bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of follicular dendritic cells on HIV dynamics
Authors: Hlavacek William S. , Stilianakis Nikolaos I. , Perelson Alan S.
Published: July 2002

In patients infected with human immunodeficiency virus type 1 (HIV-1), a large amount of virus is associated with follicular dendritic cells (FDCs) in lymphoid tissue. To assess the influence of FDCs on viral dynamics during antiretroviral therapy, we have developed a mathematical model for treatment of HIV-1 infection that includes FDCs. Here, we use this model to analyse measurements of HIV-1 dynamics in the blood and lymphoid tissue of a representative patient, who was treated with a combination of HIV-1 reverse transcriptase and protease inhibitors. We show that loss of virus from FDCs during therapy can make a much larger contribution to plasma virus than production of virus by infected cells. This result challenges the notion that long-lived infected cells are a significant source of HIV-1 during drug therapy. Due to release of FDC-associated virus, we find that it is necessary to revise upward previous estimates ofc, the rate at which free virus is cleared, andδ, the rate at which productively infected cells die. Furthermore, we find that potentially infectious virus, present before treatment, is released from FDCs during therapy and that the persistence of this virus can be affected by whether therapy includes reverse transcriptase inhibitors.
Hydrodynamic image formation by the peripheral lateral line system of the Lake Michigan mottled sculpin,Cottus bairdi
Authors: Coombs Sheryl , Finneran James J. , Conley Ruth A.
Published: July 2002

Lake Michigan mottled sculpin (Cottus bairdi) have a lateral–line–mediated prey–capture behaviour that consists of an initial orientation towards the prey, a sequence of approach movements, and a final strike at the prey. This unconditioned behaviour can be elicited from blinded sculpin in the laboratory by both real and artificial (vibrating sphere) prey. In order to visualize what Lake Michigan mottled sculpin might perceive through their lateral line when approaching prey, we have combined anatomical, neurophysiological, behavioural and computational modelling techniques to produce three–dimensional maps of how excitation patterns along the lateral line sensory surface change as sculpin approach a vibrating sphere. Changes in the excitation patterns and the information they contain about source location are consistent with behavioural performance, including the approach pathways taken by sculpin to the sphere, the maximum distances at which approaches can be elicited, distances from which strikes are launched, and strike success. Information content is generally higher for laterally located sources than for frontally located sources and this may explain exceptional performance (e.g. successful strikes from unusually long distances) in response to lateral sources and poor performance (e.g. unsuccessful strikes) to frontal sources.
Enhancer–promoter specificity mediated by DPE or TATA core promoter motifs
Authors: Butler Jennifer E.F. , Kadonaga James T.
Published: July 2002

To investigate the basis for enhancer–promoter specificity, we compared the ability of enhancers to activate transcription in vivo from core promoters containing either downstream promoter element (DPE) or TATA box motifs. To eliminate position effects, we generated and analyzed pairs of sister Drosophila lines that contain a DPE- or TATA-dependent reporter gene at precisely the same genomic position relative to each enhancer. These studies revealed transcriptional enhancers that are specific for promoters that contain either DPE or TATA box elements. Thus, the core promoter not only mediates the initiation of transcription, but also functions as a regulatory element.
vhnf1, the MODY5 and familial GCKD-associated gene, regulates regional specification of the zebrafish gut, pronephros, and hindbrain
Authors: Sun Zhaoxia , Hopkins Nancy
Published: July 2002

Mutations in the homeobox gene vHnf1 are associated with human diseases MODY5 (maturity-onset diabetes of the young, type V) and familial GCKD (glomerulocystic kidney disease). In an insertional mutagenesis screen in zebrafish, we isolated mutant alleles of vhnf1. Phenotypes of these mutants include formation of kidney cysts, underdevelopment of the pancreas and the liver, and reduction in size of the otic vesicles. We show that these abnormalities arise from patterning defects during development. We further provide evidence that vhnf1 regulates the expression of key patterning genes for these organs. vhnf1 is required for the proper expression of pdx1 and shh (sonic hedgehog) in the gut endoderm, pax2 and wt1 in the pronephric primordial, and valentino (val) in the hindbrain. Complementary to the loss-of-function phenotypes, overexpression of vhnf1 induces expansion of the valexpression domain in the hindbrain. We propose that vhnf1controls development of multiple organs through regulating regional specification of organ primordia. The similarity betweenvhnf1-associated fish phenotypes and human symptoms suggests a correlation between developmental functions of vhnf1 and the molecular etiology of MODY5 and GCKD.
Emotional Memory Formation Is Enhanced across Sleep Intervals with High Amounts of Rapid Eye Movement Sleep
Authors: Wagner Ullrich , Gais Steffen , Born Jan
Published: July 2002

Recent studies indicated a selective activation during rapid eye movement (REM) sleep of the amygdala known to play a decisive role in the processing of emotional stimuli. This study compared memory retention of emotional versus neutral text material over intervals covering either early sleep known to be dominated by nonREM slow wave sleep (SWS) or late sleep, in which REM sleep is dominant. Two groups of men were tested across 3-h periods of early and late sleep (sleep group) or corresponding retention intervals filled with wakefulness (wake group). Sleep was recorded polysomnographically. Cortisol concentrations in saliva were monitored at acquisition and retrieval testing. As expected, the amount of REM sleep was about three times greater during late than during early retention sleep, whereas a reversed pattern was observed for SWS distribution (P < 0.001). Sleep improved retention, compared with the effects of wake intervals (P < 0.02). However, this effect was substantial only in the late night (P < 0.005), during which retention was generally worse than during the early night (P < 0.02). Late sleep particularly enhanced memory for emotional texts. This effect was highly significant in comparison with memory for neutral texts (P < 0.01) and in comparison with memory after late and early wake intervals (P < 0.001). Cortisol concentration differed between early and late retention intervals but not between sleep and wake conditions. Results are consonant with a supportive function of REM sleep predominating late sleep for the formation of emotional memory in humans.
Direct proton magnetic resonance determination of the pKa of the active center histidine in thiolsubtilisin
Authors: Kahyaoglu Ara , Jordan Frank
Published: July 2002

The serine proteases constitute a group of endopeptidases whose members owe their catalytic activity to the presence of a catalytic triad of amino acids consisting of a serine, a histidine and an aspartate. The pKa values for this histidine have been determined for several cases in which there is a negative charge installed at the serine to mimic the oxyanionic intermediate and related transition state for the catalytic pathway. Instances from this laboratory include (1) replacement of the serine by a cysteine in subtilisin to create a thiolate; (2) formation of monoisopropylphosphoryl‐Ser 195 monoanionic phosphodiesters (in trypsin and chymotrypsin, Ser 221 in subtilisins); and (3) tetrahedral boronates formed with peptide boronic acids. The nuclear magnetic resonance (NMR) signals pertinent to this histidine, or signals indirectly reflecting the state of ionization of this histidine, have been used effectively to monitor changes in the active center ionization state. In every case studied, there is elevation of the pKa at the histidine when the negative charge is installed at the serine position. Herein is reported the first NMR measurement of the active center His 63 pKa in thiolsubtilisin Carlsberg; it is elevated by 3 units compared with the parent enzyme. Using a numerical solution (finite difference) of the Poisson‐Boltzmann equation, a protein dielectric constant of 4 provides a good estimate of the experimentally observed pKa elevations. Very significantly, a very low protein dielectric constant (εp = 3–5) is required in all of the comparisons, and for all three enzymes used (chymotrypsin, trypsin, and subtilisin). Finally, we discuss why the electrostatic perturbation sensed at His of the active center is more amplified by a negative charge on the Ser side than the same charge on the Asp side. A plausible explanation is that the positive charge on the imidazolium ring of the His is localized, with the Nδ1 carrying a smaller fraction, the Nε2 carrying the bulk of the positive charge.
Comparison of I‐125 sources used for permanent interstitial implants
Authors: Heintz Bret H. , Wallace Robert E. , Hevezi James M.
Published: July 2002

The increase in the number of manufacturers of sources used in prostate brachytherapy has generated many questions in the radiation oncology community. In this investigation, the physical and dosimetric characteristics were evaluated for the following sources listed by marketing company and source model: Nycomed‐Amersham 6711 (OncoSeed), Nycomed‐Amersham 6702, Mentor IoGold, UroMed Symmetra, Imagyn IsoSTAR, UroCor, (PSA, Mallincrkrodt) ProstaSeed, Syncor PharmaSeed, SourceTech Medical, (BARD) (BrachySource), Med‐Tec I‐Plant, Best Medical Model 2301, DraxImage BrachySeed, and International Brachytherapy, Inc. (IBT) The investigation examined the differences in design, construction, and the dosimetric characteristics created from each source. The dosimetric characteristics of the new sources were compared to that of the Amersham 6711 source. Parameter studies have led to the development of a simple equation that can be used to clinically convert the standard 6711 source strength to an equivalent strength of a new source.
Characterization of a commercial multileaf collimator used for intensity modulated radiation therapy
Authors: Low Daniel A. , Sohn Jason W. , Klein Eric E. , Markman Jerry , Mutic Sasa , Dempsey James F.
Published: July 2002

The characteristics of a commercial multileaf collimator (MLC) to deliver static and dynamic multileaf collimation (SMLC and DMLC, respectively) were investigated to determine their influence on intensity modulated radiation therapy (IMRT) treatment planning and quality assurance. The influence of MLC leaf positioning accuracy on sequentially abutted SMLC fields was measured by creating abutting fields with selected gaps and overlaps. These data were also used to measure static leaf positioning precision. The characteristics of high leaf‐velocity DMLC delivery were measured with constant velocity leaf sequences starting with an open field and closing a single leaf bank. A range of 1–72 monitor units (MU) was used providing a range of leaf velocities. The field abutment measurements yielded dose errors (as a percentage of the open field max dose) of 16.7±0.7% mm−1 and 12.8±0.7% mm−1 for 6 MV and 18 MV photon beams, respectively. The MLC leaf positioning precision was 0.080±0.018 mm (single standard deviation) highlighting the excellent delivery hardware tolerances for the tested beam delivery geometry. The high leaf‐velocity DMLC measurements showed delivery artifacts when the leaf sequence and selected monitor units caused the linear accelerator to move the leaves at their maximum velocity while modulating the accelerator dose rate to deliver the desired leaf and MU sequence (termed leaf‐velocity limited delivery). According to the vendor, a unique feature to their linear accelerator and MLC is that the dose rate is reduced to provide the correct cm MU−1 leaf velocity when the delivery is leaf‐velocity limited. However, it was found that the system delivered roughly 1 MU per pulse when the delivery was leaf‐velocity limited causing dose profiles to exhibit discrete steps rather than a smooth dose gradient. The root mean square difference between the steps and desired linear gradient was less than 3% when more than 4 MU were used. The average dose per MU was greater and less than desired for closing and opening leaf patterns, respectively, when the delivery was leaf‐velocity limited. The results indicated that the dose delivery artifacts should be minor for most clinical cases, but limit the assumption of dose linearity when significantly reducing the delivered dose for dosimeter characterization studies or QA measurements.
A least squares method of estimating length to target strength relationships from in situ target strength distributions and length frequencies
Authors: Cordue Patrick L. , Coombs Roger F. , Macaulay Gavin J.
Published: July 2002

A least squares method is presented for estimating length to target strength relationships for a target species and associated species using a series of target strength distributions and associated trawl catches. A by-product of the estimation procedure is an objective determination of the correspondence between modal lengths in the trawl catches and the modal lengths in the associated target strength distributions. The method is illustrated by applying it to a data set collected to determine the length to target strength relationship for hoki (Macruronus novaezelandiae).
Searching for the time constant of neural pitch extraction
Authors: Wiegrebe Lutz
Published: July 2002

Multichannel, auditory models have been repeatedly used to explain many aspects of human pitch perception. Among the most successful ones are models where pitch is estimated based on an analysis of periodicity in the simulated auditory-nerve firing. This periodicity analysis is typically implemented as a running autocorrelation, i.e., the autocorrelation is calculated within a temporal window which is shifted along the time axis. The window was suggested to have an exponential decay with time-constant estimates between 1.5 and 100 ms. The window length determines the minimal integration time of pitch extraction. The present experiments are designed to quantify the temporal window of pitch extraction using regular-interval noises (RINs). RINs were generated by concatenating equal-duration noise samples which produce a pitch corresponding to the reciprocal of the sample duration when the samples are identical (periodic noise). When the samples are independent, the stimulus is Gaussian noise and produces no pitch. Using RIN stimuli where periodic portions interchange with aperiodic portions, it is shown that the temporal window of pitch extraction cannot be modeled using a single time constant but that the size of the temporal window depends on the pitch itself.
Consonant identification under maskers with sinusoidal modulation: Masking release or modulation interference?
Authors: Kwon Bom Jun , Turner Christopher W.
Published: July 2002

The present study investigated the effect of envelope modulations in a background masker on consonant recognition by normal hearing listeners. It is well known that listeners understand speech better under a temporally modulated masker than under a steady masker at the same level, due to masking release. The possibility of an opposite phenomenon, modulation interference, whereby speech recognition could be degraded by a modulated masker due to interference with auditory processing of the speech envelope, was hypothesized and tested under various speech and masker conditions. It was of interest whether modulation interference for speech perception, if it were observed, could be predicted by modulation masking, as found in psychoacoustic studies using nonspeech stimuli. Results revealed that masking release measurably occurred under a variety of conditions, especially when the speech signal maintained a high degree of redundancy across several frequency bands. Modulation interference was also clearly observed under several circumstances when the speech signal did not contain a high redundancy. However, the effect of modulation interference did not follow the expected pattern from psychoacoustic modulation masking results. In conclusion, (1) both factors, modulation interference and masking release, should be accounted for whenever a background masker contains temporal fluctuations, and (2) caution needs to be taken when psychoacoustic theory on modulation masking is applied to speech recognition.
Towards a measure of auditory-filter phase response
Authors: Oxenham Andrew J. , Dau Torsten
Published: July 2002

This study investigates how the phase curvature of the auditory filters varies with center frequency (CF) and level. Harmonic tone complex maskers were used, with component phases adjusted using a variant of an equation proposed by Schroeder [IEEE Trans. Inf. Theory 16, 85–89 (1970)]. In experiment 1, the phase curvature of the masker was varied systematically and sinusoidal signal thresholds were measured at frequencies from 125 to 8000 Hz. At all signal frequencies, threshold differences of 20 dB or more were observed between the most effective and least effective masker phase curvature. In experiment 2, the effect of overall masker level on masker phase effects was studied using signal frequencies of 250, 1000, and 4000 Hz. The results were used to estimate the phase curvature of the auditory filters. The estimated relative phase curvature decreases dramatically with decreasing CF below 1000 Hz. At frequencies above 1000 Hz, relative auditory-filter phase curvature increases only slowly with increasing CF, or may remain constant. The phase curvature of the auditory filters seems to be broadly independent of overall level. Most aspects of the data are in qualitative agreement with peripheral physiological findings from other mammals, which suggests that the phase responses observed here are of peripheral origin. However, in contrast to the data reported in a cat auditory-nerve study [Carney et al., J. Acoust. Soc. Am. 105, 2384–2391 (1999)], no reversal in the sign of the phase curvature was observed at very low frequencies. Overall, the results provide a framework for mapping out the phase curvature of the auditory filters and provide constraints on future models of peripheral filtering in the human auditory system.
Detection of frequency modulation by hearing-impaired listeners: Effects of carrier frequency, modulation rate, and added amplitude modulation
Authors: Moore Brian C. J. , Skrodzka Ewa
Published: July 2002

It has been proposed that the detection of frequency modulation (FM) of sinusoidal carriers can be mediated by two mechanisms: a place mechanism based on FM-induced amplitude modulation (AM) in the excitation pattern, and a temporal mechanism based on phase-locking in the auditory nerve. The temporal mechanism appears to be “sluggish” and does not play a role for FM rates above about 10 Hz. It also does not play a role for high carrier frequencies (above about 5 kHz). This experiment examined FM detection in three young subjects with normal hearing and four elderly subjects with cochlear hearing loss. Carrier frequencies were 0.25, 0.5, 1, 2, 4, and 6 kHz and modulation rates were 2, 5, 10, and 20 Hz. FM detection thresholds were measured both in the absence of AM, and with AM of a fixed depth (m=0.33) added in both intervals of a forced-choice trial. The added AM was intended to disrupt cues based on FM-induced AM in the excitation pattern. Generally, the hearing-impaired subjects performed markedly more poorly than the normal-hearing subjects. For the normal-hearing subjects, the disruptive effect of the AM tended to increase with increasing modulation rate, for carrier frequencies below 6 kHz, as found previously by Moore and Sek [J. Acoust. Soc. Am. 100, 2320–2331 (1996)]. For the hearing-impaired subjects, the disruptive effective of the AM was generally larger than for the normal-hearing subjects, and the magnitude of the disruption did not consistently increase with increasing modulation rate. The results suggest that cochlear hearing impairment adversely affects both temporal and excitation pattern mechanisms of FM detection.
A revised model of the inner-hair cell and auditory-nerve complex
Authors: Sumner Christian J. , Lopez-Poveda Enrique A. , O’Mard Lowel P. , Meddis Ray
Published: July 2002

A revised computational model of the inner-hair cell (IHC) and auditory-nerve (AN) complex is presented and evaluated. Building on previous models, the algorithm is intended as a component for use in more comprehensive models of the auditory periphery. It combines smaller components that aim to be faithful to physiology in so far as is practicable and known. Transduction between cochlear mechanical motion and IHC receptor potential (RP) is simulated using a modification of an existing biophysical IHC model. Changes in RP control the opening of calcium ion channels near the synapse, and local calcium levels determine the probability of the release of neurotransmitter. AN adaptation results from transmitter depletion. The exact timing of AN action potentials is determined by the quantal and stochastic release of neurotransmitter into the cleft. The model reproduces a wide range of animal RP and AN observations. When the input to the model is taken from a suitably nonlinear simulation of the motion of the cochlear partition, the new algorithm is able to simulate the rate-intensity functions of low-, medium-, and high-spontaneous rate AN fibers in response to stimulation both at best frequency and at other frequencies. The variation in fiber type arises in large part from the manipulation of a single parameter in the model: maximum calcium conductance. The model also reproduces quantitatively phase-locking characteristics, relative refractory effects, mean-to-variance ratio, and first- and second-order discharge history effects.
Pure-tone threshold estimation from extrapolated distortion product otoacoustic emission I/O-functions in normal and cochlear hearing loss ears
Authors: Boege Paul , Janssen Thomas
Published: July 2002

A new method for direct pure-tone threshold estimation from input/output functions of distortion product otoacoustic emissions (DPOAEs) in humans is presented. Previous methods use statistical models relating DPOAE level to hearing threshold including additional parameters e.g., age or slope of DPOAE I/O-function. Here we derive a DPOAE threshold from extrapolated DPOAE I/O-functions directly. Cubic 2 f1−f2 distortion products and pure-tone threshold at f2 were measured at 51 frequencies between f2=500 Hz and 8 kHz at up to ten primary tone levels between L2=65 and 20 dB SPL in 30 normally hearing and 119 sensorineural hearing loss ears. Using an optimized primary tone level setting (L1=0.4L2+39 dB) that accounts for the nonlinear interaction of the two primaries at the DPOAE generation site at f2, the pressure of the 2 f1−f2 distortion product pDP is a linear function of the primary tone level L2. Linear regression yields correlation coefficients higher than 0.8 in the majority of the DPOAE I/O-functions. The linear behavior is sufficiently fulfilled for all frequencies in normal and impaired hearing. This suggests that the observed linear functional dependency is quite general. Extrapolating towards pDP=0 yields the DPOAE threshold for L2. There is a significant correlation between DPOAE threshold and pure-tone threshold (r=0.65, p<0.001). Thus, the DPOAEs that reflect the functioning of an essential element of peripheral sound processing enable a reliable estimation of cochlear hearing threshold up to hearing losses of 50 dBHL without any statistical data.
A behavioral measure of basilar-membrane nonlinearity in listeners with normal and impaired hearing
Authors: Oxenham Andrew J. , Plack Christopher J.
Published: July 2002

This paper examines the possibility of estimating basilar-membrane (BM) nonlinearity using a psychophysical technique. The level of a forward masker required to mask a brief signal was measured for conditions where the masker was either at, or one octave below, the signal frequency. The level of the forward masker at masked threshold provided an indirect measure of the BM response to the signal, as follows. Consistent with physiological studies, it was assumed that the BM responds linearly to frequencies well below the characteristic frequency (CF). Thus the ratio of the slopes of the masking functions between a masker at the signal frequency and a masker well below the signal frequency should provide an estimate of BM compression at CF. Results obtained from normally hearing listeners were in quantitative agreement with physiological estimates of BM compression. Furthermore, differences between normally hearing listeners and listeners with cochlear hearing impairment were consistent with the physiological effects of damage to the cochlea. The results support the hypothesis that BM nonlinearity governs the nonlinear growth of the upward spread of masking, and suggest that this technique provides a straightforward method for estimating BM nonlinearity in humans.
Use of pseudo-random sequences and a single microphone to measure surface impedance at oblique incidence
Authors: Li Jing-Fang , Hodgson Murray
Published: July 2002

The use of a pseudo-random sequence and a single microphone is suggested for the experimental determination of the acoustical properties (surface impedance, reflection coefficient, etc.) of sound-absorbing materials. An experimental system is developed with which the surface impedance and reflection coefficient at oblique incidence are determined from measurements of the impulse-response function sequentially at two locations close to the surface of the material using a pseudo-random sequence and a single microphone. This technique is validated using the measurement of a residual pressure-intensity index. The advantage of this technique is that it is possible to perform measurements of the surface properties of materials without phase-mismatch errors that occur with two-microphone methods. Models for estimating the surface impedance from plane-wave and spherical-wave hypotheses are reviewed and compared. Measurements of impedance at oblique incidence are carried out on a sheet of glass fiber in an anechoic room, as well as in a semi-reverberant room, and the results are compared. Surface impedances and reflection coefficients are presented as a function of angle of incidence. The proposed experimental system can be used to measure the acoustical properties of materials at oblique angles of incidence and in semi-reverberant environments.
Modeling auditory processing of amplitude modulation. II. Spectral and temporal integration
Authors: Dau Torsten , Kollmeier Birger , Kohlrausch Armin
Published: July 2002

A multi-channel model, describing the effects of spectral and temporal integration in amplitude-modulation detection for a stochastic noise carrier, is proposed and validated. The model is based on the modulation filterbank concept which was established in the accompanying paper [Dau et al., J. Acoust. Soc. Am. 102, 2892–2905 (1997)] for modulation perception in narrow-band conditions (single-channel model). To integrate information across frequency, the detection process of the model linearly combines the channel outputs. To integrate information across time, a kind of “multiple-look” strategy, is realized within the detection stage of the model. Both data from the literature and new data are used to validate the model. The model predictions agree with the results of Eddins [J. Acoust. Soc. Am. 93, 470–479 (1993)] that the “time constants” associated with the temporal modulation transfer functions (TMTF) derived for narrow-band stimuli do not vary with carrier frequency region and that they decrease monotonically with increasing stimulus bandwidth. The model is able to predict masking patterns in the modulation-frequency domain, as observed experimentally by Houtgast [J. Acoust. Soc. Am. 85, 1676–1680 (1989)]. The model also accounts for the finding by Sheft and Yost [J. Acoust. Soc. Am. 88, 796–805 (1990)] that the long “effective” integration time constants derived from the data are two orders of magnitude larger than the time constants derived from the cutoff frequency of the TMTF. Finally, the temporal-summation properties of the model allow the prediction of data in a specific temporal paradigm used earlier by Viemeister and Wakefield [J. Acoust. Soc. Am. 90, 858–865 (1991)]. The combination of the modulation filterbank concept and the optimal decision algorithm proposed here appears to present a powerful strategy for describing modulation-detection phenomena in narrow-band and broadband conditions.
An analytical model for bandlimited response of acoustic-structural coupled systems. I. Direct sound field excitation
Authors: Sum K. S. , Pan J.
Published: July 2002

An analytical model is proposed in this paper for predicting time-averaged energies of boundary structures and enclosed sound field. The sound field is directly driven by an acoustic source and the structures are excited through acoustic-structural coupling. The present model is based on the classical modal coupling method but is developed in such a way to improve the computational efficiency in estimating the bandlimited response of acoustic-structural coupled systems particularly in the medium frequency range where a large number of acoustic and/or structural modes is involved. In this frequency range, one often has to deal with manipulation of large complex matrices in order to obtain full mathematical solutions to the system response using the classical modal coupling method. However, this is avoided if the present bandlimited model is used. This paper describes the mathematical development of the model. Numerical examples for a panel-cavity system are presented and the proposed model is compared with the classical modal coupling method in terms of computational efficiency and accuracy in the prediction of the system energies.
Changes in ultrasonic images of tissue damaged by high-intensity focused ultrasound in vivo
Authors: Wu Feng , Wang Zhi B. , Wang Zhi L.
Published: July 2002

In order to clarify the effects of high-intensity focused ultrasound (HIFU) on the liver in vivo, the morphological changes in a large animal model were detected by quantitative analysis of ultrasonic image. One region of the liver was selected as a target tissue by ultrasonic imaging. Then, using the method of focal planes, the target part of the liver was resected by ultrasound-monitored HIFU with a 1.6-MHz extracorporeal spherical-bowl transducer. Ultrasonic images of the liver at the selective region were acquired before, immediately, and consecutively after HIFU treatment. The bit difference of ultrasonic image at the selective damage of the liver in vivo before and after HIFU treatment was detected by a quantitative analysis system. It was observed immediately after focused extracorporeal pyrotherapy. Sharp changes in ultrasonic image were also detected by consecutive monitoring after treatment. It corresponded to the histological characteristics of the changes of the damaged tissue. These results suggest that as a method to detect necrosed tissue, the quantitative analysis of ultrasonic image may also be used as an indicator of morphological changes after HIFU treatment.
Nonlinear surface acoustic waves in crystals
Authors: Hamilton Mark F. , Il’inskii Yurii A. , Zabolotskaya Evgenia A.
Published: July 2002

A theory for nonlinear surface acoustic waves in isotropic solids [E. A. Zabolotskaya, J. Acoust. Soc. Am. 91, 2569–2575 (1992)] is generalized to include the anisotropy of crystals. There is no restriction to material symmetry, orientation of the free surface with respect to crystal axes, or propagation direction in the plane of the free surface. Numerical simulations of waveform distortion, shock formation, and harmonic propagation curves are presented for two different cuts of potassium chloride.
Correlational analysis of acoustic cues for the discrimination of auditory motion
Authors: Lutfi Robert A. , Wang Wen
Published: July 2002

The sound of a source moving in a straight path and passing directly in front of the listener on the azimuthal plane was synthesized over headphones to include three dynamic cues for motion: Doppler effect, overall intensity, and interaural time difference. Discriminability of a change in displacement, velocity, and acceleration of this source was measured using a standard two-interval, forced-choice procedure. In each case, the relative reliance or weight given to the three acoustic cues was estimated from correlations of the listener’s response with small independent perturbations imposed on cues from trial to trial. Group estimates of threshold agreed well with results from past studies, while the obtained pattern of weights depended on the individual, starting velocity, and discrimination task. For the discrimination of displacement at moderate velocity (10 m/s), responses were most highly correlated with intensity or interaural time difference. For the discrimination of velocity and, to a lesser extent, acceleration, responses were most highly correlated with Doppler effect. At higher velocity (50 m/s) responses in all discrimination tasks were most strongly correlated with Doppler effect with few exceptions. Randomizing source spectrum or roving distance of the source from trial to trial did not significantly affect the pattern of results. The results suggest that motion perception is mutable, and not in all cases based on a single invariant acoustic cue.
Measurement of acoustic dispersion using both transmitted and reflected pulses
Authors: He Ping
Published: July 2002

Traditional broadband transmission method for measuring acoustic dispersion requires the measurements of the sound speed in water, the thickness of the specimen, and the phase spectra of two transmitted ultrasound pulses. When the sound speed in the specimen is significantly different from that in water, the overall uncertainty of the dispersion measurement is generally dominated by the uncertainty of the thickness measurement. In this paper, a new water immersion method for measuring dispersion is proposed which eliminates the need for thickness measurement and the associated uncertainty. In addition to recording the two transmitted pulses, the new method requires recording two reflected pulses, one from the front surface and one from the back surface of the specimen. The phase velocity as well as the thickness of the specimen can be determined from the phase spectra of the four pulses. Theoretical analysis and experimental results from three specimens demonstrate the advantages of this new method.
Tori of confusion: Binaural localization cues for sources within reach of a listener
Authors: Shinn-Cunningham Barbara G. , Santarelli Scott , Kopco Norbert
Published: July 2002

To a first-order approximation, binaural localization cues are ambiguous: many source locations give rise to nearly the same interaural differences. For sources more than a meter away, binaural localization cues are approximately equal for any source on a cone centered on the interaural axis (i.e., the well-known “cone of confusion”). The current paper analyzes simple geometric approximations of a head to gain insight into localization performance for nearby sources. If the head is treated as a rigid, perfect sphere, interaural intensity differences (IIDs) can be broken down into two main components. One component depends on the head shadow and is constant along the cone of confusion (and covaries with the interaural time difference, or ITD). The other component depends only on the relative path lengths from the source to the two ears and is roughly constant for a sphere centered on the interaural axis. This second factor is large enough to be perceptible only when sources are within one or two meters of the listener. Results are not dramatically different if one assumes that the ears are separated by 160 deg along the surface of the sphere (rather than diametrically opposite one another). Thus for nearby sources, binaural information should allow listeners to locate sources within a volume around a circle centered on the interaural axis on a “torus of confusion.” The volume of the torus of confusion increases as the source approaches the median plane, degenerating to a volume around the median plane in the limit.
Effects of phase duration and electrode separation on loudness growth in cochlear implant listeners
Authors: Chatterjee Monita , Fu Qian-Jie , Shannon Robert V.
Published: July 2002

Loudness estimates were obtained in a group of four adult subjects implanted with the Nucleus-22 multielectrode cochlear implant device, for a range of pulse amplitudes and different fixed phase durations and electrode separations. The stimulus was a 200-ms long train of biphasic pulses presented at 500 pulses/s. Subjects estimated loudness as a number from 0 (“don’t hear it”) to 100 (“uncomfortably loud”). Loudness was found to grow exponentially with pulse amplitude, at a rate that was dependent upon the phase duration as well as the electrode separation. An equation of the form L=e(λ+γM)(Dθ)I, where L is the estimated loudness, M is the separation between electrodes of a stimulating pair, D is the phase duration, I is current amplitude, and λ, γ, and θ are constants, appears to describe the observed data adequately. The findings are remarkably consistent across subjects.
A model of the perceptual asymmetry between peaks and troughs of frequency modulation
Authors: de Cheveigné Alain
Published: July 2002

Pitch discrimination at peaks of frequency modulation is better than at troughs [L. Demany and K. I. McAnally, J. Acoust. Soc. Am. 96, 706–715 (1989)]. A similar asymmetry emerges within a time-domain pitch perception model based on autocorrelation. The model requires the following assumptions: (a) The neural discharge patterns must be temporally sharpened to a single narrow pulse per period (possibly by neural convergence within the cochlear nucleus). (b) Autocorrelation must be implemented as a cross correlation between the neural pulse train and a delayed pulse train convolved with a short kernel function. This kernel function must be asymmetric in time. (c) Pitch discrimination must rely on higher-order modes of the autocorrelation function. This particular implementation of the autocorrelation model produces modes that are sharper for peaks than for troughs, and thus accounts for the pitch discrimination asymmetry observed experimentally. As a by-product it can account for “hyperacute” discrimination observed at peaks of triangular modulation.
Perception and production of English vowels by Spanish adult L2 learners: Effects of experience and proficiency
Authors: Wayland Ratree P. , Flege James E.
Published: July 2002

This study examined the effects of experience and proficiency on the perception and the production of English vowels by native Spanish adults. The 60 subjects were assigned to subgroups according to the length of their residence in the United States (3 LOR groups) and overall degree of foreign accent in English (three proficiency groups). Experiment 1 assessed the perceived relationship between 11 English and 5 Spanish vowels. Experiment 2 examined the subject’s categorial discrimination of pairs of the English vowels, and exp. 3 assessed the subjects’ accuracy in producing eight English vowels. The native Spanish subjects’ perception and production of English vowels changed as a function of their overall proficiency in pronouncing English. An examination of relation between perception and production suggested that perceived similarity of English vowels to Spanish vowels, but not the subjects’ categorial discrimination of vowels, was correlated with subjects’ vowel production accuracy. Also, a stronger correlation was found to exist between the perceived relation between English and Spanish vowels and subjects’ overall degree of foreign accent than between their vowel discrimination scores and overall degree of foreign accent.
Investigation of the solid–liquid transition of highly concentrated suspensions in oscillatory amplitude sweeps
Authors: Heymann Lutz , Peukert Sigrid , Aksel Nuri
Published: July 2002

Suspensions of quasimonodisperse polymethylmethacrylate spheres with mean diameters of 4.7 and 3.1 μm, dispersed in a low-molecular-weight polydimethylsiloxane, were characterized using oscillatory shear amplitude sweeps. Thereby, the solid volume concentration was varied. The influence of the sample preparation, the mode of the experiment (controlled shear rate, controlled shear stress), and the parameters of the amplitude sweep such as logarithmic ramp time, measurement time, and frequency were investigated. The logarithmic ramp and the measurement time were found to be the substantial factors which especially influence the experimental results at low shear stress amplitudes. The frequency has an effect only at higher shear stress amplitudes where the material behaves linearly again. All suspensions showed a Hookean solid behavior at low shear stress amplitudes and a Newtonian fluid behavior at high shear stress amplitudes. In the transition range between the Hookean and the Newtonian behavior the analysis of the primary shear strain-time signal showed that the nonlinear effects were coupled with the occurrence of higher odd harmonics.
Viscoelastic material functions of noncolloidal suspensions with spherical particles
Authors: Aral Birnur K. , Kalyon Dilhan M.
Published: July 2002

We have characterized various steady and time-dependent material functions of suspensions of a non-Newtonian binder, poly(dimethyl siloxane), incorporated with 10%–60% by volume of hollow and spherical glass beads. The material functions included storage and the loss moduli, shear stress and first normal stress difference growth and relaxation, relaxation modulus upon step strain and creep and recovery behavior. Both constant shear stress and shear rate experiments were carried out using multiple rheometers over a broad temperature range (−35 to 40 °C) while following sample fracture and wall slip effects. With increasing volume fraction, φ, of the noncolloidal particles, the strain range, over which linear viscoelastic behavior is observed, became narrower and the relaxation time of the suspension increased. Increasing solid content gave rise to the development of the yield stress and the dependence of large amplitude oscillatory shear properties on time and deformation history. The yield stress values increased with φ, but were not sensitive to temperature. For φ⩾0.3 the first normal stress difference values reached reproducible and steady negative values (with tensile force positive). Larger negative values of the first normal stress difference were observed with increasing deformation rate and solid concentration. The manifestations of the material functions resulting from the incorporation of the solids into the non-Newtonian binder included the suppression of the extrudate swell and the dipping of the free surface in the Weissenberg experiment.
Deliberate Self-injury in Children and Associations With Negative Adjustment
Authors: Willoughby Teena , Heffer Taylor , Borg Meghan E.
Published: July 2022

This study examines patterns between known childhood and adolescence self-injury behavior and longitudinal patterns with negative adjustment.
Repurposing open‐source data from weather radars to reduce the costs of aerial waterbird surveys
Authors: Rogers Rebecca M. , Buler Jeffrey , Clancy Timothy , Campbell Hamish
Published: July 2022

Aerial counts are the primary means of monitoring waterbird populations. A valid population assessment requires a significant proportion of the population to be surveyed. For broad‐ranging species, this requires costly reconnaissance flights and surveys over large areas of potential habitat.

Here, we assess whether free, autonomously collected weather radar reflectivity data can identify waterbird aggregations over broad areas of potential habitat, thereby providing a low‐cost means of directing the timing and location of aerial survey counts.

Our study was undertaken over a large flood plain known to be a key seasonal nesting area of the Magpie Goose (Anseranas semipalmata). A standardized aerial survey technique was employed, firstly using reconnaissance flights to determine when the birds were nesting and then 400‐m wide transects 3 km apart over approximately 1100 km, visually counting the geese. Radar reflectivity data from an operational weather radar in Darwin, Australia, 2 weeks prior to and during the aerial survey, were processed to link averaged radar reflectivity to terrestrial habitat at a spatial polar resolution of 250 m × 0.5°. A binary classification approach evaluated the accuracy, precision, sensitivity and specificity of reflectivity data in identifying areas where the aerial surveys recorded geese.

Aerial surveys of Magpie Geese are most effective when the geese are nesting, which is usually identified by reconnaissance flights. Here, we show nesting correlated with a decline in radar reflectivity and a concentration of hotspots. By achieving reasonable accuracy and precision (77% and 67%, respectively), the weather radar reflectivity identified high aggregations of Magpie Geese and demonstrated high efficacy when identifying areas where Magpie Geese did not occur (specificity, 94%).

We conclude that using weather radar data to guide aerial survey timing would reduce reconnaissance flight needs, and enable aerial surveys to focus on areas with a large proportion of the target waterbird population.
Tissue Engineering Cartilage with Deep Zone Cytoarchitecture by High‐Resolution Acoustic Cell Patterning
Authors: Armstrong James P. K. , Pchelintseva Ekaterina , Treumuth Sirli , Campanella Cristiana , Meinert Christoph , Klein Travis J. , Hutmacher Dietmar W. , Drinkwater Bruce W. , Stevens Molly M.
Published: July 2022

The ultimate objective of tissue engineering is to fabricate artificial living constructs with a structural organization and function that faithfully resembles their native tissue counterparts. For example, the deep zone of articular cartilage possesses a distinctive anisotropic architecture with chondrocytes organized in aligned arrays ≈1–2 cells wide, features that are oriented parallel to surrounding extracellular matrix fibers and orthogonal to the underlying subchondral bone. Although there are major advances in fabricating custom tissue architectures, it remains a significant technical challenge to precisely recreate such fine cellular features in vitro. Here, it is shown that ultrasound standing waves can be used to remotely organize living chondrocytes into high‐resolution anisotropic arrays, distributed throughout the full volume of agarose hydrogels. It is demonstrated that this cytoarchitecture is maintained throughout a five‐week course of in vitro tissue engineering, producing hyaline cartilage with cellular and extracellular matrix organization analogous to the deep zone of native articular cartilage. It is anticipated that this acoustic cell patterning method will provide unprecedented opportunities to interrogate in vitro the contribution of chondrocyte organization to the development of aligned extracellular matrix fibers, and ultimately, the design of new mechanically anisotropic tissue grafts for articular cartilage regeneration.