440 research outputs found
Uniform Interpolation and Forgetting for ALC Ontologies with ABoxes
Uniform interpolation and the dual task of forgetting restrict the ontology to a specified subset of concept and role names. This makes them useful tools for ontology analysis, ontology evolution and information hiding. Most previous research focused on uniform interpolation of TBoxes. However, especially for applications in privacy and information hiding, it is essential that uniform interpolation methods can deal with ABoxes as well. We present the first method that can compute uniform interpolants of any ALC ontology with ABoxes. ABoxes bring their own challenges when computing uniform interpolants, possibly requiring disjunctive statements or nominals in the resulting ABox. Our method can compute representations of uniform interpolants in ALCO. An evaluation on realistic ontologies shows that these uniform interpolants can be practically computed, and can often even be presented in pure ALC
The Trouble with Hubble Types in the Virgo Cluster
Quantitative measures of central light concentration and star formation
activity are derived from R and Halpha surface photometry of 84 bright S0-Scd
Virgo Cluster and isolated spiral galaxies. For isolated spirals, there is a
good correlation between these two parameters and assigned Hubble types. In the
Virgo Cluster, the correlation between central light concentration and star
formation activity is significantly weaker. Virgo Cluster spirals have
systematically reduced global star formation with respect to isolated spirals,
with severe reduction in the outer disk, but normal or enhanced activity in the
inner disk. Assigned Hubble types are thus inadequate to describe the range in
morphologies of bright Virgo Cluster spirals. In particular, spirals with
reduced global star formation activity are often assigned misleading early-type
classifications, irrespective of their central light concentrations. 45+-25% of
the galaxies classified as Sa in the Virgo Cluster sample have central light
concentrations more characteristic of isolated Sb-Sc galaxies. The misleading
classification of low concentration galaxies with low star formation rates as
early-type spirals may account for part of the excess of `early-type' spiral
galaxies in clusters. Thus the morphology-density relationship is not all due
to a systematic increase in the bulge-to-disk ratio with environmental density.Comment: Accepted for publication in ApJ Letters. Latex aaspp4.sty, 9 pages, 2
Postscript (embedded) figures. Also available at
http://www.astro.yale.edu/koopmann/preprint.htm
Weak- to strong pinning crossover
Material defects in hard type II superconductors pin the flux lines and thus
establish the dissipation-free current transport in the presence of a finite
magnetic field. Depending on the density and pinning force of the defects and
the vortex density, pinning is either weak-collective or strong. We analyze the
weak- to strong pinning crossover of vortex matter in disordered
superconductors and discuss the peak effect appearing naturally in this
context.Comment: 4 pages, 2 figure
Ongoing Gas Stripping in the Virgo Cluster Spiral NGC 4522
The Virgo cluster galaxy NGC 4522 is one of the best spiral candidates for
ICM-ISM stripping in action. Optical broadband and H-alpha images from the WIYN
telescope of the highly inclined galaxy reveal a relatively undisturbed stellar
disk and a peculiar distribution of H-alpha emission. Ten percent of the
H-alpha emission arises from extraplanar HII regions which appear to lie within
filamentary structures >3 kpc long above one side of the disk. The filaments
emerge from the outer edge of a disk of bright H-alpha emission which is
abruptly truncated beyond 0.35R(25). Together the truncated H-alpha disk and
extraplanar H-alpha filaments are reminiscent of a bow shock morphology, which
strongly suggests that the interstellar medium (ISM) of NGC 4522 is being
stripped by the gas pressure of the intracluster medium (ICM). The galaxy has a
line-of-sight velocity of 1300 km/sec with respect to the mean Virgo cluster
velocity, and thus is expected to experience a strong interaction with the
intracluster gas. The existence of HII regions apparently located above the
disk plane suggests that star formation is occuring in the stripped gas, and
that newly formed stars will enter the galaxy halo and/or intracluster space.
The absence of HII regions in the disk beyond 0.35R(25), and the existence of
HII regions in the stripped gas suggest that even molecular gas has been
effectively removed from the disk of the galaxy.Comment: to appear in The Astronomical Journal, 16 pages, 5 figures, 1 tabl
Polyvinylidene Fluoride Aerogels with Tailorable Crystalline Phase Composition
In this work, polyvinylidene fluoride (PVDF) aerogels with a tailorable phase composition
were prepared by following the crystallization-induced gelation principle. A series of PVDF wet gels
(5 to 12 wt.%) were prepared from either PVDF–DMF solutions or a mixture of DMF and ethanol
as non-solvent. The effects of the non-solvent concentration on the crystalline composition of the
PVDF aerogels were thoroughly investigated. It was found that the nucleating role of ethanol can be
adjusted to produce low-density PVDF aerogels, whereas the changes in composition by the addition
of small amounts of water to the solution promote the stabilization of the valuable β and γ phases.
These phases of the aerogels were monitored by FTIR and Raman spectroscopies. Furthermore, the
crystallization process was followed by in-time and in situ ATR–FTIR spectroscopy. The obtained
aerogels displayed specific surface areas > 150 m2 g−1, with variable particle morphologies that are
dependent on the non-solvent composition, as observed by using SEM and Synchrotron Radiation
Computed micro-Tomography (SR-μC
The Arecibo Legacy Fast ALFA Survey: VI. Second HI Source Catalog of the Virgo Cluster Region
We present the third installment of HI sources extracted from the Arecibo
Legacy Fast ALFA extragalactic survey. This dataset continues the work of the
Virgo ALFALFA catalog. The catalogs and spectra published here consist of data
obtained during the 2005 and 2006 observing sessions of the survey. The catalog
consists of 578 HI detections within the range 11h 36m < R.A.(J2000) < 13h 52m
and +08 deg < Dec.(J2000) < +12 deg, and cz_sun < 18000 km/s. The catalog
entries are identified with optical counterparts where possible through the
examination of digitized optical images. The catalog detections can be
classified into three categories: (a) detections of high reliability with S/N >
6.5; (b) high velocity clouds in the Milky Way or its periphery; and (c)
signals of lower S/N which coincide spatially with an optical object and known
redshift. 75% of the sources are newly published HI detections. Of particular
note is a complex of HI clouds projected between M87 and M49 that do not
coincide with any optical counterparts. Candidate objects without optical
counterparts are few. The median redshift for this sample is 6500 km/s and the
cz distribution exhibits the local large scale structure consisting of Virgo
and the background void and the A1367-Coma supercluster regime at cz_sun ~7000
km/s. Position corrections for telescope pointing errors are applied to the
dataset by comparing ALFALFA continuum centroid with those cataloged in the
NRAO VLA Sky Survey. The uncorrected positional accuracy averages
27 arcsec ~(21 arcsec ~median) for all sources with S/N > 6.5 and is of order
~21 arcsec ~(16 arcsec ~median) for signals with S/N > 12. Uncertainties in
distances toward the Virgo cluster can affect the calculated HI mass
distribution.Comment: 25 pages, 1 Table, 8 figures, Accepted by the Astronomical Journa
Atomic and Molecular Gas Components in Spiral Galaxies of the Virgo Cluster
Based on two models, we investigate the molecular-to-atomic gas ratio in
Virgo cluster galaxies in comparison with field galaxies. We show that the
enhanced metallicity for cluster members and the ram pressure stripping of
atomic gas from the disk periphery cannot fully explain the observed gas
component ratios. The additional environmental factors affecting the
interstellar medium and leading to an increase in the molecular gas fraction
should be taken into account for cluster galaxies.Comment: 11 pages, 4 figure
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