一类广义Hamilton系统的辛格式

通过引人泊松括号，分析了无限维Hamilton的性质，并将其推广到广义Hamilton系统，且从理论和实用角度讨论了这类广义Hamilton系统的辛格式构造问题，从而为辛几何算法在一般的时间发展方程的数值求解提供新的具体途径。     

反扩散格式在二维锋生数值模拟中的应用

把无粘流中能成功捕捉接触间断的反扩散差分格式，用在了准地转二维理想锋生的数值模拟中，并将计算结果与Cullen的计算结果和半地转方程的精确解进行了比较。用反扩散格式模拟的锋面较Cullen的结果更加显，而且更接近半地转方程的精确解。     

A mechanism for decadal changes of ENSO behavior: roles of background wind changes

This study explains why a number of El Nino properties (period, amplitude, structure, and propagation) have changed in a coherent manner since the late 1970s and why these changes had almost concurred with the Pacific decadal climate shift. Evidence is presented to show that from the pre-shift (1961-1975) to the post-shift (1981-1995) epoch, significant changes in the tropical Pacific are found in the surface winds and temperature, whereas changes in the thermocline are uncertain. Numerical experiments with the Cane and Zebiak model demonstrate that the decadal changes in the surface winds qualitatively reproduce the observed coherent changes in El Nino properties. The fundamental factor that altered the model's El Nino is the decadal changes of the background equatorial winds and associated upwelling. The annual cycle is also necessary for the mean state to modulate El Nino. From the pre- to post-shift epoch, the changes in the background winds and upwelling modify the structure of the coupled mode (eastward displacement of the equatorial westerly anomalies) by reallocating anomalous atmospheric heating and SST gradient along the equator. This structural change amplifies the ENSO cycle and prolongs the oscillation period by enhancing the coupled instability and delaying transitions from a warm to a cold state or vice versa. The changes in the mean currents and upwelling reduce the effect of the zonal temperature advection while enhance that of the vertical advection; thus, the prevailing westward propagation is replaced by eastward propagation or standing oscillation. Our results suggest a critical role of the atmospheric bridge that rapidly conveys the influences of extratropical decadal variations to the tropics, and the possibility that the Pacific climate shift might have affected El Nino properties in the late 1970s by changing the background tropical winds and the associated equatorial upwelling.     

利用“3S”技术进行北京地区土壤水分监测应用技术研究

该文主要对适合于北京地区的土壤水分卫星遥感监测方法，利用GIS及GPS工具，提高对土壤水分卫星遥感监测结果的分析能力进行了探讨。在分析研究北京地区土壤水分卫星遥感监测模式及适宜使用的下垫面状况和时段的基础上，提出了一批具有一定物理意义和应用价值的遥感模式。利用GIS和GPS技术实现包括遥感信息在内的多种数据的复合，以影像的方式，将地表地理状况与土壤水分卫星遥感监测结果结合起来，实现了RS、GIS及GPS的融合，提高了土壤水分卫星遥感监测的精度。     

北京北部城区 SO2和NO2浓度垂直分布特点初探

2001年1～3月在中国科学院大气物理研究所320 m铁塔10个不同高度(320、240、200、140、100、80、47、15、8 m和地面)使用无动力扩散采样器对SO2和NO2日平均总量及夜间平均浓度进行了观测.结果表明,200m以下高度SO2和NO2浓度较大.北京城区不同高度大气中SO2的浓度1月份最高.NO2浓度1月份和2月份呈现高值.不同高度SO2和NO2浓度与逆温强度有明显的正相关.     

岷江上游干扰岸坡主要表生地质灾害分布特征及成因浅析

岷江上游地处我国著名的南北向地震带的中段，因其特定的地质环境导致区内表生地质灾害极为严重。通过对岷江上游（汶川以上）河段的崩塌、滑坡、泥石流等表生地质灾害的调查研究，其分布沿岷江两岸具有明显的分段特征与河谷地貌分段基本一致，它们形成发展与特定地形地貌、易崩滑或软弱地层、特殊的构造部位、降雨等密切相关。     

GPS进行长边控制测量分析

采用基准和基准转换模型的不同会导致GPS观测边长与坐标计算边长不一致。因此由GPS测量的WGS－84坐标系向我国的北京54坐标系转换计算时，应尽可能选择参考点作对比分析。若满足精度要求，可采用全国精密参数作转换计算，若不能满足精度要求或达不到实测点的定位精度，可先将边长作高程异常改正，再对起算点作方位改正。     

古炭屑与古森林火?

森林火普遍发生在地质历史时期中，它对自然植被系统的演替起着重要作用。不同强度和频率的森林火培育出不同类型的植被：频繁的森林火导致草甸的形成，而热带雨林形成的原因之一是森林火的缺乏。古炭屑作为古森林火的遗迹，具有分布广泛、细胞结构保存完好以及原地埋藏等特点，为研究古森林火发生的强度和频率提供了宝贵的材料。古炭屑的出现与当时的气候因素、植被类型和地理状况有密切关系：干旱、少雨的气候常常伴随高频率森林火的发生，表现出古炭屑的数量增多；易燃物种组成的植被易发生森林火，古炭屑的出现也会增多，而耐火树种会降低森林火的强度，古炭屑则出现少。因此，从古炭屑的数量和种类的变化，可探讨古森林火的发生规律，进而推断长期地质历史时期的气候、植被、地理状况的演变。     

Probabilistic analysis of peak response of MDOF systems with uncertain PSD function

The use of uniform hazard spectra which have the same probability of exceedance at different frequencies has been proposed for the future version of the National Building Code of Canada. Commonly used combination rules to estimate the peak responses of multi‐degree‐of‐freedom (MDOF) systems are the square root of sum of squares rule and the complete quadratic combination rule. However, the probability that the peak response of a MDOF system exceeds the one estimated by using these rules with the peak modal responses from the uniform hazard spectra cannot be inferred directly. The assessment of the probability of exceedance of the peak response of MDOF systems is presented by considering that the uncertainty in seismic excitation due to all potential earthquakes can be lumped in the power spectral density function of the ground acceleration with uncertain model parameters. This probability is evaluated based on the random vibration of linear systems and the first‐order reliability method. It is found that the under‐ or over‐estimations are less than about 5 or 10% if the modal contributions are not within 10–90% of, or not within 20–80% of, the absolute sum of the effective modal peak responses, respectively. Otherwise, severe under‐ or over‐estimation could result. Copyright © 2002 John Wiley & Sons, Ltd.