State-dependent distributed-delay model of orthogonal cutting

In this paper we present a model of turning operations with state-dependent distributed time delay. We apply the theory of regenerative machine tool chat- ter and describe the dynamics of the tool-workpiece sys- tem during cutting by delay-diferential equations. We model the cutting-force as the resultant of a force sys- tem distributed along the rake face of the tool, which results in a short distributed delay in the governing equation superimposed on the large regenerative de- lay. According to the literature on stress distribution along the rake face, the length of the chip-tool inter- face, where the distributed cutting-force system is act- ing, is function of the chip thickness, which depends on the vibrations of the tool-workpiece system due to the regenerative efect. Therefore, the additional short de- lay is state-dependent. It is shown that involving state- dependent delay in the model does not afect linear sta- bility properties, but does afect the nonlinear dynamics of the cutting process. Namely, the sense of the Hopf bi- furcation along the stability boundaries may turn from sub- to supercritical at certain spindle speed regions

Specialized Movement on the Rowing Ergometer and Post-workout Changes in Selected Peripheral Blood Parameters – a Case Report.

Rowing is a sport discipline, which requires extreme physical strength and endurance and appropriate aerobic and anaerobic capacity as well. However, when the workout intensity and load is very high, exercise is associated with temporary changes in cellular metabolism and the immune system. The study included one male rower aged 28 years – the highly-skilled and experienced athlete. We determined basic cardiorespiratory fitness measures, complete blood count, and 24 clinical chemistry parameters including relevant biochemical and haematological parameters and matrix metaloproteinases activities. Maximal exercise on the rowing ergometer induced 2-fold increase in absolute counts of all leukocytes subsets. There was observed an increase in C-reactive protein concentrations as well. MMP-9 activity increased 1.3-fold compared to the baseline value. Exhaustive exercise caused significant changes in creatinine and urea serum levels, but the most prominent changes were found in total and direct bilirubin concentrations. Maximal exercise induced also a decrease in the iron and magnesium levels. No changes in ALT, GGT and ALP activity were observed, while increase in CK, AST and LDH activity in post-exercise time and the decrease during the recovery was found. Therefore acute specialized movement on the rowing ergometer is not the cause of muscular damage, but rather indicate efficient adaptation to the physical exercise. Moreover, it seems that maximal exercise induces an inflammatory response characterized by greater count of all subpopulations of leukocytes, elevated levels of CRP and MMP-9 serum activity