Дисертації з теми "First order dynamic"

The relationship between symbolicism and connectionism has been one of the major issues in recent Artificial Intelligence research. An increasing number of researchers from each side have tried to adopt desirable characteristics of the other. These efforts have produced a number of different strategies for interfacing connectionist and symbolic AI. One of them is <I>connectionist and symbol processing</I> which attempts to replicate symbol processing functionalaties using connectionist components. In this direction, this thesis develops a connectionist inference architecture which performs standard symbolic inference on a subclass of first-order predicate calculus. Our primary interest is in understanding how formulas which are described in a limited form of first-order predicate calculus may be implemented using a connectionist architecture. Our chosen knowledge representation scheme is a subset of <I>first-order Horn clause expressions</I> which is a set of universally quantified expressions in first-order predicate calculus. As a focus of attention we are developing techniques for <I>compiling</I> first-order Horn clause expressions into a connectionist network. This offers practical benefits but also forces limitations on the scope of the compiled system, since we are, in fact, merging an <I>interpreter</I> into the connectionist networks. The compilation process has to take into account not only first-order Horn clause expressions themselves but also the strategy which we intend to use for drawing inferences from the. Thus, this thesis explores the extent to which this type of a translation can build a connectionist inference model to accommodate desired symbolic inference. This work first involves constructing efficient connectionist mechanisms to represent symbol components, dynamic bindings, basic symbolic inference procedures, and devising a set of algorithms which automatically translates input descriptions to neural networks using the above connectionist mechanisms. These connectionist mechanisms are built by taking an existing temporal synchrony mechanism and extending it further to obtain desirable features to represent and manipulate basic symbol structures. The existing synchrony mechanism represents dynamic bindings very efficiently using temporal synchronous activity between neuron elements but it has fundamental limitations in supporting symbolic inference. The extension addresses these limitations.

During the last decade, the use of time scales as a means of unifying and extending results about various types of dynamic equations has proven to be both prolific and fruitful. Many classical results from the theories of differential and difference equations have time scale analogues. In this thesis we derive new oscillation criteria for second order dynamic equations on time scales.

This thesis is focused on state-of-art numerical optimization methods for nonlinear (discrete-time) optimal control. These challenging problems arise when dealing with complex tasks for autonomous systems (e.g. vehicles or robots) which require the generation of a trajectory that satisfies the system dynamics and, possibly, input and state constraints due to, e.g, actuator limits or safety region of operation. A general formulation is proposed that allows the implementation of different descent optimization algorithms on optimal control problems exploiting the beneficial effects of state feedback in terms of efficiency and stability. The main idea is the following: at each iteration a new (infeasible) state-input curve is conveniently updated by any descent method, e.g, gradient descent or Newton methods, then a nonlinear feedback controller maps the curve to a trajectory satisfying the dynamics. Thanks to its inherent flexibility, this strategy provides the opportunity to speed-up the resolution of optimization problems by conveniently choosing the descent method. This thesis proposes, for example, to exploit the Heavy-ball method to speed up the convergence. It is important to underline that this methodology enjoys recursive feasibility during the algorithm evolution, i.e. at each iteration a system trajectory is available. This feature is extremely important in real-time control schemes since it allows one to stop the algorithm at any iteration and yet have a (suboptimal) system trajectory. Furthermore, tasks which require the introduction of state and input constraints can be managed introducing an approximate barrier function which embeds the constraints within the cost function. The second main contribution of this thesis is an original Python toolbox developed in order to implement and compare different optimization methods. Moreover, thanks to a modular approach, with just few adjustments it is possible to change system, cost function and constraints.

The theory of dynamic equations on time scales provides an important bridge between the fields of differential and difference equations. It is particularly useful in describing phenomena that possess a hybrid continuous-discrete behaviour in their growth, like many temperate--2one insect populations and crops. A dynamic equation on a time scale is a generalised. 'two-in-one' model, it serves as a differential equation for purely continuous domains and as a difference equation for purely discrete ones. The field of "dynamic equations on time scales" is about 20 years old. As such, much of the basic (yet very important) linear theory has been established, however the non-linear extensions are yet to be fully developed. This thesis aims to fill this gap by providing the foundational framework of non-linear results from which further lines of inquiry can be launched. This thesis answers several important questions regarding the qualitative and quantitative properties of solutions to non-linear dynamic equations on time scales. Namely, (i) When do solutions exist? (ii) If solutions exist, then are they unique? (iii) How can such solutions be closely approximated? (iv) How can we explicitly solve certain problems to extract their solutions? The methods employed to address the above questions include: dynamic inequalities; iterative techniques and the method of successive approximations; and the fixed point approaches of Banach and Schauder.

The field of physical modelling and simulation plays a vital role in advancing numerous scientific and engineering disciplines. To cope with the increasing size and complexity of physical models, a number of modelling and simulation languages have been developed. These languages can be divided into two broad categories: causal and noncausal. Causal languages express a system model in terms of directed equations. In contrast, a noncausal model is formulated in terms of undirected equations. The fact that the causality can be left implicit makes noncausal languages more declarative and noncausal models more reusable. These are considered to be crucial advantages in many physical domains. Current, mainstream noncausal languages do not treat equational models as first-class values; that is, a model cannot be parametrised on other models or generated at simulation runtime. This results in very limited higher-order and structurally dynamic modelling capabilities, and limits the expressiveness and applicability of noncausal languages. This thesis is about a novel approach to the design and implementation of noncausal languages with first-class models supporting higher-order and structurally dynamic modelling. In particular, the thesis presents a language that enables: (1) higher-order modelling capabilities by embedding noncausal models as first-class entities into a functional programming language and (2) efficient simulation of noncausal models that are generated at simulation runtime by runtime symbolic processing and just-in-time compilation. These language design and implementation approaches can be applied to other noncausal languages. This thesis provides a self-contained reference for such an undertaking by defining the language semantics formally and providing an in-depth description of the implementation. The language provides noncausal modelling and simulation capabilities that go beyond the state of the art, as backed up by a range of examples presented in the thesis, and represents a significant progress in the field of physical modelling and simulation.

The equiatomic FeRh alloy undergoes a first-order phase transition from an antiferromagnetic (AFM) to a ferromagnetic (FM) state at about 370 K with a small thermal hysteresis of about 10 K around the phase transition. The transition is accompanied by a unit cell volume expansion about 1% in the c lattice parameter. During the transition the new phase nucleates in the matrix of the original phase by reaching the critical temperature followed by a growth in size upon increasing temperature further. Therefore, to understand the transition process with more details, it is desirable to investigate the nucleation and growth of both phases within the first order phase transition. In the present thesis the main focus is on the growth of FeRh thin films by means of Molecular Beam Epitaxy (MBE) technique and characterization of the magnetic and structural properties. To develop an understanding of the phase transformation in FeRh thin films the ways in which one can tune it were investigated. The following aspects concerning the FeRh system have been examined here: 1) influence of annealing temperature on the magnetic and structural response, 2) effect of film thickness on the first-order phase transition temperature as well as the saturation magnetization, 3) influence of chemical composition on the magnetic properties and 4) magnetic field-induced phase transition. To get insight to details of the transition process the magnetization dynamic has been addressed by performing Ferromagnetic resonance (FMR) experiment across the phase transition. FMR measurements determined the existence of two areas with different magnetic properties inside the film. A huge temperature difference for the beginning of the phase transition in comparison with the static magnetization measurement was observed for the equiatomic FeRh thin film prepared by MBE. Tuning of the AFM to FM phase transition in the FeRh thin film by means of low-energy/low fluence Ne+ ion irradiation was studied. Ion irradiation technique offers a quantitative control of the degree of chemical disorder by adjusting the ion fluence applied, while the penetration depth of the disordered phase can be adjusted by the ion-energy. The main results of ion irradiation are the shifting of the phase transition temperature to lower temperature and irradiation with 3×1014 ion/cm2 leads to the disappearance the AFM phase completely.

This study is concerned with the development and implementation of a preconditioner for a set of hyperbolic partial differential equations resulting from a new 5-moment closure for the prediction of gas flows both in and out of local equilibrium. This new 5-moment closure offers a robust and efficient system of first-order hyperbolic partial differential equations that has proven to provide an accurate treatment of one-dimensional gases, both in and for significant departures from local thermodynamic equilibrium. However, numerical computations using this model have proven to be difficult as a result of a singularity in the closing flux of the system. This also causes infinitely large wavespeeds in the system. The main goal of this work is to mitigate these numerical issues. Since the solution of a hyperbolic system is characterized by the waves of the system, one could suggest to scale these wavespeeds to remove the arbitrarily large speeds without altering the solution of the system. To accomplish this, this work starts with a detailed study of the behaviour of the system’s wavespeeds, given by the eigenvalues of the flux Jacobian of the system. Since, it is not possible to solve for these eigenvalues explicitly, it is suggested to approximate them by interpolation between the few states at which these waves can be solved for explicitly. With an estimate for the wavespeeds, the nature of the singularity in the system can be analyzed mathematically. The results of this mathematical analysis are used to develop a preconditioner matrix to remove the singularity from the model. To implement the proposed preconditioned model numerically, a centred-difference scheme with artificial dissipation is proposed. A dual-time-stepping strategy is developed and implemented with implicit Euler time marching for both physical and pseudo time iteration. This dual-time treatment allows the preconditioned system to remain applicable to time-accurate problems and is found to greatly increase the robustness of the solution of the steady-state problems. Solutions to several canonical problems for both continuum and non-equilibrium flow are computed and comparisons are made to classical models.

Cette thèse porte sur l’expressivité de la logique du premier ordre et d’autres formalismes sur différentes classes de structures ordonnées, parmi lesquelles les MSC (Message Sequence Charts), un modèle standard pour les exécutions de systèmes concurrents avec échange de messages. Cette étude est motivée par deux questions classiques : celle de l’équivalence, pour certaines classes de structures, entre la logique du premier ordre et son fragment avec k variables, et celle de la comparaison entre automates et logique, dans l’esprit du théorème de Büchi-Elgot-Trakhtenbrot. Notre approche repose sur la logique dynamique propositionnelle sans étoile (PDL sans étoile), une variante de PDL équivalente à la logique du premier ordre avec 3 variables. On étudie d’abord l’expressivité de PDL sans étoile sur des structures linéairement ordonnées avec des prédicats unaires et binaires. On montre que sous certaines conditions de monotonie, PDL sans étoile devient aussi expressive que la logique du premier ordre. Cela implique que toute formule de la logique du premier ordre peut alors être réécrite en une formule équivalente qui utilise au plus 3 variables. Ce résultat s’applique, directement ou indirectement, à un certain nombre de classes naturelles, généralisant des résultats connus et répondant à des questions ouvertes.On se concentre ensuite sur les MSC, auxquels ce premier résultat s’applique également. PDL sans étoile nous permet d’aborder un autre problème important: celui de la synthèse d’automates communicants à partir de spécifications écrites en logique du premier ordre. Les automates communicants sont un modèle de systèmes concurrents dans lequel un nombre fixé d’automates finis échangent des messages via des canaux FIFO. Ils définissent des langages de MSC. Bien que des caractérisations de l’expressivité des automates communicants aient déjà été établies pour certaines restrictions (borne sur la taille des canaux de communications, ou omission de la relation “arrivé-avant” au niveau de la logique), la question suivante restait ouverte dans le cas général : toute formule du premier ordre sur les MSC peut-elle être traduite en un automate communicant équivalent ? On montre que c’est le cas, en utilisant PDL sans étoile comme langage intermédiaire<br>This thesis is concerned with the expressive power of first-order logic and other formalisms over different classes of ordered structures, among which MSCs (Message Sequence Charts), a standard model for executions of message-passing systems. This study is motivated by two classic problems: the k-variable property, that is, the equivalence of first-order logic and its k-variable fragment over certain classes of structures, and the study of logic-automata connections, in the spirit of Büchi-Elgot-Trakhtenbrot theorem. Our approach relies on star-free propositional dynamic logic (star-free PDL), a variant of PDL with the same expressive power as the 3-variable fragment of first-order logic. We start by studying the expressive power of star-free PDL over linearly ordered structures with unary and binary predicates. We show that under certain monotonicity conditions, star-free PDL becomes as expressive as first-order logic. This implies that any first-order formula can then be rewritten into an equivalent formula with at most 3 variables. This result applies to various natural classes of structures, generalizing several known results and answering some open questions.We then focus on MSCs, to which this first result also applies. We use star-free PDL to address another important problem: the synthesis of communicating finite-state machines (CFMs) from first-order specifications. CFMs are a model of concurrent systems in which a fixed number of finite-state automata communicate through unbounded FIFO channels. They accept languages of MSCs. While logical characterizations of the expressive power of CFMs have been established under different restrictions (bounding the size of the communication channels, or removing the “happened-before” relation from the logic), the following question had remained open in the general case: can every first-order formula over MSCs be translated into an equivalent CFM? We prove that this is the case, using star-free PDL as an intermediate language

Doktorska disertacija prezentuje nov i opštiji način analiziranja&nbsp;semantike strukturiranih i objektno orijentisanih programa i to&nbsp;isključivo u okvirima predikatske logike prvog reda. Doktorska&nbsp;disertacija razmatra sledeće teme:1.) S-programski račun,2.) Definicija i osobine dinamičkih postuslova u S-računu,3.) Konceptualne definicije objekta, klase i invarijante,4.) Analiza invarijanata u klasi (SP-analiza i DP-analiza).<br>Doctoral thesis presents a new and more general method for analizing of&nbsp;structured and object-oriented program semantics, based on the first-order&nbsp;predicate logic. Doctoral thesis consideres next topics:1.) S-program calculus,2.) Definition and characteristics of dynamic postconditions in S-calculus,3.) Conceptual definitions of object, class and invariant,4.) Analyses of invariants in class (SP-analyses and DP-analyses).

Les algorithmes convexes de résolution pour les régressions linéaires parcimonieuses possèdent de bonnes performances pratiques et théoriques. Cependant, ils souffrent tous des dimensions du problème qui dictent la complexité de chacune de leur itération. Nous proposons une approche pour réduire ce coût calculatoire au niveau de l'itération. Des stratégies récentes s'appuyant sur des tests d'élimination de variables ont été proposées pour accélérer la résolution des problèmes de régressions parcimonieuse pénalisées tels que le LASSO. Ces approches reposent sur l'idée qu'il est profitable de dédier un petit effort de calcul pour localiser des atomes inactifs afin de les retirer du dictionnaire dans une étape de prétraitement. L'algorithme de résolution utilisant le dictionnaire ainsi réduit convergera alors plus rapidement vers la solution du problème initial. Nous pensons qu'il existe un moyen plus efficace pour réduire le dictionnaire et donc obtenir une meilleure accélération : à l'intérieur de chaque itération de l'algorithme, il est possible de valoriser les calculs originalement dédiés à l'algorithme pour obtenir à moindre coût un nouveau test d'élimination dont l'effet d'élimination augmente progressivement le long des itérations. Le dictionnaire est alors réduit de façon dynamique au lieu d'être réduit de façon statique, une fois pour toutes, avant la première itération. Nous formalisons ce principe d'élimination dynamique à travers une formulation algorithmique générique, et l'appliquons en intégrant des tests d'élimination existants, à l'intérieur de plusieurs algorithmes du premier ordre pour résoudre les problèmes du LASSO et Group-LASSO<br>Applications in signal processing and machine learning make frequent use of sparse regressions. Resulting convex problems, such as the LASSO, can be efficiently solved thanks to first-order algorithms, which are general, and have good convergence properties. However those algorithms suffer from the dimension of the problem, which impose the complexity of their iterations. In this thesis we study approaches, based on screening tests, aimed at reducing the computational cost at the iteration level. Such approaches build upon the idea that it is worth dedicating some small computational effort to locate inactive atoms and remove them from the dictionary in a preprocessing stage so that the regression algorithm working with a smaller dictionary will then converge faster to the solution of the initial problem. We believe that there is an even more efficient way to screen the dictionary and obtain a greater acceleration: inside each iteration of the regression algorithm, one may take advantage of the algorithm computations to obtain a new screening test for free with increasing screening effects along the iterations. The dictionary is henceforth dynamically screened instead of being screened statically, once and for all, before the first iteration. Our first contribution is the formalisation of this principle and its application to first-order algorithms, for the resolution of the LASSO and Group-LASSO. In a second contribution, this general principle is combined to active-set methods, whose goal is also to accelerate the resolution of sparse regressions. Applying the two complementary methods on first-order algorithms, leads to great acceleration performances

Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2019<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 85-87).<br>Gradient based optimization algorithms are among the most fundamental algorithms in optimization and machine learning, yet they suffer from slow convergence. Consequently, accelerating gradient based methods have become an important recent topic of study. In this thesis, we focus on explaining and understanding the acceleration results. In particular, we aim to provide insights into the acceleration phenomenon and further develop new algorithms based on this interpretation. To do so, we follow the line of work on the continuous ordinary differential equation representations of momentum based acceleration methods. We start by proving that acceleration can be achieved by stable discretization of ODEs using standard Runge-Kutta integrators when the function is smooth enough and convex. We then extend this idea and develop a distributed algorithm for solving convex finite sum problems over networks. Our proposed algorithm achieves acceleration without resorting to Nesterov's momentum approach. Finally we generalize the result to functions that are quasi-strongly convex but not necessarily convex. We show that acceleration can be achieved in a nontrivial neighborhood of the optimal solution. In particular, the neighborhood can grow larger as the condition number of the function increases. The results altogether provide a systematic way to prove nonasymptotic convergence rates of algorithms derived from ODE discretization.<br>by Jingzhao Zhang.<br>S.M.<br>S.M. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

In dieser Arbeit wird das dynamische Auswertungsproblem über dynamische Datenbanken betrachtet, bei denen Tupel hinzugefügt oder gelöscht werden können. Die Aufgabe besteht darin einen dynamischen Algorithmus zu konstruieren, welcher unmittelbar nachdem die Datenbank aktualisiert wurde, die Datenstruktur, die das Resultat repräsentiert, aktualisiert. Die Datenstruktur soll in konstanter Zeit aktualisiert werden und das Folgende unterstützen: * Teste in konstanter Zeit ob ein Tupel zur Ausgabemenge gehört, * gebe die Anzahl der Tupel in der Ausgabemenge in konstanter Zeit aus, * zähle die Tupel aus der Ausgabemenge mit konstanter Taktung auf und * zähle den Unterschied zwischen der neuen und der alten Ausgabemenge mit konstanter Taktung auf. Im ersten Teil werden konjunktive Anfragen und Vereinigungen konjunktiver Anfragen auf relationalen Datenbanken betrachtet. Die Idee der q-hierarchischen Anfragen (und t-hierarchische Anfragen für das Testen) wird eingeführt und es wird gezeigt, dass das Resultat für jede q-hierarchische Anfrage auf dynamischen Datenbanken effizient in dem oben beschriebenen Szenario ausgewertet werden können. Konjunktive Anfragen mit Aggregaten werden weiterhin betrachtet. Es wird gezeigt, dass das Lernen von polynomiellen Regressionsfunktionen in konstanter Zeit vorbereitet werden kann, falls die Trainingsdaten aus dem Anfrageergebnis kommen. Mit logarithmischer Update-Zeit kann folgende Routine unterstützt werden: Bei Eingabe einer Zahl j, gebe das j-te Tupel aus der Aufzählung aus. Im zweiten Teil werden Anfragen, die Formeln der Logik erster Stufe (FO) und deren Erweiterung mit Modulo-Zähl Quantoren (FO+MOD) sind, betrachtet, und es wird gezeigt, dass diese effizient unter Aktualisierungen ausgewertet können, wobei die dynamische Datenbank die Gradschranke nicht überschreitet, und bei der Auswertung die Zähl-, Test-, Aufzähl- und die Unterschied-Routine unterstützt werden.<br>This thesis investigates the query evaluation problem for fixed queries over fully dynamic databases, where tuples can be inserted or deleted. The task is to design a dynamic algorithm that immediately reports the new result of a fixed query after every database update. In particular, the goal is to construct a data structure that allows to support the following scenario. After every database update, the data structure can be updated in constant time such that afterwards we are able * to test within constant time for a given tuple whether or not it belongs to the query result, * to output the number of tuples in the query result, * to enumerate all tuples in the new query result with constant delay and * to enumerate the difference between the old and the new query result with constant delay. In the first part, conjunctive queries and unions of conjunctive queries on arbitrary relational databases are considered. The notion of q-hierarchical conjunctive queries (and t-hierarchical conjunctive queries for testing) is introduced and it is shown that the result of each such query on a dynamic database can be maintained efficiently in the sense described above. Moreover, this notion is extended to aggregate queries. It is shown that the preparation of learning a polynomial regression function can be done in constant time if the training data are taken (and maintained under updates) from the query result of a q-hierarchical query. With logarithmic update time the following routine is supported: upon input of a natural number j, output the j-th tuple that will be enumerated. In the second part, queries in first-order logic (FO) and its extension with modulo-counting quantifiers (FO+MOD) are considered, and it is shown that they can be efficiently evaluated under updates, provided that the dynamic database does not exceed a certain degree bound, and the counting, testing, enumeration and difference routines is supported.

Specification for process oriented applications tends to use languages that suffer from infinite, intractable or unpredictably irregular state spaces that thwart exhaustive searches by verification heuristics. However, conceptual schemas based on FOL, offer techniques for both integrating and verifying specifications in finite spaces. It is therefore of interest to transform process based specifications into conceptual schemata. Process oriented languages have an additional drawback in that reliable inputs to the integration of diverse specifications can result in unreliable outputs. This problem can more easily be addressed in a logic representation in which static and dynamic properties can be examined separately. The first part of the text describes a translation method from the process based language SDL, to first order logic. The usefulness of the method for industrial application has been demonstrated in an implementation. The method devised is sufficiently general for application to other languages with similar characteristics. Main contributions consist of: formalising the mapping of state transitions to event driven rules in dynamic entity-relationship schemas; analysing the complexity of various approaches to decomposing transitions; a conceptual representation of the source language that distinguishes meta- and object models of the source language and domain respectively. The second part of the text formally describes a framework for the integration of schemata that allows the exploration of their properties in relation to each other and to a set of integration assertions. The main contributions are the formal framework; an extension to conflicts between agents in a temporal action logic; complexity estimates for various integration properties.<br>QC 20101004

Orientador: Alex Antonelli<br>Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin<br>Made available in DSpace on 2018-08-14T11:09:53Z (GMT). No. of bitstreams: 1 Michelon_MateusFontana_D.pdf: 2538667 bytes, checksum: 7cf68d701030ed6e318c7312b4f25a03 (MD5) Previous issue date: 2009<br>Resumo: Um dos objetivos da simulação atomística na ciência dos materiais é calcular as propriedades de um material virtual e propor rotas para sua fabricação em laboratório. Uma das principais propriedades que o material deve apresentar antes de ser sintetizado é a estabilidade termodinâmica. Como a estabilidade é determinada pela energia livre, o cálculo preciso desta quantidade é de fundamental importância na construção de um laboratório virtual. Neste contexto, desenvolvemos uma metodologia alternativa para a determinação da energia livre de ligas substitucionais, que leva em conta os graus de liberdade vibracionais e configuracionais com precisão controlada. A metodologia utiliza o método de Monte Carlo para simular a dinâmica de trocas e vibrações atômicas e determina a energia livre através dos métodos de ligação adiabática e escalamento reversível. Além disso, a metodologia é capaz de avaliar a influência de mecanismos associados à entropia vibracional, através da relaxação sucessiva de vínculos na dinâmica. Especificamente, permite quantificar os mecanismos de a) proporção de ligações entre átomos distintos, b) discrepância entre volumes atômicos e c) relaxação volumétrica, e identificar a origem da diferença de entropia vibracional na transição ordem-desordem. Testamos e aplicamos a metodologia para estudar um modelo semiempírico da liga Ni3Al. Observamos um aumento da entropia vibracional na transição ordem-desordem comparável com o aumento da entropia configuracional e explicado pelo aumento de volume na transição. Outra característica de um laboratório virtual é possuir modelos que descrevam satisfatoriamente os sistemas de interesse. Investigamos um potencial do tipo tight-binding e descobrimos que não é transferível para descrever fenômenos de ordem-desordem em diversas ligas. Além de investigar o fenômeno ordem-desordem em ligas, estudamos transições de fase líquido-líquido em substâncias puras. Apresentamos uma evidência teórica de transição líquido-líquido de primeira ordem em um modelo semiempírico do gálio, fornecendo suporte a uma recente evidência experimental de transição líquido-líquido no regime super-resfriado deste elemento. Além disso, as simulações atomísticas sugerem um mecanismo microscópico para esta transição. Outras características de um laboratório virtual são a possibilidade de estudar sistemas em condições experimentais inacessíveis e a capacidade de propor novos experimentos. Neste contexto, apresentamos uma evidência teórica de transição líquido-líquido em um modelo ab initio para o dióxido de carbono. A transição ocorre entre um líquido molecular e um líquido polimérico em uma região do diagrama de fases atualmente inacessível experimentalmente. Em um futuro próximo, esperamos que seja possível testar esta previsão teórica e sintetizar fases poliméricas por meios físicos.<br>Abstract: One of the goals of atomistic simulation in materials science is to calculate properties of a virtual material and suggest routes for its fabrication in laboratory. One of the main properties that the material must have before being synthesized is the thermodynamical stability. As the thermodynamical stability is determined by the free energy, its accurate calculation is of fundamental importance for the construction of a virtual laboratory. In this context, we developed an alternative methodology to determine the free energy of substitutional alloys, which takes into account both the vibrational and configurational degrees of freedom with controlled accuracy. The methodology uses the Monte Carlo method to simulate both the vibrational and exchange dynamics and uses the adiabatic switching and reversible scaling methods to calculate the free energy efficiently. In addition, the methodology is able to evaluate the effect of three mechanisms in the vibrational entropy, through successive relaxations of constraints associated with the dynamics. Specifically, it allows to quantify the mechanisms of a) bond proportion, b) atomic size mismatch and c) bulk volume, and thus identify the origin of the vibrational entropy difference at the order-disorder transition. We tested and applied the methodology to study a semiempirical model of the Ni3Al alloy. We observed an increasing of the vibrational entropy at the order-disorder transition comparable to the configurational entropy increasing and explained by an increasing of the bulk volume. Another expected feature of a virtual laboratory is to offer models that describe satisfactorily the systems of interest. We investigated a tight-binding potential and found out that it is not transferable to describe the order-disorder phenomena in several alloys. In addition to the study of the order-disorder phenomena in alloys, we investigated phase transitions between two liquids of a pure substance. We present a theoretical evidence of a first-order liquid-liquid phase transition in a semiempirical model of gallium, which lend support to the recent experimental evidence of a first-order liquid-liquid transition in the supercooled regime of this element. Moreover, the atomistic simulations suggest a microscopic mechanism for this phase transition. Another expected features of a virtual laboratory are the possibility to investigate systems in unreachable experimental conditions and the capacity to suggest new experiments. In this context, we present an ab initio theoretical evidence of a liquid-liquid phase transition in carbon dioxide. We predict a transition between a molecular liquid and a polymeric liquid at a temperature and pressure which are presently unreachable experimentally. We hope that in the near future it will be possible to test this theoretical prediction and synthesize polymeric phases through physical means.<br>Doutorado<br>Física da Matéria Condensada<br>Doutor em Ciências

This study investigates what classroom participants do with literary texts and how literary texts are pedagogically recontextualized through classroom activities in L2 tertiary literature classrooms. Premised upon the pedagogic processes of decontextualization and recontextualization that take place in the meaning-making practices of the literature classroom, the current study examines the process of literary text recontextualization via the multimodal partnership of vocalization and gesticulation. Through this process, esoteric literary meanings requiring specialist knowledge are transformed into mundane meanings from one semiotic-institutional domain to another, where the literary text qua cultural artifact is recontextualized via first-order languaging by dint of pedagogic activities. To understand the real-time first-order languaging dynamics (Thibault, 2011a) that enable the pedagogic recontextualization of literary texts to take place, a micro analytical toolkit grounded in qualitative multimodal interaction analysis is used. This toolkit draws upon the concept of the Growth Point (McNeill & Duncan, 2000) in conjunction with Systemic Functional Grammar (Halliday & Matthiessen, 2004) and McNeill‘s (1992) theory of language and gesture. Classroom observation and video recording in university literature classrooms in Hong Kong and Taiwan provide multimodal data on students‘ languaging behaviours when they engage with literary texts in classroom talk. In order to make links with second-order socio-cultural norms that regulate first-order classroom interactivity (Thibault, 2011a), Bernstein‘s (1990) sociological theory of recontextualization in education is re-thought from the distributed language view (Cowley, 2011; Steffensen, 2011; Thibault, 2011a). Maton‘s (2007) Legitimation Codes of Specialization and Hunter‘s (1988) Foucaultian analysis of literature education (Foucault, 1972, 1985/1984) also inform the conceptual framework. The findings indicate the stability of the textual and lexicogrammatical constructions that function as second-order constraints and the variations in gesture use in its embodied coordination with speech in the pedagogic process of literary text recontextualization through different pedagogic activities. The semantic cohesive relations of Elaboration, Extension, Enhancement, Engagement, and Equipment, fostered by different gesture types together with their corresponding linguistic constructs in the recontextualized texts, demonstrate that the semiotic integration of speech and gesture comprise a single languaging system in the meaning-making process. Based on the production of literary meaning in moral judgement, the specialized consciousness of the ethical self is raised, with ethical subjects constituted through processes of subjectivity, self-reflexivity, and self-confession in the process of literary interpretation and appreciation. The conceptual framework integrating macro- and micro-levels of analysis manifests its theoretical originality by establishing both the methodological framework for multimodal interaction analysis and the cognitive framework for languaging dynamics. The understanding of the meaning-making process in the first-order languaging dynamics suggests that language is an embodied multimodal process. This major conclusion stimulates a re-thinking of important aspects of classroom interaction that have received little attention. Hopefully, the analysis and findings in the current study illustrate the significance of English literature education and suggest new directions for multimodal research in classroom interaction studies.<br>published_or_final_version<br>Education<br>Doctoral<br>Doctor of Philosophy

Many agricultural fields that have received long-term applications of P often contain levels of P exceeding those required for optimal crop production. Knowledge of the effect of the P remaining in the soil (residual effect) is of great importance for fertilization management. In order to characterize P forms in soils, a wide variety of methods have been proposed. The use of dialysis membrane tubes filled with hydrous ferric oxide (DMT-HFO) has recently been reported as an effective way to characterize P desorption over a long-term in laboratoty studies. However, there is little information on the relationship between kinetics of P release using this new method and plant P uptake. This method consist of a procedure of shaking a sample for a long period of time there by exploiting the whole volume of the soil which is in contrast to the actual plant mode of uptake. This method has also practical limitations in employing it for a routine soil analysis, as it is very expensive and time consuming. The objectives of this study were (i) to study the changes in labile, non-labile and residual P using successive P desorption by DMT-HFO followed by a subsequent fractionation method (combined method) (ii) to assess how the information gained from P desorption kinetic data relates to plant growth at green house and field trials (iii) to investigate the effect of varying shaking time on DMT-HFO extractable P and (iv) to propose a short cut approach to the combined method. The release kinetics of the plots from long term fertilizer trials at the University of Pretoria and Ermelo were studied. P desorption kinetics were described relatively well by a two-component first-order model (R2 = 0.947, 0.918,&0.993 for NPK, MNK,&MNPK treatments respectively). The relative contributions of both the labile pool (SPA) and the less labile pool (SPB) to the total P extracted increased with increased P supply levels. Significant correlations were observed between the rate coefficients and maize grain yield for both soil types. The correlation between the cumulative P extracted and maize yield (r = 0.997**) however was highly significant for Ermelo soils. This method was also used to determine the changes in the different P pools and to relate these P fractions with maize yield. Highly significant correlations were observed between maize grain yield and the different P fractions including total P. In both soil types the contribution of both the labile and non-labile inorganic P fractions in replenishing the solution Pi was significant where as the contributions from the organic fractions were limited. The C/HCl-Pi is the fraction that decreased most in both cases as well. Investigation was carried out to evaluate the effect of varying shaking periods on the extractable DMT-HFO-Pi for UP soils of varying P levels. Four shaking options were applied. Significant difference was observed for the treatment of high P application. Shaking option 2 seemed relatively better than the others since it showed the strongest correlation. Thus for soils with high releasing kinetics and high total P content, provided that the P release from the soil is a rate limiting step, reducing the length of shaking time could shorten the duration one needs to complete the experiment with out influencing the predicting capacity of the methodology. The other objective of this thesis was also to present a short cut method alternative to the combined fractionation method. Comparison of the sum of DMT-HFO-Pi, NaHCO3-Pi, NaOH-Pi, D/HCl-Pi and C/HCl-Pi extracted by a conventional step-by-step method with the sum of DMT-HFO-Pi and a single C/HCl-Pi extraction as a short cut approach for all extraction periods resulted in strong and significant correlations. The C/HCl-Pi fraction extracted by both methods was correlated with maize grain yield and it was found to be highly significant. This study revealed that this short cut approach could be a simplified and economically viable option to study the P dynamics of soils especially for soils where the P pool acting as a source in replenishing the labile portion of P is already identified. The method employed here therefore could act as an analytical tool to approximate successive cropping experiments carried out under green house or field condition. However, data from a wider range of soils is needed to evaluate the universality of this method. More work is also required in relating desorption indices of this method with yield parameters especially at field level.<br>Thesis (PhD)--University of Pretoria, 2009.<br>Plant Production and Soil Science<br>PhD<br>unrestricted

The author presents some generalized Burgers' equations for incompressible and isothermal flow of viscous non-Newtonian fluids based on the Cross model, the Carreau model, and the Power-Law model and some simple assumptions on the flows. The author numerically solves the traveling wave equations for the Cross model, the Carreau model, the Power-Law model by using industrial data. The author proves existence and uniqueness of solutions to the traveling wave equations of each of the three models. The author also provides numerical estimates of the shock thickness as well as maximum strain $\varepsilon_{11}$ for each of the fluids.

Ce travail se place dans le contexte des recherches sur les mémoires quantiques pour la lumière. L'information quantique est stockée dans un état de superposition atomique, dont la durée de vie détermine le temps maximum de stockage.On s'intéresse particulièrement aux matériaux capables de capturer la lumière par excitation résonnante d'une raie d'absorption, puis de conserver l'information quantique dans un état de superposition du fondamental électronique.Dans Tm3+:YAG, l'information est enregistrée dans un état de spin nucléaire. Cependant le champ magnétique qui lève la dégénérescence nucléaire entraîne les différents spins à des vitesses de précession différentes, ce qui tend à détruire l'aimantation initiale, porteuse de l'information.Une étude quantique du cristal est réalisée lors du premier chapitre de ce manuscrit. Les trois chapitres suivants traitent des différents mécanismes conduisant au déphasage des spins nucléaires. On y trouvera différente analyses théoriques qui seront confirmées par un ensemble de résultats expérimentaux, ainsi qu'une description détaillée du dispositif expérimental. Enfin le dernier chapitre, prospectif, exploite les outils développés au cours de la thèse pour préserver les cohérences optiques. Il présente quelques résultats expérimentaux prometteurs sur l'allongement du temps de vie de ces cohérences optiques.

碩士<br>國立政治大學<br>應用數學研究所<br>97<br>In this thesis, we are concernd with nonlinear first-order periodic boundary value problems of impulsive dynamic equations on time scales. By using Schaefer’s theorem and Banach’s fixed point theorem we acquire some new existence results.

Standard techniques used to analyze a system's response with uncertain system parameters or inputs, are generally Importance sampling methods. Sampling methods require a large number of simulation runs before the system output statistics can be analyzed. As model fidelity increases, sampling techniques become computationally infeasible, and Reliability methods have gained popularity as an analysis method that requires significantly fewer simulation runs. Reliability analysis is an analytic technique which finds a particular point in the design space that can accurately be related to the probability of system failure. However, application to dynamic systems have remained limited. In the following thesis a First Order Reliability Method (FORM) is used to determine the failure probability of a dynamic system due to system/input uncertainties. A pendulum cart system is used as a case study to demonstrate the FORM on a dynamic system. Three failure modes are discussed which correspond to the maximum pendulum angle, the maximum system velocity, and a combined requirement that neither the maximum pendulum angle or system velocity are exceeded. An explicit formulation is generated from the implicit formulation using a Response Surface Methodology, and the FORM is performed using the explicit estimate. Although the analysis converges with minimal simulation computations, attempts to verify FORM results illuminate current limitations of the methodology. The results of this initial study conclude that, currently, sampling techniques are necessary to verify the FORM results, which restricts the potential applications of the FORM methodology. Suggested future work focuses on result verification without the use of Importance sampling which would allow Reliability methods to have widespread applicability.<br>text

The equiatomic FeRh alloy undergoes a first-order phase transition from an antiferromagnetic (AFM) to a ferromagnetic (FM) state at about 370 K with a small thermal hysteresis of about 10 K around the phase transition. The transition is accompanied by a unit cell volume expansion about 1% in the c lattice parameter. During the transition the new phase nucleates in the matrix of the original phase by reaching the critical temperature followed by a growth in size upon increasing temperature further. Therefore, to understand the transition process with more details, it is desirable to investigate the nucleation and growth of both phases within the first order phase transition. In the present thesis the main focus is on the growth of FeRh thin films by means of Molecular Beam Epitaxy (MBE) technique and characterization of the magnetic and structural properties. To develop an understanding of the phase transformation in FeRh thin films the ways in which one can tune it were investigated. The following aspects concerning the FeRh system have been examined here: 1) influence of annealing temperature on the magnetic and structural response, 2) effect of film thickness on the first-order phase transition temperature as well as the saturation magnetization, 3) influence of chemical composition on the magnetic properties and 4) magnetic field-induced phase transition. To get insight to details of the transition process the magnetization dynamic has been addressed by performing Ferromagnetic resonance (FMR) experiment across the phase transition. FMR measurements determined the existence of two areas with different magnetic properties inside the film. A huge temperature difference for the beginning of the phase transition in comparison with the static magnetization measurement was observed for the equiatomic FeRh thin film prepared by MBE. Tuning of the AFM to FM phase transition in the FeRh thin film by means of low-energy/low fluence Ne+ ion irradiation was studied. Ion irradiation technique offers a quantitative control of the degree of chemical disorder by adjusting the ion fluence applied, while the penetration depth of the disordered phase can be adjusted by the ion-energy. The main results of ion irradiation are the shifting of the phase transition temperature to lower temperature and irradiation with 3×1014 ion/cm2 leads to the disappearance the AFM phase completely.

The probabilistic design of dynamic systems with degrading components is difficult. Design of dynamic systems typically involves the optimization of a time-invariant performance measure, such as Energy, that is estimated using a dynamic response, such as angular speed. The mechanistic models developed to approximate this performance measure are too complicated to be used with simple design calculations and lead to lengthy simulations. When degradation of the components is assumed, in order to determine suitable service times, estimation of the failure probability over the product lifetime is required. Again, complex mechanistic models lead to lengthy lifetime simulations when the Monte Carlo method is used to evaluate probability. Based on these problems, an efficient methodology is presented for probabilistic design of dynamic systems and to estimate the cumulative distribution function of the time to failure of a performance measure when degradation of the components is assumed. The four main steps include; 1) transforming the dynamic response into a set of static responses at discrete cycle-time steps and using Singular Value Decomposition to efficiently estimate a time-invariant performance measure that is based upon a dynamic response, 2) replacing the mechanistic model with an approximating function, known as a “metamodel” 3) searching for the best design parameters using fast integration methods such as the First Order Reliability Method and 4) building the cumulative distribution function using the summation of the incremental failure probabilities, that are estimated using the set-theory method, over the planned lifetime. The first step of the methodology uses design of experiments or sampling techniques to select a sample of training sets of the design variables. These training sets are then input to the computer-based simulation of the mechanistic model to produce a matrix of corresponding responses at discrete cycle-times. Although metamodels can be built at each time-specific column of this matrix, this method is slow especially if the number of time steps is large. An efficient alternative uses Singular Value Decomposition to split the response matrix into two matrices containing only design-variable-specific and time-specific information. The second step of the methodology fits metamodels only for the significant columns of the matrix containing the design variable-specific information. Using the time-specific matrix, a metamodel is quickly developed at any cycle-time step or for any time-invariant performance measure such as energy consumed over the cycle-lifetime. In the third step, design variables are treated as random variables and the First Order Reliability Method is used to search for the best design parameters. Finally, the components most likely to degrade are modelled using either a degradation path or a marginal distribution model and, using the First Order Reliability Method or a Monte Carlo Simulation to estimate probability, the cumulative failure probability is plotted. The speed and accuracy of the methodology using three metamodels, the Regression model, Kriging and the Radial Basis Function, is investigated. This thesis shows that the metamodel offers a significantly faster and accurate alternative to using mechanistic models for both probabilistic design optimization and for estimating the cumulative distribution function. For design using the First-Order Reliability Method to estimate probability, the Regression Model is the fastest and the Radial Basis Function is the slowest. Kriging is shown to be accurate and faster than the Radial Basis Function but its computation time is still slower than the Regression Model. When estimating the cumulative distribution function, metamodels are more than 100 times faster than the mechanistic model and the error is less than ten percent when compared with the mechanistic model. Kriging and the Radial Basis Function are more accurate than the Regression Model and computation time is faster using the Monte Carlo Simulation to estimate probability than using the First-Order Reliability Method.

An increase in the co-operativity in the motion of particles and a growth of a suitably defined dynamical correlation length seem to be generic features exhibited by all liquids upon supercooling. These features have been observed both in experiments and in numerical simulations of glass-forming liquids. Specially designed NMR experiments have estimated that the rough magnitude of this correlation length is of the order of a few nanometers near the glass transition. Simulations also predict that there are regions in the system which are more liquid-like than other regions. A complete theoretical understanding of this behaviour is not available at present. In recent calculations, Berthier, Biroli and coworkers [1, 2] extended the simple mode coupling theory (MCT) to incorporate the effects of dynamic heterogeneity and predicted the existence of a growing dynamical correlation length associated with the cooperativity of the dynamics. MCT also predicts a power law divergence of different dynamical quantities at the mode coupling temperature and at temperatures somewhat higher than the mode coupling temperature, these predictions are found to be consistent with experimental and simulation results. The system size dependence of these quantities should exhibit finite size scaling (FSS) similar to that observed near a continuous phase transition in the temperature range where they show power law growth. Hence we have used the method of finite size scaling in the context of the dynamics of supercooled liquids. In chapter 2, we present the results of extensive molecular dynamics simulations of a model glass forming liquid and extract a dynamical correlation length ξ associated with dynamic heterogeneity by performing a detailed finite size scaling analysis of a four-point dynamic susceptibility χ4(t) [3] and the associated Binder cumulant. We find that although these quantities show the “normal” finite size scaling behaviour expected for a system with a growing correlation length, the relaxation time τ does not. Thus glassy dynamics can not be fully understood in terms of “standard” critical phenomena. Inspired by the success of the empirical Adam-Gibbs relation [4] which relates dynamics with the configurational entropy, we have calculated the configurational entropy for different system sizes and temperatures to explain the nontrivial scaling behaviour of the relaxation time. We find that the behaviour of the relaxation time τ can be explained in terms of the Adam-Gibbs relation [4] for all temperatures and system sizes. This observation raises serious questions about the validity of the mode coupling theory which does not include the effects of the potential energy (or free energy) landscape on the dynamics. On the other hand, in the “random first order transition” theory (RFOT), introduced by Wolynes and coworkers [5], the configurational entropy plays a central role in determining the dynamics. So we also tried to explain our simulation results in terms of RFOT. However, this interpretation has the drawback that the value of one of the exponents of this theory extracted from our numerical results does not satisfy an expected physical bound, and there is no clear explanation for the obtained values of other exponents. Thus we find puzzling values for the exponents relevant to the applicability of RFOT, which are in need of explanation. This can be due to the fact that RFOT focuses only near the glass transition, while all our simulation results are for temperatures far above the glass transition temperature (actually, above the mode coupling temperature). Interestingly, results similar to ours were obtained in a recent analysis [6] of experimental data near the laboratory glass transition, on a large class of glass-forming materials. Thus right now we do not have any theory which can explain our simulation data consistently from all perspectives. There have been some attempts to extend the RFOT analysis to temperatures above the mode coupling temperature [7, 8] and to estimate a length scale associated with the configurational entropy at such temperatures. We compare our results with the predictions arising from these analyses. In chapter 3, we present simulation results that suggest that finite size scaling analysis is probably the only feasible method for obtaining reliable estimates of the dynamical correlation length for supercooled liquids. As mentioned before, although there exists a growing correlation length, the behaviour of all measured quantities (specifically, the relaxation time) is not in accordance with the behaviour expected in “standard” critical phenomena. So one might suspect the results for the correlation length extracted from the scaling analysis. To find out whether the results obtained by doing finite size scaling are correct, we have done simulations of very large system sizes for the same model glass forming liquid. In earlier studies, the correlation length has been extracted from the wave vector dependence of the dynamic susceptibility in the limit of zero wave vector, but to estimate the correlation length with reasonable accuracy one needs data in the small wave vector range. This implies that one needs to simulate very large systems. But as far as we know, in all previous studies typical system sizes of the order of 10, 000 particles have been used to do this analysis. In this chapter we show by comparing results for systems of 28, 000 and 350, 000 particles that these previous estimates are not reliable. We also show that one needs to simulate systems with at least a million particles to estimate the correlation length correctly near the mode coupling temperature and this size increases with decreasing temperature. We compare the correlation length obtained by analyzing the wave vector dependence of the dynamic susceptibility for a 350, 000particle system with the results obtained from the finite size scaling analysis. We were only able to compare the results in the high temperature range due to obvious reasons. However the agreement in the high temperature range shows that the finite size scaling analysis is robust and also establishes the fact that finite size scaling is the only practical method to extract reliable correlation lengths in supercooled liquids. In chapter 4, we present a free energy landscape analysis of dynamic heterogeneity for a monodisperse hard sphere system. The importance of the potential energy landscape for particles interacting with soft potentials is well known in the glass community from the work of Sastry et al. [9] and others, but the hard sphere system which does not have any well defined potential energy landscape also exhibits similar slow dynamics in the high density limit. Thus it is not clear how to treat the hard sphere systems within the same energy landscape formalism. Dasgupta et al. [10, 11, 12, 13, 14, 15] showed that one can explain the slow dynamics of these hard core systems in term of a free energy landscape picture. They and other researchers showed that these system have many aperiodic local minima in its free energy landscape, with free energy lower than that of the liquid. Using the Ramkrishnan-Yussouff free energy functional, we have performed multi parameter variational minimizations to map out the detailed density distribution of glassy free energy minima. We found that the distribution of the widths of local density peaks at glassy minima is spatially heterogeneous. By performing hard sphere event driven molecular dynamics simulation, we show that there exists strong correlation between these density inhomogeneity and the local Debye-Waller factor which provides a measure of the dynamic heterogeneity observed in simulations. This result unifies the system of hard core particles with the other soft core particles in terms of a landscapebased description of dynamic heterogeneity. In chapter 5, we extend the same free energy analysis to a polydisperse system and show that there is a critical polydispersity beyond which the crystal state is not stable and glassy states are thermodynamically stable. We also found a reentrant behaviour in the liquid-solid phase transition within this free-energy based formalism. These results are in qualitative agreement with experimental observations for colloidal systems.

In structural mechanics there are several occasions where a linearized formulation of the original nonlinear problem reduces considerably the computational effort for the response analysis. In a broader sense, a linearized formulation can be viewed as a first-order expansion of the dynamic equilibrium of the system about a `static¿ configuration; yet caution should be exercised when identifying the `correct¿ static configuration. This paper uses as a case study the rocking response of a rigid block stepping on viscoelastic supports, whose non-linear dynamics is the subject of the companion paper, and elaborates on the challenge of identifying the most appropriate static configuration around which a first-order expansion will produce the most dependable results in each regime of motion. For the regime when the heel of the block separates, a revised set of linearized equations is presented, which is an improvement to the unconservative equations published previously in the literature. The associated eigenvalues demonstrate that the characteristics of the foundation do not affect the rocking motion of the block once the heel separates.

碩士<br>逢甲大學<br>自動控制工程學系<br>106<br>While much work has been performed in the research of the Coanda effect and related mechanical design of the Coanda effect aircraft, little discussion has been found on the control of the Coanda effect saucer. The focus of this thesis is to derive the dynamical equations and controller for a special-structured Coanda effect saucer that will allow the aircraft to reach a stable and controllable state. There are two kinds of lifts: the lift caused by the momentum change and the lift caused by the air pressure difference. In this thesis, dynamical equations are derived based on these two kinds of lifts, by utilizing Newton-Euler equations together with coordinate systems and Euler angles. And, linearization is used to analyze the stability and controllability of the Coanda effect saucer’s dynamical equations. Then, the first-order perturbation is used with dynamical equations to establish feedforward controller and PID feedback controller. Coanda effect saucer is proved to be an unstable and fully controllable system. Matlab/Simulink is used to build a numerical program, and simulations for both the open loop and closed loop numerical programs are performed and verified.

In this thesis, we study advanced reasoning about dynamical systems in a logical framework -- the situation calculus. In particular, we consider promoting the efficiency of reasoning about action in the situation calculus from three different aspects. First, we propose a modified situation calculus based on the two-variable predicate logic with counting quantifiers. We show that solving the projection and executability problems via regression in such language are decidable. We prove that generally these two problems are co-NExpTime-complete in the modified language. We also consider restricting the format of regressable formulas and basic action theories (BATs) further to gain better computational complexity for reasoning about action via regression. We mention possible applications to formalization of Semantic Web services. Then, we propose a hierarchical representation of actions based on the situation calculus to facilitate development, maintenance and elaboration of very large taxonomies of actions. We show that our axioms can be more succinct, while still using an extended regression operator to solve the projection problem. Moreover, such representation has significant computational advantages. For taxonomies of actions that can be represented as finitely branching trees, the regression operator can sometimes work exponentially faster with our theories than it works with the BATs current situation calculus. We also propose a general guideline on how a taxonomy of actions can be constructed from the given set of effect axioms. Finally, we extend the current situation calculus with the order-sorted logic. In the new formalism, we add sort theories to the usual initial theories to describe taxonomies of objects. We then investigate what is the well-sortness for BATs under such framework. We consider extending the current regression operator with well-sortness checking and unification techniques. With the modified regression, we gain computational efficiency by terminating the regression earlier when reasoning tasks are ill-sorted and by reducing the search spaces for well-sorted objects. We also study that the connection between the order-sorted situation calculus and the current situation calculus.

The diploma thesis is focused on an analysis of the first sentences of newspaper articles namely from an aspect of the topic-focus articulation, which is expressed in Czech primarily by word order. The word order depending on the increasing communicative dynamism of words in the sentence might be changed from an objective word order if new information follows known or before mentioned information into subjective word order resulting in a reverse order. E.g.: The CEZ group showed record profit of 52 milliard CZK last year, a reverse word order: (literal translation) Record profit (Obj) of 52 milliard CZK the CEZ group(Subj) showed last year. In our thesis, we describe the above mentioned changes and we determine sets of cases comprising the modifications and we attempt to specify kinds of rules and principles resulting in different word orders. The sentence in the case of the subjective word order begins with an object, an adverbial of time, place, or condition. Anyway, not always a sentence constituent at the beginning of the sentence indicates the subjective word order. A significant role in the analysis is played by head- lines, which affect considerably the result. We focus ou attention on sentences expressing a placement on the scene. These sentences are assessed in relation with the head-lines...