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      Volume 72, Issue 5

      May 2009,   pages  765-914

    • Complementarity controversy in wave–particle duality revisited

      D Sen

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      On the face of some recent experiments claiming the simultaneous presence of both `sharp interference' and `highly reliable which way information' and some others casting light on the origin of complementarity in quantum interferometric experiments, the whole issue is reviewed on the basis of our earlier precise formulation of Bohr's complementarity principle. It is pointed out that contradicting the principle (in this specific formulation) is impossible without contradicting quantum mechanics and a lack of general consensus regarding the origin of the mutual exclusiveness is at the root of the controversy and confusions.

    • Quantum-classical correspondence of the Dirac equation with a scalar-like potential

      Mai-Lin Liang Shun-Lin Shu Bing Yuan

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      Quantum matrix elements of the coordinate, momentum and the velocity operator for a spin-1/2 particle moving in a scalar-like potential are calculated. In the large quantum number limit, these matrix elements give classical quantities for a relativistic system with a position-dependent mass. Meanwhile, the Klein–Gordon equation for the spin-0 particle is discussed too. Though the Heisenberg equations for both the spin-0 and spin-1/2 particles are unlike the classical equations of motion, they go to the classical equations in the classical limit.

    • Bianchi Type V magnetized string dust cosmological models with Petrov-type degenerate

      Raj Bali Umesh K Pareek

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      Bianchi Type V massive string cosmological models with free gravitational field of Petrov Type degenerate in the presence of magnetic field with variable magnetic permeability are investigated. The magnetic field is due to an electric current produced along the 𝑥-axis. The $F_{23}$ is the only non-vanishing component of electromagnetic field tensor $F_{ij}$. Maxwell's equations $F_{[ij;k]} = 0$ and $F_{ij}^{ij} = 0$ are satisfied by $F_{23}$ = constant. The behaviour of the model in the presence and absence of magnetic field and other physical aspects are also discussed.

    • Experimental studies of the transient fluctuation theorem using liquid crystals

      Soma Datta Arun Roy

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      In a thermodynamical process, the dissipation or production of entropy can only be positive or zero, according to the second law of thermodynamics. However, the laws of thermodynamics are applicable to large systems in the thermodynamic limit. Recently a fluctuation theorem, known as the transient fluctuation theorem (TFT), which generalizes the second law of thermodynamics to small systems has been proposed. This theorem has been tested in small systems such as a colloidal particle in an optical trap. We report for the first time an analogous experimental study of TFT in a spatially extended system using liquid crystals.

    • Superfield approach to symmetry invariance in quantum electrodynamics with complex scalar fields

      R P Malik B P Mandal

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      We show that the Grassmannian independence of the super-Lagrangian density, expressed in terms of the superfields defined on a $(4,2)$-dimensional supermanifold, is a clear-cut proof for the Becchi–Rouet–Stora–Tyutin (BRST) and anti-BRST invariance of the corresponding four $(3+1)$-dimensional (4D) Lagrangian density that describes the interaction between the $U(1)$ gauge field and the charged complex scalar fields. The above 4D field theoretical model is considered on a $(4,2)$-dimensional supermanifold para- metrized by the ordinary four space-time variables $x^{\mu}$ (with $\mu = 0, 1, 2, 3$) and a pair of Grassmannian variables 𝜃 and $\bar{\theta}$ (with $\theta^{2} = \bar{\theta}^{2} = 0$, $\theta\bar{\theta} + \bar{\theta}\theta = 0$). Geometrically, the (anti-)BRST invariance is encoded in the translation of the super-Lagrangian density along the Grassmannian directions of the above supermanifold such that the outcome of this shift operation is zero.

    • Multiple recycling of fuel in prototype fast breeder reactor

      G Pandikumar V Gopalakrishnan P Mohanakrishnan

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      In a thermal neutron reactor, multiple recycle of U–Pu fuel is not possible due to degradation of fissile content of Pu in just one recycle. In the FBR closed fuel cycle, possibility of multi-recycle has been recognized. In the present study, Pu-239 equivalence approach is used to demonstrate the feasibility of achieving near constant input inventory of Pu and near stable Pu isotopic composition after a few recycles of the same fuel of the prototype fast breeder reactor under construction at Kalpakkam. After about five recycles, the cycle-to-cycle variation in the above parameters is below 1%.

    • Electric field distribution and simulation of avalanche formation due to the passage of heavy ions in a parallel grid avalanche counter

      D Kanjilal S Saha

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      Electric field distributions and their role in the formation of avalanche due to the passage of heavy ions in parallel grid avalanche type wire chamber detectors are evaluated using a Monte Carlo simulation. The relative merits and demerits of parallel and crossed wire grid configurations are studied. It is found that the crossed grid geometry has marginally higher gain at larger electric fields close to the avalanche region. The spatial uniformity of response in the two wire grid configurations is also compared.

    • Stability of gold cages (Au16 and Au17) at finite temperature

      Prachi Chandrachud Kavita Joshi Sailaja Krishnamurty D G Kanhere

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      We have employed ab initio molecular dynamics to investigate the stability of the smallest gold cages, namely Au16 and Au17, at finite temperatures. First, we obtain the ground state structure along with at least 50 distinct isomers for both the clusters. This is followed by the finite temperature simulations of these clusters. Each cluster is maintained at 12 different temperatures for a time period of at least 150 ps. Thus, the total simulation time is of the order of 2.4 ns for each cluster. We observe that the cages are stable at least up to 850 K. Although both clusters melt around the same temperature, i.e. around 900 K, Au17 shows a peak in the heat capacity curve in contrast to the broad peak seen for Au16.

    • Self-interstitial configuration in molybdenum studied by modified analytical embedded atom method

      Jian-Min Zhang Zhang Fang Wang Ke-Wei Xu

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      The stability of various atomic configurations containing a self-interstitial atom (SIA) in a model representing Mo has been investigated using the modified analytical embedded atom method (MAEAM). The lattice relaxations are treated with the molecular dynamics (MD) simulation at absolute zero of temperature. Six relatively stable self-interstitial configurations and formation energies have been described and calculated. The results indicate that the [1 1 1] dumbbell interstitial S111 has the lowest formation energy, and in ascending order, the sequence of the configurations is predicted to be S111, C, S110, T, S001 and O. From relaxed displacement field up to the fifth-NN atoms of six configurations, we know that the relaxed displacements depend not only on separation distances of the NN atoms from the defect centre but also strongly on the direction of the connected line between the NN atoms and the defect centre. The equilibrium distances between two nearest atoms in the core of the S111, C, S110, T, S001 and O configurations are $0.72a, 0.72a, 0.71a, 0.72a, 0.70a$ and $0.70a$, respectively.

    • Crystal growth, electrical and photophysical properties of Tl2S layered single crystals

      A M Badr H A Elshaikh I M Ashraf

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      The Tl2S compound was prepared in a single crystal form using a special local technique, and the obtained crystals were analysed by X-ray diffraction. For the resultant crystals, the electrical properties (electrical conductivity and Hall effect) and steady-state photoconductivity were elucidated in this work. The electrical measurements extend from 170 to 430 K, where it was found that $\sigma_{\perp} = 8.82 \times 10^{−5}$ Sm-1 when current flow direction makes right angle to the cleavage plane of the crystals. In the same range of temperatures, it was found that $\sigma_{\parallel} = 4.73 \times 10^{−5}$ Sm-1 when the current flow is parallel to the cleavage plane. In line with the investigated range of temperatures, the widths of the band gaps were calculated and discussed as also the results of the electrical conductivity and Hall effect measurements. In addition, the anisotropy of the electrical conductivity $(\sigma_{\perp} / \sigma_{\parallel})$ for the obtained crystals was also studied in this work. Finally the photosensitivity was calculated for different levels of illumination as a result of the photoconductivity measurements, which showed that the recombination process in Tl2S single crystals is a monomolecular process.

    • Inter-dot coupling effects on transport through correlated parallel coupled quantum dots

      Shyam Chand G Rajput K C Sharma P K Ahluwalia

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      Transport through symmetric parallel coupled quantum dot system has been studied, using non-equilibrium Green function formalism. The inter-dot tunnelling with on-dot and inter-dot Coulomb repulsion is included. The transmission coefficient and Landaur–Buttiker like current formula are shown in terms of internal states of quantum dots. The effect of inter-dot tunnelling on transport properties has been explored. Results, in intermediate inter-dot coupling regime show signatures of merger of two dots to form a single composite dot and in strong coupling regime the behaviour of the system resembles the two decoupled dots.

    • Inflation with hyperbolic potential in the braneworld model

      Dilip Paul Bikash Chandra Paul Xin-He Meng

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      In this paper we study inflationary dynamics with a scalar field in an inverse coshyperbolic potential in the braneworld model. We note that a sufficient inflation may be obtained with the potential considering slow-roll approximation in the high energy limit. We determine the minimum values of the initial inflaton field required to obtain sufficient inflation and also determine the relevant inflationary parameters. The numerical values of spectral index of the scalar perturbation spectrum are determined by varying the number of e-foldings for different initial values of the inflaton field. The result obtained here is in good agreement with the current observational limits.

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