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1
Sloggett, Clare Physics Faculty of Science UNSW. "Electron correlations in mesoscopic systems." Awarded by:University of New South Wales. School of Physics, 2007. http://handle.unsw.edu.au/1959.4/31875.
Повний текст джерелаАнотація:
This thesis deals with electron correlation effects within low-dimensional, mesoscopic systems. We study phenomena within two different types of system in which correlations play an important role. The first involves the spectra and spin structure of small symmetric quantum dots, or "eartificial atoms"e. The second is the "e0.7 structure"e, a well-known but mysterious anomalous conductance plateau which occurs in the conductance profile of a quantum point contact. Artificial atoms are manufactured mesoscopic devices: quantum dots which resemble real atoms in that their symmetry gives them a "eshell structure"e. We examine two-dimensional circular artificial atoms numerically, using restricted and unrestricted Hartree-Fock simulation. We go beyond the mean-field approximation by direct calculation of second-order correlation terms; a method which works well for real atoms but to our knowledge has not been used before for quantum dots. We examine the spectra and spin structure of such dots and find, contrary to previous theoretical mean-field studies, that Hund's rule is not followed. We also find, in agreement with previous numerical studies, that the shell structure is fragile with respect to a simple elliptical deformation. The 0.7 structure appears in the conductance of a quantum point contact. The conductance through a ballistic quantum point contact is quantised in units of 2e^2/h. On the lowest conductance step, an anomalous narrow conductance plateau at about G = 0.7 x 2e^2/h is known to exist, which cannot be explained in the non-interacting picture. Based on suggestive numerical results, we model conductance through the lowest channel of a quantum point contact analytically. The model is based on the screening of the electron-electron interaction outside the QPC, and our observation that the wavefunctions at the Fermi level are peaked within the QPC. We use a kinetic equation approach, with perturbative account of electron-electron backscattering, to demonstrate that these simple features lead to the existence of a 0.7-like structure in the conductance. The behaviour of this structure reproduces experimentally observed features of the 0.7 structure, including the temperature dependence and the behaviour under applied in-plane magnetic fields.
2
Connolly, Malcolm. "Magnetometry of high temperature superconducting micro-disks and single crystals." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492292.
Повний текст джерелаАнотація:
Local Hall probe measurements and differential magneto-optical imaging with high spatial resolution have been used to investigate the magnetic state of high temperature superconducting Bi2Sr2CaCu2O8+� (BSCCO) micro-disks and platelet single crystals. The results obtained by magneto-optical imaging demonstrate that the field at which flux quantised vortices enter the disks decays exponentially with increasing temperature and the measured data agree well with analytic models for the thermal excitation of individual pancake vortices over Bean-Livingston surface barriers. Scanning Hall probe microscopy images are used to directly map the magnetic induction profiles of individual micro-disks at different applied fields and the results can be quite successfully fitted to analytic models which assume a continuous distribution of flux in the sample. At low fields, however, the characteristic mesoscopic compression of vortex clusters in increasing magnetic fields has been observed. Even at higher fields, where single vortex resolution is lost, it is still possible to track configurational changes in the vortex patterns, since competing vortex orders impose unmistakable signatures on local magnetisation curves as a function of the applied field. These observations are in excellent agreement with molecular dynamics numerical simulations which lead to a natural definition of the lengthscale for the crossover between discrete and continuum behaviours in this system. In closely related experiments, Hall magnetometry is used to probe the out-of-plane local magnetisation of platelet BSCCO single crystals. The magnetisation is found to depend on the strength and direction of an in-plane magnetic field in the crossing vortex lattices regime. The remanent magnetisation in zero out-of-plane field is found to exhibit a pronounced anisotropy, being largest with the in-plane field parallel to the crystalline a-axis, and smallest when it is parallel to the orthogonal b-axis. This behaviour is attributed to the presence of underlying linear disorder. Finally, spectral analysis of the local magnetisation data is used to estimate a lower cutoff for the characteristic frequency of thermal fluctuations of vortex positions.
3
Inkaya, Ugur Yigit. "Ratchet Effect In Mesoscopic Systems." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606929/index.pdf.
Повний текст джерелаАнотація:
Rectification phenomena in two specific mesoscopic systems are reviewed. The phenomenon
is called ratchet effect, and such systems are called ratchets. In this thesis,
particularly a rocked quantum-dot ratchet, and a tunneling ratchet are considered.
The origin of the name is explained in a brief historical background. Due to rectification,
there is a net non-vanishing electronic current, whose direction can be reversed
by changing rocking amplitude, the Fermi energy, or applying magnetic field
to the devices (for the rocked ratchet), and tuning the temperature (for the tunneling
ratchet). In the last part, a theoretical examination based on the Landauer-Bü<br>ttiker
formalism of mesoscopic quantum transport is presented.
4
Ožana, Marek. "Mesoscopic superconductivity : quasiclassical approach." Doctoral thesis, Umeå universitet, Institutionen för fysik, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-91484.
Повний текст джерелаАнотація:
This Thesis is concerned with the quasiclassical theory of meso-scopic superconductivity. The aim of the Thesis is to introduce the boundary conditions for a quasiclassical Green’s function on partially transparent interfaces in mesoscopic superconducting structures and to analyze the range of applicability of the quasiclassical theory. The linear boundary conditions for Andreev amplitudes, factoring the quasiclassical Green’s function, are presented. The quasiclassical theory on classical trajectories is reviewed and then generalized to include knots with paths intersections. The main focus of the Thesis is on the range of validity of the quasiclassical theory. This goal is achieved by comparison of quasiclassical and exact Green’s functions. The exact Gor’kov Greens function cannot be directly used for the comparison because of its strong microscopic variations on the length-scale of λF. It is the coarse-grain averaged exact Green’s function which is appropriate for the comparison. In most of the typical cases the calculations show very good agreement between both theories. Only for certain special situations, where the classical trajectory contains loops, one encounters discrepancies. The numerical and analytical analysis of the role of the loop-like structures and their influence on discrepancies between both exact and quasiclassical approaches is one of the main results of the Thesis. It is shown that the terms missing in the quasiclassical theory can be attributed to the loops formed by the interfering paths. In typical real samples any imperfection on the scale larger than the Fermi wavelength disconnects the loops and the path is transformed into the tree-like graph. It is concluded that the quasiclassical theory is fully applicable in most of real mesoscopic samples. In the situations where the conventional quasiclassical theory is inapplicable due to contribution of the interfering path, one can use the modification of the quasiclassical technique suggested in the Thesis.
5
Cipiloglu, Mustafa Ali. "Thermoelectric Effects In Mesoscopic Physics." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12604753/index.pdf.
Повний текст джерелаАнотація:
The electrical and thermal conductance and the Seebeck coefficient are calculated for one-dimensional systems, and their behavior as a function of temperature and chemical potential is investigated. It is shown that the conductances are proportional to an average of the transmission probability around the Fermi level with the average taken for the thermal conductance being over a wider range. This has the effect of creating less well-defined plateaus for thermal-conductance quantization experiments.
For weak non-linearities, the charge and entropy currents across a quantum point contact are expanded as a series in powers of the applied bias voltage and the temperature difference. After that, the expansions of the Seebeck voltage in temperature difference and the Peltier heat in current are obtained. Also, it is shown that the linear thermal conductance of a quantum point contact displays a half-plateau structure, almost flat regions appearing around half-integer multiples of the conductance quantum. This structure is investigated for the saddle-potential model.
6
Burghout, Wilco. "Hybrid microscopic-mesoscopic traffic simulation." Doctoral thesis, KTH, Infrastruktur, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-72.
Повний текст джерелаАнотація:
Traffic simulation is an important tool for modelling the operations of dynamic traffic systems and helps analyse the causes and potential solutions of traffic problems such as congestion and traffic safety. Microscopic simulation models provide a detailed representation of the traffic process, which makes them most suitable for evaluation of complicated traffic facilities and Intelligent Transportation Systems that often consist of complex traffic management, safety and information systems. Macroscopic and mesoscopic models on the other hand, capture traffic dynamics in lesser detail, but are faster and easier to apply and calibrate than microscopic models. Therefore they are most suitable for modelling large networks, while microscopic models are usually applied to smaller areas. The objective of this thesis is to combine the strengths of both modelling approaches and diminish their individual weaknesses by constructing a hybrid mesoscopic-microscopic model that applies microscopic simulation to areas of specific interest, while simulating a surrounding network in lesser detail with a mesoscopic model. Earlier attempts at hybrid modelling have concentrated on integrating macroscopic and microscopic models and have proved difficult due to the large difference between the continuous-flow representation of traffic in macroscopic models and the detailed vehicle-and driver-behaviour represented in microscopic models. These problems are solved in this thesis by developing a mesoscopic vehicle-based and event-based model that avoids the (dis)aggregation problems of traffic flows at the inter-model boundaries. In addition, this thesis focuses on the general problems of consistency across the entire hybrid model. The requirements are identified that are important for a hybrid model to be consistent across the models at different levels of detail. These requirements vary from network and route-choice consistency to consistency of traffic dynamics across the boundaries of the micro- and mesoscopic submodels. An integration framework is proposed that satisfies these requirements. This integration framework has been implemented in a prototype hybrid model, MiMe, which is used to demonstrate the correctness of the solutions to the various integration issues. The hybrid model integrates MITSIMLab, a microscopic traffic simulation model, and Mezzo, the newly developed mesoscopic model. Both the hybrid model and the new Mezzo model are applied in a number of case studies, including a network in the North of Stockholm, which show their validity and applicability. The results are promising and support both the proposed integration architecture and the importance of integrating microscopic and mesoscopic models.<br>QC 20100520
7
Metalidis, Georgo. "Electronic transport in mesoscopic systems." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985476753.
Повний текст джерела
8
Maassen, Ralph. "Mesoscopic particles in polymer solutions." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=964969610.
Повний текст джерела
9
Bartels, Guido. "Mesoscopic Aspects of Solid Friction." Gerhard-Mercator-Universitaet Duisburg, 2006. http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-01272006-083621/.
Повний текст джерелаАнотація:
The phenomenon of friction is on the one hand useful, for example for walking, which would not be so easy without friction, and on the other hand disturbing, for example in wheel bearings, where it slows down desired motion. Therefore, the origin and effect of friction is under intense research. One main point in this work is the analytic investigation of the coupling between friction force and (torsion) friction torque of a sliding and spinning disk. The local friction force at a contact area element was chosen to be an algebraic function of the local relative velocity with an exponent α > 0. It could be shown, that for α < 1 sliding and torsion friction dynamically reduce each other, while for α > 1 they amplify each other. In case of α = 1 sliding and torsion friction are decoupled. With respect to the velocity ratio of sliding and angular velocity, the final motion mode has been investigated, i.e. whether both motions stop together or whether one motion gets dominant. For α < 1 both motions stop together, while for α > 1 it depends on the initial velocity ratio. The mass distribution and contact area radius, which are encoded in the key parameter C of the corresponding differential equation, are the second important influence on the final motion mode. A phase diagram shows for given values C and α the possible final motion modes. The influence of an inhomogenous pressure distribution within the contact area on the coupling was investigated exemplarily for α = 0 with a cylinder as object. In contrast to the disk (homogenous pressure distribution) the cylinder is deflected from its initial sliding direction. In this context the motion of a curling rock on ice is discussed, as it is deflected towards the opposite direction compared to that of the cylinder. Another focal point is the investigation of the role of friction torques (rolling and torsion friction) in the compaction of nano-powders. For this three dimensional contact dynamics simulations with phenomenologically chosen contact laws were performed. With this it could be shown that torsion and rolling friction contribute significantly to the final porosity. Furthermore, these contributions of torsion and rolling friction are independent of each other and can be represented by a sum. In the chapter Conclusions and Outlook a brief introduction on recent research of atomic scale torsion friction is presented.
10
Constas, Styliani. "Reactions in mesoscopic liquid clusters." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0005/NQ27896.pdf.
Повний текст джерела
11
Huffelen, Wim Michel van. "Mesoscopic silicon-coupled superconducting junctions." [S.l. : Groningen : s.n.] ; University Library Groningen [Host], 1992. http://irs.ub.rug.nl/ppn/136234755.
Повний текст джерела
12
Robledo, Esparza Lucio Martín. "Optical manipulation of mesoscopic systems." München Verl. Dr. Hut, 2008. http://d-nb.info/989622711/04.
Повний текст джерела
13
De, Fabritiis Gianni. "Stochastic dynamics of mesoscopic fluids." Thesis, Queen Mary, University of London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268402.
Повний текст джерела
14
Bruun, John Thomas. "Statistical properties of mesoscopic superconductors." Thesis, Lancaster University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238960.
Повний текст джерела
15
Ryder, Jennifer F. "Mesoscopic simulations of complex fluids." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422696.
Повний текст джерела
16
Sulaiman, Nidhal A. "Mesoscopic modelling of nematic emulsions." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432255.
Повний текст джерела
17
Mason, Douglas Joseph. "Analytical Methods in Mesoscopic Systems." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10548.
Повний текст джерелаАнотація:
The propsect of designing technologies around the quantum behavior of mesoscopic devices is enticing. This thesis present several tools to facilitate the process of calculating and analyzing the quantum properties of such devices – resonance, boundary conditions, and the quantum-classical correspondence are major themes that we study with these tools. In Chapter 1, we begin by laying the groundwork for the tools that follow by defining the Hamiltonian, the Green’s function, the scattering matrix, and the Landauer formalism for ballistic conduction. In Chapter 2, we present an efficient and easy-to-implement algorithm called the Outward Wave Algorithm, which calculates the conductance function and scattering density matrix when a system is coupled to an environment in a variety of geometries and contexts beyond the simple two-lead schematic. In Chapter 3, we present a unique geometry and numerical method called the Boundary Reflectin Matrix that allows us to calculate the full scattering matrix from arbitrary boundaries of a lattice system, and introduce the phenomenon of internal Bragg diffraction. In Chapter 4, we present a new method for visualizing wavefunctions called the Husimi map, which uses measurement by coherent states to form a bridge between the quantum flux operator and semiclassics. We extend the formalism from Chapter 4 to lattice systems in Chapter 5, and comment on our results in Chapter 3 and other work in the literature. These three tools – the Outward Wave Algorithm, the Boundary Reflection Matrix, and the Husimi map – work together to throw light on our interpretation of resonance and scattering in quantum systems, effectively codifying the expertise developed in semiclassics over the past few decades in an efficient and robust package. The data and images that they make available promise to help design better technologies based on quantum scattering.<br>Physics
18
Kaerger, Joerg Sebastian. "Controlled crystallisation of mesoscopic particles." Thesis, University of Bath, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425636.
Повний текст джерела
19
Cobden, David Henry. "Individual defects in mesoscopic transistors." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386908.
Повний текст джерела
20
Zhou, Fei. "Coherence effects in mesoscopic systems /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9787.
Повний текст джерела
21
Liu, Xiya. "Mesoscopic effects in ferromagnetic materials." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24669.
Повний текст джерелаАнотація:
Thesis (Ph.D.)--Physics, Georgia Institute of Technology, 2008.<br>Committee Chair: Davidovic, Dragomir; Committee Member: Citrin, David; Committee Member: Kindermann, Markus; Committee Member: Marchenkov, Alexei; Committee Member: Riedo, Elisa
22
Radtke, Paul Kaspar. "Mesoscopic Models of Stochastic Transport." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19152.
Повний текст джерелаАнотація:
Transportphänomene treten in biologischen und künstlichen Systemen auf allen Längenskalen auf. In dieser Arbeit untersuchen wir sie für verschiedene Systeme aus einer mesoskopischen Perspektive, in der Fluktuationen physikalischer Größen um ihre Mittelwerte eine wichtige Rolle spielen.
Im ersten Teil untersuchen wir die persistente Bewegung aktiver Brownscher Teilchen mit zusätzlichem Drehmoment, wie sie z.B. für Spermien oder Janus Teilchen auftritt. Wird ihre Bewegung auf einen Tunnel variierender Breite beschränkt, so setzt im thermischen Nichtgleichgewicht Transport ein; ungerichtete Fluktuationen des rauschhaften Antriebs werden gleichgerichtet. Hierdurch wird ein neuer Ratschentyp realisiert.
Im zweiten Teil untersuchen wir den intrazellulären Cargotransport in den Axonen von Nervenzellen mithilfe molekularer Motoren. Sie werden als asymmetrischer Ausschlussprozess simuliert. Zusätzlich können die Cargos zwischen benachbarten Motoren ausgetauscht werden. Dadurch lassen sich charakteristische Eigenschaften des langsamen axonalen Transports mit einer einzigen Motorspezies reproduzieren. Bewerkstelligt wird dies durch die transiente Anbindung der Cargos an rückwärtslaufende Motorstaus.
Im dritten Teil diskutieren wir resistive switching, die nicht volatile Widerstandsänderung eines Dielektrikums durch elektrische Impulse. Es wird für Anwendungen im Computerspeicher ausgenutzt, dem resistive RAM. Wir schlagen ein auf Sauerstoffvakanzen basierendes stochastisches Gitterhüpfmodell vor. Wir definieren binäre logische Zustände mit Hilfe der zugrunde liegenden Vakanzenverteilung und definieren Schreibe- und Leseoperationen durch Spannungsimpulse für ein solches Speicherelement. Überlegungen über die Unterscheidbarkeit dieser Operationen unter Fluktuationen zusammen mit der Deutlichkeit der unterschiedlichen Widerstandszustände selbst ermöglichen es uns, eine optimale Vakanzenzahl vorherzusagen.<br>Transport phenomena occur in biological and artificial systems at all length scales. In this thesis, we investigate them for various systems from a mesoscopic perspective, in which fluctuations around their average properties play an important role.
In the first part, we investigate the persistent diffusive motion of active Brownian particles with an additional torque. It can appear in many real life systems, for example in sperm cells or Janus particles. If their motion is confined to a tunnel of varying width, transport arises out of thermal equilibrium; unbiased fluctuations of the noisy drive are rectified. This way, we have realized a novel kind of ratchet.
In the second part, we study intracellular cargo transport in the axons of nerve cells by molecular motors. They are modeled by an asymmetric exclusion process. In a new approach, we add a cargo exchange interaction between the motors. This way, the characteristics of slow axonal transport can be accounted for with a single motor species. It is explained by the transient attachment of cargos to reverse walking motors jams.
In the third part, we discuss resistive switching, the non-volatile change of resistance in a dielectric due to electric pulses. It is exploited for applications in computer memory, the resistive random access memory (ReRAM). We propose a stochastic lattice hopping model based on the on oxygen vacancies. We define binary logical states by means of the underlying vacancy distributions, and establish a framework of writing and reading such a memory element with voltage pulses. Considerations about the discriminability of these operations under fluctuations together with the markedness of the resistive switching effect itself enable us to predict an optimal vacancy number.
23
Sarkozy, Stephen Joseph. "Mesoscopic transport in undoped heterostructures." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612534.
Повний текст джерела
24
Good, Kevin. "Mesoscopic lattice Boltzmann nemato-dynamics." Thesis, Sheffield Hallam University, 2001. http://shura.shu.ac.uk/19702/.
Повний текст джерелаАнотація:
In this thesis we have developed an anisotropic lattice Boltzmann (LB) model that recovers the incompressible isentropic Ericksen-Leslie-Parodi (ELP) equations of continuum nemato-dynamics in two dimensions with the director confined to the plane. Suitable validations of the developed model against known solutions of the continuum theory are undertaken as. well as investigations into nematic flow in interesting geometries. The model is based upon two coupled LBE schemes, the standard momentum density distribution and a new link angle distribution. To achieve evolution, the link angle distribution undergoes a Bhatnagar-Gross-Krook (BGK) collision step and advects (propagates) in unit time with the momentum densities. Anisotropy is introduced into the momentum density evolution scheme through a linearized Lattice Boltzmann (1LB) collision process which is made anisotropic. Correctly to capture the macroscopic dynamics, 6th order isotropy of the underlying lattice structure is required, accordingly we introduce a new variant on the standard 1LB scheme : a two-dimensional thirteen link (D2Q13) model. Chapmann-Enskog expansions of the momentum and angle evolution schemes are shown, through a suitable selection of equilibrium distribution functions and forcing terms, correctly to map onto the target macroscopic ELP equations of continuum nemato-dynamics. Results are presented which validate the new scheme against known analytical solutions of the governing equations to a high degree of accuracy. The validated scheme is subsequently applied to nemato-dynamic behavior in an applied magnetic field, i.e the Freedericksz transition and velocity back-flow with director kick-back. Finally we simulate the geometrically complex Zenithly Bi-stable Display (ZBD) device to illustrate some of the advantages of the LB schemes.
25
Grimbert, François. "Mesoscopic models of cortical structures." Nice, 2008. http://www.theses.fr/2008NICE4071.
Повний текст джерелаАнотація:
Cette thèse traite de modèles mésoscopiques de colonnes et d’aires corticales. Nous modélisons une colonne corticale comme un petit réseau de masses neuronales et une aire comme un réseau continu de telles colonnes, formant un champ neuronal. La première partie de cette thèse est consacrée aux colonnes corticales. Nous faisons une revue des connaissances actuelles sur la circuiterie columnaire puis nous présentons une étude mathématique d’un modèle mésoscopique de colonne basée sur les bifurcations. Dans la seconde partie, nous étudions deux modèles non-linéaires de champs neuronaux. Le premier modèle est un champ infini à deux dimensions qui nécessite une instanciation précise des connectivités et de la forme des solutions que l’on cherche. Pour ce modèle, nous nous intéressons à l’analyse de bosses d’activités. Le second modèle de champ, neuronal est défini sur un modèle compact. Nous discutons l’existence, l’unicité et la stabilité des solutions de ces équations, et la capacité d’un tel modèle à exhiber de la synchronie, en utilisant des techniques d’analyse fonctionnelle. La dernière partie de cette thèse est consacrée à la modélisation des signaux d’imagerie optique extrinsèque. Nous montrons d’abord que les champs neuronaux constituent des modèles d’aires corticales satisfaisants. Nous proposons ensuite une formule biophysique pour le problème direct de l’imagerie optique extrinsèque. Finalement, nous présentons des simulations numériques qui reproduisent des signaux optiques observés dans le cortex visuel des mammifères ainsi que dans le cortex barrelé du rat<br>This thesis deals with mesoscopic models of cortical columns and cortical areas. We model a cortical column as a small network of neural masses and a cortical area as a two-dimensional continuous network of such cortical columns, forming then a neural field. The first part of this thesis is dedicated to cortical columns. We review the current biological knowledge on columnar circuitry and present a mathematical study of a mesoscopic column model based on bifurcation techniques. In the second part, we study two nonlinear neural field models. The first model consists in infinite two-dimensional fields that need a precise instantiation of the connectivities and a precise definition of the patterns we expect it to produce. In this framework, we focus on the analysis of bumps. The second neural field model is defined on a compact domain? We discuss its well-posedness, stability and ability to show synchrony via functional analysis techniques. The last part of this thesis deals with the modelling of voltage sensitive dye optical imaging signals. We show that neural fields are suitable models of cortical areas. Then we propose a biophysical formula, based on neural fields, for the direct problem of VSDO ! Finally, we make numerical simulations and reproduce optical signals that have been observed in the visual cortex of mammals and the barrel cortex of the rat
26
Yang, Ping 1961. "Thermal transport in mesoscopic dielectric systems." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85107.
Повний текст джерелаАнотація:
Although the study of thermal transport in condensed matter has a very long history, it continues to be an active field of work due to its importance in many applications. The research subject reported in this thesis is on theoretical investigations of thermal energy transport in systems whose linear dimension is less than the wavelength of thermal phonons. Such situations occur in mesoscopic and nanoscopic scale dielectric structures which can now be fabricated in a number of laboratories. Due to the small system dimensions, phonons must be treated as waves. Thermal energy transport, therefore, must be treated as phonon wave propagation through the system.<br>After reviewing the general physics of thermal energy transport in the classical regime, we derive, for dielectric materials, a formula for thermal energy flux in devices involving multi-terminals each connected to a thermal reservoir at local equilibrium. The energy flux is driven by a temperature bias and traverses the system by virtue of phonon wave scattering. A multi-terminal thermal conductance formula is derived in terms of phonon transmission coefficient. Using our theoretical formulation, we investigate thermal transport properties of both two-terminal and four-terminal dielectric devices by solving the quantum scattering problem using a mode matching numerical technique.<br>For thermal transport in a T-shaped dielectric nanostructure with two-terminals at low temperature, due to quantum interference the transmission coefficient of phonons becomes quite complicated. We found that the value of phonon transmission coefficients at zero energy may be unity or zero depending on a geometrical ratio of the nanostructure. The transmission has an oscillation behavior with quasi-periodicity and irregularity. The thermal conductance is found to increase monotonically with temperature---a result that we conclude to be generally true for any two-terminal device. We confirm the existence of the universal quantum of thermal conductance which exists at the low temperature limit, and such a quantum is robust against all the system parameters.<br>The physical behavior of four-terminal thermal conductance for mesoscopic dielectric systems with arbitrary shapes of scattering region is also investigated in detail. If we make a two-terminal measurement in the four-terminal device, the two-terminal conductance is a monotonically increasing function of temperature, and is equal to the universal quantum of thermal conductance masked by a geometric factor. If we make a four-terminal measurement, the four-terminal conductance has a non-monotonic dependence. In the low temperature limit, we predict that the four-terminal conductance diverges inversely proportional to temperature.<br>Finally, we discuss an interesting theoretical problem on the general behavior of thermal conductance for multi-terminal systems when thermal carriers satisfy fractional exclusion statistics. Our analysis allows us to conclude that results for fractional exclusion statistics are quite different from those of the Bose-Einstein statistics.
27
Zhang, Xusheng. "Mesoscopic models of block copolymer rheology." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=96823.
Повний текст джерелаАнотація:
We develop a mesoscopic theoretical framework to study viscoelastic response of block copolymers in the vicinity of their order-disorder transition point. We use it to study orientation selection of lamellar phases of diblock copolymers under oscillatory shears. We examine the effect of hydrodynamics on the relaxation of lamellar phases, and include anisotropic viscous stresses that follow from the uniaxial nature of the phase. We also introduce network viscoelastic effects that model chain entanglements, also made consistent with the symmetry of the phase. A numerical algorithm has been developed to solve the governing equations, which has been implemented on a parallel computer architecture. Simple cases involving the relaxation of small transverse perturbations, or viscoelasticity arising from diffusive relaxation of the order parameter have been investigated, and used to validate the numerical code. We also address the issue of spontaneous orientation selection from an initially disordered state due to an imposed oscillatory shear. In the absence of hydrodynamic coupling, we observe that the so called parallel orientation is selected for small shear frequency and amplitude, crossing over to a perpendicular orientation at higher shear frequencies and amplitudes. Hydrodynamic effects are seen to shift this crossover region. We have also examined the effect of network entanglement at finite frequencies. We find that network entanglement can lead to faster alignment, and that anisotropic network stresses can significantly influence the orientation selection process.<br>Nous developpons un cadre theorique propre a l'echelle me oscopique dans le but d'etudier la reponse viscoelastique des blocs de copolymeres pres du point de transition entre leur etat ordonne et desordonne. Nous utilisons cette theorie pour e tudier la selection de l'orientation des phases de lamelles des blocs de copolymeres subissant des cisaillements oscillatoires. Nous examinons les effets hydrodynamiques de la relaxation des phases lamellaires et nous incluons les stress visqueux anisotropes, dues a la nature uniaxiale des phases. Nous introduisons aussi les effets viscoelastique relatifs aux r eseaux modelisant l'enchevetrement des chaines dans une approche consistante avec la symetrie des phases. Un algorithme nume rique sous implementation parallele a ete developpe pour resoudre les equations relatives a cette etude. Des cas simples impliquant la relaxation diffuse du parametre relatif a l'ordre ont ete examines et utilises pour verifier le code numerique. Nous adressons aussi la question de la selection de l'orientation spontane d'un etat initialement desordonne due a un cisaillement oscillatoire impose au systeme. Dans l'absence d'interaction hydrodynamique, nous observons que l'orientation denomme e parallele est selectionnee pour des petites frequences et amplitudes de cisaillement mais adopte une orientation perpendiculaire pour de grandes frequences et amplitudes de cisaillement. Les effets hydrodynamiques changent la region de transition. Nous avons aussi examin e l'effet d'enchevetrement du reseau pour des frequences finies. Nous trouvons que l'enchevetrement du reseau mene a un alignement plus rapide et que les stress des reseaux anisotropes peuvent influencer de maniere significative le processus de se lection d'orientation.
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Lui, Chi-keung Arthur. "Transport properties of hybrid mesoscopic systems." Click to view the E-thesis via HKUTO, 2004. http://sunzi.lib.hku.hk/hkuto/record/B30727339.
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Reguera, D. (David). "Mesoscopic Nonequilibrium Kinetics of Nucleation Processes." Doctoral thesis, Universitat de Barcelona, 2001. http://hdl.handle.net/10803/663185.
Повний текст джерелаАнотація:
Esta tesis está dedicada al estudio de la cinética de la nucleación centrada en sus aspectos mesoscópicos y fuera equilibrio. Hemos desarrollado y presentado un marco teórico, basado en la Termodinámica Mesoscópica y de No Equilibrio (MNET), que garantiza una descripción flexible, bien fundamentada y conectada con las simulaciones de la dinámica de procesos fuera de equilibro, y en particular de la cinética de la nucleación.
Este marco se ha mostrado especialmente útil para desvelar las sutilezas mesoscópicas y las influencias potenciales del carácter de no equilibrio del proceso.
En particular, hemos analizado y resuelto algunos aspectos importantes y controvertidos en el ámbito de la nucleación, como son el Teorema de la Nucleación, donde hemos presentado una prueba termodinámica que ratifica su validez general; o la controversia que rodea a la incorporación de las contribuciones asociadas a los grados de libertad traslacionales y rotacionales, donde hemos incorporado por primera vez los efectos del movimiento y la rotación de los núcleos.
También hemos analizado la influencia que puede tener la dinámica y las inhomogeneidades del medio en el proceso de nucleación. En particular, hemos estudiado detalladamente dos situaciones de interés práctico y experimental, como son la nucleación en presencia de gradientes térmicos, y en presencia de flujos cortantes, comparando las predicciones teóricas con los experimentos.
Finalmente, también hemos señalado cómo se pueden incorporar estas influencias en las etapas avanzadas de la transición de fase, más allá de la etapa inicial de nucleación, lo cual permite una descripción más realista del proceso de cristalización.
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Diaconescu, Dorina. "Ballistic electron transport in mesoscopic samples." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=962295191.
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Magnée, Petrus Hubertus Cornelis. "Mesoscopic transport in superconductor - semiconductor structures." [S.l. : [Groningen] : s.n.] ; [University Library Groningen] [Host], 1996. http://irs.ub.rug.nl/ppn/14856769X.
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Robinson, Simon Jon. "Quantum electronic properties of mesoscopic superconductors." Thesis, Lancaster University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332082.
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Pooley, Christopher M. "Mesoscopic modelling techniques for complex fluids." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398125.
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Lui, Chi-keung Arthur, and 呂智強. "Transport properties of hybrid mesoscopic systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B30727339.
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趙學安 and Xuean Zhao. "Electrochemical capacitance in a mesoscopic structure." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31239778.
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Garcia, Coello J. L. "Quantum information processing in mesoscopic systems." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1370589/.
Повний текст джерелаАнотація:
This thesis discusses various schemes and protocols for quantum information processing in mesoscopic systems with particular focus on using the spin of a particle as the bearer of information. The first chapter introduce various aspects of the field of quantum information used in this thesis such as qubits, entanglement, its quantification, quantum logic gates and entanglement swapping. In this chapter concepts such as AKLT states, decoherence and adiabatic elimination are introduced as they will be relevant in the thesis. In chapter 2 we introduce the Quantum Dots as the solid state system that will primarily be used as the hardware for the development of Quantum Information Processing (QIP). The different properties of quantum dots depending on their size are discussed. The exchange interaction between tunnel coupled quantum dots and the background of quantum computation in quantum dots is described. The principal sources of decoherence and the measurement techniques for spin qubits are presented. In chapter 3, carbon nanowires filled with N@C60 dimers are studied to analyse the entanglement between nuclear spins. The dimer is modelled as a two coupled nuclear spin- electron spin pair with a Heisenberg interaction. The entanglement have been studied depending on the temperature and the intensity of an external magnetic field. Witnessing the entanglement, and particularly bound entanglement are discussed. In chapter 4, the way to extract a singlet from a quantum dot is explored. The system that we model will be consisting of a triple dot and analyse the best way to get the singlet out, with each electron in a separate dot. The chief motivation is to create a singlet between separate dots in a time-scale much faster than that given by spinspin exchange interactions. In chapter 5, quantum logic gates in a triple dot system has been studied. Such gates have been widely studied in double and single quantum dots. Motivated by the advent of experimental set ups of triple dots, we have studied the natural quantum gates that came out of a triple dot system. There are still two spin quantum bits in the three dots and there is an empty intervening dot, which imparts the scheme some advantages, as well as a substantial difference from the class of schemes studied so far. In chapter 6, we model a large square dot. As we describe in chapter 2, the properties of the large dots make them behave with some interesting properties such as hosting Wigner molecules of electrons inside. We explore the application of these structures for quantum information processing. We show here how to get singlet/triplet measurement, entanglement swapping, and how to prepare a 1D AKLT state, using the square dot as a construction block of the system. Finally in chapter 7 conclusions and further work. Here we indicate the further work that could be done with the knowledge present in this thesis and motivated by future advances in the technology.
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Irfachsyad, Danial. "Mesoscopic simulation of polymers and colloids." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252212.
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Dzurak, Andrew Steven. "Ballistic hot-electrons in mesoscopic transistors." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308185.
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Stroh, Rüediger Joachim. "Fluctuation phenomena in mesoscopic silicon devices." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358804.
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Rozhkov, Alexandr Vladimirovich. "Josephson tunneling through interacting mesoscopic system /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3022187.
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Zhao, Xuean. "Electrochemical capacitance in a mesoscopic structure /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20978716.
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Purbach, Ulrich. "Electron transport in mesoscopic metallic structures /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Armata, Federico. "Light matter interaction in mesoscopic systems." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/55876.
Повний текст джерелаАнотація:
The study of light-matter interaction has led to many fundamental discoveries as well as to the development of new technology. In this thesis, we investigate the interaction between light and matter in different mesoscopic systems such us Fabry-Perot cavities with fixed and/or moving mirrors (optomechanical cavities) and superconducting circuits. In the context of optomechanical cavities, we isolate genuine quantum contributions of the interaction between an optical field and a mechanical mirror and study how to probe nonlinearities of the mechanical motion. We also investigate dynamical corrections, arising from an initial non-equilibrium configuration of the system, to the Casimir energy induced by the interaction between a quantum multimode field and the quantum fluctuations of the movable mirror. In a cavity scenario, we further consider such kind of dynamical corrections for the Casimir-Polder force between an excited atom and a perfectly conducting mirror, finding new features that can allow for an easier way to single-out the dynamical Casimir-Polder effect. In the context of superconducting circuits, we explore the light-matter interaction between microwave fields and artificial atoms in the ultrastrong coupling regime, where the system displays a high degree of entanglement. We show how to extract these (otherwise inaccessible) quantum correlations, and how such correlations can potentially be exploited as a resource for entanglement-based applications. In all these investigations we provide feasible experimental scenarios where such new effects can be probed.
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Lee, Hyunwoo. "Electric current fluctuations in mesoscopic systems." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38380.
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Ferone, Raffaello. "Thermoelectric transport in disordered mesoscopic systems." Université Joseph Fourier (Grenoble), 2006. http://www.theses.fr/2006GRE10036.
Повний текст джерелаАнотація:
Landau theory of Fermi liquids foresees that the charge and heat are tranported by the same objects: the fermionic Landau quasi-particles. In a very general way, it is true if the screening among particles is quite strong to can consider the system as composed yet by independent particles. This is the case for the electron sea in an ordinary bulk metal. The existance of just one responsible for charge and heat transport is expressed by the Wiedemann-Franz (WF) law. It states that the ratio between the thermal and electrical conductivity depends on temperature by a constant which is more or less the same for several metals. The constant of proportionality is called the Lorenz number. What happens if the above-mentioned condition on screening is no longer satisfied, as for example in low-dimensional systems or electronic low-density systems ? The thesis is diveded into two parts. In the first one, we studied the thermal and electrical transport in a disordered quantum wire; in the second one, the influence of superconducting fluctuations on thermal conductivity in granular metals<br>La théorie de Landau des liquides de Fermi prévoit que la charge et la chaleur sont transportées par les mêmes objets: les quasi-particules fermionics de Landau. De façon très général, ceci est vrai, si l'écrantage parmi les particules dans le système est assez fort pour pouvoir continuer à considérer le système comme composé de particules indépendantes. C'est le cas, par exemple, pour la mer d'électrons dans un métal ordinaire. L'existence d'un même responsable pour le transport de la charge et de la chaleur est exprimé par la lois de Wiedemann-Franz (WF) qui affirme que le rapport entre la conductivité thermique et électrique dépend de la température par une constante qui est plus au moins la même pour plusieurs métaux. La constante de proportionnalité est appelé nombre de Lorenz. Que se passe-t-il si les conditions concernant l'écrantage que nous avons mentionnées ne sont plus satisfaites, comme par exemple dans les systèmes à dimensionalité réduite, ou des système à basse densité électronique ? Le travail de thèse est divisé en deux parties. Dans la première partie, nous avons étudié le transport thermique et électrique dans un fil quantique désordonné; dans la deuxième, l'influence des fluctuations supraconductives sur la conductivité thermique dans un métal granulaire
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WICKRAMASINGHE, J. M. A. S. P. "MESOSCOPIC FEATURES OF CLASSICALLY INTEGRABLE SYSTEMS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1140806635.
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Yue, Huanyu. "Mesoscopic Fuel Consumption and Emission Modeling." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/26695.
Повний текст джерелаАнотація:
The transportation sector is a major contributor to U.S. fuel consumption and emissions. Consequently, assessing the environmental impacts of transportation activities is essential for air-quality improvement programs. Current state-of-the-art models estimate vehicle emissions based on typical urban driving cycles. Most of these models offer simplified mathematical expressions to compute fuel consumption and emission rates based on average link speeds while ignoring transient changes in a vehicleâ s speed and acceleration level as it travels on a highway network. Alternatively, microscopic models capture these transient effects; however, the application of microscopic models may be costly and time consuming. Also, these tools may require a level of input data resolution that is not available. Consequently, this dissertation attempts to fill the void in energy and emission modeling by a framework for modeling vehicle fuel consumption and emissions mesoscopically. This framework is utilized to develop the VT-Meso model using a number of data sources. The model estimates average light-duty vehicle fuel consumption and emission rates on a link-by-link basis using up to three independent variables, namely: average travel speed, average number of stops per unit distance, and average stop duration.
The mesoscopic model utilizes a microscopic vehicle fuel consumption and emission model that was developed at Virginia Tech to compute mode-specific fuel consumption and emission rates. This model, known as VT-Micro, predicts the instantaneous fuel consumption and emission rates of HC, CO and NOx of individual vehicles based on their instantaneous speed and acceleration levels. The mesoscopic model utilizes these link-by-link input parameters to construct a synthetic drive cycle and compute average link fuel consumption and emission rates. After constructing the drive cycle, the model estimates the proportion of time that a vehicle typically spends cruising, decelerating, idling and accelerating while traveling on a link. A series of fuel consumption and emission models are then used to estimate the amount of fuel consumed and emissions of HC, CO, CO2, and NOX emissions for each mode of operation. Subsequently, the total fuel consumed and pollutants emitted by a vehicle while traveling along a segment are estimated by summing across the different modes of operation and dividing by the distance traveled to obtain distance-based average vehicle fuel consumption and emission rates. The models are developed for normal and high emitting vehicles.
The study quantifies the typical driver deceleration behavior for incorporation within the model. Since this model constructs a drive cycle which includes a deceleration mode, an accurate characterization of typical vehicle deceleration behavior is critical to the accurate modeling of vehicle emissions. The study demonstrates that while the deceleration rate typically increases as the vehicle approaches its desired final speed, the use of a constant deceleration rate over the entire deceleration maneuver is adequate for environmental modeling purposes.
Finally, the study validates the model on a freeway and urban arterial network. The results demonstrate that the model provides accurate estimates of vehicle fuel consumption and emission rates and is adequate for the evaluation of transportation operational projects.<br>Ph. D.
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Carlisle, Andrew Alan William. "Quantum features in mesoscopic bosonic systems." Thesis, Queen's University Belfast, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.725499.
Повний текст джерелаАнотація:
We study the means and extent to which quantum features can persist on a scale between that of microscopic and macroscopic, the mesoscopic scale. We examine first the dynamics of quantum features during the sudden quench of two coupled harmonic oscillators in contact with a thermal bath and we uncover a clear functional relation between quantum characteristics and thermodynamic figures of merit We then turn our attention to the system of a movable mirror in an optical cavity and assess its potential to generate a macroscopically quantum superposition using a Wigner function based measure. We conclude that with present techniques and technology such a superposition is out of reach experimentally. Finally we consider the potential of photon-reduced-squeezed Fock states to approximate a superposition of coherent states large enough to be considered macroscopically quantum. Our conclusion is that this route is promising and could potentially lead to the production of a macroscopically quantum superposition with only small advancement in present technology and techniques.
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Golod, Taras. "Mesoscopic phenomena in hybrid superconductor/ferromagnet structures." Doctoral thesis, Stockholms universitet, Fysikum, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-56629.
Повний текст джерелаАнотація:
This thesis explores peculiar effects of mesoscopic structures revealed at low temperatures. Three particular systems are studied experimentally: Ferromagnetic thin films made of diluted Pt1-xNix alloy, hybrid nanoscale Nb-Pt1-xNix-Nb Josephson junctions, and planar niobium Josephson junction with barrier layer made of Cu or Cu0.47Ni0.53 alloy. A cost-effective way is applied to fabricate the sputtered NixPt1-x thin films with controllable Ni concentration. 3D Focused Ion Beam (FIB) sculpturing is used to fabricate Nb-Pt1-xNix-Nb Josephson junctions. The planar junctions are made by cutting Cu-Nb or CuNi-Nb double layer by FIB. Magnetic properties of PtNi thin films are studied via the Hall effect. It is found that films with sub-critical Ni concentration are superparamagnetic at low temperatures and exhibit perpendicular magnetic anisotropy. Films with over-critical Ni concentration are ferromagnetic with parallel anisotropy. At the critical concentration the films demonstrate canted magnetization with the easy axis rotating as a function of temperature. The magnetism appears via two consecutive crossovers, going from paramagnetic to superparamagnetic to ferromagnetic, and the extraordinary Hall effect changes sign at low temperatures. Detailed studies of superconductor-ferromagnet-superconductor Josephson junctions are carried out depending on the size of junction, thickness and composition of the ferromagnetic layer. The junction critical current density decreases non-monotonically with increasing Ni concentration. It has a minimum at ~ 40 at.% of Ni which indicates a switching into the π state. The fabricated junctions are used as phase sensitive detectors for analysis of vortex states in mesoscopic superconductors. It is found that the vortex induces different flux shifts, in the measured Fraunhofer modulation of the Josephson critical current, depending on the position of the vortex. When the vortex is close to the junction it induces a flux shift equal to Φ0/2 leading to switching of the junction into the 0-π state. By changing the bias current at constant magnetic field the vortices can be manipulated and the system can be switched between two consecutive vortex states. A mesoscopic superconductor can thus act as a memory cell in which the junction is used both for reading and writing information (vortex).
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Maciejko, Joseph. "Time-dependent quantum transport in mesoscopic structures." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99346.
Повний текст джерелаАнотація:
In this thesis, we present a theory to calculate the time-dependent current flowing through an arbitrary noninteracting nanoscale phase-coherent device connected to arbitrary noninteracting external leads, in response to sharp step- and square-shaped voltage pulses. Our analysis is based on the Keldysh nonequilibrium Green's functions formalism, and provides an exact analytical solution to the transport equations in the far from equilibrium, nonlinear response regime. The essential feature of our solution is that it does not rely on the commonly used wideband approximation where the coupling between device scattering region and leads is taken to be independent of energy, and as such provides a way to perform transient transport calculations from first principles on realistic systems, taking into account the detailed electronic structure of the device scattering region and the leads. As an illustration of the general theory, we perform a toy model calculation for a quantum dot with Lorentzian linewidth and show how interesting finite-bandwidth effects arise in the time-dependent current dynamics. Finally, we describe possible generalizations of our theory to the cases of superconducting leads (an example of broken symmetry) and one-dimensional leads in the Luttinger liquid regime (an example of an interacting system).