Low threshold amplified spontaneous emission based on coumarin 151 encapsulated in mesoporous SBA-15

Amplified spontaneous emission (ASE) characteristics of a blue dye coumarin 151 encapsulated in a highly ordered mesoporous SBA-15 were studied. The spectra narrowing was observed and found that the threshold and loss were greatly reduced, and the gain is significantly increased compared with spin-coated coumarin 151 doped poly(4-vinylphenol) film. The ASE threshold, gain, and loss, respectively, reached 0.55 mJ pulse(-1) cm(-2), 44.78 cm(-1), and 8.9 cm(-1) for the coumarin 151 encapsulated in mesoporous SBA-15 film. The optimized lasing action owes much to the effects of the better spatial confinement of the molecules in the ordered mesoporous structure of the host SBA-15.

A METHOD OF FITTING TO MOSSBAUER SPECTRUM OF EU-151 AND ITS APPLICATION TO EUROPIUM COMPOUNDS

A method of fitting to Mossbauer spectrum of 151Eu has been proposed. The intensities and the positions of all the possible transitions between the sublevels of the ground state and those of the excited state of nucleus with spin I> 3/2 can be considered at one time in fitting to experimental Mossbauer spectra by this method. The method has been used to fit to the experimental Mossbauer spectra of europium orthophosphate crystal and of europium pentaphosphate crystal, and to derive Mossbauer parameters from...

一种拟合~(151)Eu穆斯堡尔谱的方法及其对铕化合物的应用

本文提出了一种拟合~(151)Eu的穆斯堡尔谱的计算方法。用这种方法拟合~(151)Eu(I>3/2)的实验穆斯堡尔谱时,可以同时对所有可能跃迁线的位置和相对强度进行拟合。我们用这种方法对EuPO_4晶体和EuPsO_(14)晶体的穆斯堡尔谱进行了拟合,得到了相应的穆斯堡尔参数。对方法及拟合的结果也进行了讨论。

Surface Tension and Its Temperature Coefficient of Molten Tin Determined with the Sessile Drop Method at Different Oxygen Partial Pressures

The surface tension of molten tin has been determined by the sessile drop method at The surface tension of molten tin has been determined by the sessile drop method at temperatures ranging from 523 to 1033 K and in the oxygen partial pressure (P-O2) range from 2.85 x 10(-19) to 8.56 x 10(-6) MPa, and its dependence on temperature and oxygen partial pressure has been analyzed. At P-O2 = 2.85 x 10(-19) and 1.06 x 10(-15) MPa, the surface tension decreases linearly with the increase of temperature and its temperature coefficients are -0.151 and -0.094 mNm(-1) K-1, respectively. However, at high P-O2 (3.17 x 10(-10), 8.56 x 10(-6) MPa), the surface tension increases with the temperature near the melting point (505 K) and decreases above 723 K. The surface tension decrease with increasing P-O2 is much larger near the melting point than at temperatures above 823 K. The contact angle between the molten tin and the alumina substrate is 158-173degrees, and the wettability is poor.

Shock tube study of JP-10 ignition delay time

JP-10 (exo-tetrahydrodicyclopentadiene, C10H16) ignition delay times were measured in a preheated shock tube. The vapor pressures of the JP-10 were measured directly by using a high-precision vacuum gauge, to remedy the difficulty in determining the gaseous concentrations of heavy hydrocarbon fuel arising from the adsorption on the wall in shock tube experiments. The whole variation of pressure and emission of the OH or CH radicals were observed in the ignition process by a pressure transducer and a photomultiplier with a monochromator. The emission of the OH or CH radicals was used to identify the time to ignition. Experiments were performed over the pressure range of 151-556 kPa, temperature range of 1000-2100 K, fuel concentrations of 0.1%-0.55% mole fraction, and stoichiometric ratios of 0.25, 0.5, 1.0 and 2.0. The experimental results show that for the lower and higher temperature ranges, there are different dependency relationships of the ignition time on the temperature and the concentrations of JP-10 and oxygen.

先进复合材料研究的发展动向——第五届国际复合材料学术会议概述

<正> 1985年7月29日至8月1日作者有机会参加了在美国圣地亚哥举行的第五届国际复合材料学术会议(Fifth Intanational Confereneon Composite Materials,ICCM—V)。会议有17个国家近六百人参加,是历届国际复合材料学术会议参加人数最多的一次。会上宣谈论文151篇。其中除大会报告一篇外,其它分22个专题在六个分会场报告。这些论文包括复合材料科学6篇,新型复合材料研制与高温聚合

论侧向应力与疲劳裂纹扩展

本文通过对Ⅰ型平裂纹及复合型斜裂纹的疲劳试验说明:虽然平行于裂纹面的正应力(侧向应力)对应力强度因子不起作用,但是对裂纹顶端的塑性变形,从而对疲劳裂纹扩展速率却有明显的影响.相应于同样的应力强度因子幅值,当双轴载荷比λ=1时,侧向应力为零,裂纹扩展最慢;随着λ值减小,裂纹扩展速率增大.因此,在估算疲劳寿命时,如果只考虑应力强度因子幅值的作用,而忽略实验加载条件和实际加载条件下侧向应力差别的影响,必然会带来较大的误差,甚至是不安全的.

利用有限差分法求解扩散混合化学反应二维平行流动

利用隐式有限差分方法,对两股平行流的扩散混合、化学反应问题进行了计算。计算中,使用了层流压缩边界层方程并考虑了HF化学激光器的化学反应。计算结果表明:HF(2)振动激发态的浓度要比HF(1),HF(3)、HF(0)的浓度都高,从而获得了粒子数反转条件。另外,在计算中不需要混合长度的假设,就可以求得主流(无化学反应区)与化学反应区的两条界面曲线。当然,本文的计算方法要比直接求解二维Navier-stokes方程要简单得多。

磁层亚暴时环电流的局部加速机制

本文讨论了一种使环电流增强的局部湍流发电机过程。由于磁层内部的磁场很强,其位形基本满足无作用力磁场近似。另一方面,磁场的涨落值与其平均值相当。当涨落场电动势局部增强时,可以使平均场以及平均电流密度增强,形成环电流的增强。这时,亚暴过程中维持环电流所需要的能量是由湍流或波动的涨落场提供的,这是一种使粒子局部加速的过程。 本文还具体讨论了一种α~2湍流发电机模型,求出了具有随时间增长特性的本征模式。将分析结果应用于讨论亚暴时的环电流过程,并进行了定量估计。

二维流体-弹塑性流动计算

<正> 在经典力学中,传统的看法是把物质严格区分为流体和固体两大类,相应地有流体动力学和固体动力学。但在自然界中物质并不总是能如此区分的,而且物质状态也不是一成不变的。例如核装置在岩石中爆炸时能产生几百万大气压的高压和几百万度的高温,足以使周围岩石汽化和液化,这时岩石剪切强度可忽略不计,因而能够把它看作流体;但是地冲击波向外传播时强度逐渐减弱,岩石的固体特性就越来越明显,呈现出弹塑性特性。由此可见,在爆炸荷载作用下岩石既可能是流体也可能是固体。研究这类特殊过程中物质运动规律的学科

纵场边值线性无力场解的唯一性

<正> 无作用力磁场在天体物理中有广泛的应用。用磁面函数讨论线性无力场,若无力因子α不等于本征值,给定纵场边值时有唯一的本征值解。文献[2]中用格林函数分析线性无力场时认为,纵场边值不能唯一确定问题的解。本文对此进行分析和讨论。

曲线叶栅的绕流问题

<正> 关于一般叶栅的繞流問題,現有的許多解法,如格利克(Garrick,J.E.)、馬特波尔(Murterperl,W.)和波略霍夫()等法,都以直綫叶柵的繞流問題为基礎。这些方法有个共同缺点,就是当叶片弯度較大时,計算甚繁而不准确。針对这个缺点,本文給出一系列曲綫叶棚的准确解,所用的保角变換和一般直线叶柵的保角变换一样簡單,可用來代替上述各法中的直綫叶栅部分,使它們适合于弯度較大的叶片;因为变換簡單,同时又有四个参数,故可用來調整叶棚的稠度、柵角以及叶片的進出口角度。本方法可用來計算叶柵中叶片的相互位置和形狀,尤其是弯度对于叶栅性能的影响,同时这些准确解可用來鑑定渦旋分佈法所給曲线叶棚近似解的准确度。我們应当指出:本方法所給的曲緣叶柵当稠度較大时,棚角有一定限度,所以只适

Hopf bifurcation in wakes behind a rotating and translating circular cylinder

A low-dimensional Galerkin method, initiated by Noack and Eckelmann [Physica D 56, 151 (1992)], for the prediction of the flow field around a stationary two-dimensional circular cylinder in a uniform stream at low Reynolds number is generalized to the case of a rotating and translating cylinder. The Hopf bifurcation describing the transition from steady to time-periodic solution is investigated. A curve indicating the transitional boundary is given in the two-dimensional parameter plane of Reynolds number Re and rotating parameter alpha. Our results show that rotation may delay the onset of vortex street and decrease the vortex-shedding frequency. (C) 1996 American Institute of Physics.

Influence of convections on dopant segregation in floating-zone crystal-growth system

The steady and axisymmetric crystal growth process of floating zone model was studied numerically to concern with the influence of convection and phase change on effective segregation. An iteration method of numerical simulation considering both thermocapillary and buoyancy effects for GaAs crystal growth gave the effective segregation coefficient, which was compared with the space experiment of GaAs on board the Chinese recoverable satellite. The calculated segregation coefficient of a two-dimensional model was found to be smaller than the one suggested by space experiment with the simplified assumption of an one-dimensional model.