In the present research, possibility of predicting average summer-monsoon rainfall over India has been analyzed through Artificial Neural Network models. In formulating the Artificial Neural Network based predictive model, three layered networks have been constructed with sigmoid non-linearity. The models under study are different in the number of hidden neurons. After a thorough training and test procedure, neural net with three nodes in the hidden layer is found to be the best predictive model.

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The present article reports studies to develop a univariate model to forecast the summer monsoon (June-August) rainfall over India. Based on the data pertaining to the period 1871-1999, the trend and stationarity within the time series have been investigated. After revealing the randomness and non-stationarity within the time series, the autoregressive integrated moving average (ARIMA) models have been attempted and the ARIMA(0,1,1) has been identified as a suitable representative model. Consequently, an autoregressive neural network (ARNN) model has been attempted and the neural network has been trained as a multilayer perceptron with the extensive variable selection procedure. Sigmoid non-linearity has been used while training the network. Finally, a three-three-one architecture of the ARNN model has been obtained and after thorough statistical analysis the supremacy of ARNN has been established over ARIMA(0,1,1). The usefulness of ARIMA(0,1,1) has also been described.

Among different candidates to play the role of Dark Energy (DE), modified gravity has emerged as offering a possible unification of Dark Matter (DM) and DE. The purpose of this work is to develop a reconstruction scheme for the modified gravity with f (T ) action using holographic energy density. In the framework of the said modified gravity we have considered the equation of state of the Holographic DE (HDE) density. Subsequently we have developed a reconstruction scheme for modified gravity with f (T ) action. Finally we have obtained a modified gravity action consistent with the HDE scenario. PACS numbers: 98.80.-k, 95.36.+x, 04.50.Kd I. INTRODUCTION Cosmological observations obtained with Supernovae Ia (SNeIa), the Cosmic Microwave Background (CMB) radiation anisotropies, the Large Scale Structure (LSS) and X-ray experiments have well established the accelerated expansion of our universe [1-7]. A missing energy component also known as Dark Energy (DE) with negative pressure is widely considered by scientists as responsible of this accelerated expansion. Recent analysis of cosmological observations indicates that the two-thirds of the total energy of the universe is been occupied by the DE whereas DM occupies almost the remaining part (the baryonic matter represents only a few percent of the total energy density of the universe) [8]. The contribution of the radiation is practically negligible.The nature of DE is still unknown and many candidates have been proposed in order to describe it [9][10][11][12][13][14][15][16]. The simplest one is represented by a tiny positive cosmological constant, with a negative constant equation of state (EoS) parameter ω, i.e. ω = −1. However, cosmologists know that the cosmological constant suffers from two well-known difficulties, the fine-tuning and the cosmic coincidence problems: the former asks why the vacuum energy density is so small (of the order of * Electronic address: surajit˙2008@yahoo.co.in, surajcha@iucaa.ernet.in † Electronic address: toto.pasqua@gmail.com

In this work, we consider the reconstruction scenario of new agegraphic dark energy (NADE) model and f (G) theory of gravity with G representing the Gauss-Bonnet invariant in the flat FRW spacetime. In this context, we assume a solution of the scale factor in power-law form and study the correspondence scenario. A new agegraphic f (G) model is constructed and discussed graphically for the evolution of the universe. Using this model, we investigate the different eras of the expanding universe and stability with the help of the equation of state (EoS) parameter ω ef f and squared speed of sound v 2 s , respectively. It is mentioned here that the reconstructed model represents the quintessence era of the accelerated expansion of the universe with instability. Moreover, the statefinder trajectories are studied and we find out that the model is not capable of reaching the ΛCDM phase of the universe.PACS numbers: 95.36.+x, 04.50.Kd

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Motivated by the work of Yang et al. (Mod. Phys. Lett. A 26:191, 2011), we report on a study of the new holographic dark energy (NHDE) model with energy density given by ρ D = 3φ 2 4ω (μH 2 + νḢ ) in the framework of chameleon Brans-Dicke cosmology. We have studied the correspondence between the quintessence, the DBI-essence, and the tachyon scalar-field models with the NHDE model in the framework of chameleon Brans-Dicke cosmology. Deriving an expression of the Hubble parameter H and, accordingly, ρ D in the context of chameleon Brans-Dicke chameleon cosmology, we have reconstructed the potentials and dynamics for these scalar-field models. Furthermore, we have examined the stability for the obtained solutions of the crossing of the phantom divide under a quantum correction of massless conformally invariant fields, and we have seen that the quantum correction could be small when the phantom crossing occurs and the obtained solutions of the phantom crossing could be stable under the quantum correction. It has also been noted that the potential increases as the matterchameleon coupling gets stronger with the evolution of the universe.