信息网络系统可靠性问题的探讨

探讨了网络安全受到主动威胁时的网络可靠性,通过信息网络可靠性定义的确定,建立了信息网络的一般可靠性模型以及受有无主动攻击时信息网络的受损情况,得到了信息网络系统的可靠性评估方法,为信息网络的免遭破坏提供预防措施。     

上海半自然森林更新苗物种组成与多样性研究

城市半自然森林具有独特的群落结构和生物多样性特征,研究城市化影响的半自然森林更新特征,可以为城市生物多样性保育与地带性植被恢复重建提供借鉴。文章以上海辰山残存半自然森林1 hm^2固定监测样地为对象,调查分析半自然森林更新苗的物种组成特征。结果表明:1 hm^2样地更新苗共5 937株,分属22科32属37种,其中上海自然分布的乡土种占57.89%,明显高于城市人工林的乡土树种比例;香樟、构树、天竺桂、朴树和小蜡等5种更新苗占总数的57.2%,聚集性分布格局明显;在11个植被群落类型中,各类型更新苗的丰富度普遍较高,不同树种的更新苗存活和发育潜力存在差异。     

网络攻防技术综述

随着互联网络技术的发展,在享受网络带来方便、快捷的服务的同时,还需要防备网络的攻击,以保证网络的安全运行。     

1941年日军对湖南常德的细菌攻击

1941年11月4日,日本第731部队远征队使用细菌武器对湖南常德发动恐怖袭击,由此造成大规模的鼠疫流行,夺去了7000多中国人民的生命。这次袭击是日本最高军事当局精心策划的一系列对华恐怖行动的一部分,是日本违反国际公法、实行国家恐怖主义的罪证之一。     

Distribution of trust model in P2P network based on equilibrium theory

There are a large number of malicious attack nodes and collusion groups in P2P(peer to peer) network, and the existing trust models improve the P2P network environment to some extent, but the emphasis of the models are different, which are unable to fully solve large-scale malicious attacks and deception. Therefore, a P2P trust model based on equilibrium theory is presented. The model consists of the construction of the trust structure, the malicious node detection and trust speculation. It constructs trust network according to the equilibrium theory, uses the equilibrium theory to define nodes balance factor, detects balance malicious nodes by calculating the impact of malicious behavior on the network, and adopts trust inference algorithm to estimate trust nodes to prevent distrust network nodes being added. Experimental results show that the model is reliable, and the algorithm is efficient and robust.     

Utilization of semi-natural grassland through integrated generation of solid fuel and biogas from biomass. I. Effects of hydrothermal conditioning and mechanical dehydration on mass flows of organic and mineral plant compounds, and nutrient balances

The use of semi-natural grasslands for the production of renewable energy through conventional conversion techniques faces major limitations because of chemical and physical properties of the biomass. A new conversion procedure was developed which separates the biomass, as silage, into a liquid phase for biogas production and into a solid fraction to be used as fuel. Separation (mechanical dehydration) is carried out with a screw press after mashing with water (hydrothermal conditioning). The effect of hydrothermal conditioning at different temperatures (5, 60 and 80°C) and mechanical dehydration on mass flows of plant compounds into the press fluid was investigated for five grassland pastures typical of mountain areas of Germany. Results show that 0·18 of the crude fibre was transferred into the fluid, whereas more digestible organic compounds, such as crude protein and nitrogen-free extract, showed mass flows of 0·40 and 0·31 respectively. While 0·52–0·89 of potassium (K), magnesium (Mg) and chloride (Cl), which are detrimental for the combustion of the press cake, were transferred into the press fluid, more than 0·50 of calcium, which has positive combustion properties, remained in the press cake. Significantly ( P  <   0·05) higher mass flows were detected at conditioning temperatures of 60°C (K and Mg) and 80°C (crude fibre and nitrogen-free extract) compared with the 5°C treatment. Because of the separation of solids and liquids, high proportions of P (0·61–0·74) and K (0·64–0·85) but only 0·32–0·45 of nitrogen exported from the grassland would be recycled with an application of the digestates from the anaerobic digestion of the press liquid.     

Inheritance of several sources of resistance to Phomopsis stem canker (Diaporthe helianthi Munt.-Cvet.) in sunflower (Helianthus annuus L.)

The hybrids from 2 factorial crosses involving a total of 7 female lines and 11 restorers, representing the known range of reaction of sunflower to Phomopsis stem canker and most of the resistance sources used in breeding programmes, were studied in multilocational semi-natural attack trials and by artificial infections on leaves and stems in 1996, 1997 and 1998. The results confirm that resistance is quantitative, with predominantly additive effects, although there were some female × male interactions when individual trials were analysed. For lines used in both crosses, relative general combining abilities were stable. Some lines not bred for Phomopsis resistance showed good or intermediate levels of resistance. Lines from or including Yugoslavian, Rumanian and Russian sources of resistance and interspecific hybrids all provided good levels of resistance. The majority of parental lines showed the same relative reactions to semi-natural attack and artificial infections on leaves or stems indicating that their resistance is characterised by a slow rate of mycelial extension. However, one genotype showed resistance to passage of Phomopsis stem canker from the petiole to the stem and two genotypes appeared susceptible to tests but resistant to semi-natural attack, indicating that their resistance is controlled by factors not measured by the mycelium tests. The use of combinations of these resistance sources to give high levels of stable resistance to Phomopsis stem canker is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

不同密度下近天然落叶松云冷杉林各土层土壤理化特征

本研究以8块不同林分密度近天然落叶松云冷杉林为对象, 研究不同林分下密度对不同土层土壤的理化特征。结果表明, 相同林分密度条件下, 土壤物理性质随土层深度增加呈显著变化(P0.05);除全氮外, 其他养分元素浓度差异不显著(P0.05)。不同密度条件下的土壤养分浓度并未表现出明显的变化规律, 也没有在某一密度之后出现明显的下降现象。林分密度为1 058株·hm-2时, 虽然土壤养分浓度有所降低, 但总体差异并不显著。这说明在试验区目前林分密度下, 土壤养分状况并未受影响, 可适当补植, 增加林地的利用效率。     

浅析DDoS攻击和防范

DDoS的英文缩写是Distributed Denial of Service，即“分布式拒绝服务”。DDoS的攻击通过很多“僵尸主机”（被攻击者入侵过或可间接利用的主机）向受害主机发送大量看似合法的网络包，从而造成网络阻塞或服务器资源耗尽而导致拒绝服务。本文介绍了DDoS攻击原理、攻击形式、检测方法和防范措施。