We develop a theory of fertility, distinguishing its intensive margin from its extensive margin. The deep parameters are identified using facts from the 1990 US Census: (i) fertility of mothers decreases with education; (ii) childlessness exhibits a U-shaped relationship with education; (iii) the relationship between marriage rates and education is hump-shaped for women and increasing for men. ...

We show that for a broad class of technologies the relationship between policy stringency and the rate of technology adoption is inverted U-shaped. This happens when the marginal abatement cost (MAC) curves of conventional and new technologies intersect, which invariably occurs when emissions are proportional to output and technological progress reduces emissions per output. This outcome does n...

There are recent observational indications (lack of convergent electric ®eld signatures above the auroral oval at 4 RE altitude) that the U-shaped potential drop model for auroral acceleration is not applicable in all cases. There is nevertheless much observational evidence favouring the U-shaped model at low altitudes, i.e., in the acceleration region and below. To resolve the puzzle we propos...

Relative growth intensity of various longitudinally measured body segments in larvae of several species of fishes was distributed across the body in a continuous, U-shaped gradient. Juveniles lacked a simple pattern ofgrowth but appeared to grow nearly isometrically. Body depth exhibited a shallow, U-shaped gradient while body width lacked a discernible pattern. Most intense growth, in three or...