基于时域有限差分法的冰晶粒子群多次散射特性

为了精确地利用雷达回波信号反演降雪粒子的微观物理参数,建立满足Gamma谱分布的两类非球形降雪粒子群模型,利用XFDTD软件计算了这两类非球形冰晶粒子群模型在94 GHz频率下的雷达散射截面,分别为-37.690 0和-40.301 0dB·m~2,与简单叠加计算的结果对比后发现绝对误差分别达到0.334 4和0.733 7 dB.在冰水含量一定时,满足Gamma谱分布的两类非球形降雪粒子群模型在分别考虑多次散射和单次散射下雷达反射率因子的绝对误差分别为0.334 6和0.733 7 dB,因此粒子群的多次散射效应在实际气象探测中必须加以考虑.     

基于CST软件的零度层亮带成因分析

利用南京信息工程大学C波段雷达和南京市六合区气象局的风廓线雷达观测资料,得到了2014年4月15日层状云降水零度层亮带的基本特征.总结出零度层亮带形成的5个因素,对零度层亮带中的粒子模型进行假设,建立了冰晶、雪、冰水混合粒子和雨滴等10种粒子的假设模型.利用计算机仿真CST软件对10种假设模型进行了理论计算,分析了不同高度下不同模型对应的雷达散射截面(RCS)的变化趋势,模拟了毫米波雷达观测零度层亮带的特征.结果表明,当冰晶融化成冰水混合粒子时RCS值增大;在下降过程中,冰水混合粒子有强烈的碰并聚合作用,粒子尺度增加,使其散射电磁波的能力大大增强;冰水混合粒子完全融化之后,将迅速破碎成小的椭球形水滴粒子,下降速度也会增加,导致单位体积内粒子数目减少,总的散射能力减小.     

基于一维散射中心模型的RCS频率全角度外推

目标RCS频率外推是减小目标RCS数据存储的有效手段之一。利用FEKO电磁仿真软件得到目标回波数据,结合经典谱估计算法,提出了一种基于GTD散射中心模型的目标RCS频率全角度外推方法。以弹头目标为例,首先利用1～2GHz频率后向电磁散射数据,提取GTD散射中心模型参数;其次利用RCS频率全角度外推方法,实现了弹头目标在3GHz、4GHz频率上的RCS全角度外推;最后通过将外推数据与FEKO仿真数据进行对比,验证了外推方法的准确性与可靠性。仿真实验表明,外推结果与FEKO的仿真结果在整体趋势及强散射点对应的位置上具有较高的吻合度,可有效描述雷达目标的散射特性。     

94 GHz频率下冰晶粒子多次散射特性的研究

为了认识冰晶粒子群在94 GHz频率下的散射特性,利用互散射、相干Mie散射以及简单叠加法进行研究.结果表明,这3种方法得到的粒子群散射结果明显不同,目前的雷达气象方程使用简单叠加法计算粒子群的散射时不能精确地反演云的微物理特征,如冰水含量及有效半径等.利用3种方法比较了不同位置、不同复折射指数、不同尺度参数以及不同数量的粒子群散射强度特性后发现云的多次散射特性不能被忽略.     

雷暴云中冰晶粒子对电磁波的极化作用

为了研究雷暴云中冰晶粒子在带电情况下对电磁波传播的影响,利用冰晶粒子的介电常数模型和瑞利近似条件下带电粒子对电磁波的散射模型,推导了电磁波经过雷暴云中冰晶粒子区域时产生极化的计算模型,并进行了仿真和分析。结果表明:在传播过程中,电磁波的极化会受到冰晶粒子所带电荷的影响;冰晶粒子所带电荷量越多,对电磁波极化影响越大;冰粒表面电荷分布角越小,对电磁波的极化影响也越严重;电磁波频率和冰晶浓度越高,对电磁波造成的极化作用也越大,影响电磁波的传输质量。因此,在电磁波经过雷暴云时必须考虑带电冰晶粒子对其传播的影响。     

椭球粒子对电磁波散射的系统辨识模型

利用球形粒子的Mie解逼近椭球粒子的内外透射场与散射场,首先建立了求解任意椭球粒子对电磁波散射的系统辨识模型,在毫米波段,数值计算了非球形雨滴的内外电磁场和微分散射截面.结果表明雨滴的前向散射场大于后向散射场,后向散射场无径向分量,较大的球粒子的Mie解对椭球粒子的内外场的贡献较大,椭球引起的交叉极化分辨率随观察点的变化而变化;讨论了进一步提高计算精度的方法.     

典型隐身飞机动态RCS时间序列研究

定义和推导了目标机体坐标系与地面雷达坐标系之间的坐标转换关系式,得到了雷达视线在目标坐标系中的方位角和高低角.通过软件FEKO对典型隐身飞机目标F-22进行建模,计算得到了目标全空域的静态RCS值,并利用Matlab仿真分析了动态目标的RCS特性变化.仿真结果表明:不同飞行高度以及不同的航路捷径均可以影响机动目标的RCS序列,且当目标作适当的俯仰机动后,可以减小目标RCS值,给隐身飞机设计飞行航线模拟主动进攻提供仿真依据.     

等效球理论计算冰晶粒子毫米波散射的误差分析

利用4种等效Lorenz-Mie理论以及离散偶极子近似理论(DDA)计算了毫米波频率下卷云中随机取向六角形冰晶粒子的散射特性.对比结果表明:在毫米波频率下,利用等效体积与投影面积比值(V/A)Lorenz-Mie理论计算的结果与DDA的结果最接近,最后利用最小二乘法拟合出误差公式,为等效球理论代替DDA计算复杂的六角形冰晶粒子散射特性提供参考依据.     

基于改进型CLEAN算法三维成像的雷达散射截面积反演

基于三维成像的雷达散射截面积(radar cross section,RCS)测量可以获得目标散射系数的三维空间分布,与一维和二维RCS测量相比,它具有更好的空间分辨能力.但是,在基于成像的RCS测量中,散射中心的提取至关重要,它在很大程度上决定着RCS的反演精度.采用CLEAN算法完成对目标散射中心的提取,有效抑制了图像的三维旁瓣,并针对CLEAN算法存在估计误差的迭代累加效应,设计了一种可以更新估计的改进的相干CLEAN算法,进一步提高了RCS的反演精度.用MATLAB和FEKO测量仿真,结果表明改进型CLEAN算法能更有效地提取散射中心,且提高了RCS的反演精度.     

角反射器表面粗糙度对单站RCS的影响

研究了角反射器表面粗糙度对其雷达散射截面的影响.角反射器的粗糙表面由随机高斯面模拟,散射计算采用全波数值算法完成.计算结果与实测数据吻合,对实验数据进行了解释,验证了计算模型.通过多组计算结果得出结论,随着粗糙面均方根高度的增加和相关长度的减小,角反射器的非主散射区雷达横截面(RCS)均值提高,到达一定数值后角反射器的主散射区RCS也将受到显著影响.研究结论对角反射器用于RCS标定具有重要应用意义.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with