bluuebunny/crossref_metadata_2025 huggingface dataset:
Near-normal incidence scattering from rough, finite surfaces: Kirchhoff theory and data comparison for arctic sea ice
Authors: Mourad P. D. , Williams K. L.
Published: October 2005

The Kirchhoff theory is applied for the target strength of a rough, circular surface whose roughness is characterized by a two-dimensional, isotropic power-law wave number spectrum, W2(κ) = η2κ−p2. The reflection coefficient for ice and three nondimensional parameters are found to govern the target strength. These parameters are ζ=κ0a, η≡η2ap2−4, and p1=p2−1, where κ0 is the acoustic wave number, a is the radius of the surface, and p1 is the spectral exponent of the one-dimensional power-law wave-number spectrum from which W2(κ) is derived. The general influence of ζ, p1, and η on the target strength is discussed. Calculations of average target strength of the ice/water interface of a submerged cylindrical block of ice are shown, which are then compared with individual realizations of measured target strengths of ice blocks for ζ between 25 and 100, corresponding to frequencies between 20 and 80 kHz for a=0.29 m. Data and theory show that the (smooth surface) form function for a finite surface does not describe the observed diffraction pattern. Instead, the lobes of the pattern diminish and the nulls fill in—i.e., the total backscatter becomes more incoherent—as frequency increases or as the large wave-number components of the roughness spectrum contribute more to the total acoustic return. These comparisons also allowed us to infer the rough surface statistics of the ice surface and the compressional sound-speed structure within the skeletal zone of the ice.
Propagation of strongly nonlinear plane wavesa)
Authors: Inoue Yoshinori , Yano Takeru
Published: October 2005

The nonlinear propagation of plane waves at high acoustic Reynolds number is studied without the restriction of low amplitude, namely, the weak nonlinearity. The wave is emitted from an infinite plate executing harmonic oscillations into a perfect gas. The method of analysis is based on the simple wave theory up to the shock formation time, and beyond the time on the numerical calculation by means of the upwind finite difference scheme (and partly the weakly nonlinear theory is used jointly with it). The initial sinusoidlike wave profile is progressively distorted as the wave propagates and this leads to the formation of shocks, as well as in the propagation of the weakly nonlinear wave. Then it evolves into a sawtoothlike wave as a whole. The strongly nonlinear wave, however, possesses the following outstanding distinctive features, as contrasted with its counterpart in the weakly nonlinear regime: (i) shock waves that form in a near field propagate with supersonic speed in a quasi-steady state; (ii) the waveform does not have any symmetry between the rarefactive phase and the compressive phase in a wave cycle; (iii) acoustic streaming occurs in one direction after shock formation; and (iv) the leading shock and the following shock are merged into one shock.
Acoustic pulse propagation in Maxwell fluids
Authors: Leander Johan L.
Published: October 2005

Transient linear acoustic wave propagation in fluids exhibiting Maxwell relaxation processes is investigated theoretically. The case of a single relaxation proces is studied in detail. The inverse problem concerning the estimation of the governing parameters of Maxwell fluids on the basis of measured transients is analyzed. First, a method based on numerical Fourier transformation is discussed. Then, it is shown how the governing parameters can be estimated via certain moments of a distorted pulse. The above two methods involve formally the entire pressure–time history of a distorted pulse. Since part of it can also be influenced by other effects than dissipative it is of interest to establish complementary methods. The full solution to the distortion problem is derived and the governing parameters can be estimated by means of, for example, least-mean-square approximation. This method requires only that a finite part of a pulse be solely influenced by dissipation. However, it results in two overdetermined nonlinear equations and a first-order approximation is needed. By evaluation of the time derivatives of the pressure signature at the wave front it is shown that a first-order approximation can be obtained.
On reporting the precision of scattering calculations
Authors: Beattie P. , Chivers R. C.
Published: October 2005

Scattering calculations often produce a series solution which, for the purposes of practical computation, requires restriction to a finite number of terms. The conventional approach simply specifies the arbitrary number of terms to be included, and is of unknown accuracy. An improved procedure is proposed in which the number of terms included in the calculation is defined by the accuracy required over the whole of the ka range considered.
Influence of variations in loss factor of a panel and line impedances of attached ribs
Authors: Maidanik G. , Dickey J.
Published: October 2005

This is a companion paper to a preceding paper entitled: ‘‘Quadratic and energy estimates of the partial response of ribbed panels’’ [J. Dickey and G. Maidanik, J. Acoust. Soc. Am. 94, (1993)]. A ribbed panel is used as a complex structure in which the bays form an ensemble of coupled dynamic systems which can be made identical. In the companion paper a quadratic analysis (QA) is employed to yield the quadratized linear response of a ribbed panel which is then compared with the responses that are yielded by an energy analysis (EA) and a statistical energy analysis (SEA). The comparison is extended herein to include variations in the loss factor of the panel and in the line impedance of the ribs. It is found that such variations may significantly influence the quadratic (global) and the energy (local) responses of a ribbed panel as well as the correspondence between these types of responses.
Ultrasonic method for determining attenuation coefficients in plate-shaped materials
Authors: Guidarelli G. , Marini A. , Palmieri L.
Published: October 2005

Measurements of elastic wave transmission through a fluid-loaded plate are usually employed for studying acoustic properties of materials. In this work an experimental method has been introduced for investigating the attenuation effect on plate transmittivity of ultrasonic waves at normal incidence, and for determining the attenuation coefficient as a function of frequency in plate-shaped materials. The method, based on the well-known transmission selective properties of layers, has been developed by resorting to swept frequency techniques analogous to those usually employed for network analysis. A simplified theoretical formalism is also developed, whose predictions are compared with the experimental results, showing good agreement.
Contributions of comodulation masking release and temporal resolution to the speech-reception threshold masked by an interfering voice
Authors: Festen Joost M.
Published: October 2005

Two experiments are presented to explain the difference in speech-reception threshold (SRT) between conditions with a steady-state noise masker or an interfering voice. Literature shows for normal hearing a masking release of 6–8 dB with an interfering voice and a substantial reduction of this release with hearing impairment. In experiment I the possible role of comodulation masking release (CMR) is investigated by manipulating the comodulation in the interfering voice by the introduction of temporal shift among filter bands of various width. The spectral spread of masking from the manipulated interfering voice was controlled by interleaving the mutually shifted speech bands with 1/3-octave bands of noise. Although comodulation in the interfering speech appears to be very important for the low SRT, the contribution of across-frequency processing of masker fluctuations—commonly considered as the origin of CMR—is only 1.3 dB. In experiment II the level dependence of masking release with an interfering voice is investigated. The data fit in with the hypothesis by Festen and Plomp [J. Acoust. Soc. Am. 88, 1725–1736 (1990)] that the release from masking with an interfering voice is limited by forward masking. It appears that up to about 55 dBA the release from masking increases with level up to about 7 dB. Above 55 dBA the difference in SRT obtained with a noise masker or an interfering voice is constant due to the limited average modulation depth of speech.
A computational theory of spectral cue localization
Authors: Zakarauskas Pierre , Cynader Max S.
Published: October 2005

This paper presents a computational theory of localization based on analysis of the cues contained in the spectrum received at the eardrum. It is well established that monaural localization, and binaural localization onto the cone of confusion, for pure tone stimuli are unrelated to the actual source position. On the other hand, broad spectrum stimuli are localized with some accuracy. This paper outlines the properties that the operations performed on a received spectrum must have in order for the source to be localized accurately. The use of the two simplest nontrivial such operations, the first and second finite differences of the spectrum, respectively, are explored in detail. This analysis shows that so long as the spectrum of the sound source has a locally constant slope, accurate localization using such operators is possible. A simulation of the localization process making use of measured human head-related transfer functions (HRTF’s) and two recorded spectra demonstrates that the second-order finite difference operator produces much more accurate and robust estimates than the first-order operator.
On the potential of fixed arrays for hearing aids
Authors: Stadler R. W. , Rabinowitz W. M.
Published: October 2005

Microphone arrays with fixed (time-invariant) weights are directed at enhancing a desired signal from one direction (straight ahead) while attenuating spatially distributed interference and reverberation. Using the theory of sensitivity-constrained optimal beamforming [Cox et al., IEEE Trans. Acoust. Speech Sig. Process. ASSP-34, 393–398 (1986)], free-field arrays of head-sized extents were studied. The key parameters affecting array design and performance are the set of transfer functions from the target direction to each array microphone [H(f )] and the intermicrophone cross-spectral densities for isotropic noise [Szz(f )]. Design variables included the orientation of the array, the number, and [as motivated by Soede, Ph.D. thesis, Delft University of Technology (1990)] the directionality of the microphones within the array, and the complexity and robustness of the required processing. Performance was characterized by the broadband intelligibility-weighted directivity (gain against isotropic noise) and noise sensitivity (reflecting the array’s sensitivity to uncorrelated noise, as well as device tolerances). For broadside orientation, a variety of arrays based on cardioid and hypercardioid microphones gave very similar performance. They can provide directivities of 7–8 dB with easily implemented weights (simple scalars). For end-fire orientation, as Soede (1990) recognized, similar directivities result with weights based on analog gains and pure time delays. However, with weightings chosen independently for each frequency, directivities up to ∼11 dB may be obtained, although the increased noise sensitivities of these arrays require practical evaluation. Because of sound diffraction, placement of arrays onto the head potentially impacts both their design and performance. In situ measurements of H(f ) and Szz(f ) as well as simplified theoretical models are suggested to explore the optimization of head-mounted arrays.
Target motion analysis in the presence of false alarms
Authors: Jauffret C. , Bar-Shalom Y.
Published: October 2005

Usually, target motion analysis (TMA) is based upon the Gaussian statistical assumption for the additive corrupting measurement noise and ignores the presence of false alarms. In this paper, a realistic maximum likelihood estimator (MLE) is developed for TMA problems when the available measurement at each sampling time is either a true detection or a false alarm. By using appropriate statistical assumptions, the Cramer–Rao lower bound (CRLB) is computed for the bearings-only TMA under the realistic assumption that the data set is contaminated by false alarms. A comparison is then made between the least-squares estimator and MLE-based TMA.
Active isolation of a vibration source from a thin beam using a single active mount
Authors: Pan Jiaqiang , Hansen Colin H. , Pan Jie
Published: October 2005

When active control is used to reduce the vibration transmission through machine mounts into supporting structures, the vibratory power flow through the mounts is often used as the cost function to be minimized. This is because the mounts behave as vibration ‘‘sources’’ for the supporting structure and they have a finite number of degrees of freedom. To apply active control effectively to suspension systems, it is necessary to investigate the nature of the power flow from a vibrating machine to its supporting structure through the mounts. In this study the transmission of harmonic vibratory power flow from a vibrating rigid body into a thin support beam through a single isolating mount is investigated theoretically and experimentally, and the possibility of active control of the transmission of vibratory power is explored. Power flow resulting from moments as well as horizontal and vertical forces is considered. It is shown that over a wide frequency range, significant reduction in vibratory power flow can be achieved by using a control actuator that exerts a control force on the rigid body and support structure simultaneously.
Quadratic and energy estimates of the partial response of ribbed panels
Authors: Maidanik G. , Dickey J.
Published: October 2005

Two formalisms of the response of a ribbed uniform panel excited by a line drive are considered. In the first a quadratic analysis (QA) of the linear response is obtained. In this response phases among the responses of the bays are preserved and accounted for. (A bay is the portion of the panel that lies between two adjacent ribs.) The preservation of the phases yield responses that exhibit the phenomena of pass and stop bands and of localization and delocalization when the separations between adjacent ribs are equal. In the second an energy analysis (EA) of the response is obtained. The response is estimated in terms of the energy densities in the individual bays. In this formalism the phases among the responses of the bays are inconsequential. Therefore the phenomena of pass and stop bands and of localization and delocalization are not manifested in the EA response. It is thus suggested that formalisms that are akin to the statistical energy analysis (SEA) and SEA itself cannot be expected to exhibit some of the features in the response of a complex structure, especially if the structure is composed of a number of regular substructures; e.g., the identical bays in a ribbed panel. The generic example presented in this paper illustrates that in certain situations and for certain purposes the missing features in the EA response, as compared with the QA response, may be significant.
Local consonance and the relationship between timbre and scale
Authors: Sethares William A.
Published: October 2005

The principle of local consonance is based on an explicit parametrization of Plomp and Levelt’s [J. Acoust. Soc. Am. 38, 548–560 (1965)] consonance curves. It explains the relationship between the spectrum of a sound (its timbre) and a tuning (or scale) in which the timbre will appear most consonant. This relationship is defined in terms of the local minima of a family of dissonance curves. For certain timbres with simple spectral configurations, dissonance curves can be completely characterized, and bounds are provided on the number and location of points of local consonance. Computational techniques are presented which answer two complementary questions: Given a timbre, what scale should it be played in? Given a desired scale, how can appropriate timbres be chosen? Several concrete examples are given, including finding scales for nonharmonic timbres (the natural resonances of a uniform beam, ‘‘stretched’’ and ‘‘compressed’’ timbres, FM timbres with noninteger carrier-to-modulation ratios), and finding timbres for arbitrary scales.
Training Japanese listeners to identify English /r/ and /l/. II: The role of phonetic environment and talker variability in learning new perceptual categories
Authors: Lively Scott E. , Logan John S. , Pisoni David B.
Published: October 2005

Two experiments were carried out to extend Logan et al.’s recent study [J. S. Logan, S. E. Lively, and D. B. Pisoni, J. Acoust. Soc. Am. 89, 874–886 (1991)] on training Japanese listeners to identify English /r/ and /l/. Subjects in experiment 1 were trained in an identification task with multiple talkers who produced English words containing the /r/–/l/ contrast in initial singleton, initial consonant clusters, and intervocalic positions. Moderate, but significant, increases in accuracy and decreases in response latency were observed between pretest and posttest and during training sessions. Subjects also generalized to new words produced by a familiar talker and novel words produced by an unfamiliar talker. In experiment 2, a new group of subjects was trained with tokens from a single talker who produced words containing the /r/–/l/ contrast in five phonetic environments. Although subjects improved during training and showed increases in pretest–posttest performance, they failed to generalize to tokens produced by a new talker. The results of the present experiments suggest that variability plays an important role in perceptual learning and robust category formation. During training, listeners develop talker-specific, context-dependent representations for new phonetic categories by selectively shifting attention toward the contrastive dimensions of the non-native phonetic categories. Phonotactic constraints in the native language, similarity of the new contrast to distinctions in the native language, and the distinctiveness of contrastive cues all appear to mediate category acquisition.
Manipulations of the duration and relative onsets of two-tone forward maskersa)
Authors: Champlin Craig A. , Wright Beverly A.
Published: October 2005

The effects of absolute and relative masker duration were investigated using one- and two-tone forward maskers. In the absolute-duration conditions, the duration (D) of a one-component on-frequency (M1; Dm1-alone) or off-frequency (M2; Dm2-alone) masker or the common duration of a two-component masker (Dm1=Dm2) was varied. Masked threshold increased as duration increased in all three conditions. In the relative-duration conditions, the duration of one masker component was fixed at a relatively long value and the duration of the other component was varied (Dm1≳Dm2 or Dm2≳Dm1). In the Dm1≳Dm2 condition, masked threshold decreased as the duration of Dm2 was increased. In the Dm2≳Dm1 conditions, masked threshold increased and then decreased slightly as the duration of Dm1 was increased. Masked threshold was frequently lower in the M1+M2 than in the M1-alone conditions, indicating psychophysical suppression. Further, masked threshold in the Dm2≳Dm1 condition was always higher than in the corresponding absolute-duration condition (Dm1=Dm2) having the same M1 duration, indicating masker enhancement. A two-stage neural model was proposed to account for these forward-masking data.
Physical limitation on the quality factor of quartz resonators
Authors: El Habti A. , Zarka A. , Bastien F.
Published: October 2005

Several quartz resonators have been studied at very low temperature (1.5 K<T<20 K). The measurement of the resonator quality factor as a function of temperature for different overtones gives a method for distinguishing between different causes of acoustic wave damping. Several quartz resonators with different surface finishing have been measured and compared. The general quality of quartz can be evaluated by x-ray diffraction. Furthermore, the different causes of damping are analyzed theoretically. The conclusions derived both from a theoretical analysis and from the measurements are the following. The intrinsic absorption of crystalline quartz is the main cause of attenuation at T=15 K; but this attenuation decreases very rapidly with temperature (as T4). Therefore, at T=4.2 K, for good resonators, three residual causes can be considered. The first is the damping due to the mounting structure. In fact, this cause diminishes rapidly as the overtone rank increases. For this reason, this damping can be neglected for higher rank overtones. The second is the diffraction of acoustic waves by the quartz surface. This loss can be greatly reduced with good mechanical polishing of the quartz surface. The last reason is the absorption due to a disturbed layer near the surface. The measurement of Q at low temperatures for different overtones provides a tool for the analysis of the different origins of acoustic wave attenuation, especially the attenuation in the superficial layers of the crystal. It seems possible to reach a Q value near the intrinsic crystal quartz limit at 4.2 K, that is to say, about 100 million at a frequency of 10 MHz.
Thermoacoustics in pin-array stacks
Authors: Swift G. W. , Keolian R. M.
Published: October 2005

A new thermoacoustic stack geometry, the pin array, is described. Analytical expressions for velocity and temperature in the pin array are derived, and potential advantages of the pin stack are demonstrated.
Sensitivity of the deconvolution of acoustic transients to Green’s function mismatch
Authors: Broadhead Michael K. , Field Robert L. , Leclere James H.
Published: October 2005

In this paper various measurements of acoustic time series recorded in the Atlantic over source-to-receiver ranges of 600 to 12 900 m are analyzed. The transmitted source signature with a monitor hydrophone mounted on the source array was also recorded. The signature distortion introduced by propagation effects was treated by the use of single-channel deconvolution. In situations where the Green’s function structure is simple (e.g., direct arrival and surface reflection), single-channel deconvolution gave satisfactory results. When multipath effects (due to interaction with layered bottom sediments) were present, it was difficult to get a good source estimate. A way was developed of perturbing the Green’s functions such that the source estimates were guaranteed to improve. In most cases it was found that very small changes could produce significant improvement in the source estimates. This sensitivity was quantified by using the correlation coefficient. This sensitivity is not to be confused with the well-known fact that the single-channel deconvolution problem is ill-posed. That issue was treated separately.
Study of surface elastic wave induced on backing material and diffracted field of a piezoelectric polymer film hydrophone
Authors: Nakamura Yasuhiro , Otani Takahiko
Published: October 2005

A distinctive irregularity in the frequency response of a piezoelectric polymer film hydrophone, which is not predicted by the use of conventional theory, has been observed. It was confirmed in a previous study [Y. Nakamura and T. Otani, Jpn. J. Appl. Phys. Suppl. 31-1 31, 266–268 (1992)] that the irregularity can be attributed to the radial resonance of a surface wave induced by the incident pressure on the hydrophone’s backing material. To estimate theoretically the frequency response of the hydrophone, the transient acoustic field on the receiving surface of the hydrophone was studied by time-domain analysis. The field is theoretically described in the time domain as the superposition of an incident wave, a reflected plane wave, a diffracted edge wave, and a leaky elastic wave that originates from a surface wave propagating along the radius on the hydrophone’s backing material. The validity of the theoretical analysis of the acoustic field on receiving surface is verified by experimental observations. Thus it is shown that the frequency response of the piezoelectric polymer film hydrophone is estimated from the analytical results of the acoustic field.
Sound localization: Effects of reverberation time, speaker array, stimulus frequency, and stimulus rise/decay
Authors: Giguère Christian , Abel Sharon M.
Published: October 2005

This research assessed the ability of human listeners to localize one-third octave noise bands in the horizontal plane. The effects of reverberation time (absorbent versus reverberant room), stimulus center frequency (500, 1000, 2000, and 4000 Hz), stimulus rise/decay time (5 vs 200 ms) and speaker array (frontal versus lateral) were investigated for four subjects using a forced-choice speaker-identification paradigm. Sound localization scores were consistently lower in the reverberant room than in the absorbent room. They also revealed strong frequency and azimuthal effects. The benefit of a shorter rise/decay time was small and limited to low frequencies. The identification of a speaker position depended strongly upon the array in which it was embedded, primarily because localization in the lateral array led to frequency-dependent front/back confusions and response bias. The results also illustrated the importance of choosing a coordinate system based on the auditory cone-of-confusion to analyze localization data for speaker arrays spanning the aural axis.
The perception of temporal modulations by cochlear implant patients
Authors: Busby P. A. , Tong Y. C. , Clark G. M.
Published: October 2005

The perception of temporal modulations of pulsatile electric stimuli was measured in seven cochlear implant patients using the Cochlear Pty. Limited prosthesis. Four patients were postlingually deafened adults and three patients were young adults who were deafened very early in life. The first study measured detection thresholds for modulated pulse duration for a series of modulation frequencies and pulse rates. The shape of the detection thresholds as a function of modulation frequency, the temporal modulation transfer function, often resembled a low-pass filter with a 50–100-Hz cut-off frequency. Thresholds did not markedly vary across the different pulse rates for most patients. Thresholds were less than 10%–20% of the range of usable hearing for most patients. The second study compared detection thresholds for modulated pulse durations around different reference pulse durations: 50, 100, and 300 μs. Detection thresholds were generally proportional to the different reference pulse durations. The third study measured difference limens for the discrimination of modulation depth. The difference limens were similar to the detection thresholds for the same reference pulse duration and pulse rate. The three patients deafened very early in life showed more within-group variation in performance, and their overall levels of performance were poorer than those of the postlingually deafened adults.
Waves in stratified viscoelastic media with microstructure
Authors: Burridge Robert , de Hoop Maarten V. , Hsu Kai , Le Lawrence , Norris Andrew
Published: October 2005

An extension of the O’Doherty and Anstey theory [R. F. O’Doherty and N. A. Anstey, Geophys. Prosp. 19, 430–458 (1971)] is derived for waves in finely layered, anisotropic, viscoelastic media. Multiple scattering effects cause the direct wave to be delayed and broadened, subject to a deterministic integrodifferential delay equation. The kernel depends upon time-domain autocorrelations of reflectivities and the relaxation functions defining the viscoelastic effects. The medium differs from a slowly varying medium by O(ε), and propagation over O(1/ε2) distances is considered. Both smoothly varying media and interfaces are considered simultaneously. A regular perturbation technique is used to show how an approximation to the field may be rapidly calculated. The signal delay predicted by the theory is identified with the retardation (drift) in the equivalent effective medium for the same interval. Numerical examples using synthetic fractal media show the approximate solutions to be in very good agreement with exact computations but 30–30 000 times faster.
Some acoustic effects of listening to noise on speech production
Authors: Tartter Vivien C. , Gomes Hilary , Litwin Elissa
Published: October 2005

An experiment was performed to corroborate earlier findings of a spectral shift in speech produced in 80 dB or greater noise, and to determine whether a spectral shift relative to quiet also occurs at 35- and 60-dB white noise. Both speakers studied incrementally decreased spectral tilt (the amount of energy at low frequencies relative to high) with noise above 35 dB. Both speakers increased duration and average speech amplitude incrementally with each noise increase. One speaker steadily increased fundamental frequency, while the other speaker decreased it. Speech changes are discussed as possible compensations for a distorted sidetone.
Finite element and finite difference models for the fast-field program in outdoor sound propagation
Authors: Gilbert Kenneth E. , Hansen Scott D.
Published: October 2005

The so-called ‘‘fast-field program’’ (FFP) has become a popular method for predicting sound pressure levels in outdoor sound propagation. The method requires the solution of a one-dimensional Green’s function equation. The usual approach in outdoor sound propagation has been to obtain the solution in terms of sinusoids or special functions. Here, a simple direct method is demonstrated that uses either finite elements or finite differences in much the same way as does the parabolic equation method. The finite element method presented here is adapted from a range-dependent FFP model developed for underwater acoustics [K. E. Gilbert and R. B. Evans, in OceanSeismo-Acoustics, edited by T. Akal and J. M. Berkson (Plenum, New York, 1986)]. The finite element FFP has been used successfully for propagation problems in atmospheric acoustics for several years. The finite difference approach, which has been developed only recently, is more straightforward than finite elements but equally accurate. We compare the FFP solutions in terms of speed and accuracy using several existing benchmark problems as test cases.
Low-frequency sound waves associated with avalanches, atmospheric turbulence, severe weather, and earthquakes
Authors: Bedard Alfred J.
Published: October 2005

Recent measurements of naturally occurring atmospheric sound waves near 1 Hz indicate potential uses for monitoring and studying a variety of geophysical processes including avalanches, atmospheric turbulence, severe weather, and earthquakes. A review presents typical signal characteristics including spectral content, showing clear differences between signals from various sources. Possible generation mechanisms are discussed in the context of these data and possible potential practical uses indicated.
Insight into the learning process of neural networks for classifying acoustic signatures
Authors: DeMetz Fred C. , Brooks Lowell W.
Published: October 2005

Feedforward networks employing the backward propagating delta rule for error correction were tested utilizing simulated target signatures and noise to provide insight into the network learning process. Network training histories and weight evolutions were studied for alternating signal and noise input vectors for two network architectures. Contour plots of the input-to-hidden layer weights clearly indicate the relationship between the evolving features of the network weights as they respond to the input signatures during the learning process. Singular value decomposition of the input-to-hidden layer transfer matrix provides insight into the similarities of a trained neural network and a classical matched filter.
A new approach for measurement telephone systems and teleconferencing applications
Authors: Gierlich H. W.
Published: October 2005

New telephone and teleconference systems show increasingly nonlinear time variant behavior. Measurement results of such systems are highly correlated to the measurement procedure used especially for conformance tests and measurements according to several standards. It is highly desirable to achieve comparable measurement results in different labs. These results should correlate well to the subjective impression the user has when telephoning with the measured device. To achieve the desired performance, a suitable test signal must have voice signal properties. On the other hand, measurements have to be carried out in a very short period of time in order to guarantee quasistationary behavior during the time of measurement. To achieve this, a ‘‘composite source signal’’ was developed. The signal consists of a voiced sound on 50 ms at the initial phase. This voiced sound is followed by a measurement signal, a pseudorandom noise sequence. To get a modulation typical for speech, the signal is followed by 100-ms pause. Variations of the signal are described for different measurement applications. Measurement results derived from different systems, including various signal processing techniques, are presented.
Speech synthesis by rule, text-to-speech, and aids for persons with disabilities
Authors: Javkin Hector Raul
Published: October 2005

Speech synthesis by rule and its subsequent development into text-to-speech have progressed into both science and technology for use by the general population, particularly by persons with disabilities. This paper briefly reviews the advances in speech synthesis by rule and text-to-speech and then focuses on a new development—the use of text-to-speech in a speech training system for deaf children. The method uses the acoustic parameters that a text-to-speech system supplies to its formant synthesizer and converts them to pseudoarticulatory parameters equivalent to parameters measured from instruments monitoring the child’s production. For example, the relative frequencies of the nasal pole and nasal zero are converted to a ‘‘nasalization index’’ equivalent to the output of a nasal sensor. The method enables a student to type any utterance she/he wants to learn and see a representation of the articulation of that utterance that corresponds to the feedback received from instruments. Preliminary testing of the use of the method will be reported.
Two-dimensional modeling of low-angle backscatter from geologically realistic seafloors
Authors: Stephen R. A. , Swift S. A.
Published: October 2005

The numerical scattering chamber has been used to quantitatively predict low-angle backscatter coefficients for a suite of seafloor models. A number of issues have been addressed: (a) How finely does seafloor bathymetry need to be resolved in order to predict the backscattered field? Corollary issues in this area are (i) at what resolution can one go from a deterministic to a stochastic representation and (ii) how should one interpolate between bathymetric data points? (b) How important are shear (rigidity) properties of the sediment and basement in a predictive model of seafloor backscatter? (c) How important is intrinsic attenuation (anelasticity) in a predictive model of seafloor backscatter? (d) How do the magnitude and mechanisms of backscatter vary with increasing sediment cover? (e) How effective are isolated facets on the seafloor in generating strong backscatter? (f) Can realistic volume heterogeneities within the sediment and basement generate comparable backscatter levels to realistic seafloor roughness? These issues will be discussed by comparing backscatter coefficients for various seafloor representations.
Viscoelastic characterization of materials using a dynamic hardness tester
Authors: Madigosky W. , Fiorito R. , Überall H.
Published: October 2005

The Shore or IRHD hardness test has been widely used for many years and has become one of the standards for characterizing materials in the rubber and plastics industries. The obtained hardness scale values, ASTM or IRHD, are often related to the static elastic properties of rubber-like materials. The classical Hertz equation has also been used to correlate the hardness scale values to the static elastic properties. Recently, progress has been made on the problem of obtaining dynamic viscoelastic properties through the use of a vibrating spherical indentor and modeling the measured input impedance by the radiation impedance of a sphere radiating into a half-space. In the limiting case where the sphere radius is small, such that ka≪1 for longitudinal waves, it is shown that the measured shear modulus and loss factor are in good agreement with that found using other dynamic methods such as the DMTA or the resonance method. The model is most appropriate for relatively soft materials or very thick hard materials where the thickness of the material can be ignored. The problem of very hard materials and finite thickness where the terminating boundary is important will be discussed.
Metal-Insulator Transition in Disordered Two-Dimensional Electron Systems
Authors: Punnoose Alexander , Finkel'stein Alexander M.
Published: October 2005

We present a theory of the metal-insulator transition in a disordered two-dimensional electron gas. A quantum critical point, separating the metallic phase, which is stabilized by electronic interactions, from the insulating phase, where disorder prevails over the electronic interactions, has been identified. The existence of the quantum critical point leads to a divergence in the density of states of the underlying collective modes at the transition, causing the thermodynamic properties to behave critically as the transition is approached. We show that the interplay of electron-electron interactions and disorder can explain the observed transport properties and the anomalous enhancement of the spin susceptibility near the metal-insulator transition.
Sequence Variants in
SLITRK1
Are Associated with Tourette's Syndrome
Authors: Abelson Jesse F. , Kwan Kenneth Y. , O'Roak Brian J. , Baek Danielle Y. , Stillman Althea A. , Morgan Thomas M. , Mathews Carol A. , Pauls David L. , Rašin Mladen-Roko , Gunel Murat , Davis Nicole R. , Ercan-Sencicek A. Gulhan , Guez Danielle H. , Spertus John A. , Leckman James F. , Dure Leon S. , Kurlan Roger , Singer Harvey S. , Gilbert Donald L. , Farhi Anita , Louvi Angeliki , Lifton Richard P. , Šestan Nenad , State Matthew W.
Published: October 2005

Tourette's syndrome (TS) is a genetically influenced developmental neuropsychiatric disorder characterized by chronic vocal and motor tics. We studied
Slit and Trk-like 1
(
SLITRK1
) as a candidate gene on chromosome 13q31.1 because of its proximity to a de novo chromosomal inversion in a child with TS. Among 174 unrelated probands, we identified a frameshift mutation and two independent occurrences of the identical variant in the binding site for microRNA hsa-miR-189. These variants were absent from 3600 control chromosomes.
SLITRK1
mRNA and hsa-miR-189 showed an overlapping expression pattern in brain regions previously implicated in TS. Wild-type SLITRK1, but not the frameshift mutant, enhanced dendritic growth in primary neuronal cultures. Collectively, these findings support the association of rare
SLITRK1
sequence variants with TS.
Structure and Freezing of MgSiO
3
Liquid in Earth's Lower Mantle
Authors: Stixrude Lars , Karki Bijaya
Published: October 2005

First-principles molecular-dynamics simulations show that over the pressure regime of Earth's mantle the mean silicon-oxygen coordination number of magnesium metasilicate liquid changes nearly linearly from 4 to 6. The density contrast between liquid and crystal decreases by a factor of nearly 5 over the mantle pressure regime and is 4% at the core-mantle boundary. The ab initio melting curve, obtained by integration of the Clausius-Clapeyron equation, yields a melting temperature at the core-mantle boundary of 5400 ± 600 kelvins.
A Fine-Scale Map of Recombination Rates and Hotspots Across the Human Genome
Authors: Myers Simon , Bottolo Leonardo , Freeman Colin , McVean Gil , Donnelly Peter
Published: October 2005

Genetic maps, which document the way in which recombination rates vary over a genome, are an essential tool for many genetic analyses. We present a high-resolution genetic map of the human genome, based on statistical analyses of genetic variation data, and identify more than 25,000 recombination hotspots, together with motifs and sequence contexts that play a role in hotspot activity. Differences between the behavior of recombination rates over large (megabase) and small (kilobase) scales lead us to suggest a two-stage model for recombination in which hotspots are stochastic features, within a framework in which large-scale rates are constrained.
Wolbachia
Establishment and Invasion in an
Aedes aegypti
Laboratory Population
Authors: Xi Zhiyong , Khoo Cynthia C. H. , Dobson Stephen L.
Published: October 2005

A proposed strategy to aid in controlling the growing burden of vector-borne disease is population replacement, in which a natural vector population is replaced by a population with a reduced capacity for disease transmission. An important component of such a strategy is the drive system, which serves to spread a desired genotype into the targeted field population. Endosymbiotic
Wolbachia
bacteria are potential transgene drivers, but infections do not naturally occur in some important mosquito vectors, notably
Aedes aegypti
. In this work, stable infections of
w
AlbB
Wolbachia
were established in
A. aegypti
and caused high rates of cytoplasmic incompatibility (that is, elimination of egg hatch). Laboratory cage tests demonstrated the ability of
w
AlbB to spread into an
A. aegypti
population after seeding of an uninfected population with infected females, reaching infection fixation within seven generations.
Akt-Mediated Phosphorylation of EZH2 Suppresses Methylation of Lysine 27 in Histone H3
Authors: Cha Tai-Lung , Zhou Binhua P. , Xia Weiya , Wu Yadi , Yang Cheng-Chieh , Chen Chun-Te , Ping Bo , Otte Arie P. , Hung Mien-Chie
Published: October 2005

Enhancer of Zeste homolog 2 (EZH2) is a methyltransferase that plays an important role in many biological processes through its ability to trimethylate lysine 27 in histone H3. Here, we show that Akt phosphorylates EZH2 at serine 21 and suppresses its methyltransferase activity by impeding EZH2 binding to histone H3, which results in a decrease of lysine 27 trimethylation and derepression of silenced genes. Our results imply that Akt regulates the methylation activity, through phosphorylation of EZH2, which may contribute to oncogenesis.
Current and Developing Technologies for Monitoring Agents of Bioterrorism and Biowarfare
Authors: Lim Daniel V. , Simpson Joyce M. , Kearns Elizabeth A. , Kramer Marianne F.
Published: October 2005

Recent events have made public health officials acutely aware of the importance of rapidly and accurately detecting acts of bioterrorism. Because bioterrorism is difficult to predict or prevent, reliable platforms to rapidly detect and identify biothreat agents are important to minimize the spread of these agents and to protect the public health. These platforms must not only be sensitive and specific, but must also be able to accurately detect a variety of pathogens, including modified or previously uncharacterized agents, directly from complex sample matrices. Various commercial tests utilizing biochemical, immunological, nucleic acid, and bioluminescence procedures are currently available to identify biological threat agents. Newer tests have also been developed to identify such agents using aptamers, biochips, evanescent wave biosensors, cantilevers, living cells, and other innovative technologies. This review describes these current and developing technologies and considers challenges to rapid, accurate detection of biothreat agents. Although there is no ideal platform, many of these technologies have proved invaluable for the detection and identification of biothreat agents.
Extended-Spectrum β-Lactamases: a Clinical Update
Authors: Paterson David L. , Bonomo Robert A.
Published: October 2005

Extended-spectrum β-lactamases (ESBLs) are a rapidly evolving group of β-lactamases which share the ability to hydrolyze third-generation cephalosporins and aztreonam yet are inhibited by clavulanic acid. Typically, they derive from genes for TEM-1, TEM-2, or SHV-1 by mutations that alter the amino acid configuration around the active site of these β-lactamases. This extends the spectrum of β-lactam antibiotics susceptible to hydrolysis by these enzymes. An increasing number of ESBLs not of TEM or SHV lineage have recently been described. The presence of ESBLs carries tremendous clinical significance. The ESBLs are frequently plasmid encoded. Plasmids responsible for ESBL production frequently carry genes encoding resistance to other drug classes (for example, aminoglycosides). Therefore, antibiotic options in the treatment of ESBL-producing organisms are extremely limited. Carbapenems are the treatment of choice for serious infections due to ESBL-producing organisms, yet carbapenem-resistant isolates have recently been reported. ESBL-producing organisms may appear susceptible to some extended-spectrum cephalosporins. However, treatment with such antibiotics has been associated with high failure rates. There is substantial debate as to the optimal method to prevent this occurrence. It has been proposed that cephalosporin breakpoints for theEnterobacteriaceaeshould be altered so that the need for ESBL detection would be obviated. At present, however, organizations such as the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) provide guidelines for the detection of ESBLs in klebsiellae andEscherichia coli. In common to all ESBL detection methods is the general principle that the activity of extended-spectrum cephalosporins against ESBL-producing organisms will be enhanced by the presence of clavulanic acid. ESBLs represent an impressive example of the ability of gram-negative bacteria to develop new antibiotic resistance mechanisms in the face of the introduction of new antimicrobial agents.
Baylisascariasis
Authors: Gavin Patrick J. , Kazacos Kevin R. , Shulman Stanford T.
Published: October 2005

The raccoon roundworm,Baylisascaris procyonis, is the most common and widespread cause of clinical larva migrans in animals. In addition, it is increasingly recognized as a cause of devastating or fatal neural larva migrans in infants and young children and ocular larva migrans in adults. Humans become infected by accidentally ingesting infectiveB. procyoniseggs from raccoon latrines or articles contaminated with their feces. Two features distinguishB. procyonisfrom other helminthes that cause larva migrans: (i) its aggressive somatic migration and invasion of the central nervous system and (ii) the continued growth of larvae to a large size within the central nervous system. Typically,B. procyonisneural larva migrans presents as acute fulminant eosinophilic meningoencephalitis. Once invasion of the central nervous system has occurred, the prognosis is grave with or without treatment. To date, despite anthelmintic treatment of cases ofB. procyonisneural larva migrans, there are no documented neurologically intact survivors. Epidemiologic study of human cases of neural larva migrans demonstrate that contact with raccoon feces or an environment contaminated by infective eggs and geophagia or pica are the most important risk factors for infection. In many regions of the United States, increasingly large populations of raccoons, with high rates ofB. procyonisinfection, live in close proximity to humans. Although documented cases of human baylisascariasis remain relatively uncommon, widespread contamination of the domestic environment by infected raccoons suggests that the risk of exposure and human infection is probably substantial. In the absence of early diagnosis or effective treatment, prevention of infection is the most important public health measure.