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11.
Effects of orientation and shape of holes on the band gaps in water waves over periodically drilled bottoms 下载免费PDF全文
The complete band gaps (CBGs) of shallow water waves
propagating over bottoms with periodically drilled holes are
investigated numerically by the plane wave expansion method. Four
different patterns are considered, containing triangular, square,
hexagonal and circular cross-sectioned holes arranged into
triangular lattices. Results show that the width of CBGs can be
changed by adjusting the orientation of noncircular holes and the
effect of hole shape on the width of the maximal CBGs is discussed. 相似文献
12.
化学反应中的双稳性的临界现象及Landau相变理论 总被引:4,自引:0,他引:4
本文通过两个典型事例,即Langmuir形式的交换过程和Schlogle用以模拟一级相变的自催化反应,阐明化学反应系统的双稳性临界现象同样可以纳入Landau相变理论的模式。从而进一步揭示了双稳系统一级相变线临界点的二级(连续)相变特征,同时也揭示了作为远离平衡的化学反应双稳性临界现象的共性,以至于在更大范围内临界现象的共性。将相变的Landau理论,由原来的处于热平衡的凝聚物质推广到范围更宽广,表现更为丰富多彩的远离平衡系统的临界现象。 相似文献
13.
Novel structures and mechanical properties of Zr2N:Ab initio description under high pressures 下载免费PDF全文
With the formation of structural vacancies,zirconium nitrides(key materials for cutting coatings,super wearresistance,and thermal barrier coatings) display a variety of compositions and phases featuring both cation and nitrogen enrichment.This study presents a systematic exploration of the stable crystal structures of zirconium heminitride combining the evolutionary algorithm method and ab initio density functional theory calculations at pressures of 0 GPa,30 GPa,60 GPa,90 GPa,120 GPa,150 GPa,and 200 GPa.In addition to the previously proposed phases P42/mnm-,Pnnn-,and Cmcm-Zr2 N,five new high-pressure Zr2N phases of PA/nmm,IA/mcm,P21/m,P3 m1,and C2/m are discovered.An enthalpy study of these candidate configurations reveals various structural phase transformations of Zr2 N under pressure.By calculating the elastic constants and phonon dispersion,the mechanical and dynamical stabilities of all predicted structures are examined at ambient and high pressures.To understand the structure-property relationships,the mechanical properties of all Zr2N compounds are investigated,including the elastic moduli,Vickers hardness,and directional dependence of Young’s modulus.The Cmncm-Zr2 N phase is found to belong to the brittle materials and has the highest Vickers hardness(12.9 GPa) among all candidate phases,while the I4/mcm-Zr2 N phase is the most ductile and has the lowest Vickers hardness(2.1 GPa).Furthermore,the electronic mechanism underlying the diverse mechanical behaviors of Zr2 N structures is discussed by analyzing the partial density of states. 相似文献
14.
从理论上提出一种由局域共振单元组成的声子晶体低频多通道滤波模型.在二维三组元局域共振声子晶体中引入不同填充率的共振单元构成波导结构,通过有限元法计算出其能带结构、透射曲线和透射场图.结果显示:这种设计能够在低频带隙范围内不同填充率散射体的共振频率附近产生新的分立模,且这些分立模能够使相应的声波在声子晶体中沿波导方向传播;这些分立模只与相应的共振单元相关,抗干扰能力强.所得结果为低频多通道滤波器的设计提供了一种新的理论依据. 相似文献
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16.
存在双稳性的激光系统中的临界现象 总被引:1,自引:0,他引:1
通过实际事例研究了可能出现光学双稳性的激光系统中的临界现象,并且用平均场理论作详细描述,这里揭示了在作为远离平衡系统的上述激光器中一种更为特殊的临界点,它意味着一级相变与二级相变之间的转变。它十分类似于Landau(1937)在他著名二级(平衡)相变理论中所预见的“第二类相变(线)的临界点”。 相似文献
17.
本文通过两个典型事例,即Langmuir形式的交换过程和Schl(?)gle用以模拟一级相变的自催化反应,阐明化学反应系统的双稳性临界现象同样可以纳入Landau相变理论的模式,从而进一步揭示了双稳系统一级相交线临界点的二级(连续)相变特征,同时也揭示了作为远离平衡的化学反应双稳性临界现象的共性,以至于在更大范围内临界现象的共性.将相变的Landau理论,由原来的处于热平衡的凝聚物质推广到范围更宽广,表现更为丰富多彩的远离平衡系统的临界现象. 相似文献
18.
The study of boron structure is fascinating because boron has various allotropes containing boron icosahedrons under pressure. Here, we propose a new boron structure (space group $Fm\overline{3}m$) that is dynamically stable at 1.4 tera-Pascal (TPa) using density functional theory and an evolutionary algorithm. The unit cell of this structure can be viewed as a structure with a boron atom embedded in the icosahedron. This structure behaves as a metal, and cannot be stable under ambient pressure. Furthermore, we found electrons gather in lattice interstices, which is similar to that of the semiconductor Na or Ca$_{2}$N-II under high pressure. The discovery of this new structure expands our comprehension of high-pressure condensed matter and contributes to the further development of high-pressure science. 相似文献
19.
用超元胞的平面波展开法,计算了存在点缺陷的二维水/水银声子晶体的能带结构和压强分布。通过改变5×5超元胞中心圆柱体的半径而引入缺陷,发现缺陷填充率(Fd)小于或大于正常柱体填充率(F0)一定数值时(如当F0=0.35,Fd<0.10或Fd>0.50),都将出现缺陷态,且Fd对缺陷态的频率有重要影响。还比较了当Fd=0.03和Fd=0.90两种情况下缺陷态的压强分布,计算结果表明压强分布均具有局域性,Fd的大小对单模缺陷态的局域程度有影响,而对二重简并模无显著影响。 相似文献
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