Thermal Diffusivity in Supercritical Fluids Measured by Thermal Lensing

Thermal diffusivities of supercritical CO₂ and C₂H₆ were determined over a wide density range with a photothermal technique. The thermal lens, formed by the degradation of the absorbed light energy as heat by the sample, allows the employment of a nonequilibrium method in the critical region. Controlling the refractive-index gradient, i.e., a density gradient, perturbations can be maintained at levels where convection is negligible. An easy-to-operate setup allowed us to measure thermal diffusivities in the density ranges 5 to 20 mol·dm^–3 for CO₂ at 308 and 313 K and 2 to 12 mol·dm^–3 for C₂H₆ at 308 K with a standard precision of 15%.     

Characteristics of a NaOH-Activated Blast Furnace Slag Blended with a Fine Particle Silica Waste

Mortars of blast furnace slag blended with a geothermal silica waste at various replacement levels of 0%, 5%, 10%, 15%, and 20% were cured for up to 90 days. The binder was activated by 6 wt% Na₂O equivalent of sodium hydroxide. Lime was added as an activating agent and also to promote pozzolanic reaction with the silica. It was found that the presence of the silica waste increased the reactivity of the cementitious materials, as measured by means of nonevaporable water. The compressive strength was increased in the presence of the silica, except at the highest replacement level of 20%, the optimum silica replacement was that of 5%–10%. The microstructures of blended slag showed less porosity than those of neat slag mortars. The lime was completely consumed after 90 days of hydration.     

Identification of aroma components of Spanish ‘Verdejo’ wine

Aroma components of ine resulting from fermentation of grape must from the Verdejo cultivar ere isolated by continuous liquid-liquid extraction and further fractionation on a silica gel column. One hundred and thirty-to substances, including alcohols, esters, carbonyl compounds, terpenes, acids and sulphur compounds, ere identified by using GC-MS; some had not been previously detected in ines. Data are given hich could lead to the characterisation of the Verdejo cultivar and the effect of the elaboration of young ines. The sensory contribution of some volatile compounds to the flavour of Verdejo ine is also studied.     

Fractionation and characterisation for antioxidant activity of hydrolysed whey protein

Whey protein isolate (WPI) was hydrolysed for 1 h using Alcalase, Protamex and Flavourzyme. Native WPI, hydrolysed WPI and two commercial WPI hydrolysates were subjected to fractionation by size exclusion chromatography. Antioxidant activity of WPI fractions was measured with a liposome‐oxidising system (50 µM FeCl₃/0.1 µM ascorbate, pH 7.0). Lipid oxidation was measured as thiobarbituric acid‐reactive substances (TBARS). Gel electrophoresis and amino acid analysis were run to identify the peptide composition. The influence of amino acid composition on antioxidant activity was evaluated using multivariate analysis methods (correlation analysis, principal component analysis, multiple linear regression and discriminant analysis). TBARS assays indicated the presence of antioxidant activity in all protein fractions, including non‐hydrolysed WPI. For native and hydrolysed WPI samples the first fraction (> 45 kDa) showed a higher TBARS inhibition effect (24–27%) when compared with lower‐molecular‐weight fractions and hydrolysate mixtures. In contrast, for commercial WPI hydrolysates a higher inhibitory effect was found in most of the lower‐molecular‐weight fractions (30–55%). The ability of WPI fractions to delay lipid oxidation was found to be related to the prevalence of histidine and hydrophobic amino acids. Copyright © 2004 Society of Chemical Industry     

Potential applications of poly(vinyl alcohol)‐congo red aqueous solutions and hydrogels as liquids for hydraulic fracturing

The authors report on the viscoelastic characterization of guar hydrogels obtained through complexation reactions with borax ions. These gels are compared with hydrogels obtained from poly(vinyl alcohol) of different degree of hydrolysis through complexation reactions with congo red. The effect of the degree of hydrolysis and both, the concentration of PVA and the concentration of congo red, on the viscoelastic properties of the hydrogels is analyzed. The potential use of the PVA‐based hydrogels as hydraulic fracturing liquids is discussed in relation to the commonly used fracturing liquid based on the guar–borax system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

MTCLAB: A MATLAB®-based program for traveltime quality analysis and pre-inversion velocity tuning in 2D transmission tomography

A MATLAB^®-based computer code that analyses the traveltime distribution and performs quality analysis at the pre-inversion stage for 2D transmission experiments is presented. The core tools of this approach are the so-called mean traveltime curves. For any general recording geometry, the user may select any pair of subsets of contiguous sources and receivers. The portion of the domain swept by the implied rays defines a zone of analysis, and for each source (receiver) the outcoming (incoming) ray fan is named a source (receiver) gather. The empirical mean traveltime curves are constructed, for each zone, by assigning the average and the standard deviation of the traveltimes in the gathers to the positions of the sources (receivers).The theoretical expressions assume isotropic homogeneous velocity inside each zone. The empirical counterparts use the observed traveltimes and make no assumptions. Isotropic velocity in each zone is inferred by least-squares fitting of the empirical mean traveltime curves. The user may refine the analysis considering different zones (multi-zone analysis). Initially the whole domain is modelled as a single zone. The procedure compares empirical versus theoretical curves. In addition, residuals can be plotted using source–receiver positions as plane coordinates. The results are used to unravel the possible presence of anomalous gathers, heterogeneities, anisotropies, etc. Depending on the kind of anomalies, velocity estimation and mean time residuals are different in the source and receiver gather curves.This software helps to grasp a better understanding of the data variability before the inversion and provides to the geophysicist an approximate zonal isotropic model and a range of velocity variation that can be used in the inverse problem as a priori information (regularization term). Its use is described through tutorial examples. A guided user interface leads the user through the algorithm steps.     

Laser welding of Al55-Zn coated steel sheet

A study has been made of the procedures used for the lap and butt welding of 0.62 and 1.16 mm thickness steel sheets coated with Al55-Zn alloy, using laser-beam technology. The main problems arise in lap welding as a result of zinc evaporation from the coating. The vapour pressures of this element lead to cratering and blistering of the welds which are visible from the external surface and imply severe weld defects. An efficient solution to this problem consists in leaving a gap between the internal faces, thus allowing the zinc vapours to escape. Excessive gaps, however, lead to the molten metal collapse and to lack of penetration. In the present work, acceptable results were obtained with a maximum interface separation of 0.1 mm. This allows excellent continuity of the joints, without cracks, pores or non-metallic inclusions and with moderate hardnesses, thus demonstrating the good laser weldability of the coated material. A difficulty arises, however, in relation to the coating in zones close to the weld. In these high-temperature zones the coating is lost, and in the immediately adjacent areas the coating microstructure and phases are altered, as was shown by scanning electron microscope analyses.