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Ahmed N.,National Research Institute of Astronomy and Geophysics | Moss I.G.,Newcastle University
Nuclear Physics B | Year: 2010

Moduli stabilisation is explored in the context of low-energy heterotic M-theory to show that a small value of the cosmological constant can result from a balance between the negative potential energy left over from stabilising the moduli and a positive Casimir energy from the higher dimensions. Supersymmetry breaking is induced by the fermion boundary conditions on the two branes in the theory. An explicit calculation of the Casimir energy for the gravitino reveals that the energy has the correct sign, although the size of the contribution is close to the edge of the parameter range for which the calculation is valid. © 2010 Elsevier B.V.

Ahmed N.,Taibah University | Ahmed N.,National Research Institute of Astronomy and Geophysics | Pradhan A.,Hindu Post graduate College
International Journal of Theoretical Physics | Year: 2014

A new class of cosmological models in f(R,T) modified theories of gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011), where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar R and the trace of the stress-energy tensor T, have been investigated for a specific choice of f(R,T)=f1(R)+f2(T) by considering time dependent deceleration parameter. The concept of time dependent deceleration parameter (DP) with some proper assumptions yield the average scale factor a(t) = sinh1\n(αt), where n and α are positive constants. For 01, the models of universe exhibit phase transition from early decelerating phase to present accelerating phase which is in good agreement with the results from recent astrophysical observations. Our intention is to reconstruct f(R,T) models inspired by this special law for the deceleration parameter in connection with the theories of modified gravity. In the present study we consider the cosmological constant Λ as a function of the trace of the stress energy-momentum-tensor, and dub such a model "Λ(T) gravity" where we have specified a certain form of Λ(T). Such models may display better uniformity with the cosmological observations. The statefinder diagnostic pair {r,s} parameter has been embraced to characterize different phases of the universe. We also discuss the physical consequences of the derived models. © 2013 Springer Science+Business Media New York.

Gahalaut K.,CSIR - Central Electrochemical Research Institute | Hassoup A.,National Research Institute of Astronomy and Geophysics
Journal of Geophysical Research: Solid Earth | Year: 2012

Continuing seismicity for about 30 years near a large western embayment of the Lake Nasser, about 50 km from the Aswan High Dam in Egypt, has led to a debate about the possibility of its relation with the reservoir impoundment. The largest event in the region occurred on 14 November 1981 (M 5.3), 20 km beneath the Wadi Kalabsha embayment, a westward extension of the Lake Aswan. Since then, continuous monitoring of seismic activity has given an excellent opportunity to study the spatiotemporal distribution of seismicity in the area. Most of the immediate aftershocks of the 1981 main shock were located in the Gebel Marawa area at depths between 15 and 30 km. Depths of almost all earthquakes away from this zone were shallower than 12 km. To quantify the effect of the reservoir impoundment on the seismicity of the Aswan area, we calculated changes in stress and pore pressure due to the reservoir impoundment using Green's function approach. The change in Coulomb stress (ΔS) is calculated on the fault planes responsible for majority of the seismicity of the region. We found that for all the seismogenic faults, ΔS is negative, i.e., stabilizing, when we consider the effect of the reservoir load only, whereas it is positive, i.e., destabilizing, when we include pore pressure. For example, at the hypocenter of the main earthquake, shear stress, normal stress, and pore pressure due to reservoir operation are estimated as 5.5, 13.2, and 13.5 kPa, respectively, which suggest that ΔS is -3.1 kPa when we do not consider the effect of pore pressure and 5.7 kPa when contribution from pore pressure is considered. Hence, the seismicity in the Aswan lake region is driven by the pore pressure due to reservoir impoundment. Copyright 2012 by the American Geophysical Union.

Abd El-Aal A.K.,National Research Institute of Astronomy and Geophysics
Natural Hazards and Earth System Science | Year: 2010

This paper reviews the likely source characteristics, focal source mechanism and fault patterns of the nearest effective seismogenic zones to Greater Cairo Area. Furthermore, Mmax and ground accelerations related to the effective seismic events expected in future from those seismogenic zones are well evaluated. For this purpose, the digital waveform of earthquakes than MLCombining double low line3 that occurred in and around Greater Cairo Area from 1997 to 2008 which have been recorded by the Egyptian National Seismological Network, are used to study source characterization, focal mechanism and fault pattern of the seismogenic zones around Greater Cairo Area. The ground motions are predicted from seismogenic zones to assess seismic hazard in the northeastern part of Greater Cairo, where three effective seismogenic zones, namely Abou Zabul, southeast Cairo trend and Dahshour area, have the largest effect to the Greater Cairo Area. The M max was determined, based upon an empirical relationship between the seismic moment and the rupture length of the fault during the earthquake. The estimated Mmax expected from Abou Zabul, southeast Cairo trend, Dahshour seismic sources are of Mw magnitudes equal to 5.4, 5.1, and 6.5, respectively. The predominant fundamental frequency and soil amplification characteristics at the area were obtained using boreholes data and in-situ ambient noise measurement. © 2010 Author(s).

Sanad M.R.,National Research Institute of Astronomy and Geophysics
Astrophysical Journal | Year: 2015

Ultraviolet spectra of two intermediate polars (IPs), PQ Gem and V405 Aur, observed with Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph and Faint Object Spectrograph and International Ultraviolet Explorer (IUE) satellites were analyzed during the period between 1994-2000. We estimated the reddening of the two systems from the 2200 feature. Six spectra of the two systems revealing modulations of line fluxes at different times are presented. PQ Gem and V405 Aur are featured by spectral lines in different ionization states. This paper focuses on the third ionized carbon emission line at 1550 and the first ionized helium emission line at 1640 produced in the optically thin outer region of the accretion curtain for the two systems by calculating spectral line fluxes. From HST and IUE data, we deduced ultraviolet luminosities and ultraviolet accretion rates for the two binary stars. The average temperature of the accretion streams for PQ Gem and V405 Aur are ∼4500 K and 4100 K, respectively. The results reveal that there are modulations in fluxes of spectral lines, ultraviolet luminosities, and ultraviolet accretion rates with time for both systems. These modulations are referred to the changes of both density and temperature as a result of the variations of mass transfer rate from the secondary star to the primary star. The current results are consistent with an accretion curtain model for IPs. © 2015. The American Astronomical Society. All rights reserved.

Abd El-Aal A.K.,National Research Institute of Astronomy and Geophysics
Journal of Geophysics and Engineering | Year: 2010

The importance of the northeastern part of the greater Cairo metropolitan area is due to the presence of a nuclear power plant and the dense population and its extent towards seismic sources. This paper reviews the likely ground acceleration related to the effective seismic events initiated from the closest seismic sources to the area. For this purpose, a deterministic seismic hazard approach followed by ground stochastic simulation was performed to assess the seismic hazard in the area. Seismic sources of hazardous effects were defined. A controlling earthquake was determined, based upon an empirical relationship between the seismic moment and the rupture length of the fault during the earthquake. The soil amplification characteristics in the area were obtained by in situ ambient noise measurements with great precautions. An H/V technique has been used to estimate the fundamental frequency and amplification factors at the sites of ambient noise measurements. The values of the fundamental frequency and the corresponding amplification factor were estimated at the investigated sites within the area of interest. The maximum possible earthquake magnitude Mmax was estimated for the effective seismic sources surrounding the study area and the hazard parameter peak ground acceleration (PGA) calculated for given zones. The work on the estimation of PGAs will contribute to the determination of national seismic codes, giving guidance on which buildings must take seismic risk into consideration and the necessity to re-appraise the seismic risk for existing buildings. © 2010 Nanjing Institute of Geophysical Prospecting.

Abd El-Aal A.K.,National Research Institute of Astronomy and Geophysics
Geophysical Journal International | Year: 2010

In conventional vibroseis signal processing, algorithms including cross-correlation and deconvolution are applied to convert the raw trace data into a seismic section. However, their performance deteriorates when the trace data are corrupted by the harmonic noise. An important issue of vibroseis data enhancement is the treatment or suppression upper harmonics. In this contribution, I present algorithm to eliminate the harmonic distortion, all at once, in both down- and up-sweep conventional vibroseis data using a simulation process for harmonic distortion in the correlated data. This technique consists of four steps: (1) cross-correlating the raw data with fundamental sweep then dividing the trace to several windows and detecting the windows contain fundamental energy for each response reflector; (2) calculating the harmonic amplitude ratio when applying the Fourier transform on the upper harmonic components and the fundamental, and dividing the upper harmonic components by the fundamental to remove the unknown convolutional effects; (3) using the harmonic amplitude ratio to simulate the upper harmonics associated with the fundamental energy in down- and up-sweep data. When the harmonic amplitude ratio is convolved with a portion of data containing the fundamental energy in the correlated data in time domain, I can get simulation for the upper harmonics existed in the original data and (4) subtracting the simulated harmonics from correlated traces using direct optimization procedure. Accordingly, I developed a procedure for attenuating upper harmonics in the positive and negative times of the correlated traces depending on accurate simulation for the correlated harmonics. The procedure was tested on both synthetic and field data sets. The correlated trace thus obtained will be freed substantially of correlation noise; that is the correlation-ghost sweeps (produced by severe harmonic distortion at positive and negative correlation times) are eliminated without degrading the seismic information content of the trace. © 2010 The Author Journal compilation © 2010 RAS.

Tadross A.L.,National Research Institute of Astronomy and Geophysics
Journal of the Korean Astronomical Society | Year: 2011

A sample of 145 JHK{2MASS observations of NGC open star clusters is studied, of which 132 have never been studied before. Twelve are classified as non-open clusters and 13 are re-estimated self-consistently, after applying the same methods in order to compare and calibrate our reduction procedures. The fundamental and structural parameters of the 120 new open clusters studied here are derived using color-magnitude diagrams of JHK Near-IR photometry with the fitting of solar metallicity isochrones. We provide here, for the first time, a catalog of the main parameters for these 120 open clusters, namely, diameter, distance, reddening and age. © 2011 The Korean Astronomical Society.

Tadross A.L.,National Research Institute of Astronomy and Geophysics
Research in Astronomy and Astrophysics | Year: 2012

We present the first in a series studying the astrophysical parameters of open clusters using the PPMXL* database whose data are applied to study Ruprecht 15. The astrophysical parameters of Ruprecht 15 have been estimated for the first time. © 2012 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd..

Araffa S.A.S.,National Research Institute of Astronomy and Geophysics
Geophysical Journal International | Year: 2013

SUMMARY This study aims to investigate the shallow and deeper section to delineate the groundwater aquifer and structural elementswhich dissect the study area. Added, the study aims to define the depth to a basaltic body and evaluate the quality of groundwater through interpretation of the geophysical, geological and boreholes data. Geophysical data have been measured, processed and interpreted in two- and three dimensions using special codes prepared by authors and commercial software. The results of interpretation indicate that the study area composed of two aquifers, the first is the Miocene aquifer and the second is Oligocene aquifer. The depth of the Miocene aquifer is ranging from 32.5 to 80 m. Its water quality is good and suitable for drinking and agricultural purposes; where the salinity ranges from 550 to 2200 g l-1 and the total hardness is ranging between 16.7 and 108.5 g l-1. The depth of the upper surface of basaltic body is ranging from 70 to 375m and the depth of lower surface of basaltic sheet is ranging from 133 to 410 m. The area is dissected by fault elements of NW-SE, NE-SW and N-S trend. © The Authors 2012.

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