Normal-mode analysis suggests important flexibility between the two N-terminal domains of CD4 and supports the hypothesis of a conformational change in CD4 upon HIV binding

Human CD4 is the receptor for human immunodeficiency virus (HTV).It is well established that the first domain of CD4 binds withhigh affinity to gp120, an envelope protein of HIV, but it hasalso been demonstrated that amino acids located in its seconddomain, within or close to residues 120–127 or 163–166(lying 15 Å away from the binding site), play a role invirus infectivity. We show here that these two stretches ofamino acids happen to be important for the largest amplitudemotion obtained with the normal-mode theory for the two N-terminaldomains of human CD4: an overall rigid-body displacement ofone domain with respect to the other. Such a ‘hinge-bending’motion is unexpected since these two domains were found by crystallographersto be tightly abutting. On the other hand, since for severalproteins the hinge-bending motion experimentally observed uponligand binding was found to be similar to the largest amplitudemotion obtained with the normal-mode theory for these proteins,our results suggest that CD4 may undergo such a kind of conformationalchange upon HTV binding.     

Acoustic determination of ideal-gas heat capacity and second virial coefficients of some refrigerants between 250 and 420 K

An apparatus for speed-of-sound measurements with a spherical resonator was adapted for temperatures up to 42(I K. This included new microphones with a special wiring, a pressure indicator which can be thermostatted to 420 K, and some installations to avoid temperature gradients. Calibration of the radius of the resonator with argon was extended to higher temperatures. Speed-of-sound measurements up to 420 K and 0.5 MPa were done onl,l-dilluoroethane (R152a). 1.l,l-trilluoroethane (R 143a ),l,l,l-chlorodifluoroethane (R 142b ), l,1,1,2-tetralluoroethane (R134a), and 2.2.2-trifluoroethanol. The ideal-gas heat capacities coincide with the statistical mechanical values, except for R134a, where our values as well as recent literature data are below the values calculated from spectroscopy. The reduced second virial coefficients can be interpreted in terms of the dipole moment and the angle between dipole moment and molecular axis. For the associated substance trifluoroethanol values of the third virial coefficient are given, which are appreciably negative at low temperatures.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994 Boulder, Colorado, U.S.A.     

带中吊杆下承式系杆拱桥稳定性研究

带中吊杆的下承式系杆拱桥存在着稳定方面的脆弱性。对京津二通道某带中吊杆下承式系杆拱桥进行了成桥状态稳定性分析。介绍了恒载和活载作用下的第一类稳定分析和第二类稳定分析,并进行了对比。通过分析说明,在实际工程中,材料非线性和几何非线性等非线性因素的影响是很大的。由此得出该类型桥梁稳定问题主要体现在横撑和拱肋上的结论,具有参考意义。     

空间钢框架几何非线性分析的一种新单元

介绍了一种新的用于空间钢框架几何非线性分析用的单元,可有效考虑P-δ效应的影响,达到了一个单元模拟一根杆件的精度要求,用于非线性分析是行之有效的,并可使截断误差的影响得到满意的控制,计算实例证明,该单元是可靠和高效率的。     

Properties of second harmonic generation in nonlinear optical crystals CsLiB_6O_(10) and K_2Al_2B_2O_7

1 Introduction In recent years short wavelength coherent radiation lying in th blue and UV range has attracted wide attention for a variety o applications, including laser printing, undersea communicatio etc. In view of this, several studies of nonlinear-…     

Blind Multiuser Channel Identification Based on Rate Doubling and Modulation-Induced Cyclostationarity

1　IntroductionInthemultiuseruplink ,eachuser’ssignalgoesthroughitschanneltothebasestationreceiver,wherethechannelhastobeidentifiedinordertoperformmultiuserdetection .Mostofthemultiuserdetectorsarelinear,includingZeroForcing (ZF)andMinimumMeanSquareError (MMSE)detec tors.Andtheyalldependontheestimationofthemultiuserchannels.Thetraditionalwayofestimat ingchannelsisbytraining .Buttheblindestimationofchannelsareadvantageous;besidesthefactthatitmaysaveagreatdealofbandwidth ,therearesitua ti…     

静电摇摆器自由电子激光器的高次谐波分析

讨论了一种静电摇摆器中电子的自发辐射谱和高次谐波的增益 ,其形式与平面磁摇摆器中的类似。这种静电摇摆器可由等离子体流波纹产生。当存在轴向静电力时 ,高次谐波就可能产生     

A New equation of state for square-well molecules

This paper presents a new equation of state for the square-well fluid based on perturbation theory. This equation has the exact second virial coefficient behavior, converges to the correct mean-field behavior at high densities, and accurately interpolates between the two limits. Monte Carlo simulations were performed to evaluate the limiting behavior of the theory in the dilute-gas regime. Comparison of the theory with the simulation results shows excellent agreement between the equation-of-state predictions and the data.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

位相畸变三次谐波转换

研究了KDP晶体TypeⅠ /TypeⅡ角度匹配的三倍频方案中 ,离散效应和基波位相畸变对三次谐波的影响。重点考虑了位相畸变所带来的在光束全口径上e光折射率以及相位失配等的变化 ,分析了功率密度分布为超高斯型且具有Zernike多项式表述的各阶像差的光束的三次谐波转换过程 ,得到了不同像差对三次谐波横向光功率密度分布的影响以及转换效率变化曲线。     

采用外调制方式产生5 Gbit/s的非归零码光脉冲

采用外调制方式得到了重复频率为５ＧＨｚ的非归零码光脉冲。采用二次谐波强度自相关法测量了光脉冲。对实验中的关键技术进行了理论和实验研究。