Conventional coupling paradigms used nowadays to couple various physics components in reactor analysis problems can be inconsistent in their treatment of the nonlinear terms. This leads to usage of smaller time steps to maintain stability and accuracy requirements thereby increasing the computational time. These inconsistencies can be overcome using better approximations to the nonlinear operator in a time stepping strategy to regain the lost accuracy. This research aims at finding remedies that provide consistent coupling and time stepping strategies with good stability properties and higher orders of accuracy. Consistent coupling strategies, namely predictive and accelerated methods, were introduced for several reactor transient accident problems and the performance was analyzed for a 0-D and 1-D model. The results indicate that consistent approximations can be made to enhance the overall accuracy in conventional codes with such simple nonintrusive techniques. A detailed analysis of a monoblock coupling strategy using time adaptation was also implemented for several higher order Implicit Runge-Kutta (IRK) schemes. The conclusion from the results indicate that adaptive time stepping provided better accuracy and reliability in the solution fields than constant stepping methods even during discontinuities in the transients. Also, the computational and the total memory requirements for such schemes make them attractive alternatives to be used for conventional coupling codes.

This research focuses on the modeling of dendrimer molecules for their application as delivery vectors within drug and gene therapy systems. We examine how the architecture and composition of dendrimers affect their drug and gene binding efficacies along with their interactions with anionic bilayers. We specifically focus on how the weakly basic nature of dendrimer monomers and the addition of neutral grafts to dendrimer surface groups affect their interactions with drugs, linear polyelectrolytes, and bilayers. By using polymer self-consistent field theory (SCFT) to model such systems, we develop a computationally efficient means to provide physical insights into these systems, which are intended to guide dendrimer design for delivery applications.We study the conformational properties of weakly basic (annealed) polyelectrolyte dendrimers by developing a SCFT model that explicitly accounts for the acid-base equilibrium reaction of the weakly basic monomers. We specifically focus on the role of local counterion concentration upon the charge and conformations of the annealed polyelectrolyte dendrimers. We compare our results to existing polymer scaling theories and develop a strong stretching theory for the dendrimer molecules.We extend the previous study to model the interactions between weakly basic dendrimers and weakly acidic, hydrophobic drug molecules. We specifically examine the effects of excluded volume, electrostatic, and enthalpic interactions on the binding efficacies between dendrimers and drugs under a variety of dendrimer generations, solution pOH conditions, drug sizes, and Bjerrum length values.We study the role of neutral dendrimer grafts on the conformations and drug binding efficacies of dendrimers. We then elucidate how the observed conformational changes affect the charge of the dendrimers. Furthermore, we examine how the presence of grafts affects the steric, electrostatic, and hydrophobic interactions between the drugs and dendrimers under a variety of solution conditions. We compare our results with the binding efficacies observed for non-grafted dendrimers to delineate the conditions under which the grafted dendrimers are better suited as drug hosts.We include semi-flexible, anionic linear polyelectrolyte (LPE) molecules in our grafted dendrimer SCFT framework to model the interactions between dendrimers and negatively charged genetic materials. Specifically, we examine how neutral dendrimer grafts, LPE stiffness, and solution pOH affect the interactions between dendrimers and LPEs. We then use our SCFT potential fields as input into Monte Carlo simulations in order to determine the dendrimer-LPE potentials of mean force and the resulting loop and tail statistics of the dendrimer-adsorbed LPE chains.We incorporate a negatively charged bilayer into our grafted dendrimer SCFT framework to model dendrimer interactions with a cellular membrane. We specifically examine the role of dendrimer grafting length, solution pH, and membrane tension on such interactions. By comparing our results with SCFT calculations of fixed dendrimer conformations and hard sphere nanoparticles in the presence of membranes, we delineate the role of dendrimer flexibility and porosity on the interactions between dendrimers and anionic bilayers. / text

Ο κύριος σκοπός της παρούσας εργασίας είναι να συγκεντρωθούν συγκεκριμένες θεωρήσεις που χρησιμοποιούν τον φορμαλισμό των συνεπών ιστοριών σε βασικά προβλήματα της κβαντικής θεωρίας και κβαντικής κοσμολογίας. Ο φορμαλισμός αυτός είναι πολλά υποσχόμενος για τον τομέα της κανονικής κβαντικής βαρύτητας. Ο λόγος που θα κάνουμε αυτή την ανασκόπηση είναι για να δώσουμε μία ενοποιημένη εικόνα στα ζητήματα αυτά και να μπορέσουμε να τα συγκρίνουμε. Συγκεκριμένα, το πρώτο μέρος αφορά δύο διαφορετικές προσεγγίσεις για το πρόβλημα του χρόνου άφιξης στην κβαντομηχανική, εκ των οποίων και οι δύο χρησιμοποιούν φορμαλισμό ιστοριών. Η πρώτη έγινε από τους Halliwell και Yearsly (2009) και η δεύτερη από τους Anastopoulo και Saviddou (2012). Από την σύγκριση αυτών καταλήγουμε στο συμπέρασμα ότι και οι δύο δίνουν μία αδρομερή μορφή της εξίσωσης του Kijowski. Το δεύτερο μέρος αφορά την κβαντική κοσμολογία. Σε αυτό αρχικά παρουσιάζεται μία προσέγγιση με συνεπείς ιστορίες για την πυκνότητα πιθανότητας στην κβαντική κοσμολογία η οποία έγινε από τον Halliwell (2009). Στην συνέχεια παρουσιάζεται μία προσέγγιση με ιστορίες για μοντέλα μίνι-υπερχώρου από τους Anastopoulo and Savidou (2005). Σε αυτή κατασκευάζονται μοντέλα μίνι-υπερχώρου με όρους προβολικών τελεστών ιστοριών (HPO). Η σπουδαιότητα αυτού του φορμαλισμού έγκειται στο γεγονός ότι η γενική σχετικότητα σε αυτή την μορφή ικανοποιεί και τους χωροχρονικούς διαφορομορφισμούς και την άλγεβρα Dirac, με αποτέλεσμα να είναι εύκολα κβαντίσιμη. / The major purpose of this study is to consecrate specific approaches to some problems of quantum theory and quantum cosmology, in terms of decoherence histories formalism which is a very promising formalism for the canonical quantum gravity theories. The reason is to give a unified picture to these issues in order to be possible to compare them. Specifically, the first part contains two different approaches to the time of arrival in quantum mechanics, both of these use a histories formalism. The first is from Halliwell and Yearsly (2009) and the second from Anastopoulos and Saviddou (2012). By comparing them we deduce that both of them first gives a coarse-grain form of the Kijowski' s probability distribution. The second part concerns quantum cosmology. In this, we presented a decoherent histories approach to quantum cosmological probabilities, in which was used a complex potential, from Halliwell (2009). After that we present a histories approach to minisuperspace models by Anastopoulos and Savidou (2005). In this, minisuperspace models is written in terms of histories projector operator (HPO) formalism. The spectacular of this is that in that form general relativity satisfies both spacetime diffeomorfisms and Dirac algebra, which is very important because it is easier to be quantized.

The area of ultrafast (sub-nanosecond) magnetization dynamics of ferromagnetic elements and thin films, usually driven by a strong femtosecond laser pulse, has experienced intense research interest. In this dissertation, laser-induced demagnetization is theoretically studied by taking into account interactions among electrons, spins, and lattice. We propose a microscopic approach under the three temperature framework and derive the equations that govern the demagnetization at arbitrary temperatures.To address the question of magnetization reversal at high temperatures, the conventional Landau-Lifshitz equation is obviously unsatisfactory, since it fails to describe the longitudinal relaxation. So by using the equation of motion for the quantum density matrix within the instantaneous local relaxation time approximation, we propose an effective equation that is capable of addressing magnetization dynamics for a wide range of temperatures. The longitudinal and transverse relaxations are analyzed, magnetization reversal processes near Curie temperatures is also studied. Furthermore, we compared our derived Self-consistent Bloch equation and Landau-Lifshitz-Bloch equation in detail. Finally, the demagnetzation dynamics for ferromagnetic and ferrimagnetic alloys is studied by solving the Self-consistent Bloch equation.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (p. 114-121).

A presente dissertação tem por objetivo discutir diferentes aspectos de um método de modelagem econômica conhecido por Modelos Stock-Flow Consistent (SFC). Essa classe de modelos tem como principais características a presença de matrizes que representam os balanços patrimoniais dos setores modelados, bem como os fluxos de transações e de fundos financeiros. A primeira etapa do trabalho consiste em analisar as origens dos modelos SFC, apresentando os trabalhos que precederam as primeiras formulações. Em seguida, é feito um survey completo da literatura SFC corrente. Essas duas etapas são realizadas através de uma revisão bibliográfica de artigos, working papers, teses e dissertações. A terceira etapa do trabalho consiste em discutir aspectos metodológicos da modelagem SFC, em especial a modelagem de equações comportamentais de expectativas. Por fim, um modelo SFC é elaborado com o objetivo de analisar o comportamento de uma economia sob quatro regimes fiscais diferentes: (i) balanço equilibrado; (ii) meta de gastos do governo como proporção do PIB; (iii) meta de déficit do governo como proporção do PIB; (iv) meta de dívida pública como proporção do PIB. O comportamento em estado estacionário desses regimes é analisado, bem como sua resiliência a choques. Entre as conclusões, percebeu-se que o segundo regime apresenta a maior taxa de crescimento no steady state, além de ser mais resiliente a choques negativos. / The general goal of this dissertation is to discuss different dimensions of a class of Post-Keynesian models known as Stock-Flow Consistent Models. The main features of these models are: (i) the presence of balance sheets matrices of the sectors to be modeled, guaranteeing the consistency in the economic stocks; (ii) the flow of funds matrix, that records the real and financial transactions of the economy. The first step of the work is to analyze the origins of the SFC models, presenting the works that preceded the first elaborations. Next to it, the current SFC literature is surveyed. These two steps are accomplished by means of a survey of the literature in academic journals, working papers, dissertations and thesis. The third step of the work is a discussion of methodological issues such as the role of expectations in the behavioral functions for consumption. Finally, the fourth step consists of elaborating a SFC model in order to analyze four fiscal policy regimes: (i) balanced budget, (ii) a target for government’s expenditures , (iii) a target for government deficit, and (iv) a target for government debt. The steady state behavior of each regime is analyzed, as well as its resilience to adverse shocks. The second regime is the one with the higher steady state growth rate and also is the more resilient to negative shocks.

This thesis presents work done on the calculation of the effects of anharmonic nuclear motion on the properties of solid materials from first principles. Such anharmonic effects can be significant in many cases. A vibrational self-consistent field (VSCF) method is used as the basis for these calculations, which is then improved and applied to a variety of solid state systems. Firstly, work done to improve the efficiency of the VSCF method is presented. The standard VSCF method involves using density functional theory (DFT) to map the Born-Oppenheimer (BO) energy surface that the nuclei move in, a computationally expensive process. It is shown that the accurate forces available in plane-wave basis DFT can be used to help map the BO surface more accurately and reduce the computational cost. This improved VSCF+f method is tested on molecular and solid hydrogen, as well as lithium and zirconium, and is found to give a speed-up of up to 40%. The VSCF method is then applied to two different systems of physical interest. It is first applied to the case of the neutral vacancy in diamond, in order to resolve a known discrepancy between harmonic ab initio calculations and experiment -- the former predict a static Jahn-Teller distortion, whilst the latter leads to a dynamic Jahn-Teller effect. By including anharmonic corrections to the energy and nuclear wavefunction, we show that the inclusion of these effects results in agreement between first-principles calculations and experiment for the first time. Lastly, the VSCF method is applied to barium titanate, a prototypical ferroelectric material which undergoes a series of phase transitions from around 400 K downwards. The nature of these phase transitions is still unclear, and understanding them is an active area of research. We describe the physics of the phase transitions of barium titanate, including both anharmonicity and the effect of polarisation caused by long wavelength vibrations, to help understand the important physics from first principles.

Na área de simulação de processos, existe uma visível tendência da migração das ferramentas seqüenciais modulares, que hoje são as mais amplamente utilizadas, para as baseadas em equações. Uma das principais vantagens do paradigma baseado em equações ou simultâneo é que este se mostra eficiente na solução de problemas de simulação, otimização, estimação de parâmetros e reconciliação de dados, todos baseados em um mesmo conjunto de modelos, evitando retrabalho de modelagem. Porém, a tecnologia simultânea também apresenta algumas deficiências, onde destacam-se os problemas de robustez tanto na modelagem quanto na obtenção de resultados numéricos. Este trabalho tem como objetivo reunir e desenvolver técnicas que permitam reduzir estas deficiências. Para tanto, as técnicas conhecidas para depuração de sistemas de equações que representam problemas estacionários e dinâmicos foram estudadas em detalhe. Pôde-se observar que para o caso estático os métodos disponíveis para depuração de modelos, já se apresentam em um nível bem desenvolvido. Já para o caso dinâmico, onde há uma maior complexidade, as técnicas conhecidas encontram-se em um nível de desenvolvimento muito menor. Neste ponto encontram-se as principais contribuições deste trabalho. / In the field of process simulation the movement from the sequential modular tools, which are currently the most widely used, to the equation based approach is clear. One of the key advantages of the equation based or simulatneous approach is that using a single model one can solve simulation, optimization, parameter estimation, and optimization problems. This fact avoids modeling rework for each application. However, the simultaneous technology has problems regarding modeling and solving robustness. This work aims to group and develop methods capable of minimize these deficiencies. In order to achieve this goal, available debugging approaches for both steady-state and dynamic system of equations were studied in detail. For the steady-state case well stablished debugging techniques are known. For dynamic models, where the complexity is higher, the analysis and debugging methods are much less mature. This was the source for the major contributions of this work.

Social networks tend to shape our views about the world. Our study conducts an empirical analysis of social network dynamics using Twitter data. We ask whether social networks influence voting decisions, and determine whether or not people make consistent choices based on their tweets or what they believe. We collect Twitter data on a daily basis, with dynamic social network measurements before, during, and after the 2012 Presidential election. We identify how people should believe based on their ideological profiles. We use lexicographical analysis to check if ideological key words are present in a user's tweets, and if the overall sentiment on this issue is positive or negative. We utilize this data to determine how people should have chosen an outcome which may conflict with an individual's observed declaration of political ideology. We are able to determine what percentage of the population made a consistent choices based on their Tweets during the 2012 presidential election. Additionally, we examine the social network structure in Twitter and how it affects voting. We illustrate that an individual's political ideology is influenced by others in their network.\\ Consumer confidence is an economic indicator which measures the degree of optimism that consumers feel about the overall state of the economy as well as their personal financial situation. We will show that consumer sentiment can be measured via analysis of social networks. Specifically, we perform a lexicographic analysis of Twitter data over a three month period. After careful analysis, we find that not only does talk intensity of economic issues cause shifts in the daily stock market prices but has a significant negative affect.\\ The study of religion has enjoyed distinction and legitimacy within sociology, psychology, anthropology, and political science for many years. This paper concerns the extent to which economic opinion is embedded in structure of religious social relations. We hope to enhance the empirical study of homophily and the economics of behavior by showing how beliefs, norms, and values are affected by religion and, by extension, morals, and culture. We utilize a technique called cluster analysis to determine homophilic ties within a single attribute, religiosity. We see that religion affects economic attitudes and activities of individuals, groups, and societies. Further, religion influences how behavior and institutions are affected by social relations and in our case homophily. This influence is one of the classic questions of social theory.

A presente dissertação tem por objetivo discutir diferentes aspectos de um método de modelagem econômica conhecido por Modelos Stock-Flow Consistent (SFC). Essa classe de modelos tem como principais características a presença de matrizes que representam os balanços patrimoniais dos setores modelados, bem como os fluxos de transações e de fundos financeiros. A primeira etapa do trabalho consiste em analisar as origens dos modelos SFC, apresentando os trabalhos que precederam as primeiras formulações. Em seguida, é feito um survey completo da literatura SFC corrente. Essas duas etapas são realizadas através de uma revisão bibliográfica de artigos, working papers, teses e dissertações. A terceira etapa do trabalho consiste em discutir aspectos metodológicos da modelagem SFC, em especial a modelagem de equações comportamentais de expectativas. Por fim, um modelo SFC é elaborado com o objetivo de analisar o comportamento de uma economia sob quatro regimes fiscais diferentes: (i) balanço equilibrado; (ii) meta de gastos do governo como proporção do PIB; (iii) meta de déficit do governo como proporção do PIB; (iv) meta de dívida pública como proporção do PIB. O comportamento em estado estacionário desses regimes é analisado, bem como sua resiliência a choques. Entre as conclusões, percebeu-se que o segundo regime apresenta a maior taxa de crescimento no steady state, além de ser mais resiliente a choques negativos. / The general goal of this dissertation is to discuss different dimensions of a class of Post-Keynesian models known as Stock-Flow Consistent Models. The main features of these models are: (i) the presence of balance sheets matrices of the sectors to be modeled, guaranteeing the consistency in the economic stocks; (ii) the flow of funds matrix, that records the real and financial transactions of the economy. The first step of the work is to analyze the origins of the SFC models, presenting the works that preceded the first elaborations. Next to it, the current SFC literature is surveyed. These two steps are accomplished by means of a survey of the literature in academic journals, working papers, dissertations and thesis. The third step of the work is a discussion of methodological issues such as the role of expectations in the behavioral functions for consumption. Finally, the fourth step consists of elaborating a SFC model in order to analyze four fiscal policy regimes: (i) balanced budget, (ii) a target for government’s expenditures , (iii) a target for government deficit, and (iv) a target for government debt. The steady state behavior of each regime is analyzed, as well as its resilience to adverse shocks. The second regime is the one with the higher steady state growth rate and also is the more resilient to negative shocks.