bluuebunny/crossref_metadata_2025 huggingface dataset:
An enhanceosome containing the Jun B/Fra‐2 heterodimer and the HMG‐I(Y) architectural protein controls HPV18 transcription
Authors: Bouallaga Isabelle , Massicard Séverine , Yaniv Moshe , Thierry Françoise
Published: July 2002

Recent studies have reported new mechanisms that mediate the transcriptional synergy of strong tissue‐specific enhancers, involving the cooperative assembly of higher‐order nucleoprotein complexes called enhanceosomes. Here we show that the HPV18 enhancer, which controls the epithelial‐specific transcription of the E6 and E7 transforming genes, exhibits characteristic features of these structures. We used deletion experiments to show that a core enhancer element cooperates, in a specific helical phasing, with distant essential factors binding to the ends of the enhancer. This core sequence, binding a Jun B/Fra‐2 heterodimer, cooperatively recruits the architectural protein HMG‐I(Y) in a nucleoprotein complex, where they interact with each other. Therefore, in HeLa cells, HPV18 transcription seems to depend upon the assembly of an enhanceosome containing multiple cellular factors recruited by a core sequence interacting with AP1 and HMG‐I(Y).
Cell‐nonautonomous function of the retinoblastoma tumour suppressor protein: new interpretations of old phenotypes
Authors: Whyatt David , Grosveld Frank
Published: July 2002

Loss of the retinoblastoma protein (pRb) induces a cell‐nonautonomous defect in both erythroid and neuronal differentiation. It has previously been thought that this reflects a requirement for pRb function in cells that normally support erythropoiesis and neurogenesis, rather than in the erythrocytes or neurons themselves. However, recent studies have challenged this interpretation, and it appears that erythrocytes and neurons themselves have the intrinsic requirement for pRb function. This requirement can be bypassed by signals supplied by wild‐type erythroid or neuronal cells. The existence of such a signalling mechanism has implications not only in understanding pRb function but also in the interpretation of other cell‐nonautonomous phenotypes.
The origin of alternation of generations in land plants: a focus on matrotrophy and hexose transport
Authors: Graham Linda K. E. , Wilcox Lee W.
Published: July 2002

A life history involving alternation of two developmentally associated, multicellular generations (sporophyte and gametophyte) is an autapomorphy of embryophytes (bryophytes + vascular plants). Microfossil data indicate that Mid–Late Ordovician land plants possessed such a life cycle, and that the origin of alternation of generations preceded this date. Molecular phylogenetic data unambiguously relate charophycean green algae to the ancestry of monophyletic embryophytes, and identify bryophytes as early–divergent land plants. Comparison of reproduction in charophyceans and bryophytes suggests that the following stages occurred during evolutionary origin of embryophytic alternation of generations: (i) origin of oogamy; (ii) retention of eggs and zygotes on the parental thallus; (iii) origin of matrotrophy (regulated transfer of nutritional and morphogenetic solutes from parental cells to the next generation); (iv) origin of a multicellular sporophyte generation; and (v) origin of non–flagellate, walled spores. Oogamy, egg/zygote retention and matrotrophy characterize at least some modern charophyceans, and are postulated to represent pre–adaptative features inherited by embryophytes from ancestral charophyceans. Matrotrophy is hypothesized to have preceded origin of the multicellular sporophytes of plants, and to represent a critical innovation. Molecular approaches to the study of the origins of matrotrophy include assessment of hexose transporter genes and protein family members and their expression patterns. The occurrence in modern charophyceans and bryophytes of chemically resistant tissues that exhibit distinctive morphology correlated with matrotrophy suggests that Early–Mid Ordovician or older microfossils relevant to the origin of land plant alternation of generations may be found.
The genetic basis of cardiac function: dissection by zebrafish (Danio rerio) screens
Authors: Warren Kerri S. , Wu Justina C. , Pinet Florence , Fishman Mark C.
Published: July 2002

The vertebrate heart differs from chordate ancestors both structurally and functionally. Genetic units of form, termed ‘modules’, are identifiable by mutation, both in zebrafish and mouse, and correspond to features recently acquired in evolution, such as the ventricular chamber or endothelial lining of the vessels and heart. Zebrafish (Danio rerio) genetic screens have provided a reasonably inclusive set of such genes. Normal cardiac function may also be disrupted by single–gene mutations in zebrafish. Individual mutations may perturb contractility or rhythm generation. The zebrafish mutations which principally disturb cardiac contractility fall into two broad phenotypic categories, ‘dilated’ and ‘hypertrophic’. Interestingly, these correspond to the two primary types of heart failure in humans. These disorders of early cardiac function provide candidate genes to be examined in complex human heart diseases, including arrhythmias and heart failure.
Associating Genes with Gene Ontology Codes Using a Maximum Entropy Analysis of Biomedical Literature
Authors: Raychaudhuri Soumya , Chang Jeffrey T. , Sutphin Patrick D. , Altman Russ B.
Published: July 2002

Functional characterizations of thousands of gene products from many species are described in the published literature. These discussions are extremely valuable for characterizing the functions not only of these gene products, but also of their homologs in other organisms. The Gene Ontology (GO) is an effort to create a controlled terminology for labeling gene functions in a more precise, reliable, computer-readable manner. Currently, the best annotations of gene function with the GO are performed by highly trained biologists who read the literature and select appropriate codes. In this study, we explored the possibility that statistical natural language processing techniques can be used to assign GO codes. We compared three document classification methods (maximum entropy modeling, naïve Bayes classification, and nearest-neighbor classification) to the problem of associating a set of GO codes (for biological process) to literature abstracts and thus to the genes associated with the abstracts. We showed that maximum entropy modeling outperforms the other methods and achieves an accuracy of 72% when ascertaining the function discussed within an abstract. The maximum entropy method provides confidence measures that correlate well with performance. We conclude that statistical methods may be used to assign GO codes and may be useful for the difficult task of reassignment as terminology standards evolve over time.
A simplified intensity modulated radiation therapy technique for the breast
Authors: Chui Chen‐Shou , Hong Linda , Hunt Margie , McCormick Beryl
Published: July 2002

A simplified intensity modulated radiation therapy (sIMRT) technique for the breast is presented. The technique aims to produce a uniform dose distribution in the entire breast volume. Using the standard tangential beam arrangement, we first determine for each pencil beam the midpoint of the segment that intersects the treatment volume. The dose to the midpoint from the open field is then calculated. The intensity of the pencil beam is determined as proportional to the inverse of the open field dose. With this intensity modulated beam, the dose delivered to the midpoint of each pencil beam segment that intersects the treatment volume is now equalized. The dose distribution in the entire treatment volume is nearly as uniform as can be achieved under the given beam arrangement. Fifteen left breast patients were planned with the sIMRT technique. For comparison, the same group of patients was also planned with the standard wedged pair technique and the full‐fledged volume‐based IMRT (vIMRT) technique. Both the sIMRT and the vIMRT techniques achieved more homogeneous dose in the treatment volume than the standard plan. Doses to the heart, the ipsilateral lung, and the contralateral breast were also reduced. The planning time and the treatment time for the sIMRT technique were comparable to that of the standard technique, and significantly less than that required by the vIMRT technique. The sIMRT technique is practical for large‐scale implementation in a busy clinic without requiring significant increase of resources.
Monte Carlo calculations and GafChromic film measurements for plugged collimator helmets of Leksell Gamma Knife unit
Authors: Cheung Joel Y. C. , Yu K. N. , Ho Robert T. K. , Yu C. P.
Published: July 2002

The Monte Carlo technique and GafChromic films were employed to verify the accuracy of the dose planning system used in Gamma Knife (type B) radiosurgery when plugged collimator helmets were used. The EGS4 Monte Carlo code was used to calculate the dose distribution along the x, y, and z axes when a single shot was delivered at the center point (unit center point: of a spherical polystyrene phantom, with gamma angle of 90°. Two different sizes of the plugged collimator helmets, 4 and 18 mm, were studied. Two typical plugged patterns, 51 plugs and 99 plugs along the y direction, were examined. The results of our Monte Carlo trials showed good consistency with GammaPlan calculations and GafChromic film measurements. Furthermore, the Monte Carlo results showed that radiation leakage from the plugs was too small to affect the overall isodose curve distribution even when the heavily plugged pattern of up to 99 plugs was employed. The results of this project provide confidence to all Gamma Knife centers using the Leksell GammaPlan treatment planning system.
Surface charges and fields of simple circuits
Authors: Preyer Norris W.
Published: July 2002

Interest in the surface charges on circuits, and their utility in the conceptual understanding of circuit behavior, has recently increased. Papers and textbooks have discussed surface charges either with qualitative diagrams or analytic results for very special geometries. Here, I present the results of numerical calculations showing the surface charges on several simple resistor-capacitor circuits. Surface charges are seen to guide the motion of charges and create the appropriate electric potential and Poynting vectors for the circuit, and hence are an important factor in the teaching of circuit theory.
Image charges revisited: Beyond classical electrostatics
Authors: Roulet Bernard , Saint Jean Michel
Published: July 2002

The method of images in electrostatics seems to lead to a paradox: The charges induced on the surface of a grounded conductor by an external point charge do not spread out although the electrostatic field is normal to the surface. This effect can be understood if one takes into account the spreading of the charges inside the conductor due to the kinetic energy (either thermal or quantum mechanical) of the electrons. Corrections to the usual electrostatics of images are then calculated (in particular, it is shown that the conductor surface is not an exact equipotential) when the distance of the point charge to the surface is much larger than the screening length. Applications are discussed.
A computational acoustic field reconstruction process based on an indirect boundary element formulation
Authors: Zhang Zhidong , Vlahopoulos Nickolas , Raveendra S. T. , Allen T. , Zhang K. Y.
Published: July 2002

The objective of the work presented in this paper is to develop a computational capability based on the indirect boundary element method (IBEM) for evaluating appropriate velocity boundary conditions on an assembly of piston type sources in order to recreate a prescribed acoustic field. Information for the acoustic pressure of the original acoustic field at certain field points constitutes the input to the developed process. The velocities on the piston type sources are computed from transfer functions evaluated between the field points where the acoustic pressure of the original field is prescribed and the velocity boundary condition on each element of the generic source. The IBEM is employed for computing the transfer functions in order to accommodate the presence of openings in the model and radiation from both sides of the piston type sources. Simulating the generic source as a thin surface that radiates from both sides eliminates the presence of irregular frequencies in the analysis. A singular value decomposition (SVD) solver is integrated with the IBEM computations in order to evaluate the velocity boundary conditions from the transfer functions. The number of field points where the acoustic pressure is defined can be considerably smaller than the number of elements where the velocity is computed. The solution that demonstrates the smallest magnitude is selected from all possible solutions. An algorithm is also developed for identifying the optimum field points where the acoustic pressure of the original field must be prescribed. The optimum field points are selected from a set of prescribed candidate points. The number of optimum points is considered smaller than the number of elements where the velocity is computed. The properties of the transformation matrix and the quality of the reconstruction depend on the location of the field points. Thus, the selection of the optimum points is based on achieving the highest possible orthogonality among the vectors that comprise the range of the transformation matrix. Several validation and application cases are presented.
Minimum entropy deconvolution of pulse-echo signals acquired from attenuative layered media
Authors: Olofsson Tomas , Stepinski Tadeusz
Published: July 2002

In this article deconvolution of ultrasonic pulse-echo data acquired from attenuative layered media is considered. The problem is divided in two subproblems: treating the sparse reflection sequence caused by the layered structure of the media and treating the frequency-dependent attenuation. The first subproblem is solved by means of joint maximum a posteriori estimation of the assumed zero mean, white, nonstationary reflection sequence and its corresponding sequence of unknown standard deviations. This approach leads to an algorithm that seeks minimum entropy solutions for the reflection sequence and therefore the algorithm serves as a novel link between the classical Wiener filter and methods for sparse or minimum entropy deconvolution. The second subproblem is solved by introducing a new signal processing-oriented, linear discrete-time model for frequency-dependent attenuation in isotropic and homogeneous media. The deconvolution algorithm is tested using simulated data and its performance for real normal incidence pulse-echo data from a composite material is also demonstrated. The results show that the algorithm, in combination with the attenuation model, yields estimates that reveal the internal structure of the composite and, thus, simplify the interpretation of the ultrasonic data.
Effects of low-pass filtering on the intelligibility of speech in quiet for people with and without dead regions at high frequencies
Authors: Vickers Deborah A. , Moore Brian C. J. , Baer Thomas
Published: July 2002

A dead region is a region of the cochlea where there are no functioning inner hair cells (IHCs) and/or neurons; it can be characterized in terms of the characteristic frequencies of the IHCs bordering that region. We examined the effect of high-frequency amplification on speech perception for subjects with high-frequency hearing loss with and without dead regions. The limits of any dead regions were defined by measuring psychophysical tuning curves and were confirmed using the TEN test described in Moore et al. [Br. J. Audiol. 34, 205–224 (2000)]. The speech stimuli were vowel–consonant–vowel (VCV) nonsense syllables, using one of three vowels (/i/, /a/, and /u/) and 21 different consonants. In a baseline condition, subjects were tested using broadband stimuli with a nominal input level of 65 dB SPL. Prior to presentation via Sennheiser HD580 earphones, the stimuli were subjected to the frequency-gain characteristic prescribed by the “Cambridge” formula, which is intended to give speech at 65 dB SPL the same overall loudness as for a normal listener, and to make the average loudness of the speech the same for each critical band over the frequency range important for speech intelligibility (in a listener without a dead region). The stimuli for all other conditions were initially subjected to this same frequency-gain characteristic. Then, the speech was low-pass filtered with various cutoff frequencies. For subjects without dead regions, performance generally improved progressively with increasing cutoff frequency. This indicates that they benefited from high-frequency information. For subjects with dead regions, two patterns of performance were observed. For most subjects, performance improved with increasing cutoff frequency until the cutoff frequency was somewhat above the estimated edge frequency of the dead region, but hardly changed with further increases. For a few subjects, performance initially improved with increasing cutoff frequency and then worsened with further increases, although the worsening was significant only for one subject. The results have important implications for the fitting of hearing aids.
Second-order temporal modulation transfer functions
Authors: Lorenzi Christian , Soares Catherine , Vonner Thomas
Published: July 2002

Detection thresholds were measured for a sinusoidal modulation applied to the modulation depth of a sinusoidally amplitude-modulated (SAM) white noise carrier as a function of the frequency of the modulation applied to the modulation depth (referred to as fm′). The SAM noise acted therefore as a “carrier” stimulus of frequency fm, and sinusoidal modulation of the SAM-noise modulation depth generated two additional components in the modulation spectrum: fm−fm′ and fm+fm′. The tracking variable was the modulation depth of the sinusoidal variation applied to the “carrier” modulation depth. The resulting “second-order” temporal modulation transfer functions (TMTFs) measured on four listeners for “carrier” modulation frequencies fm of 16, 64, and 256 Hz display a low-pass segment followed by a plateau. This indicates that sensitivity to fluctuations in the strength of amplitude modulation is best for fluctuation rates fm′ below about 2–4 Hz when using broadband noise carriers. Measurements of masked modulation detection thresholds for the lower and upper modulation sideband suggest that this capacity is possibly related to the detection of a beat in the sound’s temporal envelope. The results appear qualitatively consistent with the predictions of an envelope detector model consisting of a low-pass filtering stage followed by a decision stage. Unlike listeners’ performance, a modulation filterbank model using Q values ⩾2 should predict that second-order modulation detection thresholds should decrease at high values of fm′ due to the spectral resolution of the modulation sidebands (in the modulation domain). This suggests that, if such modulation filters do exist, their selectivity is poor. In the latter case, the Q value of modulation filters would have to be less than 2. This estimate of modulation filter selectivity is consistent with the results of a previous study using a modulation-masking paradigm [S. D. Ewert and T. Dau, J. Acoust. Soc. Am. 108, 1181–1196 (2000)].
Second-order modulation detection thresholds for pure-tone and narrow-band noise carriers
Authors: Lorenzi C. , Simpson M. I. G. , Millman R. E. , Griffiths T. D. , Woods W. P. , Rees A. , Green G. G. R.
Published: July 2002

Modulation perception has typically been characterized by measuring detection thresholds for sinusoidally amplitude-modulated (SAM) signals. This study uses multicomponent modulations. “Second-order” temporal modulation transfer functions (TMTFs) measure detection thresholds for a sinusoidal modulation of the modulation waveform of a SAM signal [Lorenzi et al., J. Acoust. Soc. Am. 110, 1030–2038 (2001)]. The SAM signal therefore acts as a “carrier” stimulus of frequency fm, and sinusoidal modulation of the SAM signal’s modulation depth (at rate fm′) generates two additional components in the modulation spectrum at fm−fm′ and fm+fm′. There is no spectral energy at the envelope beat frequency fm′ in the modulation spectrum of the “physical” stimulus. In the present study, second-order TMTFs were measured for three listeners when fm was 16, 64, and 256 Hz. The carrier was either a 5-kHz pure tone or a narrow-band noise with center frequency and bandwidth of 5 kHz and 2 Hz, respectively. The narrow-band noise carrier was used to prevent listeners from detecting spectral energy at the beat frequency fm′ in the “internal” stimuli’s modulation spectrum. The results show that, for the 5-kHz pure-tone carrier, second-order TMTFs are nearly low pass in shape; the overall sensitivity and cutoff frequency measured on these second-order TMTFs increase when fm increases from 16 to 256 Hz. For the 2-Hz-wide narrow-band noise carrier, second-order TMTFs are nearly flat in shape for fm=16 and 64 Hz, and they show a high-pass segment for fm=256 Hz. These results suggest that detection of spectral energy at the envelope beat frequency contributes in part to the detection of second-order modulation. This is consistent with the idea that nonlinear mechanisms in the auditory pathway produce an audible distortion component at the envelope beat frequency in the internal modulation spectrum of the sounds.
Hearing protector attenuation: Models of attenuation distributions
Authors: Murphy William J. , Franks John R. , Krieg Edward F.
Published: July 2002

Current hearing protector rating standards estimate the protection performance for a given frequency as the mean attenuation minus a multiple of the standard deviation. Distributions of real-ear attenuation at threshold data are fit with maximum likelihood estimation procedures using both normal and mixed-normal models. Attenuations from six hearing protectors, Bilsom UF-1 earmuff, Bilsom Quietzone, E•A•R® Classic®, E•A•R® EXPRESS® Pod Plugs®, Howard Leight MAX, and Wilson EP100 earplugs, measured with a subject-fit protocol are reported. The mixed-normal (bimodal) model provides a better fit to the empirical data than the unimodal model for most frequencies and protectors. Primarily, the bimodal model fits the shape of the distributions caused by data from poorly-fit protectors. This paper presents an alternative method for estimating the protection performance either with the more accurate bimodal model or directly from the empirical cumulative distributions of the attenuation data.
An experimental study of tire standing waves
Authors: Cusumano Joseph P. , Zolock John D.
Published: July 2002

Small-scale test rigs for experimental investigations of tire standing wave instability are described. The rigs are used in experiments in which tire rotational speed is gradually increased past the critical speed at which standing waves appear around the circumference of the tire. Detailed results from one of the rigs are presented. Images grabbed from live video are processed to extract the spatial structure of the standing waves. Frequency and time domain vibrational data and temperature histories are also collected and presented. The spatial frequencies, strains, and logarithmic decrement for the standing wave are computed for four different tire pressures, and the results are shown to be in qualitative agreement with numerical results of previous researchers.
Condition monitoring on engines using response noise estimates and reconstructed excitation
Authors: Abram Kwin , Hayes Paul , Bernhard Robert
Published: July 2002

A condition monitoring technique is developed for engines and similar machines whereby only external response measurements are used to determine the condition of the machine. The method assumes the response signal is composed of components due to an event of interest and other events which are not of interest. The response due to the events of no interest are treated as deterministic noise. An identification process is used to identify the noise and the frequency response function between the event of interest and the response. This identification procedure uses operating conditions which span the faults of interest. This model is used in an inverse filter process to determine the excitation during operation. Signal filtering and time gating are used to enhance the procedure. The method is verified for combustion faults on a diesel engine. [See NOISE-CON Proceedings for full paper.]
Extraction of periodic modulation of rotational speed from machinery vibration signals using a modulation template matching algorithm
Authors: Van Dyke Michael B. , Reichard Karl , Swanson Dave
Published: July 2002

The periodic modulation of the rotational speed of a machine element, such as a bearing element or a gear, is recognized as a valuable feature in characterizing the physical condition of the machine component. A time-domain template-matching algorithm is introduced as a robust nonlinear frequency modulation estimation technique for extracting this feature from perturbations in the acoustic signal emitted from a damaged machine component. The technique is applied to both synthetic signals as well as real accelerometer and microphone data taken from damaged railroad car roller bearings. The results are compared with those obtained using a standard baseband phase demodulation technique. Although the template-matching algorithm is computationally more expensive, it can be applied directly to a limited-duration, raw input signal, unlike the baseband demodulation technique, which relies on bandpass filtering and synchronous averaging over a lengthy time duration. [See NOISE-CON Proceedings for full paper.]
Acoustic tomography in the autonomous oceanographic sampling network
Authors: Schmidt Henrik , Bellingham James , Elisseeff Pierre , Deffenbaugh Max
Published: July 2002

Ocean acoustics plays a central role in the new autonomous oceanographic sampling network (AOSN) concept. Thus, as in most other underwater systems, acoustics provides the only reliable means for wireless communication and navigation. Also, the sensor suite applied in the AOSN includes various sonars for object avoidance and imaging, and acoustic Doppler current profilers. By adding a tomographic component, the performance of the AOSN in highly dynamic littoral environments can be significantly improved. Thus, the tomography can provide a low resolution, but also a synoptic image of the oceanography which can eliminate the space-time aliasing inherent to the point measurements made by the AUVs. Using real-time processing the tomographic map is used to adaptively focus the AUV measurements in areas with high gradients or large uncertainty. In addition, the AUVs can enhance the tomographic coverage by equipping them with acoustic sources. The feasibility of this acoustically focused oceanographic sampling (AFOS) concept was investigated in the June 1996 Haro Strait PRIMER experiment. The experiment clearly demonstrated the feasibility of the tomographic components. Robust and efficient algorithms have been developed, capable of performing real-time tomographic inversion within a littoral AOSN. The results of the experiment are reviewed, including frontal mapping performed in more than 80 AUV missions. The experiment also clearly demonstrated the severity of the littoral acoustic environment in terms of ambient noise, reverberation, and variability, significantly affecting the robustness of the acoustic communication and navigation systems crucial to the AOSN. [Work supported by ONR.]
Twinkling of low-frequency tones from a moored source transmitting through and away from the surf zone
Authors: D’Spain Gerald L. , Berger Lewis P. , McArthur K. Megan , Hodgkiss William S. , Ritter Michael J. , Kuperman William A.
Published: July 2002

During a recent seismoacoustics experiment, a moored, near-bottom, source just outside the surf zone (approximately 500-m seaward) in 9-m deep water, transmitted 8 tones from 70 to 700 Hz. Recordings were made by several fixed sensor systems, including: 1) a bottom hydrophone/3-component geophone package 15-m distant; 2) two horizontal bottom hydrophone arrays in a nearly perpendicular configuration in 12-m water 1.23 km away and 1.06 km farther offshore; and 3) five 3-component geophones buried at approximate 14-m spacing across the beach at 480–530 m range. These data were used to create 5-min time series of the spectral levels and directionality of the tones every 1/2 h over an 8-h period. Results indicate that within a 5-min period, fluctuations of 10–15 dB occur in the bottom hydrophone array signal levels which, typically, are not correlated from frequency to frequency. Fluctuations in the land geophone data are somewhat smaller, and only the 2 or 3 highest-frequency tones are detectable. Variations in water depth, measured by a package also located just outside the surf zone, are used with an adiabatic normal mode model to predict the fluctuation effects of ocean surface wave activity alone. [Work supported by ONR, Code 32].
A review of the shelf edge studies acoustic measurement experiments—SESAME I and II
Authors: Field Robert L.
Published: July 2002

The shelf edge studies acoustic measurement experiments (SESAME) were performed in the North West Approaches to the British Isles. The SESAME experiments were a collaborative effort between the Natural Environment Research Council, the Defence Research Agency (both of the United Kingdom), and the Naval Research Laboratory (Stennis Space Center). The objective of the experiments was to determine the effects of internal waves formed at the shelf edge on acoustic propagation. Oceanographic measurements were gathered continuously over an 18-month period and acoustic experiments were performed during the summers of 1995 and 1996. Measurements of temperature, conductivity, and current were made within the water column, sediment cores were taken of the ocean bottom, and SAR images of the sea surface were taken of the experimental area. Range and time-varying acoustic experiments were performed in the along shelf and cross shelf directions over a frequency band of 100–2100 Hz. Both narrow- and broadband (frequency modulated) signals were transmitted. A review of the two experiments and some of the oceanographic and acoustic data collected will be presented. [Work supported by ONR and NRL.]
Modeling of the out-of-plane pulse propagation in the SWARM95 experiment
Authors: Tang X. , Badiey M.
Published: July 2002

The acoustical data collected in the shallow water acoustics in a random medium (SWARM95) experiment on the continental shelf off New Jersey in 1995 have shown that the temporal variations of the time series of the airgun signals (center frequency 75 Hz and bandwidth 50 Hz) are both range and azimuthal dependent. A full-wave broadband PE model is used to simulate such shallow water pulse propagation at different horizontal bearings. The time-dependent shallow water internal wave fluctuations constructed with a broad spectrum of excitation and the solitonlike thermocline displacements based on the in situ observations are included in the numerical simulation as well as the bathmetry. The vertical wavefronts and the 2-h time histories of the repeated transmissions from airgun positions above and below the thermocline are calculated and displayed. The simulated data and the experimental data of the receiver arrays at different locations with an approximately 10-km cross-range distance are compared. The results suggest that the azimuthal dependence of the received signals correlate to both the internal wave fields and the bathmetric variations.
Issues in mechanical draft cooling tower noise
Authors: Jameson Randall W.
Published: July 2002

Sound from cooling towers in power plants can be a significant contributor to the overall noise level at plant boundaries. Because of their size, cooling towers cannot be treated as a single noise source, and special considerations must be made in determining the contribution of the cooling tower to the overall plant noise level. The significant sound sources of a cooling tower will be identified, as well as how the total sound emitted from a cooling tower is affected by operational and design changes in these sources. Data from field sound measurements of cooling towers will be used to illustrate some of these points. Discussion of measures to reduce cooling tower sound levels in a new installation will also reviewed. [See NOISE-CON Proceedings for full paper.]
Spatial scales on fluid-loaded plates and shells
Authors: McDaniel J. Gregory , Allik Henno , Haberman Robert
Published: July 2002

This paper attempts to quantify in a general way the spatial scales that occur on fluid-loaded plates and shells for the purpose of assessing various modeling techniques. Modelers using the SARA finite-element code typically follow a ‘‘quarter-wavelength rule,’’ which states that the size of a quadratic element should be less than a quarter of the minimum wavelength in the problem. The minimum wavelength for fluid-loaded plates and shells is often the flexural wavelength. Questions naturally arise regarding the accuracy of this rule near discontinuities. In this paper, a straightforward theoretical justification for the quarter-wavelength rule is presented in terms of a Taylor series expansion of the wave field. This justification is extended to the local evanescent fields generated near discontinuities. The complex wave numbers describing these fields, as well as SARA finite-element data for some canonical problems, are examined to determine the expected accuracy of a given discretized model. The fundamental conclusion is that modeling rules based on the propagating wave fields also give convergent answers for the evanescent fields generated near discontinuities.
Optimal processing and performance evaluation of passive acoustic systems
Authors: Greene Peter L.
Published: July 2002

The acoustic spectrogram is a fundamental input for many underwater acoustic signal detectors. This presentation describes an effort to place theoretical bounds on the performance of these detectors and to provide insight into the structure of practical processors. The presentation begins with a description of the Neyman–Pearson optimal detector, the likelihood ratio test, and its use for signal detection in colored Gaussian noise scenarios. The presentation continues by developing successively more complex detection scenarios that necessitate the use of background estimation and, consequently, the generalized likelihood ratio test (GLRT). Parameter estimation from several common noise spectral estimation (NSE) techniques is included in the GLRT detection scenarios. In addition, the presentation develops guidelines for matching NSE parameter settings to signal characteristics. Then, the relationships among several relevant signal-to-noise ratios (SNRs) is developed and their correlation with detection performance is considered. Finally, the presentation considers departures from the Gaussian distribution assumption for background and signal processes and the resulting consequences. a)Ensign, USN
A tomographic algorithm applied to imaging bubbly water
Authors: Rouseff Daniel , Henyey Frank S.
Published: July 2002

A tomographic algorithm believed appropriate for reconstructing the effective index of the refraction structure of bubbly water is developed. The method is optimum in a least-squares sense if the medium can be interpreted as a realization of a Gaussian random process. In contrast to other tomographic algorithms, it can be applied when the number of ray paths is sparse. The measured input may be acoustic travel time, to reconstruct sound speed, or log intensity, to reconstruct attenuation. The data are multiplied by a precalculated matrix that depends on the geometry and the assumed autocorrelation function of the medium. This gives the weights used in the imaging step. To produce an image, the data from each ray are weighted, then backprojected over a smeared region centered about the original ray path. Superimposing the weighted smeared images produces the final reconstruction. The computationally expensive work can be done prior to processing any data, giving the potential to do nearly real-time imaging. The algorithm is tested in numerical simulations of the March 1997 shallow water bubbles experiment. The locations of the sources and receivers are varied. The effects of environmental mismatch are studied.
Forward projection of transient signals obtained from a fiber-optic pressure sensor
Authors: Clement Gregory , Liu Ruiming , Letcher Stephen , Stepanishen Peter
Published: July 2002

An analytical/experimental approach is presented to reconstruct the space-time pressure field in a plane and forward project the resultant space-time pressure field using tomographic and wave-vector frequency-domain methods. Transient pressure signals from an underwater ultrasonic planar transducer are first measured using a fiber-optic pressure sensor which is scanned across a plane at a fixed distance from the transducer. The resulting spatial line integrals in the plane are time-dependent signals that are first used to reconstruct the space-time pressure field in the plane via simply implemented tomographic methods. These signals are then used to forward project the space-time pressure field to arbitrary planes further from the transducer. Numerical results will be presented for transient signals to illustrate both the projection and the detection techniques. The results of the projected fields will be compared at various distances for synthetic signals and experimental data. [Work supported, in part, by the URI Ocean Technology Center and by ONR.]
A laser-based experimental-numerical technique for evaluating the bulk and shear dynamic elastic moduli of viscoelastic materials
Authors: Stone T. Shane , Willis R. Lance , Berthelot Yves H.
Published: July 2002

A laser-based numerical/experimental technique suitable for laboratory studies has been designed and tested to simultaneously measure the bulk and shear complex dynamic moduli of a viscoelastic sample excited harmonically in the 0.5–3 kHz range by a shaker. The method consists of measuring the dynamic response (amplitude and phase) of the sample at five surface points with noncontact laser Doppler interferometric probes measuring in-plane (tangential) and out-of-plane (normal) surface velocities. To determine the bulk and shear moduli as functions of frequency, the measured dynamic surface response is matched to the predictions obtained from a finite element model of the sample in which the two complex elastic moduli are the adjustable parameters. This inversion procedure is based on a classical multi-dimensional direction set method (Powell’s method) of optimization theory. The results are based on measurements made in air under standard pressure and temperature conditions. However, work is under way to build a similar system that would allow for measurements at high static pressure and controlled temperature. [Work supported by ONR, Code 334.]
On the estimation of uncertainties for the calibration of standard accelerometers using the fringe counting method
Authors: Silva-Pineda Guillermo
Published: July 2002

The uncertainties calculation procedure for the estimation of errors when the fringe counting method is used to get the sensitivity of standard accelerometers is developed. The fringe counting method is used in the frequency range from 50 to 800 Hz and into a dynamic range from 20 to 100 m s−2. Also, the reference condition is set up at 160 Hz and 50 m s−2, where the main objective is to get the lowest uncertainty between all the frequency and dynamic ranges mentioned above. This calculation procedure agrees with both the ‘‘Guide to the expression of uncertainty in measurement’’ and the ISO 5347-1 ‘‘Primary vibration calibration by laser interferometry.’’ Furthermore, type B uncertainties are received from specific technical information from the equipment used during the calibration procedure and the type A uncertainty is received from periodic measurements performed on the standard accelerometer which have been monitored. Data from primary calibrations have been used to validate the estimation of uncertainties. Moreover, this paper shows the differences on the levels of error sources involved in a standard accelerometer calibration.
Transient axisymmetric response of a finite cylindrical shell with internal fluid loading. Part 2. Comparison of theory and experiment
Authors: Hassan Scott E. , Stepanishen Peter R.
Published: July 2002

An experimental investigation addressing the transient axisymmetric response of a finite length cylindrical shell with a base plate and internal fluid loading is presented. The configuration consists of a steel cylindrical shell with a circular base plate welded to one end. The shell and base plate contain an internal volume of water with a free surface. Data are presented for the special case of an axisymmetric transient excitation due to a force impulse hammer acting on the base plate. The in-vacuo and fluid-loaded response of the shell and base plate measured with an accelerometer will be presented and compared with numerical results. Transient field point pressure measurements taken with a hydrophone will also be presented and compared with numerical results. The agreement between experiment and numerical results is noted to be excellent.
Nonstationary vibrations of an elastic nonlinear cylindrical shell in external contact with an elastic isotropic medium.
Authors: Yuriy A. Rossikhin , Shitikova Marina V.
Published: July 2002

Nonlinear nonstationary vibrations of an infinite elastic isotropic cylindrical shell of constant thickness in welded or smooth contact with a continuous elastic isotropic medium are considered. Nonstationary vibra- tions are excited by snap-action loads, resulting in two types of cylindrical shock waves propagating in the medium. Behind the wavefronts, the solution for the desired functions is constructed along the rays in terms of a power series (ray series), whose coefficients are the discontinuities in various orders of partial derivatives of the functions to be found with respect to time. A variable value is the time needed for a disturbance to propagate along the ray from the point under consideration up to the wavefront. In so doing, the power of the variable value corresponds to the order of partial time derivative of the desired function.
Investigation on relationships between STI and speech intelligibility in listening tests on Japanese language for sound system design of auditoria
Authors: Komoda Motoo
Published: July 2002

In order to clarify the applicability of STI as a parameter in sound system design, a series of investigations on speech intelligibility were carried out. This report summarizes the results of the investigation on the following items: (1) STI round-robin tests with different measuring systems; (2) relationships between measured STI and the intelligibility in listening tests on Japanese language; (3) STI measurements in various types of auditoria in Japan.
Flow-induced self noise in hydrophones resting on the sea floor
Authors: Strasberg M.
Published: July 2002

Measurements of underwater sound at very low frequencies made with a hydrophone resting on the sea bottom may be contaminated by flow noise. Although the flow velocity may be negligible at the very bottom, the turbulent boundary layer of natural currents flowing above the bottom induces nonacoustic local pressure fluctuations on the bottom which may cause self-noise interference. Estimates of these pressure fluctuations are presented based on pressures measured on the ground in an open field in the presence of wind, using dimensional analysis to extrapolate from air to water. The estimated values are compared with underwater ambient noise levels measured with bottomed hydrophones to determine how large the current must be to cause concern with self-noise interference at very low frequencies. Methods for reducing the interference are discussed.
Education in acoustics and noise control
Authors: Kihlman Tor
Published: July 2002

The tasks of designing quieter products, a quieter society, and acoustically good environments demand skilled engineers. It is essential to develop good curricula for the education of the engineers, also considering the difficulties that many students have in developing a deep understanding in the acoustic discipline. However, it is also necessary to develop strategies within the university in order to attract some of the best students. Such strategies may partly be based on judgments and demands from industry and society. Results of some inquiries to industry will be reported. They show that the universities’ own judgments and experiences from the past also need to be taken into account, otherwise the tasks will be difficult to solve.
Mass flux resonance and the threshold for light emission in single bubble sonoluminescence
Authors: Holt R. Glynn , Gaitan D. Felipe
Published: July 2002

The acoustic pressure, equilibrium, and time-varying radius of single air bubbles acoustically levitated in a 20-kHz acoustic standing wave have been measured in the region of parameter space where light emission from bubbles is observed. A resonancelike response of the bubble oscillation is observed along the path in parameter space to which the bubble equilibrium radius is constrained by an unknown mass flux mechanism. A partial explanation of the anomalous stability observed previously [R. G. Holt and D. F. Gaitan, Phys. Rev. Lett. 77, 3791 (1996)] is presented. The bubble response is correlated with the threshold for light emission and light intensity as a function of increasing acoustic pressure. Finally, the measured bubble response is shown to agree with the Rayleigh–Plesset equation, even though the theory cannot predict the equilibrium path in parameter space. [Work supported by NASA.]
The psychophysics of complex envelope processing
Authors: Bacon Sid P.
Published: July 2002

During the past decade, psychophysical research on the processing of amplitude modulation (AM) has expanded to relatively complex situations where subjects are asked to make detection or discrimination judgments regarding some aspect of AM in the presence of competing AM. This AM-masking paradigm has been referred to as modulation masking when the signal and masker carriers are overlapping noise bands, and as modulation detection (or discrimination) interference (MDI) when the two carriers are sinusoids. An important finding in the MDI paradigm is that this AM masking occurs even when the sinusoidal carriers are 2 or more oct apart, and hence under conditions where peripheral interactions within a single auditory filter are unlikely. It also occurs when the signal and masker carriers are presented to opposite ears, further evidence that at least some of the AM masking is occurring at a relatively central site in the auditory system. Finally, a common finding in these masking experiments is a rather broad tuning for the detection (or discrimination) of AM. Whether this turning should be taken as evidence for AM channels in the auditory system will be discussed, as will recent research on subjects with cochlear hearing loss. [Work supported by NIDCD.]
Effects of transducer mass on resonance frequency and quality factor of free–free bars
Authors: Guo Qiushuang , Brown David
Published: July 2002

The use of resonant free–free bars to determine the elastic properties of materials has been presented previously [Garrett, ‘‘Resonant acoustic determination of elastic moduli,’’ J. Acoust. Soc. Am. 88, 210–221; Brown, ‘‘Characterization of viscoelastic materials using the resonant modes of a ‘free–free’ bar,’’ J. Acoust. Soc. Am. 94, 2294(A) (1993)]. The preferred excitation and detection method is based on electrodynamic transduction in which a coil of wire is attached to each bar end, which in turn is subjected to a strong magnetic field. The effect of the added transducer mass on the observed resonant frequency and quality factors of longitudinally driven bars used to determine Young’s modulus and damping will be reported. [Work supported by the University of Massachusetts Dartmouth.]