利用超声波在线检测液态金属洁净度的模拟研究

通过水模型实验研究了利用超声波在线检测液态金属中夹杂物的可能性。首先考察和比较了不同性质的夹杂物对超声波传播规律的影响,发现当溶液中存在夹杂物时超声波声压减小,超声波的波形也发生明显变化,而且不同性质的夹杂物对超声波的影响也存在较大差异。进一步考察夹杂物浓度和粒径对超声波传播的影响,发现随着夹杂物浓度的增加和粒径的增大,超声波声压逐渐减小,而且声压对上述因素的微小变化反应灵敏。研究表明,利用超声波在线检测液态金属洁净度是可能的。     

科技打造残障人士的康美之翼——“非常美”残障人士康健服装展演举办

本刊讯为弘扬残奥会精神,切实体现科技对发展残疾事业的支持,并作为对北京2008残奥会的献礼,首都科技集团和北京服装学院于2008年9月15日在奥林匹克公园祥云剧场举办了"非常美"残障人士康健服装展演。这是国内首次为残障人士举办的康健服装展演,它表达了科技界对残疾人事业发展的支持,展示了"科技、时尚、和谐"完美的结合,体现了残障人士热爱生活、     

旋转源近场声学特性进一步研究

旋转运动源近场声学频域解可以表示为在远场解基础上叠加近场修正项．在此解基础上，本文得到宽频源和简谐源的近场声压谱密度，指出此２种声源近声场各自的特点及源的旋转半径和轴向位置对声场结构的影响．     

海洋气候声学测温计划

温室效应引起的地球变暖是威胁人类生存的全球性环境问题。海洋在缓解全球气候变暖的过程中起着十分重要的作用,因此,测定海洋变暖趋势受到世界的关注。大范围海洋声学测温是基于声波能在大洋中远距离传播以及海水中声速是温度灵敏函数的原理,通过测量远距离脉冲声信号的传播时间可以推算海洋温度的时、空变化。SCOR已成立了声学监测大洋的96工作组,决定在全球大洋设网进行常年观测,名为海洋气候声学测温(ATOC)计划。本文着重介绍该计划及我国参加该计划的意义。     

九龙江河口湾新沉积层及其声学地层特征的研究

近三十余年来,由于九龙江入海泥沙成倍增加和厦门东渡湾多条栏湾大坝的修建导致了河口湾沉积环境的明显改变,首先是沉积速率的加快,应用Klein-510型浅地层剖面仪进行了不同沉积层声学效应的探测试验取得新的认识,详细分析了图象清晰、连续性完好的沉积界面特征,并与钻孔岩蕊逐层地进行对比,证明了海湾沉积环境的变化能很好地反映在沉积界面上,与过去的其他研究方法比较,本区近30多年来的沉积平均速率:内湾区大部分为6～7cm/a,河口湾前沿可达到8～10cm/a。     

Relationship between the temperature and the acoustic nonlinearity parameter in biological tissues

Recently with the rapid development of the high-intensity focused ultrasound (HIFU) in biomedical ultrasound, much attention has been paid to the noninvasive temperature estimation in biological tissue in order to determine the region and degree of the ultrasound-induced lesions. In ultrasound hyperthermal therapy it is highly desirable to study the real-time noninvasive monitoring of temperature distribution in biological tissue. In this paper, the relationship between the nonlinearity parameter B/A and the temperature in biological tissue is studied and compared with the theoretical model as well as the experimental results from the thermocouple. Results indicated that B/A could be used as an effective tool to monitor the temperature distribution in biological media.     

Identification of diesel front sound source based on continuous wavelet transform

Acoustic signals from diesel engines contain useful information but also include considerable noise components. To extract information for condition monitoring purposes, continuous wavelet transform (CWT) is used for the characterization of engine acoustics. This paper first reviews CWT characteristics represented by short duration transient signals. Wavelet selection and CWT are then implemented and wavelet transform is used to analyze the major sources of the engine front's exterior radiation sound. The research provides a reliable basis for engineering practice to reduce vehicle sound level. Comparison of the identification results of the measured acoustic signals with the identification results of the measured surface vibration showed good agreement.     

我院小礼堂音响系统的设计与设备选择

根据我院实际提出建设小礼堂音响扩音系统设计思想,设备选型原则,并就工程的施工、投入使用后进行回顾和小结.     

Head rotation and sound image localization in the median plane

The effect of head rotation on median plane sound source (or image) localization is studied. It is suggested that, at low frequency, the change of interaural time difference (ITD) caused by head rotation supplies information for determining sound source direction in the median plane. Based on the suggestion, the summed sound image Ioealization equations for multiple loudspeakers arranged in the median plane are derived. Especially, for a pair of loudspeakers arranged front-back symmetrically in the median plane, the localization equations are similar to that of stereophonic sound in horizontal plane. A sound image localization experiment was carried out to prove the theoretical analysis. The results of this paper are not only available to virtual spatial auditory, but also supply a quantitative validation of the hypothesis that head rotation is a cue for sound source localization in the median plane at low frequency.