bluuebunny/crossref_metadata_2025 huggingface dataset:
Alloantigen–induced specific immunological unresponsiveness
Authors: Wood Kathryn J. , Jones Nick D. , Bushell Andrew R. , Morris Peter J.
Published: July 2002

When the immune system encounters alloantigen it can respond in any one of a number of different ways. The choice that is made will take into account factors such as where, when and how the contact with the alloantigen takes place, as well as the environmental conditions that prevail at the time the alloantigen is encountered. Alloantigen administration before transplantation either alone or in combination with therapeutic agents that modulate the functional activity of the responding leucocytes can be a powerful way of inducing specific unresponsiveness to alloantigensin vivo.The molecular mechanisms that influence the way the outcome of the immune response to alloantigen develops, either activation or unresponsiveness to the triggering antigen, hold the key to our ability to manipulate the immune system effectively by exposing it to donor antigen for therapeutic purposes. This review will focus on alloantigen–induced immunological unresponsiveness and how insights into the mechanisms of unresponsiveness have driven the development of novel tolerance–induction strategies that show promise for translation into the clinic in the future.
A flu optical immunoassay (ThermoBioStar'sFLU OIA): a diagnostic tool for improved influenza management
Authors: Tucker S. P. , Cox C. , Steaffens J.
Published: July 2002

ThermoBioStar'sand Biota'sflu optical immunoassay (FLU OIA) is a rapid test designed to diagnose influenza A and B infection using a variety of specimen types. The assay uses highly sensitive thin–film detection methods, coupled with specific monoclonal antibodies to the nucleoprotein. The test is simple to perform, requires no instrumentation and is intended to provide a result within 15min of test initiation in the ‘point–of–care’ environment. In initial clinical studies, the assay was demonstrated to be equivalent to culture in identifying infected individuals. Subsequent independent studies using a variety of sample types have demonstrated sensitivity ranging from 48 to 100% and specificities ranging from 93 to 97%. In addition to detecting human strains, this assay has been demonstrated to be capable of detecting a variety of avian and non–human mammalian influenza viruses. The FLU OIA test has been used in large–scale surveillance schemes intended to provide rapid epidemiological data during normal influenza seasons and has demonstrated the potential for fulfilling a similar role for multispecies surveillance in, for example, conditions that offer challenges for conventional virus isolation methods. Conceivably, such use should facilitate the timely recognition of influenza outbreaks and prioritization of positive specimens for more conventional, laboratory characterization, leading to improved interpandemic surveillance and rapid reaction in the face of the next pandemic.
The S. cerevisiae SET3 complex includes two histone deacetylases, Hos2 and Hst1, and is a meiotic-specific repressor of the sporulation gene program
Authors: Pijnappel W.W.M. Pim , Schaft Daniel , Roguev Assen , Shevchenko Anna , Tekotte Hille , Wilm Matthias , Rigaut Guillaume , Séraphin Bertrand , Aasland Rein , Stewart A. Francis
Published: July 2002

Set3 is one of two proteins in the yeast Saccharomyces cerevisiae that, like Drosophila Trithorax, contains both SET and PHD domains. We found that Set3 forms a single complex, Set3C, with Snt1, YIL112w, Sif2, Cpr1, and two putative histone deacetylases, Hos2 and NAD-dependent Hst1. Set3C includes NAD-dependent and independent deacetylase activities when assayed in vitro. Homology searches suggest that Set3C is the yeast analog of the mammalian HDAC3/SMRT complex. Set3C represses genes in early/middle of the yeast sporulation program, including the key meiotic regulators ime2and ndt80. Whereas Hos2 is only found in Set3C, Hst1 is also present in a complex with Sum1, supporting previous characterizations of Hst1 and Sum1 as repressors of middle sporulation genes during vegetative growth. However, Hst1 is not required for meiotic repression by Set3C, thus implying that Set3C (−Hst1) and not Hst1–Sum1, is the meiotic-specific repressor of early/middle sporulation genes.
Structural properties of trimers and tetramers of ribonuclease A
Authors: Nenci Arianna , Gotte Giovanni , Bertoldi Mariarita , Libonati Massimo
Published: July 2002

Ribonuclease A aggregates (dimers, trimers, tetramers, pentamers) can be obtained by lyophilization from 40% acetic acid solutions. Each aggregate forms two conformational isomers distinguishable by different basic net charge. The crystal structure of the two dimers has recently been determined; the structure of the higher oligomers is unknown. The results of the study of the two trimeric and tetrameric conformers can be summarized as follows: (1) RNase A trimers and tetramers form by a 3D domain‐swapping mechanism. N‐terminal and C‐terminal types of domain swapping could coexist; (2) the secondary structures of the trimeric and tetrameric conformers do not show significant differences if compared with the secondary structure of monomeric RNase A or its two dimers; (3) a different exposure of tyrosine residues indicates that in the aggregates they have different microenvironments; (4) the two trimeric and tetrameric conformers show different susceptibility to digestion by subtilisin; (5) dimers, trimers, and tetramers of RNase A show unwinding activity on double‐helical poly(dA‐dT) • poly(dA‐dT), that increases as a function of the size of the oligomers; (6) the less basic conformers are more stable than the more basic ones, and a low concentration in solution of trimers and tetramers favors their stability, which is definitely increased by the interaction of the aggregates with poly(dA‐dT) • poly(dA‐dT); (7) the products of thermal dissociation of the two trimers indicate that their structures could be remarkably different. The dissociation products of the two tetramers allow the proposal of two models for their putative structures.
Observer variation and the performance accuracy gained by averaging ratings of abnormality
Authors: Swensson Richard G. , King Jill L. , Good Walter F. , Gur David
Published: July 2002

Six radiologists used continuous scales to rate 529 chest‐film cases for likelihood of five different types of abnormalities (interstitial disease, nodule, pneumothorax, alveolar infiltrate, and rib fracture) in each of six replicated readings, yielding 36 separate ratings of each case for the five abnormalities. Separate data analyses of all cases and subsets of the difficult/subtle cases for each abnormality estimated the relative gains in accuracy (linear‐scaled area below the ROC curve) obtained by averaging the case‐ratings across (a) six independent replications by each reader (25% gain), (b) six different readers within each replication (34% gain), or (c) all 36 readings (48% gain). Although accuracy differed among both readers and abnormalities, ROC curves for the median ratings showed similar relative gains in accuracy, somewhat greater than those predicted from the measured rating correlations. A model for variance components in the observer's latent decision variable could predict these gains from measured correlations in the single ratings of cases. Depending on whether the model's estimates were based on realized accuracy gains or on rating correlations, about 48% or 39% of each reader's total decision variance (summed variance for positive and negative cases) consisted of random (within‐reader) error that was uncorrelated between replications, another 10% or 14% came from idiosyncratic responses to individual cases, and about 43% or 47% was systematic variation that all readers found in the sampled cases.
Measurements and calculations of thermal neutron fluence rate and neutron energy spectra resulting from moderation of fast neutrons: Applications for neutron capture therapy
Authors: Rivard Mark J.
Published: July 2002

is a neutron emitting radioisotope which has promise for both standard brachytherapy and neutron capture enhanced brachytherapy. In this study, experimental measurements and calculations were used to determine the thermal neutron fluence rate, in the vicinity of applicator tube (AT) type sources. Results of these measurements were confirmed with Monte Carlo calculations performed in a distributed manner on multiple workstations using MCNP. Three studies were executed: (1) relative as a function of distance from a AT source in an A‐150 tissue equivalent plastic phantom using thermoluminescent dosimeters (TLDs) of varying enrichment, (2) measured with gold foils in a 114 liter water phantom 5 cm from two AT sources, and (3) calculations of the impact of phantom material composition (e.g., A‐150, water, brain, muscle) on from moderated fast neutrons. TLD results and Monte Carlo calculations in A‐150 of relative typically agreed within 1% and at most differed by 3% for distances from 1 to 6 cm. Foil measurements followed the ASTM E 262‐86e protocol, and the ratio of activated plain and Cd encased gold foils (7.31) agreed well with the calculated ratio (7.26). Measured at 5 cm was 10% greater than that determined using MCNP but was within the combined uncertainties. Compared with A‐150 at a distance of 1 cm, was 20%, 22%, and 32% less for water, brain, and muscle, respectively; these ratios decreased to 16%, 16%, and 24% less, respectively, at a distance of 5 cm from the source in a 15 cm diameter phantom. Comparisons of these results generally agreed with those in the literature for a value of in water at 3 cm.
Autoactivation of source dwell positions for HDR brachytherapy treatment planning
Authors: Giannouli S. , Baltas D. , Milickovic N. , Lahanas M. , Kolotas C. , Zamboglou N. , Uzunoglu N.
Published: July 2002

The most accurate classical dose optimization algorithms in HDR brachytherapy strongly depend on an appropriate selection of source dwell positions which fulfill user‐defined geometrical boundary conditions which are relative to patient anatomy. Most anatomical situations, such as for prostate and head and neck tumors, are complex and can require geometries with 5–15 catheters with 48 possible dwell positions per catheter depending on the tumor volume. The manual selection of dwell positions using visual checks by trial and error is very time consuming. This can only be improved by the use of a technique which automatically recognizes and selects the optimum dwell positions for each catheter. We have developed an algorithm, termed an autoactivation algorithm, which improves implant planning by providing a facility for the necessary automatic recognition of HDR source dwell positions.
Irregular field calculation on the central beam axis of photon beams using sector‐integration
Authors: Sanz Darı́o E. , Romaguera Antinógenes L. , Acosta Norma B.
Published: July 2002

A method is proposed for calculation of irregular field factors on the central beam axis and homogeneous medium for x‐ray beams. The irregular field factor is introduced as the ratio of the output of a field with and without blocks on the central beam axis. The algorithm is based on the sector‐integration method and the circular field quantities are calculated from in‐phantom measurements. These circular field quantities are the output per beam monitor unit for circular fields defined by a hypothetical secondary collimator and reduced to a circular field by blocking. A derivation of the sector‐integration equation is given from first principles. As it is shown, the circular field quantities are evaluated from data measured for rectangular, block shaped fields. Such quantities contain all beam components, including photons scattered from the blocks, the block tray, and photons scattered in the phantom. Consequently, the so called primary and secondary beam components are readily incorporated in this approach. Once the circular field quantities have been determined from rectangular field data, the irregular field factors for other geometry can be calculated. Irregular field factors for square, rectangular and circular block‐shaped fields were calculated for 6 MV photon beams and compared with measured values. The results agree within 0.7%, even for heavy blocked field cases, i.e., a collimator field blocked to a field. The method was tested for a particular source to surface distance, depth, phantom composition, and source to block distance. Calculation of irregular field factors in another set up conditions requires the measurement of the appropriate input data.
Computer‐based collection of mammographic exposure data for quality assurance and dosimetry
Authors: Rosenberg R. D. , Kelsey C. A. , Williamson M. R. , Houston J. D. , Hunt W. C.
Published: July 2002

PURPOSE: There is potentially more to quality assurance in mammography than the MQSA mandated tests. In this paper we describe a method of capturing individual mammogram technical parameters and the creation of new measures. These include the numbers of images required for each screening examination by technologist, median compression by technologist, and the radiation dose of the examination to the general population of patients. METHOD/MATERIALS: With this method we describe a semiautomated method of the collection of technical data from mammography exposures. The data that are automatically created by the mammography unit are saved on a computer for later analysis. The method was used on 2738 consecutive screening mammography examinations and 13 621 exposures from one machine. Data were obtained from November 1998 through December 1999. RESULTS: Using standard methods, the mean glandular dose (MGD) per exposure was 2.62 mGy (SD 1.2). The mean dose per bilateral screening examination was 6.53 mGy (SD 3.07), the median dose was 6.11 mGy, and the dose range was 1.13–34.23 mGy. Rhodium filtration was used for 18% of the exposures. The average and median breast thickness was 4.9 cm. The ACR phantom MGD for this machine was 2.44 mGy at 25 kVp, and 1.97 mGy at 26 kVp. The mean number of exposures for a bilateral mammogram was 4.9, and varied by a technologist from 4.7 to 5.2. The mean compression pressure varied by technologist from 13 to 30 lbs (58–134 N). CONCLUSIONS: The mean dose per mammogram is slightly greater than the ACR phantom dose at 25 kVp. Almost five exposures were necessary for a standard bilateral examination, and this varied by technologist. The compression used also varied by technologist. The semiautomated collection of technical data can aid in maintaining an effective mammography QA program.
Accurate localization of intracavitary brachytherapy applicators from 3D CT imaging studies
Authors: Lerma F. A. , Williamson J. F.
Published: July 2002

Purpose: To present an accurate method to identify the positions and orientations of intracavitary (ICT) brachytherapy applicators imaged in 3D CT scans, in support of Monte Carlo photon‐transport simulations, enabling accurate dose modeling in the presence of applicator shielding and interapplicator attenuation. Materials and methods: The method consists of finding the transformation that maximizes the coincidence between the known 3D shapes of each applicator component (colpostats and tandem) with the volume defined by contours of the corresponding surface on each CT slice. We use this technique to localize Fletcher–Suit CT‐compatible applicators for three cervix cancer patients using post‐implant CT examinations (3 mm slice thickness and separation). Dose distributions in 1‐to‐1 registration with the underlying CT anatomy are derived from 3D Monte Carlo photon‐transport simulations incorporating each applicator's internal geometry (source encapsulation, high‐density shields, and applicator body) oriented in relation to the dose matrix according to the measured localization transformations. The precision and accuracy of our localization method are assessed using CT scans, in which the positions and orientations of dense rods and spheres (in a precision‐machined phantom) were measured at various orientations relative to the gantry. Results: Using this method, we register 3D Monte Carlo dose calculations directly onto post insertion patient CT studies. Using CT studies of a precisely machined phantom, the absolute accuracy of the method was found to be ±0.2 mm in plane, and ±0.3 mm in the axial direction while its precision was ±0.2 mm in plane, and ±0.2 mm axially. Conclusion: We have developed a novel, and accurate technique to localize intracavitary brachytherapy applicators in 3D CT imaging studies, which supports 3D dose planning involving detailed 3D Monte Carlo dose calculations, modeling source positions, shielding and interapplicator shielding, accurately.
Rapid objective measurement of gamma camera resolution using statistical moments
Authors: Hander Trish A. , Lancaster Jack L. , Kopp David T. , Lasher John C. , Blumhardt Ralph , Fox Peter T.
Published: July 2002

An easy and rapid method for the measurement of the intrinsic spatial resolution of a gamma camera was developed. The measurement is based on the first and second statistical moments of regions of interest (ROIs) applied to bar phantom images. This leads to an estimate of the modulation transfer function (MTF) and the full‐width‐at‐half‐maximum (FWHM) of a line spread function (LSF). Bar phantom images were acquired using four large field‐of‐view (LFOV) gamma cameras (Scintronix, Picker, Searle, Siemens). The following factors important for routine measurement of gamma camera resolution with this method were tested: ROI placement and shape, phantom orientation, spatial sampling, and procedural consistency. A 0.2% coefficient of variation (CV) between repeat measurements of MTF was observed for a circular ROI. The CVs of less than 2% were observed for measured MTF values for bar orientations ranging from −10° to +10° with respect to the x and y axes of the camera acquisition matrix. A 256×256 matrix (1.6 mm pixel spacing) was judged sufficient for routine measurements, giving an estimate of the FWHM to within 0.1 mm of manufacturer‐specified values (3% difference). Under simulated clinical conditions, the variation in measurements attributable to procedural effects yielded a CV of less than 2% in newer generation cameras. The moments method for determining MTF correlated well with a peak–valley method, with an average difference of 0.03 across the range of spatial frequencies tested (0.11–0.17 line pairs/mm, corresponding to 4.5–3.0 mm bars). When compared with the NEMA method for measuring intrinsic spatial resolution, the moments method was found to be within 4% of the expected FWHM.
Experimental determination of fluence correction factors at depths beyond for a Farmer type cylindrical ionization chamber in clinical electron beams
Authors: Huq M. Saiful , Yue Ning , Suntharalingam N.
Published: July 2002

Recently, it has been recommended that electron beam calibrations be performed at a new reference depth [Burns et al., Med. Phys. 23, 383 (1996)] given by where is the depth of 50% depth dose. In order to calibrate electron beams at with a Farmer type cylindrical ionization chamber, the values of the perturbation correction factors and at are required. Using a parallel plate Holt chamber as a reference chamber, the product has been determined for a 6.1‐mm‐diameter PTW cylindrical ionization chamber at as a function of of clinical electron beams ( energy ). Assuming that for the PTW chamber is unity in electron beams, the measured values ranged from 0.96 to 0.98 as the energy is increased. These results are in close agreement with recently reported calculated values. Determination of requires the knowledge of A relation between and is given in the IAEA Protocol [TRS No. 277 (IAEA, Vienna, 1987), pp. 1–98] for broad beams at SSD=100 cm. It has been shown experimentally that the equation derived by Ding et al. [Med. Phys. 22, 489 (1995)] from Monte Carlo simulations of realistic clinical electron beams, can be used satisfactorily to obtain from where is the depth of 50% ionization. The largest difference between the measured value of and that calculated by using the above equation has been found to be about 1 mm at 22 MeV.
Improvement of signal‐to‐noise and contrast‐to‐noise ratios in dual‐screen computed radiography
Authors: Shaw Chris C. , Wang TienPeng , Breitenstein Darryl S. , Gur David
Published: July 2002

A dual‐screen computed radiography (CR) technique has been developed to improve and optimize the overall image signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR). With this technique, two CR screens are exposed together and separately scanned to form a front and a back image. These two images are then superimposed to form an image of improved SNR and CNR. A mathematical model has been derived to describe the improvement and optimization of the SNR and CNR. Based on this model, the front and back images should be weighted in proportion to their SNR squared to optimize the SNR of the composite image. Imaging experiments have been conducted to verify the theoretical model under mammographic and chest imaging conditions. The results largely agree with the theoretical predictions. It has also been found that optimization of the SNR results in nearly optimal CNR and vice versa. For mammographic imaging, a 14%–22% improvement in the SNR and a 13%–19% improvement in the CNR have been demonstrated. For chest imaging, a 31%–36% improvement in the SNR and a 28%–30% improvement in the CNR has been demonstrated.
Measurement of factors in electron beams and in a beam for plane‐parallel chambers
Authors: Ding G. X. , Cygler J. E.
Published: July 2002

This paper describes a method to measure the product of correction factors for ionization chambers and presents our measured values of for Markus plane‐parallel chambers in electron beams. It is shown that the measured values of can be fitted to an equation, for Markus chambers at the new reference depth for electron beams ( energy ). We also present our measured values of for NACP and Markus chambers in a water phantom irradiated in a beam.
A room‐based diagnostic imaging system for measurement of patient setup
Authors: Schewe James E. , Lam Kwok L. , Balter James M. , Ten Haken Randall K.
Published: July 2002

A room‐based diagnostic x‐ray imaging system for routine measurement of radiotherapy patient orientation has been developed. The system consists of a pair of room‐mounted x‐ray tubes and a portable imager consisting of an orthogonal pair of phosphor screens, a mirror/lens system, a CCD camera, and computer software for comparing images of the patient to reference images. Orthogonal pairs of images can be acquired quickly and with relatively little exposure, allowing correction of patient setup on a daily basis. This could limit patient setup error to the uncertainty in the measurement and repositioning processes, a potentially significant improvement over the present standard.
Monte Carlo calculations of dose rate distributions around the Amersham CDCS‐M‐type source
Authors: Casal E. , Ballester F. , Lluch J. L. , Pérez‐Calatayud J. , Lliso F.
Published: July 2002

The Amersham CDCS‐M‐type stainless‐steel encapsulated source is widely used in low dose rate brachytherapy with manual afterloading. However there is a need for more accurate dosimetry data. In this study we present Monte Carlo calculations of absolute dose rate in water around this source using the Monte Carlo code GEANT, discuss dosimetric features of these data, and compare them with Krishnaswamy's results for intracavitary sources. Dose rate distributions are presented in the form of along‐away tables and in the TG43 formalism. Simulated absolute dose rate values can be used as benchmark data to verify the treatment planning system calculation results or directly as input data for treatment planning. Best‐fit values of attenuation coefficients suitable for use in Sievert integral type calculations have been derived comparing dose rate distributions calculated using this algorithm with those obtained from Monte Carlo calculations.
Dosimetric characteristics of the InterSource103 palladium brachytherapy source
Authors: Meigooni A. S. , Sowards K. , Soldano M.
Published: July 2002

brachytherapy sources are being used for interstitial implants in tumor sites such as the prostate. Recently, the palladium source has been introduced, which has a design different from that of other sources presently on the market. Dosimetric characteristics (i.e., dose rate constant, radial dose function, and anisotropy function) of this source were experimentally and theoretically determined following the AAPM Task Group 43 (TG‐43) recommendations and were related to the 1999 NIST calibration assigned to this source 99std]. Measurements were performed in a solid water phantom using LiF thermoluminescent dosimeters. The measured data was compared with Monte Carlo simulations performed in solid water using the PTRAN code. The calculations were then performed in liquid water to obtain the dosimetric information for clinical applications as per TG‐43 recommendation. The results indicated that the dose rate constant, Λ, of the palladium source was using TLD measurements and using Monte Carlo simulations in solid water. The calculated value in liquid water was found to be The radial dose function, of the new source was measured at distances ranging from 0.5 to 10 cm using LiF TLD in solid water phantom material. The Monte Carlo simulations were performed at distances ranging from 0.1 to 10 cm from the source center in solid water and liquid water. The anisotropy function, was measured at distances of 2, 3, 5, and 7 cm from the source center and calculated at distances of 0.5, 1, 2, 3, 5, and 7 cm from the source center. Complete dosimetric data are described in this paper. Per TG‐43, the values reported in water should be used for clinical treatment planning systems.
Detecting electron beam energy shifts with a commercially available energy monitor
Authors: Evans Michael D. C. , Moftah Belal A. , Olivares Marina , Podgorsak Ervin B.
Published: July 2002

Routine electron beam quality assurance requires an accurate, yet practical, method of energy characterization. Subtle shifts in beam energy may be produced by the linac bending magnet assembly, and the sensitivity of a commercially available electron beam energy‐monitoring device for monitoring these small energy drifts has been evaluated. The device shows an 11% change in signal for a 2 mm change in the energy parameter for low energy electron beams (in the vicinity of 6 MeV) and a 2.5% change in signal for a 2 mm change in the energy parameter for high energy electron beams (in the vicinity of 22 MeV). Thus the device is capable of detecting small energy shifts resulting from bending magnet drift for all clinically relevant electron beams.
Fluid-like properties of the probability densities in quantum mechanics
Authors: Mita Katsunori
Published: July 2002

The transport properties of the probability fluid are investigated. The transport equation is derived as a generalization of the equation of continuity. This equation is used to examine the properties of the mass flux density, momentum flux density, and kinetic energy flux density of the probability fluid. It is shown that the transport equations of the probability fluid can be represented in a form identical to those of the classical, Eulerian fluid. It is also shown that the transport equations are differential forms of Ehrenfest’s theorem. Local conservation of the mass density and kinetic energy density for the stationary states are examined. Explicit expressions of the mass flux density and kinetic energy flux density are obtained for the 2p state of the hydrogen atom.
Measuring and modeling cosmic ray showers with an MBL system: An undergraduate project
Authors: Jackson David P. , Welker Matthew T.
Published: July 2002

Following a brief historical introduction, a novel method for inducing and measuring cosmic ray showers using a low-cost microcomputer-based laboratory system is described. This reproduction of Bruno Rossi’s classic experiment uses low counting-rate radiation monitors. The advantage of this is that a simple AND gate can be used to trigger coincidences, which makes the workings of the experiment completely transparent to undergraduate students. The disadvantage is that data must be taken for many days to get reasonably accurate results. A simple theory is presented that models the resulting shower curve quite well.
Expectation value analysis of wave packet solutions for the quantum bouncer: Short-term classical and long-term revival behaviors
Authors: Doncheski M. A. , Robinett R. W.
Published: July 2002

We discuss the time development of Gaussian wave packet solutions of the “quantum bouncer” (a quantum mechanical particle subject to a uniform downward force, above an impermeable flat surface). We focus on the evaluation and visualization of the expectation values and uncertainties of position and momentum variables during a single quasi-classical period as well as during the long-term collapsed phase and several revivals. This approach complements existing analytic and numerical analyses of this system, as well as being useful for comparison with similar results for the harmonic oscillator and infinite well cases.
A conjugated infinite element method for half-space acoustic problems
Authors: Coyette Jean-Pierre , Van den Nieuwenhof Benoı̂t
Published: July 2002

Many acoustic problems (especially in environmental acoustics) involve half-space domains bounded by a plane subjected to normal admittance boundary conditions. In the “low” frequency domain, the numerical treatment of such problems usually relies on boundary element methods based on a particular Green’s function suited for the half-(admittance) plane. In the present paper, an alternative hybrid finite/infinite element scheme is proposed. The method relies on a direct treatment of nonhomogeneous boundary conditions along infinite element edges (or faces). The procedure is validated through comparisons with an available reference solution.
Three-dimensional optical measurement of instantaneous pressure
Authors: Pitts Todd A. , Greenleaf James F.
Published: July 2002

Local perturbations in material density induced in a material by a compressional wave give rise to local perturbations in refractive index. Accurate, high-resolution, three-dimensional, optical measurements of an instantaneous refractive index perturbation in a homogeneous, optically transparent medium may be obtained from measurements of scattered optical intensity alone. The method of generalized projections allows incorporation of optical intensity measurements into an iterative algorithm for computing the phase of the interrogating optical pulse as the solution of a fixed point equation. The complex optical field amplitude, computed in this manner, is unique up to a constant unit magnitude complex coefficient. The three-dimensional refractive index distribution may be computed via the Fourier slice reconstruction algorithm from the optical phase data under the assumption of weak optical scattering. The refractive index perturbation is related to local instantaneous pressure under a linear, small-displacement model for the mechanical wave. A numerical simulation of the measurement experiment, phase recovery, and reconstruction process for a plane piston ultrasound transducer with a semicircular aperture and center frequency of 1.5 MHz is described and corresponds very well with experiment. Experimental data obtained using an 810-nm laser source are used to reconstruct the three-dimensional pressure field from two elements of a 2.5-MHz linear array. Comparison with a measurement obtained via a 500-μm needle hydrophone shows excellent agreement.
Characterization of particle size and its distribution during the crystallization of organic fine chemical products as measured in situ using ultrasonic attenuation spectroscopy
Authors: Mougin Patricia , Wilkinson Derek , Roberts Kevin J. , Tweedie Richard
Published: July 2002

The potential application of ultrasonic attenuation spectroscopy to the in situ examination of solution phase crystallization processes is examined through studies carried out on two organic compounds: urea and (L)-glutamic acid. For this study a commercial ultrasonic spectrometer [Ultrasizer by Malvern Instruments Ltd., F. Alba, U.S. Patent 5,121,629 (1992)] was used. A particle size analysis was carried out in an attempt to monitor the crystal size distributions of the crystals growing within the mother liquor. While this technique was found to be of limited effectiveness for the monitoring of the crystallization of urea, due to the formation of high aspect ratio needle crystals, whose long axial size is beyond the range of the technique (0.01 μm–1000 μm), good results were obtained with prismatic (L)-glutamic acid crystals. The size evolution of the latter during crystal growth was successfully monitored throughout the crystallization process.
Surface waves in orthotropic incompressible materials
Authors: Destrade Michel
Published: July 2002

The secular equation for surface acoustic waves propagating on an orthotropic incompressible half-space is derived in a direct manner, using the method of first integrals.
A study of wave propagation in varying cross-section waveguides by modal decomposition. Part II. Results
Authors: Amir N. , Pagneux V. , Kergomard J.
Published: July 2002

The full derivation of the equations governing the generalized impedance matrix Z, the pressure, and the velocity were presented in Part I of this series [Pagneux et al., J. Acoust. Soc. Am. 100, 2034–2048 (1996)]. Here only the results of that paper, i.e., the final set of equations which needed to be solved are repeated. Other factors influencing the solution are the boundary conditions at the end of the waveguide: Source and radiation conditions are also presented. Finally, the details of the numerical implementation are also relevant, and will be discussed in some detail.
Acoustic transient radiation and scattering from fluid-loaded elastic shells using convolution methods
Authors: Stepanishen Peter R.
Published: July 2002

A general time-domain approach is presented to address the acoustic transient radiation and scattering problem from fluid-loaded elastic shells. The approach is based on utilizing an in-vacuo eigenvector expansion with time-dependent coefficients for the velocity field of the shell. The time-dependent modal velocity coefficients of the shell are described by a universal set of coupled convolution integral equations. Substitution of the eigenvector expansion into the Kirchhoff integral solution leads to the external pressure field being expressed as a modal sum of convolution integrals of mode and space-dependent pressure impulse response functions with the modal velocity coefficients. Special cases which include an unbaffled finite plate and an arbitrarily shaped shell of revolution are addressed using the general approach. Simple closed-form expressions are presented for the pressure impulse response functions for the unbaffled finite plate and the on-axis response of a general shell of revolution. The characteristics of the mode and space-dependent far-field pressure impulse response functions for an unbaffled simply supported plate and a spherical shell are presented to illustrate the general characteristics of the impulse response functions.
Internal wave strength inversion and localization using long-range acoustic signals
Authors: Heaney Kevin D.
Published: July 2002

The ATOC95 experiment was conducted in the winter of 1995 with transmission paths from Pioneer Seamount to Hawaii (range = 3515 km). The internal wave environment is strongly range dependent, and significant mode coupling occurs to the late arriving energy. The ability to localize a source is an indication of the remaining source information in the signal. A mode travel time difference range estimator was developed and shown to be biased by internal wave-induced mode coupling. A range estimator was developed which matched the received wavefronts with those of predicted wavefronts at various ranges. Forward simulations were done using a frequency interpolation method of the PE, and a set of random realizations of the Garrett–Munk spectra for internal waves. With this ensemble of calculations as a forward model, three different measures were calculated from the data and simulations to do an inversion for the background internal wave strength in the ocean. A method was developed to simultaneously invert the source location and the internal wave strength using the mode arrival time and mode spread as the two observables. a)Present address: Sci. Applications Intl. Corp., 10260 Campus Pt. Dr., San Diego, CA 92121.
Acoustic detections of singing humpback whales (Megaptera novaeangliae) in the eastern North Pacific during their northbound migration
Authors: Norris Thomas F. , Mc Donald Mark , Barlow Jay
Published: July 2002

Numerous (84) acoustic detections of singing humpback whales were made during a spring (08 March–09 June 1997) research cruise to study sperm whales in the central and eastern North Pacific. Over 15 000 km of track-line was surveyed acoustically using a towed hydrophone array. Additionally, 83 sonobuoys were deployed throughout the study area. Detection rates were greatest in late March, near the Hawaiian Islands, and in early April, northeast of the islands. Only one detection was made after April. Detection rates for sonobuoys were unequal in three equally divided longitudinal regions of the study area. Two high density clusters of detections occurred approximately 1200–2000 km northeast of the Hawaiian Islands and were attributed to a large aggregation of migrating animals. The distribution of these detections corroborates findings of previous studies. It is possible that these animals were maintaining acoustic contact during migration. Two unexpected clusters of singing whales were detected approximately 900 to 1000 km west of central and southern California. The location of these detections may indicate a previously undocumented migration route between an offshore breeding area, such as the Revillagigedo Islands, Mexico, and possible feeding areas in the western North Pacific or Bering Sea.
Effects of lengthened formant transition duration on discrimination and neural representation of synthetic CV syllables by normal and learning-disabled children
Authors: Bradlow Ann R. , Kraus Nina , Nicol Trent G. , McGee Therese J. , Cunningham Jenna , Zecker Steven G. , Carrell Thomas D.
Published: July 2002

In order to investigate the precise acoustic features of stop consonants that pose perceptual difficulties for some children with learning problems, discrimination thresholds along two separate synthetic /da-ga/ continua were compared in a group of children with learning problems (LP) and a group of normal children. The continua differed only in the duration of the formant transitions. Results showed that simply lengthening the formant transition duration from 40 to 80 ms did not result in improved discrimination thresholds for the LP group relative to the normal group. Consistent with previous findings, an electrophysiologic response that is known to reflect the brain’s representation of a change from one auditory stimulus to another—the mismatch negativity (MMN)—indicated diminished responses in the LP group relative to the normal group to /da/ versus /ga/ when the transition duration was 40 ms. In the lengthened transition duration condition the MMN responses from the LP group were more similar to those from the normal group, and were enhanced relative to the short transition duration condition. These data suggest that extending the duration of the critical portion of the acoustic stimulus can result in enhanced encoding at a preattentive neural level; however, this stimulus manipulation on its own is not a sufficient acoustic enhancement to facilitate increased perceptual discrimination of this place-of-articulation contrast.
The impact of sound speed errors on medical ultrasound imaging
Authors: Anderson M. E. , McKeag M. S. , Trahey G. E.
Published: July 2002

The results of a quantitative study of the impact of sound speed errors on the spatial resolution and amplitude sensitivity of a commercial medical ultrasound scanner are presented in the context of their clinical significance. The beamforming parameters of the scanner were manipulated to produce sound speed errors ranging over ±8% while imaging a wire target and an attenuating, speckle-generating phantom. For the wire target, these errors produced increases in lateral beam width of up to 320% and reductions in peak echo amplitude of up to 10.5 dB. In the speckle-generating phantom, these errors produced increases in speckle intensity correlation cell area of up to 92% and reductions in mean speckle brightness of up to 5.6 dB. These results are applied in statistical analyses of two detection tasks of clinical relevance. The first is of low contrast lesion detectability, predicting the changes in the correct decision probability as a function of lesion size, contrast, and sound speed error. The second is of point target detectability, predicting the changes in the correct decision probability as function of point target reflectivity and sound speed error. Representative results of these analyses are presented and their implications for clinical imaging are discussed. In general, sound speed errors have a more significant impact on point target detectability over lesion detectability by these analyses, producing up to a 22% reduction in correct decisions for a typical error.
Rheological Properties of Viscoelastic Fluids from Continuous Flow Through a Channel Approximating Infinite Parallel Plates
Authors: Novotny E. J. , Eckert Roger E.
Published: July 2002

Important rheological properties of viscoelastic fluids can be obtained by studying continuous flow through a channel approximating infinite parallel plates. This flat plate rheometer eliminates or reduces some problems of conventional ones and extends the region of useful measurements to high shear rates. Four pressure transducers are flush mounted on the top plate to measure the normal stress T22. From these measurements the shear stress can also be obtained. The normal stress in the direction of flow (T11) is obtained from the measurement of the impact of the exit stream. A Weissenberg rheogoniometer (WRG) is used to measure the shear stress and the primary normal stress difference (N1=T11−T22). Data are presented for polyethylene oxide (M̄w=4×106) solutions of 0.25%, 0.9%, 2.0%, and 3.0% in water. Newtonian fluids were used to test and compare the apparatus. Fluid viscosities from 0.01 to 6000 poise and normal stresses from 100 to 450,000 dynes/cm2 were determined for shear rates from 0.03 to 130,000 sec−1. The rotational geometry of the WRG limits its use to shear rates under 102–103 sec−1. Further, the precision of normal stress measurement with the parallel plates is better than obtained with the WRG. The shear stress values obtained with the plates are of equivalent precision and higher accuracy. Normal stress dependence upon shear rate is fit by the molecular dumbbell model of Bird et al. over a wide range of conditions. In the upper region the model predicts a slope of 2/3 and 0.66±0.03 is obtained by regression analysis of the data. In the lower region a slope of 2 is predicted and 2.08±0.37 obtained. Extrapolation of T11 and T22 data using this model allows N1 to be obtained at shear rates far higher than with the WRG. The magnitude of the ratio T22/T11 decreases as Polyox concentration increases and the fluid becomes more elastic. The complete state of stress is determined for all Polyox solutions, and pressures at the exit surface and exit centerline are found to contribute substantially to the total stress tensor.
A Generalized Strain Measure in a Single-Integral Constitutive Equation
Authors: Phillips Mike
Published: July 2002

The Bird-Carreau single-integral constitutive equation is considered with an unspecified and unrestricted form of non-linear memory function, and with an arbitrary strain measure, I, in place of the normally used Finger and Cauchy strain tensors. It is shown that the form of the shear component of the strain measure, I12, can be derived from experimental results obtained in the start-up of steady shear flow; and that normal stresses can be predicted from shear stresses. In contrast to the Finger and Cauchy tensors, the form of I12 obtained from experiment is decidedly non-linear in the amount of shear, and this results in markedly improved normal stress predictions. It is concluded that some of the previous failures of the Bird-Carreau type of equation have been due to a poor choice of strain measure, and not (as has been suggested) to the use of an inappropriate form of memory function. The new strain measure might usefully be applied to other flows.
Elongational flow of polyethylenes in isothermal melt spinning
Authors: Revenu Pascale , Guillet Jacques , Carrot Christian
Published: July 2002

The elongational behavior of two polyethylenes with different structures, namely, a low-density polyethylene and a linear low-density polyethylene, has been investigated by isothermal melt spinning. The length along the spinline has been rescaled according to time. The evolution of the calculated elongational viscosity versus time has been compared to the transient elongational viscosities measured after imposition of a constant extension rate. The data demonstrate that these two situations, which are in many ways similar, give nearly the same results. Consequently, the viscosity which can be obtained from a fiber spinning experiment is a transient elongational viscosity. Differences in the elongational behavior between the long branched and the linear polyethylene are presented such as displayed in the spinning experiment. The strong influence on practical parameters such as melt strength or breaking stretch ratio is demonstrated.
Molecular-level modeling of the viscoelasticity of crosslinked polymers: Effect of time and temperature
Authors: Simon Philip P. , Ploehn Harry J.
Published: July 2002

We present a new molecular-level picture of chain dynamics for describing the viscoelasticity of crosslinked polymers. The associated mathematical model consists of a time-dependent momentum balance on a representative polymer segment in the crosslinked network, plus phenomenological expressions for forces acting on the segments. These include a cohesive force that accounts for intermolecular attraction, an entropic force describing the thermodynamics governing chain conformations, and a frictional force that captures the temperature dependence of relative chain motion. We treat the case of oscillatory uniaxial deformation. Solution of the model equations in the frequency domain yields the dynamic moduli as functions of temperature and frequency. The model reproduces all of the qualitative features of experimental dynamic modulus data across the complete spectrum of time and temperature, spanning the glassy zone, the β transition, the dynamic glass transition, and the rubbery zone. All of the model parameters can be evaluated through the use of independent experimental data. Comparison of model predictions with experimental data yields good quantitative agreement outside of the glass transition region.
OPCs reduce ODs; post‐OD intervention reduces deaths
Authors: Knopf Alison
Published: March 2023

Two studies together show that having a place to inject opioids and be rescued by naloxone reduces overdoses but not deaths, and that what is needed to prevent subsequent overdose deaths is outreach after an overdose to the victim and family.