No description available.

No description available.

Reproduction de : Thèse de doctorat : Terres solides et enveloppe superficielle : Poitiers : 2008. / Titre provenant de l'écran-titre. Bibliogr. 61 réf.

Starting from a classical mechanical model, a set of Langevin equations for the surface diffusion of adsorbed molecules is developed. In contrast to previous work, these Langevin equations take full account of the rotations and internal vibrations of the adsorbed molecule. These equations are then applied to a stiff dimer diffusing in one dimension, and the results compared with previous calculations for the same system. It is shown that the modifications in our new approach give significantly different results than this previous calculation, and therefore must be taken into account in future calculations for systems of this kind. Next a new approximation method is developed by assuming that the motion of the molecule is confined to the lowest energy path between adsorption sites. This method is applicable to an arbitrarily complex molecule, and is complimentary to the first method, in that it can account for deformation of the molecule by the surface but not the internal vibrations of the molecule (whereas the first method accounts for internal vibrations but not deformation). This approximation method is then applied to a flexible dimer in two dimensions (one dimension along the surface and one perpendicular). The results are discussed and compared with those of the stiff dimer in one dimension, explaining and clarifying the difference between our results and those of previous calculations.

Andre Langevin's novels, Evade de la nuit (1951), Poussiere sur la ville (1953), Le temps des hommes (1956), L'elan d'Amerique (1972) and Une chaine daps le parc (1974) show numerous lonely characters. Abandoned, secluded or uncivilized, they remain unable to communicate with others: "C'est ce rapport difficile et jamais termine de l'individu avec "autrui" qui constitue la trame essentielle et la continuite de l'oeuvre romanesque d'Andre Langevin", wrote Jean-Louis Major in 1977, in an article about the author. / The purpose of this study is to look at the representation of the "Other" when it refers specifically to a woman. The feminine characters in Langevin's novels are shown as strangers: obviously different from men, women are struck by passions that are unknown and incomprehensible to the male heros or to any other man of her environment. In the first part, this study will demonstrate that the majority of heroines lived a painful chidhood with an absent father and an unkind mother. The second part will look at the love relationships of the female protagonists, unions that remain disappointing and are doomed to failure. Finally, the conclusion will examine the tragic death of several heroines (suicide, death in child-birth...). / This study of Andre Langevin's feminine characters relies on the feminist critic, using, among others, the work of Barbara Godard and Lori Saint-Martin. This model will offer an innovative perspective of a literary work that has been greatly studied, but for which one important aspect appears to have been neglected: women who inhabit it.

No description available.

Stuttgart, Univ., Diss., 2001.

Theories with a chemical potential are difficult to treat numerically because the action is complex and therefore methods based on a probability interpretation of the weight break down. This is an issue known as the sign problem. Complex Langevin dynamics was first proposed in the early 1980s and does not rely in a probability interpretation of the weight, so it can in principle l)e applied even where there is a severe sign problem. However, the combined problems of numerical instabilities and incorrect convergence impeded such early studies. In this work, the problem of runaway trajectories is cured l)y the use of a general adaptive stepsize procedure, which can be applied to both abelian and non-abelian theories. A study of the three-dimensional XY model at non-zero chemical potential follows, in which the problem of incorrect convergence is encountered. A formal justification of complex Langevin dynamics is given, from which a set of criteria are derived which can be used to test the validity of results. These ideas are applied to the SU(3) spin model, which is found to pass them all and therefore give correct results. An improved integration algorithm, which eliminates leading order step size corrections, is outlined and shown to give improved results.

DNA sequencing via nanopore translocation was a pipedream two decades ago. Today, biotech companies are releasing commercial devices. Yet many challenges still hover around the simple concept of threading a long DNA molecule through a small nanoscopic pore with the aim of extracting the DNA’s sequence along the process. In this thesis I use computer simulations to create what are in essence virtual pro- totypes for testing design ideas for the improvement of nanopore translocation devices. These ideas are based on the general concept of modifying the average shape of the initial DNA conformations. This is done, for example, by introducing new geometrical features to the nanopore’s surrounding or by the means of some external force. The goal of these simulations is not just to test design improvements, but also to systematically deconstruct the physical mechanisms involved in the translocation process. The roles of pore friction, initial polymer conformations, monomer crowding on the trans- side of the membrane, Brownian fluctuations, and polymer rigidity can, with careful consideration, be essentially muted at will. Computer simulations in this sense play the role of a sandbox in which the physics can be tinkered with, in order to assess and evaluate the magnitude of certain approximations found in theoretical modelling of translocation. This enables me to construct theoretical models that contain the necessary features pertaining to the different designs tested by simulations. The work presented here is thus constituted of both Langevin Dynamics simulations and adaptations of the Tension-Propagation theory of polymer translocation when the polymer is subject to the various test conditions.

No description available.