含孔洞和裂纹压电板问题的研究

压电陶瓷因具有良好的压电性而被广泛应用于智能结构。在工作状态下，由力或电载荷引起的应力或电位移的集中会导致压电元件的力电失效。本论文对压电陶瓷板的力电集中和断裂问题进行探讨。首次应用Rei ssner理论对含孔、裂纹压电板的弯曲问题进行了研究，得出了孔边和裂纹尖端场的力电分布形式；应用半权函数方法分析计算含裂纹压电板应力强度因子。全文包括以下几部分：（一）含孔压电板的弯曲基于Reissner板理论，结合有限元法和解析法研究含孔压电板的力电集中问题。给出了上下表面电源短路、含孔压电板方程的通解。计算了含圆孔无穷大压电板受纯弯曲作用的力电集中问题。结果表明：1）压电效应对面内弯曲正应力的影响很小，可忽略不计。2）压电效应对剪应力影响较大，切向电场强度和电位移的集中程度随径厚比变化趋势和切向剪力的变化趋势相同。3）中面上孔边电势和垂直于板中面的电场强度的集中程度随径厚比的减小而减弱，垂直于中面的电位移的集中程度随着径厚比的减小而增强。（二）含裂纹压电板的拉伸和弯曲（极化轴垂直于板的中面）用双重级数展开方法给出了基于Reissner板理论压电板的裂纹尖端奇异场。研究得出：垂直于板面的电场强度不奇异，但是电位移是奇异的；在裂纹尖端的奇异场里，板面内弯曲应力与电场无关，同时面内电位移奇异且只与剪力有关，垂直于板面的电位移与弯曲应力有关。计算了受纯弯矩作用含中心裂纹的压电矩形板，并与非压电材料板情况进行了比较，结果表明：压电效应对应力强度因子影响不大，可以忽略不计，因此可以用含裂纹的各向同性非压电板计算应力强度因子，并得出垂直于板面的电位移。（三）含裂纹压电板的拉伸和弯曲（极化轴平行于板的中面）基于Reissner板理论，分析了含裂纹且极化轴平行于板中面的压电板拉伸和弯曲问题。研究表明，当板的上下表面没有剪力和电荷载，只在板边加电荷载和力的情况下，此问题可以分解为压电材料的平面应力断裂和各向异性板的弯曲断裂问题。对于含裂纹压电材料的平面应力问题，利用Stroh理论导出压电材料平面问题尖端场Wiiliams形式的展开式。计算了有限压电板含中心裂纹受纯弯曲和板边加电荷载作用的断裂问题。得出以下结论：各向异性板受纯弯曲作用时，由线性压电材料的本构关系可以得出电位移的奇异性；整个问题电位移奇异性是由受电荷载作用的平面应力问题和受纯弯曲作用的各向异性板弯曲问题各自引起的电位移奇异性的叠加。（四）计算含裂纹压电板应力强度因子的半权函数法本文对含裂纹压电板的应力强度因子计算都采用了半权函数法。由功能互等定理导出用半权函数和积分围道裂纹尖端的参考场所表示的所研究情况的应力强度因子的表达式。对多种情况进行了计算，并与相关结果进行了比较，结果表明：此方法需要的单元少，精度高，实用性好。利用本文方法对实际应用中出现的有限尺寸压电介质断裂问题进行分析，为压电元件的力电祸合性态研究及其可靠性预测提供理论依据。

滇西北地区冬虫夏草和阔孢虫草的遗传分化研究

应用随机扩增多态性DNA(RAPD)技术对来自云南西北部高黎贡山和丽江玉龙雪山的6个冬虫夏草Cordyceps sinensis (Berk.) Sacc.,来自德钦地区三个地方的8个阔孢虫草C. crassispora Zang,Yang et Li以及来自云南昆明的一个蛹虫草C. militaris (Vuill) Fr.进行分析。18个随机引物获得的RAPD谱带清晰并呈现多态。遗传距离分析表明,冬虫夏草/阔孢虫草与蛹虫草之间存在显著的遗传差异。

Proteomic detection of changes in protein expression induced by cordycepin in human hepatocellular carcinoma BEL-7402 cells

The nucleoside analogue cordycepin (3'-deoxyodenosine, 3'-dA), one of the components of cordyceps militaris, has been shown to inhibit the growth of various tumor cells. However, the probable mechanism is still obscure. In this study, the inhibition of cell growth and changes in protein expression induced by cordycepin were investigated in BEL-7402 cells. Using the MTT assay and flow cytometry, we found that cordycepin inhibits cell viability and induces apoptosis in BEL 7402 cells. Additionally. the proteins were separated using two-dimensional polyacrylamide gel electrophoresis, and eight proteins were found to be significantly, affected by cordycepin compared to untreated control; among them, two were downregulated and six were upregulated. Of the eight proteins, six were identified with peptide mass fingerprinting using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) after in-gel trypsin digestion. These proteins are involved in various aspects of cellular metabolism. It is suggested that the effect of cordycepin on the growth of tumor cells is significantly related to the metabolism-associated protein expression induced by cordycepin. Copyright 2008 Prous Science, S.A.U. or its licensors. All rights reserved.

Effects of temperature on CO2 exchange between the atmosphere and an alpine meadow

The alpine meadow ecosystem on the Qinghai-Tibetan Plateau is characterized by low temperatures because of its high elevation. The low-temperature environment may limit both ecosystem photosynthetic CO2 uptake and ecosystem respiration, and thus affect the net ecosystem CO2 exchange (NEE). We clarified the low-temperature constraint on photosynthesis and respiration in an alpine meadow ecosystem on the northern edge of the plateau using flux measurements obtained by the eddy covariance technique in two growing seasons. When we compared NEE during the two periods, during which the leaf area index and other environmental parameters were similar but the mean temperature differed, we found that NEE from 9 August to 10 September 2001, when the average temperature was low, was greater than that during the same period in 2002, when the average temperature was high, but the ecosystem gross primary production was similar during the two periods. Further analysis showed that ecosystem respiration was significantly higher in 2002 than in 2001 during the study period, as estimated from the relationship between temperature and nighttime ecosystem respiration. The results suggest that low temperature controlled the NEE mainly through its influence on ecosystem respiration. The annual NEE, estimated from 15 January 2002 to 14 January 2003, was about 290 g CO2 m(-2) year(-1). The optimum temperature for ecosystem NEE under light-saturated conditions was estimated to be around 15 degrees C.

CO2 fluxes of alpine shrubland ecosystem on the north-eastern Tibetan plateau

We measured ecosystem CO2 fluxes for an alpine shrubland on the north-eastern Tibetan Plateau, Qinghai, China. The study is to understand (1) the seasonal variation of CO2 flux and (2) how environmental factors affect the seasonality of CO2 exchange in the alpine ecosystem. Daytime ecosystem respiration was extrapolated from the relationship between temperature and nighttime CO2 fluxes under high turbulent conditions.Seasonal patterns of gross ecosystem production, ecosystem respiration and net ecosystem CO2 exchange followed highly the seasonal change of aboveground biomass in the alpine shrubland. The net ecosystem CO2 exchange was mainly controlled by the variation of photosynthetic photon flux density, while the ecosystem respiration was closely correlated to the soil temperature at 5-cm depth. Integrated values of gross ecosystem production, ecosystem respiration and net ecosystem CO2 exchange for the period from November 1, 2002 to October 31 2003 were estimated to be 1418, 1155 and 222 g CO2 m(-2) yr(-1), respectively.