Objective Measurement of Posture and Movement in Young Children Using Wearable Sensors and Customised Mathematical Approaches: A Systematic Review.

Given the importance of young children's postures and movements to health and development, robust objective measures are required to provide high-quality evidence. This study aimed to systematically review the available evidence for objective measurement of young (0-5 years) children's posture and movement using machine learning and other algorithm methods on accelerometer data. From 1663 papers, a total of 20 papers reporting on 18 studies met the inclusion criteria. Papers were quality-assessed and data extracted and synthesised on sample, postures and movements identified, sensors used, model development, and accuracy. A common limitation of studies was a poor description of their sample data, yet over half scored adequate/good on their overall study design quality assessment. There was great diversity in all aspects examined, with evidence of increasing sophistication in approaches used over time. Model accuracy varied greatly, but for a range of postures and movements, models developed on a reasonable-sized (n > 25) sample were able to achieve an accuracy of >80%. Issues related to model development are discussed and implications for future research outlined. The current evidence suggests the rapidly developing field of machine learning has clear potential to enable the collection of high-quality evidence on the postures and movements of young children.

Resolving Point Defects in the Hydration Structure of Calcite (10.4) with Three-Dimensional Atomic Force Microscopy.

It seems natural to assume that defects at mineral surfaces critically influence interfacial processes such as the dissolution and growth of minerals in water. The experimental verification of this claim, however, is challenging and requires real-space methods with utmost spatial resolution, such as atomic force microscopy (AFM). While defects at mineral-water interfaces have been resolved in 2D AFM images before, the perturbation of the surrounding hydration structure has not yet been analyzed experimentally. In this Letter, we demonstrate that point defects on the most stable and naturally abundant calcite (10.4) surface can be resolved using high-resolution 3D AFM-even within the fifth hydration layer. Our analysis of the hydration structure surrounding the point defect shows a perturbation of the hydration with a lateral extent of approximately one unit cell. These experimental results are corroborated by molecular dynamics simulations.

A Supramolecular Ice Growth Inhibitor.

Safranine O, a synthetic dye, was found to inhibit growth of ice at millimolar concentrations with an activity comparable to that of highly evolved antifreeze glycoproteins. Safranine inhibits growth of ice crystals along the crystallographic a-axis, resulting in bipyramidal needles extended along the <0001> directions as well as and plane-specific thermal hysteresis (TH) activity. The interaction of safranine with ice is reversible, distinct from the previously reported behavior of antifreeze proteins. Spectroscopy and molecular dynamics indicate that safranine forms aggregates in aqueous solution at micromolar concentrations. Metadynamics simulations and aggregation theory suggested that as many as 30 safranine molecules were preorganized in stacks at the concentrations where ice growth inhibition was observed. The simulations and single-crystal X-ray structure of safranine revealed regularly spaced amino and methyl substituents in the aggregates, akin to the ice-binding site of antifreeze proteins. Collectively, these observations suggest an unusual link between supramolecular assemblies of small molecules and functional proteins.

Resorcinol Crystallization from the Melt: A New Ambient Phase and New "Riddles".

Structures of the α and ß phases of resorcinol, a major commodity chemical in the pharmaceutical, agrichemical, and polymer industries, were the first polymorphic pair of molecular crystals solved by X-ray analysis. It was recently stated that "no additional phases can be found under atmospheric conditions" (Druzbicki, K. et al. J. Phys. Chem. B 2015, 119, 1681). Herein is described the growth and structure of a new ambient pressure phase, ε, through a combination of optical and X-ray crystallography and by computational crystal structure prediction algorithms. α-Resorcinol has long been a model for mechanistic crystal growth studies from both solution and vapor because prisms extended along the polar axis grow much faster in one direction than in the opposite direction. Research has focused on identifying the absolute sense of the fast direction-the so-called "resorcinol riddle"-with the aim of identifying how solvent controls crystal growth. Here, the growth velocity dissymmetry in the melt is analyzed for the ß phase. The ε phase only grows from the melt, concomitant with the ß phase, as polycrystalline, radially growing spherulites. If the radii are polar, then the sense of the polar axis is an essential feature of the form. Here, this determination is made for spherulites of ß resorcinol (ε, point symmetry 222, does not have a polar axis) with additives that stereoselectively modify growth velocities. Both ß and ε have the additional feature that individual radial lamellae may adopt helicoidal morphologies. We correlate the appearance of twisting in ß and ε with the symmetry of twist-inducing additives.

Can Point Defects in Surfaces in Solution be Atomically Resolved by Atomic Force Microscopy?

While the atomic force microscope (AFM) is able to image mineral surfaces in solution with atomic resolution, so far, it has been a matter of debate whether imaging point defects is also possible under these conditions. The difficulties stem from the limited knowledge of what types of defects may be stable in the presence of an AFM tip, as well as from the complicated imaging mechanism involving interactions between hydration layers over the surface and around the tip apex. Here, we present atomistic molecular dynamics and free energy calculations of the AFM imaging of vacancies and ionic substitutions in the calcite (101[over ¯]4) surface in water, using a new silica AFM tip model. Our results indicate that both calcium and carbonate vacancies, as well as a magnesium substitution, could be resolved in an AFM experiment, albeit with different imaging mechanisms.

Understanding 2D atomic resolution imaging of the calcite surface in water by frequency modulation atomic force microscopy.

Frequency modulation atomic force microscopy (FM-AFM) experiments were performed on the calcite (10[Formula: see text]4) surface in pure water, and a detailed analysis was made of the 2D images at a variety of frequency setpoints. We observed eight different contrast patterns that reproducibly appeared in different experiments and with different measurement parameters. We then performed systematic free energy calculations of the same system using atomistic molecular dynamics to obtain an effective force field for the tip-surface interaction. By using this force field in a virtual AFM simulation we found that each experimental contrast could be reproduced in our simulations by changing the setpoint, regardless of the experimental parameters. This approach offers a generic method for understanding the wide variety of contrast patterns seen on the calcite surface in water, and is generally applicable to AFM imaging in liquids.

Twisted aspirin crystals.

Banded spherulites of aspirin have been crystallized from the melt in the presence of salicylic acid either generated from aspirin decomposition or added deliberately (2.6-35.9 mol %). Scanning electron microscopy, X-ray diffraction analysis, and optical polarimetry show that the spherulites are composed of helicoidal crystallites twisted along the <010> growth directions. Mueller matrix imaging reveals radial oscillations in not only linear birefringence, but also circular birefringence, whose origin is explained through slight (∼1.3°) but systematic splaying of individual lamellae in the film. Strain associated with the replacement of aspirin molecules by salicylic acid molecules in the crystal structure is computed to be large enough to work as the driving force for the twisting of crystallites.

Tip dependence of three-dimensional scanning force microscopy images of calcite-water interfaces investigated by simulation and experiments.

In this study, we have investigated the influence of the tip on the three-dimensional scanning force microscopy (3D-SFM) images of calcite-water interfaces by experiments and simulations. We calculated 3D force images by simulations with the solvent tip approximation (STA), Ca, CO3 and OH tip models. For all the 3D images, the z profiles at the surface Ca and CO3 sites alternately show oscillatory peaks corresponding to the hydration layers. However, the peak heights and spacings become larger when the mechanical stability of the tip becomes higher. For analyzing the xy slices of the 3D force images, we developed the extended STA (E-STA) model which allowed us to reveal the strong correlation between the hydration structure just under the tip and the atomic-scale force contrasts. Based on these understandings on the image features showing the strong tip dependence, we developed a method for objectively estimating the similarity between 3D force images. With this method, we compared the simulated images with the three experimentally obtained ones. Among them, two images showed a relatively high similarity with the image obtained by the simulation with the Ca or the CO3 tip model. Based on these agreements, we characterized the hydration structure and mechanical stability of the experimentally used tips. The understanding and methodology presented here should help us to derive accurate information on the tip and the interfacial structure from experimentally obtained 3D-SFM images.

Molecular Dynamics Visualization (MDV): Stereoscopic 3D Display of Biomolecular Structure and Interactions Using the Unity Game Engine.

Molecular graphics systems are visualization tools which, upon integration into a 3D immersive environment, provide a unique virtual reality experience for research and teaching of biomolecular structure, function and interactions. We have developed a molecular structure and dynamics application, the Molecular Dynamics Visualization tool, that uses the Unity game engine combined with large scale, multi-user, stereoscopic visualization systems to deliver an immersive display experience, particularly with a large cylindrical projection display. The application is structured to separate the biomolecular modeling and visualization systems. The biomolecular model loading and analysis system was developed as a stand-alone C# library and provides the foundation for the custom visualization system built in Unity. All visual models displayed within the tool are generated using Unity-based procedural mesh building routines. A 3D user interface was built to allow seamless dynamic interaction with the model while being viewed in 3D space. Biomolecular structure analysis and display capabilities are exemplified with a range of complex systems involving cell membranes, protein folding and lipid droplets.

The interaction of EDTA with barium sulfate.

Ethylenediaminetetraacetic acid (EDTA) is a known complexing agent that interacts with a host of cations. In this paper, various techniques are used to elucidate the mechanism of interaction between EDTA and barium sulfate surfaces. It is shown that complexation with metal ions is not sufficient to explain the inhibition of barite crystallization but that other processes such as chemisorption must also occur. EDTA is shown to always adsorb as the mono-protonated species - suggesting that the molecule is able to lose a proton when it adsorbs at lower pH. Molecular modelling shows that the interaction of the surface barium ions with the carboxylate group is an important one. Finally, in situ turbidity measurements provide information about the mechanism of nucleation/growth modification. It is found that the EDTA molecule inhibits barium sulfate nucleation and that this could be its primary means of inhibiting precipitation of barium sulfate.

Atomistic simulation of the measurement of mechanical properties of gold nanorods by AFM.

Mechanical properties of nanoscale objects can be measured with an atomic force microscope (AFM) tip. However, the continuum models typically used to relate the force measured at a certain indentation depth to quantities such as the elastic modulus, may not be valid at such small scales, where the details of atomistic processes need to be taken into account. On the other hand, molecular dynamics (MD) simulations of nanoindentation, which can offer understanding at an atomistic level, are often performed on systems much smaller than the ones studied experimentally. Here, we present large scale MD simulations of the nanoindentation of single crystal and penta-twinned gold nanorod samples on a silicon substrate, with a spherical diamond AFM tip apex. Both the sample and tip sizes and geometries match commercially available products, potentially linking simulation and experiment. Different deformation mechanisms, involving the creation, migration and annihilation of dislocations are observed depending on the nanorod crystallographic structure and orientation. Using the Oliver-Pharr method, the Young's moduli of the (100) terminated and (110) terminated single crystal nanorods, and the penta-twinned nanorod, have been determined to be 103 ± 2, 140 ± 4 and 108 ± 2 GPa, respectively, which is in good agreement with bending experiments performed on nanowires.

The controlled disassembly of mesostructured perovskites as an avenue to fabricating high performance nanohybrid catalysts.

Versatile superstructures composed of nanoparticles have recently been prepared using various disassembly methods. However, little information is known on how the structural disassembly influences the catalytic performance of the materials. Here we show how the disassembly of an ordered porous La0.6Sr0.4MnO3 perovskite array, to give hexapod mesostructured nanoparticles, exposes a new crystal facet which is more active for catalytic methane combustion. On fragmenting three-dimensionally ordered macroporous (3DOM) structures in a controlled manner, via a process that has been likened to retrosynthesis, hexapod-shaped building blocks can be harvested which possess a mesostructured architecture. The hexapod-shaped perovskite catalyst exhibits excellent low temperature methane oxidation activity (T90%=438 °C; reaction rate=4.84 × 10-7 mol m-2 s-1). First principle calculations suggest the fractures, which occur at weak joints within the 3DOM architecture, afford a large area of (001) surface that displays a reduced energy barrier for hydrogen abstraction, thereby facilitating methane oxidation.

Powder diffraction and crystal structure prediction identify four new coumarin polymorphs.

Coumarin, a simple, commodity chemical isolated from beans in 1820, has, to date, only yielded one solid state structure. Here, we report a rich polymorphism of coumarin grown from the melt. Four new metastable forms were identified and their crystal structures were solved using a combination of computational crystal structure prediction algorithms and X-ray powder diffraction. With five crystal structures, coumarin has become one of the few rigid molecules showing extensive polymorphism at ambient conditions. We demonstrate the crucial role of advanced electronic structure calculations including many-body dispersion effects for accurate ranking of the stability of coumarin polymorphs and the need to account for anharmonic vibrational contributions to their free energy. As such, coumarin is a model system for studying weak intermolecular interactions, crystallization mechanisms, and kinetic effects.

Molecular modeling of phosphonate molecules onto barium sulfate terraced surfaces.

The adsorption of phosphonate molecules onto mineral surfaces is of interest due to their use as scale inhibitors. Molecular modeling is an important tool that can aid the fundamental understanding of how these inhibitors operate. This paper presents an empirical molecular mechanics study of the adsorption of a series of straight chain phosphonate molecules onto barium sulfate. It has been found that inhibition can be predicted for this straight chain series of molecules, which differ by the number of phosphonate groups present as well as by the chain length. Even more importantly, the modeling results can predict which faces will be preferred, and this has been verified by scanning and transmission electron microscopy on the resultant barite particles. It has been found that, in general, lattice matching results in the lowest replacement energy for all of the organic molecules investigated. The agreement between the experiment and the model confirms that the dominant mechanism of interaction for the additives on barium sulfate is via the deprotonated phosphonate groups with the barium ions on the surface.

Silver(I), gold(I) and palladium(II) complexes of a NHC-pincer ligand with an aminotriazine core: a comparison with pyridyl analogues.

Dinuclear silver, di- and tetra-nuclear gold, and mononuclear palladium complexes with chelating C,N,C diethylaminotriazinyl-bridged bis(NHC) pincer ligands were prepared and characterised. The silver and gold complexes exist in a twisted, helical conformation in both the solution- and the solid state. In contrast, an analogous dinuclear gold complex with pyridyl-bridged NHCs exists in a linear conformation. Computational studies have been performed to rationalise the formation of twisted/helical vs. linear forms.

Structure, Energetics, and Dynamics of Screw Dislocations in Even n-Alkane Crystals.

Spiral hillocks on n-alkane crystal surfaces were observed immediately after Frank recognized the importance of screw dislocations for crystal growth, yet their structures and energies in molecular crystals remain ill-defined. To illustrate the structural chemistry of screw dislocations that are responsible for plasticity in organic crystals and upon which the organic electronics and pharmaceutical industries depend, molecular dynamics was used to examine heterochiral dislocation pairs with Burgers vectors along [001] in n-hexane, n-octane, and n-decane crystals. The cores were anisotropic and elongated in the (110) slip plane, with significant local changes in molecular position, orientation, conformation, and energy. This detailed atomic level picture produced a distribution of strain consistent with linear elastic theory, giving confidence in the simulations. Dislocations with doubled Burgers vectors split into pairs with elementary displacements. These results suggest a pathway to understanding the mechanical properties and failure associated with elastic and plastic deformation in soft crystals.

Benchmarking Calculated Lattice Parameters and Energies of Molecular Crystals Using van der Waals Density Functionals.

The development of new functionals and methods to accurately describe van der Waals forces in density functional theory (DFT) has become popular in recent years, with the vast majority of studies assessing the accuracy of the energetics of collections of molecules, and to a lesser extent molecular crystalline systems. As the energies are a function of the atom positions, we assess the accuracy of DFT calculations from both a geometric and energetics point of view for the C21 reference data set of Otero-de-la-Roza and Johnson for molecular crystals, and a set of monosaccharide molecular crystals. In particular, we examine the performance of exchange-correlation functionals designed to handle van der Waals forces, including the vdW-DF, vdW-DF2, and XDM methods. We also assess the effect of using small and large basis sets, the choice of basis functions (local atomic orbitals using the SIESTA code versus planewaves using the Quantum ESPRESSO code), and the effect of corrections for basis set superposition errors. Finally, we examine the geometries and energies of the S22 reference set of molecular complexes. Overall, the most accurate geometries for both choices of basis functions are obtained with the vdW-DF2 functional, while the most accurate lattice energies are obtained using vdW-DF2 with local atomic orbitals and XDM with planewaves with mean absolute errors of less than 4 kJ/mol.

Noncovalent Interactions in SIESTA Using the vdW-DF Functional: S22 Benchmark and Macrocyclic Structures.

We investigate the performance of the vdW-DF functional of Dion et al. implemented in the SIESTA code. In particular, the S22 data set and several calixarene-based host-guest structures are examined to assess the performance of the functional. The binding energy error statistics for the S22 data set reveal that the vdW-DF functional performs very well when compared to a range of other methods of treating dispersion in density functional theory, and to vdW-DF implementations in other codes. For the calixarene host-guest structures, the structural properties and binding energies are compared to previous experimental and computational studies, and in most cases we find that vdW-DF provides superior results to other computational studies.

Ab Initio Molecular Dynamics Simulations of (101) Surfaces of Potassium Dihydrogenphosphate.

We present an ab initio molecular dynamics study of bare and hydrated (101) surfaces of KDP. We examine the dynamical nature of the hydrogen bonding in the high and low temperature phases of bulk KDP and find evidence to support the theory that hydrogen atoms oscillate between two off-center positions in the high-temperature phase. We report the translational relaxation of the surface species on the (101) surface and find good agreement with experimental results, particularly with reference to the direction of the relaxation. We find a strongly hydrogen bound water layer close to the KDP surface, comparing closely to a highly ordered water layer observed experimentally. Overall, there is good agreement with the results of nanoscale experimental studies, demonstrating the effectiveness of ab initio molecular dynamics calculations at simulating bulk and surface properties.