• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 93
  • 37
  • 18
  • 17
  • 4
  • 3
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 239
  • 39
  • 37
  • 36
  • 36
  • 34
  • 29
  • 24
  • 23
  • 20
  • 20
  • 20
  • 19
  • 19
  • 19
  • 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.
191

Eat Your Heart Out: Framing Design, Experience, Street Foods, and Globalization

January 2018 (has links)
abstract: Eat Your Heart Out is a visually rich qualitative ethnic food research that examines consumption, production, and distribution practices transnationally. Through the example of Mumbai’s street foods, the study aims to discover how design participates in fashioning the street food experiences locally and globally. Food is an important cultural artifact in the world. However, past research in design suggests that the discipline has mainly focused on food as a catalyst for creativity and imagination or as a tool to examine materialistic, economical, sensorial, and emotional connections. Studying the user-focused involvement in the creation of food artifacts and focusing on cultural, global, and historical aspects of that participation are important to address the gaps in the knowledge required to solve increasingly “wicked problems” (Buchanan, 1992; Rittel, 1971). To achieve this goal, Eat Your Heart Out implemented a comparative practice-based study of the Indian street foods in Mumbai and Phoenix to examine consumption, production, and distribution practices at both places. The methodological design was highly multi-disciplinary in nature and included rapid ethnographic assessment, interviews, visual research, and a generative method of co-creation. The study revealed that street foods as cultural artifacts were deeply rooted in specific traditional values specific to the context, which significantly influenced personal and communal consumption, production, and distribution practices of Indian street foods in Mumbai and Phoenix. The values of standardization, formality, and higher food regulation practices limited the diversity and radically transformed the central values of Mumbai’s street foods when the foods re-territorialized in Phoenix. This resulted in lowering the consumption. Eat Your Heart Out presents cultural and practical insights into the interactions between contexts, artifacts, practices, and participants. Eat Your Heart Out recommends new frameworks of correlation for various consumption and production practices and suggests how street food artifacts alter when they move across cultures. Such knowledge can be valuable for similar ethnic food culture studies and the development of innovative research tools incorporating transnational and multidisciplinary methods in the future. On a broader scope, Eat Your Heart Out provides a unique opportunity to study a culture that has not been examined by scholars much in the past. It also focuses on gaining knowledge about ethnic culinary practices of Indian immigrants in the United States and encouraging enhanced cross-cultural acceptance. / Dissertation/Thesis / Doctoral Dissertation Design, Environment and the Arts 2018
192

Dinâmica adaptativa em populações de predadores e presas / Adaptive dynamics in predator and prey populations

Araújo, Sabrina Borges Lino 17 August 2018 (has links)
Orientador: Marcus Aloizio Martinez de Aguiar / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-17T01:49:08Z (GMT). No. of bitstreams: 1 Araujo_SabrinaBorgesLino_D.pdf: 18627531 bytes, checksum: aed18ab505ee489e8cde08b6d2850bba (MD5) Previous issue date: 2010 / Resumo: Neste trabalho estudamos a dinâmica espaço-temporal de cadeias alimentares compostas por duas e três espécies. Utilizamos uma modelagem baseada nos indivíduos, que consiste em tratar cada membro da população de forma explícita. Um dos ingredientes do modelo é a possibilidade de restringir a área de forrageio dos predadores à uma região circular, de raio R, em torno da sua residência. O tamanho desta região é tratado como uma característica adaptativa, sujeita à pequenas variações aleatórias ao longo das gerações. Observamos que existe um raio de predação ótimo R', para o qual os predadores evoluem. Desenvolvemos cálculos analíticos utilizando aproximações de Campo Médio com correlações de pares e verificamos que a estratégia de predação é um mecanismo crucial para a ocorrência do raio ótimo. Observamos também que a distribuição da abundância de indivíduos por região espacial pode exibir um comportamento invariante de escala, indicando que o sistema é criticamente auto-organizado, e que a ocorrência de surtos populacionais locais é uma característica intrínseca do sistema / Abstract: In this work we study the spatial dynamics of two and three species food chains. We use an individual based model, which treats each member of the population explicitly. One of the model ingredients is the possibility to control the size of the predators foraging area, defined as a circular neighborhood, of radius R, around their home position. This home range size is treated as an adaptive, subject to small random variations along generations. We find that the predators evolve to a optimum predation radius R'. We develop analytical approximations using mean field and pair correlation techniques that indicate that the predation strategy is crucial for existence of this optimum radius. We also find that the population abundance distributions display a scale invariant power law tail, indicating self-organized criticality and that the occurrence of local outbreaks is an intrinsic characteristic of the system / Doutorado / Ciências Exatas e da Terra / Doutora em Ciências
193

Obtenção de reatividade subcrítica por meio de medidas de APSD e CPSD utilizando detectores modo pulso no reator IPEN/MB-01 / Obtainment of subcritical reactivity by mean of measurement of APSD and CPSD employing pulse mode detectors in the IPEN/MB-01 reactor

LEE, SEUNG M. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:42:36Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:07Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Este trabalho apresenta uma nova abordagem experimental para determinar a reatividade de sistemas subcríticos. O método a ser apresentado utiliza o modelo da cinética subcrítica desenvolvido por Gandini e Salvatores e baseia-se apenas em grandezas medidas, tais como a taxa de contagem no detector, e nos parâmetros que surgem do ajuste dos mínimos quadrados APSD (Auto Power Spectral Density) e CPSD (Cross Power Spectral Density), não sendo necessário lidar com as quantidades de maior complexidade como a eficiência de detector. A única hipótese feita neste método foi que a fração efetiva de nêutrons atrasados e o tempo de geração de nêutrons prontos fossem independentes do nível de subcriticalidade do sistema. O método proposto foi aplicado nas medidas de reatividade de várias configurações subcríticas do reator IPEN/MB-01. Foram realizadas medidas da APSD e CPSD em diversos graus de subcriticalidade (até em torno de -7000 pcm). Nos dados das densidades espectrais foram feitos ajustes por meio do método de mínimos quadrados para obter a constante de decaimento pronto (α) e outras grandezas. Com a finalide de melhorar as estatísticas de contagem de nêutrons, fonte externa de nêutrons de Am-Be foi instalada próximo ao núcleo, além da fonte de partida. O método experimental proposto mostra claramente que, a teoria da cinética pontual clássica não descreve a reatividade medida. Em vez disso, a reatividade inferida a partir do modelo da cinética pontual clássica é próxima, em seus valores absolutos, ao índice de subcriticalidade (ζ) para um determinado arranjo das fontes do experimeno. A concordância dos resultados obtidos por MCNP5 e GPT-TORT, ambos utilizando os dados nucleares da biblioteca ENDF/B-VII.0, com os resultados experimentais correspondentes são de boa qualidade. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP:09/54838-0
194

Determinacao experimental de indices espectrais por varredura gama de vareta combustivel no reator IPEN/MB-01 / Experimental determination of spectral indices by scanning of fuel rod in the IPEN/MB-01 reactor

FANARO, LEDA C.C.B. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:26:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:28Z (GMT). No. of bitstreams: 0 / Neste trabalho foram determinados experimentalmente os índices espectrais 28r* e 25d* e o fator de eficiência de contagem gama através da técnica de varredura gama de varetas combustíveis no reator nuclear IPEN/MB-01. A vantagem deste método experimental consiste no fato de terem sido eliminados a maioria dos fatores de correção advindos dos cálculos, permanecendo somente os fatores de rendimento médio de fissão e a fração de fissão no 235U na determinação do 25d*. Os experimentos foram efetuados com luvas de cádmio de diferentes espessuras: 0,55 mm, 1,10 mm e 2,20 mm. As incertezas experimentais inferiores a 1% e a excelente caracterização dos dados geométricos e materiais do reator IPEN/MB-01 permitem utilizar os resultados obtidos como benchmark para a validação de bibliotecas de dados nucleares. Sendo assim, foi utilizado o programa MCNP-5 com as bibliotecas de dados nucleares: ENDF/B-VI.8, ENDF/B-VII.0, JENDL-3.3 e JEFF-3.1. A comparação entre os valores advindos dos cálculos e os resultados experimentais mostrou que houve progressos sensíveis com as bibliotecas de dados nucleares atuais. Os desvios entre a comparação dos valores calculados e os resultados experimentais são inferiores a 2 %, sendo que o melhor desempenho foi obtido com a biblioteca de dados nucleares ENDF/B-VII.0 e a incerteza máxima na comparação dos resultados foi de -1,4 %, para as bibliotecas de dados nucleares JEFF-3.1 e JENDL-3.3. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
195

Avaliacao neutronica de reator carregado com combustivel metalico e refrigerado por chumbo

NASCIMENTO, JAMIL A. do 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:44:01Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:25Z (GMT). No. of bitstreams: 1 06864.pdf: 11106654 bytes, checksum: 851c7803db872d59fc1f49dc465fa8af (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
196

Matemática financeira e tecnologia: espaços para o desenvolvimento da capacidade crítica dos educandos da educação de jovens e adultos

Costa, Luciano Pecoraro 03 October 2012 (has links)
Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-06-02T12:06:21Z No. of bitstreams: 1 lucianopecorarocosta.pdf: 3438112 bytes, checksum: 3896600479f38ac7e056d633475793f4 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-06-28T14:35:07Z (GMT) No. of bitstreams: 1 lucianopecorarocosta.pdf: 3438112 bytes, checksum: 3896600479f38ac7e056d633475793f4 (MD5) / Made available in DSpace on 2016-06-28T14:35:07Z (GMT). No. of bitstreams: 1 lucianopecorarocosta.pdf: 3438112 bytes, checksum: 3896600479f38ac7e056d633475793f4 (MD5) Previous issue date: 2012-10-03 / Este trabalho é fruto de reflexões acerca dos questionamentos inerentes ao dia a dia de uma sala de aula, de estudantes jovens e adultos. A disciplina Matemática não necessita, exclusivamente, trabalhar conteúdos explícitos, contemplando “resolva” e “calcule”. Tendo como intenção, proporcionar aos estudantes, além de trazer os conteúdos pertinentes à disciplina, mas também, a emersão, em caráter reflexivo. Um aluno terá condições de apoderar-se de seus conhecimentos advindos do meio escolar e de mundo, a fim de conjecturar sobre possíveis caminhos, em tomadas de decisão. Diante da intenção de incorporar debate de cunho crítico às aulas, tomamos como prerrogativa, as características da Educação Matemática Crítica, de Ole Skovsmose, em que consequentemente acarretam reflexões de cunho social, perante questões relacionadas à Cidadania, descritas nas obras de Nilson José Machado. A pesquisa foi desenvolvida num colégio público estadual da cidade de Miguel Pereira/RJ, cujo pré-teste ocorrera em uma turma de 9° ano do Ensino Fundamental, sendo o pós-teste, aplicado no 3° ano do Ensino Médio, ambos na modalidade da Educação de Jovens e Adultos – EJA. A fim de aglutinar aos aspectos de criticidade e cidadania, foram incorporadas ferramentas tecnológicas – calculadora e computador – como meio de intencionar a inclusão digital, e paralelamente, como instrumento auxiliador diante de tomadas de decisão. Diante da escassez de materiais destinados ao público da EJA, seja no âmbito editorial quanto por meio de publicações no meio acadêmico, forçou-nos a planejar aulas, tanto quanto materiais, destinados a esta modalidade de ensino. As atividades aplicadas tanto no pré-teste quanto no pós-teste converteram-se em produto educacional, os quais aduziram neste trabalho. / This work is the reflections result on the questions about everyday life of a classroom of young and adult students. The mathematics course does not require exclusively working explicit content, contemplating "settle" and "calculate". The intention is to provide students, in addition to bring in relevant content to the discipline, but also the emergence, in reflective nature. A student will be able to seize his knowledge from the school and the world in order to speculate on possible paths indecision making. Faced with the intention of incorporating critical debate of nature classes, we take the prerogative, the characteristics of Critical Mathematics Education, Ole Skovsmose, which consequently cause reflections of social; faces issues related to citizenship, described in the works of José Nilson Machado. The research was conducted in a public state school in Miguel Pereira/RJ, whose pre test occurred in a class of 9th grade of elementary school and the post-test, applied in the 3rd year of high school, both in the form Education of Youth and Adults-EJA. In order to unite the aspects of criticality and citizenship were incorporated technological tools-calculator and computer-as means of intending digital inclusion, and in parallel, as a tool helper before making decisions. Given the scarcity of materials intended for EJA public, is under editorial and through publications in academic, forced us to plan lessons as well as material intended for this type of education. The activities implemented both pretest and post-test have become educational product, which did this work.
197

Définition des indicateurs clés de performance et évaluation multicritère de filières durables de recyclage des polymères renforcés de fibres de carbone issus de l’industrie aéronautique / Definition of key sustainability performance indicators and multicriteria evaluation of recycling sector for carbon fiber reinforced polymers from the aerospace industry

Pillain, Baptiste 30 June 2017 (has links)
La consommation globale de plastique renforcé de fibres de carbone (PRFC) est en constante augmentation, ce qui induit la nécessité de créer un secteur de recyclage capable de traiter l’ensemble des fibres de carbone actuellement consommées et qui représente la quantité de déchets à traiter en devenir. Cette thèse porte sur le développement et l'application d’une méthodologie d’évaluation multicritère du développement durable pour la création d’une filière de recyclage des plastiques renforcés de fibres de carbone (PRFC) issus du secteur aéronautique, mais aussi des autres secteurs consommateurs de fibres de carbone tels que l’automobile et l’éolien. Cette méthodologie a pour but d’identifier les indicateurs les plus pertinents ainsi que les méthodes qui leurs sont associés, c'est-à-dire qu’elle vise à la création et l’adaptation d’indicateurs clé de performance du développement durable pour caractériser au mieux les impacts environnementaux et sociaux-économique de cette filière de recyclage. Le résultat final de ce travail est la création d’une méthodologie d’évaluation du développement durable dédiée à la filière de recyclage des fibres de carbone par la considération des différents aspects de celui-ci. Cette méthodologie, aidant à l’identification et la définition des indicateurs clé de performances du développement durable peut être aussi appliquée à d’autres secteurs souhaitant s’implanter en suivant les principes de ce développement. / The global consumption of carbon-fiber reinforced plastic (CFRP) is constantly growing since the last decade, leading to the need to create a recycling sector able to manage the amount of carbon fibers currently consumed and representing the amount of waste to be treated in the future. This thesis focus on the creation of a methodology for evaluating the sustainability potential for the implementation of a carbon fiber reinforced plastics recycling (CFRP) sector. CFRP coming from the aeronautics sector as well as other sectors such as the automobile and wind-energy industries. This methodology aims at identifying the most relevant indicators and associated methods, but also aims at the creation and adaptation of indicators to best assess the environmental and socioeconomic impacts of this recycling sector. The final result of this work, is the creation of a sustainability assessment methodology dedicated to the carbon fiber recycling sector, considering the different sustainability pillars. However this methodology also define more widely a tool that helps to identify sustainability performance indicators and that can be applied to other sectors if necessary.
198

Criticalité quantique ferromagnétique dans les composés ternaires à base d'uranium URhSi, URhAl et UCoAl / Ferromagnetic quantum criticality in the uranium-based ternary compounds URhSi, URhAl, and UCoAl

Combier, Tristan 27 February 2014 (has links)
Dans cette thèse, on étudie la criticalité quantique ferromagnétique dans trois composés ternaires à base d'uranium, par des mesures thermodynamiques et de transport sur des échantillons monocristallins, à basse température et sous haute pression. URhSi et URhAl sont des systèmes ferromagnétiques itinérants, tandis que UCoAl est un système paramagnétique étant proche d'une instabilité ferromagnétique. Tous ont une phase ordonnée de type Ising. Dans le composé orthorhombique URhSi, on montre que la température de Curie diminue lorsqu'un champ magnétique est appliqué perpendiculairement à l'axe facile d'aimantation, et une transition de phase quantique est attendue autour de 40~T. Dans le système hexagonal URhAl, on établit le diagramme de phase pression--température pour la première fois, lequel indique une transition de phase quantique vers 5~GPa. Dans le composé isostructural UCoAl, on étudie la transition métamagnétique par des mesures d'aimantation, d'effet Hall, de résistivité et de dichroïsme circulaire magnétique des rayons X. On observe des phénomènes de relaxation magnétique intrigants, avec des sortes de marches. L'effet Hall et la résistivité ont été mesurés à des températures de réfrigérateur à dilution, sous pression hydrostatique jusqu'à 2,2~GPa, et sous champ magnétique jusqu'à 16~T. La transition métamagnétique se termine sous pression et champ magnétique au niveau d'un point critique quantique terminal. Dans cette région, il se produit une forte augmentation de la masse effective, et une différence intrigante entre champ montant et descendant apparaît dans la résistivité transverse. Ce pourrait être la signature d'une nouvelle phase, éventuellement reliée aux phénomènes de relaxation observés dans les mesures d'aimantation, et résultant de frustrations au sein du réseau quasi-Kagomé que forment les atomes d'uranium dans cette structure cristalline. / In this thesis we explore the ferromagnetic quantum criticality in three uranium-based ternary compounds, by means of thermodynamical and transport measurements on single crystal samples, at low temperature and high pressure. URhSi and URhAl are itinerant ferromagnets, while UCoAl is a paramagnet being close to a ferromagnetic instability. All of them have Ising-type magnetic ordering. In the orthorhombic compound URhSi, we show that the Curie temperature decreases upon applying a magnetic field perpendicular to the easy magnetization axis, and a quantum phase transition is expected around 40~T. In the hexagonal system URhAl, we establish the pressure--temperature phase diagram for the first time, indicating a quantum phase transition around 5~GPa. In the isostructural compound UCoAl, we investigate the metamagnetic transition with measurements of magnetization, Hall effect, resistivity and X-ray magnetic circular dichroism. Some intriguing magnetic relaxation phenomena are observed, with step-like features. Hall effect and resistivity have been measured at dilution temperatures, under hydrostatic pressure up to 2.2 GPa and magnetic field up to 16~T. The metamagnetic transition terminates under pressure and magnetic field at a quantum critical endpoint. In this region, a strong effective mass enhancement occurs, and an intriguing difference between up and down field sweeps appears in transverse resistivity. This may be the signature of a new phase, supposedly linked to the relaxation phenomena observed in magnetic measurements, arising from frustration on the quasi-Kagome lattice of uranium atoms in this crystal structure.
199

Fission fragment angular distribution and fission cross section validation / Distributions angulaires de fragments de fission et validation de sections efficaces de fission

Leong, Lou Sai 27 September 2013 (has links)
La connaissance actuelle de la distribution angulaire de la fission induite par neutrons est limitée à une énergie maximum de 15~MeV, avec de grands écarts autour de 14~MeV. Seulement 238U et 232Th ont été étudiés jusqu'à 100 MeV et un seul jeu de données existe. Nous avons réalisé une expérience à n_TOF au CERN pour mesurer les distributions angulaires de fragments de fission jusqu'à 1~GeV pour les isotopes 232Th, 235U , 238U , 237Np.L'expérience a été réalisée à l'aide d'un dispositif expérimental à base de compteurs à avalanche à plaques parallèles (PPAC). La méthode basée sur la détection des 2 fragments en coïncidence permet d'identifier sans ambiguïté la fission des autres réactions, notamment dans le domaine de spallation. Au-dessous de 10 MeV nos résultats sont cohérents avec les données existantes. Par exemple, dans le cas de 232Th , en dessous de 10 MeV ils montrent clairement la variation d'anisotropie se produisant dans les résonances vibrationnelles (1.6 MeV) correspondant à des états de transition de J et K donnés (spin total et sa projection sur l'axe de fission), et après l'ouverture de la deuxième chance de fission (7 MeV). Ils apportent une meilleure précision autour de la troisième chance de fission (14 MeV). Aux énergies intermédiaires, au-dessus de 20 MeV nous avons constaté une anisotropie significative mais bien inférieure à l'unique résultat antérieur. Notre résultat est en accord avec la systématique en fissilité du système composite et avec un modèle incluant les phénomènes essentiels, en particulier le preéquilibre. Dans le cadre de cette comparaison l'anisotropie plus grande que pour la fission induite par protons s'explique parfaitement. J'ai par ailleurs exploré et simulé les expériences de criticité qui permettent de tester la précision des données nucléaires. La section efficace de fission de 237Np induite par neutrons avait été mesurée sur l'installation n_TOF au CERN. Par rapport aux résultats antérieurs la section efficace de fission n_TOF était apparue plus élevée de 6-7% au-delà du seuil de fission. Pour vérifier la pertinence des données de n_TOF, nous avons simulé une expérience de criticité effectuée à Los Alamos avec une sphère contenant 6 kg de 237Np. Cette sphère est entourée par de l'uranium hautement enrichi en 235U de façon à approcher la criticité avec des neutrons rapides. La simulation prédit un facteur de multiplication keff en meilleur accord avec l'expérience (l'écart de -0.75% est réduit à +0.25%) quand on remplace la section efficace de fission de 237Np des bibliothèques évaluées par celle de n_TOF. Nous avons également exploré d'autres effets pouvant expliquer l'écart qui existait entre la mesure de criticité et sa prédiction par les simulations, en particulier nous avons testé la section inélastique de 235U et la multiplicité de neutrons de fission de 237Np. Dans les 2 cas la modification requise pour réconcilier l'écart de criticité n'est pas en accord avec les mesures. Des mesures de taux de fission dans des flux de neutrons dont le spectre est connu indiquent également que la section de fission du 237Np pourrait être plus grande de 4 à 5% par rapport à ce qui était admis aujourd'hui. / The present knowledge of angular distributions of neutron-induced fission is limited to a maximal energy of 15 MeV, with large discrepancies around 14 MeV. Only 238U and 232Th have been investigated up to 100 MeV in a single experiment. The n_TOF Collaboration performed the fission cross section measurement of several actinides (232Th, 235U, 238U, 234U, 237Np) at the n_TOF facility using an experimental set-up made of Parallel Plate Avalanche Counters (PPAC), extending the energy domain of the incident neutron above hundreds of MeV. The method based on the detection of the 2 fragments in coincidence allowed to clearly disentangle the fission reactions among other types of reactions occurring in the spallation domain. I will show the methods we used to reconstruct the full angular resolution by the tracking of fission fragments. Below 10 MeV our results are consistent with existing data. For example in the case of 232Th, below 10 MeV the results show clearly the variation occurring at the first (1 MeV) and second (7 MeV) chance fission, corresponding to transition states of given J and K (total spin and its projection on the fission axis), and a much more accurate energy dependence at the 3rd chance threshold (14 MeV) has been obtained. In the spallation domain, above 30 MeV we confirm the high anisotropy revealed in 232Th by the single existing data set. I'll discuss the implications of this finding, related to the low anisotropy exhibited in proton-induced fission. I also explore the critical experiments which is valuable checks of nuclear data. The 237Np neutron-induced fission cross section has recently been measured in a large energy range (from eV to GeV) at the n TOF facility at CERN. When compared to previous measurements, the n TOF fission cross section appears to be higher by 5-7 % beyond the fission threshold. To check the relevance of n TOF data, we simulate a criticality experiment performed at Los Alamos with a 6 kg sphere of 237Np. This sphere was surrounded by enriched uranium 235U so as to approach criticality with fast neutrons. The simulation predicts a multiplication factor keff in better agreement with the experiment (the deviation of 750 pcm is reduced to 250 pcm) when we replace the ENDF/B- VII.0 evaluation of the 237Np fission cross section by the n TOF data. We also explore the hypothesis of deficiencies of the inelastic cross section in 235U which has been invoked by some authors to explain the deviation of 750 pcm. The large distortion that should be applied to the inelastic cross sections in order to reconcile the critical experiment with its simulation is incompatible with existing measurements. Also we show that the nubar of 237Np can hardly be incriminated because of the high accuracy of the existing data. Fission rate ratios or averaged fission cross sections measured in several fast neutron fields seem to give contradictory results on the validation of the 237Np cross section but at least one of the benchmark experiments, where the active deposits have been well calibrated for the number of atoms, favors the n TOF data set. These outcomes support the hypothesis of a higher fission cross section of 237Np.
200

The Integrated Method Utilizing Graph Theory and Fuzzy Logic for Safety and Reliability Assessment / The Integrated Method Utilizing Graph Theory and Fuzzy Logic for Safety and Reliability Assessment

Janhuba, Luboš January 2018 (has links)
Dizertační práce se zabývá návrhem integrované metody hodnocení bezpečnosti a spolehlivosti palubních leteckých systém za použití teorie grafů a fuzzy logiky. Navržená integrovaná metoda je univerzálně použitelná v oblasti hodnocení bezpečnosti a spolehlivosti, nicméně je primárně navržená pro použití v oblasti General Aviation a civilních bezpilotních prostředků. Současná podoba hodnocení spolehlivosti je téměř výhradně závislá na úsudku analytika. Použití komerčních softwarových nástrojů pro hodnocení spolehlivosti je extrémně nákladné, přičemž možnost přístupu a úpravy použitých algoritmů je minimální. Současný prudký vývoj palubních letecký systému je spojen s jejich zvyšující se komplexností a sofistikovaností. Integrovaná metoda používá teorii grafů, jako nástroj modelování funkčních závislostí mez jednotily prvky systému. Použití teorie grafu současně umožňuje daný systém analyzovat, hodnotit hustotu vzájemné funkční vazebnosti, identifikovat důsledky případných poruchových stavů. Aplikace fuzzy logiky umožňuje manipulovat s expertní znalostí a stanovit kritičnost daného prvku a systému. Kritičnost prvku zohledňuje pravděpodobnost jeho selhání, možnost detekce dané poruchy, závažnost těchto selhání vzhledem k vlivu na alokované funkce.

Page generated in 0.0439 seconds