3He-Driven Mixing in Low-Mass Red Giants: Convective Instability in Radiative and Adiabatic Limits

We examine the stability and observational consequences of mixing induced by 3He burning in the envelopes of first ascent red giants. We demonstrate that there are two unstable modes: a rapid, nearly adiabatic mode that we cannot identify with an underlying physical mechanism, and a slow, nearly radiative mode that can be identified with thermohaline convection. We present observational constraints that make the operation of the rapid mode unlikely to occur in real stars. Thermohaline convection turns out to be fast enough only if fluid elements have finger-like structures with a length to diameter ratio l/d > 10. We identify some potentially serious obstacles for thermohaline convection as the predominant mixing mechanism for giants. We show that rotation-induced horizontal turbulent diffusion may suppress the 3He-driven thermohaline convection. Another potentially serious problem for it is to explain observational evidence of enhanced extra mixing. The 3He exhaustion in stars approaching the red giant branch (RGB) tip should make the 3He mixing inefficient on the asymptotic giant branch (AGB). In spite of this, there are observational data indicating the presence of extra mixing in low-mass AGB stars similar to that operating on the RGB. Overmixing may also occur in carbon-enhanced metal-poor stars.Comment: 25 pages, 6 figures, modified version, accepted by Ap

What interventions do general practitioners recommend avoiding? A nationwide survey from Switzerland

Background: To address low-value interventions in healthcare, “Choosing Wisely” campaigns provide recommendations of interventions to avoid (RIAs). These are usually developed by expert panels rather than general practitioners (GPs). The aim of our study was to develop RIAs for ambulatory general medicine based on the suggestions of GPs, with their involvement from the very beginning. Methods: This was a nationwide online Delphi survey among Swiss Society of General Internal Medicine members. In round one, each participant suggested two interventions perceived as particularly inappropriate. In round two, the 16 most frequent RIAs were rated by importance on a 0–100 scale and compared with “Choosing Wisely” lists. We calculated descriptive statistics for suggestions and importance ratings, and used regression models to search for associations with GP characteristics. Results: Response rates were 7.4% (538/7318) for round one and 18.2% (1357/7468) for round two. GPs provided 1074 suggestions. Out of the 16 most frequent RIAs, 13 corresponded to existing “Choosing Wisely” lists. The RIAs rated most important were: antibiotics in viral infections, unnecessarily duplicated tests and imaging in unspecific low back pain (means 88.5–91.7, standard deviations 18.6–19.9). None of the GPs’ characteristics were associated with any of the five highest rated RIAs except for working in a hospital setting. Conclusion: Most RIA suggestions from GPs were concordant with previously published recommendations of interventions to avoid, independently of GPs knowledge of these and reflecting their high clinical relevance. In addition, our study revealed some more relevant topics and may help to develop future “Choosing Wisely” recommendations, with the final goal to reduce low-value care

Perfusion-CT guided intravenous thrombolysis in patients with unknown-onset stroke: a randomized, double-blind, placebo-controlled, pilot feasibility trial

Introduction: Patients with unknown stroke onset are generally excluded from acute recanalisation treatments. We designed a pilot study to assess feasibility of a trial of perfusion computed tomography (PCT)-guided thrombolysis in patients with ischemic tissue at risk of infarction and unknown stroke onset. Methods: Patients with a supratentorial stroke of unknown onset in the middle cerebral artery territory and significant volume of at-risk tissue on PCT were randomized to intravenous thrombolysis with alteplase (0.9mg/kg) or placebo. Feasibility endpoints were randomization and blinded treatment of patients within 2h after hospital arrival, and the correct application (estimation) of the perfusion imaging criteria. Results: At baseline, there was a trend towards older age [69.5 (57-78) vs. 49 (44-78) years] in the thrombolysis group (n = 6) compared to placebo (n = 6). Regarding feasibility, hospital arrival to treatment delay was above the allowed 2h in three patients (25%). There were two protocol violations (17%) regarding PCT, both underestimating the predicted infarct in patients randomized in the placebo group. No symptomatic hemorrhage or death occurred during the first 7days. Three of the four (75%) and one of the five (20%) patients were recanalized in the thrombolysis and placebo group respectively. The volume of non-infarcted at-risk tissue was 84 (44-206) cm3 in the treatment arm and 29 (8-105) cm3 in the placebo arm. Conclusions: This pilot study shows that a randomized PCT-guided thrombolysis trial in patients with stroke of unknown onset may be feasible if issues such as treatment delays and reliable identification of tissue at risk of infarction tissue are resolved. Safety and efficiency of such an approach need to be establishe

Core Formation by a Population of Massive Remnants

Core radii of globular clusters in the Large and Small Magellanic Clouds show an increasing trend with age. We propose that this trend is a dynamical effect resulting from the accumulation of massive stars and stellar-mass black holes at the cluster centers. The black holes are remnants of stars with initial masses exceeding 20-25 solar masses; as their orbits decay by dynamical friction, they heat the stellar background and create a core. Using analytical estimates and N-body experiments, we show that the sizes of the cores so produced and their growth rates are consistent with what is observed. We propose that this mechanism is responsible for the formation of cores in all globular clusters and possibly in other systems as well.Comment: 5 page

Studying deformation mechanisms of nanocrystalline nickel by thermal activation analysis at subambient temperatures and high strain rates

Electrodeposition and magnetron sputtering are promising methods for depositing thin films with nanocrystalline (nc) microstructures. Nc metals are attractive materials, as they show considerably higher mechanical strength compared to their poly- or monocrystalline counterparts. However, they also feature pronounced time- and rate-dependent inelastic behavior and their microstructure may change drastically when exposed to elevated temperatures or ion irradiation. Therefore, in order to assess the mechanical behavior and deformation mechanisms of these materials under controlled conditions and at a constant microstructure, it is desirable to perform thermal activation analysis at subambient temperatures and high strain rates on pristine samples. Large arrays of micropillars were fabricated by electrodeposition of nc Ni into lithography molds by LIGA leading to non-tapered, damage-free microspecimens. X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) imaging revealed a grain size of approximately 28nm. EDX analysis showed a homogeneous elemental composition and no concentration of impurities at the grain boundaries. A micromechanical testing device was developed that allows performing nanomechanical experiments at sub-ambient temperatures down to 120K in a large range of strain rates between 10-4 and 103s-1. Please click Additional Files below to see the full abstract

DASH: Dynamic Attention-Based Substructure Hierarchy for Partial Charge Assignment

We present a robust and computationally efficient approach for assigning partial charges of atoms in molecules. The method is based on a hierarchical tree constructed from attention values extracted from a graph neural network (GNN), which was trained to predict atomic partial charges from accurate quantum-mechanical (QM) calculations. The resulting dynamic attention-based substructure hierarchy (DASH) approach provides fast assignment of partial charges with the same accuracy as the GNN itself, is software-independent, and can easily be integrated in existing parametrization pipelines as shown for the Open force field (OpenFF). The implementation of the DASH workflow, the final DASH tree, and the training set are available as open source / open data from public repositories

Design and processing of low-range piezoresistive LTCC force sensors

Low-temperature cofired ceramic (LTCC) combines many advantageous features for low-range (force & pressure) piezoresistive sensors: ease of 3D structuration, availability of very thin sheets, low elastic modulus and yet reasonable mechanical strength. This work covers the design and fabrication low-range LTCC force sensors down to ideally 10 mN, together with mechanical characterisation of LTCC substrates. We show that LTCC is a viable substrate for piezoresistive sensing, and that 3D structuration can be used to both increase the output signal and simplify production. Moreover, very sensitive LTCC sensors may be manufactured, provided specific thick-film conductors with a sintering behaviour closely matched to that of the LTCC are applied

Fabrication of a Millinewton Force Sensor Using Low Temperature Co-fired Ceramic (LTCC) Technology

This study is aimed at outlining the fabrication of a novel piezoresistive force sensor using LTCC technology, which operates at millinewton range, yet is compatible with low cost thick-film fabrication process. Mechanical and electrical characterization of the device is explained in terms of processing conditions, including the principle of force sensing and materials employed. The improvement of device functionality by modifying commercially-available thick- film conductors is described. The sensors are found to be efficient in responding to forces below 100 mN

Angular Momentum Transport In Solar-Type Stars: Testing the Timescale For Core-Envelope Coupling

We critically examine the constraints on internal angular momentum transport which can be inferred from the spin down of open cluster stars. The rotation distribution inferred from rotation velocities and periods are consistent for larger and more recent samples, but smaller samples of rotation periods appear biased relative to vsini studies. We therefore focus on whether the rotation period distributions observed in star forming regions can be evolved into the observed ones in the Pleiades, NGC2516, M34, M35, M37, and M50 with plausible assumptions about star-disk coupling and angular momentum loss from magnetized solar-like winds. Solid body models are consistent with the data for low mass fully convective stars but highly inconsistent for higher mass stars where the surface convection zone can decouple for angular momentum purposes from the radiative interior. The Tayler-Spruit magnetic angular momentum transport mechanism, commonly employed in models of high mass stars, predicts solid-body rotation on extremely short timescales and is therefore unlikely to operate in solar-type pre-MS and MS stars at the predicted rate. Models with core-envelope decoupling can explain the spin down of 1.0 and 0.8 solar mass slow rotators with characteristic coupling timescales of 55+-25 Myr and 175+-25 Myr respectively. The upper envelope of the rotation distribution is more strongly coupled than the lower envelope of the rotation distribution, in accord with theoretical predictions that the angular momentum transport timescale should be shorter for more rapidly rotating stars. Constraints imposed by the solar rotation curve are also discussed (Abridged)Comment: 42 pages, 16 figures, submitted to Ap