323,987 research outputs found
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, formed from
O and CO preadsorbed at 90 K, is detected at 260 K and 500 K. Ab-initio
simulations suggest two reaction routes, with Pd(CO)O and Pd(CO)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
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