Helix packing in membrane proteins

A survey of 45 transmembrane (TM) helices and 88 helix packing interactions in three independent transmembrane protein structures reveals the following features. (1) Helix lengths range from 14 to 36 residues with an average length of 26.4 residues. There is a preference for lengths greater than 20 residues. (2) The helices are tilted with respect to the bilayer normal by an average of 21 degrees, but there is a decided preference for smaller tilt angles. (3) The distribution of helix packing angles is very different than for soluble proteins. The most common packing angles for TM helices are centered around +20 degrees while for soluble proteins packing angles of around -35 degrees are the most prevalent. (4) The average distance of closest approach is 9.6 A, which is the same as soluble proteins. (5) There is no preference for the positioning of the point of closest approach along the length of the helices. (6) It is almost a rule that TM helices pack against neighbors in the sequence. Of the 37 helices that have a sequence neighbor, 36 of them are in significant contact with a neighbor. (7) An antiparallel orientation is more prevalent than a parallel orientation and antiparallel interactions are more intimate on average. The general features of helix bundle membrane protein architecture described in this survey should prove useful in the modeling of helix bundle transmembrane proteins.     

材质对蜂窝纸板缓冲性能的影响

对两种不同材质的蜂窝纸板静态应力应变性能和动态缓冲结果进行了比较分析。讨论了蜂窝纸板力学性能对应变速度的敏感性及两种纸板的缓冲性能差异。缓冲试验结果表明。在不同的冲击应变率下蜂窝纸板的材质影响蜂窝纸板缓冲性能。     

固井水泥环缺陷对套管强度影响仿真分析

固井水泥环质量对套管的强度影响很大。建立了水泥环缺少1／12的井筒平面应变有限元模型，通过对固井水泥环缺陷引起的套管应力变化进行仿真模拟分析，得出无内压下套管的最大径向位移是水泥环完整时的3．9倍，水泥环的缺少导致Mises应力集中系数为2．0，套管外壁的最大塑性应变达到0．0152，定量分析固井质量对套管强度的影响，为热采井套管损坏提供一些定量数据。     

无线移动自组网络的动态源路由策略

文章介绍无线移动自组网中动态源路由策略的路由发现和路由维护,并提出改进思路和今后研究的方向。     

液氮温区同轴脉冲管制冷机的实验研究

脉冲管制冷机冷头朝上布置可以使制冷机与超导器件的耦合更方便 ,但对G -M型脉冲管制冷机 ,重力会对这种布置方式产生不利影响。对双向进气型脉冲管制冷机 ,直流和耦合传热会共同影响脉冲管制冷机的性能。介绍了液氮温区G -M型同轴脉冲管制冷机的实验结果 ,主要研究了蓄冷器温度分布和重力对脉冲管制冷机性能的影响     

ECAP细化晶粒法的仿真与分析

ECAP(Equal Channel Angular Extrusion)方法，是实现材料纯剪切变形的有效方法。本文采用有限元（FEA）分析软件ANSYS对Al的挤压过程进行仿真与分析。分析结果表明：外切角Φ、圆角半径、试样与凹模之间的摩擦系数、凹模本身的特性（如弹性模量、泊松比等）等等，对材料的变形量都有不同程度的影响。     

The Research of ST-OFDM in Physical Layer of IEEE 802.16a

This paper briefly introduces one of the three physical layer implementations of IEEE 802.16a~[1],WirelessMAN-OFDM PHY.Based on the implementation,the combination of Orthogonal Frequency Division Multiplexing(OFDM)and Space-Time Coding(STC)which is briefly called ST-OFDM in IEEE 802.16a,is investigated under thechannel provided in Ref.[2].Especially,this paper is focused on the influence of the optimal decision threshold on the sys-tern Bit-Error-Rate(BER)performance based on unequal probabilities of sources.The simulations show that when Signal-Noise-Ratio(SNR)is low the optimal decision threshold is obviously superior to the usual one;when SNR is high to someextent,such as 10 dB for 4QAM and 16 dB for 16QAM,we can use the usual decision threshold instead of the optimal     

从会计信息的质量特征看财务报告的改进

基于财务报告目标的实现，首先分析了会计信息的两大质量特征——可靠性与相关性。然后对传统财务报告模式的改进提出了看法：不断健全法制以提高可靠性；财务报告后增加预测性财务报表；提供更加丰富的报表附注内容等，目的是为报表使用者做决策提供相关性更强的信息。最后，针对报告的这些改进可能遇到的障碍及如何应对进行了探索和思考。     

二高炉4号热风炉烘炉实践

介绍了二高炉4号热风炉烘炉的特点、前期准备工作、具体操作过程中的注意事项及烘炉后的相关作业。此次生产实践对今后类似情况的热风炉烘炉具有参考价值。     

永久式防倒灌隔水采油工艺在长庆油田的应用

长庆油田存在严重的套管腐蚀损坏,采取的主要治理措施是隔水采油工艺技术。原有隔水采油工艺存在隔采周期短、检泵时水层倒灌污染油层、多次隔采后坐封难度大等问题,为此,试验应用了永久式防倒灌隔水采油工艺。现场试验、应用表明,该工艺具有隔采成功率高、隔采周期长等优点,能有效防止检泵时上部水层倒灌污染油层,具有很好的应用价值和推广前景。