939 resultados para Instability, Natural convection, Non-uniform cooling, Pitchfork bifurcation, Triangular enclosure


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O abacaxizeiro é uma planta de grande importância econômica, porém seu florescimento natural causa sérios problemas, tornando seu manejo difícil devido à desuniformidade de frutos e colheitas, elevando o custo de produção. O objetivo deste trabalho foi manipular o florescimento do abacaxizeiro, contribuindo para uma produção uniforme colocada no mercado, nos meses de menor oferta. Utilizou-se o Paclobutrazol (PBZ) nas concentrações de 100; 150 e 200 mg L-1, em 2; 3 ou 4 aplicações via foliar, em plantas de abacaxi cv. Smooth Cayenne, no município de Presidente Alves-SP. O delineamento empregado foi em blocos ao acaso, com 10 tratamentos e três repetições, com 40 plantas por parcela experimental. No período de 100 a 150 dias após a primeira aplicação dos tratamentos, efetuaram-se as contagens de inflorescências presentes no centro da roseta foliar das plantas. Todos os tratamentos com Paclobutrazol inibiram a diferenciação floral natural do abacaxizeiro, recomendando-se a concentração de 150 mg L-1 em duas aplicações, com início em abril, a intervalo de 15 dias.

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Biological control is a relatively benign method of pest control. However, considerable debate exists over whether multiple natural enemies often interact to produce additive or non-additive effects on their prey or host populations. Based on the large data set stored in the Sao Joao and Barra sugarcane mills (state of São Paulo, Brazil) regarding the programme of biological control of Diatraea saccharalis using the parasitoids Cotesia flavipes and tachinid flies, in the present study the author investigated whether the parasitoids released into sugarcane fields interfered significantly with the rate of parasitized D. saccharalis hosts. The author also observed whether there was an additive effect of releasing C. flavipes and tachinids on the rate of parasitized hosts, and looked for evidence of possible negative effects of the use of multiple parasitoid species in this biological control programme. Results showed that C. flavipes and the tachinids were concomitantly released in the Barra Mill, but not in the Sao Jao Mill. Furthermore, in the Barra Mill there was evidence that the parasitoids interacted because the percentage of parasitism did not increase after the release of either C. flavipes or tachinids. In the Sao Joao Mill, when both parasitoid species were released out of synchrony, both the percentage of parasitism by C. flavipes as well as that of the tachinids increased. When large numbers of tachinids were released in the Barra Mill, they caused a significant lower percentage of parasitism imposed by C. flavipes. The implications of the results as evidence of non-additive effects of C. flavipes plus tachinids on D. saccharalis populations are discussed.

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CONTEXTUALIZAÇÃO: A dor e a disfunção no complexo articular do ombro é comumente encontrada na prática fisioterapêutica. Essas anormalidades musculoesqueléticas estão relacionadas à instabilidade e inadequado funcionamento cinemático, que dependem da integridade dos tecidos musculares. Assim, no sentido de prevenir e reabilitar esses sintomas, o uso da haste oscilatória vem sendo implantado para melhorar os resultados de técnicas cinesioterapêuticas. OBJETIVOS: Analisar a atividade eletromiográfica (EMG) dos músculos que estabilizam a articulação do ombro durante a realização de exercícios com haste oscilatória e haste não-oscilatória. MÉTODOS: Participaram do estudo 12 voluntárias com idade de 20,4±1,9 anos. Os dados EMG foram coletados nos músculos trapézio superior (TrS), trapézio inferior (TrI) e deltoide médio (DM) durante três diferentes exercícios realizados com haste oscilatória e haste não-oscilatória. O sinal EMG foi analisado no domínio do tempo pelo cálculo do Root Mean Square (RMS). Os valores de RMS foram normalizados pelo valor de pico obtido em todas as tentativas por cada músculo. A análise estatística foi feita com os testes ANOVA para medidas repetidas e post-hoc de Bonferroni. RESULTADOS: A atividade EMG dos músculos TrS, TrI e DM foi significativamente maior nos exercícios com haste oscilatória do que com haste não-oscilatória (todos p<0,001). Não foram significativas as diferenças na ativação desses músculos entre os exercícios. CONCLUSÃO: Os resultados do presente estudo indicaram que a haste oscilatória requisitou maior atividade EMG dos músculos do ombro e, assim, pode ser um instrumento útil no treinamento desses músculos.

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The tegu lizard Tupinambis merianae exhibits an episodic ventilatory pattern when dormant at 17 degrees C but a uniform ventilatory pattern when dormant at 25 degrees C. At 17 degrees C, ventilatory episodes were composed of 1-22 breaths interspaced by non-ventilatory periods lasting 1.8-26min, Dormancy at the higher body temperature was accompanied by higher rates of O-2 consumption and ventilation. The increase in ventilation was due only to increases in breathing frequency with no change observed in tidal volume. The air convection requirement for O-2 did not differ at the two body temperatures. The respiratory quotient was 0.8 at 17 degrees C and 1.0 at 25 degrees C. We found no consistent relationship between expired gas composition and the start/end of the ventilatory period during episodic breathing at 17 degrees C. However, following non-ventilatory periods of increasing duration, there was an increase in the pulmonary O-2 extraction that was not coupled to an equivalent increase in elimination of CO2 from the lungs. None of the changes in the variables studied could alone explain the initiation/termination of episodic ventilation in the tegus, suggesting that breathing episodes are shaped by a complex interaction between many variables. The estimated oxidative cost of breathing in dormant tegus at 17 degrees C was equivalent to 52.3% of the total metabolic rate, indicating that breathing is the most costly activity during dormancy.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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The seasonal density fluctuation, phenology and sex ratio of Peucetia flava (Oxyopidae) on Rhyncanthera dichotoma (Melastomataceae) were investigated during a year in a swamp in southeastern Brazil. Peucetia flava displayed an unusual non-seasonal life cycle and the population size varied little over the year. The density of Peucetia spiders increased with the increase in abundance of leaves and number of arthropods adhered to glandular trichomes on R. dichotoma leaves. Our findings suggest that seasonal density fluctuation of Peucetia may be influenced by foraging site availability (i.e. leaves) and prey supply (i.e. arthropods adhering to glandular trichomes). The unusual seasonal stability of P. flava may be related to the type of habitat in which this spider occurs (swamp), because of the constant input of allochthonous resources from the water source, i.e. aquatic insects that migrate to the terrestrial environment.

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The boundary conditions of the bosonic string theory in non-zero B-field background are equivalent to the second class constraints of a discretized version of the theory. By projecting the original canonical coordinates onto the constraint surface we derive a set of coordinates of string that are unconstrained. These coordinates represent a natural framework for the quantization of the theory.

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Based on the equivalence between a gauge theory for the translation group and general relativity, a teleparallel version of the non-Abelian Kaluza-Klein theory is constructed. In this theory, only the fiber-space turns out to be higher dimensional, spacetime being kept always four dimensional. The resulting model is a gauge theory that unifies, in the Kaluza-Klein sense, gravitational and gauge fields. In contrast with the ordinary Kaluza-Klein models, this theory defines a natural length scale for the compact submanifold of the fiber space, which is shown to be of the order of the Planck length.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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We investigate the spin of the electron in a non-relativistic context by using the Galilean covariant Pauli-Dirac equation. From a non-relativistic Lagrangian density, we find an appropriate Dirac-like Hamiltonian in the momentum representation, which includes the spin operator in the Galilean covariant framework. Within this formalism, we show that the total angular momentum appears as a constant of motion. Additionally, we propose a non-minimal coupling that describes the Galilean interaction between an electron and the electromagnetic field. Thereby, we obtain, in a natural way, the Hamiltonian including all the essential interaction terms for the electron in a general vector field.

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