RESUMEN
The abundance of refractory elements in giant planets can provide key insights into their formation histories1. Owing to the low temperatures of the Solar System giants, refractory elements condense below the cloud deck, limiting sensing capabilities to only highly volatile elements2. Recently, ultra-hot giant exoplanets have allowed for some refractory elements to be measured, showing abundances broadly consistent with the solar nebula with titanium probably condensed out of the photosphere3,4. Here we report precise abundance constraints of 14 major refractory elements on the ultra-hot giant planet WASP-76b that show distinct deviations from proto-solar and a sharp onset in condensation temperature. In particular, we find nickel to be enriched, a possible sign of the accretion of the core of a differentiated object during the evolution of the planet. Elements with condensation temperatures below 1,550 K otherwise closely match those of the Sun5 before sharply transitioning to being strongly depleted above 1,550 K, which is well explained by nightside cold-trapping. We further unambiguously detect vanadium oxide on WASP-76b, a molecule long suggested to drive atmospheric thermal inversions6, and also observe a global east-west asymmetry7 in its absorption signals. Overall, our findings indicate that giant planets have a mostly stellar-like refractory elemental content and suggest that temperature sequences of hot Jupiter spectra can show abrupt transitions wherein a mineral species is either present or completely absent if a cold trap exists below its condensation temperature8.
RESUMEN
Mixtures of active and passive colloids show an intriguing dynamics of self-assembling, which is driven by the active component. Self-phoretic active colloids generate sinks in a chemical concentration field that cause passive colloids to drift toward active colloids by diffusiophoresis. The strength of this effective attraction is governed by the diffusiophoretic parameter, which determines the drift velocity. Simulating the Langevin dynamics of the colloids, we determine the state diagram for increasing diffusiophoretic strength and fixed active velocity. Three main states are distinguished. For weak attraction, passive particles are first scattered in the simulation box and then form a colloidal cloud around its center. Increasing the diffusiophoretic parameter further, passive particles oscillate between the cloud and a compact cluster, which embeds active colloids. Ultimately, in the third state, all particles collapse into a single stable cluster. In the collapse regime, the clustering dynamics of the largest cluster follows a logistic function and the mean cluster velocity vs cluster size decays with a power law. Throughout this article, we discuss our simulation results with regard to the experiments of Singh et al., Adv. Mater. 29(32), 1701328 (2017).
RESUMEN
Effects of nicotine on neurocognitive performance have been shown but are influenced by nonpharmacological expectancies in smokers, whereas there is little knowledge about expectancy effects in nonsmokers. A half balanced placebo design provides no drug but only placebo and tests the effects of expectations elicited by the information that nicotine was given. Sixty-four healthy participants balanced for smoking status and sex were told that a chewing gum may contain either nicotine or is a placebo in a double-blinded and randomized fashion. One hour later and immediately before neurocognitive function testing (Parametric Go/No-Go task) they were informed--balanced for smoking status and sex--that they belong to the nicotine or to the placebo group. Reaction times of Go responses (RT) and the number of false No-Go responses were analyzed. A significant interaction of all three factors (information, smoking status, sex) was found, indicating that the information to have received nicotine compared with placebo shortened RTs in female smokers but increased it in female nonsmokers, whereas results in men are in part reversed. No effects on No-Go errors were found, and beliefs about nicotine effects had no influence on results. Therefore, the known effects of nicotine on RTs could be influenced by stimulus expectancy not only in smokers but also in nonsmokers. Furthermore, previous results on sex-specific responsiveness to nicotine instructions are supported.
