The canonical 8-form on manifolds with holonomy group Spin(9)

An explicit expression of the canonical 8-form on a Riemannian manifold with a Spin(9)-structure, in terms of the nine local symmetric involutions involved, is given. The list of explicit expressions of all the canonical forms related to Berger's list of holonomy groups is thus completed. Moreover, some results on Spin(9)-structures as G-structures defined by a tensor and on the curvature tensor of the Cayley planes, are obtained

Composition algebras and the two faces of G2G_{2}

We consider composition and division algebras over the real numbers: We note two r\^oles for the group $G_{2}$: as automorphism group of the octonions and as the isotropy group of a generic 3-form in 7 dimensions. We show why they are equivalent, by means of a regular metric. We express in some diagrams the relation between some pertinent groups, most of them related to the octonions. Some applications to physics are also discussed.Comment: 11 pages, 3 figure

The G_2 sphere over a 4-manifold

We present a construction of a canonical G_2 structure on the unit sphere tangent bundle S_M of any given orientable Riemannian 4-manifold M. Such structure is never geometric or 1-flat, but seems full of other possibilities. We start by the study of the most basic properties of our construction. The structure is co-calibrated if, and only if, M is an Einstein manifold. The fibres are always associative. In fact, the associated 3-form results from a linear combination of three other volume 3-forms, one of which is the volume of the fibres. We also give new examples of co-calibrated structures on well known spaces. We hope this contributes both to the knowledge of special geometries and to the study of 4-manifolds.Comment: 13 page

Adjunct therapies to improve outcomes after botulinum toxin injection in children: A systematic review

BACKGROUND: Botulinum toxin (BTX) injection alone is not sufficient to treat spasticity in children, notably those with cerebral palsy; thus, there is an emerging trend for adjunct therapies to offer greater outcomes than BTX alone. OBJECTIVE: The aim of this systematic review was to evaluate the general effectiveness of adjunct therapies regardless of their nature in children with spasticity. METHODS: Medline, Cochrane and Embase databases were searched from January 1980 to March 15, 2018 for reports of parallel-group trials (randomized controlled trials [RCTs] and non-RCTs) assessing adjunct therapies after BTX injection for treating spasticity in children. Two independent reviewers extracted data and assessed the risk of bias by using the PEDro scale for RCTs and Downs and Black scale (D&B) for non-RCTs. RESULTS: Overall, 20 articles involving 662 participants met the inclusion criteria. The average quality was good for the 16 RCTs (mean PEDro score 7.4 [SD 1.6]) and poor to moderate for the 4 non-RCTs (D&B score 9 to 17). Adjunct therapies consisted of casting/posture, electrical stimulation, resistance training and rehabilitation programmes. Casting associated with BTX injection improved the range of passive and active motion and reduced spasticity better than did BTX alone (9 studies), with a follow-up of 1 year. Resistance training enhanced the quality and performance of muscles without increasing spasticity. Only 3 rehabilitation programmes were studied, with encouraging results for activities. CONCLUSION: Lower-limb posture with casting in children has a high level of evidence, but the long-term efficacy of short-leg casting needs to be evaluated. A comparison between the different modalities of casting is missing, and studies specifically devoted to testing the different kinds of casting are needed. Moreover, the delay to casting after BTX injection is not clear. Data on electrical stimulation are not conclusive. Despite the small number of studies, resistance training could be an interesting adjunct therapy notably to avoid loss of strength after BTX injection. Rehabilitation programmes after BTX injection still need to be evaluated

Developments and Further Applications of Ephemeral Data Derived Potentials

Machine-learned interatomic potentials are fast becoming an indispensable tool in computational materials science. One approach is the ephemeral data-derived potential (EDDP), which was designed to accelerate atomistic structure prediction. The EDDP is simple and cost-efficient. It relies on training data generated in small unit cells and is fit using a lightweight neural network, leading to smooth interactions which exhibit the robust transferability essential for structure prediction. Here, we present a variety of applications of EDDPs, enabled by recent developments of the open-source EDDP software. New features include interfaces to phonon and molecular dynamics codes, as well as deployment of the ensemble deviation for estimating the confidence in EDDP predictions. Through case studies ranging from elemental carbon and lead to the binary scandium hydride and the ternary zinc cyanide, we demonstrate that EDDPs can be trained to cover wide ranges of pressures and stoichiometries, and used to evaluate phonons, phase diagrams, superionicity, and thermal expansion. These developments complement continued success in accelerated structure prediction.Comment: 22 pages, 15 figure

Changes in balance and joint position sense during a 12-day high altitude trek: The British Services Dhaulagiri medical research expedition

<div><p>Postural control and joint position sense are essential for safely undertaking leisure and professional activities, particularly at high altitude. We tested whether exposure to a 12-day trek with a gradual ascent to high altitude impairs postural control and joint position sense. This was a repeated measures observational study of 12 military service personnel (28±4 years). Postural control (sway velocity measured by a portable force platform) during standing balance, a Sharpened Romberg Test and knee joint position sense were measured, in England (113m elevation) and at 3 research camps (3619m, 4600m and 5140m) on a 12-day high altitude trek in the Dhaulagiri region of Nepal. Pulse oximetry, and Lake Louise scores were also recorded on the morning and evening of each trek day. Data were compared between altitudes and relationships between pulse oximetry, Lake Louise score, and sway velocity were explored. Total sway velocity during standing balance with eyes open (p = 0.003, d = 1.9) and during Sharpened Romberg test with eyes open (p = 0.007, d = 1.6) was significantly greater at altitudes of 3619m and 5140m when compared with sea level. Anterior-posterior sway velocity during standing balance with eyes open was also significantly greater at altitudes of 3619m and 5140m when compared with sea level (p = 0.001, d = 1.9). Knee joint position sense was not altered at higher altitudes. There were no significant correlations between Lake Louise scores, pulse oximetry and postural sway. Despite a gradual ascent profile, exposure to 3619 m was associated with impairments in postural control without impairment in knee joint position sense. Importantly, these impairments did not worsen at higher altitudes of 4600 m or 5140 m. The present findings should be considered during future trekking expeditions when developing training strategies targeted to manage impairments in postural control that occur with increasing altitude.</p></div

The Impact of Recent European Droughts and Heatwaves on Trace Gas Surface Fluxes: Insights from Land Surface Data Assimilation

Heatwave and drought extremes can have significant impacts on vegetation, which can in turn lead to important effects on reactive trace gas fluxes at the land-atmosphere interface that can ultimately alter atmospheric composition. We present results from the EU-funded Sentinel EObased Emission and Deposition Service (SEEDS) project, which aimed at developing upgrades to the existing Copernicus Atmospheric Monitoring Service (CAMS) component on European air quality. In this work, we used land surface modelling (SURFEX – Surface Externalisée) combined with data assimilation (Extended Kalman Filter - EKF) of satellite leaf area index (LAI) to deliver improved estimation of the land surface state. The land surface model is coupled with an online model for dry deposition and an offline model (MEGANv3.1) for biogenic volatile organic compounds (BVOCs) to estimate trace gas losses and emissions, respectively. This approach exploits methods at the forefront of land surface modelling (dynamic vegetation simulation and data assimilation) and combines them with the latest algorithms to estimate trace gas fluxes at the surface. We present findings from two extreme events in Europe: the 2018 drought and the 2019 June/July heat waves. SURFEX was forced using ECMWF meteorology at 0.1° × 0.1° resolution that captured both events. Both extreme events provoked strong responses in the models for dry deposition velocity and BVOC emissions. The 2018 drought began in spring and endured through summer, during which dry deposition velocities declined steadily beyond seasonal norms due to increased stomatal resistance forced by the vegetation response to drought. Over continental Europe, BVOCs initially increased in the early phase of the drought, but then sharply declined into July in the worst-affected regions in Germany, Denmark, and Poland. Meanwhile, BVOCs increased in Scandinavia relative to seasonal norms due to the warmer-than-average conditions. The first episode of severe heat in 2019 arrived in late June, which initially caused a large increase in BVOC emissions compared to seasonal norms. Then drought set in during July and despite a second large heat wave BVOC emissions were lower overall compared to seasonal norms. In fact, the European-wide BVOC emissions were higher in June compared to July due to the drought effects that commenced later in the heat wave cycle. This reverses the normal seasonal cycle in BVOC emissions, and drought impacts on vegetation were the primary driver behind this. Dry deposition velocities are reduced during both heat waves, but we see a larger decline in the second heat wave in July when drought conditions are more severe. Our findings suggest that these impacts on trace gas surface fluxes would have a strong effect on atmospheric composition, and on photochemical ozone formation. We, therefore, conclude that these effects likely played a contributory role to the ozone pollution episodes that occurred coincidentally in time with the heat wave events in both 2018 and 2019. The project aim within SEEDS is to eventually test the BVOC emissions and dry deposition velocities within a chemical transport model participating within the CAMS regional ensemble (MOCAGE) and to therefore evaluate the impact on ozone

Contribution of isoprene to chemical budgets:A model tracer study with the NCAR CTM MOZART-4

We present a study of the sensitivity of isoprene emission calculations in a global chemistry transport model (CTM) to input land cover characteristics and analyze the impacts of changes in isoprene on the tropospheric budgets of atmospheric key species. The CTM Model for Ozone and Related Chemical Species, version 4 (MOZART-4) includes the online calculation of isoprene emissions based on the Model of Emissions of Gases and Aerosols from Nature (MEGAN), which is driven by three different land parameter inputs. We also included a tagging scheme in the CTM, which keeps track of the production of carbon containing species from isoprene oxidation. It is found that the amount of tropospheric carbon monoxide (CO), formaldehyde (HCHO) and peroxyacetylnitrate (PAN) explained by isoprene oxidation ranges from 9-16%, 15-27%, and 22-32%, depending on the isoprene emissions scenario. Changes in the global tropospheric burden with different land cover inputs can reach up to 10% for CO, 15% for HCHO, and 20% for PAN. Changes for ozone are small on a global scale, but regionally differences are as large as 3DU in the tropospheric column and as large as 5 ppbv in the surface concentrations. Our results demonstrate that a careful integration of isoprene emissions and chemistry in CTMs is very important for simulating the budgets of a number of atmospheric trace gases. We further demonstrate that the model tagging scheme has the capability of improving conventional methods of constraining isoprene emissions from space-borne HCHO column observations, especially in regions where a considerable part of the variability in the HCHO column is not related to isoprene. Copyright 2008 by the American Geophysical Union