Scalar field cosmology with polytropic and causal viscous fluids

In this paper, we have considered a model for FRW space-time in the presence of coupled scalar field φ and potential V(φ) with causal viscous fluid and polytropic fluid. We have shown that irrespective of fluid the causality theory provides late time acceleration of the universe. In all cases, the potential always decreases due to evolution of the universe.     

Study of a new class of cylindrically symmetric space-time in general relativity

A new class of solutions of Einstein field equations is investigated for a cylindrically symmetric space-time when the source of gravitation is a perfect fluid. To get the deterministic solution a relation between metric coefficients A=(BC) ⁿ is assumed. Certain physical and geometric properties of the model are also discussed.     

Charged analogue of Vlasenko-Pronin superdense star in general relativity

In this article we have derived a set of three static spherical symmetric well behaved solutions of Einstein-Maxwell field equations is obtained for a specific choice of electric field involving a parameter K. The solutions so obtained can be seen as a charge analogue of the neutral solution due to Vlasenko and Pronin. The physical features of solutions so obtained and that of Vlasenko and Pronin are investigated subject to the reality and the causality conditions i.e. Pressure, density (greater than pressure), pressure-density ratio and velocity of sound (less than the velocity of light) are positive and monotonically decreasing and the electric intensity is monotonically increasing in nature away from the centre. The maximum mass and radius occupied by the neutral solution are 2.1434 M _Θ and 16.7300 km respectively. For the charged solution, overall maximum mass and corresponding radius are found to be 6.8714 M _Θ and 20.6166 km respectively (for K=1.343).     

Dynamics of a triaxial gyrostat at a Lagrangian equilibrium of a binary asteroid

The non-canonical Hamiltonian dynamics of a triaxial gyrostat in Newtonian interaction with two punctual masses is considered. This serves as a model for the study of the attitude dynamics of a spacecraft located at a Lagrangian equilibrium point of the system formed by a binary asteroid and a spacecraft. Using geometric-mechanics methods, the approximated dynamics that arises when developing the potential in series of Legendre functions and truncating the series to the second harmonics is studied. Working in the reduced problem, the existence of equilibria in Lagrangian form are studied, in analogy with classic results on the topic. In this way, the classical results on equilibria of the three-body problem, as well as other results by different authors that use more conventional techniques for the case of rigid bodies, are generalized. The rotational Poisson dynamics of a spacecraft located at a Lagrangian equilibrium and the study of the nonlinear stability of some important equilibria are considered. The analysis is done in vectorial form avoiding the use of canonical variables and the tedious expressions associated with them.     

Higher dimensional exact solutions for a charged fluid sphere in general theory of relativity

The exact higher dimensional solutions of Einstein-Maxwell field equations for spherically symmetric distribution of charged perfect fluid are obtained by using the method originally used by Hajj-Boutros and Sfeila (Gen. Relativ. Gravit. 18(4):395, 1986) for four-dimensional space-time. The new exact solutions have been generated from those of Khadekar et al. (J. Indian Math. Soc. 68(1–4):33, 2001), Humi and Mansour (Phys. Rev. D 29(6):1076, 1984) and Banerjee and Santos (J. Math. Phys. 22(4):824, 1981) in the frame work of higher dimensional space-time. The various physical properties are also discussed.     

A simple derivation of level spacing of quasinormal frequencies for a black hole with a deficit solid angle and quintessence-like matter

In this paper, we investigate analytically the level space of the imaginary part of quasinormal frequencies for a black hole with a deficit solid angle and quintessence-like matter by the Padmanabhan’s method (Padmanabhan in Class. Quantum Gravity 21:L1, 2004). Padmanabhan presented a method to study analytically the imaginary part of quasinormal frequencies for a class of spherically symmetric spacetimes including Schwarzschild-de Sitter black holes which has an evenly spaced structure. The results show that the level space of scalar and gravitational quasinormal frequencies for this kind of black holes only depend on the surface gravity of black-hole horizon in the range of $-1<w<-\frac{1}{3}$ , respectively. We also extend the range of w to w≤?1, the results of which are similar to that in $-1<w<-\frac{1}{3}$ case. Particularly, a black hole with a deficit solid angle in accelerating universe will be a Schwarzschild-de Sitter black hole, fixing w=?1 and ε ²=0. And a black hole with a deficit solid angle in the accelerating universe will be a Schwarzschild black hole,when ρ ₀=0 and ε ²=0. In this paper, w is the parameter of state equation, ε ² is a parameter relating to a deficit solid angle and ρ ₀ is the density of static spherically symmetrical quintessence-like matter at r=1.     

Periodic motions of a small body in the Newtonian field of a regular polygonal configuration of ν+1 bodies

We study the simple periodic orbits of a particle that is subject to the gravitational action of the much bigger primary bodies which form a regular polygonal configuration of (ν+1) bodies when ν=8. We investigate the distribution of the characteristic curves of the families and their evolution in the phase space of the initial conditions, we describe various types of simple periodic orbits and we study their linear stability. Plots and tables illustrate the obtained material and reveal many interesting aspects regarding particle dynamics in such a multi-body system.     

Remote Sensing of the Heliosphere with the Murchison Widefield Array

The Murchison Widefield Array (MWA) is one of the new technology low frequency radio interferometers currently under construction at an extremely radio-quiet location in Western Australia. The MWA design brings to bear the recent availability of powerful high-speed computational and digital signal processing capabilities on the problem of low frequency high-fidelity imaging with a rapid cadence and high spectral resolution. Solar and heliosphere science are among the key science objectives of the MWA and have guided the array design from its very conception. We present here a brief overview of the design and capabilities of the MWA with emphasis on its suitability for solar physics and remote-sensing of the heliosphere. We discuss the solar imaging and interplanetary scintillation (IPS) science capabilities of the MWA and also describe a new software framework. This software, referred to as Haystack InterPlanetary Software System (HIPSS), aims to provide a common data repository, interface, and analysis tools for IPS data from all observatories across the world.     

Role of a tachyonic field in accelerating the Universe in the presence of a perfect fluid

Recently, a tachyonic field was presented as a dark energy model to represent the present acceleration of the Universe. In this paper, we consider a mixture of tachyonic fluid with a perfect fluid. For this purpose we consider barotropic fluid and Generalized Chaplygin gas (GCG). We present a particular form of the scale factor. We solve the equations of motion to get exact solutions of the density, tachyonic potential and the tachyonic field. We introduce a coupling term to show that the interaction decays with time. We also show that the nature of the potentials vary, so the interaction term reduces the potential in both cases.     

Statefinder description of a cosmological model based on a mixture of five fluids

In this paper, we have considered a model of our universe containing five components as its constituents. Then, we have done here the statefinder diagnostics for this model. This model can successfully explain the accelerated expansion of the universe given that it satisfies a certain condition. Here we have considered the modified Chaplygin gas as the dynamically changing part of the dark energy component of our universe. Chaplygin gas provides early deceleration and late time acceleration of the universe. The graphical representation of statefinder parameters shows that the total evolution of the universe starts from radiation era to phantom model.     

Charged particles’ areas of three-dimensional motions in a system of two magnetic stars

We study the parametric evolution of the regions where three-dimensional motions of a charged particle are allowed in the combined electromagnetic field produced by two rotating magnetic stars. We discuss the changes in the topology of the zero-velocity surfaces, as well as in the trapping regions of the particle motion for various values of the dipoles’ magnetic moments.     

Dynamic evolution of recurrent mass ejections observed in Hα and Civ lines

During a coordinated SMY program, the consecutive formation of two new active centers merging together within AR 2646 was observed from 28 August, to 5 September, 1980. The two preceding spots compressed an inverse polarity spot on 1 September 1980, causing recurrent ejecta of matter with time intervals around 10 min. The observations of the MSDP spectrograph operating in H at the Meudon Solar tower and of the UVSP spectrometer on SMM in the Civ 1548 Å line show that cold and hot material had the same projection, although the upward Civ velocity structure was more extended than the H one. We present evidence that observed contrasts of the H absorbing structure can be interpreted in terms of a dynamic cloud model overlying the chromosphere. H matter follows a magnetic channel with upward velocity around 20–30 km s^–1 in the first phase of the event and with downward velocity ( - 40 km s^–1) in the second phase. The stored energy is not sufficient to trigger a flare, nor even to propulse matter along the full length of an arch, because of the periodic reorganisation of the magnetic field.     

Exact Kantowski–Sachs cosmological models in general theory of relativity

We have studied cosmological model generated by perfect fluid coupled with mass less scalar field for Kantowski–Sachs space–time in general theory of relativity. Two different physically viable models of the universe are obtained by using a special law of variation for Hubble’s parameter that yields a constant value of deceleration parameter. Some physical consequences of the models have been discussed in case of Zel’dovich fluid.     

Plane symmetric inhomogeneous cosmological models with a perfect fluid in General Relativity II

We investigate a class of solutions of Einstein equations for the plane symmetric perfect fluid case. If these solutions have shear, they must necessarily be non-static. Some physical and geometric properties of the models are also discussed.      

Bianchi type-I cosmological models with variable G and Λ-term in general relativity

Einstein’s field equations with variable gravitational and cosmological “constant” are considered in presence of perfect fluid for Bianchi type-I space-time. Consequences of the four cases of the phenomenological decay of Λ have been discussed which are consistent with observations. The physical significance of the cosmological models have also been discussed.      

The Minimum Activity Epoch as a Precursor of the Solar Activity

This paper considers the indices characterizing the minimum activity epoch, according to the data of large-scale magnetic fields and polar activity. Such indices include: dipole–octopole index, area and average latitude of the field with dominant polarity in each hemisphere, polar activity seen in polar faculae and Ca?ii K line bright points, coronal emission line intensity (5303?Å) and others. We studied the correlation between these indices and the amplitude of the following sunspot cycle, and the relation between the duration of the cycle of large-scale magnetic fields and the duration of the sunspot cycle. The obtained relationships allow us to presume that the polar field is formed from the sources of both preceding and the current activity cycles during the decay phase and at the activity minimum. The balance in these sources would therefore determine the features of the following sunspot cycle. The prediction for the 24th activity cycle using these results leads to W=102±13.     

Massive scalar field quasinormal modes of a black hole with quintessence-like matter and a deficit solid angle

Using the third-order WKB approximation, we evaluate the quasinormal frequencies of massive scalar field perturbation around a black hole with quintessence-like matter and a deficit solid angle. The mass u of the scalar field plays an important role in studying the quasinormal frequencies. We find that as the scalar field mass increases when the other parameters are fixed, so do the real parts and the magnitudes of the imaginary parts of the quasinormal frequencies decrease. The imaginary parts are almost linearly related to the real parts.     

A new law emerging from the recurrences of the ‘critical-acceleration’ of MOND, suggesting a clue to unification of fundamental forces

Keeping apart the problem, whether Modified Newtonian Dynamics [MOND] can replace ‘dark matter’, this letter considers seven different theoretical recurrences of ‘critical acceleration’ of MOND noticed by Sivaram in various physical situations; adds five more observational recurrences to the list; and arrives at a set of laws which seem to be followed by all the systems bound by different fundamental forces; suggesting a clue to unification of fundamental forces. This attempt proposes a general explanation for ‘flattening of galaxies’ rotation-curves’ as well as the ‘expansion of the universe’.     

Statistical Comparison of Magnetic Clouds with Interplanetary Coronal Mass Ejections for Solar Cycle 23

We compare the number and characteristics of interplanetary coronal mass ejections (ICMEs) to those of magnetic clouds (MCs) by using in-situ solar wind plasma and magnetic field observations made at 1 AU during solar cycle 23. We found that ≈ 28% of ICMEs appear to contain MCs, since 103 magnetic clouds (MCs) occurred during 1995  – 2006, and 307 ICMEs occurred during 1996 – 2006. For the period between 1996 and 2006, 85 MCs are identified as part of ICMEs, and six MCs are not associated with ICMEs, which conflicts with the idea that MCs are usually a subset of ICMEs. It was also found that solar wind conditions inside MCs and ICMEs are usually similar, but the linear correlation between geomagnetic storm intensity (Dst _min) and relevant solar wind parameters is better for MCs than for ICMEs. The differences between average event duration (Δt) and average proton plasma β (〈β〉) are two of the major differences between MCs and ICMEs: i) the average duration of ICMEs (29.6 h) is 44% longer than for MCs (20.6 hours), and ii) the average of 〈β〉 is 0.01 for MCs and 0.24 for ICMEs. The difference between the definition of a MC and that for an ICME is one of the major reasons for these average characteristics being different (i.e., listed above as items i) and ii)), and it is the reason for the frequency of their occurrences being different.