A review of commonly used analytical and empirical formulae for predicting sound diffracted by a thin screen

This paper reviews some useful analytical and empirical formulae that are used for the calculation of sound diffracted by a barrier. A brief historic overview of the study of spherical waves diffracted by a rigid half plane is presented also. The physical principles of sound diffraction by a thin plane are explained. The mathematical expressions are cast in a convenient form for ease of numerical implementation. Accurate analytical solutions are expressed in terms of standard mathematical functions that can be computed readily. Among the approximate solutions quoted, quite a few empirical formulations are adequate for most engineering purposes. The information presented in this paper should also be helpful for those who are interested in the study of sound diffracted by a barrier in a room or in a long industrial space.     

Influence of vehicle noise emission directivity on sound level distribution in a canyon street. Part II: Experimental verification

In the paper, predictions of relative sound level distribution on building façades in city-centres obtained by using the simulation PROP11 program are compared with measurements. The simulation involves the geometry of surrounding buildings, road geometry (number of lanes and their positions) and traffic structure (vehicle flow rates and their average speeds). The agreement between measurement and simulation results is tested for different directivity characteristics of an equivalent point source representing the vehicles.     

Adsorption-transport modeling of anions through PVD membrane in the presence of the screen phenomenon

A mathematical model for transport and adsorption of chloride and sulphate ions through PVD membrane is presented at two pressures; 8 and 15 bar and 40 °C. The PVD membrane is negatively charged. Saturated brine containing NaCl with the concentration higher than 97% was challenged with the membrane as the feed. Other available ions in the solution were Fe²⁺, Ca²⁺, Mg²⁺ and SO₄²⁻. The screen effect of the cations on the membrane surface charge facilitates the passage of the anions through the membrane without any noticeable electrostatic repulsion. Hermia blocking laws combined with experimental results indicate that the internal pore closure of the membrane by anions and cake deposition on the membrane surface by cations are the separation mechanisms. The transmission of anions through the membrane may be predicted with a simple transport equation (convection and diffusion) combined with an adsorption isotherm. Both Langmuir and Freundlich adsorption isotherms were employed due to the simplicity and validity in liquid systems. The isotherm’s parameters were determined at 10 bar during the unsteady state filtration. Under this condition, the permeate flux and concentration varied sharply due to adsorption. Finally, the model was compared with the experimental rejection data. An acceptable agreement around 95% at 8 bar and 92% at 15 bar was observed between theoretical model and experimental data.     

高蒸发率下筛网通道式液体获取装置的金属筛网毛细性能研究

筛网通道式液体获取装置是低温推进剂在轨管理的关键技术之一,其中具有高蒸发速率的低温推进剂在金属筛网的毛细性能是影响筛网通道式液体获取装置工作性能的主要因素.以筛网通道式液体获取装置的常用金属筛网——荷兰斜纹编织网为研究对象,以乙醇和丙酮为工质,采用红外热像仪实验研究了在高蒸发率下易挥发工质在荷兰斜纹编织网经丝方向的毛细...     

墨粉灌装车间噪声测试分析与控制

本文应用峰值频率声压级对比方法并结合相干分析技术对某墨粉灌装车间主噪声源进行了诊断，分析了声源特性，在此基础上提出了经济合理的治理措施，实施后取得了满意的结果，车间噪声达到了相应的国家标准。     

室内超大面积探测区域测速光幕设计

针对大横截面室内靶道弹丸测速需求,提出了一种大面积探测区域测速光幕构建方法。采用90°探测视场的广角天幕靶作为接收装置和多段等长的排布成L形状的LED线阵列作为光源,各段LED线阵列光源均朝向广角天幕靶扇形视场中心,完全填充广角天幕靶的视场,在空域形成10m×10m的探测区域。给出了L形光源的详细设计,采用气枪弹进行了靶面内灵敏度验证试验和系统实弹射击试验。试验结果表明,所提出的方法是有效可行的,可满足10m×10m横截面室内靶道的测速需要。     

Effect of surface morphology on screen printed solar cells

Surface texturing is well known as one of the major paths to improving the efficiency of silicon solar cells by increasing the short circuit current through effective photon trapping. However, the effects of the pyramids created after surface texturing on the other properties remain obscure. In this work, we studied the effect of the surface morphologies on the formation of both the emitter layer and metal electrode using the screen printing method, which is a cost-effective method of fabricating silicon solar cells. Various textured surfaces, such as with large, small, sharp or smooth pyramids, were investigated in comparison with a flat surface. The contact resistance was measured from a TLM patterned cell by I–V measurement under dark conditions and SEM, TEM and UV–vis spectrophotometer were used to evaluate the surfaces.     

Utilizing noise mapping for environmental impact assessment in a downtown redevelopment area of Seoul, Korea

In environmental impact assessment, noise impact assessment usually consists of three stages: surveying the existing noise levels, predicting noise levels induced by future construction works and predicting noise levels after the completion of a project. The distance-attenuation relation of a point source, which has been used in Korea to predict the noise level due to its simplicity, does not consider complex acoustic phenomena like multi-reflections, diffractions and absorptions that arise due to the complex topographic configurations of surrounding buildings and terrains. To consider such physical and acoustical complexities, a noise mapping tool is adopted to produce a series of three noise maps: for the present environment, for the planned construction works and for the future. For meaningful noise mapping, both acoustically- and topographically-good information is essential. Standard sound power levels and directivities of various construction equipments are required. Exact scheduling of construction processes and equipment locations must be provided. When the legal limit is exceeded, mitigation measures are applied to satisfy these limits and a subsequent noise map is constructed to verify the effect of these measures. Foreign prediction models are adopted for the situations in Korea if a certain validation condition is satisfied.     

Estimation and application of spatially variable noise fields in diffusion tensor imaging

Optimal interpretation of magnetic resonance image content often requires an estimate of the underlying image noise, which is typically realized as a spatially invariant estimate of the noise distribution. This is not an ideal practice in diffusion tensor imaging because the noise distribution is usually spatially varying due to the use of fast imaging and noise suppression techniques. A new estimation approach for spatially varying noise fields (NFs) is proposed in this article. The approach is based on a noise invariance property in scenarios in which more than one image, each with potentially different signal levels, is acquired on each slice, as in diffusion-weighted MRI. This technique leads to improved NF estimates in simulations, phantom experiments and in vivo studies when compared to traditional NF estimators that use regional variability or background intensity histograms. The proposed method reduces the NF estimation error by a factor of 100 in simulations, shows a strong linear correlation (R²=0.99) between theoretical and estimated noise changes in phantoms and demonstrates consistent (<5% variability) NF estimates in vivo. The advantages of spatially varying NF estimation are demonstrated for power analysis, outlier detection and tensor estimation.     

Are adverse impacts of neighbourhood noisy areas the flip side of quiet area benefits?

Soundscape researchers have studied how localized areas of noise and quiet within a neighbourhood have an effect upon residential noise annoyance. In this paper, noisy and quiet areas are studied simultaneously using data from three surveys and a noise mapping effort for Oslo. Results indicate that noisy neighbourhoods have the potential to increase residential noise annoyance primarily for apartments exposed to low residential noise levels whereas quiet neighbourhood areas have the potential to reduce noise annoyance the most at intermediate and high residential noise levels. Adverse neighbourhood soundscapes are shown to increase residential noise annoyance also after adjusting for possible absence of quiet areas. Whereas Swedish research results document benefits of living in an apartment having access to a quiet facade, no beneficial impacts of quiet neighbourhood areas were found. Results indicate that adjustment factors for apartment having quiet façades and/or adverse soundscapes respectively, can be independently applied.     

耦合生物细胞体系中噪声诱导钙信号的传递和增强

研究了耦合细胞体系中钙振荡的动力学行为,发现体系的一端受到噪声扰动时,能够产生噪声诱导的钙振荡信号,这种信号在沿着耦合体系有效传递的同时,信号本身也能显著增强,并且在体系的另一端能够得到一个规则的信号.分别讨论了耦合强度、噪声强度和耦合方式对信号传递的影响,发现存在合适的耦合强度和噪声强度更有利于钙信号的传递和增强,与以往不同的是,还分别从信号和噪声背景两方面给出了定性的解释;同时发现单向耦合比双向耦合更有利于信号的传递和增强.     

Research on photoelectronics properties of array emitting diode and its light energy distribution in detection screen

According to the principle of multi-screen intersection target measure flying projectile parameters, the photoelectronics properties of array emitting diode that form detection screen in multi-screen intersection target and its light energy distributing were studied. The form of detection screen using array emitting diode and the measure principle of four screens intersection were analyzed. The properties of emitting diode were analyzed based on its compound emitting mechanism and P–N ties internal current carrier. The light energy superposition principle was applied to set up light energy distributing model and give out its arithmetic. Through calculation and analysis, the light energy distributing is asymmetric when being close to diode position and the output variation range of light energy is large relatively. When test position is far from diode, the light energy distributing is uniformity, but the energy is relatively feebleness in edge of screen. Detection screen light energy distribution is trapezoidal in whole screen. The variety of emitting diode luminous flux is very distinct when projectile close to pointing light source, the output signal in received detective circuit is very high which is propitious to improve acquirement rate.     

金属烧结丝网在内场消声中的应用

利用试验手段研究暂冲式风洞稳定段内安装不同规格烧结金属丝网对风洞上游控制阀后气流噪声和湍流度抑制作用。试验结果表明:多层金属烧结丝网可在全频段内大幅度降低上游气流的噪声,最大可达21 dB;消声量与金属烧结丝网无量纲的压力损失系数成正比,压力降与金属烧结丝网层数呈现出非线性叠加的结果。另外发现烧结金属烧结丝网对气流速度脉动亦具有突出的抑制效果。例如,试验段马赫数Ma=1.5时,120目26层+160目26层组合烧结金属丝网出口气流速压脉动幅值减小为入口来流的18%,湍流度由11.7%降至3%。因此金属烧结丝网适合于暂冲式风洞的内场降噪。     

A study of noise reduction by acoustic shock waves

I.IntroductionAcousticshockwavcs(ASW)isanimportantphcnomcnoninnonlinearacoustics.Experimentalrcsultshavcshownthatwhenanaircraftcngincinletopcratesneartheson-iccondition,vcrystrongnoisegcncratedbythcfanscanbcreduccdgreat1yowingtothcformationofASWatthcthroatofthcin1etll].ASWisadiscontinuityofacousticvaria-bles,whichisdifTcrcntfromthcshockwavesoccurringinhighspcedsteadyflowinducts.Theformer'sintensityismuch1cssthanthelattcr's.Furthcrmorc,thepositionandintensityofASWisalwayschangedwithtime.l…     

High temperature oxidation behavior of interconnect coated with LSCF and LSM for solid oxide fuel cell by screen printing

The current study examined the effect of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) and La_0.7Sr_0.3MnO₃ (LSM) coatings on the electrical properties and oxidation resistance of Crofer22 APU at 800 °C hot air. LSCF and LSM were coated on Crofer22 APU by screen printing and sintered over temperatures ranging from 1000 to 1100 °C in N₂. The coated alloy was first checked for compositions, morphology and interface conditions and then treated in a simulated oxidizing environment at 800 °C for 200 h. After measuring the long-term electrical resistance, the area specific resistance (ASR) at 800 °C for the alloy coated with LSCF was less than its counterpart coated with LSM. This work used LSCF coating as a metallic interconnect to reduce working temperature for the solid oxide fuel cell.     

Procedures for determining the acoustic efficiency of edge-modified noise barriers

This paper describes the noise shielding efficiency of barriers with an acoustic device mounted on their top edge for reducing sound diffraction. Diffraction behind the edge-modified barrier is investigated by scale model experiments in which the positions of a source and a receiver are aligned along a circular arc around the barrier top. The result indicates that the acoustic efficiency of the edge device is a function of the angles of the source and receiver and independent of their radii. Based on this finding, a novel procedure for determining the efficiency of manufactured edge devices is established. This procedure is very beneficial for estimating the edge device efficiency by eliminating ground and meteorological effects. The measured efficiency of the device will be quite useful for the prediction of noise propagation behind the edge-modified barriers.     

高层住宅阳台降噪量的计算分析

高层住宅中的阳台不仅具有居住及建筑上的功能,对道路交通噪声也有衰减作用。本文通过建立噪声传播模型计算高层住宅阳台的插入损失,并探讨了影响阳台降噪量的一些因素。同时对阳台内部吸声处理的效果进行了理论预测。     

螺旋线行波管电子效率改善的数值模拟

运用全电磁2.5维粒子模拟软件MAGIC和3维高频结构仿真软件HFSS,模拟仿真了正-负双跳变慢波结构对螺旋线行波管电子效率的改善,从慢波系统高频参量、非同步参量、增益参量和电子注相位等角度进行了讨论。设计并加工了一支采用双跳变结构的螺旋线行波管,实测结果表明：采用双跳变结构后可将电子效率从19%提高到29%;模拟仿真方法得到的平均相对误差为5%左右。     

An empirical model for the noise propagation in open cast mines - A case study

Data obtained from 312 measurement stations of sound propagation in panel 48 of the Tuncbilek open cast mine, Western Lignite Corporation, Turkey have been used to create an empirical model for such propagation. As well as the noise level recorded at these stations, atmospheric conditions were recorded also by the meteorological station located at the same panel. A total of 95,000 noise values were recorded at these stations. In addition the distances of the measurement stations to the effective source of noise and to the working slope, the meteorological effects and the number of noise sources were defined for each of 312 measurement stations. Using these data, the proposed model was tested against the noise measurements.