scholarly journals Low frequency events at Mt. Etna: some problems and open questions

1996 ◽  
Vol 39 (2) ◽  
Author(s):  
S. Alparone ◽  
S. Gresta
Keyword(s):  
Low Frequency ◽  
Seismic Array ◽  
Open Questions ◽  
Short Period ◽  
Spectral Peaks ◽  
Mt Etna ◽  
Low Amplitude

A short period seismic array setting at Mt. Etna symmetrically in regard to the fracture of the 1991-1993 eruption allowed an analysis of low frequency events which occurred in the first phase of the mentioned eruption. We recorded about 50 events, 19 of them belong to a family. They show very low amplitude values and spectral peaks ranging 0.5-4.5 Hz. The evidence of this family of events shows how the process driving the dynamics of the fluid in the volcano is often the same.

Frequency Response Analysis of Piecewise Nonlinear Vibration Isolator

2005 ◽  
Author(s):  
Patrick Stahl ◽  
G. Nakhaie Jazar
Keyword(s):  
Low Frequency ◽  
High Amplitude ◽  
Relative Displacement ◽  
Response Analysis ◽  
Frequency Response Analysis ◽  
State Behavior ◽  
Vibration Isolators ◽  
Short Period ◽  
Secondary Suspension ◽  
Low Amplitude

Non-smooth piecewise functional isolators are smart passive vibration isolators that can provide effective isolation for high frequency/low amplitude excitation by introducing a soft primary suspension, and by preventing a high relative displacement in low frequency/high amplitude excitation by introducing a relatively damped secondary suspension. In this investigation a linear secondary suspension is attached to a nonlinear primary suspension. The primary is assumed to be nonlinear to model the inherent nonlinearities involved in real suspensions. However, the secondary suspension comes into action only during a short period of time, and in mall domain around resonance. Therefore, a linear assumption for the secondary suspension is reasonable. The dynamic behavior of the system subject to a harmonic base excitation has been analyzed utilizing the analytic results derived by applying the averaging method. The analytic results match very well in the transition between the two suspensions. A sensitivity analysis has shown the effect of varying dynamic parameters in the steady state behavior of the system.

scholarly journals Seismic monitoring of Campi Flegrei and Vesuvius by stand-alone instruments

2015 ◽  
Vol 58 (5) ◽  
Author(s):  
Mario La Rocca ◽  
Danilo Galluzzo
Keyword(s):  
Signal To Noise Ratio ◽  
Broad Band ◽  
Low Frequency ◽  
Volcanic Tremor ◽  
Seismic Signal ◽  
Seismic Monitoring ◽  
Campi Flegrei ◽  
Array Data ◽  
Short Period ◽  
Low Amplitude

<p>A seismic network of more than 20 broad band stations and two arrays of 10 short period stations each, all working in local acquisition mode, are used to improve the seismic monitoring of Campi Flegrei and Vesuvius for research purposes. Data provided by stand-alone instruments are characterized by high quality and very continuous data streams, therefore they are appropriate to detect and analyze any seismic signals possibly related with the volcanic activity. Array data are particularly useful to discover and analyze seismic events characterized by low amplitude, low signal to noise ratio and emergent onset, but whose signals are more coherent among the array stations than the background noise. Since the background seismic signal is very high at both volcanoes, particularly at Campi Flegrei, seismic arrays and dense station networks are necessary to discriminate volcanic events from the many transient signals produced by artificial sources. In Campi Flegrei area the analysis with array methods of data recorded by ARF array permitted the discovery of low amplitude volcanic tremor of hydrothermal origin occurred in January 2015, a seismic signal never observed before in the area. At Mt. Vesuvius the analysis of VAS array data has shown the occasional occurrence of short bursts of low amplitude volcanic tremor. Small low-frequency earthquakes have also been revealed in the two volcanic areas.</p>

scholarly journals Characteristics of volcanic tremor accompanying the September 24th, 1986 explosive eruption of Mt. Etna (Italy)

1996 ◽  
Vol 39 (2) ◽  
Author(s):  
S. Gresta ◽  
G. Lombardo ◽  
R. Cristofolini
Keyword(s):  
Low Frequency ◽  
Volcanic Tremor ◽  
Spectral Amplitude ◽  
Spectral Bands ◽  
Eruptive Episode ◽  
Spectral Peaks ◽  
Large Fluctuations ◽  
Mt Etna ◽  
Planar Source ◽  
Frequency Variations

Features of the volcanic tremor recorded before, during and after the eruptive event which occurred at Mt. Etna on September 24th 1986, are described. The whole eruption was particularly short in time (about eight hours) and characterized by an extremely violent explosive activity with lava fountains a few hundred meters high. As the complete record of the seismic signals generated during the whole eruptive episode was available, a detailed spectral analysis of the volcanic tremor recorded at four stations, located at increasing distance from the summit of the volcano, was carried out. Fourier analysis, that was performed using temporal windows of about 11 min in duration, pointed to some large fluctuations of the overall spectral amplitude, as well as some frequency variations of the dominant spectral peaks. The ratio of the overall spectral amplitude recorded at the highest station and at the peripheral ones, was calculated in the two spectral bands 1.0-2.5 and 2.6-6.0 Hz, respectively. The significant contribution of energy at low frequency values supports the hypothesis of a subvertical planar source, which was active during the paroxysmal stage of the eruption. Such results are also supported by the analysis of the attenuation function of the spectral amplitude.

scholarly journals Absence of spectral peaks in short-period oscillations from the Chilean Earthquake

1963 ◽  
Vol 68 (16) ◽  
pp. 4884-4884 ◽  
Author(s):  
Hitoshi Takeuchi ◽  
Hiroo Kanamori ◽  
Masanori Saito
Keyword(s):  
Short Period ◽  
Spectral Peaks ◽  
Chilean Earthquake

Oxygen Consumption by the Sea Anemone Calliactis Parasitica (Couch)

1980 ◽  
Vol 88 (1) ◽  
pp. 367-374
Author(s):  
A. E. BRAFIELD
Keyword(s):  
Oxygen Consumption ◽  
Oxygen Concentration ◽  
Low Frequency ◽  
High Amplitude ◽  
Total Oxygen ◽  
Strip Chart ◽  
Calliactis Parasitica ◽  
Cycle Lengths ◽  
Mean Cycle ◽  
Low Amplitude

Oxygen consumption by Calliactis parasitica, measured in a continuousflow polarographic respirometer, yielded a slope of 0·92 when plotted against body weight on log scales. This high value is discussed in terms of the sea anemone's basically laminate nature. Strip-chart records of the oxygen concentration of water which had just passed a specimen of Calliactis commonly showed rhythmic fluctuations, either of low amplitude and high frequency or high amplitude and low frequency (mean cycle lengths 11 and 34 min respectively). The fluctuations are explained in terms of rhythmic muscular contractions which irrigate the enteron for respiratory purposes. Analysis of the slow fluctuations indicates that the endoderm is responsible for about 18% of the total oxygen consumption. The oxygen concentration of water in the enteron, measured and recorded continuously, was 4–27% of the air-saturation level. These strip chart records also frequently showed rhythmic fluctuations (mean cycle length 12 min), apparently resulting from the muscular contractions.

A procedure for calibrating short-period telemetered seismograph systems

1988 ◽  
Vol 78 (6) ◽  
pp. 2077-2088
Author(s):  
M. C. Chapman ◽  
J. A. Snoke ◽  
G. A. Bollinger
Keyword(s):  
Dynamic Range ◽  
Low Frequency ◽  
Inertial Mass ◽  
System Response ◽  
Total System ◽  
Electronic Components ◽  
Amplitude Response ◽  
Motion System ◽  
Short Period ◽  
The Hilbert Transform

Abstract Efficient low-frequency calibration of the entire seismograph system can be accomplished by Fourier analysis of the system response to automatically generated transient test functions applied to the seismometer calibration coil. Typically, such calibrations are restricted to frequencies less than 10 Hz by the ambient ground motion, system noise, and limited dynamic range. To extend the calibration to a broader frequency range, we disconnect the seismometer and take advantage of the fact that the relative amplitude response of the electronic components in most systems can be measured with high accuracy at frequencies from as low as 0.02 Hz to the Nyquist frequency (e.g., 50 Hz) using standard electronics test equipment. The low-frequency amplitude response of the seismometer can then be isolated by dividing the total system response by that obtained for the electronic components. An iterative least-squares procedure is used to estimate the natural frequency and damping coefficient of the seismometer, along with a scaling parameter that specifies the absolute gain of the system. The phase response of the system is calculated directly from the amplitude response using the Hilbert transform. The procedure assumes that the seismometer is an ideal damped harmonic oscillator and that the system as a whole acts as a minimum phase filter. The only instrumental constants that must be known from independent measurement are the seismometer calibration coil force constant and the inertial mass.

Electrical Resistive Spiking of Fungi

2021 ◽  
pp. 1-7 ◽  
Author(s):  
Andrew Adamatzky ◽  
Alessandro Chiolerio ◽  
Georgios Sirakoulis
Keyword(s):  
Electrical Resistance ◽  
Electronic Devices ◽  
Low Frequency ◽  
High Amplitude ◽  
Average Amplitude ◽  
Average Width ◽  
C 23 ◽  
C 30 ◽  
Low Amplitude

We study long-term electrical resistance dynamics in mycelium and fruit bodies of oyster fungi P. ostreatus. A nearly homogeneous sheet of mycelium on the surface of a growth substrate exhibits trains of resistance spikes. The average width of spikes is c. 23[Formula: see text]min and the average amplitude is c. 1[Formula: see text]k[Formula: see text]. The distance between neighboring spikes in a train of spikes is c. 30[Formula: see text]min. Typically, there are 4–6 spikes in a train of spikes. Two types of electrical resistance spikes trains are found in fruit bodies: low frequency and high amplitude (28[Formula: see text]min spike width, 1.6[Formula: see text]k[Formula: see text] amplitude, 57[Formula: see text]min distance between spikes) and high frequency and low amplitude (10[Formula: see text]min width, 0.6[Formula: see text]k[Formula: see text] amplitude, 44[Formula: see text]min distance between spikes). The findings could be applied in monitoring of physiological states of fungi and future development of living electronic devices and sensors.

Remnants of the Amalgamation of the East and West Cathaysia Blocks Revealed by a Short-period Dense Seismic Array

2022 ◽  
Author(s):  
He Huang ◽  
Xuzhang Shen ◽  
Jian Xu ◽  
Rui Gao ◽  
Wentian Wang ◽  
...  
Keyword(s):  
Seismic Array ◽  
Short Period ◽  
East And West ◽  
Dense Seismic Array

Radial Velocity Variations in Cool Supergiants

1984 ◽  
Vol 88 ◽  
pp. 283-288
Author(s):  
Hugh C. Harris
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Short Period ◽  
Cool Stars ◽  
Synchronous Rotation ◽  
Red Supergiants ◽  
Velocity Variations ◽  
Orbital Periods ◽  
Low Amplitude ◽  
Good Agreement

AbstractA survey of F, G, and W supergiants has been carried out with the DAO radial velocity spectrometer, an efficient instrument for detecting low-amplitude velocity variations in cool stars. Observations of 78 stars over five seasons show generally good agreement with OORAVEL results for spectroscopie binaries. The majority of supergiants show low-amplitude variability, with amplitudes typically 1 to 2 km s−1. The width of the cross-correlation profile has been measured for 58 supergiants. It reveals 14 stars with unusually broad lines, indicative of rotation velocities of 15 to 35 km s−1. Several have short-period binary companions and may be in synchronous rotation. The other broad-lined stars are apparently single or with long orbital periods; they may be making their first transition from the main sequence to become red supergiants.

Three-dimensional mode growth in boundary layers with tuned and detuned subharmonic resonance

1995 ◽  
Vol 352 (1700) ◽  
pp. 453-471 ◽  
Keyword(s):  
Three Dimensional ◽  
Low Frequency ◽  
Phase Speed ◽  
Subharmonic Resonance ◽  
Oblique Waves ◽  
Periodic Disturbances ◽  
Wave Numbers ◽  
Interaction Order ◽  
Tollmien Schlichting ◽  
Low Amplitude

This work involves the use of controlled periodic disturbances to excite a plane Tollmien-Schlichting (TS) wave at one frequency ( f 2D) along with pairs of oblique waves with equal but opposite wave angles at a different frequency ( f 3D) in order to study the resonant growth of 3D modes in a Blasius boundary layer. In our earlier work (Corke & Mangano 1989; Corke 1990), the frequency of the oblique modes was exactly the subharmonic of the plane Tollmien-Schlichting (TS) mode. These modes were also phase-speed locked so that in terms of their streamwise wave numbers, α2D=1/2 α3D. This so-called ‘tuned’ subharmonic resonance leads to the enhanced growth of the otherwise linearly damped oblique waves, as well as the growth of higher harmonic 3D modes with frequencies and wave numbers: (3/2 f2d, 3/2 α2D, ±β3D), (5/2 f2d, 5/2 α2D, ±β3D), (f2d, α2D, ±2β3D) and (0, 0, ±2β3D). Even when the initial 3D oblique waves have frequencies which are close to the TS subharmonic frequency, a ‘detuned’ subharmonic resonance leads to the enhanced growth of the 3D mode. In addition, it promotes the growth of numerous discrete modes produced by successive sum and difference interactions. These interacted modes are also three dimensional, with higher amplification rates that increase with the interaction order. The growth of these modes accounts for the rapid spectral filling, and low-frequency modulation commonly observed in natural subharmonic transition. Starting from a ‘tuned' resonance, this scenario then provides a mechanism for the generation of a broad spectrum at the later stages of subharmonic mode transition. However, the results also suggest that with ‘natural’ transition, starting from low-amplitude broadband disturbances, the most likely 2D/3D resonance will be ‘detuned’.

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