G.K. Dey

Bio: G.K. Dey is an academic researcher from Bhabha Atomic Research Centre. The author has contributed to research in topics: Alloy & Microstructure. The author has an hindex of 21, co-authored 178 publications receiving 1873 citations. Previous affiliations of G.K. Dey include Homi Bhabha National Institute.

Luminescence study on Eu(3+) doped Y(2)O(3) nanoparticles: particle size, concentration and core-shell formation effects.

Abstract: Nanoparticles of Eu3+ doped Y2O3 (core) and Eu3+ doped Y2O3 covered with Y2O3 shell (core?shell) are prepared by urea hydrolysis for 3?h in ethylene glycol medium at a relatively low temperature of 140??C, followed by heating at 500 and 900??C. Particle sizes determined from x-ray diffraction and transmission electron microscopic studies are 11 and 18?nm for 500 and 900??C heated samples respectively. Based on the luminescence studies of 500 and 900??C heated samples, it is confirmed that there is no particle size effect on the peak positions of Eu3+ emission, and optimum luminescence intensity is observed from the nanoparticles with a Eu3+ concentration of 4?5?at.%. A luminescence study establishes that the Eu3+ environment in amorphous Y (OH)3 is different from that in crystalline Y2O3. For a fixed concentration of Eu3+ doping, there is a reduction in Eu3+ emission intensity for core?shell nanoparticles compared to that of core nanoparticles, and this has been attributed to the concentration dilution effect. Energy transfer from the host to Eu3+ increases with increase of crystallinity.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Thermodynamically-consistent phase-field models for solidification

Abstract: In an effort to unify the various phase-field models that have been used to study solidification, we have developed a class of phase-field models for crystallization of a pure substance from its melt. These models are based on an entropy functional, as in the treatment of Penrose and Fife, and are therefore thermodynamically consistent inasmuch as they guarantee spatially local positive entropy production. General conditions are developed to ensure that the phase field takes on constant values in the bulk phases. Specific forms of a phase-field function are chosen to produce two models that bear strong resemblances to the models proposed by Langer and Kobayashi. Our models contain additional nonlinear functions of the phase field that are necessary to guarantee thermodynamic consistency.

Alloy Phase Diagrams

Abstract: With the presentation of a theory of liquid alloys, we have now assembled all the necessary tools for the ab initio construction of an alloy phase diagram.