas y las revistas que sirvieron de consulta para realizar el Reporte.

PROCESO DE MEJORA PARA LA OPTIMIZACIÓN DE TIEMPOS EN EL ÁREA DE COTIZACIONES DE MITSUBISHI ELECTRIC DE MÉXICO S.A. C.V.
MITSUBISHI ELECTRIC DE MÉXICO S.A. de C.V., es una empresa dedicada a la fabricación, venta, instalación y mantenimiento de elevadores para el mercado mexicano. Mitsubishi Electric de México S.A. de C.V., ha vendido más de 2000 elevadores y escaleras eléctricas, y ha exportado un número similar de elevadores. Como referencia, es importante mencionar que en la actualidad más del 50% de los equipos que son utilizados en el metro de la Ciudad de México han sido fabricados por Mitsubishi Electric de México S.A. de C.V. Considerando que la calidad en el servicio al cliente es uno de los puntos primordiales que se deben cumplir dentro de cada una de las empresas; sin importar el tamaño, estructura y naturaleza de sus operaciones, deben de demostrar la capacidad que tienen para desempeñarse en esta área, ya que al ser la primera imagen que se da a los clientes ayuda a mantenerse en la preferencia de los mismos, y si se llega a alterar pueden convertirse en una amenaza. Sin embargo, en muchas ocasiones puede llegar a ser empleado por las organizaciones incorrectamente, afectando tanto al desarrollo y crecimiento de las mismas, por lo cual, principalmente se debe definir la importancia de dicho servicio al cliente, para poder estructurar adecuadamente la forma más óptima de llevarlo a cabo. En la actualidad las Empresas no pueden sobrevivir por simple hecho de realizar un buen trabajo o crear un buen producto. Es por eso que cada empresa debe de poner particular atención en la queja de sus clientes y poder solucionar estos problemas. A medida que pasa el tiempo, se hace más urgente y necesaria la aplicación correcta y efectiva del servicio al cliente en establecimientos comerciales de pequeñas, medianas y grandes empresas; así como en instituciones e incluso en nuestra vida diaria, esto debido a que en la actualidad todos ofrecemos, desde bienes y servicios hasta la imagen que proyectamos a los demás. En este sentido y considerando que la empresa no solo vende equipo sino también servicio tiene puntos de mejora que son imprescindibles de atender para garantizar al cliente un servicio de calidad. Actualmente en Mitsubishi Electric de México S.A. de C.V. en el área de cotizaciones se presentan descontentos por parte de los clientes debido a que argumentan que la empresa les ofrece un mal servicio en el excesivo tiempo de elaboración de cotizaciones. La inconformidad del cliente está justificada debido a que cuando sus equipos requieren refacciones por mantenimiento preventivo o correctivo estas no son adquiridas a tiempo por falta del presupuesto que permita dar solución a su problema ya que a su vez estos no ofrecen buen servicio en sus equipos generando conflicto con el servicio que ofrecen, convirtiéndose esta situación en una cadena de inconformidades. Por lo anterior en este trabajo se pretende encontrar un método de mejora para la optimización de tiempos en el área de cotizaciones que permita tener un proceso más eficiente para dar mejor servicio. Este proceso consiste esencialmente en detectar las principales inconformidades de los clientes y de la problemática en el área de cotizaciones ya que es demasiado tardado de esta manera identificar la causa raíz de la demora, posteriormente la información es analizada para establecer los procedimientos a seguir y establecer el procedimiento de mejora de acuerdo al análisis y la identificación del área de oportunidad en la elaboración de cotización de refacciones para elevadores y escaleras eléctricas, con base en el diagnóstico. Las herramientas metodológicas de apoyo para realizar este trabajo son: encuestas de servicio, diagrama de Pareto, diagramas de causa y efecto, histograma y teoría de colas.

La stima della risposta sismica di edifici storici in muratura a carattere monumentale costituisce un argomento di estrema rilevanza, ma allo stesso tempo, di difficile soluzione. I metodi di modellazione piu' accurati agli elementi finiti non lineari, capaci di cogliere la risposta non lineare e il progressivo degrado del solido murario soggetto ad azioni cicliche, richiedono la definizione di legami costitutivi complessi cui e' associato un enorme onere computazionale rendendo questi approcci non ancora pronti per essere applicati nella pratica ingegneristica. Nel passato diversi autori hanno sviluppato metodi semplificati alternativi che, a fronte di un ridotto onere computazionale, forniscono risultati sufficientemente accurati per poter essere utilizzati in ambito professionale. Tuttavia la maggior parte dei metodi semplificati proposti nella letteratura sono basati su ipotesi restrittive che rendo tali metodi inappropriati per essere applicati agli edifici monumentali. Nella tesi viene sviluppato un elemento discreto tridimensionale, capace di predire la risposta non lineare di elementi murari a geometria curva, quale evoluzione non banale di un approccio per macro-elementi sviluppato per la stima della risposta sismica di edifici in muratura. Il nuovo elemento discreto introdotto e sviluppato nella tesi arricchisce un nuovo approccio di modellazione per macroelementi dedicato alla modellazione sismica degli edifici storici a carattere monumentale.
The assessment of the seismic response of historical masonry buildings represents a subject of considerable importance but, at the same time, of very difficult task. Refined finite element numerical models, able to predict the non-linear dynamic mechanical behavior and the degradation of the masonry media, require sophisticated constitutive law and a huge computational cost that makes these methods nowadays not suitable for practical application. In the past many authors developed simplified or alternative methodologies that, with a reduced computational effort, should be able to provide numerical results that can be considered sufficiently accurate for engineering practice purposes. However most of these methods are based on simplified hypotheses that make these approaches inappropriate for monumental buildings. In this thesis a three dimensional discrete element model, able to predict the nonlinear behaviour of masonry shell elements, is presented as an extension of a previously introduced spatial discrete-element conceived for the simulation of both the in-plane and the out-of-plane behavior of masonry plane elements. The new macro-element enriches a larger computational framework, based on macro-element approach, devoted to the numerical simulation of the seismic behaviour of historical masonry structures.

DISEÑO DEL PROCESO DE MANUFACTURA DE CERÁMICOS AVANZADOS DE ÓXIDO DE ALUMINIO: EFECTO DE LA TEMPERATURA DE SINTERIZACIÓN PARA SU POSIBLE APLICACIÓN EN LA INDUSTRIA TEXTIL.
Durante los últimos años se han investigado y desarrollado diferentes materiales para diversos ámbitos de aplicación industrial, sin necesidad de indagar, solo basta con observar nuestro alrededor y son tangibles los avances y aplicaciones de nuevos materiales por ejemplo en la industria del transporte, aeronáutica, militar, naval, del deporte entre otras. Con este contexto, en esta investigación se han desarrollado materiales cerámicos para posibles aplicaciones en particular en la industria textil basados en la investigación de materiales cerámicos avanzados en donde se ha considerado principalmente el diseño del proceso de manufactura; buscando un material con propiedades específicas para mejorar las propiedades físicas de densidad y porosidad, sus propiedades mecánicas de dureza, tenacidad a la fractura, así como el de un proceso de menor costo, fácil, y con ahorro de energía. Se pretende establecer condiciones ideales para la fabricación de estos materiales que se proponen en este proyecto, a través del rediseño del proceso, en la busca de mejorar las propiedades físicas y mecánicas de las ya existentes en el mercado y así mismo cumplir con materiales que tengan características que puedan aportar nuevos resultados para la industria textil. La cerámica avanzada utilizada en este trabajo es oxido de aluminio también conocido como Alúmina (Al2O3) y la consolidación de este material se realiza mediante el proceso de sinterización en estado sólido considerando como variable de estudio la temperatura en el proceso de sinterización y el agregado de aglutinantes de las muestras durante la compactación. Considerado que la etapa de conformado o compactado es el primer paso antes de la sinterización. La etapa de compactado inicia tomando en cuenta la no aplicación de aglutinantes en el material; es decir, se compactan muestras de material de únicamente polvos de alúmina comercial que servirán como referencia y comparativo cuando en esta misma etapa se compacten materiales usando aglutinantes como: Alcohol Polivinílico (PVA) y Polietileno Glycol (PEG) teniendo en cuenta que este hecho tiene un efecto en la consolidación del material. 5 El compactado de las muestras se realiza a partir de polvos de alúmina utilizando un dado de acero grado herramienta aplicando una presión uniaxial de 200 MPa en frio para obtener muestras cilíndricas de 20 mm de diámetro y 4 mm de espesor también llamadas muestras “en verde”, y son llamadas así porque han pasado por el proceso de sinterización, el tiempo de la carga máxima de trabajo es aplicada durante 30 segundos. Posteriormente los compactos en verde se someten al proceso de sinterizado o consolidación en estado sólido a 1600°C durante 1 hora utilizando un horno de resistencia eléctrica de alta temperatura. Una vez consolidados los materiales se le hace un análisis microestructural mediante microscopia óptica (MO), y sus propiedades físicas de densidad y porosidad se determinan por el principio de Arquímedes, y después son determinadas sus propiedades mecánicas de dureza y tenacidad a la fractura. Los resultados de las pruebas físicas de densidad y porosidad indican que la incorporación de los aglutinantes en la etapa del conformado como Alcohol Polivinílico (PVA) y Polietileno Glycol (PEG), mejoran las características físicas para el manejo de los materiales en verde, mientras que las muestras sinterizadas no presentan rastro de estos aglutinantes con respecto a las muestras que no lo contienen, además se observan cambios microestructurales en estos mismos materiales.

Manual de procedimientos para la selección de materias primas en el desarrollo de insecticidas de industrias h-24 s.a. De c.v.
El departamento de Aseguramiento y Control de la Calidad de Industrias H24 S.A. DE C.V., cuenta con un sistema de gestión de calidad, que se encarga de diversas actividades, una de estas es la selección de materia prima para los productos de la compañía. Esta actividad no contaba con un manual de procedimientos para realizar las pruebas de selección de materia prima (fragancias); al no contar con un manual se corre el riesgo de cometer errores antes, durante y después de las pruebas por parte del analista que las realiza y también, por otra parte, se corría el riesgo de seleccionar materia prima no óptima para el producto y por ende se obtenían productos de baja calidad. Dado lo anterior se consideró que el sistema de gestión de calidad para esta actividad era ineficiente debido a que no se contaban con las pruebas redactadas ni con los formatos de evidencia para la mayoría de las pruebas; es por ello que surgió la necesidad de crear un manual de procedimientos para las pruebas. Este manual se desarrollo bajo la gruía técnica para elaborar o actualizar manuales de procedimientos de la PROFECO, con el fin de obtener un documento físico para el departamento, para ser utilizado por los analistas que realizan las pruebas o para capacitar al personal que se integre en un futuro al departamento. El desarrollo de este manual se baso en una investigación de información primaria (Toda la información con la que contaba la empresa con respecto a las pruebas: procedimientos, formatos, manuales, entrevistas, etc.) y de información secundaria (Páginas de internet, libros, revistas, guía técnica de la PROFECO, etc.), esta información recabada sirvió para hacer un análisis, establecer y estructurar el trabajo. El manual, resultado de este trabajo, va permitir capacitar a nuevo personal, se tendrá un orden y una secuencia en la aplicación de las pruebas. Y por otra parte se va contar con una trazabilidad de los materiales seleccionados y de los productos de la compañía, sirviendo esta información para las auditorias que se realicen al departamento.

DISEÑO E IMPLEMENTACIÓN DE UN COMPENDIO DE MÉTODOS DE PRUEBA APLICADOS AL CONTROL DE CALIDAD EN LA MANUFACTURA DE PERFILES DE ALUMINIO PARA EL LABORATORIO DE ANÁLISIS INDUSTRIALES E INVESTIGACIÓN DEL PROGRAMA EDUCATIVO DE INGENIERÍA INDUSTRIAL DEL CENTRO UNIVERSITARIO UAEM VALLE DE MÉXICO
El presente proyecto registra un contenido completo sobre los requerimientos del diseño e implementación de un compendio de métodos de prueba aplicados al control de calidad en la manufactura de perfiles de aluminio para el laboratorio de análisis industriales e investigación del programa educativo de ingeniería industrial del centro universitario UAEM valle de México. Para poder ejemplificar y dar a conocer estos métodos, la información se basa en las actividades realizadas dentro de la empresa Cuprum S.A. de C.V., lo cual ayuda a otorgar las tareas que hoy en día se llevan a cabo en este sector de la industria. En el capítulo 1 se da a conocer los pasos base del proceso de extrusión del aluminio de cómo se va formando hasta su figura final y traslado. En el capítulo 2 se aborda sobre los procesos de acabado y mecanizado de los perfiles de aluminio, lo cual da una mayor visión de las condiciones en las que los perfiles de aluminio son ocupados en sus múltiples usos y ocupaciones. En el capítulo 3 se detallan los elementos esenciales para que un perfil de aluminio tenga la condición de uso propicia para su usó ya que esto lo determina la aleación, el temple y las propiedades químicas y mecánicas que cada perfil requiera. En el capítulo 4 y 5 se aborda el tema de calidad y las normas que rigen nacional e internacionalmente la fabricación de perfiles de aluminio y de cuáles son las características que cada perfil debe cumplir para poder ser usado. En el capítulo 6 se dan a conocer los usos y aplicaciones más comunes en los que son usados los perfiles de aluminio. En el capítulo 7 se enuncian las soluciones propuestas a implementar en el laboratorio de Ingeniería, así como las evaluaciones de las mismas. Por último, se muestran como anexos las prácticas de liberación de los perfiles de aluminio con acabado anodizado, lo cual ayuda a los alumnos a conocer la importancia de los requisitos que debe cumplir cada perfil de aluminio y poder ser usado en el mercado.

IMPLEMENTACIÓN DE LA NORMA OFICIAL MEXICANA NOM-002-STPS-2010 EN LA EMPRESA TEXTIL BLUE GIANT.
Este documento muestra una implementación y propuestas dentro de la empresa textil “BLUE GIANT” tal implementación se basó acorde a la norma oficial mexicana NOM-002-STPS-2010 condiciones de seguridad - prevención y protección contra incendios en los centros de trabajo. Al implementar esta norma se buscaba establecer condiciones de seguridad de las instalaciones de la empresa para su adecuado funcionamiento y conservación y así prevenir riesgos a los trabajadores. Al igual se pretende generar una cultura de seguridad en los espacios donde se generan actividades directas e indirectas al producto fabricado. Se muestran resultados tangibles y las evidencias de antes y después de tal implementación del mismo modo se presentan propuestas que se pueden aplicar en un futuro y así mejorar aún más las condiciones de seguridad dentro de la empresa. Lo anterior se puede lograr con la aplicación de conocimientos de seguridad e higiene adquiridos en mencionadas unidades de aprendizaje, mismos que sin duda es un campo en el cual el estudiante de ingeniería industrial al terminar sus estudios puede incursionar de manera eficiente en el mundo laboral para la solución de problemas que mencionado campo conlleva.

The exploitation of nonlinear dynamics behavior in ferroelectric material toward the realization of innovative transducers for the detection of weak and low frequency electric fields is the focus of this thesis. A nonlinear dynamical system based on ferroelectric capacitors coupled into a unidirectional ring circuit is considered with particular interest for developing novel electric field sensors. The focused approach is based on the exploitation of circuits made up by the ring connection of an odd number of elements containing a ferroelectric capacitor, which under particular conditions exhibits an oscillating regime of behavior. For such a device a weak, external, target electric field interacts with the system thus inducing perturbation of the polarization of the ferroelectric material; this, the target signal can be indirectly detected and quantified via its effect on the system response. The conceived devices exploit the synergetic use of bi-stable ferroelectric materials, micromachining technologies that allow us to address charge density amplification, and implement novel sensing strategies based on coupling non-linear elemental cells. Advanced simulation tools have been used for modeling a system including electronic components and non linear elements as the conceived micro-capacitors. Moreover, Finite Element Analysis (FEM) has allowed us to steer the capacitor electrodes design toward optimal geometries and to improve the knowledge of effects of the external target E-field on the electric potential acting on the ferroelectric material. An experimental characterization of the whole circuit, including three cells coupled in a ring configuration has also been carried out.

A particular form of winged seed (samara) dispersal technique adopted by nature uses autorotative (unpowered rotation of the wing generating thrust force against gravity) descent; for eg. in Maple and Mahagony trees. This technique provides the lowest descent velocities among various seed dispersal techniques found in nature ensuring the safety of the delicate seeds. Bio-mimicked solutions to important engineering problems in aerospace as well as in disaster management - air dropping of life-saving packages during floods can be inspired from the samara. The samara is a complex structure having a bluff root containing the seed attached to a three dimensional wing. The dynamics of the samara from the instant of release is entirely unsteady, involving an initial transition phase where the samara tumbles until it achieves autorotation leading to a steady descent velocity. The distribution of mass and aerodynamic forces in this single structure ensures its stability during descent. Studies to comprehensively understand the physics of the samaras are limited. Recently, Leading Edge Vortex (LEV) has been found to be responsible for the high thrust forces achieved during autorotation. The dependence of LEV on the morphology of the seed needs to be understood to design optimal devices for engineering applications. The principal aim of this study is to understand the effect of morphology on the aerodynamics of the samara with a particular focus on the characteristics of the LEV. The flow field around the autorotating samara is experimentally obtained using Particle Image Velocimetry (PIV) in a specially designed vertical wind tunnel. However, since each natural samara is intricate, optimal, and unique, it has limited utility for parametric studies. Therefore, 3D printed models are developed that closely mimic the functions of the natural samara. A new design methodology has been developed to generate autorotating samara models. Drop tests of the natural samara and the 3D printed models show that the dynamics of the models and the samara are similar. Three 3D-printed samara models with different spanwise distributions of chord and mass are considered. For the first time, a complete characterization of the spanwise distribution of LEV has been carried out on the samara models. We show that in the neighborhood of the maximum chord location multiple LEVs are present, which leads to significantly higher local lift forces compared to other cross-sections near the root and the tip. The elaborate spanwise survey also shows that the locations near the wing tip behave similar to a bluff body, while sections near the root undergo a reversal of flow topology. A new non-dimensional parameter has been defined using Buckingham 𝜋 analysis that encompasses the dominant parameters involved in the study. This enabled us to understand the inter-relationship between observed flow physics, morphology and performance parameters.

The aim of this work is to develop high performance cryosorption (or cryoadsorption) pumps specifically for fusion applications. An actual cryopump for the above application will use the supercritical liquid helium flow through the channels embedded in the large scale cryopanels. In this case, the liquid helium requirement (both as normal and as supercritical fluids) will be large, depending on the size of the cryosorption pump. However, in a research laboratory wherein such large quantities of liquid helium are not available, an alternate arrangement of cooling the cryopanels has to be considered. One of the possible options can then be as follows. A scaled-down version of the cryopanel can be used and cooled by a two stage cryo-refrigerator system with adequate cooling power. This system is known as cryocooler based cryosorption pump. Due to the availability of a two stage GM cryocooler with a refrigeration power of ~ 1.5 W at 4.2 K in our laboratory, which can be used for the above purpose, the main objective of this work is the “development of a cryocooler based high performance cryosorption pump”. The cryopanel which is mounted on the second stage cold head of the cryocooler is not necessarily a single panel, but is usually a set of panels (stacked one over the other) and consists of mainly three components and they are: (a) the metallic panel made of copper and cooled by the cryocooler (b) the adhesive to bind the adsorbent onto the metallic panel and (c) the adsorbent (in the present case, activated carbon (AC)) which is used to adsorb the gas molecules. By this arrangement, the adsorbent gets cooled to the lowest possible temperature to enable cryopumping. To develop the cryocooler based high performance cryosorption pump, we need to select: (a) the best adsorbent (with large adsorption surface area) and adhere it on a cryopanel to evaluate its performance as a cryopump and (b) the best adhesive with high thermal conductivity, high bonding strength and ability to withstand several thermal cycles. The surface area of an adsorbent in the range of temperatures range from 4.5 K to 77 K can be arrived at by a micropore analyser ( Model: ASIQ, Quantachrome, USA) integrated with a two stage GM cryocooler (Janis: SRDK415D), with helium as adsorbate gas at 4.5 K and nitrogen as adsorbate gas at 77 K. Based on the above studies, we can choose the best activated carbon with high surface area. Next, the best adhesive which is used for binding the adsorbent onto the panel is chosen on the basis of its high thermal conductivity. The thermal conductivity of the adhesive has been measured using two dedicated thermal conductivity measurement systems namely: (a) liquid helium based Janis SuperVariTemp (SVT) cryostat and (b) two-stage GM cryocooler based experimental setup developed in our laboratory in the temperature range from 4.5 K to 300 K. In order to make comparative studies of cryosorption of different activated carbons, a standard cryopanel, such as the one used in the commercial cryopump (Make: Varian, Model Ebara SP8) has been chosen in our studies. (Henceforth, this will be designated as “Commercial cryopanel”). In other words, the physical dimensions of all the cryopanels fabricated with indigenous activated carbons are exactly the same as that of the commercial cryopanel. By this, the experimental results of pumping speeds of different indigenous AC cryopanels can be benchmarked against the commercial cryopanel and the best performing activated carbon cryopanel can be arrived at. In the following, we discuss the works carried out for the development of the cryocooler based high performance cryosorption pump. a) A specially prepared indigenously developed Knitted Carbon Cloth (KCC/IIS01) is found to have a larger surface area for adsorption compared to the other adsorbents. This adsorbent has a surface area of ~ 3000 m2/g for helium adsorption at 4.5 K, which is significantly higher than those of granular charcoals which are in the range of ~ 1600 m2/g for similar experimental conditions. This AC cloth has been used for the development of our cryosorption pump. b) A special epoxy based adhesive (SEBA/IIS01) with higher thermal conductivity, (measured using the experimental setups mentioned earlier) in the temperature range from 4.5 K to 7 K (which is generally the operating temperature range of a cryosorption pump for efficient pumping of helium gas) compared to the commercially available epoxy adhesives such as STYCAST 2850 FT and G10 Cryocomp has been developed indigenously and used. c) Using the above Knitted Carbon Cloth KCC/IIS01 and the epoxy adhesive SEBA/IIS01, cryopanel has been prepared and studied for its performance. The pumping speeds of the developed cryopanel are improved on an average by factors of 1.55 and 1.54 when compared with those of commercial panel for gases such as hydrogen (H2) and helium (He) respectively in the specific pressure range. To enhance the thermal conductivity of SEBA/IIS01, fine powders of metallic fillers (such as aluminium, silver etc.) can be added to the pure epoxy adhesive. However it is also essential that the epoxy-aluminium composite adhesive should withstand the thermal cycling from 4.5 K to 300 K during its functioning as a cryosorption pump. d) Now the thermal conductivities of epoxy-aluminium composites in the temperature range from 4.5 K to 300 K has been measured using the dedicated experimental setups for measurements of thermal conductivity (developed in-house). The measurements of thermal conductivity using the above experimental setups are based on one-dimensional Fourier heat conduction with longitudinal steady state heat flow method. Detailed experimental studies on thermal conductivity of epoxy and epoxy-aluminium composites have been carried out by the above experimental setups. e) Further the thermal conductivities of the epoxy-aluminium composites have been theoretically predicted by analytical heat conduction models. Here, the epoxy forms the base matrix and aluminium powder forms the filler. Appropriate models have been developed both for the low and high volume fractions of the filler in the epoxy base matrix. The thermal conductivity values predicted by the models match quite well with the experimentally measured values of the epoxy-aluminium composite samples. Also the developed models are able to predict the thermal conductivity values of the published data. f) By the addition of metallic (aluminium) filler particles to the epoxy adhesive, the thermal conductivity of the epoxy adhesive is increased. However, the downside of adding aluminium fine powder is the reduction of the bonding strength of the epoxy onto the cryopanel. An experimental setup has been developed to measure the strength of epoxy- aluminium composite adhesive. Based on the experimental studies, an optimum composition of the aluminium powder filler in the epoxy adhesive has been estimated as ~ 35 % by volume fraction. This epoxy-aluminium composite adhesive is designated henceforth as “EAL35”. g) A new cryopanel has been fabricated wherein the activated carbon cloth KCC/IIS01 is bonded using EAL35. The pumping speeds of the newly developed cryopanel are improved on an average by factors of 3.63 and 3.60 when compared with those of commercial panel for gases such as hydrogen and helium respectively in the pressure range from 5E-6 to 4E-5 mbar. Our studies have led to the development of a cryocooler based cryosorption pump with higher pumping speeds for gases such as H2 and He compared to the commercial cryopumps. Hence the present studies will be quite useful to the development of the appropriate cryosorption pumps for the Tokamak related applications.

UV light detection has a lot of applications including secured satellite communication, solar and celestial observation and biological imaging. Wide bandgap materials are used to sense UV light. SiC is an excellent material for UV detection, having properties like high hardness, chemical inertness, thermal stability, high breakdown voltage etc. making it a very reliable and stable material for use in harsh/unknown environments. Growing SiC is a difficult task as it shows 250 different crystal structures and needs very high temperature to form crystalline film. Most of the studies use SiH4 (toxic) and other gaseous precursors for growth of SiC. We are proposing formation of crystalline SiC thin film with DC magnetron sputtering using highly pure, naturally and commercially abundant Silicon, Argon and Methane at relatively lower temperature. The technique is well known in industry and is compatible with silicon technology. SiC thin films were grown on Si Substrate. For the study of formation of crystalline films, we varied the deposition parameters. Flow rate of methane inside the chamber and DC power supplied to the target were varied to observe the change in film’s bonding, structure and crystallinity. Deposited films were characterized using FTIR, Raman, X-Ray Diffraction, Optical profilometer and UV Visible spectroscopy. Films grown were found to be polycrystalline and the study gave the clear picture to get high quality reproducible cubic SiC thin films. Optimized films were used to make a heterostructure of Al/SiC/Si/Al configuration and a planar structure of Al/SiC/Al on quartz substrate to observe the response in UV region. Study proposes that the deposited film could be used for UV detection in various applications

Currently, there is an enormous demand for the development of high performance nitrogen dioxide (NO2) gas sensors for environmental pollution monitoring. Hence, there is a constant quest to replace traditional metal oxide nanostructures as gas sensing materials due to the challenges associated with high temperature working condition. Carbon nanomaterials, particularly graphene because of its unique properties have recently attracted a great deal of interests for gas sensing applications. Abundant defects and functional groups on reduced graphene oxide (rGO), a derivative of graphene, not only facilitate gas adsorption but also provide the ease of selective functionalization with specific organic and inorganic groups for achieving selectivity. The interfacial interactions at the junctions of rGO and nanostructures support the modulation of electronic properties, making the graphene hybrid highly responsive to external chemical perturbations. A chemiresistor device based on Sr nanoparticles (NPs) decorated rGO (rGO-Sr) is presented for detecting NO2 gas over a wide concentration range of 500 ppb to 104 ppm. It is a unique study using hybrid of rGO with a low work function alkaline earth metal. At a concentration of 1 ppm, rGO-Sr exhibited an approximate 222% increase in response as compared to rGO. The calculated detection limit (DL) of the sensor was 478 ppb that is close to the experimentally observed limit. The hybrid sensor was also highly selective to NO2 amongst other gases like CO, SO2, CH4, NH3 and exhibited good sensing responses at different humidity conditions at room temperature, thus presenting it as a promising candidate for selective NO2 sensing at room temperature. Electron transfer from Sr to rGO is induced by work function difference due to which more electrons populate the rGO, thus facilitating rapid charge transfer to electrophilic NO2. Also, Sr NPs, possess high adsorption energy for NO2 which plays an important role in fast and selective adsorption of NO2 at room temperature. Thus, engineering the work function of rGO triggered by the work function differences in graphene hybrid can efficiently create a highly sensitive and selective NO2 sensor. The study was further extended to develop interfaces of rGO with semiconductor, molybdenum disulphide (MoS2) and a noble metal, silver (Ag). Thus, chemiresistive devices based on rGO-MoS2 hybrid (GM) and rGO-MoS2-Ag (GMA) were fabricated for NO2 interaction over a wide concentration range. Both the devices showed much higher sensor responses than rGO alone. Also, both the devices revealed an approximate 500% increase in response to NO2 exposure than rGO device at a concentration of 1 ppm. Moreover, the calculated DL of the GM and GMA sensors were 147 ppb and 70 ppb, respectively. The increased sensor performance of GM compared to rGO is attributed to the defect-dominated adsorption of NO2 molecules on rGO and MoS2. Also, modulation of fermi level at the p-p interface of rGO and MoS2 on NO2 exposure provides enhanced sensitivity. Further, on integration of Ag NPs onto rGO-MoS2 matrix, an interfacial electron transfer occurs from Ag to rGO and MoS2 induced by the work function differences, thus facilitating electron withdrawal by NO2. Moreover, the Ag NPs provide catalytic effect due to which more active intermediate species like NO- and O- are formed that are adsorbed on both rGO and MoS2 thus leading to enhanced sensitivity. Again, such an approach effectively pave the way for engineering nanostructures for tailoring sensitivity and selectivity. Various allotropes of carbon facilitate a unique study on the effect of size on the gas interaction. Thus, the interaction of NO2 gas with zero dimensional carbon nanodots (CNDs) has been further exploited. It is observed that the reduction in dimension of carbon structure, from two-dimensional rGO to zero-dimensional CND has a great impact on the electronic interaction process with NO2. The usual charge transfer sensing mechanism observed in rGO was found hindered in CNDs on exposure to NO2, because charge traps induced by water molecules screen any charge transfer due to NO2 molecules. The functional groups on the surface of CNDs attract ambient water molecules, which in turn act as charge traps and thus, result in the hysteresis in the current–voltage response, where area of hysteresis revealed a strong dependence on gas interaction time. Thus, this study leads to not only develop a deep understanding on the effect of size but also a novel functionality is presented on the gas interaction at small scale interfaces.

Excitons are quasiparticles formed due to electrostatic attraction between the electrons and the holes in a semiconductor. This Coulomb attraction is very strong in the mono- layers of Transition Metal Dichalcogenides (TMDs) mainly because of strong quantum confinement, reduced dielectric screening, and high effective mass of electrons and holes in these material systems. A 2D hydrogen atom is a simple model to describe confined excitons in these monolayer films. A more formal way to describe excitons in thin semi- conductors is through the Bethe-Salpeter formalism which describes these excitons as a superposition of the electronic states in momentum space. In order to understand exci- tons further, we explore the following excitonic features in this thesis: Probing intrinsic exciton linewidth: Monolayer TMDs are highly luminescent materials despite being sub-nanometer thick. This is due to the ultrashort radiative life- time of the strongly bound bright excitons hosted by these materials. The intrinsically short radiative lifetime results in a large broadening in the exciton band with a magnitude that is about two orders greater than the spread of the light cone itself. The situation calls for a need to revisit the conventional light cone picture. We present a modified light cone concept which places the light line as the generalized lower bound for allowed radia- tive recombination. A self-consistent methodology, which becomes crucial upon inclusion of large radiative broadening in the exciton band, is proposed to segregate the radiative and the nonradiative components of the homogeneous exciton linewidth. We estimate a fundamental radiative linewidth of 1:54 0:17 meV, owing purely to finite radiative lifetime in the absence of nonradiative dephasing processes. As a direct consequence of the large radiative limit, we nd a surprisingly large ( 0:27 meV) linewidth broadening due to zero-point energy of acoustic phonons. This obscures the precise experimental determination of the intrinsic radiative linewidth and sets a fundamental limit on the nonradiative linewidth broadening at T=0 K. Modulating exciton binding energy: Screening due to the surrounding dielectric medium reshapes the electron-hole interaction potential and plays a pivotal role in decid- ing the binding energies of strongly bound exciton complexes in quantum confined TMD monolayers. However, owing to strong quasiparticle band-gap renormalization in such systems, a direct quantification of estimated shifts in binding energy in different dielectric media remains elusive using optical studies. By changing the dielectric environment, we show a conspicuous photoluminescence peak shift at low temperature for higher energy excitons (2s,3s,4s,5s) in monolayer MoSe2, while the 1s exciton peak position remains unaltered a direct evidence of varying compensation between screening induced exciton binding energy modulation and quasiparticle band-gap renormalization. The estimated modulation of binding energy for the 1s exciton is found to be 58.6% (72.8% for 2s, 75.85% for 3s, and 85.6% for 4s) by coating an Al2O3 layer on top, while the correspond- ing reduction in quasiparticle band-gap is estimated to be 246 meV. Such direct evidence of large tunability of the binding energy of exciton complexes as well as the band-gap in monolayer TMDs holds promise of novel device applications. Enhancing exciton valley coherence time: In monolayer TMDs, valley coher- ence degrades rapidly due to a combination of fast scattering and inter-valley exchange interaction. This leads to a sub-picosecond valley coherence time, making coherent manip- ulation of exciton a highly formidable task. Using monolayer MoS2 sandwiched between top and bottom graphene, we demonstrate perfect valley coherence by observing 100% degree of linear polarization (DOLP) of excitons in steady state photoluminescence. This is achieved in this unique design through a combined effect of (a) suppression in exchange interaction due to enhanced dielectric screening, (b) reduction in exciton lifetime due to a fast inter-layer transfer to graphene, and (c) operating in the motional narrowing regime. We disentangle the role of the key parameters affecting valley coherence by using a com- bination of calculation (solutions of Bethe-Salpeter and steady-state Maialle-Silva-Sham equations) and choice of systematic design of experiments using four different stacks with varying screening and exciton lifetime. To the best of our knowledge, this is the first time where the valley coherence timescale has been significantly enhanced in monolayer semiconductors. Probing the role of motional narrowing in exciton valley coherence: We observe a strong effect of motional narrowing (regime of random phase cancellation) by observing a high DOLP from a defected MoS2 sample, as compared to a clean MoS2 sam- ple which shows relatively lower exciton DOLP. Similar observations hold good for both monolayer and bilayer MoS2 samples, which results from random phase cancellation in the exciton pseudospin in the motional narrowing regime. This highlights the counter- intuitive role of sample quality in the exciton DOLP measurements: a clean sample does not necessarily guarantee large exciton DOLP and vice versa. Generating highly luminescent, highly-polarized, ultra-narrow exciton peak : On generation, the excitons relax to the lowest energy 1s state by scattering with phonons through multiple possible pathways. We use a simple technique in which, by tuning the excitation laser wavelength, the excitons resonantly come down to the 1s state in a single- shot manner through scattering with a specific phonon mode. Using this technique in a monolayer WS2 sample sandwiched between few-layer graphene flakes, we obtain exciton peaks that are: (1) highly luminescent, (2) highly linearly polarized - demonstrating near- perfect valley coherence, and (3) ultra-narrow - due to a reduction in the inhomogeneous broadening. The lowest exciton linewidth obtained using this technique is 1:5 meV, which after deconvolution with the excitation laser gives an upper bound of 0:23 meV on the homogeneous linewidth of the exciton peak. We demonstrate the above features all the way from cryogenic temperature to room-temperature.

Environmental pollution and energy storage are two important issues in the modern day society. In this regard, Carbon nanomaterials have attained immense importance, due to their high surface area and electrical conductivity along with thermal and electrochemical stability. Various classes of mesoporous materials have been studied for energy storage and environmental applications especially waste water treatment and greener alternative to the materials in synthesis. In this regard, the present dissertation discusses the synthesis, characterization of carbon nanomaterials, such as exfoliated graphite (EG) and reduced graphene oxide (rGO), with reference to energy, as well as, environmental applications. EG has been prepared in bulk quantity within one minute using microwave irradiation technique in different methods. As prepared EG material shows outstanding application performance including adsorption of various dyes in aqueous solutions, acts as a filter, absorption of broad range of chemical solvents, as well as, oils, pseudocapacitors, EMI shielding over a broad frequency region, novel flatform for SERS detection for various dyes, adsorption various types of heavy metal ions under aqueous solution. Moreover, rGO has been prepared by the room temperature as well as green reduction methods from graphite oxide (GO), where graphite is oxidized into GO by Hummer’s method. As prepared rGO materials show excellent performance as electrodes for supercapacitor applications. It was observed that, porosity is the dominant factor responsible for overall performance of EG, whereas, surface area is the dominant factor for rGO.

Surface structuring on a micro-nano scale, combined with a low surface energy coating, leads to anti-wetting properties. Such surfaces also exhibit other properties such as self-cleaning, antifouling, bacteriostatic, drag reduction, and anti-icing. Hierarchical structures with dual-scale roughness provide the superhydrophobic surface with lower droplet adhesion and better protection against failure (i.e., Wenzel transition). This understanding has led to the study of nanostructured sieves, as the sieve wires (having diameters ranging from 10 to 100 microns) provide the higher-level roughness required in dual-scale surfaces. Thus, for sieves, a single nano-structuring step leads to dual-scale rough surfaces. Further, the pores in sieves provide an additional structural feature for enabling other applications such as oil-water separation. Hence, nanostructured sieves are being investigated today for novel applications. Studying the impact of droplets on sieves with different wettability is fascinating as their porosity leads to several exciting scenarios that can be explored for potential use. This thesis investigates the different outcomes of droplet impact on sieves and explores new possibilities. The first part of the study explores droplet impact at the low Weber number regime. The formation of different cavities and their collapse have been studied. The focusing of kinetic energy in the cavity collapse process and the associated singularity leads to the generation of a single droplet. This work reports a new kind of cavity formation phenomenon unique to sieve configurations. In contrast to cavities observed for droplet impact on solid surfaces, this cavity is formed during the droplet impact's recoil phase. Hence, it is called the recoil cavity. The cavity formation and collapse are explained using experimental results and theoretical modeling. The collapse of the recoil cavity leads to the generation of a satellite-free single droplet underneath the sieve. Essentially this phenomenon of ejecting a single drop opens up avenues for novel applications. This thesis explores the drop-on-demand technique for material jetting and printing. Interestingly, we found that using superhydrophobic sieves could eliminate a long-standing problem of clogging in printing. We explored the clogging issue in-depth and showed our technique's unique capability in printing high mass loading and large particle size. We report printing of ink with mass loading as high as 71% using our technique. Further, the use of this printing technique has been demonstrated for various applications. Electronic circuits and devices have been printed on flexible substrates. 3D printing has also been demonstrated using high mass loading ink. Printing of live cells and bacteria has also been achieved using this technique. This thesis explores droplet impact at a high Weber number regime in the second part. We developed double sieve-based air-transparent surfaces capable of repelling rain droplets impacting at terminal velocities. Such air-transparent surfaces will find use in roofs and windows of homes and public places. Current understanding would point towards the use of nanostructured superhydrophobic sieves. However, liquid leaks through such superhydrophobic sieves when the dynamic pressure of the impacting droplet is larger than the anti-penetration Laplace pressure. When the droplet penetrates through the sieve, it comes out in the form of jets. Due to Rayleigh-Plateau instability, the ejected jets break into smaller droplets. This jetting dictates the outcome of the impact. Contrary to the common understanding, we explain our experimental results, which show that the jet velocity can be larger than the impact velocity. This increase in velocity of the ejected droplet makes it difficult to stop the ejected jet using a second superhydrophobic sieve. We use a combination of superhydrophilic and superhydrophobic sieves to repel raindrops impacting at the terminal velocity. Overall, this thesis deals with the droplet interaction with sieves of different wettability. The present work evolves to innovate interesting applications and solve significant problems.

The moisture content of residual soils above the water table, and near ground surface (≤ 6 m) is influenced by the environmental relative humidity (RH). The focus of this thesis is to examine the physico-chemical and physical mechanisms of moisture retention and moisture loss in unsaturated residual soils in response to environmental RH and the implications of such changes on the engineering behavior of soils. The physicochemical drivers of moisture retention include forces and energy responsible for adsorption and desorption of water molecules on soil particle surfaces and capillaries, while the micro-structural features include, tortuosity and pore structure in influencing moisture retention and transport in unsaturated soils. In this study, laboratory experiments were performed with representative fraction of residual soil collected from Indian Institute of Science Campus, Bengaluru and five different saturated salt solutions were used to maintain environmental RH of 97%, 76%, 64.4%, 33% and 7% in the desiccators. The thermodynamics of moisture loss from the residual soil specimens were explored by performing experiments with moist powder soil specimens that were exposed to environmental RH of 33 to 97% at various constant temperatures (16 to 35°C). Distribution constant (Kc) is employed to account for the affinity of desorption of water molecules from soil particles. Analysis of laboratory results revealed that moisture desorption is an endothermic process associated with positive entropy changes and the trend of ΔGo (free energy change) variations indicated that moisture desorption is most favored at low environmental RH. Similar to SWRC (soil water retention curves), the ability of GAB (Guggenheim- Anderson-de Boer) isotherm to characterize the equilibrium soil moisture content - RH relations of compacted residual soil specimens along the drying path were explored and was successful in predicting the equilibrium water contents inspite of the variations in initial compaction conditions. The preferential desorption of water molecules from monoand multi-layers at low relative humidity required relatively larger (1.68 to 3.42 kJ/mol) desorption energy, while, from capillary condensation layer at higher relative humidity required lesser (0.08 to 0.5 kJ/mol) desorption energy. The influence of controlled environmental RH on the moisture loss behavior of compacted residual soil specimens was explored. As the RH of water in soil pores was in excess of the environmental RH of the desiccator, moisture desorption occurred from the compacted soil specimens exhibiting a falling rate segment. The moisture loss under RH gradients caused rapid increase in total suction of the specimens during the falling rate segment. Although the void ratios of the compacted specimens were unaffected by moisture loss, the micro-structure of the soils were affected; increase in very fine (< 0.002 μm) and fine pore (0.002 to 0.01 μm) contents at the expense of medium pores (0.01 to 6.0 μm) content was exhibited by most specimens. Analysis of the moisture loss - exchange period data showed that moisture loss from the compacted soil specimens is driven by diffusion and prevalence of lower RH in the environment facilitates speedier diffusion of moisture from soil pores. The thesis also develops an approach to select appropriate tortuosity (τ) equation based on dominant mode of moisture transport (liquid water or vapor) for correct prediction of moisture flux from the unsaturated soil when using Fick’s equation. Analysis of the laboratory results revealed that during the moisture loss process, as long as θ (volumetric water content) remains greater than a critical water content (θcr) value, capillary controlled flow of water dominates the moisture loss process and the τ is dependent on θ. When θ becomes less than θcr, vapor diffusion through connected air-filled pores becomes important and τ is dependent on air-filled porosity (θa). Knowledge of the final water content (wf) achieved by the unsaturated soil specimen during moisture loss under controlled environmental RH defines θcr for the soil. Good agreement is obtained between predicted and experimental moisture flux (qv) obtained by using τ values based on the dominant mode of moisture transport. Lastly, the thesis examines the influence of moisture loss under controlled environmental RH on compressive strength and collapse behavior of compacted residual soil specimens. Comparing the influence of moisture loss across specimens, it is observed that the initial water content and initial dry density had profound influence on magnitude of strength gain and stiffness respectively. The gain in strength and stiffness upon moisture loss is temporary as the improved strength and stiffness of the compacted specimens are lost on soaking. Examination of critical state stress ratios of compacted specimens upon moisture loss revealed that the critical state stress ratio for changes in net mean stress (Ma) and changes in matric suction (Mb) are strongly influenced by moisture loss. At Sr (degree of saturation) values < 1, Ma exceeds Ms (critical stress ratio at saturation) as particle aggregation at lower Sr causes the soil to behave in a coarser manner. In comparison, the Mb values are less than Ms at Sr < 1 as lowering the Sr causes the water phase to recede into the fine pores of the aggregates and the capillary bonds do not strengthen the aggregate - aggregate contact during shear. Exposure to environmental RH influences the swell and collapse tendency of the compacted residual soil specimens. At a given vertical pressure, exposure to lower RH renders the specimen more collapsible. The increased collapse potential upon moisture loss is attributed to existence of high matric suction in the unsoaked state that stabilizes the inter granular contacts; loss of inter-granular contacts on wetting leads to collapse of soil. In addition to suction, the wetting load to swell pressure ratio also influences the nature of wetting induced volumetric strains. At ratios < unity, the compacted specimen swells and at ratios > unity, the compacted specimen collapse. Further for wetting load < swell pressure ratio, the specimen with lower ratio swells more. Likewise, for wetting load > swell pressure ratio, the specimen with larger ratio collapses more.

Gallium Nitride (GaN) based high electron mobility transistors (HEMTs) are extensively considered for power switching and RF applications by the virtue of their unique properties. However, despite of its attractive performance/cost ratio, AlGaN/GaN HEMT suffers from poor reliability which limits its penetration in the ever-growing power device market. Therefore, reliability of AlGaN/GaN HEMT has become a topic of intense research. In last one decade, the long-term reliability of GaN devices, has been greatly studied in literature. However, the ability to withstand high power under extreme conditions and related safe operating area (SOA) concerns in GaN HEMT, including the failure mechanisms which determine its SOA boundary are still not clearly understood. This thesis aims to investigate devices under pulse stress conditions, the scenario which is more realistic to the practical power electronic circuits. Integrated electrical and mechanical stress characterization routines involving Raman/PL mapping and CL spectroscopy are used to understand the evolution of failure. SEM and TEM analysis of damaged regions provided physical insight into the underlying degradation phenomena. Distinct device behaviour of AlGaN/GaN HEMT is observed in high current regime with dependence on various design and technology parameters. Failure power, shows power law-type behaviour. Device degrades in cumulative manner attributed to deep level traps and the degradation is nicely correlated with the failure threshold. Increased voltage stress leads to defect generation and increased trap density in gate-drain region and carrier trapping leads to electric field shift and peaking towards drain edge. Non-uniform carrier trapping across the device width, triggers avalanche instability and lowers the SOA boundary. Avalanche instability is absent when carrier trapping is suppressed with sub-bandgap UV light. Device failed in gate-source region with carrier trapping and in absence of trapping (with UV exposure), failure occurred in gate-drain region. Stress accumulation at drain edge creates defects underneath drain contact. ON-state SOA is limited by tensile stress in the gate-to-drain region. SOA boundary in OFF-state was found to deteriorate due to compressive stress at drain-gate edge. Furthermore, different techniques are used to compensate for the trap induced field shift and restore SOA. Field shift can be can be tuned by gate recess depth. At optimum recess depth, field peaks at gate/drain are suppressed and relatively more uniform field distribution is achieved and improves SOA. To further improve SOA; polarization doping is added to AlGaN/GaN HEMT. Nearly a two-fold improvement in SOA is realized with PSJ. Failure in OFF-state occurs with gate stack degradation while ON-state failure happens due to hotspot formation at the PSJ edge and is thermally driven. SOA reliability of GaN HEMT is also be limited by premature failure of Schottky gate. Robustness of Schottky diodes with recesses and non-recessed anode is studied. Failure in forward mode is found to be assisted by generation of traps at the GaN/Schottky interface and Schottky barrier gradually turns Ohmic in nature. Failure under reverse mode, is observed to be governed by piezoelectric stress distribution in anode-cathode region. The stress induced trap generation is found to slow down when UV light is exposed, which is due to fast de-trapping of carrier. During pulse operation, the SOA of GaN HEMT is observed to shrink with time. Such shift in SOA boundary is not seen in Si power transistors. To investigate the root cause, devices are realized on commercially available AlGaN/GaN stack which is qualified for 10-year lifetime under DC conditions. Surprisingly, the stack fails faster under cyclic pulse transient stress posing serious limitation to device reliability and SOA. Interestingly, TTF was found to improve when pulse rise time was increased. In depth investigations are done using On-the-fly electrical, optical and materials characterization to understand the root cause. Rapid and more sever changes in device’s RON, ION and VTH are observed under pulse stress compared to that under DC condition. Drain to substrate vertical leakage hysteresis is found to increases with stress time PL mapping of drain-source region reveals increased defect generation introducing deep level traps. Highest PL intensity is observed near the drain contact. CL depth profiling reveals spatial location of newly formed defects, in GaN buffer in the drain contact vicinity. Raman map further confirms mechanical strain builds up at AlGaN transition-region/GaN interface in buffer region underneath the drain contact. Post failure cross-sectional SEM shows a catastrophic damage in GaN buffer, in vicinity of drain contact. HR-TEM of defected region reveals fine cracks near GaN buffer and AlGaN transition interface. However, under DC stress, damage is localized to device surface and no failure signature is observed in the bulk. An electrical shock-based fatigue phenomenon is found to be responsible for time dependent GaN Epi stack failure. A comprehensive failure model is proposed and is experimentally verified

High power fiber lasers due to their immense utility in both industry and research divisions, have seen a dramatic level of power scaling in the last two decades. This is due to the superior beam quality, thermal handling and compact nature inherently offered by all-fiber based systems as compared to other forms of laser systems. As of now, the rare earth doped Ytterbium (Yb), Erbium (Er) and Thulium/Holmium (Th-Hm) fiber lasers have shown remarkable levels of power with Yb outperforming the rest by order of magnitude levels. However as the power in the tightly confined fiber modes scale up, fiber nonlinearity sets into action. Nonlinear effects such as self-phase modulation, modulation instability (MI), supercontinuum (SC) generation, etc alters the spectral and temporal properties of lasers. Similarly nonlinear effects based on photon-phonon interactions, i.e. Raman and Brillouin scattering as well as thermal Rayleigh scattering also hinders or enhances the features of a laser depending upon the application. More recently stimulated Raman scattering (SRS) has evolved to be the only known power scalable technology for generating new wavelength bands, otherwise nonexistent in the rare earth platform. Stimulated Brillouin scattering (SBS) and stimulated thermal Rayleigh scattering (STRS) on the other hand, have been the primary bottleneck in power scaling of narrow linewidth high power lasers. This thesis consisting of two main parts dealing with some new applications and novel effects of SRS and SBS. In the first, we exploit the properties of SRS in silica fiber medium to generate highly spectrally flat SC lasers and subsequently explore their utility in different frontiers. In the second, we demonstrate a widely linewidth tunable high power fiber amplifier which generates an SBS limited kW class narrow linewidth fiber laser showing a previously unseen unique visible light generation phenomena. Raman fiber lasers (RFL) aided by SRS have very recently been established as the only power scalable route to filling in the gaps between Yb, Er and Th emission windows. Similarly spectrally broad lasers, SC lasers too allow a path to spectrally populate these otherwise inaccessible gaps, though not yet known to be power scalable. We identified the shortcomings in bandwidth, conversion efficiency, power scalability and flatness in the existing SC modules and propose utilizing Raman fiber lasers to simultaneously mitigate all of them. Thus we demonstrated a CW RFL with 24 W power (highest at the time of publishing) tunable across the L-band and subsequently generated a 700 nm broad, 35 W SC with ~40% conversion efficiency. The SC had a remarkable flatness of ~5 dB across at least 400 nm which is highest ever reported so far in all fiber and CW format. Flat SC generation was followed by exploring the spectral and temporal properties of such lasers. Femtosecond pulse shaping technology enables one to generate light sources with user defined amplitude, phase and polarization in the ultrafast regime. However due to power handling limitations of the components, this technology lacks a bridge with the modern high power fiber lasers. We propose and demonstrate a scalable design for a high power Fourier shaper capable of handling 20 W of CW laser power with simultaneously covering over 450 nm bandwidth between 1-1.5 micron band. Our design implements several modifications from conventional designs to conform with the demands of high power fiber laser technology. We believe that the ability to shape high power SC or RFL sources will potentially aid controlled Raman conversion to increase spectral purity and many more applications. Further, in the experiments concerning the temporal properties of SCs, we proposed a new method of characterizing high speed photodetectors in a spectrally resolved manner. This is enabled by the stochastic pulse nature of CW SCs while simultaneously having broad optical bandwidth. Our method also gives an insight to how the RF source spectra of CW SC varies across the optical bandwidth as well as its evolution from a single wavelength laser through SRS, MI regime etc. In the second part of the thesis, we demonstrate a high power tunable narrow linewidth laser source at 1064 nm. This was achieved by stepwise amplification of a 1064 nm polarization maintained (PM) DBR (Distributed Bragg reflector) laser, externally phase modulated by a power and bandwidth tunable noise source. This resulted in a tunable linewidth, SBS limited at 10 GHz linewidth laser delivering more than 500 W CW power. This laser operating in the NIR (1064 nm), showed some surprising visible light flashes at a fusion splice point when operated in the SBS regime. Subsequent experimental analysis showed that at the onset of SBS, the backward propagating SBS pulses in the core of the fiber also undergo SRS. This generates multiple Stoke orders of 1064 nm and they eventually undergo Cherenkov type phase matching to the second harmonics of the respective Stoke orders in the cladding of the fiber. Thus any part of the laser with the cladding exposed dissipated the visible light. The analysis was also validated by numerical simulations carried out conforming to the fiber parameters. We believe any laser system with high enough power irrespective of the temporal dynamics could possibly trigger this effect.

Electrostatic Discharge (ESD) reliability is one of the major reliability concerns in integrated circuits (IC), which if not addressed while designing devices and circuits, can lead to a permanent damage to the Integrated Circuits. The same becomes a rather more stringent in case of system level ESD events (System level ESD), which usually occurs in uncontrolled or harsh environments. To address these issues physical insights into the non-equilibrium electron-phonon (electro-thermal) behaviour of these devices, under nano-second time scale high-current conditions, are required to be developed. These insights are subsequently used to develop reliability aware device. Keeping this larger problem in mind, in this work, we focus on developing physical insights into ESD behaviour of advanced high voltage CMOS/BiCMOS & beyond CMOS device options. Using the physical insights developed, this work also demonstrates using computations and experiment’s reliability aware device design. The thesis/work is divided into following threads: In the first part of this work, insights into various system level ESD problems in advanced High Voltage CMOS devices is developed. High voltage functionalities are the key for building system on chips (SoC) in mobile and automotive products. However, high voltage LDMOS/DeNMOS devices are prone to early ESD induced damages with charge modulation induced current _laments. To withstand extremely high current levels ( 30 A), during system level ESD events, in lowest possible area footprint, Silicon Controlled Rectifier (SCR) solutions are preferred. SCR can switch from a high voltage blocking state to an ohmic state and conduct high current levels. However, implementing SCR in High voltage LDMOS/DeNMOS technologies presents different challenges. First part of the thesis focuses on three of such major challenges i.e. Power scalability, Window failures when stressed through Common Mode Choke (CMC) and Air discharge failures. Furthermore, HBM and CDM qualified HV-SCR devices have found to cause early failures during system level stress conditions. System level discharges can last longer than HBM & CDM time scales (100ns), SCR should survive for pulse widths > 100ns. In this thesis, a unique low current ESD failures in LDMOS based SCRs during snapback is reported for the first time. Failure is universal to LDMOS-SCR devices designed as an efficient MOS switch and found to be specific to a window of current between trigger and holding state and can only be captured using high resistance load-line in Transmission Line Pulse (TLP) test system. This resulted in severe power scalability issues in LDMOS-SCRs for longer stress durations (Pulse width>100 ns). While using systematic experiments and 3D Technology Computer Aided Design (TCAD) simulations, we have developed detailed physical insights into the low current ESD failure phenomenon in LDMOS-SCR devices. Physical insights developed has resulted in design solutions to avoid low current failure and mitigate power scalability issue without interfering with functional operation and MOS performance. Further, the severity of the power scalability problem with increasing LDMOS voltage classes (from 40V Design to 80V LDMOS) is highlighted with a need for novel design strategies. A systematic design approach is presented to evaluate the effect of different design parameters on LDMOS _lament and SCR turn-on near the snapback region. New design guidelines are presented to improve the power scalability without compromising on its ON-state DC (functional) and Safe Operating Area (SOA) characteristics. On the other hand, signalling at certain high voltage I/Os can go below ground levels. Hence, Bidirectional SCR (BDSCR) protection elements are needed to block high voltage under different stress polarities. Power Scalability of High Voltage BDSCR for long duration pulse discharges (PW >100 ns), is also studied in this thesis. Power scalability trends are found to be sensitive to the Transmission Line Pulse (TLP) measurement set-up. Detailed physical insights into the early formation of current filaments along with filament motion in BDSCR is presented in detail using 3D TCAD. Dynamic current filament motion in Bi-directional high voltage SCRs is found. Back and forth current filament motion is found to improve the power scalability trends in BDSCR devices for long stress durations. Finally, impact of silicide blocking in mitigating filament strength has been studied, which in turn improves the ESD robustness and overall power scalability. The device design and physical understanding from investigations in helped to come-up with a new approach to engineer LDMOS drivers for safe snapback. Proposed method considers engineering both static filament & Dynamic/Moving current filaments in LDMOS design. Dynamic filament motion and its relation to NPN turn-on engineering is studied. A unique window failure in LDMOS near snap-back discussed for the first time in LDMOS designs. The presented approach resulted in 10-time improvement in ESD robustness for self-protecting concepts. Finally, different fundamental questions related to origin of filament motion are explored with the help of engineered LDMOS Designs. Another major challenge in development of HVSCR is, its survival against system level ESD stress through Common Mode Choke (CMC). Some of the communication pins (CAN) in automotive ICs need to pass system level IEC test through choke. CMC is an on-chip component present in ESD stress path. A unique failure mechanism for system level ESD stress through a CM choke is investigated. Presence of choke in stress path is found to change current waveform shape that ESD protection devices experience on-chip. Minor variations in the stress current waveform shape for specific IEC stress levels are found to cause an unexpected window failure in Drain Extended NMOS SCRs (DeNMOS-SCR). 3D TCAD simulations are used to understand the device behaviour and failure under the peculiar two-pulse shaped IEC current waveform. A novel DeNMOS-SCR design is demonstrated to increases ESD robustness against the peculiar two pulse stimulus and to avoid system level ESD failures. Air discharge failure in HV-SCRs is another major bottleneck in developing on- chip system level protections. High voltage BDSCR devices are found to be vulnerable to system level air discharge failures. The failure observed is sporadic in nature and found to be function of pulse rise time. Root cause for such SCR failure sensitivity to specific rise times is studied in detail using Multi-Finger 3D TCAD Simulations. A novel design solution is prosed to improve BDSCR robustness against the air discharge failures. Second part of the thesis focuses on understanding ESD device physics of new transistor concepts such as Tunnel FETs and graphene-based FETs. Current as well as the time evolution of the junction breakdown, device turn-ON, voltage snapback, and finally the failure mechanism is studied using both 2-D and 3-D TCAD simulations In Tunnel FETs. The interaction between the band-to-band tunnelling, avalanche multiplication, and thermal carrier generation leading to voltage snapback and failure is presented in detail, along with the electro-thermal instability initiated _lamentation. Impact of various technology and device design parameters on the ESD behavior and robustness of TFETs is discussed. The obtained details will be useful in designing ESD protection concepts in future TFET technologies. Experimental ESD studies on Graphene FETs using matured technology platform are carried out to study the impact of diffusive vs. ballistic carrier transport and top-gate vs. back-gate on failure mechanisms. Insights on current saturation in graphene FET in ESD time scales and a novel step by step failure in dielectric capped transistors is presented. Finally, influence of various top-gate designs on the ESD performance is reported. Safe Operating area boundary definitions in Graphene FETs is also explored. Obtained insights on device failures in these budding technologies, will help in building stronger ESD protection concepts in graphene-based technologies.

Power semiconductor devices have been the key to growth of power electronics market, and cover application areas ranging from mobile stations (commercial) to missile seekers (military). Continuously increasing demand for improving the power handling capacities and need for higher bandwidth capable devices has impelled the need for search of novel device structures and materials other than Silicon (Si). High electron mobility transistors (HEMT) based on Gallium Nitride (GaN) have emerged as one of the most promising candidates to replace Si based power semiconductor devices. AlGaN/GaN HEMTs offer several advantages over their Si counterpart, such as high electron mobility (~2000 cm^2/Vs), high sheet carrier density (~ 1E13 cm^-2), and higher critical electric field (~ 3MV/cm). These properties result in devices based on GaN to have superior and efficient ON-state performance, while achieving voltage handling capacities better than their Si counterparts. The theoretical material limits for GaN shows promising applications in power as well as RF domain. These application areas, combined with the widespread LED market, is expected to bring down the cost of development of GaN based devices to be competitive to that of Si-based devices. However, despite very high-power density and operational frequency figures already demonstrated for GaN HEMTs, there is yet to be wide-scale deployment of these devices. One of the major challenges in GaN HEMTs is the development of high performance yet reliable and fail-safe normally-OFF or enhancement-mode (e-mode) devices. Normally-OFF devices are the devices that conduct current only when a positive voltage is applied at one of its terminals, referred to as gate terminal. These devices have a positive threshold voltage (Vth) beyond which they conduct current or become ON. Such devices are desirable in power applications to improve reliability of the power electronic system. Further, extensive application of the GaN based devices is also limited by reliability challenges unique to this material system, such as dynamic ON resistance (Ron), ambient light dependent behavior, and hot electron induced degradation. This work follows a physics-based approach to demonstrate high performance and reliable e-mode devices using a device performance-reliability co-design approach. Physical insights gained into the mechanism governing e-mode operation, besides the reliability challenges, allowed the development of novel methods to demonstrate reliable normally-OFF AlGaN/GaN HEMTs in this work. Firstly, to demonstrate high-performance e-mode AlGaN/GaN HEMTs, we have designed and developed a novel p-type and high-κ ternary oxide AlxTi1-xOy [1]-[2]. The p-type nature of the oxide resulted in an increase in Vth of the device, demonstrating a possibility to achieve positive Vth and hence e-mode operation. The oxide was developed in a thermal Atomic Layer Deposition system by depositing alternate films of Al2O3 and TiO2. By changing the deposition cycles of these films, the Al% and thickness of AlTiO could be precisely controlled. The p-type and high-κ nature of the resulting oxide was found to be a strong function of Al%. This allowed complete control over the p-type nature of developed AlTiO and hence threshold voltage of AlTiO gate oxide-based devices. Using the developed high-κ (25) and p-type Al0.5Ti0.5Oy as gate oxide, in conjunction with a thinner AlGaN barrier under gate, 600-V e-mode AlGaN/GaN HEMTs were demonstrated with performance metrices comparable to the best in literature. The HEMTs showed superior ON-state performance (ON current ~400 mA/mm and ON resistance = 8.9 ohm-mm) and gate control over channel (Ion / Ioff= 1E7, subthreshold slope = 73 mV/dec, and gate leakage < 200 nA/mm). Given that the developed p-type AlTiO was first of its kind, the next area of focus was to probe into the physical mechanism governing the 2-Dimensional Electron Gas (2-DEG) depletion or positive Vth shift achieved by the integration of these oxides in the gate stack. Given the wide band gap nature of AlTiO and AlGaN/GaN system, an electro-optical experiment-based method was used to probe the underlying mechanism [3], [4]. Experiments were carried out on devices with various gate oxides (Al2O3,TiO2, AlTiO) and GaN buffer stacks (varied carbon doping) with 365 nm UV exposure. These experiments revealed maximum negative Vth shift with UV exposure in AlTiO-gated devices. Moreover, the negative Vth shift was a function of Al% in AlTiO. Further, the negative Vth shift was established to be due to deionization of deep-level negative states in AlTiO, induced due to presence of Al at Ti sites ([Al]'Ti), at/near the oxide/nitride interface under the gate metal. The study thus identified the presence of negatively ionized deep-level states at room temperature to result in p-type doping of AlTiO, thereby leading to the positive Vth shift in AlTiO-based HEMTs. Post demonstration of high-performance e-mode GaN HEMTs and the related physical mechanisms, the next part of the work dealt with gaining physical insights into reliability challenges plaguing AlGaN/GaN HEMTs with a view to achieving robust devices. Measure-Stress-Measure routines were followed to evaluate the dynamic ON resistance (dynamic Ron) of AlGaN/GaN HEMTs on carbon (C)-doped GaN buffer. The experiments revealed a unique stress time-dependent OFF-state drain-to-source critical stress voltage (Vcr), above which the dynamic Ron of AlGaN/GaN HEMTs increased significantly [5] – [7]. The Vcr was found to be a strong function of device design parameters, such as, gate-drain distance, field plate length, and passivation thickness. Moreover, the Vcr was observed for both Schottky and Metal-Insulator-Semiconductor (MIS)-HEMTs. With the help of detailed experiments with varying substrate bias, temperature and C-doping in GaN buffer, electron trapping in C-doping induced buffer acceptor traps is proposed and validated to be the source of the dynamic Ron degradation in these devices. This electron trapping is shown to be controlled by the electric field near gate connected field plate of the devices, as it modulates the trap ionization probability and injection of carriers into the GaN buffer. Thus, the HEMTs exhibit a Vcr beyond which high dynamic Ron is observed. Further experimentation on the gate bias dependence of the dynamic Ron of devices with different gate stacks revealed the carrier density in the GaN buffer to be a function of gate control over the channel [8]. This results in an OFF-state gate bias-dependent dynamic Ron degradation in AlGaN/GaN MISHEMTs. This is attributed to the MISHEMTs having an inferior channel control due to the insertion of the gate dielectric. Discovery of an electron trapping controlled dynamic Ron in GaN HEMTs encouraged us to examine the same under semi-ON state stressing as well [9]. Semi-ON state, where channel is in semi-ON condition, stresses the device in a condition where significant electron density exists in the presence of high electric field. This condition results in the generation of highly energized electrons, known as hot electrons. Dynamic Ron experimentations on GaN HEMTs under semi-ON conditions revealed that the interaction of hot electrons with the GaN buffer results in significant self-heating in the GaN buffer near the field plate edge and enhances electron de-trapping from these traps. On the other hand, trapping was found to be determined by field conditions near the field plate edge. This trapping-de-trapping process determines the net electron density trapped in the GaN buffer traps and thus determines the dynamic Ron of the HEMTs under semi-ON state stressing. Furthermore, the study revealed Schottky-HEMTs to have a better dynamic Ron behavior under semi-ON state stressing, as compared to the MISHEMTs. This was due to higher hot electron-induced self-heating and related de-trapping in the Schottky HEMTs. Besides analysing dynamic Ron behavior, reliability aspects related to device breakdown were also analysed [10]. Experiments revealed a slew rate dependent dynamic breakdown voltage in AlGaN/GaN HEMTs on a C-doped buffer. Detailed analysis revealed the role of electron transport through the C-doped GaN buffer in the observed HEMT breakdown behavior. Further, besides gaining insights into the mechanisms governing dynamic Ron in GaN HEMTs, this work also demonstrates a methodology to improve the dynamic Ron of GaN HEMTs even in the presence of C-doping induced acceptor traps, which are introduced to improve the device breakdown. The developed methodology is based on the understanding gained from this work that electron trapping in the GaN buffer can be controlled by relaxing electric field magnitude near the field plate edge. The same was achieved in this work by incorporation of p-type Al0.5Ti0.5Oy as surface protection layer over SiNx passivation [7]. The proposed approach successfully relaxed electric field near field plate edge and resulted in mitigation of dynamic Ron in AlGaN/GaN HEMTs, even in the presence of C-doping induced buffer traps. This work thus resulted in the development of high performance and reliable AlGaN/GaN HEMTs on C-doped GaN-on-Si epi-stack, which was achieved through detailed physical insights into the governing mechanisms. Moreover, by solving the fundamental reliability challenge of dynamic Ron and demonstrating a novel AlGaN/GaN HEMT technology based on AlTiO, this work paves the way towards commercial deployment of a novel technology for high performance and reliable e-mode power HEMTs.

Inverse problems pose a significant challenge as they aim to estimate the causal factors that result in a measured response. However, the responses are often truncated, partially available, and corrupted by measurement noise, rendering the problems ill-posed, and may have multiple or no solutions. Solving such problems using regularization transforms them into a family of well-posed functions. While physics-based models are interpretable, they operate under approximations and assumptions. Data-driven models such as machine learning and deep learning have shown promise in solving mechanics-based inverse problems, but they lack robustness, convergence, and generalization when operating under partial information, compromising the interpretability and explainability of their predictions. To overcome these challenges, hybrid physics-data-driven models can be formulated by integrating prior knowledge of physical laws, expert knowledge, spatial invariances, empirically validated rules, etc., acting as a regularizing agent to select a more feasible solution space. This approach improves prediction accuracy, robustness, generalization, interpretability, and explainability of the data-driven models. In this dissertation, we propose various physics-data-driven models to solve inverse problems related to engineering mechanics by integrating prior knowledge and its representation into a data-driven pipeline at different stages. We have used these hybrid models to solve six different inverse problems, such as leakage estimation of a pressurized habitat, estimating dispersion relations of a waveguide, structural damage identification, filtering temperature effects in guided waves, material property prediction, and guided wave generation and material design. The dissertation presents a detailed overview of inverse problems, definitions of the six inverse problems, and the motivation behind using hybrid models for their solution. Six different hybrid models, such as adaptive model calibration, physics-informed neural networks, inverse deep surrogate, deep latent variable, and unsupervised representation learning models, are formulated, and arranged on different levels of a pyramid, showing the trade-off between autonomy and explainability. All these new methods are designed with practical implementation in mind. The first model uses an adaptive real-time calibration framework to estimate the severity of leaks in a pressurized deep space habitat before they become a threat to the crew and habitat. The second model utilizes a physics-informed neural network to estimate the speed of wave propagation in a waveguide from limited experimental observations. The third model uses deep surrogate models to solve structural damage identification and material property prediction problems. The fourth model proposes a domain knowledge-based data augmentation scheme for ultrasonic guided waves-based damage identification. The fifth model uses unsupervised feature learning to solve guided waves-based structural anomaly detection and filtering the temperature effects on guided waves. The final model employs a deep latent variable model for structural anomaly detection, guided wave generation, and material design problems. Overall, the thesis demonstrates the effectiveness of hybrid models that combine prior knowledge with machine learning techniques to address a wide range of inverse problems. These models offer faster, more accurate, and more automated solutions to these problems than traditional methods.

Hypersonic air-breathing cruise vehicles powered by supersonic combustion ramjet engines are the potential candidate for future space and defense applications. The air intake of the scramjet engine is a vital component that uses shock waves to compress the air to pressure and temperatures suitable for supersonic combustion. Understanding the unstart dynamics of such intakes is of prime importance for the seamless operation of scramjet intakes. While the unstart dynamics in supersonic intakes are studied widely by various researchers, only a few such studies are reported in hypersonic intakes. The mechanisms associated with the same are not clearly understood. In the current work, a design optimization framework is established by coupling (a) oblique-shock theory and Non-dominated Sorting Genetic Algorithm II (NSGA-II) and (b) Computational fluid dynamics (CFD) and NSGA - II to minimize total pressure loss and maximize intake exit temperature of planar mixed compression intake at a design Mach number of 6. The ramp and cowl angles constitute the design space. The intake with maximum exit temperature is chosen to study its unstart dynamics using a combination of experiments in a hypersonic wind tunnel (M = 6 and Re = 8.86 × 106/m) and unsteady numerical investigations using the open-source suite SU2. The intake model is equipped with a movable cowl and flap to study the internal contraction and throttling induced unstart. Simultaneous pressure measurements and schlieren flow visualization are carried out to study unsteady flow physics associated with intake unstart. The dynamic content in the flow is analyzed using Fast Fourier Transform (FFT) and spectrogram of the unsteady pressure signal and Dynamic Mode Decomposition (DMD) of the schlieren images and density contours. In this work, two different modes of shock oscillation during unstart are observed when the flap is moved while the cowl is held stationary. At ICR = 1.19, the intake shows started behavior for throttling ratio up to 0.31, and a dual behavior, where it remains started in dynamic flap runs but unstarted in fixed flap runs for throttling ratios of 0.35 and 0.42. The intake exhibits a staged evolution to a large amplitude oscillatory unstart for throttling ratios of 0.55 and 0.69, with frequencies of 950 and 1100 Hz, respectively. A staged evolution (5 stages) to a subsonic spillage oscillatory unstart is detailed using corroborative evidence from both time-resolved schlieren and pressure measurements. The ramp side separation bubble drives the high amplitude oscillatory unstart. At ICR = 1.37, the shear layer emanating from the triple point of shock interaction drives the low amplitude oscillatory unstart with a dominant frequency of about 3.7 kHz for a throttling ratio of 0.69. A criterion for demarcating the modes of unstart is evolved using current and previous data. The actual shock on lip condition during started operation demarcates the two modes of oscillatory unstart. Unsteady numerical computations are performed to study the effect of enthalpy on the unstart frequency. The frequency of unstart varies linearly with stagnation acoustic speed and is an appropriate velocity scale. During unstart, the extent of the subsonic region is the appropriate length scale to be used in the quarter-wave resonance model to estimate unstart frequency pertaining to high mechanical blockage

Mankind’s desire is to replicate the nature’s creation provided an impetus and inspiration to the rapid advancements, especially progress made in the sensors and other devices for next generation technologies from nanoscience and engineering. Generally, human being has five basic sensory organs, which helps to perform routine tasks in normal life. This clearly signify the importance of basic sensory organs in a human life. In a similar way, sensors and other devices are very important for most of the scientific and engineering applications. The aim of the present thesis work is to explore the application possibilities of graphene and its derivative based films deposited on a flexible substrate for the development of sensors and other devices. Different types of flexible/rigid substrates such as Kapton, Cotton Cloth and Stainless Steel were chosen for different applications. Drop casting and Dip coating techniques were adopted for the deposition of graphene and its derivative based films onto the above-mentioned substrates. The necessary process parameters were optimized to achieve good quality films. To explore the applications in sensors and other devices have been developed by utilizing the direct transformation of graphene and its derivative nanomaterial-based films deposited on flexible/rigid substrates by above mentioned techniques. These devices include temperature sensor for measurement of environmental parameters, heating element devices on cotton cloth for wearable body warmer (in clod places). On the other hand, using piezoresistive effect of graphene and its derivative nanomaterial film strain gauges for force sensor have also been developed. This includes, a film nanomaterial of graphene and its derivatives was used for tensile test of force sensor/device, which work as a load cell. The present thesis work is divided into the following six chapters.

Concrete is a heterogeneous material whose constituents (e.g., cement paste, aggregate etc.) range from a characteristic length-scale dimension of a nanometre to a metre. Owing to the heterogeneity of concrete and the contrasting nature of its constituent’s (cement paste, aggregate) response at ambient and high temperatures, applying a homogeneous macroscopic model to predict concrete’s mechanical and thermo-mechanical performance is questionable. Hence, in this thesis, multiple physical and chemical processes that occur within the concrete constituents at different length scales are considered, and a multi-scale model is developed to study the mechanical and thermo-mechanical behaviour of concrete in a hygral-thermal-chemical-mechanical (HTCM) framework. Firstly, the governing equations of HTCM processes are described at meso-scale, a length-scale where coarse aggregate is explicitly modelled in a binding medium called mortar. After that, a hierarchical homogenization approach is employed, and the evolution of mechanical properties etc., are upscaled (from micro to meso) and used at the meso-scale. The proposed methodology is then used to predict the evolution of mechanical properties (e.g., compressive strength) and time-dependent deformation (e.g., shrinkage and creep) of cement paste, mortar and concrete for a wide variety of factors (e.g., type and content of constituents, different curing conditions, etc.). Like ambient conditions, the developed model is used to simulate thermo-mechanical responses (e.g., in terms of spalling, deformation, residual capacity, etc.) of both plain and reinforced concrete structural elements. Further, the effect of several other meso and macroscopic parameters (e.g., interfacial transition zone, aggregate shape, random configurations of aggregates etc.) on concrete’s mechanical and thermo-mechanical behaviour is studied numerically at the meso-scale. Validation of the proposed methodology with the available experimental results at both ambient and high temperatures for a wide variety of cases highlights the general applicability of the model. It has been shown that on several occasions, existing macro, meso or multi-scale models unable to reproduce the mechanical and thermos-mechanical behaviour of concrete structures. Such limitations can be overcome with the present developed approach. Further, empiricism in several calibrated parameters in the existing thermal-hygral-mechanical macroscopic models (associated with elasticity, strength, shrinkage, and creep prediction) can be avoided by using the present developed multi-scale and multi-physics-based methodology. Similarly, simulated results at high temperatures highlight several crucial aspects related to obtaining a more precise residual capacity of a concrete structure, which is impossible to reproduce with a homogenized macroscopic model. For instance, spalling out of random concrete parts at different times during high-temperature exposure cannot be simulated with a homogenized assumption. Further, unlike macroscopic models, a mesoscopic model does not require transient creep strain to be specified explicitly in the analysis. The primary influencing mechanisms behind this transient creep strain are implicitly taken into account in the present developed meso-scale model that results in such advantages.
Ministry of Human Resource and Development, Government of India

Дана дисертація присвячена теоретичному й експериментальному дослідженню ефективних електродинамічних властивостей двокомпонентних метало-діелектрич-них метаматеріалів у надвисокочастотному (НВЧ) діапазоні, а також створенню кон-цепції мініатюризації мікросмужкових прямокутних антен НВЧ-діапазону з підклад-ками на основі зазначених метаматеріалів із поліпшеними характеристиками ближ-нього і далекого полів. Розглянуті в дисертації метаматеріали являють собою ізотропні діелектрики (матриці) з періодично вбудованими в них металевими включеннями циліндричної або сферичної форми. У дисертації були окремо розглянуті випадки немагнітних (мідних) металевих включень і феромагнітних (залізовмісних) металевих включень. У другому випадку розглядалися режими повного та часткового намагнічування фе-ромагнітних включень під дією зовнішнього постійного магнітного поля з позицій розповсюдження електромагнітних хвиль як у напрямку зовнішнього магнітного поля, так й перендикулярно до цього напрямку. Дисертація складається з шести розділів. Перший розділ присвячений огляду літератури за темою дисертації та обґрунту-ванню вибору напрямку дослідження, його мети, а також завдань, які необхідно розв’язати для досягнення мети. Другий розділ дисертації присвячений створенню теорії ефективного середо-вища для безмежного ізотропного діелектрика з періодично вбудованими в нього не-магнітними металевими включеннями циліндричної і сферичної форми. Уперше отримані мікрохвильові наближення для ефективних електромагнітних відгуків для таких композитних середовищ. Уперше показано, що в НВЧ-діапазоні ці композитні середовища мають приріст ефективної відносної діелектричної проник-ності і діамагнітну ефективну відносну магнітну проникність, а також володіють ни-зькими як діелектричними, так і магнітними втратами. Уперше дано фізичне пояснення явища приросту ефективної відносної діелект-ричної проникності та явища діамагнітної ефективної відносної магнітної проникно-сті для розглянутих в даному розділі безмежних немагнітних мета матеріалів. Третій розділ дисертації присвячений експериментальному підтвердженню тео-рії, створеної у другому розділі. З цією метою було виготовлено композитні матеріали у вигляді діелектричних матриць паралелепіпедної форми з періодично вбудованими в них металевими включеннями циліндричної форми. Також даний розділ присвячений вимірюванням ефективних проникностей та-ких метаматеріалів. У розділі розроблений і практично апробований новий та недо-рогий метод вимірювання ефективних проникностей метаматеріалів. Уперше експе-риментально показано, що метаматеріали у вигляді діелектричних матриць правиль-ної форми з періодично вбудованими в них металевими включеннями циліндричної форми мають такі властивості:– приріст дійсної частини ефективної відносної діелектричної проникності і діамагнітний характер дійсної частини ефективної відносної магнітної проникності; – приріст дійсної частини ефективної відносної діелектричної і магнітної проникностей у випадку феромагнітних металевих включень; – такі метаматеріали можуть бути використані для поліпшення характеристик дале-кого поля мікросмужкової антени при повному покритті її випромінювального еле-менту (патча) цими матеріалами; – S-параметри даних метаматеріалів містять аномальні піки, що є обумовлені розмірним резонансом. Четвертий розділ дисертації присвячено аналітичному дослідженню в НВЧ-діапазоні ефективних електродинамічних параметрів шаруватих метал-діелектрич-них композитів та розробці чисельно-аналітичного алгорітму пошарової декомпо-зиції плоских композитних/метаматеріальних середовищ. Показано, що плоскі метало-діелектричні композитні середовища характеризу-ються приростом дійсної частини ефективної відносної діелектричної проникності і діамагнітною дійсною частиною ефективної відносної магнітної проникності, при-чому дані ефекти виявляються сильнішими, якщо в композиті можна виділити елеме-нтарну комірку, тобто якщо композит є метаматеріалом. П'ятий розділ присвячено створенню теорії ефективного середовища для безмежного ізотропного діелектрика з періодично вбудованими в нього феромагнітними металевими включеннями циліндричної і сферичної форм, намагнічений повністю або частково під дією зовнішнього постійного магнітного поля. Уперше отримані тензори ефективної магнітної проникності для таких магнітних метаматеріалів. Уперше показано, що метаматеріали в НВЧ-діапазоні мають такі властивості: – при повній магнетизації включень розповсюдження електромагнітної (ЕМ) хвилі в напрямку зовнішнього намагнічування або в напрямку, що є перпендикулярним до зовнішнього намагнічування, характеризується тим, що тангенс кута магнітних втрат поза резонансів коливається в межах 3 1 10 10  для циліндричних включень і є на два порядки вищим для сферичних включень; – при частковому намагнічуванні включень елементи тензора ефективної магнітної проникності мають малі магнітні втрати, причому в разі циліндричних включень такі втрати на два порядки вище, ніж в разі сферичних втрат; – при частковому намагнічуванні включень розповсюдження ЕМ-хвилі в напрямку зовнішнього намагнічування або в напрямку, шо є перпендикулярним до зовнішнього намагнічування, характеризується тим, що тангенс кута магнітних втрат поза резонансів коливається в межах 8 1 10 10  ; – як при частковому, так і при повному намагнічуванні включень, в залежності від напрямку розповсюдження ЕМ-хвилі, у розглянутих метаматеріальних середовищах виявляються ефекти, що супроводжуються: а) приростом дійсної частини ефективної відносної магнітної проникності; б) ультранизькими значеннями дійсної частини ефективного коефіцієнта заломлення; в) негативними значеннями дійсної частини ефективної відносної магнітної проникності. Теоретичні результати якісно підтверджуються експериментальними резуль- татами, які було отримано для феромагнітних включень і відображено в третьому розділі. У даному розділі також уперше отримано умова відсутності втрат у слабкому полі для композитних магнітних середовищ у вигляді безмежного ізотропного діеле- ктрика з періодично вбудованими у нього частково намагнічених металевих ферома- гнітних включень циліндричної і сферичної форми. Уперше показано, що при різних значеннях зовнішнього постійного магнітного поля дані магнітні метаматеріали можуть замикати проходження монохроматичних компонентів НВЧ-хвилі, забезпечувати її повне проходження в заданому діапазоні частот або інвертувати її фазу. Отримані вище результати дозволяють використовувати досліджувані магнітні метаматеріали для синтезу штучних феритів НВЧ-діапазону, які можуть бути вико- ристані для: – створення метаферитних ізоляторів, метаферитних фазообертачів і метаферитних циркуляторів НВЧ-діапазону; – створення керованих метаповерхонь НВЧ діпазону; – створення альтернативних до вже існуючих НВЧ-фільтрів, конверторів і ретрансляторів/транспондерів ЕМ-хвиль; – створення компактних бездротових систем передачі електромагнітної енергії в НВЧ-діапазоні з високими значеннями коефіцієнта корисної дії. Шостий розділ дисертації присвячено розробці принципів мініатюризації мікросмужкових прямокутних антен НВЧ-діапазону з подальшим поліпшенням ха- рактеристик ближнього та далекого полів таких антен. Уперше показано, що можна домогтися суттєвої мініатюризації профілю пря-мокутної мікросмужкової антени і поліпшення її коефіцієнта посилення за потуж-ністю і коефіцієнта корисної дії при використанні в якості підкладки метаматеріалів або композитів з приростом ефективної відносної діелектричної проникності і/або ефективної відносної магнітної проникності. Причому, поліпшення даних параметрів антен також відбувається при збільшенні кількості метаматеріальних шарів у випадку композитних підкладок, при збереженні об'ємного профілю антени. У даному розділі вперше отримані основні співвідношення між резонансною ча-стотою хвилі і бажаною товщиною метаматеріальної підкладки антени або резонанс-ною довжиною хвилі і бажаним значенням ефективної відносної діелектричної про-никності метаматеріальної підкладкою в припущенні мінімально можливого об'ємного профілю антени з немагнітною підкладкою з приростом ефективної віднос-ної діелектричної проникності. Також у даному розділі вперше показано, що при заміні діелектричної підкладки на метаматеріальну підкладку з приростом ефективної відносної діелек-тричної проникності або ефективної відносної магнітної проникності інтенсивність полів у ближній зоні істотно зменшується, що відкриває широкі перспективи для використання таких метаматеріальних антен у мобільному зв'язку, а також при ви-робництві гаджетів. При цьому, найбільш корисним виявляється використання ба-гатошарових немагнітних композитних підкладок, що містять один магнітний мета-матеріальний шар.

We consider the problem of status updates of a physical process over an unreliable channel. In this setting, one may not be able to reliably transmit the current state at all times. Instead, one is interested in the timeliness of the accurately received information. This is a setting for several cyber-physical system applications that require real-time monitoring and control. In this thesis, fi rst we have studied the periodic data transmission schemes for highly correlated source, that can always exploit the temporal correlation in the source messages. When the source has no feedback, it can periodically send the actual information, interspersed with differential messages. On the availability of receiver's feedback at the source, it can decide to send either the differential or the actual information, at each transmission opportunity. We show a stochastic ordering among the update schemes, to conclude that the differential encoding improves the timeliness performance, only if the receiver's feedback is available. We also identify the scenarios when it is advantageous to use differential encoding with feedback, considering a cost for feedback messages. Second, we have studied the data transmission scheme for general correlated sources that can elect to transmit actual or differential state information depending on the current state. This encoding scheme generalizes the actual and differential updates schemes. Using this generalized scheme, we quantify the timeliness gains for general Markov sources using block Markov chains.

Low-dimensional systems are an exciting platform for exploring new physics and realizing novel devices. The intriguing features, such as the existence of strongly bound multiparticle complexes and thickness-dependent band structures, enable us to utilize them to overcome many challenges faced by bulk materials and conceive new technologies. Since the isolation of graphene, the class of two-dimensional materials has grown tremendously. The array of materials one can choose from for implementing an idea is vast. Nevertheless, understanding the underlying physics is essential for utilizing these properties for real-life applications. Here, we explore the optical, electrical, and optoelectrical characteristics of heterostructures based on 2D layered systems. The strongly bound excitonic complexes hosted by monolayer transition metal dichalcogenide semiconductors (TMDC) are an excellent platform for probing many-body physics. The strong luminescence and a plethora of exciting properties make them a good candidate for applications such as single photon emitters and light-emitting diodes. In the first work, we explore new ways to tune the emission from these particles without compromising their luminescence. Using a high-quality graphene/hBN/WS2/hBN/Au vertical heterojunction, we demonstrate for the first time an out-of-plane electric field-driven change in the sign of the Stark shift from blue to red for four different excitonic species, namely, the neutral exciton, the charged exciton (trion), the charged biexciton, and the defect-bound exciton. We also find that the encapsulating environment of the monolayer TMDC plays a vital role in wave function spreading and hence in determining the magnitude of the blue Stark shift. We also provide a theoretical framework to understand the underlying physics better. The findings have important implications in probing many-body interaction in the two dimensions and developing layered semiconductor-based tunable optoelectronic devices. A significant advantage of the 2D material system is its robustness against lattice mismatch between the successive layers and the ability to extract exciting characteristics from the resultant system. The final system's behavior greatly depends on how the energy bands of the individual materials line up and can result in drastically different properties. In the second work, we demonstrate how an additional ultra-thin barrier layer modifies the properties of a black phosphorus (BP)/SnSe2 tunnel diode. While the system without the barrier layer showed a linear relationship between current and voltage, the additional barrier layer modified it to a highly nonlinear relation and exhibited negative differential resistance (NDR). Moreover, the tunnel diodes exhibited highly repeatable, ultra-clean, and gate tunable NDR characteristics with a signature of intrinsic oscillation and a large peak-to-valley current ratio (PVCR) of 3.6 at 300 K (4.6 at 7 K), making them suitable for practical applications. We then show that the thermodynamic stability of the van der Waals (vdW) tunnel diode circuit can be tuned from astability to bistability by altering the constraint by choosing a voltage or a current bias, respectively. After exploring the dynamics of the device, we assess its viability for designing systems with real-life applications. In the astable mode under voltage bias, we demonstrate a compact, voltage-controlled oscillator without needing an external tank circuit. In the bistable mode under current bias, we demonstrate a highly scalable, single element, a one-bit memory cell promising for dense random access memory applications in memory-intensive computation architectures. In the third work, we explore the usage of vdW materials for generating a cryptographically secure true random number generator. Such generators rely on external entropy sources for their indeterminism. Physical processes governed by the laws of quantum mechanics are excellent sources of entropy available in nature. However, extracting enough entropy from such systems for generating truly random sequences is challenging while maintaining the feasibility of the extraction procedure for real-world applications. Here, we design a compact and an all-electronic vdW heterostructure-based device capable of detecting discrete charge fluctuations for extracting entropy from physical processes and use it for the generation of independent and identically distributed (IID) true random sequences. Using the proposed scheme, we extract a record high value (> 0.98 bits/bit) of min-entropy. We demonstrate an entropy generation rate tunable over multiple orders of magnitude and show the persistence of the underlying physical process for temperatures ranging from cryogenic to ambient conditions. We verify the random nature of the generated sequences using tests such as the NIST SP 800-90B standard and other statistical measures and verify the suitability of our random sequence for cryptographic applications using the NIST SP 800-22 standard. The generated random sequences are then used to implement various randomized algorithms in real life without preconditioning steps. We then investigate how knowledge of the dynamics of optically generated carriers, ability to sense discrete charge fluctuation, and transport of carriers across vdW heterostructure can be combined to design a comprehensive system to detect single photons. Single-photon detectors (SPDs) are crucial in applications ranging from space and biological imaging to quantum communication and information processing. The SPDs operating at room temperature are particularly interesting to broader application spaces as the energy overhead introduced by cryogenic cooling can be avoided. Although silicon-based single photon avalanche diodes (SPADs) are well matured and operate at room temperature, the bandgap limitation restricts their operation at telecommunication wavelength (1550 nm) and beyond. On the other hand, InGaAs-based SPADs are sensitive to 1550 nm photons but suffer from relatively lower efficiency, high dark count rate, afterpulsing probability, and pose hazards to the environment from the fabrication process. By coupling a low bandgap (~350 meV) absorber (black phosphorus) to a sensitive van der Waals probe capable of detecting discrete electron fluctuation, we demonstrate a room-temperature single-photon detector. While the device is capable of covering up to a wavelength of ~3.5 um, we optimize the device for operation at 1550 nm and demonstrate an overall quantum efficiency of 21.4% (estimated as 42.8% for polarized light) and a minimum dark count of ~720 Hz at room temperature.

A significant fraction of the materials handled in the chemical, food-processing, and pharmaceutical industries are particulate in nature. Screw feeder systems are often employed in such scenarios to achieve their bulk transport. Several studies have attempted to characterize the overall flow behavior of granular material in screw feeder systems by linking the flow rate with rotational speed and the design parameters of the screw. However, a detailed description of the flow mechanics of granular material in the screw feeder systems is lacking. This thesis describes a detailed experimental study of the flow of dry (cohesionless) granular materials in different helical screws of the different pitch-to-barrel-diameter ratios in the horizontal screw feeder system. We measured stress profiles at different axial positions on the barrel surface, flow rate, and detailed kinematics using the particle tracking velocimetry (PTV) technique for every helical screw. The qualitative behavior of local stress variation with time, measured at different axial positions, on the barrel’s surface remains the same in comparison to the previous study by our group, which relied on the discrete element method (DEM). Stress values decrease from inlet to outlet in every helical screw, which was not observed previously because of the assumptions of a completely filled and fully developed system. The fill level of granular material also decreases from the inlet to the outlet. Combining these results allows us to illustrate gravity’s vital role in reducing the fill level of the granular material in the screw feeder systems, which has been overlooked in previous investigations. Furthermore, the particle tracking velocimetry technique also highlights the crucial dependence of flow mechanics on the pitch-to-barrel-diameter ratio of the helical screw. We observed a similar trend in experimentally obtained flow rate variation with a pitch-to-barrel-diameter ratio of the helical screw compared to the analytical model and DEM simulations obtained from a previous study. We also performed the DEM simulations, where we simulated the entire system by combining the inlet hopper and screw feeder geometry without employing periodic boundary conditions (allowing the system to vary along the axial direction). These DEM simulations confirmed that the fill level decreases along the axial direction in the presence of gravity. We have also performed sensitivity analysis on the coefficient of friction of the screw and barrel surface to see its effect on the flow rate. We observed an increase in flow rate with an increase in the barrel surface’s coefficient of friction and a decrease in flow rate with an increase in the screw surface’s coefficient of friction.
International Fine Particle Research Institute (IFPRI)

The occurrence of a severe natural disaster causes loss of life and destruction of properties. The overall criticality of the disaster depends on the nature of the disaster and the physical characteristics of the affected locations. In the aftermath of a natural disaster, multiple emergencies often evolve at different geographical locations with casualties and infrastructure damage. In post-disaster scenarios, responsible authorities should initiate relevant disaster management activities to mitigate the devastating effects of natural disaster. Resource allocation is an integral part of the post-disaster activities. In general, resource allocation deals with the issue of distributing necessary resources to multiple users depending on their demand and the availability of resources. It aims to achieve efficient and fair assignment of limited resources. The devastation caused by a natural disaster enforces the need for various critical resources in disaster-affected locations to reduce the impact of the disaster. When adequate resources are available, the problem of allocating resources becomes trivial, and all the crisis locations can be fully satisfied in terms of their resource requirements. However, if there is a scarcity of essential resources after the simultaneous occurrence of multiple emergencies at distinct geographical locations, providing resources to all those regions and fulfilling their demands simultaneously becomes challenging. In such situations, efficient decision-making is necessary to execute a fair and socially agreeable allocation of resources to the affected locations. One cannot rely on human-controlled decision-making since it can have a bias for, or prejudice against, some of the disaster locations. A fair and impartial approach to the allocation of resources can be implemented by designing an automated decision-making system. This thesis proposes a game-theoretic framework which can form the basis for such a system. In this thesis, we develop a multi-event emergency management system using a non-cooperative, single-stage, strategic form game model to facilitate the allocation of resources to the respective disaster locations. Each emergency event is assumed to occur at different locations simultaneously, and some amount of resources are demanded by each location to mitigate the impact of disasters. These locations are represented as players in the game, which are assumed to play in a self-interested manner with the other players to get an allocation of scarce resources available at the resource station. However, it should be noted that the disaster locations are not actively involved in playing a game. It is a centralized decision-making executed by the responsible disaster management authority, which implements the algorithm designed using the game-theoretic framework to decide reasonable allocations to the players. The authority assumes different allocations to be the possible strategies of the players and arrive at a fair solution. As a game utility, the authority imposes a non-monetary cost on each player for obtaining a certain amount of resource units. The objective of the proposed game is to derive socially acceptable strategies for an effective and fair allocation of resources to the respective players. In the thesis, it is established that the game model is unique in structure and always possesses pure strategy Nash equilibria (PSNE). Each PSNE consists of possible allocations to the players; hence, those can be implemented by the disaster management authority as potential allocation vectors. As the resources needed during disaster management can be both divisible and indivisible, we investigate the game for both types of resources. Mathematical analysis shows that the existence of PSNEs is independent of the nature of resources. The only difference it makes is that in the case of indivisible resources, the players have a discrete set of strategies, and divisible resources make their strategy sets continuous. It is also shown that the game-theoretic algorithm can be used for any number of players or disaster locations at various stages of resource allocations. The investigation is conducted using twoplayer, three-player and n-player game models. Different case studies are presented in the chapters of this thesis to validate the mathematical results developed in this work and to indicate how this proposed method can be helpful in practical disaster resource allocations. This work also includes the statistical analysis of the game-theoretic algorithm and the study of its computational complexity. This thesis also includes a study on the preparedness and damage assessment of a natural disaster using unmanned aerial vehicles (UAV). Preparedness is a pre-disaster activity which is essential to build resilience against natural disasters. Damage assessment is one of the post-disaster activities which estimates the loss of human lives, properties, and infrastructure. This phase is important to initiate the response and recovery work after a natural disaster. These activities become challenging and time-consuming when human effort is the only option. In our study, we focus on the possible applications of UAVs to make these activities speedy and effective.

The generation and detection of surface acoustic waves (SAWs) using interdigital transducers (IDTs) on a piezoelectric surface have been used to produce many high performance Band Pass Filters. This thesis focuses on the design and simulation of various SAW Band Pass Filters. IDTs can be fabricated on many piezoelectric substrates. The effect of substrate properties – electromechanical coupling coefficient and SAW velocity, on filter frequency response is analyzed. The IDT design properties comprise film thickness ratio, metallization ratio, acoustic aperture, and number of finger pairs. The behavior of electrical equivalent circuit of an IDT that consists of impedance parameters – radiation conductance, radiation susceptance, and capacitance, is simulated and analyzed for different piezoelectric materials. Different IDT designs offer different propagation environment to SAWs. The IDT designs based on electrode spacing – uniform and non-uniform, direction of SAW propagation – bidirectional and unidirectional, acoustic aperture – apodized and unapodized, and electrode configuration – solid electrode and split electrode, are studied. The effect of IDT design on filter performance is assessed. The design of linear phase SAW filter using fourier transform, and effect of truncation on filter specifications – amplitude ripple, side lobe rejection ratio, insertion loss, and transition bandwidth is thoroughly depicted and analyzed. The cosine window function technique is used to improve filter performance. The second order effects – bulk wave interference, diffraction, impedance matching, electromagnetic feedthrough, triple transit interference, and harmonics that corrupt the filter performance are elaborated. The effect of metallization ratio on higher harmonic suppression is studied. Design of advanced SAW band pass filters – comb filters and resulting frequency response is also explored.

Ribbons exhibit fascinating buckling-dominated behavior under mechanical loading because of a unique combination of geometric dimensions. The recent interest in examining engineering applications of ribbon-like structures underscores the need for dedicated structural mechanics models to predict their complex behavior. In this thesis, we deal with ribbons that have at unstressed con figurations. Due to their physical appearance, such ribbons are typically modeled either as rods with highly anisotropic cross-sections (width of the cross-section is much larger than the thickness) or narrow plates. We speci fically examine the predictive capabilities of the Geometrically exact two-director Cosserat rod and Geometrically exact one-director Cosserat plate models. We measure ribbon shapes in various bending-dominated experiments and compare them with predictions computed using detailed finite element simulations of these models. We nd the plate theory to be particularly useful under a broad range of loading conditions, mainly because it captures nontrivial (and nonlinear) curvature distributions realized in the material bers oriented along the ribbon's width. This feature, which is noticeably absent in rod models, contributes to their poor predictive capabilities. We then propose a phenomenological one-dimension ribbon model by dimensional reduction from the Cosserat plate theory. Speci fically, we impose kinematic assumptions on the displacement field's dependence along the width direction of a ribbon to permit non-trivial lateral surface curvatures observed in the Cosserat plate solutions corresponding to various experiments. We speci fically examine polynomial dependences for the displacement field on the coordinate along the width. In principle, we expect a quadratic dependence to suffice since it helps to reproduce non-zero curvatures along the width. However, we nd that the resulting restricted kinematics is prone to membrane locking. Presuming a cubic dependence helps circumvent the issue. Alternately, resorting to selective reduced integration techniques during numerical approximation using finite element methods helps alleviate the issue.

In recent times, usage of electronic devices inside cars while driving has increased due to the introduction of new technologies to keep drivers comfortable and entertained. Systems like satnav ease out the navigation by offering optimised traffic plans at times of complex traffic and road conditions. Though technologies like music, radio and phone facilitate onboard communication and entertainment, they have potential in distracting drivers. The interaction with such technologies while driving takes the attention of drivers away from driving. As distraction of drivers leads to car crashes and fatal accidents, the research community investigated detecting and reducing such distractions. Operating a secondary task while driving is one of the key reasons for driver distraction. It is challenging to detect the inattention blindness of drivers compared to detecting instances of eyes-off road. Recent studies have found that high perceptional load results in increased inattention blindness. This dissertation investigates methods to reduce driver distraction caused due to operating secondary tasks. It proposes new interactive technologies involving virtual touch and eye gaze tracker to undertake secondary tasks in both head down and head up displays. It also proposes a new machine learning model to estimate cognitive load from ocular parameters and validates with respect to EEG parameters from studies involving professional drivers operating real vehicles. Finally, grounded theory method of qualitative research is used to understand and explore concerns and issues of professional drivers, resolve them, and look for factors contributing to acceptance of the proposed interaction technologies. This dissertation discusses the potential of the proposed methods for applications beyond automotive context. As the proposed systems are tested in simulation and real driving environments, they are considered to be deployed by industries.

Random walks and algorithms based upon them are used widely to explore large state spaces that arise while studying physical systems. In this thesis, we will discuss some quantum generalizations of such algorithms and study their complexity. In the first part of this talk, we will discuss quantum search in the presence of spatial constraints. One of the main results in this thesis is an efficient search algorithm that can find multiple marked elements under spatial constraints imposed by regular graphs. Next, we will focus attention on two-dimensional square lattices. Building on our earlier algorithmic framework, we will show that optimal quantum search is possible on the square lattice by only mildly violating the locality constraints imposed by the graph. This investigation leads to a general prescription for dealing with the graph powering operation in the quantum walk framework. After this, we will move on to discussing mixing times of quantum walks. We will show that a fully decohered quantum walk mixes asymptotically at the same rate as its classical counterpart only if its degree is a constant function of its size. We will also present some numerical evidence showing that faster mixing is possible using a weakly decohered quantum walk, if the decoherence probability is tuned in relation to the spectral gap of the graph. Finally, we will also discuss the implementation of quantum walks and spatial search on IBM's quantum computing platform.
EMR/2016/006312

Experimental techniques to measure and visualize kinematics in structural and solid mechanics range from humble strain gage rosettes to sophisticated digital image correlation methods. This thesis develops a stereo visionbased optical measurement technique and evaluates its efficacy for measuring three-dimensional elastic deformations of slender structures. Our motivation to develop the technique stems from the need to quantify/digitize the kinematics of slender elastic structures undergoing large displacements and rotations within the small strain regime. As devices composed of highly flexible elements become ubiquitous in engineering applications, especially at small length scales, it is imperative to examine the mechanics underlying their functioning through a combination of modeling and experimental studies. The technique proposed here is a step towards addressing challenges in the context of the latter. We adopt elastic ribbons as prototypical examples in our study. Owing to the disparities in their dimensions (length ≫ width ≫ thickness), ribbons naturally contort into complex three-dimensional energy-minimizing configurations in response to simple loading scenarios. For this reason, elastic ribbons furnish excellent test cases to investigate the capabilities of the proposed technique. Besides, such measurements complement on-going efforts within the research group to understand the mechanics and envision novel applications of elastic ribbons. The proposed technique relies on familiar principles of stereo vision— a pair of calibrated digital cameras, an ansatz for pixel correspondences, and triangulation of corresponding pixel pairs to reconstruct points of interest in the scene. Hence, we will photograph a ribbon sample from multiple vantage points using a pair of digital cameras and reconstruct the locations of markers labeling its surface. The novel aspects of the technique include: the choice of fiducial markers to paint flexible surfaces, an algorithm to encode/decode 5-letter marker dictionaries that helps limit the number of distinct markers required to label surfaces, and an optimization-based algorithm to determine full-field approximations of deformations mappings by unifying independent Lagrangian marker and Eulerian shape measurements. The set of markers labeling ribbon surfaces serve multiple purposes. They define Lagrangian coordinates that can be tracked during deformation, establish pixel correspondences between cameras in a stereo arrangement, and aid in registering partial reconstructions to a common coordinate system. Throughout our study, we adopt the ArUco marker system that is commonly used for positioning and alignment of coordinate systems in virtual reality and robotics applications. This choice is mainly based on convenience; alternate marker systems (e.g., AprilTags, color-based markers, shape-based markers) along with reliable detection algorithm can be employed as well. Through a detailed set of measurements of shapes and displacements of straight and annular ribbons, we quantify the accuracy of the proposed technique at a desktop-scale. When available, we also compare the measurements with idealized finite element simulations available in the literature. We conclude the thesis by listing possible strategies to improve the technique.

Printed antennas play an significant role in satellite, mobile, and other wireless communications networks, military systems and several more emerging applications in- cluding radar sensing and imaging. Several of these new applications not only have special demands for antenna designs but also require incorporation of smart features into it. In addition, research for high gain, wideband and compact antennas for several emerging technologies like 5G and IoT are rapidly progressing. In this work, design and analysis of several variants of wideband microstrip patch antennas are taken up. We begin with the design of a single layer suspended antenna where a small coplanar capacitive strip is used as the feed. Following a recent research from the group, di erent radiating patch shapes like rectangular, triangular and semi- elliptical patch geometries are compared with each other for various performance parameters. It is important that these wideband antennas must be able to transmit and receive short time pulses without any distortion and dispersion. Thus, parameters like group delay(GD) and fidelity factor(FF) are studied along with other parameters like re ection loss (S11), gain, polarisation, e ciency and radiation pattern. Full wave electromagnetic simulations using CST microwave studio is used to analyze these antenna characteristics. Triangular and semi-elliptical patches are fed in two di erent configurations (edge-feed and vertex-feed). Simulation studies showed that among the five configurations the vertex fed triangular antenna has the best performance in terms of at gain and low group delay variation over the frequency band of operation. Fabricated antenna has a return loss bandwidth from 3.1 GHz to 4.2 GHz at S11 better than -10 dB where the group delay variation is less than 2 ns. This antenna has a peak gain of 7 dBi and a beamwidth of 60 in both principal planes at the center frequency. Pulse propagation characteristics of this antenna is also studied using modulated sinusoid waveforms as the transmit signal. The degradation of pulse shape with angle is studied through simulations. The transmitted and received pulses are compared with two identical antennas at boresight to experimentally analyze the impact on time domain waveforms. A similar performance has been obtained for an antenna with the feedstrip embedded within the patch by providing a slot surrounding the strip. While retaining most of the performances the footprint of the antenna could be reduced by this approach. Surface wave generation is considered a common drawback in relatively thick microstrip configurations including suspended microstrip patch antennas (MPA) as this may cause less gain, asymmetry in the radiation pattern at higher frequencies within the operational band and increased mutual coupling when these antennas are used in arrays. To address these issues, conducting walls are introduced surrounding the above suspended MPA. The resulting configuration is a wideband cavity backed microstrip patch antenna (WCMPA). The proposed configuration has the widest impedance bandwidth reported for a cavity backed MPA. Measured S11 band- width at -10 dB return loss is from 2.89 GHz to 5.18 GHz (% BW > 55%) with peak gain of 7.6 dBi. The radiation pattern is symmetrical throughout the operational frequencies. The group delay variation is < 1ns and FF is above 0.9. In addition to these performance improvements, the addition of cavity walls provides physical stability to the antenna. Further, a modification to this antenna is investigated to increase its gain. By increasing the lateral dimensions of the cavity the gain is increased from 7.6 dBi to 10.2 dBi. However, this results in an overall footprint of about 1.3 for the entire antenna. The impact of having conducting sidewalls on mutual coupling is also studied for two element arrays in both E-plane and H-plane. A comparison of arrays with and without cavity showed that, the isolation between elements improves by 14 dB with cavity walls for a similar distance between elements in the E-plane. Furthermore, these two-element arrays can be designed for combined peak gain of 11 dBi by choosing appropriate inter-element spacing. Another modification to this antenna is proposed here, where a short horn is mounted on the substrate to increase the overall gain. The gain throughout the frequency range of the antenna can be improved by appropriately choosing the dimensions and are angle of the horn-like structure. Extensive parametric studies have been conducted on this wideband quasi-planar antenna (WQA) to analyze the impact of various design parameters. Measured peak gain for this antenna is 13.2 dBi. This low profile antenna o ers the best gain for similar quasi-planar configurations. The measured impedance bandwidth is 46.7% from 3.1 GHz to 4.6 GHz and the beamwidth is around 35 in both principal planes. While the calculated aperture efficiency is comparable to any other horn antenna, the proposed antenna geometry has a lower height compared to horn antennas and the coaxial transition is similar to those used in planar technologies. In these respects, the proposed quasi-planar an- tenna eliminates the complexity involved in integrating conventional horn antennas for compact wireless terminals. Furthermore, it has been shown that the design can be appropriately modified for di erent frequencies of operation and similar performance is achieved for these designs. One of these designs have been employed in a passive radar developed by the group. The wideband high gain antennas proposed in this research may find several applications in wideband RADAR and imaging. As a case study, we integrated this with a wideband frequency modulated continuous wave (FMCW) RADAR. A WCMPA is used as the transmitter and a two-element array of WCMPA is used as the receiver. A rat race hybrid circuit is integrated with the receiver antennas to obtain sum and di erence patterns in a monopulse configuration. This information can be used to measure the angular position to track a target. 2D and 3D tracking antenna integrated circuits are designed and the results are validated experimentally. Another case study dealt with application of high gain antenna WQA for passive radar since this wideband antenna with large beamwidth helps locate the target with good res- olution. Thermal radiations emitted by the human body in the microwave range are sensed using radiometric system. Experimental results demonstrated capability of the system to detect the presence of a person upto a distance of 2 m where the range improvement may be attributed to the high gain of the WQA used. In summary, the work reported in this dissertation enables the design and analysis of several variants of wideband microstrip antennas with low profile. In addition to extensive simulation studies, some of these designs are experimentally validated and employed in practical wideband radar applications.

The biological membrane is a thin fluidic matrix composed of a lipid bilayer that forms the primary cellular barrier against the extracellular environment. The high-density of embedded proteins and glycosylated molecules confer further complexity with unique specificities for signalling and transport across the membrane. Many pathogenic bacteria have evolved dedicated proteins, pore-forming toxins (PFTs), to form nanoscale ring-like pores on cellular membranes that lead to cell lysis and death. However, it is challenging to study how PFTs function due to the considerable heterogeneity in their assembly intermediates and their complex interaction with lipid components. In this work, we have employed single-particle tracking and single-molecule photobleaching to investigate the assembly pathway of ClyA (a representative αPFT) on supported lipid bilayers (SLB). We show that cholesterol in the membrane greatly enhances the ClyA lytic activity by stabilizing the membrane inserted protomer intermediate and assisting in oligomerization by acting as a ’molecular glue’ between the protomer-protomer interfaces. We identify the role of different membrane-bound motifs of ClyA responsible for defining the initial membrane binding and the large conformational change required to form the pore. In the concluding part, we show how biomolecular assembly of PFTs can be enhanced in complex ways by crowded membrane surfaces using polyethylene glycol (PEG) grafted to lipids as crowders. As the PEG crowder transition from mushroom to an elongated polymer called brush regime, membrane-embedded molecules display correlated changes in their mobility and biomolecular assembly. Overall, this work elucidates how molecular and physical interactions modulate the biomolecular assembly of PFTs on lipid bilayer membranes.

Fiber reinforcement plays an important role in the structure and function of biological materials. Soft connective tissues in human body like artery, heart tissues, skin etc. exhibit anisotropic material responses due to the orientation of fibers along specific directions. At a cellular level, stress fibers in the cytoskeleton play an important role in maintaining cellular shape and influence cell adhesion, migration, and contractility. Cells respond to changes in their mechanical milieu and drive biochemical processes which induce growth and remodeling of the underlying material properties. This results in non-uniform changes to the structural form and function over time. Continuum mechanics-based approaches to address biological growth and remodeling demonstrate an intimate relationship between the cellular level mechanobiology and the underlying tissue properties. How does orientation of fibers affect mechanical response of tissues? How do mechanosensing processes influence cellular growth and remodeling under stretch? I have combined experimental techniques and analytical models, to quantify structure-property correlations in cells and biomimetic materials under stretch. In the first study, we investigated the role of fiber orientations in the mechanics of bioinspired fiber reinforced elastomers (FRE) fabricated to mimic tissue architectures. We fabricated FRE materials in transversely isotropic layouts and characterized the nonlinear stress-strain relationships using uniaxial and equibiaxial experiments. We used these data within a continuum mechanical framework to propose a novel constitutive model for incompressible FRE materials with embedded extensible fibers. The model shows that the interaction between the fiber and matrix along with individual contributions from the matrix and fibers were crucial in capturing the stress-strain responses in the FRE composites. The deviatoric stress components show inversion at fiber orientation angles near the magic angle (54.7°) in the FRE composites. These results are useful in soft robotic applications and in the biomechanics of fiber reinforced tissues. Secondly, we apply these formulations at a cellular level to quantify the role of stress fiber elongation and realignment to changes in cellular morphomechanics under uniaxial cyclic stretch. Cyclic uniaxial stretching results in cellular reorientation orthogonal to the applied stretch direction via a strain avoidance reaction. We show that uniaxial cyclic stretch induces stress fiber lengthening, realignment and increase in cortical actin in fibroblasts stretched over varied amplitudes and durations. Higher amounts of actin and realignment of stress fibers were accompanied with an increase in the effective elastic modulus of cells. We modelled stress fiber growth and reorientation dynamics using a nonlinear, orthotropic, fiber-reinforced continuum representation of the cell. The model predictions match the observed increased cellular stiffness under uniaxial cyclic stretch. As a final study, we have designed and fabricated a microscope mountable cell-stretching device and used it to quantify stretch-induced changes in cellular contractility by measuring the changes cellular traction forces. Our results show a significant 2 increase in cellular traction forces when subjected to prolonged duration of cyclic stretch. Together, these studies demonstrate the importance of uniaxial stretching in mechanotransduction processes which are essential in understanding growth processes and in disease models of fibrosis.

In this thesis, we develop different modelling frameworks to capture the processes of opinion formation and disease spread. The common theme binding them is a nearest-neighbour-based interaction rule; while the closeness of opinions fosters inter-personal interactions, physical proximity facilitates disease spread. Since the nearest-neighbour rules with dynamic local interactions have been shown to enable consensus about the heading of self-propelled particles in a non-equilibrium system, we adapt the Vicsek model. In the first part of the thesis, we discuss two modelling frameworks that are rendered suitable for the study of opinion formation and influence diffusion. We work on the presumption that the agents' opinions are analogous to directions in the opinion space. We assume that the agents with vectorial opinions related to a common subject form groups. We characterise these groups by the distribution of the initial opinions of the agents, and accordingly, they are either Conservative or Liberal. This modelling aspect exclusive to our work is intended to capture the impact of opinion bias of the group on the eventual behaviour. We also account for the heterogeneity among agents and broadly classify them into rigid and flexible. Although this classification does not seem unique, their characterisation differs from the conventional ones. It is based upon the inclination of agents to update one's opinion and susceptibility to the influence of peers with contrasting opinions. Since the interactions among agents of a group on virtual social platforms are oblivious to the physical distances separating them, we assume them to be arranged on a time-varying and directed influence network. In the first model, the agents are placed on directed influence networks based on opinions, individual tolerance and familiarity. In contrast, the network is generated using Watt-Strogatz's model in the second. This arrangement of agents is unlike the uniform random distribution of particles inside the square box. Additionally, not all interactions are equal; some are more important than others and is quantified using inter-personal weights. The two processes, opinion formation and evolution of the network, in tandem, give rise to several behavioural patterns. We evaluate trends in the behaviour of groups upon varying several model-specific parameters through extensive simulations. In the second part of this thesis, we discuss two other modelling frameworks proposed to capture trends in disease spread due to human mobility. While the opinion models borrow the directional attributes of particles from the original formulation of the Vicsek model, the motion of the self-propelled particles is of interest in the context of the spread of infectious diseases. However, the rules governing the movement of particles cannot describe the human movement straight away, thereby necessitating suitable modifications. We propose an agent-based framework equipped with a population mixing algorithm and stochastic disease transmission and evolutionary dynamics. The population mixing algorithm incorporates the simple rules governing the movement of particles in the Vicsek model, together with collision avoidance and goal following to mimic human motion. This algorithm generates human motion patterns ranging from short-distance and long-distance movement to activity-driven mobility. On the other hand, the disease models characterise the health condition of agents using three crucial traits of the disease, (1) infection status, (2) severity and (3) awareness, endowed with age-dependent probabilities for transmission, progress and recovery of the disease. The representative population, motion model and stochastic age-specific disease transmission dynamics are used to evaluate different scenarios. The scenarios are combinations of different motion patterns of the agents; we have chosen them to reflect restricted human mobility during phases of the COVID-19 outbreak from the past.

In the first part of the thesis, the results of our studies on the classification of phonological categories in imagined words are presented. We have investigated whether there are any statistically significant differences in the mean phase coherence values in six cortical regions when the participants imagined uttering nasal and bilabial consonants. The cortical regions considered are prefrontal, premotor, motor, somatosensory, sensorimotor and auditory cortices, which are normally involved in speech production. We have observed statistically significant differences in the MPC values in all the six cortical regions in the beta band and in the motor cortex alone in the gamma band. The results obtained support the dual stream prediction model for imagined speech. Further, we have tried to classify the speech imagery EEG epochs based on the phonological category of the prompt using a shallow neural network. We have obtained an accuracy of 84.9% in the classification task when beta band MPC values are used. This is around 12% higher than the benchmark result on this dataset. The accuracies of our model dropped to 59.0% and 69.1%, respectively when only alpha or gamma band MPC values are used. The fact that EEG carries correlates of the phonological categories of the imagined phonemes can help in designing better prompts for a speech imagery-based BCI system. In part two of the thesis, we have investigated as to whether we can classify the imagined prompt from the EEG recorded during speech imagery. For this, we have developed three different architectures. All these architectures address the problem of lack of sufficient training data. In the first one, which we call the CSP-based architecture, the issue of limited training data is addressed by treating the features extracted from selected EEG channels as distinct inputs to the classifier. Common spatial pattern (CSP) is used for channel selection. The primary classifier is a deep neural network (DNN) with four hidden layers whereas the secondary classifier is a majority voting classifier. The second model, which we call the TL-based architecture handles the problem of limited training data by using data augmentation and transfer learning (TL). In this architecture, MPC and MSC values from the alpha, beta and gamma bands are arranged as a 3D data, and are input to a ResNet50-based classifier, where ResNet50 is used as a fixed feature extractor. The third one, which we call the LSTM-based architecture employs overlapping window-based data augmentation to increase the amount of data, which is possible because the ASU dataset involves repeated imagination by the subjects. The LSTM-based architecture uses CSP for feature extraction, linear discriminant analysis (LDA) for dimensionality reduction and long short-term memory (LSTM) network as the primary classifier and a majority voting classifier as the secondary classifier. All the three architectures have achieved above chance-level accuracies on the publicly available ASU speech imagery EEG dataset. The TL-based and the LSTM-based architectures have achieved average accuracies of 92.8% and 85.2%, respectively, for the classification of "short-long" words, which are better than the state-of-the-art. Although the LSTM-based architecture has lower accuracy than the TL-based architecture, the former can classify a 5 s EEG epoch in less than 110 ms, making it a suitable algorithm for online BCI systems. We have also performed ablation studies to identify the optimal number of EEG channels in the case of the CSP-based architecture and the optimal EEG frequency band in the case of the TL-based and the LSTM-based architectures. The optimal number of EEG channels in the case of CSP-based architecture is nine whereas the optimal EEG band for both the TL-based and the LSTM-based architectures is the gamma band. In the last part of the thesis, we have proposed three architectures for classifying the altered state of consciousness during Rajayoga meditation from the resting state. Classification of Rajayoga meditation is challenging since it is probably unique in that the practitioners meditate with their eyes open. The first model, which we call the CSP-LDA architecture, uses CSP for feature extraction and LDA as the classifier. The second one, which we call the CSP-LDA-LSTM architecture is similar to the LSTM-based architecture used for decoding imagined speech. The third model, which we call the SVD-DNN architecture uses singular value decomposition (SVD) for choosing the relevant subspace of the signal and DNN for classification. The best intra-subject classification performance of 98.2% is obtained using the CSP-LDA-LSTM architecture whereas the best inter-subject performance of 96.4% is obtained using the SVD-DNN architecture. Both these architectures are able to capture subject-invariant features and can be deployed for grading the depth of meditation and for classifying other altered states of consciousness such as disorders of consciousness and hypnosis.

Landslides are major natural disasters which pose a significant risk to lives and infrastructure globally. As urbanization is increasing due to the increasing population in mountainous regions, the risk due to landslides draws grave concern owing to the damage and disruption since the last decade. Hence, regional-scale and local-scale landslide analyses are necessary to reduce the impact of landslides on lives and infrastructure; and efficiently prevent the landslide risk. The landslide analysis must be conducted separately for different triggering factors as the slope materials follow different failure mechanisms under various triggering factors. In this thesis, efficient models for landslide analysis at regional-scale as well as local-scale are developed, focusing mainly on understanding the relationship between actuating factors and slope failure events; and the slope failure mechanism. These models are developed for different causal factors, including rainfall and earthquakes. For regional scale analysis of landslides, a methodology is introduced for landslide mapping, which aims at the accurate and faster demarcation of slope areas affected by landslides. Fast and accurate landslide mapping forms the basis of research and practice of landslide hazard and risk analysis. A systematic framework is also presented to estimate landslide hazard at regional-scale using previous landslide incidents and establish a relationship between different triggering factors and landslide incidents. Further, a predictive model is proposed to estimate the evolution of seismically induced slope displacement with time. The developed model is based on the dynamic response surface method (DRSM). Various methodologies are proposed for local-scale analysis of slope systems under various causal factors, i.e., rainfall and earthquakes to estimate the uncertainty in soil parameters using probabilistic methods and machine learning algorithms. Several algorithms are developed and implemented in Python and MATLAB to add new features that introduce complexity in the numerical models and interface the deterministic and probabilistic analysis. Overall, it is anticipated that the work presented in this thesis will facilitate guidelines for 1) landslide inventory and hazard mapping due to rainfall infiltration, 2) estimation of evolution of seismically-induced slope displacement with time using predictive models, and 3) probabilistic back analysis of slope system under various causal factors.

Sedimentation – settling of particles in a fluid- is observed in nature like rain droplets and dust particles in the atmosphere, and in a variety of industrial processes, like to clarify liquid as well as separate particles of different size and density. The simplest system is the sedimentation of mono-disperse particles in a vast stationary fluid. The main parameters are Particle Reynolds Number (〖Re〗_p based on terminal velocity), ratio of particle density to fluid density (ρ_p/ρ_f ), particle volume fraction (φ), and container dimensions for experimental and numerical methods. Two main questions arise: what is the mean settling velocity (V_g), and nature and values of fluctuation in particle velocity (V^/), and how do they compare with the terminal velocity (V_t) of an isolated particle in an infinite fluid. At low particle Reynolds number, V_t is given by the Stokes law. Experiments have been typically performed in a tank containing the fluid with particles initially well mixed and tracking the motion of the particles or performing PIV to obtain mean settling velocity (V_g), fluctuating particle velocities (V^/) etc. The main focus of these studies has been to correlate different parameters like mean settling velocity, velocity fluctuation, correlation length with volume fraction, and dimension of the container. Though this apparently simple problem has been studied theoretically, experimentally, and numerically over many decades, there are several unanswered questions. For example, the experimental results for velocity fluctuations do not agree with the theoretical predictions. The origin of scalings for velocity fluctuations are unclear. In our study, we try to address some of these issues using a new type of experiment. In our experiment, particles are fed at a constant rate at the top and allowed to settle in a long vertical tube containing quiescent fluid, closed at the bottom. The constant particle feed rate ensures mean steady particle settling in contrast to the standard experiments done previously where the settling process is transient. Also, the long vertical extent of the tube ensures Axial Homogeneity. We have done two types of experiments: water droplets (10 μm, 〖Re〗_p~〖10〗^(-3)) falling in the air, and spherical glass beads (110 μm, 〖Re〗_p~1 ) settling in water. The estimated volume fractions for the former is 〖10〗^(-7) and for the latter, it is〖 10〗^(-3). For the droplet-air system, the tube dimension is 5×5 〖cm〗^2 and for the particle-water system, three tube dimensions (4×4 〖cm〗^2 , 5×5 〖cm〗^2, 7×7 〖cm〗^2 ) have been used. Experiments have been done with different mass flux values. We have used high-speed imaging illuminated by a sheet of laser light to visualize the particle motion fields and Particle Image Velocimetry (PIV) to get the mean and fluctuating particle velocities and the spatial and temporal correlations. We have observed a variety of sedimentation-induced convective motions, including regions of particle patches moving upwards. The conditions at the tube end significantly alter the convective patterns and the fluctuating velocities. Convective motions, though hypothesized to exist, have not been observed in earlier experiments. We present results for the mean and fluctuating velocities and spatial and temporal correlations of the velocity fields for the range of mass fluxes and different tube dimensions. Besides the existence of convective motion, the main findings are: the mean settling velocity varies between 0.80-1.1 V_t. The fluctuating velocities are in the range 0.30-0.80 V_t and strongly depend on mass flux. Correlation lengths scale with tube width. We present these results in a non-dimensional form which suggest different scaling laws.

Environmental issues caused by the non-biodegradability of synthetic thermoplastics have increased interest in more environmentally friendly alternatives that should be derived from renewable resources. This work focuses on producing green composites and biofilms by synthesizing nanocellulose (NC) from readily available natural and renewable sources like cellulose. The term NC refers to cellulose that has been reduced to the nanoscale. NC is used to describe a variety of cellulose nanostructures, including Micro Crystal Cellulose (MCC), Cellulose Micro Fibrils (CMF), Cellulose nanocrystals (CNC), and Cellulose nanofibers (CNF). Because of its versatility, low toxicity, biodegradability, and carbon neutrality, nanocellulose has attracted considerable attention for generating new materials in several industrial, technological, and biological applications. Nanocellulose has a sizable global market and demand because of these numerous applications. One of the challenges for commercial and industrial production of nanocellulose is finding a source of cellulose that is economically viable, abundant, and sustainable. Bacteria, plants (including trees, shrubs, and herbs), algae, and animals (Tunicates) are the primary sources of nanocellulose. In this study, cellulose nanofibers are synthesized from the bamboo pulp through TEMPO oxidation, high- pressure homogenization, and ultrasonication treatment. Characterization of CNF was done using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), X-ray powder Diffraction (XRD), and Dynamic Mechanical Analysis (DMA). After characterization, the synthesized NC was evaluated by turning it into films and using it as reinforcement to prepare composites. Bamboo particles are reinforced with CNF suspension to prepare composites using the hot press (HP) and oven-dried (OD) methods. The mechanical properties of these fabricated composites are investigated, such as modulus of elasticity (MOE), modulus of rupture (MOR), and interfacial strength. The properties of the NC and composites are compared for 1st , and 3rd homogenization passes. The mechanical characteristics of the film have been investigated using uniaxial tensile and nanoindentation experiments. The morphological characteristics examined using SEM and TEM showed that the cellulose in the bamboo pulp is reduced to the nanoscale, confirming the formation of CNF. The average diameter of nanofibres of bamboo calculated from TEM images was 8 to 10 nm, respectively. The CNF analyzed using FTIR spectroscopy exhibited the presence of functional groups and their vibrational modes. Further, crystal size (CS)andcrystallinity index (CI) of CNF synthesized from different homogenization passes were calculated usingthe XRD technique. Properties like viscosity, storage modulus, and loss modulus were determined from the rheological characterization, which confirmed the non-Newtonian behavior of pure NC suspension. In addition to morphology analysis, mechanical properties of NC films computed from uniaxial tensile test and nanoindentation showed a 58 MPa tensile strength and a 0.2228 GPa hardness, respectively. Also, dynamic mechanical properties like storage modulus, loss modulus, and tanδ were determined to examine the viscoelastic behavior of the film as a function of temperature. However, from the results, no phase transformation was noticed until 75°C. Furthermore, composites reinforced with 1 % weight consistency of CNF showed an increase in interfacial strength, MOE, and MOR as a function of density. The MOE increased 9 times for HP samples compared to the OD samples. MOR nearly increased by a factor of 4, and the energy-absorbing capacity also increased to 182% in the case of HP samples. From these results, it can be inferred that hot-pressing was an effective manufacturing method than oven drying as it removes maximum moisture content and enhances adhesion between bamboo powder and CNF. Therefore, it can be concluded from the results that nanocellulose derived from bamboo has highly entangled fibers, which can be transformed into a film and used in packaging and biomedical applications. Also, bamboo CNF acts as a binding agent to prepare composites. Hence, the concept of using matrix and reinforcement derived from the same natural sources can be used to make green composites. Consequently, there is a great deal of potential for the TEMPO-oxidized bamboo celluloses to develop into ground-breaking nanotechnology that will connect the domains of biomass and forest refinement with cutting-edge high-tech research.

Efficient preparation and characterization of layered materials and their van der Waals heterojunctions lay the foundation for various opportunities in both fundamental studies and device applications. The vast library of 2D materials displays a range of electronic properties, including conductors, semiconductors, insulators, semimetal, and superconductors, and shows strong light-matter interaction. The fact that each layer in the layered material is bonded via van der Waals interaction opens up the possibility of assembling different layers arbitrarily without any consideration over the precision of lattice match- ing. This unique stacking with one-atomic-plane precision can unfold diverse van der Waals heterostructure devices by efficiently engineering its energy band alignment. This paves a path to design novel devices such as solar cells, photodetectors, light-emitting diodes and transistors. In this thesis, our motivation is to explore the electronic and optoelectronic characteristics of 2D materials and their heterojunctions. We focus on designing 2D heterostructures for the multi-functional devices including electronic (diode/transistor) and optoelectronic (highly sensitive photodetection) applications. As the initial step, we realized SnSe2 based photoconductor which shows a very high responsivity of 10^3 A/W at 1 mV voltage bias. We investigated the role of trap states present at the channel- substrate interface on the observed gain mechanism in typical planar 2D photoconductors. Next, in order to improve the speed for a photodetector, we designed a heterostructure composed of ITO/WSe2/SnSe2 vertical heterojunction. This novel design helped us to achieve a large responsivity at near IR region while maintaining high operational speed. We achieved a high responsivity of more than 1100 A/W and fast transient response time in the order of 10 us. Considering the interest of broad band detection, we then fabricated a graphene-absorption-based photodetector where graphene can act as the absorbing medium, utilizing its zero-band gap nature. The absorbed photo-carriers are vertically transported in a fast time scale to a floating MoS2 quantum well, providing photo-gating. This structure exhibited the responsivity of 4.4 * 10^6 A/W at 30 fW incident power which is higher than that of any reported graphene absorption-based photodetectors. As a continuation of the study of heterostructure transport characteristics, we realized a backward diode with WSe2/SnSe2 structure which exhibits an ultra-high reverse recti cation ratio of 2.1 *10^4 with an impressive curvature coefficient of 37 V^(-1). Finally, we proposed a novel methodology for the extraction of Schottky Barrier Height (SBH) using a vertical heterojunction of multilayer transition metal dichalcogenide with asymmetric contacts which allow easy and direct quantitative evaluation of SBH for two contacts simultaneously.
Visvesvarayya PhD Scheme

Directed testing is a technique to analyze user-specified target locations in the program. It reduces the time and effort of developers by excluding irrelevant parts of the program from testing and focusing on reaching the target location. Existing tools for directed testing employ either symbolic execution with heavy-weight program analysis or fuzz testing mixed with hand-tuned heuristics. In this thesis, we explore the feasibility of using a data-driven approach for directed testing. We aim to leverage the data generated by fuzz testing tools. We train an agent on the data collected from the fuzzers to learn a better mutation strategy based on the program input. The agent then directs the fuzzer towards the target location by instructing the optimal action for each program input. We use reinforcement learning based algorithms to train the agent. We implemented a prototype of our approach and tested it on synthetic as well as real-world programs. We evaluated and compared different reward functions. In our experiments, we observe that for simple synthetic programs, our approach can reach the target location with fewer mutations compared to AFL and AFLGo that employ random mutations. However, for complex programs, the results are mixed. No one technique can perform consistently for all programs.

Remediation of the existing MSW dumpsites has received considerable attention these days and there is an urgent need to address this issue in order to maintain the over hygiene of the urban environment. An approach consisting of experimental and numerical studies to understand the behavior of the waste to be remediated is essential in this regard. In this study, laboratory scale experimental studies were carried out to characterize the mechanically and biologically treated (MBT) waste of Bangalore city. The physical composition, index, engineering and biochemical properties of the waste which are essential for the design of a bioreactor landfill were estimated. The moisture retention characteristics (MRC) and the hydraulic conductivity of the waste influence the design and performance of the leachate recirculation system in a bioreactor landfill. Estimation of MRC and hydraulic conductivity of waste were carried out under varying conditions of overburden stress and density. Their behavior in the fresh and degraded waste was also estimated to predict its influence on LRS as a function of time. Laboratory scale bioreactor studies to assess the biodegradability of the MBT waste under aerobic and anaerobic conditions were carried out. The performance of the bioreactors in terms of the organic content of waste, the gas generated, leachate characteristics and the settlement were evaluated for around 574 days. Experimental studies representing the methane oxidation process in the biocover systems were studied using anaerobically digested MBT waste as the cover material by means of column studies. The modeling studies consisted of the validating the experimental results of the laboratory scale anaerobic bioreactor using a Landfill Degradation and Transport model (LDAT). Parametric study was conducted using the model to study the influence of various parameters such as the growth rates, initial biomass concentration, pH, moisture content, recirculation rate, ambient temperature, heat transfer coefficients on the biogas production. An approach to incorporate the influence of temporal changes on the performance of the LRS due to variations in the MRC and hydraulic conductivity of waste is proposed. The methodology was verified by performing the hydraulic performance of the LRS using HYDRUS-2D model. The application of both the experimental and numerical studies for remediating an existing MSW dumpsite in Bangalore City is given. This involved studying the existing site conditions, modeling studies to understand the influence of installation of the LRS using HELP model, design of the leachate collection and recirculation system and the control of landfill gas emissions using biocover systems. The overall aim of the study was to explore the possibilities of implementing sustainability practices in landfilling.

The ferromagnetic (FM) material finds its applications due to the property of spontaneous magnetization. An FM object can hold its state of magnetization unless any external stimuli change it. The easy manipulation of its state by an external magnetic field or spin current manifests FMs usability for digital data storage and logic devices. The efficiency and speed of magnetic data storage and logic devices should be optimized to match the existing semiconductor devices. This thesis has mainly proclaimed the fundamental dependence of magnetism on the composition of the layers and geometry, established the nexus to understand the underlying physics to identify the promising candidates for data storage applications in the future. In the first work, systematically modifying the strength of the induced moment in the bottom Pt layer by the thickness variation of the adjacent Ta buffer layer, the Pt spin depth profiles in Ta/Pt/Co/Pt multilayers induced by the magnetic proximity effect due to the adjacent Co layer have been quantified. The Pt spin depth profiles by hard x-ray resonant magnetic reflectivity measurements have been identified, which have been carried out at the third-generation synchrotron PETRA III at DESY. It has been found that the top Pt layer has a comparable induced magnetic moment with the bottom one. The induced magnetic moment in the bottom Pt layer reduces with increasing Ta thickness. Grazing incidence x-ray diffraction measurements have been carried out to show that the Ta buffer layer induces the growth of Pt(011) rather than Pt(111) which in turn reduces the induced moment as confirmed by detailed density functional theory calculations presented in our manuscript. In the second work, the tilt in magnetic anisotropy and strength of the interfacial Dzyaloshinskii-Moriya interaction (iDMI), in the Pt/Co interface of the Pt/Co/Pt trilayers simultaneously have been quantified. The differential polar-Kerr microscopy technique in the creep regime of the domain wall motion for these measurements has been used. It has been found that an oblique angle sputter deposition technique results in a slight tilt of magnetic anisotropy from the film normal (quasi-perpendicular magnetic anisotropy). The effective in-plane field at the domain wall due to iDMI has been determined by decomposing the symmetric and asymmetric contributions of the domain wall motion. Furthermore, the asymmetric contribution has been decomposed into two contributions due to the tilted magnetic anisotropy and the exponentially decaying chiral damping. The collective coordinate model for a system with iDMI and quasi-PMA has been developed to study the nature of the asymmetric contribution owing to the tilted anisotropy and a functional form of the total asymmetric contribution has been determined from the simulation result. In the third work, the effective strength of the iDMI, in the Ta/Pt/Co/Au multilayers has been estimated using the field-induced domain wall motion and spin-orbit torque efficiency estimation studies. The current-induced magnetization switching phase diagram has also been constructed. It has been found that from the phase diagram, the effective strength of the iDMI can be quantified. Multilayers with the heavy metal Pt and the novel metal Au on either side of the ferromagnetic Co layer break the structural inversion symmetry, enhancing the iDMI strength.

Carbon nanotubes (CNTs) have been extensively researched for diverse applications in recent years. In the present work, the use of low frequency non-uniform alternating electric fields to manipulate the alignment behavior of CNTs in an epoxy matrix has been explored for use in structural applications. CNT alignment was accomplished based on the dielectrophoresis (DEP) principle. The alignment methodology was developed and CNT alignment effectiveness was assessed through in-situ current measurements and polarized Raman spectroscopy data in addition to optical microscopy. Electrical and mechanical characterization studies were then performed on the nanocomposites containing aligned CNTs and the improvement in properties with respect to the control samples was evaluated. Further, the alignment methodology was extended to the case of hierarchical composites with geometric discontinuities. The effect of CNT orientation on the open hole tensile behavior of uni-directional glass fiber-epoxy hierarchical composites containing CNTs was evaluated as a typical case of structural loading. Different electrode configurations were employed to control CNT orientation locally around the hole with respect to the loading direction. The results indicate that altering CNT orientation locally around the hole influences the overall response of the hierarchical composite. The thesis then discusses multiphysics simulations performed to model CNT behavior in epoxy resin considering time varying non-uniform electric fields and matrix viscosity. Considering a nanocomposite plate with a rectangular filleted notch subjected to tensile loading as a case study, numerical models were developed to enable electrode configuration design to control CNT orientation around the notch to mitigate stress concentration effects. Experimental studies were then performed with inputs from simulation studies facilitating the development of electrode set-up. The results indicate a significant enhancement in notched strength of the nanocomposite plates. Numerical and experimental studies on the development of nanocomposites containing varying concentration of aligned CNTs are also presented.