Sound Extinction Research Articles

Slope does not affect autonomous recorder detection shape: considerations for acoustic monitoring in forested landscapes

ABSTRACT To date, there are no published guidelines on how to optimally install recorders on sloped terrain, although slope could potentially affect a recorder’s detection space. This study experimentally investigated the effect of microphone orientation in relation to slope of recorders from two cost classes. We installed four recorders at each plot centre (n = 16), oriented either parallel or perpendicular to the slope. We played standard tones of 1–11 kHz at distances of 10, 20, 40 and 80 m from the recorders. Our two response variables were the presence/absence of each tone (coarse spatial scale) and predicted sound extinction distance (fine spatial scale), which were tested for effects of microphone orientation and sound source direction (SSD). We observed a significant effect of microphone orientation on extinction distance when recorders were perpendicular to the slope at the finer spatial scale as an interaction with SSD, indicating that microphones are biased towards the direction they face. Despite the advertised directionality of most recorder microphones, detection space is not circular. This trend was observed across all frequencies, for both high- and low-cost recorders. Microphone orientation in relation to slope is not an important methodological consideration, instead dominant factors such as frequency and prevailing wind direction drive detection space shape.

Sound extinction by fish schools: forward scattering theory and data analysis.

A model used previously to study collective back scattering from fish schools [Feuillade et al., J. Acoust. Soc. Am. 99(1), 196-208 (1996)], is used to analyze the forward scattering properties of these objects. There is an essential physical difference between back and forward scattering from fish schools. Strong frequency dependent interference effects, which affect the back scattered field amplitude, are absent in the forward scattering case. This is critically important for data analysis. There is interest in using back scattering and transmission data from fish schools to study their size, the species and abundance of fish, and fish behavior. Transmission data can be processed to determine the extinction of the field by a school. The extinction of sound depends on the forward scattering characteristics of the school, and data inversion to provide information about the fish should be based upon a forward scattering paradigm. Results are presented of an analysis of transmission data obtained in September 1995 during an experiment performed in the Gulf of Lion in the Mediterranean Sea [Diachok, J. Acoust. Soc. Am. 105(4), 2107-2128 (1999)]. The analysis shows that using forward scattering leads to significantly larger estimates of fish abundance than previous analysis based upon back scattering approaches.

Preoperative planning of calcium deposit removal in calcifying tendinitis of the rotator cuff - possible contribution of computed tomography, ultrasound and conventional X-Ray.

BackgroundThe purpose of the present study was to investigate the accuracy of Ultrasound (US), conventional X-Ray (CX) and Computed Tomography (CT) to estimate the total count, localization, morphology and consistency of Calcium deposits (CDs) in the rotator cuff.MethodsUS, CX and CT imaging was performed pre-operatively in 151 patients who underwent arthroscopic removal of CDs in the rotator cuff. In all procedures: (1) total CD counts were determined, (2) the CDs appearance in each image modality was correlated to the intraoperative consistency and (3) CDs were localized in their relation to the acromion using US, CX and CT.ResultsUsing US158 CDs, using CT 188 CDs and using CX 164 CDs were identified. Reliable localization of the CDs was possible with all used diagnostic modalities. CT revealed 49% of the CDs to be septated, out of which 85% were uni- and 15% multiseptated. CX was not suitable for prediction of CDs consistency. US reliably predicted viscous-solid CDs consistency only when presenting with full sound extinction (PPV 84.6%) . CT had high positive and negative predictive values for detection of liquid-soft (PPV 92.9%) and viscous-solid (PPV 87.8%) CDs.ConclusionUS and CX are sufficient for preoperative planning of CD removal with regards to localization and prediction of consistency if the deposits present with full sound extinction. This is the case in the majority of the patients. However, in patients with missing sound extinction CT can be recommended if CDs consistency of the deposits should be determined. Satellite deposits or septations are regularly present, which is of importance if complete CD removal is aspired.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2474-15-385) contains supplementary material, which is available to authorized users.

Pilomatrixoma - an important differential diagnosis of facial masses

Pilomatrixoma are rare tumors usually arising from the sebaceous glands in the subcutaneous tissue. They are the most frequent superficially localized tumors of the cheek and parotid region in children. About 20% of all tumors in this area in children are pilomatrixoma. Currently there are only a few studies in the literature which describe characteristic findings in these tumors. The purpose of the present study was to describe clinical, sonographical and morphological characteristics of these rare tumors. Clinical records of 6 patients which were operated on for a pilomatrixoma were retrospectively analyzed. All tumors were completely excised followed by an histopathological examination on H&E stained specimens. All patients reported about a slowly growing painless mass in the parotid area or nuchal. Sonographically tumors displayed as hyperechoic masses with a dorsal sound extinction, due to hypercalcification. Histopathologically all tumors were characterized by typical basaloid and ghost cells, accompanied by a foreign-body reaction. Pilomatrixoma are an important differential diagnosis of unclear masses in the head and neck especially in children. The sonographical characteristics are variable and unspecific. A fine-needle aspiration biopsy is not recommended, since false malignant cytologic findings occur quite often. Therapeutically complete excision is required. Usually no adjuvant therapy is necessary, and the prognosis is good.

Experimental study of targeted energy transfer from an acoustic system to a nonlinear membrane absorber

Abstract This paper deals with the application of the concept of targeted energy transfer to the field of acoustics, providing a new approach to passive sound control in the low frequency domain, where no efficient dissipative mechanism exists. The targeted energy transfer, also called energy pumping, is a phenomenon that we observe by combining a pure nonlinear oscillator with a linear primary system. It corresponds to an almost irreversible transfer of vibration energy from the linear system to the auxiliary nonlinear one, where the energy is finally dissipated. In this study, an experimental set-up has been developed using the air inside a tube as the acoustic linear system, a thin circular visco-elastic membrane as an essentially cubic oscillator and the air inside a box as a weak coupling between those two elements. In this paper, which mainly deals with experimental results, it is shown that several regimes exist under sinusoidal forcing, corresponding to the different nonlinear normal modes of the system. One of these regimes is the quasi-periodic energy pumping regime. The targeted energy transfer phenomenon is also visible on the free oscillations of the system. Indeed, above an initial excitation threshold, the sound extinction in the tube follows a quasi-linear decrease that is much faster than the usual exponential one. During this linear decrease, the energy of the acoustic medium is irreversibly transferred to the membrane and then damped into this element called nonlinear energy sink. We present also the frequency responses of the system which shows a clipping of the original resonance peak of the acoustic medium and we finally demonstrate the ability of the nonlinear absorber to operate in a large frequency band, tuning itself to any linear system.

Prognostic factors in nonoperative therapy for chronic symptomatic calcific tendinitis of the shoulder

To define prognostic factors in chronically symptomatic patients with calcific tendinitis of the shoulder. We evaluated 420 patients (488 shoulders) in the context of a prospective cohort study. Epidemiologic data were assessed. The radiographic and sonographic appearance of the calcific deposits was classified. The mean period of nonoperative therapy was 4.4 years (range 0.5-13.7 years). After referral to our institution, standardized nonoperative therapy was continued for a minimum of 3 months. Failure of nonoperative therapy was defined as the persistence of symptomatic calcific tendinitis of the shoulder after a minimum of 6 months. Prognostic factors (determined at P < 0.05 by chi-square test) were analyzed by logistic regression. Of the 420 patients, 269 (64%) were women, 151 (36%) were men. The mean age of the patients was 51.3 years (range 28-84 years). Occurrence of calcific tendinitis of the shoulder was unilateral in 84% and bilateral in 16%. Gärtner type I calcific deposits were found in 37%, type II in 32%, and type III in 31%. Failure of nonoperative therapy was observed in 114 patients (27%). Negative prognostic factors were bilateral occurrence of calcific tendinitis of the shoulder, localization to the anterior portion of the acromion, medial (subacromial) extension, and high volume of the calcific deposit. Positive prognostic factors were a Gärtner type III deposit and a lack of sonographic sound extinction of the calcific deposit. Our findings demonstrate the existence of prognostic factors in the nonoperative treatment of chronic symptomatic calcific tendinitis of the shoulder. Guidelines for optimal treatment can be implemented according to these factors to avoid a long-term symptomatic disease course.

Energy pumping in acoustics

Energy pumping corresponds to a particular vibratory regime of a non‐linear system coupled to a linear primary structure. Its non‐linear behaviour allows to reduce vibrations of the primary structure, and is thus a new passive vibration control technique. This phenomenon has mainly been studied in mechanical engineering, so we transposed its principle to noise control in an acoustic medium. The presentation will focus on results about acoustic energy pumping that we observed both experimentally and numerically, in the time and frequency domains. These results highlight two main points: physically, energy pumping corresponds to an irreversible transfer of energy from the primary system to the non‐linear absorber, and practically, its effects are a noise level limitation in the acoustic medium in permanent regime and a much faster sound extinction in transient regime.

Localized and cumulative nonlinearity in wind instruments

Nonlinearities are very common in wind instruments. A crucial one localized at the input of the wind instrument is responsible for the sound production mechanism. As an illustration, some recent measurements done at clarinet mouthpieces will be shown. Some other localized nonlinear effects take place at the open tube ends. They imply extra losses whose amount depends on the internal geometry of the termination. They control the sound extinction phenomena. It will be shown how the playing range of a clarinet-like instrument is determined by these extra losses. Besides localized nonlinearity, cumulative nonlinearity effects are present as well. The cumulative nonlinear propagation phenomena along the tube of brass instruments can lead to shock waves obtained when the player is playing very loudly with a ‘‘brassy sound.’’

Some aspects of sound extinction by zooplankton.

To address the importance of sound extinction (or the shadowing effect) in the presence of a densely aggregated zooplankton layer, acoustic scattering by weakly scattering fluid objects is studied theoretically. An analytical expression for the extinction cross section is obtained based on the forward scattering theorem and the analytical formula for the forward scattering amplitude is derived from the Modal Based-Deformed Cylinder Model (MB-DCM). The validity of the MB-DCM solution for the forward scattering amplitude and its sensitivity to geometrical and physical parameters is studied. Comparison with the PC-DWBA (Phase-Compensated-Distorted Wave Born Approximation) shows a reasonable agreement between the two models. The extinction cross section is shown to be proportional to (ka)2 and the induced attenuation is predicted for various species of zooplankton over a wide frequency range. It is shown that, under certain realistic conditions, such as the presence of a swarm of aggregated krill, sound extinction by zooplankton could influence the acoustic measurements significantly, as much as an 85% reduction in acoustic intensity for Euphausia superba with n = 5000 ind./m3 over a range of 50 m.

Evaluation of Carotid Artery Stenosis by Power Doppler Imaging

To the Editor: Steinke and coworkers1 recently reported on the possible advantages of power Doppler imaging (PDI) for quantification of stenoses of the internal carotid artery (ICA): similar to angiography, it should be possible to assess the degree of stenosis of the ICA as the percentage of the diameter reduction from the longitudinal image. We have tested this examination procedure by comparison with the usual, validated sonography criteria on 40 cases of ICA stenosis. Included in the observation period of the study were all consecutive stenosis findings for which color-coded duplex sonography (CCDS) fulfilled the following criteria: (1) detection of a local flow acceleration in the ICA, (2) peak flow velocity of ≥1 m/s (measurement of the jet flow at the stenosis maximum or, in cases of sound extinction there, directly distal from it), and (3) detection of flow disturbances. Quantification was achieved using the known Doppler criteria.2 In 22% of the cases an adequate evaluation by PDI was not possible: in 6 stenoses the residual lumen could not be demonstrated because of sound extinction; in an additional 3 stenoses, the vessel wall could not be imaged adequately for determination of the degree of stenosis. In the remaining cases the degree of stenosis was regularly underestimated in comparison with the Doppler criteria (Figure 1⇓). Figure 2⇓ illustrates this for the example of a high-grade stenosis of the ICA: the stenosis is very poorly demonstrated in the PDI (panel A). Angiography and conventional CCDS findings with determination of the peak systolic velocity were in agreement, and both revealed the high-grade stenosis (panels B and C). The problem of underestimation …

On acoustic attenuation by swimbladder fish

This letter presents a theoretical study of sound attenuation by swimbladder fish. Since the sound attenuation is related to the sound extinction cross section, the focus of the letter is on theoretical calculation of the extinction cross section of swimbladder fish. A forward scattering theorem is used for the purpose. Based on simple scattering models for swimbladder fish, the frequency dependence of the extinction cross section is obtained. The result shows that while the air-filled swimbladder dominates the forward scattering of sound at low frequencies, the fish body may dominate the forward scattering in the high-frequency range. Without fitting parameters, the theoretical results compare favorably with some existing experimental data.

Acoustic sounding of rain intensity

The numerical solution of the scalar wave equation is generalized for the case of a polydispersed medium. The analytical expressions are given for the dependence of sound extinction on the intensity of rain and acoustic frequency. The method of acoustic sounding of rain intensity proposed on the basis of these analytical expressions is theoretically analyzed.

A bistatic scheme for radioacoustic sounding of the atmosphere

Abstract The problem of radioacoustic sounding of the atmosphere is considered with diffraction effects taken into account for the bistatic scheme of sounding. Formulae are obtained for the power and frequency of the scattered signal. The influence of wind displacement, sound extinction and the finite dimensions of wave packets upon the scattered signal frequency is proved to be significant and should be taken into account mainly for the calculation of power characteristics

Societies and Academies

Societies and Academies