The equilibrium structures and dynamics of a nanoscale system are regulated by a complex potential energy surface (PES). This is a key target of theoretical calculations but experimentally elusive. ...We report the measurement of a key PES parameter for a model nanosystem: size-selected Au nanoclusters, soft-landed on amorphous silicon nitride supports. We obtain the energy difference between the most abundant structural isomers of magic number Au
clusters, the decahedron and face-centred-cubic (fcc) structures, from the equilibrium proportions of the isomers. These are measured by atomic-resolution scanning transmission electron microscopy, with an ultra-stable heating stage, as a function of temperature (125-500 °C). At lower temperatures (20-125 °C) the behaviour is kinetic, exhibiting down conversion of metastable decahedra into fcc structures; the higher state is repopulated at higher temperatures in equilibrium. We find the decahedron is 0.040 ± 0.020 eV higher in energy than the fcc isomer, providing a benchmark for the theoretical treatment of nanoparticles.
The Morphometry of Impact Craters on Bennu Daly, R. T.; Bierhaus, E. B.; Barnouin, O. S. ...
Geophysical research letters,
28 December 2020, Letnik:
47, Številka:
24
Journal Article
Recenzirano
Odprti dostop
Bennu is an ~500‐m‐diameter rubble‐pile asteroid that is the target of detailed study by the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS‐REx) ...mission. Here we use data from the OSIRIS‐REx Laser Altimeter to assess depth‐to‐diameter ratios (d/D) of 108 impact craters larger than 10 m in diameter. The d/D of craters on Bennu ranges from 0.02 to 0.19. The mean is 0.10 ± 0.03. The smallest craters show the broadest range in d/D, consistent with d/D measurements on other asteroids. A few craters have central mounds, which is interpreted as evidence that a more competent substrate lies a few meters beneath them. The range of d/D narrows as crater size increases, with craters larger than 80 m tending toward smaller d/D. At large scales, increases in target strength with depth, combined with target curvature, may affect crater morphometry.
Plain Language Summary
Between 2018 and 2020, National Aeronautics and Space Administration (NASA)'s Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS‐REx) spacecraft orbited a small asteroid called Bennu in preparation to collect a sample for return to Earth. Bennu is a “rubble‐pile” asteroid, meaning an aggregate of rock fragments that have coalesced together in space. OSIRIS‐REx observations showed that Bennu has many craters on its surface, which formed when other, smaller objects collided with it in the past. Crater depths and widths (diameters), in addition to relating to the size and speed of the impacting object, also reflect the physical characteristics of the impacted surface. Accordingly, we measured the depths and diameters of many of Bennu's craters to better understand the surface and interior properties of this rubble‐pile asteroid and how it compares to other asteroids. The smaller craters on Bennu have a variety of depths, even among similarly sized craters. The largest are so wide that they appear to be affected by the curvature of Bennu's surface and by the presence of stronger material at depth. We observe mounds inside some of the smaller craters, supporting the idea that a more competent substrate underlies the surface material.
Key Points
The depth‐to‐diameter ratio (d/D) of asteroid Bennu's craters >10 m in diameter ranges from 0.02 to 0.19 with a mean of 0.10 ± 0.03
Small craters show the greatest diversity in d/D, whereas larger craters (>80 m) span a narrower range in d/D and tend to be shallower
For craters >80 m, increases in target strength with depth, combined with target curvature, likely contribute to smaller d/D
Although the changes in melting behaviour on the nanoscale have long attracted the interest of researchers, the mechanism by which nanoparticles melt remains an open problem. We report the direct ...observation, at atomic resolution, of surface melting in individual size-selected Au clusters (2-5 nm diameter) supported on carbon films, using an in situ heating stage in the aberration corrected scanning transmission electron microscope. At elevated temperatures the Au nanoparticles are found to form a solid core-liquid shell structure. The cluster surface melting temperatures, show evidence of size-dependent melting point suppression. The cluster core melting temperatures are significantly greater than predicted by existing models of free clusters. To explore the effect of the interaction between the clusters and the carbon substrate, we employ a very large-scale ab initio simulation approach to investigate the influence of the support. Theoretical results for surface and core melting points are in good agreement with experiment.
Aims/hypothesis
In this study we aimed to replicate the previously reported association between the glycaemic response to metformin and the SNP rs11212617 at a locus that includes the ataxia ...telangiectasia mutated (
ATM
) gene in multiple additional populations.
Methods
Incident users of metformin selected from the Diabetes Care System West-Friesland (DCS,
n
= 929) and the Rotterdam Study (
n
= 182) from the Netherlands, and the CARDS Trial (
n
= 254) from the UK were genotyped for rs11212617 and tested for an association with both HbA
1c
reduction and treatment success, defined as the ability to reach the treatment target of an HbA
1c
≤7 % (53 mmol/mol). Finally, a meta-analysis including data from literature was performed.
Results
In the DCS cohort, we observed an association between rs11212617 genotype and treatment success on metformin (OR 1.27, 95% CI 1.03, 1.58,
p
= 0.028); in the smaller Rotterdam Study cohort, a numerically similar but non-significant trend was observed (OR 1.45, 95% CI 0.87, 2.39,
p
= 0.15); while in the CARDS cohort there was no significant association. In meta-analyses of these three cohorts separately or combined with the previously published cohorts, rs11212617 genotype is associated with metformin treatment success (OR 1.24, 95% CI 1.04, 1.49,
p
= 0.016 and OR 1.25, 95% CI 1.33, 1.38,
p
= 7.8 × 10
−6
, respectively).
Conclusions/interpretation
A gene variant near
ATM
is significantly associated with metformin treatment response in type 2 diabetic patients from the Netherlands and the UK. This is the first robustly replicated common susceptibility locus found to be associated with metformin treatment response.
An unambiguous determination of the three-dimensional structure of nanoparticles is challenging. Electron tomography requires a series of images taken for many different specimen orientations. This ...approach is ideal for stable and stationary structures. But ultrasmall nanoparticles are intrinsically structurally unstable and may interact with the incident electron beam, constraining the electron beam density that can be used and the duration of the observation. Here we use aberration-corrected scanning transmission electron microscopy, coupled with simple imaging simulation, to determine with atomic resolution the size, three-dimensional shape, orientation and atomic arrangement of size-selected gold nanoclusters that are preformed in the gas phase and soft-landed on an amorphous carbon substrate. The structures of gold nanoclusters containing 309±6 atoms can be identified with either Ino-decahedral, cuboctahedral or icosahedral geometries. Comparison with theoretical modelling of the system suggests that the structures are consistent with energetic considerations. The discovery that nanoscale gold particles function as active and selective catalysts for a variety of important chemical reactions has provoked much research interest in recent years. We believe that the detailed structure information we provide will help to unravel the role of these nanoclusters in size- and structure-specific catalytic reactions. We note that the technique will be of use in investigations of other supported ultrasmall metal cluster systems.
The equilibrium ground state atomic structures of nanoparticles are critical to understanding the relationship between their structure and functionality, e.g., in catalysis, and are the standard ...output of first principles and semiempirical theoretical treatments. We demonstrate a method of obtaining a stable population of the structural isomers of supported Au clusters from a metastable initial array via electron beam irradiation. Statistical investigation of size-selected Au clusters containing 923±23 atoms via aberration-corrected scanning transmission electron microscopy shows that virtually all of the icosahedral (Ih) clusters undergo structural transformations into decahedral (Dh) (primarily) or fcc isomers while Dh and FCC clusters generally retain their atomic structures after electron irradiation of each cluster individually for up to 400 s at a dose of 2.4×10(4) e-/angstrom2/frame. Intermediate phases are often observed in the image series (videos) before the appearance of the new stable isomers, the relative structural populations of which can be controlled via the electron beam dose. The comprehensive results reported here should provide a valuable experimental reference for testing or refining potential models and for kinetic or dynamical treatments of the atomic configurations.
We report the atomic-scale structures and fluctuating dynamical behavior of size-selected Au55 clusters obtained by aberration-corrected scanning transmission electron microscopy (STEM) coupled with ...systematic STEM simulations. No high-symmetry structures (face-centered cubic polyhedron, icosahedron, or decahedron) were observed in our statistical investigation. We find Au55 clusters that are characteristic of the theoretically predicted chiral structure and similar sister isomers (which together we define as the chiral structural zone). The chiral structural zone was found to arise repeatedly in the time-lapse sequences of images we measured, though other amorphous-like structures are also frequently observed. The approach demonstrated here can be applied to identify specific low-symmetry atomic structures in other small clusters and distinguish them unambiguously from high-symmetry isomers.
Numerous pharmacogenetic clinical guidelines and recommendations have been published, but barriers have hindered the clinical implementation of pharmacogenetics. The Translational Pharmacogenetics ...Program (TPP) of the National Institutes of Health (NIH) Pharmacogenomics Research Network was established in 2011 to catalog and contribute to the development of pharmacogenetic implementations at eight US healthcare systems, with the goal to disseminate real‐world solutions for the barriers to clinical pharmacogenetic implementation. The TPP collected and normalized pharmacogenetic implementation metrics through June 2015, including gene–drug pairs implemented, interpretations of alleles and diplotypes, numbers of tests performed and actionable results, and workflow diagrams. TPP participant institutions developed diverse solutions to overcome many barriers, but the use of Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines provided some consistency among the institutions. The TPP also collected some pharmacogenetic implementation outcomes (scientific, educational, financial, and informatics), which may inform healthcare systems seeking to implement their own pharmacogenetic testing programs.
Synthetically versatile alkyl sulfinates can be prepared from readily available amines, using Katritzky pyridinium salt intermediates. In a catalyst-free procedure, primary, secondary, and benzylic ...alkyl radicals are generated by photoinduced or thermally induced single-electron transfer (SET) from an electron donor–acceptor (EDA) complex, and trapped by SO2 to generate sulfonyl radicals. Hydrogen atom transfer (HAT) from Hantzsch ester gives alkyl sulfinate products, which are used to prepare a selection of medicinal chemistry relevant sulfonyl-containing motifs.
Summary Objective Femoroacetabular Impingement (FAI) and Acetabular Dysplasia are common deformities, which have been implicated as a major cause of hip osteoarthritis (OA). We examined whether these ...subtle deformities of the hip are associated with the development of radiographic OA and total hip replacement (THR) in women. Design A population-based, longitudinal cohort of 1003 women underwent pelvis radiographs at years 2 and 20. Alpha Angle, Triangular Index Height, Lateral Centre Edge (LCE) angle and Extrusion Index were measured. An alpha angle of greater than 65° was defined as Cam-type FAI. Radiographic OA and the presence of a THR were then determined at 20 years. Results Cam-type FAI was significantly associated with the development of radiographic OA. Each degree increase in alpha angle above 65° was associated with an increase in risk of 5% (Odds Ratio (OR) 1.05 95% confidence interval (CI) 1.01–1.09) for radiographic OA and 4% (OR 1.04 95% CI 1.00–1.08) for THR. For Acetabular Dysplasia, each degree reduction in LCE angle below 28° was associated with an increase in risk of 13.0% (OR 0.87 95% CI 0.78–0.96) for radiographic OA and 18% (OR 0.82 95% CI 0.75–0.89) for THR. Conclusions This study demonstrates that Cam-type FAI and mild Acetabular Dysplasia are predictive of subsequent OA and THR in a large female population cohort. These are independent of age, BMI and joint space and significantly improve current predictive models of hip OA development.
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