Numerical simulation of the radar echo from a ship in ocean clutter

A comprehensive approach which combines the generalized forward-backward method (GFBM) with the spectral acceleration algorithm (SAA) is developed. The angular radar echo from a rough ocean surface with a ship present, and with the transverse electric (TE) and transverse magnetic (TM) components incidencing at low grazing angle, is numerically simulated; and its functional dependences upon the polarization, observation angle, sea surface wind speed, ship location and other parameters are analyzed.     

Multivariate analyses of variation pattern in the Deutzia multiradiata group（Hydrangeaceae）in Mt．Jin－fo of Nanchuan

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Numerical Investigation of the Influence of Reynolds Number on Probe Measurements

Multi-holepneumaticprobesarecommonlyusedinturbomachinerymeasurementsbecausetheyaresimple,cheap,anddurable,especiallysincetheycansimultaneouslymeasurevelocityandpressure.TheprobemeasurementsarebasedonflowsimilaritywithReasoneofthebasicsimilaritycriteria.However,theinfluenceofReonprobemeasurementsisnotconsideredinprobecalibrationsbecauseofthedifficultiesinherentinRebasedcalibration.MostofthelimitedexperimentalinvestigationsonthisproblemfocusedondeterminingRerangeinwhichtheinfluencecanbeneglect…     

A synthetical evaluation about the catastropha－bility of urban geomorphic environment in Chongqing

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Numerical simulation of topography effects on the “00.7” severe rainfall in Beijing

In an effort to study the severe rainfall event of 4?5th July 2000 in Beijing (with 24h accumulated precipitation of 240 mm), we perform numerical simulations to investigate this event using the MM5v3.6 model. The model is initialized with the MM5/WRF 3DVAR analysis, which incorporates the ground-based GPS precipitable water vapor, automatic and conventional meteorological observations in its assimilation step. For 24 h accumulated precipitation forecast, the threat scores are 0.72, 0.76, 0.67 and 0.63, for thresholds of 1, 5, 10, and 20 mm, respectively. Holding other factors unchanged, sensitivity experiments were conducted with different topographic resolutions of 110, 50 and 3.7 km to investigate the topographic effects on precipitation over the Beijing area. In these sensitivity experiments, we attempt to preserve the realistic orographic distribution in the model topography under the condition of keeping the dynamic-thermodynamic consistency of the initial model atmosphere to the extent possible. Results indicate that the unique topographic distribution and variations in the Beijing area play an important role in determining the location, distribution and intensity of heavy precipitation.     

Investigation on abnormal group velocities in 1D coaxial photonic crystals

Recently, controlling the propagation velocity of electromagnetic wave has been the object of many re- searches because it offers an extra degree of flexibility for processing signals. Reducing the transmission ve- locity, even stopping and storing the mi…     

Influence of variation in precipitation on the δD values of terrestrial n-alkanes on the southern Tibetan Plateau

A short lake sedimentary core and ice core were recovered from Lake Chen Co and Noijingangsang Glacier,respectively,in the Lake Yamdrok watershed of the southern Tibetan Plateau.Hydrogen isotope ratios of the ice core(δDice) and δD values of terrestrial n-alkanes(δDwax) in the sediments showed a linear correlation(R2 = 0.41,P = 0.047) over the past 80 years,indicating the effect of hydrogen isotope ratios of precipitation(δDp) on δDwax.However,apparent fractionation(εwax-p) values of δDwax relative to δDice increased with decreasing ice core accumulation(amount of precipitation;R2 = 0.65,P = 0.0051),revealing that dry or wet climate variation had a significant impact on δDwax.Thus,precipitation amount and δDp are both important in determining δDwax.     

Numerical study on the flow features of U-beam inertial separator

Detailed parametric study of three-dimensional gas-particle multiphase flow characteristics in Ubeam tube bundle ntertial separators was conducted by numerical simulation.The carrier phase was treated in the Eulerian frame,the particles were tracked in the Lagrangian frame,and particle-wall collision was considered.Simulation carried out at different inflow rate and mass loading ratios revealed the pressure losses in the separators,velocity field of the gas phase,and the trajectories of particles.The study results revealed the multiphase flow-dynamic features of the separators,and the relationship between separator pressure losses and different inlet velocity.The numerical simulation can provde basis both for optimal disign of mpacting-inertial separator used in circulating fluidized bed boiler;and for study of gas-particle multiphase circumfluence flow.     

Numerical investigation on the self-excited oscillation of wet steam flow in a supersonic turbine cascade

The self-excited flow oscillation due to supercritical heat addition during the condensation process in wet steam turbine is an important issue. With an Eulerian/Eulerian model, the self-excited oscillation of wet steam flow in a supersonic turbine cascade is investigated. A proper inlet supercooling results in the transition from steady flow to self-excited oscillating flow in the cascade of steam turbine. The frequency dependency on the inlet supercooling is not monotonic. The flow oscillation leads to non-synchronous periodical variation of the inlet and outlet mass flow rate. The aerodynamic force on the blade varies periodically due to the self-excited flow oscillation. With the frequency lies between 18.1?80.64 Hz, the oscillating flow is apt to act with the periodical variation of the inlet supercooling due to stator rotor interaction in a syntonic pattern, and results in larger aerodynamic force on the blade. The loss in the oscillating flow increases 20.64% compared with that in the steady flow.     

番荔枝科糠秕鳞杜氏木群及其近缘种的修订(Ⅱ)——种的描述、地理分布及其相互亲缘关系

杜氏木属(Duguetia St.Hilaire)约80种,全产新热带.它的系统修订系由联合国教科文组织资助的《新热带植物志》(Flora Neotropica)中番荔枝科研究的子课题,本文第一作者有幸参加了该项研究.这里报告的是第一作者于1990年2月至1991年3月在荷兰乌德勒支大学系统植物学研究所进修期间,在 P.J.M.Maas教授指导下完成的番荔枝科杜氏木属中糠秕鳞杜氏木群(Duguetia furfuracea group,为非正式分类学等级)及其近缘种(共16种,现修订至12种)系统修订专著连载的第二部分.它给出了隶属糠秕鳞杜氏木群的叉鳞杜氏木(D.dicholepidota)、莫里杜氏木(D.moricandiana)、马格杜氏木(D.marcgraviana)及具刺杜氏木(D.echinophora)四种的详尽描述、地方名、应用价值、地理分布、分类界定和它们间的相互亲缘关系.短梗杜氏木(D.brevipedunculata)被归并为马格杜氏木的新异名;叉鳞杜氏木与莫里杜氏木不象R.E.Fries(1934,1959)认为那样与马格杜氏木直接亲缘而是与糠秕鳞杜氏木亲缘关系非常密切.     

木瓜属(Chaenomeles)栽培品种与近缘种的数量分类

选取木瓜属(Chaenomeles)18个栽培品种和4个近缘种的24个形态学性状,利用SPSS10.0软件进行聚类分析,以探讨品种间的亲缘关系。Q型聚类分析显示供试样本可分为2类：木瓜和‘豆青’自成一类,与其他种类和品种关系疏远;其余种类和品种聚合成一类。而第2类分为4个亚类,贴梗海棠、木瓜海棠、倭海棠以及5个杂交品种分别聚合。根据聚类结果,‘猩红与金黄’和‘碧雪’等品种的分类地位值得进一步探讨。数量分类结果能够反映品种之间的亲缘关系。R型聚类结果表明,各分类性状之间没有明显的逻辑关系,24个形态学性状对品种的演化具有较独立的意义。主成分分析表明,前6个主成分的累计贡献率达85.9%,根据其与性状间的相关性可知,影响力较大的性状有花径、花梗颜色、花瓣形状、花瓣宽、瓣爪长、幼叶颜色、花托和果实形状、重瓣性和花瓣数目等。     

军队院校群际关系存在的问题及对策

院校群际关系是院校教、管、学三方在日常教育训练活动中形成的相互作用的心理机制与行为模式。和谐的院校群际关系对于提升院校集体凝聚力具有重要的作用。研究表明：当前军队院校群际关系存在一些问题,已经成为影响院校全面建设和可持续发展的重要因素。军队院校要加强文化管理,重视群际沟通,推进群际参与,改善院校群际关系,把院校建设成公平正义、诚信友爱、充满活力、安定有序的和谐军营。     

复杂空区群露天开采境界三维可视化及其应用

为了预防露天开采境界下复杂空区群对矿山生产造成重大安全事故,研究以不规则三角网(TIN)为基础的复杂地质体三维可视化建模技术,并以Surpac软件为平台制定出相应的复杂空区群露天开采境界三维可视化实施方案。将该方案应用于某矿区,建立该矿区内露天开采境界地表、地下矿体以及复杂空区群的三维可视化模型,重点对空区群内部错综复杂的通透关系进行三维描述。研究结果表明:复合模型的建立明确了地表、地下矿体及各水平采空区之间的空间位置关系,可利用其分析空区群的安全隐患及空区间的连带破坏作用,为露天境界内复杂空区群的灾害控制、安全性评判及矿区地表开采的施工设计提供了参考依据,从而解决了多空区矿山的盲目开采问题,有效预防了重大安全事故的发生。     

应用基团键贡献法计算烯烃的折光指数

:根据分子中基团的特性和连接性 ,发展了一种计算烯烃折光指数的新方法———基团键贡献法 ,该方法考虑分子中基团的特性 ,又考虑基团间的连接性 (化学键 ) ,同时具有基团贡献法和拓扑方法的特点。对 2 16种烯烃折光指数的计算结果表明 ,计算值与实验值的一致性令人满意 ,平均误差 0 .48%。     

《天津理工学院学报》作者群的统计与评价

阐述科技期刊作者信息在科技交流、文献检索、人才学、编辑学等方面的情报价值.运用文献计量学的方法,通过对本刊的高产作者,作者的职称、机构、地区、年龄,作者论文的合作情况的统计,指出作者信息在提高科技情报传递效果和文献检索效率方面,以及在了解科技人才结构和分布状况,准确选择审稿人,提高期刊质量等方面均能发挥重要作用.     

几个超可解性定理的推广

设Ｎ是有限可解群Ｇ的正规子群,使得Ｇ／Ｎ超可解,若Ｆ（Ｎ）的极小子群在Ｇ中Ｃ－正规,且以下条件之一被满足,则Ｇ超可解：（１）Ｆ（Ｎ）的４阶循环子群在Ｇ中Ｃ－正规;（２）Ｇ中不含Ｄ２ｑ型子群。     

基于线粒体COI基因对5种切梢小蠹种间关系的研究

切梢小蠹属各种之前形态差异很小,种类鉴定困难.采用线粒体DNA细胞色素c氧化酶亚单位I(COI基因)部分序列,对5种切梢小蠹进行PCR扩增和测序.研究分析发现:华山松切梢小蠹与其他4种切梢小蠹存在明显的遗传分化,再次证明华山松切梢小蠹是1个新种;云南切梢小蠹与华山松切梢小蠹在各种分析数据结果都显示出很小的差异,但二者的寄主完全不同,这暗示着二者最初可能起源于同1个祖先,产生分化的原因可能是寄主的差异所致.通过探索5种切梢小蠹之间的关系,为其防控提供科学数据.