Griffiths' singularities in diluted ising models on the Cayley tree

The Griffiths singularities are fully exhibited for a class of diluted ferromagnetic Ising models defined on the Cayley tree (Bethe lattice). For the deterministic model the Lee-Yang circle theorem is explicitly proven for the magnetization at the origin and it is shown that, in the thermodynamic limit, the Lee-Yang singularities become dense in the entire unit circle for the whole ferromagnetic phase. Smoothness (infinite differentiability) of the quenched magnetizationm at the origin with respect to the external magnetic field is also proven for convenient choices of temperature and disorder. From our analysis we also conclude that the existence of metastable states is impossible for the random models under consideration.     

压力下Ti60Si40纳米晶的固相反应

 利用球磨方法制备出Ti₆₀Si₄₀纳米晶混合物，研究了该混合物在不同静压力下固态反应，利用X射线衍射和电子显微镜分别研究了样品中的相组成。实验结果表明，球磨过程中生成的微量新的亚稳相可以在适当的压力和温度条件下长大，但其长大速率却随压力的增加而减小。在常压下进行相同温度和时间的热处理，则只有纳米晶的长大而没有固相反应发生。     

Phase behavior of four homologous compounds of 4-n-alkyl-4′-isothiocyanatobiphenyl (nBT) under pressure

The phase behavior of four homologous compounds of 4-n-nonyl-, 4-n-decyl-, 4-n-undecyl-, and 4-n-dodecyl-4′-isothiocyanatobiphenyl (9BT, 10BT, 11BT, and 12BT) was re-investigated to characterize their high-pressure mesophases under pressures up to 150 MPa using a polarizing optical microscope equipped with a high-pressure optical cell and a wide-angle X-ray diffractometer equipped with a high-pressure sample vessel. The pressure-induced mesophases of 9BT and 10BT appearing under pressures above about 60 and 100 MPa, respectively, were identified as nematic (N) and SmA phases, which indicate the reversible Cr–CrE–N–I and Cr–CrE–SmA–I phase transitions under elevated pressure. 11BT and 12BT exhibited the reversible transition of Cr–CrE–SmA–I in the low-pressure regions below about 5 and 23 MPa, respectively. Both the stable CrE phases changed into the monotropic (and metastable) one under higher pressures, in which the Cr–SmA–I and I–SmA–CrE–Cr phase transitions on heating and cooling processes, respectively, were recognized.     

高压下Pd82Si18合金凝固过程中形成的亚稳相

 使用X射线衍射、差热分析、透射电镜及Ｘ射线能谱分析，研究了Pd₈₂Si₁₈合金在高压下的凝固特点及所形成的相的结构和稳定性。在5.5 GPa压力下以100 K/s的冷却速率淬火，得到了面心立方结构钯硅固溶体（MS-Ⅰ），其点阵常数为a=0.388 3 nm。与钯硅固溶体共存的还有另一未知结构亚稳相（MS-Ⅱ）。在700 K时上述亚稳相转变成平衡相Pd+Pd₃Si。     

高压下液态Ag-20 at%Ge合金的凝固及密排六方亚稳相的形成

 利用高压淬火方法，在液态Ag-20at%Ge合金的凝固过程中，对比液态急冷低四个数量级的冷却速率得到了单相密排六方结构亚稳相，其点阵参数为a=0.289 8 nm，c=0.470 8 nm，c/a=1.625。     

Clusters,metastability, and nucleation: Kinetics of first-order phase transitions

We describe and interpret computer simulations of the time evolution of a binary alloy on a cubic lattice, with nearest neighbor interactions favoring like pairs of atoms. Initially the atoms are arranged at random; the time evolution proceeds by random interchanges of nearest neighbor pairs, using probabilities compatible with the equilibrium Gibbs distribution at temperatureT. For temperatures 0.59T_c, 0.81 T_c, and 0.89T _c, with density of A atoms equal to that in the B-rich phase at coexistence, the density C₁ of clusters ofl A atoms approximately satisfies the following empirical formulas: C₁ w(1 –)³ andC ₁, (1 –)⁴Q₁w¹ (2 l 10). Herew is a parameter and we defineQ _l = _K e ^–E(K) , where the sum goes over all translationally nonequivalentl-particle clusters andE(K) is the energy of formation of the clusterK. Forl > 10,Q ₁ is not known exactly; so we use an extrapolation formulaQ _l Aw _s ^–l l ^– exp(–bl ), wherew _s is the value ofw at coexistence. The same formula (withw > w _s) also fits the observed values of C, (for small values ofl) at densities greater than the coexistence density (forT=0.59T_c): When the supersaturation is small, the simulations show apparently metastable states, a theoretical estimate of whose lifetime is compatible with the observations. For higher supersaturation the system is observed to undergo a slow process of segregation into two coexisting phases (andw therefore changes slowly with time). These results may be interpreted as a more quantitative formulation (and confirmation) of ideas used in standard nucleation theory. No evidence for a spinodal transition is found.Supported by AFOSR Grant No. 73-2430D and by ERDA Contract No. EY-76-C-02-3077*000.     

氨基甲酸铵的水解动力学及其对碳化过程的影响

用氨基甲酸铵直接水解的方法,在总氨浓度2.6～6.1 mol/L,温度5～35℃范围内,进行了水解动力学研究,获得对氨基甲酸铵为一级的水解反应速率常数表达式及反应活化能。按照本文提出的“介稳”态模型,对工业碳化塔进行了剖析,得出了在氨基甲酸铵水解阻尼下碳化主塔的合适操作温度范围。     

液晶性芳族共聚酯的DSC研究

<正> 近年来热致液晶性的全芳族共聚酯的研究受到了人们的极大的关注,某些具有刚性主链和主链上包含介晶段的聚酯能显示出热致液晶性,这种高聚物在熔融态表现出自发取向的倾向,通过简单熔融纺丝有希望制备出高强、高模纤维。     

Li~ ,Na~ //SO_4~(2-),B_4O_7~(2-)-H_2O交互四元体系288K介稳相平衡研究

采用等温蒸发法研究了四元体系Li ,Na //SO42-,B4O72--H2O288K介稳相平衡及平衡液相物化性质(密度、电导率、折光率、粘度和pH值),测定了该四元体系288K条件下介稳平衡溶液溶解度及物化性质。根据实验数据绘制了相应的介稳相图及物化性质组成图。研究发现:该体系介稳平衡中有复盐Li2SO·4Na2SO4形成。其介稳相图中有3个共饱和点,7条单变量曲线,平衡固相为:Li2SO·4H2O,Na2SO4,Li2SO·4Na2SO4,Li2B4O7·3H2O,Na2B4O·710H2O。复盐Li2SO·4Na2SO4和一水硫酸锂(Li2SO·4H2O)有较小的结晶区,而Li2B4O7·3H2O和Na2B4O7·10H2O有较大的结晶区;该四元体系介稳平衡条件下未发现Na2SO·410H2O的结晶区。