The genetic diversity of cen-tral and peripheral popula-tions of ratlike hamster(Cricetulus triton)

The impact of habitat fragmentation and isolation on the genetic diversity of populations has attracted much attention in studies of meta-population and conservation biology. In this work, using the randomly amplified polymorphic DNA (RAPD) technique, we studied the genetic diversity of central, peripheral and peninsular populations of ratlike hamster, which were collected in five locations of the North China Plain and its surrounding areas, in 1999. The study revealed that, ⅰ) the genetic diversity of central population of Raoyang County＞the sub-central populations of Gu'an County and Taikang County＞the peripheral population of Shunyi District＞the peninsular population of Mentougou District; ⅱ) the genetic diversities of the five populations were positively correlated to the nearest distances to the peripheral line of population distribution; ⅲ) there were significant differences of gene frequencies of some RAPD fragments among the five populations. More RAPD fragments disappeared in peripheral populations than in central or sub-central populations. The frequencies of two RAPD fragments were correlated to the latitude. This study clearly indicated that the variation of the genetic diversities of the five populations was caused by edge effect and frag- mentation through the enhanced inbreeding and genetic drift, and thus supported the view that habitat fragmentation and related edge effect reduce the population genetic diversity.     

网络路径容量测量算法仿真研究

网络路径容量的测量在网络管理、网络规划与设计、提高网络应用程序的性能等方面，都具有重要意义。现有的网络路径容量测量工具都是采用Pacbt Pair测量算法设计的，这些测量工具在实际使用中的性能不尽人意。Packet Pair测量算法的ns-2仿真测量分析表明：网络在重载时Packet Pair测量算法不能正确测量出网络路径的容量；Packet Pair测量算法中的测量分组的长度并不是采用最大值为最佳。根据仿真测量分析的结论，提出了Double Packet Pair网络路径容量测量算法，改进了原有算法测量速度慢，重载环境下测量精度不高的缺点。     

一种分层多播的带宽适应策略

提出了一种基于接收端意见反馈的带宽适应策略。在该策略中，为了避免反馈信息在源端的爆炸，给出了一个路由器分流合并的方法，使得带宽适应策略具有良好的缩放性。     

互生共长的长青藤与参天大树——从文学作品改编看20世纪中国文学与现代传播之电影

20世纪中国文学十分幸运地发生、发展在一个现代传播飞速发展的时代.电影,是现代传播的一种形式.在过去的近百年的中国文学发展的历史中有许多的文学作品借助电影这一现代传播的形式得以广泛传播,经久不衰;电影也从20世纪中国文学的宝库中汲取了丰富的创作源泉.近百年来,它们互生互长,共同繁荣,结出了累累硕果.     

基于PSO磁悬浮球系统自适应灰预测控制

目的 针对磁悬浮球系统非线性不稳定和滞后性的问题,提出一种基于粒子群优化的自适应灰色预测 PID (Proportion Integration Differentiation)复合控制策略。 方法 通过在 PID 控制模块的反馈环中引入具有等维新息特征的灰色预测器,对系统误差进行及时反馈修正,以提高控制系统的响应速度和鲁棒性;同时,融合粒子群智能算 法对控制器参数迭代优化,以提高控制系统控制精度和抗干扰能力;最后,在 MATLAB / Simulink 环境下搭建仿真 平台进行对比实验。 结果 验证基于粒子群优化的自适应灰预测控制系统模型的超调量、峰值时间、调节时间显著 改善。 结论 证实该策略可以有效抑制系统滞后性,具有良好的稳定性和鲁棒性。     

有限规模下网络话音复用带宽的近似评估

通过对网络话音业务的近似分析和仿真，建立了相对简单的复用带宽分配机制．首先对规模较小、性能参数比较确定的接入网进行建模和具体分析，然后利用网络仿真器对所建模型丢失率随带宽变化的特性等进行了仿真，对缓冲区与时延等影响网络话音复用带宽的重要因素进行了讨论．仿真结果表明，在网络为有限规模时，本文的结论对于确定区分服务中应当分配给IP电话业务的网络带宽有实用意义．     

多码DS／CDMA传输自适应系统的序列优化

为了优化多码DS／CDMA系统性能，提出了一种自适应序列优化及功率控制方法，通过优化系统扩频码设计，使系统能有效地克服多径多址干扰，降低系统传输功率。此方法中，为提高接收端用户的信号干扰噪声比(SINR)，提出了一种快速收敛的优化序列设计算法，通过优化发送扩频序列和接收解扩序列，降低了多址干扰，提高了多径分集增益；通过调整发射功率，使接收端达到设定服务质量要求，是一种有效的多码DS／CDMA传输自适应方法。     

Rapid cold hardening process of insects and its ecologically adaptive significance

In contrast to overwintering cold hardening, a rapid cold hardening process has recently been described in insects. This process can rapidly enhance cold tolerance of insects in several hours or even minutes. The characteristics of rapid cold hardening include inducing conditions, cold hardening effects, and fitness costs. Physiological and biochemical mechanisms of rapid cold hardening include rapid changes in the phospholipid composition and the increase in hemolymph osmolalities, polyols production, proline and cold-induced proteins. Moreover, there are different views about the ecologically adaptive significance of rapid cold hardening in insects. This paper reviews research results about rapid cold hardening of insects since 1987, focusing on forms of cold injury, strategies of cold tolerance, and definitions, characteristics, physiological and biochemical mechanisms and adaptive significance of rapid cold hardening.     

皖南传统聚落的生态适应性

以景观生态的视角，对皖南传统聚落的选址、布局以及巷道空间、单体建筑形态等进行了分析与研究，以对当代建筑设计有所启迪．     

带宽控制技术分析及其实现

针对目前Internet技术中热门的QoS问题,讨论了带宽控制的基本方法和带宽动态划分的算法,分析了Linux内核和iproute2工具包中的关键数据结构,以及过滤器和队列调度规则,并对在Linux环境下,利用改进的双今牌桶算法对带宽的动态划分,实现对带宽的有效控制,从代码角度上作了分析和探索。