Pradhan G.K.,Jawaharlal Nehru Centre for Advanced Scientific Research |
Kumar A.,Jawaharlal Nehru Centre for Advanced Scientific Research |
Deb S.K.,INDUS Technology |
Waghmare U.V.,Jawaharlal Nehru Centre for Advanced Scientific Research |
Narayana C.,Jawaharlal Nehru Centre for Advanced Scientific Research
Physical Review B - Condensed Matter and Materials Physics | Year: 2010
We use in situ high-pressure angle dispersive x-ray diffraction measurements to determine the equation of state of cubic tin nitride (γ -Sn3 N4) under pressure up to 26 GPa. While we find no evidence for any structural phase transition, our estimate of the bulk modulus (B0) is 149 (±1.2) GPa, much lower than the earlier theoretical estimates and that of other group IV-nitrides. We corroborate and understand these results with complementary first-principles analysis of structural, elastic, and vibrational properties of group IV-nitrides, and predict a structural transition of Sn3 N4 at a higher pressure of 88 GPa compared to earlier predictions of 40 GPa. Our comparative analysis of cubic nitrides shows that bulk modulus of cubic C3 N 4 is the highest (379 GPa) while it is structurally unstable and should not exist at ambient conditions. © 2010 The American Physical Society.
Haque S.M.,Bhabha Atomic Research Center |
Sagdeo P.R.,Indian Institute of Technology Indore |
Sagdeo A.,INDUS Technology |
Jha S.N.,Bhabha Atomic Research Center |
And 2 more authors.
Applied Optics | Year: 2015
A set of titanium dioxide thin films have been deposited on fused silica substrates by the novel asymmetric bipolar pulsed dc reactive sputtering technique using different oxygen partial pressures in the sputtering ambient in the range of 0%-21%. For investigating long-range structural properties of the samples, grazing incidence x-ray diffraction (GIXRD) measurements and for probing local structure surrounding Ti sites, extended x-ray absorption fine structure (EXAFS) measurements have been carried out. Optical properties of the films have been investigated by transmission spectrophotometry in UV-visible-near IR range and it has been observed that as oxygen partial pressure in the sputtering ambient is increased, refractive index of the films varies in a nonlinear fashion. Microscopically, it has been found that this nonlinear variation can be explained by the local structure tool EXAFS, while GIXRD which works on average long-range order fails to explain this. Such a variation of optical properties with increase in oxygen partial pressure during deposition of the films is attributed to the competition between the two processes, viz., improvement in the stoichiometry of the films and reduction in the mobility of the adatoms on the surface of the growing films. © 2015 Optical Society of America.
Sood K.,Space Applications Center |
Jyoti R.,Space Applications Center |
Sharma S.B.,INDUS Technology
International Journal of Microwave and Wireless Technologies | Year: 2013
A waveguide shunt slot-fed microstrip patch antenna (WGMPA) element is proposed and analyzed with method of moments (MOM) using entire-domain basis functions. The developed analysis has been utilized to obtain parametric observation of power-coupling versus transverse offset of feeding slot from the waveguide axis. Expressions for the radiation pattern as a summation of contributions of individual basis functions are reported. The proposed element is amenable to building-up series-fed linear arrays by a simple cascading of elements at the through-end of the feeding waveguide. The authors propose that arbitrary amplitude excitations may be applied to such linear arrays for desired tailored array pattern characteristics. The required transverse offsets for each array element may be computed using the reported parametric result. As a demonstration of concept, two distributions are designed - uniform amplitudes and Dolph-Chebyshev for reduced side lobes. Computed element patterns from MOM are used with an array factor formulation for arbitrary element positions. Both modules show radiation characteristics closely matching the expected directivity and sidelobe envelopes. Analysis validation is achieved using a proven finite element method (FEM)-based solver; the comparison is close and is reported. Efficacy of the waveguide shunt-slot fed patch element for building linear array modules with prescribed amplitude distributions is thus established. Copyright © Cambridge University Press and the European Microwave Association 2013.
Mahajan M.,Antenna Systems Group |
Jyoti R.,Antenna Systems Group |
Sood K.,Antenna Systems Group |
Sharma S.B.,INDUS Technology
IEEE Transactions on Antennas and Propagation | Year: 2013
This communication deals with simultaneous generation of a contoured and a pencil beam from a single shaped reflector with two feeds. A novel concept of generating a high gain pencil beam from a shaped reflector is presented using focal plane conjugate field matching method. The contoured beam is generated from the shaped reflector by introducing deformations in a parabolic reflector surface. This communication proposes a simple method to counteract the effects of shaping and generate an additional high gain pencil beam from the shaped reflector. This is achieved by using a single feed which is axially and laterally displaced from the focal point. The proposed method is successfully applied to generate an Indian main land coverage contoured beam and a high gain pencil beam over Andaman Islands. The contoured beam with peak gain of 33.05 dBi and the pencil beam with 43.8 dBi peak gain is generated using the single shaped reflector and two feeds. This technique saves mass and volume otherwise would have required for feed cluster to compensate for the surface distortion. © 2013 IEEE.
Kaur G.,Punjabi University |
Gupta S.,Punjabi University |
Tiwari M.K.,INDUS Technology |
Mittal R.,Punjabi University
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2014
M sub shell X-ray emission cross sections of Pt, Au, Hg, Pb, Th and U at 8 and 10 keV photon energies have been determined with linearly polarized photon beam from Indus-2 synchrotron source. The measured cross sections have been reported for the first time and were used to check the available theoretical Dirac-Hartree-Slater (DHS) and Dirac-Fock (DF) values reported in literature and also the presently derived Non Relativistic Hartree-Slater (NRHS), DF and DHS values for Mξ, Mδ, Mα, M β, Mγ, Mm1 and Mm2 group of X-rays. © 2013 Elsevier B.V. All rights reserved.