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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Local council's response to street homelessness in Welkom

Okumu, Moses 26 October 2006 (has links)
Faculty of Arts School of Humanities 0400617v mosmakoso@yahoo.com Degree of master housing / The aim of the study was to investigate, how Welkom council is responding to street homelessness in Welkom. The democratic government adopted, the Reconstruction and Development Programme, as an integrated socio-economic policy framework, to mobilize national, and human resources, towards a sustainable housing for urban, and rural poor. However, despite, the government’s concerted commitment to providing massive housing for its citizens, the problem of homelessness, remains pervasive. Three themes, which emerged as critical during the study, are discussed in detail, namely, lack of housing policy, addressing specifically street homelessness; lack of financial and legal mandate, by the local council, to house street homelessness; and lack of research department, and human resources for effective conceptualization of the issue. It is argued that the department of research is critical in providing strategic research facilities, in areas of housing policy, and legislation frameworks. Equally critical, is the need for skilled human resources, necessary for strategic and holistic provision of efficient and effective services. The study suggests complete overhaul of the national housing policy making it holistically inclusive. Equally suggested, is capacity building necessary for sustainable, efficient, and effective housing delivery and eradication of homelessness.
2

Strategies to enhance efficiency of microbial protein production in cattle consuming tropical forages

Tanda Sahat Sastradarmaja Panjaitan Unknown Date (has links)
Microbial crude protein (MCP) is the main source of protein supplied to ruminants. Several studies report that the efficiency of MCP production (eMCP) from tropical forages is low due to low rumen degradable protein (RDP) content. The studies reported in this thesis determined the eMCP from tropical forages varying in crude protein (CP) and dry matter digestibility (DMD), examined strategies to increase eMCP and the possible practical methods of application under extensive cattle production systems. This was done through four metabolism experiments, one rate of digestion experiment and a preference test experiment. In Experiment 1, the eMCP of 3 tropical forages (speargrass (Heteropogon contortus), Mitchell grass (Astrebla spp) and pangola grass (Digitaria eriantha)), and temperate ryegrass (Lolium multiflorum cultivar aristocrat) was measured. All tropical forages were associated with low eMCP (102 - 110 g MCP/kg digestible organic matter (DOM)) due to low CP and RDP content. The RDP content of the tropical forages ranged from 43 - 103 g RDP/kg DOM compared to 214 g RDP/kg DOM in ryegrass. Retention time of Cr-EDTA and Ytterbium in the rumen ranged from 13 - 34 and 29 - 59 h for tropical forages respectively, compared to 10.2 and 13.2 h for ryegrass. In Experiment 2, the rate of digestion of speargrass, Mitchell grass and ryegrass varied when incubated in the rumen of steers consuming speargrass hay (1.8% CP). Addition of a variety of nitrogen supplements; urea-ammonium sulphate (US), US plus branch chain amino acids (leucine, isoleucine and valine) plus phenylalanine (USAA), casein, cottonseed meal (CSM), yeast and Chlorella (Chlorella pyrenoidea) algae to supply approximately 170 g RDP/kg DOM improved the rate of digestion of all three substrates. However, there was no difference in rate of digestion of the three substrates between the different nitrogen supplements. In Experiments 3 and 4, steers fed medium quality pangola grass hay (9.9% CP and 61% DMD) or low quality Mitchell grass hay (4.5% CP and 41% DMD) were supplemented with US, casein and USAA. US was provided at 130, 170, 210 and 250 g RDP/kg DOM. The USAA treatment was provided at a RDP/DOM of 170 with US and then amino acids (USAA) were provided in the same ratio and level as the amino acids in the casein treatment at 130, 170, 250 and 300 g RDP/kg DOM. Increased RDP intake from all supplements increased the rumen ammonia-N concentration for both hays. The molar percentage of branch chain fatty acids (BCFA) increased 3 - 4 fold (6.6% of total VFA) above control with increasing intake of USAA or casein supplements for both hays. However, eMCP did not increase in response to increasing RDP intake from either supplement for both hays. The RDP supplementation also had no effect on intake, rate of digestion and retention time of Cr-EDTA in the rumen. In Experiment 5, steers fed Mitchell grass hay (3.8% CP and 44% DMD) were supplemented with US and Spirulina (Spirulina platensis) algae. The US was supplied to provide 90, 130, 170 and 210 g RDP/kg DOM and the Spirulina supplied to provide 90, 130, 170 and 290 g RDP/kg DOM. Increased RDP intake from US and Spirulina was associated with linear and quadratic increases in eMCP respectively. The eMCP at the highest level of US (93 g MCP/kg DOM) was below the minimum feeding standards value of 130 g MCP/kg DOM, whilst the highest level of Spirulina reached the higher end of the feeding standards (166 g MCP/kg DOM). Increasing RDP intake resulted in increased hay DM intake and total DOM intake, which were both higher for the Spirulina than the US supplement (24.5 vs.18.5 g DM/kg W/d and 11.9 vs. 7.6 g DOM/kg W/d). The retention time of Cr-EDTA and lignin in the rumen decreased with increasing RDP intake and were both shorter with Spirulina compared with US supplementation (15 vs. 21 h for Cr-EDTA; 45 vs. 56 h for lignin). In addition, Spirulina increased the BCFA concentration to 4.2% of total VFA. In Experiment 6, four different concentrations of Spirulina solution were offered to steers fed restricted amounts (14 g DM/kg W/d) of pangola hay (3.4% CP). Drinking water containing Spirulina was highly preferred and had no deleterious effect on water or hay intake. Steers strongly preferred Spirulina solution to water, when offered both solutions. Approximately 20.5% of imbibed water by-passed the rumen, which was not influenced by the Spirulina concentration in the drinking water. It may be concluded that RDP is the primary factor affecting eMCP. High eMCP was associated with low retention time of water in the rumen and high intake. Once RDP is not limiting eMCP, a source of RDP rich in true protein, nucleic acids, fatty acids, vitamins and minerals, such as Spirulina algae, may be required for cattle fed low quality tropical hay to achieve the maximum eMCP reported in the feeding standards.
3

Effect of low-cost housing on household and environmental health of residents in Phumlani Village, City of Cape Town

Daries, Louella M. January 2011 (has links)
Magister Public Health - MPH / Many poor households in South Africa find themselves living in informal housing and only become proprietors of formal housing via the government subsidy scheme for core low-cost housing, thereby also realizing their constitutional right to housing. The subsidy is however limited and it largely determines materials, and construction methods used. Obtaining a formal low-cost dwelling means that basic services such as electricity, sanitation, water and waste collection, is available to the home owner. Formal low-cost housing settlements are commonly located in poor areas and recipients of the housing subsidy are commonly unemployed or have low-income jobs, and frequently originate from informal settlements where services, albeit limited and often communal, were provided at no cost. This study sought to assess the combined effect of relocating from an informal dwelling to a formal low-cost dwelling and receiving individual house-based basic services of electricity, water, sanitation and waste collection, on environmental- and household health. An ecological study design was used whereby data was collected at "baseline" while households were living in the informal settlement, and again at "2 years relocated" i.e. 2 years after moving in to the formal low-cost dwelling. The study population included all households residing in the Phumlani- and Pelican Park- Zeekoevlei Informal area in the year 2000, who were on the waiting list to receive low-cost core housing units in Phumlani Village and were due to be relocated there. Due to the rapid pace at which construction of new homes occurred not all households could be captured whilst living in the informal settlement, i.e. at "baseline". The actual sample subsequently consisted of 53 households at "baseline", and all, i.e. 124 households at "2 years relocated". Data was collected via a structured interview, whereby one respondent per household was interviewed by a trained fieldworker. Positive health improvements were reported by households in terms of personal and household health. Significant (p<0.05) positive improvements were found for households in formal lowcost housing at "2 years relocated" for exposures to: overcrowded living conditions (PR=1.159, 95%CI=1.153 – 3.328); indoor air pollution due to cooking and heating (PR=2.185, 95%CI=1.655 – 2.885); improper household waste management (PR=7.381, 95%CI=4.313 – 12.633 and inadequate sanitation (PR=0.365, 95%CI=0.255 – 0.523). The incidence of childhood diarrhoea episodes decreased significantly (PR=5.588, 95%CI=1.284 – 24.315) at "2 years relocated". Water access, availability and use also increased significantly (PR=0.212, 95%CI=0.125 – 0.358) 2 years after relocation. Factors that did not improve include levels of employment for which households were found to be worse off, with 16% of households having no person employed at "2 years relocated" as opposed to only 2% at ‘baseline”. Other factors remaining unchanged included incidences of respiratory, skin and eye infections amongst children ≤ 6 years old. Although exposure levels to indoor air pollution decreased for some households, this remained present for others as electricity in combination with bio-mass fuels are still being used for heating and cooking. Environmental health conditions for a variety of factors remained unchanged and there was a reversion back to living conditions and habits of the informal settlement. Littering, dumping of waste within the neighbourhood and a high pest presence, remained unchanged. Subsidised formal housing and associated basic services does have a positive impact on health. However, the amount of free basic services, specifically electricity, provided, in lieu of household energy requirements, does not satisfactorily cover all household needs. Factors such as unemployment and low-incomes hamper the household’s ability to maintain the electricity supply as is needed and for this reason alternatives to reliance on electricity should be included in the design and construction of the low-cost house. The manifestation of poor environmental health conditions indicates that provision of low-cost housing by itself is not sufficient to ensure good environmental health. Therefore hygiene promotion should be included as part of the total beneficiary package.
4

Sustainable subsidy housing provision : a planning approach / Elmarie Yolandé Scheepers

Scheepers, Elmarie Yolandé January 2014 (has links)
South Africa is plagued with a staggering housing backlog (estimated at approximately 2.1 million units at present) due, in part, to the poor planning principles advocated by the Apartheid regime. Concerted efforts were made by the newly elected government since 1994 to provide houses for the urban poor who were previously disadvantaged. As such, a subsidised housing scheme in South Africa was introduced as a method to provide adequate housing to citizens who could not afford to do so themselves. However, despite the construction of approximately 3 million dwellings over the past 19 years, the backlog today is larger than the initial backlog experienced in 1994. Two questions were therefore raised in this research: 1) Whether the current approach to subsidised housing provision is sustainable, given the socio-economic conditions present in South African cities and 2) Which planning principles could be applied with regards to subsidised housing in order to ensure the development of sustainable human settlements. In order to address these issues, research regarding sustainable human settlements, and the South African context in terms of housing provision, was done in the form of a literature review and empirical study. The literature reviewed shed light on (a) urban models, (b) the elements of sustainable human settlements, (c) policies and legislation relating to subsidised housing provision in South Africa and (d) the criticisms against the South African policies and the current method of subsidised housing provision in South Africa. Information gained during the literature review phase was used to compile a set of criteria by which housing provision for the urban poor could be evaluated. This evaluation took the form of an empirical study which consisted of structured questionnaires and interviews, and a comparative analysis of international and local pilot studies. The following subsidised housing projects were scrutinised to establish best practices that may be applied to the South African context: * Bairro Carioca and Taroni Condiminiums in Rio de Janeiro, Brazil, * Haram City in October 6 City, Egypt, * Cosmo City, South Africa, * Community Residential Units in Potchefstroom, South Africa, and * Reconstruction and Development Program Units in Potchefstroom, South Africa. Through the critical evaluation of the above mentioned projects, it became clear that the typical South African method of subsidised housing provision, in which beneficiaries receive a loose standing dwelling house on a single erf, is in fact unsustainable, and that this approach is not facilitating the formation of sustainable human settlements. Alternative methods of housing delivery that can be implemented in the South African context were identified and led to the formulation of planning related recommendations in terms of sustainable subsidised housing provision, focussing on (1) increased densities, (2) improved location and (3) providing a range of household types. Mention was also made of non-planning related recommendations such as (4) alternative services delivery, (5) including different forms of tenure and (6) increasing financial responsibility. / MArt et Scien (Urban and Regional Planning), North-West University, Potchefstroom Campus, 2014
5

Sustainable subsidy housing provision : a planning approach / Elmarie Yolandé Scheepers

Scheepers, Elmarie Yolandé January 2014 (has links)
South Africa is plagued with a staggering housing backlog (estimated at approximately 2.1 million units at present) due, in part, to the poor planning principles advocated by the Apartheid regime. Concerted efforts were made by the newly elected government since 1994 to provide houses for the urban poor who were previously disadvantaged. As such, a subsidised housing scheme in South Africa was introduced as a method to provide adequate housing to citizens who could not afford to do so themselves. However, despite the construction of approximately 3 million dwellings over the past 19 years, the backlog today is larger than the initial backlog experienced in 1994. Two questions were therefore raised in this research: 1) Whether the current approach to subsidised housing provision is sustainable, given the socio-economic conditions present in South African cities and 2) Which planning principles could be applied with regards to subsidised housing in order to ensure the development of sustainable human settlements. In order to address these issues, research regarding sustainable human settlements, and the South African context in terms of housing provision, was done in the form of a literature review and empirical study. The literature reviewed shed light on (a) urban models, (b) the elements of sustainable human settlements, (c) policies and legislation relating to subsidised housing provision in South Africa and (d) the criticisms against the South African policies and the current method of subsidised housing provision in South Africa. Information gained during the literature review phase was used to compile a set of criteria by which housing provision for the urban poor could be evaluated. This evaluation took the form of an empirical study which consisted of structured questionnaires and interviews, and a comparative analysis of international and local pilot studies. The following subsidised housing projects were scrutinised to establish best practices that may be applied to the South African context: * Bairro Carioca and Taroni Condiminiums in Rio de Janeiro, Brazil, * Haram City in October 6 City, Egypt, * Cosmo City, South Africa, * Community Residential Units in Potchefstroom, South Africa, and * Reconstruction and Development Program Units in Potchefstroom, South Africa. Through the critical evaluation of the above mentioned projects, it became clear that the typical South African method of subsidised housing provision, in which beneficiaries receive a loose standing dwelling house on a single erf, is in fact unsustainable, and that this approach is not facilitating the formation of sustainable human settlements. Alternative methods of housing delivery that can be implemented in the South African context were identified and led to the formulation of planning related recommendations in terms of sustainable subsidised housing provision, focussing on (1) increased densities, (2) improved location and (3) providing a range of household types. Mention was also made of non-planning related recommendations such as (4) alternative services delivery, (5) including different forms of tenure and (6) increasing financial responsibility. / MArt et Scien (Urban and Regional Planning), North-West University, Potchefstroom Campus, 2014
6

Modélisation des flux d'information dans un système de e-maintenance.

Tararykine, Viatcheslav 07 November 2005 (has links) (PDF)
Le maintien des équipements de production était toujours un élément clé pour la productivité des usines aussi bien que pour la qualité des produits. Premièrement, le coût de la maintenance représente une partie importante du coût total de la production et, deuxièmement, un défaut d'équipement peut avoir un impact considérable sur la qualité du produit et sur la disponibilité de l'équipement. La maintenance reste aujourd'hui un défi industriel impliquant la remise en cause des structures figées et la promotion de méthodes nouvelles adaptées à la nature moderne des matériels. Les avancées technologiques dans le domaine de communication ont favorisé l'apparition de nouveaux types et formes de maintenance : télémaintenance distribuée .... Le problème majeur de ces solutions, basées sur l'utilisation des moyens d'échange d'information modernes, tel que Internet, reste leur nature non-déterministe. L'impossibilité de garantir la Qualité de Service, peut avoir des impacts considérables sur le fonctionnement des applications faisant partie du système de maintenance, et par conséquent, sur la disponibilité des équipements. Le modèle du système d'information de la fonction maintenance, proposé dans cette thèse, permettra de prédire le comportement du système de communication choisi, vis-à-vis du flux d'information généré par le système.
7

Comportamento alimentar, metabolismo ruminal e estabilidade do leite de vacas alimentadas com milho floculado e diferentes níveis de degradabilidade da proteína / Feeding behavior, ruminal metabolism and milk stability of cows fed steam flakes and different levels of protein degradability

Fonseca, Danielle de Cássia Martins da 09 February 2018 (has links)
O presente estudo foi desenvolvido em dois experimentos: 1) Tipo de processamento do milho e a relação PDR:PNDR sobre a fermentação ruminal, comportamento alimentar e seletividade ingestiva de vacas leiteiras cujos objetivos foram: a) avaliar o efeito do tipo de processamento do milho (floculado ou moído) e a relação da proteína degradável (PDR) e não degradável no rúmen (PNDR) (alta ou baixa) sobre a fermentação ruminal, o comportamento alimentar e a seletividade ingestiva de vacas leiteiras durante o período experimental; b) avaliar o efeito a curto prazo da troca da dieta contendomilho moído ou floculado e alta ou baixa relação PDR:PNDR sobre o consumo de matéria seca, produção e estabilidade do leite (teste do álcool, pH, cálcio iônico, estabilidade térmica e alcoólica) de vacas leiteiras durante período de adaptação. Foram utilizadas 20 vacas da raça Holandesa, com 162 &#177; 70 DEL, 666 &#177; 68 kg de peso corporal, 3,15 &#177; 0,48 de escore de condição corporal e 36,0 &#177; 7,78 kg/vaca/ dia de produção de leite. Os resultados de metabolismo ruminal indicaram que o milho floculado reduziu a relação acetato:propionato e a concentração de ácido acético (%) e aumentou as concentrações dos ácidos valérico (&micro;mol/L) e de propiônico (%) e o pH fecal em relação ao milho moído. Quanto ao comportamento alimentar, observou-se que o uso de milho floculado associado à alta relação PDR:PNDR e a utilização de milho moído associado à baixa relação PDR:PNDR reduziram os tempos de alimentação (TAL/ kg de MS ingerida) e de ruminação (TRU/ kg de MS ingerida) entretanto, o uso de milho floculado associado à alta ou à baixa relação PDR:PNDR aumentaram o tempo de ruminação (TRU/ kg de FDN consumido). Já para índice de seleção notou-se que a rejeição de partículas longas (&gt; 19,0 mm) foi menor em vacas alimentadas com milho floculado em relação às alimentadas com moído. 2) Efeito a curto prazo da troca da dieta sobre a produção e estabilidade do leite de vacas da raça Holandesa que teve por objetivo avaliar o efeito do dia de troca da dieta com diferentes fontes de carboidrato não fibroso associado ou não a inclusão de tamponante/alcalinizante sobre CMS, produção e estabilidade do leite (teste do álcool, pH, cálcio iônico, estabilidade térmica e alcoólica). Foram utilizadas 16 vacas da raça Holandesa, com 130 &#177; 81 DEL, peso corporal de 660 &#177; 62 kg e produção média de leite de 28,5 &#177; 4,79 kg/vaca/dia. O milho moído associado à alta ou à baixa relação PDR:PNDR aumentou o CMS, entretanto o fornecimento de dieta contendo a alta relação PDR:PNDR associada ao milho moído ou floculado apresentaram redução na PL. O uso de milho floculado associado à alta relação PDR:PNDR aumentou o valor de pH das amostras de leite e em todos os tratamentos testados a concentração de Cai apresentou redução. O uso de milho floculado associado ao aumento da relação PDR:PNDR causou redução na estabilidade alcoólica do leite e o uso do milho moído associado a baixa relação PDR:PNDR aumentou a estabilidade do leite ao teste do álcool. O CMS foi a única variável que apresentou efeito da dieta, em que o uso de milho moído sem a inclusão de tamp/alc aumentou o CMS. Sendo assim, durante o período de adaptação, o efeito a curto prazo de troca foi mais nítido nas dietas contendo milho processado associado à proteínas de diferentes degradabilidades ruminal do que nas dietas contendo fontes de carboidratos não fibrosos associados à inclusão ou não de tamp/alc. / The present study was developed in two experiments: 1) Corn processing type and the RDP:RUP ratio on ruminal fermentation, feeding behavior and ingestive selectivity of dairy cows. The objectives were: to evaluate the effect of corn processing type (flocculated or ground) and the ratio (hight or low) of degradable (RDP) and non-degradable protein (RUP) on ruminal fermentation, feed behavior and ingestive selectivity of dairy cows during the experimental period. Indeed to evaluate the short-term effect of dietary exchange containing either ground or flocculated corn and high or low RDP: RUP ratio on dry matter intake, milk yield and stability (alcohol test, pH, ionic calcium, of dairy cows during adaptation period. Twenty Holstein cows were used, with 162 &#177; 70 DIM, 666 &#177; 68 kg body weight, 3.15 &#177; 0.48 body condition score and 36.0 &#177; 7.78 kg / cow / day of milk yield. The results of ruminal metabolism indicated that the flocculated corn reduced the acetate: propionate ratio and the acetic acid concentration (%) and increased the concentrations of valeric (&micro;mol / L) and propionic acid (%) and fecal pH in relation to ground corn. As regards feed behavior, it was observed that the use of flocculated corn associated with high RDP:RUP ratio and the use of milled corn associated with low RDP:RUP ratio reduced feeding times (TAL / kg of intake DM) and rumination (TRU / kg of DM ingested). However, the use of flocculated corn associated with high or low RDP:RUP ratios increased rumination time (TRU / kg of NDF consumed). For the selection index, it was noted that the rejection of long particles (&gt; 19.0 mm) was lower in cows fed flocculated maize than those fed with milled corn. 2) Short-term effect of the diet change on the production and stability of Holstein cows milk that aimed to evaluate the effect of the diet change day with different sources of non-fibrous carbohydrate associated or not with the inclusion of buffer / alkalinizing on DMI, milk production and stability (alcohol test, pH, ionic calcium, thermal and alcoholic stability). Sixteen Holstein cows, 130 &#177; 81 DIM, body weight of 660 &#177; 62 kg and mean milk yield of 28.5 &#177; 4.79 kg / cow / day were used. Ground corn associated with high or low RDP:RUP ratios increased of intake DM; however, the diet containing the high RDP:RUP ratio associated to ground or flocculated corn showed a decrease in milk yield. The use of flocculated corn associated with high RDP:RUP ratio increased the pH value of milk samples; and in all tested treatments; the concentration of Cai presented reduction. The use of flocculated corn associated with the increase of the RDP:RUP ratio caused a decrease in the milk alcoholic stability while the use of ground corn associated with a low RDP:RUP ratio increased this variable. The intake DM was the only variable that presented a dietary effect, in which the use of ground corn without the inclusion of buffer/alk increased intake DM. Thus, during the adaptation period, the short-term effect of exchange was more pronounced in diets containing processed corn associated with proteins of different ruminal degradability than in diets containing sources of non-fibrous carbohydrates associated with the inclusion of buffer/alk .
8

Factors contributing to misallocation of RDP-Low cost houses to beneficiaries at Namakgale in Mopani District of Limpopo Province

Malatji, M.P. January 2011 (has links)
Thesis (MPA.) --University of Limpopo, 2011 / Refer to document
9

Construction d'un espace sanitaire transfrontalier : le recours aux soins des Laotiens en Thaïlande

Bochaton, Audrey 17 December 2009 (has links) (PDF)
Dans le monde globalisé contemporain, les hommes sont de plus en plus mobiles pour des motifs aussi divers que la recherche d'un emploi, la poursuite des études ou encore la quête d'exotisme. La santé n'échappe pas à cette tendance et ainsi certains malades n'hésitent pas à traverser les frontières et à parcourir parfois des milliers de kilomètres pour consulter tel médecin renommé, bénéficier d'une prise en charge rapide, de qualité ou à bas coût. Notre étude s'intéresse à ces questions, les flux de patients, appréhendés à l'échelle régionale et plus précisément au sein de l'espace frontalier lao-thaïlandais où apparaissent des dynamiques thérapeutiques transfrontalières : le recours aux soins des Laotiens dans des hôpitaux thaïlandais limitrophes. Cette pratique engagée par une partie de la population vivant dans les bordures frontalières accompagne l'ouverture récente du Laos et souligne l'écart de développement existant entre les deux pays. La discontinuité géographique entre le Laos et la Thaïlande se double d'une discontinuité sanitaire, propice à la mobilité des patients et facilitée en outre par la proximité et les liens historiques entretenus par les populations riveraines du Mékong. Que révèlent ces mobilités de patients sur le fonctionnement de l'espace lao-thaïlandais et sur les relations entre les deux pays ? Comment participent-elles à une recomposition du territoire transfrontalier ? En utilisant les recours aux soins transfrontaliers comme révélateur, notre objectif, en tant que géographe est d'analyser les processus socio-territoriaux en présence actuellement au sein de l'espace lao-thaïlandais. L'entrée par la santé constitue un point de vue original pour renouveler la réflexion sur la notion de frontière.
10

Surveillance des systèmes de production automatisés : détection et aide au diagnostic

Rayhane, Hassan 02 July 2004 (has links) (PDF)
Le but de la thèse est de développer une nouvelle approche de surveillance des systèmes à événements discrets. La méthode proposée est basée sur la surveillance du temps de service en utilisant l'automate temporisé comme outil de modélisation.<br />Partant d'un système commandé, le premier objectif est la surveillance des différentes activités de ce système afin d'améliorer sa disponibilité. Ceci se traduit par la minimisation du nombre d'arrêts qui pénalisent la production, en suivant en temps réel, l'état de fonctionnement des différents capteurs du système. Ainsi pour chaque tâche, la surveillance du temps écoulé entre deux événements (l'instant où la commande a donné l'ordre de démarrer une tâche et l'instant où le capteur indique la fin d'exécution de la tâche) permet de détecter au plutôt d'éventuelles défaillances. La deuxième phase correspond au diagnostic qui consiste en la détermination des causes du problème observé.<br />Jusqu'à présent les approches de surveillance utilisent un modèle de référence basé sur la connaissance à priori de toutes les situations interdites du système. Le modèle de surveillance proposé présente un réel avantage. En effet, la détection d'éventuelles défaillances ne nécessite pas une liste exhaustive de toutes les défaillances possibles du système. En fonction de la catégorie du système de production et de la nature des tâches à surveiller nous introduisons une tolérance sur la durée de la tâche à surveiller. Ainsi, la notion de fonctionnement en ‘ mode dégradé' est introduite. Au-delà de cette tolérance, le système sera effectivement dans un état de ‘défaillance'. Différents exemples illustrent la démarche proposée. Ils permettent de montrer la puissance d'une telle approche. De plus, un algorithme permettant le calcul du seuil optimal de tolérance est proposé, ainsi que l'évaluation des performances du système de surveillance.

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