50,785 research outputs found
Line Emission in the Brightest Cluster Galaxies of the NOAO Fundamental Plane and Sloan Digital Sky Surveys
We examine the optical emission line properties of Brightest Cluster Galaxies
(BCGs) selected from two large, homogeneous datasets. The first is the X-ray
selected National Optical Astronomy Observatory Fundamental Plane Survey
(NFPS), and the second is the C4 catalogue of optically selected clusters built
from the Sloan Digital Sky Survey Data Release ~3 (SDSS DR3). Our goal is to
better understand the optical line emission in BCGs with respect to properties
of the galaxy and the host cluster. Throughout the analysis we compare the line
emission of the BCGs to that of a control sample made of the other bright
galaxies near the cluster centre. Overall, both the NFPS and SDSS show a modest
fraction of BCGs with emission lines (~15%). No trend in the fraction of
emitting BCGs as a function of galaxy mass or cluster velocity dispersion is
found. However we find that, for those BCGs found in cooling flow clusters,
71^{+9}_{-14}% have optical emission. Furthermore, if we consider only BCGs
within 50kpc of the X-ray centre of a cooling flow cluster, the emission-line
fraction rises further to 100^{+0}_{-15}%. Excluding the cooling flow clusters,
only ~10% of BCGs are line emitting, comparable to the control sample of
galaxies. We show that the physical origin of the emission line activity
varies: in some cases it has LINER-like line ratios, whereas in others it is a
composite of star-formation and LINER-like activity. We conclude that the
presence of emission lines in BCGs is directly related to the cooling of X-ray
gas at the cluster centre.Comment: Accepted for publication in MNRAS. 13 pages mn2e style with 7 figures
and 2 table
Jets in Effective Theory: Summing Phase Space Logs
We demonstrate how to resum phase space logarithms in the Sterman-Weinberg
(SW) dijet decay rate within the context of Soft Collinear Effective theory
(SCET). An operator basis corresponding to two and three jet events is defined
in SCET and renormalized. We obtain the RGE of the two and three jet operators
and run the operators from the scale to the phase space scale . This phase space scale, where is the
cone half angle of the jet, defines the angular region of the jet. At we determine the mixing of the three and two jet operators. We
combine these results with the running of the two jet shape function, which we
run down to an energy cut scale . This defines the resumed SW
dijet decay rate in the context of SCET. The approach outlined here
demonstrates how to establish a jet definition in the context of SCET. This
allows a program of systematically improving the theoretical precision of jet
phenomenology to be carried out.Comment: 25 pages, 4 figures, V2: Typos fixed, writing clarified, detail on
PSRG added. Matching onto jet definition changed to taking place at collinear
scal
The Role of Definitions in Biomedical Concept Representation
The Foundational Model (FM) of anatomy, developed as an anatomical enhancement of UMLS, classifies anatomical entities in a structural context. Explicit definitions have played a critical role in the establishment of FM classes. Essential structural properties that distinguish a group of anatomical entities serve as the differentiae for defining classes. These, as well as other structural attributes, are introduced as template slots in Protege, a frame-based knowledge acquisition system, and are inherited by descendants of the class. A set of desiderata has evolved during the instantiation of the FM for formulating definitions. We contend that 1. these desiderata generalize to non-anatomical domains and 2. satisfying them in constituent vocabularies of UMLS would enhance the quality of information retrievable through UMLS
Crusted (Norwegian) scabies treated with oral ivermectin : a case report and overview
Crusted (Norwegian) scabies is a severe and highly contagious form of infestation caused by the mite Sarcoptes scabiei var. hominis. It occurs in a subgroup of patients who are either immunocompromised or physically or mentally debilitated. Due to its atypical clinical presentation as well as difficulties associated with its management it presents a number of challenges both from a therapeutic aspect as well as from public health perspective. Failure to diagnose this condition may give rise to a massive epidemic when the patient is in an institutional setting.
We describe a case of crusted scabies which occurred in a nursing home leading to an institutional outbreak. She received a combination of oral ivermectin and topical scabicidal with good results.
This case highlights the importance of being alert to the possible diagnosis of crusted scabies and gives an overview of the condition as well as management strategies.peer-reviewe
Optimal Online Selection of a Monotone Subsequence: a Central Limit Theorem
Consider a sequence of independent random variables with a common
continuous distribution , and consider the task of choosing an increasing
subsequence where the observations are revealed sequentially and where an
observation must be accepted or rejected when it is first revealed. There is a
unique selection policy that is optimal in the sense that it
maximizes the expected value of , the number of selected
observations. We investigate the distribution of ; in particular,
we obtain a central limit theorem for and a detailed
understanding of its mean and variance for large . Our results and methods
are complementary to the work of Bruss and Delbaen (2004) where an analogous
central limit theorem is found for monotone increasing selections from a finite
sequence with cardinality where is a Poisson random variable that is
independent of the sequence.Comment: 26 page
The Low-Redshift Intergalactic Medium
The low-redshift Ly-alpha forest of absorption lines provides a probe of
large-scale baryonic structures in the intergalactic medium, some of which may
be remnants of physical conditions set up during the epoch of galaxy formation.
We discuss our recent Hubble Space Telescope (HST) observations and
interpretation of low-z Ly-alpha clouds toward nearby Seyferts and QSOs,
including their frequency, space density, estimated mass, association with
galaxies, and contribution to Omega-baryon. Our HST/GHRS detections of 70
Ly-alpha absorbers with N_HI > 10^12.6 cm-2 along 11 sightlines covering
pathlength Delta(cz) = 114,000 km/s show f(>N_HI) ~ N_HI^{-0.63 +- 0.04} and a
line frequency dN/dz = 200 +- 40 for N_HI > 10^12.6 cm-2 (one every 1500 km/s
of redshift). A group of strong absorbers toward PKS 2155-304 may be associated
with gas (400-800) h_75^-1 kpc from 4 large galaxies, with low metallicity (<
0.003 solar) and D/H < 2 x 10^-4. At low-z, we derive a metagalactic ionizing
radiation field from AGN of J_0 = 1.3^{+0.8 -0.5} x 10^-23 ergs/cm2/s/Hz/sr and
a Ly-alpha-forest baryon density Omega-baryon = (0.008 +- 0.004) h_75^-1 [J_-23
N_14 b_100]^{1/2} For clouds of characteristic size b = (100 kpc)b_100.Comment: 5 figure
Summing the Instanton Series in N=2 Superconformal Large-N QCD
We consider the multi-instanton collective coordinate integration measure in
N=2 supersymmetric SU(N) gauge theory with N_F fundamental hypermultiplets. In
the large-N limit, at the superconformal point where N_F=2N and all VEVs are
turned off, the k-instanton moduli space collapses to a single copy of
AdS_5*S^1. The resulting k-instanton effective measure is proportional to
N^{1/2} g^4 Z_k^(6), where Z_k^(6) is the partition function of N=(1,0) SYM
theory in six dimensions reduced to zero dimensions. The multi-instanton can in
fact be summed in closed form. As a hint of an AdS/CFT duality, with the usual
relation between the gauge theory and string theory parameters, this precisely
matches the normalization of the charge-k D-instanton measure in type IIB
string theory compactified to six dimensions on K3 with a vanishing two-cycle.Comment: 12 pages, amslate
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