Effect of point source and heterogeneity on the propagation of SH-Waves in a viscoelastic layer over a viscoelastic half space

The present paper is concerned with the propagation of shear waves in a homogeneous viscoelastic isotropic layer lying over a semi-infinite heterogeneous viscoelastic isotropic half-space due to point source. The inhomogeneity parameters associated to rigidity, internal friction and density are assumed to be functions of depth. The dispersion equation of shear waves has been obtained using Green’s function technique. The dimensionless angular frequency has been plotted against dimensionless wave number for different values of inhomogeneity parameters. The effects of inhomogeneity have been shown in the dispersion curves. graphical user interface (GUI) software in MATLAB has been developed to show the effect of various inhomogeneity parameters on angular frequency. The topic can be of interest for geophysical applications in propagation of shear waves on the Earth’s crust.     

Interaction between phantom field and modified Chaplygin gas

In this letter, we have considered a flat FRW universe. Instead of considering only one candidate for the dark energy, we have considered the interaction between phantom field and modified Chaplygin gas. It has been shown that the potential of the phantom field increases from a lower value with evolution of the universe. It has been observed that the field has an increasing tendency and the potential has also an increasing tendency with passage of cosmic time. In the evolution of the universe the crossing of w=−1 has been realized by this interacting model.     

Power spectrum analysis of atmospheric ozone content over north India

Summary Atmospheric total ozone contents over three stations in north India have been studied. A power spectrum analysis has been made of daily values recoreded at these stations during the winter season. Three types of periodicities have been observed in the available records, namely, oscillations with a period of (a) 2.5–3.5 days, (b) 4.0–5.3 days and (c) 8.0–9.6 days. The first and third type of oscillations were also observed when the data were extended to cover an entire year, instead of the winter season alone. A possible mechanism for the occurrence of these periodicities is discussed.     

Development of a hard x-ray focal plane compton polarimeter: a compact polarimetric configuration with scintillators and Si photomultipliers

X-ray polarization measurement of cosmic sources provides two unique parameters namely degree and angle of polarization which can probe the emission mechanism and geometry at close vicinity of the compact objects. Specifically, the hard X-ray polarimetry is more rewarding because the sources are expected to be intrinsically highly polarized at higher energies. With the successful implementation of Hard X-ray optics in NuSTAR, it is now feasible to conceive Compton polarimeters as focal plane detectors. Such a configuration is likely to provide sensitive polarization measurements in hard X-rays with a broad energy band. We are developing a focal plane hard X-ray Compton polarimeter consisting of a plastic scintillator as active scatterer surrounded by a cylindrical array of CsI(Tl) scintillators. The scatterer is 5 mm diameter and 100 mm long plastic scintillator (BC404) viewed by normal PMT. The photons scattered by the plastic scatterer are collected by a cylindrical array of 16 CsI(Tl) scintillators (5 mm × 5 mm × 150 mm) which are read by Si Photomultiplier (SiPM). Use of the new generation SiPMs ensures the compactness of the instrument which is essential for the design of focal plane detectors. The expected sensitivity of such polarimetric configuration and complete characterization of the plastic scatterer, specially at lower energies have been discussed in [11, 13]. In this paper, we characterize the CsI(Tl) absorbers coupled to SiPM. We also present the experimental results from the fully assembled configuration of the Compton polarimeter.     

The initiation and linkage of surface fractures above a buried strike-slip fault: An experimental approach

Surface fractures in the overburdened sedimentary rocks, formed above a deep-seated basement fault, often provide important information about the kinematics of the underlying master fault. It has already been established that these surface fractures dynamically evolve and link one another with progressive displacement on the master fault below. In the present study, two different series of riedel-type experiments were carried out with clay analogue models under different boundary conditions viz., (i) heterogeneous simple shear of the cover rocks above a buried strike slip fault (wrench system) and (ii) heterogeneous simple shear with a component of shear-normal compression of the overburden package above a basement fault (transpressional system), to observe the initiation and linkage of surface fractures with varying T′ (where T′ = thickness of the overburden normalized with respect to the width of the master fault). In the wrench system, Riedel (R) shears were linked by principal displacement (Y) shears at early stages (shear strain of 0.8 to 1) in thin (2 < T′ < 18) models and finally (at a minimum shear strain of 1.4) gave rise to a through-going fault parallel to the basement fault without development of any other fracture. Conjugate Riedel (R′) shears develop only within the thicker (T′ > 18) clay models at a minimum shear strain of 0.7. With increasing deformation (at a minimum shear strain of 1.2) two R′ shears were joined by an R shear and finally opened up to make a sigmoidal vein with an asymmetry antithetic to the major fault-movement sense. Under transpression, the results were similar to that of heterogeneous simple shear for layers 2 < T′ < 15. In layers of intermediate thickness (15 < T′ < 25) early formed high angle R shears were cross cut by low angle R shears (at a minimum shear strain of 0.5 and shortening of 0.028) and “Riedel-within-Riedel” shears were formed within thick (T′ > 25) models (at minimum shear strain of 0.7 and shortening of 0.1), with marked angularity of secondary fault zone with the master fault at depth.     

REFLECTION AND TRANSMISSION OF SHEAR WAVES IN MONOCLINIC MEDIA

This paper deals with the propagation, reflection and transmission of shear waves in monoclinic media. The dispersion equation for a monoclinic layer overlying a monoclinic half-space has been obtained and curves are plotted. The amplitude ratios for both the reflected and transmitted waves due to reflection of shear waves at the interface of two monoclinic half-spaces have also been computed and the numerical results are presented graphically. The results are compared with the isotropic case. It has been observed that, in monoclinic media, the amplitude ratios for reflected and transmitted wave increases approximately by 25 and 50 per cent respectively, in comparison to the isotropic case. © 1997 John Wiley & Sons, Ltd.     

Multivariate forecast of winter monsoon rainfall in India using SST anomaly as a predictor: Neurocomputing and statistical approaches

In this article, the complexities in the relationship between rainfall and sea surface temperature (SST) anomalies during the winter monsoon over India were evaluated statistically using scatter plot matrices and autocorrelation functions. Linear, as well as polynomial trend equations were obtained, and it was observed that the coefficient of determination for the linear trend was very low and it remained low even when polynomial trend of degree six was used. An exponential regression equation and an artificial neural network with extensive variable selection were generated to forecast the average winter monsoon rainfall of a given year using the rainfall amounts and the SST anomalies in the winter monsoon months of the previous year as predictors. The regression coefficients for the multiple exponential regression equation were generated using Levenberg-Marquardt algorithm. The artificial neural network was generated in the form of a multilayer perceptron with sigmoid non-linearity and genetic-algorithm based variable selection. Both of the predictive models were judged statistically using the Willmott's index, percentage error of prediction, and prediction yields. The statistical assessment revealed the potential of artificial neural network over exponential regression.     

Acceleration of the Universe in presence of tachyonic field

In this letter, we have assumed that the Universe is filled in tachyonic field with potential, which gives the acceleration of the Universe. For certain choice of potential, we have found the exact solutions of the field equations. We have shown the decaying nature of potential. From recently developed statefinder parameters, we have investigated the role of tachyonic field in different stages of the evolution of the Universe.