887 resultados para Redundant Manipulator
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This paper presents a general methodology for estimating and incorporating uncertainty in the controller and forward models for noisy nonlinear control problems. Conditional distribution modeling in a neural network context is used to estimate uncertainty around the prediction of neural network outputs. The developed methodology circumvents the dynamic programming problem by using the predicted neural network uncertainty to localize the possible control solutions to consider. A nonlinear multivariable system with different delays between the input-output pairs is used to demonstrate the successful application of the developed control algorithm. The proposed method is suitable for redundant control systems and allows us to model strongly non Gaussian distributions of control signal as well as processes with hysteresis.
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We consider the direct adaptive inverse control of nonlinear multivariable systems with different delays between every input-output pair. In direct adaptive inverse control, the inverse mapping is learned from examples of input-output pairs. This makes the obtained controller sub optimal, since the network may have to learn the response of the plant over a larger operational range than necessary. Moreover, in certain applications, the control problem can be redundant, implying that the inverse problem is ill posed. In this paper we propose a new algorithm which allows estimating and exploiting uncertainty in nonlinear multivariable control systems. This approach allows us to model strongly non-Gaussian distribution of control signals as well as processes with hysteresis. The proposed algorithm circumvents the dynamic programming problem by using the predicted neural network uncertainty to localise the possible control solutions to consider.
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The work describes the programme of activities relating to a mechanical study of the Conform extrusion process. The main objective was to provide a basic understanding of the mechanics of the Conform process with particular emphasis placed on modelling using experimental and theoretical considerations. The experimental equipment used includes a state of the art computer-aided data-logging system and high temperature loadcells (up to 260oC) manufactured from tungsten carbide. Full details of the experimental equipment is presented in sections 3 and 4. A theoretical model is given in Section 5. The model presented is based on the upper bound theorem using a variation of the existing extrusion theories combined with temperature changes in the feed metal across the deformation zone. In addition, constitutive equations used in the model have been generated from existing experimental data. Theoretical and experimental data are presented in tabular form in Section 6. The discussion of results includes a comprehensive graphical presentation of the experimental and theoretical data. The main findings are: (i) the establishment of stress/strain relationships and an energy balance in order to study the factors affecting redundant work, and hence a model suitable for design purposes; (ii) optimisation of the process, by determination of the extrusion pressure for the range of reduction and changes in the extrusion chamber geometry at lower wheel speeds; and (iii) an understanding of the control of the peak temperature reach during extrusion.
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PURPOSE: To design and validate a vision-specific quality-of-life assessment tool to be used in a clinical setting to evaluate low-vision rehabilitation strategy and management. METHODS: Previous vision-related questionnaires were assessed by low-vision rehabilitation professionals and patients for relevance and coverage. The 74 items selected were pretested to ensure correct interpretation. One hundred and fifty patients with low vision completed the chosen questions on four occasions to allow the selection of the most appropriate items. The vision-specific quality of life of patients with low vision was compared with that of 70 age-matched and gender-matched patients with normal vision and before and after low-vision rehabilitation in 278 patients. RESULTS: Items that were unreliable, internally inconsistent, redundant, or not relevant were excluded, resulting in the 25-item Low Vision Quality-of-Life Questionnaire (LVQOL). Completion of the LVQOL results in a summed score between 0 (a low quality of life) and 125 (a high quality of life). The LVQOL has a high internal consistency (α = 0.88) and good reliability (0.72). The average LVQOL score for a population with low vision (60.9 ± 25.1) was significantly lower than the average score of those with normal vision (100.3 ± 20.8). Rehabilitation improved the LVQOL score of those with low vision by an average of 6.8 ± 15.6 (17%). CONCLUSIONS: The LVQOL was shown to be an internally consistent, reliable, and fast method for measuring the vision-specific quality of life of the visually impaired in a clinical setting. It is able to quantify the quality of life of those with low vision and is useful in determining the effects of low-vision rehabilitation. Copyright (C) 2000 Elsevier Science Inc.
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Objectives: The Competitive Aggressiveness and Anger Scale (CAAS) was developed to measure antecedents of aggression in sport. The critique attacks the CAAS on three points: (1) the definition of aggression in sport adopted, (2) the‘‘one size fits all’’ element in the thinking behind the scale’s development, (3) the nature of the CAAS Anger and Aggressiveness items. The objectives of this response is to address misunderstandings in the critique. Methods: We identified a number of false assumptions that undermine the validity of the critique and attempt to clarify our position with respect to the criticisms made. Results: (1) The CAAS is being criticised for a definition that it did not use. (2) We accepted that the CAAS may not be suitable for everyone in our limitations section and fully accept the limitations of any scale. We have since undertaken a large research project to establish whether the scale is valid across and within specific sports. (3) The fundamental misunderstanding inherent throughout the critique is that the CAAS was designed as a measure of aggression, rather than anger and aggressiveness, rendering the critique of its items redundant. Conclusions: The critique misrepresents the authors of the CAAS and fails to present a coherent argument against its use. We hope to clarify our position here. The evidence to date suggests that the CAAS is a valid measure of anger and aggressiveness in many sports and that these concepts reliably differentiate players who admit unsanctioned aggression from those who do not.
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Amino acid substitution plays a vital role in both the molecular engineering of proteins and analysis of structure-activity relationships. High-throughput substitution is achieved by codon randomisation, which generates a library of mutants (a randomised gene library) in a single experiment. For full randomisation, key codons are typically replaced with NNN (64 sequences) or NNG CorT (32 sequences). This obligates cloning of redundant codons alongside those required to encode the 20 amino acids. As the number of randomised codons increases, there is therefore a progressive loss of randomisation efficiency; the number of genes required per protein rises exponentially. The redundant codons cause amino acids to be represented unevenly; for example, methionine is encoded just once within NNN, whilst arginine is encoded six times. Finally, the organisation of the genetic code makes it impossible to encode functional subsets of amino acids (e.g. polar residues only) in a single experiment. Here, we present a novel solution to randomisation where genetic redundancy is eliminated; the number of different genes equals the number of encoded proteins, regardless of codon number. There is no inherent amino acid bias and any required subset of amino acids may be encoded in one experiment. This generic approach should be widely applicable in studies involving randomisation of proteins. © 2003 Elsevier Ltd. All rights reserved.
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This thesis sets out to investigate the role of cohesion in the organisation and processing of three text types in English and Arabic. In other words, it attempts to shed some light on the descriptive and explanatory power of cohesion in different text typologies. To this effect, three text types, namely, literary fictional narrative, newspaper editorial and science were analysed to ascertain the intra- and inter-sentential trends in textual cohesion characteristic of each text type in each language. In addition, two small scale experiments which aimed at exploring the facilitatory effect of one cohesive device (i.e. lexical repetition) on the comprehension of three English text types by Arab learners were carried out. The first experiment examined this effect in an English science text; the second covered three English text types, i.e. fictional narrative, culturally-oriented and science. Some interesting and significant results have emerged from the textual analysis and the pilot studies. Most importantly, each text type tends to utilize the cohesive trends that are compatible with its readership, reader knowledge, reading style and pedagogical purpose. Whereas fictional narratives largely cohere through pronominal co-reference, editorials and science texts derive much cohesion from lexical repetition. As for cross-language differences English opts for economy in the use of cohesive devices, while Arabic largely coheres through the redundant effect created by the high frequency of most of those devices. Thus, cohesion is proved to be a variable rather than a homogeneous phenomenon which is dictated by text type among other factors. The results of the experiments suggest that lexical repetition does facilitate the comprehension of English texts by Arab learners. Fictional narratives are found to be easier to process and understand than expository texts. Consequently, cohesion can assist in the processing of text as it can in its creation.
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This study aims to investigate to what extent the views of the managers of the enterprises to be privatized are a barrier to smooth implementation of privatization as opposed to other problems. Accordingly, the research tackles two main issues: Identification and analysis of the major problems encountered in the implementation of the Egyptian privatization programme and at which level these problems exist while proposing different approaches to tackle them; and views of public sector top and middle-level managers regarding the main issues of privatization. The study relies upon a literature survey, interviews with stakeholders, a survey of managers' attitudes and several illustrative case studies. A model of "good practice" for the smooth and effective implementation of privatization has been designed. Practice in Egypt has then been studied and compared with the "good practice" model. Lack of strictness and firmness in implementing the announced privatization programme has been found to be a characteristic of Egyptian practice. This is partly attributable to the inadequacy of the programme and partly to the different obstacles to implementation. The main obstacles are doubtful desirability of privatization on the part of the managers at different implementation levels, resistance of stakeholders, in adequately of the legal framework governing privatization, redundant labour, lack of an efficient monitoring system allowing for accountability, inefficient marketing of privatization, ineffective communication, insufficient information at different levels and problems related to valuation and selling procedures. A large part of the thesis is concerned with SOE (State Owned Enterprise) managers' attitudes on and understanding of the privatization (appraised through surveys). Although most managers have stated their acceptance of privatization, many of their responses show that they do not accept selling SOEs. They understand privatization to include enterprise reform and restructuring, changing procedures and giving more authority to company executives, but not necessarily as selling SOEs. The majority of managers still see many issues that have to be addressed for smooth implementation of privatization e.g. insufficiency of information, incompleteness of legal framework, restructuring and labour problems. The main contribution to knowledge of this thesis is the study of problems of implementing privatization in developing countries especially managers' resistance to privatization as a major change, partly because of the threat it poses and partly because of the lack of understanding of privatization and implications of operating private businesses. A programme of persuading managers and offsetting the unfavourable effects is recommended as an outcome of the study. Five different phrases and words for the national Index to theses are: Egypt, privatization, implementation of privatization, problems of implementing privatization and managers' attitudes towards privatization.
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During the last decade the use of randomised gene libraries has had an enormous impact in the field of protein engineering. Such libraries comprise many variations of a single gene in which codon replacements are used to substitute key residues of the encoded protein. The expression of such libraries generates a library of randomised proteins which can subsequently be screened for desired or novel activities. Randomisation in this fashion has predominantly been achieved by the inclusion of the codons NNN or NNGCor T, in which N represents any of the four bases A,C,G, or T. The use of thesis codons however, necessities the cloning of redundant codons at each position of randomisation, in addition to those required to encode the twenty possible amino acid substitutions. As degenerate codons must be included at each position of randomisation, this results in a progressive loss of randomisation efficiency as the number of randomised positions is increased. The ratio of genes to proteins in these libraries rises exponentially with each position of randomisation, creating large gene libraries, which generate protein libraries of limited diversity upon expression. In addition to these problems of library size, the cloning of redundant codons also results in the generation of protein libraries in which substituted amino acids are unevenly represented. As several of the randomised codons may encode the same amino acid, for example serine which is encoded six time using the codon NNN, an inherent bias may be introduced into the resulting protein library during the randomisation procedure. The work outlined here describes the development of a novel randomisation technique aimed at a eliminating codon redundancy from randomised gene libraries, thus addressing the problems of library size and bias, associated with the cloning of redundant codons.
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We have simulated the performance of various apertures used in Coded Aperture Imaging - optically. Coded pictures of extended and continuous-tone planar objects from the Annulus, Twin Annulus, Fresnel Zone Plate and the Uniformly Redundant Array have been decoded using a noncoherent correlation process. We have compared the tomographic capabilities of the Twin Annulus with the Uniformly Redundant Arrays based on quadratic residues and m-sequences. We discuss the ways of reducing the 'd. c.' background of the various apertures used. The non-ideal System-Point-Spread-Function inherent in a noncoherent optical correlation process produces artifacts in the reconstruction. Artifacts are also introduced as a result of unwanted cross-correlation terms from out-of-focus planes. We find that the URN based on m-sequences exhibits good spatial resolution and out-of-focus behaviour when imaging extended objects.
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Particulate solids are complex redundant systems which consist of discrete particles. The interactions between the particles are complex and have been the subject of many theoretical and experimental investigations. Invetigations of particulate material have been restricted by the lack of quantitative information on the mechanisms occurring within an assembly. Laboratory experimentation is limited as information on the internal behaviour can only be inferred from measurements on the assembly boundary, or the use of intrusive measuring devices. In addition comparisons between test data are uncertain due to the difficulty in reproducing exact replicas of physical systems. Nevertheless, theoretical and technological advances require more detailed material information. However, numerical simulation affords access to information on every particle and hence the micro-mechanical behaviour within an assembly, and can replicate desired systems. To use a computer program to numerically simulate material behaviour accurately it is necessary to incorporte realistic interaction laws. This research programme used the finite difference simulation program `BALL', developed by Cundall (1971), which employed linear spring force-displacement laws. It was thus necessary to incorporate more realistic interaction laws. Therefore, this research programme was primarily concerned with the implementation of the normal force-displacement law of Hertz (1882) and the tangential force-displacement laws of Mindlin and Deresiewicz (1953). Within this thesis the contact mechanics theories employed in the program are developed and the adaptations which were necessary to incorporate these laws are detailed. Verification of the new contact force-displacement laws was achieved by simulating a quasi-static oblique contact and single particle oblique impact. Applications of the program to the simulation of large assemblies of particles is given, and the problems in undertaking quasi-static shear tests along with the results from two successful shear tests are described.
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Wavelet families arise by scaling and translations of a prototype function, called the mother wavelet. The construction of wavelet bases for cardinal spline spaces is generally carried out within the multi-resolution analysis scheme. Thus, the usual way of increasing the dimension of the multi-resolution subspaces is by augmenting the scaling factor. We show here that, when working on a compact interval, the identical effect can be achieved without changing the wavelet scale but reducing the translation parameter. By such a procedure we generate a redundant frame, called a dictionary, spanning the same spaces as a wavelet basis but with wavelets of broader support. We characterize the correlation of the dictionary elements by measuring their 'coherence' and produce examples illustrating the relevance of highly coherent dictionaries to problems of sparse signal representation.
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Non-uniform B-spline dictionaries on a compact interval are discussed in the context of sparse signal representation. For each given partition, dictionaries of B-spline functions for the corresponding spline space are built up by dividing the partition into subpartitions and joining together the bases for the concomitant subspaces. The resulting slightly redundant dictionaries are composed of B-spline functions of broader support than those corresponding to the B-spline basis for the identical space. Such dictionaries are meant to assist in the construction of adaptive sparse signal representation through a combination of stepwise optimal greedy techniques.
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A property of sparse representations in relation to their capacity for information storage is discussed. It is shown that this feature can be used for an application that we term Encrypted Image Folding. The proposed procedure is realizable through any suitable transformation. In particular, in this paper we illustrate the approach by recourse to the Discrete Cosine Transform and a combination of redundant Cosine and Dirac dictionaries. The main advantage of the proposed technique is that both storage and encryption can be achieved simultaneously using simple processing steps.
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This paper provides a preliminary comparative longitudinal analysis of the impact on workers made redundant due to the closure of the Mitsubishi plant in Adelaide and the MG Rover plant in Birmingham. Longitudinal surveys of ex-workers from both firms were undertaken over a 12-month period in order to assess the process of labour market adjustment. In the Mitsubishi case, given the skills shortage the state of Adelaide was facing, together with the considerable growth in mining and defence industries, it would have been more appropriate if policy intervention had been redirected to further training or re-skilling opportunities for redundant workers. This opportunity was effectively missed and as a result more workers left the workforce, most notably for retirement, than could have otherwise been the case. The MG Rover case was seen as a more successful example of policy intervention, with greater funding assistance available and targeted support available, and with more emphasis on re-training needs to assist adjustment. However, despite the assistance offered and the rhetoric of successful adjustment in both cases, the majority of workers have nevertheless experienced deterioration in their circumstances particularly in the Australian case where casual and part-time work were often the only work that could be obtained. Even in the UK case, where more funding assistance was offered, a majority of workers reported a decline in earnings and a rise in job insecurity. This suggests that a reliance on the flexible labour market is insufficient to promote adjustment, and that more active policy intervention is needed especially in regard to further up-skilling.