气相色谱-质谱测定香烟灰中的多环芳烃

采用正己烷-二氯甲烷(体积比为1:1)索氏提取,硅胶柱净化技术,用气相色谱-质谱(GC-MS)的分段选择性离子监测(SIM)对烟灰中多环芳烃(PAHs)进行定性定量分析.通过优化19种PAHs的分离条件,SIM法实现烟灰中19种PAHs的同时测定,检出限达到0.02ng/mL.该法灵敏、准确,适合于烟灰等食品中多环芳烃含量的测定.     

土壤的光谱特征及氮含量的预测研究

应用近红外光谱分析技术(NIR)测定土壤参数具有快速、方便的特点.文章分析了不同含水率、不同颗粒大小的土壤样本在不同测试角、不同测试高度对土壤光谱的影响,并得到了不同含水率和不同粒径土壤的含氮量预测模型.研究了这些因素对含氮率测量的影响,分析了NIR技术在田间实地应用预测的可能性.研究表明,光谱仪在距土壤高度为100 mm,测试角为45°时,具有最大的吸光度.土壤粒径和含水率这2个参数明显影响,当粒径在0.5～5 mm变化时,含氮量预测相关系数r为0.81左右,当土壤粒径在＜0.25和＞5 mm模型的预测能力变差.当土壤样品呈天然潮湿状态时,氮的预测结果较差.而样品干燥以后,预测相关系数较高.为土壤原位光谱测试提供了依据.     

Thermal Performance of Laser Diode Array under Constant Convective Heat Transfer Boundary Condition

Three-dimensional heat transfer model of laser diode array under constant convective heat transfer coefficient boundary condition is established and analytical temperature profiles within its heat sink are obtained by separation of variables. The influences on thermal resistance and maximum temperature variation among emitters from heat sink structure parameters and convective heat transfer coefficient are brought forward. The derived formula enables the thermal optimization of laser diode array.     

Observation of Quantum Beat in Rb by Parametric Four-Wave Mixing

Two coupled paralnetric four-wave-mixing processes in Rb atoms are studied using perturbation theory, which reveals clear evidence of tile appearance of quantum beat at 608cm^-1, corresponding to the energy difference of the 7s - 5d states of Rb atoms, in the parametric four-wave-mixing signals. A pump-probe technique is utilized to observe the quantum beat. Tinle-varying characteristics of the quantum beat are investigated using time-dependellt Fourier transform. The results show that the time-varying characteistics of the quantum beat not oldy offers a sensitive detecting method for observing the decay of atomic wave packets, but also provides a potential tool for monitoriHg the dissociation of molecules.     

Effect of Temperature on the Void Growth in Pure Aluminium at High Strain-Rate Loading

With the environment temperature varying from 273 K to 773 K, the dynamic process of void growth in pure aluminium at high strain-rate loading is calculated based on the dynamic growth equation of a void with internal pressure. The result shows that the effect of temperature on the growth of void should be emphasized. Because the initial pressure of void with gas will increase and the viscosity of materials will decrease with the rising of temperature, the growth of void is accelerated. Furthermore, material inertia restrains the growth of void evidently when the diameter exceeds 10 μm. The effect of surface tension is very weak in the whole process of void growth.     

Mechanism of Striation in Dielectric Barrier Discharge

The mechanism of striations in dielectric barrier discharge in pure neon is studied by a two-dimensional particle- in-cell/Monte Carlo collision （PIC-MCC） model. It is shown that the striations appear in the plasma background, and non-uniform electrical field resulting from ionization and the negative wall charge appear on the dielectric layer above the anode. The sustainment of striations is a non-local kinetic effect of electrons in a stratified field controlled by non-elastic impact with neutral gases. The striations in the transient dielectric barrier discharge are similar to those in dc positive column discharge.     

Measurement and Analysis of Spall Characteristics of High-Pure Aluminium at One-Dimensional Strain Loading

With an impact velocity varying from 196.9m/s to 317.9m/s and ratios of flyer/sample thickness of 2：4 and 3：6, the free-surface velocity profiles of the shock compressed high purity aluminium （HPA 99.999%） samples are measured with a velocity interferometer system for any reflector. Based on the vibrating features of the velocity profiles, the damage behaviour of HPA is analysed. The results indicate that the vibrating amplitude increases with increasing shock stress, and the subsequent reverberations describing the spall become more obvious. When the shock stress in the material is below a critical or smaller than the threshold level, the free-surface velocity profile replicates virtually the form of the compression pulse inside the sample. When the impact stress exceeds a critical value （1.4 GPa）, the micro damage would appear, and the free-surface velocity profile changes significantly, showing a series of short-duration reverberations in the profile. When the impact stress exceeds the threshold of damage, a compressive disturbance called the ＂spall pulse＂ appears in the free-surface velocity profile, and the subsequent reverberation becomes regular again. The measured spall strength of HPA is much higher than those of commercially pure aluminium reported in many references. In addition, the strength of HPA is similar to that of single-crystal aluminium.     

First-Principles Study of Structural and Electronic Properties of Layered B2CN Crystals

Based on the hexagonal BN structure, six possible layered B~ CN structures are constructed. Their total energies, lattice constants as well as electronic properties are calculated using the ab initio pseudopotential density functional method within the local density approximation. The calculated results show that the B2 CN-V configuration with AA stacking sequence is the most stable among the six B2CN layered structures. The characteristics of electronic structures indicate that the B2 CN-V shows metallicity, which mainly comes from -B1-C-B1-C- chains.     

Bounce-Averaged Acceleration of Energetic Electrons by Whistler Mode Chorus in the Magnetosphere

We construct the bounce-averaged diffusion coefficients and study the bounce-averaged acceleration for energetic electrons in gyroresonance with whistler mode chorus. Numerical calculations have been performed for a band of chorus frequency distributed over a standard Gaussian spectrum specifically in the region near L = 4.5, where peaks of the electron phase space density occur. It is found that whistler mode chorus can efficiently accelerate electrons and can increase the phase space density at energies of about 1 MeV by more than one order of magnitude about one day, in agreement with the satellite observations during the recovery phase of magnetic storms.     

CMOS星敏感器光学系统的设计

基于对恒星星表V/50的统计,在确保一定捕获概率的前提下,确定了星敏感器光学系统的视场角和所能探测的极限星等,在此基础上,结合所选用的STAR-250CMOS探测器的性能,在保证一定信噪比的前提下,确定了光学系统的通光孔径、焦距、工作光谱范围和中心波长、弥散元大小等主要参数。以改进双高斯型结构为初始结构,在ZE-MAX平台上实现了具有良好像质的大孔径(F/1.198)、大视场(22.6°)、宽光谱范围(0.5μm~0.8μm)的光学系统的设计,满足了对弥散斑、能量集中度等的特殊要求。