人工智能在新型冠状病毒肺炎中的研究综述

新型冠状病毒肺炎（corona virus disease,COVID-19）的暴发对全球人类的生命财产安全造成了巨大威胁。人工智能（artificial intelligence,AI）为助力打赢这场疫情攻坚战发挥了不可替代的作用。由于AI的助力,医疗资源紧张的问题得到大幅度缓解,并提高了医疗诊断效率,同时也避免接触感染的风险。阐述了COVID-19和AI的背景知识,从疫情趋势预测、疫情溯源追踪、检测诊断、药物开发、疫苗研制、药物再利用、网络舆论管控以及基因组测序这8个疫情防控的环节讨论了AI在本次COVID-19中的研究进展,并列举本次疫情中AI所面临的挑战,浅谈本次疫情对我国AI产业影响以及两者的辩证关系,对全文进行总结。     

一种基于Arnold置乱和DCT编码的无载体信息隐藏方法北大核心CSCD

近年来十分火热的搜索映射式无载体信息隐藏虽具有一定的鲁棒性,但其隐藏容量较低、传输负载大且算法复杂度高。针对以上问题,该文章提出一种基于Arnold置乱和离散余弦变换(discrete cosine transform,DCT)编码的无载体信息隐藏方法。该算法先对图片进行Arnold置乱,再对DCT后的低频系数进行编码,接着更换置乱参数来构建索引表。选择索引表中与秘密信息相同的编码值所对应的参数构建候选队列,最后筛选出鲁棒性强的参数作为密钥发送给接收方。实验结果表明,该方法与现有方法相比大大提高了嵌入容量,拥有更强的抗JPEG压缩性能。并且减少了传输负载,算法简捷,具有较强的应用价值。     

基于改进遗传模拟退火算法的WSN路径优化

针对无线传感器网络路径优化问题,提出了一种改进的最优保存的遗传模拟退火算法。利用LEACH算法构建初始路由表,使用GASA的高效率搜索,将路由计算和遗传演化计算同时进行,并直至寻找到近似最优路径为止。将最优保存遗传算法和模拟退火算法相结合,引入自适应的概率变化,有效地解决了这两种算法的早熟现象和时间问题。仿真实验表明,该算法有效地解决了无线传感器路径优化问题,具有定位准确、节能和搜索能力较强等优点。     

建筑业企业工程项目群管理组织架构设计

工程项目群管理是传统项目管理的升级,是建筑业企业新形势下进一步发展的有效管理模式,研究项目群管理组织问题是成功推广项目群管理模式的前提.文章在对工程项目群管理理论进行阐述并界定研究对象后,基于优化的传统矩阵式项目型组织架构和联邦德国统一铁路改造工程项目总控组织模型,通过项目总控理论、扁平化组织架构和学习型组织研究,探索设计了工程项目群管理组织架构模型,分析了该模型架构内涵、各管理元素及其职责,并重点对项目群管理组织模型的核心——企业级和项目级项目群管理办公室进行了分析和职能定位.该架构基于传统项目管理组织,面向项目群管理要求,提供项目管理模式递进的组织路径.     

基于分簇的WSN多项式随机密钥管理方案

结合多项式的密钥预分配方案和基于分簇管理的随机预分配方案,提出了一种改进的密钥管理方案,并在该方案中添加距离参数来提高无线传感器网络的安全性。对该方案的分析和评估结果表明,该方案提高了无线传感器网络的安全性,并能降低节点的存储空间和计算开销。     

Characterization of heat transfer along a silicon nanowire using thermoreflectance technique

We studied heat transfer along a silicon nanowire suspended between two thin-film heaters using a thermoreflectance imaging technique. The thermoreflectance imaging system achieved submicrometer spatial resolution and 0.1/spl deg/C temperature resolution using visible light. The temperature difference across the nanowire was measured, and then its thermal resistance was calculated. Knowing the dimension of the nanowire (115 nm in width and 3.9 /spl mu/m in length), we calculated the thermal conductivity of the sample, which is 46 W/mK. Thermal conductivity decreases with decreasing wire size. For a 115-nm-wide silicon nanowire, the thermal conductivity is only one-third of the bulk value. In addition, the transient response of the thin-film heaters was also examined using three-dimensional thermal models by the ANSYS program. The simulated thermal map matches well with the experimental thermoreflectance results.     

电流互感器二次阻抗的现场测试计算

介绍了电流互感器实际二次阻抗的现场测试、计算方法。该方法所需设备少、重量轻，操作简便；不需新增专用设备，不需三相电源；通用性强，适用于各种形式接线的电流互感器。     

Synthesis and Photocatalytic Properties of Single Crystalline (Ga1-xZnx)(N1-xOx) Nanotubes

Recently, (Ga_1-xZn_x)(N_1-xO_x) has gained widespread attention as a comparatively high efficiency photocatalyst for visible-light-driven overall water splitting. Despite significant gains in efficiency over the past several years, a majority of the photogenerated carriers recombine within bulk powders. To improve the photocatalytic activity, we used an epitaxial casting method to synthesize single-crystalline, high surface area (Ga_1-xZn_x)(N_1-xO_x) nanotubes with ZnO compositions up to x=0.10. Individual nanotubes showed improved homogeneity over powder samples due to a well defined epitaxial interface for ZnO diffusion into GaN. Absorption measurements showed that the ZnO incorporation shifts the absorption into the visible region with a tail out to 500 nm. Gas chromatography (GC) was used to compare the solar water splitting activity of (Ga_1-xZn_x)(N_1-xO_x) nanotubes (x=0.05–0.10) with similar composition powders. Cocatalyst decorated samples were dispersed in aqueous solutions of CH₃OH and AgO₂CCH₃ to monitor the H⁺ reduction and H₂O oxidation half reactions, respectively. The nanotubes were found to have approximately 1.5–2 times higher photocatalytic activity than similar composition powders for the rate limiting H⁺ reduction half reaction. These results demonstrate that improvements in homogeneity and surface area using the nanotube geometry can enhance the photocatalytic activity of GaN:ZnO for solar water splitting.     

预制装配式梁板桥板缝错台的成因和预防

预应力钢筋混凝土空心梁板在我国桥梁界有着广泛的应用,其矩形横断面和结构特征决定了相邻2片梁板紧挨着安装,2片梁板底水平间距只有10 mm。在预应力钢筋混凝土空心梁板简支结构桥梁中,经常会出现相邻梁板板缝错台问题,高差较大时在后续的梁板勾缝工序中难以衬平弥补,从而影响桥梁外观质量,特别是在城市跨线互通桥梁上这种影响尤为严重。     

Effect of temperature on the performance of laterally constrained dielectric elastomer actuators with failure modes

This article analytically investigates the temperature influence on the performance of laterally constrained dielectric elastomer actuators. The effects of both temperature and stretches on the permittivity are taken into consideration. The governing equations of state are established by modeling the actuator as a thermodynamic system of three degrees of freedom. Various failure modes, including electromechanical instability, electric breakdown, loss of tension, and tensile rupture are considered to restrict the operation state and to determine the region of allowable state. Numerical calculations are performed to depict the variations of some important physical quantities with generalized coordinates and to gain insight on the influence of temperature on the critical curves of failures. It is shown that the temperature has obvious effects on the operation state and the allowable region. The present results can be used for designing and optimizing an actuator, and the present approach can be extended to other kinds of dielectric elastomer actuators with complex geometries.