域名系统的部署及安全性分析与建议

针对传统DNS结构可能存在的问题,为应对分布式拒绝服务攻击行为,提出了基于AnyCast的DNS部署方式,以进一步提高DNS的可靠性和性能。从DNS服务技术层面和域名注册业务流程等环节对域名系统进行了安全性分析,并提出了一些安全性建议。     

A novel user’s authentication scheme for pervasive on-line media services

Due to the explosive growth of the Internet and the pervasion of multimedia, protection of intellectual property (IP) rights of digital content in transactions induces people’s concerns. Current security requirements and copyright protection mechanisms especially need to work in real-time and on-line for communication and networking. For media service systems in the Internet, user’s authentication is most essential in association with the access control of the media system. The authentication scheme is a trivial but crucial issue for maintaining user’s information. Up to now, many one-time password-based authentication schemes have been proposed. However, none is secure enough. The purpose of a one-time password (OTP) is to make it more difficult to gain unauthorized access to restricted resources. Traditionally static passwords can more easily be obtained by an unauthorized intruder given enough attempts and time. By constantly altering the password, as is done with a one-time password, this risk can be greatly reduced. These schemes are specially fit for media services in the Internet since they will frustrate the attacker’s attempt. Lin, Shen and Hwang proposed a strong-password authentication scheme in association with one-time password by using smart cards, and claimed their scheme can resist guess attack, replay attack, impersonation attack and stolen attack. Later, Ku, Tsai, and Chen showed that Lin-Shen-Hwang’s scheme suffers from a replay attack and a denial-of-service attack. Furthermore, Ku proposed a hash-based strong-password authentication scheme to enhance the security. In this paper, we show the weaknesses and devise some attacks against Ku’s scheme. Then, we revise Ku’s scheme and propose a novel user’s authentication scheme in pervasive on-line media services for current communication and networking.     

滑模控制永磁同步电动机的矢量控制技术

本文为了解决传统PI控制器鲁棒性差、系统抗扰能力弱和动态响应的问题,针对永磁同步电动机矢量控制系统,设计了一阶滑模变结构速度环控制器。分析滑模转速控制器抖振产生的原因和影响,利用饱和函数设计了边界层滑模控制器,削弱了滑模控制器的抖振。搭建了在Matlab/Simulink环境下的仿真模型,并进行了仿真分析。仿真结果表明该控制策略减小了系统的超调与振荡,使系统具有较好的鲁棒性和动、静态性能。     

Direct-methane solid oxide fuel cells with Cu1.3Mn1.7O4 spinel internal reforming layer

Cu_1.3Mn_1.7O₄ spinel oxide has been synthesized and characterized as anode internal reforming layer for Ni–SDC anode-supported solid oxide fuel cells (SOFCs) directly operating on methane fuel. XRD and Cu mapping image results of Cu_1.3Mn_1.7O₄ oxide after in-situ reduction by methane show that a highly dispersed nano-Cu metal network has been obtained. By adopting Cu_1.3Mn_1.7O₄ as an internal reforming layer, the cell demonstrated maximum power densities of 242 and 311 mW cm^?2 at 650 and 700 °C, respectively using methane as fuel and ambient air as oxidant. More importantly, Cu_1.3Mn_1.7O₄ internal reforming layer has significantly improved the cell performance stability. The cell with the Cu_1.3Mn_1.7O₄ internal reforming layer has demonstrated reasonably stable performance while the cell without it degraded very rapidly.     

Excited‐State Dynamics of the Metal String Complex Co3(dpa)4(NCS)2 from Femtosecond Transient Absorption Spectra

Transient absorption spectroscopy is used to study the excited‐state dynamics of Co₃(dpa)₄(NCS)₂, where dpa is the ligand di(2‐pyridyl)amido. The ππ*, charge‐transfer, and d–d transition states are excited upon irradiation at wavelengths of 330, 400 and 600 nm, respectively. Similar transient spectra are observed under the experimental temporal resolution and the transient species show weak absorption. We thus propose that a low‐lying metal‐centered d–d state is accessed immediately after excitation. Analyses of the experimental kinetic traces reveal rapid conversion from the ligand‐centered ππ* and the charge‐transfer states to this metal‐centered d‐d state within 100 fs. The excited molecule then crosses to a second d–d state within the ligand‐field manifold, with a time coefficient of 0.6–1.4 ps. Because the ground‐state bleaching band recovers with a time coefficient of 10–23 ps, we propose that an excited molecule crosses from the low‐lying d–d state either directly within the same spin system or with spin crossing via the state ²B to the ground state ²A₂ (symmetry group C₄). In this trimetal string complex, relaxation to the ground electronic surface after excitation is thus rapid.     

Symmetry forbidden vibronic spectra and internal conversion in benzene

The spectra of symmetry-forbidden transitions and internal conversion were investigated in the present work. Temperature dependence was taken into account for the spectra simulation. The vibronic coupling, essential in the two processes, was calculated based on the Herzberg-Teller theory within the Born-Oppenheimer approximation. The approach was employed for the symmetry-forbidden absorption/fluorescence, and internal conversion between 1(1)A(1g) and 1(1)B(2u) states in benzene. Vibrational frequencies, normal coordinates, electronic transition dipole moments, and non-adiabatic coupling matrix elements were obtained by ab initio quantum chemical methods. The main peaks, along with the weak peaks, were in good agreement with the observed ones. The rate constant of the 1(1)A(1g)← 1(1)B(2u) internal conversion was estimated within the order of 10(3) s(-1). This could be regarded as the lower limit (about 4.8 × 10(3) s(-1)) of the internal conversion. It is stressed that the distortion effect was taken into account both in the symmetry-forbidden absorption/fluorescence, and the rate constants of internal conversion in the present work. The distortion effects complicate the spectra and increase the rate constants of internal conversion.