bluuebunny/crossref_metadata_2025 huggingface dataset:
A maximum‐entropy method for the planning of conformal radiotherapy
Authors: Wu Xingen , Zhu Yunping
Published: July 2002

The maximum entropy method (MEM) is a powerful inverse analysis technique that is used in many fields of science and engineering to perform tasks such as image reconstruction and processing of nuclear magnetic resonance signals. Unlike other methods, MEM naturally incorporates a priori knowledge of the problem into the optimized cost function. This feature is especially important in radiotherapy planning, because some knowledge is usually available about the stage of tumor development and about the prescription doses, including some dose constraints to the surrounding normal organs. Inverse planning is inherently consistent with the ability of MEM to estimate parameters inversely. In this investigation, an entropy function determines the homogeneity of dose distribution in the planning target volume; a least‐squares function is added to the maximum entropy function as a constraint to measure the quality of reconstructed doses in organs at risk; and an iterative Newton–Ralphson algorithm searches for the optimization solution. Here we provide two examples that validate this application of MEM and the results were compared with manual plans. Although the examples involve conformal radiotherapy, we think MEM can be adopted to optimize intensity‐modulated radiation therapy.
Matching tomographic IMRT fields with static photon fields
Authors: Sethi A. , Leybovich L. , Dogan N. , Emami B.
Published: July 2002

The matching of abutting radiation fields presents a challenging problem in radiation therapy. Due to sharp penumbra of linear accelerator beams, small (1–2 mm) errors in field positioning can lead to large (>30%) hot or cold spots in the abutment region. With head and neck immobilization devices (thermoplastic mask/aquaplast) an average setup error of 3 mm has been reported. Therefore hot or cold spots approaching 50% of the prescription dose may occur along the matchline. Although abutting radiation fields have been investigated for static fields, there is no reported study regarding matching of tomographic IMRT and static fields. Compared to static fields, the matching of tomographic IMRT fields with static fields is more complicated. Since IMRT and static fields are planned on separate treatment planning computers, the dose in the abutment region is not specified. In addition, commonly used techniques for matching fields, such as feathering of junctions, are not practical. We have developed a method that substantially reduces dose inhomogeneity in the abutment region. In this method, a “buffer zone” around the matchline was created and was included as part of the target for both IMRT and static field plans. In both fields, a small dose gradient (⩽3%/mm) in the buffer zone was created. In the IMRT plan, the buffer zone was divided into three sections with dose varying from 83% to 25% of prescription dose. The static field dose profile was modified using either a specially designed physical (hard) or a dynamic (soft) wedge. When these modified fields were matched, the combined dose in the abutment region varied by ⩽10% in the presence of setup errors spanning 4 mm (±2 mm) when the hard wedge was used and 10 mm (±5 mm) with the soft wedge.
Remote control for a stand‐alone freely movable treatment couch with limitation system
Authors: Van de Vondel Iwein , Coppens Luc , Verellen Dirk , Linthout Nadine , Van Acker Swana , Storme Guy
Published: July 2002

One of our linear accelerators is equipped with a free‐movable treatment couch. An additional projects was to develop a system that first protects the free‐movable couch against collisions, secondly build a remote control for moving the couch from outside the treatment room and finally implement this remote control/limitation system in an automatic position algorithm using an electronic portal image. The latter has been the subject of an on‐going departmental investigation on intra‐fractional correction of set‐up errors. A few years ago, we developed a limitation system to protect both the table and the accelerator against collisions. In this paper we describe the second part of this project, the remote control system.
Development and application of a small gamma camera
Authors: Matthews Kenneth L.
Published: July 2002

This work investigates the design, construction, and application of a portable gamma camera based on a single position‐sensitive photomultiplier tube (PSPMT) rather than an array of conventional phototubes. The PSPMT is an innovation in photomultiplier design that allows two‐dimensional position information to be obtained from a single phototube. PSPMT‐based portable gamma cameras can have several distinct advantages over portable systems using conventional technology: lower weight, reduced electronics, and smaller size. This design can be incorporated as modules in conjugate imaging, orthogonal view, or ring detector systems, or even in large‐area planar imagers. The PSPMT design is applicable for diagnostic clinical procedures and for basic biomedical research. Two small gamma camera (SGC) systems have been constructed. Computer simulations and physical measurements have been applied to the performance characterization of the SGC. The SGC incorporates a maximum‐likelihood position estimation scheme. The intrinsic resolution of the SGC is 1.7 mm FWHM (3.2 mm FWTM) at the center of the 48 mm×48 mm field of view. The SGC has been evaluated for several nuclear medicine imaging applications as well as laboratory research imaging. The clinical applications include planar and tomographic imaging. Radiotracer imaging with the SGC has been applied to the in vivo investigation of electroporation injury and tissue repair.
Measurement of the effective size of the input phosphor of an x‐ray image intensifier
Authors: Feldman Arnold , Cox Ronald , Rosser Jeffrey
Published: July 2002

A technique is described, using a mobile radiographic x‐ray unit, for determining the effective size of the input phosphor of an image intensifier (I.I.), in particular for a unit with over‐table x‐ray tube, under‐table II, and with the I.I. physically inaccessible. The techniques described also enable (1) locating the central axis of the I.I.; (2) the ratio, , of the dimensions of the radiological image incident upon the front of the I.I. to the dimensions of the image on the monitor screen; and (3) the distance between the input phosphor and the table top, which is needed to determine the distance from focal spot to input phosphor.
Photoacoustic ultrasonography and its potential application in mammography
Authors: Fang Yuncai
Published: July 2002

In this thesis, photoacoustic ultrasonography (PAUS) and its applicability in breast cancer detection were investigated. PAUS employs a short pulse of electromagnetic energy, at either near‐infrared or microwave frequency, to heat breast tissue. Rapid heating, resulting from inhomogeneous absorption of the energy pulse, generates ultrasonic waves. The energy absorption patterns can be reconstructed from these pressure waves recorded at locations around the periphery of the tissue. This study concentrated on microwave‐induced PAUS (434 MHz). The principle of the photoacoustic signal generation was analyzed, and the image reconstruction method was implemented and validated by imaging experiments. Extensive studies of microwave‐induced PAUS demonstrated that an adequate absorption difference of microwaves at 434 MHz exists between benign and malignant breast tissues. Experiments suggest that adequate ultrasonic signals can be detected using proper instrumentation, which allow the microwave absorption patterns to be reconstructed. I conclude that microwave‐induced PAUS is likely to be a useful imaging modality for breast screening.
A new convolution/superposition dose calculation method for external photon beam radiation therapy using beam modifiers and/or independent collimators
Authors: Liu Hui Helen
Published: July 2002

This thesis was dedicated to developing a convolution/superposition dose calculation method for computing patient dose distributions as well as radiation output (monitor units) for photon radiotherapy. A new dual source photon beam model based on Monte Carlo simulation of clinical linear accelerators was developed and incorporated in the convolution method. This allowed for more accurate computation of dose distributions and output factors for photon fields, because both the primary and extra‐focal photons from clinical accelerators can be accounted for accurately. This convolution method was tested extensively for a variety of photon fields including those using independent jaws and/or beam modifiers, such as wedges and blocks. To use this convolution method for wedged fields, an extended phantom model was developed to integrate a wedge along with a patient phantom. Thus, dosimetric effect of wedges regarding beam hardening effect and secondary radiation generated by the wedge was taken into account. The new convolution method was also applied to calculate dose and output factors for dynamic or intensity modulated fields such as dynamic wedges. To use the convolution method for clinical situations, corrections for beam divergence and beam hardening were also developed. The parameters for the convolution calculation related to spatial resolution were investigated to optimize the speed and accuracy of the convolution calculation.
A bandwidth indicator for magnetic resonance imagers
Authors: Date Takuji , Redpath Thomas W. , Bussell David M.
Published: July 2002

Signal‐to‐noise ratios in magnetic resonance imaging are crucial in determining image quality, and dependent on a number of factors, one being the signal bandwidth per pixel. Not all manufacturers clearly state the bandwidth per pixel used for all sequences. A small battery‐powered portable device is described which produces bright sharp lines on the magnetic resonance image at 10 kHz intervals in the frequency encoding direction. The bandwidth per pixel can then easily be calculated using electronic distance callipers, provided the image matrix and field of view are known. The device is expected to be especially of value when acceptance testing on poorly documented imaging systems.
Development of a CCD array imaging system for measurement of dose distributions in doped agarose gels
Authors: Tarte B. J. , Jardine P. A. , van Doorn T. , Nitschke K. N. , Poulsen M. G.
Published: July 2002

An imaging system for agarose gel sections has been investigated for applications in rapid two‐dimensional radiation dosimetry. The imaging system, with white light illumination and CCD camera detection, was designed for measurement of the radiation‐induced optical density changes in iron‐ and xylenol orange dye‐doped agarose gels. The performance of the imaging system was compared with that of a laser scanning system for the gels and with the accepted dosimetry standard, the ionization chamber. In measurement of beam profiles of two therapeutic radiation fields, relative dose values from the CCD camera imaging system were on average within 3% (ranging from 0.005% to 7.5%) of values recorded with a parallel plate ionization chamber. In comparison with the laser scanner, the CCD camera imaging system provided comparable spatial resolution and an increased rate of data acquisition, although a consistently reduced signal to noise ratio was observed. Suggestions for improving the camera imaging technique include noise reduction through camera cooling and further frame averaging.
Beam profiles for x‐ray rotation therapy
Authors: Cormack R. A.
Published: July 2002

Determining the beam configuration necessary to deliver a desired dose distribution with rotation therapy is equivalent to solving an integral equation. The equation has been solved analytically for a handful of dose distributions having specific radial variation and either rotational or reflective angular symmetry. In this work a numerical method for calculating beam profiles appropriate for producing distributions having arbitrary radial variation and angular symmetry of order is presented. The accuracy of the technique is demonstrated by comparison with one of the few dose distributions for which an analytic solution exists, and the ability to produce both more general and conformal distributions is also shown. The problems of negative intensity and scatter are discussed.
Combined use of FLUKA and MCNP‐4A for the Monte Carlo simulation of the dosimetry of neutron capture enhancement of fast neutron irradiations
Authors: Pignol Jean‐Philippe , Cuendet Pascal , Brassart Nicole , Fares Georges , Colomb Florence , M'Bake Diop Cheikh , Sabattier Roland , Hachem Ahmed , Prevot Gilles
Published: July 2002

Boron neutron capture enhancement (BNCE) of the fast neutron irradiations use thermal neutrons produced in depth of the tissues to generate neutron capture reactions on within tumor cells. The dose enhancement is correlated to the concentration and to thermal neutron flux measured in the depth of the tissues, and in this paper we demonstrate the feasibility of Monte Carlo simulation to study the dosimetry of BNCE. The charged particle FLUKA code has been used to calculate the primary neutron yield from the beryllium target, while MCNP‐4A has been used for the transport of these neutrons in the geometry of the Biomedical Cyclotron of Nice. The fast neutron spectrum and dose deposition, the thermal flux and thermal neutron spectrum in depth of a Plexiglas phantom has been calculated. The thermal neutron flux has been compared with experimental results determined with calibrated thermoluminescent dosimeters (TLD‐600 and TLD‐700, respectively, doped with or ). The theoretical results were in good agreement with the experimental results: the thermal neutron flux was calculated at and measured at at 4 cm depth of the phantom and with a irradiation field. For fast neutron dose deposition the calculated and experimental curves have the same slope but different shape: only the experimental curve shows a maximum at 2.27 cm depth corresponding to the build‐up. The difference is due to the Monte Carlo simulation which does not follow the secondary particles. Finally, a dose enhancement of, respectively, 4.6% and 10.4% are found for or fields, provided that 100 μg/g of is loaded in the tissues. It is anticipated that this calculation method may be used to improve BNCE of fast neutron irradiations through collimation modifications.
Techniques to alleviate the effects of view aliasing artifacts in computed tomography
Authors: Galigekere R. R. , Wiesent K. , Holdsworth D. W.
Published: July 2002

Due to practical limitations in data acquisition, 3‐D computed tomography systems must attempt to provide rapid reconstructions of acceptable quality from a limited number of views. The use of convolution backprojection (CBP) for image reconstruction from an inadequate number of projections, results in view aliasing artifacts. In this paper we investigate different post‐processing methods of alleviating the effects of view aliasing artifacts. Two distinct methods and their variants are considered. The first, termed the intermediate view reprojection (IVR) method, involves estimating a set of intermediate views by reprojection, followed by a reconstruction using the augmented set of views. The second, termed the error‐correction (EC) method, incorporates a correction on the initial reconstruction based on the projection‐domain error. Suitable modifications and variants of the above methods are indicated. Of the methods discussed, the IVR method is simple, tends to reduce the effects of artifacts with less susceptibility to secondary effects, and is applicable to region‐of‐interest reconstructions.
Spatially varying longitudinal aliasing and resolution in spiral computed tomography
Authors: Yen Shin Yi , Rubin Geoffrey D. , Napel Sandy
Published: July 2002

Spiral computed tomography (CT) has revolutionized conventional CT as a truly three‐dimensional imaging modality. A number of studies aimed at evaluating the longitudinal resolution in spiral CT have been presented, but the spatially varying nature of the longitudinal resolution in spiral CT has been largely left undiscussed. In this paper, we investigate the longitudinal resolution in spiral CT as affected by the spatially varying longitudinal aliasing. We propose the treatment of aliasing as a signal dependent, additive noise, and define a new image quality parameter, the contrast‐to‐aliased‐noise ratio that relates to possible image degradation or loss of resolution caused by aliasing. We performed CT simulations and actual phantom scans using a resolution phantom consisting of sequences of spherical beads of different diameters, extending along the longitudinal axis. Our results show that the off‐isocenter longitudinal resolution differs significantly from the longitudinal resolution at the isocenter and that the decreases with distance from the isocenter, and is a function of pitch and the helical interpolation algorithm used. The longitudinal resolution was observed to worsen with decreasing We conclude that the longitudinal resolution in spiral CT is spatially varying, and can be characterized by the measured at the transaxial location of interest.
Estimation of the dose at the maze entrance for x‐rays from radiotherapy linear accelerators
Authors: Al‐Affana I. A. M.
Published: July 2002

Recent measurements have shown that the NCRP formula to estimate the x radiation dose at the maze entrance of high energy radiotherapy rooms underestimates the dose by an order of magnitude. In the present work the Monte Carlo Code MCNP was used to model a radiotherapy room and investigate the NCRP formula. The dose of the scattered photons was calculated for 6‐MV and 10‐MV x‐rays for the following situations: primary beam in vacuum, primary beam with air in the room, collimated primary beam (by the jaws) with air in the room and primary beam collimated with air in the room, and phantom at 100‐cm SSD. It was found that for 6‐MV x‐rays the dose, when these materials were present in the beam path, was 1.2, 1.6, 5.3, and respectively. Therefore the presence of all these materials together increased the dose by a factor of 11. The dose due to leakage was calculated separately to be This adds another factor of 8. The 10‐MV results were similar to those at 6 MV. There was good agreement between MCNP calculations and the published measurements. The spectrum and average energy of scattered photons at different locations in the radiotherapy room and the maze were also calculated by MCNP.
A method for achieving variable widths of the spread‐out Bragg peak using a ridge filter
Authors: Nakagawa Takafumi , Yoda Kiyoshi
Published: July 2002

A method for designing a variable‐SOBP (spread‐out Bragg peak) ridge filter has been proposed. First, ridge filter parameters are determined by using a Monte Carlo calculation followed by a fast two‐step iterative optimization. Then, tilting the ridge filter results in continuous variation of the SOBP width. Monte Carlo calculations show that depth dose uniformity changes from ±1.3% to ±1.6% for SOBP widths ranging from 10.3 cm to 14.5 cm. Advantages of the proposed tilting ridge filter include a capability of continuous SOBP variation and cost‐effective installation for a given SOBP width range.
Megavoltage computed tomography for tomotherapeutic verification
Authors: Ruchala Kenneth J.
Published: July 2002

A helical tomotherapy system is being developed at the University of Wisconsin—Madison as a means of improving Intensity Modulated Radiotherapy (IMRT) delivery. The goal of this thesis was to develop megavoltage computed tomography (MVCT) capabilities to image the patient in the treatment position, before, during, or after IMRT treatment. This MVCT system uses a 738‐channel xenon detector and is similar to helical kilovoltage CT (kVCT) except that it utilizes the treatment linac as the x‐ray source. Due to the high (4 MV) photon energy, MVCT contrast is inferior to kVCT, but should be adequate to verify patient positioning for radiotherapy. Techniques were developed to preprocess transmission data and to correct for artifacts. Image quality was compared for several different reconstruction algorithms. MVCT scans on a tomotherapy research system demonstrated relative contrasts below 1% for 25 mm objects using a 7 cGy dose to the center of the phantom. High‐contrast resolutions are 1.25 mm for air cavities. Through calibration of this system with known materials, the reconstructed values have been demonstrated to be linear with electron density, which benefits subsequent dose calculations. MVCT using transmission data collected during IMRT treatment delivery was also investigated. By overcoming the problems of incomplete data availability and difficulty normalizing modulated beams, treatment data was incorporated into the reconstruction process. This has demonstrated improved image contrast while reducing the additional imaging dose, and also presents the opportunity to collect all of the data necessary for image reconstruction during the treatment delivery.
American radium engenders telecurie therapy during World War I
Authors: Robison Roger
Published: July 2002

From 1899 to 1912 there was a European monopoly controlling the sale of radium for cancer therapy. This trust was finally broken, albeit only temporarily, in 1912/13 by American entrepreneurs J. Flannery, H. Kelly, and J. Douglas. Joe Flannery was a former mortician turned mining magnate. Dr. Howard Kelly was the renowned gynecological surgeon at Johns Hopkins Hospital and Medical School who defied tradition by maintaining his own private hospital. Professor James Douglas was the Arizona copper king who helped support Memorial Hospital in New York City as America's first cancer hospital. During 1913–1916 surgeons Howard Kelly (Baltimore) and H. H. Janeway (Memorial Hospital) began using radium and radon for the treatment of deep seated cancers. Their technique required placement of the sources several centimeters away from the skin surface. As this new concept, telecurie therapy, resulted in a significant decrease in dose rate, it was necessary for both surgeons to have several grams of radium, costing $180 000/gram, in their possession. Fortunately, Kelly and Janeway were the sole beneficiaries of a radium mining company, the National Radium Institute, from 1913 to 1916. With this unique American source of radium and with Europe otherwise preoccupied, these two American surgeons pioneered megavoltage telecurie therapy, using the 1.2 MeV gamma rays of “mass radium.”
Absorbed fractions in a voxel‐based phantom calculated with the MCNP‐4B code
Authors: Yoriyaz Hélio , dos Santos Adimir , Stabin Michael G. , Cabezas Roberto
Published: July 2002

A new approach for calculating internal dose estimates was developed through the use of a more realistic computational model of the human body. The present technique shows the capability to build a patient‐specific phantom with tomography data (a voxel‐based phantom) for the simulation of radiation transport and energy deposition using Monte Carlo methods such as in the MCNP‐4B code. MCNP‐4B absorbed fractions for photons in the mathematical phantom of Snyder et al. agreed well with reference values. Results obtained through radiation transport simulation in the voxel‐based phantom, in general, agreed well with reference values. Considerable discrepancies, however, were found in some cases due to two major causes: differences in the organ masses between the phantoms and the occurrence of organ overlap in the voxel‐based phantom, which is not considered in the mathematical phantom.
Rotating slant‐hole single‐photon emission‐computed tomography
Authors: Wessell Daniel Edward
Published: July 2002

This dissertation presents a detailed investigation of the use of rotating slant‐hole (RSH) collimators in single‐photon emission‐computed tomography (SPECT). We propose RSH SPECT as an alternative imaging technique, which may have advantages over more traditional SPECT techniques, in certain imaging applications. The basic imaging properties of RSH collimators are derived. This includes the derivation of expressions for the size and location of the common volume of view and the geometric resolution and efficiency. In addition, we derive an analytical expression for the geometric response and transfer functions of RSH collimators. The theoretical expressions for the aforementioned imaging characteristics are verified via Monte Carlo simulations and phantom experiments. Next, we present the development of a three‐dimensional (3‐D) analytic reconstruction algorithm for RSH SPECT. This includes the derivation of both a backprojection of the filtered projections and a filtering of the simple backprojections (BpjF) algorithm. The relationship between the derived 3‐D RSH reconstruction filter and a number of other reconstruction filters is discussed. In addition, the implementation of the BpjF reconstruction algorithm is described and its performance is demonstrated via simulations and phantom experiments. We have also implemented an iterative ordered‐subsets expectation‐maximization (OS‐EM) reconstruction algorithm for RSH SPECT. A detailed description of the development of the projector/backprojector employed by the OS‐EM algorithm is provided. Simulation and phantom experiments are again used to demonstrate the performance of the projector/backprojector and the iterative OS‐EM reconstruction algorithm. Rotating slant‐hole SPECT has potential applications in cardiac and breast imaging. Thus, we demonstrate the feasibility, advantages, and disadvantages of using RSH SPECT via a comparison with conventional SPECT in a cardiac and breast imaging phantom experiment. In conclusion, we summarize the results presented and discuss their implications on the current and future state of RSH SPECT research.
Testing the development of student conceptual and visualization understanding in quantum mechanics through the undergraduate career
Authors: Cataloglu E. , Robinett R. W.
Published: July 2002

In order to probe various aspects of student understanding of some of the core ideas of quantum mechanics, and especially how they develop over the undergraduate curriculum, we have developed an assessment instrument designed to test conceptual and visualization understanding in quantum theory. We report data obtained from students ranging from sophomore-level modern physics courses, through junior–senior level quantum theory classes, to first year graduate quantum mechanics courses in what may be the first such study of the development of student understanding in this important core subject of physics through the undergraduate career. We discuss the results and their possible relevance to the standard curriculum as well as to the development of new curricular materials.
The shape of “the Spandex” and orbits upon its surface
Authors: White Gary D. , Walker Michael
Published: July 2002

What is the shape that results when a flat rubber sheet is warped by placing a heavy ball upon it? We show that, at distance R far from the center of a ball of mass M, the height h of the surface above the ball’s center is given by h(R)=AM1/3R2/3, where A is a constant determined by the stretchiness of the rubber and the earth’s gravitational constant. This happy result allows one to analyze the orbits of marbles and coins as they roll across the surface in some detail, providing very nice analogues for a wealth of topics in celestial mechanics, from Kepler’s laws to tides and the Roche limit.
1D toy model for magnetic trapping
Authors: Gov S. , Shtrikman S. , Thomas H.
Published: July 2002

We study, both classically and quantum mechanically, the problem of a neutral particle with a spin angular momentum S, mass m, and magnetic moment μ, moving in one dimension in an inhomogeneous magnetic field given by B=B0ẑ+B⊥′xŷ. This problem serves for us as a toy model to study the trapping of neutral particles. We identify K≡[S2(B⊥′)2/μmB03], which is the ratio between the precessional frequency of the particle and its vibrational frequency, as the relevant parameter of the problem. Classically, we find that when μ is antiparallel to B, the particle is trapped provided that K<0.5. We also find that viscous friction, be it translational or precessional, destabilizes the system. Quantum mechanically, we study the problem of a spin S=ℏ/2 particle in the same field. Treating K as a small parameter for the perturbation from the adiabatic Hamiltonian, we find that the lifetime Tesc of the particle in its trapped ground state is Tesc=(Tvib/2π)(1/8πK)exp(2/K), where Tvib=2πmB0/μ(B⊥′)2 is the classical period of the particle when placed in the adiabatic potential V=μ|B|.
Evidence for spatial tuning in informational masking using the probe-signal method
Authors: Arbogast Tanya L. , Kidd Gerald
Published: July 2002

Auditory spatial attention is one mechanism that may contribute to the ability to identify one sound source in a multi-source environment. The role of auditory spatial attention in a multi-source environment was investigated using the probe-signal method. The experiment took place in a quiet room with seven speakers arranged in a semi-circle in front of the listener. The speakers were placed at 30-degree intervals at a distance of 5 ft from the listener. The signal was comprised of eight contiguous, 60-ms pure-tone bursts arranged in either a rising or falling frequency pattern. Masker components were also comprised of eight contiguous pure-tone bursts but with durations that varied randomly from 20 to 100 ms. The six maskers were played with the signal and were constructed in order to result in informational rather than energetic masking. The frequency of each masker component was chosen randomly on each burst from a narrow frequency band, independent from the signal frequency band. The task was 1I-2AFC fixed-level identification with response time measurement. The listener was instructed to focus attention on a specified speaker (expected location) for a block of trials. Accuracy and response time were compared across two conditions: (1) signal presented at the expected location and (2) signal presented at an unexpected location. Results indicate a significant increase in accuracy and faster response time when the signal was presented at the expected location as compared to an unexpected location. These results suggest that auditory spatial attention plays an important role in multi-source listening, especially when the listening environment is complex and uncertain.
The short-wave model and waves in two directions
Authors: de Boer Egbert
Published: July 2002

In the region where a sinusoidal wave in the cochlea reaches its maximum amplitude, the long-wave (or one-dimensional) model of the cochlea is deficient. In this region a short-wave model is more appropriate. However, in its current form, the short-wave model supports only waves in one direction. Therefore, it cannot cope with reflection effects associated with, e.g., inhomogeneities. Theoretical explorations of creation and internal reflection of otoacoustic emissions have almost exclusively been based on the long-wave model. In this article the road is paved for future explorations on a generalized form of the short-wave model, one that supports forward as well as backward waves, and thus can include internal reflections.
Binaural coherence edge pitch
Authors: Hartmann William M. , McMillon Colleen D.
Published: July 2002

The binaural coherence edge pitch (BICEP) is a dichotic broadband noise pitch effect similar to the binaural edge pitch (BEP). The BICEP stimulus is made by summing spectrally dense sine wave components with random phases. The interaural phase angle is a constant (0 or π) for components with frequencies below (or above) a chosen edge frequency, and it is a random variable for the remaining components. The chosen edge frequency is a coherence edge because the noises to the two ears are mutually coherent within any band of frequencies on one side of the edge and they are mutually incoherent in any band on the other side. Pitch-matching experiments show that the BICEP exists for coherence edge frequencies between about 300 and 1000 Hz. It is matched by a pure-tone frequency that differs from the edge frequency by 5% to 10%. The matching frequency lies on the incoherent side of the edge, an important result that is consistent with the way that the equalization-cancellation model has been applied to binaural pitch effects, especially the BEP. The results of BICEP experiments depend upon whether the coherent components are presented in 0 or π interaural phase for some listeners but not for all. The BICEP persists if the noise to one of the ears is delayed, but it becomes weaker and less well matched as the delay increases beyond 2 ms. The BICEP does not depend on whether the component amplitudes are all created equal or are given a Rayleigh distribution. Some reliable pitch sensation exists even when the component amplitudes are entirely independent in the two ears, so long as the phase coherence conditions of the BICEP stimulus are maintained. The existence of the BICEP is a challenge for current models of dichotic pitch because none of them predicts all its features.
Nonlinear two-dimensional model for thermoacoustic engines
Authors: Hamilton Mark F. , Ilinskii Yurii A. , Zabolotskaya Evgenia A.
Published: July 2002

A two-dimensional model and efficient solution algorithm are developed for studying nonlinear effects in thermoacoustic engines. There is no restriction on the length or location of the stack, and the cross-sectional area of the resonator may vary with position along its axis. Reduced model equations are obtained by ordering spatial derivatives in terms of rapid variations across the pores in the stack, versus slow variations along the resonator axis. High efficiency is achieved with the solution algorithm because the stability condition for numerical integration of the model equations is connected with resonator length rather than pore diameter. Computation time is reduced accordingly, by several orders of magnitude, without sacrificing spatial resolution. The solution algorithm is described in detail, and the results are verified by comparison with established linear theory. Two examples of nonlinear effects are investigated briefly, the onset of instability through to saturation and steady state, and nonlinear waveform distortion as a function of resonator shape.
Frequency derivative approach for identification of the wave resonances on immersed elastic bodies
Authors: Dubus Bertrand , Lavie Antoine , Veksler Naum D.
Published: July 2002

Acoustic scattering by elastic bodies is usually analyzed in terms of resonances, the frequency, width, and order of which should be determined. In this paper, a simple approach based on a frequency derivative of the scattered pressure is proposed for resonance order identification on bodies of arbitrary shape. The method is applied to the acoustic scattering of a plane wave by a spherical shell for validation and by a cylindrical shell bounded by hemispherical end caps. In both cases, the A and S0 wave resonances are identified.
Comments on “Biot model of sound propagation in water-saturated sand” [J. Acoust. Soc. Am. 97, 199–214 (1995)]
Authors: Stoll R. D.
Published: July 2002

Input parameters to the Biot theory, used by N. P. Chotiros [J. Acoust. Soc. Am. 97, 199–214 (1995)] in an effort to claim that a slow wave propagating at 1200 m/s was experimentally observed in near-bottom sand, are shown to be inconsistent with generally accepted results from prior theoretical and experimental studies of granular media.
The spectrogram correlation and transformation receiver, revisited
Authors: Peremans H. , Hallam J.
Published: July 2002

The spectrogram correlation and transformation (SCAT) receiver has been proposed as a model for the receiver structure used by fm bats. The main contribution of this paper lies in the analysis of which features of the proposed model are responsible for its high accuracy in estimating arrival times of overlapping echoes. Apart from providing an answer to this question, the analysis will also indicate the limitations of the SCAT receiver. In particular, it is shown that the temporal block of the SCAT receiver returns erroneous results for interecho delays <20 μs and for interecho amplitude ratios >6 dB. It is also shown that the spectral block of the SCAT receiver generates spurious arrival times if more than two overlapping echoes are present. Finally, it is discussed how the characteristic measurement errors predicted by this analysis can be used to further investigate the accuracy of the SCAT receiver as a model of the receiver structure used by fm bats.
Air cavity modes in sound boxes recorded by TV holography
Authors: Runnemalm Anna , Molin Nils-Erik
Published: July 2002

Amplitude and phase distribution of air cavity modes in a rectangular box, in a guitar, and in a violin are measured using TV holography. The box and the top and back plates of the guitar and the violin are made transparent using 5-mm-thick and flat PMMA plates. Standing waves in the enclosed cavities are generated by a loudspeaker. Object laser light is sent through the cavities to a rigid white-painted steel block and reflected back again through the cavities to the optical unit of the TV holography interferometer. Laser light traveling through a sound pressure field will experience a phase delay, since an increased air pressure is accompanied by a higher air density as well as a higher index of refraction which in turn gives a slower speed of the laser light, which generates a phase delay compared to undisturbed air. This often small phase change is made visible by the highly sensitive phase-modulated TV holography technique. The optical system will be described and air cavity modes in a simple rectangular box, in a guitar, and in a violin will illustrate the presentation.
Elastic wave propagation and scattering in heterogeneous, anisotropic media: Textured polycrystalline materials
Authors: Turner Joseph A.
Published: July 2002

The propagation of elastic waves through heterogeneous, anisotropic media is considered. Appropriate ensemble averaging of the elastic wave equation leads to the Dyson equation which governs the mean response of the field. The Dyson equation is given here in terms of anisotropic elastic Green’s dyadics for the medium with and without heterogeneities. The solution of the Dyson equation for the mean response is given for heterogeneities that are weak. The formalism is further specified for the case of equiaxed cubic polycrystalline metals with a single aligned axis. The Green’s dyadics in this case are those for a transversely isotropic medium. Simple expressions for the attenuations of the shear horizontal, quasicompressional, and quasishear waves are given in terms of integrations on the unit circle. The derived expressions are limited to frequencies below the geometric optics limit, but give the attenuations in a direct manner. Comparisons with previous results are also discussed. It is anticipated that a similar approach is necessary for the study of wave propagation in complex anisotropic materials such as fiber-reinforced composites. In addition, the results are applicable to diffuse ultrasonic inspection of textured polycrystalline media.
Acoustic attenuation in very shallow water due to the presence of bubbles in rip currents
Authors: Caruthers J. W. , Stanic S. J. , Elmore P. A. , Goodman R. R.
Published: July 2002

An experiment was performed just off the research pier at the Scripps Institute of Oceanography to determine the acoustic effects of small bubbles in very shallow water (∼6 m depth). The distance offshore was ∼300 m. The propagation lengths were 2–10 m, and the frequency range was from 39 to 244 kHz. During the experiment, rip currents passed through the field of measurement instruments. These rip currents were laden with bubbles created in the surf between the instruments and the shore. The effects of these rip currents on the spatial distributions of the resulting acoustic attenuation are discussed. From the attenuation data, the bubble distributions are calculated using a new iterative approach [Caruthers et al., in press, J. Acoust. Soc. Am.] that is based on the well-known resonant bubble approximation. Calculated bubble distributions varied from an essentially uniform lack of bubbles during quiescent periods to highly inhomogeneous and dense bubbly regions within rip events. Such observed distributions were consistent with measurements made by other investigators during the experiment.
Underwater temporary threshold shift induced by octave-band noise in three species of pinniped
Authors: Kastak David , Schusterman Ronald J. , Southall Brandon L. , Reichmuth Colleen J.
Published: July 2002

Pure-tone sound detection thresholds were obtained in water for one harbor seal (Phoca vitulina), two California sea lions (Zalophus californianus), and one northern elephant seal (Mirounga angustirostris) before and immediately following exposure to octave-band noise. Additional thresholds were obtained following a 24-h recovery period. Test frequencies ranged from 100 Hz to 2000 Hz and octave-band exposure levels were approximately 60–75 dB SL (sensation level at center frequency). Each subject was trained to dive into a noise field and remain stationed underwater during a noise-exposure period that lasted a total of 20–22 min. Following exposure, three of the subjects showed threshold shifts averaging 4.8 dB (Phoca), 4.9 dB (Zalophus), and 4.6 dB (Mirounga). Recovery to baseline threshold levels was observed in test sessions conducted within 24 h of noise exposure. Control sessions in which the subjects completed a simulated noise exposure produced shifts that were significantly smaller than those observed following noise exposure. These results indicate that noise of moderate intensity and duration is sufficient to induce TTS under water in these pinniped species.
Mode-locking of acoustic resonators and its application to vibration cancellation in acoustic heat engines
Authors: Spoor P. S. , Swift G. W.
Published: July 2002

Vibration induced in engine hardware by a working fluid can be very significant in high-power, high-amplitude acoustic heat engines, and is a serious impediment to their practical use. This vibration can cause fatigue and destruction of engine components as well as fuel lines, cooling lines, and sensor wires. The forces involved make anchoring such an engine to an “immovable” object impractical. Rigidly attaching two such engines together, and acoustically coupling them with a duct of such a length and diameter that the two engines mode-lock in antiphase (thus canceling the longitudinal vibration) appears to be an inexpensive, viable solution. This paper describes in detail experiments demonstrating the feasibility of this idea, and the underlying theory.
The dependence of target strength of the northern right whale (Eubalaena glacialis) on the acoustic properties of blubber
Authors: Miller James H. , Weber Thomas , Tuttle Angela , Potter David C.
Published: July 2002

Whale detection and tracking using active sonar is a subject of recent study [J. H. Miller, D. C. Potter, T. Weber, and J. Felix, J. Acoust. Soc. Am. 105, 992 (1999)]. In that previous work, the measured target strength of a northern right whale (Eubalaena glacialis) was found to be less than that measured for a humpback whale (Megaptera novaeangliae) of the same size and aspect (about 0 and 5 dB, respectively). The difference was explained by modeling the thicker blubber of the right whale as a lossy layer in a plane wave reflection coefficient. However, values for the acoustic properties of the blubber were estimated from tissue properties of other mammals [R. C. Chivers and R. J. Parry, J. Acoust. Soc. Am. 63 (1978)]. In April, 1999, a 60-ton northern right whale named Staccato was found dead near Cape Cod. Blubber samples were acquired by the National Marine Fisheries Service and acoustic properties determined using a multi-sensor core logger in URI Marine Geomechanics Laboratory. Sound speed and density data have been used to refine the plane wave reflection coefficient model and corroborate the earlier work. [Work supported by NMFS.]
Auditory hazard from airbag noise exposure
Authors: Price G. Richard , Kalb Joel T.
Published: July 2002

Airbag deployment includes very intense acoustic stimulation, yet almost no tests of auditory hazard have been done with real ears. Therefore 32 anesthetized cats, positioned at the driver and passenger locations in a pickup truck, were exposed in pairs to one airbag deployment (electrically initiated). Hearing was tested at 1, 2, 4, 8, and 16 kHz by evoked-response audiometry just before exposure, immediately after and at 1 month and 6 months. Exposure conditions included doors open, compartment closed, and closed compartment sealed with tape: seven exposures to passenger bag only and nine to driver and passenger bags. Peak pressures ranged from 167 to 173 dB with unweighted energies as high as 4000 J/m2 (or 8 hr LEQA=95.5 dB). The immediate threshold shift averaged 60 dB at 4.0 kHz that resolved to an average permanent shift of 37 dB. By extrapolation, these data from cats may indicate that susceptible human ears risk permanent hearing loss from airbag noise.
Seismic/electromagnetic system for landmine detection
Authors: Scott Waymond R. , Larson Gregg D. , Martin James S. , Rogers Peter H.
Published: July 2002

A system has been designed for the detection of buried landmines. The system uses a stationary seismic source in conjunction with a movable displacement sensor that is based on an 8 GHz CW radar. The sensor measures the surface displacement by analog demodulation of the radar signal, which is reflected from the soil surface and modulated by the surface motion. The sensor is not in direct contact with the soil surface and is, therefore, capable of interrogating surface motion immediately above a buried mine. This configuration provides the dual advantage of removing half the seismic propagation path that would be encountered with a classical pulsed echo technique and detecting localized fields that would not propagate to a remote receiver. The system has been used in the laboratory to image inert antipersonnel mines and simulated antitank mines buried in damp compacted sand. Signal processing in the wave number domain provides significant improvement in the contrast between mine-related and background motion. The simplest detection cue for antipersonnel mines was found to be low-frequency resonances of their trigger mechanisms. These responded to seismic excitations with substantial local displacement. The resonances made these mines easily discernable from buried clutter such as rocks and sticks. [Work supported by ARO.]
Maximum a posteriori deconvolution of ultrasonic signals using multiple transducers
Authors: Olofsson Tomas , Stepinski Tadeusz
Published: July 2002

A new method for deconvolution of ultrasonic pulse-echo measurements employing multiple-transducer setup is proposed in the paper. An optimal way of estimating the material reflection sequence for a linear signal generation model using maximum a posteriori estimation is proposed. The method combines the measurements from a number of transducers covering different frequency bands yielding an optimal estimate of the reflection sequence. The main idea of this approach is to complement the information unavailable from one transducer in some frequency bands with the information from the other transducers. The method is based on the assumption that the measurements are performed using transducers with identical apertures and apodization, which are located exactly at the same position relative to the test object during the measurement. An error analysis presented in the paper proves that when the above assumptions are fulfilled, the proposed method, by utilizing more data for estimation, consistently yields more accurate reflection sequence estimates than the classical Wiener filter. Experimental evidence is presented using both simulated and real ultrasonic data as a verification of the correctness of the multiple-transducer model and the estimation scheme. An illustration of the advantages of the method is also given using real ultrasonic data.