No description available.

[pt] As fibras ópticas são suscetíveis ao estresse mecânico e podem ser danificadas ou quebradas, portanto, a supervisão da camada física é essencial para identificar essas falhas e remediá-las o mais rápido possível. Com o objetivo de agilizar e simplificar o processo de agendamento de unidades de reparo em campo, foi desenvolvido um sistema automatizado de medição de fibras baseado em uma unidade de processamento digital de sinal (DSP) capaz de identificar as posições das falhas de forma autônoma. Combinando esta unidade de DSP com um OTDR de contagem de fótons, é possível criar tal dispositivo. Este trabalho apresenta o desenvolvimento dos blocos de construção para tal dispositivo. / [en] Optical fibers are susceptible to mechanical stress and may be damaged or broken, thus physical layer supervision is essential to identify these failures and remediate them as quickly as possible. In order to hasten and simplify the scheduling process of the in-field repairing units, an automated fiber measurement system based on a digital signal processing (DSP) unit capable of autonomously identifying fault positions was developed. By combining this DSP unit with a Tunable Photon-Counting OTDR, it is possible to create such a device. This work presents the development of the building blocks for such device.

MSc (Applied Mathematics) / Mathematics and Applied Mathematics Department / In this study the iteration of boundary conditions method (Chizhonkov and Kargin, 2006) is used together with the well known Finite difference numerical method to solve the Stokes problem over a rectangular domain as well as in irregular domain. The iteration of boundary conditions method has been applied to the Stokes problem in a rectangular domain, 􀀀 2 <x< 2 , 􀀀 d 2 < y < d 2 , by the above mentioned researchers. Our main task here is to validate the results of the approximate methods by this analytical method in case of the rectangular domain and extend that to the case of irregular domain.The (Chizhonkov and Kargin, 2006) algorithm is typically the best choice for validation purposes because of its high accuracy. It is known in literature that increasing the parameter d, which represents the ratio of the sides, leads to slow down in convergence of the approximate methods like the conjugate Gradients of Uzawa (Kobelkov and Olshanskii, 2000). It is therefore important that an algorithm that converges uniformly with respect to the parameter d is considered. The (Chizhonkov and Kargin, 2006) algorithm is typical of such an algorithm, and hence our choice of the method in this work. In this project the non-homogeneous Stokes problem is transformed into a homogeneous Stokes problem and the resulting problem is then decomposed into two sub problems that are solvable by the eigenfunction expansion method. Once all necessary coefficients of the generalised Fourier series are known and the functions describing the boundary conditions are prescribed and represented in terms of the Fourier series, we then proceed to formulate the iteration of boundary conditions numerical algorithm. Finally we develop a numerical scheme, using the finite difference methods, for solving the problem in both rectangular and irregular domains. Coding of the numerical algorithm is done using MATLAB 9.0,R2016a programming language, and implemented by the author. The results of the two methods in both cases of boundary conditions are then compared for validation of our purely numerical results. / NRF

Asynchronous iterative algorithms are parallel iterative algorithms in which communications and iterations are not synchronized among processors. Thus, as soon as a processing unit finishes its own calculations, it starts the next cycle with the latest data received during a previous cycle, without waiting for any other processing unit to complete its own calculation. These algorithms increase the number of updates in some processors (as compared to the synchronous case) but suppress most idle times. This usually results in a reduction of the (execution) time to achieve convergence. Optimized Schwarz methods (OSM) are domain decomposition methods in which the transmission conditions between subdomains contain operators of the form \linebreak $\partial/\partial \nu +\Lambda$, where $\partial/\partial \nu$ is the outward normal derivative and $\Lambda$ is an optimized local approximation of the global Steklov-Poincar\'e operator. There is more than one family of transmission conditions that can be used for a given partial differential equation (e.g., the $OO0$ and $OO2$ families), each of these families containing a particular approximation of the Steklov-Poincar\'e operator. These transmission conditions have some parameters that are tuned to obtain a fast convergence rate. Optimized Schwarz methods are fast in terms of iteration count and can be implemented asynchronously. In this thesis we analyze the convergence behavior of the synchronous and asynchronous implementation of OSM applied to solve partial differential equations with a shifted Laplacian operator in bounded rectangular domains. We analyze two cases. In the first case we have a shift that can be either positive, negative or zero, a one-way domain decomposition and transmission conditions of the $OO2$ family. In the second case we have Poisson's equation, a domain decomposition with cross-points and $OO0$ transmission conditions. In both cases we reformulate the equations defining the problem into a fixed point iteration that is suitable for our analysis, then derive convergence proofs and analyze how the convergence rate varies with the number of subdomains, the amount of overlap, and the values of the parameters introduced in the transmission conditions. Additionally, we find the optimal values of the parameters and present some numerical experiments for the second case illustrating our theoretical results. To our knowledge this is the first time that a convergence analysis of optimized Schwarz is presented for bounded subdomains with multiple subdomains and arbitrary overlap. The analysis presented in this thesis also applies to problems with more general domains which can be decomposed as a union of rectangles. / Mathematics

Au cours des dernières années, l'informatique “green” est devenue un sujet important dans le calcul intensif. Cependant, les plates-formes informatiques continuent de consommer de plus en plus d'énergie en raison de l'augmentation du nombre de noeuds qui les composent. Afin de minimiser les coûts d'exploitation de ces plates-formes de nombreuses techniques ont été étudiées, parmi celles-ci, il y a le changement de la fréquence dynamique des processeurs (DVFS en anglais). Il permet de réduire la consommation d'énergie d'un CPU, en abaissant sa fréquence. Cependant, cela augmente le temps d'exécution de l'application. Par conséquent, il faut trouver un seuil qui donne le meilleur compromis entre la consommation d'énergie et la performance d'une application. Cette thèse présente des algorithmes développés pour optimiser la consommation d'énergie et les performances des applications parallèles avec des itérations synchrones et asynchrones sur des clusters ou des grilles. Les modèles de consommation d'énergie et de performance proposés pour chaque type d'application parallèle permettent de prédire le temps d'exécution et la consommation d'énergie d'une application pour toutes les fréquences disponibles.La contribution de cette thèse peut être divisé en trois parties. Tout d'abord, il s'agit d'optimiser le compromis entre la consommation d'énergie et les performances des applications parallèles avec des itérations synchrones sur des clusters homogènes. Deuxièmement, nous avons adapté les modèles de performance énergétique aux plates-formes hétérogènes dans lesquelles chaque noeud peut avoir des spécifications différentes telles que la puissance de calcul, la consommation d'énergie, différentes fréquences de fonctionnement ou encore des latences et des bandes passantes réseaux différentes. L'algorithme d'optimisation de la fréquence CPU a également été modifié en fonction de l'hétérogénéité de la plate-forme. Troisièmement, les modèles et l'algorithme d'optimisation de la fréquence CPU ont été complètement repensés pour prendre en considération les spécificités des algorithmes itératifs asynchrones.Tous ces modèles et algorithmes ont été appliqués sur des applications parallèles utilisant la bibliothèque MPI et ont été exécutés avec le simulateur Simgrid ou sur la plate-forme Grid'5000. Les expériences ont montré que les algorithmes proposés sont plus efficaces que les méthodes existantes. Ils n’introduisent qu’un faible surcoût et ne nécessitent pas de profilage au préalable car ils sont exécutés au cours du déroulement de l’application. / In recent years, green computing has become an important topic in the supercomputing research domain. However, the computing platforms are still consuming more and more energy due to the increase in the number of nodes composing them. To minimize the operating costs of these platforms many techniques have been used. Dynamic voltage and frequency scaling (DVFS) is one of them. It can be used to reduce the power consumption of the CPU while computing, by lowering its frequency. However, lowering the frequency of a CPU may increase the execution time of the application running on that processor. Therefore, the frequency that gives the best trade-off between the energy consumption and the performance of an application must be selected.This thesis, presents the algorithms developed to optimize the energy consumption and theperformance of synchronous and asynchronous message passing applications with iterations runningover clusters or grids. The energy consumption and performance models for each type of parallelapplication predicts its execution time and energy consumption for any selected frequency accordingto the characteristics of both the application and the architecture executing this application.The contribution of this thesis can be divided into three parts: Firstly, optimizing the trade-offbetween the energy consumption and the performance of the message passing applications withsynchronous iterations running over homogeneous clusters. Secondly, adapting the energy andperformance models to heterogeneous platforms where each node can have different specificationssuch as computing power, energy consumption, available frequency gears or network’s latency andbandwidth. The frequency scaling algorithm was also modified to suit the heterogeneity of theplatform. Thirdly, the models and the frequency scaling algorithm were completely rethought to takeinto considerations the asynchronism in the communication and computation. All these models andalgorithms were applied to message passing applications with iterations and evaluated over eitherSimGrid simulator or Grid’5000 platform. The experiments showed that the proposed algorithms areefficient and outperform existing methods such as the energy and delay product. They also introducea small runtime overhead and work online without any training or profiling.

Cables are highly nonlinear structural members under transverse loading. This nonlinearity is mainly due to the close relationship between the final geometry under transverse loads and the resulting stresses in its equilibrium state rather than the material properties. In practice, the cables are usually used as isolated single-segment elements fixed at the ends. Various studies and solution procedures suggested by researchers are available in the literature for such isolated cables. However, not much work is available for continuous cables with multiple supports. In this study, a multi-segment continuous cable is defined as a cable fixed at the ends and supported by a number of stationary roller supports in between. Total cable length is assumed constant and the intermediate supports are assumed to be frictionless. Therefore, the critical issue is to find the distribution of the cable length among its segments in the final equilibrium state. Since the solution of single-segment cables is available the additional condition to be satisfied for multi-segment continuous cables with multiple supports is to have stress continuity at intermediate support locations where successive cable segments meet. A predictive/corrective iteration procedure is proposed for this purpose. The solution starts with an initially assumed distribution of total cable length among the segments and each segment is analyzed as an independent isolated single-segment cable. In general, the stress continuity between the cable segments will not be satisfied unless the assumed distribution of cable length is the correct distribution corresponding to final equilibrium state. In the subsequent iterations the segment lengths are readjusted to eliminate the unbalanced tensions at segment junctions. The iterations are continued until the stress continuity is satisfied at all junctions. Two alternative approaches are proposed for the segment length adjustments: Direct stiffness method and tension distribution method. Both techniques have been implemented in a software program for the analysis of multi-segment continuous cables and some sample problems are analyzed for verification. The results are satisfactory and compares well with those obtained by the commercial finite element program ANSYS.

Dans cette thèse, une nouvelle manière de générer des nombres pseudo-aléatoires est présentée.La proposition consiste à mixer deux générateurs exitants avec des itérations chaotiquesdiscrètes, qui satisfont à la définition de chaos proposée par Devaney. Un cadre rigoureux estintroduit, dans lequel les propriétés topologiques du générateur résultant sont données. Deuxréalisations pratiques d’un tel générateur sont ensuite présentées et évaluées. On montre que lespropriétés statistiques des générateurs fournis en entrée peuvent être grandement améliorées enprocédant ainsi. Ces deux propositions sont alors comparées, en profondeur, entre elles et avecun certain nombre de générateurs préexistants. On montre entre autres que la seconde manièrede mixer deux générateurs est largement meilleure que la première, à la fois en terme de vitesseet de performances.Dans la première partie de ce manuscrit, la fonction d’itérations considérée est la négation vectorielle.Dans la deuxième partie, nous proposons d’utiliser des graphes fortement connexescomme critère de sélection de bonnes fonctions d’itérations. Nous montrons que nous pouvonschanger de fonction sans perte de propriétés pour le générateur obtenu. Finalement, une illustrationdans le domaine de l’information dissimulée est présentée, et la robustesse de l’algorithmede tatouage numérique proposé est évalué. / In this thesis, a new way to generate pseudorandom numbers is presented. The propositionis to mix two exiting generators with discrete chaotic iterations that satisfy the Devaney’sdefinition of chaos. A rigorous framework is introduced, where topological properties of theresulting generator are given, and two practical designs are presented and evaluated. It is shownthat the statistical quality of the inputted generators can be greatly improved by this way, thusfulfilling the up-to-date standards. Comparison between these two designs and existing generatorsare investigated in details. Among other things, it is established that the second designedtechnique outperforms the first one, both in terms of performance and speed.In the first part of this manuscript, the iteration function embedded into chaotic iterations isthe vectorial Boolean negation. In the second part, we propose a method using graphs havingstrongly connected components as a selection criterion.We are thus able to modify the iterationfunction without deflating the good properties of the associated generator. Simulation resultsand basic security analysis are then presented to evaluate the randomness of this new family ofpseudorandom generators. Finally, an illustration in the field of information hiding is presented,and the robustness of the obtained data hiding algorithm against attacks is evaluated.

Projektet undersökte olika verktyg och metoder som i skrivande stund används för att lära ut programmering. Den sammanfattar tidigare undersökningar och drar slutsatser kring hur lämpliga de är. Utifrån dessa slutsatser utformades en webbapplikation för undervisning.   Rapporten redogör för hur webbapplikationen konstruerades, samt vilka metoder och verktyg som användes i dess utveckling.   Detta ämne är högaktuellt idag då Sveriges regering ämnar införa programmering i grundskolan och då krävs både bra metoder och verktyg för detta. / This project investigated different tools and methods used today in teaching programming. It summarizes earlier studies and draws conclusions about how suited they are for the job. The accompanying web application would be crafted based on the conclusions made.   The report intends to describe how the web application was constructed, and which methods and tools were used during its development.   The subject of the report is highly relevant today since the Swedish government is discussing the introduction of programming classes in the elementary school. Thus demanding both suitable methods and tools.

Une large classe de méthodes numériques possède une propriété d’échelonnabilité connue comme étant la loi d’Amdahl. Elle constitue l’inconvénient majeur limitatif du calcul parallèle, en ce sens qu’elle établit une borne supérieure sur le nombre d’unités de traitement parallèles qui peuvent être utilisées pour accélérer un calcul. Des activités de recherche sont donc largement conduites à la fois sur les plans mathématiques et informatiques, pour repousser cette limite afin d’être en mesure de tirer le maximum des machines parallèles. Les méthodes de décomposition de domaine introduisent une approche naturelle et optimale pour résoudre de larges problèmes numériques de façon distribuée. Elles consistent en la division du domaine géométrique sur lequel une équation est définie, puis le traitement itératif de chaque sous-domaine, séparément, tout en assurant la continuité de la solution et de sa dérivée sur leur interface de jointure. Dans le présent travail, nous étudions la suppression de la limite d’accélération en appliquant des itérations asynchrones dans différents cadres de décomposition, à la fois de domaines spatiaux et temporels. Nous couvrons plusieurs aspects du développement d’algorithmes asynchrones, de l’analyse théorique de convergence à la mise en oeuvre effective. Nous aboutissons ainsi à des méthodes asynchrones efficaces pour la décomposition de domaine, ainsi qu’à une nouvelle bibliothèque de communication pour l’expérimentation asynchrone rapide d’applications scientifiques existantes. / An important class of numerical methods features a scalability property well known as the Amdahl’s law, which constitutes the main limiting drawback of parallel computing, as it establishes an upper bound on the number of parallel processing units that can be used to speed a computation up. Extensive research activities are therefore conducted on both mathematical and computer science aspects to increase this bound, in order to be able to squeeze the most out of parallel machines. Domain decomposition methods introduce a natural and optimal approach to solve large numerical problems in a distributed way. They consist in dividing the geometrical domain on which an equation is defined, then iteratively processing each sub-domain separately, while ensuring the continuity of the solution and of its derivative across the junction interface between them. In the present work, we investigate the removal of the scalability bound by the application of the asynchronous iterations theory in various decomposition frameworks, both for space and time domains. We cover various aspects of the development of asynchronous iterative algorithms, from theoretical convergence analysis to effective parallel implementation. Efficient asynchronous domain decomposition methods are thus successfully designed, as well as a new communication library for the quick asynchronous experimentation of existing scientific applications.

Optical testing in adverse environments, ophthalmology and applications where characterization by curvature is leveraged all have a common goal: accurately estimate wavefront shape. This dissertation investigates wavefront sensing techniques as applied to optical testing based on gradient and curvature measurements. Wavefront sensing involves the ability to accurately estimate shape over any aperture geometry, which requires establishing a sampling grid and estimation scheme, quantifying estimation errors caused by measurement noise propagation, and designing an instrument with sufficient accuracy and sensitivity for the application. Starting with gradient-based wavefront sensing, a zonal least-squares wavefront estimation algorithm for any irregular pupil shape and size is presented, for which the normal matrix equation sets share a pre-defined matrix. A Gerchberg–Saxton iterative method is employed to reduce the deviation errors in the estimated wavefront caused by the pre-defined matrix across discontinuous boundary. The results show that the RMS deviation error of the estimated wavefront from the original wavefront can be less than λ/130~ λ/150 (for λ equals 632.8nm) after about twelve iterations and less than λ/100 after as few as four iterations. The presented approach to handling irregular pupil shapes applies equally well to wavefront estimation from curvature data. A defining characteristic for a wavefront estimation algorithm is its error propagation behavior. The error propagation coefficient can be formulated as a function of the eigenvalues of the wavefront estimation-related matrices, and such functions are established for each of the basic estimation geometries (i.e. Fried, Hudgin and Southwell) with a serial numbering scheme, where a square sampling grid array is sequentially indexed row by row. The results show that with the wavefront piston-value fixed, the odd-number grid sizes yield lower error propagation than the even-number grid sizes for all geometries. The Fried geometry either allows sub-sized wavefront estimations within the testing domain or yields a two-rank deficient estimation matrix over the full aperture; but the latter usually suffers from high error propagation and the waffle mode problem. Hudgin geometry offers an error propagator between those of the Southwell and the Fried geometries. For both wavefront gradient-based and wavefront difference-based estimations, the Southwell geometry is shown to offer the lowest error propagation with the minimum-norm least-squares solution. Noll’s theoretical result, which was extensively used as a reference in the previous literature for error propagation estimate, corresponds to the Southwell geometry with an odd-number grid size. For curvature-based wavefront sensing, a concept for a differential Shack-Hartmann (DSH) curvature sensor is proposed. This curvature sensor is derived from the basic Shack-Hartmann sensor with the collimated beam split into three output channels, along each of which a lenslet array is located. Three Hartmann grid arrays are generated by three lenslet arrays. Two of the lenslets shear in two perpendicular directions relative to the third one. By quantitatively comparing the Shack-Hartmann grid coordinates of the three channels, the differentials of the wavefront slope at each Shack-Hartmann grid point can be obtained, so the Laplacian curvatures and twist terms will be available. The acquisition of the twist terms using a Hartmann-based sensor allows us to uniquely determine the principal curvatures and directions more accurately than prior methods. Measurement of local curvatures as opposed to slopes is unique because curvature is intrinsic to the wavefront under test, and it is an absolute as opposed to a relative measurement. A zonal least-squares-based wavefront estimation algorithm was developed to estimate the wavefront shape from the Laplacian curvature data, and validated. An implementation of the DSH curvature sensor is proposed and an experimental system for this implementation was initiated. The DSH curvature sensor shares the important features of both the Shack-Hartmann slope sensor and Roddier’s curvature sensor. It is a two-dimensional parallel curvature sensor. Because it is a curvature sensor, it provides absolute measurements which are thus insensitive to vibrations, tip/tilts, and whole body movements. Because it is a two-dimensional sensor, it does not suffer from other sources of errors, such as scanning noise. Combined with sufficient sampling and a zonal wavefront estimation algorithm, both low and mid frequencies of the wavefront may be recovered. Notice that the DSH curvature sensor operates at the pupil of the system under test, therefore the difficulty associated with operation close to the caustic zone is avoided. Finally, the DSH-curvature-sensor-based wavefront estimation does not suffer from the 2π-ambiguity problem, so potentially both small and large aberrations may be measured.