kHz Peak Research Articles

In vitro experimental study on interventional ultrasound-mediated microbubble cavitation lithotripsy

Abstract Ultrasound-mediated microbubble cavitation lithotripsy as a new minimally invasive approach has received great attention for the treatment of urinary stones. However, the attenuation of ultrasonic waves in human tissues and stone displacement during lithotripsy are two key issues limiting the development of this technology. In this paper, a method of interventional ultrasound-mediated microbubble cavitation lithotripsy is proposed, which can realize the in-situ delivery of ultrasonic waves and microbubbles. A piezoelectric ultrasound transducer with the center frequency of 461 kHz and output peak to peak acoustic pressures of 3.2 MPa is fabricated, and microbubbles with the concentration of 1.33×109/ml are synthesized. An extracorporeal experiment platform is built and in vitro tests of ultrasound mediated microbubble cavitation lithotripsy are conducted by using microbubbles with different concentrations and water. The results show that the proposed interventional ultrasound-mediated microbubble cavitation lithotripsy is an efficient method for the fragmentation of ureteral stones. The maximum mass reduction of the stone is 9.4 mg within 30 minutes of treatment under the combined action of ultrasound with the peak-negative pressure of 1.6 MPa and center frequency of 461 kHz and microbubbles with the concentration of 3.325×107/ml. The research results will provide a technical basis for further optimization of subsequent tentative schemes, in vivo experiments with animals and future clinical applications.

High-peak-power structured beams by an Nd:YAG/Cr4+:YAG laser in a near-hemispherical cavity.

An Nd:YAG/Cr4+:YAG passively Q-switched (PQS) laser in a near-hemispherical cavity is exploited to generate high-order structured pulsed fields. Under tightly focused on-axis pumping, radial-order Laguerre-Gaussian (LG) modes with controllable mode orders by the input pump power are realized to exhibit quite stable temporal behavior. The pulse repetition rates of radial-LG modes can reach up to 78 kHz with an average output power of 0.57 W and peak power beyond 300 W under a 5-W pump level. Furthermore, by introducing 1D off-axis pumping into the PQS laser, various structured pulsed fields with transverse morphologies as high-order Ince-Gaussian (IG) modes are further created. With clean and well-defined beam structures, the IG pulsed fields can be nicely reconstructed by the resonant modes of the inhomogeneous Helmholtz equation for spherical cavities. More importantly, these high-order PQS IG modes reveal highly regular pulse trains with the maximum pulse repetition rate beyond 20 kHz and overall peak power higher than 1.5 kW.

One-dimensional surface phononic crystal ring resonator and its application in gas sensing

We introduce a ring resonator, which employs a one-dimensional phononic crystal on its inner surface, and investigate its performance as a gas sensor both numerically and experimentally. Having periodic equilateral trapezoidal protrusions, the ring resonator with 207 periods is optimized through band structure calculations via the finite-element method. A surface band linear around 58 kHz is observed. The resonator exhibits sharp transmission peaks with a broad free-spectral range of 0.54 kHz. Accordingly, a peak at 58.49 kHz with a high-quality factor of 8196 appears. Application in detection of the carbon dioxide level in air with high sensitivity is demonstrated. The 58.49 kHz peak red shifts linearly at 17.3 mHz/ppm and 17.8 mHz/ppm rates, as obtained from numerical calculations and experiments, respectively. Besides, the peak shape and maximum intensity are preserved. Due to the linear shift of the resonance peak with respect to the carbon dioxide concentration, acoustic intensity at initial peak frequency can be utilized as an auxiliary means for concentrations up to 1000 ppm. The proposed ring resonator can be adapted to a variety of acoustic devices such as liquid concentration sensors based on phononic crystals, surface acoustic wave sensors, and micromechanical resonators.

Deep residual network for off-resonance artifact correction with application to pediatric body MRA with 3D cones.

To enable rapid imaging with a scan time-efficient 3D cones trajectory with a deep-learning off-resonance artifact correction technique. A residual convolutional neural network to correct off-resonance artifacts (Off-ResNet) was trained with a prospective study of pediatric MRA exams. Each exam acquired a short readout scan (1.18 ms ± 0.38) and a long readout scan (3.35 ms ± 0.74) at 3 T. Short readout scans, with longer scan times but negligible off-resonance blurring, were used as reference images and augmented with additional off-resonance for supervised training examples. Long readout scans, with greater off-resonance artifacts but shorter scan time, were corrected by autofocus and Off-ResNet and compared with short readout scans by normalized RMS error, structural similarity index, and peak SNR. Scans were also compared by scoring on 8 anatomical features by two radiologists, using analysis of variance with post hoc Tukey's test and two one-sided t-tests. Reader agreement was determined with intraclass correlation. The total scan time for long readout scans was on average 59.3% shorter than short readout scans. Images from Off-ResNet had superior normalized RMS error, structural similarity index, and peak SNR compared with uncorrected images across ±1 kHz off-resonance (P < .01). The proposed method had superior normalized RMS error over -677 Hz to +1 kHz and superior structural similarity index and peak SNR over ±1 kHz compared with autofocus (P < .01). Radiologic scoring demonstrated that long readout scans corrected with Off-ResNet were noninferior to short readout scans (P < .05). The proposed method can correct off-resonance artifacts from rapid long-readout 3D cones scans to a noninferior image quality compared with diagnostically standard short readout scans.

False killer whale and short-finned pilot whale acoustic identification

False killer whales Pseudorca crassidens and short-finned pilot whales Globicephala macrorhynchus are known to interact with long-line fishing gear in Hawaiian waters, causing eco- nomic loss and leading to whale injuries and deaths. The main Hawaiian Islands' insular popula- tion of false killer whales is listed as endangered and the offshore population is considered 'strate- gic' under the Marine Mammal Protection Act due to relatively high bycatch levels. Discriminating between these species acoustically is problematic due to similarity in the spectral content of their echolocation clicks. We used passive acoustic monitoring along with data from satellite tags to dis- tinguish signals from these 2 species. Acoustic encounters recorded with autonomous instruments offshore of the islands of Hawai'i and Kaua'i were matched with concurrent and nearby location information obtained from satellite tagged individuals. Two patterns of echolocation clicks were established for the 2 species. The overall spectral click parameters were highly similar (22 kHz peak and 25 kHz center frequency), but false killer whales had shorter duration and broader bandwidth clicks than short-finned pilot whales (225 µs, 8 kHz (�3 dB bandwidth) and 545 µs, 4 kHz, respectively). Also, short-finned pilot whale clicks showed distinct spectral peaks at 12 and 18 kHz. Automated classification techniques using Gaussian mixture models had a 6.5% median error rate. Based on these findings for echolocation clicks and prior published work on whistle classification, acoustic encounters of false killer whales and short-finned pilot whales on auto - nomous instruments should be identifiable to species level, leading to better long-term monitoring with the goal of mitigating bycatch.

Studying biological membranes with extended range high-speed atomic force microscopy.

High—speed atomic force microscopy has proven to be a valuable tool for the study of biomolecular systems at the nanoscale. Expanding its application to larger biological specimens such as membranes or cells has, however, proven difficult, often requiring fundamental changes in the AFM instrument. Here we show a way to utilize conventional AFM instrumentation with minor alterations to perform high-speed AFM imaging with a large scan range. Using a two—actuator design with adapted control systems, a 130 × 130 × 5 μm scanner with nearly 100 kHz open—loop small-signal Z—bandwidth is implemented. This allows for high-speed imaging of biologically relevant samples as well as high-speed measurements of nanomechanical surface properties. We demonstrate the system performance by real-time imaging of the effect of charged polymer nanoparticles on the integrity of lipid membranes at high imaging speeds and peak force tapping measurements at 32 kHz peak force rate.

Behavioral audiogram of two Arctic foxes (Vulpes lagopus)

With increased polar anthropogenic activity, such as from the oil and gas industry, there are growing concerns about how Arctic species will be affected. Knowledge of species’ sensory abilities, such as auditory sensitivities, can be used to mitigate the effects of such activities. Herein, behavioral audiograms of two captive adult Arctic foxes (Vulpes lagopus) were measured using a yes/no paradigm and descending staircase method of signal presentation. Both foxes displayed a typical mammalian U-shaped audiometric curve, with a functional hearing range of 125 Hz–16 kHz (sensitivity ≤ 60 dB re: 20 μPa) and average peak sensitivity of 24 dB re: 20 μPa at 4 kHz. The foxes had a lower frequency range and sensitivity than would be expected when compared to previous audiograms of domestic dogs (Canis familiaris) and other carnivores. These differences indicate Arctic foxes (V. lagopus) may have a lower frequency range than previously expected, which was similar to the only other fox species tested to date, kit foxes (Vulpes macrotis). Alternatively, differences may be due to testing constraints, such as masking of test signals by ambient noise and/or an unintentionally trained conservative response bias, which most likely resulted in underestimated hearing curves. While results of this study should be interpreted with caution due to its limitations, findings indicate that foxes have a narrower frequency range than formerly presumed. Anthropogenic activities near fox habitats can mitigate their impacts by reducing noise at frequencies within the functional hearing range and peak sensitivities of this species.

Towards quantized current arbitrary waveform synthesis

The generation of ac modulated quantized current waveforms using a semiconductor non-adiabatic single electron pump is demonstrated. In standard operation, the single electron pump generates a quantized output current of I = ef, where e is the charge of the electron and f is the pumping frequency. Suitable frequency modulation of f allows the generation of ac modulated output currents with different characteristics. By sinusoidal and saw tooth like modulation of f accordingly modulated quantized current waveforms with kHz modulation frequencies and peak currents up to 100 pA are obtained. Such ac quantized current sources could find applications ranging from precision ac metrology to on-chip signal generation.

Diagnostics of nocturnal calls of Sciaena umbra (L., fam. Sciaenidae) in a nearshore Mediterranean marine reserve

Calls emitted by the brown meagre Sciaena umbra (L., fam. Sciaenidae) were recorded at the Natural Marine Reserve of Miramare (Trieste, Italy) in seven nocturnal surveys (12-h continuous sampling) during the summer of 2009. Calls consist of pulses, with the main energy content below 2 kHz and mean peak frequency of c. 270 Hz. Pulses were short, with an average duration of 20 ms and a pulse period of 100 ms. Sounds lasted approximately 500 ms. Three types of sound patterns were recognized: irregular (I), regular (R) and the chorus (C). Their acoustic parameters are described showing that I, R and C differ in pulse duration, pulse peak frequency and pulse period. Occurrence of the three call types changes throughout the night: the R pattern occurred mainly at dawn and dusk, C predominated after nightfall, while I calls were produced sporadically during the whole nocturnal period. Our results indicate that S. umbra has a pronounced nocturnal rhythm in vocalizing behaviour and highlight how the diagnostic time–frequency pattern of S. umbra calls can be used to identify the species in the field. Considering that the abundance of S. umbra is currently declining, the information presented here will be relevant in developing non-invasive and low-cost monitoring acoustic systems for managing S. umbra conservation and fishery along the Mediterranean Sea.

550-mW Output Power From a Narrow Linewidth All-Phosphate Fiber Laser

We present a compact monolithic all-phosphate glass fiber laser with up to 550 mW of output power operating on a single longitudinal mode. We measured a linewidth of less than 60 kHz and relaxation oscillation peak amplitudes below -100 dB/Hz without active RIN-supression. The laser cavity has been formed by inscribing fiber Bragg gratings (FBG) directly into heavily Er3+ Yb3+ doped phosphate glass fiber using femtosecond laser pulses and a phasemask. The compact form factor and higher output power combined with the low noise and narrow line width characteristic make this laser an ideal candidate for ranging, interferometry and sensing applications.

Evaluation of Partial Discharge in Power Transformers by Acoustic Emission Method and Propagation Modeling of Acoustic Signal

Transformers are one of the most important and costly components of any power system. Proper monitoring of the health of a transformer is thus inevitable. Online monitoring of partial discharges (PD) is one of the ways by which the risk of catastrophic failure of a power apparatus can be reduced. Common insulation in power transformers are pressboard and oil. Unconventional PD measurement was developed for several decades ago as a form of PD detection system. In these PD measurement systems that are named unconventional method PD is analyzed by indirect features of this phenomenon, which includes electrical, acoustic, UHF, optical, and chemical methods. The main advantage of unconventional method is the ability of this method in order to decrease the amount of signal to noise ratio for on-site or on-line measurement. A study of the correlation between acoustic emission signals generated by PD and electrical PD charges is inevitable. By developing the speed of measuring devices like digital signal processor (DSP) the possibility of evaluation and calculation of acoustic signals in very short time have been increased. The aim of this paper is evaluation of acoustic signals for two different kind of pressboard (new and aged) with two types of sensors (75 kHz and 150 kHz peak frequency) and simulation of Acoustic Emission (AE) signals propagation which are produced due to PD inside a sample transformer tank by using Finite Element Method (FEM). 

Behavioral in-air audiogram of two Arctic fox (Alopex lagopus) at the Columbus Zoo and Aquarium

The aerial audiograms of two captive adult, male Arctic fox (Alopex lagopus) were measured using a two-alternative, forced-choice paradigm and descending staircase method of signal presentation at the Columbus Zoo and Aquarium. Both fox displayed a typical mammalian U-shaped audiometric curve, with a functional hearing range of 125 Hz to 16 kHz (sensitivity &amp;lt; 60 dB re: 20 μPa) and average peak sensitivity of 22 dB re: 20 μPa at 4 kHz. This range is similar to airborne hearing thresholds previously measured for two closely related species, the kit fox (Vulpes marotis) and the domestic dog (Canis familiaris). There was little variability around threshold and no significant difference between the hearing curves of the two fox. The peak sensitivities of the Arctic fox overlaps their vocal range, the vocal range of their prey; field voles (Microtus agrestis), collared lemmings (Dicrostonyx groenlandicus), Canada geese (Branta canadensis), and the hearing range of a predator; the polar bear (Ursus maritimus). Ambient noise levels were monitored and test frequencies below 5 kHz were possibly masked. Potential response bias was examined using Receiver Operator Characteristic analysis and had a conservative bias. Masking effects and conservative response bias may have resulted in slightly underestimated hearing curves.

Quantifying Snowfall Rates using Underwater Sound

It is well known that rainfall rate can be estimated by analyzing the spectral character and level of the underwater sound that it generates. There have been a few field reports of increased sound levels associated with the occurrence of snow; these reports suggest an increase in sound levels above 20 kHz. It has previously been demonstrated that snowflakes can generate both a small impact sound and a separate high frequency pulse that is consistent with the sound generated by a resonant bubble. One aspect that these earlier studies have not explored is the dependence of this sound generation on the type or intensity of snowfall. We report on observations of sound generated by snow falling into a tank of water, quantifying snowfall rate using an Optical Scientific precipitation gauge. Recorded signals allowed analysis of frequencies between 1 and 50 kHz. Using the classification scheme of the International Association of Hydrological Sciences for snow, seven distinct snow types, as well as rain and freezing rain, were observed with a range of precipitation rates. Snow types that produced a signal included column, needle, irregular crystal, graupel and ice pellet. Snow types for which no signal was detected were plate, stellar crystal and spatial dendrite. The previously reported rise in high frequency sound could not be distinguished unambiguously in the present data. A small peak at around 12 kHz was seen in spectra of some snow types similar to the characteristic 14 kHz peak seen in some rain-generated sounds. There was a clear correlation between sound level and snowfall rate at frequencies above 10 kHz.

The acoustic features of the long distance advertisement call produced by Panthera tigris altaica, the Amur (Siberian) tiger.

The long distance advertisement call (LDAC) frequently referred to as a moan, an intense mew or a territorial roar, is commonly exchanged by adult members of Panthera tigris living both in captivity and in the wild. While the functionality of the call is not understood ethologically, its social nature is unambiguous, and isolated individuals living in captivity exchange the call repeatedly over extended periods of time. In this report, we concentrate on LDACs produced by P. tigris altaica. The average duration of the LDAC was just under 2 s. The average fundamental frequency, f0, was 0.155 kHz, ranging from ∼0.113 to 0.176 kHz. Spectrograms were dominated by distinct harmonically related frequency modulated frequency sweeps, although subharmonics were also observed. Overall peak frequency, the frequency exhibiting maximum acoustic power, was centered at ∼0.330 kHz and instantaneous peak frequency frequently shifted from one harmonic to another throughout the call’s time course. The bulk of broadcast energy was contained in a band of frequencies ranging from ∼0.1 to 0.8 kHz at 20 dB down from the peak frequency, and bandwidth expanded to ∼3.7 and 4.9 octaves at the 30 and 40 dB down points, respectively. [Funding provided by NSF Grant 0823417.]

Development of a superconducting magnet for nuclear magnetic resonance using bulk high‐temperature superconducting materials

AbstractWe developed a trapped‐field magnet system using a bulk high‐temperature superconducting (HTS) material (Sm‐Ba‐Cu‐O; abbreviated as Sm123) and used it to observe a signal of 1H nuclear magnetic resonance (NMR). The compact magnet system can fit on a table and needs no conventional refrigerant such as liquid helium. The magnet has a c‐axis‐oriented single‐domain Sm123 bulk superconductor containing 20 wt.% Ag and was synthesized in the melt‐textured process. The magnet is constructed of two cylindrical pieces, 36‐mm outer and 7‐mm inner diameters, respectively, and 16‐mm thickness. This configuration results in magnetic field stability and suitable homogeneity for observation of NMR signal. The magnet was magnetized to 3 T by an ordinary NMR superconducting magnet by using a field cooling (FC) method. The bulk magnet was magnetized at 60K and has been kept at the temperature under 58K by using a pulse tube refrigerator. We observed 1H NMR signal from the silicon rubber with the size of 1.2 mm diameter and 1.5 mm length at 2.89 Tesla (123 MHz) and 228 kHz peak width. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 31B: 65–70, 2007.

HELMHOLTZ BEHAVIOR OF A NITROGEN PLASMA ARC CHAMBER

The dynamic behaviour of an original double anode plasma torch which provides a long lifetime and highly stable supersonic low-pressure nitrogen plasma jet is analyzed by means of classical tools such as FFT, correlation function and Wigner distribution. At both arc chamber stages, the plasma is investigated by means of spectroscopic diagnostics. They reveal that the anode attachments are diffuse rather than local. Electron temperature and number density are comparable to those derived from a simple LTE model. Voltage, arc current and light intensity temporal series exhibit two main characteristic frequencies: the electric generators yield very stable and reproducible 150 Hz oscillations, whereas the firing of the second arc gives birth to a sharp 6.7 kHz peak which is ascribed to the generation of acoustic waves in the region of the first anode attachment. The value of this frequency that depends neither on the electrical injected power nor on the mass flow rate is interpreted by assuming that the arc chamber acts as a Helmholtz oscillator.

Neuroethology of the katydid T-cell. II. Responses to acoustic playback of conspecific and predatory signals.

Although early work on the tettigoniid T large fiber suggested that it might mediate early-warning and escape behavior in katydids, the majority of research thereafter has focused on the ability of the T-cell to detect, localize and/or discriminate mate-calling song. Interestingly, T-cell responses to conspecific song are rarely examined for more than a few seconds, despite the fact that many katydids sing for minutes or hours at a time. In this paper, the second of a pair examining the physiology of the T-cell in Neoconocephalus ensiger, we recorded T-cell responses using longer-duration playbacks (3 min) of conspecific song (Katydid signal 30 ms syllables, 9-25 kHz bandwidth, 12-15 kHz peak frequency) and two types of bat-like ultrasound, a 10 ms, 80->30 kHz frequency-modulated sweep (Bat 10 signal) and a 30 ms, 80->30 kHz frequency-modulated sweep (Bat 30 signal). Spiking responses were distinctly biased towards the short-duration ultrasonic signal, with more spikes per pulse, at a shorter spike latency and at a higher instantaneous firing frequency to the Bat 10 signal than to the Katydid signal or, surprisingly, to the Bat 30 signal. The ability of the T-cell to encode the temporal pattern of the stimulus was particularly striking. Only for the predatory bat signals did T-cell spiking faithfully copy the stimulus; playbacks of conspecific song resulted in significantly weaker spiking responses, particularly in male katydids. The results demonstrate that responses from the T-cell alone may be sufficient for katydids to discriminate biologically relevant signals pertinent to the phonotactic behavior patterns involved in mate attraction and predator avoidance.

Discovery of Kilohertz Quasi-periodic Oscillations in the Z source GX 340+0

We have discovered two simultaneous kHz quasi-periodic oscillations (QPOs) in the Z source GX 340+0 with the Rossi X-ray Timing Explorer. The X-ray hardness-intensity and color-color diagram each show a full Z-track, with an extra limb branching off the flaring branch of the Z. Both peaks moved to higher frequencies when the mass accretion rate increased. The two peaks moved from 247 +/- 6 and 567 +/- 39 Hz at the left end of the horizontal branch to 625 +/- 18 and 820 +/- 19 Hz at its right end. The higher frequency peak's rms amplitude (5-60 keV) and FWHM decreased from ~5% and 383 +/- 135 Hz to ~2%, and 145 +/- 62 Hz, respectively. The rms amplitude and FWHM of the lower peak were consistent with being constant near 2.5 % and 100 Hz. The kHz QPO separation was consistent with being constant at 325 +/- 10 Hz. Simultaneous with the kHz QPOs we detected the horizontal branch oscillations (HBO) and its second harmonic, at frequencies between 20 and 50 Hz, and 38 and 69 Hz, respectively. The normal branch oscillations were only detected on the upper and middle normal branch, and became undetectable on the lower normal branch. The HBO frequencies do not fall within the range predicted for Lense-Thirring (LT) precession, unless either the ratio of the neutron star moment of inertia to neutron star mass is at least 4, 10^45 gcm^2/M_sun, the frequencies of the HBO are in fact the sub-harmonic oscillations, or the observed kHz peak difference is half the spin frequency and not the spin frequency. During a 1.2 day gap between two observations, the Z-track in the hardness-intensity diagram moved to higher count rates by about 3.5%. Comparing data before and after this shift, we find that the HBO properties are determined by position on the Z-track and not directly by count rate or X-ray colors.

Hearing and hunting in red bats (Lasiurus borealis, Vespertilionidae): audiogram and ear properties.

We examined aspects of hearing in the red bat (Lasiurus borealis) related to its use of biosonar. Evoked potential audiograms, obtained from volume-conducted auditory brainstem responses, were obtained in two bats, and the sound pressure transformation of the pinna was measured in three specimens. Field-recorded echolocation signals were analysed for comparison. The fundamental sonar search calls sweep from 45 to 30 kHz (peak energy at 35 kHz), approach-phase calls sweep from 65 to 35 kHz (peak 40 kHz) and terminal calls sweep from 70 to 30 kHz (peak 45 kHz). The most sensitive region of the audiogram extended from 10 kHz to 45-55 kHz, with maximum sensitivity as low as 20 dB SPL occurring between 25 and 30 kHz. A relative threshold minimum occurred between 40 and 50 kHz. With increasing frequency, the acoustic axis of the pinna moves upwards and medially. The sound pressure transformation was noteworthy near 40-45 kHz; the acoustic axis was closest to the midline, the -3 dB acceptance angles showed local minima, and the pinna gain and interaural intensity difference were maximal. These results are related to the known echolocation and foraging behavior of this species and match the spectral components of approach- and final-phase calls. We conclude that co-evolution with hearing prey has put a higher selective pressure on optimizing localization and tracking of prey than on improving detection performance.

Average spectrum of cochlear activity: a possible synchronized firing, its olivo-cochlear feedback and alterations under anesthesia

Average spectrum of electrophysiological cochlear activity (ASECA) recorded from the cochlea or the eighth nerve is related to firing of auditory neurons and has been used recently in search of an objective measure of tinnitus both in animal models and in humans. Little is known about neuro-sensory processes underlying the spectral features of ASECA. The present study used awake and/or anesthetized animals and investigated effects of various sounds presented contralaterally and ipsilaterally. Contralateral stimulation with noise bands at frequencies above about 8 kHz and below acoustic interaural cross-talk decreased the amplitude of the 1 kHz peak of ASECA. When presented ipsilaterally noises produced either an increase or a decrease of this spectral peak when the acoustic bandwidth was respectively above or below 1.5 kHz. Pure tones when presented contralaterally had no detectable effect. When presented ipsilaterally pure tones with frequencies higher than about 4 kHz decreased the 1 kHz peak of ASECA. The detailed time course of sound-induced variations of the 1 kHz peak was measured by time averaging. The resulting response patterns resemble PST histograms of the auditory nerve. Sedation and anesthesia deepened the 500 Hz trough of ASECA and shifted it towards 400 Hz. Sedation induced a diminution and anesthesia an almost complete suppression of the decrease of the 1 kHz peak induced by contralateral noise. Overall these data indicate that ASECA would reflect synchronized firings and they provide evidence for an influence of olivo-cochlear feedback sensitive to the state of awakeness.