High‐pressure Raman spectra of deuterated L‐alanine crystal

Raman spectra of deuterated L ‐alanine have been obtained at high‐pressure conditions. A phase transition at ∼1.5 GPa associated with the splitting of some internal modes and increase of the wavenumber of the external modes was observed. Similarly to the hydrogenated L ‐alanine crystal, this first transition was related to a symmetry change. Moreover, further modifications of the Raman spectra were observed at 4.4 GPa, which may be associated to conformational changes of the molecule. To give further support to such a hypothesis, neutron powder diffraction measurements were performed. Information about the cell parameter at atmospheric pressure gave valuable information about the N D distances, shedding light on the behavior of the torsional vibration of ND₃⁺. Copyright © 2009 John Wiley & Sons, Ltd.     

Analytical solution of a multidimensional Langevin equation at high friction limits and probability passing over a two-dimensional saddle

The analytical solution of a multidimensional Langevin equation at the overdamping limit is obtained and the probability of particles passing over a two-dimensional saddle point is discussed. These results may break a path for studying further the fusion in superheavy elements synthesis.     

基于物理光学法的建筑物内高功率微波耦合场分布计算

利用物理光学法计算了高功率微波在建筑物内的耦合场分布。根据建筑物墙壁和窗户的透射率可以得到墙壁内侧的透射场,将它代入到矢量衍射公式中直接计算出在整个建筑物内的透射场;根据建筑物地面的反射率得到地板表面的反射场,将它代入到矢量衍射公式中可计算出整个建筑物内的反射场;对透射场与反射场进行矢量相加,得到叠加场。将本文方法得到的场分布情况和时域有限差分法得到的场分布进行比较,二者结果一致。物理光学法的优点在于其物理图像清晰,计算量小,计算速度快,适合应用在大型建筑物内部耦合场分布计算上。     

瓦级大功率InGaN蓝光LED的光色电特性

封装并测量了瓦级大功率InGaN蓝色发光二极管(LED)在不同正向电流I_F驱动下的光通量、电功率、发光效率、发射光谱和色品坐标等参数的变化。研究表明, 光通量与电功率随I_F的增大呈亚线性增加,而发光效率η则下降。当I_F从50 mA一直增大到450 mA左右时,发射光谱的峰值波长λ_p随I_F的增加发生蓝移,蓝移现象可能与InGaN蓝光LED芯片在较大电流时能带被拉平以及In成分的作用有关。当I_F大于500 mA或800 mA后,λ_p又发生红移,红移现象可能与大电流注入下InGaN蓝光LED芯片产生的热效应以及电子-空穴对辐射复合有关。此外,光谱的半峰全宽(FWHM)产生宽化现象,色坐标x和y值也发生变化。     

激光核聚变与高功率激光:历史与进展

回顾激光聚变近50年来的发展历程,评述聚变物理与高功率激光驱动器的研究进展,展望聚变能源未来前景.     

多功能抗激光损伤高反射膜

为了能同时满足半导体激光器和YAG激光器对薄膜的特殊要求,在分析高反射膜理论的基础上,选取TiO2和SiO2为高、低折射率材料镀制了周期性多层介质高反射膜。研究了材料的光学及机械特性,重点解决了薄膜的消偏振和抗激光损伤问题。实验采用电子束真空镀膜并加以考夫曼离子源辅助沉积,利用TFC软件进行膜系设计,通过调整镀膜工艺参数和监控方法,在10mm×1．8mm的K9基底上镀制了符合要求的高反射膜,结果表明,当激光以45°入射时,薄膜在900～1100nm的P光与s光的反射率均大于99．95％。所制备的高反射膜性能稳定,抗激光损伤阈值高,能同时满足两种激光器的使用要求。     

Vibronic origins of high T c

In this paper we present a detailed development of our vibronic mechanism for the explanation of high temperature superconductivity. We first review the evidence for believing that some unified mechanism for “low” and “high” T _c is required. We then develop the case for the existence of the double-well motions, required by our theory, in these systems, and proceed to develop our ideas further to the point of unifying, the T _c ～ 100 K, and the T _c ～ 40 K systems. We also advance a possible explanation of the anomalous isotope effects in these systems, and conclude with an extended discussion of non-cuprate systems and general criteria for high T _c theories, including the gap to kT _c ratio.     

Probability of fatigue failure in glass fibers

Abstract

Fracture mechanics provides the background for making long-term failure predictions to assure the mechanical reliability of glass fibers. The fatigue parameters necessary for making these predictions can be obtained from static and dynamic fatigue strength experiments. The failure calculations are best understood by expressing the predictions in terms of a design diagram. The probability of failure in service as well as the proof test stress necessary to ensure a minimum lifetime in service can be obtained from a design diagram.     

Thermoelastic behaviour of hexagonal graphite-like boron nitride

Abstract

A synchrotron X-ray diffraction study on hexagonal graphite-like boron nitride (h-BN) was performed under high pressures and temperatures. From the measured P-V-Trelation for h-BN (with a three-dimensional ordering parameter P₃ = 0.9) in the temperature range from 298 to 1273 K and up to 6.7 GPa, the thermoelastic parameters are derived by fitting a modified high temperature Birch-Murnaghan equation of state. The results are: bulk modulus B₀[GPa] = 27.6-0.0081(T[K]-298) and its pressure derivative B¹ = 10.5 + 0.0016(T [K] - 298). These values are for samples with P₃ = 0.9 and are quite different for samples with different values of the order parameter. This parameter is shown to have a leading role in the determination of the thermoelastic properties of h-BN, which explains and reconciles the differences between previous results.