摘要:

A 5‐MHz pulsed ultrasonic system has been designed which can detect microparticles in a free‐flowing liquid, monitoring particles between 10 and 400 μm in diameter. As in an earlier version by the same authors [J. Acoust. Soc. Am.60, S53–S54(A) (1976)], the transducer is mounted in the plexiglass wall of a cylindrical dielectric cell (interior diameter 1.27 cm) so that a thin section of plexiglass of plano‐concave shape exists between the transducer and the liquid stream, serving as an acoustic lens and focusing the ultrasonic beam at a point 1.36 cm from the surface of the lens. The return reflections from density discontinuities within the liquid are converted to digital signals by use of a 100‐MHz A‐D converter. This information is then analyzed by means of a PDP‐11/40 computer. Both the video signal and the RF signal from the ultrasonic transmitter‐receiver are used to provide information on the size and type of particle detected. Air bubbles return a symmetric pulsed echo, while various solid particles examined return asymmetric pulses. The RF signal can also be used to provide phase information, thus distinguishing particles with acoustic impedance less than that of the flowing liquid from those with higher acoustic impedance.

ISSN:0001-4966    

DOI:10.1121/1.2004302

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Pulsed chemical laser devices require a high degree of fluid homogeneity to meet electrical discharge and optical beam‐steering requirements. However, the lasing initiation process generates relatively large pressure and temperature (and thus, critically, density) disturbances which propagate upstream and downstream at fluid and acoustic velocities. These disturbances can interact with each other and with other system components and later return to the cavity to degrade subsequent lasing pulses. A quasi‐one‐dimensional numerical fluid analysis program has been developed, using the “discrete element” technique, which permits examination of the various forms of acoustic attenuation being considered for use in such systems. This technique has been used to establish fluid supply system characteristics for an actual 1000‐Hz pulse rate lasing system. A design was arrived at that could supply adequate acoustic attenuation within the required 1 ms. Some details of the numerical technique and correlation with experimental data will be presented. Major emphasis will be on the application of the technique to at least one particular laser system, and a generally applicable convective/acoustic design philosophy, which developed as a result of parameterization studies carried out using the numerical model.

ISSN:0001-4966    

DOI:10.1121/1.2004305

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Brainstem evoked response (BSER) techniques have been developed to study the electrode‐nerve interface in cats implanted with intracochlear stimulating electrode arrays. These methods may be useful in measuring nerve and electrode function in prosthesis recipients. One method is used to estimate the stimulus current level at which neural excitation, generated by one electrode, overlaps the spatial excitation pattern generated by a second electrode. This technique is useful in determining whether each electrode is capable of exciting a restricted and unique sector of the auditory nerve. Initial experiments have confirmed that “The number of excited auditory nerve fibers versus BSER magnitude” can be estimated. Because “BSER magnitude versus stimulus current amplitude” can be noninvasively measured, “The number of excited fibers versus stimulus current amplitude” may be determined noninvasively. With this function and information from previous excitation mapping studies in the inferior colliculus, an estimate of “Fiber threshold versus cochlear place” can be made for most practical bipolar electrodes. [Work supported by NIH Grant ♯NS‐11S04 and NIH Contract ♯N01‐NS‐7‐2367.]

ISSN:0001-4966    

DOI:10.1121/1.2004313

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

For cochlear prostheses, environmental stimuli can be translated into electrical currents in a variety of ways. This study explores some of the variables relevant to prosthetic stimulation using psychophysical and biophysical techniques in an experimental animal model. Macaque monkeys trained to perform a simple reaction time task were used to test thresholds and dynamic ranges for sinusoidal, pulsatile, and white noise electrical stimulation via prostheses implanted in the scala tympani. In addition, biophysical techniques were used to examine current spread and electrode damage in relation to these variables. Results show that stimulus frequency, pulse duration, and stimulus intensity have major effects on threshold and suprathreshold measures while pulse repetition rate, electrode spacing and location, and stimulus waveform have relatively less effect. Limits within which these variables can be usefully manipulated will be discussed. [Supported by NIH grants NS13056 and RR00166.]

ISSN:0001-4966    

DOI:10.1121/1.2004316

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Waveform and latency of BERs elicited by filtered, monaurally presented clicks (major energy, 2.4–7.4 kHz) were determined for Rhesus monkeys,N= 6 (M. mulata) and humansN= 46. Similar measurement conditions were maintained for the two species. BERs derived from monkeys consistently displayed a greater number of identifiable components then did those of humans, particularly at moderate and high click intensities. Values of absolute latency and intercomponent latency difference were foreshortened in Rhesus monkeys compared to these values in humans. The magnitude of this relative foreshortening was found to increase with later components. Possible anatomic bases for the interspecific response differences observed will be discussed. [Work supported by EPA and NIEHS.]

ISSN:0001-4966    

DOI:10.1121/1.2004324

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

An asymptotic long wave technique is applied to a two‐dimensional cochlear model. The method leads to an ordinary differential equation for either the pressure difference across the cochlear partition or the partition velocity. The lowest order approximation appears to be identical to the equation describing one‐dimensional models; the complete approach is equivalent to that of Viergever and Kalker [J. Eng. Math.9, 353–365 (1975) and11, 11–28 (1977)] and that of Sondhi [Proc. 9th ICA, Madrid, ( 1977)], which thus are shown to be long wave methods as well. The validity of the one‐dimensional solution is confined to waves along the basilar membrane whose wavelength λ satisfies λ>>2πh; h is the scalaheight. The presented technique is applicable when λ>2h, which is not only a factor of π, but also an order of magnitude better. The asymptotic approach is especially useful since it makes the physical principles in the cochlea comprehensible. The limited validity however asks for a comparison of the results of the present method with exact numerical results of the two‐dimensional cochlear model, which indeed will be made in the lecture.

ISSN:0001-4966    

DOI:10.1121/1.2004326

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Participation in athletics is a privilege involving both responsibilities and rights. The athlete's responsibilities are to play fair, keep in training, and to conduct himself with credit to his sport and his school. In turn, he has a right to optimal protection against injury and this may be assured through good conditioning and technical instruction, proper regulations and conditions of play, and adequate health supervision. With the number of people involved in all types of recreation in sports, and the high injury rate even in noncontact sports, there is an ever increasing. need to make these activities as safe as possible. There are a number of factors that must be considered if sports and recreational activities are to be kept safe and if proper treatment is to be administered. What is sports medicine? Sports medicine is the study of problems and the application of solution to the problems as they relate to the physiological, psychological, and pathological nature of the athlete. It involves sports, but is not limited to organized athletics; it involves medicine, but is not limited to injuries. Sports medicine concerns itself with the health implications of the organism and physical activity; thus, sports medicine spans the gamut from the highly trained athlete who is endowed with sufficient skill and a physique to participate in modern competitive athletics with great intensity and diversity, to the neophyte “little leaguer,” who often lacks skill and physique and who might play in the vacant lot without supervision.

ISSN:0001-4966    

DOI:10.1121/1.2004328

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The dynamic properties of golf shafts and golf balls were measured. This includes natural frequencies and damping factors. Both steady‐state and transient procedures were used in the test evaluations. Different types of golf shafts were used, including different steel alloys, aluminum, and graphite. Damping values are reported for the entire golf shaft portion, with and without the clubhead. Damping is also reported for smaller sections of the golf shaft by cutting the shaft into three parts and measuring each part. This was done to examine the influence of the manufacturing process since the small diameter end is processed differently from the large diameter end. Golf‐ball measurements were made of a coefficient of restitution which is converted to an equivalent viscous damping factor. This value is reported for different impact velocities and for different types of manufactured balls. This includes the solid ball with and without a covering layer as well as the core wound ball. The significance of the golf shaft and golf‐ball properties is discussed in the light of the entire golf swing and ball impact process. The aim is to assess the possibility of designing and manufacturing a better double impedance match between the initiation of the swing through the final stages of impact with the ball.

ISSN:0001-4966    

DOI:10.1121/1.2004332

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Rapid developments in new materials helped to achieve superior performance in sports equipment. The art of manufacturing skis, tennis racquets, vaulting poles, and fishing rods benefited from many of the so‐called space age materials. Better material properties and light weight contributed to superior achievements by sports enthusiasts, but also gave rise to injuries to the human body or other qualitative deterioration for which damping can be a useful parameter for safety and performance. Experiments describing damping on skis and fishing rods will be shown, indicating how the amplitude of vibration can be reduced without impairing weight and structural performance and, in some instances, improve the quality associated with good performance.

ISSN:0001-4966    

DOI:10.1121/1.2004336

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Rapid improvements in integrated circuit technology have made it possible for complex speech processing algorithms to be implemented in compact, real‐time, low cost circuits. In this session, the evolution of this technology will be traced from early discrete‐component systems up to current practice. In a complementary way, speech processing algorithms will be described structurally so as to reveal the opportunity for custom circuit designs. The session papers describe several such custom devices of wide utility for speech processing research and applications, including both speech analysis and synthesis. A projection of future integrated circuit capability will also be given.

ISSN:0001-4966    

DOI:10.1121/1.2004337

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP