CPLD技术及其在现代时统中的应用

对CPLD(复杂可编程逻辑器件)技术的基本特征和发展趋势作了简要介绍,揭示了该技术在现代数字系统中的重要地位及作用.利用CPLD对时统设备IRIG-B码产生器进行集成,其实验结果表明,集成了的B码产生器不但简单、可靠,而且便于调试,克服了以往硬件电路复杂的缺点.     

Numerical prediction of blast‐induced stress wave from large‐scale underground explosion

This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd.     

The Statistical Analysis of Migration of Strong Earthquakes-Taking the North China Region as an Example

The migration of strong earthquakes is an important research topic because the migration phenomena reflect partly the seismic mechanism and involve the prediction of tendency of seismic activity. Research on migration of strong earthquakes has mostly focused on finding the phenomena. Some attempts on getting regularity were comparatively subjective. This paper suggests that there should be indices of migration in earthquake dataset and the indexes should have statistical meaning if there is regularity in the migration of strong earthquakes. In this study, three derivative attributes of migration, i.e., migration orientation, migration distance and migration time interval, were statistically analyzed. Results in the North China region show that the migration of strong earthquakes has statistical meaning. There is a dominant migration orientation (W by S to E by N), a dominant distance (≤100km and on the confines of 300～700km), and a dominant time interval (≤1a and on the confines of 3～4a). The results also show that the migration will differ slightly with different magnitude range or earthquake activity phase.     

Isotopic studies of leaf water. Part 1: A physically based two-dimensional model for pine needles

Understanding of isotopic variations in leaf water is important for reconstruction of paleoclimate and assessment of global biochemical processes. We report here a study of isotopic distributions within a single needle of two pine species, Pinus resinosa Ait and Pinus strobes L., with the objective of understanding how isotopic compositions of leaf water are controlled by environmental and physiological variables. A 2D model was developed to simulate along-leaf isotopic variations and bulk leaf water isotopic compositions. In addition to variables common to all leaf water isotopic models, this 2D model also takes into account the specific geometry and dimensions of pine needles and the isotopic transport in xylem and mesophyll. The model can successfully simulate oxygen isotopic variations along a single needle and averaged over a leaf (bulk leaf water). The simulations suggest that isotopic composition of the bulk leaf water does not always depend only upon the average transpiration rate, which in turn raises questions about using leaf water isotopic values to estimate transpiration rates. An unsuccessful attempt to simulate along-needle hydrogen isotopic variations suggests that certain unknown biological process(es) may not have been incorporated into our 2D model, and if so, it calls for a reevaluation of all other models for hydrogen isotopic simulations of leaf water since they too lack these processes.Existing leaf water isotopic models are reviewed in this work. In particular, we evaluate the most frequently used model, the stomatal boundary layer model (also referred to as the Craig-Gordon model). We point out that discrepancy between the boundary layer model and the measured bulk leaf water seems to depend upon relative humidity. Using our 2D model, we show that this humidity dependency is a result of an interplay between environmental and physiological conditions: if the transpiration rate of plant leaves decreases with increasing relative humidity, our 2D model can reproduce the pattern of isotopic discrepancy between boundary layer model predictions and observations, enabling us to understand better the reason behind this discrepancy.     

藻类分子生物技术两年评─—与藻类活性物质研究有关的生物技术

根据１９９２年６月－１９９４年６月国内外发表资料，评述海洋藻类活性物质研究的生物技术及最新成果。认为，海洋生物活性物质研究的重心正转向与海洋生物技术有关的研究。运用生物技术筛选、提取并生产藻类活性物质已经成为这一领域的主流。综合文献表明，藻类活性物质的生物技术正走向成熟，大量的活性物质被发现，光生物反应器将成为主要的下游生产技术，通过藻类基因工程生产药物已初现端倪。     

从第九届国际光合作用大会看藻类分子遗传学发展趋势

根据１９９２年８月３０日－９月４日在日本名古层如开的第九届国际光合作用大会上交流的以藻类为材料的研究论文，综述了分子遗传学方面的研究成果。认为这些成果体现了光合作用研究的最新进展，蕴含有一定的应用前景；表明类分子遗传学不仅是藻类学研究领域的带头学科，而且已经活跃在光合作用等重大生物学问题研究的前沿；反映了藻类分子遗传学向解决生物学重大问题和推动藻类资料开发方向发展的趋势。     

哀牢山-红河断裂带中段应变分析

对哀牢山—红河断裂带中段和平—水塘剖面、墨江—元江剖面和其它地段的岩石应变及磁组构进行了分析，表明应变强度的校正磁各向异性度PJ从断裂带向西至三叠系明显降低，变形强度向西迅速减弱。磁化率椭球体主轴展布反映出剪切带内、外变形方式的改变。剪切带内，以水平走滑运动为主；向西则以水平缩短为主。在应变分析中，对断裂带内的S—C组构两组面理夹角、杏仁体和石榴石应变标志体进行了测量，结果显示，剪切带内的磁组构和岩石组构间关系较差。此外，还对这两条剖面中的三叠系进行了应变和磁组构分析，找出了它们与磁化率椭球体对应轴率间的相关性。     

城市景观三维重建中的三角剖分算法

在构建城市景观时,为了快速精确地重建建筑物、绿地、河流等三维模型,提高自动化程度,缩短建设周期,需对用户采集的矢量地物数据进行三角剖分,再以OpenGL重绘三维模型。本文提出了一种对多边形进行三角剖分的递归分割算法,并以VisualC++实现,以实际的4万多个建筑物进行三角剖分实验,充分证明其是有效的。