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It is unclear whether sex steroids influence melatonin secretion in the human. In an attempt to find an answer to this important question 36 women within an age range of 19 to 40 years were studied within a 3-month period under the following conditions: natural menstrual cycle, ovulation induction with gonadotrophins, early pregnancy, and intake of monophasic or triphasic oral contraceptives. Except in the case of pregnancy, repeated measurements in the same individual were done because of the well-known large inter-individual variations in melatonin secretion. Melatonin concentration was measured in plasma samples obtained at 4-hourly intervals in a 24 h period and < 200 lux for all subjects studied. No consistent change in melatonin blood concentrations was demonstrated in response to the varying endogenous or exogenous concentrations of sex steroids. These observations suggest that circadian melatonin secretion is not significantly modulated by sex steroids.

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Breakout of objects from soft, clayey seafloors is a common, potentially hazardous and costly task, but there is little information about it beyond results of small-scale laboratory studies extracting decimetre-scale objects from 'model' soils. In this study, a unique dataset is presented, comprising thirty-five immediate breakout events of a seafloor template from very soft clay in 200 m to 2000 m water. The measured breakout forces were compared to operational variables and soil characteristics at the exact location of breakout, which were known because geotechnical soil investigations were performed at each site. Predictions from three existing theories, namely Muga (1968), Rapoport and Young (1983), and Das (1991) were tested. The three theories appear to predict breakout force well, and with comparable accuracy. Predictions from all these methods could be valuable in lifting/extraction risk assessments.

No abstract