Abstract This master thesis describes the use of Condition Monitoring Systems and its appli- cation in maintenance optimization for wind turbines. The focus is on the gearbox, one of the most critical compenents,in terms of high failure rates and long mean down,time. Two different models for cost optimal maintenance,are presented and discussed. The thesis include also a basic description of the gearbox and its sub- components,togheter with the most common,techniques for condition monitoring. iii Acknowledgements

Previous works have reported circadian rhythms for several cardiovascular parameters. A chronobiologic rhythm is characterized by: mesor (a rhythm-determined average), amplitude (half difference between the highest and lowest values), and acrophase (timing of high point in degrees and/or in hours) along with 95% confidence limits. We performed 24-hour ECG Holter monitoring in seven patients (mean age, 50.6 years) with ventricular parasystole (VP) in order to determine whether the chronotropic activity of parasystolic foci has a circadian rhythm similar to that of the sinus node. For each Holter recording parasystolic rates (PRs) and heart rates (HRs) were calculated every hour. Furthermore, a mean hourly PR and a mean hourly HR were calculated from the hourly PRs and HRs of the patients. The statistic chronobiologic analysis was done by single and mean cosinor methods. Correlation between mean hourly PR and HR was evaluated by Pearson's 'r' coefficient. A statistically significant rhythm (P less than 0.05) was found for the single and mean rhythms both of HR and PR. In our patients, HR had acrophase at 1.27 P.M., mesor at 73.28 beats/min, and amplitude at 9.53 beats/min, whereas PR had acrophase at 1.42 P.M., mesor at 38.31 beats/min, and amplitude at 3.64 beats/min. Chronobiological data and the high direct correlation between mean hourly HRs and mean hourly PRs (r = 0.96, P less than 0.001) indicate a similar circadian variability of the chronotropic activity of sinus nodes and parasystolic foci. Although several hypotheses can be made, responsiveness of parasystolic foci to circadian variations of the autonomic nervous system tone (sympathetic and/or vagal) and/or circulating substances (particularly catecholamines) seems the more probable one for explaining our findings.

To the Editor Poblete et al1Poblete PF Kennedy HL Caralis DG Detection of ventricular ectopy in patients with coronary heart disease and normal subjects by exercise testing and ambulatory electrocardiography.Chest. 1978; 74: 402-407Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar documented that the pattern of ventricular ectopy was best detected by continuous electrocardiographic recording (Holter monitor) than with exercise testing in both apparently normal subjects and patients with coronary heart disease. In this context, we would like to point out this new tool of investigation in the field of chronobiology. In a group of 13 ambulatory patients, ages 46-69 years, with coronary heart disease, synchronized for a week according to the following protocol: light/dark 07.00-22.00; meals at 08:00, 13:00 and 20:00, a continuous electrocardiographic recording was performed. For each subject the number of ventricular ectopic beats was grouped hourly, in order to observe the period of maximal occurrence in a 24-hr period. The data were evaluated according to the least square method (Halberg's Cosinor method2Halberg F Tong YL Johnson EA Circadian system phase: an aspect of temporal morphology; procedures and illustrative examples.in: Von Mayersbach H The Cellular Aspect of Biorhythms. Springer-Verlag, Berlin1967: 20-48Crossref Google Scholar). It was possible to detect a statistically significant circadian rhythm of the rate of ventricular ectopic beats/hour with a peak of maximal occurrence—acrophase—at 15:34 (degrees −231.1), 95 percent confidence limits between 10:48 and 19:13 (degrees −162.2; −288.4), the mean (± SEM) of individual oscillations—mesor–60.14 ± 17.82 ectopic beats/hour, and the mean (± SEM) of individual differences between maximum and mesor—amplitude–64.73 ±: 29.10 ectopic beats/ hour. We have work in progress to observe if apparently healthy subjects presenting ventricular ectopic beats exhibit a circadian rhythm as well, and if so, if a shift of rhythm takes place in patients with cardiac disease. In addition, it must be emphasized that these results could have importance from a chronotherapeutic point of view, since the peak of ventricular ectopy occurs in the early afternoon; hence, the suggestion to administer antiarrhythmic drugs especially active during this period of the day.