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S. K. Gupta

Publications and source records attributed to S. K. Gupta.

31 records · Page 2Linked to original sources
arXiv2010

Exhaustive Verification of Weak Reconstruction For Self Complementary Graphs

This paper presents an exhaustive approach for verification of the weak reconstruction of Self Complementary Graphs up to 17 vertices. It describes the general problem of the Reconstruction Conjecture, explaining the complexity involved in checking deck-isomorphism between two graphs. In order to improve the computation time, various pruning techniques have been employed to reduce the number of graph-isomorphism comparisons. These techniques offer great help in proceeding with a reconstructive approach. An analysis of the numbers involved is provided, along with the various limitations of this approach. A list enumerating the number of SC graphs up till 101 vertices is also appended.

cs.DM↗
arXiv2010

Optical Emission Based Oxygen Sensing by ZnO Nanoparticles

ZnO nanoparticles (NP) of size less than around 20 nm inside a chamber exhibits complete reduction in their visible photoluminescence (PL) intensity when partial pressure of oxygen in the surrounding gaseous environment is decreased by evacuation. However the visible PL from ZnO nanoparticles are insensitive to the gases like N2, He and Ar. The rate of change of PL intensity with pressure (or the sensitivity) is inversely proportional to the ambient air pressure. Sensitivity increases when surface to volume ratio increases for lower particle size. The charged oxygen vacancies are attributed as the responsible candidates for surface related visible PL from ZnO NP.

cond-mat.mtrl-sci↗
arXiv2010

Photovoltaic Properties of ZnO Nanoparticle Based Solid Polymeric Photoelectrochemical Cells

In this work, we report optical and photovoltaic properties of ZnO based solid polymeric photoelectrochemical (PEC) cell. In this device construction, film of ZnO nanoparticle (NP) has been sandwiched between ITO and LiClO4-PEO solid electrolyte. ZnO NP has been used as photo-anode and the electrolyte LiClO4 has been dissolved in a solid solution polyethylene oxide that makes the device lightweight and portable. The charge transfer is performed by Li+ and ClO4- ions which serve the purpose of a redox couple in a conventional dye sensitize solar cell (DSSC). Short Circuit Current (JSC) shows maximum when the ZnO/ITO interface has been illuminated by a UV light (350 +/- 15 nm) passing through the transparent ITO glass substrate. JSC and Open Circuit Voltage (VOC) of the best performing device are found to be 7 microA/cm2 and 0.24 V respectively under white light of intensity 15 mW/cm2.

cond-mat.mtrl-sci↗
arXiv2009

Titanium dioxide synthesized using titanium chloride: Size effect study using Raman and Photoluminescence

Titanium dioxide (TiO2) nanocrystals were prepared by wet chemical method and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Raman scattering (RS) and photoluminescence (PL). The X-ray diffraction shows the formation of nanocrytalline TiO2 of average sizes 7 nm and 15 nm for two samples. The x-ray diffraction, transmission electron microscopy (TEM) and Raman scattering shows that the TiO2 nanocrystals has anatase crystal structure for both samples. The PL intensity of the smaller particle is more, which has been attributed to defects and particle size variation. A modified phonon confinement model with the inclusion of size distribution, a new confinement function for TiO2 nanocrystals and averaged dispersion curves for most dispersion phonon branch (G-X direction) has been used to interpret the size variation of Raman spectra. The obtained Raman peak shift and FWHM agree will the experimental data. Our observations suggest that phonon confinement effects are responsible for a significant shift and broadening for the Raman peaks.

cond-mat.mes-hall↗
arXiv2008

Forbush decreases and turbulence levels at CME fronts

We seek to estimate the average level of MHD turbulence near coronal mass ejection (CME) fronts as they propagate from the Sun to the Earth. We examine the cosmic ray data from the GRAPES-3 tracking muon telescope at Ooty, together with the data from other sources for three well observed Forbush decrease events. Each of these events are associated with frontside halo Coronal Mass Ejections (CMEs) and near-Earth magnetic clouds. In each case, we estimate the magnitude of the Forbush decrease using a simple model for the diffusion of high energy protons through the largely closed field lines enclosing the CME as it expands and propagates from the Sun to the Earth. We use estimates of the cross-field diffusion coefficient $D_{\perp}$ derived from published results of extensive Monte Carlo simulations of cosmic rays propagating through turbulent magnetic fields. Our method helps constrain the ratio of energy density in the turbulent magnetic fields to that in the mean magnetic fields near the CME fronts. This ratio is found to be $\sim$ 2% for the 11 April 2001 Forbush decrease event, $\sim$ 6% for the 20 November 2003 Forbush decrease event and $\sim$ 249% for the much more energetic event of 29 October 2003.

astro-ph↗
arXiv2007

Nonlinear response and observable signatures of equilibrium entanglement

We investigate how equilibrium entanglement is manifested in the nonlinear response of an $N$-qubit system. We show that in the thermodynamic limit the irreducible part of the $n$th-order nonlinear susceptibility indicates that the eigenstates of the system contain entangled $(n+1)$-qubit clusters. This opens the way to a directly observable multiqubit entanglement signature. We show that the irreducible part of the static cubic susceptibility of a system of four flux qubits, as a function of external parameters, behaves as a global 4-qubit entanglement measure introduced in Ref.\cite{Love}. We discuss the possibility of extracting purely-entanglement-generated contribution from the general multipoint correlators in a multiqubit system.

quant-ph↗
arXiv2001

HD 12098 - A new norhtern hemisphere roAp star

We present the analysis of 65 hours of high speed photometric observations of HD 12098 taken from State Observatory, Naini Tal and Gurushikhar Observatory, Mt.Abu on sixteen nights spanning from November 1999 to November 2000. HD 12098 is the first rapidly oscillating Ap star discovered from the `Naini Tal-Cape survey for northern hemisphere roAp stars'. It is the 32nd in the complete list. HD 12098 exhibits one predominant mode of oscillation at nu_1 = 2.1738 mHz. The second-most significant frequency in our data is at nu_2 = 2.1641 mHz with a 1 cycle/day alias ambiguity. We argue that nu_2 is a rotational sidelobe of nu_1, rather than an independent pulsation mode. Evidence for the presence of two other frequencies at 2.1807 and 2.3056 mHz is also presented.

astro-ph↗
arXiv2000

Dynamical growth of the hadron bubbles during the quark-hadron phase transition

The rate of dynamical growth of the hadron bubbles in a supercooled baryon free quark-gluon plasma, is evaluated by solving the equations of relativistic fluid dynamics in all regions. For a non-viscous plasma, this dynamical growth rate is found to depend only on the range of correlation $ξ$ of order parameter fluctuation, and the radius $R$ of the critical hadron bubble, the two length scales relevant for the description of the critical phenomena. Further, it is shown that the dynamical prefactor acquires an additive component when the medium becomes viscous. Interestingly, under certain reasonable assumption for the velocity of the sound in the medium around the saddle configuration, the viscous and the non-viscous parts of the prefactor are found to be similar to the results obtained by Csernai-Kapusta and Ruggeri-Friedman (for the case of zero viscosity) respectively.

hep-ph↗
arXiv2000

Inhomogeneous nucleation in quark hadron phase transition

The effect of subcritical hadron bubbles on a first-order quark-hadron phase transition is studied. These subcritical hadron bubbles are created due to thermal fluctuations, and can introduce a finite amount of phase mixing (quark phase mixed with hadron phase) even at and above the critical temperature. For reasonable choices of surface tension and correlation length, as obtained from the lattice QCD calculations, we show that the amount of phase mixing at the critical temperature remains below the percolation threshold. Thus, as the system cools below the critical temperature, the transition proceeds through the nucleation of critical-size hadron bubbles from a metastable quark-gluon phase (QGP), within an inhomogeneous background populated by an equilibrium distribution of subcritical hadron bubbles. The inhomogeneity of the medium results in a substantial reduction of the nucleation barrier for critical bubbles. Using the corrected nucleation barrier, we estimate the amount of supercooling for different parameters controlling the phase transition, and briefly discuss its implications to cosmology and heavy-ion collisions.

hep-ph↗
arXiv1998

A Preshower Photon Multiplicity Detector for the WA98 Experiment

A high granularity preshower detector has been fabricated and installed in the WA98 Experiment at the CERN SPS for measuring the spatial distribution of photons produced in the forward region in lead ion induced interactions. Photons are counted by detecting the preshower signal in plastic scintillator pads placed behind a 3 radiation length thick lead converter and applying a threshold on the scintillator signal to reject the minimum ionizing particles. Techniques to improve the imaging of the fibre and performance of the detector in the high multiplicity environment of lead-lead collisions are described. Using Monte-Carlo simulation methods and test beam data of pi- and e- at various energies the photon counting efficiency is estimated to be 68% for central and 73% for peripheral Pb+Pb collisions.

hep-ex↗
arXiv1997

phi-Meson Mass Modification in Heavy-Ion Collisions

We recently presented a method of analyzing invariant-mass spectra of kaon pairs resulting from decay of $ϕ$ mesons produced in high-energy heavy-ion collisions. It can be used to extract the shifts in the mass and the width ($ΔM$ and $ΔΓ$) of the $ϕ$ mesons when they are inside the dense matter formed in these collisions. We have now performed a Monte-Carlo simulation of this process. We illustrate our method with the help of available preliminary data. Extracted value of $ΔM$ is significantly larger than that obtained with an earlier method. Our results are consistent with the experimentally observed $p_T$ dependence of the mass shift.

hep-ph↗
arXiv1997

Apparent and Actual Shifts in Mass and Width of Phi Mesons Produced in Heavy-Ion Collisions

We present a method of analyzing invariant-mass spectra of kaon pairs resulting from decay of $ϕ$ mesons produced in high-energy heavy-ion collisions. It can be used to extract the shifts in the mass and the width ($ΔM$ and $ΔΓ$) of the $ϕ$ mesons when they are inside the dense matter formed in these collisions. We illustrate our method with the help of available preliminary data. Extracted values of $ΔM$ and $ΔΓ$ are significantly larger than those obtained with an earlier method. Our results are consistent with the experimentally observed $p_T$ dependence of the mass shift. Finally, we present a phenomenological relation between $ΔM$ and $ΔΓ$. It provides a useful constraint on theories which predict the values of these two quantities.

hep-ph↗