2,156 research outputs found
A new and flexible method for constructing designs for computer experiments
We develop a new method for constructing "good" designs for computer
experiments. The method derives its power from its basic structure that builds
large designs using small designs. We specialize the method for the
construction of orthogonal Latin hypercubes and obtain many results along the
way. In terms of run sizes, the existence problem of orthogonal Latin
hypercubes is completely solved. We also present an explicit result showing how
large orthogonal Latin hypercubes can be constructed using small orthogonal
Latin hypercubes. Another appealing feature of our method is that it can easily
be adapted to construct other designs; we examine how to make use of the method
to construct nearly orthogonal and cascading Latin hypercubes.Comment: Published in at http://dx.doi.org/10.1214/09-AOS757 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
The magnetic properties of the planet host star Kepler-78
Kepler-78 is host to a transiting 8.5-hour orbit super-Earth. In this paper,
the rotation and magnetic properties of the planet host star are studied. We
first revisit the Kepler photometric data for a detailed description of the
rotation properties of Kepler-78, showing that the star seems to undergo a
cycle in the spot pattern of ~1,300 day duration. We then use
spectropolarimetric observations with CFHT/ESPaDOnS to measure the circular
polarization in the line profile of the star during its rotation cycle, as well
as spectroscopic proxies of the chromospheric activity. The average field has
an amplitude of 16 G. The magnetic topology is characterized by a poloidal and
a toroidal component, encompassing 60% and 40% of the magnetic energy,
respectively. Differential rotation is detected with an estimated rate of
0.105+-0.039 rad/d. Activity tracers vary with the rotation cycle of the star;
there is no hint that a residual activity level is related to the planetary
orbit at the precision of our data. The description of the star magnetic
field's characteristics then may serve as input for models of interactions
between the star and its close-by planet, e.g., Ohmic dissipation and unipolar
induction
Interaction of Close-in Planets with the Magnetosphere of their Host Stars I: Diffusion, Ohmic Dissipation of Time Dependent Field, Planetary Inflation, and Mass Loss
The unanticipated discovery of the first close-in planet around 51 Peg has
rekindled the notion that shortly after their formation outside the snow line,
some planets may have migrated to the proximity of their host stars because of
their tidal interaction with their nascent disks. If these planets indeed
migrated to their present-day location, their survival would require a halting
mechanism in the proximity of their host stars. Most T Tauri stars have strong
magnetic fields which can clear out a cavity in the innermost regions of their
circumstellar disks and impose magnetic induction on the nearby young planets.
Here we consider the possibility that a magnetic coupling between young stars
and planets could quench the planet's orbital evolution. After a brief
discussion of the complexity of the full problem, we focus our discussion on
evaluating the permeation and ohmic dissipation of the time dependent component
of the stellar magnetic field in the planet's interior. Adopting a model first
introduced by C. G. Campbell for interacting binary stars, we determine the
modulation of the planetary response to the tilted magnetic field of a
non-synchronously spinning star. We first compute the conductivity in the young
planets, which indicates that the stellar field can penetrate well into the
planet's envelope in a synodic period. For various orbital configurations, we
show that the energy dissipation rate inside the planet is sufficient to induce
short-period planets to inflate. This process results in mass loss via Roche
lobe overflow and in the halting of the planet's orbital migration.Comment: 47 pages, 12 figure
Finite volume effects using lattice chiral perturbation theory
Lattice regularization is used to perform chiral perturbation theory
calculations in finite volume. The lattice spacing is chosen small enough to be
irrelevant, and numerical results are obtained from simple summations.Comment: Lattice2004(spectrum), 3 page
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