1,379 research outputs found
Begin, After, and Later: a Maximal Decidable Interval Temporal Logic
Interval temporal logics (ITLs) are logics for reasoning about temporal
statements expressed over intervals, i.e., periods of time. The most famous ITL
studied so far is Halpern and Shoham's HS, which is the logic of the thirteen
Allen's interval relations. Unfortunately, HS and most of its fragments have an
undecidable satisfiability problem. This discouraged the research in this area
until recently, when a number non-trivial decidable ITLs have been discovered.
This paper is a contribution towards the complete classification of all
different fragments of HS. We consider different combinations of the interval
relations Begins, After, Later and their inverses Abar, Bbar, and Lbar. We know
from previous works that the combination ABBbarAbar is decidable only when
finite domains are considered (and undecidable elsewhere), and that ABBbar is
decidable over the natural numbers. We extend these results by showing that
decidability of ABBar can be further extended to capture the language
ABBbarLbar, which lays in between ABBar and ABBbarAbar, and that turns out to
be maximal w.r.t decidability over strongly discrete linear orders (e.g. finite
orders, the naturals, the integers). We also prove that the proposed decision
procedure is optimal with respect to the complexity class
Chemical abundances in M31 from HII regions
We have obtained multi-slit spectroscopic observations from 3700A to 9200A
with LRIS at the Keck I telescope for 31 HII regions in the disk of the
Andromeda galaxy (M31), spanning a range in galactocentric distance from 3.9
kpc to 16.1 kpc. In 9 HII regions we measure one or several auroral lines
([OIII]4363, [NII]5755, [SIII]6312, [OII]7325), from which we determine the
electron temperature (Te) of the gas and derive chemical abundances using the
'direct Te-based method'. We analyze, for the first time in M31, abundance
trends with galactocentric radius from the 'direct' method, and find that the
Ne/O, Ar/O, N/O and S/O abundance ratios are consistent with a constant value
across the M31 disc, while the O/H abundance ratio shows a weak gradient. We
have combined our data with all spectroscopic observations of HII regions in
M31 available in the literature, yielding a sample of 85 HII regions spanning
distances from 3.9 kpc to 24.7 kpc (0.19 - 1.2 R25) from the galaxy center. We
have tested a number of empirical calibrations of strong emission line ratios.
We find that the slope of the oxygen abundance gradient in M31 is
-0.023+/-0.002 dex/kpc, and that the central oxygen abundance is in the range
12+log(O/H) = 8.71 - 8.91 dex (i.e. between 1.05 and 1.66 times the solar
value, for 12+log(O/H)_solar=8.69), depending on the calibration adopted. The
HII region oxygen abundances are compared with the results from other
metallicity indicators (supergiant stars and planetary nebulae). The comparison
shows that HII region O/H abundances are systematically ~0.3 dex below the
stellar ones. This discrepancy is discussed in terms of oxygen depletion onto
dust grains and possible biases affecting Te-based oxygen abundances at high
metallicity.Comment: 21 pages and 11 figures. Accepted for publication in MNRA
Aging-dependent functional alterations of mitochondrial DNA (mtDNA) from human fibroblasts transferred into mtDNA-less cells
To investigate the role that aging-dependent accumulation of mitochondrial DNA (mtDNA) mutations plays in the senescence processes, mitochondria from fibroblasts of 21 normal human individuals between 20 weeks (fetal) and 103 years of age were introduced into human mtDNA-less (Ï0) 206 cells by cytoplast Ă Ï0 cell fusion, and 7-31 transformant clones were isolated from each fusion. A slight cell donor age-dependent decrease in growth rate was detected in the transformants. Using an O2 consumption rate of 1 fmol/min/cell, which was not observed in any transformant among 158 derived from individuals 20 weeks (fetal) to 37 years of age, as a cut-off to identify respiratory-deficient clones, 11 such clones were found among 198 transformants derived from individuals 39-103 years of age. Furthermore, conventional and nonparametric analysis of the respiratory rates of 356 clones revealed a very significant decrease with donor age. In other analyses, a very significant age-dependent decline in the mtDNA content of the clones was observed, without, however, any significant correlation with the decrease in O2 consumption rate in the defective transformants. These observations clearly indicate the occurrence in the fibroblast-derived transformants of two independent, age-related functional alterations of mtDNA, presumably resulting from structural damage to this genome
The Araucaria Project: The effect of blending on the Cepheid distance to NGC 300 from Advanced Camera for Surveys images
We have used the Advanced Camera for Surveys aboard the Hubble Space
Telescope to obtain F435W, F555W and F814W single-epoch images of six fields in
the spiral galaxy NGC 300. Taking advantage of the superb spatial resolution of
these images, we have tested the effect that blending of the Cepheid variables
studied from the ground with close stellar neighbors, unresolved on the
ground-based images, has on the distance determination to NGC 300. Out of the
16 Cepheids included in this study, only three are significantly affected by
nearby stellar objects. After correcting the ground-based magnitudes for the
contribution by these projected companions to the observed flux, we find that
the corresponding Period-Luminosity relations in V, I and the Wesenheit
magnitude W_I are not significantly different from the relations obtained
without corrections. We fix an upper limit of 0.04 magnitudes to the systematic
effect of blending on the distance modulus to NGC 300.
As part of our HST imaging program, we present improved photometry for 40
blue supergiants in NGC 300.Comment: To be published in the Astrophysical Journa
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