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Gamma射线爆光曲线的一个简单激波模型

采用一个简单的激波模型来讨论了珈玛射线爆光变曲线的轮廓。根据激波理论,爆炸产生压力脉冲并以压力波的形式传播,既有压缩波也有膨胀波。压缩波的合并产生激波,它的强度被随后并入的压缩波或膨胀波分别增强或减弱。该模型能自然地描述珈玛爆光变曲线和光变曲线具有的"快速上升指数下降"的轮廓特征。我们认为这一特征是压缩波和膨胀波的传播特性导致的。     

River suspended sediment modelling using a fuzzy logic approach

Correct estimation of sediment volume carried by a river is very important for many water resources projects. Conventional sediment rating curves, however, are not able to provide sufficiently accurate results. In this paper, a fuzzy logic approach is proposed to estimate suspended sediment concentration from streamflow. This study provides forecasting benchmarks for sediment concentration prediction in the form of a numerical and graphical comparison between fuzzy and rating‐curve models. Benchmarking was based on a 5‐year period of continuous streamflow and sediment concentration data of Quebrada Blanca Station operated by the United States Geological Survey. The benchmark results showed that the fuzzy model was able to produce much better results than rating‐curve models. The fuzzy model proposed in the study is site specific and does not simulate the hysteresis effects. Copyright © 2006 John Wiley & Sons, Ltd.     

Density distribution in massive galactic disks with a central black hole

We developed an efficient method for determining the surface-density distribution in a self-gravitating disk with an isolated central point mass from a specified angular-velocity distribution in the disk. An upper limit for the galactic-disk mass is shown to exist at a given black-hole mass. This limit significantly depends on the choice of rotation curves.     

Adaptive criterion curves describing incipient motion of sediment under wave and current conditions

Sediment incipient motion is a fundamental issue in sediment transport theory and engineering practice. Whilst Shields curve often is used to determine the threshold of sediment movement under unidirectional current conditions, it is unclear whether it can be directly applied for the wave or combined wave-current conditions. The study developed adaptive criterion curves describing incipient motion of sediment under wave and current conditions based on the flow pattern around the sediment particles. Firstly, the flow pattern law for fixed particles was recognized based on the friction law under various dynamic conditions (wave, current, and their combinations), and the flow pattern demarcations for incipient sediment motion were obtained with the threshold conditions for sediment movement under various dynamic conditions combined. Secondly, the exact shape of the Shields curve in each flow regime was derived under the current condition. By combining the flow pattern demarcations for incipient sediment motion under the wave condition, the criterion curve under the wave condition was derived. By combining the flow pattern demarcations for incipient sediment motion under the combined current-wave condition, the criterion curve for sediment incipient motion under the combined current-wave condition was derived. The results indicated that the flow pattern around incipient particles includes laminar, laminar-rough turbulent transition, and rough turbulent regimes. The criterion curves for sediment incipient motion under various dynamic conditions stayed the same in the laminar and rough turbulent regimes, but different in the transition regime. Depending on the relative strengths of the currents and waves, the shape of the criterion curve under the combined current-wave condition transitions adaptively between the criterion curve under the current condition and the criterion curve under the wave conditions.     

云南漾濞6.4级地震强地面运动三要素基本特征分析

2021年5月21日云南漾濞发生6.4级地震,中国数字化强震动观测网络在主震中捕获28组加速度数据。对84条三分向加速度记录进行常规处理,计算出对应的地震动参数,并绘制震中附近水平向PGA和PGV等值线图,结果显示其走向和形态与震后烈度调查结果相近。将实际观测的相对持时进行曲线回归,求得相关系数,并据此计算出T_d(5%～95%)持时对应的震源持续时间在10.22～13.06 s间,与震源破裂过程反演结果基本一致。再通过分析近场6个台站记录的加速度反应谱,并与抗震设计谱比较,总结此次地震的频谱特性,为该区域抗震设防提供参考依据。     

兰州半荒漠植被区红砂(Reaumurta soongorica)种群数量动态

对兰州市永登县半荒漠植被区天然分布的红砂(Reaumurta soongorica)种群实地调查取样,利用红砂植株地径大小与相应年轮年龄的关系,得出回归方程,求出各地径对应年龄,编制静态生命表、分析动态指数、存活曲线、生存分析曲线。结果表明:各生境红砂种群均表现出新苗和幼株丰富,占种群株数的比例大;所有样地存活曲线均接近于Deevev-Ⅲ型(凹型);静态生命表显示,生境异质性,特别是水分差异,致使红砂种群表现出2种不同的环境适应策略;各生境种群动态指数均基本为正值,充分说明样地内的红砂种群基本处于发育状态,整体上是稳定增长的。     

基于径向基函数神经网络的混合像元分解

遥感图像中普通存在着混合像元。对这部分像元进行分类（即混合像元分解）是遥感图像处理中的难点。基于主分量分析的混合像元分解 法是一种较为成熟的算法，但它存在着计算量大，适应性差等缺点。在深入研究混合像元分解原理的基础上，提出了用径向基函数神经网络拟合分解结果超平面，以实现混合像元分解的算法，实验结果证明：该算法的结果与基于主分量分析的混合像元分解算法结果相近（相关系数达到0．00），而计算量大大减少，具有较强的适应性。     

MODIS 1B 影像条带检测与去除

MODIS 1B 影像中存在横向和纵向条带, 基于均衡化曲线补偿技术, 提出了一种快速检测和去除条带的 算法, 给出了条带检测判定参数, 即: 如果A帧和B 帧的10 组传感器校正系数Ci值分别位于0 的两侧, 且ABS(Ci)> 0.008, 则存在宽条带; 如果10 组传感器的校正系数MAX(Ci)>0.05 时, 则存在单行条带。去除宽条带时, 需以当前 列为首列, 从其后连续的100 列影像中提取各传感器相对当前列的校正系数。结果表明, 条带检测模型能有效识别 单行条带和宽条带, 多行条带需目视识     

钢铅组合防屈曲支撑的滞回性能与参数研究

为简化防屈曲支撑的加工工艺,提高防屈曲支撑的初始刚度和在小变形下的耗能能力,基于现有防屈曲支撑在截面形式与构造方式上的特点,提出了一种新型钢铅组合防屈曲支撑并进行了构造设计。通过有限元数值模拟,分析了钢铅组合防屈曲支撑的耗能特性与效果,建立了恢复力简化模型,并根据理想弹塑性材料本构关系推导出滞回规则。通过对不同设计参数的理论分析和数值模拟,分析了钢铅屈服力比、铅剪切面长宽比、核心段宽厚比和耗能段长度等参数对防屈曲支撑滞回性能的影响。研究结果表明,钢铅组合防屈曲支撑能够提供较大的抗侧刚度,耗能效果良好,加工工艺简单,适合工程应用。