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

In the present article, we have studied the two dimensional tangent hyperbolic fluid flow towards a stretching sheet with a magnetic field. Governing equations for the proposed model are modelled and then simplified using boundary layer approach and similarity transformations. Simplified governing equations are then solved numerically with the help of fourth and fifth order Runge–Kutta–Fehlberg method. Physical features of the involved parameters are presented and discussed.

Numerical solutions of Magnetohydrodynamic boundary layer flow of tangent hyperbolic fluid towards a stretching sheet

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

Studies on the shift in the frequency of the first Schumann resonance mode during a solar proton event

The results from the measurements of some of the fundamental parameters (amplitude of sferics and transmitted signal, conductivity of lower ionosphere) of the ionospheric responses to the 22 July 2009 solar eclipse (partial: 91.7%) are shown. This study summarizes our results from sferics signals at 81 kHz and subionospheric transmitted signals at 19.8 and 40 kHz recorded at Agartala, Tripura (latitude: 23°N, longitude: 91.4°E). We observed significant absorption in amplitude of these signals during the eclipse period compared to their ambient values for the same period during the adjacent 7 days. The signal strength along their propagation paths was controlled by the eclipse associated decrease in ionization in the D-region of the ionosphere. Waveguide mode theory calculations show that the elevation of the height of lower ionosphere boundary of the Earth-ionosphere waveguide to a value where the conductivity parameter was 10 6 unit. The absorption in 81 kHz sferics amplitude is high compared to the absorption in the amplitude of 40 kHz signal transmitted from Japan. The simultaneous changes in the amplitudes of sferics and in the amplitude of transmitted signals assert some sort of coupling between the upper atmosphere and the Earth’s near-surface atmosphere prevailing clouds during solar eclipse.

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Effects of a Solar Eclipse on the Propagation of VLF-LF Signals: Observations and Results

Several experiments were undertaken at Kolkata (latitude: 22°34′N, longitude: 88°30′E) on the solar eclipse day of August 1, 2008 to observe the effects of the solar eclipse on Fair Weather Field (FWF) and VLF amplitude and phase. The experimental results presented here show significant deviations of the observed parameters from their normal values, as they are determined by the average of the records obtained on 5 days adjacent to the day of the solar eclipse.

The Effects of Solar Eclipse of August 1, 2008 on Earth’s Atmospheric Parameters

Studies on the seasonal variation of atmospheric electricity parameters at a tropical station in Kolkata, India

Large amplitude ion-acoustic solitary waves have been theoretically studied in a non-collisional plasma consisting of warm positive ions, positrons and isothermal electrons using pseudo-potential (effective potential) method. The expressions of phase velocities of slow- and fast- modes of the wave have been derived and graphically analyzed. The critical values of densities of the positrons and the ions, Mach number and positron temperature for the excitation of ion-acoustic solitary wave have also been obtained. The solutions of the first-order and next higher order solitary waves have been obtained and the profiles of the solitary waves have been drawn taking different values of the plasma parameters. It has been observed that both compressive and rarefactive solitary waves are being excited in presence of positrons in the plasma. The variation of amplitudes of the solitary waves has been shown graphically for different values of density and temperature of positrons, drift velocity and temperature of the ions.

Suman Paul

Papers

Studies on the shift in the frequency of the first Schumann resonance mode during a solar proton event

Effects of a Solar Eclipse on the Propagation of VLF-LF Signals: Observations and Results

The Effects of Solar Eclipse of August 1, 2008 on Earth’s Atmospheric Parameters

Studies on the seasonal variation of atmospheric electricity parameters at a tropical station in Kolkata, India

Ion acoustic solitary waves in an electron–ion–positron plasma