Thermoelastic Stresses in SiC Single Crystals Grown by the Physical Vapor Transport Method

A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method. The composite structure of the growing SiC crystal and graphite lid is considered in the model. The thermal expansion match between the crucible lid and SiC crystal is studied for the first time. The influence of thermal stress on the dislocation density and crystal quality is discussed.

Sensitivity improvement by UV-light recording in LiNbO3 : Ce : Cu crystals

Modulated UV light is used to increase the sensitivity of the two-centre holographic recording. Inherent mechanisms of nonvolatile holographic recording in oxidized and reduced crystals are numerically analysed based on solving the two-centre material equations modilied for UV-Iight recording. Experiments verification is performed with an oxidized crystal and a reduced crystal, and the role of UV intensity on the sensitivity is presented.

一种检测光刻机激光干涉仪测量系统非正交性的新方法

提出一种精确检测光刻机激光干涉仪测量系统非正交性的新方法。将对准标记曝光到硅片表面并进行显影;利用光学对准系统测量曝光到硅片上的对准标记理论曝光位置与实际读取位置的偏差;由推导的位置偏差与非正交因子、坐标轴尺度比例、过程引入误差的线性模型,根据最小二乘原理计算出干涉仪测量系统的非正交性。实验结果表明,利用该方法使用同一硅片在不同旋转角下进行测量,干涉仪测量系统非正交因子的测量重复精度优于0.01 μrad,坐标轴尺度比例的测量重复精度优于0.7×10-6。使用不同的硅片进行测量,非正交因子的测量再现性优于

Diode-pumped Q-switched Tm:YAP laser with a pump recycling scheme

We reported on a diode end-pumped AO Q-switched Tm:YAP laser at 1937 nm. The average output power was 3.9 W, with a slope efficiency of 29.4% and optical-optical conversion efficiency of 21.6% at a 5-kHz repetition rate. The temperature dependency of the output power and the pulse width at different repetition rates were investigated in details.

Origin and evolution of new exons in the rodent zinc finger protein 39 gene

The origin of new structures and functions is an important process in evolution. In the past decades, we have obtained some preliminary knowledge of the origin and evolution of new genes. However, as the basic unit of genes, the origin and evolution of exons remain unclear. Because young exons retain the footprints of origination, they can be good materials for studying origin and evolution of new exons. In this paper, we report two young exons in a zinc finger protein gene of rodents. Since they are unique sequences in mouse and rat genome and no homologous sequences were found in the orthologous genes of human and pig, the young exons might originate after the divergence of primates and rodents through exonization of intronic sequences. Strong positive selection was detected in the new exons between mouse and rat, suggesting that these exons have undergone significant functional divergence after the separation of the two species. On the other hand, population genetics data of mouse demonstrate that the new exons have been subject to functional constraint, indicating an important function of the new exons in mouse. Functional analyses suggest that these new exons encode a nuclear localization signal peptide, which may mediate new ways of nuclear protein transport. To our knowledge, this is the first example of the origin and evolution of young exons.

哺乳动物胚胎冷冻技术的研究进展

胚胎冷冻保存已广泛用于胚胎移植、动物克隆以及动物资源保护。此技术的应用需保证胚胎在冷冻—解冻后具有较高的成活率。自从1972年小鼠胚胎冷冻保存获得成功以来,许多学者在简化冷冻程序、缩短冷冻时间等方面进行了深入的研究。文章就胚胎冷冻的原理、保护剂、冷冻方法以及解冻方法等方面进行了综述。

巢湖微囊藻和浮游甲壳动物昼夜垂直迁移的初步研究

2002年10月进行了巢湖微囊藻和几种优势浮游甲壳动物的昼夜垂直变化的研究,结果表明:微囊藻具有明显的昼夜垂直变化现象。白天上层水中的微囊藻密度显著高于下层水中,夜晚逐渐下沉使得下层水中的密度相对高于上层水。微囊藻与叶绿素a、水温、溶解氧和pH等均呈显著的正相关(p<0.01)。几种优势浮游甲壳动物的昼夜垂直迁移存在较大的差异。短尾秀体溞和角突网纹溞白天在下层水(1.5m和2.5m)中的密度较高,夜晚则倾向于在上层水(0m和0.5m)中活动。相反,卵形盘肠溞白天在上层水中密度较高,象鼻溞则在11:00和1

The molecular characterization of RNA segment S9 of grass carp hemorrhage virus (GCHV), an aquareovirus

Although reovirus infection is one of the major virus diseases of grass carp in China, the available knowledge on the structure and function of genes and proteins of the virus is limited. The complete sequence of the S9 genome segment of grass carp hemorrhage virus (GCHV) was determined. The segment consists of 1130 nucleotides and has a large open reading frame (ORF) encoding a protein of 352 amino acids with predicted molecular mass of 37.7 kDa. Amino acid sequence comparison revealed that the deduced protein encoded by GCHV S9 is closely related to the sigma NS proteins of mammalian reovirus (MRV) and avian reovirus (ARV). Secondary structure analysis displayed that the form of alpha -helices (40.1%) and beta -sheets (49.4%) are the richest two contents in the protein encoded by S9, and this protein is predicted to be a nonstructural protein. (C) 2001 Elsevier Science B.V. All rights reserved.

On a Certain Algebraic Property of Block Ciphers

This is a study on a certain group theoretic property of the set of encryption functions of a block cipher. We have shown how to construct a subset which has this property in a given symmetric group by a computer algebra software GAP4.2 (Groups, Algorithms, and Programming, Version 4.2). These observations on group structures of block ciphers suggest us that we may be able to set a trapdoor based on meet-in-the-middle attack on block ciphers.

一种多信任域内的直接匿名证明方案

针对可信计算平台的原始直接匿名证明方案在多信任域的环境下存在的不足,提出了一种多信任域内的直接匿名证明方案.该方案扩展了原始的直接匿名证明方案,解决了可信计算平台在多信任域内的隐私性保护问题.利用理想系统/现实系统模型对该方案进行了安全性的分析和证明.分析表明,该方案满足匿名性和不可伪造性.最后分析方案的计算性能,实验验证了方案的有效性和可行性.

稀土(III)及铜(II)、锌(II)有机磷（膦）酸酯配合物的晶体结构和振动光谱研究

本文包括标题配合物的结构和振动光谱两部分，共涉及了M(DMP)_n {n=2.3, M=2a, Nd, Cu. Zn}, Ln(DPP)_3{2n=2a-2u, Y}和Ln(BBP)_3 {Ln=La-Lu. Y}三类三十四个配合物。在结构方面，首次测定了Zn(DMP)_2和Cu(DMP)_2呈现出链状配位高聚结构，而La(DMP)_3, La(DMP)_3则为平面网状配位高聚结构。在Zn(DMP)_2, La(DMP)_3和Nd(DMP)_3中，配体以对称“O－P－O”桥键与金属原子配位，在相邻金属原子间形成双桥键。在Zn(DMP)_2中，每个Zn原子通过“O－P－O”双桥键与另两个Zn原子连接，Zn原子配位数为4，配位多面体为四面体构型；在La(DMP)_3和Nd(DMP)_3中，每个稀土原子通过“O－P－O”双桥键与另外三个稀土原子相连接，稀土原子的配位数为6，配位多面体LnO_6为八面体构型。在Cu(DMP)_3中， 配体以对称和非对称“O－P－O”桥键两种形式存在，其中非对称配位的配体形成为“Cu-O-P_O-Cu"-Cu，在铜原之间形成了一个单氧桥键。每个Cu原子通过双“O－P－O”桥键以及双单氧原子桥键与另外三个Cu原子相连接，Cu原子配位数为5，配位多面体为四角锥构型。在振动光谱方面，得到了上述配合物较为完整的光谱数据，并对主要光谱带进行了归属，如V_(M-O), V_(PO_2), V_(P-O(c)),VC-O, VP-C及σ_PO_2等。在稀土配合物中，稀土配位键的伸缩振动V_(vn-o)位于250cm~(-1)附近。V_(Cu)和V_(Zn-o)，在Cu(DMP)_2和Zn(DMP)_2中，分别为(412cm~(-1), 370cm~(-1))和(393cm~(-1), 386cm~(-1))。V_(as)PO_2和V_sPO_2，在配合物振动光谱中，分别在1130－1249cm~(-1)区和1084－1156cm~(-1)区。在稀土配合物中，VL_(n-o), V_(as)PO_2频率值，随镧系收缩逐渐递增。在Cu(DMP)_2红外谱中，非对称配体和对称配体的V_(as)PO_2和V_sPO_2, 分别为(1249cm~(-1)，1156cm~(-1))及(1177cm~(-1)，1090cm~(-1))，其劈裂值△V(V_(as)PO_2-V_sPO_2)为93cm~(-1)和87cm~(-1)。通过对配合物的常温和低温红外光谱的比较，确认了La(DMP)3和Nd(DMP)_3的176cm~(-1)、Ln(DPP)_3和Ln(BBP)_3的150cm~(-1)附近吸收为晶格振动。Ln(DPP)_3、Ln(BBP_3)的光谱性质与Ln(DMP)_3相似，我们认为它们之间具有相同的骨架结构－平面网状配位高聚结构。

紫外光直写杂化溶胶-凝胶SiO_2光波导器件

利用有机/无机杂化方法制备了光敏性溶胶-凝胶(sol-gel)SiO_2材料,在硅基片上旋涂成膜.研究了薄膜折射率和厚度随紫外曝光时间、后烘温度及时间等外界工艺条件的变化关系.利用紫外光直写技术,制作出1×2,1×4多模干涉(MMI)型分束器,并且观测到了分光效果较好的近场输出图像.