Clarté cognitive et apprentissage de la lecture-écriture

Apprendre à lire c'est entrer dans l'écrit, comprendre et intégrer un système aux formes complexes. La clarté cognitive faciliterait la compréhension et la structuration progressive de la langue écrite. Comment se met-elle en place, et que font les enseignants dans leurs pratiques de classe pour aller dans ce sens. Quant aux méthodes de lecture, quelles aides peuvent-elles apporter

Esca, BDA and Eutypiosis: foliar symptoms, trunk lesions and fungi observed in diseased vinestocks in two vineyards in Alsace

The French vineyard is affected by three principal wood diseases: Eutypa dieback, esca and black dead arm (BDA). Phaeomoniella chlamydospora, Phaeocremonium aleophilum, Eutypa lata, Fomitiporia mediterranea, Diplodia seriata, Diplodia mutila and Neofusicoccum parvum are the main fungi isolated in France and associated with grapevine trunk diseases. The aim of this study was to highlight the type of wood lesions and the fungus present in the Alsace vineyards (France) and to compare it with those identified in the other french vine-growing regions or with the German vineyards. Therefore, we have studied two vineyards with two different grapevine varieties ('Auxerrois', 'Gewürztraminer'). The foliar symptoms showed that the plots planted with 'Auxerrois' and 'Gewürztraminer' varieties had respectively 12 and 21 % grapevines with symptoms in 2005. Different cross sections were made on trunks and arms of 55 vines showing foliar symptoms, totalizing 162 microbiological isolations. Visual characterisations of the different lesions were described. The isolations made from the different necrosis showed the presence of species of fungi involved in grapevine trunk diseases and other fungi. Microbiological observations showed that for the Auxerrois vineyard the majority of the vines were infected with D. seriata, P. chlamydospora, E. lata and F. mediterranea. In the Gewürztraminer vineyard, the fungus most frequently isolated was P. chlamydospora, followed by D. seriata. The presence of D. seriata in different parts of the grapevine wood and in young wood is related to the severe damages observed on the vegetation.

Late harvest as factor affecting esca and Botryosphaeria dieback prevalence of vineyards in the Alsace region of France

The decline of grapevines due to esca and Botryosphaeria dieback (Bot. dieback) is a serious problem in the Alsace region of France. A survey of 82 vineyards over 8 years showed that among a set of agronomical and cultural variables, esca and Bot. dieback prevalence correlated to the harvest dates, especially late harvest dates for the production of sweet wines. The interpretation of this finding that points to the carbon balance of the vine and its reserves status as possible causation is discussed. Under this hypothesis the data also point to climatic variables as factors in the disease epidemiology, with a lag phase of about one year.

Surface spin magnetism controls the polarized exciton emission from CdSe nanoplatelets

The surface of nominally diamagnetic colloidal CdSe nanoplatelets can demonstrate paramagnetism owing to the uncompensated spins of dangling bonds (DBSs). We reveal that by optical spectroscopy in high magnetic fields up to 15 Tesla using the exciton spin as probe of the surface magnetism. The strongly nonlinear magnetic field dependence of the circular polarization of the exciton emission is determined by the DBS and exciton spin polarization as well as by the spin-dependent recombination of dark excitons. The sign of the exciton-DBS exchange interaction can be adjusted by the nanoplatelet growth conditions

Conidia dispersal of Diplodia species in a French vineyard

Diseases caused by species of Botryosphaeriaceae lead to significant losses of grape yield. Species in this family produce foliar symptoms similar to, but distinguishable from esca, and the diseases they cause are generally named black dead arm (BDA). Botryosphaeriaceae species are ascomycetes frequently isolated from grapevine stocks showing decline or dieback symptoms. It is therefore useful to know what is the spore dissemination period of Botryosphaeriaceae in the vineyard. The objective of this study was to determine the peak periods of conidial release by some Diplodia spp. in the Botryosphaeriaceae in grapevines and to ascertain the climatic factors that influence inoculum availability and dispersal. Spore dispersal from Vitis vinifera was studied from 2005 to 2006 in a French vineyard. Spores of Diplodia seriata and D.  mutila were trapped throughout the year. Spore release from D. seriata peaked during the vegetative growth period, while D. mutila  released its spores later

Addressing the exciton fine structure in colloidal nanocrystals: the case of CdSe nanoplatelets

We study the band-edge exciton fine structure and in particular its bright-dark splitting in colloidal semiconductor nanocrystals by four different optical methods based on fluorescence line narrowing and time-resolved measurements at various temperatures down to 2 K. We demonstrate that all these methods provide consistent splitting values and discuss their advances and limitations. Colloidal CdSe nanoplatelets with thicknesses of 3, 4 and 5 monolayers are chosen for experimental demonstrations. The bright-dark splitting of excitons varies from 3.2 to 6.0 meV and is inversely proportional to the nanoplatelet thickness. Good agreement between experimental and theoretically calculated size dependence of the bright-dark exciton slitting is achieved. The recombination rates of the bright and dark excitons and the bright to dark relaxation rate are measured by time-resolved techniques

Dynamic analysis of repetitive decision-free discreteevent processes: The algebra of timed marked graphs and algorithmic issues

A model to analyze certain classes of discrete event dynamic systems is presented. Previous research on timed marked graphs is reviewed and extended. This model is useful to analyze asynchronous and repetitive production processes. In particular, applications to certain classes of flexible manufacturing systems are provided in a companion paper. Here, an algebraic representation of timed marked graphs in terms of reccurrence equations is provided. These equations are linear in a nonconventional algebra, that is described. Also, an algorithm to properly characterize the periodic behavior of repetitive production processes is descrbed. This model extends the concepts from PERT/CPM analysis to repetitive production processes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44155/1/10479_2005_Article_BF02248590.pd