摘要:

The field experiments of the noise propagating over the ground were carried out, varying the combination of height of an artificial noise source and a receiving point. We pay attention to the excess attenuation obtained from the noise propagating over the ground. The results obtained are as follows: (1) The excess attenuation of the low frequency obtained from the noise propagating over the soft ground is larger than we expected and also affected by the wind; (2) the excess attenuation obtained is, as a whole, larger in summer than in winter. From the data obtained, the empirical equation predicting the excess attenuation is introduced. [T. F. Embleton, J. E. Piercy, and N. Olson, J. Acoust. Soc. Am.59, 267–277 (1976)] Furthermore, referring to the data measured by other researchers [P. H. Parkin and W. E. Scholes, J. Sound Vib.2, 353–374 (1965)], it is shown that the equation is applicable to predict the excess attenuation over the ground.

ISSN:0001-4966    

DOI:10.1121/1.2004016

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Due to the adverse intensity of the acoustic noise within Spacelab, which will be generated during the launch of Space Shuttle, it has been determined that mitigating measures must be implemented in order to preserve the integrity of certain data to be collected during in‐orbit amphibious life sciences experiments. Because of dynamic experimentation constraints, the preliminary design of the noise abatement system required the utilization of performance trade‐offs resulting in the development of a multicomponent system to achieve effective noise control capabilities. A double‐walled life support container fully filled with water and a specimen cadaver has been experimentally modelled in full scale. Its design is intended to merge noise control capabilities with life support, data acquisition, and dynamic requirements in order to achieve the significant noise reduction required by the project.

ISSN:0001-4966    

DOI:10.1121/1.2004023

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This paper reviews diverse observations of acoustic emission from materials and attempts to interpret them on the basis of current knowledge of plastic deformation and fracture. An attempt is made to unify diverse and often conflicting findings paying special attention to microstructural conditions. Observed acoustic emission characteristics have been classified according to their probable origins such as heterogeneous and homogeneous yielding, dynamic strain aging, twinning, decoheston and fracture of second phase particles, and deformation‐induced transformation. Temperature effects and sources of burst‐type emissions are considered. The micro‐yielding concept and other mechanisms are correlated to various acoustic emission behavior observed. Fracture processes generally produce high levels of acoustic emission. Various fracture mechanisms found in different classes of materials are correlated to observed acoustic emission behavior. Relationships between different AE parameters and stress intensity factor or crack tip opening displacement are discussed. It is shown that the consideration of second phase particles is of crucial importance in identifying the mechanisms of acoustic emission. [Work supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2004028

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A review of the application of acoustic emission (microseismic) techniques to the geotechnical area will be given. The approach will be somewhat historical starting with the pioneering work (in the 1930's) by Obert and Duvall in the coal and metal mines and continuing up to the present where currently a host of materials and engineering problems are being investigated with acoustic emission techniques. Acoustic emission measurements in the laboratory will be described which have given insight into the mechanical behavior of rocks, soils, coal and ice. Field applications which will be dealt with include determination of the stability of mine tunnels, open pit mine slopes, underground gas storage reservoirs, and earthem dikes and dams. The use of acoustic emission techniques in earthquake prediction studies will be reviewed. [The authors' work has been supported by EPA.]

ISSN:0001-4966    

DOI:10.1121/1.2004030

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A selected review of ultrasonic propagation in mammalian tissues, organs, and aqueous solutions of biologically pertinent macromolecules is presented. The influence of water and proteinaceous constituents on absorption, attenuation, scattering, and velocity is discussed. It is observed that the ultrasonic propagation properties and organ function form a correspondence allowing for tissue characterization. [Portions of the research reported were supported by the NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2004032

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A reverberation method is used to determine the total acoustic energy absorbed by a mouse when exposed to ultrasound at clinical frequencies. The specimen is exposed in a cylindrical stainless steel tank supported by wires to minimize acoustic losses using a diffuse field created by frequency modulating the 1.03 MHz carrier signal with white noise having a bandwidth of 285 kHz. In the reverberation method, the rate of change of acoustic intensity, also referred to as the decay rate, is measured using a piezoelectric probe when the source is modulated. The energy absorbed by the specimen is given by the product of the total acoustic input power, the exposure time, and the fractional increase in decay rate caused by the specimen. The decay rate for samples of castor oil enclosed in spherical glass vessels was measured at two temperatures, 20° and 30°C. The absorption coefficient was calculated from the decay rate by assuming the energy density within the specimen was uniform and equal to the average energy density within the tank. The results obtained were within 15% of previously reported values for castor oil. Anesthetized ICR mice were exposed using the apparatus and typical results are presented.

ISSN:0001-4966    

DOI:10.1121/1.2004040

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The subject in our study has spent between 2000 and 2500 h learning to read speech spectrograms. We tested the subject's ability to identify the phonetic content of broadband speech spectrograms of unknown utterances during eight separate sessions of about 4 h each. The expert was presented with 23 spectrograms of English sentences and sequences of words and nonsense words, and 50 English words embedded in a known carrier phrase. The phonetic labels produced by the expert agreed with the phonetic labels produced by trained phoneticians (who listened to the speech) between 80% and 90% of the time, depending upon the scoring method used. When presented with words in a known carrier phrase, labeling performance improved to about 95%. A linguist who was presented with the phonetic transcriptions produced by the spectrogram reader was able to identify all of the words in 10 of 15 utterances, and missed only a single word in each of the remaining five. A film will be shown of the expert segmenting and labeling two spectrograms of unknown utterances.

ISSN:0001-4966    

DOI:10.1121/1.2004042

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The acoustic characteristics of voiceless affricates have not been clearly determined. The voiceless affricates /ts/ and /t∫/ in CV syllables are analyzed in this paper to obtain acoustic features useful for their discrimination from the voiceless fricatives /s/ and /∫/ as well as for distinguishing between /ts/ and /t∫/ themselves. The maximum rate of increase in short‐term power at consonantal onset was found to be useful for separating the affricates from the fricatives, while the frequency of the spectral zero, extracted by assuming a model with one zero and two poles for the frequency spectrum up to 7 kHz, was found to be effective for separating the two affricates [H. Fujisaki and O. Kunisaki, IEEE Trans.ASSP‐26, 21–27 (1978)]. Based on these results, a recognition test was carried out on 100 CV syllables consisting of /ts/, /t∫/, /s/, or /∫/ followed by one of the five Japanese vowels uttered by a male speaker, and a recognition rate of 99% was achieved. [Work supported by Ministry of Education Grant‐in‐Aid for Scientific Research No. 239005.]

ISSN:0001-4966    

DOI:10.1121/1.2004050

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A decision rule which assigns an unknown signal to the class for which its average distance to theKnearest samples is minimum is derived. It is shown that this decision rule is equivalent to the classical maximum posterior probability rule based on nonparametric estimates of the local class conditional density functions. We have used the rule successfully in an isolated word recognition experiment and have found that it performs better than other nearest neighbor classification rules. Part of the improved performance is due to the selection of the appropriate value ofK. We show how this choice can be tailored to the training set and why the rule is particularly appropriate for our speech recognition work.

ISSN:0001-4966    

DOI:10.1121/1.2004058

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A spoken word recognition system for unspecified male speakers is outlined. The system operates in the following four stages. (I) Seven acoustic parameters are extracted every 10 ms from the outputs of the filter bank. The parameters are the frequencies of three spectral local peaks, the speech power and three parameters expressing the gross pattern of the spectrum. (II) Segmentation and the phoneme recognition are carried out. (III) Errors in the segmentation and phoneme recognition are corrected by means of phoneme connecting rules. (IV) The recognized sequence is determined to be the item of the dictionary having a maximum similarity to the recognized phonemic sequence. The similarity between the item of the dictionary and the recognized phonemic sequence is computed using confusion matrices made from the recognition of 17 040 phonemes. Every item of the dictionary is written in phonemic symbols derived from the word in Japanese “kana” letters by simple rules, so that the contents of the dictionary can be easily changed. The scores for word recognition were found to be 84.0% for 166 words uttered by 25 male speakers and 95.0% for 51 words selected from these 166.

ISSN:0001-4966    

DOI:10.1121/1.2004062

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP