bluuebunny/crossref_metadata_2025 huggingface dataset:
The emergence of rabbit haemorrhagic disease virus: will a non-pathogenic strain protect the UK?
Authors: White P.J. , Norman R.A. , Trout R.C. , Gould E.A. , Hudson P.J.
Published: July 2002

Rabbit haemorrhagic disease virus emerged in China in 1984, and has killed hundreds of millions of wild rabbits in Australia and Europe. In the UK there appears to be an endemic non–pathogenic strain, with high levels of seroprevalence being recorded, in the absence of associated mortality. Using a seasonal, age–structured model we examine the hypothesis that differences in rabbit population demography differentially affect the basic reproductive rates (R0) of the pathogenic and non–pathogenic strains, leading to each dominating in some populations and not others. The strain with the higherR0excluded the other, with the dynamics depending upon the ratio of the twoR0values. When the non–pathogenic strain dominated, the pathogenic strain caused only transient mortality, although this could be significant when the twoR0values were similar. When the pathogenic strain dominated, repeated epidemics led to host eradication. Seroprevalence data suggest that the non–pathogenic strain may be protecting some, but not all UK populations, with half being ‘at risk’ from invasion by the pathogenic strain and a fifth prone to significant transient mortality. We identify key questions for empirical research to test this prediction.
The regulation of circadian clocks by light in fruitflies and mice
Authors: Foster Russell G. , Helfrich-Forster Charlotte
Published: July 2002

A circadian clock has no survival value unless biological time is adjusted (entrained) to local time and, for most organisms, the profound changes in the light environment provide the local time signal (zeitgeber). Over 24 h, the amount of light, its spectral composition and its direction change in a systematic way. In theory, all of these features could be used for entrainment, but each would be subject to considerable variation or ‘noise’. Despite this high degree of environmental noise, entrained organisms show remarkable precision in their daily activities. Thus, the photosensory task of entrainment is likely to be very complex, but fundamentally similar for all organisms. To test this hypothesis we compare the photoreceptors that mediate entrainment in both flies and mice, and assess their degree of convergence. Although superficially different, both organisms use specialized (employing novel photopigments) and complex (using multiple photopigments) photoreceptor mechanisms. We conclude that this multiplicity of photic inputs, in highly divergent organisms, must relate to the complex sensory task of using light as azeitgeber.
Ku DNA end-binding protein modulates homologous repair of double-strand breaks in mammalian cells
Authors: Pierce Andrew J. , Hu Peng , Han Mingguang , Ellis Nathan , Jasin Maria
Published: July 2002

Chromosomal double-strand breaks (DSBs) in mammalian cells are repaired by either homology-directed repair (HDR), using a homologous sequence as a repair template, or nonhomologous end-joining (NHEJ), which often involves sequence alterations at the DSB site. To characterize the interrelationship of these two pathways, we analyzed HDR of a DSB in cells deficient for NHEJ components. We find that the HDR frequency is enhanced in Ku70−/−,XRCC4−/−, and DNA-PKcs−/−cells, with the increase being particularly striking inKu70−/− cells. Neither sister-chromatid exchange nor gene-targeting frequencies show a dependence on these NHEJ proteins. A Ku-modulated two-ended versus one-ended chromosome break model is presented to explain these results.
Structural basis for abrogated binding between staphylococcal enterotoxin A superantigen vaccine and MHC‐IIα
Authors: Krupka Heike I. , Segelke Brent W. , Ulrich Robert G. , Ringhofer Sabine , Knapp Mark , Rupp Bernhard
Published: July 2002

Staphylococcal enterotoxins (SEs) are superantigenic protein toxins responsible for a number of life‐threatening diseases. The X‐ray structure of a staphylococcal enterotoxin A (SEA) triple‐mutant (L48R, D70R, and Y92A) vaccine reveals a cascade of structural rearrangements located in three loop regions essential for binding the α subunit of major histocompatibility complex class II (MHC‐II) molecules. A comparison of hypothetical model complexes between SEA and the SEA triple mutant with MHC‐II HLA‐DR1 clearly shows disruption of key ionic and hydrophobic interactions necessary for forming the complex. Extensive dislocation of the disulfide loop in particular interferes with MHC‐IIα binding. The triple‐mutant structure provides new insights into the loss of superantigenicity and toxicity of an engineered superantigen and provides a basis for further design of enterotoxin vaccines.
Mechanism of pressure‐induced thermostabilization of proteins: Studies of glutamate dehydrogenases from the hyperthermophile Thermococcus litoralis
Authors: Sun Michael M.C. , Caillot Raphaele , Mak Gary , Robb Frank T. , Clark Douglas S.
Published: July 2002

In this study, we investigated the effect of pressure on protein structure and stability at high temperature. Thermoinactivation experiments at 5 and 500 atm were performed using the wild‐type (WT) enzyme and two single mutants (D167T and T138E) of the glutamate dehydrogenase (GDH) from the hyperthermophile Thermococcus litoralis. All three GDHs were stabilized, although to different degrees, by the application of 500 atm. Interestingly, the degree of pressure stabilization correlated with GDH stability as well as the magnitude of electrostatic repulsion created by residues at positions 138 and 167. Thermoinactivation experiments also were performed in the presence of trehalose. Addition of the sugar stabilized all three GDHs; the degree of sugar‐induced thermostabilization followed the same order as pressure stabilization. Previous studies suggested a mechanism whereby the enzyme adopts a more compact and rigid structure and volume fluctuations away from the native state are diminished under pressure. The present results on the three GDHs allowed us to further confirm and refine the proposed mechanism for pressure‐induced thermostabilization. In particular, we propose that pressure stabilizes against thermoinactivation by shifting the equilibrium between conformational substates of the GDH hexamer, thus inhibiting irreversible aggregation.
A model for photon detection and dosimetry with superheated emulsions
Authors: d'Errico Francesco , Nath Ravinder , Nolte Ralf
Published: July 2002

A model is presented for the analysis and prediction of the photon response of detectors based on superheated emulsions of light halocarbons in tissue equivalent gels. It is shown that on the basis of a nondimensional thermodynamic quantity, called reduced superheat, it is possible to identify the degree of superheat, or the operating temperature, corresponding to the photon sensitization of the emulsions. Moreover, on the basis of the mass energy absorption coefficients, it is possible to determine the energy dependence of the photon response. The vaporization energy necessary for bubble nucleation is estimated by means of the thermal spike theory developed for bubble chambers. The energy deposition requirements are consistent with the energy transferred by secondary electrons at the end of their range in the halocarbons. These findings provide design criteria for photon detectors based on superheated emulsions. It is shown that light halocarbons of low effective atomic numbers present the best dosimetric properties. In particular, by manufacturing superheated emulsions with octafluoropropane, or halocarbon R‐218, photon sensitivity is achieved at room temperature along with a fairly constant air‐kerma response.
Millikan Lecture 1999: The Workplace, Student Minds, and Physics Learning Systems
Authors: Van Heuvelen Alan
Published: July 2002

We review three important ideas concerning physics education. First, what do surveys from the workplace indicate about the relative importance in student education of scientific process knowledge, personal skills, and conceptual physics knowledge? Second, what are the characteristics of student minds that need to acquire this knowledge and these skills? Finally, what can we do with physics learning systems to help these minds better acquire this knowledge and these skills?
Cautious revolutionaries: Maxwell, Planck, Hubble
Authors: Brush Stephen G.
Published: July 2002

Three scientists exemplified the cautious behavior that we might like all scientists to display: indeed, they were so critical of their own ideas that they risked losing credit for them. Nevertheless, they finally earned at least as much fame as they deserved, leaving historians to wonder about what they really believed. Maxwell initially rejected the kinetic theory of gases because two of its predictions disagreed with experiments; later he revived the theory, showed that one of those experiments had been misinterpreted, and eventually became known as one of the founders of the modern theory. Planck seems to have intended his 1900 quantum hypothesis as a mathematical device, not a physical discontinuity; later he limited it to the emission (not absorption) of radiation, thereby discovering “zero-point energy.” Eventually he accepted the physical quantum hypothesis and became known as its discoverer. Hubble (with Humason) established the distance–velocity law, which others used as a basis for the expanding universe theory; later he suggested that redshifts may not be due to motion and appeared to lean toward a static model in place of the expanding universe.
Comparison of an integral equation on energy and the ray-tracing technique in room acoustics
Authors: Le Bot A. , Bocquillet A.
Published: July 2002

This paper deals with a comparison of two room acoustic models. The first one is an integral formulation stemming from power balance and the second is the ray-tracing technique with a perfectly diffuse reflection law. The common assumptions to both models are the uncorrelated wave hypothesis and the perfectly diffuse reflection law. The latter allows the use of these methods for nondiffuse fields beyond the validity domain of Sabine’s formula. Comparisons of numerical simulations performed with the softwares RAYON and CeReS point out that these results are close to each other and finally, a formal proof is proposed showing that both methods are actually equivalent.
Three-dimensional modeling of acoustic backscattering from fluid-like zooplankton
Authors: Lavery Andone C. , Stanton Timothy K. , McGehee Duncan E. , Chu Dezhang
Published: July 2002

Scattering models that correctly incorporate organism size and shape are a critical component for the remote detection and classification of many marine organisms. In this work, an acoustic scattering model has been developed for fluid-like zooplankton that is based on the distorted wave Born approximation (DWBA) and that makes use of high-resolution three-dimensional measurements of the animal’s outer boundary shape. High-resolution computerized tomography (CT) was used to determine the three-dimensional digitizations of animal shape. This study focuses on developing the methodology for incorporating high-resolution CT scans into a scattering model that is generally valid for any body with fluid-like material properties. The model predictions are compared to controlled laboratory measurements of the acoustic backscattering from live individual decapod shrimp. The frequency range used was 50 kHz to 1 MHz and the angular characteristics of the backscattering were investigated with up to a 1° angular resolution. The practical conditions under which it is necessary to make use of high-resolution digitizations of shape are assessed.
Effect of reducing temporal intensity modulations on sentence intelligibility
Authors: Noordhoek Ingrid M. , Drullman Rob
Published: July 2002

Modulations in the temporal intensity envelope of 24 1/4-octave bands were reduced by proportionally raising the troughs and lowering the peaks relative to the mean intensity in each band. The effect on intelligibility of various degrees of modulation reduction was investigated by measuring the speech-reception threshold (SRT) in noise. For conditions of severe modulation reduction, the number of correctly received sentences in quiet was scored. The effect of this deterministic modulation reduction was compared to the effect of stochastic modulation reduction obtained with addition of noise. Results for 12 normal-hearing subjects show that in the case of deterministic modulation reduction, intelligibility is reduced to 50% when the modulation-transfer factor equals 0.10, whereas in the case of modulation reduction by addition of noise, this intelligibility is reached already at a modulation-transfer factor of 0.27. This confirms that the effect of additive noise on intelligibility cannot be understood completely as a result of only modulation reduction. As suggested by Drullman [J. Acoust. Soc. Am. 97, 585–592 (1995)] two other factors associated with the addition of noise have to be taken into account: (1) the introduction of nonrelevant modulations, and (2) the corruption of the fine structure.
A new approach to comparing binaural masking level differences at low and high frequencies
Authors: van de Par Steven , Kohlrausch Armin
Published: July 2002

A new experimental technique for studying binaural processing at high frequencies is introduced. Binaural masking level differences (BMLDs) for the conditions N0Sπ and NπS0 were measured for a tonal signal in narrow-band noise at 125, 250, and 4000 Hz. In addition, “transposed” stimuli were generated, which were centered at 4000 Hz, but were designed to preserve within the envelope the temporal “fine-structure” information available at the two lower frequencies. The BMLDs measured with the 125-Hz transposed stimuli were essentially the same as BMLDs from the regular 125-Hz condition. The transposed 250-Hz stimuli generally produced smaller BMLDs than the stimuli centered at 250 Hz, but the pattern of results as a function of masker bandwidth was the same. The patterns of results from the transposed stimuli are different from those of the 4000-Hz condition and, consistent with the low-frequency masker data, generally show higher BMLDs. The results indicate that the mechanisms underlying binaural processing at low and high frequencies are similar, and that frequency-dependent differences in BMLDs probably reflect the inability of the auditory system to encode the temporal fine structure of high-frequency stimuli.
Acoustic wave propagation in two-phase viscoelastic fluids: The case of polymer emulsions
Authors: Verdier Claude , Piau Monique
Published: July 2002

Wave propagation in two-phase viscoelastic fluid media is studied. A theory based on previous ones for liquid–liquid or liquid–solid mixtures is developed. Acoustical parameters, i.e., velocity of propagation and attenuation, are related to the morphological properties (concentration and size of inclusions) through the thermal and viscoelastic effects. This general theory includes the Newtonian and elastic behaviors as limiting cases. In the case of molten polymer blends, viscoelastic effects may be dominant, unlike most of the Newtonian emulsions studied previously, where thermal effects usually prevail. Moreover, by taking into account the viscoelastic character of the fluids, important changes are obtained not only for the absorption due to the individual components, but also for the excess attenuation in the emulsion.
Issues in predicting community noise for power plants
Authors: Brittain Frank H.
Published: July 2002

The normal method of predicting community noise levels involves first computing sound power levels from near-field sound-pressure levels and then assuming that the noise radiates from one or several point sources. This approach makes several major leaps of faith. Some of these leaps of faith or issues in predicting community noise levels for power plants are identified. The issues include validity of near-field sound-pressure levels, accuracy of sound power levels computed, radiation from large sources, transmission through building walls, and screening and reflection of noise by power plant equipment and buildings. The validity of representing large sources as one or a series of point sources is reviewed. The role of atmospheric effects and the dangers inherent in typical noise prediction software is briefly reviewed. Several examples and suggestions for making more accurate predictions are given. [See NOISE-CON Proceedings for full paper.]
High-frequency reciprocal transmissions across a coastal front in Haro Strait, British Columbia
Authors: Elisseeff Pierre , Schmidt Henrik , Johnson Mark
Published: July 2002

The Haro Strait experiment was conducted in Haro Strait, British Columbia (Canada) in order to determine the feasibility of acoustically focused oceanographic sampling (AFOS). In the course of the experiment 15-kHz pseudorandom sequences with a bandwidth of 3 kHz were reciprocally transmitted across a front driven by estuarian and tidal forcing. Temperature profiles were continuously measured at the array locations, and array elements were acoustically tracked. Transmissions were performed over a period of 36 h, providing an exhaustive acoustic characterization of the frontal dynamics. The sensitivity of arrival times to the environmental variability is first investigated. Both current and temperature fields across the front are estimated using travel-time tomography. Resolution issues associated with source–receiver parameters such as geometry, frequency, and bandwidth are discussed in light of the experimental data. Finally, the relevance of the high-frequency acoustic tomographic inversion to AFOS is assessed. [Work supported by ONR.]
Wavelet analysis of internal waves in SESAME II data, and the effects on acoustic transmission
Authors: George Jacob , Field Robert L.
Published: July 2002

In continential shelf regions, large-amplitude internal tides are believed to spawn smaller wavelength solitonlike waves. During the summers of 1995 and 1996, the SESAME experiments were performed in the North West Approaches to the British Isles. The purpose of these experiments was to measure the properties (length scales, amplitudes, velocities, and the time of occurrence) of these solitonlike waves and determine their effects on acoustic propagation. In this paper wavelet analysis is applied to some of the long-term temperature measurements in order to determine soliton properties. The results of the wavelet analysis and its implications on acoustic transmission will be discussed. [Work supported by ONR and NRL.]
Pulsed beam propagation in lossless dispersive media. I. Background
Authors: Felsen Leopold B. , Melamed Timor
Published: July 2002

Pulsed beams (PB) are highly collimated wave objects which can simulate actual acoustic fields radiated by time-domain (TD) compact transducers and, by superposition, can analytically synthesize arbitrary pulsed source distributions. While much progress has been made in tracking PB wave packets through nondispersive environments, the TD phenomenologies characterizing PB interaction with dispersive media are as yet inadequately understood. To initiate this study, we review known TD asymptotic techniques for pulsed noncollimated wave objects with real frequency and wave number constituents. The results can be interpreted in terms of space-time ray theory and instantaneous dispersion relations, with interesting graphical representations (in the configuration–spectrum phase space) that highlight the relevant wave physics. Of special interest are inputs which focus the pulsed signal at a specified space-time point inside the medium. The extension to pulsed beams requires consideration of complex spectra, as performed in part II.
Effect of flexibility on rattle noise: Experimental and theoretical analysis
Authors: Fegelman Karen J. L. , Grosh Karl
Published: July 2002

Rattle has become an important issue in the automotive and aerospace industries. In order to understand the fundamental mechanics of rattle, a model problem involving a hinged plate rattling against a stiff contact point was formulated. In a previous study, this plate was modeled as a rigid body and the linearized equations of motion were solved explicitly. The calculated tip accelerations were compared to those measured from an experimental test stand and agreed qualitatively. Currently, the model has been expanded to include flexible modes in order to capture higher frequency behavior. In addition, instrumentation has been added to the test stand to measure sound-pressure level (SPL) and contact forces. The data for accelerations, contact forces, and SPL were compared in the time and frequency domains. Finally, the closed form flexible body solutions were analyzed with regard to stability to predict transitions from periodic to chaotic rattling behavior.
Preliminary results on environmentally robust vertical array design for shallow water mode filtering
Authors: Buck John R.
Published: July 2002

Many shallow water acoustics techniques require accurate estimates of the propagating modes from pressure observations at a vertical array. The noise in these estimates is a function of the conditioning of the vertical modes as sampled by the hydrophone array. However, the sound-speed profile and thus vertical mode shapes are usually not known when the array is designed. In addition, economic considerations often dictate the same array be used in a wide range of environments. Consequently, optimizing the array for a specific environment risks a degradation in performance if the experimental environment differs from the environment assumed by the array design. Conventional wisdom holds that in the absence of precise environmental knowledge, the safest approach is to space the hydrophones evenly throughout the water column. This work presents several simplified mode filtering scenarios demonstrating that nonuniform hydrophone spacings exist which are more robust in the minimax sense than uniform spacing, if it is possible to specify a range of operating environments for the array. This means that their worst case performance is better than the worst case performance of the uniformly spaced array over the range of environments.
Detection of low-level broadband signals using adaptive matched-field processing
Authors: Booth Newell O. , Schey Phil , Hodgkiss William S.
Published: July 2002

The detection performance of low spectral level, broadband signals from a submerged acoustic source in the presence of strong surface interference is described and illustrated with examples obtained in the May 1996 shallow water evaluation cell experiment (SWellEx-96). The experiment was carried out west of Point Loma in 200-m water of complex bathymetry. A vertical line array (VLA) was deployed next to an identical line array tilted at 45 deg. The detection performance of each of the arrays with linear and adaptive matched-field processing is measured and compared. [Work sponsored by Office of Naval Research, Code 321(US).]
Vibration isolation and detection using a mesoscopic photomechanical unit
Authors: Kwiatkowski Christopher S. , Welker David , Kuzyk Mark G.
Published: July 2002

Due to the high bandwidth of light, optical fibers are being used extensively in data communication systems, and more recently have found applications in sensors capable of monitoring environmental changes such as stress, displacement, temperature, and chemical concentrations. An active region consisting of a Fabry–Perot cavity inside a nonlinear polymer optical fiber, called a Mesoscopic Photomechanical Unit (MPU), has been studied that has applications in both sensing and vibration isolation. These devices consist of a PMMA core doped with DR1 organic dye. It has been shown that the length of these MPUs has a series of stable states, the stability of which is dependent on the intensity of guided light inside the fiber. Preliminary data show that a vibration sensor incorporating an MPU as its sensing element has the advantage of having an intensity-dependent response. This effect could be used to include all-optical logic within the device, making external electronics unnecessary. [Research supported by NASA and ARO.]
Room noise criteria—Time for common sense
Authors: Hale Marlund E. , Burke Richard E.
Published: July 2002

The acoustical environments of the many types of rooms designed for occupancy are supposed to be established in the design phase of a new project or during a project retro-fit so that the intended use of a room is not compromised by intrusive noise sources. A major tool in accomplishing the desired environment is the application of room noise criteria. However, given the many types of noise sources with a wide range in sound quality, frequency content, and temporal features, it seems impossible to achieve a desired, yet cost effective, acoustical room environment by using venerable noise criteria (NC) curves alone. ANSI S12.2-1995 is an attempt to include the means to account for different characteristics in noise sources by introducing the balanced noise criteria (NCB) and room criteria (RC) methods for evaluating noise. As a result of the introduction of ANSI S12.2-1995, a controversy has arisen over the practicality and even the viability of the new standard(s). The people who must live or work in the designed space will ultimately determine whether an adequate acoustical room environment has been achieved. The economics of the acoustical design often dictates whether a working solution is ever implemented at all. A practical basic criteria with just a handful of adjustment factors and guidelines to account for quality, frequency, and temporal anomalies, would be better suited to standardizing the design methodology in room acoustics. This paper provides examples of applications of standards in the everyday world of environmental acoustics. [See NOISE-CON Proceedings for full paper.]
Acoustic source location using a neural network
Authors: Bhatt Tarun , Ososanya Esther T. , Darvennes Corinne M.
Published: July 2002

This paper presents an artificial neural network (ANN) approach to locate an acoustic source and determine its distance from a microphone. First, two sets of experiments were performed to locate a rattling bolt on a plate using the unwrapped phase method, by comparing the acceleration signal from the vibrating plate to the acoustic signal received by an array of four microphones. The first test used a wide frequency bandwidth random signal and the second test used a short frequency bandwidth signal. Then the neural network was trained using this experimental data. The effectiveness of the ANN at locating a source using four microphones was evaluated, in light of experimental problems associated with frequency resolution and effects of reflecting surfaces. The ANN was also used to locate the same source using only three microphones. The expectation is that fewer microphones will be needed if an ANN is used and still provide the same level of accuracy on source location. This would result in better accuracy, or substantial savings for acoustic source location evaluation.
Pulsed beam propagation in lossless dispersive media. II. Implementation
Authors: Melamed Timor , Felsen Leopold B.
Published: July 2002

The space-time asymptotic analysis in lossless dispersive media for noncollimated pulsed wave objects with real spectra, as performed in Part I is here extended to the complex frequency and wavenumber spectra that characterize pulsed beam (PB) wave packets. To address the problem systematically, all spectral components in the formal asymptotic wave number frequency synthesis are expanded to second order away from the beam axis, which represents a real space-time ray with real spectra. Off-axis observation points in the paraxial region are reached by complex space-time rays with complex spectra. The complex off-axis spectra lead to corrections of the real on-axis spectra, in addition to introducing an imaginary (evanescent) decay component. Efforts are in progress to assess the wave physics that accompany these results, and to determine the modifications, due to dispersion, of the highly resolved PB in a nondispersive environment. Synthesizing PB profiles for focusing at a given space–time point in the dispersive medium are also considered.
Sonic band structure and surface localized modes in a density-modulated system: An experimental and theoretical study
Authors: Carr Christopher , Yu Roger
Published: July 2002

A result of the Bloch theory is that the eigenstates of an electron in a strictly periodic potential are extended and the corresponding energy levels form clustered energy bands separated by gaps. In the study reported here, a finite air-filled tube with arbitrary mass density modulation which permits the inclusion of disorder in the study of the acoustic frequency bands is theoretically considered. Since the theoretical model is finite, direct comparisons can be made with the experiment. The baffled tube is excited with a sound source at one end. The source can deliver short pulses as well as harmonic oscillations. Both normal mode analysis (NMA) and pulse analysis (PA) have been used. The spectra obtained from both methods are compared with our theoretical prediction. For the tube with evenly spaced baffles, three passing frequency bands have been found. More interestingly, some localized resonant modes are discovered whose frequencies lie in the gaps. The wave functions of these modes are confined within a few sections of divided tube at both ends.
Propagation and loss in layered viscoelastic composites
Authors: George Wallace R. A. , Schoenberg Michael
Published: July 2002

The acoustic response of a source in an anisotropic viscoelastic medium has not only a directionally dependent speed of propagation, but also a directionally dependent rate of attenuation. The long wavelength properties of a layered composite comprised of two alternating constituent layers, both of which are isotropic, but with one elastic and the other viscoelastic (modeled as a ‘‘standard solid’’), are investigated. Such a structure behaves as a homogeneous transversely isotropic viscoelastic medium. The plane-wave phase slowness and quality factor as a function of direction are shown for three cases. The first two are (a) when the slower medium is lossy and (b) when the faster medium is lossy. In these cases, the curves for loss versus angle are highly directional, but the actual patterns depend dramatically upon the choice of (a) or (b). The third case examines the behavior when the velocities of the constituents are approximately the same, but the loss is such that which constituent is fast and which is slow is dependent on frequency.
Speckle statistics of scatterer distributions described by marked regularity models
Authors: Cramblitt Robert M. , Parker Kevin J.
Published: July 2002

Speckle images characterized by a non-Rayleigh amplitude probability density function (pdf) are formed when the assumptions underlying fully developed speckle are violated, such as when the number of scatterers in a resolution cell is small, or scatterers are organized with some periodicity, leading to nonuniform scatterer phasing. Various random-walk models have been developed to explain how non-Rayleigh cases such as the K, Rician, and homodyned-K pdf’s arise. Marked regularity models provide an alternative to specialized random-walk models, because they describe the physical spatial placement of point scatterers in one dimension in a parametric manner. Spatial distributions ranging from clustered to random to periodic can be obtained by adjusting the model parameters governing the scatterer’s density and ‘‘regularity.’’ It is shown that the amplitude statistics of the coherently detected speckle pattern of a collection of scatterers described by the model may be either Rayleigh or non-Rayleigh, and that it is possible to generate the special cases of Rician, K, and homodyned-K pdf’s through various settings of the regularity parameters. The model’s second-order properties are known and can be varied, eliminating the need to incorporate nonstochastic variations into the random-walk models.
‘‘Through the sensor’’ environmental estimation
Authors: Smith George B.
Published: July 2002

Classification of an echo at tactical ranges in a shallow-water environment is made difficult by dynamic shallow-water multipath. Stable deconvolution (or other) techniques can adapt the processing to the environment if reasonable and dynamic estimates of the environmental impulse response can be obtained. Technology that obtains real-time environmental impulse responses directly from the data record being analyzed acoustically is called ‘‘through the sensor environmental estimation.’’ This work develops a new technique to be added to the already existing arsenal of ‘‘through the sensor’’ techniques and is meant to complement the already-existing technology. This technique uses the ambient noise field and the fact that spatial diversity of the noise sources results in uncorrelated modes. As a consequence of this, the depth modal eigenfunctions for the waveguide can be obtained directly from an eigenvector decomposition of the data spatial covariance matrix, and the wave numbers can be obtained from beamforming these eigenfunctions. The estimated environment is tested here with passive matched-field simulations with limited success and with active matched-filter and biosonar simulations. [This work was supported by the Office of Naval Research. Technical management was provided by the Naval Research Laboratory, Stennis Space Center, Mississippi.]
Factors influencing perceived listening quality in university classrooms
Authors: Hodgson Murray R. , Kennedy Susan M.
Published: July 2002

The speech transmission index (STI) can be used to describe acoustical quality in classrooms. The objective of the work reported here was to establish the relationship between STI and user subjective perception of the listening environment by studying thirty university classrooms. STI measurements were made in these rooms when unoccupied. A questionnaire was developed to create a summary measure of perceived listening quality (PLQ) and to enquire about user-related factors that could affect PLQ. The questionnaire was administered to over 5700 students in 107 classes in the 30 rooms. Preliminary results suggest that the main factors contributing to increased PLQ are the perceived instructor speech level, the perceived quality of the classroom air and lighting, the proportion of time that the instructor speaks toward the audience, and the ‘‘unoccupied’’ STI. Use of a speech-reinforcement system reduced PLQ. [See NOISE-CON Proceedings for full paper.]
A virtual sound level meter for use in acoustics distance education
Authors: Capone Dean E. , Lauchle Gerald C.
Published: July 2002

A virtual sound level meter has been designed using the LabVIEW■ programming language for use in a CD/ROM-based distance education course, developed and taught by instructors from the Penn State Graduate Program in Acoustics. The purpose of the virtual instrument is to reinforce concepts presented in the lectures by providing students hands-on experience in applying the principles. The meter was designed using ANSI standard S1.4, Specification for Sound Level Meters. All of the functionality prescribed by standard S1.4 is incorporated in the virtual sound level meter. As a signal input the user can specify the frequency and magnitude of a number of deterministic signals, such as a sine wave. Uniform or Gaussian random noise of a user selected magnitude can then be added to the deterministic signal. The student can apply various weightings, third-octave filters, and integration times to the signals. The raw time series, filtered time series, and calculated SPL are displayed on the front panel of the virtual instrument allowing the student to visualize the original signal and the results of the signal conditioning.
Phase relations in the lip reed flow controller
Authors: Hoekje P. L.
Published: July 2002

Recent research into the mechanism of the lip reed flow controller provide stroboscopic confirmation [Copley and Strong, J. Acoust. Soc. Am. 99, 1219–1226 (1996)] and theoretical support [Adachi and Sato, J. Acoust. Soc. Am. 99, 1200–1209 (1996)] of the two-dimensional model of lip motion. In this model the lips undergo a rotary motion in which the phase difference between the (upper) lip’s upward and outward components may shift in a manner that favors self-sustained oscillation near the impedance peaks of the air column. In the present work, the pressure difference p across the lips and the flow u into the instrument are estimated from measurements of pressures pu and pd upstream and downstream of the lips and the input impedance Zd of the instrument. The measured relations between p and u are consistent with the predictions of the two-dimensional model, and in particular illustrate how the brass player is able to vary the blown frequency both above and below the impedance maximum of a given mode. [Work supported by the Carver Foundation and a UNI Graduate College Project Grant.]
Internal sound field of vibrating trombone bell
Authors: Morrison Andrew , Hoekje P. L.
Published: July 2002

Many of the vibration patterns of a free trombone bell show rotational symmetry, with equal numbers of oppositely moving anti-node regions of equal size. Thus it is predicted that the acoustic sources due to these patterns will cancel, particularly at low frequencies, resulting in little or no net coupling between the body vibrations and the air. This has implications for both the radiated field and the acoustic response of the instrument as seen by the player. An isolated trombone bell was driven at certain of its structural resonance frequencies by attaching a magnet chip and exciting with a solenoid carrying an oscillating current. The resulting acoustic field was probed with a miniature microphone throughout the bell. For each structural mode, the acoustic field pattern was also compared with the corresponding structural vibration pattern imaged with holographic interferometry. The results show acoustic short circuiting between adjacent anti-nodes of the structure, as expected, contributing little bell-to-air coupling. However, there are also significant asymmetries in the acoustic field that do not result in cancellation, and therefore can produce increased signals in the radiated field, as well as at remote regions in the bore. [Research supported by a UNI College of Natural Sciences SOAR grant.]
Oscillations of a water drop with surfactant Triton X-100 in zero gravity
Authors: Chen Xiaohui , Tian Yuren , Jankovsky Joe , Apfel Robert , Shi William Tao
Published: July 2002

Large amplitude nonlinear oscillations of an axially symmetric water drop of 2.51-cm diameter, initial aspect ratio 3.4, with surfactant Triton X-100 of 0.5 mM, in zero gravity are studied by a boundary element method. Included in the analysis are surface-shear and dilatational viscos- ity, under the assumption that the shear viscosity of the bulk phase is small. Numerical simulations of the drop oscillations are in good agreement with the experimental results of drop oscillations measured in space during the second United States Microgravity Laboratory, USML-2. The evolution of the drop oscillations for both experiment and simulation is given. The simulation provides predictions for the values of both surface dilatational viscosity and shear viscosity of 0.20 sp and 0.10 sp, respectively. In addition, with the simulated data, the damping constants, frequencies, and decomposed oscillation modes are computed. [Work supported by NASA through JPL, Contract No. 958722.]
Improved active stabilization of capillary bridges using acoustic radiation pressure and dynamics of a breaking bridge
Authors: Marr-Lyon Mark J. , Thiessen David B. , Marston Philip L.
Published: July 2002

Liquid bridges between two solid surfaces have applications in low gravity, such as the solidification of floating zones. Long bridges naturally become unstable to a symmetric mode by bulging near one end while the opposite end thins. For a cylindrical bridge of radius R and length L, the slenderness S=L/2R has a natural (Rayleigh) limit of π beyond which the bridge breaks. Using acoustic radiation pressure in simulated low gravity as described previously [J. Acoust. Soc. Am. 99, 2540 (1996)], stable bridges significantly beyond the Rayleigh limit can be produced. Improvements in the acoustics, optics, and electronics have enabled stabilization of bridges with S as large as 4.3. To be useful in low gravity, this technique will have to be modified to work on liquid bridges in air. Currently, acoustic resonators in air that have the required property that the sound amplitude can be spatially redistributed rapidly are being investigated. The laboratory experiments with simulated low gravity have made it possible to observe the dynamics of a breaking super-long bridge. [Work supported by NASA.]
Encoding of amplitude modulation in the peripheral auditory system
Authors: Joris Philip X. , Yin Tom C. T.
Published: July 2002

Auditory-nerve fibers synchronize to the envelope of SAM stimuli over a wide range of modulation parameters. Synchronization is found at all characteristic frequencies and shows moderate gain differences between fibers of different spontaneous rate. Modulation transfer functions are uniformly low pass, with an upper frequency limit that systematically increases with characteristic frequency. As expected, envelope phase locking in bushy cells of the anteroventral cochlear nucleus is nervelike, but marked transformations occur in other cell classes. Phase-locking gain is very high in onset cells in posteroventral cochlear nucleus. High gains are also seen in the dorsal cochlear nucleus; however, small changes in stimulus parameters often result in large changes in gain and phase. In general, it is unclear whether high gains are functionally significant, or rather a mere reflection of the transient response properties of cells. There is evidence for the latter in one class of high-gain cell. Effects of modulation on average rate are small in the auditory nerve, but can be large in cochlear nucleus and, with binaural stimulation, in the olivary complex. The lateral superior olive and its bushy cell afferents provide an example of a circuit in which temporal envelope information is converted into average rate changes. [Work supported by NIDCD.]
Spatial statistics of plate vibration modes with irregular boundary conditions
Authors: Bakker Michael J. , DeJong Richard G.
Published: July 2002

The spatial statistics of several resonant bending modes in an irregularly shaped flat plate have been measured experimentally and calculated in a finite element model. The variations due to changes in the boundary conditions have also been included. The spatial statistics for one boundary condition are essentially the same as the statistics obtained over random variations in the boundary conditions. This is consistent with an ergodic model for the vibration pattern in an irregular plate in that one realization of the plate boundary condition represents the same statistics as the ensemble over varying boundary conditions.
Moment method formulation for piezoceramic plate vibrations
Authors: Dökmeci M. Cengiz , Altay G. Aşkar
Published: July 2002

Presented herein is a numerical algorithm based on the method of moments that has been used recently in structural electroelastic elements [e.g., M. C. Dökmeci and G. A. Altay, Z. angew. Math. Mech. 77, 1–17 (1997) and references therein] in order to predict the dynamic response of a piezoceramic plate. The piezoceramic plate of uniform thickness is coated completely with very thin perfectly conducting electrodes on and under an electric potential applied to its faces. In the first part of the paper, the two-dimensional equations for the piezoceramic plate are derived in both variational and differential forms by use of the differential variational principle [M. C. Dökmeci and G. A. Altay, Int. J. Eng. Sci. 34(7), 769–782 (1996)] together with a series expansion of the field variables. In the second part, the method of moments [M. C. Dökmeci, Proceedings of the 1992 Ultrasonics Symposium (IEEE, New York, 1992), pp. 1025–1028] is described for the dynamic response. The significant mechanical and electrical effects are all taken into account. The equations derived accommodate all the types of motions as well as coupled motions of the piezoceramic plate. In the third part, attention is focused on certain cases involving special geometry, motions, and polarization directions of the piezoceramic plate. [Work supported in part by TÜBA.]
Measurement of typical speech and background noise levels in university classrooms during lectures
Authors: Hodgson Murray R. , Rempel Rod
Published: July 2002

A measurement system has been developed for determining typical long-term speech and background noise levels in university classrooms during lectures. A particular objective was to determine typical levels of student activity noise. A total of 18 lectures were recorded at up to four positions in 14 classrooms. These recordings were digitized and filtered using digital octave-band and A-weighting filters. Software processed the resulting pressure time histories as follows: The signals were squared; short-term mean-square pressures were calculated; sound-pressure levels were calculated; sound-pressure-level frequency distributions were determined and plotted; and the resulting distributions were fitted by one, two, or three normal-distribution curves to identify peaks. Three curves generally gave the best fit. The levels of the peaks so identified were associated with speech, student activity, and background noise levels. The corresponding values were determined for each test case; the results are summarized and conclusions are drawn.
Considerations in loudspeaker system directivity and power response
Authors: Forsythe Kenton G. , Gunness David , Rocha Jeff
Published: July 2002

The influence of power response of a loudspeaker system on sound quality and intelligibility is an often overlooked aspect of a speaker system’s performance. This paper will examine the importance of achieving uniformly predictable power response and directivity and the factors leading to a successful design. Traditional axial response, beamwidth, and directivity plots fail to convey a complete information set. Data sets from traditional and recent designs will be compared to demonstrate the important factors and the means of identifying them in proposed products. This will be examined for a range of loudspeaker system sizes and applications.
The DTC loudspeaker
Authors: Weinreich Gabriel
Published: July 2002

The property of ‘‘directional tone color,’’ especially characteristic of a violin [G. Weinreich, J. Acoust. Soc. Am. 101 (to be published)], consists of a directional radiation pattern which is a very strong function both of angle and of frequency. This can produce the illusion that each note (in fact, each harmonic of each note) is coming from a different direction, confusing the common psychoacoustic cues and endowing the sound with a specially striking spatial sense. A loudspeaker has been constructed in which a single driver drives four pipes of different lengths, with their mouths forming a three-dimensional pattern of roughly 20-cm spacing. This produces four sources whose phases vary rapidly with frequency, and which interfere with each other so as to produce the type of pattern desired. The result (which will be demonstrated), when driven by a monophonic signal, appears to ‘‘fill space’’ more strikingly than many stereo systems. The paper will also discuss other ways in which the effect might be produced (for example, by using a number of drivers with varying signal delays), various applications (in particular, for pipe organ music), and implications for the way in which stereo music is perceived. [Work supported by NSF.]