大规模围垦对香港维多利亚港水动力环流的影响

运用一个已校正的珠江口三维水动力数学模型,研究现存的大规模围垦和进一步最大可能的中环围垦对香港维多利亚港(维港)水动力环流的影响.数值计算显示,与1975年(大规模围垦前)海岸线相比,现存的大规模围垦使维港的水动力有几点关键性变化:①流量峰值降低了8%～17%,平均降低约11.5%;②维港东部流速峰值由于流量的减少而减少,维港西部,尽管流量减少,但由于横断面剧减,流速峰值反而增加;③雨季由于珠江径流的作用,盐度垂向分布呈明显的二层结构,而在枯季则比较均匀;④枯、雨季的潮流冲洗时间分别增加约30%和50%.在现存的海岸线下,维港枯、雨季的潮流冲洗时间分别为5～7 d和1.5～2.5 d.进一步的中环围垦不会对维港潮流冲洗率和流量产生明显影响.     

圆弧形沉积谷地对Rayleigh波三维散射解析解

采用假定的大圆弧面来模拟半空间,利用波函数展开法和有限项Fourier级数展开技术,在频域内给出圆弧形沉积谷地对Rayleigh波三维散射的一个解析解．以此解答为基础,进一步分析入射波的频率和入射角度以及谷地深度对圆弧形沉积谷地场地反应的影响．数值结果表明,入射频率和入射角度以及沉积谷地深度对沉积谷地地表位移有重要影响．     

降雨时黏性土边坡的离心模型试验

为研究降雨引起的黏性土边坡变形破坏,进行了边坡的降雨离心模型试验。试验中利用自主研制的离心场降雨模拟设备,用图像采集和相关分析方法,观测了降雨过程中土坡的破坏形态和位移场变化过程。结果表明:降雨对边坡稳定性产生很大影响。降雨引起均质土坡发生浅层土体滑移破坏,雨水入渗至土坡较深的位置。降雨引起土坡位移逐渐增大,且变形区域也逐渐扩展,最终形成明显的位移集中区域。土坡中一点位移发展可分为小位移阶段、迅速增大阶段和缓慢增大阶段。     

Bayes Inference for Technological Substitution Data with Data-based Transformation

Bayesian inference via Gibbs sampling is studied for forecasting technological substitutions. The Box–Cox transformation is applied to the time series AR(1) data to enhance the linear model fit. We compute Bayes point and interval estimates for each of the parameters from the Gibbs sampler. The unknown parameters are the regression coefficients, the power in the Box–Cox transformation, the serial correlation coefficient, and the variance of the disturbance terms. In addition, we forecast the future technological substitution rate and its interval. Model validation and model choice issues are also addressed. Two numerical examples with real data sets are given.©1997 John Wiley & Sons, Ltd.     

一种基于可靠性的设备顺序预防性维护模型

等周期预防性维护策略不可避免地会使设备的可靠性随着役龄及维护次数的增加而逐步降低．为此,结合役龄递减因子和故障率递增因子的优点,通过引入基于两类调整因子的混合式故障率演化规则,建立了基于设备可靠性的顺序预防性维护优化模型,并以威布尔分布为例,利用蒙特卡罗仿真方法对其进行了优化．结果显示,该模型符合设备的实际维护情况,可为设备的维护决策提供有力的支持．     

阳生与阴生环境梓树叶片的比较解剖学研究

采用光学显微技术,对不同生长环境的梓树Catalpa ovata G.Don叶片进行了比较解剖研究.结果表明:梓树的阳生叶比阴生叶大得多,为1.94～2.64倍;阳生叶的栅栏组织厚度是阴生叶的1.96倍左右.阳生叶的气孔微下陷,有利于减少水分蒸腾;阴生叶的气孔大部分微上拱.阳生叶的上表皮比阴生叶厚,为1.91倍左右;阳...     

用于手写签名识别的演化超网络

手写签名作为易被大众所接受的生物特征身份认证方式,已成为模式识别领域一个重要研究热点.针对现有手写签名存在易模仿难鉴定的问题,提出一种结合演化超网络模型的手写签名认证方法.为了平滑噪声,构造出可读性强的笔迹特征集,采用向量化和平滑采集点的方法对手写签名样本进行预处理,从而提取出位置和方向特征属性,采用演化超网络模型对签名进行学习和鉴定.为验证该方法的有效性,对20个签名用户分别采集了40个真实签名和20个伪造签名数据进行实验.实验结果表明,该方法对用户签名的误拒率(false rejection rate,FRR)为4.75％,误纳率(false acceptance rate,FAR)为3.75％,识别率(verification accuracy,VA)为95.75％.同时和其他传统的识别算法相比,具有更高的识别率.     

Extrusion Freeforming of Millimeter-Wave Electromagnetic Bandgap (EBG) Photonic Crystals

Extrusion freeforming can be used for the rapid prototyping of millimeter-wave electromagnetic bandgap (EBG) structures. In this work, an alumina-polymer paste with a relatively high volatility solvent (propanol) was used and the characteristics of the ceramic paste, particularly the rheological features are described. The advantage of high volatility solvent is that the viscosity and elastic modulus of the paste are increased sharply as the solvent evaporates. Thus, the rigidity of the extruded filament is quickly increased as a small amount of solvent evaporates. Finally, by employing this procedure, different EBG structures such as 2-D, 3-D woodpile and aperiodic structures were fabricated and their bandgaps were measured. The experimental results show that extrusion freeforming is a relatively simple and easy method to fabricate these woodpile structures with a bandgap in the 90-110 GHz region.     

西周天象和绝对年代

文章依据殷末和西周的天象记录，推定了武王伐纣年和西周诸王年代。根据“五星合聚”、“岁在鹑火”及“月相干支”的记载，得出天文受命元年是公元前１０５８年，伐纣之年为元前１０４６年。把“天再旦”现象解释为发生在郑州地方的日食的“懿王元年”算出是公元前９０３年，但公元前９２５年也有成为“懿王元年”的可能性。     

Application of Standardization for Initial Design of Plastic Injection Moulds

Today, the time-to-market for plastic products ar e getting shorter, thus the lead-time for making the injection mould is decreasin g. There is potential in timesavings in the mould design stage because the design process that is repeatable for every mould design can be standardized. T he preliminary work of any final plastic injection mould design is to always pro vide an initial design of the mould assembly for product designers (customers) p rior to receiving the final product CAD data. Traditiona...