58 research outputs found
A Survey of Stellar Families: Multiplicity of Solar-type Stars
I present the results of a comprehensive assessment of companions to 454 solar-type stars within 25 pc. New observational aspects of this work include surveys for (1) very close companions with long-baseline interferometry at the Center for High Angular Resolution Astronomy (CHARA) Array, (2) close companions with speckle interferometry, and (3) wide proper motion companions identified by blinking multi-epoch archival images. I have also obtained and included unpublished results from extensive radial velocity monitoring programs. The many sources utilized enable a thorough evaluation of stellar and brown dwarf companions. The results presented here include eight new companion discoveries, four of which are wide common proper motion pairs discovered by blinking archival images, and four more are from the spectroscopic data. The overall observed fractions of single, double, triple, and higher order systems are 57%±3%, 33%±2%, 8%±1%, and 3%±1%, respectively, counting all stellar and brown dwarf companions. The incompleteness analysis indicates that only a few undiscovered companions remain in this well-studied sample, showing that a majority of the solar-type stars are single. Bluer, more massive stars are more likely to have companions than redder, less massive ones. I confirm earlier expectations that more active stars are more likely to have companions. A preliminary, but important indication is that brown dwarfs, like planets, prefer stars with higher metallicity, tentatively suggesting that brown dwarfs may form like planets when they are companions to stars. The period distribution is unimodal and roughly Gaussian with peak and median values of about 300 years. The period-eccentricity relation shows a roughly flat distribution beyond the circularization limit of about 12 days. The mass-ratio distribution shows a clear discontinuity near a value of one, indicating a preference for twins, which are not confined to short orbital periods, suggesting that stars form by multiple formation mechanisms. The ratio of planet hosts among single, binary, and multiple systems are statistically indistinguishable, suggesting that planets are as likely to form around single stars as they are around components of binary or multiple systems at sufficiently wide separations
A Case Study in Matching Service Descriptions to Implementations in an Existing System
A number of companies are trying to migrate large monolithic software systems
to Service Oriented Architectures. A common approach to do this is to first
identify and describe desired services (i.e., create a model), and then to
locate portions of code within the existing system that implement the described
services. In this paper we describe a detailed case study we undertook to match
a model to an open-source business application. We describe the systematic
methodology we used, the results of the exercise, as well as several
observations that throw light on the nature of this problem. We also suggest
and validate heuristics that are likely to be useful in partially automating
the process of matching service descriptions to implementations.Comment: 20 pages, 19 pdf figure
Towards Efficient Controller Synthesis Techniques for Logical LTL Games
Two-player games are a fruitful way to represent and reason about several
important synthesis tasks. These tasks include controller synthesis (where one
asks for a controller for a given plant such that the controlled plant
satisfies a given temporal specification), program repair (setting values of
variables to avoid exceptions), and synchronization synthesis (adding
lock/unlock statements in multi-threaded programs to satisfy safety
assertions). In all these applications, a solution directly corresponds to a
winning strategy for one of the players in the induced game. In turn,
\emph{logically-specified} games offer a powerful way to model these tasks for
large or infinite-state systems. Much of the techniques proposed for solving
such games typically rely on abstraction-refinement or template-based
solutions. In this paper, we show how to apply classical fixpoint algorithms,
that have hitherto been used in explicit, finite-state, settings, to a symbolic
logical setting. We implement our techniques in a tool called GenSys-LTL and
show that they are not only effective in synthesizing valid controllers for a
variety of challenging benchmarks from the literature, but often compute
maximal winning regions and maximally-permissive controllers. We achieve
\textbf{46.38X speed-up} over the state of the art and also scale well for
non-trivial LTL specifications
Relationship Between Information System Project Characteristics and Project Management Activities: An Empirical Investigation
The activities of a project manager in overseeing the development of a software system are many and varied. Not all such activities are performed in managing every project. If so, a natural ensuing question is whether project managers adapt their managerial functions to the projects being managed. Prior research suggests that they do adapt, and that project characteristics may be the factors determining this adaptation. This assertion is investigated by considering three characteristics of a project (size, type, and environment) and investigating their association with four traditionally recognized management functions (planning, organizing, controlling, and motivating). Results indicate that project managers do modify some managerial functions based on size and type of the project but not based on the environmental characteristics of the project
Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems
We present results of a reconnaissance for stellar companions to all 131
radial-velocity-detected candidate extrasolar planetary systems known as of
July 1, 2005. CPM companions were investigated using the multi-epoch DSS
images, and confirmed by matching the trigonometric parallax distances of the
primaries to companion distances estimated photometrically. We also attempt to
confirm or refute companions listed in the Washington Double Star Catalog, the
Catalogs of Nearby Stars, in Hipparcos results, and in Duquennoy & Mayor
(1991).
Our findings indicate that a lower limit of 30 (23%) of the 131 exoplanet
systems have stellar companions. We report new stellar companions to HD 38529
and HD 188015, and a new candidate companion to HD 169830. We confirm many
previously reported stellar companions, including six stars in five systems
that are recognized for the first time as companions to exoplanet hosts. We
have found evidence that 20 entries in the Washington Double Star Catalog are
not gravitationally bound companions. At least three, and possibly five, of the
exoplanet systems reside in triple star systems. Three exoplanet systems have
potentially close-in stellar companions ~ 20 AU away from the primary. Finally,
two of the exoplanet systems contain white dwarf companions. This comprehensive
assessment of exoplanet systems indicates that solar systems are found in a
variety of stellar multiplicity environments - singles, binaries, and triples;
and that planets survive the post-main-sequence evolution of companion stars.Comment: 52 pages, 7 figures, Accepted for publication in Ap
Know the Star, Know the Planet. II. Speckle Interferometry of Exoplanet Host Stars
A study of the host stars to exoplanets is important to understanding their
environment. To that end, we report new speckle observations of a sample of
exoplanet host primaries. The bright exoplanet host HD 8673 (= HIP 6702) is
revealed to have a companion, although at this time we cannot definitively
establish the companion as physical or optical. The observing lists for planet
searches and for these observations have for the most part been pre-screened
for known duplicity, so the detected binary fraction is lower than what would
otherwise be expected. Therefore, a large number of double stars were observed
contemporaneously for verification and quality control purposes, to ensure the
lack of detection of companions for exoplanet hosts was valid. In these
additional observations, ten pairs are resolved for the first time and sixty
pairs are confirmed. These observations were obtained with the USNO speckle
camera on the NOAO 4m telescopes at both KPNO and CTIO from 2001 to 2010.Comment: 2 figures, 3 table
Samanantar: The Largest Publicly Available Parallel Corpora Collection for 11 Indic Languages
We present Samanantar, the largest publicly available parallel corpora
collection for Indic languages. The collection contains a total of 49.7 million
sentence pairs between English and 11 Indic languages (from two language
families). Specifically, we compile 12.4 million sentence pairs from existing,
publicly-available parallel corpora, and additionally mine 37.4 million
sentence pairs from the web, resulting in a 4x increase. We mine the parallel
sentences from the web by combining many corpora, tools, and methods: (a)
web-crawled monolingual corpora, (b) document OCR for extracting sentences from
scanned documents, (c) multilingual representation models for aligning
sentences, and (d) approximate nearest neighbor search for searching in a large
collection of sentences. Human evaluation of samples from the newly mined
corpora validate the high quality of the parallel sentences across 11
languages. Further, we extract 83.4 million sentence pairs between all 55 Indic
language pairs from the English-centric parallel corpus using English as the
pivot language. We trained multilingual NMT models spanning all these languages
on Samanantar, which outperform existing models and baselines on publicly
available benchmarks, such as FLORES, establishing the utility of Samanantar.
Our data and models are available publicly at
https://indicnlp.ai4bharat.org/samanantar/ and we hope they will help advance
research in NMT and multilingual NLP for Indic languages.Comment: Accepted to the Transactions of the Association for Computational
Linguistics (TACL
Angular Diameters of the G Subdwarf Cassiopeiae A and the K Dwarfs Draconis and HR 511 from Interferometric Measurements with the CHARA Array
Using the longest baselines of the CHARA Array, we have measured the angular
diameter of the G5 V subdwarf Cas A, the first such determination for a
halo population star. We compare this result to new diameters for the higher
metallicity K0 V stars, Dra and HR 511, and find that the metal-poor
star, Cas A, has an effective temperature ( K),
radius (), and absolute luminosity
() comparable to the other two stars with later
spectral types. We show that stellar models show a discrepancy in the predicted
temperature and radius for Cas A, and we discuss these results and how
they provide a key to understanding the fundamental relationships for stars
with low metallicity.Comment: Accepted for publication in The Astrophysical Journa
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