’94北京检测技术交流会在京召开

由北京机械工程学会无损检测分会、中国声学学会检测声学分会、中国机械工程学会无损检测分会超声专业委员会和促进无损检测器材发展工作委员会联合主办，北京NDT技术交流中心承办的“’94北京检测技术交流会”于1994年10月8日一10日在北京国际会议中心隆重召开．这是无损检测学会与声学检测学会第一次在北京联合召开的全国性大规模学术交流会，也是第一次由从事无损检测与声学检测两个方面的科技工作者联合参加的检测技术交流会．出席大会的代表近200人．大会共收到论文110篇．特邀大会报告6篇：中科院院士应崇福先生的“激光超声研究与…     

北京七色光儿童艺术剧院的声学设计

北京七色光儿童艺术剧院是一个以演出儿童话剧为主，同时还可以进行歌舞、音乐等其他文艺形式的演出的多功能剧场，该剧院形式活泼，音质良好。本文从音质和噪声控制的几个方面对其声学设计进行了介绍。     

Practical absorption limits of MPP absorber

The construction and properties of microperforated panel (MPP) absorber are discussed. The absorption limit of the absorber had been shown that low values of the perforate constant k = d(f/10)1/2 and the orifice diameter d (in mm) are essential for MPP to have high absorption in wide frequency band. To find the exact limits, take 1 for k as a start, because both specific resistance and high absorption require k around one. And the orifice diameter d is chosen as 0.1 mm, so that the peak absorption coefficient (resonance absorption) is at 1000 Hz, and high sound frequency may be in the absorption region. Is it possible for a single layer of such an MPP to cover the whole absorption region required in practice? The half-absorption limit is not a good criterion, because low absorption comes in also in some cases. The 0.5 absorption coefficient limit is suggested for practical region, as a standard for comparison. Absorption curves were drawn for different load resistances, of absorption coefficients versus frequency. Ordinary MPP absorber absorbs in slightly over two octaves, and the new absorber with r = 1 (specific resistance equal to the characteristic impedance in air)is slightly better than these, 2.5 octaves. The new absorbers with r > 1, are much better than these, and some satisfies high absorption in broad frequency range. Realization of these will mean great progress of MPP absorbers.     

第十六届国际非线性声学会议在莫斯科市举行

第十六届国际非线性声学会议(InternationalSymposium on Nonlinear Acoustics,简称16thISNA)于2002年8月19日至23日在俄罗斯首都莫斯科市举行。来自全世界28个国家和地区约300人参加了会议,其中俄罗斯160人,美国32人,法国16人,日本11人,德国9人,英国7人,瑞典7人,….等等;中国代表有3人,他们是南京大学龚秀芬教授和王耀俊教授,江西吉安师范学院李化茂教授。ISNA是由国际非线性声学学术委员会主办的国际学术会议,每3年举行一次,自1968年以来已举办了16次,在声学和非线性声学领域具有很大的影响。本届会议由俄罗斯的莫斯科大学组织和承办。会议     

Elimination of Spiral Waves and Competition between Travelling Wave Impulses and Spiral Waves

The interaction between travelling wave impulses and spiral waves is studied and the results of their competition are related to the exciting period. From the results, it is known that the formation and development of spiral waves in cardiac tissue depend on the period by which the travelling wave impulses are excited. A method is proposed to eliminate spiral waves, which is easily operated.     

美国国家标准与技术研究所简介

美国国家标准与技术研究所 (NIST)是国际上著名的两大参考物质供应单位之一。她的前身是美国国家标准局 (NBS) ,创建于 190 1年 ,迄今已有10 1年历史。总部设在Madison州Gaithersburg市 ,分部设在Colorado州Boulder市。该所隶属于美国商务部。该所的宗旨是与工业界携手合作 ,发展和应用测量、标准与技术 ,以推动美国经济日益壮大 ,为贯彻这一宗旨 ,在新千年来临之际制订并实施下述计划 :①测量与标准实验所计划 ;②先进技术计划 ,其任务是帮助填补先进基础研究与其产业化之间的缺口 ,以开发高风险而具有广阔商业前景的新技术 ;③延伸制…     

Langlands和Taylor教授共同获得2007年邵逸夫奖数学奖

2007年(第四届)邵逸夫奖数学奖由普林斯顿高等研究所的Robert Langlands教授和哈佛大学的RichardTaylor教授共同获得,是因为“for initiating and developing a grand unifying vision of mathematics that connects primenumbers with symmetry.”而获奖.他们两人分享一百万美元的奖金.颁奖典礼是于2007年9月11日在香港举行。邵逸夫奖于2002年设立,以表彰在学术及科学研究或应用获得突破成果,和该成果对人类生活产生意义深远影响的科学家。现代微分几何学的奠基者陈省身(S.S.Chern)教授、费马大定理的终结者怀尔斯(A.Wiles)教授分别获…     

Lower Hearing Threshold by Noise

We demonstrate that noise can be a benefit factor that enables us to hear weaker signals. We measured the hearing thresholds of subjects for pure tone in different noise levels. The results show that pure tone thresholds with noise of some levels are lower than that without noise. The largest down-shift of the threshold by noise among the examined subjects is 5.7 dB, and the smallest is 1.7 dB.     

Sound Field Calculations of Elliptical Pistons by the Superposition of Two—Dimensional Gaussian Beams

We present an alternative approach to calculate the sound field of ultrasonic transducers.The distribution function of sources is expanded into the superposition of a series of two-dimensional Gaussian functions.The corresponding radiated sound field is expressed as the superposition of these two-dimensional Gaussian beams and is then reduced to the computation of these simple functions.This treatment does not require the condition that the shape of the source is of circular axial symmetry.A numerical example is presented for the uniform elliptical piston transducer and this is in good agreement with the results given by complicated computation.