多孔微结构光纤中飞秒激光脉冲超连续谱的产生

报道了利用800nm飞秒激光脉冲在多孔微结构光纤中产生超连续谱展宽的现象，连续谱展宽范围为440—890nm.基于标量波近似理论对微结构光纤包层的有效折射率和基模的有效面积以及光纤的色散特性进行了计算，发现微结构光纤具有特殊的控制色散和波导特性的能力，对超连续谱展宽的机理进行了初步解释.本文的理论分析和实验结果有较好的一致性，认为即使包层由无序填充气线组成的多孔微结构光纤也可以出现超连续谱展宽效应. 关键词： 多孔微结构光纤 超连续谱 有效折射率 色散     

Microstructure of nanocrystalline powders of nonstoichiometric vanadium VC<Subscript>0.875</Subscript> and niobium NbC<Subscript>0.93</Subscript> carbides

The evolution of the microstructure of nonstoichiometric vanadium VC_0.875 and niobium NbC_0.93 carbide powders subjected to high-energy ball milling is investigated by neutron diffraction. It is established that milling produces non uniform powders and two distinct fractions with differing microstructure can be identified in them. It is shown that the time-of-flight neutron-diffraction technique is promising for studying the microstructure of highly deformed nonstoichiometric carbides and for quantitative determination of the anisotropy of microstrains.     

微结构光纤中超短激光脉冲传输的数值模拟

在传统求解广义非线性薛定谔方程(GNSE)分步傅里叶方法的基础上，提出了利用自适应分步 傅里叶方法(ASSFM)求解GNSE.数值模拟发现：在发生显著孤子峰值频移且微结构光纤的色散 和非线性参数随频率显著变化的情况下，采用ASSFM对超短脉冲在光纤中传输进行模拟是很 必要的，微结构光纤色散特性对超短脉冲在微结构光纤中的演化以及超连续光谱展宽有很大 影响.ASSFM可以合理地考虑到微结构光纤特性参数随脉冲演化过程中峰值功率所对应波长（ 或频率）的变化，从而更精确地模拟超短脉冲在微结构光纤中的传输. 关键词： 微结构光纤 超短脉冲 色散 自适应分步傅里叶方法     

Strain-induced grain growth in non-oriented electrical steels

The present work considers a method of columnar microstructure development in vacuum-degassed non-oriented electrical steels. Samples after temper rolling were annealed under special heat treatment conditions. The influence of the applied thermo-mechanical treatments on microstructure progress in the investigated non-oriented steels is studied. Columnar microstructure is obtained after combining the temper rolling and appropriate annealing conditions. The dependence of texture on the applied conditions was studied by EBSD facilities in the investigated material. It was confirmed that the obtained columnar microstructure possesses pronounced cube texture components.     

纳米CaCO3作固硫剂的基础研究

本文主要研究纳米碳酸钙与固硫有关的微观物理特性和固硫特性。研究表明,纳米碳酸钙有较好的利于固硫反应的微观物理特性和固硫特性,但固硫效果的好坏同结构特性有关,并且固硫特性受温度条件的支配影响,纳米碳酸钙用作喷钙吸收剂已具备一定的实用意义     

Microstructural analysis of Nd1.85Ce0.15CuO4−y superconductor sintered under high pressure and ambient pressure

The microstructure of Nd_1.85Ce_0.15CuO_4−y superconductor sintered under high pressure and ambient pressure has been characterized by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HREM). It has been observed that the conventional sample is porous, while the high-pressure sample is almost pore-free. It is confirmed that the thermal treatment under high pressure recovers fairly well connections between grains which were partly crushed during the compression process; hence the weak links at grain boundary are improved. Furthermore, a high density of defects induced by pressure is observed in the high-pressure sample. In contrast, the conventional sample is nearly perfect. For comparison, the microstructure of a sample pressed at high pressure at room temperature is also examined. The influence of pressure on the microstructure and the superconductivity is discussed.     

Enhancing light extraction from tapered internal reflection microstructure

The internal transmittance characteristics of the taper surface microstructure grating with the feature size in a large dimension range from subwavelength nanostructure to microstructure are investigated to improve the light extraction efficiency of light emitting diodes. It is found that subwavelength taper nanostructure can not overcome the total internal reflection, but it is interesting that the taper microstructure can effectively surmount the total internal reflection at a larger emitted angle over the critical angle also with higher transmittance. Besides, the emission characteristics of light intensity for subwavelength nano-grating and taper micro-grating are demonstrated. Also, the simple approaches of the scalar diffraction theory and the effective medium method can accurately analyze respectively the taper microstructure and subwavelength nanostructure grating. It is expected that the taper microstructure could be integrated into light emitting diodes to tremendously enhance the emission efficiency.     

Twin-microstructure enhanced magnetoresistance in La0.67Ba0.33MnO3 oxides

The grain growth dependence of microstructure and its effects on magnetic and transport properties are studied in the polycrystalline La_0.67Ba_0.33MnO₃ oxides. It is found that a lateral growth manner along a certain direction and a concentric terrace pattern along three orthogonal axes occur in the samples sintered at 1573 and 1673 K, respectively. Lamella-like twin microstructure forms in the concentric terrace growth pattern and the magnetoresistance properties can be enhanced by the twin microstructure. It suggests that the twin-boundaries in twin-grains may possibly induce spin-dependent scattering of electrons that is field reduced, or spin-polarized tunneling of electrons that is field enhanced, thus strengthening the effect of grain boundaries.     

三氨基三硝基苯材料微孔结构的小角x射线散射实验研究

应用同步辐射x射线小角散射技术研究了不同工艺制备的三氨基三硝基苯样品中的微孔状况 ，得到了样品材料有关微结构参数，包括微孔平均孔径及孔径分布、分形特征、Porod常数 及界面参数等，并分析了微孔结构参数的变化规律.结果表明，不同工艺制备的TATB样品材 料其微孔结构有较大差别，都有较显著的特征. 关键词： 小角x射线散射 TATB材料微孔分布     

Fabrication of a random convex-lens-shaped microstructure using a laser ablation

A convex-lens-shaped microstructure with a diameter of 50 μm on a metallic mold substrate was fabricated in this paper. A laser ablation process, in which the laser beam was focused and irradiated on the metallic mold substrate in order to remove a part of the substrate, was used for that. The convex-lens-shaped microstructure has not been reported in any studies of microstructure using the laser ablation process. It was proposed that the unbalanced ablation and re-adherence of the melted particles was the processing mechanism of the convex lens shape. The convex-lens-shaped microstructure fabricated in this study is smaller than the focused spot. It was expected that the same convex-lens-shaped microstructure can be fabricated even if the focused spot size is increased, so long as the fluence of the laser can be maintained. Therefore, the method proposed in this paper will improve the low processing speed, which has been the problem of a laser ablation process. The fabricated convex-lens-shaped microstructure on the metallic substrate can be used as the mold for the micro lens.     

急冷条件下Cu-Pb偏晶合金的相分离研究

研究了Cu-Pb偏晶合金的急冷快速凝固和组织形成规律，并通过将金属熔体的热传导方程和Navier-Stokes方程相耦合, 理论分析了合金熔体的冷却速率、液固相变时间等物理参量与液相分离之间的相关性. 研究结果表明，在急冷快速凝固条件下，熔体的快速冷却对偏晶合金组织形成的影响要比熔体内部液相流动的影响更为显著. 快速凝固使液相分离受到抑制，Cu-Pb偏晶合金均可获得均匀的微观组织结构. 随着冷速的增大，晶粒尺寸明显减小，凝固组织显著细化，晶体形态由粗大枝晶向均匀细小的等轴晶过渡. 提高冷却速率，缩短液固相变时间是重力场中抑制液相分离、获得均匀偏晶组织结构的重要条件. 关键词： 偏晶合金 快速凝固 液相分离 微观结构     

The concentration-dependence of the resistivity anomaly in dilute magnetic alloys at low temperatures

Ice single crystals were produced, which were homogeneously doped by HF. Distribution coefficients were determined, and ageing experiments were done. It is assumed: for fluorine-concentrations less than 10^?6 m/l the whole solute is concentrated in the grainboundaries of the microstructure, but at higher concentrations there exists no microstructure and the solute is regularly distributed in the bulk. The ageing experiments showed that the fluorineconcentration decreases while stored until a limiting concentration of 10^?6 m/l is reached. Then the microstructure may be rebuilt.     

Training, constraints, and high-cycle magneto-mechanical properties of Ni-Mn-Ga magnetic shape-memory alloys

Magneto-mechanical experiments with a rotating magnetic field of 0.97 T were performed with a Ni-Mn-Ga single crystal. Periodic strains exceeding 1% were recorded over a hundred million magneto-mechanical cycles. The twin microstructure of the cycled crystal was characterized using atomic force microscopy (AFM) and magnetic force microscopy (MFM). In the center of the sample, no twin boundaries were found. At the sample edges, the microstructure shows a dense twin pattern. The results are compared with previous experiments of differently trained crystals. It is useful to distinguish between “ineffective training”, which results in a nearly self-accommodated martensite, and “effective training”, which results in a nearly single-variant crystal. The evolution of twin structure is discussed in terms of training, magneto-mechanical cycling, and extrinsic constraints imposed by the experimental setting. It is concluded that the response of a magnetic shape memory alloy to an alternating excitation depends strongly on the initial twin microstructure established through training. In particular, ineffective training results in a twin microstructure which can adapt to extrinsic constraints resulting in continued large periodic magnetic-field-induced deformation. In contrast, the twin microstructure of an effectively trained crystal can not adapt to extrinsic constraints resulting in early failure by fracture.     

Microstructure and properties of single-crystal rare-earth oxide fibers

Single-crystal Ln₂O₃ (Ln = Sm, Eu, Gd) fibers are grown by the laser-heated miniature pedestal technique. The relationship between the microstructure of fibers and their plasticity is analyzed using scanning electron microscopy, energy-dispersive microanalysis, electron backscatter diffraction, and X-ray methods. It is shown that the distinction between ductile and brittle fibers is determined basically by the difference in their microstructure. The fracture of samarium oxide fibers is associated with the formation of oxycarbonate phases on their surface. The most promising are the fibers of gadolinium oxide, having the most perfect microstructure, moisture and a carbon dioxide resistance, and a wide range of transparency.     

Light induced microstructure transformation in a-Si：H films

A series of a-Si:H films are deposited by hot wire assisted microwave electron cyclotron resonant chemical vapour deposition (HW-MWECR-CVD), subsequently exposed under simulated illumination for three hours. This paper studies the microstructure change during illumination by Fourier Transformation Infrared (FTIR) spectra. There are two typical transformation tendencies of microstructure after illumination. It proposes a model of light induced structural change based on the experimental results. It is found that all samples follow the same mechanism during illumination, and intrinsic structure of samples affect the total H content.     

Microstructure of the current channels in a nanosecond spark discharge in atmospheric-pressure air in uniform and highly nonuniform electric fields

The microstructure of a nanosecond spark discharge in atmospheric-pressure air in uniform and highly nonuniform electric fields is investigated. It is found that an 0.1-to 0.4-mm spark channel consists of a large number (from 100 to 1000) of 5-to 10-μm-diameter microchannels distributed nearly uniformly over the channel cross section. The current amplitude in the spark is 1.5–3 kA, and the current density in a microchannel is 10⁷ A/cm². It is shown that the formation of the microstructure cannot be attributed to ionization-heating instability. The instability of the ionization wave front is suggested as a mechanism for the microstructure formation.     

Formation of the microstructure in the course of low-temperature annealing of cryogenically deformed copper

The formation of the microstructure in the course of annealing of cryogenically deformed copper is investigated. It is shown that this material is very unstable, and the primary recrystallization in it is finished already after 1-h annealing at 150°C. The formation of the microstructure and texture in the course of the recrystallization are determined by the selective growth of grains with orientations close to (90;27;45), (80;31;35), and (55;30/60;0).     

Highly Birefringent Microstructure Fiber with Zero Dispersion Wavelength at 0.64 Micrometer

Abstract

In this article, we have designed a microstructure fiber, which consists of elliptical air holes at the core region. We have investigated its optical properties using finite difference time domain method. The fundamental mode of the proposed microstructure fiber can induce very high birefringence. It has been realized that the value of birefringence is mainly decided by the shape of the air holes present in the first and second rings. The zero dispersion wavelengths of both fast and slow axes have been shifted to 0.64 micrometer. The proposed birefringent microstructure fiber may be useful in optical communication and sensors.