Y. Kumar

Y. Kumar
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Physics - Materials Science (6)
 
Solar and Stellar Astrophysics (6)
 
High Energy Physics - Phenomenology (3)
 
Computer Science - Computer Vision and Pattern Recognition (2)
 
Physics - Mesoscopic Systems and Quantum Hall Effect (2)
 
Computer Science - Information Theory (1)
 
Mathematics - Information Theory (1)
 
Computer Science - Architecture (1)
 
Physics - Accelerator Physics (1)
 
Instrumentation and Methods for Astrophysics (1)
 
Physics - Other (1)

Publications Authored By Y. Kumar

After more than a decade of extensive research on the magnetic order triggered by lattice defects in a wide range of nominally non-magnetic materials, we report its application in a spintronic device. This device is based on a spin-filter phenomenon we discovered at the interfaces between defect-induced magnetic and non-magnetic regions, produced at the surface of a Li doped ZnO microwire by low-energy proton implantation. Positive magnetoresistance is observed at 300~K and scales with the number of interfaces introduced along the wire. Read More

We report on the magnetic properties of zinc ferrite thin film deposited on SrTiO$_3$ single crystal using pulsed laser deposition. X-ray diffraction result indicates the highly oriented single phase growth of the film along with the presence of the strain. In comparison to the bulk antiferromagnetic order, the as-deposited film has been found to exhibit ferrimagnetic ordering with a coercive field of 1140~Oe at 5~K. Read More

2017Jan
Affiliations: 1ARIES Nainital, 2SAO, Russia, 3SAO, Russia, 4Delhi University Delhi, 5ARIES, Nainital, 6INASAN, Russia, 7Delhi University Delhi, 8National Astronomical Observatories, China

The combination of photometry, spectroscopy and spectropolarimetry of the chemically peculiar stars often aims to study the complex physical phenomena such as stellar pulsation, chemical inhomogeneity, magnetic field and their interplay with stellar atmosphere and circumstellar environment. The prime objective of the present study is to determine the atmospheric parameters of a set of Am stars to understand their evolutionary status. Atmospheric abundances and basic parameters are determined using full spectrum fitting technique by comparing the high-resolution spectra to the synthetic spectra. Read More

In this work, we propose a Triangle based approach to classify flower images. Initially, flowers are segmented using whorl based region merging segmentation. Skeleton of a flower is obtained from the segmented flower using a skeleton pruning method. Read More

In this work, we propose a method for the classification of animal in images. Initially, a graph cut based method is used to perform segmentation in order to eliminate the background from the given image. The segmented animal images are partitioned in to number of blocks and then the color texture moments are extracted from different blocks. Read More

We present spectroscopic measurements on the night sky of Xinglong Observatory for a period of 12 years from 2004 to 2015. The spectra were obtained on moonless clear nights using the OMR spectrograph mounted on a 2.16-m reflector with a wavelength coverage of 4000-7000A. Read More

We use the spectra of Pleiades and field stars from LAMOST DR2 archive to study how spottedness and activity vary as a function of mass at young ages. We obtained standard TiO band strength by measuring TiO bands near 7050 $\AA$ from LAMOST spectra (R$\approx$1800) for large sample of field GKM dwarfs with solar metallicity. Analysis show that active dwarfs, including late G- and early K-type, have extra TiO absorption compare to inactive counterparts, indicating the presence of cool spots on their surface. Read More

An emerging branch of electronics, the optospintronics, would be highly boosted if the control of magnetic order by light is implemented in magnetic semiconductors nanostructures being compatible with the actual technology. Here we show that the ferromagnetic magnetization of low Fe-doped ZnO nanowires prepared by carbothermal process is enhanced under illumination up to temperatures slightly below room temperature. This enhancement is related to the existence of an oxygen vacancy V$_{\rm O}$ in the neighbouring of an antiferromagnetic superexchange Fe$^{3+}$-Fe$^{3+}$ pair. Read More

The electric noise can be an important limitation for applications of conducting elements of size in the nanometer range. The intrinsic electrical noise of prospective materials for opto-spintronics applications like ZnO has not been characterized yet. In this study we have investigated the conductivity fluctuations in 10~nm thick current paths produced by proton implantation of ZnO microwires at room temperature. Read More

2016Mar
Affiliations: 1Aryabhatta Research Institute of Observational Sciences, 2SpaceLab, Department of Electrical Engineering, University of Cape Town, South Africa, 3Department of Physics, Christ University, Hosur Road, Bangalore, India, 4School of Studies in Physics and Astrophysics, Pt Ravishankar Shukla University, Raipur, India, 5ARIES-India, 6SAAO, South Africa, 7Department of Physics, University of the North-West, South Africa, 8National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China, 9SAAO, South Afirca

The Nainital-Cape survey is a dedicated ongoing survey programme to search for and study pulsational variability in chemically peculiar (CP) stars to understand their internal structure and evolution. The main aims of this survey are to find new pulsating Ap and Am stars in the northern and southern hemisphere and to perform asteroseismic studies of these new pulsators. The survey is conducted using high-speed photometry. Read More

The detection of defect-induced magnetic order in single low-dimensional oxide structures is in general difficult because of the relatively small yield of magnetically ordered regions. In this work we have studied the effect of an external magnetic field on the transient photocurrent measured after light irradiation on different ZnO samples at room temperature. We found that a magnetic field produces a change in the relaxation rate of the transient photocurrent only in magnetically ordered ZnO samples. Read More

We searched for a correlation between the two anomalous properties of K giants: Li enhancement and IR excess from an unbiased survey of a large sample of RGB stars. A sample of 2000 low-mass K giants with accurate astrometry from the Hipparcos catalog was chosen for which Li abundances have been determined from low-resolution spectra. Far-infrared data were collected from the $WISE$ and $IRAS$ catalogs. Read More

The structure and dielectric properties of 6% $\rm{Sr}^{2+}$-substituted, modified Lead Zirconium Titanate (PZT) piezoelectric ceramic, with composition $[\rm{Pb}_{0.94}\rm{Sr}_{0.06}][(\rm{Mn}_{1/3}\rm{Sb}_{2/3})_{0. Read More

A fireball of QGP is evoluted at temperature dependent chemical potential by a statistical model in the pionic medium. We study the dilepton emission rate at temperature dependent chemical potential (TDCP) from such a fireball of QGP. In this model, we take the dynamical quark mass as a finite value dependence on temparature and parametrization factor of the QGP evolution. Read More

Weak G-band (WGB) stars are a rare class of cool luminous stars that present a strong depletion in carbon, but also lithium abundance anomalies that have been little explored in the literature since the first discovery of these peculiar objects in the early 50's. Here we focus on the Li-rich WGB stars and report on their evolutionary status. We explore different paths to propose a tentative explanation for the lithium anomaly. Read More

The effects of 200-MeV Ag^{+15} ion irradiation on the optical properties of TiO_{2} and SnO_{2} thin films prepared by using the RF magnetron sputtering technique were investigated. These films were characterized by using UV-vis spectroscopy, and with increasing irradiation fluence, the transmittance for the TiO_{2} films was observed to increase systematically while that for SnO_{2} was observed to decrease. Absorption spectra of the irradiated samples showed minor changes in the indirect bandgap from 3. Read More

In this Letter, we report on a low-resolution spectroscopic survey for Li-rich K giants among 2000 low mass (M <= 3 Msun) giants spanning the luminosity range from below to above the luminosity of the clump. Fifteen new Li-rich giants including four super Li-rich K giants (A(Li) >= 3.2) were discovered. Read More

Dielectric response has been studied for a new manganocuprate, Gd3Ba2Mn2Cu2O12 (Gd3222) as a function of temperature (100 - 300 K) and frequency (75 kHz to 1 MHz). The dielectric constant (e) exhibits a two step increase (two peaks) in e(T) with increasing temperature from 100 to 300 K. The first peak is seen around 150 K and the second one around 210 K (both for 75 kHz). Read More

The free energy of a Quark-Gluon Plasma fireball in the hadronic medium is calculated in the Ramanathan et al. statistical model including the effect of curvature. The result with this curvature is found to produce significant improvement from earlier results in all the parameters we calculated. Read More

A model of statistical quark-gluon plasma formation is considered.We look the dilepton production at critical temperature $T_{c}\sim170 Mev $ and completely free out temperature $T=150 MeV$ with the initial temperature as $T_{0}=570,400 (250) MeV$. Now we consider that quark mass is depending on the coupling value through parameterisation factor of the fireball formation and temperature. Read More

Since the advent of new nanotechnologies, the variability of gate delay due to process variations has become a major concern. This paper proposes a new gate delay model that includes impact from both process variations and multiple input switching. The proposed model uses orthogonal polynomial based probabilistic collocation method to construct a delay analytical equation from circuit timing performance. Read More

Construction of signal sets with low correlation property is of interest to designers of CDMA systems. One of the preferred ways of constructing such sets is the interleaved construction which uses two sequences a and b with 2-level autocorrelation and a shift sequence e. The shift sequence has to satisfy certain conditions for the resulting signal set to have low correlation properties. Read More