An earlier model of deep-penetration laser welding has been simplified in order to provide a useful model of process analysis. This work involves the modelling of the various energy-absorption mechanisms which determine the keyhole shape and thus the dimensions of the melt pool. The penetration depth and weld width (top and bottom) predicted by the model are shown to be in close agreement with experimental results. The widening of the top of the weld seam as a result of Marangoni flow is accurately modelled by introducing an artificially enhanced value for the workpiece's thermal conductivity towards the top of the weld. The model allows analysis of the dependence of the weld profile on the process parameters.

Oxygen consumption by human oocytes and blastocysts was analysed using a sensitive micro-spectrophotometric technique. Oocytes were obtained from women undergoing laparotomy for sterilization or hysterectomy, and blastocysts were obtained as spare embryos from the local in-vitro fertilization programme. There was no significant difference between oocyte oxygen consumption on the day of isolation and after 1 day of culture, 0.53 +/- 0.08 (n = 9) and 0.35 +/- 0.06 (n = 5) nl/h oocyte, respectively. Blastocyst oxygen consumption was measured after a culture period of 5-8 days after in-vitro fertilization. Mean oxygen consumption by healthy looking blastocysts was 0.34 +/- 0.03 (n = 15) nl/h blastocyst, and there was no change in oxygen consumption with culture time. This level of respiration was lower than expected, both when compared with the oocytes and when compared with levels reported for blastocysts of other species.

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It is known that dibutyryl cyclic AMP (dbcAMP) and theophylline inhibit the spontaneous maturation of isolated mouse oocytes. The present study demonstrates that dbcAMP (0.01-1.0 mM) as well as cyclic AMP (cAMP, 10 mM) and a phosphodiesterase inhibitor (IBMX, 0.01-1.0 mM) prevent spontaneous maturation of isolated rat oocytes. As reported earlier an increase in oxygen consumption by the oocyte was found following maturation. When the oocytes were cultured in the presence of dbcAMP or cAMP no change in respiration occurred during culture. These results argue against the theory that cAMP acts as a direct mediator of the action of luteinizing hormone (LH) on oocyte maturation. Furthermore they suggest that changes in oocyte energy metabolism are closely related to the maturation process.

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