• S Sarkar

      Articles written in Pramana – Journal of Physics

    • Mechanical prototype of tracking chamber in station 2 in dimuon spectrometer of ALICE

      P Bhattacharya S Bose S Chattopadhyay D Das P Datta T Ghosh N Majumdar S Mukhopadhyay S Pal L Paul P Roy A Sanyal S Sarkar P Sen S Sen M Sharan T Sinha B C Sinha

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    • Dust acoustic shock wave generation due to dust charge variation in a dusty plasma

      M R Gupta S Sarkar M Khan Samiran Ghosh

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      In a dusty plasma, the non-adiabaticity of the charge variation on a dust grain surface results in an anomalous dissipation. Analytical investigation shows that this results in a small but finite amplitude dust acoustic (DA) wave propagation which is described by the Korteweg-de Vries-Burger equation. Results of the numerical investigation of the propagation of large-amplitude dust acoustic stationary shock wave are presented here using the complete set of non-linear dust fluid equations coupled with the dust charging equation and Poisson equation. The DA waves are of compressional type showing considerable increase of dust density, which is of significant importance in astrophysical context as it leads to enhanced gravitational attraction considered as a viable process for star formation. The DA shock transition to its far downstream amplitude is oscillatory in nature due to dust charge fluctuations, the oscillation amplitude and shock width depending on the ratioωpd/Vch and other plasma parameters

    • Temperature effects on the structure of liquid D-methanol through neutron diffraction

      A Sahoo S Sarkar P S R Krishna R N Joarder

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      The study of changes in the structure (H-bonded) of liquid alcohols at elevated temperatures is rare probably due to low flash points of these liquids. An indigenously devised special quartz cell is now used to carry out the structural studies of these liquids at elevated temperatures through neutron diffraction. Here, the liquid consists of deuterated methanol and neutron data was collected on the high-Q diffractometer at Dhruva, BARC. The corrected data at elevated temperatures (BP (boiling point) and double the BP) show that there is a large change in the H-bonded structure of this liquid. The pre-peak or hump, known to be signature of H-bonded clusters appears to be present at all the three temperatures studied. In the low-Q (scattering vector) data Ornstein Zernike (OZ) behaviour is also observed. It is, however, seen that the intramolecular structure does not change very much at higher temperatures. A detailed model analysis is in progress and would be reported later.

    • An effective pair potential for liquid semiconductor, Se: Structure and related dynamical properties

      P P Nath S Sarkar R N JOarder

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      The effective pair potential of liquid semiconductor Se is extracted from its experimental structure factor data using an accurate liquid state theory and this shows important basic features. A model potential incorporating the basic features of the structure factor extracted potential is suggested. This model potential is then used to describe through low-order perturbation theory, the structure and related dynamical properties like self-diffusion coefficient and shear viscosity of this complex liquid over a wide range of temperatures.

    • Pulverization of the flux line lattice, the phase coexistence and the spinodal temperature of the order—disorder transition in a weakly pinned crystal of Yb3Rh4Sn13

      S Sarkar C V Tomy A D Thakur G Balakrishnan D McK Paul S Ramakrishnan A K Grover

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      We have studied metastability effects pertaining to the peak effect (PE) in critical current density (Jc) via isofield scans in AC susceptibility measurements in a weakly pinned single crystal of Yb3Rh4Sn13 (Tc(0) ≈ 7.6 K). The order-disorder transition in this specimen proceeds in a multi-step manner. The phase coexistence regime between the onset temperature of the PE and the spinodal temperature (where metastability effects cease) seems to comprise two parts, where ordered and disordered regions dominate the bulk behavior, respectively. The PE line in the vortex phase diagram is argued to terminate at the low field end at a critical point in the elastic (Bragg) glass phase.

    • Critical points in the Bragg glass phase of a weakly pinned crystal of Ca3Rh4Sn13

      S Sarkar A D Thakur C V Tomy G Balakrishnan D McK Paul S Ramakrishnan A K Grover

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      New experimental data are presented on the scan rate dependence of the magnetization hysteresis width ΔM(H) (∞ critical current densityJc(H)) in isothermalMH scans in a weakly pinned single crystal of Ca3Rh4Sn13, which displays second magnetization peak (SMP) anomaly as distinct from the peak effect (PE). We observe an interesting modulation in the field dependence of a parameter which purports to measure the dynamical annealing of the disordered bundles of vortices injected through the sample edges towards the destined equilibrium vortex state at a givenH. These data, in conjunction with the earlier observations made while studying the thermomagnetic history dependence inJc(H) in the tracing of the minor hysteresis loops, imply that the partially disordered state heals towards the more ordered state between the peak field of the SMP anomaly and the onset field of the PE. The vortex phase diagram in the given crystal of Ca3Rh4Sn13 has been updated in the context of the notion of the phase coexistence of the ordered and disordered regions between the onset field of the SMP anomaly and the spinodal line located just prior to the irreversibility line. A multi-critical point and a critical point in the (H,T) region of the Bragg glass phase have been marked in this phase diagram and the observed behavior is discussed in the light of recent data on multi-critical point in the vortex phase diagram in a single crystal of Nb.

    • Chiral dynamics of baryon resonances and hadrons in a nuclear medium

      E Oset D Cabrera V K Magas L Roca S Sarkar M J Vicente Vacas A Ramos

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      In these lectures I make an introduction to chiral unitary theory applied to the meson-baryon interaction and show how several well-known resonances are dynamically generated, and others are predicted. Two very recent experiments are analyzed, one of them showing the existence of two Λ(1405) states and the other one providing support for the Λ(1520) resonance as a quasi-bound state of Σ(1385)π. The use of chiral Lagrangians to account for the hadronic interaction at the elementary level introduces a new approach to deal with the modification of meson and baryon properties in a nuclear medium. Examples of it for $$\bar K$$ andø modification in the nuclear medium are presented

    • Molecular conformation and structural correlations of liquid D-1-propanol through neutron diffraction

      A Sahoo S Sarkar P S R Krishna V Bhagat R N Joarder

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      An analysis of neutron diffraction data of liquid deuterated 1-propanol at room temperature to extract its molecular conformation is presented. Being a big molecule with twelve atomic sites, the analysis is tricky and needs careful consideration. The resulting molecular parameters are compared with electron diffraction (gas phase), X-ray diffraction (liquid phase) and MD simulation results. Information about the hydrogen-bonded intermolecular structure in liquid is extracted and nature of the probable molecular association suggested.

    • Molecular conformation and liquid structure of 2-propanol through neutron diffraction

      A Sahoo S Sarkar P S R Krishna R N Joarder

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      The neutron diffraction data analysis of deuterated liquid 2-propanol at room temperature to define its molecular conformation is presented. 2-Propanol being a large molecule with twelve atomic sites, the conformation analysis is tricky and an improved method of data analysis is given. The intermolecular structural correlations, i.e., hydrogen-bonded liquid structure, can be modelled accurately to extract the nature of the average hydrogen-bonded molecular association in liquid state at room temperature. Like other alcohols these are mostly hexamer ring chain (HRC) clusters. The cluster analysis of recent X-ray data available in the literature also support the same liquid structure.

    • Quantifying uncertainties in the high-energy neutrino cross-section

      A Cooper-Sarkar P Mertsch S Sarkar

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      The predictions for high-energy neutrino and antineutrino deep inelastic scattering cross-sections are compared within the conventional DGLAP formalism of next-to-leading order QCD, using the latest parton distribution functions (PDF) such as CT10, HERAPDF1.5 and MSTW08 and taking account of PDF uncertainties. From this, a benchmark cross-section and uncertainty are derived which is consistent with the results obtained earlier using the ZEUS-S PDFs. The use of this is advocated for analysing data from neutrino telescopes, in order to facilitate comparison between their results.

    • 136Sn and three-body forces

      M Saha Sarkar S Sarkar

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      New experimental data on 2+ energies of 136,138Sn confirm the trend of lower 2+ excitation energies of even–even tin isotopes with 𝑁 > 82 compared to those with N < 82. However, none of the theoretical predictions using both realistic and empirical interactions can reproduce experimental data on excitation energies as well as the transition probabilities (𝐵(𝐸2; 6+ $\to$ 4+)) of these nuclei, simultaneously, apart from the ones whose matrix elements have been changed empirically to produce mixed seniority states by weakening the pairing. We have shown that the experimental result also shows good agreement with the theory in which three-body forces have been included in a realistic interaction. The new theoretical results on transition probabilities are discussed to identify the experimental quantities which will clearly distinguish between different views.

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