Characterization and modification of fillers for paints and coatings

This paper highlights the possibility of inverse gas chromatography for the surface characterization of common fillers (CaCO₃, talc, SiO₂,) for paints and coatings. Divided solids are described, on the one hand, by the dispersive component of their surface energy and, on the other, by a specific parameter indicating their acid-base interaction potential. The role of the surface morphology at a molecular level is also examined. It is demonstrated that steric effects play an important role in the adsorption of probes on lamellar solids like talc. The consequences of surface treatments as well as examples of practical applications are also reported.     

Validation of a Method of Determination of Apparent Diffusivity Versus Composition in Solids

A method is presented for computing the values of apparent diffusivity in solids with respect to the concentration of the diffusing substance (water or sodium chloride). This method does not require any assumption upon the mathematical relationship between diffusivity and concentration. It can be applied to experimental measurements of local concentration versus position within the solid (profiles) with relatively few measurements (circa 10) and a mathematical smoothing of the experimental data by using an artificial neural network model. The method was first validated on simulated data obtained by using a constant diffusivity value and on experimental profiles when the relation between diffusivity and concentration was given. It was then applied to original experimental moisture profiles obtained by putting gelatin gels with different initial moisture contents into contact for up to 14 days. The method was also successfully applied to five sets of experimental moisture and sodium chloride profiles taken from the literature and obtained from different food products. Apparent diffusivities calculated by our method were found in agreement with those obtained by authors using different numerical methods to compute the diffusivity values.     

Prebiotic synthesis of sequential peptides on the Hadean beach by a molecular engine working with nitrogen oxides as energy sources

Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry.     

Characterization of the ntrBC genes of Azospirillum brasilense Sp7: their involvement in the regulation of nitrogenase synthesis and activity

The in vitro effect of citric acid application on periodontally involved root surfaces was investigated using scanning electron microscopy. Teeth were selected following specific criteria. The specimens were prepared for observation, and the features of the root surface were studied. The results demonstrated that a 3-minute application of citric acid (pH = 1.0) to the root surface after scaling and root planing demineralized the outer root surface, opened the dentinal tubules, and exposed collagen fibers. Scaling and root planing alone left the surface with a smear layer, scattered islands of cementum, and no collagen fibers or exposed dentinal tubules.     

Oil yield and compressibility modeling during microscale expression: Criteria for linseed breeding

Seven linseed varieties were harvested at seven times before complete maturity. Microscale oilseed expressions were subsequently carried out on it. A pressure of 10 MPa was applied for 1 h under uniaxial stress. The results were characterized in terms of oil, water and mucilage content, harvest date and oil yield. The piston displacement versus time (creep curves) was described by a four‐Kelvin‐Voigt elements viscoelastic model. Parameters were derived from the model, such as the mechanical properties of seeds (compressibility moduli), showing that the viscoelastic model fits well the experimental data (R² ≈ 0.999). The modeling parameters were combined with some biochemical data in order to predict the kinetics of oil extraction.     

Nitrogen dioxide effect in the reduction of nitric oxide by propane in oxidizing atmosphere

The role of nitrogen dioxide in the selective reduction of NO by propane over a Cu-MFI zeolite is investigated. NO₂ and NO reductions were carried out under similar conditions of reaction. In the presence of oxygen, the reduction of NO by C₃H₈ does not differ significantly from that of NO₂. In the absence of oxygen, the reduction of NO₂ by propane occurs with a partial decomposition of the nitric dioxide molecule. Such a decomposition leads to the formation of oxygen, which is responsible for the increase in catalytic activity by comparison with the same reaction performed with NO. NO₂ formed and released in the gas phase during the reduction of NO by propane in the presence of oxygen does not play a predominant role in the catalytic process.     

The Dübendorf Study: a population-based investigation on normal values of blood pressure self-measurement

In a retrospective study of 50 consecutive children with posterior fossa tumors treated at Texas Children's Hospital, Houston, Tex., in 1989-1992, we evaluated perioperative factors which might influence the development of postoperative cerebrospinal fluid leaks. Factors analyzed included the presence of preoperative hydrocephalus, the institution of cerebrospinal fluid diversion, and the method of dural closure. No statistically significant impact on subsequent cerebrospinal fluid leakage was demonstrated.