Time-domain numerical computation of noise reduction by diffraction and finite impedance of barriers

A new time-domain numerical method is presented for the estimation of noise reduction by the diffraction and finite impedance of barriers. High order finite difference schemes conventionally used for computational aeroacoustics, and time-domain impedance boundary conditions are utilized for the development of the time-domain method. Compared with other methods, this method can be applied more easily to the problems related to nonlinear noise propagation such as impulsive noise and broadband noise. Linearized Euler equations in Cartesian co-ordinates are considered and solved numerically. Straight and T-shaped barriers with and without surface admittance are calculated. In order to assess the accuracy of this time-domain method, comparison with the results of SYSNOISE software (Ver. 5.3) are made. There are very good agreements between the results of the present time-domain numerical method and the boundary element method of the SYSNOISE software.     

A Facile Synthesis of α-Phenylthio-α,β-Unsatuated Esters

α-phenylthio-α，β-unsaturated esters 6 were synthesized by Witting reaction of 3.which were prepared by a phenylsulfenyllation-trans-ylidation reaction.     

Effects of B′-site transition metal on the properties of double perovskites Sr2FeMO6 (M=Mo, W): B′ 4d-5d system

The crystal structure, magnetic and magnetotransport properties of the variation of B′-site transition metal in Sr₂FeMO₆ (M=Mo, W) with double perovskites structure have been investigated systematically. Measurements of magnetization vs. temperature at H=5 T show that Sr₂FeMoO₆ is a ferromagnet and Sr₂FeWO₆ is an antiferromagnet with T_N∼35 K. Additionally, the large magnetoresistance ratio (MR) of ∼22% (H=3 T) at room temperature (RT) was observed in the Sr₂FeWO₆ compound. However, the Sr₂FeMoO₆ compound did not show any significant MR even at high fields and RT (MR∼1%; H=3 T and 300 K). The implications of these findings are supported by band structure calculations to explain the interaction between the 4d(Mo) and 5d(W) orbitals of transition metal ions and oxygen ions.     

氢原子光谱实验研究

氢原子的结构简单，其光谱具有明显的规律，各种原子光谱线规律性的研究首先是在氢原子上得到突破。通过测量氢光谱可见谱线的波长，能较准确测定氢的里德伯常数，可使学生对近代物理测量有初步了解。     

Analytical Study of Nonlinear Dust Acoustic Waves in Two-Dimensional Dust Plasma with Dust Charge Variation

The nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation is analytically investigated by using the formally variable separation approach. New analytical solutions for the governing equation of this system have been obtained for dust acoustic waves in a dust plasma for the first time. We derive exact analytical expressions for the general case of the nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation.     

“神龙一号”注入器研制

“神龙一号”注入器是直线感应加速器的束流源，它采用了感应叠加的高压加载方式，包括脉冲功率系统、感应腔、阴阳极杆、绝缘支撑、二极管和束流传输系统等子系统. 在研制中采用了径向绝缘支撑、对中支撑调节系统、类Pierce阴极等先进技术，以及二极管线圈内置和外径为800mm的铁氧体大环等创新. 参数测试显示，3.5MeV注入器达到了世界先进水平.     

Photoluminescence linewidth broadening due to alloy/thickness fluctuation of CdxZn1 − xSe/ZnSe triple quantum wells

Photoluminescence (PL) linewidth broadening of Cd_xZn_{1 − x}Se/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced.     

Synthesis and characterization of new bis(1-aryliminomethylenylnaphthalen-2-oxy)nickel complexes and their catalytic behavior for vinyl polymerization of norbornene

The synthesized 1-aryliminomethylenylnaphthalen-2-ol derivatives reacted with nickel chloride to form bis(1-aryliminomethylenylnaphthalen-2-oxy)nickel complexes. All resultant compounds were structurally characterized by elemental analyses, IR and H NMR, and the structures of the formed complexes were elucidated by X-ray crystal structure analysis. The complexes show high catalytic activities for the vinyl polymerization of norbornene in the presence of methylaluminoxane. The catalytic activity variations have been followed by gas chromatography through monitoring the conversion of norbornene.     

Characterization of a 4-miktoarm star copolymer of the (PS-b-PI)3 PS type by temperature gradient interaction chromatography

Temperature gradient interaction chromatography (TGIC) was applied for the separation of a complex miktoarm star copolymer which has one polystyrene (PS) arm and three polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer arms. Such miktoarm star polymers are much more difficult to characterize than branched homopolymers since the byproduct, typically polymers with missing arm(s) or coupled products, have not only different molecular weights but also different compositions. TGIC was able to fully separate the byproducts, and the composition of the molecular species corresponding to the different separated elution peaks was determined by two methods, fractionation/NMR and multiple detection (UV and RI). A reasonable agreement between the results of the two methods was obtained. By using the composition found, the corresponding molecular weights were determined by multi-angle light scattering detection. Based on the composition and the molecular weight we were able to identify the structure of the different molecular species.     

技术创新与增长期权定价

本采用了净现值(NPV)和实物期权定价方法对一个实际的MMDS的发射放大器项目进行了定价，并对两种方法定价的结果进行了分析和对比。由于实物期权方法定价的结果包含项目中的增长期权和放弃期权的价值，因而实物期权方法定价的结果比NPV方法定价的结果更合理和更高。