6,500 research outputs found
Labyrinthic granular landscapes
We have numerically studied a model of granular landscape eroded by wind. We
show the appearance of labyrinthic patterns when the wind orientation turns by
. The occurence of such structures are discussed. Morever, we
introduce the density of ``defects'' as the dynamic parameter governing
the landscape evolution. A power law behavior of is found as a function
of time. In the case of wind variations, the exponent (drastically) shifts from
2 to 1. The presence of two asymptotic values of implies the
irreversibility of the labyrinthic formation process.Comment: 3 pages, 3 figure, RevTe
Bounds on the Magnetic Fields in the Radiative Zone of the Sun
We discuss bounds on the strength of the magnetic fields that could be buried
in the radiative zone of the Sun. The field profiles and decay times are
computed for all axisymmetric toroidal Ohmic decay eigenmodes with lifetimes
exceeding the age of the Sun. The measurements of the solar oblateness yield a
bound <~ 7 MG on the strength of the field. A comparable bound is expected to
come from the analysis of the splitting of the solar oscillation frequencies.
The theoretical analysis of the double diffusive instability also yields a
similar bound. The oblateness measurements at their present level of
sensitivity are therefore not expected to measure a toroidal field
contribution.Comment: 15 pages, 6 figure
Patterns in hydraulic ripples with binary granular mixtures
An experimental study of a binary granular mixture submitted to a transient
shear flow in a cylindrical container is reported. The formation of ripples
with a spiral shape is observed. The appearance of phase segregation in those
spiral patterns is shown. The relative grain size bewteen sand species is found
to be a relevant parameter leading to phase segregation. However, the relative
repose angle is an irrelevant parameter. The formation of sedimentary
structures is also presented. They result from a ripple climbing process. The
``sub-critical'' or ``super-critical'' character of the lamination patterns is
shown to depend on the rotation speed of the container.Comment: 9 pages, 9 figures, LateX (using elsart package), submitted to Phys.
Ripple and kink dynamics
We propose a relevant modification of the Nishimori-Ouchi model [{\em Phys.
Rev. Lett.} {\bf 71}, 197 (1993)] for granular landscape erosion. We explicitly
introduce a new parameter: the angle of repose , and a new process:
avalanches. We show that the parameter leads to an asymmetry of the
ripples, as observed in natural patterns. The temporal evolution of the maximum
ripple height is limited and not linear, according to recent
observations. The ripple symmetry and the kink dynamics are studied and
discussed.Comment: 7 pages, 10 figure, RevTe
Fine and ultrafine particle number and size measurements from industrial combustion processes : primary emissions field data
This study is to our knowledge the first to present the results of on-line measurements of residual nanoparticle numbers downstream of the flue gas treatment systems of a wide variety of medium- and large-scale industrial installations. Where available, a semi-quantitative elemental composition of the sampled particles is carried out using a Scanning Electron Microscope coupled with an Energy Dispersive Spectrometer (SEM-EDS). The semi-quantitative elemental composition as a function of the particle size is presented. EU's Best Available Technology documents (BAT) show removal efficiencies of Electrostatic Precipitator (ESP) and bag filter dedusting systems exceeding 99% when expressed in terms of weight. Their efficiency decreases slightly for particles smaller than 1 mu m but when expressed in terms of weight, still exceeds 99% for bag filters and 96% for ESP. This study reveals that in terms of particle numbers, residual nanoparticles (NP) leaving the dedusting systems dominate by several orders of magnitude. In terms of weight, all installations respect their emission limit values and the contribution of NP to weight concentrations is negligible, despite their dominance in terms of numbers. Current World Health Organisation regulations are expressed in terms of PM2.5 wt concentrations and therefore do not reflect the presence or absence of a high number of NP. This study suggests that research is needed on possible additional guidelines related to NP given their possible toxicity and high potential to easily enter the blood stream when inhaled by humans
Using risk adjustment to improve the interpretation of global inpatient pediatric antibiotic prescribing.
Objectives
Assessment of regional pediatric last-resort antibiotic utilization patterns is hampered by potential confounding from population differences. We developed a risk-adjustment model from readily available, internationally used survey data and a simple patient classification to aid such comparisons.
Design
We investigated the association between pediatric conserve antibiotic (pCA) exposure and patient / treatment characteristics derived from global point prevalence surveys of antibiotic prescribing, and developed a risk-adjustment model using multivariable logistic regression. The performance of a simple patient classification of groups with different expected pCA exposure levels was compared to the risk model.
Setting
226 centers in 41 countries across 5 continents.
Participants
Neonatal and pediatric inpatient antibiotic prescriptions for sepsis/bloodstream infection for 1281 patients.
Results
Overall pCA exposure was high (35%), strongly associated with each variable (patient age, ward, underlying disease, community acquisition or nosocomial infection and empiric or targeted treatment), and all were included in the final risk-adjustment model. The model demonstrated good discrimination (c-statistic = 0.83) and calibration (p = 0.38). The simple classification model demonstrated similar discrimination and calibration to the risk model. The crude regional pCA exposure rates ranged from 10.3% (Africa) to 67.4% (Latin America). Risk adjustment substantially reduced the regional variation, the adjusted rates ranging from 17.1% (Africa) to 42.8% (Latin America).
Conclusions
Greater comparability of pCA exposure rates can be achieved by using a few easily collected variables to produce risk-adjusted rates
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