bluuebunny/crossref_metadata_2025 huggingface dataset:
On energy absorption in classical electromagnetism
Authors: Goedecke G. H.
Published: July 2002

Using only classical electromagnetic energy conservation laws and causality, we show that the net average power absorbed by any mechanically isolated illuminated medium in steady state must be zero, but that for linear model media it is nonzero. This contradiction implies that all media must behave inelastically. We also show in general that the average power absorbed at an incident frequency, which is equal to the total taken from an incident wave minus that scattered elastically, is also equal to the average power scattered inelastically plus that carried off mechanically, if any. Finally, we infer that while the conventional linear theory cannot predict the spectral distribution of inelastic scattering, it may be applied as always to predict the propagation, absorption, and elastic scattering of weak illumination in passive media.
The field oscillator approach to classical electrodynamics
Authors: Case William B.
Published: July 2002

The field oscillator approach offers a more transparent view of many features of classical electromagnetic radiation. It also offers a powerful technique for determining the energy radiated from a given combination of conductors, dielectrics, and currents. In this approach, the vector potential is expanded in a complete set of fields which depend only on position and are consistent with the conductors and dielectrics present. The expansion coefficients depend only on time and describe the field oscillators. When the currents are added, one finds that the coefficients obey the equation of the driven harmonic oscillator. This paper is a tutorial presentation of the background of the field oscillator approach along with several examples of its application.
A recursion relation for matrix elements of the quantum bouncer. Comment on “A quantum bouncing ball,” by Julio Gea-Banacloche [Am. J. Phys. 67 (9), 776–782 (1999)]
Authors: Goodmanson David M.
Published: July 2002

This paper describes a recursion relation for matrix elements of the quantum bouncer. The relation provides an exact expression for the normalization integral, and allows recursive calculation of matrix elements of the form 〈n|zp|m〉, where z is the spatial coordinate and |m〉,|n〉 are quantum bouncer eigenstates.
Thermodynamical interpretation of the variational Maxwell theorem in dc circuits
Authors: Pérez José-Philippe
Published: July 2002

We point out a thermodynamic interpretation of the variational Maxwell theorem relative to dc circuits, based on the minimum of the entropy production. We thus complete the interesting pedagogical analysis of D. A. Van Baak in a recent paper concerning the use of variational methods on dc circuits.
Laplace–Runge–Lenz vector for a light ray trajectory in r−1 media
Authors: Rangwala Abbas A. , Kulkarni Vaman H. , Rindani Amishi A.
Published: July 2002

Using the variational formulation of the Fermat principle and exploiting its analogy with the Hamilton principle of mechanics, we introduce an optical Lagrangian to show that the Euler–Lagrange equations result in the ray equation of optics. For a medium with refractive index given by n2(r)=C+2k/r we show that there exists an additional conservation law as in the Kepler problem of mechanics giving the Laplace–Runge–Lenz vector. We consider its two applications: (a) bending of a light ray near a massive star and (b) its bending in a nonmagnetized thermal plasma.
Reinventing the wheel: Hodographic solutions to the Kepler problems
Authors: Derbes David
Published: July 2002

There are two Kepler problems: given the inverse-square law, find the trajectories; or, given Kepler’s laws, find the inverse-square law. Traditionally these problems are solved in the classroom via calculus, but the amount of calculus needed may be prohibitively high for a first-year course. Alternative solutions to the Kepler problems have been discovered, forgotten, and rediscovered for centuries. Many of these employ Hamilton’s hodograph, a graphical representation of an object’s velocity. This article demonstrates hodographic solutions to the Kepler problems, including an algorithm for the construction of parabolic trajectories.
The proper homogeneous Lorentz transformation operator eL=e−ω⋅S−ξ⋅K: Where’s it going, what’s the twist?
Authors: Berk H. L. , Chaicherdsakul K. , Udagawa T.
Published: July 2002

A discussion of the proper homogeneous Lorentz transformation operator eL=exp[−ω⋅S−ξ⋅K] is given where eL transforms coordinates of an observer 𝒪 to those of an observer O′. Two methods of evaluation are presented. The first is based on a dynamical analog. It is shown that the transformation can be evaluated from the set of equations that are identical to the set of equations that determine the four-velocity of a charged particle in response to a combined spatially uniform and temporally constant electric field E and magnetic field B, where E is parallel to ξ and B is antiparallel to ω, and E/B=ξ/ω. The principal difference in the two problems is that in the dynamics problem, the initial conditions for the four-velocity u must satisfy the constraint, uu=1, whereas the inner product of the coordinates acted on by eL can have any real value. In order to evaluate eL, one can then apply the simplifying techniques of transforming to the frame where E is parallel or antiparallel to B, whereupon the transformation eL in this special frame is trivially evaluated. Then we transform back to the original frame. We determine the β and the rotation Ω that results from a successive boost and rotation that the operator eL produces. A second method is based on a direct summation of the power series of the matrix elements of eL that has been used in relativistic quantum theory. The summation is facilitated by observing that the operators J±≡K±iS commute with each other, and can be represented in terms of the Pauli spin matrices. Indeed, we can reduce the Lorentz transformation to the product of spinor operators to give a compact way to compute the elements of the Lorentz operator eL.
Why bows get stiffer and racquets get softer when the strings are added
Authors: Cross Rod
Published: July 2002

The frame of a string instrument is subject to a large tension force when the strings are installed. Intuitively, one might expect that the frame would be stiffened by the strings. Experimental data and a theoretical analysis are presented to show that this is not generally the case. An archer’s bow is much stiffer when it is strung, but a tennis racquet is softened when the strings are added. As a result, the mode frequencies for transverse vibrations increase for a bow and decrease for a racquet when the strings are added. The effect of the strings depends on the extent to which the frame is bent at equilibrium.
Physics goes practical
Authors: Usher T. D. , Dixon P. K.
Published: July 2002

A new applied physics program at California State University San Bernardino is described. The applied program incorporates many aspects that may be of interest to others. For example, a required course in introductory electronics is offered at the freshman level. This program is not a “watered down” version of the traditional B.S. degree. We also stress that this applied physics option was not created by a few minor curriculum changes with the name “applied physics option” attached; it represents a major commitment by the department to offer a viable and marketable alternative to the traditional physics major. We believe that a balance must be struck by providing the type of liberal arts education that will sustain students throughout their careers and enrich their lives on the one hand, while offering specific skills that will help them land that all important first position on the other hand.
Sadi Carnot on Carnot’s theorem
Authors: Güémez J. , Fiolhais C. , Fiolhais M.
Published: July 2002

We reproduce the original calculations of Sadi Carnot that led him to formulate the so-called Carnot’s theorem. We rephrase Carnot’s calculations in SI units and compare his results with those obtained using modern data.
Understanding wave characteristics via linear superposition of retarded fields
Authors: Lai H. M. , Lau Y. P. , Wong W. H.
Published: July 2002

The Feynman–Schwartz method of linearly superposing retarded fields to understand the origin of the refractive index is generalized to an obliquely incident electromagnetic wave interacting with a planar medium. Different integral equations for the wave field in the medium are obtained for the TE-state and the TM-state of wave polarization. The two states of polarization are shown to satisfy the same differential equation for the spatial variation of the fields and thus they have the same dispersion relation (or the index of refraction) and change of phase velocity upon penetration into the medium. The integral equations are also used to deduce the well-known reflection and transmission coefficients in various cases.
The Bertrand theorem revisited
Authors: Zarmi Yair
Published: July 2002

The Bertrand theorem, which states that the only power-law central potentials for which the bounded trajectories are closed are 1/r2 and r2, is analyzed using the Poincaré–Lindstedt perturbation method. This perturbation method does not generate secular terms and correctly incorporates the effect of nonlinearities on the nature of periodic solutions. The requirement that the orbits be closed implies that the theorem holds in each order of the expansion.
Bohmian mechanics as a heuristic device: Wave packets in the harmonic oscillator
Authors: Bowman Gary E.
Published: July 2002

Although Bohmian mechanics has attracted considerable interest as a causal interpretation of quantum mechanics, it also possesses intrinsic heuristic value, arising from calculational tools and physical insights that are unavailable in “standard” quantum mechanics. We illustrate by examining the behavior of Gaussian harmonic oscillator wave packets from the Bohmian perspective. By utilizing familiar classical concepts and techniques, we obtain a physically transparent picture of packet behavior. This example provides, at a level accessible to students, a concrete illustration of Bohmian mechanics as a heuristic device that can enhance both understanding and discovery.
Which way does the light go?
Authors: Wünscher Thilo , Hauptmann Holger , Herrmann Friedrich
Published: July 2002

Pictures of the energy density and the energy flow in distributions of incoherent light for various two-dimensional situations are shown and discussed. Rules are introduced that allow one to sketch and to interpret such pictures.
A simple special relativistic perturbation scheme for yielding the general relativistic behavior of point particles and photons in the gravitational field of stars
Authors: Alaniz Alex
Published: July 2002

Using the principle of the equivalence of mass and energy of the special theory of relativity, it is shown that a Lagrangian yielding the same equations of motion that Einstein originally derived for the precession of the perihelion of Mercury and the bending of light by the sun may be derived by using a new perturbation scheme applied to the Lagrangian for an orbiting point particle. The magnitude of the Newtonian potential energy term appearing in the Lagrangian of an orbiting point particle is divided by c2 to yield a first-order mass correction to the potential energy. The corrected first-order potential energy term is in turn divided by c2 to yield a second-order mass correction to the total potential energy, and so forth. Successive correction terms are shown to yield successively smaller mass corrections to the total potential energy. This scheme, up to the first-order term in perturbation, leads to the astronomically observed corrections to the advance of the perihelion of Mercury and the bending of light by the sun attributable to general relativistic effects.
An undergraduate biophysics program: Curricular examples and lessons from a liberal arts context
Authors: Amador Kane Suzanne
Published: July 2002

The undergraduate concentration in biophysics at Haverford College is described, along with references to similar programs nationwide and reflections on the construction of sample curricula, administrative issues, and resources available for starting up related programs.
An experiment to demonstrate the canonical distribution
Authors: Sturge M. D. , Toh Song Bac
Published: July 2002

We describe a simple experiment, suitable for an undergraduate laboratory, in which the collector current in a transistor is measured as a function of the base–emitter voltage at various temperatures. The experiment gives a very convincing demonstration of the canonical distribution of statistical mechanics, in which the probability of occupancy of a state of energy E is proportional to e−E/kT.
Atoms in nanotubes: Small dimensions and variable dimensionality
Authors: Stan George , Gatica Silvina M. , Boninsegni Massimo , Curtarolo Stefano , Cole Milton W.
Published: July 2002

Newly discovered carbon nanotubes provide an environment in which small atoms move relatively freely. An assembly of such atoms provides a realization of a quasi-one-dimensional system which can be used to illustrate the concepts of statistical physics.
A simple model for Brownian motion leading to the Langevin equation
Authors: de Grooth Bart G.
Published: July 2002

A simple one-dimensional model is presented for the motion of a Brownian particle. It is shown how the collisions between a Brownian particle and its surrounding molecules lead to the Langevin equation, the power spectrum of the stochastic force, and the equipartition of kinetic energy.
Holography without photography
Authors: Walker Thad G.
Published: July 2002

I detail a method for producing high quality Fourier transform holograms using a computer, laser printer, and overhead transparency film. The method should be useful for lecture demonstration and holography laboratories.
An introduction to laser modeling studies with a nitrogen-pumped dye laser
Authors: Guerra David V. , Morgan Michael A. , Coyle D. Barry
Published: July 2002

The following exercises, which are suitable for an intermediate physics or physical chemistry class, provide an introduction to the use of computer modeling in the study of laser dynamics. The first exercise is performed with a tunable nitrogen-pumped dye laser to investigate empirically the effects that changes in gain and internal loss have on laser pulse characteristics. The second exercise employs a numerical model, based on the laser rate equations, to perform a quantitative study of the same effects. Since the model is constructed with the parameters that characterize the laser used in the first exercise, it can be exploited to gain deeper insight into the dynamics of the system. Together, these exercises expose students to the fundamentals of laser dynamics and techniques used to understand the buildup of a laser pulse.
Relativity and the electric dipole moment of a moving, conducting, magnetized sphere
Authors: Krotkov Robert V. , Pellegrini Gerald N. , Ford Norman C. , Swift Arthur R.
Published: July 2002

A classic experiment in the history of special relativity was designed to test the prediction that a moving magnetic dipole m develops an electric dipole moment p=v×m/c. In 1913 the competing theory was Lorentz’s electron theory. The experiment used a rotating magnetic medium composed of steel spheres embedded in wax. The results of the experiment agreed with the prediction of special relativity. A paper by Pellegrini and Swift reanalyzed the experiment using rotating coordinates. Their calculation disagreed with special relativity. One possible source of the disagreement is the nature of medium used in the experiment. This paper presents a straightforward calculation of the electric field of a steel sphere moving in a uniform magnetic field. The result demonstrates that any method of calculation consistent with Maxwell’s equations in the laboratory frame predicts a p=v×m/c contribution to the electric dipole moment. The calculations are carried out for a single moving sphere, while the Wilson experiment was done on an assembly of many spheres. We present arguments making it plausible that our result holds for such an assembly.
The whole-partial derivative
Authors: Brownstein K. R.
Published: July 2002

We discuss two types of partial derivatives which occur, e.g., in the Euler–Lagrange equations. To avoid confusion, a different notation (ðF/ðxμ) and a new name (whole-partial derivative) are suggested for what is usually written as ∂F/∂xμ but acts on both the explicit and implicit dependence of F upon the coordinate xμ.
Algebraic identities relating first- and second-quantized operators
Authors: Lawrence W. E.
Published: July 2002

Second-quantized operators are derived algebraically from first-quantized counterparts, thus providing an alternative to all existing methods, most of which rely upon demonstrating the equivalence of matrix elements of the two operators. This derivation establishes an operator identity between a second-quantized operator and a first-quantized operator whose domain of definition is extended explicitly from an N-particle Hilbert space to Fock space. The existence of such an identity eliminates the need to address the issue of the representations used for the two operators, which often obscures the underlying simple relationship between them.
Lifting of magnetic degeneracy in a parity-nonconserved atom by arbitrarily polarized light
Authors: Wagnière Georges H.
Published: July 2002

We show that in a one-electron atom in which parity-nonconserving interactions are operative, electromagnetic radiation of arbitrary polarization lifts the magnetic degeneracy of a spin–orbit coupled state. This result, arising from basic symmetry principles, occurs to second (and higher) order in the interaction of the atom with the electromagnetic field. It is a manifestation of the inverse magnetochiral effect.
The kinematical roots of dynamics
Authors: Rao S. R. Madhu
Published: July 2002

Whenever the total kinetic energy of an isolated collection of interacting bodies changes, the amount of its change as measured from different inertial frames has identical values. This remarkable invariance implies two of the principal conservation laws of Newtonian as well as relativistic mechanics. Moreover, together with the relevant rule of velocity addition, it even determines the exact form of the kinetic energy as a scalar function of the speed of motion in either context.
General relativistic treatment of the Colella–Overhauser–Werner experiment on neutron interference in a gravitational field
Authors: Varjú Katalin , Ryder Lewis H.
Published: July 2002

In the Colella–Overhauser–Werner (COW) experiment a gravity-induced phase shift of spin 1/2 particles was detected. The experimental results were explained by using the Newtonian theory of gravity. The explanation can be easily given using general relativistic arguments and the highest order term reproduces the result of Colella, Overhauser, and Werner together with additional, lower order corrections. The derivation can be considered as an interesting exercise for students with basic knowledge of the field of general relativity.
Self-force approach to synchrotron radiation
Authors: Burko Lior M.
Published: July 2002

We analyze radiation reaction for synchrotron radiation by computing, via a multipole expansion, the near field and derive from it the Lorentz four-force, which we evaluate on the world-line of the charge. We find that the temporal component of the self four-force agrees with the radiated power, which one calculates in the radiation zone. This is the case for each mode in the multipole decomposition. We also find agreement with the Abraham–Lorentz–Dirac equation.
Culvert whistlers: Harmonizing the wave and ray models
Authors: Karlow Edwin A.
Published: July 2002

Culvert whistlers created from acoustic waves in air confined by large cylinders are analyzed with both wave and geometrical ray models. Two distinct types of whistlers, on-axis and off-axis, are shown to have compatible explanations from both models that completely account for their time-dependent and frequency characteristics. The work of previous authors is revised and extended.
Bounded beam interaction with thin inclusions. Characterization by phase differences at Rayleigh angle incidence
Authors: Briers R. , Leroy O. , Shkerdin G.
Published: July 2002

A theoretical study of the reflection of a bounded Gaussian ultrasonic beam, incident onto a rectangular inclusion located near a fluid/solid half-space interface, is presented. The thickness of the inclusion is assumed to be much smaller than the ultrasonic wavelength in the solid. It is shown that, at critical Rayleigh angle incidence, the phase in the point of maximum amplitude of the shifted reflected lobe is very sensitive to dimension variations of the inclusion, and thus useful for inclusion characterization. The modelization of the problem is based on mode theory.
The influence of interaural stimulus uncertainty on binaural signal detection
Authors: Breebaart Jeroen , Kohlrausch Armin
Published: July 2002

This paper investigated the influence of stimulus uncertainty in binaural detection experiments and the predictions of several binaural models for such conditions. Masked thresholds of a 500-Hz sinusoid were measured in an NρSπ condition for both running and frozen-noise maskers using a three interval, forced-choice (3IFC) procedure. The nominal masker correlation varied between 0.64 and 1, and the bandwidth of the masker was either 10, 100, or 1000 Hz. The running-noise thresholds were expected to be higher than the frozen-noise thresholds because of stimulus uncertainty in the running-noise conditions. For an interaural correlation close to +1, no difference between frozen-noise and running-noise thresholds was expected for all values of the masker bandwidth. These expectations were supported by the experimental data: for interaural correlations less than 1.0, substantial differences between frozen and running-noise conditions were observed for bandwidths of 10 and 100 Hz. Two additional conditions were tested to further investigate the influence of stimulus uncertainty. In the first condition a different masker sample was chosen on each trial, but the correlation of the masker was forced to a fixed value. In the second condition one of two independent frozen-noise maskers was randomly chosen on each trial. Results from these experiments emphasized the influence of stimulus uncertainty in binaural detection tasks: if the degree of uncertainty in binaural cues was reduced, thresholds decreased towards thresholds in the conditions without any stimulus uncertainty. In the analysis of the data, stimulus uncertainty was expressed in terms of three theories of binaural processing: the interaural correlation, the EC theory, and a model based on the processing of interaural intensity differences (IIDs) and interaural time differences (ITDs). This analysis revealed that none of the theories tested could quantitatively account for the observed thresholds. In addition, it was found that, in conditions with stimulus uncertainty, predictions based on correlation differ from those based on the EC theory.
Resolution of front–back confusion in virtual acoustic imaging systems
Authors: Hill P. A. , Nelson P. A. , Kirkeby O. , Hamada H.
Published: July 2002

A geometric model of the scattering of sound by the human head is used to generate a model of localization cues based on interaural time delay (ITD). The ITD is calculated in terms of the interaural cross-correlation function (IACC) for sources placed at a series of azimuthal angles in the horizontal plane. This model is used to simulate the pressures generated at the ears of a listener due to real sources and due to a two-channel and a four-channel virtual source imaging system. Results are presented in each case for the variation of ITD with head rotation. The simulations predict that the rate of change of the ITD with head rotation produced by a real source and replicated by the four-channel virtual source imaging system, cannot be replicated by the two-channel system. These changes to the ITD provide cues which allow resolution of front–back confusion. The results of subjective experiments are also presented for the three cases modeled. These results strongly support the findings from the modeling work indicating that, for the systems described here, front–back confusion is resolved through changes to the ITD arising from head motion.
Numerical simulation of acoustic wave phase conjugation in active media
Authors: Khelil S. Ben , Merlen A. , Preobrazhensky V. , Pernod Ph.
Published: July 2002

Godunov-type computation schemes are applied to numerical simulations of wave propagations in time-dependent heterogeneous media (solids and liquids). The parametric phase conjugation of a wide band ultrasound pulse is considered. The supercritical dynamics of the acoustic field is described for one-dimensional systems containing a parametrically active solid. The impulse response function, numerically calculated for a finite active zone in an infinite medium above the threshold of absolute parametric instability, is in a good agreement with the analytical asymptotic theory. The supercritical evolution of the acoustic field spatial distribution is studied in detail for parametric excitations in an active zone of a solid layer, loaded by a semi-infinite liquid on one side and free on the other.
An updated perspective on basin-scale tomography
Authors: Spiesberger John L.
Published: July 2002

There seems to be little doubt that pulse-like acoustic transmissions at 1000 to 5000 km can be used to measure small changes in average temperature in many oceanic regions, given the numerous results published by different groups. The early experimental results in this field which led to these conclusions have been confirmed by recent experiments. Our purpose in this Letter is to summarize the work in this field in the context of addressing a few reservations expressed about the early experiments.
On the modeling of the vent path in hearing aid systems
Authors: Rafaely B. , Hayes J. L.
Published: July 2002

The unamplified response of a vented hearing aid can be significant, in particular at the low frequencies. This letter discusses two different, previously published configurations, in which the vent response is included in the hearing aid model. Any confusion that can potentially arise from the difference in the models is clarified, and a preferred configuration is proposed, which is more consistent with measurable quantities.
Ultrasound-mediated disruption of cell membranes. II. Heterogeneous effects on cells
Authors: Guzmán Héctor R. , Nguyen Daniel X. , Khan Sohail , Prausnitz Mark R.
Published: July 2002

Ultrasound has been shown to reversibly and irreversibly disrupt membranes of viable cells through a mechanism believed to involve cavitation. Because cavitation is both temporally and spatially heterogeneous, flow cytometry was used to identify and quantify heterogeneity in the effects of ultrasound on molecular uptake and cell viability on a cell-by-cell basis for suspensions of DU145 prostate cancer and aortic smooth muscle cells exposed to varying peak negative acoustic pressures (0.6–3.0 MPa), exposure times (120–2000 ms), and pulse lengths (0.02–60 ms) in the presence of Optison (1.7% v/v) contrast agent. Cell-to-cell heterogeneity was observed at all conditions studied and was classified into three subpopulations: nominal uptake (NUP), low uptake (LUP), and high uptake (HUP) populations. The average number of molecules within each subpopulation was generally constant: 104–105 molecules/cell in NUP, ∼106 molecules/cell in LUP, and ∼107 molecules/cell in HUP. However, the fraction of cells within each subpopulation showed a strong dependence on both acoustic pressure and exposure time. Varying pulse length produced no significant effect. The distribution of cells among the three subpopulations correlated with acoustic energy exposure, which suggests that energy exposure may govern the ability of ultrasound to induce bioeffects by a nonthermal mechanism.
Quasistatic coupling coefficients for electrostrictive ceramics
Authors: Piquette Jean C.
Published: July 2002

A generalized definition of the coupling coefficient, useful for the evaluation of transducers that incorporate an electrostrictive active element, is introduced. The definition is expressed under quasistatic conditions and becomes zero when no bias is applied (assuming that the effects of remanence are negligible), and remains zero under zero bias even when a significant prestress is present. This reflects a property of the piezoelectric coupling coefficient, which vanishes when the ceramic becomes depoled. The behavior of this definition thus differs from that of another definition, introduced elsewhere, which produces a significant nonzero result at zero bias. [See C. Hom et al., “Calculation of quasi-static electromechanical coupling coefficients for electrostrictive ceramic materials,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control 41, 542–551 (1994).] The present definition also leads in a natural way to a coupling coefficient for biased piezoelectric ceramics, and an equation is given for that case. Moreover, in the case of a biased electrostrictive ceramic it is found that a coupling coefficient derived from an equivalent circuit [J. C. Piquette and S. E. Forsythe, “Generalized material model for lead magnesium niobate (PMN) and an associated electromechanical equivalent circuit,” J. Acoust. Soc. Am. 104, 2763–2772 (1998)] gives an excellent approximation to the exact value, and is found to be accurate to within a few percent for drive amplitudes as high as 75% of the bias. It is shown that maximizing the coupling coefficient automatically discriminates against transducer designs (and operating conditions) that would produce significant harmonic distortion.
Relative rates of growth of annoyance of impulsive and non-impulsive noises
Authors: Fidell Sanford , Silvati Laura , Pearsons Karl
Published: July 2002

Twenty-nine people judged the relative annoyance of five variable level signals and 29 impulsive and non-impulsive fixed-level signals in an adaptive paired comparison study. Signals were presented for judgment as heard indoors in a facility capable of accurately reproducing the very low-frequency content of sonic booms. When the annoyance of sonic booms unaccompanied by rattle was compared with that of sounds containing more higher-frequency energy (an aircraft flyover and an octave band of noise centered at 1 kHz), the relative rate of growth of annoyance, as expressed in C-weighted SEL units, was nearly 2:1. In other words, to maintain subjective equality of annoyance, each increase in level of sonic booms had to be matched by nearly twice the increase in level of an aircraft flyover or an octave band of noise centered at 1 kHz. Relative rates of growth of annoyance of sonic booms accompanied by rattle and of non-impulsive sounds, including both low- (63-Hz octave band of noise) and high-frequency energy (1-kHz octave band of noise and an aircraft flyover), were closer to 1:1. Relative rates of growth of annoyance for sonic booms unaccompanied by rattle and low-frequency sounds (63 Hz) were also about 1:1. These differences in relative rates of growth of annoyance of impulsive and non-impulsive sounds are as plausibly attributed to their relative low-frequency content as to impulsiveness per se. It may therefore be more useful for some purposes to express the annoyance of impulsive signals and other environmental noises containing substantial low-frequency energy in terms of effective (duration-corrected) loudness level rather than commonplace ASEL or CSEL.
Three-dimensional modeling of hearing in Delphinus delphis
Authors: Aroyan James L.
Published: July 2002

Physical modeling is a fertile approach to investigating sound emission and reception (hearing) in marine mammals. A method for simulation of hearing was developed combining three-dimensional acoustic propagation and extrapolation techniques with a novel approach to modeling the acoustic parameters of mammalian tissues. Models of the forehead and lower jaw tissues of the common dolphin, Delphinus delphis, were created in order to simulate the biosonar emission and hearing processes. This paper outlines the methods used in the hearing simulations and offers observations concerning the mechanisms of acoustic reception in this dolphin based on model results. These results include: (1) The left and right mandibular fat bodies were found to channel sound incident from forward directions to the left and right tympanic bulla and to create sharp maxima against the lateral surfaces of each respective bulla; (2) The soft tissues of the lower jaw improved the forward directivity of the simulated receptivity patterns; (3) A focal property of the lower-jaw pan bones appeared to contribute to the creation of distinct forward receptivity peaks for each ear; (4) The reception patterns contained features that may correspond to lateral hearing pathways. A “fast” lens mechanism is proposed to explain the focal contribution of the pan bones in this dolphin. Similar techniques may be used to study hearing in other marine mammals.
Extinction theorem for object scattering in a stratified medium
Authors: Ratilal Purnima , Makris Nicholas C.
Published: July 2002

A simple relation for the rate at which energy is extinguished from the incident wave of a far field point source by an obstacle of arbitrary size and shape in a stratified medium is derived from wave theory. This relation generalizes the classical extinction theorem, or optical theorem, that was originally derived for plane wave scattering in free space and greatly facilitates extinction calculations by eliminating the need to integrate energy flux about the obstacle. The total extinction is shown to be a linear sum of the extinction of each wave guide mode. Each modal extinction involves a sum over all incident modes that are scattered into the extinguished mode and is expressed in terms of the object’s plane wave scatter function in the forward azimuth and equivalent plane wave amplitudes of the modes. The only assumptions are that multiple scattering between the object and wave guide boundaries is negligible, and the object lies within a constant sound speed layer. Modal extinction cross sections of an object for the extinction of the individual modes of a wave guide are then defined. Calculations for a shallow water wave guide show that, after correcting for absorption loss in the medium, the modal cross section of an object for mode 1 in a typical ocean wave guide is very nearly equal to its free space cross section. This new extinction theorem may be applied to estimate the cross section of an object submerged in a wave guide from a measurement of its forward scattered field.
An approximate analytic solution for the radiation from a line-driven fluid-loaded plate
Authors: DiPerna Daniel T. , Feit David
Published: July 2002

In the analysis of a fluid loaded line-driven plate, the fields in the structure and the fluid are often expressed in terms of a Fourier transform. Once the boundary conditions are matched, the structural displacement can be expressed as an inverse transform, which can be evaluated using contour integration. The result is then a sum of propagating or decaying waves, each arising from poles in the complex plane, plus a branch cut integral. The branch cut is due to a square root in the transform of the acoustic impedance. The complex layer analysis (CLA) used here eliminates the branch cut singularity by approximating the square root with a rational function, causing the characteristic equation to become a polynomial in the transform variable. An approximate analytic solution to the characteristic equation is then found using a perturbation method. The result is four poles corresponding to the roots of the in vacuo plate, modified by the presence of the fluid, plus an infinity of poles located along the branch cut of the acoustic impedance. The solution is then found analytically using contour integration, with the integrand containing only simple poles.
Coupled modes of the resonance box of the guitar
Authors: Elejabarrieta M. J. , Ezcurra A. , Santamarı́a C.
Published: July 2002

Vibrations of the resonance box of the guitar have been studied by means of the modal analysis technique and the finite-element method. An expert craftsman constructed the guitar box with all the structures, internal and external, characteristic of a real instrument for the experimental measurements. The boundary conditions were chosen in order to clarify the soundboard–back interaction only via the internal air coupling. The numerical model allows one to study the influence of each component on the whole box, and the contribution of the modes of the components (wooden box and its parts, and air), to the coupled modes by calculating their participation factors. The coupled modes of the guitar box are discussed taking into account both the finite-element and modal analysis results.
Robust active control of broadband noise in finite ducts
Authors: Liu S. , Yuan J. , Fung K.-Y.
Published: July 2002

This study focuses on robust active control of broadband noise in finite ducts. Our analytical and experimental studies suggest the existence of several technical flaws in the path models of conventional active noise control (ANC) systems. These are sensitivity of the path model with respect to boundary conditions, and nonminimum phase (NMP) secondary and reference paths. For finite ducts with small cross sections, the traveling wave model (TWM) may be adopted to find an effective solution to these problems and lead to a robust ANC system. Since many practical “noisy” ducts are finite with small cross sections, the proposed ANC has many practical applications. Its robustness and ability to suppress broadband noise will be explained theoretically and verified experimentally.
Analysis of harmonic distortion in electroacoustic transducers under indirect drive conditions
Authors: Sherman Charles H. , Butler John L. , Butler Alexander L.
Published: July 2002

Nonlinear transducer equations for the six major types of electroacoustic transducers (electrostatic, variable reluctance, moving coil, piezoelectric, electrostrictive, and magnetostrictive) are formulated in a common way and solved approximately by perturbation analysis for indirect drive, i.e., current drive of electric field transducers and voltage drive of magnetic field transducers. The direct drive analysis, i.e., voltage drive of electric field transducers and current drive of magnetic field transducers, was given in J. Acoust. Soc. Am. 98, 1596–1611 (1995). Expressions and graphs are given for some of the indirect drive harmonics which apply to all six transducer types. The solutions for direct and indirect drive are compared, and some of the differences are discussed with emphasis on the question of which drive gives lower harmonic distortion. No answer to this question has been found that is applicable to all nonlinear mechanisms in all transducers at all frequencies. However, it is shown that for transducers of all types with low electrical loss operated near resonance direct drive usually gives lower second harmonics. The exceptions occur when mechanical springs are the dominant nonlinearity and the electromechanical coupling is very high; then indirect drive gives lower second harmonics. It is shown how the results, although based on simple lumped parameter models, can be applied in some cases to more complex transducer structures.
The application of analytical/numerical matching to structural discontinuities in structural/acoustic problems
Authors: Loftman Rickard C. , Bliss Donald B.
Published: July 2002

Analytical/numerical matching (ANM) is introduced to more efficiently model structural discontinuities in structural/acoustic problems. The general method is explained in detail for the simple example problem of normal incidence acoustic scattering from a periodically line-supported elastic membrane. A modal series solution exists for this problem. The most slowly convergent part of this solution, the dominant high-resolution (large wave number) content, is removed from the series representation and summed in closed form in what is called the ANM local solution. This local solution is represented by a piecewise polynomial that is zero outside of a small region. The remaining part of the solution, containing the overall low resolution content, is called the ANM global solution and converges very rapidly. In the present example, the series representing the global solution falls by three powers of the index faster than the classical modal solution. The result is an ANM composite (local plus global) solution that requires far less computational effort to resolve. In addition to providing a clear abstraction of the method, the example problem allows the equivalence of the ANM solution to be verified, and indicates the importance of resolving the fine scale effects of discontinuities in constrained scattering problems.
In vitro and in vivo enhancement of sonodynamically active cavitation by second-harmonic superimposition
Authors: Umemura Shin-ichiro , Kawabata Ken-ichi , Sasaki Kazuaki
Published: July 2002

Acoustic cavitation, the primary mechanism of sonochemical effects, is known to be induced more easily by standing waves than by progressive waves. It has been found that acoustic cavitation can be an order of magnitude enhanced by superimposing the second harmonic on the fundamental. Significant synergistic effects between the fundamental and the second harmonic were observed in both in vitro and in vivo experiments employing a progressive wave field. Second-harmonic superimposition induces in vitro sonochemical reaction as well as fractional harmonic emission at a relatively low ultrasonic intensity even in a progressive wave field. The effect of second-harmonic superimposition was also investigated using exteriorized mouse livers suspended in degassed saline. The intensity threshold for the production of focal tissue damage, paired with fractional harmonic emission was significantly lowered by second-harmonic superimposition especially when a sonodynamically active agent had been administered to the mouse. Insonation with second-harmonic superimposition in combination with such administration may have potential use for selective tumor treatment.
Elastic wave band gaps and defect states in two-dimensional composites
Authors: Sigalas M. M.
Published: July 2002

Using the plane-wave expansion method, we study the propagation of elastic waves through two-dimensional (2-D) periodic composites which exhibit full band gaps for all the polarizations and directions of the displacements. Defect states created inside those band gaps are also studied by disturbing the periodicity of the lattice. Systems exhibiting such kinds of states can be used as acoustical filters.
Matched-field source localization in a random ocean
Authors: Minassian George R.
Published: July 2002

This paper is devoted to the statistical approach to matched-field processing (MFP). In Sec. I, a statistical model of the Green’s function of a random oceanic waveguide is described using the mean field and the second moment. In Sec. 2, using Bayesian approach, optimum target detection and localization algorithms matched to a deterministic and a stochastic ocean are derived. First, the optimum decisive statistic (log-likelihood ratio) is derived for a deterministic ocean. In the general case, ocean parameter fluctuations make the Green’s function random and so we need to average the log-likelihood ratio. The MFP algorithms for a random ocean waveguide developed on the basis of the Bayesian approach are less precise than the algorithms for a deterministic oceanic waveguide model, but they are more robust. In Sec. 3 a comparative analysis of the proposed MFP methods and the known suboptimum MFP techniques is carried out. The ambiguity surfaces for the proposed algorithms, Bartlett, Minimum Variance (MV), MV with neighboring location constraints, and MV with sound-speed perturbation constraints methods are presented. The proposed MFP method outperformed other algorithms under random ocean conditions, giving the least bias error and the lowest sidelobes.
Rotorcraft noise model
Authors: Lucas Michael J. , Marcolini Michael A.
Published: July 2002

The rotorcraft noise model (RNM) is a multiplatform computer program being developed for NASA-Langley Research Center which calculates sound levels at receiver positions on the ground from helicopter and tiltrotor operations. RNM calculates levels at positions on a uniform grid or a specific defined locations. The basic computational model written in FORTRAN calculates maximum A-weighted sound level, sound exposure level (overall, C- and A-weighted), and effective perceived noise level (EPNL). Contained within the program are sound propagation and EPNL algorithms that are the same as, or equivalent to, corresponding algorithms in NASA’s Aircraft Noise Prediction Program (ANOPP). Acoustic properties of the noise source are defined by a set of sound-pressure noise spheres. One set of noise spheres provides broadband data in the form of one-third octave band sound-pressure levels. The other set of noise spheres provides narrow-band data in the form of pure-tone sound-pressure levels and phase. RNM outputs a file that is input to NMPLOT, a noise contouring/smoothing program used by the Department of Defense (DOD) and other government agencies. This paper will describe the basic element of the noise model and compare the noise models prediction with XV-15 noise data collected by NASA-Langley.
Coherence masking protection in brief noise complexes: Effects of temporal patterns
Authors: Gordon Peter C.
Published: July 2002

Three experiments examined listeners’ thresholds for classifying the pitch of a target signal in a masking noise when it was presented alone as compared to when it was presented with a “cosignal.” The target signal was a narrow band of noise centered on either 375 or 625 Hz and the masker was noise low-pass filtered at 1000 Hz. The cosignal provided no information about the pitch of the target signal but could potentially combine with it to form an auditory object; it was spectrally well separated from the target signal, consisting of a band of noise ranging from 2200 to 2900 Hz. Experiment 1 showed that identification thresholds were lower when the target signal was paired with the cosignal than when it was presented alone if the onsets and offsets of the target signal and cosignal were temporally synchronous. This is an instance of “coherence masking protection,” a phenomenon that has previously been established in the perception of vowels [P. C. Gordon, Percept. Psychophys. 59, 232–242 (1997)]. The effect disappears when the cosignal leads and lags the target signal by short durations, a finding that also matches that observed previously with vowels. The finding that temporal relations between the components of a stimulus have similar effects on the perception of nonspeech noise complexes and speech sounds suggests that speech perception makes use of general auditory mechanisms for perceptual integration of this sort. Experiments 2 and 3 examine further the role of temporal relations between the onsets and offsets of the target signal and the cosignal in producing coherence masking protection. The results show that either onset synchrony or offset synchrony is sufficient to produce the effect when the cosignal is of greater duration than the target signal, but that only onset synchrony produces the effect when the target signal has greater duration than the cosignal. This pattern indicates that the target signal and cosignal do not contribute equally to the formation of auditory objects.