8,511 research outputs found
Nonlinear stratospheric variability: multifractal detrended fluctuation analysis and singularity spectra
Characterising the stratosphere as a turbulent system, temporal fluctuations
often show different correlations for different time scales as well as
intermittent behaviour that cannot be captured by a single scaling exponent. In
this study, the different scaling laws in the long term stratospheric
variability are studied using Multifractal de-trended Fluctuation Analysis. The
analysis is performed comparing four re-analysis products and different
realisations of an idealised numerical model, isolating the role of topographic
forcing and seasonal variability, as well as the absence of climate
teleconnections and small-scale forcing. The Northern Hemisphere (NH) shows a
transition of scaling exponents for time scales shorter than about one year,
for which the variability is multifractal and scales in time with a power law
corresponding to a red spectrum, to longer time scales, for which the
variability is monofractal and scales in time with a power law corresponding to
white noise. Southern Hemisphere (SH) variability also shows a transition at
annual scales. The SH also shows a narrower dynamical range in multifractality
than the NH, as seen in the generalised Hurst exponent and in the singularity
spectra. The numerical integrations show that the models are able to reproduce
the low-frequency variability but are not able to fully capture the shorter
term variability of the stratosphere
Reviewing model calculations of the Collins fragmentation function
The Collins fragmentation function describes a left/right asymmetry in the
fragmentation of a transversely polarized quark into a hadron in a jet. Four
different model calculations of the Collins function have been presented in the
literature. While based on the same concepts, they lead to different results
and in particular to different signs for the Collins function. The purpose of
the present work is to review the features of these models and correct some
errors made in previous calculations. A full study of the parameter dependence
and the possible modifications to these models is beyond the scope of the
paper. However, some general conclusions are drawn
Static and slowly rotating neutron stars in scalar-tensor theory with self-interacting massive scalar field
Binary pulsar observations and gravitational wave detections seriously
constrained scalar-tensor theories with massless scalar field allowing only
small deviations from general relativity. If we consider a nonzero mass of the
scalar field, though, significant deviations from general relativity are
allowed for values of the parameters that are in agreement with the
observations. In the present paper we extend this idea and we study
scalar-tensor theory with massive field with self-interaction term in the
potential. The additional term suppresses the scalar field in the neutron star
models in addition to the effect of the mass of the scalar field but still,
large deviations from pure GR can be observed for values of the parameters that
are in agreement with the observations.Comment: 9 pages, 5 figure
Towards a gauge-polyvalent Numerical Relativity code
The gauge polyvalence of a new numerical code is tested, both in
harmonic-coordinate simulations (gauge-waves testbed) and in
singularity-avoiding coordinates (simple Black-Hole simulations, either with or
without shift). The code is built upon an adjusted first-order
flux-conservative version of the Z4 formalism and a recently proposed family of
robust finite-difference high-resolution algorithms. An outstanding result is
the long-term evolution (up to 1000M) of a Black-Hole in normal coordinates
(zero shift) without excision.Comment: to appear in Physical Review
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Dynamics of Dinitrosyl Iron Complex (DNIC) Formation with Low Molecular Weight Thiols.
Dinitrosyl iron complexes (DNICs) are ubiquitous in mammalian cells and tissues producing nitric oxide (NO) and have been argued to play key physiological and pathological roles. Nonetheless, the mechanism and dynamics of DNIC formation in aqueous media remain only partially understood. Here, we report a stopped-flow kinetics and density functional theory (DFT) investigation of the reaction of NO with ferrous ions and the low molecular weight thiols glutathione (GSH) and cysteine (CysSH) as well as the peptides WCGPC and WCGPY to produce DNICs in pH 7.4 aqueous media. With each thiol, a two-stage reaction pattern is observed. The first stage involves several rapidly established pre-equilibria leading to a ferrous intermediate concluded to have the composition FeII(NO)(RS)2(H2O)x (C). In the second stage, C undergoes rate-limiting, unimolecular autoreduction to give thiyl radical (RS•) plus the mononitrosyl Fe(I) complex FeI(NO)(RS)(H2O)x following the reactivity order of CysSH > WCGPC > WCGPY > GSH. Time course simulations using the experimentally determined kinetics parameters demonstrate that, at a NO flux characteristic of inflammation, DNICs will be rapidly formed from intracellular levels of ferrous iron and thiols. Furthermore, the proposed mechanism offers a novel pathway for S-nitroso thiol (RSNO) formation in a biological environment
Dynamics of relativistic solitons
Relativistic solitons are self-trapped, finite size, electromagnetic waves of
relativistic intensity that propagate without diffraction spreading. They have
been predicted theoretically within the relativistic fluid approximation, and
have been observed in multi-dimensional particle in cell simulations of laser
pulse interaction with the plasma. Solitons were observed in the laser
irradiated plasmas with the proton imaging technique as well. This paper
reviews many theoretical results on relativistic solitons in electron-ion
plasmas.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
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