Observations dans les semiconducteurs à l'aide du mode induit

Short discussion of an experiment to detect an intrinsic dislocation contrast in planar structure. Unfortunately, a negative result do not give a clear cut answer to the question to know if the contrast generally observed is due to a decoration in the diffusion process.On discute de difficultés rencontrées dans un essai de mise en évidence d'un contraste intrinsèque dû aux dislocations d'une structure planar. Il semble bien en effet que les contrastes généralement observés soient dus à une décoration des dislocations lors du processus de dopage par diffusion

Instantaneous intake rate of free-grazing cattle as affected by herbage characteristics in heterogeneous tropical agro-pastoral landscapes

Numerous territories of Sub-Saharan Africa are composed of a mosaic of very different landscape units: cropland, forest, and savannah. This spatial, but also temporal heterogeneity leads to complexity in the analysis of cattle intake behaviour. The instantaneous intake rate (IIR) is generally analysed in relation to forage biomass density (Bm), i.e. the functional response. We analysed the relationship between IIR and Bm and effects of other vegetation and animal factors for two herds of N’Dama cattle grazing freely during the dry season in the complex Sare Yoro Bana landscape located in the Kolda region in Southern Senegal. The available forages included crop residues (from rice, millet and maize), grass and hay, fruits and litter. The amount and quality of biomass declined throughout the dry season. The variation in IIR was large and could be attributed to differences in Bm (for 30%) and differed between seasons and vegetation types (also 30% of variation explained). Effects of animal characteristics such as wither height and requirements were significant but small compared to herbage-related factors. In the middle of the dry season (MDS) the IIR was higher than in the early dry season (EDS), probably due to better herbage prehensibility, whereas in the late dry season total herbage stocks were very low and also IIR was lower than in EDS and MDS. Two different relations were observed between IIR and the bite rate. In the EDS higher bite rate resulted in higher IIR, compared to an absence of such effect in later stages of the season indicating a compensation between ingestion rate and bite size. Based on these result, we conclude that the relation between intake rate and biomass density generally follows a type-2 functional response, modelled by a monotonically saturating function, but is strongly affected by many factors related to herbage palatability. Despite the inherent spatio-temporal complexity of the vegetation and the challenges in observations and data collection these relationships can be quantified for cattle grazing in a heterogeneous semi-arid landscape

Structural characterization of the exocellular polysaccharides produced by Streptococcus thermophilus SFi39 and SFi12.

We investigated the structures of the exopolysaccharides (EPSs) produced by Streptococcus thermophilus SFi39 and SFi12. Both polymers were found to have molecular masses of greater than 2 x 10(6) Da. The SFi39 EPS consisted of D-glucose and D-galactose in a molar ratio of 1:1, whereas the SFi12 EPS was composed of D-galactose, L-rhamnose, and D-glucose in a molar ratio of 3:2:1. Methylation analysis of and nuclear magnetic resonance spectra recorded from the native polysaccharide, as well as oligosaccharides released by partial acid hydrolysis, allowed the complete structural determination of the SFi39 EPS, which consists of the following tetrasaccharide repeating unit: [formula: see text] Similar spectra recorded only from the native polysaccharide were sufficient to allow the structural determination of the SFi12 EPS, which consists of the following hexasaccharide repeating unit: [formula: see text] This study shows that the texturizing properties of different S. thermophilus ropy strains are based on the production of EPSs exhibiting chemical similarities but structural differences

Detonation properties of condensed explosives calculated with an equation of state based on intermolecular potentials

Available from CEN Saclay, Service de Documentation, 91191 Gif-Sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Understanding the impact and adoption of conservation agriculture in Africa: a multi-scale analysis

Conservation agriculture (CA) is increasingly promoted in Africa as an alternative for coping with the need to increase food production on the basis of more sustainable farming practices. Success with adopting CA on farms in Africa has been limited, despite more than two decades of research and development investments. Through analyzing past and on-going CA experiences in a set of case studies, this paper seeks to better understand the reasons for the limited adoption of CA and to assess where, when and for whom CA works best. CA is analyzed and understood within a framework that distinguishes the following scales of analysis: field, farm, village and region. CA has a potential to increase crop yields in the fields, especially under conditions of erratic rainfall and over the long-term as a result of a gradual increase of overall soil quality. The impact on farm income with the practice of CA on some fields of the farm is far less evident, and depends on the type of farm. The lack of an immediate increase in farm income with CA explains in many cases the non-adoption of CA. Smallholders have often short-term time horizons: future benefits do not adequately outweigh their immediate needs. Another key factor that explains the limited CA adoption in mixed crop-livestock farming systems is the fact that crop harvest residues are preferably used as fodder for livestock, preventing their use as soil cover. Finally, in most case studies good markets for purchase of inputs and sale of produce – a key prerequisite condition for adoption of new technologies – were lacking. The case studies show clear evidence for the need to target end users (not all farmers are potential end user of CA) and adapt CA systems to the local circumstances of the farmers, considering in particular the farmer's investment capacity in the practice of CA and the compatibility of CA with his/her production objectives and existing farming activities. The identification of situations where, when and for whom CA works will help future development agents to better target their investments with CA

Efeito do conteúdo e da natureza da lignina residual na eficiência e na seletividade do branqueamento com ozônio Effect of residual lignin content and nature on the efficiency and selectivity of ozone bleaching

Neste estudo foram avaliados os efeitos do conteúdo e da natureza da lignina residual na eficiência e na seletividade do branqueamento com ozônio de polpa kraft convencional (kraft) e pré-deslignificada com oxigênio (kraft-O). Constatou-se que a eficiência do branqueamento com ozônio se eleva com o aumento do conteúdo de lignina residual da polpa. O tratamento com ozônio é mais seletivo para polpas kraft-O, mas para um mesmo tipo de polpa a seletividade de branqueamento com ozônio se eleva com o aumento de lignina residual. A eficiência do branqueamento com ozônio aumenta com o teor de lignina fenólica na polpa, entretanto a seletividade é negativamente afetada pela presença destas estruturas.<br>This study aimed to evaluate the effect of residual lignin content and nature on the efficiency and selectivity of ozone bleaching of conventional (kraft) and oxygen delignified (kraft-O) pulps. Ozone bleaching efficiency was found to be enhanced by increasing pulp residual lignin content. Ozone treatment is more selective for kraft-O pulps, but for a given type of pulp (kraft or kraft-O), ozone bleaching selectivity increases with increasing pulp lignin content. Ozone bleaching efficiency increases with increasing pulp lignin phenolic hydroxyl content whereas selectivity is negatively affected by these structures