248 research outputs found
The Spin Glass Transition : Exponents and Dynamics
Numerical simulations on Ising Spin Glasses show that spin glass transitions
do not obey the usual universality rules which hold at canonical second order
transitions. On the other hand the dynamics at the approach to the transition
appear to take up a universal form for all spin glasses. The implications for
the fundamental physics of transitions in complex systems are addressed.Comment: 4 pages (Latex) with 3 figures (postscript), accepted for publication
in Physica
Phonons and specific heat of linear dense phases of atoms physisorbed in the grooves of carbon nanotube bundles
The vibrational properties (phonons) of a one-dimensional periodic phase of
atoms physisorbed in the external groove of the carbon nanotube bundle are
studied. Analytical expressions for the phonon dispersion relations are
derived. The derived expressions are applied to Xe, Kr and Ar adsorbates. The
specific heat pertaining to dense phases of these adsorbates is calculated.Comment: 4 PS figure
Critical exponents in Ising spin glasses
We determine accurate values of ordering temperatures and critical exponents
for Ising Spin Glass transitions in dimension 4, using a combination of finite
size scaling and non-equilibrium scaling techniques. We find that the exponents
and vary with the form of the interaction distribution, indicating
non-universality at Ising spin glass transitions. These results confirm
conclusions drawn from numerical data for dimension 3.Comment: 6 pages, RevTeX (or Latex, etc), 10 figures, Submitted to PR
Coronal mass ejections as expanding force-free structures
We mode Solar coronal mass ejections (CMEs) as expanding force-fee magnetic
structures and find the self-similar dynamics of configurations with spatially
constant \alpha, where {\bf J} =\alpha {\bf B}, in spherical and cylindrical
geometries, expanding spheromaks and expanding Lundquist fields
correspondingly. The field structures remain force-free, under the conventional
non-relativistic assumption that the dynamical effects of the inductive
electric fields can be neglected. While keeping the internal magnetic field
structure of the stationary solutions, expansion leads to complicated internal
velocities and rotation, induced by inductive electric field. The structures
depends only on overall radius R(t) and rate of expansion \dot{R}(t) measured
at a given moment, and thus are applicable to arbitrary expansion laws. In case
of cylindrical Lundquist fields, the flux conservation requires that both axial
and radial expansion proceed with equal rates. In accordance with observations,
the model predicts that the maximum magnetic field is reached before the
spacecraft reaches the geometric center of a CME.Comment: 19 pages, 9 Figures, accepted by Solar Physic
Atenolol versus losartan in children and young adults with Marfan's syndrome
BACKGROUND : Aortic-root dissection is the leading cause of death in Marfan's syndrome. Studies suggest that with regard to slowing aortic-root enlargement, losartan may be more effective than beta-blockers, the current standard therapy in most centers.
METHODS : We conducted a randomized trial comparing losartan with atenolol in children and young adults with Marfan's syndrome. The primary outcome was the rate of aortic-root enlargement, expressed as the change in the maximum aortic-root-diameter z score indexed to body-surface area (hereafter, aortic-root z score) over a 3-year period. Secondary outcomes included the rate of change in the absolute diameter of the aortic root; the rate of change in aortic regurgitation; the time to aortic dissection, aortic-root surgery, or death; somatic growth; and the incidence of adverse events.
RESULTS : From January 2007 through February 2011, a total of 21 clinical centers enrolled 608 participants, 6 months to 25 years of age (mean [+/- SD] age, 11.5 +/- 6.5 years in the atenolol group and 11.0 +/- 6.2 years in the losartan group), who had an aorticroot z score greater than 3.0. The baseline-adjusted rate of change (+/- SE) in the aortic-root z score did not differ significantly between the atenolol group and the losartan group (-0.139 +/- 0.013 and -0.107 +/- 0.013 standard-deviation units per year, respectively; P = 0.08). Both slopes were significantly less than zero, indicating a decrease in the degree of aortic-root dilatation relative to body-surface area with either treatment. The 3-year rates of aortic-root surgery, aortic dissection, death, and a composite of these events did not differ significantly between the two treatment groups.
CONCLUSIONS : Among children and young adults with Marfan's syndrome who were randomly assigned to losartan or atenolol, we found no significant difference in the rate of aorticroot dilatation between the two treatment groups over a 3-year period
Progressive transformation of a flux rope to an ICME
The solar wind conditions at one astronomical unit (AU) can be strongly
disturbed by the interplanetary coronal mass ejections (ICMEs). A subset,
called magnetic clouds (MCs), is formed by twisted flux ropes that transport an
important amount of magnetic flux and helicity which is released in CMEs. At 1
AU from the Sun, the magnetic structure of MCs is generally modeled neglecting
their expansion during the spacecraft crossing. However, in some cases, MCs
present a significant expansion. We present here an analysis of the huge and
significantly expanding MC observed by the Wind spacecraft during 9 and 10
November, 2004. After determining an approximated orientation for the flux rope
using the minimum variance method, we precise the orientation of the cloud axis
relating its front and rear magnetic discontinuities using a direct method.
This method takes into account the conservation of the azimuthal magnetic flux
between the in- and out-bound branches, and is valid for a finite impact
parameter (i.e., not necessarily a small distance between the spacecraft
trajectory and the cloud axis). Moreover, using the direct method, we find that
the ICME is formed by a flux rope (MC) followed by an extended coherent
magnetic region. These observations are interpreted considering the existence
of a previous larger flux rope, which partially reconnected with its
environment in the front. These findings imply that the ejected flux rope is
progressively peeled by reconnection and transformed to the observed ICME (with
a remnant flux rope in the front part).Comment: Solar Physics (in press
Small-scale anisotropy and intermittency in high and low-latitude solar wind
We analyze low and high--latitude fast solar wind data from the Ulysses
spacecraft from 1992 to 1994 using a a systematic method to analyse the
anisotropic content of the magnetic field fluctuations. We investigate all
available frequencies, 1-10^{-6} Hz, for both high and low--latitudes datasets
and are able to quantify the relative importance of the anisotropic versus the
isotropic fluctuations. We analyse, up to sixth order, longitudinal, transverse
and mixed magnetic field correlations. Our results show that strongly
intermittent and anisotropic events are present in the solar wind plasma at
high frequencies/small scales, indicating the absence of a complete recovery of
isotropy. Anisotropic scaling properties are compatible for high and
low--latitude data, suggesting a universal behaviour in spite of the different
rate of evolution of the fast solar wind streams in the two environments.Comment: 26 pages, 8 figures. Submitted to Astrophysical Journa
Dynamical parton distributions of the nucleon and very small-x physics
Utilizing recent DIS measurements (F_{2,L}) and data on dilepton and
high-E_{T} jet production we determine the dynamical parton distributions of
the nucleon generated radiatively from valence-like positive input
distributions at optimally chosen low resolution scales. These are compared
with `standard' distributions generated from positive input distributions at
some fixed and higher resolution scale. It is shown that up to the next to
leading order NLO(\bar{MS}, DIS) of perturbative QCD considered in this paper,
the uncertainties of the dynamical distributions are, as expected, smaller than
those of their standard counterparts. This holds true in particular in the
presently unexplored extremely small-x region relevant for evaluating ultrahigh
energy cross sections in astrophysical applications. It is noted that our new
dynamical distributions are compatible, within the presently determined
uncertainties, with previously determined dynamical parton distributions.Comment: 21 pages, 2 tables, 16 figures, v2: added Ref.[60], replaced Fig.
How Many CMEs Have Flux Ropes? Deciphering the Signatures of Shocks, Flux Ropes, and Prominences in Coronagraph Observations of CMEs
We intend to provide a comprehensive answer to the question on whether all
Coronal Mass Ejections (CMEs) have flux rope structure. To achieve this, we
present a synthesis of the LASCO CME observations over the last sixteen years,
assisted by 3D MHD simulations of the breakout model, EUV and coronagraphic
observations from STEREO and SDO, and statistics from a revised LASCO CME
database. We argue that the bright loop often seen as the CME leading edge is
the result of pileup at the boundary of the erupting flux rope irrespective of
whether a cavity or, more generally, a 3-part CME can be identified. Based on
our previous work on white light shock detection and supported by the MHD
simulations, we identify a new type of morphology, the `two-front' morphology.
It consists of a faint front followed by diffuse emission and the bright
loop-like CME leading edge. We show that the faint front is caused by density
compression at a wave (or possibly shock) front driven by the CME. We also
present high-detailed multi-wavelength EUV observations that clarify the
relative positioning of the prominence at the bottom of a coronal cavity with
clear flux rope structure. Finally, we visually check the full LASCO CME
database for flux rope structures. In the process, we classify the events into
two clear flux rope classes (`3-part', `Loop'), jets and outflows (no clear
structure). We find that at least 40% of the observed CMEs have clear flux rope
structures. We propose a new definition for flux rope CMEs (FR-CMEs) as a
coherent magnetic, twist-carrying coronal structure with angular width of at
least 40 deg and able to reach beyond 10 Rsun which erupts on a time scale of a
few minutes to several hours. We conclude that flux ropes are a common
occurrence in CMEs and pose a challenge for future studies to identify CMEs
that are clearly not FR-CMEs.Comment: 26 pages, 9 figs, to be published in Solar Physics Topical Issue
"Flux Rope Structure of CMEs
Risk factor burden, heart failure, and survival in women of different ethnic groups insights from the women's health initiative
BACKGROUND: The higher risk of heart failure (HF) in African-American and Hispanic women compared with white women is related to the higher burden of risk factors (RFs) in minorities. However, it is unclear if there are differences in the association between the number of RFs for HF and the risk of development of HF and death within racial/ethnic groups. METHODS AND RESULTS: In the WHI (Women's Health Initiative; 1993-2010), African-American (n=11996), white (n=18479), and Hispanic (n=5096) women with 1, 2, or 3+ baseline RFs were compared with women with 0 RF within their respective racial/ethnic groups to assess risk of developing HF or all-cause mortality before and after HF, using survival analyses. After adjusting for age, socioeconomic status, and hormone therapy, the subdistribution hazard ratio (95% confidence interval) of developing HF increased as number of RFs increased (P<0.0001, interaction of race/ethnicity and RF number P=0.18)-African-Americans 1 RF: 1.80 (1.01-3.20), 2 RFs: 3.19 (1.84-5.54), 3+ RFs: 7.31 (4.26-12.56); Whites 1 RF: 1.27 (1.04-1.54), 2 RFs: 1.95 (1.60-2.36), 3+ RFs: 4.07 (3.36-4.93); Hispanics 1 RF: 1.72 (0.68-4.34), 2 RFs: 3.87 (1.60-9.37), 3+ RFs: 8.80 (3.62-21.42). Risk of death before developing HF increased with subsequent RFs (P<0.0001) but differed by racial/ethnic group (interaction P=0.001). The number of RFs was not associated with the risk of death after developing HF in any group (P=0.25; interaction P=0.48). CONCLUSIONS: Among diverse racial/ethnic groups, an increase in the number of baseline RFs was associated with higher risk of HF and death before HF but was not associated with death after HF. Early RF prevention may reduce the burden of HF across multiple racial/ethnic groups
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