室内声场模拟中的界面声散射

室内声场模拟中引入扩散反射对提高模拟的准确性具有重要意义,但采用单值散射系数无法完整表示界面的扩散反射特性。受几何声学中扩散反射模拟方法的限制,界面有效散射系数存在不确定性。通过改变一个矩形房间中的吸声量、吸声布置方式及表面几何复杂程度等声场条件,对混响时间的模拟值与实测值进行比较,分析了由界面散射系数不确定性产生的模拟偏差与房间内声场扩散的关系。     

随机起伏界面声散射的实验与理论研究

进行了二维粗糙海面声波散射特性的水池实验,测量了不同入射角、散射角以及方位角条件下所对应的散射强度。实验通过不同位置风扇对水面的吹拂获得粗糙水面,分别对水平面上互相垂直的两个方向上的水面波高变化进行了测量,利用周期图法估计出这两个方向上的空间功率谱,验证了实验中的粗糙水面是各向同性的。利用改进的空间域处理技术去除了总声波信号中的直达波和其他固定位置散射体的散射信号,获得了粗糙水面的声波散射信号。利用小斜率近似方法计算了二维粗糙海面的声散射特性。实验与模拟计算结果比较,证实了计算二维粗糙海面声波散射特性的小斜率近似方法的有效性与准确性,相互印证了实验与理论。     

小斜率近似方法分析粗糙界面声散射问题

利用小斜率近似方法计算了起伏海面的声散射特性,得到了具有高斯分布粗糙海面的平均反射系数（即镜反射系数）计算公式,并与微扰法和Kirchhoff近似做了比较,结果表明小斜率近似是一种非常有效的分析起伏表面散射特性的近似方法。最后讨论了海面镜反射系数随海面的不平整度（波浪的均方根高度）、声波频率和声波入射方向的变化关系,得出了只有在声波波长和起伏波浪高度可比拟时,才有明显的镜反射的结论。这为分析浅海目标声散射特性时,选择是否需要考虑海面（海底）所引起的多途效应提供了理论依据。     

粗糙面上声散射的算子展开法研究

采用算子展开法研究了粗糙面的声散射问题。首先,给出了算子展开法级数展开的理论推导过程,并对q^因子进行了修改,使其得以用FFT实现。然后,给出了在修改后q^因子作用下前三阶的算子展开式。最后,将计算结果和速度与积分方程法、小斜率近似法进行了比较,比较发现算子展开法计算精度很高,对q^因子修改后,计算速度也得到了有效的改善。因此,算子展开法是一种处理粗糙面声散射问题的较好方法。     

厅堂中早期反射声能分布的测量

厅堂中的早期反射声能是决定厅堂音质的重要因素,ＥＤＴ、Ｃ５０、Ｃ６０、响度等音质参量都是由早期反射声能决定的。为探讨早期反射声能在厅堂中的分布及随距离的衰减规律,本文对同济大学的大礼堂（容积为２７０００ｍ２）进行了实测。声源为脉冲电火花发声器,传声器接收到声信号后经１／３倍频程滤波器,采样后得到接收点的脉冲响应,再经积分获得早期反射声能累积值ＲＥＣ（ｔ）,其中ｔ是对脉冲响应的积分时间。实验中测量了礼堂中２０个位置上的ＲＥＣ（ｔ）分布及其随接收点到声源距离的衰减率,同时测量了稳态声场声压级在厅内的…     

反射声对室内声景主观评价的影响初探

梳理了近年来地面反射声和室内声景观的研究情况,结合实验心理学以及室内声景观主观评价等研究框架,通过三个基于反射声感知的声学可听化实验,确定了在四间房间内人耳对有无地面反射声参与的三种声音信号的绝对感觉阈。结果表明语音信号高于本底噪声10 dB(A)即可被察觉,而水流声及音乐声高于本底噪声17 dB(A)才能够被明显察觉,最后结合实验结果对地面反射声的处理给出了建议。     

界面声散射数值模拟中的突变边界处理及有效性分析

利用在边界突变点处设置两个速度值的方法,解决界面声散射数值模拟中的阻抗突变边界的积分奇异性问题。同时把界面对入射声音的响应局限在声散射方面,仅关心散射声场的声压方向性分布而不考虑吸声效果,可以通过边界元法得到较准确的界面散射极响应图。精确理论解和实验分析表明该处理方法在界面散射的预测中是有效的。     

热声热机系统的测量与实验研究

对热声热机驱动耗散性负载的性能进行了实验研究和分析,对热声热机系统起振温度和谐振频率进行了测量和标定。得出导致热声发动机工作在二附谐振频率模态下的影响因素。测量和分析了气体充气压力、频率以及谐振管长度对系统驱动制冷机,产生了25℃的温差。     

活动靶标模拟声特性与反射声特性的差异及其影响

本文从理论上分析计算了典型的大口径活动靶标的目标散射回波机理和目标强度值,探讨了其对模拟声学特性的影响.研究结论认为,靶标航行体产生的目标强度具有强烈的方位"收敛"特性,除正横方位外散射回波都很弱,几乎淹没在混响背景里,攻击武器在远、中场时多处于侧尾追方位,靶标的弱散射回波不会对其产生影响,在近场,则由于攻击武器已由探测跟踪阶段转为攻击过靶阶段,靶标自身的散射回波影响也变的没有意义.     

Biosensor Measurements on Diffusion Coefficients of Physiologically Active Substances in Brain Tissue

Three methods are proposed for determining the diffusion coefficient D for several substances in vivo. The results are discussed along with the prospects for using chemical biosensors for examining the variations in D produced by external physical factors (vortex magnetic fields).     

动态光散射在颗粒检测中的应用

动态光散射是常用的一种用于检测颗粒粒径分布的方法。本文详细介绍了该技术在测量颗粒粒径、介电常数、传导率、旋转扩散系数、环境的影响以及结晶条件等方面的研究进展,并对该技术的发展及应用做出了进一步的讨论,提出了动态光散射方法存在的问题,以及克服动态光散射的背景噪声、提高光源质量以及建立更智能化的算法等研究方向。     

Determination of Binary Diffusion Coefficients of Gases Using Holographic Interferometry in a Loschmidt Cell

A measuring system for the determination of binary diffusion coefficients of gases has been developed. The lower and upper half cells of the Loschmidt diffusion cell are fixed, one upon the other, contrary to the usual shearing cells. A sliding component between the half cells is moved to connect them and to start the diffusion. The concentration changes due to diffusion are determined by the optical method of real-time holographic interferometry. In this way the concentration is obtained as a function of time and location resulting from the analysis of the interference pattern. The data are evaluated by using the integrated diffusion equation for the closed-tube technique. First, measurements on the system argon-propane have been successfully performed at 1 bar and at room temperature. The results show an uncertainty of 1 per cent and are in good agreement with data by Wakeham and Slater (1974). Furthermore, refractive index measurements on the pure gases, argon and propane, as a function of gas density have been performed and evaluated to derive values of the first refractivity virial coefficient.     

Spectral radiative properties of a living human body

Spectral radiative properties of the human body were studied experimentally in the region from the ultraviolet to the far-infrared to know the thermal response of the human body exposed to solar radiation and infrared radiation. The measuring equipment for reflectance and transmittance of a semitransparent scattering medium was developed and measurement on a living human skin was performed in vivo. The measured parts are forearm, cheek, dorsum hand, hip, and hair. The values obtained by the present study are much different from those of previous in vitro measurements. Fairly large values for hemispherical reflectances are observed in the visible and near-infrared regions but very small values for hemispherical reflectances are observed in the infrared region, below 0.05. By applying the four-flux treatment of radiative transfer, the absorption coefficient and scattering coefficient in the human skin are determined. The scattering coefficient is large in the visible region but negligible in the infrared region. The absorption coefficient is very close to that of water and large in the infrared region.     

高浓度超细颗粒系后向散射研究

为了研究高浓度状态下颗粒系后向散射规律 ,基于Beer-Lambert定律、Mie散射理论及复散射的相关理论建立了消光 -散射衰减模型 ,并针对具体算例进行了数值计算 ,给出计算结果。     

扩散泵的世纪回顾与发展

本文叙述了盖得的发明专利,从初期的汞扩散泵到分馏油扩散泵的演变过程.讨论了泵体结构、喷咀型式、泵油性能和几个关键技术问题.现代油扩散泵的何氏系数达0.65以上,返油率达10-5 mg/cm2·min,1 kW功率抽气量可达200 Pa L/s.最后对泵的性能、结构和应用前景作了展望.     

The Permeability and Solubility of Hydrogen in a Lead-Bismuth Melt of Eutectic Composition

The permeability of hydrogen through a lead-bismuth melt of eutectic composition is investigated, as well as the solubility of hydrogen in this melt in the ranges of temperature from 425 to 810°C and of hydrogen pressure from 1 to 3 kg/cm². The experimental setup and procedure are described. The calculated value of the coefficient of hydrogen diffusion in the melt is used to estimate the solubility of hydrogen in the melt.