A new method for computing turbulence in compressible laminar-turbulent transition and boundary layers--PSE＋DNS

A new method for computing laminar-turbulent transition and turbulence in compressible boundary layers is proposed. It is especially useful for computation of laminar-turbulent transition and turbulence starting from small-amplitude disturbances. The laminar stage, up to the beginning of the breakdown in laminar-turbulent transition, is computed by parabolized stability equations (PSE). The direct numerical simulation (DNS) method is used to compute the transition process and turbulent flow, for which the inflow condition is provided by using the disturbances obtained by PSE method up to that stage. In the two test cases incfuding a subsonic and a supersonic boundary layer, the transition locations and the turbulent flow obtained with this method agree well with those obtained by using only DNS method for the whole process. The computational cost of the proposed method is much less than using only DNS method.     

端羟基丁腈与二异氰酸酯反应动力学研究

本文对端羟基液体丁二烯/丙烯腈共聚物与二异氰酸酯的反应动力学进行了研究。通过化学分析方法测定反应速率,确定该反应为二级反应,反应活化能E_a =6.44kcal/mol。同时研究了一些因素对反应速率的影响。结果表明,共聚物中丙烯腈含量愈高,反应速度愈快,即氰基对反应有自催化作用。二月桂酸二丁基锡是反应的有效催化剂。不同异氰酸酯与端羟基液体丁二烯/丙烯腈共聚物的反应活性的顺序为4,4′-二苯基甲烷二异氰酸酯、2,4-甲苯二异氰酸醋、2,4/2,6-甲苯二异氰酸酯、1,6-六次甲基二异氰酸酯。     

柠檬酸燃烧法制备Gd3Ga5O12:Eu3+纳米晶及发光性质

以柠檬酸为燃烧剂,乙二醇为分散剂,采用燃烧法制备了Gd3Ga5O12∶Eu3+纳米晶.利用X射线衍射仪、扫描电镜和荧光光谱对样品的结构、形貌和发光性能进行了研究.XRD研究结果表明:合成的样品均为单一的Gd3Ga5O12晶相,纳米晶的一次性粒径分布在16～ 30nm.发射光谱和激发光谱的研究表明:主发射峰来自于Eu3+的5D0→7F1的跃迁;宽激发带主要来自于Eu-O电荷迁移带.讨论了柠檬酸和乙二醇用量对晶粒尺寸、品格常数、发射和激发强度的影响.结果表明:过量的柠檬酸和适量的乙二醇有利于晶体发育和发光强度的提高.     

计算柱面上对面积的曲面积分的一种新方法

给出了利用对弧长的曲线积分计算柱面上对面积的曲面积分的一种新方法,其计算公式为∫∫_Σf(x,y,z)dS=∫_(L*)ds∫z_1(x,y) z_2(x,y)f(x,y,z)dz,其中积分曲面Σ为垂直于xoy坐标面的柱面片,L*为Σ在xoy坐标面上的投影曲线(平面曲线),z=z1(x,y),z=z2(x,y)分别为过Σ的下边界曲线和上边界曲线的任一不同于Σ的曲面的方程.     

稀土钙钛矿型过氧化氢分解催化剂研究

柠檬酸盐热分解法合成了一系列稀土钙钛矿型过氧化氢分解催化剂，90％和30％H2O2实验表明，点火延迟时间主要取决于催化剂的润湿程度，而催化剂活性则主要取决于催化剂化学组成；所合成催化剂的活性顺序是LaNiO3〈〈LaCoO3〈LaMnO3〈LaMn0．5Co0．5O3〈LaMn0．8Co0.2O3〈La0．7Sr0．3Mn0．8Co0．2O3。为了制备商用催化剂，将30％的La0．7Sr0．3Mn0．8Co0.2O3浸渍在γ—Al2O3微球上；模拟发动机试验表明，在大于5g·cm^-2·s的较高床载荷下，催化分解89．6％的推进剂级过氧化氢的寿命达到4000s以上。     

分段函数的分类及分离型分段函数与初等函数之间的关系

将分段函数划分为连结型分段函数，分离型分段函数和它们的组合形式三种类型，得到了分离型分段函数是初池数的充分必要条件，完整地解决了分离型分段函数与初等函数之间的关系，并且给出了初等函数在其行一截取集上的限制函数（截取函数）仍然是初等函数的结果。     

Oxide-apertured VCSEL with short period superlattice

Novel distributed Bragg reflectors (DBRs) with 4.5 pairs of GaAs/AlAs short period superlattice (SPS)used in oxide-apertured vertical-cavity surface-emitting lasers (VCSELs) were designed. The structure of a 22-period Al0.9Ga0.1As (69.5 nm)/4.5-pair [GaAs (10 nm)-AlAs (1.9 nm)] DBR was grown on an n+ GaAs substrate (100) 2° off toward (111)A by molecular beam epitaxy. The emitting wavelength was 850 nm with low threshold current of about 2 mA, corresponding to the threshold current density of 2 kA/cm2. The maximum output power was more than 1 mW. The VCSEL device temperature was increased by heating ambient temperature from 20 to 100 ℃ and the threshold current increased slowly with the increase of temperature.     

新型MSM结构砷化镓半导体探测器的性能

研究一种新型双金属接触GaAs半导体探测器的性能,测量了²⁴¹Am 5.48MeVα粒子、⁵⁷Co 122keV的光子和⁹⁰Sr 2.27MeVβ粒子的最小电离粒子谱,比较了一个3×3mm²的GaAs芯片在经过¹³⁷Cs 662keV光子约1300rad辐照前后的电荷收集效率和能量分辨率.测量结果显示这种新型金属─半导体─金属(MSM)结构的半导体探测器不仅在室温下对各种粒子具有良好的探测能力,而且具有很好的抗辐照性能.     

阴极适应多丝室电荷灵敏放大器的研制

 电荷放大器是粒子描迹仪系统中一个重要组成部分，它的目的是把多丝正比室输出的弱电信号进行放大并处理为准高斯信号以供CIA(电流积分型ADC）电路进行数字化。整个电路主要包括放大、成型两个部分。可把不同幅度的输入脉冲放大成型为宽度600ns的准高斯波形。     

Verification of parabolized stability equations for its application to compressible boundary layers

Parabolized stability equations (PSE) were used to study the evolution of disturbances in compressible boundary layers.The results were compared with those ob- tained by direct numerical simulations (DNS),to check if the results from PSE method were reliable or not.The results of comparison showed that no matter for subsonic or supersonic boundary layers,results from both the PSE and DNS method agreed with each other reasonably well,and the agreement between temperatures was better than those between velocities.In addition,linear PSE was used to calculate the neutral curve for small amplitude disturbances in a supersonic boundary layer.Compared with those obtained by linear stability theory (LST),the situation was similar to those for incom- pressible boundary layer.