Thèses : « Nonlinear interfaces »

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Poznic, Milan. « Nonlinear Interaction Between Ultrasonic Waves and Cracks and Interfaces ». Doctoral thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4604.

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The subject of this thesis is the development of new ultrasound inspection techniques for detection of cracks that are smaller than the wavelength of the inspecting wave and the characterization of cracks in fluid-filled pipes as either surface-breaking or subsurface. The spectrum of the scattered field of a partially closed crack comprises harmonic components not expected to be found in the case of linear scatterers such as pores or inclusions. Paper A presents an experimental investigation into the linear reflection and generation of the 2nd harmonic component following the incidence of an ultrasonic wave onto a dry or water-confining interface formed by elasto-plastic steel-steel surfaces in contact. The results indicate that water has an unexpected effect on the reflection, at low interfacial pressures, suggesting that fluid mediated forces play a role not accounted for in current models. The level of the generation of the 2nd harmonic measured provides support for further development of the technique for detection of dry, partially closed cracks or fluid-filled, nearly open cracks. A theoretical model describing the nonlinear scattering of acoustic waves by surface-breaking cracks with faces in partial contact is presented in Paper B. Both linear and nonlinear response of the crack are shown to be the largest for a SV wave incident on the surface containing the crack at an angle just above the critical angle for longitudinal waves. A method which provides information on whether a fracture is surface-breaking or subsurface has been modelled and its optimal experimental set-up examined in Paper C. The main assumption of the model is that water carried by pressurized pipes infiltrates and fills a surface-breaking crack, while a subsurface crack is dry. The model simulates an inspection in which the modulation technique is employed and the surface hosting the crack is not accessible. A parameter, constructed with signals recorded in backscattering configuration during a modulation cycle, is examined and shown to provide a clear criterion to distinguish subsurface from surface-breaking cracks when a SV wave at 45 degree incidence is employed as a probe. Finally, in Paper D the modulation technique is experimentally tested on steel beams that host surface-breaking fatigue cracks. The method is shown to be a successful tool to distinguish a dry from a fluid-filled crack. Furthermore, it is revealed that the dynamics of the fluid needs to be accounted for in a more accurate simulation tool.
QC 20100906

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Poznić, Milan. « Interaction between ultrasonic waves and nonlinear cracks and interfaces / ». Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4087.

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Poznić, Milan. « Nonlinear interaction between ultrasonic waves and cracks and interfaces / ». Stockholm : Farkost- och flyg, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4604.

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Shelford, Leigh. « Ultrafast nonlinear optical studies of multilayered thin films and interfaces ». Thesis, University of Exeter, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506859.

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Van, Wyck Neal Edward. « MULTIPHOTON SPECTROSCOPY OF THIN FILMS AND SURFACES (NONLINEAR, WAVEGUIDES, INTERFACES) ». Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/291294.

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Ojaghlou, Neda. « Adhesion at Solid/Liquid Interfaces ». VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6079.

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The adhesion at solid/liquid interface plays a fundamental role in diverse fields and helps explain the structure and physical properties of interfaces, at the atomic scale, for example in catalysis, crystal growth, lubrication, electrochemistry, colloidal system, and in many biological reactions. Unraveling the atomic structure at the solid/liquid interface is, therefore, one of the major challenges facing the surface science today to understand the physical processes in the phenomena such as surface coating, self-cleaning, and oil recovery applications. In this thesis, a variety of theory/computational methods in statistical physics and statistical mechanics are used to improve understanding of water adhesion at solid/liquid interfaces. In here, we addressed two separated, but interconnected problems: First, we consider water adhesion on fiber/surface, responsible for the emergence of droplet residue upon droplet detachment. In this project, we study the mechanism of water droplet detachment and retention of residual water on smooth hydrophilic fibers and surfaces using nonequilibrium molecular dynamics simulations. We investigate how the applied force affects the breakup of a droplet and how the minimal detaching force per unit mass decreases with droplet size. We extract scaling relations that allow extrapolation of our findings to larger length scales that are not directly accessible by molecular models. We find that the volume of the residue on a fiber varies nonmonotonically with the detaching force, reaching the maximal size at an intermediate force and associated detachment time. The strength of this force decreases with the size of the drop, while the maximal residue increases with the droplet volume, V, sub-linearly, in proportion to the V2/3. Second, we address the adhesion on conducting graphene. We improved the graphene model by incorporating the conductivity of graphene sheet using the fluctuating charge technique of Constant Potential Molecular Dynamics (CPMD). We evaluated the wettability by measuring the contact angle of cylindrical water drops on a conducting graphene sheet. We found that the CA of a water droplet on a graphene sheet supported by water is lower than in the absence of water under graphene. Our calculations reveal effective attractions between partial charges of equal sign across the conducting graphene sheet. Attractive correlations are attributed to the formation of the highly localized image charges on carbon atoms between the partially charged sites of water molecules on both sides of graphene. By performing additional computations with nonpolar diiodomethane, we confirm that graphene transmits both polar and dispersive interactions. These findings are important in applications including sensors, fuel cell membranes, water filtration, and graphene-based electrode material to enhance the supercapacitor performance. A challenge for future work concerns dynamic polarization response of wetted graphene at alternating (AC) field condition.

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Lombardi, Giulia. « Unified nonlinear electrical interfaces for hybrid piezoelectric-electromagnetic small-scale harvesting systems ». Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI101.

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Ce travail de recherche présente des interfaces électroniques non-linéaires pour des systèmes hybrides de récupération d'énergie combinant des transducteurs piézoélectriques et électromagnétiques. Ces systèmes ont reçu un grand intérêt en raison de leur capacité à convertir les vibrations mécaniques en énergie électrique suffisante pour alimenter des capteurs à faible puissance. Afin d'alimenter ces appareils microélectroniques, une fois l'énergie convertie, une extraction efficace et intelligente doit être mise en place avec une unité dédiée. Les interfaces hybrides non-linéaires proposées dans ce travail, visant à inclure autant de parties électroactives que possible dans le même circuit, permettent une augmentation de la puissance de sortie finale des microgénérateurs concernés, ainsi qu'une solution pour obtenir une valeur commune de charge optimale, même si chacun des éléments traités présentent des principes de fonctionnement et des valeurs de charge optimale différents. Une première solution est dérivée du SSHI (Synchronized Switch Harvesting on Inductor) et se base sur la technique de commutation synchronisée. Cette méthode vise à remplacer l'inductance passive dans l'interface SSHI par un système électromagnétique actif, conduisant à une interface de microgénérateurs entièrement actifs et augmentant la puissance de sortie finale. Une deuxième solution est issue de la combinaison des techniques SECE (Synchronous Electric Charge Extraction) et SMFE (Synchronous Magnetic Flux Extraction), respectivement développées pour les systèmes piézoélectriques et électromagnétiques. Son principe de base consiste à transférer l'énergie de l’élément piézoélectrique vers le transducteur électromagnétique, et ensuite à extraire l'énergie du système électromagnétique, préalablement amplifiée par le transfert de charges issues du dispositif piézoélectrique. La stratégie consistant à inclure autant de parties électroactives que possible dans la même interface électrique ouvre de nouvelles possibilités de combiner plusieurs systèmes électroactifs, constituant des récupérateurs d'énergie hybride, sans inclure des étages supplémentaires dans les circuits, ce qui permet de maintenir une relative simplicité sans perte de puissance significative
In this research work, electronic nonlinear interfaces for hybrid energy harvesting systems combining piezoelectric and electromagnetic transducers are presented. Such systems have received great attention due to their ability to detect mechanical vibrations and convert them into electrical energy sufficient to power low-power sensors. In order to supply these microelectronic devices the generated sinusoidal signal needs to be rectified into a constant DC voltage. In other words, once the energy is converted, a proper and smart extraction of such energy needs to be implemented with a dedicated unit. The proposed nonlinear hybrid interfaces developed in this work, aimed at incorporating as much as electroactive parts as possible in the circuit, not only increase the final output power of the involved transducers but also provide a solution for obtaining a common optimal load value, despite dealing with elements singularly presenting different working principles and values of optimal load, without the use of additional load adaptation stages. A first solution is derived from the previously developed SSHI (Synchronized Switch Harvesting on Inductor) and based on the Synchronized Switching technique. This method aims at replacing the passive inductor in the SSHI interface with an active electromagnetic system, leading to an all-active microgenerators interface and increasing the final output power. A second solution is derived from a combination of the SECE (Synchronous Electric Charge Extraction) and SMFE (Synchronous Magnetic Flux Extraction) techniques. Its main principle consists of transferring the energy from the piezoelectric to the electromagnetic transducer and then extracting the boosted energy from the electromagnetic system. The strategy of including as much as electroactive parts within the same electrical interface open many different possibilities of interfacing more than one electroactive system, constituting hybrid energy harvesters, without including extra circuit stages, thus maintaining a relative simplicity without high power losses

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Costard, Rene. « Ultrafast dynamics of phospholipid-water interfaces studied by nonlinear time-resolved vibrational spectroscopy ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/16955.

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Geladene Phosphatgruppen sind von wesentlicher Bedeutung für die Hydratisierung von Phospholipiden und DNS. Hydratisierungshüllen spielen eine wichtige Rolle für die Ausbildung und Stabilisierung von Zellmembranen und der DNS-Doppelhelixstruktur. In dieser Arbeit werden elementare Phosphat-Wasser-Wechselwirkungen in einem Phospholidmodellsystem – sogenannten inversen Mizellen - mit variablen Wassergehalt zwischen einem und 16 Wassermolekülen pro Phospholipid untersucht. Die schnellsten Prozesse an den Grenzflächen wie z.B. Phosphat-Wasser-Wasserstoffbrückendynamik und Schwingungsenergieumverteilung finden auf einer Femto- bis Pikosekundenzeitskala statt. Molekulare Schwingungen sind sensitive lokale Sonden für die Struktur und Dynamik. Deshalb ermöglicht Femtosekunden-Schwingungsspektroskope, insbesondere zweidimensionale Infrarotspektroskopie (2D IR) und Pump-Probe-Spektroskopie in einem breiten Spektralbereich, die Dynamik mikroskopischer Phosphat-Wasser-Wechselwirkungen in Echtzeit zu beobachten. Wir zeigen die ersten zweidimensionalen Infrarotspektren von Phosphat-Streckschwingungen, die unabhängig vom Wassergehalt grenzflächensensitive Sonden darstellen. Solche Spektren belegen, dass die schnellsten strukturellen Fluktuationen der Phospholipid-Kopfgruppen auf einer 300-fs Zeitskala ablaufen, wohingegen die Phosphat-Wasser-Wasserstoffbrücken länger als 10 ps bestehen bleiben. Die Schwingungsdynamik intramolekularer Wasserschwingungen, d.h. der OH-Streck- und Biegeschwingung, zeigen, dass sich kleine Wasserpools um die Phosphatgruppen bilden, sobald drei oder mehr Wassermoleküle pro Phospholipid vorliegen. Solche Wasserpools dienen als effiziente Wärmesenken für intramolekulare Schwingungen des Wassers und der Phosphatgruppen.
Charged phosphate groups are the major hydration sites of biomolecules such as phospholipids and DNA. Hydration shells play a key role in the formation and stabilization of cell membranes and the DNA double helix structure. Here, we introduce phospholipid reverse micelles with variable water content (between one and sixteen water molecules per phospholipid) as a model system to study elementary phosphate-water interactions. The fastest processes at phosphate-water interfaces , e.g. hydrogen-bond dynamics and vibrational energy transfer occur on a femto- to picosecond time scale. Since molecular vibrations are sensitive local probes of the structure and dynamics, the use of femtosecond vibrational spectroscopy, in particular two-dimensional infrared spectroscopy (2D IR) and pump-probe spectroscopy in a broad spectral range, allow for the observation of microscopic phosphate-water interactions in real time. We present the first two-dimensional infrared spectra of phosphate stretching vibrations that represent true interfacial probes independent of the hydration level. Such spectra reveal that the fastest structural fluctuations of phospholipid headgroups occur on a 300-fs timescale whereas phosphate-water hydrogen bonds are preserved for >10 ps. Vibrational dynamics of intramolecular water vibrations, i.e., the OH stretching and bending modes show that small water pools around the phosphate groups form when three or more water molecules per phospholipid are present. Such water pools act as efficient heat sinks of excess energy deposited in intramolecular vibrations of water or the phosphate groups.

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RIZZOGLIO, FABIO. « Nonlinear dimensionality reduction for human movement analysis with application to body machine interfaces ». Doctoral thesis, Università degli studi di Genova, 2021. http://hdl.handle.net/11567/1038287.

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For my PhD project, I set to explore how a nonlinear dimensionality reduction (DR) technique - autoencoder networks (AEs) - can identify low-dimensional latent manifolds of movement data. The thesis focuses on the application of this technique to body machine interfaces (BoMIs). I begin by comparing nonlinear AEs to Principal Component Analysis (PCA), a linear DR method, in capturing essential information of kinematic signals, including hand gestures and object manipulations, as well as electromyographic signals (EMG) obtained from unconstrained movements of shoulders and arms. AEs exhibited higher performance than PCA in the reconstruction of hand kinematic and EMG data from a latent manifold. Therefore, a non-linear DR method has the potential to provide a more effective coding platform for human-machine interfaces (HMIs). I therefore investigated how the choice of hyperparameters (e.g., type of activation function, number of hidden layers, etc.) affected the shape of the latent manifold, particularly its local curvature, and whether these potential effects were correlated with changes in reconstruction performance. To gain more consistent insights on the structure of the nonlinear latent manifold, I developed a visual tool based on classic concepts of cartography. This display offers a direct and intuitive assessment of the AE’s nonlinear transformation. I was able to demonstrate that the cartographic approach makes the visible structure of the latent manifold stable and independent of the AE’s training parameters. As such, the proposed approach is a step toward defining a unique latent manifold. After analyzing the properties of both linear (PCA) and nonlinear (AE) DR techniques, I focused on their applications within the control-scheme of a BoMI. First, I aimed at providing BoMI users with the possibility to switch seamlessly between movement and EMG control. Such approach is essential to utilize the BoMI as a therapeutic tool for promoting recovery of muscle control after neurological injury. In the clinical context it is essential to adapt the operation of the BoMI to the evolving state of its users. My guiding hypothesis for this purpose is that the operation of the interface is facilitated if the BoMI forward map is updated online to match the evolving latent manifold of the user’s motions. Results show that this adaptive approach increased the representational efficiency of the interface and significantly improved users’ task-related performance. As an extension of the application of AE-based BoMI, I developed a non-linear BoMI designed to control an assistive 4D virtual robotic manipulator and tested the interface on a cohort of unimpaired participants, who successfully acquired a high level of robot control. To conclude, I investigated whether AEs can represent and estimate motor learning during the operation of a BoMI. This final study demonstrates that in fact this nonlinear method is effective to accurately track users’ learning process.

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Aanensen, Nina Sasaki. « Nonlinear Laser-induced Deformations and Forces at Liquid-Liquid Interfaces near the critical Point ». Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14264.

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The theory of laser-induced liquid-liquid interface deformation has been presented and used to derive a differential equation describing the shape of the deformation. The differential equation has been investigated and solved numerically, and the results have been compared to the experimental results of the Bordeaux group. A model describing the maximum depth of the deformation based on the theory of a sphere in an electric field has also been investigated.The deformations from the numerical solutions of the differential equation are too wide compared to the experimental results. The shoulder-shape that has been observed in the experiments is not present in the numerical solutions. There is reason to believe that the differential equation may be too simple in order to describe the liquid-liquid interface deformation for nonlinear cases. There may be thermal effects that changes the liquid properties due to local temperature variations induced by the laser, causing the liquid parameters to change along the deformation.The model used to estimate the deformation depth does not give reasonable results, as it leads to a deformation that is more than 100 times larger than what is observed in the corresponding experiments. The assumptions made for this model may not be valid, and a discussion on what should be done in order to improve the model is included in this text.

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Barbano, Émerson Cristiano. « Third-harmonic generation at interfaces with femtosecond pulses : self-focusing contribution and nonlinear microscopy ». Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-20012017-154741/.

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Third-harmonic generation (THG) is a fundamental nonlinear optical process that has been used in different applications such as third-order nonlinear materials characterization and nonlinear microscopy. It is widely employed since the third-order nonlinearity is the most important in isotropic materials and THG occurs in all media regardless of symmetry. In the tightly focused laser beam condition THG is observed only at the materials interfaces, where the focal symmetry is broken due to the presence of two media with different refractive index and/or third-order susceptibilities. Measuring slabs of different types of optical glasses, using femtosecond laser pulses, we could explain the asymmetric THG intensity profile observed at the interfaces. The harmonic generated at the exit interface is systematically stronger than the one generated at the entrance and this phenomenon can be understood by taking into account the presence of self-focusing effects. Basically, the self-focusing reduces the beam waist radius at the exit interface, resulting in greater laser irradiance and, consequently, higher THG. This study was then extended to the interfaces of a cuvette filled with organic solvents. Such systems present four interfaces and a mixture of nonlinear processes contributions since the cuvette walls present only electronic nonlinearity and the solvents present both electronic and orientational ones. In this way, the solvents may present an additional self-focusing contribution and, due to the noninstantaneous nature of the orientational process, the self-focusing from the solvent may be influenced by the pulse duration. In this case, the THG, which is an instantaneous electronic phenomenon, can be indirectly affected by pulse duration by means of the self-focusing effect. Usually, the slow orientational contribution is not considered for materials characterization by THG which may lead to incorrect nonlinear coefficient values, that means our study is important from the fundamental physics point of view and also for applications such as materials characterization. Based on the application of THG in nonlinear microscopy, we also present a microscopy technique which makes use of spatial frequency-modulated imaging (SPIFI) with single element detection. The microscope was developed at Colorado School of Mines (CSM) during an internship. The system uses a spatial light modulator (SLM) to provide the spatial frequency modulation and permits enhanced resolution images. THG SPIFI images are shown for the first time and we also report images obtained by other nonlinear optical process. In summary, the studies presented in this PhD work are of great importance for THG fundamental understanding, materials characterization and nonlinear optical microscopy.
Geração de terceiro harmônico (GTH) é um processo óptico não linear fundamental que tem sido usado em diferentes aplicações, como em caracterização óptica não linear de materiais e microscopia não linear. Ele é amplamente empregado uma vez que a não linearidade de terceira ordem é a mais importante em materiais isotrópicos e GTH ocorre em todos os meios independente da simetria. Na condição de feixe fortemente focalizado a GTH é observada apenas nas interfaces do material, onde a simetria focal é quebrada devido à presença de dois meios com diferentes índices de refração e/ou susceptibilidades de terceira ordem. Medindo lâminas de diferentes tipos de vidros ópticos, com pulsos de laser de femtossegundos, nós explicamos o perfil assimétrico de intensidade de GTH observado nas interfaces. O harmônico gerado na interface de saída é sistematicamente mais intenso do que o gerado na entrada e este fenômeno pode ser entendido levando-se em conta a presença do efeito de autofocalização. Basicamente, a autofocalização reduz a cintura do feixe na interface de saída do material, resultando em uma maior irradiância e, consequentemente, maior GTH. Este estudo foi estendido para o caso de interfaces de uma cubeta preenchida com diferentes solventes orgânicos. Tais sistemas apresentam quatro interfaces e uma mistura na contribuição dos processos não lineares, dado que as paredes da cubeta apresentam apenas não linearidade eletrônica e os solventes podem apresentar não linearidades tanto eletrônicas quanto orientacionais. Neste sentido, os solventes podem apresentar uma contribuição adicional de autofocalização e, devido à natureza não instantânea do processo orientacional, a autofocalização proveniente do solvente pode ser influenciada pela duração do pulso. Neste caso, a GTH, que é um fenômeno eletrônico (instantâneo), pode ser indiretamente afetada pela duração do pulso por meio do efeito de autofocalização. Usualmente, a contribuição orientacional não é considerada na caracterização de materiais por GTH, o que pode levar à valores incorretos para os coeficientes não lineares, o que significa que nosso estudo é importante do ponto de vista de física fundamental como também em aplicações como caracterização de materiais. Por conta da aplicação da GTH em microscopia não linear, apresentamos também nesta tese uma técnica de microscopia, que baseia-se em uma modulação em frequência espacial para imageamento (SPIFI) com uso de um detector de elemento único. O microscópio foi desenvolvido na Colorado School of Mines (CSM) durante um período de estágio. O sistema utiliza um modulador espacial de luz (SLM) para produzir a modulação em frequência espacial e permite obtenção de imagens em alta resolução. Imagens por GTH SPIFI são mostradas pela primeira vez e também apresentamos imagens obtidas por outros processos ópticos não lineares. Em resumo, os estudos apresentados neste trabalho de doutorado são de grande importância para o entendimento fundamental do processo de GTH, caracterização de materiais e microscopia óptica não linear.

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Yang, Dengliang. « Investigations of amino acid-based surfactants at liquid interfaces ». Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/2689.

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Herein are presented collective studies of amino acid-based surfactants, also known as lipoamino acids, at liquid interfaces. Chapter III describes an investigation of domain morphology of N-Stearoylglutamic acid (N-SGA) Langmuir monolayers at the air/water interface by epifluorescence microscopy. Anisotropic feather-like domains were observed in L-enantiomeric monolayers while symmetric circular domains were found in racemic N-SGA monolayers. At a surface pressure of 30 mN/m the enantiomeric domains melted at 31 ??C while the racemic domains melted at 27 ??C. This result is exactly opposite to the behavior found in bulk crystals where the racemate melts at a higher temperature. These results were explained in terms of different molecular packing and hydrogen bonding between bulk crystals and two-dimensional thin films for enantiomeric and racemic compounds. Chapter IV summarizes the investigations of hydrogen bonding in N-acyl amino acid monolayers by vibrational sum-frequency spectroscopy (VSFS). The intermolecular hydrogen bonding interaction between the adjacent molecules through amide-amide groups in N-stearoylalanine (N-SA) is characterized by an NH stretch peak at 3311 cm-1. This is the first time that the amide NH stretching signals have been detected with the VSFS technique. A similar peak was detected at 3341 cm-1on N-SGA monolayer. The higher frequency indicates that the H-bond strength is weaker due to the larger size of the glutamic acid residue. The NH stretch mode can thus be used as a fingerprint of hydrogen bonding among amide-amide groups. A peak at 3050 cm-1 due to hydrogen bonding among carboxyl groups was also resolved from the VSFS spectra. Molecular models of intermolecular hydrogen bonding were proposed.

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WANG, JIH-FU TREVOR. « OPTICAL PROPERTIES OF Si-SiO₂ INTERFACES BY LINEAR AND NONLINEAR OPTICAL TECHNIQUES ». NCSU, 2002. http://www.lib.ncsu.edu/theses/available/etd-20020304-114240.

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WANG, JIH-FU TREVOR. Optical Properties of Si-SiO Interfaces by Linear and Nonlinear Optical Techniques. ( Under the direction of Professor D. E. Aspnes. ) The objective of this research is to understand the physics of (001)Si-SiO data can be realized by the SBHM. From the SHG analysis we find effective angles of incidence and observation of about 12°, indicating that the SHG intensity originates at the Si side of the interface. This work further demonstrates the advantages of SBHM for interpreting SHG data with respect to conventional approaches. By expressing nonlinear polarizations in terms of complex hyperpolarizabilities associated with each of bonds in a unit cell, the description is not only much simpler but also provides more physical information and insight that can otherwise be obtained on a microscopic scale.

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Isaienko, Oleksandr. « Development of ultra-broadband ultrafast infrared sources and applications to nonlinear vibrational spectroscopy of interfaces ». Diss., Temple University Libraries, 2011. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/141408.

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Chemistry
Ph.D.
Interfaces play a crucial role in the exchange of energy and matter in various physical, chemical and biological systems. A particular interest has been to study interfaces between aqueous phases and various minerals because of their importance in understanding geochemical phenomena as well as for applications such as enhanced oil recovery. The nonlinear optical technique of vibrational sum-frequency generation (SFG) spectroscopy, introduced over 20 years ago, has become a powerful tool to investigate various surfaces, in particular, mineral-water interfaces. One of the challenges of the SFG spectroscopy of aqueous surfaces is the need to tune the central frequency of relatively narrowband IR lasers through the broad range of the OH-stretch frequencies of water molecules (3000 - 4000 cm-1). We have developed a novel ultrabroadband IR laser source that generates infrared pulses in the ~2800-6000 cm-1 range (lambda~3300-1800 nm) with bandwidths Delta(nu)>1000 cm-1, and bandwidths >2000 cm-1 in the near-IR range (lambda~1000-2000 nm). Pulse front tilt of signal pulse has been corrected allowing for compression of signal pulses down to 25 fsec. Such ultrabroadband IR pulses allow us to perform SFG spectroscopy of aqueous surfaces over the entire frequency range of water molecule spectrum (extending from ~2900 cm -1 to ~3800 cm -1) simultaneously, without tuning the laser ("in one shot"). We have used this novel ultrabroadband IR source to investigate the vibrational SFG spectra of silica/water interfaces. The high signal-to-noise ratio of our spectroscopic setup has allowed us to study low-intensity features that were not studied in detail, or recognized previously in the SFG-spectroscopy investigations, including: 1) non-hydrogen bonded OH vibrations at hydrophilic silica/water interfaces; 2) combination [stretch+bend] bands of water at the silica surface appearing at ~5000-5200 cm -1. 3) Overtones of water stretching modes at silica/water interfaces. The most important conclusions from these studies are outlined below. 1. Non-hydrogen bonded hydroxyls at silica/water interface. Typically SFG-studies of mineral/water interfaces (in particular, silica/water) have focused on the most pronounced features - peaks of H-bonded hydroxyls at ~3150 and ~3450 cm -1. We have been able to systematically observe and study a weaker peak at ~3670 - 3700 cm -1. This peak becomes more pronounced as the pH of aqueous phase decreases, as well as the ionic strength increases, indicating that the hydroxyls corresponding to this spectral feature are situated in a very close proximity to the surface. Isotopic dilution experiments indicate that the 3700 cm -1 feature is not due to asymmetric OH stretches as was suggested before. Based on our results, we suggest that this spectral feature corresponds to hydroxyls of water molecules at the silica surface that cannot hydrogen bond with silanol groups because of the lower density of silanols compared to H2O. We believe this to be the first surface-specific study of non-hydrogen bonded hydroxyls at silica, a surface widely accepted as hydrophilic. 2. SFG spectroscopy of [ν(OH)+δ(HOH)] combination bands of water at silica surface. We have extended SFG spectroscopy of the interfacial hydroxyls at mineral/water surfaces into the near-IR frequency range. The studies of overtones of interfacial OH(OD) groups will provide information on the anharmonicity of such species, and thus on the energy of dissociation. In addition, the positions of the overtone frequencies of the hydroxyls are more sensitive to interactions with the environment than the fundamental stretch frequencies. Our particular focus has been to study the stretch+bend combination band nu comb nu;(OH)+delta;(HOH) of liquid water which occurs in the near-IR spectral range at ~5000-5200 cm -1. It is typically much weaker in the FTIR absorption spectra than the fundamental transitions of the OH stretches or HOH bending, similar to overtones of these modes. We have performed, what we believe to be, the first surface-specific vibrational SFG spectroscopic measurements of combination bands of water molecules at silica surfaces. SFG spectroscopy of water combination band allows access to the water bending mode (delta~1600 cm -1), which still has not been observed in sum-frequency.
Temple University--Theses

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Bao, Bin. « Distributed, broadband vibration control devices using nonlinear approaches ». Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI086/document.

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L’amélioration du confort des usagers ainsi que l’augmentation du niveau de sécurité des structures requièrent le développement de techniques permettant de limiter efficacement les vibrations. Dans cette optique, les travaux exposés ici proposent le développement et l’analyse de méthodes de contrôle vibratoire pour des structures de faibles dimensions et utilisant peu d’énergie. Afin de satisfaire à ces deux critères, il est ici proposé d’utiliser des éléments piézoélectriques électriquement interfacés de manière non-linéaire et périodiquement distribués sur la structure-cible à contrôler. Ainsi, l’approche proposée permet de bénéficier à la fois des avantages des techniques de contrôle non-linéaires appliquées aux matériaux intelligents de type piézoélectrique, offrant des performances remarquables tout en étant peu consommatrices d’énergie, avec ceux des structures périodiques exhibant des bandes fréquentielles interdites présentant de fortes atténuations de la propagation d’onde. Plus particulièrement, ce mémoire s’intéresse à différentes architectures d’interconnexion des interfaces électriques non-linéaires permettant un bon compromis entre la bande fréquentielle contrôlée et les performances en termes d’atténuation des vibrations. Ainsi, trois architectures principales sont proposées, allant de structures totalement périodiques, tant au niveau mécanique qu’électrique (interconnexions), à des structures présentant un certain degré d’apériodicité sur le plan électrique (entrelacement), impactant ainsi la propagation de l’onde acoustique en élargissant la bande de contrôle, pour enfin proposer une architecture hybride entre interconnexion et entrelacement conduisant à des systèmes large bande performants
For ameliorating vibration reduction systems in engineering applications, miscellaneous vibration control methods, including vibration damping systems, have been developed in recent years. As one of intelligent vibration damping systems, nonlinear electronic damping system using smart materials (e.g., piezoelectric materials), is more likely to achieve multimodal vibration control. With the development of meta-structures (a structure based upon metamaterial concepts), electronic vibration damping shunts, such as linear resonant damping or negative capacitance shunts, have been introduced and integrated abundantly in the electromechanical meta-structure design for wave attenuation and vibration reduction control. Herein, semi-passive Synchronized Switch Damping on the Inductor (SSDI) technique (which belongs to nonlinear electronic damping techniques), is combined with smart meta-structure (also called smart periodic structure) concept for broadband wave attenuation and vibration reduction control, especially for low frequency applications. More precisely, smart periodic structure with nonlinear SSDI electrical networks is investigated from the following four aspects, including three new techniques for limiting vibrations: First, in order to dispose of a tool allowing the evaluation of the proposed approaches, previous finite element (FE) modeling methods for piezoelectric beam structures are summarized and a new voltage-based FE modeling method, based on Timoshenko beam theory, is proposed for investigating smart beam structure with complex interconnected electrical networks; then, the first developed technique lies in smart periodic structure with nonlinear SSDI interconnected electrical networks, which involves wave propagation interaction between continuous mechanical and continuous nonlinear electrical media; the second proposed topology lies in smart periodic structures with nonlinear SSDI interleaved / Tri-interleaved electrical networks involving wave propagation interaction between the continuous mechanical medium and the discrete nonlinear electrical medium. Due to unique electrical interleaved configuration and nonlinear SSDI electrical features, electrical irregularities are induced and simultaneously mechanical irregularities are also generated within an investigated periodic cell; the last architecture consists in smart periodic structures with SSDI multilevel interleaved-interconnected electrical networks, involving wave propagation interaction between the continuous mechanical medium and the multilevel continuous nonlinear electrical medium. Compared with the SSDI interconnected case, more resonant-type band gaps in the primitive pass bands of purely mechanical periodic structures can be induced, and the number of such band-gaps are closely related to the interconnection / interleaved level. Finally, the main works and perspectives of the thesis are summarized in the last chapter

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Yang, Yifan. « Modélisation numérique de l'amortissement induit par les interfaces des structures assemblées ». Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC044/document.

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Déterminer la durée de vie d'une pièce sous excitation vibratoire est l'un des enjeux majeurs dans l'ingénierie mécanique. Afin de donner une estimation fiable de la durée de vie, un calcul correct de champ de contrainte, qui est fortement lié à la forme et l'amplitude modale est obligatoire. Cependant, le calcul de réponse d'une structure assemblée est difficile, surtout avec la présence de frottement sec aux interfaces de liaisons qui entraîne un amortissement non linéaire. La recherche de la thèse commence par une identification phénoménologique de l'amortissement induit par le frottement sec avec 3 modèles analytiques, notamment la plaque sandwich, la rotule frottante et la plaque von Kármán. Après la caractérisation de l'amortissement structural au 1er et 2ème ordre, les influences des paramètres comme la pression de serrage, le rapport d'épaisseurs ainsi que le nombre de soudures sont analysés. La deuxième partie des travaux traite les problèmes d'amortissement avec une géométrie de dimension finie. La plaque de von Kármán est reprise dans l'étude et une méthode hybride de différences finies et d'éléments finis est adopté pour résoudre le couplage entre la flexion et les efforts internes. Une attention particulière est portée à la notion de modes non linéaires dans le cas de la plaque von Kármán. Les conditions nécessitant l'introduction de modes non linéaires sont identifiées. Le champ de force fictif qui est proposé dans l'étude sur la plaque von Kármán est ensuite introduit dans le cas de la plaque sandwich. Puis la propagation de glissement et l'influence de champ fictif sont étudiées. Afin de vérifier les phénomènes trouvés dans les études théoriques, une installation expérimentale est conçue et montée pour l'amortissement structural au premier ordre. Dans la dernière partie qui est basée sur les observations faites dans les études précédentes, une méthode de calcul de l'amortissement dans un environnement industriel est proposée. Cette méthode permet de donner un amortissement pour chaque mode isolé
The determination of a component's lifetime under vibrational excitation is one of the most difficult challenges in mechanical engineering. In order to provide a reliable estimation of lifetime, a correct calculation of stress field, which depends on the modal form and its amplitude, is needed. However, the vibrational response calculation on an assembled structure is not easy, especially with the nonlinear structural damping induced by frictional contact surface. The research in the current thesis starts from the phenomenological identification of damping with the help of 3 analytical models, in particular the sandwich plate, rotational joint and von Karman plate. Structural damping of 1st and 2nd order are identified. The influence of parameters like clamping pressure, thickness ratio and number of welding points are also analyzed. The second part of the research focuses on problems with finite dimensions. The von Karman plate serves as the subject of the study and a hydride method which combines FDM and FEM is proposed to solve the coupling between defection and in-plane force field. A special attention is paid to nonlinear mode theory, the conditions under which the nonlinear mode is necessary are identified. The fictive force field proposed in the study of von Kármán plate is then applied to the sandwich plate model. The slipping's propagation as well as the influence of fictive force field are studied. To verify the existence of the found phenomena in the previous studies, an experimental setup is designed and mounted for the 1st order structural damping. In the last part of the research, which is based on the observations previously obtained from academic models, a calculation method of friction-induced damping in structures with complex geometries is proposed for the application in the industrial environment. This methods enables the estimation of damping for each isolated mode

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Perry, Angela S. « A theoretical description of the vibrational sum frequency generation spectroscopy of interfaces ». [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001252.

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Miles, Aaron R. « The effect of initial conditions on the nonlinear evolution of perturbed interfaces driven by strong blast waves ». College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1374.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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Johnson, Magnus. « Vibrational Sum Frequency and Infrared Reflection/Absorption Spectroscopy Studies of the Air/Liquid and Liquid/Metal Interfaces ». Doctoral thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-455.

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Green, Anthony. « Applications of Molecular Dynamics Techniques and Spectroscopic Theories to Aqueous Interfaces ». Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3457.

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The primary goal of spectroscopy is to obtain molecularly detailed information about the system under study. Sum frequency generation (SFG) vibrational spectroscopy is a nonlinear optical technique that is highly interface specific, and is therefore a powerful tool for understanding interfacial structure and dynamics. SFG is a second order, electronically nonresonant, polarization experiment and is consequently dipole forbidden in isotropic media such as a bulk liquid. Interfaces, however, serve to break the symmetry and produce a signal. Theoretical approximations to vibrational spectra of O-H stretching at aqueous interfaces are constructed using time correlation function (TCF) and instantaneous normal mode (INM) methods. Detailed comparisons of theoretical models and spectra are made with those obtained experimentally in an effort to establish that our molecular dynamics (MD) methods can reliably depict the system of interest. The computational results presented demonstrate the potential of these methods to accurately describe fundamentally important systems on a molecular level.

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Beerman, Michael. « Transverse freezing of thin liquid films / ». Thesis, Connect to this title online ; UW restricted, 2007. http://hdl.handle.net/1773/10573.

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Mastricola, Nicholas Palma. « Nonlinear Stiffness and Edge Friction Characterization of Coned Disk Springs ». The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480346443676492.

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Andersen, Audrée. « Surfactant dynamics at interfaces : a series of second harmonic generation experiments ». Phd thesis, Universität Potsdam, 2005. http://opus.kobv.de/ubp/volltexte/2006/655/.

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Adsorption layers of soluble surfactants enable and govern a variety of phenomena in surface and colloidal sciences, such as foams. The ability of a surfactant solution to form wet foam lamellae is governed by the surface dilatational rheology. Only systems having a non-vanishing imaginary part in their surface dilatational modulus, E, are able to form wet foams. The aim of this thesis is to illuminate the dissipative processes that give rise to the imaginary part of the modulus.

There are two controversial models discussed in the literature. The reorientation model assumes that the surfactants adsorb in two distinct states, differing in their orientation. This model is able to describe the frequency dependence of the modulus E. However, it assumes reorientation dynamics in the millisecond time regime. In order to assess this model, we designed a SHG pump-probe experiment that addresses the orientation dynamics. Results obtained reveal that the orientation dynamics occur in the picosecond time regime, being in strong contradiction with the two states model.

The second model regards the interface as an interphase. The adsorption layer consists of a topmost monolayer and an adjacent sublayer. The dissipative process is due to the molecular exchange between both layers. The assessment of this model required the design of an experiment that discriminates between the surface compositional term and the sublayer contribution. Such an experiment has been successfully designed and results on elastic and viscoelastic surfactant provided evidence for the correctness of the model.

Because of its inherent surface specificity, surface SHG is a powerful analytical tool that can be used to gain information on molecular dynamics and reorganization of soluble surfactants. They are central elements of both experiments. However, they impose several structural elements of the model system. During the course of this thesis, a proper model system has been identified and characterized. The combination of several linear and nonlinear optical techniques, allowed for a detailed picture of the interfacial architecture of these surfactants.
Amphiphile vereinen zwei gegensätzliche Strukturelemente in einem Molekül, eine hydrophile Kopfgruppe und ein hydrophobe, meist aliphatische Kette. Aufgrund der molekularen Asymmetrie erfolgt eine spontane Adsorption an der Wasser-Luft Grenzfläche. Die Adsorptionsschicht verändert die makroskopischen Eigenschaften des Materials, z.B. die Grenzflächenspannung wird erniedrigt. Amphiphile sind zentrale Bauelemente der Kolloid- und Grenzflächenforschung, die Phänomene, wie Schäume ermöglichen.

Eine Schaumlamelle besteht aus einem dünnen Wasserfilm, der durch zwei Adsorptionsschichten stabilisiert wird. Die Stabilität der Lamelle wird durch die Grenzflächenrheologie entscheidend geprägt. Die wesentliche makroskopische Größe in diesem Zusammenhang ist das so genannte Grenzflächendilatationsmodul E. Es beschreibt die Fähigkeit des Systems die Gleichgewichtsgrenzflächenspannung nach einer Expansion oder Dilatation der Adsorptionschicht wieder herzustellen. Das Modul E ist eine komplexe Größe, in dem der Imaginärteil direkt mit der Schaumstabilität korreliert.

Diese Arbeit widmet sich der Grenzflächenrheologie. In der Literatur werden zwei kontroverse Modelle zur Interpretation dieser Größe diskutiert. Diese Modelle werden experimentell in dieser Arbeit überprüft. Dies erfordert die Entwicklung neuer experimenteller Aufbauten basierend auf nichtlinearen, optischen Techniken. Mit diesen Experimenten konnte eines der Modelle bestätigt werden.

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Dianne, Soule Melissa C. Kido. « Nonlinear vibrational spectroscopic studies of the absorption and orientation of environmentally important molecules at the vapor/water interface / ». view abstract or download file of text, 2007. http://proquest.umi.com/pqdweb?did=1335361671&sid=2&Fmt=2&clientId=11238&RQT=309&VName=PQD.

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Thesis (Ph. D.)--University of Oregon, 2007.
Typescript. Includes vita and abstract. Includes bibliographical references (leaves 146-156). Also available for download via the World Wide Web; free to University of Oregon users.

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Karami, Armine. « Study of electrical interfaces for electrostatic vibration energy harvesting ». Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS134/document.

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Les récupérateurs d'énergie vibratoire électrostatiques (REV) sont des systèmes convertissant une partie de l'énergie cinétique de leur environnement en énergie électrique, afin d'alimenter de petits systèmes électroniques. Les REV inertiels sont constituées d'un sous-système mécanique bâti autour d'une masse mobile, ainsi que d'une interface électrique. Ces deux blocs sont couplés par un transducteur électrostatique. Cette thèse étudie l'amélioration des performances des REV par la conception optimisée de leur interface électrique. La première partie de cette thèse étudie une famille d'interfaces électriques appelées pompes de charge (PC). On commence par la construction d'une théorie formelle des PC. Des interfaces rapportées dans la littérature sont identifiées comme membres de cette famille. Cette dernière est ensuite complétée par une nouvelle topologie de PC. Une comparaison des différents PC est alors faite dans le domaine électrique, puis un outil semi-analytique est présenté pour la comparaison des PC en prenant en compte le couplage électromécanique. L'étude des PC se termine par la présentation d'une nouvelle méthode de mesure du potentiel d'électret des REV. La deuxième partie de la thèse présente une approche de conception radicalement différente de ce qui est présenté dans les travaux actuels sur les REV. Elle préconise une synthèse active de la dynamique de la masse des REV à travers leur interface électrique. Nous montrons d'abord que cela permet la conversion d'énergie en quantités proches des limites physiques, et ce à partir de vibrations d'entrée de forme arbitraire. Enfin, une architecture pour un tel REV est proposée et testée en simulation
Electrostatic vibration energy harvesters (e-VEHs) are systems that convert part of their surroundings' kinetic energy into electrical energy, in order to supply small-scale electronic systems. Inertial E-VEHs are comprised of a mechanical subsystem that revolves around a mobile mass, and of an electrical interface. The mechanical and electrical parts are coupled by an electrostatic transducer. This thesis is focused on improving the performances of e-VEHs by the design of their electrical interface. The first part of this thesis consists in the study of a family of electrical interfaces called charge-pumps conditioning circuits (CPCC). It starts by building a formal theory of CPCCs. State-of-the-art reported conditioning circuits are shown to belong to this family. This family is then completed by a new CPCC topology. An electrical domain comparison of different CPCCs is then reported. Next, a semi-analytical tool allowing for the comparison of CPCC-based e-VEHs accounting for electromechanical effects is reported. The first part of the thesis ends by presenting a novel method for the measurement of e-VEHs' built-in electret potential. The second part of the thesis presents a radically different design approach than what is followed in most of state-of-the-art works on e-VEHs. It advocates for e-VEHs that actively synthesize the dynamics of their mobile mass through their electrical interface. We first show that this enables to convert energy in amounts approaching the physical limits, and from arbitrary types of input vibrations. Then, a complete architecture such an e-VEH is proposed and tested in simulations submitted to human body vibrations

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Khan, Md Rubel. « Adsorption and Self-Assembly of Surfactants at Air-Liquid and Liquid-Metal Interfaces Studied by Sum Frequency Generation (SFG) Spectroscopy ». Ohio University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1620212735093219.

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Khan, Md Rubel. « Adsorption and Self-Assembly of Surfactants at Air-Liquid and Liquid-Metal Interfaces Studied by Sum Frequency Generation (SFG) Spectroscopy ». Ohio University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1620212735093219.

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Motti, Silvia Genaro. « Espectroscopia não linear de interfaces aplicada ao estudo de transistores poliméricos ». Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-20102014-130245/.

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O uso de materiais orgânicos em dispositivos eletrônicos, além de menor custo e facilidade de processamento, permite obter flexibilidade e transparência. Entretanto, para que a aplicação comercial desses materiais seja viável, os processos que ocorrem nos dispositivos ainda precisam ser mais bem compreendidos, visando maior eficiência e tempo de vida. É de grande importância o estudo das interfaces entre o semicondutor orgânico e os contatos metálicos, onde ocorre transferência de portadores de carga, e a interface com o dielétrico em transistores orgânicos (OFETs), onde se forma o canal de condução. As interfaces de dispositivos eletrônicos poliméricos foram estudadas, utilizando-se Espectroscopia SFG (do inglês Sum Frequency Generation). Esta técnica obtém um sinal com a soma das frequências de dois feixes incidentes sobrepostos, em um processo seletivo a meios onde não há simetria de inversão, como no caso de interfaces. Com aplicação de um feixe de excitação na região visível e outro sintonizável no infravermelho médio, a espectroscopia SFG fornece um espectro vibracional da interface e permite o estudo do ordenamento e da orientação dos grupos moleculares. Foram construídos e analisados OFETs de poli-3-hexiltiofeno (P3HT) preparados sobre substrato de vidro ou silício, utilizando como isolante óxido de silício e/ou poli-metil-metacrilato (PMMA). Foram obtidos espectros in situ do canal de OFETs em operação, observando pequenas alterações na forma de linha, porém a baixa relação sinal/ruído não permitiu obter conclusões detalhadas. Foi constatada a manifestação de bandas da camada isolante de PMMA como consequência da aplicação de campo elétrico. Este fenômeno foi considerado como uma nova ferramenta para estudar a distribuição de cargas e campo elétrico no canal de transistores. Não foram detectados sinais de degradação irreversível no polímero semicondutor a curto prazo, e a mudança de comportamento elétrico foi atribuída majoritariamente a dopagem por oxigênio absorvido no material.
The usage of organic materials in electronic devices allows not only low cost and ease of processing but also flexibility and transparency. However, to achieve viable commercial application, the processes involved on the devices operation must still be better comprehended, aiming for improved efficiency and life time. There is great importance in the study of the interfaces between organic semiconductors and metallic contacts, where charge transfer takes place, and between the dielectric and semiconductor layers of organic transistors (OFETs), where the conducting channel is formed. The interfaces in polymeric electronic devices were studied by SFG spectroscopy (Sum Frequency Generation). In this technique, a signal with frequency that equals the sum of those of two incident beams is generated in a process only allowed in media without inversion symmetry, such as interfaces. Using a visible excitation beam and a tunable infrared one, SFG spectroscopy yields a vibrational spectrum of the interface and provides information about the conformation and orientation of molecular groups. Poly-3-hexylthiophene (P3HT) OFETs were fabricated using glass or silicon substrates and silicon oxide and/or poly-methyl-methacrylate (PMMA) for the dielectric layer. SFG spectra were acquired in situ from the channel region of operating OFETs, observing small changes in lineshape, but low signal-to-noise ration did not allow a detailed interpretation. It was found that PMMA vibrational bands appeared when polarizing the device. This phenomenon was considered a new tool for studying the electric field and charge distribution along transistor channels. It was not noted any sign of short term irreversible degradation of the semiconducting polymer, and the change in the electrical behavior was attributed mainly to doping of the polymer by oxygen absorbed in the material.

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Oiticica, Pedro Ramon Almeida. « Microscopia por geração de soma de frequências em interfaces líquidas e sólidas ». Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-13042015-112958/.

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Estudos em interfaces são importantes para o completo entendimento de muitos processos em química, física e biologia. Esses sistemas são governados principalmente pelas propriedades interfaciais dos materiais. Nas duas últimas décadas, o desenvolvimento de novos métodos experimentais melhorou o nosso entendimento das propriedades interfaciais. O advento de uma série de técnicas de espectroscopia a laser baseadas em óptica não linear e o desenvolvimento das técnicas de microscopia por ponta de prova, possibilitaram estudos antes inimagináveis em superfícies e interfaces. Entre as técnicas de espectroscopia não linear, destacamos a espectroscopia por Geração de Soma de Frequências (espectroscopia SFG). Essa técnica foi desenvolvida por Shen et al. em 1987 e, desde então, é aplicada a muitos estudos em superfícies e interfaces. A espectroscopia SFG pode fornecer informações sobre a natureza química por meio do espectro vibracional e sobre o ordenamento médio das moléculas em uma única monocamada. O sinal SFG só pode ser gerado em meios não centrossimétricos, isso inclui superfícies ou interfaces entre meios centrossimétricos, onde há quebra da simetria de inversão. A combinação da espectroscopia SFG com a microscopia óptica tem sido proposta como uma nova técnica experimental para obter imagens em interfaces com sensibilidade química pelo espectro vibracional e contraste pela orientação e ordenamento das moléculas. Neste trabalho, apresentamos o desenvolvimento, construção e caracterização de um Microscópio SFG (MSFG). Esse MSFG foi especialmente projetado para estudos em superfícies ou interfaces tanto líquidas quanto sólidas. Testes iniciais de desempenho do MSFG foram realizados na interface líquido/ar da solução binária água/acetonitrila (H2O⁄CH3CN). Foram obtidas imagens do sinal SFG ressonante com o estiramento simétrico do grupo metil (CH3) da acetonitrila na interface líquido⁄ar da solução binária. Variando a fração molar da acetonitrila na solução entre 4% e 20% observamos a dependência da intensidade do sinal SFG na interface em função da fração molar de acetonitrila no volume do líquido. Testes também foram feitos em filmes Langmuir-Blodgett multicamada de ácido esteárico (CH3(CH2)16COOH). Obtivemos a espectromicroscopia SFG na ressonância dos grupos CH2 e CH3 do ácido graxo. Pelas diferenças entre os espectros SFG das regiões ordenadas e desordenadas, a espectromicroscopia revelou distribuições microscópicas do ordenamento das cadeias alquila que formam o filme. A sensibilidade da detecção do sinal SFG foi caracterizada e revelou a possibilidade de obter imagens na superfície da água em menos de um minuto. A caracterização óptica e os testes nas interfaces líquido⁄ar e sólido⁄ar demonstraram a completa capacidade do MSFG como ferramenta para investigar qualquer superfície ou interface, seja essa líquida ou sólida.
Interface studies are important for the complete understanding of many processes in chemistry, physics and biology. These systems are mainly governed by the interfacial properties of the materials. In the last two decades, the development of new experimental methods improved our understanding of interfacial properties. The advent of a host of laser spectroscopy techniques based on nonlinear optics and the development of the scanning probe microscopy techniques, opened up unimaginable possibilities of studies at surfaces and interfaces. Among these nonlinear spectroscopies we turned our attention to Sum Frequency Generation spectroscopy (SFG spectroscopy). This technique was developed by Shen et al. in 1987 and, since then, it has been applied to many studies of surfaces and interfaces. SFG spectroscopy can provide information about the chemical nature by the vibrational spectra and about the average of molecular ordering in a single monolayer. The SFG signal only can be generated in a noncentrossymetric media, this includes surfaces or interfaces between centrossymetric media, where there is a broken in the inversion symmetry. The combination of SFG spectroscopy with optical microscopy has been proposed as a novel experimental technique to obtain images at interfaces with chemical sensitivity by the vibrational spectra as well as contrast by the ordering and orientation of the molecules. In this work we present the development, construction and characterization of an SFG Microscope (SFGM). This SFGM was specially designed to perform studies on surfaces or interfaces of liquids and solids. Initial SFGM performance tests were performed at the liquid/air interface of the water/acetonitrile (H2O/CH3CN) binary solution. The images of the SFG signal were acquired on the resonance of the methyl group (CH3) of acetonitrile present at the liquid⁄air interface of the binary solution. By varying the molar fraction of acetonitrile in the solution between 4% and 20% we observed the dependency of the SFG signal intensity as a function the acetonitrile bulk mole fraction. We also performed tests in multi-layered Langmuir-Blodgett films of stearic acid (CH3(CH2)16COOH). We obtained the SFG spectromicroscopy in the resonance of CH2 and CH3 groups of the fatty acid. By the differences between the SFG spectra of ordered and disordered regions, the spectromicroscopy revealed microscopic distribution of the conformational ordering in the alkyl chains that composes the film. The sensitivity of the SFG microscope was characterized and it was shown that images could be acquired at the water surface in less than one minute. The optical characterization and the performed tests at the liquid/air and solid/air interfaces demonstrated the full capabilities of the SFGM as a tool for investigations in any liquid or solid interface.

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Costard, René [Verfasser], Thomas Akademischer Betreuer] Elsässer, Peter [Akademischer Betreuer] Hamm et Oliver [Akademischer Betreuer] [Benson. « Ultrafast dynamics of phospholipid-water interfaces studied by nonlinear time-resolved vibrational spectroscopy / Rene Costard. Gutachter : Thomas Elsässer ; Peter Hamm ; Oliver Benson ». Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://d-nb.info/1051371902/34.

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Nicola, Ernesto Miguel. « Interfaces between Competing Patterns in Reaction-diffusion Systems with Nonlocal Coupling ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2002. http://nbn-resolving.de/urn:nbn:de:swb:14-1036499969687-26395.

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In this thesis we investigate the formation of patterns in a simple activator-inhibitor model supplemented with an inhibitory nonlocal coupling term. This model exhibits a wave instability for slow inhibitor diffusion, while, for fast inhibitor diffusion, a Turing instability is found. For moderate values of the inhibitor diffusion these two instabilities occur simultaneously at a codimension-2 wave-Turing instability. We perform a weakly nonlinear analysis of the model in the neighbourhood of this codimension-2 instability. The resulting amplitude equations consist in a set of coupled Ginzburg-Landau equations. These equations predict that the model exhibits bistability between travelling waves and Turing patterns. We present a study of interfaces separating wave and Turing patterns arising from the codimension-2 instability. We study theoretically and numerically the dynamics of such interfaces in the framework of the amplitude equations and compare these results with numerical simulations of the model near and far away from the codimension-2 instability. Near the instability, the dynamics of interfaces separating small amplitude Turing patterns and travelling waves is well described by the amplitude equations, while, far from the codimension-2 instability, we observe a locking of the interface velocities. This locking mechanism is imposed by the absence of defects near the interfaces and is responsible for the formation of drifting pattern domains, i.e. moving localised patches of travelling waves embedded in a Turing pattern background and vice versa.

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Nicola, Ernesto Miguel. « Interfaces between Competing Patterns in Reaction-diffusion Systems with Nonlocal Coupling ». Doctoral thesis, Technische Universität Dresden, 2001. https://tud.qucosa.de/id/qucosa%3A24181.

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In this thesis we investigate the formation of patterns in a simple activator-inhibitor model supplemented with an inhibitory nonlocal coupling term. This model exhibits a wave instability for slow inhibitor diffusion, while, for fast inhibitor diffusion, a Turing instability is found. For moderate values of the inhibitor diffusion these two instabilities occur simultaneously at a codimension-2 wave-Turing instability. We perform a weakly nonlinear analysis of the model in the neighbourhood of this codimension-2 instability. The resulting amplitude equations consist in a set of coupled Ginzburg-Landau equations. These equations predict that the model exhibits bistability between travelling waves and Turing patterns. We present a study of interfaces separating wave and Turing patterns arising from the codimension-2 instability. We study theoretically and numerically the dynamics of such interfaces in the framework of the amplitude equations and compare these results with numerical simulations of the model near and far away from the codimension-2 instability. Near the instability, the dynamics of interfaces separating small amplitude Turing patterns and travelling waves is well described by the amplitude equations, while, far from the codimension-2 instability, we observe a locking of the interface velocities. This locking mechanism is imposed by the absence of defects near the interfaces and is responsible for the formation of drifting pattern domains, i.e. moving localised patches of travelling waves embedded in a Turing pattern background and vice versa.

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FERHATOGLU, ERHAN. « Effects of non-unique friction forces on the dynamic behavior of turbine bladed disks with contact interfaces ». Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2967027.

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Morel, Adrien. « Interfaces électriques adaptatives dynamiquement au spectre fréquentiel pour la récupération d'énergie vibratoire large bande ». Electronic Thesis or Diss., Chambéry, 2020. http://www.theses.fr/2020CHAMA035.

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La récupération d’énergie est un domaine émergent dont la visée principale est le développement de systèmes de capteurs autonomes énergétiquement, ne nécessitant pas de maintenance. La récupération de l’énergie contenue dans les vibrations ambiantes est d’un intérêt tout particulier lorsque le capteur à alimenter se trouve dans un environnement clos, confiné, où les gisements d’énergie solaire et les gradients thermiques ne sont pas suffisamment abondants. Cependant l’industrialisation et la mise sur le marché de récupérateurs d’énergie vibratoire sont freinées par la faible robustesse des récupérateurs d’énergie actuels. En effet, comment garantir l’autonomie d’un système pendant plusieurs années si le vieillissement du récupérateur d’énergie, les dérives en température de l’environnement, ou les variations de la source vibratoire peuvent écarter la fréquence de la source vibrante de la fréquence de résonance du récupérateur d’énergie, diminuant ainsi drastiquement l’énergie récupérée ? Cette thèse propose l’étude théorique et expérimentale d’approches permettant de régler électriquement la fréquence de résonance d’un récupérateur d’énergie vibratoire à transduction piézoélectrique, afin de pouvoir l’ajuster en temps réel. Après avoir expliqué le contexte dans lequel s’inscrit cette thèse, nous avons développé un modèle électromécanique du récupérateur d’énergie couplé à l’interface électrique. L’analyse de ce modèle nous a permis de rassembler l’ensemble des influences de l’interface électrique sur la dynamique du système sous la forme de deux paramètres : l’amortissement électrique et la raideur électrique. L’ajustement de ces deux paramètres a été tout d’abord analysé, puis, dans un second temps, réalisé grâce à des combinaisons de charges linéaires résistives, capacitives et inductives. La généralisation de ces influences aux interfaces électriques non-linéaires a permis l’élaboration de plusieurs stratégies innovantes d’extraction de l’énergie, permettant le réglage dynamique de la fréquence de résonance du récupérateur. La validation expérimentale de ces stratégies avec des récupérateurs d’énergie utilisant des matériaux piézoélectriques a permis de vérifier notre modèle tout en démontrant le potentiel de notre approche, notamment pour des structures présentant de forts couplages électromécaniques. La comparaison quantitative de ces stratégies a été rendue possible grâce au développement de plusieurs outils d’analyse et d’une figure de mérite prenant en compte le comportement fréquentiel du récupérateur associé à une stratégie donnée. Cette comparaison nous a permis de choisir la meilleure stratégie à implémenter dans un circuit intégré dédié. Cette intégration microélectronique constitue la dernière étape de cette thèse. Le circuit réalisé inclut un chemin de puissance, un démarrage à froid, un ensemble de capteurs auto-alimentés et un algorithme très basse consommation permettant le réglage en temps réel de la fréquence de résonance du récupérateur. Le rendement maximal atteint par notre circuit est de 94%. Outre ses performances, ce circuit est le premier à combiner auto-alimentation et réglage de la fréquence de résonance du récupérateur, tout en ne nécessitant pas de calibration préalable et en présentant une consommation inférieure au micro-watt. La comparaison de notre circuit avec des solutions de l’état de l’art (réglage magnétique, piézoélectrique ou mécanique) démontre tout le potentiel de notre approche
Energy harvesting is an emerging field whose main aim is the development of autonomous sensor nodes that do not require maintenance. Scavenging the energy contained in ambient vibrations is of particular interest when the sensor lies in a closed and confined environment, where there are few solar radiations or thermal gradients. However, a massive industrialization of vibration energy harvesters is currently hindered by their low robustness. Indeed, aging of the energy harvester, temperature drifts, or variations of the vibrating source might deviate the vibration frequency away from the energy harvester’s resonant frequency, drastically reducing the harvested energy. This thesis studies approaches allowing to electrically tune the resonant frequency of a piezoelectric vibration energy harvester, in order to monitor its dynamics in real-time. After establishing the background of this thesis, we develop an electromechanical model of the piezoelectric energy harvester coupled to the electrical interface. A normalized analysis of this model allows us to reduce all the influences of the electrical interface on the dynamics of the system to two physically meaningful variables: the electrical damping and the electrical stiffness. The adjustment of these two parameters is first analyzed, then achieved through combinations of resistive, capacitive and inductive linear loads. Extending this analysis to non-linear electrical interfaces has enabled the development of several innovative energy extraction strategies. The experimental validations of these strategies with energy harvesters made with strongly coupled piezoelectric materials are in great agreement with our model and demonstrate the value of our approach. The quantitative comparison of these strategies is made possible thanks to the development of several analysis tools and a figure of merit taking into account the frequency behavior of the harvester associated with a given electrical strategy. This comparison allows us to determine and justify which strategy to implement thanks to a dedicated integrated circuit. The microelectronic integration of this energy extraction strategy is the last step of this thesis. Our integrated circuit includes a power path, a cold-start, self-powered sensors and a low-power algorithm allowing real-time monitoring of the harvester’s resonant frequency. The maximum efficiency reached by our circuit is 94%. In addition to its performance, this circuit is the first self-powered solution that adjusts the resonant frequency of the harvester without any prior calibration and with a sub-microwatt power consumption. Finally, the favorable comparison between our approach and state-of-the-art solutions (based on magnetic, piezoelectric or mechanical frequency adjustment) confirms the potential of electrically-based frequency tuning

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Crémoux, Tatiana. « Physico-chimie aux interfaces de systèmes vitreux à charge d'espace ». Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR14972/document.

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Le but de ce travail de thèse est de contrôler via un traitement de polarisation les propriétés physico-chimiques de surface des verres. Pour cela, l'implémentation d'une charge d'espace au sein de différents verres silicates et borosilicates a été caractérisée. Ces études comparatives ont montré que la déplétion des cations de l’anode vers la cathode induit l’apparition d’un champ électrique et des modifications structurales localisées. De plus, nous avons démontré que la formation d’un plasma entre l’anode et le verre pouvait être à l’origine de phénomènes d'échanges ioniques conduisant notamment à la formation d’entités azotées NO2/N2O4 piégées dans le verre. Par la suite, une étude des propriétés physico-chimiques des surfaces polarisées a été conduite. Les résultats préliminaires obtenus concernent l'influence de la charge d'espace sur (i) la mouillabilité, (ii) la chimie de surface et (iii) les réponses optiques de molécules adsorbées
The purpose of this work is to control physicochemical properties of glasses surfaces using a thermal polarization treatment. For this, the implementation of a space charge layer has been characterized for various silicates and borosilicates glasses. These comparative studies have shown that cations depletion from anode toward cathode induces both an electric field and structural local changes. To go further, we demonstrated that there is a plasma formation between anode and glass surfaces which could be the cause of ionic exchange phenomena leading to the formation of nitrogen NO2/N2O4 entities entrapped inside glass network. Subsequently, physicochemical properties studies of polarized surfaces were performed. Preliminary results concerning the space charge influence on (i) surface wettability, (ii) surface chemistry and (iii) optical responses of adsorbed molecules on poled glass surface have been obtained

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Salles, Loïc. « Etude de l'usure par fretting sous chargements dynamiques dans les interfaces frottantes : application aux pieds d'aubes de turbomachines ». Phd thesis, Ecole Centrale de Lyon, 2010. http://tel.archives-ouvertes.fr/tel-00600613.

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Les parties tournantes des turbomachines aéronautiques sont composées d'une succession de roues aubagées qui permettent le transfert de l'énergie entre l'air et le rotor. Ces roues aubagées constituent des pièces particulièrement sensibles car elles doivent répondre en termes de dimensionnement à des impératifs de performances aérodynamiques, d'aéroacoustique et de tenue mécanique à la rotation,à la température et à la charge aérodynamique. Le contact avec frottement existant au niveau des attaches aube-disque joue un rôle important sur les niveaux vibratoires.Ce travail porte sur l'étude de l'usure par fretting sous chargements dynamiques dans les interfaces frottantes. En effet, les vibrations de l'aube peuvent produire des micro-glissements en pied d'aubequi peuvent entraîner un phénomène d'usure par fretting. Les connaissances sur le comportement de l'usure sous sollicitations dynamiques sont faibles. Seuls existent des outils numériques pour modéliser l'usure dans le cas de sollicitations quasi-statiques. Nous proposons dans cette thèse des méthodes pour calculer l'évolution de l'usure au cours des cycles de chargement dynamique basées sur une approche multi-échelle en temps. La réponse vibratoire de la structure est liée à une échelle de temps rapide qui est calculée par une méthode d'équilibrage harmonique, dans laquelle les déplacements et les efforts sont projetés sur la base de Fourier. Différentes approches temps-fréquence de calcul des coefficients de Fourier des forces de contact sont présentées. La cinétique d'usure est liée à une échelle lente et différentes méthodes sont proposées pour l'intégrer. La prise en compte des géométries usées dans le modèle éléments finis se fait par l'ajout d'un vecteur des profondeurs d'usure dans le terme de pénalité des lagrangiens dynamiques. Des exemples académiques valident et illustrent les méthodes proposées. Ces méthodes sont ensuite appliquées à l'étude de l'usure par fretting en pied d'aube de soufflante. L'étude numérique met en lumière le couplage entre vibration et usure par fretting aux interfaces de contact. La modification du comportement dynamique global de la roue aubagée est aussi observée.

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Maurice, Anthony. « Diffusion de second harmonique en milieux liquides : approche comparée des réponses de volume et de surface ». Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1337/document.

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Ce manuscrit décrit le processus optique non linéaire de Génération de Second Harmonique (acronyme anglais SHG pour Second Harmonic Generation) réalisé en phase liquide. En particulier, la propriété de cohérence de ce processus est étudiée en détail. En effet, en raison de la parité du processus SHG, cette cohérence est perdue dans les liquides. Ces études portent ainsi sur plusieurs géométries afin d’accéder aux réponses de volume et de surface. Les avantages d’une méthode combinée sont aussi discutés. Dans une première partie, la configuration classique de la Diffusion Hyper Rayleigh (acronyme anglais HRS pour Hyper Rayleigh Scattering ou SHS Second harmonic scattering) est utilisée pour l’étude de systèmes simples comme les solvants purs. Cette étude porte en particulier sur les méthodes de normalisation des hyperpolarisabilités moléculaires. Une voie alternative est proposée basée sur l’introduction d’une section efficace HRS ou SHS. Par la suite, les effets liés aux ordres non linéaires supérieurs sont démontrés et interprétés, ceux-ci pouvant altérer les valeurs absolues qui peuvent être mesurées.La seconde partie porte sur l’introduction de plusieurs améliorations dans les mesures HRS ou SHS. En particulier, l’évolution vers des géométries non conventionnelles s’éloignant de la géométrie standard ainsi que sur des évolutions permettant d’accéder aux aspects dynamiques sont proposées. Des expériences sont réalisées sur des systèmes simples comme les solvants purs, des composés moléculaires et des nanoparticules, tous présentant des spécificités propres. Cette partie finit sur l’exploration des systèmes aléatoires diffusants et les problèmes associés. Enfin, dans une dernière partie, la réponse HRS ou SHS de solutions aqueuses de sels est discutée. Les mesures portent plus particulièrement sur une étude comparée des aspects cohérents et incohérents et les propriétés qu’il est possible de mesurer dans ces systèmes
This manuscript describes the nonlinear optical process of Second Harmonic Generation (SHG acronym for Second Harmonic Generation) carried out in liquid phase. In particular, this process coherence property is studied in detail. Indeed, due to the parity of the SHG process, this coherence is lost in liquids. These studies covers several geometries to access the volume and surface responses. The benefits of a combined method are also discussed. In the first part, the typical configuration of the Hyper Rayleigh Scattering(HRS or SHS for Second harmonic scattering) is used for the study of simple systems like pure solvents. This particular study focuses on methods of standardization of molecular hyperpolarizabilities. An alternative route is proposed based on the introduction of a HRS or SHS cross. Subsequently, the effects of the higher nonlinear orders are demonstrated and interpreted, they can alter the absolute values that can be measured.The second part deals with the introduction of several improvements in the HRS or SHS measurement. In particular, the trend towards unconventional geometries away from the standard geometry as well as developments for accessing dynamic aspects are proposed. Experiments are performed on simple systems such as pure solvents, molecular compounds and the nanoparticles, all presenting specificities. This part ends on exploring the random scattering systems and associated problems. Finally, in the last part, the HRS or SHS response of aqueous salt solutions is discussed. The measures focus specifically on a comparative study of coherent and incoherent aspects and properties that can be measured in these systems

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Gagliardi, Luca. « Modèle de film mince pour la croissance et la dissolution de cristaux confinées ». Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1211/document.

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Cette thèse traite de la modélisation de la croissance et de la dissolution de cristaux confinés. Nous nous concentrons sur la dynamique dans les contacts lubrifiés (ou hydrophiles) et dérivons un modèle de continu de couche mince prenant en compte la diffusion, la cinétique de surface, l’hydrodynamique, la tension de surface et les interactions avec le substrat (pression de disjonction). Premièrement, nous étudions la dissolution induite par une charge extérieure (dissolution sous contrainte). Nous trouvons que la forme fonctionnelle de la pression de disjonction -finie ou divergente au contact- est cruciale dans la détermination des taux de dissolution et des morphologies stationnaires. Ces formes conduisent respectivement à des taux de dissolution dépendant ou indépendants de la charge, et à des profils de surface plats ou pointus. Deuxièmement, nous avons considéré la croissance des cristaux à proximité d’un mur plat. Nous avons constaté qu’une cavité apparaît sur la surface cristalline confinée. Nous obtenons un diagramme de morphologie hors équilibre en accord avec les observations expérimentales. En traversant la ligne de transition, une cavité peut apparaître de manière continue ou discontinue en fonction de la forme de la pression de disjonction (répulsive ou attractive). Pour les épaisseurs de film nanométriques, la viscosité peut entraver la formation de la cavité. Enfin, nous étudions la force de cristallisation exercée par un cristal croissant entre deux parois planes. Nous soulignons l’importance d’une définition précise de l’aire de contact pour définir la pression d’équilibre thermodynamique. Pendant la croissance, la ligne triple subit une transition cinétique dépendant uniquement du rapport entre: la constante de diffusion, et le produit de la constante cinétique de surface et de la distance entre les murs. Après cette transition, la force de cristallisation diminue jusqu’à s’annuler, et un film macroscopique se forme
This thesis discusses the modeling of growth and dissolution of confined crystals. We focus on the dynamics within lubricated (or hydrophilic) contacts and derive a thin film continuum model accounting for diffusion, surface kinetics, hydrodynamics, surface tension and interactions with the substrate (disjoinining pressure). First, we study dissolution induced by an external load (pressure solution). We find the functional form of the disjoining pressure -finite or diverging at contact- to be crucial in determining steady state dissolution rates and morphologies. These forms respectively lead to load-dependent or load-independent dissolution rates, and to flat or pointy surface profiles.Second, we considered crystal growth in the vicinity of a flat wall. We found that a cavity appears on the confined crystal surface. We obtain a non-equilibrium morphology diagram in agreement with experimental observations. When crossing the transition line, a cavity can appear continuously or discontinuously depending on the form of the disjoining pressure (repulsive or attractive). For nanometric film thicknesses, viscosity can hinder the formation of the cavity.Finally, we study the force of crystallization exerted by a crystal growing between two flat walls. We point out the importance of a precise definition of the contact area to define the thermodynamic equilibrium pressure. During growth, the triple-line undergoes a kinetic pinning transition depending solely on the ratio between the diffusion constant and the product of the surface kinetic constant and distance between the walls. After this transition, the crystallization force decreases to zero, and a macroscopic film forms

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Aceves, Alejandro Borbolla. « Snell's laws at the interface between nonlinear dielectrics ». Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184467.

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A theory is presented which describes the global reflection and transmission characteristics of a self-focused channel propagating at an oblique angle of incidence to an interface separating two or more self-focusing nonlinear dielectric media. A complete characterization of the different behavior of the channel is given in the proper parameter space. In the dominant region, the nonlinear wavepacket representing the self-focused channel is represented as an equivalent particle moving in an equivalent potential. The dynamics of the particle is described by Newton's equations of motion, with the asymptotic propagation paths of the channel being read off from the associated phase planes of the equivalent potential. This theory provides therefore, the nonlinear Snell's Laws of refleciton or transmission since the particle dynamics gives the critical angle of total reflection and in the case of transmission, the corresponding angle of transmission. This theory also gives the stability characteristics of nonlinear surface waves, which had only been partially established in the past through numerical simulations. Finally, some applications of the theory are presented such as the design of an all-optical power adjustable spatial scanning element and an all optical switch. Extensions of the theory to waveguides with multiple interfaces are also given and possible new directions are also suggested.

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Monteiro, Eric. « Contributions aux méthodes numériques pour traiter les non linéarités et les discontinuités dans les matériaux hétérogènes ». Phd thesis, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00601050.

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Motivé par l'étude de tissus biologiques, ce travail contribue aux développements d'outils numériques permettant de prédire la réponse mécanique de matériaux hétérogènes non linéaires dans lesquels les énergies d'interfaces deviennent prépondérantes. Ainsi, une méthode d'homogénéisation multi échelle combinée à une technique de réduction de modèle basée sur la décomposition orthogonale aux valeurs propres est proposée dans un cadre thermique et hyperélastique. Les énergies d'interfaces entre les différentes phases des composites sont décrites par un modèle d'interface cohérent et prises en compte numériquement par une approche liant la méthode des éléments finis étendus et la méthode level-set. Une étude de l'étalement d'une cellule vivante entre deux lamelles fixes est ensuite réalisée. Les deux modèles utilisés pour les simulations montrent que l'assemblage cortex d'actine-membrane plasmique ne joue qu'un rôle minime dans la réponse mécanique cellulaire

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Li, Xiangwei. « Measuring friction at an interface using nonlinear ultrasonic response ». Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/22514/.

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Contacts of rough surfaces are present in almost all machines and mechanical components. Friction at the rough interface cause energy dissipation, wear and damage of surfaces. Engineers are interested in knowing the frictional conditions at contact interfaces. Despite friction being such a fundamental phenomenon, it is surprisingly difficult to measure reliably as results depend on the test method measurement environment. Methods have been developed to measure the friction and sliding contact tribometers are devised mostly in a laboratory environment. Their applications in measuring friction in-situ in a real contact is a challenge. Therefore, the aim of this research is to develop an ultrasonic method to measure friction and friction coefficient in-situ in a contact interface. Ultrasonic methods developed for non-destructive testing have been used to measure tribological parameters, such as oil film thickness, viscosity and pressure, in-situ bearings and machines. In conventional ultrasonic techniques, pulses are low power and when they strike an interface they do not result in a change in the contact state. The process is linear and elastic. However, high power sound waves can cause opening or closing of an interface, or interfacial slip; this is non-linear. Recently Contact Acoustic Nonlinearity (CAN) has drawn interest due to its potential in the non-destructive evaluation. When high power bulk shear ultrasound propagates through a compressed rough contact interface, higher order frequency components, higher odd order harmonics (3f, 5f, etc.) are generated in both transmitted and reflected waves. The nonlinear nature of the stick-slip phenomenon in friction may be the source of nonlinearity. In this study, nonlinearity due to the interaction of a shear ultrasonic wave with a frictional interface has been initially investigated numerically. A one-dimensional numerical model has been employed to understand contact nonlinearity generation and its dependence on incident ultrasonic amplitude, contact pressure and friction coefficient. The third harmonic increases and then decreases when contact stress rises, which suggests that nonlinearity generation due to the 'stick-slip' motion occurs at low contact stress and is restricted at high contact pressure. Harmonic generation at the contact was secondly investigated experimentally using a high frequency nonlinear ultrasonic technique. Methods were developed to separate the contact nonlinearity from the measured ultrasonic nonlinearity. Contact nonlinearity originating from a rough interface are assessed under various test conditions. Experimental measurement shows good agreement with the numerically computed nonlinearity. Two strategies were developed to estimate the friction coefficient using experimentally measured contact nonlinearity in conjunction with the numerical computation. The ultrasonically measured friction coefficient agrees reasonably with the sliding test results and published data. Using the contact nonlinearity, the ultrasonic method shows the usefulness in measuring the friction coefficient in-situ in a contact interface.

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Katsouli, Maria. « Seismic response of dam-foundation systems with nonlinear interface behavior ». Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61712.

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DANTAS, Henrique Cunha. « Brain-machine interface using nonlinear Kalman filters and channel selection ». Programa de Pos Graduacao em Ciencia da Computacao, 2015. https://repositorio.ufpe.br/handle/123456789/14238.

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Submitted by Isaac Francisco de Souza Dias (isaac.souzadias@ufpe.br) on 2015-10-22T16:37:20Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_Henrique_Dantas_2015.pdf: 1887462 bytes, checksum: 0e4a34db6ecb36db533670b19464128c (MD5)
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This dissertation describes the use of Kalman Filter to decode neural signals, which were recorded using cortical surface potentials, acquired with dense grids of microelectrodes, for brain-computer interfaces (BCIs). This work represents a combination of electronic and biomedical engineering, machine learning and neural science. Kalman filters have been used to decode neural signals and estimate hand kinematics in many studies. However, most prior work assumes a linear system model, an assumption that is violated by neural systems. In this dissertation, I added nonlinearities to the decoding algorithm improving the accuracy of tracking hand movements using neural signal acquired via a 32-channel micro-electrocorticographic (µECoG) grid placed over the arm and hand representations in the motor cortex. Experimental comparisons indicate that a Kalman filter with a fifth order polynomial generative model with cross product relating the hand kinematics signals to the neural signals improved the mean-square tracking performance in the hand movements over a conventional Kalman filter employing a linear system model. While in other works the channel delays were estimated using algorithm based on hill climbing or assuming the uniformity of delay across all the channels. In this work, Particle Swarm of Optimization was applied to better estimate the delays. Also, I was also able to develop a generalized feature selection algorithm and apply to it, to select the most significant channels. As expected this caused a loss in accuracy, but the results of a 16 neural channels system were comparable with the full 32 channel system. This dissertation represents a comprehensive investigation of addition of non linearities, delay estimation and feature selection for Kalman Filter, when used as interface between man and machine.
Essa dissertação descreve o uso dos Filtros de Kalman para decodificar sinais neurais, que são gravados na superfície do córtex cerebral por uma malha densa de micro eletrodos, para interfaces cérebro computador. Esse trabalho representa a combinação entre os campos das engenharia eletrônica e biomédica, aprendizagem de máquina e neuro ciência. Filtros de Kalman tem sido usados para decodificar sinais neurais e estimar os estados cinemáticos da mão em diversos estudos. No entanto, na maioria dos trabalhos anteriores é assumido linearidade, tal premissa é quase certa de ser falsa em sistemas neurais. Nessa dissertação, foi adicionado não linearidades ao algoritmo de decodificação, que resultou em uma melhora na acurácia da predição dos movimentos da mão para sinais adquiridos por uma malha de 32 micro canais eletrocortigráfico (µECoG), colocados sobre as áreas que representam mão e braços no córtex motor. Comparações experimentais indicam que os Filtros de Kalman com quinta ordem polinomial no modelo generativo com o produto cruzado para relacionar o estado cinemático da mão com os sinais neurais melhoram o erro quadrático se comparado com os Filtros de Kalman tradicionais. Enquanto em outros trabalhos os retardos dos canais são estimados com algoritmos de subida de encosta ou assumindo uniformidade entre os atrasos. Nesse trabalho, foi usado otimização po exame (PSO) para estimar os melhores retardos para cada canal. Nesse trabalho, também foi desenvolvido uma generalização da informação mutua para selecionar os melhores canais. Como o esperado a redução para 16 canais neurais, levou a uma perda de desempenho, porém os resultados são comparáveis. Essa dissertação representa uma compreensiva investigação sobre a adição de não linearidades, estimação de atrasos e seleção de características para Filtros de Kalman, quando usados como interface entre homem e máquina.

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Varatharajah, Paramanathan. « Propagation of light beams at the interface separating nonlinear diffusive dielectrics ». Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185543.

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Diffusion effects on the stationary TE nonlinear surface waves and guided waves and the beam propagation characteristics at the interface separating two or more nonlinear diffusive Kerr-like media are studied extensively. The shape of the nonlinear surface and guided waves are computed for differing diffusion mechanisms and diffusion lengths. Stability of these waves is determined using the beam propagation method. The power and the shape of the nonlinear surface or guided waves are seen to be sensitive to the scaled diffusion length. However, many features including the stability criteria from the diffusionless case remain in the presence of the diffusion. An equivalent particle theory, describing the propagation of a self-focused light channel at the interface of two nonlinear dielectric media, is extended to include diffusion of the nonlinear excitation within each medium. The theory replaces the computationally intensive beam propagation problem by a much simpler Newtonian dynamical problem of studying the motion of an equivalent particle in an effective potential. This simpler Newtonian dynamical problem provides quantitative information on the asymptotes of the reflected, transmitted or trapped channels as well as the stability of the latter as a function of increasing diffusion length. The main results are that increased diffusion makes light transmission more difficult and tends to wash out the local equilibria of the equivalent potential representing unstable or stable TE nonlinear surface waves. The dynamics of two beams interacting at an interface separating two nonlinear dielectrics is studied. Using the two-soliton solution of the nonlinear Schrodinger equation (NLS) and performing a perturbation analysis, ordinary differential equations (ODE) approximation for the two beam interaction dynamics are derived. The numerical results of the ODE model are verified by comparison with numerical solutions of the governing full partial differential equation (PDE). This ODE model is reduced to a simple form to carry out a useful analysis for a special case where a single beam propagating as a trapped surface wave acts as a power controllable switch to direct a second beam incident at a finite angle to the interface. In this case the shape of the effective potential for the second beam is obtained and predicts the behavior of such a beam using the equivalent particle theory.

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Thakore, Vaibhav. « Nonlinear dynamic modeling, simulation and characterization of the mesoscale neuron-electrode interface ». Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5529.

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Extracellular neuroelectronic interfacing has important applications in the fields of neural prosthetics, biological computation and whole-cell biosensing for drug screening and toxin detection. While the field of neuroelectronic interfacing holds great promise, the recording of high-fidelity signals from extracellular devices has long suffered from the problem of low signal-to-noise ratios and changes in signal shapes due to the presence of highly dispersive dielectric medium in the neuron-microelectrode cleft. This has made it difficult to correlate the extracellularly recorded signals with the intracellular signals recorded using conventional patch-clamp electrophysiology. For bringing about an improvement in the signal-to-noise ratio of the signals recorded on the extracellular microelectrodes and to explore strategies for engineering the neuron-electrode interface there exists a need to model, simulate and characterize the cell-sensor interface to better understand the mechanism of signal transduction across the interface. Efforts to date for modeling the neuron-electrode interface have primarily focused on the use of point or area contact linear equivalent circuit models for a description of the interface with an assumption of passive linearity for the dynamics of the interfacial medium in the cell-electrode cleft. In this dissertation, results are presented from a nonlinear dynamic characterization of the neuroelectronic junction based on Volterra-Wiener modeling which showed that the process of signal transduction at the interface may have nonlinear contributions from the interfacial medium. An optimization based study of linear equivalent circuit models for representing signals recorded at the neuron-electrode interface subsequently proved conclusively that the process of signal transduction across the interface is indeed nonlinear. Following this a theoretical framework for the extraction of the complex nonlinear material parameters of the interfacial medium like the dielectric permittivity, conductivity and diffusivity tensors based on dynamic nonlinear Volterra-Wiener modeling was developed. Within this framework, the use of Gaussian bandlimited white noise for nonlinear impedance spectroscopy was shown to offer considerable advantages over the use of sinusoidal inputs for nonlinear harmonic analysis currently employed in impedance characterization of nonlinear electrochemical systems. Signal transduction at the neuron-microelectrode interface is mediated by the interfacial medium confined to a thin cleft with thickness on the scale of 20-110 nm giving rise to Knudsen numbers (ratio of mean free path to characteristic system length) in the range of 0.015 and 0.003 for ionic electrodiffusion. At these Knudsen numbers, the continuum assumptions made in the use of Poisson-Nernst-Planck system of equations for modeling ionic electrodiffusion are not valid. Therefore, a lattice Boltzmann method (LBM) based multiphysics solver suitable for modeling ionic electrodiffusion at the mesoscale neuron-microelectrode interface was developed. Additionally, a molecular speed dependent relaxation time was proposed for use in the lattice Boltzmann equation. Such a relaxation time holds promise for enhancing the numerical stability of lattice Boltzmann algorithms as it helped recover a physically correct description of microscopic phenomena related to particle collisions governed by their local density on the lattice. Next, using this multiphysics solver simulations were carried out for the charge relaxation dynamics of an electrolytic nanocapacitor with the intention of ultimately employing it for a simulation of the capacitive coupling between the neuron and the planar microelectrode on a microelectrode array (MEA). Simulations of the charge relaxation dynamics for a step potential applied at t = 0 to the capacitor electrodes were carried out for varying conditions of electric double layer (EDL) overlap, solvent viscosity, electrode spacing and ratio of cation to anion diffusivity. For a large EDL overlap, an anomalous plasma-like collective behavior of oscillating ions at a frequency much lower than the plasma frequency of the electrolyte was observed and as such it appears to be purely an effect of nanoscale confinement. Results from these simulations are then discussed in the context of the dynamics of the interfacial medium in the neuron-microelectrode cleft. In conclusion, a synergistic approach to engineering the neuron-microelectrode interface is outlined through a use of the nonlinear dynamic modeling, simulation and characterization tools developed as part of this dissertation research.
Ph.D.
Doctorate
Physics
Sciences
Physics

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Ros, Ida. « NONLINEAR OPTICAL PROCESSES IN MOLECULAR SYSTEMS AT THE INTERFACE WITH METAL NANOSTRUCTURES ». Doctoral thesis, Università degli studi di Padova, 2010. http://hdl.handle.net/11577/3427355.

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Surface plasmon excitations, i.e. collective oscillations of the conduction electrons, strongly influence the optical properties of metal nanostructures. Furthermore, under resonance conditions, a giant local electromagnetic field develops on the nanostructure surface. By controlling the size and shape of the nanostructures, it is possible to control the surface plasmon resonance frequency and so the frequency at which the local field will be amplified. If a molecule is located at the interface with metal nanostructures, its optical properties will be affected by the local field and can be enhanced or suppressed by the metal. Here, the effect on the optical properties of molecules due to the interaction with metal nanostructures is investigated by different techniques. Emphasis is placed on the synthesis and the study of the nonlinear properties of nude and functionalized gold nanoshells (NSs). Different shape gold nanoparticles are synthesized: spherical particles in water and in toluene, rod like particles in water subsequently transferred in organic solvents, core-shells in water. Gold nanostructures have been functionalized with spiropyran, PEP-C3-SH and PEP-C12-SH (two heterocyclic dyes), Rhodamine B. Fluorescence decay times for PEP-C3-SH and PEP-C12-SH free and bound to nanorods (NRs) have been measured to study the interaction between the dye and the nanostructure and to evaluate the effects of the chain length. The PEP moieties present a two exponential decay times: a short one of 6.2 ± 0.5 ns and a long one of 61 ± 2 ns. When the dye is bound to NRs, the interaction between the molecules and the nanoparticles provoked a change in the PEP dynamics. Both PEP-C3 and PEP-C12 bound to NRs, decay faster, indicating quenching of fluorescence. Nanoshells functionalized with Rhodamine B have been characterized with Pump and Probe technique. The dye clearly modified the dynamics of naked NSs and shortened the electron-phonon time decay from 4.9 ps (naked NSs) to 3.7 ps (RhB-NSs) introducing an additional channel by which hot electrons can decay. SERS measurements of NSs, deposited on glass substrates, covered by benzenethiol were performed. Incomplete shells with sharp tips may turn out to be quite interesting for SERS analysis due to the strong local field that take place at tip apexes. Enhancement of the Raman signal has been clearly observed because the concentration of benzenethiol is too low to give Raman signal except in case of strong enhancement field effects. Z-scan measurements, with fs laser pulses, were performed at 20 and 200 Hz and at different energy to study the nonlinear response of naked NRs and NSs. Both nanostructures behaved like saturable absorber and reshaped during laser pulse illumination. NSs z-scan data, fitted with Sheik-Bahae model, yielded an effective value of the non linear absorption coefficient β = (–1.1 ÷ –9.6) X 10-11 cmW-1 dependent on the pulse energy and repetition rate. The absolute value of the nonlinear absorption coefficient increased both with energy and pulse repetition rate. The effect of increasing the repetition rate is likely related to thermal effects, also confirmed by an increase of the beam waist radius used for fitting the z-scan data. The dependence on the energy, instead, indicated that the process is not a third order phenomenon, but higher order contributions should be taken into account. Together with the plasmonic effects, the NSs deposition onto a transparent electrode potentially allows for improved efficiency both for light collection and charge collection. With this motivation, work function measurements on NSs deposited ITO substrates have been performed by the Kelvin probe method. They showed that by selectively choosing the shell thickness, ITO pre-functionalization and nanoparticle coverage, it is possible to fine-tune the WF of the transparent electrode within the range of 3.9 – 4.4 eV.
L’eccitazione dei plasmoni di superficie, cioè dell’oscillazione collettiva degli elettroni di conduzione, influenza fortemente le proprietà ottiche delle nanostrutture metalliche. Inoltre, in condizioni di risonanza, si sviluppa, sulla superficie della nanostruttura, un fortissimo campo elettrico localizzato. Controllando le dimensioni e la forma delle nanostrutture, è possibile controllare la frequenza di risonanza del plasmone superficiale e, di conseguenza, la frequenza alla quale il campo elettrico locale verrà amplificato. Se una molecola è posizionata all’interfaccia con la nanostruttura metallica, le sue proprietà ottiche risentiranno del campo locale e potranno essere amplificate o ridotte dal metallo. In questo lavoro di tesi, sono stati studiati, con diverse tecniche, gli effetti, sulle proprietà ottiche di molecole, dell’interazione con nanostrutture metalliche. In particolare, ci si è concentrati sulla sintesi e sullo studio delle proprietà non lineari di nanoshell (NSs) nude e funzionalizzate. Sono state sintetizzate nanoparticelle di oro di forma diversa: particelle sferiche in acqua e toluene, a forma di rod in acqua (successivamente trasferite in solventi organici), core-shell in acqua. Le nanostrutture d’oro sono state funzionalizzate con spiropirani, PEP-C3-SH e PEP-C12-SH (due molecole eterocicliche), Rodamina B. I tempi di decadimento di fluorescenza per PEP-C3-SH e PEP-C12-SH liberi e legati alle nanorods (NRs) sono stati misurati per studiare l’interazione tra il colorante e la nanostruttura e per valutare gli effetti della diversa lunghezza della catena alchilica. Il colorante, indipendentemente dalla lunghezza della catena, presenta un decadimento biesponenziale con un tempo breve di 6.2 ± 0.5 ns e uno lungo di 61 ± 2 ns. In seguito alla funzionalizzazione, l’interazione tra la molecola e le NRs provoca un cambiamento nella dinamica di decadimento del PEP. Sia il PEP-C3 che il PEP-C12 legati alle NRs, decadono più rapidamente, indicando un’attenuazione della fluorescenza. Le nanoshell funzionalizzate con la Rodamina B sono state caratterizzate con la tecnica Pump and Probe. Il colorante modifica la dinamica delle NSs e riduce il tempo di decadimento dell’accoppiamente elettrone-fonone da 4.9 ps (NS nude) a 3.7 ps (RhB-NSs), introducendo un canale addizionale attraverso cui gli elettroni caldi possono decadere. Sono state effettuate delle misure SERS su benzentiolo attaccato a nanoshell, depositate su substrati di vetro. Shell incompleti caratterizzati da punte acuminate possono risultare molto interessanti per la Spettroscopia SERS per i forti campi locali che si sviluppano sulle punte. Un aumento del segnale Raman è stato chiaramente osservato, dato che la concentrazione di benzentiolo era troppo bassa per dare segnale Raman eccetto in caso di effetti di campo locale. Sono state effettuare misure Z-scan con impulsi di durata di centinaia di femtosecondi, a frequenza di ripetizione di 20 e 200 Hz e a diverse energie, per studiare la risposta non lineare di NRs e NSs non funzionalizzate. Entrambe le nanostrutture si comportano come assorbitori saturabili e subiscono delle modifiche morfologiche per effetto dell’illuminazione con impulsi laser. I dati z-scan per le nanoshell, fittati con il modello Sheik-Bahae, producono un valore effettivo del coefficiente di assorbimento non lineare β = (–1.1 ÷ –9.6) X 10-11 cmW-1 che dipende sia dall’energia dell’impulso che dalla frequenza di ripetizione. Il valore assoluto del coefficiente di assorbimento non lineare aumenta sia con l’energia che con la frequenza di ripetizione. L’aumento con la frequenza di ripetizione è dovuto a effetti termici, confermati anche da un aumento del raggio del beam waist usato per fittare i dati z-scan. Invece, la dipendenza dall’energia indica che il processo non è un fenomeno al terzo ordine ma si deve tenere conto di contributi di ordine superiore. Insieme agli effetti plasmonici, le nanoshell depositate su elettrodi trasparenti, come l’ITO (Indium Tin Oxide), potrebbero potenzialmente migliorare l’efficienza sia dell’assorbimento della luce che della separazione di carica. Per questa ragione, è stata misurata la funzione lavoro di nanoshell depositate su substrati di ITO con la tecnica Kelvin probe. Scegliendo opportunamente lo spessore dello shell, se pre-funzionalizzare l’ITO e il livello di ricoprimento di particelle, è possibile variare la funzione lavoro dell’elettrodo nell’intervallo 3.9 – 4.4 eV.

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Dinh, Anh thi. « Finite Element Methods for nonlinear interface problems. Application to a bioﬁlm growth model ». Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCD083.

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Un biofilm est un ensemble de micro-organismes tels que les bactéries, les champignons ou encore les algues qui vivent en communauté. Les biofilms ont la capacité d’être présents en tout lieu. Ils sont observés dans les milieux aqueux ou humides. Ils peuvent se développer sur n’importe quel type de surface naturelle ou artificielle,qu’elle soit minérale (roche, interfaces air-liquide...) ou organique (peau, tube digestif,racines et feuilles des plantes), industrielle (canalisations, coques des navires) ou médicale comme les prothèses et les cathéters. Cette ubiquité est à l’origine de nombreuses infections bactériennes. Les infections nosocomiales contractées dans les hôpitaux sont un exemple majeur. Certaines de ces infections pouvant être mortelles.Le traitement médical des biofilms est souvent inefficace pour lutter contre ce type d’infection. Il est donc important de comprendre les mécanismes de croissance d’un biofilm. Telle est la motivation de la présente thèse. Afin de réaliser des simulations numériques d’un modèle décrivant la croissance d’un biofilm, nous combinons différentes méthodes de calcul basées sur la méthode Nitsche-Extended Finite Element Method (NXFEM) ainsi que sur la méthode des lignes de niveau. Ces méthodes nous permettent d’étudier des modèles complexes dans lesquels l’interface entre le biofilm et son environnement est capable de se déformer tout en dépendant du temps. Ceci permet de considérer une discrétisation à l’aide d’un maillage ne coïncidant pas avec l’interface biofilm/environnement.Nous présentons également une technique de découplage d’un système d’équations aux dérivées partielles semi-linéaires et la fac¸on dont nous appliquons la méthode NXFEM pour résoudre un tel problème. Ce système est en relation avec le modèle de croissance du biofilm qui est traité dans cette thèse. Pour l’implémentation, une boite à outils NXFEM, développée en Matlab, a été entièrement conçue pour résoudre un tel problème. Nous donnons dans ce document les détails des algorithmes et techniques numériques utilisés afin que chacun puisse utiliser cette boite à outils pour ses propres projets
A biofilm is a collective of living, reproducing microorganisms, such as bacteria, that stick together as a colony or community. They appear everywhere in human life and have impacts on our environment. Biofilm modeling, together with laboratory experiments,has risen toproduce quantitative tools for scientists to better understand the biofilm’s growth. This thesis is motivated to research on this subject.A combination of computational methods which are based on Nitsche-Extended Finite Element Method (NXFEM), Level Set Method and some other stabilized techniques is used to solve and simulate a biofilm growth model. These methods allow us to work with a complex scheme in which the interface between the biofilm and its environment may change with time and on an unfitted mesh. We also present a technique of decoupling a system of semilinear differential equations and how we apply the NXFEM method to solve such a problem. This system has a relation to a model of biofilm’s growth which will be examined carefully in the work.For the implementations, NXFEM toolbox which is a Matlab based toolbox is built for solving such a problem. We also give the details of all algorithms and numerical techniques so that everyone can use this toolbox for their own projects

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Radhakrishnan, Vikram. « Cohesive zone modeling of the interface in linear and nonlinear carbon nano-composites ». Cincinnati, Ohio : University of Cincinnati, 2008. http://rave.ohiolink.edu/etdc/view.cgi?acc_num=ucin1206453509.

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Thesis (M.S.)--University of Cincinnati, 2008.
Advisor: Kumar Vemaganti. Title from electronic thesis title page (viewed Feb.25, 2009). Includes abstract. Keywords: carbon nano-composites; cohesive zone modeling (CZM); interface; finite element analysis. Includes bibliographical references.

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Zhang, Ziyin. « Nonlinear Assessment of Material and Interface Imperfections Based on Non-Collinear Shear Wave Mixing ». University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1458814847.

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Guo, Xinxin. « Nonlinear architected metasurfaces for acoustic wave scattering manipulation ». Thesis, Le Mans, 2018. http://www.theses.fr/2018LEMA1030/document.

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Ces dernières années, les métamatériaux acoustiques sont largement étudiés pour leur intérêt dans la réalisation de divers types de contrôle des ondes à une échelle sub-longueur d’onde. En particulier, les métasurfaces acoustiques ont montré leur capacité à manipuler des ondes en limites de milieux de propagation via les processus de réflexion, de transmission et de réfraction. Contrairement au régime linéaire qui concerne l’immense majorité des travaux sur les métamatériaux acoustiques, les études sur les propriétés non linéaires des métamatériaux, de surcroit des métasurfaces, restent peu nombreuses, malgré la possibilité de générer des phénomènes acoustiques riches et variés. Les principaux freins au développement des métamatériaux non linéaires sont l'efficacité généralement faible de la réponse non linéaire et le manque de contrôle sur cette non-linéarité. Les travaux de recherche présentés ici ont donc pour objectif de concevoir des architectures de métasurfaces élastiques, permettant un contrôle des ondes acoustiques dans le régime non linéaire. En particulier l’effet de conversion d’une onde fondamentale vers son deuxième harmonique est étudié dans le processus de réflexion et de transmission unidirectionnelle. Cela nécessite le design de la non-linéarité élastique, qui est réalisé à base de modélisations discrètes de systèmes masses-ressorts et d'architectures composées d'éléments tournants. Les métasurfaces ainsi conçues, résonantes et à non-linéarité contrôlée, permettent de générer des effets non linéaires acoustiques inhabituels, potentiellement intéressants pour la manipulation d'ondes acoustiques
In recent years, acoustic metamaterials have proven to be of great interest for their ability to achieve a variety of wave control at sub-wavelength scale. In particular, acoustic metasurfaces have shown their ability to manipulate waves from the boundaries of propagation media, via the reflection, transmission and refraction processes. Unlike the linear regime which has been extensively investigated in acoustic metamaterials, studies of the nonlinear acoustic properties of metamaterials, especially nonlinear acoustic metasurfaces, are quite scarce, despite the possibility to lead to a rich and diverse set of non-trivial acoustic phenomena. The key limitations in the development of nonlinear acoustic metamaterials are the typically weak efficiency of their nonlinear response together with the lack of control on this nonlinearity. This PhD research is thus dedicated to the design of nonlinear elastic metamaterial and metasurface architectures, enabling acoustic wave control in the nonlinear regime. Specifically, the conversion effect from a fundamental wave to its second harmonic is studied through the one-dimensional scattering process (reflection and transmission) by metasurfaces. This requires the elastic nonlinearity management, realized via the discrete modeling of lumped-element systems and architectures made of rotating units. Such designed metasurfaces, resonating and with harnessed nonlinearity, can create unusual nonlinear acoustic effects, potentially interesting for wave control. This research open the path to a more systematic study of nonlinear acoustic wave manipulation by metamaterials

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