空间抛物面状通讯天线振动模态浓缩现象分析

应用摄动理论分析了空间大型抛物面状通讯天线振动模态发生“浓缩”现象的机理．这类天线属于对质量缺陷很敏感的周期对称性结构，这种结构具有高密度（近频）模态，当近频模态发生联合使结构内部振动发生“浓缩”现象时，强烈的振动被“浓缩”到天线结构中某一小区域．研究结果表明，具有大量弱联子结构的天线当其肋架质量存在缺陷后容易激起模态“浓缩”现象．以８肋架天线为计算机模拟计算模型验证了分析结果的正确性．对影响天线结构模态“浓缩”现象的结构参数也作了分析讨论．     

The T cell receptor

The primary structure of T cell receptor proteins and genes is well understood. Immunologists are now trying to understand the properties of these interesting molecules. Evidence suggests that T cell alpha beta receptors recognize a complex of an antigen-derived peptide bound to one of the cell-surface products of the major histocompatibility complex (MHC) genes. It is likely that alpha beta receptors and MHC proteins have coevolved to have some affinity for each other. During T cell development in the thymus, cells bearing self-reactive receptors are deleted by the mechanisms of tolerance, and cells are preferentially allowed to mature if they bear receptors that will be able to recognize antigen plus self-MHC after they have become full-fledged T cells. Some explanations for these phenomena have been tested, but no satisfactory theory can yet be proposed to account for them.     

脉冲掺铒波导激光器研究进展

目前发展的用于脉冲掺铒光波导激光器的技术主要有：调Q技术、半导体饱和吸收镜被动锁模技术以及带尾纤的碳纳米管（CNTs）饱和吸收被动锁模技术。对基于调Q技术的波导嫩光器、基于半导体饱和吸收镜被动锁模技术的波导激光器、带尾纤的碳纳米管（CNTs）饱和吸收被动锁模技术的波导激光器的发展现状以及存在的问题进行了分析研究,并针对目前存在的问题,指出了其发展方向。     

The role of the T cell receptor in positive and negative selection of developing T cells

Although many combinations of alpha beta T cell receptors are available to the T cells in any given organism, far fewer are actually used by mature T cells. The combinations used are limited by two selective processes, positive selection of T cells bearing receptors that will be useful to the host, and clonal elimination or inactivation of T cells bearing receptors that will be damaging to the host. The ways in which these two apparently contradictory processes occur, and the hypotheses that have been suggested to reconcile them, are discussed.     

Chemoreceptors in lepidoptera: stereochemical differentiation of dual receptors for an achiral pheromone

The racemate and optically pure enantiomers of 9-(2-cyclopenten-1yl)nonyl acetate have been synthesized and shown to mimic certain biological properties of (Z)-11-tetradecenyl acetate. European corn borers and red-banded leaf rollers respond differently to the racemate and to the enantiomers in precopulatory behavior bioassay. The responses demonstrate the presence of two stereospecific chemoreceptors, show the chiral character of these receptors, and define the conformation of carbon atoms 10 to 14 of (Z)-11-tetradecenyl acetate in these receptors.     

New perspectives in cell adhesion: RGD and integrins

Rapid progress has been made in the understanding of the molecular interactions that result in cell adhesion. Many adhesive proteins present in extracellular matrices and in the blood contain the tripeptide arginine-glycine-aspartic acid (RGD) as their cell recognition site. These proteins include fibronectin, vitronectin, osteopontin, collagens, thrombospondin, fibrinogen, and von Willebrand factor. The RGD sequences of each of the adhesive proteins are recognized by at least one member of a family of structurally related receptors, integrins, which are heterodimeric proteins with two membrane-spanning subunits. Some of these receptors bind to the RGD sequence of a single adhesion protein only, whereas others recognize groups of them. The conformation of the RGD sequence in the individual proteins may be critical to this recognition specificity. On the cytoplasmic side of the plasma membrane, the receptors connect the extracellular matrix to the cytoskeleton. More than ten proved or suspected RGD-containing adhesion-promoting proteins have already been identified, and the integrin family includes at least as many receptors recognizing these proteins. Together, the adhesion proteins and their receptors constitute a versatile recognition system providing cells with anchorage, traction for migration, and signals for polarity, position, differentiation, and possibly growth.     

Positron emission tomography reveals elevated D2 dopamine receptors in drug-naive schizophrenics

In postmortem studies of patients with schizophrenia, D2 dopamine receptors in the basal ganglia have been observed to be more numerous than in patients with no history of neurological or psychiatric disease. Because most patients with schizophrenia are treated with neuroleptic drugs that block D2 dopamine receptors in the caudate nucleus, it has been suggested that this increase in the number of receptors is a result of adaptation to these drugs rather than a biochemical abnormality intrinsic to schizophrenia. With positron emission tomography (PET), the D2 dopamine receptor density in the caudate nucleus of living human beings was measured in normal volunteers and in two groups of patients with schizophrenia--one group that had never been treated with neuroleptics and another group that had been treated with these drugs. D2 dopamine receptor densities in the caudate nucleus were higher in both groups of patients than in the normal volunteers. Thus, schizophrenia itself is associated with an increase in brain D2 dopamine receptor density.     

3种边界条件下足尺定向刨花板的模态灵敏度和振动模态研究

  目的  研究完全自由、四节点支承和两对边简支3种边界条件下足尺定向刨花板的模态灵敏度和振动模态,为开展3种边界条件下足尺定向刨花板弹性常数振动检测结果的对比研究奠定基础。  方法  以4种厚度的足尺定向刨花板为研究对象,采用有限元软件COMSOL Multiphysics对完全自由、四节点支承和两对边简支的足尺定向刨花板进行了模态灵敏度分析,分别确定这3种边界条件下对其长度和宽度方向的弹性模量与面内剪切模量这3个弹性常数灵敏度最高的模态;通过试验模态分析测得足尺定向刨花板在这3种边界条件下的前9阶振动模态参数,并对比和分析其在这3种边界条件下的振动模态参数检测结果。  结果  计算和试验模态分析得到的这3种边界条件下足尺定向刨花板的前9阶模态振型形状和阶次分别是相同的;足尺定向刨花板在这3种边界条件下的前9阶模态中,除模态（m, 0）、（0, 2）和（1, 1）外,其余模态均为单一方向的弯曲和扭转或不同方向弯曲的叠加模态;用于计算足尺定向刨花板长度和宽度方向的弹性模量与面内剪切模量的最高灵敏度模态,在完全自由下为模态（2, 0）、（0, 2）和（1, 1）,对应阶次分别为第2、4和1阶;在四节点支承下为模态（2, 0）、（0, 2）和（2, 1）,对应阶次分别为第1、4和3阶;在两对边简支下为模态（2, 0）、（2, 2）和（2, 1）,对应阶次分别为第1、5和2阶。  结论  从振型角度说明基于计算模态分析方法和试验模态分析方法分别进行3种边界条件下足尺定向刨花板的模态灵敏度分析和振动模态测试具有可行性。      

高层建筑加强层粘滞阻尼系统的优化分析

提出了一种设加强层的框架-核心筒结构耗能减振系统，利用加强层与外围框架柱二者之间相对大的位移差，布设竖向粘滞阻尼器.基于结构简化计算简图，分别得到了采用假定振型法和有限单元法的数学模型.基于模态阻尼比，参数分析确定了阻尼器的最优阻尼系数.以一个安装了加强层阻尼系统的高层建筑为例，仿真分析了其在地震激励下的动力响应.研究表明，加强层阻尼系统可以大幅提高结构的模态阻尼比，有效减小结构的动力响应.     

虚拟仪器技术在振动测试中的应用

该文介绍了一种使用虚拟仪器(virtual instrument,简称VI)技术进行机械结构模态分析的新方法.利用虚拟仪器开发软件LabVIEW与模态分析软件Star System来完成传统上复杂的机械测试过程.该方法是:通过虚拟仪器开发软件LabVIEW(G语言)编程控制数据采集卡采集数据,生成具有一定数据格式的文件,然后用Star System专业软件对此文件进行分析,最后完成机械结构模态分析过程.该方法使模态分析实验过程得到了简化,降低了设备成本.用此方法对不同的机械结构进行模态分析,与传统测试方法进行比较,结果证明该方法行之有效.     

拼板结构的古筝共鸣面板振动模态研究

  目的  古筝共鸣面板的结构是影响其振动性能的重要因素之一,不同结构的共鸣面板发出的音质与音色会有所差异,迄今很少有学者就拼板古筝共鸣面板的振动发声特点展开研究。  方法  本研究以拼板古筝共鸣面板为研究对象,利用两种模态分析方法探讨其声学振动性能。采用实验模态分析法,运用数字信号处理技术对采集到的激励力信号和振动响应信号进行分析,经过数据转换求得系统的频响函数,进而得出各阶次共振频率及其对应模态振型;采用计算模态分析法,建立拼板结构共鸣面板的三维模型,运用有限元法对其进行离散,通过近似方法求解出各阶次共振频率及其对应模态振型。  结果  实验模态结果显示:拼板共鸣面板能够识别到的阶次有(0, n)和(1, n)阶,且多集中在(0, n)阶,(1, 4)、(1, 6)、(1, 7)和(1, 10)阶为沿横纹理方向和顺纹理方向弯曲振动叠加的复合振动,识别较困难。从振型上看,拼板共鸣面板各阶的模态振型相对清晰易识别。与实验模态结果相比,计算模态分析能够识别到选定阶次范围的所有阶次,所得振型图更加均匀且理想,而实验模态分析时个别阶次较难识别。拼板共鸣面板计算模态结果与实验模态结果呈显著的线性相关性,相关系数为0.999 6。  结论  从模态分析结果来看,相对整板结构,拼板共鸣面板各阶共振频率对应的模态振型整体清晰易识别,振动频率更高;从木材利用率方面来讲,相对于制作整板,拼板共鸣面板更有利于节约木材资源。通过两种模态分析结果综合对比,验证了计算模态分析应用于拼板结构古筝共鸣面板的振动模态研究具有可行性。      

Quinoxalinediones: potent competitive non-NMDA glutamate receptor antagonists

The N-methyl-D-aspartate (NMDA)-subtype of glutamate receptors has been well described as a result of the early appearance of NMDA antagonists, but no potent antagonist for the "non-NMDA" glutamate receptors has been available. Quinoxalinediones have now been found to be potent and competitive antagonists at non-NMDA glutamate receptors. These compounds will be useful in the determination of the structure-activity relations of quisqualate and kainate receptors and the role of such receptors in synaptic transmission in the mammalian brain.     

渡槽模型实测模态合成的研究

分别对渡槽模型的桩及槽墩两部分进行了模态实测.为了能把两个部分的实测结果合成一个整体，并且能在实测中最大限度地减少对桩中已安装传感器的破坏，利用模型的对称性以组合系统的频响特性、结构的位移协调条件，推导出简单易行振型合成方法，实现了对桩模态与槽墩模态的组合.实测组合结果与有限元计算结果基本吻合，从而验证了该方法在实际工程中的可行性.     

Identification of a T3-associated gamma delta T cell receptor on Thy-1+ dendritic epidermal Cell lines

The murine epidermis contains a subpopulation of bone marrow-derived lymphocytes that have a dendritic morphology and that express Thy-1 and T3 cell-surface antigens but not other markers (L3T4 or Lyt-2) characteristic of mature peripheral T lymphocytes. An alternative type of T cell receptor was earlier identified on a subpopulation of murine thymocytes with a similar phenotype (T3+, L3T4-, Lyt-2-), but not on peripheral murine T lymphocytes. Two independently derived Thy-1+, L3T4-, and Lyt-2- dendritic cell lines of epidermal origin that express a T3-associated disulfide-linked heterodimer composed of a 34-kilodalton gamma-chain and 46-kilodalton partner (the delta chain) have now been identified. Analysis of N-linked glycosylation revealed that this receptor is similar to that detected on thymocytes. These results demonstrate that Thy-1+ dendritic epidermal cell lines can express gamma delta T cell receptors in vitro and suggest that Thy-1+ dendritic epidermal cells express such receptors in vivo. The localization of these gamma delta T cell receptor-expressing cells in the epidermis may be of importance for understanding the function of these receptors.     

Trout leukocytes: growth in oxygenated cultures

A reproducible method of culturing leukocytes from rainbow trout (Salmo gairdneri) has been found. Using an atmosphere of 100 percent oxygen, we stimulated peripheral blood leukocytes to divide at 19 degrees C. Cultured cells were used for a karyological study; they had a modal chromosome number of 60 and a constant arm number of 104, a value previously reported for other tissues in these fish.     

Presynaptic kainate receptor mediation of frequency facilitation at hippocampal mossy fiber synapses

Inhibition of transmitter release by presynaptic receptors is widespread in the central nervous system and is typically mediated via metabotropic receptors. In contrast, very little is known about facilitatory receptors, and synaptic activation of a facilitatory autoreceptor has not been established. Here we show that activation of presynaptic kainate receptors can facilitate transmitter release from hippocampal mossy fiber synapses. Synaptic activation of these presumed ionotropic kainate receptors is very fast (<10 ms) and lasts for seconds. Thus, these presynaptic kainate receptors contribute to the short-term plasticity characteristics of mossy fiber synapses, which were previously thought to be an intrinsic property of the synapse.     

Steroid binding at sigma receptors suggests a link between endocrine, nervous, and immune systems

Specific sigma binding sites have been identified in the mammalian brain and lymphoid tissue. In this study, certain gonadal and adrenal steroids, particularly progesterone, were found to inhibit sigma receptor binding in homogenates of brain and spleen. The findings suggest that steroids are naturally occurring ligands for sigma receptors and raise the possibility that these sites mediate some aspects of steroid-induced mental disturbances and alterations in immune functions.     

N-Formylmethionyl peptide receptors on equine leukocytes initiate secretion but not chemotaxis

The chemotaxis of leukocytes appears to be initiated by the binding of chemotactic factors to the surface of these cells. N-Formylated peptides induce chemotaxis and lysosomal enzyme secretion of leukocytes; because these peptides are available in a purified radiolabeled form, they have been useful in the characterization of receptors for chemotactic factors. Equine polymorphonuclear leukocytes secrete lysosomal enzymes but do not exhibit chemotaxis in respone to the N-formylated peptides, even though they have a high-affinity cell surface receptor for these agents. The specificity of the equine receptor resembles the specificity of the receptor on chemotactically responsive leukocytes from other species. Equine polymorphonuclear leukocytes may thus be an excellent model for the study of the events that lead to a biological response following receptor occupancy.     

北京黑猪染色体组型

家猪的染色体组型研究,国内、外皆有报导。其目的是研究家猪的正常染色体组型:进一步探讨猪的遗传性疾患与染色体的关系,以及种族间在遗传结构上的变异。一、材料和方法由于组织培养技术的发展,对于染色体的研究已成为方便易行之事。因为血液中的单核     

Zebrafish Dpr2 inhibits mesoderm induction by promoting degradation of nodal receptors

Nodal proteins, members of the transforming growth factor-beta (TGFbeta) superfamily, have been identified as key endogenous mesoderm inducers in vertebrates. Precise control of Nodal signaling is essential for normal development of embryos. Here, we report that zebrafish dapper2 (dpr2) is expressed in mesoderm precursors during early embryogenesis and is positively regulated by Nodal signals. In vivo functional studies in zebrafish suggest that Dpr2 suppresses mesoderm induction activities of Nodal signaling. Dpr2 is localized in late endosomes, binds to the TGFbeta receptors ALK5 and ALK4, and accelerates lysosomal degradation of these receptors.