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Improved effective charge density in MOS capacitors with PECVD SiOxNy dielectric layer obtained at low RF power

Torres, Katia Franklin Albertin; Pereyra, Ines
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
55.85%
In this work SiOxNy films are produced and characterized. Series of samples were deposited by the plasma enhanced chemical vapor deposition (PECVD) technique at low temperatures from silane (SiH4), nitrous oxide (N2O) and helium (He) precursor gaseous mixtures, at different deposition power in order to analyze the effect of this parameter on the films structural properties, on the SiOxNy/Si interface quality and on the SiOxNy effective charge density. In order to compare the film structural properties with the interface (SiOxNy/Si) quality and effective charge density, MOS capacitors were fabricated using these films as dielectric layer. X-ray absorption near-edge spectroscopy (XANES), at the Si-K edge, was utilized to investigate the structure of the films and the material bonding characteristics were analyzed through Fourier transform infrared spectroscopy (FTIR). The MOS capacitors were characterized by low and high frequency capacitance (C-V) measurements, in order to obtain the interface state density (D-it) and the effective charge density (N-ss). An effective charge density linear reduction for decreasing deposition power was observed, result that is attributed to the smaller amount of ions present in the plasma for low RF power. (C) 2008 Elsevier B.V. All rights reserved.

Concreto de alto desempenho aplicado a sistemas de processamento e armazenagem de alimentos em baixas temperaturas; High performance concrete applied to storage and processing system buildings at low temperatures

Lima, Sandra Maria de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 20/10/2008 PT
Relevância na Pesquisa
66%
O desenvolvimento de um concreto de alto desempenho aplicado a sistemas de processamento e armazenagem de alimentos em baixas temperaturas teve por objetivo atender às indústrias de alimentos no Brasil que se utilizam da tecnologia do frio em seu processo industrial. A hegemonia mundial do mercado de carnes é brasileira, sendo que nossas indústrias são responsáveis por 33% desse mercado. A ausência de estudos para aprimorar e tornar as plantas industriais mais duráveis e condizentes com a importância do setor foi determinante na delineação do tema desta tese. Desenvolveu-se um concreto de alto desempenho frente às possíveis situações em uma planta industrial: baixas temperaturas em ambientes secos e baixas temperaturas em ambientes sujeitos à umidade. A temperatura mínima a qual foram submetidos os concretos analisados foi de 35°C. O método de dosagem e as diretrizes calcadas no reforço da matriz da pasta de cimento e refinamento de poros mostraram-se como uma alternativa para vencer as agressividades causadas pelas baixas temperaturas ao concreto. Até então, estudos sugeriam um sistema de ar cujos vazios teriam diâmetros em torno de 250 µm espaçados com esta mesma distância entre eles e com conteúdo de 6±1% para a proteção de concretos expostos a baixas temperaturas. A produção de um concreto coeso...

Determinação das fronteiras de fase de sistemas antiferromagnéticos anisotrópicos a baixas temperaturas; Determination of the boundaries of the anisotropic antiferromagnetic systems phase at low temperatures

Figueiredo, Wagner
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/11/1980 PT
Relevância na Pesquisa
55.8%
A combinação das funções de Green para operadores de criação e destruição de bosons com as transformações de Holstein e Primakoff é utilizada na análise de sistemas antiferromagnéticos, isolantes e anisotrópicos, na região de baixas temperaturas. Os limites de estabilidade das fases antiferromagnética e "spin-flop", assim como a transição "spin-flop"-paramagnética são determinados em função da temperatura. A Hamiltoniana modelo considerada leva em conta as interações de intercâmbio anisotrópicas entre primeiros e segundos dos vizinhos numa rede cúbica simples e anisotropias de íon único, dos tipos uniaxial e ortorrômbico. Em particular, as fronteiras de fase "spin-flop"-paramagnéticas dos antiferromagnetos NiCl2.6H2O, CoCl2. 6H2O, NiCl2.4H2O e MnCl2.4H2O são determinadas e comparadas com os dados experimentais. As interações dipolares são consideradas explicitamente no circulo da fronteira de fase "spin-flop"-paramagnética do EuTe, obtendo-se boa concordância com a experiência.; The combination of Greens functions for boson creation and destruction operators with the Holstein - Primakoff transformations is employed in the analysis of insulating and anisotropic antiferromagnetic systems at very low temperatures. The stability limits of antiferromagnetic and spin- flop phases...

Armazenamento a baixas temperaturas de diferentes cultivares de bananas: efeito nos atributos de qualidade; Storage at low temperatures of different banana cultivars: effect on quality attributes.

Facundo, Heliofabia Virginia de Vasconcelos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 06/05/2013 PT
Relevância na Pesquisa
46.01%
A banana é altamente susceptível a injúrias causadas pelo frio, mas o efeito da refrigeração nos atributos que caracterizam a qualidade do fruto maduro é ainda pouco explorado. Neste trabalho, alguns desses atributos foram analisados em duas cultivares de banana escolhidas por sua diferença em relação à susceptibilidade ao frio: Nanicão e Prata. As duas cultivares foram armazenadas a baixas temperaturas (cv. Nanicão a 13 ºC e cv. Prata a 13 ºC e 10 ºC) por 15 dias e o efeito do frio sobre os compostos voláteis responsáveis pelo aroma e sabor, índices de cor da casca, níveis de carotenoides, açúcares e amido foram analisados comparativamente durante a maturação dos frutos e o perfil de proteínas diferentemente abundantes foi analisado na cultivar Nanicão. Com o auxílio das ferramentas da estatística multivariada, verificou-se que a produção dos compostos voláteis é altamente sensível as baixas temperaturas. A cv. Prata apresentou uma maior resistência ao efeito negativo do armazenamento, mesmo armazenada a 10 ºC. Na cv. Nanicão, as amostras maduras do grupo frio (13 ºC) foram caracterizadas pela presença dos carotenoides majoritários devido ao fato de que as vias metabólicas que utilizam carotenoides terem sido afetadas pelo armazenamento em baixas temperaturas. Para a cv. Prata teve um efeito negativo com o armazenamento...

Structural transition of ZnO thin films produced by RF magnetron sputtering at low temperatures

Rosa, A. M.; Da Silva, E. P.; Chaves, M.; Trino, L. D.; Lisboa Filho, Paulo Noronha; Da Silva, T. F.; Durrant, S. F.; Bortoleto, J. R R
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 3143-3148
ENG
Relevância na Pesquisa
55.83%
Zinc oxide (ZnO) thin films were prepared using reactive radio-frequency magnetron sputtering of a pure metallic zinc target onto glass substrates. The evolution of the surface morphology and the optical properties of the films were studied as a function of the substrate temperature, which was varied from 50 to 250 C. The surface topography of the samples was examined using atomic force microscopy (AFM), and their optical properties were studied via transmittance measurements in the UV-Vis-NIR region. DRX and AFM analyses showed that the surface morphology undergoes a structural transition at substrate temperatures of around 150 C. Actually, at 50 C the formation of small grains was observed while at 250 C the grains observed were larger and had more irregular shapes. The optical gap remained constant at ∼3.3 eV for all films. In the visible region, the average optical transmittance was 80 %. From these results, one can conclude that the morphological properties of the ZnO thin films were more greatly affected by the substrate temperature, due to mis-orientation of polycrystalline grains, than were the optical properties. © 2013 Springer Science+Business Media New York.

Relação entre o rendimento do motor de partida e o torque resistivo de um motor diesel submetido à partida em baixas temperaturas; Relationship between of starter efficiency and the resistive torque of a diesel engine submitted for starting at low temperatures

Anderson Almeida Carlos
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/06/2011 PT
Relevância na Pesquisa
65.95%
Em baixas temperaturas, as condições de partida do motor tornam-se mais difíceis devido a diversos fatores, como por exemplo, a menor lubrificação devido ao aumento da viscosidade do óleo lubrificante, a diminuição da massa de ar e a diminuição das folgas entre as partes móveis do motor como virabrequim, pistão e conseqüentemente o aumento do atrito entre estas partes. Foi construído um dispositivo para estimar o torque resistivo em baixas temperaturas na faixa entre - 20°C a 0ºC em um motor diesel NGD 3,0 litros, quatro cilindros de fabricação da MWM International com o objetivo de estudar a correlação entre o rendimento do motor de partida nestas condições e o torque resistivo solicitado na partida. Este dispositivo permite o levantamento do torque resistivo nos motores diesel sem combustão, onde a lubrificação é mínima e o atrito entre as partes móveis do motor são máximas. Para a medição do torque foi utilizada uma flange de torque modelo T40 de fabricação da HBM acoplada ao dispositivo de arraste, composto por um volante e motor de partida de um motor com 9,3 litros também de fabricação MWM International e o volante do motor que foi testado, através de um eixo cardam. Os testes para o levantamento dos dados foram realizados em um "contêiner" frigorífico utilizado para transportes de cargas perecíveis...

Estudo da deposição de lignina em genótipos de cana-de-açúcar sob condição de déficit hídrico e baixa temperatura; Study of lignin deposition in sugarcane genotypes under condition of water deficit and low temperature

Adriana Brombini dos Santos
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 14/05/2014 PT
Relevância na Pesquisa
55.94%
A cana-de-açúcar (Saccharum spp.), uma gramínea C4, representa uma abundante e promissora fonte de biomassa vegetal para a produção de biocombustíveis. O uso da biomassa para a conversão em etanol é limitada pela recalcitrância do material lignocelulósico, principalmente, devido à presença da lignina. O conteúdo e a composição da lignina variam entre diferentes táxons, tipos celulares e podem ser afetados por diversos fatores ambientais. Considerando a demanda mundial por fontes de energia renovável e o alto potencial da biomassa da cana-de-açúcar para a produção de etanol celulósico, o objetivo desse estudo foi avaliar os efeitos do déficit hídrico e da baixa temperatura sobre a deposição de lignina no colmo em diferentes genótipos de cana. Os resultados obtidos para o conteúdo de lignina somados à caracterização anatômica da lignina no caule indicaram que as plantas IACSP94-2094 são mais lignificadas que IACSP95-5000, sob condições normais de crescimento, o que foi principalmente associado aos maiores teores de lignina na região do córtex dos entrenós maduros. O déficit hídrico influenciou negativamente a produção de biomassa nas plantas de cana e o genótipo IACSP94-2094 foi mais fortemente afetado...

Acclimation to short-term low temperatures in two Eucalyptus globulus clones with contrasting drought resistance

Silva, F.Costa e; Shvaleva, A.; Broetto, F.; Ortuño, M.F.; Rodrigues, M.L.; Almeida, M.H.; Chaves, M.M.; Pereira, J.S.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
Publicado em //2009 ENG
Relevância na Pesquisa
46.01%
We tested the hypothesis that Eucalyptus globulus Labill. genotypes that are more resistant to dry environments might also exhibit higher cold tolerances than drought-sensitive plants. The effect of low temperatures was evaluated in acclimated and unacclimated ramets of a drought-resistant clone (CN5) and a drought-sensitive clone (ST51) of E. globulus. We studied the plants’ response via leaf gas exchanges, leaf water and osmotic potentials, concentrations of soluble sugars, several antioxidant enzymes and leaf electrolyte leakage. Progressively lowering air temperatures (from 24/16 to 10/ 2 C, day/night) led to acclimation of both clones. Acclimated ramets exhibited higher photosynthetic rates, stomatal conductances and lower membrane relative injuries when compared to unacclimated ramets. Moreover, low temperatures led to significant increases of soluble sugars and antioxidant enzymes activity (glutathione reductase, ascorbate peroxidase and superoxide dismutases) of both clones in comparison to plants grown at control temperature (24/16 C). On the other hand, none of the clones, either acclimated or not, exhibited signs of photoinhibition under low temperatures and moderate light. The main differences in the responses to low temperatures between the two clones resulted mainly from differences in carbon metabolism...

Is cold the new hot in sudden unexpected death in epilepsy? Effect of low temperature on heart rate of rats with epilepsy

Sonoda,Eliza Y.F.; Colugnati,Diego B.; Scorza,Carla A.; Arida,Ricardo M.; Pansani,Aline P.; Almeida,Antonio-Carlos G. de; Cavalheiro,Esper A.; Scorza,Fulvio A.
Fonte: Academia Brasileira de Neurologia - ABNEURO Publicador: Academia Brasileira de Neurologia - ABNEURO
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2008 EN
Relevância na Pesquisa
55.93%
Sudden unexpected death in epilepsy (SUDEP) is the commonest cause of seizure-related mortality in people with refractory epilepsy. Several risk factors for SUDEP are described; however, the importance of including low temperatures as risk factor for SUDEP was never explored. Based on this, the aim of this study was to evaluate the heart rate of rats with epilepsy during low temperature exposure. Our results showed that low temperature clearly increased the heart rate of rats with epilepsy. Taken together, we concluded that exposure to low temperatures could be considered important risk factors from cardiovascular abnormalities and hence sudden cardiac death in epilepsy.

Construction and testing of a system for the electrical characterization of ceramic thermistors at low temperatures

Luz,F. C. S.; Pianaro,S. A.; Yurk,C. E.; Capobianco,G.; Zara,A. J.; Tebcherani,S. M.
Fonte: Associação Brasileira de Cerâmica Publicador: Associação Brasileira de Cerâmica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2014 EN
Relevância na Pesquisa
55.92%
A high-precision and low cost system was built for the electrical characterization of ceramic thermistors at low temperatures, using components readily available in materials research laboratories. The system presented excellent reproducibility in the electrical characterization of NTC ceramic sensors from -75 ºC (195 K) to 23 ºC (296 K). The behavior of the NTC sensor was comparable to that of commercial thermistors only below room temperature (α = -3.2%/K), demonstrating the importance of fully characterizing these materials at both low and high temperatures.

Critical role of anteiso-C15:0 fatty acid in the growth of Listeria monocytogenes at low temperatures.

Annous, B A; Becker, L A; Bayles, D O; Labeda, D P; Wilkinson, B J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1997 EN
Relevância na Pesquisa
46.05%
Listeria monocytogenes is a food-borne pathogen capable of growth at refrigeration temperatures. Membrane lipid fatty acids are major determinants of a sufficiently fluid membrane state to allow growth at low temperatures. L. monocytogenes was characterized by a fatty acid profile dominated to an unusual extent (> 95%) by branched-chain fatty acids, with the major fatty acids being anteiso-C15:0, anteiso-C17:0, and iso-C15:0 in cultures grown in complex or defined media at 37 degrees C. Determination of the fatty acid composition of L. monocytogenes 10403S and SLCC 53 grown over the temperature range 45 to 5 degrees C revealed two modes of adaptation of fatty acid composition to lower growth temperatures: (i) shortening of fatty acid chain length and (ii) alteration of branching from iso to anteiso. Two transposon Tn917-induced cold-sensitive mutants incapable of growth at low temperatures had dramatically altered fatty acid compositions with low levels of i-C15:0, a-C15:0, and a-C17:0 and high levels of i-C14:0, C14:0, i-C16:0, and C16:0. The levels of a-C15:0 and a-C17:0 and the ability to grow at low temperatures were restored by supplementing media with 2-methylbutyric acid, presumably because it acted as a precursor of methylbutyryl coenzyme A...

Translocation of Carbohydrates and Proline in Young Grapefruit Trees at Low Temperatures 1

Purvis, Albert C.; Yelenosky, George
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1983 EN
Relevância na Pesquisa
46.01%
Girdling and defoliation of fruit-bearing grapefruit (Citrus paradisi Macf.) branches inhibited the accumulation of soluble carbohydrates and proline in fruit tissues during low temperature treatment of trees. These treatments did not inhibit hydrolysis of sucrose to reducing sugars. Flavedo and albedo tissues responded similarly to low temperatures but little or no change occurred in the juice. Therefore, soluble carbohydrates and proline do not appear to interchange between different tissues of the fruit at low temperatures but instead are translocated into the fruit from other parts of the plant. Girdling fruit-bearing branches immediately after low temperature treatments inhibited the accumulation of sucrose in fruit tissues at dehardening temperatures. Also, proline levels decreased rapidly in fruit on girdled branches at dehardening temperatures. This rapid decrease suggests proline may serve as a source for respiratory energy in grapefruit during rapidly changing temperatures that favor active growth and during recovery of citrus from environmental stress.

Neonatal exposure to short days and low temperatures blunts stress response and yields low fluctuating asymmetry in Siberian hamsters

Benderlioglu, Zeynep; Dow, Eliot; Pyter, Leah M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.04%
Fluctuating asymmetry (FA) refers to small, non-directional deviations from perfect bilateral symmetry in morphological characters. Individuals with low FA presumably either developed in a relatively stable environment and/or were better able to buffer against developmental stressors. The present study investigated the effects of seasonal factors measured by day length and ambient temperature manipulations on the development of bilateral characters and concomitant changes in stress responses. Siberian hamsters were exposed to either long days (16 h of light per day) or short days (8 h of light per day) combined with either standard temperatures (21 ± 2°C) or low temperatures (8 ± 2°C) on the day of birth until weaning. Cortisol concentrations at baseline and following acute restraint stress, and FA values were measured in adulthood. Females reared in winter-like conditions with short day lengths and low temperatures had low FA and low cortisol concentrations following restraint stress compared to other females. Females reared in long day lengths and standard temperatures had the highest rate of increase in cortisol concentrations after restraint among other female groups. No group effects were observed in males regarding day length and temperature manipulations. Baseline and post-restraint cortisol concentrations were higher in females than males for all groups except in animals reared in short day lengths and low temperatures. Our results suggest that winter-like conditions during neonatal period evoke hyposensitivity to stress in adult females and this blunted response to stress is a key factor in achieving ideal growth patterns.

Effects of Low Temperatures on Three Embryonic Stages of the Codling Moth (Lepidoptera: Tortricidae)

Moffitt, H. R.; Burditt, A. K.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica Formato: text/html
EN
Relevância na Pesquisa
55.93%
Base don mortality, the order of tolerance of three embryonic stages of codling moth, Cydia pomonella (L.), eggs for temperatures near 0°C was red ring > white > blackhead. Red ring stage eggs were 1.5 times more tolerant of low temperature than were white stage eggs and 2.5 times more tolerant than blackhead stage eggs. Thirty-six to 42 d exposure was required for complete mortality on mature ‘Red Delicious’ or ‘Golden Delicious’ apples. Tolerance of low temperature was not affected by the apple variety used as the substrate for oviposition. Eggs deposited on a substrate other than apples, such as plastic film, were significantly more susceptible to the effects of low temperature. Exposure to low temperatures such as those commonly used for short- or long-term fruit storage shows promise as an alternative to fumigation as a treatment for codling moth eggs on apples and pears after harvest.

Identifica????o de fam??lias mutantes de arroz (Oryza sativa L.) para caracter??sticas de import??ncia agron??mica e toler??ncia a baixas temperaturas na germina????o; Identifica????o de fam??lias mutantes de arroz (Oryza sativa L.) para caracter??sticas de import??ncia agron??mica e toler??ncia a baixas temperaturas na germina????o; Identification of mutant families of rice for traits of agronomic importance and tolerance to low temperatures during germination.; Identification of mutant families of rice for traits of agronomic importance and tolerance to low temperatures during germination.

LUZ, Viviane Kopp da
Fonte: Universidade Federal de Pelotas; Agronomia; Programa de P??s-Gradua????o em Agronomia; UFPel; BR Publicador: Universidade Federal de Pelotas; Agronomia; Programa de P??s-Gradua????o em Agronomia; UFPel; BR
Tipo: Tese de Doutorado Formato: application/pdf
POR
Relevância na Pesquisa
46.05%
The existence of variability is essential for successful breeding. The use of mutagens can increase the mutation frequency, enabling the development of variation for traits of interest. The occurrence of low temperatures is a common stress in rice cultivation in temperate regions, therefore the tolerance to low temperatures is a desirable feature of Brazilian rice genotypes grown in the South, where low temperatures affect the germination and crop establishment causing reductions in the grain yield. This work aimed to identify mutants of rice genotypes for traits of agronomic importance and to evaluate the low temperature stress tolerance of genotypes on germination stage. In stage germination, 400 M3 families and control genotypes BRS Quer??ncia, BR IRGA 409 and Nourim Mochi, were subjected to treatments with different temperatures (13 C and 25 C) and compared for their relative performance, measured by the coleoptile, root and shoot length. To evaluate the traits of agronomic importance, M3 rice seeds were sown in the experimental field at Embrapa Clima Temperado. The experimental design was a completely randomized block with four replications. Seven traits of agronomic importance were evaluated: length of main panicle in cm...

Estresses abi??ticos em h??bridos de canola: Efeito do alagamento e de baixas temperaturas; Abiotic stress in canola hybrids: Effect of flooding and low temperatures

PERBONI, Anelise Tessari
Fonte: Universidade Federal de Pelotas; Biologia; Programa de P??s-Gradua????o em Fisiologia Vegetal; UFPel; BR Publicador: Universidade Federal de Pelotas; Biologia; Programa de P??s-Gradua????o em Fisiologia Vegetal; UFPel; BR
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
46.02%
Oilseed rape (Brassica napus L.) belongs to the family Brassicaceae and constitutes the third most produced oilseed in the world, surpassed only by soybean and palm. Flooding of soil and low temperatures can cause alterations in cellular metabolism and impair plant growth, generating a stress condition. Two experiments were conducted using the canola hybrid Hyola 43, Hyola 401, Hyola 420 and Hyola 432. The first was conducted in greenhouse where 10 plants of each hybrid were subjected to stress by flooding for a period of six days. Were evaluated parameters and differences in the kinetics of emission of chlorophyll fluorescence, chlorophyll content, leaf area and dry weight of shoot and root. The flooding caused a reduction of leaf area, root dry mass and root dry mass/shoot dry mass ratio of all hybrids studied. In relation to chlorophyll fluorescence were identified differences in parameters related to specific flows that have undergone changes as a function of stress the latter being more pronounced for Hyola 432. The performace photosynthetic index (PIABS and PIABS,total) showed a decrease after 6 days of the experiment except for hybrid Hyola 420. The analysis of the kinetics of chlorophyll a fluorescence transient showed differential effects of stress application in different sites of photosynthetic apparatus...

Rela????o entre a concentra????o de gelo marinho Ant??rtico e a temperatura m??nima na Am??rica do Sul; Relation between the Antarctic Sea ice concentration and low temperatures in South America

Blank, Dionis Mauri Penning
Fonte: Universidade Federal de Pelotas; Meteorologia; Programa de P??s-gradua????o em Meteorologia; UFPel; BR Publicador: Universidade Federal de Pelotas; Meteorologia; Programa de P??s-gradua????o em Meteorologia; UFPel; BR
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
55.98%
The Antarctic Sea Ice Concentration (ASIC) is thought to be an important element in the analysis of the world climate. However, few studies have investigated its relation to other climatic elements. Thus, the aim of this study was to verify the relation between the ASIC and low temperatures in South America through two approaches. The first, regional, investigated the occurrence of a connection between the ASIC and the cold and hot quantiles of the daily lowest temperature as observed in some weather stations in Rio Grande do Sul in the 1982 2005 period. For such, low temperature values were transformed into cold and hot quantiles through the quantile technique, and correlated to ASIC sectors. The correlation coefficient showed a connection between the elements, with emphasis on the influence of Weddell, Ross Sea sectors and Bellingshausen and Amundsen Sea sector, especially because the Indian Ocean and the Western Pacific Ocean are farther away. The second approach, continental, analyzed the ASIC variability and its connection with low temperatures observed in South America by means of NCEP-NCAR reanalysis in the 1982 2007 period. For such, the sectors of larger ASIC variability were identified through the principal component analysis technique...

Compressive residual strength at low temperatures of composite laminates subjected to low-velocity impacts

Sánchez-Sáez, Sonia; Barbero, Enrique; Navarro Ugena, Carlos
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em /10/2008 ENG
Relevância na Pesquisa
55.93%
Compression after impact behaviour of different carbon fibre reinforced composite laminates (tape and woven) was studied at low temperatures. Low-velocity impact tests on thin plates at room temperature were made, followed by compression after impact tests at −60°C and −150°C. The results of these tests were compared with those of non-impacted specimens to study the variation of the residual strength at different impact energies. In tape laminates, the lower temperature decreased compression after impact strength, although no influence was detected regarding temperature in the variation of the compressive-strength-retention factor. However, at low temperatures, the woven laminate showed greater strength and a less loss of the retention factor than at room temperature.; The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT-98/0273) for the financial support of this work.; 7 pages, 8 figures.

Concreto de alto desempenho em ambientes com baixas temperaturas ; High performance concrete in low temperature environment

Lima, Sandra Maria de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 06/03/2006 PT
Relevância na Pesquisa
55.99%
O objetivo de colaborar com o equacionamento da problemática do crescimento populacional por meio de uma proposta viável economicamente, e com vantagens tecnológicas com vistas à durabilidade para a armazenagem de gêneros alimentícios em baixas temperaturas motivou o desenvolvimento desta pesquisa, na qual se propõe o uso do concreto como material alternativo para a construção de sistemas de guarda e conservação de alimentos. A partir de um adequado método de dosagem e da tecnologia desenvolvida pelo grupo de pesquisadores do Laboratório de Materiais Avançados à Base de Cimento, foram elaborados dois concretos diferenciados pela incorporação ou não de ar. A durabilidade do concreto para ambientes com baixas temperaturas tem sido relacionada a um sistema de vazios de ar com volume de 6 '+ OU -' 1 % e adequado espaçamento entre as bolhas de ar. O desempenho desses concretos em ambientes com baixas temperaturas foi avaliado acondicionando-os em uma câmara fria com temperatura de - 35 ± 2 graus Celsius. A sanidade dos corpos-de-prova foi monitorada por meio de ensaios não destrutivos (i.e. determinação da freqüência natural). O período de exposição foi de trinta e cinco dias, sendo que após o sétimo dia ocorreu a estabilização dos valores da freqüência natural dos corpos-de-prova. Os dois tipos de concretos ensaiados - com ar incorporado e sem ar incorporado - mostraram-se resistentes nestas condições de ensaio. Os resultados obtidos demonstram que os concretos...

Influence by proximity effect on ultrasound attenuation in Cu-Nb composite system at low temperatures

Ledenyov, Viktor O.; Ledenyov, Dimitri O.; Ledenyov, Oleg P.; Tikhonovsky, Mikhail A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/04/2012
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The attenuation of longitudinal ultrasonic wave with the frequency of 30 MHz in Cu-Nb copper-niobium (40 vol%) composite system at low temperatures from 0.35 K up to 2 K is researched. It was found that the ultrasonic attenuation decreases in a Cu-Nb multi-filamentary composite sample at low temperatures in distinction to the pure Cu copper or Nb niobium homogeneous bulk samples. It is well known that the contact between the normal metal N and the superconductor S is characterized by an appearance of superconducting properties in the thin surface layer of normal metal N, because of the presence of proximity effect at low temperatures T. This phenomenon is observed on the temperature dependent distance \xi_N(T) in the normal metal N at the normal metal - superconductor NS boundary. It is assumed that the transition from the normal state N to the superconducting state S must be accompanied by the decrease of magnitude of ultrasonic wave's electronic energy absorption in normal metal N. The experimental results show that the superconducting electron coherence length in the normal thin layer is temperature dependent \xi_N(T). The electron mean free path l, which is dependent on the impurity scattering in volume and near Cu-Nb interfaces...