Resonant diffraction radiation from inclined gratings and bunch length measurements

A simple scheme for the measurement of sub-mm bunch lengths using coherent resonant diffraction radiation (CRDR) from a tilted grating is proposed. The CRDR spectral-angular characteristics have been calculated using an adapted Kirchhoff model, taking into account the pre-wave zone effect. It is shown that the latter leads to a distortion of the CRDR monochromaticity. Choosing the appropriate distance between grating and detector such that the pre-wave zone effect becomes negligible, it is possible to measure the CRDR yield in the sub-THz range by a broadband detector. While changing the grating inclination angle with respect to the beam axis, the CRDR line is shifted and it is possible to obtain information about the bunch length, measuring the signal ratio from two detectors located at fixed observation angles instead of complicated spectral measurements which rely on absolute values of the intensity.     

Local field effect in diffraction radiation from a periodical system of dielectric spheres

We present a theory of diffraction radiation from a two-dimensional system that consists of small spherical particles on a metal substrate. The interaction between a moving charge and single particles is described in the frames of local field theory. The local field effects are proved to lead to a sharp increase of the radiation intensity at certain frequencies, similar to the effect of giant Raman scattering. The case of nanoparticles is explored and it is shown that the possible enhancement of radiation can reach some thousands of times in the THz range. The Smith-Purcell effect is investigated for the case when the system of particles is periodically arranged.     

水平受荷桩非线性m法研究

大量试验表明,水平荷载作用的单桩的m值随桩身泥面位移增大逐渐减小,然而现有相关规范没有给出大位移情况下m值的取值范围和选取方法,这对于实际工程设计的参数选择造成了一定困难。在大量的桩基水平静载荷试验实测资料的基础上,采用数理统计的方法建立了不同土质条件下土体的m值与桩身泥面位移的相互关系式,可用来计算水平推力桩在大位移情况下的m值,算例表明该方法具有较可靠的精度和较强的实用性。     

浅谈中小户型的设计

针对有关方面提出的“90m^2及以下住房比重要达到新建项目的70％,中小户型将成为市场的主流”这一实际问题,介绍了小面积住宅套型设计的历史,并通过对住宅使用空间的分析,探讨了中小户型的设计原理和方法,进而解决了小面积住宅套型设计的一些问题,说明中小户型住宅一般说来是可行的。     

薄壁高墩连续梁移动模架法设计与施工

介绍了扬中夹江二桥引桥40 m跨等高预应力混凝土连续梁的设计与施工情况,重点介绍了移动模架造桥机在薄壁高墩连续梁结构中的成功应用,指出该工程使用的移动模架造桥机具有承载力大、滑移方便等优点,确保了施工进度,值得推广应用。     

三峡船闸四级运行方式优化研究

针对三峡船闸在四级运行方式下,二闸室充水过程中一闸室待闸条件不佳和充水时间超过设计允许值的问题,采用在二闸室充水前关闭一闸首人字门+快速开启阀门的运行方式,并在原型上进行了调试优化.水力学观测、实船试验及分析表明,这一运行方式从根本上改善了一闸室的待闸条件,显著提高了船舶待闸的安全性,并使一、二闸室充水时间缩短到与后续闸室一致,满足了不大于12 min的设计要求,彻底改变了四级运行方式下二闸室充水过程成为延长船舶过闸时间关键的现状,可使日通过闸次由一闸室不待闸的13～14.5次提高到18.7～22.1次.     

300 m级超高土质心墙坝的长期变形特性研究

 目前国内即将列项修建的 300 m 级高土质心墙坝,在高应力状态下,坝料的长期变形特性对坝体的沉降影响大。为研究 300 m 级超高土质心墙坝的长期变形特性,采用长江科学院九参数幂级数流变本构模型及其试验参数,对 300 m 级高土质心墙坝填筑过程及流变过程进行数值模拟。计算得到的流变位移约为 47 cm 左右,考虑了流变后的变形会更真实反映实际坝体的运行状况。     

Performance of wireless multihop communications systems with cooperative diversity over fading channels

We present closed‐form bounds for the performance of wireless multihop communications systems with cooperative diversity over Nakagami‐m fading channels. The end‐to‐end signal‐to‐noise ratio is formulated and upper bounded by using the inequality between harmonic and geometric means of positive random variables. Closed‐form expression is derived for the moment‐generating function and is used to obtain lower bounds for the average error probability. Numerical results are compared with computer simulations showing the tightness of the proposed bounds. Copyright © 2007 John Wiley & Sons, Ltd.     

双排桩丁坝在涌潮作用下的内力测试和分析

基于现场测试的成果,利用常数法、m法和编制的有限元程序对实际工况进行计算比较,研究分析了双排桩丁坝在涌潮作用下的受力机理.由于前排桩和后排桩的受荷模式不同、刚度不同,从而桩头弯矩不同.测试结果和理论分析表明,双排桩丁坝的桩体约束条件介于桩头自由和桩头固接之间,常数法和m法的计算都基于桩头完全固接的假设,其计算结果与实际情况相差较大,而有限元法计算假设较少,计算结果与实测值吻合较好.     

HY沸石催化合成2-叔丁基-5-甲基苯酚

以HY沸石为催化剂,在固定床反应器中,进行间甲酚与叔丁醇的烷基化反应合成2-叔丁基-5-甲基苯酚的实验。考察了反应温度、液态空速、间甲酚与叔丁醇投料摩尔比对HY沸石催化性能的影响,并考察了催化剂的稳定性。实验结果表明,HY沸石在相对低的反应温度下表现出高活性、高选择性及稳定性,有潜在的应用价值。