1,196 research outputs found
Three-Dimensional Simulations of Massive Stars: II. Age Dependence
We present 3D full star simulations, reaching up to 90% of the total stellar
radius, for three stars of different ages (ZAMS, midMS and TAMS). A
comparison with several theoretical prescriptions shows the generation spectra
for all three ages are dominated by convective plumes. Two distinct
overshooting layers are observed, with most plumes stopped within the layer
situated directly above the convective boundary (CB); overshooting to the
second, deeper layer becomes increasingly more infrequent with stellar age.
Internal gravity wave (IGW) propagation is significantly impacted in the midMS
and TAMS models as a result of some IGWs getting trapped within their
Brunt-V\"{a}is\"{a}l\"{a} frequency spikes. A fundamental change in the wave
structure across radius is also observed, driven by the effect of density
stratification on IGW propagation causing waves to become evanescent within the
radiative zone, with older stars being affected more strongly. We find that the
steepness of the frequency spectrum at the surface increases from ZAMS to the
older models, with older stars also showing more modes in their spectra.Comment: 24 pages, 14 figures / Accepted at Ap
SDSS J013655.91+242546.0 - an A-type hyper-velocity star from the outskirts of the Galaxy
Hyper-velocity stars (HVS) are moving so fast that they are unbound to the
Galaxy. Dynamical ejection by a supermassive black hole is favoured to explain
their origin. Locating the place of birth of an individual HVS is of utmost
importance to understanding the ejection mechanism. SDSS J013655.91+242546.0
(J0136+2425 for short) was found amongst three high-velocity stars (drawn from
a sample of more than 10000 blue stars), for which proper motions were
measured. A kinematical as well as a quantitative NLTE spectral analysis was
performed. When combined with the radial velocity (RV) and the spectroscopic
distance, the trajectory of the star in the Galactic potential was
reconstructed. J0136+2425 is found to be an A-type main-sequence star
travelling at 590 \kms, possibly unbound to the Galaxy and originating
in the outer Galactic rim nowhere near the Galactic centre. J0136+2425 is the
second HVS candidate with measured proper motion, besides the massive B star HD
271791, and also the second for which its proper motion excludes a Galactic
centre origin and, hence, the SMBH slingshot mechanism. Most known HVS are late
B-type stars of about 3 M. With a mass of 2.45 M, J0136+2425
resembles a typical HVS far more than HD 271791 does. Hence, this is the first
time that a typical HVS is found not to originate in the Galactic centre. Its
ejection velocity from the disk is so high (550 \kms) that the extreme
supernova binary scenario proposed for HD 271791 is very unlikely.Comment: 4 pages, 5 figures, accepted for publication in A&
Range Variability in CMR Feature Tracking Multilayer Strain across Different Stages of Heart Failure
Heart failure (HF) is associated with progressive ventricular remodeling and impaired contraction that affects distinctly various regions of the myocardium. Our study applied cardiac magnetic resonance (CMR) feature tracking (FT) to assess comparatively myocardial strain at 3 distinct levels: subendocardial (Endo-), mid (Myo-) and subepicardial (Epi-) myocardium across an extended spectrum of patients with HF. 59 patients with HF, divided into 3 subgroups as follows: preserved ejection fraction (HFpEF, N = 18), HF with mid-range ejection fraction (HFmrEF, N = 21), HF with reduced ejection fraction (HFrEF, N = 20) and a group of age- gender- matched volunteers (N = 17) were included. Using CMR FT we assessed systolic longitudinal and circumferential strain and strain-rate at Endo-, Myo- and Epi- levels. Strain values were the highest in the Endo- layer and progressively lower in the Myo- and Epi- layers respectively, this gradient was present in all the patients groups analyzed but decreased progressively in HFmrEF and further on in HFrEF groups. GLS decreased with the severity of the disease in all 3 layers: Normal > HFpEF > HFmrEF > HFrEF (Endo-: 1223.0 \ub1 3.5 > 1220.0 \ub1 3.3 > 1216.4 \ub1 2.2 > 1211.0 \ub1 3.2, p 1217.5.0 \ub1 2.6 > 1214.5 \ub1 2.1 > 129.6 \ub1 2.7, p 1212.2 \ub1 2.1 > 1210.6 \ub1 2.3 > 127.7 \ub1 2.3, p HFmrEF > HFrEF (Endo-: 1234.5 \ub1 6.2 > 1220.0 \ub1 4.2 > 12.3 \ub1 4.2, p 1213.0 \ub1 3.4 > 128.0 \ub1 2.7. p 127.9 \ub1 2.3 > 124.5 \ub1 1.9. p < 0.001). CMR feature tracking multilayer strain assessment identifies large range differences between distinct myocardial regions. Our data emphasizes the importance of sub-endocardial myocardium for cardiac contraction and thus, its predilect role in imaging detection of functional impairment. CMR feature tracking offers a convenient, readily available, platform to evaluate myocardial contraction with excellent spatial resolution, rendering further details about discrete areas of the myocardium. Using this technique across distinct groups of patients with heart failure (HF), we demonstrate that subendocardial regions of the myocardium exhibit much higher strain values than mid-myocardium or subepicardial and are more sensitive to detect contractile impairment. We also show comparatively higher values of circumferential strain compared with longitudinal and a higher sensitivity to detect contractile impairment. A newly characterized group of patients, HF with mid-range ejection fraction (EF), shows similar traits of decompensation but has relatively higher strain values as patients with HF with reduced EF
Nuclear shadowing in polarized DIS on ^6LiD at small x and its effect on the extraction of the deuteron spin structure function g_{1}^{d}(x,Q^2)
We consider the effect of nuclear shadowing in polarized deep inelastic
scattering (DIS) on ^6LiD at small Bjorken x and its relevance to the
extraction of the deuteron spin structure function g_{1}^{d}(x,Q^2). Using
models, which describe nuclear shadowing in unpolarized DIS, we demonstrate
that the nuclear shadowing correction to g_{1}^{d}(x,Q^2) is significant.Comment: 17 pages, 2 figure
Impact of propofol on mid-latency auditory-evoked potentials in childrenâ
Background Propofol is increasingly used in paediatric anaesthesia, but can be challenging to titrate accurately in this group. Mid-latency auditory-evoked potentials (MLAEPs) can be used to help titrate propofol. However, the effects of propofol on MLAEP in children are unclear. Therefore, we investigated the relationship between propofol and MLAEP in children undergoing anaesthesia. Methods Fourteen healthy children aged 4-16 yr received anaesthesia for elective surgery. Before surgery, propofol was administered in three concentrations (3, 6, 9 ”g mlâ1) through a target-controlled infusion pump using Kataria and colleagues' model. MLAEPs were recorded 5 min after having reached each target propofol concentration at each respective concentration. Additionally, venous propofol blood concentrations were assayed at each measuring time point. Results Propofol increased all four MLAEP peak latencies (peaks Na, Pa, Nb, P1) in a dose-dependent manner. In addition, the differences in amplitudes were significantly smaller with increasing propofol target concentrations. The measured propofol plasma concentrations correlated positively with the latencies of the peaks Na, Pa, and Nb. Conclusions Propofol affects MLAEP latencies and amplitudes in children in a dose-dependent manner. MLAEP measurement might therefore be a useful tool for monitoring depth of propofol anaesthesia in childre
RhoJ interacts with the GIT-PIX complex and regulates focal adhesion disassembly
RhoJ is a Rho GTPase expressed in endothelial cells and tumour cells, which regulates cell motility, invasion, endothelial tube formation and focal adhesion numbers. This study aimed to further delineate the molecular function of RhoJ. Using timelapse microscopy RhoJ was found to regulate focal adhesion disassembly; small interfering RNA (siRNA)-mediated knockdown of RhoJ increased focal adhesion disassembly time, whereas expression of an active mutant (daRhoJ) decreased it. Furthermore, daRhoJ co-precipitated with the GITâPIX complex, a regulator of focal adhesion disassembly. An interaction between daRhoJ and GIT1 was confirmed using yeast two-hybrid experiments, and this depended on the Spa homology domain of GIT1. GIT1, GIT2, ÎČ-PIX (also known as ARHGEF7) and RhoJ all colocalised in focal adhesions and depended on each other for their recruitment to focal adhesions. Functionally, the GITâPIX complex regulated endothelial tube formation, with knockdown of both GIT1 and GIT2, or ÎČ-PIX phenocopying RhoJ knockdown. RhoJ-knockout mice showed reduced tumour growth and diminished tumour vessel density, identifying a role for RhoJ in mediating tumour angiogenesis. These studies give new insight into the molecular function of RhoJ in regulating cell motility and tumour vessel formation
HVS7: a chemically peculiar hyper-velocity star
Context: Hyper-velocity stars are suggested to originate from the dynamical
interaction of binary stars with the supermassive black hole in the Galactic
centre (GC), which accelerates one component of the binary to beyond the
Galactic escape velocity. Aims: The evolutionary status and GC origin of the
HVS SDSS J113312.12+010824.9 (HVS7) is constrained from a detailed study of its
stellar parameters and chemical composition. Methods: High-resolution spectra
of HVS7 obtained with UVES on the ESO VLT were analysed using state-of-the-art
NLTE/LTE modelling techniques that can account for a chemically-peculiar
composition via opacity sampling. Results: Instead of the expected slight
enrichments of alpha-elements and near-solar Fe, huge chemical peculiarities of
all elements are apparent. The He abundance is very low (<1/100 solar), C, N
and O are below the detection limit, i.e they are underabundant (<1/100, <1/3
and <1/10 solar). Heavier elements, however, are overabundant: the iron group
by a factor of ~10, P, Co and Cl by factors ~40, 80 and 440 and rare-earth
elements and Hg even by ~10000. An additional finding, relevant also for other
chemically peculiar stars are the large NLTE effects on abundances of TiII and
FeII (~0.6-0.7dex). The derived abundance pattern of HVS7 is characteristic for
the class of chemical peculiar magnetic B stars on the main sequence. The
chemical composition and high vsini=55+-2km/s render a low mass nature of HVS7
as a blue horizontal branch star unlikely. Conclusions: Such a surface
abundance pattern is caused by atomic diffusion in a possibly magnetically
stabilised, non-convective atmosphere. Hence all chemical information on the
star's place of birth and its evolution has been washed out. High precision
astrometry is the only means to validate a GC origin for HVS7.Comment: 9 pages, 3 figure
The Subluminous and Peculiar Type Ia Supernova PTF09dav
PTF09dav is a peculiar subluminous type Ia supernova (SN) discovered by the
Palomar Transient Factory (PTF). Spectroscopically, it appears superficially
similar to the class of subluminous SN1991bg-like SNe, but it has several
unusual features which make it stand out from this population. Its peak
luminosity is fainter than any previously discovered SN1991bg-like SN Ia (M_B
-15.5), but without the unusually red optical colors expected if the faint
luminosity were due to extinction. The photospheric optical spectra have very
unusual strong lines of Sc II and Mg I, with possible Sr II, together with
stronger than average Ti II and low velocities of ~6000 km/s. The host galaxy
of PTF09dav is ambiguous. The SN lies either on the extreme outskirts (~41kpc)
of a spiral galaxy, or in an very faint (M_R>-12.8) dwarf galaxy, unlike other
1991bg-like SNe which are invariably associated with massive, old stellar
populations. PTF09dav is also an outlier on the light-curve-width--luminosity
and color--luminosity relations derived for other sub-luminous SNe Ia. The
inferred 56Ni mass is small (0.019+/-0.003Msun), as is the estimated ejecta
mass of 0.36Msun. Taken together, these properties make PTF09dav a remarkable
event. We discuss various physical models that could explain PTF09dav. Helium
shell detonation or deflagration on the surface of a CO white-dwarf can explain
some of the features of PTF09dav, including the presence of Sc and the low
photospheric velocities, but the observed Si and Mg are not predicted to be
very abundant in these models. We conclude that no single model is currently
capable of explaining all of the observed signatures of PTF09dav.Comment: Accepted for publication in Ap
Hot subdwarfs from the ESO Supernova Ia Progenitor Survey: II. Atmospheric parameters of subdwarf O stars
We address the origin and evolutionary status of hot subdwarf stars by
studying the optical spectral properties of 58 subdwarf O (sdO) stars.
Combining them with the results of our previously studied subdwarf B (sdB)
stars, we aim at investigating possible evolutionary links. We analyze
high-resolution ESO VLT UVES spectra from the ESO Supernova Ia Progenitor
Survey (SPY). Effective temperatures, gravities, and helium abundances are
determined simultaneously by fitting the profiles of H and He lines using
dedicated synthetic spectra in NLTE. Evidence for cool companions to 8 sdOs as
well as a binary consisting of two sdO stars is found. A correlation between He
abundances and the presence of carbon and/or nitrogen lines emerges: below
solar He abundance, no sdO shows C or N lines. In contrast, C and/or N lines
are present in ALL sdOs with super- solar He abundance. We thus use the solar
He abundance to divide our sample into He-deficient and He-enriched sdOs. While
He-deficient sdOs are scattered in a wide range of the Teff-log(g)-diagram,
most of the He-enriched sdOs cluster in a narrow region at Teff = 40,000 ...
50,000K and log(g)=5.5 ... 6.0. An evolu- tionary link between sdBs and sdOs
appears plausible only for the He-deficient sdOs indicating that they are the
likely successors to sdBs. The properties of He-enriched sdOs cannot be
explained with canonical single star evolutionary models. Alternative scenarios
(late hot flasher) as well as for binary evolution (white dwarf merger;
post-RGB evolution) are tested. While we regard the post-RGB scenario as
inappropriate, the white dwarf merger and the late hot flasher scenarios remain
viable to explain the origin of He-enriched sdOs.Comment: 14 pages, 10 figures, Astronomy & Astrophysics accepte
Generalized Polarizabilities of the Nucleon in Chiral Effective Theories
Using the techniques of chiral effective field theories we evaluate the so
called generalized polarizabilities of the nucleon, which characterize the
structure dependent components in virtual Compton scattering (VCS) as probed in
the electron scattering reaction e N \to e' N gamma. Results are given for both
spin-dependent and spin-independent structure effects to O(p^3) in SU(2) Heavy
Baryon Chiral Perturbation Theory and to O(epsilon^3) in the SU(2) Small Scale
Expansion. Finally we compare our calculations with results from the pioneering
VCS experiment on the proton from Mainz.Comment: 39 pages, 12 figures, revte
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