Etched sections of agates examined by scanning electron microscopy show three types of compositional zonation'. (1) two-unit oscillatory sequences in which the successive zones are of the same width, on a micron scale, but show a uniform difference in the content of (OH) in structural sites; (2) three-unit oscillatory sequenc€s of various palindromic types in which successive zones are of the s...

UNLABELLED In this work, we have obtained colloidal solutions of Si nanocrystals (Si-ncs), starting from free-standing porous silicon (PSi) layers. PSi layers were synthesized using a two-electrode Teflon electrochemical cell; the etching solution contained hydrogen peroxide 30%, hydrofluoric acid 40% (HF), and methanol. The anodizing current density was varied to 250 mA cm(-2), 1 A cm(-2), and...

The interactions of alkali fluorides with D-xylose have been studied by X-ray diffraction (XRD), infrared spectroscopy (IR), nuclear magnetic resonance (NMR, 1H and 13C) and atomic absorption spectrophotometry. KF and CsF form complexes with D-xylose in a 1:1 molar ratio. These complexes can be obtained by solid state milling the reactants in an agate mortar or from methanolic solutions of the ...

We describe the synthetic route towards a novel class of salts, trifluoromethylsulfonylsulfates, as exemplified by the silver(I) derivative (AgS2O6CF3). Formation proceeds via direct reaction between a triflate precursor, AgSO3CF3, and SO3. The title compound crystallizes in the P2(1)/c unit cell with a = 5.15746(14) Å, b = 25.8563(9) Å, c = 5.53970(14) Å and β = 101.1749(19)°. The structure is...

In the dating of sediments by luminescence methods, to obtain a sample the purest possible as to its mineralogy determines the rest of the analytical procedures. The isolation of the sample minerals is a critical stage due to the impossibility of quantifying the relative contributions to the dose from the different minerals. In this paper we propose a non chemical method to isolate quartz from ...

In the residual∗ cost sharing game with a convex technology, the equilibrium demands maximize total surplus, but total payment may differ from the actual cost, and a user with a null demand may be subsidized. If the cost function is totally monotone (e.g., polynomial with positive coefficients, or exponential), participation is voluntary and total payment covers actual cost. The ratio of excess...

The effect of carbon materials on TiO2 for the photocatalytic hydrogen gas production from water / alcohol mixtures was investigated. Single walled carbon nanotubes (SWNTs), multi walled carbon nanotubes (MWNTs), carbon nanofiber (CNF), fullerene (FLN), graphite (GP), and graphite silica (GS) were used as co-catalysts by directly mixing with TiO2. Drastic synergy effects were found with increas...