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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
171

Links between international child abduction and relocation: moving towards likemindedness in relocation disputes internationally - Is it time for a protocol regulating international relocation disputes

Andrews, Pearl Deidre January 2012 (has links)
Magister Legum - LLM / This by implication would mean that the best way to prevent child abduction is to desist from international marriages and moving abroad.The modern reality is that relationships are being formed internationally. In the same breath, relationships are easily un-formed and the family fractured. The emotional impact of any breakup is usually tense, and it follows by implication that this will be exacerbated if a child is involved. For reasons that will be expounded on in the thesis, many caregivers, usually mothers have opted to abduct their children. Some have opted to apply formally to relocate. Relocation disputes are widely regarded as one of the most controversial and difficult issues in family law internationally. These disputes usually arise pursuant to a relational breakdown, when the resident parent (usually the mother) seeks to relocate with the children either domestically or internationally. This causes a significant impact on contact arrangements with the other parent (usually the father). Depending on the country in which they find themselves and the laws applicable to relocation with the child, mothers are faced with the decision to remove the child either lawfully or wrongfully. International family law jurisprudence has been developed over time to assist with custody and relocation disputes. ‘Much has been written on the Hague Convention – its flaws and its successes, its effectiveness and utilization. This thesis aims to look specifically at relocation disputes within the context of international parental child abduction; more specifically, it sets out to explore whether there is a link between those phenomena, and whether the Hague Convention is sufficient for dealing with relocation disputes. I hope to make a convincing argument that if there were an international instrument regulating relocation, there would be uniformity and consistency. People’s confidence in the legal processes would be restored, motivating them to apply formally to relocate and, in doing so, the incidence of child abductions would be reduced. / South Africa
172

Simulation multi-échelle des procédés de fabrication basée sur la plasticité cristalline / Multi-scale simulation of manufacturing processes based on the crystal plasticity

Soho, Komi Dodzi Badji 21 March 2016 (has links)
Dans cette thèse, deux méthodes de couplage sont proposées pour la simulation multi-échelle des procédés de mise en forme. Dans la première partie, une procédure simplifiée (couplage indirect) est adoptée pour coupler les codes éléments finis (Abaqus et LAM3) au modèle polycristallin avec un schéma de transition autocohérente basée sur le comportement élastoplastique du monocristal écrit dans le formalisme des grandes déformations. Cette procédure simplifiée consiste à lier le modèle polycristallin avec l'analyse EF par l'extraction de l'histoire de l'incrément de déformation et de contrainte macroscopique, obtenue à partir d'une simulation EF préliminaire avec une loi phénoménologique, et à l'utiliser comme trajet de chargement dans le modèle polycristallin. Cette méthode est appliquée pour la simulation multi-échelle du procédé de skin-pass. Le suivi du trajet de chargement extrait dans la demi-épaisseur de la tôle a permis de prédire l'évolution des grandeurs physiques associées au modèle de plasticité en particulier la texture cristallographique, la texture morphologique et l'écrouissage. Dans la seconde partie de cette thèse, un modèle polycristallin élastoplastique du type autocohérent en petites déformations est couplé au code EF Abaqus via la routine utilisateur UMAT. Ce couplage (dit couplage direct) consiste à utiliser la théorie de la plasticité cristalline comme loi de comportement à chaque point d'intégration du maillage EF. Le polycristal est représenté par un ensemble de N monocristaux. Chaque fois que le code EF a besoin d'information sur le comportement mécanique aux points d'intégration de chaque EF, le modèle polycristallin est appelé. Pour valider ce couplage développé, nous avons effectué des cas tests de simulation de trajets rhéologiques. Les résultats issus de ce couplage ont été validés avec des modèles de référence. À la différence des modèles phénoménologiques, ce couplage permet non seulement d'avoir des informations sur le comportement macroscopique de la structure mais aussi d'obtenir des informations sur l'état de la microstructure du matériau. / In this thesis, two coupling methods are proposed for the multiscale simulation of forming processes. In the first part, a simplified procedure (indirect coupling) is adopted to couple the finite element codes (Abaqus and LAM3) with a polycrystalline selfconsistent model based on the large strain elastoplastic behavior of single crystals. This simplified procedure consists in linking the polycrystalline model with the FE analysis by extracting the history of the increment of macroscopic strain and stress, obtained from a preliminary FE simulation with a phenomenological law, and then using it as loading path prescribed to the polycrystalline model. This method is applied to multiscale simulation of skin-pass processes. By following on the loading path extracted at the halfthickness of the sheet, we can predict the evolution of some physical parameters associated with the plasticity model, in particular the crystallographic texture, the morphological texture and hardening. In the second part on this thesis, a small strain version of the elastoplastic polycristalline self-consistent model is coupled to the Abaqus FE code via the user material subroutine UMAT. This coupling (called direct coupling) consists in using crystal plasticity theory as constitutive law at each integration point of the FE mesh. The polycristal is represented by a set of N single crystals. Each time the FE code needs information on the mechanical behavior at the integration points considered, the full polycrystalline constitutive model is called. In order to validate this coupling, simulations of simple mechanical tests have been conducted. The results of this coupling have been validated through comparison with reference models. Unlike phenomenological models, this coupling provides not only information on the overall macroscopic response of the structure, but also important information related to its microstructure
173

Påverkar äktheten i socialt ansvarstagande den finansiella lönsamheten i företag? : En kvantitativ studie av 280 europeiska bolag

Adebäck, Julia, Eriksson, Ludvig January 2017 (has links)
Syfte: Det ställs idag högre krav på att företag inte enbart kan fokusera på att tjäna pengar utan att de också måste börja ta ansvar för miljö, samhälle och ekonomi. Till följd av de ökade kraven på företagen har vikten av begreppet Corporate social responsibility (CSR) ökat de senaste årtiondena. En populär inriktning hos tidigare studier inom området CSR är om CSR påverkar företagets finansiella prestation (CFP), vilka visat på motsägelsefulla resultat. Dock har forskning identifierat ett äkthets-gap mellan företags uttalade ansvarstagande och vad som i verkligheten utförs. Det har även konstaterats att en CSR-kommitté samt att konsekvent CSR påverkar äktheten i CSR. Syftet med denna studie är därför att undersöka hur äktheten hos investeringar i Corporate social responsibility, CSR, med avseende på hur en CSR-kommitté och konsekvent CSR, påverkar företagens lönsamhet, CFP. Metod: Studien antar en positivistisk forskningsfilosofi med en hypotetiskt deduktiv ansats. Utifrån ett kvantitativt tillvägagångssätt har sekundärdata inhämtats från databasen Thomson Reuters Datastream. En longitudinell design har använts där data har inhämtats över en sexårsperiod där det slutgiltiga urvalet har analyserats med hjälp av multipla regressionsanalyser i statistikprogrammet IBM SPSS. Resultat & slutsats: Studien visar att lönsamheten är högre hos företag som innehar en CSR-kommitté, än för företag utan CSR-kommitté, vilket indikerar att företag genom ett äkta engagemang i CSR uppnår ökad lönsamhet. Ledningens benägenhet att förmedla socialt ansvarstagande leder till ett bättre samarbete med företagets intressenter som ger ett högre finansiellt utfall. Förslag till fortsatt forskning: Studier som undersöker företags konsekventa CSR-aktiviteter över en längre tidsperiod för att identifiera effekterna av den nya hållbarhetslagen. Eftersom förekomsten av en CSR-kommitté påverkar företags lönsamhet önskar vi även ytterligare forskning angående vilka faktorer som kan förstärka eller försvaga utfallet. Uppsatsens bidrag: Ur ett teoretiskt perspektiv bidrar denna studie till redovisningslitteraturen genom att undersöka sambandet mellan finansiell prestation och äktheten hos bolagens CSR-motiv. Ur ett praktiskt perspektiv kan denna studie vara betydelsefull för företag som planerar att implementera en CSRkommitté eftersom detta bidrar till företags lönsamhet. / Aim: Todays’ companies are facing an increased demand from society that they need to shift their priorities from just making money to being socially responsible. Due to the increased demand, the importance of the concept Corporate social responsibility (CSR) has also increased in the last decades. A popular branch in prior CSR studies has been to investigate if CSR-investments affects the Corporate financial performance (CFP) which has shown conflicting results. However, previous research has identified an authentic gap between what companies are promising and what they implement in reality. Therefore the aim with this study is to investigate how authentic investments in CSR, with regard to how a CSR committee and consistent CSR, influence corporate financial performance (CFP). Method: The study is based on the philosophy of positivism with a hypothetical deductive approach. Secondary data has been collected from Thomson Reuters Datastream with a quantitative approach. A longitudinal design has been used where data has been collected over a period of six years and the final sample has been processed and analyzed with regression analysis in IBM SPSS. Result & Conclusions: This study shows that companies’ financial performance is higher in the presence of a CSR-committee, which indicates that a company by engaging in authentic CSR-activities gets a higher financial performance. Management preferences to communicate the company's social responsibility results in a better financial performance due to a better relationship with the stakeholders Suggestions for future research: Suggestions for future research may investigate how the consistency of companies CSR is influenced by the new legislation over a longer period of time. Since the CSR-committee is influential for the financial performance we would also like to see further studies involving factors that might weaken or strengthen this relationship. Contribution of the thesis: From a theoretical perspective this study contributes to the accounting literature by investigating the relationship between financial performance and authentic CSR motives. From a practical perspective this study can be of interest for companies that are planning to implement a CSR-committee since this is an influential factor for the financial performance.
174

Calculs théoriques avec le couplage spin orbitales pour les molécules diatomiques YS, YN, ZrS, et ZrN / Theoretical calculations with spin orbit effects of the diatomic molecules YS, YN, ZrS, ZrN

Farhat, Ayman 21 June 2012 (has links)
Cette thèse est consacrée à l'étude ab initio des structures électroniques des molécules diatomiques polaires YN, YS, ZrN, et ZrS. Cette étude est motivé par le manque d’informations dans la littérature sur la structure électronique de ces molécules, alors qu’elles ont clairement été identifiées dans le spectre de certaines étoiles. Des calculs théoriques sont ainsi nécessaire puisqu’ils peuvent fournir d'importantes informations quant aux propriétés des états électroniques fondamentaux et excités qui ne sont pas accessibles expérimentalement. Dans ce travail les calculs ab initio ont été effectués par la méthode du champ auto-cohérent de l'espace actif complet (CASSCF), suivie par l'interaction de configuration multiréférence (MRSDCI). La correction de Davidson, notée (MRSDCI+ Q), a ensuite été appliquée pour rendre compte de clusters ou agrégats quadruples non liés. Les calculs ont été effectués selon deux schémas. Dans le premier les effets spin-orbite ont été négligés alors que dans le second les effets spin orbite ont été inclus par la méthode des potentiels de noyau efficaces. Tous les calculs ont été effectués en utilisant le programme de calcul de chimie physique MOLPRO et en tirant parti de l’interface graphique Gabedit. Les courbes d'énergie potentielle ont été construites et des constantes spectroscopiques calculées, ainsi que les moments dipolaires électriques permanent, les champs électriques moléculaires intenses et les structures énergétiques de vibration-rotation. Nous avons détecté dans la molécule ZrS plusieurs niveaux vibrationnels dégénérés ceux-ci peuvent être utilisés pour rechercher les variantes possibles de la constante de structure fine α etdu rapport de masse μ de l’electron par rapport au proton dans trois étoiles de type S, du nomde Rand, les RCas, et χCyg. La comparaison des données expérimentales et théoriques pour la plupart des constantes calculées a montré une bonne précision pour nos prédictions avec une différence relative (en pourcentage) qui varie entre 0,1% et 10%. Ces résultats devraient ainsi mener à des études expérimentales plus poussées pour ces molécules. / This dissertation is dedicated to the ab initio study of the electronic structures of the polardiatomic molecules YN, YS, ZrN, and ZrS. The identification of these molecules in the spectraof stars as well as the lack in literature on the electronic structures of these molecules motivatedthe present study. Theoretical calculations are useful in this respect since they can provideimportant data for the properties of the ground and excited electronic states that are not availablefrom experimental means. In the present work the ab initio calculations were performed at thecomplete active space self-consistent field method (CASSCF) followed by multireference singleand double configuration interaction method (MRSDCI). The Davidson correction noted as(MRSDCI+Q) was then invoked in order to account for unlinked quadruple clusters. Thecalculations were performed on two stages in the first spin orbit effects were neglected while inthe second type of calculations spin orbit effects were included by the method of effective corepotentials. All of the calculations were done by using the computational physical chemistryprogram MOLPRO and by taking advantage of the graphical user interface Gabedit. In thepresent work potential energy curves were constructed and spectroscopic constants computed,along with permanent electric dipole moments, internal molecular electric fields, and vibrationalrotationalenergy structures. We detected in the ZrS molecule several degenerate vibrationalenergy levels which can be used to search for possible variations of the fine structure constant αand the electron to proton mass ratio μ in three S-type stars, named Rand, RCas, and χCyg. Acomparison with experimental and theoretical data for most of the calculated constantsdemonstrated a good accuracy for our predictions giving a percentage relative difference thatranged between 0.1% and 10%. Finally, we expect that the results of the present work shouldinvoke further experimental investigations for these molecules.
175

Systematic Approaches to Predictive Computational Chemistry using the Correlation Consistent Basis Sets

Prascher, Brian P. 05 1900 (has links)
The development of the correlation consistent basis sets, cc-pVnZ (where n = D, T, Q, etc.) have allowed for the systematic elucidation of the intrinsic accuracy of ab initio quantum chemical methods. In density functional theory (DFT), where the cc-pVnZ basis sets are not necessarily optimal in their current form, the elucidation of the intrinsic accuracy of DFT methods cannot always be accomplished. This dissertation outlines investigations into the basis set requirements for DFT and how the intrinsic accuracy of DFT methods may be determined with a prescription involving recontraction of the cc-pVnZ basis sets for specific density functionals. Next, the development and benchmarks of a set of cc-pVnZ basis sets designed for the s-block atoms lithium, beryllium, sodium, and magnesium are presented. Computed atomic and molecular properties agree well with reliable experimental data, demonstrating the accuracy of these new s-block basis sets. In addition to the development of cc-pVnZ basis sets, the development of a new, efficient formulism of the correlation consistent Composite Approach (ccCA) using the resolution of the identity (RI) approximation is employed. The new formulism, denoted 'RI-ccCA,' has marked efficiency in terms of computational time and storage, compared with the ccCA formulism, without the introduction of significant error. Finally, this dissertation reports three separate investigations of the properties of FOOF-like, germanium arsenide, and silicon hydride/halide molecules using high accuracy ab initio methods and the cc-pVnZ basis sets.
176

A Self-Consistent Model for Thermal Oxidation of Silicon at Low Oxide Thickness

Gerlach, Gerald, Maser, Karl 11 January 2017 (has links)
Thermal oxidation of silicon belongs to the most decisive steps in microelectronic fabrication because it allows creating electrically insulating areas which enclose electrically conductive devices and device areas, respectively. Deal and Grove developed the first model (DG-model) for the thermal oxidation of silicon describing the oxide thickness versus oxidation time relationship with very good agreement for oxide thicknesses of more than 23 nm. Their approach named as general relationship is the basis of many similar investigations. However, measurement results show that the DG-model does not apply to very thin oxides in the range of a few nm. Additionally, it is inherently not self-consistent. The aim of this paper is to develop a self-consistent model that is based on the continuity equation instead of Fick’s law as the DG-model is. As literature data show, the relationship between silicon oxide thickness and oxidation time is governed—down to oxide thicknesses of just a few nm—by a power-of-time law. Given by the time-independent surface concentration of oxidants at the oxide surface, Fickian diffusion seems to be neglectable for oxidant migration. The oxidant flux has been revealed to be carried by non-Fickian flux processes depending on sites being able to lodge dopants (oxidants), the so-called DOCC-sites, as well as on the dopant jump rate.
177

Effects of non-covalent interactions on electronic structure and anisotropy in lanthanide-based single-molecule magnets: theoretical studies

Dubrovin, Vasilii 08 November 2021 (has links)
This work describes theoretical studies on molecular and electronic structures of lanthanide-based single-molecule magnets focusing on their magnetic properties. In this work, two main problems are covered: the structural ordering of endohedral fullerenes in different supramolecular arrangements, and the magnetic anisotropy of lanthanides in different charge coordinations. The basic methodes used in this work are density functional theory and multiconfigurational self-consistent field.:CHAPTER 1. THEORETICAL FOUNDATIONS OF RARE-EARTH MAGNETISM 12 1.1. Single-molecule magnetism and 4f-elements 14 1.1.1. Electronic structure of 4f-elements 16 1.1.2. LS-coupling scheme 19 1.1.3. Parameterization of the Crystal-Field splitting effect. 20 1.1.4. Zeeman splitting for a free ion 24 1.1.5. Spin Hamiltonian and pseudospin approximation 24 1.1.6. Kramers theorem 25 1.1.7. Weak and strong molecular interactions. 26 1.2. Computational methods in application to Ln-based SMMs 27 1.2.1. Density functional theory (DFT). 28 1.2.2. Multiconfigurational methods in quantum chemistry 33 1.3. Role of molecular structure in single-molecular magnetism 41 1.3.1. Complexes of SMMs with organic molecules 45 1.3.2. SMMs deposited on surfaces 46 CHAPTER 2. STRUCTURAL ORDERING IN COCRYSTALS OF EMFs AND Ni(OEP) 49 2.1. Ordering in endohedral metallofullerenes 49 2.2. Modeling details 51 2.3. Conformer analysis 54 2.4. Electrostatic potential 58 CHAPTER 3. ISOMERISM OF Dy2ScN@C80 DEPOSITED ON SURFACES 61 3.1. Modeling details 62 3.2. Cluster conformation analysis 69 3.3. Charge density analysis 75 CHAPTER 4. Ho|MgO AS A SINGLE-ATOMIC MAGNET. FV-MAGNETISM. 80 4.1. DFT description of Ln|MgO 85 4.2. Ho|MgO system: ab initio calculations 92 4.3. Magnetic properties of lanthanides with FV magnetism 99 4.4. Generalized ligand field and spin Hamiltonians for FV systems. 101 CHAPTER 5. FV-MAGNETISM IN [Ln2+] METALLOCENE COMPLEXES 107 5.1. TbII(CpiPr5)2 DFT-model 108 5.2. FV-interaction in terms of ab initio multiconfigurational approach 113 5.3. Point-charge model 115
178

Modélisation des écoulements dans des milieux poreux fracturés par la méthode des équations aux intégrales singulières / Modelling of fluide flow in fractured porous media by the ingular integral equations method

Vu, Minh Ngoc 26 September 2012 (has links)
Cette thèse est consacrée au développement d'une méthode numérique visant à modéliser des écoulements dans des milieux poreux fissurés, ainsi qu'à déterminer leur perméabilité effective à partir des avancements théoriques récents. En parallèle, elle a été aussi l'occasion de continuer sur la voie théorique et d'obtenir de nouveaux résultats sur ce plan.Les équations générales gouvernant l'écoulement dans de tels matériaux sont rappelées, et plus particulièrement, la conservation de la masse à l'intersection entre fissures est établie explicitement [132, 139]. Des solutions générales du potentiel sont proposées sous la forme d'une équation intégrale singulière décrivant l'écoulement dans et autour des fissures entourées par une matrice infinie soumise à un champ lointain [136, 139]. Ces solutions représentent le champ de pression dans le milieu infini en fonction de l'infiltration dans les fissures qui prennent en compte complètement l'interaction et l'intersection entre fissures. En considérant le problème d'une fissure super-conductrice, des solutions analytiques de l'écoulement ont été développées et ces solutions sont utilisées comme cas de référence pour valider la solution numérique. De plus, la solution théorique de ce problème dans le cas 3D permet de comparer le modèle d'écoulement de Poiseuille dans une fissure elliptique d'épaisseur nulle et le modèle d'inclusion ellipsoïdale aplatie soumise à l'écoulement de Darcy [140]. Des outils numériques ont été développés en se basant sur la méthode des équations intégrales singulières afin de résoudre les équations générales du potentiel [132, 180]. Cela permet, d'une part, de modéliser l'écoulement stationnaire dans un domaine poreux contenant un grand nombre de fissures et, d'autre part, de proposer une solution semi-analytique de l'infiltration dans une fissure isolée dépendant de la perméabilité de la matrice, de la conductivité de la fissure et de la variable géométrique de la fissure. Cette dernière est l'élément essentiel pour déterminer de la perméabilité effective d'un milieu poreux fissuré en utilisant des schémas d'homogénéisation. Ce modèle auto-cohérent révèle un seuil de percolation qui est alors applicable pour l'estimation de la perméabilité effective d'un matériau contenant un grand nombre de fissures. L'approche par sous-structuration permet l'extension de la solution générale du potentiel, écrite pour un domaine infini, à celle d'un domaine fini [181]. Une solution analytique de l'écoulement dans et autour d'une fissure partiellement saturée est établie, fondée sur la solution analytique pour la fissure super-conductrice. Celle-ci est alors utilisée pour estimer la perméabilité effective d'un milieu poreux fissuré non-saturé [141]. Le modèle de la perméabilité effective est appliqué dans le contexte du stockage géologique du CO2 en vue d'étudier le comportement d'une zone de faille constituée par un noyau argileux et des zones fissurées. La pression d'injection provoque l'augmentation de la pression interstitielle dans le réservoir. Cette surpression engendrée dans le réservoir peut affecter la perméabilité de zones fissurées ce qui conduit à des phénomènes hydromécaniques couplés. Les résultats de simulations numériques permettent d'évaluer, d'une part, le risque de la remontée de la saumure à l'aquifère supérieur, et d'autre part, le risque de l'initiation d'une rupture sur le plan de la faille / This thesis aims to develop a method for numerical modelling of fluid flow through fractured porous media and for determination of their effective permeability by taking advantage of recent results based on formulation of the problem by Singular Integral Equations. In parallel, it was also an occasion to continue on the theoretical development and to obtain new results in this area. The governing equations for flow in such materials are reviewed first and mass conservation at the fracture intersections is expressed explicitly. Using the theory of potential, the general potential solutions are proposed in the form of a singular integral equation that describes the steady-state flow in and around several fractures embedded in an infinite porous matrix under a far-field pressure condition [136, 139]. These solutions represent the pressure field in the whole body as functions of the infiltration in the fractures, which fully take into account the fracture interaction and intersections. Closed-form solutions for the fundamental problem of fluid flow around a single fracture are derived, which are considered as the benchmark problems to validate the numerical solutions. In particular, the solution obtained for the case of an elliptical disc-shaped crack obeying to the Poiseuille's law has been compared to that obtained for ellipsoidal inclusions with Darcy's law [140].The numerical programs have been developed based on the singular integral equations method to resolve the general potential equations [132, 180]. These allow modeling the fluid flow through a porous medium containing a great number of fractures. Besides, this formulation of the problem also allows obtaining a semi-analytical infiltration solution over a single fracture depending on the matrice permeability, the fracture conductivity and the fracture geometry. This result is the important key to upscalling the effective permeability of a fractured porous medium by using different homogeneisation schemes. The results obtained by the self-consistent scheme have been in particular established. The multi-region approach can be used to extend the general potential solution written for the infinite domain to that for a finite domain [181]. A closed-form solution for flow in and around a single partially saturated fracture, surrounded by an infinite matrix subjected to a far-field condition, is also derived combining the solutions for a superconductive fracture and for an imprevious fracture. This solution is then employed to estimate the effective permeability of unsaturated fractured porous media [141].The effective permeability model is applied to study the hydromechanical behaviour of a fault zone constituted by a clay core surrounded by fractured zones in the context of CO2 geological storage. The pressure injection induces an overpressure in the reservoir that may affect the permeability of the fractured zones leading to complexe coupled hydromechanical phenomena. The simulation results allow evaluating the risk of leakage of the reservoir brine to higher aquifers as well as the risk of fault reactivation
179

Flux vacua and compactification on smooth compact toric varieties / Vides avec flux et compactification sur des variétés toriques compactes

Terrisse, Robin 16 September 2019 (has links)
L’étude des vides avec flux est une étape primordiale afin de mieux comprendre la compactification en théorie des cordes ainsi que ses conséquences phénoménologiques. En présence de flux, l’espace interne ne peut plus être Calabi-Yau, mais admet tout de même une structure SU(3) qui devient un outil privilégié. Après une introduction aux notions géométriques nécessaires, cette thèse examine le rôle des flux dans la compactification supersymétrique sous différents angles. Nous considérons tout d’abord des troncations cohérentes de la supergravité IIA. Nous montrons alors que des condensats fermioniques peuvent aider à supporter des flux et générer une contribution positive à la constante cosmologique. Ces troncations admettent donc des vides de Sitter qu’il serait autrement très difficile d’obtenir, si ce n’est impossible. L’argument est tout d’abord employé avec des condensats de dilatini puis améliorer en suggérant un mécanisme pour générer des condensats de gravitini à partir d’instantons gravitationnels. Ensuite l’attention se tourne sur les branes et leur comportement sous T-dualité non abélienne. Nous calculons les configurations duales à certaines solutions avec D branes de la supergravité de type II, et examinons les flux ainsi que leurs charges afin d’identifier les branes après dualité. La solution supersymétrique avec brane D2 est étudiée plus en détails en vérifiant explicitement les équations sur les spineurs généralisés, puis en discutant de la possibilité d’une déformation massive. Le dernier chapitre fournit une construction systématique de structures SU(3) sur une large classe de variétés toriques compactes. Cette construction définit un fibré en sphère au-dessus d’une variété torique 2d quelconque, mais fonctionne tout aussi bien sur une base Kähler-Einstein / The study of flux vacua is a primordial step in the understanding of string compactifications and their phenomenological properties. In presence of flux the internal manifold ceases to be Calabi-Yau, but still admits an SU(3) structure which becomes thus the preferred framework. After introducing the relevant geometrical notions this thesis explores the role that fluxes play in supersymmetric compactification through several approaches. At first consistent truncations of type IIA supergravity are considered. It is shown that fermionic condensates can help support fluxes and generate a positive contribution to the cosmological constant. These truncations thus admit de Sitter vacua which are otherwise extremely difficult to get, if not impossible. The argument is initially performed with dilatini condensates and then improved by suggesting a mechanism to generate gravitini condensates from gravitational instantons. Then the focus shifts towards branes and their behavior under non abelian T-duality. The duals of several D-brane solutions of type II supergravity are computed and the branes are tracked down by investigating the fluxes and the charges they carry. The supersymmetric D2 brane is further studied by checking explicitly the generalized spinor equations and discussing the possibility of a massive deformation. The last chapter gives a systematic construction of SU(3) structures on a wide class of compact toric varieties. The construction defines a sphere bundle on an arbitrary two-dimensional toric variety but also works when the base is Kähler-Einstein
180

Electrokinetics as an alternative to neutron reflectivity for evaluation of segment density distribution in PEO brushes

Zimmermann, Ralf, Romeis, Dirk, Bihannic, Isabelle, Stuart, Martien Cohen, Sommer, Jens-Uwe, Werner, Carsten 09 December 2019 (has links)
Unravelling details of charge, structure and molecular interactions of functional polymer coatings defines an important analytical challenge that requires the extension of current methodologies. In this article we demonstrate how streaming current measurements interpreted with combined self consistent field (SCF) and soft surface electrokinetic theories allow the evaluation of the segment distribution within poly(ethylene oxide) (PEO) brushes beyond the resolution limits of neutron reflectivity technique.

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