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An exact solution of the observable universe in Bianchi V space-time

Prasad Rajendra, Singh Manvinder, Yadav Anil Kumar, Beesham A.
06 Oct 2020 physics.gen-ph arxiv.org/abs/2010.02728

In this paper we investigate an observable universe in Bianchi type V space-time by taking into account the cosmological constant as the source of energy. We have performed a $\chi^{2}$ test to obtain the best fit values of the model parameters of the universe in the derived model. We have used two types of data sets, viz: i) 31 values of the Hubble parameter and ii) the 1048 Phanteon data set of various supernovae distance moduli and apparent magnitudes. From both the data sets, we have estimated the current values of the Hubble constant, density parameters $(\Omega_{m}){0}$ and $(\Omega{\Lambda}){0}$. The present value of deceleration parameter of the universe in derived model is obtained as $q{0} = 0.59^{+0.04}{-0.03}$ and $0.59^{+0.02}{-0.03}$ in accordance with $H(z)$ and Pantheon data respectively. Also we observe that there is a signature flipping in the sign of deceleration parameter from positive to negative and transition red-shift exists. Thus, the universe in derived model represents a transitioning universe which is in accelerated phase of expansion at present epoch. We have estimated the current age of the universe $(t_{0})$ and present value of jerk parameter $(j_{0})$. Our obtained values of $t_{0}$ and $j_{0}$ are in good agreement with its values estimated by Plank collaborations and WMAP observations.

On bi-slant submersions in complex geometry

Sayar Cem, Akyol Mehmet Akif, Prasad Rajendra
09 Nov 2019 math.GM arxiv.org/abs/1911.04889

In the present paper, we introduce bi-slant submersions from almost Hermitian manifolds onto Riemannian manifolds as a generalization of invariant, anti-invariant, semi-invariant, slant, semi-slant and hemi-slant Riemannian submersions. We mainly focus on bi-slant submersions from Kaehler manifolds. We provide a proper example of bi-slant submersion, investigate the geometry of foliations determined by vertical and horizontal distributions, and obtain the geometry of leaves of these distributions. Moreover, we obtain curvature relations between the base space, the total space and the fibres, and find geometric implications of these relations.

Ricci Solitons on submanifolds of $(LCS)_n$-Manifolds

Hui Shyamal Kumar, Prasad Rajendra, Pal Tanumoy
21 Jul 2017 math.DG arxiv.org/abs/1707.06815

The present paper deals with the study of Ricci solitons on invariant and anti-invariant submanifolds of $(LCS)_n$-manifolds with respect to Riemannian connection as well as quarter symmetric metric connection.

Optical Anisotropy in Bismuth Titanate: An Experimental and Theoretical Study

Roy Amritendu, Prasad Rajendra, Auluck Sushil, Garg Ashish
16 Sep 2013 cond-mat.mtrl-sci arxiv.org/abs/1309.4056

We report experimental and theoretical investigation of anisotropy in optical properties and their origin in the ferroelectric and paraelectric phases of bismuth titanate. Room temperature ellipsometric measurements performed on pulsed laser deposited bismuth titanate thin films of different orientations show anisotropy in the dielectric and optical constants, Subsequent first-principles calculations performed on the ground state structures of ferroelectric and high temperature paraelectric phases of bismuth titanate show that the material demonstrates anisotropic optical behavior in both ferroelectric and paraelectric phases. We further show that O 2p to Ti 3d transition is the primary origin of optical activity of the material while optical anisotropy results from the asymmetrically oriented Ti-O bonds in TiO6 octehdra in the unit cell.

Room Temperature Nanoscale Ferroelectricity in Magnetoelectric GaFeO3 Epitaxial Thin Films

Mukherjee Somdutta, Roy Amritendu, Auluck Sushil, Prasad Rajendra, Gupta Rajeev, Garg Ashish
16 Feb 2013 cond-mat.mtrl-sci arxiv.org/abs/1302.3983

We demonstrate room temperature ferroelectricity in the epitaxial thin films of magnetoelectric GaFeO3. Piezo-force measurements show a 180o phase shift of piezoresponse upon switching the electric field indicating nanoscale ferroelectricity in epitaxial thin films of gallium ferrite. Further, temperature dependent impedance analysis with and without the presence of an external magnetic field clearly reveals a pronounced magneto-dielectric effect across the magnetic transition temperature. In addition, our first principles calculations show that Fe ions are not only responsible for ferrimagnetism as observed earlier, but also give rise to the observed ferroelectricity, making GFO an unique single phase multiferroic.

Engineering Polarization Rotation in Ferroelectric Bismuth Titanate

Roy Amritendu, Prasad Rajendra, Auluck Sushil, Garg Ashish
24 Jan 2013 cond-mat.mtrl-sci arxiv.org/abs/1301.5743

Here, we report a combined experimental-theoretical study showing that collective application of rare earth doping on A-site and epitaxial strain to ferroelectric bismuth titanate does not lead to a very large c-axis polarization as reported previously. Further first principles calculations based on the examination of polarization tensor suggest that simultaneous Bi and Ti site doping could result in moderate polarization along c-axis of bismuth titanate which is typically a preferential axis of film growth and thus enabling c axis oriented films to have appreciable polarization. This approach could also be applicable to other ferroic oxides where one can correlate the doping, epitaxial strain, and polarization to design materials compositions resulting in epitaxial films grown along desired directions yielding substantial polarization.

Effect of Site-disorder, Off-stoichiometry and Epitaxial Strain on the Optical Properties of Magnetoelectric Gallium Ferrite

Roy Amritendu, Mukherjee Somdutta, Sarkar Surajit, Auluck Sushil, Prasad Rajendra, Gupta Rajeev, Garg Ashish
01 Oct 2012 cond-mat.mtrl-sci arxiv.org/abs/1210.0356

We present a combined experimental-theoretical study demonstrating the role of site disorder, off-stoichiometry and strain on the optical behavior of magnetoelectric gallium ferrite. Optical properties such as band-gap, refractive indices and dielectric constants were experimentally obtained by performing ellipsometric studies over the energy range 0.8 eV to 4.2 eV on pulsed laser deposited epitaxial thin films of stoichiometric gallium ferrite with b-axis orientation and the data was compared with theoretical results. Calculations on the ground state structure show that the optical activity in GaFeO3 arises primarily from O2p-Fe3d transitions. Further, inclusion of site disorder and epitaxial strain in the ground state structure significantly improves the agreement between the theory and the room temperature experimental data substantiating the presence of site-disorder in the experimentally derived strained GaFeO3 films at room temperature. We attribute the modification of the ground state optical behavior upon inclusion of site disorder to the corresponding changes in the electronic band structure, especially in Fe3d states leading to a lowered band-gap of the material.

Semi-slant submersions

Park Kwang-Soon, Prasad Rajendra
03 Jan 2012 math.DG arxiv.org/abs/1201.0814

Let F be a Riemannian submersion from an almost Hermitian manifold (M; gM; J) onto a Riemannian manifold (N; gN). We introduce the notion of the semi-slant submersion. And then we obtain some properties about it. In particular, we give some examples for it.

Power comparison of CMOS and adiabatic full adder circuit

Reddy Sunil Gavaskar, prasad Rajendra
07 Oct 2011 cs.AR arxiv.org/abs/1110.1549

Full adders are important components in applications such as digital signal processors (DSP) architectures and microprocessors. Apart from the basic addition adders also used in performing useful operations such as subtraction, multiplication, division, address calculation, etc. In most of these systems the adder lies in the critical path that determines the overall performance of the system. In this paper conventional complementary metal oxide semiconductor (CMOS) and adiabatic adder circuits are analyzed in terms of power and transistor count using 0.18UM technology.

First Principle Study of Magnetism and Magneto-structural Coupling in Gallium Ferrite

Roy Amritendu, Prasad Rajendra, Auluck Sushil, Garg Ashish
13 Aug 2011 cond-mat.mtrl-sci arxiv.org/abs/1108.2773

We report a first-principles study of the magnetic properties, site disorder and magneto-structural coupling in multiferroic gallium ferrite (GFO) using local spin density approximation (LSDA+U) of density functional theory. The calculations of the ground state A-type antiferromagnetic structure predict magnetic moments consistent with the experiments whilst consideration of spin-orbit coupling yields a net orbital moment of ~ 0.025 Bohr magneton/Fe site also in good accordance with the experiments. We find that though site disorder is not spontaneous in the ground state, interchange between Fe2 and Ga2 sites is most favored in the disordered state. The results show that ferrimagnetism in GFO is due to Ga-Fe site disordering such that Fe spins at Ga1 and Ga2 sites are antiferromagnetically aligned while maintaining ferromagnetic coupling between Fe spins at Ga1 and Fe1 sites as well as between Fe spins at Ga2 and Fe2 sites. The effect of spin configuration on the structural distortion clearly indicates presence of magneto-structural coupling in GFO.