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Shear viscosity to entropy density ratio in nuclear multifragmentation
Subrata Pal
Physics , 2010, DOI: 10.1103/PhysRevC.81.051601
Abstract: Nuclear multifragmentation in intermediate energy heavy ion collisions has long been associated with liquid-gas phase transition. We calculate the shear viscosity to entropy density ratio eta/s for an equilibrated system of nucleons and fragments produced in multifragmentation within an extended statistical multifragmentation model. The temperature dependence of eta/s exhibits surprisingly similar behavior as that for water. In the coexistence phase of fragments and light particles, the ratio eta/s reaches a minimum of comparable depth as that for water in the vicinity of the critical temperature for liquid-gas phase transition. The effects of freeze-out volume and surface symmetry energy on eta/s in multifragmentation are studied.
Shear viscosity to entropy density ratio of a relativistic Hagedorn resonance gas
Subrata Pal
Physics , 2010, DOI: 10.1016/j.physletb.2010.01.017
Abstract: The new state of matter produced at Relativistic Heavy Ion Collider reveals a strongly coupled quark-gluon plasma with an extremely small shear viscosity to entropy density ratio eta/s. We calculate the eta/s of an equilibrated hadron matter characterized by a relativistic hadron resonance gas with a Hagedorn mass spectrum that grows exponentially with the hadron mass. We find with increase in temperature of the system the eta/s value decreases due to rapid increase in the multiplicity of massive resonances. In the vicinity of the critical temperature for deconfinement transition, the minimum value of eta/s in the Hagedorn resonance gas is found to be consistent with the current estimates for a strongly coupled quark-gluon plasma.
Entropy Production at RHIC
Subrata Pal,Scott Pratt
Physics , 2003, DOI: 10.1016/j.physletb.2003.10.054
Abstract: For central heavy ion collisions at the RHIC energy, the entropy per unit rapidity dS/dy at freeze-out is extracted with minimal model dependence from available experimental measurements of particle yields, spectra, and source sizes estimated from two-particle interferometry. The extracted entropy rapidity density is consistent with lattice gauge theory results for a thermalized quark-gluon plasma with an energy density estimated from transverse energy production at RHIC.
Hadron production from resonance decay in relativistic collisions
Subrata Pal,Pawel Danielewicz
Physics , 2005, DOI: 10.1016/j.physletb.2005.08.121
Abstract: A statistical model for decay and formation of heavy hadronic resonances is formulated. The resonance properties become increasingly uncertain with increasing resonance mass. Drawing on analogy with the situation in low-energy nuclear physics, we employ the Weisskopf approach to the resonance processes. In the large-mass limit, the density of resonance states in mass is governed by a universal Hagedorn-like temperature T_H. As resonances decay, progressively more and more numerous lighter states get populated. For T_H \simeq 170 MeV, the model describes data for the hadron yield ratios at the RHIC and SPS energies under the extreme assumption of a single heavy resonance giving rise to measured yields.
Quark recombination and elliptic flow
Scott Pratt,Subrata Pal
Physics , 2004, DOI: 10.1103/PhysRevC.71.014905
Abstract: Elliptic flow systematics for different hadron species have been explained by quark coalescence models. It has been argued that the elliptic asymmetry v_2 should scale with the number of quarks that comprise the hadron. We show how these arguments are sensitive to the relative role of asymmetries in the phase space density vs. asymmetries in the effective volume of emission. We also discuss the degree to which coalescence arguments differ from thermal models. Illustrative calculations based on solving the Boltzmann equation are presented along with the results of blast-wave models. Although the issue is complicated, ambiguities might be clarified by measurements of source-size parameters for nucleons at higher transverse momenta.
Finding the remnants of lost jets at RHIC
Subrata Pal,Scott Pratt
Physics , 2003, DOI: 10.1016/j.physletb.2003.08.064
Abstract: A fast jet propagating through partonic matter loses energy by medium-induced gluon radiation. We propose a method to detect the energy loss of jets and the final-state interaction of the radiated gluons and the jets with the partonic medium. By embedding jets and radiated energy into a parton cascade, we find that the fate of lost jets can be studied by analyzing the momentum distribution of soft hadrons relative to the jet axis.
Suppression of high transverse momenta hadrons in Pb+Pb collisions at LHC
Subrata Pal,Marcus Bleicher
Physics , 2012, DOI: 10.1016/j.physletb.2012.01.070
Abstract: Hadron production and their suppression in Pb+Pb collisions at LHC at a center-of-mass energy of s_NN = 2.76 TeV are studied within a multiphase transport (AMPT) model whose initial conditions are obtained from the recently updated HIJING 2.0 model. The centrality dependence of charged hadron multiplicity dN_ch/deta at midrapidity was found quite sensitive to the largely uncertain gluon shadowing parameter s_g that determines the nuclear modification of the gluon distribution. We find final-state parton scatterings reduce considerably hadron yield at midrapidity and enforces a smaller gluon shadowing to be consistent with dN_ch/deta data at LHC. With such a constrained parton shadowing, charged hadron and neutral pion production over a wide transverse momenta range are investigated in AMPT. Relative to nucleon-nucleon collisions, the particle yield in central heavy ion collisions is suppressed due to parton energy loss. While the calculated magnitude and pattern of suppression is found consistent with that measured in Au+Au collisions at s_NN = 0.2 TeV at RHIC, at the LHC energy the suppression is overpredicted which may imply the medium formed at LHC is less opaque than expected from simple RHIC extrapolations. Reduction of the QCD coupling constant alpha_s by ~30% in the higher temperature plasma formed at LHC as compared to that at RHIC was found to reproduce the measured suppression at LHC.
Medium information from anisotropic flow and jet quenching in relativistic heavy ion collisions
Subrata Pal,Marcus Bleicher
Physics , 2012, DOI: 10.1088/1742-6596/420/1/012027
Abstract: Within a multiphase transport (AMPT) model, where the initial conditions are obtained from the recently updated HIJING 2.0 model, the recent anisotropic flow and suppression data for charged hadrons in Pb+Pb collisions at the LHC center of mass energy of 2.76 TeV are explored to constrain the properties of the partonic medium formed. In contrast to RHIC, the measured centrality dependence of charged hadron multiplicity dN_ch/deta at LHC provides severe constraint to the largely uncertain gluon shadowing parameter s_g. We find final-state parton scatterings reduce considerably hadron yield at midrapidity and enforces a smaller s_g to be consistent with dN_ch/deta data at LHC. With the parton shadowing so constrained, hadron production and flow over a wide transverse momenta range are investigated in AMPT. The model calculations for the elliptic and triangular flow are found to be in excellent agreement with the RHIC data, and predictions for the flow coefficients v_n(p_T, cent) at LHC are given. The magnitude and pattern of suppression of the hadrons in AMPT are found consistent with the measurements at RHIC. However, the suppression is distinctly overpredicted in Pb+Pb collisions at the LHC energy. Reduction of the QCD coupling constant alpha_s by ~30% in the higher temperature plasma formed at LHC reproduces the measured hadron suppression.
Fine-needle aspiration cytology of leishmanial lymphadenitis in an HIV-reactive patient: Report of a rare case
Biswajit Biswas,Subrata Pal
- , 2018, DOI: 10.4103/tp.TP_61_16
Abstract:
FDTD Modeling of Lorentzian DNG Metamaterials by Auxiliary Differential Equation Method  [PDF]
Chiranjib Goswami, Saptarshi Mukherjee, Subrata Karmakar, Manimala Pal, Rowdra Ghatak
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2014, DOI: 10.4236/jemaa.2014.65010
Abstract:

In this paper, Finite Difference Time Domain (FDTD) is utilized to simulate metamaterials of Double Negative (DNG) origin that refers to those materials having simultaneous negative permittivity and permeability. The problem regarding space formulation is achieved by means of auxiliary differential equation method (ADE), which is easy, reliable and also causal process in nature thus making it proficient. It uses fair approximations to explicate the model. Mur’s boundary condition is used for 1-D problem space and convolution perfectly matched layer boundary is implemented for 2-D problem space. The properties of metamaterial conform their speculations of energy absorption, enhancement and backward propagation property with the aid of graphs engineered by Matlab simulation both in 1-D and 2-D. Also, the interaction of fields on DNG and Double Positive (DPS) layers is contrasted. The results achieved elucidate the validity and effectiveness of the ADE method and the Convolution Perfectly Match Layer (CPML) in designing DNG metamaterials.

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