38,081 research outputs found
All-sky Relative Opacity Mapping Using Night Time Panoramic Images
An all-sky cloud monitoring system that generates relative opacity maps over
many of the world's premier astronomical observatories is described.
Photometric measurements of numerous background stars are combined with
simultaneous sky brightness measurements to differentiate thin clouds from sky
glow sources such as air glow and zodiacal light. The system takes a continuous
pipeline of all-sky images, and compares them to canonical images taken on
other nights at the same sidereal time. Data interpolation then yields
transmission maps covering almost the entire sky. An implementation of this
system is currently operating through the Night Sky Live network of CONCAM3s
located at Cerro Pachon (Chile), Mauna Kea (Hawaii), Haleakala (Hawaii), SALT
(South Africa) and the Canary Islands (Northwestern Africa).Comment: Accepted for publication in PAS
Chiral spin-orbital liquids with nodal lines
Strongly correlated materials with strong spin-orbit coupling hold promise
for realizing topological phases with fractionalized excitations. Here we
propose a chiral spin-orbital liquid as a stable phase of a realistic model for
heavy-element double perovskites. This spin liquid state has Majorana fermion
excitations with a gapless spectrum characterized by nodal lines along the
edges of the Brillouin zone. We show that the nodal lines are topological
defects of a non-Abelian Berry connection and that the system exhibits
dispersing surface states. We discuss some experimental signatures of this
state and compare them with properties of the spin liquid candidate Ba_2YMoO_6.Comment: 5 pages + supplementary materia
A water level relationship between consecutive gauge stations along Solim\~oes/Amazonas main channel: a wavelet approach
Gauge stations are distributed along the Solim\~oes/Amazonas main channel to
monitor water level changes over time. Those measurements help quantify both
the water movement and its variability from one gauge station to the next
downstream. The objective of this study is to detect changes in the water level
relationship between consecutive gauge stations along the Solim\~oes/Amazonas
main channel, since 1980. To carry out the analyses, data spanning from 1980 to
2010 from three consecutive gauges (Tefe, Manaus and Obidos) were used to
compute standardized daily anomalies. In particular for infra-annual periods it
was possible to detect changes for the water level variability along the
Solim\~oes/Amazonas main channel, by applying the Morlet Wavelet Transformation
(WT) and Wavelet Cross Coherence (WCC) methods. It was possible to quantify the
waves amplitude for the WT infra-annual scaled-period and were quite similar to
the three gauge stations denoting that the water level variability are related
to the same hydrological forcing functions. Changes in the WCC was detected for
the Manaus-Obidos river stretch and this characteristic might be associated
with land cover changes in the floodplains. The next steps of this research,
will be to test this hypotheses by integrating land cover changes into the
floodplain with hydrological modelling simulations throughout the time-series
Non-Collinear Ferromagnetic Luttinger Liquids
The presence of electron-electron interactions in one dimension profoundly
changes the properties of a system. The separation of charge and spin degrees
of freedom is just one example. We consider what happens when a system
consisting of a ferromagnetic region of non-collinearity, i.e. a domain wall,
is coupled to interacting electrons in one-dimension (more specifically a
Luttinger liquid). The ferromagnetism breaks spin charge separation and the
presence of the domain wall introduces a spin dependent scatterer into the
problem. The absence of spin charge separation and the effects of the electron
correlations results in very different behaviour for the excitations in the
system and for spin-transfer-torque effects in this model.Comment: 6 pages, submitted to Journal of Physics: Conference Series for JEMS
201
Modeling non-thermal emission from stellar bow shocks
Runaway O- and early B-type stars passing throughout the interstellar medium
at supersonic velocities and characterized by strong stellar winds may produce
bow shocks that can serve as particle acceleration sites. Previous theoretical
models predict the production of high energy photons by non-thermal radiative
processes, but their efficiency is still debated. We aim to test and explain
the possibility of emission from the bow shocks formed by runaway stars
traveling through the interstellar medium by using previous theoretical models.
We apply our model to AE Aurigae, the first reported star with an X-ray
detected bow shock, to BD+43 3654, in which the observations failed in
detecting high energy emission, and to the transition phase of a supergiant
star in the late stages of its life.From our analysis, we confirm that the
X-ray emission from the bow shock produced by AE Aurigae can be explained by
inverse Compton processes involving the infrared photons of the heated dust. We
also predict low high energy flux emission from the bow shock produced by BD+43
3654, and the possibility of high energy emission from the bow shock formed by
a supergiant star during the transition phase from blue to red supergiant.Bow
shock formed by different type of runaway stars are revealed as a new possible
source of high energy photons in our neighbourhood
Properties improvement of poly(o-methoxyaniline) based supercapacitors : experimental and theoretical behaviour study of self-doping effect
The support of this research by FAPESP (2011/10897-2, 2013/07296-2), CsF-PVE (99999.007708/2015-07), CAPES and CNPq is gratefully acknowledged. We also thank the University of Aberdeen for providing computational time on MaxwellPeer reviewedPostprin
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