Single Atom Dynamics in Chemical Reactions.

Many heterogeneous chemical reactions involve gases catalyzed over solid surfaces at elevated temperatures and play a critical role in the production of energy, healthcare, pollution control, industrial products, and food. These catalytic reactions take place at the atomic level, with active structures forming under reaction conditions. A fundamental understanding of catalysis at the single atom resolution is therefore a major advance in a rational framework upon which future catalytic processes can be built. Visualization and analysis of gas-catalyst chemical reactions at the atomic level under controlled reaction conditions are key to understanding the catalyst structural evolution and atomic scale reaction mechanisms crucial to the performance and the development of improved catalysts and chemical processes. Increasingly, dynamic single atoms and atom clusters are believed to lead to enhanced catalyst performance, but despite considerable efforts, reaction mechanisms at the single atom level under reaction conditions of gas and temperature are not well understood. The development of the atomic lattice resolution environmental transmission electron microscope (ETEM) by the authors is widely used to visualize gas-solid catalyst reactions at this atomic level. It has recently been advanced to the environmental scanning TEM (ESTEM) with single atom resolution and full analytical capabilities. The ESTEM employs high-angle annular dark-field imaging where intensity is approximately proportional to the square of the atomic number (Z). In this Account, we highlight the ESTEM development also introduced by the authors for real time in situ studies to reliably discern metal atoms on lighter supports in gas and high temperature environments, evolving oxide/metal interfaces, and atomic level reaction mechanisms in heterogeneous catalysts more generally and informatively, with utilizing the wider body of literature. The highlights include platinum/carbon systems of interest in fuel cells to meet energy demands and reduce environmental pollution, in reduction/oxidation (redox) mechanisms of copper and nickel nanoparticles extensively employed in catalysis, electronics, and sensors, and in the activation of supported cobalt catalysts in Fischer-Tropsch (FT) synthesis to produce fuels. By following the dynamic reduction process at operating temperature, we investigate Pt atom migrations from irregular nanoparticles in a carbon supported platinum catalyst and the resulting faceting. We outline the factors that govern the mechanism involved, with the discovery of single atom interactions which indicate that a primary role of the nanoparticles is to act as reservoirs of low coordination atoms and clusters. This has important implications in supported nanoparticle catalysis and nanoparticle science. In copper and nickel systems, we track the oxidation front at the atomic level as it proceeds across a nanoparticle, by directly monitoring Z-contrast changes with time and temperature. Regeneration of deactivated catalysts is key to prolong catalyst life. We discuss and review analyses of dynamic redox cycles for the redispersion of nickel nanoparticles with single atom resolution. In the FT process, pretreatment of practical cobalt/silica catalysts reveals higher low-coordination Co0 active sites for CO adsorption. Collectively, the ESTEM findings generate structural insights into catalyst dynamics important in the development of efficient catalysts and processes.

You talkin' to me? An assessment of commands as play signals during dog-human play.

During play with a dog, humans commonly command the dog to engage in particular activities. How effective are commands during play, and do they serve as play signals? To answer this question, I examined commands issued to dogs by 21 familiar and 17 unfamiliar persons who played with a dog, and the dog's responses. Specifically, I examined dogs' actions following commands containing the words (in decreasing order of frequency) come/come here, go get/get/go, give/gimme, bring, look, and drop, to see if they satisfied the commands and whether play followed the commands. Dogs more often ignored than satisfied most commands during play interactions, and more often played than not following commands. However, dogs playing after commands as often satisfied as ignored a command, suggesting that commands do not serve as play signals. Play activity dogs were engaged in following commands, most commonly object-keepaway and chase the object, resulted in actions (e.g., getting closer or farther away from the play partner) that could either satisfy or not satisfy a given command. Commands were likely a response to dogs' activities, spoken to direct a dog to engage in a particular activity or exhort the dog to continue engaging in an activity that supported the human's play activities, rather than a play signal.

Atom-by-atom analysis of sintering dynamics and stability of Pt nanoparticle catalysts in chemical reactions.

Supported Pt nanoparticles are used extensively in chemical processes, including for fuel cells, fuels, pollution control and hydrogenation reactions. Atomic-level deactivation mechanisms play a critical role in the loss of performance. In this original research paper, we introduce real-time in-situ visualization and quantitative analysis of dynamic atom-by-atom sintering and stability of model Pt nanoparticles on a carbon support, under controlled chemical reaction conditions of temperature and continuously flowing gas. We use a novel environmental scanning transmission electron microscope with single-atom resolution, to understand the mechanisms. Our results track the areal density of dynamic single atoms on the support between nanoparticles and attached to them; both as migrating species in performance degradation and as potential new independent active species. We demonstrate that the decay of smaller nanoparticles is initiated by a local lack of single atoms; while a post decay increase in single-atom density suggests anchoring sites on the substrate before aggregation to larger particles. The analyses reveal a relationship between the density and mobility of single atoms, particle sizes and their nature in the immediate neighbourhood. The results are combined with practical catalysts important in technological processes. The findings illustrate the complex nature of sintering and deactivation. They are used to generate new fundamental insights into nanoparticle sintering dynamics at the single-atom level, important in the development of efficient supported nanoparticle systems for improved chemical processes and novel single-atom catalysis. This article is part of a discussion meeting issue 'Dynamic in situ microscopy relating structure and function'.

A critique and empirical assessment of Alexandra Horowitz and Julie Hecht's "Examining dog-human play: the characteristics, affect, and vocalizations of a unique interspecific interaction".

Horowitz and Hecht (Anim Cog 19:779-788, 2016) presented data about activities and vocalizations during brief videotaped dog-owner play provided by owners, examined these in relation to human affect during play, and made comparisons from their results to other research on activities and vocalizations during dog-human play. In this critique, I describe problems with Horowitz and Hecht's methodology, analyses, and evidence; in their interpretations of the data, evidence, and categorizations provided in other research, particularly my own studies of dog-human play; and in their claims of novelty for their findings. I argue that, to support their ideas about vocalizations and play types during dog-human play and their comparisons to other studies, their study requires fuller descriptions and reliability for their coding of vocalizations and play types, appropriate statistical analyses, and accurate descriptions of prior research. I also argue that their methodology provides results strikingly similar in many aspects to those of other researchers studying dog-human play, contrary to their claims of novel findings. Finally, I examine their suggestions about relationships between human affect and types of play activities and vocalizations using the videos of dog-human play I discussed in earlier publications, discovering minimal, if any, relationship.

Self-awareness without inner speech: a commentary on Morin.

Morin's identification of inner speech with self-awareness is problematic. Taylor's description of her experience before, during, and after her stroke and operation is also problematic; it is at times confusing and difficult to comprehend conceptually. Rather than being global, her deficits in self-awareness seem piecemeal. She describes self-awareness that exists independent of inner speech. I offer interpretations of her experience alternative to those of Morin and Taylor.

A resolution between mentalism and teleonomy, or fodder for a continuing dialogue?

Scientists, including psychologists, are often disturbed by the psychological interpretation of animal behavior. Nick Thompson offered a teleonomic approach to the use of psychological terms to describe behavior that avoided the assumption that mental states (or other entities or processes) caused the behavior. I describe tensions between teleonomic and mentalistic conceptualizations of animals by some early comparative psychologists, and offer our skill at kinesthetic-visual matching as an explanation as to why humans so often assume that mental states cohere with behavior. My explanation elucidates why mentalistic interpretations of behavior remain after teleonomic description.