121 |
High redundancy actuatorDu, Xinli January 2008 (has links)
High Redundancy Actuation (HRA) is a novel type of fault tolerant actuator. By comprising a relatively large number of actuation elements, faults in the elements can be inherently accommodated without resulting in a failure of the complete actuation system. By removing the possibility of faults detection and reconfiguration, HRA can provide high reliability and availability. The idea is motivated by the composition of human musculature. Our musculature can sustain damage and still function, sometimes with reduced performance, and even complete loss of a muscle group can be accommodated through kinematics redundancy, e.g. the use of just one leg. Electro-mechanical actuation is used as single element inside HRA. This thesis is started with modelling and simulation of individual actuation element and two basic structures to connect elements, in series and in parallel. A relatively simple HRA is then modelled which engages a two-by-two series-in-parallel configuration. Based on this HRA, position feedback controllers are designed using both classical and optimal algorithms under two control structures. All controllers are tested under both healthy and faults injected situations. Finally, a hardware demonstrator is set up based simulation studies. The demonstrator is controlled in real time using an xPC Target system. Experimental results show that the HRA can continuously work when one element fails, although performance degradation can be expected.
|
122 |
Regression Wavelet Analysis for Lossless Coding of Remote-Sensing DataMarcellin, Michael W., Amrani, Naoufal, Serra-Sagristà. Joan, Laparra, Valero, Malo, Jesus 08 May 2016 (has links)
A novel wavelet-based scheme to increase coefficient
independence in hyperspectral images is introduced for lossless
coding. The proposed regression wavelet analysis (RWA) uses
multivariate regression to exploit the relationships among wavelettransformed
components. It builds on our previous nonlinear
schemes that estimate each coefficient from neighbor coefficients.
Specifically, RWA performs a pyramidal estimation in the wavelet
domain, thus reducing the statistical relations in the residuals
and the energy of the representation compared to existing
wavelet-based schemes. We propose three regression models to
address the issues concerning estimation accuracy, component
scalability, and computational complexity. Other suitable regression
models could be devised for other goals. RWA is invertible, it
allows a reversible integer implementation, and it does not expand
the dynamic range. Experimental results over a wide range of
sensors, such as AVIRIS, Hyperion, and Infrared Atmospheric
Sounding Interferometer, suggest that RWA outperforms not only
principal component analysis and wavelets but also the best and
most recent coding standard in remote sensing, CCSDS-123.
|
123 |
Organizational resilience and the humanitarioan sector : Exploring Organizational Resilience in Policy and Practice within the United NationsÅslund, Robin January 2019 (has links)
The notion of ‘organizational resilience’ has risen exponentially in recent years; it is the ability of an organization to ‘bounce back’ and continue key functions during disruptive events. The rise follows the will to better face the unforeseen and complex adversity that modern times throws at organizations. This study, following a single-case exploratory research design, aims to establish knowledge regarding organizational resilience in the humanitarian sector; by exploring the policy and practice of the United Nations. The author builds an Analytical Framework based on the leading research in the field of organizational resilience, in order to grasp an understanding of the organization's different beliefs, capabilities, and proficiencies necessary to establish and maintain a resilient organization. Concluding with the statement that while there are areas of challenges, the humanitarian sector provides a case not only to scrutinize, but also to learn from.
|
124 |
Controle de um manipulador planar paralelo com redundância cinemática / Control of a parallel planar manipulator with kinematic redundancyFontes, João Vitor de Carvalho 01 March 2019 (has links)
Manipuladores paralelos são aqueles que possuem mais de uma cadeia cinemática que liga a base ao efetuador final. Esta característica proporciona vantagens sobre os manipuladores em série, como maior robustez, maior carga útil e maior velocidade. Por outro lado, as singularidades presentes nos manipuladores paralelos diminuem a área de trabalho prejudicando o desempenho dos mesmos. Uma técnica para evitar as singularidades é a redundância cinemática, que consiste em adicionar atuadores às cadeias cinemáticas possibilitando a reconfiguração do manipulador. Além disso, a redundância cinemática pode melhorar também a rigidez, a robustez, a precisão do sistema, entre outras características, provando ser uma boa alternativa para melhorar o desempenho de manipuladores. Entretanto, alguns dos problemas encontrados em manipuladores paralelos com níveis de redundância altos são os modelos com dinâmica acoplada, que dificultam a implementação de simulações, e o controle ainda mais complexo do que manipuladores paralelos não redundantes. Portanto, esta tese apresenta um estudo sobre o controle de um manipulador paralelo versátil redundante e o impacto dos níveis de redundância cinemática sobre seu desempenho dinâmico. O protótipo consiste de um manipulador paralelo planar atuado por três motores rotacionais e três guias lineares acionadas por motores rotacionais. O acionamento ou não do movimento da guia linear define a redundância do sistema garantindo a versatilidade do protótipo, que pode apresentar de nenhum a três níveis de redundância cinemática. Essa variação permite a avaliação do impacto de diferentes níveis de redundância cinemática no manipulador. Além disso, dois controles baseados no modelo do manipulador, o controle torque calculado e o controle com linearização por retroalimentação, foram implementados para minimizar o impacto da dinâmica acoplada e não linearidades. Estes controles foram comparados com um controle tradicional como referência de comparação. Os resultados demonstraram que o desempenho do manipulador é melhorado utilizando três níveis de redundância e o controle torque calculado em termos de erro de posição e torques executados. / Parallel manipulators are those that have more than one kinematic chain linking the base to the end-effector. This feature provides advantages over serial manipulators, such as greater robustness, higher payload and higher speed. On the other hand, the singularities present in the parallel manipulators decrease the workspace and impair their performance. One technique to avoid the singularities is the kinematic redundancy, which consists of adding actuators to the kinematic chains allowing the reconfiguration of the manipulator. In addition, kinematic redundancy can also improve stiffness, robustness, accuracy, and other features proving to be a good alternative to improve the performance of manipulators. However, some of the problems encountered in parallel manipulators with high levels of redundancy are models with coupled dynamics, that hamper simulations, and even more complex control than non-redundant parallel manipulators. Therefore, this thesis presents a study on the control of a versatile redundant parallel manipulator and the impact of kinematic redundancy levels on its dynamic performance. The prototype consists of a parallel planar manipulator actuated by three rotational motors and three linear guides driven by rotational motors. Whether or not linear motion is triggered defines the redundancy of the robotic system, ensuring the versatility of the prototype, which can vary from no to three levels of kinematic redundancy. This variation allows the impact evaluation of different levels of kinematic redundancy in the manipulator. In addition, two controls based on the manipulator model, the computed torque control and the feedback linearization control were implemented to minimize the impact of coupled dynamics and nonlinearities. These controls were compared with a traditional control as reference. The results demonstrated that the manipulator performance is improved by using three levels of redundancy and the computed torque control in terms of position error and executed torques.
|
125 |
Contribution à la commande des robots parallèles à câbles à redondance d'actionnement / Contribution to the control of redundantly actuated cable-driven parallel robotsLamaury, Johann 08 October 2013 (has links)
Les Robots Parallèles à Câbles (RPC) sont particulièrement adaptés pour des applications telles que le transport de charges lourdes au travers de grands espaces de travail. Afin de contrôler l'ensemble des degrés de liberté de la plate-forme tout en optimisant la taille de l'espace de travail du robot par rapport au volume de sa structure, la redondance d'actionnement est nécessaire. Dans cette thèse, un algorithme de distribution des tensions des câbles compatible temps-réel est introduit. Il permet de calculer efficacement différentes solutions optimales au problème de la distribution des tensions des RPC à deux degrés de redondance. Des schémas de commande adaptés aux RPC, intégrant l'algorithme de distribution des tensions, sont ensuite proposés. Un schéma de commande en espace double est introduit pour compenser la dynamique de la plate-forme et des enrouleurs. Afin de pallier les incertitudes et les variations des paramètres des modèles, une commande adaptative en espace double est finalement proposée. Des résultats expérimentaux prouvent la compatibilité temps-réel des algorithmes et des lois de commande développés dans cette thèse, ainsi que leur stabilité le long de la trajectoire suivie. / Cable-driven parallel robots (CDPR) are particularly well adapted for some applications such as handling of heavy payloads over large workspaces. However, in order to fully control all the degrees of freedomof the mobile platformand to obtain large workspace to footprint ratios, redundant actuation may be required, which implies the determination of feasible cable tension distributions. In this thesis, in the case of CDPR with two degrees of actuation redundancy, real-time compatible algorithms capable of efficiently calculating various continuous tension distribution are introduced. Furthermore, efficient control schemes are proposed in order to increase the CDPR tracking performances. First, an dual-space feedforward control scheme is introduced to compensate for the plate-formeand whinches dynamics. In order to deal with parametric variations and incertainties in the models, an adaptive dual-space motion control scheme for CDPR is finally presented. Experimental results validate the reel-time efficiency of the proposed tension distribution algorithmand control schemes as well as their stability along the tracked trajectory.
|
126 |
Atributos microbiológicos na mudança de uso da terra para produção de cana-de-açúcar na região centro-sul do Brasil / Microbiological attributes in the land use change for the production of sugarcane in the center-south region of BrazilMaísa Helena Heluany 03 March 2015 (has links)
Com a grande demanda por derivados da cana-de-açúcar no Brasil a expansão de área para produção, assim como o aumento da produtividade tem sido foco para áreas agrícolas na região centro-sul. Portanto áreas que anteriormente eram dedicadas a pastagem estão tornando-se cultivo de cana-de-açúcar. Essa mudança está ocorrendo com uma grande rapidez e por esse motivo preocupações com a sustentabilidade do solo estão sendo levantadas. O objetivo deste trabalho foi verificar como a atual mudança de uso da terra de pastagem para cultivo de canade- açúcar impacta atributos microbiológicos quantitativos e funcionais do solo em um transecto edafoclimático na região centro-sul do Brasil tendo a vegetação nativa como referência. Para isso foram feitas análises do carbono e nitrogênio da biomassa microbiana do solo segundo Vance, Brookes e Jenkinson (1987) e análises da atividade enzimática da β-glicosidase, fosfatase ácida e alcalina segundo Tabatabai (1994). Verifica-se a tendência de reduzir a fertilidade na pastagem em relação a mata nativa e posteriormente aumentar com o uso de fertilizantes na cana-de-açúcar. O estoque de C tem um menor valor na pastagem quando não manejada em Lat S 17º, diminui na sequencia de mudança dos sistemas de uso da terra em Lat S 21º, porém uma recuperação na mudança para cultivo de cana-de-açúcar e é maior em Lat S 23º quando a textura do solo é mais argilosa. Existe uma diminuição do estoque de CBM das matas nativas para as pastagens e um aumento nos cultivos de cana-de-açúcar em Lat S 17º e Lat S 21º. Em Lat S 23º a pastagem apresenta maior CBM do que os outros sistemas de uso da terra. Nos locais de estudo a menor relação CBM/C Total foi de 2,54% na mata nativa em Lat S 17º e a maior de 5,74% na pastagem de Lat S 23º. O N é um elemento muito sensível, em todos os atributos analisados a mudança de uso da terra causou uma grande diminuição, e a degradação do solo é o fator que causa o grande impacto nesses atributos. A textura argilosa do solo garante maior atividade enzimática, porém em cultivos de cana-de-açúcar a atividade diminui independente da classe textural. Os mesmos usos da terra em diferentes locais não podem ser analisados como repetições. Sendo assim pode-se concluir que nos casos analisados o impacto da mudança de uso da terra de pastagem para cultivo de cana-de-açúcar se manifestou de forma diferente em cada local, não permitindo uma generalização. / The great demand for derivatives of sugarcane in Brazil is the motive for the area expansion for production as well as the increase of productivity have been the focus of agricultural areas in the center-south region. So areas that were previously pastures have been changing for sugarcane cultivation. This change has occured with great speed and therefore concerns about the sustainability of soil have been raised. The aim of this study was to determine how the current change from pasture to sugarcane cultivation impacts quantitative and functional microbiological attributes of soil in a soil climatic zone in the central-south region of Brazil considering the native vegetation as reference. For it were made analysis of soil microbial biomass carbon and nitrogen according to Vance, Brookes and Jenkinson (1987) and analysis of enzymatic activity of β-glucosidase, acid and alkaline phosphatase according to Tabatabai (1994). There is a tendency to reduce fertility in pasture compared to native vegetation and then increase with the use of fertilizers in sugarcane cultivation. The stock of C has a lower value in the pasture when there is no fertilizers in Lat S 17º, decreases in the land use change in Lat S 21º, but there is a recovery in the switch over to sugarcane cultivation and it is the biggest in Lat S 23º when the soil texture is clayey. There is a decrease in the stock of CBM from native forests to pastures and an increase in sugarcane cultivation in Lat S 17º and Lat S 21º. In Lat S 23º the pasture has higher CBM stock than other land use systems. In the study sites the reason between CBM and C Total was 2.54% in the native vegetation in Lat S 17º and the highest 5.74% in the pasture of Lat S 23º. The N is a very sensitive element, in all attributes analyzed, the land use change caused a large decrease, and soil degradation is the factor that causes serious impact on those attributes. The clayey soil ensures greater enzymatic activity, but in sugarcane cultivation decreases the activity independent of the texture. The same land uses in different locations can\'t be analyzed as repetitions. Therefore in the cases analyzed the impact of the change from pasture to sugarcane cultivation was differently in each place, not allowing a generalization.
|
127 |
New solution schemes in constrained redundancy optimizatin [sic.]. / New solution schemes in constrained redundancy optimizationJanuary 1999 (has links)
by Lam Ngok. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 111-114). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Overview --- p.1 / Chapter 1.2 --- Organization outline --- p.2 / Chapter 2 --- Fundamentals of reliability theory --- p.4 / Chapter 2.1 --- State vector --- p.4 / Chapter 2.2 --- Minimal path sets --- p.4 / Chapter 2.3 --- Minimal cut sets --- p.7 / Chapter 2.4 --- Structure functions --- p.7 / Chapter 2.5 --- The structure functions and the systems reliability --- p.10 / Chapter 3 --- Literature review --- p.12 / Chapter 3.1 --- Introduction --- p.12 / Chapter 3.2 --- Approximation schemes --- p.13 / Chapter 3.3 --- Heurisitic search schemes --- p.14 / Chapter 3.4 --- Exact solution schemes --- p.16 / Chapter 3.5 --- Software reliability --- p.17 / Chapter 4 --- Characteristics of Series-parallel network --- p.18 / Chapter 4.1 --- Series-parallel network problem formulation --- p.18 / Chapter 4.2 --- Characteristics of series-parallel networks --- p.19 / Chapter 4.3 --- Some further properties of Maximal Monotonicity --- p.20 / Chapter 4.3.1 --- Definitions and the background --- p.20 / Chapter 4.3.2 --- The proper and the improper MMPs --- p.22 / Chapter 4.4 --- Examples --- p.37 / Chapter 4.5 --- Computational results --- p.39 / Chapter 4.6 --- New progress --- p.40 / Chapter 5 --- Extensions for the series-parallel reducible networks --- p.43 / Chapter 5.1 --- Some new notations for computation --- p.44 / Chapter 5.1.1 --- Notation --- p.44 / Chapter 5.2 --- Problem formulation --- p.46 / Chapter 5.3 --- The series-parallel reducible networks --- p.46 / Chapter 5.4 --- The algorithm --- p.54 / Chapter 6 --- "On ""Successive Solution Scheme For Constrained Redun- dancy Optimization In Reliability Networks"" [1]" --- p.56 / Chapter 6.1 --- Introduction --- p.56 / Chapter 6.2 --- The contents --- p.56 / Chapter 6.2.1 --- The motivation --- p.56 / Chapter 6.2.2 --- The Successive Solution Scheme --- p.57 / Chapter 6.3 --- Illustrative examples --- p.62 / Chapter 6.3.1 --- Example 1 --- p.62 / Chapter 6.3.2 --- Example 2 --- p.67 / Chapter 7 --- Conclusions --- p.76 / Chapter 8 --- Appendix --- p.79 / Chapter 8.1 --- Computational results --- p.79 / Chapter 8.2 --- Programme codes --- p.97
|
128 |
Le licenciement pour motif personnel en France et au Sénégal : [étude de droit comparé] / The redundancy for personal reasons in France and in Senegal : [compared study]N'doye, N'deye 20 April 2012 (has links)
Le licenciement pour motif personnel, à la différence du licenciement pour motif économique, est intimement lié à la personne du salarié. Il constitue une notion essentielle en droit du travail, qu'on retrouve dans la plupart des États au monde, mais souvent, sous une terminologie différente. Face à ce constat, on serait tenté de se demander si laréglementation du licenciement pour motif personnel est réellement variable d'un pays à un autre. La réponse à cette question suppose une analyse comparée des législations de certains États. À ce titre, seuls la France et le Sénégal, deux États qui sont par ailleurs fortement liés par l'histoire, ont retenu notre attention. L'étude du droit du licenciement pour motif personnel en France et au Sénégal laisse entrevoir à la fois des similitudes et des divergences. Cette situation se justifierait d'ailleurs à plus d'un titre. En effet, parce que la France a constitué la puissance colonisatrice du Sénégal de 1854 jusqu'en 1960, le droit français a largement influencé le droit sénégalais et ce, depuis belle lurette. Mais, on ne peut s'empêcher de constater que cet impact a tendance à s'amenuiser de plus en plus. En effet, il apparait qu'à un moment donné, le législateur sénégalais a pris conscience du fait que l'idéal serait, non pas de mettre en place un droit du travail qui serait en grande partie calqué sur le droit de son ancienne puissance colonisatrice, mais plutôt d'élaborer un droit qui prendrait en compte les spécificités locales et les réalités nationales. Cette volonté du législateur est d'ailleurs visible aussi bien à travers l'ancien Code du travail sénégalais de 1961 qu'au niveau du nouveau Code de 1997. Le législateur de l'OHADA, de son coté, a su quelque peu freiner cette tendance. Une analyse minutieuse des dispositions de l'avant-projet d'acte uniforme portant sur le droit du travail laisse supposer un réel rapprochement avec le droit français actuel. Notre étude constitue donc l'occasion d'analyser cette évolution originale. De façon plus précise, elle permet, non seulement de recenser et d'expliquer les divergences notées au sein des droits français et sénégalais, mais aussi de mettre en exergue les innovations apportées par l'avant-projet d'acte uniforme de l'OHADA portant sur le droit du travail. / The redundancy for personal reason, unlike the redundancy for economic reason,is intimately linked to the person of the employee. It is an essential concept inlabor law, found in most states in the world but often under different terminology. ln front of this report, wc wouId be tried to wonder if the regulations of the redundancy for personal reason are really variable from a country to another.The answer to this question requires a comparative analysis of the laws of certain states. For this reason, only France and Senegal, two States which are, in addition, strongly bound by the history, held our attention. The study of the law of dismissal for personal reason in France and in Senegal suggests both similarities and differences. This is justified also in more ways. Indeed, because France constituted the colonizing power of Senegal from 1854 to1960, French law largely influenced Senegalese law. But today, it seems that this impact tends to fade more and more. Indeed, it appears that at sorne point, Senegalese legislators realized that the ideal would be not to establish a labor law that is largely modeled on the Law of its old colonizing power but rather to develop a law that takes into account local and national realities. This assertion is also visible both through the Senegalese former Labour Code of 1961 than at the new Code of 1997. The OHADA legislator, for his part, has curb this trend. Careful analysis of the provisions of the preliminary Uniform Act on employment law suggests a real reconciliation with current French law. Our study is therefore an opportunity to analyze this original evolution. In a more precise way, it constitutes the occasion to count and explain the divergences noted within the French and Senegalese laws, but also to put forward the innovations brought by the OHADA Law.
|
129 |
Investigating techniques to reduce soft error rate under single-event-induced charge sharing / Investigando técnicas para reduzir a taxa de erro de soft sob evento único induzido de carga compartilhadaAlmeida, Antonio Felipe Costa de January 2014 (has links)
The interaction of radiation with integrated circuits can provoke transient faults due to the deposit of charge in sensitive nodes of transistors. Because of the decrease the size in the process technology, charge sharing between transistors placed close to each other has been more and more observed. This phenomenon can lead to multiple transient faults. Therefore, it is important to analyze the effect of multiple transient faults in integrated circuits and investigate mitigation techniques able to cope with multiple faults. This work investigates the effect known as single-event-induced charge sharing in integrated circuits. Two main techniques are analyzed to cope with this effect. First, a placement constraint methodology is proposed. This technique uses placement constraints in standard cell based circuits. The objective is to achieve a layout for which the Soft-Error Rate (SER) due charge shared at adjacent cell is reduced. A set of fault injection was performed and the results show that the SER can be minimized due to single-event-induced charge sharing in according to the layout structure. Results show that by using placement constraint, it is possible to reduce the error rate from 12.85% to 10.63% due double faults. Second, Triple Modular Redundancy (TMR) schemes with different levels of granularities limited by majority voters are analyzed under multiple faults. The TMR versions are implemented using a standard design flow based on a traditional commercial standard cell library. An extensive fault injection campaign is then performed in order to verify the softerror rate due to single-event-induced charge sharing in multiple nodes. Results show that the proposed methodology becomes crucial to find the best trade-off in area, performance and soft-error rate when TMR designs are considered under multiple upsets. Results have been evaluated in a case-study circuit Advanced Encryption Standard (AES), synthesized to 90nm Application Specific Integrated Circuit (ASIC) library, and they show that combining the two techniques, the error rate resulted from multiple faults can be minimized or masked. By using TMR with different granularities and placement constraint methodology, it is possible to reduce the error rate from 11.06% to 0.00% for double faults. A detailed study of triple, four and five multiple faults combining both techniques are also described. We also tested the TMR with different granularities in SRAM-based FPGA platform. Results show that the versions with a fine grain scheme (FGTMR) were more effectiveness in masking multiple faults, similarly to results observed in the ASICs. In summary, the main contribution of this master thesis is the investigation of charge sharing effects in ASICs and the use of a combination of techniques based on TMR redundancy and placement to improve the tolerance under multiple faults.
|
130 |
A system failure detection method -- failure projection methodLou, Xi-Cheng January 1982 (has links)
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982. / Includes bibliographical references. / by Xi-Cheng Lou. / M.S.
|
Page generated in 0.0233 seconds