A note on the prediction method of reverberation absorption coefficient of double layer micro-perforated membrane

The absorption performance of micro-perforated absorber (MPA) has been usually estimated by equivalent circuit (EC), however, it has been noted that the predicted absorption coefficient by EC does not agree completely with the experiment in some frequency range. Hence impedance transfer method (ITM) is adopted to predict the reverberation absorption coefficient of a double layer micro-perforated membrane (MPM) structure. Experimental studies show that the prediction of ITM is better than that of EC.     

使用脉冲声和矢量传声器的现场测量吸声系数

使用不同声源利用矢量传声器对毛毡材料进行现场吸声系数测试,研究了不同背景下不同声源的抗噪能力。矢量传声器可以同时测得声压和质点振速信号,进而可计算得到阻抗,利用自由空间和材料表面的阻抗可计算得到材料的吸声系数。在此次实验中,使用不同声源分别在无干扰和有一白噪声干扰源的两种情况下进行测试。结果表明,使用对数扫频脉冲和巴特沃斯脉冲测试所得的吸声系数曲线更平滑,说明脉冲声可以有效降低环境反射的影响,在高噪声背景下使用对数扫频脉冲测试所得的结果基本没有受到背景噪声的影响,说明对数扫频脉冲的抗噪能力更强。因此,使用对数扫频脉冲作为声源进行测试可有效减弱环境反射和背景噪声的影响。     

穿孔率和穿孔直径耦合下微穿孔板吸声体整体吸声性能

微穿孔板几何参数的耦合性及其对整体吸声性能的影响,对于设计微穿孔板吸声体和优化其工作性能具有指导作用。根据微穿孔板吸声体基本理论,研究了穿孔率和穿孔直径双参数耦合作用下微穿孔板吸声体的整体吸声性能。穿孔率和穿孔直径之间的耦合性与其本身取值密切相关,而与板厚和板后腔深无明显关系;在穿孔率-穿孔直径参数域上,吸声体存在吸声系数为1.0的吸收峰,整体吸声性能随穿孔率或穿孔直径从小到大变化,呈现出先增强后减弱的变化趋势。该结论能够准确解释微穿孔板受粉尘污染后吸声性能的变化规律和演变路径。论文的工作为设计微穿孔板吸声体提供了一种新的理论依据和实施方法。     

The relationship between absorption coefficient and temperature and their effect on the atmospheric cooling rate

Several approaches are considered to determine the temperature effect on the absorption coefficient within a correlated k-distribution method. Taking in the 610- region for example, the absorption coefficients and atmospheric cooling rates calculated using these approaches are compared with line-by-line integration. It is emphasized in this paper by numerical calculation that the effect of pressure on absorption coefficient is related to temperature and vise versa; the larger the pressure, the larger the effect of temperature on absorption coefficient. Results show that the temperature effect must be considered in radiative calculations although its effect on the absorption coefficient is much smaller than that of pressure.     

微穿孔板几何参数估算及其对吸声性能的影响

不规则孔微穿孔板几何参数无法直接获知,造成吸声性能计算困难,故提出一种微穿孔板几何参数估算方法。将不规则孔等效处理为圆孔,利用马氏理论关于圆孔微穿孔板的基本理论,建立了微穿孔板几何参数估算模型;将参数估算结果用于吸声性能预测,理论计算与实验结果吻合。根据微穿孔板几何参数对高吸声性能区域的影响,探讨了马氏理论适用极限与微穿孔板几何参数的关系,以及微穿孔板受粉尘污染后吸声性能演变规律。将微穿孔板参数点取在面积较大的高吸声性能区域中间部位,可获得较大的马氏理论适用极限;微穿孔板参数点位于高吸声性能区域右上部位时,一定程度的粉尘污染不会降低吸声性能.     

A note on the relationship between the sound absorption by microperforated panels and panel/membrane-type absorbers

The sound absorption mechanism of microperforated panel (MPP) absorbers and panel/membrane-type absorbers is both based on a certain resonance system and utilising its resonance effect. However, the relationship between the absorption mechanisms of MPPs and panel/membrane-type absorbers has not been discussed: it is not clarified whether they can occur simultaneously, or how they interfere each other. On the other hand, in a previous study there is an attempt to cause both absorption mechanisms simultaneously. In this paper, using an electro-acoustical equivalent circuit model, their sound absorption mechanisms and their relationship are discussed. In this study, three cases are considered: (1) the case in which only the mass reactance of the MPP is considered, (2) the case in which the losses of the panel is considered, and (3) the case in which the sound absorption of the back wall surface is considered. The results suggest that the microperforated panel absorption, which is Helmhotz-type resonance, and the panel/membrane-type absorption can be regarded as phenomena of the same kind which can be smoothly transformed into each other by changing a parameter, and can be consistently modelled and comprehensively discussed.     

基于最小二乘法的声速测定实验数据处理及分析

用振幅极大值法比振幅极小值法测声速的误差小和声波在传播过程中声压按指数函数关系衰减。     

Multi-resolution error analysis of predicted absorption coefficients. Method and application to the infrared spectrum of methane at high temperature

A general method for the estimation of the confidence interval of molecular absorption coefficients is presented. Statistical numerical experiments are implemented to quantify the propagation of errors from line parameters to absorption coefficients as a function of the resolution. The method uses line parameter predictions (position and intensity) with estimated uncertainties derived from global polyad models. This work is especially intended to provide expert information for applications requiring theoretical predictions for which the present state of the art of line by line high-resolution modeling is not accurate enough to meet the desired precision. As an illustration, it is applied to predict the absorption coefficient of methane at high temperature involving simultaneously well known lower energy levels (cold bands) and higher energy levels with much lower precisions (hot bands). Potential extensions are discussed in the context of atmospheric remote sensing of astrophysical objects.     

Effects of methyl red acidity and UV illumination on absorption coefficient of MR/PVA thin films

The absorption coefficient spectra of poly(vinyl alcohol), PVA, mixed with methyl red (MR) thin films on glass substrates, prepared by the spin coating method has been investigated using scanning electron microscopy (SEM) and spectroscopic ellipsometry. SEM imaging indicates that the surface of the MR/PVA film is smooth, uniform, and no crack could be observed. Spectroscopic ellipsometry measurements of PVA and MR/PMMA thin films were carried out at three angles of incidence, over the wavelength range 400-800 nm. Optical models were used to obtain the absorption coefficients for the prepared samples. These models include Cauchy formula for the glass substrate and PVA film, Lorentz model with three oscillators for MR layer, and a Bruggeman effective medium approximation for MR/PVA films. Absorption coefficients were found to be in the range 5×10³−5×10⁴ cm⁻¹ with a maximum being at about 475 nm. Changing the absorption coefficient as a function of increasing the pH of MR causes a shift of the absorption band toward higher wavelengths. Our results show that the absorption coefficient of the film decreases upon increasing the UV illumination time.     

Effect of interdiffusion on band structure and intersubband absorption coefficient of GaAs/GaAlAs double quantum well

The influence of Ga and Al atoms interdiffusion on the band structure and absorption coefficient of coupled double quantum wells are investigated on the basis of a potential composed of four modified Wood–Saxon potentials. Wave functions of the real potential are expressed as a superposition of the stationary state wave functions of the “basal” potential. It is shown that interdiffusion leads to the smearing of the rectangular profile of the potential and to the disappearance of the barrier between the wells, as a result of which, the degradation of doublet character of the electron energetic spectrum is observed. It is also shown that interdiffusion leads to the significant change in oscillator strength and in the enhancement of the thermal stability of the absorption spectrum of the considered heterostructure.     

Low frequency in situ metrology of absorption and dispersion of sound absorbing porous materials based on high power ultrasonic non-linearly demodulated waves

The present work is related to acoustic in situ free-field measurements of sound absorption in porous materials, such as cellular plastic foams, glass-wool or recycled felt materials. The emphasis is given towards fine metrology of absorption in view of potential industrial applications. A powerful ultrasonic array working at 40 kHz is used. It enables to measure absorption acoustical data down to 100 Hz due to the exploitation of the non-linear ultrasonic demodulation phenomenon in air. Fine measurements of acoustic absorption are compared to numerical predictions based on the “equivalent-fluid” model (when the squeleton frame is motionless), and to some measurements performed on a Brüel and Kjaer impedance tube. Dispersion curves are also measured and compared to the numerical predictions for some automotive felt materials which are compressed at various ratios. Data obtained with a dedicated portable instrument are also discussed for the same type of materials and configurations.     

双传声器法测量斜入射吸声系数研究

本文从理论和实验两方面研究了双传声器法测量斜入射吸声系数时,双传声器间距,双传声器离材料表面距离,材料面积大小等因素对测量结果的影响。     

Experimental measurement of the electrical conductivity of pyroxenite at high temperature and high pressure under different oxygen fugacities

Electrical conductivities of pyroxenite were measured between frequencies of 10^?1 and 10⁶ Hz in a multi-anvil pressure apparatus using different solid buffers (Ni+NiO, Fe+Fe₃O₄, Fe+FeO and Mo+MoO₂) to stabilize the partial pressure of oxygen. The temperature ranged from 1073 to 1423 K (800 to 1200 °C) and the pressure from 1.0 to 4.0 GPa. We observe that: (1) the electrical conductivity (σ) of pyroxenite depends on frequency; (2) σ tends to increase with rising temperature (T), and Log σ and 1/T obey a linear Arrhenius relationship; (3) under control of the buffer Fe+Fe₃O₄, σ tends to decrease with rising pressure, nevertheless the activation enthalpy tends to increase. For the first time we have obtained values for the activation energy and activation bulk volume of the main charge carriers, which are (1.60±0.07) eV and (0.05±0.03) cm³/mol, respectively; (4) for a given pressure and temperature, σ tends to rise with increased oxygen fugacity, whereas the activation enthalpy and preexponential factor tend to decrease; and (5) the behaviour of the electrical conductivity at high temperature and high pressure can be reasonably interpreted by assuming that small polarons provide the dominant conduction mechanism in the pyroxenite samples.     

弯管对末端带弹性障板充液管路辐射声能量的影响

基于声固耦合有限元方法建立了末端带弹性障板的充液管路数值模型,重点分析了不同激励下弯管对管口辐射声能量的影响。结果表明:弯管引入的高阶周向模式耦合使结构振动和流体声传播都发生明显改变,以致系统辐射声能量及主要能量贡献源也发生转移,并随激励方式和频率而不同。对本文管路模型,平面波激励下弯管系统在低频的结构辐射声能量明显增加,在高频段呈流体声与结构声交替主导的特点。径向力激励下直管系统的总声能量几乎全部来自于弹性障板辐射结构声,而弯管的声固耦合使得管口流体声功率显著增加。在轴向力激励下弯管耦合使系统总辐射声功率显著下降的同时管出口的流体声功率反而增加。     

Evaluation of the effect of high pressure carbon dioxide-pasteurized food on animal health

ABSTRACT

High pressure-carbon dioxide processing (HPCDP) is used as a non-thermal technology for food pasteurization to produce newer flavors for bread. However, there is no evidence that this process does not produce undesirable toxic materials. To confirm the safety of high pressure carbon dioxide-processed food, we fed high pressure carbon dioxide-processed bread to mice and evaluated their health by monitoring body weight, stress biomarkers, and gut microbiota. There was no significant difference in the body weight of normal and HPCDP bread-fed mice. Similarly, no significant difference in expression of genes important for maintaining the health of the mice was found. Although the mice’s gut microbiota showed a significant difference between the control and the two bread-fed groups, there was no significant difference between the HPCDP and the normal bread-fed groups. Therefore, we found no conclusive evidence to suggest that the processed bread contained toxic materials in comparison to the unprocessed bread.     

霜形成对翅片管换热器空气侧表面传热系数影响的实验研究

在空冷系统中,换热器空气侧的表面结霜问题是影响其应用和发展的主要问题。通过对结霜条件下翅片管换热器空气侧换热性能的实验研究,得出了空气湿度、翅片间距、风速等参数变化对空气侧当量表面传热系数的影响;结果表明在一定的范围内,结霜前期h0值随结霜时间τ急剧下降,在结霜后期,这些参数对h0值的影响大为削弱。     

偶极相互作用存在的前提下Kerr介质对系统纠缠度的影响

在Milburn方程的支配下,研究了在偶极相互作用存在的前提下Kerr介质对两原子系统纠缠度的影响.通过concurrence计算了系统的纠缠度,讨论了concurrence随时间的振荡情况.结果表明,在偶极相互作用存在的前提下,通过适当选取Kerr介质的耦合常数χ,可以更好地提高系统的纠缠度,从而有效地抑制内禀消相干的作用.同时还发现在增大纠缠度方面,对于Ω的不同取值,倍数Λ的取值也不同. 关键词： Milburn理论 偶极相互作用 Kerr介质 concurrence     

Experimental investigation of the effect of ambient pressure on laser-induced bubble dynamics

The effect of ambient pressure on the dynamics of laser-induced bubbles was investigated by a fiber-optic diagnostic technique based on probe beam deflection (PBD). The experimental criterion for judging the maximum bubble radius is modified to the average value of the detecting distances at which the characteristic waveform signals appear. The ambient pressure affects the maximum radius and collapse of bubble strongly. The experimental results indicate that the maximum bubble radius and the collapse time both decrease nonlinearly while the ambient pressure increases linearly, and the decreasing velocities of them are smaller at a larger ambient pressure. The predicted value of collapse time has a good agreement with experiment at larger ambient pressure.     

激光烧蚀等离子体射流与固体靶相互作用实验研究

利用激光烧蚀等离子体射流可以获得数km/s 甚至上千km/s 的射流速度，远超目前绝大多数设备所能提供的模拟速度，并且覆盖了极大的温度与密度范围，作为加载手段具有广阔的应用前景。通过实验方法，探索和发展激光烧蚀等离子体射流这一新型实验模拟手段，利用高功率激光烧蚀产生高温高压等离子体射流，实现超高速气体动力学实验室模拟的新途径。以此作为加载条件，研究超高速物体与气体相互作用的气体动力学特性。通过建立激光烧蚀等离子体射流与固体靶相互作用实验方法，可进一步研究等离子体射流的产生、发展以及高速物体气体动力学，为下一步开展天体物理、小行星形貌、超高速陨石与行星大气相互作用机制等相关研究奠定基础。