A new VLF radio receiver in Greece for the detection of lower ionosphere anomalies before strong seismic events and the preliminary results for a strong (6.7 Mw) earthquake that occurred in Samos (Greece) on 30/10/2020.

2021 ◽  
Author(s):  
Dimitrios Politis ◽  
Stelios Potirakis ◽  
Sagardweep Biswas ◽  
Sudipta Sasmal ◽  
Masashi Hayakawa
Keyword(s):  
Fresnel Zone ◽  
Focal Depth ◽  
Lower Ionosphere ◽  
Aegean Sea ◽  
Propagation Path ◽  
Radio Receiver ◽  
Preliminary Results ◽  
Amplitude Data ◽  
Recorded Data ◽  
The University

<p>A new VLF/LF (10 - 47.5 kHz) radio receiver has recently been installed in the University of West Attica, in Athens (Greece), and has been operating in trial mode since April 2020 for the study of sub-ionospheric propagation variations, mainly aiming at the identification of possible earthquake (EQ) precursors or signatures of other extreme geophysical phenomena. The receiver is monitoring signals from a number of transmitters. Most of them are located in Europe, while some are located in Asia, Australia and North America. The recorded data (amplitude and phase) from this receiver are sampled at a rate of 1 sample per second. In this paper we present information about the new VLF/LF receiver as well as preliminary results concerning a very recent, strong (Mw = 6.7), shallow (focal depth = 12 km), EQ that occurred in Greece (epicenter located in the Aegean Sea, off-coast of the Samos island, close to the Greece-Turkey borders) on 30/10/2020, hereafter referred to as Samos’ EQ. The subionospheric propagation data associated with two specific transmitters were analyzed. Τhe first transmitter, with call sign TBB, is located in Denizköy (Turkey) and the location of Samos’ EQ epicenter is within of 5<sup>th</sup> Fresnel zone of the corresponding propagation path. The second transmitter, with call sign ISR, is located in Negev (Israel) and the location of Samos’ EQ epicenter is in close distance to the borders of the 5<sup>th</sup> Fresnel zone, so that, considering the magnitude of the specific EQ, the corresponding propagation path could possibly be disturbed. In this paper we present the analysis of the receiver’s amplitude data by means of the Terminator Time Method (TTM) in order to reveal any possible pre-seismic anomaly in the lower ionosphere. Our preliminary results show that there are indications for disturbance of the lower ionosphere a few days before the EQ occurrence.</p>

scholarly journals Statistical and Criticality Analysis of the Lower Ionosphere Prior to the 30 October 2020 Samos (Greece) Earthquake (M6.9), Based on VLF Electromagnetic Propagation Data as Recorded by a New VLF/LF Receiver Installed in Athens (Greece)

Entropy ◽  
2021 ◽  
Vol 23 (6) ◽  
pp. 676
Author(s):  
Dimitrios Z. Politis ◽  
Stelios M. Potirakis ◽  
Yiannis F. Contoyiannis ◽  
Sagardweep Biswas ◽  
Sudipta Sasmal ◽  
...  
Keyword(s):  
Time Series ◽  
Fresnel Zone ◽  
Lower Ionosphere ◽  
Propagation Path ◽  
Northern Coast ◽  
Analysis Method ◽  
Ionospheric Propagation ◽  
Amplitude Data ◽  
Natural Time ◽  
Criticality Analysis

In this work we present the statistical and criticality analysis of the very low frequency (VLF) sub-ionospheric propagation data recorded by a VLF/LF radio receiver which has recently been established at the University of West Attica in Athens (Greece). We investigate a very recent, strong (M6.9), and shallow earthquake (EQ) that occurred on 30 October 2020, very close to the northern coast of the island of Samos (Greece). We focus on the reception data from two VLF transmitters, located in Turkey and Israel, on the basis that the EQ’s epicenter was located within or very close to the 5th Fresnel zone, respectively, of the corresponding sub-ionospheric propagation path. Firstly, we employed in our study the conventional analyses known as the nighttime fluctuation method (NFM) and the terminator time method (TTM), aiming to reveal any statistical anomalies prior to the EQ’s occurrence. These analyses revealed statistical anomalies in the studied sub-ionospheric propagation paths within ~2 weeks and a few days before the EQ’s occurrence. Secondly, we performed criticality analysis using two well-established complex systems’ time series analysis methods—the natural time (NT) analysis method, and the method of critical fluctuations (MCF). The NT analysis method was applied to the VLF propagation quantities of the NFM, revealing criticality indications over a period of ~2 weeks prior to the Samos EQ, whereas MCF was applied to the raw receiver amplitude data, uncovering the time excerpts of the analyzed time series that present criticality which were closest before the Samos EQ. Interestingly, power-law indications were also found shortly after the EQ’s occurrence. However, it is shown that these do not correspond to criticality related to EQ preparation processes. Finally, it is noted that no other complex space-sourced or geophysical phenomenon that could disturb the lower ionosphere did occur during the studied time period or close after, corroborating the view that our results prior to the Samos EQ are likely related to this mainshock.

scholarly journals Analysis of Predistortion Techniques on Fresnel Zone Plates in Ultrasound Applications

Sensors ◽  
2021 ◽  
Vol 21 (15) ◽  
pp. 5066
Author(s):  
José Miguel Fuster ◽  
Sergio Pérez-López ◽  
Francisco Belmar ◽  
Pilar Candelas
Keyword(s):  
Intensity Distribution ◽  
Fresnel Zone ◽  
Focal Depth ◽  
Acoustic Intensity ◽  
Fresnel Zone Plates ◽  
Therapeutic Applications ◽  
Zone Plates ◽  
Ultrasound Applications

In this work, we analyze the effect of predistortion techniques on the focusing profile of Fresnel Zone Plates (FZPs) in ultrasound applications. This novel predistortion method is based on either increasing or decreasing the width of some of the FZP Fresnel rings by a certain amount. We investigate how the magnitude of the predistortion, as well as the number and location of the predistorted rings, influences the lens focusing profile. This focusing profile can be affected in different ways depending on the area of the lens where the predistortion is applied. It is shown that when the inner area of the lens, closer to its center, is predistorted, this technique allows the control of the focal depth at the main focus. However, when the predistortion is applied to an area farther from the center of the lens, the acoustic intensity distribution among the main focus and the closest adjacent secondary foci can be tailored at a certain degree. This predistortion technique shows great potential and can be used to control, modify and shape the FZP focusing profile in both industrial and therapeutic applications.

High-resolution imaging: An approach by incorporating stationary-phase implementation into deabsorption prestack time migration

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. S317-S331 ◽  
Author(s):  
Jianfeng Zhang ◽  
Zhengwei Li ◽  
Linong Liu ◽  
Jin Wang ◽  
Jincheng Xu
Keyword(s):  
Stationary Phase ◽  
Fresnel Zone ◽  
Computational Cost ◽  
Computational Effort ◽  
Propagation Path ◽  
Time Migration ◽  
Resolution Imaging ◽  
Prestack Time Migration ◽  
Dip Angle ◽  
Absorption And Dispersion

We have improved the so-called deabsorption prestack time migration (PSTM) by introducing a dip-angle domain stationary-phase implementation. Deabsorption PSTM compensates absorption and dispersion via an actual wave propagation path using effective [Formula: see text] parameters that are obtained during migration. However, noises induced by the compensation degrade the resolution gained and deabsorption PSTM requires more computational effort than conventional PSTM. Our stationary-phase implementation improves deabsorption PSTM through the determination of an optimal migration aperture based on an estimate of the Fresnel zone. This significantly attenuates the noises and reduces the computational cost of 3D deabsorption PSTM. We have estimated the 2D Fresnel zone in terms of two dip angles through building a pair of 1D migrated dip-angle gathers using PSTM. Our stationary-phase QPSTM (deabsorption PSTM) was implemented as a two-stage process. First, we used conventional PSTM to obtain the Fresnel zones. Then, we performed deabsorption PSTM with the Fresnel-zone-based optimized migration aperture. We applied stationary-phase QPSTM to a 3D field data. Comparison with synthetic seismogram generated from well log data validates the resolution enhancements.

scholarly journals Mandarin Language Students Illocutionary Acts in Japanese Language Learning at the University of Sumatera Utara

2021 ◽  
Vol 10 (1) ◽  
pp. 6-11
Author(s):  
Taulia Taulia ◽  
Laraiba Nasution
Keyword(s):  
Language Learning ◽  
Speech Acts ◽  
Speech Act ◽  
Japanese Language ◽  
Mandarin Language ◽  
Written Form ◽  
Recorded Data ◽  
Directive Speech Acts ◽  
The University ◽  
Department Faculty

Speech acts play an essential role in language learning as an aspect that can improve a learner's ability to speak orally. In this research, illocutionary speech-acts  were described in the Japanese language learning process for students of the Mandarin Language Department, Faculty of Cultural Sciences, University of Sumatera Utara. This research is qualitative. The data are speech acts in the lecture process in class, especially in the discussion. The data sources were 40 fourth-semester students of the Mandarin Language Department. The theory used was the Searle speech act theory. Data collection techniques were carried out through observation, recording , and note-taking techniques. Data analysis techniques were carried out applying Miles & Huberman's opinion by condensing data through transcription of recorded data into written form, identifying forms, speech act functions, data presentation, and concluding. As a result, there were forms of illocutionary speech acts, namely directive, expressive, and declarative. Furthermore, the purpose used in class was in directive speech acts which were to order, ask, invite (engage). In other words, in expressive speech-act was praising, and in declarative speech-act was prohibiting. In conclusion, Japanese speech acts in Japanese class occured between lecturers and students and only consisted of several types of speech acts due to students' limited mastery of Japanese.

scholarly journals INSTALLATION AND PRELIMINARY RESULTS FROM A SMALL APERTURE SEISMIC ARRAY IN TRIPOLI, GREECE

2004 ◽  
Vol 36 (3) ◽  
pp. 1499 ◽  
Author(s):  
M. Pirli ◽  
Ν. Voulgaris ◽  
J. Alexopoulos ◽  
K. Makropoulos
Keyword(s):  
Body Wave ◽  
Seismic Array ◽  
Small Aperture ◽  
Preliminary Results ◽  
Seismic Waveforms ◽  
Equipment Safety ◽  
Array Calibration ◽  
Array Performance ◽  
The University ◽  
Of Greece

A small aperture seismic array was installed by the University of Athens, in the area of Tripoli, Greece, on July 16th 2003, in order to test the performance of seismic array processing in the area of Greece and assess its contribution to earthquake location, especially in offshore areas not azimuthally covered by the existing, conventional seismological networks. The array consists of four three-component seismological stations, one of them in the middle of a small, almost equilateral triangle, formed by the deployment of the other three stations. Despite the fact that array siting is a compromise of array installation criteria, equipment safety and logistics, the test character of the experiment can be served successfully. The array transfer function depicts good azimuthal coverage nonetheless the existence of side-lobes and a rather wide main lobe is characteristic of spatial aliasing and low resolution in the two-dimensional wavenumber domain. The resolvable wavenumber passband of the array permits the determination of most of the common seismic body wave phases (Pn, Pg, Sn, Sg, etc.) for local and regional events in the area of Greece. Location of recorded events was performed using slowness and backazimuth data, calculated by f-k analysis of the seismic waveforms. Preliminary results have been compared to epicentres calculated by the Geodynamic Institute of the National Observatory of Athens. Although some differences are observed, these are not significant and location results as well as overall array performance can be improved by array calibration and travel-time, azimuth and slowness correction calculations.

scholarly journals The sanctuary of Punta Stilo at Kaulonia-Monasterace (Rc, Italy): preliminary results of the close range photogrammetric surveys 2012-2013

2014 ◽  
Vol XL-5 ◽  
pp. 559-563
Author(s):  
E. Taccola ◽  
M. C. Parra ◽  
C. Ampolo
Keyword(s):  
Preliminary Results ◽  
3D Data ◽  
Close Range ◽  
The University ◽  
First Time

During the 2012–2013 excavations at the Sanctuary of Punta Stilo at Kaulonia, carried out by the University of Pisa and the Scuola Normale Superiore of Pisa, close range aerial and terrestrial photogrammetric surveys were tested for the first time. The aim of the test was to verify the accuracy of the site planimetry currently used, dating back also to a century ago. The 3D data obtained have allowed new data to be acquired for correcting and updating the mapping of the site.

scholarly journals The Rise of Urbanized Landscapes in Mesopotamia: The QADIS Integrated Survey Results and the Interpretation of Multi-Layered Historical Landscapes

2019 ◽  
Vol 109 (2) ◽  
pp. 214-237 ◽  
Author(s):  
Nicolò Marchetti ◽  
Abbas Al-Hussainy ◽  
Giacomo Benati ◽  
Giampaolo Luglio ◽  
Giulia Scazzosi ◽  
...  
Keyword(s):  
Dense Network ◽  
Urbanization Process ◽  
Anthropogenic Transformation ◽  
Preliminary Results ◽  
The Core ◽  
Survey Results ◽  
The University ◽  
Artificial Water ◽  
Over Time ◽  
Archaeological Landscape

Abstract This paper draws on the preliminary results of the QADIS survey project, conducted by the University of Bologna and the Iraqi State Board of Antiquities and Heritage since 2016 in the Qadisiyah province. The project addresses phenomena related to anthropogenic transformation of landscapes in a region that was at the core of the early Mesopotamian urbanization process. Building upon the seminal work conducted by R. McC. Adams in the 1960 s and 1970 s, we implemented an integrated documentation technique to reconstruct at regional levels the changes in the dense network of human settlements and artificial water infrastructures characterizing the evolution of this archaeological landscape over time. The aim of the article is that of providing a finer-grained regional picture of 4th and 3rd millennium BC urban developments which can be useful for better conceptualizing the scale and pace of early Mesopotamian urbanism.

scholarly journals Spectroscopic and Polarimetric Observations of AC Her and UU Her

1989 ◽  
Vol 106 ◽  
pp. 296-296
Author(s):  
M.A. Nook ◽  
J.A. Cardelli ◽  
K.H. Nordsieck
Keyword(s):  
Wavelength Range ◽  
Spectral Resolution ◽  
Preliminary Results ◽  
Cassegrain Telescope ◽  
The University

We present preliminary results obtained between March and August of 1987 of a two-year spectropolarimetric study of 10 RV Tauri stars. The observations were made at the University of Wisconsin's Pine Bluff Observatory using the 36 inch cassegrain telescope with a Lyot polarimeter. The spectral resolution of the instrument was 6 A and covered the range between 4350 A and 7500 A. The polarimetry covered the same wavelength range but is binned in four broad bands at 4828 A, 5361 A, 6025 A, and 6877 A.

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