bluuebunny/crossref_metadata_2025 huggingface dataset:
Serodiversity and ecological distribution of Vibrio parahaemolyticus in the Venetian Lagoon, Northeast Italy
Authors: Caburlotto Greta , Haley Bradd J. , Lleò Maria M. , Huq Anwar , Colwell Rita R.
Published: January 2010

Vibrio parahaemolyticus is a natural inhabitant of estuarine and marine environments constituting part of the autochthonous microflora. This species is associated with human gastroenteritis caused by ingestion of contaminated water and undercooked seafood. During the past several years, the number of V. parahaemolyticus gastroenteritis cases have increased worldwide, causing over half of all food‐poisoning outbreaks of bacterial origin. Vibrio populations in water are known to be influenced by environmental factors. Notably, it has been shown that in different parts of the world the distribution of V. parahaemolyticus in the marine environment is related to the water temperature. In this study, we identified environmental determinants affecting distribution of V. parahaemolyticus in the Venetian Lagoon, in the Italian North Adriatic Sea. Data obtained revealed that sea surface temperature constitutes the key factor influencing occurrence of V. parahaemolyticus, but salinity and chlorophyll concentration are also important. Serotyping of a collection of V. parahaemolyticus environmental isolates revealed high serodiversity, with serotypes O3:KUT and O1:KUT, belonging to the ‘pandemic group’, occurring with higher frequency. From our results, we conclude that there is no correlation between serotype and specific geographic site or season of the year. However, certain serotypes were isolated in the Lagoon during the entire 18 months of the study, strongly suggesting persistence in this environment.
Putatively free‐living ‘Endomicrobia’– ancestors of the intracellular symbionts of termite gut flagellates?
Authors: Ikeda‐Ohtsubo Wakako , Faivre Nicolas , Brune Andreas
Published: January 2010

Endomicrobia represent a candidate class in the Elusimicrobia phylum (formerly Termite Group 1) and were originally described as obligate intracellular symbionts of gut flagellates in lower termites. However, 16S rRNA gene sequences of Endomicrobia have been detected also in the gut of insects that do not possess such flagellates, e.g. higher termites and cockroaches. When we eliminated the large gut flagellates of Reticulitermes santonensis by feeding a starch diet, we discovered novel lineages of Endomicrobia that were hitherto undetected in normally faunated specimens. The new phylotypes are clearly separated from the endosymbionts of gut flagellates and fall into the radiation of those from flagellate‐free insects. Comprehensive phylogenetic analysis documented that Endomicrobia comprise an apical cluster of endosymbionts that is not necessarily monophyletic and several apparently basal lineages that include bacteria present in the gut of defaunated lower termites, the naturally flagellate‐free guts of higher termites and scarab beetle larvae, and in the cow rumen. We propose that these lineages represent hitherto undetected free‐living Endomicrobia that share a common ancestor with the intracellular symbionts.
Presence of the siderophores pyoverdine and pyochelin in the extracellular medium reduces toxic metal accumulation in Pseudomonas aeruginosa and increases bacterial metal tolerance
Authors: Braud Armelle , Geoffroy Valérie , Hoegy Françoise , Mislin Gaëtan L. A. , Schalk Isabelle J.
Published: January 2010

In order to get access to iron, Pseudomonas aeruginosa strain PAO1 produces two major siderophores pyoverdine (PVD) and pyochelin (PCH). Both siderophores are able to chelate many other metals in addition to iron. However, despite this property, only iron is transported efficiently into the bacteria by the PVD and PCH uptake pathways. Growth studies with P. aeruginosa strains showed a lower sensitivity to toxic metals for the siderophore‐producing strain than for the mutants unable to produce siderophores. Moreover, addition of PVD or PCH to the growth medium of a siderophore‐deficient strain considerably reduced the toxicity of toxic metals present at concentrations of 100 µM in iron‐limited and iron‐supplemented growth conditions. Measurement by Inductively Coupled Plasma‐Atomic Emission Spectrometry of the concentration of metals present in bacteria incubated with metals in the presence or absence of PVD or PCH indicated that both siderophores were able to sequester metals from the extracellular medium of the bacteria, decreasing metal diffusion into the bacteria. Pyoverdine was able to sequester Al3+, Co2+, Cu2+, Eu3+, Ni2+, Pb2+, Tb3+ and Zn2+ from the extracellular medium, and PCH, Al3+, Co2+, Cu2+, Ni2+, Pb2+ and Zn2+. Moreover, the presence of 100 µM Cu2+ and Ni2+ increased PVD production by 290% and 380%, respectively, in a medium supplemented with iron. All these data suggest that PVD and PCH may contribute to P. aeruginosa resistance to heavy metals.
Zebrafish (Danio rerio) gill neuroepithelial cells are sensitive chemoreceptors for environmental CO2
Authors: Qin Z. , Lewis J. E. , Perry S. F.
Published: January 2010

Adult zebrafish exhibit hyperventilatory responses to absolute environmental CO2 levels as low as 0.13% ( mmHg), more than an order of magnitude lower than the typical arterial levels (∼40 mmHg) monitored by the mammalian carotid body. The sensory basis underlying the ability of fish to detect and respond to low ambient CO2 levels is not clear. Here, we show that the neuroepithelial cells (NECs) of the zebrafish gill, known to sense O2 levels, also respond to low levels of CO2. An electrophysiological characterization of this response using both current and voltage clamp protocols revealed that for increasing CO2 levels, a background K+ channel was inhibited, resulting in a partial pressure‐dependent depolarization of the NEC. To elucidate the signalling pathway underlying K+ channel inhibition, we used immunocytochemistry to show that these NECs express carbonic anhydrase (CA), an enzyme involved in CO2 sensing in the mammalian carotid body. Further, the NEC response to CO2 (magnitude of membrane depolarization and time required to achieve maximal response), under conditions of constant pH, was reduced by ∼50% by the CA‐inhibitor acetazolamide. This suggests that the CO2 detection mechanism involves an intracellular sensor that is responsive to the rate of acidification associated with the hydration of CO2 and which does not require a change of extracellular pH. Because some cells that were responsive to increasing also responded to hypoxia with membrane depolarization, the present results demonstrate that a subset of the NECs in the zebrafish gill are bimodal sensors of CO2 and O2.
Effect of Autofrettage in the Thick-Walled Cylinder With a Radial Cross-Bore
Authors: Li Hongjun , Johnston Richard , Mackenzie Donald
Published: January 2010

The effect of autofrettage on the stress level in thick-walled cylinders with a radial cross-bore is investigated by applying inelastic finite element analysis with cyclic pressure loading. A macro is created in ANSYS to calculate the equivalent alternating stress intensity, Seq, based on the ASME Boiler and Pressure Vessel Code. The value of Seq is used to evaluate the fatigue life of the vessel. For a specific cyclic load level, a distinct optimum autofrettage pressure is identified by plotting autofrettage pressure against the number of cycles from design fatigue data. The fatigue life of the autofrettaged vessel with such an optimum pressure is significantly increased compared with the case where no autofrettage is used.
Convection Calibration of Schmidt–Boelter Heat Flux Gauges in Stagnation and Shear Air Flow
Authors: Gifford A. , Hoffie A. , Diller T. , Huxtable S.
Published: January 2010

Experiments were performed to characterize the performance of Schmidt–Boelter heat flux gauges in stagnation and shear convective air flows. The gauges were of a standard design (25.4 mm and 38 mm in diameter), using a copper heat sink with water cooling channels around the active sensing element. A simple model of the gauges using an internal thermal resistance between the sensor surface and the heat sink is used to interpret the results. The model predicts a nonlinear dependence of the gauge sensitivity as a function of the heat transfer coefficient. Experimental calibration systems were developed to simultaneously measure the heat flux gauge response relative to a secondary standard under the same flow and thermal conditions. The measured gauge sensitivities in the stagnation flow matched the model, and were used to estimate the value of the internal thermal resistance for each of the four gauges tested. For shear flow, the effect of the varying gauge surface temperature on the boundary layer was included. The results matched the model with a constant factor of 15–25% lower effective heat transfer coefficient. When the gauge was water cooled, the effect of the internal thermal resistance of the gauge was markedly different for the two flow conditions. In the stagnation flow, the internal resistance further decreased the apparent gauge sensitivity. Conversely, in shear flow, the resistance was effectively offset by the cooler heat sink of the gauge, and the resulting sensitivities were nearly the same as, or larger than, for radiation.
Natural Convection From a Porous Cavity With Sublayers of Nonuniform Thickness: A Lumped System Analysis
Authors: Marvel R. L. , Lai F. C.
Published: January 2010

A numerical study has been performed to further investigate the flow and temperature fields in layered porous cavity. The geometry considered is a two-dimensional square cavity comprising of three or four vertical sublayers with nonuniform thickness and distinct permeability. The cavity is subjected to differential heating from the vertical walls. The results obtained are used to further evaluate the capacity of the lumped-system analysis in the prediction of heat transfer results of layered porous cavities. It has been found that predictions by the lumped-system model are reasonably good for the range of Rayleigh numbers encountered in engineering applications. In addition, the predictions improve when the number of sublayers increases as well as the sublayer thickness becomes more uniform. Thus, it proves that the lumped-system analysis can offer a quick estimate of heat transfer result from a layered porous cavity with reasonable accuracy.
Flow Boiling Visualization of R-134a in a Vertical Channel of Small Diameter
Authors: Martín-Callizo Claudi , Palm Björn , Owhaib Wahib , Ali Rashid
Published: January 2010

The present work reports on flow boiling visualization of refrigerant R-134a in a vertical circular channel with an internal diameter of 1.33 mm and 235 mm in heated length. A quartz tube with a homogeneous Indium Tin Oxide coating is used to allow heating and simultaneous visualization. Flow patterns have been observed along the heated length with the aid of high-speed complementary metal oxide semiconductor (CMOS) digital camera. From the flow boiling visualization, seven distinct two-phase flow patterns have been observed: isolated bubbly flow, confined bubbly flow, slug flow, churn flow, slug-annular flow, annular flow, and mist flow. Two-phase flow pattern observations are presented in the form of flow pattern maps. The effects of the saturation temperature and the inlet subcooling degree on the two-phase flow pattern transitions are elucidated. Finally, the experimental flow pattern map is compared with models developed for conventional sizes as well as to a microscale map for air-water mixtures available in literature, showing a large discrepancy.
Flow Visualization and Local Measurement of Forced Convection Heat Transfer in a Microtube
Authors: Schilder Boris , Man Simon Yu Ching , Kasagi Nobuhide , Hardt Steffen , Stephan Peter
Published: January 2010

The pressure drop and the convective heat transfer characteristics of ethanol and water in a circular tube with a diameter of 600 μm with and without phase change have been studied experimentally. The test section consists of a glass tube coated with a transparent indium tin oxide heater film. For single-phase liquid flow (including superheated liquid) it was found that the measured Nusselt numbers and friction factors are in good agreement with the theoretical values expected from Poiseuille flow. Subsequently, the boiling heat transfer of ethanol was studied. It was found that boiling with bubble growth in both upstream and downstream directions leaving behind a thin evaporating liquid film on the tube wall is the dominant phase change process. Wavy patterns on the film surface indicate shear forces between vapor and liquid phase during slug flow. Temporary dryout phenomena occur even at a low mean vapor quality due to film rupture as a result of film instabilities. Local Nusselt numbers are calculated for the two-phase flow at different heat fluxes and Reynolds numbers. Compared with single-phase flow the heat transfer is enhanced by a factor of 3–8.
Equilibrium Molecular Dynamics Study of Lattice Thermal Conductivity/Conductance of Au-SAM-Au Junctions
Authors: Luo Tengfei , Lloyd John R.
Published: January 2010

In this paper, equilibrium molecular dynamics simulations were performed on Au-SAM (self-assembly monolayer)-Au junctions. The SAM consisted of alkanedithiol (–S–(CH2)n–S–) molecules. The out-of-plane (z-direction) thermal conductance and in-plane (x- and y-direction) thermal conductivities were calculated. The simulation finite size effect, gold substrate thickness effect, temperature effect, normal pressure effect, molecule chain length effect, and molecule coverage effect on thermal conductivity/conductance were studied. Vibration power spectra of gold atoms in the substrate and sulfur atoms in the SAM were calculated, and vibration coupling of these two parts was analyzed. The calculated thermal conductance values of Au-SAM-Au junctions are in the range of experimental data on metal-nonmetal junctions. The temperature dependence of thermal conductance has a similar trend to experimental observations. It is concluded that the Au-SAM interface resistance dominates thermal energy transport across the junction, while the substrate is the dominant media in which in-plane thermal energy transport happens.
Ultra-Low Thermal Conductivity in Nanoscale Layered Oxides
Authors: Alvarez-Quintana J. , Peralba-Garcia Ll. , Lábár J. L. , Rodríguez-Viejo J.
Published: January 2010

The cross-plane thermal conductivity of several nanoscale layered oxides SiO2/Y2O3, SiO2/Cr2O3, and SiO2/Al2O3, synthesized by e-beam evaporation was measured in the range from 30 K to 300 K by the 3ω method. Thermal conductivity attains values around 0.5 W/m K at room temperature in multilayer samples, formed by 20 bilayers of 10 nm SiO2/10 nm Y2O3, and as low as 0.16 W/m K for a single bilayer. The reduction in thermal conductivity is related to the high interface density, which produces a strong barrier to heat transfer rather than to the changes of the intrinsic thermal conductivity due to the nanometer thickness of the layers. We show that the influence of the first few interfaces on the overall thermal resistance is higher than the subsequent ones. Annealing the multilayered samples to 1100°C slightly increases the thermal conductivity due to changes in the microstructure. These results suggest a route to obtain suitable thermal barrier coatings for high temperature applications.
Computational Analysis of Pin-Fin Arrays Effects on Internal Heat Transfer Enhancement of a Blade Tip Wall
Authors: Xie Gongnan , Sundén Bengt , Utriainen Esa , Wang Lieke
Published: January 2010

Cooling methods are strongly needed for the turbine blade tips to ensure a long durability and safe operation. Improving the internal convective cooling is therefore required to increase the blade tip life. A common way to cool the tip is to use serpentine passages with 180-deg turns under the blade tip cap. In this paper, enhanced heat transfer of a blade tip cap has been investigated numerically. The computational models consist of a two-pass channel with a 180-deg turn and various arrays of pin fins mounted on the tip cap, and a smooth two-pass channel. The inlet Reynolds number is ranging from 100,000 to 600,000. The computations are 3D, steady, incompressible, and nonrotating. Details of the 3D fluid flow and heat transfer over the tip walls are presented. The effects of pin-fin height, diameter, and pitches on the heat transfer enhancement on the blade tip walls are observed. The overall performances of ten models are compared and evaluated. It is found that due to the combination of turning, impingement, and pin-fin crossflow, the heat transfer coefficient of the pin-finned tip is a factor of 2.67 higher than that of a smooth tip. This augmentation is achieved at the expense of a penalty of pressure drop around 30%. Results show that the intensity of heat transfer enhancement depends upon pin-fin configuration and arrangement. It is suggested that pin fins could be used to enhance the blade tip heat transfer and cooling.
Investigation of Heat Transfer Enhancement Through Permeable Fins
Authors: Khaled A.-R. A.
Published: January 2010

Heat transfer through rectangular permeable fins is modeled and analyzed theoretically in this work. The free stream fluid flow is considered to be normal to the upper surface of the permeable fin. The flow across the permeable fin is permitted in this work. The continuity, momentum, and energy equations are solved for the fluid flow using a similarity transformation and an iterative tridiagonal finite difference method. As such, a correlation for the Nusselt number is generated as functions of the Prandtl number (Pr) and dimensionless suction velocity (fo) for 0.7<Pr≤10 and 0<fo≤5, respectively. The energy equation for the permeable fin is generated and solved analytically using the developed correlation. It was found that permeable fins may have superiority in transferring heat over ordinary solid fins, especially at large fo values and moderate holes-to-fin surface area ratios. In addition, the critical holes-to-fin surface area ratios, below which the permeable fins transfer more heat than solid fins, is found to increase as Pr and fo increase. Finally, this work paves a way for a new passive method for enhancing heat transfer.
Thermal Analysis and Optimization of Orthotropic Pin Fins: A Closed-Form Analytical Solution
Authors: Zubair Syed M. , Arif A. F. M. , Sharqawy Mostafa H.
Published: January 2010

Analytical solutions for temperature distribution, heat transfer rate, and fin efficiency and fin effectiveness are derived and presented for orthotropic two-dimensional pin fins subject to convective-tip boundary condition. The generalized results are presented and discussed in terms of dimensionless variables such as radial and axial Biot numbers (Bir,Biz), fin aspect ratio, L/R, and radial-to-axial conductivity ratio k∗. Several special cases are derived from the general solution, which includes the insulated-tip boundary condition. It is also demonstrated that the classical temperature distribution and heat transfer rate from the two-dimensional isotropic pin fin introduced earlier in literature can easily be recovered from the general solutions presented in this paper. Furthermore, dimensionless optimization results are presented for orthotropic pin fins that can help to solve many natural and forced convection pin fin problems.
A Comparison Between Measured and Modeled Residual Stresses in a Circumferentially Butt-Welded P91 Steel Pipe
Authors: Yaghi A. H. , Hyde T. H. , Becker A. A. , Sun W. , Hilson G. , Simandjuntak S. , Flewitt P. E. J. , Pavier M. J. , Smith D. J.
Published: January 2010

Residual macrostresses in a multipass circumferentially butt-welded P91 ferritic steel pipe have been determined numerically and experimentally. The welded joint in a pipe with an outer diameter of 290 mm and a wall thickness of 55 mm is typical of power generation plant components. An axisymmetric thermomechanical finite element model has been used to predict the resulting residual hoop and axial stresses in the welded pipe. The effects of the austenite to martensite phase transformation have been incorporated into the simulation. Residual stresses have been measured using the X-ray diffraction technique along the outer surface of the pipe and using the deep-hole drilling technique through the wall thickness at the center of the weld. Good correlation has been demonstrated between the residual hoop and the axial stresses obtained numerically and experimentally. The paper demonstrates the importance of using a mixed experimental and numerical approach to determine accurately the residual macrostress distribution in welded components.
Lower and Upper Bound Shakedown Analysis of Structures With Temperature-Dependent Yield Stress
Authors: Chen Haofeng
Published: January 2010

Based upon the kinematic theorem of Koiter (1960, “General Theorems for Elastic Plastic Solids,” in Progress in Solid Mechanics 1, J. N. Sneddon and R. Hill, eds., North-Holland, Amsterdam, pp. 167–221) the linear matching method (LMM) procedure has been proved to produce very accurate upper bound shakedown limits. This paper presents a recently developed LMM lower bound procedure for shakedown analysis of structures with temperature-dependent yield stress, which is implemented into ABAQUS using the same procedure as for upper bounds. According to the Melan’s theorem (1936, “Theorie statisch unbestimmter Systeme aus ideal-plastichem Baustoff,” Sitzungsber. Akad. Wiss. Wien, Math.-Naturwiss. Kl., Abt. 2A, 145, pp. 195–210), a direct algorithm has been carried out to determine the lower bound of shakedown limit using the best residual stress field calculated during the LMM upper bound procedure with displacement-based finite elements. By checking the yield condition at every integration point, the lower bound is calculated by the obtained static field at each iteration, with the upper bound given by the obtained kinematic field. A number of numerical examples confirm the applicability of this procedure and ensure that the upper and lower bounds are expected to converge to the theoretical solution after a number of iterations.
Depth dependent variation of the echolocation pulse rate of bottlenose dolphins (Tursiops truncatus)
Authors: Simard Peter , Hibbard Ashley L. , McCallister Kimberly A. , Frankel Adam S. , Zeddies David G. , Sisson Geoffrey M. , Gowans Shannon , Forys Elizabeth A. , Mann David A.
Published: January 2010

Trained odontocetes appear to have good control over the timing (pulse rate) of their echolocation clicks; however, there is comparatively little information about how free-ranging odontocetes modify their echolocation in relation to their environment. This study investigates echolocation pulse rate in 14 groups of free-ranging bottlenose dolphins (Tursiops truncatus) at a variety of depths (2.4–30.1 m) in the Gulf of Mexico. Linear regression models indicated a significant decrease in mean pulse rate with mean water depth. Pulse rates for most groups were multi-modal. Distance to target estimates were as high as 91.8 m, assuming that echolocation was produced at a maximal rate for the target distance. A 5.29-ms processing lag time was necessary to explain the pulse rate modes observed. Although echolocation is likely reverberation limited, these results support the hypotheses that free-ranging bottlenose dolphins in this area are adapting their echolocation signals for a variety of target detection and ranging purposes, and that the target distance is a function of water depth.
Detecting overblown flute fingerings from the residual noise spectrum
Authors: Verfaille Vincent , Depalle Philippe , Wanderley Marcelo M.
Published: January 2010

Producing a tone by increasing the blowing pressure to excite a higher frequency impedance minimum, or overblowing, is widely used in standard flute technique. In this paper, the effect of overblowing a fingering is explored with spectral analysis, and a fingering detector is designed based on acoustical knowledge and pattern classification techniques. The detector performs signal analysis of the strong broadband signal, that is, spectrally shaped by the pipe impedance, and measures the spectral energy during the attack around multiples of the fundamental frequency sub-multiples over the first octave and a half. It is trained and evaluated on sounds recorded with four expert performers. They played six series of tones from overblown and regular fingerings, with frequencies that are octave- and non-octave-related to the playing frequency. The best of the four proposed sound descriptors allows for a detection error below 1.3% for notes with two and three fingerings (C5, D5, C6, and C♯6) and below 14% for four (E6) or five fingerings (G6). The error is shown to dramatically increase when two fingerings’ impedance become too similar (E6 and A4 and G6 and C5).
Analytical study of the acoustic field in a spherical resonator for single bubble sonoluminescence
Authors: Dellavale Damián , Urteaga Raúl , Bonetto Fabián J.
Published: January 2010

The acoustic field in the liquid within a spherical solid shell is calculated. The proposed model takes into account Stoke’s wave equation in the viscous fluid, the membrane theory to describe the solid shell motion and the energy loss through the external couplings of the system. A point source at the resonator center is included to reproduce the acoustic emission of a sonoluminescence bubble. Particular calculations of the resulting acoustic field are performed for viscous liquids of interest in single bubble sonoluminescence. The model reveals that in case of radially symmetric modes of low frequency, the quality factor is mainly determined by the acoustic energy flowing through the mechanical coupling of the resonator. Alternatively, for high frequency modes the quality factor is mainly determined by the viscous dissipation in the liquid. Furthermore, the interaction between the bubble acoustic emission and the resonator modes is analyzed. It was found that the bubble acoustic emission produces local maxima in the resonator response. The calculated amplitudes and relative phases of the harmonics constituting the bubble acoustic environment can be used to improve multi-frequency driving in sonoluminescence.
Sound velocities and thermodynamic properties of water to 700 MPa and −10 to 100 °C
Authors: Vance Steve , Brown J. Michael
Published: January 2010

Sound velocities in liquid water were measured by the method of impulsive stimulated scattering in a sapphire-windowed high-pressure cell from −10 to 100 °C and pressures as high as 700 MPa. Velocity measurements are compared with previous experimental efforts relative to the International Association for the Properties of Water and Steam (IAPWS-95) formulation for the equations of state. At 0 and −10 °C, sound velocities are in agreement with the one previously published study at sub-zero temperatures to 350 MPa. At ambient and elevated temperatures, differences between the present measurements and IAPWS-95 velocities approach 0.5% near 700 MPa. Inversion of velocity data for density yields results within IAPWS-95 uncertainties, except at the highest temperatures, where elevated sound velocity at high pressure corresponds to as much as −0.2% disagreement with IAPWS-95.
Forward-masking patterns produced by symmetric and asymmetric pulse shapes in electric hearing
Authors: Macherey Olivier , van Wieringen Astrid , Carlyon Robert P. , Dhooge Ingeborg , Wouters Jan
Published: January 2010

Two forward-masking experiments were conducted with six cochlear implant listeners to test whether asymmetric pulse shapes would improve the place-specificity of stimulation compared to symmetric ones. The maskers were either cathodic-first symmetric biphasic, pseudomonophasic (i.e., with a second anodic phase longer and lower in amplitude than the first phase), or “delayed pseudomonophasic” (identical to pseudomonophasic but with an inter-phase gap) stimuli. In experiment 1, forward-masking patterns for monopolar maskers were obtained by keeping each masker fixed on a middle electrode of the array and measuring the masked thresholds of a monopolar signal presented on several other electrodes. The results were very variable, and no difference between pulse shapes was found. In experiment 2, six maskers were used in a wide bipolar (bipolar+9) configuration: the same three pulse shapes as in experiment 1, either cathodic-first relative to the most apical or relative to the most basal electrode of the bipolar channel. The pseudomonophasic masker showed a stronger excitation proximal to the electrode of the bipolar pair for which the short, high-amplitude phase was anodic. However, no difference was obtained with the symmetric and, more surprisingly, with the delayed pseudomonophasic maskers. Implications for cochlear implant design are discussed.
Sound absorption of a micro-perforated panel backed by an irregular-shaped cavity
Authors: Wang Chunqi , Cheng Li , Pan Jie , Yu Ganghua
Published: January 2010

In the pursuit of more effective noise control devices, the cavity backed micro-perforated panel absorber (CBMPPA) is developed in this study. A CBMPPA differs from the conventional micro-perforated panel (MPP) absorber in that the MPP is backed by a trapezoidal cavity, which allows more effective vibroacoustic coupling between the MPP and the cavity. A two-dimensional theoretical model is established and tested both numerically and experimentally. Based on the verified theoretical model, sound absorption performance of a trapezoidal CBMPPA is investigated numerically. Results show that the shape of the backing cavity can significantly alter the sound absorption mechanisms and frequency distribution of overall sound absorption coefficient of the absorber. Further analyses show that acoustic modes that are initially decoupled from the MPP in the rectangular configuration are coupled with the air motion in the MPP, which accounts for the change in absorption pattern of the trapezoidal CBMPPA. By the same token, it also provides the flexibility for tuning the effective absorption range of the absorber. Due to the varying impedance matching conditions, the absorption performance of the trapezoidal CBMPPA exhibits obvious local characteristics over the MPP surface, which contrasts with the spatially uniform absorption in the conventional MPP absorber.
Computation of the head-related transfer function via the fast multipole accelerated boundary element method and its spherical harmonic representation
Authors: Gumerov Nail A. , O’Donovan Adam E. , Duraiswami Ramani , Zotkin Dmitry N.
Published: January 2010

The head-related transfer function (HRTF) is computed using the fast multipole accelerated boundary element method. For efficiency, the HRTF is computed using the reciprocity principle by placing a source at the ear and computing its field. Analysis is presented to modify the boundary value problem accordingly. To compute the HRTF corresponding to different ranges via a single computation, a compact and accurate representation of the HRTF, termed the spherical spectrum, is developed. Computations are reduced to a two stage process, the computation of the spherical spectrum and a subsequent evaluation of the HRTF. This representation allows easy interpolation and range extrapolation of HRTFs. HRTF computations are performed for the range of audible frequencies up to 20kHz for several models including a sphere, human head models [the Neumann KU-100 (“Fritz”) and the Knowles KEMAR (“Kemar”) manikins], and head-and-torso model (the Kemar manikin). Comparisons between the different cases are provided. Comparisons with the computational data of other authors and available experimental data are conducted and show satisfactory agreement for the frequencies for which reliable experimental data are available. Results show that, given a good mesh, it is feasible to compute the HRTF over the full audible range on a regular personal computer.
Extracting guided waves from cross-correlations of elastic diffuse fields: Applications to remote structural health monitoring
Authors: Duroux Adelaide , Sabra Karim G. , Ayers James , Ruzzene Massimo
Published: January 2010

Due to their apparent complexity, diffuse fields are not commonly used by conventional structural health monitoring methodologies. However, recent theoretical and experimental studies have demonstrated that local Green’s functions (GFs) can be estimated from the cross-correlation of elastic diffuse fields (CDFs) recorded between any points of a sensor grid and generated by sources located remotely from the monitoring area. Hence, this CDF technique effectively transforming each measurement point into a virtual elastic source, thus allowing to measure the local structural response (or GF). Theoretical and experimental studies are conducted to assess the broadband performance of the CDF technique for the extraction of low-frequency coherent Lamb waves (4–90kHz) propagating in a thin aluminum plate of complex geometry using a scanning laser Doppler vibrometer. The coherent signal-to-noise ratio and the accuracy of the phase and group velocity measurements of the coherent A0 mode obtained from CDF are also measured to quantify the influence of the spatio-temporal characteristics of the recorded diffuse field, the number and spatial configuration of the remote ultrasonic sources, and the influence of incoherent measurement noise (e.g., sensor noise). In addition, a criterion to assess the emergence rate of late coherent coda arrivals from CDF is also formulated.
Short pulse multi-frequency phase-based time delay estimation
Authors: Assous Said , Hopper Clare , Lovell Mike , Gunn Dave , Jackson Peter , Rees John
Published: January 2010

An approach for time delay estimation, based on phase difference detection, is presented. A multiple-frequency short continuous wave pulse is used to solve the well-known phase ambiguity problem when the maximum distance exceeds a full wavelength. Within an unambiguous range defined with the lowest frequency difference between components, the corresponding phase difference is unique and any distance within this range can be determined. Phase differences between higher frequency components are used to achieve a finer resolution. The concept will be presented and the effectiveness of the approach will be investigated through theoretical and practical examples. The method will be validated using underwater acoustic measurements, simulating noisy environments, demonstrating resolutions better than a 50th of a wavelength, even in the presence of high levels (−5dB) of additive Gaussian noise. Furthermore, the algorithm is simple to use and can be easily implemented, being based on phase detection using the discrete Fourier transform.
Intelligibility and listener preference of telephone speech in the presence of babble noise
Authors: Hall Joseph L. , Flanagan James L.
Published: January 2010

Two procedures for improving the intelligibility of wideband telephone speech in the presence of competing babble noise are evaluated. One procedure is differentiation, the other consists of equalizing the speech spectrum by applying the inverse of the average spectrum of formant amplitudes for adult male speakers (“formant equalization”). Speech processed by these two methods was evaluated both for intelligibility and for listener preference. Both methods produced a clear increase in intelligibility compared to unprocessed wideband telephone speech. Formant equalization was found to be preferred over differentiation, more so at low signal-to-noise ratios than at high ones.
Catalan speakers’ perception of word stress in unaccented contexts
Authors: Ortega-Llebaria Marta , del Mar Vanrell Maria , Prieto Pilar
Published: January 2010

In unaccented contexts, formant frequency differences related to vowel reduction constitute a consistent cue to word stress in English, whereas in languages such as Spanish that have no systematic vowel reduction, stress perception is based on duration and intensity cues. This article examines the perception of word stress by speakers of Central Catalan, in which, due to its vowel reduction patterns, words either alternate stressed open vowels with unstressed mid-central vowels as in English or contain no vowel quality cues to stress, as in Spanish. Results show that Catalan listeners perceive stress based mainly on duration cues in both word types. Other cues pattern together with duration to make stress perception more robust. However, no single cue is absolutely necessary and trading effects compensate for a lack of differentiation in one dimension by changes in another dimension. In particular, speakers identify longer mid-central vowels as more stressed than shorter open vowels. These results and those obtained in other stress-accent languages provide cumulative evidence that word stress is perceived independently of pitch accents by relying on a set of cues with trading effects so that no single cue, including formant frequency differences related to vowel reduction, is absolutely necessary for stress perception.
The role of temporal fine structure in harmonic segregation through mistuning
Authors: Moore Brian C. J. , Glasberg Brian R.
Published: January 2010

Bernstein and Oxenham [(2008). J. Acoust. Soc. Am. 124, 1653–1667] measured thresholds for discriminating the fundamental frequency, F0, of a complex tone that was passed through a fixed bandpass filter. They found that performance worsened when the F0 was decreased so that only harmonics above the tenth were audible. However, performance in this case was improved by mistuning the odd harmonics by 3%. Bernstein and Oxenham considered whether the results could be explained in terms of temporal fine structure information available at the output of a single auditory filter and concluded that their results did not appear to be consistent with such an explanation. Here, it is argued that such cues could have led to the improvement in performance produced by mistuning the odd harmonics.
Simplified expressions of the subtracted Kramers–Kronig relations using the expanded forms applied to ultrasonic power-law systems
Authors: Mobley Joel
Published: January 2010

The Kramers–Kronig (KK) relations are a large class of integral transformations that exploit the broad principle of simple causality in order to link the physical properties of matter and materials. In applications to the complex-valued wavenumber for acoustic propagation, the method of subtractions is used to form convergent integral relations between the phase velocity and the attenuation coefficient. When the method of subtractions is applied in the usual manner, the integrands in the relations become unnecessarily complicated. In this work, an expanded form of the subtracted relations is presented, which is essentially a truncated Taylor series expansion of the Hilbert transforms. The implementation of the relations only requires the explicit evaluation of two simply expressed integrals involving the Hilbert transform kernel. These two integrals determine the values of the other terms in the subtracted relations, demonstrating the computational efficiency of the technique. The method is illustrated analytically through its application to power-law attenuation coefficients and its associated dispersion, which are observed in a wide variety of materials. This approach explicitly shows the central role of the Hilbert transform kernel in the KK relations, which can become obscured in other formulations.
Observations and modeling of angular compression and vertical spatial coherence in sea surface forward scattering
Authors: Dahl Peter H.
Published: January 2010

Measurements and modeling of spatial coherence and related angular spreading associated with forward scattering from the sea surface are presented. The measurements were taken in waters 80 m deep off the New Jersey coast in August 2006. Acoustic signals from a source at depth 40 m were recorded on a vertical line array of length 1.4 m, centered at depth 25 m, and at range 200 m. Measurements in the 14–20-kHz frequency range are reported; the rms waveheight H was 0.16 m, setting kH as ∼10 where k is acoustic wavenumber. A systematic study of measurements taken over four source–receiver bearing angles separated by 90° suggests a null influence of changing bearing angle or equivalently directional wave effects. Sound speed was characterized by a downward-refracting profile. Refraction modifies the vertical angular spread due to rough sea surface scattering, which can be understood from Snell’s law. The Snell mapping is smooth, so an approximation based on the mean grazing angle provides a functional relation between the angular variance near the surface and that at the receiver. The latter is measurably reduced owing to refraction, the effect called angular compression, and a parameter that quantifies this effect is defined.
Normal modes of a musical drumhead under non-uniform tension
Authors: Worland Randy
Published: January 2010

The effect of non-uniform tension on the normal modes of musical drumheads is examined. Using the standard (m,n) designation for the number of nodal diameters and circles, ideal circular membrane modes with m>0 are doubly degenerate. These degeneracies can be lifted by perturbations to the circular symmetry. Of practical interest to drummers are perturbations caused by non-uniform tension applied at the rim of the drum, leading in some cases to audible frequency splitting. The role of the (1,1) mode in practical drum tuning is analyzed using data obtained using time-averaged electronic speckle-pattern interferometry along with finite element analysis. The resulting model is then generalized to include all modes, using symmetry arguments along with a selection rule taken from group theory. The model compares favorably with both perturbation theory and finite element analysis, and is consistent with experimental observations.
On Dowell’s simplification for acoustic cavity-structure interaction and consistent alternatives
Authors: Ginsberg Jerry H.
Published: January 2010

A widely employed description of the acoustical response in a cavity whose walls are compliant, which was first proposed by Dowell and Voss [(1962). AIAA J. 1, 476–477], uses the modes of the corresponding cavity with rigid walls as basis functions for a series representation of the pressure. It yields a velocity field that is not compatible with the movement of the boundary, and the system equations do not satisfy the principle of reciprocity. The simplified formulation is compared to consistent solutions of the coupled field equations in the time and frequency domains. In addition, this paper introduces an extension of the Ritz series method to fluid-structure coupled systems that satisfies all continuity conditions by imposing constraint equations to enforce any such conditions that are not identically satisfied by the series. A slender waveguide terminated by an oscillator is analyzed by each method. The simplified formulation is found to be very accurate for light fluid loading, except for the pressure field at frequencies below the fundamental rigid-cavity resonance, whereas the Ritz series solution is found to be extremely accurate in all cases.
Full bandwidth calibration procedure for acoustic probes containing a pressure and particle velocity sensor
Authors: Basten Tom G. H. , de Bree Hans-Elias
Published: January 2010

Calibration of acoustic particle velocity sensors is still difficult due to the lack of standardized sensors to compare with. Recently it is shown by Jacobsen and Jaud [J. Acoust. Soc. Am. 120, 830–837 (2006)] that it is possible to calibrate a sound pressure and particle velocity sensor in free field conditions at higher frequencies. This is done by using the known acoustic impedance at a certain distance of a spherical loudspeaker. When the sound pressure is measured with a calibrated reference microphone, the particle velocity can be calculated from the known impedance and the measured pressure. At lower frequencies, this approach gives unreliable results. The method is now extended to lower frequencies by measuring the acoustic pressure inside the spherical source. At lower frequencies, the sound pressure inside the sphere is proportional to the movement of the loudspeaker membrane. If the movement is known, the particle velocity in front of the loudspeaker can be derived. This low frequency approach is combined with the high frequency approach giving a full bandwidth calibration procedure which can be used in free field conditions using a single calibration setup. The calibration results are compared with results obtained with a standing wave tube.
Efficient frequency-domain finite element modeling of two-dimensional elastodynamic scattering
Authors: Wilcox Paul D. , Velichko Alexander
Published: January 2010

A frequency-domain finite element technique is presented that enables the complete characterization of a finite-sized scatterer using a minimum number of separate model executions and a relatively small spatial modeling domain. The technique is implemented using a commercial finite element package. A certain forcing profile is applied at a set of points surrounding the scatterer to cause a uni-modal plane wave to be incident on the scatterer from a specified direction. The scattered field is recorded and decomposed first into modes and then into far-field scattering coefficients in different directions. The data obtained from the model are represented in a scattering matrix that describes the far-field scattering response for all combinations of incident and scattering angles. The information in the scattering matrix can be efficiently represented in the Fourier domain by another matrix containing a finite number of Fourier coefficients. It is shown how the complete scattering behavior in both the near- and far-field can be extracted from the matrix of Fourier coefficients. Modeling accuracy is examined in various ways, including a comparison with the analytical solution for a circular cavity, and guidelines for the selection of modeling parameters are given.
An acoustical study of vocal pitch matching in congenital amusia
Authors: Hutchins Sean , Zarate Jean Mary , Zatorre Robert J. , Peretz Isabelle
Published: January 2010

Vocal pitch matching is a foundational skill for singing and is an interesting place to study the relationship between pitch perception and production. To better understand this relationship, we assessed pitch-matching abilities in congenital amusics, who have documented disabilities in pitch perception, and in matched controls under normal, masked, and guided feedback conditions. Their vocal productions were analyzed for fundamental frequency and showed that amusics were significantly less accurate at pitch matching than the controls. However, five of the six amusics showed a significant correlation between their produced pitches and the target pitch. Feedback condition had no effect on pitch-matching accuracy. These results show impaired vocal pitch-matching abilities in amusics but also show a relationship between perceived and produced pitches.