Dissertations / Theses on the topic 'Tunneling Time'

Fractures and fracture networks govern the mechanical and fluid flow behavior of rock masses. Tunneling and other rock mechanics applications therefore require the characterization of rock fractures based on geological data. Field investigations produce only a limited amount of data from boreholes, outcrops, cut slopes, and geophysical surveys. In tunneling, the process of excavation creates a priceless opportunity to gather more data during construction. Typically, however, these data are not utilized due to the impedance of sampling and analysis on the flow of construction, and safety concerns with sampling within unlined tunnel sections. However, the use of this additional data would increase the overall safety, quality, and cost savings of tunneling. This study deals with several aspects of the above, with the goal of creating methods and tools to allow engineers and geologists to gather and analysis fracture data in tunnels without interrupting the excavation and without compromising safety. Distribution-independent trace density and mean trace length estimators are developed using principles of stereology. An optimization technique is developed utilizing Differential Evolution to infer fracture size and shape from trace data obtained on two or more nonparallel sampling planes. A method of producing nearly bias free empirical trace length CDF's is also introduced. These new methods and tools were validated using Monte Carlo simulations. A field study was conducted in an existing tunnel allowing the above methods and tools to be further validated and tested. A relational database was developed to aid in storage, retrieval, and analysis of field data. Fracture models were built and updated using fracture data from within the tunnel. Utilization of state of the art imaging techniques allowed for remote sampling and analysis, which were enhanced by the use of 3d visualization techniques.
Ph. D.

L’excavation d’un tunnel profond dans des terrains poussants pose des difficultés particulières de conception et d’exécution. Ce type de terrain est caractérisé par des fortes convergences en paroi du tunnel de nature différée et souvent anisotrope. Le comportement d’un tunnel excavé en terrain poussant est très influencé par la technique d’excavation utilisée. Le cas d’étude du tunnel routier du Fréjus et de sa galerie de sécurité permet d’illustrer ce phénomène. Il s’agit de deux tunnels parallèles qui montrent une configuration très intéressante étant donné qu’ils traversent des conditions géotechniques similaires et qu’ils sont creusés avec des techniques d’excavation différentes : le tunnel routier a été creusé par méthode conventionnelle à l’explosif tandis que la galerie de sécurité a été creusée avec un tunnelier à bouclier simple. Les mesures d’auscultation réalisées pendant l’excavation des deux tunnels ont été analysées et comparées. Des modélisations numériques pour simuler la réponse des deux tunnels ont été développées avec le logiciel Flac3D. Le comportement du terrain est simulé avec un modèle visco-elasto-plastique et anisotrope. L’anisotropie liée à la schistosité du terrain est introduite dans le modèle par la présence de plans de faiblesse d’orientation donnée (ubiquitous joint model) insérés dans une matrice rocheuse caractérisée par un comportement visco-elasto-plastique isotrope. Une rétro-analyse a été réalisée sur les mesures de convergence obtenues lors du creusement du tunnel routier du Fréjus. Le comportement du terrain identifié dans le tunnel routier est ensuite extrapolé pour prédire la réponse de la galerie de sécurité. L’objectif est de reproduire l’état des contraintes observé dans les voussoirs de la galerie de sécurité et d’extrapoler les sollicitations à long terme. L’influence que la technique d’excavation, en particulier sur le comportement différé du terrain a été prise en compte dans les simulations numériques. On a mis en évidence que les déformations différées du terrain sont réduites lorsque l’excavation est réalisée au tunnelier.Par ailleurs, une synthèse critique de la méthode convergence-confinement et de ses variantes a été réalisée. Une discussion a été menée sur l’applicabilité des méthodes convergence-confinent quand elles sont utilisées pour le dimensionnement des tunnels circulaires excavés en section pleine avec l’installation d’un soutènement raide près du front d’excavation comme c’est le cas lors d’une excavation au tunnelier. Dans ce contexte, un ensemble de formules empiriques sont proposées. Elles permettent d’obtenir avec une bonne précision l’état d’équilibre entre le terrain et le soutènement et peuvent être utilisées dans la phase de pré-dimensionnement des ouvrages
During the excavation of deep tunnels, squeezing ground conditions are often encountered. The squeezing behavior of the ground is characterized by large time-dependent and usually anisotropic convergences that take place at the tunnel wall. The technique of excavation has a strong influence on the tunnel response when it is excavated under squeezing conditions. This phenomenon is illustrated throughout the case study of the Fréjus road tunnel excavated with conventional drill and blast methods and of its safety gallery excavated with a single shield tunneling boring machine. They exhibit a very interesting configuration of two tunnels excavated in parallel under the same geotechnical conditions but with different excavation techniques. Monitored geotechnical data from both tunnels are analyzed and compared. Numerical simulations of both tunnels have been carried out with Flac3D. An anisotropic creep model which includes weakness planes of given orientation embedded in a visco-elasto-plastic matrix has been used for describing the behavior of the ground. A back-analysis of convergence measurements of the Fréjus road tunnel has been carried out. The behavior of the ground identified from the Fréjus road tunnel is extrapolated to predict the response of the Fréjus safety gallery in terms of the stress state in the lining. The influence of the technique of excavation on the time-dependent parameters of the ground is taken into account in the computations and its effects are discussed. It is shown that the long term ground deformation are significantly reduced with TBM excavation as compared to traditional blast and drill method.Furthermore, the convergence-confinement methods are reviewed and their applicability is discussed when they are applied to full face circular tunnels excavated in rock masses with a stiff support system near the face. In this context, a set of empirical formula are proposed which allows to accurately predict the equilibrium state between the ground and the lining in circular tunnels excavated in full section. These formula are useful in the preliminary phase of tunnel design

Vid kalkylering inför en tunneldrivning finns det vissa svårigheter med att bestämma hur lång tid arbetet tar och framför allt vid uppstarten av produktionen. Det kan leda till att anbudsofferter blir felberäknade med avseende på både tiden och kostnaden. Vid en felberäkning av hur mycket tid ett projekt kan tänkas behöva kan det i längden ge högre kostnader och därmed lägre intäkter. För att förhindra sådana fallgropar är ett steg att identifiera de problem som kan uppstå under produktionen och förhindra dem. Mätningar har därför utförts under uppstarten av ett tunneldrivningsprojekt i Norsborg. Även om mätningarna utförs på ett specifikt projekt är förhoppningen att det även ska kunna användas vid andra tunneldrivningsprojekt. Många resultat och slutsatser kan också tillämpas vid andra tunneldrivningsprojekt och kanske även vid helt andra byggprojekt. Mätningarna har skett ute på projektet och har innefattat tidtagning på de olika arbetsmoment som har skett under uppstarten och inom varje cykel. En cykel omfattar alla de arbeten som sker vid sprängning av en hel stuff, det vill säga från det att borrning påbörjas inför en laddning av salva till dess att salvan sprängts av och allt berg har lastats och rensats bort från stuffen. Problem som har uppstått under tiden och anledningen till dem har även noterats. Kvantiteter på hur många borrhål som har borrats och hur långa dessa är, hur mycket sprängmedel som har använts och hur många hål som har laddats har dokumenterats för att kunna ta fram kapaciteten under de olika momenten. Uppstarten redovisas per vecka med cirkeldiagram som visar hur mycket av den totala arbetstiden som har gått åt för varje moment. Här redovisas också hur mycket stopp som har skett för respektive vecka. Diagrammen ger en bra överblick över vad som har skett under uppstarten och vilka moment som har varit mer tidskrävande än andra.   Av diagrammen vid uppstarten kan utläsas att många problem som uppstod vid uppstarten hade kunnat förhindras om det funnits bättre maskiner eller att tillgången till maskinist från leverantör hade funnits på plats redan från starten. En del av problemen hade alltså kunnat förhindras eller reduceras redan vid kalkyleringen. Av resultaten som kan avläsas kring cyklerna har många olika faktorer spelat en stor roll kring huruvida effektiviteten och kapaciteterna förbättras. Dessa resultat redovisas i diagram där helheten visas kring de cykler som uppmätts och i mer specifika diagram där varje moment behandlas var för sig. Många olika slutsatser har dragits gällande de olika faktorer som påverkar effektiviteten. Lastningen, som är det mest kritiska momentet i cykeln, har visat sig kunna effektiviseras desto längre projektet fortskridit.
Planning a tunnel project presents certain difficulties in deciding how long the job will take, particularly at the start of production. This can lead to miscalculated quotations concerning both time and cost. A miscalculation of how much time a project may need can increase costs long-term and thus lead to lower revenues. In order to avoid such pitfalls, one measure is to identify the problems that can arise during production and prevent them. Therefore, measuring’s have been made during the start-up of a tunnel project in Norsborg. Even if measuring’s have been performed on a specific project, the expectation is that they can be used at later tunnel projects as well. Many results and conclusions can also be applied to other tunnel projects, and possibly even to completely different types of construction projects. The measuring’s have taken place at the project site and have included timekeeping of the various work tasks that have taken place during start-up and each cycle. A cycle covers all work that happens when blasting a full tunnel opening; that is, from the initial drilling for a charge until the charge has burst and all the rock has been cleared and loaded from the tunnel opening. Any problems and their respective causes during this process have been recorded. The number of drill holes and their length, how much explosives that have been used and how many holes that have been primed with charges, has been documented so that capacity during the various tasks could be outlined. The start-up is recorded on a weekly circle chart showing how much of the total work time has been spent on each task. It also shows any stoppages during the week. The charts provide a good overview of the proceedings during start-up and what tasks have taken more time than others. The charts show that many of the problems that arose during start-up could have been prevented if better machinery or an operator from the contractor had been available on-site from the start. Some problems could also have been prevented or diminished as early as the project planning stage.  By the results that can be read from the cycles many factors have played a big role of the improvement of the efficiency and the capacity. These results are shown in charts where the whole cycles can be studied and in more specific charts where every task are examined individually. Many conclusions have been read regarding the different factors that affects the efficiency. The loading that is the most critical task within the cycle have been able to become more efficient the longer the project has proceeded.

The present work is divided in two part. The first is dedicated to the investigation of the gas-metal interactions, an interesting area in the basic surface science but also in applied one, since it could provide a more efficient way to design corrosion-resistant structural metals. In particular, we concentrate our attention on the study H2S on Fe surface. Experimental studies, of adsorption of H2S on Fe, and first-principle calculations were carried out for these systems, clarifying some important questions, such as adsorption geometry and dissociation pathways for H2S, on the above close-packed metal surfaces. However, real samples will also include a number of defects, in particular step edges where bonding of adsorbates is usually stronger than at facets. It is therefore interesting to investigate adsorption of H2S on a stepped Fe surface, a task which has not been considered yet to the best of our knowledge. In the present work we study the H2S interaction with Fe(310) surfaces by DFT calculations in order to understand the role of step defects in the adsorption properties. We recall that the (310) surface is relatively stable, and its surface energy predicted to be even smaller than that of Fe(110). We do not only obtain the binding sites and adsorption energies of H2S and its components, but we also relate bonding to the detailed features of the localdensity of states (LDOS). The second part of the present thesis is devoted to the dynamics of scattering. Scattering underlies various physical processes in different field of physics, mainly in solid state, as for example in thermoelectricity, about the filtering of hot electrons by defects, or adsorption and desorption by a surface, or in charge injection and field emission trough interface, usually associated with tunneling mechanisms. The recent developments of nanotechnology and the advent of modern high-speed high-density MOS devices, have revived the technological and theoretical interest of the scientific community on the scattering problem and in particular on quantun tunneling mechanism usually associated. Ultrascaled nanometric CMOS compatible single electron transistors (SETs) and single atom trasistors has lead the emergence of density of states graining and fluctuations in the contacts which may determine discretization of energy levels, charge localization at intradopant length scale and selection rules on quantum states in tunnelling. Consequently, the understanding of dependence of charge dynamics, across a barrier, from the initial position constitutes a relevant aspect in such systems. In this work we study the scattering process in the non stationary framework using Gaussian wave packet (GWP) to describe the particle wave function of the system so as to consider the dependence of scattering dynamics from the initial conditions. Through a numerical solution of the Schr¨odinger equation we analyse the evolution of the system calculating the transmission of the scattering GWP as a function of the initial spread and position x(0), and comparing simulated data with theoretical results. By our analysis a new important issue emerges: the time spent by the particle to reach its asymptotic probability to be observed beyond the barrier ( that we call formation time), strongly depends on initial conditions, and in particular on x(0). Finally, to analytically express such a dependence, we propose a semi-classical approximated model in which tf is described as the time spent by a finite support (accounting for the 0.99 of the probability) of the incident wave packet to cross the barrier, namely the time required to locate, in coordinate space, the greatest amount of the GWP’s probability distribution beyond the barrier interface.

La tesis propuesta es una investigación cuantitativa de diseño longitudinal, el objetivo de este estudio es implementar una metodología de Gestión en proyectos en Tunelería Subterránea con similares características a la analizada. (SIMAREG S.R.L), que involucra los procesos de Gestión de Costos y Tiempo, tomando como referencia la Metodología del Project Management Body of Knowledge (PMBOK), para el análisis, se identificaron los factores que afectan el cumplimiento de labores en la operación, como también los métodos de trabajo, y los sistemas de control; a este análisis se acompañan propuestas que mejoran y/o complementan las entradas, herramientas y técnicas y salidas, con la finalidad de poder controlar y demostrar que el proyecto puede realizarse dentro del tiempo requerido así como optimizar una adecuada distribución de recursos y una reducción de los costos generando así una mayor rentabilidad. The thesis proposal is a quantitative research and a longitudinal design, the objective of this study is to implement a project management methodology in Tunnelling Underground with similar characteristics to that analyzed. (SIMAREG SRL), involving processes about Costs and Time Management with reference to the methodology of the Project Management Body of Knowledge (PMBOK), for analyze, the factors affecting the performance of functions in the operation were identified as the working methods and control systems; this analysis proposals that enhance and / or complement the inputs, tools and techniques and outputs,, in order to be able to control and demonstrate that the project can be accomplished within the required time and optimize the appropriate distribution of resources and cost Reduction Generating support profitability.

Les travaux présentés dans cette thèse s'inscrivent dans le cadre général de la description de l'effet tunnel dans la limite semiclassique $\hbar \rightarrow 0$. Nous présentons une nouvelle méthode de calcul direct de la largeur des doublets tunnel. L'expression obtenue est basée sur l'utilisation de traces d'opérateurs quantiques, dont l'opérateur d'évolution $\hat{U}(T)$ prolongé analytiquement à l'aide d'un temps complexe $T$. L'étape suivante consiste en un développement semiclassique de ces traces. Nous nous plaçons dans le cadre des systèmes intégrables unidimensionnels afin d'insister sur l'importance d'un temps complexe et on montre que le choix d'un chemin du temps $[t]$ adapté, lors du calcul semiclassique des traces, fournit un critère de sélection efficace des trajectoires complexes dominantes. Nous verrons que cette approche retrouve la technique des instantons dans la limite d'un temps purement imaginaire et qu'elle permet d'inclure les descriptions, inaccessibles par une rotation de $\textsc{Wick}$ complète, de l'effet tunnel dynamique et résonant. Nous montrons également comment adapter cette méthode au taux de transmission tunnel d'un état localisé dans un minimum local vers un continuum d'états. Enfin, nous proposerons, en guise de perspectives, d'étudier l'effet tunnel résonant à partir de modèles intégrables présentant des îlots stables entourés de chaînes de tores pour lesquels nous tenterons d'adapter la théorie de l'effet tunnel assisté par les résonances.

Orientador: Amir Ordacgi Caldeira
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-08-18T12:04:56Z (GMT). No. of bitstreams: 1 GarciaRodriguez_AlexisOmar_D.pdf: 2441638 bytes, checksum: 00dfa78fb7b0c9f69778a51704c587b7 (MD5) Previous issue date: 2011
Resumo: Este trabalho foi motivado por várias dificuldades encontradas no estudo do artigo de M. Ueda, Transmission Spectrum of a Tunneling Particle Interacting with Dynamical Fields: Real- Time Functional Integral Approach, Phys. Rev. B 54, 8676 (1996). Nesse artigo, num formalismo de tempo real, é descrito o tunelamento de uma partícula através de uma barreira utilizando tempos não reais de travessia através dessa barreira. No presente trabalho é proposto um formalismo mais amplo de tempo real para uma introdução mais natural de valores complexos do tempo na descrição do tunelamento de uma partícula cm interação com o ambiente. Esta proposta está baseada no chamado método do tempo complexo utilizado no caso do tunelamento de uma partícula sem interação com o ambiente estudado nos trabalhos de D. W. McLaughlin, J. Math. Phys. 13, 1099 (1972) c B. R. Holstein c A. R. Swift, Am. J. Phys. 50, 833 (1982). Seguindo o trabalho citado de Ueda, o ambiente da partícula é representado através de um conjunto, ou banho térmico, de osciladores harmônicos caracterizados por uma função de densidade espectral J(w). Utilizando o método de Feynman de integrais de trajetória, integramos sobre as coordenadas dos osciladores do banho c obtemos uma expressão exata para o espectro de transmissão da partícula para uma temperatura do banho T > O. Limitando-nos então ao caso mais simples T = O, estudamos o tunelamento dissipativo da partícula através da barreira. Considerando h um parâmetro pequeno (limite semiclássico), aproximamos o espectro de transmissão da partícula através da contribuição das trajetórias clássicas c suas trajetórias vizinhas. Nesta aproximação consideramos a variação da ação efetiva da partícula para tempos dados de duração das trajetórias c deste modo substituímos o procedimento variacional seguido no trabalho indicado de Ueda onde não é considerada a variação nos tempos de travessia da partícula através da barreira. Num segundo problema variacional nos tempos de duração das trajetórias clássicas de acordo com o método do tempo complexo e considerando também a variação nas posições iniciais c finais dessas trajetórias, obtemos as equações de movimento das chamadas trajetórias clássicas especiais. Este tratamento das coordenadas iniciais c finais das trajetórias clássicas substitui o procedimento seguido no trabalho de Ueda onde é considerc1da uma aceleração nula durante todo o trajeto de movimento incluindo o trajeto na região da barreira. Diferentemente do artigo citado de Ueda, no presente trabalho utilizamos pacotes de ondas relativamente bem localizados para descrever os estados inicial e final da partícula. Em consequência, aproximamos o espectro de transmissão da partícula através de trajetórias clássicas especiais com coordenadas iniciais c finais iguais ao valor médio da coordenada para esses pacotes de ondas. O procedimento seguido neste trabalho, baseado no método do tempo complexo, permite obter o fator ele acoplamento apropriado entre as duas trajetórias que descrevem a ação efetiva ela partícula substituindo assim o procedimento de tipo ad hoc seguido com este fim no trabalho indicado de Ueda. O método do tempo complexo permite obter também o termo ela diferença entre a ação efetiva da partícula c o expoente ele tunelamento, sendo que estas grandezas são tratadas como iguais no trabalho citado de Ueda. Considerando termos até primeira ordem num campo elétrico externo c na interação da partícula com o banho de osciladores, obtemos expressões gerais para o expoente de tunelamento, o espectro de transmissão, a taxa total de tunelamento c o tempo de travessia da partícula através da barreira, válidas para um banho de osciladores com uma função de densidade espectral arbitrária. Assim temos que a interação da partícula com um banho de osciladores com uma função de densidade espectral arbitrária diminui a taxa total de tunelamento. Adicionalmente, obtemos que a interação da partícula com os osciladores do banho com frequências ?a = ?C ~ 1.9 T , onde T0 é o tempo característico de travessia através da barreira no caso cm que não há interação da partícula com o banho de osciladores nem campo elétrico, não afeta o tempo característico de travessia através da barreira. Por outro lado, a interação da partícula com os osciladores do banho que têm frequências ?a < ?C (?a > ?C) diminui (aumenta) o tempo característico de travessia através da barreira. No caso de um banho de osciladores com uma única frequência w c uma constante de acoplamento com a partícula dada por Ca = Ca (wT)a , são identificados cinco comportamentos diferentes em função de w para o expoente característico de tunelamento e o tempo característico de travessia através da barreira. Estes comportamentos correspondem aos valores de s < 1, s = 1, 1 < s < 2, s = 2 e s > 2. No trabalho de M. Ueda, Phys. Rev. B 54, 8676 (1996), foi considerado somente o expoente característico de tunelamento no caso s = 1. No caso de um banho ôhmico de osciladores a temperatura zero, assim corno no caso de um banho de osciladores com uma única frequência, obtemos que o espectro de transmissão da partícula é zero para urna energia final característica da partícula maior que a energia inicial característica. Este resultado corrige o resultado correspondente no trabalho citado de Ueda, o qual não é consistente do ponto de vista físico, permitindo também obter de um modo mais coerente a corrente de tunelamento entre dois metais separados por um material isolante a temperatura zero. Obtém-se também que a interação da partícula com um banho ôhmico de osciladora não afeta o tempo característico de travessia através da barreira até primeira ordem nessa interação
Abstract: This work was motivated by several difficulties found when studying the article by M . Ueda, Transmission Spectrum of a Tunneling Particle Interacting with Dynamical Fields: Real-Time Functional-Integral Approach, Phys. Rev. B 54, 8676 (1996). In that paper, using a real-time formalism, a tunneling particle is described by complex traversal times of tunneling. In the present work we propose a broader real-time formalism that allows for a more natural introduction of complex values of time in the description of a tunneling particle interacting with the environment. This proposal is based on the well-known complex time method used in the case of a tunneling particle with no interaction with the environment studied in the works of D. W. McLaughlin, J. Math. Phys. 13, 1099 (1972) and B. R. Holstein and A. R. Swift, Am. J. Phys. 50, 833 (1982). Following the cited work of Ueda, the environment of the particle is represented by a set, or heat bath, of harmonic oscillators which is characterized by a spectral density function J(w). Using the Feynman path integrals method, we integrate out the coordinates of the bath oscillators and obtain an exact expression for the transmission spectrum of the particle for a bath temperature T > O. Limiting ourselves to the simpler case T = O, we study the case of a dissipative tunneling of the particle. Considering h a small parameter (semiclassical limit) we approximate the transmission spectrum of the particle by the contribution of the classical trajectories and its neighboring paths. In this approach we consider the variation of the effective action of the particle for given duration times of the paths and replace the variation procedure followed in the cited work of Ueda where the variation in the traversal times of tunneling is not considered. In a second variation problem for the duration times of the classical paths, according to the complex time method and considering also the variation in the initial and final positions of these paths, we obtain the equations of motion for the so-called special classical paths. This treatment of the initial and final coordinates of the classical paths replaces the procedure followed in the cited work of Ueda where an acceleration equal to zero is considered during the entire path of motion including the region under the barrier. Unlike the cited article of Ueda, we use in the present work wave packets relatively well localized to describe the init.ial and final statics of the particle. Conscqncnt.ly, we approximate the transmission spectrum of the particle through special classical paths with initial and final coordinates equal to the average value of the coordinate for those wave packets. The procedure followed in this work, based on the complex time method, gives the appropriate coupling factor between the two paths describing the effective action of the particle and thus replaces the ad hoc procedure followed for this purpose in the cited work of Ueda. The complex time method also allows us to obtain the difference term between the effective action of the particle and the tunneling exponent. These quantities are treated as equal in Ueda\'s work. Considering terms up to first order in an external electric field and the interaction of the particle with the bath of oscillators, we obtain general expressions for the tunneling exponent, transmission spectrum, total tunneling rate and traversal time of tunneling, which are valid for a bath of oscillators with an arbitrary spectral lenity function. We find that the interaction of the particle with a bath of oscillators with an arbitrary spectral density function decreases the total tunneling rate. Also, we find that the interaction of the particle with the bath oscillators with frequencies ?a = ?C ~ 1.9 T , where To is the characteristic traversal time of tunneling when there is no interaction of the particle with the bath of oscillators nor electric field. , does not affect the characteristic traversal time of tunneling. On the other hand, the interaction of the particle with the bath oscillators having frequencies ?a< ?c (?a: > ?c decreases (increases) the characteristic traversal time of tunneling. In the case of a bath of oscillators with a single frequency w and a coupling constant with the particle given by Ca = Ca (wT)a we identify five different behaviors deepening on w for the characteristic tunneling exponent and the characteristic traversal time of tunneling. These behaviors correspond to the values of s < 1, s = 1, 1 < s < 2, s = 2 and s > 2. In the work of M. Ueda, Phys. Rev. B 54, 8676 (1996), it was only considered the characteristic tunneling exponent in the case s = 1. In the case of an ohmic bath of oscillators at zero temperature, as well as in the case of a bath of oscillators with a single frequency, we obtain that the transmission spectrum of the particle is ;1,cro for a final characteristic energy of the particle greater than the initial characteristic energy. This result corrects the corresponding result in Ueda work, which is not consistent from a physical point of view, allowing also for a more coherent derivation of the tunneling current between two metals separated by an insulating material at zero temperature. It is also obtained that the interaction of the particle with an ohmic bath of oscillators does not affect the characteristic traversal time of tunneling up to first order in that interaction
Doutorado
Física
Doutor em Ciências

In this thesis different mechanical properties for shotcrete (sprayed concrete) such as compression strength, bond strength, bending tensile strength, elastic modulus, free and restrained shrinkage as a function of its age was investigated. One of the main issues was to investigate the difference between ordinary cast concrete and shotcrete. Reliable material data for young and hardening shotcrete is scarce which in the past have made such comparisons difficult. Also, less accurate data representative for cast concrete has often been used in numerical modelling and design analyses. The focus of the project has particularly been on the properties bond strength and restrained shrinkage for which two new testing methods has been developed and evaluated. Microstructural studies have also been performed as a complement to the bond strength testing. The bond to rock is one of the most important properties for shotcrete used as rock reinforcement. During the very first time after spraying the physical properties and the bond to the rock depend on the set accelerator and the micro structure that is formed. The investigation of early age bond strength of shotcrete is of great importance both from a production perspective and a safety perspective. The newly developed method was tested and evaluated and proved that it can be used for bond strength testing already from a couple of hours after shotcreting. The bond, or adhesion, depends on several factors such as texture of the rock, the type of accelerator, application technique, etc. In this work the development of the microstructure in the interfacial transition zone (ITZ) and strength of the bond was investigated. The results show that the bond strength is related to the hydration process, i.e. the strength gain of the shotcrete. The early development of the ITZ was here studied using a scanning electron microscope (SEM) making it possible to observe changes over time, before and after proper cement hydration. Restrained shrinkage cracking of shotcrete, especially in the case of shotcrete sprayed on soft drains that are parts of a tunnel lining not continuously bonded to the rock, can be detrimental for the sustainability of an infrastructure tunnel system. Maintenance and repair costs can be high over time. It is shown that the developed test method realistically captures the behaviour of shotcrete drains on hard rock in situ. The method can be used in the evaluation of different technical solutions for avoiding or minimizing shrinkage cracks in shotcreted soft drains. It can also be used to assess the performance of shotcrete fully bonded to a rock surface, with respect to the ability to prevent cracking or to distribute possible shrinkage damage into several fine cracks instead of one wide.

QC 20140526

Cette thèse porte sur la description théorique de processus dynamiques ultra-rapides de molécules polyatomiques et de leur contrôle par impulsions laser. Nous avons d’abord étudié la photochimie de l’aniline à l’aide de calculs de structure électronique. Nous avons d´écrit plusieurs régions clé des surfaces d’énergie potentielle et analysé ces résultats en relation avec les données expérimentales existantes. La photochimie de la pyrazine a été étudiée par des calculs de dynamiques quantique basés sur un Hamiltonien modèle incluant les quatre états électroniques excités de plus basse énergie et seize modes de vibration. Nous montrons que l’état sombre Au(nπ∗) joue un rôle important dans la dynamique de la molécule après photo-excitation. Un modèle simplifié à deux états et quatre modes a été utilisé pour étudier le contrôle par laser de la dynamique de la pyrazine photo-excitée. Nous proposons un mécanisme visant à augmenter la durée de vie de l’état B2u(ππ∗) en utilisant l’effet Stark induit par une impulsion laser intense non-résonante
The central subject of this thesis is the theoretical description of ultrafast dynamical processes in molecular systems of chemical interest and of their control by laser pulses. We first use electronic structure calculations to study the photochemistry of aniline. A umber of previously unknown features of the potential energy surfaces of the low-lying elec-tronic states are reported, and analyzed in relation with the experimental results available. We use quantum dynamics simulations, based on a model Hamiltonian including the four lowest excited electronic states and sixteen vibrational modes, to investigate the photochem-istry of pyrazine. We show that the dark Au(nπ∗) state plays an important role in the ultrafast dynamics of the molecule after photoexcitation. The laser control of the excited state dynamics of pyrazine is studied using a simplified two-state four-mode model Hamiltonian. We propose a control mechanism to enhance the lifetime of the bright B2u(ππ∗) state using the Stark effect induced by a strong non-resonant laser pulse. We finally focus on the laser control of the tunneling dynamics of the NHD2 molecule, using accurate full-dimensional potential energy and dipole moment surfaces. We use simple effective Hamiltonians to explore the effect of the laser parameters on the dynamics and design suitable laser fields to achieve the control. These laser fields are then used in MCTDH quantum dynamics simulations. Both enhancement and suppression of tunneling are achieved in our model

In semiconductor superlattices, the carrier band structure can be tailored by the proper choice of their geometry. Therefore, superlattices are a model system for the study of coherent high-field transport phenomena in a periodic potential with applied static electric field. This thesis is structured in two parts. I. Zener Tunneling in Semiconductor Superlattices. In this work,semiconductor superlattices with shallow barriers and narrow band gaps were employed to investigate the Zener breakdown. In these samples, tunneling in the electron Wannier-Stark ladder spectrum is addressed as coupling of the electron states of a single bound below-barrier band to the states of the above-barrier spectrum. The field-dependent evolution of the Wannier-Stark ladder states was traced in the optical interband spectrum. Superlattices with different geometries were employed, to clarify the influence of the particular miniband structure on the Zener tunneling behavior. It was shown that in the presence of Zener tunneling, the Wannier-Stark ladder picture becomes invalid. Tunneling is demonstrated to lead to a field-induced delocalization of Wannier-Stark ladder states. In addition, the coherent polarization lifetime was analyzed as a measure of the tunneling probability. II. Terahertz Emission of Exciton Wave Packets in Semiconductor Superlattices. By means of Terahertz spectroscopy, the coherent intraband dynamics of exciton wave packets in biased superlattices after the selective ultrafast excitation of the Wannier-Stark ladder spectrum was investigated. The dynamics of Bloch oscillations was investigated under broadband excitation. It is demonstrated, that the Bloch oscillation amplitude can be controlled by altering the pump pulse energy. The xperimental results can only be explained in a full exciton picture, incorporating bound 1s exciton states and the associated exciton in-plane continuum. The intraband dipole of single Wannier-Stark ladder excitons was measured by detecting the Terhartz response after excitation of the Wannier-Stark ladder with a spectrally narrow rectangular pump pulse. In addition, experiments revealed a previously unknown mechanism for the generation of Bloch oscillating exciton wave packets. This was demonstrated for an incident pump spectrum which was too narrow to excite a superposition of Wannier-Stark ladder states. The effect is based on the sudden, non-adiabatic, change in the net dc internal field due to creation of electron-hole pairs with permanent dipole moments. The non-adiabatic generation of Bloch oscillations is a highly nonlinear effect mediated by strong exciton-exciton interactions.The central role that play exciton-exciton interactions in the intraband dynamics became especially evident when the Wannier-Stark ladder was selectively excited by two spectrally narrow laser lines. The experiments demonstrated a resonant enhancement of the intraband transition matrix element when 1s exciton wavepackets are excited
In Halbleiter-Übergittern kann die Bandstruktur von Ladungsträgern durch die geeignete Wahl der Geometrie eingestellt werden. Deshalb sind Halbleiter-Übergitter ein Modellsystem für Untersuchungen des kohärenten Ladungstransportes im periodischen Potential bei hohen, statischen, elektrischen Feldern. Diese Doktorarbeit ist in zwei Teile untergliedert. I. Zener-Tunneln in Halbleiter-Übergittern In dieser Arbeit werden Halbleiter-Übergitter mit flachen Barrieren und schmalen Bandlücken eingesetzt, um den Effekt des Zener-Durchbruchs zu untersuchen. In diesen Strukturen wird das Zener-Tunneln im Elektronen-Spektrum der Wannier-Stark-Leiter adressiert. Dabei handelt es sich um die Kopplung von Elektronen-Zuständen eines einzelnen Minibandes unterhalb der Potentialbarriere des Quantentopfes mit Zuständen oberhalb der Barriere. Die Feldabhängigkeit der Wannier-Stark-Leiter-Zustände wurde im optischen Interband-Spektrum detektiert. Übergitter mit unterschiedlichen Geometrien wurden untersucht, um den Einfluss der spezifischen Miniband-Struktur auf die Charakteristiken des Zener-Tunnelns aufzuklären. Es wurde gezeigt, dass im Regime des Zener-Tunnelns das Wannier-Stark-Leiter-Bild nicht mehr gültig ist. Dabei wird demonstriert, dass Tunneln zu einer feldabhängigen Delokalisierung der Wannier-Stark-Leiter-Zustände führt. Außerdem wird die Kohärenz-Lebensdauer der Polarisation analysiert. Sie bildet die Tunneln-Wahrscheinlichkeit ab. II. Terahertz Emission von Exzitonen-Wellen-Paketen in Halbleiter-Übergittern Mit Hilfe von Terahertz-Spektroskopie wurde die kohärente Intraband-Dynamik von Exzitonen-Wellen-Paketen in vorgespannten Halbleiter-Übergittern nach der selektiven, ultrakurzen Anregung des Wannier-Stark-Leiter-Spektrums untersucht. Die Dynamik von Bloch-Oszillatonen wurde durch spektral breitbandiger Anregung detektiert. Es wird gezeigt, dass die Amplitude von Bloch-Oszillationen durch die Änderung der Energie des Anrege-Pulses beeinflusst werden kann. Die experimentellen Resultate können nur in einem ganzheitlichen Exzitonenbild erklärt werden. Es umfaßt die gebundenen 1s-Exziton-Zustände und das zugehörige Exzitonen-Kontinuum in der Quantentopfschicht. Der Intraband-Dipol einzelner Wannier-Stark-Leiter-Exzitonen wurde durch die Detektion der Terahertz-Antwort auf die Anregung der Wannier-Stark-Leiter mit einem spektral schmalen Anrege-Puls vermessen. Außerdem wird in den Experimenten ein zuvor ungekannten Mechanismus der Anregung von bloch-oszillierenden Wellen-Paketen beobachtet. Dieser Effekt wird für ein eingestrahltes Anrege-Spektrum, welches spektral zu schmal für die Anregung einer Überlagerung von Wannier-Stark-Leiter-Zuständen ist, demonstriert. Der Mechanismus basiert auf die unmittelbare, nicht-adiabatische Änderung des effektiven, internen, statischen Feldes auf Grund der Anregung von Elektron-Loch-Paaren mit permanentem Dipolmoment. Die nicht-adiabatische Anregung von Bloch-Oszillationen ist ein hoch nicht-linearer Effekt, der durch starke Exziton-Exziton Wechselwirkung vermittelt wird. Die zentrale Rolle, die die Exziton-Exziton Wechselwirkung in der Intraband-Dynamik spielt, wurde besonders deutlich bei der selektiven Anregung der Wannier-Stark-Leiter durch zwei spekral schmale Laserlinien. Die Experimente demonstrieren eine resonante Überhöhung des Intraband-Übergangs-Matrix-Elements, wenn 1s-Exziton-Wellen-Pakete angeregt werden

In semiconductor superlattices, the carrier band structure can be tailored by the proper choice of their geometry. Therefore, superlattices are a model system for the study of coherent high-field transport phenomena in a periodic potential with applied static electric field. This thesis is structured in two parts. I. Zener Tunneling in Semiconductor Superlattices. In this work,semiconductor superlattices with shallow barriers and narrow band gaps were employed to investigate the Zener breakdown. In these samples, tunneling in the electron Wannier-Stark ladder spectrum is addressed as coupling of the electron states of a single bound below-barrier band to the states of the above-barrier spectrum. The field-dependent evolution of the Wannier-Stark ladder states was traced in the optical interband spectrum. Superlattices with different geometries were employed, to clarify the influence of the particular miniband structure on the Zener tunneling behavior. It was shown that in the presence of Zener tunneling, the Wannier-Stark ladder picture becomes invalid. Tunneling is demonstrated to lead to a field-induced delocalization of Wannier-Stark ladder states. In addition, the coherent polarization lifetime was analyzed as a measure of the tunneling probability. II. Terahertz Emission of Exciton Wave Packets in Semiconductor Superlattices. By means of Terahertz spectroscopy, the coherent intraband dynamics of exciton wave packets in biased superlattices after the selective ultrafast excitation of the Wannier-Stark ladder spectrum was investigated. The dynamics of Bloch oscillations was investigated under broadband excitation. It is demonstrated, that the Bloch oscillation amplitude can be controlled by altering the pump pulse energy. The xperimental results can only be explained in a full exciton picture, incorporating bound 1s exciton states and the associated exciton in-plane continuum. The intraband dipole of single Wannier-Stark ladder excitons was measured by detecting the Terhartz response after excitation of the Wannier-Stark ladder with a spectrally narrow rectangular pump pulse. In addition, experiments revealed a previously unknown mechanism for the generation of Bloch oscillating exciton wave packets. This was demonstrated for an incident pump spectrum which was too narrow to excite a superposition of Wannier-Stark ladder states. The effect is based on the sudden, non-adiabatic, change in the net dc internal field due to creation of electron-hole pairs with permanent dipole moments. The non-adiabatic generation of Bloch oscillations is a highly nonlinear effect mediated by strong exciton-exciton interactions.The central role that play exciton-exciton interactions in the intraband dynamics became especially evident when the Wannier-Stark ladder was selectively excited by two spectrally narrow laser lines. The experiments demonstrated a resonant enhancement of the intraband transition matrix element when 1s exciton wavepackets are excited.
In Halbleiter-Übergittern kann die Bandstruktur von Ladungsträgern durch die geeignete Wahl der Geometrie eingestellt werden. Deshalb sind Halbleiter-Übergitter ein Modellsystem für Untersuchungen des kohärenten Ladungstransportes im periodischen Potential bei hohen, statischen, elektrischen Feldern. Diese Doktorarbeit ist in zwei Teile untergliedert. I. Zener-Tunneln in Halbleiter-Übergittern In dieser Arbeit werden Halbleiter-Übergitter mit flachen Barrieren und schmalen Bandlücken eingesetzt, um den Effekt des Zener-Durchbruchs zu untersuchen. In diesen Strukturen wird das Zener-Tunneln im Elektronen-Spektrum der Wannier-Stark-Leiter adressiert. Dabei handelt es sich um die Kopplung von Elektronen-Zuständen eines einzelnen Minibandes unterhalb der Potentialbarriere des Quantentopfes mit Zuständen oberhalb der Barriere. Die Feldabhängigkeit der Wannier-Stark-Leiter-Zustände wurde im optischen Interband-Spektrum detektiert. Übergitter mit unterschiedlichen Geometrien wurden untersucht, um den Einfluss der spezifischen Miniband-Struktur auf die Charakteristiken des Zener-Tunnelns aufzuklären. Es wurde gezeigt, dass im Regime des Zener-Tunnelns das Wannier-Stark-Leiter-Bild nicht mehr gültig ist. Dabei wird demonstriert, dass Tunneln zu einer feldabhängigen Delokalisierung der Wannier-Stark-Leiter-Zustände führt. Außerdem wird die Kohärenz-Lebensdauer der Polarisation analysiert. Sie bildet die Tunneln-Wahrscheinlichkeit ab. II. Terahertz Emission von Exzitonen-Wellen-Paketen in Halbleiter-Übergittern Mit Hilfe von Terahertz-Spektroskopie wurde die kohärente Intraband-Dynamik von Exzitonen-Wellen-Paketen in vorgespannten Halbleiter-Übergittern nach der selektiven, ultrakurzen Anregung des Wannier-Stark-Leiter-Spektrums untersucht. Die Dynamik von Bloch-Oszillatonen wurde durch spektral breitbandiger Anregung detektiert. Es wird gezeigt, dass die Amplitude von Bloch-Oszillationen durch die Änderung der Energie des Anrege-Pulses beeinflusst werden kann. Die experimentellen Resultate können nur in einem ganzheitlichen Exzitonenbild erklärt werden. Es umfaßt die gebundenen 1s-Exziton-Zustände und das zugehörige Exzitonen-Kontinuum in der Quantentopfschicht. Der Intraband-Dipol einzelner Wannier-Stark-Leiter-Exzitonen wurde durch die Detektion der Terahertz-Antwort auf die Anregung der Wannier-Stark-Leiter mit einem spektral schmalen Anrege-Puls vermessen. Außerdem wird in den Experimenten ein zuvor ungekannten Mechanismus der Anregung von bloch-oszillierenden Wellen-Paketen beobachtet. Dieser Effekt wird für ein eingestrahltes Anrege-Spektrum, welches spektral zu schmal für die Anregung einer Überlagerung von Wannier-Stark-Leiter-Zuständen ist, demonstriert. Der Mechanismus basiert auf die unmittelbare, nicht-adiabatische Änderung des effektiven, internen, statischen Feldes auf Grund der Anregung von Elektron-Loch-Paaren mit permanentem Dipolmoment. Die nicht-adiabatische Anregung von Bloch-Oszillationen ist ein hoch nicht-linearer Effekt, der durch starke Exziton-Exziton Wechselwirkung vermittelt wird. Die zentrale Rolle, die die Exziton-Exziton Wechselwirkung in der Intraband-Dynamik spielt, wurde besonders deutlich bei der selektiven Anregung der Wannier-Stark-Leiter durch zwei spekral schmale Laserlinien. Die Experimente demonstrieren eine resonante Überhöhung des Intraband-Übergangs-Matrix-Elements, wenn 1s-Exziton-Wellen-Pakete angeregt werden.

Representing the time-dependent plastic behaviour of geomaterials is a critical issue in the correct application of tunnelling design techniques such as the convergence-confinement method or numerical modelling. Furthermore, during underground excavations below the water table, the effect of seepage flow cannot be ignored, and the behaviour of the tunnel must be analysed in a coupled hydro-mechanical framework. The main objective of this thesis is to analyse the response of tunnels excavated in saturated time-dependent plastic rock masses. For this purpose, a time-dependent plastic constitutive model has been developed and implemented in the software CODE_BRIGHT to simulate the time-dependent, strain-softening and creep-induced failure behaviour of geomaterials. Moreover, a coupled hydro-mechanical model is utilised to simulate the interaction between solid deformations and fluid flows. The obtained results provide relevant insights into the response of tunnels excavated in saturated time-dependent plastic rock masses. However, numerical difficulties might occur when modelling multi-stage excavations problems, when considering multi-physics coupled processes or non-linear mechanical material models, especially if the layers or pieces of excavated material are relatively coarse. In order to mitigate these numerical difficulties, a smoothed excavation (SE) method has been proposed and implemented in the software CODE_BRIGHT, which can improve numerical efficiency and mitigate non-convergence issues. Subsequently, to analyse the stability of tunnels with a combined support system, numerical solutions have been developed for tunnels excavated in strain-softening rock masses, considering the whole process of tunnel advancement, and the sequential installation of primary and secondary support systems. For this purpose, the actual compatibility conditions at both the rock-support interface and the support-support interface are considered. This method provides a convenient alternative method for the preliminary design of supported tunnels.
La adecuada representación del comportamiento plástico y dependiente del tiempo de los geomateriales es una cuestión crítica en la correcta aplicación de técnicas de diseño de túneles como el método de convergencia-confinamiento o el modelado numérico. Por otro lado, durante las excavaciones subterráneas por debajo del nivel freático no se puede ignorar el efecto del flujo de filtración y, por tanto, el comportamiento del túnel debe analizarse en un marco hidromecánico acoplado. El principal objetivo de esta tesis es analizar la respuesta de túneles excavados en macizos rocosos plásticos saturados y dependientes del tiempo. Para este propósito, se ha desarrollado e implementado un modelo constitutivo plástico dependiente del tiempo en el software CODE_BRIGHT, que permite simular el comportamiento dependiente del tiempo, el de reblandecimiento por deformación y el inducido por fluencia de los geomateriales. Además, se ha utilizado un modelo hidromecánico acoplado para simular la interacción entre la deformación del sólidas y el flujo de fluido. Los resultados obtenidos proporcionan información relevante sobre la respuesta de los túneles excavados en macizos rocosos plásticos, saturados y dependientes del tiempo. Sin embargo, pueden surgir dificultades numéricas al modelar problemas de excavaciones en varias etapas, al considerar procesos multifísicos acoplados o modelos de materiales mecánicos no lineales, especialmente si las capas o piezas de material excavado son relativamente gruesas. Para mitigar estas dificultades numéricas, se ha propuesto e implementado un método de excavación suavizada (SE) en el software CODE_BRIGHT, que puede mejorar la eficiencia numérica y mitigar los problemas de no convergencia. Posteriormente, para analizar la estabilidad de túneles con sistemas de sostenimiento combinado, se han desarrollado soluciones numéricas para túneles excavados en macizos con reblandecimiento por deformación, considerando todo el proceso de avance del túnel y la instalación secuencial de los sistemas de sostenimiento primario y secundario. Con este propósito, se han considerado las condiciones reales de compatibilidad tanto en la interfaz roca- sostenimiento como en la interfaz sostenimiento-sostenimiento. Este método proporciona un método alternativo conveniente para el diseño preliminar de túneles con sostenimiento.

Den här rapporten grundar sig i problematiken med att kombinera TCP/IPv4 ochTCP/IPv6 med varandra. De två protokollen är inte kompatibla att skicka paket mellansig och bara delar av internet använder sig av, eller har stöd för, det nyare protokolletIPv6. På grund av att de publika IPv4-adresserna är slut i världen så måsteförr eller senare en fullständig migrering ske på internet. Fram till dess behövs dockmigreringsmetoder som kan hantera både de äldre och de nyare TCP/IP-protokolletsimultant.I rapporten kommer olika migreringsmetoder plockas fram där fokus ligger påkomplexitet, alltså tidsåtgång för implementering. Metoderna som presenteras utgören laboration där testpersoner har fått utföra simulerade migreringar med de olikateknikerna för att få fram tidsdata. Med hjälp av tidsdatan presenteras sedan denminst komplexa migreringsmetoden. En minimalt komplex metod kan hjälpa bådeprivatpersoner och företag kopplade till internet att migrera från IPv4 till IPv6 på ettsmidigare sätt.Migreringslösningarna i den här rapporten riktar sig dock främst till en målgruppav medelstora företag som vill använd sig av IPv6 men samtidigt ha möjlighet attvara anslutna till internet.Resultatet visade att med hjälp av en teknik kallad Dual Stacking kunde bådeIPv4 och IPv6 användas på ett nätverk simultant. Våra testpersoner pekade också påatt denna teknik är den minst komplexa, alltså lättast att implementera och förstå.Resultatet av rapporten kan göra att fler vågar använda sig av IPv6 och när dagenkommer då internet går över till IPv6 så kommer dessa företag ligga i framkant ochvara väl förberedda.
This report is based on the problem of combining TCP/IPv4 and TCP/IPv6 with eachother. The two protocols are not compatible to send packets between themselves andonly parts of the Internet make use of, or supports, the newer IPv6 protocol. Due tothe shortage of public IPv4 addresses in the world we need to, sooner or later, makea complete migration from IPv4 to IPv6 over the Internet. However, until needed,we can make use of migration methods that can handle both the older and the newerTCP/IP protocols simultaneously.In the report, various migration techniques are evaluated with the main focusbeing complexity, as in: the time it takes to implement the solution. The methodpresented constitute a laboratory task where the test persons performs simulated migrationswith the different techniques to get a time data. With the help of time datathe least complex migration method is later presented. A minimally complex methodcan help both individuals and companies connected to the Internet to migrate fromIPv4 to IPv6 in a smoother manner.Migration solutions in this report are mainly addressed to a target group of mediumsizedcompanies that want to use the IPv6-protocol but at the same time want to havethe opportunity to be connected to the Internet.The results showed that by using a technique called Dual Stacking, both IPv4 andIPv6 can be used on a network simultaneously. Our testers also pointed out that thistechnique is the least complex, therefore the easiest to implement and understand.The outcome of the report might result in more companies daring to use IPv6, andwhen the day comes when the Internet completely migrates to IPv6 these companieswill be in the forefront and well prepared.

The current thesis aims at benchmarking strong- eld physics with the help of precision measurements performed on the simplest atomic (H) and molecular (H2) systems. The importance of H in validating strong- eld models is demonstrated through the rst set of experimental data. It aims at calibrating the absolute Carrier-envelope phase (CEP) of few-cycle laser pulses using H against complete ab initio solution of the three dimensional time-dependent Schr odinger equation (3D-TDSE). Subsequent set of measurements with noble gases against widely used strong- eld models based on single-active electron (SAE) approximation, is shown to reveal a systematic o set of 0:25 radians in tagging CEP, questioning the validity of such models. The second experimental study forms the main result of this thesis, that attempts to resolve the ongoing debate on tunnelling times (tunnelling delays in the context of strong- eld physics). We address this by employing the `attoclock' technique with 6 fs pulses on H and validating the results against full numerical solutions of ab initio 3D-TDSE. The validated numerical codes are then used to arti cially screen the parent ion-electron interaction, concluding that the tunnelling time 1.8 as. The nal experimental results presented in this dissertation are the alignmentdependent attoclock measurements using both few-cycle (7 fs) and multi-cycle (28 fs) pulses on H2. The measured attoclock observable for various molecular orientations (in laser polarisation frame) shows a strong modulation with a periodicity of . Initial ab initio simulations for few-cycle pulses under the frozen-nuclei and SAE approximations, fail to explain these observations. Further experimental studies with H2/D2 (50:50 mixed gases) show no signi cant relative di erences among the attoclock observables, suggesting a prominent role of the electron-electron correlations at play. The ongoing study is believed to have far reaching implications in applications such as studying molecular dissociation processes and tomography.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)
Muitos fatores t?m sido pautados como atributos que podem ajudar a entender melhor o padr?o de escava??o de t?neis em cupins. Dentre estes destacam-se o comportamento auto-organizado, fatores ambientais, caracter?sticas morfol?gicas dos oper?rios, comunica??o qu?mica e f?sica, a escava??o por ?escavadores de topo?, e a teoria do forrageamento ?timo. Desta forma, atrav?s do presente trabalho objetivou-se investigar se o n?mero de oper?rios influencia no padr?o de escava??o de t?neis em Cortaritermes silvestrii. Para as observa??es do comportamento de escava??o foram utilizadas arenas bidimensionais preenchidas por areia com diferentes n?meros de indiv?duos em cada bateria, variando de 20 a 200 oper?rios. Uma vez registrada a atividade de escava??o, ap?s 24 horas de experimento, foram medidos a ?rea escavada, a taxa de escava??o, o n?mero total de t?neis, o tempo para in?cio da escava??o (TIE), o tempo para in?cio da bifurca??o (TIB) e os ?ngulos entre as bifurca??es observadas. Al?m disso, tamb?m foi feita uma simula??o, utilizando dados emp?ricos, para estimar a efici?ncia de forrageio em C. silvestrii com diferentes n?meros de oper?rios e diferentes tipos de distribui??o do recurso no substrato. Em rela??o aos resultados obtidos, observou-se que existe uma rela??o entre a ?rea escavada (?= 0,4959, p < 0.001), a taxa de escava??o, o n?mero total de t?neis escavados (? = 0,3917, p < 0.001), o TIE (? = -0,2935, p < 0,001), TIB (? = - 0,0729, p <0,001), e o n?mero de oper?rios em cada arena. Ao analisar os ?ngulos, observou-se uma frequ?ncia maior de ?ngulos menos redundantes (muito pequenos ou muito maiores). Os resultados obtidos na simula??o indicam que o n?mero de oper?rios n?o influencia no retorno energ?tico obtido durante a escava??o, e que provavelmente C. silvestrii explora recursos distribu?dos de forma aglomerada ou aleat?ria, muito mais eficiente do que recursos distribu?dos uniformemente no substrato. Portanto, concluiu-se que o n?mero de oper?rios est? relacionado ao padr?o de escava??o de t?neis em C. silvestrii e que este padr?o observado possivelmente est? ligado ? forma com que esta esp?cie explora seus recursos.
Disserta??o (Mestrado) ? Programa de P?s-gradua??o em Biologia Animal, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017.
Several factors have been ruled as attributes that may help better understand the pattern of tunneling in termites. These include self-organized behavior, environmental factors, morphological characteristics of workers, chemical and physical communication, excavation by "top-excavators", and optimal foraging theory. In this way, the objective of this work was to investigate whether the number of workers influences the tunneling pattern in Cortaritermes silvestrii. For the observations of the excavation behavior, two-dimensional arenas filled with sand with different numbers of individuals in each battery were used, ranging from 20 to 200 workers. Once the excavation activity was observed, after 24 hours, it was measured the excavated area, total number of tunnels, time to start of excavation (TIE), time to start of bifurcation (TIB), and the angles between the observed bifurcations. In addition, a simulation using empirical data was used to estimate the foraging efficiency in C. silvestrii with different numbers of workers and different types of distribution of the resource in the substrate. In relation to the results obtained, it was observed that there is a relation between the excavated area (? = 0.4959, p <0.001), the excavation rate, the total number of excavated tunnels (? = 0.3917, p <0.001), the TIE (? = -0.2935, p <0.001), TIB (? = - 0.0729, p <0.001), and the number of workers in each arena. When analyzing the angles, a greater frequency of less redundant angles (very small or much larger angles) was observed. The results obtained in the simulation indicate that the number of workers does not influence the energetic return obtained during the excavation, and that probably C. silvestrii exploits resources distributed in agglomerated or random ways, much more efficiently than resources evenly distributed in the substrate. Therefore, it was concluded that the number of workers is related to the pattern of tunnel excavation in C. silvestrii and that this observed pattern is possibly related to the way in which this species exploits its resources.

碩士
國立交通大學
理學院碩士在職專班網路學習學程
97
The main structure of a scanning tunneling microscope involves three parts—namely Mechanical part, Electrics part, and Computer program. The purpose of the research is to develop a computer image system mainly based on a homemade scanning tunneling microscope. Except for the ordinary function of outputting scanned images, the design of the image system provides various parameters to satisfy the needs of the experiment, two features--real time and variety. According to the result of the experiment, the researcher found that the factors that influence the quality of outputting images are not only the design of tips and mechanical system but also the software that processes the images. In addition, the data retrieved from the circuit system have to be processed adequately. That is, by improving the contrast and the tone of colors, the same images quality retrieved from commercial system can be achieved. Besides, to improve the image quality, solve the problem of thermal drifting of tips, and make the scanning output more authentic, the researcher devised a deslope algorithm to overcome the difficulties which may occur when the scanning tunneling microscope working under the room temperature. Moreover, to make the image quality more stable, some possible defects of the making of scanning tips were taken into consideration because this may directly influence the clarity of the retrieved images. Furthermore, to solve the problem of blur images resulted from asymmetry tips, the design the system allow the scanning tips to do arbitrary angle scanning, and provides the users two different options of tips movements.

博士
國立中興大學
土木工程學系所
107
Slate is a metamorphic rock with well developed sheeted texture called slaty cleavages. The ease of split along the cleavages weakens the slate and its resistance to weathering and erosion. For the tunnel excavation in slate formations, it is common to observe anisotropic deformation; in addition, the deformation caused by stress release also shows time-dependent behavior. Hence, Anisotropic and time-dependent behaviors must be taken into account to more properly estimate the deformation of tunnel excavation in slate formation. In this paper, the computer software FLAC was adopted for the analysis. Firstly, tunnel deformation was analyzed by numerical analysis to evaluate tunnel support effect and safety. The ubiquitous joint (UBI) model was adopted for the analysis of the anisotropic tunnel deformation. Secondly, the the Burger-creep viscoplastic (CVISC) model was coupled with the UBI model and is implemented for the analysis of the time-dependent anisotropic behavior of slate formations. Back calculations were performed to obtain relevant parameters of the new hybrid model. The new model was calibrated by the monitoring data from a slate tunnel excavation project, i.e., the Wanta-Sunglin Project in Taiwan Power Company, and then was applied for detailed analyses. The results indicate that the hybrid model developed in this study is better than the conventional models, and can be used for the simulation of tunnel excavation in similar anisotropic time-dependent slate formations.

碩士
國立交通大學
土木工程系所
97
The first part of this paper analyzes the surface settlement-time relationship due to shield tunneling. This study collects 198 sets of field measurement data due to shield tunneling cases reported in different parts of the world from 1980 to 2008. A hyperbolic model is proposed to simulate the surface settlement-time relationship due to shield tunneling constructed in different types of soils with different shields. Based on the collected data, this paper suggests empirical tables to estimate initial rate of settlement 1/a and the maximum surface settlement Smax=1/b to estimate the surface settlement-time relationship. Base on this study, the following conclusions are made. （1）Field monitored data indicate that the surface settlement-time relationship induced by shield tunneling can be properly described by the hyperbolic model. （2）The initial rate of ground settlement 1/a in the empirical table, it is found that the initial rate of settlement in sandy soil is faster than that in clayey soil. For soft clays, the initial rate of ground settlement is faster than that in clayey soil. （3）Base on the maximum surface settlement Smax=1/b table suggested in this thesis indicate, when compared with Smax due to tunneling with an open shield and an EPB shields, the slurry shield induces the smallest Smax. The second part of this paper analyzes the subsurface settlement due to shield tunneling. Based on 21 sets of field cases, the relationship between surface and subsurface settlement troughs has been established. Based on the normal distribution curve suggested by Peck(1969), an empirical method is suggested to evaluate the subsurface settlement trough due to shield tunneling. Base on this study, the following conclusions are made. （1）Field monitored data indicate that subsurface settlement trough can be described by the distribution curve. （2）This study established the relationship between the surface and subsurface settlement trough parameter iz/is and Smax,z/Smax,s. It is concluded that at a deeper elevation, the width of settlement trough is narrower and the maximum settlement is larger. （3）The suggested empirical method can successfully estimate the subsurface settlement trough in clayey soil induced by shield tunneling.

碩士
國立中興大學
土木工程學系所
104
Cleavage is a major structure in slates, and its orientation is critical for the anisotropy property of stress field. As a soft rock, the cleavages in slate tend to be weathered and form opening with or without filling material. For the tunnel excavation in slates, it is common to have anisotropy deformation. Its behavior can not be described by a simple elastic or plastic model. To consider the deformation characteristics of the stress release process during tunneling, more sophisticated model including anisotropy property and time-dependent behavior is essential. In this study, we use the Ubiquitous-joint model (UBI) to simulate tunnel excavation in slate, for different stages of stress release and tunnel support. Then, we use Burger-creep visco-plastic model (CVISC) to study time-dependent behavior of slates. For the above two model, we can obtain the material parameters by back analysis based on the monitoring data. However, this study established a UDM model to combine UBI and CVISC model, named UBI/BUR, which integrates CVISC mode and UBI mode. This model can more properly describe the behavior of slates, and good for the simulation of tunneling in slates. The results of this study suggest that UBI can effectively represents the influence of cleavage, however, the displacement history curve does not closely conform to the monitoring data. And the reason for this discrepancy is the model is short of time-dependent behavior of the slate. CVISC can describe time-dependent behavior, but it can’t consider the anisotropy of cleavage. In this case analysis, the results show that the UBI/BUR model can more properly match the monitoring data.

碩士
國立臺灣師範大學
化學系
100
Fluorescent nanodiamond (FND), a relatively new nanocarbon material, has recently emerged as a novel fluorescent probe for biological applications. The material exhibits unique optical properties and is highly biocompatible with very low toxicity. Also, the surface of FND is easy to be functionalized for specific targeting. In this work, high energy helium ion beam was used to irradiate 100-nm type Ib nanodiamonds, followed by annealing, to create a high density of negatively charged nitrogen-vacancy (NV−) defect centers. The center emits far red fluorescence under excitation by green yellow light. Excellent optical properties such as no photobleaching, no photoblinking and nontoxicity make FND distinct from conventional fluorescent probes for cell labeling and long-term tracking applications. This work applies FNDs as a single particle tracker in tunneling nanotubes (TNTs) and neurites. The intercellular vesicles transportation through TNTs formed between cells and organelle trafficking in neurites is related to many diseases, such as HIV infection, prion protein infection, Alzheimer's disease and Parkinson's disease. In order to study the transportation, we first coated FNDs with bovine serum albumin (BSA) and then performed single particle tracking of these nanoparticle bioconjugates inside TNTs (HEK293T cells) and neurites (N18 cells) by confocal fluorescence microscopy. We analyzed the transportation of the BSA-coated FNDs individually and obtained an average speed of 0.05 to 1 μm/s in both TNTs and neurites. The success of these experiments opens new ways to explore cellular transports in detail by using specifically labeled FNDs in future experiments.

Plasmonic structures are utilized in many applications ranging from bio-medicine to solar energy generation and transfer. Numerical schemes capable of solving equations of classical electrodynamics have been the method of choice for characterizing scattering properties of such structures. However, as dimensions of these plasmonic structures reduce to nanometer scale, quantum mechanical effects start to appear. These effects cannot be accurately modeled by available classical numerical methods. One of these quantum effects is the tunneling, which is observed when two structures are located within a sub-nanometer distance of each other. At these small distances electrons “jump" from one structure to another and introduce a path for electric current to flow. Classical equations of electrodynamics and the schemes used for solving them do not account for this additional current path. This limitation can be lifted by introducing an auxiliary tunnel with material properties obtained using quantum models and applying a classical solver to the structures connected by this auxiliary tunnel. Early work on this topic focused on quantum models that are generated using a simple one-dimensional wave function to find the tunneling probability and assume a simple Drude model for the permittivity of the tunnel. These tunnel models are then used together with a classical frequency domain solver. In this thesis, a time domain surface integral equation solver for quantum corrected analysis of transient plasmonic interactions is proposed. This solver has several advantages: (i) As opposed to frequency domain solvers, it provides results at a broad band of frequencies with a single simulation. (ii) As opposed to differential equation solvers, it only discretizes surfaces (reducing number of unknowns), enforces the radiation condition implicitly (increasing the accuracy), and allows for time step selection independent of spatial discretization (increasing efficiency). The quantum model of the tunnel is obtained using density functional theory (DFT) computations, which account for the atomic structure of materials. Accuracy and applicability of this (quantum corrected) time domain surface integral equation solver will be shown by numerical examples.

碩士
國立臺灣大學
土木工程學研究所
97
The controlling of convergence deformation is an important concept in modern tunneling technique, and the second lining well be installed when deformation of rock surrounding tunnel is under control as the NATM method. In Taiwan, numbers of tunnels in middle to old ages increase with time rapidly, which deteriorate after years of performance, but there are no ruptures during construction and few numbers of deformations on rock when tunneling. So it is important to know well about the factors affecting their long-term stability. In order to know well about tunnel structure systems in long-term stability characteristics, we must understand how time-dependent deformations occur during tunneling in first. Secondly, it is necessary to consider the influences by visco-elastio-plastic mechanics behavior of geo-materials. Time-dependent deformation behaviors usually appear when geo-materials are abide by stress which is larger than creep critical stress threshold. It is different between time-dependent deformation behaviors and elasto-plastic constitutive model which is been applied extensively in tunnel convergence mechanisms. Some models combine elasto-plastic constitutive law with time-dependent characters which are too many complex procedures for analysis and the parameters are too hard to obtain, so they are difficult to use in engineering application. This research aims to know well about tunnel time-dependent convergence deformations by using: (1) the influences of long-term factors and mechanics mechanisms during tunneling; (2) a non-linear visco-elasto-plastic constitutive model; (3) numerical simulations and monitoring measurements data for parameters by back-analysis; (4) time-dependent constitutive numerical model of different excavation forms and support systems and discuss stress around tunnel and convergence behaviors. Base on the original Burgers rheological model, the model in this research modifies the viscous parameter as a function relative to different stress states. After test and verify confidentially, the model can improved the defects that classic visco-elastic model cannot consider different stress states mechanics mechanisms. The numerical results show that the model can understand the phenomena at time-dependent deformation for geo-materials and underground structures during tunneling, and it also can be used for tunnel long-term stability research.

碩士
國立交通大學
物理研究所
87
The adsorption and desorption processes which occur during the interaction of phosphine with Si(100) surfaces have received extensive attention. However, we found that there were still some ambiguous points remaining for explanation in the process. In this thesis, we apply the real-time STM technique to study the adsorption and decomposition of phosphine on Si(100)2 x 1 surfaces at the substrate temperature between 620 K and 850 K. We also observed the continuing PH$_3$ deposition process as functions of time and temperature. From the data, temperature plays an important role on the surface morphology and surface composition. Thus, we divide the descriptions and discussions of the data into three parts based on three ranges of temperature: the temperature below 620 K as low temperature, that between 650 and 730 K as middle temperature, and that between 770 and 850 K as high temperature. At these temperatures, the P coverages were calculated and the surface morphology and composition were discussed. The main results are summarized as follows. At low temperature (620 K), the surface was covered with Si$_2$H$_2$ and short 1-D islands composed of P-P dimers. At middle temperature (650 K and 700 K), the surface morphology and composition depended on the competition between hydrogen desorption rate and PH$_3$ deposition rate. At high temperature (790 K and 850 K), for initial PH$_3$ exposure, the hydrogens desorbed from the surface upon PH$_3$ adsorption, and the P atoms exchanged with substrate Si atoms to form Si-P dimers, which annihilated the thermally-induced 2 x n structure; at high P coverage ($>$ 0.5 ML), P-P dimers formed on the surface and reapplied the compressive strain to the surface, and thus defect lines reappeared. Our study revealed the evolution of surface morphology during phosphorus CVD in atomic resolution and, thereby providing comprehensive insight into the growth processes which occur on the Si(100) surface.

碩士
國立交通大學
物理研究所
87
Under the procedure of P and Si growth on Si (100) by chemical vapor deposition from phosphine and disilane, the hydrogen of adsorbed on Si (100) impedes the growth. We investigated, using real-time variable-temperature scanning tunneling microscopy, the image of hydrogen desorption from Si (100)-2×1: H at several temperature. According to the annealing time and hydrogen desorption coverage by directly counting the site on image, then desorption rate of hydrogen from surface in 585-668K temperature range has known to obeys the first-order kinetics. The data of isothermal desorption at temperature 611, 622, 633, 644 and 668K give us the kinetic parameter activity energy Ed = 1.9 eV and pre-exponential factor νd= 2.0×1012 S-1. In addition, the disilane and phosphine grow to 1D line structure on Si (100) surface at 611K. Then we compare the difference of hydrogen desorption from Si (100) surface and 1D line structure, the 1D line structure dimers that hydrogen has desorbed repel each other.

碩士
國立臺灣大學
電信工程學研究所
102
The finite-di ffrence time-domain(FDTD) method is applied to solve the Dirac-like equation of a graphene sheet. A virtual absorbing layer (VAL) is proposed to achieve low reflection of wave function at the boundary of a graphene sheet. Empirical parameters are tuned to optimize the performance of the VAL. The Klein tunneling effects on a graphene sheet are simulated to confirm the effectiveness of this FDTD scheme and the VAL.

碩士
國立清華大學
物理學系
85
Understanding growth kinetics is essential to achieving controlled film growth. We have investigated, using real-time variable-temperature scanning tunneling microscopy, the Si homoepitaxy on Si(100) surface during chemical vapor deposition from disilane. Our STM results show different growth modes in different temperature range. At low temperature regime (RT-450℃), both 2D and 3D islands formation and hydrogen adsorption at the surface are observed, and hydrogen adsorption influence the film growth rate. At higher substrate temperature (450-550℃), the surface hydrogen desorb completely here, 2D islands formation and coalescence with step occur. At high temperature regime (>550℃), the step flow growth mode dominates, and because of the adatoms diffusion anisotropic causes to a preference growth of 1x2 surface structure, the percentage of the 1x2 structure of the total surface is close to 80~85%.

碩士
國立交通大學
電子物理系所
103
In this study, we analyze the optical and electrical properties of the strain-relaxed InAs/InGaAs quantum dot (QD) samples with two different InAs deposition thicknesses, 2.7 and 3.3 ML, and discuss the influence of strain relaxation on the Photo-capacitance of InAs QDs with InGaAs capping layer. Relaxation-induced defect reduces the background concentration beneath the QD layer , lowering the carrier emission rate of QDs, and formation of the Photo-capacitance by relaxed QDs Schottky diode. We demonstrate the photocurrent generated by GaAs Schottky diode can be suppressed by the relaxed QDs .When electrons are programmed into the relaxed QDs ,the potential drop is caused by the charged QDs, then reduced the Schottky diode’s depletion width, and suppressed the photocurrent. First, we compared with the effective RC circuit model is proved to interpret the mechanism by using the GaAs bulk sample series connected with a ceramic capacitor and the relaxed QDs have significantly suppress the photocurrent effect , then we can understand the relaxed QDs play a role as a capacitor. Therefore, the photo-capacitance can induced by relaxed QDs sample. Furthermore, we using the time-resolved measurement and tunneling rate theory to estimate the photo-capacitance of relaxed QDs is about 2000~3000 pF.

There has been much work on electron emission. It has lead to the concept of the photon and new electron sources for imaging such as electron microscopes and the rst formulation of holographic reconstructions [1-6]. Analytical derivations are important to gain physical insight into the problem of developing better electron sources. However, to date, such formulations have su ered by a number of approximations that have masked important physics. In this thesis, a new approach is provided that solves the Schrodinger wave equation for photoemission from a single atom tungsten tip barrier or more generally, for photoemission from a Schottky triangular barrier potential, with or without image potential e ects. We describe the system, then introduce the mathematical derivation. We conclude with the applications of the theory.

Tesis (Doctorado en Física)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física, 2007.
En esta tesis usamos la ecuación maestra cuántica generalizada de Lioville von Neumann para resolver la dinámica de sistemas de muchos espines interactuando con un baño de espines. También obtuvimos la dinámica de espines dentro del formalismo de Keldysh. Ambos métodos con idénticas soluciones juntos, nos posibilitaron realizar predicciones que concuerdan con las observaciones de experimentos de RMN. Los resultados, fueron usados para la caracterización molecular, el desarrollo de nuevas metodologías numéricas y el control de dinámica cuántica en implementaciones experimentales. Aún más importante, ha sido el surgimiento de interpretaciones físicas fundamentales de la dinámica cuántica de sistemas cuánticos abiertos tales como la manifestación de una transición de fase en la dinámica cuántica inducida por el ambiente. El control de sistemas cuánticos abiertos tiene una relevancia fundamental en campos que van desde el procesamiento de la información cuántica hasta la nanotecnología. Típicamente, el sistema cuya dinámica coherente se desea manipular, interactúa con un ambiente que suavemente degrada su dinámica cuántica. Es así que el entendimiento preciso de los mecanismos internos de este proceso, llamado decoherencia, es crítico para el desarrollo de estrategias para el control de la dinámica cuántica. En esta tesis usamos la ecuación maestra cuántica generalizada de Liouville-von Neuman para resolver la dinámica de sistemas de muchos espines interactuando con un baño de espines. También obtuvimos la dinámica de espines dentro del formalismo de Keldysh. Ambos métodos nos llevaron a idénticas soluciones y juntos nos dieron la posibilidad de realizar numerosas predicciones que concuerdan con las observaciones de experimentos de Resonancia Magnética Nuclear. Estos resultados son usados para la caracterización molecular, el desarrollo de nuevas metodologías numéricas y el control de la dinámica cuántica en implementaciones experimentales. Pero aún más importante es el surgimiento de interpretaciones físicas fundamentales de la dinámica cuántica de sistemas cuánticos abiertos, tales como la manifestación de una transición de fase dinámica cuántica inducida por el ambiente.
Gonzalo Agustín Alvarez.

This thesis describes experimental studies of semiconductor heterostructures, using optical techniques. The work presented concerns two topics in the study of semiconductor heterostructures: the escape of confined electrons and holes by tunneling, and the accommodation of lattice mismatch by strain. Time-resolved photoluminescence techniques have been used to measure the times required for electrons and holes to escape by tunneling through the A1As barriers of GaAs/A1As/GaAs/A1As/GaAs double barrier heterostructures. The effect of the indirect (X-point) levels in the AlAs barriers upon escape of confined electrons has been investigated using continuous (CW) photoluminescence. Time-resolved studies of electrically biased double-barrier heterostructures have been made, using both photoluminescence and photocurrent techniques. Finally, the accommodation of the large (6%) lattice mismatch in CdTe/ZnTe superlattices has been studied using Raman scattering. In Chapter 2 we describe the measurement of tunneling escape times for electrons and holes confined in the quantum well of undoped GaAs/A1As/GaAs/A1As/GaAs double-barrier heterostructures. Photoluminescence from carriers photoexcited in the quantum well by short optical pulses was used to study escape from the quantum well. By using the two-beam technique of photoluminescence excitation correlation spectroscopy (PECS), the first experimental measurements of the tunneling escape times for both the electrons and the holes were obtained. The tunneling escape times were seen to be exponentially dependent upon the barrier thickness for barriers between 16 and 34 A. Escape times for both electrons and holes were found to be fast, and were as short as 12 ps in structures with 16 A (6 monolayer) A1As barriers. The rapid escape of heavy holes that was observed experimentally was in disagreement with simple calculations of the heavy-hole tunneling escape times, which indicated that the heavy holes should escape on a time scale many orders of magnitude longer than the times observed experimentally. This drastic difference can be explained theoretically by considering a four-band model for holes in confined systems. For finite carrier densities and temperatures, mixing of the quantum well heavy hole levels with light hole levels, due to dispersion perpendicular to the growth direction, can explain the experimental observations. This observation that heavy holes can escape rapidly by tunneling is quite general, and is applicable to a wide variety of problems involving tunneling of holes in semiconductor heterostructures. Chapter 3 describes a study of the effect of indirect (X-point) levels in the A1As barriers on the tunneling escape of electrons in undoped GaAs/AlAs/GaAs/AlAs/GaAs double-barrier heterostructures. The X-point levels, thought to be important in the electrical characteristics of double-barrier heterostructures, were found to affect the escape of photoexcited electrons in devices where the energy of the electron state confined in the GaAs quantum well is nearly equal to, or higher than, that of the X-point levels in the AlAs barriers. In Chapter 4, we present time-resolved photoluminescence and photocurrent studies of tunneling in doped devices under electrical bias, in which current is flowing. Studies of the photoluminescence decay indicate that significant transport of photoexcited carriers from the electrodes into the quantum well occurs. This transport of photoexcited carriers constitutes a photocurrent, and the two-beam PECS technique for photoluminescence has been extended to a study of photocurrents in these devices. This technique may be useful for the study of tunneling in devices not amenable to photoluminescence techniques. Chapter 5 describes a study of the accommodation of lattice mismatch in CdTe/ZnTe strained layer superlattices. Using resonance Raman scattering, the energies of the ZnTe-like phonons were determined in a series of superlattices of varying average CdTe content. The ZnTe-like phonon energies decrease with increasing average CdTe content, indicative of the increasing strain of the ZnTe layers. The observed energies agree well with calculations of the strain shift of the phonons. The results indicate that the superlattice layers adopt a lattice constant independent of the buffer layer on which they are grown, and are coherently strained to a lattice constant that minimizes the strain energy of the superlattice. Finally, the Appendix describes operation of the colliding pulse mode-locked (CPM) dye laser used in the time-resolved photoluminescence and photocurrent experiments. Alignment of the laser, and routine operation are documented.