CO oxidation on a single Pd atom supported on magnesia

The oxidation of CO on single Pd atoms anchored to MgO(100) surface oxygen vacancies is studied with temperature-programmed-reaction mass-spectrometry and infrared spectroscopy. In one-heating-cycle experiments CO$_2$, formed from O$_2$ and CO preadsorbed at 90 K, is detected at 260 K and 500 K. Ab-initio simulations suggest two reaction routes, with Pd(CO)$_2$O$_2$ and Pd(CO$_3$)CO found as precursors for the low and high temperature channels, respectively. Both reactions result in annealing of the vacancy and induce migration and coalescence of the remaining Pd-CO to form larger clusters.Comment: 4 pages, 3 figures, scheduled for publication in PRL 18 June 200

Study of the long-term evolution of the accretion dynamics of GX 339-4

We study the dynamical behaviour of the galactic black hole source GX 339-4 during 2002-2011 outbursts using RXTE, Swift(XRT), XMM-Newton(PN) archival data. We present the spectral evolution of the source using four outbursts data and discuss their similarities/differences between outbursts. We infer that the second peak in 2002/03 and 2004/05 outbursts can be due to a second instant of triggered instability in the accretion disc due to irradiation from the central X-ray source after peak-I. This propagates in viscous time scale and takes ~80-90 days after peak-I to produce peak-II. This unifies all four outbursts having a long rising time of ~90 days. The dynamical evolution of accretion parameters have been studied by modeling the individual observed spectrum with two-component accretion disc model where a Keplerian accretion disc produces the soft photons and the hard part of the spectrum originates from a hot sub-Keplerian central corona. A generic mathematical model has been proposed to understand the evolution of accretion parameters for sources like GX 339-4 which have longer rising time. Also, the possible differences of physical scenario for outbursts with shorter rising time are also discussed.Comment: Accepted for publication in mnra

Method of crystallization

A method is described for refining or growing bulk single crystals in an environment substantially free of gravity. The base material is suspended, positioned, and shaped as a containerless melt by wetting forces. Because no crucible is required, high temperature refractory materials can be processed

Generation of non-Gaussian statistics and coherent structures in ideal magnetohydrodynamics

Spectral method simulations of ideal magnetohydrodynamics are used to investigate production of coherent small scale structures, a feature of fluid models that is usually associated with inertial range signatures of nonuniform dissipation, and the associated emergence of non-Gaussian statistics. The near-identical growth of non-Gaussianity in ideal and nonideal cases suggests that generation of coherent structures and breaking of self-similarity are essentially ideal processes. This has important implications for understanding the origin of intermittency in turbulence

Criticality of tuning in athermal phase transitions

We experimentally address the importance of tuning in athermal phase transitions, which are triggered only by a slowly varying external field acting as tuning parameter. Using higher order statistics of fluctuations, a singular critical instability is detected for the first time in spite of an apparent universal self-similar kinetics over a broad range of driving force. The results as well as the experimental technique are likely to be of significance to many slowly driven non-equilibrium systems from geophysics to material science which display avalanche dynamics.Comment: 5 pages, 4 figure

Dynamics and symmetries of a field partitioned by an accelerated frame

The canonical evolution and symmetry generators are exhibited for a Klein-Gordon (K-G) system which has been partitioned by an accelerated coordinate frame into a pair of subsystems. This partitioning of the K-G system is conveyed to the canonical generators by the eigenfunction property of the Minkowski Bessel (M-B) modes. In terms of the M-B degrees of freedom, which are unitarily related to those of the Minkowski plane waves, a near complete diagonalization of these generators can be realized.Comment: 14 pages, PlainTex. Related papers on accelerated frames available at http://www.math.ohio-state.edu/~gerlac