Search

The primarily aim of this work is to investigate the feasibility of using an unfocused acoustic transducer for monitoring of blood perfusion. The current market available technology for clinical assessment of blood perfusion, which include Positron Emission Tomography (PET) and ultrasound imaging, lacks portability. Meanwhile the performance of photoplethysmography (PPG) is subjected to motion artifacts. A single point of transducer is used in this study to identify the blood perfusion in a group of four human volunteers. This technology is based on phase signals obtained from acoustic waves collected for different experimental conditions, which are at rest, warm water and blood flow occlusion conditions. It was found that phase difference is proportional to the changes in velocity of blood flow within vessels. The mean and standard deviation of phase changes for these volunteers are calculated as 0.446° ± 0.087° and -0.427° ± 0.105° for warm water and occlusion experimental condition, respectively. This work concluded that the capabilities and simplicity of this employed system renders it a promising technique for non-invasive assessment and visualization of blood perfusion and to predict blood flow rate within microcirculation environment. [ABSTRACT FROM AUTHOR]

Temperature measurement by acoustic is a new kind of temperature visualization measurement technology. It is very important to develop three-dimensional temperature field reconstruction algorithm in acoustic application. In order to get the three-dimensional temperature field distribution, a three-dimensional temperature field reconstruction algorithm based on multi-objective optimization is proposed in this paper. A multi-objective optimization model is set up considering least square criterion, smoothness criterion and maximum entropy criterion. Numerical experiments show that the algorithm of image quality is improved obviously compared with that of least squares algorithm. [ABSTRACT FROM AUTHOR]

The indoor environment much more important for people health and comfort than the outdoor environment. This scenario would make the performance of occupants at their work more important than energy costs in the building. So, this task is to upgrade indoor environmental quality conditions for comfort and work performance of occupants in Kompleks Eureka, USM while conserving energy of the building.. Recent studies have shown an important impact of the indoor thermal environment on occupants' work performance. Also studies on occupants medical leave show a very high loss of work time and working performance, which have important economical consequences for companies. The paper will mainly dealing with the indoor environmental qualities, such as thermal comfort level, air quality, lighting, and acoustic quality. The studies before showing that comfortable room temperatures, increased air ventilation above normal recommendation, comfortable acoustic surrounding will increases the work performance of occupants in Kompleks Eureka, USM. [ABSTRACT FROM AUTHOR]

Low-order moment around the mean (mean, standard deviation and skewness) analysis of the time evolving acoustic emission of an air atmospheric pressure plasma jet is performed as a function of nozzle-to-surface gap (7 to 0.5 cm), drive frequency (19 and 25 kHz) and air flow rate (35.7 and 76.6 l/m). The shapes of the probability distribution of each measurement dataset (containing 433 samples) are found to exhibit deterministic correlations with contrasting entropy process regions. The results indicate that the heated air is channeled along the surface and has a preferred backscatter angular distribution. Separation between the blown arc process (gap = 0.5 cm and 1740 ±100 K) and the afterglow (gap = 1 to 7 cm and 300-400 K) is observed in the mean acoustic amplitude and standard deviation. In addition the blown arc process exhibits a skewness of +0.055 and the afterglow has skewness values from -0.05 to -0.4. These results illustrate how acoustic information can be used to differentiate plasma-surface entropy states. [ABSTRACT FROM AUTHOR]

Sand on the leeward face of a large desert dune may create a persistent, low-frequency sound during a slumping event or natural avalanche. The sound may last for several minutes and be audible at far distances. The current manuscript describes the waveguide model and presents the mathematical derivation for the booming frequency from the waveguide model. The spatial and temporal variations of the waveguide influence the ability of a dune to produce the mysterious sounds of the desert. [ABSTRACT FROM AUTHOR]

Large (>100 W cooling capacity at 80 K) ‘pulse-tube’ coolers are ideal candidates for emerging applications such as HTS transmission lines, transformers, and motor windings, meso-scale oxygen liquefaction on-demand, cryopumping, and cryogen boiloff recovery. A number of successful large ‘in-line’ pulse-tube coolers have been built, but these require embedded shell-and-tube process heat exchangers, hence transport of the process fluid/gas to and from the coldhead, and often a high degree of process fluid purity, to avoid clogging in the narrow inlets and outlets of these heat exchangers. It is far preferable in most circumstances to have a coldfinger design that presents a salient cold tip, with the coldhead at the end of a flexible transfer line, as is done with Gifford-McMahon or Joule-Thomson coolers. This paper presents some design details and data from the development of our first high-capacity coldfinger, as well as the results of its application to a 55 gallon/day oxygen liquefier for the Navy. [ABSTRACT FROM AUTHOR]

The spatial damping of acoustic, neutron and thermal branches of oscillations are found in neutron multiplying medium with coolant. All three branches give additive contribution to the neutron density oscillations. However, their wave numbers and coefficients of spatial damping (at the same frequency) differ greatly from the sound with its high phase velocity and small attenuation to the neutron wave with the damping length, which is comparable with its wavelength. A spatial growth of neutron density oscillations is found in the case of large frequency of neutron capture and weak coupling of neutron density and temperature branches of oscillations. This fact is of importance for the noise diagnostics of the multiplying medium with coolant. The results can be applied to the development of the methods of noise diagnostics of the in core reactor equipment. [ABSTRACT FROM AUTHOR]

Polymer piezoelectric materials offer lower density and more flexibility than piezoelectric ceramics for applications where rugged and lightweight acoustic sensors are required. This paper discusses constraints imposed by material stiffness and dielectric constants and aims to derive a generalized closed-form solution for optimizing charged foamed polymers. Optimized solutions are reached in the limits of very large and small void fraction and permittivity ratio. The permittivity ratio is the ratio of the dielectric constants of the polymer and the material that fills the voids. Demonstrations indicate that, in the oblique asymptote, the optimized void fraction becomes equivalent to the permittivity ratio. This effort was conducted under the auspices of the Undersea Warfare Business Area (UWBA) Independent Research & Development (IRAD) Board of the Johns Hopkins University Applied Physics Laboratory (JHU/APL). [ABSTRACT FROM AUTHOR]

A newly developed optimization based method is followed to locate the point of impact in anisotropic composite plates for which conventional triangulation technique fails. The new technique works for both anisotropic and isotropic plates. Experiments are carried out by dropping a steel ball on a graphite-epoxy composite plate and picking up acoustic signals by passive transducers adhesively bonded to the plate at different locations. Predicted points of impact are compared with the true impact point. [ABSTRACT FROM AUTHOR]

The ultrasonic wave velocity and the thermal expansion of the rare earth glasses have been measured as functions of temperature and pressure to test predictions of the soft potential model for the acoustic and thermal properties. The longitudinal ultrasonic wave velocities increase under pressure. The hydrostatic pressure derivative of the bulk modulus is positive: these glasses show a normal elastic response as compressed. However, the pressure derivative of the shear modulus is negative and small, indicating weak softening of shear modes under pressure. The results found are used to determine the Gruneisen parameters. This is to obtain the acoustic mode contribution to thermal expansion. After subtraction of the relaxation and anharmonic contributions, the temperature dependence of the shear wave ultrasound velocity follows a linear law as predicted by the Soft Potential Model. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The vibration interaction between the top-plate of a buried VS 2.2 plastic, anti-tank landmine and the soil above it appears to exhibit similar characteristics to the nonlinear mesoscopic/nanoscale effects that are observed in geomaterials like rocks or granular materials. [J. Acoust. Soc. Am. 116, 3354–3369 (2004)]. When airborne sound at two primary frequencies f1 and f2 (closely spaced near resonance) undergo acoustic-to-seismic coupling, (A/S), interactions with the mine and soil generate combination frequencies | n f1 ± m f2 | which affect the surface vibration velocity. Profiles at f1, f2, f1 -(f2 - f1) and f2 +(f2 - f1) exhibit single peaks whereas other combination frequencies may involve higher order modes. A family of increasing amplitude tuning curves, involving the surface vibration over the landmine, exhibits a linear relationship between the peak particle velocity and corresponding resonant frequency. Subsequent decreasing amplitude tuning curves exhibit hysteresis effects. New experiments for a buried VS 1.6 anti-tank landmine and a “plastic drum head” mine simulant behave similarly. Slow dynamics explains the amplitude difference in tuning curves for first sweeping upward and then downward through resonance, provided the soil modulus drops after periods of high strain. [Support by U.S. Army RDECOM CERDEC, NVESD, Fort Belvoir, VA.] © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We report the first experimental evidence of selective generation of a confined acoustic mode in a Ga0.85In0.15As nanocavity enclosed by two Ga0.85In0.15As/AlAs phonon Bragg mirrors. Femtosecond pump-probe experiments reveal the generation of a cavity mode within the acoustic mini-gap of the mirrors, in addition to their folded acoustic modes. Selective generation of the confined mode alone is achievable for certain energies below the absorption of the quantum wells in the phonon mirrors. These energies are experimentally identified with the cavity spacer electronic transitions. The amplitude of the acoustic nanocavity mode can be controlled by detuning the excitation from the spacer transitions. The present work finds a direct interest in the seek of monochromatic MHz-THz acoustic sources. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]