990 resultados para 455


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对复相材料二维截面中第二相的空间分布状况的多级判别的模式识别方法作了较全面的综述,并对第二相的三维空间分布状况的一些体视学观测研究方法,尤其是近年来发展的新方法作了较为系统的介绍。指出在实际材料微结构设计和性能预测的过程中,应针对所研究的具体的材料特点、具体的机械性能类型以及材料性能力学计算工作的需求来确定恰当的描述尺度,选择合适的描述方法,以确定夹杂物或第二相的空间分布对材料机械性能的定量影响,尤其应注意发挥体视学在其中的重要作用。

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El estudio consistió en evaluar rendimiento en madera aserrada de trozas de Cedro Macho (Carapa guianensis) Aublet y Nancitón ( Hyeronima alchorneoides) Allemao, en los dos aserríos portátiles tipo Wood Mizer LT 40 y Wood Mizer LT70, de la empresa MAPIINIC, S.A, en el municipio de Rosita (RAAN), Nicaragua. Se utilizó una base de datos del período agosto 2010-julio 2011, facilitada por la empresa, correspondientes a la cubicación de 5,570 trozas de Cedro macho y 7,785 trozas de Nancitón. Para el cálculo del volumen de la trozas se utilizó la fórmula de Smalian y para determinar el rendimiento en madera aserrada de cada especie se utilizó el volúmen promedio obtenido de las tablas sobre el volúmen promedio de la trozas, multiplicado por cien. Para Cedro macho se obtuvo un volúmen de madera aserrada de 455,722.66 pt lo que representó un rendimiento del 18.86% del volúmen en troza; para Nancitón se obtuvo un volúmen de madera aserrada de 584,698.91 pt para un rendimiento del 10.72% del volúmen en troza. En relación al rendimiento de otras especies y otros aserríos estos rendimientos se consideran bajos, atribuidos a que las trozas, por haber estado mucho tiempo tumbadas en el campo, presentaban daños que obviamente incidieron en la cantidad y calidad de madera aserrada obtenida, además que la metodología aplicada no llevó sistemáticamente el registro de cubicación de la madera aserrada por cada troza cubicada, lo que pudo influir en estos resultados.

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Con el objetivo de conocer los principales helmintos gastrointestinales que afectan a bovinos menores de un año en la zona del municipio de Matagalpa, se realizó este estudio en diez (10) fincas representativas de la zona que se encuentran en distintos puntos geográficos del municipio. Investigación que se llevó a efecto entre noviembre del 2005 - abril del 2006. Los parámetros climáticos del municipio en esta época oscila entre 26 - 28 °C de temperatura y 80 % de humedad relativa, ± un 5 %. Se realizaron cuatro muestreos en serie a 91 terneros menores de un año, correspondiente al 20 % del total de una población de 455 animales, la que se les extrajo del recto aproximadamente de 80 a l 00 gramos de heces fecales, de los cuales se utilizó 5 gramos para realizar el método cualitativo de presencia de huevos de helmintos por medio del método de flotación de Sheather. Posterior al análisis cualitativo, se procedió a realizar el cálculo de la carga parasitaria, utilizando para esto la metodología de Gordon & Whitllock (Macmaster modificado). Para la identificación de especies, se realizaron cultivos de larva de las que se obtuvieron muy pocas formas larvarias, se observó baja eclosión de larvas, posiblemente a la no viabilidad de los huevos. Se encontraron 82 animales positivos, de los cuales los géneros Strongyloides s y Cooperia presentaron 33 % y 16.5 % respectivamente siendo los más predominantes, seguido por Trichuris 6.6 %, Toxocara; 2.2 %, Oesophagostomum; 1.1%, Bunostomum; l.l %. Además se presentaron asociaciones de helmintos con una prevalencia de 29.6 % de los casos positivos.

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We demonstrate the growth of crack-free blue and greenemitting LED structures grown on 2-inch and 6-inch Si(111) substrates by metalorganic vapour phase epitaxy (MOVPE), using AlN nucleation layers and AlGaN buffer layers for stress management. LED device performance and its dependence on threading dislocation (TD) density and emission wavelength were studied. Despite the inherently low light extraction efficiency, an output power of 1.2 mW at 50 mA was measured from a 500 μm square planar device, emitting at 455 nm. The light output decreases dramatically as the emission wavelength increases from 455 nm to 510 nm. For LED devices emitting at similar wavelength, the light output was more than doubled when the TD density was reduced from 5×1 09 cm-2 to 2×109 cm-2. Our results clearly show that high TD density is detrimental to the overall light output, highlighting the need for further TD reduction for structures grown on Si. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

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The optical efficiency of GaN-based multiple quantum well (MQW) and light emitting diode (LED) structures grown on Si(111) substrates by metal-organic vapor phase epitaxy was measured and compared with equivalent structures on sapphire. The crystalline quality of the LED structures was comprehensively characterized using x-ray diffraction, atomic force microscopy, and plan-view transmission electron microscopy. A room temperature photoluminescence (PL) internal quantum efficiency (IQE) as high as 58% has been achieved in an InGaN/GaN MQW on Si, emitting at 460 nm. This is the highest reported PL-IQE of a c-plane GaN-based MQW on Si, and the radiative efficiency of this sample compares well with similar structures grown on sapphire. Processed LED devices on Si also show good electroluminescence (EL) performance, including a forward bias voltage of ∼3.5 V at 20 mA and a light output power of 1 mW at 45 mA from a 500 ×500 μm2 planar device without the use of any additional techniques to enhance the output coupling. The extraction efficiency of the LED devices was calculated, and the EL-IQE was then estimated to have a maximum value of 33% at a current density of 4 A cm-2, dropping to 30% at a current density of 40 A cm-2 for a planar LED device on Si emitting at 455 nm. The EL-IQE was clearly observed to increase as the structural quality of the material increased for devices on both sapphire and Si substrates. © 2011 American Institute of Physics.

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(Ga, Gd, As) film was fabricated by the mass-analyzed dual ion-beam epitaxy system with the energy of 1000 eV at room temperature. There was no new peak found except GaAs substrate peaks (0 0 2) and (0 0 4) by X-ray diffraction. Rocking curves were measured for symmetric (0 0 4) reflections to further yield the lattice mismatch information by employing double-crystal X-ray diffraction. The element distributions vary so much due to the ion dose difference from AES depth profiles. The sample surface morphology indicates oxidizing layer roughness is also relative to the Gd ion dose, which leads to islandlike feature appearing on the high-dose sample. One sample shows ferromagnetic behavior at room temperature. (C) 2003 Elsevier B.V. All rights reserved.

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动脉粥样硬化(atherosclerosis)的非随机分布与当地的血流动力环境有关,借助平行平板式平直流槽和以T型分叉流槽为代表的平行平板式异型流槽,可以模拟血管的主要形状特征,首,先在数值模拟的基础上分布了流型特征参数,确定了流的设计尺寸。然后,通过实验研究,探讨流型改变对内皮细胞血管活性物质分泌的影响,发现扩张效应流线偏转和驻点效应使得异型流槽前列环素和内定素的沁泌水平与相同入口雷诺数(Re)条件下的平直流槽分别有降低趋势和显著差异。为进一步研究流型对血管内皮细胞的影响提供了实验数据。

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[EN]Bresnan and Nikitina (2009) and Rappaport Hovav and Levin (2008) show that, contrary to standard assumptions, fixed-theme idioms may appear in to-constructions under certain pragmatic circumstances. Bruening (2010a) contends that the cases they present are in fact R(ightward)-dative shifts, double object constructions with the object projected to the right. In this article, we argue that Bruening’s proposed theoretical apparatus is unnecessarily complex and ad hoc and falls short of explaining the main facts it is supposed to deal with, massively overgenerating. A regular PP structure is argued to be empirically more adequate and conceptually simpler, avoiding the main problems of the R-dative shift analysis. New empirical evidence concerning pairlist readings and scope freezing also suggests that the empirical facts about idioms should be reconsidered in completely different terms.

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为了反映近岸区域实际存在的多孔介质海底效应,并且考虑到波浪在刚性海底上传播模型的最新研究进展,运用Green第二恒等式建立了波浪在非平整、多孔介质海底上传播的复合方程.假设水深和多孔介质海底层厚度均由两种分量组成:慢变分量,其水平变化的长度尺度大于表面波的波长;快变分量,其水平变化的长度尺度与表面波的波长等阶,但其振幅小于表面波的振幅.另外,多孔介质层下部边界的快变分量比水深的快变分量小1个量级.针对水体层和多孔介质层,选择Green第二恒等式方法给出了波浪传播和渗透的复合方程,它在交接面上满足压力和垂直渗透速度的连续性条件,可充分考虑波数变化的一般连续性,并包含了某些著名的扩展型缓坡方程.

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利用神舟3号飞船(SZ-3)上的多样品空间晶体炉制备出GaMnSb材料.所设计的石英安瓿使用氧化铝棉毡和特殊设计制造的氮化硼坩锅进行减震,经受住了严峻的力学环境的考验,完成了材料的空间生长实验,达到了空间生长材料的初步要求.对空间生长的GaMnSb晶体进行了X射线能谱分析和X射线衍射分析,发现空间生长的GaMnSb是多晶结构.对未获得GaMnSb单晶的原因进行了分析,发现空间晶体炉温度的波动和提供能量的不足是导致生成GaMnSb多晶结构的主要原因.由于在晶体生长的初始阶段晶体炉提供的能量不足,使GaSb单晶部分未能熔化,从而导致GaMnSb材料的生长在没有籽晶的情况下进行.

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On September 7, 2000 the National Marine Fisheries Service announced that it was reinitiating consultation under Section 7 of the Endangered Species Act on pelagic fisheries for swordfish, sharks, tunas, and billfish. 1 Bycatch of a protected sea turtle species is considered a take under the Endangered Species Act (PL93-205). On June 30, 2000 NMFS completed a Biological Opinion on an amendment to the Highly Migratory Pelagic Fisheries Management Plan that concluded that the continued operation of the pelagic longline fishery was likely to jeopardize the continued existence of loggerhead and leatherback sea turtles.2 Since that Biological Opinion was issued NMFS concluded that further analyses of observer data and additional population modeling of loggerhead sea turtles was needed to determine more precisely the impact of the pelagic longline fishery on turtles. 3,4 Hence, the reinitiation of consultation. The documents that follow constitute the scientific review and synthesis of information pertaining to the narrowly defined reinitiation of consultation: the impact of the pelagic longline fishery on loggerhead and leatherback sea turtles The document is in 3 parts, plus 5 appendices. Part I is a stock assessment of loggerhead sea turtles of the Western North Atlantic. Part II is a stock assessment of leatherback sea turtles of the Western North Atlantic. Part III is an assessment of the impact of the pelagic longline fishery on loggerhead and leatherback sea turtles of the Western North Atlantic. These documents were prepared by the NMFS Southeast Fisheries Science Center staff and academic colleagues at Duke University and Dalhousie University. Personnel involved from the SEFSC include Joanne Braun-McNeill, Lisa Csuzdi, Craig Brown, Jean Cramer, Sheryan Epperly, Steve Turner, Wendy Teas, Nancy Thompson, Wayne Witzell, Cynthia Yeung, and also Jeff Schmid under contract from the University or Miami. Our academic colleagues, Ransom Myers, Keith Bowen, and Leah Gerber from Dalhousie University and Larry Crowder and Melissa Snover from Duke University, also recipients of a Pew Charitable Trust Grant for a Comprehensive Study of the Ecological Impacts of the Worldwide Pelagic Longline Industry, made significant contributions to the quantitative analyses and we are very grateful for their collaboration. We appreciate the reviews of the stock definition sections on loggerheads and leatherbacks by Brian Bowen, University of Florida, and Peter Dutton, National Marine Fisheries Service Southwest Fisheries Science Center, respectively, and the comments of the NMFS Center of Independent Experts reviewers Robert Mohn, Ian Poiner, and YouGan Wang on the entire document. We also wish to acknowledge all the unpublished data used herein which were contributed by many researchers, especially the coordinators and volunteers of the nesting beach surveys and the sea turtle stranding and salvage network and the contributors to the Cooperative Marine Turtle Tagging Program. (PDF contains 349 pages)

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Eterio Pajares, Raquel Merino y José Miguel Santamaría (eds.)

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ENGLISH: Yellowfin and skipjack tuna occur in commercial quantities in the Eastern Pacific Ocean from California to Chile. They are captured in the high seas at distances from the mainland up to several hundred miles (see Alverson, 1960). The Inter-American Tropical Tuna Commission has been engaged for several years in research on the biology, ecology, and population dynamics of the stocks of these species supporting the commercial fishery, in order to elucidate the effects of the fishery and of fishery independent factors on their abundance and behavior, to provide the scientific basis for rational management of the fishery. An important aspect of this research is the investigation of the migrations of these species in the Eastern Pacific, and the determination of whether each consists of but a single population or is composed of various sub-populations. One direct means of approaching these problems is the tagging, and subsequent recovery, of specimens in the region of the commercial fishery. This also provides direct information on growth rates, by comparison of sizes of specimens at tagging and upon later recovery, and can furnish the basis of estimating rates of mortality. These are two of the important elements of the vital statistics of the tuna populations. SPANISH: El atún aleta amarilla y el barrilete se encuentran en cantidades comerciales en el Océano Pacífico Oriental, desde California hasta Chile. Estos peces son capturados en alta mar a varios cientos de millas de distancia de tierra firme (ver Alverson, 1960). La Comisión Interamericana del Atún Tropical ha estado dedicada durante varios años a la investigación de la biología, ecología y dinámica de las poblaciones de los stocks de las indicadas especies que mantienen la pesquería comercial, a fin de elucidar los efectos de ésta y de los factores independientes de la explotación sobre la abundancia y hábitos de estos peces, para obtener una base científica que permita una administración racional de la pesquería. Un aspecto importante de esta investigación es el estudio de los movimientos migratorios de estas especies en el Pacífico Oriental, y la determinación de que si cada una constituye una sola población o está compuesta de varias subpoblaciones. Un medio directo de abordar estos problemas es el de la marcación, y subsecuente recuperación, de especímenes en la región de la pesquería comercial. Esto también proporciona una información directa sobre la tasa de crecimiento, por la comparación de los tamaños de los especímenes al ser marcados y recuperados más tarde y puede proveer la base para estimar las tasas de mortalidad. Estos son dos de los elementos importantes de las estadísticas vitales de las poblaciones de atún.

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Menlicirrhus americanus in the northwestern Gulf of Mexico mature at 150-220 mm TL and 12-14 months of age, with males maturing when 10-40 mm smaller than females. Spawning occurs within a broad period from February through November with two discrete peaks which coincide with the periodicity of downcoast alongshore currents (towards Mexico) in spring and fall. This species occurs at depths of less than 5 to 27 m, being most abundant at 5 m or shallower. Young-of-the-year recruit primarily at 5-9 m or shallower and gradually expand their bathymetric range. Age determination by length frequency is feasible in M. americanus but not as simple as in species that spawn in one major period of the year. Only one or two spawned groups normally predominated at anyone time and no more than three co-occurred with few possible exceptions. Observed mean sizes were 138 mm TL at 6 months, and 192 and 272 mm at ages I and II, respectively. Typical maximum size was 296-308 mm and typical maximum age is probably 2-3 years. The largest fISh captured were 392 and 455 mm. Observed sex ratio was 1.2 females to 1 male. Weight, girth, and length-length regressions are presented.(PDF file contains 27 pages.)