ASPE: attribute-based secure policy enforcement in vehicular ad hoc networks

Vehicular ad hoc networks (VANETs) are usually operated among vehicles moving at high speeds, and thus their communication relations can be changed frequently. In such a highly dynamic environment, establishing trust among vehicles is difficult. To solve this problem, we propose a flexible, secure and decentralized attribute based secure key management framework for VANETs. Our solution is based on attribute based encryption (ABE) to construct an attribute based security policy enforcement (ASPE) framework. ASPE considers various road situations as attributes. These attributes are used as encryption keys to secure the transmitted data. ASPE is flexible in that it can dynamically change encryption keys depending on the VANET situations. At the same time, ASPE naturally incorporates data access control policies on the transmitted data. ASPE provides an integrated solution to involve data access control, key management, security policy enforcement, and secure group formation in highly dynamic vehicular communication environments. Our performance evaluations show that ASPE is efficient and it can handle large amount of data encryption/decryption flows in VANETs.     

共聚物混溶性热力学-分子内排斥作用与附加共聚焓

基于聚合物分子间物理相互作用和统计平均场理论,引入附加共聚焓定义,使聚合物分子间的作用得到量化,同时推导出二元共混体系相互作用参数和三元共混体系混合焓关系式.利用所导出的公式解释一些常见聚合物共混体系和增溶体系.导出的关系式很好地解释了聚合物的热力学混溶性,但不能解释聚合物共混增溶作用.     

共聚物混溶性热力学-分子内排斥作用与附加共聚焓

基于聚合物分子间物理相互作用和统计平均场理论,引入附加共聚焓定义,使聚合物分子间的作用得到量化,同时推导出二元共混体系相互作用参数和三元共混体系混合焓关系式.利用所导出的公式解释一些常见聚合物共混体系和增溶体系.导出的关系式很好地解释了聚合物的热力学混溶性,但不能解释聚合物共混增溶作用.     

Unlinkability Measure for IEEE 802.11 Based MANETs

In this paper, we propose a two-step unlinkability measuring approach for MANET, i.e., (a) evidence collection using statistical packet-counting traffic analysis, (b) evidence theory-based unlinkability measure. We use IEEE 802.11b-based MANETs as our analytical systems. Using our approach, we can collect a set of evidence to set up a probability assignment for each possible communication relation (i.e., the data sender and corresponding receiver); and then we can apply the evidence theory-based unlinkability measuring methods to derive the unlinkability evaluations of the 802.11b MANET.     

Modeling Pairwise Key Establishment for Random Key Predistribution in Large-Scale Sensor Networks

Sensor networks are composed of a large number of low power sensor devices. For secure communication among sensors, secret keys are required to be established between them. Considering the storage limitations and the lack of post-deployment configuration information of sensors, random key predistribution schemes have been proposed. Due to limited number of keys, sensors can only share keys with a subset of the neighboring sensors. Sensors then use these neighbors to establish pairwise keys with the remaining neighbors. In order to study the communication overhead incurred due to pairwise key establishment, we derive probability models to design and analyze pairwise key establishment schemes for large-scale sensor networks. Our model applies the binomial distribution and a modified binomial distribution and analyzes the key path length in a hop-by-hop fashion. We also validate our models through a systematic validation procedure. We then show the robustness of our results and illustrate how our models can be used for addressing sensor network design problems.     

A secure group key management scheme for hierarchical mobile ad hoc networks

In this paper, we present a secure group key management scheme for hierarchical mobile ad hoc networks. Our approach aims to improve both scalability and survivability of group key management for large-scale wireless ad hoc networks. To achieve our goal, we propose the following approaches: (1) a multi-level security model, which follows a modified Bell-La Padula security model that is suitable in a hierarchical mobile ad hoc networking environment, and (2) a decentralized group key management infrastructure to achieve such a multi-level security model. Our approaches reduce the key management overhead and improve resilience to any single point failure problem. In addition, we have developed a roaming protocol that is able to provide secure group communication involving group members from different groups without requiring new keys; an advantage of this protocol is that it is able to provide continuous group communication even when the group manager fails.     

LMPM／PP复合材料的导电性能

通过挤出拉伸制备了ＬＭＰＭ／ＰＰ复合材料。测定了ＬＭＰＭ／ＰＰ复合材料的体积电阻率，并由此计算了复合材料对电磁波辐射的屏蔽效率。结果表明，复合材料导电的临界体积分数φｃ与ＬＭＰＭ的形态结构密切相关，ＬＭＰＭ越细，φｃ越低；当ＬＭＰＭ形成纤维后，φｃ更低。ＬＭＰＭ为０．１μｍ时，φｃ＝６％，再挤出拉伸时，φｃ＝２％。只有当φ〉φ，ＬＭＰＭ／ＰＰ复合材料对电磁波辐射才有屏幕作用，且屏蔽效率与（φ－φｃ     

聚合物粘结磁体用Nd—Fe—B微晶磁粉的氧化行为及防护

采用有机硅树脂、硅烷偶联剂和重铬酸盐处理快淬Ｎｄ－Ｆｅ－Ｂ微晶粉表面，通过热氧化增重试验２、湿热环境试验以及差示热分析法（ＤＴＡ）研究了上分的氧化行为和抗化效果，实验表明，上述方法能提高磁粉的抗氧化行为。     

Porous-conductive chitosan scaffolds for tissue engineering, 1. Preparation and characterization

Novel porous-conductive chitosan scaffolds were fabricated by incorporating conductive polypyrrole (PPy) particles into a chitosan matrix and employing a phase separation technique to build pores inside the scaffolds. Conductive polypyrrole particles were prepared with a microemulsion method using FeCl3 as a dopant. The preparation conditions were optimized to obtain scaffolds with controlled pore size and porosity. The conductivity of the scaffolds was investigated using a standard four-point probe technique. It was found that several kinds of scaffolds showed a conductivity close to 10(-3) S.cm(-1) with a low polypyrrole loading of around 2 wt.-%. The main mechanical properties, such as tensile strength, breaking elongation and Young's modulus of the scaffolds, were examined both in the dry and in the hydrated states. The results indicated that a few different kinds of scaffolds exhibited the desired mechanical strength for some tissue engineering applications. The miscibility of polypyrrole and chitosan was also evaluated using a dynamic mechanical method. The presence of significant phase separation was detected in non-porous PPy/chitosan scaffolds but enhanced miscibility in porous PPy/chitosan scaffolds was observed.