Department of Physics

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The investigation addresses the effect of Mn incorporation for Ni on the properties of a series of Ni77-xMnxGa23 (x=2229; at%) ferromagnetic shape memory alloys prepared in the form of ribbons by a melt spinning technique. Phase transformation studies in these ribbons by differential scanning calorimetry revealed that austenitic start and martensitic start temperatures decreased with the increase in Mn content. The Curie temperature (TC) of these alloys determined from thermal variation of magnetisations was found to rise with increasing Mn content. The martensitic transformation temperatures were above TC in low Mn containing (x=22 and 23) alloys. Morphology observed through transmission electron microscopy manifested complex martensitic features in the alloy with x=22 while x=29 had an austenitic phase. The alloys with intermediate Mn content (x=24, 25) had overlapping magnetic and martensitic transformations close to room temperature. The thermal lag between austenitic and martensitic characteristic temperatures in these alloys has been corroborated to their structural state. X-ray diffraction indicated a predominant martensite phase and austenite phase in low and high Mn containing alloys respectively. In-situ diffraction studies during thermal cycle indicate martensiteaustenite transformations. © 2011 Elsevier B.V. All rights reserved.

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Journal of Magnetism and Magnetic Materials

Effect of Mn incorporation for Ni on the properties of melt spun off-stoichiometric compositions of NiMnGa alloys

We perform a comprehensive study of the impact of new-physics operators with different Lorentz structures on decays involving the b → sμ + μ - transition. We examine the effects of new vector-axial vector (VA), scalar-pseudoscalar (SP) " and tensor (T) interactions on the differential branching ratios and forward-backward asymmetries (A FB 's) of B o s → μ + μ - , B o d X s + μ - , B o s → μ + μ - γ, B o d → Kμ + μ - , and B o d → K*μ + μ - , taking the new-physics couplings to be real. In B o d → K*μ + μ - , we further explore the polarization fraction f L , the angular asymmetry A (2) T , and the longitudinaltransverse asymmetry A LT . We identify the Lorentz structures that would significantly impact these observables, providing analytical arguments in terms of the contributions from the individual operators and their interference terms. In particular, we show that while the new VA operators can significantly enhance most of the asymmetries beyond the Standard Model predictions, the SP and T operators can do this only for A FB in B o d → Kμ + μ - . © SISSA 2011.

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Journal of High Energy Physics

New physics in b → sμ + μ - : CP-conserving observables

We perform a comprehensive study of the impact of new-physics operators with different Lorentz structures on CP-violating observables involving the b → sμ+μ- transition. We examine the effects of new vector-axial vector (VA), scalar-pseudoscalar (SP) and tensor (T) interactions on the CP asymmetries in the branching ratios and forwardbackward asymmetries of Bo s → μ+μ -, Bo d Xs +μ -, Bo s → μ+μ -γ, Bo d → Kμ+μ -, and Bo d → K*μ+μ -. In Bo d → K*μ+μ -, we also explore the direct CP asymmetries in the longitudinal polarization fraction fL and the angular asymmetries A (2) T and ALT, as well as the triple-product CP asymmetries A(im) T and A(im) LT. We find that, in almost all cases, the CP-violating observables are sensitive only to new physics which involves VA operators. The VA new physics may therefore be unambiguously identified by a combined analysis of future measurements of these CP-violating observables. © SISSA 2011.

New physics in b → sμ+μ-: CP-violating observables

In this work, we study quantum correlations in mixed states. The states studied are modeled by a two-qubit system interacting with its environment via a quantum non de-molition (purely dephasing) as well as dissipative type of interaction. The entanglement dynamics of this two qubit system is analyzed. We make a comparative study of various measures of quantum correlations, like Concurrence, Bell's inequality, Discord and Tele-portation fidelity, on these states, generated by the above evolutions. We classify these evoluted states on basis of various dynamical parameters like bath squeezing parameter r, inter-qubit spacing r12, temperature T and time of system-bath evolution t. In this study, in addition we report the existence of entangled states which do not violate Bell's inequality, but can still be useful as a potential resource for teleportation. Moreover we study the dynamics of quantum as well as classical correlation in presence of dissipative coherence. © Rinton Press.

Quantum Information and Computation

A study of quantum correlations in open quantum systems

Discrete nanoparticles of MnAs with distinct magnetostructural properties have been prepared by small modifications of solution-phase arrested precipitation reactions. Rietveld and X-ray atomic pair distribution function based approaches were used to explore the evolution of the structure of the samples with temperature, and these data were compared to the magnetic response measured with ac susceptibility. Relative to a bulk standard, one type of MnAs nanoparticles was found to demonstrate similar but smaller structural transitions and corresponding magnetic changes. However, both magnetic and structural transitions in the second type of nanoparticles are strongly suppressed. © 2011 American Chemical Society.

ACS Nano

Diverse structural and magnetic properties of differently prepared MnAs nanoparticles

A new q-deformed logistic map is proposed and it is found to have concavity in parts of the x-space. Its one-cycle and two-cycle non-trivial fixed points are obtained which are found to be qualitatively and quantitatively different from those of the usual logistic map. The stability of the proposed q-logistic map is studied using the Lyapunov exponent, and with a change in the value of the deformation parameter q, one is able to go from the chaotic to regular dynamical regime. The implications of this q-logistic map on Parrondo's paradox are examined. © 2011 IOP Publishing Ltd.

Journal of Physics A: Mathematical and Theoretical

A q-deformed logistic map and its implications

Recent results and data suggest that high magnetic fields in neutron stars (NS) strongly affect the characteristics (radius, mass) of the star. Such stars are even separated into a class known as magnetars, for which the surface magnetic field is greater than 1014G. In this work we discuss the effect of such a high magnetic field on the phase transition of a NS to a quark star (QS). We study the effect of magnetic field on the transition from NS to QS including the magnetic-field effect in the equation of state (EoS). The inclusion of the magnetic field increases the range of baryon number densities for which the flow velocities of the matter in the respective phase are finite. The magnetic field helps in initiation of the conversion process. The velocity of the conversion front, however, decreases due to the presence of the magnetic field, as the presence of the magnetic field reduces the effective pressure (P). The magnetic field of the star is decreased by the conversion process, and the resultant QS has lower magnetic field than the initial NS. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Monthly Notices of the Royal Astronomical Society

Possible conversion of a neutron star to a quark star in the presence of high magnetic field

In this paper an effort has been made to plasma nitride the ball bearing steel AISI 52100. The difficulty with this specific steel is that its tempering temperature (̃170-200°C) is much lower than the standard processing temperature (̃460-580°C) needed for the plasma nitriding treatment. To understand the mechanism, effect of heat treatment on the nitrided layer steel is investigated. Experiments are performed on three different types of ball bearing races i.e. annealed, quenched and quench-tempered samples. Different gas compositions and process temperatures are maintained while nitriding these samples. In the quenched and quench-tempered samples, the surface hardness has decreased after plasma nitriding process. Plasma nitriding of annealed sample with argon and nitrogen gas mixture gives higher hardness in comparison to the hydrogen-nitrogen gas mixture. It is reported that the later heat treatment of the plasma nitrided annealed sample has shown improvement in the hardness of this steel. X-ray diffraction analysis shows that the dominant phases in the plasma nitrided annealed sample are ε (Fe2-3N) and γ (Fe4N), whereas in the plasma nitrided annealed sample with later heat treatment only a-Fe peak occurs. © Indian Academy of Sciences.

Bulletin of Materials Science

Plasma nitriding of AISI 52100 ball bearing steel and effect of heat treatment on nitrided layer

Optical limiting measurements are carried out with the 3D polystyrene (PS) photonic crystals (PhCs) fabricated by vertical deposition method using the reflection Z-scan (RZ-scan) technique. Interestingly we found that nonlinear reflectance decreases up to 80% which leads to good optical limiting (OL) behavior for PS PhCs compared with the thin films prepared by spin coating. © 2011 American Institute of Physics.

AIP Conference Proceedings

Application of 3D polystyrene photonic crystals for optical limiting studies

The joining behavior of 304SS and Cu joint is important for the component materials of the first wall and divertor in the International Thermonuclear Fusion Experiment Reactor (ITER). In this research, the joining of 304 stainless steel (SS) and pure copper is done by rapidly solidified Cu-40Mn-10Ni brazing alloy at 920 °C for 5 min. The SEM-BSE image of joint area shows homogeneous microstructure. The butt joint of 304SS and pure Cu breaks at the tensile strength of 260 MPa and several dimples are observed at the fracture surface. It reveals ductile nature and strong bonding between two dissimilar metals. The X-ray diffraction of fracture surface explains the formation of solid solution phases with a little amount of intermetallics. © 2011 Elsevier B.V.