School of Physics

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    1/N expansion and the uncertainty principle
    ( 1985-12-01) Chatterjee, A.
    The leading-order term of the 1/N expansion is derived in a new way and is thus given a simple physical interpretation.
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    1/N expansion for Gaussian potential
    ( 1985-12-01) Chatterjee, A.
    The method of large-N expansion has been applied to an attractive radial Gaussian potential to obtain its bound state energy levels. It has been shown that the shifted 1/N expansion technique provides a better approximation than the method of unshifted 1/N expansion and yields energy values which are in good agreement with the accurate numerical and analytic results.
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    1/N expansion for the Yukawa potential revisited
    ( 1985-06-01) Chatterjee, Ashok
    In a recent paper, Moreno and Zepeda have applied the 1/N expansion to obtain an approximate analytic formula for the ground state energy of a panicle bound by a Yukawa potential. Using the method of Mlodinow and Shatz we caiculate the energies of the ground state and the first excired state of the system to show that the results provided by the i/N expansion are identical with tiiose obtained by applqing either the analytic perturbation theory or the hypenirial equations with the Hellman-Feynman theorem..Also an approximate analytic formula for the ground state energq is proposed. © 1985 The Institute of Physics.
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    1/N expansion for the Yukawa potential revisited: II
    ( 1986-12-01) Chatterjee, A.
    Using the form prescribed by Moreno and Zepeda for the N-dimensional Yukawa potential and employing the method of 1/N expansion we have obtained in a recent paper the energies of the ground state and the first excited state of a three-dimensional Yukawa potential. In the present addendum we introduce a modified prescription for the N-dimensional Yukawa potential which enables us also to calculate the energies of the higher angular momentum states. Our results are in very good agreement with the accurate numerical values.
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    331- Z′ mediated FCNC effects on b → d μ < sup > + < /sup > μ < sup > - < /sup > Transitions
    ( 2018-12-30) Singh, Soram Robertson ; Mawlong, Barilang
    We study the rare semileptonic B → πμ+μ- and B → pμ+μ- decay modes mediated by the quark level b → dμ+μ- transition in this paper. We analyze observables such as the differential branching ratio, lepton polarization asymmetry and forward-backward asymmetry within the standard model in the large hadronic recoil region. We then analyze these observables within the 331 or SUC(3) × SUL(3) × UX(1) model in which a new heavy Z′ boson contributes. The effects of the Z′-mediated flavor changing neutral current (FCNC) transitions on these modes are examined by varying the mass MZ′ and the model parameter β. The new Z′ couplings are constrained by flavor observables of Bd -Bd mixing. For the obtained parameter space, we observe Z′ sensitivities of our observables of interest and deviations from standard model can range from moderate to large depending on the β value.
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    A < inf > 4 < /inf > Realization of Linear Seesaw and Neutrino Phenomenology
    ( 2019-01-01) Sruthilaya, M. ; Mohanta, R. ; Patra, Sudhanwa
    We consider the A4 realization of linear seesaw by extending the standard model (SM) particle content with two types of right-handed neutrinos along with the flavon fields, and the SM symmetry with A4 × Z4 × Z3 and a global symmetry U(1)X . We also discuss the scope of this model to explain the baryon asymmetry of the Universe through leptogenesis.
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    A < inf > 4 < /inf > realization of linear seesaw and neutrino phenomenology
    ( 2018-09-01) Sruthilaya, M. ; Mohanta, Rukmani ; Patra, Sudhanwa
    Motivated by the crucial role played by the discrete flavor symmetry groups in explaining the observed neutrino oscillation data, we consider the A4 realization of linear seesaw by extending the standard model (SM) particle content with two types of right-handed (RH) neutrinos along with the flavon fields, and the SM symmetry with A4× Z4× Z3 and a global symmetry U(1) X, which is broken explicitly by the Higgs potential. We scrutinize this model to see if it can explain the recent results from neutrino oscillation experiments, by searching for parameter space that can accommodate the observables such as the reactor mixing angle θ13, the CP violating phase δCP, sum of active neutrino masses Σ imi, solar and atmospheric mass-squared differences, and the lepton number violating parameter called the effective Majorana mass parameter, in line with recent experimental results. We also discuss the scope of this model to explain the baryon asymmetry of the Universe through leptogenesis. We also investigate the possibility of probing the non-unitarity effect in this scenario, but it is found to be rather small.
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    A comparative study of a (0-3) connectivity type composite and core-shell structure of CoFe < inf > 2 < /inf > O < inf > 4 < /inf > - BaTiO < inf > 3 < /inf > based on microstructure and magnetic property
    ( 2018-04-10) Das, Avisek ; Gorige, Venkataiah
    In this work CoFe2O4 (CFO)-BaTiO3 (BTO) composite and core-shell CFO-BTO have been prepared to investigate the effect of microstructure on the magnetic properties. Detailed microstructure analysis has been carried out using X-ray diffraction, field emission scanning electron microscope and transmission electron microscope. Although uniform distribution of CFO is found in BTO matrix for the composite sample, magnetization and coercivity values are more enhanced in core-shell CFO-BTO.
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    A comparative study of the structure, stability and energetic performance of 5,5′-bitetrazole-1,1′-diolate based energetic ionic salts: Future high energy density materials
    ( 2018-01-01) Abraham, B. Moses ; Ghule, Vikas D. ; Vaitheeswaran, G.
    Developing novel energetic materials of high detonation performance and low sensitivity is one of the primary objectives related to explosive research. By employing ab initio calculations, a series of energetic ionic salts based on 5,5′-bitetrazole-1,1′-diolate (BTO) were thoroughly investigated to understand the structure-property-performance interrelationship. The physicochemical and detonation characteristics of these energetic ionic salts including structural, electronic, vibrational and performance parameters (heats of formation, detonation pressures, and detonation velocities) were discussed in detail. The strong intermolecular hydrogen bonding environment between the BTO2- anion and various cations is mainly responsible for prominent detonation performance and enhanced molecular stability. Such strong intermolecular hydrogen bonds are observed in hydrazine and hydroxylammonium cations compared to other cations. To predict an accurate band gap, electronic band structures of the studied energetic ionic salts (EIS) were calculated using the HSE06 hybrid functional and they are found to be wide band gap insulators with a bandwidth ranging from 4.33-5.05 eV. Careful inspection of various EIS revealed that the hydroxylammonium and hydrazine cations produce the highest density relative to other cations when combined with the BTO anion. The detonation characteristics of BTO2- are computed using EXPLO5 code. In particular, HA-BTO and TKX-50 exhibit high detonation pressure (38.85 and 40.23 GPa) and detonation velocities (9.94 and 9.91 km s-1), superior to those of traditional nitrogen-rich energetic materials with moderate sensitivities. These results highlight the importance of hydrogen bonding interactions in designing energetic salts for next-generation explosives, propellants, and pyrotechnics.
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    A comparative study on structural, dielectric and multiferroic properties of CaFe < inf > 2 < /inf > O < inf > 4 < /inf > /BaTiO < inf > 3 < /inf > core-shell and mixed composites
    ( 2017-01-01) Woldu, Tesfakiros ; Raneesh, B. ; Hazra, Binoy Krishna ; Srinath, S. ; Saravanan, P. ; Reddy, M. V.Ramana ; Kalarikkal, Nandakumar
    The core-shell CaFe2O4@BaTiO3and (1−x) CaFe2O4- xBaTO3(x = 0.3, 0.5, 0.7) mixed composites were synthesized using a combination of solution processing and solid state reaction method respectively followed by high temperature calcinations. The presence of the constituent spinel-ferrite phases in both core-shell and mixed nanocomposites were confirmed by X-ray diffraction patterns and transmission electron microscopy. High-resolution transmission electron microscope images indicate a clear view of ferrite and ferroelectric phases in each core-shell and mixed composite, where the ME coupling effect of ferrite and ferroelectric phase happened. Dependence of dielectric constant (ε′), loss tangent (tan δ) and AC conductivity (σAC) with frequency (100 Hz–2 MHz) and temperature (25 °C–550 °C) with increasing probing frequency (1 kHz–2 MHz) of the composites have been investigated. The peak observed in mixed composites and core-shell nanostructures in the low temperature range (130 °C–150 °C) are attributed to ferroelectric to paraelectric phase transition of BaTO3. The second peak observed at high temperature attributed to TC(Curie temperature) of the ferrite (CaFe2O4) phase. The core-shell composite did not show any magnificent improvement in dielectric properties than mixed composites. The presence of ordered FE and FM behavior at room temperature was confirmed by observation of P-E and M-H hysteresis loops; respectively and core-shell composite shows drastic improvement in ferroelectric, magnetic and magneto-electric properties than the mixed composites. In addition, the calculated linear ME coupling coefficient results reveal strong ME coupling effect and the maximum recorded value is ∼30.32 mV/cmOe for the core-shell composite. The larger value of ME coupling coefficient may arise from larger saturation magnetization and remnant magnetization of the core-shell composite.
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    A complete theory for the magnetism of an ideal gas of electrons
    ( 2013-05-01) Biswas, Shyamal ; Sen, Swati ; Jana, Debnarayan
    We have explored Pauli paramagnetism, Landau diamagnetism, and de Haas-van Alphen effect in a single framework, and unified these three effects for all temperatures as well as for all strengths of magnetic field. Our result goes beyond Pauli-Landau result on the magnetism of the 3-D ideal gas of electrons, and is able to describe crossover of the de Haas-van Alphen oscillation to the saturation of magnetization. We also have obtained a novel asymptotic series expansion for the low temperature properties of the system. © 2013 AIP Publishing LLC.
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    A comprative study of sol-gel and solid-state prepared La < sup > 3+ < /sup > doped multiferroic BiFeO3
    ( 2014-02-01) Suresh, Pittala ; Srinath, S.
    LaxBi1-xFeO3 (LBFO) samples were prepared by sol-gel route using citric acid as chelating agent for x = 0.0 - 0.4. The structure, dielectric and magnetic properties of the LBFO compounds were studied and compared with the corresponding properties of the materials prepared by a conventional solid state reaction. The use of the sol-gel method in preparation lowered the reaction threshold temperature by 200 oC. Effects of the preparation routes and conditions on the phase and microstructures of the materials were investigated in this study using XRD and SEM. The pure BFO without bismuth loss, which cannot be prepared by the solid state reaction, was obtained by the sol-gel method. Sol-gel synthesis could yield a pure phase material at relatively lower temperatures while the solid state method yielded powder with a small amount of the secondary Bi25FeO40 phase. Single phase LBFO prepared by sol-gel method (SG) revealed huge value of dielectric constant than same obtained by the solid state reaction method (SS). Maxwell-Wagner type dielectric dispersion is observed in sol-gel method. Dielectric constant and loss tangent are found to be higher for SG as compared to SS. Huge coercivity (HC) of the order of ~ 15 kOe is observed in both SG and SS samples due to the high anisotropy in these samples. The increase in the magnetization is observed due to the destruction of spin cycloid structure. The enhanced properties made LBFO a promising candidate for the applications in novel memory devices and spintronics. © 2014 VBRI press.
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    A comprehensive study of the discovery potential of NOνA, T2K, and T2HK experiments
    ( 2016-01-01) Soumya, C. ; Deepthi, K. N. ; Mohanta, R.
    With the recent measurement of reactor mixing angle θ13 the knowledge of neutrino oscillation parameters has improved significantly except the CP violating phase δCP, mass hierarchy, and the octant of the atmospheric mixing angle θ23. Many dedicated experiments are proposed to determine these parameters which may take at least 10 years from now to become operational. It is therefore very crucial to use the results from the existing experiments to see whether we can get even partial answers to these questions. In this paper we study the discovery potential of the ongoing NOνA and T2K experiments as well as the forthcoming T2HK experiment in addressing these questions. In particular, we evaluate the sensitivity of NOνA to determine neutrino mass hierarchy, octant degeneracy, and δCP after running for its scheduled period of 3 years in neutrino mode and 3 years in antineutrino mode. We then extend the analysis to understand the discovery potential if the experiments will run for (5ν+ 5 ¯ ν) years and (7ν+ 3 ¯ ν) years. We also show how the sensitivity improves when we combine the data from NOνA, T2K, and T2HK experiments with different combinations of run period. The CP violation sensitivity is marginal for T2K and NOνA experiments even for ten-year data taking of NOνA. T2HK has a significance above 5 σ for a fraction of two-fifths values of the δCP space. We also find that δCP can be determined to be better than 35°, 21°, and 9° for all values of δCP for T2K, NOνA, and T2HK respectively.
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    A confocal laser scanning microscopic study on thermoresponsive binary microgel dispersions incorporated with CdTe quantum dots
    ( 2010-01-01) Brijitta, J. ; Tata, B. V.R. ; Saravanan, K. ; Panigrahi, B. K. ; Kaliyappan, T.
    onodisperse poly(N-isopropylacrylamide) (PNIPAM) particles loaded with cadmium telluride (CdTe) quantum dots (QDs) of two diFFent sizes (4.7 nm and 5.6 nm) were synthesized in aqueous medium by bonding the capping agent on the quantum dots to the amide groups of PNIPAM and incubating the samples at 45°huge increase in the photoluminescence (PL) intensity (green and red regions) is observed for the PNIPAM- CdTe QDs composites compared to the parent CdTe QDs. We report here for the First time the imaging of binary dispersion of green and red luminescent PNIPAM-CdTe QDs composites using a fuorescence confocal laser scanning microscope. These composites have potential applications both in material science and biology. © Academy of Sciences.
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    A Confocal microscopic study on colony morphology and sporulation of Bacillus sp.
    ( 2008-11-01) Mary, M. S. ; Gopal, Judy ; Tata, B. V.R. ; Rao, T. S. ; Vincent, S.
    Hexavalent chromium Cr(VI) is one of the dominant oxidation states of chromium that exist in the environment and is highly toxic to all forms of life. In the present study, we employ a confocal laser scanning microscope (CLSM) and investigate the effect of Cr(VI) on colony morphology of a Bacillus sp. isolated from soil exposed to tannery effluent. The colonies grown at chromium concentrations, control and 100 ppm are found to be opaque and beyond 200 ppm the colonies were translucent thus exhibiting phase variation. CLSM studies on colonies grown on control plates showed significant increase in height and in biovolume as a function of time whereas, the translucent colonies showed very little change in height and biovolume corresponding to the colony growth. Exopolymeric substance (EPS) content of translucent colonies was lesser than that of opaque colonies, indicating that EPS also plays a role in the observed phenomenon of phase variation. Studies on the effect of Cr(VI) on spore formation showed that Cr(VI) concentrations up to 100 ppm favored spore formation, while concentrations beyond 100 ppm showed a steady decline in spore formation. © 2008 Springer Science+Business Media B.V.
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    A correlation between dielectric permittivity and wettability for low energy surface (Bismuth Zinc Niobate) on fused silica
    ( 2011-11-07) Madhurima, V. ; Purkayastha, Debarun Dhar ; Sudheendran, K. ; Raju, K. C.James
    Theoretical contact angle of Diiodomethane on Bismuth Zinc Niobate thin film on fused silica substrate is calculated and the results are compared with experimental values. The theoretical calculation of contact angle is by the determination of the Hamaker's constant from the dielectric data and applying Lifshitz-van der Waals dispersive interaction and Young-Dupree equation and the experimental value is found using a contact angle goniometer using the sessile drop method. The results from the experiment were seen to be close to that from the theoretical calculation. © 2011 IEEE.
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    A critical look at quantum diffusion and some of its interesting aspects
    ( 2007-09-01) Mukhopadhyay, S. ; Saglam, M. ; Chatterjee, A.
    A fresh and critical look has been given to the long-time behaviour of the quantum diffusion problem and a marginally more accurate solution has been obtained as compared to the one reported in the recent literature. Attempt has also been made to bring out a few interesting generic features of this problem which may have important bearing on real systems in the quantum domain. © 2007 EDP Sciences/Società Italiana di Fisica/Springer-Verlag.
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    A customized optical trap for mechanobiological studies to elucidate the molecular basis of the viscoelastic response in nerve fibres
    ( 2020-11-05) Mohapatra, Subhransu Sekhar ; Saraswati, Sudipta ; Ananthamurthy, Sharath
    We present here, a design and schematic of a single Gaussian laser beam trap built around a customized open microscope setup to carry out mechanobiological measurements on the nerve fibre of Drosophila melanogaster. In particular, the laser trap and setup is for micro stretching dissected nerve fibres from the larvae. This is achieved through the position modulation of an optically trapped bead attached to a fibre, that serves as a handle. The resultant extension of the fibre is studied by applying a stretching force following tethering of the fibre to the cover slip. We propose to carry out such measurements and obtain theviscoelastic parameters of the nerve fibre. We choose Drosophila for the following reasons:(l) It is an established genetically amenable model organism, and (2) Nerve fibres in Drosophila larvae are easily identifiable and require only simple dissections in Drosophila saline solution to be exposed.
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    A Detailed Investigation of the Polarization-Dependent Surface-Relief-Grating Formation Process on Azo Polymer Films
    ( 1999-01-01) Viswanathan, Nirmal K. ; Balasubramanian, Srinivasan ; Li, Lian ; Tripathy, Sukant K. ; Kumar, Jayant
    We have carried out two-beam interference experiments to form surface-relief gratings (SRGs) on azo polymer films under different polarization combinations. The mechanism of SRG formation on azobcnzcnc chromophorc functionalizcd polymer films has been shown to depend on both the spatial variation of the intensity as well as the polarization state of the incident field pattern. The treatment presented in this paper clearly defines the intensity and polarization distribution across the twobeam interference region for different polarization configurations of the interfering beams. The efficient photoisomerization process due to the spatial variation of the optical field renders the material anisotropic and the surface mobile. The simultaneous presence of a component of electric field gradient in the grating vector direction results in largc-modulation-depth SRGs. We have carried out this investigation in one class of prototypical amorphous cpoxy-based azo polymer thin films. Our results confirm that efficient SRG formation on azo functionalizcd polymer film requires photoinduccd anisotropy and a component of optical field gradient in the direction of the grating vector. ©1999 Publication Board, Japanese Journal of Applied Physics.
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    A DFT study on structural, vibrational properties, and quasiparticle band structure of solid nitromethane
    ( 2013-05-14) Appalakondaiah, S. ; Vaitheeswaran, G. ; Lebègue, S.
    We report a detailed theoretical study of the structural and vibrational properties of solid nitromethane using first principles density functional calculations. The ground state properties were calculated using a plane wave pseudopotential code with either the local density approximation, the generalized gradient approximation, or with a correction to include van der Waals interactions. Our calculated equilibrium lattice parameters and volume using a dispersion correction are found to be in reasonable agreement with the experimental results. Also, our calculations reproduce the experimental trends in the structural properties at high pressure. We found a discontinuity in the bond length, bond angles, and also a weakening of hydrogen bond strength in the pressure range from 10 to 12 GPa, picturing the structural transition from phase I to phase II. Moreover, we predict the elastic constants of solid nitromethane and find that the corresponding bulk modulus is in good agreement with experiments. The calculated elastic constants show an order of C 11 > C22 > C33, indicating that the material is more compressible along the c-axis. We also calculated the zone center vibrational frequencies and discuss the internal and external modes of this material under pressure. From this, we found the softening of lattice modes around 8-11 GPa. We have also attempted the quasiparticle band structure of solid nitromethane with the G0W0 approximation and found that nitromethane is an indirect band gap insulator with a value of the band gap of about 7.8 eV with G0W0 approximation. Finally, the optical properties of this material, namely the absorptive and dispersive part of the dielectric function, and the refractive index and absorption spectra are calculated and the contribution of different transition peaks of the absorption spectra are analyzed. The static dielectric constant and refractive indices along the three inequivalent crystallographic directions indicate that this material has a considerable optical anisotropy. © 2013 AIP Publishing LLC.