波叠加声场重构精度的影响因素分析

波叠加法是利用等效源的思想来求解声辐射问题的一种数值方法.其原理并没有确切地规定如何配置等效源.正由于这些不确切性的存在,当将它应用到声场重构时,有必要检验重构的准确性,分析影响重构精度的各种因素,目的是通过分析而获得一些提高重构精度的规律.通过理论分析和数值仿真,分析了各因素对重建准确性的影响.证明等效源必须配置在辐射体内部,而且最好能与辐射体表面共形;但测量面并不需要与辐射体表面共形,而且也不需要在近场测量;还发现,Tikhonov和TSVD正则化方法很适合与波叠加法结合用于声场重构.依据这些规律能更好地应用波叠加法进行声场重构,也将拓宽其应用范围. 关键词： 声场重构 波叠加法 误差影响因素 正则化方法     

基于波束形成和波叠加法的复合声全息技术

近场声全息是一种准确的噪声源识别技术.然而,由于存在测量要求严格、测点数多等缺点,一定程度上限制了它在工业现场的广泛应用.基于此,提出一种基于波束形成和波叠加法的复合声全息技术.首先利用传声器阵列获取声压场信息;再通过波束形成对声源进行定位;然后在这些声源位置附近配置等效源;最后应用波叠加法进行声场重构.该技术的优点是只需要少量传声器,在中、远距离测量,可以方便快速地实现声场重构.采用两个脉动球的声源模型进行了数值仿真,并在半消声室内采用音箱模拟噪声源进行了实验,都准确地重构了模型的外部声场.这表明,该技术可以准确地对辐射体进行声场重构,为其在工业现场中的应用奠定了基础.     

Elastic behavior of comb-like polymer chains

<正>Three-dimensional Monte Carlo simulations of comb-like polymer chains with various backbone lengths N_b,arm lengths N_a and arm densities m are carried out to study the elastic behavior of comb-like polymer chains.The radius of gyration,the shape factors and bond length in different cases during elastic process are calculated,and it is found that the comb-like polymer molecules with longer backbone or shorter arm are more close to linear chains.But the arm density m affects the chain conformation non-monotonously.Some thermodynamic properties are also studied.Average Helmholtz free energy and elastic force f all increase with elongation ratioλfor all chains.     

An Unusual Organometallic Supramolecule Composed of Chiral Dirhodium Units and Sulfato Bridging Ligands

A chiral supramolecular compound (H3O){[cis-Rh2((C6H5)2P(C6H4))2(SO4)- (DMF)]2(μ- OC2H5)}·6C2H5OH (1) has been synthesized and characterized by X-ray single-crystal analysis. Compound 1 crystallizes in monoclinic, space group C2/c with a = 26.752(3), b = 13.5868(16), c = 26.611(3) , β = 103.891(2)°, V = 9389.5(19) 3, Z = 4, C92H114N2O18P4Rh4, Mr = 2135.49, Dc = 1.511 g/cm3, F(000) = 4384 and μ(MoKα) = 0.870 mm-1. The final R = 0.0441 and wR = 0.1186 for 8283 observed reflections with I > 2σ(I) and R = 0.0567 and wR = 0.1290 for all data. The structure of the compound is unique. It contains two inherent chiral {cis-Rh2[(C6H5)2P(C6H4)]2}2+ units which are connected not only in the equatorial positions by two sulfato ligands, but also in two of their axial positions by a μ2 ethoxide anion. The remaining axial positions of Rh24+ units in 1 are occupied by the DMF molecules. The sulfato ligands act as μ4 tridentate bridges to connect the Rh24+ units. The Rh-Rh metal-metal bond distances are comparable to those in analogous dirhodium compounds.     

基于总体最小二乘算法的平稳声信号二阶盲分离方法

利用声源信号相互独立的已知条件,提出分离平稳声信号的总体最小二乘二阶盲分离算法,该算法在联合近似对角化相关函数矩阵的约束下估计分离矩阵,在同时考虑估计矩阵与观测信号误差的情况下给出修正模型,在修正模型总体误差最小时分离源信号。提出的算法具有无需选择非线性函数,不存在收敛到局部最小值与计算速度快的特点,分离的声源信号具有较小的失真。半消音室电机噪声分离实验验证了上述算法的有效性。     

BESⅢ RPC宇宙线测试系统

北京谱仪(BESⅢ)采用阻性板室(Resistive Plate Chambers)作为其muon探测器, 总使用面积达1200m². 为保证探测器的质量, 每一块阻性板室都要求通过宇宙线测试. 宇宙线测试系统使用3个流光管室作为其触发和寻迹系统, 其空间分辨可达2—3mm, 覆盖面积约4m², 测试系统可同时测量8块RPCs. 最后, 还报道了RPC的初次测试结果.     

Study of RPC gas composition using Daya Bay RPCs

This study uses Daya Bay RPCs operating in streamer mode to investigate gas mixtures of at least 50% argon, at most 6% isobutane, and with small amounts of SF6. Isobutane is reduced to 2% without degradation of performance, and SF6 reduces the noise rate and current, as well as the signal size. This study provides quantitative relationships between basic RPC operating parameters and various gas compositions.     

简易溶液法快速制备Cu2ZnSnS4纳米晶工艺研究

采用一种简易溶液法成功快速制备出低成本薄膜太阳能电池用Cu2ZnSnS4(CZTS)纳米晶.探讨合成温度和时间对CZTS纳米晶的结构、形貌、元素比例及光学特性的影响,实现可控的CZTS纳米晶合成.以上特性分别采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能量色散谱仪(EDX)、紫外-可见光谱仪(UV-vis)进行表征.结果表明:温度为250℃,时间为1h时可获得锌黄锡矿结构,团聚颗粒约为200～500 nm,化学计量比约为Cu∶ Zn∶ Sn∶S=2.17∶ 1∶1.23∶4.69,禁带宽度为1.5 eV的纳米晶,适合印刷法制备CZTS薄膜太阳能电池吸收层.     

溶胶-凝胶软模板法合成锂钛离子筛

以乙酸锂和钛酸丁酯为锂源和钛源,十六烷基三甲基溴化铵(CTAB)为软模板,采用溶胶-凝胶法,通过焙烧得到添加CTAB的锂钛化合物(Li₄Ti₅O₁₂),经过盐酸酸洗,制备出锂钛离子筛(H₄Ti₅O₁₂, HTO)。经过热重分析(TG-DTG)、X射线(XRD)、扫描电镜(SEM)、接触角及性能测试,考察了锂钛离子筛的晶相、形貌及时间对吸附容量的影响。对比CTAB的加入量,0.1 g的CTAB的离子筛前驱体杂质更少,晶相比较纯。HTO准二级动力学相关系数R²(0.997 24)大于准一级动力学相关系数R²(0.984 35),该吸附过程符合化学吸附。HTO在Li⁺溶液中24 h的吸附容量达到24.44 mg/g,经过8次吸附脱附后,吸附容量仍保持在23.68 mg/g,仅降低3.1%。因此,HTO有良好的循环吸附性能和稳定性,具有很广阔的市场前景。     

正常人与肝气郁结证人指甲中无机元素的比较分析

为探讨正常人与肝气郁结证指甲中特殊无机元素谱的差别,进而为人指甲的临床诊断及药效物质基础的探讨提供实验依据,采用扫描电子探针法测定了正常人与肝气郁结证患者指甲中炭化灰中无机元素。结果表明,正常人指甲炭化灰无机元素特征谱,有Ca和S两个呈正态分布趋势的特征性高峰;肝气郁结证指甲炭化无机元素特征谱只有一个Ca呈正态分布趋势的高峰。提示正常人与肝气郁结证具有不同的无机元素谱,肝气郁结证与体内无机元素发生代谢紊乱有关。