923 research outputs found
The spin-orbit alignment of visual binaries
The angle between the stellar spin-axis and the orbital plane of a stellar or
planetary companion has important implications for the formation and evolution
of such systems. A study by Hale (1994) found that binaries with separations au are preferentially aligned while binaries on wider orbits are
frequently misaligned. We aim to test the robustness of the Hale (1994) results
by reanalysing the sample of visual binaries with measured rotation periods
using independently derived stellar parameters and a Bayesian formalism. Our
analysis is based on a combination of data from Hale (1994) and newly obtained
spectroscopic data from the Hertzsprung SONG telescope, combined with
astrometric data from Gaia DR2 and the Washington Double Star Catalog. We
combine measurements of stellar radii and rotation periods to obtain stellar
rotational velocities . Rotational velocities are combined with
measurements of projected rotational velocities to derive posterior
probability distributions of stellar inclination angles . We determine
line-of-sight projected spin-orbit angles by comparing stellar inclination
angles with astrometric orbital inclination angles. We find that the precision
of the available data is insufficient to make inferences about the spin-orbit
alignment of visual binaries. The data are equally compatible with alignment
and misalignment at all orbital separations. We conclude that the previously
reported trend that binaries with separations au are preferentially
aligned is spurious. The spin-orbit alignment distribution of visual binaries
is unconstrained. Based on simulated observations, we predict that it will be
difficult to reach the sufficient precision in , rotation periods, and
orbital inclination required to make robust statistical inferences about the
spin-orbit alignment of visual binaries.Comment: Accepted for publication in A&A. 10 pages, 5 figures, 1 tabl
Quantum Bit String Commitment
A bit string commitment protocol securely commits classical bits in such
a way that the recipient can extract only bits of information about the
string. Classical reasoning might suggest that bit string commitment implies
bit commitment and hence, given the Mayers-Lo-Chau theorem, that
non-relativistic quantum bit string commitment is impossible. Not so: there
exist non-relativistic quantum bit string commitment protocols, with security
parameters and , that allow to commit
bits to so that 's probability of successfully cheating when revealing
any bit and 's probability of extracting more than bits of
information about the bit string before revelation are both less than
. With a slightly weakened but still restrictive definition of
security against , can be taken to be for a positive
constant . I briefly discuss possible applications.Comment: Published version. (Refs updated.
An Improved Interactive Streaming Algorithm for the Distinct Elements Problem
The exact computation of the number of distinct elements (frequency moment
) is a fundamental problem in the study of data streaming algorithms. We
denote the length of the stream by where each symbol is drawn from a
universe of size . While it is well known that the moments can
be approximated by efficient streaming algorithms, it is easy to see that exact
computation of requires space . In previous work, Cormode
et al. therefore considered a model where the data stream is also processed by
a powerful helper, who provides an interactive proof of the result. They gave
such protocols with a polylogarithmic number of rounds of communication between
helper and verifier for all functions in NC. This number of rounds
can quickly make such
protocols impractical.
Cormode et al. also gave a protocol with rounds for the exact
computation of where the space complexity is but the total communication . They managed to give round protocols with
complexity for many other interesting problems
including , Inner product, and Range-sum, but computing exactly with
polylogarithmic space and communication and rounds remained open.
In this work, we give a streaming interactive protocol with rounds
for exact computation of using bits of space and the communication is . The update
time of the verifier per symbol received is .Comment: Submitted to ICALP 201
Constraints on the Obliquities of Kepler Planet-Hosting Stars
Stars with hot Jupiters have obliquities ranging from 0-180 degrees, but
relatively little is known about the obliquities of stars with smaller planets.
Using data from the California-Kepler Survey, we investigate the obliquities of
stars with planets spanning a wide range of sizes, most of which are smaller
than Neptune. First, we identify 156 planet hosts for which measurements of the
projected rotation velocity (vsini) and rotation period are both available. By
combining estimates of v and vsini, we find nearly all the stars to be
compatible with high inclination, and hence, low obliquity (less than about 20
degrees). Second, we focus on a sample of 159 hot stars (> 6000K) for which
vsini is available but not necessarily the rotation period. We find 6 stars for
which vsini is anomalously low, an indicator of high obliquity. Half of these
have hot Jupiters, even though only 3% of the stars that were searched have hot
Jupiters. We also compare the vsini distribution of the hot stars with planets
to that of 83 control stars selected without prior knowledge of planets. The
mean vsini of the control stars is lower than that of the planet hosts by a
factor of approximately pi/4, as one would expect if the planet hosts have low
obliquities. All these findings suggest that the Kepler planet-hosting stars
generally have low obliquities, with the exception of hot stars with hot
Jupiters.Comment: AJ, in pres
Bootstrapping Conditional GANs for Video Game Level Generation
Generative Adversarial Networks (GANs) have shown im-pressive results for
image generation. However, GANs facechallenges in generating contents with
certain types of con-straints, such as game levels. Specifically, it is
difficult togenerate levels that have aesthetic appeal and are playable atthe
same time. Additionally, because training data usually islimited, it is
challenging to generate unique levels with cur-rent GANs. In this paper, we
propose a new GAN architec-ture namedConditional Embedding Self-Attention
Genera-tive Adversarial Network(CESAGAN) and a new bootstrap-ping training
procedure. The CESAGAN is a modification ofthe self-attention GAN that
incorporates an embedding fea-ture vector input to condition the training of
the discriminatorand generator. This allows the network to model
non-localdependency between game objects, and to count objects. Ad-ditionally,
to reduce the number of levels necessary to trainthe GAN, we propose a
bootstrapping mechanism in whichplayable generated levels are added to the
training set. Theresults demonstrate that the new approach does not only
gen-erate a larger number of levels that are playable but also gen-erates fewer
duplicate levels compared to a standard GAN
Quantum fingerprinting
Classical fingerprinting associates with each string a shorter string (its
fingerprint), such that, with high probability, any two distinct strings can be
distinguished by comparing their fingerprints alone. The fingerprints can be
exponentially smaller than the original strings if the parties preparing the
fingerprints share a random key, but not if they only have access to
uncorrelated random sources. In this paper we show that fingerprints consisting
of quantum information can be made exponentially smaller than the original
strings without any correlations or entanglement between the parties: we give a
scheme where the quantum fingerprints are exponentially shorter than the
original strings and we give a test that distinguishes any two unknown quantum
fingerprints with high probability. Our scheme implies an exponential
quantum/classical gap for the equality problem in the simultaneous message
passing model of communication complexity. We optimize several aspects of our
scheme.Comment: 8 pages, LaTeX, one figur
EPIC 219217635: A Doubly Eclipsing Quadruple System Containing an Evolved Binary
We have discovered a doubly eclipsing, bound, quadruple star system in the
field of K2 Campaign 7. EPIC 219217635 is a stellar image with that
contains an eclipsing binary (`EB') with d and a second EB with
d. We have obtained followup radial-velocity (`RV')
spectroscopy observations, adaptive optics imaging, as well as ground-based
photometric observations. From our analysis of all the observations, we derive
good estimates for a number of the system parameters. We conclude that (1) both
binaries are bound in a quadruple star system; (2) a linear trend to the RV
curve of binary A is found over a 2-year interval, corresponding to an
acceleration, cm s; (3) small
irregular variations are seen in the eclipse-timing variations (`ETVs')
detected over the same interval; (4) the orbital separation of the quadruple
system is probably in the range of 8-25 AU; and (5) the orbital planes of the
two binaries must be inclined with respect to each other by at least
25. In addition, we find that binary B is evolved, and the cooler and
currently less massive star has transferred much of its envelope to the
currently more massive star. We have also demonstrated that the system is
sufficiently bright that the eclipses can be followed using small ground-based
telescopes, and that this system may be profitably studied over the next decade
when the outer orbit of the quadruple is expected to manifest itself in the ETV
and/or RV curves.Comment: Accepted for publication in MNRA
MASCARA-2 b: A hot Jupiter transiting the A-star HD185603
In this paper we present MASCARA-2 b, a hot Jupiter transiting the
A2 star HD 185603. Since early 2015, MASCARA has taken more than 1.6 million
flux measurements of the star, corresponding to a total of almost 3000 hours of
observations, revealing a periodic dimming in the flux with a depth of .
Photometric follow-up observations were performed with the NITES and IAC80
telescopes and spectroscopic measurements were obtained with the Hertzsprung
SONG telescope. We find MASCARA-2 b orbits HD 185603 with a period of
at a distance of , has a radius of and place a
upper limit on the mass of . HD 185603 is a
rapidly rotating early-type star with an effective temperature of
and a mass and radius of
, , respectively. Contrary
to most other hot Jupiters transiting early-type stars, the projected planet
orbital axis and stellar spin axis are found to be aligned with . The brightness of the host star and the high equilibrium
temperature, , of MASCARA-2 b make it a suitable target for
atmospheric studies from the ground and space. Of particular interest is the
detection of TiO, which has recently been detected in the similarly hot planets
WASP-33 b and WASP-19 b.Comment: 8 pages, 4 figures, Accepted for publication in A&
UdsÊdsbÄrne sygdomme i Þkologisk sÄsÊd - betydning og skadetÊrskler
Det Þkologiske projekt ORGSEED har givet ny viden om skadetÊrsklerne for de vigtigste udsÊdsbÄrne sygdomme i korn og Êrter. I projektets sidste del vil disse tÊrskelvÊrdier blive vurderet med henblik pÄ justering. Sammenholdt med nye metoder til bestemmelse af den faktiske forekomst af udsÊdsbÄrne sygdomme, vil det give en mere sikker karakterisering af den Þkologiske sÄsÊd og hermed mindre unÞdig kassation
Measuring health inequality among children in developing countries: does the choice of the indicator of economic status matter?
Background
Currently, poor-rich inequalities in health in developing countries receive a lot of attention from both researchers and policy makers. Since measuring economic status in developing countries is often problematic, different indicators of wealth are used in different studies. Until now, there is a lack of evidence on the extent to which the use of different measures of economic status affects the observed magnitude of health inequalities.
Methods
This paper provides this empirical evidence for 10 developing countries, using the Demographic and Health Surveys data-set. We compared the World Bank asset index to three alternative wealth indices, all based on household assets. Under-5 mortality and measles immunisation coverage were the health outcomes studied. Poor-rich inequalities in under-5 mortality and measles immunisation coverage were measured using the Relative Index of Inequality.
Results
Comparing the World Bank index to the alternative indices, we found that (1) the relative position of households in the national wealth hierarchy varied to an important extent with the asset index used, (2) observed poor-rich inequalities in under-5 mortality and immunisation coverage often changed, in some cases to an important extent, and that (3) the size and direction of this change varied per country, index, and health indicator.
Conclusion
Researchers and policy makers should be aware that the choice of the measure of economic status influences the observed magnitude of health inequalities, and that differences in health inequalities between countries or time periods, may be an artefact of different wealth measures used
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