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    Wyświetlanie 1-8 z 8
    Tytuł:
    Studies on Isotope Shift Exponent and Pressure Coefficient for Extended Superconductors within BCS Formalism
    Autorzy:
    Banerjee, B.
    Roy, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1808029.pdf
    Data publikacji:
    2009-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.+f
    74.25.Bt
    74.25.Ha
    Opis:
    A tight-binding model comprising a hopping and an attractive interaction term was considered for high temperature superconductors. Explicit calculations on the effects of isotopic substitution of atoms and application of pressure on the transition temperatures were made in this work. Exact analytical expressions for the isotope-shift exponent (α) and pressure coefficient $(γ_P)$ of transition temperature $(T_C)$ considering the isotopic mass and pressure dependence of the hopping and attractive interaction strengths from a minimal model describing superconductivity were obtained. Theoretical predictions for α and $γ_P$ with proper choice of parameters are found to be qualitatively consistent with the results of the experiments of high $T_C$ oxides. The results depend on the band dispersion chosen.
    Źródło:
    Acta Physica Polonica A; 2009, 115, 5; 914-919
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Matter-Wave Bright Solitons of $\text{}^7Li$ Gas in an Expulsive Potential
    Autorzy:
    Golam Ali, Sk.
    Talukdar, B.
    Roy, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1814020.pdf
    Data publikacji:
    2007-12
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    03.75.Fi
    05.45.Yv
    Opis:
    A Lagrangian based method is used to derive an analytical model for studying the dynamics of matter-wave bright soliton created in a harmonic potential which is attractive in the transverse direction and expulsive in the longitudinal direction. By means of sech trial functions and a Ritz optimization procedure, evolution equations are constructed for width, amplitude and nonlinear frequency chirp of the propagating soliton of the atomic condensate. Our equation for the width is an exact agreement with that of Carr and Castin, obtained by more detailed analysis. In agreement with the experiment of Paris group, the expulsive potential is found to cause the soliton to explode for N|$a_s$|=0.98, N being the number of atoms in the condensate and $a_s$ -- the scattering length of the atom-atom interaction.
    Źródło:
    Acta Physica Polonica A; 2007, 112, 6; 1165-1170
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Bright Solitons in Asymmetrically Trapped Bose-Einstein Condensates
    Autorzy:
    Golam Ali, Sk.
    Talukdar, B.
    Roy, S. K.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047288.pdf
    Data publikacji:
    2007-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    03.75.-b
    03.75.Kk
    05.30.Jp
    Opis:
    We study the dynamics of bright solitons in a Bose-Einstein condensate confined in a highly asymmetric trap. While working within the framework of a variational approach we carry out the stability analysis of the Bose-Einstein condensate solitons against collapse. When the number of atoms in the soliton exceeds a critical number N$\text{}_{c}$, it undergoes the so-called primary collapse. We find an analytical expression for N$\text{}_{c}$ in terms of appropriate experimental quantities that are used to produce and confine the condensate. We further demonstrate that, in the geometry of the problem considered, the width of the soliton varies inversely as the number of constituent atoms.
    Źródło:
    Acta Physica Polonica A; 2007, 111, 3; 289-297
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    A Green Function Estimation of Correction to Vegards Law for isovalent Substitutional Defects in Alkali Halide Crystals
    Autorzy:
    Datta Roy (Paul), S.
    Das, S. K.
    Powiązania:
    https://bibliotekanauki.pl/articles/2013286.pdf
    Data publikacji:
    2000-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.72.Bb
    61.82.Bg
    Opis:
    A Green function method is developed for estimation of lattice parameter r(χ) of an AX-BX solid solution over entire composition range (χ=0 to 1). The r(χ) obtained in the present method is different from the value r$\text{}_{V}$(χ) suggested by Vegard's law. We estimated the deviation from Vegard's law, r(χ)-r$\text{}_{V}$(χ), over entire composition range for isovalent substitutional defect in alkali halide crystals. When compared to X-ray diffraction measurements, we find that the deviation is in correct direction, variation of r(χ) with χ is consistent with experiment and the overall agreement is fairly good considering the accuracy of the experiment.
    Źródło:
    Acta Physica Polonica A; 2000, 97, 4; 671-679
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Calculation of Lattice Relaxation in Some Substitutional Alloys Using a Green Function
    Autorzy:
    Das, S. K.
    Datta Roy (Paul), S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1995663.pdf
    Data publikacji:
    1999-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.72.Bb
    61.82.Bg
    Opis:
    In this paper we calculate nearest neighbour relaxation in some dilute substitutional alloys using a lattice static Green function and the Morse potential function. Distant neighbour relaxation is calculated by invoking a continuum approximation. The potential parameters for the unlike interactions are calculated using simple interpolation formulae. Using the above relaxation, we calculate volume changes in the above alloys. It is observed that the simple model predicts values which are in reasonably good agreement with the experimental values in all cases. The calculated values are also compared with those obtained from the Vegard law. For Au-Ag alloy, our model reproduces both the correct sign and the magnitude of the volume change, whereas the Vegard law cannot even give the sign of the volume change. This shows the inherent strength of the present model.
    Źródło:
    Acta Physica Polonica A; 1999, 95, 3; 359-366
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron-ion Recombination at Sub-zero Temperature
    Autorzy:
    Bhattacharyya, S.
    Roy, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2008325.pdf
    Data publikacji:
    1999-06
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    32.70.Fw
    34.80.Kw
    Opis:
    In this paper we have considered two-step radiative recombination channel over the existing spontaneous radiative recombination channel to explain the causes of experimentally obtained enhanced recombination rate at sub-zero temperature. The existing recombination rate due to spontaneous radiative recombination is 4 times smaller than the recent experimental data. In the case of Ne$\text{}^{10+}$ we obtain good agreement between theory and experiment when contribution from two-step radiative recombination channel is added to the spontaneous radiative recombination channel. Recombination rate for Ar$\text{}^{18+}$ is calculated. The radiation spectrum given out by two-step radiative recombination and spontaneous radiative recombination in the recombination rate processes are discrete spectrum and continuous spectrum, respectively. Experimental identification of these two channels through the spectral signatures is suggested.
    Źródło:
    Acta Physica Polonica A; 1999, 95, 6; 911-920
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Three-Particle Recombination at Low Temperature: a QED Approach
    Autorzy:
    Bhattacharyya, S.
    Roy, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2027431.pdf
    Data publikacji:
    2001-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    32.80.Fb
    33.55.Ad
    Opis:
    A theoretical study of the three-body recombination of proton and electron in presence of a spectator electron with electronic beam at near-zero temperature is presented using field theory and invariant Lorentz gauge. Contributions from the Feynman diagrams of different orders give an insight into the physics of the phenomena. Recombination rate coefficient is obtained for low lying principal quantum number n=1 to 10. At a fixed ion beam temperature (300 K) recombination rate coefficient is found to increase in general with n, having a flat and a sharp peak at quantum states 3 and 5, respectively. In absence of any other theoretical and experimental results for low temperature formation of H-atom by three-body recombination at low lying quantum states, we have presented the theoretical results of Stevefelt and group for three-body recombination of deuteron with electron along with the present results. Three-body recombination of antihydrogen in antiproton-positron plasma is expected to yield similar result as that for three-body recombination of hydrogen formation in proton-electron plasma. The necessity for experimental investigation of low temperature three-body recombination at low quantum states is stressed.
    Źródło:
    Acta Physica Polonica A; 2001, 100, 1; 23-40
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Static Local Field Factor and Ground State Properties of Interacting Electron Gas
    Autorzy:
    Sarkar, A.
    Haldar, S.
    Roy, D.
    Sen, D.
    Powiązania:
    https://bibliotekanauki.pl/articles/2038378.pdf
    Data publikacji:
    2004-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.-w
    71.45.Gm
    Opis:
    In the most general case, the calculation of the static local field factor G(q) for the unpolarised electron gas requires the knowledge of exchange-correlation energy functionals for both the parallel and antiparallel relative spin orientations of the electron gas system. Accurate density interpolation formulae using the quantum Monte Carlo data of Ceperley-Alder for the correlation energy of electron gas in both the "para" and "ferro" states, respectively, in the given density range are used for the calculation of G( q). Fulfilment of relevant consistency criteria is ensured and the local field factor so obtained renders significant improvement of ab initio pseudopotential calculation of effective interaction of Al. The Levin like interpolant of the correlation energy Ceperley-Alder data has been further used to study the ground state properties of the electron gas. It is also noted that a better understanding of the interacting electron gas properties requires a more accurate spin interpolation formula for the correlation energy than the existing ones.
    Źródło:
    Acta Physica Polonica A; 2004, 106, 4; 497-514
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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