10,847 research outputs found
Factor V Leiden and thrombosis in patients with systemic lupus erythematosus: a meta-analysis.
The aim of this study was to perform a meta-analysis of the association between the factor V Leiden polymorphism (FVL) and thrombosis among patients with systemic lupus erythematosus (SLE) and/or antiphospholipid antibody (aPL) positivity. Included studies recruited patients based on SLE or aPL-positive status, confirmed subjects' SLE diagnosis as defined by the American College of Rheumatology, and documented thrombotic events. Excluded studies were non-English or considered only arterial thrombosis. Individual patient data, available from 5 studies, together with unpublished data from 1210 European-American SLE patients from the UCSF Lupus Genetics Collection genotyped for FVL, were further analyzed. Seventeen studies (n=2090 subjects) were included in the initial meta-analysis. Unadjusted odds ratios (OR) were calculated to assess association of FVL with thrombosis. The OR for association of thrombosis with FVL was 2.88 (95% confidence interval (CI) 1.98-4.20). In the secondary analysis with our individual patient dataset (n=1447 European-derived individuals), SLE subjects with the FVL polymorphism still had more than two times the odds of thrombosis compared to subjects without this polymorphism, even when adjusting for covariates such as gender, age and aPL status. SLE and/or aPL-positive patients with the FVL variant have more than two times the odds of thrombosis compared to those without this polymorphism
Subnanosecond Fluctuations in Low-Barrier Nanomagnets
Fast magnetic fluctuations due to thermal torques have useful technological
functionality ranging from cryptography to probabilistic computing. The
characteristic time of fluctuations in typical uniaxial anisotropy magnets
studied so far is bounded from below by the well-known energy relaxation
mechanism. This time scales as , where parameterizes the
strength of dissipative processes. Here, we theoretically analyze the
fluctuating dynamics in easy-plane and antiferromagnetically coupled
nanomagnets. We find in such magnets, the dynamics are strongly influenced by
fluctuating intrinsic fields, which give rise to an additional dephasing-type
mechanism for washing out correlations. In particular, we establish two time
scales for characterizing fluctuations (i) the average time for a nanomagnet to
reverse|which for the experimentally relevant regime of low damping is governed
primarily by dephasing and becomes independent of , (ii) the time scale
for memory loss of a single nanomagnet|which scales as and is
governed by a combination of energy dissipation and dephasing mechanism. For
typical experimentally accessible values of intrinsic fields, the resultant
thermal-fluctuation rate is increased by multiple orders of magnitude when
compared with the bound set solely by the energy relaxation mechanism in
uniaxial magnets. This could lead to higher operating speeds of emerging
devices exploiting magnetic fluctuations
Redshift-space Distortions of the Power Spectrum of Cosmological Objects on a Light Cone : Explicit Formulations and Theoretical Implications
We examine the effects of the linear and the cosmological redshift-space
distortions on the power spectrum of cosmological objects on a light cone. We
develop theoretical formulae for the power spectrum in linear theory of density
perturbations in a rigorous manner starting from first principle corresponding
to Fourier analysis. Approximate formulae, which are useful properly to
incorporate the redshift-space distortion effects into the power spectrum are
derived, and the validity is examined. Applying our formulae to galaxy and
quasar samples which roughly match the SDSS survey, we will show how the
redshift-space distortions distort the power spectrum on the light cone
quantitatively.Comment: 30 pages, Accepted for publication in the Astrophysical Journal
Supplement Serie
The Galaxy Cluster Luminosity-Temperature Relationship and Iron Abundances - A Measure of Formation History ?
Both the X-ray luminosity-temperature (L-T) relationship and the iron
abundance distribution of galaxy clusters show intrinsic dispersion. Using a
large set of galaxy clusters with measured iron abundances we find a
correlation between abundance and the relative deviation of a cluster from the
mean L-T relationship. We argue that these observations can be explained by
taking into account the range of cluster formation epochs expected within a
hierarchical universe. The known relationship of cooling flow mass deposition
rate to luminosity and temperature is also consistent with this explanation.
From the observed cluster population we estimate that the oldest clusters
formed at z>~2. We propose that the iron abundance of a galaxy cluster can
provide a parameterization of its age and dynamical history.Comment: 13 pages Latex, 2 figures, postscript. Accepted for publication in
ApJ Letter
Curie-like paramagnetism due to incomplete Zhang-Rice singlet formation in La2-xSrxCuO4
In an effort to elucidate the origin of the Curie-like paramagnetism that is
generic for heavily-overdoped cuprates, we have performed high transverse-field
muon spin rotation (TF-muSR) measurements of La2-xSrxCuO4 single crystals over
the Sr content range 0.145 < x < 0.33. We show that the x-dependence of the
previously observed field-induced broadening of the internal magnetic field
distribution above the superconducting transition temperature Tc reflects the
presence of two distinct contributions. One of these becomes less pronounced
with increasing x and is attributed to diminishing antiferromagnetic
correlations. The other grows with increasing x, but decreases above x ~ 0.30,
and is associated with the Curie-like term in the bulk magnetic susceptibility.
In contrast to the Curie-like term, however, this second contribution to the
TF-muSR line width extends back into the underdoped regime. Our findings imply
a coexistence of antiferromagnetically correlated and paramagnetic moments,
with the latter becoming dominant beyond x ~ 0.185. This suggests that the
doped holes do not neutralize all Cu spins via the formation of Zhang-Rice
singlets. Moreover, the paramagnetic component of the TF-muSR line width is
explained by holes progressively entering the Cu 3d_{x^2-y^2} orbital with
doping.Comment: 8 pages, 7 figure
Comment about constraints on nanometer-range modifications to gravity from low-energy neutron experiments
A topic of present interest is the application of experimentally observed
quantum mechanical levels of ultra-cold neutrons in the earth's gravitational
field for searching short-range modifications to gravity. A constraint on new
forces in the nanometer-range published by Nesvizhevsky and Protasov follows
from inadequate modelling of the interaction potential of a neutron with a
mirror wall. Limits by many orders of magnitude better were already derived
long ago from the consistency of experiments on the neutron-electron
interaction.Comment: three page
Near term measurements with 21 cm intensity mapping: neutral hydrogen fraction and BAO at z<2
It is shown that 21 cm intensity mapping could be used in the near term to
make cosmologically useful measurements. Large scale structure could be
detected using existing radio telescopes, or using prototypes for dedicated
redshift survey telescopes. This would provide a measure of the mean neutral
hydrogen density, using redshift space distortions to break the degeneracy with
the linear bias. We find that with only 200 hours of observing time on the
Green Bank Telescope, the neutral hydrogen density could be measured to 25%
precision at redshift 0.54<z<1.09. This compares favourably to current
measurements, uses independent techniques, and would settle the controversy
over an important parameter which impacts galaxy formation studies. In
addition, a 4000 hour survey would allow for the detection of baryon acoustic
oscillations, giving a cosmological distance measure at 3.5% precision. These
observation time requirements could be greatly reduced with the construction of
multiple pixel receivers. Similar results are possible using prototypes for
dedicated cylindrical telescopes on month time scales, or SKA pathfinder
aperture arrays on day time scales. Such measurements promise to improve our
understanding of these quantities while beating a path for future generations
of hydrogen surveys.Comment: 6 pages, 5 figures. Submitted to Phys. Rev. D. Addressed reviewer
comments. Changed figure format, added more detailed technical discussion,
and added forecasts for aperture arrays. Added references
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