18,896 research outputs found
An Empirical Study of the Influence of User Tailoring on Evaluative Argument Effectiveness
The ability to generate effective evaluative arguments is critical for systems intended to advise and persuade their users. We have developed a system that generates evaluative arguments that are tailored to the user, properly arranged and concise. We have also devised an evaluation framework in which the effectiveness of evaluative arguments can be measured with real users. This paper presents the results of a formal experiment we performed in our framework to verify the influence of user tailoring on argument effectiveness.
Rapid rotators revisited: absolute dimensions of KOI-13
We analyse Kepler light-curves of the exoplanet KOI-13b transiting its
moderately rapidly rotating (gravity-darkened) parent star. A physical model,
with minimal ad hoc free parameters, reproduces the time-averaged light-curve
at the ca. 10 parts per million level. We demonstrate that this Roche-model
solution allows the absolute dimensions of the system to be determined from the
star's projected equatorial rotation speed, v(e)sin(i), without any additional
assumptions; we find a planetary radius 1.33+/-0.05 R(Jup), stellar polar
radius 1.55+/-0.06 R(sun), combined mass M(*) + M(P) (\simeq M*) = 1.47 +/-
0.17 M(sun), and distance d \simeq 370+/-25 pc, where the errors are dominated
by uncertainties in relative flux contribution of the visual-binary companion
KOI-13B. The implied stellar rotation period is within ca. 5% of the
non-orbital, 25.43-hr signal found in the Kepler photometry. We show that the
model accurately reproduces independent tomographic observations, and yields an
offset between orbital and stellar-rotation angular-momentum vectors of
60.25+/-0.05 degrees.Comment: Accepted in MNRA
On generalized Abelian deformations
We study sun-products on , i.e. generalized Abelian deformations
associated with star-products for general Poisson structures on . We show
that their cochains are given by differential operators. As a consequence, the
weak triviality of sun-products is established and we show that strong
equivalence classes are quite small. When the Poisson structure is linear
(i.e., on the dual of a Lie algebra), we show that the differentiability of
sun-products implies that covariant star-products on the dual of any Lie
algebra are equivalent each other.Comment: LaTeX 16 pages. To be published in Reviews in Mathematical Physic
Smoothed Particle Hydrodynamic Simulations of Viscous Accretion Discs Around Black Holes
Viscous Keplerian discs become sub-Keplerian close to a black hole since they
pass through sonic points before entering into it. We study the time evolution
of polytropic viscous accretion discs (both in one and two dimensional flows)
using Smoothed Particle Hydrodynamics. We discover that for a large region of
the parameter space, when the flow viscosity parameter is less than a critical
value, standing shock waves are formed. If the viscosity is very high then the
shock disappears. In the intermediate viscosity the disc oscillates very
significantly in viscous time-scale. Our simulations indicate that these
centrifugally supported high density region close to a black hole plays an
active role in the flow dynamics, and consequently, the radiation dynamics.Comment: MNRAS style 6 pages of output, macros included. MNRAS (submitted
Polarized thermal emission by thin metal wires
We report new measurements of the linear polarization of thermal radiation
emitted by incandescent thin tungsten wires, with thicknesses ranging from five
to hundred microns. Our data show very good agreement with theoretical
predictions, based on Drude-type fits to measured optical properties of
tungsten.Comment: 12 pages, 4 encapsulated figures. This new version matches the one
published in New. J. Phys.. Improved presentation, more references added, and
one new figure include
High-precision stellar limb-darkening in exoplanetary transits
Characterization of the atmospheres of transiting exoplanets relies on
accurate measurements of the extent of the optically thick area of the planet
at multiple wavelengths with a precision 100 parts per million (ppm).
Next-generation instruments onboard the James Webb Space Telescope (JWST) are
expected to achieve 10 ppm precision for several tens of targets. A
similar precision can be obtained in modelling only if other astrophysical
effects, including the stellar limb-darkening, are accounted for properly. In
this paper, we explore the limits on precision due to the mathematical formulas
currently adopted to approximate the stellar limb-darkening, and to the use of
limb-darkening coefficients obtained either from stellar-atmosphere models or
empirically. We propose a new limb-darkening law with two coefficients,
`power-2', which outperforms other two-coefficient laws adopted in the
literature in most cases, and particularly for cool stars. Empirical
limb-darkening based on two-coefficient formulas can be significantly biased,
even if the light-curve residuals are nearly photon-noise limited. We
demonstrate an optimal strategy to fitting for the four-coefficients
limb-darkening in the visible, using prior information on the exoplanet orbital
parameters to break some of the degeneracies that otherwise would prevent the
convergence of the fit. Infrared observations taken with the James Webb Space
Telescope (JWST) will provide accurate measurements of the exoplanet orbital
parameters with unprecedented precision, which can be used as priors to improve
the stellar limb-darkening characterization, and therefore the inferred
exoplanet parameters, from observations in the visible, such as those taken
with Kepler/K2, JWST, other past and future instruments
The Structure and Dynamical Evolution of Dark Matter Halos
(Shortened) We use N-body simulations to investigate the structure and
dynamical evolution of dark matter halos in galaxy clusters. Our sample
consists of nine massive halos from an EdS universe with scale free power
spectrum and n = -1. Halos are resolved by ~20000 particles each, with a
dynamical resolution of 20-25 kpc. Large scale tidal fields are included up to
L=150 Mpc using background particles. The halo formation process can be
characterized by the alternation of two dynamical configurations: a merging
phase and a relaxation phase, defined by their signature on the evolution of
the total mass and rms velocity. Halos spend on average one 1/3 of their
evolution in the merging phase and 2/3 in the relaxation phase. Using this
definition, we study the density profiles and their change during the halo
history. The average density profiles are fitted by the NFW analytical model
with an rms residual of 17% between the virial radius Rv and 0.01 Rv. The
Hernquist (1990) profiles fits the same halos with an rms residual of 26%. The
trend with mass of the scale radius of these fits is marginally consistent with
that found by Cole & Lacey (1996): in comparison our halos are more centrally
concentrated, and the relation between scale radius and halo mass is slightly
steeper. We find a moderately large scatter in this relation, due both to
dynamical evolution within halos and to fluctuations in the halo population. We
analyze the dynamical equilibrium of our halos using the Jeans' equation, and
find that on average they are approximately in equilibrium within their virial
radius. Finally, we find that the projected mass profiles of our simulated
halos are in very good agreement with the profiles of three rich galaxy
clusters derived from strong and weak gravitational lensing observations.Comment: 20 pages, Latex, with all figures included. Modified to match the
published versio
Quantum annealing of the Traveling Salesman Problem
We propose a path-integral Monte Carlo quantum annealing scheme for the
symmetric Traveling Salesman Problem, based on a highly constrained Ising-like
representation, and we compare its performance against standard thermal
Simulated Annealing. The Monte Carlo moves implemented are standard, and
consist in restructuring a tour by exchanging two links (2-opt moves). The
quantum annealing scheme, even with a drastically simple form of kinetic
energy, appears definitely superior to the classical one, when tested on a 1002
city instance of the standard TSPLIB.Comment: 5 pages, 2 figure
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