Representation of Coarse-grained Potentials for Polymer Simulations

In order to be able to simulate long time and large space scale properties of polymer melts one has to resort to coarse grained models, for example by subdividing all polymers into parts and restricting attention to the center of mass positions and velocities of these parts. The dynamics of these variables is governed by Langevin equations in which the free energy obtained by integrating the remaining variables provides the potential of the conservative forces. In general this leads to many particle interactions on the coarse-grained level. Methods suggested in the literature to represent these many particle interactions by effective two body interactions are reviewed and a new method, based on the Gibbs-Bogoliubov inequality, is proposed. The reason why none of these methods is able to reproduce the pressure of the underlying atomistic model is discussed.     

以肺部病变为主要表现的韦格纳肉芽肿1例并文献复习

目的:促进韦格纳肉芽肿的早期诊断和治疗,提高患者的生存率.方法:回顾性分析我院收治的1例韦格纳肉芽肿患者的发病诊治过程的临床资料并结合文献进行复习.结果:入院后行胸部CT、抗中性粒细胞胞浆抗体(ANCA)等检查,明确诊断后给予糖皮质激素、细胞毒类药物等治疗后短期缓解,5个月后死亡.结论:韦格纳肉芽肿的临床表现多种多样,诊断困难,实验室检查无特异性,临床上对于多系统受累的疾病应警惕此病,应结合患者临床表现及辅助检查做出早期诊断,及早治疗,从而提高患者的生存率.     

Chemotaxonomic Screening of Seed Oils from the Family Saxifragaceae and Comparison with Data on Seed Oils from Grossulariaceae Obtained from Literature

Seeds of 25 members of the family Saxifragaceae, 1 × Astilbe, 1 × Darmera, 1 × Leptarrhena, 1 × Tellima, 3 × Mitella, and 18 × Saxifraga were investigated regarding oil content, as well as composition and content of fatty acids and vitamin E active compounds. The results were compared with results obtained from literature for members of the genus Ribes belonging to the closely related family Grossulariaceae to find chemometric differences between the different genera and between members of the family Saxifragaceae and Grossulariaceae, respectively. Members of the family Saxifragaceae are dominated by high amounts of linoleic and α‐linolenic acid which together account for about 80% of the total fatty acids. While α‐linolenic acid is characteristic for members of the genus Saxifraga, in other genera, linoleic acid is predominant. In comparison to members of the family Saxifragaceae members of the family Grossulariaceae also contain γ‐linolenic acid and stearidonic acid which allow a significant differentiation between both families. By principle component analysis, members of both families were divided into three distinct groups, i) species with a high content of α‐linolenic acid (genus Saxifraga), ii) species with high amounts of γ‐linolenic acid and stearidonic acid (genus Ribes), and iii) species with higher amounts of linoleic acid (other members of the family Saxifragaceae). The composition of the vitamin E active compounds was characterized by a high content of γ‐tocopherol in most members of the family Saxifragaceae, but no chemotaxonomic relevance.     

Modelling the optimal timing in metabolic pathway activation—Use of Pontryagin's Maximum Principle and role of the Golden section

The time course of enzyme concentrations in metabolic pathways can be predicted on the basis of the optimality criterion of minimizing the time period in which an essential product is generated. This criterion is in line with the widely accepted view that high fitness requires high pathway flux. Here, based on Pontryagin's Maximum Principle, a method is developed to solve the corresponding constrained optimal control problem in an almost exclusively analytical way and, thus, to calculate optimal enzyme profiles, when linear, irreversible rate laws are assumed. Three different problem formulations are considered and the corresponding optimization results are derived. Besides the minimization of transition time, we consider an operation time in which 90% of the substrate has been converted into product. In that case, only the enzyme at the lower end of the pathway rather than all enzymes are active in the last phase. In all cases, biphasic or multiphasic time courses are obtained. The biological meaning of the results in terms of a consecutive just-in-time expression of metabolic genes is discussed. For the special case of two-enzyme systems, the role of the Golden section in the solution is outlined.     

When carnivores are “full and lazy”

Are animals usually hungry and busily looking for food, or do they often meet their energetic and other needs in the 24 h of a day? Focusing on carnivores, I provide evidence for the latter scenario. I develop a model that predicts the minimum food abundance at which a carnivore reaches satiation and is released from time constraints. Literature data from five invertebrate and vertebrate species suggest that food abundances experienced in the field often exceed this threshold. A comparison of energetic demands to kill rates also suggests that carnivores often reach satiation: for the 16 bird and mammal species analyzed, this frequency is 88% (average across species). Because pressure of time would likely lead to trade-offs in time allocation and thus to a nonsatiating food consumption, these results suggest that carnivores are often released from time constraints.     

噬菌体展示技术发展

噬菌体表面展示技术是一种将外源蛋白或抗体可变区与噬菌体表面特定蛋白质融合并展示于其表面,构建蛋白质或抗体库,并从中筛选特异蛋白质或抗体的基因工程技术。随着该项技术的不断完善和发展,噬菌体展示技术已被广泛应用于生命科学研究的不同领域,并显示了良好的应用前景。     

Analyzing steady states of dynamics of bio-molecules from the structure of regulatory networks

Regulatory relations between biological molecules constitute complex network systems and realize diverse biological functions through the dynamics of molecular activities. However, we currently have very little understanding of the relationship between the structure of a regulatory network and its dynamical properties. In this paper we introduce a new method, named “linkage logic” to analyze the dynamics of network systems. By this method, we can restrict possible steady states of a given complex network system from the knowledge of regulatory linkages alone. The regulatory linkage simply specifies the list of variables that affect the dynamics of each variable. We formalize two aspects of the linkage logic: the “Principle of Compatibility” determines the upper limit of the diversity of possible steady states of the dynamics realized by a given network; the “Principle of Dependency” determines the possible combinations of states of the system. By combining these two aspects, (i) for a given network, we can identify a cluster of nodes that gives an alternative representation of the steady states of the whole system, (ii) we can reduce a given complex network into a simpler one without loss of the ability to generate the diversity of steady states, (iii) we can examine the consistency between the structure of network and observed set of steady states, and (iv) sometimes we can predict unknown states or unknown regulations from an observed set of steady states alone. We illustrate the method by several applications to an experimentally determined regulatory network for biological functions.     

广东罗坑自然保护区鳄蜥夏季生境特征

2005年6—8月,在广东省罗坑自然保护区对36处鳄蜥的生境特征进行了研究。采用样线调查法,在保护区内鳄蜥分布区随机选取了30条溪沟进行调查,对每处有鳄蜥分布的生境测量了15个相关的生态因子。通过主成分分析发现,回水塘长度和宽度、水源距离、水流速度、栖枝高度、栖枝直径、干扰距离、植被类型、植被盖度等9个生态因子对鳄蜥的生境选择有显著影响,而回水塘底质组成、回水塘水深、栖枝枯活状况、栖枝角度、溪沟类型和溪沟坡向6个生态因子的影响不显著。鳄蜥偏好的生境可归结为回水塘长度、宽度中等(均为1.0—2.0m),有位于水源正上方的栖枝,水流速度缓慢,栖枝高度0.5—1.0m、栖枝直径≤1.00cm,干扰距离>500m,植被类型为常绿阔叶林、植被盖度>60%的生境。建议提高当地居民的保护意识,重点保护水源林和溪沟两侧的植被。     

The Precautionary Principle,Epidemiology and the Ethics of Delay

Ethics tells us: do good and do no harm and invokes the norms of justice, equity and respect for autonomy in protecting and promoting health and well-being. The Precautionary Principle, a contemporary re-definition of Bradford Hill's case for action, gives us a common sense rule for doing good by preventing harm to public health from delay: when in doubt about the presence of a hazard, there should be no doubt about its prevention or removal. It shifts the burden of proof from showing presence of risk to showing absence of risk, aims to do good by preventing harm, and subsumes the upstream strategies of the DPSEEA (Driving Forces Pressure Stress Exposure Effect Action) model and downstream strategies from molecular epidemiology for detection and prevention of risk. The Precautionary Principle has emerged because of the ethical import of delays in detection of risks to human health and the environment. Ethical principles, the Precautionary Principle, the DPSEEA model and molecular epidemiology all imply re-emphasizing epidemiology's classic rôle for early detection and prevention. Delays in recognizing risks from past exposures and acting on the findings (e.g., cigarette smoking and lung cancer, asbestos, organochlorines and endocrine disruption, radiofrequency, raised travel speeds) were examples of failures that were not only scientific, but ethical, since they resulted in preventable harm to exposed populations. These may delay results from, among other things, external and internal determinants of epidemiologic investigations of hazard and risk, including misuse of tests of statistical significance. Furthermore, applying the Precautionary Principle to ensure justice, equity, and respect for autonomy raises questions concerning the short-term costs of implementation to achieve long-term goals and the principles that guide compensation.