3,308 research outputs found
Genetic modification of lignin concentration affects fitness of perennial herbaceous plants
Populations of four perennial herbaceous species that were genetically modified for altered lignin content (or associated forage digestibility) by conventional plant breeding were evaluated for two agricultural fitness traits, plant survival and plant biomass, in three Northcentral USA environments for more than 4 years. Reduced lignin concentration or increased digestibility resulted in increased winter mortality in two of four species and reduced biomass in one species. Results from other experiment indicate that these apparent genetic correlations may be ephemeral, suggesting that selection for fitness can be successful within high-digestibility or low-lignin germplasm. Results indicate that perennial plants genetically engineered with altered lignin concentration or composition for use in livestock, pulp and paper, or bioenergy production should be evaluated for fitness in field environments prior to use in agriculture
The "universal" radio/X-ray flux correlation : the case study of the black hole GX 339-4
The existing radio and X-ray flux correlation for Galactic black holes in the
hard and quiescent states relies on a sample which is mostly dominated by two
sources (GX 339-4 and V404 Cyg) observed in a single outburst. In this paper,
we report on a series of radio and X-ray observations of the recurrent black
hole GX 339-4 with the Australia Telescope Compact Array, the Rossi X-ray
Timing Explorer and the Swift satellites. With our new long term campaign, we
now have a total of 88 quasi-simultaneous radio and X-ray observations of GX
339-4 during its hard state, covering a total of seven outbursts over a
15--year period. Our new measurements represent the largest sample for a
stellar mass black hole, without any bias from distance uncertainties, over the
largest flux variations and down to a level that could be close to quiescence,
making GX 339-4 the reference source for comparison with other accreting
sources (black holes, neutrons stars, white dwarfs and active galactic nuclei).
Our results demonstrate a very strong and stable coupling between radio and
X-ray emission, despite several outbursts of different nature and separated by
a period of quiescence. The radio and X-ray luminosity correlation of the form
L_X ~L_Rad^0.62 +/-0.01 confirms the non-linear coupling between the jet and
the inner accretion flow powers and better defines the standard correlation
track in the radio-X-ray diagram for stellar mass black holes. We further note
epochs of deviations from the fit that significantly exceed the measurement
uncertainties, especially during the formation and destruction of the compact
jets ...[abridged]. We incorporated our new data in a more global study of
black hole candidates strongly supporting a scale invariance in the
jet-accretion coupling of accreting black holes, and confirms the existence of
two populations of sources in the radio/X-ray diagram.Comment: Paper accepted in MNRAS. 18 pages, 9 figure
Multi-Wavelength Coverage of State Transitions in the New Black Hole X-Ray Binary Swift J1910.2-0546
Understanding how black holes accrete and supply feedback to their
environment is one of the outstanding challenges of modern astrophysics. Swift
J1910.2-0546 is a candidate black hole low-mass X-ray binary that was
discovered in 2012 when it entered an accretion outburst. To investigate the
binary configuration and the accretion morphology we monitored the evolution of
the outburst for ~3 months at X-ray, UV, optical (B,V,R,I), and near-infrared
(J,H,K) wavelengths using Swift and SMARTS. The source evolved from a hard to a
soft X-ray spectral state with a relatively cold accretion disk that peaked at
~0.5 keV. A Chandra/HETG spectrum obtained during this soft state did not
reveal signatures of an ionized disk wind. Both the low disk temperature and
the absence of a detectable wind could indicate that the system is viewed at
relatively low inclination. The multi-wavelength light curves revealed two
notable features that appear to be related to X-ray state changes. Firstly, a
prominent flux decrease was observed in all wavebands ~1-2 weeks before the
source entered the soft state. This dip occurred in (0.6-10 keV) X-rays ~6 days
later than at longer wavelengths, which could possibly reflect the viscous time
scale of the disk. Secondly, about two weeks after the source transitioned back
into the hard state, the UV emission significantly increased while the X-rays
steadily decayed. We discuss how these observations may reflect changes in the
accretion flow morphology, perhaps related to the quenching/launch of a jet or
the collapse/recovery of a hot flow.Comment: 8 pages, 5 figures, 1 table. To be published in Ap
Ground State Properties of Anderson Impurity in a Gapless Host
Using the Bethe ansatz method, we study the ground state properties of a
Anderson impurity in a ``gapless'' host, where a density of band
states vanishes at the Fermi level as . As
in metals, the impurity spin is proven to be screened at arbitrary parameters
of the system. However, the impurity occupancy as a function of the bare
impurity energy is shown to acquire novel qualitative features which
demonstrate a nonuniversal behavior of the system. The latter explains why the
Kondo screening is absent (or exists only at quite a large electron-impurity
coupling) in earlier studies based on scaling arguments.Comment: 5 pages, no figure, RevTe
Local quantum phase transition in the pseudogap Anderson model: scales, scaling and quantum critical dynamics
The pseudogap Anderson impurity model provides a paradigm for understanding
local quantum phase transitions, in this case between generalised fermi liquid
and degenerate local moment phases. Here we develop a non-perturbative local
moment approach to the generic asymmetric model, encompassing all energy scales
and interaction strengths and leading thereby to a rich description of the
problem. We investigate in particular underlying phase boundaries, the critical
behaviour of relevant low-energy scales, and single-particle dynamics embodied
in the local spectrum. Particular attention is given to the resultant universal
scaling behaviour of dynamics close to the transition in both the GFL and LM
phases, the scale-free physics characteristic of the quantum critical point
itself, and the relation between the two.Comment: 39 pages, 19 figure
Long range transcriptional control of virulence critical genes in Mycobacterium tuberculosis by nucleoid-associated proteins?
The impact of an operation and management intervention on toilet usability in schools in the Philippines:A cluster randomised controlled trial
Multichannel pseudogap Kondo model: Large-N solution and quantum-critical dynamics
We discuss a multichannel SU(N) Kondo model which displays non-trivial
zero-temperature phase transitions due to a conduction electron density of
states vanishing with a power law at the Fermi level. In a particular large-N
limit, the system is described by coupled integral equations corresponding to a
dynamic saddle point. We exactly determine the universal low-energy behavior of
spectral densities at the scale-invariant fixed points, obtain anomalous
exponents, and compute scaling functions describing the crossover near the
quantum-critical points. We argue that our findings are relevant to recent
experiments on impurity-doped d-wave superconductors.Comment: 4 pages, 3 figs; extended discussion of large-N spin representations,
added references; accepted for publication in PR
The 2002 Outburst of the Black-Hole X-ray Binary 4U 1543-47: Optical and Infrared Light Curves
We have obtained simultaneous optical and near infrared observations of 4U
1543-47 during its 2002 outburst. The most striking feature of the outburst
light curve is the secondary maximum which appears after the object transitions
into the low-hard state. This secondary maximum is much stronger in the
infrared bands than optical. We suggest that the origin of the secondary
maximum flux may be synchrotron radiation associated with a jet. Close infrared
monitoring may lead to reliable triggers for simultaneous multiwavelength
campaigns to study jet formation processes.Comment: Accepted for publication in Ap
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