摘要:

When blood particles travel through an intravascular ultrasound imaging plane, the received echo signals decorrelate at a rate that is related to the flow velocity. In this paper, the feasibility of extracting blood velocity from the decorrelation function of radio frequency signals was investigated through theoretical analysis and computer simulation. A computer model based on the impulse response method was developed to generate the ultrasound field of a 30-MHz intravascular transducer. The decorrelation due to the scatterer displacement as well as other nonmotion related decorrelation sources were studied. The computer simulations show that the decorrelation function is linearly related to the lateral displacement. The monotonic relationship between correlation and displacement provides possibilities to estimate flow velocity with decorrelation measurements. Because of the complexity of the beam profile in the near field, assessment of local velocities requires detailed knowledge of the decorrelation at each axial beam position. Sources of signal decorrelation other than the lateral displacement may cause a bias in the decorrelation based velocity measurements. For localized decorrelation estimation, measurement variations in small range windows present a major challenge. An approach based on multiple decorrelation measurements should be adopted in order to reduce the variations. In conclusion, results of this study suggest that it is feasible to measure flow velocity by quantifying the decorrelation of intravascular ultrasound signals from blood.

ISSN:0001-4966    

DOI:10.1121/1.420141

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Notch-noise masking was used to measure frequency tuning in a dolphin (Tursiops truncatus) in a simultaneous-masking paradigm in conjunction with auditory brain-stem evoked potential recording. Measurements were made at probe frequencies of 64, 76, 90, and 108 kHz. The data were analyzed by fitting the rounded-exponent model of the auditory filters to the experimental data. The fitting parameter values corresponded to the filter tuning as follows:QER(center frequency divided by equivalent rectangular bandwidths) of 35 to 36.5 andQ10 dBof 18 to 19 at all tested frequencies.

ISSN:0001-4966    

DOI:10.1121/1.420142

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Large liquid drops were deformed by an acoustic standing wave in a resonant air chamber called the Drop Physics Module, which was carried on Space Shuttle Columbia as part of the second United States Microgravity Laboratory mission. When this deforming force was suddenly reduced, the drops executed free oscillations about a perfect spherical equilibrium. The complex frequency of these oscillations was measured. The first results from a series of experiments are presented here. Results for pure water compare favorably with fundamental theoretical predictions. Drops containing aqueous solutions of soluble surfactants exhibited remarkable differences in both frequency and damping, and these are explained phenomenologically by a discussion of the multiple time scales introduced by the addition of surfactants.

ISSN:0001-4966    

DOI:10.1121/1.420405

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Natural frequencies of two-span beams have been studied in the presence of different amounts of deterministic disorder (mistuning) arising from displacement of the intermediate simple support (prop) to different locations away from its tuned (periodic) position. The two beam-segments are assumed to be fully (strongly) coupled in the absence of any torsional constraint offered by the prop. Conditions under which the beam systems with different end conditions and support locations have the same natural frequencies have been identified and explained. Unlike the tuned multi-span beams, the natural frequencies of disordered beams with extreme ends simply supported and clamped have been found to coincide even when they do not belong to the same group(s) of natural frequencies. The deflection mode shapes and the phenomenon of normal mode localization have been presented and discussed for some specific prop locations. Conditions have been identified under which the disordered beams can behave as ordered (tuned, periodic) beams and their normal modes become perfectly collective with peak deflections exactly the same in both spans. Normal modes of fully coupled multi-span beams can become and appear to be strongly localized only if they are strongly disordered. Just as in the case of periodic beams, study of natural modes of two-span disordered beams is also helpful in understanding the natural modes of disordered beams having more than two spans.

ISSN:0001-4966    

DOI:10.1121/1.420406

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

In this paper the extent to which the response of a linear cochlear model has the “minimum-phase” property is discussed, along with the topic of what it should mean when experiments confirm or deny the validity of minimum-phase in the response of the actual cochlea. This paper shows that short-wave, long-wave and three-dimensional cochlear models of the “classical” type, in which the operation of the cochlear partition is described by alocalfunction (namely, a driving-point impedance) that produces a cochlear map (from frequency to place), have a response that is minimum-phase, or very close to minimum-phase. Conversely, when the response is found to be non-minimum-phase, the best-fitting model cannot be a classical one.

ISSN:0001-4966    

DOI:10.1121/1.420356

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

43.40.Dx, 43.40.Rj, 43.10.Vx [CBB]

ISSN:0001-4966    

DOI:10.1121/1.421018

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.420287

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.420283

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP