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Search Results: 1 - 10 of 362634 matches for " D. L. Sastry "
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DC Electrical Conductivity Studies of GeO2 Doped Lead Vanadate Glass System  [PDF]
P. Tejeswararao, D. L. Sastry
New Journal of Glass and Ceramics (NJGC) , 2017, DOI: 10.4236/njgc.2017.73005
Abstract: Temperature dependent DC electrical conductivity studies of GeO2 substituted lead vanadate glass systems xGeO2(50-x)PbO:50V2O5 (x = 5, 10, 15 mole%) were carried out and the results are reported. X-ray diffraction results reveal that all samples are perfect amorphous in nature. DSC results indicate that the substituent GeO2 is replacing PbO in the glass network in such a way that the eutectic composition is maintained. DC electrical conductivity studies of the glass samples indicate that the systems are characterized by different activation energies in different temperature ranges which in turn depend on the annealing temperature. These results are interpreted in terms of temperature dependent microstructural changes in these glass systems.
Ion Association Methods for the Determination of Fexofenadine in Pharmaceutical Preparations
L. D. Srinivas,P. Ravi Kumar,B. S. Sastry
Journal of Chemistry , 2005, DOI: 10.1155/2005/370478
Mn Site Substitution Of La0.67Ca0.33MnO3 With Closed Shell Ions: Effect on Magnetic Transition Temperature
L. Seetha Lakshmi,V. Sridharan,D. V. Natarajan,V. Sankara Sastry,T. S. Radhakrishnan
Physics , 2002,
Abstract: Mn site is substituted with closed shell ions (Al, Ga. Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at. %. Substitution did not change either the crystal symmetry or the oxygen stiochiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (TP(r) and TC respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii (rMn3+-rM) between the substituent (rM) and the Mn3+ ion (rMn3+) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.
Universal behavior of transition temperatures Vs residual resistivity in Mn site doped La-Ca-Mn-O perovskites
L. Seetha Lakshmi,V. Sridharan,D. V. Natarajan,V. Sankara Sastry,T. S. Radhakrishnan
Physics , 2003,
Abstract: We discuss here a comparative study of the role of local structure and/or nature of local magnetic coupling on the electrical transport properties of Mn site substituted La-Ca-Mn-O perovskites. Particular emphasis is being paid to explore the strong correlation between the insulator-metal transition (TIM) and the residual resistivity (rhoo) upon substitution. There exists an inverse relationship between ro and TIM in the compounds under present discussion. Best fit for TIM Vs ro could be obtained for the compounds understudy to a first order exponential decay with a functional form TIM = TIMO + Aexp (-rhoo/t) than that to a power law. There is a previous report wherein the similar correlation in the case of rare earth substituted manganites has been attributed to Anderson-type electron localization. The "universal behavior" as has been observed between ro and TIM irrespective of the electronic, magnetic and chemical nature of the substituting elements in the Mn site substituted La-Ca-Mn-O perovskites needs a rigorous theoretical investigation.
Double metal-insulator transitions and MR in La(0.67)Ca(0.33)Mn(1-x)Ru(x)O(3) (x
L. Seetha Lakshmi,V. Sridharan,D. V. Natarajan,Rajeev Rawat,Sharat Chandra,V. Sankara Sastry,T. S. Radhakrishnan,.
Physics , 2003,
Abstract: This paper is in continuation of our previous work on the structural, electrical and magnetic properties of Ru doped La(0.67)Ca(0.33)MnO(3) compounds (Ref.: L.Seetha Lakshmi et.al, J. Magn. Magn. Mater. 257, 195 (2003)). Here we report the results of magnetotransport measurements on La(0.67)Ca(0.33)Mn(1-x)Ru(x)O(3) (0
Possible Magnetic separation in Ru doped La0.67Ca0.33MnO3
L. Seetha Lakshmi,V. Sridharan,D. V. Natarajan,Sharat Chandra,V. Sankara Sastry,T. S. Radhakrishnan,Ponn Pandian,A. Narayanasamy
Physics , 2002, DOI: 10.1016/S0304-8853(02)01171-X
Abstract: X-ray diffraction, resistivity, ac susceptibility and magnetization studies on La0.67Ca0.33Mn1-xRuxO3 (0 x < 0.1) were carried out. A significant increase in the lattice parameters indicated the presence of mixed valance state of Ru: Ru3+ and Ru4+. The resistivity of the doped compounds exhibited two features: a broad maximum and a relatively sharp peak. While a para to ferromagnetic transition could be observed for the latter peak, no magnetic signal either in ac susceptibility or in magnetization measurements could be observed for the broad maximum. The magnetic moment decreases non linearly from 3.55 to 3 mB over the Ru composition from 0 to 8.5 at.%. Based on the results of the present studies and on existing literature on the Mn-site substituted systems, we argue that a magnetic phase separation occurs in the Ru doped system. While the sharp peak in the resistivity corresponds to Ru4+ enriched region with a ferromagnetic coupling with neighboring Mn ions, the broad peak corresponds to a Ru3+ rich regions, with an antiferromagnetic coupling with neighboring Mn ions.
Electrical and Spectroscopic Studies of the CdO Substituted Lead Vanadate Glass System vs Crystalline Form  [PDF]
Ponnada Tejeswara Rao, Kocharlakota V. Ramesh, Devulapalli L. Sastry
New Journal of Glass and Ceramics (NJGC) , 2012, DOI: 10.4236/njgc.2012.21006
Abstract: Results of the direct current (DC) Electrical Conductivity, thermoelectric power and Electron Spin Resonance (ESR) of CdO substituted PbO-V2O5 glass system are reported. Conduction in these glasses is found to be electronic and the hoping of polaron seems to be the dominant process in the transport mechanism. There is a remarkable decrease in the activation energy for conduction in the annealed and devitrified samples when compared to their amorphous counter parts. It is observed that there is remarkable improvement in the conductivity of the crystalline samples when compared to their amorphous counter parts. The thermoelectric power measurements indicates that the amorphous samples are n-type at room temperature where as the crystalline samples are p-type at room temperature. In crystalline samples the hyperfine structure is nearly smeared out and a relatively broad line with an isotropic g value characterizes the spectra.
Evidence for anomalous structural behavior in CaFe2As2
S. K. Mishra,R. Mittal,P. S. R. Krishna,P. U. Sastry,S. L. Chaplot,P. D. Babu,S. Matsuishi,H. Hosono
Physics , 2013,
Abstract: The structural properties of the CaFe2As2 have been investigated by x-ray and neutron powder diffraction techniques as a function of temperature. Unambiguous experimental evidence is shown for coexistence of tetragonal and orthorhombic phases below 170 K in contrast to existing literature. Detailed Rietveld analyses of thermo-diffractograms show that the sample does not transform completely in to the orthorhombic phase at the lowest temperature even though it is the majority phase. We have found that the unit cell volume of the orthorhombic phase is higher compared to that of the tetragonal phase for all the temperatures. X-ray data on CaFe2As2 shows anomalous (at) lattice parameter contraction with increasing temperature and phase co-existence behavior below 170 K unlike other members of the 122 family of compounds like SrFe2As2 and EuFe2As2. Temperature dependent magnetization of polycrystalline CaFe2As2 sample show weak anomalies below 170 K. This behavior of the polycrystalline sample is in contrast to that of a single crystal reported earlier.
Absolute Zero Occurs in Black Holes  [PDF]
Sanjay Sastry
Journal of Modern Physics (JMP) , 2016, DOI: 10.4236/jmp.2016.711124
Abstract: The black hole is a region in space in which nothing can escape its pull. The two important parts of the anatomy of a stable black hole are the event horizon and gravitational singularity. The main discussion is regarding the temperature of a black hole. Absolute zero is a state which enthalpy and entropy is zero. The temperature of a black hole approaches the gravitational singularity in which space-time possibly ceases and entropy is zero producing absolute zero or possible sub- absolute zero.
Persistent memory in athermal systems in deformable energy landscapes
D. Fiocco,G. Foffi,S. Sastry
Physics , 2013, DOI: 10.1103/PhysRevLett.112.025702
Abstract: We show that memory can be encoded in a model amorphous solid subjected to athermal oscillatory shear deformations, and in an analogous spin model with disordered interactions, sharing the feature of a deformable energy landscape. When these systems are subjected to oscillatory shear deformation, they retain memory of the deformation amplitude imposed in the training phase, when the amplitude is below a "localization" threshold. Remarkably, multiple, persistent, memories can be stored using such an athermal, noise-free, protocol. The possibility of such memory is shown to be linked to the presence of plastic deformations and associated limit cycles traversed by the system, which exhibit avalanche statistics also seen in related contexts.
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