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We study by computer simulation the behavior at low energy of two-dimensional Lennard-Jones systems, with square or triangular cells and a number of degrees of freedom $N$ up to 128. These systems exhibit a transition from ordered to stochastic motions, passing through a region of intermediate behavior. We thus find two stochasticity borders, which separate in the phase space the ordered, intermediate, and stochastic regions. The corresponding energy thresholds have been determined as functions of the frequency $\ensuremath{\omega}$ of the initially excited normal modes; they generally increase with $\ensuremath{\omega}$ and appear to be independent of $N$. Their values agree with those found by other authors for one-dimensional LJ systems. We computed also the maximal Lyapunov characteristic exponent ${\ensuremath{\chi}}^{*}$ of our systems, which is a typical measure of stochasticity; this analysis shows that even in the ordered region certain stochastic features may persist. At higher energies, ${\ensuremath{\chi}}^{*}$ increases linearly with the energy per degree of freedom $e$. The law ${\ensuremath{\chi}}^{*}(e)$ has been determined in the thermodynamic limit by extrapolation. The values found for the stochasticity thresholds fall in a physically significant energy range. The behavior of the thresholds as a function of $\ensuremath{\omega}$ and $N$ is compatible with the hypothesis on the existence of a classical zero-point energy, advanced by Cercignani, Galgani, and Scotti.

Five patients with severe hypothyroidism were studied to determine diurnal variations in serum TSH and thyroid hormones. The results were based on blood samples withdrawn at 1-h intervals during a 24-h period. A statistically significant circadian rhythm in TSH was detected with the acrophase at 23(30); no significant diurnal periodicity was observed for serum T3. The TSH pattern was similar to that observed in normal and midly hypothyroid subjects, with low levels during the day and higher levels at night. The findings are consistent with the following concepts: a. the TSH circadian rhythm is retained in patients with severe hypothyroidism; b. the abnormality in thyroid function does not effect the regulation of the TSH periodicity.

The main studies on silver fir were aimed at investigating the relationship between annual ring growth rhythms and climate factors. The aim of the present work is to know how the silver fir responds to both the environmental factors and meteorological parameters as a function of altitude and soil characteristics. The results are that the ring growth depends mainly on winter mean temperature of the same year considered in the chronologies, from summer precipitation and from mean summer temperature of the preceding year. The influence of winter mean temperature appears more pronounced in shallow soil at high altitude. The effect of mean summer temperature and of summer precipitation is greater at low altitude, and at high altitude only in shallow soil.