• Volume 69, Issue 2

August 2007,   pages  159-316

• Bianchi Type-I, V and VIo models in modified generalized scalar–tensor theory

In modified generalized scalar–tensor (GST) theory, the cosmological term 𝛬 is a function of the scalar field 𝜙 and its derivatives $\dot{\phi}^{2}$. We obtain exact solutions of the field equations in Bianchi Type-I, V and VIo space–times. The evolution of the scale factor, the scalar field and the cosmological term has been discussed. The Bianchi Type-I model has been discussed in detail. Further, Bianchi Type-V and VIo models can be studied on the lines similar to Bianchi Type-I model.

• Regge behaviour of distribution functions and 𝑡 and 𝑥-evolutions of gluon distribution function at low-𝑥

In this paper, 𝑡 and 𝑥-evolutions of gluon distribution function from Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGLAP) evolution equation in leading order (LO) at low-𝑥 are presented assuming the Regge behaviour of quarks and gluons at this limit. We compare our results of gluon distribution function with MRST 2001, MRST 2004 and GRV 1998 parametrizations and show the compatibility of Regge behaviour of quark and gluon distribution functions with perturbative quantum chromodynamics (PQCD) at low-𝑥. We also discuss the limitations of Taylor series expansion method used earlier to solve DGLAP evolution equations in the Regge behaviour of distribution functions.

• $q\bar{q}$ Pair production in non-Abelian gauge fields

We calculate the $q\bar{q}$ pair production probability in the colour-flux tube model by considering the effect of non-Abelian interactions in the theory. Non-Abelian interactions in the colour field are time-dependent and hence should oscillate with a characteristic frequency $\omega_{0}$ , which depends on the amplitude of the field strength. Using the WKB approximation in complex time, we calculated the pair production probability. When the strength of the field is comparable to the quark masses, the corresponding pair creation probability is maximum, and for the static field $w_{0} \rightarrow 0$, we recovered the well-known Schwinger result.

• Single-sheet identification method of heavy charged particles using solid state nuclear track detectors

The theoretical and experimental investigations of the penetration of charged particles in matter played a very important role in the development of modern physics. Solid state nuclear track detectors have become one of the most important tools for many branches of science and technology. An attempt has been made to examine the suitability of the single-sheet particle identification technique in CR-39 and CN-85 polycarbonate by plotting track cone length vs. residual range for different heavy ions in these detectors. So, the maximum etchable ranges of heavy ions such as 93Nb, 86Kr and 4He in CR-39 and 4He and 132Xe in CN-85 polycarbonate have been determined. The ranges of these ions in these detectors have also been computed theoretically using the Henke–Benton program. A reasonably good agreement has been observed between the experimentally and theoretically computed values.

• Measurement of mass attenuation coefficients in some Cr, Co and Fe compounds around the absorption edge and the validity of the mixture rule

The total mass attenuation coefficients for elements Cr, Co and Fe and compounds CrCl2, CrCl3, Cr2(SO4)$_{3}𝐾_{2}$SO4·24H2O, CoO, CoCl2, Co(CH3COO)2, FePO4, FeCl3·6H2O, Fe(SO4)2NH4·12H2O were measured at different energies between 4.508 and 14.142 keV using secondary excitation method. Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr were chosen as secondary exciters. 59.5 keV 𝛾-rays emitted from a 241Am annular source were used to excite a secondary exciter and K$_{\alpha}$ (K-L3, L2) lines emitted by the secondary exciter were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. It was observed that mixture rule method is not a suitable method for determination of the mass attenuation coefficients of compounds, especially at an energy that is near the absorption edge. The obtained values were compared with theoretical values.

• Collision strengths for transitions in Ni XIX

In this paper we present calculations of electron impact excitation collision strengths for transitions among the 89 fine-structure levels of the 2s22p6, 2s22p53$\ell$, 2s2p63$\ell$, 2s22p54$\ell$, and 2s2p64$\ell$ configurations of Ni XIX, for which flexible atomic code (FAC) has been adopted. Comparisons are made with the earlier available results in the literature, and the anomalies observed have been discussed.

• Single-photon all-optical switching using coupled microring resonators

We study the nonlinear phase response of a microring resonator coupled to a bus waveguide and the use of this nonlinear phase shift to store information in the microring resonator and enhance the switching characteristics of a Mach–Zehnder interferometer (MZI). By introducing coupling between adjacent microring resonators, the switching characteristics of the MZI can be exponentially enhanced as a function of the number of microring resonators, when compared to the linear enhancement for uncoupled resonators. With only a few moderate-finesse microring resonators, the switching power can be reduced to attowatt level, allowing for photonic switching devices that operate at single-photon level in ordinary optical waveguides.

• Nonlinearity management and diffraction management for the stabilization of two-dimensional spatial solitons

The nonlinear Schrödinger equation which governs the dynamics of two-dimensional spatial solitons in Kerr media with periodically varying diffraction and nonlinearity has been analyzed in this paper using variational approach and numerical studies. Analytical expressions for soliton parameters have been derived using variational analysis. Variational equations and partial differential equation have been simulated numerically. Analytical and numerical studies have shown that nonlinearity management and diffraction management stabilize the pulse against decay or collapse providing undisturbed propagation even for larger energies of the incident beam.

• Propagation of ion-acoustic waves in a dusty plasma with non-isothermal electrons

For an unmagnetised collisionless plasma consisting of warm ions, non-isothermal electrons and cold, massive and charged dust grains, the Sagdeev potential equation, considering both ion dynamics and dust dynamics has been derived. It has been observed that the Sagdeev potential $V (\phi)$ exists only for $\phi &gt; 0$ up to an upper limit $(\phi \simeq 1.2)$. This implies the possibility of existence of compressive solitary wave in the plasma. Exhaustive numerics done for both the large-amplitude and small-amplitude ion-acoustic waves have revealed that various parameters, namely, ion temperature, non-isothermality of electrons, Mach numbers etc. have considerable impact on the amplitude as well as the width of the solitary waves. Dependence of soliton profiles on the ion temperature and the Mach number has also been graphically displayed. Moreover, incorporating dust-charge fluctuation and non-isothermality of electrons, a non-linear equation relating the grain surface potential to the electrostatic potential has been derived. It has been solved numerically and interdependence of the two potentials for various ion temperatures and orders of non-isothermality has been shown graphically.

• Atomic displacements due to interstitial hydrogen in Cu and Pd

The density functional theory (DFT) is used to study the atomic interactions in transition metal-based interstitial alloys. The strain field is calculated in the discrete lattice model using Kanzaki method. The total energy and hence atomic forces between interstitial hydrogen and transition metal hosts are calculated using DFT. The norm-conserving pseudopotentials for H, Cu and Pd are generated self-consistently. The dynamical matrices are evaluated considering interaction up to first nearest neighbors whereas impurity-induced forces are calculated with M32H shell (where M = Cu and Pd). The atomic displacements produced by interstitial hydrogen at the octahedral site in Cu and Pd show displacements of $7.36$% and $4.3$% of the first nearest neighbors respectively. Both Cu and Pd lattices show lattice expansion due to the presence of hydrogen and the obtained average lattice expansion $\Delta V /V = 0.177$ for Cu and 0.145 for Pd.

• Appearance of an inhomogeneous superconducting state in La0.67Sr0.33MnO3–YBa2Cu3O7–La0.67Sr0.33MnO3 trilayers

An experimental study of proximity effect in La0.67Sr0.33MnO3–YBa2Cu3O7–La0.67Sr0.33MnO3 trilayers is reported. Transport measurements on these samples show clear oscillations in critical current ($I_{c}$) as the thickness of La0.67Sr0.33MnO3 layers ($d_{F}$) is scanned from $\sim 50$ Å to $\sim 1100$ Å. In the light of existing theories of ferromagnet–superconductor (FM–SC) heterostructures, this observation suggests a long range proximity effect in the manganite, modulated by its weak exchange energy ($\sim 2$ meV). The observed modulation of the magnetic coupling between the ferromagnetic LSMO layers as a function of $d_{F}$, also suggests an oscillatory behavior of the SC order parameter near the FM–SC interface.

• Synthesis and characterization of silica–gold core-shell (SiO$_{2} \@$ Au) nanoparticles

This paper reports a systematic investigation of the growth and attachment of small gold nanoparticles to the functionalized surface of larger silica nanoparticles by three different methods. Nearly monodispersed silica particles and gold nanoparticles were prepared by sol–gel method. The size of the particle could be altered by changing the concentration of reactants, temperature and the time for which they react. The nanocore-shell particles prepared by three different methods were studied using scanning electron microscopy (SEM), UV–vis spectroscopy and Fourier transform infrared spectroscopy. We have found that the third method (c), a combination of the first two methods (a) and (b), has given better results.

• Theoretical approach to the magnetic properties of Mn(II), Cr(III), and Cu(II) complexes in the newly reported 12- and 15-membered macrocyclic ligands

The magnetic properties of Cu2+, Cr3+, and Mn2+ ions in the newly reported 12- and 15-membered macrocyclic complexes are analysed by a theoretical approach. The calculated magnetic moment and magnetic anisotropy for various situations, especially for Cu(II) ion, suggest that the magnetic properties may lead to a better interpretation about the geometry. It is also suggested that the zero-field splitting Hamiltonian may be used for magnetic properties of some metal ions, which have orbital singlet ground term in these complexes.

• Equation of state for inert gas solids

The equation of state is a fundamental relation to analyse the thermophysical properties of different class of solids and it plays a key role in basic and applied condensed matter physics research. A lot of work has been done in the field of ionic solids, minerals and metals but a very little work is done in the field of inert gas solids. Most of the equations of state failed to explain the properties of inert gas solid because of their abnormal behavior in the low temperature range. In the present paper, Singh–Gupta equation of state has been used to study the properties of these solids. The results obtained using these equations have shown a good agreement with available experimental results. Thus it is shown that these equations of states successfully explain the behavior of inert gas solids.

• Theoretical explanation of electron paramagnetic resonance and optical parameters for Cu2+ ion in LiNbO3 crystal

The EPR parameters, anisotropic 𝑔-factors $g_{x}$, $g_{y}$ and $g_{z}$ for Cu2+ ion and hyperfine structure constants $A_{x}$, $A_{y}$ and $A_{z}$ for Cu2+ in LiNbO3 crystal are calculated by the method of diagonalizing the full Hamiltonian matrix. The crystal-field parameters contact with the crystal structure by the aid of the superposition model. The optical transition parameters are calculated using Zhao crystal-field model. The calculated results are in good agreement with the observed values. The results are discussed.

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