531 research outputs found
DArTseq-based analysis of genomic relationships among species of tribe Triticeae
Precise utilization of wild genetic resources to improve the resistance of their cultivated relatives to environmental growth limiting factors, such as salinity stress and diseases, requires a clear understanding of their genomic relationships. Although seriously criticized, analyzing these relationships in tribe Triticeae has largely been based on meiotic chromosome pairing in hybrids of wide crosses, a specialized and labourious strategy. In this study, DArTseq, an efficient genotyping-by-sequencing platform, was applied to analyze the genomes of 34 Triticeae species. We reconstructed the phylogenetic relationships among diploid and polyploid Aegilops and Triticum species, including hexaploid wheat. Tentatively, we have identified the diploid genomes that are likely to have been involved in the evolution of five polyploid species of Aegilops, which have remained unresolved for decades. Explanations which cast light on the progenitor of the A genomes and the complex genomic status of the B/G genomes of polyploid Triticum species in the Emmer and Timopheevi lineages of wheat have also been provided. This study has, therefore, demonstrated that DArTseq genotyping can be effectively applied to analyze the genomes of plants, especially where their genome sequence information are not available
Novel molecular marker-assisted strategy for production of wheat-Leymus mollis chromosome addition lines
Developing wheatâalien chromosome introgression lines to improve bread wheatâs resistance to stresses, such as drought, salinity stress and diseases, requires reliable markers to identify and characterize the alien chromatins. Leymus mollis is a wild relative of bread wheat resistant to salinity and economically important diseases of wheat, but its genome sequence and cytological markers are not available. We devised a molecular marker-assisted strategy for L. mollis chromosome identification and applied it to produce 10 wheatâL. mollis chromosome addition lines. Using 47âL. racemosus genome polymorphic PCR markers and DArTseq genotyping, we distinguished the L. mollis chromosomes and differentiated disomic and monosomic lines by progeny test. DArTseq genotyping generated 14,530âL. mollis SNP markers and the chromosome-specific SNP markers were used to determine the homoeologous groups of L. mollis chromosomes in the addition lines. To validate the marker-based results, genomic in situ hybridization was applied to confirm the presence and cytological status of L. mollis chromosomes in the lines. This study demonstrates that adequate molecular markers allow the production and characterization of wheatâalien addition lines without in situ hybridization, which saves considerable time and effort
Suzaku Detection of Super-hard X-ray Emission from the Classical Nova V2491 Cygni
We report the detection of super-hard (>10 keV) X-ray emission extending up
to 70 keV from the classical nova V2491 Cygni using the Suzaku observatory. We
conducted two ~20 ks target-of-opportunity observations 9 and 29 days after the
outburst on 2008 April 11, yielding wide energy range spectra by combining the
X-ray Imaging Spectrometer and the Hard X-ray Detector. On day 9, a spectrum
was obtained at 1.0-70 keV with the Fe XXV K\alpha line feature and a very flat
continuum, which is explained by thermal plasma with a 3 keV temperature and
power-law emission with a photon index of 0.1 attenuated by a heavy extinction
of 1.4x10^{23} cm^{-2}. The 15-70 keV luminosity at 10.5 kpc is 6x10^{35} ergs
s^{-1}. The super-hard emission was not present on day 29. This is the highest
energy at which X-rays have been detected from a classical nova. We argue a
non-thermal origin for the emission, which suggests the presence of accelerated
charged particles in the nova explosion.Comment: Accepted for publication in ApJL (4 pages, 3 figures
Astrophysical Fluids of Novae: High Resolution Pre-decay X-ray spectrum of V4743 Sagittarii
Eight X-ray observations of V4743 Sgr (2002), observed with Chandra and
XMM-Newton are presented. The nova turned off some time between days 301.9 and
371, and the X-ray flux subsequently decreased from day 301.9 to 526 following
an exponential decline time scale of days. We use the absorption
lines present in the SSS spectrum for diagnostic purposes, and characterize the
physics and the dynamics of the expanding atmosphere during the explosion of
the nova. The information extracted from this first stage is then used as input
for computing full photoionization models of the ejecta in V4743 Sgr. The SSS
spectrum is modeled with a simple black-body and multiplicative Gaussian lines,
which provides us of a general kinematical picture of the system, before it
decays to its faint phase (Ness et al. 2003). In the grating spectra taken
between days 180.4 and 370, we can resolve the line profiles of absorption
lines arising from H-like and He-like C, N, and O, including transitions
involving higher principal quantum numbers. Except for a few interstellar
lines, all lines are significantly blue-shifted, yielding velocities between
1000 and 6000 km/s which implies an ongoing mass loss. It is shown that
significant expansion and mass loss occur during this phase of the explosion,
at a rate . Our measurements show that the efficiency of the amount of
energy used for the motion of the ejecta, defined as the ratio between the
kinetic luminosity and the radiated luminosity , is
of the order of one.Comment: 25 pages, 9 figures. Accepted in book: Recent Advances in Fluid
Dynamics with Environmental Applications, pp.365-39
X-ray Eclipse Diagnosis of the Evolving Mass Loss in the Recurrent Nova U Scorpii 2010
We report the Suzaku detection of the earliest X-ray eclipse seen in the
recurrent nova U Scorpii 2010. A target-of-opportunity observation 15 days
after the outburst found a 27+/-5% dimming in the 0.2-1.0 keV energy band at
the predicted center of an eclipse. In comparison with the X-ray eclipse depths
seen at two later epochs by XMM-Newton, the source region shrank by about
10-20% between days 15 and 35 after the outburst. The X-ray eclipses appear to
be deeper than or similar to contemporaneous optical eclipses, suggesting the
X-ray and optical source region extents are comparable on day 15. We raise the
possibility of the energy dependency in the photon escape regions, and that
this would be a result of the supersoft X-ray opacity being higher than the
Thomson scattering optical opacity at the photosphere due to bound-free
transitions in abundant metals that are not fully ionized. Assuming a
spherically symmetric explosion model, we constrain the mass-loss rate as a
function of time. For a ratio of actual to Thomson opacity of 10-100 in
supersoft X-rays, we find a total ejecta mass of about 10^{-7}-10^{-6}
M_{\odot}.Comment: To appear in the Astrophysical Journal Letters; 5 pages, 3 figure
Magnetoelectric ordering of BiFeO3 from the perspective of crystal chemistry
In this paper we examine the role of crystal chemistry factors in creating
conditions for formation of magnetoelectric ordering in BiFeO3. It is generally
accepted that the main reason of the ferroelectric distortion in BiFeO3 is
concerned with a stereochemical activity of the Bi lone pair. However, the lone
pair is stereochemically active in the paraelectric orthorhombic beta-phase as
well. We demonstrate that a crucial role in emerging of phase transitions of
the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order
types belongs to the change of the degree of the lone pair stereochemical
activity - its consecutive increase with the temperature decrease. Using the
structural data, we calculated the sign and strength of magnetic couplings in
BiFeO3 in the range from 945 C down to 25 C and found the couplings, which
undergo the antiferromagnetic-ferromagnetic transition with the temperature
decrease and give rise to the antiferromagnetic ordering and its delay in
regard to temperature, as compared to the ferroelectric ordering. We discuss
the reasons of emerging of the spatially modulated spin structure and its
suppression by doping with La3+.Comment: 18 pages, 5 figures, 3 table
Discrete series representations for sl(2|1), Meixner polynomials and oscillator models
We explore a model for the one-dimensional quantum oscillator based upon the
Lie superalgebra sl(2|1). For this purpose, a class of discrete series
representations of sl(2|1) is constructed, each representation characterized by
a real number beta>0. In this model, the position and momentum operators of the
oscillator are odd elements of sl(2|1) and their expressions involve an
arbitrary parameter gamma. In each representation, the spectrum of the
Hamiltonian is the same as that of the canonical oscillator. The spectrum of
the momentum operator can be continuous or infinite discrete, depending on the
value of gamma. We determine the position wavefunctions both in the continuous
and discrete case, and discuss their properties. In the discrete case, these
wavefunctions are given in terms of Meixner polynomials. From the embedding
osp(1|2)\subset sl(2|1), it can be seen why the case gamma=1 corresponds to the
paraboson oscillator. Consequently, taking the values (beta,gamma)=(1/2,1) in
the sl(2|1) model yields the canonical oscillator.Comment: (some minor misprints were corrected in this version
Formation of Galactic Systems in Light of the Magnesium Abundance in Field Stars.III.the Halo
We analyze the relations between the relative magnesium abundances,
metallicities, and Galactic orbital elements for halo stars. We show that the
relative magnesium abundances in protodisk halo stars are virtually independent
of metallicity and lie within a fairly narrow range while presumably accreted
stars demonstrate a large spread in relative magnesium abundances up to
negative [Mg/Fe]. The mean metallicity of magnesium-poor ([Mg/Fe]<0.2 dex)
accreted stars has been found to be displaced toward the negative values when
passing from stars with low azimuthal velocities to those with high ones at
\Delta[Fe/H]=0.5dex. The mean apogalactic radii and inclinations of the orbits
also increase while their eccentricities decrease. As a result negative radial
and vertical gradients in relative magnesium abundances are observed in the
accreted halo in the absence of correlations between the [Mg/Fe] ratios and
other orbital elements, while these correlations are found at a high
significance level for genetically related Galactic stars. We surmise that as
the masses of dwarf galaxies decrease, the maximum SNII masses and hence, the
yield of \alpha-elements in them also decrease. In this case, the relation
between the [Mg/Fe] ratios and the inclinations and sizes of the orbits of
accreted stars is in complete agreement with numerical simulations of dynamical
processes during the interaction of galaxies. Thus the behavior of the
magnesium abundance in accreted stars suggests that the satellite galaxies are
disrupted and lose their stars en masse only after dynamical friction reduces
significantly the sizes of their orbits and drags them into the Galactic plane.
Less massive satellite galaxies are disrupted even before their orbits change
appreciably under tidal forces.Comment: accepted 2006, Astronomy Letters, Vol. 32 No. 8, P.545, 18 pages, 6
figure
X-Ray Spectroscopy of Stars
(abridged) Non-degenerate stars of essentially all spectral classes are soft
X-ray sources. Low-mass stars on the cooler part of the main sequence and their
pre-main sequence predecessors define the dominant stellar population in the
galaxy by number. Their X-ray spectra are reminiscent, in the broadest sense,
of X-ray spectra from the solar corona. X-ray emission from cool stars is
indeed ascribed to magnetically trapped hot gas analogous to the solar coronal
plasma. Coronal structure, its thermal stratification and geometric extent can
be interpreted based on various spectral diagnostics. New features have been
identified in pre-main sequence stars; some of these may be related to
accretion shocks on the stellar surface, fluorescence on circumstellar disks
due to X-ray irradiation, or shock heating in stellar outflows. Massive, hot
stars clearly dominate the interaction with the galactic interstellar medium:
they are the main sources of ionizing radiation, mechanical energy and chemical
enrichment in galaxies. High-energy emission permits to probe some of the most
important processes at work in these stars, and put constraints on their most
peculiar feature: the stellar wind. Here, we review recent advances in our
understanding of cool and hot stars through the study of X-ray spectra, in
particular high-resolution spectra now available from XMM-Newton and Chandra.
We address issues related to coronal structure, flares, the composition of
coronal plasma, X-ray production in accretion streams and outflows, X-rays from
single OB-type stars, massive binaries, magnetic hot objects and evolved WR
stars.Comment: accepted for Astron. Astrophys. Rev., 98 journal pages, 30 figures
(partly multiple); some corrections made after proof stag
The stellar and sub-stellar IMF of simple and composite populations
The current knowledge on the stellar IMF is documented. It appears to become
top-heavy when the star-formation rate density surpasses about 0.1Msun/(yr
pc^3) on a pc scale and it may become increasingly bottom-heavy with increasing
metallicity and in increasingly massive early-type galaxies. It declines quite
steeply below about 0.07Msun with brown dwarfs (BDs) and very low mass stars
having their own IMF. The most massive star of mass mmax formed in an embedded
cluster with stellar mass Mecl correlates strongly with Mecl being a result of
gravitation-driven but resource-limited growth and fragmentation induced
starvation. There is no convincing evidence whatsoever that massive stars do
form in isolation. Various methods of discretising a stellar population are
introduced: optimal sampling leads to a mass distribution that perfectly
represents the exact form of the desired IMF and the mmax-to-Mecl relation,
while random sampling results in statistical variations of the shape of the
IMF. The observed mmax-to-Mecl correlation and the small spread of IMF
power-law indices together suggest that optimally sampling the IMF may be the
more realistic description of star formation than random sampling from a
universal IMF with a constant upper mass limit. Composite populations on galaxy
scales, which are formed from many pc scale star formation events, need to be
described by the integrated galactic IMF. This IGIMF varies systematically from
top-light to top-heavy in dependence of galaxy type and star formation rate,
with dramatic implications for theories of galaxy formation and evolution.Comment: 167 pages, 37 figures, 3 tables, published in Stellar Systems and
Galactic Structure, Vol.5, Springer. This revised version is consistent with
the published version and includes additional references and minor additions
to the text as well as a recomputed Table 1. ISBN 978-90-481-8817-
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