To investigate whether the derangements in calcium kinetics in patients with renal osteodystrophy are similar in the various histologic forms of this metabolic bone disease, 43 patients on chronic maintenance dialysis underwent calcium kinetic studies using the double isotope technique, iliac crest bone biopsies for mineralized bone histology and histomorphometry and determinations of serum indices of calcium and bone metabolism. Intestinal calcium absorption was not different among the three histologic groups. However, women exhibited lower calcium absorption in each histologic form (P < 0.01). Patients with predominant hyperparathyroid bone disease showed plasma calcium efflux, calcium accretion rate and calcium retention markedly above normal values. Patients with low turnover bone disease exhibited a normal or slightly decreased plasma calcium efflux and calcium accretion rate together with a disproportionately low calcium retention. Patients with mixed uremic osteodystrophy presented with a calcium kinetic profile intermediary to the two other forms. Good relationships existed between plasma calcium efflux, calcium accretion rate, calcium retention and histomorphometric parameters of bone turnover as well as serum levels of parathyroid hormone. However, no serum parameter could indicate with certainty the underlying bone disease. These findings demonstrate that adynamic bone disease does not merely represent an academic finding but is characterized by a very low bone capacity to buffer calcium and inability to handle an extra calcium load. This is particularly relevant for the daily care of end-stage renal failure patients presently receiving higher than ever amounts of vitamin D and calcium salts.

The formation of pure single crystalline silicon nanoparticles by microwave induced decomposition of silane in a low pressure flow reactor is reported. The morphology and crystal structure of the particles are characterized in situ by particle mass spectrometry (PMS) and ex situ by means of X-ray diffraction, high resolution transmission electron microscopy, electron energy loss spectroscopy, and infrared spectroscopy. The preparation method allows for the adjustment of the mean particle diameter in the range 6 nm < or = dPM < or = 11 nm by controlling the precursor concentration, gas pressure, and microwave power. Spectroscopic investigations reveal that the particles are single crystal silicon. The potential on n- or p-type doping is in progress.

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The kinetics of C2 radical reactions during the first stage of acetylene high-temperature pyrolysis was studied by monitoring C, C2 and C3 radicals. Quantitative C2 detection was performed by ring dye laser absorption spectroscopy, C atoms were measured by applying atomic resonance absorption spectroscopy, and C3 radicals were monitored by their emission using a combination of a spectrograph and an intensified CCD camera system. The experiments were performed behind reflected shock waves and cover the temperature range of 2580−4650 K at pressures around 2 bar. In the first part of the study initial mixtures containing Ar with 5−50 ppm C2H2 were used. In this very low concentration range, rate coefficients for the following four reactions were determined:  C2H2 + M C2H + H + M (R1); C2H + M C2 + H + M (R2); C2 + C2 C + C3 (R3); C2 + M C + C + M (R4); where k 1 = 6.96 × 1039 T -6.06 exp(−67 130/T) cm3 mol-1 s-1, k 2 = 1.74 × 1035 T -5.16 exp(−57 367/T) cm3 mol-1 s-1, k 3 = 3.2 × 1014 cm3 mol-1 s-1, and k 4 = 1.5 × 1016 exp(−71 650/T) cm3 mol-1 s-1. Furthermore, this experiments indicate that a modification of the JANAF thermodynamic data of either C, C2 or C3 seems to be necessary. In the second part, some experiments with relatively high initial acetylene concentrations up to 500 ppm C2H2 in Ar were carried out to check the validity of a more complex mechanism for the acetylene pyrolysis. Finally in a third part, a perturbation study was performed by adding 1000 ppm H2 to the initial mixtures of Ar with 20 and 50 ppm of C2H2. For the most important perturbation reactions, C2 + H2 C2H + H (R5) and C2H + H2 C2H2 + H (R6), rate coefficients of k 5 = 6.6 × 1013 exp(−4000/T) cm3 mol-1 s-1 and k 6 = 7.4 × 1014 exp(−3400/T) cm3 mol-1 s-1 were obtained.

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