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In this paper, using a large venue as the scene of the crowd evacuation, we put forward a crowd evacuation model based on ellipse sound wave diffusion, and analyse the impact to the evacuation time caused by various factors such as the area of the venue, the population density, the width of the door, the number of doors, the proportion of men and women, the proportion of the old and the young. We use MATLAB to simulate our model, and the simulation results show that our model has certain advantages in the evacuation time and can offer some reference for realistic evacuation.

The scattering problem of acoustic wave by pre-fractal curvilinear rings system is considered. Making use of the integral equation technique, three dimensional mathematical model is reduce to two dimensional one. Application of the mechanical cubature method to the case of the parabolic ring is analyzed.

We consider the classification utility of time- domain moment-like features of a wave that are invariant to dispersion and damping. Simulations of the sonar backscatter from metallic shells in a dispersive, damped waveguide are conducted for single mode and multi-mode propagation. Random variations in the waveguide parameters are also investigated. Results show our invariant moment features have greater discriminability, as quantified by ROC curves, at low false alarm rates when compared to ordinary temporal moments, and the invariant features perform best for single mode propagation.

Here we address the problem of remotely interrogating the shallow subsurface of soil using low power mechanical energy transmission and sensing the subsequent backscattering from the soil bed to find small buried objects at very shallow depths (~ 15 cm or less). The effort is geared towards the development of better technologies for the remote detection and imaging of buried land mines, improvised explosive devices (IEDs) and other undesirable objects. We present our studies against the backdrop of what is known in this field today. Our ongoing work is briefly summarized with an outline of the underlying physics of acoustic backscattering from shallow buried objects and of how such backscattering can be inexpensively and remotely detected and interpreted for possible use in automated mine clearance operations.

During The Technical Cooperation Program's T-MAST 02 sea trial in July of 2002, direct-path measurements of bottom backscattering strength were made at 2-5 kHz at 18 sites on the Outer Hebrides Platform and the Stanton Banks (west of Scotland). This is a complex area, with sediment types including mud, sand, gravel and bedrock, and strewn throughout with stones, pebbles, and rocks. When stones, etc. were present in accompanying bottom grabs, bottom backscattering strengths were generally high and flatfish in angle (over 10 to 40 deg), with many sites empirically exhibiting a sinthetas or flatter angular dependence. The frequency dependence in these cases was mild. When stones, etc. were absent, bottom backscattering strengths were less high and less flat in angle, with stronger frequency dependence. These results illustrate the inadequacies of using Lambert's Law to model bottom backscattering strengths, as well as relying on archival databases, and argue for in-situ environmental characterization

We formulate a time harmonic acoustic inverse scattering problem involving a smart obstacle and we propose a method to solve it. The smart obstacles have been introduced to model obstacles that when hit by an incoming wave take actions to try to make difficult their identification. We restrict our attention to time harmonic problems. In this case a natural way of formulating the direct problems for the smart obstacles is, Acoustic Time Harmonic Smart Direct Scattering Problem. we concentrate our attention on two kinds of smart obstacles: furtive obstacles and masked obstacles.

Resonances for close shells are studied. This work is a comparison between experimental data and numerical results of a previous paper (P.Y. Le Bas et al, J. Acoustic Soc. Am., no.115(4), p.1460-1467, 2004). For shells close enough, a split of A-waves resonances of one shell is shown. For N aligned shells, N resonances are shown in eclipse configuration. For other incidence angles, each of them seems to split again. For shells at the apexes of a triangle, an extra resonance appears.

Ultrasound contrast agent applications have expanded in recent years to the assessment of perfusion and microvascularity. A new system that measures the acoustic properties of single microbubbles can provide information that can shed new light on contrast enhanced imaging. A polymer shelled agent, BiSphere/sup /spl reg// (Point Biomedical, San Carlos, CA, USA) was used. A very diluted hydrodynamically focused flow of microbubbles was exposed to ultrasound beams of 1 to 4 MHz transmit frequency and 0.2 to 1 MPa peak negative pressure. RF data were captured using an ultrasound scanner (Sonos5500, Philips, Andover, MA, USA). The microbubbles were subjected to consecutive triggered pulses and their survival rate was also assessed. At 0.5 MPa fundamental scattering cross section (SCS) was maximum below 1.5 MHz, while the second harmonic SCS was constant up to 2.3 MHz and greater than the fundamental between 2 and 2.4 MHz. A strong ultraharmonic was present in the majority of the scattered echoes above 0.8 MPa. At 0.5 MPa the microbubble echoes disappeared after the first insonation, suggestive of rapid dissolution. In conclusion BiSphere/sup TM/ displayed compatibility with myocardial perfusion requirements, but most importantly the investigated scattered pulses provided spectral and temporal characteristics that could be used to optimise ultrasound examinations.

Detailed computer modeling has conclusively shown that out-of-plane scattering and small-scale bathymetric roughness influence the backscattered acoustic intensity in nontrivial ways for acoustically hard surfaces such as sand, gravel, shells and rock. This paper presents a preliminary technique for including these effects statistically in sonar performance modeling by adjusting the sea floor material parameter presently used in sonar models to account for them.

It is attempted to explain some backscattering strengths measurements by means of plane wave theories of scattering from a fluid sediment. In the absence of a precise knowledge of the physical properties of the sediment, the interpretation is not evident. Nevertheless, vertical insonification appears to be a useful tool.

Accurate acoustic interpretation of zooplankton scattering data requires a reliable knowledge of the material properties of the zooplankton. The lack of ability in predicting or measuring in situ material properties of these marine animals greatly affects and limits the capability to estimate the zooplankton biomass acoustically. To provide in situ measurements of the material properties, a new apparatus, the Acoustic Properties Of zooPlankton, (APOP) was developed. The system combines acoustic and resistivity measurements and can be used for in situ applications. This system can be operated under various environmental conditions (temperature and pressure). In addition, a new method (dual-density) of measuring density of live zooplankton is presented. A series of laboratory and in situ measurements were made on various marine organisms using the APOP system. The results from these measurements suggest that the material properties obtained from laboratory measurements, even if they are accurate and reliable under certain environmental conditions, may vary significantly in the ocean under different environmental conditions. Therefore, to correctly model and interpret the zooplankton acoustic survey data, one needs to take into account the variations in zooplankton material properties as a function of the environmental conditions, or oceanographic parameters.

Ultrasound is useful in evaluating the integrity of silicone breast implants, but is highly operator dependent. A system for computer assisted image interpretation is being developed to reduce operator dependability. Feasibility was examined by measuring the ultrasonic properties of breast implants in vitro. Silicone gel from 17 explanted devices (11 intact and 6 ruptured) were placed in sealed acoustic test chambers and 60 RF A-lines were acquired from each. The mean speed of sound was 1073 m/sp53.76 m/s in intact implants and 1120 m/sp32.34 m/s in ruptured ones (pl0.05). The difference in attenuation between intact and ruptured devices was not statistically significant. The mean integrated backscatter was -68.7 dBp8.98 dB in intact prostheses and -62.8 dBp7.46 dB in ruptured implants. This result shows statistical significance on a 10% level. Changes in speed of sound and integrated backscatter of silicone breast implants have been demonstrated in vitro. While more implants need to be evaluated, the results do indicate the potential for quantitative assessment of the integrity of silicone breast implants performed in vivo