400 research outputs found
Discovery Of Cold, Pristine Gas Possibly Accreting Onto An Overdensity Of Star-Forming Galaxies At Redshift z ~ 1.6
We report the discovery of large amounts of cold (T ~ 10^4 K), chemically
young gas in an overdensity of galaxies at redshift z ~ 1.6 in the Great
Observatories Origins Deep Survey southern field (GOODS-S). The gas is
identified thanks to the ultra-strong Mg II absorption features it imprints in
the rest-frame UV spectra of galaxies in the background of the overdensity.
There is no evidence that the optically-thick gas is part of any massive galaxy
(i.e. M_star > 4x10^9 M_sun), but rather is associated with the overdensity;
less massive and fainter galaxies (25.5 < z_850 < 27.5 mag) have too large an
impact parameter to be causing ultra-strong absorption systems, based on our
knowledge of such systems. The lack of corresponding Fe II absorption features,
not detected even in co-added spectra, suggests that the gas is chemically more
pristine than the ISM and outflows of star-forming galaxies at similar
redshift, including those in the overdensity itself, and comparable to the most
metal-poor stars in the Milky Way halo. A crude estimate of the projected
covering factor of the high-column density gas (N_H >~ 10^20 cm-2) based on the
observed fraction of galaxies with ultra-strong absorbers is C_F ~ 0.04. A
broad, continuum absorption profile extending to the red of the interstellar Mg
II absorption line by <~ 2000 km/s is possibly detected in two independent
co-added spectra of galaxies of the overdensity, consistent with a large-scale
infall motion of the gas onto the overdensity and its galaxies. Overall, these
findings provides the first tentative evidence of accretion of cold, chemically
young gas onto galaxies at high redshift, possibly feeding their star formation
activity. The fact that the galaxies are members of a large structure, as
opposed to field galaxies, might play a significant role in our ability to
detect the accreting gas.Comment: 57 pages, 17 figures, 1 table; accepted for publication by ApJ (Aug
9, 2011); minor modifications to match the accepted versio
The Magellanic Bridge as a DLA System: Physical Properties of Cold Gas toward PKS0312-770
We measure the physical properties of a local multi-component absorption-line
system at V_sol ~ 200 km/s toward the quasar PKS0312-770 behind the Magellanic
Bridge (MB) using Hubble Space Telescope STIS spectroscopy in conjunction with
photoionization modeling. At an impact parameter of ~ 10 kpc from the Small
Magellanic Cloud (SMC), this sightline provides a unique opportunity to probe
the chemical properties and ionization structure in a nearby absorption line
system with a column density of logN(HI) ~ 20.2, at the transition between
Damped Lyman Alpha (DLA) and sub-DLA systems. We find that metallicity of -1.0
< logZ < -0.5 and ionization parameter of -6 < logU < -5 for three
low-ionization components and logU ~ -2.6 for one high-ionization component.
One component at V_sol = 207 km/s shows an alpha-element abundance log(Si/H) ~
-5.0, making it ~ 0.2 dex more metal rich than both SMC H II regions and stars
within the MB and the SMC. The N/Si ratio in this component is log(N/Si) =
-0.3+/-0.1, making it comparable to other N-poor dwarf galaxies and ~ 0.2 dex
lower than H II regions in the SMC. Another component at V_sol = 236 km/s shows
a similar Si/H ratio but has log(N/Si) = -1.0+/-0.2, indicating a nitrogen
deficiency comparable to that seen in the most N-poor DLA systems. These
differences imply different chemical enrichment histories between components
along the same sightline. Our results suggest that, if these absorbers are
representative some fraction of DLA systems, then 1) DLA systems along single
sight-lines do not necessarily represent the global properties of the absorbing
cloud, and b) the chemical composition within a given DLA cloud may be
inhomogeneous.Comment: 28 pages, including 16 figures; accepted for publication in the
Astrophysical Journa
ROBINS-I: a tool for assessing risk of bias in non-randomized studies of interventions
Non-randomised studies of the effects of interventions are critical to many areas of healthcare evaluation, but their results may be biased. It is therefore important to understand and appraise their strengths and weaknesses. We developed ROBINS-I ("Risk Of Bias In Non-randomised Studies-of Interventions"), a new tool for evaluating risk of bias in estimates of the comparative effectiveness (harm or benefit) of interventions from studies that did not use randomisation to allocate units (individuals or clusters of individuals) to comparison groups. The tool will be particularly useful to those undertaking systematic reviews that include non-randomised studies
The Connection between a Lyman Limit System, a very strong OVI Absorber, and Galaxies at z~0.203
With a column density log N(OVI) = 14.95+/-0.05, the OVI absorber at
z_abs~0.2028 observed toward the QSO PKS0312-77 (z_em=0.223) is the strongest
yet detected at z<0.5. At nearly identical redshift (z_abs=0.2026), we also
identify a Lyman limit system (LLS, log N(HI)=18.22). Combining FUV and NUV
spectra of PKS0312-77 with optical observations of galaxies in the surrounding
field (15'x32'), we present an analysis of these absorbers and their connection
to galaxies. The observed OI/HI ratio and photoionization modelling of other
low ions indicate the metallicity of the LLS is [Z/H]_LLS=-0.6 and that the LLS
is nearly 100% photoionized. In contrast, the OVI-bearing gas is collisionally
ionized at T~(3-10)x10^5 K as derived from the high-ion ratios and profile
broadenings. Our galaxy survey reveals 13 (0.3<L/L*<1.6) galaxies at \rho<2
h^{-1}_{70} Mpc and |\delta v|<1100 km/s from the LLS. A probable origin for
the LLS is debris from a galaxy merger, which led to a 0.7L* galaxy
([Z/H]_gal=+0.15) at\rho~38 h^{-1}_{70} kpc. Outflow from this galaxy may also
be responsible for the supersolar ([Z/H]_abs=+0.15), fully ionized absorber at
z_abs=0.2018 (-190 km/s from the LLS). The hot OVI absorber likely probes
coronal gas about the 0.7 L* galaxy and/or (~0.1 keV) intragroup gas of a
spiral-rich system. The association of other strong OVI absorbers with LLS
suggests they trace galactic and not intergalactic structures.Comment: Accepted for publication in the Ap
The Maternally Expressed WRKY Transcription Factor TTG2 Controls Lethality in Interploidy Crosses of Arabidopsis
The molecular mechanisms underlying lethality of F1 hybrids between diverged parents are one target of speciation research. Crosses between diploid and tetraploid individuals of the same genotype can result in F1 lethality, and this dosage-sensitive incompatibility plays a role in polyploid speciation. We have identified variation in F1 lethality in interploidy crosses of Arabidopsis thaliana and determined the genetic architecture of the maternally expressed variation via QTL mapping. A single large-effect QTL, DR. STRANGELOVE 1 (DSL1), was identified as well as two QTL with epistatic relationships to DSL1. DSL1 affects the rate of postzygotic lethality via expression in the maternal sporophyte. Fine mapping placed DSL1 in an interval encoding the maternal effect transcription factor TTG2. Maternal parents carrying loss-of-function mutations in TTG2 suppressed the F1 lethality caused by paternal excess interploidy crosses. The frequency of cellularization in the endosperm was similarly affected by both natural variation and ttg2 loss-of-function mutants. The simple genetic basis of the natural variation and effects of single-gene mutations suggests that F1 lethality in polyploids could evolve rapidly. Furthermore, the role of the sporophytically active TTG2 gene in interploidy crosses indicates that the developmental programming of the mother regulates the viability of interploidy hybrid offspring
cis-Urocanic Acid Attenuates Acute Dextran Sodium Sulphate-Induced Intestinal Inflammation
On exposure to sunlight, urocanic acid (UCA) in the skin is converted from trans to the cis form and distributed systemically where it confers systemic immunosuppression. The aim of this study was to determine if administration of cis-UCA would be effective in attenuating colitis and the possible role of IL-10. Colitis was induced in 129/SvEv mice by administering 5% dextran sodium sulfate (DSS) for 7 days in drinking water. During this period mice received daily subcutaneously injections of cis-UCA or vehicle. To examine a role for IL-10, 129/SvEv IL-10−/− mice were injected for 24 days with cis-UCA or vehicle. Clinical disease was assessed by measurement of body weight, stool consistency, and presence of blood. At sacrifice, colonic tissue was collected for histology and measurement of myeloperoxidase and cytokines. Splenocytes were analyzed for CD4+CD25+FoxP3+ T-regulatory cells via flow cytometry. Murine bone-marrow derived antigen-presenting cells were treated with lipopolysaccharide (LPS) ± UCA and cytokine secretion measured. Our results demonstrated that cis-UCA at a dose of 50 µg was effective in ameliorating DSS-induced colitis as evidenced by reduced weight loss and attenuated changes in colon weight/length. This protection was associated with reduced colonic expression of CXCL1, an increased expression of IL-17A and a significant preservation of splenic CD4+CD25+FoxP3+ T-regulatory cells. cis-UCA decreased LPS induced CXCL1, but not TNFα secretion, from antigen-presenting cells in vitro. UCA reduced colonic levels of IFNγ in IL-10−/− mice but did not attenuate colitis. In conclusion, this study demonstrates that cis-urocanic acid is effective in reducing the severity of colitis in a chemically-induced mouse model, indicating that pathways induced by ultraviolet radiation to the skin can influence distal sites of inflammation. This provides further evidence for a possible role for sunlight exposure in modulating inflammatory disorders
Variation in paranasal pneumatisation between Mid-Late Pleistocene hominins
There is considerable variation in mid-late Pleistocene hominin paranasal sinuses, and in some taxa distinctive craniofacial shape has been linked to sinus size. Extreme frontal sinus size has been reported in mid-Pleistocene specimens often classified as Homo heidelbergensis, and Neanderthal sinuses are said to be distinctively large, explaining diagnostic Neanderthal facial shape. Here, the sinuses of fossil hominins attributed to several mid-late Pleistocene taxa were compared to those of recent H. sapiens. The sinuses were investigated to clarify differences in the extent of pneumatisation within this group and the relationship between sinus size and craniofacial variation in hominins from this time period. Frontal and maxillary sinus volumes were measured from CT data, and geometric morphometric methods were used to identify and analyse shape variables associated with sinus volume. Some mid
Ethylene-induced differential gene expression during abscission of citrus leaves
The main objective of this work was to identify and classify genes involved in the process of leaf abscission in Clementina de Nules (Citrus clementina Hort. Ex Tan.). A 7 K unigene citrus cDNA microarray containing 12 K spots was used to characterize the transcriptome of the ethylene-induced abscission process in laminar abscission zone-enriched tissues and the petiole of debladed leaf explants. In these conditions, ethylene induced 100% leaf explant abscission in 72 h while, in air-treated samples, the abscission period started later and took 240 h. Gene expression monitored during the first 36 h of ethylene treatment showed that out of the 12 672 cDNA microarray probes, ethylene differentially induced 725 probes distributed as follows: 216 (29.8%) probes in the laminar abscission zone and 509 (70.2%) in the petiole. Functional MIPS classification and manual annotation of differentially expressed genes highlighted key processes regulating the activation and progress of the cell separation that brings about abscission. These included cell-wall modification, lipid transport, protein biosynthesis and degradation, and differential activation of signal transduction and transcription control pathways. Expression data associated with the petiole indicated the occurrence of a double defensive strategy mediated by the activation of a biochemical programme including scavenging ROS, defence and PR genes, and a physical response mostly based on lignin biosynthesis and deposition. This work identifies new genes probably involved in the onset and development of the leaf abscission process and suggests a different but co-ordinated and complementary role for the laminar abscission zone and the petiole during the process of abscission
The Memory Politics of Becoming European: The East European Subalterns and the Collective Memory of Europe
The situation in collective memory studies that share a nexus with
the discipline of International Relations (IR) is currently reflective
of the traditionally West-centric writing of European history. This
order of things has become increasingly challenged after the eastern
enlargement of the European Union (EU). This article examines
Poland’s and the Baltics’ recent attempts to enlarge the mnemonic
vision of ‘the united Europe’ by placing their ‘subaltern pasts’ in contest
with the conventionally Western European-bent understanding of the
consequences of World War II in Europe. I argue that their endeavours
to wrench the ‘European mnemonical map’ apart in order to become
more congruent with the different historical experiences within the
enlarged EU encapsulate the curious trademark of Polish and Baltic
post-Cold War politics of becoming European: their combination of
simultaneously seeking recognition from and resisting the hegemonic
‘core European’ narrative of what ‘Europe’ is all about
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