• Issue front cover thumbnail

      Volume 68, Issue 1

      January 2007,   pages  1-140

    • Calculation of CWKB envelope in boson and fermion productions

      S Biswas I Chowdhury

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      We present the calculation of envelope of boson and of both low- and high- mass fermion production at the end of inflation when the coherently oscillating inflatons decay into bosons and fermions. We consider three different models of inflation and use CWKB technique to calculate the envelope to understand the structure of resonance band formation. We observe that though low-mass fermion production is not effective in pre-heating because of Pauli blocking, it is quite probable for high-mass fermion to take part in pre-heating.

    • Energy–momentum localization in Marder space–time

      S Aygün M Aygün I Tarhan

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      Considering the Einstein, Møller, Bergmann–Thomson, Landau–Lifshitz (LL), Papapetrou, Qadir–Sharif and Weinberg's definitions in general relativity, we find the momentum four-vector of the closed Universe based on Marder space–time. The momentum four-vector (due to matter plus field) is found to be zero. These results support the viewpoints of Banerjee–Sen, Xulu and Aydoġdu–Saltı. Another point is that our study agrees with the previous works of Cooperstock–Israelit, Rosen, Johri et al.

    • Unified approach to photo- and electro-production of mesons with arbitrary spins

      G Ramachandran M S Vidya J Balasubbramanyam

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      A new approach to identify the independent amplitudes along with their partial wave multipole expansions, for photo- and electro-production is suggested, which is generally applicable to mesons with arbitrary spin-parity. These amplitudes facilitate direct identification of different resonance contributions.

    • Optimization of C5+ Balmer-𝛼 line intensity at 182 Å from laser-produced carbon plasma

      A Chowdhury R A Joshi P A Naik P D Gupta

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      Parametric dependence of the intensity of 182 Å Balmer-𝛼 line $(C^{5+}; n = 3 \rightarrow 2)$, relevant to xuv soft X-ray lasing schemes, from laser-produced carbon plasma is studied in circular spot focusing geometry using a flat field grating spectrograph. The maximum spectral intensity for this line in space integrated mode occurred at a laser intensity of $1.2 \times 10^{13}$ W cm-2. At this laser intensity, the space resolved measurements show that the spectral intensity of this line peaks at $\sim 1.5$ mm from the target surface indicating the maximum population of C5+ ions $(n = 3)$, at this distance. From a comparison of spatial intensity variation of this line with that of C5+ Ly-𝛼 $(n = 2 \rightarrow 1)$ line, it is inferred that $n = 3$ state of C5+ ions is predominantly populated through three-body recombination pumping of C$^{6+}$ ions of the expanding plasma consistent with quantitative estimates on recombination rates of different processes.

    • Synthesis of carbon nanotubes by catalytic vapor decomposition (CVD) method: Optimization of various parameters for the maximum yield

      Kanchan M Samant Santosh K Haram Sudhir Kapoor

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      This paper describes an effect of flow rate, carrier gas (H2, N2 and Ar) composition, and amount of benzene on the quality and the yield of carbon nanotubes (CNTs) formed by catalytical vapour decomposition (CVD) method. The flow and mass control of gases and precursor vapors respectively were found to be interdependent and therefore crucial in deciding the quality and yield of CNTs. We have achieved this by modified soap bubble flowmeter, which controlled the flow rates of two gases, simultaneously. With the help of this set-up, CNTs could be prepared in any common laboratory. Raman spectroscopy indicated the possibilities of formation of single-walled carbon nanotubes (SWNTs). From scanning electron microscopy (SEM) measurements, an average diameter of the tube/bundle was estimated to be about 70 nm. The elemental analysis using energy dispersion spectrum (EDS) suggested 96 at.wt.% carbon along with ca. 4 at.wt. % iron in the as-prepared sample. Maximum yield and best quality CNTs were obtained using H2 as the carrier gas.

    • On non-extensive nature of thermal conductivity

      Ashok Razdan

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      In this paper we study non-extensive nature of thermal conductivity. It is observed that there is similarity between non-extensive entropic index and fractal dimension obtained for the silica aerogel thermal conductivity data at low temperature.

    • Electron–electron interactions and the electrical resistivity of lithium at low temperatures

      O N Awasthi V K Pundhir

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      The electron–electron interactions in lithium metal have been examined keeping in view the recent developments. The contribution of the electron–electron Umklapp scattering processes in the electrical resistivity of lithium at low temperatures has been evaluated using a simplified spherical Fermi surface model with isotropic transition probability. Our values of the electrical resistivity so obtained compare fairly well with the experimental results for lithium.

    • The kinetics of Cr layer coated on TiNi films for hydrogen absorption

      M Singh Vaibhav Kulsherstha Anil Kumar N K Acharaya Y K Vijay

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      The effect of hydrogen absorption on electrical resistance with temperature for TiNi and TiNi–Cr thin films was investigated. The TiNi thin films of thickness 800 Å were deposited at different angles ($\theta = 0^{\circ}, 30^{\circ}, 45^{\circ}, 60^{\circ}$ and $75^{\circ}) under 10$^{−5}$ Torr pressure by thermal evaporation on the glass substrate at room temperature. A layer of Cr of thickness 100 Å was coated on the TiNi thin films. The changing rate of hydrogen absorption increases after Cr layer coating because Cr enhances the catalytic properties of hydrogen absorption in thin films. The rate of hydrogen absorption increases with temperature at lower range but at higher range of temperature it was found to decrease and also it was found that the hydrogen absorption increases with angle of deposition.

    • Giant magnetoresistance of electrodeposited Cu–Co–Ni alloy films

      İ H Karahan Ö F Bakkaloğlu M Bedir

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      Electrodeposition of CuCoNi alloys was performed in an acid–citrate medium. Nickel density parameter was varied in order to analyse its influence on the magnetoresistance. The structure and giant magneto- resistance (GMR) effect of CuCoNi alloys have been investigated. The maximum value for GMR ratio, at room temperature is 1% at a field of 12 kOe, and at 20 K is $2.1$% at a field of 8.5 kOe for 3.1 Ni. The MR ratio of Cu$_{100−y−x}$Co$_{y}$Ni$_{x}$ alloys first increases and then decreases monotonically with increasing Ni content. The GMR and its dependence on magnetic field and temperature were discussed.

    • Electronic structure of hafnium: A Compton profile study

      S Khera S Mathur B L Ahuja

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      In this paper, we report the first-ever isotropic Compton profile of hafnium measured at an intermediate resolution, with 661.65 keV 𝛾-radiation. To compare our experimental data, the theoretical computations have also been carried out within the framework of pseudopotential using CRYSTAL03 code and the renormalized-free-atom (RFA) model. It is found that the present experimental profile is in better agreement with the RFA calculations if the outer electronic configuration is chosen as 5d3.26s0.8. The cohesive energy of Hf is also deduced from the experimental data and is compared with the available data.

    • Experimental investigation of the response of a harmonically excited hard Duffing oscillator

      N S Patil A K Malik

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      A single degree-of-freedom torsional vibratory system, which constitutes a third-order dissipative dynamical system, has been fabricated as a mechanical analogue of hard Duffing equation with strong nonlinearity. The forced response of the system reveals complicated and chaotic motion at low frequency regime. Besides usual jump phenomenon, unpredictable jump phenomenon with two and three coexisting periodic attractors is also observed.

    • Shape evolution in 76,78Kr nuclei at high spins in tilted axis cranking Hartree–Fock–Bogoliubov approach

      A Ansari P Sharma U R Jakhar H L Yadav

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      A two-dimensional tilted axis cranking Hartree–Fock–Bogoliubov (CHFB) calculation is performed for 76Kr and 78Kr nuclei up to high spins $J = 30$ employing a pairing-plus-quadrupole (PPQ) model interaction Hamiltonian. Intricate details of the evolution of single particle structures and shapes as a function of spin have been investigated. The results show the existence of energy levels with high 𝐾 quantum numbers lying close to the yrast line in both the nuclei. Such high 𝐾 states should exhibit isomeric characteristics due to the 𝐾-selection rules for the 𝛾-decays. Moreover, in 78Kr a new band with $J = 20–30$ lying below the observed ground band is predicted.

    • Odd–even effect in fragment angular momentum in low-energy fission of actinides

      B S Tomar R Tripathi A Goswami

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      Quantitative explanation for the odd–even effect on fragment angular momenta in the low-energy fission of actinides have been provided by taking into account the single particle spin of the odd proton at the fragment's scission point deformation in the case of odd-𝑍 fragments along with the contribution from the population of angular momentum bearing collective vibrations of the fissioning nucleus at scission point. The calculated fragment angular momenta have been found to be in very good agreement with the experimental data for fragments in the mass number region of 130–140. The odd–even effect observed in the fragment angular momenta in the low-energy fission of actinides has been explained quantitatively for the first time.

    • Linear delta expansion technique for the solution of anharmonic oscillations

      P K Bera J Datta

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      The linear delta expansion technique has been developed for solving the differential equation of motion for symmetric and asymmetric anharmonic oscillators. We have also demonstrated the sophistication and simplicity of this new perturbation technique.

    • Diffusion-induced parametric dispersion and amplification in doped semiconductor plasmas

      N Yadav S Ghosh

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      Using the hydrodynamic model of semiconductor plasma, the diffusion-induced nonlinear current density and the consequent second-order effective susceptibility are obtained under off-resonant laser irradiation. The analysis deals with the qualitative behaviour of the anomalous parametric dispersion and the gain profile with respect to the excess doping concentration and pump electric field. The analysis suggests that a proper selection of doping level and pump field may lead to either positive or negative enhanced parametric dispersion, which can be of great use in the generation of sequeezed states. It is found that gain maximizes at moderate doping concentration level, which may drastically reduce the fabrication cost of parametric amplifier based on this interaction.

    • Analysis of thermal expansivity of iron (Fe) metal at ultra high temperature and pressure

      Deepika Kandpal B R K Gupta

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      In the present investigation we have explained the thermal and compression properties of HCP iron (Fe) at high pressure with variable temperature (isobars) and at high temperature with variable pressure (isotherm). The usual Tait equation of state is modified by incorporating the effect of thermal pressure. The calculated values of pressure for different isotherms and isochors and thermal expansivity (𝛼) as a function of both temperature and pressure have been compared with those values obtained by Isaak et al and Wasserman et al.

    • Corrosion behavior of low energy, high temperature nitrogen ion-implanted AISI 304 stainless steel

      M Ghorannevis A Shokouhy M M Larijani S H Haji Hosseini M Yari A Anvari M Gholipur Shahraki A H Sari M R Hantehzadeh

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      This work presents the results of a low-energy nitrogen ion implantation of AISI 304 type stainless steel (SS) at a moderate temperature of about 500° C. The nitrogen ions are extracted from a Kauffman-type ion source at an energy of 30 keV, and ion current density of 100 𝜇A cm-2. Nitrogen ion concentration of $6 \times 10^{17}$, $8 \times 10^{17}$ and 1018 ions cm-2, were selected for our study. The X-ray diffraction results show the formation of CrN polycrystalline phase after nitrogen bombardment and a change of crystallinity due to the change in nitrogen ion concentration. The secondary ion mass spectrometry (SIMS) results show the formation of CrN phases too. Corrosion test has shown that corrosion resistance is enhanced by increasing nitrogen ion concentration.

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