bluuebunny/crossref_metadata_2025 huggingface dataset:
Smile Alabama! Initiative: Interim Results From a Program to Increase Children's Access to Dental Care
Authors: Greene‐Mclntyre Mary , Finch Mary Hayes , Searcy John
Published: April 2008

Abstract: Alabama faced an oral health crisis, with decreasing dental provider participation and increasing enrollment of Medicaid‐eligible children. In response, the Smile Alabama! initiative was designed to improve oral health care services for Medicaid‐eligible children by increasing the number of participating dentists by 15% and the number of children receiving dental care annually by 5% by January 31, 2004. The initiative is composed of 4 specific components: claims processing, dental reimbursement, provider education and recruitment, and recipient education. Specific interventions were implemented for each component. From fiscal year 1999 to fiscal year 2002, enrollment of targeted Medicaid children increased 32.7%. During this same period, the number of participating dental providers in the Alabama Medicaid dental program increased by 127 providers, a 38.7% increase. The number of children receiving dental services increased from 82 600 in fiscal year 1999 to 130 208 in fiscal year 2002, a 57.1% total increase, with a 4.8% increase in the annual dental visit rate. The experience suggests that access to oral health care services can be improved through a multidimensional, strategically planned dental outreach initiative in spite of dramatic increases in Medicaid enrollment
Strain‐Associated Variations in Abnormal PrP Trafficking of Sheep Scrapie
Authors: Jeffrey Martin , McGovern Gillian , Goodsir Caroline M. , González Lorenzo
Published: April 2008

Prion diseases are associated with the accumulation of an abnormal form of the host‐coded prion protein (PrP). It is postulated that different tertiary or quaternary structures of infectious PrP provide the information necessary to code for strain properties. We show here that different light microscopic types of abnormal PrP (PrPd) accumulation found in each of 10 sheep scrapie cases correspond ultrastructurally with abnormal endocytosis, increased endo‐lysosomes, microfolding of plasma membranes, extracellular PrPd release and intercellular PrPd transfer of neurons and/or glia. The same accumulation patterns of PrPd and associated subcellular lesions were present in each of two scrapie strains present, but they were present in different proportions. The observations suggest that different trafficking pathways of PrPd are influenced by strain and cell type and that a single prion strain causes several PrPd–protein interactions at the cell membrane. These results imply that strains may contain or result in production of multiple isoforms of PrPd.
Performance of Spur Gears Considering Surface Roughness and Shear Thinning Lubricant
Authors: Akbarzadeh S. , Khonsari M. M.
Published: April 2008

A model is developed for predicting the performance of spur gears with provision for surface roughness. For each point along the line of action, the contact of pinion and gear is replaced by that of two cylinders. The radii of cylinders, transmitted load, and contact stress are calculated, and lubricant film thickness is obtained using the load-sharing concept of Johnson et al. (1972, “A Simple Theory of Asperity Contact in Elastohydrodynamic Lubrication,” Wear, 19, pp. 91–108) To validate the analysis, the predicted film thickness and the friction coefficient are compared to published theoretical and experimental data. The model is capable of predicting the performance of gears with non-Newtonian lubricants—such as that of shear thinning lubricants—often used in gears. For this purpose, a correction factor for shear thinning film thickness introduced by Bair (2005, “Shear Thinning Correction for Rolling/Sliding Electrohydrodynamic Film Thickness,” Proc. Inst. Mech. Eng., Part J: J. Eng. Tribol., 219, pp. 1–6) has been employed. The results of a series of simulations presenting the effect of surface roughness on the friction coefficient are presented and discussed. The results help to establish the lubrication regime along the line of action of spur gears.
Performance of Graphite and Boron-Nitride-Silicone Based Lubricants and Associated Lubrication Mechanisms in Warm Forging of Aluminum
Authors: Ngaile Gracious , Botz Frank
Published: April 2008

Although water/oil-graphite emulsions are widely used in warm forging processes, they carry environmental concerns. In an attempt to replace graphite-based lubricants in warm forging of aluminum alloys, two variants of boron-nitride-silicone lubricants were formulated. The two variants were made by dispersing boron nitride powder in polydimethyl siloxane oil at concentrations of 1% and 8%. The formulated lubricants were initially tested for their thermal degradation characteristics using a thermogravimetric analyzer and compared to the thermal degradation behavior of graphite and silicone oil lubricants. Ring compression tests were then carried out at 260°C and 370°C. Boron-nitride-silicone lubricant variants did not show significant difference in performance as die temperature was increased from 260°Cto370°C. This is in contrast to graphite, which performed much better at 260°C than at 370°C, due to thermal oxidation. On the other hand, silicone oil exhibited the worst performance at 260°C and the best performance at 370°C. In both boron nitride lubricant variants, the polydimethyl siloxane facilitated hydrostatic/hydrodynamic lubrication at 260°C, with boron nitride acting as a barrier film that reduced friction. However, the lubrication mechanisms changed at 370°C, where the depolymerization of polydimethyl siloxane led to formation of silica due to thermal oxidation. Silica, together with boron nitride, acted as a film barrier with low shear strength. The dual lubrication mechanisms make boron-nitride-silicone lubricants suitable for a wide range of aluminum forging temperatures.
Windage Power Loss Modeling of a Smooth Rotor Supported by Homopolar Active Magnetic Bearings
Authors: Raymond M. Saint , Kasarda M. E. F. , Allaire P. E.
Published: April 2008

Rotors supported by active magnetic bearings (AMBs) can spin at high surface speeds with relatively low power losses. This makes them particularly attractive for use in flywheels for energy storage in applications such as electric vehicles and uninterruptible power supplies. In order to optimize efficiency in these and other applications, the loss mechanisms associated with magnetic bearings and rotating machinery must be well understood. The primary parasitic loss mechanisms in an AMB include complex magnetic losses, due to eddy currents and hysteresis, and windage losses along the entire rotor in nonvacuum environments. In low-loss magnetic bearing designs, the windage loss component along the rotor can become dominant at high speeds, and the need for accurate windage models becomes even more critical. This study extends previous AMB power loss work by evaluating five different windage loss models using the experimental rundown data from the previous work. Each of the five windage models, along with standard models of eddy current and hysteresis losses, are used to reduce the rundown data into the associated power loss components. A comparison is then completed comparing the windage power loss component extracted through the rundown data reduction scheme to the associated analytical windage prediction in order to identify the most accurate model for calculating windage losses along a smooth rotor. Five empirical flat-plate drag coefficient models are implemented, four turbulent and one laminar. An empirical flat-plate turbulent boundary layer formula (referred to here as “Model 2”) developed by Prandtl and Schlichting displayed the best agreement between experimentally extracted and analytically predicted windage loss values. The most accurate model formula (Model 2) dictates that the frequency dependency of windage loss is both logarithmic and power based and represents the minimum error between experimentally extracted and analytically predicted losses of all models in the study of high-speed power losses in a smooth rotor supported in AMBs.
Experimental Investigation on the Stick-Slip Phenomenon in Granular Collision Lubrication
Authors: Elkholy Karim N. , Khonsari M. M.
Published: April 2008

An investigation on the nature of stick-slip associated with granular materials sheared between two parallel disks within the context of granular lubrication is presented. Experiments are carried out in an annular shear cell apparatus to demonstrate the effect of the stick-slip on the friction coefficient. Results are presented for the friction coefficient and the displacement as a function of the rotational speed and the applied load. The results reveal the occurrence of stick-slip at low speed and provided further evidence for the formation of granular lift between two disks undergoing sliding motion.
A Full-System Approach of the Elastohydrodynamic Line/Point Contact Problem
Authors: Habchi W. , Eyheramendy D. , Vergne P. , Morales-Espejel G.
Published: April 2008

The solution of the elastohydrodynamic lubrication (EHL) problem involves the simultaneous resolution of the hydrodynamic (Reynolds equation) and elastic problems (elastic deformation of the contacting surfaces). Up to now, most of the numerical works dealing with the modeling of the isothermal EHL problem were based on a weak coupling resolution of the Reynolds and elasticity equations (semi-system approach). The latter were solved separately using iterative schemes and a finite difference discretization. Very few authors attempted to solve the problem in a fully coupled way, thus solving both equations simultaneously (full-system approach). These attempts suffered from a major drawback which is the almost full Jacobian matrix of the nonlinear system of equations. This work presents a new approach for solving the fully coupled isothermal elastohydrodynamic problem using a finite element discretization of the corresponding equations. The use of the finite element method allows the use of variable unstructured meshing and different types of elements within the same model which leads to a reduced size of the problem. The nonlinear system of equations is solved using a Newton procedure which provides faster convergence rates. Suitable stabilization techniques are used to extend the solution to the case of highly loaded contacts. The complexity is the same as for classical algorithms, but an improved convergence rate, a reduced size of the problem and a sparse Jacobian matrix are obtained. Thus, the computational effort, time and memory usage are considerably reduced.
Characterization of Thermally Actuated Pole Tip Protrusion for Head-Media Spacing Adjustment in Hard Disk Drives
Authors: Lee Sung-Chang , Strom Brian D.
Published: April 2008

The effect of thermomechanically actuated pole tip protrusion on adhesive forces is characterized through model and experiment. The roughness of a thermomechanically actuated region is characterized by atomic force microscopy. Using the extracted roughness parameters and estimated apparent area associated with thermal actuation, the intermolecular forces at the head-disk interface (HDI) are calculated using the ISBL (improved sub-boundary lubrication) code. Both roughness and nominal area of contact are found to be significant factors determining adhesive forces. The adhesive forces for various HDI designs—including thermal actuation—are also characterized experimentally in situ using commercial hard disk drive samples. The experimental results are found to be consistent with the model calculations and imply certain advantages for thermally actuated HDI designs. However, the experiments also raise concerns regarding the field application of the technology.
Quantification of the Surface Morphology of Lubricant Films With Polar End Groups Using Molecular Dynamics Simulation: Periodic Changes in Morphology Depending on Film Thickness
Authors: Ogata Susumu , Zhang Hedong , Fukuzawa Kenji , Mitsuya Yasunaga
Published: April 2008

Using a coarse-grained molecular dynamics simulation based on the bead-spring polymer model, we reproduced the film distribution of molecularly thin lubricant films with polar end groups coated on the disk surface and quantified the film-surface morphology using a molecular-probe scanning method. We found that the film-surface morphology changed periodically with increasing film thickness. The monolayer of a polar lubricant that entirely covers the solid surface provides a flat lubricant surface by exposing its nonpolar backbone outside of the monolayer. By increasing film thickness, the end beads aggregate to make clusters, and bulges form on the lubricant surface, accompanying an increase in surface roughness. The bulges continue to grow even though the averaged film thickness reaches or exceeds the bilayer thickness. With further increases in film thickness, the clusters start to be uniformly distributed in the lateral direction to clearly form a third layer. As for the formation of fourth and fifth layers, the process is basically the same as that for the second and third layers. Through our calculations of the intermolecular potential field and the intermolecular force field, these values are found to change periodically and are synchronized with the formation of molecule aggregations, which explains the mechanism of forming the layered structure that is inherent to a polar lubricant.
Novel Synthetic Total Disk Model for Mechanical Testing of Nucleus Replacement Devices
Authors: Spenciner David , Walkenhorst Jared W. , Lee Dennis Y. , Paller David
Published: April 2008

We are presenting a novel, non-biologic model of the healthy human annulus. This lumbar Total Disc Model (TDM) ideally would be both biofidelic and sufficiently robust to withstand long-term fatigue testing without breaking down or tearing apart. Mechanical validation testing was performed to confirm that the compressive and torsional properties were similar to literature values of denucleated human lumbar discs in two-body constructs. Long-term fatigue tests were performed to establish the durability of the model. We have reported data for both our empty TDM and the TDM filled with a representative nucleus replacement device (NRD). The silicone model is geometrically equivalent to the healthy human lumbar disc, including the discoid cavity present following a total nuclectomy, the annulus fibrosis with micro-annulotomy, and the cartilaginous endplates. The pressure transmitted through the center of the disc went from negligible when the TDM was empty to over 40% when the TDM was filled. The compression stiffness was 992±15 N/mm for the empty TDM and 1583±136 N/mm for the filled TDM. The torsional stiffness was 0.505±0.024 Nm/° for the empty and 0.550±0.056 Nm/° for the filled TDM. Lastly, the only mechanical damage suffered by either empty or filled TDMs during dynamic testing came from debonding from the endplates at higher torque levels. No damage was seen during dynamic compression testing. After determining the appropriate geometry for the TDM, validation testing was performed to ensure that the load sharing, compressive, and torsional properties were similar to the native human disc. The silicone model was durable enough to avoid tearing or mechanical failure at physiologic loads. This study demonstrated that a silicone total disc model was developed with appropriate properties necessary for determining the mechanical degradation properties of a NRD and will not mechanical fail at physiologic loads.
Studies on Design Optimization of Coronary Stents
Authors: Srinivas K. , Nakayama T. , Ohta M. , Obayashi S. , Yamaguchi T.
Published: April 2008

The stent design itself seems to be one of the factors responsible for restenosis. As a remedy, the present work attempts to perform a design optimization of coronary stents from a hemodynamic point of view. For the purpose, we have applied the principles of modern exploration of design space restricting ourselves to two-dimensional considerations. Width, thickness, and spacing of the struts of the stent formed the design variables. The objectives chosen for optimization were the vorticity generated, length of recirculation zone, and the reattachment distance in between the struts. Both semicircular and rectangular cross sections of stents were included. Starting with the range of design variables, sample stent cases were generated using Latin hypercube sampling. Objective functions were calculated for each of these by computing the two-dimensional flow using software FLUENT under the assumption of a steady, Newtonian flow considering a model stent with three struts. This was followed by Kriging to construct a response surface, which gives the relationship between the objectives and the design variables. The procedure gave nondominated fronts, which consist of optimized designs. Stents with minimum vorticity, with minimum recirculation distance, and the ones with maximum reattachment length in between struts were generated. The procedure is capable of producing the optimum set of design variables to achieve the prescribed objectives.
A Simplified Method for Examining Profile Deviations of Conjugate Disk Cams
Authors: Chang Wen-Tung , Wu Long-Iong
Published: April 2008

The profile errors of conjugate disk cams can be indirectly examined by means of measuring the conjugate condition of the assembled conjugate cam mechanism. This paper demonstrates how to measure the conjugate condition of the assembled conjugate cam mechanism to reveal the cam profile errors and also develops an analytical approach for relating the variation of the conjugate condition with the cam profile errors. For the machined conjugate cams with profile errors, if the subtending angle of the oscillating follower arms is intentionally changed to be variable, the variation of the subtending angle of the follower arms may indicate the variation of profile errors when the cams rotate. According to the magnitude of the subtending angle variation, the profile deviations of conjugate disk cams can be analyzed analytically. The profile errors of a pair of conjugate cams can be evaluated by means of the corresponding motion variation of the indicator reading. For such an examining method, the only required measuring instrument is a dial indicator. A pair of conjugate cams were examined by the method and also measured using a coordinate measuring machine to test the accuracy and efficiency of the method.
An Extended Myard Linkage and its Derived 6R Linkage
Authors: Chen Y. , You Z.
Published: April 2008

In this paper, a 6R linkage suitable as a building block for the construction of large deployable structures is presented. First, we report the possibility of construct an extended 5R Myard linkage by combining two complimentary Bennett linkages. Unlike the original 5R Myard linkage (also called Myard’s “number 1” linkage), the angle of twists in the Bennett linkages is not necessary to be π∕2. Then we show that a 6R linkage can be produced by merging two extended Myard linkages together and removing the common links. The closure equations for the 6R linkage are derived and its motion characteristics are discussed. Moreover, we demonstrate that a number of such 6R linkages can be assembled together to form a large-scale deployable structure, which opens to a flat profile.
Noncircular Bevel Gear Transmission With Intersecting Axes
Authors: Xia Jiqiang , Liu Yuanyuan , Geng Chunming , Song Jiangbin
Published: April 2008

Noncircular bevel gear can achieve variable transmission between intersecting axes. Based on polar coordinates, a design method for noncircular bevel gears is presented. The geometric characteristic of tooth profiles of the gears can be obtained by means of geometry principles for spherical engagement and a pair of conjugated crown racks, which can engage with the driver noncircular bevel gear and driven one, respectively. A series of new conception such as tangent azimuth angle, concavity of conical surfaces, and module angle are proposed to describe spherical geometry relationship in meshing. Meanwhile, geometrical characters of the crown rack cutter are derived. Based on this cutter, the accurate mathematical model of noncircular bevel gear tooth profile is deduced, and the determinant criterion for undercutting is presented. As an example, the three-dimensional models of noncircular bevel gear pair are established to demonstrate the feasibility of the proposed method. A noncircular bevel gear set can be designed by this method if the special included angle for intersecting axes and transmission function ratio are given.
Design of Laser Interferometric Measuring Device of Involute Profile
Authors: Takeoka Fumi , Komori Masaharu , Kubo Aizoh , Fujio Hiroshige , Taniyama Shigeaki , Ito Takehiro , Takatsuji Toshiyuki , Osawa Sonko , Sato Osamu
Published: April 2008

The vibration and noise of gears is one of the serious problems for devices, such as vehicles and wind turbines. The characteristics of the vibration and noise of gears are considerably affected by the tooth flank form deviation of micrometer order. The quality of product gears is controlled using a gear measuring instrument and calibrated with an involute artifact. However, the conventional calibration of the involute artifact cannot achieve a sufficient accuracy. In this report, a direct method of measuring the involute artifact using a laser interferometer is proposed. Fundamental experiments are carried out, in which the effects of the surface condition of the measured object and the effect of the driving of the artifact are investigated. It is confirmed that the proposed method enables the measurement of the detailed form of an involute tooth flank and has the potential of accomplishing a highly precise measurement of an involute artifact.
Dynamic Transmission Error Prediction of Helical Gear Pair Under Sliding Friction Using Floquet Theory
Authors: He Song , Singh Rajendra
Published: April 2008

An analytical solution to the dynamic transmission error of a helical gear pair is developed by using a single-degree-of-freedom model with piecewise stiffness functions that characterize the contact plane dynamics and capture the velocity reversal at the pitch line. By assuming a constant mesh stiffness density along the contact lines, a linear time-varying model (with parametric excitations) is obtained, where the effect of sliding friction is quantified by an effective mesh stiffness term. The Floquet theory is then used to obtain closed-form solutions to the dynamic transmission error, and responses are derived to both initial conditions and the forced periodic function under a nominal preload. Analytical models are validated by comparing predictions with numerical simulations, and the effect of viscous damping is examined. Stability analysis is also briefly conducted by using the state transition matrix. Overall, the sliding friction has a marginal effect on the dynamic transmission error of helical gears, as compared with spur gears, in the context of the torsional model.
Illusory spectrotemporal ripples created with binaurally correlated noise
Authors: Nassiri Reza , Escabí Monty A.
Published: April 2008

Binaural disparities are the primary acoustic cues employed in sound localization tasks. However, the degree of binaural correlation in a sound serves as a complementary cue for detecting competing sound sources [J. F. Culling, H. S. Colburn, and M. Spurchise, “Interaural correlation sensitivity,” J. Acoust. Soc. Am. 110(2), 1020–1029 (2001) and L. R. Bernstein and C. Trahiotis, “On the use of the normalized correlation as an index of interaural envelope correlation,” J. Acoust. Soc. Am. 100, 1754–1763 (1996)]. Here a random chord stereogram (RCS) sound is developed that produces a salient pop-out illusion of a slowly varying ripple sound [T. Chi et al., “Spectro-temporal modulation transfer functions and speech intelligibility,” J. Acoust. Soc. Am. 106(5), 2719–2732 (1999)], even though the left and right ear sounds alone consist of noise-like random modulations. The quality and resolution of this percept is systematically controlled by adjusting the spectrotemporal correlation pattern between the left and right sounds. The prominence and limited time-frequency resolution for resolving the RCS suggests that envelope correlations are a dominant binaural cue for grouping acoustic objects.
Effects of upper-frequency boundary and spectral warping on speech intelligibility in electrical stimulation
Authors: Goupell Matthew J. , Laback Bernhard , Majdak Piotr , Baumgartner Wolf-Dieter
Published: April 2008

Speech understanding was tested for seven listeners using 12-electrode Med-El cochlear implants (CIs) and six normal-hearing listeners using a CI simulation. Eighteen different types of processing were evaluated, which varied the frequency-to-tonotopic place mapping and the upper boundary of the frequency and stimulation range. Spectrally unwarped and warped conditions were included. Unlike previous studies on this topic, the lower boundary of the frequency and stimulation range was fixed while the upper boundary was varied. For the unwarped conditions, only eight to ten channels were needed in both quiet and noise to achieve no significant degradation in speech understanding compared to the normal 12-electrode speech processing. The unwarped conditions were often the best conditions for understanding speech; however, small changes in frequency-to-place mapping (<0.77 octaves for the most basal electrode) yielded no significant degradation in performance from the nearest unwarped condition. A second experiment measured the effect of feedback training for both the unwarped and warped conditions. Improvements were found for the unwarped and frequency-expanded conditions, but not for the compressed condition. These results have implications for new CI processing strategies, such as the inclusion of spectral localization cues.
Nonlinear source–filter coupling in phonation: Vocal exercises
Authors: Titze Ingo , Riede Tobias , Popolo Peter
Published: April 2008

Nonlinear source–filter coupling has been demonstrated in computer simulations, in excised larynx experiments, and in physical models, but not in a consistent and unequivocal way in natural human phonations. Eighteen subjects (nine adult males and nine adult females) performed three vocal exercises that represented a combination of various fundamental frequency and formant glides. The goal of this study was to pinpoint the proportion of source instabilities that are due to nonlinear source–tract coupling. It was hypothesized that vocal fold vibration is maximally destabilized when F0 crosses F1, where the acoustic load changes dramatically. A companion paper provides the theoretical underpinnings. Expected manifestations of a source–filter interaction were sudden frequency jumps, subharmonic generation, or chaotic vocal fold vibrations that coincide with F0–F1 crossovers. Results indicated that the bifurcations occur more often in phonations with F0–F1 crossovers, suggesting that nonlinear source–filter coupling is partly responsible for source instabilities. Furthermore it was observed that male subjects show more bifurcations in phonations with F0–F1 crossovers, presumably because in normal speech they are less likely to encounter these crossovers as much as females and hence have less practice in suppressing unwanted instabilities.
Acoustic energy harvesting using an electromechanical Helmholtz resonator
Authors: Liu Fei , Phipps Alex , Horowitz Stephen , Ngo Khai , Cattafesta Louis , Nishida Toshikazu , Sheplak Mark
Published: April 2008

This paper presents the development of an acoustic energy harvester using an electromechanical Helmholtz resonator (EMHR). The EMHR consists of an orifice, cavity, and a piezoelectric diaphragm. Acoustic energy is converted to mechanical energy when sound incident on the orifice generates an oscillatory pressure in the cavity, which in turns causes the vibration of the diaphragm. The conversion of acoustic energy to electrical energy is achieved via piezoelectric transduction in the diaphragm of the EMHR. Moreover, the diaphragm is coupled with energy reclamation circuitry to increase the efficiency of the energy conversion. Lumped element modeling of the EMHR is used to provide physical insight into the coupled energy domain dynamics governing the energy reclamation process. The feasibility of acoustic energy reclamation using an EMHR is demonstrated in a plane wave tube for two power converter topologies. The first is comprised of only a rectifier, and the second uses a rectifier connected to a flyback converter to improve load matching. Experimental results indicate that approximately 30 mW of output power is harvested for an incident sound pressure level of 160dB with a flyback converter. Such power level is sufficient to power a variety of low power electronic devices.
Seeing pitch: Visual information for lexical tones of Mandarin-Chinese
Authors: Chen Trevor H. , Massaro Dominic W.
Published: April 2008

Mandarin perceivers were tested in visual lexical-tone identification before and after learning. Baseline performance was only slightly above chance, although there appeared to be some visual information in the speakers’ neck and head movements. When participants were taught to use this visible information in two experiments, visual tone identification improved significantly. There appears to be a relationship between the production of lexical tones and the visible movements of the neck, head, and mouth, and this information can be effectively used after a short training session.
A glimpsing account for the benefit of simulated combined acoustic and electric hearing
Authors: Li Ning , Loizou Philipos C.
Published: April 2008

The benefits of combined electric and acoustic stimulation (EAS) in terms of speech recognition in noise are well established; however the underlying factors responsible for this benefit are not clear. The present study tests the hypothesis that having access to acoustic information in the low frequencies makes it easier for listeners to glimpse the target. Normal-hearing listeners were presented with vocoded speech alone (V), low-pass (LP) filtered speech alone, combined vocoded and LP speech (LP+V) and with vocoded stimuli constructed so that the low-frequency envelopes were easier to glimpse. Target speech was mixed with two types of maskers (steady-state noise and competing talker) at −5 to 5dB signal-to-noise ratios. Results indicated no advantage of LP+V in steady noise, but a significant advantage over V in the competing talker background, an outcome consistent with the notion that it is easier for listeners to glimpse the target in fluctuating maskers. A significant improvement in performance was noted with the modified glimpsed stimuli over the original vocoded stimuli. These findings taken together suggest that a significant factor contributing to the EAS advantage is the enhanced ability to glimpse the target.
Application of Biot’s theory to ultrasonic characterization of human cancellous bones: Determination of structural, material, and mechanical properties
Authors: Pakula Michal , Padilla Frederic , Laugier Pascal , Kaczmarek Mariusz
Published: April 2008

This paper is devoted to the experimental determination of distinctive macroscopic structural (porosity, tortuosity, and permeability) and mechanical (Biot–Willis elastic constants) properties of human trabecular bones. Then, the obtained data may serve as input parameters for modeling wave propagation in cancellous bones using Biot’s theory. The goal of the study was to obtain experimentally those characteristics for statistically representative group of human bones (35 specimens) obtained from a single skeletal site (proximal femur). The structural parameters were determined using techniques devoted to the characterization of porous materials: electrical spectroscopy, water permeametry, and microcomputer tomography. The macroscopic mechanical properties, Biot–Willis elastic constants, were derived based on the theoretical consideration of Biot’s theory, micromechanical statistical models, and experimental results of ultrasonic studies for unsaturated cancellous bones. Our results concerning structural parameters are consistent with the data presented by the other authors, while macroscopic mechanical properties measured within our studies are situated between the other published data. The discrepancies are mainly attributed to different mechanical properties of the skeleton frame, due to strong structural anisotropy varying from site to site. The results enlighten the difficulty to use Biot’s theory for modeling wave propagation in cancellous bone, implying necessity of individual evaluation of input parameters.
Spatial averaging of oceanic rainfall variability using underwater sound: Ionian sea rainfall experiment 2004
Authors: Nystuen Jeffrey A. , Amitai Eyal , Anagnostou Emmanuel N. , Anagnostou Marios N.
Published: April 2008

An experiment to evaluate the inherent spatial averaging of the underwater acoustic signal from rainfall was conducted in the winter of 2004 in the Ionian Sea southwest of Greece. A mooring with four passive aquatic listeners (PALs) at 60, 200, 1000, and 2000m was deployed at 36.85°N, 21.52°E, 17km west of a dual-polarization X-band coastal radar at Methoni, Greece. The acoustic signal is classified into wind, rain, shipping, and whale categories. It is similar at all depths and rainfall is detected at all depths. A signal that is consistent with the clicking of deep-diving beaked whales is present 2% of the time, although there was no visual confirmation of whale presence. Co-detection of rainfall with the radar verifies that the acoustic detection of rainfall is excellent. Once detection is made, the correlation between acoustic and radar rainfall rates is high. Spatial averaging of the radar rainfall rates in concentric circles over the mooring verifies the larger inherent spatial averaging of the rainfall signal with recording depth. For the PAL at 2000m, the maximum correlation was at 3–4km, suggesting a listening area for the acoustic rainfall measurement of roughly 30–50km2.
Speech segregation in rooms: Monaural, binaural, and interacting effects of reverberation on target and interferer
Authors: Lavandier Mathieu , Culling John F.
Published: April 2008

Speech reception thresholds were measured in virtual rooms to investigate the influence of reverberation on speech intelligibility for spatially separated targets and interferers. The measurements were realized under headphones, using target sentences and noise or two-voice interferers. The room simulation allowed variation of the absorption coefficient of the room surfaces independently for target and interferer. The direct-to-reverberant ratio and interaural coherence of sources were also varied independently by considering binaural and diotic listening. The main effect of reverberation on the interferer was binaural and mediated by the coherence, in agreement with binaural unmasking theories. It appeared at lower reverberation levels than the effect of reverberation on the target, which was mainly monaural and associated with the direct-to-reverberant ratio, and could be explained by the loss of amplitude modulation in the reverberant speech signals. This effect was slightly smaller when listening binaurally. Reverberation might also be responsible for a disruption of the mechanism by which the auditory system exploits fundamental frequency differences to segregate competing voices, and a disruption of the “listening in the gaps” associated with speech interferers. These disruptions may explain an interaction observed between the effects of reverberation on the targets and two-voice interferers.
A simulation tool for brassiness studies
Authors: Gilbert Joël , Menguy Ludovic , Campbell Murray
Published: April 2008

A frequency-domain numerical model of brass instrument sound production is proposed as a tool to predict their brassiness, defined as the rate of spectral enrichment with increasing dynamic level. It is based on generalized Burger’s equations dedicated to weakly nonlinear wave propagation in nonuniform ducts, and is an extension of previous work by Menguy and Gilbert [Acta Acustica 86, 798–810 (2000)], initially limited to short cylindrical tubes. The relevance of the present tool is evaluated by carrying out simulations over distances longer than typical shock formation distances, and by doing preliminary simulations of periodic regimes in a typical brass trombone bore geometry.
Target detection and location with ambient noise
Authors: Harrison Christopher H.
Published: April 2008

By placing a vertical array in an ambient noise field and forming an upward and a downward beam one obtains two time series which can be cross correlated to reveal a subbottom profile of the seabed [Siderius et al., J. Acoust. Soc. Am. 120, 1315–1323 (2006)]. Here the cross-correlation approach is applied to the location in range and bearing of a point target. An experiment was designed using floats and weights mounted (and dismounted) on the same cable as the vertical array. Careful measurements were made of the location of all likely floats, ballast weights, array terminations, and so on. After suitable coherent averaging, peaks were seen at delays (correlation offsets) agreeing with the reflector positions and were shown to be absent when reflectors were removed. A trivial extension of the theory developed in Harrison and Siderius [J. Acoust. Soc. Am. 123, 1282–1296 (2008)] is used to explain the rough amplitudes of the reflections. The approach differs from “acoustic daylight” principally in having a capability to determine a target range.
An acoustic intensity-based method for reconstruction of radiated fields
Authors: Yu Chao , Zhou Zhengfang , Zhuang Mei
Published: April 2008

An acoustic intensity-based method is proposed for the reconstruction of acoustic radiation pressure. Unlike the traditional inverse acoustic methods, the proposed method includes the acoustic pressure gradient as an input in addition to its simultaneous, co-located acoustic pressure in a radiated field. As a result, the reconstruction of acoustic radiation pressure from the input acoustic data over a portion of a surface enclosing all the acoustic sources, i.e., an open surface, becomes unique due to the unique continuation theory of elliptic equations. Hence the method is more stable and the reconstructed acoustic pressure is less dependable on the locations of the input acoustic data. Furthermore, the proposed method can be applied for both inverse and forward problems up to the minimum sphere enclosing the sources of interest. The effectiveness of the method is demonstrated by the results of several acoustic radiation examples with single or multi-frequency source in a two-dimensional configuration. The results from the method also show a measurable improvement in accuracy and consistency of reconstructed acoustic radiation pressure, in particular when the effect of the signal-to-noise ratio is included.
Sound velocity and attenuation in bubbly gels measured by transmission experiments
Authors: Leroy Valentin , Strybulevych Anatoliy , Page John H. , Scanlon Martin G.
Published: April 2008

Measurements of the phase velocity and attenuation of sound in concentrated samples of bubbly gels are presented. Hair gel was used as a matrix material to obtain well characterized distributions of bubbles. Ultrasonic measurements were conducted over a large range of frequencies, including the resonance frequencies of the bubbles. Surprisingly good agreement with Foldy’s prediction was found, even for monodisperse samples at resonance frequencies, up to volume fraction of 1%. Beyond this concentration, the effects of high-order multiple scattering were observed. These results support the feasability of ultrasonic techniques to investigate the size distribution of bubbles in a weak gel or liquid.
The effect of stimulus range on two-interval frequency discrimination
Authors: Matthews William J. , Stewart Neil
Published: April 2008

It has traditionally been thought that performance in two-interval frequency discrimination tasks decreases as the range over which the standard tone varies is increased. Recent empirical evidence and a reexamination of previous results suggest that this may not be the case. The present experiment found that performance was significantly better when the standard roved over a wide range (1500Hz) than a narrow range (30Hz). This pattern cannot readily be accommodated by traditional models of frequency discrimination based on memory or attention, but may be explicable in terms of neural plasticity and the formation of perceptual anchors.
Causal impulse response for circular sources in viscous media
Authors: Kelly James F. , McGough Robert J.
Published: April 2008

The causal impulse response of the velocity potential for the Stokes wave equation is derived for calculations of transient velocity potential fields generated by circular pistons in viscous media. The causal Green’s function is numerically verified using the material impulse response function approach. The causal, lossy impulse response for a baffled circular piston is then calculated within the near field and the far field regions using expressions previously derived for the fast near field method. Transient velocity potential fields in viscous media are computed with the causal, lossy impulse response and compared to results obtained with the lossless impulse response. The numerical error in the computed velocity potential field is quantitatively analyzed for a range of viscous relaxation times and piston radii. Results show that the largest errors are generated in locations near the piston face and for large relaxation times, and errors are relatively small otherwise. Unlike previous frequency-domain methods that require numerical inverse Fourier transforms for the evaluation of the lossy impulse response, the present approach calculates the lossy impulse response directly in the time domain. The results indicate that this causal impulse response is ideal for time-domain calculations that simultaneously account for diffraction and quadratic frequency-dependent attenuation in viscous media.
Finite element simulation of the generation and detection by air-coupled transducers of guided waves in viscoelastic and anisotropic materials
Authors: Hosten Bernard , Biateau Christine
Published: April 2008

The measured characteristics (efficiency and sensitivity) of two air-coupled transducers allow for the prediction of the absolute values of the pressure of the bulk waves generated in air and for the measurement of the pressure of the field radiated in air by guided waves propagating in a structure. With finite element software, the pressure field generated by an air-coupled transducer is simulated by introducing a right-hand side member in the Helmholtz equation, which is used for computing the propagation from the transducer to a plate. The simulated source is rotated in order to impose an angle of incidence with respect to the normal of the plate and generate the corresponding guided mode. Inside the plate, the propagation is simulated with the dynamic equations of equilibrium and a complex stiffness tensor to take into account the viscoelastic anisotropy of the material. For modeling the three-dimensional fields of the guided modes propagating in a two-dimensional non-symmetry plane, a 2.5 dimensional model is introduced. The model computes the value of the pressure field radiated in air by the plates for any guided modes and can predict the detectability of the system for a known defect in a structure. A test bed incorporating two air-coupled transducers is used to generate and receive various guided modes. Two plates made of Perspex and carbon-epoxy composite are tested. The pressure measured by the receiver at various positions is compared to the results of the model to validate it.
Optimized translation of microbubbles driven by acoustic fields
Authors: Toilliez Jean O. , Szeri Andrew J.
Published: April 2008

The problem of a single acoustically driven bubble translating unsteadily in a fluid is considered. The investigation of the translation equation identifies the inverse Reynolds number as a small perturbation parameter. The objective is to obtain a closed-form, leading order solution for the translation of the bubble, assuming nonlinear radial oscillations and a pressure field as the forcing term. In a second part, the periodic attractor of the Rayleigh–Plesset equation serves as basis for an optimal acoustic forcing designed to achieve maximized bubble translation over one dimensionless period. At near-resonant or super-resonant driving frequencies, it seems one cannot improve much on sinusoidal forcing. However at moderate acoustic intensity and sub-resonant frequencies, acoustic wave forms that enhance bubble collapse lead to displacement many times larger than the case of purely sinusoidal forcing. The survey covers a wide spectrum of driving ratios and bubble diameters including those relevant to biomedical applications. Shape stability issues are considered. Together, these results suggest new ways to predict some of the direct and indirect effects of the acoustic radiation force in applications such as targeted drug delivery, selective bubble driving, and accumulation.
In Vitro Antifungal Susceptibility and Molecular Characterization of Clinical Isolates of
Fusarium verticillioides
(
F. moniliforme
) and
Fusarium thapsinum
Authors: Azor Mónica , Gené Josepa , Cano Josep , Sutton Deanna A. , Fothergill Annette W. , Rinaldi Michael G. , Guarro Josep
Published: April 2008

A microdilution method was used to test 11 antifungal drugs against clinical isolates of
Fusarium thapsinum
and three different phylogenetic clades of
Fusarium verticillioides
that were characterized by sequencing a region of the β-tubulin gene. Terbinafine was the most-active drug against both species, followed by posaconazole against
F. verticillioides
.
Production of Enterocins L50A, L50B, and IT, a New Enterocin, by
Enterococcus faecium
IT62, a Strain Isolated from Italian Ryegrass in Japan
Authors: Izquierdo Esther , Bednarczyk Audrey , Schaeffer Christine , Cai Yimin , Marchioni Eric , Van Dorsselaer Alain , Ennahar Saïd
Published: April 2008

Enterococcus faecium
IT62, isolated from ryegrass in Japan, was shown to produce three different bacteriocins, two of which had molecular masses and amino acid sequences that corresponded to those of enterocin L50A and enterocin L50B. These peptides existed, however, as chemically modified forms that were either N formylated or N formylated and oxidized at Met
24
. The third bacteriocin, named enterocin IT, had a molecular mass of 6,390 Da, was made up of 54 amino acids, and did not correspond to any known bacteriocin. However, enterocin IT was identical to the C-terminal part of the 16-amino-acid-longer bacteriocin 32 (T. Inoue, H. Tomita, and Y. Ike, Antimicrob. Agents Chemother., 50:1202-1212, 2006). For the first time, the antimicrobial activity spectra for enterocins L50A and L50B were determined separately and included a wide range of gram-positive bacteria but also a few gram-negative strains that were weakly sensitive. Slight differences in the activities of enterocins L50A and L50B were observed, as gram-positive bacteria showed an overall higher level of sensitivity to L50A than to L50B, as opposed to gram-negative ones. Conversely, enterocin IT showed a very narrow antimicrobial spectrum that was limited to
E. faecium
strains, one strain of
Bacillus subtilis
, and one strain of
Lactococcus lactis
. This study showed that
E. faecium
IT62, a grass-borne strain, produces bacteriocins with very different activity features and structures that may be found in strains associated with food or those of clinical origin, which demonstrates that a particular enterocin structure may be widespread and not related to the producer's origin.