Instability mechanisms in amorphous oxide semiconductors leading to a threshold voltage shift in thin film transistors

Amorphous indium gallium zinc oxide (a-IGZO) has been successfully employed commercially as the channel layer in thin film transistors (TFTs) for active-matrix flat panel displays. However, these TFTs are known to suffer from a threshold voltage shift upon application of a gate bias. The threshold voltage shift is reversible through annealing. A similar phenomenon is observed in other TFTs with an amorphous oxide semiconductor channel. The migration of oxygen vacancies is proposed as being the microscopic mechanism causing this effect as it can lead to a change in the equilibrium distribution of defect states in the band gap of the semiconductor. This would manifest itself as a reversible threshold voltage shift in the TFT transfer characteristics, as observed experimentally.The support of this work by the Engineering and Physical Sciences Research Council (EPSRC) through project EP/M013650/1 is acknowledged

Aménagements hydro-agricoles et santé (vallée du fleuve Sénégal)

L'étude de l'évolution spatiale et temporelle de la desserte médicale et du recours aux soins de Santé Primaires dans l'arrondissement de Ross-Béthio fait apparaître des discontinuités importantes entre les périodes étudiées (1983, 1988 et 1992). La desserte médicale a connu une amélioration quantitative et qualitative. L'exploitation des registres de consultation des postes de santé montre que le recours aux soins a considérablement augmenté passant de 70% en 1983 à 83% en 1992. Cependant, le recours aux soins présente des disparités spatiales créées autant par la distribution des structures de soins que par les comportements thérapeutiques des populations. L'application de l'Initiative de Bamako a également contribué à accentuer ces disparités spatiales en instaurant ces différences dans les coûts de soins des postes de santé. (Résumé d'auteur

Self-cleaning on a higher order mode in ytterbium-doped multimode fiber with parabolic profile

We experimentally demonstrate polarization-dependent Kerr spatial beam self-cleaning into the LP11 mode of an Ytterbium-doped multimode optical fiber with parabolic gain and refractive index profiles

The Mae I assay for scoring atrazine resistance is codon-usage dependent in legumes

A research experiment on herbicide atrazine usages as observed out in Zimbabwe.Nine different cowpea varieties were grown and total deoxyribonucleic acid (DNA) isolated from the young leaves. This DNA was used to amplify a 291 base pair fragment that contained codon 264 of the psb A gene. The primers used were designed based on the soybean psb A gene sequence. The 291 base pair fragment was digested with the restriction enzyme Mae I to assay for sensitivity/resistance to atrazine using a published method. When Mae I did not cut the 291 base fragment, the whole gene was amplified by the polymerase chain reaction, cloned into pBSK+ll (Stratagene, CA, USA) and sequenced around codon 264. Codons 263 and 264 were found to be GCA and AGT respectively. UWGCG and BLASTsearchesofthepsbAgenesequences in the databases confirmed that Mae I has a recognition site that overlaps with codons 263 and 264 in some legumes but not in others. The Mae I assay used by Cheung and co-workers is therefore not universal but depends on codon usage in legumes

Pluie de solitons dans un laser à fibre co-dopée Er:Yb en forme de huit

Nous rapportons ici l\u27observation expérimentale d\u27un comportement collectif d\u27un ensemble de soliton, appelé pluie de solitons, dans un laser à fibre en forme de huit avec un miroir à boucle non linéaire (NOLM). Cette dynamique non linéaire a été précédemment observée dans un laser à fibre verrouillé passivement par la technique de rotation de polarisation non linéaire. A partir d\u27un fond continu, des solitons se créent et dérivent vers la phase condensée de plusieurs solitons. L\u27observation de cette dynamique tend à renforcer l\u27idée de l\u27universalité du comportement collectif des solitons. 

Soliton pattern formation in figure-of-eight laser

We investigate the soliton pattern formation in an erbium-doped figure-of-eight double-clad fiber laser. The mode-locking is realized with a nonlinear amplifying loop mirror. Different soliton complexes have been obtained similar to those obtained when the mode-locking is achieved through the nonlinear polarization rotation technique

Urban sprawl development and flooding at Yeumbeul suburb (Dakar-Senegal)

Rapid development of urban centers in Africa is becoming a serious challenge for the coming decades with a wide range of foreseen social, economical and environmental implications. With the natural growth of the population, urban demography has been boosted by rural exodus triggered by serious droughts and increasing rural poverty. With the small resources available for an adequate urban management and the lack of efficient urban policy, Dakar capital of Senegal is characterized by an out of control urbanization process. Among the many impacts noted, flooding has appeared recently as a major threat for poor population leaving in the suburbs of Dakar. This study carried out at the outskirts of the town, in Yeumbeul District (17°24’ North, 14°46’ West), tries from rainfall variability, Digital Terrain Model and land cover change analysis since 1954 to track the interactions between natural and human causes of flooding occurring regularly since 1989. This integrated approach shows that the flooding process is not a mere climate variability related issue, it is tightly bound with poor urban management and occupation of irregular, unsuited land devoted to natural process. Satisfaction of housing needs was, for most poor rural dwellers, only possible through informal land markets, forcing them to settle in cheap yet risky lands. The recent extreme rainfall events reveal that most of these urban sprawls are located in flood prone areas. Environmental impacts of these flooded settlements have been examined. Serious flooding of 2005 has been a great momentum for the State and several other stakeholders to initiate various strategies that are discussed in this paper.Key words: Flooding, rural migration, irregular settlements, Dakar, Senegal