Physics

A conceptual framework for variational formulations of physical theories is proposed. Such a framework is displayed here just for statics, but it is designed to be subsequently adapted to variational formulations of static field theories and dynamics.

There are currently two - main - continuum models of entropy: a 'reversible' entropy model and an 'irreversible' entropy model. It is shown that the 'reversible' entropy model and the 'irreversible' entropy model are equivalent with respect to entropy accumulation - which entails same values of entropy change and, thus, same values of entropy. The context of the analysis is continuum physics. The spatial non-continuity of the physical reality poses restrictions to domains of continuous field equations: There are lower limits for the sizes of the systems, for which the continuum assumption is valid. The scope of the analysis is the 'mechanical theory of heat' of Clausius, i.e. the heat and work phenomena of i) heat transfer, ii) heat generation, iii) heat absorption, and iv) work transfer

We define the Mie-Grüneisen form in five different ways, then demonstrate their equivalence.

In the present paper, we have investigated the Friedmann Robertson Walker (FRW) model in viable f(R,T) gravity with f(R,T) function proposed as f(R,T)=R+ξ T 1/2 , where ξ is an arbitrary constant, R is the scalar curvature and T is the trace of stress energy tensor. Defining the scale factor, the field equations are solved numerically and the energy conditions are analyzed. Further, determining Hubble parameter and deceleration parameter, their present values are estimated. Furthermore, 57 redshift data (42 redshift data from Supernova Cosmology project and 15 redshift data from Calán/ Tolono Supernova survey) are used to estimate the age of the universe and to find the best fit curves for luminosity distance and apparent magnitude.

An evanescent wave is a non-propagating wave with an imaginary wave vector. In this study, we prove that these are solutions of the tachyon-like Klein Gordon equation, and that in the tunneling of ultrarelativistic half integer spin particles they describe superluminal states arising from interactions between a particle and barrier. These states decay as a particle emerges from the opposite side of a potential barrier, conserving the same initial energy but not necessarily the same mass. The obtained theory is applied to the neutrino, to explain flavor oscillations during free flight and determine the conditions that maximize the probability of their occurrence.

Here we study the essence of f(R,T) gravitation theory in five dimensional Universe and see the role of dark energy in the form of wet dark fluid in such a Universe. It is found that the dark energy is not exaggerated in contributing to the accelerating expansion of the Universe though the expansion is inherent as a result of the theory itself and due to the geometric contribution of matter. It is interesting to see that in some model it is found that there was some era before the beginning of the present era, and some of the model Universe came out to be either oscillatory or cyclic. Some of the models are seen to go to ΛCDM models in late future as in Einstein gravitation theory, starting the evolution with a big bang. Most of the models undergo early inflation as well as late time accelerating expansion thus defining as good models for real astrophysical situations, with dark energy playing fundamental role in these Universe.

The exact harmonic metric for a moving Reissner-Nordström black hole with an arbitrary constant speed is presented. As an application, the post-Newtonian dynamics of a non-relativistic particle in this field is calculated.

Based on the cosmological principle and quantum Yang-Mills gravity in the super-macroscopic limit, we obtain an exact recession velocity and cosmic redshift z, as measured in an inertial frame F≡F(t,x,y,z). For a matter-dominated universe, we have the effective cosmic metric tensor G μν (t)=( B 2 (t),− A 2 (t),− A 2 (t),− A 2 (t)), A∝B∝ t 1/2 , where t has the operational meaning of time in F frame. We assume a cosmic action S≡ S cos involving G μν (t) and derive the `Okubo equation' of motion, G μν (t) ∂ μ S ∂ ν S− m 2 =0 , for a distant galaxy with mass m . This cosmic equation predicts an exact recession velocity, r ˙ =rH/[1/2+ 1/4+ r 2 H 2 / C 2 o − − − − − − − − − − − − − √ ]< C o , where H= A ˙ (t)/A(t) and C o =B/A , as observed in the inertial frame F . For small velocities, we have the usual Hubble's law r ˙ ≈rH for recession velocities. Following the formulation of the accelerated Wu-Doppler effect, we investigate cosmic redshifts z as measured in F . It is natural to assume the massless Okubo equation, G μν (t) ∂ μ ψ e ∂ ν ψ e =0 , for light emitted from accelerated distant galaxies. Based on the principle of limiting continuation of physical laws, we obtain a transformation for covariant wave 4-vectors between and inertial and an accelerated frame, and predict a relationship for the exact recession velocity and cosmic redshift, z=[(1+ V r )/(1− V 2 r ) 1/2 ]−1 , where V r = r ˙ / C o <1 , as observed in the inertial frame F . These predictions of the cosmic model are consistent with experiments for small velocities and should be further tested.

In this paper we have investigated a bulk viscous universe in f(R,T) gravity where R and T are the Ricci scalar and trace of energy momentum tensor respectively. We have obtained explicit solutions of field equations in modified gravity by considering the power law form of scale factor. The Hubble parameter and deceleration parameter are derived in terms of cosmic time and redshift both. We have estimated the present values of these parameters with observational Hubble data and SN Ia data sets. At 1 σ level, the estimated values of q 0 and m are obtained as q 0 =−0.30±0.05 \& m=0.70±0.02 where q 0 is the present value of deceleration parameter and m is the model parameter. The energy conditions and Om(z) analysis for the anisotropic LRS Bianchi type I model are also discussed.

The Gravity Probe B (GP-B) Experiment of NASA was aimed to test the theoretical predictions of Einstein's 1916 relativistic tensor theory of gravity in curved space-time (General Relativity (GR)) concerning the spin axis precession of a gyroscope moving in the field of a slowly rotating massive body, like the Earth. In 2011, GP-B mission reported its measured data on the precession (displacement) angles of the spin axes of the four spherical gyroscopes housed in a satellite orbiting 642 km (400 mi) above the Earth in polar orbit. The reported results are in agreement with the predictions of GR. For the first time, here we report an undergraduate level explanation of the GP-B experimental results using Heaviside-Maxwellian (vector) Gravity (HMG) in flat space-time, first formulated by Heaviside in 1893, and later considered/re-discovered by many authors. Our new explanation of the GP-B results provides a new test of HMG apart from the existing ones, which deserves the attention of researchers in the field for its simplicity and new perspective.