Analysis on the effectiveness of the 20-H rule for printed-circuit-board layout to reduce edge-radiated coupling

This paper presents the quantified study of the electromagnetic radiation mechanism of the 20-H rule using a numerical approach that has not yet been systematically addressed. The 20-H rule is a rule-of-thumb layout technique recommended to minimize radiated fields propagating from the edges of a printed circuit board (PCB) coupling onto nearby structures. Propagating electromagnetic fields may corrupt adjacent cable assemblies, sheet metal enclosures, and aperture openings. The magnitude of this design rule is investigated using the full-wave finite-difference time-domain (FDTD) method. An analysis on whether benefits exist from use of this rule is examined and under what conditions the rule is valid when correctly implemented. The purpose of this paper is to provide insight into the validity of the 20-H rule, recognizing that every PCB will have different simulation results. FDTD is used to capture a snapshot view of field propagation. This view allows one to determine the validity of the 20-H rule at a single point of time within a dynamic structure and what may be expected when digital components are finally added to a PCB assembly, which generally negates simulated results.     

Four-scanning attack on hierarchical digital watermarking method for image tamper detection and recovery

In a recent paper presented by Lin et al., a block-based hierarchical watermarking algorithm for digital images is proposed. It adopts parity check and the intensity-relation check to conduct the experiment of image tamper detection. Their experimental results indicate that the precision of tamper detection and localization is 99.6% and 100% after level-2 and level-3 inspections, respectively. The proposed attacks demonstrate that this watermarking algorithm is fundamentally flawed in that the attacker can tamper a watermarked image easily without being detected. In this paper, a four-scanning attack aimed to Lin et al.'s watermarking method is presented to create tampered images. Furthermore, in case they use encryption to protect their 3-tuple-watermark, we proposed a blind attack to tamper watermarked images without being detected. Experimental results are given to support and enhance our conclusions, and demonstrate that our attacks are successful in tampering watermarked images.     

无线Ad Hoc网络支持QoS的研究进展与展望

无线ad hoc网络的应用环境以及与Internet的互连要求它必须提供一定的服务质量(QoS)保证,然而,无线信道固有的特点及节点移动造成网络拓扑的频繁变化,使得在无线ad hoc网络中支持QoS面临许多新的挑战.从无线ad hoc网络的QoS体系结构、QoS路由、QoS信令、支持业务区分和资源预留的介质访问控制协议这4个方面出发,对近年来国内外在该方向取得的研究成果作了全面的概括总结和比较分析,系统阐述了在无线ad hoc网络中支持QoS的问题,指出了亟待解决的问题和今后的研究方向.     

三角褐指藻源岩藻黄素功能活性及其生物合成研究进展

海洋硅藻三角褐指藻(Phaeodactylum tricornutum)含有丰富的岩藻黄素且生长速度快,被认为是生产岩藻黄素的最佳物种之一。其中岩藻黄素作为一种天然类胡萝卜素,具有抗肿瘤、抗氧化、抗糖尿病、抗炎症、抗肥胖等生理活性,在生物医药和功能食品领域具有重要应用价值。岩藻黄素因合成机制的复杂性而表现出一定的不稳定性,使其在生产中存在着产量低、成本高等问题。本文详细介绍了三角褐指藻源岩藻黄素的功能活性,对岩藻黄素的合成机制及合成过程中不同因素对其积累量的影响因素的研究进展进行系统综述旨在深入研究海洋微藻来源的岩藻黄素的作用价值,为岩藻黄素进一步的开发利用提供技术支撑,有望为功能性食品领域的开发提供理论依据,为未来海洋硅藻产业化发展提供参考。     

智能合约漏洞检测技术综述

智能合约作为可信的去中心化应用,获得了广泛的关注,但其安全漏洞问题对其可靠性带来了巨大威胁.为此,研究者们利用各种前沿技术(如模糊测试、机器学习、形式化验证等)研究了多种漏洞检测技术,并取得了可观的效果.为了系统性地梳理与分析现有智能合约漏洞检测技术,搜集截至2021年7月关于智能合约漏洞检测的84篇论文,根据它们的核心方法进行分类,从每种技术的实现方法、漏洞类型、实验数据等方面展开分析,同时对比国内外研究现状在这些方面的差异.最后,对现有的智能合约漏洞检测技术进行总结,探讨面临的挑战,并展望了未来的研究方向.     

非线性扰动微分方程解的估计

目的是研究非线性扰动微分方程dx/dt=ψ（t，x） f(t,x)解的估计。     

Simultaneous interpenetrating polymer networks of epoxy and N-phenylmaleimide-styrene copolymers

Ductile thermoplastic N-phenylmaleimide-styrene copolymers (PMS) have been introduced into diglycidyl ether of bisphenol A (epoxy) by a simultaneous polymerization technique. The tensile strength and fracture toughness increased with increasing PMS content and reached a maximum value at a PMS/epoxy ratio of about 20/80 (w/w). The mechanical properties decreased significantly beyond that ratio, because of phase inversion.     

Mathematical model and tooth surfaces of recess action worm gears with double-depth teeth

In this study, the surface equations of recess action (RA) worm gears with double-depth teeth, generated by a ZN worm-type hob cutter, are proposed. Based on the generation mechanism and the theory of gearing, a mathematical model of a series of worm gears, semi RA, full RA and standard proportional tooth types, with double-depth teeth is developed as the function of design parameters of the ZN worm-type hob cutter. According to the derived tooth surface equations, computer graphs of a series of worm gears with double-depth teeth are plotted. Tooth surface variations of the generated RA worm gears due to the varying pitch line, pressure angle and tooth height of the hob cutter are also investigated.     

RWBO（pd, w）： A Novel Backoff Algorithm for IEEE 802.11 DCF

The Probability Distribution of Slot Selection (PDoSS) of IEEE 802.11 DCF is extremely uneven, which makes the packet collision probability very high. In this paper, the authors explore how to make the stations select the slots uniformly, and give an RWBO(pd,w) algorithm for 802.11 DCF to make the PDoSS even and decrease the packet collision probability. A Markov model is given to analyze the PDoSS of RWBO(pa, w). The performance of RWBO(pd, w) is evaluated by simulation in terms of saturation throughput and packet collision probability. The simulation results indicate that RWBO(pa, w) can decrease the packet contention probability to a large extent, and utilize the channel more efficiently as compared to the 802.11 DCF. Moreover, the relation between saturation throughput and walking probability (pd), the relation between saturation throughput and contention windows (w), the relation between packet collision probability and walking probability (pal), and the relation between packet collision probability and contention windows (w) are analyzed. The analysis indicates that RWBO(pd, w) has some remarkable features: its saturation throughout keeps high and packet collision probability keeps very low (under 0.1) in a large range of pd and w, which allow users to configure Pd and w more flexibly.