3,250 research outputs found
An evaluation of the ATM man/machine interface. Phase 3: Analysis of SL-3 and SL-4 data
The functional adequacy of human factored crew operated systems under operational zero-gravity conditions is considered. Skylab ATM experiment operations generated sufficient telemetry and voice transcript data to support such an assessment effort. Discussions are presented pertaining to the methodology and procedures used to evaluate the hardware, training and directive aspects of Skylab 3 and Skylab 4 manned ATM experiment operations
A Force-Balanced Control Volume Finite Element Method for Multi-Phase Porous Media Flow Modelling
Dr D. Pavlidis would like to acknowledge the support from the following research grants: Innovate UK âOctopusâ, EPSRC âReactor Core-Structure Re-location Modelling for Severe Nuclear Accidentsâ) and Horizon 2020 âIn-Vessel Melt Retentionâ. Funding for Dr P. Salinas from ExxonMobil is gratefully acknowledged. Dr Z. Xie is supported by EPSRC âMulti-Scale Exploration of Multi-phase Physics in Flowsâ. Part funding for Prof Jackson under the TOTAL Chairs programme at Imperial College is also acknowledged. The authors would also like to acknowledge Mr Y. Debbabi for supplying analytic solutions.Peer reviewedPublisher PD
Higher-order conservative interpolation between control-volume meshes: Application to advection and multiphase flow problems with dynamic mesh adaptivity
© 2016 .A general, higher-order, conservative and bounded interpolation for the dynamic and adaptive meshing of control-volume fields dual to continuous and discontinuous finite element representations is presented. Existing techniques such as node-wise interpolation are not conservative and do not readily generalise to discontinuous fields, whilst conservative methods such as Grandy interpolation are often too diffusive. The new method uses control-volume Galerkin projection to interpolate between control-volume fields. Bounded solutions are ensured by using a post-interpolation diffusive correction. Example applications of the method to interface capturing during advection and also to the modelling of multiphase porous media flow are presented to demonstrate the generality and robustness of the approach
Photometry of supernovae in an image series : methods and application to the Supernova Legacy Survey (SNLS)
We present a technique to measure lightcurves of time-variable point sources
on a spatially structured background from imaging data. The technique was
developed to measure light curves of SNLS supernovae in order to infer their
distances. This photometry technique performs simultaneous PSF photometry at
the same sky position on an image series. We describe two implementations of
the method: one that resamples images before measuring fluxes, and one which
does not. In both instances, we sketch the key algorithms involved and present
the validation using semi-artificial sources introduced in real images in order
to assess the accuracy of the supernova flux measurements relative to that of
surrounding stars. We describe the methods required to anchor these PSF fluxes
to calibrated aperture catalogs, in order to derive SN magnitudes. We find a
marginally significant bias of 2 mmag of the after-resampling method, and no
bias at the mmag accuracy for the non-resampling method. Given surrounding star
magnitudes, we determine the systematic uncertainty of SN magnitudes to be less
than 1.5 mmag, which represents about one third of the current photometric
calibration uncertainty affecting SN measurements. The SN photometry delivers
several by-products: bright star PSF flux mea- surements which have a
repeatability of about 0.6%, as for aperture measurements; we measure relative
astrometric positions with a noise floor of 2.4 mas for a single-image bright
star measurement; we show that in all bands of the MegaCam instrument, stars
exhibit a profile linearly broadening with flux by about 0.5% over the whole
brightness range.Comment: Accepted for publication in A&A. 20 page
A mixed discontinuous/continuous finite element pair for shallow-water ocean modelling
We introduce a mixed discontinuous/continuous finite element pair for ocean
modelling, with continuous quadratic pressure/layer depth and discontinuous
velocity. We investigate the finite element pair applied to the linear
shallow-water equations on an f-plane. The element pair has the property that
all geostrophically balanced states which strongly satisfy the boundary
conditions have discrete divergence equal to exactly zero and hence are exactly
steady states of the discretised equations. This means that the finite element
pair has excellent geostrophic balance properties. We illustrate these
properties using numerical tests and provide convergence calculations which
show that the discretisation has quadratic errors, indicating that the element
pair is stable
Self-consistent modelling of hot plasmas within non-extensive Tsallis' thermostatistics
A study of the effects of non-extensivity on the modelling of atomic physics
in hot dense plasmas is proposed within Tsallis' statistics. The electronic
structure of the plasma is calculated through an average-atom model based on
the minimization of the non-extensive free energy.Comment: submitted to "Eur. Phys. J. D
Two superluminous supernovae from the early universe discovered by the Supernova Legacy Survey
We present spectra and lightcurves of SNLS 06D4eu and SNLS 07D2bv, two
hydrogen-free superluminous supernovae discovered by the Supernova Legacy
Survey. At z = 1.588, SNLS 06D4eu is the highest redshift superluminous SN with
a spectrum, at M_U = -22.7 is one of the most luminous SNe ever observed, and
gives a rare glimpse into the restframe ultraviolet where these supernovae put
out their peak energy. SNLS 07D2bv does not have a host galaxy redshift, but
based on the supernova spectrum, we estimate it to be at z ~ 1.5. Both
supernovae have similar observer-frame griz lightcurves, which map to restframe
lightcurves in the U-band and UV, rising in ~ 20 restframe days or longer, and
declining over a similar timescale. The lightcurves peak in the shortest
wavelengths first, consistent with an expanding blackbody starting near 15,000
K and steadily declining in temperature. We compare the spectra to theoretical
models, and identify lines of C II, C III, Fe III, and Mg II in the spectrum of
SNLS 06D4eu and SCP 06F6, and find that they are consistent with an expanding
explosion of only a few solar masses of carbon, oxygen, and other trace metals.
Thus the progenitors appear to be related to those suspected for SNe Ic. A high
kinetic energy, 10^52 ergs, is also favored. Normal mechanisms of powering
core- collapse or thermonuclear supernovae do not seem to work for these
supernovae. We consider models powered by 56Ni decay and interaction with
circumstellar material, but find that the creation and spin-down of a magnetar
with a period of 2ms, magnetic field of 2 x 10^14 Gauss, and a 3 solar mass
progenitor provides the best fit to the data.Comment: ApJ, accepted, 43 pages, 15 figure
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