基于博弈论的融资租赁保证金确定方法研究

针对融资租赁中租金偿还违约风险的防范问题,研究了如何合理设置租赁保证金来防范违约风险.运用博弈理论建立了租金偿还的动态博弈模型,采用逆向归纳法求解该博弈模型并推导出了预防性保证金确定方法及其适用条件,通过边界条件的改变继而推导出了补偿性保证金确定方法及其适用条件.算例分析表明,运用两种方法来计算租赁保证金时,只需已知租赁项目各期租金和租赁资产的价值而无需知道租赁项目的各期收益,仅以出租人预期租赁项目在各期的收益与租金之间的大小作为判据来选择保证金确定方法.两种保证金确定方法具有较高的实用性和可操作性,是出租人合理地确定租赁保证金的有效方法.     

Adult survival in Partridge-Barton model of biological aging

A Monte Carlo simulation of the Partridge-Barton model is presented which in a limiting case gives extreme senescence in the sense of immediate death after sexual maturity.     

Non‐homogeneous infinitely many sites discrete‐time model with exact coalescent

Kingman's coalescent is among the most fertile concepts in mathematical population genetics. However, it only approximates the exact coalescent process associated with the Wright–Fisher model, in which the ancestry of a sample does not have to be a binary tree. The distinction between the approximate and exact coalescent becomes important when population size is small and time has to be measured in discrete units (generations). In the present paper, we explore the exact coalescent, with mutations following the infinitely many sites model. The methods used involve random point processes and generating functionals. This allows obtaining joint distributions of segregating sites in arbitrary intervals or collections of intervals, and generally in arbitrary Borel subsets of two or more chromosomes. Using this framework it is possible to find the moments of the numbers of segregating sites on pairs of chromosomes, as well as the moments of the average of the number of pairwise differences, in the form that is more general than usually. In addition, we demonstrate limit properties of the first two moments under a range of demographic scenarios, including different patterns of population growth. This latter part complements results obtained earlier for Kingman's coalescent. Finally, we discuss various applications, including the analysis of fluctuation experiments, from which mutation rates of biological cells can be inferred. Copyright © 2009 John Wiley & Sons, Ltd.     

拉米夫定治疗慢性乙型肝炎YMDD变异的相关因素分析

目的分析拉米夫定治疗后慢性乙型肝炎酪氨酸(Y)、蛋氨酸(M)、天冬氨酸(D)、天冬氨酸(D)变异的相关因素.方法对169例经拉米夫定治疗12个月后的慢性乙型肝炎患者发生YMDD变异情况进行回顾性分析.采用荧光定量PCR和PCR产物测序等方法检测慢性乙型肝炎拉米夫定治疗前、治疗后HBV基因型、HBV DNA水平、HBeAg状态、ALT水平等指标.结果在169例患者中,基因型B共76例(44.97%),基因型C共93例(55.03%).拉米夫定治疗12个月后,46例(27.22%)患者发生YMDD变异,其中,基因型B变异27例(35.53%),基因型C变异19例(20.43%),两者有统计学差异(P<0.05).YMDD变异组患者治疗前HBV DNA水平显著高于YMDD未变异组[(7.26±0.58 vs6.44±0.65)log拷贝/ml,P<0.05].HBeAg阳性患者YMDD变异率显著高于HBeAg阴性患者(38.10%vs20.75%,P<0.05).YMDD变异组与未变异组在治疗前ALT水平上无明显差异[(136.09±28.21 vs 124.15±26.52)U/L,P>0.05].结论拉米夫定治疗慢性乙型肝炎发生YMDD变异与HBV基因型、HBV DNA水平、HBeAg状态等密切相关.拉米夫定治疗前,检测HBV基因型、HBV DNA水平,HBeAg状态等指标对慢性乙型肝炎抗病毒治疗具有重要意义.     

Updating Insights into the Catalytic Domain Properties of Plant Cellulose synthase (CesA) and Cellulose synthase-like (Csl) Proteins

The wall is the last frontier of a plant cell involved in modulating growth, development and defense against biotic stresses. Cellulose and additional polysaccharides of plant cell walls are the most abundant biopolymers on earth, having increased in economic value and thereby attracted significant interest in biotechnology. Cellulose biosynthesis constitutes a highly complicated process relying on the formation of cellulose synthase complexes. Cellulose synthase (CesA) and Cellulose synthase-like (Csl) genes encode enzymes that synthesize cellulose and most hemicellulosic polysaccharides. Arabidopsis and rice are invaluable genetic models and reliable representatives of land plants to comprehend cell wall synthesis. During the past two decades, enormous research progress has been made to understand the mechanisms of cellulose synthesis and construction of the plant cell wall. A plethora of cesa and csl mutants have been characterized, providing functional insights into individual protein isoforms. Recent structural studies have uncovered the mode of CesA assembly and the dynamics of cellulose production. Genetics and structural biology have generated new knowledge and have accelerated the pace of discovery in this field, ultimately opening perspectives towards cellulose synthesis manipulation. This review provides an overview of the major breakthroughs gathering previous and recent genetic and structural advancements, focusing on the function of CesA and Csl catalytic domain in plants.     

Molecular insight for the role of key residues of calreticulin in its binding activities: A computational study

Calreticulin (CRT) is localized to and has functions in multiple cellular compartments, including the cell surface, the endoplasmic reticulum, and the extracellular matrix. Mutagenesis studies have identified several residues on a concave β-sheet surface of CRT critical for CRT binding to carbohydrate and other proteins/peptides. How the mutations of these key residues in CRT affect the conformation and dynamics of CRT, further influencing CRT binding to carbohydrates and other proteins to signal the important biological activities remain unknown. In this study, we investigated the effect of three key point mutations (C105A, C137A and W319A) on CRT conformation and dynamics via atomistic molecular dynamics simulations. Results show that these three key residues mutations induced the changes of CRT local backbone flexibility and secondary structure of CRT N-domain, which could further affect CRT’s binding activity. C137A mutation led to dramatic decrease of the overall size of CRT due to the P-domain fold back to the globular domain and formed new inter-domain contacts, which can cause blockage of CRT’s binding with other large substrates. Furthermore, for CRT concave β-strand surface patch containing lectin binding site, CRT C105A, C137A and W319A point mutation resulted in the changes in solvent accessible surface area, key residues’ side chain atom positions and dynamical correlated motions between residues. All these changes could directly affect CRT binding behavior. Results of this study provide molecular and structural insights into understanding the role of key residues of CRT in its binding behavior.     

吴大猷先生点评《经典力学》

文章介绍了吴大猷先生对《经典力学》中一些基本问题的意见以及他的近期工作。吴先生认为,Hamilton原理是一个物理原则,而不仅仅是数学变分问题。他还对“齐次问题”和“猝变运动”作了讨论。     

滑动移除小波分析法在动力学结构突变检验中的应用

标度指数计算的即时性与准确性对相关时间序列的动力学结构突变分析至关重要,然而现有方法在即时性与准确性上一直无法兼顾.将小波分析方法与滑动移除窗口技术相融合,提出一种新的动力学结构突变检测方法——滑动移除小波分析法.通过选取不同的滑动移除窗口,分别对构建的线性、非线性理想时间序列进行动力学结构突变分析,结果表明不论是线性时间序列还是非线性时间序列,滑动移除小波分析能够准确地检测到序列的动力学结构突变点及突变区间,对于滑动移除窗口长度依赖性较小,具有很强的稳定性,而且在计算速度上明显优于滑动移除重标极差和滑动移除方差分析方法,将在大数据处理中具有一定的优势.同时分别对线性、非线性理想时间序列添加高斯白噪声,结果表明滑动移除小波分析具有很强的抗噪能力,能够准确地检测到加噪后序列的突变点.对佛坪站日最高温度实测资料的动力学结构突变的准确检测进一步验证了该方法的有效性.滑动移除小波分析法可为具有相关性的系统动力学结构突变的快速、准确检测提供一种途径.