bluuebunny/crossref_metadata_2025 huggingface dataset:
Coherent phonons in semiconductor superlattice under DC electrical bias
Authors: Kent Anthony , Beardsley Ryan , Akimov Andrey , Henini Mohamed
Published: May 2008

Resonant pumping of superlattices SLs by femtosecond laser pulses results in the generation of coherent phonons with frequency centred approximately on s/dSL, where s is the speed of longitudinal sound and dSL is the SL period. The phonons can be detected by measuring the changes in reflectance of time-delayed probe pulses. To date, measurements have been made on nominally undoped SLs, and phonon frequencies are typically in the range 100 GHz - 1 THz. The motivation for these studies is that such hypersound could be used for acoustic probing of nanostructures. Here we describe the generation and detection of coherent phonons in a doped and electrically-biased SL. The studied SL consisted of 50×(6 nm GaAs and 4 nm AlAs), uniformly doped with Silicon to density 2×1022 m−3. Pump-probe measurements were made at λ∼770 nm on an optical MESA at T=12K. At zero bias, we observed a similar phonon spectrum as previously observed in comparable but undoped SLs, with a mode at ̃ 450GHz. Under applied bias this mode increased in amplitude, and the decay time was also increased. We discuss these observations in terms of the effects of the bias on the coherent phonon generation and detection process and also the possibility of coherent phonon amplification occurring in the structure.
Strain wave induced electron transport in superlattices
Authors: Kent Anthony , Fowler Daivid , Henini Mohamed , Greenaway Mark , Belanov Alexander , Fromhold Mark
Published: May 2008

We show that propagating high-amplitude coherent strain pulses, generated by ultrafast optical excitation of a metal film can induce a charge current in a GaAs/AlAs superlattice (SL). The studied SL had a period of of 12.5 nm and a miniband width of 12 meV. It was grown by MBE on a 0.35 mm-thick semi-insulating GaAs substrate, and a 100 micron device MESA fabricated. On the other side of the substrate a 100 nm-thick Al film was deposited. A coherent picosecond strain pulse was generated opposite the device by exciting the Al film with 40 fs, 800 nm pulses from a 5 KHz, 2.5 mJ Ti:Sapphire amplifier. A strong current pulse from the device was observed about 80 ns after the laser pulse was incident on the Al film, this time delay being equal to the time of flight of longitudinal polarized strain pulses across the GaAs substrate. We attribute the current pulse to electrons that are confined and dragged along by the potential generated by the strain wave. Theoretical calculations show that this "wave dragging" effect in the presence of the SL potential can give rise to the generation of ultra-high (THz) frequency electron dynamics.
Thickness dependence of the acoustical response of ultra-thin metallic films studied by Colored Picosecond Ultrasonics
Authors: Le Louarn Arnaud , Devos Arnaud , Rossignol Clément
Published: May 2008

We have previously demonstrated [1,2] that a connection exists between Colored Picosecond Ultrasonic (CPU) experiments and electronic structure of metallic thin films. Indeed, a strong change of the detected acoustic echoes is observed when the laser is tuned around an interband transition wavelength. This connection suggests that CPU can be an useful tool for measuring interband transitions in thin metallic films. Surprisingly, by doing such a measurement on a series of ultra-thin Aluminium films, we observed a significant shift of the transition (from 880 to 970 nm) as the film thickness is reduced (from 400 to 120 A). We will discuss the origin of the phenomenon and propose some applications to the characterization of ultra-thin metallic films. [1] A. Devos and C. Lerouge, Phys. Rev. Lett. 86, 2669 (2001) [2] A. Devos and A. Le Louarn, Phys. Rev. B 68, 045405 (2003)
Monochromatic high frequency coherent phonons propagation with superlattice transducers
Authors: Huynh Agnès , Pascual Winter Maria Florencia , Perrin Bernard , Jusserand Bernard , Lemaitre Aristide , Fainstein Alejandro
Published: May 2008

The availability of efficient and compact phonons transducers in the THz range would be very interesting for phonons spectroscopy, acoustic microscopy and study of vibrational and electronic properties of nanostructures. Thanks to epitaxial growth of semiconductors multilayers, high quality phononic nanostructures with standard semiconductors, such as superlattices (SL) and nanocavities can be obtained for the GHz and THz transduction. Picosecond ultrasonics experiments have been performed in transmission geometry with pump and probe incident on opposite sides of the substrate, allowing discoupling acoustic generation and detection processes. By these means, we have shown independently that SL are very efficient high frequency monochromatic phonon generators and detectors. We report on experiments where two superlattices have been grown on the opposite sides of a substrate: a first SL with uniform layer thickness over the whole surface sample is used as a generator; the other one, used as the detector, presents a thickness gradient and the location of the detection is chosen in order to have the best matching with the emitted frequency. This setup is used to study the propagation of monochromatic high frequency coherent phonons as a function of temperature.
Progress on coherent generation of terahertz acoustic phonons by resonant absorption of nanosecond-pulsed far-infrared laser radiation in silicon doping superlattices
Authors: Wilson Thomas E.
Published: May 2008

We report progress on experiments to generate and detect coherent terahertz acoustic phonons. Coherent phonons are generated1 in a silicon-doping superlattice by the absorption of grating-coupled high peak-power cavity-dumped far-infared laser radiation2. The superlattice period is chosen to match the phonon wavelength at the excitation frequency of the laser radiation. The phonons propagate across the Si:B substrate and are detected by a novel superconducting granular aluminium/palladium bilayer microbolometer3 with sub-nanosecond resolution. The phonon spectrum is obtained by piezo-phonon spectroscopy4 via the boron impurities in the silicon substrate. (1) P. Ruden and G.H. Dohler, "Anistropy Effects and Optical Excitation of Acoustic Phonons in n-i-p-i Doping Superlattices", Solid State Commun. 45 (1), 23 (1983). (2) T.E. Wilson, "A High-Power NH3 Laser Pumped in a Three-Mirror CO2 Laser Cavity with Optically-Switched Cavity-Dumping", International Journal of Infrared and Millimeter Waves 14 (2), 303 (1993). (3) T E Wilson, "Fabrication and characterization of granular aluminum/palladium bilayer microbolometer", Meas. Sci. Technol. 18 N53-N59 (2007). (4) S. Roshko and W. Dietsche, "Phonon Spectroscopy in High Magnetic Fields: The B+ Center in Si", Solid State Comm. 98(5), 453 (1996).
Escape time of an acoustic nanocavity mode
Authors: Pascual Winter Maria Florencia , Rozas Guillermo , Fainstein Alejandro , Jusserand Bernard , Perrin Bernard , Lemaitre Aristide
Published: May 2008

We present a study of the escape time of a 1 THz nanocavity phonon mode as a function of the Q-factor of the cavity. We compare results from picosecond acoustics and high resolution Raman scattering experiments, the latter obtained by means of a Fabry-Perot/triple-additive spectrometer tandem. A nanocavity consists of a GaAs spacer enclosed by two acoustic GaAs/AlAs Bragg mirrors. The number of periods of the inner mirror varies from sample to sample, spanning a range 64<Q<2470. This means that the cavity mode tunnels through the inner mirror to the substrate at theoretical time intervals that vary from 64 to 2470 ps for the different samples. An optic AlGaAs/AlAs Bragg mirror was grown between the substrate and the inner acoustic mirror in order to allow for the observation of the cavity mode in a backscattering configuration of the Raman experiments, otherwise forbidden by symmetry. At room temperature we observe escape times that vary from 65 to 278 ps. The theoretical values match the experimental results if a 3.0-GHz-wide lorentzian convolution is included to account for broadening effects. Possible explanations for this broadening will be discussed, as well as low temperature results.
Acoustic dynamics in glasses in the mesoscopic range
Authors: Monaco Giulio
Published: May 2008

The investigation of the high-frequency acoustic excitations in glasses and of their connection to the universal anomalies in the thermal properties remains a largely debated topic. For instance, one interpretation is based on the observation that the high-frequency acoustic dynamics in simulated harmonic glasses shares the same main features as those found in experiments on real glasses [1]. Another interpretation is based on the observation that both acoustic dispersion and attenuation measured in glasses and in the corresponding poly-crystals are indistinguishable [2]. A further interpretation is based on the observation that in some glasses the high-frequency acoustic attenuation increases as a power of q with an exponent of four or larger up to frequencies corresponding to the Boson peak [3]. Here, I will discuss the above approaches on the basis of recent inelastic x-ray scattering results on the high-frequency acoustic dynamics of glasses. [1] G. Ruocco et al., Phys. Rev. Lett. 84, 5788 (2000). [2] A. Matic et al., Phys. Rev. Lett. 93, 145502 (2004). [3] B. Rufflè et al., Phys. Rev. Lett. 96, 045502 (2006).
High frequency ultrasonic waves in metals and dielectrics
Authors: Eleftheriou Maria , Bakarezos Makis , Lyras Andreas , Kosmidis Costas , Tatarakis Michael , Papadogiannis Nektarios
Published: May 2008

We theoretically study the generation of high frequency ultrasonic waves by short laser pulses, as well as their propagation, in metals and dielectrics. For this purpose, we employ a theoretical model that applies to both cases of materials. In the case of the dielectric the theoretical model is reduced properly. We compute key physical quantities of the lattice deformation such as the temperature, the strain and the displacement of the bulk while we compare the obtained results for the two different abovementioned types of materials. The dependence of these quantities on the generating laser intensity and pulse duration is investigated, revealing interesting differences in their behavior.
Phonons rectification in picosecond laser ultrasonics
Authors: Perrin Bernard , Zhang Shuo , Belliard Laurent , Péronne Emmanuel
Published: May 2008

In standard ultrafast acoustic experiments very short coherent acoustic pulses are generated by the absorption of a femtosecond laser pulse in a thin metallic transducer deposited on the sample. Subsequently the acoustic pulses and the heat generated in the transducer cross the sample and are partially transmitted in the underlaying substrate. At low temperature, heating of the metallic transducer gives rise to the emission of incoherent phonons wave packets which propagate ballistically over large distances in the substrate. We report on a series of experiments which demonstrate the acoustic rectification [1-3] of these wave packets as they propagate through large GaAs or Si substrates. [1] B. Perrin, J. de Phys. C8 (1979) 216. [2] S. M. Avanesyan, V. E. Gusev, Solid State. Commun. 54 (1985) 1065. [3] B. Perrin, E. Péronne, L. Belliard, Ultrasonics, 44 (2006) 1277.
Picosecond ultrasonics in a single biological cell
Authors: Audoin Bertrand , Rossignol Clément , Chigarev Nikolay , Durrieu Marie-Christine , Guillemot Fabien , Forget Guillaume
Published: May 2008

The picosecond ultrasonic technique has been developed during the last 20 years due to permanent interest in the study of mechanical properties of nano- and micro-layers made of metals and semiconductors used in solid state physics and microelectronics. The technique relies on generation, propagation and detection of ultra-short acoustic waves by femtosecond laser pulses. Important advantages of these techniques are the absence of direct contact to the sample and extremely high frequency range. In this presentation, the picosecond ultrasonics technique is applied to generate and detect acoustic waves with a frequency as high as 15 GHz in a single biological cell. Hypersound velocity and attenuation can thus be mapped in the cell with the small lateral resolution provided by optics, ie 1μm. In addition to single cell imaging, the sensitivity of the measurements to cell compressibility suggests promising perspectives in the field of biology. An application to the analysis of mouse cells grafting on biomaterials will illustrate the potentialities for quantitative evaluation of implants bio compatibility.
Acoustic phonon generation by intrinsically localized vibrational modes in double-helices of DNA macromolecules and transition from inter-strand energy exchange to nonlinear self-trapping
Authors: Kosevich Yuriy A. , Savin Alexander V. , Golo Voislav L. , Volkov Yuriy S.
Published: May 2008

We study ultrafast dynamics of intrinsically localized vibrational modes (breathers) in a double helix of two weakly coupled chains of nonlinear oscillators. With this we model nonlinear dynamics of DNA-type macromolecules, which can be studied by means of femtosecond infrared pump-probe laser spectroscopy similar to the case of protein α-helices [1]. We show that there are two regimes of coupled breathers: the time-periodic wandering of low-amplitude breather between the chains, and the one-chain-localization (self-trapping) of high-amplitude breather. We also find bound states of two breathers, localized in different chains, with different positions in the chains. The helix symmetry of the system results in a specific chiral mode which accomplishes the interaction between torsional and longitudinal acoustic modes in the constituent chains. In both nonlinear regimes, the inter-strand energy exchange gives rise to acoustic phonon generation in the coupled chains, and the generation is much stronger in the wandering-breather regime. Ultrafast acoustic phonon generation can be detected by means of optoacoustics, which can therefore provide a tool to study in time domain the inter-strand energy exchange and the transition to nonlinear self-trapping in DNA-type macromolecules. 1. J. Edler, R. Pfister, V. Pouthier, C. Falvo, and P. Hamm, 2004, Phys. Rev. Lett. v. 93, 106405.
Nanoultrasonics based on piezoelectric semiconductor nanolayers
Authors: Sun Chi-Kuang
Published: May 2008

In this presentation, we will review our recent work on the development of nanoultrasonics based on piezoelectric semiconductor nanolayers. Through epitaxial growth of multiple or single piezoelectric semiconductor layers with a period on the order of 10 nm, nanoacoustic waves with a frequency of 1 terahertz and a wavelength of 10 nm can be excited and measured with femtosecond optical pulses. Using temperal coherent and spatial nonlinear optical controls, we are able to synthesize nanoacoustic waveforms and generate a lateral acoustic spot on the order of 100 nm without the need of the near-field optical techniques. In this presentation, we will also discuss the potential use of this terahertz acoustic source for various nanoacoustic applications, including nanoultrasonic imaging.
Photoelastic transduction in photo-phononic nanodevices
Authors: Fainstein Alejandro , Jusserand Bernard , Pascual Winter Maria Florencia , Lanzillotti Kimura Norberto Daniel , Rozas Guillermo , Perrin Bernard , Huynh Agnès , Lemaitre Aristide
Published: May 2008

We will discuss the new possibilities that semiconductor superlattices and acoustic nanocavities open for the controlled manipulation of quasi-monochromatic acoustic waves in the terahertz range. Playing with the specific electronic properties of quantum wells constituting acoustic nanodevices allows to selectively generate or detect phonons with a specific spatial distribution of the deformation along the acoustic device propagation axis. We could for instance demonstrate the selective generation of cavity phonons at resonance with cavity excitonic transitions or the increased photoelastic coupling of folded acoustic modes in mirrors when the number of nodes of the acoustic mode coincide with the one of the dominantly resonant excitonic transition. We also used the combination of photonic and phononic cavities to ensure phase matching with cavity phonons in the standard detection scheme corresponding to transient reflectivity in the time domain or Raman backscattering in the frequency domain. Photonic cavities moreover provide a strong increase of the internal optical fields by quality factors up to 100 typically, resulting in high enhancements of the transduction efficiency of monochromatic phonons to the benefit of the envisioned high speed modulation of optoelectronic properties of coupled photo-phononic nanodevices.
Bubbles, surfactants, shape oscillations, optical levitation, and light scattering: a survey
Authors: Marston Philip L. , Thiessen David B.
Published: May 2008

Research emphasizing relatively slow aspects of bubble dynamics will be summarized. Though the attention is mainly on acoustically levitated bubbles larger than the size for monopole resonance, early experiments on stable optical levitation of gas bubbles in water [J. Acoust. Soc. Am. 83, 970-975 (1988)] will also be noted as well as fundamental aspects of light scattering by bubbles [J. Opt. Soc. Am. and/or Applied Optics (1979-1991)]. Modulated radiation pressure was demonstrated to be an effective way for mode-specific excitation of shape oscillations of acoustically levitated bubbles [J. Acoust. Soc. Am. 93, 706-713 (1993)]. The damping of shape oscillations was demonstrated to be strongly influenced by the presence of insoluble or soluble surfactants [J. Fluid Mech. 300, 149-167 (1995); Phys. Rev. Let. 75, 2686-2689 (1995); J. Acoust. Soc. Am. 102, 3372-3377 (1997)]. A convenient way of measuring the damping was to use laser beam extinction to monitor freely decaying shape oscillations. This technique was sufficiently sensitive to reveal the strong dependence of the damping on surface elasticity. Even for clean bubbles, an improved analysis of the damping was needed. [Sponsored in part by NASA and by ONR.]
Bubble-bubble interaction in disperse bubble clouds
Authors: Szeri Andrew J. , Toilliez Jean O. , Heckman Chris , Eslami Parastou
Published: May 2008

Disperse bubble fields driven by pressure waves feature effects of time delays associated with the finite speed of travel of the driving acoustic wave, and the finite travel time of pressure waves between bubbles. The relative spatial arrangement of bubble nuclei in a disperse field, and the direction of the incoming pressure wave, both influence the cavitation behavior of a cloud of nuclei. In this paper, we consider the dynamics of a disperse field of bubble nuclei driven by a strong rarefaction, such as one sees in shock wave lithotripsy. We make comparisons to experimental work published in J. I. Iloreta, A. J. Szeri, Y. Zhou, G. Sankin and P. Zhong, Assessment of shock wave lithotripters via cavitation potential, Physics of Fluids 19, 086103 (2007). Bubble-bubble interactions are the key ingredient to resolving a mystery concerning the extent of cavitation bubble growth.
The effects of sonication on bacteria
Authors: Mason Timothy J , Paniwnyk L , Joyce E
Published: May 2008

High power ultrasound at frequencies around 20kHz is capable of killing bacteria and for many years has been standard technique in microbiology for the disruption of living cells to release their contents. So successful is this effect that ultrasound has been studied as a possible method for water disinfection. The energies required for using ultrasound alone are high but commercial equipment is available and is often used for disinfection in conjunction with other techniques such as ozonation or uv irradiation. Now evidence is emerging that is possible to induce effects on bacteria other than kill by modifying the acoustic energy entering the suspension (Ultrason. Sonochem. 10:315, 2003). This can be done by altering the duration of exposure, the acoustic power used or the frequency of the ultrasound. In this way sonication can lead to such effects as deagglommeration, enhanced reaction to biocides and gene transfer (Nucleic Acids Res. 35:e129, 2007).
Bubbles in piezo-acoustic inkjet printing
Authors: Lohse Detlef , Jeurissen Roger , De Jong Jos , Versluis Michel , Wijshoff Herman , Van Den Berg Marc , Reinten Hans
Published: May 2008

Ink-jet printing is considered as the hitherto most successful application of microfluidics. A notorious problem in piezo-acoustic ink-jet systems is the formation of air bubbles during operation. They seriously disturb the acoustics and can cause the droplet formation to stop. We could show by a combination of acoustical detection and high-speed visualization that the air-bubbles are entrained at the nozzle and then grow by rectified diffusion. Experimental results on the droplet velocity as a function of the equilibrium radius R0 of the entrained bubble are presented, too. Surprisingly, the droplet velocity shows a pronounced maximum around R0=17 micrometer before it sharply drops to zero around R0=19 micrometer. A simple one-dimensional model is introduced to describe this counterintuitive behavior which turns out to be a resonance effect of the entrained bubble. We show that the bubble counteracts the pressure buildup necessary for the droplet formation. The channel acoustics and the air bubble dynamics are modeled. It is crucial to include the confined geometry into the model: The air bubble acts back on the acoustic field in the channel and thus on its own dynamics. This two-way coupling limits further bubble growth and thus determines the saturation size of the bubble.
Equilibrium state of a multi-size bubble population in a liquid
Authors: Kovinskaya Svetlana
Published: May 2008

A propagation of a linear pressure wave in the liquid with multi-size bubble population is investigated. The wave in the bubbly mixture is modeled as wave in the waveguide interacting with distributed resonators having different resonance frequencies. Each bubble sub-population has the frequency range of effective influence on the wave propagation. This range is started from the resonance frequency of the individual bubble and ended in dependency on the partial void fraction of this sub-population. Mutual influence of sub-populations leads to additional sound attenuation that in essence is a Landau damping. The dispersive equation for the propagating wave lets introduce a criterion for the equilibrium state of the bubbly mixture with multi-size bubble population. The equilibrium distribution which meets this criterion is found analytically. It is shown that the equilibrium distribution is an exact result from the resonant acoustical absorption theory. This theory is employed to find the bubble distribution from measured attenuation of the acoustical wave with assumption that only resonating bubbles contribute attenuation at the frequency of their resonance (neglecting off-resonance contributions). The deviation from the equilibrium contributes Landau damping into the resonant absorption. A dependency of Landau damping on the bubble size distribution is presented.
Optical measurements of the hot spot and incandescent shock from high pressure cavitation in water
Authors: Hiller Robert , Gaitan D. Felipe
Published: May 2008

Spontaneous acoustic cavitation in water at static pressure up to 300 bar has been experimentally investigated. Cavities are initiated by negative pressure and then collapse due to both acoustic pressure and shock waves reflected from the inner surface of the spherical resonator. The implosions result in intense (Mbar) shock waves and bright (1 nJ) light flashes which last from 5 to 40 nanoseconds. The optical spectrum of the flash is measured with a grating monochromator and intensified array detector for high wavelength resolution (̃5 nm) but slow time resolution, and with a multiple-anode microchannel plate photomultiplier tube along with bandpass filters for fast time resolution (̃1 ns) but poor wavelength resolution. The spectrum is generally broad-band and featureless, matching roughly to a Planck spectrum at 5000 to 8000K. The spectral and temporal structure of the flashes is matched to hydrocode simulations. The model suggest the flashes are due to a shell of hot, opaque, shocked water which surrounds and obscures the central hot core. (SMDC contract W9113M-07-C-0178)
Modeling of the effect of boundaries on ultrasound contrast agent microbubbles response
Authors: Dollet Benjamin , Van Wijngaarden Leen , De Jong Nico , Lohse Detlef , Versluis Michel
Published: May 2008

Ultrasound contrast agents are coated microbubbles currently extensively studied to target endothelial cells, for local drug delivery. It is therefore important to distinguish acoustically free-floating bubbles from bubbles located close, or targeted to blood vessels. Here, we propose a theoretical study to understand the effect of boundaries on bubble response to ultrasound. We consider the hydrodynamic interaction of a single bubble with a wall, including all possible bubble motions: volumetric oscillations, translation, and nonspherical deformations. We also include the friction in the viscous boundary layer along the wall. We derive the coupled equations of the bubble dynamics using a Lagrangian approach. We predict the bubble response to ultrasound, as a function of various parameters (applied frequency and amplitude, bubble size and coating, bubble/wall distance). We show that our new model predicts a decrease of the resonance frequency as a bubble gets closer to a wall, in agreement with experiments. We reproduce correctly the observed decrease of oscillation amplitude for a close close to the wall, showing that it is due to the coupling between oscillation and translation rather than the friction in the boundary layer. The threshold for nonspherical oscillations is also discussed and compared to experimental measurements.
Acoustic characterization of an ultrasound surgical transmitter in the linear and nonlinear regime of working
Authors: Petosic Antonio , Ivančević Bojan , Svilar Dragoljub
Published: May 2008

The method for measurement of a derived acoustic power of an ultrasound surgical transducer has been suggested in the free field conditions. The pressure field of the transmitter, immersed in depth of quater wavelength and vibrating at the fundamental frequency (≈25kHz), has been measured with calibrated hydrophone at different excitation levels. In the linear regime, the transmitter has been theoretically described as an acoustic dipole, the source parameters have been found and good agreement between theoretical and experimental results is obtained. When transmitter is excitated at higher excitation levels, the nonlinear behaviour in loading medium appears, with strong cavitation activity. In the averaged power spectrum of the recorded acoustic pressure signal, is evident the presence of harmonics (n⋅f), subharmonics (f/q), ultraharmonics (n⋅f/q) of excitation frequency. The spatial pressure distribution of each discrete frequency component in the free acoustic field has been measured and its contribution to total acoustic power has been calculated. The total acoustic power in the cavitation noise signal is estimated integrating the averaged pressure power spectrum with appropriate contributions of each frequency component in the signal.
From sounds to melodies: Memory for sequences of pitch and loudness
Authors: Cousineau Marion , Pressnitzer Daniel , Demany Laurent
Published: May 2008

In order to understand speech or appreciate music, listeners have to process and remember patterns of sounds that vary along many perceptual dimensions. Here we investigated the perception of pitch sequences and loudness sequences, using a psychophysical method that uncouples discriminability and memory capacity. Pitch could be produced by either resolved or unresolved harmonics. Random sequences were constructed for which a single attribute (pitch or loudness) could take only two different values. These values were selected individually for each participant to produce equal discriminability (d') for isolated sounds. The participants then had to perform Same-Different judgments on pairs of sequences of two, four or eight elements each. We found that performance decreased rapidly with the number of elements for the loudness and pitch of unresolved harmonics conditions. With sequences of four and eight elements, performance was markedly better for the pitch of resolved harmonics condition. These findings show that short-term auditory memory capacity changes with the type of attribute that is varied within a sequence. For pitch, resolved harmonics yield a higher capacity than do unresolved harmonics; this could explain part of the difficulties encountered by cochlear implant users when listening to music.
Pitch discrimination: Combination of information across frequency
Authors: Gockel Hedwig E. , Carlyon Robert P. , Plack Christopher J.
Published: May 2008

Performance (d') for fundamental frequency (F0) discrimination was measured for two complex tones (A and B) presented either individually or simultaneously. The objective was to investigate how information is combined in pitch processing. For most subjects, tones A and B were filtered from 1350-1650 and 3300-4200 Hz, respectively, such that both contained only unresolved components (components were added in sine phase). The tones had identical nominal F0s of 75 Hz, and the difference in F0 between the two intervals of a 2AFC trial was the same for A and B. When A and B were tested individually, performance was equal for the two tones (d' value ̃ 1). For some subjects, to achieve equal d' for the two tones, all components were added in alternating phase, F0 was increased to 90 Hz, and tones A and B were filtered from 1375-1875 and 3900-5400 Hz, respectively. Presenting the tones simultaneously should increase d' by a factor of 1.41, if information from both were combined optimally. The results showed no increase in d' above that measured for the individual tones for three subjects, and only a very small improvement for another three subjects (factor of about 1.1) [supported by EPSRC Grant EP/D501571/1].
Additivity of auditory masking using Gaussian-shaped tones
Authors: Laback Bernhard , Balazs Peter , Toupin Gwenael , Necciari Thibaud , Savel Sophie , Meunier Sabine , Ystad Solvi , Kronland-Martinet Richard
Published: May 2008

Both temporal and spectral masking have been studied extensively in the literature. Mostly, they have been regarded as separate phenomena. Very little is known about the interaction between these two effects, i.e. masking in the time-frequency domain. Data on the time-frequency spread of masking evoked by a single Gaussian-shaped tone pulse are presented in an accompanying study at the same conference (Necciari et al.). The current study gathers data on the additivity of masking by up to four, approximately equally effective Gaussian maskers (ERB=600 Hz), separated either along the time or the frequency axis. For temporal separation, the amount of masking increases with the number of maskers, with excess masking (exceeding linear additivity) of up to 25 dB. For frequency separation (preliminary data) excess masking amounts up to 15 dB, and the higher-frequency masker (relative to the target) contributes more to the additivity than the lower-frequency maskers. Experiments with multiple maskers combining both temporal and frequency separation are underway. Combined with the single maker data, these data may serve as a basis for modeling time-frequency masking effects in complex signals. Work partly supported by OEAD (WTZ project AMADEUS) and ANR
Evaluation of auditory processing disorder and auditory efferent system functionality in adult dyslexics: towards a unification theory of auditory-language processing impairments
Authors: Hoen Michel , Grataloup Claire , Veuillet Evelyne , Thai-Van Hung , Collet Lionel , Meunier Fanny
Published: May 2008

In a recent paper, Veuillet et al., (2007) suggested that some auditory processing mechanism could be impaired in children with dyslexia. They reported a link between children's ability to perceive phonemic boundaries and the physiological functionality of their medial olivocochlear system (MOC), an auditory efferent pathway functioning under central control. In the present experiment, we extended this observation by comparing speech-in-speech comprehension performances in a group of control participants (N=40) and a group of adults who had been diagnosed dyslexic as children (N=49). Confirming the idea that patients with dyslexia present auditory processing disorders (APD), we show that adult dyslexics exhibit greater difficulty in comprehending speech in noise. Data moreover suggest a link between speech-in-noise comprehension difficulty and the MOC functionality in these participants. More precisely, it appears that the absolute functionality of the left and right MOC bundles does not differ in dyslexic patients compared to controls. What appears to be differing is the functional asymmetry in the MOC functionality between both ears, normal readers showing a classical functional asymmetry, while dyslexic adults show an absence of, or reduced functional asymmetry between MOC bundles. These results will be discussed in the context of current models of APD and Dyslexia.
The Role of Auditory-Visual Integration in Object Recognition
Authors: Suied Clara , Bonneel Nicolas , Viaud-Delmon Isabelle
Published: May 2008

Combining auditory and visual information about the same external event enhances perception and behavioural performance. Numerous factors have been shown to contribute to the integration of visual and auditory stimuli, like spatial or semantic relationships between the two stimuli. We studied the influence of spatial disparity between the auditory and the visual stimuli on bimodal object recognition in a go/no-go task, under realistic virtual environment. Participants were asked to react as fast as possible to a target object, presented in the visual and/or the auditory modality, and to inhibit a distractor object. Reaction times were significantly shorter for semantically congruent bimodal stimuli than would be predicted by independent processing of information about the auditory and the visual targets. Moreover, reaction times were significantly shorter for semantically congruent bimodal stimuli (i.e. visual and auditory targets) than for semantically incongruent bimodal stimuli (i.e. target represented in only one sensory modality). Importantly, these results were not altered by a large spatial disparity between the auditory and the visual targets. Altogether our findings suggest that rules governing multisensory integration vary according to the purpose for which auditory and visual stimuli are combined.
Fluid-structure interaction and computational aeroacoustics of the flow past a thin flexible structure
Authors: Schäfer Frank , Uffinger Thomas , Becker Stefan , Grabinger Jens , Kaltenbacher Manfred
Published: May 2008

In many technical applications the interaction between a fluid flow and a thin flexible structure leads to the generation of acoustic noise which is caused by flow induced structural vibrations. Examples for such applications are coverings and panelings of cars and airplanes. In many cases the generated noise is unwanted so that noise reduction is a topic of major interest. In the present work we investigate the acoustic field resulting from the interaction of a thin flexible structure with a turbulent flow field by means of numerical simulation. Two different model configurations are considered: one is the flow over a flexible plate, in the second case the flexible plate is located in the wake of a square cylinder. The major aim of this work is to provide a better understanding of the noise generation processes in these flow cases. The numerical methodology applied is utilized for a decomposition of the acoustic field into one part generated by the structural vibrations and another part which is due to stream noise. Finally, comparisons to experimental data available at our institute are provided.
Noise reduction prediction of Ariane 5 fairing with acoustic protection made of porous-elastic material
Authors: Frikha Slaheddine , Hamdi Mohamed Ali , Roux Philippe , Mebarek Lassen , Omrani Abderrazak
Published: May 2008

ESI Group (Formerly STRACO) has been involved during the last two decades in the numerical prediction of noise reduction index of ARIANE 5 fairing. During the 1990's, STRACO developed an axi-symmetric, boundary element model of the fairing where the fairing protection made of distributed Helmholtz Resonator is modeled by equivalent local impedance. Recently, the fairing acoustic protection has been replaced by a foam-made insulator. Such porous materials are widely used by transportation industries to improve the payload acoustic comfort. In collaboration with automotive industry, ESI group developed RAYON-VTM, a powerful tool allowing the predicting of fully trimmed vehicle vibroacoustic response up to 500 Hz. RAYON VTM model the porous-elastic material using a 3D Finite Element (PEM), based on the Modified-Biot-Equations. This new module of RAYON software has been applied to predict the vibroacoustic response of the ARIANE 5 fairing allowing a detailed modeling of the acoustic protection. A fully 3-D model of the fairing has been developed. The results show the influence of intrinsic modeling of the porous-elastic protection as well as the influence of non-axi-symmetric details usually neglected in the axi-symmetric approach.
Smart panels with active wedges
Authors: Gardonio Paolo , Aoki Yohko , Elliott Stephen J.
Published: May 2008

This paper presents an experimental study comparing the vibration and sound radiation control performance obtained from six different rectangular panels with various geometries of active wedge. Each panel is equipped with sixteen triangular piezoceramic actuators along the panel border and accelerometer sensors located at the top vertex of the triangular actuators. These sensor-actuator pairs are used to implement decentralized velocity feedback loops that produce active damping on the plate. The primary objective of this paper is to investigate the effect of the size and geometry of the triangular actuators on stability and control performance. Narrow frequency band measurements highlight that vibration reductions at the first few resonant frequencies are significantly improved by increasing the height of the triangular actuators. However, the increase of the height also results in spillover effects at frequencies higher than around 700Hz. In contrast, an increase of the base length of the triangular actuators improves the overall control performance up to 1 kHz without increasing the spillover effect.
The performance trade off of decentralised, distributed and centralised controllers
Authors: Baumann Oliver N. , Frampton Kenneth , Gardonio Paolo
Published: May 2008

Direct velocity feedback control of structures is well known to increase structural damping and thus reduce vibration. In multichannel systems the way in which the velocity signals are used to inform the actuators ranges from decentralised controller through distributed or clustered controllers to the fully centralised controller. The objective of distributed controllers is to exploit the anticipated performance advantage of the centralised controller whilst maintaining the ease of implementation and robustness of the decentralised controller. It has been observed, however, that in many vibration control systems the centralised controller struggles to perform significantly better than a decentralised controller. This paper compares a number of distributed controllers and optimisation techniques for the reduction of kinetic energy and radiated sound power and identifies the conditions under which the centralised and distributed controllers offer a significant performance advantage.
Decentralised active control of single - frequency panel vibrations using piezoelectric actuator - sensor pairs
Authors: Berry Alain , Micheau Philippe , Louviot Rémi , Brunet Yvonnick
Published: May 2008

This paper addresses active control of the bending response of a panel using independent PZT (piezoceramic) actuator - PVDF (piezopolymer) sensor pairs distributed on the panel. Previous work showed that under the assumption of collocated, dual actuator - sensor pairs, decentralised static gain control is stable due to plant matrix passivity at all frequencies. However, duality is not guaranteed for collocated PZT - PVDF pairs because of the coupling of piezoelectric transducers with both bending and extensional modes of the panel. Moreover, the spatially local nature of PZT actuator to PVDF sensor transfers on the panel can lead to a diagonal - dominant FRF matrix but is detrimental to global control of the panel vibration or acoustic radiation; hence, a non-diagonal dominant plant matrix is more likely to result in global control for this problem. In the case of single-frequency disturbance, stability analysis shows that plant matrix passivity is only required at the disturbance frequency and that a phase - shift compensation, identical for all independent units, can ensure stable decentralized control. Guidelines for the design of decentralised PZT - PVDF pairs are provided, with the objective of global vibroacoustic control of a panel.
Numerical study of volume sources associated with displacement flow during phonation
Authors: Park Jong Beom , Mongeau Luc
Published: May 2008

The glottal displacement flow is a volume flow induced by the motion of the vocal folds in the absence of transglottal pressure. This source may eventually contribute to the radiated sound, in particular during glottal opening. The volume source strength was numerically computed for a time-varying rigid M5 geometry, and decomposed into monopole and dipole components. The air mass entrained by the dipole moment was found to have a length equivalent to the glottal dimension based on the net force exerted on the fluid by the vocal folds wall. The dipole moment, associated with asymmetric geometries and/or motion, is significant even for the case of motion of a incompressible deformable solid with constant volume, but having a time-varying shape.
Calculation model of the influence of the vocal fold shape on the vocal fold oscillation form
Authors: Gömmel Andreas , Butenweg Christoph , Kob Malte
Published: May 2008

Vocal fold (VF) oscillation is driven by fluid-structure interaction effects. A possible way of modeling these effects is the finite-element (FE) method. The presented FE model consists of two coupled domains: A fluid domain representing the air, and a structural domain representing the VFs. In principle, each of the domains is a stand-alone simulation model. In the current implementation a thin three-dimensional frontal slice of the vocal folds and the sub- and supraglottal areas is modeled. Flow calculation is done using the standard Navier-Stokes equations. The air is modeled as a transient, viscous, and laminar flow. Constant physiologic values of pressure are used as driving force. For structural analysis, linear volume elements are used. There are two different models which differ in the VF shape. The first one is an assumed shape of a normal voice while the second shape was measured at an excised larynx and resembles more a falsetto voice. The results support two observations and assumptions: During normal phonation the VF touch each other in a constantly changing converging and diverging shape while during the more falsetto-like phonation, no converging/diverging shape is visible and no closure occurs.
Intraglottal pressure distributions for oblique glottal angles
Authors: Scherer Ronald C.
Published: May 2008

Asymmetric vocal fold oscillation occurs for both normal and pathological phonation. The pressures on the right and left glottal walls receive different pressures when the glottis is oblique, as we have shown previously. Different driving forces may affect the motion, although to what extent is not yet known. We have continued empirical modeling of various oblique glottal shapes using a Plexiglas model (M5), and report the findings of those studies. In general, an oblique glottis tends to receive higher pressures on the more convergent side, and the cross-channel pressure differences may shift polarity between upstream and downstream sections. The effects on intraglottal pressures for a wide range of obliquity, minimal glottal diameter, transglottal pressure, and included glottal angle will be shown and discussed relative to potential oscillatory effects. [supported by NIH R01DC03577]
Separated flow behavior in an in-vitro rigid model of the laryngeal channel
Authors: Sciamarella Denisse , Chisari Elisa , Artana Guillermo , Bailly Lucie , Pelorson Xavier
Published: May 2008

Flow through an in-vitro rigid model of the scaled-up laryngeal channel is measured using pressure sensors and visualized using the Schlieren technique for different geometrical configurations. Three downstream flow-conditions are considered: steady, quasi-impulsive and periodical using an electromechanical device controlling the inflow and producing the cyclic jet emerging from the glottis. The separated flow behavior in the presence of a ventricular constriction ("false vocal folds") is also examined. Direct theoretical flow predictions and numerical simulations are proposed to quantify the aerodynamic impact involved by the ventricular bands on the pressure distribution. Two parameters are investigated: the aperture of the ventricular bands and the distance between the vocal folds and the ventricular bands. The influence of both parameters are measured and compared to the theoretical outcome.
The Influence of Constriction Geometry on Sound Generation in Fricative Consonants
Authors: Ramsay Gordon
Published: May 2008

Sound generation in fricative consonants is traditionally supposed to depend only on the Reynolds Number, usually defined in terms of the constriction area and the volume velocity at the constriction. The potential influence of the detailed three-dimensional geometry of the constriction is often ignored, even though previous empirical studies have shown this to have an important effect on the spectral shape of the source and the overall sound strength. At present, the physical processes governing turbulent jet formation and aeroacoustic source generation in fricative consonants are not fully understood. In this paper, we use large-eddy simulations of three-dimensional viscous incompressible flow to visualize the development of the turbulent flow field and aeroacoustic source distribution in an elliptical duct representing the vocal tract, for elliptical, laminar, and grooved constriction shapes that share the same cross-sectional area function. By contrasting results for these geometries, we test the hypothesis that turbulent jet formation is determined largely by the shape of the boundary layer where flow separates at the exit of the constriction, and that the perimeter of the constriction, rather than the cross-sectional area, may therefore be a more appropriate parameter for characterizing properties of the aeroacoustic source.