343 research outputs found
Conceptual Organization is Revealed by Consumer Activity Patterns
Computational models using text corpora have proved useful in understanding the nature of language and human concepts. One appeal of this work is that text, such as from newspaper articles, should reflect human behaviour and conceptual organization outside the laboratory. However, texts do not directly reflect human activity, but instead serve a communicative function and are highly curated or edited to suit an audience. Here, we apply methods devised for text to a data source that directly reflects thousands of individuals’ activity patterns. Using product co-occurrence data from nearly 1.3-m supermarket shopping baskets, we trained a topic model to learn 25 high-level concepts (or topics). These topics were found to be comprehensible and coherent by both retail experts and consumers. The topics indicated that human concepts are primarily organized around goals and interactions (e.g. tomatoes go well with vegetables in a salad), rather than their intrinsic features (e.g. defining a tomato by the fact that it has seeds and is fleshy). These results are consistent with the notion that human conceptual knowledge is tailored to support action. Individual differences in the topics sampled predicted basic demographic characteristics. Our findings suggest that human activity patterns can reveal conceptual organization and may give rise to it
A Photometric Metallicity Estimate of the Virgo Stellar Overdensity
We determine photometric metal abundance estimates for individual
main-sequence stars in the Virgo Overdensity (VOD), which covers almost 1000
deg^2 on the sky, based on a calibration of the metallicity sensitivity of
stellar isochrones in the gri filter passbands using field stars with
well-determined spectroscopic metal abundances. Despite the low precision of
the method for individual stars, we derive [Fe/H] = -2.0 +/-0.1 (internal)
+/-0.5 (systematic) for the metal abundance of the VOD from photometric
measurements of 0.7 million stars in the Northern Galactic hemisphere with
heliocentric distances from ~10 kpc to ~20 kpc. The metallicity of the VOD is
indistinguishable, within Delta [Fe/H] < 0.2, from that of field halo stars
covering the same distance range. This initial application suggests that the
SDSS gri passbands can be used to probe the properties of main-sequence stars
beyond ~10 kpc, complementing studies of nearby stars from more
metallicity-sensitive color indices that involve the u passband.Comment: 5 pages, 3 figures, Accepted for publication in ApJ Letter
Cut-free Calculi and Relational Semantics for Temporal STIT Logics
We present cut-free labelled sequent calculi for a central formalism in logics of agency: STIT logics with temporal operators. These include sequent systems for Ldm , Tstit and Xstit. All calculi presented possess essential structural properties such as contraction- and cut-admissibility. The labelled calculi G3Ldm and G3Tstit are shown sound and complete relative to irreflexive temporal frames. Additionally, we extend current results by showing that also Xstit can be characterized through relational frames, omitting the use of BT+AC frames
Probabilistic Consensus of the Blockchain Protocol
We introduce a temporal epistemic logic with probabilities as an extension of temporal epistemic logic. This extension enables us to reason about properties that characterize the uncertain nature of knowledge, like “agent a will with high probability know after time s same fact”. To define semantics for the logic we enrich temporal epistemic Kripke models with probability functions defined on sets of possible worlds. We use this framework to model and reason about probabilistic properties of the blockchain protocol, which is in essence probabilistic since ledgers are immutable with high probabilities. We prove the probabilistic convergence for reaching the consensus of the protocol
A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy: VI. s-Process and Titanium Abundance Variations Along the Sagittarius Stream
We present high-resolution spectroscopic measurements of the abundances of
titanium (Ti), yttrium (Y) and lanthanum (La) for M giant candidates of the
Sagittarius (Sgr) dwarf spheroidal (dSph) + tidal tail system pre-selected on
the basis of position and radial velocity. The majority of these stars show
peculiar abundance patterns compared to those of nominal Milky Way (MW) stars.
The overall [Ti/Fe], [Y/Fe], [La/Fe] and [La/Y] patterns with [Fe/H] of the Sgr
stream plus Sgr core do resemble those seen in the Large Magellanic Cloud (LMC)
and other dSphs, only shifted [Fe/H] by ~+0.4 from the LMC and by ~+1 dex from
the other dSphs; these relative shifts reflect the faster and/or more efficient
chemical evolution of Sgr compared to the other satellites, and show that Sgr
has had an enrichment history more like the LMC than the other dSphs. By
tracking the evolution of the abundance patterns along the Sgr stream we can
follow the time variation of the chemical make-up of dSph stars donated to the
MW halo by Sgr. This evolution demonstrates that while the bulk of the stars
currently in the Sgr dSph are quite unlike those of the MW halo, an increasing
number of stars farther along the Sgr stream have abundances like MW halo
stars, a trend that shows clearly how the MW halo could have been contributed
by present day satellite galaxies even if the present chemistry of those
satellites is now different from typical halo field stars. Finally, we analyze
the chemical abundances of a moving group of M giants among the Sgr leading arm
stars at the North Galactic Cap, but having radial velocities unlike the
infalling Sgr leading arm debris there. Through use of "chemical
fingerprinting", we conclude that these northern hemisphere M giants also are
Sgr stars, likely trailing arm debris overlapping the leading arm in the north.Comment: Accepted for publication in Ap
Update on the Nature of Virgo Overdensity
We use the Eighth Data Release of Sloan Digital Sky Survey (SDSS DR8) catalog
with its additional sky coverage of the southern Galactic hemisphere, to
measure the extent and study the nature of the Virgo Overdensity (VOD; Juric et
al. 2008). The data show that the VOD extends over no less than 2000 deg^2,
with its true extent likely closer to 3000 deg^2. We test whether the VOD can
be attributed to a tilt in the stellar halo ellipsoid with respect to the plane
of the Galactic disk and find that the observed symmetry of the north-south
Galactic hemisphere star counts excludes this possibility. We argue that the
Virgo Overdensity, in spite of its wide area and cloud-like appearance, is
still best explained by a minor merger. Its appearance and position is
qualitatively similar to a near perigalacticon merger event and, assuming that
the VOD and the Virgo Stellar Stream share the same progenitor, consistent with
the VSS orbit determined by Casetti-Dinescu et al. (2009).Comment: 9 pages,6 figures; accepted for publication in A
Alignment of a digital watershed and land use game to national education standards
Digital games, especially simulations, have supported student learning outcomes in the areas of science and agriculture in classrooms and nonformal settings. Simulations contribute robustly to student achievement in science, technology, engineering, and mathematics (STEM), and agriculture content areas, especially when they are aligned with national education standards. The People in Ecosystems Watershed Integration (PEWI) simulation is a digital game that was evaluated for fit to two national standards: the Next Generation Science Standards (NGSS) and the Agriculture, Food, and Natural Resources Standards (AFNR). The evaluation of alignment of PEWI to NGSS provided “extensive” evidence on a four‐point scale for meeting Criterion A: Explaining phenomenon/designing solutions; Criterion B: 3‐D learning, science and engineering practices, rated for three areas: (a) “extensive” for science and engineering practices, (b) “adequate” for disciplinary core ideas, and (c) “extensive” for cross‐cutting concepts. Additionally, PEWI aligned with nine high school–level NGSS student performance expectations categories. For AFNR Standards, the PEWI evaluation provided evidence for alignment to 10 standards and 17 indicators from the AFNR areas of Environmental Service Systems, Natural Resource Systems, and Plant Systems
Light Curve Templates and Galactic Distribution of RR Lyrae Stars from Sloan Digital Sky Survey Stripe 82
We present an improved analysis of halo substructure traced by RR Lyrae stars
in the SDSS stripe 82 region. With the addition of SDSS-II data, a revised
selection method based on new ugriz light curve templates results in a sample
of 483 RR Lyrae stars that is essentially free of contamination. The main
result from our first study persists: the spatial distribution of halo stars at
galactocentric distances 5--100 kpc is highly inhomogeneous. At least 20% of
halo stars within 30 kpc from the Galactic center can be statistically
associated with substructure. We present strong direct evidence, based on both
RR Lyrae stars and main sequence stars, that the halo stellar number density
profile significantly steepens beyond a Galactocentric distance of ~30 kpc, and
a larger fraction of the stars are associated with substructure. By using a
novel method that simultaneously combines data for RR Lyrae and main sequence
stars, and using photometric metallicity estimates for main sequence stars
derived from deep co-added u-band data, we measure the metallicity of the
Sagittarius dSph tidal stream (trailing arm) towards R.A.2h-3h and Dec~0 deg to
be 0.3 dex higher ([Fe/H]=-1.2) than that of surrounding halo field stars.
Together with a similar result for another major halo substructure, the
Monoceros stream, these results support theoretical predictions that an early
forming, smooth inner halo, is metal poor compared to high surface brightness
material that have been accreted onto a later-forming outer halo. The mean
metallicity of stars in the outer halo that are not associated with detectable
clumps may still be more metal-poor than the bulk of inner-halo stars, as has
been argued from other data sets.Comment: Submitted to ApJ, 68 pages, 26 figures, supplemental material (light
curves, templates, animation) can be downloaded from
http://www.astro.washington.edu/bsesar/S82_RRLyr.htm
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