2,159 research outputs found
Solar-type Stars Observed by LAMOST and Kepler
Obtaining measurements of chromospheric and photometric activity of stars
with near-solar fundamental parameters and rotation periods is important for a
better understanding of solar-stellar connection. We select a sample of 2603
stars with near-solar fundamental parameters from the Large Sky Area
Multi-Object Fiber Spectroscopic Telescope (LAMOST)-Kepler field and use LAMOST
spectra to measure their chromospheric activity and Kepler light curves to
measure their photospheric activity (i.e., the amplitude of the photometric
variability). While the rotation periods of 1556 of these stars could not be
measured due to the low amplitude of the photometric variability and highly
irregular temporal profile of light curves, 254 stars were further identified
as having near-solar rotation periods. We show that stars with near-solar
rotation periods have chromospheric activities that are systematically higher
than stars with undetected rotation periods. Furthermore, while the solar level
of photospheric and chromospheric activity appears to be typical for stars with
undetected rotation periods, the Sun appears to be less active than most stars
with near-solar rotation periods (both in terms of photospheric and
chromospheric activity).Comment: 7 pages, 6 figure
Self-regulated reionization
Recently, we have presented the first large-scale radiative transfer
simulations of reionization. Here we present new simulations which extend the
source halo mass range downward to 10^8M_solar, to capture the full range of
halo masses thought to be primarily responsible for reionization by their star
formation following atomic hydrogen radiative cooling and gravitational
collapse. Haloes below about 10^9M_solar, however, are subject to Jeans-mass
filtering in the ionized regions, which suppresses their baryonic content and
their ability to release ionizing radiation. By including these smaller-mass
haloes but accounting for their suppression, too, we find that reionization is
``self-regulating,'' as follows. As the mean ionized fraction rises, so does
the fraction of the volume within which suppression occurs. Hence, the degree
of suppression is related to the mean ionized fraction. Since low-mass haloes
with high emissivity achieve a given mean ionized fraction earlier than do
those with low efficiency, Jeans-mass filtering compensates for the difference
in the emissivity of the suppressible haloes in these two cases. As a result,
in the presence of lower-mass source haloes, reionization begins earlier, but
the later stages of reionization and the time of overlap are dictated by the
efficiency of the higher-mass haloes, independent of the efficiency of the
suppressible, lower-mass haloes. Reionization histories consistent with current
observational constraints are shown to be achievable with standard stellar
sources in haloes above 10^8M_solar. Neither minihalos nor exotic sources are
required, and the phenomenon of ``double reionization'' previously suggested
does not occur. (abridged)Comment: 16 pages, 10 figures, most in color. MNRAS, in print. Replaced to
match the accepted version. High-quality images and movies can be found at
http://www.cita.utoronto.ca/~iliev/dokuwiki/doku.php?id=reionization_sim
Glimpsing through the high redshift neutral hydrogen fog
We analyze the transmitted flux in a sample of 17 QSOs spectra at
5.74<zem<6.42 to obtain tighter constraints on the volume-averaged neutral
hydrogen fraction, xHI, at z~6. We study separately the narrow transmission
windows (peaks) and the wide dark portions (gaps) in the observed absorption
spectra. By comparing the statistics of these spectral features with Lyalpha
forest simulations, we conclude that xHI evolves smoothly from 10^{-4.4} at
z=5.3 to 10^{-4.2} at z=5.6, with a robust upper limit xHI<0.36 at z=6.3. The
frequency and physical sizes of the peaks imply an origin in cosmic underdense
regions and/or in HII regions around faint quasars or galaxies. In one case
(the intervening HII region of the faint quasar RD J1148+5253 at z=5.70 along
the LOS of SDSS J1148+5251 at z=6.42) the increase of the peak spectral density
is explained by the first-ever detected transverse proximity effect in the HI
Lyalpha forest; this indicates that at least some peaks result from a locally
enhanced radiation field. We then obtain a strong lower limit on the foreground
QSO lifetime of tQ>11 Myr. The observed widths of the peaks are found to be
systematically larger than the simulated ones. Reasons for such discrepancy
might reside either in the photoionization equilibrium assumption or in
radiative transfer effects.Comment: 12 pages, 9 figures, revised to match the accepted version including
a detailed analysis of the foreground QSO redshift and of the relativistic
effects on the HII region shape; MNRAS in pres
Proteomic screening and identification of differentially distributed membrane proteins in Escherichia coli
Bacteria show asymmetric subcellular distribution of many proteins involved in diverse cellular processes such as chemotaxis, motility, actin polymerization, chromosome partitioning and cell division. In many cases, the specific subcellular localization of these proteins is critical for proper regulation and function. Although cellular organization of the bacterial cell clearly plays an important role in cell physiology, systematic studies to uncover asymmetrically distributed proteins have not been reported previously. In this study, we undertook a proteomics approach to uncover polar membrane proteins in Escherichia coli . We identified membrane proteins enriched in E. coli minicells using a combination of two-dimensional electrophoresis and mass spectrometry. Among a total of 173 membrane protein spots that were consistently detected, 36 spots were enriched in minicell membranes, whereas 15 spots were more abundant in rod cell membranes. The minicell-enriched proteins included the inner membrane proteins MCPs, AtpA, AtpB, YiaF and AcrA, the membrane-associated FtsZ protein and the outer membrane proteins YbhC, OmpW, Tsx, Pal, FadL, OmpT and BtuB. We immunolocalized two of the minicell-enriched proteins, OmpW and YiaF, and showed that OmpW is a bona fide polar protein whereas YiaF displays a patchy membrane distribution with a polar and septal bias.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72089/1/j.1365-2958.2004.04040.x.pd
Genetic analysis of water loss of excised leaves associated with drought tolerance in wheat
BACKGROUND: . Wheat is widely affected by drought. Low excised-leaf water loss (ELWL) has frequently been associated with improved grain yield under drought. This study dissected the genetic control of ELWL in wheat, associated physiological, morphological and anatomical leaf traits, and compared these with yield QTLs. Methods. Ninety-four hexaploid wheat (Triticum aestivum L.) doubled haploids, mapped with over 700 markers, were tested for three years for ELWL from detached leaf 4 of glasshouse-grown plants. In one experiment, stomata per unit area and leaf thickness parameters from leaf cross-sections were measured. QTLs were identified using QTLCartographer. Results. ELWL was significantly negatively correlated with leaf length, width, area and thickness. Major QTLs for ELWL during 0-3 h and 3-6 h were coincident across trials on 3A, 3B, 4B, 5B, 5D, 6B, 7A, 7B, 7D and frequently coincident (inversely) with leaf size QTLs. Yield in other trials was sometimes associated with ELWL and leaf size phenotypically and genotypically, but more frequently under non-droughted than droughted conditions. QTL coincidence showed only ELWL to be associated with drought/control yield ratio. Discussion. Our results demonstrated that measures of ELWL and leaf size were equally effective predictors of yield, and both were more useful for selecting under favourable than stressed conditions
Experimental Constraints on Self-consistent Reionization Models
A self-consistent formalism to jointly study cosmic reionization and thermal
history of the IGM is presented. The model implements most of the relevant
physics governing these processes, such as the inhomogeneous IGM density
distribution, three different sources of ionizing photons (PopIII stars, PopII
stars and QSOs), and radiative feedback. By constraining the free parameters
with available data on redshift evolution of Lyman-limit systems, Gunn-Peterson
and electron scattering optical depths, Near InfraRed Background (NIRB), and
cosmic star formation history, we select a fiducial model, whose main
predictions are: (i) H was completely reionized at z \approx 15, while HeII
must have been reionized by z \approx 12. At z \approx 7, HeIII suffered an
almost complete recombination as a result of the extinction of PopIII stars, as
required by the interpretation of the NIRB. (ii) A QSO-induced complete HeII
reionization occurs at z=3.5; a similar double H reionization does not take
place due to the large number of photons above 1 Ryd from PopII stars and QSOs,
even after PopIII stars have disappeared. (iii) Following reionization, the
temperature of the IGM corresponding to the mean gas density is boosted to
15000 K. Observations of T_0 are consistent with the fact that He is singly
ionized at z > 3.5, while they are consistent with He being doubly ionized at z
< 3.5. This might be interpreted as a signature of (second) HeII reionization.
(iv) Only 0.3% of the stars produced by z=2 need to be PopIII stars in order to
achieve the hydrogen reionization. Such model not only relieves the tension
between the Gunn-Peterson optical depth and WMAP observations, but also
accounts self-consistently for all known observational constraints (abridged).Comment: Revised version. Accepted for publication in MNRA
LETSGO: A spacecraft-based mission to accurately measure the solar angular momentum with frame-dragging
LETSGO (LEnse-Thirring Sun-Geo Orbiter) is a proposed space-based mission
involving the use of a spacecraft moving along a highly eccentric heliocentric
orbit perpendicular to the ecliptic. It aims to accurately measure some
important physical properties of the Sun and to test some post-Newtonian
features of its gravitational field by continuously monitoring the Earth-probe
range. Preliminary sensitivity analyses show that, by assuming a cm-level
accuracy in ranging to the spacecraft, it would be possible to detect, in
principle, the Lense-Thirring effect on it at a 10^-3-10^-4 level over a
timescale of 2 yr, while the larger Schwarzschild component of the solar
gravitational field may be sensed with a relative accuracy of about 10^-8-10^-9
during the same temporal interval. The competing range perturbation due to the
non-sphericity of the Sun would be a source of systematic error, but it turns
out that all the three dynamical features of motion examined affect the
Earth-probe range in different ways, allowing for a separation in data
analyses. The high eccentricity would help in reducing the impact of the
non-gravitational perturbations whose impact would certainly be severe when
LETSGO would approach the Sun at just a few solar radii. Further studies should
be devoted to investigate both the consequences of the non-conservative forces
and the actual measurability of the effects of interest by means of extensive
numerical data simulations, parameter estimations and covariance analyses. Also
an alternative, fly-by configuration is worth of consideration.Comment: LaTex2e, double column, 19 pages, 3 figures, 3 tables, 97 references.
Accepted for publication in Acta Astronautica. Proof corrections inserte
Co-circulation of genetically distinct highly pathogenic avian influenza A clade 2.3.4.4 (H5N6) viruses in wild waterfowl and poultry in Europe and East Asia, 2017–18
Highly pathogenic avian influenza (HPAI) H5 clade 2.3.4.4 viruses were first introduced into Europe in late 2014 and re-introduced in late 2016, following detections in Asia and Russia. In contrast to the 2014–15 H5N8 wave, there was substantial local virus amplification in wild birds in Europe in 2016–17 and associated wild bird mortality, with evidence for occasional gene exchange with low pathogenic avian influenza (LPAI) viruses. Since December 2017, several European countries have again reported events or outbreaks with HPAI H5N6 reassortant viruses in both wild birds and poultry, respectively. Previous phylogenetic studies have shown that the two earliest incursions of HPAI H5N8 viruses originated in Southeast Asia and subsequently spread to Europe. In contrast, this study indicates that recent HPAI H5N6 viruses evolved from the H5N8 2016–17 viruses during 2017 by reassortment of a European HPAI H5N8 virus and wild host reservoir LPAI viruses. The genetic and phenotypic differences between these outbreaks and the continuing detections of HPAI viruses in Europe are a cause of concern for both animal and human health. The current co-circulation of potentially zoonotic HPAI and LPAI virus strains in Asia warrants the determination of drivers responsible for the global spread of Asian lineage viruses and the potential threat they pose to public health
Cosmological models in scalar tensor theories of gravity and observations: a class of general solutions
We consider cosmological models in scalar tensor theories of gravity that
describe an accelerating universe, and we study a family of inverse power law
potentials, for which exact solutions of the Einstein equations are known. We
also compare theoretical predictions of our models with observations. For this
we use the following data: the publicly available catalogs of type Ia
supernovae and high redshift Gamma Ray Bursts, the parameters of large scale
structure determined by the 2-degree Field Galaxy Redshift Survey (2dFGRS), and
measurements of cosmological distances based on the Sunyaev-Zel'dovich effect,
among others.Comment: 26 pages,23 figures, accepted for publication in A&
The growth of structure in the intergalactic medium
A {\it stochastic adhesion} model is introduced, with the purpose of
describing the formation and evolution of mildly nonlinear structures, such as
sheets and filaments, in the intergalactic medium (IGM), after hydrogen
reionization. The model is based on replacing the overall force acting on the
baryon fluid -- as it results from the composition of local gravity, pressure
gradients and Hubble drag -- by a mock external force, self-consistently
calculated from first-order perturbation theory. A small kinematic viscosity
term prevents shell-crossing on small scales (which arises because of the
approximate treatment of pressure gradients). The emerging scheme is an
extension of the well-known adhesion approximation for the dark matter
dynamics, from which it only differs by the presence of a small-scale `random'
force, characterizing the IGM. Our algorithm is the ideal tool to obtain the
skeleton of the IGM distribution, which is responsible for the structure
observed in the low-column density Ly forest in the absorption spectra
of distant quasars.Comment: 26 pages, 6 figures, MNRAS in press (accepted version
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