3,647 research outputs found
PO and PN in the wind of the oxygen-rich AGB star IK Tau
Phosphorus-bearing compounds have only been studied in the circumstellar
environments (CSEs) of the asymptotic giant branch (AGB) star IRC +10216 and
the protoplanetary nebula CRL 2688, both C-rich objects, and the O-rich red
supergiant VY CMa. The current chemical models cannot reproduce the high
abundances of PO and PN derived from observations of VY CMa. No observations
have been reported of phosphorus in the CSEs of O-rich AGB stars. We aim to set
observational constraints on the phosphorous chemistry in the CSEs of O-rich
AGB stars, by focussing on the Mira-type variable star IK Tau. Using the IRAM
30m telescope and the Submillimeter Array (SMA), we observed four rotational
transitions of PN (J=2-1,3-2,6-5,7-6) and four of PO
(J=5/2-3/2,7/2-5/2,13/2-11/2,15/2-13/2). The IRAM 30m observations were
dedicated line observations, while the SMA data come from an unbiased spectral
survey in the frequency range 279-355 GHz.
We present the first detections of PN and PO in an O-rich AGB star and
estimate abundances X(PN/H2) of about 3x10^-7 and X(PO/H2) in the range
0.5-6.0x10^-7. This is several orders of magnitude higher than what is found
for the C-rich AGB star IRC +10216. The diameter (<=0.7") of the PN and PO
emission distributions measured in the interferometric data corresponds to a
maximum radial extent of about 40 stellar radii. The abundances and the spatial
occurrence of the molecules are in very good agreement with the results
reported for VY CMa. We did not detect PS or PH3 in the survey. We suggest that
PN and PO are the main carriers of phosphorus in the gas phase, with abundances
possibly up to several 10^-7. The current chemical models cannot account for
this, underlining the strong need for updated chemical models that include
phosphorous compounds.Comment: Accepted for publication in Astronomy & Astrophysics, 10 pages, 8
figure
Thermodynamics of lattice QCD with two light quark flavours on a 16^3 x 8 lattice II
We have extended our earlier simulations of the high temperature behaviour of
lattice QCD with two light flavours of staggered quarks on a
lattice to lower quark mass (m_q=0.00625). The transition from hadronic matter
to a quark-gluon plasma is observed at corresponding to a
temperature of MeV. We present measurements of observables
which probe the nature of the quark-gluon plasma and serve to distinguish it
from hadronic matter. Although the transition is quite abrupt, we have seen no
indications that it is first order.Comment: 23 pages, RevteX, 6 encapsulated postscript figure
Quarkonium mass splittings in three-flavor lattice QCD
We report on calculations of the charmonium and bottomonium spectrum in
lattice QCD. We use ensembles of gauge fields with three flavors of sea quarks,
simulated with the asqtad improved action for staggered fermions. For the heavy
quarks we employ the Fermilab interpretation of the clover action for Wilson
fermions. These calculations provide a test of lattice QCD, including the
theory of discretization errors for heavy quarks. We provide, therefore, a
careful discussion of the results in light of the heavy-quark effective
Lagrangian. By and large, we find that the computed results are in agreement
with experiment, once parametric and discretization errors are taken into
account.Comment: 21 pages, 17 figure
Pure rotational spectra of TiO and TiO_2 in VY Canis Majoris
We report the first detection of pure rotational transitions of TiO and TiO_2
at (sub-)millimeter wavelengths towards the red supergiant VY CMa. A rotational
temperature, T_rot, of about 250 K was derived for TiO_2. Although T_rot was
not well constrained for TiO, it is likely somewhat higher than that of TiO_2.
The detection of the Ti oxides confirms that they are formed in the
circumstellar envelopes of cool oxygen-rich stars and may be the "seeds" of
inorganic-dust formation, but alternative explanations for our observation of
TiO and TiO_2 in the cooler regions of the envelope cannot be ruled out at this
time. The observations suggest that a significant fraction of the oxides is not
converted to dust, but instead remains in the gas phase throughout the outflow.Comment: to appear in Astronomy and Astrophysic
Multiconfigurational Hartree-Fock theory for identical bosons in a double well
Multiconfigurational Hartree-Fock theory is presented and implemented in an
investigation of the fragmentation of a Bose-Einstein condensate made of
identical bosonic atoms in a double well potential at zero temperature. The
approach builds in the effects of the condensate mean field and of atomic
correlations by describing generalized many-body states that are composed of
multiple configurations which incorporate atomic interactions. Nonlinear and
linear optimization is utilized in conjunction with the variational and
Hylleraas-Undheim theorems to find the optimal ground and excited states of the
interacting system. The resulting energy spectrum and associated eigenstates
are presented as a function of double well barrier height. Delocalized and
localized single configurational states are found in the extreme limits of the
simple and fragmented condensate ground states, while multiconfigurational
states and macroscopic quantum superposition states are revealed throughout the
full extent of barrier heights. Comparison is made to existing theories that
either neglect mean field or correlation effects and it is found that
contributions from both interactions are essential in order to obtain a robust
microscopic understanding of the condensate's atomic structure throughout the
fragmentation process.Comment: 21 pages, 13 figure
Preliminary heavy-light decay constants from the MILC collaboration
Preliminary results from the MILC collaboration for , , ,
and their ratios are presented. We compute in the quenched
approximation at , 6.0 and 5.7 with Wilson light quarks and static
and Wilson heavy quarks. We attempt to quantify systematic errors due to finite
volume, finite lattice spacing, large , and fitting and extrapolation
uncertainties. The hopping parameter approach of Henty and Kenway is used to
treat the heavy quarks; the sources are Coulomb gauge gaussians.Comment: 3 pages, compressed postscript (uufiles), talk given at Lattice '9
Symanzik flow on HISQ ensembles
We report on a scale determination with gradient-flow techniques on the HISQ ensembles generated by the MILC collaboration. The lattice
scale , originally proposed by the BMW collaboration, is computed using
Symanzik flow at four lattice spacings ranging from 0.15 to 0.06 fm. With a
Taylor series ansatz, the results are simultaneously extrapolated to the
continuum and interpolated to physical quark masses. We give a preliminary
determination of the scale in physical units, along with associated
systematic errors, and compare with results from other groups. We also present
a first estimate of autocorrelation lengths as a function of flowtime for these
ensembles.Comment: 7 pages, 6 pdf figures, 2 tables, presented at the 31st International
Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013,
Mainz, German
Cytomegalovirus Management in Solid Organ Transplant Recipients: A Pre-COVID-19 Survey From the Working Group of the European Society for Organ Transplantation
Infections are leading causes of morbidity/mortality following solid organ transplantation (SOT) and cytomegalovirus (CMV) is among the most frequent pathogens, causing a considerable threat to SOT recipients. A survey was conducted 19 July–31 October 2019 to capture clinical practices about CMV in SOT recipients (e.g., how practices aligned with guidelines, how adequately treatments met patients’ needs, and respondents’ expectations for future developments). Transplant professionals completed a ∼30-minute online questionnaire: 224 responses were included, representing 160 hospitals and 197 SOT programs (41 countries; 167[83%] European programs). Findings revealed a heterogenous approach to CMV diagnosis and management and, sometimes, significant divergence from international guidelines. Valganciclovir prophylaxis (of variable duration) was administered by 201/224 (90%) respondents in D+/R− SOT and by 40% in R+ cases, with pre-emptive strategies generally reserved for R+ cases: DNA thresholds to initiate treatment ranged across 10–10,000 copies/ml. Ganciclovir-resistant CMV strains were still perceived as major challenges, and tailored treatment was one of the most important unmet needs for CMV management. These findings may help to design studies to evaluate safety and efficacy of new strategies to prevent CMV disease in SOT recipients, and target specific educational activities to harmonize CMV management in this challenging population
Perturbative approach to the penguin-induced
Using a modified perturbative approach that includes the Sudakov resummation
and transverse degrees of freedom we analyze the penguin-induced decay by applying the next-to-leading order effective weak
Hamiltonian. The modified perturbative method enables us to include
nonfactorizable contributions and to control virtual momenta appearing in the
process. Besides, we apply the three-scale factorization theorem for
nonleptonic processes that offers the possibility of having the
scale-independent product of short- and long-distance parts in the amplitude of
the weak Hamiltonian. The calculation supports the results obtained in the BSW
factorization approach, illustrating the electroweak penguin dominance and the
branching ratio of order . However, the estimated prediction
of 16% for the CP asymmetry is much larger than that obtained in the
factorization approach.Comment: RevTex, 25 pages, 4 PostScript figures included, revised version, to
be published in Phys.Rev.
Structure preserving schemes for mean-field equations of collective behavior
In this paper we consider the development of numerical schemes for mean-field
equations describing the collective behavior of a large group of interacting
agents. The schemes are based on a generalization of the classical Chang-Cooper
approach and are capable to preserve the main structural properties of the
systems, namely nonnegativity of the solution, physical conservation laws,
entropy dissipation and stationary solutions. In particular, the methods here
derived are second order accurate in transient regimes whereas they can reach
arbitrary accuracy asymptotically for large times. Several examples are
reported to show the generality of the approach.Comment: Proceedings of the XVI International Conference on Hyperbolic
Problem
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