一种自适应的网络拓扑自动发现算法

针对现有网络拓扑发现算法的不足，提出并实现了一种自适应网络拓扑自动发现算法——RANTAD(Robust and Adaptive Network Topology Auto Discovery)。BANTAD算法以TCP／IP网络管理体系结构为依托，将现有的各协议和发现技术进行有机地整合，在发现过程的每个阶段，能根据网络的实际情况对所采用的协议和技术进行自适应调整。模拟实验表明RANTAD算法能快速有效地自动发现网络拓扑信息，并且具有很好的健壮性。     

无线自组织网络覆盖网络资源发现算法研究

从无线自组织网络特点及其资源发布并发现的特性出发,提出了分布式的覆盖网络资源发现算法PARD.PARD以哈希资源名称作为路由地址,利用覆盖网络技术,使资源信息分布存储在多个节点上,提高了整个网络的负载均衡能力.通过代理及本地技术,使得对1个附近节点的资源查询尽量不需和远端节点通信,最大程度地避免了全网范围的信息洪泛,有助于网络的扩展和管理.实验结果表明,PARD算法具有良好的稳定性和可扩展性,与Broadcast算法相比,PARD算法能有效的降低网络流量,提高了网络的效用和性能.     

Global mapping of the yeast genetic interaction network

A genetic interaction network containing approximately 1000 genes and approximately 4000 interactions was mapped by crossing mutations in 132 different query genes into a set of approximately 4700 viable gene yeast deletion mutants and scoring the double mutant progeny for fitness defects. Network connectivity was predictive of function because interactions often occurred among functionally related genes, and similar patterns of interactions tended to identify components of the same pathway. The genetic network exhibited dense local neighborhoods; therefore, the position of a gene on a partially mapped network is predictive of other genetic interactions. Because digenic interactions are common in yeast, similar networks may underlie the complex genetics associated with inherited phenotypes in other organisms.     

Global genetic change tracks global climate warming in Drosophila subobscura

Comparisons of recent with historical samples of chromosome inversion frequencies provide opportunities to determine whether genetic change is tracking climate change in natural populations. We determined the magnitude and direction of shifts over time (24 years between samples on average) in chromosome inversion frequencies and in ambient temperature for populations of the fly Drosophila subobscura on three continents. In 22 of 26 populations, climates warmed over the intervals, and genotypes characteristic of low latitudes (warm climates) increased in frequency in 21 of those 22 populations. Thus, genetic change in this fly is tracking climate warming and is doing so globally.     

Identifying global centers of genetic diversity for grain sorghum with the use of rice DNA markers

STS and InDel markers developed on the basis of DNA sequences of certain rice genes are used for a comparative study of grain sorghum accessions. The main sorghum genetic diversity centers are revealed, two in Africa and a third in regions of Central, East, and South Asia.     

全球大豆贸易网络演化特征与政策启示

大豆是我国进口贸易依存度较高的农产品之一,作为大豆的下游加工品,豆油和豆粕的贸易状况对大豆供求结构也存在显著影响,分析全球大豆及其加工品的贸易网络演化特征,对于贸易摩擦背景下的大豆稳定供应具有重要意义。本文选择2002年和2017年全球大豆、豆油、豆粕进口量前五十位国家的贸易数据,分别构建无权贸易网络和加权贸易网络,对总体网络特征、国别关系特征和国别地位特征进行分析。结果显示:全球大豆、豆油、豆粕贸易规模逐渐扩大,贸易密集性和聚集程度不断增强,出口较进口更为集中,核心国在网络中占有重要地位并一定程度掌控贸易流向。随着大豆国际贸易发展,网络结构趋于均衡,更多国家参与到大豆贸易中来。在中美贸易摩擦与高进口依存度背景下,我国应立足大豆的基本供求特征,通过积极开发大豆贸易市场、寻求豆油和豆粕的替代品、推进我国大豆期货市场国际化等手段,扭转进口集聚导致的被动地位,构建我国为主导地位的大豆供应体系。     

基于神经网络和遗传算法的池塘溶解氧预测模型

水产养殖池塘是一个多变量、非线性和大时延系统,其中溶解氧的预测也是一个复杂的问题。针对大连某水产养殖池塘,作者建立了一个基于Levenberg—Marquardt（LM）神经网络和遗传算法（GA）的溶解氧预测模型GA—LM,并将该模型与传统的BP神经网络进行比较分析。结果表明：使用本研究中建立的GA-LM模型预测的溶解氧值和实际测定值吻合较好,预测更为精准,运行时间明显减少。     

基于神经网络和遗传算法的池塘溶解氧预测模型

水产养殖池塘是一个多变量、非线性和大时延系统,其中溶解氧的预测也是一个复杂的问题。针对大连某水产养殖池塘,作者建立了一个基于Levenberg-Marquardt(LM)神经网络和遗传算法(GA)的溶解氧预测模型GA-LM,并将该模型与传统的BP神经网络进行比较分析。结果表明:使用本研究中建立的GA-LM模型预测的溶解氧值和实际测定值吻合较好,预测更为精准,运行时间明显减少。     

A global geometric framework for nonlinear dimensionality reduction

Scientists working with large volumes of high-dimensional data, such as global climate patterns, stellar spectra, or human gene distributions, regularly confront the problem of dimensionality reduction: finding meaningful low-dimensional structures hidden in their high-dimensional observations. The human brain confronts the same problem in everyday perception, extracting from its high-dimensional sensory inputs-30,000 auditory nerve fibers or 10(6) optic nerve fibers-a manageably small number of perceptually relevant features. Here we describe an approach to solving dimensionality reduction problems that uses easily measured local metric information to learn the underlying global geometry of a data set. Unlike classical techniques such as principal component analysis (PCA) and multidimensional scaling (MDS), our approach is capable of discovering the nonlinear degrees of freedom that underlie complex natural observations, such as human handwriting or images of a face under different viewing conditions. In contrast to previous algorithms for nonlinear dimensionality reduction, ours efficiently computes a globally optimal solution, and, for an important class of data manifolds, is guaranteed to converge asymptotically to the true structure.     

A genomic regulatory network for development

Development of the body plan is controlled by large networks of regulatory genes. A gene regulatory network that controls the specification of endoderm and mesoderm in the sea urchin embryo is summarized here. The network was derived from large-scale perturbation analyses, in combination with computational methodologies, genomic data, cis-regulatory analysis, and molecular embryology. The network contains over 40 genes at present, and each node can be directly verified at the DNA sequence level by cis-regulatory analysis. Its architecture reveals specific and general aspects of development, such as how given cells generate their ordained fates in the embryo and why the process moves inexorably forward in developmental time.     

A combinatorial approach to materials discovery

A method that combines thin film deposition and physical masking techniques has been used for the parallel synthesis of spatially addressable libraries of solid-state materials. Arrays containing different combinations, stoichiometries, and deposition sequences of BaCO(3), Bi(2)O(3), CaO, CuO, PbO, SrCO(3), and Y(2)O(3) were generated with a series of binary masks. The arrays were sintered and BiSrCaCuO and YBaCuO superconducting films were identified. Samples as small as 200 micrometers by 200 micrometers in size were generated, corresponding to library densities of 10,000 sites per square inch. The ability to generate and screen combinatorial libraries of solid-state compounds, when coupled with theory and empirical observations, may significantly increase the rate at which novel electronic, magnetic, and optical materials are discovered and theoretical predictions tested.     

Ex situ conservation of plant genetic resources: global development and environmental concerns

Conservation of plant genetic resources is achieved by protection of populations in nature (in situ) or by preservation of samples in gene banks (ex situ). The latter are essential for users of germplasm who need ready access. Ex situ conservation also acts as a back-up for certain segments of diversity that might otherwise be lost in nature and in human-dominated ecosystems. The two methods are complementary, yet better understanding of this interrelation and the role of ex situ conservation in global environmental considerations is needed. Inclusion of ex situ conservation efforts within current environmental policies conserving global diversity would focus greater international attention on the safeguarding of these efforts.