The challenges of nanostructures for theory

It is tempting to believe that modelling in nanotechnology is much the same as that for conventional solid-state physics. However, important areas of nanotechnology address different systems. The mechanics of DNA (for instance) resembles spaghetti more than silicon, the statistical physics needed is often not carrier statistics, and the role of viscosity (the low Reynolds number limit) is not always the familiar one. The idea of equilibrium may be irrelevant, as the kinetics of nonequilibrium (perhaps quasi-steady state) can be crucial. Even when the issues are limited to nanoscale structures (rather than functions), there is a complex range of ideas. Some features, like elasticity and electrostatic energies, have clear macroscopic analogies, but different questions emerge, such as the accuracy of self-organisation. Others concepts like epitaxy and templating are usually micro- or mesostructural. Some of the ideas, which emerge in modelling for the nanoscale, suggest parallels between molecular motors and recombination enhanced diffusion in semiconductors. (C) 2002 Elsevier Science B.V. All rights reserved

Blending isogeometric analysis and local maximum entropy meshfree approximants

We present a method to blend local maximum entropy (LME) meshfree approximants and isogeometric analysis. The coupling strategy exploits the optimization program behind LME approximation, treats isogeometric and LME basis functions on an equal footing in the reproducibility constraints, but views the former as data in the constrained minimization. The resulting scheme exploits the best features and overcomes the main drawbacks of each of these approximants. Indeed, it preserves the high fidelity boundary representation (exact CAD geometry) of isogeometric analysis, out of reach for bare meshfree methods, and easily handles volume discretization and unstructured grids with possibly local refinement, while maintaining the smoothness and non-negativity of the basis functions. We implement the method with B-Splines in two dimensions, but the procedure carries over to higher spatial dimensions or to other non-negative approximants such as NURBS or subdivision schemes. The performance of the method is illustrated with the heat equation, and linear and nonlinear elasticity. The ability of the proposed method to impose directly essential boundary conditions in non-convex domains, and to deal with unstructured grids and local refinement in domains of complex geometry and topology is highlighted by the numerical examples

Lubrication of dislocation glide in forsterite by Mg vacancies: insights from Peierls-Nabarro modeling

Dislocation glide is an important contributor to the rheology of olivine under conditions of high stress and low to moderate temperature, such as occur in mantle wedges. Interactions between point defects and dislocation core may alter the Peierls stress, σp, and has been suggested that vacancy-related defects may selectively enhance glide on certain slip systems, changing the olivine deformation fabric. In this study, the Peierls-Nabarro model, parameterized by generalized stacking fault (GSF) energies calculated atomistically using empirical interatomic potentials, is used to determine the effect of bare Mg vacancies on the Peierls stresses of [100](010) and [001](010) dislocations in forsterite. Mg vacancies considerably reduce GSF energies and, consequently, σp for dislocations gliding on (010) in olivine. The magnitude of this decrease depends strongly on dislocation and the type of the lattice site, with vacant M2 sites producing the largest reduction of σp. The [001](010) slip system is found to be more sensitive than the [100](010) slip system to the presence of vacancies. Although, at ambient pressure, σp is lower for [100](010) than [001](010) edge dislocations, dσp/dP is greater for [100](010) dislocations, resulting in a change in the preferred slip system at 1.5 GPa. By preferentially lubricating [001](010) glide, Mg vacancies reduce the pressure at which this cross-over occurs. An M2 vacancy concentration at the glide plane of 0.125 defects/site is sufficient to reduce cross-over to 0.7 GPa. This may account for the existence of the B-type olivine deformation fabric in the corners of mantle wedges

Second order convex maximum entropy approximants with applications to high order PDE

We present a new approach for second order maximum entropy (max-ent) meshfree approximants that produces positive and smooth basis functions of uniform aspect ratio even for non-uniform node sets, and prescribes robustly feasible constraints for the entropy maximization program defining the approximants. We examine the performance of the proposed approximation scheme in the numerical solution by a direct Galerkin method of a number of partial differential equations (PDEs), including structural vibrations, elliptic second order PDEs, and fourth order PDEs for Kirchhoff-Love thin shells and for a phase field model describing the mechanics of biomembranes. The examples highlight the ability of the method to deal with non-uniform node distributions, and the high accuracy of the solutions. Surprisingly, the first order meshfree max-ent approximants with large supports are competitive when compared to the proposed second order approach in all the tested examples, even in the higher order PDEs

Can homogeneous nucleation resolve the inner core nucleation paradox?

The formation of Earth's solid inner core is thought to mark a profound change in the evolution of the deep Earth and the power that is available to generate the geomagnetic field. Previous studies generally find that the inner core nucleated around 0.5–1 billion years ago, but neglect the fact that homogeneous liquids must be cooled far below their melting point in order for solids to form spontaneously. The classical theory of nucleation predicts that the core must be undercooled by several hundred K, which is incompatible with estimates of the core's present-day temperature. This “inner core nucleation paradox” therefore asserts that the present inner core should not have formed, leaving a significant gap in our understanding of deep Earth evolution. In this paper we explore the nucleation process in as yet untested iron-rich systems which may comprise the Earth's early core. We find that 1 mol.% Si and S increase the supercooling required to freeze the inner core compared to pure iron by 400 K and 1000 K respectively. 10 mol.% O reduces the required inner core nucleation supercooling to 730 K and 3 mol.% C to only 612 K, which is close to resolving the paradox but still requires that the inner core formed recently

Benefits and Harms of Electrical Neuromodulation for Chronic Pelvic Pain: A Systematic Review

Context: Patients with chronic pelvic pain (CPP) may have pain refractory to conventional pain management strategies. Neuromodulation could provide relief of pain. / Objective: To evaluate the benefits and harms of neuromodulation for CPP. / Evidence acquisition:: A comprehensive search of EMBASE, PUBMED, and SCOPUS was performed for the entire database to January 2018. Studies were selected, data were extracted, and quality was assessed by two independent reviewers. A meta-analysis was used to combine randomized controlled trials (RCTs); otherwise, a narrative analysis was used. / Evidence synthesis: After screening 1311 abstracts, 36 studies including eight RCTs were identified, enrolling 1099 patients. Studies covered a broad range in terms of phenotypes of CPP and methods of neuromodulation. A meta-analysis was possible for percutaneous tibial nerve stimulation and transcutaneous electrical nerve stimulation, which showed improvement in pain. Only narrative synthesis was possible for other modalities (sacral nerve stimulation, spinal cord stimulation, intravaginal electrical stimulation, and pudendal nerve stimulation) which appeared to reduce pain in patients with CPP. Treatments generally improved quality of life but with variable reporting of adverse events. Many studies showed high risks of bias and confounding. / Conclusions: While electrical neuromodulation may improve symptoms in CPP, further work is needed with high-quality studies to confirm it. / Patient summary: Neuromodulation may be useful in reducing pain and improving quality of life in patients with chronic pelvic pain, but more research is needed

Examining the power supplied to Earth's dynamo by magnesium precipitation and radiogenic heat production

We examine magnesium and potassium solubility in liquid Fe mixtures, representative of Earth's core composition, in equilibrium with liquid silicate mixtures representative of an early magma ocean. Our study is based on the calculation of the chemical potentials of MgO and K2O in both phases, using density functional theory. For MgO, we also study stability against precipitation of the solid phase. We use thermal evolution models of the core and mantle to assess whether either radiogenic heating from 40K decay or Mg precipitation from the liquid core can resolve the new core paradox by powering the geodynamo prior to inner core formation. Our results for K show that concentrations in the core are likely to be small and the effect of 40K decay on the thermal evolution of the core is minimal, making it incapable of sustaining the early geodynamo alone. Our results also predict small concentrations of Mg in the core which might be sufficient to power the geodynamo prior to inner core formation, depending on the process by which it is transported across the core mantle boundary

Behaviour change interventions to improve medication adherence in patients with cardiac disease: Protocol for a mixed methods study including a pilot randomised controlled trial

© 2017 Australian College of Nursing Ltd Background: Suboptimal adherence to medication increases mortality and morbidity; individually tailored supportive interventions can improve patients’ adherence to their medication regimens. Aims: The study aims to use a pilot randomised controlled trial (RCT) to test the hypothesis that a theory-based, nurse-led, multi-faceted intervention comprising motivational interviewing techniques and text message reminders in addition to standard care will better promote medication adherence in cardiac patients compared to standard care alone. The pilot study will assess self-reported adherence or non-adherence to cardiovascular medication in patients referred to a cardiac rehabilitation program following hospital admission for an acute cardiac event and test the feasibility of the intervention. The study will examine the role of individual, behavioural and environmental factors in predicting medication non-adherence in patients with CVD. Methods: This is a mixed- methods study including a nested pilot RCT. Twenty-eight cardiac patients will be recruited; an estimated sample of nine patients in each group will be required for the pilot RCT with 80% power to detect a moderate effect size at 5% significance, and assuming 50% loss to follow-up over the six month intervention. Participants will complete a paper-based survey (Phase one), followed by a brief semi-structured interview (Phase two) to identify their level of adherence to medication and determine factors predictive of non-adherence. Participants identified as ‘non-adherent’ will be eligible for the pilot randomised trial, where they will be randomly allocated to receive either the motivational interview plus text message reminders and standard care, or standard care alone. Discussion: Nurse-led multi-faceted interventions have the potential to enhance adherence to cardiac medications. The results of this study may have relevance for cardiac patients in other settings, and for long-term medication users with other chronic diseases

Interactions between bare and protonated Mg vacancies and dislocation cores in MgO

Water can be incorporated into the lattice of mantle minerals in the form of protons charge-balanced by the creation of cation vacancies. These protonated vacancies, when they interact with dislocations, influence strain rates by affecting dislocation climb, pinning the dislocation, and, potentially, by altering the Peierls barrier to glide. We use atomic scale simulations to investigate segregation of Mg vacancies to atomic sites within the core regions of dislocations in MgO. Energies are computed for bare and V′′Mg protonated Mg vacancies occupying atomic sites close to ½ 〈110〉 screw dislocations, and ½ 〈110〉 {100} and ½ 〈110〉 {110} edge dislocations. These are compared with energies for equivalent defects in the bulk lattice to determine segregation energies for each defect. Mg vacancies preferentially bind to ½ 〈110〉 {100} edge dislocations, with calculated minimum segregation energies of − 3.54 eV for and − 4.56 eV for 2HxMg . The magnitudes of the minimum segregation energies calculated for defects binding to ½ 〈110〉 {110} edge or ½ 〈110〉 screw dislocations are considerably lower. Interactions with the dislocation strain field lift the threefold energy degeneracy of the 2HxMg defect in MgO. These calculations show that Mg vacancies interact strongly with dislocations in MgO, and may be present in sufficiently high concentrations to affect dislocation mobility in both the glide- and climb-controlled creep regimes

Mouse models for preeclampsia: disruption of redox-regulated signaling

The concept that oxidative stress contributes to the development of human preeclampsia has never been tested in genetically-defined animal models. Homozygous deletion of catechol-Omethyl transferase (Comt-/-) in pregnant mice leads to human preeclampsia-like symptoms (high blood pressure, albuminurea and preterm birth) resulting from extensive vasculo-endothelial pathology, primarily at the utero-fetal interface where maternal cardiac output is dramatically increased during pregnancy. Comt converts estradiol to 2-methoxyestradiol 2 (2ME2) which counters angiogenesis by depleting hypoxia inducible factor-1 alpha (HIF-1 alpha) at late pregnancy. We propose that in wild type (Comt++) pregnant mice, 2ME2 destabilizes HIF-1 alpha by inhibiting mitochondrial superoxide dismutase (MnSOD). Thus, 2ME2 acts as a pro-oxidant, disrupting redox-regulated signaling which blocks angiogenesis in wild type (WT) animals in physiological pregnancy. Further, we suggest that a lack of this inhibition under normoxic conditions in mutant animals (Comt-/-) stabilises HIF-1 alpha by inactivating prolyl hydroxlases (PHD). We predict that a lack of inhibition of MnSOD, leading to persistent accumulation of HIF-1 alpha, would trigger inflammatory infiltration and endothelial damage in mutant animals. Critical tests of this hypothesis would be to recreate preeclampsia symptoms by inducing oxidative stress in WT animals or to ameliorate by treating mutant mice with Mn-SOD-catalase mimetics or activators of PHD