The effect of K+ on freshly precipitated BaSO4 is seen to increase the area of the crystals. The exchange rate of Ba2+ with these crystals is found to be proportional to this increased area. The extent of234Th precipitation is found to be, increased more than can be accounted for by the area change, and it is suggested that the
concentration of Th4+ adsorption sites increases as more K+ is incorporated into the lattice. Activation energy measurements show the reaction mechanisms to be unchanged by the presence
of K+. Values of 11.4 and 24.4 Kcal·mol−1 for the Ba2+ and Th4+ reactions, respectively, are consistent with an activation process involving loss of water of hydration.
Earlier work on the coprecipitation of230Th and234Th with BaSO4 has been confirmed and in particular the influence of other ions was investigated. Potassium ions, both in the solution and
in the crystals, promote the coprecipitation, while polyvalent cations tend to prevent it. It is shown that increased concentration
of K+ causes a marked change in the BaSO4 crystal form, with a concomitant increase in surface area. At the same time, the rate of exchange of133Ba2+ with the BaSO4 surface is also increased. This can be roughly accounted for by the change in surface area. It is conjectured that an equilibrium
occurs involving foreign cations in the lattice.
Authors:F Köteles, Z Dömötör, T Berkes, and R Szemerszky
Polar watches with heart rate monitoring function have become popular among recreational and professional athletes. In addition to monitoring functions, they calculate a specific index called OwnIndex which is claimed to measure aerobic training status. The current research attempted to shed light on the factors determining the OwnIndex. In Study 1, OwnIndex calculated by the RS-400 Polar watch was estimated using anthropometric (gender, age, height, weight), cardiovascular (resting HR, RMSSD), and exercise-related (maximal oxygen uptake, self-reported physical activity) data of 45 young adults. In Study 2, the OwnIndex was measured in 21 young adults twice, first with self-reported physical activity set to the lowest, then to the highest value. In the regression analysis (Study 1), the only significant predictor of OwnIndex was self-reported physical activity (R2 = 0.883; β = 0.915, p < 0.001). A significant difference with a large effect size (t(20) = −16.657, p <0.001, d = 3.635) and no significant correlation (r = −0.32; p = 0.155) were found between the OwnIndices calculated with different levels of activity in Study 2. As anthropometric and cardiac variables play a practically negligible role in the calculation of the OwnIndex, it cannot be considered an appropriate measure of aerobic fitness.