Many portions of energy generated in the U.S. are not used and take the form of wasted heat due to a poor heat transfer efficiency. This fact leads research communities to focus on thermoelectrics as a means for using waste heat through direct thermal to electrical energy conversion. One way to enhance thermoelectric efficiency is to reduce thermal conductivity through nanostructuring. In nanostructures, understanding energy transport across the interface of two materials is important because interfaces dominate the resistance to overall thermal transport of the system and can be described by thermal boundary conductance (TBC). Also of note, an understanding of thermal transport cannot be achieved without an understanding of transfer via atomic vibration, known as phonons. In this study, two different techniques of molecular dynamics (MD) simulation are introduced in order to improve the understanding of the phonon transport at the interface of dissimilar materials and the impact of different material properties on TBC. Non-equilibrium MD simulations are used to study relative and combined contributions of mass and bond energy difference on TBC and phonon wave-packet simulations are used to obtain a detailed description of phonon interactions at the interface. At the end of this study, a simple analytical model for the prediction of effective thermal conductivity, using knowledge of thermal boundary resistance, an inverse of TBC, and the interface geometry, is developed.

Although an iontophoretic trans-dermal drug delivery is known as an effective means for drug transportation through the human skin, it is not widely used because of the various side effects that come to life due to a high applied voltage of up to 80V. This study introduces an alternative means of drug transportation through the skin by means of sweat gland activation and reduction of an applied voltage to ensure that the iontophoresis is safe. The skin conductance studies performed on the pulmar area using 50mM of NaCl showed that the activation of sweat glands led to the increase of the skin conductance up to 8-10 times which enabled us to use a lower voltage of 2V in order to achieve noticeable results during the actual drug delivery experiment performed in the points of low ionic resistance that are located on a human biceps, also the application of Vaseline on the experimental surface does not allow the decrease of a skin conductance for as long as 11 hours which enables us to do the drug delivery over a long period of time. Finally, the drug delivery was performed and tested by means of HPLC method.

Analytical baseflow separation techniques such as those used in the automated hydrograph separation program HYSEP rely on a single input parameter that defines the period of time after which surface runoff ceases and all streamflow is considered baseflow. In HYSEP, this input parameter is solely a function of drainage basin contributing area. This method cannot be applied universally since in most regions the time of surface runoff cessation is a function of a number of different hydrologic and hydrogeologic basin characteristics, not just contributing drainage area. This study demonstrates that streamflow conductivity can be used as a natural tracer that integrates the different hydrologic and hydrogeologic basin characteristics that influence baseflow response. Used as an indicator of baseflow as a component of total flow, streamflow conductivity allows for an empirical approach to hydrograph separation using a simple mass balance algorithm. Although conductivity values for surface-water runoff and ground-water baseflow must be identified to apply this mass balance algorithm, field studies show that assumptions based on streamflow at low flow and high flow conditions are valid for estimating these end member conductivities. The only data required to apply the mass balance algorithm are streamflow conductivity and discharge measurements. Using minimal data requirements, empirical hydrograph separation techniques can be applied that yield reasonable estimates of baseflow. This procedure was performed on data from 10 USGS gaging stations for which reliable, real-time conductivity data are available. Comparison of empirical hydrograph separations using streamflow conductivity data with analytical hydrograph separations demonstrates that uncalibrated, graphical estimation of baseflow can lead to substantial errors in baseflow estimates. Results from empirical separations can be used to calibrate the runoff cessation input parameter used in analytical separation for each gaging station. In general, collection of stream conductivity data at gaging stations is relatively recent, while discharge measurements may extend many decades into the past. Results demonstrate that conductivity data available for a relatively short period of record can be used to calibrate the runoff cessation input parameter used for analytical separation. The calibrated analytical method can then be applied over a much longer period record since discharge data are the only requirement.

In this dissertation, we study properties of quantum interaction phenomena in two-dimensional (2D) and one-dimensional (1D) electronic systems in p-GaAs micro- and nano-scale devices. We present low-temperature magneto-transport data from three forms of low-dimensional systems 1) 2D hole systems: in order to study interaction contributions to the metallic behavior of 2D systems 2) Bilayer hole systems: in order to study the many body, bilayer quantum Hall state at nu = 1 3) 1D hole systems: for the study of the anomalous conductance plateau G = 0.7 ???? 2e2/h The work is divided into five experimental studies aimed at either directly exploring the properties of the above three interaction phenomena or the development of novel device structures that exploit the strong particle-particle interactions found in p-GaAs for the study of many body phenomena. Firstly, we demonstrate a novel semiconductor-insulator-semiconductor field effect transistor (SISFET), designed specifically to induced 2D hole systems at a ????normal???? AlGaAs-on-GaAs heterojunction. The novel SISFETs feature in our studies of the metallic behavior in 2D systems in which we examine temperature corrections to ????xx(T) and ????xy(T) in short- and long-range disorder potentials. Next, we shift focus to bilayer hole systems and the many body quantum Hall states that form a nu = 1 in the presence of strong interlayer interactions. We explore the evolution of this quantum Hall state as the relative densities in the layers is imbalanced while the total density is kept constant. Finally, we demonstrate a novel p-type quantum point contact device that produce the most stable and robust current quantization in a p-type 1D systems to date, allowing us to observed for the first time the 0.7 structure in a p-type device.

This thesis deals with electron correlation effects within low-dimensional, mesoscopic systems. We study phenomena within two different types of system in which correlations play an important role. The first involves the spectra and spin structure of small symmetric quantum dots, or &quoteartificial atoms&quote. The second is the &quote0.7 structure&quote, a well-known but mysterious anomalous conductance plateau which occurs in the conductance profile of a quantum point contact. Artificial atoms are manufactured mesoscopic devices: quantum dots which resemble real atoms in that their symmetry gives them a &quoteshell structure&quote. We examine two-dimensional circular artificial atoms numerically, using restricted and unrestricted Hartree-Fock simulation. We go beyond the mean-field approximation by direct calculation of second-order correlation terms; a method which works well for real atoms but to our knowledge has not been used before for quantum dots. We examine the spectra and spin structure of such dots and find, contrary to previous theoretical mean-field studies, that Hund's rule is not followed. We also find, in agreement with previous numerical studies, that the shell structure is fragile with respect to a simple elliptical deformation. The 0.7 structure appears in the conductance of a quantum point contact. The conductance through a ballistic quantum point contact is quantised in units of 2e^2/h. On the lowest conductance step, an anomalous narrow conductance plateau at about G = 0.7 x 2e^2/h is known to exist, which cannot be explained in the non-interacting picture. Based on suggestive numerical results, we model conductance through the lowest channel of a quantum point contact analytically. The model is based on the screening of the electron-electron interaction outside the QPC, and our observation that the wavefunctions at the Fermi level are peaked within the QPC. We use a kinetic equation approach, with perturbative account of electron-electron backscattering, to demonstrate that these simple features lead to the existence of a 0.7-like structure in the conductance. The behaviour of this structure reproduces experimentally observed features of the 0.7 structure, including the temperature dependence and the behaviour under applied in-plane magnetic fields.

<p>We study the spin polarization and conductance in infinitely long quasi one-dimensionalquantum wires under various conditions in an attempt to reproduce and to explain some of theanomalous conductance features as seen in various experiments. In order to accomplish thistask we create an idealized model of a quantum wire in a split-gate semiconductorheterostructure and we perform self-consistent Hartree-Fock calculations to determine theelectron occupation and spin polarization. Based on those results we calculate the currentthrough the wire as well as the direct and differential conductances. In the frame of theproposed model the results show a high degree of similarity to some of the experimentallyobserved conductance features, particularly the 0.25- and 0.85-plateaus. These results lead usto the conclusion that those conductance anomalies are in fact caused by the electronsspontaneously polarizing due to electron-electron interactions when an applied potentialdrives a current through the wire.</p>

We developed and implemented a first-principles based theory of the Landauer ballistic conductance, to determine the transport properties of nanostructures and molecular-electronics devices. Our approach starts from a quantum-mechanical description of the electronic structure of the system under consideration, performed at the density-functional theory level and using finite-temperature molecular dynamics simulations to obtain an ensemble of the most likely microscopic configurations. The extended Bloch states are then converted into maximally-localized Wannier functions to allow us to construct the Green's function of the conductor, from which we obtain the density of states (confirming the reliability of our microscopic calculations) and the Landauer conductance. A first application is presented to the case of pristine and functionalized carbon nanotubes. / Singapore-MIT Alliance (SMA)

La personnalité et les émotions sont des concepts étroitement liés théoriquement comme empiriquement, cependant, la question de savoir quels aspects de la réactivité émotionnelle modulent la personnalité a été peu étudiée en soi. Cette question est abordée dans ce travail au moyen de méthodes psychophysiologiques (en particulier la réponse électrodermale et les potentiels évoqués), afin disoler les différents éléments de la réponse émotionnelle. Les résultats montrent que la personnalité module à la fois les aspects somatique et cognitif de la réponse émotionnelle. Finalement, le présent travail fait état de possibles implications de ces différences de réactivité émotionnelle liées à la personnalité sur le fonctionnement psychologique en situation de prise de décision, ainsi que dans lépisode dépressif. Personality and emotions are theoretically and empirically related concepts; however which emotional responsiveness aspect is modulated by personality has been hardly addressed. This issue is thus investigated here with psychophysiological methods (namely skin conductance response and event-related potentials), in order to separately focus on different parts of the emotional response. The results show that both somatic and cognitive aspects of the emotional response are modulated by personality. Finally, the present work reports that personality-related differences regarding emotional responsiveness might be implicated in psychological functioning in a decision-making task, as well as in depression.

Irreversible thermodynamics is a widely-applicable toolset that extends thermodynamics to describe systems undergoing irreversible processes. It is particularly useful for describing macroscopic flow of system components, whether conserved (e.g., particle number) or non-conserved (e.g., spin). We give a general introduction to this toolset and calculate the entropy production due to bulk and interfacial flow. We compare the entropy production and heating rate of bulk and interfacial transport, as well as interfacial charge and spin transport. We then demonstrate the power and applicability of this toolset by applying it to three systems. We first consider metal oxide growth, and discuss inconsistency in previous theory by Mott. We show, however, that Mott's solution is the lowest order of a consistent asymptotic solution, with the ion and electron concentrations and fluxes going as power series in t^-k/2, where k = 1, 2, .... We find that this gives corrections to the "parabolic growth law" that has oxide thickness going as t^1/2; the lowest order correction is logarithmic in t. We then consider the effect on spin of electric currents crossing an interface between a ferromagnet (FM) and non-magnetic material (NM). Previous theories for electrical potential and spin accumulation neglect chemical or magnetic contributions to the energy. We apply irreversible thermodynamics to show that both contributions are pivotal in predicting the spin accumulation, particularly in the NM. We also show that charge screening, not considered in previous theories, causes spin accumulation in the FM, which may be important in ferromagnetic semiconductors. Finally, we apply irreversible thermodynamics to thermal equilibration in a thin-film FM on a substrate. Recent experiments suggest that applying a thermal gradient across the length of the system causes a spin current along the thickness; this spin current is present much farther from the heat sources than expected. We find that, although the interaction between the separate thermal equilibration processes increases the largest equilibration length, thermal equilibration does not predict a length as large as the experimentally measured length; it does predict, however, a thermal gradient along the thickness that has the shape of the measured spin current.

Individual carbon nanotubes (CNTs) have superior thermal conductivity than conventional materials. The applications for CNTs range from heat sinks, thin films to thermal interface materials. However, when CNTs are grouped together in macroscopic quantities and embedded in different media their thermal conductivity changes. Therefore, it is important to determine the thermal conductance changes when CNTs are embedded in different media. In my research, CNTs were embedded in thin films and as aligned structures (fins) in water. Analytical and experimental methods were used to determine the thermal conductances of these aligned structures and thin films. The primary goals of this research were to develop novel analytical methods to determine thermal conductivity and also experimental techniques to determine effectiveness of the embedded CNTs as carriers of heat by thermal conductance evaluation. It is observed that CNTs fins are effective carriers of heat and result in up to 57% decrease in thermal resistance. In the case of CNTs embedded in thin films, it is important to consider non Fourier effects and neglecting non Fourier effects would lead to an underestimation of the thermal conductivity. In addition to the thermal conductivity value, the analysis also provides a way to determine the thermal relaxation time of thin films.