The PERMIS X.509 role based privilege management infrastructure

This paper describes the EC PERMIS project, which has developed a role based access control infrastructure that uses X.509 attribute certificates (ACs) to store the users’ roles. All access control decisions are driven by an authorisation policy, which is itself stored in an X.509 AC, thus guaranteeing its integrity. All the ACs can be stored in one or more LDAP directories, thus making them widely available. Authorisation policies are written in XML according to a DTD that has been published at XML.org. The Access Control Decision Function (ADF) is written in Java and the Java API is simple to use, comprising of just three methods and a constructor. There is also a Privilege Allocator, which is a tool that constructs and signs ACs and stores them in an LDAP directory for subsequent use by the ADF.     

Simplified molecular gas film lubrication equation and accommodation coefficient effects

As the spacing between the flying head/slider and the rotating disk in hard disk drives (HDDs) continues to decrease, the interaction between the molecular gas and the surfaces of the disk and the head/slider becomes significant. The influence of surface accommodation coefficient (AC) is an important factor to govern the static characteristics of the head/slider. Starting from the polynomial logarithm fitting equations of Poisueille flow rate and Couette flow rate, a new simplified molecular gas film lubrication (MGL) equation is proposed to simulate the ultra-thin air bearing film in HDDs. The new MGL equation is simpler than that of the polynomial logarithm form of MGL equation. The new approach produces very good approximations for both Poisueille flow rate and Couette flow rate with very little differences to those based on the original MGL equation. The new simplified MGL equation is solved by using a meshless method, called least square finite difference (LSFD) method. Effects of ACs on the static characteristics of air bearing films in HDDs with ultra-low flying heights are investigated. Numerical results show that effects of ACs on the static characteristics are significant for the case of symmetric molecular interaction. On the other hand, effects of ACs at the disk surface on the static characteristics are significant for the case of non-symmetric molecular interaction, while effects of ACs at the slider surface on the static characteristics are weak.     

A PKI approach for deploying modern secure distributed e-learning and m-learning environments

While public key cryptography is continuously evolving and its installed base is growing significantly, recent research works examine its potential use in e-learning or m-learning environments. Public key infrastructure (PKI) and attribute certificates (ACs) can provide the appropriate framework to effectively support authentication and authorization services, offering mutual trust to both learners and service providers. Considering PKI requirements for online distance learning networks, this paper discusses the potential application of ACs in a proposed trust model. Typical e-learning trust interactions between e-learners and providers are presented, demonstrating that robust security mechanisms and effective trust control can be obtained and implemented. The application of ACs to support m-learning is also presented and evaluated through an experimental test-bed setup, using the general packet radio service network. The results showed that AC issuing is attainable in service times while simultaneously can deliver flexible and scalable solutions to both learners and e-learning providers.     

The effects of the format of two-sided online reviews: A linguistic perspective

Drawing on the linguistic theory that differentiates between foreground and background content in narratives, this research proposes that consumer product attitude differs significantly between reviews written in the mixed narrative (MN) format and the divided narrative (DN) format. Results of three experiments show that reviewers are more likely to use adversative conjunctions (ACs) in the MN format than in the DN format when composing two-sided reviews. The presence of ACs affects readers’ attitudes by shifting the allocation of attention between positive and negative content in a review. Moreover, this effect is stronger when positive content is presented first.     

A Novel Hybrid Slot Allocation Mechanism for 802.11e EDCA Protocol

This letter proposes a novel Hybrid Slot Allocation Mechanism (HSAM) to solve the high collision problem among four Access Categories (ACs) introduced by IEEE 802.11e EDCA protocol. In the HSAM, three time slots are assembled into a super-slot, each slot in the super slot is allocated to a particular AC according to its priority. The main idea of HSAM is to stagger the transmission slots of different ACs to reduce collisions, while maintaining the service differentiation. Extensive results from simulations have demonstrated good performance of HSAM comparing with EDCA protocol in terms of throughput, packet loss and MAC delay.     

JAC: an aspect‐based distributed dynamic framework

In this paper, we present the Java Aspect Components (JAC) framework for building aspect‐oriented distributed applications in Java. This paper describes the aspect‐oriented programming model and the architectural details of the framework implementation. The framework enables extension of application semantics for handling well‐separated concerns. This is achieved with a software entity called an aspect component (AC). ACs provide distributed pointcuts, dynamic wrappers and metamodel annotations. Distributed pointcuts are a key feature of our framework. They enable the definition of crosscutting structures that do not need to be located on a single host. ACs are dynamic. They can be added, removed, and controlled at runtime. This enables our framework to be used in highly dynamic environments where adaptable software is needed. Copyright © 2004 John Wiley & Sons, Ltd.     

基于属性证书的权限管理平台GoAccessPMI

该文介绍基于X.509属性证书的权限管理平台GoAccessPMI。该系统使用X.509属性证书(Acs)来存储用户的角色以及相关的访问控制策略,这样可以保证信息的完整性。该系统将属性证书(Acs)存储在LDAP目录中,客户系统通过LDAP接口访问属性证书。     

一种新型软件鉴别系统

该文设计了一个基于Ｃｈｉ－Ｓｕｎｇ公钥鉴别方案的软件鉴别系统。它有三个权利中心，对公钥证书的信任可达到等级３［６］。由于ＫＡＣｓ与ＩＤＣ处于不等地位，所以ＩＤＣ与ＫＡＣ合谋的可能性很小。     

Performance analysis of a threshold-based dynamic TXOP scheme for intra-AC QoS in wireless LANs

The IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol has been proposed for provisioning of differentiated Quality-of-Service (QoS) between various Access Categories (ACs), i.e., inter-AC QoS, in Wireless Local Area Networks (WLANs). However, the EDCA lacks the support of the intra-AC QoS provisioning, which is indispensable in practical WLANs since the network loads are always asymmetric between traffic flows of ACs with the same priority. To address the intra-AC QoS issue, this paper proposes a Threshold-Based Dynamic Transmission Opportunity (TBD-TXOP) scheme which sets the TXOP limits adaptive to the current status of the transmission queue based on the pre-setting threshold. An analytical model is further developed to evaluate the QoS performance of this scheme in terms of throughput, end-to-end delay, and frame loss probability. NS-2 simulation experiments validate the accuracy of the proposed analytical model. The performance results demonstrate the efficacy of TBD-TXOP for the intra-AC QoS differentiation.     

Squeeze film effects on dynamic performance of MEMS μ-mirrors-consideration of gas rarefaction and surface roughness

The squeeze film behavior of MEMS torsion mirrors is modeled, analyzed and discussed. Effects of gas rarefaction (first-order slip-flow model with non-symmetric accommodation coefficients, ACs) and surface roughness are considered simultaneously by using the average Reynolds type equation (ARTE). Based on the operating conditions with small variations in film thickness and pressure, the ARTE is linearized. A coordinate transformation, by stretching or contracting the axes by referring to the roughness flow factors, is proposed to transform the linearized ARTE into a diffusion type modal equation. The dynamic coefficients (stiffness and damping coefficients) are then derived and expressed in analytical form. The results show that the tilting frequency (or Γ₀ squeeze number), roughness parameters (γ Peklenik numbers, σ standard deviation of composite roughness) and gas rarefaction parameters (D inverse Knudsen number, ACs) are all important parameters on analyzing the dynamic performance of MEMS torsion mirrors.     

一种用于无线局域网可伸缩视频传输的跨层结构与SBED算法*

为了增强802.11e无线局域网上的视频传输质量,提出了一种跨层结构与自适应映射算法。将H.264可伸缩视频编码（SVC）的层次信息与802.11e MAC层的访问类（AC）相结合,基于重要性早期检测（SBED）策略将SVC数据包动态映射到合适的AC上,在基础层损失率与平均重要性损失度间实现良好的平衡。仿真表明,该方案的PSNR性能明显优于现有的静态与随机映射方案。     

基于属性证书的RBAC实现模型研究

基于角色的访问控制提供了灵活安全管理授权机制,公钥基础设施(PKI)提供了一个强有力的认证系统,授权管理基础设施(PMI)作为一项新的技术提供了有效授权和访问控制管理。为了满足现在的安全需求,结合X．509公钥证书(PKCs)和属性证书(ACs),本文提出了一个基于角色的访问控制模型。     

模拟电路故障字典开发平台

针对模拟电路板故障诊断和维修中存在的困难,引入基于故障字典法的模拟电路故障字典开发平台,该平台集成了电路模型图形化输入、元器件故障自动插入、交流频率自动选取、诊断测试点优选等关键技术,通过对电路的自动仿真与数据分析实现了模拟电路故障诊断用故障字典的自动生成;通过结合实际模拟电路板验证表明,应用陔平台可有效避免传统依赖人工分析进行故障诊断遇到的各种难题,对提高模拟电路板故障诊断效率以及实现模拟电路板的自动测试都具有重要意义。     

A Puzzle-Based Genetic Algorithm with Block Mining and Recombination Heuristic for the Traveling Salesman Problem

In this research, we introduce a new heuristic approach using the concept of ant colony optimization (ACO) to extract patterns from the chromosomes generated by previous generations for solving the generalized traveling salesman problem. The proposed heuristic is composed of two phases. In the first phase the ACO technique is adopted to establish an archive consisting of a set of non-overlapping blocks and of a set of remaining cities (nodes) to be visited. The second phase is a block recombination phase where the set of blocks and the rest of cities are combined to form an artificial chromosome. The generated artificial chromosomes (ACs) will then be injected into a standard genetic algorithm (SGA) to speed up the convergence. The proposed method is called "Puzzle-Based Genetic Algorithm" or "p-ACGA". We demonstrate that p-ACGA performs very well on all TSPLIB problems, which have been solved to optimality by other researchers. The proposed approach can prevent the early convergence of the genetic algorithm (GA) and lead the algorithm to explore and exploit the search space by taking advantage of the artificial chromosomes.     

无线局域网EDCA机制MAC接入延时分析

提出一种分析模型,基于信号流图和母函数方法分析了无线局域网中EDCA(enhanced distribution channel access)机制的MAC(medium access control)接入延时.得到了MAC接入延时的概率分布和相关的数字特征,包括接入延时的均值、方差、标准差和变异系数.仿真结果与模型的分析结果吻合良好,验证了模型和计算方法的正确性.进一步分析了各类AC(access category)的发送概率、碰撞概率、挂起概率和延时均值随终端数目变化的规律;分析了MAC接入延时的成因;指出了AIFS(arbitration inter frame spacing)值对MAC接入延时的影响;指出接入延时的变异系数大于1,因此,采用负指数分布作为MAC接入延时的近似分布,会错误地估计系统的服务能力.     

Frequency‐dependent behavioral‐model‐based nonlinear analysis and design of a low‐profile transmit active phased array antenna

Design and behavioral‐model‐based nonlinear analysis of a 3‐GHz active‐phased array antenna (APAA) are presented. Four nonlinear power amplifiers are employed in the output ports of the feeding network (FN) and analyzed based on a 5‐order polynomial model with frequency‐dependent coefficients. The FN is based on 4‐port new Gysel power dividers and combiners arranged in such a way to feed the array with Gaussian‐like amplitude and in‐phase distributions. Beam steering capability is obtained in 2 directions by a new technique including a phase shifter and an amplitude controller (AC). The features result in a low‐profile APAA whose design and fabrication complexity and cost are reduced. Single and 2‐tone power tests are performed to develop analytical expressions in nonlinear region for array factor as a function of the model, FN and the phase and ACs. A similar system with frequency‐independent model is also analyzed for comparison in terms of scan loss, beamwidth, side‐lobe level, beam position, and gain. A microstrip array antenna including the power amplifiers, pre‐amplifiers, AC, delay‐line‐based phase shifters and Gysels is fabricated and measured. The simulation results at the single and dual tones and the intermodulation products are presented which have a good agreement with the measurements.     

Theoretical study of chlordecone and surface groups interaction in an activated carbon model under acidic and neutral conditions

Activated carbons (ACs) are widely used in the purification of drinking water without almost any knowledge about the adsorption mechanisms of the persistent organic pollutants. Chlordecone (CLD, Kepone) is an organochlorinated synthetic compound that has been used mainly as agricultural insecticide. CLD has been identified and listed as a persistent organic pollutant by the Stockholm Convention. The selection of the best suited AC for this type of contaminants is mainly an empirical and costly process. A theoretical study of the influence of AC surface groups (SGs) on CLD adsorption is done in order to help understanding the process. This may provide a first selection criteria for the preparation of AC with suitable surface properties. A model of AC consisting of a seven membered ring graphene sheet (coronene) with a functional group on the edge was used to evaluate the influence of the SGs over the adsorption. Multiple Minima Hypersurface methodology (MMH) coupled with PM7 semiempirical Hamiltonian was employed in order to study the interactions of the chlordecone with SGs (hydroxyl and carboxyl) at acidic and neutral pH and different hydration conditions. Selected structures were re-optimized using CAM-B3LYP to achieve a well-defined electron density to characterize the interactions by the Quantum Theory of Atoms in Molecules approach. The deprotonated form of surface carboxyl and hydroxyl groups of AC models show the strongest interactions, suggesting a chemical adsorption. An increase in carboxylic SGs content is proposed to enhance CLD adsorption onto AC at neutral pH conditions.     

Performance analysis of trigger frame in enhanced UL and DL MU MIMO transmissions

In an Internet-of-Things (IoT) environment, congestion and scarcity problems may occur because many mobile stations (STAs) access wireless networks simultaneously. The IEEE 802.11ax/802.11be standards for large-scale wireless communications have defined a trigger frame (TF) to control multiple STAs. During resource allocation, the downlink (DL) transmission is divided in a control period from the access point (AP) to multiple STAs. The resource allocation (RA) is then assigned to an uplink (UL) transmission by a TF and a DL period from the AP to STAs. However, because the DL transmission should be considered separately in terms of the control and DL periods, it is necessary to analyze the DL transmission. We propose a scheduled MU transmission (SMT) algorithm for enhanced UL and DL MU MIMO transmissions. In this study, we analyze and systematically model medium access control (MAC) performance when the DL transmission is divided in the control and data periods when the UL coexists with the DL data transmission. To achieve this, we mathematically analyze the time-efficient throughput, estimate the transmission and collision probabilities for wireless local area network (WLAN) STAs, and generalize the transmission interval. In addition, we propose an access category (AC) for the TF that is defined in the DL transmission. All data transmissions are defined as the ACs for basic channel access, but the AC is not defined for the TF. Therefore, we clarify the transmission by defining the AC of the TF to control the UL transmissions of various STAs. Evaluation results demonstrate that the SMT algorithm can improve the MAC throughput by up to 70% – 87% compared to UL and DL MU MIMO transmissions.