初应力位形上的附加变形和拱的弹性屈曲

从初应力位形上的附加变形场论出发,导出了弹性屈曲问题的控制方程和变分原理的普遍形式,并在该理论框架下,对于平面拱的弹性屈曲问题,通过降维处理,得到了求临界载荷条件的变分方程、控制方程及相应的线性齐次微分方程的特征值(平面拱面内、侧向屈曲临界值).分析结果表明,对于临界载荷问题,面内屈曲与侧向屈曲彼此独立;与建立控制方程的几何分析方法相比,该方法具有理性化的优点.在曲线形构件等几何复杂情况下,按该方法导出的变分方程或控制方程条理清晰,改善了微小变形几何分析方法的不足之处.     

曲杆有限元与拱的临界载荷算法

从初应力位形上附加变形的场论出发,提出弹性屈曲问题的控制方程和变分原理的普遍形式;在这个理论框架下,通过降维处理,导出平面拱弹性屈曲问题求解临界载荷的变分方程、控制方程以及相应的线性齐次微分方程的特征值问题;进一步放弃平截面假设,考虑剪切变形,给出曲杆截面含6个自由度的一维有限元法算法.推导过程和计算结果表明,该理论体系导出曲杆有限元方程准确,易于数值实施,计算结果更符合实际情况.     

非理想边界拱的面内失稳模式与屈曲荷载

将拱结构中既非固结也非铰支的非理想边界考虑为沿不同方向的具有一定刚度的弹性约束,利用变形几何关系和能量变分原理推导了拱的非线性平衡方程.以圆弧拱为例建立了径向均布荷载下外荷载与结构内力、径向位移之间的关系,通过定义拱的深浅参数和临界约束刚度进行分析并得到了跳跃屈曲、分岔屈曲等的发生条件及存在区间.本文方法所得屈曲路径和屈曲荷载与有限元法所得结论吻合良好,且用数值法分析了不同约束刚度时的屈曲路径和临界荷载.结果表明,临界深浅参数和临界约束刚度对圆弧拱的屈曲模式及屈曲临界荷载影响显著.     

静水压荷载下功能梯度圆环的弹性屈曲

管道屈曲问题中,结构通常被考虑为平面应力圆环,但若存在轴向位移约束,其状态更接近平面应变圆环的状态.文中从理论上研究静水压作用下平面应力和平面应变功能梯度材料圆环的弹性屈曲问题.假定材料沿厚度方向弹性物性按照幂律分布连续变化,结合一阶剪切变形理论和Kárman几何关系,应用虚位移原理,导出结构的基本平衡方程;采用本征值方法得到了屈曲控制方程和结构屈曲临界荷载的解析解.通过算例比较了平面应力和平面应变状态下结构理论屈曲性能,同时考察了结构径厚比和材料组分参数的影响.结果表明:平面应变功能梯度材料圆环屈曲临界荷载略高于平面应力的结果;当材料组分参数介于0.1至10区间内时,两种圆环的屈曲临界荷载均下降得较为明显.     

弹性支撑圆弧拱考虑几何缺陷的面内屈曲特性

通过变分原理推导了弹性支撑圆弧拱考虑几何缺陷时的平衡方程,得到了外荷载与径向位移和轴力的关系,以及圆弧拱发生跳跃和分岔屈曲的平衡条件．用解析法和有限元法分析了几何缺陷和弹性支撑刚度对面内稳定性的影响．研究结果表明,两种方法在展开角较小时吻合良好;几何缺陷对屈曲路径有一定的影响,而弹性支撑刚度对跳跃屈曲的路径和临界值均有...     

矩形薄板在非保守力作用下的动力稳定性

用弹性非保守系统自激振动的似固有频率变分原理,导出矩形薄板受均胡从力的变分方程,进而导出此问题的有限元基本方程及求解临界力和固有频率的特征方程,用载荷增量法计算了在不同边界条件下,不同边长比的矩形薄板在面内受均布随从力作用的临界载荷,分析了两相材料组合板的临界载荷与模量比的关系,计算结果表明,边界条件对薄板的动力稳定性有较大影响,它不仅影响临界载荷,而且对板的屈曲形式起决定性作用。     

不可移简支几何非线性铁磁梁式板的磁弹性屈曲与后屈曲分析

采用基于薄板挠曲变形的广义变分原理导出的磁力计算公式和运用电磁弹性耦合的非线性数值计算程序,定量分析了不可移简支几何非线性铁磁梁式板的屈曲与后屈曲路径,给出了非线性静态解的分叉图象．然后对于在斜磁场作用下这一铁磁板的磁弹性弯曲与失稳情形,得到了梁由两个半波的挠曲构形演变为单半波挠曲构形的跳跃失稳临界磁场与失稳后的路径等;并且随着倾斜磁场的倾角增大,简支梁式板磁弹性的临界磁场值随之增加．这一结果表明简支梁式板的磁弹性系统对安装偏差之类的缺陷是不敏感的．     

轴向拉力对薄壁梁的侧向屈曲临界载荷值的影响

分析了几种特殊约束下，薄壁梁出现侧向屈曲的临界载荷受轴向拉力的影响，推导出含有轴向拉力的变系数线性齐次微分方程．采用了逐次逼近法解出狭长矩形截面梁的侧向屈曲临界载荷值，并与弹性稳定理论中的同类问题作了比较得出了轴向拉力的影响使得梁的侧向屈曲临界载荷值有较明显提高的结论．     

线性弹性Timoshenko梁的屈曲与分叉

在假定梁不可伸长的基础上,给出了描述几何非线性、物理线性的大挠度Timoshenko梁的变分原理,由此导出了大挠度Timoshenko梁平面静动力学分析的边值问题.在几类边界条件下,具体求解了线性弹性Timoshenko梁的临界载荷,并与Euler梁的结果进行比较.讨论了细长比(横向剪切变形)对梁的临界载荷的影响,给出了不同端部条件下,线性弹性Timoshenko梁的无量纲临界载荷.通过数值计算,分析了弹性Timoshenko梁在临界载荷处的屈曲和分叉以及稳定性,并与理论值进行了比较.     

具有不同表层夹层扁锥壳的非线性稳定性问题

研究了具有不同质、不等厚表层和软夹心的夹层扁锥壳在均布压力作用下的非线性稳定性,利用变分原理导出夹层扁锥壳非线性稳定问题的基本方程,采用修正迭代法得到临界屈曲压力的解析表达式,讨论了几何参数和物理参数对壳体屈曲的影响．     

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.     

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     

Journal of Donghua University ( English Edition) Contents of Volume 31

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Brief Introduction to “Journal of Jilin University( Science Edition) ”

<正>"Journal of Jilin University(Science Edition)"is a comprehensive academic journal in the fields of science sponsored by Jilin University and administrated by the Ministry of Education of the Peoples Republic of China.The journal started publication in 1955.The original name at starting publication was"Journal of Natural Science of Northeast People University",which was changed into"Acta Scientiarum Naturalium Universitatis Jilinensis"in 1958 owing to the name change of the university.The present journal name has