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      Volume 74, Issue 4

      April 2010,   pages  491-673

    • Observability of the effects of curl-free magnetic vector potential on the macroscale and the nature of the ‘transition amplitude wave’

      Ram K Varma

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      We discuss here the prediction, based on a formalism by the author, on the observable effects of a curl-free magnetic vector potential on the macroscale as against the microscale of the Aharonov–Bohm effect. A new quantum concept – the ‘transition amplitude wave’ – postulated in the formalism has already been shown to exhibit matter wave manifestations in the form of one-dimensional interference effects on the macroscale. It was predicted by the formalism that the same entity would lead to the detection of a curl-free magnetic vector potential on the macroscale. We describe here the manner of generation of this quantum entity in an inelastic scattering episode and work out an algorithm to observe this radically new phenomenon, the detection of a curl-free magnetic vector potential on the macroscale. We determine the various characteristic features of such an observation which can then be looked for experimentally so as to verify the predicted effect, establishing thereby the physical reality of the new quantum entity, and to fully validate the formalism predicting it. It is also shown that this ‘transition amplitude wave’ can be regarded as a novel kind of ‘quasiparticle’ excited in the charged particle trajectory as a consequence of the scattering episode.

    • Relativistic star solutions in higher-dimensional pseudospheroidal space-time

      P K Chattopadhyay B C Paul

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      We obtain relativistic solutions of a class of compact stars in hydrostatic equilibrium in higher dimensions by assuming a pseudospheroidal geometry for the space-time. The space-time geometry is assumed to be ($D - 1$) pseudospheroid immersed in a 𝐷-dimensional Euclidean space. The spheroidicity parameter (𝜆) plays an important role in determining the equation of state of the matter content and the maximum radius of such stars. It is found that the core density of compact objects is approximately proportional to the square of the space-time dimensions (𝐷), i.e., core of the star is denser in higher dimensions than that in conventional four dimensions. The central density of a compact star is also found to depend on the parameter 𝜆. One obtains a physically interesting solution satisfying the acoustic condition when 𝜆 lies in the range $\lambda$ > $(D + 1)/(D − 3)$ for the space-time dimensions ranging from $D = 4$ to 8 and $(D + 1)/(D − 3)$ < $\lambda$ < ($D^{2} - 4D + 3$)/($D^{2} - 8D - 1$) for space-time dimensions $\geq 9$. The non-negativity of the energy density (𝜌) constrains the parameter with a lower limit (> 1). We note that in the case of a superdense compact object the number of space-time dimensions cannot be taken infinitely large, which is a different result from the braneworld model.

    • Structure of negative parity yrast bands in odd mass 125-131Ce nuclei

      Arun Bharti Suram Singh S K Khosa

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      The negative parity yrast bands of neutron-deficient 125-131Ce nuclei are studied by using the projected shell model approach. Energy levels, transition energies and $B(M1)/B(E2)$ ratios are calculated and compared with the available experimental data. The calculations reproduce the band-head spins of negative parity yrast bands and indicate the multi-quasiparticle structure for these bands.

    • The investigation of $0^{+} \leftrightarro 0^{−} \beta$ decay in some spherical nuclei

      Necla Cakmak Kaan Manisa Serdar Unlu Cevad Selam

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      The $0^{+} \leftrightarrow 0^{−}$ first-forbidden 𝛽 decay transitions have been investigated for some spherical nuclei. The theoretical framework is based on a proton–neutron quasiparticle random phase approximation (pnQRPA). The Woods–Saxon potential basis has been used in our calculations. The transition probabilities have been calculated within the 𝜉 approximation. The relativistic 𝛽 moment matrix element has been calculated both directly without any assumption and assuming that it is proportional to the non-relativistic one.

    • Effective atomic numbers of some H-, C-, N- and O-based composite materials derived from differential incoherent scattering cross-sections

      S Prasanna Kumar V Manjunathaguru T K Umesh

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      In this work, we have made an effort to determine whether the effective atomic numbers of H-, C-, N- and O-based composite materials would indeed remain a constant over the energy grid of 280–1200 keV wherein incoherent scattering dominates their interaction with photons. For this purpose, the differential incoherent scattering cross-sections of Be, C, Mg, Al, Ca and Ti were measured for three scattering angles 60°, 80° and 100° at 279.1, 661.6 and 1115.5 keV using which an expression for the effective atomic number was derived. The differential incoherent scattering cross-sections of the composite materials of interest measured at these three angles in the same set-up and substituted in this expression would yield their effective atomic number at the three energies. Results obtained in this manner for bakelite, nylon, epoxy, teflon, perspex and some sugars, fatty acids as well as amino acids agreed to within 2% of some of the other available values. It was also observed that for each of these samples, $Z_{\text{eff}}$ was almost a constant at the three energies which unambiguously justified the conclusions drawn by other authors earlier [Manjunathaguru and Umesh, J. Phys. B: At. Mol. Opt. Phys. 39, 3969 (2006); Manohara et al, Nucl. Instrum. Methods B266, 3906 (2008); Manohara et al Phys. Med. Biol. 53, M377 (2008)] based on total interaction cross-sections in the energy grid of interest.

    • Measurement of the bremsstrahlung spectra generated from thick targets with $Z=2–78$ under the impact of 10 keV electrons

      Namita Yadav Pragya Bhatt Raj Singh V S Subrahmanyam R Shanker

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      We present new experimental data on thick target bremsstrahlung spectra generated from the interaction of energetic electrons with bulk matter. The ‘photon yields’ in terms of double differential cross-sections (DDCS) are measured for pure elements of thick targets: Ti ($Z = 22$), Ag ($Z = 47$), W ($Z = 74$) and Pt ($Z = 78$) under the impact of 10 keV electrons. Comparison of DDCS obtained from the experimental data is made with those predicted by Monte-Carlo (MC) calculations using PENELOPE code. A close agreement between the experimental data and the MC calculations is found for all the four targets within the experimental error of 16%. Furthermore, the ratios of DDCS of bremsstrahlung photons emitted from Ag, W and Pt with those from Ti as a function of photon energy are examined with a relatively lower uncertainty of about 10% and they are compared with MC calculations. A satisfactory agreement is found between the experiment and the calculations within some normalizing factors. The variations of DDCS as a function of Z and of photon energy are also studied which show that the DDCS vary closely with Z; however, some deviations are observed for ‘tip’ photons emitted from high Z targets.

    • Switching behaviour of a nonlinear Mach–Zehnder interferometer

      Arpita Srivastava Punya Prasanna Paltani S Medhekar

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      In the present paper, a detailed investigation on the switching behaviour of a nonlinear Mach–Zehnder interferometer (NMZI) has been carried out using beam propagation method (BPM). A thorough investigation on input vs. output characteristic has been carried out by varying different parameters like length of the arms, refractive index of the linear/nonlinear arm, wavelength of the input beams and nonlinear coefficient of the material of the nonlinear arm. The input vs. output characteristic has also been investigated by shifting the balance point of the NMZI. The present paper provides a physically intuitive understanding of the effect of change in different parameters of the NMZI on its switching behaviour.

    • Investigation of bending loss in a single-mode optical fibre

      A Zendehnam M Mirzaei A Farashiani L Horabadi Farahani

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      Loss of optical power in a single-mode optical fibre due to bending has been investigated for a wavelength of 1550 nm. In this experiment, the effects of bending radius (4–15 mm, with steps of 1 mm), and wrapping turns (up to 40 turns) on loss have been studied. Twisting the optical fibre and its influence on power loss also have been investigated.

      Variations of bending loss with these two parameters have been measured, loss with number of turns and radius of curvature have been measured, and with the help of computer curve fitting method, semi-empirical relationships between bending loss and these two parameters have been found, which show good agreement with the obtained experimental results.

    • Kadomstev–Petviashvili (KP) equation in warm dusty plasma with variable dust charge, two-temperature ion and nonthermal electron

      Hamid Reza Pakzad

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      In this work, the propagation of nonlinear waves in warm dusty plasmas with variable dust charge, two-temperature ion and nonthermal electron is studied. By using the reductive perturbation theory, the Kadomstev–Petviashvili (KP) equation is derived. The energy of the soliton and the linear dispersion relation are obtained. The effects of variable dust charge on the energy of soliton and the angular frequency of linear wave are also discussed.

    • Many-body Hamiltonian with screening parameter and ionization energy

      Andrew Das Arulsamy

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      We prove the existence of a Hamiltonian with ionization energy as part of the eigenvalue, which can be used to study strongly correlated matter. This eigenvalue consists of total energy at zero temperature ($E_{0}$) and the ionization energy (𝜉). We show that the existence of this total energy eigenvalue, $E_{0} \pm \xi$, does not violate the Coulombian atomic system. Since there is no equivalent known Hamilton operator that corresponds quantitatively to 𝜉, we employ the screened Coulomb potential operator (Yukawa-type), which is a function of this ionization energy to analytically calculate the screening parameter (𝜎) of a neutral helium atom in the ground state. In addition, we also show that the energy level splitting due to spin-orbit coupling is inversely proportional to 𝜉 eigenvalue, which is also important in the field of spintronics.

    • On the excited state wave functions of Dirac fermions in the random gauge potential

      H Milani Moghaddam

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      In the last decade, it was shown that the Liouville field theory is an effective theory of Dirac fermions in the random gauge potential (FRGP). We show that the Dirac wave functions in FRGP can be written in terms of descendents of the Liouville vertex operator. In the quasiclassical approximation of the Liouville theory, our model predicts 22.2 that the localization length 𝜉 scales with the energy 𝐸 as $\xi \sim E^{−b^{2}(1+b^{2})^{2}}$, where 𝑏 is the strength of the disorder. The self-duality of the theory under the transformation $b \rightarrow 1/b$ is discussed. We also calculate the distribution functions of $t_{0} = |\psi_{0} (x)|^{2}$, (i.e. $p(t_{0}$); $\psi_{0}(x)$ is the ground state wave function), which behaves as the log-normal distribution function. It is also shown that in small $t_{0}$, $p(t_{0})$ behaves as a chi-square distribution.

    • Theoretical study of the electron paramagnetic resonance parameters and local structure for the tetragonal Ir2+ centre in NaCl

      Y-X Hu S-Y Wu X-F Wang P Xu

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      The electron paramagnetic resonance (EPR) parameters (the 𝑔 factors, hyperfine structure constants and the superhyperfine parameters) for the tetragonal Ir2+ centre in NaCl are theoretically investigated from the perturbation formulas of these parameters for a 5d7 ion in tetragonally elongated octahedra. This impurity centre is attributed to the substitutional [IrCl6]4- cluster on host Na+ site, associated with the 4% relative elongation along the $C_{4}$-axis due to the Jahn–Teller effect. Despite the ionicity of host NaCl, the [IrCl6]4- cluster still exhibits moderate covalency and then the ligand orbital and spin-orbit coupling contributions should be taken into account. In addition, the theoretical EPR parameters based on the Jahn–Teller elongation show good agreement with the observed values.

    • Density functional study of ferromagnetism in alkali metal thin films

      Prasenjit Sen

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      Electronic and magnetic structures of (1 0 0) films of K and Cs, having thicknesses of one to seven layers, are calculated within the plane-wave projector augmented wave (PAW) formalism of the density functional theory (DFT), using both local spin density approximation (LSDA) and the PW91 generalized gradient approximation (GGA). Only a six-layer Cs film is found to have a ferromagnetic (FM) state which is degenerate with a paramagnetic (PM) state within the accuracy of these calculations. These results are compared with those obtained from calculations on a finite-thickness uniform jellium model (UJM), and it is argued that within LSDA or GGA, alkali metal thin films cannot be claimed to have an FM ground state. Relevance of these results to the experiments on transition metal-doped alkali metal thin films and bulk hosts are also discussed.

    • Non-intrusive refractometer sensor

      Pabitra Nath

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      An experimental realization of a simple non-intrusive refractometer sensor is demonstrated in this communication. The working principle of the sensor is based on intensity modulation of the back-reflected light when output light from an optical fibre end focusses onto air–medium interface. The change in the refractive index of the medium affects the reflectance of the incident light signal and thus modulates the back-reflected signal. Refractive index variation as small as 0.002 RIU can be measured using the present technique. The advantages of the technique are its simplicity, cost efficiency and usefulness in monitoring refractive indices of acidic solutions.

    • Einstein–Rosen inflationary Universe in general relativity

      S D Katore R S Rane K S Wankhade N K Sarkate

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      Einstein–Rosen inflationary Universe is investigated in the presence of mass-less scalar field with a flat potential. To get an inflationary Universe, we have considered a flat region in which the potential V is constant. Some physical properties of the model are discussed.

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