Dissertations / Theses on the topic 'Electric transport mechanisms'
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1
Costantino, Mauro. "Low-frequency noise spectroscopy as an effective tool for electric transport analysis." Doctoral thesis, Universita degli studi di Salerno, 2018. http://elea.unisa.it:8080/xmlui/handle/10556/4375.
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2016 - 2017In this work, several experiments and analyses performed by means of noise spectroscopy, on a broad typology of materials and compounds, are presented. Structural, DC electrical transport and noise properties are exposed for each investigated sample, and theoretical models and possible explanations of the experimental results are given to unravel physical phenomena. In particular, two distinct types of iron-chalcogenide superconductors are investigated, in their pristine and aged state, suggesting the more likely mechanism which generates the resistance fluctuations and resorting to Weak Localization theory. In the case of the polymer/carbon nanotubes composites, the fluctuation-induced tunneling model is introduced to explain the measured temperature dependence of the electrical conductance and the I-V curve behaviors. Then, noise measurements prove the existence of a structural phase transition occurring around 160 K within the perovskite compound and highlight the correlation between electronic defect states distribution and device performance. The variety of investigated devices and materials validates the soundness of the noise spectroscopy as an effective tool for electric transport analysis. [edited by author]
XXX ciclo
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Wachtmeister, Marcus. "Driving towards more flexibility? : China's environmental and climate policy in the automotive sector." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:a525684b-072d-4288-9216-52a9321051ee.
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This doctoral dissertation examines the mode and efficacy of environmental and climate policy in China’s automotive sector. The ascent of China’s automobile market to the largest worldwide has detrimental effects on the country’s energy security situation, worsens environmental pollution, and increases greenhouse gas emissions. Environmental and climate policy measures to ameliorate these repercussions are the most apt tools available to the Chinese government. The objective of this dissertation is to identify the dominant mode of environmental and climate policies in China’s automotive industry and to assess the efficacy of select policy instruments. It does so by asking whether a uniform national approach to policy instrument adoption can be discerned that reflects China’s institutional and administrative history or whether modal exceptions exist. Secondly, if modal differences exist, to what extent do different instruments confirm the current understanding of the advantages and pitfalls of individual policy instrument types? And finally, how do Chinese instruments compare to those in other ambits in terms of policy mode and instrument efficacy? The literature on policy instruments holds that, due to their alleged efficiency advantages, incentive-based instruments dominate the political agenda of industrialised countries and international organisations (environmental consensus). This favouring of flexible instruments in academic and political circles contrasts with an evident lack of incentive-based instruments in practice and an observed lack of efficiency of some of those instruments actually implemented. Moreover, the policy mode adopted in developing countries and emerging markets has not yet received sufficient academic attention despite significant differences in institutional design, enforcement capacities, resources, and development paths that may imply reason for modal deviation. Applying a blend of qualitative and quantitative social sciences research methods, I add the case of China to the comparative literature and show that command-and-control regulation indeed forms the backbone of environmental and climate policy in China’s automotive industry. At the same time, modal differences exist between national regulation and local/ municipal incentive-based policy as well as in the electric vehicle sector, which shows a trend towards more incentive-based instruments and flexibility mechanisms in conventional regulation. Compared to other ambits, China has established a relatively flexible policy regime, at least for the case of vehicle efficiency standards. For the time being, incentive-based instruments remain comparatively ineffective and flexibility mechanisms in conventional regulation have an erosive effect on instrument stringency.
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Thomson, Susmita. "Local feedback regulation of salt & water transport across pumping epithelia : experimental & mathematical investigations in the isolated abdominal skin of Bufo marinus." University of Western Australia. Dept. of Physiology, 2003. http://theses.library.uwa.edu.au/adt-WU2003.0022.
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[Truncated abstract] This study describes the results of a four and a half year investigation examining local regulation of ion transport through pumping epithelial cells. The study focussed on the standard isolated toad skin preparation, made famous by Hans Ussing. Originally, the objective was to perform some simple manipulations on the isolated toad skin, a standard and well-tested epithelial layer, which, according to the literature, was a well-behaved and stable preparation. The purpose of doing these toad skin experiments was to gain familiarity with the experimental techniques, such as measuring the open-circuit voltage (Voc) and the short-circuit current (Isc) across an epithelium. In the process, the experimental information that was obtained was to assist in the development and refinement of a mathematical model of a single pumping epithelial cell . . . Finally, it should be emphasised the toad skin was a convenient tissue model for exploring more general issues such as: (i) how pumping epithelial cells may adjust to changes in the extracellular environment by locally regulating their membrane conductances; (2) how the topology of a cell can influence its function (i.e. the topology can determine whether a cell is optimised for salt transport or water transport). (3) how different cells, with different functions, may be positioned in apposition in a pumping epithelial tissue so that gradients generated by one cell type can be utilised by another. From a broader perspective, it is likely that such issues are also applicable to other pumping epithelia, and ultimately, may assist in understanding how these epithelia function.
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Grange, Michael. "Integrative imaging and electron cryo-tomography of viral transport mechanisms." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:704e3459-053a-4a1c-b95a-9aaeca809cb2.
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To comprehensively understand a biological process or mechanism from molecule to cell it requires the combination of multiple techniques across a range of resolutions and scales. We currently rely on a variety of different approaches to highlight given aspects of biology that are then interlinked through interpretation. Intracellular transport is a process whereby vesicles and organelles are transported to different parts of cells with a precise spatial and temporal accuracy. This process is often hijacked by viruses, which utilize cellular machineries for active transport to and from the nucleus during their entry and egress. In this thesis I focus on the intracellular transport of adenoviruses, which are able to recruit and bind to the cytoskeletal motor, dynein, and use it to travel to the nucleus. I apply electron cryo-microscopy and fluorescence microscopy to elucidate the basis for this process, and link this to the behaviour of adenoviruses as they are recruited to microtubules. I then apply electron cryo-tomography to directly observe proteins in their native cellular environment. I discuss the ability of this technique to be utilized in the in situ determination of the structure of viruses as they infect a cell. I show that (i) in situ sub-volume averaging from single tomograms can guide and complement segmentation of biological features and (ii) that novel, transient processes can be imaged with high levels of detail. As a second example of transport in cells, I study the nuclear egress of herpesvirus capsids, utilizing a multi-modal approach in an attempt to characterize this process from cellular to molecular level, and ask how herpesviruses modulate the nuclear membrane during capsid egress into the cytosol. Finally, I discuss an emergent technique in the field of electron cryo-microscopy, the Volta phase plate, its potential application in molecular tomography, and how it may enhance our current ability to discern contextual molecular mechanism.
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Zhang, Tong. "Electrical conduction transport mechanisms of barium titanate- based multilayer ceramic capacitors." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43074.
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dThe major objectives of this study were to examine electrical conduction properties of BaTiO3-based multilayer ceramic ( MLC ) capacitors in order to gain a better understanding of the conduction transport mechanisms inside the devices. The experiments involved mainly leakage current versus time measurements under both low temperature-low voltage stress and high temperature-high voltage stress.
It was established that leakage current conduction in a MLC capacitor under temperature-voltage stress can be divided into three different conduction regions due to different mechanisms. Those regions are polarization current, DC conduction current and degradation current. The polarization current decreases with time as a power law relation, i.e. Ic(t) t-m where the exponent value m is strongly dependent on the type of capacitor and temperature, but is only weakly dependent on the applied voltage.
It has been proposed that two degradation models ( a charge carrier concentration model and a reduction of grain boundary barrier height model ) can explain the degradation behavior for the Z5U devices tested. Degradation measurements indicate that the lifetime for Z5U capacitors can be described by Minford's expression. However, these models account only partly for X7R degradation. X7R behavior, is characterized by an early power law time dependence, followed by exponential voltage dependence.
The most probable conduction transport mechanism in X7R capacitors is small polaron hopping, while grain boundary transmission may be the predominant conduction transport mechanism in Z5U capacitors.
Master of Science
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Storti, Mattia. "Adaptation of mechanisms for regulation of photosynthetic electron transport upon land colonization." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3425893.
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In eukaryotic organisms, oxygenic photosynthesis is catalyzed by 4 multiprotein complexes present on the thylakoid membranes inside the chloroplasts: Photosystem (PS) II, Cytochrome b6f (Cyt b6f), PSI and chloroplast ATP synthase (ATPase). The three former mediate a Linear Electron Flow (LEF) from H2O to NADP+ to synthetize NADPH. LEF also generate a proton gradient across the thylakoid membrane, supporting ATP synthesis. NADPH and ATP are exploited by Calvin Benson cycle to fix inorganic CO2 in sugars available for the metabolism.
Photosynthetic process is accompanied by the formation of unstable molecules that can generate reactive oxygen species (ROS) harmful for the cell. Particular regulatory mechanisms prevent the formation of these molecules. Among these, the Alternative Electron Flow (AEF) divert electrons from photosynthetic processes preventing over-reduction of electron transporters and ROS production. AEF mechanisms can be divided in Cyclic Electron Flow (CEF) and Pseudo-CEF (PCEF) according to the acceptors of the pathways, respectively the plastoquinone and O2. Two major CEF are known and mediated by PGR5/PGRL1 or by NDH-1 complex. PCEF is instead mediated by Flavodiiron proteins (FLV). In this thesis I focused on the early land plant Physcomitrella patens, this moss presents all the main AEF identified in algae and vascular plants and is thus a suitable model to directly compared their activity in the same organisms.
FLV proteins were lost in Angiosperms, one of the plausible explanations to this loss is that another AEF mechanism replaces their function, making FLV dispensable. FLV were shown to be fundamental to respond to light fluctuation that occurs in the natural environments, a function that in angiosperms was replaced by PGR5/PGRL1.
To evaluate the hypothesis that PGRL1/PGR5 CEF mediated pathway can replace FLV, in chapter 3 we isolated a P. patens mutant defective for both FLV and PGRL1. Our experiments highlighted a strong synergy between the 2 pathways especially when plants were exposed to stressful light regimes, suggesting a functional overlap and the possible replacement of one pathway over the other during evolution. Further analysis allowed us to establish that FLV and PGRL1 are particularly important for protection of PSI from over-reduction, thus preventing photodamage.
In chapter 4, we characterized NDH-1 complex in P. patens isolating a line defective for NDH-1 function. NDH-1 defective mutants showed a small defect in PSI functionality in the first moment after light exposure. Reiterating cycle of dark and light, the defect observed increased significantly in NDH-1 defective plants suggesting that this complex may operates in first seconds after light exposure to avoid PSI over-reduction. However, this defect did not impact the plant growth not even in fluctuating light conditions, probably because of the compensation from other mechanisms present in the chloroplast.
In order to entangle this possible compensation in chapter 5 NDH-1 was depleted in plants knock out for both PGRL1 and FLV, by isolating a double mutant lacking both CEF pathways (pgrl1-ndhm) and a triple mutant defective for both CEF and PCEF (flva-pgrl1-ndhm). Both exhibited a drastic decrease in growth and photosynthetic performances showing that NDH-1 depletion has a much larger effect if other mechanisms for AEF are also absent, eliminating compensating effects. The triple mutant showed growth defects even in non-stressing conditions suggesting these mechanisms are important also for steady state photosynthesis. Spectroscopic and biochemical characterization detected extensive damage to PSI, correlated with the growth defects.Negli organismi eucarioti la fotosintesi ossigenica è catalizzata da 4 complessi localizzati sulle membrane tilacoidali dei cloroplasti: il fotosistema (PS) II, il citocromo b6f, il PSI e l’ATPasi cloroplastica. I primi tre mediano un trasporto lineare degli elettroni (LEF) dall’H2O al NADP+ per formare NADPH. L’ATPasi invece sfrutta il gradiente protonico generato dal LEF per sintetizzare ATP. NADPH e ATP sono utilizzati dal ciclo di Calvin per fissare la CO2 in zuccheri disponibili per il metabolismo. Durante la fotosintesi si formano molecole instabili che possono generare molecole dannose per la cellula quali le specie reattive dell’ossigeno (ROS). Particolari meccanismi regolatori prevengono la formazione di queste molecole, tra questi i trasporti elettronici alternativi (AEF) rimuovono elettroni dal LEF prevenendo l’over-riduzione dei traportatori e a formazione di ROS. Gli AEF possono essere divisi in trasporti ciclici (CEF) e pseudo-ciclici (PCEF) a seconda dell’accettore finale della via, rispettivamente il plastochinone o l’O2. I due principali CEF conosciuti sono mediati dalle proteine PGR5/PGRL1 e dal complesso NDH-1. Il PCEF è invece mediato dalle proteine FLV. In questa tesi è stato studiato Physcomitrella patens, un muschio che presenta tutti i principali AEF identificati in alghe e piante vascolari ed è quindi un buon modello dove poter comparare l’attività dei diversi AEF presenti. Le proteine FLV non sono presenti nelle angiosperme, una possibile spiegazione alla loro perdita è che un altro AEF abbia sostituito il loro ruolo rendendole dispensabili. Le FLV sono importanti nella risposta alla luce fluttuante, ruolo che nelle angiosperme è ricoperto da PGR5/PGRL1. Per valutare l’ipotesi che PGR5/PGRL1 abbia rimpiazzato le FLV, nel capitolo 3 di questa tesi abbiamo isolato un mutante di P. patens difettivo per entrambe le vie. Abbiamo individuato una forte sinergia tra le 2 vie, in particolare quando i mutanti sono stati esposti a regimi luminosi restrittivi, suggerendo una sovrapposizione funzionale e un possibile sostituzione di uno con l’altro nel corso dell’evoluzione. Inoltre, abbiamo stabilito che le FLV e PGR5/PGRL1 sono importanti per proteggere il PSI dalla sovra-riduzione, prevendendo cos’ danni ossidativi. Nel capitolo 4, abbiamo caratterizzato il complesso NDH-1 di P. patens, grazie all’isolamento di una linea difettiva per la sua funzione. Questi mutanti hanno evidenziato solo una piccola differenza nella funzionalità del PSI al momento in cui le piante sono state esposte ad una luce. Reiterando cicli di buio è luce, il difetto osservato aumentava significativamente suggerendo che NDH-1 possa essere attivo nei primi secondo dopo l’esposizione ad una fonte luminosa, proteggendo il PSI. Tuttavia, anche cresciute in una condizione di luce fluttuante le piante difettive di NDH-1 non hanno mostrato fenotipi di crescita, probabilmente a causa di un meccanismo di compensazione durante il processo di acclimatazione a questa condizione. Per identificare questa possibile compensazione, nel capitolo 5 abbiamo rimosso la funzione NDH-1 in piante già mancanti di PGRL1 e FLV, isolando un doppio mutante difettivo per entrambi CEF e un triplo mutante mancante sia di CEF che di PCEF. Per Entrambi abbiamo riscontrato ridotta crescita e capacità fotosintetica, evidenziando che la funzione di NDH-1 è molto più evidente quando gli altri AEF sono assenti, eliminando l’effetto di compensazione. Il triplo mutante inoltre ha mostrato una ridotta crescita anche in condizioni non stressanti dimostrando che i AEF sono indispensabili per una corretta attività fotosintetica. Analisi spettroscopiche e biochimiche hanno mostrato che i difetti individuati sono dovuti a evidenti danni a carico del PSI in queste piante.
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Tzamos, Christos. "Mechanism design : from optimal transport theory to revenue maximization." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112000.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 191-196).
A central problem in Economics and Algorithmic Game Theory is the design of auctions that maximize the auctioneer's expected revenue. While optimal selling of a single item has been well-understood since the pioneering work of Myerson in 1981, extending his work to multi-item settings has remained a challenge. In this work, we obtain such extensions providing a mathematical framework for finding optimal mechanisms. In the first part of the work, we study revenue maximization in single-bidder multi-item settings, connecting this problem to a well-studied problem in measure theory, namely the design of optimal transport maps. By establishing strong duality between these two problems, we obtain a characterization of the structure of optimal mechanisms. As an important application, we prove that a grand bundling mechanism is optimal if and only if two measure-theoretic inequalities are satisfied. Likewise, we obtain necessary and sufficient conditions for the optimality of any mechanism in terms of a collection of measure-theoretic inequalities. Using our machinery we derive closed-form solutions in several example scenarios, illustrating the richness of mechanisms in multi-item settings, and we prove that the mechanism design problem in general is computationally intractable even for a single bidder. In the second part of the work, we study multi-bidder settings where bidders have uncertainty about the items for sale. In such settings, the auctioneer may wish to reveal some information about the item for sale in addition to running an auction. While prior work has focused only on the information design part keeping the mechanism fixed, we study the combined problem of designing the information revelation policy together with the auction format. We find that prior approaches to this problem are suboptimal and identify the optimal mechanism by connecting this setting to the multi-item mechanism design problem studied in the first part of the work.
by Christos Tzamos.
Ph. D.
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Philipp, Martin. "Electrical Transport and Scattering Mechanisms in Thin Silver Films for Thermally Insulating Glazing." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-70920.
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Thin silver films are widely used in low-emissivity coatings for building glazing due to their high reflectance in the infrared and high transmittance in the visible spectrum. The determining parameter for the infrared reflectance is the electrical conductance of the layer stack - the better the conductance the higher the reflectance. Electrically conductive films of thicknesses smaller than the electron mean free path exhibit a strong increase in the residual resistivity proportional to the inverse of the film thickness. Despite intensive discussions, which have extended over tens of years, it is not understood yet if this conductive behavior originates from electron scattering at interfaces (Fuchs-Sondheimer model) or grain boundaries (Mayadas-Shatzkes model). To achieve a fundamental understanding of the prevailing electron scattering mechanisms, aluminum-doped zinc oxide (ZnO:Al) / Ag / ZnO:Al layer stacks produced by magnetron sputtering were investigated concerning their electronic structure and electrical transport properties. The electronic structure of the layer stacks was probed and analyzed by electron energy-loss spectroscopy. By this technique, plasmonic excitations are observed, which can be categorized into excitations of the electrons in the bulk silver and excitations at the ZnO:Al / Ag interface. The plasmons were analyzed with respect to their dispersion and the peak width, and brought into relation with electrical conductivity measurements by calculating the plasmon lifetime and the electron scattering rate. The difficulty in determining the relative contributions of the interface and grain boundary scattering in experimental conditions is due to the fact that the way in which these scattering mechanisms depend on the film thickness, is very similar. Understanding the electron transport in thin films is of paramount importance, because the differentiation between the scattering mechanisms is a key issue for the improvement of the coatings. In the present work, the solution came from the expected difference in the temperature-dependent behavior of the resistivity between electron scattering at interfaces and electron scattering at grain boundaries. Hence, the resistivity was measured as a function of the temperature on layer stacks with different silver film thickness varying in the range of 4 to 200 nm. The data were analyzed using the extended Mayadas-Shatzkes model involving both electron scattering at interfaces (Fuchs-Sondheimer model), and electron scattering at grain boundaries. The results demonstrate that electron scattering at grain boundaries dominates for all film thicknesses. The basic layer stack was compared to more sophisticated systems, obtained either by adding a thin titanium layer in between silver and ZnO:Al, or by exposing the growing silver film to an oxygen partial pressure (oxidizing the film). Furthermore, the effect of annealing at 250°C was studied for all these systemsDünne Silberfilme werden aufgrund ihres hohen Reflexionsvermögens im infraroten Spektrum und ihres hohen Transmissionsvermögens im Spektrum des Sonnenlichtes als Wärmeschutzbeschichtungen für Fensterglas verwendet. Der entscheidende Parameter für das Reflexionsvermögen der Schicht ist die elektrische Leitfähigkeit - je höher die Leitfähigkeit, desto stärker wird Infrarotlicht reflektiert. Elektrisch leitende Schichten mit Schichtdicken dünner als die mittlere freie Weglänge der Elektronen weisen einen starken Anstieg des spezifischen Widerstandes auf, der sich proportional zur inversen Schichtdicke verhält. Trotz ausführlicher Diskussionen während der letzten Jahrzehnte, ist noch nicht geklärt ob dieses Verhalten auf Streuung von Elektronen an Grenzflächen (Fuchs-Sondheimer-Modell) oder an Korngrenzen (Mayadas-Shatzkes-Modell) zurückzuführen ist. Um ein grundlegendes Verständnis der vorherrschenden Streumechanismen zu erlangen, wurden Schichtstapel der Struktur Aluminium-dotiertes Zinkoxid (ZnO:Al) / Ag / ZnO:Al, welche mittels Magnetron-Sputtern hergestellt wurden, hinsichtlich ihrer Transporteigenschaften und elektronischen Struktur untersucht. Die elektronische Struktur der Schichtsysteme ist mittels Elektronen-Energieverlust-Spektroskopie untersucht und bezüglich ihrer plasmonischen Anregungen analysiert wurden. Diese können in Anregungen der Volumenelektronen des Silbers und Anregungen der Elektronen aus der ZnO:Al / Ag Grenzfläche unterteilt werden. Die Plasmonen wurden hinsichtlich ihrer Impulsabhängigkeit und Anregungsbreite analysiert und durch Berechnung der Plasmonenstreurate mit den Messungen der elektrischen Leitfähigkeit verglichen. Aufgund der Tatsache, dass Genzflächen- und Korngrenzstreuung eine ähnliche Schichtdickenabhängigkeit aufweisen, gestaltet sich die Bestimmung der relativen Beiträge beider Streumechanismen als schwierig. Diese Problem kann durch die Untersuchung der Temperaturabhängigkeit der Streumechanismen, die sich für Grenzflächen- und Korngrenzstreuung unterscheidet, gelöst werden. Der spezifische Widerstand wurde in Abhängigkeit von der Temperatur an mehreren Proben unterschiedlicher Silberschichtdicke (im Bereich von 4 bis 200 nm) gemessen. Die Daten wurden anhand des erweiterten Mayadas-Shatzkes-Modells, welches sowohl Streuung an Grenzflächen (Fuchs-Sondheimer-Modell) als auch an Korngrenzen berücksichtigt, evaluiert. Die Ergebnisse zeigen eindeutig, dass für alle Schichtdicken die Elektronenstreuung an Korngenzen der dominierende Streumechanismus ist. Die Ergebnisse der Analyse des fundmentalen Schichtsystems wurden mit denen komplexerer Systeme verglichen, bei denen zum einen durch Hinzufügen einer dünnen Titanschicht die Grenzfläche zwischen Silber und ZnO:Al modifiziert wurde und zum anderen der Silberfilm durch einen erhöhten Sauerstoff-Partialdruck während der Beschichtung oxidiert wurde. Des Weiteren wurde der Effekt einer Temperung bei 250°C an allen Systemen untersucht
Les vitrages bas-émissifs sont fréquemment élaborés par dépôts de revêtements dont la couche active est un film mince d'argent. Le paramètre qui détermine la réflexion dans l'infra-rouge est la conductance électrique de l'empilement. La résistivité électrique résiduelle de films dont l'épaisseur est inférieure au libre parcours moyen des électrons croît fortement en fonction de l'inverse de l'épaisseur. En dépit d'intenses recherches menées pendant des dizaines d'années, l'origine de cet accroissement de résistivité - réflexion des électrons par les interfaces (modèle de Fuchs-Sondheimer) ou par les joints de grains (modèle de Mayadas-Shatzkes). Pour comprendre les mécanismes à l'œuvre dans le transport des électrons, des couches ZnO dopé aluminium (ZnO:Al) / Ag / (ZnO:Al) produites par pulvérisation plasma ont été étudiée concernant leur structure électronique et propriétés de transport électrique. Les empilements ont été examinés par spectroscopie de pertes d'énergie d'électrons. Les spectres font apparaître les excitations des électrons de volume de l'argent et les excitations à l'interface ZnO:Al / Ag. Les excitations ont été analysés concernant leur dispersion. En outre, la durée de vie moyenne des plasmons déterminée d'après la largeur du pic de plasmon d'interface se compare bien à la l'inverse de la fréquence de diffusion des électrons qui se déduit de l'application du modèle de Drude aux données relatives à la résistivité. La difficulté dans la détermination des contributions relatives des modèles de Fuchs-Sondheimer et Mayadas-Shatzkes dans les conditions expérimentales est due au fait que ces deux modèles présentent des variations très similaires en fonction de l'épaisseur des films. D'importance primordiale pour la compréhension du transport dans les films minces, la question est une clé pour l'amélioration des revêtements bas-émissifs. La solution a été apportée ici par la différence de comportement en fonction de la température des diffusions des électrons aux interfaces et aux joints de grains. D'après cela, la résistance d'empilements comportant des films d'argent d'épaisseurs comprises entre 4 et 200 nm a été mesurée en fonction de la température. Les données ont été analysées au moyen de la version du modèle de Mayadas-Shatzkes qui inclut à la fois la diffusion des électrons aux interfaces (modèle de Fuchs-Sondheimer) et la diffusion des électrons aux joints de grains. Il a té démontré que, pour toutes les épaisseurs, la diffusion des électrons aux joints de grains constitue l'effet dominant. Les résultats de l'analyse du système fondamental ont été comparées avec les résultats de systèmes plus sophistiqués, obtenus soit en intercalant une couche additionnelle de titane entre l'argent et le ZnO (méthode communément utilisée pour améliorer le mouillage du ZnO par l'argent), soit par exposition à une pression partielle du film d'argent encours de croissance (pour oxyder le film). En outre, l'effet du recuit à 250°C a été étudié pour tous ces systèmes
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Sivakumar, Praveen. "Analysis of Electron Transport and Luminance Mechanisms in SrS Based Blue Emitting ACTFEL Devices." UKnowledge, 2003. http://uknowledge.uky.edu/gradschool_theses/243.
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The purpose of this thesis is to contribute to the understanding of SrS based ACTFEL devices. Better understanding of the processes in the host phosphor will give us the possibility to design more efficient blue emitting ACTFEL devices. Towards this aim, a physical model, that describes the optoelectronic processes taking place in the phosphor, was developed and analytical equations were written. The analytical model was numerically simulated and the plots of flux flowing through the device and luminance output by the device were obtained. Experiments were performed to obtain the plots of current flowing through the device and luminance output by the device. These plots were then qualitatively compared and the results of comparisons are presented. The numerical simulations qualitatively verify the accuracy of the model. The drive parameters were varied in order to study its effect on the VIL characteristics of the device. On varying the voltage applied to the device and its rise and fall times, a good insight was obtained into device behavior. Simulations were also performed to obtain responses to qualitatively match the experimentally obtained responses. Various What-If scenarios have been studied by varying the device parameters. These studies have indicated the importance of these parameters in determining device performance.
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Downs, Christopher Stephen Charles. "A route to strain-engineering electron transport in graphene." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/18897.
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Graphene, a single atomic layer of graphite, has many exciting electronic and mechanical properties. On a fundamental level, the quasi-relativistic behaviour of the charge carriers in graphene arises from the honeycomb-like atomic structure. Deforming the lattice changes the lengths of the carbon-carbon bonds, breaking the hopping symmetry between carbon sites. Mathematically, elastic strain in a graphene membrane can be described by additional terms in the low-energy effective Hamiltonian, analogous to the vector potential of an external magnetic field. Hence, certain non-uniform strain geometries produce so-called `pseudo-magnetic fields', leading to a predicted zero-field quantum Hall effect. These fictitious magnetic fields are distinct from an external magnetic field in that they are only observed by charge carriers within the membrane, and have opposing polarity for electrons in the K and K' valleys, preserving time-reversal symmetry of the lattice as a whole. Deforming graphene in the non-uniform manner required to produce a homogeneous pseudo-magnetic field has proven to be a huge technological challenge, however, restricting experimental evidence to scanning tunnelling spectroscopy measurements on, for example, highly deformed nanobubbles formed by the thermal expansion of an epitaxially grown sheet on a platinum substrate. These results stimulated a large amount of interest in strain-engineering electron transport in graphene, partly due to the extreme magnitude of the observed pseudo-magnetic field, a direct consequence of the strain components strongly varying over the space of a few nanometres, but the formation of nanobubbles is a highly stochastic process which cannot be reliably reproduced. Subsequent research found a way to fabricate nanobubbles with a high degree of consistency, but the measurements were still limited to local-probe techniques due to the nanoscale size of the devices. As such, a method to reliably induce a homogeneous pseudo-magnetic field within a micron-sized membrane would be an attractive proposition, and is the basis for the work presented within this thesis. The non-uniform strain required precludes a simple bending or elongation of the substrate, hence a more local method is required. A novel nanostructure consisting of suspended gold beams surrounding a graphene membrane will deform upon cooling to cryogenic temperatures, and crucially, the actuation mechanism can be designed to produce any configuration of strain, including uniaxial strain, triaxial strain and a fan-shaped deformation, the latter two of which are predicted to create homogeneous pseudo-magnetic fields within a membrane. Strain patterns which are predicted to produce experimentally significant pseudo-magnetic fields (~1 T) may be generated with complex actuation beams that are physically achievable. Furthermore, the actuation mechanisms may be utilised as electrical contacts to the membrane, allowing its conductivity to be measured in the context of a two- or multi-terminal measurement, in conjunction with an external magnetic field. The design of the devices was developed using finite-element analysis, and the behaviour verified by low-temperature imaging of prototypes. While, after careful annealing, some conventional two-terminal suspended devices exhibited quantum Hall features at very low fields, the fabricated strain-inducing devices did not display pseudo-Landau quantisation, nor Landau quantisation, due to the difficulties of using current annealing to clean devices post-fabrication. The presented work, however, could pave the way towards observing signatures of pseudo-magnetic fields in a range of experimental measurements, as well as creating alternative strain geometries.
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Kaya, Savas. "Electrical transport in strained silicon quantum wells on vicinal substrates." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313699.
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Alarcón, Pardo Alfonso. "Quantum many-particle electron transport in time-dependent systems with Bohmian trajectories." Doctoral thesis, Universitat Autònoma de Barcelona, 2011. http://hdl.handle.net/10803/42002.
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Es conocido que a escalas nanométricas se debe tratar con en el problema de muchas partículas a la hora de estudiar dispositivos electrónicos. Es estos escenarios, la ecuación de Schrödinger dependiente del tiempo para muchas partículas solo se puede resolver para unos pocos grados de libertad. En este sentido, diferentes formalismos han sido desarrollados en la literatura (tales como time-dependent Density Functional Theory, Green's functions técnicas o Quantum Monte Carlo técnicas) para tratar sistemas cuánticos de muchos electrones. Estas aproximaciones modelizan de forma razonable el transporte electrónico en sistemas de muchas partículas. Una propuesta alternativa ha sido desarrollada por el Dr. Oriols para descomponer la ecuación de Schrödinger de N-partículas en un sistema de N-ecuaciones de Schrödinger para una sola partícula usando trayectorias (cuánticas) de Bohm. Basado en esta propuesta se presenta un 3D, general, versátil y dependiente del tiempo simulador de transporte de dispositivos electrónicos llamado BITLLES (Bohmian Interacting Transport for non-equiLibrium eLEctronic Structures). Las novedades que aporta el simulador BITLLES se basan en dos puntos. El primero, éste representa un modelo de transporte cuántico de electrones para muchas partículas en el cual se tiene en cuenta de forma explicita las correlaciones de Coulomb y de intercambio entre electrones usando trayectorias de Bohm. En segundo lugar, el simulador proporciona una completa información de los momentos de la corriente (i.e., DC, AC, fluctuaciones o incluso momentos mayores).
A continuación resumimos las contribuciones que esta tesis aporta al desarrollo del simulador BITLLES. De esta forma, introducimos de forma explicita la interacción de intercambio entre electrones. En este contexto, mostramos como la interacción de intercambio es la responsable final para determinar la corriente total a través del sistema. Además presentamos una nueva aproximación para estudiar sistemas de muchas partículas donde los espines de los electrones tienen diferente orientación. Hasta donde llega nuestro conocimiento, es la primera vez que la interacción de intercambio es introducida de forma práctica en un simulador de transporte de electrones. Además presentamos la computación de la corriente total dependiente del tiempo en un contexto de alta frecuencia donde se tienen que tener en cuenta las variaciones del campo eléctrico dependientes del tiempo (i.e., la corriente de desplazamiento) para asegurar la conservación de la corriente. También discutimos el cálculo de la corriente total (conducción más desplazamiento) usando los teoremas de Ramo-Shockley-Pellegrini. Diferentes capacidades del simulador BITLLES como AC y fluctuaciones de la corriente se presentan para el diodo túnel resonante. También hemos usado el simulador BITLLES para testear un nuevo tipo de dispositivo nanoeléctronico diseñado para procesar señales dentro del espectro de los THz. Hemos llamado a este dispositivo Driven Tunneling Device. Se trata de un dispositivo de tres terminales donde la conductancia entre el drain y el source se controla por el terminal del gate el cual oscila a frecuencias de THz. También presentamos ejemplos prácticos de la funcionalidad de este dispositivo como un rectificador y un multiplicador de frecuencia. Finalmente, hemos desarrollado una aproximación numérica para resolver la ecuación de Schrödinger usando el modelo de tight-binding con el propósito de mejorar la descripción de la estructura de bandas del simulador BITLLES.It is known that at nanoscale regime we must deal with the many-particle problem in order to study electronic devices. In this scenario, the time-dependent many-particle Schrödinger equation is only directly solvable for very few degrees of freedom. However, there are many electrons (degrees of freedom) in any electron device. In this sense, many-particle quantum electron formalisms (such as time-dependent Density Functional Theory, Green's functions techniques or Quantum Monte Carlo techniques) have been developed in the literature to provide reasonable approximations to model many-particle electron transport. An alternative proposal has been developed by Dr. Oriols to decompose the N-particle Schrödinger equation into a N-single particle Schrödinger equation using Bohmian trajectories. Based on this proposal a general, versatile and time-dependent 3D electron transport simulator for nanoelectronic devices, named BITLLES (Bohmian Interacting Transport for non-equiLibrium eLEctronic Structures) is presented. The novelty of the BITLLES simulator is based on two points. First, it presents a many-particle quantum electron transport model taking into account explicitly the Coulomb and exchange correlations among electrons using Bohmian trajectories. Second, it provides full information of the all current distribution moments (i.e. DC, AC, fluctuations and even higher moments). We summarize the important contributions of this thesis to the development of BITLLES simulator. Thus, we introduce explicitly the exchange correlations among electrons. In this context, we show how exchange interaction is the final responsible for determining the total current across the system. We also present a new approximation to study many-particle systems with spin of different orientations. Some practical examples are studied taking into account the exchange interaction. To the best of our knowledge, it is the first time that the exchange interaction is introduced explicitly (imposing the exchange symmetry properties directly into the many-particle wavefunction) in practical electron transport simulators. We present the computation of the time-dependent total current in the high-frequency regime where one has to compute time-dependent variations of the electric field (i.e. the displacement current) to assure current conservation. We discuss the computation of the total (conduction plus displacement) current using Bohmian trajectories and the Ramo-Shockley-Pellegrini theorems. Different capabilities of BITLLES simulator such as AC and current fluctuations are presented for Resonant Tunneling Devices. We have used the BITLLES simulator to test a new type of nanoelectronic device designed to process signals at THz regime named Driven Tunneling Device. It is a three terminal device where the drain-source conductance is controlled by a gate terminal that can oscillate at THz frequencies. We also present practical examples on the functionality of this device such as rectifier and frequency multiplier. Finally, we have developed a numerical approximation to solve the Schrödinger equation using tight-binding model to improve the band structure description of the BITLLES simulator.
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Ädelroth, Pia. "Mechanisms and pathways for proton transfer in cytochrome-c oxidase." Göteborg : Göteborg University, 1998. http://catalog.hathitrust.org/api/volumes/oclc/68945135.html.
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Zhang, Bo. "Ferritin : mechanistic studies and electron transfer properties /." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1533.pdf.
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Kite, Jason T. "Secondary Electron Production and Transport Mechanisms By Measurement of Angle-Energy Resolved Cross Sections of Secondary and Backscattered Electron Emission from Gold." DigitalCommons@USU, 2006. https://digitalcommons.usu.edu/etd/2089.
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This work provides information about interactions that produce emitted electrons from polycrystalline Au. Emission energy- angle- dependent electron spectra from a polycrystalline Au surface have been measured at several incident electron beam energies. The range of incident energies (~100 eV to 2500 eV) extends from below the first crossover energy, through Emaxo, to above the second crossover energy. The conventional distinction between secondary electrons (SE) (50 eV) is found to be crude for the investigation of electron yields using these energy- angle- resolved measurements. A more realistic boundary occurs at the local minima of the emission spectra; this feature is studied as a function of incident energy and emission angle. In addition, deviations observed in the angular resolved emission spectra from isotropic behavior suggests that residual signatures exist in the emission spectra resulting from the anisotropic SE production mechanisms. Based on the disparity between our observations and recent modeling of the emission spectra, the most recent theory and simulation studies may overestimate the occurrence of randomizing collisions of scattered secondary electrons in the model of the transport mechanism. Finally, description of extensive modification to instrumental and analysis methods are described, and their effectiveness is evaluated.
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Pirbadian, Sahand. "Bacterial nanowires of Shewanella oneidensis MR-1| electron transport mechanism, composition, and role of multiheme cytochromes." Thesis, University of Southern California, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3704250.
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In this thesis, we discuss three topics concerning extracellular electron transfer in the Dissimilatory Metal Reducing Bacterium (DMRB) Shewanella oneidensis MR-1. One proposed strategy to accomplish extracellular charge transfer in Shewanella involves forming a conductive pathway to electrodes by incorporating redox components on outer cell membranes and along extracellular appendages known as bacterial nanowires within biofilms. In the first part of this dissertation, to describe extracellular charge transfer in microbial redox chains, we employed a model based on incoherent hopping between sites in the chain and an interfacial treatment of electrochemical interactions with the surrounding electrodes. Based on this model, we calculated the current-voltage (I-V) characteristics and found the results to be in good agreement with I-V measurements across and along individual microbial nanowires produced by the bacterium S. oneidensis MR-1. Based on our analysis, we propose that multistep hopping in redox chains constitutes a viable strategy for extracellular charge transfer in microbial biofilms.
In the second part, we report the first in vivo observations of the formation and respiratory impact of nanowires in the model metal-reducing microbe S. oneidensis MR-1. Live fluorescence measurements, immunolabeling, and quantitative gene expression analysis point to S. oneidensis MR-1 nanowires as extensions of the outer membrane and periplasm that include the multiheme cytochromes responsible for EET, rather than pilin-based structures as previously thought. These membrane extensions are associated with outer membrane vesicles, structures ubiquitous in Gram-negative bacteria, and are consistent with bacterial nanowires that mediate long-range EET by our proposed multistep redox hopping mechanism. Redox-functionalized membrane and vesicular extensions may represent a general microbial strategy for electron transport and energy distribution.
In addition, to elucidate the membranous nature of Shewanella nanowires, we imaged these filaments using Transmission Electron Microscopy. The TEM images reported in this thesis also provide the most accurate estimates of bacterial nanowire dimensions to date. Future TEM and cryo-TEM imaging can establish the specific alignment and configuration of outer membrane cytochromes that facilitate electron transport along bacterial nanowires.
In the third part of this thesis, we focus on the molecular conductance of MtrF, the first decaheme outer membrane cytochrome with a solved crystal structure. Decaheme outer membrane cytochromes of Shewanella play a crucial role in all the suggested pathways of extracellular electron transfer. An understanding of the electron transfer properties in MtrF will therefore impact all aspects of extracellular electron transfer research. In this thesis, using purified MtrF, we form monolayers of the protein on atomically flat gold substrates and address the dry monolayer with a Scanning Tunneling Microscope (STM) tip. This technique can be used in the future to examine the conductivity of individual MtrF molecules within the monolayer in the form of I-V curves. This methodology will allow experimental comparison with recently developed simulations of MtrF conductance.
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Poehler, Scott A. "Transport Phenomena of CVD Few-Layer MoS2 As-grown on an Al2O3 Substrate." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440181154.
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Mosbacker, Howard L. IV. "Control of Electrical Transport Mechanisms At Metal-Zinc Oxide Interfaces By Subsurface Defect Engineering With Remote Plasma Treatment." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204733572.
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Halavaty, Andrei Stepanovich. "The "shuttle" mechanism of the electron transport by the ruthenium(II) bipyridyl complex-modified bovine adrenodoxin in the steroid hydroxylase crystal structure and intramolecular electron transfer /." [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2005/340/index.html.
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Puglisi, Armando. "Transport coefficients and early time dynamics of the Quark-Gluon Plasma created in ultra-relativistic heavy ion collisions." Doctoral thesis, Università di Catania, 2016. http://hdl.handle.net/10761/4016.
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The phase diagram of QCD is actually under exploration both theoretically and experimentally searching for the phase transition from ordinary matter to a deconfined phase of quarks and gluons, namely the Quark-Gluon Plasma. Being a very complex theory, such a task is very difficult however there are several indications that the phase transition occurs as indicated by Lattice QCD calculations, in the low baryon density region, at a critical temperature of Tc 155 MeV. The only way to access the QGP in a laboratory is to collide heavy ion collision at ultra-relativistic (uRHIC) energies as actually carry out at LHC at CERN and at RHIC at BNL.
One of the most amazing discovery was that the system created in these collisions behaves like a perfect fluid. Indeed hydrodynamics calculations show that the large anisotropic flows measured are in agreement with a shear viscosity to entropy density ration eta/s close to the minimum value predicted by AdS/CFT eta/s = 1/4pi.
In this thesis we discuss about two main subjects of QGP produced in uRHIC: transport coefficients, in particular shear viscosity and electric conductivity, and a modeling of initial fields
and their early time dynamics of the system produced in uRHIC.
Our challenge is to develop a very precise transport based approach with a fixed value of eta/s, being the physical quantity that describes a fluid in strong coupling. We compute the shear viscosity solving the Relativistic Boltzmann Transport (RBT) equation and using the Green-Kubo relation that, being not affected by any kind of approximation, gives us the possibility to find the correct formula among the analytical derivations in Relaxation Time Approximation and in Chapman-Enskog scheme.
Using our numerical solution to the RTB equation we also compute the electric conductivity sigma-el of the QGP. This transport coefficient represents the response of the system to an applied external electric field and only very recently has captured the attention in the field of QGP due to the strong electric and magnetic fields present in the early stage of the collision. Our focus was to characterize the relation between the sigmael and the relaxation time tau . Moreover we study the relationship between eta and sigmael investigating the ratio between eta/s and sigma-el/T, taking into account the QCD thermodynamics, and predicting that the ratio supplies a measure of the quark to gluon scattering rates.
Once we have developed a transport based approach describing a fluid with a given eta/s, our interest moved into describing, using a single consistent approach, the fireball created in uRHIC starting from the initial time. We modeled the early time dynamics considering only a color electric field which decays to pair particles thanks to the Schwinger mechanism.
Our studies focused on the isotropization and thermalization of the system in the early stage in order to quantify the isotropization time, which is assumed to be tau-iso = 0.6 ÷ 0.8 f m/c in hydrodynamics calculations. We investigate in a sistematic way different systems: the static box, the longitudinal expanding system and the 3+1D expanding case. We compute the ratio PL/PT , with PL (PT ) the longitudinal (transverse) pressure, finding that for the relevant cases of 1+1D and 3+1D the system reaches PL/PT about 1, which characterizes the isotropization of the system, in about 1fm/c for eta/s = 1/4pi while for higher value of shear viscosity the ratio PL/PT is quite smaller than 1, meaning that the system does not isotropize.
Moreover we study also the effects of eta/s on the elliptic flow v2. The first studies show that the final v2 developed by the system is not significantly affected by the strong early non-equilibrium dynamics. Hence, such a result provides a justification of the assumptions exploited in hydrodynamical approach.
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Kabengele, Kantu. "Identification of flow patterns for coarse particles transported in a non-Newtonian carrier using electrical resistance tomography." Thesis, Cape Peninsula University of Technology, 2012. http://hdl.handle.net/20.500.11838/1247.
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A dissertation submitted to the Faculty of Engineering, Cape Peninsula University of Technology, Cape Town, in partial fulfilment of the requirements for the MTech Degree in Mechanical Engineering
2012Flow features provide considerable guidance for the rational selection of techniques to predict hydraulic behaviour and for suitable operating conditions for pipelines. Traditionally, water was used to transport coarse particles, and it was necessary to operate at velocities at which the flow was turbulent in order to avoid blockage. Consequently the friction losses were too high for economic operation. In addition, wear on pipes, fittings and pumps presented serious problems. Nowadays, it is well established that it is possible to operate at very high solids concentration in a heavy vehicle (carrier fluid). Similar solids throughputs may be achieved at very much lower velocities by operating in the laminar flow regime. This results not only in lower power requirement, but it also reduces wear and water consumption. In spite of these potential benefits, only a few studies dealing with the transport of coarse particles in heavy media have been reported. Since the distinction between different flow patterns is of paramount importance for modelling purposes, as equations are flow pattern dependent, and given the importance of avoiding excessive wear of pipes at low and high velocities, the present work was carried out in the context of dense or non-Newtonian carrier fluid. This project comprised analysis of existing data acquired at the Flow Process and Rheology Centre of the Cape Peninsula University of Technology. Kaolin in the range of 6% to 15% volumetric concentration was used as a carrier fluid and coarse material in the range of 10% to 30% volumetric concentration was simulated by silica sand ranging in size from 1 mm to 3 mm. For the purpose of this study flow patterns derived from resistance curves for various mixtures, particle concentrations, particle grading and flow conditions were compared with “concentration profiles” and images obtained from electrical resistance tomography (ERT). It appeared from this work that the sand concentration does not change the flow pattern but increases or reduces the pressure gradients depending on the case. The concentration of kaolin carrier can change the flow patterns from layered to homogeneous flow, inducing an increase in total pressure gradients as it increases. Flow patterns obtained from ERT compared reasonably well with those derived from pressure gradients profiles. The transition velocities from layered to heterogeneous flow obtained from both methods were similar, especially for low and moderate carrier concentrations. As the kaolin carrier concentration or as the sand concentration increased it became more difficult to distinguish the transition velocity between heterogeneous and layered flow. More work is still needed to improve the ERT instrument and its image reconstruction software.
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Colomés, Capón Enrique. "Quantum transport with Bohmian mechanics: application to graphene devices." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/663823.
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La ley de Moore ha sido una piedra fundamental en la mejora de la electónica
y la causa del aumento de nuestra capacidad computacional y de la existencia de la
electónica. En estas dimensiones, herramientas de simulación clásica deben ser susti-
tuidas por cuánticas. Dicha substitución implica enfrentarse a nuevos problemas fun-
damentales. Primero, el problema de muchos cuerpos imposibilita la exacta simulación
de sistemas con muchas partículas. Por otra parte, el problema de la medida, que es
especialmente relevante en escenarios de alta frequencia donde se debe medir muchas
veces.
Alternativamente a la teoría ortodoxa, la mecánica cuántica Bohmiana emerge como una
teoría cuántica especialmente bien equipada para simular parámetros de alta frecuencia
en dispositivos electrónicos cuánticos, gracias a la función de onda condicional que guía
a las partículas con posiciones bien definidas.
En esta tesis, el transporte cuántico fue explorado bajo la mecánica cuántica Bohmiana,
poniendo especial atención en grafeno, un novedoso material con estructura de bandas
lineal, del que se espera que ocupe una posición central en el futuro próximo de la
electrónica. Difiere de otros materiales en que obedece la ecuación biespinor de Dirac y
el electrón se comporta entonces como una partícula sin masa, exhibiendo efectos como
el Klein tunneling.
Durante la tesis, el simulador cuántico BITLLES fue mejorado y ahora es capaz de sim-
ular correctamente nanodispositivos con materials de banda parabólica o linear (gracias
a la inclusión de la ecuación de Dirac) en sistemas balísticos o con disipación (gracias
a la inclusión del método completamente positivo de scattering Bohmiano). Por tanto,
el BITLLES se ha convertido en un excelente candidato a ocupar el lugar del versátil
método Monte Carlo en el régimen cuántico, manteniendo su versatibilidad para calcular
parámetros de DC, AC y ruido.
Como aplicaciones prácticas, durante la tesis se predijeron probabilidades (no esperadas)
de encontrar dos electrones en el mismo lugar. También se obtuvieron curvas IV en
diferentes escenarios. Finalmente, se encontró un nuevo límite (debido a la naturaleza
discreta de los electrones) para nanodispositivos para aplicaciones lógicas trabajando a
altas frecuencias.Moore’s law has been the milestone for electronics improvement, and the cause for the exponential growth in our computational abilities and for reaching nanoscale electron devices. At such dimensions, classical simulation tools must be substituted by quan- tum ones. Such substitution implies to tackle new fundamental problems. First, the many-body problem makes (almost) impossible the exact simulation of many particles scenarios. Second, the measurement problem is especially relevant in high-frequency scenarios where multi-time measurements are mandatory. Alternatively to the orthodox theory, Bohmian mechanics emerges as a quantum theory which is specially well-equipped for the simulation of high-frequency characteristic of quantum electron devices. The Bohmian theory provides the conditional wave function that guides particles with well-defined positions. In this thesis, I explored quantum transport using Bohmian mechanics, putting special emphasis to graphene, a 2D material with linear bandstructure, which is expected to play an important role in the next future electronics. Differently from other materi- als, graphene obeys the bispinor Dirac equation, electrons behave as massless particles, exhibiting exotic behaviors, such as the Klein Tunneling effect. During the thesis, the quantum BITLLES simulator has been improved to correctly model electron nanodevices with either linear (by the inclusion of the complex bispinor Dirac equation) or parabolic bandstructures in either ballistic or dissipative (by the inclusion of the complete positive Bohmian scattering approach) systems. Thus, the BITLLES has become the candidate for substituting the versatile semiclassical Monte Carlo approach in the quantum regime, while keeping the versatility to predict DC, AC and noise performances. As practical applications, during the thesis, unexpected scattering probabilities in a Hong-Ou-Mandel experiment were predicted. In addition, different current-voltage char- acteristics were analyzed. Finally, a new limit (due to the discrete nature of charge) for ultra-small logic applications working at THz frequencies was predicted.
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Sixou, Bruno. "Proprietes de transport dans les polymeres conducteurs electroniques." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10271.
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Ce travail est consacre a l'etude des proprietes de transport, conductivite et pouvoir thermoelectrique, de plusieurs polymeres conducteurs electroniques. Le suivi de l'evolution de ces proprietes en fonction d'un seul parametre de structure, a savoir: le desordre cree par le vieillissement dans le polypyrrole ou dans la polyaniline protonee a l'acide camphre sulfonique, le taux de reticulation dans des reseaux a base de polyoctylthiophene, ou la composition dans des composites polyaniline-nafion ou polyaniline-polyoxyde d'ethylene, nous a permis de preciser la nature du processus de conduction dans chacun de ces materiaux, et de degager des caracteristiques communes a ces systemes. Dans les polymeres conducteurs tres desordonnes, on observe un processus de sauts limite par l'energie de charge entre ilots conducteurs polaroniques separes par des barrieres isolantes. Nous montrons que la variation thermique de la conductivite observee experimentalement peut etre obtenue par des simulations numeriques a partir de methodes de milieu effectif. Dans les reseaux de polyoctylthiophene, une correlation est fortement suggeree entre ilots conducteurs et ilots cristallins. Dans les melanges a base de polyaniline, les ecarts observes par rapport a la theorie classique de la percolation sont attribues a ces processus de hopping. Pour des niveaux de conduction croissants, interviennent un effet tunnel entre gros ilots induit par les fluctuations thermiques puis des processus de conduction de type metallique, lies a la structure interne des grains conducteurs et de nature quasi-unidimensionnel. Les mesures de pouvoir thermoelectrique confirment cette image heterogene de la structure. De facon generale, a un terme lineaire en fonction de la temperature, de type metallique, se superpose, une contribution de type semi-conducteur amorphe. Dans les polymeres conducteurs, c'est la microstructure, les heterogeneites de dopage ou les zones plus ou moins cristallines qui determinent en premier lieu les proprietes de transport macroscopiques. La structure locale des chaines intervient dans les processus de conduction a l'interieur des ilots conducteurs et en filigrane dans les proprietes de transport macroscopiques. Dans cette perspective, le vieillissement peut etre decrit comme un grignotage d'ilots conducteurs au profit de barrieres isolantes
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Philipp, Martin [Verfasser], Bernd [Akademischer Betreuer] Büchner, Jacques [Akademischer Betreuer] Jupille, Bourhis Eric [Akademischer Betreuer] Le, and Rüdiger [Akademischer Betreuer] Klingeler. "Electrical Transport and Scattering Mechanisms in Thin Silver Films for Thermally Insulating Glazing / Martin Philipp. Gutachter: Bernd Büchner ; Eric Le Bourhis ; Rüdiger Klingeler. Betreuer: Bernd Büchner ; Jacques Jupille." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://d-nb.info/1067189971/34.
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Zeng, Sheng. "Mycobacterium bovis BCG chaperonin 60.1 contributes to adaptations under stresses: implication for escaping isoniazid bactericidal mechanism and for mycobacterial biofilm growth." Doctoral thesis, Universite Libre de Bruxelles, 2019. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/286394.
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Tuberculosis, caused by Mycobacterium tuberculosis, still poses a huge global health threat today. During infection, the bacilli are believed to confront with various stresses, including hypoxia. Hypoxia is known to trigger the bacteria to adapt into a nonreplicating dormant state associated with reduced drug susceptibility. In addition to dormancy, mycobacteria, like other bacteria, may switch to sessile biofilm growth that is generally associated with augmented drug and stress tolerance. Bacterial biofilm is physically heterogeneous and may harbor cells displaying distinct metabolic activities. It is therefore likely that some cell populations within an established biofilm are in a nonreplicating dormant state. A better understanding of mycobacterial dormancy establishment and biofilm growth could unveil crucial bacillary survival strategies that will provide insights into a rational design of chemotherapy regimen.The mycobacterial chaperonin 60.1 (Cpn60.1, also known as GroEL1), a probable chaperonin and/or nucleoid associated protein, is necessary for mycobacterial cell wall virulence lipid biosynthesis, which was reported to be enhanced at the early stage of mycobacterial hypoxic adaptation, and for reduced drug susceptibility under aerobic condition. We therefore investigated whether Cpn60.1 was essential for mycobacterial adaptation to hypoxic dormancy using Mycobacterium bovis BCG as the model organism. We found that Cpn60.1, although nonessential for mycobacterial survival, reduced isoniazid (INH) susceptibility under hypoxia. Unexpectedly and interestingly, INH’s bactericidal activity was found to involve electron transport chain perturbation (e.g. enhanced oxygen consumption and increased adenosine triphosphate level) via NADH dehydrogenases, succinate dehydrogenases, cytochrome bc1 and F0F1 ATP synthase. Moreover, respiratory reprogramming to cytochrome bd was observed to protect against INH-induced killing.Intriguingly, we found that Cpn60.1 was required for respiratory and energetic downregulation under excess glycerol as well as in response to drugs (such as Q203 inhibiting cytochrome bc1). Cpn60.1 also played a role in lipidomic adaptation under excess glycerol (e.g. enhanced phthiocerol dimycocerosate and glycerol-based lipids synthesis but repressed trehalose-based lipids synthesis). Defective energetic downregulation in the absence of Cpn60.1 compromised the establishment of the Crabtree effect characterized by respiratory downregulation, glycolytic enhancement and secretion of several metabolites (i.e. pyruvate, succinate, acetate and glutamate). The Crabtree effect was necessary for mycobacterial adaptation to excess glycerol and biofilm growth. Due to a compromised Crabtree effect, a Cpn60.1-deficient Mycobacterium bovis BCG strain, i.e. the Δcpn60.1 strain, suffered from methylglyoxal-induced growth stasis under excess glycerol, leading to the biofilm defect under the standard biofilm medium. Given the essentiality for Cpn60.1 in mycobacterial respiratory adaptation under stresses, it is likely that the enhanced INH susceptibility of the Δcpn60.1 strain under hypoxia was due to a problematic respiratory reprogramming.In summary, Mycobacterium bovis BCG Cpn60.1 is not required for bacillary survival under hypoxic dormancy. However, it participates in various adaptations (e.g. respiratory downregulation) necessary for mycobacterial biofilm growth and for escaping INH’s bactericidal mechanism.Doctorat en Sciences biomédicales et pharmaceutiques (Pharmacie)
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Llano, Jorge. "Modern Computational Physical Chemistry : An Introduction to Biomolecular Radiation Damage and Phototoxicity." Doctoral thesis, Uppsala University, Department of Cell and Molecular Biology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4224.
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The realm of molecular physical chemistry ranges from the structure of matter and the fundamental atomic and molecular interactions to the macroscopic properties and processes arising from the average microscopic behaviour.
Herein, the conventional electrodic problem is recast into the simpler molecular problem of finding the electrochemical, real chemical, and chemical potentials of the species involved in redox half-reactions. This molecular approach is followed to define the three types of absolute chemical potentials of species in solution and to estimate their standard values. This is achieved by applying the scaling laws of statistical mechanics to the collective behaviour of atoms and molecules, whose motion, interactions, and properties are described by first principles quantum chemistry. For atomic and molecular species, calculation of these quantities is within the computational implementations of wave function, density functional, and self-consistent reaction field theories. Since electrons and nuclei are the elementary particles in the realm of chemistry, an internally consistent set of absolute standard values within chemical accuracy is supplied for all three chemical potentials of electrons and protons in aqueous solution. As a result, problems in referencing chemical data are circumvented, and a uniform thermochemical treatment of electron, proton, and proton-coupled electron transfer reactions in solution is enabled.
The formalism is applied to the primary and secondary radiation damage to DNA bases, e.g., absorption of UV light to yield electronically excited states, formation of radical ions, and transformation of nucleobases into mutagenic lesions as OH radical adducts and 8-oxoguanine. Based on serine phosphate as a model compound, some insight into the direct DNA strand break mechanism is given.
Psoralens, also called furocoumarins, are a family of sensitizers exhibiting cytostatic and photodynamic actions, and hence, they are used in photochemotherapy. Molecular design of more efficient photosensitizers can contribute to enhance the photophysical and photochemical properties of psoralens and to reduce the phototoxic reactions. The mechanisms of photosensitization of furocoumarins connected to their dark toxicity are examined quantum chemically.
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Forestier-Colleoni, Pierre. "Etude expérimentale des champs magnétiques en surface d'une cible irradiée par laser et leurs implications sur le faisceau d'électrons." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0036/document.
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Cette thèse porte sur la caractérisation des champs magnétiques générés par l'interaction entre un laser d'intensité de 1017 W/cm2 à 1018 W/cm2 et de cibles solides, et leurs effets sur le faisceau d'électrons chauds. En effet, les différents champs magnétiques créés lors de cette interaction ont un rôle fondamental sur les caractéristiques du faisceau d'électrons chauds : sa source et son transport dans la matière. Des diagnostics de polarimétrie et d'interférométrie croisée ont été développés lors de cette thèse pour observer le champ magnétique en surface de la cible irradiée par laser et en particulier leurs évolutions spatiale et temporelle. Deux différents régimes ont été observés selon le contraste en intensité de l'impulsion laser : un possédant une montée rapide de champ magnétique suivie d'une décroissance plus lente créées par le déplacement des électrons chauds dans la matière, et un possédant une croissance plus lente de forme logarithmique créée par la pré-impulsion du laser par effet thermoélectrique. L'interprétation de nos résultats obtenues par ces diagnostics ont permis d'évaluer la résistivité du plasma. Cette résistivité nommée anormale dans la littérature se comprend en estimant l'influence du champ magnétique sur l'anisotropie du transport des électrons et donc sur la résistivité. Le dernier diagnostic permettant l'estimation du champ magnétique détaillé dans cette thèse est la déflectométrie protonique. Elle permet d'observer la déviation d'un faisceau de protons lors de sa propagation sous l'effet de champs électrique et magnétique. D'autres expériences se sont focalisées sur la divergence de ce faisceau d'électrons. Deux diagnostics principaux ont été utilisés : l'imagerie K α et l'imagerie du rayonnement de transition cohérente (C.T.R.) en face arrière de ciblesThis thesis concerns magnetic fields, generated by the interaction between strong laser pulse (intensity up to1018 W/cm2) and solid target, and their effects on the fast electron beam. Indeed, the various magnetic fields created during this interaction can inuence the divergence of the fast electron beam. The magnetic field createdduring this interaction have a fundamental role on the fast electron beam characteristics : its source and its transportin the material. Diagnotics of polarimetry and crossed interferometry were developed during this thesis to observethe on-surface magnetic field of the target, and in particular, their spatial and temporal evolutions. Two types oftemporal evolution of the magnetic field were observed according to the contrast in intensity of the laser pulse : afast rise of magnetic field followed by a slower decrease created by the travel of the fast electrons in the material,and a slower growth of logarithmic form created by the pre-pulse of the laser by thermoelectric effect. The interpretation of our results obtained by these diagnotics allowed us to estimate the resistivity of the plasma.This resistivity named "anomalously high resistivity" in the literature can be explained by taking into account theinuence of the magnetic field on the electrons transport (creation of an anisotropy) and thus on the resitivity.The last diagnotic allowing the estimation of the magnetic field detailed in this thesis is the proton deectometry. itallows to observe the deviation of a proton beam during its propagation under the inuence of electric and magneticfields. Other experiments were focused on the fast electron beam divergence. Two main diagnotics were used : the K α imaging and the coherent transition radiation (C.T.R) imaging at the rear side of solid targets. These diagnoticsallowed to estimate the fast electron beam divergence for two distinct energetic electron populations. The differenceof divergence coming from characteristics of both diagnotics (electrons in charge of the emissions in different energies). The diagnotics of on-surface magnetic fields of target irradiated by intense laser, such as the technics of polarimetry and crossed interferometry developed in this thesis, are dedicated to be combined with diagnotics determining the evolution of the radial size of the fast electron beam generated by the laser-matter interaction. Their simultaneous use, and the correlation between their respective data, should allow to establish experimentally, in the short term, the inuence of the on-surface magnetic fields on the fast electron beam initial characteristics, in particular the angular and energy distributions. Our results of polarimetry on the spatio-temporal evolution of the magnetic fields of surface establish the state of the art for this type of measures. There are possible improvements, in particular as regards their use in conditions of irradiation by lasers of intensities > 1018 W/cm2. These perspectives are also the object of discussions in this manuscript
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Kilian, Rolf. "From cuprates to manganites: spin and orbital liquids." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 1999. http://nbn-resolving.de/urn:nbn:de:swb:14-994411393875-11016.
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Both cuprates and manganites belong to the transition metal oxides. The physics of these compounds is characterized by a dualism of local electron interaction and itinerant charge motion. In the present work, several key issues of metallic cuprates and manganites are addressed on a theoretical level, while close connection to recent experimental work is kept. The work is based on the notion of spin and orbital liquids, representing elegant tools to handle the strongly correlated nature of the metallic state in an efficient and transparent manner. A concise introduction to the physics of cuprates and manganites as well as to the methods employed is presented at the beginning of the work. In a subsequent part, we show that the peculiar magnetic response of metallic cuprates upon impurity doping can be successfully explained within a spin-liquid picture. The remainder of the work is devoted to the metallic state of manganites. Elaborating on the notion of an orbital liquid, the interplay of electron correlations, orbital degeneracy, and double exchange is studied. Thereby, the unconventionally large incoherent optical spectrum of metallic manganites and the pronounced softening of the magnon spectrum observed in experiment can be explained. Finally, a theory of the metal-insulator transition of manganites is presented which is based upon the newly introduced notion of orbital polarons. In general, we believe the close agreement of our results with experiment to strongly support the validity of our approach, giving new insight into the spectacular and sometimes as-tonishing physics of transition metal oxides.
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Chiu, Shao-Chien, and 邱紹謙. "Electronic Transport Mechanisms of PbSe Nanoparticles." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/84547215189961694236.
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博士國立交通大學
電子物理系所
102
To understand the electrical properties of PbSe nanoparticle (NP), especially the impacts from wave function overlap, surface topography, and quantum confinement, we modulate the interparticle distance, topography and size of nanoparticle and measure the electrical properties. By observing the current to voltage, resistance to temperature relations, gate effect, photoresponse, and surface topography of nanoparticle device, systematic analysis of electronic transport and optoelectronics property can be carried out. The resistance of NP device varies over orders when the interparticle distances change. Moreover, even the electronic transport mechanism changes during the modulation of interparticle distance. For the dependence of NP topography, it was found that, the transport mechanisms are fluctuation induced tunneling conduction and hopping in the octahedral and spherical NP devices, respectively. This difference can be contributed to the difference of interparticle capacitance. The size of NP is also important, especially for the smaller NP, the quantum confinement original from the small size of NP is the main reason of Anderson localization present. From gate dependence, the mobility and carrier concentration of NP device with various interparticle distances is extracted. The photoresponse of NP is also carried out.
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Lee, Yen-Chi, and 李彥琦. "The investigation on electron transport mechanisms of magnetic tunnel junctions." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/49968271127990481258.
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博士國立彰化師範大學
物理學系
103
Electron transport mechanisms of two main structures in the field of spintronics, hybrid magnetic tunnel junctions (h-MTJs) and low RA MgO-based MTJs, have been investigated in this study. A top-down process is adopted in fabricating the devices, in which three key techniques, photolithography, electron beam lithography, and a dual-angle ion-milling etching, are used. The temperature dependent behaviors were obtained via two-probe and four-probe measurement for the former and the latter structures, respectively. First, a dramatic current enhancement is revealed in the lateral hybrid magnetic junction of NiFe/Al2O3/p-Si/ Al2O3/NiFe, and it is almost 2 orders of magnitude higher than normal nonmagnetic hybrid junction, resulting from the formation of the metal-insulator interface states in h-MTJ. This transport mechanism is associated with a trap assisted tunneling, and the results best fit to a theoretical model that obeys the Poole-Frenkel effect and gives rise to a trapping potential of 0.4 eV. Via reducing the semiconductor channel length from 3µm to 0.2 µm, a transition from the trap assisted tunneling to the hot-electron tunneling process is observed, especially for those devices with channel length down to below 1 µm. In addition, the current enhancement may be suppressed for four orders of magnitude by increasing the thickness of the oxide layer from 1nm to 2nm, in which the transport mechanism is mainly dominated by trap-assisted tunneling. In the system of CoFeB/MgO/CoFeB-based magnetic tunnel junctions (MTJs), the tunneling magnetoresistance (TMR) ratio of each deep sub-micrometer scaled device follows a similar decreasing ratio of 0.17 %/K, however there are two different tendencies in temperature dependent behaviors: (1) insulator-liked behavior at parallel (P) state and anti-parallel (AP) state; (2) insulator-like behavior and metal-liked behavior at AP state and P state, respectively. It is notable that there is a significant metal-insulator transition at P state in second type of devices at temperature below 50K. As evident by the field-independent variation in temperature dependent resistance variation (ΔR/T1/2) in this metal-insulator transition, a three-dimensional electron-electron interaction (3-D EEI) in a narrow disorder channel is accounted for such behavior. Thus, an 3-D EEI is introduced as a quantum correction term, i.e. GM=MT^0.5+M0 , to the conventional theory model. This modified model consistently describes the temperature-dependent conductance for all the MTJ devices from 300K to 2K. Moreover, it has been confirmed that the TMR ratio is not affected by the existed narrow channel having an upper limit conductance of 1 mS.
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Malvankar, Nikhil S. "Investigations of electron transport and storage mechanisms in microbial biofilms." 2010. https://scholarworks.umass.edu/dissertations/AAI3427555.
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Electron transport is a fundamental mechanism in a variety of biological systems such as photosynthesis and aerobic respiration. However, the transport has long been considered to occur only over short distances (< 1 μm), primary by metalloproteins. Recently, the conduction of electrons over large distances (> 10 μm) along networks of microbial pilin filaments known as microbial nanowires has been invoked to explain a wide range of important redox phenomena that influence carbon and mineral cycling in soils and sediments, bioremediation, corrosion, interspecies electron transfer and anaerobic conversion of organic wastes to methane or electricity. However, there has never been any direct experimental demonstration of this long-distance electron transport. In fact, previous measurements of microbial biofilms have noted just the opposite: that biofilms act as insulators, not conductors. In this thesis, we reconcile these confounding observations with the demonstration that biofilms of several species of commonly studied microorganisms do function as insulators, whereas biofilms of Geobacter sulfurreducens , common in soils and sediments can form a conductive matrix, with a conductivity comparable to synthetic conductive polymers. We show that biofilms are capable of conducting electrons over 1.25 cm, many thousands of times the size of a cell. Biofilm conductivity was found to be proportional to the abundance of pilin filaments and the conductivity of sheared pilins was comparable to biofilms. We also found that biofilm conductivity regulates fuel cell current density. We demonstrate that electron transport in the biofilms does not occur via localized charge carriers known as cytochromes, as almost universally predicted, but rather through delocalized electronic states. Moreover, we report a quantum mechanical interference phenomenon of weak localization in pilin nanowires. Additionally, we demonstrate that cytochromes can be used to store electrons with capacitance comparable to commercial supercapacitors. Furthermore, the degree of conductivity and capacitance within the films can be tuned via changes in gene expression or gate bias. This study demonstrates that pilin-associated long-distance electron transport through a microbial matrix is feasible, establishes approaches that could be used for evaluating the possibility of electron flow through natural microbial communities, and demonstrates the potential for developing novel bioelectronic materials.
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Su, Guo-Rong, and 蘇國榮. "Electronic Transport Mechanisms in Split-gate Controlled Semiconductor Quantum Devices." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/25359805127541470504.
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碩士國立聯合大學
機械工程學系碩士班
100
The thesis studies the electronic transport characteristics in semiconductor quantum devices. We use the split-gate to control the width of the quantum device. In addition, an AC-biased top-gate is applied in front of the split-gate to investigate time-dependent quantum transport mechanisms. We use the time-dependent mode-matching method to investigate the time-dependent quantum transport mechanisms of quantum devices with different geometric structures. The geometric structure may involve mode-mixing effects and induce inter-subband transisition effects. The periodic time-varing potential energy may let the conduction electrons absorb or emit photon energies to induce inter-sideband transition effects, and then to achieve the photon-assisted to photon-suppressed quantum transport characheristics. Morover, we also investigate how the frequency response and the temperature effects influence the electronic transport characteristics.
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Lin, Cheng-Pang, and 林政邦. "Electric field effect and transport mechanism research on Co-doped ZnO films." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/ycc762.
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碩士國立中山大學
物理學系研究所
96
The mechanism for the room temperature magnetic coupling and electric conduction in oxide diluted magnetic semiconductors (DMS) has been studied simultaneously on the Co:ZnO thin film by utilization of the electric field effect. We find that the carriers are bound on a defect in a radius much larger than the bounded magnetic polaron (BMP) radius, and can move by the variable range hopping (VRH) over a relative small distance. Therefore, a concentric bounded model consisting of a concentric localization configuration with a limited carrier VRH capability was proposed. In this model, the carriers localized around defects couples strongly with the doped magnetic ions forming a BMP in the inner sphere and can only itinerate with no spin coherence in the outer shell. Carriers can hop either by spin-polarized or by spin-independent VRH directly between or not directly between adjacent inner spheres, respectively. This model can explain both the electric and magnetic properties of the oxide DMS, and depicts an evolution of electric and magnetic properties associated with defect concentration.
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"Electron transfer mechanism between cytochrome C and inorganic complexes." Chinese University of Hong Kong, 1988. http://library.cuhk.edu.hk/record=b5885935.
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ZAMPONI, NICOLA. "Quantum fluid models for electron transport in graphene." Doctoral thesis, 2013. http://hdl.handle.net/2158/804472.
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We derived and studied several fluid models for quantum transport of electrons in graphene. The models have been derived from a collisional Wigner equation by means of an entropy minimization tecnique. Analytical results concerning one of the models have been achieved, showing the well-posedness of the model itself. Numerical simulations of a one-dimensional ballistic diode using two of the presented models have been performed, showing some interesting features of the considered models.
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Lee, Ping-Huan, and 李品寰. "First principle study of electron transport mechanism in phenylene-based molecular devices." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/19350571632023196677.
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碩士中原大學
物理研究所
100
The first principle calculation in molecular device is studied for electron transport. Our method is based on density functional theory and non-equilibrium Green’s function method to analyze a single phenylene-based molecular device and calculate its density of states, molecular orbits, electron density distribution and current-voltage (I-V) curves. We find that when the phenylene-based molecular is coupled to electrodes, the Fermi level and energy level of the molecule are modified, and an intrinsic potential barrier is formed at the molecule-electrode interface, which has effect on the electron transport, leading to non-linear I-V curves. Furthermore, we change the structure of the molecule. We have a hydrogen atom of the benzene replaced by a substituent-NH2 to become aniline(C6H5NH2) and analyze its electron transport. From the result of the aniline device, we find that the substituent-NH2 gives rise to the Fermi level and energy level of the molecule but its lone pair of electrons affects the π electrons of the aromatic ring, leading to the number of π-bonding of the aniline is reduced by one compared with the benzene. Thus, the current flowing through the aniline devices is slightly smaller than that of the benzene device. Finally, we conclude that the substituent-NH2 could affect the electron transport of the molecule, creating different electrical transport characteristics. On the other hand, we simulate the electrical property of polyaniline device which is composited of the benzenes and anilines. The different I-V curves of the benzene, aniline and polyaniline are compared with each other.
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Lee, Hoshik 1975. "Quantum chaos and electron transport properties in a quantum waveguide." Thesis, 2008. http://hdl.handle.net/2152/3914.
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We numerically investigate electron transport properties in an electron waveguide which can be constructed in 2DEG of the heterostructure of GaAs and AlGaAs. We apply R-matrix theory to solve a Schrödinger equation and construct a S-matrix, and we then calculate conductance of an electron waveguide. We study single impurity scattering in a waveguide. A [delta]-function model as a single impurity is very attractive, but it has been known that [delta]-function potential does not give a convergent result in two or higher space dimensions. However, we find that it can be used as a single impurity in a waveguide with the truncation of the number of modes. We also compute conductance for a finite size impurity by using R-matrix theory. We propose an appropriate criteria for determining the cut-off mode for a [delta]-function impurity that reproduces the conductance of a waveguide when a finite impurity presents. We find quantum scattering echoes in a ripple waveguide. A ripple waveguide (or cavity) is widely used for quantum chaos studies because it is easy to control a particle's dynamics. Moreover we can obtain an exact expression of Hamiltonian matrix with for the waveguide using a simple coordinate transformation. Having an exact Hamiltonian matrix reduces computation time significantly. It saves a lot of computational needs. We identify three families of resonance which correspond to three different classical phase space structures. Quasi bound states of one of those resonances reside on a hetero-clinic tangle formed by unstable manifolds and stable manifolds in the phase space of a corresponding classical system. Resonances due to these states appear in the conductance in a nearly periodic manner as a function of energy. Period from energy frequency gives a good agreement with a prediction of the classical theory. We also demonstrate wavepacket dynamics in a ripple waveguide. We find quantum echoes in the transmitted probability of a wavepacket. The period of echoes also agrees with the classical predictions. We also compute the electron transmission probability through a multi-ripple electron waveguide. We find an effect analogous to the Dicke effect in the multi-ripple electron waveguide. We show that one of the S-matrix poles, that of the super-radiant resonance state, withdraws further from the real axis as each ripple is added. The lifetime of the super-radiant state, for N quantum dots, decreases as [1/N] . This behavior of the lifetime of the super-radiant state is a signature of the Dicke effect.text
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Arora, Himani. "Charge transport in two-dimensional materials and their electronic applications." 2020. https://tud.qucosa.de/id/qucosa%3A74071.
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Semiconducting two-dimensional (2D) materials have gained considerable attention in recent years owing to their potential in future electronics. On the one hand, the conventional 2D semiconductors, such as transition metal dichalcogenides (TMDCs (MoS2, WS2, etc.) are being exhaustively studied, on the other hand, search for novel 2D materials is at a rapid pace. In this thesis, we explore 2D materials beyond graphene and TMDCs in terms of their intrinsic electronic properties and underlying charge transport mechanisms. We introduce 2D semiconducting materials of indium selenide (InSe) and gallium selenide (GaSe), and a novel π-d conjugated Fe3(THT)2(NH4)3 metal-organic framework (MOF) as potential candidates for their use as active elements in (opto)electronic applications.
Owing to the air-sensitivity of InSe and GaSe, their integration into active devices has been severely constrained. Here, we report a hexagonal boron nitride (hBN) based encapsulation, where 2D layers of InSe and GaSe are sandwiched between two layers of hBN; top hBN passivating the 2D layer from the environment and bottom hBN acting as a spacer and suppressing charge transfer to the 2D layer from the SiO2 substrate. To fabricate the devices from fully encapsulated InSe and GaSe layers, we employ the technique of lithography-free via-contacts, which are metal contacts embedded within hBN flakes. Based on our results, we find that full hBN encapsulation preserves InSe in its pristine form and suppresses its degradation with time. Consequently, the electronic properties of encapsulated InSe devices are significantly improved, leading to a mobility of 30–120 cm2 V−1 s−1 as compared to a mere ∼1 cm2 V−1 s−1 obtained for unencapsulated devices. In addition, encapsulated InSe devices are stable for a prolonged period of time, overcoming their limitation to be air-sensitive. On employing full hBN encapsulation to GaSe, a high photoresponsivity of 84.2 A W−1 at 405 nm is obtained. The full hBN encapsulation technique passivates the air-sensitive layers from various degrading factors and preserves their unaltered properties. In the future, this technique can be applied to other 2D materials that have been restricted so far in their fundamental study and applications due to their environmental sensitivity.
MOFs are another emerging class of semiconducting 2D materials investigated in this thesis. They are hybrid materials that consist of metal ions connected with organic ligands via coordination bonds. In recent years, advances in synthetic approaches have led to the development of electrically conductive MOFs as a new generation of electronic materials. However, to date, poor mobilities and hopping-type charge transport dominant in these materials have prevented them from being considered for electronic applications. In this work, we investigate a newly developed π-d conjugated Fe3(THT)2(NH4)3 (THT: 2,3,6,7,10,11-hexathioltriphenylene) MOF. The MOF films are characterized with a direct bandgap lying in the infrared (IR) region. By employing Hall-effect measurements, we demonstrate band-like transport and a record-high mobility of 230 cm2 V−1 s−1 in Fe3(THT)2(NH4)3 MOF films. The temperature-dependent conductivity confirms a thermally activated charge carrier population in the samples induced by the small bandgap of the analyzed MOFs.
Following these results, we demonstrate the feasibility of using this high-mobility semiconducting MOF as an active material in thin-film optoelectronic devices. The MOF photodetectors fabricated in this work are capable of detecting wavelengths from UV to NIR (400–1575 nm). The narrow IR bandgap of the active layer constrains the performance of the photodetector at room temperature by band-to-band thermal excitation of the charge carriers. At 77 K, the device performance is significantly improved; two orders of magnitude higher voltage responsivity, lower noise equivalent power, and higher specific detectivity of 7 × 10^8 cm Hz1/2 W−1 are achieved at 785 nm excitation, which is a direct consequence of suppressing the thermal generation of charge carriers across the bandgap. These figures of merit are retained over the analyzed spectral region (400–1575 nm) and are comparable to those obtained with the first demonstrations of graphene and black phosphorus based photodetectors, thus, revealing a promising application of MOFs in optoelectronics.Zweidimensionale (2D) Halbleiter haben dank ihres Potenzials für elektronische Anwendungen in den letzten Jahren große Aufmerksamkeit erregt. Dabei werden einerseits konventionelle 2D-Materialien, wie die Übergangsmetall-Chalkogenide (TMDCs) (MoS2, WS2, usw.) intensiv erforscht. Andererseits schreitet auch die Suche nach neuen 2D-Materialien rasch voran. Diese Dissertation stellt Forschungsergebnisse zu elektrischen Eigenschaften und den zugrundeliegenden Ladungstransportmechanismen von 2D-Materialien jenseits von Graphen und TMDCs vor. Untersucht wurden die 2D-Halbleiter Indiumselenid (InSe) und Galliumselenid (GaSe), sowie eine neuartige π-d konjugierte Metallorganische Gerüstverbindung (Metal-Organic Framework, MOF) Fe3(THT)2(NH4)3. Diese Materialien sind vielversprechende Kandidaten für elektronische und optoelektronische Anwendungen. InSe und GaSe sind besonders luftempfindliche Materialien. Aus diesem Grund ist ihre Verwendung für aktive Bauteile trotz ihrer hervorragenden elektrischen Eigenschaften bis heute sehr begrenzt. In dieser Arbeit wird ein effektives Verkapselungsverfahren vorstellt, bei dem InSe- oder GaSe-2D-Schichten zwischen zwei Schichten aus hexagonalem Bornitrid (hBN) eingebettet werden. Die untere Schicht hBN isoliert das Material vom Substrat Siliziumdioxid (SiO2), während die obere Schicht das 2D-Material luftdicht isoliert. Um Bauteile aus komplett eingekapseltem InSe oder GaSe herzustellen, wurden lithographiefreie, sogenannte via-Kontakte hergestellt. Dies sind Metallkontakte, die bereits vor der Verkapselung in die hBN-Schichten integriert werden. Die hBN-Verkapselung erhält InSe in seiner ursprünglichen Form. Die hier vorgestellten Ergebnisse zeigen, dass sich die elektronischen Eigenschaften von InSe durch Verkapselung signifikant verbessern, was zu elektrischen Mobilitäten von 30–120 cm2 V−1 s−1 gegenüber nur rund ∼1 cm2 V−1 s−1 in unverkapselten Bauteilen führt. Darüber hinaus bleiben die Eigenschaften der verkapselten InSe-Bauteile über einen langen Zeitraum erhalten und degradieren nicht mehr bei Kontakt mit Luft. Die Verkapselung von GaSe ermöglicht den Einsatz in Fotodetektoren, bei einer Wellenlänge von 405 nm wird eine Fotoempfindlichkeit von 84.2 A W−1 gemessen; auch hier bewahrt die Verkapselung die empfindlichen Schichten vor schädlichen Einflüssen und konserviert so ihre unveränderten Eigenschaften. In der Zukunft kann diese Technik auch für andere 2D-Materialien eingesetzt werden, insbesondere für solche, deren Erforschung und Anwendung durch die große Empfindlichkeit bis heute eingeschränkt ist. Darüber hinaus untersucht diese Dissertation mit Metallorganischen Gerüstverbindungen (MOFs) eine zweite Klasse halbleitender 2D-Materialien. MOFs sind hybride Materialien aus Metallionen, die mit organischen Molekülen als Verbindungselementen eine meist kristalline Struktur bilden. In den letzten Jahren haben Fortschritte in der synthetischen Herstellung zur Entwicklung von elektronisch leitfähigen MOFs geführt. Die niedrige Mobilität und der sogenannte hopping-Ladungstransport der gängigsten MOFs haben jedoch verhindert, dass diese für Anwendungen betrachtet wurden. In dieser Arbeit wird eine kürzlich neu entwickelte, π-d-konjugierte Fe3(THT)2(NH4)3 (THT: 2,3,6,7,10,11-hexathioltriphenylene) MOF vorgestellt. Der MOF Film hat eine direkte Bandlücke im Infrarot(IR)-Bereich liegend. Mithilfe von Hall-Effekt-Messungen wurde gezeigt, dass der Transport in den Fe3(THT)2(NH4)3 MOF Filmen mit dem Drude-Modell konsistent ist. Darüber hinaus wird eine bis jetzt nicht übertroffene Mobilität von 230 cm2 V−1 s−1 gemessen. Die Temperaturabhängigkeit der Leitfähigkeit bestätigt, dass die kleine Bandlücke zu thermisch aktivierten Ladungstragerdichten in den Proben führt. Auf Grundlage dieser Ergebnisse wird die Machbarkeit von hochmobilen halbleitenden Fe3(THT)2(NH4)3 MOFs als aktives Material in dünnen optoelektronischen Bauteilen gezeigt. Die hier vorgestellten MOF Fotodetektoren reagieren auf Wellenlängen im UV bis Nahinfrarotspektrum (400–1575 nm). Die schmale Bandlücke schränkt die Leistung des Fotodetektors bei Raumtemperatur durch thermische Band-zu-Band-Anregung der Ladungsträger ein. Bei einer Temperatur von 77 K verbessert sich die Leistung des Detektors signifikant: Bei 785 nm wird eine um zwei Größenordnungen erhöhte Spannungsempfindlichkeit, eine niedrigere äquivalente Rauschleistung sowie eine höhere spezifische Empfindlichkeit von 7 × 10^8 cm Hz1/2 W−1 erhalten. Dies ist eine direkte Konsequenz der Unterdrückung thermischer Anregung von Ladungsträgern über die Bandlücke. Diese Leistungszahlen sind über das analysierte Spektrum (400–1575 nm) gültig und vergleichbar mit den ersten Fotodetektoren auf Grundlage von Graphen und Schwarzem Phosphor. Die Ergebnisse zeigen deutlich das Potenzial von MOFs für optoelektronische Anwendungen.
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Chiu, Wei-Hao, and 邱偉豪. "Study on Electron Transport Mechanism in Metal Oxide Photoanode Electrode for Dye-Sensitized Solar Cells." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/71562058949139583686.
Full textAbstract:
博士國立交通大學
光電工程學系
99
In early 2011, the oil price broke through 110 U.S. dollars per barrel. People are paying more and more effort to find the alternative energy sources that would suffice in the following high-oil-price era. In this thesis, the works are associated with some fundamental research in one of the solutions to the energy sources, dye-sensitized solar cells. The dye-sensitized solar cell is taken as the system where the effects of the structure and the quality of the photoanode electrodes will be studied and rationalized. Firstly, the tetrapod-like ZnO (T-ZnO) nanopartipcles (NPs) are employed to construct an efficient electron transport network as the photoanode of the dye-sensitized solar cells (DSCs). The best performance of DSCs based on 42 μm terapod-like ZnO film showed high energy conversion efficiency of 4.9% with high short-circuit current density of 12.3 mA cm-2, open-circuit voltage of 0.6 V, and filling factor of 0.65 under AM 1.5 irradiation. High efficient electron transport may be also ascribed by long effective electron diffusion length of 46 μm determined from the electrochemical impedance spectroscopy (EIS) which is consistent with thickness dependent JSC measurement. On the other hand, from time-response photocurrent transient analysis and EIS studies on the ionic diffusion dynamics of the high-viscosity electrolyte, we observed the presence of a tetrapod-like framework as the photoanode provides more efficient ionic diffusion pathway than the conventional photoanode made of C-ZnO (commercial spherical ZnO) nanopowders. And the concept of tetrapod structure is also suitable for other semiconductor photoanode in DSCs for future applications. In the second part of this thesis, a multiple electrophoretic deposition (EPD) of binder-free TiO2 photoanode has been developed to successfully fill the crack occurring after air-drying on the first EPD-TiO2 film surface. With the slow 2nd EPD, high quality TiO2 thin films are acquired on flexible ITO/PEN substrates at room temperature and the device efficiency of the dye-sensitized solar cell achieves 5.54% with a high fill factor of 0.721. EIS measurements analyze the great enhancement of the photovoltaic performance through the multiple EPD. The electron diffusion coefficient improved by about 1 order of magnitude in crack-less multiple-EPD TiO2 films. With the scattering layer, the device reveals a high conversion efficiency of up to 6.63% under AM 1.5 one sun irradiation, having a short circuit current density, open circuit voltage, and filling factor of 12.06mA cm-2, 0.763V and 0.72, respectively. Moreover, the durability of dye-sensitized plastic solar cells using two organic iodides (TBAI and PMII) are investigated. Plastic DSCs with MPN-based electrolyte containing TBAI provide good long-term stability than PMII ones. They maintain 96.9 % of baseline efficiency after 100 h under a prolonged visible light irradiation and thermal (60 oC) stress aging. We will also report the effects of organic iodides, cell-sealing conditions, and the sheet resistance of indium tin oxide coated polyethylene naphthalate substrate on device durability using the EIS.
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Standish, Russell Kim. "On various questions in nonequilibrium statistical mechanics relating to swarms and fluid flow." Phd thesis, 1990. http://hdl.handle.net/1885/138858.
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Rieger, Felix. "Correlation between Thermal Transport Mechanisms and Microstructure of Epitaxially Grown (Sb1-xBix)2Te3 Thin Films." Doctoral thesis, 2019. http://hdl.handle.net/11858/00-1735-0000-002E-E644-A.
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Rutagemwa, Humphrey. "Performance Modeling, Design and Analysis of Transport Mechanisms in Integrated Heterogeneous Wireless Networks." Thesis, 2007. http://hdl.handle.net/10012/2770.
Full textAbstract:
Recently, wireless access to Internet applications and services has attracted a lot of attention. However, there is no single wireless network that can meet all mobile users’ requirements. Con-sequently, integrated heterogeneous wireless networks are introduced to meet diverse wireless Internet applications and services requirements. On the other hand, integrated heterogeneous wireless networks pose new challenges to the design and development of reliable transport mechanisms. Wireless Application Protocol version 2 (WAP 2.0) is one of the promising trans-port mechanisms. It uses wireless profiled TCP (WP-TCP), which is fully compatible with TCP, as one of the reliable transport protocols to cope with the wireless link impairments. For WAP 2.0 to continue providing reliable and efficient transport services in the future, one of the key is-sues is to thoroughly study, understand, and improve its performance in integrated heterogeneous wireless networks.
In this thesis, we develop analytical frameworks and propose a solution to respectively study and improve the performance of WP-TCP in integrated heterogeneous wireless networks. Spe-cifically, we consider WP-TCP short- and long-lived flows over integrated wireless local area network (WLAN) and wireless wide area network (WWAN), where WLAN can be static or mo-bile. In order to facilitate the analysis of WP-TCP performance in integrated WLAN and WWAN, we first construct a novel WLAN link model, which captures the impact of both uncor-related and correlated transmission errors, and derive mathematical expressions that describe packet loss probability and packet loss burst length over WWAN-WLAN link.
Then, we develop analytical frameworks for studying the performance of WP-TCP short- and long-lived flows. Differently from those reported in the literature, our analytical framework for WP-TCP short-lived flows takes into account both correlated and uncorrelated packet losses. Furthermore, our analytical framework for long-lived flow can be used to study the short-term (during vertical handover) and long-term performances of WP-TCP and it captures the effects of vertical handover, such as excessive packet losses and sudden change in network characteristics, which are commonly experienced in integrated static WLAN and WWAN. By using the devel-oped analytical frameworks, we extensively analyze the performance of WP-TCP flows and in-vestigate the optimal protocol design parameters over a wide range of network conditions.
Finally, based on our analytical studies, we propose a receiver-centric loosely coupled cross-layer design along with two proactive schemes, which significantly improve the vertical hand-over performance. The proposed solution is easy to implement and deploy, compatible with tra-ditional TCP, and robust in the absence of cross-layer information. Extensive simulations have been conducted to confirm the effectiveness and practicability of our schemes.
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Chen, Chun-Yin, and 陳俊吟. "A Theoretical Investigation on the Mechanism and Application of the Quantum Interference Effect in Single Molecule Electron Transport." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/20446511541381612353.
Full textAbstract:
碩士國立臺灣師範大學
化學系
103
As the size of the integrated circuits (IC) gets smaller, single-molecule electron transport becomes an important issue. Electron transport in single molecules is often accompanied and strongly influenced by quantum interference effect (QIE), which can be further divided into two parts: the constructive and the destructive quantum interference. Here we investigate QIE in single -molecule electron transport in the hope that this effect can be utilized to design different electric device component. Previous literatures have reported successful synthesis of a molecular turnstile based on the phenyl-acetylene macrocycle (PAM) architecture, which consists of a central rotor and an outer stator. The rotor, with electron donating and electron withdrawing substituents, can be rotated by an external electric field. The conductance through this molecule vary with different rotating angles. We observe a sudden transmission drop at some particular rotating angles, seemingly from the destructive QIE. The variations of the molecular orbital distribution and energy with rotation for this system are investigated in detail. In the second part of this thesis, inspired by a single-molecule electric revolving door device (SMERD) reported in a following literature, we propose an improved version for this device (2G-SMERD) which has a large on-off conductance ratio (>104) and that their open and closed states can be operated by a smaller external electric field (1.0-1.5V/nm). The above case studies raise another interesting issue. We notice that the destructive QIE can take a completely different characteristic transmission lineshapes in different molecular systems. In the last chapter, we examine the odd-even symmetry effect in the destructive QIE phenomenon, and extend this discussion to cross-conjugated systems. Keywords：Quantum Interference Effect,Single Molecule Electron Transport
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Fernández, Alcazar Lucas Jonatan. "Decoherencia en el transporte cuántico : descripciones dinámicas y procesos dependientes de espín." Doctoral thesis, 2016. http://hdl.handle.net/11086/2751.
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Tesis (Doctor en Física)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación, 2016.La pérdida de correlación de fase en un sistema cuántico es conocida como decoherencia y es consecuencia de las interacción con el ambiente. En esta tesis nos enfocamos en desarrollar herramientas teóricas y numéricas que permitan describir el efecto de la decoherencia en el transporte cuántico de sistemas con dependencia temporal o que presenten procesos de inversión de espín. En particular abordamos problemas de transporte a través de paredes de dominios magnéticos, magnetorresistencia gigante, dinámica cuántica decoherente y motores cuánticos. Los modelos y métodos desarrollados son los suficientemente generales como para ser aplicados en otras situaciones.
The loss of phase correlation in a quantum system is known as decoherence and it is consequence of interactions with the environment. In this thesis, we focus on developing theoretical and numerical tools to describe the effect of decoherence in quantum transport of systems with time dependence or with spin-flipping processes. In particular we address the problems of transport through magnetic domain walls, giant magnetoresistance, decoherent quantum dynamics and adiabatic quantum motors. The models and methods developed in this thesis are general enough to be applied in other situations.
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Halavaty, Andrei S. [Verfasser]. "The "shuttle" mechanism of the electron transport by the ruthenium(II) bipyridyl complex-modified bovine adrenodoxin in the steroid hydroxylase : crystal structure and intramolecular electron transfer / Andrei S. Halavaty." 2005. http://d-nb.info/978069064/34.
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Chuang, Su-Ting, and 莊舒婷. "On the Mechanism of Charge Transport in Single-Molecule Junction: Energy Alignment and Electronic Coupling of Bipyridine and Alkylbipyridine on Au, Pd, and Pt." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/75254929864083245039.
Full textAbstract:
碩士國立臺灣大學
化學研究所
99
Understanding the factors that influence charge transport properties in MMM devices (metal-molecule-metal devices) is a critical issue. Here especially the influence of the metal work function and the metal-molecule interface are considered. We measure the single-molecule conductance of a series of pyridyl-terminated molecules, 4,4''-bipyridine (BPY) and Py–(CH2)n–Py (n = 2, 3, and 4; Py = 4-pyridyl), on Au, Pd, and Pt electrodes by the method of STM-BJ (scanning tunneling microscopy break junction). The experimental data show that the conductance of BPY decreases as the electrode work function increases. The results demonstrate electron transport takes place via LUMO of BPY. Moreover, the conductance of Py–(CH2)n–Py molecules on Au is inferior to those on Pd and Pt. Since the α,ω-alkane moiety has large HOMO－LUMO gap, the effect of different work function is not observed. The contact resistance of Py–(CH2)n–Py (n = 2, 3, and 4) is smallest on Pt. Finally, by analyzing the transport mechanism based on transition voltage spectroscopy and density functional theory calculation, we find out the major factor that influence charge transport properties through pyridyl-terminated molecules. For BPY, disparity in the conductance is attributed to the different value of barrier height. However, for Py–(CH2)n–Py, the major factor that influence charge transport is the degree of electronic coupling between the headgroup and the electrode.
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Bäumer, Sebastian Andreas. "Mechanisms of proton translocation in Methanosarcina mazei Gö1." Doctoral thesis, 2001. http://hdl.handle.net/11858/00-1735-0000-0006-ABE7-3.
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Fernández, Alcazar Lucas Jonatan. "Elementos para una descripción dinámica de la conductancia cuántica en nanohilos magnéticos." Bachelor's thesis, 2011. http://hdl.handle.net/11086/65.
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Tesis (Lic. en Física)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física, 2011.El estudio de conductancia en sistemas ferromagnéticos ha tenido un interés creciente desde el descubrimiento de la magneto-resistencia gigante, llevando al desarrollo de la espintrónica. Desarrollamos herramientas que permitirán profundizar el tratamiento del transporte cuántico en nanohilos ferromagnéticos. La necesidad de una descripción dinámica, asociada a oscilaciones de Rabi, y la consideración de efectos producidos por la temperatura, tal como la decoherencia, nos lleva a una nueva y más eficiente implementación práctica del transporte cuántico decoherente. Esto nos acerca a los experimentos desarrollados localmente y nos abre las puertas a la descripción de fenómenos dinámicos de actual interés tales como movimiento de paredes de dominio o inversión de la magnetización inducida por corriente.
Transporte en metales ferromagnéticos -- Transporte coherente -- Propuesta dinámica : Expansión de Trotter-Suzuki -- Modelo dinámico para la decoherencia -- Propiedad del transporte con decoherencia en el nanohilo ferromagnético.
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Taubitz, Christian. "Investigation of the magnetic and electronic structure of Fe in molecules and chalcogenide systems." Doctoral thesis, 2010. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-201006096312.
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In this work the electronic and magnetic structure of the crystals Sr2FeMoO6,
Fe0.5Cu0.5Cr2S4, LuFe2O4 and the molecules FeStar, Mo72Fe30, W72Fe30 are investigated
by means of X-ray spectroscopic techniques. These advanced materials exhibit very interesting properties like magnetoresistance or multiferroic behaviour. In case of the molecules they also could be used as spin model systems. A long standing issue concerning the investigation of these materials are contradicting results found for the magnetic and electronic state of the iron (Fe) ions present in these compounds. Therefore this work focuses on the Fe state of these materials in order to elucidate reasons for these problems. Thereby the experimental results are compared to multiplet simulations.