摘要:

Airport noise has been monitored at Oakland International Airport since early 1970s using mobile noise‐monitoring terminals for one week sampling each calendar quarter in order to meet requirements of California state noise regulations. The Port of Oakland has recently installed a permanent airport noise and operations monitoring system that will enable achievement of three primary objectives: (1) gather acoustical data to meet California airport noise standards, (2) remove contribution of overflights from San Francisco International Airport to Oakland's noise exposure map, and (3) develop aircraft flight track measurements and positive identification of aircraft operators for community noise complaint resolution. Noise monitoring systems typically are passive in measuring only noise events. Oakland's system incorporates flight operations data and passive airport surveillance radar data to provide a proactive management tool for monitoring effectiveness of and compliance with existing noise abatement procedures. A discussion of this system will be made regarding its effectiveness in monitoring compliance with noise control procedures and in resolving community noise complaints.

ISSN:0001-4966    

DOI:10.1121/1.2029281

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Most theoretical formulations for the response of small gas bubbles to acoustic pressure fields assume that the ideal gas equation of state is appropriate for calculating the internal pressure of the bubble. While this assumption is adequate at low amplitudes, at higher pressure amplitudes, and thus larger bubble responses, it leads to predictions of internal gas densities that are on the order of, or greater than, those of metals. A more realistic assumption is a van der Waals equation of state for a “real” gas. In the present work a general expression for the pressure inside a bubble containing real gas is provided, as well as expressions resulting from some common simplifying assumptions. In addition, comparisons between calculated bubble responses using either an ideal gas or van der Waals equation are presented. For these computations one of two models for bubble dynamics will be employed: the Gilmore‐Akulichev formulation with temperature estimated polytropically or Flynn's equations in which temperature is calculated exactly. [Work supported by NIH and ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2029289

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Mass transfer of the dissolved gas across a bubble wall during nonlinear spherically symmetric oscillations is studied. Use of an earlier comprehensive model [Prosperettiet al., J. Acoust. Soc. Am.83, 502–514 (1988)] to determine the bubble dynamics avoids the need to usead hocpolytropic assumptions. A numerical technique based on a pseudospectral method is used to determine the dissolved gas concentration in the liquid. This formulation does not require the assumptions made in the classic theory of Eller and Flynn [J. Acoust. Soc. Am.37, 493–503 (1965)]. In some conditions results indicate a significant difference in growth rate predictions when compared to the Eller‐Flynn model. [Work supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2029293

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The sound power per unit cross‐sectional area (specific power) is measured in the ear canal using a three‐probe‐microphone system. Pressure measurements recorded from locations within the core region of the ear canal are utilized to determine the instantaneous intensity of sound waves traveling in the lengthwise direction. A direct time‐domain method provides the specific power contained in waves traveling through the region of the canal containing the microphones. The time average of the instantaneous intensity defines the specific power absorbed by the ear. Furthermore, the time average of the positive part of the intensity determines the incident specific power, or input to the ear, and the time average of the negative part of the intensity determines the reflected, or emitted, specific power. Signal averaged data are collected for pure‐tone sweeps from 4 to 15 kHz. [Work supported, in part, by the Whitaker Foundation and the National Science Foundation.]

ISSN:0001-4966    

DOI:10.1121/1.2029298

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

In vitroexperiments have demonstrated that cochlear outer‐hair cells (OHCs) can detect an increase in the extracellular osmotic pressure and, in response, regulate their internal pressure. Salicylate exposure reduces the turgor in electrically stimulated OHCs suggesting an interference with turgor regulation. Cytoplasmic pressure was determined by placing OHCs in a phosphate‐buffered saline (PBS) solution and increasing the osmotic pressure by dripping a hyperosmotic solution (PBS plus 130 mM raffinose; Osmol = 410–440 mmol/kg) into the chamber. The raffinose perfusion was stopped when cell volume decreased and the osmolarity of the chamber was measured with a vapor pressure osmometer. The cytoplasmic pressure of OHCs in the PBS was 16.1 mmol/kg (±5.7) greater than the PBS. When OHCs were exposed to a PBS solution containing an extra 10 mM NaCl or either 5 or 10 mM Na‐salicylate, the pressure difference between the cytoplasm and the bathing medium was decreased to between −4 to 6 mmol/kg. After 10 min, the pressure difference increased to 11.3 mmol/kg (±5.2) for the NaCl solution and 10.3 mmol/kg (±4.16) for the salicylate solution. [Supported by ONR and NIDCD.]

ISSN:0001-4966    

DOI:10.1121/1.2029303

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

In the characteristic differential equations governing propagation of linear one‐dimensional waves through heterogeneous media, the only properties of significance are the sound speedcand the acoustic impedance ρc. The former occurs in the differential equations governing the (curved) characteristics, while the latter appears in the differential equations governing the evolution of particle velocity and strain along the characteristics. One might attempt to approximate the spatial variation of these material properties in a periodic array of homogeneous layers by smooth interpolating functions. An implicitly stable finite difference representation of the characteristic equations is used in the present work to consider propagation of a transient wave through a bi‐material sequence of layers of thicknessL. Waveforms are compared to those obtained from a model in which the layer properties are taken to vary sinusoidally, such thatρ = ρ0[1 + ε sin(πx/L)]andc = c0[1 + δ sin(πx/L)]. Of particular interest is the case where the wavelength isL, which, according to Floquet theory, represents a condition of uncertain stability for steady‐state waves, but which leads to maximum interference for a harmonic transient wave in the sinusoidally varying medium.

ISSN:0001-4966    

DOI:10.1121/1.2029307

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

For cylindrical and spherical shells without truncation or for flat plates with infinite lateral extent, fundamental shell or plate modes propagate independently without coupling. However, at a joint of two or more plate or shell elements, these modes couple together. If a mode is incident at an oblique angle from one element, it will excite other modes propagating away from the junction in each element. The propagation direction and the excitation strength of each mode can be determined by the following boundary conditions: continuity of displacement at the joint, continuity of rotation about the axis of the joint, and vanishing net force and torque on the joint. These boundary conditions are derived from the assumption that the joint is massless and has rigid cross section but offers no resistance to extension along and twisting about the axis of the joint, and to bending transverse to the axis. To be consistent with thin plate/shell theory, it is necessary to account for the first cutoff mode in addition to the three propagating modes in each plate or shell. Numerical examples will be discussed. [Work supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2029312

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This paper relies highly on a paper by E. Eichler [J. Acoust. Soc. Am.36, 344 (1964)], which contains an analysis of the response of a semi‐infinite, thin plate excited by a time‐harmonic load applied at a stud of width 2aattached to the edge, the remainder being free. Eichler used spatial Fourier transforms in the edge direction to obtain closed form integral expressions for the plate response. The present paper provides full details on the analysis (some of them not yet published) and presents new expressions for the input power fed into the plate. Numerical results covering a wide range ofkaare presented, allowing for a simple physical interpretation in three cases: (a)ka≪ 1: point excitation, (b)ka→ ∞: line (or beam mode) excitation, and (c)ka=O(1): interference effects at intermediate frequencies, which are also present in the simple acoustical analogy of a baffled piston. [Work supported by the TNO Institute of Applied Physics, Delft, The Netherlands.]

ISSN:0001-4966    

DOI:10.1121/1.2029318

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Two prosodic categories are particularly interesting for examining the relationship between phonetic units and articulatory timing because they provide a clear contrast in prosodic function: The durational correlates of “sentence stress” mark constituent peaks (nuclear‐accented syllables), whereas phrase‐final lengthening marks constituent edges. When kinematic patterns are contrasted in nuclear‐accented versus unaccented and phrase‐final versus nonfinal syllables, it seems that final lengthening is a local decrease in stiffness, whereas lengthening for accent is a change in the phasing of the final (consonant) gesture relative to the opening (vowel) gesture. When interaction with overall tempo is examined, however, it is clear that the prosodic function cannot be equated directly with the dynamic parameters, since at slow tempo, phrase‐final lengthening affects phasing rather than stiffness. Thus prosodic structure is not the immediate goal of the dynamic representation. Rather, there must be intermediate representations of the phonetic tasks in terms of a local tempo change (for final lengthening) and an increase in the duration of the “sonority peak” of the syllable (for sentence stress). [Work supported by the NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2029320

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The kinematics of two‐dimensional human jaw motion are presented based on x‐ray microbeam recordings. The relationship between jaw translation and rotation is described and experimental records are compared with simulations based on the equilibrium point hypothesis (λ model). In general, jaw rotation and translation were found to start and end simultaneously and straight line paths were observed when rotation was plotted against translation. Several manipulations suggest that jaw rotation and translation are separately controlled. For example, when jaw movements in speech were examined, the slope of the relationship between rotation and translation varied with the consonant but did not depend on the vowel or speech rate. The kinematic patterns of jaw motion are well accounted for by the λ model. The model demonstrates that separate central commands can be defined associated with jaw translation, jaw rotation, and coactivation of muscles without motion. Central commands may be superimposed to produce combinations of rotation, translation, and coactivation. Empirical patterns can be captured by the model under the assumption of simple constant velocity shifts in equilibrium governed by central commands.

ISSN:0001-4966    

DOI:10.1121/1.2029324

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP