Artificial neural networks (ANNs) constitute a class of flexible nonlinear models designed to mimic biological neural systems. In this entry, we introduce ANN using familiar econometric terminology and provide an overview of ANN modeling approach and its implementation methods. † Correspondence: Chung-Ming Kuan, Institute of Economics, Academia Sinica, 128 Academia Road, Sec. 2, Taipei 115, Taiwan; ckuan@econ.sinica.edu.tw. †† I would like to express my sincere gratitude to the editor, Professor Steven Durlauf, for his patience and constructive comments on early drafts of this entry. I also thank Shih-Hsun Hsu and Yu-Lieh Huang for very helpful suggestions. The remaining errors are all mine.

Artificial neural networks

A comparison of methods to avoid overfitting in neural networks training in the case of catchment runoff modelling

A statistical point-process model is derived to describe the standard activity of earthquake occurrences by assuming that general seismicity is given by the superposition of aftershock sequences. The parameters are estimated ty the maximum likelihood method. Using the estimated model, the “residual point process” of the data is defined and used to find the anomalies which are included in the data set but not captured in the considered model for the standard seismicity. For instance, seismic quiescences can be measured quantitatively by using the residual process. Some examples are provided to illustrate such analyses. Furthermore, a time series of the magnitudes on the residual point process is considered, to investigate its dependence either on the time or on the history of the seismicity. By assuming the exponential distribution at each time and modelling of the b- value , we can examine such dependences and estimate them. Two practical examples are shown.

Statistical model for standard seismicity and detection of anomalies by residual analysis

Optimizing neural networks for river flow forecasting – Evolutionary Computation methods versus the Levenberg–Marquardt approach

Lightning produces electromagnetic fields and waves in all frequency ranges. In the extremely low frequency (ELF) range below 100 Hz, the global Schumann Resonances (SR) are excited at frequencies of 8 Hz, 14 Hz, 20 Hz, etc. This review is aimed at the reader generally unfamiliar with the Schumann Resonances. First some historical context to SR research is given, followed by some theoretical background and examples of the extensive use of Schumann resonances in a variety of lightning-related studies in recent years, ranging from estimates of the spatial and temporal variations in global lighting activity, connections to global climate change, transient luminous events and extraterrestrial lightning. Both theoretical and experimental results of the global resonance phenomenon are presented. It is our hope that this review will increase the interest in SR among researchers previously unfamiliar with this phenomenon.

https://www.mdpi.com/2073-4433/7/9/116/pdf

ELF Electromagnetic Waves from Lightning: The Schumann Resonances

The effects of 2009 Leonid Meteor Shower upon the two VLF subionospheric transmitted signals and vertical electric potential gradient from the ground surface have been studied from Kolkata (Lat: 22.56°N, Long: 88.5°E) on November 17, 2009. The received signals showed their peak values when ZHR (Zenithal Hourly Rate) was highest. Some typical variations in the outcome of these measurements during the meteor showers will be presented in this paper.

Studies on the Effects of 2009 Leonid Meteor Shower on Subionospheric Transmitted VLF Signals and Vertical Electric Potential Gradient

The expression for power radiated from a dipole within an anisotropic plasma has been obtained in presence of a current source and time-varying irregularities. This may be useful for numerical computation in lossy media.

Radiation from a dipole in an anisotropic plasma medium containing time-varying irregularities

Venus transited across the Sun on 06 June 2012, introducing significant contribution to the tidal characteristics of the solar atmosphere. Earth’s atmosphere was perturbed due to an anomalous Coronal Mass Ejection (CME) and γ-radiation influenced by the solar tide due to Venus transit, thereby the Earth-ionosphere waveguide characteristics were changed. In this anomalous situation we measured some atmospheric electricity parameters such as Schumann resonance (SR) amplitude, very low frequency (VLF) sferics, subionospheric transmitted signals and the point discharge current (PDC) along with the vertical electrical potential gradient (PG) at the ground surface on the day of transit. The results showed some remarkable variations during the transit as well as pre- and post-transit periods. The observed anomalies in the recorded data were interpreted in terms of the anomalous solar tidal effects initiated due to Venus transit.

/pdf/earth-s-atmospheric-electricity-parameter-response-during-2fchk5rxf4.pdf

Earth's atmospheric electricity parameter response during Venus transit

Electromagnetic fields due to earthquake have been studied in this presentation through some model calculations. The expressions of the variation of electron concentration and electron temperature as the ionospheric precursors of earthquake have been deduced in this presentation through quasihydrodynamic formulations. The outcome of the analyses of electromagnetic emissions recorded by VLF receivers at 5, 7, 9 and 12 kHz on November 16, 2008 over Kolkata (Lat. 22.56° N, Long. 88.5° E) during the large earthquake at Minahasa, Sulawesi (Lat. 1.27° N, Long. 122.09° E), under Indonesia have been presented here. Spiky variations of signals are observed few days prior to the day of occurrence of the earthquake which continued several days more, then decayed gradually and eventually ceased.

http://ieeexplore.ieee.org/iel5/5398767/5407062/05407109.pdf

On some effects of perturbations in the ionosphere due to electromagnetic precursory signals from earthquake

The non-linear heating of electrons in the ionospheric plasma due to high-power radio wave propagation has been investigated through an integro-differential equation derived from Boltzmann velocity-moment equations. Various processes appropriate to the situation under study are taken into account. The numerical solution of the derived equation is presented graphically.

Syam Sundar De

Papers

Studies on the Effects of 2009 Leonid Meteor Shower on Subionospheric Transmitted VLF Signals and Vertical Electric Potential Gradient

Radiation from a dipole in an anisotropic plasma medium containing time-varying irregularities

Earth's atmospheric electricity parameter response during Venus transit

On some effects of perturbations in the ionosphere due to electromagnetic precursory signals from earthquake

Non-linear r.f. heating of ionospheric plasma