11,658 research outputs found
Calculating the inherent visual structure of a landscape (inherent viewshed) using high-throughput computing
This paper describes a method of calculating the inherent visibility at all locations in a landscape (‘total viewshed’) by making use of redundant computer cycles. This approach uses a simplified viewshed program that is suitable for use within a distributed environment, in this case managed by the Condor system. Distributing the calculation in this way reduced the calculation time of our example from an estimated 34 days to slightly over 25 hours using a cluster of 43 workstations. Finally, we discuss the example ‘total viewshed’ raster for the Avebury region, and briefly highlight some of its implications
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Water ice clouds in a martian global climate model using data assimilation
The water cycle is one of the key seasonal cycles on Mars, and the radiative effects of water ice clouds have recently been shown to alter the thermal structure of the atmosphere. Current Mars General Circulation Models (MGCMs) are capable of representing the formation and evolution of water ice clouds, though there are still many unanswered questions regarding their effect on the water cycle, the local atmosphere and the global circulation. We discuss the properties of clouds in the LMD/UK MGCM and compare them with observations, focusing on the differences between the water ice clouds in a standalone model and those in a model which has been modified by assimilation of thermal and aerosol opacity spacecraft data
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Assimilating the Martian water cycle
Water ice clouds have been shown to alter the thermal structure of the Martian atmosphere. Here we discuss the assimilation of total column water vapour and dust optical depth data from the Thermal Emission Spectrometer (TES) into the UK/LMD MGCM, and compare the predictions of cloud and temperature in the assimilation with observations
Transillumination imaging through scattering media by use of photorefractive polymers
We demonstrate the use of a near-infrared-sensitive photorefractive polymer with high efficiency for imaging through scattering media, using an all-optical holographic time gate. Imaging through nine scattering mean free paths is performed at 800 nm with a mode-locked continuous-wave Ti:sapphire laser
Vacuum spacetimes with a spacelike, hypersurface-orthogonal Killing vector: reduced equations in a canonical frame
The Newman-Penrose equations for spacetimes having one spacelike Killing
vector are reduced -- in a geometrically defined "canonical frame'' -- to a
minimal set, and its differential structure is studied. Expressions for the
frame vectors in an arbitrary coordinate basis are given, and
coordinate-independent choices of the metric functions are suggested which make
the components of the Ricci tensor in the direction of the Killing vector
vanish.Comment: 13 pages, no figures, LaTeX, to be published in Class. Quantum
Gravity; v2: added/rephrased content, corrected typos, changed 1 referenc
RISE: a fast-readout imager for exoplanet transit timing
By the precise timing of the low amplitude (0.005 - 0.02 magnitude) transits
of exoplanets around their parent star it should be possible to infer the
presence of other planetary bodies in the system down to Earth-like masses. We
describe the design and construction of RISE, a fast-readout frame transfer
camera for the Liverpool Telescope designed to carry out this experiment. The
results of our commissioning tests are described as well as the data reduction
procedure necessary. We present light curves of two objects, showing that the
desired timing and photometric accuracy can be obtained providing that
autoguiding is used to keep the target on the same detector pixel for the
entire (typically 4 hour) observing run.Comment: Published in PROC SPIE, vol 7014, 70416
Tensor Di-Gluonium from Laplace Sum Rules at NLO
We evaluate the next-to-leading (NLO) corrections to the perturbative (PT)
and condensate and the LO constant term of the
contributions to the tensor di-gluonium two-point correlator. Using
these results into the inverse Laplace transform sum rules (LSR) moments and
their ratio, we estimate the mass and coupling of the lowest ground state. We
obtain\,: MeV and the renormalization group invariant (RGI)
coupling MeV within a vacuum saturation estimate of the
dimension gluon condensates (). We study the effect of on
the result and find: MeV and =245(32) MeV for
. Our result does not favour the pure gluonia/glueball nature of
the observed states.Comment: 7 pages, 9 figures, 1 Tabl
The Long and Short of Nuclear Effective Field Theory Expansions
Nonperturbative effective field theory calculations for NN scattering seem to
break down at rather low momenta. By examining several toy models, we clarify
how effective field theory expansions can in general be used to properly
separate long- and short-range effects. We find that one-pion exchange has a
large effect on the scattering phase shift near poles in the amplitude, but
otherwise can be treated perturbatively. Analysis of a toy model that
reproduces 1S0 NN scattering data rather well suggests that failures of
effective field theories for momenta above the pion mass can be due to
short-range physics rather than the treatment of pion exchange. We discuss the
implications this has for extending the applicability of effective field
theories.Comment: 22 pages, 9 figures, references corrected, minor modification
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