MONOFRACTAL AND MULTIFRACTAL ANALYSIS IN SHORT - TERM TIME DYNAMICS OF ULF GEOMAGNETIC FIELD MEASURED IN CRETE, GREECE

In this work, a monofractal and multifractal characterization of the short-term time dynamical fluctuations of the ultra low frequency (ULF) geomagnetic field, measured by one station installed in Creete, Greece, has been carried out. Time scale properties of the three ULF geomagnetic components, two horizontal (x, y) and one vertical (z) have been analyzed through the power spectral density, Higuchi method and Hurst R/S analysis. Results point out the presence of fractal features expressing long-range time correlation with scaling coefficients, which are the clue of persistent mechanism. Using a set of multifractal parameters, defined from the shape of the multifractal spectrum, it has been observed that the degree of multifractality, that characterizes the original signals, is "weaker" if compared to the residual signals, obtained from the original ones after removing the four observed periodicities (24-, 12-, 8- and 6-h periodicties). Furthermore the horizontal χ and y components have revealed to be less multifractal than the vertical z-component.

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(M,β)-Stability of Positive Linear Systems

Mathematical Problems in Engineering ◽

10.1155/2016/9605464 ◽

2016 ◽

Vol 2016 ◽

pp. 1-11 ◽

Cited By ~ 3

Author(s):

Octavian Pastravanu ◽

Mihaela-Hanako Matcovschi

Keyword(s):

Linear System ◽

Linear Systems ◽

Transient Behavior ◽

Short Term ◽

Time Dynamics ◽

The Right ◽

Long Term Behavior ◽

Stability Concept

The main purpose of this work is to show that the Perron-Frobenius eigenstructure of a positive linear system is involved not only in the characterization of long-term behavior (for which well-known results are available) but also in the characterization of short-term or transient behavior. We address the analysis of the short-term behavior by the help of the “(M,β)-stability” concept introduced in literature for general classes of dynamics. Our paper exploits this concept relative to Hölder vectorp-norms,1≤p≤∞, adequately weighted by scaling operators, focusing on positive linear systems. Given an asymptotically stable positive linear system, for each1≤p≤∞, we prove the existence of a scaling operator (built from the right and left Perron-Frobenius eigenvectors, with concrete expressions depending onp) that ensures the best possible values for the parametersMandβ, corresponding to an “ideal” short-term (transient) behavior. We provide results that cover both discrete- and continuous-time dynamics. Our analysis also captures the differences between the cases where the system dynamics is defined by matrices irreducible and reducible, respectively. The theoretical developments are applied to the practical study of the short-term behavior for two positive linear systems already discussed in literature by other authors.

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Limitations of the Power Spectral Density as an Indicator of Test Severity

Journal of the IEST ◽

10.17764/jiet.54.2.j3761476322338w1 ◽

2011 ◽

Vol 54 (2) ◽

pp. 116-128 ◽

Cited By ~ 2

Author(s):

Mark Paulus

Keyword(s):

Experimental Data ◽

Spectral Density ◽

Frequency Shift ◽

Natural Frequency ◽

Power Spectral Density ◽

Low Frequency ◽

Poor Correlation ◽

Frequency Change ◽

Power Spectral

This paper presents a set of experimental data comparing repetitive shock (RS) vibration, single-axis electrodynamic (ED) vibration, and multi-axis ED vibration. It was found that multi-axis testing is more severe than single-axis testing at the same level. In addition, weaknesses were found in the RS system at low frequency. Smoothing of the data or poor line resolution was also shown to change the overall severity of a test. A poor correlation was shown between the power spectral density (PSD) and the rate of natural frequency change (RFC) over a wide frequency shift. The change in natural frequency caused the initial PSD to be an ineffective indicator of test severity. Quantification of the severity of the test profile can be accomplished through characterization of the RFC.

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A climatology of infrasound detections at Kerguelen Island

10.5194/egusphere-egu2020-7047 ◽

2020 ◽

Author(s):

Olivier F.C. den Ouden ◽

Jelle D. Assink ◽

Pieter S.M. Smets ◽

Läslo G. Evers

Keyword(s):

Low Frequency ◽

Noise Model ◽

High Noise ◽

Kerguelen Island ◽

Power Spectral ◽

The World ◽

Processing Techniques ◽

Test Ban

The International Monitoring System (IMS) is in place for the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Part of the IMS are 60 infrasound arrays, of which 51 currently provide real-time infrasound recordings from around the world. Those arrays play a central role in the characterization of the global infrasonic wavefield and localization of infrasound sources.Power Spectral Density (PSD) estimates give insight into the noise levels per station and array. The IMS global low and high noise model curves have been determined in a study by Brown et al. [2014] using a distribution of computed PSDs. All the IMS infrasound arrays, except IS23, have been included in the determination of the atmospheric ambient noise curves. IS23 is located at Kerguelen Island and exist of 15 elements that have been divided into five 100 meter aperture triplets arrays. The array is located at one of the noisiest locations in the world, due to the high wind conditions that exist year-round. The resulting high noise floor appears to hamper infrasound detection at this island array.In this work, the effects of meteorological, oceanographic, and topographical conditions on the infrasound recordings at IS23 are studied. Five years of infrasound data is analyzed, as recorded by IS23, by using various processing techniques. Contributions within different frequency bands are evaluated. The infrasound detections are explained in terms of the stratospheric winds and ocean wave activity. Understanding and characterization of the low-frequency recordings of IS23 are of importance for successfully including this array for verification of the CTBT.

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Research on Morphology of N80 Casing Drilling Steel Fatigue Crack Growth with Low-Frequency Noise

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.239-242.2795 ◽

2011 ◽

Vol 239-242 ◽

pp. 2795-2798

Author(s):

Dang Hui Wang ◽

Tian Han Xu ◽

Ting Zhen Yao

Keyword(s):

Fatigue Crack ◽

Fatigue Crack Growth ◽

Crack Growth ◽

Low Frequency ◽

Frequency Noise ◽

Low Frequency Noise ◽

Power Spectral ◽

Microstructure Morphology ◽

Casing Drilling

Microstructure and low-frequency noise test were measured for N80 steel casing drilling, through SEM analyzed their morphology. Results showed that: (1) power spectral density of 1/f noise increases two orders of magnitude after fatigue crack growth. (2) 1/f noise parameters of γ and B are significantly increased, indicating that the process of fatigue produced more cracks, defects, and combination centers, which were proved by microstructure morphology. From the mechanism of fatigue crack growth of N80, defects and cracks resulting from fatigue are the numbers of kind of fluctuations. In essence, low-frequency noise is a type of fluctuations, which can serve as a viable tool to study the defects and the characterization of defects.

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Multifractal features in short-term time dynamics of ULF geomagnetic field measured in Crete, Greece

Chaos Solitons & Fractals ◽

10.1016/j.chaos.2003.10.020 ◽

2004 ◽

Vol 21 (2) ◽

pp. 273-282 ◽

Cited By ~ 10

Author(s):

Luciano Telesca ◽

Vincenzo Lapenna ◽

Filippos Vallianatos ◽

John Makris ◽

Vassilios Saltas

Keyword(s):

Geomagnetic Field ◽

Short Term ◽

Time Dynamics

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The Effect of Breath Pacing on Task Switching and Working Memory

International Journal of Neural Systems ◽

10.1142/s0129065720500288 ◽

2020 ◽

Vol 30 (06) ◽

pp. 2050028

Author(s):

Maria Paula Bonomini ◽

Mikel Val Calvo ◽

Alejandro Diaz Morcillo ◽

Florencia Segovia ◽

Jose Manuel Ferrandez Vicente ◽

...

Keyword(s):

Working Memory ◽

Processing Speed ◽

Response Times ◽

Low Frequency ◽

Cortical Activity ◽

Short Term ◽

Cognitive Domains ◽

Power Spectral ◽

Autonomic Changes ◽

Study Population

The cortical and subcortical circuit regulating both cognition and cardiac autonomic interactions are already well established. This circuit has mainly been analyzed from cortex to heart. Thus, the heart rate variability (HRV) is usually considered a reflection of cortical activity. In this paper, we investigate whether HRV changes affect cortical activity. Short-term local autonomic changes were induced by three breathing strategies: spontaneous (Control), normal (NB) and slow paced breathing (SB). We measured the performance in two cognition domains: executive functions and processing speed. Breathing maneuvres produced three clearly differentiated autonomic states, which preconditioned the cognitive tasks. We found that the SB significantly increased the HRV low frequency (LF) power and lowered the power spectral density (PSD) peak to 0.1[Formula: see text]Hz. Meanwhile, executive function was assessed by the working memory test, whose accuracy significantly improved after SB, with no significant changes in the response times. Processing speed was assessed by a multitasking test. Consistently, the proportion of correct answers (success rate) was the only dependent variable affected by short-term and long-term breath pacing. These findings suggest that accuracy, and not timing of these two cognitive domains would benefit from short-term SB in this study population.

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