Abstract.The measurement of the directions of radio meteors with an interferometric system is beset by two problems: (1) The ambiguity in the measured directions for antennas spaced by more than )•/2 and (2) the effects of mutual impedance when the antennas are spaced at )•/2 and less to avoid these ambiguities. In this paper we discuss the effects of mutual impedance between spaced antennas and describe an interferometer which both minimizes these effects and avoids the ambiguities associated with spacings larger than )•/2. We have modeled a version of this design numerically and show that under ideal conditions an interferometer of total span 4.5)• can yield directions accurate to about 0.3 ø with a signal-to-noise ratio of 20 dB. Finally, we have tested the design with observations from the 1996 Geminid and 1997 Quadrantid meteor showers and find that even without a ground plane, the interferometer provides unambiguous directions to an accuracy of the order of 1.15 ø.

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SignificanceWomen live longer than men in nearly all populations today. Some research focuses on the biological origins of the female advantage; other research stresses the significance of social factors. We studied male–female survival differences in populations of slaves and populations exposed to severe famines and epidemics. We find that even when mortality was very high, women lived longer on average than men. Most of the female advantage was due to differences in mortality among infants: baby girls were able to survive harsh conditions better than baby boys. These results support the view that the female survival advantage is modulated by a complex interaction of biological environmental and social factors.

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