ε-Dependent Controllability for Two Time-Scale Systems

This paper investigates the controllability of two time-scale systems using both the time-scale separation model and the slow-fast order reduction model.This work considers the effect of a singular perturbation parameter on the model transformations to improve the criterion precision.The Maclaurin expansion method and homotopy arithmetic are introduced to obtainε-dependent controllability criteria.Examples indicate that theε-dependent controllability criteria are more accurate and that the controllabilit...     

中国及世界风资源变化研究进展

20世纪以来.随着能源需求成倍增长,风能资源因其安全、清洁、丰富的特性已成为世界上增长最快的能源方式.有关风能资源可持续利用的近地层风和风能资源变化研究也逐渐开展起来.20世纪观测事实研究表明,①全球高纬度地区风速呈增大趋势,而中低纬度地区风速呈减小趋势变化;②中国近50年来年平均风速呈明显的减小趋势变化;⑨中国区域城市化发展、测站迁址及测风仪器的变更都对中国年平均风速的长期变化产生了一定影响,但都不是近50年来中国年平均风速呈显著减小趋势的主因;大气环流的变化才是造成中国年平均风速呈显著减小趋势的最可能原因.与风和风能资源预估相关的研究表明,21世纪由于人为温室气体排放增加和全球变暖,中国年平均和冬季平均风速和风功率密度将可能减小,夏季平均风速和风功率密度的变化不确定性较大.目前,利用气候模式模拟和预估近地层风速方面的研究才刚刚开始.今后还需要做大量和长时间的研究试验,才能得到更可靠的结论.     

硫化矿石堆自燃早期指标优选及预测方法

为研究硫化矿石自燃早期的氧化自热发展状况与规律,并寻求最优识别指标,对具有自燃倾向性的硫化矿石进行堆矿试验.试验结果表明,在矿石氧化自热的孕育期、发展期和邻近自燃期-氧浓度会有所减少,总体在17%～18%间波动,不能识别氧化所处的阶段:只有在临近自燃期才能测出SO2,同样不能作为自燃早期的征兆;矿堆温度的变化,明显反映了矿石堆氧化、自热至自燃这一过程,适宜作为早期预测矿石自燃的指标.应用指数曲线法建立了预测硫化矿石堆温度的数学模型.计算结果表明,预测模型准确、直观地反映了硫化矿石氧化自热的孕育期、发展期和邻近自燃期3个阶段,对矿石堆自燃火灾的早期预防有重要的理论价值和实践意义.     

华北冬小麦作物气候干旱指数研究

作为农业干旱指标,降水距平百分率未考虑底墒作用,不同发育期水分对产量影响不同.利用降水距平百分率指数构建了华北冬小麦作物气候冬小麦干旱指数.该指数将冬小麦不同发育阶段的水分产量反应系数应用到降水距平干旱指数中,同时量化底墒对冬小麦生长发育过程中起到的重要作用.通过对河南省卢氏县冬小麦历年干旱和减产率进行计算和分析,结果表明,作物气候指标负距平百分率和减产率的相关性明显高于降水负距平百分率和减产率的相关性.作物气候冬小麦干旱指数在评估冬小麦干旱时要优于降水距平百分率,将作物和气候干旱相结合能更准确地评估冬小麦干旱,弥补降水距平百分率作为农业干旱指数只涉及气候干旱的不足.     

强冷空气影响下的强对流天气对比分析

2007年5月和2006年6月两次相似的强对流天气给浙江省带来了强烈的雷雨大风和短时冰雹天气,这两次过程最主要的特征表现在中高层蕴含深厚的冷空气条件,而低层存在浅薄的暖湿气流.综合运用雷达卫星及NCEP实况资料,对比分析了强对流发生发展的环境条件、云图及回波特征,进而揭示出此类天气的主要特点和可预报性.分析发现,925 hPa的切变线形成中尺度触发机制,对预报雷暴的发展走向具有不可忽视的作用;冷空气南下造成的冷暖平流交汇是触发对流的主要原因;云图上,云系移动前方形成较大的亮温梯度,后方形成干涌边界;雷达回波中表现出阵风锋的影响,这些都是地面灾害性大风产生的主要征兆.另外,强回波对应较大的风向切变区和悬挂回波是冰雹产生的重要特征.     

基于激光三维成像数据的车辆目标方位估计

对目标方位进行精确估计是提高目标匹配识别效率的重要前提,而车辆目标的地面投影轮廓近似于矩形,为此提出了基于激光三维成像数据的车辆目标方位估计方法.首先依据激光成像数据的高程值对数据进行分类,从激光成像区域的三维数据中提取出车辆目标数据进而获取目标的投影轮廓数据,然后采用向量积异号排除法求解车辆目标投影轮廓数据的凸边界,在此基础上采用直接求解凸边界最小外接矩形的方法对车辆目标的方位进行初步估计,最后利用与目标投影轮廓数据邻近的地面数据,并依据最小二乘原理拟合优化凸边界的最小外接矩形,校正车辆目标初始估计方位,从而实现车辆目标方位的精确估计.仿真结果表明,该方法可实现车辆目标方位的快速准确估计.     

相位差变化率的测量方法及其测量精度分析

相位差变化率是最近提出的用于快速无源定位的观测量。分析了相位差变化率的特点,提出了相位差变化率的测量原理,从理论上分析了相位差变化率测量精度的Cramer-Rao界,指出了过窄的源信号脉冲宽度和过低的相位差变化率是造成相位差变化率测量困难的主要原因,并对此提出了解决的方法,随后进行的测量精度对比仿真分析表明,该方法是有效的。     

TGFB2 mutations cause familial thoracic aortic aneurysms and dissections associated with mild systemic features of Marfan syndrome

A predisposition for thoracic aortic aneurysms leading to acute aortic dissections can be inherited in families in an autosomal dominant manner. Genome-wide linkage analysis of two large unrelated families with thoracic aortic disease followed by whole-exome sequencing of affected relatives identified causative mutations in TGFB2. These mutations-a frameshift mutation in exon 6 and a nonsense mutation in exon 4-segregated with disease with a combined logarithm of odds (LOD) score of 7.7. Sanger sequencing of 276 probands from families with inherited thoracic aortic disease identified 2 additional TGFB2 mutations. TGFB2 encodes transforming growth factor (TGF)-β2, and the mutations are predicted to cause haploinsufficiency for TGFB2; however, aortic tissue from cases paradoxically shows increased TGF-β2 expression and immunostaining. Thus, haploinsufficiency for TGFB2 predisposes to thoracic aortic disease, suggesting that the initial pathway driving disease is decreased cellular TGF-β2 levels leading to a secondary increase in TGF-β2 production in the diseased aorta.     

Exome sequencing of extreme phenotypes identifies DCTN4 as a modifier of chronic Pseudomonas aeruginosa infection in cystic fibrosis

Exome sequencing has become a powerful and effective strategy for the discovery of genes underlying Mendelian disorders. However, use of exome sequencing to identify variants associated with complex traits has been more challenging, partly because the sample sizes needed for adequate power may be very large. One strategy to increase efficiency is to sequence individuals who are at both ends of a phenotype distribution (those with extreme phenotypes). Because the frequency of alleles that contribute to the trait are enriched in one or both phenotype extremes, a modest sample size can potentially be used to identify novel candidate genes and/or alleles. As part of the National Heart, Lung, and Blood Institute (NHLBI) Exome Sequencing Project (ESP), we used an extreme phenotype study design to discover that variants in DCTN4, encoding a dynactin protein, are associated with time to first P. aeruginosa airway infection, chronic P. aeruginosa infection and mucoid P. aeruginosa in individuals with cystic fibrosis.     

An improved neural network model for prediction of mechanical properties of magnesium alloys

An improved neural network model was developed for prediction of mechanical properties in the design and development of new types of magnesium alloys by refining the types of input variables and using a more reasonable algorithm.The results showed that the improved model apparently decreased the prediction errors,and raised the accuracy of the prediction results.Better preprocessing parameters were found to be[0.15,0.90]for the tensile strength,[0.1,0.9]for the yield strength,and[0.15,0.90]for the elongatio...