bluuebunny/crossref_metadata_2025 huggingface dataset:
An update on the multi-static model, SPADES, and its application to the reverberation workshop test suite
Authors: Brooke Gary H.
Published: September 2008

GD Canada has developed a multi-static sonar performance prediction capability called SPADES. SPADES was applied to the Reverberation Workshop test cases [November 9–13, 2006, Austin, TX] and reported consistent behavior with other models in all cases except those involving refraction. This paper outlines recent progress with the SPADES model to include multi-static target echo, Nx2D propagation environments, and its current status with respect to the reverberation workshop test suite. In particular, it is shown that the model now aligns closer with the norm in all of the test cases. Sensitivities in the SPADES model to workshop problem parameters are detailed with a view to understanding the remaining discrepancies. Included also are new results for range-dependent test cases. [Work is funded as an internal R&D program at GD Canada.]
Noise in modular dwellings
Authors: Beristain Sergio
Published: September 2008

Construction of modular dwellings in Mexico usually has had the problem of the joints; examples are given in some cases where this prob- lem shows up as a low-quality construction, due to bad joints that no one will see. Sometimes, in order to make low cost construction, with the posibility of selling high, modular isolating panels are employed, but the details are seldom observed. Builders do not care to hire an acoustician, and there are infrequent complaints by owners.
Stable cavitation in ultrasound image-guided high intensity focused ultrasound therapy
Authors: Vaezy Shahram , Luo Wenbo , Bailey Michael , Crum Lawrence , Rabkin Brian , Zderic Vesna
Published: September 2008

Microbubble activity is significantly involved in both diagnostic and therapeutic aspects of ultrasound image-guided HIFU therapy. Ultrasound interrogation techniques (A-, B-, M-mode, Doppler, harmonic and contrast imaging, and passive and active cavitation detection) were integrated with HIFU. Our results using HIFU devices of 1–5 MHz, and focal, derated intensities of 1,000–10,000 W/cm2, show the formation of microbubbles (about 100 bubbles/mm3, 5–100 microns in size) at the HIFU focus. Boiling, stable, and inertial acoustic cavitation activities were detected during therapy. The presence of bubbles allows the observation of the treatment spot as bright hyperechoic regions in ultrasound images, providing an effective method for guidance and monitoring of therapy. The stable cavitation of microbubbles may provide a mechanism for enhanced HIFU energy delivery, as well as induction of biological responses for stimulation and regulation of specific physiological events such as coagulum and thrombus formation for hemostasis applications, apoptotic activity in treating tumor margins, and stimulation of immune response. Stable cavitation of extrinsic bubbles (contrast agents) is used in detection and localization of internal occult bleeding, using harmonic imaging. There appears to be benefits in utilizing stable cavitation in both diagnostic and therapeutic objectives of ultrasound image-guided HIFU. Funding: DoD, NIH, NSBRI.
Observations of cavitation and boiling in a tissue-mimicking phantom due to high intensity focused ultrasound
Authors: Canney Michael S. , Kreider Wayne , Bailey Michael R. , Khokhlova Vera A. , Crum Lawrence A.
Published: September 2008

Bubbles generated by acoustic cavitation or boiling are often observed during high intensity focused ultrasound (HIFU) medical treatments. In this work, high-speed video imaging, a 20-MHz focused acoustic transducer, and the driving voltage to our 2-MHz HIFU source are used to distinguish between cavitation and boiling in a tissue-mimicking gel phantom at peak focal intensities up to 30,000 W/cm2. Bubble dynamics are modeled using a reduced order model that accounts for evaporation and condensation, heat and gas transfer across the interface, and temperature changes in the surrounding liquid. The model includes vapor trapping, whereby the noncondensable gas slows diffusion of vapor to the interface, thereby limiting condensation. At the transducer focus, evidence of cavitation is observed in the first millisecond before disappearing. Boiling is observed several milliseconds later, after sufficient heating of the focal volume to 100°C. The disappearance of cavitation can be explained in part by the observed motion of bubbles away from the focal region due to radiation-pressure forces and in part by the softening of bubble collapses by vapor trapping. Thus, at clinical HIFU amplitudes, bubble dynamics and their impact on image-feedback and/or therapy change dramatically in only milliseconds. [Work supported by NIH DK43881 and NSBRI SMS00402.]
Magnetic resonance imaging of boiling induced by high intensity focused ultrasound
Authors: Khokhlova Tatiana D. , Bailey Michael R. , Canney Michael S. , Khokhlova Vera A. , Lee Donghoon , Marro Kenneth I.
Published: September 2008

Bubble activity in high intensity focused ultrasound (HIFU) medical therapy is commonly but not rigorously divided between mechanically induced cavitation (μ size gas bubbles) and thermally induced boiling (mm size vapor bubbles). Our goal was to confirm that boiling occurred at 100°C. A 2 MHz focused transducer (42 mm aperture, 44 mm focal length) was used to heat tissue phantoms in a 4.7 Tesla magnet. Temperature was measured by magnetic resonance imaging (MRI) proton resonance frequency shift and calculated from acoustic absorption. The MRI voxel was 0.3×0.5×2 mm, and acquisition time was 1.3 s. Boiling was observed as a dark spot in MRI images and fluctuation in the transducer drive voltage. At 30 MPa peak pressure, boiling occurred in 7 s. Calculations yielded 100circC in 7 s and a temperature half maximum width of 1 mm. Averaging the calculated temperature field over the MRI voxel yielded a maximum of 73circC, which was the peak temperature measured in the last MRI slice before boiling. In conclusion, boiling appeared when the peak temperature reached 100°C, and the results warn that MRI monitoring alone may underestimate the peak temperatures. [Work supported by NIH DK43881, NIBIB R21EB005250, and NSBRI SMS00402.]
A study of ambiguities in the acoustic-articulatory mapping
Authors: Atal Bishnu
Published: September 2008

At Bell Laboratories, in 1976, Max Mathews, John Tukey, J. J. Chang, and I investigated the relationship between the shape of the vocal tract and its acoustic output for studying articulatory compensation. Although the mathematics of the forward transformation, from the vocal-tract shape to its acoustics, is reasonably clear, the same cannot be said about the inverse transformation from acoustics to the corresponding vocal-tract shape. Max, recognizing the increasing power of digital computers, suggested an interesting approach to the inverse problem, based on computer-sorting. Inversion by computer-sorting consisted of computing the output for many values of the input and sorting the resulting output-input pairs into a convenient order, according to the output data. The paper will highlight this approach and present some interesting results of this study on articulatory compensation. We were successful in determining articulatory regions (fibers) that map into a single point in the acoustic space and produce the same sound [Atal et al., J. Acoust. Soc. Am. 63, 1535–1555 (1978)].
Max V. Mathews, the computer music pioneer
Authors: Richard Moore F.
Published: September 2008

Max Vernon Mathews (born November 13, 1926) is the pioneer of computer music sound synthesis and control. After receiving a Sc.D in electrical engineering from M.I.T. in 1954, Mathews directed the Acoustical and Behavioral Research Center at Bell Laboratories at Murray Hill, New Jersey from 1962 to 1985, where he designed and implemented the first important computer programs to synthesize musicals sounds, starting with MUSIC I, in 1957. Mathews’ ingenious strategies traversed many computer generations of improvement, and now form the backbone of much of the music synthesis industry. In 1968, Mathews turned to real time control of musical synthesis, resulting in the GROOVE system, which, like the MUSIC programs, provided a conceptual basis for further developments in computer-based musical performance. Mathews has influenced many musicians and researchers, including Pierre Boulez, who based major research aspects of his Institute de Recherche et Coordination Acoustique/Musique (IRCAM) in Paris on the work of Mathews and his colleagues. Mathews has received awards from the NAS, NAE, ASA, AES, and IEEE, as well as the Republique Francaise, and has been a professor of musical research at Stanford University since 1987.
Max Mathews in real-time
Authors: Wessel David
Published: September 2008

Some of the most important contributions of Max Mathews stem from his emphasis on live-performance computer music. His performer-oriented perspective has won over musicians ranging from Pierre Boulez to Stevie Wonder. The most prominent real-time computer language in use today, Max/MSP, bears his name. In the 1960s, after making an overwhelmingly convincing argument for the digital computer as a musical instrument, he and F. R. Moore at Bell Labs built a hybrid system, GROOVE, consisting of analog synthesis modules under real-time digital control. Though not a fully digital system—a practical move—it anticipated much of what we in the field are currently doing with laptops and gestural controllers in performance. Indeed his GROOVE conducting program impressed both Pierre Boulez and Stevie Wonder when it was demonstrated to them in the mid-1970s. I will strive to honor Max’s contributions to musical performance with examples from his work and those influenced by him. Along the way there will be a few stories.
Noise impacts on birds: Assessing take of endangered species
Authors: West Edward W. , Dooling Robert J. , Popper Arthur N. , Buehler David M.
Published: September 2008

Section 9 of the Endangered Species Act makes it illegal to take (harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect) an endangered species. Harass includes any action that would significantly disrupt normal behavioral patterns including breeding, feeding, or sheltering. ‘‘Harm’’ includes any action that actually kills or injures a listed species. To better understand how and to what extent anthropogenic noise can harm or harass birds, we examined the potential for noise effects at three levels: Physiological stress, hearing impairment, and interference with communication through signal masking. Pile driving and blasting (≊100 dBA at 15 m) can potentially cause temporary or permanent hearing impairment in birds. Chronic intense noise (e.g., oil field compressor station: 92 dBA at 20 m) may induce physiological stress in some species if they cannot avoid exposure. Finally, highway noise as low as 45 dBA can potentially mask acoustic communication and modify breeding and other behaviors in many species. Thresholds of effect and effect distances are largely species-specific, reflecting differences in tolerance capacity, spacing requirements, and bioacoustic profiles. Indices of take can be physiological, behavioral, or ecological, but must be verifiably correlated with significant changes in species viability.
Environmental noise: Is there any significant influence on animals?
Authors: Genuit Klaus , Fiebig André
Published: September 2008

It is stated that there is no convincing evidence that animals are deterred by intense sounds (Heffner 2007). Nevertheless, it must be thoroughly examined to what extent animals are impaired by specific environmental noise with regard to their orientation, communication, behavior, etc. Such interferences would significantly influence the animals’ life. Similar to the auditory sensitivity of animals, the human hearing system shows a high performance in amplitude, frequency, and time resolution. It pays attention to more factors and noise features than only to absolute SPLs. Psychoacoustic parameters as well as further hearing-related parameters can capture such specific factors and features of noise, which allow us to draw conclusions concerning noise annoyance or, respectively, the pleasantness of noise. The adequate measurement and use of such parameters resulting in an advanced analysis and description of environmental noise—beyond simple sound pressure level considerations—provide valuable information with respect to noise annoyance, stress-related reactions, and interference of daily life activities of humans. The presentation will highlight the relevance, the determination, and interpretation of psychoacoustic and other hearing-related parameters in the context of environmental noise, with respect to the hearing sensation of humans.
Role in science in assessing noise impacts on wildlife under National Environmental Policy Act (NEPA)
Authors: Wisdom Sheyna
Published: September 2008

Data uncertainty is an unfortunate reality of wildlife management. Data gaps can lead to decision uncertainty when assessing noise impacts on terrestrial and marine wildlife through the National Environmental Policy Act (NEPA) process and other regulations. How can managers take a precautionary approach to effects of noise on wildlife in light of imperfect information without imposing unacceptable restrictions on activities? This talk will describe the existing policies and/or guidelines used to assess noise impacts to marine and terrestrial wildlife under NEPA. It will provide specific examples of how noise impacts on wildlife have been assessed using GIS-based technology and industry-accepted acoustic propagation models, such as the Federal Highway Administrations Traffic Noise Model. There will also be a discussion of important gaps in our understanding of wildlife susceptibility to noise. Using principles of adaptive management, wildlife managers can implement policies that address data gaps, protect wildlife, and yet allow human activity.
Hierarchical method for single-observer, continuous sound source observer logging
Authors: Horonjeff Richard , Anderson Grant
Published: September 2008

Sound environments, whether urban or remote, often contain a variety of audible sound sources, each with different onset and offset times. Obtaining a continuous log of these sources can be a daunting task, especially for a single observer. In situations where it is impractical to deploy several observers to a single location, a hierarchical, forced-choice method has been developed. The method stratifies the sources into layers, each layer containing sources with common attributes, such as human-related or natural-indigenous. The method collects sufficiently detailed information for study objectives, without taxing the observers’ cognitive and recording abilities, and thereby introducing large observation or recording errors. So long as the onsets and offsets of audible sources in one layer are independent of those in another, statistical descriptors, such as the percent of time audible, can be determined for each layer. The highest layer in the hierarchy becomes an exhaustive sample, whereas lower layers become statistical samples with random blocks of time removed. The method has been applied in a number of national parks over the past 15 years, by several organizations and sponsors. Advantages and disadvantages of the method, along with inter-observer logging consistency results, are presented.
Speech intelligibility in a passenger train compartment
Authors: Yip Tze Leung , Fung William W. S. , Leung Chun Wah , Frommer Glenn H. , Li Kai Ming
Published: September 2008

An effective delivery of an informative announcement through a public address system in a mass transit train is very important from the viewpoints of safety and passengers’ comfort. A high quality of speech intelligibility is needed in the compartment to facilitate the effective communication between train operators with passengers. The reverberation time is often used as one of the key elements for assessing and determining the quality and perception of the speech sound in an enclosure. Not only does it indicate the level of absorption and reflection in the train compartment, it also affects the overall noise levels and the clarity of speech. In the current study, a simple ray model is presented to estimate the sound field in a train compartment. It is then used to predict the decay curve of noise levels in which the reverberation time is calculated. Full-scale field measurements were conducted in a train compartment operating in a tunnel, for validation of the numerical model. This study aims to understand the speech intelligibility of a train compartment in a set of realistic operating conditions for setting achievable contractual specifications for the design of underground trains operating in tunnels.
Experimentally measured diffraction of sonic boom waves around a house
Authors: Sparrow Victor W. , Klos Jacob , Buehrle Ralph D.
Published: September 2008

During June 2006, a series of sonic boom flight tests were conducted as a part of the NASA low-boom/no boom program. One objective was to evaluate structural acoustic building response on a house. This presentation gives some results of that test regarding the outdoor pressure response on and near the house. The passage of the sonic booms over a nearby wall and the house itself have been examined to determine the maximum pressure loading. Both conventional N-waves and low-amplitude N-waves have been considered. The results indicate that the walls of the house facing the direction of the incoming sonic boom receive the maximum loading in agreement with image theory. The findings also confirm the temporal and spatial dependence of the structural loading. [The first author is supported by NASA and the FAA/NASA/Transport-Canada PARTNER Center of Excellence.]
Acoustic surface waves and long-range detection of mortars and artillery
Authors: Di Xiao , Talmadge Carrick L. , Waxler Roger , Gilbert Kenneth E.
Published: September 2008

A natural terrain surface, because of its porosity, can support an acoustic surface wave that is a mechanical analog of the familiar vertically polarized surface wave in AM radio transmission. At frequencies of several hundred Hertz, the acoustic surface wave is attenuated over distances of less than about 100 m. At lower frequencies (e.g., below 100 Hz) the attenuation is much less, allowing surface waves to propagate thousands of meters. Thus, understanding the low-frequency surface wave is important for detecting and locating mortars and artillery. Data from recent field experiments will be shown demonstrating the persistence of the surface wave under different meteorological conditions. Propagation calculations will be presented using typical source signatures for mortars and artillery, and the implications for long-range detection will be discussed. [Research supported by the U.S. Army TACOM-ARDEC at Picatinny Arsenal, New Jersey.]
Refraction corrections to source localization using an acoustic array suspended below an aerostat
Authors: Ostashev Vladimir E. , Scanlon Michael V. , Wilson D. Keith
Published: September 2008

Acoustic sensor arrays suspended below tethered aerostats have several advantages in detection and localization of sources on the ground in comparison with ground-based sensors. Aerostats can be elevated up to 1-2 Km above the ground where the temperature and wind velocity can significantly differ from their values close to the ground. Therefore, due to refraction, a ray trajectory that connects a source on the ground and an aerostat can bend significantly resulting in different directions of sound propagation along this trajectory. However, so far, refraction has been ignored in source localization using aerostats. In this paper, a theory is developed that allows one to find the source coordinates more accurately by taking into account refraction of sound signals emitted by the source. The source coordinates are expressed in terms of direction of sound signal propagation near the aerostat, the coordinates, and orientation of the aerostat, and the vertical profiles of temperature and wind velocity. Other meteorological parameters may also be incorporated, if available, such as time-of-day, geographical features, and historical weather trends.
Acoustic tomographic study of the mesoscale coherent structures in the lower atmosphere
Authors: Chunchuzov Petrovich Igor , Kulichkov Sergey , Perepelkin Vitali , Ziemann Astrid , Arnold Klaus , Kniffka Anke
Published: September 2008

The results of acoustic tomographic monitoring of the coherent structures in the lower atmosphere and the effects of these structures on the acoustic signal parameters (travel time, duration and direction of propagation) are studied. From the measurements of acoustic travel time fluctuations (periods 1 min-1h) by a net of distanced receivers the temporal fluctuations of the effective sound speed are retrieved along different ray paths connecting a pulse source and the receivers. By using a coherence analysis of the fluctuations near spatially distanced ray turning points, the internal wave-associated fluctuations are filtered and their spatial characteristics (coherences, horizontal translation velocities, and spatial scales) are obtained. A possible explanation of the presence of the dominant periods in the observed mesoscale variations of the acoustic parameters, wind shears and turbulent fluxes of momentum near ground is done.
Effects of internal gravity waves on acoustic pulse propagation in the atmospheric wave guides
Authors: Chunchuzov Igor , Kulichkov Sergey , Perepelkin Vitali
Published: September 2008

Recently developed theoretical model of a random internal wave field in the atmosphere is used for calculating the statistical characteristics of the parameters of acoustic pulses propagating in the atmospheric wave guides. The variances, frequency spectra and spatial structure functions of the internal wave-associated fluctuations of the acoustic pulse travel times and grazing angles are calculated and compared to those obtained in the experiments on pulse sounding of the atmosphere. The effects analyzed here include: a scattering of acoustic waves from highly anisotropic wind speed and temperature inhomogeneities into the so-called acoustic shadow zones; a discrete character of the observed frequency spectra of the fluctuations of acoustic pulse parameters in the range 1min-1h; an error caused by internal waves in determining of the angle of arrival of the acoustic signal in the waveguide.
Groundborne noise and vibration control at the Toronto Four Seasons Centre for the Performing Arts
Authors: Wolfe Steven L.
Published: September 2008

The Four Seasons Centre for the Performing Arts, Canada’s first purpose-built opera house had its grand opening on June 14, 2006. Occupying an entire block of the financial and theatre district in downtown Toronto (across from the Sheraton Hotel), the facility with its 2,000 seat auditorium, is the new home of the Canadian Opera Company and the performance venue for the National Ballet of Canada. A major challenge for the project’s downtown location was isolating the auditorium from the vibration and noise from the adjacent subway system on University Avenue and surface streetcars on Queen Street. A ‘‘building within a building’’ vibration isolation design was developed that set the entire auditorium, stage, and rehearsal hall on rubber isolation bearings. This paper provides design details and the procedures used to ensure that the groundborne noise from outside activities would be inaudible. Results of follow-up measurements are presented which confirmed that the vibration design effectively mitigated the outside vibration and noise intrusion inside the auditorium to achieve background noise levels from exterior sources equivalent to the threshold of human hearing.
An adaptive tunable dynamic vibration absorber
Authors: Tiseo Barbara , Concilio Antonio , Gianvito Antonio , Koopmann Gary
Published: September 2008

This paper examines a new concept of adaptive tuned dynamic vibration absorbers (ATDVAs) using shape memory alloy (SMA) elements instead of spring elements. Shape memory is a class of alloys that shows a reversible change in crystalline structure. In the martensite phase, the material exhibits a low elastic modulus and yield strength. Subsequent heating of the material induces the change to austenite, with a corresponding higher elastic modulus and yield strength. The result of the phase transformation is a sizable change in the geometry, in the internal tension, a considerable deformation, and a concomitant frequency shift, as in the case where the SMA is used as the stiffness component of a tuned dynamic absorber. In this research, experimental investigations have been focused to verify the capability of an ATDVA to control vibration on a free-free aluminum panel.
Somatosensory influence on the perception of speech sounds
Authors: Ito Takayuki , Tiede Mark , Ostry David J.
Published: September 2008

Along with auditory information, sensory information associated with articulatory movements may also be involved in the neural processing that subserves speech perception. Although somatosensory organs in the orofacial system provide this kind of input, there have been few studies assessing the influence of somatosensory afferents on speech perception. To explore this idea, we examined the possibility that by altering somatosensory information, we might modify the perception of speech sounds. We tested native speakers of American English in a speech identification task using a 10-step synthesized continuum between gheadh and ghad.h Subjects listened to the stimuli one at a time through headphones and classified them as gheadh or ghad.h For half of the trials, during the presentation of the auditory stimulus, we used a robotic device to stretch the facial skin stretch lateral to the oral angle in order to modulate somatosensory information. The mechanical perturbation was timed so that its start and end coincided with that of the auditory stimulus. The results show a systematic modification of speech perception due to altered somatosensory input, which varied systematically according to the direction of the skin stretch perturbation. This suggests that somatosensory information influences the neural processing of speech signals.
Neural mechanisms underlying sensory feedback control of speech
Authors: Tourville Jason , Guenther Frank
Published: September 2008

The DIVA model predicts that perturbation of speech will result in activation of sensory error cells that encode the mismatch between the expected and realized sensory consequences of speech production. Cells coding auditory and somatosensory errors are hypothesized to lie in posterior superior temporal gyrus and supramarginal gyrus, respectively. Activation of these error cells drives compensatory articulator movements, marked by increased activation of ventral motor cortex. To test these hypotheses, blood oxygen level dependent responses during normal and perturbed feedback conditions were assessed in two fMRI experiments. In one experiment, transient, unexpected auditory perturbations were induced by shifting F1 upward or downward; in another, a small balloon was inflated during speech production to induce a somatosensory perturbation. Increased bilateral activation in higher-order sensory cortices in response to the feedback perturbation was consistent with model predictions. Increased activation of frontal regions was found primarily in the right hemisphere. The results suggest that detection of feedback error by bilateral sensory error cells results in a shift from left-lateralized feedforward control of speech to feedback-based control mechanisms that rely more heavily on right hemisphere lateral frontal regions. [This work was supported by NIDCD Grant No. R01 DC02852 (F. Guenther, PI).]
Classification of impulsive-source active-sonar echoes based on a model of auditory perception
Authors: Summers Jason E. , Gaumond Charles F. , Brock Derek , Baer Ralph N.
Published: September 2008

Models of auditory perception are investigated as the basis for a biomimetic classifier of impulsive-source active-sonar echoes. Multidimensional scaling estimates the perceptual space in which listeners perform classification [J. E. Summers et al., J. Acoust. Soc. Am. 120, 3125 (A) (2006)]. In the resulting space of perceptual dimensions, stimuli form distinct clusters and target is discriminated from clutter along a single perceptual dimension. Dimensions in this space do not correspond to features having simple algorithmic representations. Consequently, conventional methods to develop a mapping from signal space to feature space fail. Instead, dimensions reflect untrained categorical perception manifested through the mixtures of top-down and bottom-up processes used by listeners: A high-level cognitive process for interclass dissimilarity ratings and a low-level signal-based process for intraclass comparisons. Behaving as expert systems, listeners rapidly assign stimuli to categories based on prior experiences, a process analogous to the statistical description of classes in the class-specific method. In contrast, within-class comparisons reflect signal-derived features found to be most efficacious for differentiating between the signals, a process similar to generation of features by singular-value decomposition. Implications of these findings for design of hybrid generative/discriminative human-mimetic classifier architectures are discussed. [Work supported by ONR.]
Acoustic dopplergram
Authors: Yang T.C.
Published: September 2008

Lofargram (or spectral gram) is widely used in sonar for detection of narrowband tonal signals and/or wideband transient signals. Such signals at a level comparable to the noise level are difficult to detect using snapshots of the signal spectrum, as they look like the noise. However, as noise is random in time while the signals are persistent over time, they can be detected by line-association (often referred to as eyeball integration) using the Lofargram. This concept for passive signal detection is carried forward to active signal detection using the Dopplergram. In an active system, the challenge is to detect a target echo from the noise and/or the reverberation signals. In a noise-limited situation, there is only so much power one can put out due to hardware and environmental (marine mammal) limitations. In a reverberation-limited environment, the problem is the high probability of false alarms due to reverberations. Active detections using a Dopplergram are rid of these problems in a natural way. [Work supported by ONR.]
The Cramer-Rao lower bound (CRLB) on the bearing estimate for a moving array of vector sensors
Authors: Sullivan Edmund J.
Published: September 2008

The Cramer-Rao lower bound (CRLB) on the variance of the bearing estimate for a moving array of vector sensors is derived. It is shown that the motion itself provides a reduction in the variance of the estimate by utilizing the bearing information inherent in the Doppler. This is referred to as the passive synthetic aperture effect. In order to achieve this, it is necessary to jointly estimate the source frequency along with the bearing. Further, depending on the estimator used, it is necessary to provide a priori information on the source frequency. This can be done by using the observed frequency as a first estimate of the source frequency. It is shown that the CRLB decreases with the processing time and array speed, thereby significantly outperforming the conventional bearing estimator. It is then shown that by including vector sensors colocated with the pressure sensors in the bearing estimate, the CRLB decreases even further. This is due both to the increase in the effective number of sensors, and the inherent directivity provided by the vector sensor.
Removal of non-Gaussian, broadband interferers using blind source separation and spatial processing
Authors: Hoppe Elizabeth , Roan Michael
Published: September 2008

A method is introduced where blind source separation of acoustical sources is combined with spatial processing to remove non-Gaussian, broadband interferers from space-time displays such as bearing track recorder (BTR displays). This is quite different from the standard technique of placing nulls in the direction of interferers. The algorithm is implemented and tested against standard adaptive beamforming techniques, such as minimum variance distortionless response beamforming. In order to illustrate the utility of the approach, experiments were carried out in an anechoic chamber using two acoustic sources. The interferer source remained stationary at boresight, while the signal source moved, in steps of two deg, from negative to positive 20 deg. At each step, one second of data was recorded using a 64-element microphone array that had been calibrated at each subband frequency. All 64 channels of the array were sampled simultaneously at a rate of 22,050 Hz. Spatial processing is implemented using a broadband beamformer. The broadband beamforming algorithm first divides the signals into subbands, basebands, resamples, and finally low-passes the subbands, so that they can be processed using standard frequency domain narrowband beamformers.
A space domain complex envelope
Authors: Park Choon-Su , Kim Yang-Hann
Published: September 2008

Sound visualization tools, for example, beam forming and acoustic holography, exhibit the spatial look of sound in time or frequency domain. However, they normally require a significant amount of computation time to draw well the sound picture in space. The picture contains a great deal of information: Sound pressure distribution, intensity pattern, or energy information with respect to space. The information is often far more than what we need in practice. For example, when we want to know only the location of the sound sources and somewhat averaged sound pressure distribution, we need a means that can provide only what we need. The complex envelope in time domain can be a good starting idea to deal with the problems we have. A method to generate a spatial domain envelope has been theoretically developed. We found that the method not only has an advantage to show rather simple spatial sound distribution, but also reduce significantly the computation time. The latter makes it possible to see the sound picture faster than before: About ten times faster. This method has been applied to many practical examples: For example, sound from a musical instrument and sound from machinery.
Acoustic source identification using a generalized regressive discrete Fourier series for tomographic reconstruction
Authors: Vanherzeele Joris , Longo Roberto , Vanlanduit Steve , Guillaume Patrick
Published: September 2008

When measuring three-dimensional phenomena such as acoustic fields using an interferometric technique, one is prone to measure different angles of view to obtain a full three-dimensional representation of the phenomenon under investigation. This is due to the fact that an interferometric technique measures a line integral across the optical path. To obtain the full three-dimensional view, the different angles of view are passed through a tomographic algorithm. The most widely used tomographic method is filtered back projection. However, this process suffers from a series of drawbacks, the most important one being the fact that substantial truncation errors occur in the back projection step. In this article, a method is devised to eliminate these errors, based on a parametric frequency domain approach called generalized regressive discrete Fourier series (GRDFS). The method will be applied to laser doppler vibrometer measurements on a loudspeaker. This source will be rotated to obtain continuous angle views of the acoustic field, hence eliminating the tedious process of rotating the measurement set-up. By demodulation of a measured signal, it is possible to determine the position of the loudspeaker in space. The results obtained with the GRDFS will be compared to the classical filtered back projection method.
Ultrasonic Doppler vibrometry using direct undersampling
Authors: Mehmood Asif , Goggans Paul M. , Sabatier James M.
Published: September 2008

In ultrasonic Doppler vibrometry (UDV) systems, sound returned from a moving point scatterer is frequency modulated by the component of the scatterer’s velocity in the direction of the system’s colocated ultrasonic transducers. Because of this, time-frequency analysis of the receiver transducer output can be used to reveal the velocities of multiple scatterers moving within the sensor’s field of view. This principle can be used, for example, as in [Zhang et al., EL110 J. Acoust. Soc. Am. 121 (2007)] to study human gait. Because it is band-pass limited, the received signal can be expressed equivalently in terms of low-pass limited in-phase and quadrature (I&Q) components. To reduce the amount of data to be stored and analyzed, it is advantageous to sample the I&Q signals rather than the received signal. This paper reports an implementation of undersampling [J. L. Brown, Jr., IEEE Trans. Information Theory IT−26, 613−−615 (1980)] to capture samples of the I&Q using a data acquisition card without the use of external oscillators or mixers. Undersampling yields I&Q samples that are interlaced rather than simultaneous in time. Here, a spectrogram using interlaced I&Q samples is derived using Bayesian spectrum analysis.
Design of multi-input interleaved multisine excitation signals for ultrasonic testing
Authors: Longo Roberto , Vanlanduit Steve , Vanherzeele Joris , Guillaume Patrick
Published: September 2008

Multisines are periodic signals consisting of harmonically-related sine waves. By optimizing the phases of the different sine waves, a periodic signal is obtained with a small crest factor resulting in high signal-to-noise ratios. One disadvantage of multisines when several ultrasonic actuators are used simultaneously is that, in general, it is very difficult to distinguish from a measured ultrasonic signal the contribution of the different actuators. This is easier when pulses are used and when they do not overlap. In this contribution, a new approach for periodic continuous wave signals will be presented to separate the contribution coming from the different actuators (senders) at every receiver. The proposed approach is based on the use of multi-input interleaved multisines. Interleaved multisines contain energy at different spectral lines allowing an easy separation by means of a discrete Fourier transform. The separation becomes more complex when non-linear effects are present, but even then it is possible to apply this approach by properly selecting the excitation lines. The use of multi-input interleaved multisine offers new applications for ultrasonic NDT (e.g., combined transmission and reflection measurements) as well as in the field of material identification and biomedical applications.
Bayesian spectrum estimation of termite signals using laser Doppler vibrometry
Authors: Mehmood Asif , Tahaineh Orwa M. , Fink Tom , Ramalingam Vijay. P. , Seiner John. M. , Lax Alan R.
Published: September 2008

Laser vibrometry provides a sensitive non-invasive means of measuring substrate vibration. These measurements include landmine detection, automotive testing, production testing, aerospace, and structural testing. We employed laser vibrometry for termite detection. The vibratory signal generated by termite head banging is picked up by the laser Doppler vibrometer. In laser vibrometry, the surface motion is monitored by heterodyne laser Doppler vibrometry, and the received heterodyne signal is sampled to produce time-series data. The time-series data thus obtained is the velocity signal of the vibrating object. We consider here a statistical signal-processing approach to termite head banging data, which is based on Bayesian inference. In this approach, the quantity of interest is the frequency of vibration caused by termite head banging, while phase and quadrature amplitudes are considered nuisance parameters. We employ a single-frequency model to determine this frequency. Because of the optimal prior knowledge about the signal of interest, the frequency can be measured with much greater precision and greater noise immunity than using Fourier transform. Our results show that the Bayesian method of processing an acoustic signal exhibits excellent performance in determining the vibrational frequency.
Reverberation modeling with BiRASP—The bistatic range-dependent active system prediction model
Authors: Fromm David
Published: September 2008

The calculation of bistatic reverberation is a computationally intensive exercise. Efficient computation of timely results typically involves numerous physical and algorithmic assumptions or approximations. Consequently, it is not unusual for predicted time series from different models to differ in level or structure. At a recent Reverberation Modeling Workshop [9–13 November 2006, Austin, TX], a set of test cases were proposed with the intent of establishing benchmark reverberation problems and solutions. This talk will focus on the test case performance of BiRASP, the Naval Research Laboratory’s bistatic reverberation model. BiRASP is a ray-based code, originally developed for deep-water, long-range, low-frequency reverberation predictions and data analysis. Results for the various test case problems will be shown. The consequences of some of the typical algorithm and physical assumptions/approximations will be demonstrated and discussed. [Work supported by the Office of Naval Research.]
Constrained comparison of ocean acoustic reverberation: Theory and observations
Authors: Holland Charles
Published: September 2008

Measurements of long-range (order 104 m) shallow-water reverberation in the Straits of Sicily at 900 and 1800 Hz are compared with theoretical predictions. All of the required environmental inputs for the theory are obtained independently, that is to say there are no free parameters. The reflection coefficient and the scattering strength are measured by direct path methods; both quantities show strong frequency dependence. The theoretical reverberation predictions using these measurements are in good agreement with directional reverberation data, i.e., within the expected uncertainty bounds. The good agreement suggests that the supporting environmental measurement techniques are robust and that the physics associated with reverberation in a waveguide is reasonably well understood, at least in simple environments. The ability to independently measure the seabed scattering strength and reflection coefficient is a crucial step for the advancement of inverse methods using reverberation (e.g., rapid environmental assessment) inasmuch as it provides the means for quantitatively measuring the robustness of those methods. [Research supported by the Office of Naval Research OA321 and the NATO Undersea Research Centre.]
A model of narrow-band normal-mode reverberation in shallow water
Authors: Ivakin Anatoliy
Published: September 2008

A unified model of reverberation in a shallow-water waveguide caused by the volume heterogeneity and rough interfaces is proposed. Normal modes are used to describe propagation of a narrow-band signal from a point source to the scattering volume (a vertical column of the waveguide including both water and sediment) and from the scattering volume to the receiver. A local scattering matrix describes a process of reradiation from one normal mode to another within the scattering volume. The case of statistically axial symmetry, where the source and receiver are separated only in the vertical direction and the medium is statistically homogeneous and isotropic in the horizontal plane, is considered in more detail. A simple relationship of the temporal dependence of the reverberation intensity with the scattering matrix, attenuation, and group velocities of the normal modes is obtained. Contributions of different components of reverberation due to rough air-water and water-sediment interfaces, volume heterogeneity of the water column, and the sediment are discussed.
The effect of different environments on shallow-water reverberation: Measurements and modeling
Authors: Gauss Roger , Preston John
Published: September 2008

Low-frequency reverberation in shallow water is a complex and difficult quantity to predict as its mean levels can be due to a combination of seafloor, sea surface, and fish scattering, coupled with propagation and system-dependent effects. In this paper the importance of having a physics-based modeling capability and the correct spatially-dependent environmental description will be demonstrated via data-model comparisons corresponding to monostatic data the authors have collected over the last 15 years in a range of distinct acoustic environments, from silt to sand to chalk to basalt. Additionally, the use of in situ measurements to both refine predictions and mitigate uncertainty is discussed. [Work supported by ONR.]
Demonstration of coherent gain from synthetic aperture for a midfrequency sonar in shallow water
Authors: LePage Kevin D.
Published: September 2008

The Clutter 07 experiment was carried out this May in the Straits of Sicily on board the R/Vs Alliance and Oceanus with the participation of NATO Undersea Research Centre, NRL, Applied Research Lab-Pennsylvania State University, and Defense Research and Development Canada. High repetition rate monostatic active sonar data collected off the alliance on the Malta Plateau during this experiment is processed to show significant inter-ping correlation indicative of the utility of performing coherent synthetic aperture sonar (SAS). Strip SAS images of scattering from a rocky outcrop on the bottom known as the Ragusa ridge show that the lateral extent of returns from compact objects can be reduced through SAS techniques for real shallow water environments using autofocusing techniques. [Work supported by ONR.]
A New Tetracycline Efflux Gene,
tet
(40), Is Located in Tandem with
tet
(O/32/O) in a Human Gut Firmicute Bacterium and in Metagenomic Library Clones
Authors: Kazimierczak Katarzyna A. , Rincon Marco T. , Patterson Andrea J. , Martin Jennifer C. , Young Pauline , Flint Harry J. , Scott Karen P.
Published: September 2008

The bacterium
Clostridium saccharolyticum
K10, isolated from a fecal sample obtained from a healthy donor who had received long-term tetracycline therapy, was found to carry three tetracycline resistance genes:
tet
(W) and the mosaic
tet
(O/32/O), both conferring ribosome protection-type resistance, and a novel, closely linked efflux-type resistance gene designated
tet
(40).
tet
(40) encodes a predicted membrane-associated protein with 42% amino acid identity to
tetA
(P). Tetracycline did not accumulate in
Escherichia coli
cells expressing the Tet(40) efflux protein, and resistance to tetracycline was reduced when cells were incubated with an efflux pump inhibitor.
E. coli
cells carrying
tet
(40) had a 50% inhibitory concentration of tetracycline of 60 μg/ml. Analysis of a transconjugant from a mating between donor strain
C. saccharolyticum
K10 and the recipient human gut commensal bacterium
Roseburia inulinivorans
suggested that
tet
(O/32/O) and
tet
(40) were cotransferred on a mobile element. Sequence analysis of a 37-kb insert identified on the basis of tetracycline resistance from a metagenomic fosmid library again revealed a tandem arrangement of
tet
(O/32/O) and
tet
(40), flanked by regions with homology to parts of the VanG operon previously identified in
Enterococcus faecalis
. At least 10 of the metagenomic inserts that carried
tet
(O/32/O) also carried
tet
(40), suggesting that
tet
(40), although previously undetected, may be an abundant efflux gene.