Magnetic Permeability and Relaxation Frequency in High Frequency Magnetic Materials.

2001 ◽  
Vol 674 ◽  
Author(s):  
M.I. Rosales ◽  
H. Montiel ◽  
R. Valenzuela
Keyword(s):  
High Frequency ◽  
Domain Walls ◽  
Magnetocrystalline Anisotropy ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Anisotropy Constant ◽  
Relaxation Frequency ◽  
Resonance Relaxation ◽  
Frequency Behavior

ABSTRACTAn investigation of the frequency behavior of polycrystalline ferrites is presented. It is shown that the low frequency dispersion (f < 10 MHz) of permeability is associated with the bulging of pinned domain walls, and has a mixed resonance-relaxation character, closer to the latter. It is also shown that there is a linear relationship between the magnetocrystalline anisotropy constant, K1, and the relaxation frequency. The slope of this correlation depends on the grain size. Such a relationship could allow the determination of this basic parameter from polycrystalline samples.

Mechanisms of Noise Transmission through Helicopter Gearbox Support Struts

1994 ◽  
Vol 116 (4) ◽  
pp. 548-554 ◽  
Author(s):  
M. J. Brennan ◽  
R. J. Pinnington ◽  
S. J. Elliott
Keyword(s):  
High Frequency ◽  
Vibration Isolation ◽  
Low Frequency ◽  
Structural Members ◽  
Vibration Transmission ◽  
Gear Noise ◽  
High Frequencies ◽  
Passive Vibration Isolation ◽  
In Series ◽  
Frequency Behavior

Helicopter gearbox support struts are structural members designed to take large compressive and tensile mechanical loads. They also act as vibration transmission paths connecting the major noise and vibration generators of the main rotor and gearbox to the fuselage and cabin. In this paper the mechanisms of vibration transmission through these struts are examined. The differences between the low frequency behavior that is important in the transmission of the rotor vibrations, and the high frequency behavior that is important in the transmission of gear noise are discussed. A flexible element is introduced in series with the strut, and the limitations of this simple passive measure in attenuating longitudinal and flexural vibrations are highlighted. The analysis shows that there is a difference in the mechanisms of vibration transmission between low and high frequencies, and that there are difficulties in applying effective passive vibration isolation measures to this system.

Required Data Collection Times for Steady and Quasi-steady Experiments

2017 ◽  
Author(s):  
Robert F. Roddy ◽  
David E. Hess
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Frequency Noise ◽  
Surface Ship ◽  
System A ◽  
Low Pass ◽  
Collection Period ◽  
Almost All ◽  
Low Pass Filters

One of the requirements in performing steady or quasi-steady experiments is the determination of adequate collection times so that the data will not be biased due to low frequency energy in the data stream. Since virtually all steady experiments run at DTMB have low pass filters in line with the signal conditioning, high frequency noise is not a consideration in determining the required collection times. At both EMB and DTMB almost all of the surface ship drag measurements were made using gravity type balances until about 1970. These balances used both springs and dampers to modify the natural frequency of the system so that a good average model drag could be determined in a 5-6 sec collection period. Submarine model experiments began using block gages to measure drag beginning in the late 1950's. For these experiments crude methods were used to damp the output data but, to the author’s knowledge, no methods were ever put into place that was analogous to the springs and damper system. A method for determining the required collection times for any steady or quasi-steady experiment is presented along with sample cases showing the necessity for, and the utility of, using such a method.

MEASURING OF ELASTIC MODULI BY MEANS OF SUB-SURFACE SOUNDING METHOD

2020 ◽  
pp. 44-53
Author(s):  
A. V. Kozlov
Keyword(s):  
Elastic Moduli ◽  
Point Contact ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Surface Measurement ◽  
Longitudinal And Shear Waves ◽  
Material Sample ◽  
Dynamic Elastic Moduli ◽  
Table Data

The method of determination of elastic moduli for different materials by means of measuring of longitudinal and shear waves’ velocities is discussed in the paper. The velocities are measured by obtaining the time of flight between a pair of low frequency ultrasonic dry point contact transducers installed on the surface of the studied material sample. Factors defining the accuracy of such measurement are indicated which mainly consist of physical velocity frequency dispersion, fundamental although small differences between static and dynamic elastic moduli measurements, velocity dependence on temperature etc. Comparison between Young’s modulus and Poisson’s ratio, obtained experimentally and from table data, is given for various plastics and steel samples. It shows good agreement of different methods’ data and demonstrates the applicability of the suggested elastic moduli ultrasonic sub-surface measurement method.

Effects of Off-Frequency Detection in Brief-Tone Audiometry

1974 ◽  
Vol 17 (4) ◽  
pp. 576-588 ◽  
Author(s):  
Michele Spence ◽  
Lawrence L. Feth
Keyword(s):  
High Frequency ◽  
Temporal Integration ◽  
Low Frequency ◽  
High Frequency Hearing Loss ◽  
Frequency Detection ◽  
Stimulus Artifact ◽  
Brief Tones ◽  
High Pass

Many studies of auditory temporal integration by pathological ears have used listeners with an abrupt high-frequency hearing loss. While this configuration may lend itself to use of the listener as his own control, it presents the opportunity for detection of the low-frequency energy of the brief-tone bursts. This study was designed to assess the role of low-frequency energy in the determination of brief-tone thresholds of listeners with such abrupt high-frequency losses. Low-frequency energy was reduced to subthreshold levels by passing the brief tones through a filter system which had a sharp high-pass characteristic. For both normal and impaired listeners, no significant differences in threshold were found between filtered and unfiltered brief tones. Thus, we must conclude that although the opportunity for off-frequency detection is present, the abnormal temporal integration functions cannot be attributed to stimulus artifact.

The Twin Clinical Method in Dermatology

1970 ◽  
Vol 19 (1-2) ◽  
pp. 257-257
Author(s):  
R. Cavalieri
Keyword(s):  
Epidermolysis Bullosa ◽  
High Frequency ◽  
Skin Diseases ◽  
Acne Vulgaris ◽  
Low Frequency ◽  
Clinical Method ◽  
Clinical Evolution ◽  
High Concordance ◽  
Mz Twins

Genetic skin diseases have been considered with respect to their population and family frequencies, as well as to their concordance values, in MZ and DZ twin pairs. The clinical evolution of the disease has been further considered in its various stages and compared in MZ and DZ twins, concordant for the disease.The material consisted of 100 twin pairs, with at least one member affected, subdivided with respect to concordance and zygosity. For each dermatosis, then, the population and family frequencies have been calculated. The following dermatoses could be studied: psoriasis, acne vulgaris, keratosis pilaris, alopecia areata, epidermolysis bullosa and dermatitis seborrheica.A high concordance of clinical evolution in MZ twins has appeared to correspond to a low frequency of the disease, while a high frequency appears to correspond to low concordance values. This finding may be very useful for a better understanding of the disease's inheritance, as well as of its penetrance and expression.It has been finally possible to evaluate the hereditary quantum vs. the environmental one in the determination of a dermatosis, by means of Holzinger's coefficient of heredity (H). The estimates of the latter vary from 35 to 50% in the various dermatoses examined.

The dielectric properties of aqueous nucleic acid solutions

1966 ◽  
Vol 291 (1426) ◽  
pp. 368-388 ◽  
Keyword(s):  
Dielectric Properties ◽  
High Frequency ◽  
Deoxyribonucleic Acid ◽  
General Pattern ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Theoretical Interpretation ◽  
Acid Solutions ◽  
Dispersion Region ◽  
Ionic Polarization

The dielectric properties of aqueous solutions of the sodium salts of ribonucleic acid and deoxyribonucleic acid have been determined. The general pattern of behaviour observed for other aqueous polyelectrolyte systems has been verified in these studies. There are indications that a low frequency dispersion region (below 2 Mc/s) is present as well as the normal high frequency dispersion region. The theoretical interpretation of the experimental results makes use of the O’Konski theory of ionic polarization and the formulation of an equilibrium between counterions ‘non-specifically bound’ and ‘free’ from the electrostatic field of the polyion. Calculations are made on the basis of this theory and estimates of the values of the specific conductivities existing at the polyion surface are made.

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