1,340 research outputs found
Temperature programed desorption of water ice from the surface of amorphous carbon and silicate grains as related to planet-forming disks
Understanding the history and evolution of small bodies, such as dust grains
and comets, in planet-forming disks is very important to reveal the
architectural laws responsible for the creation of planetary systems. These
small bodies in cold regions of the disks are typically considered as mixtures
of dust particles with molecular ices, where ices cover the surface of a dust
core or are actually physically mixed with dust. Whilst the first case,
ice-on-dust, has been intensively studied in the laboratory in recent decades,
the second case, ice-mixed-with-dust, present uncharted territory. This work is
the first laboratory study of the temperature-programmed desorption (TPD) of
water ice mixed with amorphous carbon and silicate grains. We show that the
kinetics of desorption of H2O ice depends strongly on the dust/ice mass ratio,
probably, due to the desorption of water molecules from a large surface of
fractal clusters composed of carbon or silicate grains. In addition, it is
shown that water ice molecules are differently bound to silicate grains in
contrast to carbon. The results provide a link between the structure and
morphology of small cosmic bodies and the kinetics of desorption of water ice
included in them.Comment: Submitted to the Astrophysical Journa
Improved interpolating fields for hadrons at non-vanishing momentum
We demonstrate that a reduction in the noise-to-signal ratio may be obtained
for hadrons at non-zero momenta whilst maintaining a good overlap with the
ground state through a generalisation of Gaussian/Wuppertal smearing. The use
of an anisotropic smearing wavefunction is motivated by the physical picture of
a boosted hadron.Comment: 7 pages, 6 figures, poster presented at the 30th International
Symposium on Lattice Field Theory (Lattice 2012), Cairns, Australia, June
24-29, 201
Some theories with positive induction of ordinal strength φω0
This paper deals with: (i) the theory which results from by restricting induction on the natural numbers to formulas which are positive in the fixed point constants, (ii) the theory BON(μ) plus various forms of positive induction, and (iii) a subtheory of Peano arithmetic with ordinals in which induction on the natural numbers is restricted to formulas which are Σ in the ordinals. We show that these systems have proof-theoretic strength φω
The Shape of Covariantly Smeared Sources in Lattice QCD
Covariantly smeared sources are commonly used in lattice QCD to enhance the
projection onto the ground state. Here we investigate the dependence of their
shape on the gauge field background and find that the presence of localized
concentrations of magnetic field can lead to strong distortions which reduce
the smearing radii achievable by iterative smearing prescriptions. In
particular, as , iterative procedures like Jacobi smearing require
increasingly large iteration counts in order to reach physically-sized smearing
radii 0.5 fm, and the resulting sources are strongly distorted. To
bypass this issue, we propose a covariant smearing procedure (``free-form
smearing'') that allows us to create arbitrarily shaped sources, including in
particular Gaussians of arbitrary radius.Comment: 1+15 pages, 7 figures (24 pdf images
Upper bounds for metapredicative Mahlo in explicit mathematics and admissible set theory
In this article we introduce systems for metapredicative Mahlo in explicit mathematics and admissible set theory. The exact upper proof-theoretic bounds of these systems are establishe
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