Papers by Dhananjay Kumar
Europium activated yttrium oxide (Eu:Y2O3) phosphor films have been grown in situ on (100) bare a... more Europium activated yttrium oxide (Eu:Y2O3) phosphor films have been grown in situ on (100) bare and diamond-coated silicon substrates using a pulsed laser deposition technique. Diamond-coated silicon substrates were prepared using hot filament chemical vapor deposition of diamond onto silicon. Photoluminescence brightness from Eu:Y2O3 films grown at 700 °C on diamond-coated silicon substrates was about twice that of films on
First Break, 2004
Thick Mesozoic sediments under the basalt cover of the Deccan traps along the northwest coast of ... more Thick Mesozoic sediments under the basalt cover of the Deccan traps along the northwest coast of India are considered to be potential targets for hydrocarbon exploration together with the Indus basin of Pakistan. Sub-basalt seismic imaging is difficult in these formations, as the Deccan traps are composed of multilayered lava flows. Seismic imaging issues associated with high velocity basalt include: 1. Multiples generated in interbedded units of basalt and between the top of the basalt and the sea floor. 2. Energy scattering from and absorption by heterogeneities. 3. Wave mode conversion at the top of the basalt.
The successful correction of aberrations in scanning transmission electron microscopy (STEM) has ... more The successful correction of aberrations in scanning transmission electron microscopy (STEM) has improved lateral resolution by more than a factor of two [1], brought greatly enhanced sensitivity for imaging individual atoms, and depth resolution of a few nanometers [2-4]. In zone axis crystals, columnar channeling tends to reduce the depth resolution, and image simulations are necessary to establish the depth
Physical Review B, 2000
Anuranjan Srivastava, D. Kumar * , and Rajiv K. Singh Department of Materials Science and Enginee... more Anuranjan Srivastava, D. Kumar * , and Rajiv K. Singh Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611-6400. ... Phys. 85, 2497 1997 . 12 A. Srivastava, D. Kumar, and RK Singh, J. Electtro. Chem. Lett. to be published . ...
Superconductor Science and Technology, 2005
Nanodot arrays of Y 2 O 3 were dispersed in thin films of YBa 2 Cu 3 O 7−δ (YBCO) by growing alte... more Nanodot arrays of Y 2 O 3 were dispersed in thin films of YBa 2 Cu 3 O 7−δ (YBCO) by growing alternating layers of these two species using a pulsed laser deposition method. As a result, critical current density J c both in applied magnetic field and self-field is enhanced by as much as an order of magnitude, along with a significant increase in the irreversibility field H irr . High-resolution scanning transmission electron microscopy (STEM) and Z -contrast STEM show that the nanoparticles are crystalline and coherent with the YBCO matrix. Whereas in most other studies pinning has been attributed to the strain fields around the nanoparticles, in this case pinning may actually be due to the nanoparticles themselves, since the delineation between the two species is very sharp and STEM reveals no discernible strain fields in the superconducting material around the nanoparticles.
2008 First International Conference on Emerging Trends in Engineering and Technology, 2008
Session setup time is a critical factor for multimedia applications. Some of the factors that aff... more Session setup time is a critical factor for multimedia applications. Some of the factors that affect the session setup delay are length of SIP messages, bandwidth and packet loss in wireless link. This paper aims at reducing the session setup delay in UMTS IP Multimedia ...
High Performance Computing, Networking and Communication Systems, 2008
Chemical Engineering Journal, 2009
Peepul leaves were identified as the most potent Pb(II) sorbent (qmax=127.34mgg−1), followed in d... more Peepul leaves were identified as the most potent Pb(II) sorbent (qmax=127.34mgg−1), followed in decreasing order by banana peels (72.79mgg−1), peanut hulls (69.75mgg−1), coir fibers (52.03mgg−1), rice stem (49.57mgg−1), teak saw dust (40.70mgg−1), discarded tea leaves (35.89mgg−1), mango leaves (31.54mgg−1), rice husk (31.13mgg−1) and grass clippings (29.05mgg−1). The tested plant materials sorbed Pb(II) optimally at pH 4 or 5, but peepul
Quality and Reliability Engineering International, 1995
The purpose of this paper is to illustrate some situations under which the proportional hazards m... more The purpose of this paper is to illustrate some situations under which the proportional hazards model (PHM) and its extensions can be used for identification of the most important covariates influencing a repairable system. First of all an overview of the application of the PHM in engineering is presented. Then the concepts of the PHM and its extensions, such as stratified PHM, PHM in the case of nonhomogeneous Poisson processes and PHM in the case of jumps in the hazard rate or different intensity function at failures of a large number of copies of a repairable system, are presented. Selection of a suitable extension of the PHM for given data on the basis of residual plots is also discussed. Finally applications of the PHM and its extensions are illustrated with a suitable example. Only the semiparametric method has been considered. The assumptions made in the PHM for the analysis of repairable systems have been explained graphically as far as possible. Perfect, minimal or imperfect repairs carried out on repairable systems can be taken into consideration for the reliability analysis using the PHM.
Physica C: Superconductivity, 1992
Using a KrF pulsed excimer laser, various interrelated deposition parameters governing the qualit... more Using a KrF pulsed excimer laser, various interrelated deposition parameters governing the quality of laser-ablated Y~Ba2Cu30~-6( 123 ) thin films have been systematically studied. Modification of the 123 target with increasing laser exposure has been found to affect the plume stability, and the axis of the plume has been found to shift slowly towards the direction of the laser beam. Small laser spots exposing a relatively large diameter annular track of the rotating target have been found to give better plume stability than larger spots exposing the same diameter track. Because ofbener plume stability and larger plume expansion, smaller laser spots have been found to give significantly better quality 123 films as compared with large spots under optimised growth conditions. The effects of varying O2 pressure and target-substrate distance have been found to be similar and the location of the substrates at or close to the tip of the plume has been found to be important for the realization of film stoichiometry and high quality. Results have shown that under optimised conditions of 3 J cm-2 fluence, 200 reTort 02 pressure and 4.5 cm targetsubstrate distance, films with Tc = 90 K, AT~ 1 K and critical current density, Jc >-2 × 106 Acm-2 at 77 K can be reproducibly realized on (100) MgO substrates with small (3 minx 0.8 ram) laser spots.
Seg Technical Program Expanded Abstracts, 2005
A seismic experiment was canied out in summer 2002 at the Hydrate Ridge to map the gas hydrate. S... more A seismic experiment was canied out in summer 2002 at the Hydrate Ridge to map the gas hydrate. Seismic wave velocities vary in the presence of gas hydrate and free gas in the sediments. Accuracy in the estimation of distribution and saturation of gas hydrates and ...
Nano Letters, 2008
We identify a substitutional and three distinct interstitial configurations, one of which has not... more We identify a substitutional and three distinct interstitial configurations, one of which has not been previously identified. We confirm the stability of the observed point defect configurations by density functional theory (DFT) calculations. The observed number densities of the various configurations are in accord with their calculated formation energies. The concentration of Au atoms is larger than the solubility limit, but the effect may be caused by the STEM beam.
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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2002
ABSTRACT Colossal magnetoresistive La0.7Ca0.3MnO3 (LCMO) films with improved magnetoresistance pr... more ABSTRACT Colossal magnetoresistive La0.7Ca0.3MnO3 (LCMO) films with improved magnetoresistance properties have been grown at relatively low temperatures using an ultraviolet-assisted pulsed laser deposition technique. In this technique, a low pressure Hg lamp having a fused silica envelope, which allows more than 85% of the emitted 184.9 nm radiation to be transmitted, is added inside the growth chamber during pulsed laser deposition of LCMO films. Magnetoresistance (MR) measurements carried out on LCMO films grown under identical conditions barring the presence/absence of UV radiation during thin film formation have shown that the MR ratio of UV-assisted grown LCMO films is nearly two orders of magnitude higher than that of LCMO films grown without UV. The improvement in magnetoresistive properties of LCMO film deposited in the presence of UV is assumed to be related with improvement in oxygen content, oxygen homogeneity, and crystallinity. Evidences supporting this assumption are obtained from analysis of spectra recorded using x-ray photoelectron spectroscopy and Rutherford backscattering measurements.
The mechanical engineering curriculum in our department contains two required materials courses, ... more The mechanical engineering curriculum in our department contains two required materials courses, supplemented with several technical elective courses dealing with the state of the art in advanced materials. We are involved in the introductory materials science course and in the technical elective courses. A newly-developed technical elective course Thin and Thick Films is designed for students seeking to learn about one of the most important branches of materials science, namely the science and technology of materials in the form of films. This paper reports our experiences and approaches in achieving the course objectives more effectively by means of using supplementary learning methods including pre-quizzes, multidisciplinary learning through extramural speakers and off-campus lab visits, and service learning.
Journal of Materials Research, 2002
In this paper, we report the growth of ZnO films on silicon substrates using a pulsed laser depos... more In this paper, we report the growth of ZnO films on silicon substrates using a pulsed laser deposition technique. These films were deposited on Si(111) directly as well as by using thin buffer layers of AlN and GaN. All the films were found to have c-axis-preferred orientation aligned with ...
Journal of Magnetism and Magnetic Materials, 2001
Single-domain nanoscale magnetic iron particles have been embedded uniformly in an amorphous matr... more Single-domain nanoscale magnetic iron particles have been embedded uniformly in an amorphous matrix of alumina using a pulsed laser deposition technique. Structural characterization by transmission electron microscopy (TEM) reveals the presence of a crystalline iron and an amorphous alumina phase. Fine particle magnetism have been investigated by carrying out field and temperature dependence of magnetization measurements using superconducting quantum interference device magnetometer. The particle size of Fe in Al 2 O 3 matrices prepared by changing the deposition time of Fe, have been found to be 9, 7 and 5 nm from TEM studies. At 10 K, the coercivities of these samples are found be 450, 350 and 150 Oe, respectively. At 300 K, the coercivity of Fe-Al 2 O 3 sample decreases from 100 to 50 Oe as the particle size decreases from 9 to 7 nm and finally the sample turns superparamagnetic when the Fe particle size becomes around 5 nm. Based on the calculated value of blocking temperature, T B , (481 K), magnetic anisotropy K (4.8 Â 10 5 erg/cm 3 ) for Fe, and the Boltzmann constant k B (1.38 Â 10 @16 erg/K) from T B =KV/25k B , the mean radius of Fe particles is found to be 9.3 nm. in one of the samples. This is in good agreement with the particle size measured using TEM studies. r 2001 Published by Elsevier Science B.V. 0304-8853/01/$ -see front matter r 2001 Published by Elsevier Science B.V. PII: S 0 3 0 4 -8 8 5 3 ( 0 1 ) 0 0 1 9 1 -3
Journal of The Electrochemical Society, 2006
Shallow trench isolation (STI) allows tighter device packing and reduced chip area for isolation.... more Shallow trench isolation (STI) allows tighter device packing and reduced chip area for isolation. STI is critically dependent on the global planarity that is only possible using chemical mechanical polishing (CMP). Ceria-based slurries are considered the most promising ...
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Papers by Dhananjay Kumar