二钼酸铵晶体饱和水溶液Raman光谱的变异现象及其机理

记录了常温下二钼酸铵晶体饱和水溶液的Raman光谱,并分别与二钼酸铵晶体、仲钼酸铵晶体、仲钼酸铵晶体饱和水溶液、水溶液状态下单钼酸根离子的Raman光谱进行了比较研究。结果表明：二钼酸铵晶体饱和水溶液Raman光谱相对二钼酸铵晶体Raman光谱,明显地发生了变异现象。二钼酸铵晶体饱和水溶液Raman光谱其主要特征峰最高振动频率937.6 cm^-1与仲钼酸铵晶体饱和水溶液Raman光谱主要特征峰最高振动频率937.6 cm^-1完全吻合,而其次高振动频率893.9 cm^-1,恰好介于水溶液中单钼酸根离子Raman光谱主要特征峰最高振动频率895.1 cm^-1与仲钼酸铵晶体饱和水溶液Raman光谱主要特征次高峰振动频率891.0 cm^-1之间,而且三者彼此接近。二钼酸铵晶体饱和水溶液Raman光谱主、次特征峰强度之比值为2.1,与仲钼酸铵晶体饱和水溶液Raman光谱主、次特征峰强度之比值4.4相比,一半不足。提出了一种利用Raman光谱主要特征峰振动频率及其主、次特征峰强度之比值对二钼酸铵晶体饱和水溶液组分同时进行定性和半定量分析的新方法。发现了常温下二钼酸铵晶体饱和水溶液中二钼酸根离子Mo₂O₇^2-已经不复存在,完全转变成了优势组分仲钼酸根离子Mo₇O₂₄^6-和次要组分单钼酸根离子MoO₄^2-;证明了常温下含钼水溶液酸化过程中溶液Raman光谱离散性变化现象的存在。运用结构化学和物理化学原理同时讨论了二钼酸铵晶体饱和水溶液Raman光谱发生变异现象的机理。     

临界空穴扩张比准则的适用性

用新研制成的DE36平台钢制的轴对称和平面应变试样,进一步考察了临界空穴扩张比V_(Gi)准则[1]、[2]、[3]的适用性。实验和大应变有限元理论计算结果表明,V_(Gi)准则适用于所研究材料。文中指出,按V_(Gi)准则可根据试样或构件材料中V_G的发展变化来预起裂位置。     

近壁面柱体涡激振动的迟滞效应

柱体涡激振动是典型的流固耦合问题,其响应规律标识码在升速流动和远离壁面条件下获得的. 而自然环境流动通常不断经历升速和降速过程,近壁面柱体的涡激振动可呈现与远离标识码体不同的响应特征. 本研究结合大型波流水槽,设计了具有微结构阻尼的柱体涡激振动装置. 基于量纲分析,开展系列水槽标识码验,通过同步测量柱体涡激振动位移时程和绕流流场变化,研究了升降流速作用下柱体涡激振动触发和停振的临界速度(即上临标识码临界速度)变化规律,探究了近壁面柱体涡激振动迟滞效应. 采用自下向上激光扫射的 PIV 流场测量系统,对比分析了固定柱体标识码振动柱体的绕流特征. 实验观测表明,近壁面柱体涡激振动触发的临界速度呈现随壁面间距比减小而逐渐减小的变化趋势;但标识码速条件下的涡激振动停振所对应的下临界速度却明显小于升速时的涡激振动触发所对应的上临界速度. 采用上临界与下临界约标识码差值可定量表征涡激振动迟滞程度,研究发现该值随着柱体间距比减小呈线性增大趋势. 涡激振动迟滞现象通常伴随振幅阶跃标识码阶跃值则随着间距比减小而非线性减小.     

一类五次多项式系统的奇点量与极限环分支

该文研究一类五次多项式微分系统在高次奇点与无穷远点的极限环分支问题. 该系统的原点是高次奇点, 赤道环上没有实奇点. 首先推导出计算高次奇点与无穷远点奇点量的代数递推公式,并用之计算系统原点、无穷远点的奇点量,然后分别讨论了系统原点、无穷远点中心判据. 给出了多项式系统在高次奇点分支出5个极限环同时在无穷远点分支出2个极限环的实例. 这是首次在同步扰动的条件下讨论高次奇点与无穷远点分支出极限环的问题.     

一类具功能反应的食饵--捕食者系统定性分析

研究一类具功能反应的食饵-捕食者系统:x=xg(x)-y(?)(x),y=y(-d+e(?)(x)．在g(x)=α-bxm,(?)(x)=cxθ及m+θ=1,m=1/n,n>2为正整数情形下,分析了该系统的平衡点性态,并得到了系统在正平衡点外围的极限环的不存在性、存在性与唯一性的相关条件．     

Anisotropic spin-glasses with broken replica symmetry

A simple mechanism of replica symmetry breaking for spin-glass, as suggested by Parisi, has been used to solve the anisotropic spin-glass model of Sherrington and Ghatak. Temperature variation of the correlation parameters and the resulting variations with the temperature of the thermodynamic quantities like internal energy, specific heat and entropy have been evaluated. It is found that the anisotropy has considerable effect on the properties of the spin system. At low temperatures, the specific heat varies asT ². However, the entropy is positive for temperatures above 0.1°K, which is a considerable improvement on the results of Sherrington and Ghatak. The results are expected to be in good agreement with experiment or computer simulation studies near transition temperatures.     

Part I. The 2D classical Coulomb gas near the zero-density Kosterlitz-Thouless critical point: Correlations and critical line

The 2D classical Coulomb gas undergoes the famous Kosterlitz-Thouless (KT) transition between a high-temperature conducting phase and a low-temperature insulating phase. We present various studies of the correlations in the insulating phase near the zero-density critical point. First, we briefly recall the phenomenological approach of Kosterlitz and Thouless. This theory predicts that the decay of the charge correlation is entirely controlled by the bare Coulomb potential between opposite charges only renormalized by the dielectric constante. Then, we present an analysis of the low-fugacity expansions of the correlations. The particle correlations are found to decay as 1/r⁴. The large-distance decay of the charge correlation is shown to be tightly related to the behavior of l/s in the regime of interest. Systematic resummations allow one to recover the algebraic decay predicted by the heuristic KT model. This settles on a rigorous basis various assumptions of this model. In particular, the nested pair mechanism naturally arises in the resummation scheme. Finally, we describe the phase diagram of the system according to the most recent calculations which include finite-density effects.     

Critical values of autonomous Lagrangian systems

Let M be a closed manifold and a convex superlinear Lagrangian. We consider critical values of Lagrangians as defined by R. Ma?é in [5]. Let c _u (L) denote the critical value of the lift of L to the universal covering of M and let c _a (L) denote the critical value of the lift of L to the abelian covering of M. It is easy to see that in general, . Let c ₀ (L) denote the strict critical value of L defined as the smallest critical value of where ranges among all possible closed 1-forms. We show that c _a (L) = c ₀ (L). We also show that if there exists k such that the Euler-Lagrange flow of L on the energy level k' is Anosov for all , then . Afterwards, we exhibit a Lagrangian on a compact surface of genus two which possesses Anosov energy levels with energy , thus answering in the negative a question raised by Ma?é. This example also shows that the inequality could be strict. Moreover, by a result of M.J. Dias Carneiro [4] these Anosov energy levels do not have minimizing measures. Finally, we describe a large class of Lagrangians for which c _u (L) is strictly bigger than the maximum of the energy restricted to the zero section of TM. Received: October 2, 1996     

Phase transitions in polymesomorphic compounds

Summary The results of a X-ray diffraction study, performed on N(p-n-pentyloxy benzylidene)p′-n-octylaniline (50.8) and N(p-n-pentyloxy benzylidene)p′-n-decylaniline (50.10) are presented. The investigated compounds exhibit smecticB, smecticA and nematic phases in between solid and isotropic liquid phases. In addition, after a thermal cycle the 50.8 compound exhibits a smecticG phase at room temperature. The interlayer and the in-plane intermolecular distances were obtained as functions of temperature through all the mesophases. A phase coexistence has been observed during the solid to smecticB and the smecticB to smecticA phase transitions of the 50.8 compound. The nematic to smecticA phase transitions are found to be of second order for both compounds. Pretransitional effects due to cybotactic-cluster formation in the nematic region are observed.

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Riassunto Si presentano i risultati di uno studio effettuato mediante la diffrazione dei raggi X sul N(p-n-pentilossi benzilidene)p′-n-ottilanilina (50.8) e sul N(p-n-pentilossi benzilidene)p′-n-decilanilina (50.10). Tra le fasi solida ed isotropica i composti esaminati presentano le mesofasiS _B ,S _A e nematica. Inoltre, dopo un ciclo termico il composto 50.8 presenta una faseS _G a temperatura ambiente. Sono state misurate le distanze tra i piani smettici e le distanze laterali tra le molecole in tutte le mesofasi in funzione della temperatura. Una coesistenza di fase è stata osservata durante le transizioni solido →S _B eS _B →S _A del composto 50.8. Le transizioni nematico-S _A sono risultate del second'ordine per entrambi i composti. Nelle fasi nematiche sono stati osservati effetti pretransizionali dovuti alla formazione di gruppi cibotattici.