1,568 research outputs found
OPTIMIZING AND PROMOTING MECHANICAL WEED CONTROL IN ARABLE CROPS
Within an overall strategy of weed flora management, mechanical weed control practices are complementary solutions to agronomic levers (crop rotation, tillage...) in weed control. Acquiring knowledge and communicating on the effectiveness of mechanical practices and tools appear essential. The "Mechanical Weed Control" project in France conducted between 2009 and 2012 made progress in this regard. The project shows that research activities are to be continued (experimentation, analysis of practices) and should be complemented by promotion that focuses on participatory approaches where farmers are involved in the implementation of these new practices
Quasi-equilibrium states in thermotropic liquid crystals studied by multiple quantum NMR
We study the nature of the quasiinvariants in nematic 5CB and measure their
relaxation times by encoding the multiple quantum coherences of the states
following the JB pulse pair on two orthogonal bases, Z and X. The experiments
were also performed in powder adamantane at 301 K which is used as a reference
compound having only one dipolar quasiinvariant. We show that the evolution of
the quantum states during the build up of the quasi-equilibrium state in 5CB
prepared under the S condition is similar to the case of adamantane and that
their quasi-equilibrium density operators have the same tensor structure. In
contrast, the second constant of motion, whose explicit operator form is not
known, involves a richer composition of multiple quantum coherences on the X
basis of even order, in consistency with the truncation inherent in its
definition. We exploited the exclusive presence coherences 4, 6, 8, besides 0
and 2 under the W condition to measure the spin-lattice relaxation time T_{W}
accurately, so avoiding experimental difficulties that usually impair dipolar
order relaxation measurement such as Zeeman contamination at high fields, and
also superposition of the different quasiinvariants. This procedure opens the
possibility of measuring the spin-lattice relaxation of a quasiinvariant
independent of the Zeeman and S reservoirs, so incorporating a new relaxation
parameter useful for studying the complex molecular dynamics in mesophases. In
fact, we report the first measurement of T_{W} in a liquid crystal at high
magnetic fields. The comparison of the obtained value with the one
corresponding to a lower field (16 MHz) points out that the relaxation of the
W-order strongly depends on the intensity of the external magnetic field,
similarly to the case of the S reservoir, indicating that the relaxation of the
W-quasiinvariant is also governed by the cooperative molecular motions.Comment: 7 figures. http://www.famaf.unc.edu.ar/series/AFis2005.ht
Optical microrheology using rotating laser-trapped particles
We demonstrate an optical system that can apply and accurately measure the
torque exerted by the trapping beam on a rotating birefringent probe particle.
This allows the viscosity and surface effects within liquid media to be
measured quantitatively on a micron-size scale using a trapped rotating
spherical probe particle. We use the system to measure the viscosity inside a
prototype cellular structure.Comment: 5 pages, 4 figures. v2: bibliographic details, minor text correction
Medland 2020, une parole partagée sur les forêts méditerranéennes et leurs produits
En proposant, à travers cet article, un regard extérieur sur le projet Medland 2020, l’association Forêt Méditerranéenne s’est prêtée à un exercice difficile, mais ô combien stimulant, puisqu’il touche au cœur de ses réflexions depuis maintenant 35 ans. Chaque expérience présentée dans ce numéro et réalisée dans le cadre de projets de coopération de l’Union européenne, participe à un cadre commun de gestion des territoires méditerranéens en promouvant l’utilisation et la protection des ressources naturelles, la valorisation sociale et économique de ces territoires... Cet article tente d’analyser en quoi la mise en commun et la capitalisation de ces résultats peut apporter un plus aux acteurs de la foresterie méditerranéenne..
Medland 2020, A voice in common for Mediterranean forests and their products
In this article, the association Forêt Méditerranéenne seeks to offer an outsider’s perspective on the Medland 2020 project. A difficult task indeed, but worth every effort because it reaches into the very heart of the association’s preoccupations over the last 35 years. All the experiments and experience presented in this issue took place as part of the European Union’s projects for cooperation, contributing to a shared framework for the management of Mediterranean regions and localities by fostering the use and protection of natural resources and making the most, both economically and socially, out of these territories... This article attempts to analyse how pooling the results and sharing acquired knowhow can boost the success of all those involved in Mediterranean forestry
THE COST STRUCTURE OF MICROFINANCE INSTITUTIONS IN EASTERN EUROPE AND CENTRAL ASIA
Microfinance institutions are important, particularly in developing countries, because they expand the frontier of financial intermediation by providing loans to those traditionally excluded from formal financial markets. This paper presents the first systematic statistical examination of the performance of MFIs operating in Eastern Europe and Central Asia. A cost function is estimated for MFIs in the region from 1999-2004. First, the presence of subsidies is found to be associated with higher MFI costs. When output is measured as the number of loans made, we find that MFIs become more efficient over time and that MFIs involved in the provision of group loans and loans to women have lower costs. However, when output is measured as volume of loans rather than their number, this last finding is reversed. This may be due to the fact that such loans are smaller in size; thus for a given volume more loans must be made.http://deepblue.lib.umich.edu/bitstream/2027.42/40195/3/wp809.pd
Two-Photon Doppler cooling of alkaline-earth-metal and ytterbium atoms
A new possibility of laser cooling of alkaline-earth-metal and Ytterbium
atoms using a two-photon transition is analyzed. We consider a -
transition, with excitation in near resonance with the
level. This greatly increases the two-photon transition rate, allowing an
effective transfer of momentum. The experimental implementation of this
technique is discussed and we show that for Calcium, for example, two-photon
cooling can be used to achieve a Doppler limit of 123 microKelvin. The
efficiency of this cooling scheme and the main loss mechanisms are analyzed.Comment: 7 pages, 5 figure
Strain Effects on Point Defects and Chain-Oxygen Order-Disorder Transition in 123-Structure Cuprate Superconductors
The energetics of Schottky defects in 123 cuprate superconductor series, (where RE = lanthandies) and (AE =
alkali-earths), were found to have unusual relations if one considers only the
volumetric strain. Our calculations reveal the effect of non-uniform changes of
interatomic distances within the RE-123 structures, introduced by doping
homovalent elements, on the Schottky defect formation energy. The energy of
formation of Frenkel Pair defects, which is an elementary disordering event, in
123 compounds can be substantially altered under both stress and chemical
doping. Scaling the oxygen-oxygen short-range repulsive parameter using the
calculated formation energy of Frenkel pair defects, the transition temperature
between orthorhombic and tetragonal phases is computed by quasi-chemical
approximations (QCA). The theoretical results illustrate the same trend as the
experimental measurements in that the larger the ionic radius of RE, the lower
the orthorhombic/tetragonal phase transition temperature. This study provides
strong evidence of the strain effects on order-disorder transition due to
oxygens in the CuO chain sites.Comment: In print Phys Rev B (2004
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