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1
Kosztolowicz, Tadeusz. "How to measure subdiffusion coefficient." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196926.
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We propose a method to measure a subdiffusion coefficient Dα. The method, which exploits a membrane system, relies on the so-called near-membrane layers. We experimentally study the diffusion of glucose and sucrose in a gel solvent. We find a fully analytic solution of the fractional subdiffusion equation with the initial and boundary conditions representing the system under study. Confronting the experimental data with theoretical results, we find the values of the subdiffusion coefficient for investigated substances.
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Kosztolowicz, Tadeusz. "How to measure subdiffusion coefficient." Diffusion fundamentals 2 (2005) 123, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14464.
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We propose a method to measure a subdiffusion coefficient Dα. The method, which exploits a membrane system, relies on the so-called near-membrane layers. We experimentally study the diffusion of glucose and sucrose in a gel solvent. We find a fully analytic solution of the fractional subdiffusion equation with the initial and boundary conditions representing the system under study. Confronting the experimental data with theoretical results, we find the values of the subdiffusion coefficient for investigated substances.
3
Kalnins, Juris Roberts, Eugene A. Kotomin, and Vladimir N. Kuzovkov. "Effective diffusion coefficient in one-dimensional heterogeneous solids." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198322.
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Kalnin, Juris Robert, Eugene A. Kotomin, Joachim Maier, and Vladimir N. Kuzovkov. "Calculation of the effective diffusion coefficient for heterogeneous media: Calculation of the effective diffusion coefficient forheterogeneous media." Diffusion fundamentals 2 (2005) 21, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14351.
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Kalnin, Juris Robert, Eugene A. Kotomin, Joachim Maier, and Vladimir N. Kuzovkov. "Calculation of the effective diffusion coefficient for heterogeneous media." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-195345.
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Fröba, Andreas P., Cristina Botero, Heiko Kremer, and Alfred Leipertz. "Mutual diffusion coefficient in fluids by dynamic light scattering." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196269.
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Ohkubo, Takahiro, Koh Kidena, and Akihiro Ohira. "Time-dependent diffusion coefficient of proton in polymer electrolyte membrane." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-192269.
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We investigated the time-dependent self-diffusion coefficients of water, D(T eff), in polymer electrolyte membranes at 278 K. TheD(T eff) was measured from T eff=0.7 to 100 ms by field gradient NMR techniques. The results showed that the self-diffusion coefficients of water were dependent on T eff less than 2 ms due to restricted diffusion, and were constant beyond 3 ms. The tortuosity and surface-to-volume ratio related to water diffusion were also estimated from D(T eff). The obtained values revealed the existence of large-scale restricted geometry compared with well-known nanometer-sized domain in polymer electrolyte membranes.
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Saxton, Michael J. "Diffusion coefficient as a function of mass for globular macromolecules." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198611.
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Fröba, Andreas P., Cristina Botero, Heiko Kremer, and Alfred Leipertz. "Mutual diffusion coefficient in fluids by dynamic light scattering." Diffusion fundamentals 2 (2005) 70, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14404.
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Keller, Steven Ede. "Flux-limited Diffusion Coefficient Applied to Reactor Analysis." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16126.
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A new definition of the diffusion coefficient for use in reactor physics calculations is evaluated in this thesis. It is based on naturally flux-limited diffusion theory (FDT), sometimes referred to as Levermore-Pomraning diffusion theory. Another diffusion coefficient more loosely based on FDT is also evaluated in this thesis. Flux-limited diffusion theory adheres to the physical principle of flux-limiting, which is that the magnitude of neutron current is not allowed to exceed the scalar flux. Because the diffusion coefficients currently used in the nuclear industry are not flux-limited they may violate this principle in regions of large spatial gradients, and because they encompass other assumptions, they are only accurate when used in the types of calculations for which they were intended.
The evaluations were performed using fine-mesh diffusion theory. They are in one spatial dimension and in 47, 4, and 2 energy groups, and were compared against a transport theory benchmark using equivalent energy structures and spatial discretization.
The results show that the flux-limited diffusion coefficient (FD) outperforms the standard diffusion coefficient in calculations of single assemblies with vacuum boundaries, according to flux- and eigenvalue-errors. In single assemblies with reflective boundary conditions, the FD yielded smaller improvements, and tended to improve only the fast-group results. The results also computationally confirm that the FD adheres to flux-limiting, while the standard diffusion coefficient does not.
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Ohkubo, Takahiro, Koh Kidena, and Akihiro Ohira. "Time-dependent diffusion coefficient of proton in polymer electrolyte membrane." Diffusion fundamentals 10 (2009) 21, S. 1-3, 2009. https://ul.qucosa.de/id/qucosa%3A14112.
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We investigated the time-dependent self-diffusion coefficients of water, D(T eff), in polymer electrolyte membranes at 278 K. TheD(T eff) was measured from T eff=0.7 to 100 ms by field gradient NMR techniques. The results showed that the self-diffusion coefficients of water were dependent on T eff less than 2 ms due to restricted diffusion, and were constant beyond 3 ms. The tortuosity and surface-to-volume ratio related to water diffusion were also estimated from D(T eff). The obtained values revealed the existence of large-scale restricted geometry compared with well-known nanometer-sized domain in polymer electrolyte membranes.
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Saxton, Michael J. "Diffusion coefficient as a function of mass for globular macromolecules." Diffusion fundamentals 24 (2015) 45, S. 1, 2015. https://ul.qucosa.de/id/qucosa%3A14565.
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Botero, Cristina, Heiko Kremer, Andreas P. Fröba, and Alfred Leipertz. "Particle diffusion coefficient and dynamic viscosity in non-ideal liquid mixtures by dynamic light scattering." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196233.
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Loskutov, Valentin, and Vyacheslav Sevriugin. "Analytical solution for the time dependent self-diffusion coefficient of a liquid in a porous medium." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194287.
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The purpose of our work is to attempt to find the analytical expression approximating the experimentally obtained D(t) dependence of molecules of liquids or gases, in porous systems. The statement of the problem is based on the most general representations of self-diffusion processes in porous systems.
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Farrher, Germán, Ioan Ardelean, and Rainer Kimmich. "Vapor contribution to the time dependence of the effective diffusion coefficient in partially filled porous glasses." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194345.
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NMR microscopy of silica glasses with micrometer pores (Vitrapor#5) partially filled with water reveal heterogeneous distributions of the liquid on a length scale much longer than the pore dimension. This heterogeneity, which is not observed in MRI of saturated
samples, is attributed to the spatial variation of the granular microstructure. As a consequence of the inhomogeneous filling degree, the effective transverse relaxation time varies, which in turn leads to NMR imaging contrasts. Since the spatial distribution of the transverse relaxation time prevents reliable measurements with the standard pulsed gradient stimulated echo technique (PGStE), a combination of the fringe field stimulated echo method (FFStE) on the one hand and the magnetization grid rotating frame imaging technique (MAGROFI) on the other was employed in our investigations. Using this combination four decades of the diffusion time from 100 μs to 1 s could be probed. The comparison of the experimental data with Monte Carlo simulations on a model structure has shown that the vapor phase contribution to the effective diffusivity is particularly efficient on a diffusion time scale corresponding to root mean squared displacements of the order of pores dimension.
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Salhani, Chloé. "Exploring thermoelectricity and electronic transport of molecular layers." Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7013.
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Les progrès de la science des matériaux depuis les années 70 se sont engagés dans une course constante à la miniaturisation. Aux échelles où les effets quantiques dominent la physique en jeu, l'électronique moléculaire a été considérée comme un domaine d'étude prometteur, proposant d'exploiter la physique quantique pour atteindre la fonctionnalité souhaitée d'un dispositif moléculaire. Dans cette thèse, j'étudie les propriétés électroniques et thermoélectriques des jonctions moléculaires à l'état solide à grande surface, des dispositifs composés de couches moléculaires robustes et greffées par covalence formées de plusieurs chaînes moléculaires contenant plusieurs unités moléculaires en série, contactées par des électrodes métalliques. Une première partie de cette thèse consiste en l'étude des interactions inélastiques el-ph dans des couches d'anthraquinone (AQ). La molécule AQ présente des effets d'interférence quantique (QI), provoquant une extinction de la fonction de transmission (et donc de la conductance) près du point de polarisation nulle et améliorant ainsi la visibilité des effets inélastiques (interactions el-ph). La spectroscopie IETS est réalisée sur ces couches et permet d'identifier les modes vibratoires connus de la molécule AQ. Une deuxième partie de ces travaux concerne les propriétés thermoélectriques de couches moléculaires similaires (composés de couches moléculaires d’AQ, de BTB et de NB). Les défis d'ingénierie sont relevés avec le développement d'une nouvelle géométrie d'échantillon utilisant un alliage à couche mince AuGe comme élément chauffant thermomètre, pour permettre d'établir un gradient de température contrôlé à travers l'épaisseur de la couche moléculaire (~ 15 nm). Enfin, j'explore la présence d'un potentiel thermoélectrique développé à travers la couche moléculaire. Une troisième et dernière partie de cette thèse explore une nouvelle géométrie pour les jonctions moléculaires de grande surface. Au lieu d'une approche ascendante, des nanotrenches sont utilisées pour fabriquer des jonctions moléculaires dans le plan dans une géométrie conçue pour permettre l'intégration de la porte à un stade ultérieur. Je présente la fabrication de ces nanotranches en utilisant une méthode de masque de bord d'ombre, et leur caractérisation avant et après greffe moléculaire. Les nanotranches greffées AQ révèlent des signatures de transport typiques des jonctions moléculaires qui sont comparées au comportement de la fabrication planaire plus standard<br>Progress in material science over the past half-century has been engaged in a constant race towards miniaturization. At the scales where quantum effects dominate the physics at play, molecular electronics has been considered a promising field of study, proposing to exploit quantum physics to achieve the desired functionality of a molecular device. In this thesis, I investigate electronic and thermoelectric properties of large-area solid-state molecular junctions, devices constructed of robust and covalently-grafted molecular layers formed by multiple molecular chains containing several molecular units in series contacted between metallic electrodes. A first part of this thesis concerns the investigation of inelastic el-ph interactions in layers of anthraquinone (AQ). The AQ molecule exhibits quantum interference (QI) effects, causing an extinction of the transmission function (and thus the conductance) near the zero-bias point and thus enhancing the visibility of inelastic effects (el-ph interactions). IETS spectroscopy is performed on these layers and allows to identify known vibrational modes of the AQ molecule. A second part of this work investigates the thermoelectric properties of similar molecular layers (using AQ, BTB and NB molecules). Engineering challenges are met with the development of a new sample geometry using an AuGe thin-film alloy as a heater-thermometer element, to enable establishing a controlled temperature gradient across the thickness of the molecular layer (~15nm). Finally, I explore the presence of a thermoelectric potential developed across the molecular layer. A third and final part of this thesis explores a new geometry for large area molecular junctions. Instead of a bottom-up approach, nanotrenches are used to fabricate in-plane molecular junctions in a geometry designed to allow gate integration at a later stage. I present the fabrication of these nanotrenches using a shadow-edge mask method, and their characterization before and after molecular grafting. AQ-grafted nanotrenches reveal typical transport signatures of molecular junctions that are compared to the behavior of the more standard planar fabrication
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Scharnagl, Nico, Norbert Stribeck, and Veroni Barbi. "Study of diffusion coefficient of water and homologous series of primary alcohols in PEBA membranes by NMR." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194997.
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SYAHRIR, SYAHRIR. "TRANSPORT OF RADON IN STILL WATER." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1109117669.
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Venkateshvaran, Deepak. "Seebeck coefficient in organic semiconductors." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245517.
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When a temperature differential is applied across a semiconductor, a thermal voltage develops across it in response. The ratio of this thermal voltage to the applied temperature differential is the Seebeck coefficient, a transport coefficient that complements measurements of electrical and thermal conductivity. The physical interpretation of the Seebeck coefficient is the entropy per charge carrier divided by its charge and is hence a direct measurement of the carrier entropy in the solid state. This PhD thesis has three major outcomes. The first major outcome is a demonstration of how the Seebeck coefficient can be used as a tool to quantify the role of energetic disorder in organic semiconductors. To this end, a microfabricated chip was designed to perform accurate measurements of the Seebeck coefficient within the channel of the active layer in a field-effect transistor (FET). When measured within an FET, the Seebeck coefficient can be modulated using the gate electrode. The extent to which the Seebeck coefficient is modulated gives a clear idea of charge carrier trapping and the distribution of the density of states within the organic semiconductor. The second major outcome of this work is the observation that organic semiconducting polymers show Seebeck coefficients that are temperature independent and strongly gate voltage modulated. The extent to which the Seebeck coefficient is modulated in the polymer PBTTT is found to be larger than that in the polymer IDTBT. Taken together with conventional charge transport measurements on IDTBT, the voltage modulated Seebeck coefficient confirms the existence of a vanishingly small energetic disorder in this material. In the third and final outcome of this thesis, the magnitude of the Seebeck coefficient is shown to be larger for organic small molecules as compared to organic polymers. The basis for this is not yet clear. There are reports that such an observation is substantiated through a larger contribution from vibrational entropy that adds to the so called entropy-of-mixing contribution so as to boost the magnitude of the Seebeck coefficient in organic small molecules. As of now, this remains an open question and is a potential starting point for future work. The practical implications of this PhD thesis lie in building cost-effective and environmentally friendly waste-heat to useful energy converters based on organic polymers. The efficiency of heat to energy conversion by organic polymers tends to be higher than that for conventional semiconductors owing to the presence of narrow bands in organic polymer semiconductors.
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Botero, Cristina, Heiko Kremer, Andreas P. Fröba, and Alfred Leipertz. "Particle diffusion coefficient and dynamic viscosity in non-ideal liquid mixtures by dynamic light scattering." Diffusion fundamentals 2 (2005) 67, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14401.
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Fadaei, Ehsan, and Mohsen Tafazzoli. "Study of the self-diffusion coefficient in the water-methanol binary mixture from the hydrogen bonding viewpoint using DOSY NMR." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198103.
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Furst, Jonathan Joseph. "An Investigation of Vertical Turbulent Transport Processes in Coastal Regions Using Tower Observations." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/814.
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High-resolution tower observations of turbulent transport processes in the coastal atmospheric surface layer show that the exchange coefficients for momentum, enthalpy, and moisture behave differently for different environmental and atmospheric conditions. The drag coefficient is closely tied to wind speed and turbulent intensity. The exchange coefficient for enthalpy shows a dependence on stability. Analysis of the turbulent kinetic energy budget yields a new parameterization framework that well explains the observed variation of the drag coefficient, particularly at low wind speeds.
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Loskutov, Valentin, and Vyacheslav Sevriugin. "Analytical solution for the time dependent self-diffusion coefficient of a liquid in a porous medium." Diffusion fundamentals 5 (2007) 3, S. 1-5, 2007. https://ul.qucosa.de/id/qucosa%3A14267.
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The purpose of our work is to attempt to find the analytical expression approximating the experimentally obtained D(t) dependence of molecules of liquids or gases, in porous systems. The statement of the problem is based on the most general representations of self-diffusion processes in porous systems.
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Kalnins, Juris Roberts, Eugene A. Kotomin, and Vladimir N. Kuzovkov. "Effective diffusion coefficient in one-dimensional heterogeneous solids: a comparison of continuous and discrete lattice models." Diffusion fundamentals 24 (2015) 27, S. 1, 2015. https://ul.qucosa.de/id/qucosa%3A14543.
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Scharnagl, Nico, Norbert Stribeck, and Veroni Barbi. "Study of diffusion coefficient of water and homologous series of primary alcohols in PEBA membranes by NMR." Diffusion fundamentals 3 (2005) 34, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14324.
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Fadaei, Ehsan, and Mohsen Tafazzoli. "Study of the self-diffusion coefficient in the water-methanol binary mixture from the hydrogen bonding viewpoint using DOSY NMR: Study of the self-diffusion coefficient in the water-methanol binary mixturefrom the hydrogen bonding viewpoint using DOSY NMR." Diffusion fundamentals 24 (2015) 13, S. 1, 2015. https://ul.qucosa.de/id/qucosa%3A14527.
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Tejwani, Ravindra Wadhumal. "EXPERIMENTAL AND MOLECULAR DYNAMICS SIMULATION STUDIES OF PARTITIONING AND TRANSPORT ACROSS LIPID BILAYER MEMBRANES." UKnowledge, 2009. http://uknowledge.uky.edu/gradschool_diss/738.
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Most drugs undergo passive transport during absorption and distribution in the body. It is desirable to predict passive permeation of future drug candidates in order to increase the productivity of the drug discovery process. Unlike drug-receptor interactions, there is no receptor map for passive permeability because the process of transport across the lipid bilayer involves multiple mechanisms. This work intends to increase the understanding of permeation of drug-like molecules through lipid bilayers.
Drug molecules in solution typically form various species due to ionization, complexation, etc. Therefore, species specific properties must be obtained to bridge the experiment and simulations. Due to the volume contrast between intra- and extravesicular compartments of liposomes, minor perturbations in ionic and binding equilibria become significant contributors to transport rates. Using tyramine as a model amine, quantitative numerical models were developed to determine intrinsic permeability coefficients. The microscopic ionization and binding constants needed for this were independently measured. The partition coefficient in 1,9-decadiene was measured for a series of compounds as a quantitative surrogate for the partitioning into the hydrocarbon region of the bilayer. These studies uncovered an apparent long-range interaction between the two polar substituents that caused deviations in the microscopic pKa values and partition coefficient of tyramine from the expected values. Additionally the partition coefficients in the preferred binding region of the bilayer were also measured by equilibrium uptake into liposomes.
All-atom molecular dynamics simulations of lipid bilayers containing tyramine, 4- ethylphenol, or phenylethylamine provided free energies of transfer of these solutes from water to various locations on the transport path. The experimentally measured partition coefficients were consistent with the free energy profiles in showing the barrier in the hydrocarbon region and preferred binding region near the interface. The substituent contributions to these free energies were also quantitatively consistent between the experiments and simulations. Specific interactions between solutes and the bilayer suggest that amphiphiles are likely to show preferred binding in the head group region and that the most of hydrogen bonds involving solutes located inside the bilayer are with water molecules. Solute re-orientation inside the bilayer lowers the partitioning barrier by allowing favorable interactions.
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Luffman, Ingrid E. "The effect of spatial statistics of hydraulic conductivity and distribution coefficient fields on solute transport." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq22003.pdf.
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Luffman, Ingrid Elizabeth. "The effect of spatial statistics of hydraulic conductivity and distribution coefficient fields on solute transport." Thesis, University of Ottawa (Canada), 1997. http://hdl.handle.net/10393/4458.
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The purpose of this research is twofold. First, a tool is developed to assist in the reproduction of field correlation scenarios for input into a flow and transport simulator. Second, this tool is used to generate random fields with several different velocity/retardation relationships typical of the Canada Forces Base Borden aquifer in order to determine the effect of this relationship on the retardation and dispersive processes, specifically on the macrodispersivity. The second section of the research investigates the effect of different types of spatial statistics on the behaviour of a contaminant travelling through saturated, heterogeneous porous media. The non-reactive plume travels significantly farther than the reactive plume, even when considering the effects of retardation. Transverse macrodispersivities are sensitive to changes to neither the correlation within fields, nor the correlation between velocity and retardation fields for both the reactive and non-reactive solute plumes. Longitudinal macrodispersivity for a reactive solute is significantly different than that for a non-reactive solute: the effect of the chemical heterogeneities is to enhance reactive solute macrodispersivities relative to non-reactive macrodispersivities for a negative cross-correlation between velocity and retardation, and to decease reactive solute macrodispersivities relative to non-reactive macrodispersivities when the cross-correlation is positive. (Abstract shortened by UMI.)
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Nolting, Westly. "Electronic Transport in Thermoelectric Bismuth Telluride." ScholarWorks@UNO, 2012. http://scholarworks.uno.edu/td/1539.
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An experimental investigation of the electronic transport properties of bismuth telluride nanocomposite materials is presented. The primary transport measurements are electrical conductivity, Seebeck coefficient and Hall effect. An experimental apparatus for measuring Hall effect and electrical conductivity was designed, constructed and tested. Seebeck coefficient measurements were performed on a commercial instrument. The Hall effect and Seebeck coefficient measurements are two of the most important tools for characterizing thermoelectric materials and are widely used in the semiconductor industry for determining carrier types, carrier concentration and mobility. Further, these transport parameters are used to determine the thermal to electrical conversion efficiency of a thermoelectric material. The Boltzmann transport equation was used to analyze the Seebeck coefficient, carrier mobility and electrical conductivity as a function of carrier concentration for eleven samples. The relationship between the electronic transport and material/composite composition is discussed.
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Trément, Sébastien. "Simulations gros grains de systèmes complexes et forces d’interactions : du microscopique au mésoscopique." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112227.
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Un fondu de polymères est un liquide complexe constitué de chaînes macromoléculaires. Ces chaînes présentent la particularité d'offrir une distribution de temps caractéristiques extrêmement importante. L'ensemble de ces différentes échelles représente donc un défi pour la simulation numérique de polymères longs et sont bien au-delà des capacités des ordinateurs actuels. Un thème actuel de recherche porte donc sur le développement de modèles mésoscopiques (modèle gros grains). La construction d'un tel modèle consiste à éliminer les degrés de liberté rapide en regroupant un certain nombre d'atomes en un monomère. Ce monomère est représenté par une sphère molle évoluant dans un bain thermique créé par les degrés de liberté rapides éliminés au cours du processus de nivellement. La dynamique des particules créées est donc stochastique. La dynamique particulaire dissipative qui intègre ces idées est une combinaison de dynamique moléculaire, de Lattice Gas Automata ainsi que de dynamique Brownienne. Le champ de force DPD est constitué d'une interaction molle et d'un thermostat (force dissipative et bruit) et les paramètres de ce champ de force sont généralement calibrés sur des données expérimentales (compressibilité et diffusion). Cette approche est difficilement applicable aux mélanges de polymères. Pour surmonter cette difficulté, l'intégralité du champ de force DPD est construit à partir d'une dynamique moléculaire pour des corps purs ainsi que pour des mélanges. Nous montrons également que pour calculer correctement la force dissipative, la dynamique moléculaire doit être altérée en contraignant la position des monomères. Les coefficients de transport sont calculés par DPD et comparés à ceux obtenus par dynamique moléculaire. Ce travail s'achève par une étude de la transferabilité du champ de force du monomère vers toute une chaîne de polymères<br>A molten polymer is a complex liquid consisting of macromolecular chains. These chains have many different time scales. All these scales present a real challenge to numerical simulations and exceed the computational capabilities of today's computers. A current topic of research therefore focuses on the development of mesoscopic models. The main idea behind coarse-graining is to eliminate fast degrees of freedom grouping atoms or molecules into clusters (or monomers). This monomer is represented by a soft sphere operating in a thermal bath generated by the fast degrees of freedom eliminated during the coarse-graining. Particle dynamics is therfore stochastic. Dissipative particle dyna-mics, which includes these ideas, is a combination of molecular dynamics, Lattice Gas Automata and Brownian dynamics. DPD force field consist of a soft interaction and a thermostat (dissipative and random force) and parameters of DPD interaction are generally optimized to match some macroscopic properties like compressibility or self-diffusion coefficient. This approach is difficult to apply to polymer melt. To overcome this problem, we apply an operational procedure available in the literature to the cons-truction of conservative and dissipative forces of DPD force field for pure substances and mixtures. We also show that in order to calculate the dissipative forces, the underlying molecular dynamics must be altered by constraining the position of the mo-nomers. Transport coefficients are calculated by DPD and compared with those obtained by molecular dynamics. This work concludes with a study of the transferability of the force field of the monomer to a chain of polymers
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Olynyk, Thierry. "Coefficients de transport de particules browniennes en solution : approche expérimentale et modélisation." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2001. http://tel.archives-ouvertes.fr/tel-00146787.
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Les coefficients d'autodiffusion, le coefficient de diffusion mutuelle ainsi que la conductivité sont des propriétés de transport des ions en solution pouvant être déterminées expérimentalement, par des calculs analytiques ou par simulation de dynamique brownienne.<br />Nous avons comparé ces méthodes pour trois électrolytes en solution aqueuse : le tungtosilicate de sodium avec ou sans sulfate de sodium ajouté, les chlorures de cryptate de potassium et de baryum ; le chlorure de potassium.<br />La voltammétrie à signaux carrés de potentiel a permis de mesurer le coefficient d'autodiffusion de l'ion tungstosilicate. La RMN impulsionnelle avec gradient de champ a été le moyen de mesurer le coefficient d'autodiffusion des cryptates. La conductivité a été mesurée classiquement par une cellule conductimétrique,<br />Les systèmes ont été modélisés et leurs propriétés simulées par dynamique brownienne dont les principes sont exposés. Nous montrons comment il est possible d'obtenir les différents coefficients de transport, en particulier le coefficient de diffusion mutuelle qui n'avait pas été calculé jusque là par cette méthode.<br />Nous avons montré que l'ion tungstosilicate était un bon modèle de particule brownienne et avons déterminé son coefficient d'autodiffusion à dilution infinie en solution aqueuse. Les ions cryptate sont plus difficiles à modéliser. Le calcul du coefficient de diffusion mutuelle par dynamique brownienne a fourni un résultat correct pour le système simple chlorure de potassium et pourrait être étendu à des systèmes plus complexes.
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Islam, Rakibul. "Electrical and thermal transport properties of polymer/carbonaceous nanostructured composites." Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10131/document.
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Les polymères conducteurs composites présentent des propriétés thermoélectriques qui en font une solution prometteuse, peu coûteuse, propre et efficace pour la récupération de pertes de chaleur. L’objet de cette thèse est l’étude des propriétés de composites nanostructurés à base de polyaniline (PANI) en fonction de la concentration en nanoobjets: nanotubes de carbone (1-D) et oxyde de graphène réduit (RGO) (2-D). Leur structure et morphologie ont été étudiées par MEB, MET, diffraction des rayons X et diffusion Raman. Les conductivités électrique et thermique, le coefficient Seebeck, la figure de mérite thermoélectrique ZT, ont été mesurés. La conductivité électrique montre une augmentation importante avec la concentration en charges alors que la conductivité thermique ne croît que légèrement, ceci améliore ZT de plusieurs ordres de grandeur. L’effet de la dimensionnalité des charges a été mis en évidence. Mais quelle que soit cette dimension, la conductivité électrique contrairement à la conductivité thermique, suit un comportement de percolation à travers un processus de conduction à 2-D. Ce comportement a été également observé pour la capacité thermique volumique des nanohybrides PANI/RGO ce qui en fait des candidats potentiels dans le domaine des matériaux à haute capacité thermique. Leur facteur de stockage de chaleur est traité avec un nouveau modèle analytique. Les échantillons de PANI/RGO ont été étudiés par spectroscopie diélectrique à différentes températures. Les résultats font apparaître un phénomène intéressant de piégeage de charges à l’interface PANI/RGO qui pourrait trouver des applications dans les supercondensateurs et les mémoires électroniques<br>Conducting polymer nanocomposites exhibit for instance interesting thermoelectric properties which make them a promising, inexpensive, clean and efficient solution for heat waste harvesting. This thesis reports on properties of polyaniline (PANI) nanostructured composites as a function of various carbonaceous nano-fillers content such as carbon nanotubes (1-D), and 2-D reduced graphene oxide (RGO). SEM, TEM, X-ray diffraction, and Raman spectroscopy have been employed to investigate their structure and morphology. Electrical and thermal conductivity, Seebeck coefficient, and thermoelectric figure of merit (ZT) have been systematically performed. An important increase of electrical conductivity has been observed with increasing filler fraction whereas thermal conductivity only slightly increases, which enhances ZT of several orders of magnitude. Fillers dimension effect is evidenced, but, whatever this dimension, it is shown that, in contrast with thermal conductivity, electrical conductivity follows a percolation behavior through 2D conduction process. This behavior is also observed in the case of the volumetric heat capacity of PANI/RGO nanohybrids which make them potential candidates as high heat capacitive materials. For the first time their heat storage factor is assessed with a new analytical model proposed in this study. The PANI/RGO samples have also been investigated by Dielectric Spectroscopy at different temperatures. Results evidence an interesting charge trapping phenomenon occurring at the PANI/RGO interface which might find promising applications in supercapacitors or gate memory devices
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Lee, Jangguen. "Experimental and numerical investigation of consolidation-induced solute transport." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1190048627.
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Alméras, Élise. "Étude des propriétés de transport et de mélange dans les écoulements à bulles." Thesis, Toulouse, INPT, 2014. http://www.theses.fr/2014INPT0115/document.
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Les réacteurs chimiques impliquant une phase liquide et une phase gazeuse sont couramment utilisés dans l'industrie pétrochimique et biologique car les écoulements à bulles ont de très bonnes propriétés de transfert et de mélange. Cela permet de mêler intimement différents composés et d'optimiser les réactions chimiques. Néanmoins, les mécanismes et les phénomènes mis en jeu dans le mélange au sein d'un écoulement à bulles restent encore mal connus. Ce travail a donc consisté à identifier les différents mécanismes de mélange en écoulement à bulles pour réviser le modèle physique de transport des espèces chimiques. Afin de distinguer et séparer les différents mécanismes, le mélange d'un traceur passif a été étudié dans différentes configurations expérimentales. Premièrement, l'étude du mélange dans un écoulement à bulles fortement confiné dans une cellule de Hele-Shaw a permis de mettre en évidence le mélange par capture du traceur dans les sillages. Ce mécanisme de mélange, fortement intermittent et convectif, s'est révélé être incompatible avec un processus purement diffusif. Deuxièmement, l'étude du mélange dans un essaim de bulles homogène tridimensionnel a été entreprise. Au contraire du cas confiné, le mélange, qui est causé par l'agitation induite par les bulles dans le liquide, est bien de nature diffusive. Nous avons donc pu mesurer les coefficients de diffusion effectifs en fonction de la fraction volumique de gaz. Ces coefficients sont différents dans les directions verticale et horizontale, ce qui traduit le caractère anisotrope du mélange. De plus, ils deviennent constants au-delà d'une certaine valeur de fraction volumique. Pour finir, nous avons considéré le mélange dans un essaim inhomogène de bulles, où se développe une boucle de recirculation du liquide. Dans le cas d'une recirculation modérée, la dispersion du traceur peut être estimée en combinant le mélange résultant de l'agitation des bulles avec l'advection par le mouvement moyen du fluide<br>Bubble columns are commonly used for chemical processes because of their good mixing and transfer capabilities. This work aims at understanding and modelling the mixing induced by bubbles. In order to distinguish the differents mixing mechanisms, the dispersion of a low-diffusive scalar has been investigated in various experimental configurations. The first one is a bubbly flow in a Hele-Shaw cell where the confinement prevents from the developpement of turbulence. In this case, the mixing is controlled by the capture and the transport by the bubble wakes. This mechanism, which cannot be described by an effective diffusivity, has been modelled by considering the intermittent transport of finite volumes of dye. The second configuration is a homogeneous swarm of rising bubbles where the mixing results from the dispersion by the bubble-induced turbulence. It can therefore be modelled by an anistropic effective diffusivity, which becomes independent of the gas volume fraction beyond a certain value. Finally, an inhomogenous bubbly flow, where a liquid recirculation loop is present, has been considered. In the case of a moderate inhomogeneity, shear induced-turbulence is not generated by the gradients of the mean flow and the mixing can be modelled by the sum of the bubble-induced dispersion and the advection by the mean flow
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Farrher, Germán, Ioan Ardelean, and Rainer Kimmich. "Vapor contribution to the time dependence of the effective diffusion coefficient in partially filled porous glasses: Vapor contribution to the time dependence of the effective diffusioncoefficient in partially filled porous glasses." Diffusion fundamentals 5 (2007) 9, S. 1-9, 2007. https://ul.qucosa.de/id/qucosa%3A14273.
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NMR microscopy of silica glasses with micrometer pores (Vitrapor#5) partially filled with water reveal heterogeneous distributions of the liquid on a length scale much longer than the pore dimension. This heterogeneity, which is not observed in MRI of saturated
samples, is attributed to the spatial variation of the granular microstructure. As a consequence of the inhomogeneous filling degree, the effective transverse relaxation time varies, which in turn leads to NMR imaging contrasts. Since the spatial distribution of the transverse relaxation time prevents reliable measurements with the standard pulsed gradient stimulated echo technique (PGStE), a combination of the fringe field stimulated echo method (FFStE) on the one hand and the magnetization grid rotating frame imaging technique (MAGROFI) on the other was employed in our investigations. Using this combination four decades of the diffusion time from 100 μs to 1 s could be probed. The comparison of the experimental data with Monte Carlo simulations on a model structure has shown that the vapor phase contribution to the effective diffusivity is particularly efficient on a diffusion time scale corresponding to root mean squared displacements of the order of pores dimension.
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ORCIL, KERVAJAN LOUISIANE. "Etude de l'influence des cinetiques d'echange sur les processus de transport dans les electrolytes." Paris 6, 1987. http://www.theses.fr/1987PA066561.
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Raffanel, Sylvie. "Proprietes thermodynamiques et de transport de melanges gazeux : azote/oxygene/argon dans les domaines 1p200 atm, 1000t30000 k." Toulouse 3, 1987. http://www.theses.fr/1987TOU30165.
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Calcul des compositions, des potentiels thermodynamiques et des coefficients de transport de melanges azote-oxygene supposes en equilibre thermodynamique complet. L'air est traite comme un cas particulier pour lequel la presence de 0,97 % d'argon est prise en compte. Le calcul est effectue dans des gammes etendues de pression (1 a 200 atm) et de temperature (1000 a 30000 k) pour constituer une banque de donnees pour un code numerique de calcul d'ecoulement turbulent du plasma. Etude de l'influence des particules chargees sur les compositions et potentiels thermodynamiques et sur les interactions entre particules
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Guillot, Geneviève. "Transport de macromolécules en solution à travers des membranes poreuses modèles." Paris 11, 1986. http://www.theses.fr/1986PA112297.
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Ce travail présente une étude expérimentale du transport de solutions de polymère flexible à travers des membranes à pores fins, dans le cas où polymère et pore sont de taille comparable. Les membranes ont été préparées par irradiation de films de polycarbonate aux ions lourds, une attaque chimique ultérieure révèle les traces latentes d'irradiation en pores cylindriques percés à travers toute l'épaisseur du film (5 à 100 microns), Le rayon de pore (50 à 200 manomètres) a été contrôlé par une observation directe au microscope électronique à balayage, et par des mesures de conductivité et de perméabilité. On a suivi la diffusion de grandes chaînes de polystyrène (masse supérieure au million) en solution dans l'acétate d'éthyle à travers ces membranes, en mesurant la concentration des solutions par spectroscopie d'absorption. Pour des solutions diluées, le coefficient de diffusion obtenu peut être décrit par un modèle sphère dure. Cependant les chaînes de grande taille devant la taille de pore ont une diffusion plus rapide qu'une sphère dure, de plus leur coefficient de diffusion augmente considérablement avec la concentration. Nous attribuons cette accélération à l'augmentation du coefficient de partage des chaînes entre intérieur et extérieur du pore, due à la flexibilité des chaînes qui leur permet de se déformer pour entrer dans le pore, et à la répulsion entre chaînes plus importante à forte concentration, Cet effet a aussi été observé avec des solutions de mélanges de grandes et de petites chaînes de même nature chimique. Des résultats préliminaires d'expériences de filtration sont enfin présentés, concernant la quantité de polymère transportée et l'évolution de la perméabilité de la membrane après filtration. Ils confirment un modèle proposé par S. DAOUDI et F. BROCHARD (1978) d'entraînement des chaînes par déformation à l'entrée des pores<br>An experimental study of the transport of solutions of flexible polymer chains through membranes with fine pores is presented in this work, for pores and polymers of comparable sizes. Membranes have been prepared by heavy ion irradiation of polycarbonate films, followed by chemical etching which reveals the irradiation latent tracks into cylindrical pores spanning the film (5 to 100 microns). The pore radius has been controlled by direct observation under a scanning electron microscope, and by conductivity and permeability measurements. The diffusion of large polystyrene chains (weights larger than one million) dissolved in ethyl acetate has been followed across these membranes, by measuring the solution concentrations by absorption spectroscopy. For dilute solutions, the measured diffusion coefficient can be described by a hard sphere model. However chains of size larger than the pore size diffuse more rapidly than hard spheres, moreover their diffusion coefficient increases drastically with concentration. We attribute this acceleration to the increase of the partition coefficient between the inside and outside of the pore, due to the chain flexibility which allows the chains to elongate to enter the pore, and to the larger repulsion between chains at higher concentrations. This effect has also been observed with solutions of mixtures of large and small chains of the same chemical composition. Some preliminary results of filtration experiments are also reported, about the amount of transported polymer and about the evolution of the membrane permeability after filtration. They confirm model suggested by S. Daoudi and F. Brochard (1978) for chain transport by elongation under flow at the pore entrance
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Ghorbani, Shaban Reza. "Structural and Electrical Transport Properties of Doped Nd-123 Superconductors." Doctoral thesis, KTH, Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3461.
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<p>It is generally believed that one of the key parameterscontrolling the normal state and superconducting properties ofhigh temperature superconductors is the charge carrierconcentration<i>p</i>in the CuO<sub>2</sub>planes.By changing the non-isovalent dopingconcentration on the RE site as well as the oxygen content in(RE)Ba<sub>2</sub>Cu<sub>3</sub>O<sub>7−δ</sub>, an excellent tool is obtained tovary the hole concentration over a wide range from theunderdoped up to the overdoped regime.In the present thesis thefocus is on the doping effects on the structural and normalstate electrical properties in Nd-123 doped with Ca, La, Pr,Ca-Pr, and Ca-Th.T he effects of doping have been investigatedby X-ray and neutron powder diffraction, and by measurements ofthe resistivity, thermoelectric power<i>S</i>, and Hall coefficient R<sub>H</sub>.T he thermoelectric power is a powerful tool forstudies of high temperature superconductivity and is highlysensitive to details of the electronic band structure.<i>S</i>as a function of temperature has been analyzed in twodifferent two band models.The parameters of these models arerelated to charactristic features of the electron bands and asemiempirical physical description of the doping dependence of<i>S</i>is obtained.So me important results are following:</p><p>(i)<i>The valence of Pr in the RE-123 family.</i>Results from thestructural investigations, the critical temperature Tc, and thethermoelectric power indicated a valence +4 at low dopingconcentration, which is in agreement with results of chargeneutral doping in the RE-123 family.(ii)<i>Hole localization</i>. The results of bond valence sum (BVS)calculations from neutron diffraction data showed that holelocalization on the Pr<sup>+4</sup>site was the main reason for the decrease of thehole concentration p.Differ ent types of localization wereinferred by S measurements for Ca-Th and Ca-Pr dopings.(iii)<i>Competition between added charge and disorder</i>. Theresults of RH measurements indicated that Ca doping introduceddisorder in the CuO<sub>2</sub>planes in addition to added charge.This could bethe main reason for the observed small decrease of thebandwidth of the density of states in the description of aphenomenological narrow band model.(iv) Empirical parabolic relation between γ and p.S data were analyzed and well described by a two-band modelwith an additional linear T term, γT.An empiricalparabolic relation for γ as a function of holeconcentration has been found.</p><p><b>Key words:</b>high temperature superconductors, criticaltemperature, resistivity, thermoelectric power, Hallcoefficient, X-ray diffraction, Neutron diffraction, NdBa<sub>2</sub>Cu<sub>3</sub>O<sub>7−δ</sub>, hole concentration,substitution.</p>
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Falk, Kerstin. "The molecular origin of fast fluid transport in carbon nanotubes : theoretical and molecular dynamics study of liquid/solid friction in graphitic nanopores." Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10167/document.
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Ce manuscrit présente une description théorique des propriétés de transport exceptionnelles des liquides dans les nanotubes de carbone (CNT). La perméabilité de ces canaux dépasse largement ce qui est prévu par les équations de l'hydrodynamique et la condition limite de non-glissement. Au cours des dernières années, plusieurs groupes ont effectué des expériences d'écoulement de liquides dans des membranes de CNT. Une perméabilité très supérieure à l'attente classique a été observée. Dans ce contexte, nous avons mené une étude exhaustive du frottement liquide/solide qui apparaît pendant l'écoulement d'un fluide dans un CNT, à l'aide de simulations de dynamique moléculaire. Le coefficient de frottement a été mesuré pour différents systèmes en utilisant plusieurs méthodes indépendantes. Les simulations ont montré que le coefficient de frottement était indépendant du confinement, mais qu'il dépendait considérablement de la courbure de la paroi. Pour l'eau dans un CNT, le coefficient de frottement diminue avec le rayon du tube. Nous avons ensuite établi une expression approchée du coefficient de frottement, qui le relie à des propriétés microscopiques de l'interface entre le liquide et la paroi. Cette expression reproduit la dépendance du coefficient de frottement avec la courbure, et permet de l'expliquer à partir des trois paramètres statiques suivants : la densité surfacique de l'eau, la rugosité de la paroi et la commensurabilité entre les structures de la paroi et de la première couche d'eau à l'interface. En résumé, notre étude a permis une compréhension détaillée du frottement de l'eau dans les CNT, qui explique l'origine de sa valeur extrêmement basse<br>Within the scope of this thesis, a theoretical study of liquid flow in graphitic nanopores was performed. More precisely, a combination of numerical simulations and analytic approach was used to establish the special properties of carbon nanotubes for fluid transport: Molecular dynamics flow simulations of different liquids in carbon nanotubes exhibited flow velocities that are 1-3 orders of magnitude higher than predicted from the continuum hydrodynamics framework and the no-slip boundary condition. These results support previous experiments performed by several groups reporting exceptionally high flow rates for water in carbon nanotube membranes. The reason for this important flow enhancement with respect to the expectation was so far unclear. In this work, a careful investigation of the water/graphite friction coefficient which we identified as the crucial parameter for fast liquid transport in the considered systems was carried out. In simulations, the friction coefficient was found to be very sensitive to wall curvature: friction is independent of confinement for water between at graphene walls with zero curvature, while it increases with increasing negative curvature (water at the outside of the tube), and it decreases with increasing positive curvature (water inside the tube), eventually leading to quasi frictionless flow for water in a single file configuration in the smallest tubes. A similar behaviour was moreover found with several other liquids, such as alcohol, alcane and OMCTS. urthermore, a theoretical approximate expression for the friction coefficient is presented which predicts qualitatively and semi-quantitatively its curvature dependent behavior. Moreover, a deeper analysis of the simulations according to the proposed theoretical description shed light on the physical mechanisms at the origin of the ultra low liquid/solid friction in carbon nanotubes. In fine, it is due to their perfectly ordered molecular structure and their atomically smooth surface that carbon nanotubes are quasi-perfect liquid conductors compared to other membrane pores like, for example, nanochannels in amorphous silica. The newly gained understanding constitutes an important validation that carbon nanotubes operate as fast transporters of various liquids which makes them a promising option for different applications like energy conversion or filtration on the molecular level
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Jelescu, Ileana O. "Magnetic resonance microscopy of Aplysia neurons : studying neurotransmitter-modulated transport and response to stress." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00979419.
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Recent progress in magnetic resonance imaging (MRI) has opened the way for micron-scale resolution, and thus for imaging biological cells. In this thesis work, we performed magnetic resonance microscopy (MRM) on the nervous system of Aplysia californica, a model particularly suited due to its simplicity and to its very large neuronal cell bodies, in the aim of studying cellular-scale processes with various MR contrasts. Experiments were performed on a 17.2 Tesla horizontal magnet, at resolutions down to 25 µm isotropic. Initial work consisted in conceiving and building radiofrequency microcoils adapted to the size of single neurons and ganglia. The first major part of the project consisted in using the manganese ion (Mn2+) as neural tract tracer in the buccal ganglia of Aplysia. Manganese is an MR contrast agent that enters neurons via voltage-gated calcium channels. We performed the mapping of axonal projections from motor neurons into the peripheral nerves of the buccal ganglia. We also confirmed the existence of active Mn2+ transport inside the neural network upon activation with the neurotransmitter dopamine. In the second major part of the project, we tested the potential of two diffusion MRI sequences for microscopy. On the one hand, we explored a very original mechanism for diffusion weighting, DESIRE (Diffusion Enhancement of SIgnal and REsolution), particularly suited for small samples. The two-dimensional DESIRE sequence was implemented and successfully tested on phantoms. The measured enhancement was consistent with theoretical predictions. Using this sequence to produce diffusion weighted images with an unprecedented contrast in biological tissue remains a challenge. On the other hand, a more "standard" sequence was implemented to measure the apparent diffusion coefficient (ADC) in nervous tissue with MRM. This sequence was a three-dimensional DP-FISP (Diffusion Prepared Fast Imaging with Steady-state free Precession), which met criteria for high resolution in a short acquisition time, with minimal artifacts. Using this sequence, we studied the changes in water ADC at different scales in the nervous system, triggered by cellular challenges. The challenges were hypotonic shock or exposure to ouabain. ADC measurements were performed on single isolated neuronal bodies and on ganglia tissue, before and after challenge. Both types of stress produced an ADC increase inside the cell and an ADC decrease at tissue level. The results favor the hypothesis that the increase in membrane surface area associated with cell swelling is responsible for the decrease of water ADC in tissue, typically measured in ischemia or other conditions associated with cell swelling.
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Biggs, Georgina Aimee. "The Onsager heat of transport at the liquidvapour interface of p-tert-butyltoluene." Thesis, University of Canterbury. Chemistry, 2007. http://hdl.handle.net/10092/1386.
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The Onsager heat of transport for p-tert-butyltoluene was measured, as part of a series of preliminary experiments towards the determination of the importance of temperature gradients on the air-sea flux of carbon dioxide. The results presented in this thesis imply that the temperature gradient is a major contributor to the magnitude of the air-sea flux. The heat of transport has been measured for the p-tert-butyltoluene system by measuring stationary-state pressure changes for known temperature differences on the vapour side of the interface. At the pressure ranges used the number of mean free paths was always outside the Knudsen zone, but the values of Q* were approximately 100 % of the latent heat of vaporisation. Departures from linearity of plots of P against ΔT are attributed to temperature jumps at the surface of the dry upper plate. Both the results taken for p-tert-butyltoluene and the earlier results for water from this laboratory fit to a Type III BET isotherm, where the c parameter is not constant. They also reveal the importance of the temperature gradient in determining the value of the thermal accommodation coefficient, and provide a new method of measuring thermal accommodation coefficients for a variety of surfaces and vapours
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Kockert, Maximilian Emil. "Thermoelectric transport properties of thin metallic films, nanowires and novel Bi-based core/shell nanowires." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/23001.
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Thermoelektrische Phänomene können in Nanomaterialien im Vergleich zum Volumenmaterial stark modifiziert werden. Die Bestimmung der elektrischen Leitfähigkeit, des absoluten Seebeck-Koeffizienten (S) und der Wärmeleitfähigkeit ist eine wesentliche Herausforderung für die Messtechnik in Hinblick auf Mikro- und Nanostrukturen aufgrund dessen, dass die Transporteigenschaften vom Volumenmaterial sich durch Oberflächen- und Einschränkungseffekte verändern können.
Im Rahmen dieser Abschlussarbeit wird der Einfluss von Größeneffekten auf die thermoelektrischen Eigenschaften von dünnen Platinschichten untersucht und mit dem Volumenmaterial verglichen. Dafür wurde eine Messplattform als standardisierte Methode entwickelt, um S einer dünnen Schicht zu bestimmen. Strukturelle Eigenschaften wie Schichtdicke und Korngröße werden variiert. Grenz- und Oberflächenstreuung reduzieren S der dünnen Schichten im Vergleich zum Volumenmaterial.
Außerdem wird eine Methode demonstriert um S von einzelnen metallischen Nanodrähten zu bestimmen. Für hochreine und einkristalline Silber-Nanodrähte wird der Einfluss von Nanostrukturierung auf die Temperaturabhängigkeit von S gezeigt.
Ein Modell ermöglicht die eindeutige Zerlegung des temperaturabhängigen S von Platin und Silber in einen Thermodiffusions- und Phononen-Drag-Anteil.
Des Weiteren werden die thermoelektrischen Transporteigenschaften von einzelnen auf Bismut-basierenden Kern/Hülle-Nanodrähten untersucht. Der Einfluss des Hüllenmaterials (Tellur oder Titandioxid) und der räumlichen Dimension des Nanodrahts auf die Transporteigenschaften wird diskutiert. Streuung an Oberflächen, Einkerbungen und Grenzflächen zwischen dem Kern und der Hülle reduzieren die elektrische und thermische Leitfähigkeit. Eine Druckverformung induziert durch die Hülle kann zu einer Bandöffnung bei Bismut führen, sodass S gesteigert werden kann. Das Kern/Hülle-System zeigt in eine Richtung, um die thermoelektrischen Eigenschaften von Bismut erfolgreich anzupassen.<br>Thermoelectric phenomena can be strongly modified in nanomaterials compared to the bulk. The determination of the electrical conductivity, the absolute Seebeck coefficient (S) and the thermal conductivity is a major challenge for metrology with respect to micro- and nanostructures because the transport properties of the bulk may change due to surface and confinement effects.
Within the scope of this thesis, the influence of size effects on the thermoelectric properties of thin platinum films is investigated and compared to the bulk. For this reason, a measurement platform was developed as a standardized method to determine S of a thin film. Structural properties, like film thickness and grain size, are varied. Boundary and surface scattering reduce S of the thin films compared to the bulk.
In addition, a method is demonstrated to determine S of individual metallic nanowires. For highly pure and single crystalline silver nanowires, the influence of nanopatterning on the temperature dependence of S is shown.
A model allows the distinct decomposition of the temperature-dependent S of platinum and silver into a thermodiffusion and phonon drag contribution.
Furthermore, the thermoelectric transport properties of individual bismuth-based core/shell nanowires are investigated. The influence of the shell material (tellurium or titanium dioxide) and spatial dimension of the nanowire on the transport properties are discussed. Scattering at surfaces, indentations and interfaces between the core and the shell reduces the electrical and the thermal conductivity. A compressive strain induced by the shell can lead to a band opening of bismuth increasing S. The core/shell system points towards a route to successfully tailor the thermoelectric properties of bismuth.
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Kawagoe, Daisuke. "Regularity of solutions to the stationary transport equation with the incoming boundary data." Kyoto University, 2018. http://hdl.handle.net/2433/232413.
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Guegan, Eric. "Transport characteristics using nor-dihydroguaiaretic acid (NDGA)-polymerized collagen fibers as a local drug delivery system." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002042.
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Razafinimanana, Manitra. "Etude des proprietes d'un plasma d'arc dans les melanges hexafluorure de soufre-azote (sf : :(6)-n::(2))." Toulouse 3, 1986. http://www.theses.fr/1986TOU30240.
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Methodes et resultats de calcul de composition du plasma, des grandeurs thermodynamiques a l'equilibre et des coefficients de transport. Modelisation du plasma d'arc en regime stationnaire, fondee sur la resolution de l'equation de conservation de l'energie. Interpretation quantitative de certaines proprietes caracteristiques de la colonne d'arc stabilise. Etude de l'extinction de l'arc et calcul de l'evolution de la conductance du plasma. Cette etude permet d'analyser les principaux mecanismes gouvernant l'evolution d'un arc stabilise non souffle en extinction.
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Kovalčíková, Hana. "Vliv změn v pórové struktuře betonu na aktuální trvanlivost ŽB a předpjatých konstrukcí." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2012. http://www.nusl.cz/ntk/nusl-225569.
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This master thesis deals with a durability of concrete, which has become the centre of the interests of international scientific insitutes during the last years. The resistence of reinforced concrete depends on the covercrete which the aggresive liquids and gases penetrate through from the environment to reinforcement. According to the ability of the covercrete to penetrate degradative species is possible to tell the durability of concrete constructions. In experimental part we look for the actual state of covercrete, ordinary and high strength, by combination of various experiments. We can find here the test´s results of water and gas permeability and absorbability and sorption of concrete which complete the permeability tests. In final part the impact of different concrete types on durability of reinforced concrete is discussed.
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Slováková, Kristína. "Studium ochranných vlastností fóliových a nánosovaných materiálů." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2009. http://www.nusl.cz/ntk/nusl-216474.
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The report deals with the study of the resistence of the nonporous polymer materiále against permeation of the selected TICs, with the analysis of the running difussion processes and utilization of the acquired results for the selection of suitable barrier materials for the protective means.
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Ouahid, Soumia. "Transport facilité du glucose à travers une membrane échangeuse d'anions avec l'ion borate comme transporteur." Rouen, 1994. http://www.theses.fr/1994ROUES029.
Full textAbstract:
Par couplage diffusion-réaction, le transport d'un substrat non ionique à travers une membrane échangeuse d'ions, peut être facilité en choisissant un contre-ion apte à réagir réversiblement avec le substrat. Dans ce travail, nous avons réalisé le transport facilité à travers une membrane échangeuse d'anions. L'ion borate était utilisé comme transporteur et sa teneur dans la membrane était fixée par l'activité de l'acide borique. Nous avons mené simultanément la modélisation et l'expérimentation du transport. Par des études d'équilibre et de conductivité, nous avons déterminé les paramètres physicochimiques, tels que le coefficient de stabilité du complexe glucose-borate et le coefficient de diffusion des différentes espèces présentes. Nous avons, de plus, mis en évidence en présence de glucose, deux aspects originaux: la variation de l'accessibilité des sites membranaires et la variation de leurs interactions avec certains contre-ions. Dans la majorité des cas, nous avons choisi une activité d'acide borique relativement faible afin que les polyborates soient minoritaires devant les autres contre-ions. Dans une première série de mesures, nous avons réalisé le transport facilité du glucose en fonction de son activité, en maintenant constante celle de l'acide borique. Dans une seconde série, le transport a été réalisé en fonction de l'activité du transporteur. A partir des paramètres préalablement déterminés, nous avons élaboré un modèle théorique qui permet de comparer les valeurs théoriques et expérimentales des flux du glucose. Nous parvenons à un bon accord lorsque le transport a été réalisé en imposant pour l'acide borique une activité pour laquelle les paramètres du modèle ont été caractérisés