Propagation of Audiofrequency Sound in High Polymers

1950 ◽  
Vol 23 (1) ◽  
pp. 163-171
Author(s):  
R. S. Witte ◽  
B. A. Mrowca ◽  
E. Guth
Keyword(s):  
Room Temperature ◽  
Low Frequency ◽  
Intermolecular Forces ◽  
Temperature Curve ◽  
Frequency Range ◽  
Dynamic Measurements ◽  
Time Effects ◽  
And Shifts ◽  
Viscoelastic Constants ◽  
Made In

Abstract Velocity and attenuation measurements were made in thin strips of rubber from 0.5 to 5 kc and from −5° to 90° C to obtain the dynamic viscoelastic constants of Butyl and GR-S gum stocks. Above room temperature velocity and attenuation are higher in Butyl gum than in GR-S. In all cases, the velocity increases with decreasing temperature and increasing frequency. The attenuation shows a peak with temperature. For Butyl, the peaks are broad and occur at higher temperatures than for GR-S. For both stocks an increase in frequency gives peaks which are higher, sharper, and shifted to higher temperatures. In some instances, there are indications of peaks in the attenuation versus frequency at frequencies beyond our range of measurement. The behavior of the dynamic modulus in the temperature and frequency range studied is similar to that of the velocity. These results, combined with low temperature static measurements and very low frequency dynamic measurements, indicate a U-shaped modulus-temperature curve whose minimum broadens and shifts to higher temperatures with increasing frequency. This may be explained by a generalization of the kinetic theory of rubber elasticity, taking into account intra- and intermolecular forces, and considering time effects.

Some measurements in the self-preserving jet

1969 ◽  
Vol 38 (3) ◽  
pp. 577-612 ◽  
Author(s):  
I. Wygnanski ◽  
H. Fiedler
Keyword(s):  
Low Frequency ◽  
Convection Velocity ◽  
Hot Wire ◽  
Frequency Range ◽  
Mean Velocity ◽  
Frequency Spectra ◽  
Velocity Fluctuations ◽  
Taylor’S Hypothesis ◽  
Velocity Turbulence ◽  
Made In

The axisymmetric turbulent incompressible and isothermal jet was investigated by use of linearized constant-temperature hot-wire anemometers. It was established that the jet was truly self-preserving some 70 diameters downstream of the nozzle and most of the measurements were made in excess of this distance. The quantities measured include mean velocity, turbulence stresses, intermittency, skewness and flatness factors, correlations, scales, low-frequency spectra and convection velocity. The r.m.s. values of the various velocity fluctuations differ from those measured previously as a result of lack of self-preservation and insufficient frequency range in the instrumentation of the previous investigations. It appears that Taylor's hypothesis is not applicable to this flow, but the use of convection velocity of the appropriate scale for the transformation from temporal to spatial quantities appears appropriate. The energy balance was calculated from the various measured quantities and the result is quite different from the recent measurements of Sami (1967), which were obtained twenty diameters downstream from the nozzle. In light of these measurements some previous hypotheses about the turbulent structure and the transport phenomena are discussed. Some of the quantities were obtained by two or more different methods, and their relative merits and accuracy are assessed.

Detection of geomagnetic disturbances with ionospheric calibration solutions of LOFAR astronomical observations

2021 ◽  
Author(s):  
Katarzyna Budzińska ◽  
Maaijke Mevius ◽  
Marcin Grzesiak ◽  
Mariusz Pożoga ◽  
Barbara Matyjasiak ◽  
...  
Keyword(s):  
Low Frequency ◽  
Limiting Factors ◽  
Electromagnetic Signal ◽  
Frequency Range ◽  
Geomagnetic Disturbances ◽  
Low Frequencies ◽  
Astronomical Observations ◽  
The Earth ◽  
Wavelet Transform Analysis ◽  
Made In

<p>Perturbation of an electromagnetic signal due to its passing through the Earth’s ionosphere is one of the limiting factors in obtaining high quality astronomical observations at low frequencies. Since the establishment of the Low Frequency Array (LOFAR) radio interferometer, which is operating  in the frequency range between 10  and 240 MHz, effort has been made in order to properly remove this effect during the calibration routine.</p><p>In this study we use differential TEC solutions obtained from calibration of Epoch of Reionization project’s observations and investigate their sensitivity to weak geomagnetic disturbances with wavelet transform analysis. Comparison to the different geomagnetic indices allows us to study the possible origin of medium scale ionospheric structures that have been detected.</p>

Low-frequency noise in RF-sputtered Pb-doped 2223 phase BiSrCaCuO thin films

1994 ◽  
Vol 72 (5-6) ◽  
pp. 270-273 ◽  
Author(s):  
I. Shih ◽  
A. L. Li ◽  
W. W. Lam ◽  
C. X. Qiu ◽  
L. Ngo Phong ◽  
...  
Keyword(s):  
Thin Films ◽  
Normal State ◽  
Room Temperature ◽  
Low Frequency ◽  
Thermal Fluctuation ◽  
Temperature Curve ◽  
Frequency Noise ◽  
Superconducting Thin Films ◽  
Current Dependence ◽  
Noise Measurements

Noise measurements were carried out on RF-sputtered Pb-doped 2223 phase BiSrCaCuO superconducting thin films. No definite relationship between noise and bias current was observed in the superconducting state, however, a square-current dependence of noise was found in the normal state. The magnitude of the noise in the BiSrCaCuO films at room temperature was one to five orders of magnitude larger than that in a normal metal. Near the tail of the resistance transition, noise peaks were observed that were 3–12 K below the maximum of the derivative resistance–temperature curve. Noise dependence on frequency shows an approximate 1/f relation in both normal and superconducting states. The origin of the noise in the normal state is believed to be due to thermal fluctuation or resistance fluctuation and the larger noise near zero TC is possibly caused by grain boundaries in the films.

Dielectric and impedance spectroscopy of K+-doped MgAl2O4 nanoparticles

2018 ◽  
Vol 32 (15) ◽  
pp. 1850189
Author(s):  
Javed Ahmad ◽  
S. H. Bukhari ◽  
M. Qadeer Awan ◽  
M. Ehsan Mazhar ◽  
A. R. Makhdoom
Keyword(s):  
Dielectric Constant ◽  
Impedance Spectroscopy ◽  
High Frequency ◽  
Dielectric Response ◽  
Room Temperature ◽  
Parent Compound ◽  
Low Frequency ◽  
Space Charge Polarization ◽  
Relaxation Phenomena ◽  
Frequency Range

In this study, the dielectric response of Potassium (K[Formula: see text])-doped magnesium aluminates nanoparticles (Mg[Formula: see text]K[Formula: see text]Al2O4, x = 0.0, 0.25, 0.5, 0.75, 1.0) have been investigated as a function of frequency (20 Hz to 2 MHz) at room-temperature. Interestingly, the behavior of dielectric constant indicated the ionic or space charge polarization in the low-frequency range and it remains almost constant at high frequency. However, the value of conductivity increases at higher frequencies which is consistent with the previously reported results for the parent compound MgAl2O4. Moreover, the Cole–Cole plots represent various relaxation phenomena reflecting the existence of grain (boundaries) resistance effects.

LOW‐FREQUENCY IMPEDANCE PARAMETERS OF BASALT, GRANITE, AND QUARTZITE

Geophysics ◽  
1973 ◽  
Vol 38 (1) ◽  
pp. 68-75 ◽  
Author(s):  
A. S. Khalafalla ◽  
W. J. Maegley
Keyword(s):  
Room Temperature ◽  
Electrical Impedance ◽  
Analog Circuit ◽  
Low Frequency ◽  
Frequency Variation ◽  
Frequency Range ◽  
Argand Diagram ◽  
Circular Arcs ◽  
Impedance Parameters ◽  
Zero Frequency

An analog circuit digital computer setup was used to evaluate rock electrical impedance and phase angle in the frequency range 0.05 to 2 khz. Room‐temperature measurements were made on several samples of basalt, granite, and quartz. Argand diagram presentation of rock reactance as a function of its resistance at a series of frequencies described a semicircular arc. Rock impedance circular arcs can be used to define the rock resistivity at infinite frequency and the dc resistivity at the limit of zero frequency. Variation of rock resistance with the logarithm of frequency indicated finite rock dielectric dispersions at characteristic frequency ranges. Also, variation of rock reactance with the logarithm of frequency exhibited finite relaxation peaks, which can be used to difine the rock characteristics or turnover frequency as well as a characteristic or relaxation time.

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.

scholarly journals Dielectric properties of ternary composites of triblock polymer surfactant, liquid crystal and organic solvent

2014 ◽  
Vol 04 (03) ◽  
pp. 1450022 ◽  
Author(s):  
M. R. Fisch ◽  
Clinton Braganza ◽  
L. C. Chien ◽  
R. G. Petschek
Keyword(s):  
Liquid Crystal ◽  
Organic Solvent ◽  
Room Temperature ◽  
Low Frequency ◽  
Ternary Mixtures ◽  
Frequency Range ◽  
Getter Effect ◽  
Triblock Polymer ◽  
Polymer Surfactant ◽  
Triblock Polymers

Dielectric spectroscopy, at room temperature (20°C), is used to study the dielectric response of ternary mixtures of commercial nematic liquid crystal mixtures E7 and E33, an organic solvent N-Methyl-2-Pyrrolidone (NMP) and a triblock polymers in the frequency range from 0.01 Hz to 1 MHz. The results indicate a dielectric relaxation in the hectohertz region. Individually, both E7 and NMP have rather large low frequency conductivities; however, the low frequency (0.01–10 Hz) behavior of the mixtures has no such behavior. We attribute this behavior to an ion getter effect of the triblock polymer surfactant. Optimized ternary mixtures obtain a real dielectric constant near 230, and loss tangent less than 0.05 at frequencies near 10 mHz.

Experimental Study of Low-Frequency Effects on the Dynamic Modulus of a Buna-N Rubber

1955 ◽  
Vol 28 (1) ◽  
pp. 131-138 ◽  
Author(s):  
Allen Q. Hutton ◽  
A. W. Nolle
Keyword(s):  
Dynamic Modulus ◽  
Room Temperature ◽  
Temperature Scale ◽  
Dynamic Properties ◽  
Low Frequency ◽  
Frequency Range ◽  
Frequency Increase ◽  
Frequency Effects ◽  
Similar Compound ◽  
Linear Dynamic

Abstract The linear dynamic Young's modulus of a vulcanized Buna-N gum rubber was measured at frequencies of 0.05, 0.10, and 1.00 cps, in the temperature range − 22° C to 30° C, by a method in which a small differential sinusoidal elongation is superimposed on a 5 per cent static elongation. The width of the dispersion range on the temperature scale (the range in which the logarithm of the modulus increases steeply with decreasing temperature) is only about 10° C, contrasted with widths as great as 25° C found in previous measurements on a similar compound at frequencies of several kilocycles. The modulus-temperature plot shifts upward by only about 4° C per decade of frequency increase of the present range, contrasted with about 10° C per decade in the previous measurements at higher frequencies. It is concluded that this elastomer cannot be described properly by means of the “method of reduced variables”, in which the dynamic properties are ascribed to mechanisms having identical temperature dependence, and that the low-temperature behavior is governed by mechanisms distinct from those effective in the audio-frequency range at room temperature.

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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