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Melatonin (MEL) affects the immune system by direct or indirect mechanisms. An involvement of the zinc pool in the immune-reconstituting effect of MEL in old mice has recently been documented. An altered zinc turnover and impaired immune functions are also evident in pinealectomized (px) mice. The present work investigates further the effect of "physiological" doses of MEL on the zinc pool and on thymic and peripheral immune functions in px mice. Daily injections of MEL (100 micrograms/mouse) for 1 month in px mice restored the crude zinc balance from negative to positive values. Thymic and peripheral immune functions, including plasma levels of interleukin-2, also recovered. The nontoxic effect of MEL on immune functions was observed in sham-operated mice. Because the half-life of MEL is very short (12 min), interruption of MEL treatment in px mice resulted, after 1 month, in a renewed negative crude zinc balance and a regression of immune functions. Both the zinc pool and immunological parameters were restored by 30 further days of MEL treatment. The existence of a significant correlation between zinc and thymic hormone after both cycles of MEL treatment clearly shows an involvement of the zinc pool in the immunoenhancing effects of MEL and thus suggests an inter-relationship between zinc and MEL in px mice. Moreover, the existence of significant positive correlations between zinc or thymulin and interleukin-2 suggests that interleukin-2 may participate in the action of MEL, via zinc, on thymic functions in px MEL-treated mice.

Chatter in metal cutting is a nonlinear self-excited vibration of the limit cycle type. This investigation is concerned with the analysis of chatter from the viewpoint of the describing function. Vibrations with different frequencies and amplitudes were superimposed on the steady feed motion of the tool in orthogonal cutting in order to simulate chatter. The relationships between the oscillating cutting and thrust forces and tool vibrations are discussed from the point of view of energy transfer and describing functions. Experimentally obtained describing functions of the dynamically varying cutting process are given. The stability of a typical machine tool structure under primary chatter conditions with dynamical cutting process represented by its describing function is discussed.

Several in vivoexperimental and clinical studies suggest that the production of thymic hormones, such as thymulin (Zn-FTS), is modulated by thyroid hormones. It was not determined in these studies, however whether such modulation is exerted directly on the thymic epithelial cells which synthesize and secrete thymic hormones. In order to discriminate between direct and indirect modulation, the effect of thyroid hormones on the in vitroproduction of thymulin by whole thymic organ culture, as detected by the rosette inhibition assay, has been investigated. Donors of thymuses were young 6N-propyl-2 thyouracil (PTU)-treated hypothyroid Balb/c mice and normal littermates. Thymuses from hypothyroid mice were shown to produce concentrations in vitronearly undetectable of thymic hormone, when compared to thymuses from normal mice. The in vitroaddition of triiodothyronine (T3) caused a complete recovery of the thymic hormone production by thymuses from hypothyroid mice and an increased synthesis even by normal thymuses over control values. The complete blockade of in vitrothymic hormone production with cycloheximide, which inhibits mRNA and protein synthesis but not thyroid hormone permissive actions, suggests that the T3induced increment of thymic hormone level in the supernatant is due to de novosynthesis. Furthermore, the number of thymulin-producing cells, as detected by immunofluorescence using a specific antithymulin monoclonal antibody, which is quite low in thymuses from hypothyroid mice, is completely regained after in vitroincubation with T3. These findings support the idea that the modulation of thyroid hormones on thymic endocrine activity is directly exerted at thymic level.

The occurrence of machine-tool chatter is usually undesirable as it gives rise to severe production problems. The existing theoretical and experimental studies on dynamic cutting indicate that the chip thickness and forces in cutting are related by a nonlinear equation. But the existing studies on chatter stability employ a linear relationship between these variables. In this paper, a relationship is developed between the chip thickness and forces in cutting under dynamic conditions. This relationship is based on existing experimental results and it exhibits active hysteresis. Hence, the oscillations in chip thickness lead the oscillations in cutting forces for all frequencies. A nonlinear theory is developed based on the describing function approach. An example is given of computing a stability chart giving the width of cut, frequency of chatter, and critical cutting speeds for regenerative chatter. In contrast to the linear stability analysis, the nonlinear theory can better explain the experimentally observed phenomena as well as give better correlation with the theoretical analysis of dynamic cutting.

The paper proposes a new optimization method of machining conditions. The target of optimization is getting the performance index, the unit cost of workpiece, to be minimum. A proper expression has been suggested to describe the relation between the unit cost and the cutting conditions, it becomes a complete mathematical model by means of Stepwise Regression Method. The process of optimization is divided in two steps, widespread search and partial search. Uses Embedding Method and Golden Section Method for two steps individually to search the real optimal point within the constrained range with one run of computer easily and certainly.