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Tesi sul tema "Coefficient de diffusion de l’exciton"

Autore: Grafiati

Pubblicato: 2 novembre 2024

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1

Diarra, Cheick Oumar. "Modélisation par dynamique moléculaire ab initio du transport des excitons et du transport thermique dans les semiconducteurs organiques pour la collecte d'énergie". Electronic Thesis or Diss., Strasbourg, 2024. http://www.theses.fr/2024STRAD013.

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L'exciton joue un rôle clé dans le fonctionnement des cellules solaires organiques (OSCs). Comprendre sa dynamique dans les semiconducteurs organiques est essentiel, notamment pour améliorer la longueur de diffusion, une propriété déterminante pour la performance des hétérojonctions planaires, envisagées comme une alternative plus stable aux hétérojonctions en volume (BHJ). Dans la première partie de cette thèse, nous avons développé une approche méthodologique robuste et polyvalente pour évaluer la longueur de diffusion de l'exciton dans les semiconducteurs organiques. Cette approche, basée sur AIMD-ROKS, a été validée avec succès dans le cas du polymère P3HT. Elle a également été appliquée à l'accepteur NFA O-IDTBR, révélant des longueurs de diffusion prometteuses, mais encore insuffisantes pour les hétérojonctions planaires. Dans la deuxième partie de la thèse, le transfert de chaleur dans les semiconducteurs organiques a été exploré, élément crucial pour la performance des dispositifs thermoélectriques. Ces études se sont concentrées sur le P3HT, un matériau utilisé en thermoélectricité. Dans un premier temps, la conductivité thermique au sein des chaînes de P3HT a été étudiée, révélant l'influence de la longueur des chaînes de polymère. Ensuite, les transferts de chaleur entre ces chaînes ont également été examinés
The exciton plays a central role in the functioning of organic solar cells (OSCs). Understanding its dynamics in organic semiconductors is essential, particularly to optimize the diffusion length, a key property for the performance of planar heterojunctions, which are considered as a potentially more stable alternative to bulk heterojunctions (BHJ) in certain contexts. In the first part of this thesis, we developed a robust and versatile methodological approach to evaluate the exciton diffusion length in organic semiconductors. This method, based on AIMD-ROKS, was successfully validated for the P3HT polymer. It was also applied to the NFA O-IDTBR acceptor, revealing promising diffusion lengths, though still insufficient for planar heterojunctions. The second part of the thesis explores heat transfer in organic semiconductors, a crucial element for the performance of thermoelectric devices. These studies focused on P3HT, a material used in thermoelectricity. First, the thermal conductivity within P3HT chains was studied, revealing the influence of polymer chain length. Then, heat transfers between these chains were also examined

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2

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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3

Kalnin, Juris Robert, Eugene A. Kotomin, Joachim Maier e 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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4

Sood, Eeshani. "Determination of diffusion coefficient for unsaturated soils". Texas A&M University, 2005. http://hdl.handle.net/1969.1/2318.

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The structures constructed on unsaturated soils are damaged by the movement of the soil underneath. The movement is basically due to the flow of moisture in and out of the soil. This change in moisture also affects the strength of the soil, thus resulting in failure of slopes of embankments constructed with these soils. Therefore, it is very important to study the diffusion properties of unsaturated soils. Study of the diffusion properties requires the determination of the diffusion coefficient (/). In this thesis improvements in the drying test, originally proposed by Mitchell (1979), have been discussed. The study also involves defining the evaporation coefficient (he) which has been ill-defined in previous research work. The flow through unsaturated soils is non-linear but due to the complexity involved it has been simplified to a linear problem. The nonlinear behavior has been studied during this research. Therefore, certain refinements have been applied in the determination of the diffusion coefficient. The laboratory procedure followed involves measuring the soil suction along the length of the sample and at different times using thermocouple psychrometers. The evaluation of the evaporation coefficient (he) has been made an integral part of the procedure. The diffusion coefficient is determined using the curve fitting procedure of Aubeny and Lytton, 2003.

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5

Chandler, I. D. "Vertical variation in diffusion coefficient within sediments". Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/49612/.

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River ecosystems can be strongly in uenced by contaminants in the water column, in the pore water and attached to sediment particles. Current models [TGD, 2003] predict exposure to sediments based on equilibrium partitioning between dissolved and suspended-particle-sorbed phase in the water column despite numerous studies showing significant direct mass transfer across the sediment water interface. When exchange across the interface (hyporheic exchange) is included in modelling the diffusion coefficient is assumed to be constant with depth. The overall aims of this research were to quantify the vertical variation in diffusion coefficient below the sediment water interface and asses the use of a modified EROSIMESS-System (erosimeter) in the study of hyporheic exchange. The modified erosimeter and novel fibre optic uorometers measuring in-bed concentrations Rhodamine WT were employed in an experimental investigation. Five different diameter glass sphere beds (0.15 to 5.0mm) and five bed shear velocities (0.01 to 0.04m/s) allowed the vertical variation in diffusion coefficient to be quantified to a depth of 0.134m below the sediment water interface. The vertical variation in diffusion coefficient can be described using an exponential function that was found to be consistent for all the parameter combinations tested. This function, combined with the scaling relationship proposed by O'Connor and Harvey [2008] allows a prediction of the diffusion coefficient below the sediment water interface based on bed shear velocity, roughness height and permeability. 1D numerical diffusion model simulations using the exponential function compare favourably with the experimental data.

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6

Itamunoala, G. F. "Effective diffusion coefficient in cell immobilization matrices". Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371905.

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7

Hess, Clarion Hadleigh. "The Green's function for the diffusion coefficient". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/114353.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 53-54).
The scattering diffusion coefficient between two points can theoretically be extracted from a random distribution of sources. An improved ability to measure the diffusion coefficient of the Earth's crust would simplify the process of characterizing the fracture network for applications in geothermal energy. This has the potential to make geothermal wells more economical to make, more efficient to operate, and longer lived. Previous work has shown the diffusion coefficient can be extracted from synthetic datasets in both one dimension and three dimensions using seismic interferometry. This paper attempts to recover the diffusion coefficient for a realistic source distribution taken from a microseismic dataset from a geothermal field in Indonesia. This dataset did not have an ideal distribution of sources, so the estimated diffusion coefficient did not match the expected value. A better estimate of the expected diffusion coefficient and an improved dataset with sources more evenly distributed in all directions around the receivers would likely give a better result.
by Clarion Hadleigh Hess.
S.B.

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8

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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Abstract (sommario):

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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9

Kalnins, Juris Roberts, Eugene A. Kotomin e 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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10

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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11

Kalnin, Juris Robert, Eugene A. Kotomin, Joachim Maier e 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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12

Fröba, Andreas P., Cristina Botero, Heiko Kremer e 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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13

Delattre, Sylvain. "Estimation du coefficient de diffusion d'un processus de diffusion en présence d'erreurs d'arrondi". Paris 6, 1997. http://www.theses.fr/1997PA066297.

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Soit un processus de diffusion a valeurs reelles x dont le coefficient de diffusion depend d'un parametre reel inconnu. On etudie le probleme de l'estimation de ce parametre quand on echantillonne une trajectoire de x en un grand nombre, n, d'instants equireparties entre l'instant et l'instant 1, et quand de plus les observations sont sujettes a des erreurs d'arrondi dont l'ordre de grandeur, alpha, est petit. On decrit tout d'abord le comportement, quand n tend vers l'infini et a tend vers , de la variation quadratique approchee de x calculee a partir de ces observations (et aussi d'autres fonctionnelles similaires) : sous l'hypothese que la suite alpha x racine (n) admet un limite (eventuellement infinie) et apres normalisation, la convergence en probabilite est prouvee ainsi qu'un theoreme de type central-limite associe. Un outil essentiel est le fait que si y est une variable aleatoire reelle admettant une densite reguliere alors la partie fractionnaire de (y : alpha) est approximativement uniformement distribuee. Grace a ces resultats, on construit une suite consistante d'estimateurs, qui converge a la vitesse suivante : soit racine(n) si alpha x racine(n) tend vers une limite finie, soit 1 : alpha si alpha x racine(n) tend vers l'infini. En particulier, si alpha x racine(n) tend vers , ces estimateurs sont optimaux dans la classe des estimateurs bases sur des observations sans erreur d'arrondi. En outre, dans le cas ou alpha x racine(n) tend vers une limite finie, la suite de modeles statistiques correspondante est localement asymptotiquement normale mixte (propriete lamn), avec la vitesse racine(n). La principale difficulte par rapport au cas sans erreur d'arrondi est que les observations ne constituent plus une chaine de markov.

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14

Iacus, Stefano Maria. "Statistique semi-paramétrique pour un processus de diffusion avec coefficient de diffusion petit". Le Mans, 1999. http://www.theses.fr/1999LEMAA003.

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15

Ohkubo, Takahiro, Koh Kidena e 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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16

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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17

Vasudevan, Raghavan. "Thermal diffusion coefficient modeling for high pressure combustion simulations". Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1202500574/.

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18

Fröba, Andreas P., Cristina Botero, Heiko Kremer e 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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19

Areerat, Surat. "Solubility, diffusion coefficient and viscosity in polymer/CO2 systems". 京都大学 (Kyoto University), 2002. http://hdl.handle.net/2433/149457.

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20

Minke, Mary Ann. "The diffusion and segregation coefficient of germanium in silica". Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280235.

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This research was instigated to study non-equilibrium segregation effects during the crystallization of a glass. The non-equilibrium segregation coefficient has been experimentally measured in a variety of alloys including silicon and it has been observed to increase by orders of magnitude as a function of growth rate. Monte Carlo modeling has successfully simulated this effect and has led to the analytical Jackson equation which describes it. Glass crystallization usually takes place far from equilibrium and glasses have the advantage that the glass-crystal interface does not move during quenching, and so the segregation effects can be evaluated at room temperature. The germanium in silica system was chosen for this study because germanium should substitute for the silicon and the glass matrix, and diffuse slowly enough in silica to permit evaluation of the non-equilibrium segregation. Samples were prepared by implanting silica glass with germanium, and then annealing to permit diffusion and to promote crystallization. The samples were analyzed with RBS before and after annealing to determine the distribution of germanium. Initially, the implanted germanium peak was observed to shift towards the surface which is attributed to ion drift in an electric field. This effect was eliminated with a pre-anneal which incorporated the germanium ions into the glass matrix. Since the non-equilibrium segregation depends on the dopant diffusion rate, the diffusion coefficient of germanium in amorphous and crystalline silica was measured. The diffusion coefficient in the silica glass was found to be DG=47exp(-5.8x 10⁴/T) cm²/s and the diffusion coefficient in the silica crystal was found to be DC=360exp(-(6.9x 10⁴/T)) cm²/s . The non-equilibrium segregation coefficient was evaluated based on the distribution of the dopant after crystallization, including the build-up of dopant at the crystal/glass interface. When fitted to the Jackson equation the equilibrium distribution coefficient was found to be k(eq) = 0.01. The non-equilibrium segregation coefficient increased with crystallization rate.

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21

Berg, Tobias [Verfasser]. "Non-parametric estimation of the diffusion coefficient of a branching diffusion with immigration / Tobias Berg". Mainz : Universitätsbibliothek Mainz, 2015. http://d-nb.info/1073275140/34.

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22

Ohkubo, Takahiro, Koh Kidena e 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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Abstract (sommario):

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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23

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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24

Kratschun, Filipp, Katharina Schmitz e Hubertus Murrenhoff. "Experimental investigation of the Bunsen and the diffusion coefficients in hydraulic fluids". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-199490.

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The dynamic of cavitation in hydraulic components cannot be computed accurately yet and therefore cavitation is hard to predict. The cavitation phenomenon can be divided in three sub-phenomenona: Pseudo-cavitation, Gas-cavitation and Vapour-cavitation. Pseudo-cavitation discribes the enlargement of an air bubble due to a pressure drop. Gas-cavitation refers to bubble growth which is driven by diffusion of dissolved air from the surrounding fluid into the bubble, when the solubility of air in the fluid is lowered by a pressure drop. Vapor-cavitation is the evaporation of the liquid phase on the bubble surface. Usually all three sub-phenomenona occur simultaneously when the pressure decreases and are summarised as cavitation in general. To implement the physics of gas-cavitation in a dynamic mathematical model it is necessary to know the diffusion coefficient of air in the hydraulic liquid and the maximum amount of air which can be dissolved in the liquid. The calculation can be accomplished by using the Bunsen coefficient. In this paper both coefficients for three different hydraulic oils are calculated based on experimental results.

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25

Demir, Ayhan. "Apport de l'imagerie de diffusion avec calcul du coefficient apparent de diffusion et du tenseur de diffusion dans la myélopathie cervicarthrosique". Bordeaux 2, 2000. http://www.theses.fr/2000BOR23058.

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26

Botero, Cristina, Heiko Kremer, Andreas P. Fröba e 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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27

Loskutov, Valentin, e 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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28

Farrher, Germán, Ioan Ardelean e 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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29

Masár, Lukáš. "Laboratorní a počítačové modelování difúze nízkomolekulových látek v gelových nosičích". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2011. http://www.nusl.cz/ntk/nusl-216767.

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This diploma thesis is focused on combination of experimental study and computer modelling of diffusion processes in gel phases. The aim of experimental part of the diploma thesis was to test and optimize the setting of the diffusion coefficient in gel medium by using the method of horizontal diffusion cells, commonly used for study of diffusion processes through membranes. Specific description of experiments was to determinate the impact of presence of reactive component in inert hydro-gel carrier on final value of diffusion coefficient of low-molecular model diffusion probe. The defined dependencies were subsequently combined with computer simulation of diffusion process in a properly designed model in order to determinate the experimentally unavailable system parameters. The stated combination of both approaches was proved to be an appropriate instrument for studying of hydro-gels with a wide potential especially in the field of preparation of hydro-gel carriers with controlled release of active substances.

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30

Sato, Masahide, Makio Uwaha e Yukio Saito. "Drift-Induced Step Instabilities Due to the Gap in the Diffusion Coefficient". Elsevier, 2005. http://hdl.handle.net/2237/7320.

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31

Scharnagl, Nico, Norbert Stribeck e 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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32

VOISIN, GOBIN LAURE. "Quantification de l'interaction lumiere-tissus biologiques par la mesure non invasive du coefficient d'absorption et du coefficient reduit de diffusion". Paris 12, 1999. http://www.theses.fr/1999PA120026.

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Les deux phenomenes qui interviennent dans l'interaction de la lumiere avec les tissus biologiques sont l'absorption et la diffusion. Ils sont quantifies par les coefficients optiques d'absorption et de diffusion, notes respectivement #a et #s. Une methode de mesure non invasive de ces parametres a ete elabore qui permet de separer absorption et diffusion. Cette methode repose sur l'analyse de l'image de la surface d'un echantillon eclaire ponctuellement. Cette image est integree sur des disques afin de diminuer les bruits electroniques ainsi que ceux introduits par la rugosite de l'echantillon. La courbe obtenue est alors ajustee par une fonction de relaxation du type a (1 e#r#/#b) ou r est la distance au point d'incidence. #a et #s sont alors directement deduits de a et b. Apres avoir ete elabore sur des images de simulation de monte carlo, ce modele de diffusion a ete valide experimentalement sur des etalons de diffusion avec une erreur maximale de 20%. Les coefficients #a et #s obtenus experimentalement sur la peau in vivo, pourront etre exploites comme parametres de simulation afin de determiner les performances requises d'un systeme d'imagerie tomographique a coherence optique. A terme cette technique simple et peu couteuse pourra etre utilisee pour l'optimisation des traitements photodynamiques utilisant soit des photosensibilisants, soit des lasers medicaux.

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33

VALE, JAMES MICHAEL. "MODIFICATION OF CALCIUM ALGINATE MEMBRANES WITH MONTMORILLONITE CLAY TO ALTER THE DIFFUSION COEFFICIENT". University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1093967807.

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34

Muhammad, Naim. "Hydraulic, diffusion, and retention characteristics of inorganic chemicals in bentonite". [Tampa, Fla.] : University of South Florida, 2004. http://purl.fcla.edu/fcla/etd/SFE0000383.

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35

Botero, Cristina, Heiko Kremer, Andreas P. Fröba e 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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36

Fadaei, Ehsan, e 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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37

Loskutov, Valentin, e 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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Abstract (sommario):

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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38

Kalnins, Juris Roberts, Eugene A. Kotomin e 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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39

Poole, Owen John. "A Monte Carlo simulation of percolation diffusion above the threshold in disordered lattices". Thesis, University of Portsmouth, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310385.

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40

Perez, Emmanuel. "Interdiffusion Analysis for NiCoCrAlY and NiAl vs. Various Superalloys". Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3301.

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Abstract (sommario):

Hot section components in gas turbines can be NiCoCrAlY-coated to provide the component with an Al reservoir that maintains a protective oxide layer on its surface. Over the service life of the component, the coatings degrade by composition and phase changes due to oxidation/hot-corrosion, and multicomponent interdiffusion from and into the superalloy substrate. In this study, the rate of Al interdiffusion into selected Ni-base superalloys using various diffusion couples of two-phase NiCoCrAlY (beta + gamma) and single beta-phase NiAl with the selected alloys is measured. The diffusion couples were examined with an emphasis on the composition-dependence of Al interdiffusion. Microstructural analysis of the NiCoCrAlY vs. superalloys couples is performed to examine the dependence of coatings lifetime on the superalloy composition. The beta-NiAl diffusion couples were analyzed to determine the integrated, apparent and average effective interdiffusion coefficient as a function of superalloy's composition. Concentration profiles were obtained by EPMA of the NiAl vs. superalloy diffusion couples. Findings of this study show that the lifetimes of NiCoCrAlY are heavily dependent on superalloy compositions. The rate of interdiffusion in the diffusion couples is affected by the refractory precipitate phase microstructure structures in the interdiffusion zones as well as by component interactions. The results of the beta-NiAl diffusion couples show that increasing concentrations of Cr, Mo and Ti in the superalloy increase the Al effective interdiffusion coefficient into the superalloy, while increasing concentrations of Al, Ta and W reduce it. Thus NiCoCrAlY-superalloy systems may be designed to produce optimal microstructures in the interdiffusion zone and minimize Al interdiffusion by consideration of these diffusional interactions.
M.S.M.S.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering

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41

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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42

Nugue, Frédéric. "Recherche d'une méthode rapide de détermination du coefficient de diffusion en milieu cimentaire saturé". Toulouse, INSA, 2002. http://www.theses.fr/2002ISAT0019.

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Notre étude vise à développer des méthodes rapides de détermination des coefficients de diffusion des matériaux cimentaires saturés. Une étude analytique et expérimentale de la diffusion moléculaire de HTO a été réalisée. Trois voies ont été retenues : l'exploitation du régime transitoire amont ou aval, le suivi simultané des compartiments amont et aval et le dopage préalable des échantillons. Une étude expérimentale et numérique (code de calcul Ms-Diff) de la diffusion ionique des ions Cl- a permis de réexaminer l'influence des interactions électriques sur la durée du régime transitoire. Le suivi simultané du compartiment amont et aval a, outre l'obtention d'un gain de temps sensible, permis de développer une nouvelle méthode de détermination des interactions physico-chimiques sur matériau massif. Des essais de migration aux chlorures ont permis d'étudier l'influence des conditions expérimentales. La modélisation des essais par Ms-Diff a permis de valider l'approche multi-espèces
The aim of our study consist in developing quick methods of diffusion coefficient determination in saturated cement based materials. Analytical and experimental studies of the HTO molecular diffusion have been conducted. Three ways were studied : the unsteady state in upstream or downstream compartment, the simultaneous exploitation of upstream and downstream compartments and preliminary doping of samples. Experimental and numerical studies by Ms-Diff code of chloride ionic diffusion allowed us to re-examine the influence of electrical interactions during the unsteady state regime. A new method of physico-chemical interactions determination on massive sample and a substantial reduction of time consuming have been found. Chloride migration tests allowed us to study the influence of experimental conditions. The experimental results were in good agreement with modelling by Ms-Diff. The multi-species approach has been validated

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43

Scharnagl, Nico, Norbert Stribeck e 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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44

Benkhalifa, Mohamed Tai͏̈eb. "Ecoulement visqueux de diffusion binaire dans un pore : application à la détermination du coefficient de diffusion équivalent dans un milieu poreux". Poitiers, 1994. http://www.theses.fr/1994POIT2327.

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Abstract (sommario):

Le phenomene de transport de masse constitue par le mecanisme de la diffusion binaire visqueuse de gaz a ete analyse finement au niveau d'un pore microscopique. Le phenomene de recirculation d'air est quantifie numeriquement dans un pore cylindrique en tenant compte de l'influence du fond et des parois. Les forces de viscosite le long des parois freinent la diffusion et l'on montre l'ecart a la solution de reference dite de stefan sans viscosite avec un air stagnant. Les flux d'air qui descendent le long des parois du pore montrent la possibilite d'une oxydation des composes qui impregnent la structure, comme par exemple les tanins du bois. Un fluide, diffusant dans un milieu poreux, passe a travers des capillaires microscopiques et subit deux types de resistances a la diffusion: une resistance reguliere due aux frottements visqueux aux parois de ce capillaire et une resistance singuliere due aux changements de sections. Les resultats numeriques de l'evaluation de ces resistances au niveau du pore sont utilises pour predire le coefficient de diffusion equivalent d'un assemblage de pores reconstituant des milieux poreux periodiques. On constate un bon accord avec des experiences issues de la litterature. L'effet de la viscosite est loin d'etre toujours negligeable pour la diffusion gazeuse en milieu poreux

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45

Fadaei, Ehsan, e 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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46

Mohajeri, Arash. "Effective diffusion coefficients for charged porous materials based on micro-scale analyses". Connect to thesis, 2009. http://repository.unimelb.edu.au/10187/5780.

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Abstract (sommario):

Estimation of effective diffusion coefficients is essential to be able to describe the diffusive transport of solutes in porous media. It has been shown in theory that in the case of uncharged porous materials the effective diffusion coefficient of solutes is a function of the pore morphology of the material and can be described by their tortuosity (tensor). To estimate the apparent diffusion coefficients, the values of tortuosity and porosity should be known first. In contrast with calculation of porosity, which can be easily obtained, estimation of tortuosity is intricate, particularly with increasing micro-geometry complexity in porous media. Moreover, many engineering materials (e.g, clays and shales) are characterized by electrical surface charges on particles of the porous material which can strongly affect the diffusive transport properties of ions. For these materials, estimation of effective diffusion coefficients have been mostly based on phenomenological equations with no link to underlying microscale properties of these charged materials although a few recent studies have used alternative methods to obtain the diffusion parameters.
In the first part of this thesis a numerical method based on a recently proposed up-scaled Poisson-Nernst-Planck type of equation (PNP) and its microscale counterpart is employed to estimate the tortuosity and thus the effective and apparent diffusion coefficients in thin charged membranes. Beside this, a new mathematical approach for estimation of tortuosity is applied and validated. This mathematical approach is also derived while upscaling of micro-scale Poisson-Nernst-Planck system of equations using the volume averaging method. A variety of different pore 2D and 3D micro-geometries together with different electrochemical conditions are studied here. To validate the new approaches, the relation between porosity and tortuosity has been obtained using a multi-scale approach and compared with published results. These include comparison with the results from a recently developed numerical method that is based on macro and micro-scale PNP equations.
Results confirm that the tortuosity value is the same for porous media with electrically uncharged and charged particles but only when using a consistent set of PNP equations. The effects of charged particles are captured by the ratio of average concentration to effective intrinsic concentration in the macroscopic PNP equations. Using this ratio allows to consistently take into account electro-chemical interactions of ions and charges on particles and so excludes any ambiguity generally encountered in phenomenological equations.
Steady-state diffusion studies dominate this thesis; however, understanding of transient ion transport in porous media is also important. The last section of this thesis briefly introduces transient diffusion through bentonite. To do so, the micro Nernst-Planck equation with electro-neutrality condition (NPE) is solved for a porous medium which consists of compacted bentonite. This system has been studied before in another research using an experimental approach and the results are available for both transient and steady-state phases. Three different conditions are assumed for NPE governing equations and then the numerical results from these three conditions are compared to the experimental values and analytical phenomenological solution. The tortuosity is treated as a fitting parameter and the effective diffusion coefficient can be calculated based on these tortuosity values. The results show that including a sorption term in the NPE equations can render similar results as the experimental values in transient and steady state phases. Also, as a fitting parameter, the tortuosity values were found varying with background concentration. This highlights the need to monitor multiple diffusing ion fluxes and membrane potential to fully characterize electro-diffusive transport from fundamental principles (which have been investigated in first part of this thesis) rather than phenomenological equations for predictive studies.
This research has lead to two different journal articles submissions, one already accepted in Computers and Geotechnics (October 22, 2009, 5-yrs Impact Factor 0.884) and the other one still under review.

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47

Xu, Yu. "Etude de la diffusion du carbone dans le zirconium et la zircone en volume des gaines de combustible usées par simulations multi-échelles". Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS199/document.

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Dans le cadre de la gestion des déchets nucléaires, les coques et embouts des gaines de combustibles sont coupées, compactées et empilés dans les colis CSD-C (Colis Standards de Déchets Compactés). Actuellement entreposés à la Hague, ces déchets seront stockés en milieu géologique profond dans des alvéoles en béton. Ces déchets MA-VL contiennent des RN d’intérêts dont le carbone-14 qui provient de l’activation neutronique de l’azote-14 et de l’oxygène-17 présents dans le Zircaloy. L’objectif de cette thèse, qui est menée en collaboration avec EDF et AREVA, est de répondre à la question du devenir et du comportement du carbone-14 dans ZrO₂ et Zr-métal. Cette thèse consistera à utiliser la simulation numérique, au moyen de la Théorie de la Fonctionnelle de la Densité (DFT), afin demodéliser le comportement du carbone-14 dans les CSD-C. Les simulations sont effectuées avec une approche multi-échelles : 1) Échelle atomique, optimisation de modèles atomiques permettant de représenter les différentes phases de ZrO₂ ; identification des différents sites d’insertion possibles pour l’atome de carbone en sites interstitiels et en substitutions à un atome d’oxygène ou de zirconium ; modélisation des différentes chemins d’énergie minimum associées à la migration d’un atome de carbone d’un site à un autre par mécanismes interstitiels et lacunaires. 2) Échelle macroscopique, détermination des coefficients de diffusion par la méthode Monte-Carlo dans ZrO₂ monoclinique pure et Zr pure
As part of the nuclear waste management, hulls and ends of fuel claddings are cut, compacted and put in CSD-C containers (compacted standard waste containers). Currently stored at La Hague, the waste will be stored in deep geological environment. The MA-VL waste contains RN including carbon-14, which comes from the neutron activation of nitrogen-14 and oxygen-17 present in the oxide Zircaloy. The objective of this thesis, which is taken in collaboration with EDF and AREVA, is to answer the question of the carbon-14 behavior in ZrO₂ and Zr metal. This thesis is to perform numerical simulations, using the Theory of Density Functional (DFT) to model the behavior of carbon-14 in the CSD-C. The simulations are performed with multi-scale approach: 1) At atomic scale, optimization of atomic models to represent the different phases of ZrO₂; identification of the insertion sites for the carbon atom in interstitial sites and substitutions of an oxygen or zirconium atom; modeling different minimum energy path for the migration of a carbon atom from one site to another by interstitial and vacancye mechanisms. 2) At macroscopic scale, determination of diffusion coefficients in pure bulk monoclinic ZrO₂ and pure bulk Zr by the Monte Carlo method

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48

Zhang, Zhengyu. "Laser-Induced Nucleation in a Coaxial Microfluidic Mixer". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLN023.

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La cristallisation est une des opérations élémentaires du génie chimique. Les matières produites sont extraites par cristallisation et purifiées par recristallisation. Mais la nucléation du cristal reste un mystère et la théorie classique de la nucléation est battue en brèche par de nombreuses données expérimentales. Nous avons construit un dispositif microfluidique de précipitation par mélange de solvants pour produire de manière continue et observer la formation d’un grand nombre de cristaux. La molécule étudiée est le DBDCS dont les cristaux sont fluorescents mais pas la molécule. Le germe sera ainsi le premier objet lumineux du mélange.Nous avons calculé la thermodynamique du mélange ternaire DBDCS/1,4-dioxane(diox)/eau à partir de ce qui est connu pour le mélange diox/eau et de la courbe de solubilité du DBDCS dans diox/eau, dans le cadre d’un modèle de solution régulière. Il permet de calculer les conditions de la décomposition spinodale ([DBDCS]= 59 fois la saturation) du mélange ternaire en une phase liquide hypothétique de DBDCS pratiquement pur dans un mélange diox/eau.Nous observons cette phase dans une expérience de précipitation après 6ms de mélange. La mesure du volume de cette phase liquide confirme qu’elle est pratiquement pure. L’apparition de cette phase liquide nécessite une forte sursaturation. Celle-ci fait suite à la diffusion de l’eau qui repousse et concentre le DBDCS au centre du dispositif. L’étude du temps mis à atteindre la concentration critique en fonction de la concentration initiale en DBDCS dans le flux central permet d’obtenir une valeur de 50 à 70 fois la saturation pour la concentration critique d’apparition de la phase liquide DBDCS. Le produit de cette décomposition spinodale est un nuage de gouttelettes sub-micrométriques. Mais le gradient de potentiel chimique peut, dans certaines conditions, regrouper ces nano-gouttes en un chapelet de gouttes micrométriques de même taille.Lorsque l’anti-solvant n’est pas de l’eau pure, mais un mélange diox/eau, la barrière de potentiel ne l’emporte pas sur l’entropie de la diffusion, ce que montre la répartition de la fluorescence résiduelle des molécules (rendement<10-4). Sur des temps de l’ordre de 5s, on observe la formation et la croissance de cristaux dans un mélange localement homogène. La simulation numérique indique que dans ces conditions la sursaturation relative ne dépasse pas 3,5. L’imagerie rapide et la fluorescence permettent d’observer les cristaux un par un. Trois polymorphes différents sont identifiables par leur durée de vie : les phases vertes et bleues déjà observées et une phase de courte durée de vie. Ces cristaux présentent une vitesse de croissance moyenne proportionnelle à la concentration locale.En focalisant un laser sur les nuages de nano-gouttes, on observe un effet de pince optique capable de rassembler ces gouttes. En focalisant ce laser dans la zone de super-saturation maximale dans des conditions de nucléation spontanée, on observe une multiplication du nombre de cristaux formés d’un facteur cinq. Nous sommes en présence d’une nucléation induite par laser. Ces cristaux présentent la même vitesse de croissance, la même distribution en nombre des polymorphes, que les cristaux obtenus spontanément. Cette nucléation induite par laser est donc très douce et induit un changement minimal du mécanisme de la nucléation. Un effet de pince optique qui concentre localement les précurseurs du germe et augment transitoirement la sursaturation pourrait avoir cet effet.Cette nucléation induite par laser permet de localiser la nucléation. Au point focal du laser NPLIN, nous observons l’accumulation d’une phase de durée de vie de fluorescence courte, donc peut être désordonnée. Elle disparaît après le passage dans le laser pendant qu’une phase de grande durée de vie (la phase verte) croit lentement. Ce serait une observation directe d’une nucléation en deux étapes
Crystallization is one of the elementary operations of chemical engineering. The materials produced are extracted by crystallization and purified by recrystallization. But the nucleation of the crystal remains a mystery and the classical theory of nucleation is undermined by numerous experimental data. We have chosen to build a microfluidic precipitation device by mixing solvents to produce and continuously observe the birth of a large number of crystals. The molecule chosen for the study is DBDCS, with fluorescent crystals but not the molecule. The germ will thus be the first luminous object in the mixture.We calculated the thermodynamics of the ternary mixture DBDCS/diox/water from what is known for the mixture diox/water and the solubility curve of DBDCS in diox/water, as part of a regular solution model. We calculate the conditions of the spinodal decomposition ([DBDCS]= 59 times the saturation) of the ternary mixture into a hypothetical liquid phase of DBDCS practically pure in a diox/water mixture.However, this hypothetical phase we observe it as the main initial product of this precipitation experience. The measurement of the volume produced by this liquid phase confirms that it is practically pure. The appearance of this liquid phase requires a strong oversaturation following the diffusion of water. The study of the solubility of DBDCS in diox/water shows that the chemical potential of DBDCS in water is 17 RT higher than its value in diox. The diffusion of water in diox induces the formation of an energy barrier that repels and concentrates DBDCS to the center of the device. The study of the time taken to reach the critical concentration as a function of the initial concentration of DBDCS in the central flow provides a value 50 to 70 times the saturation for the critical concentration of occurrence of the DBDCS liquid phase. This confirms that we observe a spinodal decomposition. The product of this spinodal decomposition is a cloud of sub-micrometric droplets. But the chemical potential gradient can, under certain conditions, group these nanodrops into a string of micrometric drops of the same size.When the anti-solvent is not pure water, but a diox/water mixture, the potential barrier does not outweigh the entropy of the diffusion. This is shown by the distribution of the fluorescence of the molecules (yield<10-4). Over times of the order of 5s, the formation and growth of crystals is observed. The numerical simulation indicates that under the conditions the relative oversaturation does not exceed 3.5. Rapid imaging and fluorescence allow the crystals to be observed one by one. Three different polymorphs are identifiable by their lifetime : the green and blue phases already observed and a short-lived phase. The growth rates are widely dispersed, making it difficult to locate and observe spontaneous nucleation.By focusing a laser on the clouds of nanodrops, we observe an optical tweezer effect capable of collecting these drops. By focusing this laser in the zone of maximum super-saturation under spontaneous nucleation conditions, we observe a multiplication of the number of crystals formed by a factor of five. We are in the presence of laser-induced nucleation. These crystals have the same growth rate, the same distribution in number of polymorphs, as the spontaneously obtained crystals. This laser-induced nucleation is therefore very soft and induces a minimal change in the nucleation mechanism. An optical tweezer effect that locally concentrates the precursors of the germ and increases the over-saturation could have this effect.This laser-induced nucleation makes it possible to locate the nucleation. At the focal point of the NPLIN laser, we observe the accumulation of a phase with a short fluorescence lifetime, so it can be disordered, which disappears after the passage in the laser while the green phase grows slowly. This would be a direct observation of a two-step nucleation

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49

Dhoot, Gaurav. "Estimation of eugenol diffusion coefficient in LLDPE using FTIR-ATR flow cell and HPLC techniques". Diss., Connect to online resource - MSU authorized users, 2008.

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50

Silva, Matthew S. "NMR characterization of changes in the apparent diffusion coefficient of water following transient cerebral ischemia". Link to electronic thesis, 2002. http://www.wpi.edu/Pubs/ETD/Available/etd-0327102-221251.

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