A Two-dimensional Heat Transfer Model for Atmosphere-land System in the Lake-dominated Alaskan Arctic

1 Introduction Shallow tundra lakes are one of the dominating landscape features in the Alaskan Arctic. They typically cover 20% of the total area of the North Slope of Alaska, and up to about 40% in the coastal plain [1,2]. Many lakes are, in their entirety or in part, shallower than the maximum annual ice thickness, consequently, some ice freezes completely to the lake bottom, nevertheless, large areas of water are deeper than the maximum ice thickness and the ice remains afloat througho…     

基于定位辅助按需拓扑维护的超宽带自组网路由算法

提出了一种基于定位辅助按需拓扑维护的超宽带自组网路由算法,该算法利用超宽带技术精确定位信息所获得的网络拓扑信息和路由信息进行分组转发,路由维护阶段在定位信息辅助下采用按需方式进行断链路由的修复和拓扑维护,通过基于位置信息的按需路由发现和限制路由查找范围,以及定位信息和网络拓扑信息的及时更新,在降低协议开销的同时保证了算法的有效性。仿真表明,该算法在分组丢失率、平均端到端时延和路由附加开销等方面具有良好性能,其优良的分布式控制特征能适应超宽带自组网的动态环境。     

服饰时尚中的文化变迁：以牛仔服与唐装为例

牛仔服伴随着改革开放向西方学习的思潮而来,唐装则复兴于繁荣的新世纪之初,本文以“牛仔服”和“唐装”的流行为研究对象,通过探寻其流行原因,来揭示服饰时尚中的文化变迁,并由此展现当今时代多元文化———传统的和现代的、全球的和本土的并存交融的形貌。     

倪瓒逸民遗民心态变化论

本文从对逸民遗民的界定入手,研究了身处元末明初的倪瓒心态及思想的变化,从而廓清了倪瓒在元明易祚之际逸民遗民身份及心理变化。指出倪瓒的这一思想嬗变对于后来明清之际的一些遗民画家对倪瓒传承中的一种文化认同感来说,显得尤为重要。     

基于RS和GIS的龙口市居民地动态变化研究

选择Landsat 1986.6和2002.6两个时期的TM影像,经过多波段彩色合成处理,在分析居民地等多种地物的光谱特征及谱间特征的基础上,建立了居民地信息提取的光谱模型,提取并制作了两个时段的居民地分布图.在此基础上,简要分析了胶东半岛龙口市近20年来居民地动态变化的特点.     

Improving Convergence of the HastingsMetropolis Algorithm with an Adaptive Proposal

The HastingsMetropolis algorithm is a general MCMC method for sampling from a density known up to a constant. Geometric convergence of this algorithm has been proved under conditions relative to the instrumental (or proposal) distribution. We present an inhomogeneous HastingsMetropolis algorithm for which the proposal density approximates the target density, as the number of iterations increases. The proposal density at the n th step is a non-parametric estimate of the density of the algorithm, and uses an increasing number of i.i.d. copies of the Markov chain. The resulting algorithm converges (in n ) geometrically faster than a HastingsMetropolis algorithm with any fixed proposal distribution. The case of a strictly positive density with compact support is presented first, then an extension to more general densities is given. We conclude by proposing a practical way of implementation for the algorithm, and illustrate it over simulated examples.     

Estimating rating transition probabilites with missing data

In this article we provide a rigorous treatment of one of the central statistical issues of credit risk management. GivenK-1 rating categories, the rating of a corporate bond over a certain horizon may either stay the same or change to one of the remainingK-2 categories; in addition, it is usually the case that the rating of some bonds is withdrawn during the time interval considered in the analysis. When estimating transition probabilities, we have thus to consider aK-th category, called withdrawal, which contains (partially) missing data. We show how maximum likelihood estimation can be performed in this setup; whereas in discrete time our solution gives rigorous support to a solution often used in applications, in continuous time the maximum likelihood estimator of the transition matrix computed by means of the EM algorithm represents a significant improvement over existing methods.     

浅谈当代水彩画在中国的传播与发展

水彩画作为艺术表现形式的一种,力争用鲜明的色彩与格调拨动欣赏者心灵深处的情弦。并通过水彩中水与彩的调和体现艺术的语言及其创作这种语言的目的和经历。     

新时期俄语社会政治词汇中一些词语的转义

文章通过大量的报刊中的实例,阐述俄语中的一些社会政治词语的转义用法,揭示了当今俄语在社会政治词语领域的变化。这对改善现今高校俄语专业的教学,更好地用俄语与俄罗斯人交际会起到促进作用。     

均值绝对偏差资产组合选择模型的算法

对均值绝对偏差模型进行了简化,并利用一种旋转算法求解。这种算法比单纯形算法的计算简便,且计算量更小。利用上海和深圳股市1 072支股票70期周末收盘价所作的实验结果表明,对于资产无上界限制的模型,计算20个不同最优投资组合需要1 274次旋转运算,上界为10%时需要1 570次旋转运算,每 次旋转运算约需1 14171次加法和乘法运算。