3,455 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
Supernova Remnants and Star Formation in the Large Magellanic Cloud
It has often been suggested that supernova remnants (SNRs) can trigger star
formation. To investigate the relationship between SNRs and star formation, we
have examined the known sample of 45 SNRs in the Large Magellanic Cloud to
search for associated young stellar objects (YSOs) and molecular clouds. We
find seven SNRs associated with both YSOs and molecular clouds, three SNRs
associated with YSOs but not molecular clouds, and eight SNRs near molecular
clouds but not associated with YSOs. Among the 10 SNRs associated with YSOs,
the association between the YSOs and SNRs can be either rejected or cannot be
convincingly established for eight cases. Only two SNRs have YSOs closely
aligned along their rims; however, the time elapsed since the SNR began to
interact with the YSOs' natal clouds is much shorter than the contraction
timescales of the YSOs, and thus we do not see any evidence of SNR-triggered
star formation in the LMC. The 15 SNRs that are near molecular clouds may
trigger star formation in the future when the SNR shocks have slowed down to
<45 km/s. We discuss how SNRs can alter the physical properties and abundances
of YSOs.Comment: 24 pages, 5 figures, 1 table, Accepted for publication in the August
2010 edition of the Astronomical Journa
Sub-millimeter Observations of Giant Molecular Clouds in the Large Magellanic Cloud: Temperature and Density as Determined from J=3-2 and J=1-0 transitions of CO
We have carried out sub-mm 12CO(J=3-2) observations of 6 giant molecular
clouds (GMCs) in the Large Magellanic Cloud (LMC) with the ASTE 10m sub-mm
telescope at a spatial resolution of 5 pc and very high sensitivity. We have
identified 32 molecular clumps in the GMCs and revealed significant details of
the warm and dense molecular gas with n(H2) 10 cm and
Tkin 60 K. These data are combined with 12CO(J=1-0) and 13CO(J=1-0)
results and compared with LVG calculations. We found that the ratio of
12CO(J=3-2) to 12CO(J=1-0) emission is sensitive to and is well correlated with
the local Halpha flux. We interpret that differences of clump propeties
represent an evolutionary sequence of GMCs in terms of density increase leading
to star formation.Type I and II GMCs (starless GMCs and GMCs with HII regions
only, respectively) are at the young phase of star formation where density does
not yet become high enough to show active star formation and Type III GMCs
(GMCs with HII regions and young star clusters) represents the later phase
where the average density is increased and the GMCs are forming massive stars.
The high kinetic temperature correlated with \Halpha flux suggests that FUV
heating is dominant in the molecular gas of the LMC.Comment: 74 pages, including 41 figures, accepted for publication in ApJ
The generative quantum eigensolver (GQE) and its application for ground state search
We introduce the generative quantum eigensolver (GQE), a novel method for
applying classical generative models for quantum simulation. The GQE algorithm
optimizes a classical generative model to produce quantum circuits with desired
properties. Here, we develop a transformer-based implementation, which we name
the generative pre-trained transformer-based (GPT) quantum eigensolver
(GPT-QE), leveraging both pre-training on existing datasets and training
without any prior knowledge. We demonstrate the effectiveness of training and
pre-training GPT-QE in the search for ground states of electronic structure
Hamiltonians. GQE strategies can extend beyond the problem of Hamiltonian
simulation into other application areas of quantum computing.Comment: 16 pages, 7 figure
Chk2 is a tumour suppressor that regulates apoptosis in both an ataxia telangiectasia mutad (ATM)-dependent and an ATM-independent manner
In response to ionizing radiation (IR), the tumor suppressor p53 is stabilized and promotes either cell cycle arrest or apoptosis. Chk2 activated by IR contributes to this stabilization, possibly by direct phosphorylation. Like p53, Chk2 is mutated in patients with Li-Fraumeni syndrome. Since the ataxia telangiectasia mutated (ATM) gene is required for IR-induced activation of Chk2, it has been assumed that ATM and Chk2 act in a linear pathway leading to p53 activation. To clarify the role of Chk2 in tumorigenesis, we generated gene-targeted Chk2-deficient mice. Unlike ATM-/- and p53-/- mice, Chk2-/- mice do not spontaneously develop tumors, although Chk2 does suppress 7,12-dimethylbenzanthracene-induced skin tumors. Tissues from Chk2-/- mice, including those from the thymus, central nervous system, fibroblasts, epidermis, and hair follicles, show significant defects in IR-induced apoptosis or impaired G1/S arrest. Quantitative comparison of the G1/S checkpoint, apoptosis, and expression of p53 proteins in Chk2-/- versus ATM-/- thymocytes suggested that Chk2 can regulate p53-dependent apoptosis in an ATM-independent manner. IR-induced apoptosis was restored in Chk2-/- thymocytes by reintroduction of the wild-type Chk2 gene but not by a Chk2 gene in which the sites phosphorylated by ATM and ataxia telangiectasia and rad3+ related (ATR) were mutated to alanine. ATR may thus selectively contribute to p53-mediated apoptosis. These data indicate that distinct pathways regulate the activation of p53 leading to cell cycle arrest or apoptosis
Estimated incidence of previously undetected atrial fibrillation on a 14-day continuous electrocardiographic monitor and associated risk of stroke
Aims There is uncertainty about whether and how to perform screening for atrial fibrillation (AF). To estimate the incidence of previously undetected AF that would be captured using a continuous 14-day ECG monitor and the associated risk of stroke. Methods and results We analysed data from a cohort of patients >65 years old with hypertension and a pacemaker, but without known AF. For each participant, we simulated 1000 ECG monitors by randomly selecting 14-day windows in the 6 months following enrolment and calculated the average AF burden (total time in AF). We used Cox proportional hazards models adjusted for CHA(2)DS(2)-VASc score to estimate the risk of subsequent ischaemic stroke or systemic embolism (SSE) associated with burdens of AF > and 6 min was 3.10% (95% CI 2.53-3.72). This was consistent across strata of age and CHA(2)DS(2)-VASc scores. Over a mean follow-up of 2.4 years, the rate of SSE among patients with 6 min of AF. Conclusions Approximately 3% of individuals aged >65 years with hypertension may have more than 6 min of AF detected by a 14-day ECG monitor. This is associated with a stroke risk of over 2% per year. Whether oral anticoagulation will reduce stroke in these patients is unknown
Cardiovascular disease management in people with diabetes outside North America and Western Europe in 2006 and 2015
Aim: Optimal treatment of cardiovascular disease is essential to decrease mortality among people with diabetes, but information is limited on how actual treatment relates to guidelines. We analysed changes in therapeutic approaches to anti-hypertensive and lipid-lowering medications in people with Type 2 diabetes from 2006 and 2015.
Methods: Summary data from clinical services in seven countries outside North America and Western Europe were collected for 39Â 684 people. Each site summarized individual-level data from outpatient medical records for 2006 and 2015. Data included: demographic information, blood pressure (BP), total cholesterol levels and percentage of people taking statins, anti-hypertensive medication (angiotensin-converting enzyme inhibitors, calcium channel blockers, angiotensin II receptor blockers, thiazide diuretics) and antiplatelet drugs.
Results: From 2006 to 2015, mean cholesterol levels decreased in six of eight sites (range: â0.5 to â0.2), whereas the proportion with BP levels > 140/90 mmHg increased in seven of eight sites. Decreases in cholesterol paralleled increases in statin use (range: 3.1 to 47.0 percentage points). Overall, utilization of anti-hypertensive medication did not change. However, there was an increase in the use of angiotensin II receptor blockers and a decrease in angiotensin-converting enzyme inhibitors. The percentage of individuals receiving calcium channel blockers and aspirin remained unchanged.
Conclusions: Our findings indicate that control of cholesterol levels improved and coincided with increased use of statins. The percentage of people with BP >Â 140/90Â mmHg was higher in 2015 than in 2006. Hypertension treatment shifted from using angiotensin-converting enzyme inhibitors to angiotensin II receptor blockers. Despite the potentially greater tolerability of angiotensin II receptor blockers, there was no associated improvement in BP levels.Centro de EndocrinologĂa Experimental y Aplicad
Cardiovascular disease management in people with diabetes outside North America and Western Europe in 2006 and 2015
Aim: Optimal treatment of cardiovascular disease is essential to decrease mortality among people with diabetes, but information is limited on how actual treatment relates to guidelines. We analysed changes in therapeutic approaches to anti-hypertensive and lipid-lowering medications in people with Type 2 diabetes from 2006 and 2015.
Methods: Summary data from clinical services in seven countries outside North America and Western Europe were collected for 39Â 684 people. Each site summarized individual-level data from outpatient medical records for 2006 and 2015. Data included: demographic information, blood pressure (BP), total cholesterol levels and percentage of people taking statins, anti-hypertensive medication (angiotensin-converting enzyme inhibitors, calcium channel blockers, angiotensin II receptor blockers, thiazide diuretics) and antiplatelet drugs.
Results: From 2006 to 2015, mean cholesterol levels decreased in six of eight sites (range: â0.5 to â0.2), whereas the proportion with BP levels > 140/90 mmHg increased in seven of eight sites. Decreases in cholesterol paralleled increases in statin use (range: 3.1 to 47.0 percentage points). Overall, utilization of anti-hypertensive medication did not change. However, there was an increase in the use of angiotensin II receptor blockers and a decrease in angiotensin-converting enzyme inhibitors. The percentage of individuals receiving calcium channel blockers and aspirin remained unchanged.
Conclusions: Our findings indicate that control of cholesterol levels improved and coincided with increased use of statins. The percentage of people with BP >Â 140/90Â mmHg was higher in 2015 than in 2006. Hypertension treatment shifted from using angiotensin-converting enzyme inhibitors to angiotensin II receptor blockers. Despite the potentially greater tolerability of angiotensin II receptor blockers, there was no associated improvement in BP levels.Centro de EndocrinologĂa Experimental y Aplicad
- âŠ