680 research outputs found
Photometric Variability in Kepler Target Stars: The Sun Among Stars -- A First Look
The Kepler mission provides an exciting opportunity to study the lightcurves
of stars with unprecedented precision and continuity of coverage. This is the
first look at a large sample of stars with photometric data of a quality that
has heretofore been only available for our Sun. It provides the first
opportunity to compare the irradiance variations of our Sun to a large cohort
of stars ranging from vary similar to rather different stellar properties, at a
wide variety of ages. Although Kepler data is in an early phase of maturity,
and we only analyze the first month of coverage, it is sufficient to garner the
first meaningful measurements of our Sun's variability in the context of a
large cohort of main sequence stars in the solar neighborhood. We find that
nearly half of the full sample is more active than the active Sun, although
most of them are not more than twice as active. The active fraction is closer
to a third for the stars most similar to the Sun, and rises to well more than
half for stars cooler than mid K spectral types.Comment: 13 pages, 4 figures, accepted to ApJ Letter
Programa de opinión con sátira polÃtica en plataformas como YouTube: el caso de La Pulla
61 páginasA través de los años, los medios de comunicación colombianos han debido adaptarse a la evolución de las plataformas de información, al igual que a los formatos y la manera en la que se transmite la información, pues estos son clave a la hora de generar interés en el público. Con la llegada del internet, muchos medios han tenido que adaptar su contenido para que este cumpla con las expectativas planteadas y no termine por aburrir a las personas que lo observan. Por estos motivos, este proyecto se propone investigar qué tan importante es el uso de recursos humorÃsticos y gráficos para generar engagement con las audiencias que buscan contenidos polÃticos alternativos. Se tomó el ejemplo de La Pulla, un programa de opinión y sátira polÃtica que busca informar a los colombianos, de una manera entendible, mediante una de las plataformas más utilizadas actualmente, YouTube. La respuesta a este interrogante es que este programa en especial trata la información de forma clara, sin dejar de lado su opinión, y los recursos que utiliza tanto humorÃsticos (sátira, ironÃa, sarcasmo, etc.) como gráficos (fotos, videos, audios, etc.) explican buena parte del éxito y la viralización de su contenido.Colombian media have adapted over the years as information platforms have evolved, as well as formats, because the way in which information is transmitted is very important when generating interest in the viewer. With the advent of the internet, many media have had to adapt their content so that it meets public expectations and does not result boring for people. For these reasons, this project aims to investigate how important is the use of humorous and graphic resources on the engagement of the audiences that seek for alternative political content, such as La Pulla. This program uses an opinion and political type of journalism which seeks to inform Colombians in an understandable way through one of the currently most used platforms: YouTube. This program in particular treats information clearly and without neglecting personal opinions, so, the resources it uses, both humorous (satire, irony, sarcasm, etc.) and graphic (photos, videos, audios, etc.) explain a big part of the success and spread of their content.Comunicación Social y PeriodismoComunicador Social y Periodist
The Firebreak Problem
Suppose we have a network that is represented by a graph . Potentially a
fire (or other type of contagion) might erupt at some vertex of . We are
able to respond to this outbreak by establishing a firebreak at other
vertices of , so that the fire cannot pass through these fortified vertices.
The question that now arises is which vertices will result in the greatest
number of vertices being saved from the fire, assuming that the fire will
spread to every vertex that is not fully behind the vertices of the
firebreak. This is the essence of the {\sc Firebreak} decision problem, which
is the focus of this paper. We establish that the problem is intractable on the
class of split graphs as well as on the class of bipartite graphs, but can be
solved in linear time when restricted to graphs having constant-bounded
treewidth, or in polynomial time when restricted to intersection graphs. We
also consider some closely related problems
SN 2013ab : A normal type IIP supernova in NGC 5669
We present densely-sampled ultraviolet/optical photometric and low-resolution
optical spectroscopic observations of the type IIP supernova 2013ab in the
nearby (24 Mpc) galaxy NGC 5669, from 2 to 190d after explosion.
Continuous photometric observations, with the cadence of typically a day to one
week, were acquired with the 1-2m class telescopes in the LCOGT network, ARIES
telescopes in India and various other telescopes around the globe. The light
curve and spectra suggest that the SN is a normal type IIP event with a plateau
duration of days with mid plateau absolute visual magnitude of
-16.7, although with a steeper decline during the plateau (0.92 mag 100 d in band) relative to other archetypal SNe of similar brightness.
The velocity profile of SN 2013ab shows striking resemblance with those of SNe
1999em and 2012aw. Following the Rabinak & Waxman (2011) prescription, the
initial temperature evolution of the SN emission allows us to estimate the
progenitor radius to be 800 R, indicating that the SN
originated from a red supergiant star. The distance to the SN host galaxy is
estimated to be 24.3 Mpc from expanding photosphere method (EPM). From our
observations, we estimate that 0.064 M of Ni was synthesized
in the explosion. General relativistic, radiation hydrodynamical modeling of
the SN infers an explosion energy of erg, a progenitor
mass (at the time of explosion) of M and an initial radius
of R.Comment: 22 pages, 18 figures, 5 tables. Accepted for publication in MNRA
Verus: Verifying Rust Programs using Linear Ghost Types (extended version)
The Rust programming language provides a powerful type system that checks
linearity and borrowing, allowing code to safely manipulate memory without
garbage collection and making Rust ideal for developing low-level,
high-assurance systems. For such systems, formal verification can be useful to
prove functional correctness properties beyond type safety. This paper presents
Verus, an SMT-based tool for formally verifying Rust programs. With Verus,
programmers express proofs and specifications using the Rust language, allowing
proofs to take advantage of Rust's linear types and borrow checking. We show
how this allows proofs to manipulate linearly typed permissions that let Rust
code safely manipulate memory, pointers, and concurrent resources. Verus
organizes proofs and specifications using a novel mode system that
distinguishes specifications, which are not checked for linearity and
borrowing, from executable code and proofs, which are checked for linearity and
borrowing. We formalize Verus' linearity, borrowing, and modes in a small
lambda calculus, for which we prove type safety and termination of
specifications and proofs. We demonstrate Verus on a series of examples,
including pointer-manipulating code (an xor-based doubly linked list), code
with interior mutability, and concurrent code
The K2 Mission: Characterization and Early results
The K2 mission will make use of the Kepler spacecraft and its assets to
expand upon Kepler's groundbreaking discoveries in the fields of exoplanets and
astrophysics through new and exciting observations. K2 will use an innovative
way of operating the spacecraft to observe target fields along the ecliptic for
the next 2-3 years. Early science commissioning observations have shown an
estimated photometric precision near 400 ppm in a single 30 minute observation,
and a 6-hour photometric precision of 80 ppm (both at V=12). The K2 mission
offers long-term, simultaneous optical observation of thousands of objects at a
precision far better than is achievable from ground-based telescopes. Ecliptic
fields will be observed for approximately 75-days enabling a unique exoplanet
survey which fills the gaps in duration and sensitivity between the Kepler and
TESS missions, and offers pre-launch exoplanet target identification for JWST
transit spectroscopy. Astrophysics observations with K2 will include studies of
young open clusters, bright stars, galaxies, supernovae, and asteroseismology.Comment: 25 pages, 11 figures, Accepted to PAS
Kepler Observations of Transiting Hot Compact Objects
Kepler photometry has revealed two unusual transiting companions orbiting an
early A-star and a late B-star. In both cases the occultation of the companion
is deeper than the transit. The occultation and transit with follow-up optical
spectroscopy reveal a 9400 K early A-star, KOI-74 (KIC 6889235), with a
companion in a 5.2 day orbit with a radius of 0.08 Rsun and a 10000 K late
B-star KOI-81 (KIC 8823868) that has a companion in a 24 day orbit with a
radius of 0.2 Rsun. We infer a temperature of 12250 K for KOI-74b and 13500 K
for KOI-81b.
We present 43 days of high duty cycle, 30 minute cadence photometry, with
models demonstrating the intriguing properties of these object, and speculate
on their nature.Comment: 12 pages, 3 figures, submitted to ApJL (updated to correct KOI74
lightcurve
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