Tesis sobre el tema "Transport phenomena"
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1
Swartz, Melody A. "Interstitial-lymphatic transport phenomena". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50376.
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Laohakunakorn, Nadanai. "Electrokinetic phenomena in nanopore transport". Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/252690.
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Nanopores are apertures of nanometric dimensions in an insulating matrix. They are routinely used to sense and measure properties of single molecules such as DNA. This sensing technique relies on the process of translocation, whereby a molecule in aqueous solution moves through the pore under an applied electric field. The presence of the molecule modulates the ionic current through the pore, from which information can be obtained regarding the molecule's properties. Whereas the electrical properties of the nanopore are relatively well known, much less work has been done regarding their fluidic properties. In this thesis I investigate the effects of fluid flow within the nanopore system. In particular, the charged nature of the DNA and pore walls results in electrically-driven flows called electroosmosis. Using a setup which combines the nanopore with an optical trap to measure forces with piconewton sensitivity, we elucidate the electroosmotic coupling between multiple DNA molecules inside the confined environment of the pore. Outside the pore, these flows produce a nanofluidic jet, since the pore behaves like a small electroosmotic pump. We show that this jet is well-described by the low Reynolds number limit of the classical Landau-Squire solution of the Navier-Stokes equations. The properties of this jet vary in a complex way with changing conditions: the jet reverses direction as a function of salt concentration, and exhibits asymmetry with respect to voltage reversal. Using a combination of simulations and analytic modelling, we are able to account for all of these effects. The result of this work is a more complete understanding of the fluidic properties of the nanopore. These effects govern the translocation process, and thus have consequences for better control of single molecule sensing. Additionally, the phenomena we have uncovered could potentially be harnessed in novel microfluidic applications, whose technological implications range from lab-on-a-chip devices to personalised medicine.
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Kilchherr, Rudolf. "Transport phenomena in porous media". Thesis, Kingston University, 2003. http://eprints.kingston.ac.uk/20729/.
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Non-Newtonian flow in heterogeneous media is of enormous theoretical and industrial importance. This phenomenon is studied to reveal macroscopic effects that arise due to the interaction between the non-linear flow behaviour and the spatial variation of the medium through which it is forced to move. The heterogeneity is achieved by using porous granular media, which is naturally non-homogeneous. The non-Newtonian properties of the fluid may have many causes and is an intrinsic property of the fluid that is used: One way of achieving it is by studying dense slurries of neutral particles or naturally occurring magmatic flows. Another way is to study the case where the flow is dominated by its ionic content and where the double layer thickness (the effective size of the ionic entities) is of the order of magnitude of the pore size. All cases studied in this thesis pertain to slow flow (low Reynolds number), though the fluid may be compressible. The variations in the flow are calculated in first order and these turn out to be coupled to the spatial variations in the porous medium. In this way structure formation is predicted. The structures may be either aligned with or may be perpendicular to the mean flow direction. 'Experiments to decide on which regime is relevant have been conducted. The genesis of structure formation is studied as a temporal development by considering a compressible flow. The constitutive equation that is required to couple the compressibility to the flow parameters is investigated. Two possible mechanisms have been identified: compressibility coupled to the pressure field and compressibility associated with the fluctuations in the flow. Using linear analysis the structure formation patterns associated with these two mechanisms are established for the steady state. Flow of ionically laden fluids has also been studied. Experiments done at Loughborough University (Department of Chemical Engineering) on electrowashing of filter cakes has been used to prove a major macroscopic effect. This effect takes place when the ionic diameter (which is approximately twice the double layer thickness) is of the order of magnitude of the pore size. A phenomenological set of transport equations has been set up. These contain coefficients, such as transition probabilities and mean ionic flow rates, that can be obtained from experiments by doing a first order solution of the equations for short times. A more involved numerical solution is also supplied and confirms the initial analytical estimates.
4
Varanakkottu, Subramanyan Namboodiri. "Light-Induced Microfluidic Transport Phenomena". Phd thesis, TU Darmstadt, 2013. https://tuprints.ulb.tu-darmstadt.de/3509/1/PhD%20thesis_SN.Varanakkottu.pdf.
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Abstract
Optofluidics is an emerging field which combines microfluidics and optics, having widespread applications in fundamental sciences as well as engineering. Among the research in the area of optofluidics, manipulation of small objects such as particles and droplets is of great interest. Precise control over the manipulation and confinement of such objects is a challenging task. Unification of microfluidics and optics opens a new way to achieve this goal with added advantages such as non-contact manipulation capability and tunability. This Ph.D. dissertation addresses optofluidic manipulation of particles and droplets based on some novel concepts.
The section on light-induced particle manipulation begins with optical trapping inside a microfluidic channel. Motivation of this study is to understand the influence of velocity profile on the trapped particle. An optical trapping experimental setup is constructed using a He-Cd laser (442 nm emission) as the trapping source. Optical trapping experiments are performed under two flow conditions. A particle trapped inside a microfluidic channel experiences a parabolic velocity profile. In the second method, particles are trapped inside a sample chamber where the trapped particle experiences a uniform velocity profile. Experiments are performed at different optical powers with particles having various diameters. Results showed that for particles having intermediate size the trapping force is higher in the case of particles trapped inside the microfluidic channel than that of a sample chamber. This is attributed to the contribution of Saffman lift force arising from the parabolic velocity gradient. Experimentally measured optical trapping stiffness is found to be in good agreement with the theoretical model.
Following that, a novel particle manipulation technique is presented. Here, microparticle adsorbed at the air-water interface is trapped and manipulated along the interface. The method relies on photoresponsive surfactants adsorbed to a gas-liquid interface that can be reversibly switched between two isomeric states (a trans state and a cis state) using light beams. The principle is based on local changes of the surface tension, giving rise to Marangoni stresses. Depending on the type of surfactant isomer in the region around the laser spot, a flow either radially inward or outward is created. For the trapping of microparticles, a 325 nm beam from a He-Cd laser is focused at the interface, which results in an inward flow directing towards the focal spot. This inward flow is utilized for trapping and manipulation of particles. Interfacial flow velocity is characterized using particle streak velocimetry. It is experimentally demonstrated that this trapping mechanism is capable of manipulating the trapped particle at lower intensity than conventional optical tweezers.
Finally, studies on light-induced droplet manipulation were conducted, utilizing the phase transition of temperature sensitive PNIPAM (Poly(N-isopropylacrylamide)) polymer films. PNIPAM films are prepared on UV absorbing glass plates. Absorption of the UV light by the glass raises its temperature resulting in the phase transition of PNIPAM film from a swollen (hydrophilic) to a deswollen (hydrophobic) phase. Experiments show that PNIPAM films undergo a phase transition from a hydrophilic to a hydrophobic state at around 26oC. At the hydrophobic state, water drop placed on the substrate exhibits a contact angle of about 78o while it reduces to 53o at the hydrophilic state. Experiments are performed to drive the water drop by creating a wettability gradient over the surface by locally cooling one side of the drop. Though the drop spreads towards the colder region, due to the large hysteresis in contact angle, the receding edge of the drop is pinned at the surface.
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Hamilton, C. J. "Transport phenomena in hydrogel membranes". Thesis, Aston University, 1988. http://publications.aston.ac.uk/9719/.
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In this thesis the factors surrounding the permeation of alkali and alkaline earth metal salts through hydrogel membranes are investigated. Although of relevance to aqueous separations in general, it was with their potential application in sensors that this work was particularly concerned. In order to study the effect that the nature of the solute has on the transport process, a single polymer matrix, poly (2-hydroxyethyl methacrylate), was initially studied. The influence of cation variation in the presence of a fixed anion was looked at, followed by the effect of the anion in the presence of a fixed cation. The anion was found to possess the dominant influence and tended to subsume any influence by the cation. This is explained in terms of the structure-making and structure-breaking characteristics of the ions in their solute-water interactions. Analogies in the transport behaviour of the salts are made with the Hofmeister series. The effect of the chemical composition of the polymer backbone on the water structuring in the hydrogel and, consequently, transport through the membrane, was investigated by preparing a series of poly (2-hydroxyethyl methacrylate) copolymer membranes and determining the permeability coefficient of salts with a fixed anion. The results were discussed in terms of the `free-volume' model of permeation and the water structuring of the polymer backbone. The ability of ionophores to selectively modulate the permeation of salts through hydrogel membranes was also examined. The results indicated that a dualsorption model was in operation. Finally, hydrogels were used as membrane overlays on coated wire ion-selective electrodes that employed conventional plasticised-PVC-valinomycin based sensing membranes. The hydrogel overlays were found to affect the access of the analyte but not the underlying electrochemistry.
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Badiger, M. V. "Transport phenomena in polymeric media". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 1988. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/6166.
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Sood, R. "Transport phenomena in polymeric systems". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 1985. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/3259.
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Naumov, Sergej, Rustem Valiullin y Jörg Kärger. "Adsorption hysteresis phenomena in mesopores". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194077.
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Tánczos, Ilka Christine. "Selective transport phenomena in coastal sands". [S.l. : [Groningen] : s.n.] ; [University Library Groningen] [Host], 1996. http://irs.ub.rug.nl/ppn/152328920.
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Kyriakou, Ioanna. "Coherent transport phenomena in semiconductor nanostructures". Thesis, Lancaster University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428887.
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Moore, Christopher Paul. "Tunneling Transport Phenomena in Topological Systems". Thesis, Clemson University, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=13420479.
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Originally proposed in high energy physics as particles, which are their own anti-particles, Majorana fermions have never been observed in experiments. However, possible signatures of their condensed matter analog, zero energy, charge neutral, quasiparticle excitations, known as Majorana zero modes (MZMs), are beginning to emerge in experimental data. The primary method of engineering topological superconductors capable of supporting MZMs is through proximity-coupled semiconductor nanowires with strong Rashba spin-orbit coupling and an applied magnetic field. Recent tunneling transport experiments involving these materials, known as semiconductor-superconductor heterostructures, were capable for the first time of measuring quantized zero bias conductance plateaus, which are robust over a range of control parameters, long believed to be the smoking gun signature of the existence of MZMs. The possibility of observing Majorana zero modes has garnered great excitement within the field due to the fact that MZMs are predicted to obey non-Abelian quantum statistics and therefore are the leading candidates for the creation of qubits, the building blocks of a topological quantum computer. In this work, we first give a brief introduction to Majorana zero modes and topological quantum computing (TQC). We emphasize the importance that having a true topologically protected state, which is not dependent on local degrees of freedom, has with regard to non-Abelian braiding calculations. We then introduce the concept of partially separated Andreev bound states (ps-ABSs) as zero energy states whose constituent Majorana bound states (MBSs) are spatially separated on the order of the Majorana decay length. Next, through numerical calculation, we show that the robust 2 e2/h zero bias conductance plateaus recently measured and claimed by many in the community to be evidence of having observed MZMs for the first time, can be identically created due to the existence of ps-ABSs. We use these results to claim that all localized tunneling experiments, which have been until now the main way researchers have tried to measure MZMs, have ceased to be useful. Finally, we outline a two-terminal tunneling experiment, which we believe to be relatively straight forward to implement and fully capable of distinguishing between ps-ABSs and true topologically protected MZMs.
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Kurs, André B. "Novel resonance-assisted electromagnetic-transport phenomena". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68981.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 99-105).
We first demonstrate theoretically and experimentally that electromagnetic resonators with high quality factors (Q) can be used to transfer power efficiently over distances substantially larger than the characteristic dimensions of the resonators by operating in a so-called "strongly coupled" regime. We next generalize the notion of strongly coupled resonances to a system comprising one power source and multiple receivers in a regime of broad practical applicability and show that, by appropriately tuning the parameters of the system, it is possible to significantly improve the overall efficiency of the wireless power transfer relative to the single-source and single-receiver configuration. We experimentally verify the predicted improvement in efficiency for a system consisting of one large source (area ~ 1 m2 ) coupling to two much smaller receivers of dimensions comparable to those of many portable electronic devices (area ~ 0.07 m2 ). Next, we present a novel design for an electrical conductor whose structure is optimized to have the lowest achievable resistance in the 2-20 MHz frequency range, where it can offer performance an order of magnitude better than the best currently available conductors. The two following chapters deal with energy transport in photonic crystals. We first investigate numerically how a square lattice of dielectric rods may be used to collimate a laser beam and the feasibility of using this system as a chemical sensor. Finally, we present and demonstrate through specific examples a systematic and general procedure, which is both computationally inexpensive and straightforward to implement, for coupling strongly dissimilar waveguides with 100% transmission.
by André B. Kurs.
Ph.D.
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da, Silva Santos Constantino Adriano. "Transport phenomena in random gradient flows". Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624990.
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Murphy, Benedict Andrew. "Microscopic and macroscopic spin transport phenomena". Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/15520/.
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Spintronics is the field concerned with the control of electron spin. In logic devices electron charge is manipulated, in computer data storage the magnetisation of a domain is altered; spintronics offers a hybrid between the two. This could be exploited in non-volatile random access memory cells for low power data storage. All-metal Lateral spin-valve devices were fabricated by electron beam lithography to investigate spin transport phenomena. The fabrication and measurement processes were optimised and lateral spin-valve devices were successfully fabricated with spin diffusion lengths of (200±25) nm and (310±30) nm in 100 nm and 200 nm wide Copper wires respectively. Spin filtering was previously observed by patterning nano-scale wires to be laterally asymmetric. Here, nano-scale wires were patterned to have a laterally symmetric spin diffusion path. No increase in signal due to the filtering effect was observed, thus confirming the phenomenological model put forward. Also, the spin diffusion path in a lateral spin valve was split into a ring geometry. By applying a field gradient across the ring, the operational efficiency was improved by 30%. The observation of a mechanically induced spin current has been achieved for the first time. The design of an optical measurement system that rotates a sample at up to 200~Hz is presented here. Deviation in the moment on the surface of a paramagnetic Tungsten foil from the moment induced by the Barnett effect confirms that a spin current may be induced by mechanical rotation. In summary, design and development of magneto-electrical and mechano-optical measurement systems has been achieved. The improvement in the operational efficiency in lateral spin-valves could be used alongside materials such as Heusler alloys to provide cheaper efficient logic devices. The observation of a mechanically induced spin current in Tungsten precedes the future study of the effect in other paramagnetic materials, such as Platinum or Palladium.
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Banerjee, Soumik. "Molecular Simulation Of Nanoscale Transport Phenomena". Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28252.
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Interest in nanoscale heat and mass transport has been augmented through current trends in nanotechnology research. The theme of this dissertation is to characterize electric charge, mass and thermal transport at the nanoscale using a fundamental molecular simulation method, namely molecular dynamics. This dissertation reports simulations of (1) ion intake by carbon nanotubes, (2) hydrogen storage in carbon nanotubes, (3) carbon nanotube growth and (4) nanoscale heat transfer. Ion transport is investigated in the context of desalination of a polar solution using charged carbon nanotubes. Simulations demonstrate that when either a spatially or temporally alternating charge distribution is applied, ion intake into the nanotubes is minimal. Thus, the charge distribution can either be maintained constant (for ion encapsulation) or varied (for water intake) in order to achieve different effects. Next, as an application of mass transport, the hydrogen storage characteristics of carbon nanotubes under modified conditions is reported. The findings presented in this dissertation suggest a significant increment in storage in the presence of alkali metals. The dependence of storage on the external thermodynamic conditions is analyzed and the optimal range of operating conditions is identified. Another application of mass transport is the growth mode of carbon nanostructures (viz. tip growth and base growth). A correct prediction of the dominant growth mode depends on the energy gain due to the addition of C-atoms from the carbon-metal catalyst solution to the graphene sheets forming the carbon nanostructures. This energy gain is evaluated through molecular dynamics simulations. The results suggest tip growth for Ni and base growth for Fe catalysts. Finally, unsteady nanoscale thermal transport at solid-fluid interfaces is simulated using non-equilibrium molecular dynamics simulations. It is found that the simulated temperature evolution deviates from an analytical continuum solution due to the overall system heterogeneity. Temperature discontinuities are observed between the solid-like interfaces and their neighboring fluid molecules. With an increase in the temperature of the solid wall the interfacial thermal resistance decreases.Ph. D.
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Romero, Gomez Pedro. "Transport Phenomena in Drinking Water Systems". Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/194495.
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The current computer models used for simulating water quality in potable water distribution systems assume perfect mixing at pipe junctions and non-dispersive solute transport in pipe flows. To improve the prediction accuracy, the present study examines and expands these modeling assumptions using transport phenomena analyses. Whereas the level of solute mixing at a cross-type junction is evaluated numerically via Computational Fluid Dynamics (CFD), the axial transport in laminar flows is investigated with both CFD simulations and corresponding experimental runs in a single pipe. The findings show that solute mixing at junctions is rather incomplete owing to the limited spatio-temporal interaction that occurs between incoming flows with different qualities. Incomplete mixing shifts the expected propagation patterns of a chemical or microbial constituent from widely-spread to narrowly-concentrated over the service area. On the other hand, solute dispersion is found to prevail over advective transport in laminar pipe flows. Thus, this work develops axial dispersion rates through parameter optimization techniques. By accounting for axial dispersive effects, the patterns of solute delivery shifted from high concentrations over short time periods to lower doses at prolonged exposure times. In addition, the present study integrates the incomplete mixing model into the optimal placement of water quality monitoring stations aimed at detecting contaminant intrusions.
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Wilkinson, Aidan. "Transport phenomena in two-phase systems". Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/25574.
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The physics of two-phase systems is explored here, particularly magneto-transport and low temperature d.c. conductivity in thin films. The extraordinary magnetoresistance (EMR) effect was analysed in the context of previous experimental and theoretical considerations. The magnetoresistance (MR) may be enhanced by up to two orders of magnitude by changing the geometry. This was investigated using finite element analysis. Thin film samples consisting of a layered structure of Germanium-Tin-Germanium (Ge-Sn-Ge) were created in collaboration with Shandong University in China. Ge layers were kept at a constant thickness across all samples, with variable Sn thickness. Regions of Sn form island-like shapes ten times larger than the average film thickness, as is seen in scanning electron microscope (SEM) images. Raman spectroscopy was conducted on these samples, from which it is concluded that the Ge layers are amorphous in nature. It was seen that there is a relationship between the electrical resistance and the film thickness which is indicative of a metal-insulator transition (MIT). The temperature dependence of resistivity was subsequently investigated. The temperature coefficient of resistivity (TCR) of the samples is seen to become negative as the thickness of the Sn layer is reduced below a certain critical thickness. Depending on their thickness, samples were designated as metallic or insulator, and various models associated with metals and insulators fitted to the data. While it is impossible to be absolutely certain of the validity of each of the models, some are a better fit than others. The same temperature dependence of resistivity was measured with an applied magnetic field. This is compared with the previous EMR investigation, however the MR of the samples is only of the order of a few percent which corresponds to ordinary MR, seen in most metals. The magnetic field measurements suppress a resistivity down-turn at very low temperatures (T < 10K) which suggests the presence of superconductivity. Analysis of dr=dT shows that the onset of superconductivity is lower for samples with a lower Sn thickness. Additionally, the deposition rate of the Sn layer affects the resistivity significantly; a higher deposition rate causes a decrease in resistivity. It is supposed that this is due to a change in the microstructure of the film. Finally, piezo-resistivity was considered by applying mechanical compression to the samples. The added pressure causes a drop in resistivity.
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Dias, Mariama Rebello de Sousa. "Transport phenomena in quasi-one-dimensional heterostructures". Universidade Federal de São Carlos, 2014. https://repositorio.ufscar.br/handle/ufscar/4973.
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O crescimento e caracterização de sistemas de heteroestruturas semicondutoras quasi-unidimensionais têm atraído grande interesse devido à sua potencial de aplicação tecnológica, como foto-detectores, dispositivos opto-eletrônicos assim como seu para o processamento de informação quântica e aplicações em fotônica. O objetivo desta tese é o estudo das propriedades de transporte eletrônico e de spin em sistemas semicondutores quasi-unidimensionais, especificamente trataremos de nanofios (NWs) homogêneos, NWs acoplados, NWs do tipo plano-geminado (TP), diodos de tunelamento ressonante (ETD) e cadeias de pontos quânticos (QDCS). Escolhemos o método k-p, particularmente o Hamiltoniano de Luttinger, para descrever os efeitos de confinamento e tensão biaxial. Este sugeriu uma modulação do caráter do estado fundamental que, complementada com a dinâmica fônons fornecidas pelas simulações da Dinâmica Molecular (MD), permitiu a descrição da modulação da mobilidade de buracos por emissão ou absorção de fônons. Em relação ao sistema de NWs acoplado,estudamos, através do método da matriz de transferência (TMM), as propriedades de transporte de elétrons e spin sob a interação de spin-órbita (SOI) de Eashba, localizada na região de acoplamento entre fios. Foram consideradas várias configurações de tensões de gate (Vg) aplicadas nos fios. Desse modo, compreendemos a modulação do transporte de spin quando esse é projetado no direção-z através da combinação do SOI e das dimensionalidades do sistema. Da mesma forma, a combinação de SOI e da Vg aplicada deu origem a modulação da polarização, quando o spin medido é projetado na mesma direção em que o SOI de Eashba atua, a direção y. Usando o TMM, exploramos as propriedades de transporte de um DBS e o efeito de uma resistência em série com o intuito de provar a natureza da biestabilidade das curvas características I V bem como o aumento de sua área com temperatura, resultados fornecidos por experimentos. O modelo indicou que aumentando da resistência pela diminuição sa temperatura aumenta a área biestável. A presença de uma hetero-junção adicional ao sistema induz uma densidade de carga nas suas interfaces. De acordo com esta configuração, a queda de tensão total do ETDS muda, podendo ser confirmada experimentalmente. A formação dos peculiares campos de deformação e sua influência sobre a estrutura eletrônicas e propriedades de transporte em superredes de TP foi estudada sistematicamente. Assim, as propriedades de transporte, de ambos os elétrons e buracos, pode ser sintonizada eficientemente, mesmo no caso de elétrons r em sistemas de blenda de zinco, contrastando com a prevista transparência de elétrons r em superredes de semicondutores III-V heteroestruturados. Além disso, constatamos que a probabilidade de transmissão para buracos da banda de valência também poderia ser efetivamente modificada através de uma tensão externa.Por fim, colaboradores sintetizaram com sucesso sistemas de QDCs de InGaAs através da epitaxia de feixe molecular e engenharia de tensão. Um comportamento anisotrópico da condutância com a temperatura foi observado em QDCs com diferentes concentrações de dopagem, medida realizada ao longo e entre os QDCs. O modelo teórico 1D de hoppíng desenvolvido mostrou que a presença de estados OD modela a resposta anisotrópica da condutância neste sistemas.
The growth and characterization of semiconductor quasi-one-dimensional heterostructure systems have attracted increasing interest due to their potential technological application, like photo-detectors, optoelectronic devices and their promising features for quantum information processing and photonic applications. The goal of this thesis is the study of electronic and spin transport properties on quasi-one-dimensional semiconductor systems; specifically, homogenous nanowires (NWs), coupled NW s, twin-plane (TP) NWs, resonant tunneling diodes (RTDs), and quantum dot chains (QDCs). The k-p method, in particular the Luttinger Hamiltonian, was chosen to describe the effects of biaxial confinement and strain. This suggested a modulation of the ground state character that, complemented with the phonon dynamics provided by Molecular Dynamics (MD) simulations, allowed the description of the hole mobility modulation by either phonon emission or absorption. Regarding the coupled NW s system, the electron and spin transport properties affected by a Rashba spin-orbit interaction (SOI) at the joined region were unveiled through the Transfer Matrix Method (TMM). Various configurations of gate voltages (Vg), applied on the wire structure, were considered. We were able to understand the modulation of the spin transport projected in the z-direction trough the combination of the SOI and the system dimensionalities. Likewise, the combination of SOI and applied Vg gave rise to a modulation of the polarization, when the measured spin is projected in the same direction where the Rashba SOI acts, the y-direction. The transport properties of a DBS and the effect of a resistance in series was explored within the TMM to prove the nature of a bistability of the I V characteristics and its enhanced area with temperature provided by the experiment. The model indicates that increasing the resistente by decreasing the temperature, the bistable area enhances. The presence of an additional heterojunction induces a sheet charge at its interfaces. Under this configuration, the total voltage drop of the RTD changes and can be confirmed experimentally.The formation of the peculiar strain fields and their influence on the electronic structure and transport properties of a TP superlattice was systematically studied. Hence, the transport properties of both electrons and holes could be effectively tuned even in the case of T-electrons of zincblende systems, contrasting to the predicted transparency of T-electrons in heterolayered III-V semiconductor superlattices. Also, the transmission probability for holes at valence band could also be effectively modified by applying an external stress. Finally, using molecular-beam-epitaxy and skillful strain engineering, systems of In-GaAs QDCs were successfully synthesized by collaborators. The QDCs with different doping concentrations showed an anisotropic behavior of the conductance, measured along and across the QDCs, with temperature. The theoretical ID hopping model developed found that the presence of OD states shapes the anisotropic response of the conductance in this system.
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Bergeson, Jeremy D. "Spin-dependent transport phenomena in organic semiconductors". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1167674229.
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Greenfield, Claire. "Numerical modelling of transport phenomena in reactors". Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263981.
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Spiechowicz, Jakub. "Anomalous transport phenomena in driven periodic systems". Doctoral thesis, Katowice : Uniwersytet Śląski, 2015. http://hdl.handle.net/20.500.12128/5723.
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Praca zawiera przegląd procesów anomalnego transportu zachodzących w czasowo i przestrzennie periodycznych układach fizycznych. Złącza Josephsona są używane jako wygodna motywacja fizyczna ruchu Browna w periodycznym potencjale, która może zostać wykorzystana w celu doświadczalnej weryfi kacji otrzymanych rezultatów. Zidentyfi kowano wiele intrygujących zjawisk, wśród nich efekt zębatkowy, ujemną mobilność czy anomalną dyfuzję. W pracy zaprezentowano konstruktywny wpływ ruchu Browna ilustrując w jaki sposób fluktuacje pochodzenia termicznego lub nierównowagowego mogą zostać wykorzystane w celu kontroli stopni swobody rozmaitej natury. Nacisk położono na wkład własny autora w ten obszar badawczy, niemniej jednak, użyta metodyka jest uniwersalna i ma wiele zastosować w różnorodnych układach fizycznych.
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Mostaghimi, Peyman. "Transport phenomena modelled on pore-space images". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9180.
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Fluid flow and dispersion of solute particles are modelled directly on three-dimensional pore-space images of rock samples. To simulate flow, the finite-difference method combined with a standard predictor-corrector procedure to decouple pressure and velocity is applied. We study the permeability and the size of representative elementary volume (REV) of a range of consolidated and unconsolidated porous media. We demonstrate that the flow-based REV is larger than for geometry-based properties such as porosity and specific surface area, since it needs to account for the tortuosity and connectedness of the flow paths. For solute transport we apply a novel streamline-based algorithm that is similar to the Pollock algorithm common in field-scale reservoir simulation, but which employs a semi-analytic formulation near solid boundaries to capture, with sub-grid resolution, the variation in velocity near the grains. A random walk method is used to account for mixing by molecular diffusion. The algorithm is validated by comparison with published results for Taylor-Aris dispersion in a single capillary with a square cross-section. We then accurately predict experimental data available in the literature for longitudinal dispersion coefficient as a function of Peclet number. We study a number of sandpack, sandstone and carbonate samples for which we have good quality three-dimensional images. There is a power-law dependence of dispersion coefficient as a function of Peclet number, with an exponent that is a function of pore-space heterogeneity: the carbonates we study have a distinctly different behaviour than sandstones and sandpacks. This is related to the differences in transit time probabilities of solute particles travelling between two neighbouring voxels. We then study the non-Fickian behaviour of solute transport in porous media by modelling the NMR propagators and the time-dependent dispersion coefficients of different rock types. The behaviour is explained using Continuous Time Random Walk (CTRW) theory: transport is qualitatively different for the complex porous media such as carbonates compared to the sandstone or sandpack, with long tailing and an almost immobile peak concentration. We discuss extensions of the work to reactive transport and the simulation of transport in finely-resolved images with billions of voxels.
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Naumov, Sergej, Rustem Valiullin y Jörg Kärger. "Adsorption hysteresis phenomena in mesopores". Diffusion fundamentals 6 (2007) 67, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14247.
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Takada, Satoshi. "Studies on transport phenomena of cohesive granular particles". 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215293.
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Khosravi, Elham [Verfasser]. "Time-dependent phenomena in quantum transport / Elham Khosravi". Berlin : Freie Universität Berlin, 2013. http://d-nb.info/1034300261/34.
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Sirisathitkul, C. "Studies of transport phenomena at ferromagnet/semiconductor interfaces". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325445.
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Aboelsoud, Walid. "Study of Transport Phenomena in Carbon-Based Materials". Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5593.
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In air-cooled heat exchangers, air-side thermal resistance is usually the largest compared to conduction and liquid-side thermal resistances. Thus, reducing the air-side thermal resistance with fin-like structures can greatly improve overall cooling performance. The performance of these structures is usually characterized by the rate of heat which can be transferred and the pumping power required. One promising solution is to use a high-thermal-conductivity material with a large surface per unit volume such as carbon foam. This study presents a method of utilizing V-shape corrugated carbon foam. The air-side heat transfer coefficient and the pressure drop across the foam have been investigated using different V-shape foam geometrical configurations obtained by varying its length and height. Based on design considerations and availability, the foam length has been chosen to be 25.4, 38.1 and 52.1 mm while its height is 4.4, 6.8 and 11.7 mm, resulting in nine different test pieces of foam with different heights and lengths.
A total number of 81 experiments were carried out and results show that of the nine V-shape configurations, the foam with the shortest length and tallest height gives the best performance. Experimental results are also compared with the results of prior work using different carbon foam geometries. It is shown that V-shape corrugated carbon foam provides higher heat transfer coefficient and better overall performance.
Numerical method is performed next. The effect of the foam length and height on thermal and hydraulic performance is demonstrated and discussed. There is excellent agreement between numerical and experimental results. An analysis is also made to better understand the transport phenomena that occur within the porous matrix. For laminar flow of air, one of the findings is the high heat transfer effectiveness of the foam which means a foam thickness of 1 mm or less is sufficient for heat transfer enhancement for air speed of up to 4 m/s.
To demonstrate the feasibility of using carbon foam, an analytical case study of carbon foam heat exchanger was performed and compared to traditional heat exchanger with the same heat load. Results show that a volume saving of up to 55% can be obtained by using carbon foam instead of traditional aluminum fins.
Another attractive carbon-based material is the highly oriented pyrolytic graphite (HOPG) which has an in-plane thermal conductivity of about 1700 W/m.K and an out-of-plane k of about 8 W/m.K at room temperature. HOPG is a graphite material with a high degree of preferred crystallographic orientation. HOPG can be very useful in thermal applications when axial conduction is critical and needed to be minimized as in recuperators used in cryocoolers and compact power generation. Also, an analysis of HOPG for micro-channel applications shows that the high in-plane thermal conductivity of HOPG, which is far greater than that of copper and aluminum, allows a taller height for the micro-channel. This translates to an increase in the heat flux removal rate by two to three times.Ph.D.
Doctorate
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering
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Powell, Adam Clayton IV. "Transport phenomena in electron beam melting and evaporation". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/39623.
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Holland, Emilie Charlotte. "Computational modelling of transport phenomena in cerebral aneurysms". Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:72471f90-9d97-4fbe-b2c3-499430678277.
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An estimated 85% of haemorrhagic strokes are secondary to the rupture of an intracranial aneurysm (IA), a localised, blood-filled dilation of the artery wall. The clinically observed rupture of occluded IAs has led to hypothesise that the presence of thrombus may restrict the transport of nutrients, most notably oxygen, to the aneurysmal wall, thus heightening the risk of rupture through the deleterious effects of hypoxia on cellular functionality. The limited research into O2 transport within IAs demonstrate the need for further exploration into the possible detrimental hypoxic conditions as a result of intrasaccular haemodynamics and thrombusformation in untreated, treated and evolving IAs, with the ultimate goal of further understanding disease evolution and developing prognostic decision support models for clinical intervention. Preliminary computational fluid dynamic simulations conducted on a 2Daxisymmetric model of a thrombosed artery highlighted the relative importance of wall-side versus the fluid-side mass transport of oxygen. A sensitivity analysis demonstrated that variations in thrombus thickness, and arterial wall cellular respiration rates have the greatest influence on the oxygen distribution to the portion of wall in direct contact with the thrombus. The results of the coupled flow-mass transport computational fluid dynamic simulations within patient-specific IA show that a reduction in intrasaccular flow as a consequence of stent deployment affects the rate at which oxygenated blood reaches the entirety of the dome. Nonetheless, the distribution ofO2 to the aneurysmal wall itself does not differ from the observed oxygen distribution across the wall when the same IA is left untreated. Conversely, the low velocity recirculations observed in an IA presenting with a very high aspect ratio (i.e a narrow neck and high sack height) limited the transport of oxygen to such an extent as to completely deprive the delivery of oxygen to the fundus. The presence of thrombus within the IA dome results in a dramatic reduction in oxygen delivery to the wall, the extent of which is dependent on the local thrombus thickness. Finally, a novel fluid-solid-growth-mass transport (FSGT) mathematical model is conceived to explore the biochemical role of thrombus on the evolution of an IA. The shear-regulate propagation of a thrombus layer during membrane expansion leads to the gradual decrease in oxygen tension within the wall. Moreover, as a consequence of coupling this oxygen deficiency to fibroblast functionality, the collagen fibre mass density was shown to increase at an insufficient rate to compensate for the transfer in load from the degrading elastinous consitituents to the collagenous constituents, thus resulting in the increased stretch of collagen fibres in order to maintain mechanical equilibrium. Moreover this over-expansion results in the gradual unstable evolution of the IA. The observed obstruction to oxygen delivery as a result of intrasaccular haemodynamics and thrombosis compounds the need for further development of more comprehensive chemo-mechano-biological models of IAs so as to better ascertain the level of rupture risk posed by a hypoxic environment. Refinement to the models proposed within this work would prove invaluable to creating a fully integrated multi-physics, multi-scale in silico framework in aid to patient diagnostics and individual treatment planning of IAs.
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Balasubramanian, Ganesh. "Modeling nanoscale transport phenomena: Implications for the continuum". Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/27288.
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Transport phenomena at the nanoscale can differ from that at the continuum because the large surface area to volume ratio significantly influences material properties. While the modeling of many such transport processes have been reported in the literature, a few examples exist that integrate molecular approaches into the more typical macroscale perspective. This thesis extends the understanding of nanoscale transport governed by charge, mass and energy transfer, comparing these phenomena with the corresponding continuum behavior where applicable. For instance, molecular simulations enable us to predict the solvation structure around ions and describe the diffusion of water in salt solutions. In another case, we find that in the absence of interfacial effects, the stagnation flow produced by two opposing nanojets can be suitably described using continuum relations. We also examine heat conduction within solids of nanometer dimensions due to both the ballistic propagation of lattice vibrations in small confined dimensions and a diffusive behavior that is observed at larger length scales. Our simulations determine the length dependence of thermal conductivity for these cases as well as effects of isotope substitution in a material. We find that a temperature discontinuity at interfaces between dissimilar materials arises due to interfacial thermal resistance. We successfully incorporate these interfacial nanoscale effects into a continuum model through a modified heat conduction approach and also by a multiscale computational scheme. Finally, our efforts at integrating research with education are described through our initiative for developing and implementing a nanotechnology module for freshmen, which forms the first step of a spiral curriculum.Ph. D.
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Zhang, Hao. "Gravity-dependent transport phenomena in zeolite crystal growth". Case Western Reserve University School of Graduate Studies / OhioLINK, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1060021149.
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Feng, Jingxing. "Transport Phenomena in Polymeric Blends and Multilayer Films". Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1548202751756984.
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Grau, Ribes Alexis. "Mathematical models of transport phenomena in biological tissues". Doctoral thesis, Universite Libre de Bruxelles, 2020. https://dipot.ulb.ac.be/dspace/bitstream/2013/303032/4/contents.pdf.
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Cette thèse est consacrée à l’élaboration et l’étude théorique de modèles de transport décrivant les dynamiques cellulaires et la communication intercellulaire dans les tissus épithéliaux. Nous nous intéressons d’abord à l’influence du transport de microARNs (miRNAs) sur la dynamique spatiotemporelle de réseaux de régulation génétique. Ces courtes séquences d’ARN régulent la synthèse des protéines en bloquant l’activité des ARN messagers et leur sécrétion via des vesicules extracellulaires en font des agents de communication intercellulaire. Différents modèles faisant intervenir des miRNAs extracellulaires ont été construits et étudiés numériquement. Les premiers sont des modèles génériques destinés à mettre en évidence l'effet d'une cellule ayant une production de miRNAs anormale sur l'expression génétique dans les cellules voisines. Nous abordons ensuite des modèles plus complexes et réalistes dans lesquels des oscillations (liées à des rythmes biologiques) et de la bistabilité (liée à une différenciation cellulaire) sont observées. Ces modèles permettent d’étudier des dynamiques de communication complexes observées en biologie, comme la synchronisation de cellules couplées ou la propagation d'un changement de phénotype. Nous mettons également en évidence le rôle de défauts, tels que des mutations génétiques ou encore des variations de densité cellulaire dans les tissus, sur ces phénomènes de propagation. La deuxième partie de la thèse est dédiée à la construction de modèles de réaction-diffusion dans lesquels la dynamique des cellules dépend de leur état interne. Sur base d’études expérimentales montrant l’influence de protéines et de miRNAs sur la mobilité et la prolifération des cellules, nous établissons un modèle multi-échelle dans lequel la dynamique intracellulaire et le mouvement des cellules interagissent. En effet, certaines protéines sont responsables de l’adhésion cellulaire ou régulent la vitesse de prolifération. Dans notre modèle, chaque cellule synthétise ces espèces d’intérêt et les processus cellulaires (migration, prolifération) dépendent de la concentration de ces espèces biochimiques. Ce modèle permet de reproduire des expériences de migration cellulaire et de prédire, notamment, l'influence d'E-cadherin, une protéine clé dans l'adhesion cellulaire, sur la dynamique de régénération d'un tissu.Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Nagata, Koji. "TURBULENCE STRUCTURE AND TRANSPORT PHENOMENA IN DENSITY STRATIFICATION". Kyoto University, 2000. http://hdl.handle.net/2433/151546.
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Lloyd, Kenneth P. "Understanding Human Erythrocyte Glucose Transporter (GLUT1) Mediated Glucose Transport Phenomena Through Structural Analysis". eScholarship@UMMS, 2018. https://escholarship.umassmed.edu/gsbs_diss/962.
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GLUT1-mediated, facilitated sugar transport is proposed to be an example of transport by a carrier that alternately presents exofacial (e2) and endofacial (e1) substrate binding sites, commonly referred to as the alternating access carrier model. This hypothesis is incompatible with observations of co-existent exo- and endofacial ligand binding sites, transport allostery, and e1 ligand (e.g. cytochalasin B) induced GLUT1 sugar occlusion. The fixed-site carrier model proposes co-existent, interacting e2 and e1 ligand binding sites but involves sugar translocation by geminate exchange through internal cavities. Demonstrations of membrane-resident dimeric and tetrameric GLUT1 and of e2, e1 and occluded GLUT conformations in GLUT crystals of monodisperse, detergent-solubilized proteins suggest a third model. Here, GLUT1 is an alternating access carrier but the transporter complex is a dimer of GLUT1 dimers, in which subunit interactions produce two e2 and two e1 conformers at any instant. The crystallographic structures in different conformations can be utilized to further understand the transport cycle, ligand binding behavior and complex kinetics observed in GLUT1. Specifically, the GLUT1 crystal structure and homology models based upon related major facilitator superfamily proteins were used in this study, to understand inhibitor binding, ligand binding induced GLUT1 transport allostery and the existence of helix packing/oligomerization motifs and glycine induced flexibility. These studies suggest that GLUT1 functions as an oligomeric allosteric carrier where cis-allostery is an intramolecular behavior and trans-allostery is an intermolecular behavior. Additionally, mutations of a dynamic glycine affect the turnover of the transporter while mutations to helix packing motifs affect affinity.
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Pongsaksawad, Wanida. "Numerical modeling of interface dynamics and transport phenomena in transport-limited electrolysis processes". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36209.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 111-117).
Electrochemical reactions in materials and processes induce morphological instability on the cathode, which can lead to porous deposits or system failure. The growth of the protrusion is a complex phenomenon which involves chemical, electrical, and momentum driving forces in the system. Thus, it is important to understand the effect of electrochemistry in phase boundary evolution in order to optimize the performance of such processes. This thesis contributes to predicting and controlling such interface instability phenomena by developing a computational model that captures them. Successful application of the model to emerging metal extraction processes demonstrates its usefulness. A phase field model of electrochemical interface is developed for transport-limited electrolysis with rapid charge redistribution. This new Cahn-Hillard phase field formulation includes a model electrostatic free energy term, which captures the behavior of the diffuse interface under the applied electric field, in addition to transport by free energy gradient and convection. The model agrees with published stability criterion for a solid cathode. When the electrodes and electrolyte are low-viscosity fluids, flow stabilizes the interface.
(cont.) A new stability criterion for metal reduction in a liquid-liquid system is derived and agrees well with the model results. Next, the phase field model is extended for a ternary system to model titanium reduction in a supported electrolyte system. The model can simulate phase boundaries migration depending on the composition of the electrolyte and also electronically mediated reactions. Finally, Solid Oxide Membrane Electrolytic Smelting with Rotating Cathode (SOMERC), an emerging technology to electrolytically reduce titanium oxide from molten salt, is investigated. In the SOMERC process, rotational flow is introduced to create shear force that is expected to stabilize the interface. Computational fluid dynamics models of rotational flow are carried out to estimate the relationship between cathode rotational speed, shear strain rate, and boundary layer thicknesses. The phase field model presented in this thesis can be applied to any electrochemical reduction processes that are in the mass-transport controlled regime. Stability criteria and detailed morphology in two and three dimensions can be explored.
by Wanida Pongsaksawad.
Ph.D.
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De, Virgiliis Andres y Kurt Binder. "Monte Carlo study of transport phenomena in surface binary alloys". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194655.
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Shangguan, Minhui. "Charge and spin transport in mesoscopic systems". Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39557583.
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Shangguan, Minhui y 上官敏慧. "Charge and spin transport in mesoscopic systems". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39557583.
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Daumer, Volker. "Phase coherent transport phenomena in HgTe quantum well structures". Doctoral thesis, [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=979460352.
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Racec, Paul Nicolae. "Transport phenomena and capacitance of open quantum semiconductor nanostructures". [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=965463613.
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Zahn, Peter. "Transport phenomena in metallic nanostructures: an ab initio approach". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2005. http://nbn-resolving.de/urn:nbn:de:swb:14-1117186073142-40775.
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Im Rahmen der vorliegenden Arbeit werden ab initio Berechnungen des Restwiderstandes von metallischen Nanostrukturen vorgestellt. Die elektronische Struktur der idealen Systeme wird mit Hilfe einer Screened KKR Greenschen Funktionsmethode im Rahmen der Vielfachstreutheorie auf der Grundlage der Dichtefunktionaltheorie berechnet. Die Potentiale von Punktdefekten werden selbstkonsistent mit Hilfe einer Dyson-Gleichung für die Greensche Funktion des gestörten Systems berechnet. Unter Nutzung der ab initio Ubergangswahrscheinlichkeiten wird der Restwiderstand durch Lösung der quasi-klassischen Boltzmann-Gleichung bestimmt. Ergebnisse für ultradünne Cu-Filme und die Leitfähigkeitsanomalie während des Wachstums von Co/Cu-Vielfachschichten werden vorgestellt. Der Einfluss von Oberflächen, geordneten und ungeordneten Grenzflächenlegierungen und von Defekten an verschiedenen Positionen in der Vielfachschicht auf den Effekt des Giant Magnetoresistance wird untersucht. Die selbstkonsistente Berechnung der Streueigenschaften und die verbesserte Lösung der Boltzmann-Transportgleichung unter Einbeziehung der Vertex-Korrekturen stellen ein leistungsfähiges Werkzeug zur umfassenden theoretischen Beschreibung dar. Sie verhelfen zu nützlichen Einsichten in die mikroskopischen Prozesse, die die Transporteigenschaften von nanostrukturierten Materialen bestimmenA powerful formalism for the calculation of the residual resistivity of metallic nanostructured materials without adjustable parameters is presented. The electronic structure of the unperturbed system is calculated using a screended KKR multiple scattering Green's function formalism in the framework of density functional theory. The scattering potential of point defects is calculated self-consistently by solving a Dyson equation for the Green's function of the perturbed system. Using the ab initio scattering probabilities the residual resistivity was calculated solving the quasiclassical Boltzmann equation. Examples are given for the resistivity of ultrathin Cu films and the conductance anomaly during the growth of a Co/Cu multilayer. Furthermore, the influence of surfaces, ordered and disordered interface alloys and defects at different positions in the multilayer on the effect of Giant Magnetoresistance is investigated. The self-consistent calculation of the scattering properties and the improved treatment of the Boltzmann transport equation including vertex corrections provide a powerful tool for a comprehensive theoretical description and a helpful insight into the microscopic processes determining the transport properties of magnetic nanostructured materials
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Schoofs, Frank. "Defect-induced magnetism and transport phenomena in epitaxial oxides". Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/243639.
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This work focuses on the impact of defects, intrinsic or artificially introduced, on the functional properties of thin, epitaxial oxide films. In the first part, the origin of the ferromagnetic properties of Mn-doped and undoped zinc oxide is studied. The deposition conditions are found to have a significant impact on the structural, transport and magnetic properties of the thin films. Combining x-ray magnetic circular dichroism and magnetometry experiments, it is established that the transition metal dopants (i.e. Mn) have no influence on the ferromagnetic nature of the zinc oxide, but that localised magnetic moments on intrinsic defects are in fact responsible for the ferromagnetic behaviour. A relation between strain (related to defect concentration) and magnetisation is established. In the second part of this dissertation, artificially introduced defects are employed in order to discover the fundamental conduction mechanism behind the two-dimensionally conductive LaAlO3/SrTiO3 interface. All experiments, from varying deposition temperature, to oxygen pressure, to laser fluence or to the insertion of (doped) perovskite layers, point towards a structurally governed conduction mechanism, although the exact details are still unclear. Distinct transitions in the resistance versus temperature curves are observed at different values than the bulk phase transformation temperature. These transitions form the boundaries of different conduction modes, with tendencies towards non-Fermi-liquid behaviour observed in certain two-dimensionally conducting samples in limited temperature regimes. By optimising the (defect) structure at the interface, i.e. by introducing a single unit cell of (La0.5,Sr0.5)TiO3 or SnTiO3, it is shown that the sheet carrier density can be dramatically enhanced, up to an order of magnitude higher than unmodified LaAlO3/SrTiO3 interfaces with a value of 1e14 cm−2 at 200 K. Finally, attempts at functionalising the conductive heterointerface by doping and inserting (anti)ferromagnetic layers are made.
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Mielke, Eric. "Study on the Transport Phenomena in Complex Micro-Reactors". Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36040.
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Continuous processing in the pharmaceutical and fine chemical industries, particularly in micro/milli-scale reactors, has been a topic of interest in literature in recent years due to the advantages offered over batch reactions. One such advantage is the enhanced transport properties of operating at smaller scales, although the quantification of the transport phenomena is not straightforward when wall and entrance effects cannot be neglected.
In the first study presented, various micro-mixer geometries and scales were considered to increase the mixing efficiency in liquid-liquid systems of diverse interfacial tensions for fast reactions. The conditions were varied over different flow regimes; including slug flow, parallel flow, and drop flow. A mass-transfer-limited test reaction was used to evaluate the overall volumetric mass transfer coefficients (Korga) as a function of the average rate of energy dissipation (ε) for each mixer design. The onset of drop flow occurred at a lower ε for the LL-Triangle mixer when compared with the Sickle or LL-Rhombus mixers for low interfacial-tension systems (i.e., n-butanol-water). In the drop flow regime for energy dissipation rates of around 20 to 500 W/kg, Korga values ranged from approximatively 0.14 to 0.35 s-1 and 0.004 to 0.015 s-1 for the relatively low and high interfacial-tension (i.e., toluene-water) systems, respectively.
The second investigation explored the heat transfer properties of a FlowPlate® system by Ehrfeld Mikrotechnik BTS. First, in a non-reactive system with rectangular serpentine channels (d_h<1mm, 400
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Sadomba, Clara P. (Clara Petronella). "A computational study of transport phenomena in RH-ladles". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23377.
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A numerical study was carried out to predict three dimensional turbulent flow heat and mass transfer in RH-ladles. To model the turbulence in the system, the popular Launder and Sharma (7) version of the low Reynolds number k-$ varepsilon$ model was employed. The governing equations for fluid flow and heat transfer were solved using a control volume-based finite difference method. The buoyancy effect in the axial momentum equation was incorporated through the Boussinesq approximation. From the fluid flow and turbulence characteristics predicted by the numerical model, the mass transfer occurring from the dissolution of steel rods immersed in the liquid steel was computed using the Sherwood number correlation recently proposed by Mazumdar et al. (25). The parameters studied include: the flow rate of steel, the heat flux from the solid walls and various radial positions of the vertically immersed steel rod. The fluid flow results are presented as vector plots. The heat transfer aspects are shown through temperature contours at various vertical planes and the mass transfer results are graphically presented in plots showing variance of mass transfer coefficients with key parameters.The flow field results were found to be in qualitative agreement with previously reported 3D numerical studies for similar systems. Due to the lack of any experimental or numerical results related to heat and/or mass transfer in RH-ladles, the heat and mass transfer results obtained in the present study could not be compared and verified.
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Grauer, Stefan [Verfasser]. "Transport Phenomena in Bi2Se3 and Related Compounds / Stefan Grauer". München : Verlag Dr. Hut, 2018. http://d-nb.info/1155058925/34.
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Messina, Luca. "Multiscale modeling of atomic transport phenomena in ferritic steels". Doctoral thesis, KTH, Reaktorfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177525.
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Defect-driven transport of impurities plays a key role in the microstructure evolution of alloys, and has a great impact on the mechanical properties at the macroscopic scale. This phenomenon is greatly enhanced in irradiated materials because of the large amount of radiation-induced crystal defects (vacancies and interstitials). For instance, the formation of nanosized solute clusters in neutron-irradiated reactor pressure vessel (RPV) ferritic steels has been shown to hinder dislocation motion and induce hardening and embrittlement. In Swedish RPV steels, this mechanical-property degradation is enhanced by the high content of manganese and nickel impurities. It has been suggested that the formation of Mn-Ni-rich clusters (which contain also Cu, Si, and P) might be the outcome of a dynamic process, where crystal defects act both as nucleation sites and solute carriers. Solute transport by point defects is therefore a crucial mechanism to understand the origin and the dynamics of the clustering process. The first part of this work aims at modeling solute transport by point defects in dilute iron alloys, to identify the intrinsic diffusion mechanisms for a wide range of impurities. Transport and diffusion coefficients are obtained by combining accurate ab initio calculations of defect transition rates with an exact mean-field model. The results show that solute drag by single vacancies is a common phenomenon occurring at RPV temperature (about 300 °C) for all impurities found in the solute clusters, and that transport of phosphorus and manganese atoms is dominated by interstitial-type defects. These transport tendencies confirm that point defects can indeed carry impurities towards nucleated solute clusters. Moreover, the obtained flux-coupling tendencies can also explain the observed radiation-induced solute enrichment on grain boundaries and dislocations. In the second part of this work, the acquired knowledge about solute-transport mechanisms is transferred to kinetic Monte Carlo (KMC) models, with the aim of simulating the RPV microstructure evolution. Firstly, the needed parameters in terms of solute-defect cluster stability and mobility are calculated by means of dedicated KMC simulations. Secondly, an innovative approach to the prediction of transition rates in complex multicomponent alloys is introduced. This approach relies on a neural network based on ab initio-computed migration barriers. Finally, the evolution of the Swedish RPV steels is simulated in a "gray-alloy" fashion, where impurities are introduced indirectly as a modification of the defect-cluster mobilities. The latter simulations are compared to the experimental characterization of the Swedish RPV surveillance samples, and confirm the possibility that solute clusters might form on small interstitial clusters. In conclusion, this work identifies from a solid theoretical perspective the atomic-transport phenomena underlying the formation of embrittling nanofeatures in RPV steels. In addition, it prepares the ground for the development of predictive KMC tools that can simulate the microstructure evolution of a wide variety of irradiated alloys. This is of great interest not only for reactor pressure vessels, but also for many other materials in extreme environments.QC 20151123
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Tsuda, Taizo. "STUDIES ON BIOLOGICAL TRANSPORT PHENOMENA OF ENVIRONMENTAL CHEMICAL POLLUTANTS". Kyoto University, 1992. http://hdl.handle.net/2433/168761.
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本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・論文博士
博士(工学)
乙第7828号
論工博第2578号
新制||工||874(附属図書館)
UT51-92-J240
(主査)教授 乾 智行, 教授 渡部 良久, 教授 宗宮 功
学位規則第4条第2項該当
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Zahn, Peter. "Transport phenomena in metallic nanostructures: an ab initio approach". Doctoral thesis, Technische Universität Dresden, 2003. https://tud.qucosa.de/id/qucosa%3A24499.
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Im Rahmen der vorliegenden Arbeit werden ab initio Berechnungen des Restwiderstandes von metallischen Nanostrukturen vorgestellt. Die elektronische Struktur der idealen Systeme wird mit Hilfe einer Screened KKR Greenschen Funktionsmethode im Rahmen der Vielfachstreutheorie auf der Grundlage der Dichtefunktionaltheorie berechnet. Die Potentiale von Punktdefekten werden selbstkonsistent mit Hilfe einer Dyson-Gleichung für die Greensche Funktion des gestörten Systems berechnet. Unter Nutzung der ab initio Ubergangswahrscheinlichkeiten wird der Restwiderstand durch Lösung der quasi-klassischen Boltzmann-Gleichung bestimmt. Ergebnisse für ultradünne Cu-Filme und die Leitfähigkeitsanomalie während des Wachstums von Co/Cu-Vielfachschichten werden vorgestellt. Der Einfluss von Oberflächen, geordneten und ungeordneten Grenzflächenlegierungen und von Defekten an verschiedenen Positionen in der Vielfachschicht auf den Effekt des Giant Magnetoresistance wird untersucht. Die selbstkonsistente Berechnung der Streueigenschaften und die verbesserte Lösung der Boltzmann-Transportgleichung unter Einbeziehung der Vertex-Korrekturen stellen ein leistungsfähiges Werkzeug zur umfassenden theoretischen Beschreibung dar. Sie verhelfen zu nützlichen Einsichten in die mikroskopischen Prozesse, die die Transporteigenschaften von nanostrukturierten Materialen bestimmen.A powerful formalism for the calculation of the residual resistivity of metallic nanostructured materials without adjustable parameters is presented. The electronic structure of the unperturbed system is calculated using a screended KKR multiple scattering Green's function formalism in the framework of density functional theory. The scattering potential of point defects is calculated self-consistently by solving a Dyson equation for the Green's function of the perturbed system. Using the ab initio scattering probabilities the residual resistivity was calculated solving the quasiclassical Boltzmann equation. Examples are given for the resistivity of ultrathin Cu films and the conductance anomaly during the growth of a Co/Cu multilayer. Furthermore, the influence of surfaces, ordered and disordered interface alloys and defects at different positions in the multilayer on the effect of Giant Magnetoresistance is investigated. The self-consistent calculation of the scattering properties and the improved treatment of the Boltzmann transport equation including vertex corrections provide a powerful tool for a comprehensive theoretical description and a helpful insight into the microscopic processes determining the transport properties of magnetic nanostructured materials.
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Leichsenring, Peter y Thomas Wallmersperger. "Modeling and simulation of transport phenomena in ionic gels". SPIE, 2015. https://tud.qucosa.de/id/qucosa%3A35028.
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Ionic hydrogels belong to the class of polyelectrolyte gels or ionic gels. Their ability to swell or shrink under different environmental conditions such as change of pH, ion concentration or temperature make them promising materials, e.g. for microsensoric or microactuatoric devices. The hydrogel swelling exhibits nonlinear effects due to the occurrence of different interacting transport phenomena.
Numerical simulations are an essential part in the ongoing development of microsensors and microactuators. In order to determine transport effects due to diffusion, migration and convection a multiphase mesoscale model based on the Theory of Porous Media is applied. The governing field equations are solved in the transient regime by applying the Finite Element Method.
By means of the derived numerical framework a detailed investigation of the different transport phenomena is carried out. Numerical experiments are performed to characterize the dominating transfer phenomena for ionic gels under chemical stimulation.