204 research outputs found
Brief communication:getting Greenland’s glaciers right – a new data set of all official Greenlandic glacier names
Place names in Greenland can be difficult to get right, as they are a mix of
Greenlandic, Danish, and other foreign languages. In addition, orthographies
have changed over time. With this new data set, we give the researcher
working with Greenlandic glaciers the proper tool to find the correct name
for glaciers and ice caps in Greenland and to locate glaciers described in
the historic literature with the old Greenlandic orthography. The data set
contains information on the names of 733 glaciers, 285 originating from the
Greenland Ice Sheet (GrIS) and 448 from local glaciers and ice caps (LGICs)
High-dimensional quantum dynamics of adsorption and desorption of H at Cu(111)
We performed high-dimensional quantum dynamical calculations of the
dissociative adsorption and associative desorption of hydrogen on Cu(111). The
potential energy surface (PES) is obtained from density functional theory
calculations. Two regimes of dynamics are found, at low energies sticking is
determined by the minimum energy barrier, at high energies by the distribution
of barrier heights. Experimental results are well-reproduced qualitatively, but
some quantitative discrepancies are identified as well.Comment: 4 two column pages, revtex, 4 figures, to appear in Phys. Rev. Let
Three decades of volume change of a small greenlandic glacier using ground penetrating radar, structure from motion, and aerial photogrammetry
Glaciers in the Arctic are losing mass at an increasing rate. Here we use surface topography derived from Structure from Motion (SfM) and ice volume from ground penetrating radar (GPR) to describe the 2014 state of Aqqutikitsoq glacier (2.85 km2) on Greenland's west coast. A photogrammetrically derived 1985 digital elevation model (DEM) was subtracted from a 2014 DEM obtained using land-based SfM to calculate geodetic glacier mass balance. Furthermore, a detailed 2014 ground penetrating radar survey was performed to assess ice volume. From 1985 to 2014, the glacier has lost 49.8 ± 9.4 106 m3 of ice, corresponding to roughly a quarter of its 1985 volume (148.6 ± 47.6 106 m3) and a thinning rate of 0.60 ± 0.11 m a-1. The computations are challenged by a relatively large fraction of the 1985 DEM (∼50% of the glacier surface) being deemed unreliable owing to low contrast (snow cover) in the 1985 aerial photography. To address this issue, surface elevation in low contrast areas was measured manually at point locations and interpolated using a universal kriging approach. We conclude that ground-based SfM is well suited to establish high-quality DEMs of smaller glaciers. Provided favorable topography, the approach constitutes a viable alternative where the use of drones is not possible. Our investigations constitute the first glacier on Greenland's west coast where ice volume was determined and volume change calculated. The glacier's thinning rate is comparable to, for example, the Swiss Alps and underlines that arctic glaciers are subject to fast changes
In Situ Detection of Active Edge Sites in Single-Layer MoS Catalysts
MoS2 nanoparticles are proven catalysts for processes such as
hydrodesulphurization and hydrogen evolution, but unravelling their
atomic-scale structure under catalytic working conditions has remained
significantly challenging. Ambient pressure X-ray Photoelectron Spectroscopy
(AP-XPS) allows us to follow in-situ the formation of the catalytically
relevant MoS2 edge sites in their active state. The XPS fingerprint is
described by independent contributions to the Mo3d core level spectrum whose
relative intensity is sensitive to the thermodynamic conditions. Density
Functional Theory (DFT) is used to model the triangular MoS2 particles on
Au(111) and identify the particular sulphidation state of the edge sites. A
consistent picture emerges in which the core level shifts for the edge Mo atoms
evolve counter-intuitively towards higher binding energies when the active
edges are reduced. The shift is explained by a surprising alteration in the
metallic character of the edge sites, which is a distinct spectroscopic
signature of the MoS2 edges under working conditions
Modelling and Simulation of Asynchronous Real-Time Systems using Timed Rebeca
In this paper we propose an extension of the Rebeca language that can be used
to model distributed and asynchronous systems with timing constraints. We
provide the formal semantics of the language using Structural Operational
Semantics, and show its expressiveness by means of examples. We developed a
tool for automated translation from timed Rebeca to the Erlang language, which
provides a first implementation of timed Rebeca. We can use the tool to set the
parameters of timed Rebeca models, which represent the environment and
component variables, and use McErlang to run multiple simulations for different
settings. Timed Rebeca restricts the modeller to a pure asynchronous
actor-based paradigm, where the structure of the model represents the service
oriented architecture, while the computational model matches the network
infrastructure. Simulation is shown to be an effective analysis support,
specially where model checking faces almost immediate state explosion in an
asynchronous setting.Comment: In Proceedings FOCLASA 2011, arXiv:1107.584
Metamaterial anisotropic flux concentrators and magnetic arrays
A metamaterial magnetic flux concentrator is investigated in detail in
combination with a Halbach cylinder of infinite length. A general analytical
solution to the field is determined and the magnetic figure of merit is
determined for a Halbach cylinder with a flux concentrator. It is shown that an
ideal flux concentrator will not change the figure of merit of a given magnet
design, while the non-ideal will always lower it. The geometric parameters
producing maximum figure of merit, i.e. the most efficient devices, are
determined. The force and torque between two concentric Halbach cylinders with
flux concentrators is determined and the maximum torque is found. Finally, the
effect of non-ideal flux concentrators and the practical use of flux
concentrators, as well as demagnetization issues, is discussed.Comment: 11 pages, 5 figure
Quantum-mechanical calculation of H on Ni(001) using a model potential based on first-principles calculations
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