Particle Velocity Signals Research Articles

Microacoustics: maintaining an ecologically relevant scale in insect bioacoustics

A major challenge when studying an organism is to maintain its environment and context as reliably as possible. When looking at sensory systems it is crucial not to assume the animal's perception the same as ours and instead measure and mimic more accurately the natural stimuli driving the sensors. In insect bioacoustics the usual practice in playback and recording techniques overlooks differences in scale and context in which the organism's sensory system evolved. Here we present an approach to emit and record low‐amplitude near‐field sound, while maintaining an ecologically relevant scale, in Drosophila melanogaster. To mimic the effect of male courtship song on the female sound receiver (antennae) a mechanical microwing was constructed simulating, in power and geometry, particle velocity signals emitted by singing males, with its efficacy tested by behavioural assay. Development of a miniature particle velocity microphone was also initiated for recording signals in the fly's immediate vicinity (<2 mm) to elucidate the magnitude, temporal and radiation characteristics of the produced sound‐field.

The solid flow structure in a circulating fluidized bed riser/downer of 0.42-m diameter

Local transient solid fraction and particle velocity signals were measured in a 0.418-m I.D. and 18-m high large-scale circulating fluidized bed (CFB) by a dual-optical fiber density probe and a Laser Doppler Velocimeter (LDV) system. The probability density distributions (PDD) of transient solid fraction and particle velocity show bimodal distributions in the riser, while in the downer, the PDD curves only exhibit single peak distribution. The results indicate that two-phase solid flow structure exists in the riser: i.e. a dense cluster phase and a dispersed particle phase. Although there are solid aggregations in the downer, the solid concentration of which is much lower than that in the riser, and they could not form a dense cluster phase with solid fraction 1−εmf as those in the riser. From the analysis and comparison of transient solid fraction signal and the PDD of solid fraction and particle velocity in the riser and downer, it is clear that significant difference exist in the solid flow structure and the particle cluster mechanism between the gravity-assisted gas–solid flow in the downer and the against-gravity flow in the riser.

Wavelet analysis of turbulence in the glottal jet flow

Airflow from the lungs drives the vocal folds into oscillation and exits the glottis as a turbulent jet, even though laminar flow is documented entering the glottis. Incomplete glottal closure may result in air leakage that becomes turbulent. This turbulence is thought to be the main source of breathiness in the voice. Few studies have measured degree of turbulent noise in the glottis. This turbulent noise adds significant amounts of energy to the voice signal and cannot be extracted easily without changing the voice. In this study, the turbulent jet was investigated in an excised canine larynx model with simultaneous recordings of air particle velocity, subglottal pressure, airflow rate, and EGG signal for various conditions of phonation. The velocity was measured with a constant-temperature hot-wire anemometer system. To separate the turbulence from the periodic component of the velocity signal, the technique of wavelet denoising was employed. In this method, unlike the Fourier transform which decomposes the signal into periodic components, wavelet denoising uses template matching transform to approximate the signal with different resolution or scale. Results indicate that the high resolution part contains the turbulent noise. [Work supported by NIDCD Grant No. R01 DC03566.]

On unified dual fields and Einstein deconvolution

In many physical phenomena, the laws governing motion can be looked at as the relationship between unified dual fields which are continuous in time and space. Both fields are activated by a single source. The most notable example of such phenomena is electromagnetism, in which the dual fields are the electric field and the magnetic field. Another example is acoustics, in which the dual fields are the particle‐velocity field and the pressure field. The two fields are activated by the same source and satisfy two first‐order partial differential equations, such as those obtained by Newton’s laws or Maxwell’s equations. These equations are symmetrical in time and space, i.e., they obey the same wave equation, which differs only in the interface condition changing sign. The generalization of the Einstein velocity addition equation to a layered system explains how multiple reflections are generated. This result shows how dual sensors at a receiver point at depth provide the information required for a new deconvolution method. This method is called Einstein deconvolution in honor of Albert Einstein. Einstein deconvolution requires measurements of the pressure signal, the particle velocity signal, and the rock impedance, all at the receiver point. From these measurements, the downgoing and upgoing waves at the receiver are computed. Einstein deconvolution is the process of deconvolving the upgoing wave by the downgoing wave. Knowledge of the source signature is not required. Einstein deconvolution removes the unknown source signature and strips off the effects of all the layers above the receiver point. Specifically, the output of Einstein deconvolution is the unit‐impulse reflection response of the layers below the receiver point. Compared with the field data, the unit‐impulse reflection response gives a much clearer picture of the deep horizons, a desirable result in all remote detection problems. In addition, the unit‐impulse reflection response is precisely the input required to perform dynamic deconvolution. Dynamic deconvolution yields the reflectivity (i.e., reflection‐ coefficient series) of the interfaces below the receiver point. Alternatively, predictive deconvolution can be used instead of dynamic deconvolution.

Turbulent glottal flow during phonation

Human phonation is the flow-induced oscillation of the vocal folds, producing pulsatile jet through the glottis, which may become turbulent. This turbulent jet was investigated in an excised canine larynx model with simultaneous recordings of air particle velocity, subglottal pressure, airflow rate, and EGG signal for various conditions of phonation. Canine larynges were mounted on a plastic air tube and sustained oscillations were established and maintained by mechanically manipulating the cartilages to mimic the function of laryngeal muscles. The major control parameters were the airflow rate and the glottal adduction. The velocity was measured with a constant-temperature hot-wire anemometer system. To separate the turbulence from the periodic component of the velocity signal, the technique of phase shift averaging was employed. Results suggest that subglottal inlet flow to the larynx is pulsatile but mostly laminar, while the exiting jet is nonuniform and turbulent. The Reynolds number based on the mean glottal velocity and glottal hydraulic diameter varied between 1600 and 7000, the Strouhal number varied between 0.002 and 0.032, and the Womersley number ranged from 2.6 to 15.9. These results help define the conditions required for computational models of laryngeal flow. [This work was supported by NIDCD Grant No. DC03566-01.]

Evaluation of the air particle velocity signal from the binaural pressure impulse response

From the Lagrangian theory in linear acoustics one clearly infers that the generalized momenta of the sound field are the acoustic pressure and the three components of the air particle velocity. This means that only through the knowledge of the full set of these four quantities a complete physical identification of the sound field can be achieved. The binaural technology represents an important tool for this goal, since it offers a method for reconstructing the pressure sound field by means of a couple of pressure impulse responses measured in two close points. An additional improvement of the binaural signal processing can be obtained using the two pressure input signals for evaluating the velocity component along the direction determined by the measurement points. First the velocity impulse response component is evaluated by means of the Euler equation and then, by convolving this signal with the usual anechoic signal, the velocity is reconstructed. In this paper the rigorous mathematical procedure for accomplishing the above task is presented.

Acoustico-Lateralis System of Fishes: Cross-Modal Coupling of Signal and Noise in the Grunt, Haemulon parrai

Behavioral studies on sailor's choice (bony shallow-water fish) determined that, at 200 Hz, sonic particle velocity noise received by the lateral line did not mask a sonic pressure signal received by the ear; but sonic pressure noise received by the ear can mask the sonic particle velocity signal received by the lateral line. At 50 Hz, the fish failed to respond to the pressure signal, but pressure noise was still coupled into the velocity-sensitive lateral-line system.