bluuebunny/crossref_metadata_2025 huggingface dataset:
Aversion-related changes in the call structure of Squirrel monkey vocalizations
Authors: Hammerschmidt Kurt , Fichtel Claudia
Published: July 2002

It is generally assumed that the variation in primate calls is, to a certain extent, correlated with the internal state of a caller. However, it remains difficult to describe this relationship because it is difficult to get reliable information of the internal state of a caller. Therefore, the vocalizations given by Squirrel monkeys were analyzed in a self-stimulation study done by Uwe Jürgens (1978). In this study it was measured how certain intracerebral stimulations were experienced by the subject. The Squirrel monkeys were in a cage with two compartments. Presence in one compartment was followed by a stimulation, whereas presence in the other compartment was stimulus free. As the animals were free to move from one compartment to the other, they could decide whether they wanted to avoid the stimulus or not. The multiparametric analysis revealed significant correlations between call parameters and the degree of aversion. Whereas single call types showed partly different parameter correlations, a shift in call pitch was found for all call types. In other words, the more intense the aversion was, the higher the frequency parameters (e.g., peak frequency or frequency range) were. =20
Estimating the ocean bottom properties from multifrequency data
Authors: Xiao Ling , Zhang Renhe , Gong Zaixiao
Published: July 2002

The inversion for the ocean bottom properties can be divided into two parts: constructing the cost function and the search strategy. In this paper, a cost function based on the multifrequency signal is given. The cost function is robust to the error caused by the range measurement. A controlled exhausted search method, named the box division algorithm (BDA), is adopted for the search strategy. BDA is a reliable search method with high efficiency. A numerical result is given for the benchmark inversion problem. An inversion test for real data is also presented. All the tests show that BDA and the cost function can play a robust role in the inversion for the ocean bottom properties. [Work supported by NSF of China.]
Pulse waveform design using time reversal for cardiac ultrasound imaging
Authors: Maniatis T. M. , Nikita Konstantina S. , Stergiopoulos Stergios , Uzunoglu Nikoloas K.
Published: July 2002

The time-reversal method is being used to design pulse waveform signals for cardiac ultrasound imaging. The objective is to remove the impact of the dominant scatterers of the human body located between the sensors and the heart’s near region. The proposed pulse waveform design method has been evaluated with numerical experiments that simulate the acoustical scattering effects of generic cardiac ultrasound imaging operations. Moreover, it is shown that the time-reversal method, when it is being applied on a portion of the received signal, provides a direct real-time assessment of the dominant scatterers’ relevant transfer function.
Noise reduction strategies employing interaural parameters
Authors: Wittkop Thomas , Hohmann Volker , Kollmeier Birger
Published: July 2002

The binaural noise reduction algorithm for hearing aids employing directional filtering and dereverberation introduced by Peissig [J. Peissig, V. Hohmann, and B. Kollmeier, DAGA ’92, 1049–1052 (1992)] was already studied and developed further in the past [T. Wittkop and V. Hohmann, DAGA ’97, 246–247 (1997)]. In this paper, a new noise reduction algorithm will be described which is based in part on the above-mentioned algorithm and was developed with particular respect to the sound quality of the processed signal. An additional stage of processing is introduced which is able to attenuate a single lateral jammer sound source while preserving high signal quality in simple acoustical environments. Moreover, a decision unit is introduced and described which is used to rate the complexity of the acoustical environment and to switch off processing stages automatically if the environment does not match the prerequisites for a particular processing stage, i.e., if the processing is assumed to deteriorate the signal rather than to give any benefit. Measurements of quality judgments employing paired comparisons will be described and the results will be discussed and compared to former results obtained with the old algorithm.
Real-time combined compression and linear gain processing for digital hearing aids
Authors: Tejero-Calado Juan Carlos , Rutledge Janet , Nelson Peggy
Published: July 2002

Amplitude compression processing is used to reduce amplitude-level variations of speech to fit reduced dynamic ranges of hard-of-hearing (HoH) listeners. However, compression processing results in spectral smearing due in part to reduced peak-to-valley ratios. HoH listeners have difficulty detecting important spectral peaks in speech [Nelson and Revoile, 1998]. Thus spectral smearing due to compression processing may have unwanted negative effects on speech understanding. Presented here is a real-time processing algorithm based on a sinusoidal speech model that preserves the important spectral peaks through hybrid compression and linear gain processing. Primary spectral peaks are identified in 7.5-ms analysis frames using 30-ms Hamming windows. A 256-pt FFT is used for speech sampled at 8.013 kHz. The stimuli are divided into frequency bands surrounding the spectral peaks, and the desired compression ratio for each frequency band is applied [Tejero-Calado et al., 1998]. For speech synthesis, an inverse FFT and overlap-add method is used with a triangular window that is double the analysis frame length. The algorithm is currently implemented using a TMS320C30 EVM. The resulting processed speech has good sound quality, compressed amplitude, and preserved spectral contrast. Preliminary tests indicate that HoH listeners benefit from the processing algorithm over conventionally amplified speech signals.
Trading level for number of aircraft immissions: A full-factorial laboratory design
Authors: Vogt Joachim , Kalveram Karl Theodor
Published: July 2002

To what extent can the number of overflights be increased without enhancing annoyance, if airplanes become softer? An original B737 take-off sound (A-weighted sound-pressure level: Lmax=76 dB) was either reduced or amplified by 4.8 dB. In a 3×3 factorial design, nine groups of ten subjects were exposed for 27 min to 3, 9, or 27 copies of one of these three sounds. Regarding energy equivalence defined by LeqA=const, a 4.8-dB sound-pressure reduction compensated for three times the number of the higher level, achieving constant Leq levels in the diagonals of the design. After noise exposure, cardiovascular responses and the subject ratings of loudness, annoyance, and quality of an imagined living area with comparable noise load were analyzed statistically. Comparison of the equal-energy conditions revealed no difference regarding heart rate and blood pressure, but subjective loudness increased with both level and number, and 27 soft aircraft were rated extremely loud. However, annoyance decreased, when 3 loud overflights were converted to 9 medium events, but increased again under 27 soft events. Imagined living quality always decreased with increasing numbers of events, and could not be compensated for by energy-preserving reduction of single-event levels. Conclusion: Beyond 10 events per 30 min the number probably has an increasing over-energetic impact on subjective noise effects.
Calculation of noise contours for Belgian airports
Authors: Peeters Elisabeth M. J. , Thoen Jan , Geusens Ghislain
Published: July 2002

Noise contours are an objective way to represent the long-term noise load from departing and arriving aircraft. Many major European airports have a long history of noise contour calculations and related land use planning. For Belgian airports, several noise contour calculations have been made since the 1970s, but have always been based on limited information. Recently, noise contours for the airports of Brussels, Antwerp, and Ostend have been calculated based on detailed flight information. Long-term noise measurements around Brussels airport validated the accuracy of the Brussels airport noise contours. Up to today, neither for the development of noise contours, nor for the land use planning based on airport noise contours, official guidelines or practices exist, and new houses can still be built around the airports. On the other hand, with international harmonization efforts in mind, Belgian airports are not, as some other European airports restrained by legislation, based on dated technology noise contours, but have taken the opportunity to choose noise descriptors and calculation methods based on current evolutions in the international ways of calculating noise contours, as well as on international guidelines.
Modeling centrifugal fan blade trailing edge noise
Authors: Schlinker Robert H. , Morin Bruce L. , Coffen C. D. , Davis Roger L.
Published: July 2002

Centrifugal fan noise contains numerous aeroacoustic mechanisms, one of them being trailing edge noise due to turbulent boundary layer flows convecting over the blade trailing edge. A fundamental research program was conducted to develop a trailing edge noise database and assess the ability of existing aeroacoustic models to predict this mechanism. The database included unsteady surface pressure spectra, trailing edge wake characteristics, and acoustic sound power. To focus on trailing edge noise, a mixed flow radial fan was simulated with a circumferential array of nonrotating vanes located in a radial diffuser. Both loaded and unloaded vane geometries were tested to simulate varying pressure gradients in an actual fan blade passage. It was demonstrated that the trailing edge noise mechanism can be accurately predicted if the trailing edge wall pressure spectrum is known a priori. However, for radial fans the strong adverse pressure gradients appear to rule out the existence of a ‘‘universal’’ wall spectrum shape typically observed in flat plate zero pressure gradient boundary layer flows. Hence, futher trailing edge noise modeling needs to focus on predicting surface pressure spectrum shape, in addition to, amplitude and frequency content.
Experimental investigation of noise sources in cross-flow fans
Authors: Herrmann Michael , Neise Wolfgang , Schlinker Robert H.
Published: July 2002

Cross-flow fans are unusual types of blowers which operate in a fundamentally different way from axial or centrifugal fans. The flow enters and leaves the impeller in a direction vertical to its axis and passes the blade row twice, first radially inward and then radially outward. Hence, cross-flow fans are basically two-stage fans. Aerodynamic and acoustic modeling of cross-flow fans is extremely difficult because of the complexity of the flow field in the rotating impeller channels with a reversal of the flow direction during each revolution and large regions of severe flow separations. To obtain experimental input data for modeling efforts, experiments were performed with a scaled up model fan. The fan was installed in an open-inlet/ducted outlet test rig. Measurements were made of the unsteady pressures on the impeller blades and on the fan casing, in particular the vortex wall. The flow fields inside the impeller and at its outer periphery were studied by using hot wire anemometry and a three-hole probe. The effect of different casing geometries was examined. A simple model for broadband noise radiation involving surface dipole sources as suggested in an early paper by Sharland [JSV 1, 302–322 (1964)] predicts the spectrum measured in an anechoically terminated outlet duct reasonably well for Now with Behr GmbH & Co., Mauserstrasse 3, 70469 Stuttgart, Germany
Rotational noise generation in peripheral fans
Authors: Weise Volkmar
Published: July 2002

Peripheral fans are used in technical applications where radial and axial fans cannot supply the required pressure ratio at a low mass flux rate. Characteristic for peripheral fans is their high noise emission in the range above 1000 Hz. In comparison to the theory of noise generation in axial fans the sound sources in peripheral fans are not only the rotational blade forces. From an aeroacoustic viewpoint the main difference between axial fans and peripheral fans is the stripper which is necessary to separate inlet and outlet. The sound generation at the outlet is related to the circulating flow between rotor and side channel. This circulation is the main reason for the momentum and energy transfer from the rotor to the gas. The stripper divides the flow in the side channel from the flow between the blades. The result is the modulation of the circulating flow with monopole sources of aerodynamic noise. At the inlet the relief of the blade chambers filled with higher pressure proved to be the main aeroacoustic source by time-dependent periodical mass flux. According to the theory of aerodynamic sound generation this expansion flow represents a monopole source of noise. [Work supported by DFG.]
Experiences with attenuation of low-frequency noise in duct
Authors: Jiříček Ondřej , Koníček Petr
Published: July 2002

Fan noise still represents a serious component of noise pollution in the working place. Fan noise contains both random and discrete frequency components. This paper presents results of experiments with the ANC system useful for low noise design of air-conditioning systems. Computer simulation and measurements were used to examine the performance of the tested feedforward system. The control algorithm is designed for the optimum least square control in the time domain. Experimental results of an investigation of active control of sound are presented.
The effects of rail support stiffness on railway rolling noise
Authors: Thompson David J. , Jones Chris J. C. , de France Guillaume
Published: July 2002

Rolling noise from trains is radiated by both wheel and track vibrations, the track being dominant in many cases. The stiffness of the rail fastener system, especially the elastomeric rail pad usually inserted between the rails and the sleepers, has a significant influence on the noise emitted by the track. Railways are increasingly using softer pads to reduce potential damage to sleepers and ballast. Softer pads decouple the rail from the sleeper. This reduces the noise from the sleeper but also reduces the decay of vibration with distance along the rail and hence leads to an increase of the noise radiated by the rail. The paper describes experimental and theoretical work to investigate the influence of pad stiffness on the dynamic and acoustic behavior of track. The vibrational behavior has been measured on a dedicated 36-m section of railway track, with different types of rail pad installed. The results are compared with predictions using theoretical models of the track behavior. This allows the effective pad stiffness and damping to be determined, laboratory measurements also being available for comparison. The attenuation of vertical and lateral vibration along the track is measured in order to estimate the effect on radiated noise.
Reduction of ground-borne noise from rail systems
Authors: Wilson George P.
Published: July 2002

Over the last 35–40 years there has been an ever increasing awareness of ground-borne noise from rail system train operations and an increasing need for mitigation. In response there have been extensive and continuing efforts to develop rail fixation and support systems which will reduce or control the ground-borne noise which originates at the wheel/rail interface. The rail fixation systems have varied from simple resilient boots on sleepers or resilient pads under rail fixation plates to elaborate concrete floating slab trackforms. Intermediate mitigation designs have included ballast mats, booted duo-block sleepers, and many configurations of resilient rail fixation baseplate assemblies. A review of the various types of ground-borne noise mitigation trackform designs is presented along with indication of the effectiveness for each type or class of design. Further, characteristics or design parameters of the various classes of design which result in poor performance are discussed, particularly for floating slab trackform.
The real sound emission of ‘‘Rasengleis’’
Authors: Fuerst P.
Published: July 2002

The ‘‘Rasengleis’’ (railway lines which are covered by meadow and bedded on conventional ballasted tracks) has indeed a lower noise emission level. Various investigations focusing on the acoustical behavior of the ‘‘Rasengleis’’ were carried out in the last years. The results were rather different. The first sequence of measurements took place before changing the construction of the second part of the railway line. That was to counterbalance errors due to locality, time (the last measurement was carried out almost 2 years later than the first one), and other ambient conditions. The levels could be easily compared among each other using the results of the reference point. Additionally, the measurements were repeated after at least a year to take aging processes of the meadow into account. Two different types of trams were used. They differ among other things in the kind of absorption used for the wheels. One wheel type contains rubber parts stressed of shearing (Tatra T4D), the other wheel rubber parts are stressed of pressure (Bochum). ‘‘Rasengleis’’ reduces noise emission depending on the kind of wheel up to 3 dB (minimum 2 dB). There will be measured levels of drive past, standardized values, and sonograms.
Space-wave number representation of transient waves. Experimental determination of the space location origin of Lamb waves on cylindrical shells
Authors: Martinez Loic , Duclos Jean , Tinel Alain
Published: July 2002

A new space-frequency-wave number representation is introduced. This representation is obtained by space-sliding window FFT of the space-frequency representation. This new method is used to experimentally define the space origin of the pulse-generated Lamb wave on an air-filled cylindrical shell immersed in water (relative thickness is equal to 0.03). The space-wave number slices also allow the measurement of the Lamb-wave complex wave numbers and their propagation direction (reduced frequencies range from 20 to 1000). The reflected field is experimentally separated from multiple propagating Lamb waves. This efficient method is complementary to the surface wave analysis method (S.W.A.M.) [Martinez et al., 16th ICA and 135th ASA Congress, II, 1359–1360 (1998)]. In particular, the space-wave number representations are not limited by space windowing. The experimental results confirm the theoretical computations performed on waves propagating on a plane plate.
Experimental determination of the angular width of plate modes
Authors: Durinck Guy , Thys Willy , Rembert Pascal , Izbicki Jean-Louis
Published: July 2002

The reflection and transmission coefficient of a plate can be expressed as a function of frequency at fixed angle of incidence or as a function of angle of incidence at fixed frequency. In the first situation, the transmission coefficient can be considered as a superposition of frequency resonances, while in the latter case it can be considered as a superposition of angular resonances [R. Fiorito, W. Madigosky, and H. Uberall, J. Acoust. Soc. Am. 66, 1857–1866 (1979)]. Using this approximation the properties of frequency resonances of a plate can be determined experimentally [Derible et al., Ultrasonics International 93 Conf. Proc. 483–486 (1993)]. In this work, this approximation is used to determine the properties of the angular resonances. The transmission coefficient as a function of frequency is determined for a large set of angles of incidence by insonifying the plate with an ultrasonic pulse. Then, at fixed frequency, the data are plotted as a function of angle of incidence. The properties of the angular resonances are extracted using the Argand representation of the transmission coefficient. A comparison with theoretical values is made.
Characterization of bonding quality of composites with the nonlinear modulation method
Authors: Donskoy Dimitri , Ekimov Alexander , Sutin Alexander
Published: July 2002

The nonlinear ultrasonic nondestructive testing technique is emerging as a valuable tool for material characterization and diagnostics. The most widely used nonlinear method is based on measurements of harmonic distortion of the probing ultrasonic wave. Another approach, developed by the authors, utilizes effect of modulation of ultrasound by low-frequency vibration. This method is more sensitive to various material and structural flaws, such as cracks, debonding, delamination, etc. It is also much easier to implement in practice. The present work focuses on characterization of bonding quality of composite plates used in the aerospace industry. The test was performed on 14 samples with various (known) degrees of bonding. The ultrasonic frequencies in the range of 50 kHz to 1.5 MHz were examined to determine the most sensitive frequencies. The modulating vibrations were in much lower frequency range up to 1 kHz. It was found that the average (across the frequency range) normalized modulation level is proportional to the bonding quality and can be used for its quantitative assessment.
Ultrasonic weld testing using the laser vibrometer detection of a time-reversed A wave
Authors: Morvan Bruno , Tinel Alain , Duclos Jean
Published: July 2002

This study presents a method of weld inspection by a surface wave called A wave. The A wave propagates without attenuation in an immersed plane plate, so it is suitable for a long-range inspection of large structures. The studied structure consists of a brass plate perpendicularly soldered on to another one. For convenience, the welding is discontinuous and a nonsoldered zone is chosen as reference. The A wave is very dispersive, so a time-reversed method is used to temporally focus it on the weld: this improves the signal-to-noise ratio. An immersed transducer transmits a reversed A-wave signal. A laser vibrometer collects, at several locations along a line parallel to the weld, the incident A-wave signal and its reflection on the weld. At each position, owing to the A-wave time-reversal excitation, the two detected signals have the same duration. The correlation of the two signals allows one to determine the time delay between the incident and the reflected signal. Once the group velocity is known, the topography of the weld can be built and the defects localized.
Backscattering time-reversal of acoustic waves in random media
Authors: Tourin Arnaud , Derode Arnaud , Fink Mathias
Published: July 2002

Three years ago, the first experiments showing the reversibility of acoustic waves propagating through high-order multiple scattering media were reported [A. Derode, P. Roux, and M. Fink, Phys. Rev. Lett. 75, 4206 (1995)]. These experiments were performed in a transmission mode by means of a time reversal mirror (TRM). Here, new time-dependent experimental results obtained in a backscattering mode are reported. The experiment can be described as follows: the TRM used is a linear array of 128 transducers. One of the elements transmits a pulsed wave into the sample which is a random set of 2400 steel rods. In the 128 recorded backscattered signals, short windows are selected which are time-reversed and retransmitted. Surprisingly, it is found that the synthesized time-reversed waves revive their past and converge onto the initial emitting element, despite disorder. Thus the image of the source is recreated, what is referred to as the mirror effect. The spatial refocusing is found to be improved when selecting windows farther and farther in the backscattered signals. The refocused spot time-evolution is well explained by a simple model including both single and multiple scattering contributions.
Effects of micro bubbles vibration for increase of acoustic streaming
Authors: Sakamoto Shinichi , Watanabe Yoshiaki
Published: July 2002

The effects of the existence of micro bubbles in water for the increasing of acoustic streaming velocity are experimentally discussed. Velocity of acoustic streaming is observed on the sound axis by LDV (laser Doppler velocimeter). Acoustic streaming is generated by continuous ultrasonic sound transmitted by some PZT transducers whose diameter is 15 mm and resonant frequencies are 2.98 or 3.46 MHz. Sound pressures of ultrasonic sound are set to 80, 160, and 240 kPa at the last peak position on the sound axis. Micro bubbles are generated by extracting water with a syringe mechanism, decreasing the pressure of water down to 6.4% below static pressure. Average radius of micro bubbles is approximately 220 μm. The experimental results clearly show the velocity of acoustic streaming increases; the velocity increases from 9 to 13.5 mm/s when the micro bubbles exist. The harmonics are observed when the micro bubbles are generated. The mechanism for the increase of acoustic streaming is discussed from the point of view of the nonlinear effect of the bubble vibration.
Measuring cavitation conditions by multibubble sonoluminescence
Authors: Suslick Kenneth S. , McNamara William B. , Didenko Yuri T.
Published: July 2002

Multibubble sonoluminescence (MBSL) arising from ultrasonic irradiation of solutions containing volatile transition metal car- bonyls have been collected and analyzed. The principal emission is the atomic line spectrum from excited states of the metal atoms. This metal atom MBSL has been used to determine the effective emission temperature of cavitation as a function of the dissolved gas, and the effects of changes in the ratio of the heat capacities and of the thermal conductivity of the dissolved gas have been examined. The results strongly support a simple near-adiabatic compression model of cavitation. The results also indicate that the continua in MBSL spectra are due to emission from small molecules, and not due to plasma emission. [Work supported by the NSF and in part by the DOE.]
Simulation of bubble motion in acoustic cavitation
Authors: Mettin Robert , Luther Stefan , Ohl Claus-Dieter , Lauterborn Werner
Published: July 2002

The motion of cavitation bubbles in an acoustic field is investigated both experimentally and numerically. To simulate the experimental results, a particle approach is employed which calculates the trajectories of many individual bubbles. For this purpose, added mass, drag, and Bjerknes forces are considered, and nucleation and coalescence of bubbles are modeled. Though the particle model is based on simplifying assumptions, it can reproduce different cavitation structure types observed in experiments. [Work partially supported by ‘‘Graduiertenkolleg Strömungsinstabilität und Turbulenz.’’]
Single-bubble large-scale cavitation
Authors: Simonenko Vadim A. , Nogin Vladimir N. , Karlykhanov Nikolay G. , Kovalenko Gennadiy V. , Moss William C.
Published: July 2002

Recent successes in experimental and theoretical studies of single-bubble sonoluminescence (SBSL) suggest the possibility of achieving high energy densities in the collapsed bubble. Scaling analyses and efficient ways for cavitation enhancement are discussed, with particular attention to the geometrical size of the system components and ambient pressure level. The goal is to increase the energy density in the collapsed bubble and increase the size and mass of the heated region. Theoretical estimations and results of direct hydrodynamic numerical simulations are presented for a prospective system with a 0.01- to 0.1-mm-radius gas-filled cavity that is surrounded by a 0.3-m-radius liquid-filled shell. The liquid-filled shell is surrounded by two concentric gas-filled spherical shells. The inner shell contains pressurized hydrogen, whereas, the outer shell contains oxygen. The initial rarefaction phase, which caused bubble expansion, is caused by a sudden release of the hydrogen gas into the outer oxygen-filled shell. The subsequent compression phase results from the combustion of the hydrogen and oxygen gases. [Work was partly supported by CRDF].
Modeling of air-jet-driven instruments: An unstable jet driven by pressure gradient
Authors: Adachi Seiji
Published: July 2002

A new model of the jet deflection is developed to understand the sound production of an organ flue pipe, which is representative of air-jet-driven instruments. This model provides a dynamical equation governing the displacement of a jet, which has the aerodynamical instability and is driven by the acoustic pressure gradient in the direction perpendicular to jet travel. Due to the instability, the growth factor of the deflection becomes exponential, as found in measurements of the jet movement such as hot-wire anemometry and flow visualization. The oscillation condition of an experimental E4 organ pipe is examined by considering the phase difference between the jet displacement at the labium and the acoustic pressure at the mouth. The sound is simulated by means of the physical modeling technique. The simulated pipe behavior is compared with that found in an actual pipe. Similarities and differences found in the transition between oscillation regimes are discussed.
A computer program for optimization of brass instruments. Part II. Applications, practical examples
Authors: Anglmayer Paul , Kausel Wilfried , Widholm Gregor
Published: July 2002

The brass instrument optimization program presented in Part I has been used in a variety of practical cases, demonstrating its power for the improvement of existing brass instruments. In the first and possibly most difficult step, bore lists describing the instrument’s geometry have to be obtained. Sometimes data can be imported directly from a CAD system, otherwise mechanical measurements must be done. Next, the dimensions which are to be varied by the program have to be specified. Constraints can be defined. Specific parametric modification rules representing typical working steps of instrument makers (inserting sleeves, narrowing and widening of certain areas) can be applied. Finally, optimization targets have to be defined. Any combination of intonation, impedance magnitude matching, shape, or envelope goals in user-defined frequency intervals is possible. The optimizer will search for the best possible compromise. During the optimization run, all activities can be observed on screen, and target parameters can be adjusted dynamically. In practical examples, real instruments have been optimized and the proposed modifications have been performed by an instrument maker. Measurements and evaluation results made before and after the modifications have been compared. It was shown that the actual performance improvement matches the predicted one well.
Vortex dynamics, transition to turbulence, and aeroacoustics in rectangular free jets
Authors: Grinstein Fernando F.
Published: July 2002

An overview of recent studies of compressible, rectangular, free jets is presented, with special focus on understanding the dynamics and topology of coherent vortical structures controlling the jet development, and identifying major near-jet noise generation mechanisms. Relevant issues of subgrid and supergrid modeling in free-jet numerical simulations are addressed in this context. The vortex dynamics underlying axis-switching and vortex bifurcation phenomena are examined, including: the roles of self-induced vortex-ring deformation, reconnection, braid vortices, aspect ratio (AR), and the transition to turbulence from laminar initial jet conditions. Qualitatively different vorticity geometries characterizing the near field of low-AR, M<2, ideally expanded, rectangular jets are demonstrated, involving: (i) self-deforming and (ii) bifurcating vortex rings; interacting ring and rib (braid) vortices—including, (iii) single ribs aligned with corner regions (AR>1), and (iv) rib pairs aligned with the corners (AR=1); (v) smaller-scale, elongated, ‘‘worm’’ vortices in the turbulent jet regime. The near-field entrainment of low-AR rectangular jets is shown to be largely determined by the characteristic geometry of the ring–rib interactions; progress in the study of noise-generation mechanisms in low-AR jets is discussed. [Work sponsored by AFOSR, ONR, and the DoD HPC-MP.]
The thermoacoustic oscillator as a musical instrument
Authors: Lauterborn Werner , Müller Georg
Published: July 2002

The air in a tube with a short stack of thin parallel plates inside starts to oscillate when a steep heat gradient is applied. The known device can be considered as an oscillator, more specifically a thermoacoustic oscillator (TAO). It radiates sound when the tube is open to the ambient air. The pitch is determined by the tube length. Thus different pitches can be generated by altering the tube length, allowing the possibility to build musical instruments based on TAOs. As in other instruments with tubes, there are several possibilities to alter the tube length. It may be adjusted by holes that are opened and closed as in a recorder, or by a sliding piston with a hole in it to transmit the sound to the exterior. With the sliding piston, trombonelike sliding sounds can be generated. Examples of musical sounds out of a TAO will be given. A thermoacoustic organ is easily conceivable consisting of TAOs of different lengths played by keys opening and closing the respective TAOs.
Measurements of the performance of a thermoacoustic refrigerator prototype
Authors: Minner B. L. , Braun J. E. , Mongeau L.
Published: July 2002

The performance of a thermoacoustic prototype designed for a cooling capacity of 140 W and operating stack end temperatures of 282 and 306 K was measured. The device was operated using a 55%–45% helium–argon mixture at a mean pressure lower than or equal to 20 bars. The electrodynamic moving coil driver coupled to the half-wavelength resonator was tuned such that the system resonance frequency (i.e., the operating frequency) was around 180 Hz. The stack was made of a coiled polyester film and nylon filament spacers. The secondary system included finned-tube heat exchangers with water as the operating fluid. The power delivered to the driver coil was measured using a power meter. The cooling power was estimated from the water-side temperature drop across the heat exchangers measured using thermopiles, and from the water flow rate. Acoustic pressure, piston acceleration, and temperature measurements were also made at various locations inside the resonator. The measured values were compared with predictions obtained using DeltaE.
Conventional heat exchanger design methods and their applicability to thermoacoustics
Authors: Herman Cila
Published: July 2002

Heat exchangers (HEX) play an important role in many engineering applications, and well established methods for their modeling and optimization are available. Conventional heat exchangers take advantage of forced convection or phase change to transport thermal energy from the hot to the cold fluid, as opposed to thermoacoustic applications where the mean velocity of the oscillatory flow is zero. Conventional HEX are typically classified according to flow arrangement and type of construction. The most commonly implemented methods for HEX analysis are the logarithmic mean temperature difference (LMTD) method and the number of transport units (NTU) approach. Both methods require a set of input parameters and the analysis yields, for example, the appropriate heat exchanger size, i.e., the heat transfer surface area, and type that achieve the desired fluid outlet temperature. The applicability of conventional heat exchanger design methods to thermoacoustic HEX is explored. HEX design solutions developed for thermoacoustics are analyzed in light of the LMTD and NTU approaches. Key differences and issues requiring further research are addressed in the study. [Work supported by the Office of Naval Research.]
Experimental verification of Rayleigh’s interpretation for thermoacoustic Sondhauss-type oscillations
Authors: Huelsz Guadalupe , Ramos Eduardo
Published: July 2002

A century ago, Rayleigh [J. W. S. Rayleigh, The Theory of Sound (Dover, New York, 1945), Vol. 2, Sec. 322] gave a qualitative explanation of the acoustic power production in terms of the relative phase of the pressure wave and the heat transferred to the fluid. In quantitative terms his interpretation is equivalent to saying that a wave is promoted if the absolute value of this relative phase is less than π/2, otherwise the wave is attenuated. The authors have demonstrated [G. Huelsz and E. Ramos, Int. Comm. Heat Mass Transfer 22, 71–80 (1995)] that in standing waves Rayleigh’s criterion for acoustic power production can be translated to the relative phase of the pressure and the temperature oscillations in the limit when the distance to the solid boundary goes to zero; if the absolute value of this quantity is larger than π/2 there is local acoustic power production. In the experimental work reported here, this criterion was used to provide experimental verification for Rayleigh’s interpretation of the acoustic power production in a standing wave parallel to a wall with an axial temperature gradient. [Partial support for this work has been provided by DGAPA-UNAM IN103197 and CONACYT G0044E projects.]
Acoustic wave field imaging and measurement by scanning probe methods
Authors: Chilla Eduard
Published: July 2002

Acoustic waves are widely utilized for the investigation of elastic properties of solids and layered systems. However, since the spatial resolution is limited due to Abbe’s criteria, small structures can not be investigated by elastic waves using conventional techniques. These limitations can be overcome by applying scanning probe methods. A scanning acoustic force microscope (SAFM) and a scanning acoustic tunneling microscope (SATM) for the measurement of high-frequency surface acoustic waves were developed. The methods are based on the mixing at the nonlinearities of the tip-to-sample interactions. The amplitude and phase of the surface oscillation can be imaged with a lateral resolution in the nanometer range. The phase velocities of surface acoustic wave for propagation distances as small as 20 nm were measured. By using the SATM the surface oscillation was measured on the atomic scale. The SAFM was applied for the investigation of high-frequency interdigital transducers up to some GHz. Scattering and dispersion of elastic waves were studied. Recently, it has been shown that in-plane polarized surface acoustic waves can be detected by using a scanning acoustic probe technique. The phase velocity of Love waves in quartz-layered systems was determined.
Comparison between first and second harmonic imaging in ultrasound tomography
Authors: Kourtiche D. , Chitnalah A. , Nadi M.
Published: July 2002

In biomedical ultrasound imaging, quality of images can be enhanced using the second harmonic generated by nonlinear distorsion in the biological medium. Recent works have showed that the use of harmonics improves lateral resolution. The goal of this paper is to show the advantage of ultrasound tomography imaging using the second harmonic. The method of image reconstruction is based on diffraction Fourier theorem which relates the Fourier transform of the measured scattered field with the Fourier transform of the object function. This experimental setup is based on a 3-MHz circular transducer 2 cm in diameter. The transmitted field is measured by a wide bandwidth hydrophone 1 mm in diameter. A cylindrical object is centered at 10 cm from the emitting transducer. A mechanical system permits the translation of the hydrophone step by step (λ/2). For each position, the signal is detected by a numerical oscilloscope and digitized. Data are transferred to the PC for posttreatment. The first and the second harmonics are then obtained from measurement by FFT. Tomographic imaging is obtained from the first and second harmonic measurements. These images are compared and the performance of the second harmonic imaging in terms of resolution is discussed.
Objective and subjective evaluation of performance precision in piano chords
Authors: Tro Jan
Published: July 2002

Analysis of timing precision and dynamic patterns in piano performances using sound recordings may not become a trivial task due to the influence of the recording technique, the room acoustics, and the need for a well-defined attack position for single tone events. During the last ten years the use of standardized registration and transmission of musical performance events makes it a lot easier to do performance analyses even if the present commercially available tools (MIDIized acoustical pianos) still are questioned concerning reliability and reproducibility. This paper discusses the use of a MIDIized piano for multiple recordings of piano performances by several professional artists. The results are based on statistical analyses of both precision and dynamics variation among the performers and deviation for each performer. Subjective listening tests have been used for evaluating musical variables on a subjective quality scale. [B. Repp, ‘‘Individual Differences in Shaping a Musical Phrase,’’ 5th ICMPC, Seoul (1998); J. Tro, ‘‘Micro Dynamics Deviation as a Measure of Musical Quality in Piano Performances?,’’ 5th ICMPC, Seoul (1998).]
Noise annoyance assessment around Paris airports
Authors: Defrance Jerome , Abramowitch Jean-Marc , Bonfil Ferit
Published: July 2002

Within the context of the French Noise and Sound Annoyance Survey ordered by the General Direction of Civil Aviation (DGAC) and the French Environment Ministry, a complete noise impact study concerning Paris-Charles-de-Gaulle and Paris-Orly airports is carried out. On the one hand, a survey of noise annoyance due to aircraft activity around these airports is led through a sounding out of opinion. On the other hand and later on, a complete campaign of 24-hours-a-day measurement of air traffic is carried out around the same previous zones on a total of 36 fixed receiver points. The aim of this work is to establish the correlation between the annoyance perceived by the local residents and the physical characterization of noise expressed through different exposure-to-the-noise indexes which exist at the moment. The results of this survey bring some technical elements able to validate the choice of the future exposure index(es) used in France for the setting up of Noise Annoyance Maps and Noise Exposure Maps around airports.
Resonant scattering phenomenon by in-plane periodic cracks
Authors: Danicki Eugene J. , Hurley Donna C.
Published: July 2002

Two isotropic elastic halfspaces, with periodic domains of perfect bonding and with perfect disbonds (cracks) in between, are considered. In such a system, a free-interface vibration may exist, the frequency of which depends on the crack period and width. This vibration occurs when a bulk wave is scattered by the cracks. There is a deep drop in the transmission coefficient of the wave through the interface, and a corresponding rise in the reflection coefficient, dependent on frequency and the propagation direction of the incident wave. Steel and aluminium halfspaces are considered in each of three combinations, with either perfect or sliding contact between cracks. Numerical results are obtained by extending an existing theory [E. Danicki, J. Acoust. Soc. Am. 100, 2942–2948 (1994)] to account for near-normal incidence. This phenomenon is important for understanding the operation of comb transducers, which may be used for the ultrasonic investigation of materials. Analysis of the interface wave can aid in optimization of the comb material and its groove-to-period relative width, for either solid or sliding contact between the comb and the sample.
Radiation of a sphere near reflecting planes
Authors: Yashkin Vladimir B.
Published: July 2002

A numerical solution by the equivalent sources method to the radiation problem for a sphere in fluid near a rigid plane, in a wedge, and in a corner, is presented and discussed. Distributed circular equivalent sources are used. Dependencies of the radiation impedance and power flow on the geometry parameters are analyzed. It is shown that finite dimensions of the radiator lead to an increase in radiation power flow more than an order of magnitude compared to its value in the free space.
Thermoacoustic sensors
Authors: Fay Burkhard , Reimann Hans-Peter
Published: July 2002

The two procedures mainly used for determining ultrasonic power—the sound radiation force method and the planar scanning technique—are complicated, and require a relatively expensive measuring setup. These procedures are therefore unsuitable for the routine inspection of ultrasonic equipment used in medical and technical applications. In contrast to these procedures, the thermoacoustic sensor is well-suited for this purpose. It is of simple design, small in dimension, and its application requires only relatively inexpensive equipment. The ultrasonic power is determined from the heat produced by the ultrasonic signal in a suitable absorbing material. A disadvantage of this first sensor type is that the power of the ultrasonic signal can be determined only if its amplitude spectrum is known. The new thermoacoustic sensor allows the power of ultrasonic signals to be determined even if their amplitude spectra are unknown. When this sensor type is used, the ultrasonic signal first travels a short distance in a weakly absorbing propagation medium before it enters the absorber, where its energy is completely transformed into heat. In this case, the ultrasonic power is determined from the frequency-independent temperature gradient originating in the weakly absorbing propagation medium immediately in front of the absorber.
Quantitative measurements of solid and fluid properties with near-field acoustics
Authors: Cretin Bernard , Vairac Pascal , Patois Raphael
Published: July 2002

Local measurement of the elastic or viscoelastic properties of solids and fluids has been widely investigated with far-field acoustics e.g., (determination of resonance frequencies and damping, interference between different waves or modes). However, actual techniques need high operating frequencies to shorten the wavelength. Conversely, the proposed method is based on near-field acoustics: a subwavelength acoustic source interacts with the investigated medium within a short distance related to the radius of the source. The resonance frequency of a cantilever is used to measure the interaction between this small vibrating source and the investigated medium. For the characterization of solids, this device is a part of the scanning microdeformation microscope (SMM) that is a kind of ac contact force microscope. For the characterization of fluids, the vibrating tip is replaced by a small sphere. Standard operating frequency of the resonator is 20–30 kHz. The paper presents both theoretical and experimental aspects of the electromechanical resonator, the vibrating element (the tip with radius in the 0.5 to 10-mm range for the investigation of solid samples and the sphere having a 100- to 500-mm diameter for the investigation of fluids), and the interaction. Main features, advantages, and limitations of the presented method will be discussed.
Behavior of the LSAW loss in multi-layer systems
Authors: Wallner Paul , Ruile Werner , Weigel Robert
Published: July 2002

Compared with common SAW, the leaky SAW shows attenuation even if material-dependent loss types like viscosity, dielectric damping, or airloading are neglected. In fact, this typically LSAW loss is caused by a pure bulk wave emission into the piezoelectric substrate. For the search of low-loss crystal cuts it is important that this kind of loss strongly depends on the crystal cut. Only such crystal cuts are important for technical use where this leaky loss shows a minimum. Moreover, former investigations confirmed that an additional metal layer on the piezoelectric substrate can shift the minimum loss to other crystal cut angles, e.g., the shift from 36rotYX to 42rotYX LiTaO3 with 10% Al. New computations show that this behavior can be understood as a general effect: The shift depends on the material constants of layer and substrate. In multi-layer structures all the material constants influence the angle of minimum propagation loss. A distinct angle of minimum can be reached by using a distinct ratio of the layers. This means, if the ratio differs from 10% Al or the aluminum layer is covered with a second layer, the minimum of propagation loss due to bulk wave emission is shifted away from 42rotYX LiTaO3.