摘要：化学取代是有效调节分子电导,产生多通道输运、量子干涉效应和其他机制的关键方法.但分子骨架和侧基之间存在复杂的相互作用,目前仍未被研究清楚.在本工作中,我们结合扫描隧道显微镜裂结实验技术和第一性原理计算方法,深入研究了具有不同σ和π侧基的分子电导.实验结果及理论分析表明,σ侧基的加入引起了分子前线轨道的对称性破缺并加剧了分子内散射,从而导致电导的降低.相反,π侧基引入了额外的电荷传输通道,实现了电荷传输的多通道效应,增加了分子的电导.这些发现为未来分子功能化和分子电子器件的设计提供了坚实的基础.

摘要：The recent decade has witnessed an upsurge in the demands of intelligent and simplified Internet of Things(IoT)networks that provide ultra-low-power communication for numerous miniaturized *** the research community has paid great attention to wireless protocol designs for these networks,researchers are handicapped by the lack of an energy-efficient software-defined radio(SDR)platform for fast implementation and experimental *** SDRs perform well in battery-equipped systems,but fail to support miniaturized IoT devices with stringent hardware and power *** paper takes the first step toward designing an ultra-low-power SDR that satisfies the ultra-low-power or even battery-free requirements of intelligent and simplified IoT *** achieve this goal,the core technique is the effective integration ofµW-level backscatter in our SDR to sidestep power-hungry active radio frequency *** carefully develop a novel circuit design for efficient energy harvesting and power control,and devise a competent solution for eliminating the harmonic and mirror frequencies caused by backscatter *** evaluate the proposed SDR using different modulation schemes,and it achieves a high data rate of 100 kb/s with power consumption less than 200µW in the active mode and as low as 10µW in the sleep *** also conduct a case study of railway inspection using our platform,achieving 1 kb/s battery-free data delivery to the monitoring unmanned aerial vehicle at a distance of 50 m in a real-world environment,and provide two case studies on smart factories and logistic distribution to explore the application of our platform.

摘要：There are a lot of security issues in block cipher *** analysis and enhanced design of a dynamic block cipher was ***,the safety of ciphertext was enhanced based on confusion substitution of S-box,thus disordering the internal structure of data blocks by four steps of matrix ***,the diffusivity of ciphertext was obtained by cyclic displacement of bytes using column ambiguity *** dynamic key was finally generated by using LFSR,which improved the stochastic characters of secret key in each of round of *** safety performance of proposed algorithm was analyzed by simulation *** results showed the proposed algorithm has a little effect on the speed of encryption and decryption while enhancing the ***,the proposed algorithm has highly scalability,the dimension of S-box and the number of register can be dynamically extended according to the security requirement.

摘要：Role based access control is one of the widely used access control *** are investigations in the literature that use knowledge representation mechanisms such as formal concept analysis(FCA),description logics,and Ontology for representing access control ***,while using FCA,investigations reported in the literature so far work on the logic that transforms the three dimensional access control matrix into dyadic formal *** transformation is mainly to derive the formal concepts,lattice structure and implications to represent role hierarchy and constraints of *** this work,we propose a methodology that models RBAC using triadic FCA without transforming the triadic access control matrix into dyadic formal *** discussion is on two lines of *** present how triadic FCA can provide a suitable representation of RBAC policy and we demonstrate how this representation follows role hierarchy and constraints of RBAC on sample healthcare network available in the literature.

摘要：Since most ad hoc mobile devices today operate on batteries,the power consumption becomes an important *** paper proposes a cross-layer design of energy-aware ad hoc on-demand distance vector(CEAODV) routing protocol which adopts cross-layer mechanism and energy-aware metric to improve AODV routing protocol to reduce the energy consumption and then prolong the life of the whole *** CEAODV,the link layer and the routing layer work together to choose the optimized transmission power for nodes and the route for *** link layer provides the energy consumption information for the routing layer and the routing layer chooses route accordingly and conversely controls the link layer to adjust the transmission *** simulation result shows that CEAODV can outperform AODV to save more *** can reduce the consumed energy by about 8%over traditional energy-aware *** the performance is better when the traffic load is higher in the network.

摘要：本文提出一种在特殊任务下基于Chebychev映射的移动机器人混沌全覆盖路径规划器的设计新策略。所设计的混沌路径规划器包含一个二维的Chebychev映射,该映射由两个一维的Chebychev映射构建而成。对规划器所产生的时间序列,进行反正弦变换,可以改善系统的混沌特性和均匀分布特性,从而提高机器人在完成特殊任务时的覆盖率和随机特性。通过仿射变换,Chebychev混沌系统映射到机器人工作空间的可行区域内,然后设计有障碍物环境下全覆盖路径规划的通用方法。仿真结果显示,所设计的混沌路径规划器在可行空间能够安全运行,不需要设计避障算法。所设计策略能够满足特殊任务下随机性、遍历性和高效率的需求。

摘要：Not So Cooperative Caching(NSCC) considers a network comprised of selfish nodes; each is with caching capability and an objective of reducing its own access cost by fetching data from its local cache or from neighboring caches. These nodes would cooperate in caching and share cached content if and only if they each benefit. The challenges are to determine what objects to cache at each node and to implement the system in the context of information Centric Networking(ICN). This work includes both a solution for the NSCC problem and a design and implementation of an NSCC system in Named Data Networking(NDN), a large effort that exemplifies ICN. Our design applies NDN synchronization protocol to facilitate the information exchange among nodes, adopts group key encryption to control data access within the NSCC group, and offers an error checker to detect error events in the system. Our approach is validated by deploying the system we developed on Planet Lab.

摘要：To deal with the key-exposure problem in signature systems, a new framework named parallel key-insulated signature (PKIS) was introduced, and a concrete PKIS scheme was proposed. Compared with traditional key-insulated signature (KIS) schemes, the proposed PKIS scheme allows a frequent updating for temporary secret keys without increasing the risk of helper key-exposure. Moreover, the proposed PKIS scheme does not collapse even if some (not all) of the helper keys and some of the temporary secret keys are simultaneously exposed. As a result, the security of the PKIS scheme is greatly enhanced, and the damage caused by key-exposure is successfully minimized.

摘要：数据完整性公开验证对提高云存储系统的适用性、可服务性至关重要。最近,Tan和Jia(2014)提出了一种基于身份的云数据完整性公开验证(NaEPASC)协议,以简化用户密钥管理和减轻完整性验证负担。NaEPASC可以使第三方审计人员(third-party auditor,TPA)能够在云计算环境中高效和安全地验证外包数据的完整性。然而,本文指出NaEPASC在数据签名阶段容易遭受签名伪造攻击,即恶意云服务器可以通过使用两个正确的签名来伪造任意数据块的有效签名。此外,证明了NaEPASC在挑战阶段受到数据隐私威胁,即TPA或冒充TPA的外部攻击者可以分析出外包数据的内容。本文分析表明NaEPASC在数据验证过程中不安全。本文的工作有助于密码学家和工程师设计、实施更安全高效的基于身份的云存储数据完整性公开审计方案。

摘要：Cobalt nanoparticles(NPs)catalysts are extensively used in heterogeneous catalytic reactions,and the addition of alkali metal promoters is a common method to modulate the catalytic performance because the catalyst's surface structures and morphologies are sensitive to the addition of ***,the underlying modulation trend remains ***,the adsorption of alkali metal promoters(Na and K)on the surfaces of face-centered-cubic(FCC)and hexagonal-closest packed(HCP)polymorphous cobalt was systematically investigated using density functional ***,the effect of alkali promoters on surface energies and nanoparticle morphologies was revealed on the basis of Wulff *** FCC-Co,the exposed area of the(111)facet in the nanoparticle increases with the adsorption coverage of alkali metal ***,the(311),(110),and(100)facets would disappear under the higher adsorption coverage of alkali *** HCPCo,the Wulff morphology is dominated by the(0001)and(1011)facets and is independent of the alkali metal adsorption *** work provides insights into morphology modulation by alkali metal promoters for the rational design and synthesis of cobalt-based nanomaterials with desired facets and morphologies.