4,453 research outputs found
Adherence to secondary stroke prevention strategies - Results from the German stroke data bank
Only very limited data are available concerning patient adherence to antithrombotic medication intended to prevent a recurrent stroke. Reduced adherence and compliance could significantly influence the effects of any stroke prevention strategies. This study from a large stroke data bank provides representative data concerning the rate of stroke victims adhering to their recommended preventive medication. During a 2-year period beginning January 1, 1998, all patients with acute stroke or TIA in 23 neurological departments with an acute stroke unit were included in the German Stroke Data Bank. Data were collected prospectively, reviewed, validated and processed in a central data management unit. Only 12 centers with a follow-up rate of 80% or higher were included in this evaluation. 3,420 patients were followed up after 3 months, and 2,640 patients were followed up one year after their stroke. After one year, 96% of all patients reported still adhere to at least one medical stroke prevention strategy. Of the patients receiving aspirin at discharge, 92.6% reported to use that medication after 3 months and 84% after one year, while 81.6 and 61.6% were the respective figures for clopidogrel, and 85.2 and 77.4% for oral anticoagulation. Most patients who changed medication switched from aspirin to clopidogrel. Under the conditions of this observational study, adherence to stroke prevention strategies is excellent. The highest adherence rate is noticed for aspirin and oral anticoagulation. After one year, very few patients stopped taking stroke preventive medication. Copyright (C) 2003 S. Karger AG, Basel
Quasar outflow energetics from broad absorption line variability
Quasar outflows have long been recognized as potential contributors to the
co-evolution between supermassive black holes (SMBHs) and their host galaxies.
The role of outflows in AGN feedback processes can be better understood by
placing observational constraints on wind locations and kinetic energies. We
utilize broad absorption line (BAL) variability to investigate the properties
of a sample of 71 BAL quasars with PV broad absorption. The
presence of PV BALs indicates that other BALs like CIV
are saturated, such that variability in those lines favours clouds crossing the
line of sight. We use these constraints with measurements of BAL variability to
estimate outflow locations and energetics. Our data set consists of
multiple-epoch spectra from the Sloan Digital Sky Survey and MDM Observatory.
We detect significant (4) BAL variations from 10 quasars in our sample
over rest frame time-scales between < 0.2-3.8 yr. Our derived distances for the
10 variable outflows are nominally < 1-10 pc from the SMBH using the
transverse-motion scenario, and < 100-1000 pc from the central source using
ionization-change considerations. These distances, in combination with the
estimated high outflow column densities (i.e. > 10
cm), yield outflow kinetic luminosities between ~ 0.001-1 times the
bolometric luminosity of the quasar, indicating that many absorber energies
within our sample are viable for AGN feedback.Comment: 19 pages, 3 figures, 4 tables, 1 supplementary figure, accepted to
MNRA
Axions and saxions from the primordial supersymmetric plasma and extra radiation signatures
We calculate the rate for thermal production of axions and saxions via
scattering of quarks, gluons, squarks, and gluinos in the primordial
supersymmetric plasma. Systematic field theoretical methods such as hard
thermal loop resummation are applied to obtain a finite result in a
gauge-invariant way that is consistent to leading order in the strong gauge
coupling. We calculate the thermally produced yield and the decoupling
temperature for both axions and saxions. For the generic case in which saxion
decays into axions are possible, the emitted axions can constitute extra
radiation already prior to big bang nucleosynthesis and well thereafter. We
update associated limits imposed by recent studies of the primordial helium-4
abundance and by precision cosmology of the cosmic microwave background and
large scale structure. We show that the trend towards extra radiation seen in
those studies can be explained by late decays of thermal saxions into axions
and that upcoming Planck results will probe supersymmetric axion models with
unprecedented sensitivity.Comment: 16 pages, 7 figures; v2: references added, minor clarifying
additions, matches published versio
4D visualization of embryonic, structural crystallization by single-pulse microscopy
In many physical and biological systems the transition from an amorphous to ordered native structure involves complex energy landscapes, and understanding such transformations requires not only their thermodynamics but also the structural dynamics during the process. Here, we extend our 4D visualization method with electron imaging to include the study of irreversible processes with a single pulse in the same ultrafast electron microscope (UEM) as used before in the single-electron mode for the study of reversible processes. With this augmentation, we report on the transformation of amorphous to crystalline structure with silicon as an example. A single heating pulse was used to initiate crystallization from the amorphous phase while a single packet of electrons imaged selectively in space the transformation as the structure continuously changes with time. From the evolution of crystallinity in real time and the changes in morphology, for nanosecond and femtosecond pulse heating, we describe two types of processes, one that occurs at early time and involves a nondiffusive motion and another that takes place on a longer time scale. Similar mechanisms of two distinct time scales may perhaps be important in biomolecular folding
A Brachistochrone Approach to Reconstruct the Inflaton Potential
We propose a new way to implement an inflationary prior to a cosmological
dataset that incorporates the inflationary observables at arbitrary order. This
approach employs an exponential form for the Hubble parameter without
taking the slow-roll approximation. At lowest non-trivial order, this
has the unique property that it is the solution to the brachistochrone problem
for inflation.Comment: 13 pages, 2 figures, version matches published versio
The Metallicity of the Redshift 4.16 Quasar BR2248-1242
We estimate the metallicity in the broad emission-line region of the redshift
z=4.16 quasar, BR2248-1242, by comparing line ratios involving nitrogen to
theoretical predictions. BR2248-1242 has unusually narrow emission lines with
large equivalent widths, thus providing a rare opportunity to measure several
line-ratio abundance diagnostics. The combined diagnostics indicate a
metallicity of ~2 times solar. This result suggests that an episode of vigorous
star formation occurred near BR2248-1242 prior to the observed z=4.16 epoch.
The time available for this enrichment episode is only ~1.5 Gyr at z=4.16 (for
H_{0}=65 km s^-1 Mpc^-1, Omega_{m}=0.3 and Omega_Lambda ~< 1). This evidence
for high metallicities and rapid star formation is consistent with the expected
early-epoch evolution of dense galactic nuclei.Comment: 8 pages, 3 figures. Prepared in AAStex. Submitted to the
Astrophysical Journal Revised version: added 1 referenc
The rapid evolution of the exciting star of the Stingray Nebula
SAO244567, the exciting star of the Stingray nebula, is rapidly evolving.
Previous analyses suggested that it has heated up from an effective temperature
of about 21kK in 1971 to over 50kK in the 1990s. Canonical post-asymptotic
giant branch evolution suggests a relatively high mass while previous analyses
indicate a low-mass star. Fitting line profiles from static and expanding
non-LTE model atmospheres to the observed UV and optical spectra, taken during
1988-2013, allowed us to study the temporal change of effective temperature,
surface gravity, mass-loss rate, and terminal wind velocity. In addition, we
determined the chemical composition of the atmosphere. We find that the central
star has steadily increased its effective temperature from 38kK in 1988 to a
peak value of 60kK in 2002. During the same time, the star was contracting, as
concluded from an increase in surface gravity from log g = 4.8 to 6.0 and a
drop in luminosity. Simultaneously, the mass-loss rate declined from log
(dM/dt/Msun/yr)=-9.0 to -11.6 and the terminal wind velocity increased from
1800km/s to 2800km/s. Since around 2002, the star stopped heating and has
cooled down again to 55kK by 2006. It has a largely solar surface composition
with the exception of slightly subsolar carbon, phosphorus, and sulfur. By
comparison with stellar-evolution calculations, we confirm that SAO244567 must
be a low-mass star (M < 0.55 Msun). However, the slow evolution of the
respective stellar evolutionary models is in strong contrast to the observed
fast evolution and the young planetary nebula with a kinematical age of only
about 1000 years. We speculate that the star could be a late He-shell flash
object. Alternatively, it could be the outcome of close-binary evolution. Then
SAO244567 would be a low-mass (0.354 Msun) helium prewhite dwarf after the
common-envelope phase, during which the planetary nebula was ejected.Comment: 16 pages, 13 figures, accepted for publication in A&
A rare early-type star revealed in the Wing of the Small Magellanic Cloud
Sk 183 is the visually-brightest star in the N90 nebula, a young star-forming
region in the Wing of the Small Magellanic Cloud (SMC). We present new optical
spectroscopy from the Very Large Telescope which reveals Sk 183 to be one of
the most massive O-type stars in the SMC. Classified as an O3-type dwarf on the
basis of its nitrogen spectrum, the star also displays broadened He I
absorption which suggests a later type. We propose that Sk 183 has a composite
spectrum and that it is similar to another star in the SMC, MPG 324. This
brings the number of rare O2- and O3-type stars known in the whole of the SMC
to a mere four. We estimate physical parameters for Sk 183 from analysis of its
spectrum. For a single-star model, we estimate an effective temperature of
46+/-2 kK, a low mass-loss rate of ~10^-7 Msun yr^-1, and a spectroscopic mass
of 46^+9_-8 Msun (for an adopted distance modulus of 18.7 mag to the young
population in the SMC Wing). An illustrative binary model requires a slightly
hotter temperature (~47.5 kK) for the primary component. In either scenario, Sk
183 is the earliest-type star known in N90 and will therefore be the dominant
source of hydrogen-ionising photons. This suggests Sk 183 is the primary
influence on the star formation along the inner edge of the nebula.Comment: Accepted by ApJ, 10 pages, 7 figures, v2 after proof
Increased plasma viscosity as a reason for inappropriate erythropoietin formation
The aim of this study was to examine whether altered plasma viscosity could contribute to the inappropriately low production rate of erythropoietin (EPO) observed in patients suffering from hypergammaglobulinemias associated with multiple myeloma or Waldenström's disease. We found that the EPO formation in response to anemia in these patients was inversely related to plasma viscosity. A similar inverse relationship between plasma viscosity and EPO production was seen in rats in which EPO formation had been stimulated by exchange transfusion and the plasma viscosity of which was thereby altered by using exchange solutions of different composition to alter plasma viscosity and thus whole blood viscosity independently from hematocrit. Raising the gammaglobulin concentration to approximately 40 mg/ml plasma in the rats almost totally blunted the rise in serum EPO levels despite a fall of the hematocrit to 20%. Determination of renal EPO mRNA levels by RNase protection revealed that the reductions in serum EPO levels at higher plasma viscosities were paralleled by reductions in renal EPO mRNA levels. Taken together, our findings suggest that plasma viscosity may be a significant inhibitory modulator of anemia-induced EPO formation. The increased plasma viscosity in patients with hypergammaglobulinemias may therefore contribute to the inappropriate EPO production, which is a major reason for the anemia developing in these patients
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