bluuebunny/crossref_metadata_2025 huggingface dataset:
A new penumbra generator for electron fields matching
Authors: Lachance B. , Tremblay D. , Pouliot J.
Published: July 2002

Abutment of two or more electron fields to irradiate extended areas may lead to significant dose inhomogeneities in the junction region. This paper describes the geometric and dosimetric characteristics of a device developed to modify the penumbra of an electron beam and thereby improve the dose uniformity in the overlap region when fields are abutted. The device is a Lipowitz metal block placed on top of the electron applicator's insertion plate and positioned to stop part of the electron beam on the side of field abutment. The air‐scattered electrons beyond the block increase the penumbra width from about 1.4 to 2.7–3.4 cm with an SSD of 100 cm. The modified penumbra is broad and almost linear at all depths for the 9 and 12 MeV electron beams used in this study. Film dosimetry was used to obtain beam profiles and isodose distributions of single modified beams and matched fields of 9 and 12 MeV as well as matched fields of both energies. Computer simulation was used to optimize the skin gap to be used and to quantify the dose uniformity as a function of the field separation for both modified and nonmodified beams. Results are presented for various field configurations. Without the penumbra generator, lateral setup errors of 2–3 mm may introduce dose variations of 20% or more in the junction region. Similar setup errors cause less than 5% dose variations when the penumbra generator is used to match the fields. The potential of the technique for the irradiation of curved surfaces is presented. A possible method for implementing the modified penumbra into a conventional treatment planning system is evaluated.
Treatment planning for prostate implant with loose seeds
Authors: Chen Yan , Stanton Robert E. , Holst Rodger J. , Koprowski Christopher D. , Krisch Evan B.
Published: July 2002

A new method of treatment planning for the I‐125 and Pd‐103 permanent interstitial prostate implant is developed, which does not use the traditional nomograms but automatically generates optimized source configurations. An iterative algorithm is used that places one seed at a step. The volume dose of target is calculated at each step to determine the coldest spot where the next source is to be placed, so that the dose uniformity of target is best improved as source placement proceeds. At each step, the total activity required for the seed configuration as so established is calculated by normalizing the minimal dose to the prescribed dose. An optimized configuration is the one that takes the minimized total activity. Around its minimum the total activity has a very small variation with the number of seeds. Consequently multiple clinically acceptable seed configurations with similar total activity but different individual activities are generated simultaneously. In our computer generated treatment plans most of the seeds are distributed in the periphery of the target, similar to the Paterson–Parker pattern of a volume implant.
Optimized accelerator based epithermal neutron beams for boron neutron capture therapy
Authors: Kudchadker Rajat J.
Published: July 2002

Current accelerator based neutron source concepts for boron neutron capture therapy (BNCT) are centered on the lithium reaction which has a reaction threshold energy of 1.881 MeV. Bombarding energies several hundred keV above the reaction threshold are used (2.3 MeV–2.5 MeV), resulting in neutrons having energies approaching 1 MeV. Large inefficient moderator reflector assemblies are required to reduce the energies of these neutrons to the desired therapy beam energy (1 eV to 10 keV). Operating with proton energies near the reaction threshold decreases the neutron yield but produces neutrons with energies less than 200 keV. In addition, all the neutrons emitted from the lithium target are kinematically collimated in the forward direction. This allows for a smaller more efficient moderator reflector arrangement, increasing the useful epithermal neutron flux available at the irradiation position and reducing gamma and fast neutron contamination. This concept has been proved by comparing Monte Carlo (MCNP) calculations with benchmark experiments. Neutron properties (energies, yields and angular distribution), moderator reflector design concepts, optimum accelerator proton energy, which maximize performance for BNCT, have also been studied. The results indicate that for a lithium target, 3 mA of 1.91 MeV protons can produce an epithermal flux of 109 n/cm2/s at the patient irradiation position.
An accelerator‐based epithermal photoneutron source for boron neutron capture therapy
Authors: Mitchell Hannah E.
Published: July 2002

Boron neutron capture therapy is an experimental cancer radiotherapy modality in which a boronated pharmaceutical that preferentially accumulates in malignant tissue is administered, followed by exposure of the tissue in the treatment volume to a thermal neutron field. Presently in the US and Europe, for treatment of deeper‐seated tumors, an epithermal beam is felt preferable in generating the necessary thermal neutron field. Boronated cells are selectively destroyed via energy deposition resulting from the interaction. Current usable beams are reactor‐based; a viable alternative is production of the epithermal neutron beam using an accelerator. Various proposed accelerator‐based designs exist, most based on proton beams with beryllium or lithium targets. This dissertation examines the efficacy of a novel approach incorporating an electron linear accelerator (4 to 8 MeV) in the production of a photoneutron source, which may help to resolve present concerns associated with some accelerator‐based sources, including target cooling. A conceptual design to produce epithermal photoneutrons, with high energy bremsstrahlung on deuterium targets, is presented along with computational and experimental neutron production data. A clinically acceptable epithermal neutron flux on the order of neutrons/second per milliampere of electron current is shown obtainable. Additionally, the neutron beam is modified and characterized, employing two unique moderating materials (an composite and a stacked Al/Teflon design).
Tissue equivalence correction for silicon microdosimetry detectors in boron neutron capture therapy
Authors: Bradley P. D. , Rosenfeld A. B.
Published: July 2002

Reverse‐biased silicon junction arrays have been proposed as microdosimetry detectors. The tissue equivalence of such detectors in boron neutron capture therapy (BNCT) is discussed. A comparison of the range‐energy relationships of H, He, C, and Li ions in tissue (ICRU‐muscle) and silicon is given. A simple geometrical scaling (∼0.63) of linear dimensions is required to convert microdosimetric energy deposition measurements performed in silicon to equivalent deposition in tissue. The Monte Carlo technique is used to examine energy deposition for two simple geometrical cases applicable to BNCT.
Delivery and verification of intensity‐modulated x‐ray beams in radiotherapy
Authors: Curtin‐Savard Arthur J.
Published: July 2002

This thesis deals with the implementation of intensity‐modulated radiation therapy into the clinic and a method of quality assurance which can be used on each intensity‐modulated beam prior to treatment. The first component of the thesis was to write a step‐and‐shoot leaf sequence algorithm to control the multileaf collimator (MLC) fitted to our Clinac 2300 C/D linear accelerator. Our algorithm takes into account the MLC transmission, MLC penumbra, and change in scatter conditions with field size and is also slightly more efficient than other published step‐and‐shoot type algorithms. The second (and major) component of the thesis was to investigate the use of a portal imaging device for dosimetric verification purposes. We show that an electronic portal imaging device of the scanning liquid ionization chamber type yields images which, once calibrated from a previously determined calibration curve, provide highly precise planar maps of the incident dose rate. For verification of an intensity‐modulated x‐ray beam delivered in the segmented approach with a MLC, a portal image is acquired for each subfield of the leaf sequence. Subsequent to their calibration, the images are multiplied by their respective associated monitor unit settings, and summed to produce a planar dose distribution at the measurement depth in phantom. The excellent agreement of our portal imager measurements with calculations of our treatment planning system and data from a one‐dimensional beam profiler attests to the usefulness of this method for the planar verification of intensity‐modulated fields produced in the segmented approach on a computerized linear accelerator equipped with a multileaf collimator.
Intrapatient consistency of imaging biodistributions and their application to predicting therapeutic doses in a phase I clinical study of ‐based radioimmunotherapy
Authors: Clarke K. G. , Odom‐Maryon T. L. , Williams L. E. , Liu A. , Lopatin G. , Chou J. , Farino G. M. , Raubitschek A. A. , Wong J. Y. C.
Published: July 2002

Intrapatient variation in the biodistribution of the chimeric monoclonal antibody cT84.66 was assessed in 19 patients having a variety of carcinoembryonic antigen (CEA) positive tumors. The two studies, including whole‐body imaging and blood and urine specimen collections, were conducted within 14 days of each other using at a fixed total protein dose of 5 mg per patient per study. An initial pretherapy infusion of was administered followed by a therapy coinfusion of and A closed five‐compartment model was used to integrate source organ activity curves as residence time inputs into the MIRDOSE3 program. Normal organ absorbed doses were estimated for the corresponding radiotherapeutic agent. For the two biodistributions, all data were modeled with a value of between 0.72 and 1.00 with the exception of the urine data taken during therapy. This was due to the need of diethylenetriaminepentaacetic acid during the therapy phase because of the possibility that yttrium might escape from the chelator attached to the antibody. With the assurance that the biodistributions were reproducible, we were able to estimate the absorbed doses on a per‐patient basis. Concordance coefficients showing the agreement between the imaging and therapy phase dose estimates were between the 0.60 and 0.99 levels for liver, spleen, red marrow, total body, and other organ systems. Median results were: 27, 17, and 2.7 rad/mCi of for liver, spleen, and red marrow, respectively. Because of decreases in platelets and white cells as the amount of was increased, dose‐limiting toxicity was found at 22 mCi/m2. We conclude that patient biodistributions were consistent over time to 14 days so as to allow absorbed dose estimation in a radioimmunotherapy trial involving the cT84.66 anti‐CEA antibody.
Monte Carlo studies of the exit photon spectra and dose to a metal/phosphor portal imaging screen
Authors: Yeboah C. , Pistorius S.
Published: July 2002

The energy spectra and the dose to a Cu phosphor portal imaging detector were investigated for monoenergetic incident beams of photons (1.25, 2, and 5 MeV). The Monte Carlo method was used to characterize the influence of the patient/detector geometry, detector material and design, and incident beam energy on the spectral distribution and the dose, at the imaging detector plane, of a photon beam scattered from a water phantom. The results show that radiation equilibrium is lost in the air gap and that, for the geometries studied, this effect led to a reduction in the exit dose of up to 40%. The finding that the effects of the air gap and field size are roughly complementary has led to the hypothesis that an equivalent field size concept may be used to account for intensity and spectral changes arising from air gap variations. The copper plate preferentially attenuates the low‐energy scattered photons incident on it, while producing additional annihilation, bremsstrahlung, and scattered photons. As a result, the scatter spectra at the copper surface entrance of the detector differs significantly from that at the Cu/phosphor interface. In addition, the mean scattered photon energy at the interface was observed to be roughly 0.4 MeV higher than the corresponding effective energy for 2 MeV incident beams. A comparison of the dose to various detector materials showed that exit dosimetry errors of up to 24% will occur if it is assumed that the Cu phosphor detector is water equivalent.
The maximal invariance group of Newton’s equations for a free point particle
Authors: Jahn O. , Sreedhar V. V.
Published: July 2002

The maximal invariance group of Newton’s equations for a free nonrelativistic point particle is shown to be larger than the Galilei group. It is a semidirect product of the static (nine-parameter) Galilei group and an SL(2,R) group containing time translations, dilations, and a one-parameter group of time-dependent scalings called expansions. This group was first discovered by Niederer in the context of the free Schrödinger equation. We also provide a road map from the free nonrelativistic point particle to the equations of fluid mechanics to which the symmetry carries over. The hitherto unnoticed SL(2,R) part of the symmetry group for fluid mechanics gives a theoretical explanation for an observed similarity between numerical simulations of supernova explosions and numerical simulations of experiments involving laser-induced implosions in inertial confinement plasmas. We also give examples of interacting many-body systems of point particles which have this symmetry group.
Conceptual astronomy. II. Replicating conceptual gains, probing attitude changes across three semesters
Authors: Zeilik Michael , Schau Candace , Mattern Nancy
Published: July 2002

We report on a long-term, large-scale study of a one-semester, conceptually based, introductory astronomy course with data from more than 400 students over three semesters at the University of New Mexico. Using traditional and alternative assessment tools developed for the project, we examined the pre- and postcourse results for Fall 1994, Spring 1995, and Fall 1995. We find our results are robust: novice students show large, positive gains on assessments of conceptual understanding and connected understanding of the knowledge structure of astronomy. We find no relationship between course achievement and completion of prior courses in science or math; we do find a small to moderate relationship between students’ science self-image and course achievement. Also, we detect little change over each semester in students’ mildly positive incoming attitudes about astronomy and science.
Visualizing the collapse and revival of wave packets in the infinite square well using expectation values
Authors: Robinett R. W.
Published: July 2002

We investigate the short-, medium-, and long-term time dependence of wave packets in the infinite square well. In addition to emphasizing the appearance of wave packet revivals, i.e., situations where a spreading wave packet reforms with close to its initial shape and width, we also examine in detail the approach to the collapsed phase where the position-space probability density is almost uniformly spread over the well. We focus on visualizing these phenomena in both position- and momentum-space as well as by following the time-dependent expectation values of and uncertainties in position and momentum. We discuss the time scales for wave packet collapse, using both an autocorrelation function analysis as well as focusing on expectation values, and find two relevant time scales which describe different aspects of the decay phase. In an Appendix, we briefly discuss wave packet revival and collapse in a more general, one-dimensional power-law potential given by V(k)(x)=V0|x/a|k which interpolates between the case of the harmonic oscillator (k=2) and the infinite well (k=∞).
Ultrasound-mediated disruption of cell membranes. I. Quantification of molecular uptake and cell viability
Authors: Guzmán Héctor R. , Nguyen Daniel X. , Khan Sohail , Prausnitz Mark R.
Published: July 2002

Ultrasound-mediated drug delivery is a nonchemical, nonviral, and noninvasive method for targeted transport of drugs and genes into cells. Molecules can be delivered into cells when ultrasound disrupts the cell membrane by a mechanism believed to involve cavitation. This study examined molecular uptake and cell viability in cell suspensions (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. With increasing pressure and exposure time, molecular uptake of a marker compound, a calcein, increased and approached equilibrium with the extra cellular solution, while cell viability decreased. Varying pulse length produced no significant effect. All viability and molecular uptake measurements collected over the broad range of ultrasound conditions studied correlated with acoustic energy exposure. This suggests that acoustic energy exposure may be predictive of ultrasound’s nonthermal bioeffects.
Boundary element method calculation of individual head-related transfer function. II. Impedance effects and comparisons to real measurements
Authors: Katz Brian F. G.
Published: July 2002

Following previous work by the author involving the calculation of an individual head-related transfer function (HRTF) using a Boundary Element Method (BEM) approach, impedance conditions are now included to take account of the acoustic properties of human hair. In addition, comparisons are made here between calculations and measured values for the HRTF of a specific individual. Numerous works have been published regarding the measurement of HRTFs, but rarely are several methods compared for the same individual. The results presented in the work compare two different measurement techniques and a computational BEM for acquiring an individual HRTF. Impedance effects have been incorporated in the BEM model for hair based on measured data, providing a final set for comparison. Measurement results show significant variations for the same individual. Computational results show good agreement within the range of experimental variations. Definite trends are observed for many directions, while the limitations of the methods are also highlighted for others. The effects of incorporating hair impedance are shown to provide an improvement in the correlation of computational results, indicating an affect of hair impedance on the HRTF.
Frame-borne surface waves in air-saturated porous media
Authors: Allard J. F. , Jansens G. , Vermeir G. , Lauriks W.
Published: July 2002

A Rayleigh-type surface wave at an air–air saturated porous layer interface is predicted and detected experimentally in the audible frequency range. Applications of this surface wave for the metrology of sound-absorbing media are suggested.
Numerical implementation of the lumped parameter model for the acoustic power output of a vibrating structure
Authors: Fahnline John B. , Koopmann Gary H.
Published: July 2002

In a previous paper, a lumped parameter model for the acoustic radiation from a vibrating structure was defined by dividing the surface of the structure into elements, expanding the acoustic field from each of the elements in a multipole expansion, and truncating all but the lowest-order terms in the expansion. Here, the lumped parameter model is implemented numerically by requiring the boundary condition for the normal surface velocity to be satisfied in a lumped parameter sense. This alleviates the difficulties typically encountered in enforcing the boundary condition, leading to a relatively simple numerical solution with well-defined convergence properties. The basis functions for the numerical analysis are taken as the acoustic fields of discrete simple, dipole, and tripole sources located at the geometrical centers of the surface elements. The different source types are used to represent the radiation from different kinds of surface elements: simple sources for elements in the plane of an infinite baffle, dipole sources for very thin structures which deform only in bending, and tripole sources for elements associated with parts of a structure enclosing a finite volume. The convergence of the numerical solution for the power output as a function of both frequency and element size is demonstrated through several example problems.
Use of reciprocity to characterize ultrasonic transducers in air above 100 kHz
Authors: Anderson Michael J. , Liu Xu
Published: July 2002

The three-transducer free-field reciprocity calibration technique has been extended to apply to ultrasonic transducers operating in air at frequencies above 100 kHz. The reciprocity method was extended to apply to this frequency range by correcting for attenuation, which is severe in air, and for diffraction. Validation of the extended reciprocity calibration technique was performed by comparing experimental determinations of receive and transmit sensitivity with predictions obtained from a mathematical model for the test transducers and calibration system. It is believed that these are the first comprehensive, broadband experimental determinations of absolute transmit and receive sensitivity to appear in the technical literature for transducers operating in air over the frequency range 100–500 kHz. Receive and transmit sensitivity measurements obtained with the extended reciprocity calibration technique agreed to within 2.5 dB of model predictions. The location of the resonance peaks in the sensitivity measurements had a maximum difference of 7% from those inferred from measurements of transducer admittance and those predicted by the transducer model. It was concluded that both the extended reciprocity calibration technique and the transducer model were accurate to within this level of discrepancy.
Plane-wave reflection from a solid layer with nonuniform density, sound speed, and shear speed
Authors: Robins Alvin J.
Published: July 2002

This paper considers the problem of calculating the reflection coefficient of a plane wave incident on an inhomogeneous elastic solid layer of finite thickness, overlying a semi-infinite, homogeneous solid substrate. The physical properties of the inhomogeneous layer, namely the density, compressional (sound) speed, shear speed, and attenuation, are all assumed to vary with depth. It is shown that, provided terms involving the gradient of the shear speed and of the shear modulus are ignored, and volume coupling between compressional and shear waves is neglected, analytical solutions of the resulting equations can be obtained. The assumptions made are justified at most frequencies of practical interest in underwater acoustics. In the case of a solid whose density and shear speed are constant, the results obtained are exact solutions of the full equations of motion, and may usefully be compared with numerical solutions in which the variation in sound speed through the layer is represented by a number of homogeneous sublayers. It is concluded that, with realistic sediment and substrate properties, a surprisingly large number of sublayers can be needed to give accurate results.
Ultrasonic propagation in metal powder-viscous liquid suspensions
Authors: Schulitz Frederick T. , Lu Yichi , Wadley Haydn N. G.
Published: July 2002

The need to measure the volume fraction of metal powder during the slurry casting synthesis of metal matrix composites has stimulated a new interest in ultrasonic propagation in metal powder-viscous liquid suspensions. Using model slurries, a systematic series of ultrasonic tests have been conducted to experimentally identify the frequency dependent relationships between ultrasonic velocity/attenuation and the particle volume fraction, the suspending liquid’s viscosity and the particle’s shape. For slurries with the compositions and viscosities typical of those used in slurry casting, the velocity decreases and the attenuation increases with particle fraction. The data have been compared to predictions of the Harker–Temple hydrodynamic model for these systems. The velocity measurements were well predicted by the model with a difference between measured and predicted velocities of about 0.25%. The ultrasonic attenuation was underpredicted by this model in part by its use of a rule of mixtures and by its failure to incorporate the intrinsic absorption/scattering within the powder phase.
Jet-wave amplification in organ pipes
Authors: Yoshikawa Shigeru
Published: July 2002

An envelope-based method to estimate both the jet-wave amplification factor and the mouth-field strength in organ pipes is developed by using flow visualization of a smoked jet with a high-speed digital video camera. A theoretical envelope of wave growth, which is approximated using a negative displacement model of the jet drive, is compared with an experimental envelope derived from superposing many instantaneous shapes of jet deflection in the steady-state oscillation. The estimation results are presented in dimensional terms with respect to two particular models, where the flue-to-edge distances are, respectively, 15.8 and 10.2 mm, with a common flue thickness of 2.2 mm. In our experiment the jet velocity ranges from 7 to 33 m/s, the Reynolds number from 1000 to 5000, and the sounding frequency from 130 to 580 Hz. The amplification factor of organ pipe jets, estimated to lie in the 0.18–0.26-mm−1 range, tends to decrease and saturate with increasing blowing velocity in each oscillation mode; the mouth-field strength defined as the acoustic displacement amplitude, roughly estimated to be 0.5–1.5 mm, tends to increase and saturate with increasing blowing velocity. A hot-wire anemometer is then used to measure the mouth-field strength, whose value shows a good agreement with the estimated one. This result confirms the validity of our envelope-based method. A dimensionless representation of the experimental data is used to compare wave characteristics between an organ pipe jet and an acoustically perturbed free jet. The applicability of the spatial and temporal theories of jet instability is discussed to analyze them. If we can assume a Poiseuille flow at the flue exit and a subsequent Bickley jet, the spatial theory seems to be relevant to our organ pipe jets. However, for lack of a reliable experimental measurement of the jet half-thickness we cannot draw a definite conclusion about the wave characteristics of organ pipe jets.
Ultrasonic spectroscopy of imperfect contact interfaces between a layer and two solids
Authors: Lavrentyev Anton I. , Rokhlin S. I.
Published: July 2002

Ultrasonic waves reflected from the front and back surfaces of a thin layer are often not separated in the time domain, and interfere. The spectrum of the resulting interference signal depends on (a) the thickness of the layer and the elastic moduli and density of the layer and the surrounding material (substrates), and (b) properties of the layer/substrate interface which can be described in terms of the interfacial stiffness. In this paper the effect of interfacial stiffness is isolated by considering the ultrasonic wave interaction with a solid layer compressed between two substrates of the same material. Since the layer and the substrate have identical properties the effect of impedance difference on the layer reflection vanishes. An aluminum system is selected for the experiment; the contacting surfaces are roughened and varying pressure is applied to model imperfect interface changes. It is shown both theoretically and experimentally that the contact pressure increase results in increase of the interfacial stiffness and spectral minima shift to higher frequency. A simple analytical expression relating the reflection minimum position to the interfacial stiffness is derived and shows good agreement with experimental results. It is shown that in the high-interfacial-stiffness limit the resonance minima positions are given by the condition h=λ/4+nλ/2, n=0,1,2,… . In the limit of low interfacial stiffness the first minimum shifts to zero and higher order resonances are given by h=nλ/2. Since the resonance minima measurements can be done with high precision it is proposed to use the frequency minimum shift for determination of interfacial stiffness and, consequently, the quality of the interfacial contact.
Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part III. The validity of using subject-fit data
Authors: Berger Elliott H. , Franks John R. , Behar Alberto , Casali John G. , Dixon-Ernst Christine , Kieper Ronald W. , Merry Carol J. , Mozo Ben T. , Nixon Charles W. , Ohlin Doug , Royster Julia Doswell , Royster Larry H.
Published: July 2002

The mandate of ASA Working Group S12/WG11 has been to develop “laboratory and/or field procedure(s) that yield useful estimates of field performance” of hearing protection devices (HPDs). A real-ear attenuation at threshold procedure was selected, devised, tested via an interlaboratory study, and incorporated into a draft standard that was approved in 1997 [J. D. Royster et al., “Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S12, Noise,” J. Acoust. Soc. Am. 99, 1506–1526 (1996); ANSI S12.6-1997, “American National Standard Methods for Measuring Real-Ear Attenuation of Hearing Protectors” (American National Standards Institute, New York, 1997)]. The real-world estimation procedure utilizes a subject-fit methodology with listeners who are audiometrically proficient, but inexperienced in the use of HPDs. A key factor in the decision to utilize the subject-fit method was an evaluation of the representativeness of the laboratory data vis-à-vis attenuation values achieved by workers in practice. Twenty-two field studies were reviewed to develop a data base for comparison purposes. Results indicated that laboratory subject-fit attenuation values were typically equivalent to or greater than the field attenuation values, and yielded a better estimate of those values than did experimenter-fit or experimenter-supervised fit types of results. Recent data which are discussed in the paper, but which were not available at the time of the original analyses, confirm the findings.
A novel boundary integral formulation for three-dimensional analysis of thin acoustic barriers over an impedance plane
Authors: de Lacerda L. A. , Wrobel L. C. , Power H. , Mansur W. J.
Published: July 2002

This article presents a three-dimensional formulation for the analysis of acoustic barriers over an impedance plane as infinitely thin structures. The barriers are therefore modeled as simple surfaces rather than volumetric structures. Using this approach, the problems caused by near-singular integrations and near-degenerate systems of equations are averted, and mesh generation is made easier. A dual-boundary-element method is used in the analysis, involving the simultaneous solution of standard and hypersingular boundary integral equations. An optimization procedure is used to speed up the assembling of the system of equations, increasing the applicability of the method to a wider range of frequencies.
Experimental confirmation of the two-source interference model for the fine structure of distortion product otoacoustic emissions
Authors: Talmadge Carrick L. , Long Glenis R. , Tubis Arnold , Dhar Sumit
Published: July 2002

High-resolution measurements of distortion product otoacoustic emissions (DPOAEs) from three different experimental paradigms are shown to be in agreement with the implications of a realistic “two-source” cochlear model of DPOAE fine structure. The measurements of DPOAE amplitude and phase imply an interference phenomenon involving one source in the region of strong nonlinear interaction of the primary waves (the strong “overlap” or generation region), and the other source region around the DPOAE tonotopic place. The component from the DPOAE place can be larger than the one from the generator region. These findings are supported by the analysis of the onset and offset of the DPOAE when the higher-frequency primary is pulsed on and off. The two-source hypothesis was further tested by adding a third tone closer in frequency to the DPOAE which modifies the amplitude of the component from the DPOAE place and leaves the one from the generator region unchanged. The results agree well with the model prediction that the variation with frequency, and implied latency, of the phase of the DPOAE tonotopic-place component are greater than the corresponding quantities for the component from the generation region.
Scattering from rigid and soft targets near a planar boundary: Numerical results
Authors: Bishop Garner C. , Smith Judy
Published: July 2002

A T-matrix formalism for plane-wave scattering from a fluid-loaded elastic spherical shell near a rough fluid–elastic boundary that includes target–boundary scattering effects [J. Acoust. Soc. Am. 101, 767–788 (1997)] is specialized to scattering from a planar boundary and generalized to include scattering from rigid and soft spheres and finite cylinders with hemispherical endcaps and rigid, soft, fluid, viscoelastic, and fluid-saturated poroelastic sediments. Scattering from a variety of target and sediment combinations is considered, and numerical results are shown that indicate some of the effects of target–boundary scattering and the dependence of target–boundary scattering on target and sediment parameters.
Fast numerical scheme of computing acoustic pressure fields for planar circular ultrasound transducers
Authors: Liauh Chihng-Tsung , Lin Win-Li
Published: July 2002

The velocity potential field and thus the acoustic-pressure field of planar circular ultrasound transducers are theoretically derived. By applying the Hankel transform, the solution of the wave equation induced by the transducer can be expressed as a single integral in which both the wavelength of the emitted ultrasound and the radius of the transducer become mere parameters. Two-dimensional surface and contour plots of acoustic pressure fields for planar circular transducers with different values of a/λ, the ratio of transducer radius to wavelength, are compared with previously published plots calculated by other methods. The comparison reveals that the computational time in obtaining accurate calculations is dramatically reduced for high frequency and/or large transducers.
Killer whale (Orcinus orca) hearing: Auditory brainstem response and behavioral audiograms
Authors: Szymanski Michael D. , Bain David E. , Kiehl Kent , Pennington Scott , Wong Scott , Henry Kenneth R.
Published: July 2002

Killer whale (Orcinus orca) audiograms were measured using behavioral responses and auditory evoked potentials (AEPs) from two trained adult females. The mean auditory brainstem response (ABR) audiogram to tones between 1 and 100 kHz was 12 dB (re 1 μ Pa) less sensitive than behavioral audiograms from the same individuals (±8 dB). The ABR and behavioral audiogram curves had shapes that were generally consistent and had the best threshold agreement (5 dB) in the most sensitive range 18–42 kHz, and the least (22 dB) at higher frequencies 60–100 kHz. The most sensitive frequency in the mean Orcinus audiogram was 20 kHz (36 dB), a frequency lower than many other odontocetes, but one that matches peak spectral energy reported for wild killer whale echolocation clicks. A previously reported audiogram of a male Orcinus had greatest sensitivity in this range (15 kHz, ∼35 dB). Both whales reliably responded to 100-kHz tones (95 dB), and one whale to a 120-kHz tone, a variation from an earlier reported high-frequency limit of 32 kHz for a male Orcinus. Despite smaller amplitude ABRs than smaller delphinids, the results demonstrated that ABR audiometry can provide a useful suprathreshold estimate of hearing range in toothed whales.
Backscattering enhancements due to reflection of meridional leaky Rayleigh waves at the blunt truncation of a tilted solid cylinder in water: Observations and theory
Authors: Gipson Karen , Marston Philip L.
Published: July 2002

Leaky surface waves once launched on an elastic object in water will undergo partial reflection at the truncations of the object. Under certain conditions, such reflections can radiate locally flat acoustic wavefronts with a reversal of the acoustic wave vector, and thus a large backscattered signal is produced. A stainless-steel circular rod with flat ends was ensonified through an angular region appropriate for launching meridional Rayleigh waves, and the resulting backscattering enhancement is consistent with the hypothesized end-reflection process. The observed backscattering peak is in general agreement with predictions from a convolution formulation [P. L. Marston, J. Acoust. Soc. Am. 102, 358–369 (1997)]. The tilt of the cylinder was varied to explore the peak’s width, and the results are consistent with an extension of the theory for the dephasing of the Rayleigh wave given here. The amplitude measurements used ultrasonic tone bursts having ka of 50 and 83, and the enhancement is predicted to be significant over a wide range of ka.
The influence of carrier level and frequency on modulation and beat-detection thresholds for sinusoidal carriers
Authors: Kohlrausch Armin , Fassel Ralf , Dau Torsten
Published: July 2002

This paper is concerned with modulation and beat detection for sinusoidal carriers. In the first experiment, temporal modulation transfer functions (TMTFs) were measured for carrier frequencies between 1 and 10 kHz. Modulation rates covered the range from 10 Hz to about the rate equaling the critical bandwidth at the carrier frequency. In experiment 2, TMTFs for three carrier frequencies were obtained as a function of the carrier level. In the final experiment, thresholds for the detection of either the lower or the upper modulation sideband (beat detection) were measured for “carrier” frequencies of 5 and 10 kHz, using the same range of modulation rates as in experiment 1. The TMTFs for carrier frequencies of 2 kHz and higher remained flat up to a modulation rate of about 100–130 Hz and had similar values across carrier frequencies. For higher rates, modulation thresholds initially increased and then decreased rapidly, reflecting the subjects’ ability to resolve the sidebands spectrally. Detection thresholds generally improved with increasing carrier level, but large variations in the exact level dependence were observed, across subjects as well as across carrier frequencies. For beat rates up to about 70 Hz (at 5 kHz) and 100 Hz (at 10 kHz), beat detection thresholds were the same for the upper and the lower sidebands and were about 6 dB higher than the level per sideband at the modulation-detection threshold. At higher rates the threshold for both sidebands increased, but the increase was larger for the lower sideband. This reflects an asymmetry in masking with more masking towards lower frequencies. Only at rates well beyond the maximum of the TMTF did detection for the lower sideband start to be better than that for the upper sideband. The asymmetry at intermediate frequency separations can be explained by assuming that detection always takes place in filters centered above the stimulus spectrum. The shape of the TMTF and the beat-detection data reflects a limitation in resolving fast amplitude variations, which must occur central to the inner-ear filtering. Its characteristic resembles that of a first-order low-pass filter with a cutoff frequency of about 150 Hz.
Study of Flow Induced in Viscoelastic Liquid by a Rotating Cone
Authors: Hoppmann W. H. , Baronet C. N.
Published: July 2002

An extensive series of photographs of lines of flow induced in a viscoelastic liquid by a rotating cone has been obtained for polyisobutylene in cetane at various vertex angles. Torque and thrust were measured at various angular velocities, concentrations, and temperatures. Concentrations above 5% resulted in departures from Newtonian behavior. They exhibited multiple vortices and in addition, the thrust-to-angular-velocity relationships were different from those for Newtonian liquids. The higher concentrations show well defined maxima of thrust and torque at definite angular velocities.
On Generalized Torsional Flow
Authors: Huilgol R. R.
Published: July 2002

This paper provides a derivation of the axial stress distribution and the total thrust in the generalized torsional flow of Pipkin and Tanner. A new interpretation of the formula in the inverted-cone technique of Cowsley to find the second normal stress difference is also given, along with the use of a shallow spherical shell to find the normal stress differences.
Flow profiles of electrorheological suspensions: An alternative model for ER activity
Authors: Henley S. , Filisko F. E.
Published: July 2002

This paper shows the effect of the coupling of an electric field with a shear field on a suspension of polarizeable or ER active particles. It demonstrates that the elementary particles in an electrorheologically active suspension, when the suspension is under flow and simultaneously under the influence of a large electric field, organize into tight packed lamellar formations, the type and orientation being related to the shear field or type of device imposing the shear field. These formations resemble walls between parallel plates, cylinders between parallel disks, and disks between concentric cylinders. In all cases, the columns making up these formations are oriented in the field direction. When exposed to a field but not under flow, the particles assemble together into numerous columnar like clusters of similar diameter (100–200 μm), which are uniformly but randomly distributed between the electrodes and oriented in the field direction. Flow alone in the absence of an electric field produces no segregation of the elementary particles in the suspension. An alternative model for the electrorheological phenomenon is proposed.
Pressure and temperature effects in slit rheometry
Authors: Hay Grant , Mackay M. E. , Awati K. M. , Park Y.
Published: July 2002

We present an approximate theoretical treatment of pressure and viscous heating effects on the flow of a power law fluid through a slit die. It is assumed that the flow remains one dimensional, and the accuracy of this approximation is checked via finite element simulations of the complete momentum and energy equations. For pressures typically achieved in the laboratory it is seen that the one dimensional approximation compares well with the simulations. The model therefore offers a method of including pressure and viscous heating effects in the analysis of experiments and is used to rationalize experimentally obtained pressure profiles for the flow of polymer melts through a slit die. Data for the flow of a linear low density polyethylene and a polystyrene melt in a slit die show these two effects are significant under normal laboratory conditions. Thus, the shear stress–shear rate curves will be affected to the point of being inaccurate at high shear rates. In addition, it is found that the typical technique to correct for a pressure dependent viscosity is also inaccurate being affected by the viscous heating and heat transfer from the melt to the die.
The Monte Carlo method for finding missing atoms in solving crystal structures from powder diffraction data without applying a rigid-body approximation
Authors: Nakamura Hisayoshi , Yamazaki Satoru , Ohnishi Tomohiko , Ida Takashi , Toraya Hideo
Published: July 2002

The Monte Carlo method is applied to finding missing atoms in solving inorganic crystal structures without applying a rigid-body approximation. Whole powder patterns of α-SiO2 and Mg2SiO4 were used for testing a procedure. Four atoms among the six in the asymmetric unit of Mg2SiO4 could be found in the present analysis. The use of well-refined profile parameters enhanced the frequency of correct structure configurations in the Monte Carlo search. Utilizing structural information available for constructing a trial configuration is also considered to be important for efficiently searching the structure solution. A procedure for assignment of equivalent positions to respective atoms is presented. The method can be used as a powerful tool for finding missing atoms in a partially solved structure. A histogram of weighted reliability index in Monte Carlo calculations is very informative for evaluating the performance of the method. ©
Synthesis and X-ray diffraction study of calcium salts of some carboxylic acids
Authors: Valor A. , Reguera E. , Sa´nchez-Sinencio F.
Published: July 2002

An experimental X-ray diffraction (XRD) study of calcium salts of four carboxylic acids is presented. Calcium salts of propionic, butyric, valeric, and caproic acids were synthesized mixing in a mortar Ca(OH)2 with the liquid acids. Measuring the thermogravimetric analysis curves it was determined that the salts were actually monohydrates. The densities of the synthesized samples were measured using a density gradient column. The measured values for the densities were as follows: Dm(propionate)=1.38 g/cm3, Dm(butyrate)=1.30 g/cm3, Dm(valerate)=1.26 g/cm3, Dm(caproate)=1.22 g/cm3. The XRD analysis revealed that these compounds have monoclinic cells with symmetry described by the P21/a space group. Calcium propionate hydrate has cell parameters: a=2.437 51(5) nm, b=0.681 24(1) nm, c=0.591 43(1) nm, β=95.320(2)°. For calcium butyrate hydrate the cell parameters are: a=2.966 84(8) nm, b=0.680 74(2) nm, c=0.589 29(2) nm, β=95.442(3)°. The cell parameters for calcium valerate hydrate are: a=3.566 36(4) nm, b=0.682 49(1) nm, c=0.592 77(1) nm, β=107.280(1)° and for calcium caproate hydrate a=4.180 30(5) nm, b=0.682 61(1) nm, c=0.592 13(1) nm, β=110.230(1)°. The calculated density values from the XRD results, taking into account that the number of chemical formulas in the unit cell equals four, agree very well with the measured ones. It was established that the unit cell parameter a grows with the increase of the number of carbon atoms in the aliphatic chain, while parameters b and c remain almost constant. This is an indication of the stacking layer character of the structure as has been suggested for calcium stearate monohydrate. This fact points to the possibility of the refinement of the crystalline structures taking as the starting point the reported structure for calcium stearate monohydrate.
Doubly curved crystal (DCC) X-ray optics and applications
Authors: Chen Zewu , Gibson Walter M.
Published: July 2002

Doubly curved crystal (DCC) X-ray optics provide an enabling technology for new portable, remote, andin situapplications of monochromatic X-rays for composition and structure analysis of amorphous, polycrystalline, and crystalline solids. Femtogram sensitivity for surface contamination, parts-per-billion (ppb) impurity levels for solids, and composition, structure and uniformity of thin films with compact, low power (20–50 W) source optic combinations are possible.
Technology: Health Outcomes
Authors: Robertson Brett W. , Kee Kerk F.
Published: November 2022

Health outcomes are defined as a change in the health of an individual, group of people, or population that is attributable to an intervention or series of health communication interventions. The purpose of this entry is to explore how technology relates to and impacts health outcomes. We draw from the notion of information and communication technologies (ICTs) to examine how communication with technology and information‐related processes is a critical structure that can positively influence health outcomes. Three types of health ICTs are described: information technologies, Web 2.0, and 3D represented technologies. We then link these ICTs to positive health outcomes through several examples.