Higher-order analysis of crack tip fields in elastic power-law hardening materials

A HIGHER-ORDER asymptotic analysis of a stationary crack in an elastic power-law hardening material has been carried out for plane strain, Mode 1. The extent to which elasticity affects the near-tip fields is determined by the strain hardening exponent n. Five terms in the asymptotic series for the stresses have been derived for n = 3. However, only three amplitudes can be independently prescribed. These are K1, K2 and K5 corresponding to amplitudes of the first-, second- and fifth-order terms. Four terms in the asymptotic series have been obtained for n = 5, 7 and 10; in these cases, the independent amplitudes are K1, K2 and K4. It is found that appropriate choices of K2 and K4 can reproduce near-tip fields representative of a broad range of crack tip constraints in moderate and low hardening materials. Indeed, fields characterized by distinctly different stress triaxiality levels (established by finite element analysis) have been matched by the asymptotic series. The zone of dominance of the asymptotic series extends over distances of about 10 crack openings ahead of the crack tip encompassing length scales that are microstructurally significant. Furthermore, the higher-order terms collectively describe a spatially uniform hydrostatic stress field (of adjustable magnitude) ahead of the crack. Our results lend support to a suggestion that J and a measure of near-tip stress triaxiality can describe the full range of near-tip states.

High-order asymptotic field of tensile plane-strain nonlinear crack problems

In this paper, the governing equations and the analytical method of the secondorder asymptotic field for the plane-straln crack problems of mode I have been presented. The numerical calculation has been carried out. The amplitude coefficients k2 of the second term of the asymptotic field have been determined after comparing the present results with some fine results of the finite element calculation. The variation of coefficients k2 with changes of specimen geometry and developments of plastic zone have been analysed. It is shown that the second term of the asymptotic field has significant influence on the near-crack-tip field. Therefore, we may reasonably argue that both the J-integral and the coefficient k2 can beeome two characterizing parameters for crack initiation.

立波作用下海床的有效应力与液化分析

波浪作用下海床的稳定性与液化分析是海底管线、防波堤和海洋平台设计中必须仔细考虑的问题。本文推荐了一个循环荷载作用下土体的弹塑性实用本构模型，并给出了一种粉土的模型参数。该模型直接根据初始应力状态和循环应力的大小与作用时间计算土体的塑性应变增量，在有限元计算中不需要引入弹塑性矩阵。采用Biot理论和有限单元法，对海床有效应力的变化过程分析表明，波腹点下海床存在较大的液化可能性。波浪作用对海床存在一定的压密作用。

激光诱导放电复合毛化坑形貌与电极侵蚀问题研究

利用高重频YAG激光作用在固体表面所产生的等离子体使工件和电极之间在大气环境中并且电压远低于击穿闭值的条件下产生可控定向放电。实验结果显示，放电坑基本上呈火山坑形，既有单坑结构，也有多坑结构，其形貌受到放电波形、电源极性、放电介质等因素的影响。放电坑表面形貌的规律是：①除了涂油时的阳极放电坑是单坑结构以外，其他条件下的放电坑都是复合多坑结构；②单坑结构呈火山坑形，坑底为圆弧形，熔凝物堆积在坑的边缘，而多坑结构则是一个大的放电坑中有多个凸起的尖峰，这种结构有利于毛化加工。研究表明，对于碳钢、铸铁、黄铜三种材料，放电坑直径d与电源参数的关系可以表示成：d∝Iαp（对于三角波），或d∝Υβ（对于矩形波）。α的范围在0.40～0.71，β的范围在0.23～0.47。在工件表面涂油，有利于提高放电的能量密度，使放电坑变深。介质的密度和粘性系数可作为控制放电通道扩展的有效因素。放电能量一定时，有固态相变材料的相变区深度的变化遵从以下规律：①放电波形和电源极性一定时，涂油时的深度＞大气时的深度；②极性和介质一定时，矩形波时的深度≥三角波时的深度；③介质和波形一定时，阳极时的深度≥阴极时的深度。与一般的研究电极损耗即放电前后电极的质量差所不同的是，认为在激光诱导放电毛化技术中，对工件电极应该研究放电的侵蚀作用，即实验上可观测到的能量作用的范围所对应的体积V，它不仅包括脱落下来的那部分物质，也包括发生了组织变化的那部分物质。对于有固态相变的材料，V通常就是相变区边界所对应的球冠体积；对于无固态相变的材料，V通常是放电坑的体积。通过量纲分析，揭示出V是一个多元函数。当电极材料和放电介质一定时，对于电流峰值一定的矩形波放电，v主要取决于脉冲宽度γ，其函数关系为：V＝K1·Υ1.41～1.45；对于脉冲宽度一定的三角波放电，V主要取决于电流峰值IP，V＝K2·I1.30～2.15P，K1、K2为与材料和放电介质有关的常量。在比较分析了脉冲激光束与激光诱导放电在功率密度、作用时间和坑的深度等方面对材料的影响之后，认为：高重频激光束适合于对材料表面进行薄层熔凝和毛化，低重频长脉冲激光束适合于对材料进行表面改性处理，而激光诱导放电具有对材料表面进行造型强化和组织强化的双重作用。设计了一种转动式圆盘电极，延长了工具电极的连续工作时间。

Cytokine control of neuronal phenotype

Diffusible proteins regulate neural development at a variety of stages. Using a novel neuronal culture assay, I have identified several cytokines that regulate the expression of neurotransmitters and neuropeptides in sympathetic neurons. These cytokines fall into two families. The first group is termed the neuropoietic cytokines, while including CDF/LIF, CNTF, OSM and GPA, induces expression of the same set of neuropeptide mRNAs in cultured sympathetic neurons. These four factors not only exhibit similar biological activities; they also share a predicted secondary structure and bind to a signal-transducing receptor subunit in common with IL-6 and IL-11. The latter two cytokines display a weaker activity in this assay. In addition, I find that several members of the TGF-β superfamily, activin A, BMP-2, and BMP-6, have a selective overlap with the neuropoietic family in the spectrum of neuropeptides that these cytokines induce in sympathetic neurons. Different patterns of neuropeptides induced by the TGF-β family members, however, demonstrate that the activities of these cytokines are distinct from those of the neuropoietic family. Another 30 cytokines are without detectable effect in this neuronal assay.

Activin A induces a set of neurotransmitters and neuropeptides that is somewhat similar to the phenotype of sympathetic neurons innervating sweat glands in rat footpads. In situ hybridization and RNase protection were carried out to test whether activins were involved in the phenotypic transition when sympathetic neurons contact sweat glands. I find that activin mRNA is present in both cholinergic and noradrenergic targets. Moreover, homogenates of footpads do not contain activin-like activity in the neuronal assay in vitro. Taken together, these data do not support activins as the best candidates for the sweat gland factor.

Several novel factors that regulate neuropeptide expression exist in heart cell conditioned medium. I attempted to purify these factors in collaboration with Dr. Jane Talvenheimo. Our results suggest that these factors are sensitive to the storage conditions used. Several modifications of purification strategy are discussed.

Aquarienanlage im Kontrollbereich

Seit Februar betreibt das Labor für Radioökologie der Gewässer für Versuche mit radioaktiven Stoffen an Fischen eine Aquarienanlage mit einem geschlossenen Wasserumlauf im Kontrollbereich (Kulturraum Ost) des Laboratoriums Sülldorf. Erste Untersuchungen an Karpfen (K2) zur Bestimmung der biologischen Halbwertszeit bei der Aufnahme von Phosphor aus dem Futter wurden mit dem radioaktiven Tracer P-32 inzwischen erfolgreich durchgeführt.

Contribuição para a elaboração de um sistema de gestão ambiental dos diques de manutenção e reparo do Arsenal de Marinha do Rio de Janeiro

A Baía de Guanabara, ambiente de localização do Arsenal de Marinha do Rio de Janeiro (AMRJ), sofre com a intensa pressão antrópica, principalmente no aspecto da qualidade das águas. Neste contexto, uma fração considerável da poluição decorre das atividades dos estaleiros, uma vez que a atividade industrial naval no Rio de Janeiro não tem mecanismo de controle de poluição à altura do seu real potencial poluidor. Esta ausência de fiscalização possibilita o lançamento na Baía de resíduos sólidos, esgotos sanitários, efluentes químicos, oleosos e tóxicos, tornando crescente a contaminação dessas águas, margens e mangues. Estes descartes cada vez mais são alvo das exigências ambientais da sociedade e das legislações. Devido a isto, a gestão de efluentes líquidos do Arsenal tornou-se prioritária, para tal, esse estudo foi proposto, tendo iniciado pela análise das oficinas do estaleiro, na qual as operações no dique foram identificadas como uma das mais impactantes do estaleiro. A partir desta constatação, estão apresentadas duas fontes de pesquisas para a redução dos impactos. Na primeira etapa, há o estudo das atividades geradoras de efluentes no dique de reparo, com os objetivos de propor a implantação das diretrizes de melhores práticas de gestão, de minimizar a geração de efluentes líquidos e de contribuir para a adoção de práticas ambientais proativas. Como segunda pesquisa, com base nas tecnologias mundiais, há a proposta de tratamento dos efluentes de um dique, na qual foram identificados os processos que irão atender às necessidades ambientais do estaleiro, com as opções de escolha entre o tratamento parcial, para o descarte na rede pública, ou com o prosseguimento do processo até o seu reúso. As conclusões deste estudo apontam para a implantação da gestão ambiental do dique sistematizada, rigorosa e integrada com a gestão das embarcações, acrescentando-se a isto, as necessidades de incorporação de tecnologias modernas e de sistema de tratamento dos efluentes, propiciando de maneira sustentável que haja a continuação do processo de produção do estaleiro e, ao mesmo tempo, permitindo o retorno da biodiversidade da Baía de Guanabara.

Final Evaluation Memorandum: Strategies for Resolving Low Dissolved Oxygen and Methylmercury Events in Northern Suisun Marsh

The purpose of the project is to improve our understanding about best management practices that can be utilized on diked managed wetlands in Suisun Marsh for reducing the occurrence of low dissolved oxygen (DO) and high methylmercury (MeHg) events associated primarily with fall flood-up practices. Low DO events are of concern because they can lead to undue stress and even mortality of sensitive aquatic organisms. Elevated MeHg levels are of concern because MeHg is a neurotoxin that bio-magnifies up the food chain and can cause deleterious effects to higher trophic level consumers such as piscivorous fish, birds, and mammals (including humans). This study involved two years (2007-2008) of intensive field data collection at two managed wetland sites in northwest Suisun Marsh and their surrounding tidal sloughs, an area with prior documented low DO events. In addition, the study collected limited soils and water quality field data and mapped vegetation for three managed wetland sites in the central interior of Suisun Marsh, for the purpose of examining whether wetlands at other locations exhibit characteristics that could indicate potential for similar concerns. In Year 1 of the study, the objective was to identify the baseline conditions in the managed wetlands and determine which physical management conditions could be modified for Year 2 to reduce low DO and MeHg production issues most effectively. The objective of Year 2 was to evaluate the effectiveness of these modified management actions at reducing production of low DO and elevated MeHg conditions within the managed wetlands and to continue improving understanding of the underlying biogeochemical processes at play. This Final Evaluation Memorandum examined a total of 19 BMPs, 14 involving modified water management operations and the remaining five involving modified soil and vegetation management practices. Some of these BMPs were previously employed and others have not yet been tested. For each BMP this report assesses its efficacy in improving water quality conditions and potential conflicts with wetland management. It makes recommendations for further study (either feasibility assessments or field testing) and whether to consider for future use. Certain previously used BMPs were found to be important contributors to poor water quality conditions and their continued use is not recommended. Some BMPs that could improve water quality conditions appear difficult to implement in regards to compatibility with wetland management; these BMPs require further elaboration and feasibility assessment to determine whether they should be field tested. In practice for any given wetland, there is likely a combination of BMPs that would together have the greatest potential to address the low DO and high MeHg water quality concerns. Consequently, this report makes no sweeping recommendations applicable to large groups of wetlands but instead promotes a careful consideration of factors at each wetland or small groups of wetlands and from that assessment to apply the most effective suite of BMPs. This report also identifies a number of recommended future actions and studies. These recommendations are geared toward improving the process understanding of factors that promote low DO and high MeHg conditions, the extent of these problems in Suisun Marsh, the regulatory basis for the DO standards for a large estuarine marsh, the economics of BMPs, and alternative approaches to BMPs on diked managed wetlands that may address the water quality issues. The most important of these recommendations is that future BMP implementation should be carried out within the context of rigorous scientific evaluation so as to gain the maximum improvement in how to manage these water quality issues in the diked managed wetlands of Suisun Marsh.

Premiers résultats sur l'excrétion et la production du zooplancton de la Lagune Ebrié (Côte d'Ivoire)

Biomass and metabolic rates (total nitrogen and phosphorus excretion and respiration) were measured at 4 stations, representative of the lagoon environment, during high-water (Oct-Nov), dry (Dec-Jan) and rainy (July) seasons. In low-salinity waters (4o/oo) Acartia clausi is almost the only species, whereas a marine and diversified fauna is brought in from the ocean during the dry season. O/NT and O/PT atomic ratios between respiration (O) and total nitrogen (NT) and phosphorus (PT) excretions are high (15.1 and 111, respectively) and show a marked hydrocarbon feeding of zooplankton. Production was assessed from excretion via the net growth efficiency coefficient, K2 , calculated from N/P ratios for particles (a1), zooplankton excretion (a2) and constitution (a3). Daily productivity indices (i.e. daily production/biomass ratio) are high and equivalent to 1.2-3.8 day turn-over times. These high values may be ascribed to high temperatures (26.5-30 C) and phytoplankton richness (surface chlorophyll 'a' concentrations are always greater than 4 mg/m-3). Finally, the paper deals with trophic relationships between phyto- and zooplankton (ingestion /primary production ratio and transfer coefficient) and the question of relationships between zooplankton and predators.

Estudo fenotípico da região Aorta-Gônada-Mesonefros, de embriões de galinhas Gallus gallus domesticus, com ênfase na aorta dorsal

Acredita-se que os primeiros progenitores da hematopoese definitiva surjam da diferenciação do endotélio da aorta dorsal, na altura da região da Aorta-Gônada-Mesonefros (AGM). Com o intuito de estudar esta região e o fenótipo das células do endotélio da aorta dorsal nesta posição topográfica, ovos galados de Gallus gallus domesticus L. foram incubados em chocadeira, classificados em estádios de E16 a E25 e processados histotecnologicamente para obtenção de secções seriadas na altura da região AGM. Estas passaram por coloração por Hematoxilina-Eosina, histoquímica para PAS, PAS-diastase e Alcian Blue pH 1.0 e pH 2.5, histoquímica por lectinas fluoresceinadas e imunofluorescência para moléculas de superfície, citoesqueleto e matriz extracelular. Foi observada hipertrofia endotelial no assoalho da aorta nos estádios observados, o qual se apresentava positivo ao PAS, com ocorrência frequente de vacuolizações basais PAS negativas, e o surgimento ocasional de grupamentos celulares intravasculares. Nestes, as células que se destacavam da membrana basal do endotélio expressavam progressivamente mais material PAS positivo, o qual, no entanto, em nenhum momento pareceu se tratar de glicogênio. Em relação às glicosaminoglicanas, notamos a presença predominante de ácido hialurônico por todo o mesênquima da região e em outras estruturas como periferia da notocorda, tubo neural e mesoderma lateral. Ocorreu co-expressão de fibronectina e α-actina de músculo liso em células circunjacentes à aorta, na face ventral do vaso. GFAP e BMP-4 são expressas entre as células do tubo neural e em sua periferia, assim como na notocorda do embrião. As lectinas Abrus precatorius, Lens culinarise Ricinus communis mostraram-se positivas principalmente na região subedotelial do assoalho da aorta nos estádios observados neste trabalho. Bandeiraea simplicifolia exibiu pouca marcação na aorta dorsal e a Arachis hypogeae foi negativa. Outras estruturas da região AGM também expressaram resíduos de açúcares revelados por estas lectinas, tais como: notocorda, tubo neural, mesênquima, intestino primitivo e saco vitelínico. Estes resultados acrescentam elementos morfológicos e bioquímicos ao conhecimento sobre a região AGM de embriões de galinha e sobre o endotélio, possivelmente hemogênico, da aorta dorsal.

The effect of dopants on the twist elastic constant and the rotational viscosity coefficient for nematics

The twist elastic constant, K2, and the rotational viscosity coefficient, γ1, are of importance when the response lime for the in-plane switching mode is studied. Since adding dopants is one technique to improve the response characteristics, the effect of dopants on these physical properties is significant. The effect on K2 and γ1 of adding alkyl(alkoxy) phenylcyclopentenones and alkyl(alkoxy) cyanobiphenyls to the base mixture ZLI-4792 together with their temperature dependence have been investigated using different temperature scales. The reduced temperature scale showed the effect of these dopants on K2 is small. On the other hand, the temperature dependence of γ1 depends on both the absolute temperature scale and the reduced temperature scale. Therefore, it is clear that the choice of temperature scale with which to compare γ1 for different systems raises fundamental questions which way not have a unique answer. 2000 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.

体外分步诱导猕猴胚胎干细胞为肝细胞

采用分阶段诱导方法模拟肝细胞体内发育,建立体外诱导猕猴胚胎干细胞(rhesus monkey embryonic stem cells,rESCs)分化为成熟肝细胞的体系,对研究以ES细胞为基础的临床替代治疗人类晚期肝脏疾病具有重要的意义.将rESCs团块在含有10%FBS的DMEM培养基中悬浮培养11d,形成含有早期内胚层细胞的拟胚体(embryonic bodies,EB)并开始表达早期肝细胞的部分基因或蛋白,将11日龄EB接种至包被有ECM的组织培养皿,分阶段加入aFGF、BMP-4及OSM.经aFGF和BMP-4诱导7～10d后,分化细胞形态变为具有双核的多角形细胞,表达早期和中期肝细胞特异性的蛋白(AFP、ALB及CK18)和基因(AFP、ALB、APOH,G-6-P及TAT),并具有储存糖原的功能.撤除aFGF和BMP-4,添加OSM继续诱导7～10 d,分化的细胞表达成熟肝细胞所特有基因CYP1B1和ADH1C,并具有摄取靛青绿的能力.

S7核糖体蛋白基因序列变异与亚科鱼类的单系性研究

使用分子生物学的方法对亚科鱼类的单系性进行了探讨。通过PCR方法 ,获得了 13种鲤科鱼类S7核糖体蛋白基因第 1内含子序列 ,其中包括 6种亚科鱼类。使用MEGA软件中的Neighbor Joining法和Most Parsimony法分别构建分支系统图。研究结果显示目前所确认的亚科鱼类实际上没有形成单系类群。其中属、波鱼属和低线属位于系统树基部 ,显示出原始性。而由细鲫属、马口鱼属和属构成的类群相对于亚科中的原始种类起源较晚 ,可能和较晚起源的东亚鲤科类群之间有更为密切的关系。

人工饲养鲸类动物的繁殖

介绍多年来对鲸类动物在人工饲养条件下繁殖问题的研究成果 ,包括 :雌雄性生殖器官的组织解剖 ,饲养和采精训练 ,人工饲养条件下的繁殖 ,孕豚护理 ,分娩和幼豚饲养。为推动我国鲸类动物的人工繁殖提供科学资料。

保安湖沉水植物分布的GIS模拟

以 GPS为辅助 ,在保安湖主体湖和桥墩湖进行沉水植物调查。将野外调查数据构建 GIS数据库 ,基于 GIS软件平台 ,运用 Kringing插值法对保安湖沉水植物分布进行模拟。模拟结果清楚地显示出调查时保安湖沉水植物及 4优势种 (金鱼藻 Ceratophyllum demersum L.、穗状狐尾藻 Myriophyllum spicatum L .、微齿眼子菜 Potamogeton maackianus A.Benn.及苦草 Vallisneria spiralis L.)分别在湖中的分布情况。统