Imaging Ferroelastic Domain Walls in Hybrid Improper Ferroelectric Sr3Sn2O7.

We combined synchrotron-based near field infrared spectroscopy and atomic force microscopy to image the properties of ferroelastic domain walls in Sr3Sn2O7. Although frequency shifts at the walls are near the limit of our sensitivity, we can confirm semiconducting rather than metallic character and widths between 20 and 60 nm. The latter is significantly narrower than in other hybrid improper ferroelectrics like Ca3Ti2O7. We attribute this trend to the softer lattice in Sr3Sn2O7, which may enable the octahedral tilt and rotation order parameters to evolve more quickly across the wall without significantly increased strain. These findings are crucial for the understanding of phononic properties at interfaces and the development of domain wall-based devices.

Pressure-Temperature-Magnetic Field Phase Diagram of Multiferroic (NH4)2FeCl5·H2O.

We combined synchrotron-based infrared absorbance and Raman scattering spectroscopies with diamond anvil cell techniques and a symmetry analysis to explore the properties of multiferroic (NH4)2FeCl5·H2O under extreme pressure-temperature conditions. Compression-induced splitting of the Fe-Cl stretching, Cl-Fe-Cl and Cl-Fe-O bending, and NH4+ librational modes defines two structural phase transitions, and a group-subgroup analysis reveals space group sequences that vary depending upon proximity to the unexpectedly wide order-disorder transition. We bring these findings together with prior high-field work to develop the pressure-temperature-magnetic field phase diagram uncovering competing polar, chiral, and magnetic phases in this system.

Rapid trial-and-error learning with simulation supports flexible tool use and physical reasoning.

Many animals, and an increasing number of artificial agents, display sophisticated capabilities to perceive and manipulate objects. But human beings remain distinctive in their capacity for flexible, creative tool use-using objects in new ways to act on the world, achieve a goal, or solve a problem. To study this type of general physical problem solving, we introduce the Virtual Tools game. In this game, people solve a large range of challenging physical puzzles in just a handful of attempts. We propose that the flexibility of human physical problem solving rests on an ability to imagine the effects of hypothesized actions, while the efficiency of human search arises from rich action priors which are updated via observations of the world. We instantiate these components in the "sample, simulate, update" (SSUP) model and show that it captures human performance across 30 levels of the Virtual Tools game. More broadly, this model provides a mechanism for explaining how people condense general physical knowledge into actionable, task-specific plans to achieve flexible and efficient physical problem solving.

Partial mental simulation explains fallacies in physical reasoning.

People can reason intuitively, efficiently, and accurately about everyday physical events. Recent accounts suggest that people use mental simulation to make such intuitive physical judgments. But mental simulation models are computationally expensive; how is physical reasoning relatively accurate, while maintaining computational tractability? We suggest that people make use of partial simulation, mentally moving forward in time only parts of the world deemed relevant. We propose a novel partial simulation model, and test it on the physical conjunction fallacy, a recently observed phenomenon [Ludwin-Peery et al. (2020). Broken physics: A conjunction-fallacy effect in intuitive physical reasoning. Psychological Science, 31(12), 1602-1611. https://doi.org/10.1177/0956797620957610] that poses a challenge for full simulation models. We find an excellent fit between our model's predictions and human performance on a set of scenarios that build on and extend those used by Ludwin-Peery et al. [(2020). Broken physics: A conjunction-fallacy effect in intuitive physical reasoning. Psychological Science, 31(12), 1602-1611. https://doi.org/10.1177/0956797620957610], quantitatively and qualitatively accounting for deviations from optimal performance. Our results suggest more generally how we allocate cognitive resources to efficiently represent and simulate physical scenes.

Developing the Pressure-Temperature-Magnetic Field Phase Diagram of Multiferroic [(CH3)2NH2]Mn(HCOO)3.

We combined Raman scattering and magnetic susceptibility to explore the properties of [(CH3)2NH2]Mn(HCOO)3 under compression. Analysis of the formate bending mode reveals a broad two-phase region surrounding the 4.2 GPa critical pressure that becomes increasingly sluggish below the order-disorder transition due to the extensive hydrogen-bonding network. Although the paraelectric and ferroelectric phases have different space groups at ambient-pressure conditions, they both drive toward P1 symmetry under compression. This is a direct consequence of how the order-disorder transition changes under pressure. We bring these findings together with prior magnetization work to create a pressure-temperature-magnetic field phase diagram, unveiling entanglement, competition, and a progression of symmetry-breaking effects that underlie functionality in this molecule-based multiferroic. That the high-pressure P1 phase is a subgroup of the ferroelectric Cc suggests the possibility of enhanced electric polarization as well as opportunity for strain control.

Redox Isomeric Surface Structures Are Preferred over Odd-Electron Pt1.

The formation of metal-ligand coordination networks on surfaces that contain redox isomers is a topic of considerable interest and is important for bifunctional metallochemistry, including heterogeneous catalysis. Towards this end, a tetrazine with two electron withdrawing pyrimidinyl substituents was co-deposited with platinum metal on the Au(100) surface. In a 2:1 metal:ligand ratio, only half of the platinum is oxidized to the +2 oxidation state, with the remainder coordinating to the ligand without charge transfer, as Pt0 . The resultant Pt0 /PtII mixed valence structure is thought to form due to the aversion of the ligand towards a four-electron reduction and the strong preference of Pt towards 0 and +2 oxidation states. These results were confirmed through a series of experiments varying the on-surface metal:ligand stoichiometry in the redox assembly formed: added oxidant does not oxidize the already complexed Pt0 . Scanning tunneling microscopy reveals irregular chain structures that are attributed to the mixture of Pt valence states, each with distinct local coordination geometries. Density functional theory calculations give further detail about these local geometries. These results demonstrate the formation of a mixture of valence states in on-surface redox assembly of metal-organic networks that extends the library of single-site metal structures for surface chemistry and catalysis. Redox-isomeric Pt0 versus Pt2+ surface structures can coexist in this ligand environment.

Two- and Three-Electron Oxidation of Single-Site Vanadium Centers at Surfaces by Ligand Design.

Rational, systematic tuning of single-site metal centers on surfaces offers a new approach to increase selectivity in heterogeneous catalysis reactions. Although such metal centers of uniform oxidation states have been achieved, the ability to control their oxidation states through the use of carefully designed ligands had not been shown. To this end, tetrazine ligands functionalized by two pyridinyl or pyrimidinyl substituents were deposited, along with vanadium metal, on the Au(100) surface. The greater oxidizing power of the bis-pyrimidinyltetrazine facilitates the on-surface redox formation of V(3+), compared to V(2+) when paired with the bis-pyridinyltetrazine, as determined by X-ray photoelectron spectroscopy. This demonstrates the ability to control metal oxidation states in surface coordination architectures by altering the redox properties of organic ligands. The metal-ligand complexes take the form of one-dimensional polymeric chains, resolved by scanning tunneling microscopy. The chain structures in the first layer are very uniform and are based on the same quasi-square-planar coordination geometry around single-site V with either ligand. Formation of a different, dimer structure is observed in the early stages of the second layer formation. These systems offer new opportunities in controlling the oxidation state of single-site transition metal atoms at a surface for new advances in heterogeneous catalysts.

Redox-active on-surface polymerization of single-site divalent cations from pure metals by a ketone-functionalized phenanthroline.

Metallic iron, chromium, or platinum mixing with a ketone-functionalized phenanthroline ligand on a single crystal gold surface demonstrates redox activity to a well-defined oxidation state and assembly into thermally stable, one dimensional, polymeric chains. The diverging ligand geometry incorporates redox-active sub-units and bi-dentate binding sites. The gold surface provides a stable adsorption environment and directs growth of the polymeric chains, but is inert with regard to the redox chemistry. These systems are characterized by scanning tunnelling microscopy, non-contact atomic force microscopy, and X-ray photoelectron spectroscopy under ultra-high vacuum conditions. The relative propensity of the metals to interact with the ketone group is examined, and it is found that Fe and Cr more readily complex the ligand than Pt. The formation and stabilization of well-defined transition metal single-sites at surfaces may open new routes to achieve higher selectivity in heterogeneous catalysts.

Redox-active on-surface assembly of metal-organic chains with single-site Pt(II).

The formation and stabilization of well-defined transition-metal single sites at surfaces may open new routes to achieve higher selectivity in heterogeneous catalysts. Organic ligand coordination to produce a well-defined oxidation state in weakly reducing metal sites at surfaces, desirable for selective catalysis, has not been achieved. Here, we address this using metallic platinum interacting with a dipyridyl tetrazine ligand on a single crystal gold surface. X-ray photoelectron spectroscopy measurements demonstrate the metal-ligand redox activity and are paired with molecular-resolution scanning probe microscopy to elucidate the structure of the metal-organic network. Comparison to the redox-inactive diphenyl tetrazine ligand as a control experiment illustrates that the redox activity and molecular-level ordering at the surface rely on two key elements of the metal complexes: (i) bidentate binding sites providing a suitable square-planar coordination geometry when paired around each Pt, and (ii) redox-active functional groups to enable charge transfer to a well-defined Pt(II) oxidation state. Ligand-mediated control over the oxidation state and structure of single-site metal centers that are in contact with a metal surface may enable advances in higher selectivity for next generation heterogeneous catalysts.

Unconventional insulator-to-metal phase transition in Mn3Si2Te6.

The nodal-line semiconductor Mn3Si2Te6 is generating enormous excitment due to the recent discovery of a field-driven insulator-to-metal transition and associated colossal magnetoresistance as well as evidence for a new type of quantum state involving chiral orbital currents. Strikingly, these qualities persist even in the absence of traditional Jahn-Teller distortions and double-exchange mechanisms, raising questions about exactly how and why magnetoresistance occurs along with conjecture as to the likely signatures of loop currents. Here, we measured the infrared response of Mn3Si2Te6 across the magnetic ordering and field-induced insulator-to-metal transitions in order to explore colossal magnetoresistance in the absence of Jahn-Teller and double-exchange interactions. Rather than a traditional metal with screened phonons, the field-driven insulator-to-metal transition leads to a weakly metallic state with localized carriers. Our spectral data are fit by a percolation model, providing evidence for electronic inhomogeneity and phase separation. Modeling also reveals a frequency-dependent threshold field for carriers contributing to colossal magnetoresistance which we discuss in terms of polaron formation, chiral orbital currents, and short-range spin fluctuations. These findings enhance the understanding of insulator-to-metal transitions in new settings and open the door to the design of unconventional colossal magnetoresistant materials.

Mental jenga: A counterfactual simulation model of causal judgments about physical support.

From building towers to picking an orange from a stack of fruit, assessing support is critical for successfully interacting with the physical world. But how do people determine whether one object supports another? In this paper, we develop a counterfactual simulation model (CSM) of causal judgments about physical support. The CSM predicts that people judge physical support by mentally simulating what would happen to a scene if the object of interest was removed. Three experiments test the model by asking one group of participants to judge what would happen to a tower if one of the blocks were removed, and another group of participants how responsible that block was for the tower's stability. The CSM accurately captures participants' predictions by running noisy simulations that incorporate different sources of uncertainty. Participants' responsibility judgments are closely related to counterfactual predictions: a block is more responsible when many other blocks would fall if it were removed. By construing physical support as preventing from falling, the CSM provides a unified account of how causal judgments in dynamic and static physical scenes arise from the process of counterfactual simulation. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

An approximate representation of objects underlies physical reasoning.

People make fast and reasonable predictions about the physical behavior of everyday objects. To do so, people may use principled mental shortcuts, such as object simplification, similar to models developed by engineers for real-time physical simulations. We hypothesize that people use simplified object approximations for tracking and action (the body representation), as opposed to fine-grained forms for visual recognition (the shape representation). We used three classic psychophysical tasks (causality perception, time-to-collision, and change detection) in novel settings that dissociate body and shape. People's behavior across tasks indicates that they rely on coarse bodies for physical reasoning, which lies between convex hulls and fine-grained shapes. Our empirical and computational findings shed light on basic representations people use to understand everyday dynamics, and how these representations differ from those used for recognition. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Lifelong learning of cognitive styles for physical problem-solving: The effect of embodied experience.

'Embodied cognition' suggests that our bodily experiences broadly shape our cognitive capabilities. We study how embodied experience affects the abstract physical problem-solving styles people use in a virtual task where embodiment does not affect action capabilities. We compare how groups with different embodied experience - 25 children and 35 adults with congenital limb differences versus 45 children and 40 adults born with two hands - perform this task, and find that while there is no difference in overall competence, the groups use different cognitive styles to find solutions. People born with limb differences think more before acting but take fewer attempts to reach solutions. Conversely, development affects the particular actions children use, as well as their persistence with their current strategy. Our findings suggest that while development alters action choices and persistence, differences in embodied experience drive changes in the acquisition of cognitive styles for balancing acting with thinking.

Real-Space Infrared Spectroscopy of Ferroelectric Domain Walls in Multiferroic h-(Lu,Sc)FeO3.

We employ synchrotron-based near-field infrared spectroscopy to image the phononic properties of ferroelectric domain walls in hexagonal (h) Lu0.6Sc0.4FeO3, and we compare our findings with a detailed symmetry analysis, lattice dynamics calculations, and prior models of domain-wall structure. Rather than metallic and atomically thin as observed in the rare-earth manganites, ferroelectric walls in h-Lu0.6Sc0.4FeO3 are broad and semiconducting, a finding that we attribute to the presence of an A-site substitution-induced intermediate phase that reduces strain and renders the interior of the domain wall nonpolar. Mixed Lu/Sc occupation on the A site also provides compositional heterogeneity over micron-sized length scales, and we leverage the fact that Lu and Sc cluster in different ratios to demonstrate that the spectral characteristics at the wall are robust even in different compositional regimes. This work opens the door to broadband imaging of physical and chemical heterogeneity in ferroics and represents an important step toward revealing the rich properties of these flexible defect states.

The Biomedical Resource Ontology (BRO) to enable resource discovery in clinical and translational research.

The biomedical research community relies on a diverse set of resources, both within their own institutions and at other research centers. In addition, an increasing number of shared electronic resources have been developed. Without effective means to locate and query these resources, it is challenging, if not impossible, for investigators to be aware of the myriad resources available, or to effectively perform resource discovery when the need arises. In this paper, we describe the development and use of the Biomedical Resource Ontology (BRO) to enable semantic annotation and discovery of biomedical resources. We also describe the Resource Discovery System (RDS) which is a federated, inter-institutional pilot project that uses the BRO to facilitate resource discovery on the Internet. Through the RDS framework and its associated Biositemaps infrastructure, the BRO facilitates semantic search and discovery of biomedical resources, breaking down barriers and streamlining scientific research that will improve human health.

Polycyclic aromatic hydrocarbons in soil of the Canadian river floodplain in Oklahoma.

The accumulation of polycyclic aromatic hydrocarbons (PAH) in soil, plants, and water may impart negative effects on ecosystem and human health. We quantified the concentration and distribution of 41 PAH (n = 32), organic C, total N, and S (n = 140) and investigated PAH sources using a chronosequence of floodplain soils under a natural vegetation succession. Soil samples were collected between 0- and 260-cm depth in bare land (the control), wetland, forest, and grassland areas near a closed municipal landfill and an active asphalt plant (the contaminant sources) in the north bank of the Canadian River near Norman, OK. Principal component, cluster, and correlation analyses were used to investigate the spatial distribution of PAH, in combination with diagnostic ratios to distinguish pyrogenic vs. petrogenic PAH suites. Total PAH concentration (SigmaPAH) had a mean of 1300 ng g(-1), minimum of 16 ng g(-1), and maximum of 12,000 ng g(-1). At 0- to 20-cm depth, SigmaPAH was 3500 +/- 1600 ng g(-1) (mean +/- 1 SE) near the contaminant sources. The most common compounds were nonalkylated, high molecular weight PAH of pyrogenic origin, i.e., fluoranthene (17%), pyrene (14%), phenanthrene (9%), benzo(b)fluoranthene (7%), chrysene (6%), and benzo(a)anthracene (5%). SigmaPAH in the control (130 +/- 23 ng g(-1)) was comparable to reported concentrations for the rural Great Plains. Perylene had a unique distribution pattern suggesting biological inputs. The main PAH contamination mechanisms were likely atmospheric deposition due to asphalt production at the 0- to 20-cm depth and past landfill operations at deeper depths.

Site-specific spectroscopic measurement of spin and charge in (LuFeO3)m/(LuFe2O4)1 multiferroic superlattices.

Interface materials offer a means to achieve electrical control of ferrimagnetism at room temperature as was recently demonstrated in (LuFeO3)m/(LuFe2O4)1 superlattices. A challenge to understanding the inner workings of these complex magnetoelectric multiferroics is the multitude of distinct Fe centres and their associated environments. This is because macroscopic techniques characterize average responses rather than the role of individual iron centres. Here, we combine optical absorption, magnetic circular dichroism and first-principles calculations to uncover the origin of high-temperature magnetism in these superlattices and the charge-ordering pattern in the m = 3 member. In a significant conceptual advance, interface spectra establish how Lu-layer distortion selectively enhances the Fe2+ â†’  Fe3+ charge-transfer contribution in the spin-up channel, strengthens the exchange interactions and increases the Curie temperature. Comparison of predicted and measured spectra also identifies a non-polar charge ordering arrangement in the LuFe2O4 layer. This site-specific spectroscopic approach opens the door to understanding engineered materials with multiple metal centres and strong entanglement.

Quantitative Analysis of Glycine Oligomerization by Ion-Pair Chromatography.

This paper describes a method for the quantitative analysis of mixtures of glycine and its oligomers by ion-pair high-performance liquid chromatography (IP-HPLC), with a particular focus on applications in origins-of-life research. We demonstrate the identification of glycine oligomers (Gly n ) up to 14 residues long-the approximate detectable limit of their solubility in water-and measurement of the concentration of these species in the product mixture of an oligomerization reaction. The molar response factors for higher oligomers of glycine-which are impractical to obtain as pure samples-are extrapolated from direct analysis of pure standards of n = 3-6, which established a clear linear trend. We compare and contrast our method to those in previous reports with respect to accuracy and practicality. While the data reported here are specific to the analysis of oligomers of glycine, the approach should be applicable to the design of methods for the analysis of oligomerization of other amino acids.

Sources of uncertainty in intuitive physics.

Recent work suggests that people predict how objects interact in a manner consistent with Newtonian physics, but with additional uncertainty. However, the sources of uncertainty have not been examined. In this study, we measure perceptual noise in initial conditions and stochasticity in the physical model used to make predictions. Participants predicted the trajectory of a moving object through occluded motion and bounces, and we compared their behavior to an ideal observer model. We found that human judgments cannot be captured by simple heuristics and must incorporate noisy dynamics. Moreover, these judgments are biased consistently with a prior expectation on object destinations, suggesting that people use simple expectations about outcomes to compensate for uncertainty about their physical models.

Multiply-constrained semantic search in the Remote Associates Test.

Many important problems require consideration of multiple constraints, such as choosing a job based on salary, location, and responsibilities. We used the Remote Associates Test to study how people solve such multiply-constrained problems by asking participants to make guesses as they came to mind. We evaluated how people generated these guesses by using Latent Semantic Analysis to measure the similarity between the guesses, cues, and answers. We found that people use two systematic strategies to solve multiply-constrained problems: (a) people produce guesses primarily on the basis of just one of the three cues at a time; and (b) people adopt a local search strategy--they make new guesses based in part on their previous guesses. These results inform how people combine constraints to search through and retrieve semantic information from memory.