bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous display of all the Fresnel diffraction patterns of one-dimensional apertures
Authors: Furlan Walter D. , Saavedra Genaro , Granieri Sergio
Published: July 2002

An optical setup is implemented for observation and analysis of diffraction phenomena. The device provides a two-dimensional ordered continuous display of all the diffraction patterns of any one-dimensional signal. This result allows a direct comparison between the observed light intensity and the prediction of diffraction theory, both in the near-field and the far-field regions. The arrangement is built with conventional laboratory optical components plus a single ophthalmic progressive lens. Experimental results for typical diffracting apertures are shown.
Quantitative experiments in electric and fluid flow field mapping
Authors: Young Richard A.
Published: July 2002

A system employing a voltage probe attached to an XY recorder is used to sample the electrical potential over a grid of points on conducting paper. Using commercial plotting software, the three-dimensional (3D) perspective of the potential (or equipotential contour lines) may then be displayed as a function of position. The charge density and the associated electric field are obtained by direct numerical differentiation of the potential data, and charge densities are displayed in a 3D perspective to reveal their spatial variation. Experimental results for screening and image charge densities on conductors are in excellent agreement with theoretical predictions obtained using conformal mapping methods. In addition, by exploiting the analogy between electric fields and fluid flow, the experimental system may also be used to model two-dimensional fluid dynamics. In this context, results for the velocity profile and the pressure distribution surrounding a wing moving through a fluid are presented.
Resource Letter: MesP-1: Mesoscopic physics
Authors: Glazman L. I.
Published: July 2002

This Resource Letter provides a guide to the literature on mesoscopic electron physics of solids. Journal articles, conference proceedings, and books are cited for the following topics: conductance fluctuations in disordered and quantum-chaotic systems, conductance quantization, conduction of a Luttinger liquid, electron noise in mesoscopic devices, mesoscopic superconductivity, electron–electron interactions in mesoscopic systems and the Coulomb blockade phenomenon, and Kondo effect in quantum dots.
The missing wave momentum mystery
Authors: Rowland David R. , Pask Colin
Published: July 2002

The usual suggestion for the longitudinally propagating momentum carried by a transverse wave on a string is shown to lead to paradoxes. Numerical simulations provide clues for resolving these paradoxes. The usual formula for wave momentum should be changed by a factor of 2 and the involvement of the cogenerated longitudinal waves is shown to be of crucial importance.
Measurement of air resistance on an air track
Authors: Andereck Barbara S.
Published: July 2002

An extension of a standard air track experiment is described in which the effects of air resistance can be studied. A circular disk is placed on one end of an air track cart to provide air drag. The data analysis consists of subtracting the “ideal” velocity for a frictionless situation from the measured velocity and plotting the difference as a function of the ideal velocity. The resulting curve is fitted with a modified power-law and the coefficient of the cubic term is studied as a function of the area of the disk, a behavior that can be predicted theoretically. Frictional effects in addition to the air drag on the disk were found to be significant and were accounted for.
Brightness and color of rapidly moving objects: The visual appearance of a large sphere revisited
Authors: Kraus U.
Published: July 2002

An object at relativistic speed is seen as both rotated and distorted when it is large or close by so that it subtends a large solid angle. This is a consequence of the aberration effect and is obtained by purely geometric considerations. In this paper it is pointed out and illustrated that a photorealistic image of such an object would actually be dominated by the Doppler and searchlight effects, which would be so prominent as to render the geometric apparent shape effectively invisible.
Measurements and mechanisms of Thomson’s jumping ring
Authors: Tjossem Paul J. H. , Cornejo Victor
Published: July 2002

Measurements of the phase delay of the current and force on a ring floated on a commonly available Thomson’s jumping ring apparatus were performed for phase angles from 12° to 88°. The force and phase data show excellent agreement with a linear inductive model. We find that the demonstration, as usually performed with large highly conducting rings, operates in the inductance-dominated regime at 60-Hz line frequency. Stroboscopic photographs of the jumping ring, for both room-temperature and 78-K rings, confirm that the same time-averaged inductive phase lag mechanism, not an electrical transient, accounts for the jump height. We introduce a simple room-temperature demonstration that illustrates the importance of the phase lag: Despite its greater weight, a stack of thin rings will float higher than a single ring as the inductive phase lag comes to dominate the parallel resistance of the combined rings.
Newton’s absolute time and space in general relativity
Authors: Gautreau Ronald
Published: July 2002

I describe a reference system in a spherically symmetric gravitational field that is built around times recorded by radially moving geodesic clocks. The geodesic time coordinate t and the curvature spatial radial coordinate R result in spacetime descriptions of the motion of the geodesic clocks that are exactly identical with equations following from Newton’s absolute time and space used with his inverse square law. I show how to use the resulting Newtonian/general-relativistic equations for geodesic clocks to generate exact relativistic metric forms in terms of the coordinates (R,t). Newtonian theory does not describe light. However, the motion of light can be determined from the (R,t) general-relativistic metric forms obtained from Newtonian theory by setting ds2(R,t)=0. In this sense, a theory of light can be related to absolute time and space of Newtonian gravitational theory. I illustrate the (R,t) methodology by first solving the equations that result from a Newtonian picture and then examining the exact metric forms for the general-relativistic problems of the Schwarzschild field, gravitational collapse and expansion of a zero-pressure perfect fluid, and zero-pressure big-bang cosmology. I also briefly describe other applications of the Newtonian/general-relativistic formulation to: embedding a Schwarzschild mass into cosmology; continuously following an expanding universe from radiation to matter domination; Dirac’s Large Numbers hypothesis; the incompleteness of Kruskal–Szekeres spacetime; double valuedness in cosmology; and the de Sitter universe.
Neutron activation analysis of a penny
Authors: Stevens Richard E.
Published: July 2002

Neutron activation analysis has been used for many years as an analysis tool and as an educational tool to teach students about nuclear properties. This article presents an exercise in the neutron activation analysis of a penny which, due to the simplicity of the resulting gamma-ray spectra, is appropriate for general physics classes. Students express a great deal of interest both in seeing the reactor in use as well as determining the composition of something that is familiar to them.
The magnetic field of current-carrying polygons: An application of vector field rotations
Authors: Grivich Matthew I. , Jackson David P.
Published: July 2002

We calculate the magnetic field around a current loop consisting of a regular N-sided polygon by successively rotating the field obtained from a straight, finite, current-carrying wire. This involves developing and applying a vector field rotation operator, which transforms vector fields the way a rotation matrix transforms scalar fields. Using this result, we explore the various magnetic field components about the current loop and notice an interesting structure that results from the geometry of the polygons. The magnetic field on the axis of the current loop as well as the field at all points around a circular loop are considered as limiting cases.
What quantum mechanics is trying to tell us
Authors: Mohrhoff Ulrich
Published: July 2002

This article presents a novel interpretation of quantum mechanics. It extends the meaning of “measurement” to include all property-indicating facts. Intrinsically, space is undifferentiated: There are no points on which a world of locally instantiated physical properties could be built. Instead, reality is built on facts, in the sense that the properties of things are extrinsic, or supervenient on property-indicating facts. The actual extent to which the world is spatially and temporally differentiated (that is, the extent to which spatiotemporal relations and distinctions are warranted by the facts) is necessarily limited. Notwithstanding that the state vector does nothing but assign probabilities, quantum mechanics affords a complete understanding of the actual world. If there is anything that is incomplete, it is the actual world, but its incompleteness exists only in relation to a conceptual framework that is more detailed than the actual world. Two deep-seated misconceptions are responsible for the interpretational difficulties associated with quantum mechanics: the notion that the spatial and temporal aspects of the world are adequately represented by sets with the cardinality of the real numbers, and the notion of an instantaneous state that evolves in time. The latter is an unwarranted (in fact, incoherent) projection of our apparent “motion in time” into the world of physics. Equally unwarranted, at bottom, is the use of causal concepts. There nevertheless exists a “classical” domain in which language suggestive of nomological necessity may be used. Quantum mechanics not only is strictly consistent with the existence of this domain but also presupposes it in several ways.
A noninvasive method for estimating acoustic admittance at the tympanic membrane
Authors: Huang Gregory T. , Rosowski John J. , Puria Sunil , Peake William T.
Published: July 2002

The acoustic admittance at the tympanic membrane (TM), YTM, describes the linear acoustic properties of the ear. Here, a noninvasive measurement procedure is developed for estimating YTM in intact ears. The method consists of (1) measuring the admittance in the ear canal YEC with a commercially available earphone-and-microphone system, and (2) estimating YTM via a uniform-tube approximation of the space between the measurement point and the TM. The dimensions of this space are estimated from YEC via an area-estimation algorithm [Keefe et al., J. Acoust. Soc. Am. 91, 470 (1992)] and measurements made with controlled static pressures in the canal. Measurements in artificial loads are used to test the accuracy of the measurement system and to determine sources of error. For accurate admittance measurements: (1) extension of the microphone tube medially beyond the earphone’s port is necessary for frequencies above 2 kHz; (2) the acoustic system must be calibrated in known loads with diameters within 15% of the canal diameter, because the source’s output characteristics vary with load diameter. The method is applied to intact ears of anesthetized domestic cats; for frequencies below 5 kHz, the estimated YTM in four ears have features that are similar to those of previous measurements made at the cat TM. Sources of error include nonuniform waves generated at the earphone’s narrow port, inaccuracy in estimation of canal dimensions, irregular geometry of the canal, and earphone-microphone cross talk.
Measurements of anisotropic sound propagation in glass wool
Authors: Tarnow Viggo
Published: July 2002

The attenuation coefficient and phase velocity of plane sound waves propagating in three perpendicular directions in glass wool were measured in the frequency range 50–10 000 Hz. For glass wool of mass density 14 kg/m3 at the frequency 1000 Hz, the attenuation constant for propagation perpendicular to the glass wool sheets was 75 dB/m, and for propagation parallel with the sheets 57 dB/m. For mass density 30 kg/m3, the corresponding numbers were 140 and 100 dB/m. The measured values were compared with calculated ones taking into account the movements of the fiber skeleton. The calculations need the elastic moduli, which were measured. For density 14 kg/m3 and deformation perpendicular to the glass wool sheets, the static modulus was 2.0 kPa, and for parallel deformation 120 kPa. The corresponding numbers for mass density 30 kg/m3 were 16 and 390 kPa.
A variational method for identification of viscoelastic parameters from experimental data
Authors: Di Meglio Alberto , Wang Lian Sheng
Published: July 2002

An identification method based on a variational algorithm is proposed for the determination of the viscoelastic properties of plates from a set of experimental data. A pulse-transmission configuration with parametric sources is used for the experimental measurements, whereby two electrically mixed high-frequency pulses are combined to generate a low-frequency, narrow-beam signal to minimize the edge-diffraction effect from a finite-sized panel. The variational method is based on an optimization technique adapted from an approach normally used in dynamics for the identification of motion parameters. The fluid–panel–fluid system is initially represented by a transmission matrix model. The model and the known experimental data are then used to build an optimization functional to be minimized by means of a collocation method based on the Hamilton principle analogy. The plate viscoelastic parameters are then calculated by application of well-established numerical procedures to the resulting set of integral-differential equations.
Low-frequency scattering of acoustic waves by a bounded rough surface in a half-plane
Authors: Sabina F. J. , Babich V. M.
Published: July 2002

The problem of the scattering of harmonic plane waves by a rough half-plane is studied here. The surface roughness is finite. The slope of the irregularity is taken as arbitrary. Two boundary conditions are considered, those of Dirichlet and Neumann. An asymptotic solution is obtained, when the wavelength λ of the incident wave is much larger than the characteristic length of the roughness l, by means of the method of matched asymptotic expansions in terms of the small parameter ε=2πl/λ. For the Dirichlet problem, the solution of the near and far fields is obtained up to O(ε2). The far field solution is given in terms of a coefficient that have a simple explicit expression, which also appears in the corresponding solution to the Neumann problem, already solved. Also the scattering cross section is given by simple formulas to O(ε3). It is noted that, for the Dirichlet problem, the leading term is of order ε3 which, by contrast, is different from that of the circular cylinder in full space, that is, of order ε−1 (log ε)−2. Some examples display the simplicity of the general results based on conformal mapping, which involve arcs of circle, polygonal lines, surface cracks and the like.
Audio-visual enhancement of speech in noise
Authors: Girin Laurent , Schwartz Jean-Luc , Feng Gang
Published: July 2002

A key problem for telecommunication or human–machine communication systems concerns speech enhancement in noise. In this domain, a certain number of techniques exist, all of them based on an acoustic-only approach—that is, the processing of the audio corrupted signal using audio information (from the corrupted signal only or additive audio information). In this paper, an audio-visual approach to the problem is considered, since it has been demonstrated in several studies that viewing the speaker’s face improves message intelligibility, especially in noisy environments. A speech enhancement prototype system that takes advantage of visual inputs is developed. A filtering process approach is proposed that uses enhancement filters estimated with the help of lip shape information. The estimation process is based on linear regression or simple neural networks using a training corpus. A set of experiments assessed by Gaussian classification and perceptual tests demonstrates that it is indeed possible to enhance simple stimuli (vowel-plosive-vowel sequences) embedded in white Gaussian noise.
Verifying a vocal tract model with a closed side-branch
Authors: Jackson Michel Tah-Tung , Espy-Wilson Carol , Boyce Suzanne E.
Published: July 2002

In this article an implementation of a vocal tract model and its validation are described. The model uses a transmission line model to calculate pole and zero frequencies for a vocal tract with a closed side-branch such as a sublingual cavity. In the validation study calculated pole and zero frequencies from the model are compared with frequencies estimated using elementary acoustic formulas for a variety of vocal tract configurations.
An efficient formulation of Krylov’s prediction model for train induced vibrations based on the dynamic reciprocity theorem
Authors: Degrande Geert , Lombaert Geert
Published: July 2002

In Krylov’s analytical prediction model, the free field vibration response during the passage of a train is written as the superposition of the effect of all sleeper forces, using Lamb’s approximate solution for the Green’s function of a halfspace. When this formulation is extended with the Green’s functions of a layered soil, considerable computational effort is required if these Green’s functions are needed in a wide range of source–receiver distances and frequencies. It is demonstrated in this paper how the free field response can alternatively be computed, using the dynamic reciprocity theorem, applied to moving loads. The formulation is based on the response of the soil due to the moving load distribution for a single axle load. The equations are written in the wave-number-frequency domain, accounting for the invariance of the geometry in the direction of the track. The approach allows for a very efficient calculation of the free field vibration response, distinguishing the quasistatic contribution from the effect of the sleeper passage frequency and its higher harmonics. The methodology is validated by means of in situ vibration measurements during the passage of a Thalys high-speed train on the track between Brussels and Paris. It is shown that the model has good predictive capabilities in the near field at low and high frequencies, but underestimates the response in the midfrequency band.
Minimum spectral contrast needed for vowel identification by normal hearing and cochlear implant listeners
Authors: Loizou Philipos C. , Poroy Oguz
Published: July 2002

The minimum spectral contrast needed for vowel identification by normal-hearing and cochlear implant listeners was determined in this study. In experiment 1, a spectral modification algorithm was used that manipulated the channel amplitudes extracted from a 6-channel continuous interleaved sampling (CIS) processor to have a 1–10 dB spectral contrast. The spectrally modified amplitudes of eight natural vowels were presented to six Med-El/CIS-link users for identification. Results showed that subjects required a 4–6 dB contrast to identify vowels with relatively high accuracy. A 4–6 dB contrast was needed independent of the individual subject’s dynamic range (range 9–28 dB). Some cochlear implant (CI) users obtained significantly higher scores with vowels enhanced to 6 dB contrast compared to the original, unenhanced vowels, suggesting that spectral contrast enhancement can improve the vowel identification scores for some CI users. To determine whether the minimum spectral contrast needed for vowel identification was dependent on spectral resolution (number of channels available), vowels were processed in experiment 2 through n (n=4,6,8,12) channels, and synthesized as a linear combination of n sine waves with amplitudes manipulated to have a 1–20 dB spectral contrast. For vowels processed through 4 channels, normal-hearing listeners needed a 6 dB contrast, for 6 and 8 channels a 4 dB contrast was needed, consistent with our findings with CI listeners, and for 12 channels a 1 dB contrast was sufficient to achieve high accuracy (>80%). The above-mentioned findings with normal-hearing listeners suggest that when the spectral resolution is poor, a larger spectral contrast is needed for vowel identification. Conversely, when the spectral resolution is fine, a small spectral contrast (1 dB) is sufficient. The high identification score (82%) achieved with 1 dB contrast was significantly higher than any of the scores reported in the literature using synthetic vowels, and this can be attributed to the fact that we used natural vowels which contained duration and spectral cues (e.g., formant movements) present in fluent speech. The outcomes of experiments 1 and 2, taken together, suggest that CI listeners need a larger spectral contrast (4–6 dB) than normal-hearing listeners to achieve high recognition accuracy, not because of the limited dynamic range, but because of the limited spectral resolution.
Polynomial relations for quasi-static mechanical characterization of isotropic poroelastic materials
Authors: Langlois Christian , Panneton Raymond , Atalla Noureddine
Published: July 2002

This paper proposes a quasi-static method for the characterization of the elastic properties of poroelastic materials. The method is based on the development of polynomial relations among compression stiffness, Young’s modulus, Poisson’s ratio, and shape factor derived from high order axisymmetrical finite element simulations on a disk-shaped poroelastic sample under static compression. The shape factor is defined as half the radius to thickness ratio of the sample. The polynomial relations account for the fact that the disk sample “wants” to bulge sideways when compressed between two rigid plates on which it is bonded. A compression test setup is used to measure the compression stiffness of two disk samples of different large shape factors. The measured stiffnesses together with the polynomial relations lead to a system of two equations and two unknowns. The solution of the system yields the Young’s modulus and Poisson’s ratio of the poroelastic material. Employing the proposed quasi-static method, Young’s modulus, Poisson’s ratio, and loss factor are measured for a poroelastic foam. The measured elastic properties are used in the Biot poroelasticity theory to predict the sound absorption coefficient of the foam. The prediction is finally compared with a standing wave tube measurement. A good correlation is obtained.
Modal degeneracy in square wave guides
Authors: McCartin Brian J.
Published: July 2002

Issues relating to modal degeneracy in a square wave guide are herein treated. Specifically, it is determined precisely which cutoff frequencies can be present, the multiplicity of each such frequency is ascertained, and a procedure is developed which provides a prescription for finding all the modes associated with each of these frequencies. As an added dividend, we characterize the family of harmonic series into which these frequencies naturally assemble. Just enough of the requisite number theory is included to make this account reasonably self-contained.
Intensity-importance functions for bandlimited monosyllabic words
Authors: Studebaker Gerald A. , Sherbecoe Robert L.
Published: July 2002

A study was carried out to determine the relative importance to speech intelligibility of different intensities within the speech dynamic range. The functions that were derived are analogous to previous descriptions of the relative importance of different frequencies and are referred to here as intensity-importance functions (IIFs). They were obtained as follows. Sharply filtered bands of speech (NU6 monosyllabic words) were mixed with filtered noise and presented alone or in pairs at 19 signal-to-noise ratios (−25 to 41 dB). When paired bands were tested, the level and signal-to-noise ratio (SNR) of one band were held constant while the level and SNR of the other band were varied. The listeners were 100 normal hearers, organized into five 20-person groups. Each group provided speech recognition data for one of five frequency regions (141–562, 562–1122, 1122–1778, 1778–2818, and 2818–8913 Hz). Comparisons of the results for each group indicated that IIFs vary with frequency and SNR. Current methods for predicting intelligibility from physical measurements of speech audibility would need to be revised in order to take such findings into consideration.
Investigations of sound waves generated by the Hall effect in electrolytes
Authors: Campanella Angelo J.
Published: July 2002

Electrolyte ions moving in a magnetic field produce a velocity component transverse to the electric and magnetic fields. This phenomenon can be alternatively termed as the Hall effect, a magnetohydrodynamic transducer, or a liquid-state electromagnetic transducer. In electrolytes, the viscous drag of the electrolyte fluid is dominant, so the ion deflection soon reaches a terminal velocity dependent only on the electric field strength. The alternating velocity component transverse to the electric and magnetic fields produces a pressure wave due to the viscous drag of the fluid on the ions. Acoustic waves of very high frequencies can be produced since the mass of an ion is very small. Theory for this method of generating sound waves by ultrahigh frequency (UHF) electromagnetic wave impinging on a conducting medium in a magnetic field, causing a conduction current to flow near the surface (skin effect), is presented. Experiments were performed in an electrolyte at frequencies from 8 kHz to 1 MHz to study the effects of electrode size, ionic mobility, and ionic concentration. In the reciprocal effect, ions moving en masse with the particle velocity of a passing acoustic wave induce an alternating voltage between a pair of electrodes in a transverse magnetic field.
Efficiency, accuracy, and stability issues in discrete-time simulations of single reed wind instruments
Authors: Avanzini Federico , Rocchesso Davide
Published: July 2002

A quantitative study of discrete-time simulations for a single reed physical model is presented. It is shown that when the continuous-time model is discretized, a delay-free path is generated in the computation. A general solution is proposed to this problem, that amounts to operating a geometrical transformation on the equations. The transformed equations are discretized using four different numerical methods. Stability properties of each method are assessed through analysis in the frequency domain. By comparing the discrete and continuous frequency responses, it is studied how the physical parameters are mapped by each method into the discrete-time domain. Time-domain simulations are developed by coupling the four digital reeds to an idealized bore model. Quantitative analysis of the simulations shows that the discrete-time systems produced by the four methods have significantly different behaviors, even when high sampling rates are used. As a result of this study, a general scheme for accurate and efficient time-domain simulations of the single reed model is proposed.
Characterizing holes in duct walls using resonance frequencies
Authors: de Salis M. H. F. , Movchan N. V. , Oldham D. J.
Published: July 2002

The current paper demonstrates that the technique recently used by de Salis and Oldham for the sizing and location of blockages in ducts using resonance and antiresonance value shifts [J. Sound Vib. 221(1), 180–186 (1999)] may be successfully applied to the detection, location, and sizing of small holes in duct walls. It is shown that when the blockage area function reconstruction process is applied using resonance and antiresonance frequencies determined from a single measurement of sound pressure within a duct, the position of a hole in the duct wall is revealed as the beginning of an apparent gradual expansion. This expansion is termed the effective expansion function and emanates from an initial positive dc shift. Once the hole has been located, a simple impedance model of the duct incorporating the hole location and the measured wave number at the first-order duct resonance may be derived which allows the determination of the radius of the side hole from a simple quadratic equation. This hole-sizing technique is also successfully applied to thin slits in duct walls using an equivalent radius approach, and is shown to be highly accurate for slit-shaped holes with cross-sectional length to width aspect ratios of up to 28:1.
Reflection of drill-string extensional waves at the bit-rock contact
Authors: Poletto Flavio , Malusa Massimo
Published: July 2002

Downward propagating extensional waves are partially reflected at the bit-rock contact. The evaluation of the reflection coefficient is important to obtain while drilling information about the acoustic properties of the formations. The scope of this work is to estimate the bit-rock reflection coefficient, assuming a flat drill bit in perfect contact with the formation. Using the low-frequency approximation, which holds when the wavelength is much larger than the lateral dimensions of the borehole, the drill-string is assumed to be a laterally free rod, and the formation an homogeneous and isotropic medium. This work shows that the reflection coefficient of the extensional waves depends, along with the elastic properties of the formation, on the ratio of the cross sections of the drill-string and borehole. The impedance of the drilled rock can be calculated from the measured reflection coefficient, which is related to the amplitude of waves produced in the string and in the formation by a working drill-bit.
Numerical analysis of dipole sound source around high speed trains
Authors: Takaishi Takehisa , Sagawa Akio , Nagakura Kiyoshi , Maeda Tatsuo
Published: July 2002

As the maximum speed of high speed trains increases, the effect of aeroacoustic noise on the sound level on the ground becomes increasingly important. In this paper, the distribution of dipole sound sources at the bogie section of high speed trains is predicted numerically. The three-dimensional unsteady flow around a train is solved by the large eddy simulation technique. The time history of vortices shows that unstable shear layer separation at the leading edge of the bogie section sheds vortices periodically. These vortices travel downstream while growing to finally impinge upon the trailing edge of the section. The wavelength of sound produced by these vortices is large compared to the representative length of the bogie section, so that the source region can be regarded as acoustically compact. Thus a compact Green’s function adapted to the shape can be used to determine the sound. By coupling the instantaneous flow properties with the compact Green’s function, the distribution of dipole sources is obtained. The results reveal a strong dipole source at the trailing edge of the bogie section where the shape changes greatly and the variation of flow with time is also great. On the other hand, the bottom of the bogie section where the shape does not change, or the leading edge and boundary layer where the variation of flow with time is small, cannot generate a strong dipole source.
Acoustic signal-to-noise ratio for an inclusion beneath a randomly rough surface and in the presence of microstructure
Authors: Bilgen Mehmet , Rose James H.
Published: July 2002

The effects of surface roughness on the signal-to-noise ratio (SNR) for the phase-sensitive detection of an inclusion in a sample with microstructure is explored in a simple model. It is assumed that a phase-sensitive transducer is used in pulse-echo mode, that the sample is immersed in a water bath, and that the noise is dominated by scattering from the sample’s microstructure. Since there is interest in roughness-induced changes in the SNR, calculations are reported of the normalized signal-to-noise ratio (NSNR), i.e., the SNR with the rough surface divided by the SNR with the smooth surface. The dependence of the NSNR on transducer parameters (radius and focal length), on surface parameters (root-mean-square height and autocorrelation length), and on material parameters (scattering strength, average crystalline size) is reported. In this paper, approximate analytic series solutions, previously obtained for the signal and the noise, are combined to estimate the NSNR as a function of the inclusion’s depth beneath the surface. It is found that for unfocused transducers even moderately rough surfaces can substantially degrade the NSNR for the most typical case, a relatively large inclusion in a background of small microcrystallites. The calculations predict two other results that initially surprised us. First, surface roughness is predicted to increase the SNR for a relatively small strongly scattering inclusion in a sample with relatively large but weakly scattering microstructure. Second, moderate roughness is predicted to have little effect on the SNR for focused transducers at the focal depth.
Reflection of a plane sound wave from a semi-infinite periodic transversely isotropic set of layers
Authors: Shenderov Evgeni L.
Published: July 2002

A novel method is presented to calculate the reflection coefficient of sound from a semi-infinite periodic system of elastic layers. Each layer may consist of sublayers, and may be either isotropic, or transversely anisotropic. The reflection coefficient is given in an explicit form for alternating solid and liquid layers at an oblique incidence of a sound wave as well as for all solid layers at normal incidence. For all solid layers at oblique incidence a quadratic matrix equation with respect to the input impedance matrix is obtained. The method of solving this equation and the coefficients of a transfer matrix for transversely isotropic layers are presented in the Appendices. Resonance properties of the system of layers follow from the results of computations of the frequency and angular dependencies.
Meteorology and elephant infrasound at Etosha National Park, Namibia
Authors: Larom David , Garstang Michael , Lindeque Malan , Raspet Richard , Zunckel Mark , Hong Yvonne , Brassel Kevin , O’Beirne Sean , Sokolic Frank
Published: July 2002

Measured vertical profiles of temperature and wind are used to model infrasound propagation over a representative high savanna habitat typically occupied by the African elephant, Loxodonta africana, to predict calling distance and area as a function of the meteorological variables. The profiles were measured up to 300 m above the surface by tethered balloon-borne instruments in Etosha National Park, Namibia, during the late dry season. Continuous local surface layer measurements of wind and temperature at 5 and 10 m provide the context for interpreting the boundary layer profiles. The fast field program (FFP) was used to predict the directionally dependent attenuation of a 15-Hz signal under these measured atmospheric conditions. The attenuation curves are used to estimate elephant infrasonic calling range and calling area. Directionality and calling range are shown to be controlled by the diurnal cycle in wind (shear) and temperature. Low-level nocturnal radiative temperature inversions and low surface wind speeds make the early evening the optimum time for the transmission of low-frequency sound at Etosha, with range at a maximum and directionality at a minimum. As the night progresses, a nocturnal low-level wind maximum (jet) forms, reducing upwind range and calling area. The estimated calling area drops rapidly after sunrise with the destruction of the inversion. Daytime calling areas are usually less than 50 km2, while early evening calling areas frequently exceed 200 km2 and are much less directional. This marked diurnal cycle will be present in any dry savanna climate, with variations due to local topography and climate. Calling range and low-frequency sound propagation cannot be effectively understood without knowledge of meteorological controls.
Background contributions and coupling coefficients for backscattering by thick shells
Authors: Kargl Steven G. , Marston Philip L.
Published: July 2002

Approximations for leaky wave coupling coefficients and background scattering contributions are usually derived by assuming the shell response is governed by thin shell theory. Comparisons are described with approximations derived by other methods for a thick spherical shell at frequencies above coincidence. The variation of the phase of the coupling coefficient from numerical evaluation of the Watson transformation residue by Kargl [Ph.D. thesis, Washington State University (1990)] is evident in an analytical approximation. The phase of the background includes inertial and wave-kinematic contributions and is related to research by Gaunaurd and Werby [J. Acoust. Soc. Am. 90, 2536–2550 (1991)]. The inertial contribution to the background phase is derived directly from the reflectivity of a plate in the limit of small phase shift for propagation across the thickness of the shell. The frequency and angle dependence of the phase of the exact reflection coefficient of a plate (having the same thickness as the shell) is also examined.
A generalized network formulation for acoustic scattering
Authors: Titterton, Jr. Paul J.
Published: July 2002

The discretized Helmholtz and equivalence integral equations yield the impedance representation of a generalized network formulation for acoustic scattering. Trans- and self-impedances relate the ensonification, the scattered field, and the pressure and velocity on the scatterer’s surface, S; the scatterer’s dry impedance loads S. This formulation suggests applying analysis tools from electrical circuit theory: network element abstraction and change of field-variable basis. The scatterer’s wet admittance (impedance) corresponds to the augmented driving point admittance (impedance) from electrical network theory. The lower-branch modes of the scattering from a submerged spherical shell occur when the reactance looking into the fluid from S negates that looking into the shell. Change of basis on S transforms the impedance representation into the admittance, arbitrary-reference, and network-scattering representations. The impedance, admittance, and arbitrary-reference representations naturally separate hard, soft, and intermediate background scattering, respectively. Scattering from passive objects with limited vibrational degrees of freedom is bounded: the lower-branch modes of the submerged spherical shell approach this bound. No bound exists when the vibrational degrees of freedom are unlimited.
The static-dynamic superposition method applied to uniaxial waves in a bi-periodic stack
Authors: El-Raheb Michael
Published: July 2002

The method of El-Raheb [J. Acoust. Soc. Am. 94, 172–184 (1993)] that treats transient uniaxial waves in a weakly coupled bi-periodic stack is modified in the way external force is applied. An inhomogeneous static solution and a homogeneous dynamic solution are superimposed. The modified method accurately predicts stress in the excited layer and converges rapidly with number of terms in the eigenfunction expansion.
Model calculations of the effects of wide-band inhibitors in the dorsal cochlear nucleus
Authors: Reed Michael C. , Blum Jacob J.
Published: July 2002

In two previous papers [Reed and Blum, J. Acoust. Soc. Am. 97, 425–438 (1995), Blum et al., J. Acoust. Soc. Am. 98, 181–191 (1995)] a computational model for signal processing in the dorsal cochlear nucleus (DCN) was developed. In those modelling studies, stellate cells inhibited only type II cells. In this study, the effect of including wide-band inhibitory (WBI) connections from stellate cells to type IV cells, as proposed by Nelken and Young [J. Neurophysiol. 71, 2446–2462 (1994)], is examined. Inclusion of the WBI connections improves the fit to the experimental pure tone response maps for both the “standard”and “non-standard” cells examined by Spirou and Young [J. Neurophysiol. 66, 1750–1768 (1991)]. Thus, these modelling studies support the hypothesis of Nelken and Young [J. Neurophysiol. 71, 2446–2462 (1994)]. The degree of improvement is greatest for cells with prominent upper inhibitory sidebands. The qualitative features of the pure tone response map and the theoretical model allow one to deduce the probable frequency bias of the type II to type IV and stellate to type IV connections.
Specifying spectra for musical scales
Authors: Sethares William A.
Published: July 2002

The sensory consonance and dissonance of musical intervals is dependent on the spectrum of the tones. The dissonance curve gives a measure of this perception over a range of intervals, and a musical scale is said to be related to a sound with a given spectrum if minima of the dissonance curve occur at the scale steps. While it is straightforward to calculate the dissonance curve for a given sound, it is not obvious how to find related spectra for a given scale. This paper introduces a “symbolic method” for constructing related spectra that is applicable to scales built from a small number of successive intervals. The method is applied to specify related spectra for several different tetrachordal scales, including the well-known Pythagorean scale. Mathematical properties of the symbolic system are investigated, and the strengths and weaknesses of the approach are discussed.
Leaky-Rayleigh wave detection at air–solid interfaces by optical heterodyne interferometry
Authors: de Billy Michel , Adler Laszlo , Quentin Gerard
Published: July 2002

Recent developments have proven optical heterodyne interferometry to be a sensitive detector for ultrasonic amplitude and phase measurements in transparent materials. In this letter it is shown that this optical technique is sensitive enough to detect leaky-Rayleigh as well as leaky-Lamb waves in air reradiated from solids in the megaHertz region. Probing the leaky wave field at several positions parallel to the solid surface can yield the Rayleigh wave velocity of both transparent and opaque solids. This method can be used for low optical reflectivity solid surfaces: thus it can be extended for noncontact nondestructive evaluation applications.
Phenomenon of leaky free waves in the modal response of a uniform cylinder
Authors: Maidanik G. , Becker K. J.
Published: July 2002

The phenomenon of leaky free waves in the modal response of a uniform shell is manifest if (1) in the absence of fluid loading the locus of the free waves as a function of frequency crosses from the subsonic region to the supersonic region across the sonic locus and (2) in the presence of fluid loading the fluid surface impedance at and in the vicinity of the sonic locus is high and the introduction of this fluid loading does not, in itself, prevent the free waves of concern from reaching the sonic locus. In this consideration the sonic locus remains fixed relative to the properties of the shell and, therefore, changes in the fluid loading, on a given shell, are induced by changes in the fluid density only. The phenomenon of leaky free waves in the modal response of a uniform cylinder is investigated. It is found that two distinct examples of leaky free waves are manifested. The first is associated with the flexural free waves that reside in a frequency range that lies above the critical frequency with respect to the speed of sound in the fluid, and the second is associated with the curvature free waves that reside in a frequency range that lies below the ring frequency. The phenomenon of leaky free waves in these two examples is computed, displayed, and discussed.
Aeroelastic structural acoustic coupling: Implications on the control of turbulent boundary-layer noise transmission
Authors: Clark Robert L. , Frampton Kenneth D.
Published: July 2002

A method of formulating a model to evaluate the aeroelastic structural acoustic response of a panel subjected to turbulent boundary layer (TBL) noise sources and coupled with full potential flow aerodynamics is presented. Reduced-order models of both the aerodynamics and the structural acoustic coupling are presented such that a state-variable realization of the entire system dynamics can be developed for future active control system design and synthesis with modern and robust control theory. Results from this study demonstrate the importance of including aeroelastic coupling in modeling the structural acoustic response of panels for interior noise control on modern aircraft. At subsonic flow conditions, the aeroelastic coupling serves to increase the transmission loss across the panel with increasing Mach number; however, the power spectrum of the TBL noise source increases with increasing Mach number as well and thus offsets this benefit to some degree. Results from this study also serve to demonstrate that for future analysis of robust stability and performance, variations in the plant dynamics due to variations in flow conditions must be considered in the design of broadband, feedback, active structural acoustic control systems.
Free-mass reciprocity calibration
Authors: Gabrielson Thomas B.
Published: July 2002

A simple method for reciprocity calibration of accelerometers and velocity sensors is presented. The useful frequency range is from about 1 Hz to a kilohertz or more and the method is capable of subpercent accuracy. Calibrations with excitation levels from 1 to 300 mm/s2 (0.1 mg to 0.03 g) were produced in prototype fixtures. The device to be calibrated and two geophones are used in the calibration fixture. Since the geophones are both reciprocal, a direct test of reciprocity can be done prior to the calibration to evaluate the apparatus. In contrast to standard techniques, the method requires only one relatively inexpensive mechanical setup.
Interaction of a slender vortex with a rigid sphere: Dynamics and far-field sound
Authors: Knio Omar M. , Ting Lu , Klein Rupert
Published: July 2002

Interactions between a slender vortex filament and a stationary rigid sphere are analyzed using a vortex element scheme which tracks the motion of the filament centerline. The filament velocity is expressed as the sum of a self-induced velocity and potential velocity due to the presence of the sphere. The self-induced velocity is estimated numerically using a line Biot–Savart integral which is carefully desingularized so as to reflect the correct asymptotic behavior of the core vorticity distribution under the influence of stretching and viscous diffusion. Meanwhile, the potential velocity is evaluated from a recently derived formula, which expresses it as a line integral along the image of the filament centerline in the sphere with regular weight functions. From the far-field behavior of an unsteady vortical flow outside a stationary sphere, formulas for the acoustic far field are obtained. It is shown that the interaction between the slender vortex filament and the sphere generates dipoles and quadrupoles in addition to the quadrupoles generated by the filament alone in space. The strengths and orientations of the dipoles and quadrupoles are completely determined by the time evolution of the weighted first and second moments of vorticity. The formulas are applied to compute the far-field sound generated by the passage of a slender vortex ring over the sphere. Both coaxial and noncoaxial passage events are analyzed in the computations, as well as the effects of initial core size and asymmetric perturbations.
A theoretical formulation of active control eardefenders
Authors: Pan Jiaqiang , Liu Yingshu , Pan Jie
Published: July 2002

This paper is concerned with the analysis and design of a feedback control active eardefender. By using classical control theory, the authors investigated the system stability and robustness of stability, the noise reduction level and its parameter sensitivity, and the working frequency range of the active eardefender. A general method for designing a stable feedback control eardefender is developed. In this theory, a special type of second-order compensator is used to improve the robustness of stability, the noise reduction level and its robustness, and the working area of the active eardefender, particularly at the low-frequency range of interest.