bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of bromodeoxyuridine incorporation and neuropeptide immunoreactivity during arm regeneration in the starfish Asterias rubens
Authors: Moss Claire , Jackie Hunter A. , Thorndyke Michael C.
Published: July 2002

Regeneration of the arm of the starfish,Asterias rubens(L.) (Echinodermata: Asteroidea) was examined using two preparations. The first involved regeneration of the entire arm tip and its associated sensory structures and the second examined regeneration of a small section of radial nerve cord in the mid–arm region. Cell cycle activity was investigated by incorporation of the thymidine analogue, bromodeoxyuridine (BrdU). Details of neuroanatomy were obtained by immunocytochemistry (ICC) using an antiserum to the recently isolated starfish neuropeptide, GFNSALMFamide (S1). BrdU labelling indicated that initial events occur by morphallaxis, with cell cycle activity first apparent after formation of a wound epidermis. As regeneration proceeded, BrdU immunoreactive (IR) nuclei revealed cell cycle activity in cells at the distal ends of the radial nerve cord epidermis, in the coelomic epithelium, the perihaemal and water vascular canal epithelia, and in the forming tube feet of both preparations. By varying the time between BrdU pulses and tissue fixation, the possible migration or differentiation of labelled cells was investigated. Neuropeptide ICC indicated the extension of S1–IR nerve fibres into the regenerating area, soon after initial wound healing processes were complete. These fibres were varicose and disorganized in appearance, when compared to the normal pattern of S1–IR in the radial nerve. S1–IR was also observed in cell bodies, which reappeared in the reforming optic cushion and radial nerve at later stages of regeneration. Double labelling studies with anti–BrdU and anti–S1 showed no co–localization in these cell bodies, in all the stages examined. It appeared that S1–IR cells were not undergoing, and had not recently undergone, cell cycle activity. It cannot be confirmed whether S1–IR neurons were derived from proliferating cells of epithelial origin, or from transdifferentiation of epithelial cells, although the former mechanism is suggested. Differentiation of the regenerating structures to replace cells such as S1–containing neurons, is thought to involve cell cycle activity and differentiation of epithelial cells in the epidermal tissue, possibly in association with certain types of coelomocytes which move into the regenerating area.
From genotype to phenotype: genetics and medical practice in the new millennium
Authors: Weatherall David
Published: July 2002

The completion of the human genome project will provide a vast amount of information about human genetic diversity. One of the major challenges for the medical sciences will be to relate genotype to phenotype. Over recent years considerable progress has been made in relating the molecular pathology of monogenic diseases to the associated clinical phenotypes. Studies of the inherited disorders of haemoglobin, notably the thalassaemias, have shown how even in these, the simplest of monogenic diseases, there is remarkable complexity with respect to their phenotypic expression. Although studies of other monogenic diseases are less far advanced, it is clear that the same level of complexity will exist. This information provides some indication of the difficulties that will be met when trying to define the genes that are involved in common multigenic disorders and, in particular, in trying to relate disease phenotypes to the complex interactions between many genes and multiple environmental factors.
Coherence in nervous system design: the visual system of
Pantodon buchholzi
Authors: Saidel William M.
Published: July 2002

One of the more unusual visual systems of the Actinopterygii is that of
Pantodon buchholzi
(Osteoglossomorpha: Osteoglossidae). Its adaptations associate neuroanatomy at different levels of the visual system with ecological and behavioural correlates and demonstrate that the visual system of this fish has adapted for simultaneous vision in air and water. The visual field is divided into three distinct areas: for viewing into the water column, into air, and for viewing the aquatic reflection from the underside of the water surface. Cone diameters in different retinal areas correlate with the differing physical constraints in the respective visual field. Retinal differentiation between the aquatic and aerial views is paralleled at different levels of the central nervous system. A diencephalic nucleus receives both direct and indirect (tectal) afferent input from only the aerial visual system and a specific type of cell in the optic tectum is preferentially distributed in the tectum processing aerial inputs. Distinctions within a single sensory system suggest that some behaviours may be organized according to visual field. For Pantodon , feeding is initiated by stimuli seen by the ventral hemiretina so the anatomical specializations may well play an important role as elements in a feeding circuit.
Developing vaccines against pandemic influenza
Authors: Wood John M.
Published: July 2002

Pandemic influenza presents special problems for vaccine development. There must be a balance between rapid availability of vaccine and the safeguards to ensure safety, quality and efficacy of vaccine. Vaccine was developed for the pandemics of 1957, 1968, 1977 and for the pandemic alert of 1976. This experience is compared with that gained in developing vaccines for a possible H5N1 pandemic in 1997–1998. Our ability to mass produce influenza vaccines against a pandemic threat was well illustrated by the production of over 150 million doses of ‘swine flu’ vaccine in the USA within a 3 month period in 1976. However, there is cause for concern that the lead time to begin vaccine production is likely to be about 7–8 months. Attempts to reduce this time should receive urgent attention. Immunogenicity of vaccines in pandemic situations is compared over the period 1968–1998. A consistent feature of the vaccine trials is the demonstration that one conventional 15μg haemagglutinin dose of vaccine is not sufficiently immunogenic in naive individuals. Much larger doses or two lower doses are needed to induce satisfactory immunity. There is some evidence that whole–virus vaccines are more immunogenic than split or subunit vaccines, but this needs substantiating by further studies. H5 vaccines appeared to be particularly poor immunogens and there is evidence that an adjuvant may be needed. Prospects for improving the development of pandemic vaccines are discussed.
The yeast SAS (something about silencing) protein complex contains a MYST-type putative acetyltransferase and functions with chromatin assembly factor ASF1
Authors: Osada Shigehiro , Sutton Ann , Muster Nemone , Brown Christine E. , Yates John R. , Sternglanz Rolf , Workman Jerry L.
Published: July 2002

It is well established that acetylation of histone and nonhistone proteins is intimately linked to transcriptional activation. However, loss of acetyltransferase activity has also been shown to cause silencing defects, implicating acetylation in gene silencing. The something about silencing (Sas) 2 protein of Saccharomyces cerevisiae, a member of the MYST (MOZ,Ybf2/Sas3, Sas2, and TIP60) acetyltransferase family, promotes silencing at HML and telomeres. Here we identify a ∼450-kD SAS complex containing Sas2p, Sas4p, and the tf2f-related Sas5 protein. Mutations in the conserved acetyl-CoA binding motif of Sas2p are shown to disrupt the ability of Sas2p to mediate the silencing at HML and telomeres, providing evidence for an important role for the acetyltransferase activity of the SAS complex in silencing. Furthermore, the SAS complex is found to interact with chromatin assembly factor Asf1p, and asf1 mutants show silencing defects similar to mutants in the SAS complex. Thus, ASF1-dependent chromatin assembly may mediate the role of the SAS complex in silencing.
Subunit composition of a bicomponent toxin: Staphylococcal leukocidin forms an octameric transmembrane pore
Authors: Miles George , Movileanu Liviu , Bayley Hagan
Published: July 2002

Staphylococcal leukocidin pores are formed by the obligatory interaction of two distinct polypeptides, one of class F and one of class S, making them unique in the family of β‐barrel pore‐forming toxins (β‐PFTs). By contrast, other β‐PFTs form homo‐oligomeric pores; for example, the staphylococcal α‐hemolysin (αHL) pore is a homoheptamer. Here, we deduce the subunit composition of a leukocidin pore by two independent methods: gel shift electrophoresis and site‐specific chemical modification during single‐channel recording. Four LukF and four LukS subunits coassemble to form an octamer. This result in part explains properties of the leukocidin pore, such as its high conductance compared to the αHL pore. It is also pertinent to the mechanism of assembly of β‐PFT pores and suggests new possibilities for engineering these proteins.
Theoretical estimation of absorbed dose to organs in radioimmunotherapy using radionuclides with multiple unstable daughters
Authors: Hamacher K. A. , Sgouros G.
Published: July 2002

The toxicity and clinical utility of long‐lived alpha emitters such as Ac‐225 and Ra‐223 will depend upon the fate of alpha‐particle emitting unstable intermediates generated after decay of the conjugated parent. For example, decay of Ac‐225 to a stable element yields four alpha particles and seven radionuclides. Each of these progeny has its own free‐state biodistribution and characteristic half‐life. Therefore, their inclusion for a more accurate prediction of absorbed dose and potential toxicity requires a formalism that takes these factors into consideration as well. To facilitate the incorporation of such intermediates into the dose calculation, a previously developed methodology (model 1) has been extended. Two new models (models 2 and 3) for allocation of daughter products are introduced and are compared with the previously developed model. Model 1 restricts the transport to a function that yields either the place of origin or the place(s) of biodistribution depending on the half‐life of the parent radionuclide. Model 2 includes the transient time within the bloodstream and model 3 incorporates additional binding at or within the tumor. This means that model 2 also allows for radionuclide decay and further daughter production while moving from one location to the next and that model 3 relaxes the constraint that the residence time within the tumor is solely based on the half‐life of the parent. The models are used to estimate normal organ absorbed doses for the following parent radionuclides: Ac‐225, Pb‐212, At‐211, Ra‐223, and Bi‐213. Model simulations are for a 0.1 g rapidly accessible tumor and a 10 g solid tumor. Additionally, the effects of varying radiolabled carrier molecule purity and amount of carrier molecules, as well as tumor cell antigen saturation are examined. The results indicate that there is a distinct advantage in using parent radionuclides such as Ac‐225 or Ra‐223, each having a half‐life of more than 10 days and yielding four alpha particles per parent decay, in that lower doses to normal organs result for a given tumor dose in comparison to those radionuclides yielding fewer alpha particles. In model 2, which accounts for transit time through the blood, a dose of 20 Gy to a rapidly accessible 0.1 g tumor will result in a liver and kidney dose of 1.7 and 0.9 Gy, respectively from Ac‐225. An equivalent dose to tumor from Ra‐223 would yield a maximum normal organ dose of 0.4 and 0.3 Gy to bone and small intestines, respectively; the corresponding absorbed dose to small intestines from Pb‐212 and Bi‐213 is 2.2 and 3.0 Gy, respectively.
Fetal dose estimates for electron‐beam treatment to the chest wall of a pregnant patient
Authors: Antolak John A. , Strom Eric A.
Published: July 2002

The purpose of this report is to discuss dosimetry and shielding for electron‐beam radiotherapy of pregnant patients. Specifically, we have determined fetal dose for a pregnant patient considering electron radiotherapy for a chest wall recurrence of breast cancer. The treatment was simulated using an anthropomorphic phantom, and the measured dose to the unshielded fetus for this plan was 5.3 cGy, a level at which risk to the fetus is uncertain. Therefore abdominal shielding, consisting of 6.6 cm of lead, was used to reduce the dose to the fetus to less than 1.5 cGy, a level considered to be of little risk. We further found that using the lower (instead of upper) variable trimmer bars to define the field edge closest to the fetus resulted in approximately 30% lower dose to the fetus. These results show that it is possible to reduce fetal dose to acceptable limits in electron‐beam radiotherapy of the chest wall using the general principles recommended for photon‐beam radiotherapy.
A Monte Carlo study of x‐ray fluorescence in x‐ray detectors
Authors: Boone John M. , Seibert J. Anthony , Sabol John M. , Tecotzky Melvin
Published: July 2002

Advances in digital x‐ray detector systems have led to a renewed interest in the performance of x‐ray phosphors and other detector materials. Indirect flat panel x‐ray detector and charged coupled device (CCD) systems require a more technologically challenging geometry, whereby the x‐ray beam is incident on the front side of the scintillator, and the light produced must diffuse to the back surface of the screen to reach the photoreceptor. Direct detector systems based on selenium have also enjoyed a growing interest, both commercially and academically. Monte Carlo simulation techniques were used to study the x‐ray scattering (Rayleigh and Compton) and the more prevalent x‐ray fluorescence properties of seven different x‐ray detector materials, CsI, Se, BaFBr, and The redistribution of x‐ray energy, back towards the x‐ray source, in a forward direction through the detector, and lateral reabsorption in the detector was computed under monoenergetic conditions (1 keV to 130 keV by 1 keV intervals) with five detector thicknesses, 30, 60, 90, 120, and 150 mg/cm2 (Se was studied from 30 to 1000 mg/cm2). The radial distribution (related to the point spread function) of reabsorbed x‐ray energy was also determined. Representative results are as follows: At 55 keV, more (31.3%) of the incident x‐ray energy escaped from a detector than was absorbed (27.9%). Approximately 1% of the total absorbed energy was reabsorbed greater than 0.5 mm from the primary interaction, for 90 mg/cm2 CsI exposed at 100 kVp. The ratio of reabsorbed secondary radiation to the primary radiation absorbed in the detectors (90 mg/cm2) was determined as 10%, 16%, 2%, 12%, 3%, 3%, and 0.3% for a 100 kVp tungsten anode x‐ray spectrum, for the CsI, Se, BaFBr, and detectors, respectively. The results indicate significant x‐ray fluorescent escape and reabsorption in common x‐ray detectors. These findings suggest that x‐ray fluorescent radiation redistribution should be considered in the design of digital x‐ray imaging systems.
Methods for the determination of effective monitor chamber thickness
Authors: Sjögren Rickard , Karlsson Magnus G. , Karlsson Mikael
Published: July 2002

There are a number of models, both analytical and Monte Carlo, which are used to describe the fluence from the treatment head of accelerators. One common problem in these simulations is to find relevant information about details in the treatment head. A complex unit in the treatment head for which reliable data is seldom given is the monitor chamber. In this work two methods are described for obtaining this information by analyzing the increased scattering of an electron beam when the monitor chamber is introduced in the beam. It was found that the effective thickness of the electrodes in a monitor chamber can be determined with sufficient accuracy by using experimental results combined with Fermi–Eyges theory or Monte Carlo simulations.
The potential for radiation‐induced skin damage in interventional neuroradiological procedures: A review of 522 cases using automated dosimetry
Authors: O'Dea Thomas J. , Geise Richard A. , Ritenour E. Russell
Published: July 2002

The Food and Drug Administration (FDA) has recommended the monitoring of radiation skin dose to patients during procedures having the potential for radiation damage. Radiologists need information about typical radiation doses during interventional procedures. The skin doses to patients during 522 interventional neuroradiological procedures have been monitored using an automated dosimetry system. Estimated entrance skin doses (ESD) were binned into 0.5 Gy increments and compared to FDA recommended thresholds for inclusion in the patient record. Percentages of procedures exceeding the above mentioned thresholds are presented. In addition, the percentage of dose in each view and the percentage of dose in fluoroscopic and digital angiographic modes are shown. Six percent of embolization procedures and one percent of cerebral angiograms are estimated to have potential for main erythema All types of procedures have potential for temporary erythema and exceed the threshold for inclusion in the patient record at the 95% percentile. The types of procedures with most potential for skin damage also have significant percentages of dose in the digital angiographic mode. Thus, monitoring fluoroscopic time alone underestimates the potential for skin injury. On the other hand, combining the doses in the posterior‐anterior and lateral views, tends to overestimate the potential for radiation injury.
Three‐dimensional computed tomographic reconstruction using a C‐arm mounted XRII: Image‐based correction of gantry motion nonidealities
Authors: Fahrig R. , Holdsworth D. W.
Published: July 2002

The image quality of 3D reconstructions produced using a C‐arm mounted XRII depends on precise determination of the geometric parameters that describe the detector system in the laboratory frame of reference. We have designed a simplified calibration system that depends on images of a metal sphere, acquired during rotation of the gantry through 200°. Angle‐dependent shift corrections are obtained, accounting for nonideal motion in two directions: perpendicular to the axis of rotation and tangential to the circular trajectory (τ), and parallel to the axis of rotation (ξ). Projection images are corrected prior to reconstruction using a simple shift‐interpolation algorithm. We show that the motion of the gantry is highly reproducible during acquisitions within one day (mean standard deviation in τ and ξ is 0.11 mm and 0.08 mm, respectively), and over 21 months (mean standard deviation in τ and ξ is 0.10 mm and 0.06 mm, respectively). Reconstruction of a small‐bead phantom demonstrates uniformity of the correction algorithm over the full volume of the reconstruction [standard deviation of full‐width‐half‐maximum of the beads is ∼0.25 pixels (0.13 mm) over the volume of reconstruction]. Our approach provides a simple correction technique that can be applied when trajectory deviations are significant relative to the pixel size of the detector but small relative to the detector field of view, and when the fan angle of the acquisition geometry is small (<20°). A comparison with other calibration techniques in the literature is provided.
Do we really understand quantum mechanics? Strange correlations, paradoxes, and theorems
Authors: Laloë F.
Published: July 2002

This article presents a general discussion of several aspects of our present understanding of quantum mechanics. The emphasis is put on the very special correlations that this theory makes possible: They are forbidden by very general arguments based on realism and local causality. In fact, these correlations are completely impossible in any circumstance, except for very special situations designed by physicists especially to observe these purely quantum effects. Another general point that is emphasized is the necessity for the theory to predict the emergence of a single result in a single realization of an experiment. For this purpose, orthodox quantum mechanics introduces a special postulate: the reduction of the state vector, which comes in addition to the Schrödinger evolution postulate. Nevertheless, the presence in parallel of two evolution processes of the same object (the state vector) may be a potential source for conflicts; various attitudes that are possible to avoid this problem are discussed in this text. After a brief historical introduction, recalling how the very special status of the state vector has emerged in quantum mechanics, various conceptual difficulties are introduced and discussed. The Einstein–Podolsky–Rosen (EPR) theorem is presented with the help of a botanical parable, in a way that emphasizes how deeply the EPR reasoning is rooted into what is often called “scientific method.” In another section the Greenberger–Horne–Zeilinger argument, the Hardy impossibilities, as well as the Bell–Kochen–Specker theorem are introduced in simple terms. The final two sections attempt to give a summary of the present situation: One section discusses nonlocality and entanglement as we see it presently, with brief mention of recent experiments; the last section contains a (nonexhaustive) list of various attitudes that are found among physicists, and that are helpful to alleviate the conceptual difficulties of quantum mechanics.
Diamagnetically stabilized magnet levitation
Authors: Simon M. D. , Heflinger L. O. , Geim A. K.
Published: July 2002

Stable levitation of one magnet by another with no energy input is usually prohibited by Earnshaw’s theorem. However, the introduction of diamagnetic material at special locations can stabilize such levitation. A magnet can even be stably suspended between (diamagnetic) fingertips. A very simple, surprisingly stable room temperature magnet levitation device is described that works without superconductors and requires absolutely no energy input. Our theory derives the magnetic field conditions necessary for stable levitation in these cases and predicts experimental measurements of the forces remarkably well. New levitation configurations are described which can be stabilized with hollow cylinders of diamagnetic material. Measurements are presented of the diamagnetic properties of several samples of bismuth and graphite.
Investigating vortical dipolar flows using particle image velocimetry: An experiment for the advanced undergraduate laboratory
Authors: Afanasyev Yakov
Published: July 2002

This paper describes a laboratory experiment designed to study vortex dipoles, fascinating structures that occur in geophysical and industrial turbulent flows. A particle image velocimetry measurement system is used to measure the velocity and vorticity fields in the flow. The apparatus required for the experiment is inexpensive and easy to construct.
A simple experiment for determining Verdet constants using alternating current magnetic fields
Authors: Jain Aloke , Kumar Jayant , Zhou Fumin , Li Lian , Tripathy Sukant
Published: July 2002

A simple experiment suitable for a senior undergraduate and graduate laboratory on the measurement of Faraday rotation using ac magnetic fields is described. The apparatus was used to measure the wavelength dependence of Verdet constants for several materials. A concentration-dependent study on ferric chloride water solution was also carried out to demonstrate that the diamagnetic and paramagnetic contributions to Faraday rotation have opposite signs.
Solving for the dynamics of the universe
Authors: Faraoni Valerio
Published: July 2002

A new method of solving the Einstein–Friedmann dynamical equations of a spatially homogeneous and isotropic universe is presented. The method is applicable when the equation of state of the material content assumes the form P=(γ−1)ρ, γ=constant. The solution for the expansion factor is commonly given only for γ=0, 1, and 4/3 when the curvature index is K=±1. The proposed procedure is valid for general γ and K and it allows for ease of derivation of the solutions. This alternative method is useful pedagogically to introduce basic cosmology.
Free vibration analysis of laminated piezoceramic hollow spheres
Authors: Chen W. Q.
Published: July 2002

This paper presents an exact three-dimensional analysis of the general nonaxisymmetric free vibration of a piezoceramic hollow sphere by employing a state-space approach. By introducing three displacement functions and two stress functions, the basic equations of a spherically isotropic piezoelectric medium are eventually turned into two separated state equations with variable coefficients. The solutions of these two equations are then obtained by virtue of Taylor’s expansion theorem. Relationships between the state variables at the inner and outer surfaces of a laminated hollow sphere are established. Exact frequency equations corresponding to two independent classes of vibrations are then derived from the free conditions at the spherical boundary surfaces. Numerical results are finally presented.
New piezoelectric polymer for air-borne and water-borne sound transducers
Authors: Kressmann Reiner
Published: July 2002

Acoustic transducers made of a charged cellular polymer called EMFi have been designed and investigated with respect to air-borne and water-borne sound. The longitudinal transducer constant is around 90 pC/N, strongly exceeding the values of other piezoelectric polymers. This is mainly attributed to the very low Young’s modulus of about 2 MPa. The acoustic impedance is only 2.6×104 kg/(m2 s) and results in good matching to air but strong loading under water. Due to this strong loading, a pronounced reduction of resonance frequency from 300 kHz in air down to 17 kHz under water is observed. The experiments indicate that fluid loading is not only mass-like but also compliant, reducing the transducer’s sensitivity below the resonance frequency of about −63 dB re 1 V/Pa (0.7 mV/Pa) in air to −71 dB re 1 V/Pa under water. This compliance is attributed to the medium’s compressibility. Piezoelectricity of EMFi films is limited to temperatures below 70 °C; above, irreversible discharge of trapped charges takes place. Furthermore, a second type of EMFi, called “OS” was investigated, having a piezoelectric constant of 15 pC/N and a Young’s modulus of 6 MPa. In quasi-static sensor measurements, the piezoelectric constant increases with the applied load. This nonlinearity explains the higher values reported in other publications on the same materials.
The surface variational principle applied to an acoustic cavity
Authors: Franco F. , Cunefare K. A.
Published: July 2002

This paper presents the development and application of the Surface Variational Principle (SVP) for the evaluation of axisymmetric interior acoustic domains. The interior form of the SVP is first developed in the same manner as the existing exterior form. Then, the surface pressure and normal velocity are represented with a Ritz expansion using basis functions that span the entire wetted surface of the object of interest. The resultant formulation is used to analyze the interior acoustic response of a harmonically forced, right circular elastic cylinder. This validation model was chosen as both the structural and acoustic responses can be solved analytically. Results are presented for two models: one with a length to radius ratio of 2.4, and another with a ratio of 12.3. The SVP is shown to well reproduce the analytical solution for this geometry, and displays the asymptotic convergence expected of its variational formulation. The SVP formulation developed here is not restricted to right-circular cylindrical geometries, and may, indeed, be readily applied to any axisymmetric body.
Binaural processing model based on contralateral inhibition. II. Dependence on spectral parameters
Authors: Breebaart Jeroen , van de Par Steven , Kohlrausch Armin
Published: July 2002

This and two accompanying articles [Breebaart et al., J. Acoust. Soc. Am. 110, 1074–1088 (2001); 110, 1105–1117 (2001)] describe a computational model for the signal processing in the binaural auditory system. The model consists of several stages of monaural and binaural preprocessing combined with an optimal detector. In the present article the model is tested and validated by comparing its predictions with experimental data for binaural discrimination and masking conditions as a function of the spectral parameters of both masker and signal. For this purpose, the model is used as an artificial observer in a three-interval, forced-choice adaptive procedure. All model parameters were kept constant for all simulations described in this and the subsequent article. The effects of the following experimental parameters were investigated: center frequency of both masker and target, bandwidth of masker and target, the interaural phase relations of masker and target, and the level of the masker. Several phenomena that occur in binaural listening conditions can be accounted for. These include the wider effective binaural critical bandwidth observed in band-widening NoSπ conditions, the different masker-level dependence of binaural detection thresholds for narrow- and for wide-band maskers, the unification of IID and ITD sensitivity with binaural detection data, and the dependence of binaural thresholds on frequency.
Origin of cubic difference tones generated by high-intensity stimuli: Effect of ischemia and auditory fatigue on the gerbil cochlea
Authors: Mom Thierry , Bonfils Pierre , Gilain Laurent , Avan Paul
Published: July 2002

Cubic difference tone (CDT) otoacoustic emissions are thought to arise from the feedback loop allowing outer hair cells to enhance the sensitivity and tuning of the organ of Corti. The existence of residual CDTs during complete cochlear ischemia is therefore disturbing. That stimulus intensities must exceed 50–60 dB SPL for residual CDTs to be recorded and for level notches to be present in CDT growth functions is often cited as evidence for a two-component, “active/passive” model: one component, the residual one, would originate from a passive, hardly vulnerable mechanism and thus be unsuitable for hearing screening purposes. This model was probed in gerbil ears after complete interruption of the cochlear blood flow. Cochlear potentials and CDTs were controlled simultaneously through continuous monitoring of CDT level and phase for 50 and 60 dB SPL stimuli and group-delay measurements. After a clear initial decay, CDT levels elicited at 60 dB SPL plateaued for several minutes at about 20 dB below initial level, and when early level notches were observed, CDT phase changes remained minor. The CDT group delays decreased by less than 30%. Later CDT level notches were associated with sharp phase reversals but the similarity between CDT characteristics before and after a notch was hardly consistent with a two-component interpretation. When mild sound overexposure (pure tone, 90–95 dB SPL, 15–30 min) had been performed prior to ischemia, little or no ischemic CDT came from the frequency bands where auditory fatigue had been detected (within 1 kHz), irrespective of the stimulus intensity. It suggests that instead of being passive, residual ischemic CDTs were vulnerable and produced according to a near-normal tonotopy by the same mechanisms that were sensitive to auditory fatigue. All the results lined up with a simple feedback model of cochlear function assuming a single CDT source related to mechano-electrical transduction in outer hair cells. More parsimonious than a two-component model, it posits that although early stages of ischemia dramatically impair the overall performance of the cochlea, the nonlinear mechanical stages responsible for the existence of CDTs keep working albeit at higher intensities.
A level of stimulus representation model for auditory detection and attention
Authors: Hafter Ervin R. , Saberi Kourosh
Published: July 2002

A model is offered here to address an asymmetry of cueing in signal detection [Hafter et al. (1992)] where the effect of frequency uncertainty on the detection of a randomly chosen tone was ameliorated by cueing with a sequence of its harmonics, but detection of a randomly chosen sequence of harmonics was not improved by cueing with their fundamental. The model proposes that signal detection can be based on various levels of neural representation that, for the case at hand, refer to levels organized either by frequency or by complex pitch. Experiments offered to test the model used three-tone complexes for both cues and signals. These stimuli consisted of either three randomly chosen frequencies or three randomly chosen harmonics (from the set 2 f1 to 7f1) of a randomly chosen fundamental. Support for the idea of cueing and detection at different levels of representation was found in higher performance with uncued detection of harmonic complexes relative to that found with complexes of unrelated tones and by successful cueing of each type of information with cues created to remove uncertainty about the relevant information. A final comparison suggests independence of performance (presumably of the limiting noise) at each of the putative levels of representation.
Interface scattering by poroelastic seafloors: First-order theory
Authors: Williams Kevin L. , Grochocinski James M. , Jackson Darrell R.
Published: July 2002

A perturbation model is developed for sound scattering by a poroelastic seafloor having roughness small compared to the acoustic wavelength. The sediment is assumed to be homogeneous and isotropic with wave propagation described by Biot’s equations. When applied to sandy sediments, the model predicts backscattering levels that are substantially lower than those of a fluid model having the same roughness, density, sound speed, and attenuation.
Quantitative investigation of acoustic streaming in blood
Authors: Shi Xuegong , Martin Roy W. , Vaezy Shahram , Crum Lawrence A.
Published: July 2002

Acoustic streaming may have practical utility in diagnostic medical ultrasound in distinguishing between stagnant blood and tissue as well as clotted and unclotted blood. This distinction can be difficult with conventional ultrasound but have high value in managing trauma patients with internal hemorrhage. Ultrasound energy applies a force to blood by momentum transfer, resulting in bulk streaming that is a function of the acoustic attenuation, sound speed, acoustic intensity, blood viscosity, and the boundary conditions posed by the geometry around the hematoma. A simple tubular model was studied analytically, by finite element simulation, and experimentally by in vitro measurement. The simulation agreed closely with measurements while the analytic solutions were found to be valid only for beam diameters approximating the diameter of the tubular channel. Experimentally, the acoustic streaming in blood decreased as the blood began to clot and the streaming flow was not detected in clotted blood. In contrast, the echogenicity of the same blood samples did not change appreciably from the unclotted to the clotted state for the stagnant blood studied. Streaming detection appears to offer a potential tool for improving hemorrhage diagnosis.
Hybrid laser/broadband EMAT ultrasonic system for characterizing cracks in metals
Authors: Bernstein Johanna R. , Spicer James B.
Published: July 2002

Detection and characterization of defects in metal parts in industrial and commercial settings has typically been carried out by nondestructive ultrasonic inspection systems. Correct measurement of crack size is critical for lifetime prediction inspections. Normally, measurements are made based on far-field ultrasonic diffraction models and time-of-flight reflection signals making accurate measurements for parts less than approximately 25 mm in thickness impossible. In this work a hybrid noncontacting laser generation/broadband electromagnetic acoustic transducer (EMAT) detection system is used to characterize ideal cracks in aluminum in which the far-field condition for ultrasonic diffraction cannot be met. Time domain signals show that diffracted energy is measured in the geometrical shadow zone of the crack. Fourier transform methods are used to show that the frequency content of the diffracted signals is different than those from the waves that do not interact with the crack. Crack size measurements are made by using the frequency content of the ultrasonic signal rather than time-of-flight information.
Formant transition duration and speech recognition in normal and hearing-impaired listeners
Authors: Turner Christopher W. , Smith Sarah J. , Aldridge Patricia L. , Stewart Suzanne L.
Published: July 2002

Listeners with sensorineural hearing loss often have difficulty discriminating stop consonants even when the speech signals are presented at high levels. One possible explanation for this deficit is that hearing-impaired listeners cannot use the information contained in the rapid formant transitions as well as normal-hearing listeners. If this is the case, then perhaps slowing the rate of frequency change in formant transitions might assist their ability to perceive these speech sounds. In the present study, sets of consonant plus vowel (CV) syllables were synthesized corresponding to /ba, da, ga/ with formant transitions for each set ranging from 5 to 160 ms in duration. The listener’s task was to identify the consonant in a three-alternative, closed-set response task. The results for normal-hearing listeners showed nearly perfect performance for transitions of 20 ms and longer, whereas the shortest transitions yielded poorer performance. A group of eight hearing-impaired listeners pure-tone averages (PTAs) ranging from 30 to 62 dB HL) was also tested. The hearing-impaired listeners tended to show poorer performance than the normals for transitions of all durations; however, the performance of a few hearing-impaired subjects was equal to that of normals for the shortest-duration transitions. A strong inverse relation was observed between degree of hearing loss and improvement in score as a function of transition duration. These results suggest that increasing the duration of formant transitions for listeners with more severe hearing losses may not provide a helpful solution to their speech recognition difficulties.
Theory of the time-reversal process in solids
Authors: Draeger Carsten , Cassereau Didier , Fink Mathias
Published: July 2002

In this paper, a theoretical formulation is proposed to describe a time-reversal process in a solid medium with two propagation modes, longitudinal and transverse waves. A plane time-reversal mirror (TRM) is used, installed in a fluid which is in contact with the solid through a plane interface parallel to the TRM. The basic approach is similar to the case of a plane fluid–fluid interface [D. Cassereau and M. Fink, J. Acoust. Soc. Am. 96, 3145–3154 (1994)]; it is extended to take into account the different wave types. It is shown that the TRM is able to recreate properly in time and space the reversed fields of the longitudinal wave and the vertical polarization SV of the transverse waves, but not the horizontal polarization SH. The focusing quality of the backpropagating waves is limited by their respective wavelengths, so the slower SV wave can be better focused. Additional, unwanted wavefronts are created in the solid, too, but they are of weak amplitude and they are not focused. Numerical simulations illustrate the dependence of the focal pattern on parameters like distance–source interface, size, and eccentricity of the mirror.
Frequency tuning of the dolphin’s hearing as revealed by auditory brain-stem response with notch-noise masking
Authors: Popov Vladimir V. , Supin Alexander Ya. , Klishin Vladimir O.
Published: July 2002

Notch-noise masking was used to measure frequency tuning in a dolphin (Tursiops truncatus) in a simultaneous-masking paradigm in conjunction with auditory brain-stem evoked potential recording. Measurements were made at probe frequencies of 64, 76, 90, and 108 kHz. The data were analyzed by fitting the rounded-exponent model of the auditory filters to the experimental data. The fitting parameter values corresponded to the filter tuning as follows: QER (center frequency divided by equivalent rectangular bandwidths) of 35 to 36.5 and Q10 dB of 18 to 19 at all tested frequencies.
The effect of a free-field auditory target’s motion on its detectability in the horizontal plane
Authors: Xiao Xin , Grantham D. Wesley
Published: July 2002

Masked thresholds were measured for five subjects in an anechoic chamber. The signal (a 500-Hz tone, an 8000-Hz tone, or a broadband noise) was presented from a movable loudspeaker located in the horizontal plane at ear level. A continuous noise masker came from two fixed loudspeakers at ±14° azimuth. In different threshold runs the signal was either stationary (positioned at 0° or at 15° azimuth), or it moved during its on-time (at a velocity of 30°/s or 90°/s) through an arc from −15° to +15°. There was no evidence that any of the moving signals was more detectable than a stationary signal when threshold variation due to position changes of the stationary signal was taken into account. Likewise, there was no evidence that signal velocity affected detectability when signal duration was taken into account. These results agree with previous reports obtained with simulated moving signals presented via earphones and suggest that if horizontal motion-sensitive mechanisms exist in the auditory system, such mechanisms do not contribute to signal detectability.
Calculation of acoustical scattering from a cluster of scatterers
Authors: Koc S. , Chew W. C.
Published: July 2002

The problem of determining the field scattered by a cluster of scatterers when they are insonified by a known acoustical field is addressed. The problem is formulated by using the T-matrix method and the resulting system of linear equations is solved by using the multilevel fast multipole algorithm (MLFMA) and the fast multipole method–fast Fourier transform (FMMFFT) method, and the efficiency of the two methods is compared. It was observed that, in general, the MLFMA performs better than the FMMFFT algorithm. However, when the scatterers are distributed uniformly on a rectangular grid, the FMMFFT algorithm performs as good as the MLFMA. The accuracy of the methods is evaluated by modeling a spherical scatterer as composed of many small spheres.
Binaural detection as a function of interaural correlation and bandwidth of masking noise: Implications for estimates of spectral resolution
Authors: van der Heijden Marcel , Trahiotis Constantine
Published: July 2002

Detection thresholds were measured for an antiphasic (Sπ) 500-Hz tone masked by a binaural noise, as a function of the bandwidth of the noise. Several values of interaural correlation of the masking noise were used, ranging from −1 to +1. The bandwidth dependence of the thresholds showed a pattern consistent with a 100-Hz-wide critical band for most values of interaural correlation, even for those values which resulted in a considerable binaural release of masking. Only when the interaural correlation of the masking noise was very close to, or equal to, unity was the bandwidth dependence of the thresholds in accord with an approximately 300-Hz-wide “binaural” critical band measured in previous studies. Our analysis of the data calls into question the commonly stated notion that binaural processing is characterized by a wider critical band than is monaural processing.
Scattering by a horizontal strip on a hard side wall
Authors: Ouis Djamel , Lindblad Sven
Published: July 2002

The study of the effect of a horizontal hard striplike element on a side wall is presented. This may give an estimate of the usefulness of such elements in reinforcing the early sound components in a listening room. The theoretical calculations are based on geometrical assumptions in combination with a diffraction model to take into account the diffraction by the edge of the scattering element. This latter is based on the time-domain theory of Biot and Tolstoy for the diffraction by a hard wedge applied to the half-plane. An accurate and useful approximation for the diffracted field in the frequency domain using Fresnel integrals is presented. Some measurements on a scale model are also presented.
Numerical simulation of remote acoustic sensing of ocean temperature in the Fram Strait environment
Authors: Naugolnykh Konstantin A. , Johannessen Ola M. , Esipov Igor B. , Ovchinnikov Oleg B. , Tuzhilkin Yury I. , Zosimov Viktor V.
Published: July 2002

An important part of the general problem of the Arctic climate change is the monitoring of the Fram Strait, which lies between Greenland and Spitsbergen. For this reason it is reasonable to apply acoustic methods which are proven to be effective in acoustic ocean thermometry, acoustic tomography, etc. Knowledge of the main peculiarities of sound signal propagation in this region is needed to estimate the feasibility of applying remote acoustic methods. To this end computer simulation of sound signal propagation in the Fram Strait environment was performed, based on oceanographic data obtained by the R/V POLARSTERN expedition. The presence of stable eigenrays in Fram Strait environmental conditions is demonstrated, typical values of acoustic signal travel time fluctuations due to environmental variations are determined, and the temperature effect on the signal travel time variation is considered. Sensitivity estimates for measurement of the average ocean temperature across Fram Strait is considered in two approaches: by calculating travel time changes along selected stable eigenrays, and by determining the cumulative sum of the whole envelope of the signals passed along water-borne paths.
Array element localization for horizontal arrays via Occam’s inversion
Authors: Dosso Stan E. , Fallat Mark R. , Sotirin Barbara J. , Newton John L.
Published: July 2002

Accurate locations for the individual elements of an acoustic sensor array are required for the application of advanced array processing methods. This paper develops a general method of localizing horizontal line array (HLA) elements which overcomes bandwidth constraints of low-frequency arrays and uncertainty in the experimental configuration. Array elements are localized for two HLA’s associated with the Spinnaker Array, a three-dimensional sensor array located in the high Arctic. Recordings were made of imploding glass light bulbs deployed at a series of locations surrounding the array site. Implosion instants were not measured; hence, the data consist of relative travel times. In addition, the source locations were measured only approximately in the field, and are treated as unknown parameters. The inverse problem of determining hydrophone and source locations is nonunique and ill-conditioned. To determine the most physically meaningful solution, an iterative linearized inversion is developed which applies the method of regularization to include a priori information about the solution. Available a priori information includes source–location estimates from on-ice measurements, depth estimates for the array end points, and the expectation that each HLA is essentially linear. The inversion is formulated to jointly minimize the parameter-estimate residuals and the three-dimensional curvature of each HLA, subject to fitting the array element localization (AEL) data to a statistically appropriate level. Minimizing HLA curvature produces the simplest array shape that is consistent with the data: any deviations from a straight array are definitely required by the data, and are not artifacts of the inversion algorithm or starting model.