Selective formation of VO2(A) or VO2(R) polymorph by controlling the hydrothermal pressure

Missing VO₂(A) usually occurs during the preparation of VO₂ polymorphs. This leads to an ambiguous understanding of the transformation between VO₂ polymorphs. The calculation of the ground state energies for different VO₂ polymorphs indicated that there is only a small energy gap between VO₂(A) and VO₂(R), which destined that the transformation from VO₂(A) to VO₂(R) should be pressure sensitive. This hypothesis was verified during the synthesizing of VO₂ polymorphs by reducing V₂O₅ with oxalic acid through hydrothermal treatment process. Selective formation of pure phase VO₂(A) or VO₂(R) was achieved by controlling the hydrothermal pressure through varying the filling ratio at 270 °C. It was found that a filling ratio over 0.5 favors the formation of pure VO₂(R) while a reduced filling ratio to 0.4 or lower results in the formation of VO₂(A). Based on our experiments, VO₂(B) nanobelts were always first formed and then it transformed to VO₂(A) by assembling process at increased temperature or extended reaction time. Under further higher pressure, the VO₂(A) transformed spontaneously to VO₂(R) initialized from the volume shrinkage due to the formation of denser VO₂(R).     

Aspect-Ratio Scaling of Domain Wall Entropy for the 2D ±<Emphasis Type="Italic">J</Emphasis> Ising Spin Glass

The ground state entropy of the 2D Ising spin glass with +1 and −1 bonds is studied for L×M square lattices with L≤M and p=0.5, where p is the fraction of negative bonds, using periodic and/or antiperiodic boundary conditions. From this we obtain the domain wall entropy as a function of L and M. It is found that for domain walls which run in the short, L direction, there are finite-size scaling functions which depend on the ratio , where d _S =1.22±0.01. When M is larger than L, very different scaling forms are found for odd L and even L. For the zero-energy domain walls, which occur when L is even, the probability distribution of domain wall entropy becomes highly singular, and apparently multifractal, as becomes large.     

坝基岩体错位的发现与分析

由寒武系坚硬白云岩组成的汾河二库坝基开挖后,岩体沿顺层开裂面发生错位,错位波及几乎整个坝基,错距达1～7cm.本文对坝基岩体错位进行了分析研究,认为岩体错位是基坑开挖后地应力释放的结果。     

四阶椭圆方程基态解的集中性态

该文分析了四阶椭圆方程△^２u=|x|^au^p-1,x∈Ω; u=\Delta u=0 , x ∈аΩ, (Ω表示Rⁿ中以原点为中心的球)基态解的集中性态,并证明了当p趋近于 2^*=\frac{2n}{n-4} (n>4)时基态解u_p集中在Ω的边界附近.     

Mon(n=2-13)和MonC(n=1-12)团簇的几何结构和电子结构

结合遗传算法和CALYPSO软件，采用密度泛函理论，对Mo_n(n=2-13)及Mo_nC(n=1-12)团簇基态的几何结构与电子结构展开详细研究.通过计算其基态结构的平均键长、平均结合能、二阶差分能、分裂能和前线轨道能级，对基态结构的稳定性随总原子数变化的关系展开了研究.计算结果表明，Mo_n团簇基态结构的稳定性可通过掺杂单个C原子而提高.综合团簇的二阶差分能、分裂能可知，n=6,9时Mo_n团簇的稳定性较高，n=4,7,10时Mo_nC团簇的稳定性较高.