The stress dependence of the subgrain size in aluminium

Etch-pit (EP) technique and transmission electron microscopy (TEM) have been used to investigate the subgrain size, , as a function of applied shear stress, , during high-temperature creep of aluminium. Examination of thin foils, prepared from deformed specimens, in the electron microscope shows the presence of very large equiaxed sub-grains that approximate those observed in etch-pit photographs. By measuring the average subgrain size from transmission micrographs of representative areas of the foils, two observations are made. First, the average subgrain size is smaller than that determined from etch-pit procedure, but exhibits the same stress dependence: /b (/G)^– where b is the Burgers vector and G is the shear modulus. Second, the TEM subgrain size data of aluminium and those of other metals and alloys, when plotted in the normalized form of /Gb against /Gb on a logarithmic scale, where is the stacking-fault energy of the material, fall within a narrow, horizontal band, confirming earlier reports that the subgrain size is insensitive to stacking-fault energy.     

Stripping of copper coatings from steel in Cr(VI)-free commercial bath

In this work the electrochemical characteristics of copper and steel in chromate, cyanide, and phosphate baths as well as in a commercial bath (ENSTRIP S-180), in the absence of chromium and cyanides were determined. Average rates of copper coatings stripping from steel in the above mentioned baths and the baths influence on the morphology of steel surfaces were described. It was found that the commercial bath ENSTRIP S-180 could be successfully used for stripping of copper coatings from steel elements.     

Electropolishing and passivation of NiTi shape memory alloy

Electropolishing of NiTi alloy has been investigated. The influence of polishing bath composition and the operating conditions instead of the conditions of the process on the quality of the surface, evaluated by AFM and SEM methods, was established. Morphologically uniform surfaces were obtained only in the case of solutions containing hydrofluoric and sulfuric acids. Electropolished samples were sterilized and thermally passivated, then their corrosion resistance was measured in Tyrode's physiological solution. It was established that already after the electropolishing the corrosion resistance of NiTi alloy increases due to the spontaneously formed TiO₂ layer. The increase of the thickness of the layer during sterilization and thermal passivation causes further increase in the corrosion resistance.     

Vitamin C and plasma triglycerides in experimental animals and in humans

A chronic latent vitamin C deficiency in guinea pigs enhances triglyceride concentration in blood plasma but does not markedly alter the composition of fatty acids in serum and hepatal triglycerides. An addition of 0·5% ascorbic acid to the diet of golden hamsters tends to normalise alimentary hypertriglyceridemia provoked by a high-glucose fat-free diet not containing vitamin C. A daily administration of 2 × 500 mg of an effervescent ascorbic acid for three months to subjects aged between 50 and 75 who were in a state of a seasonal vitamin C deficiency resulted in a significant depression of triglyceridemia. The hypotriglyceridemic effect of ascorbic acid depended on the starting plasma concentration of triglycerides: the higher the initial triglyceridemia, the more striking the hypotriglyceridemic effect. An administration of 2 × 500 mg of effervescent ascorbic acid every 24 h to a selected group of subjects with an initial triglyceridemia above 200 mg % for the duration of one year brought about a very significant decline of triglyceridemia, and this still persisted six weeks following cessation of ascorbic acid administration. An intervention of vitamin C at the level of triglyceride splitting enzymes is presumed.     

Effect of dehydrated apple products on the serum and liver lipids in Syrian hamsters

The effect of two dehydrated apple products (10% in diet)--apple pulp (crude fibre 3.5%, pectin 1.4%) and apple pomaces (crude fibre 13.5%, pectin 7%)--on the serum and liver lipids of growing Syrian male hamsters were studied. The animals were fed a natural diet (38% of energy substituted by milk fat; the diet contains 53 mg of cholesterol (CH) per 100 g) which resulted in an accumulation of CH and triacylglycerols (TG) in the serum as well as in the liver, and CH-rich very low density lipoproteins (VLDL) in the circulation. After two months both apple products decreased the levels of CH and TG in serum (by 40-70%) and the content of CH in VLDL with similar efficiency. Both products reduced CH content in the liver, and the apple pulp also decreased TG content. Up to the 6th month the apple pulp studied suppresses accumulation of CH and TG in both the serum and the liver. A complete analysis of lipoproteins of main density class at the time showed that the decrease of serum CH and TG to a decisive extent is due to the decrease of their concentration in VLDL (by more than 50%). Therefore, the concentration of VLDL and the whole lipoprotein pool decreased by 50%. The apple pulp doubled the amount of CH transported by HDL. Three months after the replacement of butter in the diet by corn germ oil the CH and TG levels in the serum and TG also in the liver decreased to the physiological level.(ABSTRACT TRUNCATED AT 250 WORDS)     

Investigations on electrochemical α-methoxylation of selected dipeptides

Voltamperometric studies on the indirect electrochemical α-methoxylation of Boc-Pro-Gly-OMe and Boc-Val-Gly-OMe in MeOH in the presence of NaCl or NaBr as the mediator suggested that the first reaction step was a direct N-halogenation of the dipeptide by active chlorine or bromine adsorbed on the electrode surface. The kind of mediator (NaCl or NaBr), its concentration, the current density, and the applied electric charge had a significant influence on the reaction course. In the case of Boc-Pro-Gly-OMe, the use of sodium bromide was necessary to obtain a relatively high ratio of α-monomethoxylation to α,α-dimethoxylation. For Boc-Val-Gly-OMe, the selectivity for α-monomethoxylation was close to 100%, independently of the mediator. Optimisation of the selected electrolysis parameters allowed us to significantly improve the yield and selectivity of the α-methoxylation of Boc-Pro-Gly-OMe (Kardassis et al. Tetrahedron 54:3471, 1998) and to obtain good results in the α-methoxylation of Boc-Val-Gly-OMe.