scholarly journals Vibration Confinement Phenomena in Disordered, Mono-Coupled, Multi-Span Beams

1992 ◽  
Vol 114 (4) ◽  
pp. 521-530 ◽  
Author(s):  
D. Bouzit ◽  
C. Pierre
Keyword(s):  
Perturbation Methods ◽  
Average Rate ◽  
Wide Frequency Range ◽  
Practical Significance ◽  
Frequency Range ◽  
Engineering Structures ◽  
High Frequencies ◽  
Strong Localization ◽  
Simple Supports ◽  
Statistical Perturbation

The effects of small, periodicity-destroying irregularities on the dynamics of multi-span beams are examined. It is shown that minute deviations of the span lengths from an ideal value alter qualitatively the dynamic response by localizing vibrations and waves to small geometric regions. These confinement phenomena are studied over a wide frequency range for beams resting on simple supports and with variable interspan coupling. Approximations of the localization factor (the average rate of spatial exponential decay of the vibration amplitude) are derived by statistical perturbation methods and validated by Monte Carlo simulations. If the interspan coupling is strong, localization effects are weak and of no practical significance for most engineering structures. On the other hand, localization is severe for small interspan coupling. Confinement is also generally stronger near the edges of frequency passbands and increases nearly linearly with frequency from passband to passband. This means that strong localization occurs at high frequencies, even for large static coupling between spans.

scholarly journals Vibration Confinement Phenomena in Disordered, Mono-Coupled, Multi-Span Beams

1991 ◽  
Author(s):  
Djamel Bouzit ◽  
Christophe Pierre
Keyword(s):  
Average Rate ◽  
Wide Frequency Range ◽  
Practical Significance ◽  
Engineering Structures ◽  
High Frequencies ◽  
Strong Localization ◽  
Simple Supports ◽  
Very High Frequencies ◽  
Very High ◽  
Statistical Perturbation

Abstract The effects of small, periodicity-destroying irregularities on the dynamics of multi-span beams are examined. It is shown that minute deviations of the span lengths from an ideal value alter qualitatively the dynamic response by localizing vibrations and waves to small geometric regions. These confinement phenomena are studied over a wide frequency range for beams resting on simple supports and with variable interspan coupling. Approximations of the localization factor (the average rate of spatial exponential decay of the vibration amplitude) are derived by statistical perturbation methods and validated by Monte Carlo simulations. If the interspan coupling is strong, localization effects are weak and of no practical significance for most engineering structures. On the other hand, localization is severe for small interspan coupling. Confinement is also generally stronger near the edges of frequency passbands and increases nearly linearly with frequency from passband to passband. This means that strong localization occurs at high frequencies, even for large static coupling between spans. De-localization is also observed at very high frequencies.

Investigation of Room Temperature Mössbauer Spectroscopy and Initial Permeability Properties of Al3+ Substituted Cobalt Ferrites

SPIN ◽  
2018 ◽  
Vol 08 (01) ◽  
pp. 1840005
Author(s):  
Rabia Pandit ◽  
Pawanpreet Kaur ◽  
K. K. Sharma ◽  
Mohd. Hashim ◽  
Ravi Kumar
Keyword(s):  
Loss Factor ◽  
Room Temperature ◽  
Magnetic Hyperfine Field ◽  
Initial Permeability ◽  
Wide Frequency Range ◽  
Ion Concentration ◽  
Frequency Range ◽  
High Frequencies ◽  
Relative Loss ◽  
Cobalt Ferrites

In the present work, Al[Formula: see text] substituted cobalt ferrites (CoFe[Formula: see text]AlxO4, [Formula: see text], 0.4, 0.6, 0.8) have been synthesized via standard solid-state reaction technique. The incorporation of Al[Formula: see text] ions in cobalt ferrite has been shown to play an important role in modifying the magnetic properties. The room temperature (300[Formula: see text]K) [Formula: see text]Fe Mössbauer spectra reveals that the studied samples show two characteristic ferromagnetic zeeman sextets at A and B-sites at lower Al[Formula: see text] ion concentration (i.e., up to [Formula: see text]). However, a paramagnetic relaxation has been noted for higher Al[Formula: see text] substitution (for [Formula: see text] and 0.8) samples. The dependence of the Mössbauer parameters such as isomer shift, quadrupole splitting, line width and magnetic hyperfine field on Al[Formula: see text] ion concentration has also been noted. The variations in initial permeability over a wide frequency range (125[Formula: see text]kHz to 30[Formula: see text]MHz) at 300[Formula: see text]K have been recorded. The fairly constant values of initial permeability and the low values of the relative loss factor of the order of 10[Formula: see text] to 10[Formula: see text] over the wide frequency range are the important findings of the present work. The observed low values of relative loss factor at high frequencies suggest that the studied ferrites are promising materials to be used in microwave applications.

Metachronal Co-ordination of the Comb Plates of the Ctenophore Pleurobrachia

1968 ◽  
Vol 48 (1) ◽  
pp. 111-125
Author(s):  
M. A. SLEIGH
Keyword(s):  
Wave Velocity ◽  
Sea Water ◽  
Wide Frequency Range ◽  
Relative Importance ◽  
Frequency Range ◽  
Mechanical Contact ◽  
Low Frequencies ◽  
High Frequencies ◽  
Common Features ◽  
Rapid Transmission

1. The activity of comb plates of Pleurobrachia was analysed from cine films. 2. The interval between successive beats of a comb plate varied from several seconds to about 50 msec. in normal sea water; this variation in frequency was accompanied by a variation wave velocity. There was an almost linear relationship between wave velocity and frequency, ranging from a minimal wave velocity of about 20 mm./sec. at low frequencies to a maximal wave velocity of about 80 mm./sec. at the highest frequencies. 3. The wave velocity was accelerated at low frequencies by increased Mg2+ concentrations, by ouabain and by curare, and the same substances decreased the wave velocity at high frequencies. 4. The frequency of beat was accelerated by certain concentrations of adrenaline, serotonin, Mg2+, ouabain and curare. Decreases of frequency were found in acetylcholine (and eserine) and strychnine. These substances act on the excitability of the pacemaker. 5. It is concluded that metachronal transmission is by a flow of electric current from one comb plate to the next. Depolarization, either by a recent excitation of the comb plate or by agents like ouabain causes increased excitability and a more rapid transmission. The minimum phase difference between adjacent comb plates was about 5 msec. 6. The comb plates are almost entirely dependent on a conducted impulse for their excitation; occasionally a spontaneous excitation occurs. The membranelles of Stentor depend more on excitation within the ciliary base and less on the conducted impulse. The two systems are believed to share common features, but differ in the relative importance of these features. 7. Reverse waves involving the beating of comb plates in the normal direction were observed. The wave velocity of these waves increased only slightly over a wide frequency range. Reverse waves of this type are believed to be transmitted by mechanical contact between the comb plates.

scholarly journals EXTENSION OF THE FREQUENCY-RANGE OF INTERFEROMETERS FOR THE "MAGNETIC" COMPONENTS OF GRAVITATIONAL WAVES?

2007 ◽  
Vol 22 (13) ◽  
pp. 2361-2381 ◽  
Author(s):  
CHRISTIAN CORDA
Keyword(s):  
Data Analysis ◽  
Frequency Dependence ◽  
Gravitational Waves ◽  
Response Functions ◽  
Frequency Range ◽  
Total Response ◽  
High Frequencies ◽  
Magnetic Components ◽  
Linear Dimensions ◽  
Dominant Part

Recently, with an enlightening treatment, Baskaran and Grishchuk have shown the presence and importance of the so-called "magnetic" components of gravitational waves (GW's), which have to be taken into account in the context of the total response functions of interferometers for GW's propagating from arbitrary directions. In this paper the analysis of the response functions for the magnetic components is generalized in its full frequency dependence, while in the work of Baskaran and Grishchuk the response functions were computed only in the approximation of wavelength much larger than the linear dimensions of the interferometer. It is also shown that the response functions to the magnetic components grow at high frequencies, differently from the values of the response functions to the well-known ordinary components that decrease at high frequencies. Thus the magnetic components could in principle become the dominant part of the signal at high frequencies. This is important for a potential detection of the signal at high frequencies and confirms that the magnetic contributions must be taken into account in the data analysis. More, the fact that the response functions of the magnetic components grow at high frequencies shows that, in principle, the frequency-range of Earth-based interferometers could extend to frequencies over 10000 Hz.

Installation for testing electronic voltmeters over a wide frequency range

1976 ◽  
Vol 19 (10) ◽  
pp. 1525-1526
Author(s):  
A. M. Fedorov ◽  
V. V. Krestovskii ◽  
V. S. Kiselev ◽  
S. A. Razumovskii ◽  
V. A. Shcheglov
Keyword(s):  
Wide Frequency Range ◽  
Frequency Range
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