bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Finger Posture on the Tendon Force Distribution Within the Finger Extensor Mechanism
Authors: Lee Sang Wook , Chen Hua , Towles Joseph D. , Kamper Derek G.
Published: September 2008

Understanding the transformation of tendon forces into joint torques would greatly aid in the investigation of the complex temporal and spatial coordination of multiple muscles in finger movements. In this study, the effects of the finger posture on the tendon force transmission within the finger extensor apparatus were investigated. In five cadaver specimens, a constant force was applied sequentially to the two extrinsic extensor tendons in the index finger, extensor digitorum communis and extensor indicis proprius. The responses to this loading, i.e., fingertip force/moment and regional strains of the extensor apparatus, were measured and analyzed to estimate the tendon force transmission into the terminal and central slips of the extensor hood. Repeated measures analysis of variance revealed that the amount of tendon force transmitted to each tendon slip was significantly affected by finger posture, specifically by the interphalangeal (IP) joint angles (p<0.01). Tendon force transmitted to each of the tendon slips was found to decrease with the IP flexion. The main effect of the metacarpophalangeal (MCP) joint angle was not as consistent as the IP angle, but there was a strong interaction effect for which MCP flexion led to large decreases in the slip forces (>30%) when the IP joints were extended. The ratio of terminal slip force:central slip force remained relatively constant across postures at approximately 1.7:1. Force dissipation into surrounding structures was found to be largely responsible for the observed force-posture relationship. Due to the significance of posture in the force transmission to the tendon slips, the impact of finger posture should be carefully considered when studying finger motor control or examining injury mechanisms in the extensor apparatus.
A Generalized Maxwell Model for Creep Behavior of Artery Opening Angle
Authors: Zhang W. , Guo X. , Kassab G. S.
Published: September 2008

An artery ring springs open into a sector after a radial cut. The opening angle characterizes the residual strain in the unloaded state, which is fundamental in understanding stress and strain in the vessel wall. A recent study revealed that the opening angle decreases with time if the artery is cut from the loaded state, while it increases if the cut is made from the no-load state due to viscoelasticity. In both cases, the opening angle approaches the same value in 3h. This implies that the characteristic relaxation time is about 10,000s. Here, the creep function of a generalized Maxwell model (a spring in series with six Voigt bodies) is used to predict the temporal change of opening angle in multiple time scales. It is demonstrated that the theoretical model captures the salient features of the experimental results. The proposed creep function may be extended to study the viscoelastic response of blood vessels under various loading conditions.
Experimental and numerical investigations on melamine wedges
Authors: Schneider S.
Published: September 2008

Melamine wedges are often used as acoustic lining material for anechoic chambers. It was proposed here to study the effects of the mounting conditions on the acoustic properties of the melamine wedges used in the large anechoic chamber at the LMA. The results of the impedance tube measurements carried out show that the mounting conditions must be taken into account when assessing the quality of an acoustic lining. As it can be difficult to simulate these mounting conditions in impedance tube experiments, a numerical method was developed, which can be used to complete the experiments or for parametric studies. By combining the finite and the boundary element method, it is possible to investigate acoustic linings with almost no restrictions as to the geometry, material behavior, or mounting conditions. The numerical method presented here was used to study the acoustic properties of the acoustic lining installed in the anechoic chamber at the LMA. Further experiments showed that the behavior of the melamine foam is anisotropic. Numerical simulations showed that this anisotropy can be used to advantage when designing an acoustic lining.
Determination of thickness and elastic constants of aluminum plates from full-field wavelength measurements of single-mode narrowband Lamb waves
Authors: Deán J. Luis , Trillo Cristina , Doval Ángel F. , Fernández José L.
Published: September 2008

A method based on fitting the theoretical dispersion curves of Lamb waves to experimental data is presented to determine the thickness and two independent elastic constants of aluminum plates a few millimeters thick. The waves are generated by means of the wedge method using a narrowband source, selecting the wedge angle and the acoustic frequency f so that mainly one mode is excited. A self-developed pulsed electronic speckle pattern interferometry system renders a two dimensional map of the out-of-plane acoustic displacement field at the plate surface, which allows an accurate measurement of the acoustic wavelength λ1. For any mode, the relation between λ1 and f depends on the three unknown parameters, so at least three experimental measurements (λ1i,fi) with different frequencies and/or different modes are required to calculate them. The suitability of different Lamb modes to determine each parameter when the others are known is studied, as well as the conditions that the experimental set of values must fulfill to calculate all three parameters. Numerous Lamb modes at different frequencies are generated in each plate, and a fitting is made based on the minimization of the error function, resulting in an accuracy better than 1%.
Observed limiting cases of horizontal field coherence and array performance in a time-varying internal wavefield
Authors: Collis Jon M. , Duda Timothy F. , Lynch James F. , DeFerrari Harry A.
Published: September 2008

Using a moored source and horizontal/vertical line array combination, horizontal coherence properties of high signal to noise ratio (≥20dB) 100–1600Hz signals have been measured. Internal waves in the area of the measurement created moving episodic sound-speed anomaly structures, influencing coherence length. Measured horizontal coherence scales for 100Hz ranged from 5 to 20 acoustic wavelengths, and were inversely related to the sound-speed anomaly strength. Horizontal field properties were compared with fields computed using modal decompositions of the vertical signals. The comparison allows azimuthal field coherence properties to be studied apart from normal-mode interference effects.
Measuring distortion product otoacoustic emissions using continuously sweeping primaries
Authors: Long Glenis R. , Talmadge Carrick L. , Lee Jungmee
Published: September 2008

Distortion product otoacoustic emission (DPOAE) level from normal hearing individuals can vary by as much as 30dB with small frequency changes (a phenomenon known as DPOAE fine structure). This fine structure is hypothesized to stem from the interaction of components from two different regions of the cochlea (the nonlinear generator region and the reflection component from the DP region). An efficient procedure to separate these two components would improve the clinical and research utility of DPOAE by permitting separate evaluation of different cochlea regions. In this paper, two procedures for evaluating DPOAE fine structure are compared: DPOAE generated by fixed-frequency primaries versus continuously sweeping primaries. The sweep DPOAE data are analyzed with a least squares fit filter. Sweep rates of greater than 8s per octave permit rapid evaluation of the cochlear fine structure. A higher sweep rate of 2s per octave provided DPOAE without fine structure. Under these conditions, the longer latency reflection component falls outside the range of the filter. Consequently, DPOAE obtained with sweeping tones can be used either to get more rapid estimates of DPOAE fine structure or to obtain estimates of DPOAE from the generator region uncontaminated by energy from the reflection region.
A method for approximating acoustic-field-amplitude uncertainty caused by environmental uncertainties
Authors: James Kevin R. , Dowling David R.
Published: September 2008

In underwater acoustics, the accuracy of computational field predictions is commonly limited by uncertainty in environmental parameters. An approximate technique for determining the probability density function (PDF) of computed field amplitude, A, from known environmental uncertainties is presented here. The technique can be applied to several, N, uncertain parameters simultaneously, requires N+1 field calculations, and can be used with any acoustic field model. The technique implicitly assumes independent input parameters and is based on finding the optimum spatial shift between field calculations completed at two different values of each uncertain parameter. This shift information is used to convert uncertain-environmental-parameter distributions into PDF(A). The technique’s accuracy is good when the shifted fields match well. Its accuracy is evaluated in range-independent underwater sound channels via an L1 error-norm defined between approximate and numerically converged results for PDF(A). In 50-m- and 100-m-deep sound channels with 0.5% uncertainty in depth (N=1) at frequencies between 100 and 800Hz, and for ranges from 1to8km, 95% of the approximate field-amplitude distributions generated L1 values less than 0.52 using only two field calculations. Obtaining comparable accuracy from traditional methods requires of order 10 field calculations and up to 10N when N>1.
The effect of the base line response on self-adjustments of hearing aid gain
Authors: Keidser Gitte , Dillon Harvey , Convery Elizabeth
Published: September 2008

Self-adjustments of variable hearing aid parameters are essential for trainable hearing aids to provide customized amplification for different listening environments. Prompted by a finding of Dreschler et al. [Ear Hear. 29, 214–227 (2008)], this study investigates the effect of the base line (starting) response on self-adjustments of gain in different frequency bands. In a laboratory test, 24 hearing-impaired listeners adjusted the bass, treble, and overall gain to reach their preferred responses from two different base line responses for 12 different listening situations. The adjustments were repeated five times using the preferred response after each adjustment as base line response for the next adjustment. Half of the listeners further compared three different response shapes, within the range of preferred responses, pairwise ten times for preferential and perceptual discrimination. The results revealed that base line response biases were more pronounced at low frequencies and for listeners with a flat hearing loss configuration. While 83% of listeners reliably discriminated between the average selected biased responses, only 25% demonstrated reliable preferences for one response over the other. Listeners who showed preferential discrimination ability were those who were less biased by the base line response. The clinical implication is that self-adjustments should begin from an appropriately prescribed starting response.
On the forces in single-ended and push-pull electret transducers
Authors: Mellow Tim , Kärkkäinen Leo
Published: September 2008

The equations for the electromechanical force conversion in single-ended and push-pull electret transducers are derived. Traditionally, the charge distribution has been modeled as a concentrated layer at an arbitrary distance from the surface of the dielectric. For the purpose of this analysis, a negative charge is assumed to be evenly distributed throughout the dielectric. The membrane has a conductive coating in which a positive charge is induced, giving an overall dipole charge. The resulting formulas are used to derive the voltage sensitivity of a microphone and the equivalent electrical circuit for the electromechanical transduction part of a microphone or loudspeaker. An equivalent external polarizing voltage is then derived that would produce the same driving force in a conventional electrostatic loudspeaker without a stored charge. The condition for the static stability of a circular electret membrane is also determined.
Interference between wave modes may contribute to the apparent negative dispersion observed in cancellous bone
Authors: Anderson Christian C. , Marutyan Karen R. , Holland Mark R. , Wear Keith A. , Miller James G.
Published: September 2008

Previous work has shown that ultrasonic waves propagating through cancellous bone often exhibit a linear-with-frequency attenuation coefficient, but a decrease in phase velocity with frequency (negative dispersion) that is inconsistent with the causality-imposed Kramers–Kronig relations. In the current study, interfering wave modes similar to those observed in bone are shown to potentially contribute to the observed negative dispersion. Biot theory, the modified Biot–Attenborogh model, and experimental results are used to aid in simulating multiple-mode wave propagation through cancellous bone. Simulations entail constructing individual wave modes exhibiting a positive dispersion using plausible velocities and amplitudes, and then summing the individual modes to create mixed-mode output wave forms. Results of the simulations indicate that mixed-mode wave forms can exhibit negative dispersion when analyzed conventionally under the assumption that only one wave is present, even when the individual interfering waves exhibit positive dispersions in accordance with the Kramers–Kronig relations. Furthermore, negative dispersion is observed when little or no visual evidence of interference exists in the time-domain data. Understanding the mechanisms responsible for the observed negative dispersion could aid in determining the true material properties of cancellous bone, as opposed to the apparent properties measured using conventional data analysis techniques.
Experimental verification of a two-sensor acoustic intensity measurement in lossy ducts
Authors: Biwa Tetsushi , Tashiro Yusuke , Nomura Hiroshi , Ueda Yuki , Yazaki Taichi
Published: September 2008

Two-sensor method proposed by Fusco et al. [“Two-sensor power measurements in lossy ducts,” J. Acoust. Soc. Am. 91, 2229–2235 (1992)] is a novel technique that determines acoustic intensity of a gas column in a wide duct from measurements of pressure based on the boundary layer approximation. For further development of this method, its validity is experimentally tested through comparison with the direct method measuring the pressure and the velocity simultaneously, and its formulation is modified to include the narrow duct range where the duct radius is smaller than the viscous boundary layer thickness of the gas. It is shown that the modified two-sensor method enables quick and accurate evaluation of the acoustic intensity seamlessly from narrow to wide duct ranges.
Syllable acoustics, temporal patterns, and call composition vary with behavioral context in Mexican free-tailed bats
Authors: Bohn Kirsten M. , Schmidt-French Barbara , Ma Sean T. , Pollak George D.
Published: September 2008

Recent research has shown that some bat species have rich vocal repertoires with diverse syllable acoustics. Few studies, however, have compared vocalizations across different behavioral contexts or examined the temporal emission patterns of vocalizations. In this paper, a comprehensive examination of the vocal repertoire of Mexican free-tailed bats, T. brasiliensis, is presented. Syllable acoustics and temporal emission patterns for 16 types of vocalizations including courtship song revealed three main findings. First, although in some cases syllables are unique to specific calls, other syllables are shared among different calls. Second, entire calls associated with one behavior can be embedded into more complex vocalizations used in entirely different behavioral contexts. Third, when different calls are composed of similar syllables, distinctive temporal emission patterns may facilitate call recognition. These results indicate that syllable acoustics alone do not likely provide enough information for call recognition; rather, the acoustic context and temporal emission patterns of vocalizations may affect meaning.
Effect of the cochlear microphonic on the limiting frequency of the mammalian ear
Authors: Iwasa Kuni H. , Sul Bora
Published: September 2008

Electromotility is a basis for cochlear amplifier, which controls the sensitivity of the mammalian ear and contributes to its frequency selectivity. Because it is driven by the receptor potential, its frequency characteristics are determined by the low-pass RC filter intrinsic to the cell, which has a corner frequency about 1∕10th of the operating frequency. This filter significantly decreases the efficiency of electromotility as an amplifier. The present paper examines a proposal that the cochlear microphonic, the voltage drop across the extracellular medium by the receptor current, contributes to overcome this problem. It is found that this effect can improve frequency dependence. However, this effect alone is too small to enhance the effectiveness of electromotility beyond 10kHz in the mammalian ear.
Development and characterization of a blood mimicking fluid for high intensity focused ultrasound
Authors: Liu Yunbo , Maruvada Subha , King Randy L. , Herman Bruce A. , Wear Keith A.
Published: September 2008

A blood mimicking fluid (BMF) has been developed for the acoustic and thermal characterizations of high intensity focused ultrasound (HIFU) ablation devices. The BMF is based on a degassed and de-ionized water solution dispersed with low density polyethylene microspheres, nylon particles, gellan gum, and glycerol. A broad range of physical parameters, including attenuation coefficient, speed of sound, viscosity, thermal conductivity, and diffusivity, were characterized as a function of temperature (20–70°C). The nonlinear parameter B∕A and backscatter coefficient were also measured at room temperature. Importantly, the attenuation coefficient is linearly proportional to the frequency (2–8MHz) with a slope of about 0.2dBcm−1MHz−1 in the 20–70°C range as in the case of human blood. Furthermore, sound speed and bloodlike backscattering indicate the usefulness of the BMF for ultrasound flow imaging and ultrasound-guided HIFU applications. Most of the other temperature-dependent physical parameters are also close to the reported values in human blood. These properties make it a unique HIFU research tool for developing standardized exposimetry techniques, validating numerical models, and determining the safety and efficacy of HIFU ablation devices.
Developmental changes in the perception of pitch contour: Distinguishing up from down
Authors: Stalinski Stephanie M. , Schellenberg E. Glenn , Trehub Sandra E.
Published: September 2008

Musically untrained participants in five age groups (5-, 6-, 8-, and 11-year-olds, and adults) heard sequences of three 1s piano tones in which the first and third tones were identical (A5, or 880Hz) but the middle tone was displaced upward or downward in pitch. Their task was to identify whether the middle tone was higher or lower than the other two tones. In experiment 1, 5-year-olds successfully identified upward and downward shifts of 4, 2, 1, 0.5, and 0.3 semitones. In experiment 2, older children (6-, 8-, and 11-year-olds) and adults successfully identified the same shifts as well as a smaller shift (0.1 semitone). For all age groups, performance accuracy decreased as the size of the shift decreased. Performance improved from 5to8years of age, reaching adult levels at 8years.
Acoustic mode coupling induced by shallow water nonlinear internal waves: Sensitivity to environmental conditions and space-time scales of internal waves
Authors: Colosi John A.
Published: September 2008

While many results have been intuited from numerical simulation studies, the precise connections between shallow-water acoustic variability and the space-time scales of nonlinear internal waves (NLIWs) as well as the background environmental conditions have not been clearly established analytically. Two-dimensional coupled mode propagation through NLIWs is examined using a perturbation series solution in which each order n is associated with nth-order multiple scattering. Importantly, the perturbation solution gives resonance conditions that pick out specific NLIW scales that cause coupling, and seabed attenuation is demonstrated to broaden these resonances, fundamentally changing the coupling behavior at low frequency. Sound-speed inhomogeneities caused by internal solitary waves (ISWs) are primarily considered and the dependence of mode coupling on ISW amplitude, range width, depth structure, location relative to the source, and packet characteristics are delineated as a function of acoustic frequency. In addition, it is seen that significant energy transfer to modes with initially low or zero energy involves at least a second order scattering process. Under moderate scattering conditions, comparisons of first order, single scattering theoretical predictions to direct numerical simulation demonstrate the accuracy of the approach for acoustic frequencies upto 400Hz and for single as well as multiple ISW wave packets.
Subjective and objective evaluations of a scattered sound field in a scale model opera house
Authors: Ryu Jong Kwan , Jeon Jin Yong
Published: September 2008

Scattered sound fields in an opera house were objectively and subjectively evaluated through acoustical measurements in a 1:10 scale model and through auditory preference tests. Acoustical characteristics were measured in the stalls area with and without diffusers, both on the sidewalls close to the proscenium and in the soffit of the side balcony. Installed diffusers reduced the initial time delay gap and amplitude of the first reflected sound, and decreased sound pressure level (SPL), reverberation time (RT), and early decay time (EDT) at most seats due to the increased scattering and absorption. After diffuser installation, C80 and 1-IACCE3 increased at the front seats and decreased at the rear seats. Subjective evaluations showed that the preference of scattered sound fields correlates highly with loudness and reverberance. It was also found that EDT and SPL are dominant parameters describing subjective preference for scattered sounds in this experimental condition.
Evaluation of infrasound signals from the shuttle Atlantis using a large seismic network
Authors: de Groot-Hedlin Catherine D. , Hedlin Michael A. H. , Walker Kristoffer T. , Drob Douglas P. , Zumberge Mark A.
Published: September 2008

Inclement weather in Florida forced the space shuttle “Atlantis” to land at Edwards Air Force Base in southern California on June 22, 2007, passing near three infrasound stations and several hundred seismic stations in northern Mexico, southern California, and Nevada. The high signal-to-noise ratio, broad receiver coverage, and Atlantis’ positional information allow for the testing of infrasound propagation modeling capabilities through the atmosphere to regional distances. Shadow zones and arrival times are predicted by tracing rays that are launched at right angles to the conical shock front surrounding the shuttle through a standard climatological model as well as a global ground to space model. The predictions and observations compare favorably over much of the study area for both atmospheric specifications. To the east of the shuttle trajectory, there were no detections beyond the primary acoustic carpet. Infrasound energy was detected hundreds of kilometers to the west and northwest (NW) of the shuttle trajectory, consistent with the predictions of ducting due to the westward summer-time stratospheric jet. Both atmospheric models predict alternating regions of high and low ensonifications to the NW. However, infrasound energy was detected tens of kilometers beyond the predicted zones of ensonification, possibly due to uncertainties in stratospheric wind speeds.
Vibrational characteristics of harp soundboards
Authors: Waltham Chris , Kotlicki Andrzej
Published: September 2008

Harps exist in different forms, from large factory-made concert harps to small hand-made folk harps. This variety presents both a challenge and an opportunity for acousticians. The musical quality of a harp depends on many factors, but key among these is the soundboard. This work sets out to define some general desirable qualities of a harp soundboard. First, in order to understand the relationship between the vibrational behavior of a bare soundboard and that of a completed instrument, a 36-string harp was built from scratch. Measurements were made at each stage of construction, and the results showed how the bare soundboard properties affect those of the finished harp. Second, the soundboards of several harps of different sizes were assessed by measuring the admittances along the string bar. These data showed that one relationship crucial to the quality of the soundboard is that between the modal shapes and modal frequencies of the soundboard, and the position and fundamental frequencies of the strings attached to it. A general statement is made about this relationship, one which should be of use to harp makers.
Comparison of the Faran Cylinder Model and the Weak Scattering Model for predicting the frequency dependence of backscatter from human cancellous femur in vitro
Authors: Wear Keith A. , Padilla Frederic , Laugier Pascal
Published: September 2008

This letter presents the first side-by-side comparison of the Faran Cylinder Model and the Weak Scattering Model for predicting backscatter from human femur. Both models are applied to the same dataset of frequency-dependent backscatter coefficients from 26 human femur cancellous bone samples in vitro. The Faran Cylinder Model predicts a slightly slower rate of increase of backscatter with frequency than the Weak Scattering Model, but both models are in reasonable agreement with the data and with each other, given the uncertainty in the measurements.
Comment on “Ear Asymmetries in middle-ear, cochlear, and brainstem responses in human infants” [J. Acoust. Soc. Am. 123, 1504–1512]
Authors: Sininger Yvonne , Cone Barbara
Published: September 2008

Following Sininger and Cone-Wesson [Science 305, 1581], Sininger and Cone-Wesson [Hear. Res. 212, 203–211], Keefe et al. [J. Acoust. Soc. Am. 123(3), 1504–1512] described ear asymmetries in middle ear, cochlear, and brainstem responses of infants. Keefe et al. state that their data do not support the findings of Sininger and Cone-Wesson [Science 305, 1581] who found asymmetries in evoked otoacoustic emissions and auditory brainstem responses and proposed that stimulus-directed asymmetries in processing may facilitate development of hemispheric specialization. The Keefe et al. findings, in fact, replicated and extended the findings of Sininger and Cone-Wesson (2004, 2006) and support, rather than refute, the conclusions. Keefe et al. controlled neither the background noise nor averaging time across test conditions (ear or otoacoustic emission type) and thus their separate analyses of signal and noise magnitude exceed the limitations imposed by the data collection methods.
Harmonic segregation through mistuning can improve fundamental frequency discrimination
Authors: Bernstein Joshua G. W. , Oxenham Andrew J.
Published: September 2008

This study investigated the relationship between harmonic frequency resolution and fundamental frequency (f0) discrimination. Consistent with earlier studies, f0 discrimination of a diotic bandpass-filtered harmonic complex deteriorated sharply as the f0 decreased to the point where only harmonics above the tenth were presented. However, when the odd harmonics were mistuned by 3%, performance improved dramatically, such that performance nearly equaled that found with only even harmonics present. Mistuning also improved performance when alternating harmonics were presented to opposite ears (dichotic condition). In a task involving frequency discrimination of individual harmonics within the complexes, mistuning the odd harmonics yielded no significant improvement in the resolution of individual harmonics. Pitch matches to the mistuned complexes suggested that the even harmonics dominated the pitch for f0’s at which a benefit of mistuning was observed. The results suggest that f0 discrimination performance can benefit from perceptual segregation based on inharmonicity, and that poor performance when only high-numbered harmonics are present is not due to limited peripheral harmonic resolvability. Taken together with earlier results, the findings suggest that f0 discrimination may depend on auditory filter bandwidths, but that spectral resolution of individual harmonics is neither necessary nor sufficient for accurate f0 discrimination.
Effective medium method for sound propagation in a soft medium containing air bubbles
Authors: Liang Bin , Zou Xinye , Cheng Jianchun
Published: September 2008

An effective medium method (EMM) is developed to investigate the nonlinear propagation of acoustic waves for soft media containing air bubbles, which accounts for the effects of weak compressibility, viscosity, surrounding pressure, surface tension, and encapsulating shells. Based on the dynamics model of an individual bubble that has included these effects, the EMM is presented by employing a simple perturbation approach to “homogenize” the bubbly soft media. The equations describing the fundamental and the second harmonic waves are derived that applies to three-dimensional cases, and then solved in a one-dimensional case to obtain the effective acoustical parameters of a longitudinal wave. The EMM is compared with the previous theories in three representative cases regarded as simple models of significant practical applications. The results show that the EMM agrees well with the previous theories and can incorporate the additional effects, which may notably affect the accuracy of the results. The limitations of the EMM are also identified and stated.
Direct methods for characterizing high-intensity focused ultrasound transducers using acoustic streaming
Authors: Myers Matthew R. , Hariharan Prasanna , Banerjee Rupak K.
Published: September 2008

Two techniques are presented for noninvasively determining the intensity field of high-intensity focused ultrasound transducers in a liquid medium. The techniques are based upon the streaming velocity induced in the liquid by the absorbed ultrasound beam. The approaches are similar to an iterative streaming method previously reported, but the present approaches are “direct:” The differential operations of the Navier–Stokes equations are performed directly upon the experimentally measured streaming velocity, rather than through an iterative approach that minimizes the difference between a theoretical estimate of the streaming velocity and the one measured experimentally. As such, the direct methods are much faster than the iterative technique. The price paid for the increase in speed is smaller spatial coverage; the direct techniques are applicable only where accurate streaming velocity is available. Comparisons performed in the range 100–1000W∕cm2 focal intensity showed differences between the direct methods and the iterative streaming technique to be less than 20%. Similar differences were observed in low-power comparisons with hydrophone measurements.
Influence of flow separation location on phonation onset
Authors: Zhang Zhaoyan
Published: September 2008

The influence of flow separation location on eigenmode synchronization and phonation onset was investigated in a two-dimensional, aeroelastic, continuum model of phonation. A linear stability analysis showed that flow separation played a critical role in initiating eigenmode synchronization and phonation. For a given glottal configuration, a small variation in the flow separation location along the vocal fold surface may lead to a qualitatively different eigenmode-synchronization pattern, and different phonation threshold pressure and frequency. This high sensitivity suggests a need for phonation models to be capable of accurate prediction of the flow separation location. Analysis with different glottal channel geometries showed that a minimum phonation threshold pressure existed for a rectangular glottal channel, consistent with previous experiments. However, in contrast to previous theoretical analyses, this study showed that phonation was facilitated, rather than prohibited, by the upstream movement of the flow separation point within a divergent glottis.
Direct measurement of sediment sound speed in Shallow Water '06
Authors: Yang Jie , Tang Dajun , Williams Kevin L.
Published: September 2008

Knowledge of sediment sound speed is crucial for predicting sound propagation. During the Shallow Water '06 experiment, in situ sediment sound speed was measured using the Sediment Acoustic-speed Measurement System (SAMS). SAMS consists of ten fixed sources and one receiver that can reach a maximal sediment depth of 3m. Measurements were made in the frequency range 2–35kHz. Signal arrival times and propagation distances were recorded, from which sediment sound speed was determined. Preliminary results from three deployments show that SAMS was capable of determining sediment sound speed with uncertainties less than 1.6%. Little dispersion in sediment sound speed was observed.
Observations of the R reflector and sediment interface reflection at the Shallow Water ’06 Central Site
Authors: Choi Jee Woong , Dahl Peter H. , Goff John A.
Published: September 2008

Acoustic bottom-interacting measurements from the Shallow Water ’06 experiment experiment (frequency range 1–20kHz) are presented. These are co-located with coring and stratigraphic studies showing a thin (∼20cm) higher sound speed layer overlaying a thicker (∼20m) lower sound speed layer ending at a high-impedance reflector (R reflector). Reflections from the R reflector and analysis of the bottom reflection coefficient magnitude for the upper two sediment layers confirm both these features. Geoacoustic parameters are estimated, dispersion effects addressed, and forward modeling using the parabolic wave equation undertaken. The reflection coefficient measurements suggest a nonlinear attenuation law for the thin layer of sandy sediments.
Geoacoustic inversion on the New Jersey Margin: Along and across the shelf
Authors: Ballard Megan S. , Becker Kyle M.
Published: September 2008

This paper presents results of a range-independent perturbative inverse approach applied to data from the Shallow Water Experiment 2006. The inversion technique is based on a linearized relationship between sound speed in the sediment and modal eigenvalues. Horizontal wave numbers were estimated from data collected from two distinct source/receiver tracks oriented along and across the shelf. The specific inversion algorithm used is based on qualitative regularization and uses known information about the environment to constrain the solution. Locations of the R reflector and other layering information are used as a priori information for the inversion to emphasize the layered structure of the sediment.
Mid-frequency sound propagation through internal waves at short range with synoptic oceanographic observations
Authors: Rouseff Daniel , Tang Dajun , Williams Kevin L. , Wang Zhongkang , Moum James N.
Published: September 2008

Preliminary results are presented from an analysis of mid-frequency acoustic transmission data collected at range 550m during the Shallow Water 2006 Experiment. The acoustic data were collected on a vertical array immediately before, during, and after the passage of a nonlinear internal wave on 18 August, 2006. Using oceanographic data collected at a nearby location, a plane-wave model for the nonlinear internal wave’s position as a function of time is developed. Experimental results show a new acoustic path is generated as the internal wave passes above the acoustic source.
Intensity fluctuations of midfrequency sound signals passing through moving nonlinear internal waves
Authors: Katsnelson Boris , Grigorev Valery , Lynch James F.
Published: September 2008

The fluctuations of intensity of broadband pulses in the midfrequency range (2–4.5kHz) propagating in shallow water in the presence of intense internal waves moving approximately along the acoustic track are considered. These pulses were received by two separate single hydrophones placed at different distances from the source (∼4 and ∼12km) and in different directions. It is shown that the frequency spectra of the fluctuations for these hydrophones have different predominating frequencies corresponding with the directions of the acoustic track. Comparisons of experimental results with theoretical estimates demonstrate good consistency.
Shallow-water seismoacoustic noise generated by tropical storms Ernesto and Florence
Authors: Traer James , Gerstoft Peter , Bromirski Peter D. , Hodgkiss William S. , Brooks Laura A.
Published: September 2008

Land-based seismic observations of double frequency (DF) microseisms generated during tropical storms Ernesto and Florence are dominated by signals in the 0.15–0.5Hz band. In contrast, data from sea floor hydrophones in shallow water (70m depth, 130km off the New Jersey coast) show dominant signals in the ocean gravity-wave frequency band, 0.02–0.18Hz, and low amplitudes from 0.18to0.3Hz, suggesting significant opposing wave components necessary for DF microseism generation were negligible at the site. Florence produced large waves over deep water while Ernesto only generated waves in coastal regions, yet both storms produced similar spectra. This suggests near-coastal shallow water as the dominant region for observed microseism generation.
White Fat Progenitor Cells Reside in the Adipose Vasculature
Authors: Tang Wei , Zeve Daniel , Suh Jae Myoung , Bosnakovski Darko , Kyba Michael , Hammer Robert E. , Tallquist Michelle D. , Graff Jonathan M.
Published: September 2008

White adipose (fat) tissues regulate metabolism, reproduction, and life span. Adipocytes form throughout life, with the most marked expansion of the lineage occurring during the postnatal period. Adipocytes develop in coordination with the vasculature, but the identity and location of white adipocyte progenitor cells in vivo are unknown. We used genetically marked mice to isolate proliferating and renewing adipogenic progenitors. We found that most adipocytes descend from a pool of these proliferating progenitors that are already committed, either prenatally or early in postnatal life. These progenitors reside in the mural cell compartment of the adipose vasculature, but not in the vasculature of other tissues. Thus, the adipose vasculature appears to function as a progenitor niche and may provide signals for adipocyte development.
Catalytic Conversion of Biomass to Monofunctional Hydrocarbons and Targeted Liquid-Fuel Classes
Authors: Kunkes Edward L. , Simonetti Dante A. , West Ryan M. , Serrano-Ruiz Juan Carlos , Gärtner Christian A. , Dumesic James A.
Published: September 2008

It is imperative to develop more efficient processes for conversion of biomass to liquid fuels, such that the cost of these fuels would be competitive with the cost of fuels derived from petroleum. We report a catalytic approach for the conversion of carbohydrates to specific classes of hydrocarbons for use as liquid transportation fuels, based on the integration of several flow reactors operated in a cascade mode, where the effluent from the one reactor is simply fed to the next reactor. This approach can be tuned for production of branched hydrocarbons and aromatic compounds in gasoline, or longer-chain, less highly branched hydrocarbons in diesel and jet fuels. The liquid organic effluent from the first flow reactor contains monofunctional compounds, such as alcohols, ketones, carboxylic acids, and heterocycles, that can also be used to provide reactive intermediates for fine chemicals and polymers markets.
Innate Immunity in
Caenorhabditis elegans
Is Regulated by Neurons Expressing NPR-1/GPCR
Authors: Styer Katie L. , Singh Varsha , Macosko Evan , Steele Sarah E. , Bargmann Cornelia I. , Aballay Alejandro
Published: September 2008

A large body of evidence indicates that metazoan innate immunity is regulated by the nervous system, but the mechanisms involved in the process and the biological importance of such control remain unclear. We show that a neural circuit involving
npr-1
, which encodes a G protein–coupled receptor (GPCR) related to mammalian neuropeptide Y receptors, functions to suppress innate immune responses. The immune inhibitory function requires a guanosine 3′,5′-monophosphate–gated ion channel encoded by
tax-2
and
tax-4
as well as the soluble guanylate cyclase GCY-35. Furthermore, we show that
npr-1
– and
gcy-35
–expressing sensory neurons actively suppress immune responses of nonneuronal tissues. A full-genome microarray analysis on animals with altered neural function due to mutation in
npr-1
shows an enrichment in genes that are markers of innate immune responses, including those regulated by a conserved PMK-1/p38 mitogen-activated protein kinase signaling pathway. These results present evidence that neurons directly control innate immunity in
C. elegans
, suggesting that GPCRs may participate in neural circuits that receive inputs from either pathogens or infected sites and integrate them to coordinate appropriate immune responses.
A High Phase-Space-Density Gas of Polar Molecules
Authors: Ni K.-K. , Ospelkaus S. , de Miranda M. H. G. , Pe'er A. , Neyenhuis B. , Zirbel J. J. , Kotochigova S. , Julienne P. S. , Jin D. S. , Ye J.
Published: September 2008

A quantum gas of ultracold polar molecules, with long-range and anisotropic interactions, not only would enable explorations of a large class of many-body physics phenomena but also could be used for quantum information processing. We report on the creation of an ultracold dense gas of potassium-rubidium (
40
K
87
Rb) polar molecules. Using a single step of STIRAP (stimulated Raman adiabatic passage) with two-frequency laser irradiation, we coherently transfer extremely weakly bound KRb molecules to the rovibrational ground state of either the triplet or the singlet electronic ground molecular potential. The polar molecular gas has a peak density of 10
12
per cubic centimeter and an expansion-determined translational temperature of 350 nanokelvin. The polar molecules have a permanent electric dipole moment, which we measure with Stark spectroscopy to be 0.052(2) Debye (1 Debye = 3.336 × 10
–30
coulomb-meters) for the triplet rovibrational ground state and 0.566(17) Debye for the singlet rovibrational ground state.
Changes in mechanical loading lead to tendonspecific alterations in MMP and TIMP expression: influence of stress deprivation and intermittent cyclic hydrostatic compression on rat supraspinatus and Achilles tendons
Authors: Thornton G M , Shao X , Chung M , Sciore P , Boorman R S , Hart D A , Lo I K Y
Published: September 2008

Background

Tendinopathy commonly occurs in tendons with large in vivo loading demands like the Achilles tendon (AT) and supraspinatus tendon (SST). In addition to differences in their local anatomic environment, these tendons are designed for different loading requirements because of the muscles to which they attach, with the AT experiencing higher loads than the SST. One possible factor in the progression of tendinopathy is the interplay between mechanical loading and the regulation of enzymes that degrade the extracellular matrix (matrix metalloproteinases (MMPs)) and their inhibitors (tissue inhibitor of metalloprotienases (TIMPs)). Thus, overuse injuries may have different biological consequences in tendons designed for different in vivo loading demands.

Aim

In this study, the tendon-specific regulation of MMP-13, MMP-3 and TIMP-2 expression in rat AT and SST exposed to two different mechanical environments was investigated.

Methods

Rat AT and SST were exposed to stress deprivation (ie, detached from attachments) and intermittent cyclic hydrostatic compression (with attachments intact). Levels of MMP-13, MMP-3 and TIMP-2 mRNA were evaluated in time-zero control, attached, stressdeprived and “compressed” tendons.

Results

Stress deprivation led to elevated expression of MMP-13, MMP-3 and TIMP-2 in both tendons, although the magnitude of the increase was greater for the SST than the AT. Intermittent cyclic hydrostatic compression of attached tendons increased expression of MMP-13 in the SST, but not the AT.

Conclusions

The results of this study suggest that stress deprivation may be one contributor to the progression of tendinopathy in AT and SST, where the tendon designed for the lower in vivo loading demand (SST) was the most affected by a change in mechanical loading. The unique upregulation of MMP-13 with hydrostatic compression supports the impingement injury theory for rotator cuff tears.
World-class performance in lightweight rowing: is it genetically influenced? A comparison with cyclists, runners and non-athletes: Table 1
Authors: Muniesa Carlos A , González-Freire Marta , Santiago Catalina , Lao José I , Buxens Amaya , Rubio Juan C , Martín Miguel A , Arenas Joaquín , Gomez-Gallego Felix , Lucia Alejandro
Published: September 2008

In this study, genotype frequencies of several polymorphisms that are candidates to influence sports performance (ie,ACTN3R577X,ACEID,PPARGC1AGly482Ser,AMPD1C34T,CKMM985bp/1170bp and GDF8 (myostatin) K153R) were compared in 123 nonathletic controls, 50 professional cyclists, 52 Olympicclass runners and 39 world-class rowers (medallists in world championships, lightweight category). Significant differences in genotype distributions among the groups were not found except for theACEgene, that is, lower (p<0.05) proportion of II in rowers (10.3%) than in the total subject population (22.3%). In summary, sports performance is likely polygenic with thecombinedeffect of hundreds of genetic variants, one possibly being theACEID polymorphism (at least in the sports studied here), but many others remain to be identified.
Acute changes in arginine vasopressin, sweat, urine and serum sodium concentrations in exercising humans: does a coordinated homeostatic relationship exist?
Authors: Hew-Butler T , Noakes T D , Soldin S J , Verbalis J G
Published: September 2008

The parallel response of sweat rate and urine production to changes in plasma osmolality and volume support a role for arginine vasopressin (AVP) as the main endocrine regulator of both excretions. A maximal test to exhaustion and a steady-state run on a motorised treadmill were both completed by 10 moderately trained runners, 1 week apart. Sweat, urine and serum sodium concentrations ([Na+]) were evaluated in association with the plasma concentrations of cytokines, neurohypophyseal and natriuretic peptides, and adrenal steroid hormones. When data from both the high-intensity and steady-state runs were combined, significant linear correlations were noted between: sweat [Na+] versus postexercise urine [Na+] (r=0.80; p<0.001), postexercise serum [Na+] versus both postexercise urine [Na+] (r=0.56; p<0.05) and sweat [Na+] (r=0.64; p<0.01) and postexercise urine [Na+] versus postexercise plasma arginine vasopressin concentration ([AVP]P) (r=0.48; p<0.05). A significant positive correlation was noted between postexercise [AVP]Pand sweat [Na+] during the steady-state condition only (r=0.66; p<0.05). These correlations suggest that changes in serum [Na+] during exercise may evoke corresponding changes in sweat and urine [Na+], which are likely regulated coordinately by changes in [AVP]Pto preserve body fluid homeostasis.