一种新型径向复合压电陶瓷超声换能器径向振动特性研究

研制了一种新型径向复合压电陶瓷超声换能器,并对其径向振动特性进行了理论及实验研究.该换能器由一个厚度方向极化的压电陶瓷薄圆环及一个金属圆环组成.对压电陶瓷圆环和金属圆环的径向振动分别进行了分析,得到了各自机电等效电路.在此基础上,利用换能器径向力及径向振动速度的连续条件,得出了压电陶瓷径向复合超声换能器机电等效电路及其共振频率方程.分析了换能器的共振及反共振频率、有效机电耦合系数与其几何尺寸之间的关系.结果表明,在换能器压电陶瓷圆环内外半径保持一定情况下,换能器半径比增大时,共振及反共振频率随之增大.对于换能器第一阶径向振动,其有效机电耦合系数随半径比增大单调增大,而第二阶径向振动有效机电耦合系数随半径比增大单调减小.     

幂函数剖面薄圆环振子的扭转振动特性

对剖面厚度按幂函数变化的薄圆环振子的扭转振动进行了理论分析,导出了其等效电路;进而由等效电路得出了扭转振动频率方程及共振频率表达式;探讨了环形振子第1、第2阶共振频率及角位移放大系数与其半径比的关系;给出了薄圆环振子第1、第2阶共振频率及放大系数与其半径比的拟合关系曲线．通过有限元（FEM）模态的分析,表明理论结果与FEM仿真结果吻合,对环形扭转振子的工程设计具有参考价值．     

阶梯形截面环行聚能器扭转振动

对各向同性弹性薄圆环的扭转振动进行研究,给出了其等效电路.在此基础上,对由双金属圆环组成的阶梯形扭转振动聚能器进行了探讨,推出了其扭转振动的复合等效电路及其共振频率方程及角速度放大系数.利用数值方法分析了共振频率以及位移振幅放大系数与其集合尺寸之间的依赖关系.有限元模态分析表明:理论值与仿真值符合很好,这对阶梯形截面环状聚能器的工程设计具有参考价值.     

薄圆环扭转振动及其等效电路研究

研究了各向同性薄圆环振子的扭转振动，推导了薄圆环振子扭转振动的波动方程和机电等效电路．在此基础上，得出了振子空载时共振频率方程和振子共振频率的表达式．利用数值方法，求出了共振频率的理论值；并利用Ansys软件，对薄圆环振子进行了有限元模拟，得到了其共振频率的模拟值．     

环形振子的扭转振动等效电路及有限元模态分析

基于机电类比原理,对弹性薄圆环振子的扭转振动进行了研究,建立了圆环振子平面扭转振动的机电类比等效电路模型,从等效电路得出了其扭转振动频率方程及共振频率表达式,给出了薄圆环振子频率方程的数值根与其半径比的拟合关系曲线,通过有限元(FEM)模态分析表明,理论与FEM仿真结果符合较好,对环形扭转振子的工程设计具有参考价值.     

薄圆环振子的超声扭转振动及其等效电路研究

对薄圆环振子的扭转振动进行了研究,导出了其等效电路,从等效电路得出了其扭转振动频率方程及共振频率表达式.给出了薄圆环振子频率方程的数值根与其半径比的拟合关系曲线.通过对有限元(FEM)模态的分析表明,理论与FEM仿真结果符合较好,对环形扭转振子的工程设计具有参考价值.     

锥形截面环状聚能器扭转振动的研究

对各向同性弹性锥形薄圆环的扭转振动进行了研究,推出了其等效电路.在此基础上得到了空载时扭转振动的频率方程、共振频率表达式及角位移放大系数表达式.利用数值方法求出了共振频率和角位移放大系数的理论值.给出了频率与半径及放大系数与内外半径比的拟合关系曲线,得到了放大系数最大时的半径比.通过有限元模态分析表明,理论值与仿真值符合很好,这对锥形截面环状聚能器的工程设计具有参考价值.     

切向极化压电陶瓷薄圆环扭转振动负载特性研究

通过分析接电负载压电薄圆环的扭转振动特性,推出机电等效电路和共振频率方程.利用等效电路方法,给出了共振频率方程.得到了压电陶瓷薄圆环扭转振动的共振频率与负载阻抗曲线.电负载的阻抗改变将引起振子共振频率的改变.     

级联式变截面压电换能器尺寸对其性能的影响

研究了一种新型的级联式变截面压电换能器,它由两段金属圆柱、一段金属圆锥和两组轴向极化的压电陶瓷晶堆组成,并以机械端串联、电端并联的形式相连接,且换能器的两端半径远小于纵向振动尺寸。基于一维理论,得到了换能器的机电等效电路以及共振频率方程和反共振频率方程,进而研究了换能器在基频和二次谐频振动下的共振频率、反共振频率及有效机电耦合系数与压电陶瓷晶堆间距离和金属圆锥尺寸之间的关系。将理论计算所得共振频率、反共振频率与COMSOL模拟结果进行比较,二者所得结果一致,研究表明选择合理的换能器尺寸可以有效优化其性能。     

径向扭转复合型超声换能器等效电路研究

对径向扭转复合型超声换能器进行了研究.从波动方程出发,不考虑径向扭转振动耦合,推导了换能器中径向振动及扭转振动模式的各自机电等效电路.在此基础上,得出了换能器空载时共振频率方程及其共振频率的表达式,并用有限元方法对此换能器进行了计算机仿真实验.结果表明:等效电路计算的换能器径向及扭转共振频率的理论计算值与计算机仿真值一致.     

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.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

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.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Jane Eyre——A Feminist In The 19th Century

In the 19th century the society was controlled by men, and women were just appendants of them, they had not any rights and freedom. But Jane was an exception, she showed some characteristics of early feminist. Jane showed her characteristics of feminism in three aspects: rebellion, equality, and independence. These characteristics were helpful to her success, and feminism is the only way out for women of that time.     

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-