14,414 research outputs found
Propagation of QCD Color through Strongly Interacting Systems
The propagation of QCD color through atomic nuclei is studied via a new
analysis using a geometric model of semi-inclusive deep inelastic scattering.
The experimental data were previously published by the HERMES Collaboration and
consisted of the multiplicity ratio observable (2007) and the transverse
momentum broadening observable (2010). We perform a simultaneous fit of these
two observables to estimate (1) the color lifetime of the quark, (2) quark
energy loss, (3) the transport coefficient, and (4) the cross section
for hadronic interaction with the medium. We present preliminary results for
this fit.Comment: 4 pages, 3 figures; proceedings for the Eighth International
Conference on Quarks and Nuclear Physics (QNP2018), Tsukuba, Japan.
https://www-conf.kek.jp/qnp2018
Expansive homeomorphisms of the plane
This article tackles the problem of the classification of expansive
homeomorphisms of the plane. Necessary and sufficient conditions for a
homeomorphism to be conjugate to a linear hyperbolic automorphism will be
presented. The techniques involve topological and metric aspects of the plane.
The use of a Lyapunov metric function which defines the same topology as the
one induced by the usual metric but that, in general, is not equivalent to it
is an example of such techniques. The discovery of a hypothesis about the
behavior of Lyapunov functions at infinity allows us to generalize some results
that are valid in the compact context. Additional local properties allow us to
obtain another classification theorem.Comment: 29 pages, 22 figure
On Schwinger Pair Creation in Gravity and in Closed Superstring Theory
We investigate the Schwinger pair creation process in the context of
gravitational models with the back reaction of the electric field included in
the geometry. The background is also an exact solution of type II superstring
theory, where the electric field arises by Kaluza-Klein reduction. We obtain a
closed formula for the pair creation rate that incorporates the gravitational
back reaction. At weak fields it has the same structure as the general
Schwinger formula, albeit pairs are produced by a combination of Schwinger and
Unruh effect, the latter due to the presence of a Rindler horizon. In four
spacetime dimensions, the rate becomes constant at strong electric fields. For
states with mass of Kaluza-Klein origin, the rate has a power-like dependence
in the electric field, rather than the familiar (non-perturbative) exponential
dependence. We also reproduce the same formula from the string partition
function for winding string states. Finally, we comment on the generalization
to excited string states.Comment: 21 page
SGR 0418+5729, Swift J1822.3-1606, and 1E 2259+586 as massive fast rotating highly magnetized white dwarfs
Following Malheiro et al. (2012) we describe the so-called low magnetic field
magnetars, SGR 0418+5729, Swift J1822.3--1606, as well as the AXP prototype 1E
2259+586 as massive fast rotating highly magnetized white dwarfs. We give
bounds for the mass, radius, moment of inertia, and magnetic field for these
sources by requesting the stability of realistic general relativistic uniformly
rotating configurations. Based on these parameters, we improve the theoretical
prediction of the lower limit of the spindown rate of SGR 0418+5729; for a
white dwarf close to its maximum stable we obtain the very stringent interval
for the spindown rate of 4.1E-16< dP/dt < 6E-15, where the upper value is the
known observational limit. A lower limit has been also set for Swift
J1822.3-1606 for which a fully observationally accepted spin-down rate is still
lacking. The white dwarf model provides for this source dP/dt> 2.13E-15, if the
star is close to its maximum stable mass. We also present the theoretical
expectation of the infrared, optical and ultraviolet emission of these objects
and show their consistency with the current available observational data. We
give in addition the frequencies at which absorption features could be present
in the spectrum of these sources as the result of the scattering of photons
with the quantized electrons by the surface magnetic field.Comment: to appear in Astronomy & Astrophysic
Addition of 24âhour heart rate variability parameters to the Cardiovascular Health Study stroke risk score and prediction of incident stroke: The Cardiovascular Health Study
Background Heart rate variability (HRV) characterizes cardiac autonomic functioning. The association of HRV with stroke is uncertain. We examined whether 24âhour HRV added predictive value to the Cardiovascular Health Study clinical stroke risk score (CHSâSCORE), previously developed at the baseline examination. Methods and Results N=884 strokeâfree CHS participants (age 75.3±4.6), with 24âhour Holters adequate for HRV analysis at the 1994â1995 examination, had 68 strokes over â€8 year followâup (median 7.3 [interquartile range 7.1â7.6] years). The value of adding HRV to the CHSâSCORE was assessed with stepwise Cox regression analysis. The CHSâSCORE predicted incident stroke (HR=1.06 per unit increment, P=0.005). Two HRV parameters, decreased coefficient of variance of NN intervals (CV%, P=0.031) and decreased power law slope (SLOPE, P=0.033) also entered the model, but these did not significantly improve the câstatistic (P=0.47). In a secondary analysis, dichotomization of CV% (LOWCV% â€12.8%) was found to maximally stratify higherârisk participants after adjustment for CHSâSCORE. Similarly, dichotomizing SLOPE (LOWSLOPE <â1.4) maximally stratified higherârisk participants. When these HRV categories were combined (eg, HIGHCV% with HIGHSLOPE), the câstatistic for the model with the CHSâSCORE and combined HRV categories was 0.68, significantly higher than 0.61 for the CHSâSCORE alone (P=0.02). Conclusions In this sample of older adults, 2 HRV parameters, CV% and power law slope, emerged as significantly associated with incident stroke when added to a validated clinical risk score. After each parameter was dichotomized based on its optimal cut point in this sample, their composite significantly improved prediction of incident stroke during â€8âyear followâup. These findings will require validation in separate, larger cohorts. Keywords: autonomic nervous system, clinical stroke risk model, heart rate variability, prediction, predictors, risk prediction, risk stratification, strok
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