1,192 research outputs found
Determination of III-V/Si absolute interface energies: impact on wetting properties
Here, we quantitatively determine the impact of III-V/Si interface atomic
configuration on the wetting properties of the system. Based on a description
at the atomic scale using density functional theory, we first show that it is
possible to determine the absolute interface energies in heterogeneous
materials systems. A large variety of absolute GaP surface energies and GaP/Si
interface energies are then computed, confirming the large stability of charge
compensated III-V/Si interfaces with an energy as low as 23 meV/\r{A}.
While stable compensated III-V/Si interfaces are expected to promote complete
wetting conditions, it is found that this can be easily counterbalanced by the
substrate initial passivation, which favors partial wetting conditions.Comment: 17 pages, 14 figure
On QCD analysis of stucture function in alternative approach
The alternative approach to QCD analysis of the photon structure function
is presented. It differs from the conventional one by the
presence of the terms which in conventional approach appear in higher orders.
We show that this difference concerns also the photonic parton distribution
functions. In the alternative approach, the complete LO analysis of
can be performed as all required quantities are known. At the
NLO, however, one of the coefficient function is so far not available and thus
only the photonic parton distribution function can be computed and compared to
those of standard approach. We discuss the numerical difference of these
approaches at the LO and the NLO approximation and show that in case of
this difference is non-negligible and may play an important role
in the analysis on photon data of the future experiments.Comment: 25 page
Dissolution on Saturn's Moon Titan: A 3D Karst Landscape Evolution Model
Titan is an Earth-like world possessing a nitrogen-rich atmosphere covering a surface showing signs of lacustrine (lakes and depressions), fluvial (channels, valleys), aeolian (longitudinal dunes) activity. The chemistry implied in the geological processes is, however, strikingly different from that on Earth. Titan’s extremely cold environment (T ~ -180°C) only allows water to exist under the form of an icy “bedrock”. The presence of methane as the second major constituent in the atmosphere, as well as an active nitrogen-methane photochemistry, allows methane and ethane to drive a hydrocarbon cycle similar to the terrestrial hydrological cycle. A plethora of organic solids, more or less soluble in liquid hydrocarbons, is also produced in the atmosphere and can lead, by atmospheric sedimentation over geological timescales, to formation of some kind of organic geological sedimentary layer.
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Based on comparisons between Titan’s landscapes seen in the Cassini spacecraft data and terrestrial analogues, karstic-like dissolution and evaporitic crystallization have been suggested in various instances to take part in the landscape development on Titan. Dissolution has been invoked, for instance, for the development of the so-called “labyrinthic terrain”, located at high latitudes and resembling terrestrial cockpit or polygonal karst terrain. In this work, we aim at testing this hypothesis by comparing the natural landscapes visible in the Cassini/RADAR images of Titan’s surface, with those inferred from the use of a 3D Landscape Evolution Model (LEM) based on the Channel-Hillslope Integrated Landscape Development (CHILD), modified to include karstic dissolution as the major geological process. Digital Elevation Models (DEMs) are generated from an initial quasi-planar surface for a set of dissolution rates, diffusion coefficients (solute transport), and sink densities of the mesh. The landscape evolves over millions of years. Synthetic SAR images are generated from these DEMs in order to compare with Titan’s landforms seen in the actual SAR images and infer the possible thickness and degree of maturation of the Titan kars
Dijet photoproduction of massless charm jets at next-to-leading order of QCD
We compute the charm dijet photoproduction cross section at next-to-leading
order of QCD in the zero-mass variable flavour number scheme, i.e. with active
charm quarks in the proton and photon. The results are compared to recent
measurements from the ZEUS experiment at HERA. The predictions for various
distributions agree well with the data, in particular for large momentum
fractions of the the partons in the photon, where direct photon processes
dominate. At low momentum fractions, the predictions are quite sensitive to the
charm content in the photon. The experimental data are shown to favour
parameterizations with a substantial charm quark density such as the one
proposed by Cornet et al.Comment: 18 pages, 11 figure
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