Study of the oxygen budget of the Black Sea waters using a 3D coupled hydrodynamical-biogeochemical model

in Journal of Marine Systems (2001), 31(1-mars Sp. Iss. SI), 175-202

The ventilation of the Black Sea waters by physical and biogeochemical processes is investigated using the Geohydrodynamics and Environment Research (GHER) laboratory 3D coupled hydrodynamical ... [more ▼]

The ventilation of the Black Sea waters by physical and biogeochemical processes is investigated using the Geohydrodynamics and Environment Research (GHER) laboratory 3D coupled hydrodynamical-biogeochemical model. In particular, the penetration at depth of the winter mixing, the generation of unstable motions by frontal instabilities, the exchanges between the north-western shelf and the open sea along the shelf break, the primary production distribution, the generation of detritus and the resulting consumption of oxygen for their recycling are studied. The GHER 3D hydrodynamic model is used to simulate the Black Sea's general circulation and the associated synoptic and mesoscale structures. This model is coupled with a simple ecosystem model defined by a nitrogen cycle which is described by seven state variables: nitrate, ammonium, dissolved oxygen, phytoplankton, zooplankton, pelagic and benthic detritus. The model simulates the space-time variations of the biogeochemical state variables. In particular, the spatial variability of the phytoplankton biomass annual cycle, imparted by the horizontal and vertical variations of the physical and chemical properties of the water column, is clearly illustrated. For instance, on the north-western shelf, the seasonal variability of the circulation and in particular, the reversal of the surface current at the end of spring, has a strong influence on the transport of the rich nutrient Danube waters and, thus, on the repartition of the primary production. Furthermore, the results illustrate the seasonal and vertical variations of the dissolved oxygen concentration resulting (a) from its atmospheric and photosynthetic productions in the surface layer, (b) from its loss to the atmosphere in spring and summer and (c) from its consumption associated with the detritus decomposition, the ammonium oxidation during the nitrification process, as well as the oxidation of hydrogen sulfide. The simulated sea surface, phytoplankton fields are compared with satellite estimates of chlorophyll-a fields. Comparisons are made with seasonal mean pictures and snapshot images, illustrating the mesoscale motions of the main coastal current. In the central Black Sea and the Danube delta area, comparisons with available field data are also made. As a general rule, all these comparisons show a quite good qualitative agreement. In particular, at the surface, the simulated phytoplankton space-time distribution is in a good qualitative agreement with satellite observations. However, on a quantitative point of view, the model underestimates the bloom intensity especially in the Danube discharge area. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

Study of the physical changes of spray-dried inulin during storage.

Poster (2006, October 17)

Study of the physiological component involved in the development of crown rot in bananas and the role of phenolics in susceptibility variation mechanisms

Doctoral thesis (2012)

Crown rot is a post-harvest disease caused by a broad unspecific and opportunistic parasitic complex, which affects the quality of export bananas in Cameroon, as well as in most of the production areas ... [more ▼]

Crown rot is a post-harvest disease caused by a broad unspecific and opportunistic parasitic complex, which affects the quality of export bananas in Cameroon, as well as in most of the production areas around the world. The originality of this research is that it is sets out, not only to investigate on the conditions surrounding the development of the disease and the variable factors of fruit’s susceptibility, but equally to characterize the phenolic content of the banana crown with differential susceptibility levels. The study therefore aims at showing the influence of abiotic and biotic factors on the fruit’s physiological component at harvest and the involvement of phenolic compounds in the mechanism staked in fruit’s susceptibility variations to this pathology. At the end of this study, it appears that abiotic and biotic factors influence the fruit’s physiological component at harvest, affecting thus its susceptibility level and therefore favours the development of crown rot disease. The reliability of internal necrosis surface (INS) assessments method was improved. The influence of abiotic factors (production area and harvest date) on fruit susceptibility was demonstrated without season influence. Fruits grown in high altitudes (Ekona, 500 m) were less susceptible to crown rot than the ones grown in low altitudes (Dia-Dia, Koumba, 80 m). It was noticed that at certain harvest dates within the rainy season, fruit susceptibility was higher in plantations with low altitudes. Concerning biotic factors, Mycosphaerella leaf spot disease’s influence was shown in two geographical areas. In Cameroon, black leaf streak disease significantly influenced banana’s sensitivity to crown rot (P< 0.001). In Guadeloupe, Sigatoka disease had no effect (P> 0.05) on banana’s susceptibility to the development of crown rot disease. The influence of the source-sink ratio variations, an abiotic factor, on fruit physiology could explain these differences. The influence of severe source-sink ratio modification on fruit susceptibility to crown rot was shown. Fruits with low source-sink ratio were the most susceptible. Bananas of extreme modalities (12leaves/1hand, 1leaf/8hands) and with differential susceptibility (S-, S+) to crown rot were used for the biochemical characterization of their phenolic content at two stages: the day of harvest before inoculation (dhbi) and 13 days post-inoculation (13dpi) by chromatographic methods (GC-MS, HPLC, LC-MS). Dopamine was identified as the major secondary metabolite (phenolic alkaloid) in banana crown. Norepinephrine and normetanephrine levels were high in the dhbi, especially in the S+ crowns. Hydroxycinnamic acids (ferulic acid, coumaric acid and their derivatives) and other unidentified compounds were accumulated in highly significant quantities (P <0.001) in the dhbi in the less susceptible crown (S-) as compared to the susceptible ones (S+), with decreased 13dpi mostly in the susceptible fruits (S+). These results suggest a possible role of these phenolics in banana crown biochemical defense. However, the main role of each phenolic detected in the susceptibility variations mechanism remains unclear. This study is the starting point to understanding the function(s) of phenolics in banana crown defense. This is a pioneer study on the influence of abiotic and biotic factors on the banana fruit’s physiological component at harvest through the assessment of their incidence on crown rot development. This work appears to be the first to link the level of fruit’s susceptibility at two stages (dhbi and13dpi) with their crown phenolic content. [less ▲]

STUDY OF THE POSSIBILITY TO PRODUCE CELLULOSE MICROFIBRILS BY APPLYING SHEARING TREATMENTS TO CELLULOSE FIBERS

Poster (2007, June 04)

Cellulose is a linear biopolymer composed of glucose residues linked by β 1-4 glucosidics bonds. These characteristics enable cellulose molecules to adopt an extended rod-like configuration. In the ... [more ▼]

Cellulose is a linear biopolymer composed of glucose residues linked by β 1-4 glucosidics bonds. These characteristics enable cellulose molecules to adopt an extended rod-like configuration. In the microfibrils, the multiple hydroxyl groups on the glucose residues hydrogen bond with each other, holding the chains firmly together and contributing to their high tensile strength. This study has shown the possibility to produce cellulose microfibrils by applying shearing treatment. Homogenisation and microfluidisation treatments permit to obtain microfibrils with 5 to 20 μm length and a 20 to 50 nm diameter. This study also shows that a tridimensional network, typical of a gel, appears in the treated samples [less ▲]

Study of the powerplant of Lanaye

in Proceedings of Hydroenergia 2006 (2006)

Study of the propagation center in the anionic polymerization of (meth)acrylic monomers: NMR and MNDO study of the complexes of Di-tert-butyl 2-lithio-2,4,4-trimethylglutarate and of the living poly(tert-butyl methacrylate) oligomers with lithium chloride

in Macromolecules (1998), 31(9), 2744-2755

Interactions of living oligomers of tert-butyl methacrylate (tBuMA) with a Li counterion and of the model living dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) with LiCl (B) were studied in ... [more ▼]

Interactions of living oligomers of tert-butyl methacrylate (tBuMA) with a Li counterion and of the model living dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) with LiCl (B) were studied in tetrahydrofuran-d8 (THF-d8) solution by 7Li, 6Li, 1H, and 13C, 1D and 2D, NMR spectroscopy. Di-tert-butyl 2-lithio-2,4,4-trimethylglutarate is shown to form a 1:1 complex with lithium chloride in THF. 1H, 7Li NMR results suggest that a rapid equilibrium between free LiCl and the mixed complex takes place when the molar ratio LiCl:lithiated dimer is higher than 1. From 13C relaxation times, a dimeric aggregation (i.e. A2B2) of the complex is deduced, in full accord with MNDO calculations. Preliminary results are presented for living tBuMA oligomers prepared by initiation with diphenylhexyllithium in the presence of various amounts of lithium chloride. Fast-acquired 13C NMR spectra of the living ends were recorded using 13C-enriched monomer added at the end of the polymerization. Their structure is shown to be affected by the amount of LiCl added and to correspond to an equilibrium between free lithium chloride and a complexed end group. A higher excess of LiCl apparently does not change the nature of the complexed living end. The oligomers exhibit marked self-termination in THF at 273 K. Finally, a correlation of the structure of the living chain ends with the macromolecular parameters of the resulting polymer is attempted. [less ▲]

Study of the propagation center in the anionic polymerization of (meth)acrylic monomers: NMR study of Di-tert-butyl 2-Lithio-2.4'-trimethylglutarate and living poly(tert-butyl methacrylate) oligomers in THF/toluene mixtures

in Macromolecules (1999), 32(7), 5477-5486

Solvation influences both the stereoregularity and molecular weight distribution (MWD) of poly(tert-butyl methacrylate) (PtBMA) prepared by anionic polymerization of tBMA with a lithium counterion in THF ... [more ▼]

Solvation influences both the stereoregularity and molecular weight distribution (MWD) of poly(tert-butyl methacrylate) (PtBMA) prepared by anionic polymerization of tBMA with a lithium counterion in THF/toluene mixed solvents at −78 °C. As a probe of the structural changes of the propagating species, multinuclear 7Li, 1H, and 13C NMR analysis of di-tert-butyl 2-lithio-2,4,4‘-trimethylglutarate (a model dimer, A) and of short-length living PtBMA chains is reported and discussed. Whatever the system, the main structure of the lithium ester enolate in THF/toluene mixtures is similar to that one reported in THF. In the case of A and for toluene contents exceeding 50% v/v, partly organized pseudophases can additionally be detected in the 7Li NMR spectra, but they do not provide well-developed 1H and 13C NMR signals. The chemical shifts of 1H and 13C signals of A support the dimeric form of this model. An equilibrium between dimeric and nonaggregated living PtBMA chains has been previously proposed to dominate in pure THF. However, marked self-termination of low-molecular weight living oligomers prepared in THF/toluene mixtures can be observed at 263 K, in contrast to the stability observed in pure THF up to 298 K. Another contrasting feature is the broadening of the molecular weight distribution which can be explained by an aggregation process that stabilizes oligomers at the early stage of the anionic polymerization as supported by SEC-RI and SEC-UV eluograms. [less ▲]

Study of the protective effects of hyperimmune immunoglobulins G and M against endotoxin in mice and rats

in Medical Microbiology & Immunology (1999), 188(2), 55-64

We prepared solutions of human IgM and IgG to various lipopolysaccharide (LPS) species. These were then tested, along with solutions of non-LPS specific human IgG or IgM, for their ability to confer ... [more ▼]

We prepared solutions of human IgM and IgG to various lipopolysaccharide (LPS) species. These were then tested, along with solutions of non-LPS specific human IgG or IgM, for their ability to confer passive immunity against experimental endotoxemia in two animal models. The immunoglobulins were first tested for an effect on the lethality induced by seven different LPSs in actinomycin-D sensitized mice, or by three different bacteria in normal mice. When the immunoglobulins were administered 1 h before challenge, a small protective effect was observed. This protection was dependent upon both the anti-LPS agent, the chemical composition of the LPS, or the strain of gram-negative bacteria used for injection. The anti-LPS IgM and IgG preparations reduced the mortality induced by Escherichia coli but not by Serratia marcescens or Klebsiella pneumoniae, indicating protection by strain-specific antibodies. When the antibodies were preincubated with LPS or bacteria for 30 min before administration, almost complete protection was seen. The influence of these immunoglobulin preparations or of human albumin (as a control) on the hypotensive and vascular-permeabilizing effects of LPS in rats was then studied. A dose-dependent inhibitory effect was observed with IgG preparations and albumin. At 200 mg/kg, anti-LPS IgG reduced the effects of LPS, while at 400 mg/kg, both anti-LPS and normal IgG preparations showed protection, as did human albumin used at the same dose. The IgM-enriched preparation worsened the initial hypotensive phase after LPS, whereas the anti-LPS IgM significantly reduced the second phase of the hypotension, but only at the largest dose of 400 mg/kg. In this second model using the rat, a clear difference between the activity of IgG and IgM was thus observed. We conclude that pretreatment with human immunoglobulins from large plasma pools modestly, but significantly, attenuated the effects of murine and rat Gram-negative sepsis, but that protection was incomplete. Our results suggest that single regimen intervention strategies may not be sufficient to influence the course of the disease. [less ▲]

Study of the provenance of Belgian merovingian Garnets of cloisonné style artefacts

Poster (2008)

Study of the relationship between lipid binding properties of cyclodextrins and their effect on the integrity of liposomes

in International Journal of Pharmaceutics (2007), 338(1-2), 35-42

It is well known that cyclodextrins are able to extract lipids constituting membranes, increasing their fluidity and permeability. This behaviour towards biological membranes is directly linked to the ... [more ▼]

It is well known that cyclodextrins are able to extract lipids constituting membranes, increasing their fluidity and permeability. This behaviour towards biological membranes is directly linked to the toxicological effects of methylated cyclodextrins. However, confusion is currently made in the literature between the different methylated cyclodextrin derivatives. Moreover, a new methylated cyclodextrin derivative recently occurred in the market. the Crysmeb (R). We wanted to compare and understand the effect of the most currently used cyclodextrins on a model membrane. We studied the influence of natural cyclodextrins (beta CD and gamma CD), methylated derivatives (2,6-dimethyl-beta CD (Dimeb), 2,3,6-trimethyl-beta CD (Trimeb) and randomly methylated-beta CD (Rameb), as well as the new derivative Crysmeb), hydroxypropylated derivatives (HP beta CD of different substitution degrees and HP gamma CD) and the sulfobutylated derivative (SBE beta CD) on the release of a fluorescent marker encapsulated in the inner cavity of liposomes. It was shown that the observed effect on calcein release can be directly related to the affinity of cyclodextrins for both lipid components of liposomes, cholesterol and phosphatidylcholine. From this relationship, we were able to determine, for each cyclodextrin, a theoretical concentration giving rise to 50% or 100% calcein release. This theoretical concentration was confirmed experimentally. We have also showed that cyclodextrins which provoke calcein release also induce large structure modifications of liposomes. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]