470 research outputs found
Interstellar Comets from Post-Main Sequence Systems as Tracers of Extrasolar Oort Clouds
Interstellar small bodies are unique probes into the histories of
exoplanetary systems. One hypothesized class of interlopers are "Jurads,"
exo-comets released into the Milky Way during the post-main sequence as the
thermally-pulsing asymptotic giant branch (AGB) host stars lose mass. In this
study, we assess the prospects for the Legacy Survey of Space and Time (LSST)
to detect a Jurad and examine whether such an interloper would be
observationally distinguishable from exo-comets ejected during the (pre-)main
sequence. Using analytic and numerical methods, we estimate the fraction of
exo-Oort Cloud objects that are released from 1-8 solar mass stars during
post-main sequence evolution. We quantify the extent to which small bodies are
altered by the increased luminosity and stellar outflows during the AGB,
finding that some Jurads may lack hypervolatiles and that stellar winds could
deposit dust that covers the entire exo-comet surface. Next, we construct
models of the interstellar small body reservoir for various size-frequency
distribution slopes, characteristic sizes, and the total mass sequestered in
the minor planets of exo-Oort Clouds. Even with the LSST's increased search
volume compared to contemporary surveys, we find that detecting a Jurad is
unlikely but not infeasible given the current understanding of (exo)planet
formation.Comment: 28 pages, 13 figures; accepted to PS
Potential Melting of Extrasolar Planets by Tidal Dissipation
Tidal heating on Io due to its finite eccentricity was predicted to drive
surface volcanic activity, which was subsequently confirmed by the
spacecrafts. Although the volcanic activity in Io is more
complex, in theory volcanism can be driven by runaway melting in which the
tidal heating increases as the mantle thickness decreases. We show that this
runaway melting mechanism is generic for a composite planetary body with liquid
core and solid mantle, provided that (i) the mantle rigidity, , is
comparable to the central pressure, i.e.
for a body with density , surface gravitational acceleration , and
radius , (ii) the surface is not molten, (iii) tides deposit
sufficient energy, and (iv) the planet has nonzero eccentricity. We calculate
the approximate liquid core radius as a function of ,
and find that more than of the core will melt due to this runaway for
. From all currently confirmed exoplanets, we
find that the terrestrial planets in the L98-59 system are the most promising
candidates for sustaining active volcanism. However, uncertainties regarding
the quality factors and the details of tidal heating and cooling mechanisms
prohibit definitive claims of volcanism on any of these planets. We generate
synthetic transmission spectra of these planets assuming Venus-like atmospheric
compositions with an additional 5, 50, and SO component, which is a
tracer of volcanic activity. We find a preference for a
model with SO with 5-10 transits with for L98-59bcd.Comment: 16 pages, 8 Figures, accepted for publication in Ap
Development of an international standard set of outcome measures for patients with atrial fibrillation: a report of the International Consortium for Health Outcomes Measurement (ICHOM) atrial fibrillation working group.
AIMS: As health systems around the world increasingly look to measure and improve the value of care that they provide to patients, being able to measure the outcomes that matter most to patients is vital. To support the shift towards value-based health care in atrial fibrillation (AF), the International Consortium for Health Outcomes Measurement (ICHOM) assembled an international Working Group (WG) of 30 volunteers, including health professionals and patient representatives to develop a standardized minimum set of outcomes for benchmarking care delivery in clinical settings. METHODS AND RESULTS: Using an online-modified Delphi process, outcomes important to patients and health professionals were selected and categorized into (i) long-term consequences of disease outcomes, (ii) complications of treatment outcomes, and (iii) patient-reported outcomes. The WG identified demographic and clinical variables for use as case-mix risk adjusters. These included baseline demographics, comorbidities, cognitive function, date of diagnosis, disease duration, medications prescribed and AF procedures, as well as smoking, body mass index (BMI), alcohol intake, and physical activity. Where appropriate, and for ease of implementation, standardization of outcomes and case-mix variables was achieved using ICD codes. The standard set underwent an open review process in which over 80% of patients surveyed agreed with the outcomes captured by the standard set. CONCLUSION: Implementation of these consensus recommendations could help institutions to monitor, compare and improve the quality and delivery of chronic AF care. Their consistent definition and collection, using ICD codes where applicable, could also broaden the implementation of more patient-centric clinical outcomes research in AF
Modeling Complex Nuclear Spectra - Regularity versus Chaos
A statistical analysis of the spectrum of two particle - two hole doorway
states in a finite nucleus is performed. On the unperturbed mean-field level
sizable attractive correlations are present in such a spectrum. Including
particle-hole rescattering effects via the residual interaction introduces
repulsive dynamical correlations which generate the fluctuation properties
characteristic of the Gaussian Orthogonal Ensemble. This signals that the
underlying dynamics becomes chaotic. This feature turns out to be independent
of the detailed form of the residual interaction and hence reflects the generic
nature of the fluctuations studied.Comment: 8 pages of text (LATEX), figures (not included, available from the
authors), Feb 9
Renaissance of the ~1 TeV Fixed-Target Program
This document describes the physics potential of a new fixed-target program
based on a ~1 TeV proton source. Two proton sources are potentially available
in the future: the existing Tevatron at Fermilab, which can provide 800 GeV
protons for fixed-target physics, and a possible upgrade to the SPS at CERN,
called SPS+, which would produce 1 TeV protons on target. In this paper we use
an example Tevatron fixed-target program to illustrate the high discovery
potential possible in the charm and neutrino sectors. We highlight examples
which are either unique to the program or difficult to accomplish at other
venues.Comment: 31 pages, 11 figure
A High Statistics Search for Electron-Neutrino --> Tau-Neutrino Oscillations
We present new limits on nu_e to nu_tau and nu_e to nu_sterile oscillations
by searching for electron neutrino dissappearance in the high-energy wide-band
CCFR neutrino beam. Sensitivity to nu_tau appearance comes from tau decay modes
in which a large fraction of the energy deposited is electromagnetic. The beam
is composed primarily of muon neutrinos but this analysis uses the 2.3%
electron neutrino component of the beam. Electron neutrino energies range from
30 to 600 GeV and flight lengths vary from 0.9 to 1.4 km. This limit improves
the sensitivity of existing limits and obtains a lowest 90% confidence upper
limit in sin**2(2*alpha) of 9.9 x 10**(-2) at delta-m**2 of 125 eV**2.Comment: submitted to Phys. Rev. D. Rapid Com
Nuclear Structure Functions in the Large x Large Q^2 Kinematic Region in Neutrino Deep Inelastic Scattering
Data from the CCFR E770 Neutrino Deep Inelastic Scattering (DIS) experiment
at Fermilab contain events with large Bjorken x (x>0.7) and high momentum
transfer (Q^2>50 (GeV/c)^2). A comparison of the data with a model based on no
nuclear effects at large x, shows a significant excess of events in the data.
Addition of Fermi gas motion of the nucleons in the nucleus to the model does
not explain the excess. Adding a higher momentum tail due to the formation of
``quasi-deuterons'' makes some improvement. An exponentially falling F_2
\propto e^-s(x-x_0) at large x, predicted by ``multi-quark clusters'' and
``few-nucleon correlations'', can describe the data. A value of s=8.3 \pm
0.7(stat.)\pm 0.7(sys.) yields the best agreement with the data.Comment: 4 pages, 4 figures, 1 table. Sibmitted to PR
Shadowing in neutrino deep inelastic scattering and the determination of the strange quark distribution
We discuss shadowing corrections to the structure function in neutrino
deep-inelastic scattering on heavy nuclear targets. In particular, we examine
the role played by shadowing in the comparison of the structure functions
measured in neutrino and muon deep inelastic scattering. The importance of
shadowing corrections in the determination of the strange quark distributions
is explained.Comment: 22 pages, 7 figure
Determination of the Strange Quark Content of the Nucleon from a Next-to-Leading-Order QCD Analysis of Neutrino Charm Production
We present the first next-to-leading-order QCD analysis of neutrino charm
production, using a sample of 6090 - and -induced
opposite-sign dimuon events observed in the CCFR detector at the Fermilab
Tevatron. We find that the nucleon strange quark content is suppressed with
respect to the non-strange sea quarks by a factor \kappa = 0.477 \:
^{+\:0.063}_{-\:0.053}, where the error includes statistical, systematic and
QCD scale uncertainties. In contrast to previous leading order analyses, we
find that the strange sea -dependence is similar to that of the non-strange
sea, and that the measured charm quark mass, , is larger and consistent with that determined in other processes.
Further analysis finds that the difference in -distributions between
and is small. A measurement of the Cabibbo-Kobayashi-Maskawa
matrix element is also presented.
uufile containing compressed postscript files of five Figures is appended at
the end of the LaTeX source.Comment: Nevis R#150
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