Circadian (daily) regulation of metabolic pathways implies that food may be metabolized differentially over the daily cycle. To test that hypothesis, we monitored the metabolism of older subjects in a whole-room respiratory chamber over two separate 56-h sessions in a random crossover design. In one session, one of the 3 daily meals was presented as breakfast, whereas in the other session, a nutritionally equivalent meal was presented as a lateevening snack. The duration of the overnight fast was the same for both sessions. Whereas the two sessions did not differ in overall energy expenditure, the respiratory exchange ratio (RER) was different during sleep between the two sessions. Unexpectedly, this difference in RER due to daily meal timing was not due to daily differences in physical activity, sleep disruption, or core body temperature (CBT). Rather, we found that the daily timing of nutrient availability coupled with daily/circadian control of metabolism drives a switch in substrate preference such that the late-evening Snack Session resulted in significantly lower lipid oxidation (LO) compared to the Breakfast Session. Therefore, the timing of meals during the day/night cycle affects how ingested food is oxidized or stored in humans, with important implications for optimal eating habits.

Controlled-geometry voids were introduced into unimplanted and Ti-implanted high-purity c-axis sapphire substrates using microfabrication techniques and ion beam etching, and subsequently transferred to an internal interface by hot-pressing. The morphological evolution of cracklike and channellike defects oriented parallel to the basal plane in response to anneals at 1700°C was studied. The healing behavior of defects in the unimplanted and Ti-ionimplanted samples differs significantly. Ti additions appear to reverse the directional dependence of the healing characteristics in undoped sapphire, greatly stabilizing defects with edges aligned along the [IT001 direction, while reducing the stability of defects with edges aligned parallel to the [1120] direction relative to unimplanted sapphire. The healing characteristics of unimplanted and Ti-implanted sapphire substrates are compared and contrasted with those observed previously in Ca-and Mg-ion-implanted sapphire.