5,772 research outputs found
A deep Chandra observation of Abell 4059: a new face to radio-mode AGN feedback?
A deep Chandra observation of the cooling core cluster Abell 4059 (A4059) is
presented. Previous studies have found two X-ray cavities in the central
regions of A4059 together with a ridge of X-ray emission 20kpc south-west of
the cluster center. These features are clearly related to the radio galaxy
PKS2354-35 which resides in the cD galaxy. Our new data confirm these previous
findings and strengthen previous suggestions that the south-western ridge is
colder and denser than, but in approximate pressure equilibrium with, the
surrounding ICM atmosphere. In addition, we find evidence for a weak shock that
wraps around the north and east sides of the cavity structure. Our data allow
us to map the 2-dimensional distribution of metals in the ICM of A4059 for the
first time. We find that the SW ridge possesses an anomalously high
(super-solar) metalicity. The unusual morphology, temperature structure and
metal distribution all point to significant asymmetry in the ICM atmosphere
prior to the onset of radio-galaxy activity. Motivated by the very high
metalicity of the SW ridge, we hypothesize that the ICM asymmetry was caused by
the extremely rapid stripping of metal enriched gas from a starburst galaxy
that plunged through the core of A4059. Furthermore, we suggest that the onset
of powerful radio-galaxy activity in the cD galaxy may have been initiated by
this starburst/stripping event, either via the tidal-shocking of cold gas
native to the cD galaxy, or the accretion of cold gas that had been stripped
from the starburst galaxy.Comment: Accepted for publication in the Astrophysical Journal. 12 pages, 11
figures. A version of this paper including full resolution figures can be
found at http://www.astro.umd.edu/~chris/publications/papers/a4059_2008.pd
Pinguicula rosmarieae Casper, Bussmann & T.Henning (Lentibulariaceae), a new butterwort from the Amotape-Huancabamba Zone (northern Peru)
The insectivorous genus Pinguicula occurs along the whole Andean mountain chain from Colombia-Venezuela in the north to Tierra del Fuego in the south with a short interruption in the Peruvian-Chilean desert range. This paper describes a new and striking species of Pinguicula that occurs in the south-eastern part of the Amotape-Huancabamba Zone in north Peru. It grows either as a lithophyte on moist rocks or as an epiphyte on Polylepis multijuga Pilg. in the wet highlands of the Cordillera Central. Pinguicula rosmarieae Casper, Bussmann & T.Henning, sp. nov. is clearly distinguished by a basal rosette of ovate-obovate leaves spread out flat on the ground and especially by a two-partite corolla with a straight uniform tube-spur complex, two features unknown from other Andean Pinguicula species. The morphological similarity to P. calyptrata Kunth is discussed and the habitat and distribution of P. rosmarieae are characterised
Hybrid RHF/MP2 geometry optimizations with the Effective Fragment Molecular Orbital Method
The frozen domain effective fragment molecular orbital method is extended to
allow for the treatment of a single fragment at the MP2 level of theory. The
approach is applied to the conversion of chorismate to prephenate by chorismate
mutase, where the substrate is treated at the MP2 level of theory while the
rest of the system is treated at the RHF level. MP2 geometry optimization is
found to lower the barrier by up to 3.5 kcal/mol compared to RHF optimzations
and ONIOM energy refinement and leads to a smoother convergence with respect to
the basis set for the reaction profile. For double zeta basis sets the increase
in CPU time relative to RHF is roughly a factor of two.Comment: 11 pages, 3 figure
Introduction: A Perspective on Midwest Amphibian Declines
On March 21, 1998, approximately 300 scientists and students gathered at the Milwaukee Public Museum for two days of scientific presentations and intense discussion on amphibian declines and malformities. Never before had so many persons come together to address amphibian conservation in the Midwestern United States (Minnesota, Wisconsin, Michigan, Illinois, Indiana, Ohio, Iowa, and Missouri)
Hadron mass corrections in semi-inclusive deep-inelastic scattering
The spin-dependent cross sections for semi-inclusive lepton-nucleon
scattering are derived in the framework of collinear factorization, including
the effects of masses of the target and produced hadron at finite momentum
transfer squared Q^2. At leading order the cross sections factorize into
products of parton distribution and fragmentation functions evaluated in terms
of new, mass-dependent scaling variables. The size of the hadron mass
corrections is estimated at kinematics relevant for future semi-inclusive
deep-inelastic scattering experiments.Comment: 28 pages, 12 figures, published versio
Interface of the polarizable continuum model of solvation with semi-empirical methods in the GAMESS program
An interface between semi-empirical methods and the polarized continuum model
(PCM) of solvation successfully implemented into GAMESS following the approach
by Chudinov et al (Chem. Phys. 1992, 160, 41). The interface includes energy
gradients and is parallelized. For large molecules such as ubiquitin a
reasonable speedup (up to a factor of six) is observed for up to 16 cores. The
SCF convergence is greatly improved by PCM for proteins compared to the gas
phase
Extreme value theory and statistics for heavy tail data
A scientific way of looking beyond the worst-case return is to employ statistical
extreme value methods. Extreme Value Theory (EVT) shows that the probability on
very large losses is eventually governed by a simple function, regardless the specific
distribution that underlies the return process. This limit result can be exploited to
construct semi-parametric portfolio Value at Risk (VaR) estimates around and beyond
the largest observed loss. Such extreme VaR estimates can be useful inputs for
scenario analysis and stress testing. The aim of this chapter is to introduce the reader
to extreme value theory and the statistics of extremes
Auctions with Numerous Bidders
We study auctions in which the number of potential bidders is large, such as in Internet auctions. With numerous bidders, the expected revenue and the optimal bid function in a first price auction result in complicated expressions, except for a few simple distribution function for the bidders' valuations. We show that these expressions can be well approximated using extreme value theory without assuming a particular distribution function. The theory is applied to data from Internet auctions
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