Analysis of radial segregation of granular mixtures in a rotating drum

This paper considers the segregation of a granular mixture in a rotating drum. Extending a recent kinematic model for grain transport on sandpile surfaces to the case of rotating drums, an analysis is presented for radial segregation in the rolling regime, where a thin layer is avalanching down while the rest of the material follows rigid body rotation. We argue that segregation is driven not just by differences in the angle of repose of the species, as has been assumed in earlier investigations, but also by differences in the size and surface properties of the grains. The cases of grains differing only in size (slightly or widely) and only in surface properties are considered, and the predictions are in qualitative agreement with observations. The model yields results inconsistent with the assumptions for more general cases, and we speculate on how this may be corrected. Received 4 June 1999 and Received in final form 28 September 1999     

Scaling behavior of semiclassical gravity

Using the idea of metric scaling we examine the scaling behavior of the stress tensor of a scalar quantum field in curved space-time. The renormalization of the stress tensor results in a departure from naive scaling. We view the process of renormalizing the stress tensor as being equivalent to renormalizing the coupling constants in the Lagrangian for gravity (with terms quadratic in the curvature included). Thus the scaling of the stress tensor is interpreted as a nonnaive scaling of these coupling constants. In particular, we find that the cosmological constant and the gravitational constant approach UV fixed points. The constants associated with the terms which are quadratic in the curvature logarithmically diverge. This suggests that quantum gravity is asymptotically scale invariant.     

Neutral charm production in 400 GeV proton-emulsion interactions

A search has been carried out for neutral charm production in 5,108 proton-emulsion interactions at 400 GeV/c. Nine charm candidates have been observed in our fiducial volume which extends from 100 μm-1,000 μm in the forward cone. One of these is a 4-prong and the others are 2-prong events with opening angle>10 mrad and momenta of both decay tracks>150 MeV/c. Search for associated charm decays was made in an extended fiducial volume around the primary stars of these nine candidates. This yielded two neutral 2-prong events, one associated with the 4-prong and the other with a 2-prong candidate. All unassociated candidates are consistent with being backgrounds due toK _s , Λ decays, neutral interactions and γ conversions whereas the background to associated events is negligible. Based on the two associated decays the inclusive cross section forD ^{0, ?0} production is determined as 27±20 μb/nucleon. Detailed measurements on the 4-prong candidate lead to the identification of one decay track as an electron and another as a kaon. This is interpreted as a semi-leptonic, Cabbibo favouredD ⁰/D ^?0 decay.     

Effect of Dy substitution on structural,magnetic and optical properties of BiFeO3 ceramics

Bi_1−xDy_xFeO₃ (x=0.0, 0.03, 0.05, 0.07, 0.10 and 0.12) ceramics were synthesized by solid state reaction method. Effects of Dy substitution on structural distortion, magnetic and optical properties of BiFeO₃ were examined by X-ray diffraction, Raman and UV–Visible spectroscopy. The samples were found to crystallize in rhombohedral structure of BiFeO₃ with R3c space group. The reduction in lattice parameters and unit cell volume indicate the distortion in FeO₆ octahedra of the rhombohedral structure without any signature of phase transformation up to x=0.12. The predictable weak ferromagnetic hysteresis loops can be observed in the Dy doped samples with maximum remnant magnetization of 0.2103 emu/g for x=0.12. The weak ferromagnetism is ascribed to the suppressed spiral spin structure and magnetically active characteristic of Dy³⁺ ions together with ferromagnetic coupling between Dy³⁺ and Fe³⁺ ions. With optical band gap in visible region, Dy doped BiFeO₃ ceramics are potential material for optoelectronic device and solar cell applications.     

Deep Level Transient Spectroscopy of Defects in High-Energy Light-Particle Irradiated Si

The authors review what has been learned concerning the electrical and annealing properties of point defects in high-energy electron or proton irradiated Si from deep level transient spectroscopy (DLTS). The authors have focused mainly on the properties of electron traps, and to a lesser extent on the properties of hole traps. In addition to an in-depth discussion of hydrogen-related defects in Si, this review article provides a brief tutorial on ion-solid interactions and the theory underlying DLTS. The authors also provide a few examples of the power of high resolution Laplace DLTS in analyzing radiation induced defects. The collection of results gathered in this article may provide the fundamental information for successful defect engineering in light-particle irradiated Si.     

Long term performance evaluation of the TACTIC imaging telescope using ∼400 h Crab Nebula observation during 2003–2010

The TeV atmospheric Cherenkov telescope with imaging camera (TACTIC) γ-ray telescope has been in operation at Mt. Abu, India since 2001 to study TeV γ-ray emission from celestial sources. During the last 10 years, apart from consistently detecting a steady signal from the Crab Nebula above ～1.2 TeV energy, at a sensitivity level of ～5.0 σ in ～25 h, the telescope has also detected flaring activity from Mrk 421 and Mrk 501 on several occasions. Although we used Crab Nebula data partially, in some of the reported results, primarily for testing the validity of the full data analysis chain, the main aim of this work is to study the long term performance of the TACTIC telescope by using consolidated data collected between 2003 and 2010. The total on-source data, comprising ～402 h, yields an excess of ～(3742±192) γ-ray events with a statistical significance of ～19.9 σ. The off-source data, comprising ～107 h of observation, is found to be consistent with a no-emission hypothesis, as expected. The resulting γ-ray rate for the on-source data is determined to be ～(9.31±0.48) h ^?1. A power law fit (dΦ/dE=f ₀ E ^?Γ ) with f ₀ ～ (2.66±0.29) × 10^?11 cm^?2 s^?1 TeV^?1 and Γ ～ 2.56±0.10 is found to provide reasonable fit to the inferred differential spectrum within statistical uncertainties. The spectrum matches reasonably well with that obtained by other groups. A brief summary of the improvements in the various subsystems of the telescope carried out recently, which has resulted in a substantial improvement in its detection sensitivity (viz., ～5 σ in an observation period of ～13 h as compared to ～25 h earlier) are also presented in this paper. Encouraged by the detection of strong γ-ray signals from Mrk 501 and Mrk 421 on several occasions, there is considerable scope for the TACTIC telescope to monitor similar TeV γ-ray emission activity from other active galactic nuclei on a long-term basis.     

Band gap control and photoluminescence properties of Ba(Co2x Ti1−x )O3 thin films prepared by Sol–gel method

This paper reports on the preparation, characterization and optical properties of transparent Ba(Co_2x Ti_1?x )O₃ (0 ≤ x ≤ 0.06) thin films prepared by sol–gel method and deposited on fused quartz substrate by spin-coating technique. Their formation is confirmed by X-ray diffraction patterns, energy dispersive X-ray spectrometry and Fourier transformed infrared measurements. Hitherto unreported near-band-gap photoluminescence in ultraviolet, at 378 nm (3.28 eV), of exciton origin is observed which remains unaffected with change in excitation wavelength from 320 to 350 nm. A weak defect emission appears in green region. For larger excitation wavelength, i.e., 488 nm, emission arising from localized states again occurs in green region but with lower energy. The occurrence of efficient violet–blue PL emission is related to ‘direct’ band gap and shallow levels with high optical band gap values. Analysis of band gap variation with dopant concentration, determined using Tauc’s plot assuming them both of ‘direct’ and ‘indirect’ nature, also indicates the ‘direct’ nature. Co⁺² ions as dopants promote a decrease of band gap of films linearly. Scanning electron micrographs show the granular and flakes-like surface growth. Atomic force microscopy images show the presence of ribbon-like nanostructured grains throughout the surface of the films which is smooth with small values of surface roughness.     

Flow coupling mechanisms in two-layer Rayleigh–Benard convection

 Rayleigh-Benard convection in two-layer systems is characterized by two distinct modes of flow coupling. These are: thermal coupling and mechanical coupling. Intellegible observations of the temperature field for both coupling mechanisms are provided. The flow coupling mechanisms are experimentally characterized as a function of the contrast in the buoyancy driving forces and in the viscosities of the two layers. Aside from the flow coupling between the layers, flow patterns in each layer, and their corresponding spatial transitions are found to be similar to those reported for single layer convection in rectangular boxes. Received: 7 January 1996/Accepted: 4 February 1997     

A more chaotic and easily hardware implementable new 3-D chaotic system in comparison with 50 reported systems

This paper attempts to construct a new 3-D chaotic system which is easily hardware realisable and fulfil the requirement of a real-life application. The proposed system is relatively more chaotic (based on the first Lyapunov exponent) and has larger bandwidth than 50 available chaotic systems. Lyapunov spectrum and bifurcation diagram of the system reveal that it has chaotic behaviour for a wider range of its parameters. Such characteristic is helpful for an easy hardware realisation of the system. It is to be noted that the reported systems with hidden attractors are not considered here for the comparison. The proposed system has more complexity and disorder due to several unique properties like asymmetry to principle coordinates, dissimilar and asymmetrical equilibria, and non-uniform contraction and expansion of volume in phase space. The proposed system also exhibits asymmetric pairs of coexisting attractors during its operation in two modes. The new system has different routes to chaos including crisis, an inverse crisis, period-doubling and reverse period-doubling routes to chaos with the variation of parameters. MATLAB simulation results confirm the claims, and the results of hardware circuit realisation validate the simulation results. An application of the new system is shown by masking and retrieving an information signal. It is also shown that the proposed system is better than a well-known Lorenz chaotic system for this application. A system with the above unique properties is rare in the literature.