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 $a\to 0$, iterative procedures like Jacobi smearing require increasingly large iteration counts in order to reach physically-sized smearing radii $r_{sm}\sim$ 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