浅析计算机网络信息安全问题及对策

随着IT应用在生活中的日益普及,互联网已经覆盖了175个国家和地区的数亿台计算机,用户数量超过lO亿计算机技术广泛应用于各行各业,向着深度和广度不断地发展,构成了各自的网络,为资源共享、信息交换和分布处理提供了良好的环境,企业上网、政府上网、学校用网以及网上购物等计算机的应用表现了一个网络化的社会已经呈现在我们的面前、因此,在增加网络实用性的同时,系统的脆弱性不可避免的显露了出来,使计算机网络面临严重的安全问题。!     

LIQUID PHASE TRANSPORT PROPERTIES IN A HIGH PRESSURE PACKED COLUMN

A mathematical model of fluid flow and mass transfer in a packed bed was derived and used to evaluate the liquid phase axial dispersion and mass transfer coefficients under high pressure conditions. The least-squares method was used to evaluate the rate parameters from experimental breakthrough curves, and the agreement between the concentration curves predicted from rate parameters and those measured experimentally was good. Experiments were performed at 20 and 200°C with water as a solvent and nonporous soda-lime glass beads as packing. Although the axial dispersion coefficient was independent of temperature and pressure, the mass transport parameters were found to be pressure dependent.     

Manipulating the microstructure and rheology in polymer‐organoclay composites

A series of nanocomposites prepared by melt‐blending of cloisite‐based organoclays with poly(ethylene‐vinylacetate) (EVA) and neutralized poly (ethylene‐methacrylic acid) (EMA) copolymers were investigated via DSC, small‐angle X‐ray scattering (SAXS), and rheological techniques. SAXS results indicated partial clay exfoliation in all samples. In both EMA and EVA systems, the nominal melting temperature T_m and bulk crystallinity are not significantly affected by the presence of organoclays, suggesting that clay particles are predominantly confined in the amorphous phase. In rheological measurements (above T_m), the EVA‐clay system demonstrated a solid‐like rheological behavior under the small‐strain oscillatory shear, yet it was able to yield and flow under a steady shear, which is the characteristic of physical crosslinking. In contrast, the EMA‐clay system exhibited a melt‐like rheological behavior, where the influence of organoclay on the thermorheological behavior of the EMA composite was quite minimal. We propose that the carbonyl groups of vinylacetate in EVA interact with the clay surface, resulting in a strong physically crosslinking like interaction in the melt. On the other hand, the interaction between EMA and clay is weak because of repulsion between carboxyl anions and negatively charged clay surface.     

The viscoelastic properties of rubber–resin blends. III. The effect of resin concentration

The viscoelastic properties of a rubber–resin blend, which influences performance of the blend as a pressure-sensitive adhesive, depend upon the structure of the resin as well as its molecular weight. The effect of the concentration of a compatible resin in the blend was examined using a mechanical spectrometer. Four types of resins were used. These are the rosin esters, polyterpenes, pure monomer resins such as polystyrene and poly(vinyl cyclohexane), and petroleum stream resins. Each was examined in blends with both natural rubber and styrene–butadiene rubber over a range of concentrations. It is shown that the temperature of the tan δ peak for compatible systems can be predicted by the Fox equation, T = W₁T + W₂T, where W₁ and W₂ are the weight fractions of the resin and rubber, respectively, and the T_g's are the tan δ peak temperatures in K. The plateau modulus G for a blend can be identified as the G′ value in the rubbery plateau at the point where tan δ is at a minimum. The relationship between G and G, the plateau modulus for the undiluted elastomer, is shown to be proportional to the volume fraction of the elastomer raised to the 2.3–2.4 power for natural rubber with six different compatible resins. The exponent for styrene–butadiene rubber is 2.5–2.6 with four different resins. Using these relationships, both the tan δ peak temperature and plateau modulus can be predicted for a rubber–resin system from data on the unmodified elastomer and on one typical rubber–resin blend.     

Low-temperature catalytic combustion of methane over MnO x –CeO2 mixed oxide catalysts: Effect of preparation method

The effect of preparation method on MnO _x –CeO₂ mixed oxide catalysts for methane combustion at low temperature was investigated by means of BET, XRD, XPS, H₂-TPR techniques and methane oxidation reaction. The catalysts were prepared by the conventional coprecipitation, plasma and modified coprecipitation methods, respectively. It was found that the catalyst prepared by modified coprecipitation was the most active, over which methane conversion reached 90% at a temperature as low as 390 °C. The XRD results showed the preparation methods had no effect on the solid solution structure of MnO _x –CeO₂ catalysts. More Mn⁴⁺ and richer lattice oxygen were found on the surface of the modified coprecipitation prepared catalyst with the help of XPS analysis, and its reduction and BET surface area were remarkably promoted. These factors could be responsible for its higher activity for methane combustion at low temperature.     

肿节风注射液安全性实验评价

目的：对肿节风注射液进行异常毒性、溶血与凝聚试验、过敏反应安全性实验评价。方法：根据《中国药典》2010年版一部附录＂中药注射剂安全性检查法应用指导原则＂的要求及相关项目的技术规范进行试验。结果：按每只小鼠尾静脉注射0.5ml肿节风注射液,结果实验小鼠均无异常反应;溶血与凝聚试验供试品管中的溶液在3小时内不发生溶血和凝聚;按豚鼠腹腔注射0.5ml/只和静脉注射1.0ml/只作为本品的致敏剂量和激发剂量,结果试验豚鼠均未出现过敏反应。结论：本肿节风注射液进行的异常毒性、溶血与凝聚试验和致敏反应的安全性评价符合规定。     

Asymptotic state behaviour and its modeling for saturated sand

A new double hardening elasto-plastic model is proposed in this paper based on the existing unified hardening model (UH model). By assuming that there is part coupling effect between the plastic volumetric strain and plastic shear strain, hardening parameters consisting of a coupled and an uncoupled components are adopted in this model. A unique feature of this model is that it can describe not only the conventional drained and undrained behaviors of soil, but also the stress-strain relationships of soil under partially drained conditions which can be volumetric compression or dilation. Adopting the asymptotic state concept, simple equations for estimating the limiting stress ratio under undrained or earth pressure at rest (i.e. K ₀) conditions are derived. The new model is relatively simple to be adopted in practice for two reasons. First, the same soil parameters as in Cam-clay model are used except the addition of one extra parameter, the stress ratio at the characteristic state. Second, all the parameters can be determined using conventional triaxial compression tests. Supported by the National Natural Science Foundation of China (Grant Nos. 10672010 and 50479001) and the National Earthquake Science Item (Grant No. 200808076)     

凹凸棒石粘土悬浮液的悬浮性研究

研究了凹凸棒石粘土尺寸、悬浮液浓度、分散时间等因素对凹凸棒石粘土水和乙醇悬浮液悬浮性的影响,试验结果表明:凹凸棒石粘土水悬浮液的悬浮性显著高于乙醇悬浮液的悬浮性;水悬浮液中凹凸棒石粘土长度在38μm和71μm之间对悬浮性影响不大;使用50 W功率的超声波发生器分别分散10 min和15 min可以使凹凸棒石粘土分别在水和乙醇介质中充分分散;悬浮剂浓度为5 g/150 mL时水悬浮液的悬浮性最好。     

Relay selection with feedback beamforming information through designed sector sweep report frame for mmWave WPANs

This paper proposes a novel relay selection strategy based on the feedback beamforming （BF） information through designed sector sweep （SSW） report frame for millimeter-wave （mmWave） wireless personal networks （WPANs）. First, an SSW report frame compatible with IEEE 802.11ad standard is designed. Second, an approach collecting instantaneous channel state information （CSI） overheard during BF is devised. Third, with the aim of minimizing the outage probability and maximizing the overall network throughput capacity, the optimal relay selection issue for non-line-of-sight （NLoS） links is formulated as a bipartite graph, and Kuhn Munkres （KM） algorithm is provided to resolve it. Both theoretical analysis and simulation results show, with CSI considering NLoS conditions and selected relays according to the overall network throughput capacity maximization principle, the improvements achieved over opportunistic relay selection strategy in terms of overall network throughput capacity and outage probability with minimal modifications to IEEE 802.1lad.