1,806 research outputs found
Are beta-2-agonists or anticholinergics more effective for treating COPD?
Both β2-agonists and anticholinergics appear to improve symptoms for patients with chronic obstructive pulmonary disease (COPD). Recent research indicates that adding a long-acting anti-cholinergic to a β2-agonist may improve quality of life for patients with stable COPD more than the use of β2-agonists alone. Both drug classes increase exercise capacity and alleviate symptoms of COPD, although neither alters disease progression (strength of recommendation [SOR]: A). Combination therapy can lead to greater improvements in forced expiratory volume in 1 second (FEV1) than either drug alone (SOR: A). However, until recently there were no convincing direct head-to-head comparisons of the 2 classes, and it is unclear whether this difference is clinically significant
Magnetic chemically peculiar stars
Chemically peculiar (CP) stars are main-sequence A and B stars with
abnormally strong or weak lines for certain elements. They generally have
magnetic fields and all observables tend to vary with the same period.
Chemically peculiar stars provide a wealth of information; they are natural
atomic and magnetic laboratories. After a brief historical overview, we discuss
the general properties of the magnetic fields in CP stars, describe the oblique
rotator model, explain the dependence of the magnetic field strength on the
rotation, and concentrate at the end on HgMn stars.Comment: 9 pages, 4 figures, 2 tables, chapter in "Determination of
Atmospheric Parameters of B-, A-, F- and G-Type Stars", Springer (2014), eds.
E. Niemczura, B. Smalley, W. Pyc
Buffalo National River Ecosystems - Part II
The priorities were established for the Buffalo National River Ecosystem Studies through meetings and correspondence with Mr. Roland Wauer and other personnel of the Office of Natural Sciences, Southwest Region of the National Park Service. These priorities were set forth in the appendix of contract no. CX 700050443 dated May 21, 1975
Final Report: Buffalo National River Ecosystems
The objective of this study was to sample the Buffalo River on a seasonal basis for a year, in order to determine whether any potential water quality problems existed
The radio lighthouse CU Virginis: the spindown of a single main sequence star
The fast rotating star CU Virginis is a magnetic chemically peculiar star
with an oblique dipolar magnetic field. The continuum radio emission has been
interpreted as gyrosyncrotron emission arising from a thin magnetospheric
layer. Previous radio observations at 1.4 GHz showed that a 100% circular
polarized and highly directive emission component overlaps to the continuum
emission two times per rotation, when the magnetic axis lies in the plane of
the sky. This sort of radio lighthouse has been proposed to be due to cyclotron
maser emission generated above the magnetic pole and propagating
perpendicularly to the magnetic axis. Observations carried out with the
Australia Telescope Compact Array at 1.4 and 2.5 GHz one year after this
discovery show that this radio emission is still present, meaning that the
phenomenon responsible for this process is steady on a timescale of years. The
emitted radiation spans at least 1 GHz, being observed from 1.4 to 2.5 GHz. On
the light of recent results on the physics of the magnetosphere of this star,
the possibility of plasma radiation is ruled out. The characteristics of this
radio lighthouse provides us a good marker of the rotation period, since the
peaks are visible at particular rotational phases. After one year, they show a
delay of about 15 minutes. This is interpreted as a new abrupt spinning down of
the star. Among several possibilities, a quick emptying of the equatorial
magnetic belt after reaching the maximum density can account for the magnitude
of the breaking. The study of the coherent emission in stars like CU Vir, as
well as in pre main sequence stars, can give important insight into the angular
momentum evolution in young stars. This is a promising field of investigation
that high sensitivity radio interferometers such as SKA can exploit.Comment: Accepted to MNRAS, 8 pages, 7 figures, updated versio
Coarsening in the q-State Potts Model and the Ising Model with Globally Conserved Magnetization
We study the nonequilibrium dynamics of the -state Potts model following a
quench from the high temperature disordered phase to zero temperature. The time
dependent two-point correlation functions of the order parameter field satisfy
dynamic scaling with a length scale . In particular, the
autocorrelation function decays as . We illustrate these
properties by solving exactly the kinetic Potts model in . We then analyze
a Langevin equation of an appropriate field theory to compute these correlation
functions for general and . We establish a correspondence between the
two-point correlations of the -state Potts model and those of a kinetic
Ising model evolving with a fixed magnetization . The dynamics of this
Ising model is solved exactly in the large q limit, and in the limit of a large
number of components for the order parameter. For general and in any
dimension, we introduce a Gaussian closure approximation and calculate within
this approximation the scaling functions and the exponent . These
are in good agreement with the direct numerical simulations of the Potts model
as well as the kinetic Ising model with fixed magnetization. We also discuss
the existing and possible experimental realizations of these models.Comment: TeX, Vanilla.sty is needed. [Admin note: author contacted regarding
missing figure1 but is unable to supply, see journal version (Nov99)
Statistics of Magnetic Fields for OB Stars
Based on an analysis of the catalog of magnetic fields, we have investigated
the statistical properties of the mean magnetic fields for OB stars. We show
that the mean effective magnetic field of a star can be used as a
statistically significant characteristic of its magnetic field. No correlation
has been found between the mean magnetic field strength and
projected rotational velocity of OB stars, which is consistent with the
hypothesis about a fossil origin of the magnetic field. We have constructed the
magnetic field distribution function for B stars, , that has a
power-law dependence on with an exponent of . We have
found a sharp decrease in the function F for {\cal B}\lem 400 G
that may be related to rapid dissipation of weak stellar surface magnetic
fields.Comment: 22 pages, 7 figures, accepted Astronomy Letters, 2010, vol.36, No.5,
pp.370-379, contact E-mail: [email protected]
Neutron Beam Effects on Spin Exchange Polarized He-3
We have observed depolarization effects when high intensity cold neutron
beams are incident on alkali-metal-spin-exchange polarized He-3 cells used as
neutron spin filters. This was first observed as a reduction of the maximum
attainable He-3 polarization and was attributed to a decrease of alkali-metal
polarization, which led us to directly measure alkali-metal polarization and
spin relaxation over a range of neutron fluxes at LANSCE and ILL. The data
reveal a new alkali-metal spin-relaxation mechanism that approximately scales
as the square root of the neutron capture-flux density incident on the cell.
This is consistent with an effect proportional to the recombination-limited ion
concentration, but is much larger than expected from earlier work.Comment: submitted to Physical Review Letter
Isomer shift and magnetic moment of the long-lived 1/2 isomer in Zn: signature of shape coexistence near Ni
Collinear laser spectroscopy has been performed on the Zn
isotope at ISOLDE-CERN. The existence of a long-lived isomer with a few hundred
milliseconds half-life was confirmed, and the nuclear spins and moments of the
ground and isomeric states in Zn as well as the isomer shift were
measured. From the observed hyperfine structures, spins and
are firmly assigned to the ground and isomeric states. The magnetic moment
(Zn) = 1.1866(10) , confirms the spin-parity
with a shell-model configuration, in excellent
agreement with the prediction from large scale shell-model theories. The
magnetic moment (Zn) = 1.0180(12) supports a
positive parity for the isomer, with a wave function dominated by a 2h-1p
neutron excitation across the shell gap. The large isomer shift
reveals an increase of the intruder isomer mean square charge radius with
respect to that of the ground state:
= +0.204(6) fm, providing first evidence of shape coexistence.Comment: 5 pages, 4 figures, 1 table, Accepeted by Phys. Rev. Lett. (2016
Experimental Evidence for Simple Relations between Unpolarized and Polarized Parton Distributions
The Pauli exclusion principle is advocated for constructing the proton and
neutron deep inelastic structure functions in terms of Fermi-Dirac
distributions that we parametrize with very few parameters. It allows a fair
description of the recent NMC data on and at
, as well as the CCFR neutrino data at and . We
also make some reasonable and simple assumptions to relate unpolarized and
polarized quark parton distributions and we obtain, with no additional free
parameters, the spin dependent structure functions and
. Using the correct evolution, we have checked that they
are in excellent agreement with the very recent SMC proton data at and the SLAC neutron data at .Comment: 17 pages,CPT-94/P.3032,latex,6 fig available on cpt.univ-mrs.fr
directory pub/preprints/94/fundamental-interactions /94-P.303
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