bluuebunny/crossref_metadata_2025 huggingface dataset:
Operational transfer path analysis: Comparison with conventional methods
Authors: Lohrmann Martin
Published: May 2008

Transfer Path Analysis describes how sound and vibration propagates through complex structures. The correct determination of transfer coefficients between sources and receivers is essential for a high quality analysis. Conventional methods use artificial excitations (forces or volume velocities) to evaluate transfer functions. Therefore, they do not consider the influence of different load conditions on the transfer function behaviour of complex structures. In a second step, operational data (vibrations or sound pressures) are applied to the transfer functions to calculate the different path contributions. In order to overcome these restrictions, transfer coefficients can be evaluated directly from operational data. Thus, the actual load conditions are taken into account and the quality of transfer characteristics is improved. The relation between simultaneously measured data of sources and receivers can be derived by statistical methods. Principal Component Analysis is used to separate the total signal into individual path contributions, while operating on airborne and structure-borne contributions simultaneously. Operating in the time-domain gives direct access to auralisation and in-depth analysis of dominant path contributions. This new single-step approach has been proven to generate more precise analysis results within a much shorter testing time.
Noise Impact of Wind Farms: Uncertainties due to wind data reference at 10m
Authors: Slaviero David , Bigot Alexis
Published: May 2008

Noise impact prediction or measurement of Wind Farms requires wind reference data at 10 meters. From data collected on more than 200 Farms in France, over the last 5 years, this paper shows that, in the sampling of noise and meteolological data for noise prediction and assessment, differences in the wind profil from one site to another, in the period of the day (day, night) can lead to different estimations of emission data selection and impact assessment. Different parameter studies are presented both with regard to the effect on impact studies and farms impact monitoring and control. The work presented is in accordance with the project of acoustic standard for the assessment of noise impact of Wind Farms under study in France.
Criteria for wind farm noise: Lmax and Lden
Authors: Van Den Berg Frits
Published: May 2008

Wind turbine noise limits are based on either the highest sound immission level (Lmax) or several sound immission levels for a series of wind speed classes (Lmax,v). As yet no procedure has been proposed to determine the day-evening-night sound level (Lden) that is now commonly used in the European Union for all noise sources. Wind speed dependent rating wind turbine noise levels Lr,v can be predicted based on climatological data. This has been verified by measurements over a nine month period for a wind farm at a coastal location in the Netherlands. From these measurements also the long term average sound level Lden can be determined. Lden can also be determined from previously published wind speed measurements at an inland location over one year. The procedure shows that for a wind turbine or wind farm the Lden can be derived from Lmax by taking into account the regional climatology.
LES prediction of wall-pressure fluctuations and noise of a low-speed airfoil
Authors: Wang Meng , Moreau Stéphane , Iaccarino Gianluca , Roger Michel
Published: May 2008

The wall-pressure fluctuations and noise of a low-speed airfoil are computed using large-eddy simulation (LES). The results are compared with experimental measurements made in an open-jet anechoic wind-tunnel at Ecole Centrale de Lyon. To account for the effect of the jet on airfoil loading, a RANS calculation is conducted in the full wind-tunnel configuration, which provides velocity boundary conditions for the LES in a smaller domain within the potential core of the jet. The flow field is characterized by an attached laminar boundary layer on the pressure side and a transitional and turbulent boundary layer on the suction side. The predicted unsteady surface pressure field shows reasonable agreement with the experimental data in terms of frequency spectra and coherence in the trailing-edge region. In the nose region, characterized by unsteady separation and transition to turbulence, the wall-pressure fluctuations are highly sensitive to small perturbations and difficult to predict or measure with certainty. The LES, in combination with the Ffowcs Williams and Hall solution to the Lighthill equation, also predicts well the radiated trailing-edge noise. A finite-chord correction is derived and applied to the noise prediction, which is shown to improve the overall agreement with the experimental sound spectra.
The influence of the design parameters of centrifugal fans on the difference between outlet and inlet noise levels
Authors: Liberman Mikhail Y.
Published: May 2008

The operation of the industrial centrifugal fans is accompanied by the air-borne noise generation thanks to such phenomenon as: vortex formation within blade channels of impeller (because of flow separation in channel) and interactions between vortex wakes (at outlet of impeller) and cut-off of fan casing. Sound waves, which are formed at outlet of blade channels and within fan casing, propagate as through outlet side of casing, as in opposite direction: through rotating blade channels of impeller and inlet cone of casing. As it follows from theoretical analysis and experimental research the noise levels at outlet side of centrifugal fan are higher than noise levels at inlet of fan (as for broadband as for tonal noise), because of noise reduction, which is caused by sound wave propagation through inhomogeneous channel, consisted of impeller and inlet cone of casing. The efficiency of the noise reduction depends on the design parameters of impeller and casing. In particular, according to results of research the difference between levels of noise, radiated from outlet and inlet sides of fan, depend on: shape of blade channels, relation between width of casing and impeller.
Trailing edge noise computation of a fan blade profile
Authors: Christophe Julien , Anthoine Jerome , Moreau Stéphane
Published: May 2008

In problem involving noise generated by fans or high-lift devices in uniform stationary flow, trailing edge noise has a primary interest. This paper proposes to study the trailing edge noise produced by a Controlled-Diffusion (CD) airfoil specially developed for automotive engine cooling by Valeo. A LES flow computation is realised through the Fluent solver 6.3 for a Reynolds number based on the chord of 1.5 x 105 and an angle of attack of 8 degrees. This computation is compared to pressure and velocity measurements performed at ECL (France) and obtained by measurement techniques involing pressure probes and hot-wire anemometry. Amiet's theory using surface pressure spectra around the airfoil trailing-edge region is used to obtain far field acoustic predictions that are compared to microphone measurements.
Optimization problem for the automatic positioning of flow obstructions to control tonal fan noise
Authors: Gerard Anthony , Berry Alain , Masson Patrice
Published: May 2008

Tonal noise from subsonic axial fans can be controlled by adding obstructions in the downstream or upstream flow field of the rotor. These obstructions must be located with care to create secondary circumferential modes of the blade unsteady lift of equal magnitude but opposite in phase with the primary unsteady lift modes responsible for the tonal noise. The general optimization problem of controlling N circumferential modes using N obstructions with 2 degrees of freedom or 2N obstructions with 1 degree of freedom is first posed. This optimization problem can be greatly simplified using nB-perdiodic obstructions (where B is the number of blade) designed to control the most radiating mode of the blade unsteady lift at frequencies n×BPF. In this case, the control of each frequency is uncoupled and a single error microphone in the axis of the fan can be used to globally control the selected frequencies.
Axial fan noise: Towards sound prediction based on numerical unsteady flow data - a case study
Authors: Reese Hauke , Carolus Thomas
Published: May 2008

Objective of this work is to evaluate modern numerical methods for predicting flow induced fan noise. A generic fan assembly is investigated consisting of a low pressure axial impeller (diameter 0.3 m, hub to tip ratio of 0.45) including an optional turbulence generator. The flow field is simulated with different state of the art unsteady computational fluid dynamic methods. All results are compared with each other and with hot wire flow velocity and surface pressure measurements. From the numerical data, the relevant dipole sound sources, i.e. the unsteady forces on the fan blades are derived. Eventually both, a free field formulation in the time domain (acoustical analogy by FFOWCS WILLIAMS and HAWKINGS), and a boundary element formulation in the frequency domain (SYSNOISE®) are employed to predict the radiated sound field based on the numerical source data. The acoustical results are compared and contrasted with measurements.
Turbulence ingestion fan noise predictions using an advanced turbulence correlation model
Authors: Morris Scott C.
Published: May 2008

The generation of sound by an isolated rotating blade row results from the interaction of the blades with turbulence in the approach flow. The relationship between the unsteady velocity field and the sound produced can be expressed directly in terms of the two point velocity correlation function of the approach flow field. It is often assumed that the turbulent flow can be approximated by a number of simplifying assumptions, such as homogeneous, isotropic flow. However, in the frequency range of interest for a number of applications these assumptions are not valid, and their use can lead to significant errors in the prediction of generated sound. The present work will describe a method for using advanced models of two-point velocity correlations and outline new experimental results that validate this approach.
Recent progress on thermoacoustic heat engines and refrigerators
Authors: Luo Ercang
Published: May 2008

In this talk, recent progress on thermoacoustic heat engines and refrigerators developed at the Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences (CAS), is covered, which mainly includes three aspects: (i) Energy-focused thermoacoustic-Stirling heat engines (EF-TASHE) by using tapered resonators are highlighted for both low-frequency (̃50Hz) and medium-frequency (̃300Hz) operation; (ii) A thermoacoustically driven two-stage pulse tube cryocoolers capable of achieving liquid hydrogen temperature (̃20K) is described. In addition, a 300 Hz compact thermoacoustically driven pulse tube cryocooler operating below 80K is also covered. In this part, an acoustical pressure amplifier is highlighted; (iii) A heat-driven thermoacoustic refrigeration system with double thermoacoustic-Stirling configuration for room temperature cooling is reported. This system is able to provide a cooling power of more than 300 W at -20°C, showing good prospect as an alternative of CFC refrigeration. Finally, consideration and prospect for future development are forecasted.
Energy conversion efficiency improvement of a thermoacoustic cooling system - The influence of a lamination mesh on cooling effect-
Authors: Sakaguchi Atsushi , Sakamoto Shin-Ichi , Tsuji Yoshiyuki , Watanabe Yoshiaki
Published: May 2008

It was generally considered that energy conversion efficiency of a thermoacoustic cooling system was improved by increasing proportion of a thermal boundary layer in the stack. Thinning down a channel radius of the stack is required to increase the thermal boundary layer per unit area. A ceramic stack is difficult to satisfy this requirement. To satisfy this requirement, we propose to use a lamination mesh which is formed by piled up a stainless mesh. Since the lamination mesh has complex channel, the effect of changing the mesh number on the cooling effect is obscure. The experiments were carried out by changing the mesh number and the insertion position of the stack using the straight acoustic tube to measure the cooling effect. From the experimental results, changing mesh number causes the distribution shift of the phase difference between pressure and particle velocity. The insertion position of the stack for which the maximum temperature decrease come close to center of the acoustic tube. This is corresponded to a result using the ceramic stack. It suggests that a same design method, which is used in case of applying the ceramic stack, can be adapted to the lamination mesh.
Advanced flow measurements in thermoacoustic systems
Authors: Berson Arganthaël , Blanc-Benon Philippe
Published: May 2008

One of the bottlenecks for the conception of highly efficient thermoacoustic systems is the poor performances of heat exchangers. A better understanding of both aerodynamical and thermal phenomena that occur at the interface between the stack and the heat exchangers is necessary for the improvement of heat transport between these components, especially at high acoustic amplitudes that are required for industrial applications. To this end, a specific Particle Image Velocimetry (PIV) method has been developed and measurements are performed within a standing-wave thermoacoustic refrigerator model driven at high drive ratios (up to 5%). Vortex streets are observed behind the plates of a single stack at high acoustic level. The flow is characterized using advanced vortex analysis tools and dimensionless numbers. Vortices also appear within the gap between the stack and the heat exchangers. They will influence heat transport as was previously shown in numerical simulations from the literature. Moreover, as a first step toward enthalpy flux measurements, cold and hot wire anemometry methods are developed specifically for temperature and velocity measurements in oscillating flows. First results with these techniques will be presented and compared to available numerical and analytical models. This work is supported by ANR (project MicroThermAc NT051_42101).
Powerful, efficient, robust, electro-acoustic transducers
Authors: Corey John
Published: May 2008

The STAR™ resonant, reciprocating transducer began as a lightweight linear alternator design for a space-power free-piston Stirling engine in the early 1990's. It has since been developed into a range of commercially available motors and alternators with rated powers from 100 to over 10,000 watts (acoustic). As motors, these are acoustic pressure drivers with unlimited operating life and typical transduction efficiencies of 80-90 percent. This paper explains the electrodynamics and operation of these moving- magnet Lorentz-force devices and the unique geometric configuration that has allowed scaling over such a wide range. We discuss the design and function of the unique single-degree-of-freedom flexure suspension that enables both the compact geometry and unlimited service life without wear. Data is presented from a large sample of units placed in service during the last decade, demonstrating the durability and performance of these remarkable devices.
Interactive analysis, design, and teaching for thermoacoustics using DeltaEC
Authors: Ward William C. , Swift Greg W. , Clark John P.
Published: May 2008

The 2008 release of the Los Alamos thermoacoustics code, DeltaEC, is distinctly different from the text-based program that was first made available in 1993. The physics captured by "Design Environment for Low-Amplitude Thermoacoustic Energy Conversion" has been steadily extended over the years. Toroids and other acoustic network topologies are now possible, along with superimposed steady flow, time-averaged pressure gradients, gas diodes, Gedeon streaming, thermoacoustic mixture separation, and resonator vibration solutions. Eight different stack pore geometries are supported, and a powerful algebraic user language allows complex, custom results to be derived without source code revisions at Los Alamos. Over the last year, the numerical methods of DeltaEC were condensed into a FORTRAN computational core and wrapped with a Python-based graphical user interface to provide modern interactive features: a multi-model tabbed interface, colorizing editors, scaled schematics, and 2D plotter windows. An intricate model can now be divided into interlinked sub-models that can be solved independently (and consistently). In addition to providing usability and new capabilities, the Python front end makes the legacy code more maintainable, extensible, and verifiable. The latest download of DeltaEC is available to all researchers at www.lanl.gov/thermoacoustics/.
Cooling load and coefficient of performance of thermoacoustic refrigerators: the role of the working fluid
Authors: Herman Cila
Published: May 2008

Thermoacoustic refrigeration is a technology that uses mechanical energy in the form of sound waves to drive a heat pumping process that offers an environmentally safe, relatively low maintenance alternative to vapor compression refrigeration. Improving the design of the thermoacoustic core, composed of the stack plates and heat exchangers, may have the potential to bring thermoacoustic technology closer to commercial use. The stack plates have been analyzed to increase efficiency (expressed in terms of the coefficient of performance, COP) but in some applications a very high efficiency can lead to a smaller cooling load. The thermoacoustic stack was analytically optimized for maximum heat transfer (cooling load) and coefficient of performance (COP) for a range of working fluids of interest. Different noble gas mixtures were analyzed as the working fluid and helium was found to produce the highest cooling load because of its low molecular weight. The thermoacoustic stack plate center location, length, thickness and spacing were analyzed and optimum values to maximize cooling load and COP were found to exist for the specific input parameters considered. These optimization techniques may be used to design devices where maximum cooling load is more desirable than high efficiency.
Numerical model of boundary layer effects in Rayleigh streaming
Authors: Tuttle Brian , Sparrow Victor W.
Published: May 2008

In thermoacoustic devices such as the pulse-tube refrigerator, efficiency is diminished by the formation of a second-order mean velocity known as Rayleigh streaming. This flow emerges from the interaction of the working gas with the wall of the tube in a thin boundary layer. This research develops a numerical model to investigate Rayleigh streaming in straight and tapered tubes. Since the accuracy of the model depends on the correct representation of boundary layer effects, special consideration is given to the computation of thermal and viscous boundary layers including finite difference methods, computational grid refinement, and exaggeration of physical parameters for testing of boundary layers at low grid resolution. The model also allows for the inclusion or exclusion of temperature-dependent viscosity and thermal conductivity terms, the effects of which will be examined. [Work supported in part by the Office of Naval Research.]
Perspectives on spatial dispersion in cubic crystals provided by neutron scattering, phonon imaging, picosecond laser ultrasound and lattice dynamics models
Authors: Every Arthur G. , Jakata Kudakwashe
Published: May 2008

Spatial dispersion is the variation of acoustic wave speed with wavelength, and sets in when the wavelength approaches the natural scale of length of a medium, or lattice spacing in the case of a crystal. The first onset of dispersion can be treated within the context of continuum mechanics by the incorporation of third and fourth order spatial derivatives of the displacement field in the elastic wave equation. These additional terms yield corrections to the phase velocity which in general are quadratic in the spatial frequency k. This paper will survey the experimental techniques that give one access to the coefficients in these expansions, in particular inelastic neutron scattering, ballistic phonon imaging and picosecond laser ultrasound. The main emphasis of the paper will be on deriving the numerical values of the dispersion coefficients for four cubic crystals, Si, Ge, GaAs and InSb, from published neutron scattering data and demonstrating how modified continuum elastodynamics with these values of the coefficients is able to account well for the available dispersive phonon images of these crystals. Comparison will be made with values for the dispersion coefficients that have been obtained from laser ultrasound measurements and from lattice dynamics models.
Nanoacoustic waves in nanomaterials
Authors: Dijkhuis Jaap I. , Van Capel Peter J.
Published: May 2008

We discuss the formation and detection of acoustic soliton trains in crystal slabs. High-amplitude amplitude strain pulses are generated by impact of intense femtosecond optical pulses on a metallic film and injected into the crystal slab. Nonlinear acoustic propagation leads to the formation of shock fronts (N-waves), that, in absence of viscous damping and by virtue of dispersion, may develop into soliton trains at the leading edge and high frequency tails at the trailing edge. Interferometric pump-probe optical experiments are discussed to directly detect the ultrafast surface displacements when a soliton is reflected at the surface of the crystal slab. Finally, we experimentally prove that these acoustic solitons are capable of impulsively exciting THz transitions in electronic centers in solids. The coherent terahertz acoustic pulse trains are applied to manipulate the optical response of two-dimensional excitons in a III-V quantum well on the ultrafast timescale. By virtue of the deformation potential, the coherent exciton emission becomes strongly "chirped" when the acoustic pulse train passes the quantum well. This yields the prospect to perform pump-probe terahertz acoustic experiments with nanoacoustic waves in semiconductor nanomaterials.
Optical characterization of the acoustic response in a nanostructure using the transient reflection matrix formalism
Authors: Mounier Denis , Picart Pascal , Ruello Pascal , Breteau Jean-Marc , Gusev Vitali
Published: May 2008

The transient reflectometry and transient interferometry are the most commonly used techniques of picosecond acoustics for the study of isotropic planar stratified nanostructures. Nevertheless when anisotropy is present in the sample, the standard techniques have to be completed by transient polarimetry. The reflection properties of an anisotropic sample at oblique incidence are completely determined by the 2x2 reflection matrix (RM): R=[rpp,rps;rsp,rss]. Considering that the transient acoustic phenomena induce a perturbation ΔR of the reflection matrix, we demonstrate that the transient reflection matrix (TRM): ΔR⋅R-1, where R-1 is the inverse of the reflection matrix, can be completely determined experimentally using the three techniques: transient reflectometry, interferometry and polarimetry (TRIP). In particular, the off-diagonal components of the TRM can be determined by transient polarimetry measurements only. Moreover, theoretical calculations of the TRM point up the close relation between the off-diagonal components of the TRM and the presence of a shear strain wave propagating perpendicularly to the free surface of the sample. Experimental results using the transient polarimetry technique will be presented to support the theoretical prediction of the TRM formalism.
Coherant acoustic excitation of nanostructures probed with asynchronous optical sampling
Authors: Dekorsy Thomas
Published: May 2008

We report the high-sensitivity detection of coherent acoustic excitation in semiconductor heterostructures and metallic nanostructures by using high-speed asynchronous optical sampling. Asynchronous optical sampling is based on two tunable femtosecond Ti:sapphire lasers with slightly different repetition rates close to 1 GHz. This new technique provides the performance of an all-optical oscilloscope for coherent excitations in a pump-probe set-up without any mechanically moving part. A time delay of 1 ns is scanned with a frequency of 10 kHz and a time resolution of 100 fs. Investigations on coherent zone-folded phonons in semiconductor superlattices and nanoscale metallic structures are discussed. For the latter the influence of the substrate on the damping of acoustic excitations is investigated in detail.
Nanoscale objects as promising high frequency acoustic transducers in picosecond acoustics
Authors: Devos Arnaud
Published: May 2008

Twenty year ago, H. Maris opened up the field of nanoscale acoustics by demonstrating the opportunity of using ultrashort optical pulses for generating and detecting high frequency acoustic waves. Roughly, an optical pulse is converted in a picosecond acoustic pulse through the optical absorption in a thin metallic layer. Since then, this so-called picosecond ultrasonics has known a larger and larger success all around the world. Up to now, picosecond ultrasonics meets two main limitations. First it is difficult to reach the THz range using the usual way of producing the acoustic pulse. Second, in the common geometry only longitudinal waves are excited by the laser. Here we present some results showing that nanoscale objects could help in overcoming both difficulties. We first show that semiconductor quantum dots can be a very efficient emitter of coherent phonons whose frequency can be higher than those obtained in metallic thin films. Second we show that 2D arrays of nanosize metallic dots offers a way of generating and detecting high frequency surface acoustic waves.
High frequency acoustics in nanostructures by spontaneous Brillouin light scattering
Authors: Still Tim , Retsch Markus , Sainidou Revekka , Jonas Ulrich , Fytas George
Published: May 2008

We report on the dispersion of high frequency (GHz) acoustic excitations in three-dimensional colloidal crystalline or amorphous assemblies of sub-micron particles in different matrices by Brillouin light scattering (BLS) in order to explore the phononic and elastic properties of nanostructured materials. In air, we record eigenmodes of the individual particles, which are shown to be independent from the crystallinity and the composition of the sample but sensitively depend on the particle architecture (e.g core/shell silica/PMMA, hollow spheres) and their mechanical properties at nanoscale. In fluid matrices, the dispersion relations are recorded. We demonstrate the occurence of two hypersonic phononic band gaps of different nature. One is a Bragg gap appearing only in crystalline samples, the other one is a particle resonance-induced hybridization gap, which appears in crystalline samples along with the Bragg gap and alone in amorphous samples. Furthermore, we investigate the influence of filling fraction, crystallinity and monodispersity of size on the hypersonic behaviour of our samples.
Nonlinear dynamics of sonoluminescing bubbles
Authors: Holzfuss Joachim
Published: May 2008

The current work focuses on the acoustical and nonlinear dynamical aspects of sonoluminescence (SBSL). Several hydrodynamical instabilities in parameter space are analyzed in detail numerically. Their occurrence in experiments is discussed especially in the context of period doubled unisotropic light emission. The acoustical emissions during stable and unstable oscillations show characteristics of shock waves. The emitted sound generates a complex acoustic environment in the driving cell leading to backreactions to the bubble. Characteristic dynamical effects during unstable sonoluminescence are clarified. Chemical processes during high temperature and high pressure, spatial translations, gas diffusion, the highly nonlinear bubble oscillations and acoustic emissions are attributed to oscillations and modulations of bubble dynamics outside the range of stable SBSL. In particular reasons for quasiperiodic oscillations with incommensurate frequencies in different setups are found.
Characterizing microbubble interactions with ultrasound using flow cytometry
Authors: Matula Thomas , Swalwell Jarred
Published: May 2008

Characterizing the fundamental interaction of ultrasound with microbubbles is challenging because of the small spatial and temporal scales. High speed optical imaging is perhaps the most well-known method, as it provides direct information about their response. Although the image is in a plane, the image quality can be sufficient to obtain important information about bubble response. However, high-speed cameras are expensive, data is very limited, and difficult to process. We previously showed how light scattering can be used to obtain similar information - volume oscillations, destruction, even shell properties. Light scattering can be an inexpensive method for probing microbubbles. The difficulties with light scattering (also with optical imaging) are alignment and signal/noise. In this talk we will describe a technique to use commercially-available light-scattering systems to investigate the interaction of pulsed ultrasound with microbubbles. In particular, we developed a technique to insonify microbubbles flowing through the focal region of a flow cytometer. Attached to the quadrature side of a flow cuvette is a small piezoelectric transducer, driven in pulsed mode at various voltages to induce a bubble response. The light scattered from the bubbles can be used for sizing, destruction thresholds, and to assess volume oscillations. Funded by NIH #5R01EB000350
Interpretation of the pressure waves radiated by oscillating bubbles
Authors: Vokurka Karel , Buogo Silvano
Published: May 2008

An oscillating bubble is an excellent acoustic radiator. In a pressure wave emitted by the oscillating bubble information about the bubble properties and behavior is present. Hence, when using a suitable method, this information could be extracted and used to improve our understanding of the physical processes accompanying the bubble oscillations. However, to be able to extract this information, a number of prerequisites must be met. First, the measuring apparatus should be able to record a faithful copy of the pressure wave. Second, a large, statistically representative set of pressure records must be available for the analysis. Third, a suitable method must be used to analyze the recorded waves. All these requirements will be discussed in detail at the conference. Presented results are based on experience gained during evaluation of a large set of pressure records obtained recently in experiments with spark generated bubbles. [Work has been partly supported (K.V.) by the Czech Ministry of Education as the research project MSM 46747878501.]
Dynamics and radiation of single cavity in an abnormal compressible bubbly media
Authors: Kedrinskiy Valeriy K.
Published: May 2008

The equation of a pulsation of a single cavity in the equilibrium (on pressure) bubbly medium was suggested. The state of such medium is described by Lyakhov's equation which at the condition of pressure equilibrium in the both phases (gas/liquid) becomes essentially simpler. The numerical analysis of features of cavity dynamics and the acoustic losses was executed. The notion "acoustic losses" mean a radiation generated by cavity. The analysis of radiation parameters was restricted by the vicinity of cavity wall from a liquid side. The studies of cavity behavior, the structure and amplitude of a radiation have shown that the degree of a cavity compression by a stationary shock wave goes down when the volumetric concentration of gas phase K in the medium increases. The amplitude of pulsation essentially decrease and function R(t) (radius cavity vs. time) asymptotically (without oscillations) tends to the equilibrium state when K is equal approximately 3%. The equilibrium state is defined by amplitude of an incident shock wave and does not depend on K-value. The structure of a radiation wave takes the "soliton" form, its amplitude is essentially lesser and the width is much more in the comparison with corresponding parameters for a single-phase liquid. (RFBR 06-01-00317a financial support).
Development of an acoustics-based instrument for bubble measurement in liquids
Authors: Chahine Georges L. , Wu Xiongjun , Lu Xiaozhen
Published: May 2008

The acoustic bubble spectrometer (ABS) is an acoustics-based device that provides bubble size distribution in a bubbly liquid through measurement at various frequencies of the sound speed and attenuation and solution of an inverse problem. Acoustic bursts of varying frequencies are emitted by one hydrophone and detected by another. A PC and data boards control signal generation, detection, signal processing, inverse problem solution, and results display. Extensive validation experiments were conducted against high speed-video optical measurements. The two methods give very close results for void fractions up to 3e-3, with the ABS possessing the significant advantage of enabling near real-time measurements. The field of application is being expanded to media other than water, and the technique improved to detect larger void fractions, with the help of numerical simulations of non-linear behavior of bubble clouds in acoustic fields.
Cavitation bubbles as microfluidic actuators
Authors: Ohl Claus-Dieter , Dijkink Rory , Ed Zwaan , Le Gac Séverine , Van Den Berg Albert , Tsuji Kinko
Published: May 2008

In this talk we give an overview on the usage of single cavitation bubbles to pump, mix, and manipulate cells in microfluidics. The bubbles are generated with a laser pulse in optically transparent lab-on-a-chip devices. The bubble pulsations is inherently fast, thus although the characteristic dimensions are small high Reynolds numbers flow can be achieved. Experiments show that depending on the channel height 2-dimensional or 3-dimensional fluid flow is generated. Interestingly, there exists a regime which can be described with the Laplace equation, thus it is essentially a potential inviscid flow. We will present the current work (of others and our group) on cavitation assisted pumping using the jetting effect, mixing flows through the creation of vorticity, and the interaction of a bubble with suspension cells. The first results on the latter promise a fruitful future for biologic relevant applications in integrated lab-in-chip devices.
Ultrasonic synthesis of enzyme coated microbubbles
Authors: Ashokkumar Muthupandian , Cavalieri Francesca , Grieser Franz
Published: May 2008

Gas-filled polymer coated microbubbles are intrinsically ultrasound responsive systems and when tailored with targeting features are promising candidates for smart drug delivery. We have ultrasonically synthesised stable, versatile, biodegradable and biocompatible microbubbles using the enzyme, lysozyme. The synthesis of lysozyme microbubbles has been achieved by sonicating an aqueous solution containing denatured lysozyme. The microbubbbles have been characterised using a number of imaging techniques such as, SEM, AFM and light microscopy. We have observed that the experimental parameters such as, length of sonication, DTT concentration and denaturisation time deeply affect the yield and the size of the microbubbles. We have also investigated the secondary structure and the enzymatic activity of lysozyme coated microbubbles. The lysozyme microbubbles have retained their enzymatic antimicrobial activities.
Damage to single biological cells induced by laser-induced tandem microbubbles
Authors: Sankin Georgy , Yuan Fang , Zhong Pei
Published: May 2008

Recent studies have highlighted the potential for using laser-induced micro-cavitation in lab-on-a-chip devices. Shear stress in a liquid can be controlled and significantly enhanced by bubble-bubble interaction, providing new options for in situ cell treatment. Two micro-bubbles (10 μs life time) are generated in a 25-μm liquid layer using 5 ns tandem laser pulses delivered through the objective of a microscope. Bubble-bubble interaction in nearly two-dimensional flow is observed using high-speed video cameras. Two liquid micro-jets moving in opposite directions can be generated when the second bubble is produced at the maximum size of the first one. The jet velocity is estimated about 35 m/s. Particle imaging velocimetry reveals vortex flow motion around the oscillating bubble lasting for about 200 μs. Cell lyses produced by jetting from asymmetric oscillation of tandem microbubbles are investigated at various bubble-cell distances and compared with the results from single symmetric bubble oscillation. The interaction of tandem microbubbles can produce microjetting, leading to damage of adjacent single biological cells.
Introduction of a compliant gas-layer serves to mitigate damage to solid surfaces from the collapse of cavitation bubble clouds
Authors: Chitnis Parag V. , Manzi Nicholas J. , Cleveland Robin O. , Roy Ronald A. , Holt R. Glynn
Published: May 2008

The collapse of transient bubble clouds near a boundary was investigated. Transient cavitation bubbles were created using a shock-wave lithotripter. A porous ceramic disk (flow-pressure 7.5psi) was placed at the lithotripter focus. Air was forced through the disk to alter the boundary condition at the ceramic disk's proximal face. Gas pressure below 7.5psi resulted in a ceramic disk partially filled with fluid (rigid boundary); gas pressure over 7.5psi resulted in active bubbling at the proximal face (compliant boundary). Cavitation dynamics of bubble clouds near ceramic disks were studied for varying gas pressures (0-10psi). Images of the collapse were obtained from a high-speed camera. Additionally, a passive cavitation detector (3.5MHz focused transducer) was aligned with the lithotripter focus. Both the images and the acoustic measurements indicated that bubble clouds near a rigid boundary collapse onto the boundary, forming a re-entrant liquid jet whose impact leads to surface erosion. When a compliant boundary is introduced, bubble clouds collapse away from the surface, thus mitigating cavitation damage. The damage to the ceramic disks was quantified using micro-CT imaging. [Supported by the ORNL Spallation Neutron Source, which is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.]
Circumaural transducer arrays for binaural synthesis
Authors: Greff Raphaël , Katz Brian F.
Published: May 2008

Binaural cues such as the interaural time and level differences are the primary cues for estimation of the lateral position of a sound source, but are not sufficient to determine elevation or the exact position on the "cone of confusion". Spectral content of the head-related transfer function (HRTF) provides cues that permit this discrimination, notably high frequency peaks and notches created by diffraction effects within the pinnae. For high quality binaural synthesis, HRTFs need to be individualized, matching the morphology of the listener. Typical means for this are to measure or calculate the HRTF of the listener, but these lengthy and costly methods are not feasible for general public applications. This paper presents a novel approach for HRTF individualization, separating the head and torso effect from that of the pinnae. The head/torso component is numerically modelled while the pinnae component is created using a multiple transducer array placed around each pinna. The philosophy of this method consists in trying to excite the correct localization cues provided by the diffraction of the reconstructed wave front on the listener's own pinnae. Simulations of HRTF reconstruction with various array sizes and preliminary auditory localization tests are presented.
Interaural-time-difference sensitivity to acoustic temporally-jittered pulse trains
Authors: Goupell Matthew J. , Majdak Piotr , Laback Bernhard
Published: May 2008

Bandpass-filtered pulse trains in acoustic hearing have been used to understand the high-rate pulse trains used in electrical stimulation strategies. In a left-right discrimination test, sensitivity to interaural time differences (ITD) in 600-pulses-per-second (pps) periodic pulse trains and aperiodic (temporally-jittered) pulse trains was tested with six normal-hearing listeners. It was found that jitter significantly and systematically increased ITD performance. A second experiment using 1200-pps pulse trains was performed to show that listeners were not solely benefiting from the longest interpulse intervals and thus the instances of reduced rate by adding jitter. To better understand the effect of jitter, the output of a basilar membrane model and a higher-level physiologically-based model was observed. Results from the modeling were reminiscent of an effect called "release from binaural adaptation" where the binaural system is reactivated by a temporal irregularity and this release possibly occurs at the level of the cochlear nucleus or lower. These results help understand pulse-rate limitations of ITD in cochlear-implant listeners.
Local-pitch identification accuracy depending on the trajectory of frequency-modulated tones
Authors: Hiruma Yuki , Aikawa Kiyoaki
Published: May 2008

Local-pitch identification accuracies were analyzed for frequency-modulated (FM) tones. The problem was whether every portion of a continuous sound was perceived at the same accuracy or not. Psychophysical experiments revealed that the local-pitch identification accuracies were significantly different among the nodes of continuous FM tones. Also, the accuracies were dependent on the frequency trajectory shape. The stimuli included two types of piecewise-linear FM tones of up-down-up and down-up-down glide sequences. Each tone had four nodes; the initial, two intermediate points, and the final. The duration of each linear glide was 100 ms. The frequency range was between 1000 and 1500 Hz. A pair of FM tone was presented with one-second interval. The frequency was shifted up or down at one of the nodes in either of the tones. The shift amounts were 0%, 4%, and 8%. The subjects were requested to answer whether two pitch sequences were the same or different. The pitch identification accuracy was low at the initial for both types of FM tones. The accuracy at the final was highest for the up-down-up tone. The intermediate high frequency node showed the highest accuracy for the down-up-down tone. These results indicated that the local-pitch identification accuracies were trajectory-dependent.
The role of compression in forward masking by Schroeder-phase complexes
Authors: Wojtczak Magdalena , Oxenham Andrew J.
Published: May 2008

Waveforms with flat temporal envelopes can produce more forward masking than waveforms with more modulated, or peakier, temporal envelopes after auditory filtering, even when the rms amplitude of the two waveforms is equal. This has been explained in terms of basilar-membrane nonlinearity, which can result in a higher rms amplitude for the flatter than for the peakier temporal waveform after compression. Here, forward masking was measured as a function of the phase curvature of two Schroeder-phase complexes, one with components around the signal frequency (on-frequency masker) and the other with components well below the signal frequency (off-frequency masker). The experiment tested the hypothesis that since the basilar-membrane response to the off-frequency complex at the signal-frequency place is presumably linear, masking should not depend on the phase curvature of the complex, whereas compression of the on-frequency masker should produce phase-dependent thresholds, with the minimum corresponding to the peakiest internal representation of the masker. The results replicate prominent phase effects using on-frequency maskers, but also show some phase effects with off-frequency maskers, which are not predicted by our current understanding of basilar-membrane compression. Other possible influences, such as efferent effects and neural compression, are considered. [Supported by NIH grant R01DC03909].
Gaussian-noise discrimination as a tool to investigate auditory object formation
Authors: Goossens Tom L. , Van De Par Steven , Kohlrausch Armin
Published: May 2008

In the present study we show that, in a same/different experiment, listeners are good at discriminating 50-ms Gaussian-noise tokens with a spectral range of 350-850 Hz. However, when an identical 200-ms noise fringe, with the same statistical properties as the 50-ms target tokens, is appended to both target tokens, listeners show very poor discrimination performance. Apparently, these identical fringes cannot be ignored and these extra non-informative fringes impair the discrimination of the target tokens. It seems that a target token and the appended fringe form one auditory object and that access to subparts of these tokens is not possible. When a perceptual cue is introduced that can lead to the segregation of the target token and noise fringe, e.g., a temporal gap between target and fringe, the ability to discriminate improves implying that the non-informative noise can be (partly) ignored when it is part of a different auditory object than the target token. This method is used as a new approach to investigate the influence of cues such as spectral range, level, interaural level difference, and interaural time delay, on the formation of auditory objects.
Evidence for Poisson processes in change detection
Authors: Kaernbach Christian
Published: May 2008

Comparisons between two stimuli (e.g., "which stimulus was louder?") and change detection ("same or different?") are often assumed to operate on the same decision basis. In the Gaussian signal detection theory, each of the two stimuli to be compared is transformed into a number, and the comparison is then made between these two numbers. If both stimuli are well above absolute threshold, the numbers to be compared have to be large, which motivates the use of normal distributions. The present study tests this assumption by measuring same-different ROC curves for the detection of small changes in the intensity of sinusoids. In contrast to previous studies, change detection was measured not only when the possible direction of change was a priori unknown, but also in two conditions where changes had a fixed direction. The obtained ROCs are asymmetric. This points to Poisson processes with low means. Moreover, the sensitivity to increments was significantly higher than the sensitivity to decrements. The results put into question the Gaussian theory of sensory comparisons and change detection.
Low level auditory processing of simple and complex sounds in autism
Authors: Bonnel Anna C. , McAdams Stephen , Smith Bennett K. , Bertone Armando , Burack Jake A. , Ciocca Valter , Mottron Laurent
Published: May 2008

The documented dissociation between enhanced and diminished auditory processing performance in autistic listeners may be linked to the neural complexity required to process auditory stimuli. To test this hypothesis, four discrimination experiments were designed targeting pitch, spectral envelope, vocal timbre, and loudness. A range of pure- and complex-tone stimuli, with or without frequency or amplitude modulation, varied along spectral and temporal dimensions. An adaptive procedure was used to assess the auditory discrimination thresholds of groups of high-functioning participants with autism (HFA), Asperger syndrome (ASP), and typically developing individuals (TDs). Our research question was whether increasing the level of spectral and/or temporal complexity would have a detrimental impact on autistic listeners' ability to discriminate between acoustic stimuli. Preliminary results suggest that auditory discrimination performance of the latter group is not as dependent on levels of spectro-temporal complexity as originally predicted. The results will be interpreted in the context of current perceptually based models of enhanced and diminished perceptual functioning in autism.