Motivés par les développements récents dans le domaine des nanosciences, nous étudions les propriétés statistiques et thermodynamiques des systèmes mésoscopiques. En particulier, nous nous concentrons sur les résultats connus sous le nom de théorèmes de fluctuation. Ces relations donnent des prédictions sur le comportement de différents quantités dynamiques dans des situations loin de l'équilibre, tout en tenant compte des fluctuations de l'évolution temporelle. La première partie de notre étude est consacrée aux relations existants entre les fluctuations et la théorie de la réponse. Nous commençons par dériver une relation fonctionnelle pour les systèmes quantiques forcés dans le temps qui généralise l'égalité de Jarzynski et dont l'expansion en l'intensité du forçage permet de retrouver les résultats de la réponse linéaire. Nous poursuivons ensuite ces considérations en nous intéressant aux états stationnaires de non-équilibre. Ceci est réalisé dans le cadre des processus stochastiques, dans lequel nous dérivons une relation de fluctuation pour les courants de non-équilibre traversant le système. Cette relation lie explicitement les fluctuations aux forces thermodynamiques, ce qui nous permet de développer ses conséquences au niveau de la théorie de la réponse non-linéaire. De cette manière, nous obtenons de nouvelles relations liant fluctuations et coefficients de réponse dans le régime non-linéaire. Dans la deuxième partie de ce travail, nous développons une connexion récente liant l'irréversibilité au désordre dynamique. Nous présentons des résultats expérimentaux montrant que la production d'entropie s'exprime comme la différence de deux quantités mesurant la brisure de symétrie sous renversement du temps au niveau du désordre temporel. Nous étudions ensuite les conséquences de cette relation dans le contexte de l'énergétique du traitement de l'information. En particulier, nous présentons une généralisation du principe de Landauer pour l'effaçage d'information. De la même manière, nous relions la dissipation à la génération d'information par les entités biologiques.

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Mot bakgrund av de senaste decenniernas konjunktursvängningar i världsekonomin konstaterades det i Sverige att det fanns ett behov av att kunna möta dessa svängningar. Detta resulterade i den lagändring av Kommunallagen och Lagen om kommunal redovisning som erbjöd kommuner möjligheten till att införa en resultatutjämningsreserv i redovisningen. Denna resultatutjämningsreserv utgör ett periodiseringsverktyg där medel kan reserveras i goda tider för att sedan utnyttjas i sämre. Lagändringen är frivillig att anamma och har skapat en viss flexibilitet i kommunernas redovisning. Då kommuner har olika förutsättningar kan detta leda till att motiven till ställningstagandet kring ett införande av en resultatutjämningsreserv skiljer sig mellan kommuner. Uppsatsens syfte är att undersöka motiven till varför de valda kommunerna väljer att införa eller inte väljer att införa en resultatutjämningsreserv i redovisningen. Genom detta ämnar uppsatsen klargöra om motiven skiljer sig beroende på ekonomiska och demografiska omständigheter. En dokumentstudie genomfördes med syftet att kartlägga alla Sveriges 290 kommuners beslut rörande en resultatutjämningsreserv. Därefter valdes 40 kommuner ut till en faktorstudie för att kartlägga ekonomiska och demografiska omständigheter hos kommunerna. I ett sista skede av empiriinsamlingen intervjuades 20 av dessa 40 kommuner för att erhålla förståelse för motiven till att införa eller att inte införa en resultatutjämningsreserv. Studien visar på att kommuner som infört en resultatutjämningsreserv har samma motiv till detta som lagstiftarens intention, att möta konjunktur- svängningar. De kommuner som inte infört en resultatutjämningsreserv uppger mer spridda motiv. Motivet till att inte införa en resultatutjämningsreserv uppges vara att den leder till en inlåsning av egna medel eller att kommunen anser det onödig då kommunen har egna sätt att hantera konjunktursvängningars inverkan på ekonomin. Kommuner med mindre bra ekonomi uppger att motivet till att inte införa en resultatutjämningsreserv är att man i första hand behöver konsolidera ekonomin innan en sådan reserv kan bli aktuellt. Utifrån denna studie går det inte att se att större kommuner generellt har infört en resultatutjämningsreserv, vilket talar emot studien som Falkman et al genomfört om att större kommuner i större utsträckning anammar nya redovisningsregler. Denna avvikelse från teorin kan förklaras av frivilligheten i lagstiftningen samt den ickeexisterande praxis och rekommendationer gällande en resultat- utjämningsreserv. / Due to the last decades’ fluctuations in the world economy, it was pointed out that municipalities in Sweden needed a way to handle these fluctuations. This resulted in a change in the law of municipalities which made it possible for municipalities to implement a regulatory reserve in the accounting. This regulatory reserve is an accrual tool where funds can be reserved in good times in order to be used in worse. This legislative change has brought flexibility in to the accounting of the municipalities. Because of the different conditions in the municipalities, the motives to implement this voluntary regulatory reserve can differ among them. The study aims to examine the reasons why the chosen municipalities choose to implement or not to implement a regulatory reserve in their accounting. Through this, the study intends to clarify if the motives differ among the municipalities due to economic and demographic circumstances. A document analysis was carried out with the purpose to visualize all the municipalities of Sweden, regarding their decision to implement or not implement a regulatory reserve. After that, 40 municipalities were selected to be a part of a factor analysis in order to understand the economic and demographic circumstances in the municipalities. In a final stage of the empirical data collection, 20 of these 40 municipalities were interviewed to obtain information about the motives to implement or not to implement a regulatory reserve. The study shows that municipalities that have implemented a regulatory reserve have the same motives as the intention of the law, to meet economic fluctuations. The municipalities that haven’t implemented a regulatory reserve declare more varying motives. The motives to not implement a regulatory reserve are for instance that it leads to a locked-in effect of equity or that the municipalities can handle the fluctuations in the economy by themselves. Municipalities with less good economy declare that the motive to not implement a regulatory reserve is that they primarily focus is to consolidate their economy before it is possible to create a reserve. According to this study, it is not possible to say that bigger municipalities have implemented a regulatory reserve, which not is in accordance with the study done by Falkman et al that states that bigger municipalities tend to embrace new accounting rules. This deviation from this theory can be explained by the voluntary attribute of the law and also the non- existing practice and recommendation about a regulatory reserve.

This thesis is a partial investigation of instabilities in the interstellar gas which are driven by a coupling between the ambient radiation field and the gas, and which do not arise when this coupling is missed out. The modes of couplings considered are, firstly, the attenuation of the radiation with the concomitant effects on the temperature, density and composition of the gas, in various combinations. Secondly, velocity dependent effects are examined in various circumstances and thirdly, radiation pressure, not included in the other two, is looked at in the simple case in which temperature and compositional changes are excluded. The explanation of why these instabilities may be of interest, and an outline of the extent to which similar instabilities have been investigated, is given in Chapter 1. Chapter 2 gives details of the basic equations used in the case in which the absorption line shape is ignored. Many of the equations are used in the other chapters. The equations are linearised in perturbations of the density, temperature, radiation field and composition, and the resulting dispersion relationship is found for a harmonic perturbation. Because of the attenuation term in the radiative transfer equation, the polynomial has complex coefficients. In Chapter 3 we investigate the properties of the roots of a complex polynomial by an extension of Routh's methods, and derive a set of criteria to determine the number of roots which have positive real part. These roots correspond to exponentially growing perturbations, or, in other words, they correspond to instabilities. Later in the chapter we apply these methods to Field's dispersion relationship for thermal instabilities and derive many of his conclusions in a fairly simple way. By a slight extension the method yields estimates of the growth times of the instabilities. Some related situations are also examined in a similar way. After the detour of Chapter 3, Chapter 4 gives details of some models of the heating and cooling of the interstellar gas as well as of the reactions to be considered, namely the formation and destruction of H₂ and of carbon ions. Some of the limitations of the models are also discussed and the roots of the dispersion relation are given for different values of the parameters. New instabilities do appear; for H₂ their timescales of growth are rather too long to be of interest; for carbon no short timescale instabilities are discovered. Chapter 5 gives similar details for a system of pure hydrogen gas which may be of interest in studies of the formation of the first generation of stars. In Chapter 6 there is a criticism of an earlier work by Schatzman on a similar subject, in which it is shown that his analysis was wrong. Chapter 7 deals with a new possibility, namely that, as the gas moves, photons will be seen to be shifted in frequency and so the molecules will be exposed to a new set of destructive photons at frequencies which have not been selectively absorbed in the unperturbed gas. First the simplest case, that in which the temperature is unperturbed, is treated analytically. The attenuation of the radiation field is not considered. The effectiveness of this doppler-induced effect depends upon both the absorption profile and the radiation spectrum; these factors as well as temperature perturbations are included next. Both line absorption and continuum absorption are considered. The former is used to investigate the stability of the interstellar gas and of pure hydrogen gas, where hydrogen molecules are dissociated by line absorption; the latter is used in connection with HII regions and also the interstellar gas where the photodissociated species are hydrogen atoms and neutral carbon respectively. Radiation pressure was not included in the previous chapters but in Chapter 8 a modified version of Field's theory of instabilities driven by radiation pressure is presented. The new feature is that the frequency dependence of the absorption coefficient is included in the equations and this, in the case of a flat radiation spectrum, leads to an exact cancellation of the dominant term in Field's equation. Several restrictive features of Field's conclusions are thus modified and seem to make this instability rather more useful in the study of instabilities in the interstellar gas than it appeared in Field's work.

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Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Siu-Tat Chui, Dept. of Physics & Astronomy. Includes bibliographical references.

An interaction by exchange with the conditional mean (IECM) micromixing model is coupled to a three-dimensional single-particle Lagrangian stochastic (LS) model to estimate concentration fluctuations in plumes of a passive (i.e., non-buoyant), non-reactive (i.e., no chemistry) tracer dispersing from a variety of source configurations in four neutrally stratified flows: a horizontally-homogeneous wall shear layer flow; a horizontally-homogeneous representation of the Tombstone canopy flow; a three-dimensional inhomogeneous representation of the Tombstone canopy flow; and a three-dimensional inhomogeneous representation of the Mock Urban Setting Trials (MUST) canopy flow. The IECM micromixing model incorporates the combined effects of turbulent and molecular mixing on particle concentration. This allows the numerical estimation of all moments of the scalar concentration field, which is a significant advance over traditional LS models given that concentration fluctuations are a ubiquitous feature of a dispersing plume. The single-particle implementation of the LS-IECM model is based upon a previously reported implementation that used simultaneously computed particle trajectories to estimate the conditional mean concentration field [Cassiani, M. A., Franzese, P. A. and Giostra, U. A.: 2005, A PDF micromixing model of dispersion for atmospheric flow. Part I: development of model, application to homogeneous turbulence and to a neutral boundary layer, Atmospheric Environment 39, 1457-1469]. The model used in this thesis pre-calculates the conditional mean concentration field with an LS model for use with the IECM model, which runs as a separate simulation. The principal advantage of this single-particle approach is the performance increase on parallel computer architecture, which scales directly with the number of processors. The simulations presented in this thesis go beyond those performed with the previous model by considering three-dimensional inhomogeneous flows, as well as one-dimensional horizontally-homogeneous flows. The accuracy of the LS-IECM model was good for the flows with horizontal-homogeneity, and comparable to the results of previous simulations from older models. Rogue velocities in the simulations utilising inhomogeneous flow statistics resulted in acceptable to poor accuracy in these simulations. Suggestions for improvements to the model are made.

Wir untersuchen, welchen Einfluss die Verankerung von langen, hydrophilen Polymeren in Lipidmembranen auf deren elastische Eigenschaften ausübt. Theoretisch werden zwei Grenzbereiche für die spontane Krümmung der Membran erwartet: <br /> i) bei kleinen Oberflächenkonzentrationen des Polymers (Pilzgebiet) sollte die spontane Krümmung linear von der Oberflächendichte des verankerten Polymers abhängen;<br /> ii) bei hoher Bedeckung (Bürstengebiet) sollte die Abhängigkeit quadratisch sein. Wir versuchen, Vorhersagen für das Bürstengebiet zu prüfen, indem wir die morphologischen Veränderungen beobachten, die bei Riesen (Giant)- Vesikeln hervorgerufen werden. <br /> <br /> Als lange Polymere verwenden wir fluoreszenzmarkierte &#955;-Phage DNA Moleküle, die durch eine Biotin-Avidin-Biotin Verbindung an biotinhaltigen Lipidvesikeln befestigt sind. Wir kontrollieren die Oberflächenkonzentration der Anker durch Variation der Menge an biotinhaltigem Lipid in der Membran. Die Menge der an der Membran verankerten DNA wird durch Fluoreszenzmessungen quantifiziert. Änderungen in den elastischen Eigenschaften der Membran bei Anbindung der DNA, werden über eine Analyse der Vesikel-Fluktuationen kontrolliert. Die spontane Krümmung der Membran steigt mit der Oberflächenbeladung. Bei höheren Verankerungen bilden die Vesikel Knospen (budding). Die Größe der Knospen kann ebenfalls zur Bestimmung der Krümmung der Membran verwendet werden. Der Einfluss auf die Biegesteifigkeit ist Thema weiterer Untersuchungen. / We study the effect on the elastic properties of lipid membranes induced by anchoring of long hydrophilic polymers. Theoretically, two limiting regimes for the membrane spontaneous curvature are expected : <br /> i) at low surface polymer concentration (mushroom regime) the spontaneous curvature should scale linearly with the surface density of anchored polymers; <br /> ii) at high coverage (brush regime) the dependence should be quadratic. We attempt to test the predictions for the brush regime by monitoring the morphological changes induced on giant vesicles.<br /> <br /> As long polymers we use fluorescently labeled &#955;-phage DNA molecules which are attached to biotinylated lipid vesicles with a biotin-avidin-biotin linkage. By varying the amount of biotinylated lipid in the membrane we control the surface concentration of the anchors. The amount of anchored DNA to the membrane is quantified with fluorescence measurements. Changes in the elastic properties of the membrane as DNA grafts to it are monitored via analysis of the vesicle fluctuations. The spontaneous curvature of the membrane increases as a function of the surface coverage. At higher grafting concentrations the vesicles bud. The size of the buds can also be used to assess the membrane curvature. The effect on the bending stiffness is a subject of further investigation.

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