光纤放大器中的受激布里渊散射阈值

 从受激布里渊散射(SBS)耦合波理论出发,根据双包层光纤放大器中的受激布里渊散射阈值模型,理论仿真了信号带宽、纤芯直径、放大器增益对SBS阈值的影响,并从实验上研究了单频百纳秒脉冲信号在掺镱双包层光纤放大器中的受激布里渊散射现象。实验中输入脉冲信号重复频率1 Hz,脉宽200 ns,对不同的输入脉冲信号放大,前向放大脉冲在脉冲能量660 nJ、峰值功率3.3 W时出现畸变,产生后向SBS窄脉冲,达到了SBS阈值,实验计算的SBS阈值与理论分析结果基本一致。     

纳米Fe3 O4 颗粒的正电子湮没谱学研究

测量了磁性纳米Fe₃O₄颗粒的X射线衍射谱(XRD)、正电子湮没寿命谱(PALS)和符合多普勒展宽谱(CDBS),研究了不同压力和退火温度对磁性纳米Fe₃O₄颗粒物相、电子结构、缺陷及电子动量分布等的影响. XRD,PALS,CDBS测量结果表明:纳米Fe₃O₄颗粒的缺陷浓度随压力的增加而增大,但物相和缺陷类型并未发生变化;磁性纳米Fe₃O_{4< 关键词： 正电子 3}O₄')" href="#">Fe₃O₄ 寿命谱 多普勒展宽谱     

Fast Si magic-angle-spinning NMR acquisitions by RAPT-CP Al → Si polarization transfer

Using enhancement of the ²⁷Al central-transition magnetization by applying RAPT prior to ²⁷Al → ²⁹Si cross-polarization, we demonstrate fast acquisition of ²⁹Si one-dimensional MAS and two-dimensional ²⁷Al–²⁹Si HETCOR spectra on a new sialon phase Ba₂Al₃Si₉N₁₃O₅.     

等离子体中电磁波的粒子模拟

本文介绍了1 2/2维相对论性、电磁模等离子体粒子模拟的方法和原理。系统地以计算机模拟了由电子气体组成的等离子体中的各种电磁波。在无外加静磁场、加外横磁场、加外纵向磁场等不同情况下,分别得到静电波、电磁波、寻常波、非寻常波、ω=nω_c的磁回旋共振、左旋波、右旋波等。其色散关系、截止频率、共振频率、极限相速度均与理论结果一致。     

Investigation of the local structure variance of water molecules in laser-induced thermal desorption process

This paper presents the use of molecular dynamics simulation in the study of laser-induced thermal desorption (LITD) of water molecules adjacent to a laser-heated Au substrate. The local structure of the water molecules is investigated by considering the densities of the oxygen and hydrogen atoms, the average number of neighbors, n_NN, and the average number of H-bonds, n_HB. At an equilibrium temperature of 300 K, the simulation results show that three adsorption water layers are formed in the immediate vicinity of the Au surface, and that each four-fold hollow site on the uppermost Au(0 0 1) surface is occupied by a single water molecule. Following laser-induced heating of the Au substrate with a sub-picosecond laser pulse of 350 fs, the substrate temperature increases to 1000 K. This causes a gradual heating of the adjacent water film, which is accompanied by a decrease in the values of n_NN and n_HB. Hence, it can be concluded that an increase in the water film temperature destroys the hydrogen-bonding network throughout the water film. Although the maximum local temperature of the water film occurs in the region immediately adjacent to the Au substrate, it is determined that the attractive energy between the Au atoms and the water molecules in this region causes the water molecules to aggregate together to form three-dimensional water clusters. Furthermore, this energy prevents the hydrogen bonds in this region from breaking apart as violently as those within the phase explosion region. Finally, it is observed that the phase explosion phenomenon occurs in the region of the water film where the values of n_NN and n_HB are at a minimum.     

基于时分复用技术的吸收光谱气体温度在线测量研究

可调谐半导体激光吸收光谱技术是一种具有高灵敏度、高选择性的非接触式气体在线测量技术。通过直接扫描多条H2O特征谱线并结合最小二乘算法实现对开放环境气体温度的在线测量。利用HITRAN光谱数据库详细讨论了边界效应对气体温度浓度测量的影响,计算结果表明,扫描多特征谱线并结合最小二乘算法可有效减小边界效应对开放环境气体温度测量的影响。实验中采用时分复用技术同时扫描了7 444.36,7 185.60,7 182.95和7 447.48cm-1四条H2O特征谱线,对管式炉573～973K范围内不同工况下的气体温度进行了测量。吸收光谱测量结果与热电偶信号的最大温差小于52.4K,温度测量最大相对误差为6.8%。     

Conversion issues between microwave radiance and brightness temperature

Microwave radiances are usually converted into brightness temperatures for data assimilation and retrievals. The Rayleigh-Jeans approximation has been believed to be a good approximation for the conversion at low frequencies, but inaccurate at high frequencies. However, the simplified radiative transfer models under the Rayleigh-Jeans approximation (hereafter referred as BT-RTE) have been successfully applied in radiance simulations for frequencies below 183 GHz, which has somewhat puzzled the radiative transfer community. This paper clarifies the confusion. In addition, the conversion formula for the third and the fourth Stokes components are derived.Simulations for a polarized sensor, the Special Sensor Microwave Imager and Sounder, show that the BT-RTE is generally accurate. Results for a polarimetric sensor, WINDSAT, show that the third and the fourth Stokes radiances should be converted using the exact conversion formula given in this study rather than using a direct Planck function conversion.     

Immobilization of bovine serum albumin on TiO2 film via chemisorption of H3PO4 interface and effects on platelets adhesion

In the present study, bovine serum albumin (BSA) was successfully covalently immobilized on the surface of anatase TiO₂ film by a three-step method, i.e. application of H₃PO₄ chemisorption to increase surface -OH, which increases the amount of coupling 3-aminopropyl-triethoxylsilane (APTES), thus linking with BSA by imide bond using EDC/NHS/MES. There is no significant -OH group increase on rutile film when using the same method of phosphoric acid treatment, which suggest it is difficult for further chemical modification of the rutile film. After covalent immobilization of BSA on anatase film, an improved hemocompatibility of anti-platelet adhesion and aggregation in vitro could be recognized by LDH and SEM analysis. This study suggests BSA-immobilized anatase surface can serve as hemocompatibility material in vivo.     

高压环境下1.58μm波段CO2吸收光谱特性分析

高压气体吸收光谱特性的研究是可调谐半导体激光吸收光谱技术应用于爆轰发动机等高压燃烧环境的重要基础.为了解气体吸收光谱随压力的变化规律特别是在高压下的吸收光谱特性,本文以CO₂为气体介质对其在高压环境下近红外波段1.58μm处的吸收光谱进行了理论分析与试验研究,并给出一种高压气体浓度的计算方法.在1—10.13×10⁵Pa压力环境下,对1.58μm处CO₂吸收光谱进行了数值模拟,搭建了高压环境气体在线测量试验系统,对CO₂在波段1578.1—1579.7 nm的吸收光谱进行了试验测量.利用线性回归拟合将试验所得光谱吸收率与模拟吸收率进行对比,对高压环境下气体浓度进行了计算.结果表明,试验所得吸收光谱与数值模拟结果相吻合,1—10.13×10⁵Pa压力环境下利用线性拟合寻优法计算气体浓度最大误差为5.5%,平均误差2.6%.     

Modified adaptive algebraic tomographic reconstruction of gas distribution from incomplete projection by a two-wavelength absorption scheme

A modified adaptive algebraic reconstruction technique (MAART) with an auto-adjustment relaxation parameter and smoothness regularization is developed to reveal the tomographic reconstruction of H 2 O distribution in combustion from incomplete projections. Determinations of relaxation parameter and regularization factor are discussed with regard to the consideration of improvement in reconstruction and reduction of computational burden. A two-wavelength scheme from tunable diode laser absorption measurement, 7444.36 and 7185.59 cm 1 , is used to simplify the nonlinear solution problem for obtaining the tomographic distributions of concentration and temperature simultaneously. Results of calculations demonstrate that MAART can perform the reconstruction results more efficiently with little complex modification and much lower iterations as compared with the traditional algebraic reconstruction technique (ART) or simultaneous iterative reconstruction technique (SIRT) methods. The stability of the algorithm is studied by reconstruction from projections with random noise at different levels to demonstrate the dependence of reconstruction results on precise line-of-sight measurements.