231 research outputs found
Basin Focal Project Niger
Challenge Program Water and Food: Basin Focal Project NIGER
Faced with increasing food and water insecurity as a result of climatic and
anthropogenic (demography, land use) changes, the CGIAR Challenge Program
for Water and Food commissioned research in 10 river basins to study the links
between water, food and poverty. Looking at the Niger river basin, we carry out
a diagnosis of the hydrologic and agronomic potential, before attempting to
identify how good agricultural water management may reduce vulnerability in the
region, and preserve local ecosystems. Major future threats and opportunities,
as well as the influence of institutions on water and agricultural development are
discussed.
The study indicated that while many technical solutions are available and
identified, institutional issues as well as generalized poverty undermine their
sustained uptake by communities. Further research is required in order to
determine how to overcome socio-economic and institutional issues
Beating the teapot effect
We investigate the dripping of liquids around solid surfaces in the regime of
inertial flows, a situation commonly encountered with the so-called "teapot
effect". We demonstrate that surface wettability is an unexpected key factor in
controlling flow separation and dripping, the latter being completely
suppressed in the limit of superhydrophobic substrates. This unforeseen
coupling is rationalized in terms of a novel hydro-capillary adhesion
framework, which couples inertial flows to surface wettability effects. This
description of flow separation successfully captures the observed dependence on
the various experimental parameters - wettability, flow velocity, solid surface
edge curvature-. As a further illustration of this coupling, a real-time
control of dripping is demonstrated using electro-wetting for contact angle
actuation.Comment: 4 pages; movies at http://lpmcn.univ-lyon1.fr/~lbocque
Reshaping and Capturing Leidenfrost drops with a magnet
Liquid oxygen, which is paramagnetic, also undergoes Leidenfrost effect at
room temperature. In this article, we first study the deformation of oxygen
drops in a magnetic field and show that it can be described via an effective
capillary length, which includes the magnetic force. In a second part, we
describe how these ultra-mobile drops passing above a magnet significantly slow
down and can even be trapped. The critical velocity below which a drop is
captured is determined from the deformation induced by the field.Comment: Published in Physics of Fluids (vol. 25, 032108, 2013)
http://pof.aip.org/resource/1/phfle6/v25/i3/p032108_s1?isAuthorized=n
Gravitational oscillations of a liquid column
We report gravity oscillations of a liquid column partially immersed in a
bath of liquid. We stress in particular some peculiarities of this system,
namely (i) the fact that the mass of this oscillator constantly changes with
time; (ii) the singular character of the beginning of the rise, for which the
mass of the oscillator is zero; (iii) the sources of dissipation in this
system, which is found to be dominated at low viscosity by the entrance (or
exit) effects, leading to a long-range damping of the oscillations. We conclude
with some qualitative description of a second-order phenomenon, namely the
eruption of a jet at the beginning of the rise.Comment: 22 pages, pdf. Submitted to Physics of Fluid
Making a splash with water repellency
A 'splash' is usually heard when a solid body enters water at large velocity.
This phenomena originates from the formation of an air cavity resulting from
the complex transient dynamics of the free interface during the impact. The
classical picture of impacts on free surfaces relies solely on fluid inertia,
arguing that surface properties and viscous effects are negligible at
sufficiently large velocities. In strong contrast to this large-scale
hydrodynamic viewpoint, we demonstrate in this study that the wettability of
the impacting body is a key factor in determining the degree of splashing. This
unexpected result is illustrated in Fig.1: a large cavity is evident for an
impacting hydrophobic sphere (1.b), contrasting with the hydrophilic sphere's
impact under the very same conditions (1.a). This unforeseen fact is
furthermore embodied in the dependence of the threshold velocity for air
entrainment on the contact angle of the impacting body, as well as on the ratio
between the surface tension and fluid viscosity, thereby defining a critical
capillary velocity. As a paradigm, we show that superhydrophobic impacters make
a big 'splash' for any impact velocity. This novel understanding provides a new
perspective for impacts on free surfaces, and reveals that modifications of the
detailed nature of the surface -- involving physico-chemical aspects at the
nanometric scales -- provide an efficient and versatile strategy for
controlling the water entry of solid bodies at high velocity.Comment: accepted for publication in Nature Physic
Diagnostic criteria for multiple sclerosis: 2010 Revisions to the McDonald criteria
New evidence and consensus has led to further revision of the McDonald Criteria for diagnosis of multiple sclerosis. The use of imaging for demonstration of dissemination of central nervous system lesions in space and time has been simplified, and in some circumstances dissemination in space and time can be established by a single scan. These revisions simplify the Criteria, preserve their diagnostic sensitivity and specificity, address their applicability across populations, and may allow earlier diagnosis and more uniform and widespread use. Ann Neurol 201
Interferon β-1a in relapsing multiple sclerosis: four-year extension of the European IFNβ-1a Dose-C omparison Study
Background: Multiple sclerosis (MS) is a chronic disease requiring long-term monitoring of treatment. Objective: To assess the four-year clinical efficacy of intramuscular (IM) IFNb-1a in patients with relapsing MS from the European IFNb-1a Dose-C omparison Study. Methods: Patients who completed 36 months of treatment (Part 1) of the European IFNb-1a Dose-C omparison Study were given the option to continue double-blind treatment with IFNb-1a 30 mcg or 60 mcg IM once weekly (Part 2). Analyses of 48-month data were performed on sustained disability progression, relapses, and neutralizing antibody (NA b) formation. Results: O f 608/802 subjects who completed 36 months of treatment, 493 subjects continued treatment and 446 completed 48 months of treatment and follow-up. IFNb-1a 30 mcg and 60 mcg IM once weekly were equally effective for up to 48 months. There were no significant differences between doses over 48 months on any of the clinical endpoints, including rate of disability progression, cumulative percentage of patients who progressed (48 and 43, respectively), and annual relapse rates; relapses tended to decrease over 48 months. The incidence of patients who were positive for NAbs at any time during the study was low in both treatment groups. Conclusion: C ompared with 60-mcg IM IFNb-1a once weekly, a dose of 30 mcg IM IFNb-1a once weekly maintains the same clinical efficacy over four years
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