检测双层固接复合圆筒界面特性的周向导波

通过对层间界面固接的双层复合圆筒中周向导波频散现象的研究,以及与单层筒和层间界面光滑接触的双层复合圆筒频散曲线的比较,发现周向导波在双层复合圆筒中传播时,会发生明显的频散现象,其第一阶模态,在高频时接近于无频散Rayleigh面波。通过对比研究发现,第二阶模态具有在层间界面附近集中能量的特征,可用于层间界面缺陷的周向导波无损检测技术中。该方法可以用来研究确定激励频率的合理范围。     

任意梯度分布圆柱壳的周向导波频散分析

利用半解析方法分析了周向导波在任意梯度分布圆柱壳的频散特性.在假设材料参数沿圆柱壳径向按任意梯度变化的基础上,应用带状单元法,将功能梯度壳分成若干子层.对于细分子层可认为其材料参数为常值,并以此构造带状单元,获得导波在圆柱壳中周向传播时的特征值问题,通过求解该特征值问题,得到了导波的频散特性.最后通过算例讨论了材料参数沿径向按余弦函数分布时,不同梯度参数及内外径比对导波频散特性的影响.     

平板和管道周向Lamb波频散和波结构特性

为指导使用管道周向Lamb波进行缺陷检测的工作,分析并对比研究了弹性平板Lamb波和管道周向Lamb波的频散和波结构特性。在管道周向Lamb波频散方程的推导中引入了修正的传播方向弧长计算以提高频散曲线的计算准确度,这种修正的合理性从两个方面得到证明。计算结果表明,代表管道周向弯曲程度的内、外径之比越大则周向Lamb波的频散和波结构特性越接近于平板,这就为以平板导波研究内、外径之比较大的管道的周向导波的近似处理提供了理论依据。     

平板和管道周向Lamb波频散和波结构特性

为指导使用管道周向Lamb波进行缺陷检测的工作,分析并对比研究了弹性平板Lamb波和管道周向Lamb波的频散和波结构特性。在管道周向Lamb波频散方程的推导中引入了修正的传播方向弧长计算以提高频散曲线的计算准确度,这种修正的合理性从两个方面得到证明。计算结果表明,代表管道周向弯曲程度的内、外径之比越大则周向Lamb波的频散和波结构特性越接近于平板,这就为以平板导波研究内、外径之比较大的管道的周向导波的近似处理提供了理论依据。     

半空间多层各向异性介质的面波频散方程

将地球物理学中各向异性研究的前沿课题同半空间面波问题结合在一起，用有限元方法建立了半空间多层各向异性介质的面波频散方程；同时，对该频散方程的有关问题进行了讨论，本研究对于勘探地震学和工程勘查具有理论意义和应用价值。     

离散解析互相关的Lamb波频散特性估计方法

针对实验估计Lamb波频散特性需要借助传感器阵列或空间密集采样的问题,提出了一种基于离散解析互相关的频散特性估计方法。采用一发一收法,移动接收换能器在两个相邻位置采集Lamb波响应信号;计算两组响应信号之间以及原始激励信号与响应信号之间的离散解析互相关、估计欲知模态的群延迟和相延迟;在此基础上,求得该模态的群速度和相速度频散曲线。数值仿真和实验结果表明:当信噪比在15 dB以上时,离散解析互相关法估计A_0模态和S_0模态频散特性的最大相对误差在1%左右。该方法在待测结构几何参数和材料属性未知的情况下,仅需经过两次测试就可实现Lamb波频散特性的精确估计,测试和计算效率高,能够满足实际工程应用。     

均匀覆层梯度半空间中的Love面波

对覆盖一层均匀各向同性材料的功能梯度半空间中的Love波频散问题进行了研究，给出了Love波频散方程的一般形式．对功能梯度半空间的反平面剪切波的运动控制方程进行了求解，给出了半空间的位移、应力解析解，导出了该解析解下的Love波频散方程的一般形式．以功能梯度材料的剪切弹性模量和质量密度沿深度方向均呈指数变化和抛物线变化两种情况为例，进行了计算和分析，给出了频散曲线．结果显示：在最低阶振型频散曲线中出现了截止频率。     

基于超材料的雷达吸波材料研究进展

雷达吸波材料能够有效地抑制透射波和反射波,因而被广泛应用于隐身、电磁屏蔽和兼容以及无线通信等领域。受制于材料的电磁频散特性,传统吸波材料的宽带低频吸波性能难以进一步提高。近年来,随着超材料结构设计的不断发展,基于超材料构架设计实现的宽带电磁吸波,由于具有更加灵活的电磁调控能力,因而在其电磁性能提升方面具有更大拓展空间。围绕雷达吸波超材料的最新研究进展,结合电磁吸波超材料的发展背景、设计原理和性能表征方面的内容,着重介绍了基于多谐振叠加吸波结构、超材料与传统材料复合吸波结构、三维阵列吸波结构以及人工表面等离激元吸波结构设计的宽带雷达吸波超材料,并对于未来雷达吸波超材料的发展趋势做进一步展望。     

表面波测定涂层材料参数的反演方法

基于涂层结构中表面波的频散方程,提出了一种从实测的相速度频散数据计算材料参数的反演方法.通过引入以涂层参数、表面波相速度和频率作变量的目标函数,将实测的相速度频散数据代入目标函数,使其取最小值,从而反向计算出涂层的材料参数.为了解决单模态频散数据反演时的多值性问题,数值算例分别分析了采用表面波频散的二阶模态和三阶模态数据,同时反演3个材料参数(涂层密度、纵波速度和横波速度)的过程,验证了多模态反演方法的可行性.值得指出,该反演方法适用于任意多阶模态频散数据.     

道路结构型地层瑞利波相速度频散曲线的完整求取

研究在实数域如何完整地求取道路结构型地层的瑞利波频散曲线.在以往研究工作的基础上采用附加层法,即假定原模型的最底层介质厚度为有限,再在其下部添加一个与表层介质物性相同的半无限空间,可使原复数域的求解问题转化到实数域进行,则利用瑞利波频散方程,用二分法可得原模型的多模式相速度频散曲线.在采用附加层法进行计算时,一般假定的层厚度较大,会出现高频数值溢出现象.为此,利用二分法的特点,当计算过程中数值趋于较大时,采用较小的有限值进行替代,并且保证不改变原计算结果的正负特性,避免传递矩阵法计算中高频数值的溢出.对2个假定的三层介质模型进行模拟计算,结果表明原模型瑞利导波曲线与附加层法的计算结果完全吻合,同时附加层法计算出了高频区域泄漏波模式的相速度频散曲线,从而验证了附加层法、高频溢出处理方法的正确性和可行性.     

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     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the