1,840 research outputs found
Cyclic AMP-specific phosphodiesterase, PDE8A1, is activated by protein kinase A-mediated phosphorylation
The cyclic AMP-specific phosphodiesterase PDE8 has been shown to play a pivotal role in important processes such as steroidogenesis, T cell adhesion, regulation of heart beat and chemotaxis. However, no information exists on how the activity of this enzyme is regulated. We show that under elevated cAMP conditions, PKA acts to phosphorylate PDE8A on serine 359 and this action serves to enhance the activity of the enzyme. This is the first indication that PDE8 activity can be modulated by a kinase, and we propose that this mechanism forms a feedback loop that results in the restoration of basal cAMP levels. (C) 2012 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserve
Reduced Wolf-Rayet Line Luminosities at Low Metallicity
New NTT/EMMI spectrophotometry of single WN2-5 stars in the Magellanic Clouds
are presented, from which HeII 4686 line luminosities have been derived, and
compared with observations of other Magellanic Cloud WR stars. SMC WN3-4 stars
possess line luminosities which are a factor of 4 times lower than LMC
counterparts, incorporating several binary SMC WN3-4 stars. Similar results are
found for WN5-6 stars, despite reduced statistics, incorporating observations
of single LMC WN5-9 stars. CIV 5808 line luminosities of carbon sequence WR
stars in the SMC and IC1613 (both WO subtypes) are a factor of 3 lower than LMC
WC stars from Mt Stromlo/DBS spectrophotometry, although similar results are
also obtained for the sole LMC WO star. We demonstrate how reduced line
luminosities at low metallicity follow naturally if WR winds are Z-dependent,
as recent results suggest. We apply mass loss-Z scalings to atmospheric non-LTE
models of Milky Way and LMC WR stars to predict the wind signatures of WR stars
in the metal-poor star forming WR galaxy IZw18. WN HeII 4686 line luminosities
are 7-20 times lower than in Z-rich counterparts of identical bolometric
luminosity, whilst WC CIV 5808 line luminosities are 3-6 times lower.
Significant He^+ Lyman continuum fluxes are predicted for Z-poor early-type WR
stars. Consequently, our results suggest the need for larger population of WR
stars in IZw18 than is presently assumed, particularly for WN stars,
potentially posing a severe challenge to evolutionary models at very low Z.
Finally, reduced wind strengths from WR stars at low Z impacts upon the
immediate circumstellar environment of long duration GRB afterglows,
particularly since the host galaxies of high-redshift GRBs tend to be Z-poor.Comment: 14 pages, 12 figures, accepted for A&A, revision fixes error with Eqn
Determination of the mass of the neutron star in SMC X-1, LMC X-4 and Cen X-3 with VLT/UVES
We present the results of a spectroscopic monitoring campaign of the OB-star
companions to the eclipsing X-ray pulsars SMC X-1, LMC X-4 and Cen X-3.
High-resolution optical spectra obtained with UVES on the ESO Very Large
Telescope are used to determine the radial-velocity orbit of the OB
(super)giants with high precision. The excellent quality of the spectra
provides the opportunity to measure the radial-velocity curve based on
individual lines, and to study the effect of possible distortions of the line
profiles due to e.g. X-ray heating on the derived radial-velocity amplitude.
Several spectral lines show intrinsic variations with orbital phase. The
magnitude of these variations depends on line strength, and thus provides a
criterion to select lines that do not suffer from distortions. The undistorted
lines show a larger radial-velocity amplitude than the distorted lines,
consistent with model predictions. Application of our line-selection criteria
results in a mean radial-velocity amplitude K(Opt) of 20.2 +/- 1.1, 35.1 +/-
1.5, and 27.5 +/- 2.3 km/s (1 sigma errors), for the OB companion to SMC X-1,
LMC X-4 and Cen X-3, respectively. Adding information on the projected
rotational velocity of the OB companion (derived from our spectra), the
duration of X-ray eclipse and orbital parameters of the X-ray pulsar (obtained
from literature), we arrive at a neutron star mass of 1.06^{+0.11}_{-0.10},
1.25^{+0.11}_{-0.10} and 1.34^{+0.16}_{-0.14} M{sun} for SMC X-1, LMC X-4 and
Cen X-3, respectively. The mass of SMC X-1 is near the minimum mass (~1 M{sun})
expected for a neutron star produced in a supernova. We discuss the
implications of the measured mass distribution on the neutron-star formation
mechanism, in relation to the evolutionary history of the massive binaries.Comment: Accepted for publication in Astronomy and Astrophysic
Lexicality and frequency in specific language impairment: accuracy and error data from two nonword repetition tests
Purpose: Deficits in phonological working memory and deficits in phonological processing have both been considered potential explanatory factors in Specific Language Impairment (SLI). Manipulations of the lexicality and phonotactic frequency of nonwords enable contrasting predictions to be derived from these hypotheses. Method: 18 typically developing (TD) children and 18 children with SLI completed an assessment battery that included tests of language ability, non-verbal intelligence, and two nonword repetition tests that varied in lexicality and frequency. Results: Repetition accuracy showed that children with SLI were unimpaired for short and simple high lexicality nonwords, whereas clear impairments were shown for all low lexicality nonwords. For low lexicality nonwords, greater repetition accuracy was seen for nonwords constructed from high over low frequency phoneme sequences. Children with SLI made the same proportion of errors that substituted a nonsense syllable for a lexical item as TD children, and this was stable across nonword length. Conclusions: The data show support for a phonological processing deficit in children with SLI, where long-term lexical and sub-lexical phonological knowledge mediate the interpretation of nonwords. However, the data also suggest that while phonological processing may provide a key explanation of SLI, a full account is likely to be multi-faceted
Physical parameters of the high-mass X-ray binary 4U1700-37
We present the results of a detailed non-LTE analysis of the UV and optical
spectrum of the O6.5Iaf+ star HD153919 - the mass donor in the high-mass X-ray
binary 4U1700-37. Given the eclipsing nature of the system these results allow
us to determine the most likely masses of both components of the binary via
Monte Carlo simulations. These suggest a mass for HD153919 of 58+/-11M_sun -
implying the initial mass of the companion was rather high (>60 M_sun). The
most likely mass for the compact companion is found to be 2.44+/-0.27M_sun,
with only 3.5 per cent of the trials resulting in a mass less than 2.0M_sun and
none less than 1.65M_sun. Our observational data is inconsistent with the
canonical neutron star mass and the lowest black hole mass observed (>4.4M_sun;
Nova Vel). Significantly changing observational parameters can force the
compact object mass into either of these regimes but this results in the O-star
mass changing by factors of greater than 2, well beyond the limits determined
from its evolutionary state and surface gravity. The low mass of the compact
object implies that it is difficult to form high mass black holes through both
the Case A & B mass transfer channels and, if the compact object is a neutron
star, would significantly constrain the high density nuclear EoSComment: 13 pages, 7 figures, accepted for publication in A&
Massive stars exploding in a He-rich circumstellar medium. I. Type Ibn (SN 2006jc-like) events
We present new spectroscopic and photometric data of the type Ibn supernovae
2006jc, 2000er and 2002ao. We discuss the general properties of this recently
proposed supernova family, which also includes SN 1999cq. The early-time
monitoring of SN 2000er traces the evolution of this class of objects during
the first few days after the shock breakout. An overall similarity in the
photometric and spectroscopic evolution is found among the members of this
group, which would be unexpected if the energy in these core-collapse events
was dominated by the interaction between supernova ejecta and circumstellar
medium. Type Ibn supernovae appear to be rather normal type Ib/c supernova
explosions which occur within a He-rich circumstellar environment. SNe Ibn are
therefore likely produced by the explosion of Wolf-Rayet progenitors still
embedded in the He-rich material lost by the star in recent mass-loss episodes,
which resemble known luminous blue variable eruptions. The evolved Wolf-Rayet
star could either result from the evolution of a very massive star or be the
more evolved member of a massive binary system. We also suggest that there are
a number of arguments in favour of a type Ibn classification for the historical
SN 1885A (S-Andromedae), previously considered as an anomalous type Ia event
with some resemblance to SN 1991bg.Comment: 17 pages including 12 figures and 4 tables. Slightly revised version,
conclusions unchanged, 1 figure added. Accepted for publication in MNRA
Search for CP violation in decays
A model-independent search for direct CP violation in the Cabibbo suppressed
decay in a sample of approximately 370,000 decays is
carried out. The data were collected by the LHCb experiment in 2010 and
correspond to an integrated luminosity of 35 pb. The normalized Dalitz
plot distributions for and are compared using four different
binning schemes that are sensitive to different manifestations of CP violation.
No evidence for CP asymmetry is found.Comment: 13 pages, 8 figures, submitted to Phys. Rev.
Measurement of charged particle multiplicities in collisions at TeV in the forward region
The charged particle production in proton-proton collisions is studied with
the LHCb detector at a centre-of-mass energy of TeV in different
intervals of pseudorapidity . The charged particles are reconstructed
close to the interaction region in the vertex detector, which provides high
reconstruction efficiency in the ranges and
. The data were taken with a minimum bias trigger, only requiring
one or more reconstructed tracks in the vertex detector. By selecting an event
sample with at least one track with a transverse momentum greater than 1 GeV/c
a hard QCD subsample is investigated. Several event generators are compared
with the data; none are able to describe fully the multiplicity distributions
or the charged particle density distribution as a function of . In
general, the models underestimate the charged particle production
First observation of Bs -> D_{s2}^{*+} X mu nu decays
Using data collected with the LHCb detector in proton-proton collisions at a
centre-of-mass energy of 7 TeV, the semileptonic decays Bs -> Ds+ X mu nu and
Bs -> D0 K+ X mu nu are detected. Two structures are observed in the D0 K+ mass
spectrum at masses consistent with the known D^+_{s1}(2536) and
$D^{*+}_{s2}(2573) mesons. The measured branching fractions relative to the
total Bs semileptonic rate are B(Bs -> D_{s2}^{*+} X mu nu)/B(Bs -> X mu nu)=
(3.3\pm 1.0\pm 0.4)%, and B(Bs -> D_{s1}^+ X munu)/B(Bs -> X mu nu)= (5.4\pm
1.2\pm 0.5)%, where the first uncertainty is statistical and the second is
systematic. This is the first observation of the D_{s2}^{*+} state in Bs
decays; we also measure its mass and width.Comment: 8 pages 2 figures. Published in Physics Letters
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