基于OSG的虚拟场景漫游技术研究

虚拟场景是虚拟现实应用中必不可少的部分,但是由于其构成的复杂性使得对它的管理和编辑非常困难。文章利用OSG（OpenSceneGraph）提供的虚拟场景管理和图形渲染优化的特点,提出实现漫游设计和碰撞检测的方法。     

密集型WSN冲突避免的MAC协议

无线传感器网络媒体接触控制层存在2种冲突。提出基于概率的时隙选择算法,使不同节点在相同时隙发送概率不同,从而降低域内冲突。实验结果显示,该算法的有效能量和损失能量相比Sift协议节省了17.6%和43.9%,能量有效率提高了14.3%。提出染色预防算法,通过提前确定节点活动时序解决域间冲突问题。实验结果显示,该算法的节点平均睡眠时间在87%以上,空闲侦听导致的能量消耗仅占总能量的7%。     

Modeling and mining of dynamic trust in complex service-oriented systems

The global scale and distribution of companies have changed the economy and dynamics of businesses. Web-based collaborations and cross-organizational processes typically require dynamic and context-based interactions between people and services. However, finding the right partner to work on joint tasks or to solve emerging problems in such scenarios is challenging due to scale and temporary nature of collaborations. Furthermore, actor competencies evolve over time, thus requiring dynamic approaches for their management. Web services and SOA are the ideal technical framework to automate interactions spanning people and services. To support such complex interaction scenarios, we discuss mixed service-oriented systems that are composed of both humans and software services, interacting to perform certain activities. As an example, consider a professional online support community consisting of interactions between human participants and software-based services. We argue that trust between members is essential for successful collaborations. Unlike a security perspective, we focus on the notion of social trust in collaborative networks. We show an interpretative rule-based approach to enable humans and services to establish trust based on interactions and experiences, considering their context and subjective perceptions.     

An effective heuristic for flexible job-shop scheduling problem with maintenance activities

Most production scheduling problems, including the standard flexible job-shop scheduling problem (FJSP), assume that machines are continuously available. However, in most realistic situations, machines may become unavailable during certain periods due to preventive maintenance (PM). In this paper, a flexible job-shop scheduling problem with machine availability constraints is considered. Each machine is subject to preventive maintenance during the planning period and the starting times of maintenance activities are either flexible in a time window or fixed beforehand. Moreover, two cases of maintenance resource constraint are considered: sufficient maintenance resource available or only one maintenance resource available. To deal with this variant FJSP problem with maintenance activities, a filtered beam search (FBS) based heuristic algorithm is proposed. With a modified branching scheme, the machine availability constraint and maintenance resource constraint can be easily incorporated into the proposed algorithm. Simulation experiments are conducted on some representative problems. The results demonstrate that the proposed filtered beam search based heuristic algorithm is a viable and effective approach for the FJSP with maintenance activities.     

An accurate adaptive NURBS curve interpolator with real-time flexible acceleration/deceleration control

Parametric interpolation has been widely used in CNC machining because of its advantages over the traditional linear or circular interpolation. Many researchers focused on this field and have made great progress in the specific one, NURBS curve interpolation. These works greatly improved the CNC machining with constant feedrate, confined chord error and limited acceleration/deceleration. However, during CNC machining process, mechanical shocks to machine tool caused by the undesired acceleration/deceleration profile will dramatically deteriorate the surface accuracy and quality of the machined parts. This is, in most occasions, very harmful to machine tools. In this paper, an accurate adaptive NURBS curve interpolator is proposed with consideration of acceleration–deceleration control. The proposed design effectively reduces the machining shocks by constraining the machine tool jerk dynamically. Meanwhile, the constant feedrate is maintained during most time of machining process, and thus high accuracy is achieved while the feedrate profile is greatly smoothed. In order to deal with the sudden change of the acceleration/deceleration around the corner with large curvature, a real-time flexible acceleration/deceleration control scheme is introduced to adjust the feedrate correspondingly. Case study has been taken to verify the feasibility and advantages of the proposed design.     

Temporary bond—debond technology for high‐performance transistors on flexible substrates

Abstract— A processing technology based upon a temporary bond—debond approach has been developed that enables direct fabrication of high‐performance electronic devices on flexible substrates. This technique facilitates processing of flexible plastic and metal‐foil substrates through automated standard semiconductor and flat‐panel tool sets without tool modification. The key to processing with these tool sets is rigidifying the flexible substrates through temporary bonding to carriers that can be handled in a similar manner as silicon wafers or glass substrates in conventional electronics manufacturing. To demonstrate the power of this processing technology, amorphous‐silicon thin‐film‐transistor (a‐Si:H TFT) backplanes designed for electrophoretic displays (EPDs) were fabricated using a low‐temperature process (180°C) on bonded‐plastic and metal‐foil substrates. The electrical characteristics of the TFTs fabricated on flexible substrates are found to be consistent with those processed with identical conditions on rigid silicon wafers. These TFTs on plastic exhibit a field‐effect mobility of 0.77 cm²/V‐sec, on/off current ratio >10⁹ at Vds = 10 V, sub‐threshold swing of 365 mV/dec, threshold voltage of 0.49 V, and leakage current lower than 2 pA/μm gate width. After full TFT‐array fabrication on the bonded substrate and subsequent debonding, the flexible substrate retains its original flexibility; this enables bending of the EPD display without loss in performance.     

有意义的MD4碰撞攻击(英文)

2005年的欧密会,Wang等提出了一种构造MD4碰撞的有效方法,该方法不仅对寻找随机碰撞有效,还可以用于构造有意义的碰撞。以Wang的技术为基础,进一步分析和探讨了对构造纯文本文件有意义的MD4碰撞,给出了一种构造纯文本文件的有意义MD4碰撞的方法,概率为2-33.77。在1996年的FSE会议上,Dobbertin的"Crypt analysis of MD4"给出了一个有意义的碰撞,而其在开头包含了16个随机字符。这里给出了一个基于Latin-1字符集的有意义的碰撞。     

差分分析方法在HAVAL中的应用

差分分析方法是攻击迭代密码最有效的方法之一,它可以用来攻击任何一个用轮函数迭代的方法构造的密码系统。为此,描述差分分析方法在Hash函数HAVAL-128算法中的应用,并给出选择消息差分、确定差分路径、推导保证差分路径成立的充分条件等方法,诠释了利用差分分析方法攻击Hash函数的理论依据及步骤。     

求旅行商问题近似解的碰撞算法

提出通过寻找精确解的边获得旅行商问题(TSP)近似解的思想,并以该思想为指导,设计一种新的碰撞算法。对国际通用的TSPLIB中不同城市规模的数据进行测试表明,该算法可以得到与目前已知最优解或相同或相近的结果。该算法不仅可以计算小规模的TSP,而且同样适用较大规模的TSP。     

Flexible H2 sensor fabricated by layer-by-layer self-assembly of thin films of polypyrrole and modified in situ with Pt nanoparticles

A novel flexible H₂ gas sensor was fabricated by the layer-by-layer (LBL) self-assembly of a polypyrrole (PPy) thin film on a polyester (PET) substrate. A Pt-based complex was self-assembled in situ on the as-prepared PPy thin film, which was reduced to form a Pt-PPy thin film. Microstructural observations revealed that Pt nanoparticles formed on the surface of the PPy film. The sensitivity of the PPy thin film was improved by the Pt nanoparticles, providing catalytically active sites for H₂ gas molecules. The interfering gas NH₃ affected the limit of detection (LOD) of a targeted H₂ gas in a real-world binary gas mixture. A plausible H₂ gas sensing mechanism involves catalytic effects of Pt particles and the formation of charge carriers in the PPy thin film. The flexible H₂ gas sensor exhibited a strong sensitivity that was greater than that of sensors that were made of Pd-MWCNTs at room temperature.