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Khan M.A.,University of Central Florida | Khan M.A.,Federal Urdu University of Arts, Sciences and Technology Islamabad | Leuenberger M.N.,University of Central Florida
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We propose a two-dimensional Hong-Ou-Mandel (HOM) type interference experiment for massless Dirac fermions in graphene and 3D topological insulators. Since massless Dirac fermions exhibit linear dispersion, similar to photons in vacuum, they can be used to obtain the HOM interference intensity pattern as a function of the delay time between two massless Dirac fermions. We show that while the Coulomb interaction leads to a significant change in the angle dependence of the tunneling of two identical massless Dirac fermions incident from opposite sides of a potential barrier, it does not affect the HOM interference pattern. We apply our formalism to develop a massless Dirac fermion beam splitter (BS) for controlling the transmission and reflection coefficients. We calculate the resulting time-resolved correlation function for two identical massless Dirac fermions scattering off the BS. © 2014 American Physical Society.

Gul I.H.,National University of Sciences and Technology | Maqsood A.,National University of Sciences and Technology | Naeem M.,Federal Urdu University of Arts, Sciences and Technology Islamabad | Ashiq M.N.,Bahauddin Zakariya University
Journal of Alloys and Compounds | Year: 2010

Aluminum substituted cobalt ferrite nanoparticles CoFe2-xAl xO4 (for x = 0.00, 0.25, 0.50) have been synthesized by the chemical co-precipitation route. The average crystallite size was calculated using the Scherrer formula and found within 17-27 nm range. The optical absorption spectra of all the samples showed two clear electronic transitions, first is around 0.75 eV while the second at about 0.84 eV. The later is identified by means of 4A2 → 4T 1 (4F) transition while the former is attributed to the overlapping of the 4A2 → 4T1 (4F) transition of the tetrahedral Co2+ ions and the Co2+ + Fe3+ → Co3+ + Fe2+ metal-metal charge transfer transition. The saturation magnetization at room temperatures was found to be 61.50 emu/g for pure CoFe2O4 nanoparticles, while it decreased with increasing Al3+ concentration up to 52.00 emu/g (for x = 0.50). The Curie temperature was determined from AC magnetic susceptibility measurement. It was observed that Curie temperature decreased with Al3+ concentration (x) and DC electrical resistivity decreased with increase in temperature. Activation energy and drift mobility have been calculated from the temperature dependent DC electrical resistivity measurements for all the samples. The variation of dielectric constant, dielectric loss and tangent loss factor for all the samples have been studied as a function of frequency in the range 600 Hz to 1 MHz at room temperature. © 2010 Elsevier B.V. All rights reserved.

Khan N.A.,Federal Urdu University of Arts, Sciences and Technology Islamabad | Sandsten M.,Lund University
Signal Processing | Year: 2016

This paper proposes a time-frequency (t-f) image enhancement method for suppressing interference terms in the Wigner-Ville distribution. The proposed technique adapts the direction of the smoothing kernel locally at each t-f point, so that the smoothing kernel remains aligned with the ridges of the auto-terms. This local alignment of the smoothing kernel reduces cross-terms without degrading the energy concentration of auto-terms. The results indicate that the proposed time-frequency distribution outperforms other methods in terms of its ability to resolve close signal components. © 2016 Elsevier B.V. All rights reserved.

Imran M.,Federal Urdu University of Arts, Sciences and Technology Islamabad
Journal of Internet Banking and Commerce | Year: 2015

Since last few years social network sites (SNSs) have rapidly grown in popularity and user acceptance globally. They have become the main place for social interaction, discussion and communication. Today, many businesses advertise their products on SNSs. The current study aims to assess the effects of SNSs consumers/users’ beliefs and concerns of social network advertising (SNA) on their attitudes toward SNA and SNS banner ad-clicking behavior. Data was collected from a sample of 397 university students of Pakistan. Results show the beliefs of SNA as informative and entertaining have positive effects on user attitudes toward SNA and their ad-clicking behavior. Similarly, user concern of SNA as irritating has negative effects on both their attitudes toward SNA and ad-clicking behavior. Good for economy is an important socioeconomic belief which affects user attitudes toward SNA positively. The overall results indicate that utilitarian and hedonic aspects of SNA make SNS banner ads effective. © 2015 Imran M.

Khan N.A.,Qatar University | Khan N.A.,Federal Urdu University of Arts, Sciences and Technology Islamabad | Boashash B.,Qatar University | Boashash B.,University of Queensland
IEEE Signal Processing Letters | Year: 2013

This letter presents a novel algorithm to compute the instantaneous frequency (IF) of a multicomponent nonstationary signal using a combination of fractional spectrograms (FS). A high resolution time frequency distribution (TFD) is defined by combining FS computed using windows of varying lengths and chirp rates. The IF of individual signal components is then computed by applying a peak detection and component extraction procedure. The mean square error (MSE) of IF estimates computed with the AFS is lower than the MSE of IF estimates obtained from other TFDs for SNR varying from-5 dB to 16 dB. © 1994-2012 IEEE.

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