916 research outputs found
A Detailed Look at Chemical Abundances in Magellanic Cloud Planetary Nebulae. I. The Small Magellanic Cloud
We present an analysis of elemental abundances of He, N, O, Ne, S, and Ar in
Magellanic Cloud planetary nebulae (PNe), and focus initially on 14 PNe in the
Small Magellanic Cloud (SMC). We derived the abundances from a combination of
deep, high dispersion optical spectra, as well as mid-infrared (IR) spectra
from the Spitzer Space Telescope. A detailed comparison with prior SMC PN
studies shows that significant variations among authors of relative emission
line flux determinations lead to systematic discrepancies in derived elemental
abundances between studies that are >~0.15 dex, in spite of similar analysis
methods. We used ionic abundances derived from IR emission lines, including
those from ionization stages not observable in the optical, to examine the
accuracy of some commonly used recipes for ionization correction factors
(ICFs). These ICFs, which were developed for ions observed in the optical and
ultraviolet, relate ionic abundances to total elemental abundances. We find
that most of these ICFs work very well even in the limit of substantially
sub-Solar metallicities, except for PNe with very high ionization. Our
abundance analysis shows enhancements of He and N that are predicted from prior
dredge-up processes of the progenitors on the AGB, as well as the well known
correlations among O, Ne, S, and Ar that are little affected by nucleosynthesis
in this mass range. We identified MG_8 as an interesting limiting case of a PN
central star with a ~3.5 M_sun progenitor in which hot-bottom burning did not
occur in its prior AGB evolution. We find no evidence for O depletion in the
progenitor AGB stars via the O-N cycle, which is consistent with predictions
for lower-mass stars. We also find low S/O ratios relative to SMC H_II regions,
with a deficit comparable to what has been found for Galactic PNe.Comment: 9 figures, 6 tables; to be published in Ap
Gelatin tannate and tyndallized probiotics: a novel approach for treatment of diarrhea
Intestinal permeability impairment is implicated in many gastrointestinal (GI) diseases. Chronic diarrhea, defined as the presence of diarrhea for more than 3 weeks in adults and 2 weeks in children, requires a different diagnostic and therapeutic work-up than acute diarrhea. Gelatin tannate, by reducing the clinical activity of acute colitis and the proinflammatory effects of lipopolysaccharide (LPS), is emerging as a mucosal barrier protector
The nature of dust in compact Galactic planetary nebulae from Spitzer spectra
We present the Spitzer/IRS spectra of 157 compact Galactic PNe. These young
PNe provide insight on the effects of dust in early post-AGB evolution, before
much of the dust is altered or destroyed by the hardening stellar radiation
field. Most of the selected targets have PN-type IRS spectra, while a few
turned out to be misclassified stars. We inspected the group properties of the
PN spectra and classified them based on the different dust classes
(featureless, carbon-rich dust; oxygen-rich dust; mixed-chemistry dust) and
subclasses (aromatic and aliphatic; crystalline and amorphous). All PNe are
characterized by dust continuum and more than 80% of the sample shows solid
state features above the continuum, in contrast with the Magellanic Cloud
sample where only ~40% of the entire sample displays solid state features; this
is an indication of the strong link between dust properties and metallicity.
The Galactic PNe that show solid state features are almost equally divided
among the CRD, ORD, and MCD. We analyzed dust properties together with other PN
properties and found that (i) there is an enhancement of MCD PNe toward the
Galactic center; (ii) CRD PNe could be seen as defining an evolutionary
sequence, contrary to the ORD and MCD PNe; (iii) C- and O-rich grains retain
different equilibrium temperatures, as expected from models; (iv) ORD PNe are
highly asymmetric and CRD PNe highly symmetric; point-symmetry is statistically
more common in MCD. We find that the Galactic Disk sample does not include MCD
PNe, and the other dust classes are differently populated from high to low
metallicity environments. The MCPNe seem to attain higher dust temperatures at
similar evolutionary stages, in agreement with the observational findings of
smaller dust grains in low metallicity interstellar environments.Comment: The Astrophysical Journal, in press (76 pages, 36 figures and 6
Tables
Non-celiac gluten sensitivity in the context of functional gastrointestinal disorders
Gluten-free diets are increasingly chosen in the Western world, even in the absence of a diagnosis of celiac disease. Around 10% of people worldwide self-report gluten-related complaints, including intestinal and extra-intestinal symptoms. In most cases, these subjects would be labeled as patients suffering from irritable bowel syndrome (IBS) who place themselves on a gluten-free diet even in the absence of celiac disease. In some instances, patients report a clear benefit by avoiding gluten from their diet and/or symptom worsening upon gluten reintroduction. This clinical entity has been termed non-celiac gluten sensitivity (NCGS). The symptoms referred by these patients are both intestinal and extra-intestinal, suggesting that similarly to functional gastrointestinal disorders, NCGS is a disorder of gut–brain interaction. It remains unclear if gluten is the only wheat component involved in NCGS. The mechanisms underlying symptom generation in NCGS remain to be fully clarified, although in the past few years, the research has significantly moved forward with new data linking NCGS to changes in gut motility, permeability and innate immunity. The diagnosis is largely based on the self-reported reaction to gluten by the patient, as there are no available biomarkers, and confirmatory double-blind challenge protocols are unfeasible in daily clinical practice. Some studies suggest that a small proportion of patients with IBS have an intolerance to gluten. However, the benefits of gluten-free or low-gluten diets in non-celiac disease-related conditions are limited, and the long-term consequences of this practice may include nutritional and gut microbiota unbalance. Here, we summarize the role of gluten in the clinical features, pathophysiology, and management of NCGS and disorders of gut–brain interaction
Inflammatory and Microbiota-Related Regulation of the Intestinal Epithelial Barrier
The intestinal epithelial barrier (IEB) is one of the largest interfaces between the environment and the internal milieu of the body. It is essential to limit the passage of harmful antigens and microorganisms and, on the other side, to assure the absorption of nutrients and water. The maintenance of this delicate equilibrium is tightly regulated as it is essential for human homeostasis. Luminal solutes and ions can pass across the IEB via two main routes: the transcellular pathway or the paracellular pathway. Tight junctions (TJs) are a multi-protein complex responsible for the regulation of paracellular permeability. TJs control the passage of antigens through the IEB and have a key role in maintaining barrier integrity. Several factors, including cytokines, gut microbiota, and dietary components are known to regulate intestinal TJs. Gut microbiota participates in several human functions including the modulation of epithelial cells and immune system through the release of several metabolites, such as short-chain fatty acids (SCFAs). Mediators released by immune cells can induce epithelial cell damage and TJs dysfunction. The subsequent disruption of the IEB allows the passage of antigens into the mucosa leading to further inflammation. Growing evidence indicates that dysbiosis, immune activation, and IEB dysfunction have a role in several diseases, including irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and gluten-related conditions. Here we summarize the interplay between the IEB and gut microbiota and mucosal immune system and their involvement in IBS, IBD, and gluten-related disorders
Thermal Conductivity Enhancement of Al2O3 Nanofluid in Ethylene Glycol and Water Mixture
AbstractThe ability of nanofluids that exhibits enhanced thermal performance is acknowledged by researchers through studies since decades ago. However, the observation of thermal properties for nanofluids in water and ethylene glycol based is not fully explored yet. Hence, this paper presents the thermal conductivity of water and ethylene glycol (EG) based Al2O3 nanofluid. The 13 nm sized Al2O3 nanoparticles were dispersed into three different volume ratio of water: EG such as 40:60, 50:50 and 60:40 using a two-step method. The measurement of thermal conductivity was performed using KD2 Pro Thermal Properties Analyzer at working temperatures of 30 to 70 ̊C for volume concentration of 0.5 to 2.0%. The results indicate that the thermal conductivity increases with the increase of nanofluid concentration and temperature. While the percentage of ethylene glycol increase, the range of thermal conductivity decreases due to ethylene glycol properties. The measurement data of the nanofluids give maximum enhancement of thermal conductivity at condition 2.0% volume concentration, temperature of 70 ̊C and for all base fluid
Gastrointestinal Bleeding in COVID-19 Patients: A Systematic Review with Meta-Analysis
The novel coronavirus disease 2019 (COVID-19) has been reported to affect the gastrointestinal system with a variety of symptoms, including bleeding. The prevalence of bleeding in these patients remains unclear. The aim of this meta-Analysis is to estimate the rate of gastrointestinal bleeding in COVID-19 patients and its association with mortality. MEDLINE and Embase were searched through December 20, 2020. Studies reporting COVID-19 patients with and without gastrointestinal bleeding were included. Estimated prevalence with 95% confidence intervals (CI) was pooled; heterogeneity was expressed as I2. Metaregression analysis was performed to assess the impact of confounding covariates. Ten studies met the inclusion criteria and were included in the analysis. A total of 91887 COVID-19 patients were considered, of whom 534 reported gastrointestinal bleeding (0.6%) [409 (76.6%) upper and 121 (22.7%) lower gastrointestinal bleeding (UGIB and LGIB, resp.)]. The overall pooled gastrointestinal bleeding rate was 5% [95% CI 2-8], with high heterogeneity (I2 99.2%); "small study effect"was observed using the Egger test (p=0.049). After removing two outlier studies, the pooled bleeding rate was 2% [95% CI 0-4], with high heterogeneity (I2 99.2%), and no "small study effect"(p=0.257). The pooled UGIB rate was 1% (95% CI 0-3, I2 98.6%, p=0.214), whereas the pooled LGIB rate was 1% (95% CI 0-2, I2 64.7%, p=0.919). Metaregression analysis showed that overall estimates on gastrointestinal bleeding were affected by studies reporting different sources of bleeding. No significant association between gastrointestinal bleeding and mortality was found. In this meta-Analysis of published studies, individuals with COVID-19 were found to be at risk for gastrointestinal bleeding, especially upper gastrointestinal bleeding
Spitzer Infrared Spectrograph Observations of Magellanic Cloud Planetary Nebulae: the nature of dust in low metallicity circumstellar ejecta
We present 5 - 40 micron spectroscopy of 41 planetary nebulae (PNe) in the
Magellanic Clouds, observed with the Infrared Spectrograph on board the Spitzer
Space Telescope. The spectra show the presence of a combination of nebular
emission lines and solid-state features from dust, superimposed on the thermal
IR continuum.
By analyzing the 25 LMC and 16 SMC PNe in our sample we found that the IR
spectra of 14 LMC and 4 SMC PNe are dominated by nebular emission lines, while
the other spectra show solid-state features. We observed that the solid-state
features are compatible with carbon-rich dust grains (SiC, polycyclic aromatic
hydrocarbons (PAHs), etc.) in most cases, except in three PNe showing
oxygen-rich dust features. The frequency of carbonaceous dust features is
generally higher in LMC than in SMC PNe.
The spectral analysis allowed the correlations of the dust characteristics
with the gas composition and morphology, and the properties of the central
stars. We found that: 1) all PNe with carbonaceous dust features have C/O>1,
none of these being bipolar or otherwise highly asymmetric; 2) all PNe with
oxygen-rich dust features have C/O<1, with probable high mass progenitors if
derived from single-star evolution (these PNe are either bipolar or highly
asymmetric); 3) the dust temperature tracks the nebular and stellar evolution;
and 4) the dust production efficiency depends on metallicity, with low
metallicity environments not favoring dust production.Comment: The Astrophysical Journal, in pres
Radio Observations of the Hubble Deep Field South Region III: The 2.5, 5.2 and 8.7 GHz Catalogues and Radio Source Properties
Deep radio observations of a wide region centred on the Hubble Deep Field
South have been performed, providing one of the most sensitive set of radio
observations acquired on the Australia Telescope Compact Array to date. A
central rms of ~10 microJy is reached at four frequencies (1.4, 2.5, 5.2 and
8.7 GHz). In this paper the full source catalogues from the 2.5, 5.2 and 8.7
GHz observations are presented to complement Paper II, along with a detailed
analysis of image quality and noise. We produce a consolidated catalogue by
matching sources across all four frequencies of our survey. Radio spectral
indices are used to investigate the nature of the radio sources and identify a
number of sources with flat or inverted radio spectra, which indicates AGN
activity. We also find several other interesting sources, including a broadline
emitting radio galaxy, a giant radio galaxy and three Gigahertz Peaked Spectrum
sources.Comment: Accepted by AJ. 13 figures and 13 table
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