Showing papers by "University of the Littoral Opal Coast published in 2003"

Oxidative coupling of methane catalyzed by rare earth oxides: Unexpected synergistic effect of the oxide mixtures

Abstract: Oxidative coupling of methane (OCM) catalyzed by a series of rare earth oxides (REO) and mixtures of REO was studied using a continuous-flow quartz reactor at atmospheric pressure, 650–900 °C and variable gas flow rates of methane and air. The mixtures of the rare earth oxides available industrially (as intermediate products in commercial RE metal manufacturing) revealed good efficiency in the OCM. Catalytic performance of the light group of REO consisting of lanthanum, praseodymium, neodymium and cerium oxides with 5.5 wt.% of ceria is comparable to that of the individual oxides (samaria, ytterbia and europia). Addition of 10 wt.% of ceria to pure lanthana unexpectedly enhanced the efficiency of the catalyst. Raman spectroscopy as well as XRD suggested an oxide–oxide interaction between lanthana and ceria providing formation of additional oxygen vacancies.

Total oxidation of propene and toluene in the presence of zirconia doped by copper and yttrium

Abstract: The catalytic oxidation of propene and toluene has been investigated on pure ZrO2, pure Y2O3 and ZrO2 doped with 1, 5 and 10 mol% Y2O3 in the presence or absence of copper (0.5, 1 and 5 wt.%). A synergetic effect has been detected since ZrO2 and Y2O3 exhibit significant lower activities than the mixed oxides. The higher surface areas, related to structural change from monoclinic (ZrO2) to tetragonal (ZrO2-Y2O3), partly explained the higher activity of ZrO2-Y2O3. However, it has been shown that the number of anionic vacancies, created by the substitution of Zr4+ by Y3+, in yttria-stabilised zirconia solids depends on the yttrium contents. Their effect on propene and toluene oxidation activity is significant. The anionic vacancies should induce a better activity of the ZrO2-5 mol% Y2O3 catalyst with or without copper which presents the higher number of Zr3+ species. This support should favour the formation of CuO particles which should be the most active catalytic sites in the studied reaction. Moreover, whatever the support, copper has a promotional effect on the catalytic activity and the CO2 selectivity.

Seasonal patterns in the fish and epibenthic crustaceans community of an intertidal zone with particular reference to the population dynamics of plaice and brown shrimp

Abstract: The intertidal zone of a sandy beach located on the French coast of the Eastern Channel, was sampled during spring and summer 2000 to analyse the community structure of fish and epibenthic crustaceans. The presence of many juvenile fish (mainly O-group) and crustaceans indicated the important role played by the intertidal zone as a nursery ground. The brown shrimp, Crangon crangon and O-group plaice, Pleuronectes platessa are the two most abundant species of the intertidal ecosystem. Plaice settlement period extended from mid-March to early June. Over the survey period, densities increased to maximum numbers of about 27 ind. 10 m−2 in mid-April. In the following week, density rapidly decreased due to mortality and migration into deeper waters. The mortality was attributed mainly to predation by brown shrimp (C. crangon) and to a lesser extent by the shore crab (Carcinus maenas). The mean size of 0-group plaice increased from 19 mm in mid-April to 58 mm in July. Growth of juvenile 0-group plaice is described by an exponential equation: total length (TL, mm) = 12.602 e0.022 (post-settlement age). Post-settlement growth rates, estimated by otolith microstructure analysis, were 0.38 mm d−1 for plaice ≤30 mm and 0.61 mm d−1 for plaice >30 mm. Settlement of juvenile brown shrimp started in mid-April, peaked in early June (93 ind. 10 m−2) and continued with fluctuating intensity throughout the summer. Growth rate of juvenile C. crangon, estimated after the settlement peak, was 0.163 mm d−1. Growth conditions of juvenile plaice and C. crangon were analysed by comparing estimated growth in the field with predicted maximum growth according to temperature-growth rate models from experimental studies of growth with unlimited food supply. For plaice, the estimated growth rate was lower (plaice ≤30 mm) but similar (plaice >30 mm) to the predicted maximum growth suggesting a food limitation only for newly settled individual. The observed increase in mean length of juvenile C. crangon was lower than the maximum possible growth. The function of the intertidal zone in the early juvenile stages of marine species is discussed.

Multisensor analysis of integrated atmospheric water vapor over Canada and Alaska

Abstract: [1] Atmospheric water vapor is a key parameter for the analysis of climatic systems (greenhouse gas effect), in particular over high latitudes where water vapor displays an important seasonal variability. The sparse spatial and temporal sampling of atmospheric water vapor observations across Canada needs to be improved. A series of instruments and methods including a 940-nm solar absorption band radiometer (R) and radiosonde (S) analysis from a numerical weather prediction model and a ground-based bi-frequency Global Positioning System (GPS) were used to evaluate the integrated atmospheric water vapor (IWV) at various sites in Canada and Alaska from a multiyear database. The IWV-R measurements were collected within the framework of the North American Sun Radiometry network (AERONET/AEROCAN). Intercomparisons between [IWV-GPS and IWV-S], [IWV-R and IWV-GPS], and [IWV-R and IWV-S] show root mean square (RMS) differences of 1.8, 1.9, and 2.2 kg m � 2 , respectively. GPS meteorology appears to be the easiest approach to calibrate the solar radiometer water vapor band owing to its flexibility, and it allows us to overcome the Sun radiometry limitation in high-latitude areas like the Arctic. The sensitivity of the GPS retrieval to various parameters like GPS satellite constellation and meteorological data are discussed. The classical linear relationship between the surface temperature and the integrated weighted mean temperature profile needed for IWV-GPS retrieval may be significantly different for Arctic air masses compared with midlatitude air masses in the case of tropospheric temperature profile inversion. An ever-expanding multiyear (1994–2001) North American summer water vapor climatology, derived from AERONET/Canadian Sun Radiometer Network, is presented and analyzed, showing a mean value of 19.8 ± 6.1 kg m � 2 and variations from 17 kg m � 2 in Alaska to 23 kg m � 2 in southeastern Canada. The results in Bonanza Creek, Alaska, show significant interannual variations with a peak in 1997, which may

Block Krylov subspace methods for large algebraic Riccati equations

Abstract: In the present paper, we present numerical methods for the computation of approximate solutions to large continuous-time and discrete-time algebraic Riccati equations. The proposed methods are projection methods onto block Krylov subspaces. We use the block Arnoldi process to construct an orthonormal basis of the corresponding block Krylov subspace and then extract low rank approximate solutions. We consider the sequential version of the block Arnoldi algorithm by incorporating a deflation technique which allows us to delete linearly and almost linearly dependent vectors in the block Krylov subspace sequences. We give some theoretical results and present numerical experiments for large problems.

Pelagic dispersal of the brittle-star Ophiothrix fragilis larvae in a megatidal area (English Channel, France) examined using an advection/diffusion model

Abstract: The brittle-star Ophiothrix fragilis (Abildgaard) is widely distributed in the English Channel and particularly on pebble areas which are characterised by strong tidal currents. The main populations are located between 20 and 80 m depth. Although larval dispersal and settlement are apparently under an unfavourable high hydrodynamical constraint (a megatidal regime which generates high tidal currents, and a northeastward tidal residual current from the English Channel to the North Sea which advects larvae away from the adult populations), the density of adult populations showed little year-to-year variability. In order to determine the origin of ophioplutei larvae and recruitment patterns, larval dispersal from eight populations in the English Channel was simulated using a 2D hydrodynamical Lagrangian model integrating both the tidal residual, the wind-driven circulation and the eddy-diffusion. Simulations showed different transport patterns of the passive O. fragilis larvae under advection and eddy-diffusion control in the English Channel and highlighted a significant role of wind forcing on larval dispersal. Larval losses by mortality could exceed losses by hydrodynamic processes. For almost all populations, larval retention appeared to be sufficient to ensure local recruitment regardless of meteorological conditions or larval life span, and to explain the inter-annual stability of adult stocks. The degree of connection among populations was highly variable. While some populations were mainly self-seeding, larval supply from neighbouring populations could exceed local retention for other populations depending on wind forcing.

EPR Investigation of Fe-Exchanged Beta-Zeolites

Abstract: Iron-exchanged beta-zeolites with an exchange level (300 Fe/Al, mol/mol) of 10−97 were characterized by electron paramagnetic resonance (EPR) after calcination and a redox pretreatment (H2/N2O). According to the EPR spectra, three different types of iron species are present in the samples: isolated ions, polynuclear oxo-iron species (clusters), and superparamagnetic iron particles. Fe-exchanged beta-zeolites (Fe−BEA) with an iron exchange level lower than 24 are mainly constituted by isolated Fe(III) ions. These latter species can be located in the structure or in charge compensation of the BEA zeolite structure. The amount of interacting species above an iron exchange level of 24 increases strongly, and these species become predominant at an iron exchange level of 100. Oxidation of Fe2+−BEA by N2O leads to the generation of new oxo-iron species with superparamagnetic character. These species are considered as the active species in the selective catalytic reduction of N2O by NH3 over fully exchanged Fe−BEA.

Seasonal ichthyodiversity and growth patterns of juvenile flatfish on a nursery ground in the Southern Bight of the North Sea (France)

Abstract: The demersal fish community on a flatfish nursery ground, of the Southern Bight of the North Sea, was sampled monthly between May 1998 and 1999. The studied coastal area is a multispecific nursery area. Although 32 fish species were caught, only nine species had a major influence on the variation in total densities through the year and can be considered as key species. Juvenile sole and plaice exhibited similar seasonal growth patterns with rapid growth during late spring and summer, a growth arrest during autumn and winter and a restart of growth in March. Comparisons of observed growth in length with predicted maximal growth under optimal food conditions suggested that during the summer, growth of 0-group sole and plaice was only determined by prevailing mean water temperature. During autumn and winter, while growth in length of sole followed model predictions, observed length of plaice was less than model predictions, suggesting growth limitation. Analyses of the factors that may be responsible for differences between observed and expected length growth indicated that autumn and winter growth arrest of plaice was not only related to low winter water temperature. It is suggested that for visual feeders such as plaice, the interaction of decreasing food availability and day length during autumn and winter can reduce the access to food resource and therefore feeding success and growth.

Marine biodiversity in French Guiana: Estuarine, coastal, and shelf ecosystems under de influence of Amazonian waters

Abstract: La biodiversidad marina en la Guyana Francesa esta fuertemente influenciada por los aportes amazonicos, los cuales constituyen un factor estructurante de los ecosistemas estuarianos, costeros y de plataforma continental. Ademas, debido a las cambiantes condiciones meteorologicas y oceanograficas, la variabilidad estacional e inter-anual puede jugar un rol importante en la estabilidad o la modificacion de los parametros medio-ambientales que afectarian la biodiversidad ecologica, poblacional y genetica de los ecosistemas locales. Los estudios llevados a cabo sobre la biologia de las especies marinas y litorales se refieren principalmente a especies de interes comercial, especies protegidas en peligro de extincion, y sobre todo a las caracteristicas del funcionamiento de ciertos ecosistemas costeros y litorales caracteristicos como los estuarios, bancos de fango, playas de arena, y sobre todo los manglares. La idea de estudios o series de estudios mejor coordinados entre si a nivel regional e internacional, emerge como una necesidad para una mejor estimacion y comprension de la biodiversidad marina. Estos estudios beneficiarian de una importante cooperacion internacional que pemitiese comparar e integrar el conjunto de datos obtenidos en el pasado, llevar a cabo misiones oceanograficas conjuntas, mutualizar y homogeneizar los protocolos analiticos, y favorecer el intercambio de tecnicas y estrategias por intermedio de intercambios de cientificos y estudiantes en formacion de postgrado. Finalmente, estudios comparativos sobre la biodiversidad de sistemas costeros analogos sudamericanos permitirian de alcanzar una mejor estimacion de la biodiversidad marina de este continente.

An Overview of the Ultraviolet Index and the Skin Cancer Cases in Brazil

Abstract: This study relates regional and seasonal UV index (UVI) variations, number of skin cancer cases and population skin-color distribution in Brazil. UVI calculations were performed using the UV Global Atmospheric Model (UVGAME), whose characteristics and validations are provided in thiis article. Health and racial data sets are based on the health and census data collected by Brazilian governmental agencies in the past. The discussion covers cultural customs and details of health and educational campaigns in Brazil. Despite lower UV levels in the South and Southeast regions, the results show a number of nonmelanoma skin cancer (NMSC) cases regions, where the white population is predominant. In general, in the southern regions about 50 new NMSC cases per 100000 inhabitants have been diagnosed each year. These rates decrease almost 40% in the Central-North regions and more than 80% in Northeast region, where miscegenation is common. In addition, the UVI evaluation is extended to other South American sites with singular characteristics, e.g. populous cities located in high altitudes or those affected by the Antarctic ozone hole in the extreme south of the continent.

Role of molybdenum against ceria sulphur poisoning in the combustion of soot particles and the oxidation of propene

Abstract: The influence of molybdenum on ceria activity, CO2 selectivity and resistance to sulphur poisoning was investigated. Different molybdenum-cerium catalysts, with various atomic ratios (Mo/Ce=0.001, 0.01, 0.1, 0.2 and 0.3), have been prepared and tested with respect to carbon black (CB) combustion and the oxidation of propene before and after treatment under SO2. Based on their catalytic behaviour and according to molybdenum loadings, the catalysts have been classified into two groups: (i) ceria and low molybdenum loading catalysts (1Mo1000Ce, 1Mo100Ce) which present a good activity, an excellent CO2 selectivity and a bad resistance to sulphur poisoning; (ii) catalysts containing higher molybdenum loadings (1Mo10Ce, 2Mo10Ce, 3Mo10Ce) show lower activity and CO2 selectivity but a better resistance to sulphur poisoning. The role of molybdenum against ceria sulphur poisoning has been evidenced.

Consistent and asymptotically normal estimators for cyclically time-dependent linear models

Abstract: We consider a general class of time series linear models where parameters switch according to a known fixed calendar. These parameters are estimated by means of quasi-generalized least squares estimators. conditions for strong consistency and asymptotic normality are given. Applications to cyclical ARMA models with non constant periods are considered.

Formation of cereous sulphate phase upon interaction of So2 with ceria at room temperature

Abstract: The adsorption of SO2 gas on ceria solid at room temperature has been investigated by thermal analysis, Raman spectroscopy and electron paramagnetic resonance (EPR). The results confirm that SO2 transformation into sulphate species occurs at 25°C with a concomitant reduction of Ce4+ to Ce3+ ions. The formation of Ce(III)-sulphate phase has been evidenced on ceria surface. The thermal analysis revealed a complete decomposition of cereous sulphate phase to CeO2 at 785°C. The change of oxidation state of Ce(IV) to Ce(III) during the formation of sulphate phase has been confirmed also by EPR technique.

Blow Up for Reaction Diffusion Equations Under Dynamical Boundary Conditions

Abstract: For a class of reaction diffusion equations in a bounded domain under dissipative dynamical time lateral boundary conditions, the occurence of blow up phenomena is shown by comparison of solutions, as well as by energy and spectral methods. Moreover, the dependence of the blow up time on different boundary conditions is investigated, where the dynamical boundary condition interpolates between the Neumann boundary condition and a certain Dirichlet boundary condition related to the initial condition. Some of the techniques presented here apply also to certain parabolic equations with degenerate principal part. †Dedicated to Professor Helmut Kaul on the occasion of his 65th birthday.

Deposition of Ferroelectric BST Thin Films by Sol Gel Route in View of Electronic Applications

Abstract: We report on the deposition of Ba 0.7 Sr 0.3 TiO 3 thin films, BST (70/30), by a sol-gel process. After deposition by spin coating, the film is annealed at 750°C, one hour in air. BST films have been deposited on (111) silicon substrates (bare and platinum coated) and on (0001) sapphire. X-Ray diffration patterns show that the films are polycristalline with perovskite structure and free of secondary phase. From SEM images, we infer that the film surface is smooth, the grain size is about 50 nm and the thickness of the BST layer is 300 nm. Electrical characterizations are mainly presented on BST deposited on platinized silicon. The dielectric constant l r is about 400 at 10 kHz and slightly decreases with frequency. The leakage current density is low: typically 10 nA/cm 2 at +5 Volts. At ambient temperature, the existence of an hysterisis cycle attest that a BST (70/30) film is in the ferroelectric state. As concerns the dissipation factor, the lower value has been obtained with a BST film deposited on sap...

Environmental lead exposure and its relationship to traffic density among Senegalese children: a pilot study.

Abstract: In Senegal, as in many developing countries, traffic density is increasing in urban areas; in Dakar more than 50% of vehicles use gasoline. Yet the extent and real magnitude of the problem has neither been recognized nor assessed in these countries. Systemic data assessment of lead pollution and people's exposure are not well known in Senegal. This study was also designed to determine the impregnation levels of the lead released by the exhaust of cars and the changes of some early biological markers in Senegalese children. Blood lead (BPb) levels showed that all the children enrolled were exposed. However, lead exposure levels (from 34.7 to 145.8 mg/L) were less important for children living in rural areas (60.99-18.3 mg/L) than for those living in urban areas (106.79-16.9 mg/L). These changes could be correlated to the difference in the automobile traffic between both these regions (P B-0.001). BPb mean levels found in boys were higher than those in girls (P B-0.05). Despite elevated BPb levels, all valu...

Marine biodiversity in french guiana: estuarine, coastal, and shelf ecosystems under the influence of amazonian waters la biodiversidad marina en guyana francesa: los ecosistemas de estuarios, las costas y plataformas bajo la influencia de las aguas amazonicas

Abstract: Marine biodiversity in French Guiana is strongly influenced by the amagon River waters of the river Amazon, which constitute a major structuring factor for the estuarine, coastal, and shelf marine ecosystems. Moreover, the marked seasonal and interannual variabilities play important roles in the stability or fluctuations in the environmental parameters that influence biodiversity at the ecological, population, and genetic levels. Previous and ongoing studies of the marine and littoral biota relate mostly to comm ercial marine species, protected species in danger of extinction and, specially, to the biodiversity and functioning of local coastal and littoral ecosystems such as estuaries, mudflats, sandy beaches and, particularly, littoral mangroves. A more integrated approac h involving local, regional, and international scientific collaboration is needed for a better assessment and understanding of ma rine biodiversity. Such studies would benefit from international cooperation that would allow the gathering of new information and t he comparison of previous data, the organization of common oceanographic surveys, the homogenisation of analytical protocols, and also favour the exchange of scientists and postgraduate students for a real transfer of ideas, techniques, and know-how. Moreov er, research on the comparative biodiversity of analogous littoral and marine ecosystems in different parts of South America would allow a more accurate estimate of marine biodiversity on a continental scale.

Sky-radiance measurements for ocean-color calibration-validation.

Abstract: The calibration of an ocean-color sensor or validation of water products is generally based on ground-based extinct measurements from which the aerosol products (optical thickness tau(a) and aerosol type) are deduced Sky-radiance measurements complement the extinction measurements mainly in the aerosol-model characterization Our basic goal is to promote calibration-validation activities based on the radiative properties of the aerosols rather than their chemical or physical properties A simple method is proposed (and evaluated) to convert sky radiances measured in the principal plane into atmospheric phase functions P Indeed tau(a) and P are the required inputs to a radiative-transfer code for predicting the top-of-the-atmosphere radiances The overall error in this prediction is a few percent This method can operate on a worldwide network on ground-based sun radiometers and then be used to achieve a statistical analysis for validating satellite products

Microbial absorption and backscattering coefficients from in situ and POLDER satellite data during an El Nino-Southern Oscillation cold phase in the equatorial Pacific (180°)

Abstract: [1] Contributions of different microbial groups to absorption, backscattering, and marine reflectance (a(λ), bb(λ) and R(λ), respectively) were quantified during an El Nino-Southern Oscillation cold phase in the equatorial Pacific during the Etude du Broutage en Zone Equatoriale cruise on board the R/V L'Atalante. In situ data were collected at every degree of latitude from 8°S to 8°N, 180° (26 October to 13 November 1996), and satellite reflectances were available from POLDER-ADEOS for the 1–10 November 1996 decade. Bulk absorption and backscattering coefficients were estimated at 440 nm for the major microbial groups enumerated in the upper surface layer (heterotrophic bacteria, Prochlorococcus, Synechococcus, and <20-μm eukaryotic algae). Total absorption and backscattering coefficients were retrieved from space by a new inverse method. The observed ecosystem was typical of a well-developed equatorial upwelling, with maximal values of 0.4 mg m−3 for Tchl a, 0.026 m−1 for ap(440), 0.023 m−1 for aphy(440), and a low in situ adet (<14% of ap). Prochlorococcus and nanoeukaryotic algae (3.4-μm mean diameter) were the dominant absorbers (97%), contributing about equally to aphy. The retrieved total absorption coefficient, asat(440), from POLDER (maximum of 0.03 m−1) was higher than ap(440), as it included absorption by CDOM (estimated to be 15% of ap(440) + aw(440), where aw = absorption by pure water). Heterotrophic bacteria were the dominant contributors (73%) to total simulated microbial backscattering, bbmic (maximum = 3.7 × 10−4 m−1), but bbmic was negligible compared to the inverted total backscattering by particles, bbp (2.7 × 10−3 m−1), indicating that unidentified small nonliving particles contributed most to the satellite signal.

Transformation of vaterite into calcite in the absence and the presence of copper(II) species

Abstract: The transformation of vaterite into calcite may be performed by heating in the presence and the absence of oxygen. Vaterite remains thermally stable until a calcination temperature of 450°C. It transforms progressively to calcite up to 500°C giving two exothermic peaks: 1) at 481°C due to the transformation of vaterite surface which is in contact with a small amount of calcite phase already formed with the time on the solid surface from the humidity atmosphere; 2) at 491°C due to the transformation of pure vaterite bulk. The calcite phase remains stable until 700°C. Above this temperature the formation of CaO is observed.