Department of Physics

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Chiral symmetry is restored at high density, quarks become nearly massless and pion, the Goldstone of the symmetry breaking decouples from the quarks. What happens at high density is important for finding the density dependence of Strange Quark Matter (SQM), which in turn is relevant for understanding the structure of compact stars. © 2005 Elsevier B.V. All rights reserved.

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Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

Decoupling of pion coupling fπ from quarks at high density in three models, and its possible observational consequences

The crystallization behaviour and Curie temperature of melt-spun Co 71-xFexCr7Si8B14 (x = 0, 2, 3.2, 4, 6, 8 and 12 at.%) amorphous alloys have been studied. Differential scanning calorimetry (DSC) showed two stages of crystallization. The first stage of crystallization (TX1) in the alloy with 6 at. % Fe was the highest and it had the highest activation energy. X-ray diffraction studies revealed that the primary crystalline phase is hcp-(CoCr)2Si for Fe-free alloy, whereas (CoFeCr)2Si and (CoFeCr)3Si phases were formed with the addition of Fe. hcp-Co was also formed along with these phases. The secondary crystalline phases were fcc-Co and various boron-rich phases. The Curie temperature of the alloys also changed with the addition of Fe to the system. Like the primary crystallization temperature, the Curie temperature of the alloys did not vary systematically with the Fe content. The addition of Fe to the Co-based system changes the nearest-neighbour interaction. This changes the exchange interaction between the transition metal elements. Due to the asymmetry in the Bethe-Slater curve, a systematic variation with Fe addition was not observed in the Curie temperature measurement. © 2005 Taylor &amp; Francis Group Ltd.

Philosophical Magazine

Effect of Fe addition on the crystallization behaviour and Curie temperature of CoCrSiB-based amorphous alloys

The electrochemical response of a soft magnetic FeNbAlMnCuSiB alloy was studied through different stages of devitrification. The structural evolution including appearance of a nanocrystalline phase and intermetallics, and accompanying surface topographical changes were studied and correlated to the electrochemical behavior of this alloy. The electrochemical behavior was not directly related to changes in surface roughness but it was very responsive to the structural changes, particularly to the formation of the nanocrystalline phase and to the precipitation of Fe 7Nb 6 phase. There was a progressive passivation breakdown with the appearance of crystalline phases on annealing. © 2005 Springer Science + Business Media, Inc.

Journal of Materials Science

Effect of structural evolution and surface morphological changes on the electrochemical response of an FeNbAlMnCuSiB alloy

The wall conditioning of the ADITYA tokamak is usually done, by first producing an electron cyclotron resonance (ECR) plasma inside the vessel and then superimposing a pulsed ohmic discharge on the ECR background. Sometimes, helium gas is used as a working gas. In this article, the spectral line emissions of neutral helium for the two different plasmas - namely, the ECR and the pulsed discharge cleaning (PDC) plasmas - have been analyzed using a collisional-radiative (CR)-model code to estimate the electron density and temperature. We are able to match the experimentally obtained relative intensity ratios with those predicted by the model under the assumption of ionizing plasma condition if the possible effects of the metastable states are not ignored. This has been done by using the populations of two metastable levels (2 1S and 2 3S) as independent parameters in addition to the ground states of neutrals and ions in the CR model under a quasisteady-state approximation. It is further seen that, it is the metastables and not the recombination (including dielectronic) processes that lead to a better fit with experimental observations. The column density of neutrals inferred from this analysis implies that the emission from the PDC discharge emanates from a large region of the vessel, while in the ECR discharge, the plasma responsible for the emission is restricted to a narrow region. This is also borne out by experimental observation. © 2005 American Institute of Physics.

Journal of Applied Physics

Characterization of helium discharge cleaning plasmas in ADITYA tokamak using collisional-radiative model code

We consider the most general new physics effective Lagrangian for b→sl+l-. We derive the upper limit on the branching ratio for the processes Bs→l+l- where l=e,μ, subject to the current experimental bounds on related processes, B→Kl+l- and B→K*l+l -. If the new physics interactions are of vector/axial-vector form, the present measured rates for B→(K,K*;)l+l- constrain B(Bs→l+l-) to be of the same order of magnitude as their respective Standard Model predictions. On the other hand, if the new physics interactions are of scalar/pseudoscalar form, B→(K,K*)l+l- rates do not impose any constraint on Bs→l+l- and the branching ratios of these decays can be as large as present experimental upper bounds. If future experiments measure B(Bs→l+l-) to be ≥10-8 then the new physics giving rise to these decays has to be of the scalar/pseudoscalar form.

New physics upper bound on the branching ratio of Bs → l+l-

The crystallization behaviour and evolution of nanoparticles in amorphous Al-Ni-Mischmetal (Mm) and Al-Ni-La alloys during heat treatment have been studied. Rapidly solidified ribbons were obtained by induction melting and ejecting the melt onto a rotating Cu wheel in an Ar atmosphere. The crystallization behaviour of the melt-spun ribbons was investigated using differential scanning calorimetry and X-ray diffractometry (XRD). XRD studies confirmed that all the ribbons were fully amorphous. Al-Ni-Mm systems showed a three-stage crystallization process whereas Al-Ni-La system, in general, showed a two-stage crystallization process on annealing. Crystallization kinetics was analysed by Kissinger and Johnson-Mehl-Avrami approaches. In Al-Ni-La alloys, the crystallization pathways depend on the La concentration. Microhardness of all the ribbons was examined at different temperatures and correlated with the corresponding evolution of phases. © Indian Academy of Sciences.

Pramana - Journal of Physics

Effect of rare-earth elements on nanophase evolution, crystallization behaviour and mechanical properties in Al-Ni-R (R = La/Mischmetal) amorphous alloys

Erratum: Two new sum rules for octet-baryon magnetic moments (μ) and constraints on QCD sum rules from new experimental determination of μ-s for the decuplet (Physics Letters B (2003) 562 (63) DOI:10.1016/S0370-2693(03)00545- 8)

Surface tension (S) is due to the inward force experienced by particles at the surface and usually gravitation does not play an important role in this force. But in compact stars the gravitational force on the particles is very large and S is found to depend not only on the interactions in the strange quark matter, but also on the structure of the star, i.e. on its mass and radius. Indeed, it has been claimed recently that 511 keV photons observed by the space probe INTEGRAL from the galactic bulge may be due to e+ e- annihilation, and their source may be the positron cloud outside of an antiquark star. Such stars, if they exist, may also go a long way towards explaining away the antibaryon deficit of the universe. For that to happen S must be high enough to allow for survival of quark/antiquark stars born in early stages of the formation of the universe. High value of S may also assist explanation of delayed γ-ray burst after a supernova explosion, as conversion from normal matter to strange matter takes place. The possibility of some implications from formation of surface waves are also discussed. © ESO 2005.

Astronomy and Astrophysics

Newtonian and general relativistic contribution of gravity to surface tension of strange stars

Nanoscience deals with the materials and technologies based on them in the size range of 1-100 nm. The definition is indeed slippery. The nanoworld indeed is a weird border between the realm of individual atoms and molecules (where quantum mechanics rules) and the macroworld (where the bulk properties of materials emerge from the collective behaviour of trillions of atoms such as a steel beam). Although the existence of nanoscience can be traced both in living and non-living things existing in nature since billions of years, however, the recent and intense interest in nanomaterials and structures stem from the fact that they may boast superior and novel chemical, physical and biological properties, phenomena and processes. The development of new tools (STM, AFM, etc.) that have made characterization and manipulation of nanostructures practical and also as a result of new methods for the preparation nanosized structures and materials together with their tremendous scope of applications make nanoscience as one of the most advanced areas in science and technology. In the present paper, an overview is given on various aspects of nanomaterials including classification, approaches for synthesis and characterization, properties arising due to reduced dimensions, size confinement, interfacial phenomena, application areas, challenges, etc.

Electronics Information and Planning

An overview of science and technology of nanomaterials

Crystallisation behaviour and magnetic properties of as-spun and annealed Fe40Co40Cu0.5Zr9Al 2Si4B4.5 alloy have been studied. The annealing was performed at 873K for 15min. XRD and TEM studies shows the formation of nanocrystalline α-(Fe,Co)(SiAl) particles with 7.5±2nm in diameter dispersed in an amorphous matrix. The Curie temperature of the as-spun amorphous ribbon is 736K. Saturation magnetisation of the annealed sample decreases at a rate of 0.5emu/g/K in the measured temperature range of 300-1000K. Excellent room temperature AC magnetic properties are achieved for the nanocrystalline sample. The low value of the imaginary part of the permeability and the high cut-off frequency (20kHz) suggest that the eddy current contribution in the annealed materials is low. The coercivity of the annealed sample remains almost constant at 95A/m up to the frequency of 20kHz. High saturation magnetisation, high Curie temperature and excellent soft magnetic properties in the nanocrystalline state suggests that Fe40Co40Cu 0.5Zr9Al2Si4B4.5 alloy is a strong candidate for high temperature magnetic application. © 2004 Elsevier B.V. All rights reserved.