21,269 research outputs found
Blue, white, and red ocean planets - Simulations of orbital variations in flux and polarization colors
An exoplanet's habitability will depend strongly on the presence of liquid
water. Flux and/or polarization measurements of starlight that is reflected by
exoplanets could help to identify exo-oceans. We investigate which broadband
spectral features in flux and polarization phase functions of reflected
starlight uniquely identify exo-oceans. We compute total fluxes F and polarized
fluxes Q of starlight reflected by cloud-free and (partly) cloudy exoplanets,
for wavelengths from 350 to 865 nm. The ocean surface has waves composed of
Fresnel reflecting wave facets and whitecaps, and scattering within the water
body is included. Total flux F, polarized flux Q, and degree of polarization P
of ocean planets change color from blue, through white, to red at phase angles
alpha ranging from 134-108 deg for F, and from 123-157 deg for Q, with cloud
coverage fraction fc increasing from 0.0 to 1.0 for F, and to 0.98 for Q. The
color change in P only occurs for fc ranging from 0.03-0.98, with the color
crossing angle alpha ranging from 88-161 deg. The total flux F of a cloudy,
zero surface albedo planet can also change color, and for fc=0.0, an ocean
planet's F will not change color for surface pressures ps > 8 bars. Polarized
flux Q of a zero surface albedo planet does not change color for any fc. The
color change of P of starlight reflected by an exoplanet, from blue, through
white, to red with increasing alpha above 88 deg, appears to identify a
(partly) cloudy exo-ocean. The color change of polarized flux Q with increasing
alpha above 123 deg appears to uniquely identify an exo-ocean, independent of
surface pressure or cloud fraction. At the color changing phase angle, the
angular distance between a star and its planet is much larger than at the phase
angle where the glint appears in reflected light. The color change in
polarization thus offers better prospects for detecting exo-oceans.Comment: Accepted for publication in Astron. Astrophys; multicolumn versio
Intrinsic Magnetism in Nanosheets of SnO: A First-principles Study
We propose intrinsic magnetism in nanosheets of SnO, based on
first-principles calculations. The electronic structure and spin density reveal
that orbitals of the oxygen atoms, surrounding Sn vacancies, have a non
itinerant nature which gives birth to localized magnetism. A giant decrease in
defect formation energies of Sn vacancies in nanosheets is observed. We,
therefore, believe that native defects can be stabilized without any chemical
doping. Nanosheets of different thicknesses are also studied, and it is found
that it is easier to create vacancies, which are magnetic, at the surface of
the sheets. SnO nanosheets can, therefore, open new opportunities in the
field of spintronics.Comment: J. Magn. Magn. Mate. 2012 (Accepted
The Kinematic Properties of Double-Barred Galaxies: Simulations Vs. Integral-Field Observations
Using high resolution N -body simulations, we recently reported that a dynamically cool inner disk embedded in a hotter outer disk can naturally generate a steady double-barred (S2B) structure. Here we study the kinematics of these S2B simulations, and compare them to integral-field observations from ATLAS3D and SAURON. We show that S2B galaxies exhibit several distinct kinematic features, namely:
(1) significantly distorted isovelocity contours at the transition region between the two bars, (2) peaks in σLOS along the minor axis of inner bars, which we term “σ-humps”, that are often accompanied by
ring/spiral-like features of increased σLOS, (3) h3 − v¯ anti-correlations in the region of the inner bar for
certain orientations, and (4) rings of positive h4 when viewed at low inclinations. The most impressive of these features are the σ-humps; these evolve with the inner bar, oscillating in strength just as the inner bar does as it rotates relative to the outer bar. We show that, in cylindrical coordinates, the inner bar has similar streaming motions and velocity dispersion properties as normal large-scale bars, except for σz , which exhibits peaks on the minor axis, i.e., humps. These σz humps are responsible for producing the σ-humps. For three well-resolved early-type S2Bs (NGC 2859, NGC 2950, and NGC 3941) and a potential S2B candidate (NGC 3384), the S2B model qualitatively matches the integral-field data well, including the “σ-hollows” previously identified. We also discuss the kinematic effect of a nuclear disk in S2Bs
Data-driven modeling of systemic delay propagation under severe meteorological conditions
The upsetting consequences of weather conditions are well known to any person
involved in air transportation. Still the quantification of how these
disturbances affect delay propagation and the effectiveness of managers and
pilots interventions to prevent possible large-scale system failures needs
further attention. In this work, we employ an agent-based data-driven model
developed using real flight performance registers for the entire US airport
network and focus on the events occurring on October 27 2010 in the United
States. A major storm complex that was later called the 2010 Superstorm took
place that day. Our model correctly reproduces the evolution of the
delay-spreading dynamics. By considering different intervention measures, we
can even improve the model predictions getting closer to the real delay data.
Our model can thus be of help to managers as a tool to assess different
intervention measures in order to diminish the impact of disruptive conditions
in the air transport system.Comment: 9 pages, 5 figures. Tenth USA/Europe Air Traffic Management Research
and Development Seminar (ATM2013
Preparation of atomic oxygen resistant polymeric materials
Polyphenyl quinoxalines (PPQs) are an important family of high performance polymers that offer good chemical and thermal stability coupled with excellent mechanical properties. These aromatic heterocyclic polymers are potentially useful as films, coatings, adhesives, and composite materials that demand stability in harsh environments. Our approach was to prepare PPQs with pendent siloxane groups using the appropriate chemistry and then evaluate these polymers before and after exposure to simulated atomic oxygen. Either monomer, the bis(o-diamine)s or the bis(alpha-diketone)s can be synthesized with a hydroxy group to which the siloxane chain will be attached. Several novel materials were prepared
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