A Two—Temperature Supernova Fallback Disk Model for Anomalous X—ray Pulsars

We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approximation that such a neutron star disk with mass in the range of 10^-6-10^-5M⊙ is formed by supernova fallback. We derive several peculiar properties of the accretion disk instability: a narrow interval of X-ray pulse periods; lower X-ray luminosities; a period derivative and an evolution time scale. All these results are in good agreement with the observations of the AXPs.     

A High Precision Comprehensive Evaluation Method for Flood Disaster Loss Based on Improved Genetic Programming

Precise comprehensive evaluation of flood disaster loss is significant for the prevention and mitigation of flood disasters. Here, one of the difficulties involved is how to establish a model capable of describing the complex relation between the input and output data of the system of flood disaster loss. Genetic programming （GP） solves problems by using ideas from genetic algorithm and generates computer programs automatically. In this study a new method named the evaluation of the grade of flood disaster loss （EGFD） on the basis of improved genetic programming （IGP） is presented （IGP-EGFD）. The flood disaster area and the direct economic loss are taken as the evaluation indexes of flood disaster loss. Obviously that the larger the evaluation index value, the larger the corresponding value of the grade of flood disaster loss is. Consequently the IGP code is designed to make the value of the grade of flood disaster be an increasing function of the index value. The result of the application of the IGP-EGFD model to Henan Province shows that a good function expression can be obtained within a bigger searched function space; and the model is of high precision and considerable practical significance. Thus, IGP-EGFD can be widely used in automatic modeling and other evaluation systems.     

城市规划信息系统初探

城市规划信息系统作为城市地理信息系统的一个重要的专题分支系统 ,是城市规划体系的基础和纽带。因此 ,通过研究城市规划信息系统的基础理论来指导城市规划信息系统的具体实践 ,进而实现城市可持续发展的战略 ,具有重要意义。     

WGS-84与北京54坐标的转换问题

GPS测量得到的是WGS-84中的地心空间直角坐标，而工程施工中通常使用地方独立坐标系，要求得到地方平面坐标。如何实现两者的转换，一直是工程施工中关心的热点问题。介绍了从GPS定位结果至平面坐标的两种转换模型。平面转换模型原理简单，数值稳定可靠，但只适用于小范围的GPS测量；空间转换模型可用于大范围GPS测量，按实际情况又分为7参数转换和3参数转换两种。鉴于54坐标点的大地高通常不能精确得知，对这两种转换方法得到的平面坐标的精度进行了比较，得出大地高精度主要表现为对高程的影响，对平面坐标影响较小的结论。此外，还讨论了7参数与3参数模型对转换结果的影响。     

Runoff and sediment loss responses to rainfall and land use in two agricultural catchments on the Loess Plateau of China

Soil erosion is a severe problem hindering sustainable agriculture on the Loess Plateau of China. Plot experiments were conducted under the natural rainfall condition during 1995–1997 at Wangdongguo and Aobao catchments in this region to evaluate the effects of various land use, cropping systems, land slopes and rainfall on runoff and sediment losses, as well as the differences in catchment responses. The experiments included various surface conditions ranging from bare soil to vegetated surfaces (maize, wheat residue, Robinia pseudoacacia L., Amorpha fruticosa L., Stipa capillata L., buckwheat and Astragarus adsurgens L.). The measurements were carried out on hill slopes with different gradients (i.e. 0 ° to 36 °). These plots varied from 20 to 60 m in length. Results indicated that runoff and erosion in this region occurred mainly during summer storms. Summer runoff and sediment losses under cropping and other vegetation were significantly less than those from ploughed bare soil (i.e. without crop/plant or crop residue). There were fewer runoff and sediment losses with increasing canopy cover. Land slope had a major effect on runoff and sediment losses and this effect was markedly larger in the tillage plots than that in the natural grass and forest plots, although this effect was very small when the maximum rainfall intensity was larger than 58·8 mm/h or smaller than 2·4 mm/h. Sediment losses per unit area rose with increasing slope length for the same land slope and same land use. The effect of slope length on sediment losses was stronger on a bare soil plot than on a crop/plant plot. The runoff volume and sediment losses were both closely related to rainfall volume and maximum intensity, while runoff coefficient was mainly controlled by maximum rainfall intensity. Hortonian overland flow is the dominant runoff process in the region. The differences in runoff volume, runoff coefficient and sediment losses between the catchments are mainly controlled by the maximum rainfall intensity and infiltration characteristics. The Aobao catchment yielded much larger runoff volume, runoff coefficient and sediment than the Wangdongguo catchment. Copyright © 2001 John Wiley & Sons, Ltd.     

秦皇岛市青龙县城工程场地动力特征及分区评价

工程场地动力分区评价（即地震影响小区划），是在工程场地地震危险性分析的基础上，根据场地岩土动力特征及地形地貌、地质构造条件等对地震动影响的反应程度，从而对不同类型场地的地震效应作出评价．其成果可做为建筑抗震设计、工程加固、震害预测与对策的制定及土地合理利用和总体规划布局的依据．本文以秦皇岛市青龙县城工程场地为例，进行了工程场地动力特征研究与分区评价及震害预测（即工程场地地震影响小区划）。     

The Large-Scale, Decelerating X-ray Jets from the Microquasar Xte J1550−564: Evidence for External Shocks Caused by the Jet-Ism Interaction?

Large-scale, decelerating, relativistic X-ray jets from microquasar XTE J1550−564 has been recently discovered with Chandra by Corbel et al. (2002). We find that the dynamical evolution of the approaching jet at the late time is consistent with the well-known Sedov evolutionary phase R∝ t ^2/5. A trans-relativistic external shock dynamic model by analogy with the evolution of gamma-ray burst remnants, is shown to be able to fit the proper-motion data of the approaching jet reasonably well. The inferred interstellar medium density around the source is well below the canonical value n _ISM∼1 cm⁻³. The rapidly fading X-ray emission can be interpreted as synchrotron radiation from the non-thermal electrons in the adiabatically expanding ejecta. These electrons were accelerated by the reverse shock (moving back into the ejecta) which becomes important when the inertia of the swept external matter leads to an appreciable slowing down of the original ejecta.     

ME／EXOSAT银道扫描数据的直接解调成像

利用对象重建的直接解调方法，我们对EXOSAT卫星ME探测器银道扫描观测数据进行了重新分析，研究了在以往的分析中难以分辨的几个天区中的分立X射线源．利用Bootstrap方法，我们对成像结果进行了统计误差分析，给出了点源位置和流强的误差．     

广义相对论效应对脉冲星γ射线辐射的影响

本文研究了广义相对论效应和量子力学效应对中子量γ射线辐射的影响．通过选择磁偶极矩以及观察者视线与磁轴之间的夹角这两个观测量作为参量，我们数值计算了从中子星表面发射的、传播方向沿着磁场的光子的逃逸能量．我们得到，在磁偶极矩较小时，量子力学效应不重要，而广义相对论效应使逃逸能量显著降低；当磁偶极矩很大时，两个效应几乎相抵消，光子的逃逸能量几乎不受它们的影响．我们讨论这些结果在脉冲星γ射线谱上的意义．