Modèles Hydrodynamiques pour la Séparation des Courants dans un Décanteur Pilote

Despite of its general use in industry, particle sedimentation is still a not well understood unit operation. Hydrodynamics is complex in essence, mainly because the possible volumes are depending on the operating conditions, which in turn has consequences on the stability of the equipment in unsteady state conditions.     

On the feasibility of ocean brine pool power stations

The demonstrated existence of vast brine pools in a number of places in the ocean basin around the world offers an interesting opportunity to the production of power from ocean, which has not been yet considered. The attractiveness of these vast deposits of brine lie in the fact that can be readily dissolved with the surrounding top waters extracting the spontaneous osmotic mixing energy released. In addition, osmotic engines can pumped out the brackish streams by buoyancy without the add of pressure exchangers (PEXs) as is required in current pressure retarded osmosis (PRO) technology and then simplifying significatively the overall process. Utilizing a simplified physical model, a first estimation for the density of power per unit of membrane area was calculated.     

An estimate for thermal osmotic heat storage using precipitation of common salts

In this brief note, a first assessment on the possibilities for thermal osmotic storage by harnessing the thermal dependence of the solubility of common salts as an alternative method to sensible heat storage is discussed. In a recent study it was found that such a dependence could be used to run a heat powered cycle (osmotic heat engine). The question raised then is whether that approach could be suitable for thermal energy storage as well. The attractiveness of such a possibility lies in the capability to store energy for an indefinite period of time without using expensive isolation systems if one considers that osmotic energy only is released when both streams with different salinities are brought together. Utilizing a simplified model, a comparative study with sensible heat storage was performed. It is shown that thermal osmotic storage via thermal precipitation of common salts could be an attractive option when long thermal storage (days) and compactness is desired.     

Thermoluminescent mechanisms involving transition metal ion impurities and V-type centres in MgO crystals exposed to ultraviolet radiation

Thermoluminescent (TL) mechanisms involving Fe, Cr, Mn and V ions in both divalent and trivalent valence states, and V-type centres were studied in MgO single crystals of varying impurity content after exposure to ultraviolet radiation. Using the ESR technique, it is shown that samples containing primarily divalent impurities show no V-type centres related to the TL mechanism, which is that of charge transfer between the impurities. V-type centres, when present, are seen to be more stable in purer samples than in less pure samples, resulting in a shift of the TL peaks to higher temperatures. The TL mechanism in this case includes charge transfer between V-type centres and the impurities. The supralinear behaviour of TL peak 1 is associated with the R-emission lines of Cr³⁺.     

Production of biogenic amines by lactic acid bacteria and enterobacteria isolated from fresh pork sausages packaged in different atmospheres and kept under refrigeration

The occurrence of in vitro amino acid activity in bacterial strains associated with fresh pork sausages packaged in different atmospheres and kept in refrigeration was studied. The presence of biogenic amines in decarboxylase broth was confirmed by ion-exchange chromatography and by the presence of the corresponding decarboxylase genes by PCR. From the 93 lactic acid bacteria and 100 enterobacteria strains analysed, the decarboxylase medium underestimates the number of biogenic amine-producer strains. 28% of the lactic acid bacteria produced tyramine and presented the tdc gene. All the tyramine-producer strains were molecularly identified as Carnobacterium divergens. Differences on the relative abundance of C. divergens were observed among the different packaging atmospheres assayed. After 28 days of storage, the presence of argon seems to inhibit C. divergens growth, while packing under vacuum seems to favour it. Among enterobacteria, putrescine was the amine more frequently produced (87%), followed by cadaverine (85%); agmatine and tyramine were only produced by 13 and 1%, respectively, of the strains analysed. Packing under vacuum or in an atmosphere containing nitrogen seems to inhibit the growth of enterobacteria which produce simultaneously putrescine, cadaverine, and agmatine. Contrarily, over-wrapping or packing in an atmosphere containing argon seems to favour the growth of agmatine producer-enterobacteria. The production of putrescine and cadaverine was associated with the presence of the corresponding amino acid decarboxylase genes. The biogenic amine-producer strains were included in a wide range of enterobacterial species, including Kluyvera intermedia, Enterobacter aerogenes, Yersinia kristensenii, Serratia grimesii, Serratia ficaria, Yersinia rodhei, Providencia vermicola and Obesumbacterium proteus.     

Application of Mössbauer spectroscopy to study the formation of iron pyrite thin films

Mössbauer spectroscopy has been used to analyse FeS₂ thin films obtained by sulphidation of ⁵⁷Fe evaporated layers. Complementary characterization of the films has been carried out by X-ray diffraction and optical absorption measurements. It is concluded that the two processes (formation and crystallization of FeS₂) which lead to polycrystalline FeS₂ films are strongly influenced by the temperature at which sulphidation is accomplished. The composition of the films drastically changes at temperatures which depend on the thickness of the Fe film to be sulphidated, and their crystallization seems to show a critical temperature at which the crystallization process is severely altered. Optical properties of the pyrite films seem to depend strongly on their stoichiometry.     

Evaluation of exopolysaccharide production by Leuconostoc mesenteroides strains isolated from wine

ABSTRACT:  Exopolysaccharide (EPS)-producing lactic acid bacteria are responsible for the alteration of wine and other fermented beverages. The potential to produce EPS was investigated for Leuconostoc mesenteroides strains isolated from Spanish grape must and wine. Most strains were able to produce EPS from sucrose containing media. Based on their EPS-producing phenotype and on their EPS monosaccharide composition, the L. mesenteroides strains analyzed could be arranged in 2 groups. One group comprises mucoid strains producing a glucan polymer, and the other group includes strains producing a fructan polymer. The presence of a glucosyltransferase encoding gene in the glucan producing L. mesenteroides strains was assayed by PCR. Two primer sets, PF1-PF8 and GTFF-GTFR, were used to amplify internal fragment of known glucosyltransferase genes. None of the glucan-producing strains gave a positive amplicon by the primer sets used. Therefore, new tools need to be developed to broaden the range of potentially spoiling agents detected by PCR in fermented beverages.     

Design of semi-continuous composite steel-concrete beams at the fire limit state

A two-dimensional temperature analysis procedure based on the finite element method (FEM) is described and applied to steel-concrete composite beams. A computer program developed for the analysis is detailed. A strategy is also proposed for incorporating the influence of the partial resistance of the composite connections in reducing the sagging moment at central regions of the beam spans when the beam is calculated as semi-continuous. Finally, an example problem is discussed, comparing the design uniformly distributed loads that can be supported by a composite beam calculated as semi-continuous and with simply supported spans. The temperature distribution due to fire at the central region of the spans is taken as in the simplified procedure proposed in European Prestandard ENV 1994-1-2 [ENV 1994-1-2. Eurocode 4, Design of composite steel and concrete structures — Structural fire design. Brussels: European Committee for Standardization (CEN); 1994] and then obtained with the more rigorous calculation using the described numerical algorithm. It will be assumed that no ultimate limit state will occur due to shear force (web buckling) or due to bending moment at the hogging moment regions of the beam (web and bottom flange buckling or distortional lateral buckling).