Dielectric and mechanical alterations of snow properties near the melting temperature

2003 ◽  
Vol 81 (1-2) ◽  
pp. 233-239 ◽  
Author(s):  
I Takei ◽  
N Maeno
Keyword(s):  
Melting Temperature ◽  
Propagation Velocity ◽  
Low Frequency ◽  
Dielectric Measurements ◽  
Frequency Range ◽  
Temperature Range ◽  
Snow Properties ◽  
Response Method ◽  
Dielectric And Mechanical Properties ◽  
Snow Samples

The dielectric and mechanical properties of snow were investigated in the temperature range –15 to 0°C. Dielectric measurements were carried out in the frequency range 50 Hz – 5 MHz; the low-frequency conductivity (at 100 Hz) of snow samples shows a peak in the temperature range –3 to –0.3°C and the dielectric dispersion-strength also shows a minimum in this same range. The propagation velocity of an elastic wave through snow samples was measured with a vibration response method in the frequency range 10 Hz – 1 MHz; the propagation velocity shows an increase with the bond growth as a result of progressive sintering, and a significant decrease above –0.6°C. The temperature dependence of the low-frequency conductivity and the propagation velocity for snow samples show a hysteresis near the melting temperature. A boundary between ice particles in snow samples is discussed as a means for understanding these phenomena. PACS Nos.: 61.43Gt, 77.22Gm, 46.40-f, 73.25+i

scholarly journals The low-frequency conductivity of snow near the melting temperature

2001 ◽  
Vol 32 ◽  
pp. 14-18 ◽  
Author(s):  
Iwao Takei ◽  
Norikazu Maeno
Keyword(s):  
Activation Energy ◽  
Particle Size ◽  
Melting Temperature ◽  
Low Frequency ◽  
Dielectric Dispersion ◽  
Average Particle ◽  
Temperature Range ◽  
Ice Surfaces ◽  
Increasing Temperature ◽  
Snow Samples

AbstractDielectric measurements of snow were carried out in the temperature range –15° to 0°C and in the frequency range 50 Hz to 5 MHz. The snow samples (about 400 kg m–3 density) used were stored snow (average particle size: 2 mm) and hoar-frost (particle size: <1 to 5 mm). The frequency characteristics of dielectric parameters showed a dielectric dispersion (Davidson-Cole type) around 30 kHz and a low-frequency dielectric dispersion (Cole-Cole circular law type). The a.c. conductivity showed a dielectric dispersion around 30 kHz and two characteristic constant values in the frequency ranges above 1 MHz and below 100 Hz (the high-frequency conductivity σ∞ and the low-frequency conductivity σLOW). The low-frequency conductivity σLOW showed a peak at about –2°C. This behavior has never been noted by previous researchers. The σLOW showed an activation energy of about 1 eV below –5°C. This means that the σLOW is mainly caused by a surface conduction. The activation energy increased with increasing temperature above –5°C. This means that the σLOW in this temperature range is affected by the quasi-liquid layer on ice surfaces. The σLOW above –2°C decreased with increasing temperature. The apparently curious behavior near the melting temperature is attributed to the numerous free ice surfaces within the porous snow. This conclusion was reached because our measurements without the free ice surfaces showed no such conductivity peaks for solid polycrystalline ice samples and for snow samples soaked with kerosene in the cooling process.

scholarly journals Dielectric Properties of Ternary ( ) ( )x ( ) x ZnO MgO PO 30 2 5 70− (x = 5, 8, 13) Glasses

2014 ◽  
Vol 5 (1) ◽  
Author(s):  
S. F. Khor ◽  
Z. A. Talib ◽  
W. M. Daud ◽  
H. A. A. Sidek ◽  
W. M. M. Yunus ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
Dielectric Permittivity ◽  
Empirical Data ◽  
Loss Factor ◽  
Low Frequency ◽  
Frequency Range ◽  
Melt Quenching ◽  
Dipolar Relaxation ◽  
Temperature Range

(ZnO)30(MgO)x(P2O5)70-x glasses of the composition x = 5, 8 and 13 mol % have been prepared by melt quenching technique. The dielectric permittivity (89) and loss factor (8:) were measured in the frequency range from 0.01 Hz to 1 MHz and in the temperature range 303 to 573 K . From the results there are evidence of dipolar relaxation occurring between 103 – 106 Hz while at low frequency the spectrum is dominated by dc conduction which manifested by the 1/@ slope of loss factor plot. Value of the relaxing frequency (@p) plotted against 1/T shows one electrical transportation mechanism. The empirical data was sufficiently fitted by using Harviliak-Negami equation.

scholarly journals Ionische dielektrische Relaxationsprozesse in Festkörpern, I / Ionic Dielectric Relaxation Processes in Solids, I

1973 ◽  
Vol 28 (11-12) ◽  
pp. 721-730 ◽  
Author(s):  
Günter Schön
Keyword(s):  
Activation Enthalpy ◽  
Low Frequency ◽  
Life Time ◽  
Relaxation Processes ◽  
Dielectric Measurements ◽  
Frequency Range ◽  
Kcal Mole ◽  
Type Layer ◽  
Frequency Relaxation ◽  
Cation Sites

Dielectric measurements have been made on single-crystals of mica-type layer silicates (vermiculites) in the frequency range between 30 Hz and 10 MHz. The migration of K+-and NH4+-interlayer cations by free cation sites causes a low-frequency relaxation. It is interpreted by the orientation of large dipoles they form with parent negative layer charges. For both ions the activation enthalpy of diffusion across the lattice is 11.94 kcal/mole. Additional N-H · · · O hydrogen bonds are formed by the NH4+ ions at low temperatures. There results a bond enthalpy of 1.3 kcal/mole and a life-time of 1.2 · 10-5 sec (at 40°C). A discussion of the different rate process equations yields the applicability of the Bauer equation.

Molecular relaxation in Chitosan films in GHz frequency range

2014 ◽  
Vol 1613 ◽  
pp. 83-88
Author(s):  
Siva Kumar-Krishnan ◽  
Evgen Prokhorov ◽  
Gabriel Luna-Barcenas
Keyword(s):  
Activation Energy ◽  
Low Frequency ◽  
Bound Water ◽  
Wide Frequency Range ◽  
Frequency Range ◽  
Temperature Range ◽  
A Value ◽  
Chitosan Films ◽  
First Time

ABSTRACTThe molecular relaxations behavior of chitosan (CS) films in the wide frequency range of 0.1-3x109 Hz (by using three different impedance analyzers) have been investigated in the temperature range of -100C to 120°C using Dielectric Spectroscopy (DS). Additionally to the low frequency molecular relaxations such as α and β relaxations, for the first time, high frequency (1-3 GHz) relaxation process has been observed in the chitosan films. This relaxation exhibits Arrhenius-type dependence in the temperature range of -100 C to 54°C with negative activation energy -2.7 kJ/mol. At temperatures above 54°C, the activation energy changes from -2.7 kJ/mol to +4.4 kJ/mol. Upon cooling, the activation energy becomes negative again with a value of -1.2 kJ/mol. The bound water between chitosan molecules strongly modifies molecular motion and the relaxation spectrum, giving rise to a new relaxation at the frequency at ca. 1 GHz. In situ FTIR analysis has shown that this relaxation related to the changes in vibration of the –OH, NH and –CO functional groups.

scholarly journals Inelastic Behaviour of Ice Ih Single Crystals in the Low-Frequency Range Due to Dislocations

1978 ◽  
Vol 21 (85) ◽  
pp. 375-384 ◽  
Author(s):  
René Vassoille ◽  
Christian Maï ◽  
Joseph Perez
Keyword(s):  
High Temperature ◽  
Internal Friction ◽  
Single Crystals ◽  
Empirical Relation ◽  
Low Frequency ◽  
Frequency Range ◽  
High Temperature Range ◽  
Temperature Range ◽  
Inelastic Behaviour ◽  
Torsional Pendulum

Abstract The inelastic behaviour of ice Ih single crystals has been investigated by an inverted torsional pendulum in the low-frequency range. Three features are distinguished: (i) a relaxation peak previously observed by several authors in the higher-frequency range, (ii) an internal friction increasing with temperature in the high-temperature range (230–273 K), (iii) within this high-temperature range, internal friction becomes amplitude dependent, and this dependence becomes greater the greater the temperature. In this case, the internal friction has been interpreted in terms of movements of dislocations. Hence, the experimental results are interpreted with a model of internal friction based on an empirical relation for the velocity of dislocations. This model of internal friction is in fair agreement with experimental data . It is possible then to get an estimate of dislocation density. Hence it is shown that internal friction experiments can be useful in the study of the plastic behaviour of ice single crystals.

scholarly journals Inelastic Behaviour of Ice Ih Single Crystals in the Low-Frequency Range Due to Dislocations

1978 ◽  
Vol 21 (85) ◽  
pp. 375-384
Author(s):  
René Vassoille ◽  
Christian Maï ◽  
Joseph Perez
Keyword(s):  
High Temperature ◽  
Internal Friction ◽  
Single Crystals ◽  
Empirical Relation ◽  
Low Frequency ◽  
Frequency Range ◽  
High Temperature Range ◽  
Temperature Range ◽  
Inelastic Behaviour ◽  
Torsional Pendulum

AbstractThe inelastic behaviour of ice Ih single crystals has been investigated by an inverted torsional pendulum in the low-frequency range. Three features are distinguished:(i) a relaxation peak previously observed by several authors in the higher-frequency range,(ii) an internal friction increasing with temperature in the high-temperature range (230–273 K),(iii) within this high-temperature range, internal friction becomes amplitude dependent, and this dependence becomes greater the greater the temperature.In this case, the internal friction has been interpreted in terms of movements of dislocations. Hence, the experimental results are interpreted with a model of internal friction based on an empirical relation for the velocity of dislocations. This model of internal friction is in fair agreement with experimental data . It is possible then to get an estimate of dislocation density. Hence it is shown that internal friction experiments can be useful in the study of the plastic behaviour of ice single crystals.

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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