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The observation that some subjects with low PTH had elevated plasma magnesium (Mg) levels prompted us to analyze in 41 patients on maintenance hemodialysis for 44 +/- 36 months, their serum Mg concentrations, and the relationship between plasma Mg and PTH levels. The mean serum Mg concentration was 2.4 +/- 0.2 mg/dl. Twenty-four out of the 41 subjects (58.5%) had hypermagnesemia (serum Mg above 2.5 mg/dl). Patients were classified into 3 groups according to their PTH level: Group A, low PTH (below 120 pg/ml); group B, adequate PTH (120-250 pg/ml); and group C, high PTH (above 250 pg/ml). There were no differences among groups according to number of subjects, age, sex, time on dialysis, renal disease, serum calcium, phosphorus, bicarbonate, vitamin D or aluminum concentrations. Doses of calcium carbonate and aluminium hydroxide were also similar in all groups. Curiously, although the differences were not statistically significant, the total cumulative intake of calcium and aluminium were less in group A than in the other groups. Interestingly, patients with low PTH had a significantly higher serum Mg concentration than patients with adequate or high PTH (2.8 +/- 0.2 mg/dl vs 2.3 +/- 0.1 mg/dl and 2.2 +/- 0.1 mg/dl, respectively, p < 0.01). Moreover, regression analysis showed a negative linear correlation between serum PTH level and plasma Mg concentration (r = -0.6059, p < 0.001). Based on these findings, chronic hypermagnesemia could have a suppressive effect on PTH secretion, and it could be a risk factor for the development of adynamic bone disease in dialysis patients.

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The perovskite oxides NdNi 1−x Cu x O 3 have been synthesized for 0 x 0.2 under high oxygen pressure using a sol-gel method. Their structural, electrical, magnetic and calorimetric properties have been measured over a wide temperature range (4-300 K). All of the samples have an orthorhombic unit cell which does not change with Cu content. Nevertheless, their electrical properties change drastically with x from the very lowest values of x. The metal-insulator transition temperature decreases as x increases, up to x = 0.03; for x 0.03 the system is metallic for all temperatures. Moreover, the replacing of Ni with Cu atoms leads to magnetic disorder in the Ni sublattice.

There is a great deal of interest vested in the superconductivity of Si clathrate compounds with sp3 network, in which the structure is dominated by strong covalent bonds among silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. A joint experimental and theoretical investigation of superconductivity in Al-substituted type-I silicon clathrates is reported. Samples of the general formula Ba8Si46−xAlx, with different values of x were prepared. With an increase in the Al composition, the superconducting transition temperature TC was observed to decrease systematically. The resistivity measurement revealed that Ba8Si42Al4 is superconductive with transition temperature at TC = 5.5 K. The magnetic measurements showed that the bulk superconducting Ba8Si42Al4 is a type II superconductor. For x = 6 sample Ba8Si40Al6, the superconducting transition was observed down to TC = 4.7 K which pointed to a strong suppression of superconductivity with increasing Al content as compared with TC = 8 K for Ba8Si46. Suppression of superconductivity can be attributed primarily to a decrease in the density of states at the Fermi level, caused by reduced integrity of the sp3 hybridized networks as well as the lowering of carrier concentration. These results corroborated by first-principles calculations showed that Al substitution results in a large decrease of the electronic density of states at the Fermi level, which also explains the decreased superconducting critical temperature within the BCS framework. The work provided a comprehensive understanding of the doping effect on superconductivity of clathrates.

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