A K RayChaudhuri
Articles written in Pramana – Journal of Physics
Volume 28 Issue 2 February 1987 pp 1- Rapid Communication
Oxides of the Y-Ba-Cu-O system are found to show onset of superconductivity in the 100–120 K region.
Volume 28 Issue 5 May 1987 pp 605-605 Erratum
Volume 34 Issue 5 May 1990 pp 383-396
Spherical shells of fluid in general relativity are considered. The density is assumed to be spatially uniform and it is found that there may be three cases of positive, negative and vanishing Schwarzschild mass of the shell although the density and the pressure are both positive throughout. However the negative mass case has to be associated with a singularity representing a negative mass particle and so is unphysical. The zero mass solution has the intriguing feature that the geometry on either side of the shell is Minkowskian and the space is closed. This closure of the space saves the present result from being in contradiction with the positive energy theorems. Earlier investigations claiming zero-mass distributions are also discussed.
Volume 36 Issue 2 February 1991 pp 207-219
A detailed study of point contact tunnelling into ceramic YBCO with electrochemically etched tips of Pt, Nb and W is reported. The superconducting gap parameter (Δ) has been extracted from
Volume 36 Issue 2 February 1991 pp 231-241
We report here both hardware and software for an ac susceptibility measurement system, namely the design and construction of the cryostat, coil system, sample rod assembly and also the automation of the sample rod movement, bridge control and nulling etc with the help of an inexpensive Z-80A microprocessor via a home-made IEEE-488 interface. The variable parameters are temperature, magnitude of the rms field and frequency. An entirely new dynamic bridge nulling algorithm with continuous sample movement, which eliminates to a large extent problems related to time-dependent drifts, has been developed. We also present some experimental data collected with this system.
Volume 36 Issue 6 June 1991 pp 621-627
By making a combination of both point contact and barrier type tunnel junctions on a single sample of the high
Volume 39 Issue 4 October 1992 pp 391-404
We describe an automated calorimeter for measurement of specific heat in the temperature range 10 K>
Volume 41 Issue 5 November 1993 pp 401-419 Research Articles
In this paper we present a phenomenological model to analyze the heat release at the glass transition as observed in the continuous cooling calorimetry when a supercooled liquid freezes into the glassy state. We developed this model for the quantitative analysis of the experimental data to obtain the specific heat and the parameters which govern the structural relaxation. A description of the model and the detailed analysis are presented and the relaxation parameters are compared with the corresponding values obtained from the specific heat spectroscopy. Our analysis reveals several interesting aspects which include the effects of delayed enthalpy relaxation and the nonequilibrium structural relaxation time on the observed specific heat, the temperature dependence of the equilibrium configurational specific heat and the validity of the Vogel-Fulcher equation for the relaxation time.
Volume 44 Issue 4 April 1995 pp 1- Rapid Communication
Magnetoresistance (MR) in bulk samples of LaMnO3 has been investigated by varying the Mn4+ content from 10 to 33 per cent by chemical means, without aliovalent doping. With the increase in Mn4+ content, the structure of LaMnO3 changes first from orthorhombic to rhombohedral and then to cubic and the material becomes increasingly ferromagnetic, exhibiting a resistivity maximum akin to an insulator-metal transition at
Volume 55 Issue 4 October 2000 pp 609-615
It is an attempt to explore non-singular cosmological solutions with non-rotating perfect fluids with
Volume 58 Issue 2 February 2002 pp 343-359
In this paper we report some of the important results of experimental investigations of the flicker noise near the metal-insulator (MI) transition in doped silicon single crystals. This is the first comprehensive work to study low-frequency noise in heavily doped Si over an extensive temperature range (2 K<
Volume 94, 2020
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