Superconductivity in CaBi2.

Superconductivity is observed with critical temperature Tc = 2.0 K in self-flux-grown single crystals of CaBi2. This material adopts the ZrSi2 structure type with lattice parameters a = 4.696(1) Å, b = 17.081(2) Å and c = 4.611(1) Å. The crystals of CaBi2 were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at Tc is ΔC/γTc = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient γ = 4.1 mJ mol(-1) K(-2) and the Debye temperature ΘD = 157 K. The electron-phonon coupling strength is λel-ph = 0.59, and the thermodynamic critical field Hc is low, between 111 and 124 Oe CaBi2 is a moderate coupling type-I superconductor. Results of electronic structure calculations are reported and charge densities, electronic bands, densities of states and Fermi surfaces are discussed, focusing on the effects of spin-orbit coupling and electronic property anisotropy. We find a mixed quasi-2D + 3D character in the electronic structure, which reflects the layered crystal structure of the material.

Exercise thermoregulation in Thai and Polish male subjects.

The aim of this study was to compare the efficiency of exercise thermoregulatory functions in Thai and Polish groups. Twelve Thai and 14 Polish healthy male students were included. An exercise test on a bicycle ergometer at 53% of the maximal work load was performed at ambient air temperature of 30 degrees C and relative humidity of 70%. The test was terminated when rectal temperature (Tre) rose by 1.2 degrees C. Duration of this exercise considered as an index of the efficiency of exercise thermoregulatory functions. The duration of test exercise was evidently longer in Thais (44.8 min) than in Polish students (34.1 min). The rate of increase in the internal body temperature was lower in Thais (0.029 degrees C x min-1) than in Poles (0.037 degrees C x min-1) but exercise dehydration as well as the rate of body weight loss were significantly higher in Thais than in Poles. It can be concluded that the exercise thermoregulatory mechanisms are more efficient in Thais. Polish young athletes were poorly adapted to exercise in warm and humid environment and thus they require more exercise training in climatic chamber prior to competitions held in countries with warm and humid climate.