1,721,012 research outputs found
Introduction of a spring crop in the irrigable land of the Northern highlands of Vietnam : an approach using agroclimatic modelling.
No full textL'objectif est d'évaluer sur le plan agro-climatique les options de réalisation d'une culture de printemps dans les hautes vallées du Nord du Vietnam. A partir d'hypothèses sur les contraintes agro-climatiques s'exerçant sur ces options, un modèle de simulation et le dispositif expérimental permettant de le caler et de l'évaluer ont été élaborés. Une expérimentation virtuelle replaçant les cultures de printemps envisagées (riz, riz « aérobie », maïs et soja) dans le climat de trois régions contrastées sur ce plan a ensuite été réalisée, le long d'un gradient d'altitude, et sous différentes modalités techniques, notamment de dates de semis. Cette démarche a été appliquée successivement aux deux grands cas de figure rencontrés dans les montagnes : irrigation des parcelles dès le printemps, et conduite en régime pluvial (irrigation praticable seulement pour le cycle estival). Elle a conduit à identifier, pour chacun de ces cas de figure et chacune des régions et cultures étudiées des fenêtres de semis favorables, intervalles de dates de semis pour lesquelles la culture de printemps présente peu de risques. La taille de cette fenêtre constitue ainsi un indicateur synthétique de la contrainte climatique pour une culture donnée dans un lieu donné : plus cette fenêtre est étroite, plus on peut s'attendre à ce qu'il soit délicat pour les producteurs de pratiquer la culture. Les résultats confirment clairement que même lorsque l'eau d'irrigation est abondante, le climat des montagnes du Vietnam ne permet pas partout de pratiquer une culture de printemps. Les risques identifiés sont la destruction par le froid pendant les stades précoces de la croissance végétative, l'allongement du cycle au-delà de la date où le riz irrigué d'été doit être installé selon la pratique actuelle, l'obtention de rendements nettement abaissés du fait de la faiblesse du rayonnement global et des températures pendant la première partie de la saison. Pour ce contexte irrigué, la culture qui échappe le mieux à ces contraintes dans les simulations est le soja, suivie du maïs et du riz conduit en semis en plein champ. Le riz semé en pépinière et repiqué est apparu comme le plus sensible aux contraintes de températures.En conditions pluviales, la culture de printemps est nettement plus délicate tout particulièrement à cause des retards de levée et des stress hydriques pendant la phase de croissance végétative liés aux faibles précipitations de début de saison. Le soja reste la culture pour laquelle la contrainte de durée de cycle est la plus faible, mais son rendement simulé est fortement réduit par les stress hydriques. Le riz « aérobie » et le maïs sont des options envisageables en conditions strictement pluviales aux altitudes relativement modestes dans tous les climats étudiés. La géographie de l'extension des cultures de printemps au Vietnam est ainsi esquissée. Des perspectives de recherche sont proposées en vue d'accroître cette aire d'extension. Outre ces acquis importants pour l'agriculture locale, cette thèse confirme l'intérêt et l'efficacité d'une approche de modélisation ad hoc pour ce type de question agro-climatique.The goal of this thesis was to assess the agro-climatic feasibility of introducing a supplementary crop during the spring season in the high valleys of the mountainous northern Vietnam. From hypotheses drawn about the way climate constrained such crops, a simulation model and the experimental device required for calibrating and evaluating it were elaborated. A virtual experiment was carried out in order to submit the candidate crops (rice, “aerobic rice”, maize and soybean) under the contrasted climates of three regions, along the elevation gradient and under several technical management, especially sowing dates. This approach was applied consecutively to the two major cases occurring in these mountains: crop irrigated during the whole spring, and rainfed crop (land irrigable during summer only). This approach led to identify, for each of these two cases and for each of the studied regions and crops, favourable sowing windows, i.e. intervals of sowing dates for which the risks associated to spring crop are low. The size of such windows provides a synthetic indicator of the climatic constraint for a given crop at a given place: the narrower the window, the more difficult it is expected to be for farmers to practice the option.Results clearly confirmed that even if irrigation water is abundant, the climate of the mountains in Vietnam does not allow practicing the spring crop everywhere. The risks that were identified were crop destruction by lethally cold temperature during early vegetative stages, maturity delayed beyond the date at which the irrigated rice of summer must have been sown according to current practice, and obtaining yield neatly decreased due to low global radiation and temperature during the first half of the season. Under irrigated conditions, the simulated crop that best escaped these constraints was soybean, followed by maize and direct seeded rice. Rice sown in nurseries and transplanted showed more sensitive to temperature constraints.Spring crop showed strongly trickier under rainfed conditions, especially due to delays in seedlings emergence and water stresses during vegetative growth, in relation with low rainfall during the early part of the season. Soybean remained the crop with the shortest duration, but its simulated yield was strongly reduced by water stresses. “Aerobic rice” and maize were possible options under fully rainfed regime at relatively low elevations only, under any of the regional climates studied. Thus, the feasibility area of spring crops was thus sketched. Research perspectives were proposed, aiming at increasing this area. Additionally to these results, targeted at serving local agriculture, this work confirmed the value and effectiveness of an ad hoc modelling approach for agro-climatic studies of this kind
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Produire avec moins d'intrants, réflexions d'agronome et perspectives
No full textContact: [email protected] Événement(s) lié(s) : - CER Le Havre, Université des Métiers; Le Havre (FRA) - (2008-12-04 - 2008-12-05)National audienc
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