bluuebunny/crossref_metadata_2025 huggingface dataset:
Differences in the regulation of CD4 and CD8 T–cell clones during immune responses
Authors: Beverley Peter C. L. , Maini Mala K.
Published: July 2002

The functional units of immune response are lymphocyte clones. Analysis of lymphocyte life spanin vivoshows that the overall turnover of CD4 and CD8 lymphocytes does not differ greatly. Recently, molecular methods have been developed which allow a global analysis of T–cell clones responding to an antigenin vivo. We have used a sensitive, modified heteroduplex analysis to follow T–cell clones responding to Epstein–Barr virus in acute infectious mononucleosis (AIM). Strikingly, all the many large clones detected in freshly isolated AIM blood were found within the CD8 fraction. CD4 clonal populations responding to the soluble recall antigen tetanus toxoid could only be detected afterin vitrore–stimulation. These data imply that CD4 responses may be more polyclonal than those of CD8 cells and that the size of CD4 clones is more tightly regulated. Several molecular mechanisms may contribute to this. Up–regulation of telomerase allows very large expansions of CD8 cells to occur without exhaustion of proliferative capacity.
The molecular biology of prion propagation
Authors: Clarke Anthony R. , Jackson Graham S. , Collinge John
Published: July 2002

Prion diseases such as Creutzfeldt–Jakob disease (CJD) in humans and scrapie and bovine spongiform encephalopathy (BSE) in animals are associated with the accumulation in affected brains of a conformational isomer (PrPSc) of host–derived prion protein (PrPC). According to the protein–only hypothesis, PrPScis the principal or sole component of transmissible prions. The conformational change known to be central to prion propagation, from a predominantly α–helical fold to one predominantly comprising β structure, can now be reproducedin vitro, and the ability of β–PrP to form fibrillar aggregates provides a plausible molecular mechanism for prion propagation. The existence of multiple prion strains has been difficult to explain in terms of a protein–only infectious agent but recent studies of human prion diseases suggest that strain–specific phenotypes can be encoded by different PrP conformations and glycosylation patterns. The experimental confirmation that a novel form of human prion disease, variant CJD, is caused by the same prion strain as cattle BSE, has highlighted the pressing need to understand the molecular basis of prion propagation and the transmission barriers that limit their passage between mammalian species. These and other advances in the fundamental biology of prion propagation are leading to strategies for the development of rational therapeutics.
NHEJ regulation by mating type is exercised through a novel protein, Lif2p, essential to the Ligase IV pathway
Authors: Frank-Vaillant Marie , Marcand Stéphane
Published: July 2002

In the yeast Saccharomyces cerevisiae, DNA double strand break (DSB) repair by nonhomologous end-joining (NHEJ) requires the DNA end-binding heterodimer Yku70p–Yku80p and the ligase Dnl4p associated with its cofactor Lif1p. NHEJ efficiency is down-regulated inMATa/MATα cells relative to MATa or MATαcells, but the mechanism of this mating type regulation is unknown. Here we report the identification of Lif2p, a S. cerevisiaeprotein that interacts with Lif1p in a two-hybrid system. Disruption ofLIF2 abolishes the capacity of cells to repair DSBs by end-joining to the same extent than lif1 and dnl4mutants. In MATa/MATα cells, Lif2p steady-state level is strongly repressed when other factors involved in NHEJ are unaffected. Increasing the dosage of the Lif2p protein can suppress the NHEJ defect in a/α cells. Together, these results indicate that NHEJ regulation by mating type is achieved, at least in part, by a regulation of Lif2p activity.
Partitioning of Tissue Expression Accompanies Multiple Duplications of the Na+/K+ ATPase α Subunit Gene
Authors: Serluca Fabrizio C. , Sidow Arend , Mably John D. , Fishman Mark C.
Published: July 2002

Vertebrate genomes contain multiple copies of related genes that arose through gene duplication. In the past it has been proposed that these duplicated genes were retained because of acquisition of novel beneficial functions. A more recent model, the duplication-degeneration-complementation hypothesis (DDC), posits that the functions of a single gene may become separately allocated among the duplicated genes, rendering both duplicates essential. Thus far, empirical evidence for this model has been limited to theengrailed and sox family of developmental regulators, and it has been unclear whether it may also apply to ubiquitously expressed genes with essential functions for cell survival. Here we describe the cloning of three zebrafish α subunits of the Na(+),K(+)-ATPase and a comprehensive evolutionary analysis of this gene family. The predicted amino acid sequences are extremely well conserved among vertebrates. The evolutionary relationships and the map positions of these genes and of other α-like sequences indicate that both tandem and ploidy duplications contributed to the expansion of this gene family in the teleost lineage. The duplications are accompanied by acquisition of clear functional specialization, consistent with the DDC model of genome evolution.

[The sequence data described in this paper have been submitted to the GenBank data library under accession nos. AY028628, AY028629, and AY028630]
A directed approach to improving the solubility of Moloney murine leukemia virus reverse transcriptase
Authors: Das Debanu , Georgiadis Millie M.
Published: July 2002

One of the difficulties that can impede structural work on a molecule of interest is limited solubility. Although functionally similar to the human immunodeficiency virus type‐1 reverse transcriptase (HIV‐1 RT), the Moloney murine leukemia virus reverse transcriptase (MMLV RT) differs both in architecture and solubility properties. Reverse transcriptase is an essential retroviral enzyme that replicates the single‐stranded RNA genome of the retrovirus producing a double‐stranded DNA copy, which is subsequently integrated into the host's genome. We have introduced a single amino acid substitution in the connection domain of an N‐terminally truncated MMLV RT (L435K) that significantly improves the solubility of the enzyme eliminating the need for nonionic detergents in buffering storage solutions. The substituted enzyme retains near wild‐type polymerase activity. An important consequence of the improved solubility of the L435K MMLV RT has been the ability to obtain diffraction quality crystals.
Binding of cations in Bacillus subtilis phosphoribosyldiphosphate synthetase and their role in catalysis
Authors: Eriksen Tine A. , Kadziola Anders , Larsen Sine
Published: July 2002

The binding sites for the two cations essential for the catalytic function of 5‐phospho‐d‐ribosyl α‐1‐diphosphate (PRPP) synthases have been identified from the structure of the Bacillus subtilis phosphoribosyldiphosphate synthetase (PRPPsase) with bound Cd2+. The structure determined from X‐ray diffraction data to 2.8‐Å resolution reveals the same hexameric arrangement of the subunits that was observed in the complexes of the enzyme with the activator sulfate and the allosteric inhibitor ADP. Two cation binding sites were localized in each of the two domains of the subunits that compose the hexamer; each domain of the subunit has an associated cation. In addition to the bound Cd2+, the Cd2+‐PRPPsase structure contains a sulfate ion in the regulatory site, a sulfate ion at the ribose‐5‐phosphate binding site, and an AMP moiety at the ATP binding site. Comparison of the Cd2+‐PRPPsase to the structures of the PRPPsase complexed with sulfate and mADP reveals the structural rearrangement induced by the binding of the free cation, which is essential for the initiation of the reaction. The comparison to the cPRPP complex of glutamine phosphoribosylpyrophosphate amidotransferase from Escherichia coli, a type I phosphoribosyltransferase, provided information about the binding of PRPP. This strongly indicates that the binding of both substrates must lead to a stabilized conformation of the loop region, which remains unresolved in the known PRPPsase complex structures.
Characterizing output for the Varian enhanced dynamic wedge field
Authors: Liu Chihray , Li Zuofeng , Palta Jatinder R.
Published: July 2002

The output factor for an enhanced dynamic wedge (EDW) field, like that for a dynamic wedge field, is a complex function of the field dimension in the wedge direction. The large change in output for different field sizes (varying more than 40% for a wedge angle) is due to rescaling of the golden segmented treatment table (GSTT), which specifies the cumulative monitor unit weighting as a function of moving jaw position. The rescaling of the GSTT results in increased output on the central axis with a decrease in the value of the final moving jaw position in the wedge plane. The output factor (in air or in water) on the central axis of an EDW field can be predicted to within 1% by multiplying the output factor (in air or in water) of an open field of the same size with the ratio of the normalized GSTT (NGSTT) value at 4.5 cm, which corresponds to a 10 cm×10 cm square field, to the NGSTT value at the final moving jaw position for the EDW field. Once the NGSTT factor is separated from the output for EDW fields, the field‐size‐dependent wedge factor varies less than 1%. This approach allows a simple and accurate determination of the output factor for rectangular and asymmetric EDW fields. The equivalent square method for determining output for rectangular fields applies to EDW fields with the same precision as it does to open fields. The output for EDW fields strongly depends on the final moving jaw position. Every 5‐mm change in the final moving jaw position causes 3.5‐5.4% error in monitor unit calculation.
Selective measurement of white matter and gray matter diffusion trace values in normal human brain
Authors: Zacharopoulos Nicholas G. , Narayana Ponnada A.
Published: July 2002

The trace of the diffusion tensor (or simply the trace) is diagnostically valuable for detecting acute ischemic lesions. A number of studies indicate that the trace of human gray matter (GM) and white matter (WM) are quite similar. This is somewhat surprising considering the different cellular environments of GM and WM. It is possible that partial volume averaging (PVA) effects between GM and WM, inherent in many of the ultrafast imaging sequences used for diffusion measurements, are responsible for this observation. In order to minimize PVA effects, the trace values of GM and WM have been selectively measured by implementing double inversion recovery (DIR) echo planar imaging (EPI) pulse sequences. Results on six normal volunteers indicate that the trace values of WM and GM are not statistically different.
Noise power spectra of images from digital mammography detectors
Authors: Williams Mark B. , Mangiafico Peter A. , Simoni Piero U.
Published: July 2002

Noise characterization through estimation of the noise power spectrum (NPS) is a central component of the evaluation of digital x‐ray systems. We begin with a brief review of the fundamentals of NPS theory and measurement, derive explicit expressions for calculation of the one‐ and two‐dimensional (1D and 2D) NPS, and discuss some of the considerations and tradeoffs when these concepts are applied to digital systems. Measurements of the NPS of two detectors for digital mammography are presented to illustrate some of the implications of the choices available. For both systems, two‐dimensional noise power spectra obtained over a range of input fluence exhibit pronounced asymmetry between the orthogonal frequency dimensions. The 2D spectra of both systems also demonstrate dominant structures both on and off the primary frequency axes indicative of periodic noise components. Although the two systems share many common noise characteristics, there are significant differences, including markedly different dark‐noise magnitudes, differences in NPS shape as a function of both spatial frequency and exposure, and differences in the natures of the residual fixed pattern noise following flat fielding corrections. For low x‐ray exposures, quantum noise‐limited operation may be possible only at low spatial frequency. Depending on the method of obtaining the 1D NPS (i.e., synthetic slit scanning or slice extraction from the 2D NPS), on‐axis periodic structures can be misleadingly smoothed or missed entirely. Our measurements indicate that for these systems, 1D spectra useful for the purpose of detective quantum efficiency calculation may be obtained from thin cuts through the central portion of the calculated 2D NPS. On the other hand, low‐frequency spectral values do not converge to an asymptotic value with increasing slit length when 1D spectra are generated using the scanned synthetic slit method. Aliasing can contribute significantly to the digital NPS, especially near the Nyquist frequency. Calculation of the theoretical presampling NPS and explicit inclusion of aliased noise power shows good agreement with measured values.
An introduction to Pound–Drever–Hall laser frequency stabilization
Authors: Black Eric D.
Published: July 2002

This paper is an introduction to an elegant and powerful technique in modern optics: Pound–Drever–Hall laser frequency stabilization. This introduction is primarily meant to be conceptual, but it includes enough quantitative detail to allow the reader to immediately design a real setup, suitable for research or industrial application. The intended audience is both the researcher learning the technique for the first time and the teacher who wants to cover modern laser locking in an upper-level physics or electrical engineering course.
Integral equations of scattering in one dimension
Authors: Barlette Vania E. , Leite Marcelo M. , Adhikari Sadhan K.
Published: July 2002

A self-contained discussion of integral equations of scattering is presented in the case of centrally symmetric potentials in one dimension, which will facilitate the understanding of more complex scattering integral equations in two and three dimensions. The present discussion illustrates in a simple fashion the concept of partial-wave decomposition, Green’s function, Lippmann–Schwinger integral equations of scattering for wave function and transition operator, optical theorem, and unitarity relation. We illustrate the present approach with a Dirac delta potential.
Quantum mechanics for everyone: Hands-on activities integrated with technology
Authors: Zollman Dean A. , Rebello N. Sanjay , Hogg Kirsten
Published: July 2002

Quantum mechanics is frequently taught toward the end of the first year of physics if it is taught at all. Many physics instructors believe that quantum mechanics is a very abstract subject that cannot be understood until students have learned much of classical physics. We are challenging this belief by creating instructional materials for quantum mechanics that can be integrated throughout the first physics course. In addition, we have transferred some of the materials and the basic approach to higher-level courses. The result is a hands-on approach to learning and teaching quantum mechanics for a broad spectrum of students. We describe some of our materials and the results of using these materials with students.
An introduction to global warming
Authors: Barker John R. , Ross Marc H.
Published: July 2002

The physics of climate and of climate changes associated with increasing concentrations of greenhouse gases in the atmosphere are briefly presented. Construction of a “toy model” of the climate is discussed. Possibilities for reducing carbon dioxide emissions are indicated. Degrees of uncertainty characterizing predictions of climate responses to anthropogenic greenhouse gas emissions are presented.
Fluid instabilities and wakes in a soap-film tunnel
Authors: Vorobieff Peter , Ecke Robert E.
Published: July 2002

We present a compact, low-budget two-dimensional hydrodynamic flow visualization system based on a tilted, gravity-driven soap film tunnel. This system is suitable for demonstrations and studies of a variety of fluid mechanics problems, including turbulent wakes past bluff bodies and lifting surfaces, Kelvin–Helmholtz instability, and grid turbulence.
Student resources for learning introductory physics
Authors: Hammer David
Published: July 2002

With good reason, physics education research has focused almost exclusively on student difficulties and misconceptions. This work has been productive for curriculum development as well as in motivating the physics teaching community to examine and reconsider methods and assumptions, but it is limited in what it can tell us about student knowledge and learning. This article reviews perspectives on student resources for learning, with an emphasis on the practical benefits to be gained for instruction.
Evaluation of feedback-reduction algorithms for hearing aids
Authors: Greenberg Julie E. , Zurek Patrick M. , Brantley Merry
Published: July 2002

Three adaptive feedback-reduction algorithms were implemented in a laboratory-based digital hearing aid system and evaluated with dynamic feedback paths and hearing-impaired subjects. The evaluation included measurements of maximum stable gain and subjective quality ratings. The continuously adapting CNN algorithm (Closed-loop processing with No probe Noise) provided the best performance: 8.5 dB of added stable gain (ASG) relative to a reference algorithm averaged over all subjects, ears, and vent conditions. Two intermittently adapting algorithms, ONO (Open-loop with Noise when Oscillation detected) and ONQ (Open-loop with Noise when Quiet detected), provided an average of 5 dB of ASG. Subjects with more severe hearing losses received greater benefits: 13 dB average ASG for the CNN algorithm and 7–8 dB average ASG for the ONO and ONQ algorithms. These values are conservative estimates of ASG because the fitting procedure produced a frequency-gain characteristic that already included precautions against feedback. Speech quality ratings showed no substantial algorithm effect on pleasantness or intelligibility, although subjects informally expressed strong objections to the probe noise used by the ONO and ONQ algorithms. This objection was not reflected in the speech quality ratings because of limitations of the experimental procedure. The results clearly indicate that the CNN algorithm is the most promising choice for adaptive feedback reduction in hearing aids.
Reduction methods of the reconstruction error for large-scale implementation of near-field acoustical holography
Authors: Saijyou K. , Yoshikawa S.
Published: July 2002

New extrapolation methods in real and wave number spaces are proposed to extend near-field acoustical holography (NAH) toward a more quantitative technique applicable to the vibration measurement of actual large-scale structures. The finiteness of the measurement aperture is a serious impediment to such large-scale implementation of NAH because the measurement aperture sufficiently larger than the vibrating structure of interest is usually needed. We should thus investigate how to reduce the reconstruction error when the measurement aperture is restricted to a fraction of the vibrating structure. The following practical suggestions are derived from simulations and underwater experiments: (1) A wave number-space extrapolation method can reduce the reconstruction error to about 25% for the measurement aperture corresponding to 1/16th of the vibrating structure when 10 000 iterations of the extrapolation process are applied. (2) A real-space extrapolation method can reduce the reconstruction error to negligible degree (10−10%) for the measurement aperture corresponding to four times as large as the vibration structure when ten iterations of the extrapolation process are applied. (3) The former method may be widely and safely applied, but many iterations are necessary; the latter method can reduce the reconstruction error very quickly, but a wider measurement aperture than that in the former is needed. Therefore, when the measurement aperture cannot be larger than the vibrating structure, the former method is recommended, while when the measurement aperture is larger than the structure, the latter method is recommended. Summing up, the accuracy of our proposed methods, which is attributed to the property of data extrapolation method that the data inside the measurement aperture is conserved after adequately extrapolating the data outside the aperture, will be relevant to a more quantitative measurement and analysis of real large-scale structures.
A profiled structure with improved low frequency absorption
Authors: Wu Tao , Cox Trevor J. , Lam Y. W.
Published: July 2002

It is possible to obtain good absorption from Schroeder diffusers if suitable alterations to the design are made. Interestingly, previous work has shown that good absorption appears possible below the design frequency when the diffusers are poorly constructed. This has inspired the design of a profiled absorber using perforated plates in some wells; the absorber has extended bass response. The paper presents a theory for the enhanced absorption and the important design parameters are discussed. Good agreement is shown between the prediction model and impedance tube measurements. The design of this absorber was first carried out using a numerical optimization, although a simplified design procedure is also outlined which is almost as good. The results clearly show that this type of profiled absorber extends the absorption at low frequencies while maintaining the good absorption at mid frequencies as well.
Measurement of the scattering of a Lamb wave by a through hole in a plate
Authors: Fromme Paul , Sayir Mahir B.
Published: July 2002

Flexural waves propagating in an aluminum plate containing a circular hole are studied. In the experiments the first antisymmetric Lamb wave mode A0 is excited selectively by a piezoelectric transducer. The scattered field around a circular cavity is measured pointwise using a heterodyne laser interferometer. The measurements are compared with theoretical calculations. Different approximate analytical approaches, employing Kirchhoff and Mindlin types of plate theories to describe the scattered field, are used. Good agreement between the experimental data and the analytical solutions is found within the ranges of validity of the different models. Introduction of a small imperfection, like a notch, at the boundary of the cavity changes the measured scattered field significantly. The approach allows a fast measurement of large surfaces and might be useful for nondestructive testing purposes, e.g., the detection of cracks at fastener holes in airplane fuselage.
Implosion of an underwater spark-generated bubble and acoustic energy evaluation using the Rayleigh model
Authors: Buogo Silvano , Cannelli Giovanni B.
Published: July 2002

The growth, collapse, and rebound of a vapor bubble generated by an underwater spark is studied by means of high-speed cinematography, simultaneously acquiring the emitted acoustic signature. Video recordings show that the growth and collapse phases are nearly symmetrical during the first two or three cycles, the bubble shape being approximately spherical. After 2–3 cycles the bubble behavior changes from a collapsing/rebounding regime with sound-emitting implosions to a pulsating regime with no implosions. The motion of the bubble wall during the first collapses was found to be consistent with the Rayleigh model of a cavity in an incompressible liquid, with the inclusion of a vapor pressure term at constant temperature within each bubble cycle. An estimate of the pressure inside the bubble is obtained measuring the collapse time and maximum radius, and the amount of energy converted into acoustical energy upon each implosion is deduced. The resulting value of acoustic efficiency was found to be in agreement with measurements based on the emitted acoustic pulse.
An EMA study of VCV coarticulatory direction
Authors: Recasens Daniel
Published: July 2002

This study addresses three issues that are relevant to coarticulation theory in speech production: whether the degree of articulatory constraint model (DAC model) accounts for patterns of the directionality of tongue dorsum coarticulatory influences; the extent to which those patterns in tongue dorsum coarticulatory direction are similar to those for the tongue tip; and whether speech motor control and phonemic planning use a fixed or a context-dependent temporal window. Tongue dorsum and tongue tip movement data on vowel-to-vowel coarticulation are reported for Catalan VCV sequences with vowels /i/, /a/, and /u/, and consonants /p/, /n/, dark /l/, /s/, /∫/, alveolopalatal /ɲ/ and /k/. Electromidsagittal articulometry recordings were carried out for three speakers using the Carstens articulograph. Trajectory data are presented for the vertical dimension for the tongue dorsum, and for the horizontal dimension for tongue dorsum and tip. In agreement with predictions of the DAC model, results show that directionality patterns of tongue dorsum coarticulation can be accounted for to a large extent based on the articulatory requirements on consonantal production. While dorsals exhibit analogous trends in coarticulatory direction for all articulators and articulatory dimensions, this is mostly so for the tongue dorsum and tip along the horizontal dimension in the case of lingual fricatives and apicolaminal consonants. This finding results from different articulatory strategies: while dorsal consonants are implemented through homogeneous tongue body activation, the tongue tip and tongue dorsum act more independently for more anterior consonantal productions. Discontinuous coarticulatory effects reported in the present investigation suggest that phonemic planning is adaptative rather than context independent.
Error analysis in acoustic elastography. I. Displacement estimation
Authors: Bilgen Mehmet , Insana Michael F.
Published: July 2002

Correlation between acoustic echo signals obtained before and after application of an external compressional force provides information about the internal deformation of an elastic medium. In this paper, the variance for displacement estimated from an echo data segment and the covariance between two windowed segments that may overlap are derived. The signal and noise spectra are Gaussian and independent. The dependence of the displacement variance on input signal-to-noise ratio (SNRi), time-bandwidth product W, fractional bandwidth Y−1, and the rate of displacement variation with depth a is investigated. The relationship between a and the other experimental parameters is crucial for understanding how signal decorrelation affects displacement error. The expression for displacement variance reduces to the Cramer-Rao lower bound result when a=0 and W≫1 for both bandpass and base-band signals. When a≠0 displacement variance increases, and there is an optimal window length at W=20/a1+Y2 for which the displacement variance is minimum. Narrow-band signals produce larger errors than broadband signals for long observation windows when a≠0 and just the opposite when a=0. Errors are greatest for displacements estimated from the envelope of narrow-band signals. Finally, a general expression for the minimum displacement variance for arbitrary signal and noise spectra is derived as a function of the experimental parameters. These results form a framework for analyzing strain estimates in elastography, the subject of a companion paper.
Free vibration of a partially fluid-filled cross-ply laminated composite circular cylindrical shell
Authors: Xi Z. C. , Yam L. H. , Leung T. P.
Published: July 2002

Free vibration of a partially fluid-filled cross-ply laminated composite circular cylindrical shell is investigated using a semi-analytical procedure based on the Reissner–Mindlin theory and compressible fluid equations. The shell is modeled using unaxisymmetric shear deformable circular cylindrical shell elements. The fluid is modeled using column fluid elements. The equation of motion of the partially fluid-filled shell is derived using the Hamilton’s variational principle. Numerical examples are given for free vibrations of partially fluid-filled orthotropic and cross-ply laminated composite circular cylindrical shells with various boundary conditions. Numerical results indicate that the fluid filling can reduce significantly the natural frequencies of orthotropic and cross-ply laminated composite circular cylindrical shells.
Frequency response of a two-dimensional trusslike periodic panel
Authors: El-Raheb Michael
Published: July 2002

The frequency response of a two-dimensional trusslike periodic panel is studied adopting the transfer matrix of a repeated cell. Intracell resonance occurs at relatively low frequencies, causing high modal density of the panel. Effects of panel curvature, sag of cell diagonal member, mass added by a liquid filling the cell cavity, and damping by constrained viscoelastic layers are studied parametrically.
Temperature discontinuities between elements of thermoacoustic devices
Authors: Brewster James R. , Raspet Richard , Bass Henry E.
Published: July 2002

Significant differences in temperatures have been observed between adjoining elements of thermoacoustic prime movers [G. W. Swift, J. Acoust. Soc. Am. 92, 1551–1563 (1992)]. A simple description of the interelement heat transfer process based on the existence of this temperature difference is given. The central assumption of this approach is that the heat transfer process is sufficiently rapid that it is completed in less than the dwell time that the fluid spends in either element. Experimental measurements of the heat transfer coefficient between elements is shown to yield results close to the prediction of this complete heat exchange theory. Predictions are also compared to those based on the heat transfer description put forward by Swift [J. Acoust. Soc. Am. 92, 1551–1563 (1992)].
Dissipative effects on Bjerknes forces between two bubbles
Authors: Doinikov Alexander A.
Published: July 2002

The time-averaged forces exerted by a sound field between two gas bubbles, normally called Bjerknes forces, are examined. The surrounding medium is assumed to be an incompressible viscous liquid. It is shown that the acoustic streaming, which develops around the bubbles due to viscosity, adds one more term to the Bjerknes force that is dominant when the viscous wavelength is large compared with the bubble radii.
Use of acoustic basis functions for active control of sound power radiated from a cylindrical shell
Authors: Naghshineh Koorosh , Chen Weicheng , Koopmann Gary H.
Published: July 2002

In a previous paper by the authors [J. Acoust. Soc. Am. 92, 856–870 (1992)], a general strategy was devised for achieving minimum radiation of sound from structures subjected to a harmonic excitation force. In this strategy, a quadratic expression is written for the total sound power radiated from the structure in terms of the primary and actuator (control) forces. Using quadratic optimization of this expression, a single control force vector is found which minimizes the radiated sound power for the particular acoustic model of the structure. The structural response to this control force is referred to as the “weak radiator” response and is then used as an objective function for an adaptive algorithm. In previous work, this strategy was used to control the sound radiated from a baffled beam. The work presented in this paper extends the application of this strategy to the case of a cylindrical shell with endcaps. Numerical predictions were verified experimentally. These results show that this strategy is successful in controlling the sound radiated from the cylindrical shell by yielding large reductions in the structural supersonic wave number content.
Lateralization and binaural discrimination of patients with pontine lesions
Authors: Aharonson Vered , Furst Miriam , Levine Robert A. , Chaigrecht Michael , Korczyn Amos D.
Published: July 2002

Lateralization and just-noticeable difference (jnd) measurements relative to the center were tested in a large group of patients with pontine lesions caused either by stroke or multiple sclerosis. Stimuli included binaural clicks, and low- and high-frequency narrow-band noise bursts. Two major types of abnormalities were revealed in the lateralization performances: perception of all stimuli, regardless of interaural differences (time and/or level) in the center of head (center-oriented), or lateralization of all stimuli to one side or the other of the head (side-oriented). The only significant correlation between jnd and lateralization performances was that an elevated jnd was always manifested in abnormal lateralization, while abnormality in lateralization did not necessarily indicate an abnormal jnd. Center-oriented lateralization was observed either for both interaural differences or only for one of them, and was found in both MS and stroke patients. All side-oriented stroke patients were similarly unable to center binaural stimuli for both time and level cues, whereas only one MS patient had this abnormality for interaural time differences, while his level performance was normal. More abnormalities were detected in the narrow band stimuli tests, although in some cases performance was more degraded for click stimuli. Lateralization tasks with high-frequency stimuli were more sensitive detectors of abnormality than jnd for any kind of stimulus, or lateralization tasks with low-frequency stimuli or clicks.
Nonlinear standing waves in an acoustical resonator
Authors: Ilinskii Yurii A. , Lipkens Bart , Lucas Timothy S. , Van Doren Thomas W. , Zabolotskaya Evgenia A.
Published: July 2002

A one-dimensional model is developed to analyze nonlinear standing waves in an acoustical resonator. The time domain model equation is derived from the fundamental gasdynamics equations for an ideal gas. Attenuation associated with viscosity is included. The resonator is assumed to be of an axisymmetric, but otherwise arbitrary shape. In the model the entire resonator is driven harmonically with an acceleration of constant amplitude. The nonlinear spectral equations are integrated numerically. Results are presented for three geometries: a cylinder, a cone, and a bulb. Theoretical predictions describe the amplitude related resonance frequency shift, hysteresis effects, and waveform distortion. Both resonance hardening and softening behavior are observed and reveal dependence on resonator geometry. Waveform distortion depends on the amplitude of oscillation and the resonator shape. A comparison of measured and calculated wave shapes shows good agreement.
The direct estimation of sound speed using pulse–echo ultrasound
Authors: Anderson Martin E. , Trahey Gregg E.
Published: July 2002

A method for the direct estimation of the longitudinal speed of sound in a medium is presented. This estimator derives the speed of sound through analysis of pulse–echo data received across a single transducer array following a single transmission, and is analogous to methods used in exploration seismology. A potential application of this estimator is the dynamic correction of beamforming errors in medical imaging that result from discrepancy between the assumed and actual biological tissue velocities. The theoretical basis of this estimator is described and its function demonstrated in phantom experiments. Using a wire target, sound-speed estimates in water, methanol, ethanol, and n-butanol are compared to published values. Sound-speed estimates in two speckle-generating phantoms are also compared to expected values. The mean relative errors of these estimates are all less than 0.4%, and under the most ideal experimental conditions are less than 0.1%. The relative errors of estimates based on independent regions of speckle-generating phantoms have a standard deviation on the order of 0.5%. Simulation results showing the relative significance of potential sources of estimate error are presented. The impact of sound-speed errors on imaging and the potential of this estimator for phase aberration correction and tissue characterization are also discussed.
Method for reducing sound radiated from structures using vibration absorbers optimized with a neural network
Authors: Nagaya Kosuke , Li Lianjin
Published: July 2002

The usual design methods for the vibration absorbers are applicable to suppress vibrations of machines and structures, but they are invalid for reducing sounds. This study discusses a method for reducing sound radiated from structures by the use of vibration absorbers. In the current study, the peaks of sound power in the frequency domain are considered to be cost functions. Hence the equations for obtaining optimal parameters of the absorbers become nonlinear expressions. In order to have the optimal parameters, a neural network procedure is applied. Since it is difficult to give appropriate initial values in the usual neural network procedure which gives rapid convergence of the solution, a method for accelerating the neural network is discussed. Numerical calculations were conducted for a plate-type cantilever beam with a large width, and experimental tests were also performed for the same beam. It is proven that the present method is valid for reducing noises radiated from structures. In the usual design method for the vibration absorbers, a modal analysis has been used, so the number of absorbers should be the same as that of control modes, on the other hand the present method can treat nonlinear problems, hence there is no restriction between the number of absorbers and the modal number.
Characteristics of thermoacoustic resonance in a ducted burner
Authors: Cho Sangyeon , Lee Soogab
Published: July 2002

Combustion instability accompanied with low-frequency oscillations is one of the typical phenomena in a ducted flame burner. This is due to the interaction between unsteady heat release and the sound pressure field known as thermoacoustic feedback. A parametric study was carried out through measurements of acoustic pressure and flame radiation at various conditions not only to elucidate the effect of Reynolds number and equivalence ratio on thermoacoustic oscillation, but also to understand the mechanism of the onset of thermoacoustic resonance in a ducted flame burner. The results explain that equivalence ratio has significant effects on the magnitude of pressure and heat fluctuation as well as the fundamental frequency. It is also found that the onset of thermoacoustic resonance is strongly affected by the interacting mechanism between acoustic energy and heat release.
Predicting overall reaction to multiple noise sources
Authors: Kaku Jiro , Kato Tohru , Kuwano Sonoko , Namba Seiichiro
Published: July 2002

The validity of models predicting overall human response to complex sound environments, which are constituted of road traffic and railway noises, is discussed using results of psychological experiments carried out both in a laboratory and outdoors, as well as by using results of social surveys. Existing predictive models (energy summation model, independent effects model, response summation model, and so on) were applied to the data. The result shows that the simple energy summation model gives the poorest predicting ability in every case. It suggests that differences of response among different noise sources must be considered. The effective level D of road traffic noise relative to railway noise was calculated using Ollerhead’s response summation model as approximately 10 dB in the laboratory experiment. The D values decreased as compared to the above value in cases of field experiments and social surveys, but it was still clear that the contribution of road traffic noise to the overall judgment was greater than that of railway noise. Judging from the coefficient of determination and standard errors shown in the results, the independent effects model seems to be the most suitable to predict the overall human response to complex sound environments.
Theory of compressional and transverse wave propagation in consolidated porous media
Authors: Buckingham Michael J.
Published: July 2002

A theory of compressional and shear wave propagation in consolidated porous media (rocks) is developed by extending ideas already introduced in connection with unconsolidated marine sediments. The consolidated material is treated as an elastic medium which exhibits a specific form of stress relaxation associated with grain boundaries and microcracks. The stress relaxation, which is linear in the sense that it obeys superposition, shows hysteresis, as characterized by a material response function. Two linear wave equations are derived, one for compressional and the second for shear waves, from which expressions for the wave speeds and attenuations are established. In both cases, the attenuation is found to scale with the first power of frequency, consistent with many observations of attenuation in sandstones, limestones, and shales; the wave speeds show weak logarithmic dispersion. These expressions for the wave speeds and attenuations satisfy the Kronig–Kramers dispersion relationships, as they must if the response of the medium to disturbances is to be causal. Some comments are offered on the nature of the material response, notably that it appears to be primarily associated with grain-boundary interactions occurring at a molecular level, rather than being related to the macroscopic properties of the material, such as density or porosity.
Parallel projection and crosshole Lamb wave contact scanning tomography
Authors: McKeon James C. P. , Hinders Mark K.
Published: July 2002

Lamb waves are guided ultrasonic waves capable of propagating relatively long distances in thin plates and thin laminated structures, such as airframe skins, storage tanks, and pressure vessels. Their propagation properties in these media depend on the vibrational frequency as well as on the thickness and material properties of the structure. Structural flaws such as disbonds, corrosion, fatigue cracks, and voids represent changes in effective thickness and material properties, and therefore measurement of variations in Lamb wave propagation can be employed to assess the integrity of these structures. Lamb wave measurements can be made for a number of relative transducer positions (projections) and an image of the flawed region can be reconstructed tomographically. This paper presents a new technique in which two contact piezoelectric transducers are independently scanned along parallel lines in a fashion analogous to that commonly used in seismic crosshole tomography. These results are compared to those for parallel projection Lamb wave tomography data collected with an automated contact scanning apparatus. The advantages and drawbacks of these two methods in the development of automated tomographic Lamb wave scanners for quantitative mapping of thickness variation in platelike materials are discussed.
Automatic matched-field tracking with table lookup
Authors: Bucker Homer , Baxley Paul A.
Published: July 2002

In matched-field processing, the signals measured at sensors in an array are correlated with the expected signals for a target at a specified point in the environment. This tends to be a computer intensive process because there are a large number of possible target locations and the calculation of the sound field may be complicated. A search by an operator for the target involves examination of various cuts through a multi-dimensional search space. In this paper it is shown that use of table lookup simplifies the modeling problem. Also, by use of matched-field tracking, the data can be processed in large time (∼3 to 10 min) blocks. Using these methods, the processing can be done in real time with little, or no, operator intervention. An example of automatic matched-field tracking is presented using data collected during a shallow water test near San Clemente Island. Finally, a simple sensitivity study is made. The actual sound speed profile is replaced by one modified by low-pass filtering and, in a second case, by a constant speed profile. The results show that matched-field tracking, although degraded, still provides useful tracking data.
The perceptual tone/noise ratio of merged iterated rippled noises
Authors: Patterson Roy D. , Yost William A. , Handel Stephen , Datta A. Jaysurya
Published: July 2002

Iterated rippled noise (IRN) is constructed by delaying a random noise by d ms, adding it back to the same noise, and repeating the process iteratively. When two IRNs with the same power but slightly different delays are added together, the perceptual tone/noise ratio of the “merged” IRN is markedly reduced with respect to that of either of the component IRNs. In this paper, the reduction in the perceptual tone/noise ratio is measured for IRNs in which one of the delays is always 16 ms and the other is either 16±0.1 ms or 16±1.1 ms. The component IRNs have the same number of iterations, and the number varies across conditions from 4 to 256. The perceptual tone/noise ratio is measured using a discrimination matching procedure developed for single IRNs; each merged IRN is compared with a range of “standard” stimuli having varying proportions of a complex tone and a broadband noise [Patterson et al., J. Acoust. Soc. Am. 100, 3286–3294 (1996)]. For single IRNs, the function relating the signal-to-noise ratio of the matching standard to the number of iterations in the IRN was found to be essentially straight. This relationship was explained in terms of the height of the first peak in the autocorrelation of the stimulus wave, or by the first peak in the summary autocorrelogram produced by a time-domain auditory model. For the merged IRNs in the current experiment, the matching-point functions are found to have pronounced downward curvature, in addition to being well below the function for single IRNs. To account for the reduction in the perceptual tone/noise ratio of merged IRNs, the autocorrelation model was extended to include a simple rule for combining adjacent peaks in the autocorrelation function of the wave, and the autocorrelogram model was revised to improve the simulation of the “loss of phase locking” at higher frequencies in the autocorrelogram.
The noise emitted from vehicles at roundabouts
Authors: To W. M. , Chan T. M.
Published: July 2002

In Asian cities, many noise-sensitive receivers are located in the vicinity of highways and roundabouts because of the limited supply of usable land and the demand for good transportation. Although roundabouts can carry smooth traffic flow by minimizing the start–stop operations of drivers, the noise emitted from moving vehicles would definitely affect those people who live, work, or study in the vicinity. This article presents an analytical solution of the noise emitted from vehicles at roundabouts by assuming vehicles to be incoherent sources lying continuously on the roundabouts. A simple equation is introduced by which it is possible to relate the noise level at any distance from the center of the roundabout to the noise level measured at the center of the roundabout.
Apparent Departures from Newtonian Behavior in Liquids Caused by Viscous Heating
Authors: Gruntfest I. J.
Published: July 2002

As part of a general study of the mechanical behavior of materials with temperature-dependent properties, idealized Couette flow is considered here. The model fluid is Newtonian and incompressible. Inertial terms are neglected in the analysis. Time-dependent temperature and velocity distributions in the fluid are computed for: (1) the constant stress case, (2) the constant rate of stress increase case, and (3) the constant boundary velocity case. In each case, a range of thermal boundary conditions is also considered. The results are compared with closed form analytical solutions that can be obtained in special cases. The temperature distributions can influence the stability of laminar flow and cavitation in liquids. The derived velocity distributions influence the drag and protective action of lubricants. Furthermore, it appears that some apparently non-Newtonian flows can be described more simply when the deviation is attributed to heating than when it is attributed to intrinsic, non-Newtonian behavior. A thermistor circuit analog is demonstrated as an aid to the solution of the Couette flow equations with thermal feedback.