Host-parasitoid associations in patchy environments

Studies of insect host-parasitoid interactions have contributed much to the consensus that spatial patchiness is important in the regulation of natural populations. A variety of theoretical models predict that host and parasitoid populations, although unstable in the absence of environmental heterogeneity, may persist at roughly steady overall densities in a patchy environment owing to variation in levels of parasitism from patch to patch. Observed patterns of parasitism, however, have a variety of forms (with variation in attack rates among patches depending directly or indirectly on host density, or showing variation uncorrelated with host density). There is some confusion about the dynamical consequences of these different forms. Here we first show how the dynamical effects of all these forms of environmental heterogeneity can be assessed by a common criterion. This 'CV2 greater than 1 rule' states that the overall population densities will remain roughly steady from generation to generation if the coefficient of variation squared (CV2) of the density of searching parasitoids in the vicinity of each host exceeds approximately unity. By partitioning CV2 into components, we show that both direct and inverse patterns of dependence on host density, and density-independent patterns, all contribute to population regulation in the same way. Second, we show how a maximum-likelihood method can be applied to the kind of field data that are usually available (that is, percentage parasitism versus local host density) to estimate the components of CV2. This analysis indicates that heterogeneity is large enough to stabilize dynamics in 9 of 34 published studies, and that density-independent heterogeneity is the main factor in most cases.     

Molecular cloning of the microtubule-associated mechanochemical enzyme dynamin reveals homology with a new family of GTP-binding proteins

A complementary DNA encoding the D100 polypeptide of rat brain dynamin--a force-producing, microtubule-activated nucleotide triphosphatase--has been cloned and sequenced. The predicted amino acid sequence includes a guanine nucleotide-binding domain that is homologous with those of a family of antiviral factors, inducible by interferon and known as Mx proteins, and with the product of the essential yeast vacuolar protein sorting gene VPS1. These relationships imply the existence of a new family of GTPases with physiological roles that may include microtubule-based motility and protein sorting.     

机床整机建模的自由界面模态综合改进方法之一

对会诸多结合面的复杂机械结构(如机床)的动态分析,由于结合部位的位移不连续性,通常位移协调的动态子结构法已不再适用。本文通过引入联接子结构概念,消除了结合部的位移不连续性,并使各子结构的模态综合步骤与通常的自由界面模态综合法相似,统一了连续结构与具有形变不连续结合面的复杂结构的自由界面子结构法,扩大了自由界面法的适用范围。     

s-单式环的交换性定理(英文)

本文将文献[3]的引理1推广到s-单式环上,并用迭代技术给出文献[4]的定理2一个简易的证明,将若干有1环的交换性定理推广到s-单式环上。     

一类周期拟环的结构

本文得到了拟环满足条件ｘｙ＝ｘｙ￣（ｎ（ｘ，ｙ）ｘ或ｘｙ＝ｙｘ￣（ｎ（ｘ，ｙ）ｙ的分解定理。     

二自由度自谐式机器人动力学的研究

本文对引用弹性元件的二自由度谐式机器人的动力学进行了分析,在该模型中引入了负反馈系统。按预期的机构运动规律和系统的稳定性要求,研究了反馈放大系数的合理选择,并对构件单独和同时运动的仿真图线进行了分析。     

可用于累煤层露天矿山的多周期目标规划模型

本文给出了一个可应用于复合煤层露天矿短期生产计划优化的目标规划模型.模型考虑了与煤质、煤产量及开采程序合理性有关的亏损与盈利.该方法利用了带有客观地确定权重系数的目标规划加权法.文后又给出了一个能说明该模型应用于实际采矿问题的例子.     

Manufacturing''s Roel in Innovation Diffusion and Technological Substitution

Successful innovation management depends upon both, the intrinsic attributes of the new product to be marketed and the firm's internal performance like cost management, timely delivery and quality assurance. The impact of these latter aspects is frequently neglected in the design of models for supporting decision making in innovative firms.A model is outlined to study the market response of different manufacturing policies for innovative goods. It allows e.g. the evaluation of an aggressive strategy with large production capacities from the outset, or a more tentative behavior to. avoid the pressures stemming from high fixed cost and the risks of eventually idle capacity.     

Cloning of a probable potassium channel gene from mouse brain

Potassium channels comprise a diverse class of ion channels important for neuronal excitability and plasticity. The recent cloning of the Shaker locus from Drosophila melanogaster has provided a starting point for molecular studies of potassium channels. Predicted Shaker proteins appear to be integral membrane proteins and have a sequence similar to the sequence of the S4 segment of the vertebrate sodium channel, where the S4 segment has been proposed to be the voltage sensor. Expression studies in frog oocytes confirm that Shaker encodes a component of a potassium channel (the A channel) that conducts a fast transient potassium current. Here we report the isolation of complementary DNA clones from the mouse brain, the nucleotide sequences of which predict a protein remarkably similar to the Shaker protein. The strong conservation of the predicted protein sequence in flies and mammals suggests that these mouse clones encode a potassium channel component and that the conserved amino acids may be essential to some aspect of potassium channel function.     

A new A4 amyloid mRNA contains a domain homologous to serine proteinase inhibitors

The amyloid proteins isolated from neuritic plaques and the cerebrovasculature of Alzheimer's disease are self-aggregating moieties termed A4 protein and beta-protein, respectively. A putative A4 amyloid precursor (herein termed A4(695] has been characterized by analysis of a human brain complementary DNA. We report here the sequence of a closely related amyloid cDNA, A4(751), distinguished from A4(695) by the presence of a 168 base-pair (bp) sequence which adds 57 amino acids to, and removes one residue from, the predicted A4(695) protein. The peptide predicted from this insert is very similar to the Kunitz family of serine proteinase inhibitors. The two A4-specific messenger RNAs are differentially expressed: in a limited survey, A4(751) mRNA appears to be ubiquitous, whereas A4(695) mRNA has a restricted pattern of expression which includes cells from neuronal tissue. These data may have significant implications for understanding amyloid deposition in Alzheimer's disease.