Piezoelectric coefficients of complex semiconductor alloys from first-principles: the case of Ga(1- x)In(x)N

A first-principles-derived scheme is developed to compute the piezoelectric coefficients e(i j) of semiconductor alloys. This method is applied to study the effect of atomic arrangement and composition on e(33 ) in wurtzite Ga (1- x)In xN. Results obtained by this method for ordered structures are in good agreement with direct first-principles calculations. We predict that atomic ordering can have a large effect on piezoelectricity and that e(33 ) of disordered materials is nearly linear with composition. Microscopic origins for these features are revealed.     

Dielectric effect on the rf characteristics of a helical groove travelling wave tube

A new type of partial-dielectric-loaded helical groove slow-wave structure (SWS) for millimetre wave travelling wave tube (TWT） is presented in this paper.The radio-frequency characteristics including the dispersion properties,the longitudinal electric field distribution and the beam-wave coupling impedance of this structure are analysed.The results show that the dispersion of the helical groove circuit is weakened,the phase velocity is reduced and the position of the maximum Ez is moved from the mouth to the inside of the groove after partially filling the dielectric materials in the helical groove SWS.Therefore,the dielectric-loaded helical groove SWS is suitable for a multi-beam TWT with broad band and high gain.     

Study of nanocrystalline Fe－Al－N soft magnetic thin films

Fe－Al－N films were fabricated by reactive sputtering using a radio-frequency magnetron sputtering system. The effects of Al and N content and annealing temperature on microstructure and magnetic properties were investigated. The Fe－Al－N films, which have good soft magnetic properties, consist of nanocrystalline α-Fe grains and a small amount of other phases in the boundaries of α-Fe grains. The average α-Fe grain size is about 10－15nm. A slight amount of Fe－N and Al－N compounds precipitate in the boundaries of α-Fe grains and suppress their growth. Annealing improves the soft magnetic properties slightly by releasing the residual stress and reducing defects.     

自发喇曼成像法在线测量流场组分浓度(II)

 介绍了利用自发Raman散射光谱测量低压气流组分绝对浓度的方法，在流动状态下得到了不同压力下的自发喇曼散射光谱，检测最低压力为133帕；对于含N₂氧气流在已知N₂浓度时实时标定检测了O₂的绝对浓度，测量误差小于8%。     

Single-mode rib polymer waveguides and electro-optic polymer waveguide switches

Mode-matching and effective index methods are used to analyze single-mode operation of optical rib polymer waveguides. Their single-mode waveguiding conditions are determined. Single-mode rib waveguides fabricated from guest–host polyetherketone are presented. The estimated propagation loss of straight rib-waveguides is 0.7 dB/cm at 1.55 μm. Furthermore, by using the mode field-transfer matrix method, 2×2 and 4×4 polymer Mach–Zehnder interference switch operating at 1.55 μm wavelength has been designed based on optical multi-mode interference.     

Measurement of electro-optic coefficients of low-symmetry crystal YbCa4O(Bo3)3

In this paper, we report on all the electro-optic coefficients of the low-symmetry crystal YbCa₄O(BO₃)₃ measured by the interferometric method. The new sample orientations, which have not been reported so far, have been used for measuring the skew electro-optic coefficients γ₅₁, γ₅₃, γ₄₂ and γ₆₂ independently. The results obtained are γ₁₁=0.6, γ₂₁=0.4, γ₃₁=0.3, γ₁₃=0.3, γ₂₃=0.2, γ₃₃=2.2, γ₅₁=0.9, γ₅₃=4.1, γ₄₂=0.8 and γ₆₂=0.4×10⁻¹² m/V.     

动量相关作用对两体耗散同位旋效应的重要性

利用同位旋相关的量子分子动力学,研究了中能重离子碰撞中动量相关的状态方程对原子核阻止基于两体耗散的同位旋效应的影响.计算结果表明原子核阻止对同位旋相关和同位旋无关的核子–核子碰撞截面(两体耗散)的差值强烈地依赖于动量相关势,即在有动量相关势的情况下原子核阻止对同位旋相关和同位旋无关的核子–核子碰撞截面的差值大于没有动量相关势的情况.这就意味着动量相关作用明显地提高了原子核阻止对于核子–核子碰撞截面的灵敏性.因此,在考虑动量相关势的情况下,原子核阻止可以更准确地作为提取同位旋相关的核子–核子碰撞截面的一个探针.     

周期轨道的量子化与量子能谱中的长程关联

用二维可积系统的半经典量子化方案和二维无关联振子系统的量子能级与周期轨道之间的对应关系,讨论了一组量子能级之间具有长程关联的内在机制,在二维无关联振子系统中,发现了具有相同拓扑M(M1,M2)的周期轨道相对应的量子能级之间存在着长程关联,并以二维4次无关联振子系统为例做了具体说明.     

基于同步辐射加速器的康普顿背散射γ射线源(Ⅰ)产生MeV量级γ光子的数值计算

提出在筹建的上海同步辐射装置上建造一条MeV量级γ射线束及应用站,采用μm波长的红外(或远红外)激光与储存环中3.5GeV电子束进行康普顿背散射,从而获得能区为1—25MeV的康普顿背散射γ光子束,该光子束具有高强度、高极化度(线和圆极化)、准单色、方向性好的优点,可以广泛地应用于核物理和核天体物理基础研究及相关的应用研究领域.介绍了康普顿背散射的基本原理,并结合储存环参数给出了光子束性能的数值计算结果.     

铜(Ⅱ)/H2O2对多巴氧化作用的紫外-可见光谱研究

本文采用紫外－可见光谱法研究了在不同pH条件下铜（Ⅱ）／H2O2对多巴氧化作用的影响。结果表明，pH可影响铜离子催化多巴氧化成黑色素的效率，在弱酸性环境下铜（Ⅱ）的催化作用要比pH7.4时强。