球声源作振动时两种声强计算方法的比较

采用间接测量技术计算声强时 ,是用两传声器各自测得的声压进行算术平均 ,用其平均值代替被测点声压 ,分析发现 :在高频区误差较大。应用两测点声压的几何平均值代替被测点的声压 ,并以作振动的球声源为例 ,对基于这两种计算声压的方法得到的声强误差进行比较 ,结果表明 :对作振动的球声源 ,几何平均声强计算误差曲线比算术平均声强计算误差曲线随波数或频率的变化具有更平缓的特性 ,随着Δr/ r的增大 ,曲线上误差为零的点向着波数或频率增大的方向移动 ,且这种移动算术平均声强比几何平均声强更敏感 ,所以由几何平均声压得到的声强更适合于更宽频率范围的测量。

舰艇球鼻首金属导流罩的结构声学设计

针对舰艇球鼻首为声呐服务的主要功能,为提高其透声性能,对新型金属双壳导流罩的声学设计进行研究。研究从金属单层板和双层板的透声基本原理开始,通过计算和试验分析双层平板的透声状况,并选取钛合金材料作为新型导流罩的建造材料,用理论公式和有限元建模两种方法计算整体球鼻首的透声状况。为保证真实性能,建造实体模型对其进行了试验验证。通过此项研究验证了这种双壳结构的金属球鼻首导流罩具有良好的透声性能,实验结果满足声呐的工作要求。

轮胎噪声仿真分析专用球声源的研制

介绍轮胎噪声重放专用球声源的研制。球声源系统硬件包括扬声器、功放电路和电脑。扬声器球壳上均匀分布小孔,球体外部声场的波阵面呈球面波,声波无指向性,球面上声源的辐射声级基本相同。本研制专用球声源结构简单,实用性强,性价比高,在轮胎噪声测试分析中具有较高的应用价值。

基于二级声辐射模型的地面声场高效预测方法

建立了可用于直升机运动状态下噪声传播特性分析的高效地面声场预测方法。该方法包括计算旋翼气动、噪声的自由尾迹方法和时域FW-H方程;计入大气、地面等环境因素的声传播模型及地面声场计算模型;为提高计算效率,在声源计算与噪声传播之间引入基于"紧致球声源"的二级声辐射模型;在此基础上,还提出了通过建立"特征参数声辐射球库"以实现直升机运动状态下噪声实时预测的方法。以AH-1旋翼为算例,通过与地面声场直接计算法对比,说明了方法的有效性及高效性;此外,文中还分析了大气、地面等环境因素对噪声传播以及地面声场特性的影响。

天津体育中心扩声系统设计

本文简要介绍天津体育中心总体扩声系统的构成，并分别对主馆和大练习馆在扩声系统设计中的特点作了详细的说明．对各自建筑结构特点，容易产生的声学缺陷所采取的措施进行了阐述．

拖拉机驾驶室内噪声源识别测试与分析

为研究驾驶室内噪声问题,采用球型阵列进行拖拉机驾驶室内噪声源定位测试,分析结果表明驾驶室内声源位置主要在门锁机构附近和操纵机构附近,且在车门玻璃处出现较大的反射噪声。运用声强探头对声源泄漏位置进行特定的声强测试,以此来分析驾驶室内噪声源产生的具体原因,为下一步改善拖拉机驾驶室内的声学环境打下基础。

The Application of the Nonsplitting Perfectly Matched Layer in Numerical Modeling of Wave Propagation in Poroelastic Media

The nonsplitting perfectly matched layer （NPML） absorbing boundary condition （ABC） was first provided by Wang and Tang （2003） for the finite-difference simulation of elastic wave propagation in solids. In this paper, the method is developed to extend the NPML to simulating elastic wave propagation in poroelastic media. Biot＇s equations are discretized and approximated to a staggered-grid by applying a fourth-order accurate central difference in space and a second-order accurate central difference in time. A cylindrical twolayer seismic model and a borehole model are chosen to validate the effectiveness of the NPML. The results show that the numerical solutions agree well with the solutions of the discrete wavenumber （DW） method.

Effects of Sonic Waves at Different Frequencies on Propagation of Chlorella pyrenoidosa

[Objective] The aim was to investigate the effects of sound wave on propagation of Chlorella pyrenoidosa to explore the optimal frequency for Chlorella pyrenoidosa.[Method] In the research,Chlorella pyrenoidosa was cultured for 7 d with sound waves at different frequencies and a control group was set to study effects of sound wave at different frequencies on growth of Chlorella pyrenoidosa.[Result] Growth of Chlorella pyrenoidosa was significantly improved by sound wave,especially for wave at 400 Hz.[Conclusion] Chlorella pyrenoidosa propagation would be promoted by sound wave at certain frequencies.

中国左翼电影运动六十年

齐天乐影评怀旧深情怀旧仍堪惜·休谓乍関休戚三十年间苔痕屜齿情趣依然清晰,黄昏探笔撰电影批评照彰心迹。

Average Fidelity of Teleportation in Quantum Noise Channel

The effects of amplitude damping in quantum noise channels on average fidelity of quantum teleportation are analyzed in Bloeh sphere representation for every stage of teleportation. When the quantum channels are varied from maximally entangled states to non-maximally entangled states, it is found that the effects of noise channels on the fidelity are nearly equivalent to each other for strong quantum noise. The degree of damage on the fidelity of non-maximally entangled channels is smaller than that of maximally entangled channels. The average fidelity of values larger than 2/3 may be one representation indirectly showing how much the unavoidable quantum noise is.

Large solitary retroperitoneal echinococcal cyst:A rare case report

Echinococcal disease remains a problem within some endemic areas. Echinococcal cysts usually involve the liver and lungs, but any other organ can potentially be involved. Extrahepatic localization is reported in 14%-19% of all cases of abdominal hydatid disease. We report the case of a large echinococcal cyst localized in the lower pelvis. A 28-year-old woman was admitted to a surgical ward with lower abdominal pain and discomfort lasting for a month. Ultrasonography and computed tomography scanning revealed a large retroperitoneal cystic mass (9 cm × 4 cm) in contact with the left ovary and left ureter. There were no cysts in any other location. Serological tests were positive for Echinococcus. The patient was operated on and the entire cyst was excised intact. Histopathological results confirmed the diagnosis of echinococcosis. Antihelminthics were administered postoperatively and the patient was discharged after 6 d, and is now being closely followed up. Total cystectomy when possible represents the treatment of choice for large extrahepatic echinococcal cysts.

The Application of the Acoustic Method to the Exploration of Urban Active Faults and a Comparison with the Artificial Earthquake, and Radar Methods

The depth of upper fault point is the key data for ascertaining the active age of a buried fault on a plain. The difference of depth obtained from same fault may be dozens to several hundred meters when using different geophysical methods. It can result in the absolutely opposite conclusions when judging fault activity. Because of a lack of an artificial earthquake source with wide band and high central frequency, many kinds of methods have to be used together. The higher the frequency of the artificial earthquake wave, electromagnetic wave and sonic wave, the higher the resolution. However the attenuation is also very fast and the exploration depth is very shallow. The reverse is also true. The frequency of artificial seismic waves is in the tens of Hz. Its exploration depth is big and the resolution is poor. The frequency of radar electromagnetic waves is about a million Hz, indicating that the resolving power is better, but the exploration depth is very shallow. However, the acoustic frequency is thousands of Hz, its resolving power is better than that of the artificial earthquake method and the exploration depth is larger than that of the radar method. So it is suitable for extra shallow exploration in the thick deposit strata of the Quaternary. The preliminary results detected using the high frequency acoustic method in extra shallow layers indicates that previous inferences about some fault activity in the eastern part of the North China plain may need to be greatly corrected.

Air flow patterns and noise analysis inside high speed angular contact ball bearings

The vortex formed around the rolling ball and the high pressure region formed around the ball-raceway contact zone are the principle factors that barricades the lubricant entering the bearing cavity, and further causes improper lubrication. The investigation of the air phase flow inside the bearing cavity is essential for the optimization of the oil-air two-phase lubrication method. With the revolutionary reference frame describing the bearing motion, a highly precise air phase flow model inside the angular contact ball bearing cavity was build up. Comprehensive factors such as bearing revolution, ball rotation, and cage structure were considered to investigate the influences on the air phase flow and heat transfer efficiency. The aerodynamic noise was also analyzed. The result shows that the ball spinning leads to the pressure rise and uneven pressure distribution. The air phase velocity, pressure and cage heat transfer efficiency increase as the revolving speed increases. The operating noise is largely due to the impact of the high speed external flow on the bearing. When the center of the oil-air outlet fixes near the inner ring, the aerodynamic noise is reduced. The position near the inner ring on the bigger axial side is the ideal position to fix the lubricating device for the angular contact ball bearing.

A Comparative Study of Chinese National Vocal Music and Bel Canto

Both Chinese national vocal music and bel canto have a very long history of development, but have their own different characteristics. However, the two different ways are mutually influenced and connected along with the social economic development and globalization. This requires the absorption of the excellent western singing styles on the basis of developing Chinese national vocal music, so as to promote a common development. In this paper, Chinese national vocal music and bel canto are studied and analyzed according to the historical origins, different characteristics, effects, etc.

Voices From the Periphery？ The Polyphony of Hip Hop and the Portuguese Community

The present work fits into a wider investigation that I have been carrying on for my project on the peculiarities of Portuguese hip hop. Through our reflections today we would like to identify some of the effects of the globalizing forces that have perturbed hip-hop culture and discuss if and how these have influenced its original purposes and messages, or the nature itself of the movement. We would also like to offer our perspective on the consequences of the entrance of hip-hop music in the international marketplace since this passage represents an important moment of its history and development and one of the strongest factors of change within this culture. We will take our examples from the Lusophone, and more specifically the Portuguese, hip bop movement, having a look at what it was in the past----or at its beginning--and at what it is today, in order to understand if we can still consider it a manifestation of peripheral voices.

Effect of prestressed ultrasonic peen forming parameters on bending curvature and spherical deformation of plate

The elastic prestressed ultrasonic peen forming(UPF)was adopted in order to solve problems of insufficient bending deformation and large spherical deformation of plate during free UPF.The theoretical analysis of prestressed UPF and the influence of elastic prebending moment on deformation were analyzed.Spherical deformation coefficient was defined to quantificationally describe the spherical deformation.Experiments were conducted to compare the differences between free UPF and prestressed UPF processes and the effects of processing parameters on bending curvature and spherical deformation coefficient were studied.The results show that peening trajectory in chordwise direction is beneficial to enlarging spanwise bending deformation and decreasing spherical deformation coefficient.Large prebending curvature is helpful to increase spanwise bending deformation and decrease chordwise deformation,thereby obviously decreasing spherical deformation coefficient.Large spanwise deformation can be obtained under large firing pin velocity,small plate thickness and small offset distance.Large firing pin velocity plays a positive role in decreasing spherical deformation,while plate thickness and offset distance have little effect on it.Above all,prebending curvature and peening trajectory are the most important factors during prestressed UPF process.This study provides guidance for parameters optimization of prestressed UPF for wing plate with large thickness.

Exploration and Rethinking： Children-Voice Studies in China

This paper reviews children-voice studies in China's Mainland over the past 10 years in the context of the globalisation era. The traditional grand narrative in the field of contemporary education research in China has been challenged by individual recounts and by concemsregarding the situation in the classroom, which is reflected in the children-voice studies conducted by young researchers. The paper begins with background regarding society, culture, and schooling, continues on to describe related studies in this field, and ends with a rethinking of current research. The conclusion is that the studies were hampered both by an inherited culture of inertia and cynicism towards students＇ voices and by a dysfunction in research methodology.

Simulation of thermal field induced by concave spherical transducer in multi-layer media

High intensity focused ultrasound(HIFU)therapy is an effective method in clinical treatment of tumors,in order to explore the bio-heat conduction mechanism of in multi-layer media by concave spherical transducer,temperature field induced by this kind of transducer in multi-layer media will be simulated through solving Pennes equation with finite difference method,and the influence of initial sound pressure,absorption coefficient,and thickness of different layers of biological tissue as well as thermal conductivity parameter on sound focus and temperature distribution will be analyzed,respectively.The results show that the temperature in focus area increases faster while the initial sound pressure and thermal conductivity increase.The absorption coefficient is smaller,the ultrasound intensity in the focus area is bigger,and the size of the focus area is increasing.When the thicknesses of different layers of tissue change,the focus position changes slightly,but the sound intensity of the focus area will change obviously.The temperature in focus area will rise quickly before reaching a threshold,and then the temperature will keep in the threshold range.

A novel two-degree-of-freedom spherical ultrasonic motor using three travelling-wave type annular stators

In order to promote the tolerance and controllability of the multi-degree-of-freedom(M-DOF) ultrasonic motor, a novel two-degree-of-freedom(2-DOF) spherical ultrasonic motor using three traveling-wave type annular stators was put forward. Firstly,the structure and working principle of this motor were introduced, especially a spiral spring as the preload applied component was designed for adaptive adjustment. Then, the friction drive model of 2-DOF spherical motor was built up from spatial geometric relation between three annular stators and the spherical rotor which was used to analyze the mechanical characteristics of the motor.The optimal control strategy for minimum norm solution of three stators' angular velocity was proposed, using Moore-Penrose generalized inverse matrix. Finally, a 2-DOF prototype was fabricated and tested, which ran stably and controllably. The maximum no-load velocity and stall torque are 92 r/min and 90 m N·m, respectively. The 2-DOF spherical ultrasonic motor has compact structure, easy assembly, good performance and stable operation.

Study of Signal Processing Algorithm in the Receiving End of Through-the-Earth Communications of Elastic Wave

In the research of elastic wave signal detection algorithm, a method based on adaptive wavelet analysis and segmentation threshold processing of the channel noise removal methods is suggested to overcome the effect of noise, which is prcduced by absorption loss, scattering loss, reflection loss and multi-path effect during the elastic wave in the transmission undelgroound. The method helps to realize extraction and recovery of weak signal of elastic wave from the multi-path channel, and simulation study is carded out about wavelet de-noising effects of the elastic wave and obtained satisfactory results.