bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulent Boundary Layer With Negligible Wall Stress
Authors: Afzal Noor
Published: May 2008

The turbulent boundary layer subjected to strong adverse pressure gradient near the separation region has been analyzed at large Reynolds numbers by the method of matched asymptotic expansions. The two regions consisting of outer nonlinear wake layer and inner wall layer are analyzed in terms of pressure scaling velocities Up=(νp′∕ρ)1∕3 in the wall region and Uδ=(δp′∕ρ)1∕2 in the outer wake region, where p′ is the streamwise pressure gradient and ρ is the fluid density. In this work, the variables δ, the outer boundary layer thickness, and Uδ, the outer velocity scale, are independent of ν, the molecular kinematic viscosity, which is a better model of fully developed mean turbulent flow. The asymptotic expansions have been matched by Izakson–Millikan–Kolmogorov hypothesis leading to open functional equations. The solution for the velocity distribution gives new composite log-half-power laws, based on the pressure scales, providing a better model of the flow, where the outer composite log-half-power law does not depend on the molecular kinematic viscosity. These new composite laws are better and one may be benefited from their limiting relations that for weak pressure gradient yield the traditional logarithmic laws and for strong adverse pressure gradient yield the half-power laws. During matching of the nonlinear outer layer two cases arise: One where Uδ∕Ue is small and second where Uδ∕Ue of order unity (where Ue is the velocity at the edge of the boundary layer). In the first case, the lowest order nonlinear outer flow under certain conditions shows equilibrium. The outer flow subjected to the constant eddy viscosity closure model is governed by the Falkner–Skan equation subjected to the matching condition of finite slip velocity on the surface. The jet- and wakelike solutions are presented, where the zero velocity slip implying the point of separation, which compares well with Coles traditional wake function. In the second case, higher order terms in the asymptotic solutions for nearly separating flow have been estimated. The proposed composite log-half-power law solution and the limiting half-power law have been well supported by extensive experimental and direct numerical simulation data. For moderate values of the pressure gradient the data show that the proposed composite log-half-power laws are a better model of the flow.
Acoustic Power Calculation in Deep Cavity Flows: A Semiempirical Approach
Authors: Oshkai P. , Yan T. , Velikorodny A. , VanCaeseele S.
Published: May 2008

Acoustic power generated by turbulent flow over a coaxial side branch (deep cavity) resonator mounted in a rectangular duct is calculated using a semiempirical approach. Instantaneous flow velocity is decomposed into an irrotational acoustic component and vorticity-bearing hydrodynamic field. The total velocity at several phases of the acoustic oscillation cycle is measured using digital particle image velocimetry. The acoustic velocity field is numerically calculated. The emphasis is on the effect of the accurate geometry representation for the acoustic field modeling on the calculated acoustic power. Despite the generally low levels of acoustic radiation from the coaxial side branches, when the main duct is incorporated into the model for calculation of the acoustic velocity, the acoustic velocity exhibits substantial horizontal (streamwise) components in the vicinity of the cavity corners. This streamwise acoustic velocity correlates with hydrodynamic horizontal velocity fluctuations, thus contributing to the calculated acoustic power. Spatial structure and strength of the acoustic source change as the distance between the side branches varies. Global quantitative imaging approach is used to characterize the transformation of the acoustic source structure in terms of patterns of instantaneous and phase-averaged flow velocity, vorticity, and streamline topology as well as time-averaged acoustic power.
Characterization of Air Flow Through Sintered Metal Foams
Authors: Reutter Oliver , Smirnova Elena , Sauerhering Jörg , Angel Stefanie , Fend Thomas , Pitz-Paal Robert
Published: May 2008

This study investigates air flow in metallic foams, which are produced by the slip reaction foam sintering (SRFS) process. It was conducted as part of the collaborative research center (SFB) 561 “Thermally Highly Loaded, Porous and Cooled Multi-Layer Systems for Combined Cycle Power Plants.” The flow through a porous medium is analyzed by Darcy’s equation with the Dupuit/Forchheimer extension. All measurements can be described very well by this equation and permeability and inertial coefficients are obtained for a large quantity of samples with different base materials and different porosities. A threshold porosity of 70% is observed, above which the pressure loss significantly starts sinking with porosity. Additionally, it was found that the permeability was anisotropic. Permeability is lower in the direction of gravity during foaming. Scattering in the data of the permeability and inertial coefficients versus the porosity is observed and discussed.
Robust Design for Acetabular Cup Stability Accounting for Patient and
Surgical Variability
Authors: Ong Kevin L. , Santner Thomas J. , Bartel Donald L.
Published: May 2008

The stability of cementless acetabular cups depends on a close fit between the components and reamed acetabular cavities to promote bone ingrowth. Cup performance and stability are affected by both design and environmental (patient-dependent and surgical) factors. This study used a statistically based metamodel to determine the relative influences of design and environmental factors on acetabular cup stability by incorporating a comprehensive set of patient-dependent and surgical variables. Cup designs with 2mm or 3mm intended equatorial bone-implant interferences appeared to perform the best, improving implant stability with smaller mean and variability in cup relative motions and greater mean and smaller variability in ingrowth areas. Cup eccentricity was found to have no effect on implant performance. Design variables did not contribute as much to the variation in performance measures compared to the environmental variables, except for potential ingrowth areas.
Computational Modeling and Simulation of a Single-Jet Water Meter
Authors: Larraona Gorka S. , Rivas Alejandro , Ramos Juan Carlos
Published: May 2008

A single-jet water meter was modeled and simulated within a wide measuring range that included flow rates in laminar, transitional, and turbulent flow regimes. The interaction between the turbine and the flow, on which the operating principle of this kind of meter is based, was studied in depth from the detailed information provided by simulations of the three dimensional flow within the meter. This interaction was resolved by means of a devised semi-implicit time-marching procedure in such a way that the speed and the position of the turbine were obtained as part of the solution. Results obtained regarding the turbine’s mean rotation speed, measurement error, and pressure drop were validated through experimental measurements performed on a test rig. The role of mechanical friction on the performance of the meter at low flow rates was analyzed and interesting conclusions about its influence on the reduction of the turbine’s rotation speed and on the related change in the measurement error were drawn. The mathematical model developed was capable of reproducing the performance of the meter throughout the majority of the measuring range, and thus was shown to be a very valuable tool for the analysis and improvement of the single-jet water meter studied.
Simulation of Turbulent Airflow Using a CT Based Upper Airway Model of a Racehorse
Authors: Rakesh Vineet , Datta Ashim K. , Ducharme Normand G. , Pease Anthony P.
Published: May 2008

Computational model for airflow through the upper airway of a horse was developed. Previous flow models for human airway do not hold true for horses due to significant differences in anatomy and the high Reynolds number of flow in the equine airway. Moreover, models that simulate the entire respiratory cycle and emphasize on pressures inside the airway in relation to various anatomical diseases are lacking. The geometry of the airway was created by reconstructing images obtained from computed tomography scans of a thoroughbred racehorse. Different geometries for inhalation and exhalation were used for the model based on the difference in the nasopharynx size during the two phases of respiration. The Reynolds averaged Navier–Stokes equations were solved for the isothermal flow with the standard k-ϵ model for turbulence. Transient pressure boundary conditions for the entire breathing cycle were obtained from past experimental studies on live horses. The flow equations were solved in a commercial finite volume solver. The flow rates, computed based on the applied pressure conditions, were compared to experimentally measured flow rates for model validation. Detailed analysis of velocity, pressure, and turbulence characteristics of the flow was done. Velocity magnitudes at various slices during inhalation were found to be higher than corresponding velocity magnitudes during exhalation. The front and middle parts of the nasopharynx were found to have minimum intraluminal pressure in the airway during inhalation. During exhalation, the pressures in the soft palate were higher compared to those in the larynx, epiglottis, and nasopharynx. Turbulent kinetic energy was found to be maximum at the entry to the airway and gradually decreased as the flow moved inside the airway. However, turbulent kinetic energy increased in regions of the airway with abrupt change in area. Based on the analysis of pressure distribution at different sections of the airway, it was concluded that the front part of the nasopharynx requires maximum muscular activity to support it during inhalation. During exhalation, the soft palate is susceptible to displacements due to presence of high pressures. These can serve as critical information for diagnosis and treatment planning of diseases known to affect the soft palate and nasopharynx in horses, and can potentially be useful for human beings.
Thermodynamics of the heart: Relation between cardiac output and oxygen consumption
Authors: Uehara Mituo , Sakane Kumiko K. , Bertolotti Simone A.
Published: May 2008

A thermodynamic approach is used to derive a relation between cardiac output and rate of oxygen consumption. As an example, the relation is used to calculate the cardiac output of a young woman exercising on a treadmill. The results can be understood by undergraduates without any previous knowledge of human physiology.
Dead time correction via the time series
Authors: Meeks Craig , Siegel P. B.
Published: May 2008

We present a method that allows us to correct for dead time and check for the proper operation of a radiation detector while recording data. The method is based on the exponential probability density of the time interval between successive detector pulses, and involves examining the ratio of the moments of the time series with a delay time.
Flexural wave dispersion in orthotropic plates with heavy fluid loading
Authors: Magliula Elizabeth , McDaniel J. Gregory
Published: May 2008

Orthotropic plates support flexural waves with wavenumbers that depend on their angle of propagation. The present work investigates the effect of fluid loading on this angular dependence, and finds that the effect is relatively small for typical composite plate materials in contact with water. This finding results from an analytical model of the fluid-loaded plate, in which the plate is modeled by classical laminated plate theory and the fluid is modeled as an ideal acoustic fluid. The resulting dispersion relation is a tenth-order polynomial in the flexural wavenumber. Direct numerical solution, as well as analysis at frequencies below coincidence, reveals that the angular dependence of wavenumber is magnified but not significantly distorted by the addition of fluid loading.
Model-based detection of synthetic bat echolocation calls using an energy threshold detector for initialization
Authors: Skowronski Mark D. , Fenton M. Brock
Published: May 2008

Detection of echolocation calls is fundamental to quantitative analysis of bat acoustic signals. Automated methods of detection reduce the subjectivity of hand labeling of calls and speed up the detection process in an accurate and repeatable manner. A model-based detector was initialized using a baseline energy threshold detector, removing the need for hand labels to train the model, and shown to be superior to the baseline detector using synthetic calls in two experiments: (1) an artificial environment and (2) a field playback setting. Synthetic calls using a piecewise exponential frequency modulation function from five hypothetical species were employed to control the signal-to-noise ratio (SNR) in each experiment and to provide an absolute ground truth to judge detector performance. The model-based detector outperformed the baseline detector by 2.5dB SNR in the artificial environment and 1.5dB SNR in the field playback setting. Atmospheric absorption was measured for the synthetic calls, and 1.5dB increased the effective detection radius by between 1 and 7m depending on species. The results demonstrate that hand labels are not necessary for training detection models and that model-based detectors significantly increase the range of detection for a recording system.
Fitting data, but poor predictions: Reverberation prediction uncertainty when seabed parameters are derived from reverberation measurements
Authors: Holland Charles W.
Published: May 2008

For many decades, researchers have been developing inverse techniques for estimating seabed parameters from reverberation data, notably scattering strength. Generally, the angular dependence of the scattering kernel is unknown and is either solved for or assumed fixed. In either case, agreement is typically quite good between the measured reverberation and that modeled (by fitting scattering parameters). However, what are the resulting uncertainties in a reverberation prediction if the ocean or geometry changes? The main results of the paper are that (1) these prediction uncertainties are surprisingly large, of order 10dB at 10km and thus (2) traditional/current methods for reverberation inversion should be augmented, mitigating the large prediction uncertainties by an additional measurement. Several options for additional measurements are discussed.
Calculations of modes in circumferentially nonuniform lined ducts
Authors: Bi WenPing
Published: May 2008

This paper proposes a computationally efficient method of determining eigenfunctions and eigenvalues of acoustic modes propagating in circular lined ducts with zero or uniform flow. Linings with circumferentially nonuniform impedance, as found in nacelle acoustics, are the focus. The method of solution adapts in two important respects—the presence of flow and the imposition of impedance boundary conditions—the series expansion method first proposed by Pagneux et al. [J. Acoust. Soc. Am. 110, 1307–1314 (2001)] to calculate the eigenvalues of Lamb modes. The inclusion of flow, and a corresponding different method of solution leading to an improved convergence of eigenvalues (O(N−5), N is the truncation of radial basis of expansion), is the important new feature as compared to the previous adaptation by Bi et al. [J. Acoust. Soc. Am. 122, 280–291 (2007)]. As a result, it becomes possible to safely determine and in a simple manner the eigenvalues and eigenfunctions of circumferentially nonuniform lined ducts in the presence of uniform flow, up to relatively high frequencies (e.g., 30<kR<80). All required eigenvalues are calculated at a time and no initial values guesses are needed. Results are presented and the method is discussed.
Experimental validation and applications of a modified gap stiffness model for granular marine sediments
Authors: Kimura Masao
Published: May 2008

The author has proposed a modified gap stiffness model, which is incorporated into the Biot model; the resultant model is called the BIMGS model. By using this model, it is theoretically demonstrated that the frame bulk modulus is dependent on frequency [M. Kimura, “Frame bulk modulus of porous granular marine sediments,” J. Acoust. Soc. Am. 120, 699–710 (2006)]. In this study, the modified gap stiffness model is reinvestigated and approximated expressions are derived for low- and high-frequency ranges. In particular, experimental validation of the BIMGS model is carried out. First, for glass beads and beach sands, the modified gap stiffness at a high frequency is experimentally obtained as a function of the grain size. Second, by using the measured values of the longitudinal wave velocities in the glass beads with two types of alcohol-water-mixed liquids, it is validated that the frame bulk modulus is a linear function of the fluid bulk modulus and that the frame bulk modulus is dependent on frequency, which can be derived from the BIMGS model. Finally, for applying the BIMGS model, it is shown that the reported velocity dispersion and the frequency dependence of attenuation, which cannot be explained by using the Biot-Stoll model with a constant frame bulk modulus, can be explained.
Broadband backscatter from individual Hawaiian mesopelagic boundary community animals with implications for spinner dolphin foraging
Authors: Au Whitlow W. L. , Benoit-Bird Kelly J.
Published: May 2008

Broadband simulated dolphin echolocation signals were used to measure the ex situ backscatter properties of mesopelagic boundary community (MBC) in order to gain a better understanding of the echolocation process of spinner dolphins foraging on the MBC. Subjects were captured by trawling with a 2-m-opening Isaacs-Kidd Midwater Trawl. Backscatter measurements were conducted on the ship in a 2000L seawater tank with the transducer placed on the bottom pointed upwards. Backscatter measurements were obtained in both the dorsal and lateral aspects for seven myctophids and only in the dorsal aspect for 16 more myctophids, six shrimps, and three squids. The echoes from the myctophids and shrimps usually had two highlights, one from the surface of the animal nearest the transducer and a second probably from the signal propagating through body of the subject and reflecting off the opposite surface of the animal. The squid echoes consisted mainly of a single highlight but sometimes had a low amplitude secondary highlight. The backscatter results were used to estimate the echolocation detection range for spinner dolphins foraging on the mesopelagic boundary community. The results were also compared with multi-frequency volume backscatter of the mesopelagic boundary community sound scattering layer.
New Trends in Aeroacoustics: From acoustic analogies to direct numerical simulations
Authors: Juvé Daniel
Published: May 2008

Modern aeroacoustics started in the early 1950's when Lighthill developed his famous acoustic analogy in an attempt to understand, and reduce, the terrifying noise generated by jet aircrafts. For nearly 50 years the subject of aerodynamic sound was dominated by approaches based upon this analogy or variants of it. Recently, the availability of powerful computing facilities combined with the development of numerical algorithms specially designed to simulate sound propagation over large distances has paved the way for "a second golden age of aeroacoustics" (to quote Lighthill himself). In this talk we will first give an overview of this evolution from acoustic analogies to computational aeroacoustics (CAA). Typical illustrations of the CAA approach will then be presented and applications for transportation systems will be discussed.
Differences in perception of noise and privacy in different office types
Authors: Bodin Danielsson Christina
Published: May 2008

Differences between office types with regard to their architectural and functional features may have an impact on the employees' disturbance by noise and perception of privacy. These aspects may in its turn have an impact on employees' satisfaction and psychological responses to the office environment. In a study 469 employees in 26 different companies have rated their satisfaction with the office environment in seven different office-types: cell-office, shared room office, small open plan office, medium open plan office, large open plan office, flex-office and combi-office. This paper discusses the results concerning the employees' perception of noise and privacy and put the results in relation to the two different aspects of privacy, visual and acoustic privacy, and the role of personal control. In the statistical analysis adjustments for potential confounders as age, gender, job rank and line of business were done, which are known to have an influence on perception and satisfaction. Substantial differences between employees in different office-types were found. The fact that there were such differences between different types of offices that mean sharing of workspace and work facilities was a surprise. Architectural and functional features of the offices are discussed as the main exploratory factors for these results.
Modeling the sound field of open spaces using a diffusion equation model
Authors: Jing Yun , Xiang Ning
Published: May 2008

Steady-state and transient sound field modeling of open spaces, such as urban squares, courtyard-type traditional Chinese theaters, is discussed in this paper. It is well known that the application of the statistical room-acoustic theory is strongly limited in this case, because of the high non-uniformity of the absorption coefficient. In this study, a diffusion equation along with a recently proposed modified boundary condition [Y. Jing and N. Xiang, J. Acoust. Soc. Am., 123, 2008, 145-153] is used to predict the acoustic characteristics of open spaces, in terms of both sound pressure level distributions and reverberation times. Three different types of open spaces are presented, including urban squares, quasi-cubic open rooms, and urban streets. This paper will compare the simulation results with the experimental results conducted in all these three cases (scale model), to verify the validity and efficiency of the diffusion equation model.
Acoustical considerations in the design for ‘La Philharmonie de Paris’
Authors: Marshall Harold , Valentine Joanne O. , Scelo Thomas
Published: May 2008

The 2006 competition instructions for "La Philharmonie de Paris" included a detailed acoustical specification and the general requirement that the design should be a "new typology". The early and late sound fields respectively should be controlled independently. This paper gives an account of the acoustical aspect of the winning design, its relationship to the architecture at the competition phase, and the methodology for developing the design in subsequent phases. The new typology developed here is called the "bicameral adaptable concert hall". There are partial precedents for the concepts advanced and these will be identified. Reference is also made to a related paper (at this conference) which discusses the issue of coupling between the acoustical spaces.
Acoustical analysis of a variable roof configuration concert hall: The São Paulo Hall
Authors: Tenenbaum Roberto A. , Oliveira Lenine V. , Müller Swen
Published: May 2008

The São Paulo Hall (SPH) is recognized by musicians and musical critics in general by its good acoustical quality. It has, as an important feature, variable acoustics due to its movable roof, which is employed by musicians to tune the room according to the musical style. This work addresses the acoustical quality of SPH and its dependence on the roof configuration. Impulse responses for one source, eight microphone and two dummy head positions, using the sweep-sine technique with pre-emphasis, were obtained for seven roof configurations. Some details of the measurement procedure to ensure good accuracy are discussed. The measurement results were then used to compute the main room acoustical quality parameters, for each octave band between 63 and 8000 Hz. The spatial average and deviation of these data are presented as a function of the frequency band. The influence of the roof configurations on the obtained acoustical parameters is also discussed. Furthermore, comparative plots among SSP at the chosen roof configurations and two famous and representative halls from the classical and romantic periods are reported and discussed. It is concluded that the movable roof is very effective in modifying the room acoustics and that the musician's choices are quite good.
The acoustic design of the Elisabeth Murdoch Hall, Melbourne, Australia
Authors: Orlowski Raf
Published: May 2008

The Elisabeth Murdoch Hall is a 1000 seat recital space which will be completed in the latter half of 2008. The overall geometry is based on a classical shoebox shape to provide acoustic excellence although the internal appearance is wholly contemporary. The walls and ceiling of the hall are clad in timber panelling which is stepped in and out and also modulated to provide diffusion at mid and low frequencies. In addition, the surface layer of the panels is grooved or cut away to form an abstract pattern which is both decorative and diffusing at high frequencies. A notable aspect of the hall is that it has no orchestral reflector. The important early reflections for good orchestral ensemble are provided by articulating and shaping the surfaces around the stage. Although the hall is primarily for recitals of classical music, provision is made for amplified music by introducing acoustic drapes.
Issues in the perception of multiple speech sources under reverberant listening conditions
Authors: Darwin Chris J.
Published: May 2008

This paper will review the changes that room acoustics can make to the cues available for speech perception and those available for the localisation of sound sources, and give an overview of the perceptual mechanisms underlying the causes of the reduced intelligibility that reverberant room acoustics can make to the intelligibility of speech that is masked by additional sources of speech. Major factors that contribute to the interference of one source of speech by another are the obscuring of primary speech cues either by masking or by the failure of simultaneous grouping mechanisms, and the failure to track the sounds of an individual talker across time. The role of spatial localisation mechanisms to both these factors will be discussed.
Some Temporal and Spatial Effects of Room Acoustics on Speech Privacy
Authors: Bradley John S. , Apfel Marina , Gover Brad N.
Published: May 2008

The speech privacy of meeting rooms relates to the possibility of eavesdroppers outside the room being able to understand speech from within the meeting room. Although the speech privacy of meeting rooms is usually assumed to relate to the level of the speech transmitted from the room relative to the ambient noise outside the room, the intelligibility of the transmitted speech is also influenced by room acoustics. However, the audibility of speech is only influenced by the levels of the transmitted speech and ambient noise. This paper reports on a series of speech intelligibility tests in which the components of the problem were systematically added. As expected, adding early reflections of speech from various directions increases intelligibility but later-arriving speech sounds decrease intelligibility. While a spatial separation of speech and noise sources in free field conditions increases speech intelligibility (spatial release from masking), in more realistic conditions, representing a diffuse ambient noise field, the effects are much smaller. Conditions are further complicated by the sever filtering of the speech on transmission through typical walls. The combined effects can be estimated and are significant. If ignored costly over-design of the sound isolation of the meeting room could occur.
Monaural segregation of reverberant speech
Authors: Jin Zhaozhang , Wang Deliang
Published: May 2008

A major source of signal degradation in realistic environments is room reverberation. Monaural speech segregation in reverberant environments is a particularly challenging problem. Although inverse filtering has been proposed to partially restore the harmonicity of reverberant speech before segregation, this approach is sensitive to different room configurations. In this study, we investigate monaural segregation of reverberant speech by employing a supervised learning approach to map from a set of pitch-based auditory features to a grouping cue, which encodes the posterior probability of a time-frequency unit being target dominant given observed features. We devise a novel objective function for the learning process, which relates to the goal of maximizing SNR directly. The models trained using this new objective function yield significantly better results for unit labeling. In our segregation system, a segmentation and grouping framework is utilized in order to capture segments reliably under reverberant conditions and organize them into streams. Systematic evaluations show that our approach produces very promising results.
Spatial Audio Reproduction Using Distributed Mode Loudspeakers
Authors: Atkins Joshua , West James
Published: May 2008

For future telecommunication systems to become more pervasive in society they must have the ability to produce high quality surround sound audio for multiple listeners. Current 5.1 audio systems lack the capacity to handle large group telecommunications because of their limited optimal listening positions ("sweet spots") and their preference for sound generated in front of the listeners. This is due in part to the non-optimal position of the loudspeakers and also to the fact that very directional speakers are commonly used. Recently, a new form of speaker has been developed called a distributed mode loudspeaker (DML). These speakers use bending waves in a panel to radiate sound. Consequently, they can be very good omnidirectional sources throughout nearly all of the human hearing range. Experiments using a higher order ambisonics (HOA) approach to sound field capture and generation will be presented to show how conventional electrodynamic speaker arrays compare to equivalent DML arrays for spatial sound reproduction. This work is funded by NSF Grant IIS-0534221.
Low frequency sound absorption measurements - limits and ideas
Authors: Nocke Christian
Published: May 2008

Many (standardised) measurement procedures for sound absorption rely on geometrical approximations or statistical approaches. They fail whenever the limit of geometrical acoustics is reached. Also many room acoustic modeling procedures assume geometrical spreading of sound and neglect the wave characteristics of sound waves. In this paper various approaches towards the measurement of sound absorption are briefly reviewed and discussed in the light of low frequency applications. Approaches towards analytic descriptions for sound fields in room at low frequencies from the early 1930s are reviewed. The approaches might be the basis for future developments on new procedures for measurement techniques. Finally measurement results on the deduction of sound absorption at low frequencies are presented.
The Perforated Panel Resonator with Flexible Tube Bundles and its Appliations
Authors: Lu Yadong , Tang Huide , Wang Qiang , Tian Jing , Qu Youli , Qiu Bo
Published: May 2008

The sound absorptive mechanism and properties of the perforated panel resonator with flexible tube bundles are presented. Based upon that, some practical applications of the sound absorbing structure are introduced as follows. First of all, the perforated panel resonator with flexible tube bundles is used in designing a highly sound absorptive chamber, which is used as an audio-video laboratory. The acoustical performances of the chamber are presented. Second, the perforated panel resonator with flexible tube bundles is used in highly efficient duct silencer. The total noise level of axial fan source is attenuated to background noise level. Not only middle and high frequency noise is reduced, but also low frequency noise is suppressed considerably. Third, the perforated panel resonator with flexible tube bundles is used in a small-type centrifugal fan's casing treatments. The cut-off region of the centrifugal fan's casing is also acoustically treated. After the acoustical treatments, total sound power level of the fan is reduced obviously. Fourth, the perforated panel resonator with flexible tube bundles is used in designing the exhaust ducts and sound absorptive channel walls for an electrical transformer substation. The noise emitted from the transformer substation is reduced to surrounding background noise level.
Acoustic flexibility in singing birds under noisy urban conditions
Authors: Slabbekoorn Hans
Published: May 2008

Birds rely on song for defending a territory and attracting a mate. More and more breeding areas are affected by human activities and anthropogenic noise has become almost omnipresent. Consequently, song function in and around cities, and alongside highways, train tracks and airports, is increasingly hampered by noise interference. Several counter strategies in producing sounds, related to changes in loudness, pitch, and timing, can help out under these noisy urban conditions. Observational data have yielded several interesting patterns which show remarkable singing flexibility in different species that are typically common in cities. Here I present data for a new species, the chiffchaff (Phylloscopus collybita) showing spectral and temporal adaptation which reduces masking alongside a highway in the Netherlands. Furthermore, experimental field data reveal for the first time that this species is able to adjust immediately to exposure to highway noise via artificial playback in quiet territories. Acoustic flexibility may be key to efficient use of the 'left-over acoustic space' and may determine whether individual birds can maintain their territory and breed successfully. Variation in flexibility among species may explain which birds will remain widespread in our noisy world and which will be pushed back into 'silent' habitat pockets.
Comodulation masking release in the bottlenose dolphin (Tursiops truncatus)
Authors: Branstetter Brian K. , Finneran James J. , Green Linda S. , Robinson Erik E. , Tormey Megan N. , Dear Randall L.
Published: May 2008

The power spectrum model of masking, derived from critical band or critical ratio measurements is often cited and used to extrapolate the effects of masking noise on the signal detection abilities of marine mammals. However, the power spectrum model may not generalize well to environmental noise that is often coherently amplitude-modulated across frequency regions. The current study demonstrates a pattern of masking where temporally fluctuating comodulated noise produces lower masked thresholds (up to a 17 dB difference) compared to Gaussian noise of the same spectral density level. Noise possessing wide bandwidths, low temporal modulation rates, and across-frequency temporal envelope coherency resulted in lower masked thresholds, a phenomenon known as comodulation masking release. The results are consistent with a model where dolphins compare temporal envelope information across auditory filters to aid in signal detection. Furthermore, results suggest conventional models of masking derived from experiments using random Gaussian noise may not generalize well to environmental noise that dolphins actually encounter.
Underwater radiated noise due to the piling for the Q7 Offshore Wind Park
Authors: De Jong Christ A.f. , Ainslie Michael A.
Published: May 2008

The Q7 is the second offshore wind farm in the Dutch sector of the North Sea and, at 23 km off the Dutch coast, the world's first to be located outside the 12-mile limit. To support the wind turbines, monopiles (54 metres long steel pipes with a diameter of 4 metres) are hammered into the seabed using a pile-driver. The underwater radiated noise during the impulsive hammering of 9 out of 61 monopiles was monitored. Although there is a wide concern about the impact of piling noise on the marine life in the area, there are no criteria for the maximum acceptable noise levels. A quantitative comparison of the results of various studies in which the underwater noise from pile driving has been measured and reported is difficult, due to the lack of standardization in the level definitions and data processing. The Q7 data have been analyzed in terms of a broadband sound exposure level, peak pressure and pulse duration and a 1/3-octave band frequency spectrum of the sound pressure at different hydrophone locations, for each hammer stroke that has been recorded. The results are discussed in relation to the stroke energy and the hydrophone distance and depth.
Environmental Risk Management Capability: Advice on minimising the impact of sonar on marine mammals
Authors: Schofield Colin
Published: May 2008

The Environmental Risk Management Capability - Sonar (ERMC(S)) has now been accepted into service by the UK Royal Navy. ERMC(S) is the first operational software package that provides a comprehensive risk assessment of the common concern of the potential impact of sonar usage on marine mammals. The algorithms include allowance for extended periods of use and advice on achievable mitigation options. Now that the system has achieved this significant milestone, this paper reviews the elements of the system that have made progress to this stage so successful: -The techniques and data used by the algorithms. -The inclusive development approach that allowed all the concerned stakeholders to be satisfied with the processes utilised. -The annual review cycle that will enable the tool to maintain its links with forefront research in this area. -The application of the system to non-military sound sources as the benchmark approach. This paper will show how ERMC(S) can be develop into a tool for both commercial and military sound sources using proving and established techniques.
Acoustic navigation and communications for high latitude ocean research (ANCHOR)
Authors: Lee Craig M. , Gobat Jason I.
Published: May 2008

Recent community reports on autonomous and Lagrangian platforms and Arctic observing identify the development of under-ice navigation and telemetry technologies as one of the critical factors limiting the scope of autonomous (e.g. floats, AUVs and gliders) high-latitude measurement efforts. These platforms could provide persistent, high-resolution, basin-wide sampling in ice-covered regions and collect measurements near the critical ice-water interface. Motivated by the dramatic advances in temporal and spatial reach promised by autonomous sampling and by the need to coordinate nascent efforts to develop navigation and communication system components, an international group of acousticians, platform developers, high-latitude oceanographers and marine mammal researchers gathered in Seattle, U.S.A. from 27 February - 1 March for an NSF Office of Polar Programs sponsored Acoustic Navigation and Communication for High-latitude Ocean Research workshop. Workshop participants summarized the current state of knowledge concerning Arctic acoustics, navigation and communications, developed an overarching system specification to guide community-wide engineering efforts and established an active community and steering group to guide long-term efforts and ensure interoperability between elements developed by disparate teams. This presentation will summarize workshop findings and provide an update on recent developments stemming from the EU DAMOCLES and US NSF Arctic Observing Network programs.
Acoustical methods that provide an integrated view of the marine ecosystem
Authors: Lebourges-Dhaussy Anne , Josse Erwan
Published: May 2008

The fish stock assessment are not anymore the sole purpose of the "fisheries acoustics" as it appears clearly that the fish belongs to a whole ecosystem, of which functioning mechanisms must be understood to better assess the fish populations' health state. The biotic factors, as prey availability, are of great importance and can be studied also by acoustic tools. The multifrequency systems (echosounders or profilers), increase the size range of the organisms that can be detected; new multibeam sonars provide a high resolution allowing studies close to boundaries. The results of the SIMFAMI European program are presented. It aimed at marine organism classification through multifrequency information, including fish/plankton separation and classification of meso/macroplankton. It provided new methods to classify and describe the various biotic components of the ecosystem from fish to plankton. A link between the use of these new methods and the former micro/mesoplankton classification tools as well as passive acoustic tools allows to reach the classification of a huge range of organisms and to study their interactions. Results of such experiences done on various upwelling ecosystems are shown. Additionally for complex fields, new multibeam sonars can advantageously help in the description of fish distributions.
Acoustic assessment of trophic dominance in a marine ecosystem
Authors: Thorne Richard E. , Thomas Gary L.
Published: May 2008

High-frequency acoustic surveys over the past 15 years show that the trophic structure in Prince William Sound (PWS), Alaska, functions as a wasp-waist ecosystem. Three dominant biomasses in PWS are: (1) Pacific herring (2) walleye pollock and (3) the large-bodied copepods (Neocalanus spps.) that dominate the spring zooplankton assemblage. The acoustic surveys and associated ecosystem observations suggest that the relative dominance of herring and pollock affects the composition of the apex predators. The near-shore and near-surface distribution of herring provides access by surface-oriented marine mammal and seabird predators, such as sea lions, seals, murres and cormorants, to a crucial winter-period food source. In contrast, the deep, off-shore distribution of the pollock favors large benthic predators, such as demersal sharks, halibut, and flounder. The acoustic surveys also demonstrated that the abundance of large-bodied copepods in PWS is critical to ecosystem productivity, including survival of juvenile pink salmon, and may affect the relative dominance of herring and pollock. An additional outcome of the long-term database on Pacific herring was the discovery of linkages between the 1989 Exxon Valdez oil spill and a subsequent collapse of the herring along with associated predators.
Acoustic GIS-based monitoring of Atlantic cod ecosystems in coastal Newfoundland
Authors: Rose George A.
Published: May 2008

Several bays in Newfoundland hold the largest extent groups of overwintering and spawning Atlantic cod (Gadus morhua), and are spawning areas for capelin (Mallotus villosus), the most important forage species. These species co-exist in coastal ecosystems whose physical features and ecological sensitivities restrict monitoring using conventional fisheries methods. Active and passive acoustic methods, acoustic telemetry, oceanographic instrumentation and ROV video have been used to monitor overwintering and spawning distributions and abundance of cod, using mobile and fixed platforms. Cod behaviour is complex and features high mobility both horizontally and vertically, especially during migratory and spawning periods. Overwintering cod have school packing densities >>1 fish.m-3. Spawning features increased mobility and vertical structures or "columns" of individual fish and sound production captured using stationary hydrophones. Acoustic returns from aquatic vegetation and bottom types have been used to map juvenile habitat. Acoustic telemetry has established the movement patterns of male and female fish during spawning and the homing characteristics of cod as the basis of their stock structure. The movements and spawning behaviour of capelin can also be monitored as can interactions between predators and prey. An experiment using real-time and 3D location telemetry in a comprehensive GIS system will be described.
The feasibility of local harmonic motion imaging for the guidance and control of focused ultrasound surgery
Authors: Hynynen Kullervo , Curiel Laura , Chopra Rajiv
Published: May 2008

A local harmonic motion (LHM) can be generated within the tissues by the periodic induction of radiation force using a focused ultrasound (FUS) transducer. Tissue motion can then be tracked by collecting RF signals during the excitation using a separate transducer. Finally, displacement estimates can be obtained by cross-correlating the collected RF signals. The characteristics of the induced LHM depend on the local elastic properties of the tissues making it an attractive tool for imaging and therapy control applications. LHM measurements have been obtained in vivo on rabbit muscle and it was observed that the amplitude of the motion was significantly reduced after coagulation. LHM was successfully used to spatially detect the presence of the coagulation lesions within the tissues as a drop in LHM amplitude. It was also possible to detect the location of an implanted VX2 tumor when a spatial scan was performed as the LHM amplitude was lower inside the tumor because of an increased stiffness. Measurements of LHM during tissue heating using FUS reflected the changes in stiffness and revealed the apparition of coagulation showing the potential of these measurements as an alternative control for the FUS exposure. [Work supported by NIH GrantR33 CA102884 and CRC.]
Temperature measurements and determination of cavitation thresholds during High Intensity Focused Ultrasound (HIFU) Exposures in ex-vivo porcine muscle
Authors: Maruvada Subha , Liu Yunbo , Herman Bruce A. , Pritchard William F. , Harris Gerald R.
Published: May 2008

Cavitation in HIFU procedures can yield unpredictable results, particularly when the same location is targeted for more than several seconds. To study this effect, temperature rise was measured in fresh ex-vivo porcine tissue during HIFU exposures. Immediately following euthanasia, a section of back muscle (latissimus dorsi) was resected and a 50 μm diameter fine bare wire thermocouple was placed via needle through the tissue. 825 kHz HIFU was then applied to the tissue focused at the thermocouple junction. Thirty second HIFU exposures of increasing pressure from 1-7.5 MPa were applied and the temperature rise and decay during and after sonication were recorded. B-mode imaging was used to monitor any cavitation activity during sonication. If cavitation was noted during the sonication, the sonication was repeated at the same pressure level two more times at 20 minute intervals in order to characterize the repeatability given that cavitation has occurred. The cavitation threshold of porcine muscle was determined to be between 4 and 7 MPa. Temperature traces obtained at various pressure levels demonstrated a wide range of heating profiles in fresh ex-vivo tissue due to both the occurrence of cavitation and viscous heating artifacts. (This research was supported by DARPA IAG # 224-05-6016).