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Search Results: 1 - 10 of 312430 matches for " P. K. Sahu "
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Nuclear equation of state at high density and the properties of neutron stars
P. K. Sahu
Physics , 2000, DOI: 10.1103/PhysRevC.62.045801
Abstract: We discuss the relativistic nuclear equation of state (EOS) using a relativistic transport model in heavy-ion collisions. From the baryon flow for $Au + Au$ systems at SIS to AGS energies and above we find that the strength of the vector potential has to be reduced moderately at high density or at high relative momenta to describe the flow data at 1-10 A GeV. We use the same dynamical model to calculate the nuclear EOS and then employ this to calculate the gross structure of the neutron star considering the core to be composed of neutrons with an admixture of protons, electrons, muons, sigmas and lambdas at zero temperature. We then discuss these gross properties of neutron stars such as maximum mass and radius in contrast to the observational values.
Understanding wetland sub-surface hydrology using geologic and isotopic signatures
P. K. Sikdar ,P. Sahu
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2009,
Abstract: This paper attempts to utilize hydrogeology and isotope composition of groundwater to understand the present hydrological processes prevalent in a freshwater wetland, source of wetland groundwater, surface water/groundwater interaction and mixing of groundwater of various depth zones in the aquifer. This study considers East Calcutta Wetlands (ECW) – a freshwater peri-urban inland wetland ecosystem located at the lower part of the deltaic alluvial plain of South Bengal Basin and east of Kolkata city. This wetland is well known over the world for its resource recovery systems, developed by local people through ages, using wastewater of the city. Geological investigations reveal that the sub-surface geology is completely blanketed by the Quaternary sediments comprising a succession of silty clay, sand of various grades and sand mixed with occasional gravels and thin intercalations of silty clay. At few places the top silty clay layer is absent due to scouring action of past channels. In these areas sand is present throughout the geological column and the areas are vulnerable to groundwater pollution. Groundwater mainly flows from east to west and is being over-extracted to the tune of 65×103 m3/day. δ18O and δD values of shallow and deep groundwater are similar indicating resemblance in hydrostratigraphy and climate of the recharge areas. Groundwater originates mainly from monsoonal rain with some evaporation prior to or during infiltration and partly from bottom of ponds, canals and infiltration of groundwater withdrawn for irrigation. Relatively high tritium content of the shallow groundwater indicates local recharge, while the deep groundwater with very low tritium is recharged mainly from distant areas. At places the deep aquifer has relatively high tritium, indicating mixing of groundwater of shallow and deep aquifers. Metals such as copper, lead, arsenic, cadmium, aluminium, nickel and chromium are also present in groundwater of various depths. Therefore, aquifers of wetland and surrounding urban areas which are heavily dependent on groundwater are vulnerable to pollution. In the area south of ECW isotope data indicates no interaction between shallow and deep aquifer and hence this area may be a better location to treat sewage water than within ECW. To reduce the threat of pollution in ECW's aquifer, surface water-groundwater interaction should be minimized by regulating tubewell operation time, introducing treated surface water supply system and artificial recharging of the aquifer.
Understanding wetland sub-surface hydrology using geologic and isotopic signatures
P. K. Sikdar,P. Sahu
Hydrology and Earth System Sciences Discussions , 2009,
Abstract: This paper attempts to utilize hydrogeoloy and isotope composition of groundwater to understand the present hydrological processes prevalent in a freshwater wetland, source of wetland groundwater, surface water/groundwater interaction and mixing of groundwater of various depth zones in the aquifer. This study considers East Calcutta Wetlands (ECW) – a freshwater peri-urban inland wetland ecosystem located at the lower part of the deltaic alluvial plain of South Bengal Basin and east of Kolkata city. This wetland is well known over the world for its resource recovery systems, developed by local people through ages, using wastewater from the city. Geological investigations reveal that the sub-surface geology is completely blanketed by the Quaternary sediments comprising a succession of silty clay, sand of various grades and sand mixed with occasional gravels and thin intercalations of silty clay. Aquifer within the depths of 80 m to 120 m has the maximum potential to supply water. Groundwater mainly flows from east to west and is being over-extracted to the tune of 65×103 m3/day. δ18O and δD values of shallow and deep groundwater are similar indicating resemblance in hydrostratigraphy and climate of the recharge areas. Groundwater originates mainly from monsoonal rain with some evaporation prior to or during infiltration and partly from bottom of ponds, canals and infiltration of groundwater withdrawn for irrigation. Relatively high tritium content of the shallow groundwater indicates local recharge, while the deeper groundwater with very low tritium is recharged mainly from distant areas. At places the deeper aquifer has relatively high tritium, indicating mixing of groundwater of shallow and deep aquifers. Metals such as copper, lead, arsenic, cadmium, aluminum, nickel and chromium are also present in groundwater of various depths. Therefore, aquifers of wetland and surrounding urban areas which are heavily dependent on groundwater are vulnerable to pollution and hence surface water-groundwater interaction should be minimized by regulating tubewell operation time, introducing treated surface water supply system and artificially recharging the aquifer.
Effect of magnetic field on the strange star
S. Chakrabarty,P. K. Sahu
Physics , 1995, DOI: 10.1103/PhysRevD.53.4687
Abstract: We study the effect of a magnetic field on the strage quark matter and apply to strange star. We found that the strange star becomes more compact in presence of strong magnetic field.
Differential Flow of Protons in Au+Au Collisions at AGS Energies
P. K. Sahu,W. Cassing
Physics , 2002, DOI: 10.1016/S0375-9474(02)01287-3
Abstract: We study the proton sideward and elliptic differential flow for Au+Au collisions at AGS energies (2 -- 8 A cdot GeV) in a microscopic relativistic transport model that includes all baryon resonances up to a mass of 2 GeV as well as string degrees of freedom for the higher hadronic excitations. In order to explore the sensitivity of the various differential flows to the nuclear equation of state (EoS) we use three different parameterizations of the scalar- and vector mean-fields, i.e. NL2 (soft), NL23 (medium) and NL3 (hard), with their momentum dependence fitted to the experimental Schrodinger equivalent potential (at normal nuclear matter density rho_0) up to kinetic energies of 1 GeV. We calculate the excitation function of sideward and elliptic flow within these parameter sets for Au+Au collisions and compare with the recent data from the E895 Collaboration as a function of rapidity, impact parameter and transverse momentum, respectively. We find that the best description of the differential data is provided by a rather 'stiff' EoS at 2 A cdot GeV (NL3) while at higher bombarding energies (4--8 A cdot GeV) a 'medium' EoS leads to the lowest chi^2 with respect to the data. However, the differences in the transverse and elliptic flows (from the different parameter sets) become of minor significance at 4--8 A cdot GeV. We attribute this insensitivity to a similar reduction of the vector potential in all models and to the dominance of string degrees of freedom at these bombarding energies.
Field theoretic study of light hypernuclei
P. K. Panda,R. Sahu
Physics , 1997,
Abstract: A nonperturbative field theoretic calculation has been made for the $s$-shell hypernuclei. Here we dress the $\Lambda$- and $\Sigma$- hypernuclei with off-mass shell pion pairs. The analysis replaces the scalar isoscalar potential by quantum coherent states. The binding energies of $^{4+n\Lambda}$He $(n=0,1,2)$ agree quite well with the RMF result of Greiner. The experimental binding energies of $^4$He and $^3$He are reasonably well reproduced in our calculation. A satisfactory description of the relevant experimental $\Lambda$- and $\Sigma$- separation energies has been obtained.
SU(2) Chiral sigma model and the properties of neutron stars
P. K. Sahu,A. Ohnishi
Physics , 2000, DOI: 10.1143/PTP.104.1163
Abstract: We discuss the {\it SU}(2) chiral sigma model in the context of nuclear matter using a mean field approach at high density. In this model we include a dynamically generated isoscalar vector field and higher-order terms in the scalar field. With the inclusion of these, we reproduce the empirical values of the nuclear matter saturation density, binding energy, and nuclear incompressibility. The value of the incompressibility is chosen according to recently obtained heavy-ion collision data. We then apply the same dynamical model to neutron-rich matter in beta equilibrium, related to neutron star structure. The maximum mass and corresponding radius of stable non-rotating neutron stars are found to be in the observational limit.
Mixed phase in a compact star with strong magnetic field
Ritam Mallick,P. K. Sahu
Physics , 2012,
Abstract: Compact stars can have either hadronic matter or can have exotic states of matter like strange quark matter or color superconducting matter. Stars also can have a quark core surrounded by hadronic matter, known as hybrid stars (HS). The HS is likely to have a mixed phase in between the hadron and quark phase. Observational results suggest huge surface magnetic field in certain neutron stars (NS) called magnetars. Here we study the effect of strong magnetic field on the respective EOS of matter under extreme conditions. We further study the hadron-quark phase transition in the interiors of NS giving rise to hybrid stars (HS) in presence of strong magnetic field. The hadronic matter EOS is described based on relativistic mean field theory and we include the effect of strong magnetic fields leading to Landau quantization of the charged particles. For the quark phase we use the simple MIT bag model. We assume density dependent bag pressure and magnetic field. The magnetic field strength increases going from the surface to the center of the star. We construct the intermediate mixed phase using Glendenning conjecture. The magnetic field softens the EOS of both the matter phases. The effect of magnetic field is insignificant unless the field strength is above $10^{14}$G. A varying magnetic field, with surface field strength of $10^{14}$G and the central field strength of the order of $10^{17}$G has significant effect on both the stiffness and the mixed phase regime of the EOS. We finally study the mass-radius relationship for such type of mixed HS, calculating their maximum mass, and compare them with the recent observation of pulsar PSR J1614-2230, which is about 2 solar mass. The observations puts a severe constraint on the EOS of matter at extreme conditions. The maximum mass with our EOS can reach the limit set by the observation.
Phase transitions in neutron star and magnetars and their connection with high energetic bursts in astrophysics
Ritam Mallick,P. K. Sahu
Physics , 2012, DOI: 10.1016/j.nuclphysa.2013.11.009
Abstract: The phase transition from normal hadronic matter to quark matter in neutron stars (NS) could give rise to several interesting phenomena. Compact stars can have such exotic states up to their surface (called strange stars (SS)) or they can have quark core surrounded by hadronic matter, known as hybrid stars (HS). As the state of matter of the resultant SS/HS is different from the initial hadronic matter, their masses also differ. Therefore, such conversion leads to huge energy release, sometimes of the order of $10^{53}$ ergs. In the present work we study the qualitative energy released by such conversion. Recent observations reveal huge surface magnetic field in certain stars, termed magnetars. Such huge magnetic fields can modify the equations of state (EOS) of the matter describing the star. Therefore, the mass of magnetars are different from normal NS. The energy released during the conversion process from neutron magnetar (NM) to strange magnetar/hybrid magnetar (SS/HS) is different from normal NS to SS/HS conversion. In this work we calculate the energy release during the phase transition in magnetars. The energy released during NS to SS/HS conversion exceeds the energy released during NM to SM/HM conversion. The energy released during the conversion of NS to SS is always of the order of $10^{53}$ ergs. The amount of energy released during such conversion can only be compared to the energy observed during the gamma ray bursts (GRB). The energy liberated during NM to HM conversion is few times lesser, and is not likely to power GRB at cosmological distances. However, the magnetars are more likely to lose their energy from the magnetic poles and can produce giant flares, which are usually associated with magnetars.
Fluoride Uptake and Net Primary Productivity of Selected Crops  [PDF]
P. C. Mishra, S. K. Sahu, A. K. Bhoi, S. C. Mohapatra
Open Journal of Soil Science (OJSS) , 2014, DOI: 10.4236/ojss.2014.411039
Abstract: Crop field soil collected from Sambalpur University campus of Odisha and treated with various fluoride concentrations was used to raise selected local crops. Background concentration of total and leachable fluoride content in soil was 95.19 and 8.89 ppm respectively. At the time of harvest of the crops, the total fluoride content was found to decrease and leachable fluoride content was found to increase both in control and experimental sets. This might be due to the addition of fluoride to soil in the experimental set up as well as availability of background fluoride content in soil and the irrigated water (i.e. 0.5 ppm). The fluoride accumulation in plant tissue increased with increase in the fluoride content in soil. Net Primary Productivity (NPP) of fluoride treated plants decreased in Brinjal by 6.64% - 56.72%, Tomato by 14.46% - 62.24% and Mung by 10.27% - 53.61%, all in 20 - 100 ppm fluoride range. However, NPP of Mustard, Ladies finger and Chili decreased by 15.58% - 61.21%, 12.28% - 52.78% and 40.8% - 90.65% in 10 - 50 ppm fluoride treated sets respectively in 10 - 50 ppm fluoride range. Maize NPP decreased by 12.17% - 61.20% in 20 - 100 ppm fluoride range as Rice NPP decreased by 6.64% - 56.72% in 20 - 100 ppm fluoride range. Pod formation was inhibited at 100 ppm fluoride amended soil in case of Mung, and 50 ppm in Ladies finger, 40 - 100 ppm in Maize and 30 - 50 ppm fluoride amended soil in case of Chilli. Thus, Maize and Chilli are more sensitive to fluoride contamination than other crops. In all the crops NPP decreased with increase in fluoride content in soil with significant decrease in highest concentration of fluoride.
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