6,758 research outputs found
Genomic regions associated with common root rot resistance in the barley variety Delta
Common root rot (CRR) caused by Bipolaris sorokiniana is a serious disease constraint in the dry temperate cereal growing regions of the world. Currently little is known about the genetic control of resistance to CRR in cereals. In this study based on a Delta/Lindwall barley population we have undertaken a bulked segregant analysis (BSA) and whole genome mapping approach utilising Diversity Arrays Technology (DArT) to identified quantitative trait loci (QTL) associated with CRR expression. One QTL each was identified on chromosomes 4HL and 5HL explaining 12 and 11% of the phenotypic variance, respectively
Heteronuclear ionizing collisions between laser-cooled metastable helium atoms
We have investigated cold ionizing heteronuclear collisions in dilute
mixtures of metastable (2 3S1) 3He and 4He atoms, extending our previous work
on the analogous homonuclear collisions [R. J. W. Stas et al., PRA 73, 032713
(2006)]. A simple theoretical model of such collisions enables us to calculate
the heteronuclear ionization rate coefficient, for our quasi-unpolarized gas,
in the absence of resonant light (T = 1.2 mK): K34(th) = 2.4*10^-10 cm^3/s.
This calculation is supported by a measurement of K34 using magneto-optically
trapped mixtures containing about 1*10^8 atoms of each species, K34(exp) =
2.5(8)*10^-10 cm^3/s. Theory and experiment show good agreement.Comment: 8 pages, 6 figure
Cluster AgeS Experiment. CCD photometry of SX Phoenicis variables in the globular cluster M 55
We present CCD photometry of SX Phe variables in the field of the globular
cluster M 55. We have discovered 27 variables, three of which are probable
members of the Sagittarius dwarf galaxy. All of the SX Phe stars in M 55 lie in
the blue straggler region of the cluster color-magnitude diagram. Using period
ratio information we have identified the radial pulsation modes for one of the
observed variables. Inspection of the period-luminosity distribution permits
the probable identifications of the pulsation modes for most of the rest of the
stars in the sample. We have determined the slope of the period-luminosity
relation for SX Phe stars in M 55 pulsating in the fundamental mode. Using this
relation and the HIPPARCOS data for SX Phe itself, we have estimated the
apparent distance modulus to M 55 to be (m-M)_V=13.86 +- 0.25 mag.Comment: A&A accepted, 11 figure
A Degenerate Bose-Fermi Mixture of Metastable Atoms
We report the observation of simultaneous quantum degeneracy in a dilute
gaseous Bose-Fermi mixture of metastable atoms. Sympathetic cooling of helium-3
(fermion) by helium-4 (boson), both in the lowest triplet state, allows us to
produce ensembles containing more than 10^6 atoms of each isotope at
temperatures below 1 micro-Kelvin, and achieve a fermionic degeneracy parameter
of T/Tf=0.45. Due to their high internal energy, the detection of individual
metastable atoms with sub-nanosecond time resolution is possible, permitting
the study of bosonic and fermionic quantum gases with unprecedented precision.
This may lead to metastable helium becoming the mainstay of quantum atom
optics.Comment: 4 pages, 3 figures submitted to PR
X-ray Supercavities in the Hydra A Cluster and the Outburst History of the Central Galaxy's Active Nucleus
A 227 ksec Chandra Observatory X-ray image of the hot plasma in the Hydra A
cluster has revealed an extensive cavity system. The system was created by a
continuous outflow or a series of bursts from the nucleus of the central galaxy
over the past 200-500 Myr. The cavities have displaced 10% of the plasma within
a 300 kpc radius of the central galaxy, creating a swiss-cheese-like topology
in the hot gas. The surface brightness decrements are consistent with empty
cavities oriented within 40 degrees of the plane of the sky. The outflow has
deposited upward of 10^61 erg into the cluster gas, most of which was propelled
beyond the inner ~100 kpc cooling region. The supermassive black hole has
accreted at a rate of approximately 0.1-0.25 solar masses per year over this
time frame, which is a small fraction of the Eddington rate of a ~10^9 solar
mass black hole, but is dramatically larger than the Bondi rate. Given the
previous evidence for a circumnuclear disk of cold gas in Hydra A, these
results are consistent with the AGN being powered primarily by infalling cold
gas. The cavity system is shadowed perfectly by 330 MHz radio emission. Such
low frequency synchrotron emission may be an excellent proxy for X-ray cavities
and thus the total energy liberated by the supermassive black hole.Comment: 8 pages, 3 figures; Submitted to ApJ, revised per referee's
suggestion
The Detectability of AGN Cavities in Cooling-Flow Clusters
Chandra X-ray Observatory has revealed X-ray cavities in many nearby cooling
flow clusters. The cavities trace feedback from the central active galactic
nulceus (AGN) on the intracluster medium (ICM), an important ingredient in
stabilizing cooling flows and in the process of galaxy formation and evolution.
But, the prevalence and duty cycle of such AGN outbursts is not well
understood. To this end, we study how the cooling is balanced by the cavity
heating for a complete sample of clusters (the Brightest 55 clusters of
galaxies, hereafter B55). In the B55, we found 33 cooling flow clusters, 20 of
which have detected X-ray bubbles in their ICM. Among the remaining 13, all
except Ophiuchus could have significant cavity power yet remain undetected in
existing images. This implies that the duty cycle of AGN outbursts with
significant heating potential in cooling flow clusters is at least 60 % and
could approach 100 %, but deeper data is required to constrain this further.Comment: 4 pages, 2 figures; to appear in the proceedings of "The Monsters'
Fiery Breath", Madison, Wisconsin 1-5 June 2009, Eds. Sebastian Heinz & Eric
Wilcots; added annotation to the figur
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