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.     

用AD650作PC-XT的A/D转换接口电路

介绍V/F转换器AD650的工作原理,并且提出了一种基于AD650进行模数转换的新型结构的数据采集系统。本系统兼有模拟量输入通道隔离功能,可以远距离传递信号,可按用户要求实现10bit—16 bit不同精度要求的A/D转换,可直接与PC机及其相兼容各种机相连接.     

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。     

溅射用铁电陶瓷靶的烧结与显微结构分析

探讨了溅射用铁电陶瓷靶（ＰＺＴ，ＰＬＺＴ）的烧结工艺，并对其显微结构进行了分析。结果表明，采用新的烧结工艺（含保护措施），可以有效地抑制ＰｂＯ的挥发，制备出组织结构及成分均匀、ＰｂＯ含量正常、致密度较高、不变形的符合磁控溅射要求的铁电陶瓷烧结靶。     

时间序列AR模型参数的积分求解法

基于对时间序列实质的分析，提出了旨在减少序列的随机误差影响以及提高拟合精度的ＡＲ模型参数的积分求解法．重点讨论了ＡＲ（１）模型及ＡＲ（ｐ）模型参数的积分求解法，并与最小二乘法在计算机上进行了仿真比较．结果表明，采用积分求解法所得的ＡＲ模型参数的估计精度比最小二乘法的高．     

剩余静校正的小波包预处理方法

强反射层追踪与相对时差拾取中的“多值”现象严重影响剩余静校正的效果，为此提出的小波包预处理方法，可以实现地震道噪声与信号及不同强反射层的分离，从而能自动识别并提取“纯”的强反射层，提高强反射层追踪的可靠性和相对时差的拾取精度．     

PWM逆变电源抗冲击负荷电路研究

对几种逆变电源的抗冲击性负荷电路进行分析，给出了一种便于实现且效果很好的电路，实验证明此电路对各种冲击负荷甚至输出短路都能进行很好的限流，可以彻底解决逆变电源在负载冲击下频繁停机的问题。     

损伤材料中扩展裂纹的应力场

利用Ｇｕｒｓｏｎ本构理论，导出了损伤材料在平面应力条件下准静态定常扩展Ｉ型裂纹近裂纹线应力场和裂纹前方塑性区尺寸的解析表达式。研究结果表明：随着材料损伤量的增加，裂纹尖端处应力降低；裂纹尖端处应力不存在奇异性；裂纹前方塑性区尺寸受材料损伤程度的影响。     

单角煤粉燃烧炉中煤粉着火与稳燃的数学模型

将煤粉空气两相流在着火前和着火期间基本上仍遵从的射流发展规律作为模型基础，考虑了煤粉颗粒与气相间的速度滑移与温度滑移。气相场按射流规律发展井计及颗粒群对气相温度、速度、浓度变化的影响；颗粒群则按Ｌａｇｒａｎｇｅ处理方法追踪颗粒变化史。模型首次采用了挥发分与环境氧气匹配达着火限方能产生挥发分火焰的概念并取得了与实验现象一致的计算结果。