981 resultados para natural convection


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Free surface deformations of thermocapillary convection in a small liquid bridge of half floating-zone are studied in the present paper. The relative displacement and phase difference of free surface oscillation are experimentally studied, and the features of free surface oscillation for various applied temperature differences are obtained. It is discovered that there is a sort of surface waves having the character of small perturbation, and having a wave mode of unusually large amplitude in one corner region of the liquid bridge.

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A finite element algorithm is used to analyze the process of floating zone crystal growth under microgravity. The effect of phase change convection coupled with surface tension convection is considered. The results show that the rate of crystal growth is very important. The single-crystal-melt interface is steeper than the feed-melt interface during the process of crystal growth. When the rate exceeds a critical value, the Marangoni vortex near the feed-melt interface will become so large that a secondary vortex will exist.

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The transition processes from steady flow into oscillatory flow in a liquid bridge of the half floating zone are studied experimentally. Two methods of noncontacted diagnoses are developed to measure the distribution of critical Marangoni numbers described by the onset of the oscillation st the free surface of the liquid bridge.The experimental results obtained for both cases of the upper rod heated and the lower rod heated agree with the prediction by Rayleigh's instability theory.The sensitive relations between the relatively fat or slender liquid bridge and the onset of oscillatory convection are also discussed to reveal the insight of the pressure distribution near the free surface. The experiments have been performed in a small liquid bridge, where the Bond number is much smaller than 1, and the results can be used to simulate the experiment in the microgravity environment.

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It is suggested that the oscillation of thermocapillary convection may be excited by the buoyancy instability. By means of numerical simulation of the finite-element method, the temperature distributions in the liquid bridge are qualitatively analyzed. The temperature gradient in a certain flow region of liquid bridge may turn to be parallel to the direction of gravity when the temperature difference △T between two boundary rods of liquid bridge is larger than the critical value. The buoyancy instability may be excited, and then the thermocapillary oscillatory convection appears, as the temperature difference increases further. The distribution of the critical Marangoni number in the micro-gravity environment is derived from the data on the ground experiments. The results show that the onset of thermocapillary oscillatory convection is delayed in the case of smaller typical scale of liquid bridge and lower gravity environment.

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This paper deals with the valuation of energy assets related to natural gas. In particular, we evaluate a baseload Natural Gas Combined Cycle (NGCC) power plant and an ancillary instalation, namely a Liquefied Natural Gas (LNG) facility, in a realistic setting; specifically, these investments enjoy a long useful life but require some non-negligible time to build. Then we focus on the valuation of several investment options again in a realistic setting. These include the option to invest in the power plant when there is uncertainty concerning the initial outlay, or the option's time to maturity, or the cost of CO2 emission permits, or when there is a chance to double the plant size in the future. Our model comprises three sources of risk. We consider uncertain gas prices with regard to both the current level and the long-run equilibrium level; the current electricity price is also uncertain. They all are assumed to show mean reversion. The two-factor model for natural gas price is calibrated using data from NYMEX NG futures contracts. Also, we calibrate the one-factor model for electricity price using data from the Spanish wholesale electricity market, respectively. Then we use the estimated parameter values alongside actual physical parameters from a case study to value natural gas plants. Finally, the calibrated parameters are also used in a Monte Carlo simulation framework to evaluate several American-type options to invest in these energy assets. We accomplish this by following the least squares MC approach.

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Qualitative analyses of available photographs and maps of Merritt Island, Florida provide a large-scale, historical perspective of ecological changes of the marshes in the vicinity. Sites that deserve closer scrutiny can be identified. Secondarily, such an analysis provides a geographical orientation essential for communication not only between newcomers and those familiar with the area, but also among those familiar with the area but who refer to sites by differing methods. Photographs and maps from various sources were examined. Below are listed what we consider to be the most useful subset of these for ecological and geographical assessment of salt marsh impoundments on Merritt Island, Florida. (Document has 25 pages.)

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Background: Candida-associated denture stomatitis is a frequent infectious disease. Treatment of this oral condition is difficult because failures and recurrences are common. The aim of this study was to test the in vitro antifungal activity of pure constituents of essentials oils. -- Methods: Eight terpenic derivatives (carvacrol, farnesol, geraniol, linalool, menthol, menthone, terpinen-4-ol, and aterpineol), a phenylpropanoid (eugenol), a phenethyl alcohol (tyrosol) and fluconazole were evaluated against 38 Candida isolated from denture-wearers and 10 collection Candida strains by the CLSI M27-A3 broth microdilution method. -- Results: Almost all the tested compounds showed antifungal activity with MIC ranges of 0.03-0.25% for eugenol and linalool, 0.03-0.12% for geraniol, 0.06-0.5% for menthol, a-terpineol and terpinen-4-ol, 0.03-0.5% for carvacrol, and 0.06-4% for menthone. These compounds, with the exception of farnesol, menthone and tyrosol, showed important in vitro activities against the fluconazole-resistant and susceptible-dose dependent Candida isolates. -- Conclusions: Carvacrol, eugenol, geraniol, linalool and terpinen-4-ol were very active in vitro against oral Candida isolates. Their fungistatic and fungicidal activities might convert them into promising alternatives for the topic treatment of oral candidiasis and denture stomatitis.

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Salvinia molesta D. S. Mitchell (Salviniaceae), variously called giant salvinia, water fern or African payal, is a vegetatively reproducing, perennial, free-floating, aquatic weed, native to southeastern Brazil (Waterhouse and Norris 1987). It (hereafter called salvinia) is a very serious weed in most regions outside its native range (Harley and Mitchell 1981) including India. The purpose of this paper is to report on two fungal pathogens that were found to be the cause of a sudden decline in salvinia in Bangalore.(PDF has 4 pages.)

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Isidro de Robles reuniu e publicou em espanhol uma coletânea de onze novelas de vários autores, afirmando serem elas inéditas. Sabe-se, contudo, que as cinco primeiras, de autoria de Alfonso de Alcaláy Henares, escritor e poeta português (Lisboa, 1599 – Alcalá, 1682) já haviam sido publicadas sob o título “Vários effetos de amor en cinco novellas exemplares...”. cuja edição princeps, considerada raríssima, foi publicada em Lisboa, no ano de 1641. As cinco novelas chamaram a atenção e agradaram ao publico, que valorizou O esforço literário e a genialidade do autor por tê-las escrito omitindo uma determinada vogal. Assim, na primeira novela todas as palavras Foram escritas sem a letra a, na segunda sem a letra e, etc.

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Gvzman de Alfarache é um dos mais extensos e Importantes romances picarescos de que se tem noticia. Foi publicado, inicialmente, em duas partes: a primeira, em Madri, em 1599, intitulada ‘Primera parte de la vida dei P. Ícaro Gvzman de Alfarache’, a segunda, em Barcelona, em 1605, com o titulo ‘Segvnda parte de la vida de Gvzman de Alfarache, atalaya de la vida humana, por Mateo Aleman, su verdadero autor’. Consta que, em 1602, por ter sido publicada uma segunda parte apócrifa escrita pelo advogado valenciano Juan José Marti, Alemán acrescentou ao título a informação ‘su verdadeiro autor’. O romance é a autobiografia de um velhaco que depois de aventuras de todo gênero, conta com detalhes, a sua vida em tom cético e pessimista, com o estoicismo espanhol e características típicas do Barroco. Em seis anos o romance teve vinte e três edições e foi traduzido para o francês, o inglês e o italiano. Alemán utilizou pela primeira vez o termo pícaro para simbolizar a humanidade propensão crime

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João Franco Barreto, escritor português, nasceu em Lisboa em 1600, ignorando-se a data de sua morte. Em 1624, integrou expedição de libertação da Bahia das mãos dos holandeses. Ao regressar a Portugal dedicou-se às letras: escreveu obras como ‘Cyparisso’, ‘Biblioteca Portuguesa’, ‘Ortografia portuguesa’; traduziu a Eneida, de Virgílio; e dirigiu a edição de um Dicionário dos nomes próprios que se encontram nos Lusíadas de Luis de Camões. Segundo Inocêncio, essa tradução de Barreto, publicada em 1763, corresponde à segunda edição, ainda que esta informação não figure no corpo da obra, e ‘seja em demasia parafrástica, e que muitas vezes não reproduza fielmente o sentido do original, em razão das dificuldades da rima, a que o tradutor quis sujeitar-se, todavia, a pureza e correção de linguagem com que foi escrita juntas à louçania do estilo, e a uma versificação quase sempre fluida e harmoniosa, fazem e farão sempre com que este trabalho não seja de todo esquecido, apesar de terem aparecido depois outras versões sem dúvida mais perfeitas’. A coleção, dividida em dois volumes, traz os livros I a Vl e VII a XII. A primeira parte, que corresponde à ‘Odisséia’, narra as viagens de Enéas até a sua chegada à Itália. A segunda, a exemplo da ‘llíada’, descreve as guerras pela conquista do Lácio até a fundação do reino de Lavinio.