235,628 research outputs found
Selection Lemmas for various geometric objects
Selection lemmas are classical results in discrete geometry that have been
well studied and have applications in many geometric problems like weak epsilon
nets and slimming Delaunay triangulations. Selection lemma type results
typically show that there exists a point that is contained in many objects that
are induced (spanned) by an underlying point set.
In the first selection lemma, we consider the set of all the objects induced
(spanned) by a point set . This question has been widely explored for
simplices in , with tight bounds in . In our paper,
we prove first selection lemma for other classes of geometric objects. We also
consider the strong variant of this problem where we add the constraint that
the piercing point comes from . We prove an exact result on the strong and
the weak variant of the first selection lemma for axis-parallel rectangles,
special subclasses of axis-parallel rectangles like quadrants and slabs, disks
(for centrally symmetric point sets). We also show non-trivial bounds on the
first selection lemma for axis-parallel boxes and hyperspheres in
.
In the second selection lemma, we consider an arbitrary sized subset of
the set of all objects induced by . We study this problem for axis-parallel
rectangles and show that there exists an point in the plane that is contained
in rectangles. This is an improvement over the previous
bound by Smorodinsky and Sharir when is almost quadratic
Evidence-Informed Case Rates: A New Health Care Payment Model
Suggests a new payment model whereby providers are paid a single, risk-adjusted payment across inpatient and outpatient settings to care for a patient diagnosed with a specific condition
Morphological Dependence of Star Formation Properties for the Galaxies in the Merging Galaxy Cluster A2255
The merging cluster of galaxies A2255 is covered by the Sloan Digital Sky
Survey (SDSS) survey. In this paper we perform a morphological classification
on the basis of the SDSS imaging and spectral data, and investigate the
morphological dependence of the star formation rates (SFRs) for these member
galaxies. As we expect, a tight correlation between the normalized SFR by
stellar mass (SFR/M) and the H equivalent width is found for the
late-type galaxies in A2255. The correlation of SFR/M with the continuum
break strength at 4000 \AA is also confirmed. The SFR/M - M correlation
is found for both the early- and late-type galaxies, indicating that the star
formation activity tends to be suppressed when the assembled stellar mass
M) increases, and this correlation is tighter and steeper for the late-type
cluster galaxies. Compared with the mass range of field spiral galaxies, only
two massive late-type galaxies with M M are survived in
A2255, suggesting that the gas disks of massive spiral galaxies could have been
tidally stripped during cluster formation. Additionally, the SFR variation with
the projected radial distance are found to be heavily dependent upon galaxy
morphology: the early-type galaxies have a very weak inner decrease in
SFR/M, while the inner late-type galaxies tend to have higher SFR/M
values than the outer late-types. This may suggest that the galaxy-scale
turbulence stimulated by the merging of subclusters might have played different
roles on early- and late-type galaxies, which leads to a suppression of the
star formation activity for E/S0 galaxies and a SFR enhancement for spiral and
irregular galaxies.Comment: 21 pages, including 7 EPS figures and 1 tables, uses aastex.cls,
Accepted by the A
Obscured AGN at z~1 from the zCOSMOS-Bright Survey I. Selection and Optical Properties of a [Ne v]-selected sample
A sample of 94 narrow line AGN with 0.65<z<1.20 has been selected from the
20k-Bright zCOSMOS galaxy sample by detection of the high-ionization [NeV]3426
line. Taking advantage of the large amount of data available in the COSMOS
field, the properties of the [NeV]-selected Type-2 AGN have been investigated,
focusing on their host galaxies, X-ray emission, and optical line flux ratios.
Finally, the diagnostic developed by Gilli et al. (2010), based on the X-ray to
[NeV] luminosity ratio, has been exploited to search for the more heavily
obscured AGN. We found that [Ne v]-selected narrow line AGN have Seyfert 2-like
optical spectra, although with emission line ratios diluted by a star-forming
component. The ACS morphologies and stellar component in the optical spectra
indicate a preference for our Type-2 AGN to be hosted in early-spirals with
stellar masses greater than 10^(9.5-10)Msun, on average higher than those of
the galaxy parent sample. The fraction of galaxies hosting [NeV]-selected
obscured AGN increases with the stellar mass, reaching a maximum of about 3% at
2x10^11 Msun. A comparison with other selection techniques at z~1 shows that
the detection of the [Ne v] line is an effective method to select AGN in the
optical band, in particular the most heavily obscured ones, but can not provide
by itself a complete census of AGN2. Finally, the high fraction of
[NeV]-selected Type-2 AGN not detected in medium-deep Chandra observations
(67%) is suggestive of the inclusion of Compton-thick sources in our sample.
The presence of a population of heavily obscured AGN is corroborated by the
X-ray to [NeV] ratio; we estimated, by mean of X-ray stacking technique and
simulations, that the Compton-thick fraction in our sample of Type-2 AGN is
43+-4%, in good agreement with standard assumptions by the XRB synthesis
models.Comment: 14 pages, 12 figures, accepted for publication in A&
- …