164 research outputs found
Characterizing the transition from diffuse atomic to dense molecular clouds in the Magellanic clouds with [CII], [CI], and CO
We present and analyze deep Herschel/HIFI observations of the [CII] 158um,
[CI] 609um, and [CI] 370um lines towards 54 lines-of-sight (LOS) in the Large
and Small Magellanic clouds. These observations are used to determine the
physical conditions of the line--emitting gas, which we use to study the
transition from atomic to molecular gas and from C^+ to C^0 to CO in their low
metallicity environments. We trace gas with molecular fractions in the range
0.1<f(H2)<1, between those in the diffuse H2 gas detected by UV absorption
(f(H2)<0.2) and well shielded regions in which hydrogen is essentially
completely molecular. The C^0 and CO column densities are only measurable in
regions with molecular fractions f(H2)>0.45 in both the LMC and SMC. Ionized
carbon is the dominant gas-phase form of this element that is associated with
molecular gas, with C^0 and CO representing a small fraction, implying that
most (89% in the LMC and 77% in the SMC) of the molecular gas in our sample is
CO-dark H2. The mean X_CO conversion factors in our LMC and SMC sample are
larger than the value typically found in the Milky Way. When applying a
correction based on the filling factor of the CO emission, we find that the
values of X_CO in the LMC and SMC are closer to that in the Milky Way. The
observed [CII] intensity in our sample represents about 1% of the total
far-infrared intensity from the LOSs observed in both Magellanic Clouds.Comment: 32 pages, 21 figures, Accepted to Ap
A Search for Kinematic Evidence of Radial Gas Flows in Spiral Galaxies
CO and HI velocity fields of seven nearby spiral galaxies, derived from
radio-interferometric observations, are decomposed into Fourier components
whose radial variation is used to search for evidence of radial gas flows.
Additional information provided by optical or near-infrared isophotes is also
considered, including the relationship between the morphological and kinematic
position angles. To assist in interpreting the data, we present detailed
modeling that demonstrates the effects of bar streaming, inflow, and a warp on
the observed Fourier components. We find in all of the galaxies evidence for
either elliptical streaming or a warped disk over some range in radius, with
deviations from pure circular rotation at the level of ~20-60 km/s. Evidence
for kinematic warps is observed in several cases well inside R_{25}. No
unambiguous evidence for radial inflows is seen in any of the seven galaxies,
and we are able to place an upper limit of ~5-10 km/s (3-5% of the circular
speed) on the magnitude of any radial inflow in the inner regions of NGC 4414,
5033 and 5055. We conclude that the inherent non-axisymmetry of spiral galaxies
is the greatest limitation to the direct detection of radial inflows.Comment: 22 emulateapj pages with bitmapped colour figures, to appear in ApJ
(April 2004). For full resolution figures go to
http://www.atnf.csiro.au/people/twong/preprints
Molecular Gas in Spiral Galaxies
In this review, I highlight a number of recent surveys of molecular gas in
nearby spiral galaxies. Through such surveys, more complete observations of the
distribution and kinematics of molecular gas have become available for galaxies
with a wider range of properties (e.g., brightness, Hubble type, strength of
spiral or bar structure). These studies show the promise of both
interferometers and single-dish telescopes in advancing our general
understanding of molecular gas in spiral galaxies. In particular, I highlight
the contributions of the recent BIMA Survey of Nearby Galaxies (SONG).Comment: 8 pages, 1 figure. To appear in the proceedings of the 4th
Cologne-Bonn-Zermatt-Symposium, "The Dense Interstellar Medium in Galaxies",
which was held in Zermatt, Switzerland in September 200
Quenching of Star Formation in Molecular Outflow Host NGC 1266
We detail the rich molecular story of NGC 1266, its serendipitous discovery
within the ATLAS3D survey (Cappellari et al. 2011) and how it plays host to an
AGN-driven molecular outflow, potentially quenching all of its star formation
(SF) within the next 100 Myr. While major mergers appear to play a role in
instigating outflows in other systems, deep imaging of NGC 1266 as well as
stellar kinematic observations from SAURON, have failed to provide evidence
that NGC 1266 has recently been involved in a major interaction. The molecular
gas and the instantaneous SF tracers indicate that the current sites of star
formation are located in a hypercompact disk within 200 pc of the nucleus (Fig.
1; SF rate ~ 2 Msuns/yr). On the other hand, tracers of recent star formation,
such as the H{\beta} absorption map from SAURON and stellar population analysis
show that the young stars are distributed throughout a larger area of the
galaxy than current star formation. As the AGN at the center of NGC 1266
continues to drive cold gas out of the galaxy, we expect star formation rates
to decline as the star formation is ultimately quenched. Thus, NGC 1266 is in
the midst of a key portion of its evolution and continued studies of this
unique galaxy may help improve our understanding of how galaxies transition
from the blue to the red sequence (Alatalo et al. 2011).Comment: 1 page, Proceedings IAU symposium No. 292: Molecular gas, dust and
star formation in galaxies, ed. by Tony Wong and Juergen Ot
The Relationship Between Gas Content and Star Formation in Molecule-Rich Spiral Galaxies
We investigate the relationship between HI, H_2, and the star formation rate
(SFR) using azimuthally averaged data for seven CO-bright spiral galaxies.
Contrary to some earlier studies based on global fluxes, we find that the SFR
surface density exhibits a much stronger correlation with the H_2 than with the
HI, as the HI surface density saturates at a value of 10 Msol pc^{-2} or
even declines at large SFR surface densities. Hence the good correlation
between the SFR surface density and the total (HI+H_2) gas surface density is
driven by the molecular component in these galaxies. We find no clear evidence
for a link between the gravitational instability parameter for the gas disk
(Q_g) and the SFR, and suggest that Q_g be considered a measure of the gas
fraction. This implies that for a state of marginal gravitational stability to
exist in galaxies with low gas fractions, it must be due to instability of the
stellar disk. In regions where we have both HI and CO measurements, the ratio
of HI to H_2 surface density scales with radius R as roughly R^{1.5}, and we
suggest that the balance between HI and H_2 is determined primarily by the
midplane interstellar pressure. These results favor a "law" of star formation
in quiescent disks in which the ambient pressure and metallicity control the
formation of molecular clouds from HI, with star formation then occurring at a
roughly constant rate per unit H_2 mass. (abstract abridged)Comment: To appear in ApJ. 28 pages with 16 figures (emulateapj5). Full
resolution figures available at
http://www.atnf.csiro.au/people/twong/preprints
Hydraulic & Design Parameters in Full-Scale Constructed Wetland & Treatment Units: Six Case Studies
The efficiency of pond and constructed wetland (CW) treatment systems, is influenced by the internal hydrodynamics and mixing interactions between water and aquatic vegetation. In order to contribute to current knowledge of how emergent real vegetation affects solute mixing, and on what the shape and size effects are on the mixing characteristics, an understanding and quantification of those physical processes and interactions was evaluated.
This paper presents results from tracer tests conducted during 2015-2016 in six full-scale systems in the UK under different flow regimes, operational depths, shapes and sizes, and in-/outlet configurations. The aim is to quantify the hydraulic performance and mixing characteristics of the treatment units, and to investigate the effect of size and shape on the mixing processes. Relative comparison of outlet configuration, inflow conditions, and internal features between the six different treatment units showed variations in residence times of up to a factor of 3. A key outcome of this study, demonstrated that the width is a more important dimension for the efficiency of the unit compared to the depth. Results underlined the importance of investigating hydrodynamics and physics of flow in full-size units to enhance treatment efficiency and predictions of water quality models
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An IL1RL1 genetic variant lowers soluble ST2 levels and the risk effects of APOE-ε4 in female patients with Alzheimer’s disease
Changes in the levels of circulating proteins are associated with Alzheimer’s disease (AD), whereas their pathogenic roles in AD are unclear. Here, we identified soluble ST2 (sST2), a decoy receptor of interleukin-33–ST2 signaling, as a new disease-causing factor in AD. Increased circulating sST2 level is associated with more severe pathological changes in female individuals with AD. Genome-wide association analysis and CRISPR–Cas9 genome editing identified rs1921622, a genetic variant in an enhancer element of IL1RL1, which downregulates gene and protein levels of sST2. Mendelian randomization analysis using genetic variants, including rs1921622, demonstrated that decreased sST2 levels lower AD risk and related endophenotypes in females carrying the Apolipoprotein E (APOE)-ε4 genotype; the association is stronger in Chinese than in European-descent populations. Human and mouse transcriptome and immunohistochemical studies showed that rs1921622/sST2 regulates amyloid-beta (Aβ) pathology through the modulation of microglial activation and Aβ clearance. These findings demonstrate how sST2 level is modulated by a genetic variation and plays a disease-causing role in females with AD
A novel xylan degrading β-D-xylosidase: purification and biochemical characterization
Aspergillus ochraceus, a thermotolerant fungus isolated in Brazil from decomposing materials, produced an extracellular b-xylosidase that was purified using DEAE-cellulose ion exchange chromatography, Sephadex G-100 and Biogel P-60 gel filtration. b-xylosidase is a
glycoprotein (39 % carbohydrate content) and has a molecular mass of 137 kDa by SDS-PAGE, with optimal temperature and pH at 70 C and 3.0–5.5, respectively.b-xylosidase was stable in acidic pH (3.0–6.0) and 70 C for 1 h. The enzyme was activated by 5 mM MnCl2 (28 %)and MgCl2 (20 %) salts. The b-xylosidase produced by A. ochraceus preferentially hydrolyzed p-nitrophenyl-b- D-xylopyranoside, exhibiting apparent Km and Vmax values of 0.66 mM and 39 U (mg protein)-1 respectively, and to a lesser extent p-nitrophenyl-b-D-glucopyranoside. The enzyme was able to hydrolyze xylan from different sources,suggesting a novel b-D-xylosidase that degrades xylan.
HPLC analysis revealed xylans of different compositions which allowed explaining the differences in specificity observed by b-xylosidase. TLC confirmed the capacity.This work was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), and the Conselho de Desenvolvimento Científico e Tecnológico (CNPq). J. A. J. and M. L. T. M. P are Research Fellows of CNPq. M. M. was a recipient of a FAPESP fellowship and this work is part of her Doctoral Thesis. It is also part of the project SISBIOTA CNPq: 563260/2010-6 and FAPESP: 2010/52322-3
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