注入控制铜蒸气激光方向性时间过程测量

实验研究了注入控制对铜蒸气激光非稳腔输出光束质量的影响，从输出光发散角时间分辨过程的测量结果说明注入加速被注入腔内激光发散角的减小过程。由于被注入腔内放大自发辐射的存在，为得到较好的注入控制效果，注入光的脉宽和进入被注入腔的延时必须恰当。     

X-ray evidence for the absence of 90°-domains in polycrystalline PbTiO3 thin films with grains below a critical size

3 thin films is systematically studied by using X-ray diffraction (XRD). The PbTiO₃ thin films with different average grain sizes were prepared on various substrates by a sol-gel process. The films on NaCl and fused glass are randomly grain-oriented, while those on (111)Pt/Ti/SiO₂/Si are highly {100} cubic index grain-oriented . It is found from the XRD patterns of the films on NaCl that with decreasing average grain size from 230 to 80 nm, the intensities of high h index (h>l) peaks (hkl), such as (100), (110), (200), (201), (210), (211), etc., decrease rapidly and ultimately disappear, whereas another set of peaks (lkh), including (001), (002), (102), (112), etc., are still intense. This interesting result suggests that at grain size below a certain critical size an increasing number of grains no longer show 90°-domains, which is confirmed by TEM observations. Meanwhile, X-ray evidence of such a grain-size-related absence of 90°-domains is also found for PbTiO₃ films on Pt(111) and fused-glass substrates. The volume fractions of single-domain grains (without 90°-domains) in the films are estimated from their XRD patterns. By combining SEM and TEM investigations, the critical grain size for the formation of 90°-domains is further determined to be near 200 nm. Received: 19 December 1996/Accepted: 24 March 1997     

57Fe Mössbauer Spectroscopy Study of LaFe1−x Co x O3 (x=0 and 0.5) Formed by Mechanical Milling

Hyperfine Interactions - Perovskite-related phases of the type LaFe1?x Co x O3 (x=0 and 0.5) have been synthesised by milling techniques. The materials are of smaller particle size and more...     

AN EFFECTIVE APPROACH FOR TWO-DIMENSIONAL POLARONS IN AN ASYMMETRIC QUANTUM DOT

Within the framework of Feynman-Haken path integral theory, we calculate the ground-state energy of two-dimensional polarons in asymmetric quantum dots for arbitrary electron-phonon coupling constants. From a general three-dimensional Hamiltonian, some interesting problems, such as polarons in quasi-one-dimensional quantum wires and quasi-zero-dimensional asymmetric or symmetric quantum dots can be easily discussed only by taking different limit in the whole coupling regime. After the numerical calculation, we find that the relative polaronic correction increases monotonically with the decrease of effective dot size, and it becomes more pronounced with increasing dimension and asymmetry. Moreover, despite the insensitivity of relative polaronic enhancement to the variation of coupling constant at weak coupling, the correction is related to the coupling constant as the latter becomes larger.     

A functional modulus of continuity for Brownian motion

In this paper, we prove a sharpening of large deviation for increments of Brownian motion in (p,r)-capacity and Hölder norm case. As an application, we obtain a functional modulus of continuity for (p,r)-capacity in the stronger topology.     

Tunable negative refraction by electro-optical control in two-dimensional photonic crystal

This paper describes a simple hydrothermal procedure for high-yield synthesis of single-crystalline ZnO hexagonal nanoplates in a surfactant-free system at 70 °C. The structures and morphologies of the synthesized ZnO nanoplates are derived from characterisation by X-ray diffraction, and scanning and transmission electron microscopy. Their optical properties are recorded by Raman and photoluminescence spectroscopy. These ZnO hexagonal nanoplates exhibit the enhanced photocatalytic activity of phenol photodecomposition, suggesting that they could be served as an active system for the treatment of the waste water, in addition to their common applications. PACS 81.10.Dn; 61.10.Nz; 68.37.Hk; 78.55.Hx     

Nonlinear analysis of relativistic harmonic generation by intenselasers in plasmas

A linearly polarized, ultraintense laser field induces transverse plasma currents which are highly relativistic and nonlinear, resulting in the generation of coherent harmonic radiation in the forward direction (i.e., copropagating with the incident laser field). A nonlinear cold fluid model, valid for ultrahigh intensities, is formulated and used to analyze relativistic harmonic generation. The plasma density response is included self-consistently and is shown to significantly reduce the current driving the harmonic radiation. Phase detuning severely limits the growth of the harmonic radiation. The effects of diffraction are considered in the mildly relativistic limit. No third-harmonic signal emerges from a uniform plasma of near-infinite extent. A finite third-harmonic signal requires the use of a semi-infinite or finite slab plasma. For an initially uniform plasma, no second-harmonic radiation is generated. Generation of even harmonics requires transverse gradients in the initial plasma density profile     

平面研磨中影响工件起动力矩的因素

本文针对平面研磨过程中工件运动的随机性，从理论上求出了在机床起动瞬间磨具作用于工件上的合力矩；探讨了影响这个力矩的主要因素，偏心距和工件几何尺寸的作用规律；为选择研磨参数提供一理论依据。     

Seven novel seco-prezizaane-type sesquiterpenes from the pericarps of Illicium merrillianum

Seven new seco-prezizaane-type sesquiterpenes were isolated from the methanol extract of the pericarps of Illicium merrillianum. Their structures were elucidated as 3-deoxypseudoanisatin (1), 2beta-hydroxy-3,6-dedioxypseudoanisatin (2), 8alpha-hydroxy-10-deoxycyclomerrillianolide (3), 10beta-hydroxypseudoanisatin (4), 10beta-hydroxycyclopseudoanisatin (5), 1,6-dihydroxy-3-deoxyminwanensin (6), and 8-deoxymerrilliortholactone (7) by analyses of their spectroscopic data and chemical transformation. Compounds 4 and 5 as well as 6 and 7 coexist as a keto/acetal equilibrated mixture in methanol solution.