Evidence that the Dorsal Velvet of Barn Owl Wing Feathers Decreases Rubbing Sounds during Flapping Flight

Synopsis Owls have specialized feather features hypothesized to reduce sound produced during flight. One of these features is the velvet, a structure composed of elongated filaments termed pennulae that project dorsally from the upper surface of wing and tail feathers. There are two hypotheses of how the velvet functions to reduce sound. According to the aerodynamic noise hypothesis, the velvet reduces sound produced by aerodynamic processes, such as turbulence development on the surface of the wing. Alternatively, under the structural noise hypothesis, the velvet reduces frictional noise produced when two feathers rub together. The aerodynamic noise hypothesis predicts impairing the velvet will increase aerodynamic flight sounds predominantly at low frequency, since turbulence formation predominantly generates low frequency sound; and that changes in sound levels will occur predominantly during the downstroke, when aerodynamic forces are greatest. Conversely, the frictional noise hypothesis predicts impairing the velvet will cause a broadband (i.e., across all frequencies) increase in flight sounds, since frictional sounds are broadband; and that changes in sound levels will occur during the upstroke, when the wing feathers rub against each other the most. Here, we tested these hypotheses by impairing with hairspray the velvet on inner wing feathers (P1-S4) of 13 live barn owls (Tyto alba) and measuring the sound produced between 0.1 and 16 kHz during flapping flight. Relative to control flights, impairing the velvet increased sound produced across the entire frequency range (i.e., the effect was broadband) and the upstroke increased more than the downstroke, such that the upstroke of manipulated birds was louder than the downstroke, supporting the frictional noise hypothesis. Our results suggest that a substantial amount of bird flight sound is produced by feathers rubbing against feathers during flapping flight.

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Bending Vibrations of the Femur and the Oscillatory Behavior of a Cemented Femoral Hip Endoprosthesis

Journal of Biomechanical Engineering ◽

10.1115/1.1286317 ◽

2000 ◽

Vol 122 (4) ◽

pp. 416-422

Author(s):

M. Thomsen ◽

A. Go¨rtz ◽

U. V. Na¨gerl ◽

D. Kubein-Meesenburg ◽

W. Go¨rtz ◽

...

Keyword(s):

Degrees Of Freedom ◽

Low Frequency ◽

Oscillatory Behavior ◽

Measuring System ◽

Frequency Range ◽

Entire Frequency Range ◽

Bending Vibrations ◽

Low Frequencies ◽

Hip Endoprosthesis ◽

Resonance Frequencies

The paper presents a novel method for recording amplitude and phase of 6D-vibrations of a spatial pendulum over a wide frequency range (10 Hz up to 20 kHz). The six degrees of freedom of the pendulum mass were monitored by three electrodynamic stereo pickups. At rest, the tips of the needles and the pendulum’s center of mass defined the reference system with respect to which the oscillations of the mass were recorded in terms of their amplitudes and phases. Its small dimensions, constant transfer characteristics, linearity, high dynamics, and virtual lack of reaction onto the moving system over the entire frequency range provided the advantages of the measuring system. This method was used to analyze the spatial 6D-vibrations of the head of a cemented femoral hip endoprosthesis when the femur was stimulated to bending vibrations. The head of the prosthesis carried out axial rotational vibrations at every frequency used to stimulate the femur. The amplitudes of the axial rotations of the cortical bone were small in comparison to the ones of the prosthesis head, indicating that axial rotational vibrations following femur bending vibrations mainly stressed the spongiosa and the cement layer. This was observed over the entire frequency range, including at the low frequencies relevant for gait. Over the low-frequency range, as well as at some of the higher resonance frequencies, stationary instantaneous helical axes characterized the vibrations. The measurements suggest the mechanism that the interface “implant-bone” may already be stressed by axial torsional loads when the femur is loaded by bending impacts that are known to occur during walking. [S0148-0731(00)01604-6]

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Non-Radiative Recombination in a-Si:H

MRS Proceedings ◽

10.1557/proc-336-189 ◽

1994 ◽

Vol 336 ◽

Cited By ~ 3

Author(s):

M. Schubert ◽

R. Stachowitz ◽

R. Saleh ◽

W. Fuhs

Keyword(s):

Low Temperature ◽

Radiative Recombination ◽

Defect Density ◽

Low Frequency ◽

Lifetime Distribution ◽

Geminate Recombination ◽

Frequency Range ◽

Defect States ◽

Entire Frequency Range ◽

Radiative Tunneling

ABSTRACTFrequency-resolved photoluminescence spectroscopy (FRS) is used to study non-radiative recombination in a-Si:H using generation rates sufficiently small to garantee geminate recombination at low temperature. The quenching of the photoluminescence by a higher defect density ND and an increase of temperature influences the QFRS spectra differently: Whereas for increasing ND the quenching of the signal is more pronounced on the low frequency side raising temperature leads to a uniform decrease in the entire frequency range. The dependence of the lifetime distribution on ND is quantitatively explained in a model where radiative recombination competes with non-radiative tunneling into defect states.

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Evolution and Ecology of Silent Flight in Owls and Other Flying Vertebrates

Integrative Organismal Biology ◽

10.1093/iob/obaa001 ◽

2020 ◽

Vol 2 (1) ◽

Cited By ~ 4

Author(s):

Christopher J Clark ◽

Krista LePiane ◽

Lori Liu

Keyword(s):

Empirical Support ◽

Aerodynamic Noise ◽

Current Evidence ◽

Anatomical Location ◽

Bird Flight ◽

Acoustic Signature ◽

Apparent Relationship ◽

Frictional Sound ◽

New Perspective ◽

Frictional Noise

Synopsis We raise and explore possible answers to three questions about the evolution and ecology of silent flight of owls: (1) do owls fly silently for stealth, or is it to reduce self-masking? Current evidence slightly favors the self-masking hypothesis, but this question remains unsettled. (2) Two of the derived wing features that apparently evolved to suppress flight sound are the vane fringes and dorsal velvet of owl wing feathers. Do these two features suppress aerodynamic noise (sounds generated by airflow), or do they instead reduce structural noise, such as frictional sounds of feathers rubbing during flight? The aerodynamic noise hypothesis lacks empirical support. Several lines of evidence instead support the hypothesis that the velvet and fringe reduce frictional sound, including: the anatomical location of the fringe and velvet, which is best developed in wing and tail regions prone to rubbing, rather than in areas exposed to airflow; the acoustic signature of rubbing, which is broadband and includes ultrasound, is present in the flight of other birds but not owls; and the apparent relationship between the velvet and friction barbules found on the remiges of other birds. (3) Have other animals also evolved silent flight? Wing features in nightbirds (nocturnal members of Caprimulgiformes) suggest that they may have independently evolved to fly in relative silence, as have more than one diurnal hawk (Accipitriformes). We hypothesize that bird flight is noisy because wing feathers are intrinsically predisposed to rub and make frictional noise. This hypothesis suggests a new perspective: rather than regarding owls as silent, perhaps it is bird flight that is loud. This implies that bats may be an overlooked model for silent flight. Owl flight may not be the best (and certainly, not the only) model for “bio-inspiration” of silent flight.

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The Low Frequency Variability of Extragalactic Radio Sources

Symposium - International Astronomical Union ◽

10.1017/s0074180900155159 ◽

1987 ◽

Vol 121 ◽

pp. 211-214

Author(s):

D.R. Altschuler ◽

B.K. Dennison ◽

K.J. Mitchell ◽

S.L. O'Dell ◽

J.J. Broderick ◽

...

Keyword(s):

Low Frequency ◽

Radio Sources ◽

Frequency Range ◽

Spectral Evolution ◽

Entire Frequency Range ◽

Extragalactic Radio Sources ◽

Low Frequency Variability

The spectral evolution between 0.3 and 15 GHz of the extragalactic radio sources 0235+164 and 1611+343 (DA406) is presented. The data show two very different forms of behavior. For 0235+164 the variations over the entire frequency range are correlated and consistent with being intrinsic to the source, whereas for DA406 an extrinsic cause for the variability seems probable.

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Improved Source Characteristics of a Handclap for Acoustic Measurements: Utilization of a Leather Glove

Acoustics ◽

10.3390/acoustics2040045 ◽

2020 ◽

Vol 2 (4) ◽

pp. 803-811

Author(s):

Rick de Vos ◽

Nikolaos M. Papadakis ◽

Georgios E. Stavroulakis

Keyword(s):

Sound Pressure Level ◽

Sound Pressure ◽

Low Frequency ◽

Pressure Level ◽

Acoustic Measurements ◽

Frequency Range ◽

Acoustic Parameters ◽

Source Characteristics ◽

Sound Levels ◽

Engineering Practices

A handclap is a convenient and easily available source for room acoustic measurements. If used correctly (e.g., application of optimal hand configuration) it can provide usable results for the measurement of acoustic parameters, within an expected deviation. Its biggest drawbacks are the low sound pressure level (especially in the low frequency range) as well as its low repeatability. With this in mind, this paper explores the idea of testing a handclap with a glove in order to assess the effect on its source characteristics. For this purpose, measurements were performed with 12 participants wearing leather gloves. Sound levels were compared with simple handclaps without gloves, and between grouped results (overall A-weighted SPL, octave bands, 1/3 octave bands). Measurements were also performed several times to evaluate the effect on repeatability. Results indicate that the use of leather gloves can increase the sound levels of a handclap by 10 dB and 15 dB in the low frequency ranges (63 Hz and 125 Hz octave bands, respectively). Handclaps with leather gloves also point toward improved repeatability, particularly in the low-frequency part of the frequency spectrum. In conclusion, compared to simple handclaps without gloves, evidence from this study supports the concept that handclaps with leather gloves can be used in engineering practices for improved room acoustic measurements of room impulse response.

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Noise Spectra of Six Gey Bz:H Thermo-sensing Films for Micro-bolometers

MRS Proceedings ◽

10.1557/proc-1153-a19-05 ◽

2009 ◽

Vol 1153 ◽

Author(s):

Andrey Kosarev ◽

Ismael Cosme ◽

Alfonso Torres

Keyword(s):

Room Temperature ◽

Low Frequency ◽

Noise Spectrum ◽

Frequency Range ◽

Conductivity Activation Energy ◽

Entire Frequency Range ◽

Temperature Conductivity ◽

Room Temperature Conductivity ◽

Increasing Temperature ◽

Noise Spectra

AbstractNoise spectra in plasma deposited SixGeyBz:H thermo-sensing films for micro-bolometers have been studied. The samples were characterized by SIMS (composition) and conductivity (room temperature conductivity, activation energy) measurements. The noise spectra were measured in the temperature range from T= 300 K to T=400 K and in the frequency range from f=2 Hz to f=2×104 Hz. The noise spectra SI(f) for the samples Si0.11Ge0.88:H and Si0.04Ge0.71B0.23 can be described by SI(f) ˜ f– β with β = 1 and β = 0.4, respectively. For the sample Si0.06Ge0.67B0.26 two slopes were observed: in low frequency region f≤ 103 Hz β1= 0.7 and at higher frequencies f>103 Hz β2= 0.13. Increasing temperature resulted in an increase of noise magnitude and a change of β values. The latter depended on film composition. The correlation observed between noise and conductivity activation energies suggests that noise is due to bulk rather than interface processes. Noise spectrum of the thermo-sensing film Si0.11Ge0.88:H was compared with that for micro-bolometer structure with the same thermo-sensing film. The micro-bolometer structure showed higher noise value in entire frequency range that assumed additional processes inducing noise.

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Evaluation of Special Hearing Aids for Deaf Children

Journal of Speech and Hearing Disorders ◽

10.1044/jshd.3604.527 ◽

1971 ◽

Vol 36 (4) ◽

pp. 527-537 ◽

Cited By ~ 1

Author(s):

Norman P. Erber

Keyword(s):

Hearing Aids ◽

High Frequency ◽

Hearing Aid ◽

Low Frequency ◽

Acoustic Stimulation ◽

Deaf Children ◽

Frequency Range ◽

Frequency Limit ◽

Unpublished Studies ◽

Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

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Dynamic Damping and Stiffness Characteristics of the Rolling Tire

Tire Science and Technology ◽

10.2346/1.2135243 ◽

2001 ◽

Vol 29 (4) ◽

pp. 258-268 ◽

Cited By ~ 12

Author(s):

G. Jianmin ◽

R. Gall ◽

W. Zuomin

Keyword(s):

Dynamic Behavior ◽

Variable Parameter ◽

Low Frequency ◽

Vertical Load ◽

Frequency Range ◽

Inflation Pressure ◽

Vehicle Simulation ◽

Dynamic Damping ◽

Speed Range ◽

Stiffness Characteristics

Abstract A variable parameter model to study dynamic tire responses is presented. A modified device to measure terrain roughness is used to measure dynamic damping and stiffness characteristics of rolling tires. The device was used to examine the dynamic behavior of a tire in the speed range from 0 to 10 km/h. The inflation pressure during the tests was adjusted to 160, 240, and 320 kPa. The vertical load was 5.2 kN. The results indicate that the damping and stiffness decrease with velocity. Regression formulas for the non-linear experimental damping and stiffness are obtained. These results can be used as input parameters for vehicle simulation to evaluate the vehicle's driving and comfort performance in the medium-low frequency range (0–100 Hz). This way it can be important for tire design and the forecasting of the dynamic behavior of tires.

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