An upwind scheme based on the unstructured mesh is developed to solve ideal 2-D magnetohydrodynamics （MHD） equations. The inviscid fluxes are approximated by using the modified advection upstream splitting method （...An upwind scheme based on the unstructured mesh is developed to solve ideal 2-D magnetohydrodynamics （MHD） equations. The inviscid fluxes are approximated by using the modified advection upstream splitting method （AUSM） scheme, and a 5-stage explicit Runge-Kutta scheme is adopted in the time integration. To avoid the influence of the magnetic field divergence created during the simulation, the hyperbolic divergence cleaning method is introduced. The shock-capturing properties of the method are verified by solving the MHD shock-tube problem. Then the 2-D nozzle flow with the magnetic field is numerically simulated on the unstructured mesh. Computational results demonstrate the effects of the magnetic field and agree well with those from references.展开更多
A family of high_order accuracy explicit difference schemes for solving 2_dimension parabolic P.D.E. are constructed. Th e stability condition is r=Δt/Δx 2=Δt/Δy 2【1/2 and the truncation err or is O(Δt 3+Δx...A family of high_order accuracy explicit difference schemes for solving 2_dimension parabolic P.D.E. are constructed. Th e stability condition is r=Δt/Δx 2=Δt/Δy 2【1/2 and the truncation err or is O(Δt 3+Δx 4).展开更多
Aim To construct a third order upwind scheme for convection equation. Methods Upwind Lagrange interpolation was used. Results and Conclusion The schemes L p stability for p∈ is proved. Numerical exam...Aim To construct a third order upwind scheme for convection equation. Methods Upwind Lagrange interpolation was used. Results and Conclusion The schemes L p stability for p∈ is proved. Numerical examples show that performance of the third order upwind scheme is better than that of most second order schemes.展开更多
With the maturation of P2P technology, there are more and more challenges to the protection of digital rights. DRM for traditional Client/Server model can not satisfy the requirement of digital right protection of P2P...With the maturation of P2P technology, there are more and more challenges to the protection of digital rights. DRM for traditional Client/Server model can not satisfy the requirement of digital right protection of P2P network. With practical application of P2P network technology and new generational DRM technology, the article proposes a DRM model for P2P system based on trust degree. The proposed model shares the secret key to the trusty peers and affords necessary security ensure for digital content delivery based on P2P technology. Mathematic analyses and simulations show that, compared to the current DRM model, the proposed model is more robust toleration of transmit and security.展开更多
Resource sharing among peers is one of important application in Peer-to-Peer（P2P） network. Inexistenee of server makes P2P network to be a less trustable tool for property owners to distribute their resource. In ord...Resource sharing among peers is one of important application in Peer-to-Peer（P2P） network. Inexistenee of server makes P2P network to be a less trustable tool for property owners to distribute their resource. In order to protect intelligent property, reputation management strategy is adopted in many P2P network. As long as a P2P network reputation strategy is confirmed, application designer can employ a special detailed distribution scheme to fulfill content distribution within the net. Shmir （k, n） threshold scheme, for example, is an encryption scheme to enhance the distribution se curity of this kind of design. （k＊, n） threshold scheme is a new tool similar to Shmir scheme is proposed in this paper. The new scheme based on polynomial expansion and its security is decided by the one way function used in the secret distribution procedure. The scheme efficiency and its features as well as comparison between new and Shmir scheme are also discussed in this paper.展开更多
In order to reduce the traffic load and improve the availability of the shared resources in unstructured P2P networks, a caching scheme combining alternative index and adaptive replication （AIAR） is presented. AIAR ...In order to reduce the traffic load and improve the availability of the shared resources in unstructured P2P networks, a caching scheme combining alternative index and adaptive replication （AIAR） is presented. AIAR uses random walk mechanism to disperse the caching information of resources in the network based on its power-law characteristic, and dynamically adjusts replicas according to the visit frequency on resources and the degree information of peers. Subsequent experimental results show that the proposed AIAR scheme is beneficial to improve the search performance of success rate and respond speed. In addition, compared to some existing caching scheme, AIAR can perform much better in success rate, especially in a dynamic environment.展开更多
A class of two-level high-order accuracy explicit difference scheme for solving 3-D parabolic P.D.E is constructed. Its truncation error is (Δt2+Δx4) and the stability condition is r=Δt/Δx2=Δt/Δy2=Δt/Δz2≤1/6.
Alternating direction implicit (A.D.I.) schemes have been proved valuable in the approximation of the solutions of parabolic partial differential equations in multi-dimensional space. Consider equations in the form pa...Alternating direction implicit (A.D.I.) schemes have been proved valuable in the approximation of the solutions of parabolic partial differential equations in multi-dimensional space. Consider equations in the form partial derivative u/partial derivative t - partial derivative/partial derivative x(a(x,y,t) partial derivative u/partial derivative x) - partial derivative/partial derivative y(b(x,y,t) partial derivative u partial derivative y) = f Two A.D.I. schemes, Peaceman-Rachford scheme and Douglas scheme will be studied. In the literature, stability and convergence have been analysed with Fourier Method, which cannot be extended beyond the model problem with constant coefficients. Additionally, L-2 energy method has been introduced to analyse the case of non-constant coefficients, however, the conclusions are too weak and incomplete because of the so-called 'equivalence between L-2 norm and H-1 semi-norm'. In this paper, we try to improve these conclusions by H-1 energy estimating method. The principal results are that both of the two A.D.I. schemes are absolutely stable and converge to the exact solution with error estimations O(Delta t(2) + h(2)) in discrete H-1 norm. This implies essential improvement of existing conclusions.展开更多
在无线局域网中提供服务质量(QoS)保证的MAC算法应该满足业务区分服务的要求和系统性能的整体最优.以往的此类自适应MAC算法依赖于对不同级别的竞争业务数目进行估计,计算过于复杂.提出一种基于QoS区分的自适应p-persistentMAC算法,QDA-...在无线局域网中提供服务质量(QoS)保证的MAC算法应该满足业务区分服务的要求和系统性能的整体最优.以往的此类自适应MAC算法依赖于对不同级别的竞争业务数目进行估计,计算过于复杂.提出一种基于QoS区分的自适应p-persistentMAC算法,QDA-MAC(QoS differentiation based adaptive MAC scheme).该算法引入了新的参数-坚持因子(persistent factor),其优化值能够实时反映网络负载的变化情况,结合近似优化的自适应方法,每次发送尝试后,该算法不需要估计每类竞争业务的数目,利用坚持因子的优化值实时更新各类优先级业务的发送概率,调整相应的协议参数,系统的性能也能接近最优.仿真结果验证了该算法不仅能够根据竞争业务数目的变化对系统的性能进行整体优化,而且能够提供业务区分服务,在QoS区分的基础上可以为实时业务提供严格的QoS保证,尤其在信道利用率和时延等方面明显优于标准的IEEE802.11DCF和IEEE802.11eEDCA机制.展开更多
文摘An upwind scheme based on the unstructured mesh is developed to solve ideal 2-D magnetohydrodynamics （MHD） equations. The inviscid fluxes are approximated by using the modified advection upstream splitting method （AUSM） scheme, and a 5-stage explicit Runge-Kutta scheme is adopted in the time integration. To avoid the influence of the magnetic field divergence created during the simulation, the hyperbolic divergence cleaning method is introduced. The shock-capturing properties of the method are verified by solving the MHD shock-tube problem. Then the 2-D nozzle flow with the magnetic field is numerically simulated on the unstructured mesh. Computational results demonstrate the effects of the magnetic field and agree well with those from references.
文摘A family of high_order accuracy explicit difference schemes for solving 2_dimension parabolic P.D.E. are constructed. Th e stability condition is r=Δt/Δx 2=Δt/Δy 2【1/2 and the truncation err or is O(Δt 3+Δx 4).
文摘Aim To construct a third order upwind scheme for convection equation. Methods Upwind Lagrange interpolation was used. Results and Conclusion The schemes L p stability for p∈ is proved. Numerical examples show that performance of the third order upwind scheme is better than that of most second order schemes.
基金Supported by the National Natural Science Foun-dation of China (60502024) the Natural Science Foundation of HubeiProvince (2005ABA267) +1 种基金the Electronic Development Foundation ofMinistry of InformationIndustry of China theInnovation FundforTechnology Based Firms of Ministry of Science and Technology ofChina (04C26214201284)
文摘With the maturation of P2P technology, there are more and more challenges to the protection of digital rights. DRM for traditional Client/Server model can not satisfy the requirement of digital right protection of P2P network. With practical application of P2P network technology and new generational DRM technology, the article proposes a DRM model for P2P system based on trust degree. The proposed model shares the secret key to the trusty peers and affords necessary security ensure for digital content delivery based on P2P technology. Mathematic analyses and simulations show that, compared to the current DRM model, the proposed model is more robust toleration of transmit and security.
基金Supported by the National Natural Science Foun-dation of China (60473072)
文摘Resource sharing among peers is one of important application in Peer-to-Peer（P2P） network. Inexistenee of server makes P2P network to be a less trustable tool for property owners to distribute their resource. In order to protect intelligent property, reputation management strategy is adopted in many P2P network. As long as a P2P network reputation strategy is confirmed, application designer can employ a special detailed distribution scheme to fulfill content distribution within the net. Shmir （k, n） threshold scheme, for example, is an encryption scheme to enhance the distribution se curity of this kind of design. （k＊, n） threshold scheme is a new tool similar to Shmir scheme is proposed in this paper. The new scheme based on polynomial expansion and its security is decided by the one way function used in the secret distribution procedure. The scheme efficiency and its features as well as comparison between new and Shmir scheme are also discussed in this paper.
基金The National Natural Science Foundationof China (Nos.60403027, 60773191,and 60873225) the National High Technology Research and Development Program of China (863 Program) (No.2007AA01Z403)
文摘In order to reduce the traffic load and improve the availability of the shared resources in unstructured P2P networks, a caching scheme combining alternative index and adaptive replication （AIAR） is presented. AIAR uses random walk mechanism to disperse the caching information of resources in the network based on its power-law characteristic, and dynamically adjusts replicas according to the visit frequency on resources and the degree information of peers. Subsequent experimental results show that the proposed AIAR scheme is beneficial to improve the search performance of success rate and respond speed. In addition, compared to some existing caching scheme, AIAR can perform much better in success rate, especially in a dynamic environment.
文摘A class of two-level high-order accuracy explicit difference scheme for solving 3-D parabolic P.D.E is constructed. Its truncation error is (Δt2+Δx4) and the stability condition is r=Δt/Δx2=Δt/Δy2=Δt/Δz2≤1/6.
文摘Alternating direction implicit (A.D.I.) schemes have been proved valuable in the approximation of the solutions of parabolic partial differential equations in multi-dimensional space. Consider equations in the form partial derivative u/partial derivative t - partial derivative/partial derivative x(a(x,y,t) partial derivative u/partial derivative x) - partial derivative/partial derivative y(b(x,y,t) partial derivative u partial derivative y) = f Two A.D.I. schemes, Peaceman-Rachford scheme and Douglas scheme will be studied. In the literature, stability and convergence have been analysed with Fourier Method, which cannot be extended beyond the model problem with constant coefficients. Additionally, L-2 energy method has been introduced to analyse the case of non-constant coefficients, however, the conclusions are too weak and incomplete because of the so-called 'equivalence between L-2 norm and H-1 semi-norm'. In this paper, we try to improve these conclusions by H-1 energy estimating method. The principal results are that both of the two A.D.I. schemes are absolutely stable and converge to the exact solution with error estimations O(Delta t(2) + h(2)) in discrete H-1 norm. This implies essential improvement of existing conclusions.
文摘在无线局域网中提供服务质量(QoS)保证的MAC算法应该满足业务区分服务的要求和系统性能的整体最优.以往的此类自适应MAC算法依赖于对不同级别的竞争业务数目进行估计,计算过于复杂.提出一种基于QoS区分的自适应p-persistentMAC算法,QDA-MAC(QoS differentiation based adaptive MAC scheme).该算法引入了新的参数-坚持因子(persistent factor),其优化值能够实时反映网络负载的变化情况,结合近似优化的自适应方法,每次发送尝试后,该算法不需要估计每类竞争业务的数目,利用坚持因子的优化值实时更新各类优先级业务的发送概率,调整相应的协议参数,系统的性能也能接近最优.仿真结果验证了该算法不仅能够根据竞争业务数目的变化对系统的性能进行整体优化,而且能够提供业务区分服务,在QoS区分的基础上可以为实时业务提供严格的QoS保证,尤其在信道利用率和时延等方面明显优于标准的IEEE802.11DCF和IEEE802.11eEDCA机制.
