Patterns and bifurcations in low-Prandtl number Rayleigh-Benard convection

We present a detailed bifurcation structure and associated flow patterns for low-Prandtl number ($P=0.0002, 0.002, 0.005, 0.02$) Rayleigh-B\'{e}nard convection near its onset. We use both direct numerical simulations and a 30-mode low-dimensional model for this study. We observe that low-Prandtl number (low-P) convection exhibits similar patterns and chaos as zero-P convection \cite{pal:2009}, namely squares, asymmetric squares, oscillating asymmetric squares, relaxation oscillations, and chaos. At the onset of convection, low-P convective flows have stationary 2D rolls and associated stationary and oscillatory asymmetric squares in contrast to zero-P convection where chaos appears at the onset itself. The range of Rayleigh number for which stationary 2D rolls exist decreases rapidly with decreasing Prandtl number. Our results are in qualitative agreement with results reported earlier

Book review: Kushan, Kushano-Sasanian, and Kidarite coins: a catalogue of coins from the American Numismatic Society by David Jongeward and Joe Cribb with Peter Donovan

Accepted manuscrip

Coins of the Eastern Gangas ruler Anantavarman Chodaganga

Attributing the coins of the Eastern Gangas is a difficult task because the coins do not name the ruler, but only are dated in what are thought to be regnal years. Many authors in the past have tended to attribute the coins to the most prominent king of the dynasty, Anantavarman Chodaganga (1078-1147) (hereafter AC), but without any real justification. 2 In a recent paper, I proposed a method of attribution, based on the regnal lengths of the different kings, which would assign a sizable group of the known coins to the last four kings of the dynasty. 3 Coins attributable on a sound basis to AC remained unknown

Spacetime Singularities

We present here an overview of our basic understanding and recent developments on spacetime singularities in the Einstein theory of gravity. Several issues related to physical significance and implications of singularities are discussed. The nature and existence of singularities are considered which indicate the formation of super ultra-dense regions in the universe as predicted by the general theory of relativity. Such singularities develop during the gravitational collapse of massive stars and in cosmology at the origin of the universe. Possible astrophysical implications of the occurrence of singularities in the spacetime universe are indicated. We discuss in some detail the profound and key fundamental issues that the singularities give rise to, such as the cosmic censorship and predictability in the universe, naked singularities in gravitational collapse and their relevance in black hole physics today, and their astrophysical implications in modern relativistic astrophysics and cosmology.Comment: 45 pages, LaTex; Invited Review article for the `Springer Handbook of Spacetime' (eds A. Ashtekar and V. Petkov

Using Quantum Coherence to Enhance Gain in Atomic Physics

Quantum coherence and interference effects in atomic and molecular physics has been extensively studied due to intriguing counterintuitive physics and potential important applications. Here we present one such application of using quantum coherence to generate and enhance gain in extreme ultra-violet(XUV)(@58.4nm in Helium) and infra-red(@794.76nm in Rubidium) regime of electromagnetic radiation. We show that using moderate external coherent drive, a substantial enhancement in the energy of the lasing pulse can be achieved under optimal conditions. We also discuss the role of coherence. The present paper is intended to be pedagogical on this subject of coherence-enhanced lasing.Comment: 16 pages, 16 figures. Review Articl