REHEATING TEMPERATURE CONTRAST AND MICROSTRUCTURES OF 7075 Al ALLOY CAST BY LIQUIDUS SEMI-CONTINUOUS CASTING

In this study, reheating of liquidus semi-continuous cast billets of 7075 Al alloy was carried out in a resistance furnace, and the temperature contrast of the outer and the center of the reheated billets was investigated, then the reheating microstructures were investigated. Results show that: the difference of temperature between the outer and center is small and the difference of their microstructures are also small. During reheating at 576℃ the spheroidization of grains is significant after 5min and no rosettes are visible after 20min by optical microscopy. Similar observations were madeon materials reheated at 596℃, but the ripening process is faster. The grains growup to 30-60μm, fine enough for thixoforming.     

采用轴径向技术有效解决固定床反应器阻力降的快速升高

讨论了固定床反应器阻力降快速升高的原因，介绍了用轴径向技术解决这一问题的原理及优点，及其在铁铬系变换催化剂和钴钼系耐硫变换催化剂反应器中的实际应用。     

VTI介质中弹性参数地震反演方法

根据地震波在具有垂直对称轴的横向各向同性（VTI）介质中的运动学特征，应用传播时间反演方法，进行了水平层状VTI介质的地层弹性参数反演方法研究。在VTI介质中，P－P波的传播时间曲线不再是双曲线，尤其在长排列情况下，已不能用二项泰勒展式精确地反演P－P波的传播时间，用三项泰勒展式则可以达到更高精度；P－SV波的传播时间也可用三项泰勒展式表达，在中等及短排列长度时可达到一定精神。对P－P波、P－SV波的传播时间进行三项泰勒展开时，它们的系数中包含了地震波的各向异性信息及垂直速度信息，中以为地震波的弹性参数反演提供提供基础，模试验分析及江苏油田某地区的二维多波资料实际反演结果表明，在最大炮间距为1．5倍地层埋深时，可以很精确地得到三项泰勒展式的系数，应用这些系数能精确反演地层弹性参数，包括P波、S波的垂直速度和各向异性参数。图4表1参5（杜丽英摘）     

DC-DC变换器突加负载时的动态性能研究

提出了一种能够有效改善DC-DC变换器动态性能的方案。该方案是在全桥电路基础上并联一单端正激变换电路，使变换器负载从10%轻载突加到100%满载时，其暂态过程小于1μs输出电压达到设计要求。文中对具体电路进行了详细分析，并通过仿真进行了验证。     

填充料细度对水工沥青混凝土性能的影响

近年来沥青混凝土作为防渗材料，在我国水工建筑中得到了广泛应用。与道路工程的沥青混凝土不同的是，水工沥青混凝土具有良好的粘弹性及抗渗性。目前，国家规范对填充料的细度尚无明确规定，通过调整沥青混凝土的填充料细工，对沥青混凝土的各项性能进行了系统的试验和分析，研究表明：适宜的填充料细度及掺量，能有效地改善沥青混凝土性能，提高其抗渗性。     

Nonlinear dynamic behavior of stiffened plate under instantaneous loading

The stiffened plate subjected to both geometric and material nonlinearities under instantaneous loading is investigated by a finite element method. The effects of the two nonlinearities on the dynamic behavior of the structure are discussed. The two nonlinearities behave in different ways: the geometric nonlinearity tends to reinforce the structure stiffness owing to the resistance of the membrane forces against the bending deformation and decreases the vibration period and amplitude; while the material one possesses the function of softening the stiffness and increases the vibration period and amplitude. Thus, the dynamic behavior depends on the property of the nonlinearity which the structure experiences.     

The complexity of some reachability problems for a system on a finite group

We consider a system defined as the product of a finite set of periodic systems on cyclic groups. It is of interest to determine if certain subgroups and unions of subgroups of the state set are reachable from a specified initial state, and in particular to determine the computational complexity of verifying such reachability. These questions are motivated by certain problems that arise in the modelling and control of discrete event systems and certain forms of periodic scheduling. Our main result is that deciding whether or not the union of a certain set of subgroups is reachable or not is NP-complete.     

硫脲型整合树脂在分析上的应用 Ⅰ.岩样中微量银的中子活化分析

前言银和其他贵金属元素一样,在地壳中比较稀少,按其自然丰度为第67号元素,平均含量仅0.07 ppm。由于地质样品成分非常复杂,为测定其微量银,必须进行严格的化学分离。但是迄今文献中报道的许多分离分法,步骤都相当冗长,一般采用氯化银反     

Order–disorder phase transition induced by swift ions in MgAl2O4 and ZnAl2O4 spinels

Grazing X-ray diffraction was used to study in details the behaviour of two spinels, ZnAl₂O₄ and MgAl₂O₄ irradiated by swift ions. Such an irradiation allows to have an important irradiated depth and then accurate diffraction diagrams. Rietveld refinement done on these diagrams clearly show an order–disorder transition due to a melting of cations under irradiation in these two spinels. More especially, these results clearly exhibit that no new phase is created under irradiation in MgAl₂O₄. Raman spectroscopy, sensitive to the crystallographic space group, seems to confirm this analysis.     

用于二维非线性静磁场计算的微型计算机程序TRIM／PC

一、引言TRIM是一个相当成熟的解二维非线性静磁问题的计算程序,它在束流光学系统设计中起着越来越重要的作用。最原始的TRIM程序是A.M.Winslow(Lawrence Radi-ation Laboratory,Livermore,California)编写的,后来又经多次修改扩充,并能运行在CDC-6600,IBM-360等中型计算机上。近年来,微型计算机的应用有了很大的发展,IBM-PC/XT或其兼容机在国内已相当普及。在微型机上运行应用软件会更有利于软件的