Macroscopic Quantum Coherence in an Antiferromagnetic Spin Chain with Biaxial Anisotropy

Instanton configurations of (1+1)-dimensions in an antiferromagnetic biaxial-anisotropy-spin-chain are obtained explicitly in the strong anisotropy limit, which interpolate between degenerate equilibrium orientations of the Néel vector along easy axis and are seen to be responsible for quantum tunneling. Macroscopic quantum coherence of the domain walls is demonstrated in terms of the instantons.     

Fractal aggregates evolution of methyl red in liquid crystal

The spontaneous formation of dendritic aggregates is observed in a two-dimensional confined layered system consisting of a film composed of liquid crystal, dye and solvent cast above a polymer substrate. The observed aggregates are promoted by phase separation processes induced by dye diffusion and solvent evaporation. The growth properties of the aggregates are studied through the temporal evolution of their topological properties (surface, perimeter, fractal dimension). The fractal dimension of the completely formed structures, when they are coexistent with different types of structures, is consistent with theoretical and experimental values obtained for Diffusion-Limited Aggregates. Under different experimental conditions (temperature and local dye concentration) the structure forms without interactions with other kinds of structures, and its equilibrium fractal dimension is smaller. The fractal dimension is thus not a universal property of the observed structures, but rather depends on the experimental conditions.     

Macroscopic resonant tunneling in an rf-SQUID flux qubit under a single-cycle sinusoidal driving

We experimentally demonstrate the observation of macroscopic resonant tunneling(MRT) phenomenon of the macroscopic distinct flux states in a radio frequency superconducting quantum interference device(rf-SQUID) under a singlecycle sinusoidal driving.The population of the qubit exhibits interference patterns corresponding to resonant tunneling peaks between states in the adjacent potential wells.The dynamics of the qubit depends significantly on the amplitude,frequency,and initial phase of the driving signal.We do the numerical simulations considering the intra-well and interwell relaxation mechanism,which agree well with the experimental results.This approach provides an effective way to manipulate the qubit population by adjusting the parameters of the external driving field.     

提拉法生长高质量氟化镁单晶

设计了适合提拉法生长氟化镁单晶体的温场,采用提拉法成功生长出了直径100 mm的高质量氟化镁单晶.晶体内无气泡等宏观缺陷、无开裂;通过精密退火处理后,晶体透过率达到95;,平均应力双折射小于0.5 nm/cm.上述结果表明采用提拉法可以生长高质量的氟化镁单晶.     

Investigation of self-assembled fractal porous-silica over a wide range of length scales using a combined small-angle scattering method

The unique structure of a set of self-assembled porous silica materials was characterized through a combined small-angle scattering (CSAS) method using small- and ultra-small angle neutron scattering as well as small-angle X-ray scattering. The porous silica specimens investigated were prepared by a sol-gel method under the presence of alkylketene dimer (AKD) template particles and through calcination, which leads to the development of porous silica having a mass-fractal structure over length scales from ~ 100 nm to ~ 10 μm. Furthermore, the specimens posses a hierarchical structure, which consist of a fractal porous structure, and also contain primary silica particles less than 10 nm in size, which form a continuous silica matrix. To characterize these complex structures, observation over a broad range of length scales is indispensable. We propose a CSAS technique that serves this purpose well.     

缺陷识别反问题的研究状况与若干进展

简要回顾了缺陷识别反问题的发展状况,评述了几类典型识别方法:基于势函数理论的电学法,静态ＢＥＭ优化迭代法,射线法,Ｔ矩阵法,Ｂｏｒｎ近似法,边界积分方程及边界元法．介绍了作者建立的裂纹及夹杂识别的迭代优化法．指出了缺陷识别反问题需要研究的主要问题．      

An universal relation between fractal and Euclidean (topological) dimensions of random systems

It is shown that a dimension-invariant form for fractal dimension D of random systems (where d is Euclidean dimension of the embedding space) is in good agreement with results of numerical simulations performed by different authors for critical (p=p _c ) and subcritical (p<p _c ) percolation, for lattice animals, and for different aggregation processes. Received: 9 July 1998 / Revised and Accepted: 12 July 1998     

Quasi pulse-echo ultrasonic technique for flaw classification

One of the important flaw characterization tasks in the field of ultrasonic non-destructive evaluation (NDE) is to provide flaw type information by analysing the flaw responses acquired during an inspection. Here a new quasi pulse-echo ultrasonic classification technique is presented which utilizes the time separation and amplitude difference of mode-converted diffracted signals to distinguish between smooth and sharp-edged flaw geometries. Experiments with cylindrical cavities, surface-breaking fatigue cracks and slag inclusions have been used to test the practicality of this approach. All results of these tests show good consistency in the separation of smooth and sharp-edged flaws, provided that the signal-to-noise ratio is sufficient. Furthermore, the scattering feature used for classification in this method is also verified by detailed elastodynamic scattering calculations.     

Influence of the macroscopic distribution of platinum in PtHFAU catalysts on their activity for n-hexane isomerization

The macroscopic distribution of platinum in extrudates of bifunctional PtHFAU/Al₂O₃ catalysts is shown to have a significant effect on their activity, stability and selectivity in n-hexane transformation under hydrogen pressure. The best catalysts are those for which platinum is homogeneously dispersed. n-Hexane transformation is proposed as a model reaction for estimating the macroscopic distribution of platinum in industrial catalyst pellets.     

Macroscopic solvation of molecules in excited states: An MCSCF model including solvent polarization effects-I

An MCSCF model including the effects of solvent polarization is developed. The model is applied within the limitations of INDO approximations to look into the dominant effects of solvent polarization on the electronic structure in the excited states of a model system (e.g.nπ ^* states of H₂CO). Important features of macroscopic solvation-induced reorganization of electron density and some consequence thereof are noted.