563 research outputs found
Flambée des prix alimentaires internationaux : opportunité ou désastre pour les populations les plus pauvres ?
Cet article propose et applique un cadre d'analyse pour l'Ă©tude des consĂ©quences de la flambĂ©e des prix des denrĂ©es alimentaires sur les populations pauvres des pays du Sud. Il met en Ă©vidence la complexitĂ© des mĂ©canismes Ă l'oeuvre et la diversitĂ© des cas. Parmi les grands ensembles rĂ©gionaux, l'Afrique Sub-saharienne apparaĂźt particuliĂšrement exposĂ©e Ă des impacts nĂ©gatifs, mais les situations sont contrastĂ©es d'une nation Ă l'autre. Trois pays sont retenus pour une analyse au niveau des marchĂ©s locaux et des mĂ©nages (Cameroun, Mali, SĂ©nĂ©gal). Au SĂ©nĂ©gal, la contagion aux prix alimentaires intĂ©rieurs est la plus importante, elle a des consĂ©quences nĂ©gatives sur les mĂ©nages, en particulier les plus pauvres. Au Mali par contre, on note trĂšs peu d'impacts sur les marchĂ©s domestiques. Le Cameroun illustre une situation intermĂ©diaire entre ces deux extrĂȘmes
The lateritic ore deposits of Brazil
Au Brésil, les mécanismes d'altération supergÚne ont conduit à la formation d'un épais recouvrement latéritique sur environ 65 % de la surface totale; dans des conditions particuliÚres, l'accumulation de certains métaux dans ce manteau peut atteindre le stade économique. La latéritisation des diverses roches mÚres, tout à fait spécifiques de chaque type de gisement, est intervenue pour l'essentiel au Tertiaire, pendant des épisodes de stabilité tectonique auxquels correspondent des surfaces d'aplanissement généralisées. Le rÎle des facteurs lithologiques, climatiques et morpho-tectoniques dans le mécanisme de genÚse des gisements latéritiques est discut
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Impact of fertilization on the firmness of cranberry (Vaccinium macrocarpon AIT.)
Abstract.
QuĂ©bec is one of the leading cranberry (Vaccinium macrocarpon Ait.) or called âAtokaâ in the Iroquoian language, producers in the world. Fertilization is a key management tool to reach high fruit yield and good quality. For example, in blueberries, rates and application methods of fertilizers can affect fruit firmness. N showed the greatest effect on the development, flowering, and productivity of the cranberry plant. On the other side, hand harvesting is preferred for marketing of fresh fruit since the physical abuse of mechanical harvesting reduces fruit firmness and substantially reduces market life. The objective of this research was to study the potential of firmness reflectance TA.TX2 Texture Analyzer as a means for measurement of fresh fruit firmness. Four experimental sites were established since 2014 on podzolic acid sandy soils containing more than 90% sand at Notre Dame-de-Lourdes and St-Louis-de-Blandford in central QuĂ©bec. The experimental design was a randomized complete block with cv. âStevensâ established on permanent plots comprised five N, three P, four K and S, and also two Mg, Cu and B doses. Berries were hand-harvested on 0.37 m2 areas, 2-3 weeks before commercial harvesting. The fruits from zero N treatment were best for firmness and economic profit. Although, These N application rates discourage a good relationship between commercial yield and fruit quality. In other hand, the zero N rate resulted in lowest yield production and high quality; the fruit had the greatest N (60 kg ha-1) rate was diminished significantly firmness of the cranberry fruit. Finally, the 45 kg N ha-1 rate produced high yield with the buildup and maintenance concept and poor fruit quality
Fuel burn reduction potential from delayed deceleration approaches
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012.Cataloged from department-submitted PDF version of thesis. This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 79-80).Changing aircraft operational procedures is one strategy that can be used to reduce fuel burn and mitigate environmental impacts of aviation in relatively short timeframes with existing aircraft types. One promising modification comes from increasing the use of Delayed Deceleration Approaches where the deceleration to the standard stabilized final approach speed occurs later, which keeps the aircraft in clean aerodynamic configuration with low thrust for as long as possible. Although such approaches can reduce fuel burn, in practice aircraft often decelerate much earlier. This may be for a variety of reasons, such as airspace restrictions, slower traffic ahead, air traffic controller technique and airline procedures and/or pilot technique. In this study, operational flight data has first been used to quantify the potential fuel burn savings associated with Delayed Deceleration Approaches. Aircraft that were observed to decelerate and configure flaps later in the approach had 30-40% lower fuel burn and carbon dioxide emissions below 10,000 ft compared to those that did not. Estimates of US system-wide fuel burn and emissions reduction potential from Delayed Deceleration Approaches have also been produced. Second, radar tracks of flights to different airport areas have been analyzed to help identify reasons for early decelerations. By observing the context of evolution of the less fuel efficient flights, the role of different potential factors such as preceding traffic, traffic mix, highly constrained airspace, runway interactions and severe weather conditions affecting the airspeed schedule of a given flight have been examined. Weather appeared to be a major parameter affecting the airspeed schedule, and air traffic procedures involving early decelerations appeared to have been used in dense and complex airspaces.by Jean-Marie Dumont.S.M
Diffusion of gold nanoclusters on graphite
We present a detailed molecular-dynamics study of the diffusion and
coalescence of large (249-atom) gold clusters on graphite surfaces. The
diffusivity of monoclusters is found to be comparable to that for single
adatoms. Likewise, and even more important, cluster dimers are also found to
diffuse at a rate which is comparable to that for adatoms and monoclusters. As
a consequence, large islands formed by cluster aggregation are also expected to
be mobile. Using kinetic Monte Carlo simulations, and assuming a proper scaling
law for the dependence on size of the diffusivity of large clusters, we find
that islands consisting of as many as 100 monoclusters should exhibit
significant mobility. This result has profound implications for the morphology
of cluster-assembled materials
Nianga, laboratoire de l'agriculture irriguée en moyenne vallée du Sénégal
Les actes de l'atelier "Nianga" réunissent des analyses et des points de vue de différents spécialistes qui s'interessent à l'expérience et au devenir de la culture irriguée dans la vallée alluviale de la région du fleuve Sénégal et de son insertion dans les sytÚmes de productio
On the Propagation of Slip Fronts at Frictional Interfaces
The dynamic initiation of sliding at planar interfaces between deformable and
rigid solids is studied with particular focus on the speed of the slip front.
Recent experimental results showed a close relation between this speed and the
local ratio of shear to normal stress measured before slip occurs (static
stress ratio). Using a two-dimensional finite element model, we demonstrate,
however, that fronts propagating in different directions do not have the same
dynamics under similar stress conditions. A lack of correlation is also
observed between accelerating and decelerating slip fronts. These effects
cannot be entirely associated with static local stresses but call for a dynamic
description. Considering a dynamic stress ratio (measured in front of the slip
tip) instead of a static one reduces the above-mentioned inconsistencies.
However, the effects of the direction and acceleration are still present. To
overcome this we propose an energetic criterion that uniquely associates,
independently on the direction of propagation and its acceleration, the slip
front velocity with the relative rise of the energy density at the slip tip.Comment: 15 pages, 6 figure
Collisions of particles in locally AdS spacetimes I. Local description and global examples
We investigate 3-dimensional globally hyperbolic AdS manifolds containing
"particles", i.e., cone singularities along a graph . We impose
physically relevant conditions on the cone singularities, e.g. positivity of
mass (angle less than on time-like singular segments). We construct
examples of such manifolds, describe the cone singularities that can arise and
the way they can interact (the local geometry near the vertices of ).
We then adapt to this setting some notions like global hyperbolicity which are
natural for Lorentz manifolds, and construct some examples of globally
hyperbolic AdS manifolds with interacting particles.Comment: This is a rewritten version of the first part of arxiv:0905.1823.
That preprint was too long and contained two types of results, so we sliced
it in two. This is the first part. Some sections have been completely
rewritten so as to be more readable, at the cost of slightly less general
statements. Others parts have been notably improved to increase readabilit
Comparing automated surveillance systems for detection of pathogen-related clusters in healthcare settings
BACKGROUND: Detection of pathogen-related clusters within a hospital is key to early intervention to prevent onward transmission. Various automated surveillance methods for outbreak detection have been implemented in hospital settings. However, direct comparison is difficult due to heterogenicity of data sources and methodologies. In the hospital setting, we assess the performance of three different methods for identifying microbiological clusters when applied to various pathogens with distinct occurrence patterns. METHODS: In this retrospective cohort study we use WHONET-SaTScan, CLAR (CLuster AleRt system) and our currently used percentile-based system (P75) for the means of cluster detection. The three methods are applied to the same data curated from 1st January 2014 to 31st December 2021 from a tertiary care hospital. We show the results for the following case studies: the introduction of a new pathogen with subsequent endemicity, an endemic species, rising levels of an endemic organism, and a sporadically occurring species. RESULTS: All three cluster detection methods showed congruence only in endemic organisms. However, there was a paucity of alerts from WHONET-SaTScan (nâ=â9) compared to CLAR (nâ=â319) and the P75 system (nâ=â472). WHONET-SaTScan did not pick up smaller variations in baseline numbers of endemic organisms as well as sporadic organisms as compared to CLAR and the P75 system. CLAR and the P75 system revealed congruence in alerts for both endemic and sporadic organisms. CONCLUSIONS: Use of statistically based automated cluster alert systems (such as CLAR and WHONET-Satscan) are comparable to rule-based alert systems only for endemic pathogens. For sporadic pathogens WHONET-SaTScan returned fewer alerts compared to rule-based alert systems. Further work is required regarding clinical relevance, timelines of cluster alerts and implementation
The Glauber model and the heavy ion reaction cross section
We reexamine the Glauber model and calculate the total reaction cross section
as a function of energy in the low and intermediate energy range, where many of
the corrections in the model, are effective.
The most significant effect in this energy range is by the modification of
the trajectory due to the Coulomb field. The modification in the trajectory due
to nuclear field is also taken into account in a self consistent way.
The energy ranges in which particular corrections are effective, are
quantified and it is found that when the center of mass energy of the system
becomes 30 times the Coulomb barrier, none of the trajectory modification to
the Glauber model is really required.
The reaction cross sections for light and heavy systems, right from near
coulomb barrier to intermediate energies have been calculated. The exact
nuclear densities and free nucleon-nucleon (NN) cross sections have been used
in the calculations. The center of mass correction which is important for light
systems, has also been taken into account.
There is an excellent agreement between the calculations with the modified
Glauber model and the experimental data. This suggests that the heavy ion
reactions in this energy range can be explained by the Glauber model in terms
of free NN cross sections without incorporating any medium modification.Comment: RevTeX, 21 pages including 9 Postscript figures, submitted to Phys.
Rev.
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