1,092 research outputs found
Effective diffusivity of passive scalars in rotating turbulence
We use direct numerical simulations to compute turbulent transport
coefficients for passive scalars in turbulent rotating flows. Effective
diffusion coefficients in the directions parallel and perpendicular to the
rotations axis are obtained by studying the diffusion of an imposed initial
profile for the passive scalar, and calculated by measuring the scalar average
concentration and average spatial flux as a function of time. The Rossby and
Schmidt numbers are varied to quantify their effect on the effective diffusion.
It is find that rotation reduces scalar diffusivity in the perpendicular
direction. The perpendicular diffusion can be estimated from mixing length
arguments using the characteristic velocities and lengths perpendicular to the
rotation axis. Deviations are observed for small Schmidt numbers, for which
turbulent transport decreases and molecular diffusion becomes more significant.Comment: 10 pages, 13 figures. Slightly modified version to address referees'
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Colchicine for children with pericarditis: systematic review of clinical studies
OBJECTIVE: To review the evidence for the efficacy and safety of colchicine in children with pericarditis. DESIGN: Systematic review. SEARCH STRATEGY: The following databases were searched for studies about colchicine in children with pericarditis (June 2015): Cochrane Central, Medline, EMBASE and LILACS. ELIGIBILITY CRITERIA: All observational and experimental studies on humans with any length of follow-up and no limitations on language or publication status were included. The outcomes studied were recurrences of pericarditis and adverse events. DATA EXTRACTION: Two authors extracted data and assessed quality of included studies using the Cochrane risk of bias tool for non-randomised trials. RESULTS: Two case series and nine case reports reported the use of colchicine in a total of 86 children with pericarditis. Five articles including 74 paediatric patients were in favour of colchicine in preventing further pericarditis recurrences. Six studies including 12 patients showed that colchicine did not prevent recurrences of pericarditis. LIMITATIONS: No randomised controlled trials (RCTs) were found. CONCLUSIONS: Although colchicine is an established treatment for pericarditis in adults, it is not routinely used in children. There is not enough evidence to support or discourage the use of colchicine in children with pericarditis. Further research in the form of large double-blind RCTs is needed to establish the efficacy of colchicine in children with pericarditis
Intermittency in Hall-magnetohydrodynamics with a strong guide field
We present a detailed study of intermittency in the velocity and magnetic
field fluctuations of compressible Hall-magnetohydrodynamic turbulence with an
external guide field. To solve the equations numerically, a reduced model valid
when a strong guide field is present is used. Different values for the ion skin
depth are considered in the simulations. The resulting data is analyzed
computing field increments in several directions perpendicular to the guide
field, and building structure functions and probability density functions. In
the magnetohydrodynamic limit we recover the usual results with the magnetic
field being more intermittent than the velocity field. In the presence of the
Hall effect, field fluctuations at scales smaller than the ion skin depth show
a substantial decrease in the level of intermittency, with close to monofractal
scaling.Comment: 10 pages, 8 figure
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