RESUMO
Coherent folded acoustic phonons in a multilayered GaSb/InAs epitaxial heterostructure were generated by femtosecond laser pulses and studied by means of ultrafast x-ray diffraction. Coherent phonons excited simultaneously in the fundamental acoustic branch and the first back-folded branch were detected. This represents the first clear evidence for phonon branch folding based directly on the atomic motion to which x-ray diffraction is sensitive. From a comparison of the measured phonon-modulated x-ray reflectivity with simulations, evidence was found for a reduction of the laser penetration depth. This reduction can be explained by the self-modulation of the refractive index due to photogenerated free carriers.
RESUMO
Fifty-two patients who had had a single previous caesarean section were submitted to a trial of scar. Labour was monitored by internal tocography and direct fetal heart rate monitoring. Oxytocin infusion was employed when uterine work proved to be inadequate. The oxytocin-augmented and unstimulated groups were compared. Oxytocin augmentation improved uterine work and did not result in significant fetal or maternal morbidity or mortality. Internal tocography was found to be of value, but fetal heart rate monitoring was essential.
