370 research outputs found
Endomorphisms of Abelian Groups with Small Algebraic Entropy
We study the endomorphisms Ï of abelian groups G having a âsmallâ algebraic entropy h (where âsmallâ usually means ). Using essentially elementary tools from linear algebra, we show that this study can be carried out in the group , where an automorphism Ï with must have all eigenvalues in the open circle of radius 2, centered at 0 and Ï must leave invariant a lattice in , i.e., be essentially an automorphism of . In particular, all eigenvalues of an automorphism Ï with must be roots of unity. This is a particular case of a more general fact known as Algebraic Yuzvinskii Theorem. We discuss other particular cases of this fact and we give some applications of our main results
Oxygenation response to NO in newborns with severe pulmonary hypertension
Oxygenation Response to NO in Newborns With Severe Pulmonary Hypertensio
Dust Production and Particle Acceleration in Supernova 1987A Revealed with ALMA
Supernova (SN) explosions are crucial engines driving the evolution of
galaxies by shock heating gas, increasing the metallicity, creating dust, and
accelerating energetic particles. In 2012 we used the Atacama Large
Millimeter/Submillimeter Array to observe SN 1987A, one of the best-observed
supernovae since the invention of the telescope. We present spatially resolved
images at 450um, 870um, 1.4mm, and 2.8mm, an important transition wavelength
range. Longer wavelength emission is dominated by synchrotron radiation from
shock-accelerated particles, shorter wavelengths by emission from the largest
mass of dust measured in a supernova remnant (>0.2Msun). For the first time we
show unambiguously that this dust has formed in the inner ejecta (the cold
remnants of the exploded star's core). The dust emission is concentrated to the
center of the remnant, so the dust has not yet been affected by the shocks. If
a significant fraction survives, and if SN 1987A is typical, supernovae are
important cosmological dust producers.Comment: ApJL accepte
The First VLBI Image of the Young, Oxygen-Rich Supernova Remnant in NGC 4449
We report on sensitive 1.4-GHz VLBI radio observations of the unusually
luminous supernova remnant SNR 4449-1 in the galaxy NGC 4449, which gave us the
first well-resolved image of this object. The remnant's radio morphology
consists of two approximately parallel bright ridges, suggesting similarities
to the barrel shape seen for many older Galactic supernova remnants or possibly
to SN 1987A. The angular extent of the remnant is 65 x 40 mas, corresponding to
(3.7 x 2.3) x 10^{18} (D/3.8 Mpc) cm. We also present a new, high
signal-to-noise optical spectrum. By comparing the remnant's linear size to the
maximum velocities measured from optical lines, as well as using constraints
from historical images, we conclude that the supernova explosion occurred
between ~1905 and 1961, likely around 1940. The age of the remnant is therefore
likely ~70 yr. We find that SNR 4449-1's shock wave is likely still interacting
with the circumstellar rather than interstellar medium.Comment: 7 pages, Accepted for publication in MNRA
Carbon Monoxide in the Cold Debris of Supernova 1987A
We report spectroscopic and imaging observations of rotational transitions of
cold CO and SiO in the ejecta of SN1987A, the first such emission detected in a
supernova remnant. In addition to line luminosities for the CO J=1-0, 2-1, 6-5,
and 7-6 transitions, we present upper limits for all other transitions up to
J=13-12, collectively measured from the Atacama Large Millimeter Array (ALMA),
the Atacama Pathfinder EXperiment (APEX), and the Herschel Spectral and
Photometric Imaging REceiver (SPIRE). Simple models show the lines are emitted
from at least 0.01 solar masses of CO at a temperature > 14 K, confined within
at most 35% of a spherical volume expanding at ~ 2000 km/s. Moreover, we locate
the emission within 1'' of the central debris. These observations, along with a
partial observation of SiO, confirm the presence of cold molecular gas within
supernova remnants and provide insight into the physical conditions and
chemical processes in the ejecta. Furthermore, we demonstrate the powerful new
window into supernova ejecta offered by submillimeter observations.Comment: Accepted to the Astrophysical Journal Letters, 6 pages, 3 figure
Low Radio Frequency Observations and Spectral Modelling of the Remnant of Supernova 1987A
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present Murchison Widefield Array observations of the supernova remnant (SNR) 1987A between 72 and 230 MHz, representing the lowest frequency observations of the source to date. This large lever arm in frequency space constrains the properties of the circumstellar medium created by the progenitor of SNR 1987A when it was in its red supergiant phase. As of late-2013, the radio spectrum of SNR 1987A between 72 MHz and 8.64 GHz does not show any deviation from a non-thermal power-law with a spectral index of . This spectral index is consistent with that derived at higher frequencies, beneath 100 GHz, and with a shock in its adiabatic phase. A spectral turnover due to free-free absorption by the circumstellar medium has to occur below 72 MHz, which places upper limits on the optical depth of 0.1 at a reference frequency of 72 MHz, emission measure of 13,000 cm pc, and an electron density of 110 cm. This upper limit on the electron density is consistent with the detection of prompt radio emission and models of the X-ray emission from the supernova. The electron density upper limit implies that some hydrodynamic simulations derived a red supergiant mass loss rate that is too high, or a wind velocity that is too low. The mass loss rate of yr and wind velocity of 10 km s obtained from optical observations are consistent with our upper limits, predicting a current turnover frequency due to free-free absorption between 5 and 60 MHz.Peer reviewedFinal Published versio
Revising acute care systems and processes to improve breastfeeding and maternal postnatal health: a pre and post intervention study in one English maternity unit
Background
Most women in the UK give birth in a hospital labour ward, following which they are
transferred to a postnatal ward and discharged home within 24 to 48 hours of the birth.
Despite policy and guideline recommendations to support planned, effective postnatal care,
national surveys of womenâs views of maternity care have consistently found in-patient
postnatal care, including support for breastfeeding, is poorly rated.
Methods
Using a Continuous Quality Improvement approach, routine antenatal, intrapartum and
postnatal care systems and processes were revised to support implementation of evidence
based postnatal practice. To identify if implementation of a multi-faceted QI intervention
impacted on outcomes, data on breastfeeding initiation and duration, maternal health and
womenâs views of care, were collected in a pre and post intervention longitudinal survey.
Primary outcomes included initiation, overall duration and duration of exclusive
breastfeeding. Secondary outcomes included maternal morbidity, experiences and satisfaction
with care. As most outcomes of interest were measured on a nominal scale, these were
compared pre and post intervention using logistic regression.
Results
Data were obtained on 741/1160 (64%) women at 10 days post-birth and 616 (54%) at 3
months post-birth pre-intervention, and 725/1153 (63%) and 575 (50%) respectively postintervention.
Post intervention there were statistically significant differences in the initiation
(p = 0.050), duration of any breastfeeding (p = 0.020) and duration of exclusive breastfeeding
to 10 days (p = 0.038) and duration of any breastfeeding to three months (p = 0.016). Post
intervention, women were less likely to report physical morbidity within the first 10 days of
birth, and were more positive about their in-patient care.
Conclusions
It is possible to improve outcomes of routine in-patient care within current resources through
continuous quality improvement
Evolutionary leap in large-scale flood risk assessment needed
Current approaches for assessing large-scale flood risks contravene the fundamental principles of the flood risk system functioning because they largely ignore basic interactions and feedbacks between atmosphere, catchments, river-floodplain systems and socio-economic processes. As a consequence, risk analyses are uncertain and might be biased. However, reliable risk estimates are required for prioritizing national investments in flood risk mitigation or for appraisal and management of insurance portfolios. We review several examples of process interactions and highlight their importance in shaping spatio-temporal risk patterns. We call for a fundamental redesign of the approaches used for large-scale flood risk assessment. They need to be capable to form a basis for large-scale flood risk management and insurance policies worldwide facing the challenge of increasing risks due to climate and global change. In particular, implementation of the European Flood Directive needs to be adjusted for the next round of flood risk mapping and development of flood risk management plans focussing on methods accounting for more process interactions in flood risk systems
ALMA spectral survey of Supernova 1987A-molecular inventory, chemistry, dynamics and explosive nucleosynthesis
We report the first molecular line survey of Supernova 1987A in the millimetre wavelength range. In the Atacama Large Millimeter/submillimeter Array (ALMA) 210â300 and 340â360 GHz spectra, we detected cold (20â170 K) CO, 28SiO, HCO+ and SO, with weaker lines of 29SiO from ejecta. This is the first identification of HCO+ and SO in a young supernova remnant. We find a dip in the J = 6â5 and 5â4 SiO line profiles, suggesting that the ejecta morphology is likely elongated. The difference of the CO and SiO line profiles is consistent with hydrodynamic simulations, which show that RayleighâTaylor instabilities cause mixing of gas, with heavier elements much more disturbed, making more elongated structure. We obtained isotopologue ratios of 28SiO/29SiOâ> 13, 28SiO/30SiOâ> 14 and 12CO/13CO > 21, with the most likely limits of 28SiO/29SiO >128, 28SiO/30SiO >189. Low 29Si and 30Si abundances in SN 1987A are consistent with nucleosynthesis models that show inefficient formation of neutron-rich isotopes in a low-metallicity environment, such as the Large Magellanic Cloud. The deduced large mass of HCO+ (âŒ5 Ă 10â6âMâ) and small SiS mass (<6 Ă 10â5âMâ) might be explained by some mixing of elements immediately after the explosion. The mixing might have caused some hydrogen from the envelope to sink into carbon- and oxygen-rich zones after the explosion, enabling the formation of a substantial mass of HCO+. Oxygen atoms may have penetrated into silicon and sulphur zones, suppressing formation of SiS. Our ALMA observations open up a new window to investigate chemistry, dynamics and explosive nucleosynthesis in supernovae
Radio emission from Supernova Remnants
The explosion of a supernova releases almost instantaneously about 10^51 ergs
of mechanic energy, changing irreversibly the physical and chemical properties
of large regions in the galaxies. The stellar ejecta, the nebula resulting from
the powerful shock waves, and sometimes a compact stellar remnant, constitute a
supernova remnant (SNR). They can radiate their energy across the whole
electromagnetic spectrum, but the great majority are radio sources. Almost 70
years after the first detection of radio emission coming from a SNR, great
progress has been achieved in the comprehension of their physical
characteristics and evolution. We review the present knowledge of different
aspects of radio remnants, focusing on sources of the Milky Way and the
Magellanic Clouds, where the SNRs can be spatially resolved. We present a brief
overview of theoretical background, analyze morphology and polarization
properties, and review and critical discuss different methods applied to
determine the radio spectrum and distances. The consequences of the interaction
between the SNR shocks and the surrounding medium are examined, including the
question of whether SNRs can trigger the formation of new stars. Cases of
multispectral comparison are presented. A section is devoted to reviewing
recent results of radio SNRs in the Magellanic Clouds, with particular emphasis
on the radio properties of SN 1987A, an ideal laboratory to investigate
dynamical evolution of an SNR in near real time. The review concludes with a
summary of issues on radio SNRs that deserve further study, and analyzing the
prospects for future research with the latest generation radio telescopes.Comment: Revised version. 48 pages, 15 figure
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