Department of Physics

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Author: search.filters.author.Bandyopadhyay, DebashisEnd date: 2009

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    Randomness of random networks: A random matrix analysis
    (IOP, 2009-09) Bandyopadhyay, Debashis
    We analyze complex networks under the random matrix theory framework. Particularly, we show that Δ3 statistics, which gives information about the long-range correlations among eigenvalues, provides a measure of randomness in networks. As networks deviate from the regular structure, Δ3 follows the random matrix prediction of logarithmic behavior (i.e., ) for longer scale.
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    Magnetic phase transitions in Fe{sub 80-x}Ni{sub x}Cr{sub 20} (14 {<=} x {<=} 30) alloy studied by using {sup 57}Fe Moessbauer spectroscopy
    (ETDE Web, 1999-11) Bandyopadhyay, Debashis
    This paper reports {sup 57}Fe Moessbauer spectroscopic studies of the polycrystalline samples of the substitutionally disordered, isostructural (fcc), ternary alloy system Fe{sub 80-x}Ni{sub x}Cr{sub 20} for x = 30, 26, 19 and 14 in the temperature range of 10-295 K. The data have been analyzed in terms of the magnetic phase transitions occurring in these alloys by examining the temperature dependence of the various Moessbauer parameters like line-width, center shift, resonance area, distribution of hyperfine field, P(H), and the average hyperfine field . An estimate of the magnetic transition temperature T{sub C} is made for the alloys with x = 30 and 26 and these results are compared with those previously obtained by magnetic measurements and neutron diffraction experiments. The data for the second order Doppler shift have been analyzed to estimate the Debye temperature {theta}D for alloys with x = 30 and 26.
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    Study of hyperfine field distributions in the alloy Fe{sub 54}Ni{sub 26}Cr{sub 20} by using {sup 57}Fe Moessbauer spectroscopic technique
    (ETDE Web, 2000) Bandyopadhyay, Debashis
    This paper reports the study of hyperfine field distributions of polycrystalline Fe{sub 54}Ni{sub 26}Cr{sub 20} sample of the substitutionally disordered, isostructural (fcc), ternary alloy by using {sup 57}Fe Moessbauer spectroscopic technique. Magnetic phase transitions occurring in the alloy have been studied by examining the temperature dependence of average hyperfine field. To understand the local magnetic order in this alloy at low temperature, probability of hyperfine field distribution curves have been re-fitted by using three independent Gaussians having different positions and widths. From this fits, local magnetic order of this alloy at low temperature has been described which supports the existence of nonequilibrium ferromagnetic state below Curie temperature. (orig.)
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    The C-Hf-Ti System (Carbon-Hafnium-Titanium)
    (JOURNAL OF PHASE EQUILIBRIA, 2000) Bandyopadhyay, Debashis
    The assessed phase diagram of the Ti-C system shown in[1990Oka] conducted a detailed assessment of the C-Hf Fig. 1 is taken from [1998Oka].[1995Alb],[1996Jon], and system, where only one intermediate phase exists. The [1996Sei] reported other assessments of this system, which assessed phase diagram shown in Fig. 3 is taken from consists of two terminal solids α-Ti and β-Ti and a refractory[1990Oka]. Three terminal solids, C (graphite), α-Hf, and monocarbide TiC. The other phases present are liquid and β-Hf, are present in this system.[Massalski1] has reported graphite (C). Two eutectic and one peritectoid reaction appear the temperature of β-Hf⇔ α-Hf allotropic transformation as in this system at 1646, 2776, and 920 C, respectively. There 1743 C. There are several conflicting reports in the literature seems to be a tendency of carbon ordering at compositions([1954Cot],[1961Por],[1962Kat], and [1965Rud]) regarding below stoichiometry; as a result, the Ti2C phase does not the eutectic reaction temperature between C and Hf and its appear in the binary phase diagram. The crystal structure corresponding composition. The crystal structure data of the data shown Table 1 are taken from [Massalski2]. C-Hf system shown in Table 3 are taken from [1990Oka].
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    The C-Ti-Zr system (carbon-titanium-zirconium) (vol 22, pg 64, 1998)
    (JOURNAL OF PHASE EQUILIBRIA, 2001-04) Bandyopadhyay, Debashis
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    A study of the effect of annealing temperatures and time periods on the hyperfine field distributions of Fe79B16Si5 metallic glass near and below the crystallization temperature was carried out using 57Fe Mössbauer spectroscopy. The effect of crystallization during annealing as a function of annealing time on the average hyperfine magnetic field, , and the relative change of the probability of hyperfine fields, P(H), with respect to that of the as-received sample are also discussed.
    (Springer, 1999-11) Bandyopadhyay, Debashis
    This paper reports 57Fe Mössbauer spectroscopic studies of the polycrystalline samples of the substitutionally disordered, isostructural (fcc), ternary alloy system Fe80-xNixCr20 for x = 30, 26, 19 and 14 in the temperature range of 10–295 K. The data have been analyzed in terms of the magnetic phase transitions occurring in these alloys by examining the temperature dependence of the various Mössbauer parameters like line‐width, center shift, resonance area, distribution of hyperfine field, P(H), and the average hyperfine field 〈H〉. An estimate of the magnetic transition temperature T C is made for the alloys with x = 30 and 26 and these results are compared with those previously obtained by magnetic measurements and neutron diffraction experiments. The data for the second order Doppler shift have been analyzed to estimate the Debye temperature ΘD for alloys with x = 30 and 26.
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    A study of the effect of annealing on the hyperfine field distributions in Fe79B16Si5 metallic glass
    (Elsevier, 1999-12) Bandyopadhyay, Debashis
    A study of the effect of annealing temperatures and time periods on the hyperfine field distributions of Fe79B16Si5 metallic glass near and below the crystallization temperature was carried out using 57Fe Mössbauer spectroscopy. The effect of crystallization during annealing as a function of annealing time on the average hyperfine magnetic field, , and the relative change of the probability of hyperfine fields, P(H), with respect to that of the as-received sample are also discussed.
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    Study of hyperfine field distributions in the alloy Fe54Ni26Cr20 by using 57Fe Moessbauer spectroscopic technique
    (IAEA, 2000) Bandyopadhyay, Debashis
    This paper reports the study of hyperfine field distributions of polycrystalline Fe54Ni26Cr20 sample of the substitutionally disordered, isostructural (fcc), ternary alloy by using 57Fe Moessbauer spectroscopic technique. Magnetic phase transitions occurring in the alloy have been studied by examining the temperature dependence of average hyperfine field. To understand the local magnetic order in this alloy at low temperature, probability of hyperfine field distribution curves have been re-fitted by using three independent Gaussians having different positions and widths. From this fits, local magnetic order of this alloy at low temperature has been described which supports the existence of nonequilibrium ferromagnetic state below Curie temperature
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    Purpose-led Publishing logo. Study of hyperfine-field distributions and the lattice dynamics of Fe50Ni30Cr20 alloy by using 57Fe Mössbauer spectroscopy
    (IOP, 1999) Bandyopadhyay, Debashis
    This paper reports a 57Fe Mössbauer spectroscopic study of a polycrystalline sample of the substitutionally disordered, isostructural (fcc), ternary alloy Fe50Ni30Cr20 over the temperature range 10 to 295 K. The data have been analysed in terms of the magnetic phase transitions occurring in the alloy by examining the temperature dependence of the Mössbauer parameters. The Curie temperature has been determined by fitting the average hyperfine-field values obtained at different temperatures. In order to achieve a detailed understanding of the nature of the hyperfine-field distribution corresponding to the Mössbauer spectra of this alloy, the curves representing the probabilities of the hyperfine-field distributions versus the hyperfine field have been refitted by using two independent Gaussians. On the basis of these fits, the local magnetic ordering of this alloy at low temperature has been described. The data on the second-order Doppler shift have been analysed in order to obtain an estimate of the Debye temperature, ΘD, and a description of the lattice dynamics.
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    The Ti-V-C system (titanium-vanadium-carbon)
    (Springer, 2000-03) Bandyopadhyay, Debashis
    The assessed phase diagram of Ti-C system shown in Fig. 1 is taken from [1998Oka]. Other recent work was done on this system by [1995Alb], [1996Sei1], and [1996Jon]. The system consists of two terminal solids aTi and b Ti and a refractory monocarbide TiC. Since there is a tendency of carbon ordering at the compositions below stoichiometry, the phase Ti2C does not appear in the phase diagram. Other phases present are liquid and graphite (C). Two eutectic and one peritectoid reaction appear in this system at 1646, 2776, and 920 °C, respectively.