1,047 research outputs found
Human computer interaction for international development: past present and future
Recent years have seen a burgeoning interest in research into the use of information and communication technologies (ICTs) in the context of developing regions, particularly into how such ICTs might be appropriately designed to meet the unique user and infrastructural requirements that we encounter in these cross-cultural environments. This emerging field, known to some as HCI4D, is the product of a diverse set of origins. As such, it can often be difficult to navigate prior work, and/or to piece together a broad picture of what the field looks like as a whole. In this paper, we aim to contextualize HCI4Dâto give it some historical background, to review its existing literature spanning a number of research traditions, to discuss some of its key issues arising from the work done so far, and to suggest some major research objectives for the future
Chemical tagging can work: Identification of stellar phase-space structures purely by chemical-abundance similarity
Chemical tagging promises to use detailed abundance measurements to identify
spatially separated stars that were in fact born together (in the same
molecular cloud), long ago. This idea has not yielded much practical success,
presumably because of the noise and incompleteness in chemical-abundance
measurements. We have succeeded in substantially improving spectroscopic
measurements with The Cannon, which has now delivered 15 individual abundances
for ~100,000 stars observed as part of the APOGEE spectroscopic survey, with
precisions around 0.04 dex. We test the chemical-tagging hypothesis by looking
at clusters in abundance space and confirming that they are clustered in phase
space. We identify (by the k-means algorithm) overdensities of stars in the
15-dimensional chemical-abundance space delivered by The Cannon, and plot the
associated stars in phase space. We use only abundance-space information (no
positional information) to identify stellar groups. We find that clusters in
abundance space are indeed clusters in phase space. We recover some known
phase-space clusters and find other interesting structures. This is the
first-ever project to identify phase-space structures at survey-scale by blind
search purely in abundance space; it verifies the precision of the abundance
measurements delivered by The Cannon; the prospects for future data sets appear
very good.Comment: accepted for publication in the Ap
The Complexity of Combinations of Qualitative Constraint Satisfaction Problems
The CSP of a first-order theory is the problem of deciding for a given
finite set of atomic formulas whether is satisfiable. Let
and be two theories with countably infinite models and disjoint
signatures. Nelson and Oppen presented conditions that imply decidability (or
polynomial-time decidability) of under the
assumption that and are decidable (or
polynomial-time decidable). We show that for a large class of
-categorical theories the Nelson-Oppen conditions are not
only sufficient, but also necessary for polynomial-time tractability of
(unless P=NP).Comment: Version 2: stronger main result with better presentation of the
proof; multiple improvements in other proofs; new section structure; new
example
Influence of rain on air-sea gas exchange : lessons from a model ocean
Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S18, doi:10.1029/2003JC001806.Rain has been shown to significantly enhance the rate of air-water gas exchange in fresh water environments, and the mechanism behind this enhancement has been studied in laboratory experiments. In the ocean, the effects of rain are complicated by the potential influence of density stratification at the water surface. Since it is difficult to perform controlled rain-induced gas exchange experiments in the open ocean, an SF6 evasion experiment was conducted in the artificial ocean at Biosphere 2. The measurements show a rapid depletion of SF6 in the surface layer due to rain enhancement of air-sea gas exchange, and the gas transfer velocity was similar to that predicted from the relationship established from freshwater laboratory experiments. However, because vertical mixing is reduced by stratification, the overall gas flux is lower than that found during freshwater experiments. Physical measurements of various properties of the ocean during the rain events further elucidate the mechanisms behind the observed response. The findings suggest that short, intense rain events accelerate gas exchange in oceanic environments.Funding was provided by a generous grant from
the David and Lucile Packard Foundation
Recommended from our members
CDK2 limits the highly energetic secretory program of mature ÎČ cells by restricting PEP cycle-dependent KATP channel closure.
Hallmarks of mature ÎČ cells are restricted proliferation and a highly energetic secretory state. Paradoxically, cyclin-dependent kinase 2 (CDK2) is synthesized throughout adulthood, its cytosolic localization raising the likelihood of cell cycle-independent functions. In the absence of any changes in ÎČ cell mass, maturity, or proliferation, genetic deletion of Cdk2 in adult ÎČ cells enhanced insulin secretion from isolated islets and improved glucose tolerance in vivo. At the single ÎČ cell level, CDK2 restricts insulin secretion by increasing KATP conductance, raising the set point for membrane depolarization in response to activation of the phosphoenolpyruvate (PEP) cycle with mitochondrial fuels. In parallel with reduced ÎČ cell recruitment, CDK2 restricts oxidative glucose metabolism while promoting glucose-dependent amplification of insulin secretion. This study provides evidence of essential, non-canonical functions of CDK2 in the secretory pathways of quiescent ÎČ cells
Discovery of s-process enhanced stars in the LAMOST survey
Here we present the discovery of 895 s-process-rich candidates from 454â180 giant stars observed by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) using a data-driven approach. This sample constitutes the largest number of s-process enhanced stars ever discovered. Our sample includes 187 s-process-rich candidates that are enhanced in both barium and strontium, 49 stars with significant barium enhancement only and 659 stars that show only a strontium enhancement. Most of the stars in our sample are in the range of effective temperature and logâg typical of red giant branch (RGB) populations, which is consistent with our observational selection bias towards finding RGB stars. We estimate that only a small fraction (âŒ0.5 per cent) of binary configurations are favourable for s-process enriched stars. The majority of our s-process-rich candidates (95 per cent) show strong carbon enhancements, whereas only five candidates (<3â per cent) show evidence of sodium enhancement. Our kinematic analysis reveals that 97 per cent of our sample are disc stars, with the other 3 per cent showing velocities consistent with the Galactic halo. The scaleheight of the disc is estimated to be z_h = 0.634±0.063kpcâ , comparable with values in the literature. A comparison with yields from asymptotic giant branch (AGB) models suggests that the main neutron source responsible for the Ba and Sr enhancements is the ÂčÂłC(α,n)Âčâ¶O reaction. We conclude that s-process-rich candidates may have received their overabundances via mass transfer from a previous AGB companion with an initial mass in the range 1â3M_â
On the discovery of K-enhanced and possibly Mg-depleted stars throughout the Milky Way
Stars with unusual elemental abundances offer clues about rare astrophysical events or nucleosynthetic pathways. Stars with significantly depleted magnesium and enhanced potassium ([Mg/Fe] 1) have to date only been found in the massive globular cluster NGC 2419 and, to a lesser extent, NGC 2808. The origin of this abundance signature remains unknown, as does the reason for its apparent exclusivity to these two globular clusters. Here we present 112 field stars, identified from 454 180 LAMOST giants, that show significantly enhanced [K/Fe] and possibly depleted [Mg/Fe] abundance ratios. Our sample spans a wide range of metallicities (â1.5 < [Fe/H] < 0.3), yet none show abundance ratios of [K/Fe] or [Mg/Fe] that are as extreme as those observed in NGC 2419. If confirmed, the identified sample of stars represents evidence that the nucleosynthetic process producing the anomalous abundances ratios of [K/Fe] and [Mg/Fe] probably occurs at a wide range of metallicities. This would suggest that pollution scenarios that are limited to early epochs (such as Population III supernovae) are an unlikely explanation, although they cannot be ruled out entirely. This sample is expected to help guide modelling attempts to explain the origin of the MgâK abundance signature
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