Centrality dependence of direct photon production in (square root)S(NN) = 200 GeV Au + Au collisions

The first measurement of direct photons in Au + Au collisions at (square root)S(NN) = 200 GeV is presented. The direct photon signal is extracted as a function of the Au + Au collision centrality and compared to next-to-leading order perturbative quantum chromodynamics calculations. The direct photon yield is shown to scale with the number of nucleon-nucleon collisions for all centralities.     

多层氧化石墨烯-水泥基复合材料的力学性能与微观结构

研究了大片径多层氧化石墨烯(Graphene Oxide,GO)对水泥砂浆力学性能和微观结构的影响。发现掺入多层GO对水泥砂浆的抗压强度和抗折强度增强效果明显。随着GO掺量的增加,水泥砂浆的抗压强度和抗折强度呈现出先增大后减小的趋势。通过SEM观察其微观结构,发现GO作为载体,促使花状晶体和针状晶体等水化产物的生成,并且调节水泥的水化产物规则生长,形成致密结构。此外,GO纳米片可以形成阻止裂纹扩展的屏障,抑制裂纹在水泥砂浆中的传播,增强水泥砂浆的力学性能。相比于小片径薄层GO,大片径多层GO对水泥基材料性能的增强效果明显,经济实用性更高。     

Pure and Sn-, Ga- and Mn-doped ZnO gas sensors working at different temperatures for formaldehyde,humidity, NH<Subscript>3</Subscript>, toluene and CO

ZnO and Sn-, Ga- and Mn-doped ZnO nanoparticles were prepared by a coprecipitation method, and characterized by scanning electron microscopy (SEM), energy dispersive spectra (EDS), X-ray diffraction (XRD) and Raman spectra. The gas sensing properties were studied using formaldehyde, relative humidity, NH₃, toluene and CO as the probes. The results show that all particles have wurtzite ZnO phase, though Sn–ZnO has a relatively smaller particle (and crystallite) size than the other three samples. Gas sensing property tests reveal that the temperature where the gas sensing maximum is gained (T _M) is changed by different dopants: Sn–ZnO and Mn–ZnO have relatively lower T _M (∼100°C lower) compared with that of pure ZnO, while Ga–ZnO has the same T _M as pure ZnO except in CO sensing. Thermoluminescence (TL) spectra were used to investigate the mechanism of T _M change. The peak positions of Ga–ZnO and ZnO are the same at 300–350°C, while that of Sn–ZnO shifts to 250–300°C, which might contribute to the same T _M of Ga–ZnO and pure ZnO and relatively lower T _M of Sn–ZnO. In the case of Mn–ZnO, the luminescence emission is evidently limited by its black color.     

Antibacterial evaluation of some Schiff bases derived from 2-acetylpyridine and their metal complexes

A series of Schiff bases derived from 2-acetylpyridne and their metal complexes were characterized by elemental analysis, NMR, FT-IR and UV-Vis spectral studies. The complexes were screened for anti-bacterial activity against Methicillin-resistant Staphylococcus aureus (MRSA), Acinetobacter baumanni (AC), Klebsiella pneumonie (KB) and Pseudomonas aeruginosa (PA) using the disc diffusion and micro broth dilution assays. Based on the overall results, the complexes showed the highest activities against MRSA while a weak antibacterial activity was observed against A. baumanii and P. aeruginosa.     

Electromagnetic scattering from two-layered rough interfaces with a PEC object: vertical polarization

Electromagnetic(EM) scattering from a stack of two rough interfaces separating a homogeneous medium with a perfectly electric conducting(PEC) object has been calculated through the method of moments for vertical polarization.Theoretical formulations of EM scattering from multi-layered rough interfaces with a PEC object have been derived in detail and the total fields and their normal derivatives on the rough interfaces are solved.The two-layered model is a special case.In this work,a Gaussian rough surface was applied to simulate the rough interface.A cylinder was located above,between or below the two-layered rough interfaces.Through numerical simulations,the validity of this work is demonstrated by comparing it with existing scattering models,which are special cases that include a PEC object located above/below a single-layered rough interface and two-layered rough interfaces without an object.Subsequently,the influences of characteristic parameters,such as the relative permittivity of the medium,as well as the average height between the two rough surfaces,on the bistatic scattering coefficient are discussed.     

Measurement of identified and inclusive photon second-harmonic parameter and implications for direct photon production in [FORMULA: SEE TEXT] Au+Au

The azimuthal distribution of identified pi0 and inclusive photons has been measured in [FORMULA: SEE TEXT] Au+Au collisions with the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The second-harmonic parameter (nu2) was measured to describe the observed anisotropy of the azimuthal distribution. The measured inclusive photon is consistent with the value expected for the photons from hadron decay and is also consistent with the lack of direct photon signal over the measured pT range 1-6 GeV/c. An attempt is made to extract nu2 of direct photons.     

非线性椭圆型复方程组的一类边值问题

本文讨论了一阶非线性椭圆型复方程组于平面多连通区域上的一类复合边值问题解的先验估计及可解性.     

A novel selenization technique for fabrication of superconducting FeSex thin film

A combinative method with reactive sputtering deposition and selenization technique was applied to prepare superconducting FeSe_x films on LaAlO₃ substrates successfully. The influence of selenizing temperature on film components was studied. FeSe_0.96 and FeSe films had similar and good performances in transport measurement but little difference in magnetic property. The critical onset temperature got to 11.2 K and T_c,0 got to 4 K approximately. X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy were used to analyze the ratio of constituents and morphology of several selenized films. FeSe_x film had a porous structure on surface and no well preferred orientation, which were confirmed to have little influence on superconducting properties.     

液滴撞击液膜过程的格子Boltzmann方法模拟

本文采用格子Boltzmann方法对液滴撞击液膜过程进行了研究, 主要考察了雷诺数(Re)、韦伯数(We)、相对液膜厚度 (h) 以及表面张力 (σ) 等物理参数对界面运动过程的影响. 首先, 随着Re数和We数的增加, 可以明显观察到液滴撞击液膜过程中形成的皇冠状水花以及卷吸现象; 当Re数较大时, 液体会发生飞溅, 由液体飞溅形成的小液滴则会继续下落, 并与液膜再次发生碰撞. 其次, 当相对液膜厚度较小时, 液滴撞击液膜并最终导致液膜断裂; 然而随着相对液膜厚度的增大, 尽管撞击过程溅起的液体会越来越多, 但是液膜并不会发生断裂. 再次, 随着表面张力的增大, 界面变形阻力增大, 撞击过程中产生的界面形变也逐渐减弱. 最后还发现皇冠(由液滴溅起形成)半径r 随时间满足r/(2R) ≈ α√Ut/(2R), 这一结果与已有结论是一致的.