Long-term low-dose calcitriol treatment in predialysis chronic renal failure: can it prevent hyperparathyroid bone disease?

In an uncontrolled open study 13 patients with moderate to preterminal renal failure were treated with low doses (average 0.36 micrograms/day) of calcitriol up to the time of renal transplantation, which was performed before dialysis had been initiated. A transiliac bone biopsy was obtained both at the start and at the end of the treatment period, the latter coinciding with renal transplantation. All patients who started calcitriol treatment at a creatinine clearance (Ccr) above 30 ml/min had normal bone histology at the time of transplantation, but this was not observed when calcitriol treatment was started at Ccr below 30 ml/min. The study suggests that full benefit of calcitriol at the bone level is obtained only if prophylactic administration is started early in the course of renal failure.     

The thermal ignition of lignocellulosics in infinite slab and cubic geometries

Wood shaving samples were heated in both cubic baskets and in a previously described system realising the conditions of the ‘infinite slab’ in thermal ignition. Results from the two sets of experiment were found to be totally consistent with each other.     

The adsorption/impregnation of catalytic precursors on pure and composite oxides

Three intrinsically connected phenomena occur during adsorption/impregnation of aqueous electrolytes onto oxide carriers. They are: pH-dependent development of surface charge carriers on the oxide; pH-dependent aqueous speciation of catalytic precursors; surface adsorption by complexation and coordination. Modeling of these processes yields basic thermodynamic properties of the adsorbed phase, which could provide useful information of the catalytic properties of the metal, support, and reveal metal-support interactions, thus contributing to design criteria for supported-metal catalysts.

The spectrum of catalytic systems that can be studied using the above approach is greatly extended when both pure and composite oxide carriers are considered. This presentation will focus on three metal/support systems, each of which provides results of both practical and fundamental importance.     

Nitrogen plasma source ion implantation of AISI S1 tool steel

Significant economic savings can be achieved by improving the wear lifetime of precision manufacturing tools through nitrogen-ion implantation. This near-ambient temperature, surface modification process preserves dimensional integrity and surface finish while eliminating delamination problems that are often associated with overlay coatings. Conventional ion implantation is a line-of-sight process which requires elaborate manipulation and masking to uniformly implant components of complex shapes. A recently developed process, plasma source ion implantation (PSII), circumvents this line-of-sight restriction and makes ion implantation more attractive economically. In this article, the effects of PSII of nitrogen at a target bias of 50 kV, to a dose of 0.3 × 10¹⁸ atoms/cm² on the surface microstructure and mechanicalproperties of AISI S1 tool steel are presented.     

Absorption spectra of solid rare earth complexes obtained from the inner filter effect on luminescence

The inner filter effect is observed in luminescence whenever a second substance is present that has absorptions which overlap the luminescence. This results in a diminution of the luminescence at those wavelengths and is generally observed in solution. In the present communication we show that this effect can be observed when a solid rare earth complex is physically mixed with a solid luminescent organic matrix with which it does not interact. The resulting luminescence is reduced in emission intensity at those wavelengths corresponding to the absorptions of the rare earth ion. This is illustrated with a mixture of Na₃[Ho(ODA)₃] ·2NaClO₄·6H₂O and pyrene at 77 K, and it is shown that the absorption spectrum of the holmium complex can be extracted from the luminescence spectrum of pyrene. This absorption spectrum is in good agreement with that obtained by conventional spectroscopy with a single crystal.     

Surface electronic structure of rare earth metals

Angle-resolved UV photoemission has been used to investigate the electronic structure of the (0001) surfaces of scandium, yttrium, praseodymium and gadolinium. Off-normal emission spectra were recorded with high angular resolution, enabling detailed mapping of the dispersion of valence band features. Yttrium and gadolinium show similar results to published data from Ho(0001), suggesting minimal 4f influence in the lanthanide bandstructures. Differences seen on praseodymium and scandium may be due to 4f derived states and surface states respectively.     

Catalytic behaviour and surface properties of supported lanthana

This paper deals with the role of dispersed lanthana as an active phase in several catalytic reactions: CO hydrogenation, CO oxidation, and oxidative dimerization of methane.

Characterization of the prepared catalysts indicates that lanthana can be effectively dispersed on silica and on ceria. While in the case of silica-supported catalysts lanthana appears at the surface, leading to an almost full coverage for loadings higher than 40%, in the case of ceria-based systems, lanthana forms a solid solution with the support.

In all the reactions studied, the presence of lanthana can be related to significant changes in the catalytic properties of the bare supports. Thus, the selectivity towards the total oxidation products observed on pure ceria is decreased, and the low activity shown by silica is enhanced. For the CO+H₂ reaction, the addition of lanthana also generates upgraded products.