Body Fat is Associated with Decreased Endocrine and Cognitive Resilience to Acute Emotional Stress

*Objective:* Cortisol is elevated both in individuals with increased emotional stress as well as with higher percentages of body fat. Cortisol is also known to affect cognitive performance, particularly spatial processing, selective attention, and working memory. We hypothesized that increased body fat might therefore be associated with decreased performance on a spatial processing task, in response to an acute real-world stressor. 

*Design:* We tested two separate samples of subjects undergoing their first (tandem) skydive. In the first sample (N=78), subjects were tested for salivary cortisol and state-anxiety (Spielberger State Anxiety Scale) during the plane's fifteen-minute ascent to altitude in immediate anticipation of the jump. In a second sample (N=20), subjects were tested for salivary cortisol, as well as cardiac variables (heart rate, autonomic regulation via heart rate variability) and performance on a cognitive task of spatial processing, selective attention, and working memory. 

*Results:* In response to the skydive, individuals with greater body fat percentages showed significantly increased reactivity for both cortisol (on both samples) and cognition, including decreased accuracy of our task of spatial processing, selective attention, and working memory. These cognitive effects were restricted to the stress response and were not found under baseline conditions. There were no body fat interactions with cardiac changes in response to the stressor, suggesting that the cognitive effects were specifically hormone-mediated rather than secondary to general activation of the autonomic nervous system. 

*Conclusions:* Our results indicate that, under real-world stress, increased body fat may be associated with endocrine stress-vulnerability, with consequences for deleterious cognitive performance

Early star formation traced by the highest redshift quasars

The iron abundance relative to alpha-elements in the circumnuclear region of quasars is regarded as a clock of the star formation history and, more specifically, of the enrichment by SNIa. We investigate the iron abundance in a sample of 22 quasars in the redshift range 3.0<z<6.4 by measuring their rest frame UV FeII bump, which is shifted into the near-IR, and by comparing it with the MgII 2798 flux. The observations were performed with a device that can obtain near-IR spectra in the range 0.8-2.4 um in one shot, thereby enabling an optimal removal of the continuum underlying the FeII bump. We detect iron in all quasars including the highest redshift (z=6.4) quasar currently known. The uniform observational technique and the wide redshift range allows a reliable study of the trend of the FeII/MgII ratio with redshift. We find the FeII/MgII ratio is nearly constant at all redshifts, although there is marginal evidence for a higher FeII/MgII ratio in the quasars at z~6. If the FeII/MgII ratio reflects the Fe/alpha abundance, this result suggests that the z~6 quasars have already undergone a major episode of iron enrichment. We discuss the possible implications of this finding for the star formation history at z>6. We also detect a population of weak iron emitters at z~4.5, which are possibly hosted in systems that evolved more slowly. Alternatively, the trend of the FeII/MgII ratio at high redshift may reflect significantly different physical conditions of the circumnuclear gas in such high redshift quasars.Comment: Replaced to match the accepted version (ApJL in press), 5 page

The Smallest Molecular Switch

Ab-initio total energy calculations reveal benzene-dithiolate (BDT) molecules on a gold surface, contacted by a monoatomic gold STM tip to have two classes of low energy conformations with differing symmetries. Lateral motion of the tip or excitation of the molecule cause it to change from one conformation class to the other and to switch between a strongly and a weakly conducting state. Thus, surprisingly, despite their apparent simplicity these Au/BDT/Au nanowires are shown to be electrically bi-stable switches, the smallest two-terminal molecular switches to date. Experiments with a conventional or novel self-assembled STM are proposed to test these predictions.Comment: 8 pages, 3 figure