1,677 research outputs found
No-hole k-tuple (r + 1)-distant colorings of odd cycles
AbstractWe give a necessary and sufficient condition for the existence of near-optimal Nkr-colorings of cycles. Troxell (preprint) studied near-optimal Nkr-colorings and proved most of the result presented here; our contribution is to complete the proof for odd cycles
Multiple ionization of neon by soft X-rays at ultrahigh intensity
At the free-electron laser FLASH, multiple ionization of neon atoms was
quantitatively investigated at 93.0 eV and 90.5 eV photon energy. For ion
charge states up to 6+, we compare the respective absolute photoionization
yields with results from a minimal model and an elaborate description. Both
approaches are based on rate equations and take into acccout a Gaussian spatial
intensity distribution of the laser beam. From the comparison we conclude, that
photoionization up to a charge of 5+ can be described by the minimal model. For
higher charges, the experimental ionization yields systematically exceed the
elaborate rate based prediction.Comment: 10 pages, 3 figure
Cost optimization of offshore wind farm combination with reversible solid oxide cell system producing hydrogen using the PyPSA power system modelling tool
In the context of reaching the net zero carbon target, the UK has set an ambitious target of having a green hydrogen production capacity of 5 GW by 2030. As part of the EPSRC-funded project on high efficiency reversible solid oxide cells (rSOC) for the integration of offshore renewable energy (ORE) using hydrogen, eight scenarios where hydrogen is combined with offshore renewable energy were identified. A model using the PyPSA power system modelling tool combined with a sensitivity study, investigated optimized rSOC system capacities, hydrogen storage capacities, and subsea cable connection capacities under various combinations of infrastructure cost, rSOC system efficiencies, and electricity prices for one of the scenarios. Preliminary results for a 600 MW wind farm situated 60 km from shore combined with offshore hydrogen production illustrate the impact of electricity price on decision-making in energy dispatch and on optimization of infrastructure of an ORE-rSOC system. Results indicate that high electricity price fluctuations call for large amounts of hydrogen production and storage capacity. Further refinement of input data would make this approach a promising decision-making tool for the use in the design of an ORE-rSOC system
PERSYST, a model for ex ante assessment of cropping systems performances. Adaptation to organic farming in the Ile-de-France region
PERSYST is a web software for ex ante assessment of crop yield that takes explicitely into account the cropping system (i.e. crop rotation and crop management) perspective. Environmental and economic indicators are calculated at crop rotation scale to complete the previous yield assessment. In 2012, a research program enabled the model adaptation to organic systems, taking into account weed management and organic inputs supply. This program also allowed to parameterize the web software in the Ile-de-France region for 8 soil types and 18crops. Parameterization has been validated for the most common situations. Validation remains to be done for less common ones. When completed, validation will make it possible to test the software in promising situations of use, such as supporting organic farmers analyzing their current cropping systems, or supporting farmers thinking about converting their farms to organic farming
Optimal error estimates for non-conforming approximations of linear parabolic problems with minimal regularity
We consider a general linear parabolic problem with extended time boundary
conditions (including initial value problems and periodic ones), and
approximate it by the implicit Euler scheme in time and the Gradient
Discretisation method in space; the latter is in fact a class of methods that
includes conforming and nonconforming finite elements, discontinuous Galerkin
methods and several others. The main result is an error estimate which holds
without supplementary regularity hypothesis on the solution. This result states
that the approximation error has the same order as the sum of the interpolation
error and the conformity error. The proof of this result relies on an inf-sup
inequality in Hilbert spaces which can be used both in the continuous and the
discrete frameworks. The error estimate result is illustrated by numerical
examples with low regularity of the solution
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