Centrality dependence of elliptic flow and QGP viscosity

In the Israel-Stewart's theory of second order hydrodynamics, we have analysed the recent PHENIX data on charged particles elliptic flow in Au+Au collisions. PHENIX data demand more viscous fluid in peripheral collisions than in central collisions. Over a broad range of collision centrality (0-10%- 50-60%), viscosity to entropy ratio ($\eta/s$) varies between 0-0.17.Comment: Final version to be publiashed in J. Phys. G. 8 pages, 6 figures and 3 table

Anomalous structural and mechanical properties of solids confined in quasi one dimensional strips

We show using computer simulations and mean field theory that a system of particles in two dimensions, when confined laterally by a pair of parallel hard walls within a quasi one dimensional channel, possesses several anomalous structural and mechanical properties not observed in the bulk. Depending on the density $\rho$ and the distance between the walls $L_y$, the system shows structural characteristics analogous to a weakly modulated liquid, a strongly modulated smectic, a triangular solid or a buckled phase. At fixed $\rho$, a change in $L_y$ leads to many reentrant discontinuous transitions involving changes in the number of layers parallel to the confining walls depending crucially on the commensurability of inter-layer spacing with $L_y$. The solid shows resistance to elongation but not to shear. When strained beyond the elastic limit it fails undergoing plastic deformation but surprisingly, as the strain is reversed, the material recovers completely and returns to its original undeformed state. We obtain the phase diagram from mean field theory and finite size simulations and discuss the effect of fluctuations.Comment: 14 pages, 13 figures; revised version, accepted in J. Chem. Phy

Extraction of Projection Profile, Run-Histogram and Entropy Features Straight from Run-Length Compressed Text-Documents

Document Image Analysis, like any Digital Image Analysis requires identification and extraction of proper features, which are generally extracted from uncompressed images, though in reality images are made available in compressed form for the reasons such as transmission and storage efficiency. However, this implies that the compressed image should be decompressed, which indents additional computing resources. This limitation induces the motivation to research in extracting features directly from the compressed image. In this research, we propose to extract essential features such as projection profile, run-histogram and entropy for text document analysis directly from run-length compressed text-documents. The experimentation illustrates that features are extracted directly from the compressed image without going through the stage of decompression, because of which the computing time is reduced. The feature values so extracted are exactly identical to those extracted from uncompressed images.Comment: Published by IEEE in Proceedings of ACPR-2013. arXiv admin note: text overlap with arXiv:1403.778

Direct photon production from viscous QGP

We simulate direct photon production in evolution of viscous QGP medium. Photons from Compton and annihilation processes are considered. Viscous effect on photon production is very strong and reliable simulation is possible only in a limited $p_T$ range. For minimally viscous fluid $\eta/s$=0.08), direct photons can be reliably computed only up to $p_T \leq$ 1.3 GeV. With reduced viscosity ($\eta/s$=0.04), the limit increases to $p_T \leq$2GeV.Comment: 6 pages, 5 figure

Transverse momentum spectra and elliptic flow in ideal hydrodynamics and geometric scaling

In an ideal hydrodynamic model, with an equation of state where the confinement-deconfinement transition is a cross-over at $T_{co}=196 MeV$, we have simulated $\sqrt{s}$=200 GeV Au+Au collisions. Simultaneous description of the experimental charged particle's $p_T$ spectra and elliptic flow require that in central (0-10%) Au+Au collisions, initial energy density scales with the binary collision number density. In less central collisions, experimental data demand scaling with the participant density. Simulation studies also indicate that in central collisions viscous effects are minimal.Comment: 4 pages, 3 figures