660 research outputs found
Markov Properties of Electrical Discharge Current Fluctuations in Plasma
Using the Markovian method, we study the stochastic nature of electrical
discharge current fluctuations in the Helium plasma. Sinusoidal trends are
extracted from the data set by the Fourier-Detrended Fluctuation analysis and
consequently cleaned data is retrieved. We determine the Markov time scale of
the detrended data set by using likelihood analysis. We also estimate the
Kramers-Moyal's coefficients of the discharge current fluctuations and derive
the corresponding Fokker-Planck equation. In addition, the obtained Langevin
equation enables us to reconstruct discharge time series with similar
statistical properties compared with the observed in the experiment. We also
provide an exact decomposition of temporal correlation function by using
Kramers-Moyal's coefficients. We show that for the stationary time series, the
two point temporal correlation function has an exponential decaying behavior
with a characteristic correlation time scale. Our results confirm that, there
is no definite relation between correlation and Markov time scales. However
both of them behave as monotonic increasing function of discharge current
intensity. Finally to complete our analysis, the multifractal behavior of
reconstructed time series using its Keramers-Moyal's coefficients and original
data set are investigated. Extended self similarity analysis demonstrates that
fluctuations in our experimental setup deviates from Kolmogorov (K41) theory
for fully developed turbulence regime.Comment: 25 pages, 9 figures and 4 tables. V3: Added comments, references,
figures and major correction
Energy Norms and the Stability of the Einstein Evolution Equations
The Einstein evolution equations may be written in a variety of equivalent
analytical forms, but numerical solutions of these different formulations
display a wide range of growth rates for constraint violations. For symmetric
hyperbolic formulations of the equations, an exact expression for the growth
rate is derived using an energy norm. This expression agrees with the growth
rate determined by numerical solution of the equations. An approximate method
for estimating the growth rate is also derived. This estimate can be evaluated
algebraically from the initial data, and is shown to exhibit qualitatively the
same dependence as the numerically-determined rate on the parameters that
specify the formulation of the equations. This simple rate estimate therefore
provides a useful tool for finding the most well-behaved forms of the evolution
equations.Comment: Corrected typos; to appear in Physical Review
Molecular characterization and phylogeny of Shiga toxin–producing Escherichia coli isolates obtained from two Dutch regions using whole genome sequencing
AbstractShiga toxin–producing Escherichia coli (STEC) is one of the major causes of human gastrointestinal disease and has been implicated in sporadic cases and outbreaks of diarrhoea, haemorrhagic colitis and haemolytic uremic syndrome worldwide. In this study, we determined the molecular characteristics and phylogenetic relationship of STEC isolates, and their genetic diversity was compared to that of other E. coli populations. Whole genome sequencing was performed on 132 clinical STEC isolates obtained from the faeces of 129 Dutch patients with gastrointestinal complaints. STEC isolates of this study belonged to 44 different sequence types (STs), 42 serogenotypes and 14 stx subtype combinations. Antibiotic resistance genes were more frequently present in stx1-positive isolates compared to stx2 and stx1 + stx2–positive isolates. The iha, mchB, mchC, mchF, subA, ireA, senB, saa and sigA genes were significantly more frequently present in eae-negative than in eae-positive STEC isolates. Presence of virulence genes encoding type III secretion proteins and adhesins was associated with isolates obtained from patients with bloody diarrhoea. Core genome phylogenetic analysis showed that isolates clustered according to their ST or serogenotypes irrespective of stx subtypes. Isolates obtained from patients with bloody diarrhoea were from diverse phylogenetic backgrounds. Some STEC isolates shared common ancestors with non-STEC isolates. Whole genome sequencing is a powerful tool for clinical microbiology, allowing high-resolution molecular typing, population structure analysis and detailed molecular characterization of strains. STEC isolates of a substantial genetic diversity and of distinct phylogenetic groups were observed in this study
Novel evaluation of the two-pion contribution to the nucleon isovector form factors
We calculate the two-pion continuum contribution to the nucleon isovector
spectral functions drawing upon the new high statistics measurements of the
pion form factor by the CMD-2, KLOE, and SND collaborations. The general
structure of the spectral functions remains unchanged, but the magnitude
increases by about 10%. Using the updated spectral functions, we calculate the
contribution of the two-pion continuum to the nucleon isovector form factors
and radii. We compare the isovector radii with simple rho-pole models and
illustrate their strong underestimation in such approaches. Moreover, we give a
convenient parametrization of the result for use in future form factor
analyses.Comment: 9 pages, 2 eps figures, revtex4, CMD-2 and SND data included,
conclusions unchanged, version to appear in Phys. Lett.
SLE()and Boundary Coulomb Gas
We consider the coulomb gas model on the upper half plane with different
boundary conditions, namely Drichlet, Neuman and mixed. We related this model
to SLE() theories. We derive a set of conditions connecting the
total charge of the coulomb gas, the boundary charges, the parameters
and . Also we study a free fermion theory in presence of a boundary and
show with the same methods that it would lead to logarithmic boundary changing
operators.Comment: 10 pages, no figur
Towards surface quantum optics with Bose-Einstein condensates in evanescent waves
We present a surface trap which allows for studying the coherent interaction
of ultracold atoms with evanescent waves. The trap combines a magnetic Joffe
trap with a repulsive evanescent dipole potential. The position of the magnetic
trap can be controlled with high precision which makes it possible to move
ultracold atoms to the surface of a glass prism in a controlled way. The
optical potential of the evanescent wave compensates for the strong attractive
van der Waals forces and generates a potential barrier at only a few hundred
nanometers from the surface. The trap is tested with Rb Bose-Einstein
condensates (BEC), which are stably positioned at distances from the surfaces
below one micrometer
Extending the lifetime of 3D black hole computations with a new hyperbolic system of evolution equations
We present a new many-parameter family of hyperbolic representations of
Einstein's equations, which we obtain by a straightforward generalization of
previously known systems. We solve the resulting evolution equations
numerically for a Schwarzschild black hole in three spatial dimensions, and
find that the stability of the simulation is strongly dependent on the form of
the equations (i.e. the choice of parameters of the hyperbolic system),
independent of the numerics. For an appropriate range of parameters we can
evolve a single 3D black hole to -- , and are
apparently limited by constraint-violating solutions of the evolution
equations. We expect that our method should result in comparable times for
evolutions of a binary black hole system.Comment: 11 pages, 2 figures, submitted to PR
Standardized image interpretation and post-processing in cardiovascular magnetic resonance - 2020 update : Society for Cardiovascular Magnetic Resonance (SCMR): Board of Trustees Task Force on Standardized Post-Processing
With mounting data on its accuracy and prognostic value, cardiovascular magnetic resonance (CMR) is becoming an increasingly important diagnostic tool with growing utility in clinical routine. Given its versatility and wide range of quantitative parameters, however, agreement on specific standards for the interpretation and post-processing of CMR studies is required to ensure consistent quality and reproducibility of CMR reports. This document addresses this need by providing consensus recommendations developed by the Task Force for Post-Processing of the Society for Cardiovascular Magnetic Resonance (SCMR). The aim of the Task Force is to recommend requirements and standards for image interpretation and post-processing enabling qualitative and quantitative evaluation of CMR images. Furthermore, pitfalls of CMR image analysis are discussed where appropriate. It is an update of the original recommendations published 2013
A new measurement of the structure functions and in virtual Compton scattering at 0.33 (GeV/c)
The cross section of the reaction has been measured at
(GeV/c). The experiment was performed using the electron beam
of the MAMI accelerator and the standard detector setup of the A1
Collaboration. The cross section is analyzed using the low-energy theorem for
virtual Compton scattering, yielding a new determination of the two structure
functions P_LL}-P_{TT}/epsilon and which are linear combinations of
the generalized polarizabilities of the proton. We find somewhat larger values
than in the previous investigation at the same . This difference, however,
is purely due to our more refined analysis of the data. The results tend to
confirm the non-trivial -evolution of the generalized polarizabilities and
call for more measurements in the low- region ( 1 (GeV/c)).Comment: 9 pages, 10 figures. EPJA version. slight revisions in the text and
figure
3D simulations of linearized scalar fields in Kerr spacetime
We investigate the behavior of a dynamical scalar field on a fixed Kerr
background in Kerr-Schild coordinates using a 3+1 dimensional spectral
evolution code, and we measure the power-law tail decay that occurs at late
times. We compare evolutions of initial data proportional to f(r)
Y_lm(theta,phi) where Y_lm is a spherical harmonic and (r,theta,phi) are
Kerr-Schild coordinates, to that of initial data proportional to f(r_BL)
Y_lm(theta_BL,phi), where (r_BL,theta_BL) are Boyer-Lindquist coordinates. We
find that although these two cases are initially almost identical, the
evolution can be quite different at intermediate times; however, at late times
the power-law decay rates are equal.Comment: 12 pages, 9 figures, revtex4. Major revision: added figures, added
subsection on convergence, clarified discussion. To appear in Phys Rev
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