3,152 research outputs found
Ray methods for free boundary problems
We discuss the use of the WKB ansatz in a variety of parabolic problems involving a small parameter. We analyse the Stefan problem for small latent heat, the BlackāScholes problem for an American put option, and some nonlinear diffusion equations, in each case constructing an asymptotic solution by the use of ray methods
A neural network version of the measure correlate predict algorithm for estimating wind energy yield.
A neural network version of the measure correlate predict algorithm for estimating wind energy yiel
A Spin-Orbit Alignment for the Hot Jupiter HATS-3b
We have measured the alignment between the orbit of HATS-3b (a recently
discovered, slightly inflated Hot Jupiter) and the spin-axis of its host star.
Data were obtained using the CYCLOPS2 optical-fiber bundle and its simultaneous
calibration system feeding the UCLES spectrograph on the Anglo-Australian
Telescope. The sky-projected spin-orbit angle of was
determined from spectroscopic measurements of Rossiter-McLaughlin effect. This
is the first exoplanet discovered through the HATSouth transit survey to have
its spin-orbit angle measured. Our results indicate that the orbital plane of
HATS-3b is consistent with being aligned to the spin axis of its host star. The
low obliquity of the HATS-3 system, which has a relatively hot mid F-type host
star, agrees with the general trend observed for Hot Jupiter host stars with
effective temperatures K to have randomly distributed spin-orbit angles.Comment: 13 pages. Accepted for publication in the Astrophysical Journa
The Impact of Line Misidentification on Cosmological Constraints from Euclid and other Spectroscopic Galaxy Surveys
We perform forecasts for how baryon acoustic oscillation (BAO) scale and
redshift-space distortion (RSD) measurements from future spectroscopic emission
line galaxy (ELG) surveys such as Euclid are degraded in the presence of
spectral line misidentification. Using analytic calculations verified with mock
galaxy catalogs from log-normal simulations we find that constraints are
degraded in two ways, even when the interloper power spectrum is modeled
correctly in the likelihood. Firstly, there is a loss of signal-to-noise ratio
for the power spectrum of the target galaxies, which propagates to all
cosmological constraints and increases with contamination fraction, .
Secondly, degeneracies can open up between and cosmological parameters.
In our calculations this typically increases BAO scale uncertainties at the
10-20% level when marginalizing over parameters determining the broadband power
spectrum shape. External constraints on , or parameters determining the
shape of the power spectrum, for example from cosmic microwave background (CMB)
measurements, can remove this effect. There is a near-perfect degeneracy
between and the power spectrum amplitude for low values, where
is not well determined from the contaminated sample alone. This has the
potential to strongly degrade RSD constraints. The degeneracy can be broken
with an external constraint on , for example from cross-correlation with a
separate galaxy sample containing the misidentified line, or deeper
sub-surveys.Comment: 18 pages, 7 figures, updated to match version accepted by ApJ (extra
paragraph added at the end of Section 4.3, minor text edits
A Nearly Polar Orbit for the Extrasolar Hot Jupiter WASP-79b
We report the measurement of a spin-orbit misalignment for WASP-79b, a
recently discovered, bloated transiting hot Jupiter from the WASP survey. Data
were obtained using the CYCLOPS2 optical-fiber bundle and its simultaneous
calibration system feeding the UCLES spectrograph on the Anglo-Australian
Telescope. We have used the Rossiter-McLaughlin effect to determine the
sky-projected spin-orbit angle to be lambda = -106+19-13 degrees. This result
indicates a significant misalignment between the spin axis of the host star and
the orbital plane of the planet -- the planet being in a nearly polar orbit.
WASP-79 is consistent with other stars that have Teff > 6250K and host hot
Jupiters in spin-orbit misalignment.Comment: 8 pages, 2 figures, in press ApJL (accepted 2 August 2013
Modelling the influence of the process inputs on the removal of surface contaminants from Ti-6Al-4V linear friction welds
The linear friction welding (LFW) process is finding increasing interest from industry for the fabrication of near-net-shape, titanium alloy Tiā6Alā4V, aerospace components. Currently, the removal of surface contaminants, such as oxides and foreign particles, from the weld interface into the flash is not fully understood. To address this problem, two-dimensional (2D) computational models were developed using the finite element analysis (FEA) software DEFORM and validated with experiments. The key findings showed that the welds made with higher applied forces required less burn-off to completely remove the surface contaminants from the interface into the flash; the interface temperature increased as the applied force was decreased or the rubbing velocity increased; and the boundary temperature between the rapid flash formation and negligible material flow was approximately 970 Ā°C. An understanding of these phenomena is of particular interest for the industrialisation of near-net-shape titanium alloy aerospace components.EPSRC, Boeing Company, Welding Institut
Kinetics of Surfactant Adsorption at Fluid/Fluid Interfaces: Non-ionic Surfactants
We present a model treating the kinetics of adsorption of soluble
surface-active molecules at the interface between an aqueous solution and
another fluid phase. The model accounts for both the diffusive transport inside
the solution and the kinetics taking place at the interface using a free-energy
formulation. In addition, it offers a general method of calculating dynamic
surface tensions. Non-ionic surfactants are shown, in general, to undergo a
diffusion-limited adsorption, in accord with experimental findings.Comment: 6 pages, 3 figures, see also cond-mat/960814
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