1,704 research outputs found
Using generalized PowerFlux methods to estimate the parameters of periodic gravitational waves
We investigate methods to estimate the parameters of the gravitational-wave
signal from a spinning neutron star using Fourier transformed segments of the
strain response from an interferometric detector. Estimating the parameters
from the power, we find generalizations of the PowerFlux method. Using
simulated elliptically polarized signals injected into Gaussian noise, we apply
the generalized methods to estimate the squared amplitudes of the plus and
cross polarizations (and, in the most general case, the polarization angle),
and test the relative detection efficiencies of the various methods.Comment: 8 pages, presented at Amalid7, Sydney, Australia (July 2007), fixed
minor typos and clarified discussion to match published CQG version; updated
reference
Covariant Vortex In Superconducting-Superfluid-Normal Fluid Mixtures with Stiff Equation of State
The integrals of motion for a cylindrically symmetric stationary vortex are
obtained in a covariant description of a mixture of interacting
superconductors, superfluids and normal fluids. The relevant integrated
stress-energy coefficients for the vortex with respect to a vortex-free
reference state are calculated in the approximation of a ``stiff'', i.e. least
compressible, relativistic equation of state for the fluid mixture. As an
illustration of the foregoing general results, we discuss their application to
some of the well known examples of ``real'' superfluid and superconducting
systems that are contained as special cases. These include Landau's two-fluid
model, uncharged binary superfluid mixtures, rotating conventional
superconductors and the superfluid neutron-proton-electron plasma in the outer
core of neutron stars.Comment: 14 pages, uses RevTeX and amssymb, submitte
Measured and Calculated Neutron Spectra and Dose Equivalent Rates at High Altitudes; Relevance to SST Operations and Space Research
Results of the NASA Langley-New York University high-altitude radiation study are presented. Measurements of the absorbed dose rate and of secondary fast neutrons (1 to 10 MeV energy) during the years 1965 to 1971 are used to determine the maximum radiation exposure from galactic and solar cosmic rays of supersonic transport (SST) and subsonic jet occupants. The maximum dose equivalent rates that the SST crews might receive turn out to be 13 to 20 percent of the maximum permissible dose rate (MPD) for radiation workers (5 rem/yr). The exposure of passengers encountering an intense giant-energy solar particle event could exceed the MPD for the general population (0.5 rem/yr), but would be within these permissible limits if in such rare cases the transport descends to subsonic altitude; it is in general less than 12 percent of the MPD. By Monte Carlo calculations of the transport and buildup of nucleons in air for incident proton energies E of 0.02 to 10 GeV, the measured neutron spectra were extrapolated to lower and higher energies and for galactic cosmic rays were found to continue with a relatively high intensity to energies greater than 400 MeV, in a wide altitude range. This condition, together with the measured intensity profiles of fast neutrons, revealed that the biologically important fast and energetic neutrons penetrate deep into the atmosphere and contribute approximately 50 percent of the dose equivalant rates at SST and present subsonic jet altitudes
R-Modes in Superfluid Neutron Stars
The analogs of r-modes in superfluid neutron stars are studied here. These
modes, which are governed primarily by the Coriolis force, are identical to
their ordinary-fluid counterparts at the lowest order in the small
angular-velocity expansion used here. The equations that determine the next
order terms are derived and solved numerically for fairly realistic superfluid
neutron-star models. The damping of these modes by superfluid ``mutual
friction'' (which vanishes at the lowest order in this expansion) is found to
have a characteristic time-scale of about 10^4 s for the m=2 r-mode in a
``typical'' superfluid neutron-star model. This time-scale is far too long to
allow mutual friction to suppress the recently discovered gravitational
radiation driven instability in the r-modes. However, the strength of the
mutual friction damping depends very sensitively on the details of the
neutron-star core superfluid. A small fraction of the presently acceptable
range of superfluid models have characteristic mutual friction damping times
that are short enough (i.e. shorter than about 5 s) to suppress the
gravitational radiation driven instability completely.Comment: 15 pages, 8 figure
Atmospheric neutrons
Contributions to fast neutron measurements in the atmosphere are outlined. The results of a calculation to determine the production, distribution and final disappearance of atmospheric neutrons over the entire spectrum are presented. An attempt is made to answer questions that relate to processes such as neutron escape from the atmosphere and C-14 production. In addition, since variations of secondary neutrons can be related to variations in the primary radiation, comment on the modulation of both radiation components is made
Bogomol'nyi Limit For Magnetic Vortices In Rotating Superconductor
This work is the sequel of a previous investigation of stationary and
cylindrically symmetric vortex configurations for simple models representing an
incompressible non-relativistic superconductor in a rigidly rotating
background. In the present paper, we carry out our analysis with a generalized
Ginzburg-Landau description of the superconductor, which provides a
prescription for the radial profile of the normal density within the vortex.
Within this framework, it is shown that the Bogomol'nyi limit condition marking
the boundary between type I and type II behavior is unaffected by the rotation
of the background.Comment: 7 pages, uses RevTeX, submitted to Phys.Rev.
The r-modes in accreting neutron stars with magneto-viscous boundary layers
We explore the dynamics of the r-modes in accreting neutron stars in two
ways. First, we explore how dissipation in the magneto-viscous boundary layer
(MVBL) at the crust-core interface governs the damping of r-mode perturbations
in the fluid interior. Two models are considered: one assuming an
ordinary-fluid interior, the other taking the core to consist of superfluid
neutrons, type II superconducting protons, and normal electrons. We show,
within our approximations, that no solution to the magnetohydrodynamic
equations exists in the superfluid model when both the neutron and proton
vortices are pinned. However, if just one species of vortex is pinned, we can
find solutions. When the neutron vortices are pinned and the proton vortices
are unpinned there is much more dissipation than in the ordinary-fluid model,
unless the pinning is weak. When the proton vortices are pinned and the neutron
vortices are unpinned the dissipation is comparable or slightly less than that
for the ordinary-fluid model, even when the pinning is strong. We also find in
the superfluid model that relatively weak radial magnetic fields ~ 10^9 G (10^8
K / T)^2 greatly affect the MVBL, though the effects of mutual friction tend to
counteract the magnetic effects. Second, we evolve our two models in time,
accounting for accretion, and explore how the magnetic field strength, the
r-mode saturation amplitude, and the accretion rate affect the cyclic evolution
of these stars. If the r-modes control the spin cycles of accreting neutron
stars we find that magnetic fields can affect the clustering of the spin
frequencies of low mass x-ray binaries (LMXBs) and the fraction of these that
are currently emitting gravitational waves.Comment: 19 pages, 8 eps figures, RevTeX; corrected minor typos and added a
referenc
Effect of hyperon bulk viscosity on neutron-star r-modes
Neutron stars are expected to contain a significant number of hyperons in
addition to protons and neutrons in the highest density portions of their
cores. Following the work of Jones, we calculate the coefficient of bulk
viscosity due to nonleptonic weak interactions involving hyperons in
neutron-star cores, including new relativistic and superfluid effects. We
evaluate the influence of this new bulk viscosity on the gravitational
radiation driven instability in the r-modes. We find that the instability is
completely suppressed in stars with cores cooler than a few times 10^9 K, but
that stars rotating more rapidly than 10-30% of maximum are unstable for
temperatures around 10^10 K. Since neutron-star cores are expected to cool to a
few times 10^9 K within seconds (much shorter than the r-mode instability
growth time) due to direct Urca processes, we conclude that the gravitational
radiation instability will be suppressed in young neutron stars before it can
significantly change the angular momentum of the star.Comment: final PRD version, minor typos etc correcte
Edoxaban: an update on the new oral direct factor Xa inhibitor.
Edoxaban is a once-daily oral anticoagulant that rapidly and selectively inhibits factor Xa in a concentration-dependent manner. This review describes the extensive clinical development program of edoxaban, including phase III studies in patients with non-valvular atrial fibrillation (NVAF) and symptomatic venous thromboembolism (VTE). The ENGAGE AF-TIMI 48 study (NÂ =Â 21,105; mean CHADS2 score 2.8) compared edoxaban 60Â mg once daily (high-dose regimen) and edoxaban 30Â mg once daily (low-dose regimen) with dose-adjusted warfarin [international normalized ratio (INR) 2.0-3.0] and found that both regimens were non-inferior to warfarin in the prevention of stroke and systemic embolism in patients with NVAF. Both edoxaban regimens also provided significant reductions in the risk of hemorrhagic stroke, cardiovascular mortality, major bleeding and intracranial bleeding. The Hokusai-VTE study (NÂ =Â 8,292) in patients with symptomatic VTE had a flexible treatment duration of 3-12Â months and found that following initial heparin, edoxaban 60Â mg once daily was non-inferior to dose-adjusted warfarin (INR 2.0-3.0) for the prevention of recurrent VTE, and also had a significantly lower risk of bleeding events. Both studies randomized patients at moderate-to-high risk of thromboembolic events and were further designed to simulate routine clinical practice as much as possible, with edoxaban dose reduction (halving dose) at randomisation or during the study if required, a frequently monitored and well-controlled warfarin group, a well-monitored transition period at study end and a flexible treatment duration in Hokusai-VTE. Given the phase III results obtained, once-daily edoxaban may soon be a key addition to the range of antithrombotic treatment options
Body mass index in young men and risk of inflammatory bowel disease through adult life: A population-based Danish cohort study
Abstract Body mass index (BMI) is associated with increased future risk of inflammatory bowel disease(IBD) particularly Crohn’s disease(CD), where associations with high and low BMI have been observed. Most studies are based on adult women. We aimed to explore the impact of BMI in men entering adult life on their long-term risk of developing IBD. A total of 377,957 men born during 1939–1959, with BMI measured at draft boards at mean age 19, were followed from 1977, or time of examination, to end of 2015. Risk of IBD was assessed using Cox regression. During 13 million person-years of follow-up, 1,523 developed CD and 3,323 UC. Using normal weight as reference, for CD the following HRs were observed: BMI < 18.5, 1.35; 95% CI, 1.12–1.62, BMI 25–29.9; 0.83; 95% CI, 0.68–1.02. and BMI > 30 1.20; 95% CI, 0.75–1.90). The increased risk of CD in underweight was maintained up until age 60 not explained by known effects of smoking. For UC, minor inverse associations were observed. Restricted cubic splines revealed a U-shape association between BMI and CD, but not UC. Low BMI of men entering adult life is associated with an increased incidence of CD and UC up to 40 years later
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