950 resultados para Particle in Central Field
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This work identifies and analyzes literature about knowledge organization (KO), expressed in scientific journals communication of information science (IS). It performs an exploratory study on the Base de Dados Referencial de Artigos de Periodicos em Ciência da Informacio (BRAPCI, Reference Database of Journal Articles on Information Science) between the years 2000 and 2010. The descriptors relating to "knowledge organization" are used in order to recover and analyze the corresponding articles and to identify descriptors and concepts which integrate the semantic universe related to KO. Through the analysis of content, based on metrical studies, this article gathers and interprets data relating to documents and authors. Through this, it demonstrates the development of this field and its research fronts according to the observed characteristics, as well as noting the transformation indicative in the production of knowledge. The work describes the influences of the Spanish researchers on Brazilian literature in the fields of knowledge and information organization. As a result, it presents the most cited and productive authors, the theoretical currents which support them, and the most significant relationships of the Spanish-Brazilian authors network. Based on the constant key-words analysis in the cited articles, the co-existence of the French conception current and the incipient Spanish influence in Brazil is observed. Through this, it contributes to the comprehension of the thematic range relating to KO, stimulating both criticism and self-criticism, debate and knowledge creation, based on studies that have been developed and institutionalized in academic contexts in Spain and Brazil.
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OBJETIVO: A catarata é a principal causa tratável de cegueira e deficiência visual em países subdesenvolvidos. Este estudo foi realizado para avaliar se a catarata continua sendo uma importante causa de cegueira no centro-oeste do Estado de São Paulo. MÉTODOS: Um estudo transversal, de caráter observacional, realizado em cinco cidades da região centro-oeste do Estado de São Paulo, para as quais o centro de referência é a cidade de Botucatu. A amostra estabelecida para este estudo, de forma aleatória, seria composta por 5.555 indivíduos, sendo que foram examinados 4.229 indivíduos (8.458 olhos), ou seja, 78% da amostra pretendida. Os indivíduos foram submetidos a um exame oftalmológico completo que consistia em avaliação da acuidade visual (com e sem correção), tonometria, biomicroscopia, fundoscopia e exame refracional. O diagnóstico de catarata foi dado aos indivíduos que apresentassem opacidade de cristalino na biomicroscopia, de acordo com o Sistema de Classificação de Opacidade do Cristalino II (LOCS II). Olhos apresentando deficiência visual ou cegueira, com a melhor correção e causados por catarata, foram considerados após excluir outras patologias que pudessem causar baixa da acuidade visual (AV). Olhos com deficiência visual foram considerados quando 0,05 < AV < 0,3 e olhos cegos quando AV < 0,05. Indivíduos com deficiência visual foram considerados quando 0,05 < AV < 0,3 e indivíduos cegos quando AV < 0,3, no melhor olho com a melhor correção. Foi considerado o número de olhos com catarata, o número de olhos com deficiência visual e cegueira e o número de indivíduos com deficiência visual e cegueira. RESULTADOS: A prevalência de catarata na população estudada foi de 4,94% (209 indivíduos), afetando principalmente indivíduos com mais de 50 anos (92,34%) e do sexo feminino (61,11%). A catarata foi a causa de deficiência visual para 0,96% e a causa de cegueira para 0,52% de toda a população estudada. CONCLUSÃO: Nossos resultados mostraram que a prevalência de catarata na população estudada é semelhante aos índices de países desenvolvidos.
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Losartan, an AT1 angiotensin II (ANG II) receptor non-peptide antagonist, induces an increase in mean arterial pressure (MAP) when injected intracerebroventricularly (icv) into rats. The present study investigated possible effector mechanisms of the increase in MAP induced by icv losartan in unanesthetized rats. Male Holtzman rats (280-300 g, N = 6/group) with a cannula implanted into the anterior ventral third ventricle received an icv injection of losartan (90 µg/2 µl) that induced a typical peak pressor response within 5 min. In one group of animals, this response to icv losartan was completely reduced from 18 ± 1 to 4 ± 2 mmHg by intravenous (iv) injection of losartan (2.5-10 mg/kg), and in another group, it was partially reduced from 18 ± 3 to 11 ± 2 mmHg by iv prazosin (0.1-1.0 mg/kg), an alpha1-adrenergic antagonist (P<0.05). Captopril (10 mg/kg), a converting enzyme inhibitor, injected iv in a third group inhibited the pressor response to icv losartan from 24 ± 3 to 7 ± 2 mmHg (P<0.05). Propranolol (10 mg/kg), a ß-adrenoceptor antagonist, injected iv in a fourth group did not alter the pressor response to icv losartan. Plasma renin activity and serum angiotensin-converting enzyme activity were not altered by icv losartan in other animals. The results suggest that the pressor effect of icv losartan depends on angiotensinergic and alpha1-adrenoceptor activation, but not on increased circulating ANG II.
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Sexual dimorphism, reproduction and diet are described for Stenocercus caducus from semideciduous forest, in Mato Grosso do Sul state, Central Brazil. Lizards are collected in pitfall traps from December 2000, to December 2001. Sexual dimorphism in S. caducus is apparent, mainly in coloration; although females reach a larger SVL than males. A wide variety of arthropods are fed by S. caducus, with ants and termites numerically, and orthopterans and beetles volumetrically the most common prey items. Ontogenetic differences in diet were noted for S. caducus, with juveniles feeding on lesser prey types and smaller sized prey than adults. The reproduction was seasonal, concentrated in the rainy season, with deposition of more than one clutch per season.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)National Science Foundation (NSF)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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Maieta guianensis Aubl. and M. poeppigii Mart. ex. Triana (Melastomataceae) are among the most common myrmecophytic plants in the Amazonian forest understory. These myrmecophytes are colonized exclusively by the ants Pheidole minutula Mayr or Crematogaster sp. and usually host two other arthropods, the spider Faiditus subflavus Exline and Levi and the recently described stilt bug Jalysus ossesae Henry. In this study, the association between J ossesae and the myrmecophytic plants M. guianensis and M. poeppigii in an upland forest area in central Amazon, Brazil, is described. The presence of the stilt bugs on M. guianensis and M. poeppigii and on plants around these myrmecophytes was recorded in five transects. The number and position of the stilt bugs on the leaf surface (upper or lower) and leaf type (with or without domatia) of these myrmecophytes, as well as their behavioral acts, were recorded. Jalysus ossesae was found only on the myrmecophytic plants M. guianensis and M. poeppigii. The stilt bug occurred at similar frequencies on M. guianensis and M. poeppigii, and the number of leaves significantly influenced the presence and number of stilt bugs on these myrmecophytes. Feeding, agonistic interaction between males, and mating were observed. Our data indicate that J. ossesae uses the myrmecophytes M. guinanensis and M. poeppigii as reproductive and foraging sites.
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In this work we rederive the Lamb-Retherford energy shift for an atomic electron in the presence of a thermal radiation. Using the Dalibard, Dupont-Roc and Cohen-Tannoudji (DDC) formalism, where physical observables are expressed as convolutions of suitable statistical functions, we construct the electromagnetic field propagator of thermo field dynamics in the Coulomb gauge in order to investigate finite temperature effects on the atomic energy levels. In the same context, we also analyze the problem of the ground state stability.
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We construct the finite temperature field theory of the two-dimensional ghost-antighost system within the framework of thermo field theory. (C) 2000 Elsevier B.V. B.V. All rights reserved.
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Some dynamical properties for a classical particle confined in an infinitely deep box of potential containing a periodically oscillating square well are studied. The dynamics of the system is described by using a two-dimensional non-linear area-preserving map for the variables energy and time. The phase space is mixed and the chaotic sea is described using scaling arguments. Scaling exponents are obtained as a function of all the control parameters, extending the previous results obtained in the literature. (c) 2012 Elsevier B.V. All rights reserved.
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Some dynamical properties present in a problem concerning the acceleration of particles in a wave packet are studied. The dynamics of the model is described in terms of a two-dimensional area preserving map. We show that the phase space is mixed in the sense that there are regular and chaotic regions coexisting. We use a connection with the standard map in order to find the position of the first invariant spanning curve which borders the chaotic sea. We find that the position of the first invariant spanning curve increases as a power of the control parameter with the exponent 2/3. The standard deviation of the kinetic energy of an ensemble of initial conditions obeys a power law as a function of time, and saturates after some crossover. Scaling formalism is used in order to characterise the chaotic region close to the transition from integrability to nonintegrability and a relationship between the power law exponents is derived. The formalism can be applied in many different systems with mixed phase space. Then, dissipation is introduced into the model and therefore the property of area preservation is broken, and consequently attractors are observed. We show that after a small change of the dissipation, the chaotic attractor as well as its basin of attraction are destroyed, thus leading the system to experience a boundary crisis. The transient after the crisis follows a power law with exponent -2. (C) 2011 Elsevier Ltd. All rights reserved.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Significantly more individuals and biomass of flying insects were present at the forest edge than in the understory throughout the year, as monitored by flight interception traps, in Central Amazonia. Numbers and biomass of flying insects increased at higher rates at the edge with rainfall, associated with termite swarming behavior and increased Homopteran density. The most abundant insects were Diptera, Coleoptera, Hymenoptera and Isoptera, whose ranked abundances varied with respect to forest edge and understory, as well as with season.