323 research outputs found
Contrasting geochemical signatures on land from the Middle and Late Permian extinction events
The end of the Palaeozoic is marked by two massâextinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative δ 13 C anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new highâresolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, â W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant synâextinction and postâextinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coalâbeds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108696/1/sed12117.pd
Identification of anthranilate and benzoate metabolic operons of Pseudomonas fluorescens and functional characterization of their promoter regions
BACKGROUND: In an effort to identify alternate recombinant gene expression systems in Pseudomonas fluorescens, we identified genes encoding two native metabolic pathways that were inducible with inexpensive compounds: the anthranilate operon (antABC) and the benzoate operon (benABCD). RESULTS: The antABC and benABCD operons were identified by homology to the Acinetobacter sp. anthranilate operon and Pseudomonas putida benzoate operon, and were confirmed to be regulated by anthranilate or benzoate, respectively. Fusions of the putative promoter regions to the E. coli lacZ gene were constructed to confirm inducible gene expression. Each operon was found to be controlled by an AraC family transcriptional activator, located immediately upstream of the first structural gene in each respective operon (antR or benR). CONCLUSION: We have found the anthranilate and benzoate promoters to be useful for tightly controlling recombinant gene expression at both small (< 1 L) and large (20 L) fermentation scales
NGC 3576 and NGC 3603: Two Luminous Southern HII Regions Observed at High Resolution with the Australia Telescope Compact Array
NGC 3576 (G291.28-0.71; l=291.3o, b=-0.7o) and NGC 3603 (G291.58-0.43;
l=291.6o, b=-0.5o) are optically visible, luminous HII regions located at
distances of 3.0 kpc and 6.1 kpc, respectively. We present 3.4 cm Australian
Telescope Compact Array (ATCA) observations of these two sources in the
continuum and the H90a, He90a, C90a and H113b recombination lines with an
angular resolution of 7" and a velocity resolution of 2.6 km/s. All four
recombination lines are detected in the integrated profiles of the two sources.
Broad radio recombination lines are detected in both NGC 3576 (DV_{FWHM}>= 50
km/s) and NGC 3603 (DV_{FWHM}>=70 km/s). In NGC 3576 a prominent N-S velocity
gradient (~30 km/s/pc) is observed, and a clear temperature gradient (6000 K to
8000 K) is found from east to west, consistent with a known IR color gradient
in the source. In NGC 3603, the H90a, He90a and the H113b lines are detected
from 13 individual sources. The Y^+ (He/H) ratios in the two sources range from
0.08+/-0.04 to 0.26+/-0.10. We compare the morphology and kinematics of the
ionized gas at 3.4 cm with the distribution of stars, 10 micron emission and
H_2O, OH, and CH_3OH maser emission. These comparisons suggest that both NGC
3576 and NGC 3603 have undergone sequential star formation.Comment: 24 pages, 12 Postscript figure
Oregon 2100: projected climatic and ecological changes
Greenhouse climatic warming is underway and exacerbated by human activities. Future outcomes of these processes can be projected using computer models checked against climatic changes during comparable past atmospheric compositions. This study gives concise quantitative predictions for future climate, landscapes, soils, vegetation, and marine and terrestrial animals of Oregon. Fossil fuel burning and other human activities by the year 2100 are projected to yield atmospheric CO2 levels of about 600-850 ppm (SRES A1B and B1), well above current levels of 400 ppm and preindustrial levels of 280 ppm. Such a greenhouse climate was last recorded in Oregon during the middle Miocene, some 16 million years ago. Oregonâs future may be guided by fossil records of the middle Miocene, as well as ongoing studies on the environmental tolerances of Oregon plants and animals, and experiments on the biological effects of global warming. As carbon dioxide levels increase, Oregonâs climate will move toward warm temperate, humid in the west and semiarid to subhumid to the east, with increased summer and winter drought in the west. Western Oregon lowlands will become less suitable for temperate fruits and nuts and Pinot Noir grapes, but its hills will remain a productive softwood forest resource. Improved pasture and winter wheat crops will become more widespread in eastern Oregon. Tsunamis and stronger storms will exacerbate marine erosion along the Oregon Coast, with significant damage to coastal properties and cultural resources
Zika virus impairs the development of blood vessels in a mouse model of congenital infection
Zika virus (ZIKV) is associated with brain development abnormalities such as primary microcephaly, a severe reduction in brain growth. Here we demonstrated in vivo the impact of congenital ZIKV infection in blood vessel development, a crucial step in organogenesis. ZIKV was injected intravenously in the pregnant type 2 interferon (IFN)-deficient mouse at embryonic day (E) 12.5. The embryos were collected at E15.5 and postnatal day (P)2. Immunohistochemistry for cortical progenitors and neuronal markers at E15.5 showed the reduction of both populations as a result of ZIKV infection. Using confocal 3D imaging, we found that ZIKV infected brain sections displayed a reduction in the vasculature density and vessel branching compared to mocks at E15.5; altogether, cortical vessels presented a comparatively immature pattern in the infected tissue. These impaired vascular patterns were also apparent in the placenta and retina. Moreover, proteomic analysis has shown that angiogenesis proteins are deregulated in the infected brains compared to controls. At P2, the cortical size and brain weight were reduced in comparison to mock-infected animals. In sum, our results indicate that ZIKV impairs angiogenesis in addition to neurogenesis during development. The vasculature defects represent a limitation for general brain growth but also could regulate neurogenesis directly
Detection of the 205 um [NII] Line from the Carina Nebula
We report the first detection of the 205 um 3P1 - 3P0 [NII] line from a
ground-based observatory using a direct detection spectrometer. The line was
detected from the Carina star formation region using the South Pole Imaging
Fabry-Perot Interferometer (SPIFI) on the Antarctic Submillimeter Telescope and
Remote Observatory (AST/RO) at South Pole. The [NII] 205 um line strength
indicates a low-density (n ~ 32 cm^-3 ionized medium, similar to the
low-density ionized halo reported previously in its [OIII] 52 and 88 um line
emission. When compared with the ISO [CII] observations of this region, we find
that ~27% of the [CII] line emission arises from this low-density ionized gas,
but the large majority ~ 73% of the observed [CII] line emission arises from
the neutral interstellar medium. This result supports and underpins prior
conclusions that most of the observed [CII] 158 um line emission from Galactic
and extragalactic sources arises from the warm, dense photodissociated surfaces
of molecular clouds. The detection of the [NII] line demonstrates the utility
of Antarctic sites for THz spectroscopy.Comment: 8 pages, 2 figures. To appear in the Astrophysical Journal Letter
Anomalous X-ray Pulsars and Soft Gamma-Ray Repeaters in supernova remnants
Important constraints on the properties of the Anomalous X-ray Pulsars (AXPs)
and Soft Gamma-Ray Repeaters (SGRs) can be provided by their associations with
supernova remnants (SNRs). We have made a radio search for SNRs towards the
AXPs RX J170849-400910 and 4U 0142+61 - we find that the former lies near a
possible new SNR with which it is unlikely to be physically associated, but see
no SNR in the vicinity of the latter. We review all claimed pairings between
AXPs and SNRs; the three convincing associations imply that AXPs are young (<
10 000 yr) neutron stars with low projected space velocities (< 500 km/s).
Contrary to previous claims, we find no evidence that the density of the
ambient medium around AXPs is higher than that in the vicinity of radio
pulsars. Furthermore, the non-detection of radio emission from AXPs does not
imply that these sources are radio-silent. We also review claimed associations
between SGRs and SNRs. We find none of these associations to be convincing,
consistent with a scenario in which SGRs and AXPs are both populations of
high-field neutron stars ("magnetars") but in which the SGRs are an older or
longer-lived group of objects than are the AXPs. If the SGR/SNR associations
are shown to be valid, then SGRs must be high-velocity objects and most likely
represent a different class of source to the AXPs.Comment: 13 pages, 3 embedded EPS figures. Minor alterations following
referee's report; no significant changes. Accepted to Ap
The impact of neogene grassland expansion and aridification on the isotopic composition of continental precipitation
The late Cenozoic was a time of global cooling, increased aridity, and expansion of grasslands. In the last two decades numerous records of oxygen isotopes have been collected to assess plant ecological changes, understand terrestrial paleoclimate, and to determine the surface history of mountain belts. The δšâ¸(O) values of these records, in general, increase from the mid-Miocene to the Recent. We suggest that these records record an increase in aridity and expansion of grasslands in midlatitude continental regions. We use a nondimensional isotopic vapor transport model coupled with a soil water isotope model to evaluate the role of vapor recycling and transpiration by different plant functional types. This analysis shows that increased vapor recycling associated with grassland expansion along with biomechanistic changes in transpiration by grasses themselves conspires to lower the horizontal gradient in the δšâ¸(O) of atmospheric vapor as an air mass moves into continental interiors. The resulting signal at a given inland site is an increase in δšâ¸(O) of precipitation with the expansion of grasslands and increasing aridity, matching the general observed trend in terrestrial Cenozoic δšâ¸(O) records. There are limits to the isotopic effect that are induced by vapor recycling, which we refer to here as a âhydrostat.â In the modern climate, this hydrostatic limit occurs at approximately the boundary between forest and grassland ecosystems
Higher Level Phylogeny and the First Divergence Time Estimation of Heteroptera (Insecta: Hemiptera) Based on Multiple Genes
Heteroptera, or true bugs, are the largest, morphologically diverse and economically important group of insects with incomplete metamorphosis. However, the phylogenetic relationships within Heteroptera are still in dispute and most of the previous studies were based on morphological characters or with single gene (partial or whole 18S rDNA). Besides, so far, divergence time estimates for Heteroptera totally rely on the fossil record, while no studies have been performed on molecular divergence rates. Here, for the first time, we used maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) with multiple genes (18S rDNA, 28S rDNA, 16S rDNA and COI) to estimate phylogenetic relationships among the infraorders, and meanwhile, the Penalized Likelihood (r8s) and Bayesian (BEAST) molecular dating methods were employed to estimate divergence time of higher taxa of this suborder. Major results of the present study included: Nepomorpha was placed as the most basal clade in all six trees (MP trees, ML trees and Bayesian trees of nuclear gene data and four-gene combined data, respectively) with full support values. The sister-group relationship of Cimicomorpha and Pentatomomorpha was also strongly supported. Nepomorpha originated in early Triassic and the other six infraorders originated in a very short period of time in middle Triassic. Cimicomorpha and Pentatomomorpha underwent a radiation at family level in Cretaceous, paralleling the proliferation of the flowering plants. Our results indicated that the higher-group radiations within hemimetabolous Heteroptera were simultaneously with those of holometabolous Coleoptera and Diptera which took place in the Triassic. While the aquatic habitat was colonized by Nepomorpha already in the Triassic, the Gerromorpha independently adapted to the semi-aquatic habitat in the Early Jurassic
Rise to modern levels of ocean oxygenation coincided with the Cambrian radiation of animals.
The early diversification of animals (âź630âMa), and their development into both motile and macroscopic forms (âź575-565âMa), has been linked to stepwise increases in the oxygenation of Earth's surface environment. However, establishing such a linkage between oxygen and evolution for the later Cambrian 'explosion' (540-520âMa) of new, energy-sapping body plans and behaviours has proved more elusive. Here we present new molybdenum isotope data, which demonstrate that the areal extent of oxygenated bottom waters increased in step with the early Cambrian bioradiation of animals and eukaryotic phytoplankton. Modern-like oxygen levels characterized the ocean at âź521âMa for the first time in Earth history. This marks the first establishment of a key environmental factor in modern-like ecosystems, where animals benefit from, and also contribute to, the 'homeostasis' of marine redox conditions
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