Graduate / 0485

Graduate / 0485

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Molecular simulations performed on modern computers provide a powerful tool for the investigation of both static and dynamic properties of liquid crystals. In this thesis several properties of liquid crystal mesogens have been investigated using state-of-the-art Monte Carlo (MC) and molecular dynamics (MD) simulation techniques. The helical twisting power, βm, determines the pitch of the chiral nematic phase produced when a nematic liquid crystal is doped with a low concentration of chiral solute molecules. A new simulation technique that allows the prediction of both the sign and the magnitude of βm is described. The method employs fully atomistic MC simulations of a chiral dopant molecule in the presence of a twisted nematic solvent composed of Gay-Berne particles. Eighteen different chiral dopant molecules were examined and in all cases the results were in good agreement with existing experimental data. The Kirkwood correlation factor, g(_1), has been evaluated for the molecules PCH5, PCH5-C1, me5NF and GGP5C1 using MD simulations in the pre-transitional region of the isotropic phase. The calculations employed an all-atom force field, which was developed specifically for liquid crystal molecules. PCH5 and meSNF were seen to favour anti-parallel dipole alignment whereas, PCH5-C1 and GGP5C1 preferred a parallel arrangement of the molecular dipoles. With the exception of GGP5C1, the simulations gave g(_1) values that were in accordance with existing experimental dielectric measurements. Detailed analysis of the MD trajectories showed that certain molecular pair configurations were preferred in the bulk and indicated which molecular groups were responsible for the stabilization of these configurations. Equilibrium molecular dynamics simulations were carried out in order to evaluate the rotational viscosity coefficient, γ(_1), for a Gay-Berne mesogen using two independent analysis techniques. The methods gave consistent results, which were comparable to experimental data for real mesogens of similar shape and size.

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This thesis has taken place at ABB High Voltage Cables in Karlskrona and focuses on their reinforcement process (AR50) which reinforces the cable by application of reinforcement wires. The research is strictly limited to only the short period during the application of the wire on the cable and investigates stress differences in one reinforcing wire depending on cable - and wire dimensions as well as brake forces used in the production. The study follows a model - and theory development research process combined with a testing process to obtain the results. The study aims is to increase and expand ABB's knowledge about the reinforcing process that is used to strengthen and protect ABB’s all different high voltage cables together with a computational calculation model. The model is developed in the FEA (Finite Element Analysis) program ABAQUS through a dynamic explicit model. An explanation of how the calculation model has been built and the parameters used are described in this report. These parts then contribute to the outcome of the study which provides a sense that the brake force used in AR50’s reinforcement process does not need to be controlled with a high precision so long as it is large enough to hold the reinforcement wire stretched upon the application. The study also shows that different cable - and wire dimensions does not affect the stress levels somewhat significantly by reinforcing the process and that the nipple used in reinforcement process to press down the reinforcing wire on the cable is the main source that determines how the stress distribution looks like on the reinforcement wire. / Detta examensarbete har tagit plats på ABB High Voltage Cables i Karlskrona och fokuserar på deras armeringsprocess (AR50) som förstärker kabeln genom påläggning av armeringstrådar. Arbetet är starkt begränsat till enbart den korta perioden för själva påläggningen av tråden och undersöker spänningsskillnader i en armeringstråd beroende på olika kabel – och tråddimensioner samt bromskrafter som används i produktionen. Studien följer en modell – och teoriutvecklande forskningsprocess kombinerat med ett utprövande resultatbildande. Studiens syfte är att tillsammans med en beräkningsmodell öka och fördjupa ABBs kunskaper kring armeringstråden som idag används för att stärka och skydda ABBs alla olika högspänningskablar. Beräkningsmodellen tas fram i FEA (Finita Element Analys) prorammet ABAQUS genom en dynamisk explicit modell. En förklaring till hur beräkningsmodellen har byggts upp och vilka parametrar som används beskrivs i rapporten. Dessa delar bidrar sedan till resultatet i studien som ger en bild av att bromskraften som används i AR50s armeringsprocessen inte behöver kontrolleras med en hög precision så länge den är tillräckligt stor för att hålla armeringstråden sträckt vid påläggningen. Studien visar också att olika kabel – och tråddimensioner inte påverkar spänningsnivåerna något markant vid armeringsprocessen och att nippeln som används i armeringsprocesen för att trycka ner armeringstråden mot kabeln bestämmer hur spänningsbilden ser ut. / <p>This thesis is kept confidential</p>

On s'intéresse dans cette thèse à des questions portant sur les spécialisations de revêtements algébriques (galoisiens ou non). Le thème central de la première partie de ce travail est la construction de spécialisations de n'importe quel revêtement galoisien de la droite projective de groupe G défini sur k dont on impose d'une part le comportement local en un nombre fini d'idéaux premiers de k et dont on assure d'autre part qu'elles restent de groupe G si le corps k est hilbertien. Dans la deuxième partie, on développe une méthode générale pour qu'un revêtement galoisien f de la droite projective de groupe G défini sur k vérifie la propriété suivante : étant donné un sous-groupe H de G, il existe au moins une extension galoisienne de k de groupe H qui n'est pas spécialisation du revêtement f. De nombreux exemples sont donnés. La troisième partie consiste en l'étude de la question suivante : une extension galoisienne F/k, ou plus généralement une k-algèbre étale ∏ Fl /k, est-elle la spécialisation d'un revêtement d'une variété B défini sur k (galoisien ou non) en un certain point k-rationnel de B non-ramifié ? Notre principal outil est un twisting lemma qui réduit la question à trouver des points k-rationnels sur certaines k-variétés que nous étudions ensuite pour des corps de base k variés. / We are interested in this thesis in some questions concerning specializations of algebraic covers (Galois or not). The main theme of the first part consists in producing some specializations of any Galois cover of the projective line of group G defined over k with specified local behavior at finitely many given primes of k and which each have in addition Galois group G if k is assumed to be hilbertian. In the second part, we offer a systematic approach for a given Galois cover f of the projective line of group G defined over k to satisfy the following property: given a subgroup H of G, at least one Galois extension of k of group H is not a specialization of the cover f. Many examples are given. The central question of the third part is whether a given Galois extension F/k, or more generally a given k-étale algebra ∏ Fl /k, is the specialization of a given cover of a variety B defined over k (Galois or not) at some unramified k-rational point of B ? Our main tool is a twisting lemma which reduces the problem to finding k-rational points on some k-varieties which we then study for various base fields k.

Le sujet principal de la thèse est le transport dans les systèmes mésoscopiques. Dans une première partie de lathèse, on étudie le cas d’un branchement adiabatique d’un biais de potentiel sur un système unidiensionnel sansrépartition initiale. On démontre que le courant complet est uniformément borné par rapport à la vitesse debranchement adiabatique, lorsque celle-ci tend vers zéro. On démontre l’existence de la partie linéaire de l’étatet du courant. La seconde partie de la thèse a donné lieu à a publication d’un article et elle consiste en l’étuded’un modèle discret, sans répartition initiale. On démontre que, dans ce système et après une perturbationélectrochimique, il existe un état stationnaire hors équilibre, et on retrouve la formule de Landauer-Büttikerpour ce modèle. La dernière partie de la thèse, qui a également donné lieu à un article, porte sur l’étude del’approximation des guides d’onde quantiques par des graphes quantiques. On s’intéresse à un guide d’ondelocalement torsadé. On étudie moins le Laplacien sur ce guide d’onde torsadé. Lorsque e diamètre du guidetend vers zéro et, simultanément, lorqsue le support de la courbure tend vers zéro, on démontre que le graphelimite est la ligne droite, et que l’opérateur limite est moins le Laplacien sur L2 (R) plus une condition deDirichlet à l’origine. Cette condition de Dirichlet est la conséquence des rétrécissements faits. En Annexe, ondonne des démonstrations et explications plus détaillées et utiles pour la compréhension de points clés de lathèse. / The main topic of the thesis is the transport in mesoscopic systems. In the first part of the work, we study thecase of a connection through an adiabatic potential on a one dimensional system without initial distribution, wesaid a “partition-free approach”. It is shown that the full current is uniformly bounded with respect to theadiabatic speed of connection, when it goes to zero. We prove the existence of the linear part of the state andcurrent. The second part of the thesis has led to publication of an article and deals with the study of a discretemodel without initial distribution. We prove that in this system and after an electrochemical disturbance thereexists a nonequilibrium steady state, and the Landauer-Büttiker formula is demonstrated for this model.The last part of the thesis, which also has led to an article, concerns the study of the approximation of quantumwaveguides by quantum graphs. We are interested in a waveguide locally twisted. We studyminus theLaplacian on this locally twisted waveguide. When the diameter of the guide goes to zero and simultaneouslywhen the support of the twisting goes to zero, we prove that the limit graph is the straight line, and the limitoperator is minus the Laplacian on the straight line plus a Dirichlet condition at the origin. The Dirichletcondition is the consequence of the shrinking done. In the appendix, we

Thesis (Ph. D.)--Drexel University, 2007. / Includes abstract and vita. Includes bibliographical references (leaves 182-184).