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Acoustic Energy (acoustic + energy)
Selected AbstractsSoil creep and convex-upward velocity profiles: theoretical and experimental investigation of disturbance-driven sediment transport on hillslopesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2004Joshua J. Roering Abstract The movement of unconsolidated materials near the Earth's surface is often driven by disturbances that occur at a range of spatial and temporal scales. The nature of these disturbances ranges from highly variable, such as tree turnover, to periodic and predictable, such as frost heave or creep. To explore the effect of probabilistic disturbances on surface processes, we formulated a granular creep model with analogy to rate process theory (RPT) used for chemical reactions. According to the theory, individual particles must be energized to a height greater than adjacent particles in order for grain dilation and transport to occur. The height of neighbouring particles (which is akin to activation energy in chemical reactions) varies with slope angle such that energy barriers get smaller in the downslope direction as slopes steepen. When slopes approach the friction-limited angle of repose, the height of energy barriers approaches zero and grains ,ow in the absence of disturbance. An exponential function is used to describe the probability distribution of particle excitation height although alternative distributions are possible. We tested model predictions of granular dynamics in an experimental sandpile. In the sandpile, acoustic energy serves as the disturbance agent such that grains dilate and shear in response. Particle velocities are controlled by the frequency of energy pulses that result in grain displacement. Using tracer particles, we observed a convex-upward velocity pro,le near the surface of the sandpile, consistent with predictions of our RPT-based velocity model. In addition, we depth-integrated the velocity model to predict how ,ux rates vary with inclination of the sandpile and observed non-linear ,ux,gradient curves consistent with model predictions. By varying the acoustic energy level in the experimental sandpile, we documented changes in the rate of grain movement; similar changes in modelled velocities were achieved by varying the exponent of the particle excitation probability distribution. The general agreement between observed and modelled granular behaviour in our simple laboratory sandpile supports the utility of RPT-based methods for modelling transport processes (e.g. soil creep, frost heave, and till deformation), thus enabling us to account for the probabilistic nature of disturbances that liberate sediment in natural landscapes. Copyright © 2004 John Wiley & Sons, Ltd. [source] Tests on the vibro-acoustic behaviour of a brushless DC-motorEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 5 2000W. Heylen In the design of rotating electrical machines, the vibro-acoustic behaviour becomes an important criterion. In an electrical machine, electromagnetically induced forces may cause vibrations of, for instance, the stator. These vibrations may radiate annoying acoustic energy, especially at resonances of the stator assembly. This paper describes some techniques to analyse the vibro-acoustic behaviour of a (brushless DC-) motor. However, the technique is quite general and can be used for all types of electrical machines. The "inverse-frequency-response-function" technique (I FRF) allows the identification of the actual vibration behaviour of the motor frame from the measurement of the acoustic field around the motor. Experimental modal analysis yields the resonant behaviour of the motor. A combination of both techniques indicates the critical resonances, causing the undesired acoustic emissions. This may lead to an improved, quieter design of the electrical motor. [source] Equilibrium loading of cells with macromolecules by ultrasound: Effects of molecular size and acoustic energyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2002Héctor R Guzmán Abstract Ultrasound has been shown to deliver small compounds, macromolecules, and DNA into cells, which suggests potential applications in drug and gene delivery. However, the effect of molecular size on intracellular uptake has not been quantified. This study measured the effect of molecule size (calcein, 623 Da; bovine serum albumin, 66 kDa; and two dextrans, 42 and 464 kDa) on molecular uptake and cell viability in DU145 prostate cancer cells exposed to 500 kHz ultrasound. Molecular uptake in viable cells was shown to be very similar for small molecules and macromolecules and found to correlate with acoustic energy exposure. Molecular uptake was seen to be heterogeneous among viable cells exposed to the same ultrasound conditions; this heterogeneity also correlated with acoustic energy exposure. In a fraction of these cells, molecular uptake reached thermodynamic equilibrium with the extracellular solution for the small molecule and all three macromolecules. The results demonstrate that ultrasound provides a means to load viable cells with large numbers of macromolecules, which may be of use for laboratory and possible clinical drug delivery applications. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:1693-1701, 2002 [source] INFLUENCE OF WATER ACTIVITY ON THE ACOUSTIC PROPERTIES OF BREAKFAST CEREALSJOURNAL OF TEXTURE STUDIES, Issue 5 2006EWA GONDEK ABSTRACT Corn and wheat bran flakes were compressed in a plastic cylinder and the generated vibrations were measured by a piezoelectric accelerometer. Amplitude,time records were thoroughly analyzed and the total acoustic energy in arbitrary units, number of acoustic events and energy of a single acoustic event were calculated. Relationships between the time of compression, frequency and sound intensity are presented as acoustograms. All parameters, except the energy of a single acoustic event, were strongly dependent on water activity (Aw). The flakes differed essentially in their ability to propagate vibrations. At low Aw's, both types of flakes were alike, but at higher Aw's, corn flakes damped high-frequency waves while wheat bran flakes did not show this property. [source] Technology Advances and Tanker Spill PreventionNAVAL ENGINEERS JOURNAL, Issue 4 2001Cdr. G. Rodgers USCGR (Ret.) ABSTRACT Goals to alert the bridge watch for imminent grounding or collision with shallow underwater dangers, have long been stymied by lags in active sonar technology. Thus "lower hemisphere" designs for shallow underwater search have been unable to exploit solutions useful topside for the "upper hemisphere" guarded by radar and other technology. While the radar environment normally exhibits single path, direct line-of-sight conditions for prime targets, the shallow water sonar environment is cluttered by a mix of echoes and multipath returns for identical ranges. Thus we first must accommodate to a quirky hydroacoustic environment as a major design subsystem for any shallow water navigational sonar. Secondly, for large carriers found in the world tanker fleet, there is recognition that some simple backfit solution is needed for any electroacoustic interface, the sonar transducer. Commercial carriers have not been designed or built with special hull considerations such as sonar domes and recesses; therefore, this second vital subsystem requires particular design attention for projecting hydro-acoustic energy and receiving return echoes. Several recent patents are on file which apply to this problem. Thirdly, signal processing considerations provide a set of design-critical factors. High speed digital signal processors (DSPs) of recent "parallel" design offer opportunities to search at high speed and to unravel the confusing mix of acoustic energy found in shallow water returns. Past hurdles are endemic for these three critical subsystems: hydroacoustic environment, electroacoustic transducer design, and signal processing, but now these seem most amenable to technology transfer. [source] Radiative upper-boundary conditions for a non-hydrostatic atmosphereTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 582 2002R. James Purser Abstract A non-hydrostatic compressible model supports vertically propagating acoustic modes in addition to the modes of meteorological significance, such as the quasi-geostrophically balanced, and gravity modes. The acoustic modes are stimulated inadvertently, either by initial conditions incompatibly balanced for the model discretization, or by physical processes injecting abrupt impulses of heat or motion into the model during the integration. A standard method for removing unwanted acoustic energy is through the inclusion in the model of three-dimensional divergence damping. However, an alternative approach is to employ an upper-boundary condition designed to radiate acoustic waves, at least partially, as they impinge on the model top. This note explores this latter option through the use of an upper-boundary condition that incorporates a time filter to facilitate the selective absorption of both gravity and acoustic waves at the top. Copyright © 2002 Royal Meteorological Society [source] Temporal behaviour of global perturbations in compressible axisymmetric flows with free boundariesASTRONOMISCHE NACHRICHTEN, Issue 1 2009V.V. Zhuravlev Abstract The dynamics of small global perturbations in the form of a linear combination of a finite number of non-axisymmetric eigenmodes is studied in the two-dimensional approximation. The background flow is assumed to be an axisymmetric perfect fluid with adiabatic index , = 5/3 rotating with a power law angular velocity distribution , , r,q, 1.5 < q < 2.0, confined by free boundaries in the radial direction. The substantial transient growth of acoustic energy of optimized perturbations is discovered. An optimal energy growth G is calculated numerically for a variety of parameters. Its value depends essentially on the perturbation azimuthal wavenumber m and increases for higher values of m. The closer the rotation profile to the Keplerian law, the larger growth factors can be obtained but over a longer time. The highest acoustic energy increase found numerically is of order ,102 over ,6 typical Keplerian periods. Slow neutral eigenmodes with corotation radius beyond the outer boundary mostly contribute to the transient growth. The revealed linear temporal behaviour of perturbations may play an important role in angular momentum transfer in toroidal flows near compact relativistic objects (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||