The Hydrogen Evolution Activity of BaZrS3, BaTiS3, and BaVS3 Chalcogenide Perovskites.

Chalcogenide perovskites are a class of materials with electronic and optoelectronic properties desirable for solar cells, infrared optics, and computing. The oxide counterparts of these chalcogenides have been studied extensively for their electrocatalytic and photoelectrochemical properties. As chalcogenide perovskites are more covalent, conductive, and stable, we hypothesize that they are more viable as electrocatalysts than oxide perovskites. The goal of this synthetic, experimental, and computational study is to examine the hydrogen evolution reaction (HER) activity of three Barium-based chalcogenides in perovskite and related structures: BaZrS3, BaTiS3, and BaVS3. Potential energy surfaces for hydrogen adsorption on surfaces of these materials are calculated using density functional theory and the computational hydrogen electrode model is used to contrast overpotentials with experiment. Although both experiments and computations agree that BaVS3 is the most active of the three materials, high overpotentials of these materials make them less viable than platinum for HER. Our work establishes a framework for future studies in the chemical and electrochemical properties of chalcogenide perovskites.

A Platinum Nanowire Sensor for Ethylene in Air.

A single platinum nanowire (PtNW) chemiresistive sensor for ethylene gas is reported. In this application, the PtNW performs three functions: (1) Joule self-heating to a specified temperature, (2) in situ resistance-based temperature measurement, and (3) detection of ethylene in air as a resistance change. Ethylene gas in air is detected as a reduction in nanowire resistance by up to 4.5% for concentrations ranging from 1 to 30 ppm in an optimum NW temperature range from 630 to 660 K. This response is rapid (30-100 s), reversible, and reproducible for repetitive ethylene pulses. A threefold increase in signal amplitude is observed as the NW thickness is reduced from 60 to 20 nm, commensurate with a signal transduction mechanism involving surface electron scattering.

Nanoscale Iron Redistribution during Thermochemical Decomposition of CaTi1-x Fe x O3-δ Alters the Electrical Transport Pathway: Implications for Oxygen-Transport Membranes, Electrocatalysis, and Photocatalysis.

Potential applications of the earth-abundant, low-cost, and non-critical perovskite CaTi1-x Fe x O3-δ in electrocatalysis, photocatalysis, and oxygen-transport membranes have motivated research to tune its chemical composition and morphology. However, investigations on the decomposition mechanism(s) of CaTi1-x Fe x O3-δ under thermochemically reducing conditions are limited, and direct evidence of the nano- and atomic-level decomposition process is not available in the literature. In this work, the phase evolution of CaTi1-x Fe x O3-δ (x = 0-0.4) was investigated in a H2-containing atmosphere after heat treatments up to 600 °C. The results show that CaTi1-x Fe x O3-δ maintained a stable perovskite phase at low Fe contents while exhibiting a phase decomposition to Fe/Fe oxide nanoparticles as the Fe content increases. In CaTi0.7Fe0.3O3-δ and CaTi0.6Fe0.4O3-δ, the phase evolution to Fe/Fe oxide was greatly influenced by the temperature: Only temperatures of 300 °C and greater facilitated phase evolution. Fully coherent Fe-rich and Fe-depleted perovskite nanodomains were observed directly by atomic-resolution scanning transmission electron microscopy. Prior evidence for such nanodomain formation was not found, and it is thought to result from a near-surface Kirkendall-like phenomenon caused by Fe migration in the absence of Ca and Ti co-migration. Density functional theory simulations of Fe-doped bulk models reveal that Fe in an octahedral interstitial site is energetically more favorable than in a tetrahedral site. In addition to coherent nanodomains, agglomerated Fe/Fe oxide nanoparticles formed on the ceramic surface during decomposition, which altered the electrical transport mechanism. From temperature-dependent electrical conductivity measurements, it was found that heat treatment and phase decomposition change the transport mechanism from thermally activated p-type electronic conductivity through the perovskite to electronic conduction through the iron oxide formed by thermochemical decomposition. This understanding will be useful to those who are developing or employing this and similar earth-abundant functional perovskites for use under reducing conditions, at elevated temperatures, and when designing materials syntheses and processes.

On-Chip Optical Anodic Stripping with Closed Bipolar Cells and Cathodic Electrochemiluminescence Reporting.

The aim of this work was to develop a simple, accessible, and point-of-use sensor to measure heavy metal ions in water in low-resource areas that cannot accommodate expensive or technical solutions. This report describes a new bipolar electrochemical sensor platform that reimagines conventional anodic stripping voltammetry in a wireless bipolar format with an optical electrochemiluminescent readout that can be quantified with any simple optical sensor like that found on most modern cell phone cameras. We call this technique as optical anodic stripping. Using a new nonlithographic fabrication process, devices could be produced rapidly and simply at <$1/sensor. The sensing scheme was developed, characterized, and optimized using electrochemical and optical methods. Quantitation of Pb2+ in both lab and natural water samples was rapid (2-3 min), accurate, precise, and highly linear in the 25-1000 ppb range and was shown to be sufficiently selective in the presence of other common heavy metal ions such as Cu2+, Cd2+, and Zn2+.

Adsorbate-assisted migration of the metal atom in atomically dispersed catalysts: An ab initio molecular dynamics study.

We present a phenomenological study of dynamical evolution of the active site in atomically dispersed catalysts in the presence of reaction intermediates associated with CO oxidation and low-temperature water-gas shift reaction. Using picosecond ab initio molecular dynamics, we probe the initiation of adsorbate-induced diffusion of atomically dispersed platinum on rutile TiO2(110). NVT trajectories spanning 5 ps at 500 K reveal that the dynamical stability of the metal atom is governed by its local coordination to the support and adsorbate. Adsorbates that bind the strongest to Pt typically also lead to the fastest diffusion of the metal atom, and all adsorbates weaken Pt-support interactions, resulting in higher diffusion coefficients compared to bare Pt. We note, however, the absence of quantitative correlations between adsorption characteristics (Pt Bader charge, adsorbate binding energy) and ensemble-averaged quantities (diffusion coefficients). A recurring structural motif identified in several trajectories is a near-linear coordination between support oxygen, Pt, and specific adsorbates. These geometries, on account of enhanced metal support interactions, stabilize Pt and inhibit migration over picosecond timescales. We also identify hydrogen bonding events between the adsorbate and support for OH-containing groups. In the case of OH-bound Pt, for instance, we believe that short-lived H-bonds between OH and support promote Pt migration in the beginning of the NVT trajectory, while the subsequent formation of a near-linear geometry stabilizes the Pt atom despite the continued formation of short-lived hydrogen bonds. These observations are consistent with prior studies that report stabilization of isolated metal atoms in the presence of hydroxyl groups.

The lure of death: suicide and human evolution.

At some point in evolutionary history, human beings came to understand, as no non-human animals do, that death brings to an end a person's bodily and mental presence in the world. A potentially devastating consequence was that individuals, seeking to escape physical or mental pain, might choose to kill themselves.This article is part of the theme issue 'Evolutionary thanatology: impacts of the dead on the living in humans and other animals'.

Shamans as healers: When magical structure becomes practical function.

Singh's analysis has much to be said for it. When considering the treatment of illness, however, he begins from a shaky premise about uncontrollability and, so, fails to make the most of what shamanic treatments - as placebos - can deliver.

Dissociation of the Reach and the Grasp in the destriate (V1) monkey Helen: a new anatomy for the dual visuomotor channel theory of reaching.

Dual visuomotor channel theory proposes that reaching depends on two neural pathways that extend from visual cortex (V1) to motor cortex via the parietal lobe. The Reach pathway directs the hand to the target's location and the Grasp pathway shapes the hand and digits for purchase. Sighted human participants integrate the Reach and the Grasp, but without vision they dissociate the movements to capitalize on tactile cues. They use a Reach with a relatively open hand to locate the target and then they use touch cues to shape the fingers to Grasp. After a V1 lesion, the rhesus monkey, Helen, learned to make near-normal visual discriminations based on size and brightness but displayed visual agnosia. She also learned to reach for food with her mouth and her hands. The present analysis of film of her reaching behavior shows that she dissociated the Reach and the Grasp, as do unsighted human participants reaching for a food target at a fixed location. Her rapid and direct Reach was made with an open hand and extended fingers to contact the food with the palm whereas her Grasp was initiated after she touched the food. She also visually fixated the target during the Reach and visually disengaged after target contact, as do sighted human participants. In contrast, Helen did integrate the Reach and the Grasp to take food from her mouth, demonstrating that she could integrate the movements using online tactile cues. The finding that extrastriate pathways can direct the hand toward extrinsic target properties (location) but not intrinsic target properties (size and shape) is discussed as a novel addition to dual visuomotor channel theory.

'This chimp will kick your ass at memory games - but how the hell does he do it?'.

Extraordinary evidence generates extraordinary claims. I discuss the remarkable memory skills of chimpanzees tested in the Kyoto Primate Laboratory, and suggest a novel ­ but deflationary ­ hypothesis to explain them. Could the chimpanzees, who have been highly trained to learn the sequence of Arabic numerals, have developed number­colour synaesthesia?

CA8 mutations cause a novel syndrome characterized by ataxia and mild mental retardation with predisposition to quadrupedal gait.

We describe a consanguineous Iraqi family in which affected siblings had mild mental retardation and congenital ataxia characterized by quadrupedal gait. Genome-wide linkage analysis identified a 5.8 Mb interval on chromosome 8q with shared homozygosity among the affected persons. Sequencing of genes contained in the interval revealed a homozygous mutation, S100P, in carbonic anhydrase related protein 8 (CA8), which is highly expressed in cerebellar Purkinje cells and influences inositol triphosphate (ITP) binding to its receptor ITPR1 on the endoplasmatic reticulum and thereby modulates calcium signaling. We demonstrate that the mutation S100P is associated with proteasome-mediated degradation, and thus presumably represents a null mutation comparable to the Ca8 mutation underlying the previously described waddles mouse, which exhibits ataxia and appendicular dystonia. CA8 thus represents the third locus that has been associated with quadrupedal gait in humans, in addition to the VLDLR locus and a locus at chromosome 17p. Our findings underline the importance of ITP-mediated signaling in cerebellar function and provide suggestive evidence that congenital ataxia paired with cerebral dysfunction may, together with unknown contextual factors during development, predispose to quadrupedal gait in humans.

The society of selves.

Human beings are not only the most sociable animals on Earth, but also the only animals that have to ponder the separateness that comes with having a conscious self. The philosophical problem of 'other minds' nags away at people's sense of who--and why--they are. But the privacy of consciousness has an evolutionary history--and maybe even an evolutionary function. While recognizing the importance to humans of mind-reading and psychic transparency, we should consider the consequences and possible benefits of being--ultimately--psychically opaque.