Dissertationen zum Thema „Asynchronous dynamic“

In order to simulate both physically and visually realistic soft tissuedeformations, the Finite Element Method (FEM) is the mostpopular choice in the literature. However it is non-trivial to modelcomplex behaviour of soft tissue with sufficient refresh rates, especiallyfor haptic force feedback which requires an update rate ofthe order of 1 kHz. In this study the use of asynchronous regions isproposed to speed up the solution of FEM equations in real-time. Inthis way it is possible to solve the local neighborhood of the contactwith high refresh rates, while evaluating the more distant regions atlower frequencies, saving computational power to model complexbehaviour within the contact area. Solution of the different regionsusing different methods is also possible. To attain maximum efficiencythe size of the regions can be changed, in real-time, in responseto the size of the deformation.

Improvements in semiconductor technology have supported an exponential growth in microprocessor performance for many years. The ability to continue on this trend throughout the current decade poses serious challenges as feature sizes enter the deep sub-micron range. The problems due to increasing power consumption, clock distribution and the growing complexity of both design and verification, may soon limit the extent to which the underlying technological advances may be exploited. One approach which may ease these problems is the adoption of an asynchronous design style - one in which the global clock signal is omitted. Commonly-cited advantages include: the ability to exploit local variations in processing speed, the absence of a clock signal and its distribution network, and the ease of reuse and composability provided through the use of delay-insensitive module interfaces. While the techniques to design such circuits have matured over the past decade, studies of the impact of asynchrony of processor architecture have been less common. One challenge in particular is to develop multiple-issue architectures that are able to fully exploit asynchronous operation. Multiple-issue architectures have traditionally exploited the determinism and predictability ensured by synchronous operation. Unfortunately, this limits the effectiveness of the architecture when the clock is removed. The work presented in this dissertation describes in detail the problems of exploiting asynchrony in the design of superscalar processors. A number of techniques are presented for implementing both data forwarding and dynamic scheduling mechanisms, techniques that are central to exploiting instruction-level parallelism and achieving high-performance. A technique called instruction compounding is introduced, which appends dependency information to instructions during compilation, which can be exploited at run-time. This simplifies the implementation of both the dynamic scheduling and data-forwarding mechanisms.

This thesis introduces a new methodology for energy estimation in asynchronous circuits. Unlike existing probabilistic methods, this is the first simulative work for energy estimation in all types of asynchronous circuits. The new simulative methodology is based on Petri net modeling. A real delay model is incorporated to capture both gate delays and interconnect delays. The switching activity at each gate is captured to measure the average dynamic energy consumed per request/acknowledge handshaking pair. The new type of Petri net is called Hierarchical Colored Asynchronous Hardware Petri net (HCAHPN). The HCAHPN is able to capture the temporal and spatial correlations of signals within a circuit, while preserving gate logic behavior and timing information. While Petri nets have been previously used for simulating combinational and sequential circuits, this is the first work that uses Petri nets for simulating asynchronous circuits. While different asynchronous design styles make various assumptions on the gate and wire delays present with the circuit, the physical implementations of these circuits always have gate and interconnect delays. Unlike previous methods, the proposed methodology is independent of the asynchronous design style used and it can be adapted for all types of asynchronous circuits that use handshaking communication.

Les applications de transmission de messages distribués font partie du courant dominant des technologies de l'information car elles exploitent la puissance des systèmes informatiques parallèles pour produire des performances plus élevées. La conception de programmes distribués reste difficile car les développeurs doivent raisonner sur la concurrence, le non-déterminisme, la distribution de données… qui sont les principales caractéristiques des programmes distribués. En outre, il est pratiquement impossible de garantir l'exactitude de tels programmes via des approches de test classiques, car il est possible que l'on n'atteigne jamais avec succès l'exécution qui conduit à des comportements indésirables dans les programmes. Il existe donc un besoin de techniques de vérification plus puissantes. La vérification des modèles est l'une des méthodes formelles qui permet de vérifier automatiquement et efficacement certaines propriétés des modèles de systèmes informatiques en explorant tous les comportements possibles (états et transitions) du modèle de système. Cependant, les espaces d'état augmentent de façon exponentielle avec le nombre de processus simultanés, conduisant à une «explosion de l'espace d'état» .La réduction dynamique de l'ordre partiel basée sur le dépliage (UDPOR) est une technique récente mélangeant la réduction dynamique de l'ordre partiel (DPOR) avec des concepts de théorie de la concurrence tels que dépliages pour atténuer efficacement l'explosion de l'espace d'états lors de la vérification des modèles de programmes simultanés. Il est optimal dans le sens où chaque trace de Mazurkiewicz, c'est-à-dire une classe d'entrelacements équivalents en commutant des actions indépendantes adjacentes, est explorée exactement une fois. Et elle s'applique aux programmes en cours d'exécution, pas seulement aux modèles de programmes.La thèse vise à adapter UDPOR pour vérifier les programmes distribués asynchrones (par exemple les programmes MPI) dans le cadre du simulateur SIMGRID d'applications distribuées. Pour ce faire, un modèle de programmation abstrait de programmes distribués asynchrones est défini et formalisé en langage TLA +, permettant de définir avec précision une relation d'indépendance, ingrédient principal de la sémantique concurrentielle. Ensuite, l'adaptation de l'UDPOR, impliquant la construction d'un dépliage, est rendue efficace par une analyse précise des dépendances dans le modèle de programmation, permettant des calculs efficaces d'opérations habituellement coûteuses. Un prototype d'implémentation d'UDPOR adapté aux programmes asynchrones distribués a été développé, donnant des résultats expérimentaux prometteurs sur un ensemble significatif de références
Distributed message passing applications are in the mainstream of information technology since they exploit the power of parallel computer systems to produce higher performance. Designing distributed programs remains challenging because developers have to reason about concurrency, non-determinism, data distribution… that are main characteristics of distributed programs. Besides, it is virtually impossible to ensure the correctness of such programs via classical testing approaches since one may never successfully reach the execution that leads to unwanted behaviors in the programs. There is thus a need for more powerful verification techniques. Model-checking is one of the formal methods that allows to verify automatically and effectively some properties on models of computer systems by exploring all possible behaviors (states and transitions) of the system model. However, state spaces increase exponentially with the number of concurrent processes, leading to “state space explosion”.Unfolding-based Dynamic Partial Order Reduction (UDPOR) is a recent technique mixing Dynamic Partial Order Reduction (DPOR) with concepts of concurrency theory such as unfoldings to efficiently mitigate state space explosion in model-checking of concurrent programs. It is optimal in the sense that each Mazurkiewicz trace, i.e. a class of interleavings equivalent by commuting adjacent independent actions, is explored exactly once. And it is applicable to running programs, not only models of programs.The thesis aims at adapting UDPOR to verify asynchronous distributed programs (e.g. MPI programs) in the setting of the SIMGRID simulator of distributed applications. To do so, an abstract programming model of asynchronous distributed programs is defined and formalized in the TLA+ language, allowing to precisely define an independence relation, a main ingredient of the concurrency semantics. Then, the adaptation of UDPOR, involving the construction of an unfolding, is made efficient by a precise analysis of dependencies in the programming model, allowing efficient computations of usually costly operation. A prototype implementation of UDPOR adapted to distributed asynchronous programs has been developed, giving promising experimental results on a significant set of benchmarks

Lagrangian relaxation is a successful solution approach for many combinatorial optimisation problems, one of them being the train timetabling problem (TTP). We model this problem using time expanded networks for the single train schedules and coupling constraints to enforce restrictions like station capacities and headway times. Lagrangian relaxation of these coupling constraints leads to shortest path subproblems in the time expanded networks and is solved using a proximal bundle method. However, large instances of our practical partner Deutsche Bahn lead to computationally intractable models. In this thesis we develop two new algorithmic techniques to improve the solution process for this kind of optimisation problems. The first new technique, Dynamic Graph Generation (DGG), aims at improving the computation of the shortest path subproblems in large time expanded networks. Without sacrificing any accuracy, DGG allows to store only small parts of the networks and to dynamically extend them whenever the stored part proves to be too small. This is possible by exploiting the properties of the objective function in many scheduling applications to prefer early paths or due times, respectively. We prove that DGG can be implemented very efficiently and its running time and the size of nodes that have to be stored additionally does not depend on the size of the time expanded network but only on the length of the train routes. The second technique is an asynchronous and parallel bundle method (APBM). Traditional bundle methods require one solution of each subproblem in each iteration. However, many practical applications, e.g. the TTP, consist of rather loosely coupled subproblems. The APBM chooses only small subspaces corresponding to the Lagrange multipliers of strongly violated coupling constraints and optimises only these variables while keeping all other variables fixed. Several subspaces of disjoint variables may be chosen simultaneously and are optimised in parallel. The solutions of the subspace problem are incorporated into the global data as soon as it is available without any synchronisation mechanism. However, in order to guarantee convergence, the algorithm detects automatically dependencies between different subspaces and respects these dependencies in future subspace selections. We prove the convergence of the APBM under reasonable assumptions for both, the dual and associated primal aggregate data. The APBM is then further extended to problems with unknown dependencies between subproblems and constraints in the Lagrangian relaxation problem. The algorithm automatically detects these dependencies and respects them in future iterations. Again we prove the convergence of this algorithm under reasonable assumptions. Finally we test our solution approach for the TTP on some real world instances of Deutsche Bahn. Using an iterative rounding heuristic based on the approximate fractional solutions obtained by the Lagrangian relaxation we are able to compute feasible schedules for all trains in a subnetwork of about 10% of the whole German network in about 12 hours. In these timetables 99% of all passenger trains could be scheduled with no significant delay and the travel time of the freight trains could be reduced by about one hour on average.

Heap models in the max-plus algebra are interesting dynamical systems that can be used to model a variety of tetris-like systems, such as batch flow shops for manufacturing models. Each heap in the model can be identified with a single product to manufacture. The objective is to manufacture a group of products in such an order so as to minimize the total manufacturing time. Because this scheduling problem reduces to a variation of the Traveling Salesman Problem (known to be NP-complete), the optimal solution is computationally infeasible for many real-world systems. Thus, a feasible approximation method is needed. This work builds on and expands the existing heap model in order to more effectively solve the scheduling problems. Specifically, this work:1. Further characterizes the admissible products to these systems.2. Further characterizes sets of admissible products. 3. Presents a novel algorithm, the asynchronous $t$-step approximation, to approximate these systems.4. Proves error bounds for the system approximation, and show why these error bounds are better than the existing approximation.

A DRAM communicates with a processing unit via two interfaces: a data interface and a command interface. In today's DRAMs, also known as synchronous DRAMs (SDRAMs), both interfaces use a clock to communicate with the processing unit. The clock times the communication between the processing unit and the SDRAM on both the data interface and the command interface. We propose a self-timed DRAM. The self-timed DRAM introduces more flexibility into the DRAM interface by eliminating the clock. The command interface and the data interface each communicate with the processing unit using a handshake protocol rather than a clock. This thesis presents the data interface between the self-timed DRAM and the processing unit. The proposed data interface is self-timed. The self-timed data interface allows the DRAM to deliver data to or accept data from the processing unit as the processing unit demands rather than on a schedule set from the command interface. The self-timed data interface is designed using GasP circuits and micropipeline circuits. The design is simulated in 180nm CMOs process technology using hspice. This thesis presents the effects of width mismatch on the self-timed data interface. The micropipeline is slightly faster than the GasP. Also, the thesis compares the self-timed DRAM data interface with synchronous DRAM for the data burst rate.

L émergence des environnements omniprésents pose un nouveau défi aux systèmes informatiques. Les intergiciels asynchrones (Message-Oriented Middleware, MOM) sont reconnus comme étant la solution la plus apte à répondre aux besoins de passage à grande échelle, de flexibilité, et d' hétérogénéité des nouvelles applications distribuées. Mais l'implémentation des intergiciels asynchrones actuels reste souvent figée quels que soient les sites d'exécution et l'application (les applications) l'utilisant et sont peu voire pas configurables. Cette thèse s'intéresse à la configuration et au déploiement des intergiciels asynchrones sur système hétérogène à grande échelle. Elle vise la définition d'un modèle d'intergiciel asynchrone configurable permettant une configuration statique et à l'exécution. Elle a pour objectif d'associer les nombreux travaux dans le domaine de l'asynchrone qui ont mené à la définition des modèles de communication asynchrones et les réflexions menées dans les intergiciels synchrones autour des nouveaux besoins de configuration et d'adaptabilité. La synthèse de tous nos travaux nous a mené à la création de DREAM (Dynamic REflective Asynchronous Middleware), un intergiciel asynchrone adaptable. Les mécanismes de contrôles fournis par Dream ainsi que son architecture permettent de réaliser une configuration en se basant sur les besoins applicatifs et les contraintes imposées par le système. Nous validons notre prototype par l'implémentation d'un service à évènement à base d'agents dans lequel nous utilisons les capacités d'adaptation de DREAM pour ajouter de nouvelles fonctionnalités.

Un réseau d'automates à n composantes sur un alphabet fini Q est un système dynamique discret décrit par l'itération successive d'une fonction f : Qⁿ → Qⁿ. Dans la plupart des utilisations de ces réseaux, un paramètre important est le graphe d'interaction : un graphe sur les sommets de 1 à n ayant un arc de i vers j si f_ ј(x) dépend de x_i. Ce graphe d'interaction est en général plus facile à déterminer que la dynamique du réseau en elle-même, d'où découle une question importante : qu'est-ce que le graphe d'interaction nous apprend sur la dynamique du réseau ? Pour tenter de trouver des limites à cette question, on se pose ici la question inverse : que nous dit la dynamique sur le graphe d'interaction ? Pour cela, on étudie les réseaux à isomorphisme près. L'isomorphisme préserve la plupart des propriétés étudiées, mais ne préserve pas le graphe d'interaction. On va donc étudier G(f), l'ensemble des graphes d'interaction des réseaux isomorphes à f. On prouve notamment que K_n, le graphe d'interaction ayant tous les arcs, se trouve toujours dans G(f), qu'il est le seul à avoir cette propriété. Cela signifie que si K_n est le graphe d'interaction de f, il ne donne aucune information sur f à isomorphisme près. Réciproquement, on montre qu'il existe des réseaux f qui ne donnent aucune information sur leur graphe d'interaction : G(f) contient tous les graphes, sauf le graphe vide. Enfin, on étudie également l'impact de l'isomorphisme sur la dynamique asynchrone. On montre que celui-ci ne préserve que très peu de propriétés de ces dynamiques, hormis le nombre de points fixes
An automata network with n components on a finite alphabet Q is a discrete dynamical system described by successives iterations of a function f : Qⁿ → Qⁿ. An important parameter in most applications is the interaction graph: a graph with vertices from 1 to n and with an arc from i to j if f_j(x) depends on x_i. In general, this interaction graph is easier to approximate than the network's actual dynamic. This raises an important question: what does the interaction graph tell us about the network's dynamic? In an attempt to find limits to this question, we study the inverse: what does the network's dynamic tell us about its interaction graph? To this end, we study networks up to isomorphism. Isomorphism preserves most studied properties, but does not preserve the interaction graph. We will thus study G(f), the set of interaction graphs of all networks isomorphic to f. Notably, we prove that K_n, the interaction graph with all arcs, is always in G(f), and it's the only graph with this property. This means if K_n is the interaction graph of f, then it gives no information on f up to isomorphism. Inversely, we show there are networks f that give no information on their interaction graph: G(f) contains all graphs, except the empty one. Finally, we also study the impact of isomorphism on asynchronous dynamics. We show that it preserves very little properties of those dynamics, except the number of fixed points

Devido à complexidade das aplicações, a demanda crescente por sistemas que usam milhões de transistores e hardware complexo; tem sido desenvolvidas ferramentas que convertem C em Linguagem de Descrição de Hardware, tais como VHDL e Verilog. Neste contexto, esta tese apresenta o projeto ChipCflow, o qual usa arquitetura a fluxo de dados, para implementar lógica de alto desempenho em Field Programmable Gate Array (FPGA). Maquinas a fluxo de dados são computadores programáveis, cujo hardware é otimizado para computação paralela de granularidade fina dirigida por dados. Em outras palavras, a execução de programas é determinado pela disponibilidade dos dados, assim, o paralelismo é intrínseco neste sistema. Por outro lado, com o avanço da tecnologia da microeletrônica, o FPGA tem sido utilizado principalmente devido a sua flexibilidade, facilidade para implementar sistemas complexos e paralelismo intrínseco. Um dos desafios é criar ferramentas para programadores que usam linguagem de alto nível (HLL), como a linguagem C, e produzir hardware diretamente. Essas ferramentas devem usar a máxima experiência dos programadores, o paralelismo das arquiteturas a fluxo de dados dinâmica, a flexibilidade e o paralelismo do FPGA, para produzir um hardware eficiente, otimizado para alto desempenho e baixo consumo de energia. O projeto ChipCflow é uma ferramenta que converte os programas de aplicação escritos em linguagem C para a linguagem VHDL, baseado na arquitetura a fluxo de dados dinâmica. O principal objetivo dessa tese é definir e implementar os operadores do ChipCflow, usando a arquitetura a fluxo de dados dinâmica em FPGA. Esses operadores usam tagged tokens para identificar dados, com base em instâncias de operadores. A implementação dos operadores e das instâncias usam um modelo de implementação assíncrono em FPGA para obter maior velocidade e menor consumo
Due to the complexity of applications, the growing demand for both systems using millions of transistors and consecutive complex hardware, tools that convert C into a Hardware Description Language (HDL), as VHDL and Verilog, have been developed. In this context this thesis presents the ChipCflow project, which uses dataflow architecture to implement high-performance logics in Field Programmable Gate Array (FPGA). Dataflow machines are programmable computers whose hardware is optimized for fine-grain data-flow parallel computation. In other words the execution of programs is determined by data availability, thus parallelism is intrinsic in these systems. On the other hand, with the advance of technology of microelectronics, the FPGA has been used mainly because of its flexibility, facilities to implement complex systems and intrinsic parallelism. One of the challenges is to create tools for programmers who use HLL (High Level Language), such as C language, producing hardware directly. These tools should use the utmost experience of the programmers, the parallelism of dynamic dataflow architecture and the flexibility and parallelism of FPGA to produce efficient hardware optimized for high performance and lower power consumption. The ChipCflow project is a tool that converts application programs written in C language into VHDL, based on the dynamic dataflow architecture. The main goal in this thesis is to define and implement the operators of ChipCflow using dynamic dataflow architecture in FPGA. These operators use tagged tokens to identify data based on instances of operators and their implementation and instances use an asynchronous implementation model in FPGA to achieve faster speed and lower consumption

Baigiamajame magistro darbe nagrinėjama iešmo elektros pavara su tiesiaeigiu asinchroniniu cilindriniu varikliu. Programiniu paketu ,,Matlab“ yra sudaryti pavaros matematiniai modeliai α, β koordinačių sistemoje. Uždaviniai – tiesiaeigės iešmo elektros pavaros kompiuterinio modelio sudarymas, tyrimas ir dinaminių charakteristikų imitavimas. Literatūros analizės dalyje išnagrinėtos tiesiaeigės elektros pavaros, jų taikymo sritys bei valdymo būdai. Magistro darbo teorinėje dalyje pateikiamos tiesiaeigių elektros pavarų skaičiavimo ir valdymo metodikų analizės. Tiriamoji dalis apima iešmo elektros pavaros su tiesiaeigiu cilindriniu asinchroniniu varikliu matematinių modelių sudarymą ir dinaminių charakteristikų tyrimą programiniu paketu ,,Matlab“. Matematiniai modeliai yra sudaromi pavarai veikiant skirtingais darbo režimais (pavara perjungiama neapkrauta, pavara perjungiama apkrovus nominalia apkrova ir iešmą perjungiant pabaigoje ir pradžioje trukdant papildomai pasipriešinimo jėgai) ir tyrimo rezultatai pateikiami grafiškai. Gauti rezultatai yra palyginami ir apibendrinami. Išnagrinėjus teorinius tiesiaeigės iešmo elektros pavaros su asinchroniniu cilindriniu varikliu darbo režimų aspektus, pateikiamos išvados ir pasiūlymai. Tyrimo rezultatai gali būti panaudoti iešmo elektros pavaros su tiesiaeigiu asinchroniniu varikliu racionaliam ir optimaliam realizavimui geležinkelio transporto automatinio valdymo sistemose. Darbą sudaro 9 dalys: santrumpos ir simboliai, įvadas... [toliau žr. visą tekstą]
The final Bachelor thesis analyses point electric drive with cylinder-type linear asynchronous motor. Software package ,,Matlab“ was used to prepare mathematical models of the drive in α, β coordinate system. Objectives: preparing and analyzing a computer model of linear point electric drive, simulation of dynamic characteristics. The analysis of literary sources deals with linear electric drives, their application areas and methods of control. Theoretical part of the Master thesis presents analyses of calculation and control methods of linear electric drives. The analytical part of the thesis includes mathematical models of point electric drive with cylinder-type linear asynchronous motor and the analysis of dynamic characteristics using software package ,,Matlab“. Mathematical models were prepared when the drive operated in different modes (the drive switched without load, the drive switched with nominal load, the switch connected at the end or beginning, thereby blocking additional resistance force). Research results were presented in a graphical form. Obtained results were compared and summarized. Following the analysis of the theoretical aspects of operating modes of linear point electric drive with cylinder-type asynchronous motor, conclusions and recommendations were presented. Research results can be used for rational and optimal realization of point electric drive with linear asynchronous motor in automatic railway control systems. The thesis consists of nine parts:... [to full text]

Rapid evolution of integrated circuit technologies has paved a way to develop smaller and energy efficient biomedical devices which has put stringent requirements on data acquisition systems. These implantable devices are compact and have a very small footprint. Once implanted these devices need to rely on non-rechargeable batteries to sustain a life span of up to 10 years. Analog-to-digital converters (ADCs) are key components in these power limited systems. Therefore, development of ADCs with medium resolution (8-10 bits) and sampling rate (1 MHz) have been of great importance. This thesis presents an 8-bit successive approximation register (SAR) ADC incorporating an asynchronous control logic to avoid external high frequency clock, a dynamic comparator to improve linearity and a differential charger-distribution DAC with a monotonic capacitor switching procedure to achieve better power efficiency. This ADC is developed on a 0.18um TSMC process using Cadence Integrated Circuit design tools. At a sampling rate of 1MS/s and a supply voltage of 1.8V, this 8-bit SAR ADC achieves an effective number of bits (ENOB) of 7.39 and consumes 227.3uW of power, resulting in an energy efficient figure of merit (FOM) of 0.338pJ/conversion-step. Measured results show that the proposed SAR ADC achieves a spurious-free dynamic range (SFDR) of 57.40dB and a signal-to-noise and distortion ratio (SNDR) of 46.27dB. Including pad-ring measured chip area is 0.335sq-mm with the ADC core taking up only 0.055sq-mm

The first part of this work is devoted to the design of a traction asynchronous motor. The second part focuses on the developed method of the equivalent circuit parameters identification of the asynchronous motor in the form of -network. It is explained here that the equivalent circuit in the shape of a -network, alternatively of an inverse 'I-network, is exactly equivalent and fully-fledged to a T-network, although one of two stray inductances is formally missing. Furthermore, the relationships for the conversions of the T-network parameters to the -network parameters and back, and of the T-network to the inverse 'I-network and back are found. The third part deals with the calculation of the torque and the current characteristics of the asynchronous motor. A sensitive analysis of the torque characteristic is carried out on the individual parameters of the equivalent circuit of the asynchronous motor in the form of a -network and a method of the measurement by means of a flywheel is used for the torque characteristic measurement of the asynchronous motor. The fourth part focuses on the verification of the identified -network parameters in the Matlab-model of the traction drive.

This research study examines the dynamics of student-to-student interpersonal mediated communication motives within asynchronous discussion forums. The objective is to determine the interpersonal mediated communication motives and communicator style of students enrolled in fully asynchronous community college courses with the intention to supplement, enhance, and refine the existing research in online education through the application of relevant theories and methods from the field of communication studies. Specifically, the study seeks to determine students' communication motives for consensus-building and agonistic oriented purposes. A mixed methods approach has been utilized through the implementation of a 5-point Likert scale survey, comprised of forty questions, which was provided towards the end of a traditional 16 week semester to 125 students enrolled in five fully asynchronous courses. In an attempt to discover whether students respond to their classmates' asynchronous discussion forum posts for consensus-building motives or for purposes of engaging in agonistic confrontations, a discourse analysis of various forum responses was performed after completion of the asynchronous courses. Previous studies of community building within asynchronous contexts and interpersonal communication motives research suggest that students enrolled in fully asynchronous courses will engage in student-to-student interpersonal mediated communication for the purpose of pleasure, affection, inclusion, control, companionship, habit, receiving information, participation and functional purposes. Through the implementation of the 5-point Likert-scale survey, I discovered six interpersonal mediated communication motives (inclusion, participation, affection, receiving information, functional and pleasure) of student-to-student responses within fully asynchronous discussion forums and four communicator styles (friendly, attentive, communicator image and impression leaving). The findings from the discourse analysis overwhelmingly revealed that the student-to-student interpersonal mediated communication motive for responding to discussion forum posts was most frequently correlated with the students' rationale for consensus-building as opposed to exhibiting a rationale for agonistic pluralism.

Key words: interpersonal mediated communication motives, communicator styles, asynchronous discussion forums, higher education, consensus-building, agonistic confrontation.

Data acquisition systems for rotordynamic analysis and machine vibration were explored for the purpose of replacing the obsolete Bently Nevada ADRE 208 and ADRE for Windows system. These included the development of Matlab based custom data acquisition systems and a user interface. A model of an anisotropic rotor response undergoing transient speed was developed for the rapid prototyping and testing of data acquisition systems. Several methods for the measurement of amplitudes and phase in both the time domain and frequency domain were developed and compared. An alternate data acquisition method which is more inline with industry practices was created for the purpose of spectral analysis. Additionally, an optimized data acquisition strategy was developed for implementation within the Matlab app which included batch processing, state-based acquisition, and differentiated vector and waveform acquisition rates. A Bently Nevada 2300/20 vibration monitor was configured for use in the lab but found unsuitable for replacing the ADRE 208. Ultimately a Bently Nevada ADAPT 3701/44 Vibration Monitor was configured and found to be an adequate replacement for the ADRE 208 system for use in the Cal Poly Vibrations Lab.

L'élection de leader est importante pour les services tolérants aux pannes dans les systèmes distribués asynchrones. En coordonnant les actions d'un ensemble de processus, elle permet de résoudre des problèmes d'accord comme le consensus, un problème fondamental en informatique distribuée. Des algorithmes de consensus, tel que Paxos, s'appuient sur un service d'élection de leader ultime, également appelé Omega. Omega renvoie l'identité d'un processus du système et garantit qu'après un certain temps, l'identité du même processus correct est toujours renvoyée. Plusieurs algorithmes d'élection de leader ont été proposés dans la littérature pour implémenter Omega. Parmi ceux considérant les systèmes dynamiques, la plupart ne choisissent pas le leader selon un critère topologique. Or, la position du leader dans le réseau impacte directement les performances des algorithmes utilisant le service d'élection, car le leader doit souvent interagir avec les autres processus pour, par exemple, collecter les informations d'une majorité de processus dans le cas du consensus. Cette thèse étudie le problème d'élection de leader ultime dans les réseaux dynamiques. Deux algorithmes d'élection sont proposés pour les réseaux mobiles ad hoc. Ceux-ci maintiennent et exploitent la connaissance de la topologie du réseau pour élire à terme un unique leader par composante connexe ayant la meilleure centralité de proximité. Des évaluations sur simulateurs avec différents modèles de mobilité montrent que ces algorithmes présentent de meilleures performances que d'autres algorithmes de la littérature, notamment moins de messages, des chemins plus courts vers le leader, et une meilleure stabilité
Leader election is important for many fault-tolerant services in asynchronous distributed systems. By coordinating actions of a set of processes, it allows solving agreement problems like the consensus, a fundamental problem of distributed computing. Several consensus algorithms, such as Paxos, rely on an eventual leader election service, also known as the Omega failure detector. Omega returns the identity of a process in the system, ensuring that eventually the identity of the same correct process is always returned. Many leadership algorithms were proposed in the literature to implement Omega. Among those that consider dynamic systems, most of them do not choose the leader according to a topological criterion. However, the position of the leader in the network directly impacts the performance of algorithms using the leader election service, since the leader must often interact with other processes, for example, to collect information from a majority of processes in consensus algorithms. This thesis studies the eventual leader election problem in dynamic evolving networks and performance related issues. Two eventual leader election algorithms are proposed for Mobile Ad Hoc Networks. They maintain and exploit the knowledge of the network topology to eventually elect one leader per connected component with the best closeness centrality. Evaluations were conducted on simulators with different mobility models and performance results show that these algorithms present better performance than other algorithms of the literature, including fewer messages, shortest paths to the leader, and better stability

While online students should take charge of their own learning and form collaborative learning communities, constructivist instructors should scaffold online learning without dominating course discussions. This research continues the longitudinal investigation of web-based courses at the Faculty of Education, University of Pretoria. The mixed methodological approach this investigation followed consisted predominantly of qualitative methods, augmented with quantitative approaches. I used two distinct online tools to explore student participation in an eight-week online Masters’-level course delivered via the WebCT™ platform. First, I reviewed the use of metaphors in the literature by a framework of requirements for successful online learning. The use of metaphor supports constructivism, facilitates course interaction, helps to avoid students’ initial inertia in online discussions, and contributes to the development of virtual learning communities. I researched how an explanatory metaphor as tool supported online participation and indicated that metaphors eased students’ communication of important and difficult issues. Secondly, I used the tool of a covert virtual student that also acted as an additional facilitator and course helper. I examined the ethical implications of the carefully concealed real identity of the mythical online helper, methical Jane. As she took part in all course activities and assignments, as well as providing her co-students with cognitive and technical support, the students accepted and integrated her presence in their virtual learning community. I consequently analysed students’ reactions to her identity after disclosure of her origin after the course. Although the exposure precipitated students’ shock, disbelief and dismay as she was a convincing virtual student, they did not object to the presence of a virtual student, but rather felt betrayed due to her hidden real identity. The benefits of this teaching intervention include experts supplying technical expertise, multiple faculty enriching the learning experience, and support and teaching assistants and tutors participating with smaller groups in large online classes. I further examined how frequency of course access, discussion postings, collaborative behaviour and integration into a virtual learning community relate to learning and course completion. Quantitative indices indicated highly significant differences between the stratifications of student performance. Absent and seldom-contributing students risked missing the benefits of the online learning community. Students were discontent with peers who rarely and insufficiently contributed to group assignments. Low participation varied from only reading, skimming, or deliberately harvesting others’ contributions, to high student contributions of little value. Conclusions on the formation of an online learning community indicate that the passport to membership of the community is quality participation, rather than prior peer acquaintance. I indicated that students’ learning benefited from contributing high quality inputs to online learning communities while students with poor participation did not benefit from the online learning community. Online facilitators contribute to students’ learning through the timeliness and quality of tailored scaffolding. Recommendations for future research include uncovering the reasons for students’ stressful experiences of online learning; the effect of online assessment on student course participation; the alignment of learning metaphors in multi-cultural learning environments; and the support of non-participating online students.
Thesis (PHD)--University of Pretoria, 2009.
Curriculum Studies
unrestricted

The Diploma thesis describes the design, manufacture and testing of a universal automation machine for church bells. The research section summarizes the bell, way of use and properties. The drives and their starting and power switching characteristic are analyzed. The chain drive based on the selected engine and the whole assembly is designed and tested by using PLC. Unique controller based on a modular design was designed. Sensors based on magnetic rotary encoder were also created for this unit. The entire circuit was tested on three evangelical church bells in the town Klobouky u Brna.

This thesis describes the flexible voltage control of a multi-level-voltage-reinjection voltage source converter. The main purposes are to achieve reactive power generation flexibility when applied for HVdc transmission systems, reduce dynamic voltage balancing for direct series connected switches and an improvement of high power converter efficiency and reliability. Waveform shapes and the impact on ac harmonics caused by the modulation process are studied in detail. A configuration is proposed embracing concepts of multi level, soft-switching and harmonic cancellation. For the configuration, the firing sequence, waveform analysis, steady-state and dynamic performances and close-loop control strategies are presented. In order not to severely compromise the original advantages of the converter, the modulated waveforms are proposed based on the restrictions imposed mathematically by the harmonic cancellation concept and practically by the synthesis circuit complexity and high switching losses. The harmonic impact on the ac power system prompted by the modulation process is studied from idealistic and practical aspects. The circuit topology being proposed in this thesis is developed from a 12-pulse bridge and a converter used classically for inverting power from separated dc sources. Switching functions are deduced and current paths through the converter are analysed. Safe and steady-state operating regions of the converter are studied in phasor diagrams to facilitate the design of simple controllers for active power transfer and reactive power generations. An investigation into the application of this topology to the back-to-back VSC HVdc interconnection is preformed via EMTDC simulations.

Recent developments of high performance computing capabilities allow solving modern science problems employing sophisticated computational techniques. However, it is necessary to ensure the efficiency of state of the art computational methods to fully take advantage of modern technology capabilities. In this thesis we propose uncertainty quantification and high performance computing strategies to solve fluid dynamics systems characterized by uncertain conditions and unknown parameters. We verify that such techniques allow us to take decisions faster and ensure the reliability of simulation results. Different sources of uncertainties can be relevant in computational fluid dynamics applications. For example, we consider the shape and time variability of boundary conditions, as well as the randomness of external forces acting on the system. From a practical point of view, one has to estimate statistics of the flow, and a failure probability convergence criterion must be satisfied by the statistical estimator of interest to assess reliability. We use hierarchical Monte Carlo methods as uncertainty quantification strategy to solve stochastic systems. Such algorithms present three levels of parallelism: over levels, over realizations per level, and on the solution of each realization. We propose an improvement by adding a new level of parallelism, between batches, where each batch has its independent hierarchy. These new methods are called asynchronous hierarchical Monte Carlo, and we demonstrate that such techniques take full advantage of concurrency capabilities of modern high performance computing environments, while preserving the same reliability of state of the art methods. Moreover, we focus on reducing the wall clock time required to compute statistical estimators of chaotic incompressible flows. Our approach consists in replacing a single long-term simulation with an ensemble of multiple independent realizations, which are run in parallel with different initial conditions. The error analysis of the statistical estimator leads to the identification of two error contributions: the initialization bias and the statistical error. We propose an approach to systematically detect the burn-in time to minimize the initialization bias, accompanied by strategies to reduce the simulation cost. Finally, we propose an integration of Monte Carlo and ensemble averaging methods for reducing the wall clock time required for computing statistical estimators of time-dependent stochastic turbulent flows. A single long-term Monte Carlo realization is replaced by an ensemble of multiple independent realizations, each characterized by the same random event and different initial conditions. We consider different systems, relevant in the computational fluid dynamics engineering field, as realistic wind flowing around high-rise buildings or compressible potential flow problems. By solving such numerical examples, we demonstrate the accuracy, efficiency, and effectiveness of our proposals.
Los desarrollos relacionados con la computación de alto rendimiento de las últimas décadas permiten resolver problemas científicos actuales, utilizando métodos computacionales sofisticados. Sin embargo, es necesario asegurarse de la eficiencia de los métodos computacionales modernos, con el fin de explotar al máximo las capacidades tecnológicas. En esta tesis proponemos diferentes métodos, relacionados con la cuantificación de incertidumbres y el cálculo de alto rendimiento, con el fin de minimizar el tiempo de computación necesario para resolver las simulaciones y garantizar una alta fiabilidad. En concreto, resolvemos sistemas de dinámica de fluidos caracterizados por incertidumbres. En el campo de la dinámica de fluidos computacional existen diferentes tipos de incertidumbres. Nosotros consideramos, por ejemplo, la forma y la evolución en el tiempo de las condiciones de frontera, así como la aleatoriedad de las fuerzas externas que actúan sobre el sistema. Desde un punto de vista práctico, es necesario estimar valores estadísticos del flujo del fluido, cumpliendo los criterios de convergencia para garantizar la fiabilidad del método. Para cuantificar el efecto de las incertidumbres utilizamos métodos de Monte Carlo jerárquicos, también llamados hierarchical Monte Carlo methods. Estas estrategias tienen tres niveles de paralelización: entre los niveles de la jerarquía, entre los eventos de cada nivel y durante la resolución del evento. Proponemos agregar un nuevo nivel de paralelización, entre batches, en el cual cada batch es independiente de los demás y tiene su propia jerarquía, compuesta por niveles y eventos distribuidos en diferentes niveles. Definimos estos nuevos algoritmos como métodos de Monte Carlo asíncronos y jerárquicos, cuyos nombres equivalentes en inglés son asynchronous hierarchical Monte Carlo methods. También nos enfocamos en reducir el tiempo de computación necesario para calcular estimadores estadísticos de flujos de fluidos caóticos e incompresibles. Nuestro método consiste en reemplazar una única simulación de dinámica de fluidos, caracterizada por una ventana de tiempo prolongada, por el promedio de un conjunto de simulaciones independientes, caracterizadas por diferentes condiciones iniciales y una ventana de tiempo menor. Este conjunto de simulaciones se puede ejecutar en paralelo en superordenadores, reduciendo el tiempo de computación. El método de promedio de conjuntos se conoce como ensemble averaging. Analizando las diferentes contribuciones del error del estimador estadístico, identificamos dos términos: el error debido a las condiciones iniciales y el error estadístico. En esta tesis proponemos un método que minimiza el error debido a las condiciones iniciales, y en paralelo sugerimos varias estrategias para reducir el coste computacional de la simulación. Finalmente, proponemos una integración del método de Monte Carlo y del método de ensemble averaging, cuyo objetivo es reducir el tiempo de computación requerido para calcular estimadores estadísticos de problemas de dinámica de fluidos dependientes del tiempo, caóticos y estocásticos. Reemplazamos cada realización de Monte Carlo por un conjunto de realizaciones independientes, cada una caracterizada por el mismo evento aleatorio y diferentes condiciones iniciales. Consideramos y resolvemos diferentes sistemas físicos, todos relevantes en el campo de la dinámica de fluidos computacional, como problemas de flujo del viento alrededor de rascacielos o problemas de flujo potencial. Demostramos la precisión, eficiencia y efectividad de nuestras propuestas resolviendo estos ejemplos numéricos.
Gli sviluppi del calcolo ad alte prestazioni degli ultimi decenni permettono di risolvere problemi scientifici di grande attualità, utilizzando sofisticati metodi computazionali. È però necessario assicurarsi dell’efficienza di questi metodi, in modo da ottimizzare l’uso delle odierne conoscenze tecnologiche. A tal fine, in questa tesi proponiamo diversi metodi, tutti inerenti ai temi di quantificazione di incertezze e calcolo ad alte prestazioni. L’obiettivo è minimizzare il tempo necessario per risolvere le simulazioni e garantire alta affidabilità. Nello specifico, utilizziamo queste strategie per risolvere sistemi fluidodinamici caratterizzati da incertezze in macchine ad alte prestazioni. Nel campo della fluidodinamica computazionale esistono diverse tipologie di incertezze. In questo lavoro consideriamo, ad esempio, il valore e l’evoluzione temporale delle condizioni di contorno, così come l’aleatorietà delle forze esterne che agiscono sul sistema fisico. Dal punto di vista pratico, è necessario calcolare una stima delle variabili statistiche del flusso del fluido, soddisfacendo criteri di convergenza, i quali garantiscono l’accuratezza del metodo. Per quantificare l’effetto delle incertezze sul sistema utilizziamo metodi gerarchici di Monte Carlo, detti anche hierarchical Monte Carlo methods. Queste strategie presentano tre livelli di parallelizzazione: tra i livelli della gerarchia, tra gli eventi di ciascun livello e durante la risoluzione del singolo evento. Proponiamo di aggiungere un nuovo livello di parallelizzazione, tra gruppi (batches), in cui ogni batch sia indipendente dagli altri ed abbia una propria gerarchia, composta da livelli e da eventi distribuiti su diversi livelli. Definiamo questi nuovi algoritmi come metodi asincroni e gerarchici di Monte Carlo, il cui corrispondente in inglese è asynchronous hierarchical Monte Carlo methods. Ci focalizziamo inoltre sulla riduzione del tempo di calcolo necessario per stimare variabili statistiche di flussi caotici ed incomprimibili. Il nostro metodo consiste nel sostituire un’unica simulazione fluidodinamica, caratterizzata da un lungo arco temporale, con il valore medio di un insieme di simulazioni indipendenti, caratterizzate da diverse condizioni iniziali ed un arco temporale minore. Questo insieme 10 di simulazioni può essere eseguito in parallelo in un supercomputer, riducendo il tempo di calcolo. Questo metodo è noto come media di un insieme o, in inglese, ensemble averaging. Calcolando la stima di variabili statistiche, commettiamo due errori: l’errore dovuto alle condizioni iniziali e l’errore statistico. In questa tesi proponiamo un metodo per minimizzare l’errore dovuto alle condizioni iniziali, ed in parallelo suggeriamo diverse strategie per ridurre il costo computazionale della simulazione. Infine, proponiamo un’integrazione del metodo di Monte Carlo e del metodo di ensemble averaging, il cui obiettivo è ridurre il tempo di calcolo necessario per stimare variabili statistiche di problemi di fluidodinamica dipendenti dal tempo, caotici e stocastici. Ogni realizzazione di Monte Carlo è sostituita da un insieme di simulazioni indipendenti, ciascuna caratterizzata dallo stesso evento casuale, da differenti condizioni iniziali e da un arco temporale minore. Consideriamo e risolviamo differenti sistemi fisici, tutti rilevanti nel campo della fluidodinamica computazionale, come per esempio problemi di flusso del vento attorno a grattacieli, o sistemi di flusso potenziale. Dimostriamo l’accuratezza, l’efficienza e l’efficacia delle nostre proposte, risolvendo questi esempi numerici.
Enginyeria civil

Répondre à des requêtes de routage requiert que les entités du réseau, nommées routeurs, aient une connaissance à jour sur la topologie de celui-ci, cette connaissance est appelée table de routage. Le réseau est modélisé par un graphe dans lequel les noeuds représentent les routeurs, et les arêtes les liens de communication entre ceux ci.Cette thèse s'intéresse au calcul des tables de routage dans un modèle distribué.Dans ce modèle, les calculs sont effectués par un ensemble de processus placés sur les noeuds. Chaque processus a pour objectif de calculer la table de routage du noeud sur lequel il se trouve. Pour effectuer ce calcul les processus doivent communiquer entre eux. Dans des réseaux de grande taille, et dans le cadre d'un calcul distribué, le maintien à jour des tables de routage peut être coûteux en terme de communication. L'un des thèmes principaux abordés et celui de la réduction des coûts de communication lors de ce calcul. L'une des solutions apportées consisteà réduire la taille des tables de routage, permettant ainsi de réduire les coûts de communication. Cette stratégie classique dans le modèle centralisé est connue sous le nom de routage compact. Cette thèse présente notamment un algorithme de routage compact distribué permettant de réduire significativement les coûts de communication dans les réseaux tels que le réseau internet, i.e. le réseau des systèmes autonomes ainsi que dans des réseaux sans-échelle. Ce document contient également une étude expérimentale de différents algorithmes de routage compact distribués.Enfin, les problèmes liés à la dynamique du réseau sont également abordés. Plusprécisément le reste de l'étude porte sur un algorithme auto-stabilisant de calcul d'arbre de plus court chemin, ainsi que sur l'impact de la suppression de noeuds ou d'arêtes sur les tables de routage stockées aux routeurs.

Les effets d’extrémité jouent un rôle important dans la modélisation et la commande de la Machine Linéaire à Induction (MLI). Ces phénomènes augmentent significativement la non-linéarité du modèle de la machine et génèrent plusieurs difficultés pour contrôler et observer ses états avec de bonnes performances. Cette thèse aborde trois problématiques distinctes : la commande robuste de la MLI, l’estimation de la vitesse et du flux de la MLI et le contrôle robuste à base d’observateur en utilisant la théorie du mode glissant d’ordre supérieur.Dans la première partie de la thèse, trois contrôleurs robustes assurant la poursuite de trajectoire de la vitesse et du flux pour la MIL ont été développés : le Super Twisting (ST), le Super Twisting Adaptatif (STA) et le Twisting Adaptatif (TA). Ces commandes ont été testées en simulations et leurs performances ont été démontrées. Ainsi, le ST assure un contrôle continu avec convergence à temps fini de l’erreur à zéro malgré les perturbations, sous l’hypothèse que les bornes des incertitudes sont connues. Cette hypothèse est relaxée dans le cas du TA et du STA grâce à leurs propriétés adaptatives.Dans la deuxième partie de la thèse, un nouveau modèle du MLI a été proposé et son observabilité a été démontrée. Ensuite un Observateur par Mode Glissant d’Ordre Deux (MGOD) et un Observateur par Mode Glissant d’Ordre Supérieur (MGOS) ont été synthétisé afin d’estimer la vitesse et le flux du MLI, uniquement en utilisant la mesure des tensions et des courants statorique. La stabilité des deux observateurs a été prouvée par une approche de Lyapunov et leurs performances ont été démontrées à travers des simulations.Dans la dernière partie de la thèse, deux commandes par rejet actif des perturbations sont synthétisées. Ainsi et dans un premier temps, le modèle de la MLI est décomposé en deux sous-systèmes du second ordre. Ensuite, deux contrôleurs (le twisting et le super-twsiting) ont été synthétisés afin d’assurer la poursuite du flux et de la vitesse. Le MGOS est utilisé pour estimer les dérivées du flux et de la vitesse, ainsi que pour l’estimation en temps réel de la perturbation. Les contrôleurs quant à eux assurent la compensation des perturbations et la poursuite des trajectoires du flux et de la vitesse. La stabilité et la convergence des deux commandes proposées ont été prouvées et leurs performances démontrées par simulation
Dynamic end effects play an important role in the Linear Induction Machine (LIM) control. They increase significantly the nonlinearity of the machine model and generate several difficulties to control and observe states with good performances. This thesis addresses three distinctissues: LIM robust control, LIM speed and flux estimation and observer-based robust control using higher order sliding mode theory.In the first part, to achieve speed and flux tracking,Super Twisting Controller (STC), Adaptive Super Twisting Controller (ASTC), and Adaptive Twisting Controller (ATC) were proposed and implemented into LIM system with great performance, i.e. finite time convergence and robustness properties. Among them, STC ensures continuous control with finite time convergence of the error to zero despite disturbances, under the assumption that their bounds are known. ATC and ASTC can deal with unknown bounded disturbance thanks to their adaptive properties.In the second part, a novel simplified LIM model was proposed and its observability has been proved. Then, Second Order Sliding Mode Observer (SOSMO) and Adaptive High Order Sliding Mode Observer (HOSMO) were proposed to estimate LIM speed, only by using the measured stator voltages and stator currents. SOSMO observer is based on the super twisting algorithm and its stability has been proved with Lyapunov’s theory, which can guarantee finite time convergence with less chattering. Adaptive HOSMO strategy combines speed adaptive algorithm and HOSMO method together to estimate rotor fluxes and speed simultaneously.In the third part, the LIM is viewed as two second order subsystems. Moreover, only the speed and the flux are supposed to be measured. Based on that two differentcontrollers based on HOSMO were presented in order to achieve flux and speed tracking. In both controllers, the idea of active disturbance rejection control is applied. Hence, the HOSMO is used to estimate the derivatives of the flux and the speed, as well as the disturbance. Then, in order to deal with the uncertainty in the measured variables, two different SM controllers are proposed. Firstly, the TC is applied in the LIM. However, the control signal in this case is discontinuous. Then, in order to provide a continuous control signal, the TC is replaced with STC. The stability and convergence of proposed TC-HOSMO and STC-HOSMO approaches were given and simulation validated their performances

Les centrales nucléaires sont une source de production d'énergie importante en France. Cependant, suite aux différents accidents et aux risques encourus avec cette technologie, la sûreté nucléaire est une préoccupation mondiale. En France, des normes sont imposées continuellement sur les installations nucléaires existantes et sur les prochaines générations en développement. Parmi les nombreux aspects de la sûreté nucléaire, le dimensionnement des structures mécaniques est un sujet important pour les acteurs industriels. L'activité principale de l'entreprise Framatome concerne le dimensionnement et la justification des centrales nucléaires. Celles-ci doivent être conçues pour résister à des conditions extrêmes d'utilisation telles que des séismes, des crashs d'avion ou encore des ruptures de tuyauterie. La modélisation numérique de ce type de chargement passe par des analyses dynamiques temporelles afin de considérer ces phénomènes multi-échelles en temps. Cependant, réaliser ces analyses demande beaucoup de temps CPU et de mémoire. L'objectif de la thèse est le développement d'un nouvel intégrateur hétérogène (différents schémas d'intégration) asynchrone (différents pas de temps), basé sur la méthode de couplage GC, ayant de meilleures propriétés relatives à la conservation énergétique. En effet, les phénomènes multi-échelles en temps présents dans le bloc réacteur sont des cas d'usages favorables aux méthodes multi-échelles en temps, avec un intégrateur explicite pour les zones de contact, comportant une discrétisation temporelle fine, et un intégrateur implicite pour le reste de la structure, discrétisé par des pas de temps plus gros. Un démonstrateur de co-simulation est développé entre les logiciels Code Aster et Europlexus pour se rapprocher d'un développement industriel et ainsi montrer le gain de performance, pour un modèle tridimensionnel de bloc réacteur, apporté par les approches de co-simulation multi-échelles en temps
Nuclear power plants are an important source of energy production in France. However, following the various accidents and risks associated with this technology, nuclear safety is a global concern. In France, standards are continually being imposed on existing nuclear facilities and on the next generations under development. Among the many aspects of nuclear safety, the dimensioning of mechanical structures is an important subject for industrial players. Framatome's core business is the design and justification of nuclear power plants. These must be designed to withstand extreme operating conditions, such as earthquakes, plane crashes or pipe ruptures. Numerical modeling of this type of loading requires dynamic temporal analyses to consider these multi-scale phenomena. However, such analyses are CPU and memory intensive. The aim of this thesis is to develop a new heterogeneous (different integration schemes) and asynchronous (different time steps) integrator, based on the GC coupling method, with improved energy conservation properties. The multi-scale phenomena present in the reactor block are simulated using an explicit integrator with small time steps for the contact zones and an implicit integrator with large time steps for the rest of the structure. A co-simulation demonstrator is developed between the Code Aster and Europlexus software packages in order to get closer to an industrial development and thus demonstrate the performance gain, for a three-dimensional reactor block model, provided by the multi-time-scale co-simulation approaches

This diploma thesis describes how to create or convert traditional Java programs to desktop-like rich internet applications with the Google Web Toolkit. The Google Web Toolkit is an open source development environment, which translates Java code to browser and device independent HTML and JavaScript. Most of the GWT framework parts, including the Java to JavaScript compiler as well as important security issues of websites will be introduced. The famous Agricola board game will be implemented in the Model-View-Presenter pattern to show that complex user interfaces can be created with the Google Web Toolkit. The Google Web Toolkit framework will be compared with the JavaServer Faces one to find out which toolkit is the right one for the next web project
Diese Diplomarbeit beschreibt die Erzeugung desktopähnlicher Anwendungen mit dem Google Web Toolkit und die Umwandlung klassischer Java-Programme in diese. Das Google Web Toolkit ist eine Open-Source-Entwicklungsumgebung, die Java-Code in browserunabhängiges als auch in geräteübergreifendes HTML und JavaScript übersetzt. Vorgestellt wird der Großteil des GWT Frameworks inklusive des Java zu JavaScript-Compilers sowie wichtige Sicherheitsaspekte von Internetseiten. Um zu zeigen, dass auch komplizierte graphische Oberflächen mit dem Google Web Toolkit erzeugt werden können, wird das bekannte Brettspiel Agricola mittels Model-View-Presenter Designmuster implementiert. Zur Ermittlung der richtigen Technologie für das nächste Webprojekt findet ein Vergleich zwischen dem Google Web Toolkit und JavaServer Faces statt

碩士
國立交通大學
資訊科學系所
93
Complex jobs such as bio-genetic sequencing and protein modeling requires massive quantity of calculation and execution procedures. Today, industry applies Grid Computing technologies to delegate the intensive computational work to a farm of cluster computers in order to accelerate computing speed. This category of grid computing rely on sumptuous hardware or distinctive, specific software, thus restraining grid computing to constricted domains such as high-speed scientific computation. Despite the widespread acceptance of grid concept, high TCO(Total Cost of Ownership) intimidated the general public or even SMEs(Small-Medium Enterprises) from adopting grid technologies. Vast amount of potential computing capacity still remains untapped. Users are continually searching for more computing resources to assist solve problems. On top of these challenges, Grid itself suffers certain technical imperfections. Commercial solutions are incapable of solving single-point-of-failure issues, incapable of dynamically expanding the volume of grid network and is certainly having a difficult time migrating grid infrastructure to a universe of different electronic devices existing today. This research proposes a low-cost, pure software-based, cross-platform grid framework, eliminating the mishap of single-point of failure, allowing dynamic grid expansion. The framework also provides utility tools and Application Programming Interfaces(APIs) that simplifies the process of grid application development, thus optimizes overall productivity. Developers must focus on design and development rather than hunting for resources hidden within the enterprise.

碩士
國立臺灣師範大學
資訊工程研究所
100
The Software testing is a one of phase of software engineering. This can find out defects on Products, in the sequential program testing, the results often can be predicted, but in the concurrent testing results are always unpredicted. The concurrent program is composed by more than one Processes(or Threads) to complete the assigned tasks at the same time ,The common testing methods include Non-Deterministic Testing、Deterministic Testing and Reachability Testing , The Non- Deterministic Testing lets the Programs free running on Testing , but It may only show part of situation . Not all cases, Deterministic Testing of Concurrent Program P is carefully select a set of tests (X,S), and the forced execution determines whether S is feasible for P , But deterministic testing has additional problems to solve. One major problem is deciding which pairs of inputs and SYN-sequences to select for a concurrent program. In this paper, I will study how to use reachability testing in dynamic testing of Single-Channel-Multiple-Receivers asynchronous message passing programs. Because the reachability testing is used in test shared memory read/write event. If I use the reachability testing on asynchronous message passing programs. It will be deadlock, It is necessary for architecture to make big changes. Finally, I will use a modified version of reachability testing method on asynchronous message passing programs, and collect execution information to do analysis of whether there is message competition.

A research report subuutted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science. Degree awarded with distinction
This report describes a dynamic Quality of Service (QoS) - based call admission protocol tor distributed multimedia over ATM networks. The protocol incorporates the innovative idea of an extended QoS. This is a composite term which takes account of not only classic QoS multimedia measures, but also of the human aspect of the interaction through human receptivity. For this scenario, different QoS negotiation strategies have been formulated and then simulated with a view towards the establishment of a protocol knowledge base. Separately, a session pricing policy has been elaborated and its effect on user behaviour and network resource allocation studied.
Andrew Chakane 2018

This thesis addresses a number of issues present in the modern and future power distribution system where high penetration of distributed generation (DG) and smart sensors change the environment in which power flow must be managed. The shift in balance of power supply from the centralized to the distributed can lead to network constraint breaches such as voltage and frequency limits, fault ride through capability, system security, reliability and stability. Common regulation approaches may be inadequate in addressing these network regulation problems, leading to inefficient use of DG and unnecessary high voltage (HV) grid imports. Furthermore, the increase in intelligent Smart Grid components will lead to the transmission and processing of large volumes of data making the optimal control of a network a more challenging problem. Optimisation methods must take into consideration the increase and distributed nature of data, and account for data synchronization, latency, and privacy issues. However, if these challenges can be overcome, then the increase in the controllability and observability of smart grid components, such as distributed generators, storage and controllable demands, offers great potential for the improvement of network optimality and stability. In this thesis, a set of innovative distributed algorithms are presented that solve the optimal power flow problem of a distribution network featuring advanced nodal monitoring and control of DG, storage and loads. These algorithms exploit the network structure to produce iterative solutions to solve the global optimisation problem. They are carefully developed taking into account the realistic limitations where each node can only exchange information with adjacent neighbours but does not have sufficient information about the other nodes in a large scale system. Two partitioning strategies are considered which aim to improve the structure of the communication and control subsystem in order to better facilitate optimal control. The first strategy measures subnet optimality according to the minimisation of mismatch between DG power and local demand, therefore maximising DG utilisation, minimising line loss, and minimising HV grid imports. The second strategy is based on sets of strongly coupled buses, where the coupling of buses is characterised according to the potential for a change in power at one bus to impact the state estimation error at another, therefore improving solution optimality. Subsequently, a distributed predictive optimal control algorithm is proposed, through the method of approximate dynamic programming, that utilises a central coordinator to improve network state estimation and control sequence optimality. The centrally coordinated solution has the benefit of a near optimal solution without burdening controllers with the high dimensional state of the entire distribution network, but rather utilising only a summary of global information. Improvements to the centrally coordinated scheme are then developed through a fully distributed optimal power flow algorithm that requires no central coordination. The fully distributed approach maintains the reduced computational requirements of controllers but improves on the centrally coordinated configuration by restricting data communication to local neighbourhoods. Three variants of the distributed OPF solution are suggested for application to three distinct scenarios: Optimal DG control in a distribution network, DG optimal control in an islanded distribution network, and optimal power management in a home energy management system. These three approaches address significant issues associated with distributed control. An optimal solution to the global problem is achievable in each case, and iterations of the algorithm are shown to be stable and convergent through the use of an augmented Lagrange formulation. Global information necessary for a feasible solution is shared through the development of a new asynchronous consensus protocol, and a communication protocol is presented to enable instantiation, execution and conclusion of fully distributed optimisation sessions. For each studied approach, algorithms are carefully developed that concisely define the method of application. For each presented algorithm, a reasonable amount of computer simulation is applied to verify their applicability to a range of relevant scenarios. The simulations study the algorithms’ convergence and scalability, solutions’ optimality in a local sense, and solution feasibility. In each case the simulations successfully demonstrate the presented methods’ practicality for the studied scenarios.

碩士
國立臺北科技大學
資訊工程系
106
In recent years, the rapid development of wireless network applications has made spectrum a precious resource. However, the most licensed spectrum has not been fully used, resulting in insufficient utilization of spectrum. Since cognitive radio networks(CRNs) allow multiple users to use the same spectrum at the same time for transmission. and it can significantly increase the efficiency of spectrum usage and be therefore widely studied. In order to respond to the changes in available channels and the transmission of burst data in cognitive radio networks, this paper proposes a dynamic continuous quorum-based multichannel hopping power-saving unicast/multicast protocol for burst data in asynchronous radio networks, and to ensure two devices can still have the opportunity to have a continuous intersection in order to facilitate the transmission of burst data. As shown in the simulation result, when we transmit burst traffics, especially in the heavy load, protocols using continuous quorum systems, such as United continuous L-coterie, m-United continuous L-coterie, could outperform protocols using other quorum system by improving 10% packet arrival ratio, and 10% throughput, and reducing 20% MTIM frame quantity. It is because the continuous quorum systems have more opportunity to have continuous intersections. The sender could continuously transmit burst traffics during continuous intersections. Thus, using continuous quorum systems could reduce MTIM quantity, reduce transmission delay, increase transmission throughput, and thus, satisfy QoS for transmitting burst traffics.

碩士
國立臺北科技大學
資訊工程系
107
In recent years, due to the increasing power of mobile devices, the rapid development of wireless network applications has made the spectrum a precious resource. Cognitive radio networks (CRNs) have been widely studied by allowing multiple users to use the same spectrum for Rendezvous at the same time to facilitate the transmission of data. In order to respond to the change of available channels and the transmission of burst data in the cognitive radio network, this paper proposes a continuous composition sequence-based multichannel hopping power-saving multicast protocols for dynamic channels in asynchronous cognitive radio networks. The protocol ensures that multiple devices have the opportunity to have a continuous rendezvous even if the time is not synchronized.

Bibliography: leaves 156-165.
xvi, 174 leaves : ill. ; 30 cm.
This thesis analyses the design of a Dynamic RAM in gallium arsenide for use as a buffer in an ATM switch. The causes of leakage are investigated and methods to overcome or compensate the leakage are devised, resulting in a memory cell with a large storage time, high speed and low power dissipation. A 14 kbit RAM array is designed and laid out in gallium arsenide. The RAM array is designed to operate over a -25oC to +125oC temperature range using process parameters which vary by up to 2 [sigma] from typical.
Thesis (M.Eng.Sc.)--University of Adelaide, Dept. of Electrical & Electronic Engineering, 1996?

The overall objective of this thesis is to obtain a comprehensive understanding of the stability behavior of general parametrically excited systems. Even though the manifold resonance effects caused by time-periodic variation of system parameters have been intensively studied since the mid-19th century, several aspects still remain unexplored. While, historically, parametric excitation had been prominent predominantly for its destabilizing impact (resonance), in recent decades, also its stabilizing impact (anti-resonance) had attained significant attention. Owing to this historical development, the coexistence of resonance and anti-resonance at certain frequencies in the case of asynchronous excitation was not identified. Further, most of the existing studies dealing with the appearance of different resonance effects are limited to simple systems featuring neither circulatory nor gyroscopic terms, making the response of more complex systems to parametric excitation unpredictable. In the present contribution, the stability behavior of systems featuring circulatory and gyroscopic terms subject to asynchronous parametric excitation is investigated employing the semi-analytical method of normal forms. First, novel stability patterns are identified revealing global stabilizing and destabilizing effects. More importantly, it is shown that, contrary to the previous knowledge, resonance and anti-resonance may both simultaneously appear in the vicinity of certain resonance frequencies with a particularly steep transition between them. Even for complex systems featuring circulatory terms, these effects can be easily assessed qualitatively and quantitatively using the symbolic expressions derived for the most representative stability features. The results are validated on an electronic system following the simulation-based approach. Finally, with the enhanced understanding of the parametric stability phenomena, two exemplary mechanical systems, including a minimal model of a disk brake, are analyzed. The analysis emphasizes the practical significance of the coexistence of resonance and anti-resonance and advocates more accurate consideration of possible asymmetries, i.e., parametric excitation, in the brake squeal analysis.

碩士
國立交通大學
光電工程系所
96
Asynchronous mode-locked fiber soliton lasers have some interesting properties including slow periodic variation of the pulse parameters and excellent low noise performance. They may find applications in high speed optical communication, ultrafast optical processing, and other scientific researches. The study of the thesis is focused on how to characterize the slow periodic variation of the pulse timing position and the pulse center frequency by directly analyzing the RF spectra of the laser output pulse train. The measured results are compared with theoretical results to enhance our understanding on the laser dynamics of asynchronous mode locked fiber soliton lasers. This will also help to develop the applications of this new laser source.

碩士
國立交通大學
光電工程學系
99
Asynchronous Harmonic Mode-Locked Ytterbium Doped Fiber Lasers have many characteristics which are of great application potentials in the fields of long-distance optical communication, bio-photonics and ultrafast optics. These advantages include higher super-mode suppression ratios and the capability of generating ultrahigh repetition rate and ultra-short pulse trains. In this thesis, we demonstrate for the first time an asynchronous harmonic mode-locked ytterbium doped fiber laser with the hybrid mode-locking technique. This is the first observation of the asynchronous harmonic mode-locking in a normal dispersion fiber cavity. The deviation frequency of the laser is 94 kHz and the super-mode suppression ratio is around 60 dB at the 10 GHz asynchronous harmonic mode-locked state. The super-mode suppression ratio increases around 40 dB than the ordinary harmonic mode-locked state. The output power is around 20 mW operating at 1050 nm, a useful wavelength in many applications including bio-photonics.

碩士
國立交通大學
顯示科技研究所
100
The thesis is focused on the laser dynamics studies of asynchronous rational harmonic mode-locked Er-doped fiber soliton lasers. The rational harmonic mode-locking can provide higher repetition rates and the asynchronous mode-locking can help achieve good mode-locking performance. We stabilize the laser cavity length by locking the deviation frequency of asynchronous mode-locking to help measure the laser dynamics of the laser system. Base on the information of the RF spectra, we estimate the timing and center frequency variation of the asynchronous rational harmonic mode-locked pulse trains. We verify that the effective modulation strength is mainly from the higher order signals of the RF amplifier in asynchronous rational harmonic mode-locked lasers with only phase modulation. We also experimentally find a new operation state of synchronous harmonic mode-locking. Stable 40 GHz mode-locking operation can be achieved with RF spectral sidebands quite similar to the asynchronous mode-locking. A series of experiments have been performed to investigate the characteristics of this interesting new operation state.

Metastability is an ubiquitous phenomenon in nature. It appears in a plethora of diverse fields including physics, chemistry, biology, computer science, climatology and economics. Metastability is best described as a dynamical phenomenon that occurs when a system is close to a first order phase transition. After changing some thermodynamic parameters, the system remains for a considerable (random) time in the old phase, the metastable state, before suddenly making a transition to the new phase, the stable state. In other words, on a short time scale, the system behaves as if it was in equilibrium, while, on a long time scale, it moves between different regions of the state space. At low temperature, this motion is preceded by the appearance of a critical mesoscopic configuration of the system via a spontaneous fluctuation or some external perturbation. Thus, when the system is initiated in the metastable phase, it starts its long transition towards the stable phase. In particular, it must overcome an energy barrier to reach the stable state starting from the metastable state. Formally, an Hamiltonian or energy function and the associated dynamics characterized the detailed evolution of the system. Moreover, it is possible to define an equilibrium measure based on the Hamiltonian, for example the Gibbs measure. If the dynamics satisfies the detailed balance condition, then it is reversible with respect to this equilibrium measure. There are three interesting questions that are typically investigated in metastability. The first is the study of the transition time from the set of metastable states to the set of the stable states, i.e., the time necessary to arrive at the equilibrium phase. The second issue is the identification of the so-called critical configurations that the system creates in order to reach equilibrium. The third question concerns the study of the typical paths that the system follows with high probability during the transition from the metastable state to the stable state. The thesis is organized in five chapters. In the first two chapters, we present the different approaches and results on asynchronous (serial) and synchronous (parallel) dynamics, in Chapters 2 and 3 respectively. In particular, at the end of the third chapter, we present one of the novelties of this work: an estimate of the mixing time and of the spectral gap, and the computation of the prefactor for the mean transition time also in the case of a series of degenerate metastable states. Next, we study three models evolving under different dynamics. In Chapter 4, we examine the Ising model on the hexagonal lattice with a serial non-conservative dynamics, Glauber dynamics. In particular, we prove some model-dependent results that together with the results of Chapter 2 yield the desired metastability theorems. Indeed, we identify the metastable states proving the recurrence property and computing the maximal stability level. In addition to this, we give a geometrical description of the critical configurations and we show how these are related to polyiamonds. The characterization of the shape of the critical configurations allows us to estimate the mean transition time via potential-theoretic approach. In Chapter 5.1, we describe a particular Probabilistic Cellular Automata model to represent the metastable behavior of a system subject to parallel dynamics. In particular, using our model-independent results at the end of Chapter 3, we show the behavior of the mixing time and the spectral gap, and we find a rigorous estimate of the expected hitting time. In addition, we identify the metastable states proving recurrence property and classifying the configurations according their stability level. Finally, in Chapter 6, we study the Blume-Capel model evolving under a serial conservative dynamics, the Kawasaki dynamics. These results are still quite heuristic since this is an ongoing project. We present an heuristic study of the phase-diagram and we explain the behavior of the system showing which should be the stable and the metastable states. We suggest an idea based on the crucial role of the boundary to estimate the stability level, to prove the recurrence property and to show the asymptotic behavior of transition time.

Rotordynamics is an important area in mechanical engineering. Many machines contain rotating parts. It is well known that rotating components can develop large amplitude lateral vibrations near certain speeds called critical speeds. This large amplitude vibration is called rotor whirl. This thesis is about rotor whirl. Conventional treatments in rotordynamics use what are called gyroscopic terms and treat the rotor as a one-dimensional structure (Euler-Bernoulli or Timoshenko) with or without rigid masses added to them. Gyroscopic terms are macroscopic inertial terms that arise due to tilting of spinning cross-sections. This approach, while applicable to a large class of industrially important rotors, is not applicable to a general rotor geometry. In this thesis we develop a genuine continuum level three dimensional formulation for rotordynamics that can be used for many arbitrarily shaped rotors. The key insight that guides our formulation is that gyroscopic terms are macroscopic manifestations of the prestress induced due to spin of the rotor. Using this insight, we develop two modal projection techniques for calculating the critical speed of arbitrarily shaped rotors. These techniques along with our prestress based formulation are the primary contributions of the thesis. In addition, we also present two different nonlinear finite element based implementations of our formulation. One is a laborious load-stepping based calculation performed using ANSYS (a commercially available finite element package). The other uses our nonlinear finite element code. The latter two techniques are primarily developed to provide us with an accurate answer for comparison with the results obtained using the modal projection methods. Having developed our formulation and the subsequent modal projection approximations, we proceed to validation. First, we analytically study several examples whose solutions can be easily obtained using routine methods. Second, we consider the problem of a rotating cylinder under axial loads. We use a semi-analytical approach for this problem and offer some insights into the role played by the chosen kinematics for our virtual work calculations. The excellent match with known results obtained using Timoshenko theory validates the accuracy of our formulation. Third, we consider several rotors of arbitrary shape in numerical examples and show that our modal projection methods accurately estimate the critical speeds of these rotors. After validation, we consider efficiency. For axisymmetric rotor geometries, we implement our formulation using harmonic elements. This reduces the dimension of our problem from three to two and considerable savings in time are obtained. Finally, we apply our formulation to describe asynchronous whirl and internal viscous damping phenomena in rotors.

Rotordynamics is an important area in mechanical engineering. Many machines contain rotating parts. It is well known that rotating components can develop large amplitude lateral vibrations near certain speeds called critical speeds. This large amplitude vibration is called rotor whirl. This thesis is about rotor whirl. Conventional treatments in rotordynamics use what are called gyroscopic terms and treat the rotor as a one-dimensional structure (Euler-Bernoulli or Timoshenko) with or without rigid masses added to them. Gyroscopic terms are macroscopic inertial terms that arise due to tilting of spinning cross-sections. This approach, while applicable to a large class of industrially important rotors, is not applicable to a general rotor geometry. In this thesis we develop a genuine continuum level three dimensional formulation for rotordynamics that can be used for many arbitrarily shaped rotors. The key insight that guides our formulation is that gyroscopic terms are macroscopic manifestations of the prestress induced due to spin of the rotor. Using this insight, we develop two modal projection techniques for calculating the critical speed of arbitrarily shaped rotors. These techniques along with our prestress based formulation are the primary contributions of the thesis. In addition, we also present two different nonlinear finite element based implementations of our formulation. One is a laborious load-stepping based calculation performed using ANSYS (a commercially available finite element package). The other uses our nonlinear finite element code. The latter two techniques are primarily developed to provide us with an accurate answer for comparison with the results obtained using the modal projection methods. Having developed our formulation and the subsequent modal projection approximations, we proceed to validation. First, we analytically study several examples whose solutions can be easily obtained using routine methods. Second, we consider the problem of a rotating cylinder under axial loads. We use a semi-analytical approach for this problem and offer some insights into the role played by the chosen kinematics for our virtual work calculations. The excellent match with known results obtained using Timoshenko theory validates the accuracy of our formulation. Third, we consider several rotors of arbitrary shape in numerical examples and show that our modal projection methods accurately estimate the critical speeds of these rotors. After validation, we consider efficiency. For axisymmetric rotor geometries, we implement our formulation using harmonic elements. This reduces the dimension of our problem from three to two and considerable savings in time are obtained. Finally, we apply our formulation to describe asynchronous whirl and internal viscous damping phenomena in rotors.