微梁谐振器中的空气阻尼

为了研究空气阻尼对谐振器工作性能的影响,基于Euler-Bernoulli假设、梁弯曲振动理论和气体阻尼理论,建立了考虑气体阻尼的梁振动方程,结合边界条件对方程进行了求解,得到了两种不同情况下气体阻尼对微梁谐振器的谐振频率和品质因子的影响.通过两种阻尼对谐振器影响的比较分析,指出在梁形状保持不变(长宽比和高宽比不变)情况下,微梁谐振器存在一个临界压膜厚度,此临界厚度可为器件的设计提供参考.

纳米晶Ni疲劳行为的实验研究

系统研究了纳米晶Ni与粗晶Ni的疲劳行为。通过疲劳实验获得了这2种材料的疲劳应力--寿命曲线，并采用AFM对纳米晶Ni样品表面进行观察以研究其裂纹萌生的微观机制，利用纳米压痕仪对疲劳实验前后样品的力学性能和显微组织变化进行了研究。结果表明，纳米晶Ni具有比粗晶Ni更高的疲劳极限。AFM观察表明纳米晶疲劳后样品表面出现平均尺寸为73 nm的胞状起伏，疲劳后样品的晶粒尺寸没有发生明显改变。压痕硬度结果表明疲劳过程材料的力学性能也未发生明显变化。

Attosecond X-ray pulse obtained from linear Thomson scattering

Linear Thomson scattering by a relativistic electron of a short pulse laser has been investigated by computer simulation. Under a laser field with a pulse of 33.3-fs full-width at half-maximum, and the initial energy of an electron of gamma(0) = 10, the motion of the electron is relativistic and generates an ultrashort radiation of 76-as with a photon wave length of 2.5-nm in the backward scattering. The radiation under a high relativistic energy electron has better characteristic than under a low relativistic energy electron in terms of the pulse width and the angular distribution. (c) 2005 Elsevier GrnbH. All rights reserved.

基于电光调制的激光光谱整形技术

提出了一种新型的基于电光调制的激光光谱整形方案，该整形技术可以减轻啁啾脉冲放大系统中的增益窄化效应。傅立叶变换限的宽带种子激光脉冲通过光学展宽器线性展宽后，耦合到加载有整形电脉冲的集成波导调制器中进行整形，整形电脉冲由孔径耦合带状线电脉冲发生器产生。由于线性啁啾脉冲时间-频率的直接对应关系，在时域内对宽带种子激光脉冲整形，其光谱也得到了同样形状的整形。模拟了整形光谱形状，相应的整形电脉冲波形，分析了该整形技术的光谱整形分辨率，以及整形过程中引入的相位畸变。

Zebu Cattle Are an Exclusive Legacy of the South Asia Neolithic

Animal domestication was a major step forward in human prehistory, contributing to the emergence of more complex societies. At the time of the Neolithic transition, zebu cattle (Bos indicus) were probably the most abundant and important domestic livestock species in Southern Asia. Although archaeological evidence points toward the domestication of zebu cattle within the Indian subcontinent, the exact geographic origins and phylogenetic history of zebu cattle remains uncertain. Here, we report evidence from 844 zebu mitochondrial DNA (mtDNA) sequences surveyed from 19 Asiatic countries comprising 8 regional groups, which identify 2 distinct mitochondrial haplogroups, termed I1 and I2. The marked increase in nucleotide diversity (P < 0.001) for both the I1 and I2 haplogroups within the northern part of the Indian subcontinent is consistent with an origin for all domestic zebu in this area. For haplogroup I1, genetic diversity was highest within the Indus Valley among the three hypothesized domestication centers (Indus Valley, Ganges, and South India). These data support the Indus Valley as the most likely center of origin for the I1 haplogroup and a primary center of zebu domestication. However, for the I2 haplogroup, a complex pattern of diversity is detected, preventing the unambiguous pinpointing of the exact place of origin for this zebu maternal lineage. Our findings are discussed with respect to the archaeological record for zebu domestication within the Indian subcontinent.

Rapid and parallel chromosomal number reductions in muntjac deer inferred from mitochondrial DNA phylogeny

Muntjac deer (Muntiacinae, Cervidae) are of great interest in evolutionary studies because of their dramatic chromosome variations and recent discoveries of several new species. In this paper, we analyze the evolution of karyotypes of muntjac deer in the context of a phylogeny which is based on 1,844-bp mitochondrial DNA sequences of seven generally recognized species in the muntjac subfamily. The phylogenetic results support the hypothesis that karyotypic evolution in muntjac deer has proceeded via reduction in diploid number. However, the reduction in number is not always linear, i.e., not strictly following the order: 46-->14/13-->8/9-->6/7. For example, Muntiacus muntjak (2n = 6/7) shares a common ancestor with Muntiacus feae (2n = 13/14), which indicates that its karyotype was derived in parallel with M. feae's from an ancestral karyotype of 2n greater than or equal to 13/14. The newly discovered giant muntjac (Muntiacus vuquangensis) may represent another pa;allel reduction lineage from the ancestral 2n = 46 karyotype. Our phylogenetic results indicate that the giant muntjac is relatively closer to Muntiacus reevesi than to other muntjacs and may be placed in the genus Muntiacus. Analyses of sequence divergence reveal that the rate of change in chromosome number in muntjac deer is one of the fastest in vertebrates. Within the muntjac subfamily, the fastest evolutionary rate is found in the Fea's lineage, in which two species with different karyotypes diverged in around 0.5 Myr.

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.

马氏珠母贝Dmrt5基因的克隆及时序表达模式分析

Dmrt(Double sex and Mab-3 related transcription factor)基因是一类含有高度保守的DM(Double sex and Mab-3)结构域的基因家族,该基因家族的很多成员都参与了性别决定和分化过程的调控。目前已研究了很多物种的Dmrt基因,但对于具有重要进化地位和经济价值的贝类,却鲜见相关报道。Dmrt5作为Dmrt基因家族的重要成员,是否也参与了动物的性别决定与分化的调控,至今为止没有定论。采用RACE-PCR技术,从马氏珠母贝(Pinctadamate

鲫鱼肝脏AChE的提取及有机磷农药对AChE的抑制效应研究

本研究利用淡水鲫鱼肝脏为主要原材料提取乙酰胆碱酯酶(acetylcholinesterase,AChE),并设计正交试验确定了鲫鱼肝脏中乙酰胆碱酯酶的最佳提取条件:通过酶抑制法衡量敌敌畏、辛硫磷、三唑磷、乐果等四种不同种类有机磷农药对粗酶液的抑制作用;将鱼肝和鱼脑中乙酰胆碱酯酶活性及蛋白含量的进行对比研究。研究结果表明:提取液pH值、提取液种类以及原料与提取液的质量体积比对酶液的活性影响显著;被测四种有机磷农药中,敌敌畏对AChE活性抑制作用最强。鱼脑的AChE比酶活是肝脏的AChE比酶活的3～7倍。