Non-Radiative Recombination in a-Si:H

1994 ◽  
Vol 336 ◽  
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.

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

2020 ◽  
Vol 60 (5) ◽  
pp. 1068-1079 ◽  
Author(s):  
Krista LePiane ◽  
Christopher J Clark
Keyword(s):  
Low Frequency ◽  
Flapping Flight ◽  
Aerodynamic Noise ◽  
Tyto Alba ◽  
Frequency Range ◽  
Entire Frequency Range ◽  
Bird Flight ◽  
Sound Levels ◽  
Barn Owls ◽  
Frictional Noise

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.

Far infrared spectra and vibrational assignments of substituted benzenes

1967 ◽  
Vol 298 (1452) ◽  
pp. 51-63 ◽  
Keyword(s):  
Low Temperature ◽  
Low Frequency ◽  
Far Infrared ◽  
Marked Variation ◽  
Frequency Range ◽  
Substituted Benzenes ◽  
Low Frequencies ◽  
Vibrational Assignments ◽  
Bending Mode ◽  
Far Infrared Spectra

The vibrational absorption spectra of some substituted benzenes have been measured in the range 50 to 450 cm -1 . The compounds were measured as liquids, in solutions, as crystalline solidsat low temperature, and in polyethylene matrices. The extension of the infrared spectrum to very low frequencies has made it possible to determine new values for many fundamental vibrations. An assignment of all the vibrational frequencies in the low-frequency range has been made, from the infrared and Raman data, for p -dihalogeno-benzenes, p -halogenotoluenes, p -halogeno-nitrobenzenes, and for some mono-substituted benzenes. Some measurements have been made on the marked variation of intensity of the lowest frequency bending mode of p -dihalogeno-benzenes.

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

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]

Thermal Equilibrium, Metastable and Irreversible Defects in a-Si:H

1989 ◽  
Vol 149 ◽  
Author(s):  
R. A Street ◽  
K. Winer
Keyword(s):  
Relaxation Time ◽  
Low Temperature ◽  
Temperature Dependence ◽  
Thermodynamic Model ◽  
Thermal Equilibrium ◽  
Defect Density ◽  
Defect States ◽  
Different Types ◽  
Metastable Defect ◽  
Deposition Conditions

ABSTRACTMeasurements are reported of metastable defect states in undoped a-Si: H, with the aim of understanding the relation between the different types of metastability. The temperature dependence of the thermal equilibrium defect density agrees well with a proposed thermodynamic model and their relaxation time varies with deposition conditions. The rate of light induced defect creation and annealing in samples deposited at low temperature and with a large initial defect density, decreases progressively as the irreversible defects are removed by annealing.

scholarly journals The Low Frequency Variability of Extragalactic Radio Sources

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.

Photoluminescence and Photoacoüstic Spectroscopy of Si Single-and Multi-Step Ingot- and Wafer-Annealed GaAs Crystals

1992 ◽  
Vol 262 ◽  
Author(s):  
O. Ka ◽  
O. Oda ◽  
S. Shigetomi ◽  
T. Ikari ◽  
Y. Makita ◽  
...  
Keyword(s):  
Low Temperature ◽  
Photoacoustic Spectroscopy ◽  
Radiative Recombination ◽  
Room Temperature ◽  
Defect Density ◽  
Band Edge ◽  
Near Band Edge ◽  
Exciton Recombination ◽  
Additional Defect ◽  
Neutral Acceptor

ABSTRACTSI GaAs crystals submitted to single- or multi-step, ingot-or wafer-annealing are investigated using photoluminescence (PL) and photoacoustic spectroscopy (PA). The near-band-edge PL transitions are well resolved, with a neutral acceptor-bound exciton recombination displayed as a split doublet. The improvement induced by wafer-annealing is illustrated by the absence of additional defect-related transitions found after ingot-annealing. For the room temperature PA measurements, the intensity of a peak occuring at 1.39 eV is shown to lead to an estimation of the arsenic micro-defect density as evaluated by AB etching. The 1.39 eV PA band is also asserted to be the non-radiative recombination path of a 1.482 eV band found in the low-temperature PL spectra.

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

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.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
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.

Dynamic Damping and Stiffness Characteristics of the Rolling Tire

2001 ◽  
Vol 29 (4) ◽  
pp. 258-268 ◽  
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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