Discrete Velocity Models for Mixtures Without Nonphysical Collision Invariants

An important aspect of constructing discrete velocity models (DVMs) for the Boltzmann equation is to obtain the right number of collision invariants. It is a well-known fact that DVMs can also have extra collision invariants, so called spurious collision invariants, in plus to the physical ones. A DVM with only physical collision invariants, and so without spurious ones, is called normal. For binary mixtures also the concept of supernormal DVMs was introduced, meaning that in addition to the DVM being normal, the restriction of the DVM to any single species also is normal. Here we introduce generalizations of this concept to DVMs for multicomponent mixtures. We also present some general algorithms for constructing such models and give some concrete examples of such constructions. One of our main results is that for any given number of species, and any given rational mass ratios we can construct a supernormal DVM. The DVMs are constructed in such a way that for half-space problems, as the Milne and Kramers problems, but also nonlinear ones, we obtain similar structures as for the classical discrete Boltzmann equation for one species, and therefore we can apply obtained results for the classical Boltzmann equation.

Story Driven Web Applications

Kern der vorliegenden Arbeit ist die Modellierung komplexer Webapplikationen mit dem Story-Driven-Modeling Ansatz.Ziel ist es hierbei,die komplette Applikation allein durch die Spezifikation von Modellen zu entwickeln. Das händische Erstellen von Quelltext ist nicht notwendig. Die vorliegende Arbeit zeigt sowohl den Forschungsweg, der die angestrebte Modellierung von Webapplikationen ermöglicht, als auch die resultierenden Ergebnisse auf. Zur Unterstützung des Entwicklungsprozesses wird weiterhin ein modellgetriebener Softwareentwicklungsprozess vorgestellt, der die Modellierung einer Webapplikation von der Aufnahme der Anforderungen, bis zur abschließenden Erzeugung des Quelltextes durch Codegenerierung aus den spezifizierten Modellen, abdeckt. Für den definierten Prozess wird ferner Werkzeugunterstützung innerhalb der Fujaba Toolsuite bereitgestellt. Im Rahmen der vorliegenden Arbeit wurde die bestehede Toolsuite hierzu um alle zur Prozessunterstützung notwendigen Werkzeuge erweitert. Darüber hinaus wurden im Rahmen der vorliegenden Arbeit die in Fujaba bestehenden Werkzeuge erweitert, um neben den klassischen Möglichkeiten zur Modellierung komplexer Java-Applikationen auch die Erzeugung von Webapplikationen zu ermöglichen. Neben der genauen Beschreibung des Entwicklungsprozesses werden im Rahmen dieser Arbeit die entstehenden Webapplikationen mit ihren spezifischen Eigenschaften genau beschrieben. Zur Erzeugung dieser Applikationen wird neben dem Entwicklungsprozess die Diagrammart der Workflowdiagramme eingeführt und beschrieben. Diese Diagramme dienen der Abbildung des intendierten Userworkflows der Applikation im Rahmen der Anforderungsanalyse und stellen im weiteren Entwicklungsverlauf ein dediziertes Entwicklungsartefakt dar. Basierend auf den Workflowdiagrammen werden sowohl die grafische Benutzerschnittstelle der Webapplikation beschrieben, als auch ein Laufzeitsystem initialisiert, welches basierend auf den im Workflowdiagramm abgebildeten Abläufen die Anwendung steuert. Dieses Laufzeitsystem wurde im Rahmen der vorliegenden Arbeit entwickelt und in der Prozessunterstützung verankert. Alle notwendigen Änderungen und Anpassungen und Erweiterungen an bereits bestehenden Teilen der Fujaba Toolsuite werden unter dem Aspekt der Erstellung clientseitiger Datenmodelle einer Webapplikation genau beschrieben und in Verbindung mit den zu erfüllenden Voraussetzungen erläutert. In diesem Zusammenhang wird ebenfalls beschrieben, wie Graphtransformationen zur Umsetzung von Businesslogik auf der Clientseite einer Webapplikation eingesetzt werden können und auf welche Weise Datenmodelländerungen zwischen unterschiedlichen Clients synchronisiert werden können. Insgesamt zeigt die vorliegende Arbeit einen Weg auf, den bestehenden Ansatz des StoryDriven-Modeling für die Erzeugung von Webapplikationen einzusetzen. Durch die im Rahmen dieser Arbeit beschriebene Herangehensweise werden hierbei gleichzeitig Webbrowser zu einer neuen Klasse von Graphersetzungs-Engines erweitert, indem Graphtransformationen innerhalb der Ajax-Engine des Browsers ausgeliefert und ausgeführt werden.

A next-to-leading order calculation of the impact of primordial magnetic fields into cosmological observables

In this thesis, we perform a next-to-leading order calculation of the impact of primordial magnetic fields (PMF) into the evolution of scalar cosmological perturbations and the cosmic microwave background (CMB) anisotropy. Magnetic fields are everywhere in the Universe at all scales probed so far, but their origin is still under debate. The current standard picture is that they originate from the amplification of initial seed fields, which could have been generated as PMFs in the early Universe. The most robust way to test their presence and constrain their features is to study how they impact on key cosmological observables, in particular the CMB anisotropies. The standard way to model a PMF is to consider its contribution (quadratic in the magnetic field) at the same footing of first order perturbations, under the assumptions of ideal magneto-hydrodynamics and compensated initial conditions. In the perspectives of ever increasing precision of CMB anisotropies measurements and of possible uncounted non-linear effects, in this thesis we study effects which go beyond the standard assumptions. We study the impact of PMFs on cosmological perturbations and CMB anisotropies with adiabatic initial conditions, the effect of Alfvén waves on the speed of sound of perturbations and possible non-linear behavior of baryon overdensity for PMFs with a blue spectral index, by modifying and improving the publicly available Einstein-Boltzmann code SONG, which has been written in order to take into account all second-order contributions in cosmological perturbation theory. One of the objectives of this thesis is to set the basis to verify by an independent fully numerical analysis the possibility to affect recombination and the Hubble constant.

Classificazione spettrale delle stelle

In questo elaborato che conclude il Corso di Laurea in Astronomia vengono presentate le classificazioni spettrali di Harvard e di Yerkes, osservando anche i motivi per cui storicamente assumono il loro aspetto. Vengono poi analizzati i processi fisici che danno forma agli spettri permettendo di caratterizzarli gli uni dagli altri. In conclusione vengono osservate le tecniche osservative necessarie all'analisi dei dati.

Determination of local density of states in amorphous oxide semiconductors with Kelvin Probe Force Microscopy

Amorphous semiconductors are important materials as they can be deposited by physical deposition techniques on large areas and even on plastic substrates. Therefore, they are crucial for transistors in large active matrices for imaging and transparent wearable electronics. The most widely applied candidate for amorphous thin film transistors production is Indium Gallium Zinc Oxide (IGZO). It is attracting much interest because of its optical transparency, facile processing by sputtering deposition and notable improved charge carrier mobility with respect to hydrogenated amorphous silicon a-Si:H. Degradation of the device and long-term performance issues have been observed if IGZO thin film transistors are subjected to electrical stress, leading to a modification of IGZO channel properties and subthreshold slope. Therefore, it is of great interest to have a reliable and precise method to study the conduction band tail, and the density of states in amorphous semiconductors. The aim of this thesis is to develop a local technique using Kelvin Probe Force Microscopy to study the evolution of IGZO DOS properties. The work is divided into three main parts. First, solutions to the non-linear Poisson-Boltzmann equation of a metal-insulator-semiconductor junction describing the charge accumulation and its relation to DOS properties are elaborated. Second macroscopic techniques such as capacitance voltage (CV) measurements and photocurrent spectroscopy are applied to obtain a non-local estimate of band-tail DOS properties in thin film transistor samples. The third part of my my thesis is dedicated to the KPFM measurements. By fitting the data to the developed numerical model, important parameters describing the amorphous conduction band tail are obtained. The results are in excellent agreement with the macroscopic characterizations. KPFM result is comparable also with non-local optoelectronic characterizations, such as photocurrent spectroscopy.

Dinamica delle galassie a spirale e delle galassie ellittiche

La Dinamica Stellare è la disciplina che si occupa di descrivere la struttura e l'evoluzione dei sistemi stellari. Quest'elaborato si pone come obiettivo quello di illustrare una panoramica sui modelli e le tecniche necessari allo studio dei moti delle stelle all'interno delle galassie, per poi tradurli in pratica tramite applicazioni alle due tipologie principali di galassie. Dopo aver introdotto le principali caratteristiche delle galassie attraverso la Classificazione di Hubble, verrà affrontata la peculiarità di questi sistemi, ovvero la non collisionalità, introducendo il concetto di Tempo di Rilassamento a due corpi. In seguito, si illustreranno le equazioni che permettono di descrivere un sistema non collisionale, ovvero l'Equazione di Boltzmann e le Equazioni di Jeans, con conseguente caratterizzazione del Teorema del Viriale per questo tipo di sistemi. In conclusione, si approfondirà dapprima la dinamica delle galassie ellittiche attraverso lo studio della loro anisotropia, del profilo di brillanza e del Piano Fondamentale; successivamente, per quanto concerne le galassie a spirale, si tratterà la Curva di Rotazione, la Legge di Tully Fisher che ne descrive la luminosità e si terminerà con una descrizione della dinamica dei bracci a spirale attraverso la teoria delle Onde di Densità di Lin e Shu.

Teorema del viriale e applicazioni astrofisiche

Il teorema del viriale esprime una delle relazioni più importanti e utilizzate in astrofisica. In questo elaborato il teorema del viriale viene dimostrato in maniera classica per un generico sistema di N corpi, evidenziando in particolare la forma che esso assume in sistemi autogravitanti. Successivamente si forniscono alcune generalizzazioni del teorema e si mostra come esso possa essere dedotto dall’equazione non collisionale di Boltzmann grazie al concetto di funzione di distribuzione. Nella seconda parte della tesi si discutono alcune implicazioni del teorema del viriale per sistemi autogravitanti, quali il meccanismo di Kelvin-Helmholtz nelle stelle e la catastrofe gravotermica negli ammassi globulari. Infine si utilizza il teorema del viriale tensoriale per spiegare come forma, rotazione e anisotropia siano tra loro legate nelle galassie ellittiche.