bluuebunny/crossref_metadata_2025 huggingface dataset:
Shock Modelling of Multi-Phase Materials: Advances and Challenges
Authors: Raimondo Lucio , Iannucci Lorenzo , Robinson Paul , Curtis Paul T. , Wells Garry M.
Published: August 2008

This paper presents part of an ongoing programme of work on high velocity impact modelling on composite targets. The modelling approach aims to link existing low velocity constitutive failure models, including delamination modelling, with relevant orthotropic Equations Of State models. A methodology for predicting the Hugoniot states (shock velocity vs. particle velocity) of multi-phase materials at high compression is presented. The Gruneisen parameter of the mixture is also derived. The proposed approach is a step toward a full thermodynamic virtual characterisation of untested multi-phase materials, when tabulated shock data for the constituents is available [1]. Other approaches have been proposed [2], [3]; however, they require complex Finite Element coding and iterative procedures and are limited to two-phase materials. The approach is critically discussed in relation to shock data derived from existing flyer plate impact test data. An orthotropic Equation of State [4] has also been implemented into the LS-DYNA3D code. A flyer plate test is simulated using the implemented model, and with material parameters derived using the theory of mixture approach. The current orthotropic Equation of State formulation is discussed, within the limitation of classical Lagrangian FE techniques. Additionally, conclusions are drawn on the logical next step to model high velocity angled impacts onto orthotropic targets.
European Acceptance Criteria for Radiographic Testing
Authors: Georgiou George A. , Baylac Guy
Published: August 2008

Prior to the submission for public comment of the proposed European Standard for Unfired Pressure Vessels EN 13445, there was a long debate on acceptance criteria for radiographic testing. The committee CEN/TC 54/WG E/SG Testing initially developed criteria after wide consultation and in the absence of any other available CEN standard. When the acceptance criteria developed by CEN/TC 121 ‘Welding’ became available, the concern was whether they were workable and could achieve comparable accept/reject rates with those developed by the committee CEN/TC 54/WG E/SG Testing and could thus be adopted in place of them.
Estimating the Depths of Cracks in SS Pipes by Varying the Frequency of an ACPD Sensor
Authors: Shukert Douglas S.
Published: August 2008

Alternating Current Potential Drop (ACPD) is one nondestructive evaluation method for detecting cracks within stainless steel pipes at industrial power plants. It is well known that the penetration depth of the excitation current from the ACPD sensor depends on the frequency of the applied alternating current. With respect to a “skin effect,” lower frequencies produce deeper penetration. This frequency versus depth relationship can be used to judge the depth of cracks that may exist within stainless steel pipes. By varying the frequency of the alternating current supplied to the excitation circuit of an ACPD sensor, crack depths can be estimated. If the penetration depth of the excitation current nearly reaches the depth of the crack tip, then the existence of the crack will cause an increase in the current and a corresponding decrease in the potential drop measured by the ACPD sensor. On the other hand, if the penetration depth of the excitation current reaches beyond the depth of the crack tip, then the crack impedes the electrical current and causes a corresponding increase in the potential drop measured by the ACPD sensor. The frequency at which the measured potential drop flip-flops from a decrease to an increase corresponds to the depth of the crack tip, which can be calculated by using the standard equation for skin depth according to excitation frequency.
A Multi-Scale Approach for Prediction of Irradiation Effect on RPV Steel Toughness
Authors: Diard O.
Published: August 2008

Nuclear reactor pressure vessel steels are subjected to an irradiation-induced embrittlement in service and this may lead to a shift of the ductile-to-brittle transition temperature. The prediction of irradiation effect on toughness requires an accurate description of the elasto-visco-plastic behavior of irradiated steels. Recent progresses have been done to describe microstructural evolutions induced by irradiation. Ab-initio computations, molecular dynamics and discrete dislocations dynamics can predict the defects formation and the hardening induced by the dislocations – defects interactions. At this level, the irradiation effect is essentially reported as an increase of the critical resolved shear stress on the crystallographic slip systems. A numerical homogenization method is proposed to predict stress-strain curves of irradiated steels from the computed critical resolved shear stress evolution. Computations of realistic 3D aggregates and classical homogenization are performed with a Finite Element code [1]. Each grain is described as a single crystal with a crystal plasticity law, which naturally introduces the irradiation effect on the slip systems activity. The resulting average response over the whole aggregate corresponds to classical stress-strain curves. A Beremin type local approach is then applied to compute the fracture toughness of irradiated CT specimens. Assuming that the local approach parameters do not depend on the irradiation level, this methodology is able to take benefits of MD and DDD results to predict the irradiation effect on RPV steels toughness.
Non-Destructive Testing and Inspection of Unfired Pressure Vessels Subject to Cyclic Loads in EN 13445-5
Authors: Baylac Guy , Roberts Ian , Maddox Stephen , Zeelenberg Erik
Published: August 2008

This paper deals with non destructive testing (NDT) and inspection of cyclically-loaded unfired pressure vessels designed to EN 13445. It details specific provisions contained in Annex G of EN 13445-5 for shape imperfections and areas identified in the fatigue analysis that can limit the lifetime of the vessel (referred to as fatigue critical areas).
High Temperature Oxidation of Cr-Mo Steels in the Context of Accelerated Rupture Testing for Creep Life Prediction
Authors: Al-Mazrouee A. , Ibrahim R. N. , Singh Raman R. K.
Published: August 2008

Accelerated Rupture Testing is used to aid in assessing the remaining life for components such as pipes and tubes used in high temperature plants. Due to the high temperature nature of the test, oxide growth plays a role in affecting the test by enhancing the stress. This paper includes the study of oxide-scale growth and metal loss kinetics during air oxidation of three Cr-Mo steels used in the manufacturing of boiler tubing. These tests were carried out using cylindrical specimens similar to creep test pieces at 700°C for times up to 600 h. 1.25Cr-0.5Mo and 2.25Cr-1Mo steels showed a similar oxidation behavior, however, the 9Cr-1Mo was much higher in oxidation resistance in air. Multilayer oxide formation was observed to occur in 1.25Cr-0.5Mo and 2.25Cr-1Mo steels, involving oxides with various compositions. This paper also explains the ongoing investigations at Monash University regarding the high temperature oxidation of Cr-Mo steels and the role of oxidation in affecting the accelerated creep tests.
Aging Management Program of Large Diameter Safety Class Piping
Authors: Faidy Claude
Published: August 2008

Ageing management of Nuclear Power Plants is an essential issue for utilities, in term of safety and availability and corresponding economical consequences. Practically all nuclear countries have developed a systematic program to deal with ageing of components on their plants. This paper presents the ageing management program developed by EDF and that are compared with different other approaches in other countries (IAEA guidelines and GALL report). The paper presents an example of application to large diameter safety class piping. Different degradation mechanisms are considered like fatigue, corrosion or thermal aging. Maintenance and surveillance actions are discussed in the paper.
ENPOWER: Repair Welds and Residual Stresses in Clad Plates
Authors: Hein Hieronymus , Brown Bruce , Lawrjaniec Didier , Ohms Carsten , Truman Chris , Wimpory Robert C.
Published: August 2008

One of the tasks of the European Commission sponsored project ENPOWER was to manufacture repair welds on clad plate specimens simulating the inner wall of a Reactor Pressure Vessel (RPV) and to establish their structural integrity. The paper summarizes the main results from the repair welds carried out on clad plates with an anticipated sub-clad defect including the results from various residual stress measurements and from numerical welding simulations as well as from some fracture mechanical calculations. The results are discussed with respect to support the repair weld optimization in particular by minimizing the residual stresses. Moreover, the application ranges and capabilities of numerical simulations for this kind of weld processes are discussed.
Fracture Margins for Growing Cracks in Weld Repairs
Authors: Smith Michael C. , Bouchard Peter J. , Goldthorpe Martin R. , Lawrjaniec Didier
Published: August 2008

The residual stress field around a single-pass weld filling a slit in a thin rectangular plate has been simulated using both 2D ABAQUS and 3D SYSWELD finite element models, with good agreement between the two codes. Through-wall cracks of varying lengths have been inserted into the plate along the weld centre-line, and the non-linear crack driving force due to residual stress evaluated using three formulations of the J-integral: the standard ABAQUS J, the G-theta approach coded into SYSWELD, and a modified J-integral, Jmod, that retains its path independence under non-proportional loading. Cracks were introduced into the FE meshes either simultaneously (all crack flank nodes released in the same step) or progressively (crack opened in small increments from mid-length to tip). The results were compared with crack driving force estimates made using linear elastic fracture mechanics (LEFM) and the R6 procedure. The crack driving forces predicted by all three J–formulations agree well for simultaneous opening, showing that the crack driving force rises to a peak for a crack length equal to the weld length, and falls for longer cracks. Linear elastic fracture mechanics gives a good estimate of the crack driving force for very short defects (confirming the absence of elastic follow up), but is conservative for longer defects, overestimating the peak driving force by 20%. The R6 estimates, which incorporate plasticity corrections, are more conservative than LEFM, overestimating the peak crack driving force by up to 60%. The crack driving force for a progressively opened crack is much lower than for simultaneous opening, indicating that there may be considerable excess pessimism in conventional assessments of defects of this type.
A Brief Review of Models Representing Creep of Alloy 617
Authors: Swindeman Robert W. , Swindeman Michael J. , Ren Weiju
Published: August 2008

Alloy 617 is being considered for the construction of components to operate in the Next Generation Nuclear Plant (NGNP). Service temperatures will range from 650 to 1000°C. To meet the needs of the conceptual designers of this plant, a materials handbook is being developed that will provide information on alloy 617, as well as other materials of interest. The database for alloy 617 to be incorporated into the handbook was produced in the 1970s and 1980s, while creep and damage models were developed from the database for use in the design of high-temperature gas-cooled reactors. In the work reported here, the US database and creep models are briefly reviewed. The work reported represents progress toward a useful model of the behavior of this material in the temperature range of 650 to 1000°C.
Coupled hydrodynamic-acoustic modeling of sound generated by impacting cylindrical water jets
Authors: Chen Xuemei , Means Steven L. , Szymczak William G. , Rogers Joel C. W.
Published: August 2008

A coupled hydrodynamic-acoustic model describing acoustic propagation in a fluid containing multiple bubbles is proposed and applied to simulate noise generated by impacting water jets. The total pressure is decomposed into a “hydrodynamic” part and an “acoustic” part and computed using different schemes. The hydrodynamic pressure field is calculated independently using a generalized hydrodynamic model, and the pressure variations serve as sources in the wave equation for the acoustic pressure. A numerical algorithm developed to calculate wave propagation in an irregular region is used to account for the existence of the cavities. Noise generated by the impact of two cylindrical water jets is predicted. The computed near-field pressure is compared with the experimental data.
Stability analysis of thermally induced spontaneous gas oscillations in straight and looped tubes
Authors: Ueda Yuki , Kato Chisachi
Published: August 2008

A gas in a tube spontaneously oscillates when the temperature gradient applied along the wall of the tube is higher than the critical value. This spontaneous gas oscillation is caused by the thermal interaction between the gas and the tube wall. The stability limit of the thermally induced gas oscillation is numerically investigated by using the linear stability theory and a transfer matrix method. It is well known that an acoustic wave excited by the spontaneous gas oscillation occurring in a looped tube is different from that in a straight tube with two ends; a traveling acoustic wave is induced in a looped tube, whereas a standing acoustic wave is caused in a straight tube. The conditions for the stability limits in both tube types were calculated. The calculated and measured conditions were compared and were found to be in good agreement. Calculations performed by varying the value of the Prandtl number of the gas were used to determine the reasons for the existence of the stability limits of the looped and straight tubes.
Modeling of wave dispersion along cylindrical structures using the spectral method
Authors: Karpfinger Florian , Gurevich Boris , Bakulin Andrey
Published: August 2008

Algorithm and code are presented that solve dispersion equations for cylindrically layered media consisting of an arbitrary number of elastic and fluid layers. The algorithm is based on the spectral method which discretizes the underlying wave equations with the help of spectral differentiation matrices and solves the corresponding equations as a generalized eigenvalue problem. For a given frequency the eigenvalues correspond to the wave numbers of different modes. The advantage of this technique is that it is easy to implement, especially for cases where traditional root-finding methods are strongly limited or hard to realize, i.e., for attenuative, anisotropic, and poroelastic media. The application of the new approach is illustrated using models of an elastic cylinder and a fluid-filled tube. The dispersion curves so produced are in good agreement with analytical results, which confirms the accuracy of the method. Particle displacement profiles of the fundamental mode in a free solid cylinder are computed for a range of frequencies.
Bayesian geoacoustic inversion of ship noise on a horizontal array
Authors: Tollefsen Dag , Dosso Stan E.
Published: August 2008

This paper applies geoacoustic inversion to low-frequency narrow-band acoustic data from a quiet surface ship recorded on a bottom-moored horizontal line array in shallow water. A Bayesian matched-field inversion method is employed which quantifies geoacoustic uncertainties and allows for meaningful comparison of inversion results from different data sets. Geoacoustic inversion results for ship-noise data are compared with inversion results for multitone data from a towed controlled source collected in the same experiment, and with independent geophysical measurements. To increase the information content of low-level ship-noise data, the effect of including multiple, independent data segments in the inversion is investigated and shown to significantly reduce geoacoustic parameter uncertainties. Geoacoustic uncertainties are also shown to depend on ship range and orientation, with increased uncertainties for long ranges and for the ship stern oriented away from the array.
Noise reduction combining time-frequency ε-filter and M-transform
Authors: Abe Tomomi , Matsumoto Mitsuharu , Hashimoto Shuji
Published: August 2008

This paper introduces noise reduction combining time-frequency ε-filter (TF ε-filter) and time-frequency M-transform (TF M-transform). Musical noise is an offensive noise generated due to noise reduction in the time-frequency domain such as spectral subtraction and TF ε-filter. It has a deleterious effect on speech recognition. To solve the problem, M-transform is introduced. M-transform is a linear transform based on M-sequence. The method combining the time-domain ε-filter (TD ε-filter) and time-domain M-transform (TD M-transform) can reduce not only white noise but also impulse noise. Musical noise is isolated in the time-frequency domain, which is similar to impulse noise in the time domain. On these prospects, this paper aims to reduce musical noise by improving M-transform for the time-frequency domain. Noise reduction by using TD M-transform and the TD ε-filter is first explained to clarify its features. Then, an improved method applying M-transform to the time-frequency domain, namely TF M-transform, is described. Noise reduction combining the TF ε-filter and TF M-transform is also proposed. The proposed method can reduce not only high-level nonstationary noise but also musical noise. Experimental results are also given to demonstrate the performance of the proposed method.
Nature of orchestral noise
Authors: O’Brien Ian , Wilson Wayne , Bradley Andrew
Published: August 2008

Professional orchestral musicians are at risk of exposure to excessive noise when at work. This is an industry-wide problem that threatens not only the hearing of orchestral musicians but also the way orchestras operate. The research described in this paper recorded noise levels within a professional orchestra over three years in order to provide greater insight to the orchestral noise environment; to guide future research into orchestral noise management and hearing conservation strategies; and to provide a basis for the future education of musicians and their managers. Every rehearsal, performance, and recording from May 2004 to May 2007 was monitored, with the woodwind, brass, and percussion sections monitored in greatest detail. The study recorded dBALEQ and dBC peak data, which are presented in graphical form with accompanying summarized data tables. The findings indicate that the principal trumpet, first and third horns, and principal trombone are at greatest risk of exposure to excessive sustained noise levels and that the percussion and timpani are at greatest risk of exposure to excessive peak noise levels. However, the findings also strongly support the notion that the true nature of orchestral noise is a great deal more complex than this simple statement would imply.
Patterns of acquisition of native voice onset time in English-learning children
Authors: Lowenstein Joanna H. , Nittrouer Susan
Published: August 2008

Learning to speak involves both mastering the requisite articulatory gestures of one’s native language and learning to coordinate those gestures according to the rules of the language. Voice onset time (VOT) acquisition illustrates this point: The child must learn to produce the necessary upper vocal tract and laryngeal gestures and to coordinate them with very precise timing. This longitudinal study examined the acquisition of English VOT by audiotaping seven children at 2month intervals from first words (around 15months) to the appearance of three-word sentences (around 30months) in spontaneous speech. Words with initial stops were excerpted, and (1) the numbers of words produced with intended voiced and voiceless initial stops were counted; (2) VOT was measured; and (3) within-child standard deviations of VOT were measured. Results showed that children (1) initially avoided saying words with voiceless initial stops, (2) initially did not delay the onset of the laryngeal adduction relative to the release of closure as long as adults do for voiceless stops, and (3) were more variable in VOT for voiceless than for voiced stops. Overall these results support a model of acquisition that focuses on the mastery of gestural coordination as opposed to the acquisition of segmental contrasts.
Acoustic characterization of panel materials under simulated ocean conditions using a parametric array source
Authors: Humphrey Victor F. , Robinson Stephen P. , Smith John D. , Martin Michael J. , Beamiss Graham A. , Hayman Gary , Carroll Nicholas L.
Published: August 2008

A technique for evaluating the underwater acoustic performance of panels under simulated ocean conditions in a laboratory test facility is described. The method uses a parametric array as a source of sound within a test vessel capable of simulating ocean depths down to 700m and water temperatures from 2to35°C. The reflection loss and transmission loss of the test panel may be determined at frequencies from a few kilohertz to 50kHz. The use of the parametric array enables wideband measurements to be undertaken with short-duration pulses and reduces the effects of diffraction from the panel edges. An acoustic filter is used to truncate the array in order to provide a source-free measurement region and to simplify the measurement process. The difficulties of establishing a parametric array in the confined space of the vessel are outlined, and the experimental procedures adopted are described. The techniques were validated by undertaking measurements on two test objects that have predictable behavior. The potential of the technique is also illustrated with experimental results for test panels for hydrostatic pressures up to 2.8MPa. An extensive discussion of the measurement limitations is included.
Sound propagation in the vicinity of an isolated building: An experimental investigation
Authors: Alberts W. C. Kirkpatrick , Noble John M. , Coleman Mark A.
Published: August 2008

Recently, the study of acoustics in urban terrain has been concerned with the propagation of sound through street canyons typical of residential areas in large cities, while sparsely built suburban and rural areas have received little attention. An isolated building’s effect on propagating sound is a fundamental case of suburban acoustics and urban acoustics in general. Its study is a necessity in order to determine the processes that might be required to model the sound field in the building’s vicinity, e.g., diffraction and wind effects. The work herein presents the results of an experimental effort to characterize the interaction between propagating sound and a single story, gabled-roof building typical of some North American suburban and rural areas. Recorded data are found to reasonably compare to a common diffraction model in some instances.
Simultaneous production of low- and high-frequency sounds by neonatal finless porpoises
Authors: Li Songhai , Wang Kexiong , Wang Ding , Dong Shouyue , Akamatsu Tomonari
Published: August 2008

Phocoenids are generally considered to be nonwhistling species that produce only high-frequency pulsed sounds. Here our results show that neonatal finless porpoises (Neophocaena phocaenoides) frequently produce clear low-frequency (2–3kHz) pulsed signals, without distinct high-frequency energy, just after birth and can produce both low- (2–3kHz) and high-frequency (>100kHz) pulsed signals simultaneously until about 20days postnatal. The results indicate that low-frequency signals of neonatal finless porpoises are not an early form of high-frequency signals and suggest that low- and high-frequency signals may be produced by different sound production mechanisms.
Low frequency vocalizations attributed to sei whales (Balaenoptera borealis)
Authors: Baumgartner Mark F. , Van Parijs Sofie M. , Wenzel Frederick W. , Tremblay Christopher J. , Carter Esch H. , Warde Ann M.
Published: August 2008

Low frequency (<100Hz) downsweep vocalizations were repeatedly recorded from ocean gliders east of Cape Cod, MA in May 2005. To identify the species responsible for this call, arrays of acoustic recorders were deployed in this same area during 2006 and 2007. 70h of collocated visual observations at the center of each array were used to compare the localized occurrence of this call to the occurrence of three baleen whale species: right, humpback, and sei whales. The low frequency call was significantly associated only with the occurrence of sei whales. On average, the call swept from 82to34Hz over 1.4s and was most often produced as a single call, although pairs and (more rarely) triplets were occasionally detected. Individual calls comprising the pairs were localized to within tens of meters of one another and were more similar to one another than to contemporaneous calls by other whales, suggesting that paired calls may be produced by the same animal. A synthetic kernel was developed to facilitate automatic detection of this call using spectrogram-correlation methods. The optimal kernel missed 14% of calls, and of all the calls that were automatically detected, 15% were false positives.
Sound segregation based on temporal envelope structure and binaural cues
Authors: Schimmel Othmar , van de Par Steven , Breebaart Jeroen , Kohlrausch Armin
Published: August 2008

The ability to segregate two spectrally and temporally overlapping signals based on differences in temporal envelope structure and binaural cues was investigated. Signals were a harmonic tone complex (HTC) with 20Hz fundamental frequency and a bandpass noise (BPN). Both signals had interaural differences of the same absolute value, but with opposite signs to establish lateralization to different sides of the medial plane, such that their combination yielded two different spatial configurations. As an indication for segregation ability, threshold interaural time and level differences were measured for discrimination between these spatial configurations. Discrimination based on interaural level differences was good, although absolute thresholds depended on signal bandwidth and center frequency. Discrimination based on interaural time differences required the signals’ temporal envelope structures to be sufficiently different. Long-term interaural cross-correlation patterns or long-term averaged patterns after equalization-cancellation of the combined signals did not provide information for the discrimination. The binaural system must, therefore, have been capable of processing changes in interaural time differences within the period of the harmonic tone complex, suggesting that monaural information from the temporal envelopes influences the use of binaural information in the perceptual organization of signal components.
Active damping control unit using a small scale proof mass electrodynamic actuator
Authors: González Díaz Cristóbal , Paulitsch Christoph , Gardonio Paolo
Published: August 2008

This paper presents a study on the design and use of a small scale proof mass electrodynamic actuator, with a low mounting resonance frequency, for velocity feedback control on a thin rectangular panel. A stability-performance formula is derived, which can be effectively used to assess the down scaling effects on the stability and control performance of the feedback loop. The design and tests of a velocity feedback loop with a prototype small scale proof mass actuator are also presented. When a feedback control having a gain margin of about 6dB is implemented, so that there is little control spillover effect around the fundamental resonance of the actuator, reductions of vibration between 5dB and 10dB in the frequency band between 80Hz and 250Hz have been measured at the control position.
Temporal scales of auditory objects underlying birdsong vocal recognition
Authors: Gentner Timothy Q.
Published: August 2008

Vocal recognition is common among songbirds, and provides an excellent model system to study the perceptual and neurobiological mechanisms for processing natural vocal communication signals. Male European starlings, a species of songbird, learn to recognize the songs of multiple conspecific males by attending to stereotyped acoustic patterns, and these learned patterns elicit selective neuronal responses in auditory forebrain neurons. The present study investigates the perceptual grouping of spectrotemporal acoustic patterns in starling song at multiple temporal scales. The results show that permutations in sequencing of submotif acoustic features have significant effects on song recognition, and that these effects are specific to songs that comprise learned motifs. The observations suggest that (1) motifs form auditory objects embedded in a hierarchy of acoustic patterns, (2) that object-based song perception emerges without explicit reinforcement, and (3) that multiple temporal scales within the acoustic pattern hierarchy convey information about the individual identity of the singer. The authors discuss the results in the context of auditory object formation and talker recognition.
Courtship and agonistic sounds by the cichlid fishPseudotropheus zebra
Authors: Miguel Simões J. , Duarte Inês G. , Fonseca Paulo J. , Turner George F. , Clara Amorim M.
Published: August 2008

Courtship and agonistic interactions in an African cichlid species present a richer diversity of acoustic stimuli than previously reported. Male cichlids, including those from the genus Pseudotropheus (P.), produce low frequency short pulsed sounds during courtship. Sounds emitted by P. zebra males in the early stages of courtship (during quiver) were found to be significantly longer and with a higher number of pulses than sounds produced in later stages. During agonistic intrasexual quiver displays, males produced significantly longer sounds with more pulses than females. Also, male sounds had a shorter duration and pulse period in courtship than in male–male interactions. Taken together, these results show that the acoustic repertoire of this species is larger than what was previously known and emphasize the importance of further research exploiting the role of acoustic stimuli in intra- and interspecific communication in African cichlids.
Removing additive noise via neuro-fuzzy-based reinforcement learning
Authors: Lin Ching-Shun , Kyriakakis Chris
Published: August 2008

In this paper, a systematic treatment for developing a noise removal system based on the fundamental principle of reinforcement learning and fuzzy cerebellar model articulation controller (FCMAC) is presented. The proposed system improves its performance over time through two mechanisms. First, the modified stochastic real-valued algorithm, learning from its own mistakes via the reinforcement signal and reinforcing its action to improve future performance, is used for searching the optimal noise spectrum for the overall training system. Second, system states associated with the positive reinforcement are memorized by FCMAC-based neurons, where, in the future, similar states will share the experiences already stored there and then lead the action to a more positive situation. In this work, FCMAC’s intrinsically poor approximation of rapidly varying functions is solved by taking the complex semicepstrum. In addition, the FCMAC provides an improvement in accuracy of function approximation without losing the property of generalization, which makes the high fidelity digital signal processing possible.
Adaptive spatial combining for passive time-reversed communications
Authors: Gomes João , Silva António , Jesus Sérgio
Published: August 2008

Passive time reversal has aroused considerable interest in underwater communications as a computationally inexpensive means of mitigating the intersymbol interference introduced by the channel using a receiver array. In this paper the basic technique is extended by adaptively weighting sensor contributions to partially compensate for degraded focusing due to mismatch between the assumed and actual medium impulse responses. Two algorithms are proposed, one of which restores constructive interference between sensors, and the other one minimizes the output residual as in widely used equalization schemes. These are compared with plain time reversal and variants that employ postequalization and channel tracking. They are shown to improve the residual error and temporal stability of basic time reversal with very little added complexity. Results are presented for data collected in a passive time-reversal experiment that was conducted during the MREA’04 sea trial. In that experiment a single acoustic projector generated a 2∕4-PSK (phase-shift keyed) stream at 200∕400 baud, modulated at 3.6kHz, and received at a range of about 2km on a sparse vertical array with eight hydrophones. The data were found to exhibit significant Doppler scaling, and a resampling-based preprocessing method is also proposed here to compensate for that scaling.
Low-frequency Fourier analysis of speech rhythm
Authors: Tilsen Sam , Johnson Keith
Published: August 2008

A method for studying speech rhythm is presented, using Fourier analysis of the amplitude envelope of bandpass-filtered speech. Rather than quantifying rhythm with time-domain measurements of interval durations, a frequency-domain representation is used—the rhythm spectrum. This paper describes the method in detail, and discusses approaches to characterizing rhythm with low-frequency spectral information.
Particle filtering for dispersion curve tracking in ocean acoustics
Authors: Zorych Ivan , Michalopoulou Zoi-Heleni
Published: August 2008

A particle filtering method is developed for dispersion curve extraction from spectrograms of broadband acoustic signals propagating in underwater media. The goal is to obtain accurate representation of modal dispersion which can be employed for source localization and geoacoustic inversion. Results are presented from the application of the method to synthetic data, demonstrating the potential of the approach for accurate estimation of waveguide dispersion characteristics. The method outperforms simple time-frequency analysis providing estimates that are very close to numerically calculated dispersion curves. The method also provides uncertainty information on modal arrival time estimates, typically unavailable when traditional methods are used.
Adaptive echolocation sounds of insectivorous bats, Pipistrellus abramus, during foraging flights in the field
Authors: Hiryu Shizuko , Hagino Tomotaka , Fujioka Emyo , Riquimaroux Hiroshi , Watanabe Yoshiaki
Published: August 2008

Echolocation pulses emitted by wild Pipistrellus abramus were investigated while foraging for insects in the field. Similar to other European pipistrelles, the frequency structure during foraging varied. During the search phase, the bats emitted long shallow frequency-modulated pulses 9–11ms in duration, whereas the maximum pulse duration of the bats approaching a large target wall in the laboratory was 3ms. No significant difference was observed between decreases in the interpulse interval during these two approach flights. It is concluded that the bats use a long quasi-constant frequency pulse to find a weak echo from a small prey target.
Dispersion relation for air via Kramers-Kronig analysis
Authors: Álvarez Fernando J. , Kuc Roman
Published: August 2008

A general expression for the dispersion of acoustic waves in air is obtained by combining the attenuation coefficient given by the ISO:9613-1 standard and the twice-subtracted Kramers-Kronig relation. Good agreement is found with published data of sound velocity at different frequencies and relative humidities. The resulting expression is used to investigate changes in local dispersion with temperature and humidity.
The effect of age on auditory spatial attention in conditions of real and simulated spatial separation
Authors: Singh Gurjit , Pichora-Fuller M. Kathleen , Schneider Bruce A.
Published: August 2008

The contributions of auditory and cognitive factors to age-dependent differences in auditory spatial attention were investigated. In conditions of real spatial separation, the target sentence was presented from a central location and competing sentences were presented from left and right locations. In conditions of simulated spatial separation, different apparent spatial locations of the target and competitors were induced using the precedence effect. The identity of the target was cued by a callsign presented either prior to or following each target sentence, and the probability that the target would be presented at the three locations was specified at the beginning of each block. Younger and older adults with normal hearing sensitivity below 4kHz completed all 16 conditions (2-spatial separation method × 2-callsign conditions × 4-probability conditions). Overall, younger adults performed better than older adults. For both age groups, performance improved with target location certainty, with a priori target cueing, and when location differences were real rather than simulated. For both age groups, the contributions of natural spatial cues were most pronounced when the target occurred at “unlikely” spatial listening locations. This suggests that both age groups benefit similarly from richer acoustical cues and a priori information in difficult listening environments.
Medial olivocochlear efferent inhibition of basilar-membrane responses to clicks: Evidence for two modes of cochlear mechanical excitation
Authors: Guinan John J. , Cooper Nigel P.
Published: August 2008

Conceptualizations of mammalian cochlear mechanics are based on basilar-membrane (BM) traveling waves that scale with frequency along the length of the cochlea, are amplified by outer hair cells (OHCs), and excite inner hair cells and auditory-nerve (AN) fibers in a simple way. However, recent experimental work has shown medial-olivocochlear (MOC) inhibition of AN responses to clicks that do not fit with this picture. To test whether this AN-initial-peak (ANIP) inhibition might result from hitherto unrecognized aspects of the traveling-wave or MOC-evoked inhibition, MOC effects on BM responses to clicks in the basal turns of guinea pig and chinchilla cochleae were measured. MOC stimulation inhibited BM click responses in a time and level dependent manner. Inhibition was not seen during the first half-cycle of the responses, but built up gradually, and ultimately increased the responses’ decay rates. MOC stimulation also produced small phase leads in the response wave forms, but had little effect on the instantaneous frequency or the waxing and waning of the responses. These data, plus recent AN data, support the hypothesis that the MOC-evoked inhibitions of the traveling wave and of the ANIP response are separate phenomena, and indicate that the OHCs can affect at least two separate modes of excitation in the mammalian cochlea.
Comparison of behavioral and auditory brainstem response measures of threshold shift in rats exposed to loud sound
Authors: Heffner Henry E. , Koay Gimseong , Heffner Rickye S.
Published: August 2008

The purpose of this study was to determine how closely the auditory brainstem response (ABR) can estimate sensorineural threshold shifts in rats exposed to loud sound. Behavioral and ABR thresholds were obtained for tones or noise before and after exposure to loud sound. The results showed that the ABR threshold shift obtained with tone pips estimated the initial pure-tone threshold shifts to within ±5dB 11% of the time and the permanent pure-tone threshold shifts 55% of the time, both with large errors. Determining behavioral thresholds for the same tone pips used for the ABR did not improve the agreement between the measures. In contrast, the ABR obtained with octave noise estimated the initial threshold shifts for that noise to within ±5dB 25% of the time and the permanent threshold shifts 89% of the time, with much smaller errors. Thus, it appears that the noise-evoked ABR is more accurate in estimating threshold shift than the tone-evoked ABR.
Immunization with
Vibrio cholerae
Outer Membrane Vesicles Induces Protective Immunity in Mice
Authors: Schild Stefan , Nelson Eric J. , Camilli Andrew
Published: August 2008

The gram-negative bacterium
Vibrio cholerae
releases outer membrane vesicles (OMVs) during growth. In this study, we immunized female mice by the intranasal, intragastric, or intraperitoneal route with purified OMVs derived from
V. cholerae
. Independent of the route of immunization, mice induced specific, high-titer immune responses of similar levels against a variety of antigens present in the OMVs. After the last immunization, the half-maximum total immunoglobulin titer was stable over a 3-month period, indicating that the immune response was long lasting. The induction of specific isotypes, however, was dependent on the immunization route. Immunoglobulin A, for example, was induced to a significant level only by mucosal immunization, with the intranasal route generating the highest titers. We challenged the offspring of immunized female mice with
V. cholerae
via the oral route in two consecutive periods, approximately 30 and 95 days after the last immunization. Regardless of the route of immunization, the offspring was protected against colonization with
V. cholerae
in both challenge periods. Our results show that mucosal immunizations via both routes with OMVs derived from
V. cholerae
induce long-term protective immune responses against this gastrointestinal pathogen. These findings may contribute to the development of “nonliving,” OMV-based vaccines against
V. cholerae
and other enteric pathogens, using the oral or intranasal route of immunization.
Moraxella catarrhalis
Binding to Host Cellular Receptors Is Mediated by Sequence-Specific Determinants Not Conserved among All UspA1 Protein Variants
Authors: Brooks Michael J. , Sedillo Jennifer L. , Wagner Nikki , Wang Wei , Attia Ahmed S. , Wong Henry , Laurence Cassie A. , Hansen Eric J. , Gray-Owen Scott D.
Published: August 2008

The
Moraxella catarrhalis
ubiquitous surface proteins (UspAs) are autotransporter molecules reported to interact with a variety of different host proteins and to affect processes ranging from serum resistance to cellular adhesion. The role of UspA1 as an adhesin has been confirmed with a number of different human cell types and is mediated by binding to eukaryotic proteins including carcinoembryonic antigen-related cellular adhesion molecules (CEACAMs), fibronectin, and laminin. A distinct difference in the ability of prototypical
M. catarrhalis
strains to adhere to CEACAM-expressing cell lines prompted us to perform strain-specific structure-function analyses of UspA1 proteins. In this study, we characterized CEACAM binding by a diverse set of UspA1 proteins and showed that 3 out of 10 UspA1 proteins were incapable of binding CEACAM. This difference resulted from the absence of a distinct CEACAM binding motif in nonadhering strains. Our sequence analysis also revealed a single
M. catarrhalis
isolate that lacked the fibronectin-binding motif and was defective in adherence to Chang conjunctival epithelial cells. These results clearly demonstrate that UspA1-associated adhesive functions are not universally conserved. Instead, UspA1 proteins must be considered as variants with the potential to confer both different cell tropisms and host cell responses.
Cryptococcus neoformansEnters the Endolysosomal Pathway of Dendritic Cells and Is Killed by Lysosomal Components
Authors: Wozniak Karen L. , Levitz Stuart M.
Published: August 2008

Cryptococcus neoformansis an opportunistic fungal pathogen that primarily causes disease in immunocompromised individuals. Dendritic cells (DCs) can phagocytoseC. neoformans, present cryptococcal antigen, and killC. neoformans. However, early events followingC. neoformansphagocytosis by DCs are not well defined. We hypothesized thatC. neoformanstraffics to the endosome and the lysosome following phagocytosis by DCs and is eventually killed in the lysosome. Murine bone marrow-derived DCs (BMDCs) or human monocyte-derived DCs (HDCs) were incubated with live, encapsulatedC. neoformansyeast cells and opsonizing antibody. Following incubation, DCs were intracellularly stained with antibodies against EEA1 (endosome) and LAMP-1 (late endosome/lysosome). As assessed by confocal microscopy,C. neoformanstrafficked to endosomal compartments of DCs within 10 min and to lysosomal compartments within 30 min postincubation. For HDCs, the studies were repeated using complement-sufficient autologous plasma for the opsonization ofC. neoformans. These data showed results similar to those for antibody opsonization, withC. neoformanslocalized to endosomes within 20 min and to lysosomes within 60 min postincubation. Additionally, the results of live real-time imaging studies demonstrated thatC. neoformansentered lysosomal compartments within 20 min following the initiation of phagocytosis. The results of scanning and transmission electron microscopy demonstrated conventional zipper phagocytosis ofC. neoformansby DCs. Finally, lysosomal extracts were purified from BMDCs and incubated withC. neoformansto determine their potential to killC. neoformans. The extracts killedC. neoformansin a dose-dependent manner. This study shows thatC. neoformansenters into endosomal and lysosomal pathways following DC phagocytosis and can be killed by lysosomal components.
Toll-Like Receptor 2 Recognition of the MicrosporidiaEncephalitozoonspp. Induces Nuclear Translocation of NF-κB and Subsequent Inflammatory Responses
Authors: Fischer Jeffrey , Suire Colby , Hale-Donze Hollie
Published: August 2008

Microsporidia are obligate intracellular parasites that are ubiquitous in nature and have been recognized as causing an important emerging disease among immunocompromised individuals. Limited knowledge exists about the immune response against these organisms, and virtually nothing is known about the receptors involved in host recognition. Toll-like receptors (TLR) are pattern recognition receptors that bind to specific molecules found on pathogens and signal a variety of inflammatory responses. In this study, we show that bothEncephalitozoon cuniculiandEncephalitozoon intestinalisare preferentially recognized by TLR2 and not by TLR4 in primary human macrophages. This is the first demonstration of host receptor recognition of any microsporidian species. TLR2 ligation is known to activate NF-κB, resulting in inflammatory cytokines, such as tumor necrosis factor alpha (TNF-α) and interleukin-8 (IL-8). We found that the infection of primary human macrophages leads to the nuclear translocation of NF-κB in as early as 1 h and the subsequent production of TNF-α and IL-8. To verify the direct role of TLR2 parasite recognition in the production of these cytokines, the receptor was knocked down in primary human macrophages using small interfering RNA. This knockdown resulted in decreases in both the nuclear translocation of NF-κB and the levels of TNF-α and IL-8 after challenge with spores. Taken together, these experiments directly link the initial inflammatory response induced byEncephalitozoonspp. to TLR2 stimulation in human macrophages.