Flux des particules grossières de matière organique allochtone et autochtone dans un bras mort du Rhône

Les flux de matière organique particulaire allochtone et autochtone ont été suivis dans la Lône des Pêcheurs. Leur estimation quantitative et qualitative rend compte de l'impact de l'écotone rives sur le fonctionnement du système aquatique. Dans ce bras mort, les apports allochtones semblent plus importants que dans d'autres systèmes, comme les ruisseaux forestiers mentionnés par la littérature.Pour l'estimation des flux de matière organique particulaire nous avons utilisé, comme moyen d'échantillonnage, des bacs de plastique rectangulaires déposés sur le fond; en plus nous avons procédé à des prélèvements par benne.Le plus grand apport de feuilles terrestres a lieu en novembre, le plus grand apport de bois et autres débris en avril et dans les mois qui suivent, probablement par suite des crues. Au niveau de la lône, on note une différence entre les parties amont et aval.A surface égale, les apports grossiers (feuilles mortes et bois) sont plus abondants en amont, les éléments en voie de désintégration sont, au contraire, plus nombreux en aval. Cette différence est principalement due à la proportion des rives par rapport à la surface du plan d'eau et probablement aussi à la vitesse de dégradation de ces apports dans les deux stations. Ceci nous amène donc à penser qu'il existerait un gradient décroissant de matière organique grossière de l'amont de la lône vers l'aval.La biocénose aquatique est alimentée d'abord par les macrophytes immergés à décomposition rapide (été, automne), puis par les feuilles terrestres et les macrophytes émergés (hiver, printemps).L'analyse de la structure des invertébrés aquatiques montre la relation entre ces apports, particutièrement les feuilles mortes, et la biomasse des dilacérateurs et des collecteurs.This study concerns a side arm of the River Rhone, 20 km upstream from the city of Lyons, southeastern France. The arm opens into the channel of the river downstream, but it is closed and fed by groundwater upstream. Terrestrial particulate organic matter enters the water through the ecotone of the banks. This flow and that of carbon, nitrogen and phosphorus were measured, using sediment traps and a grab, by the monthly sedimentation of allochthonous organic matter on the bottom, corrected for the time of exposure under the water. The input seemed to be somewhat greater than in the temperate woodland streams described in the literature.The greatest input of terrestrial leaves occurred in November, the greatest input of wood and other debris in April, presumably as a consequence of the flooding of the undergrowth. The arm was narrower upstream than downstream (respectively 10-25 and 60-80 m in width). Though the banks were equally and densely forested, the bottom sediment received more coarse particulate matter upstream, and this matter was equally distributed. In contrast, less organic matter was deposited along the banks downstream and still less in the middle of the arm, where partially, decomposed matter was more abundant. These differences may be explained by the ratio between the banks and the water area, by a certain transport during the floods, and by the faster processing of particulate matter closer to the channel. Hence there seems to be a decreasing gradient of particulate organic matter as one goes downstream along the arm.The heterotrophic communities in the arm were fed successively by the decay of autochthonous submerged macrophytes such as Potamogeton in summer and autumn, then by that of terrestrial leaves (mostly alder, poplar and willow with respectively fast, medium and slow processing velocities) and emergent macrophytes such as Phragmites, during winter and spring.A comparison of invertebrate biomass and community structure shows that shredders and collectors are more numerous in winter and spring, white terrestrial leaves are being processed

Empirical Study on the Status of Moroccan Information Systems and Proposition of Approach for Choice of Best Practices for Good IT Governance

Today, the function of the chief information officer (CIO) has become part of the flow charts of many Moroccan companies [1]. Based on this statement, we did an empirical study in the first part of this work on the state of information systems (IS) Moroccan to know their strengths and weaknesses. The aim of the second part is to propose an approach based on the IT (information technology) frameworks helping CIOs to form their own repository of good practices to be applied in order to have good IT governance

Intelligent IT Governance Platform: Strategic level

The objective of this work is the implementation of a new IT governance platform adaptable to any type of Information system architecture and any kind of business. The proposed platform is intelligent and independent to understand the business needs continuously changing, is distributed to involve all stakeholders and heterogeneous components, and scalable to accumulate the know-how of the company's IT Governance through a learning asset

Empirical Study: Moroccan Information systems specificities for better IT Governance

The spread of information systems (IS) use has become an essential criterion for judging today's overall development level of a country and its attractiveness for capital and investment. Many International rankings evaluate the performance of different countries at this level. And Morocco occupies a disappointing position compared to its potential. Paradoxically, Morocco is lagging behind, although in the telecom sector, it is ahead of many developing countries, Thus, in 2015, the index NRI (Networked Readiness Index), measuring the preparation of an economy to make effective use of new information technologies (IT) published by the World Economic Forum, ranks Morocco in the 87th place. Indeed, with the exception of large companies that have implemented a set of tools to automate the process, a large number of SMEs and SMIs are very late as far as IT use is concerned. It means that IS in Morocco is still unable to achieve business perspectives for benefits and processes optimization. The aim of this article is to understand the particularities of Moroccan IS to understand the week points to correct in order to govern well enterprise Information technologies

Analysis of interactions between Information system, Communication and Marketing in Organizations

Communication, Information system and Marketing are a high and real value-added function for any organization. It needs to be clearly situated in the structure of organization to play completely their role. According to the Level of development of the organization, the company or the country, their place and their attributions are often badly defined. Their interactions also. We believe that numerous factors macro as those of the external environment and the micro as those of the business sector of the organization, its size, its structure have a determining role. To validate our hypotheses, we realized an empirical study on a sample of 262 Moroccan organizations, between companies and organizations other than companies. This work on analysis of interactions between information system, communication and marketing in organizations could server as well to the researchers, to the professionals, as to the managers

Wave packet dynamics of potassium dimers attached to helium nanodroplets

The dynamics of vibrational wave packets excited in K$_2$ dimers attached to superfluid helium nanodroplets is investigated by means of femtosecond pump-probe spectroscopy. The employed resonant three-photon-ionization scheme is studied in a wide wavelength range and different pathways leading to K$^+_2$-formation are identified. While the wave packet dynamics of the electronic ground state is not influenced by the helium environment, perturbations of the electronically excited states are observed. The latter reveal a strong time dependence on the timescale 3-8 ps which directly reflects the dynamics of desorption of K$_2$ off the helium droplets

Leaf litter degradation in highly turbid transitional waters: preliminary results from litter-bag experiments in the Gironde Estuary

The rates of decomposition of oak (Quercus robur) leaves have been examined using litter bags in a very high turbidity macrotidal estuary, the Gironde Estuary (S.W. France). The first experiments show a marked decrease in the decomposition rate of oak leaves at the water-sediment interface (mud-contact: anoxic conditions, reduced physical fragmentation) in comparison to the water column. The results point out the impact of hydrodynamic conditions on leaf litter degradation in such fluvio-estuarine systems. Regarding the aquatic-terrestrial linkage, our observations suggest direct changes in leaf decomposition kinetics and then, a potential delay on the recycling and transport processes of coarse particulate organic matter, especially in a context of modification of the natural water flow, due to global and land use changes

Ring closing reaction in diarylethene captured by femtosecond electron crystallography

The photoinduced ring-closing reaction in diarylethene, which serves as a model system for understanding reactive crossings through conical intersections, was directly observed with atomic resolution using femtosecond electron diffraction. Complementary ab initio calculations were also performed. Immediately following photoexcitation, subpicosecond structural changes associated with the formation of an open-ring excited-state intermediate were resolved. The key motion is the rotation of the thiophene rings, which significantly decreases the distance between the reactive carbon atoms prior to ring closing. Subsequently, on the few picosecond time scale, localized torsional motions of the carbon atoms lead to the formation of the closed-ring photoproduct. These direct observations of the molecular motions driving an organic chemical reaction were only made possible through the development of an ultrabright electron source to capture the atomic motions within the limited number of sampling frames and the low data acquisition rate dictated by the intrinsically poor thermal conductivity and limited photoreversibility of organic materials