COMPUTER SIMULATION ON NOISE PROCESSES

A method for generating a pseudo-random sequence with both a specified amplitude probabilitydistribution and a desired spectral property is described in this paper.This method is suitable forbeing used on a general-purpose digital computer.A pseudo-random sequence with perfectly satis-factory power spectrum is obtained by FFT first and is used as a reference sequence.Then a fun-damental sequence with a specified amplitude distribution is constructed to have the same spectralproperty as that of the reference one by the correlation transfer method(CT).The relationshipbetween the performance of the FFT-CT method and the sample number of a sequence is studied inthe paper.Some examples of simulating noise processes which have certain amplitude distributionsand desired spectral properties are given.     

SPINORS ON KAHLER–NORDEN MANIFOLDS

It is known that the complex spin group Spin(n, ?) is the universal covering group of complex orthogonal group SO(n, ?). In this work we construct a new kind of spinors on some classes of Kahler–Norden manifolds. The structure group of such a Kahler–Norden manifold is SO(n, ?) and has a lifting to Spin(n, ?). We prove that the Levi-Civita connection on M is an SO(n, ?)-connection. By using the spinor representation of the group Spin(n, ?), we define the spinor bundle S on M. Then we define covariant derivative operator ? on S and study some properties of ?. Lastly we define Dirac operator on S.     

ON THE DYNAMIC SPECTRA OF SPEECH

Using a testing sentence(Ta qu Wuxishi,wo dao Heilongjiang.)well designed for measure-ments of telephone transmission qualality,we studied some dynamic characteristics of speech.Twelvetalkers individually uttered the testing sentence in an anechoic chamber.Testing conditions included:1. different talker's efforts(SPL of speech at 1 m from talker's lips is 55,60,65,70 and 75 dB),2.different utterance rates(normal and speed up).It is shown that:(1) The long-term averagespectrum of speech is varied with the talker's effort,and variation especially appeared in low andmid band of speech.(2) The fundamental frequency F_0 and formant frequencies F_1,F_2,F_3 areincrased with the increasing of the SPL of speech.(3) If utterance picks up speed,the vowel triangletends to be smaller than normal i.e.the vowels tend to be centralized.(4) As a consequence ofincreasing SPL of speech,vowel-to-consonant ratio is increased,but it is closely related to the mannerof articulation of consonants.     

STUDY ON DURATION OF CHINESE CONSONANTS

The duration of Chinese consonants has been measured by using natural disyllabic words.Elevenyoung talkers(5 males and 6 females)and two phonetists,both males,uttered a well designed wordlist in an anechoic chamber at the normal speech sound level of 65dB.The results show that:(i)theduration of Chinese consonants is independent of the tone,syllable duration and consonant position inwords;(ii)the consonant duration is closely correlated with the manner of articulation;(iii)the rankorder of the duration of Chinese consonts is 1-unaspiraed voiceless stops,2-unaspirated voicelessaffricates,3-voiced,4-aspirated voiceless stops,5-voiceless fricatives,6-aspirated voicelessaffricates;and(iv)the closure duration of the unaspirated voiceless stops is longer than that of theaspirated voiceless stops.     

1992 INTERNATIONAL CONFERENCE ON LASERS AND OPTOELECTRONICS

The 1992 International Conference on Lasers and Opto-electronics,Beijing(ICLOE’92 Beijing)will be held at the 21st Century Hotel,Beijing on October16-18,1992.     

STUDY ON ENVIRONMENTAL NOISE EXPOSURE OF RESIDENCE

Survey on environmental noise was carried out in Beijing from April to August,1986.The data ofL_(eq) and L_(50) for every 10 minutes in all day were obtained.The reactions of inhabitants on noise and the in-formations related to noise environment were also collected.The results concerning.environmental noise ex-posure and reactions of inhabitants are mainly stated in this paper.     

ON VARIATIONAL PRINCIPLES OF A PIEZOELECTRIC BODY

The consonance of state variables of a piezoelectric body is explored and four variational princi-ples of a piezoelectric body are systematically proposed.The Lagrangian function of each of theseprinciples is the difference between a corresponding thermodynamic function and the kinetic energy.These principles correspond to different physical conditions and are to be used in different problems.Their applications are discussed.     

WIDE-BAND SOUND ABSORBER BASED ON MICROPERFORATED PANELS

It has been pointed out in a previous paper that a resonator formed by microperforated panelsexhibits the property of high absorption in a very wide frequency band without using any porous ma-terial.This fact is further analyzed quantitatively,using electrical equivalent circuits.The micro-perforated panel is characterized by its high acoustic resistance and low acoustic mass reactance,aproperty required for a wide-band absorber.And in a double resonator the reactance is furtherreduced in low and high frequency regions and remains low in several octaves.The double resonatorabsorber of microperforated panels will make a very efficient general-purpose absorber or special-purpose absorber for adverse circumstances in reverberation or noise control.Based on the analysisof the panel paramters,the situation suitable for the microperforated panels and guide-line forchoosing the design parameters are presented,with illustrating examples.     

ACOUSTIC DELAY LINE BASED ON PLATE MODES

A new kind of realizable ultrasonic delay line is proposed for long time delay application,which is basedon high efficient conversion between Rayleigh wave and plate modes by shallow groove gratings on substratesurface.The experimental devices fabricated on YZ-LiNb0_3 have exhibited the ability to delay a narrow-band singal for the delay time a couple of times longer than its Rayleigh wave counterpart.Because they aremade with the same planar lithographic technology as that used in SAW device,the new configuration retainsadvantages of reliability and reproducibility.Approximate analysis for the new device is provided forunderstanding its operation.     

EXPERIMENTAL INVESTIGATION ON THE CHARACTERISTICS OF DIAMETER-EXPANDED SILENCERS

The investigation on the characteristics of diameter-expanded silencers was carried out experi-mentally and some results were obtained:1.silencers are effective only in a limited plenum chamber(stagnation)pressure range and have maximum of noisc reduction when the condition(P_0/P_1,v)/(d_A~1/d_S~2)=0.81 is fulfilled;2.silencers also have certain expansion selection,i.e.d_S/d_A must belarger than 1.5 and smaller than 2.5;3.the length of silencers has no marked effect on their charac-teristics in the effective pressure range;4.the efflux noise of silencers in the effective pressure rangecan be calculated according to the pressure dependence of turbulent noise and the correction to theexpansion ratio.Finally,two notable phenomena,which are valuable for further study,are putforward.     

A RESEARCH ON SPEECH QUALITY OF CHANNEL VOCODER

2400 bit/s digital vocoder plays a very important role in narrow-band speech communication.This paper presents a channel vocoder designed by using multiple 8085 microprocessors and somespecial hardware. In order to improve the quality of synthesis speech of the vocoder,special attentions were paid tothe improvement of excitation signals by using an all-pass filter,the composite response and groupdelay of the synthesis filter bank adjusted by change bandwidth of filters and with anti-polarity foradjacent filters,and the efficient method of encoding and decoding for Chinese speech parameters.The effect of all these methods has been verified in the results of intelligibility tests. This paper describes the results of intelligibility tests also.     

EFFECT OF SLOW NEUTRON IRRADIATION ON SUPERCONDUCTIVE FILM

Irradiation effect by slow neutrons at a low fluence of about 108n/cm2 on YBCO and GB-CO films was reported in this paper. It was experimentally shown that appropriate slow meutron irradiation would increase the critical current densities Jcm at higher temperature (78K) and have almost no effect on Jcm at lower temperature (57K). Peak effect deduced by appropriate irradiation was observed in the field dependence of Jcm and volume flux pinning force density Fp at 78K. Based on mechanisms of slow-neutron irradiation , some discussions were made.     

STUDY ON THE ACOUSTICAL MECHANISM OF ACTIVE ABSORBER

In this paper,theoretical and experimental results for study of the acoustical mechanism ofthe active sound absorber are presented.Several conclusions have been drawn: (1)When the secondary source system is a unidirectional source,all the energy in the in-cident wave will be absorbed by the secondary source system with no energy reflection. (2)The energy absorbed by the secondary source system is lost in heat in the loudspeakercoils. (3)The process of energy absorption may be described as follows:the incident energy is partlyabsorbed by source Ⅰ in the secondary source system,the transmiting energy will be reflected backby source Ⅱ in the secondary source system and absorbed finally by source Ⅰ.     

ANALYTIC SUBJECT INDEX ON ACOUSTICAL PAPERS IN CHINA

0. Genera1The progress of the musical acoustics,Chen Tong,Acoustic Progress,1982,No.1,1.The progress of ultrasonic application in agriculture,Yuan Wanlan,Acoustic Progress,1982, No.1,11.Noise control of disk saw,Yu Yongyuan,Acoustic Progress,1982,No.1,18.The progress of the acoustic oceanography,Guan Dinghua,Acoustic Progress,1982,No.2, 1.The application of ultrasound to protect environments,Gao Dazhi,Acoustic Progress,1982, No.2,13.     

ACOUSTICAL NEWS 11TH INTERNATIONAL CONGRESS ON ACOUSTICS

The 11th ICA organized by the French-Speaking Acousticians'Association,under thePatronage of the Acoustics Committee of the Pure and Applied Physics Union(I.U.P.A.P.) was held in Paris from l9 to 27 July 1983.About 1120 acousticians from 42 countries andregions attended the meeting.Twenty two Chinese acousticians participated this meeting.More than six hundred contributed and invited papers on various topics of physical acoustics,physio-and phychoacoustics,speech communication,shocks,vibration and solid-state acous-tics,measurements,transducers, electroacoustics,applied acoustics and musital acoustics were     

RECENT DEVELOPMENTS OF RESEARCH ON HIGH FREQUENCY PHONON

A review of recent developments of research on high frequency phonon in solids is presented.Several new experimental results are emphasized,including phonon focusing effect,reflection andscattering at interfaces,and optical excitation of high frequency phonons.