bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of retinal waves and synaptic normalization in retinogeniculate development
Authors: Eglen Stephen J.
Published: July 2002

The prenatal development of the cat retinogeniculate pathway is thought to involve activity–dependent mechanisms driven by spontaneous waves of retinal activity. The role of these waves upon the segregation of the dorsal lateral geniculate nucleus (LGN) into two eye–specific layers and the development of retinotopic mappings have previously been investigated in a computer model. Using this model, we examine three aspects of retinogeniculate development. First, the mapping of visual space across the whole network into projection columns is shown to be similar to the mapping found in the cat. Second, the simplicity of the model allows us to explore how different forms of synaptic normalization affect development. In comparison to most previous models of ocular dominance, we find that subtractive postsynaptic normalization is redundant and divisive presynaptic normalization is sufficient for normal development. Third, the model predicts that the more often one eye generates waves relative to the other eye, the more LGN units will monocularly respond to the more active eye. In the limit when one eye does not generate any waves, that eye totally disconnects from the LGN allowing the non–deprived eye to innervate all of the LGN. Thus, as well as accounting for normal retinogeniculate development, the model also predicts development under abnormal conditions which can be experimentally tested.
B-chromosome evolution
Authors: Camacho Juan Pedro M. , Sharbel Timothy F. , Beukeboom Leo W.
Published: July 2002

B chromosomes are extra chromosomes to the standard complement that occur in many organisms. They can originate in a number of ways including derivation from autosomes and sex chromosomes in intraand interspecies crosses. Their subsequent molecular evolution resembles that of univalent sex chromosomes, which involves gene silencing, heterochromatinization and the accumulation of repetitive DNA and transposons. B-chromosome frequencies in populations result from a balance between their transmission rates and their effects on host fitness. Their long-term evolution is considered to be the outcome of selection on the host genome to eliminate B chromosomes or suppress their effects and on the B chromosome's ability to escape through the generation of new variants. Because B chromosomes interact with the standard chromosomes, they can play an important role in genome evolution and may be useful for studying molecular evolutionary processes.
The labile brain. II. Transients, complexity and selection
Authors: Friston Karl J.
Published: July 2002

The successive expression of neuronal transients is related to dynamic correlations and, as shown in this paper, to dynamic instability. Dynamic instability is a form of complexity, typical of neuronal systems, which may be crucial for adaptive brain function from two perspectives. The first is from the point of view of neuronal selection and self–organizing systems: if selective mechanisms underpin the emergence of adaptive neuronal responses then dynamic instability is, itself, necessarily adaptive. This is because dynamic instability is the source of diversity on which selection acts and is therefore subject to selective pressure. In short, the emergence of order, through selection, depends almost paradoxically on the instabilities that characterize the diversity of brain dynamics. The second perspective is provided by information theory.
Comparative Analysis of Chloroplast Genomes: Functional Annotation, Genome-Based Phylogeny, and Deduced Evolutionary Patterns
Authors: Rivas Javier De Las , Lozano Juan Jose , Ortiz Angel R.
Published: July 2002

All protein sequences from 19 complete chloroplast genomes (cpDNA) have been studied using a new computational method able to analyze functional correlations among series of protein sequences contained in complete proteomes. First, all open reading frames (ORFs) from the cpDNAs, comprising a total of 2266 protein sequences, were compared against the 3168 proteins from Synechocystis PCC6803 complete genome to find functionally related orthologous proteins. Additionally, all cpDNA genomes were pairwise compared to find orthologous groups not present in cyanobacteria. Annotations in the cluster of othologous proteins database and CyanoBase were used as reference for the functional assignments. Following this protocol, new functional assignments were made for ORFs of unknown function and forycfs (hypothetical chloroplast frames), which still lack a functional assignment. Using this information, a matrix of functional relationships was derived from profiles of the presence and/or absence of orthologous proteins; the matrix included 1837 proteins in 277 orthologous clusters. A factor analysis study of this matrix, followed by cluster analysis, allowed us to obtain accurate phylogenetic reconstructions and the detection of genes probably involved in speciation as phylogenetic correlates. Finally, by grouping common evolutionary patterns, we show that it is possible to determine functionally linked protein networks. This has allowed us to suggest putative associations for some unknown ORFs.
Control Genes and Variability: Absence of Ubiquitous Reference Transcripts in Diverse Mammalian Expression Studies
Authors: Lee Peter D. , Sladek Robert , Greenwood Celia M.T. , Hudson Thomas J.
Published: July 2002

Control genes, commonly defined as genes that are ubiquitously expressed at stable levels in different biological contexts, have been used to standardize quantitative expression studies for more than 25 yr. We analyzed a group of large mammalian microarray datasets including the NCI60 cancer cell line panel, a leukemia tumor panel, and a phorbol ester induction time course as well as human and mouse tissue panels. Twelve housekeeping genes commonly used as controls in classical expression studies (including GAPD, ACTB, B2M, TUBA, G6PD, LDHA, and HPRT) show considerable variability of expression both within and across microarray datasets. Although we can identify genes with lower variability within individual datasets by heuristic filtering, such genes invariably show different expression levels when compared across other microarray datasets. We confirm these results with an analysis of variance in a controlled mouse dataset, showing the extent of variability in gene expression across tissues. The results show the problems inherent in the classical use of control genes in estimating gene expression levels in different mammalian cell contexts, and highlight the importance of controlled study design in the construction of microarray experiments.

[Supplemental material available online athttp://genome.mcgill.ca/∼pdlee/control_genes and andhttp://www.genome.org.]
N‐terminal extension changes the folding mechanism of the FK506‐binding protein
Authors: Korepanova Alla , Douglas Chanel , Leyngold Ilya , Logan Timothy M.
Published: July 2002

Many of the protein fusion systems used to enhance the yield of recombinant proteins result in the addition of a small number of amino acid residues onto the desired protein. Here, we investigate the effect of short (three amino acid) N‐terminal extensions on the equilibrium denaturation and kinetic folding and unfolding reactions of the FK506‐binding protein (FKBP) and compare the results obtained with data collected on an FKBP variant lacking this extension. Isothermal equilibrium denaturation experiments demonstrated that the N‐terminal extension had a slight destabilizing effect. NMR investigations showed that the N‐terminal extension slightly perturbed the protein structure near the site of the extension, with lesser effects being propagated into the single α‐helix of FKBP. These structural perturbations probably account for the differential stability. In contrast to the relatively minor equilibrium effects, the N‐terminal extension generated a kinetic‐folding intermediate that is not observed in the shorter construct. Kinetic experiments performed on a construct with a different amino acid sequence in the extension showed that the length and the sequence of the extension both contribute to the observed equilibrium and kinetic effects. These results point to an important role for the N terminus in the folding of FKBP and suggest that a biological consequence of N‐terminal methionine removal observed in many eukaryotic and prokaryotic proteins is to increase the folding efficiency of the polypeptide chain.
Shielding for neutron scattered dose to the fetus in patients treated with 18 MV x‐ray beams
Authors: Roy S. C. , Sandison G. A.
Published: July 2002

Neutrons are associated with therapeutic high energy x‐ray beams as a contaminant that contributes significant unwanted dose to the patient. Measurement of both photon and neutron scattered dose at the position of a fetus from chest irradiation by a large field 18 MV x‐ray beam was performed using an ionization chamber and superheated drop detector, respectively. Shielding construction to reduce this scattered dose was investigated using both lead sheet and borated polyethylene slabs. A 7.35 cm lead shield reduced the scattered photon dose by 50% and the scattered neutron dose by 40%. Adding 10 cm of 5% borated polyethylene to this lead shield reduced the scattered neutron dose by a factor of 7.5 from the unshielded value. When the 5% borated polyethylene was replaced by the same thickness of 30% borated polyethylene there was no significant change in the reduction of neutron scatter dose. The most efficient shield studied reduced the neutron scatter dose by a factor of 10. The results indicate that most of the scattered neutrons present at the position of the fetus produced by an 18 MV x‐ray beam are of low energy and in the thermal to 0.57 MeV range since lead is almost transparent to neutrons with energies lower than 0.57 MeV. This article constitutes the first report of an effective shield to reduce neutron dose at the fetus when treating a pregnant woman with a high energy x‐ray beam.
Application of the mutual information criterion for feature selection in computer‐aided diagnosis
Authors: Tourassi Georgia D. , Frederick Erik D. , Markey Mia K. , Floyd Carey E.
Published: July 2002

The purpose of this study was to investigate an information theoretic approach to feature selection for computer‐aided diagnosis (CAD). The approach is based on the mutual information (MI) concept. MI measures the general dependence of random variables without making any assumptions about the nature of their underlying relationships. Consequently, MI can potentially offer some advantages over feature selection techniques that focus only on the linear relationships of variables. This study was based on a database of statistical texture features extracted from perfusion lung scans. The ultimate goal was to select the optimal subset of features for the computer‐aided diagnosis of acute pulmonary embolism (PE). Initially, the study addressed issues regarding the approximation of MI in a limited dataset as it is often the case in CAD applications. The MI selected features were compared to those features selected using stepwise linear discriminant analysis and genetic algorithms for the same PE database. Linear and nonlinear decision models were implemented to merge the selected features into a final diagnosis. Results showed that the MI is an effective feature selection criterion for nonlinear CAD models overcoming some of the well‐known limitations and computational complexities of other popular feature selection techniques in the field.
Gyroscope precession and general relativity
Authors: Holstein Barry R.
Published: July 2002

Precession of a gyroscope in the presence of a gravitational field is of considerable interest, on account of the soon to be launched satellite test and because of its connection to Mach’s principle. Nevertheless, this topic is not generally covered in the curriculum because of the mathematical sophistication required. We examine some of the simple physics involved and argue that by examining simple graviton-elementary particle couplings one can easily understand this phenomenon.
Complex tactile waveform discrimination
Authors: Bensmaı̈a Sliman J. , Hollins Mark
Published: July 2002

Complex vibrotactile waveforms consisting of two superimposed sinusoids at varying phases were presented to the fingertip, and observers made “same-different” judgments. It was found that the low-frequency (10 Hz+30 Hz) waveforms were discriminable from one another while discrimination of the high-frequency (100 Hz+300 Hz) vibrations was poor. High-frequency adaptation did not impair discrimination of the low-frequency waveforms, suggesting that the RA channel mediated discrimination. Low-frequency adaptation impaired discrimination of the high-frequency stimuli, suggesting that the RA channel likewise mediated the modest level of performance observed in the absence of an adapting stimulus. The results indicate that this channel encodes complex waveforms temporally. A simple model for low-frequency waveform discrimination is proposed. The results obtained with the high-frequency complex waveforms are compatible with the hypothesis that the PC channel integrates stimulus energy over time.
Discrimination of non-native consonant contrasts varying in perceptual assimilation to the listener’s native phonological system
Authors: Best Catherine T. , McRoberts Gerald W. , Goodell Elizabeth
Published: July 2002

Classic non-native speech perception findings suggested that adults have difficulty discriminating segmental distinctions that are not employed contrastively in their own language. However, recent reports indicate a gradient of performance across non-native contrasts, ranging from near-chance to near-ceiling. Current theoretical models argue that such variations reflect systematic effects of experience with phonetic properties of native speech. The present research addressed predictions from Best’s perceptual assimilation model (PAM), which incorporates both contrastive phonological and noncontrastive phonetic influences from the native language in its predictions about discrimination levels for diverse types of non-native contrasts. We evaluated the PAM hypotheses that discrimination of a non-native contrast should be near-ceiling if perceived as phonologically equivalent to a native contrast, lower though still quite good if perceived as a phonetic distinction between good versus poor exemplars of a single native consonant, and much lower if both non-native segments are phonetically equivalent in goodness of fit to a single native consonant. Two experiments assessed native English speakers’ perception of Zulu and Tigrinya contrasts expected to fit those criteria. Findings supported the PAM predictions, and provided evidence for some perceptual differentiation of phonological, phonetic, and nonlinguistic information in perception of non-native speech. Theoretical implications for non-native speech perception are discussed, and suggestions are made for further research.
Sensitivity to brief changes of interaural time and interaural intensity
Authors: Bernstein Leslie R. , Trahiotis Constantine , Akeroyd Michael A. , Hartung Klaus
Published: July 2002

The purpose of this study was to measure listeners’ abilities to detect brief changes in interaural temporal disparities (ITDs) or interaural intensitive disparities (IIDs) conveyed by bursts of noise (probes) temporally and symmetrically flanked by segments of diotic or uncorrelated noise. Thresholds were measured using a four-interval, two-alternative, forced-choice adaptive task and the total duration of the bursts of noise was either 20, 40, or 100 ms. Probes were temporally centered within each burst and the durations of the probes ranged from 2 to 100 ms, depending upon the duration of the (longer) total burst of noise within which they were embedded. The results indicate that, for a given total duration of noise, there is a rapid decrease in threshold ITD or threshold IID as the duration of the probe is increased so that it occupies a larger portion of the total burst of noise. Mathematical analyses revealed that both threshold ITDs and threshold IIDs could be well accounted for by assuming that the listener processes both types of binaural cues via a single, symmetric, double-exponential temporal window. Interestingly, the shapes of the temporal windows that fit the data obtained from the human listeners resemble the shapes of the temporal windows derived by Wagner [H. Wagner, J. Comp. Physiol. A 169, 281–289 (1991)], who studied the barn owl. The time constants and relative weightings yielded temporal window functions that heavily emphasize information occurring within the very temporal center of the window. This temporal window function was found to be generalizable in the sense that it also accounts for classic data reported by Grantham and Wightman [D. W. Grantham and F. L. Wightman, J. Acoust. Soc. Am. 63, 511–523 (1978)] concerning sensitivity to dynamically changing interaural disparities.
A new transducer holder mechanism for pipe inspection
Authors: Guo Dongshan , Kundu Tribikram
Published: July 2002

A new transducer holder mechanism has been designed and fabricated for pipe inspection by cylindrical guided waves. Commercially available ultrasonic transducers have been used to generate compressional ultrasonic waves in the coupling medium. Those waves are converted to cylindrical guided waves in the pipe by the new coupling mechanism. A number of advanced coupling mechanisms developed recently for large plate and pipe inspection require the presence of a coupling fluid between the ultrasonic transducer and the pipe or plate specimen. These mechanisms can be used for inspecting horizontal pipes and plates. The new coupling mechanism presented in this article uses solid material as the coupler and can be used equally well for inspecting horizontal as well as inclined or vertical pipes. The new coupling mechanism has been designed to generate efficiently different Lamb modes in the pipe. The new design has been used to inspect different kinds of anomalies in copper and aluminum pipes. The preliminary results show that a number of Lamb modes, when generated properly by the new coupling mechanism, are very sensitive to the pipe defects. These experimental results along with the new design of the coupling mechanism are presented in this article.
Crack characterization using guided circumferential waves
Authors: Valle Christine , Niethammer Marc , Qu Jianmin , Jacobs Laurence J.
Published: July 2002

This paper examines the propagation of guided circumferential waves in a hollow isotropic cylinder that contains a crack, with the goal of using these guided waves to both locate and size the crack. The crack is sized using a modified Auld’s formula, which relates the crack’s length to a reflected energy coefficient. The crack is then located by operating on the backscattered signal with a time-frequency digital signal processing (DSP) technique, and then comparing these results to those obtained if the cylinder is perfect. The guided circumferential waves are generated with a commercial finite element method (FEM) code. One objective of this work is to demonstrate the effectiveness of using sophisticated DSP techniques to describe the effect of scattering on dispersive waves, showing it is possible to characterize cracks systematically and accurately by quantifying this scattering effect. The results show that the need for high frequency signals to detect small cracks is significantly decreased by using these techniques.
Locating far-field impulsive sound sources in air by triangulation
Authors: Ferguson Brian G. , Criswick Lionel G. , Lo Kam W.
Published: July 2002

The firing of a gun generates an acoustic impulse that propagates radially outwards from the source. Acoustic gun-ranging systems estimate the source position by measuring the relative time of arrival of the impulse at a number of spatially distributed acoustic sensors. The sound-ranging problem is revisited here using improved time-delay estimation methods to refine the source position estimates. The time difference for the acoustic wavefront to arrive at two spatially separated sensors is estimated by cross correlating the digitized outputs of the sensors. The time-delay estimate is used to calculate the source bearing, and the source position is cross fixed by triangulation using the bearings from two widely separated receiving nodes. The variability in the bearing and position estimates is quantified by processing acoustic sensor data recorded during field experiments for a variety of impulsive sound sources: artillery guns, mortars, and grenades. Imperfect knowledge of the effective speed of sound travel results in bias errors in the source bearing estimates, which are found to depend on the orientation of the sensor pair axis with respect to the source direction. Combining the time-delay estimates from two orthogonal pairs of sensors reduces these bias errors.
Quantitative assessment of second language learners’ fluency: Comparisons between read and spontaneous speech
Authors: Cucchiarini Catia , Strik Helmer , Boves Lou
Published: July 2002

This paper describes two experiments aimed at exploring the relationship between objective properties of speech and perceived fluency in read and spontaneous speech. The aim is to determine whether such quantitative measures can be used to develop objective fluency tests. Fragments of read speech (Experiment 1) of 60 non-native speakers of Dutch and of spontaneous speech (Experiment 2) of another group of 57 non-native speakers of Dutch were scored for fluency by human raters and were analyzed by means of a continuous speech recognizer to calculate a number of objective measures of speech quality known to be related to perceived fluency. The results show that the objective measures investigated in this study can be employed to predict fluency ratings, but the predictive power of such measures is stronger for read speech than for spontaneous speech. Moreover, the adequacy of the variables to be employed appears to be dependent on the specific type of speech material investigated and the specific task performed by the speaker.
The detection of breast microcalcifications with medical ultrasound
Authors: Anderson Martin E. , Soo Mary S. , Bentley Rex C. , Trahey Gregg E.
Published: July 2002

Microcalcifications are small crystals of calcium apatites which form in human tissue through a number of mechanisms. The size, morphology, and distribution of microcalcifications are important indicators in the mammographic screening for and diagnosis of various carcinomas in the breast. Although x-ray mammography is currently the only accepted method for detecting microcalcifications, its efficacy in this regard can be reduced in the presence of dense parenchyma. Current ultrasound scanners do not reliably detect microcalcifications in the size range of clinical interest. The results of theoretical, simulation, and experimental studies focused on the improvement of the ultrasonic visualization of microcalcifications are presented. Methods for estimating the changes in microcalcification detection performance which result from changes in aperture geometry or the presence of an aberrator are presented. An analysis of the relative efficacy of spatial compounding and synthetic receive aperture geometries in the detection of microcalcifications is described. The impact of log compression of the detected image on visualization is discussed. Registered high resolution ultrasound and digital spot mammography images of microcalcifications in excised breast carcinoma tissue and results from the imaging of suspected microcalcifications in vivo are presented.
Vibratory power flow through a nonlinear path into a resonant receiver
Authors: Royston T. J. , Singh R.
Published: July 2002

Vibratory power flow through a nonlinear path into a resonant receiver is considered via a specific vibration isolation example case, the automotive hydraulic engine mount. System equations for the source—nonlinear path—receiver system are developed based on prior experimental and analytical studies. For periodic excitation, an efficient solution method is formulated for the calculation of the steady-state stable response using a multi-term harmonic balance approach with condensation and continuation. In this computational study it is shown that, while modeling the isolation path with a “softened” nonlinear expression may only moderately alter the predicted system behavior at the excitation harmonic, it can significantly alter it at higher harmonics. Computational studies of multi-harmonic motion and power transmission show that audible structure-borne noise may be generated from subaudio frequency excitations due to path nonlinearities. It is also observed that support base (receiver) resonances can significantly affect the overall dynamic behavior. For instance, with a multi-degree-of-freedom base model, significant levels of vibratory energy at higher harmonics of the excitation are transmitted through the path, especially when these harmonics coincide with the natural frequencies of the receiver.
Stimulus variability and spoken word recognition. II. The effects of age and hearing impairment
Authors: Sommers Mitchell S.
Published: July 2002

Three experiments were conducted to investigate the effects of variations in talker characteristics, speaking rate, and overall amplitude on perceptual identification in normal-hearing young (NHY), normal-hearing elderly (NHE), and hearing-impaired elderly (HIE) listeners. The three dimensions were selected because variations in voice characteristics and speaking rate affect features of speech signals that are important for word recognition while overall amplitude changes do not alter stimulus parameters that have direct effects on phonetic identification. Thus, the studies were designed to examine how variations in both phonetically relevant and irrelevant stimulus dimensions affect speech processing in a number of different populations. Age differences, as indicated by greater effects of variability for the NHE compared with the NHY listeners, were observed for mixed-talker and mixed-amplitude word lists. Effects of age-related hearing impairment, as indicated by reduced scores for the HIE compared with the NHE group, were observed for variations in speaking rate and talker characteristics. Considered together, the findings suggest that age-related changes in perceptual normalization and selective attention may contribute to the reduced speech understanding that is often reported for older adults.
Changes in sound pressure and fundamental frequency contours following changes in hearing status
Authors: Lane Harlan , Wozniak Jane , Matthies Melanie , Svirsky Mario , Perkell Joseph , O’Connell Michael , Manzella Joyce
Published: July 2002

Sound-pressure level (SPL) and fundamental frequency (F0) contours were obtained from four postlingually deafened adults who received cochlear implants and from a subject with Neurofibromatosis-2 (NF2) who had her hearing severely reduced following surgery to remove an auditory-nerve tumor and to implant an auditory brainstem implant. SPL and F0 contours for each phrase in passages read before and after changes in hearing were averaged over repeated readings and then normalized with respect to the highest SPL or F0 value in the contour. The regularity of each average contour was measured by calculating differences between successive syllable means and averaging the absolute values of these differences. With auditory feedback made available, the cochlear implant user with the least contour variation preimplant showed no change but all of the remaining speakers produced less variable F0 contours and three also produced less variable SPL contours. In complementary fashion, when the NF2 speaker had her auditory feedback severely reduced, she produced more variable F0 and SPL contours. The results are interpreted as supporting a dual-process theory of the role of auditory feedback in speech production, according to which one role of self-hearing is to monitor transmission conditions, leading the speaker to make changes in speech postures aimed at maintaining intelligibility.
Inertial cavitation and associated acoustic emission produced during electrohydraulic shock wave lithotripsy
Authors: Zhong Pei , Cioanta Iulian , Cocks Franklin H. , Preminger Glenn M.
Published: July 2002

The inertial cavitation and associated acoustic emission generated during electrohydraulic shock wave lithotripsy were studied using high-speed photography and acoustic pressure measurements. The dynamics of cavitation bubble clusters, induced in vitro by an experimental laboratory lithotripter, were recorded using a high-speed rotating drum camera at 20 000 frames/s. The acoustic emission, generated by the rapid initial expansion and subsequent violent collapse of the cavitation bubbles, was measured simultaneously using a 1-MHz focused hydrophone, The expansion duration of the cavitation bubble cluster was found to correlate closely with the time delay between the first two groups of pressure spikes in the acoustic emission signal. This correlation provides an essential physical basis to assess the inertial cavitation produced by a clinical Dornier HM-3 shock wave lithotripter, both in water and in renal parenchyma of a swine model. In the clinical output voltage range (16–24 kV), the expansion duration of the primary cavitation bubble cluster generated by the HM-3 lithotripter in water increases from 158 to 254 μs, whereas the corresponding values in renal parenchyma are much smaller and remain almost unchanged (from 71 to 72 μs). In contrast, subsequent oscillation of the bubble following its primary collapse is significantly prolonged (from 158–235 μs in water to 1364–1373 μs in renal parenchyma). These distinctive differences between lithotripsy-induced inertial cavitation in vitro and that in vivo are presumably due to the constraining effect of renal tissue on bubble expansion.
Comparison of elastic constant determination in anisotropic materials from ultrasonic group and phase velocity data
Authors: Degtyar A. D. , Rokhlin S. I.
Published: July 2002

A comparative analysis of elastic constant determination from the angular dependence of group and phase velocity data in orthotropic and transversely isotropic materials is performed. A nonlinear least-squares optimization procedure is used for inversion. The method allows the use of group velocity data in a cuspidal region, where for a given ray direction there are more than three distinct wave modes propagating with different velocities. Exact analytical equations are derived relating group velocities to elastic constants for arbitrary planes in transversely isotropic materials. Approximate relations for nonsymmetry planes in orthotropic materials are obtained. The procedure is generalized for determination of elastic constants from group velocities measured in arbitrary incident planes in orthotropic materials.
The sound field of an arbitrarily oriented quadrupole near ground surfaces
Authors: Li Kai Ming , Taherzadeh Shahram
Published: July 2002

The sound field due to an arbitrarily oriented quadrupole above an impedance ground is investigated. To simplify the analysis, the atmospheric and topographical effects on sound propagation are ignored. Two different methods are developed to calculate the sound field. First, an asymptotic method is used to derive a close-form analytic solution. Second, a fast field program (quad-FFP) has been developed for numerical computations of the sound field. It is found that numerical results from both methods agree well. In a recent development, it has been shown that the analytic solution of the sound field due to an arbitrarily oriented dipole can be written in the classical form similar to that due to a monopole. However, it is not possible to write the solution in such a form for the case of an arbitrarily oriented quadrupole, but rather the total sound pressure is augmented by two extra terms which are particularly important at a small separation between the source and receiver.
Performance over time of adult patients using the Ineraid or Nucleus cochlear implant
Authors: Tyler Richard S. , Parkinson Aaron J. , Woodworth George G. , Lowder Mary W. , Gantz Bruce J.
Published: July 2002

This study examined the average and individual performance over time of 49 adult cochlear implant subjects. Subjects were randomly assigned to receive either the Ineraid cochlear implant, with analog processing, or the Nucleus cochlear implant, with feature-extraction processing. All subjects had postlingual profound bilateral sensorineural hearing loss and received no significant benefit from hearing aids before implantation. Group data were examined in two ways. First, only subjects who had complete data over the test period were examined. Second, an analysis of all available data was carried out by mixed linear-model analysis. In this analysis, to account for missed follow-ups at the planned intervals, data consisting of the observations closest in time to the planned test times were modeled by natural splines with knots at the planned follow-up times. Contrasts between all pairs of planned follow-up times for each device were tested, as were contrasts between devices at each planned follow-up time. Results indicated little difference between the performance of the Ineraid and Nucleus subjects in their level of performance or their rate of learning. Postimplantation performance was typically superior to preimplantation performance within 9 months, and continued to improve up to 18–30 months depending on the speech perception measure. In some subjects, improvements in speech perception measures were observed up to four or five years postimplantation. There was also evidence that three subjects had a decrement in overall speech perception performance, although their postimplantation scores were always higher than their preimplantation scores. In at least one subject this was likely a result of age-related cognition decrements.
Do weak syllables count for newborns?
Authors: van Ooijen Brit , Bertoncini Josiane , Sansavini Alessandra , Mehler Jacques
Published: July 2002

Does the newborn’s well-known sensitivity to human speech include awareness of the distinction between strong and weak syllables, as has been shown for older infants and adults? The non-nutritive high-amplitude sucking paradigm was used to investigate whether weak syllables play a role in neonate perceptual representation. Two-day-old French infants were tested on their capacity to discriminate phonetically highly varied words containing syllables with various strong vowels versus the weak, reduced vowel schwa in natural, isolated English words. Twenty infants heard lists of weak–strong and lists of strong words (e.g., belief, control, etc. versus nose, dream, etc.) and 20 heard lists of weak–strong and strong–strong words (e.g., belief, control, etc. versus volume, rhubarb, etc.). The results show that weak–strong words were reliably distinguished from strong words, but not from strong–strong words. Taken together, the findings indicate that a weak, reduced vowel is equivalent to a strong, full vowel to the extent that both count as syllabic nuclei. Moreover, this global equivalence in terms of number of syllabic constituents apparently overrules the more local acoustic difference between strong and weak vowels. The role of syllabic/vocalic information in neonate representation is discussed.
Contact scanning Lamb wave tomography
Authors: Hinders Mark , Malyarenko Eugene , McKeon James
Published: July 2002

Lamb waves are guided ultrasonic waves capable of propagating relatively long distances in platelike structures such as airframe skins, storage tanks, and pressure vessels. Their propagation depends on frequency thickness and material properties, and, because structural flaws present changes in effective thickness and/or material properties, Lamb waves can be employed to assess the integrity of these structures. For structures with large surface areas, a full integrity evaluation can be a time-consuming operation, but with Lamb wave techniques, this evaluation can be performed with waves propagating along one dimension of the inspection area as the probing transducers are moved in the perpendicular dimension. Such an approach yields information about the presence of flaws within the scanned area. Then, in order to quantitatively characterize the flaws, Lamb wave measurements can be made for a number of projections and an image of the flawed region can be reconstructed tomographically. Contact scanning Lamb wave tomography for metallic and composite structures with flaws is discussed as a practical technique for quantitative nondestructive evaluation.
The recognition of sentences in noise by normal-hearing listeners using simulations of cochlear-implant signal processors with 6–20 channels
Authors: Dorman Michael F. , Loizou Philipos C. , Fitzke Jeanette , Tu Zhemin
Published: July 2002

Sentences were processed through simulations of cochlear-implant signal processors with 6, 8, 12, 16, and 20 channels and were presented to normal-hearing listeners at +2 db S/N and at −2 db S/N. The signal-processing operations included bandpass filtering, rectification, and smoothing of the signal in each band, estimation of the rms energy of the signal in each band (computed every 4 ms), and generation of sinusoids with frequencies equal to the center frequencies of the bands and amplitudes equal to the rms levels in each band. The sinusoids were summed and presented to listeners for identification. At issue was the number of channels necessary to reach maximum performance on tests of sentence understanding. At +2 dB S/N, the performance maximum was reached with 12 channels of stimulation. At −2 dB S/N, the performance maximum was reached with 20 channels of stimulation. These results, in combination with the outcome that in quiet, asymptotic performance is reached with five channels of stimulation, demonstrate that more channels are needed in noise than in quiet to reach a high level of sentence understanding and that, as the S/N becomes poorer, more channels are needed to achieve a given level of performance.
Internal deformation of a uniform elastic solid by acoustic radiation force
Authors: Walker William F.
Published: July 2002

Tissue elasticity estimation is a growing area of ultrasound research. One proposed approach would apply acoustic radiation force to displace tissue and use ultrasonic motion tracking techniques to measure the resultant displacement. Such a technique might allow noninvasive imaging of tissue elastic properties. The potential of this method will be limited by the magnitude of displacements which can be generated at reasonable acoustic intensity levels. This paper presents methods for estimating the internal displacements induced in an elastic solid by acoustic radiation force. These methods predict displacements on the order of 400 μm in the human vitreous body, 0.008 μm in human breast, and 0.020 μm in human liver at an acoustic intensity of 1.0 W/cm2 (in water) and an operating frequency of 10 MHz. While the displacement generated in the vitreous should be readily detectable using ultrasonic methods, the displacements generated in the breast and liver will be much more difficult to detect. Methods are also developed for predicting the time dependent temperature increases associated with attenuated acoustic fields in the absence of perfusion. These results indicate promise for radiation force imaging in the vitreous, but potential difficulties in applying these techniques in other parts of the body.
Acoustic study of texture in polycrystalline brass
Authors: Foster K. , Fairburn S. L. , Leisure R. G. , Kim S. , Balzar D. , Alers G. , Ledbetter H.
Published: July 2002

Resonant ultrasound spectroscopy was used to measure the orthorhombic elastic constants of rolled, polycrystalline plates of Cu, Cu–5% Zn, and Cu–15% Zn. The experimental results were fit to theoretical expressions to determine the orientation-distribution coefficients W400, W420, and W440. These coefficients are related to texture (the nonrandom orientation of crystallites). The experimental results were in good agreement with theory for the Cu and the Cu–15% Zn materials. The agreement was not as good for the more anisotropic Cu–5% Zn material, especially for the in-plane compressional constants C11 and C22. The ultrasonically derived W’s were compared to those obtained from neutron measurements for the Cu–Zn alloys. Pole plots based on the two types of measurements, using W400, W420, and W440, were in excellent agreement for the 15% Zn material, and in qualitative agreement for the 5% Zn material. The results support the idea that acoustic methods can be used to measure the low-order W’s in polycrystalline materials.
Time-reversal mirrors and rough surfaces: Theory
Authors: Rose James H. , Bilgen Mehmet , Roux Philippe , Fink Mathias
Published: July 2002

A systematic study is presented of the sensitivity of acoustic time-reversal mirrors (TRMs) to errors. One result is a novel acoustic method for determining the root-mean-square, rms, height and the surface-height autocorrelation function of rough surfaces. In particular, the effects of misregistering a TRM are studied with respect to a rough surface—the reflected wavefield is recorded in one place, time reversed, and then rebroadcast in a second place. This displacement causes the signal to depend importantly on the surface’s rms height and autocorrelation function. Simple closed-form formulas are presented for determining the rms height and the normalized surface-height autocorrelation function for both deterministic and randomly rough surfaces. Also presented is a numerical study that illustrates the statistical uncertainty in and the spatial resolution of the proposed method. An accompanying experimental article tests the proposed method with measurements made on a number of different rough surfaces.
Evidence for the distortion product frequency place as a source of distortion product otoacoustic emission (DPOAE) fine structure in humans. I. Fine structure and higher-order DPOAE as a function of the frequency ratio f2/f1
Authors: Mauermann Manfred , Uppenkamp Stefan , van Hengel Peter W. J. , Kollmeier Birger
Published: July 2002

Critical experiments were performed in order to validate the two-source hypothesis of distortion product otoacoustic emissions (DPOAE) generation. Measurements of the spectral fine structure of DPOAE in response to stimulation with two sinusoids have been performed with normal-hearing subjects. The dependence of fine-structure patterns on the frequency ratio f2/f1 was investigated by changing f1 or f2 only (fixed f2 or fixed f1 paradigm, respectively), and by changing both primaries at a fixed ratio and looking at different order DPOAE. When f2/f1 is varied in the fixed ratio paradigm, the patterns of 2 f1–f2 fine structure vary considerably more if plotted as a function of f2 than as a function of fDP. Different order distortion products located at the same characteristic place on the basilar membrane (BM) show similar patterns for both, the fixed-f2 and fDP paradigms. Fluctuations in DPOAE level up to 20 dB can be observed. In contrast, the results from a fixed-fDP paradigm do not show any fine structure but only an overall dependence of DP level on the frequency ratio, with a maximum for 2f1–f2 at f2/f1 close to 1.2. Similar stimulus configurations used in the experiments have also been used for computer simulations of DPOAE in a nonlinear and active model of the cochlea. Experimental results and model simulations give strong evidence for a two-source model of DPOAE generation: The first source is the initial nonlinear interaction of the primaries close to the f2 place. The second source is caused by coherent reflection from a re-emission site at the characteristic place of the distortion product frequency. The spectral fine structure of DPOAE observed in the ear canal reflects the interaction of both these sources.
The recognition of isolated words and words in sentences: Individual variability in the use of sentence context
Authors: Grant Ken W. , Seitz Philip F.
Published: July 2002

Estimates of the ability to make use of sentence context in 34 postlingually hearing-impaired (HI) individuals were obtained using formulas developed by Boothroyd and Nittrouer [Boothroyd and Nittrouer, J. Acoust. Soc. Am. 84, 101–114 (1988)] which relate scores for isolated words to words in meaningful sentences. Sentence materials were constructed by concatenating digitized productions of isolated words to ensure physical equivalence among the test items in the two conditions. Isolated words and words in sentences were tested at three levels of intelligibility (targeting 29%, 50%, and 79% correct). Thus, for each subject, three estimates of context ability, or k factors, were obtained. In addition, auditory, visual, and auditory–visual sentence recognition was evaluated using natural productions of sentence materials. Two main questions were addressed: (1) Is context ability constant for speech materials produced with different degrees of clarity? and (2) What are the relations between individual estimates of k and sentence recognition as a function of presentation modality? Results showed that estimates of k were not constant across different levels of intelligibility: k was greater for the more degraded condition relative to conditions of higher word intelligibility. Estimates of k also were influenced strongly by the test order of isolated words and words in sentences. That is, prior exposure to words in sentences improved later recognition of the same words when presented in isolation (and vice versa), even though the 1500 key words comprising the test materials were presented under degraded (filtered) conditions without feedback. The impact of this order effect was to reduce individual estimates of k for subjects exposed to sentence materials first and to increase estimates of k for subjects exposed to isolated words first. Finally, significant relationships were found between individual k scores and sentence recognition scores in all three presentation modalities, suggesting that k is a useful measure of individual differences in the ability to use sentence context.
The transmission of Lamb waves across adhesively bonded lap joints
Authors: Lowe M. J. S. , Challis R. E. , Chan C. W.
Published: July 2002

The transmission of Lamb waves across adhesively bonded lap joints is investigated using finite element analysis. The studies consider three modes for excitation and reception, s0, a0, and a1, applied to lap joints consisting of parallel aluminum sheets bonded with an epoxy adhesive. Transmission coefficient results for a two-dimensional range of bond thicknesses and bond overlap lengths are presented for all three modes. The transmission coefficients are calculated from the spectra of the received and transmitted signals using an approach which is insensitive to the presence of multimode signals and reverberated signals, and which approximates to a power transmission coefficient. Detailed analysis is then performed for one of the modes in order to investigate the nature of the mode conversion in the overlap region of the joint. It is found that the relative amplitudes of the different modes which propagate in the overlap region can be estimated reliably and simply from the properties of the incident wave mode. As well as demonstrating the physics of the mode conversion behavior, the study provides a basis for the selection of modes for nondestructive evaluation (NDE) of the bond region and for measuring the bond dimensions.