Space Science

We discuss two dark energy models on LRS Bianchi Type-I magnetized anisotropic space –time with a variable equation of state (EoS). The EoS for dark energy is found to be time dependent and its existing range for derive models is in good agreement with the recent observations. Using the suitable condition, the anisotropic models approach to isotropic scenario. We also find that during the evolution of the universe, the EoS parameter for DE changes from to in first model whereas from to in second model which is consistent with recent observations. The cosmological constant is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations. The physical and geometric properties are also discussed.

Mean Monthly, seasonal and zonal percentages of thunderstorms (TS) and rainfall (RF) frequency obtained, analyzed and depicted using fifty years (1961–2010) data of 54 Pakistani observatories spread uniformly over the country. The study has revealed that there is a significant correlation between the frequencies of said parameters, while there is a one month time lag found in the occurrence of peak activity of TS and RF. Seasonal analysis of these two parameters suggests that rainfall yield associated with post-monsoon season is marginally more than TS activity and significantly more in winter season. Considering zones of the country during winter, apart form Sindh RF activity is significantly more than TS but during May to September (most of premonsoon and monsoon) TS activity is found more than RF in all zones. This behavior is consistent with the overall seasonal behavior of the country. The monthly study has revealed two marked peaks of TS and RF while rainfall activity in end of winter and start of premonsoon is greater than in peak monsoonal months. Overall seasonal analysis of these two parameters suggests that rainfall yield associated with post-monsoon season TS seems to be higher than the pre-monsoon season. Station wise seasonal analysis of winter suggested that all stations acquire much more RF accompanied with very little TS activity. The situation is reverse for premonsoon and monsoon while in postmonsoon, situation is rather complex. All data is also demoed in graphical representations and tabulated with characterized statistical and analytical values. The aim of this paper is to promote various components of TS and RF activity over Pakistan and to help the weather forecasters, aircraft pilots, agriculturists and planners in this respect. The study also emphasizes the need for more studies in this direction.

This paper presents a comparative study on the important parameter of the ionosphere critical frequency of F2 layer (foF2) retrieved by means of ground based ionosonde radars and predicted by International Reference Ionosphere extended till plasma sphere (IRIPLAS-2011) model at two different locations including Northern Sumatra (Geographic Lat. 2.311°N,Geographic Long. 93.063°E) and Fox Island, Alaska (Geographic Lat. 52.008°N, Geographic Long.171.859°W) in the low and mid latitude during the earthquakes occurred in the years 2012 and 2011, respectively. A running median of the fof2 and linked inter quartile range (IQR), upper bound (UB) and lower bound (LB) are utilized as a reference for identifying abnormal signals during the earthquakes. The results show anomalous reductions and enhancements in the fof2 within 7 days before and after the earthquakes. A comparative study between ionosonde retrieved and IRIPLAS-2011 model derived foF2 values reveals that the ionosonde retrieved values exhibit better anomalies during both the events. The analysis during extreme quiet geophysical conditions is shown to be a useful indicator of a forthcoming earthquake.

In the Theory of relativity there are fundamental internal contradictions. The most direct of them is, between the two sides of one unequal equation, intended to transform time. These contradictions prove, that this theory is absolutely wrong.

We explore an alternate approach to the origin of primordial fluctuations using extra dimensions. A non-inflationary cosmology is considered, with the evolution of 4 + d dimensions from the initial singularity. The extra dimensions evolve more rapidly than the ordinary space and reach their maximum volume in a short interval of time, at the end of which they get stabilized. Due to random interactions between the bulk and the brane, the entropy may be sucked from the normal space. These interactions occur only for a short interval of time and hence only a small amount of entropy is consumed. An approximate equation which describes the decrease in entropy, in a region of normal space, is constructed. Finally, this violation of law of entropy is related to the increase in density of that region of space by simple thermodynamic considerations. This process occurs randomly in different regions of normal space generating the primordial fluctuations in density, which grow over time and eventually become the universe we see today.

Total electron content (TEC) is a key ionospheric parameter that describes the major impact of the ionosphere on the propagate on of radio waves which is crucial for terrestrial and space communication. The present investigation is dedicated to study the latitudinal variability of ionosphere. The study is carried out by taking three stations one each in low, mid and high latitude regions namely IISC, Bangalore, India (13.020 N, 77.570E), GUAO, Urumqi, China (43.820N, 87.600E) and NYAL, NY-Alesund, Norway (78.920N, 11.860E) respectively. To study the changes in the ionosphere at three selected station we have considered the GPS observations. The GPS derived TEC values have been collected from the SOPAC (Scripps Orbits and Permanent Array Center) data archive of the IGS (International GPS service). The study is carried out during the high solar activity period of 24th solar cycle i.e. during January 2012 to December 2012. We also studied the behaviour of ionospheric Total Electron Content (TEC) during the geomagnetic storms. We have selected 5 intense geomagnetic storms (Dst ? -100nT) that were observed during the year 2012. From our analysis we observed that TEC achieves its highest values during the months of October and March at low latitude, during the month of April and May at mid latitude and during the September and March at high latitude while the lowest values of TEC were recorded at all the station in December month. Similarly, the highest values of TEC are recorded during the equinox season while the lowest values are recorded in winter season.

A solar eclipse provides us with a rare opportunity to study the ionospheric effects associated with an accurately estimated variation of solar radiation during the eclipse period. An exceptionally long total solar eclipse occurred on Wednesday, 22 July 2009, that traversed the eastern hemisphere in a narrow corridor. The Ionosonde observations taken at Space Science Laboratory, Department of Physics and Electronics, Barkatullah University, Bhopal during the three days centered on the total solar eclipse of 22 July 2009 are described. The eclipse was sufficient to decrease the ionization of some regions of ionosphere by the solar disc which was obscured at the maximum phase. The effects on the ionospheric parameters are observed when eclipse reached its maximum totality. A magnetic disturbance occurred during the period of the observation. Therefore the Ionosonde observations are discussed in conjugation with the changes which occurred in the earth’s magnetic field and the ionosphere during the event of the eclipse.

We have studied LRS Bianchi type-I magnetized cosmological models in the presence of scalar tensor theory proposed by Saez Ballester [1]. We assume that the dark energy (DE) is minimally interacting, has dynamical energy- density, anisotropic equation of state parameter (EoS). Exact solutions of Einstein’s field equations are obtained by assuming a special law of variation for the mean Hubble parameter, which yields a constant value of the deceleration parameter. The geometrical and physical aspects for the models are also studied.

In mobile communications, the need to improve the quality of service and to predict the minimum signal power required for transmission has attracted a great deal of research attention. In this paper, the ITU-R adopted Walfisch-Bertoni (W/B) pathloss model for IMT-2000 third generation (3G) mobile networks standard, is enhanced based on experimental campaigns conducted in two CDMA2000 networks transmitting at 800MHz frequency band in South-South, Nigeria. In this enhancement method, W/B is modified to incorporate secondary knife edge diffraction and multipath reflection loss due to the buildings and objects nearest the mobile down the street. The proposed pathloss models indicate improved prediction accuracy compared to the original W/B model in terms of root mean square and relative error analysis.

An unmagnetized dusty plasma consisting of static negatively charged dust fluid, nonthermal distributed electrons, and adiabatic ion fluid has been considered. Basic properties of the dust-ion-acoustic shock waves have been made by the reductive perturbation method to derive the Burgers’ equation for nonplanar geometry. The solution of modified Burgers’ equation in nonplanar geometry is numerically analyzed and it has been found that, the nonplanar geometry effects have a very vital role in the development of shock waves. We also discovered that; the inclusion of the nonthermal electron distribution significantly modifies the shock wave profile. The change of the DIASW structure due to the effect of ion temperature and dust density is studied.