Showing papers by "University of the Littoral Opal Coast published in 2006"

Spectral dependency of optical backscattering by marine particles from satellite remote sensing of the global ocean

Abstract: [1] Knowledge of the relative proportion between small-sized and larger particles in the surface ocean is essential to understand the ocean ecology and biogeochemistry, including particle dynamics and carbon cycling. We show that this information may be assessed qualitatively from satellite observations of ocean color. Such capability is based on the estimation of spectral dependence, γ, of particulate backscattering coefficient, bbp, which is sensitive to particle size distribution. Our results obtained from satellite observations of the global ocean are supported by in situ measurements, and they demonstrate a general decrease of the spectral slope γ from oligotrophic to eutrophic regimes, although significant regional differences are observed in the relationship between γ and the chlorophyll a concentration, Chl. To first approximation, such a decrease in γ is expected to be accompanied by an increased role of larger particles. This is consistent with our field data that show relatively high concentrations of submicron particles in very clear oceanic waters. Different seasonal patterns are also observed depending on the oceanic regions. The seasonal amplitude of γ is generally higher than that of Chl and bbp in equatorial and tropical regions, and it is much lower at temperate latitudes. These spatio-temporal patterns are interpreted in terms of processes that modify the composition of particulate assemblages and physiology of phytoplankton in response to environmental forcing. The changes in γ are clearly related to variations in the mixed layer depth and photosynthetic available radiation.

Statistical demonstration of the relative effect of surface chemistry and roughness on human osteoblast short-term adhesion.

Abstract: The effects of material composition, surface chemistry or surface topography on cell attachment (short-term adhesion) have been largely studied on bone-derived cells. However, no statistical demonstration of these effects has been performed until now. With this objective, we quantified the attachment after 24 hours of human osteoblasts on pure titanium, titanium alloy and stainless steel substrates presenting 6 different surface morphologies and 2 different roughness amplitude obtained by sand-blasting, electro-erosion, acid etching, polishing and machine-tooling. The coating by a gold-palladium layer of these surfaces allowed determining the relative effect of the surface roughness and of the surface chemistry. By multiple analysis of variance, we demonstrated that neither material composition nor surface roughness amplitude influenced cell attachment except on sandblasted pure titanium substrates. On the contrary, a high significant influence of the process used to produce the surface was observed meaning that the main influent factor on cell attachment could be either the surface morphology or the surface chemistry induced by the process. As the coating of surfaces by a gold-palladium layer decreased significantly the attachment of cells on the majority of substrates, we concluded that attachment is rather influenced by surface chemistry than by surface topography.

Detection and quantification of multiple molecular species in mainstream cigarette smoke by continuous-wave terahertz spectroscopy.

Abstract: Continuous-wave terahertz spectroscopy by photomixing is applied to the analysis of mainstream cigarette smoke. Using the wide tunability of the source, spectral signatures of hydrogen cyanide (HCN), carbon monoxide (CO), formaldehyde (H2CO), and water (H2O) have been observed from 500 to 2400 GHz. The fine spectral purity allows direct concentration measurement from the pure rotational transitions of HCN and CO. The quantification of the measurement was validated by the means of a calibration gas containing CO. The potential of this technique for trace gas detection is demonstrated with an estimated detection limit of HCN equal to 9 parts in 10(6).

New Pd/hierarchical macro-mesoporous ZrO2, TiO2 and ZrO2-TiO2 catalysts for VOCs total oxidation

Abstract: Macro-mesoporous ZrO2, TiO2 and ZrO2-TiO2 have been synthesized and used as catalytic supports for volatile organic compounds (VOCs) oxidation. These supports present high surface areas. Stability of the porous structure is observed after calcination at 400 °C for ZrO2-TiO2 and TiO2 but partial breakdown of the structure occurs for ZrO2 by the crystallization into tetragonal phase. All these Pd impregnated catalysts are found to be powerful catalysts for total oxidation of toluene and chlorobenzene. Pd/TiO2 presents the highest catalytic potential. The lowest toluene adsorption enthalpy, the low coke content observed after the catalytic test, PdO particles easily reducible should explain the interesting catalytic behaviour of Pd/TiO2. However, production of polychlorinated compounds PhClx (with x = 2–6) occurs at low temperature during the chlorobenzene oxidation and this amount is lower over Pd/TiO2-ZrO2 compared to Pd/TiO2. But chlorobenzene is readily converted into HCl, CO2 and H2O at a temperature of 530 °C.

Are growth and density quantitative indicators of essential fish habitat quality? An application to the common sole Solea solea nursery grounds

Abstract: Bio-indicators were measured on juvenile fish to assess the quality of eight coastal and estuarine nursery grounds in the Eastern English Channel and in the Bay of Biscay during 3 years. Growth (size and otolith daily increment width), body condition (morphometric index) and abundance of juvenile common soles were analysed together with xenobiotic concentrations (heavy metals and organic contaminants). Condition indices displayed important variations and did not allow relevant estimation of environmental quality. On the contrary, growth and density indicators showed good steadiness above years but varied among sites. In spite of difficulties of interpreting these indicators on such a meso-scale approach, analyses highlighted the estuaries of Seine and Gironde. In these nursery areas, the levels of contamination were especially high, and the combination of fish growth performances and density was significantly lower than in other sites. The combination of these variables appears to provide reliable indicators of habitat quality and anthropogenic pressure on nursery grounds, especially highlighting contaminated areas. Such indicators may thus contribute to improve assessment of environmental quality of essential fish habitats with the aim of a sustainable management of fisheries resources. A study at a different scale, from this meso-scale nursery approach with more precise analyses, on local habitats, will nevertheless be necessary to optimize the relevance of these indicators for the assessment of essential fish habitat quality.

Effects of anthracene on development of an arbuscular mycorrhizal fungus and contribution of the symbiotic association to pollutant dissipation

Abstract: The influence of anthracene, a low molecular weight polycyclic aromatic hydrocarbon (PAH), on chicory root colonization by Glomus intraradices and the effect of the root colonization on PAH degradation were investigated in vitro. The fungus presented a reduced development of extraradical mycelium and a decrease in sporulation, root colonization, and spore germination when exposed to anthracene. Mycorrhization improved the growth of the roots in the medium supplemented containing 140 mg l−1 anthracene, suggesting a positive contribution of G. intraradices to the PAH tolerance of roots. Anthracene disappearance from the culture medium was quantified; results suggested that nonmycorrhizal chicory roots growing in vitro were able to contribute to anthracene dissipation, and in addition, that mycorrhization significantly enhanced anthracene dissipation. These monoxenic experiments demonstrated a positive contribution of the symbiotic association to anthracene dissipation in the absence of other microorganisms. In addition to anthracene dissipation, intracellular accumulation of anthracene was detected in lipid bodies of plant cells and fungal hyphae, indicating intracellular storage capacity of the pollutant by the roots and the mycorrhizal fungus.

The comparable size and overlapping nature of upper limb distal and proximal muscle representations in the human motor cortex

Abstract: The purpose of this study was to determine the relative size and location of proximal and distal upper limb muscle representations in the human motor cortex. Motor-evoked potentials (MEPs) evoked by transcranial magnetic stimulation were recorded in the proximal muscle anterior deltoid (AD) and in the distal muscles extensor carpi radialis (ECR) and first dorsal interosseus (1DI). The coil was moved in steps of 1 cm along a grid drawn on a tight-fitting polyester cap placed on the subject's head. At each location, four stimuli were delivered at 1.2 times the active motor threshold (AMT), and MEPs averaged in real-time. The peak-to-peak amplitude of each muscle's mean MEP was measured at each stimulation site. The area of a muscle's representation was measured by a pixel-counting algorithm. The optimal point of each muscle's areal representation, which corresponds to the locus near which the largest MEPs are obtained, was determined by fitting a 3D Lorentzian function to the data points. The optimal point of distal muscles tended to be situated more laterally along the motor strip than that of proximal muscles. However, there was no statistically significant difference between the size of the areal representations and they overlapped considerably. Additionally, in another five subjects, using a small 45-mm coil placed in a hyper-focal orientation, maps were obtained at a stimulus intensity of 1.1-1.15 times the AMT of the muscle with the lowest threshold, usually the 1DI. Even in this very stringent condition, the mapped representations of the AD, ECR and 1DI overlapped, notwithstanding that sharp demarcations between borders were also apparent. These observations demonstrate that stimulus spread alone does not explain the overlap of muscle representations. These results show that commonly used proximal and distal upper-limb muscles, taken individually, are controlled by motor cortical territories of approximately equal size that significantly overlap despite differences in the location of their optimal points.

The Coasean analysis of lighthouse financing: myths and realities

Abstract: In 'The Lighthouse in Economics' (Coase, R. H. Journal of Law and Economics, vol. 17, no. 2, 357-76, 1974), Coase reached the conclusion that in England there existed a relatively efficient privately financed lighthouse system, which would refute economists' traditional statements concerning the production of public goods. The purpose of this paper is to challenge his conclusion. We first show that, from a methodological and theoretical perspective, 'The Lighthouse' is consistent with 'The Problem of Social Cost' (Coase, R. H. Journal of Law and Economics, vol. 3, 1-44, 1960). Then, applying Coase's own method (historical case studies), we attempt to re-examine the respective roles and efficiencies of private initiative and government.

Variability of the relationship between the particulate backscattering coefficient and the volume scattering function measured at fixed angles

Abstract: [1] The particulate backscattering coefficient bbp is an inherent optical property that plays a central role in studies of ocean color remote sensing. Because of practical difficulties associated with measurements of the volume scattering function (VSF) over the whole backward hemisphere, bbp is currently derived using fixed-angle backscattering sensors and applying a conversion factor for particulate backscattering, referred to as χp. The underlying assumptions of the fixed-angle approach are as follows: (1) in the green band, χp is fairly constant in the angular range 100°–150° and (2) for a fixed scattering angle, χp is wavelength-independent. In this study we investigated the variability of χp based on spectral measurements of the full VSF, both in situ and for algal culture in the laboratory. The in situ data used in our study were acquired in a coastal environment outside of phytoplankton blooms, whereas the laboratory data were representative for phytoplankton bloom conditions in oceanic waters. At 555 nm, χp was found to vary significantly in the angular range 100°–130°, and at 140°, χp was found to be weakly variable in nonblooming waters only. The spectral variability of χp was studied for the first time, and the spectral slopes of χp, measured in situ, were found to vary within ±6%. Under the assumption that χp(140°) is wavelength-independent, the induced error in the estimates of bbp was found to be lower than 10%. The algal culture showed a much higher spectral variability in χp(±20%), which induced an error in the estimates of bbp up to ±25.8%.

Weathering sequences of rock-forming minerals in a serpentinite: influence of microsystems on clay mineralogy

Abstract: Under closed geochemical conditions, the weathering of a serpentinite rock composed of serpentine (70–85%) and magnesian chlorite (10–15%) associated with magnetite and chromite leads to the complete replacement of serpentine and chlorite by 2:1 layer silicates and produces new Fe oxides. The serpentine minerals crystallize under different habits issued from the serpentinization processes: mesh and hourglass pseudomorphic textures were formed from olivine, and thin-bladed pseudomorphic textures from pyroxene and amphibole crystals. Serpentine veins crosscut the whole rock with locally non-pseudomorphic interpenetrating and interlocking serpentines. Specific weathering microsystem habits with specific clay mineral crystallizations originate from these different habits: a poorly aluminous saponite in thin-bladed textures, two Fe-rich montmorillonites in mesh and hourglass (MH) textures, and in veins (V) which differentiate on Al, Mg and Fe contents. Magnesian chlorites, isolated from serpentine by hand-picking under a stereomicroscope, are found to weather to trioctahedral vermiculite. Magnetite and chromite extracted from the bulk samples are replaced by newly formed Fe oxides, maghemite, goethite and hematite, which give way to specific Fe accumulation habits in the regolith zone of the weathering profile.

Gas‐phase reaction of hydroxyl radicals with m‐, o‐ and p‐cresol

Abstract: The gas-phase reaction of oxygenated aromatic compounds m-cresol, o-cresol, and p-cresol with hydroxyl radicals has been studied by GC-MS. Experiments have been performed in a large-volume photoreactor (8000 L) at 294 ± 2 K and atmospheric pressure. The relative kinetic method was used to determine the rate constants for these reactions, with 1,3,5-trimethylbenzene as a reference compound. The rate constants obtained are kOH(m-cresol) = (5.88 ± 0.92) × 10−11 cm3 molecule−1 s−1, kOH(o-cresol) = (4.32 ± 0.52) × 10−11 cm3 molecule−1 s−1, and kOH(p-cresol) = (4.96 ± 0.75) × 10−11 cm3 molecule−1 s−1. The degradation products observed and their respective molar yields were methyl-1,4-benzoquinone 12.4 ± 1.2%, 5-methyl-2-nitrophenol 1.5 ± 0.3%, and 3-methyl-2-nitrophenol 1.4 ± 0.3% from m-cresol, methyl-1,4-benzoquinone 5.6 ± 0.9%, and 6-methyl-2-nitrophenol 4.7 ± 0.8% from o-cresol, and 4-methyl-2-nitrophenol 17.2 ± 2.5% from p-cresol. This kinetic and product data are compared with the literature, and the reaction mechanisms are discussed. Our results are in accordance with the previous studies (Atkinson, J Phys Chem Ref Data 1989, Monograph (1), 1–246; Atkinson and Aschmann, Int J Chem Kinet 1990, 22, 59–67; Atkinson et al., Environ Sci Technol 1992, 26, 1397–1403; Atkinson et al., J Phys Chem 1978, 82, 2759–2805; Olariu et al., Atmos Environ 2002, 36, 3685–3697; Semadeni et al., Int J Chem Kinet 1995, 27, 287–304) and confirm the methyl-1,4-benzoquinone yields determined by a different experimental technique (long-path Fourier transform infrared FT-IR (Olariu et al., 2002)). © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 553–562, 2006

Carbohydrate‐containing components of biofilms produced in vitro by some staphylococcal strains related to orthopaedic prosthesis infections

Abstract: The capacity of coagulase-negative staphylococci to colonize implanted medical devices is generally attributed to their ability to produce biofilms. Biofilm of the model strain of Staphylococcus epidermidis RP62A was shown to contain two carbohydrate-containing moieties, a linear poly-β-(16)-N-acetyl-d-glucosamine (PNAG) and teichoic acid. In the present study, we investigated several biofilm-producing staphylococci isolated from infected orthopaedic implants and characterized the composition of the laboratory-grown biofilms using chemical analysis and 1H nuclear magnetic resonance spectroscopy. Extracellular teichoic acid was produced by all strains studied. Some of the clinical strains were shown to produce biofilms with compositions similar to that of the model strain, containing a varying amount of PNAG. The chemical structure of PNAG of the clinical strains was similar to that previously described for the model strains S. epidermidis RP62A and Staphylococcus aureus MN8m, differing only in the amount of charged groups. Biofilms of the strains producing a substantial amount of PNAG were detached by dispersin B, a PNAG-degrading enzyme, while being unsusceptible to proteinase K treatment. On the other hand, some strains produced biofilms without any detectable amount of PNAG. The biofilms of these strains were dispersed by proteinase K, but not by dispersin B.

Cortical plasticity and motor activity studied with transcranial magnetic stimulation.

Abstract: For decades cortical representations of the parts of the body have been considered to be unchangeable. This view has changed radically during the past 20 years using new tools designed to study plasticity in the adult human brain. Transcranial magnetic stimulation (TMS) is a valuable non-invasive technique for exploring the ability of the motor cortex to change during motor skill acquisition. Results obtained with TMS in neurological patients as well as in normal subjects demonstrate that cortical plasticity is a necessity for correct adaptation to the continuously changing environment. Topographical reorganization of the motor cortex depends on the types of movements performed by the subjects. During simple training, the cortical representation is enlarged, and it returns to its initial size when the task is overlearned. These transient modifications characterize simple motor training. Motor skills in which coordination of distal and proximal muscles, precision of the task and spatio-temporal constraints are associated, has a different impact on cortical reorganization. We propose that years of practice of a complex motor skill induces a new cortical topography that must be interpreted as structural plasticity which provides the capacity to execute a plastic behaviour instead of a stereotypical movement. We review the neuronal mechanisms underlying plasticity in different types of movement. We stress new emerging notions, such as overlap of cortical maps, and system dynamics at single neuron and network levels, to explain the reorganization of movement representations that encode motor skill. Dendritic arborizations as functional computing elements, newly generated neurons in adult brain, and plastic architectures of cortical networks operating as distributed functional modules are new hypotheses for structural plasticity.

Spatial patterns and gis habitat modelling of Solea solea, Pleuronectes flesus and Limanda limanda fish larvae in the eastern English Channel during the spring

Abstract: The spring distribution of larval fish stages of flatfishes in the Dover Strait (eastern English Channel) was studied in 1995 and 1999. Fish larvae were identified and sorted according to developmental stages in order to study their ontogenic distribution. The French coastal waters are characterised by an unstable tide-dependent front, which influences larval dispersion. In spring, the French coastal waters have a high phytoplanktonic production. They have higher temperatures, lower salinities and differences in current intensity compared with the central English Channel waters. Generalised Additive Models (GAM) combined with Geographic Information Systems (GIS) were used to model the potential habitats of life stages considering data from three major surveys in this area. The models were developed by coupling presence-absence models with non-null abundance models. The potential habitat of larval stages was then mapped using a geostatistical method (kriging). This revealed different species strategies in which young stages were abundant in central waters and older ones were distributed mainly along the French and Belgian coasts. It is concluded that the central English waters are important for young stages after hatching and that coastal waters are essential nurseries for future juveniles. The models of three flatfish species having similar life cycle strategies are presented here: Limanda limanda, Platichthys flesus and Solea solea.

Spectral variation of the volume scattering function measured over the full range of scattering angles in a coastal environment.

Abstract: The spectral volume scattering function (VSF) was measured in a coastal environment from 0.6° to 177.3° by use of a recently developed device. The spectral variations of the particulate VSF and phase function (i.e., ratio of the VSF to the scattering coefficient) were examined as a function of the scattering angle. The angular dependency of both VSF and phase- function spectra was highly sensitive to the absorption and to the size distribution of the particles. As a result, the use of spectrally neutral phase functions in radiative-transfer modeling is questioned.

Influence of the angular shape of the volume-scattering function and multiple scattering on remote sensing reflectance

Abstract: Scattering phase functions derived from measured (volume-scattering meter, VSM) volume-scattering functions (VSFs) from Crimean coastal waters were found to have systematic differences in angular structure from Fournier-Forand (FF) functions with equivalent backscattering ratios. Hydrolight simulations demonstrated that differences in the angular structure of the VSF could result in variations in modeled subsurface radiance reflectances of up to ±20%. Furthermore, differences between VSM and FF simulated reflectances were found to be nonlinear as a function of scattering and could not be explained with the single-scattering approximation. Additional radiance transfer modeling demonstrated that the contribution of multiple scattering to radiance reflectance increased exponentially from a minimum of 16% for pure water to a maximum of ∼94% for turbid waters. Monte Carlo simulations demonstrated that multiple forward-scattering events were the dominant contributors to the generation of radiance reflectance signals for turbid waters and that angular structures in the shape of the VSF at forward angles could have a significant influence in determining reflectance signals for turbid waters.

The near-bottom layer as an ecological boundary in marine ecosystems: diversity, taxonomic composition and community definitions

Abstract: The near-bottom layer of the ocean represents a boundary between two oceanic biotopes (pelagial and benthal), and as a result, the animal populations living in this habitat belong to various diverse ecological groups. There is a profusion of terms to designate the organisms which live near the sea bottom, both in relation to their behaviour and to boundary-layer hydrodynamics. Do the fauna living above the sea bottom form a true community? Should the fauna in this habitat be considered as a true community or a mixed assemblage comprised of benthic and pelagic organism? Between 1988 and 1996, more than 500 suprabenthic hauls were taken with a modified Macer-GIROQ sledge at 15 sites in the English Channel and the Seine Estuary (5–70 m), at 13 sites on the southern edge of the Cap Ferret Canyon (Bay of Biscay, 350– 1100 m), and at 8 sites on the Atlantic seamounts south of the Azores (260–2235 m). This intensive sampling permitted the collection of more than several hundred species and will serve to facilitate discussion concerning the biodiversity of the fauna collected near the sea bottom. This paper proposes that in the estuary, the near-bottom layer is colonized by a mixed assemblage of both pelagic and benthic organisms, while in the coastal and in the bathyal zones, the response to the gradual extinction of light and the decreasing benthic resuspension at near-bottom depths leads to an ecocline.

Influence of the Ethylenediamine Addition on the Activity, Dispersion and Reducibility of Cobalt Oxide Catalysts Supported over ZrO2 for Complete VOC Oxidation

Abstract: A new and simple method for obtaining highly dispersed Co/ZrO2 catalyst is described. The presence of ethylenediamine during the preparation of Co/ZrO2 was studied and compared with a reference catalyst conventionally prepared. Addition of an aqueous solution of ethylenediamine to a cobalt nitrate solution had a dramatic effect on the catalytic performance of the catalyst as compared with a reference catalyst. This promotional effect was explained in terms of higher cobalt dispersion in the catalysts using ethylenediamine. The reason why ethylenediamine improves dispersion of the cobalt species was explained in terms of the size of the stable complex ions which could be formed in situ during impregnation. The best catalytic results were also explained in terms of Co-support interaction since new cobalt species were reducible at lower temperatures.

Application of a continuous-wave tunable erbium-doped fiber laser to molecular spectroscopy in the near infrared

Abstract: Development of a continuous-wave tunable fiber laser-based spectrometer for applied spectroscopy is reported. Wide wavelength tunability of an erbium-doped fiber laser (EDFL) was investigated in the near-infrared region of 1543–1601 nm. Continuous mode-hop free fine frequency tuning has been accomplished by temperature tuning in conjunction with mechanical tuning. The overall spectroscopic performance of the EDFL was evaluated in terms of frequency tunability along with its suitability for molecular spectroscopy. High-resolution absorption spectra of acetylene (C2H2) were recorded near 1544 nm with a minimum measurable absorption coefficient of about 3.5×10-7 cm-1/Hz1/2 for direct absorption spectroscopy associated with a 100-m long multipass cell. Detections of C2H2 at different concentration levels were performed as well with high dynamic detection range varying from 100% purity to sub ppmv using cavity ring down spectroscopy. A 3σ-detection-limited minimum detectable concentration (MDC) of 400 ppbv has been obtained by using the transition line Pe(22) of the ν1+ν3+ν5 1(Πg)-ν5 1(Πu) hot band near 1543.92 nm with a detection bandwidth of 2.3 Hz. This corresponds to a minimum detectable absorption coefficient of 6.6×10-11 cm-1/Hz1/2. The sensitivity limit could be further improved by almost one order of magnitude (down to ∼60 ppbv) by use of the Pe(27) line of the ν1+ν3(Σu +)-0(Σg +)combination band near 1543.68 nm.