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1.
MPEG-2先进音频编码(AAC)的研究和软件仿真   总被引:4,自引:0,他引:4       下载免费PDF全文
包益平  陈健 《应用声学》1999,18(5):19-23
MPEG-2AAC是ISO/IEC MPEG组织继 MPEG-1、MPEG-2音频编解码标准后,制定 的最新国际标准(ISO/IEC 13818-7),在64kbps/每声道低码率时能提供全透明音质。本文对其编 解码算法进行了简要介绍。论文作者对MPEG-2AAC进行了软件仿真,文中介绍了仿真结果,仿 真时对AAC标准所附编码范例中的一些不妥之处,作了改进,文中列举了6方面的修正。  相似文献   

2.
根据传统过渡态,变分过渡理论计算了H2O+Cl→HCl+OH(R1)反应中D代替的同位素动力学效应(KIE)得到了HOD+Cl→DCl+OH(R2),DOH+Cl→HCl+OD(R3)反应不同的KIE值,对KIE进行了分解,讨论了平动(trars)转动(rot)振动(vib)等各种因素的作用,在反应R2中,由于HOD中OD键直接参与反应,D同位素的KE很大,对R2的KIE分解表明,振动对KIE贡献  相似文献   

3.
包益平  陈健 《应用声学》1999,18(5):19-23
MPEG-23AAC是ISO/IECMPEG组织继MPEG-1,MPEG-2音频编解码标准后,制定的最新国际标准(ISO/IEC13818-7)在64kbps/每声道低码率时能提供全透明音质,本文对其编解码算法进行了简要介绍,论文作者对MPEG-2AAC进行了软件仿真,文中介绍了仿真结果,仿真时对AAC标准所附编码范 中的一些不妥之处,作了改进,文中列举了6方面的修正。  相似文献   

4.
YAG晶体中Ce^3+对Er^3+的敏化作用   总被引:2,自引:1,他引:1  
黄莉蕾  洪治 《光学学报》1998,18(4):03-506
通过求解(Ce,Er):YAG和Er:YAG的能级跃迁速率方程,讨论了Ce^3+对Er^3+离子的敏化作用。表明掺Ce^3+可增强Er^3+离子1.66μm波长的激光强度,但仅改变了1.66μm波长激光粒子数反转,即N2(^4I12/2)〉N1(^4I15/2)与Er^3+离子浓度的关系。  相似文献   

5.
YBa2Cu3O7-δ高温超导膜的Raman标定张鹏翔1,2,H.-U.HABERMEIER2,M.Cardona2(1云南工业大学材料科学与工程系昆明云南650051中国)(2Max-Plaud-InstitutfürFestkorperforsc...  相似文献   

6.
本文测定了Cs3Cu2 I5 晶体薄膜在室温及液氮温度下的吸收谱,并依此计算出该材料的激子参数,即激子束缚能ΔE(1)ex = (0.53±0.07)eV,激子半径aex = 0.326 nm ,禁带宽度Eg = (5.00±0.07)eV。在谱分析的基础上,论证了Cs3Cu2I5 的电子和激子激发定域在该晶体的CuI亚晶格之中,同时,揭示了在低温下Csx Cu1- x I系列化合物的第一激子峰位置随其摩尔组分变化的规律。  相似文献   

7.
RELATIVISTICCALCULATIONOFIONIZATIONENERGIESFORTITANIUMIONSTiⅠTOTiChenBo1,2TanMingliang2JiangGang2ZhuZhenghe2ZhaoYongkuan31In...  相似文献   

8.
研究了氟化膦类系列配位体(GPF2:G=F,Et2N,Me2N,C5H10N,nPrO,PhO,neoPnO,2,5diMePh,isoPr,etc.)及其与金属镍(0)铜(I)钼(0)金(I)形成的配合物的核磁共振氟谱化学位移的定量分子建模,发现了其中的一些有用规律.  相似文献   

9.
本文计算了红宝石中Al核自旋跳变引起的R1[4A2(S=-3/2)→2E(S=-1/2)]回波衰减.用随机电报过程描述每个Al核自旋(i)跳变引起Cr共振频率的起伏Δi,这个过程对光子回波衰减的贡献〈Ei(t21)〉可以用解析式表示.首先计算核自旋(i)跳变的总速率Wi及它引起的Δi,求出〈Ei(t21)〉.设对Cr光失相起主要贡献的每个Al核自旋跳变近似是独立的,所以总的回波强度是所有Al引起的〈Ei(t)21〉的乘积.计算得到非指数的回波衰减,以I=I0exp〔-(4t/tm)x〕拟合,x=2.56,tm=50.6μs,与实验及计算机模拟的结果一致  相似文献   

10.
研究了Eu(2+):BaFxCl2在紫外线辐照下的光激励发光。通过改变激励方式及激励光的扫描方向,给出了Eu(2+):BaFxCl2-x光激励发光过程中,两种F色心的浓度比值与光激励截面比值的测定方法。利用这种测定方法,进一步研究了两种F色心的浓度比值和光激励截面比值与F/CI比值的关系。  相似文献   

11.
The limitations in the use of the Impulse Precision Sound Level Meter for the assessment of the sound energy of recurrent impact noise have been investigated. For repetition rates above 30 impacts per second the meter reading and level predicted by an energy law agree to within ±2 dB. Below 30 impacts per second, for pulses with decay times in the range 2 to 28 msec, a simple empirical correction applied to the meter reading will produce results that follow the energy law. For decay times in excess of 28 msec simple corrections are not adequate and therefore the Impulse Sound Level Meter cannot be used in practice.  相似文献   

12.
Multi-Beam Echo-Sounders (MBES) designed for seafloor-mapping applications are today a major tool for ocean exploration and monitoring. Concerns have been raised about their impact towards marine life and especially marine mammals, although their inherent characteristics (high frequencies, short signals and narrow transmitting lobes) actually minimize this possibility. The present paper proposes an analysis of MBES radiation characteristics (pulse design, source level and radiation directivity pattern) accounting for the various geometries met today and expressed according to the metrics used for acoustical impact assessment (maximum Sound Pressure Level, and cumulative Sound Exposure Level). A detailed radiation model is proposed, including the transmission through directivity sidelobes, and applied to three typical MBES examples. A simplified radiation model is then defined, in order to extend it to the case of the cumulative insonification by a MBES moving along a survey line. An approximated analytical model is proposed for the accumulated intensity, showing good agreement with the complete simulation of insonification; it is applied to the worst-case configuration of a low-frequency (12 kHz) multi-sector system. The computation of ranges corresponding to impact thresholds accepted today shows that impacts in terms of injury are negligible for both SPL and SEL; however behavioural response impacts cannot be excluded, and should require specific experimentation.  相似文献   

13.
A method is reviewed for conversion of a microphone signal into calibrated Sound Pressure Level (SPL) units. The method follows American National Standards Institute (ANSI) standard for S1.4 SPL meters and requires an accurate SPL meter and an accurate calibration sound source for conversion. Accuracy and validation data from test signals and human phonation are provided. The results indicate that under typical speech conditions, an absolute accuracy of plus or minus 1.6 dB (type I SPL meter) can be obtained with a miniature head-mounted microphone.  相似文献   

14.
A study of noise conditions around a suburban rifle range was carried out in conjunction with a social survey of nearby residents. These studies were aimed at providing some information on the relationship between noise levels from rifle shooting and human reaction to the noise. The exposure at each surveyed residence was calculated in terms of eight exposure measures. All units gave similar low correlations with residents' reactions, but from other points of view the energy-mean value of the Sound Exposure Level (possibly A-weighted) seems the most useful unit. Units relying on the peak overpressure would not be generalizable to other impulsive noise sources. Even in the case of Sound Exposure Level, the relationship between exposure and reaction is not generalizable to non-impulsive noises, such as aircraft overflights, without some “correction”. This indicates that units such as Ldn in which noise exposures from different sources are added on an energy basis are inappropriate for measurement of rifle noise. Noise from the range was found to be very directional, and variable between days. It therefore appears that accurate characterization of such noise requires comparatively extensive measurements on a number of days.  相似文献   

15.
Today, analyzing of sound pressure level and frequency is considered as an important index in human society. Sound experts believe that analyzing of these parameters can help us to better understanding of work environments. Sound measurements and frequency analysis did to fix the harmful frequency in all sections in Shiraz gas power plant with sound analyzer model BSWA 308. The sound pressure levels (LP) and the one and one-third octave band were continuously measured in A and C weighting networks and slow mode for time response. Excel 2013 and Minitab 18.1 software used for statistical calculations. Results analyzed by Minitab 18.1 software. The highest harmful frequency in Shiraz Gas Power Plant (SGPP) was 50 Hz with 115 dB. The sound pressure level (SPL) ranged from 45 dB to 120 dB in one-third octave band and weighting network C. The maximum sound pressure level was in Craft electricity generator with 105.3 dB and 67 Hz. Sound pressure level in surrounded environment was 120 dB. According to the results, in this industry the sound pressure level exceeded the Occupational Exposure Level of Iran (OEL). The value of sound pressure level were higher than the Standard of occupational health. SGPP consumes 47000 cubic meters of natural gas per hour to produce 100 MW (Mega Watt) of electricity. It is very high and it is not economical and cost effective. These numbers indicate that the power plant’s efficiency is low. It could be concluded that the noise pollution is an important issue in these industries. Moreover, SGPP produce noise with loss energy. Frequencies rotation at high sound pressure levels toward low frequencies were happened.  相似文献   

16.
Exposure to sound, heat, and increased physical workload can change physiological parameters. This study was conducted to evaluate the effect of concomitant exposure to sound, heat, and physical workload changes on physiological parameters in controlled laboratory conditions. This experimental crosssectional study was conducted in 35 male university students with a mean age of 25.75 years and a mean BMI of 22.69 kg/m2 . Systolic and diastolic blood pressure and heart rate were measured after 15 min rest in the laboratory, 5 and 10 min after starting the experiment, and then after 20 min in controlled laboratory conditions in five combination modes. The combination modes were (Sound: 65 dB, WBGT: 22°C, Speed: 1.7, Slope: 10%), (Sound: 65 dB, WBGT: 22°C, Speed: 3.4, Slope: 14%), (Sound: 95 dB, WBGT: 22°C, Speed: 1.7, Slope: 10%), (Sound: 65 dB, WBGT: 32°C, Speed: 1.7, Slope: 10%), and (Sound: 95 dB, WBGT: 32°C, Speed: 3.4, Slope: 14%). Mixed model analysis and paired t-test were applied for analysis. The results showed that the mean physiological parameters (Systolic and diastolic blood pressure and heart rate) increased when different combination modes worsened (Sound from 65 to 95 dB, WBGT from 22°C to 32°C, speed from 1.7 to 3.4, and slope from 10% to 14%, and when sound: 95 dB, WBGT: 32°C, Speed: 3.4, and Slope: 14%). Moreover, the mean changes of systolic and diastolic blood pressure were significant in all conditions when compared with the reference condition (Sound: 65 dB, WBGT: 22°C, Speed: 1.7, and Slope: 10%). The mean heart rate changes were also significant except for exposure to the second condition (Sound: 65 dB, WBGT: 22°C, Speed: 3.4, Slope: 14%) and the third condition (Sound: 95 dB, WBGT: 22°C, Speed: 1.7, Slope: 10%). Exposure to hazardous levels of sound, heat, and workload has adverse effects on physiological parameters. Concomitant exposure to all three hazards has a synergistic effect and increases the adverse effect.  相似文献   

17.
Surface Science [Vol. 1] Lectures at an International Course, Trieste, 1974. (International Atomic Energy Agency, Vienna) [Pp. 505] £14.00; $31.00. Scope: Postgraduate course.

Simple Dielectric Liquids By T. J. Gallagher (Clarendon Press: Oxford University Press 1975) [Pp. vi+154] £6.00. Scope: Treatise/textbook. Level: Undergraduate to postgraduate.

Real Solids and Radiation By A. E. Hughes and D. Pooley (Wykeham Publications 1975) [Pp. xii+196] £3.00. Scope: General introduction. Level: Undergraduate, school.

New Uses for Ion Accelerators Editor: J. F. Ziegler (Plenum Press, 1975) [Pp. xii+482] $33.60.

Electrical Measurement Systems for Biological and Physical Scientists By L. J. Weber and D. L. McLean (Addison Wesley, 1975) [Pp. xiv+399] £8.25. Scope: Textbook. Level: undergraduate.

Temperature Measurement 1975 (Conference Series No. 26.) Edited by B. F. Billings and T. J. Quinn (The Institute of Physics 1975.) [Pp. xiv+454.] £20.00. Scope: Survey. Level: Specialist/postgraduate.

Theory and Application of the Boltzmann Equation By C. Cercignani (Scottish Academic Press x1975) [Pp. xii+415] £10.50. Scope: Textbook. Level: Undergraduate/postgraduate.

The Use of Physics Literature. Edited by H. Coblans. (Butterworths, 1976.) [Pp. vi+290.] £6.00. Scope: Survey; library (reference). Level: Specialist/post-graduate; undergraduate.

Authenticity in Art. By S. J. Fleming. (The Institute of Physics, 1975.) [Pp. 164.] £6.50. Level: Specialist/post-graduate; undergraduate; general reader.  相似文献   

18.
Gravity and the Earth. (Wykeham Science Series No. 6.) By A. H. Cook. (Wykeham Publications (London) Ltd., 1969.) [Pp. xi + 94.] £1.00. Scope: Survey. Level: General reader; undergraduate; school.

Relativity and High Energy Physics. (Wykeham Science Series No. 4.)

Elementary Science of Metals (Wykeham Science Series No. 1.) By J. W. MARTIN. (Wykeham Publications (London) Ltd., 1969.) [Pp. xii+ 135.] £1.00. Scope: Textbook. Level: Undergraduate; school.

The Physics of Metals. 1. Electrons. Edited by J. M. ZIMAN. (Cambridge University Press, 1969.) [Pp. xvii+ 433.] 90s. Scope: Treatise/textbook; survey. Level: Specialist/postgraduate.

Gallium Arsenide: Proceedings of 1968 conference at Dallas, Texas. The Institute of Physics and the Physical Society, 1969. [Pp. vii + 244.] £6 5s. Scope: Conference proceedings. Level: Specialist/postgraduate.

Man of Physics: L. D. Landau (II). By D. ter Haar. (Pergamon Press, 1969.) [Pp. ix + 198.] 35s. (flexi 21s.)

Arc Physics. By M. F. HOYAUX. (Berlin, Heidelberg, New York: Springer-Verlag, 1968.) [Pp. xiii + 305.] DM. 58; $14.50. Scope: Treatise/textbook. Level: Specialist/postgraduate.

Liquid Semiconductors. V. M. Glazon, S. N. Chizcheskaya and N. N. Glagoleva. (Plenum Press, 1969.) [Pp. xii + 362.] $22.50. Scope: Treatise/textbook. Level: Specialist/postgrduate.

Principles of Particle Accelerators. By E. Persico, E. Ferrari and S. E. Segre. (W. A. Benjamin, 1968.) [Pp. x + 301.] $17.75. Scope: Treatise/textbook. Level: Specialist/postgraduate.

Thermal Conductivity. Proceedings of the Eighth Conference. Edited by C. Y. Ho and R. E. Taylor. (Plenum Press, 1969.) [Pp. xx + 1169.] $40.00. Scope: Conference proceedings; library; library (reference). Level: Specialist/postgraduate.

Elementary Wave Optics. By R. H. Webb. (Academic Press, 1969.) [Pp. xi + 268.] 107S. Scope: Treatise/textbook; library. Level: Undergraduate.

Active Nitrogen. By A. N. Wright and C. A. Winkler. (Academic Press, 1968.) [Pp. x + 602.] 256s. 8d. Scope: Survey; library; library(reference). Level: Specialist/postgraduate; undergraduate; school.

Conceptual Physics: Matter in Motion. By J. R. Ballie and W. E. Dibble. (John Wiley, 1969.) [Pp. x + 637.] 88s. Scope: Survey; library. Level: General reader; undergraduate; school.

Astrophysics and Stellar Astronomy. By T. L. Swihart. (John Wiley, 1969.) [Pp. x + 299.1 88s. Scope: Textbook; library. Level: Postgraduate; undergraduate.

The Scattering of Light. By M. Kerker. (Academic Press, 1969.) [Pp. xv + 666.] £15 13s. 0d. Scope: Treatise; library. Level: Specialist/postgraduate.

Light Scattering Spectra of Solids. Edited by G. B. Wright. (Springer-Verlag, 1969.) [Pp. xix + 763.] DM. 176. Scope: Conference proceedings; library. Level: Specialist/postgraduate.  相似文献   

19.
The Community Tolerance Level (CTL) is a new indicator which characterizes the impact of aircraft noise around local airport. It corresponds to the exposure sound level (DENL or DNL) where 50% of the population is highly annoyed. Inspired by this indicator, this paper aims at calculating the Real Estate Tolerance Level (RETL) which corresponds to the exposure sound level where a property price is 50% depreciated compared to the price of the same property which would be situated in an area whose DENL is below 50 dB(A). The use of a notarial database analyzed with the Hedonic Price Model (HPM) made it possible to calculate the percentage of property price depreciation around CDG airport, with 1-dB steps of DENL, and so far to calculate the RETL. 19,891 house transactions and 23,264 apartments have been localized with a Geographic Information Systems (GIS) and crossed with the Sound Environment Curves provided by Airport of Paris. The RETL value for single houses and for apartments around CDG is 75.8 dB. It is comparable to the mean CTL value which has been estimated to 73.3 dB from the DNL data of 43 airports over the world (about 73.9 dB from DENL data). The RETL is predictable without field survey and could characterize the impact of aircraft noise around local airports. It could be a good indicator to follow the evolution of population tolerance over the years.  相似文献   

20.
Surface Science. Volume II. (Lectures at the International Course at Trieste, April 1974.) (International Atomic Energy Agency, Vienna, 1975.) [Pp. 302.] £8.50.

Landolt-Börnstein. New Series, Group IV, Volume 3, Thermodynamic Equilibria of Boiling Mixtures. By J. Weishaupt. (Springer-Verlag, Berlin, Heidelberg, New York, 1975.) [Pp. viii + 376.] DM 320; $131.20.

Advances in Nuclear Physics. Volume 8. Edited by M. Baranger and E. Vogt. (Plenum Press, 1976.) [Pp. xiii+383.] $33.00. Scope: Specialist/postgraduate.

The Physics of Metals (2) Defects. Edited by P. B. Hirsch. (Cambridge University Press, 1975.) [pp. xix + 302.] £13.50. Scope: Treatise; Library; Library(reference). Level: Specialist/post graduate; Undergraduate.

Applications of Ion Beams to Materials, 1975. Institute of Physics Conference Series No. 28. (Institute of Physics, 1976.) [Pp. xi + 364.] £19.00; $45.00. Scope: Conference Proceedings. Level: Specialist/post-graduate.

The Theory of Photons and Electrons. By J. M. Jauch and F. Rohrlich. (Springer-Verlag, 1976.) [Pp. xix + 553.] DM41; $16.80. Scope: Textbook. Level: Specialist.

An Introduction to the Physics of Ferroelectrics. By T. Mitsu, I. Tatsuzaki and E. Nakamura, translated by J. C. Burfoot. (Gordon and Breach, 1976.) [Pp. xiii + 443.] $17.00. Scope: Survey. Level: Specialist/post-graduate.

Electron Microscopy in Mineralogy. Coordinating Editor H. R. Wenk. (Springer-Verlag, 1976.) [Pp. xii + 564.] DM 96; $39.40. Scope: Survey. Level: For specialists only; specialist/postgraduate.

Vistas in Physical Reality. Edited by E. Laszlo and E. B. Sellon. (Plenum, 1976.) [pp. xii + 228.] $30.00. Scope: Survey. Level: Specialist/postgraduate; general reader.

Classical Electrodynamics (2nd Edition). By J. D. Jackson. (John Wiley, 1975.) [Pp. xxii + 848.] £10.75; £2.95. Scope: Treatise/Textbook. Level: Post-graduate; undergraduate.

Thermodynamics for Modular Instruction. By R. K. Irey, A. Ansari and J. H. Pohl. (John Wiley, 1976.) In loose sections. £18.80 complete. Scope: Treatise/Textbook. Level: Undergraduate.  相似文献   

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