bluuebunny/crossref_metadata_2025 huggingface dataset:
A large‐angle coherent/Compton scattering method for measurement in vitro of trabecular bone mineral concentration
Authors: Gigante G. E. , Sciuti S.
Published: August 2003

In this paper, experiments and related theoretical deductions on coherent/Compton scattering of 59.5‐keV Am241 gamma line by bonelike materials are described. In particular, we demonstrate that a photon scattering mineralometer (PSM) can attain the best working conditions when it operates in a backscattering geometry mode. In fact, the large scattering angle we chose, ϑ=135°, allowed us to assemble a very compact source–detector device. Further, the relative sensitivity at 135° turns out to be ≃1.7 and ≃6 times bigger than at 90° and 45°, respectively. The performances of the ϑ=135° PSM we assembled were experimentally investigated; i.e., in a measuring time of 103 s, a ≃5‰ statistical precision for bonelike materials, such as K2HPO4–water solutions, was obtained. The large‐angle PSM device seems therefore to be very promising for trabecular bone mineral density measurements in vivo in peripheral anatomic sites.
Surface acoustic wave diffraction in spectral theory of interdigital transducers
Authors: Danicki Eugene J.
Published: August 2003

A theory of interdigital transducer is presented that accounts for the surface acoustic wave diffraction. It is formulated with help of the Blotekjær, Ingebrigtsen, and Skeie expansion method used earlier in the plane-wave theory. Now, the electric field is applied to the breaks in the strips making parts of them polarized with different potentials. This way the finite aperture width transducers are modeled residing within an infinite system of periodic strips. Closed expressions are derived for system working below the Bragg condition. The theory is open for further development accounting for elastic strips, pseudo surface, leaky or even surface skimming bulk waves, for any frequency range, including Bragg reflection exploited in surface wave resonators.
The relationship between acoustic structure and semantic information in Diana monkey alarm vocalization
Authors: Riede Tobias , Zuberbühler Klaus
Published: August 2003

Mammalian vocal production mechanisms are still poorly understood despite their significance for theories of human speech evolution. Particularly, it is still unclear to what degree mammals are capable of actively controlling vocal-tract filtering, a defining feature of human speech production. To address this issue, a detailed acoustic analysis on the alarm vocalization of free-ranging Diana monkeys was conducted. These vocalizations are especially interesting because they convey semantic information about two of the monkeys’ natural predators, the leopard and the crowned eagle. Here, vocal tract and sound source parameter in Diana monkey alarm vocalizations are described. It is found that a vocalization-initial formant downward transition distinguishes most reliably between eagle and leopard alarm vocalization. This finding is discussed as an indication of articulation and alternatively as the result of a strong nasalization effect. It is suggested that the formant modulation is the result of active vocal filtering used by the monkeys to encode semantic information, an ability previously thought to be restricted to human speech.
The reflection of the fundamental torsional mode from cracks and notches in pipes
Authors: Demma A. , Cawley P. , Lowe M. , Roosenbrand A. G.
Published: August 2003

A quantitative study of the reflection of the T(0,1) mode from defects in pipes in the frequency range 10–300 kHz has been carried out, finite element predictions being validated by experiments on selected cases. Both cracklike defects with zero axial extent and notches with varying axial extents have been considered. The results show that the reflection coefficient from axisymmetric cracks increases monotonically with depth at all frequencies and increases with frequency at any given depth. In the frequency range of interest there is no mode conversion at axisymmetric defects. With nonaxisymmetric cracks, the reflection coefficient is a roughly linear function of the circumferential extent of the defect at relatively high frequencies, the reflection coefficient at low circumferential extents falling below the linear prediction at lower frequencies. With nonaxisymmetric defects, mode conversion to the F(1,2) mode is generally seen, and at lower frequencies the F(1,3) mode is also produced. The depth and circumferential extent are the parameters controlling the reflection from cracks; when notches having finite axial extent, rather than cracks, are considered, interference between the reflections from the start and the end of the notch causes a periodic variation of the reflection coefficient as a function of the axial extent of the notch. The results have been explained in terms of the wave-number-defect size product, ka. Low frequency scattering behavior is seen when ka<0.1, high frequency scattering characteristics being seen when ka>1.
Measuring the neck frequency response function of laryngectomy patients: Implications for the design of electrolarynx devices
Authors: Meltzner Geoffrey S. , Kobler James B. , Hillman Robert E.
Published: August 2003

Measurements of the neck frequency response function (NFRF), defined as the ratio of the spectrum of the estimated volume velocity that excites the vocal tract to the spectrum of the acceleration delivered to the neck wall, were made at three different positions on the necks of nine laryngectomized subjects (five males and four females) and four normal laryngeal speakers (two males and two females). A minishaker driven by broadband noise provided excitation to the necks of subjects as they configured their vocal tracts to mimic the production of the vowels /a/, /æ/, and /I/. The sound pressure at the lips was measured with a microphone and an impedance head mounted on the shaker measured the acceleration. The neck wall passed low-frequency sound energy better than high-frequency sound energy, and thus the NFRF was accurately modeled as a low-pass filter. The NFRFs of the different subject groups (female laryngeal, male laryngeal speakers, laryngectomized males, and laryngectomized females) differed from each other in terms of corner frequency and gain, with both types of male subjects presenting NFRFs with larger overall gains. In addition, there was a notable amount of intersubject variability within groups. Because the NFRF is an estimate of how sound energy passes through the neck wall, these results should aid in the design of improved neck-type electrolarynx devices.
The monopulsed nature of sperm whale clicks
Authors: Møhl Bertel , Wahlberg Magnus , Madsen Peter T. , Heerfordt Anders , Lund Anders
Published: August 2003

Traditionally, sperm whale clicks have been described as multipulsed, long duration, nondirectional signals of moderate intensity and with a spectrum peaking below 10 kHz. Such properties are counterindicative of a sonar function, and quite different from the properties of dolphin sonar clicks. Here, data are presented suggesting that the traditional view of sperm whale clicks is incomplete and derived from off-axis recordings of a highly directional source. A limited number of assumed on-axis clicks were recorded and found to be essentially monopulsed clicks, with durations of 100 μs, with a composite directionality index of 27 dB, with source levels up to 236 dB re: 1 μPa (rms), and with centroid frequencies of 15 kHz. Such clicks meet the requirements for long-range biosonar purposes. Data were obtained with a large-aperture, GPS-synchronized array in July 2000 in the Bleik Canyon off Vesterålen, Norway (69°28′ N, 15°40′ E). A total of 14 h of sound recordings was collected from five to ten independent, simultaneously operating recording units. The sound levels measured make sperm whale clicks by far the loudest of sounds recorded from any biological source. On-axis click properties support previous work proposing the nose of sperm whales to operate as a generator of sound.
The simulation of piano string vibration: From physical models to finite difference schemes and digital waveguides
Authors: Bensa Julien , Bilbao Stefan , Kronland-Martinet Richard , Smith Julius O.
Published: August 2003

A model of transverse piano string vibration, second order in time, which models frequency-dependent loss and dispersion effects is presented here. This model has many desirable properties, in particular that it can be written as a well-posed initial-boundary value problem (permitting stable finite difference schemes) and that it may be directly related to a digital waveguide model, a digital filter-based algorithm which can be used for musical sound synthesis. Techniques for the extraction of model parameters from experimental data over the full range of the grand piano are discussed, as is the link between the model parameters and the filter responses in a digital waveguide. Simulations are performed. Finally, the waveguide model is extended to the case of several coupled strings.
Ipsilateral distortion product otoacoustic emission (2 f1–f2) suppression in children with sensorineural hearing loss
Authors: Abdala Carolina , Fitzgerald Tracy S.
Published: August 2003

Distortion product otoacoustic emission (DPOAE) ipsilateral suppression has been applied to study cochlear function and maturation in laboratory animals and humans. Although DPOAE suppression appears to be sensitive to regions of specialized cochlear function and to cochlear immaturity, it is not known whether it reflects permanent cochlear damage, i.e., sensorineural hearing loss (SNHL), in a reliable and systematic manner in humans. Eight school-aged children with mild-moderate SNHL and 20 normal-hearing children served as subjects in this study. DPOAE (2 f1–f2) suppression data were collected at four f2 frequencies (1500, 3000, 4000, and 6000 Hz) using moderate-level primary tones. Features of the DPOAE iso-suppression tuning curves and suppression growth were analyzed for both subject groups. Results show that DPOAE suppression tuning curves from hearing-impaired subjects can be reliably recorded. DPOAE suppression tuning curves were generally normal in appearance and shape for six out of eight hearing-impaired subjects but showed subtle abnormalities in at least one feature. There was not one single trend or pattern of abnormality that characterized all hearing-impaired subjects. The most prominent patterns of abnormality included: broadened tuning, elevated tip, and downward shift of tip frequency. The unique patterns of atypical DPOAE suppression in subjects with similar audiograms may suggest different patterns of underlying sensory cell damage. This speculation warrants further investigation.
Influence of planar cracks in plates on reflected and transmitted fields of Gaussian acoustic beams
Authors: Vandeputte J. , Leroy O. , Shkerdin G.
Published: August 2003

The scattering of a Gaussian beam by a rectangular crack is studied by means of the radiation mode model. The orthogonal set of modes for a L/S/V structure is derived, and a general mode decomposition formula is developed. The influence of a crack on the reflected and transmitted fields of a bounded beam, incident at critical angles of the L/S/L- and the L/S/V structure, is studied and physical interpretations are given. From those interpretations, the starting point of the crack is deduced along with the length and distance to the surface. Effects on focused beams are considered as well.
Quantification of a multibeam sonar for fisheries assessment applications
Authors: Cochrane N. A. , Li Y. , Melvin G. D.
Published: August 2003

The acoustic theory is developed for a multibeam fisheries-type sonar employing a circular arc of transducer elements. Specifically, numerical relations for transmit and receive beam patterns are derived and methodologies set forth for the derivation of appropriately scaled acoustic target strength and acoustic volume backscattering strength from an ideally performing multibeam device. Predicted and measured beam characteristics of a realizable multibeam sonar, a Kongsberg Simrad-Mesotech SM 2000, are compared. Practical techniques for the extraction of calibrated acoustic volume backscattering strength from real systems are advanced.
Discriminating harmonicity
Authors: Kidd Gerald , Mason Christine R. , Brughera Andrew , Chiu Chung-Yiu Peter
Published: August 2003

Simultaneous tones that are harmonically related tend to be grouped perceptually to form a unitary auditory image. A partial that is mistuned stands out from the other tones, and harmonic complexes with different fundamental frequencies can readily be perceived as separate auditory objects. These phenomena are evidence for the strong role of harmonicity in perceptual grouping and segregation of sounds. This study measured the discriminability of harmonicity directly. In a two interval, two alternative forced-choice (2I2AFC) paradigm, the listener chose which of two sounds, signal or foil, was composed of tones that more closely matched an exact harmonic relationship. In one experiment, the signal was varied from perfectly harmonic to highly inharmonic by adding frequency perturbation to each component. The foil always had 100% perturbation. Group mean performance decreased from greater than 90% correct for 0% signal perturbation to near chance for 80% signal perturbation. In the second experiment, adding a masker presented simultaneously with the signals and foils disrupted harmonicity. Both monaural and dichotic conditions were tested. Signal level was varied relative to masker level to obtain psychometric functions from which slopes and midpoints were estimated. Dichotic presentation of these audible stimuli improved performance by 3–10 dB, due primarily to a release from “informational masking” by the perceptual segregation of the signal from the masker.
High-frequency volume and boundary acoustic backscatter fluctuations in shallow water
Authors: Gallaudet Timothy C. , de Moustier Christian P.
Published: August 2003

Volume and boundary acoustic backscatter envelope fluctuations are characterized from data collected by the Toroidal Volume Search Sonar (TVSS), a 68 kHz cylindrical array capable of 360° multibeam imaging in the vertical plane perpendicular to its axis. The data are processed to form acoustic backscatter images of the seafloor, sea surface, and horizontal and vertical planes in the volume, which are used to attribute nonhomogeneous spatial distributions of zooplankton, fish, bubbles and bubble clouds, and multiple boundary interactions to the observed backscatter amplitude statistics. Three component Rayleigh mixture probability distribution functions (PDFs) provided the best fit to the empirical distribution functions of seafloor acoustic backscatter. Sea surface and near-surface volume acoustic backscatter PDFs are better described by Rayleigh mixture or log-normal distributions, with the high density portion of the distributions arising from boundary reverberation, and the tails arising from nonhomogeneously distributed scatterers such as bubbles, fish, and zooplankton. PDF fits to the volume and near-surface acoustic backscatter data are poor compared to PDF fits to the boundary backscatter, suggesting that these data may be better described by mixture distributions with component densities from different parametric families. For active sonar target detection, the results demonstrate that threshold detectors which assume Rayleigh distributed envelope fluctuations will experience significantly higher false alarm rates in shallow water environments which are influenced by near-surface microbubbles, aggregations of zooplankton and fish, and boundary reverberation.
Auditory spatial resolution in horizontal, vertical, and diagonal planes
Authors: Grantham D. Wesley , Hornsby Benjamin W. Y. , Erpenbeck Eric A.
Published: August 2003

Minimum audible angle (MAA) and minimum audible movement angle (MAMA) thresholds were measured for stimuli in horizontal, vertical, and diagonal (60°) planes. A pseudovirtual technique was employed in which signals were recorded through KEMAR’s ears and played back to subjects through insert earphones. Thresholds were obtained for wideband, high-pass, and low-pass noises. Only 6 of 20 subjects obtained wideband vertical-plane MAAs less than 10°, and only these 6 subjects were retained for the complete study. For all three filter conditions thresholds were lowest in the horizontal plane, slightly (but significantly) higher in the diagonal plane, and highest for the vertical plane. These results were similar in magnitude and pattern to those reported by Perrott and Saberi [J. Acoust. Soc. Am. 87, 1728–1731 (1990)] and Saberi and Perrott [J. Acoust. Soc. Am. 88, 2639–2644 (1990)], except that these investigators generally found that thresholds for diagonal planes were as good as those for the horizontal plane. The present results are consistent with the hypothesis that diagonal-plane performance is based on independent contributions from a horizontal-plane system (sensitive to interaural differences) and a vertical-plane system (sensitive to pinna-based spectral changes). Measurements of the stimuli recorded through KEMAR indicated that sources presented from diagonal planes can produce larger interaural level differences (ILDs) in certain frequency regions than would be expected based on the horizontal projection of the trajectory. Such frequency-specific ILD cues may underlie the very good performance reported in previous studies for diagonal spatial resolution. Subjects in the present study could apparently not take advantage of these cues in the diagonal-plane condition, possibly because they did not externalize the images to their appropriate positions in space or possibly because of the absence of a patterned visual field.
A Born scatterer in an acoustical waveguide
Authors: Ghosh Roy D. N. , Orris Gregory J.
Published: August 2003

Scattering from a Born inhomogeneity in a homogeneous, acoustical waveguide is considered and results compared to the corresponding scattering in a homogeneous, unbounded medium. It is found that the Ewald sphere in the unbounded medium case is replaced by a Ewald “strip” in a waveguide, the strip consisting of many individual Ewald spheres embedded in a ball the radius of which is twice that of an individual sphere. The physics behind the Ewald strip is discussed along with the implications of waveguide Born data.
On the accuracy of perturbative solutions to wave scattering from rough closed surfaces
Authors: Skaropoulos Nikolaos C. , Chrissoulidis Dimitrios P.
Published: August 2003

The method of small perturbations is applied to the problem of plane-wave scattering from a soft circular surface with sinusoidal roughness. Rayleigh-theory and extinction-theorem perturbative solutions of arbitrary order are developed, and they are compared to each other as well as to an exact solution. A numerical study yields quantitative information about effects associated with the use of the Rayleigh hypothesis, about the merit of higher-order solutions, and about the reliability of the error criteria that measure a posteriori the conformity of perturbative solutions to the boundary condition. It is shown that the accuracy of perturbative solutions depends not only on the height, but also on the slope, of surface corrugations. Moreover, it is shown that the Rayleigh hypothesis does not affect the accuracy of far-field perturbative calculations. The mean extinction error is proposed as a measure for the error of the extinction-theorem perturbative solution.
Elastic wave propagation and scattering in solids with uniaxially aligned cracks
Authors: Yang Liyong , Turner Joseph A.
Published: August 2003

In this article, elastic wave propagation and scattering in a solid medium permeated by uniaxially aligned penny-shaped microcracks are studied. The crack alignment refers to the case in which the unit normals of all cracks are randomly oriented within a plane of isotropy. The analysis is restricted to the limit of the noninteraction approximation among individual cracks. Explicit expressions for attenuations and wave speeds of the shear horizontal, quasilongitudinal, and quasishear vertical waves are obtained using stochastic wave theory in a generalized dyadic approach. The ensemble average elastic wave response is governed by the Dyson equation, which is solved in terms of the anisotropic elastic Green’s dyadic. The analysis of expressions is limited to frequencies below the geometric optics limit. The resulting attenuations are investigated in terms of the directional, frequency, and damage dependence. In particular, the attenuations are simplified considerably within the low frequency Rayleigh regime. Finally, numerical results are presented and discussed in terms of the relevant dependent parameters.
On the detection of dispersion in the head-related transfer function
Authors: Constan Zachary A. , Hartmann William M.
Published: August 2003

Because of dispersion in head-related transfer functions (HRTFs), the interaural time difference (ITD) varies with frequency. This physical effect ought to have consequences for the size or shape of the auditory image of broadband noise because different frequency regions of the noise have different ITDs. However, virtual reality experiments suggest that human listeners are insensitive to head-related dispersion. The experiments of this article test that suggestion by experiments that isolate dispersion from amplitude effects in the HRTF and attempt to optimize the opportunity for detecting it. Nevertheless, the experiments find that the only effect of dispersion is to shift the lateralization of the auditory image. This negative result is explained in terms of the cross-correlation function for head-dispersed noise. Although the broad-band cross-correlation function differs considerably from 1.0, the cross-correlation functions within bands characteristic of auditory filters do not. A detailed study of the lateralization shifts show that the experimental shifts can be successfully calculated as an average of stimulus ITDs as weighted by Raatgever’s frequency-weighting function (Thesis, Delft, The Netherlands, 1980).
Audio-vocal responses to repetitive pitch-shift stimulation during a sustained vocalization: Improvements in methodology for the pitch-shifting technique
Authors: Bauer Jay J. , Larson Charles R.
Published: August 2003

The pitch-shift reflex is a sophisticated system that produces a “compensatory” response in voice F0 that is opposite in direction to a change in voice pitch feedback (pitch-shift stimulus), thus correcting for the discrepancy between the intended voice F0 and the feedback pitch. In order to more fully exploit the pitch-shift reflex as a tool for studying the influence of sensory feedback mechanisms underlying voice control, the optimal characteristics of the pitch-shift stimulus must be understood. The present study was undertaken to assess the effects of altering the duration of the interstimulus interval (ISI) and the number of trials comprising an average on measures of the pitch-shift reflex. Pitch-shift stimuli were presented to vocalizing subjects with ISI of 5.0, 2.5, 1.0, and 0.5 s to determine if an increase in ISI altered response properties. With each ISI, measures of event-related averages of the first 10, 15, 20, or 30 pitch-shift reflex responses were compared to see if increases in the number of responses comprising an event-related average altered response properties. Measures of response latency, peak time, magnitude, and prevalence were obtained for all ISI and average conditions. While quantitative measures were similar across ISI and averaging conditions, we observed more instances of “non-responses” with averages of ten trials as well as at an ISI of 0.5 s. These findings suggest an ISI of 1.0 s and an average consisting of at least 15 trials produce optimal results. Future studies using these stimulus parameters may produce more reliable data due to the fivefold decrease in subject participation time and a concomitant decrease in fatigue, boredom, and inattention.
Effect of contralateral precursor type on the temporal effect in simultaneous masking with tone and noise maskers (L)
Authors: Savel Sophie , Bacon Sid P.
Published: August 2003

A sound (contralateral precursor) presented to the nontest ear prior to the onset of a masker and probe has been shown to reduce the temporal effect in simultaneous masking with noise maskers but not with tonal maskers. The present study examined this further. The probe was a 4.0-kHz tone. In experiment 1a, the masker was a 4.4-kHz tone and the precursor was a 4.4-kHz tone or an unmodulated (UM) or amplitude-modulated (AM) band of noise (4.4–8.0 kHz). In experiment 1b, the masker was a broadband noise and the precursor was a UM or an AM broadband noise. In both experiments the precursor consistently reduced the temporal effect for only one of the seven or eight subjects, regardless of precursor type. These largely negative results indicate that it may not be possible to use contralateral precursors to gain much insight into the mechanisms underlying temporal effects in simultaneous masking.
On the optimization of the effective electromechanical coupling coefficients of a piezoelectric body
Authors: Aronov Boris
Published: August 2003

Effective electromechanical coupling coefficients are defined based on the expression for the internal energy of a piezoelectric body [B. S. Aronov, “Energy analysis of a piezoelectric body under nonuniform deformation,” J. Acoust. Soc. Am. 113, 2638–2646 (2003)]. The condition is considered under which the effective coupling coefficient can be maximized up to the value of the material coupling coefficient for any given distribution of deformation. A simple practical way to optimize the effective coupling coefficient of a transducer by changing its electrode shape is illustrated with examples of transducers vibrating in longitudinal and flexural modes.
Input–output functions for stimulus-frequency otoacoustic emissions in normal-hearing adult ears
Authors: Schairer Kim S. , Fitzpatrick Denis , Keefe Douglas H.
Published: August 2003

Input-output (I/O) functions for stimulus-frequency (SFOAE) and distortion-product (DPOAE) otoacoustic emissions were recorded in 30 normal-hearing adult ears using a nonlinear residual method. SFOAEs were recorded at half octaves from 500–8000 Hz in an L1=L2 paradigm with L2=0 to 85 dB SPL, and in a paradigm with L1 fixed and L2 varied. DPOAEs were elicited with primary levels of Kummer et al. [J. Acoust. Soc. Am. 103, 3431–3444 (1998)] at f2 frequencies of 2000 and 4000 Hz. Interpretable SFOAE responses were obtained from 1000–6000 Hz in the equal-level paradigm. SFOAE levels were larger than DPOAEs levels, signal-to-noise ratios were smaller, and I/O functions were less compressive. A two-slope model of SFOAE I/O functions predicted the low-level round-trip attenuation, the breakpoint between linearity and compression, and compressive slope. In ear but not coupler recordings, the noise at the SFOAE frequency increased with increasing level (above 60 dB SPL), whereas noise at adjacent frequencies did not. This suggests the existence of a source of signal-dependent noise producing cochlear variability, which is predicted to influence basilar-membrane motion and neural responses. A repeatable pattern of notched SFOAE I/O functions was present in some ears, and explained using a two-source mechanism of SFOAE generation.
The radiation Q factors obtained from the partial derivatives of the phase of the reflection coefficient of an elastic plate
Authors: Lenoir O. , Conoir J. M. , Izbicki J. L.
Published: August 2003

The phase gradient method is applied to study the partial derivatives of the phase of the reflection coefficient of a fluid-loaded elastic plate. We consider the derivatives with respect to the frequency f, the incidence angle θ, the phase velocities of the longitudinal and transverse waves propagating in the plate, cL and cT, respectively, and the phase velocity in the fluid cF. The partial derivatives with respect to f, cL, cT, cF are linked by a relation involving products of one of these variables with the corresponding partial derivative. At a resonance frequency, the product of frequency with the frequency phase derivative can be identified as a radiation quality factor. By analogy, the other products correspond to quality factors. It can be shown that the product assigned to the fluid phase velocity corresponds to an angular radiation quality factor. The products assigned to the longitudinal and transverse phase velocities are identified as longitudinal and transverse radiation quality factors. These quality factors are shown to be related to stored energies associated with either standing waves across the plate, guided waves, longitudinal waves or transverse waves. A reactive power balance between the plate and the fluid is also established.
Suprathreshold effects of adaptation produced by amplitude modulation
Authors: Wojtczak Magdalena , Viemeister Neal F.
Published: August 2003

This work extends the study of adaptation to amplitude modulation (AM) to the perception of highly detectable modulation. A fixed-level matching procedure was used to find perceptually equivalent modulation depths for 16-Hz modulation imposed on a 1-kHz standard and a 4-kHz comparison. The modulation depths in the two stimuli were compared before and after a 10-min exposure to a 1-kHz tone (adaptor) 100% modulated in amplitude at different rates. For modulation depths of 63% (20 log m=−4) and smaller, the perceived modulation depth was reduced after exposure to the adaptor that was modulated at the same rate as the standard. The size of this reduction expressed as a difference between the post- and pre-exposure AM depths was similar to the increase in AM-detection threshold observed after adaptation. Postexposure suprathreshold modulation depth was not appreciably reduced when the modulation depth of the standard was large (approached 100%). A much smaller or no reduction in the perceived modulation depth was also observed when the modulation rates of the adaptor and the standard tone were different. The tuning of the observed effect of the adaptor appears to be much sharper than the tuning shown by modulation-masking results.
Guided wave helical ultrasonic tomography of pipes
Authors: Leonard Kevin R. , Hinders Mark K.
Published: August 2003

Ultrasonic guided waves have been used for a wide variety of ultrasonic inspection techniques. We describe here a new variation called helical ultrasound tomography (HUT) that uses guided ultrasonic waves along with tomographic reconstruction algorithms that have been developed by seismologists for what they call “cross borehole” tomography. In HUT, the Lamb-like guided waves travel the various helical criss-cross paths between two parallel circumferential transducer arrays instead of the planar criss-cross seismic paths between two boreholes. Although the measurement itself is fairly complicated, the output of the tomographic reconstruction is a readily interpretable map of a quantity of interest such as pipe wall thickness. In this paper we demonstrate HUT via laboratory scans on steel pipe segments into which controlled thinnings have been introduced.
Robustness of multichannel equalization in an acoustic reverberant environment
Authors: Talantzis Fotios , Ward Darren B.
Published: August 2003

A theoretical framework is established, for the robustness of multichannel sound equalization in reverberant environments. Using results from statistical room acoustics, a closed-form expression is derived that predicts the degradation in performance of an equalization system as the sound source moves from its nominal position inside the enclosure. The presented analysis also provides means of identifying the performance bounds that can be expected when using such a system in an actual room. Using extensive computer simulations, the effect of physical parameters such as the relative positions of the source and the receivers, as well as effects of different design parameters are investigated. Based on the conditions imposed by these parameters, it is shown that, depending on the array geometry and the exact form of the equalizers, slight performance gains can be expected as the number of receivers is increased.
Squared error as a measure of perceived phase distortion
Authors: Pobloth Harald , Kleijn W. Bastiaan
Published: August 2003

Based on two well-known auditory models, it is investigated whether the squared error between an original signal and a phase-distorted signal is a perceptually relevant measure for distortions in the Fourier phase spectrum of periodic signals obtained from speech. Both the performance of phase vector quantizers and the direct relationship between the squared error and two perceptual distortion measures are studied. The results indicate that for small values the squared error correlates well to the perceptual measures. However, for large errors, an increase in squared error does not, on average, lead to an increase in the perceptual measures. Empirical rate-perceptual distortion curves and listening tests confirm that, for low to medium codebook sizes, the average perceived distortion does not decrease with increasing codebook size when the squared error is used as encoding criterion.
Surface-Driven Switching of Liquid Crystals Using Redox-Active Groups on Electrodes
Authors: Luk Yan-Yeung , Abbott Nicholas L.
Published: August 2003

Electrochemical control of the oxidation state of ferrocene-decorated electrodes leads to surface-driven changes in the orientations of thermotropic liquid crystals. When the electrodes possess nanometer-scale topography, voltages of 0.0 to 0.3 volts (versus a counter electrode in a two-electrode cell) can drive changes in the orientation of the liquid crystals in the plane and/or out of the plane of the electrodes. Electrodes not supporting ferrocene do not lead to surface-driven orientational transitions. The in-plane transitions are driven by the reorganization of the monolayer of ferrocene upon oxidation of ferrocene to ferrocenium. The out-of-plane transition reflects a dielectric coupling between the liquid crystal and the diffuse part of an electrical double layer that evolves upon oxidation of ferrocene to ferrocenium. These results suggest new ways to couple the orientations of liquid crystals to chemical and electrical stimuli in electro-optical devices and chemical sensors.
Extended Boltzmann Kinetic Equation for Turbulent Flows
Authors: Chen Hudong , Kandasamy Satheesh , Orszag Steven , Shock Rick , Succi Sauro , Yakhot Victor
Published: August 2003

Complex fluid physics can be modeled using an extended kinetic (Boltzmann) equation in a more efficient way than using the continuum Navier-Stokes equations. Here, we explain this method for modeling fluid turbulence and show its effectiveness with the use of a computationally efficient implementation in terms of a discrete or “lattice” Boltzmann equation.
Large Trench-Parallel Gravity Variations Predict Seismogenic Behavior in Subduction Zones
Authors: Song Teh-Ru Alex , Simons Mark
Published: August 2003

We demonstrate that great earthquakes occur predominantly in regions with a strongly negative trench-parallel gravity anomaly (TPGA), whereas regions with strongly positive TPGA are relatively aseismic. These observations suggest that, over time scales up to at least 1 million years, spatial variations of seismogenic behavior within a given subduction zone are stationary and linked to the geological structure of the fore-arc. The correlations we observe are consistent with a model in which spatial variations in frictional properties on the plate interface control trench-parellel variations in fore-arc topography, gravity, and seismogenic behavior.
A Conserved Domain in Axonal Targeting of Kv1 (Shaker) Voltage-Gated Potassium Channels
Authors: Gu Chen , Jan Yuh Nung , Jan Lily Yeh
Published: August 2003

Axonal voltage-gated potassium (Kv1) channels regulate action-potential invasion and hence transmitter release. Although evolutionarily conserved, what mediates their axonal targeting is not known. We found that Kv1 axonal targeting required its T1 tetramerization domain. When fused to unpolarized CD4 or dendritic transferrin receptor, T1 promoted their axonal surface expression. Moreover, T1 mutations eliminating Kvβ association compromised axonal targeting, but not surface expression, of CD4-T1 fusion proteins. Thus, proper association of Kvβ with the Kv1 T1 domain is essential for axonal targeting.
Structure and Mechanism of the Glycerol-3-Phosphate Transporter from
Escherichia coli
Authors: Huang Yafei , Lemieux M. Joanne , Song Jinmei , Auer Manfred , Wang Da-Neng
Published: August 2003

The major facilitator superfamily represents the largest group of secondary membrane transporters in the cell. Here we report the 3.3 angstrom resolution structure of a member of this superfamily, GlpT, which transports glycerol-3-phosphate into the cytoplasm and inorganic phosphate into the periplasm. The amino- and carboxyl-terminal halves of the protein exhibit a pseudo two-fold symmetry. Closed off to the periplasm, a centrally located substrate-translocation pore contains two arginines at its closed end, which comprise the substrate-binding site. Upon substrate binding, the protein adopts a more compact conformation. We propose that GlpT operates by a single–binding site, alternating-access mechanism through a rocker-switch type of movement.
Structure and Mechanism of the Lactose Permease of
Escherichia coli
Authors: Abramson Jeff , Smirnova Irina , Kasho Vladimir , Verner Gillian , Kaback H. Ronald , Iwata So
Published: August 2003

Membrane transport proteins that transduce free energy stored in electrochemical ion gradients into a concentration gradient are a major class of membrane proteins. We report the crystal structure at 3.5 angstroms of the
Escherichia coli
lactose permease, an intensively studied member of the major facilitator superfamily of transporters. The molecule is composed of N- and C-terminal domains, each with six transmembrane helices, symmetrically positioned within the permease. A large internal hydrophilic cavity open to the cytoplasmic side represents the inward-facing conformation of the transporter. The structure with a bound lactose homolog, β-D-galactopyranosyl-1-thio-β-D-galactopyranoside, reveals the sugar-binding site in the cavity, and residues that play major roles in substrate recognition and proton translocation are identified. We propose a possible mechanism for lactose/proton symport (co-transport) consistent with both the structure and a large body of experimental data.
Polar Localization of CheA
2
in
Rhodobacter sphaeroides
Requires Specific Che Homologs
Authors: Martin Angela C. , Nair Usha , Armitage Judith P. , Maddock Janine R.
Published: August 2003

Rhodobacter sphaeroides
is a motile bacterium that has multiple chemotaxis genes organized predominantly in three major operons (
che
Op
1
,
che
Op
2
, and
che
Op
3
). The chemoreceptor proteins are clustered at two distinct locations, the cell poles and in one or more cytoplasmic clusters. One intriguing possibility is that the physically distinct chemoreceptor clusters are each composed of a defined subset of specific chemotaxis proteins, including the chemoreceptors themselves plus specific CheW and CheA proteins. Here we report the subcellular localization of one such protein, CheA
2
, under aerobic and photoheterotrophic growth conditions. CheA
2
is predominantly clustered and localized at the cell poles under both growth conditions. Furthermore, its localization is dependent upon one or more genes in
che
Op
2
but not those of
che
Op
1
or
che
Op
3
. In
E. coli
, the polar localization of CheA depends upon CheW. The
R. sphaeroides che
Op
2
contains two
cheW
genes. Interestingly, CheW
2
is required under both aerobic and photoheterotrophic conditions, whereas CheW
3
is not required under aerobic conditions but appears to play a modest role under photoheterotrophic conditions. This suggests that
R. sphaeroides
contains at least two distinct chemotaxis complexes, possibly composed of proteins dedicated for each subcellular location. Furthermore, the composition of these spatially distinct complexes may change under different growth conditions.
Performance of Standard Phenotypic Assays for TonB Activity, as Evaluated by Varying the Level of Functional, Wild-Type TonB
Authors: Larsen Ray A. , Chen Gregory J. , Postle Kathleen
Published: August 2003

The ability of gram-negative bacterial cells to transport cobalamin and iron-siderophore complexes and their susceptibility to killing by some bacteriophages and colicins are characteristics routinely used to assay mutations of proteins in the TonB-dependent energy transduction system. These assays vary greatly in sensitivity and are subject to perturbation by overexpression of TonB and, perhaps, other proteins that contribute to the process. Thus, the choice of assay and the means by which a potential mutant is expressed can greatly influence the interpretation and recognition of a given mutant. In the present study, we expressed TonB at several different quantified levels in cells that were then subjected to a panel of assays. Our results suggest that it is reasonable to regard the assays as having windows of sensitivity. Thus, while no single assay satisfactorily spans the potential range of TonB activity, it is evident that certain assays are better suited for resolving small deviations from wild-type levels of activity, with others most useful when activity levels are very low. It is apparent from the results that the application of all possible assays to the characterization of new mutants will yield the most meaningful results.
Role of
Pseudomonas putida tol-oprL
Gene Products in Uptake of Solutes through the Cytoplasmic Membrane
Authors: Llamas María A. , Rodríguez-Herva José J. , Hancock Robert E. W. , Bitter Wilbert , Tommassen Jan , Ramos Juan L.
Published: August 2003

Proteins of the Tol-Pal (Tol-OprL) system play a key role in the maintenance of outer membrane integrity and cell morphology in gram-negative bacteria. Here we describe an additional role for this system in the transport of various carbon sources across the cytoplasmic membrane. Growth of
Pseudomonas putida tol-oprL
mutant strains in minimal medium with glycerol, fructose, or arginine was impaired, and the growth rate with succinate, proline, or sucrose as the carbon source was lower than the growth rate of the parental strain. Assays with radiolabeled substrates revealed that the rates of uptake of these compounds by mutant cells were lower than the rates of uptake by the wild-type strain. The pattern and amount of outer membrane protein in the
P. putida tol-oprL
mutants were not changed, suggesting that the transport defect was not in the outer membrane. Consistently, the uptake of radiolabeled glucose and glycerol in spheroplasts was defective in the
P. putida tol-oprL
mutant strains, suggesting that there was a defect at the cytoplasmic membrane level. Generation of a proton motive force appeared to be unaffected in these mutants. To rule out the possibility that the uptake defect was due to a lack of specific transporter proteins, the PutP symporter was overproduced, but this overproduction did not enhance proline uptake in the
tol-oprL
mutants. These results suggest that the Tol-OprL system is necessary for appropriate functioning of certain uptake systems at the level of the cytoplasmic membrane.
Rod Shape Determination by the
Bacillus subtilis
Class B Penicillin-Binding Proteins Encoded by
pbpA
and
pbpH
Authors: Wei Yuping , Havasy Teresa , McPherson Derrell C. , Popham David L.
Published: August 2003

The peptidoglycan cell wall determines the shape and structural integrity of a bacterial cell. Class B penicillin-binding proteins (PBPs) carry a transpeptidase activity that cross-links peptidoglycan strands via their peptide side chains, and some of these proteins are directly involved in cell shape determination. No
Bacillus subtilis
PBP with a clear role in rod shape maintenance has been identified. However, previous studies showed that during outgrowth of
pbpA
mutant spores, the cells grew in an ovoid shape for several hours before they recovered and took on a normal rod shape. It was postulated that another PBP, expressed later during outgrowth, was able to compensate for the lack of the
pbpA
product, PBP2a, and to guide the formation of a rod shape. The
B. subtilis pbpH
(
ykuA
) gene product is predicted to be a class B PBP with greatest sequence similarity to PBP2a. We found that a
pbpH-lacZ
fusion was expressed at very low levels in early log phase and increased in late log phase. A
pbpH
null mutant was indistinguishable from the wild-type, but a
pbpA pbpH
double mutant was nonviable. When
pbpH
was placed under the control of an inducible promoter in a
pbpA
mutant, viability was dependent on
pbpH
expression. Growth of this strain in the absence of inducer resulted in conversion of the cells from rods to ovoid/round shapes and lysis. We conclude that PBP2a and PbpH play redundant roles in formation of a rod-shaped peptidoglycan cell wall.
A Rhamnogalacturonan Lyase in the
Clostridium cellulolyticum
Cellulosome
Authors: Pagès Sandrine , Valette Odile , Abdou Laetitia , Bélaïch Anne , Bélaïch Jean-Pierre
Published: August 2003

Clostridium cellulolyticum
secretes large multienzymatic complexes with plant cell wall-degrading activities named cellulosomes. Most of the genes encoding cellulosomal components are located in a large gene cluster:
cipC
-
cel
48
F
-
cel
8
C-cel
9
G-cel
9
E
-
orfX
-
cel
9
H-cel
9
J-man
5
K-cel
9
M
. Downstream of the
cel
9
M
gene, a new open reading frame was discovered and named
rgl
11
Y
. Amino acid sequence analysis indicates that this gene encodes a multidomain pectinase, Rgl11Y, containing an N-terminal signal sequence, a catalytic domain belonging to family 11 of the polysaccharide lyases, and a C-terminal dockerin domain. The present report describes the biochemical characterization of a recombinant form of Rgl11Y. Rgl11Y cleaves the α-
l
-Rha
p
-(1→4)-α-
d
-Gal
p
A glycosidic bond in the backbone of rhamnogalacturonan I (RGI) via a β-elimination mechanism. Its specific activity on potato pectic galactan and rhamnogalacturonan was found to be 28 and 3.6 IU/mg, respectively, indicating that Rgl11Y requires galactan decoration of the RGI backbone. The optimal pH of Rgl11Y is 8.5 and calcium is required for its activity. Rgl11Y was shown to be incorporated in the
C. cellulolyticum
cellulosome through a typical cohesin-dockerin interaction. Rgl11Y from
C. cellulolyticum
is the first cellulosomal rhamnogalacturonase characterized.