低矮房屋标准模型的风洞试验研究

以国际通用的低矮建筑标准模型TIU（德州理工大学）模型为研究对象进行风洞试验,寻求适合于低矮房屋风洞试验的风场以及与风洞试验段相匹配的模型缩尺比.首先进行了1:15、1:30和1:45三种缩尺模型的风洞试验,分析了模型尺寸变化对平均、脉动风压系数和堵塞特征的影响,进而在3种不同湍流度分布的B类风场中对1:30缩尺比的模...     

含风电场的电力系统紧急电压模型预测控制

基于非线性模型预测控制理论,文中提出包含风电场的紧急电压控制器设计方法.以系统的准稳态近似模型为基础,建立滚动动态优化模型,将其滚动优化问题描述成一个具有连续—离散时间微分—代数方程组的最优控制问题,其优化目标是负荷节点电压偏差和控制成本最小.采用Radau排列法将滚动动态优化模型转化为非线性规划问题,并借助建模软件A...     

安庆天柱山机场鸟类群落季节性变化与鸟击防范

在2008年2月至2009年2月间,对安庆天柱山机场及其周边地区的鸟类种类、种群数量进行了为期一年的调查.调查共记录到鸟类102种,隶属于12个目29个科,其中留鸟38种,占总数37.25%;夏候鸟28种,占总数27.45%;冬候鸟25种,占总数24.51%;旅鸟11种,占总数14.39%.在地理类型上,机场地区鸟类呈现古北界与东洋界过渡地带的特点,其中广布种37种,占总数36.27%;东洋界种类有34种,占总数33.33%;古北界种类31种,占总数30.39%.在机场及周边地区,春季观察到鸟类物种数要明显多于秋季及冬季,春季鸟类多样性也要高于秋季与冬季.在机场地区,每年5~6月份与10~11月份鸟类活动比较频繁.机场鸟击防范工作,应该根据鸟类活动特点,通过对重点区域栖息地的改造,降低生物多样性,从而减少鸟类在机场地区的活动,避免鸟击事件的发生.     

The effects of the guide field on the structures of electron density depletions in collisionless magnetic reconnection

Two-dimensional particle-in-cell simulations are performed to investigate the formation of electron density depletions in collisionless magnetic reconnection.In anti-parallel reconnection,the quadrupole structures of the out-of-plane magnetic field are formed,and four symmetric electron density depletion layers can be found along the separatrices due to the effects of magetic mirror.With the increase of the initial guide field,the symmetry of both the out-of-plane magnetic field and electron density depletion layers is distorted.When the initial guide field is sufficiently large,the electron density depletion layers along the lower left and upper right separatrices disappear.The parallel electric field in guide field reconnection is found to play an important role in forming such structures of the electron density depletion layers.The structures of the out-of-plane magnetic field By and electron depletion layers in anti-parallel and guide field reconnection are found to be related to electron flow or in-plane currents in the separatrix regions.In anti-parallel reconnection,electrons flow towards the X line along the separatrices,and are directed away from the X line along the magnetic field lines just inside the separatrices.In guide field reconnection,electrons can only flow towards the X line along the upper left and lower right separatrices due to the existence of the parallel electric field in these regions.     

The occurrence and significance of C25HBI in Cenozoic saline lacustrine source rocks from the Western Qaidam Basin,NW China

The saline lacustrine deposit of the Oligocene Lower Ganchaigou Formation is the main source rock for the Western Qaidam Basin,NW China.In this study,abundant highly branched isoprenoids with 25 carbon atoms (C25HBI) were detected in the upper section of the Lower Ganchaigou Formation.C25HBI is a biomarker for diatoms,and can provide information regarding biogeochemical processes during production and preservation of sedimentary organic matter.The carbon isotopic values of C25HBI in these source rocks were in the range of-18‰ to-20‰.The relative enrichment in 13C of C25HBI suggests that these isoprenoids were derived from diatom blooms.In this case,the diatoms used HCO3-as an additional carbon source to dissolved CO2 in water column due to their high biological productivity.Conversely,the diatom blooms indicated an abundant nutrient supply to the environment and high primary productivity.Thus,the occurrence of 13C-enriched C25HBI could be an ideal marker for good source rocks.The decreased concentration of CO2(aq) in the water column induced by diatom blooms can result in an enrichment in 13C of organic matter synthesized by primary producers.This may be a possible reason for the occurrence of 13C-enriched organic matter in the Cenozoic source rocks of the Western Qaidam Basin.Previous studies have shown that the high carbon number n-alkanes sourced from diatoms have no carbon preference.Hence,the sources of n-alkanes in regional source rocks are complex,and should be considered when discussing the sources of organic matter in future studies.     

基于组合码字的矢量量化编码算法

传统的矢量量化编码方法总是将待编码矢量以码书中唯一的最匹配码字作为其近似输出矢量,以实现数据压缩的目的.这种方法对远离码字的矢量无法避免显著的误差.本文提出组合编码的矢量量化方法,其思想是对远离码字的矢量进行主辅组合编码,对主码字编码造成的误差通过辅码字加以补偿.实验表明,该方法在很小降低压缩比率的条件下显著提高了矢量编码精度,能够在信号处理等领域发挥有效作用.     

基于邻域粗糙集的不完整决策系统特征选择算法

针对不完整决策系统属性约简算法时间复杂度较高问题,基于正域不变条件下,决策系统分类能力保持不变原则,提出不完整决策系统前向顺序特征选择算法.该算法从约简集为空集开始,根据在约简集合中加入各属性后对正域影响程度大小将属性降序排列,采用顺序前向搜索,选择当前最佳特征加入特征约简集合,确定最佳特征子集.将该算法扩展到基于邻域...     

亚分米级精密定轨的探索

通过分析ENVISAT卫星跟踪的激光和DORIS测量数据,在完整力学模型的基础上,分别采用经验加速度修正和大气密度修正两种模式,对其进行精密轨道确定.经与精密轨道星历解进行比较,其结果达到了2~4 cm的径向轨道精度.     

基于Illustrator编排系统对长城影像图专题符号的研究

介绍了甘肃省境内明长城资源调查中形成的主要成果——长城专题影像地图,对长城影像地图专题符号制作的关键技术进行了探讨研究。提出了利用制图软件制作专题地图符号的一种新思路,并且形成完整的、规范化的系列符号,为统一化、快速化制作长城资源专题影像图奠定了坚实的基础,以满足文物管理部门对甘肃省境内明长城资源管理、保护、研究的需要。     

从舟曲泥石流灾害看我国城镇泥石流防治

2010年8月7日深夜,甘肃省甘南藏族自治州舟曲县县城后山强降雨激发三眼峪和罗家峪同时暴发泥石流.泥石流冲人城区,摧毁房屋,淤埋街道,扫荡其流路上的一切并穿城而过后,直达嘉陵江上游支流白龙江,堵塞河道,形成堰塞湖,使城区三分之一被淹没.舟曲特大泥石流灾害致使1364人遇难,401人失踪,72人受伤.这是一次十分严重的城镇泥石流灾害,也是新中国成立以来破坏性最强、死亡人数最多的一次泥石流灾害.对我国城镇泥石流防治提出了强烈警示!