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A robust control design is developed to "ize a system's response to unknown disturbances. The method consists of on-line identification of the system's state space equations coupled with an &-optimal controller design. The H , controller is designed such that the maximum of the system's closed-loop transfer function is less than y (y > 0). This robust controller is used to eliminate vibrations in cutting operations of a boring bar with an active dynamic absorber. A boring bar is a metal cutting tool with a large overhang (lenm-todiameter ratio). Due to this large overhang, a typical boring bar is characterized by a low dynamic s m e s s and is therefore susceptible to excessive vibrations during the cutting process. These vibrations o h lead to cutting instability, known as machine tool chatter. In this paper, the control of vibrations of a boring bar with an active dynamic absorber is studied. The robustness of the %-optimal controller is demonstrated by varying the system's dynamic characteristics (i.e., changing the length-todiameter ratio of the boxing bar) without adjusting the calculated control parameters. The results obtained for the H , case are compared to similar results for a linear quadratic regulator control design.

Seasonal variation of liver glycogen, lipids and melanomacrophages were investigated in a non-hibernating population of\ud Pelophylax kl. esculentus from Calabria by histochemical methods and computer-assisted image analysis. Twenty individuals\ud of both sexes were sampled in a tank in Roseto Capo Spulico (Cosenza, Calabria) in four periods of the year 2016 (February,\ud May, July, October). Portions of liver from each individual were included in paraffin for glycogen and melanomacrophages,\ud and epoxydic resin-araldite for lipid analysis. Sections were stained with periodic acid-Schiff (PAS) for glycogen (with\ud diastase-PAS as control) or osmium-tetroxide for lipids, or left unstained for melanomacrophages (appearing naturally black\ud due to melanin). Image analyses were performed on 9–12 grayscale converted pictures per individual. Total areas per μm2 of\ud glycogen, lipids and melanomacrophages, as well as counts of lipid droplets and melanomacrophages and mean area of\ud single lipid droplets and melanomacrophages, were measured. Statistical analyses were performed by analysis of variance\ud (ANOVA) with bootstrap resampling. Significant variation among sampling periods was found for each variable. Glycogen\ud and lipids co-vary, with higher values observed in October–February and lower values in May–July, whereas melanomacrophages\ud reach a peak in May and have much lower values in the other months. It is concluded that, in the absence of a\ud hibernating period, reproduction is the main force regulating the annual cycles of reserve storing and melanin production

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