Exchange Interactions in Paramagnetic Amorphous and Disordered Crystalline CrN-based Systems

We present a first principles supercell methodology for the calculation of exchange interactions of magnetic materials with arbitrary degrees of structural and chemical disorder in their high temperature paramagnetic state. It is based on a projection of the total magnetic energy of the system onto local pair clusters, allowing the interactions to vary independently as a response to their local environments. We demonstrate our method by deriving the distance dependent exchange interactions in vibrating crystalline CrN, a Ti$_{0.5}$Cr$_{0.5}$N solid solution as well as in amorphous CrN. Our method reveals strong local environment effects in all three systems. In the amorphous case we use the full set of exchange interactions in a search for the non-collinear magnetic ground state.Comment: 5 pages, 3 figure

An \emph{ab initio} method for locating characteristic potential energy minima of liquids

It is possible in principle to probe the many--atom potential surface using density functional theory (DFT). This will allow us to apply DFT to the Hamiltonian formulation of atomic motion in monatomic liquids [\textit{Phys. Rev. E} {\bf 56}, 4179 (1997)]. For a monatomic system, analysis of the potential surface is facilitated by the random and symmetric classification of potential energy valleys. Since the random valleys are numerically dominant and uniform in their macroscopic potential properties, only a few quenches are necessary to establish these properties. Here we describe an efficient technique for doing this. Quenches are done from easily generated "stochastic" configurations, in which the nuclei are distributed uniformly within a constraint limiting the closeness of approach. For metallic Na with atomic pair potential interactions, it is shown that quenches from stochastic configurations and quenches from equilibrium liquid Molecular Dynamics (MD) configurations produce statistically identical distributions of the structural potential energy. Again for metallic Na, it is shown that DFT quenches from stochastic configurations provide the parameters which calibrate the Hamiltonian. A statistical mechanical analysis shows how the underlying potential properties can be extracted from the distributions found in quenches from stochastic configurations

Transit Ly-α\alpha signatures of terrestrial planets in the habitable zones of M dwarfs

We modeled the transit signatures in the Lya line of a putative Earth-sized planet orbiting in the HZ of the M dwarf GJ436. We estimated the transit depth in the Lya line for an exo-Earth with three types of atmospheres: a hydrogen-dominated atmosphere, a nitrogen-dominated atmosphere, and a nitrogen-dominated atmosphere with an amount of hydrogen equal to that of the Earth. We calculated the in-transit absorption they would produce in the Lya line. We applied it to the out-of-transit Lya observations of GJ 436 obtained by the HST and compared the calculated in-transit absorption with observational uncertainties to determine if it would be detectable. To validate the model, we also used our method to simulate the deep absorption signature observed during the transit of GJ 436b and showed that our model is capable of reproducing the observations. We used a DSMC code to model the planetary exospheres. The code includes several species and traces neutral particles and ions. At the lower boundary of the DSMC model we assumed an atmosphere density, temperature, and velocity obtained with a hydrodynamic model for the lower atmosphere. We showed that for a small rocky Earth-like planet orbiting in the HZ of GJ436 only the hydrogen-dominated atmosphere is marginally detectable with the STIS/HST. Neither a pure nitrogen atmosphere nor a nitrogen-dominated atmosphere with an Earth-like hydrogen concentration in the upper atmosphere are detectable. We also showed that the Lya observations of GJ436b can be reproduced reasonably well assuming a hydrogen-dominated atmosphere, both in the blue and red wings of the Lya line, which indicates that warm Neptune-like planets are a suitable target for Lya observations. Terrestrial planets can be observed in the Lya line if they orbit very nearby stars, or if several observational visits are available.Comment: 17 pages, 12 figures, accepted for publication in Astronomy & Astrophysic

The top-down crystallisation of Mercury's core

The regime governing the growth of Mercury's core is unknown, but the dynamics of core growth are vital to understanding the origin and properties of the planet's weak magnetic field. Here, we use advanced first-principles methods, which include a magnetic entropy contribution, to investigate the magnetic and thermo-elastic properties of liquid Fe-S-Si and of pure liquid iron at the conditions of Mercury's core. Our results support a ‘top-down’ evolution of the core, whereby solid iron-rich material crystallises at shallow depths and sinks. This process would likely result in a compositionally driven dynamo within a stably stratified uppermost liquid layer, providing an explanation for the observed properties of the weak magnetic field of Mercury

Directional Sensitivity in Light-Mass Dark Matter Searches with Single-Electron-Resolution Ionization Detectors

We propose a method using solid state detectors with directional sensitivity to dark matter interactions to detect low-mass weakly interacting massive particles (WIMPs) originating from galactic sources. In spite of a large body of literature for high-mass WIMP detectors with directional sensitivity, no available technique exists to cover WIMPs in the mass range <1 GeV/c(2). We argue that single-electron-resolution semiconductor detectors allow for directional sensitivity once properly calibrated. We examine the commonly used semiconductor material response to these low-mass WIMP interactions.Peer reviewe

Gain-of-function R225Q mutation in AMP-activated protein kinase gamma3 subunit increases mitochondrial biogenesis in glycolytic skeletal muscle

AMP-activated protein kinase (AMPK) is a heterotrimeric complex, composed of a catalytic subunit (alpha) and two regulatory subunits (beta and gamma), that works as a cellular energy sensor. The existence of multiple heterotrimeric complexes provides a molecular basis for the multiple roles of this highly conserved signaling system. The AMPK gamma3 subunit is predominantly expressed in skeletal muscle, mostly in type II glycolytic fiber types. We determined whether the AMPK gamma3 subunit has a role in signaling pathways that mediate mitochondrial biogenesis in skeletal muscle. We provide evidence that overexpression or ablation of the AMPK gamma3 subunit does not appear to play a critical role in defining mitochondrial content in resting skeletal muscle. However, overexpression of a mutant form (R225Q) of the AMPK gamma3 subunit (Tg-AMPKgamma3(225Q)) increases mitochondrial biogenesis in glycolytic skeletal muscle. These adaptations are associated with an increase in expression of the co-activator PGC-1alpha and several transcription factors that regulate mitochondrial biogenesis, including NRF-1, NRF-2, and TFAM. Succinate dehydrogenase staining, a marker of the oxidative profile of individual fibers, was also increased in transversal skeletal muscle sections of white gastrocnemius muscle from Tg-AMPKgamma3(225Q) mice, independent of changes in fiber type composition. In conclusion, a single nucleotide mutation (R225Q) in the AMPK gamma3 subunit is associated with mitochondrial biogenesis in glycolytic skeletal muscle, concomitant with increased expression of the co-activator PGC-1alpha and several transcription factors that regulate mitochondrial proteins, without altering fiber type composition

Developing a procedure for medication reconciliation and review on admission to geriatric wards

Peer reviewe

Effect of Donor Simvastatin Treatment on Gene Expression Profiles in Human Cardiac Allografts during Ischemia-Reperfusion Injury

Purpose Numerous studies have shown that statin therapy initiated early after heart transplantation has beneficial effects on the development of cardiac allograft vasculopathy. Recently, we were able to show in a randomized clinical trial that simvastatin treatment of brain-dead donors conditions the heart transplant to withstand ischemia-reperfusion injury and to reduce the need for rejection treatments early after transplantation. In this study, we analyzed myocardial gene expression profiles in cardiac allografts after donor simvastatin treatment. Methods 84 heart transplant donors received 80 mg of simvastatin via nasogastric tube (n=42), or no treatment (n=42) in a prospective, double-blinded randomized controlled trial. Transmural Tru-Cut biopsies were taken from the apex of left ventricle of the donor heart immediately before reperfusion and 1 hour after reperfusion. 20 heart biopsies from donors without treatment and 20 heart biopsies from donors with simvastatin treatment will be analyzed with RNA sequencing. Results The preliminary analysis of RNA sequencing data from myocardial biopsies revealed altogether 137 significantly differentially expressed genes in all pairwise comparisons. The overall biological functions of these genes were related to gene ontology terms such as response to toxic substance, leukocyte migration, neutrophil mediated immunity, response to lipopolysaccharide, and response to oxidative stress. At the KEGG pathway level, our results indicated alterations in IL-17, TNF, MAPK and the AGE-RAGE signaling pathways. Conclusion We have shown in previous studies that donor simvastatin treatment induces protective effects against IRI in heart transplant recipients. In this study, we were able to detect significantly differentially expressed genes related to effects of simvastatin treatment. In order to single out genes that show beneficial effects of simvastatin treatment, further analysis will be conducted by exploring gene expression changes in specific biological functional categories, such as interleukin signaling and neutrophil degranulation. The complete analysis will be presented at the ISHLT 2019 congress.Peer reviewe

Label-Free Proteomics Approach Characterizes Plasma Protein Signature of Donor Brain Death

Purpose Despite recent advances in donation after circulatory death, transplants from brain-dead donors remain the sole source in heart transplantation (HTx) worldwide. Due to organ shortage, marginal donors are increasingly used and the utilization of transplants becomes markedly more challenging. They undergo invariably brain death that induces a systemic cytokine and catecholamine storm that lead to systemic inflammation, labile hemodynamics, and organ hypoperfusion. Together, these can damage the heart and aggravate later occurring graft injury, and ultimately, compromise graft function. However, the effect of donor brain death on allografts is not well understood. Methods In a separate prospective, blinded single-center trial, we collected donor plasma samples and relevant clinical patient data from 50 HTx brain-dead donors and as controls plasma samples from age- and gender-matched 23 healthy volunteers. Quantitative label-free proteomics in high definition MSE mode (HDMSE) was carried out on the samples. Various statistical analyses were performed on quantitative proteomics data to obtain the most reliably distinguishing proteins, which classify the donors vs controls. Results With two or more unique proteins per identification, 463 proteins were quantified in our pilot study. A complete separation between donors and controls based on a set of 278 proteins (p-valuePeer reviewe