scholarly journals Statistical Significance of Earth’s Electric and Magnetic Field Variations Preceding Earthquakes in Greece and Japan Revisited

Entropy ◽  
2018 ◽  
Vol 20 (8) ◽  
pp. 561 ◽  
Author(s):  
Nicholas Sarlis
Keyword(s):  
Magnetic Field ◽  
Statistical Significance ◽  
Low Frequency ◽  
Lead Times ◽  
Operating Characteristics ◽  
Complexity Measures ◽  
Natural Time ◽  
Experimental Findings ◽  
Precursory Phenomena ◽  
Magnetic Field Variations

By analyzing the seismicity in a new time domain, termed natural time, we recently found that the change of the entropy under time reversal (Physica A2018, 506, 625–634) and the relevant complexity measures (Entropy2018, 20, 477) exhibit pronounced variations before the occurrence of the M8.2 earthquake in Mexico on 7 September 2017. Here, the statistical significance of precursory phenomena associated with other physical properties and in particular the anomalous variations observed in the Earth’s electric and magnetic fields before earthquakes in different regions of the world and in particular in Greece since 1980s and Japan during 2001–2010 are revisited (the latter, i.e., the magnetic field variations are alternatively termed ultra low frequency (ULF) seismo-magnetic phenomena). Along these lines we employ modern statistical tools like the event coincidence analysis and the receiver operating characteristics technique. We find that these precursory variations are far beyond chance and in addition their lead times fully agree with the experimental findings in Greece since the 1980s.

scholarly journals A broadband two axis flux-gate magnetometer

1998 ◽  
Vol 41 (3) ◽  
Author(s):  
P. Palangio
Keyword(s):  
Magnetic Field ◽  
Low Frequency ◽  
High Sensitivity ◽  
Magnetic Sensors ◽  
Frequency Range ◽  
Field Station ◽  
Low Weight ◽  
Highly Sensitive ◽  
Flux Gate ◽  
Magnetic Field Variations

A broadband two axis flux-gate magnetometer was developed to obtain high sensitivity in magnetotelluric measurements. In magnetotelluric sounding, natural low frequency electromagnetic fields are used to estimate the conductivity of the Earth's interior. Because variations in the natural magnetic field have small amplitude(10-100 pT) in the frequency range 1 Hz to 100 Hz, highly sensitive magnetic sensors are required. In magnetotelluric measurements two long and heavy solenoids, which must be installed, in the field station, perpendicular to each other (north-south and east-west) and levelled in the horizontal plane are used. The coil is a critical component in magnetotelluric measurements because very slight motions create noise voltages, particularly troublesome in wooded areas; generally the installation takes place in a shallow trench. Moreover the coil records the derivative of the variations rather than the magnetic field variations, consequently the transfer function (amplitude and phase) of this sensor is not constant throughout the frequency range 0.001-100 Hz. The instrument, developed at L'Aquila Geomagnetic Observatory, has a flat response in both amplitude and phase in the frequency band DC-100 Hz, in addition it has low weight, low power, small volume and it is easier to install in the field than induction magnetometers. The sensivity of this magnetometer is 10 pT rms.

scholarly journals SIX-MONTH FOLLOW-UP OF THE EFFECT OF A MAGNETIC FIELD ON CEREBRAL MOTOR DISORDERS IN EARLY CHILDHOOD

2021 ◽  
Vol 9 (06) ◽  
pp. 543-548
Author(s):  
V. K. Kostova ◽  
◽  
A. Aleksiev ◽  
Keyword(s):  
Magnetic Field ◽  
Statistical Significance ◽  
Low Frequency ◽  
Motor Disorders ◽  
Cranial Ultrasound ◽  
Short Term ◽  
Primitive Reflexes ◽  
Frequency Impulse

Introduction:- There is a consensus about the short-term efficacy, but not about the long-term effect of the low-frequency impulse magnetic field in early childhood cerebral motor disorders. There is no consensus about the statistical significance of the two-week and six-month dynamics of the kinesiology tests, cranial ultrasound, pathological and primitive reflexes. Objective:- To compare the short-term and long-term effect of the low-frequency impulse magnetic field versus placebo control and compare the statistical significance regarding the two-week and six-month dynamics of the kinesiology tests, cranial ultrasound, pathological and primitive reflexes. Material and Methods:- 29 children (age 8.10 ± 5.98 months) with cerebral motor disorders were followed for 6 months. They were divided into two groups - physiotherapeutic and control. The physiotherapy group (n = 14) received a once-daily low-frequency impulse magnetic field for two weeks at the start of the follow-up. The control group (n = 15) received a once-daily placebo magnetic therapy for two weeks at the start of the follow-up. Kinesiology tests, cranial ultrasound, pathological and primitive reflexes were recorded at the beginning of the follow-up, after two weeks, and after six months. Results:- At the beginning of the follow-up, there was no difference between the two groups regarding all parameters (P>0.05). Both groups showed better results after two weeks versus the start of the follow-up (P<0.05) and after six months versus after two weeks (P<0.05). The physiotherapy group showed better results versus the control group after the second week (P<0.05) and after the sixth month (P<0.05). The two-week and six-month dynamics of the kinesiology tests showed the highest significance (P<0.001), followed by primitive reflexes (P<0.04), followed by pathological reflexes (P<0.05), and finally - the cranial ultrasound (P>0.05), at comparable baseline parameters (P<0.05). Conclusion:- The low-frequency impulse magnetic field showed a significant short-term and long-term therapeutic effect that exceeded the corresponding placebo effects. The statistical significance at the second week and the sixth month of kinesiology tests was the highest, followed by primitive reflexes, and pathological reflexes. The cranial ultrasound did not show significant two-week and six-month dynamics. Despite the relatively stationary morphological changes, verified by cranial ultrasound, the developing nervous system in children aged 8.10 ± 5.98 months showed significant positive dynamics and plasticity for two weeks and six months, verified by kinesiology tests, primitive and pathological reflexes.

scholarly journals Numerical Simulation Analysis and Experimental Research on Damping Performance of a Novel Magnetic Fluid Damper

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Wenrong Yang ◽  
Dejie Wei ◽  
Jianzheng Su ◽  
Xiaorui Yang ◽  
Qingxin Yang
Keyword(s):  
Magnetic Field ◽  
Magnetic Fluid ◽  
Simulation Analysis ◽  
Damping Ratio ◽  
Low Frequency ◽  
Operating Characteristics ◽  
Damping Force ◽  
Rolling Ball ◽  
High Rise ◽  
Field Coupling

Considering the low-frequency and large-amplitude vibration characteristics of the high-rise structure, a tuned magnetic fluid rolling-ball damper is proposed to suppress the vibration of the structure. By adjusting the external magnetic field to control the natural rolling frequency of the ball, the purpose of tuning vibration reduction is achieved. Firstly, the working principle of the damper is theoretically analysed, a three-dimensional (3D) magnetic-fluid-solid multiphysical field coupling mathematical model of the damper is established and the governing equations of multiphysical field coupling are derived. Secondly, the magnetic field distribution and operating characteristics of the damper are simulated and analysed. Finally, the effectiveness of the model is verified by experiments, and the damping performance of the damper with two kinds of magnetic fluid is tested and compared. The results show that the magnetic-fluid-solid multiphysical field coupling model can accurately simulate the working characteristics of the damper. The maximum damping force of the damper is about 12% of the elastic force of the structure, which can increase the damping ratio of the structure by about two times, effectively reduce the vibration response time, and suppress the vibration of the high-rise structure.

scholarly journals On Possible Electromagnetic Precursors to a Significant Earthquake (Mw = 6.3) Occurred in Lesvos (Greece) on 12 June 2017

Entropy ◽  
2019 ◽  
Vol 21 (3) ◽  
pp. 241 ◽  
Author(s):  
Stelios Potirakis ◽  
Alexander Schekotov ◽  
Yiannis Contoyiannis ◽  
Georgios Balasis ◽  
Grigorios Koulouras ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Statistical Methods ◽  
Focal Depth ◽  
Low Frequency ◽  
Electromagnetic Emission ◽  
Magnetic Field Data ◽  
Magnetometer Array ◽  
Natural Time ◽  
Electromagnetic Precursors ◽  
Criticality Analysis

This paper reports an attempt to use ultra-low-frequency (ULF) magnetic field data from a space weather monitoring magnetometer array in the study of earthquake (EQ) precursors in Greece. The data from four magnetometer stations of the HellENIc GeoMagnetic Array (ENIGMA) have been analyzed in the search for possible precursors to a strong EQ that occurred south of Lesvos Island on 12 June 2017, with magnitude Mw = 6.3 and focal depth = 12 km. The analysis includes conventional statistical methods, as well as criticality analysis, using two independent methods, the natural time (NT) method and the method of critical fluctuations (MCF). In terms of conventional statistical methods, it is found that the most convincing ULF precursor was observed in the data of ULF (20–30 mHz) depression (depression of the horizontal component of the magnetic field), which is indicative of lower ionospheric perturbation just 1 day before the EQ. Additionally, there are indications of a precursor in the direct ULF emission from the lithosphere 4 days to 1 day before the EQ. Further study in terms of NT analysis identifies criticality characteristics from 8 to 2 days before the EQ both for lithospheric ULF emission and ULF depression, while MCF reveals indications of criticality in all recorded magnetic field components, extending from 10 to 3 days before the EQ. Beyond the recordings of the geomagnetic stations of ENIGMA, the recordings of the fracto-electromagnetic emission stations of the HELlenic Seismo-ElectroMagnetics Network (ELSEM-Net) in Greece have been analyzed. The MHz recordings at the station that is located on Lesvos Island presented criticality characteristics (by means of both NT analysis and MCF) 11 days before the EQ, while a few days later (7–6 days before the EQ), the kHz recordings of the same station presented tricritical behavior. It is noted that the magnetosphere was quiet for a period of two weeks before the EQ and including its occurrence.

Effects of weak low-frequency magnetic fields on spruce seed germination under acid conditions

1998 ◽  
Vol 28 (4) ◽  
pp. 609-616 ◽  
Author(s):  
Romana Ruzic ◽  
Igor Jerman ◽  
Nada Gogala
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Physiological Stress ◽  
Statistical Significance ◽  
Low Frequency ◽  
Magnetic Flux Density ◽  
Extremely Low Frequency ◽  
Sinusoidal Magnetic Field ◽  
Delayed Germination ◽  
Intensive Growth

We studied the effects of weak and extremely low frequency magnetic fields on the growth and germination of spruce seedlings (Picea abies (L.) Karst.) that were exposed simultaneously to different pH levels. The experiments showed that a weak, sinusoidal magnetic field (50 Hz, 26 and 105 µT, stimulation 12 h/day), which was computer controlled and generated by a system of Helmholtz-like coils, slightly reduced the length of the seedlings and delayed germination at low pH levels. A 26- µT magnetic field at 50 Hz slightly reduced the length of the seedlings at pH 2, delayed germination between pH 2 and 3, and caused no effects or were even stimulatory at pH 6 and 7. At a higher magnetic flux density (105 µT) the length, fresh weight, and germination were reduced mostly at pH 2 and 3 and with a higher statistical significance than at 26 µT. Germination was influenced during the first days of germination, and later the effect diminished rapidly. A 10- µT magnetic field at 46 Hz stimulated only the length of the seedlings. This phenomenon corresponds to the observations made by some other authors, namely that biological systems during various phases of intensive growth and (or) in suboptimal environmental conditions (physiological stress) are prone to exhibit greater sensitivity to extremely low frequency fields.

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