Common fixed point theorems in modular G-metric spaces

The purpose of this paper is to prove the existence of the unique common fixed point theorems of a pair of weakly compatible mappings satisfying $\Phi$-maps in modular G-metric spaces

LMA observation of upward flashes at Säntis Tower: preliminary result

Lightning striking tall towers is mainly of the upward lightning type, which is characterized by the absence of a first return stroke and the presence of an initial continuous current (ICC) with or without superimposed pulses. The Säntis Tower is 124 m tall and it is located on the top of the Säntis Mountain (2502 m ASL) in the eastern Swiss Alps. The Tower location exhibited the highest lightning flash density in Switzerland during the period from 1999 to 2006. The Tower was instrumented in May 2010 for the measurement of lightning current parameters. In order to complement these data, a Lightning Mapping Array (LMA) was deployed around the Tower during the Summer 2017. The LMA system locates the sources of radio emissions in the very high frequency range (VHF, 60-66 MHz) in three dimensions by a time-of-arrival analysis. The LMA system allows detailed analysis of individual flashes, through the mapping of the lightning channels in the cloud with sufficient time resolution and spatial precision to locate the origin and propagation of each flash. With the help of the LMA, we intend to further investigate the initiation and propagation characteristics of upward lightning emerging from the Tower. From June 29 to August 15, 2017, 33 upward flashes initiated from the Säntis tower were registered by the LMA network. These records are the first set of VHF total lightning mapping obtained in Switzerland. Preliminary results of the campaign are presented in this paper. © 2018 IEEE.Peer ReviewedPostprint (published version

Polarimetric radar characteristics of lightning initiation and propagating channels

In this paper we present an analysis of a large dataset of lightning and polarimetric weather radar data collected in the course of a lightning measurement campaign that took place in the summer of 2017 in the area surrounding Säntis, in the northeastern part of Switzerland. For this campaign and for the first time in the Alps, a lightning mapping array (LMA) was deployed. The main objective of the campaign was to study the atmospheric conditions leading to lightning production with a particular focus on the lightning discharges generated due to the presence of the 124¿m tall Säntis telecommunications tower. In this paper we relate LMA very high frequency (VHF) sources data with co-located radar data in order to characterise the main features (location, timing, polarimetric signatures, etc.) of both the flash origin and its propagation path. We provide this type of analysis first for all of the data and then we separate the datasets into intra-cloud and cloud-to-ground flashes (and within this category positive and negative flashes) and also upward lightning. We show that polarimetric weather radar data can be helpful in determining regions where lightning is more likely to occur but that lightning climatology and/or knowledge of the orography and man-made structures is also relevant.Peer ReviewedPostprint (author's final draft

The Effect of Nuclear Elastic Scattering on Temperature Equilibration Rate of Ions in Fusion Plasma

A plasma with two different particle types and at different temperatures has been considered, so that each type of ion with Maxwell-Boltzmann distribution function is in temperature equilibrium with itself. Using the extracted nuclear elastic scattering differential cross-section from experimental data, solving the Boltzmann equation, and also taking into account the mobility of the background particles, temperature equilibration rate between two different ions in a fusion plasma is calculated. The results show that, at higher temperature differences, effect of nuclear elastic scattering is more important in calculating the temperature equilibration rate. The obtained expressions have general form so that they are applicable to each type of particle for background (b) and each type for projectile (p). In this paper, for example, an equimolar Deuterium-Hydrogen plasma with density n=5×1025 cm−3 is chosen in which the deuteron is the background particle with temperature (also electron temperature) Tb=1 keV (usual conditions for a fusion plasma at the ignition instant) and the proton is the projectile with temperature Tp>Tb. These calculations, particularly, are very important for ion fast ignition in inertial confinement fusion concept

The Polarity Reversal of Lightning‐Generated Sky Wave

The polarity reversal of the lightning‐generated first sky wave as a function of the observation distance is studied using a novel approach combining the finite‐difference time domain (FDTD) method and the superposition principle of electromagnetic waves. In this method, the sky wave is generated by radiation from the induced current produced by the motion of charged particles driven by the lightning‐radiated electromagnetic waves in the ionosphere. The horizontal and vertical components of the induced current density under the daytime and nighttime ionospheric conditions are evaluated. Their different contributions to the sky wave at different observation distances are analyzed in detail. Furthermore, a physical explanation for the polarity reversal in the time domain is proposed. It is found that, for relatively short observation distances (within ~200 km), the first sky wave is dominated by the component generated by the horizontal equivalent current in the Fresnel zone, while for longer observation distances (larger than ~300 km), the first sky wave is dominated by the component generated by the vertical equivalent current in the Fresnel zone. Since the polarities of the sky wave components generated by the vertical current source and horizontal current source are opposite, the polarity of the sky wave will reverse when increasing the observation distance

The propagation effects of lightning electromagnetic fields over mountainous terrain in the Earth-Ionosphere waveguide

This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.In this paper, a full-wave two-dimensional Finite-Difference-Time-Domain model is developed to evaluate the propagation effects of lightning electromagnetic fields over mountainous terrain in the Earth-ionosphere waveguide. In the model, we investigate the effect of the Earth-ionosphere waveguide structure and medium parameters, including the effect of the ionospheric cold plasma characteristics, the effect of the Earth curvature, and the propagation effects over mountainous terrain. For the first time, the obtained results are validated against simultaneous experimental data consisting of lightning currents measured at the Säntis Tower and electric fields measured in Neudorf, Austria, located at 380-km distance from the tower. It is shown that both the time delays and amplitudes of the lightning electromagnetic fields at 380-km distance can be strongly affected by the ionospheric electron density profile, the mountainous terrain, and the Earth curvature. After taking into account the effect of the irregular terrain between the Säntis Tower and the field measurement station, the vertical electric fields calculated by using our model are found to be in good agreement with the corresponding measured cases occurred in both daytime and nighttime. The ideal approximation used in either the classical solutions or the simplified models might lead to inaccuracies in the estimated reflection height. Furthermore, we discuss the sensitivity of our results by considering different return stroke models, as well as different typical values of the return stroke speed and of the ground conductivity. © 2019. The Authors.This work was supported by the European Research Council (ERC) under the European Union H2020 programme/ERC Grant Agreement 681257 and Swiss National Science Foundation under Project 200021_147058.Peer reviewe

Graph-based relevancy-redundancy gene selection method for cancer diagnosis

Abstract Nowadays, microarray data processing is one of the most important applications in molecular biology for cancer diagnosis. A major task in microarray data processing is gene selection, which aims to find a subset of genes with the least inner similarity and most relevant to the target class. Removing unnecessary, redundant, or noisy data reduces the data dimensionality. This research advocates a graph theoretic-based gene selection method for cancer diagnosis. Both unsupervised and supervised modes use well-known and successful social network approaches such as the maximum weighted clique criterion and edge centrality to rank genes. The suggested technique has two goals: (i) to maximize the relevancy of the chosen genes with the target class and (ii) to reduce their inner redundancy. A maximum weighted clique is chosen in a repetitive way in each iteration of this procedure. The appropriate genes are then chosen from among the existing features in this maximum clique using edge centrality and gene relevance. In the experiment, several datasets consisting of Colon, Leukemia, SRBCT, Prostate Tumor, and Lung Cancer, with different properties, are used to demonstrate the efficacy of the developed model. Our performance is compared to that of renowned filter-based gene selection approaches for cancer diagnosis whose results demonstrate a clear superiority

On the classification of self-triggered versus other-triggered lightning flashes

We present in this paper lightning current measurements and LMA (Lightning Mapping Array) data associated with upward flashes observed at the Sàntis Tower during Summer 2017. The LMA network consists of six stations located in the vicinity of the tower at distances ranging from 100 m to 11 km from it. 20 flashes simultaneously recorded by the current measurement system and the LMA are analyzed. Based on the lightning activity derived from the European Lightning Detection Network (EUCLID) in an area within 30 km from the tower and in a 5-second time window before the start of the flash, all the 20 flashes were classified as 'self-triggered' (ST). However, the investigations based on the LMA data reveal that 3 of the flashes were preceded by nearby activity and should be therefore classified as 'other-triggered' (OT) flashes. The results suggest that the number of OT flashes inferred from LLS data can be underestimated. © 2018 IEEE.Peer Reviewe