arXiv subjects

Jitendra Kumar

Publications and source records attributed to Jitendra Kumar.

52 records · Page 3Linked to original sources

arXiv2021

Pulsar PSR B0943+10 as an isotropic Vaidya-Tikekar type compact star : A comprehensive study

In this paper, we have constructed a model for well behaved isotropic compact star in the presence of charged perfect fluid, by considering a static and spherically symmetric metric in Schwarzschild's canonical coordinate system. To put the resulting differential equations into a closed system, we have employed the Vaidya & Tikekar (J. Astrophys. Astron. 3:325, 1982) form of the metric potential grr. The resulting energy-momentum components, i.e., energy density and pressure contain six constants; two of these are determined through the junction condition (matching the interior with the exterior Schwarzschild solution) and by the property of vanishing pressure on the boundary. The remaining constants are constrained by requirements of a real compact star. The physical acceptability of our model is tested using the data of the pulsar PSR B0943+10. Using graphical analysis and tabular information we have shown that our model obeys all the physical requirements. The stability of this model is evaluated using the Tolman-Oppenheimer-Volkoff equation, the adiabatic index and the Harrison-Zeldovich-Novikov Criterion and it has passed the evaluation.

gr-qc↗

arXiv2021

Anisotropic relativistic fluid spheres with a linear equation of state

In this work, we present a class of relativistic and well-behaved solution to Einstein's field equations for anisotropic matter distribution. We perform our analysis by using the Buchdahl ansatz for the metric function grr. Three different classes of new exact solution are found for anisotropy factor(delta). We have analyzed our model with various physical aspects such as pressure (radial as well as transverse), energy density, anisotropy factor, mass, compactness parameter, adiabatic index(gamma) and surface redshift. A graphical analysis of energy conditions, TOV equation and causality condition indicates the model are well behaved. The physical acceptability of the model has verified by considering compact objects with similar mass and radii, such as 4U 1820-30,Vela X-1, PSR J1614-2230, LMC X-4, SMC X-1, 4U 1538-52, Her X-1, Cyg X-2, PSR B1913+16 and PSR J1903+327.

gr-qc↗

arXiv2021

Strong gravitational lensing by rotating Simpson--Visser black holes

We investigate strong field gravitational lensing by rotating Simpson-Visser black hole, which has an additional parameter ($0\leq l/2M \leq1$), apart from mass ($M$) and rotation parameter ($a$). A rotating Simpson-Visser metric correspond to (i) a Schwarzschild metric for $l/2M=a/2M=0$ and $ M \neq 0 $, (ii) a Kerr metric for $l/2M=0$, $|a/2M|< 0.5$ and $ M \neq 0 $ (iii) a rotating regular black hole metric for $|a/2M|< 0.5$, $ M \neq 0 $ and $l/2M$ in the range $0 0.5$ and $l/2M\neq 0$. We find a decrease in the deflection angle $α_D$ and also in the ratio of the flux of the first image and all other images $ r_{mag}$. On the other hand, angular position $θ_{1}$ increases more slowly and photon sphere radius $x_{m}$ decreases more quickly, but angular separation $s$ increases more rapidly, and their behaviour is similar to that of the Kerr black hole. The formalism is applied to discuss the astrophysical consequences in the supermassive black holes and find that the rotating Simpson-Visser black holes can be distinguished from the Kerr black hole via gravitational lensing. The deviation of the lensing observables $Δθ_1$ and $Δs$ of rotating Simpson Visser black holes from Kerr black hole for $0<l/2M <0.6$ ($a/2M=0.45$), for supermassive black holes Sgr A* and M87, respectively, are in the range $0.0422-0.11658~μ$as and $0.031709-0.08758~μ$as while $|Δr_{mag}|$ is in the range $0.2037 - 0.95668$. It is difficult to distinguish the two black holes because the departure are in $\mathcal{O}(μ$as), which are unlikely to get resolved by the current EHT observations. We also derive a two-dimensional lens equation and formula for deflection angle in the strong field limit by focusing on trajectories close to the equatorial plane.

gr-qc↗

arXiv2021

Credit Card Fraud Detection using Machine Learning: A Study

As the world is rapidly moving towards digitization and money transactions are becoming cashless, the use of credit cards has rapidly increased. The fraud activities associated with it have also been increasing which leads to a huge loss to the financial institutions. Therefore, we need to analyze and detect the fraudulent transaction from the non-fraudulent ones. In this paper, we present a comprehensive review of various methods used to detect credit card fraud. These methodologies include Hidden Markov Model, Decision Trees, Logistic Regression, Support Vector Machines (SVM), Genetic algorithm, Neural Networks, Random Forests, Bayesian Belief Network. A comprehensive analysis of various techniques is presented. We conclude the paper with the pros and cons of the same as stated in the respective papers.

cs.AI↗

arXiv2021

A study on Machine Learning Approaches for Player Performance and Match Results Prediction

Cricket is unarguably one of the most popular sports in the world. Predicting the outcome of a cricket match has become a fundamental problem as we are advancing in the field of machine learning. Multiple researchers have tried to predict the outcome of a cricket match or a tournament, or to predict the performance of players during a match, or to predict the players who should be selected as per their current performance, form, morale, etc. using machine learning and artificial intelligence techniques keeping in mind extensive detailing, features, and parameters. We discuss some of these techniques along with a brief comparison among these techniques.

cs.AI↗

arXiv2021

A Secure and Multi-objective Virtual Machine Placement Framework for Cloud Data Centre

To facilitate cost-effective and elastic computing benefits to the cloud users, the energy-efficient and secure allocation of virtual machines (VMs) plays a significant role at the data centre. The inefficient VM Placement (VMP) and sharing of common physical machines among multiple users leads to resource wastage, excessive power consumption, increased inter-communication cost and security breaches. To address the aforementioned challenges, a novel secure and multi-objective virtual machine placement (SM-VMP) framework is proposed with an efficient VM migration. The proposed framework ensures an energy-efficient distribution of physical resources among VMs that emphasizes secure and timely execution of user application by reducing inter-communication delay. The VMP is carried out by applying the proposed Whale Optimization Genetic Algorithm (WOGA), inspired by whale evolutionary optimization and non-dominated sorting based genetic algorithms. The performance evaluation for static and dynamic VMP and comparison with recent state-of-the-arts observed a notable reduction in shared servers, inter-communication cost, power consumption and execution time up to 28.81%, 25.7%, 35.9% and 82.21%, respectively and increased resource utilization up to 30.21%.

cs.DC↗

arXiv2021

Behavior of anisotropic fluids with Chaplygin equation of state in Buchdahl spacetime

In the present study we have proposed a new model of an anisotropic compact star which admits the Chaplygin equation of state. For this purpose, we consider Buchdahl ansatz. We obtain the solution of proposed model in closed form which is non-singular, regular and well-behaved. In addition to this, we show that the model satisfies all the energy conditions and maintains the hydrostatic equilibrium equation. This model represents compact stars like PSR B0943+10, Her X-1 and SAX J1808.4-3658 to a very good approximate.

gr-qc↗

arXiv2019

Isotropic uncharged model with compactness and stable con gurations

In present work, we have studied a new stellar distribution model with spherically symmetric matter and an uncharged isotropic distribution in general relativity. In this model, we have considered a particular metric potential. The model is capable to represents some known compact stars like Her X-1,4U 1538-52 and SAX J1808.4-3658.The model satisfy the energy condition and hydrostatic equilibrium equation, i.e., the modified Tolman-Oppenheimer-Volkoff (TOV) equation for uncharged matter. In addition to this, we also present the velocity of sound, surface redshift, and pressure density ratio. The physical quantities such as pressure, density, redshift, etc., are compared with graphical representations that are important from theoretical and astrophysical scale.

gr-qc↗

arXiv2019

Charged Analogues of Isotropic Compact Stars Model with Buchdahl Metric in General Relativity

In this work, we examine a spherically symmetric compact body with isotropic pressure profile, in this context we obtain a new class of exact solutions of Einstein's-Maxwell field equation for compact stars with uniform charged distributions on the basis of Pseudo-spheroidal space-time with a particular form of electric field intensity and the metric potential g_rr. Indicating these two parameters takes into account further examination to be done in deciding unknown constants and depicts the compact strange star candidates likes PSR J1614-2230, 4U 1608-52, SAX J1808.4-3658, 4U 1538-52, SMC X-1, Her X-1, and Cen X-3. By the isotropic Tolman-Oppenhimer-Volkoff(TOV)equation, We explore the equilibrium among hydrostatic, gravitational and electric forces. Then, we analyze the stability of the model through the adiabatic index(gamma) and velocity of sound (0 <dp/c^2dr< 1). we additionally talk about other physical features of this model like, for example, the pressure, redshift, density, energy conditions and mass-radius of the stars in detail and demonstrate that our results are satisfying all the basic prerequisites of a physically legitimate stellar model. We have seen the measurement of basic physical parameter such as pressure, density, energy and redshift are satisfied the reality condition. All the physical quantities such as density, pressure pressure-density ratio and speed of sound is monotonically decreasing. The outcomes acquired are valuable in exploring the strength of other compact objects like white dwarfs, gravastars and neutron stars. Finally, we have shown that the obtained solutions are compatible with observational data for compact objects.

physics.gen-ph↗

arXiv2017

Charged Vaidya-Tikekar model for super compact star

In this work, we explore a class of compact charged spheres that have been tested against experimental and observational constraints with some known compact stars candidates. The study is performed by considering the self-gravitating, charged, isotropic fluids which is more pliability in solving the Einstein-Maxwell equations. In order to determine the interior geometry, we utilize the Vaidya-Tikekar geometry for the metric potential with Riessner-Nordstrom metric as an exterior solution. In this models, we determine constants after selecting some particular values of M and R, for the compact objects SAX J1808.4-3658, Her X-1 and 4U 1538-52. The most striking consequence is that hydrostatic equilibrium is maintained for different forces, and the situation is clarified by using the generalized Tolman-Oppenheimer-Volkoff (TOV) equation. In addition to this, we also present the energy conditions, speeds of sound and compactness of stars that are very much compatible to that for a physically acceptable stellar model. Arising solutions are also compared with graphical representations that provide strong evidences for more realistic and viable models, both at theoretical and astrophysical scale.

physics.gen-ph↗

arXiv2017

Analytical Approach For Solving Population Balances: A Homotopy Perturbation Method

In the present work, a new approach is proposed for finding the analytical solution of population balances. This approach is relying on idea of Homotopy Perturbation Method (HPM). The HPM solves both linear and nonlinear initial and boundary value problems without nonphysical restrictive assumptions such as linearization and discretization. It gives the solution in the form of series with easily computable solution components. The outcome of this study reveals that the proposed method can avoid numerical stability problems which often characterize in general numerical techniques related to this area. Several examples including Austin's kernel available in literature are examined to demonstrate the accuracy and applicability of the proposed method.

math.NA↗

arXiv2017

Existence and uniqueness of solutions for coagulation-fragmentation problems with singularity

In this paper, existence and uniqueness of solutions to a non-linear, initial value problem is studied. In particular, we consider a special type of problem which physically represents the time evolution of particle number density resulted due to the coagulation and fragmentation process. The coagulation kernel is chosen from a huge class of functions, both singular and non-singular in nature. On the other hand, fragmentation kernel includes practically relevant non-singular unbounded functions. Moreover, both the kernels satisfy a linear growth rate of particles at infinity. The existence theorem includes lesser restrictions over the kernels as compared to the previous studies. Furthermore, strong convergence results on the sequence of functions are used to establish the existence theory.

math.AP↗

arXiv2017

Heavy-flavour measurements in p-Pb collisions with ALICE at the LHC

The measurements of open heavy-flavours, i.e. D mesons at central rapidity and leptons from charm and beauty decays at central and forward rapidity was studied in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV using the ALICE detector. The results are presented and compared to model predictions including cold nuclear matter effects.

hep-ex↗

arXiv2015

Effect of Functionalized CNT on Nematic anchoring

Nematic phase is the most fundamental mesophase exhibited by most of the rod shaped anisotropic liquid crystalline molecules. Nematics are orientationally ordered fluids whose average orientation direction can be manipulated on application of electric and magnetic fields. Carbon nanotube (CNT), a highly shape anisotropic object can find numerous industrial application because of its interesting electronic and mechanical properties. The self-organizing properties of nematics can be used to align CNTs dispersed in them. We have dispersed functionalized CNTs in nematic liquid crystal and carried out many experimental studies. We will present results of electro-optic switching and dielectric measurements on some CNT-LC dispersion. We have observed that addition of functionalized CNTs in a liquid crystal (LC) has led to improvement in the nematic ordering which is evidential from enhancement in dielectric anisotropy (De) measurement. These results indicate that the anchoring energy at alignment layers has been influenced by presence of FCNT in the LC host. The anchoring enhancement can be attributed to p-p electron stacking between the FCNT, LC and the alignment layer.

cond-mat.soft↗

arXiv2014

Convergence analysis of a finite volume scheme for solving non-linear aggregation-breakage population balance equations

This paper presents stability and convergence analysis of a finite volume scheme (FVS) for solving aggregation, breakage and the combined processes by showing Lipschitz continuity of the numerical fluxes. It is shown that the FVS is second order convergent independently of the meshes for pure breakage problem while for pure aggregation and coupled equations, it shows second order convergent on uniform and non-uniform smooth meshes. Furthermore, it gives only first order convergence on non-uniform grids. The mathematical results of convergence analysis are also demonstrated numerically for several test problems.

math.NA↗

arXiv2005

Low field magneto-transport in La_0.7Ca_0.3MnO_3-PMMA composites synthesized by polymeric precursor route

A detailed investigation of the effect of PMMA on the structure, microstructure and magneto-transport properties of manganite La_0.7Ca_0.3MnO_3 (LCMO) is presented. LCMO-PMMA nanostructured composites have been synthesized by a unique polymeric sol-gel route, which leads to improved solubility of PMMA in the LCMO matrix. The LCMO phase is grown in the presence of varying PMMA concentration at ~500 ^0 C. This route yields single phase material and the grain size is observed to decrease slightly with increasing PMMA concentration. On increasing the PMMA concentration, T_C undergoes a small decrease, resistivity is observed to increase by two orders of magnitude, with a concomitant large decrease in T_IM, e.g., from 218 K for virgin LCMO to 108 K for 50 wt% PMMA admixed LCMO. Low field magneto-resistance measured in the temperature range 77-300 K shows considerable enhancement as a function of the PMMA concentration. These phenomena are explained by taking into account the increased intergranular disorder as a consequence of PMMA admixture.

cond-mat.mtrl-sci↗