arXiv subjects

F. Khan

Publications and source records attributed to F. Khan.

4 recordsLinked to original sources

arXiv2023

Effects of $f (R, G)$ gravity on anisotropic charged compact objects

The present study provides an in-depth analysis of the anisotropic matter distribution and various physical aspects of compact stars in the context of a $f(R,G)$-gravity framework. In order to gain an exhaustive understanding of these aspects, our study focuses on three particular compact stars: VELA X-1 (CS1), SAXJ1808.4-3658 (CS2), and 4U1820-30 (CS3). We conducted calculations on the relevant characteristics of these compact stars by employing three different models of $f(R,G)$-gravity. As a convenient approach, the $f(R,G)$-gravity is organized into two distinct components, which include $f_1(R)$ and $f_2(G)$. The $R$ dependent component is modeled similarly to the Hu-Sawicki approach, while for modeling the $G$ dependent component, we chose logarithmic and power law-like approaches and suggested three viable gravity models. Graphical methods are used to analyze the physical properties of the compact stars in the domain of suggested models of gravity.

gr-qc↗

arXiv2022

Compact relativistic geometries in $f(R,G)$ gravity

One of the possible potential candidates for describing the universe's rapid expansion is modified gravity. In the framework of the modified theory of gravity $f(R,G)$, the present work features the materialization of anisotropic matter, such as compact stars. Specifically, to learn more about the physical behavior of compact stars, the radial, and tangential pressures as well as the energy density of six stars namely $Her X-1$, $SAXJ1808.4-3658$, $4U1820-30$, $PSR J 1614 2230$, $VELA X-1$, and $Cen X-3$ are calculated. Herein, the modified theory of gravity $f(R,G)$ is disintegrated into two parts i.e. the $\tanh$ hyperbolic $f(R)$ model and the three different $f(G)$ model. The study focuses on graphical analysis of compact stars wherein the stability aspects, energy conditions, and anisotropic measurements are mainly addressed. Our calculation revealed that, for the positive value of parameter n of the model $f(G)$, all the six stars behave normally.

gr-qc↗

arXiv2021

Characterization of superconducting NbTiN films using a Dispersive Fourier Transform Spectrometer

We have built a Terahertz Dispersive Fourier Transform Spectrometer \cite{Birch1987} to study frequency properties of superconducting films used for fabrication of THz detectors. The signal reflected from the tested film is measured in time domain, which allows to separate it from the other reflections. The complex conductivity of the film depends on frequency and determines the reflection coefficient. By comparing the film reflection in the superconducting state (temperature is below $T_c$) with the reflection of the normal state, we characterise the film quality at terahertz frequencies. The method was applied to 70 and 200nm thick Nb films on a silicon wafer and to 360nm thick NbTiN films on silicon and quartz wafers. The strong-coupling coefficient, $\alpha$, was found to be 3.52 for Nb, and 3.71-4.02 for the NbTiN films. The experimental results were fitted using extended Mattis-Bardeen theory \cite{Noguchi2012} and show a good agreement.

cond-mat.supr-con↗

arXiv2007

A Multi Interface Grid Discovery System

Discovery Systems (DS) can be considered as entry points for global loosely coupled distributed systems. An efficient Discovery System in essence increases the performance, reliability and decision making capability of distributed systems. With the rapid increase in scale of distributed applications, existing solutions for discovery systems are fast becoming either obsolete or incapable of handling such complexity. They are particularly ineffective when handling service lifetimes and providing up-to-date information, poor at enabling dynamic service access and they can also impose unwanted restrictions on interfaces to widely available information repositories. In this paper we present essential the design characteristics, an implementation and a performance analysis for a discovery system capable of overcoming these deficiencies in large, globally distributed environments.

cs.DC↗