bluuebunny/crossref_metadata_2025 huggingface dataset:
Air entrapment in piezo-driven inkjet printheads
Authors: de Jong Jos , de Bruin Gerrit , Reinten Hans , van den Berg Marc , Wijshoff Herman , Versluis Michel , Lohse Detlef
Published: September 2006

The stability of inkjet printers is a major requirement for high-quality-printing. However, in piezo-driven inkjet printheads, air entrapment can lead to malfunctioning of the jet formation. The piezoactuator is employed to actively monitor the channel acoustics and to identify distortions at an early stage. Modifications of the response of the piezoactuator indicate entrapped air bubbles and these allow us to investigate them. When we employ the signal as a trigger for high-speed imaging, we can visualize the consequences of the entrained bubbles on the droplet formation. Two mechanisms are found to cause air entrapment: First, a distorted droplet formation caused by small particles, and, second, an accumulation of ink on the nozzle plate, which favors void formation once the meniscus is pulled back.
How far, how long: On the temporal scope of prosodic boundary effects
Authors: Byrd Dani , Krivokapić Jelena , Lee Sungbok
Published: September 2006

Acoustic lengthening at prosodic boundaries is well explored, and the articulatory bases for this lengthening are becoming better understood. However, the temporal scope of prosodic boundary effects has not been examined in the articulatory domain. The few acoustic studies examining the distribution of lengthening indicate that boundary effects extend from one to three syllables before the boundary, and that effects diminish as distance from the boundary increases. This diminishment is consistent with the π-gesture model of prosodic influence [Byrd and Saltzman, J. Phonetics 31, 149–180 (2003)]. The present experiment tests the preboundary and postboundary scope of articulatory lengthening at an intonational phrase boundary. Movement-tracking data are used to evaluate durations of consonant closing and opening movements, acceleration durations, and consonant spatial magnitude. Results indicate that prosodic boundary effects exist locally near the phrase boundary in both directions, diminishing in magnitude more remotely for those subjects who exhibit extended effects. Small postboundary effects that are compensatory in direction are also observed.
Detection and F discrimination of harmonic complex tones in the presence of competing tones or noise
Authors: Micheyl Christophe , Bernstein Joshua G. W. , Oxenham Andrew J.
Published: September 2006

Normal-hearing listeners’ ability to “hear out” the pitch of a target harmonic complex tone (HCT) was tested with simultaneous HCT or noise maskers, all bandpass-filtered into the same spectral region (1200–3600Hz). Target-to-masker ratios (TMRs) necessary to discriminate fixed fundamental-frequency (F0) differences were measured for target F0s between 100 and 400Hz. At high F0s (400Hz), asynchronous gating of masker and signal, presenting the masker in a different F0 range, and reducing the F0 rove of the masker, all resulted in improved performance. At the low F0s (100Hz), none of these manipulations improved performance significantly. The findings are generally consistent with the idea that the ability to segregate sounds based on cues such as F0 differences and onset/offset asynchronies can be strongly limited by peripheral harmonic resolvability. However, some cases were observed where perceptual segregation appeared possible, even when no peripherally resolved harmonics were present in the mixture of target and masker. A final experiment, comparing TMRs necessary for detection and F0 discrimination, showed that F0 discrimination of the target was possible with noise maskers at only a few decibels above detection threshold, whereas similar performance with HCT maskers was only possible 15–25dB above detection threshold.
Measurements and calculations on the simple up-down adaptive procedure for speech-in-noise tests
Authors: Smits Cas , Houtgast Tammo
Published: September 2006

The simple up-down adaptive procedure is a common method for measuring speech reception thresholds. It is used by the Dutch speech-in-noise telephone screening test [National Hearing test; Smits and Houtgast Ear Hear. 26, 89–95 (2005)]. The test uses digit triplets to measure the speech reception threshold in noise by telephone (SRTTn). About 66000 people took this test within four months of its introduction and details were stored of all individual measurements. Analyses of this large volume of data have revealed that the standard deviation of SRTTn estimates increases with hearing loss. This paper presents a calculation model which—using an intelligibility function as input—can determine the standard deviation of SRTTn estimates and the bias for the simple up-down procedure. The effects of variations in the slope of the intelligibility function, the guess rate, the starting level, the heterogeneity of the speech material, and the possibilities of optimizing SRTTn measurements were all explored with this model. The predicted decrease in the standard deviation of SRTTn estimates as a result of optimizing the speech material was confirmed by measurements in 244 listeners. The paper concludes by discussing possibilities for optimizing the development of comparable tests.
Series expansion for the sound field of rotating sources
Authors: Carley Michael
Published: September 2006

A method is derived for the fast, exact prediction of acoustic fields around rotating sources by using a series expansion which generalizes a previously published method for a circular piston. The technique gives exact predictions for the field outside the sphere containing the rotor in a computational time two orders of magnitude less than that required for direct numerical evaluation of the acoustic integrals. Its use is demonstrated by application to two sample problems characteristic of real aircraft propellers.
Reply to comment on “Auditory-nerve first-spike latency and auditory absolute threshold: A computer model”
Authors: Meddis Ray
Published: September 2006

Krisha [J. Acoust. Soc. Am., in press (2006)] has commented that an explanation based on presynaptic calcium accumulation at the inner hair cell is an incorrect explanation for the success of a model of the auditory periphery [Meddis, R., J. Acoustic. Soc. Am. 119, 406–417 (2006)] in explaining data on first-spike auditory nerve latency. This reply accepts the criticism and accepts the strength of an alternative explanation based on expected latencies in random sequences of low-probability events. This reply also goes on briefly to explore the application of this argument to other phenomena, including the dependence of absolute auditory threshold on the duration of the stimulus. This has wide-ranging implications for the concept of “temporal integration” in psychophysics.
Middle ear cavity and ear canal pressure-driven stapes velocity responses in human cadaveric temporal bones
Authors: O’Connor Kevin N. , Puria Sunil
Published: September 2006

Drive pressure to stapes velocity (Vst) transfer function measurements are collected and compared for human cadaveric temporal bones with the drive pressure alternately on the ear canal (EC) and middle ear cavity (MEC) sides of the tympanic membrane (TM), in order to predict the performance of proposed middle-ear implantable acoustic hearing aids, as well as provide additional data for examining human middle ear mechanics. The chief finding is that, in terms of the Vst response, MEC stimulation performs at least as well as EC stimulation below 8kHz, provided that the EC is unplugged. Plugging the EC causes a reduced response for MEC drive below 2kHz, due to a corresponding reduction of the pressure difference between the two sides of the TM. Between 8 and 11kHz, the MEC drive transfer functions feature an approximately 17dB drop in magnitude below the EC drive case, the cause of which remains unknown. The EC drive transfer functions reported here feature significantly less magnitude roll-off above 1kHz than previous studies [with a slope of −2.3 vs −6.7dB/octave for Aibara et al., Hear. Res. 152, 100–109 (2001)], and significantly more phase group delay (134 vs 62μs for Aibara et al.).
Temporal integration of the contralateral acoustic-reflex threshold and its age-related changes
Authors: Emmer Michele B. , Silman Shlomo , Silverman Carol A. , Levitt Harry
Published: September 2006

Although numerous studies have investigated temporal integration of the acoustic-reflex threshold (ART), research is lacking on the effect of age on temporal integration of the ART. Therefore the effect of age on temporal integration of the ART was investigated for a broad-band noise (BBN) activator. Subjects consisted of two groups of adults with normal-hearing sensitivity: one group of 20 young adults (ten males and ten females, ages 18–29years, with a mean age of 24years) and one group of 20 older adults (ten males and ten females, ages 59–75years, with a mean age of 67.5years). Activating stimulus durations were 12, 25, 50, 100, 200, 300, 500, and 1000ms. Significant main effects for duration and age were obtained. That is, as the duration increased, the acoustic reflex threshold for BBN decreased. The interactions of duration×age group and duration×hearing level were not significant. The result of pair-wise analysis indicated statistically significant differences between the two age groups at durations of 20ms and longer. The observed age effect on temporal integration of the ART for the BBN activator is interpreted in relation to senescent changes in the auditory system.
Underwater auditory localization by a swimming harbor seal (Phoca vitulina)
Authors: Bodson Anais , Miersch Lars , Mauck Bjoern , Dehnhardt Guido
Published: September 2006

The underwater sound localization acuity of a swimming harbor seal (Phoca vitulina) was measured in the horizontal plane at 13 different positions. The stimulus was either a double sound (two 6-kHz pure tones lasting 0.5s separated by an interval of 0.2s) or a single continuous sound of 1.2s. Testing was conducted in a 10-m-diam underwater half circle arena with hidden loudspeakers installed at the exterior perimeter. The animal was trained to swim along the diameter of the half circle and to change its course towards the sound source as soon as the signal was given. The seal indicated the sound source by touching its assumed position at the board of the half circle. The deviation of the seals choice from the actual sound source was measured by means of video analysis. In trials with the double sound the seal localized the sound sources with a mean deviation of 2.8° and in trials with the single sound with a mean deviation of 4.5°. In a second experiment minimum audible angles of the stationary animal were found to be 9.8° in front and 9.7° in the back of the seal’s head.
Diffraction of sound due to moving sources by barriers and ground discontinuities
Authors: Buret M. , Li K. M. , Attenborough K.
Published: September 2006

The solution for diffraction of sound by a wedge is extended to sources in uniform motion parallel to the obstacle. By means of an auxiliary transformation the problem is reduced to that of a set of stationary sources so that the resulting solution is in accordance with well-known models. Applications to prediction and abatement of transportation noise are considered. The formulation for the diffracted wave is combined with the solution for ground reflection of sound due to moving sources. New models for the sound field due to a source in motion along a barrier above the ground and for a source moving parallel to an impedance discontinuity are derived. In both situations, greater sensitivity to motion of the resulting sound pressure levels is found on source approach. However, attenuation of sound from moving sources by barriers is found to be so little affected by motion that design schemes for stationary source are relevant. On the other hand, it is noted that noise predictions must account for source motion.
Evaluation of an autoregressive spectral estimator for modal wave number estimation in range-dependent shallow water waveguides
Authors: Becker Kyle M. , Frisk George V.
Published: September 2006

In shallow water, geoacoustic properties of the seabed can be inferred from knowledge of acoustic normal modes propagating in the waveguide. For range-varying waveguides, modal content varies locally in response to changes in the environment. The problem becomes estimating the local modal content of a propagating field. For acoustic fields measured on horizontal arrays, resolution of closely spaced modal eigenvalues depends on the data aperture length. Therefore, range variability in a waveguide can only be detected for range scales of order of the resolvability of the individual modes. When only short data apertures are available for modal estimation, high-resolution methods must be used. In this paper, a high-resolution autoregressive (AR) spectral estimation method for extracting the modal information from measurements of a continuous wave acoustic field made on a horizontal array is evaluated. Performance is discussed for estimation accuracy and resolution in the presence of noise. Results are compared to previous work characterizing high-resolution wave number estimators. The AR estimator performance is comparable to other high-resolution methods and does not require prior information about the number of propagating modes. In addition, range/wave number plots obtained using a sliding window technique yield a robust method for identifying propagating modes and any changes with range.
Anterior-posterior biphonation in a finite element model of vocal fold vibration
Authors: Tao Chao , Jiang Jack J.
Published: September 2006

In this paper, a finite-element model is used to simulate anterior-posterior biphonation [Neubauer et al., J. Acoust. Soc. Am. 110(6), 3179–3192 (2001)]. The anterior-posterior stiffness asymmetric factor and the anterior-posterior shape asymmetric factor describe the asymmetry properties of vocal folds. Spatiotemporal plot, spectral analysis, anterior-posterior fundamental frequency ratio, cross covariation function, and correlation length quantitatively estimate the spatial asymmetry of vocal fold oscillations. Calculation results show that the anterior-posterior stiffness asymmetry decreases the spatial coherence of vocal fold vibration. When the stiffness asymmetry reaches a certain level, the drop in spatial coherence desynchronizes the vibration modes. The anterior and posterior sides of the vocal fold oscillate with two independent fundamental frequencies (fa and fp). The complex spectral characteristics of vocal fold vibration under biphonation conditions can be explained by the linear combination of fa and fp. Empirical orthogonal eigenfunctions prove the existence of higher-order anterior-posterior modes when anterior-posterior biphonation occurs. Then, it is found that the anterior-posterior shape asymmetry also decreases the spatial coherence of vocal fold vibration, and shape asymmetry is a possible reason for anterior-posterior biphonation.
Auditory filters and the benefit measured from spectral enhancement
Authors: DiGiovanni Jeffrey J. , Nair Padmaja
Published: September 2006

Algorithms designed to improve speech intelligibility for those with sensorineural hearing loss (SNHL) by enhancing peaks in a spectrum have had limited success. Since testing of such algorithms cannot separate the theory of the design from the implementation itself, the contribution of each of these potentially limiting factors is not clear. Therefore, psychophysical paradigms were used to test subjects with either normal hearing or SNHL in detection tasks using well controlled stimuli to predict and assess the limits in performance gain from a spectrally enhancing algorithm. A group of normal-hearing (NH) and hearing-impaired (HI) subjects listened in two experiments: auditory filter measurements and detection of incremented harmonics in a harmonic spectrum. The results show that NH and HI subjects have an improved ability to detect incremented harmonics when there are spectral decrements surrounding the increment. Various decrement widths and depths were compared against subjects’ equivalent rectangular bandwidths (ERBs). NH subjects effectively used the available energy cue in their auditory filters. Some HI subjects, while showing significant improvements, underutilized the energy reduction in their auditory filters.
Acoustic microscope lens modeling and its application in determining biological cell properties from single- and multi-layered cell models
Authors: Kundu Tribikram , Lee Joon-Pyo , Blase Christopher , Bereiter-Hahn Jürgen
Published: September 2006

The acoustic microscopy technique provides some extraordinary advantages for determining mechanical properties of living cells. It is relatively fast, of excellent spatial resolution, and of minimal invasiveness. Sound velocity is a measure of the cell stiffness. Attenuation of cytoplasm is a measure of supramolecular interactions. These parameters are of crucial interest for studying cell motility and volume regulations and to establish the functional role of the various elements of the cytoskeleton. Using a scanning acoustic microscope, longitudinal wave speed, attenuation and thickness profile of a biological cell were measured earlier by Kundu et al. [Biophys. J. 78, 2270–2279 (2000)]. In that study it was assumed that the cell properties did not change through the cell thickness but could vary in the lateral direction. In that effort the acoustic-microscope-generated signal was modeled as a plane wave striking the cell at normal incidence. Such assumptions ignored the effect of cell inhomogenity and the surface skimming Rayleigh waves. In this paper a rigorous lens model, based on the DPSM (distributed point source method), is adopted. For the first time in the literature the cell is modeled here as a multi-layered material and the effect of some external drug stimuli on a living cell is studied.
Joint estimation of water column and sediment acoustic properties from broadband towed array data using modal inverse method
Authors: Rajan Subramaniam D. , Anand G. V. , Nagesh P. V.
Published: September 2006

Broadband data, collected on a towed horizontal array of length 2375m during a geophysical survey, are used to perform joint inversion for the water column and sediment acoustic parameters using modal inverse technique [S. D. Rajan, J. F. Lynch, and G. V. Frisk, J. Acoust. Soc. Am. 82, 998–1017 (1987)]. To perform the inversion based on modal wave numbers, we first obtain the pressure field as a function of range at a discrete set of frequencies from the broadband data. The sources of errors and their impact on the estimation of modal wave number from such data are discussed. Due to the possibility of large errors in the estimation of the modal wave numbers of the higher-order modes, the inversion was performed using the modal wave numbers of the dominant lower-order modes. The resolution estimates indicate that the wave speeds in the water column and top three sediment layers have resolution lengths that are approximately 1.5 times the layer thicknesses. With respect to deeper sediment layers, the resolution lengths are large, as only lower-order modes were used in inversion. These results are consistent with a posteriori variance estimates. The model from modal inverse can serve as the initial model for nonlinear methods, such as those based on matched field processing [P. V. Nagesh, S. D. Rajan, and G. V. Anand, Conference on Underwater Acoustics Measurements: Technologies and Results, Heraklion, Crete, Greece (2005)].
Modeling auditory-nerve responses for high sound pressure levels in the normal and impaired auditory periphery
Authors: Zilany Muhammad S. A. , Bruce Ian C.
Published: September 2006

This paper presents a computational model to simulate normal and impaired auditory-nerve (AN) fiber responses in cats. The model responses match physiological data over a wider dynamic range than previous auditory models. This is achieved by providing two modes of basilar membrane excitation to the inner hair cell (IHC) rather than one. The two modes are generated by two parallel filters, component 1 (C1) and component 2 (C2), and the outputs are subsequently transduced by two separate functions. The responses are then added and passed through the IHC low-pass filter followed by the IHC-AN synapse model and discharge generator. The C1 filter is a narrow-band, chirp filter with the gain and bandwidth controlled by a nonlinear feed-forward control path. This filter is responsible for low and moderate level responses. A linear, static, and broadly tuned C2 filter followed by a nonlinear, inverted and nonrectifying C2 transduction function is critical for producing transition region and high-level effects. Consistent with Kiang’s two-factor cancellation hypothesis, the interaction between the two paths produces effects such as the C1/C2 transition and peak splitting in the period histogram. The model responses are consistent with a wide range of physiological data from both normal and impaired ears for stimuli presented at levels spanning the dynamic range of hearing.
Speech utterance clustering based on the maximization of within-cluster homogeneity of speaker voice characteristics
Authors: Tsai Wei-Ho , Wang Hsin-Min
Published: September 2006

This paper investigates the problem of how to partition unknown speech utterances into a set of clusters, such that each cluster consists of utterances from only one speaker, and the number of clusters reflects the unknown speaker population size. The proposed method begins by specifying a certain number of clusters, corresponding to one of the possible speaker population sizes, and then maximizes the level of overall within-cluster homogeneity of the speakers’ voice characteristics. The within-cluster homogeneity is characterized by the likelihood probability that a cluster model, trained using all the utterances within a cluster, matches each of the within-cluster utterances. To attain the maximal sum of likelihood probabilities for all utterances, the proposed method applies a genetic algorithm to determine the cluster in which each utterance should be located. For greater computational efficiency, also proposed is a clustering criterion that approximates the likelihood probability with a divergence-based model similarity between a cluster and each of the within-cluster utterances. The clustering method then examines various legitimate numbers of clusters by adapting the Bayesian information criterion to determine the most likely speaker population size. The experimental results show the superiority of the proposed method over conventional methods based on hierarchical clustering.
Coupling between thermoacoustic resonance pipes and piezoelectric loudspeakers studied by equivalent circuit method
Authors: Fan Li , Zhang Shu-yi , Wang Ben-ren
Published: September 2006

In order to miniaturize thermoacoustic refrigerators, piezoelectric loudspeakers are used as acoustic sources for operating at high resonance frequencies. An integrated equivalent circuit model of a thermoacoustic resonance pipe driven by a piezoelectric loudspeaker is presented to investigate the coupling conditions between the piezoelectric loudspeaker and thermoacoustic resonance pipe. Using the equivalent circuit model the optimized coupling conditions can be obtained, with which the highest electroacoustic transfer efficiency and the largest acoustic output power of a piezoelectric acoustic source can be achieved. The theoretical simulations are taken to optimize the structures and the operating frequencies of the thermoacoustic systems.
The influence of subglottal acoustics on laboratory models of phonation
Authors: Zhang Zhaoyan , Neubauer Juergen , Berry David A.
Published: September 2006

Many previous laboratory investigations of phonation involving physical models, excised larynges, and in vivo canine larynges have failed to fully specify the subglottal system. Many of these same studies have reported a variety of nonlinear phenomena, including bifurcations (e.g., various classes of phonation onset and offset, register changes, frequency jumps), subharmonics, and chaos, and attributed such phenomena to the biomechanical properties of the larynx. However, such nonlinear phenomena may also be indicative of strong coupling between the voice source and the subglottal tract. Consequently, in such studies, it has not been clear whether the underlying mechanisms of such nonlinear phenomena were acoustical, biomechanical, or a coupling of the acoustical and biomechanical systems. Using a physical model of vocal fold vibration, and tracheal tube lengths which have been commonly reported in the literature, it is hypothesized and subsequently shown that such nonlinear phenomena may be replicated solely on the basis of laryngeal interactions with the acoustical resonances of the subglottal system. Recommendations are given for ruling out acoustical resonances as the source of nonlinear phenomena in future laboratory studies of phonation.
Acoustic analysis of vocal development in a New World primate, the common marmoset (Callithrix jacchus)
Authors: Pistorio Ashley L. , Vintch Brett , Wang Xiaoqin
Published: September 2006

In contrast to humans and songbirds, there is limited evidence of vocal learning in nonhuman primates. While previous studies suggested that primate vocalizations exhibit developmental changes, detailed analyses of the extent and time course of such changes across a species’ vocal repertoire remain limited. In a highly vocal primate, the common marmoset (Callithrix jacchus), we studied developmental changes in the acoustic structure of species-specific communication sounds produced in a social setting. We performed detailed acoustic analyses of the spectral and temporal characteristics of marmoset vocalizations during development, comparing differences between genders and twin pairs, as well as with vocalizations from adult marmosets residing in the same colony. Our analyses revealed significant changes in spectral and temporal features as well as variability of particular call types over time. Infant and juvenile vocalizations changed progressively toward the vocalizations produced by adult marmosets. Call types observed early in development that were unique to infants disappeared gradually with age, while vocal exchanges with conspecifics emerged. Our observations clearly indicate that marmoset vocalizations undergo both qualitative and quantitative postnatal changes, establishing the basis for further studies to delineate contributions from maturation of the vocal apparatus and behavioral experience.
A transformation of the environment eliminates parabolic equation phase errors
Authors: Rypina Irina I. , Udovydchenkov Ilya A. , Brown Michael G.
Published: September 2006

It is shown that phase errors associated with the standard parabolic wave equation can be eliminated in a range-independent environment by appropriately transforming the environment. Solutions to the standard parabolic equation (PE) in the transformed environment are close to solutions to the Helmholtz equation in the original environment in the sense that ray and asymptotic mode contributions to the PE wave fields have no phase errors relative to their Helmholtz equation counterparts. Although phase errors are eliminated in the PE wave fields, complete asymptotic equivalence to the Helmholtz equation wave fields is not attained. Ray- and mode-based wave-field expansions are used to illustrate similarities and differences between PE and Helmholtz equation wave fields. Numerical simulations show excellent agreement between PE wave fields in the transformed environment and mode-based solutions to the Helmholtz equation in the true environment.
Optimization of multilayered panels with poroelastic components for an acoustical transmission objective
Authors: Tanneau O. , Casimir J. B. , Lamary P.
Published: September 2006

A method for optimizing acoustical linings is described and applied to multilayered panels including solid, fluid, and porous components. This optimization is based on an analytical simulation of the insulation properties and a genetic algorithm. The objective function is defined by taking into account both the acoustical frequency response over a 1/3 octave spectrum and the total mass of the panel. The optimization process gives rise to an optimal choice for the number of layers as well as for the nature and the thickness of each layer that maximizes the transmission loss. A practical example of such an optimization is described.
Brake squeal as dynamic instability: An experimental investigation
Authors: Massi Francesco , Giannini Oliviero , Baillet Laurent
Published: September 2006

This paper presents an experimental analysis performed on a simplified brake apparatus. In past years a common approach for squeal prediction was the complex eigenvalues analysis. The squeal phenomenon is treated like a dynamic instability: when two modes of the brake system couple at the same frequency, one of them becomes unstable, leading to increasing vibration. The presented experimental analysis is focused on correlating squeal characteristics with the dynamic behavior of the system. The experimental modal identification of the setup is performed and different squeal conditions and frequencies are reproduced and analyzed. Squeal events are correlated with the modal behavior of the system as a function of the main parameters. A clear distinction between squeal events involving the dynamics of the pad and squeal events involving the dynamics of the caliper is performed. The effect of the adding of damping is also investigated on the squeal phenomenon. Two opposite roles of the modal damping are described: a large modal damping can either prevent the rise of squeal instabilities or enlarge the squeal propensity of the brake apparatus. The robustness of the obtained squeal events permits a further analysis on the triggering mechanism of the squeal instability during braking.
An international key comparison of free-field hydrophone calibrations in the frequency range 1 to 500kHz
Authors: Robinson Stephen P. , Harris Peter M. , Ablitt Justin , Hayman Gary , Thompson Alex , van Buren A. Lee , Zalesak Joseph F. , Drake Robert M. , Isaev Alexander E. , Enyakov Alexander M. , Purcell Christopher , Houqing Zhu , Yuebing Wang , Yue Zhang , Botha Pierre , Krüger Dieter
Published: September 2006

A description is given of the results of a Key Comparison of primary free-field standards for underwater acoustics at frequencies from 1 to 500kHz. This is the first such Key Comparison exercise in the field of underwater acoustic calibration and measurement. Laboratories from UK, Germany, USA, Russia, China, Canada, and South Africa participated by calibrating three reference hydrophones, with project coordination provided by the National Physical Laboratory, UK. The agreement between the results obtained from the comparison was generally encouraging, with the calibration values reported by the laboratories agreeing within quoted uncertainties over the majority of the frequency range, and the results generally lying within a ±0.5-dB band for frequencies up to 300kHz. A discussion is given of the general sources of uncertainties in the calibrations, in particular those which are thought to have contributed to the differences in the results between laboratories. The results of the participants have been used to estimate the equivalence of national measurement standards within this field.
Discrimination of near-field infrasound sources based on time-difference of arrival information
Authors: Szuberla Curt A. L. , Arnoult Kenneth M. , Olson John V.
Published: September 2006

A computationally efficient method for discriminating between near- and far-field infrasound sources using array time-difference of arrival (TDOA) information is described. Rather than assess wave-front curvature, the discriminant quantifies the statistical departure of TDOA information from that of a plane wave passing the array. Since the method constrains neither the functional form nor the amplitude characteristics of a signal it is suited for discrimination of signals across large-aperture infrasound arrays. Experimental results confirm theoretical predictions to a range of order ten array apertures. The discriminant is applied to data from an Antarctic infrasound array.
The influence of spatial separation on divided listening
Authors: Best Virginia , Gallun Frederick J. , Ihlefeld Antje , Shinn-Cunningham Barbara G.
Published: September 2006

If spatial attention acts like a “spotlight,” focusing on one location and excluding others, it may be advantageous to have all targets of interest within the same spatial region. This hypothesis was explored using a task where listeners reported keywords from two simultaneous talkers. In Experiment 1, the two talkers were placed symmetrically about the frontal midline with various angular separations. While there was a small performance improvement for moderate separations, the improvement decreased for larger separations. However, the dependency of the relative talker intensities on spatial configuration accounted for these effects. Experiment 2 tested whether spatial separation improved the intelligibility of each source, an effect that could counteract any degradation in performance as sources fell outside the spatial spotlight of attention. In this experiment, intelligibility of individual sources was equalized across configurations by adding masking noise. Under these conditions, the cost of divided listening (the drop in performance when reporting both messages compared to reporting just one) was smaller when the spatial separation was small. These results suggest that spatial separation enhances the intelligibility of individual sources in a competing pair but increases the cost associated with having to process both sources simultaneously, consistent with the attentional spotlight hypothesis.
Imaging marine geophysical environments with vector acoustics
Authors: Lindwall Dennis
Published: September 2006

Using vector acoustic sensors for marine geoacoustic surveys instead of the usual scalar hydrophones enables one to acquire three-dimensional (3D) survey data with instrumentation and logistics similar to current 2D surveys. Vector acoustic sensors measure the sound wave direction directly without the cumbersome arrays that hydrophones require. This concept was tested by a scaled experiment in an acoustic water tank that had a well-controlled environment with a few targets. Using vector acoustic data from a single line of sources, the three-dimensional tank environment was imaged by directly locating the source and all reflectors.
EQUILIBRIUM MULTIPLICITY IN A CARDIOVASCULAR SYSTEM MODEL
Authors: ALVAREZ-RAMIREZ JOSE , RODRIGUEZ EDUARDO , ECHEVERRIA JUAN CARLOS , VELASCO-HERNANDEZ JORGE X.
Published: September 2006

The aim of this paper is to show that, for some parameters, a two-dimensional cardiovascular system model can exhibit intrinsic equilibrium multiplicity generated by a backward bifurcation, regardless of the baroreflex effect. The model considers the dynamics of arterial and venous compartments and a feedback effect in the stroke volume induced by venous pressure changes. The results of the mathematical analysis indicate that multiple non-trivial equilibrium points exist when the stroke volume function is convex around the origin. Interestingly, this equilibrium point structure would imply that under certain stroke volume functions, the baroreflex system would have to stabilize and regulate an unstable operating condition produced by certain values of the stroke volume. The paper ends with the discussion of some implications for the reliability and robustness of the baroreflex-feedback mechanism.
HIV/AIDS MODEL FOR ASSESSING THE EFFECTS OF PROPHYLACTIC STERILIZING VACCINES, CONDOMS AND TREATMENT WITH AMELIORATION
Authors: MUKANDAVIRE Z. , GARIRA W.
Published: September 2006

HIV/AIDS vaccination model for heterosexual transmission with explicit incubation period is presented as a system of delay differential equations. The model considers prophylactic vaccination of sexually immature (pre- and early-adolescents) and mature susceptibles in a community. We start by formulating and analyzing an HIV/AIDS vaccination model that we extend to incorporate condom use based on efficacy and compliance. Further, we extend HIV/AIDS vaccination model with condom use by incorporating treatment which allows AIDS patients to undergo amelioration. The thresholds and equilibria for the models are determined, and stabilities analyzed. The basic reproductive numbers for the models are computed and compared to assess the possible community benefits of using prophylactic vaccines, condoms and treatment with amelioration of AIDS patients. We conclude from the study that vaccination and condom use can reduce the basic reproductive number [Formula: see text] to values below unity but treatment with amelioration intended to lengthen the lives of AIDS patients may result in more numbers of HIV infections and fail to reduce [Formula: see text] to values less than unity as intended for disease control.
GLOBAL STABILITY ANALYSIS OF AN ECO-EPIDEMIOLOGICAL MODEL OF THE SALTON SEA
Authors: JIN ZHEN , HAQUE MAINUL
Published: September 2006

The Salton Sea, the largest lake of California, is now facing problems due to its massive fish and bird mortality. Haque and Chattopadhyay1have proposed and analyzed an eco-epidemiological model on Salton Sea. The present article deals with the global stability analysis of the positive interior equilibrium of that eco-epidemiological model. We use the geometric approach to the global stability analysis for ordinary differential equations which is based on the use of higher-order generalization of Bendixson's criterion. Our conclusion is that for persistence of the pelican (main predator) populations in Salton Sea, harvesting of tilapia (specially infected) populations is an utmost important factor.
RICH DYNAMICS OF A TIME-DELAYED FOOD CHAIN MODEL
Authors: MAITI ALAKES , SAMANTA G. P.
Published: September 2006

Complex dynamics of a tritrophic food chain model is discussed in this paper. The model is composed of a logistic prey, a classical Lotka-Volterra functional response for prey-predator and a ratio-dependent functional response for predator-superpredator. Dynamical behaviors such as boundedness, stability and bifurcation of the model are studied critically. The effect of discrete time-delay on the model is investigated. Computer simulation of various solutions is presented to illustrate our mathematical findings. How these ideas illuminate some of the observed properties of real populations in the field is discussed and practical implications are explored.
EXISTENCE OF E0-SEMIGROUPS FOR ARVESON SYSTEMS: MAKING TWO PROOFS INTO ONE
Authors: SKEIDE MICHAEL
Published: September 2006

For quite some time there were only two rather difficult and involved proofs available, the original one by Arveson and a more recent one by Liebscher, of the fact that for every Arveson system there exists an E0-semigroup. We put together two recent short proofs, one by Skeide and one by Arveson, to obtain a simpler one, which unifies the advantages of each proof and discards their disadvantages.
ENTANGLED MARKOV CHAINS ARE INDEED ENTANGLED
Authors: ACCARDI LUIGI , MATSUOKA TAKASHI , OHYA MASANORI
Published: September 2006

Entangled Markov chains (EMC) were so baptized on the basis of the conjecture that they provide examples of states, on infinite tensor products of matrix algebras, which are in some sense "entangled".2 In this paper we introduce the notion of multiple (or "many-body") entanglement and extend the two-body criterion of entanglement obtained in Ref. 17 to this case. We then apply this extension to EMC and prove that "generically" they satisfy the entanglement conditions.
GIBBS MEASURES FOR SOS MODELS ON A CAYLEY TREE
Authors: ROZIKOV U. A. , SUHOV Y. M.
Published: September 2006

We consider a nearest-neighbor solid-on-solid (SOS) model, with several spin values 0, 1,…, m, m ≥ 2, and zero external field, on a Cayley tree of order k (with k + 1 neighbors). The SOS model can be treated as a natural generalization of the Ising model (obtained for m = 1). We mainly assume that m = 2 (three spin values) and study translation-invariant (TI) and "splitting" (S) Gibbs measures (GMs). (Splitting GMs have a particular Markov-type property specific for a tree.) Furthermore, we focus on symmetric TISGMs, with respect to a "mirror" reflection of the spins. [For the Ising model (where m = 1), such measures are reduced to the "disordered" phase obtained for free boundary conditions, see Refs. 9, 10.] For m = 2, in the antiferromagnetic (AFM) case, a symmetric TISGM (and even a general TISGM) is unique for all temperatures. In the ferromagnetic (FM) case, for m = 2, the number of symmetric TISGMs and (and the number of general TISGMs) varies with the temperature: this gives an interesting example of phase transition. Here we identify a critical inverse temperature, [Formula: see text] such that [Formula: see text], there exists a unique symmetric TISGM μ* and [Formula: see text] there are exactly three symmetric TISGMs: [Formula: see text] (a "bottom" symmetric TISGM), [Formula: see text] (a "middle" symmetric TISGM) and [Formula: see text] (a "top" symmetric TISGM). For [Formula: see text] we also construct a continuum of distinct, symmertric SGMs which are non-TI.

Our second result gives complete description of the set of periodic Gibbs measures for the SOS model on a Cayley tree. A complete description of periodic GMs means a characterisation of such measures with respect to any given normal subgroup of finite index in the representation group of the tree. We show that (i) for an FM SOS model, for any normal subgroup of finite index, each periodic SGM is in fact TI. Further, (ii) for an AFM SOS model, for any normal subgroup of finite index, each periodic SGM is either TI or has period two (i.e. is a chess-board SGM).
Endurance exercise differentially stimulates heart and axial muscle development in zebrafish (Danio rerio)
Authors: van der Meulen T. , Schipper H. , van den Boogaart J. G. M. , Huising M. O. , Kranenbarg S. , van Leeuwen J. L.
Published: September 2006

Mechanical load is an important factor in the differentiation of cells and tissues. To investigate the effects of increased mechanical load on development of muscle and bone, zebrafish were subjected to endurance swim training for 6 h/day for 10 wk starting at 14 days after fertilization. During the first 3 wk of training, trained fish showed transiently increased growth compared with untrained (control) fish. Increased expression of proliferating cell nuclear antigen suggests that this growth is realized in part through increased cell proliferation. Red and white axial muscle fiber diameter was not affected. Total cross-sectional area of red fibers, however, was increased. An improvement in aerobic muscle performance was supported by an increase in myoglobin expression. At the end of 10 wk of training, heart and axial muscle showed increased expression of the muscle growth factor myogenin and proliferating cell nuclear antigen, but there were major differences between cardiac and axial muscle. In axial muscle, expression of the “slow” types of myosin and troponin C was increased, together with expression of erythropoietin and myoglobin, which enhance oxygen transport, indicating a shift toward a slow aerobic phenotype. In contrast, the heart muscle shifts to a faster phenotype but does not become more aerobic. This suggests that endurance training differentially affects heart and axial muscle.
Efferent projection from the bed nucleus of the stria terminalis suppresses activity of taste-responsive neurons in the hamster parabrachial nuclei
Authors: Li Cheng-Shu , Cho Young K.
Published: September 2006

Although the reciprocal projections between the bed nucleus of the stria terminalis (BNST) and the gustatory parabrachial nuclei (PbN) have been demonstrated neuroanatomically, there is no direct evidence showing that the projections from the PbN to the BNST carry taste information or that descending inputs from the BNST to the PbN modulate the activity of PbN gustatory neurons. A recent electrophysiological study has demonstrated that the BNST exerts modulatory influence on taste neurons in the nucleus of the solitary tract (NST), suggesting that the BNST may also modulate the activity of taste neurons in the PbN. In the present study, we recorded from 117 taste-responsive neurons in the PbN and examined their responsiveness to electrical stimulation of the BNST bilaterally. Thirteen neurons (11.1%) were antidromically invaded from the BNST, mostly from the ipsilateral side (12 cells), indicating that a subset of taste neurons in the PbN project their axons to the BNST. The BNST stimulation induced orthodromic responses on most of the PbN neurons: 115 out of 117 (98.3%), including all BNST projection units. This descending modulation on the PbN gustatory neurons was exclusively inhibitory. We also confirmed that activation of this efferent inhibitory projection from the BNST reduces taste responses of PbN neurons in all units tested. The BNST is part of the neural circuits that involve stress-associated feeding behavior. It is also known that brain stem gustatory nuclei, including the PbN, are associated with feeding behavior. Therefore, this neural substrate may be important in the stress-elicited alteration in ingestive behavior.
Primary Glioblastomas Express Mesenchymal Stem-Like Properties
Authors: Tso Cho-Lea , Shintaku Peter , Chen James , Liu Qinghai , Liu Jason , Chen Zugen , Yoshimoto Koji , Mischel Paul S. , Cloughesy Timothy F. , Liau Linda M. , Nelson Stanley F.
Published: September 2006

Glioblastoma is the most common and aggressive primary brain cancer. Recent isolation and characterization of brain tumor-initiating cells supports the concept that transformed neural stem cells may seed glioblastoma. We previously identified a wide array of mesenchymal tissue transcripts overexpressed in a broad set of primary glioblastoma (de novo) tumors but not in secondary glioblastoma (derived from lower-grade) tumors, low-grade astrocytomas, or normal brain tissues. Here, we extend this observation and show that a subset of primary glioblastoma tumors and their derived tumor lines express cellular and molecular markers that are associated with mesenchymal stem cells (MSC) and that glioblastoma cell cultures can be induced to differentiate into multiple mesenchymal lineage-like cell types. These findings suggest either that a subset of primary glioblastomas derive from transformed stem cells containing MSC-like properties and retain partial phenotypic aspects of a MSC nature in tumors or that glioblastomas activate a series of genes that result in mesenchymal properties of the cancer cells to effect sustained tumor growth and malignant progression. (Mol Cancer Res 2006;4(9):607–19)