827 research outputs found
A Posteriori Error Estimation for the p-curl Problem
We derive a posteriori error estimates for a semi-discrete finite element
approximation of a nonlinear eddy current problem arising from applied
superconductivity, known as the -curl problem. In particular, we show the
reliability for non-conforming N\'{e}d\'{e}lec elements based on a residual
type argument and a Helmholtz-Weyl decomposition of
. As a consequence, we are also able to derive an a
posteriori error estimate for a quantity of interest called the AC loss. The
nonlinearity for this form of Maxwell's equation is an analogue of the one
found in the -Laplacian. It is handled without linearizing around the
approximate solution. The non-conformity is dealt by adapting error
decomposition techniques of Carstensen, Hu and Orlando. Geometric
non-conformities also appear because the continuous problem is defined over a
bounded domain while the discrete problem is formulated over a weaker
polyhedral domain. The semi-discrete formulation studied in this paper is often
encountered in commercial codes and is shown to be well-posed. The paper
concludes with numerical results confirming the reliability of the a posteriori
error estimate.Comment: 32 page
Towards a user-friendly webservice architecture for statistical machine translation in the PANACEA project
This paper presents a webservice architecture for Statistical Machine Translation aimed at non-technical users. A workďŹow editor allows a user to combine different
webservices using a graphical user interface. In the current state of this project, the webservices have been implemented
for a range of sentential and sub-sentential aligners. The advantage of a common interface and a common data format allows the user to build workďŹows exchanging different aligners
Seeing statistics at the upgraded 3.8m UK infrared telescope (UKIRT)
From 1991 until 1997, the 3.8m UK Infrared Telescope (UKIRT) underwent a
programme of upgrades aimed at improving its intrinsic optical performance.
This resulted in images with a FWHM of 0."17 at 2.2 um in September 1998. To
understand and maintain the improvements to the delivered image quality since
the completion of the upgrades programme, we have regularly monitored the
overall atmospheric seeing, as measured by radial displacements of subaperture
images (i.e. seeing-generated focus fluctuations), and the delivered image
diameters. The latter have been measured and recorded automatically since the
beginning of 2001 whenever the facility imager UFTI (UKIRT Fast Track Imager)
has been in use.
In this paper we report the results of these measurements. We investigate the
relation between the delivered image diameter and the RMS atmospheric seeing
(as measured by focus fluctuations, mentioned above). We find that the best
seeing occurs in the second half of the night, generally after 2am HST and that
the best seeing occurs in the summer between the months of July and September.
We also find that the relationship between Zrms and delivered image diameter is
uncertain. As a result Zrms frequently predicts a larger FWHM than that
measured in the images.
Finally, we show that there is no correlation between near-infrared seeing
measured at UKIRT and sub-mm seeing measured at the Caltech Submillimetre
Observatory (CSO).Comment: 10 pages to appear in the SPIE proceeding vol. 4484 on Observatory
Operations to Maximize Scientific Retur
Bio-inspired two target resolution at radio frequencies
Echolocating bats show a unique ability to detect, resolve and discriminate targets. The Spectrogram Correlation and Transformation (SCAT) receiver is a model of the Eptesicus fuscus auditory system that presents key signal processing differences compared to radar which may offer useful lessons for improvement. A baseband version of the SCAT is used to investigate advantages and disadvantages of bat-like signal processing against the task of target resolution. The baseband receiver is applied to RF experimental data and results show higher range resolution than the reciprocal of the transmitted bandwidth can be achieved for two closely spaced scatterers
Grid-enabled electromagnetic optimisation (GEM) for industrial use.
We have developed a tool for parametric electromagnetic design studies using industrial analysis code for the design search and optimisation of photonic crystals. This software tool allows engineering users to transparently access Grid compute components for an end-to-end design of a photonic device using computational electromagnetics. In this paper, we give an overview of the industrial application background, present some aspects of the interface developed, and discuss some of the issues involved in the computational tasks and the storage of metadata
Inverted spin polarization of Heusler alloys for new spintronic devices
A new magnetic logic overcomes the major limitations of field programmable
gate arrays while having a 50% smaller unit cell than conventional designs
utilizing magnetic tunnel junctions with one Heusler alloy electrode. These
show positive and negative TMR values at different bias voltages at room
temperature which generally adds an additional degree of freedom to all
spintronic devices
Bio-inspired processing of radar target echoes
Echolocating bats have evolved the ability to detect, resolve and discriminate targets in highly challenging environments using biological sonar. The way bats process signals in the receiving auditory system is not the same as that of radar and sonar and hence investigating differences and similarities might provide useful lessons to improve synthetic sensors. The Spectrogram Correlation And Transformation (SCAT) receiver is an existing model of the bat auditory system that takes into account the physiology and the neural organisation of bats that emit broadband signals. In this study, the authors present a baseband receiver equivalent to the SCAT that allows an analysis of target echoes at baseband. The baseband SCAT (BSCT) is used to investigate the output of the bat-auditory model for two closely spaced scatterers and to carry out an analysis of range resolution performance and a comparison with the conventional matched filter. Results firstly show that the BSCT provides improved resolution performance. It is then demonstrated that the output of the BSCT can be obtained with an equivalent matched-filter based receiver. The results are verified with a set of laboratory experiments at radio frequencies in a high signal-to-noise ratio
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