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 analytical form of the absorption index appropriate to the D- and E-region of the ionospheric plasma is derived. It has been utilised to build up Schlomilch's integral equation. The corresponding solution is obtained in terms of certain ionospheric parameters. The variation of effective collision frequency with height has been computed numerically from the derived solution. The results are presented graphically along with an earlier work.

On Schlomilch's Integral Equation for the Ionospheric Plasma

From the measurements of atmospheric electric field and VLF sferics at Kolkata (2234 N, 8830 E), some correlation studies have been made. It is observed that the diurnal variation of vertical electric field averaged for 20 fair weather days maintains good connectivity with diurnal variation of VLF sferics activity. The variations are in contrast with the accepted unitary diurnal changes of vertical electric field and thunderstorm occurrence frequency curve with a maximum around 1900 hrs UT and a minimum around 0400 hrs UT. Some results in this context are presented in this paper.

http://nopr.niscair.res.in/bitstream/123456789/4717/1/IJRSP%2035%283%29%20187-192.pdf

Study of amplitude spectrum of VLF sferics and vertical electric field at Kolkata

In presence of non-linear perturbations of the thermospheric auroral region produced by Travelling Ionospheric Disturbances (TIDs) during the propagation of Atmospheric Gravity Waves (AGWs), an analytical expression of velocity of the constituent particles is derived through magnetohydrodynamic formalism. Using this, the expressions of Joule heating and viscous heating are derived, whose variations with time have been presented. The height-dependent ratio of the viscous heating rate to the Joule heating rate in generating AGW in the auroral electrojets is determined. Moreover, the mode coupling during transverse wave propagation within the auroral region is being explored, where the expressions of current and field during interactions are derived.

http://ieeexplore.ieee.org/iel5/5398767/5407062/05407107.pdf

Studies on non-linear Travelling Ionospheric Disturbances and mode coupling within the auroral region

Results of the detection of 2004 Leonid meteor shower over Kolkata (22°34´ N, 88°30´ E), India is presented in this paper, by using a VLF amplifier tuned at one of the transmission frequencies of Indian Navy Traffic stations at Vijayananarayanam (8o25´59.88´´ N, 77°48´ E) at 16.3 kHz. The shower was predicted to exhibit a peak activity on 19 Nov. 2004. In spite of low ZHR predicted, the peak activity had been observed earlier than the predicted times, which confirms the nongravitational ‘A2 effect’ on meteoroid trails. The observation also suggests that electromagnetic detection of meteor shower is better than the visual observation, as any time of the day and night its effect on VLF transmission can be recorded.

http://nopr.niscair.res.in/bitstream/123456789/3925/1/IJRSP%2035%286%29%20396-400.pdf

Detection of 2004 Leonid meteor shower by observing its effects on VLF transmission

In the presence of perturbations of the thermospheric auroral region produced by traveling ionospheric disturbances during the propagation of atmospheric gravity waves, an analytical expression of the velocity of the thermospheric plasma is derived through magnetohydrodynamic formalism. The expressions of the Joule heating and the viscous heating are derived, and their rates of variation are presented. A threshold height for their transition has been determined from their ratio, which is in agreement with the experimental data. The analysis indicates that the time taken by the thermospheric plasma to reach a steady-state corresponds to the nature of the traveling ionospheric disturbances in the medium.

/pdf/heating-of-the-auroral-ionosphere-by-traveling-ionospheric-3raw3s4237.pdf

Syam Sundar De

Papers

On Schlomilch's Integral Equation for the Ionospheric Plasma

Study of amplitude spectrum of VLF sferics and vertical electric field at Kolkata

Studies on non-linear Travelling Ionospheric Disturbances and mode coupling within the auroral region

Detection of 2004 Leonid meteor shower by observing its effects on VLF transmission

Heating of the auroral ionosphere by traveling ionospheric disturbances initiated by atmospheric gravity waves