• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 117
  • 109
  • 23
  • 16
  • 5
  • 5
  • 4
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 331
  • 331
  • 101
  • 100
  • 80
  • 79
  • 71
  • 51
  • 50
  • 48
  • 44
  • 43
  • 37
  • 36
  • 34
  • 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.
81

Presence of potentially pathogenic heterotrophic plate count (HPC) bacteria occurring in a drinking water distribution system in the North-West Province, South Africa / by Leandra Venter

Venter, Leandra January 2010 (has links)
There is currently growing concern about the presence of heterotrophic plate count (HPC) bacteria in drinking water. These HPC may have potential pathogenic features, enabling them to cause disease. It is especially alarming amongst individuals with a weakened immune system. South Africa, the country with the highest incidents of HIV positive individuals in the world, mainly uses these counts to assess the quality of drinking water in terms of the number of micro-organisms present in the water. These micro-organisms may be present in the bulk water or as biofilms adhered to the surfaces of a drinking water distribution system. The current study investigated the pathogenic potential of HPC bacteria occurring as biofilms within a drinking water distribution system and determined the possible presence of these micro-organims within the bulk water. Biofilm samples were taken from five sites within a drinking water distribution system. Fifty six bacterial colonies were selected based on morphotypes and isolated for the screening of potential pathogenic features. Haemolysin production was tested for using sheep-blood agar plates. Of the 56, 31 isolates were ?-haemolytic. Among the 31 ?-haemolytic positive isolates 87.1% were positive for lecithinase, 41.9% for proteinase, 19.4% for chondroitinase, 9.7% for DNase and 6.5% for hyaluronidase. All of the ?-haemolytic isolates were resistant to oxytetracycline 30 ?g, trimethoprim 2.5 ?g and penicillin G10 units, 96.8% were resistant to vancomycin 30 ?g and ampicillin 10 ?g, 93.5% to kanamycin 30 ?g, 74.2% to chloramphenicol 30 ?g, 54.8% to ciprofloxacin 5 ?g, 22.6% to streptomycin 300 ?g and 16.1% to erythromycin 15 ?g. Nineteen isolates producing two or more enzymes were subjected to Gram staining. The nineteen isolates were all Gram-positive. These isolates were then identified using the BD BBL CRYSTALTM Gram-positive (GP) identification (ID) system. Isolates were identified as Bacillus cereus, Bacillus licheniformis, Bacillus subtilis, Bacillus megaterium, Bacillus pumilus and Kocuria rosea. 16S rRNA gene sequencing was performed to confirm these results and to obtain identifications for the bacteria not identified with the BD BBL CRYSTALTM GP ID system. Additionally identified bacteria included Bacillus thuringiensis, Arthrobacter oxydans and Exiguobacterium acetylicum. Morphological properties of the different species were studied with transmission electron microscopy (TEM) to confirm sequencing results. All the isolates displayed rod shaped cells with the exception of Arthrobacter oxydans being spherical in the stationary phase of their life cycle. Bulk water samples were taken at two sites in close proximity with the biofilm sampling sites. The DNA was extracted directly from the water samples and the 16S rRNA gene region was amplified. Denaturing gradient gel electrophoresis (DGGE) was performed to confirm the presence of the isolates from the biofilm samples in the bulk water samples. The presence of Bacillus pumilus and Arthrobacter oxydans could be confirmed with DGGE. This study demonstrated the presence of potentially pathogenic HPC bacteria within biofilms in a drinking water distribution system. It also confirmed the probable presence of two of these biofilm based bacteria in the bulk water. / Thesis (M.Sc. (Microbiology))--North-West University, Potchefstroom Campus, 2010.
82

Presence of potentially pathogenic heterotrophic plate count (HPC) bacteria occurring in a drinking water distribution system in the North-West Province, South Africa / by Leandra Venter

Venter, Leandra January 2010 (has links)
There is currently growing concern about the presence of heterotrophic plate count (HPC) bacteria in drinking water. These HPC may have potential pathogenic features, enabling them to cause disease. It is especially alarming amongst individuals with a weakened immune system. South Africa, the country with the highest incidents of HIV positive individuals in the world, mainly uses these counts to assess the quality of drinking water in terms of the number of micro-organisms present in the water. These micro-organisms may be present in the bulk water or as biofilms adhered to the surfaces of a drinking water distribution system. The current study investigated the pathogenic potential of HPC bacteria occurring as biofilms within a drinking water distribution system and determined the possible presence of these micro-organims within the bulk water. Biofilm samples were taken from five sites within a drinking water distribution system. Fifty six bacterial colonies were selected based on morphotypes and isolated for the screening of potential pathogenic features. Haemolysin production was tested for using sheep-blood agar plates. Of the 56, 31 isolates were ?-haemolytic. Among the 31 ?-haemolytic positive isolates 87.1% were positive for lecithinase, 41.9% for proteinase, 19.4% for chondroitinase, 9.7% for DNase and 6.5% for hyaluronidase. All of the ?-haemolytic isolates were resistant to oxytetracycline 30 ?g, trimethoprim 2.5 ?g and penicillin G10 units, 96.8% were resistant to vancomycin 30 ?g and ampicillin 10 ?g, 93.5% to kanamycin 30 ?g, 74.2% to chloramphenicol 30 ?g, 54.8% to ciprofloxacin 5 ?g, 22.6% to streptomycin 300 ?g and 16.1% to erythromycin 15 ?g. Nineteen isolates producing two or more enzymes were subjected to Gram staining. The nineteen isolates were all Gram-positive. These isolates were then identified using the BD BBL CRYSTALTM Gram-positive (GP) identification (ID) system. Isolates were identified as Bacillus cereus, Bacillus licheniformis, Bacillus subtilis, Bacillus megaterium, Bacillus pumilus and Kocuria rosea. 16S rRNA gene sequencing was performed to confirm these results and to obtain identifications for the bacteria not identified with the BD BBL CRYSTALTM GP ID system. Additionally identified bacteria included Bacillus thuringiensis, Arthrobacter oxydans and Exiguobacterium acetylicum. Morphological properties of the different species were studied with transmission electron microscopy (TEM) to confirm sequencing results. All the isolates displayed rod shaped cells with the exception of Arthrobacter oxydans being spherical in the stationary phase of their life cycle. Bulk water samples were taken at two sites in close proximity with the biofilm sampling sites. The DNA was extracted directly from the water samples and the 16S rRNA gene region was amplified. Denaturing gradient gel electrophoresis (DGGE) was performed to confirm the presence of the isolates from the biofilm samples in the bulk water samples. The presence of Bacillus pumilus and Arthrobacter oxydans could be confirmed with DGGE. This study demonstrated the presence of potentially pathogenic HPC bacteria within biofilms in a drinking water distribution system. It also confirmed the probable presence of two of these biofilm based bacteria in the bulk water. / Thesis (M.Sc. (Microbiology))--North-West University, Potchefstroom Campus, 2010.
83

A genetic algorithm for power distribution system planning

Rivas-Davalos, Francisco January 2004 (has links)
The planning of distribution systems consists in determining the optimum site and size of new substations and feeders in order to satisfy the future power demand with minimum investment and operational costs and an acceptable level of reliability. This problem is a combinatorial, non-linear and constrained optimization problem. Several solution methods based on genetic algorithms have been reported in the literature; however, some of these methods have been reported with applications to small systems while others have long solution time. In addition, the vast majority of the developed methods handle planning problems simplifying them as single-objective problems but, there are some planning aspects that can not be combined into a single scalar objective; therefore, they require to be treated separately. The cause of these shortcomings is the poor representation of the potential solutions and their genetic operators This thesis presents the design of a genetic algorithm using a direct representation technique and specialized genetic operators for power distribution system expansion planning problems. These operators effectively preserve and exploit critical configurations that contribute to the optimization of the objective function. The constraints of the problems are efficiently handle with new strategies. The genetic algorithm was tested on several theoretical and real large-scale power distribution systems. Problems of network reconfiguration for loss reduction were also included in order to show the potential of the algorithm to resolve operational problems. Both single-objective and multi-objective formulations were considered in the tests. The results were compared with results from other heuristic methods such as ant colony system algorithms, evolutionary programming, differential evolution and other genetic algorithms reported in the literature. From these comparisons it was concluded that the proposed genetic algorithm is suitable to resolve problems of largescale power distribution system planning. Moreover, the algorithm proved to be effective, efficient and robust with better performance than other previous methods.
84

Pricing strategies in online & offline retailing

Gruber, Gottfried 11 1900 (has links) (PDF)
The thesis deals with pricing strategies for multichannel retailers, especially traditional stores which additionally manage an online shop. The problem of integrating two sales channels and applying a well-suited pricing strategy is still an emergent question. This work develops a stochastic model to represent consumer behavior on pricing. On the one hand the model contains two probability functions which render consumers' reservation prices for each individual channel. On the other hand the stochastic model is based on numerous distributions which represent switching probabilities from and to each separate channel. The various distribution functions will be estimated from the results of a survey. To highlight differences of pricing strategies due to several product categories a cross comparisons of books, clothes and digital cameras will be presented. The results show that there are differences in multichannel pricing of the various products. These inequalities stem from consumers' perceptions of the sales channels. For each product a separate sales channel is preferred by consumers. Therefore, one channel exhibits some advantage versus the alternative channels. This advantage is reflected in different pricing strategies. Further appropriate marketing strategies could help a firm to counter discounting by its competitors. So firms should keep an eye on the reservation price structure of its consumers as well as their demanded marketing activities. (author's abstract)
85

India’s Hunger Problem: A Comparative Analysis of the Performances of Food Distribution at the National level and in the State of Tamil Nadu

Madhaiyan, Raghul January 2014 (has links)
Food is fundamental for humans to survive and vital for development. Food security is a major issue and sustaining it is a challenge for the countries of the world. With climate change and other environmental andsocial factors greatly influencing the current chances for world food security, it is of prime importance for countries to work towards achieving it. A major part of the poor and vulnerable section of people lives in the developing and poor countries with rampant food insecurity issues. To achieve the UN‟s Millennium Development goal of halving hunger by 2015, food security measures are implemented in poor and developing countries with the help of world organizations to alleviate poverty and hunger. This paper studies the situation in India, where poverty and hunger is a major block for the development progress. India has proven its authority in various fields with a fast developing economy. On the other hand, poverty and hunger prevail among almost half of the country‟s people. The country has taken various measures to attain food security and curb hunger among the poor. The major welfare measure in the country is the food distribution schemes implemented by the government. The performance among different states in the country varies due to various factors. The performances of the country as a whole and of the southern state of Tamil Nadu are taken into consideration for this paper. The paper will deal with the performance and related issues such as policies, administration, operations and social influences on the food distribution system in a comparison between Tamil Nadu and the rest of the country. Based on the official records on procurement and distribution of food grains as well as on literature studies on the food security situation in India and Tamil Nadu state, this paper suggests that there is a need to modify the mechanisms that constitute the distribution system, which can be learnt from Tamil Nadu state where the performance is better than the average for India as a whole. Even though Tamil Nadu faces similar problems asother States, the better performance of Tamil Nadu does not affect the food distribution system in the country. At the national level, the situation is worse with magnified problems of performance affecting the food distribution system.
86

Análise do sistema de distribuição de medicamentos em hospital oncológico do Estado de São Paulo

Ragazzi, Susana Gabriela [UNESP] 26 August 2008 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:23:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-08-26Bitstream added on 2014-06-13T20:11:00Z : No. of bitstreams: 1 ragazzi_sg_me_arafcf.pdf: 1962785 bytes, checksum: 1c9cdbc9b2f6ca2596e4d8c529bb2b95 (MD5) / Universidade Estadual Paulista (UNESP) / A atenção farmacêutica é uma prática onde o farmacêutico tem a responsabilidade para com o paciente quanto às suas necessidades farmacoterapêuticas, garantindo a eficácia do tratamento e a segurança da farmacoterapia utilizando como instrumento o medicamento. A farmácia hospitalar é um órgão de abrangência assistencial técnico-científico e administrativo onde uma de suas principais funções é estabelecer um sistema racional de distribuição de medicamentos. O objetivo deste estudo foi analisar o sistema de distribuição de medicamentos de uma farmácia hospitalar de um hospital oncológico, bem como identificar os fatores que levam às falhas no processo de distribuição de medicamento. A pesquisa foi realizada na farmácia central de um Hospital Oncológico do Estado de São Paulo em 2007, após aprovação do Comitê de Ética em Pesquisa. A amostra constituiu-se de 3 (12%) farmacêuticos 3 (12%) assistentes de farmácia e 19 (76%) atendentes de farmácia. Todos os profissionais foram consultados quanto a sua disposição para participar do estudo e a seguir, os mesmos assinaram o temo de consentimento livre e esclarecido. Os dados coletados nos mostram que o sistema de distribuição do referido hospital é o sistema por dose individualizada diferenciada, com prescrição eletrônica. Os resultados das observações realizadas durante os 7 dias, indicam o ambiente como principal problema na distribuição de medicamentos (44,77%), pois o local é impróprio, com vários profissionais desenvolvendo atividades diferentes e interrupções freqüentes. Pela observação do ambiente foi possível demonstrar através de fluxogramas todas as ações desenvolvidas pelos profissionais da farmácia desde o momento da chegada da prescrição eletrônica até a entrega dos medicamentos à equipe de enfermagem. As entrevistas... / The pharmaceutical care is a practice where the pharmacist has the responsibility in relation to and with the patient regarding their pharmacotherapeutic needs, guaranteeing the treatment efficiency as well as the pharmacotherapy safety having as its instrument the medicine. The hospital pharmacy is an administrative technical-scientific organ where its main function is to establish a rational system of medicine distribution. The aim of this study was to analyze the medicine distribution system in a hospital pharmacy from an oncologic hospital as well as to identify the factors that lead us to failures related to the medicine distribution process. The survey took place at the central pharmacy from an oncologic hospital in the state of São Paulo after approval of the Committee of the Ethics in Research. The sample includes 3 (12%) pharmacists, 3 (12%) pharmacy assistants and 19 (76%) pharmacy attendants. All the professionals were asked about their willingness to participate in the survey and afterwards they signed on the “Free Will Participation Agreement”. The collected data show us that the distribution system from the above mentioned hospital is the individually differential dose system, with electronic prescription. The results based on the 7 days observation show the environment as the main problem in the medicine distribution (44.77%) once the place is improper and have several professionals performing different activities as well as frequent interruptions. From the environment observation was possible to demonstrate, through the fluxograms, all the actions performed by the pharmacy professionals from the electronic prescription’s arrival until the medicine delivery to the nursing team. The interviews with the professionals show us that the most frequent errors were related to the medicine dispensing (28.05%) and to the medical... (Complete abstract click electronic access below)
87

Estratégia de decomposição aplicada ao problema de planejamento da expansão de sistemas de distribuição

Baquero, John Fredy Franco [UNESP] 23 April 2012 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:30:51Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-04-23Bitstream added on 2014-06-13T18:40:59Z : No. of bitstreams: 1 baquero_jff_dr_ilha.pdf: 928776 bytes, checksum: 14beda1a12c4b74205593d8475f64232 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O problema do planejamento de sistemas de distribuição de energia elétrica consiste em determinar as mudanças que precisam ser feitas no sistema visando atender as condições de demanda futura, respeitando os critérios técnicos de operação e segurança, tudo isto sob um mínimo custo econômico (no caso da otimização monoobjetivo). A modelagem do problema de planejamento da expansão de sistemas de distribuição inclui a repotenciação de subestações existentes, a alocação e dimensionamento de novas subestações, o recondutoramento de alimentadores existentes, a construção e seleção do tipo de cabo para alimentadores novos e a seleção da topologia do sistema (reconfiguração). Além disso, o modelo considera que a expansão do sistema pode ser executada em vários estágios, propondo assim uma formulação dinâmica do problema de planejamento. É apresentada neste trabalho uma estratégia de decomposição para dividir o problema no subproblema da seleção das subestações e na solução de problemas de reconfiguração e recondutoramento dependentes. São desenvolvidos algoritmos heurísticos, que combinados com a metaheurística Busca Tabu, permitem uma exploração eficiente do espaço de busca. A estratégia de decomposição mencionada permite o uso da programação paralela, conseguindo diminuir o tempo de processamento. O método proposto é testado usando casos de grande porte da literatura, mostrando um excelente desempenho / The distribution system expansion planning problem consists of to determine the investments that need to be made in the system to meet future demand conditions, satisfying technical criteria for operation and safety, all under a minimum economic cost (in the case of mono-objective optimization). The modeling of the planning problem includes the expansion of existing substations, the allocation and design of new substations, the reconductoring of existent feeders, the selection of the type of conductor for new feeders and the selection of the system topology (reconfiguration). Furthermore, the model assumes that the expansion of the system can be performed in several stages, thus it is proposed dynamic planning problem formulation. In this paper work, it is presented a decomposition strategy to separate the problem into the subproblems of selection of the substations, reconfiguration and selection of the conductor feeders. Heuristic algorithms are developed, which combined with the Tabu Search metaheuristic, allow an efficient exploration of the space of search. The decomposition strategy aforementioned allows the use of parallel programming, achieving reduced processing time. The proposed method is tested using large cases in the literature, showing excellent performance
88

Análise do efeito da modelagem da carga nas estimativas de perdas elétricas em sistemas de distribuição

Dresch, Rodolfo de Freitas Valle January 2014 (has links)
As perdas elétricas, que no Brasil giram em torno de 14,4%, são prejudiciais ao desempenho técnico e financeiro das concessionárias de energia elétrica, principalmente em um cenário de uma eminente crise energética e alta regulação. A mitigação das perdas elétricas está diretamente relacionada com sua correta estimação. Para operar um sistema de energia elétrica, é de fundamental importância definir a correta modelagem dos elementos do sistema. As metodologias de estimação das perdas de energia, para sistemas de distribuição, vigentes não levam em conta possíveis erros na correta modelagem das cargas conectadas. Desta forma, este trabalho tem o objetivo de analisar a influência causada pela utilização dos modelos de carga, na estimação das perdas elétricas em sistemas de distribuição. Esta análise abrange as metodologias de fluxo de carga backward-forward sweep por soma de corrente, por soma de potência e Newton-Raphson. A perda de energia é calculada pela diferença entre a energia injetada no sistema, menos a energia entregue. O estudo de caso é realizado em um sistema de distribuição teste de 13 barras da IEEE. No caso proposto, são realizados cálculos das perdas de energia para o sistema de distribuição, considerando diferentes modelos de carga. Desta maneira, o trabalho estimou a diferença no cálculo das perdas para cada tipo de modelo de carga, em relação a perdas calculadas com o padrão original das cargas. Outro ponto analisado foi o desempenho das metodologias de fluxo de carga, frente à alteração dos modelos de carga. Os resultados demonstram que a alteração dos modelos de carga influência a estimação das perdas elétricas nos sistemas de distribuição, e o desempenho dos fluxos de carga. / Electrical losses, which in Brazil are around 14.4%, are harmful to the technical and financial performance of electric utilities, especially in a scenario of an imminent energy crisis and high regulation. Mitigation of electrical losses is directly related to its correct estimation. To operate an electric power system, it is of fundamental importance to define the correct model of the system elements. The methodologies for estimating energy losses, for the existing distribution systems, do not take into account possible errors in the correct model of connected loads. Thus, this study aims to examine the influence caused by the use of different load models, in the estimation of electrical losses in distribution systems. This analysis covers the backward-forward sweep load flow methodologies by the sum of current, by the sum of power and Newton-Raphson. The energy loss is calculated by the difference between the energy injected into the system, minus the energy delivered. The case study is performed on the IEEE 13 Node Test Feeder. In the proposed case, calculations of energy losses in the distribution system are performed considering different load models. Therefore, the study has estimated the difference in the calculation of energy loss for each type of load model, for the losses calculated with the original pattern of loads. Another point discussed is the performance of load flow methodologies, related to the change of load models. The results have shown that the change in load models influence the estimation of electrical losses in distribution systems and in the performance of load flows.
89

Proposta de um sistema de proteção para preservar a coordenação entre religadores e elos fusíveis de sistemas de distribuição na presença de geração distribuída / Proposal of a recloser-fuse coordination protection for distributed generation systems

Gutierres, Luiz Fernando de Freitas 11 August 2013 (has links)
This work presents a novel recloser-fuse coordination protection for distributed generation systems based on the use of RMS current comparators. In real-time, these comparators are responsible for analyzing current magnitude in upstream and downstream network directions; identify faults; and assess the recloser-fuse coordination status based on critical margins identified by the protection system. Once a miscoordination is detected, some distributed generation units are strategically disconnected from the distribution network by gate turn-off thyristors. As a result of this action, short-circuit current is reduced to a satisfactory level, restoring the coordination between recloser and fuses in the grid. The proposed protection system has been implemented in a 12.47-kV grid and simulations have been carried out in ATP/EMTP. The main contributions in this work are the results obtained mainly throughout testing fault circumstances and operational conditions. Besides, this work proposes a protection methodology in the perspective of a national standardized regulation. Significantly, the approach contributes to the adequacy and modernization of distribution systems with considerable tendency of distributed generation insertion. / Neste trabalho, apresenta-se um sistema de proteção que preserva a coordenação e a seletividade entre religadores e elos fusíveis de sistemas de distribuição na presença de geração distribuída. A ideia principal desse sistema concentra-se no uso de comparadores de corrente RMS. Em tempo real, esses comparadores são responsáveis por analisar as correntes supridas pela geração distribuída, identificar faltas e constatar a perda da coordenação e da seletividade entre religadores e elos fusíveis do sistema elétrico de distribuição. Uma vez detectado o problema, somente os geradores causadores são automaticamente desconectados temporariamente através de tiristores comutáveis pelo gatilho. Aplica-se esse sistema em uma rede elétrica de distribuição desenvolvida no ATP/EMTP. Os resultados obtidos são analisados e discutidos através de um estudo de caso. Além disso, a partir dos resultados, desenvolve-se uma metodologia de proteção de modo a colaborar com a padronização e normatização dos procedimentos de acesso à rede elétrica nacional. Dessa maneira, propõem-se mudanças nos Procedimentos de Distribuição de Energia Elétrica no Sistema Elétrico Nacional (PRODIST). Significativamente, o sistema e a metodologia de proteção propostos contribuem na adequação dos atuais sistemas de distribuição com forte tendência de inserção de geração distribuída.
90

Planning optimal load distribution and maximum renewable energy from wind power on a radial distribution system

Weerasinghe, Handuwala Dewage Dulan Jayanatha January 1900 (has links)
Doctor of Philosophy / Electrical and Computer Engineering / Ruth D. Miller / Optimizing renewable distributed generation in distribution systems has gained popularity with changes in federal energy policies. Various studies have been reported in this regard and most of the studies are based on optimum wind and/or solar generation planning in distribution system using various optimization techniques such as analytical, numerical, and heuristic. However, characteristics such as high energy density, relatively lower footprint of land, availability, and local reactive power compensation ability, have gained increased popularity for optimizing distributed wind generation (DWG) in distribution systems. This research investigated optimum distributed generation planning (ODGP) using two primary optimization techniques: analytical and heuristic. In first part of the research, an analytical optimization method called “Combined Electrical Topology (CET)” was proposed in order to minimize the impact of intentional structural changes in distribution system topology, in distributed generation/ DWG placement. Even though it is still rare, DWG could be maximized to supply base power demand of three-phase unbalanced radial distribution system, combined with distributed battery energy storage systems (BESS). In second part of this research the usage of DWG/BESS as base power generation, and to extend the ability to sustain the system in a power grid failure for a maximum of 1.5 hours was studied. IEEE 37-node, three-phase unbalanced radial distribution system was used as the test system to optimize wind turbines and sodium sulfide (NaS) battery units with respect to network real power losses, system voltage profile, DWG/BESS availability and present value of cost savings. In addition, DWG’s ability to supply local reactive power in distribution system was also investigated. Model results suggested that DWG/NaS could supply base power demand of a threephase unbalanced radial distribution system. In addition, DWG/NaS were able to sustain power demand of a three-phase unbalanced distribution system for 1.5 hours in the event of a power grid failure.

Page generated in 0.089 seconds