Precise Positioning Method for Seafloor Geodetic Stations Based on the Temporal Variation of Sound Speed Structure

At present,GNSS-Acoustic(GNSS-A)combined technology is widely used in positioning for seafloor geodetic stations.Based on Sound Velocity Profiles(SVPs)data,the equal gradient acoustic ray-tracing method is applied in high-precision position inversion.However,because of the discreteness of the SVPs used in the forementioned method,it ignores the continuous variation of sound velocity structure in time domain,which worsens the positioning accuracy.In this study,the time-domain variation of Sound Speed Structure(SSS)has been considered,and the cubic B-spline function is applied to characterize the perturbed sound velocity.Based on the ray-tracing theory,an inversion model of“stepwise iteration&progressive corrections”for both positioning and sound speed information is proposed,which conducts the gradual correction of seafloor geodetic station coordinates and disturbed sound velocity.The practical data was used to test the effectiveness of our method.The results show that the Root Mean Square(RMS)errors of the residual values of the traditional methods without sound velocity correction,based on quadratic polynomial correction and based on cubic B-spline function correction are 1.43 ms,0.44 ms and 0.21 ms,respectively.The inversion model with sound velocity correction can effectively eliminate the systematic error caused by the change of SSS,and significantly improve the positioning accuracy of the seafloor geodetic stations.

Sound Absorption Enhancement by Thin Multi-Slit Hybrid Structures

We report an extraordinary sound absorption enhancement in low and intermediate frequencies achieved by a thin multi-slit hybrid structure formed by incorporating micrometer scale micro-slits into a sub-millimeter scale meso-slit matrix. Theoretical and numerical results reveal that this exotic phenomenon is attributed to the noticeable velocity and temperature gradients induced at the junctures of the micro- and meso-slits, which cause significant loss of sound energy as a result of viscous and thermal effects. It is demonstrated that the proposed thin multi-slit hybrid structure with micro-scale configuration is capable of controling low frequency noise with large wavelength, which is attractive for applications where the size and weight of a sound absorber are restricted.

Development of a High Sound Absorption Material CEMCOM

Based on sound absorption mechanism of material,the special sound absorption material CEMCOM for road sound insulation is introduced.This high sound absorption material is mainly composed of expanded perlite.Using multiple sound absorption structure can improve sound absorption property of material.According to the preparation principle and durability design of material,a new kind of material with low cost and high durability is developed.

Magnetotelluric sounding study in the region of Zhongshan Station，East Antarctica

This paper deals with the results of the MT observations in the region of Zhongshan Station,Larsemann Hills area, East Antarctica and points out that the lithosphere thickness of the Larsemann Hills is 140 km and the crustal high conductivity layer is situated in 22 km.

北京地区五种常见鸣虫的鸣声结构

本文对寒蝉、蚱蝉、鸣鸣蝉、锐声鸣螽和大扁头蟋五种鸣虫雄虫的鸣声结构进行了较系统的研究。这些昆虫鸣声节律以及声谱和声压的瞬时变化均有显著的不同。一种昆虫的鸣声频谱范围虽然很大,但不同频率的图象却都和主频率的图象一样。

Micro-perforated structures as stand-alone sound absorbers

1 Introduction Early attempts to create a sound absorber which would function without the involvement of any fibrous or porous damping material go far back to K. A. Veliszhanina, S. N. Rschevkin and others as was outlined in Ref. [1]. 30 years ago, D. Y. MAA[2] was first in proposing a practicable design concept and calculation model for Micro-Perforated Absorber （MPA） prototypes which still forms the basis for various applications. During the past 12 years the Fraunhofer IBP developed a whole family of MPA products in close cooperation with 8 or more industrial partners operating in a variety of widely differing market segments. Meanwhile a large number of MPA modules and surface elements have evolved from MAA＇s creative pioneer work. More and more ambitious acousticians have, more recently, caught on this attractive idea of employing absorbers made of non-fibrous, non-abrasive materials with non-polluting, almost closed and optically attractive surfaces. MPA structures have played an important part in a long-standing and on-going effort at IBP to establish novel Alternative Fibreless Absorber （ALFA） tools for a better noise control and acoustic comfort.

Development of a computer vision system to monitor pig locomotion

Avoiding lameness or leg weakness in pig production is crucial to reduce cost, improve animal welfare and meat quality. Detection of lameness detection by the use of vision systems may assist the farmer or breeder to obtain a more accurate and robust measurement of lameness. The paper presents a low-cost vision system for measuring the locomotion of moving pigs based on motion detection, frame-grabbing and multivariate image analysis. The first step is to set up a video system based on web camera technology and choose a test area. Secondly, a motion detection and data storage system are used to build a processing system of video data. The video data are analyzed measuring the properties of each image, stacking them for each animal and then analyze these stacks using multivariate image analysis. The system was able to obtain and decompose information from these stacks, where components could be extracted, representing a particular motion pattern. These components could be used to classify or score animals according to this pattern, which might be an indicator of lameness. However, further improvement is needed with respect to standardization of herding, test area and tracking of animals in order to have a robust system to be used in a farm environment.

Diffusion and sound absorption properties of the quadratic residue diffuser structure with perforated panel

Acoustic structure study always is the academic research interest. Diffusion ab？sorbing structure（DiflFsorber） has good research value because it has both diflFusion property and sound absorption property. Quadratic residue diffusers（QRD） structure which had good diffusion property was combined with the perforated panel which had good sound absorption property in this study. According to standard AES-4id-2001, the diffusion experiments were carried out to study QRD structure and ones composited with perforated-panels which had1 mm-thickness and perforated percentage of 3%, 5%, 8% respectively. The polar coordinate diagrams of different structure were analyzed to derive the diffusion coefficients. Results showed that the composite structure still had good diffusion performance in the frequency range from100 Hz to 800 Hz. The reflection sound energy of composite structure reduced obviously in the perforated panel resonance frequency range where there was about 2 dB reduction averagely.The study result can provide the reference for the design and development of diifsorber.

Control of sound radiation from vibrating structure using active constrained layer: Ⅱ. Numerical calculation

The solution to the state response of active constrained layer and the expression of the sound field radiated from the vibrating structure are given, and the damping mechanisms of active constrained layer (ACL) are discussed. Compaxisons are made with the passive constrained layer (PCL) and the traditional active control method in reducing the structural vibration. The numerical results indicate that: using the active constrained layer damping (ACLD) treatment to dissipate energyt not only the vibration amplitude of structtire is reduced, but also the sound radiated from vibrating structure is suppressed