911 research outputs found
Micromagnetics of single and double point contact spin torque oscillators
In this paper we numerically conduct micromagnetic modelling to optimize
computational boundaries of magnetic thin-film elements applicable to single
and double point contact spin torque nano-oscillators. Different boundary
conditions have been introduced to compensate spin waves reflections at
boundaries that are based on extended layers, absorbing boundaries, and focal
point methods and are compared with a technique based on scattering theory. A
surface roughness boundary model is presented which is modelled according to
the Rayleigh criterion to minimize specular reflections at computational
boundaries. It is shown that the surface roughness model disperses the
reflected spin waves and improves the signal to background noise ratio. The
model is tested in comparison to conventional approaches such as extended layer
systems, variable damping constant and focal point methods for double point
contacts. The surface roughness model gives solutions that are stable in time,
in qualitative agreement with experiments and capable to reproduce phenomena
such as phase locking in double point contacts.Comment: 17 pages,) figure
Internal effective field sources for spin torque nano pillar oscillators
In this paper we numerically conduct micromagnetic modelling with an expended
micromagnetic model that includes the spin torque term and an impedance model
to investigate methods to replace external field sources with internal ones and
to investigate its tuneability on nanopillar geometries. We present results for
three methods: interlayer coupling, large perpendicular anisotropy and
magnetostatic coupling. The internal field sources are evaluated as function of
frequency shift with current, its dependency on temperature and are tested
against analytical predictions.Comment: 27 pages, 11 figures, submitted to Journal of Applied Physic
Generating QM1B with PySCF
The emergence of foundation models in Computer Vision and Natural Language
Processing have resulted in immense progress on downstream tasks. This progress
was enabled by datasets with billions of training examples. Similar benefits
are yet to be unlocked for quantum chemistry, where the potential of deep
learning is constrained by comparatively small datasets with 100k to 20M
training examples. These datasets are limited in size because the labels are
computed using the accurate (but computationally demanding) predictions of
Density Functional Theory (DFT). Notably, prior DFT datasets were created using
CPU supercomputers without leveraging hardware acceleration. In this paper, we
take a first step towards utilising hardware accelerators by introducing the
data generator PySCF using Intelligence Processing Units (IPUs).
This allowed us to create the dataset QM1B with one billion training examples
containing 9-11 heavy atoms. We demonstrate that a simple baseline neural
network (SchNet 9M) improves its performance by simply increasing the amount of
training data without additional inductive biases. To encourage future
researchers to use QM1B responsibly, we highlight several limitations of QM1B
and emphasise the low-resolution of our DFT options, which also serves as
motivation for even larger, more accurate datasets. Code and dataset are
available on Github: http://github.com/graphcore-research/pyscf-ipuComment: 15 pages, 7 figures. NeurIPS 2023 Track Datasets and Benchmark
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Teleconnections among tipping elements in the Earth system
Tipping elements are components of the Earth system that may shift abruptly and irreversibly from one state to another at specific thresholds. It is not well understood to what degree tipping of one system can influence other regions or tipping elements. Here, we propose a climate network approach to analyse the global impacts of a prominent tipping element, the Amazon Rainforest Area (ARA). We find that the ARA exhibits strong correlations with regions such as the Tibetan Plateau (TP) and West Antarctic ice sheet. Models show that the identified teleconnection propagation path between the ARA and the TP is robust under climate change. In addition, we detect that TP snow cover extent has been losing stability since 2008. We further uncover that various climate extremes between the ARA and the TP are synchronized under climate change. Our framework highlights that tipping elements can be linked and also the potential predictability of cascading tipping dynamics
Teleconnections among tipping elements in the Earth system
Tipping elements are components of the Earth system that may shift abruptly and irreversibly from one state to another at specific thresholds. It is not well understood to what degree tipping of one system can influence other regions or tipping elements. Here, we propose a climate network approach to analyse the global impacts of a prominent tipping element, the Amazon Rainforest Area (ARA). We find that the ARA exhibits strong correlations with regions such as the Tibetan Plateau (TP) and West Antarctic ice sheet. Models show that the identified teleconnection propagation path between the ARA and the TP is robust under climate change. In addition, we detect that TP snow cover extent has been losing stability since 2008. We further uncover that various climate extremes between the ARA and the TP are synchronized under climate change. Our framework highlights that tipping elements can be linked and also the potential predictability of cascading tipping dynamics.Peer reviewe
Impact of Mechanical Unloading on Microvasculature and Associated Central Remodeling Features of the Failing Human Heart
ObjectivesThis study investigates alterations in myocardial microvasculature, fibrosis, and hypertrophy before and after mechanical unloading of the failing human heart.BackgroundRecent studies demonstrated the pathophysiologic importance and significant mechanistic links among microvasculature, fibrosis, and hypertrophy during the cardiac remodeling process. The effect of left ventricular assist device (LVAD) unloading on cardiac endothelium and microvasculature is unknown, and its influence on fibrosis and hypertrophy regression to the point of atrophy is controversial.MethodsHemodynamic data and left ventricular tissue were collected from patients with chronic heart failure at LVAD implant and explant (n = 15) and from normal donors (n = 8). New advances in digital microscopy provided a unique opportunity for comprehensive whole-field, endocardium-to-epicardium evaluation for microvascular density, fibrosis, cardiomyocyte size, and glycogen content. Ultrastructural assessment was done with electron microscopy.ResultsHemodynamic data revealed significant pressure unloading with LVAD. This was accompanied by a 33% increase in microvascular density (p = 0.001) and a 36% decrease in microvascular lumen area (p = 0.028). We also identified, in agreement with these findings, ultrastructural and immunohistochemical evidence of endothelial cell activation. In addition, LVAD unloading significantly increased interstitial and total collagen content without any associated structural, ultrastructural, or metabolic cardiomyocyte changes suggestive of hypertrophy regression to the point of atrophy and degeneration.ConclusionsThe LVAD unloading resulted in increased microvascular density accompanied by increased fibrosis and no evidence of cardiomyocyte atrophy. These new insights into the effects of LVAD unloading on microvasculature and associated key remodeling features might guide future studies of unloading-induced reverse remodeling of the failing human heart
Evidence of Glycolysis Up-Regulation and Pyruvate Mitochondrial Oxidation Mismatch During Mechanical Unloading of the Failing Human Heart: Implications for Cardiac Reloading and Conditioning
This study sought to investigate the effects of mechanical unloading on myocardial energetics and the metabolic perturbation of heart failure (HF) in an effort to identify potential new therapeutic targets that could enhance the unloading-induced cardiac recovery. The authors prospectively examined paired human myocardial tissue procured from 31 advanced HF patients at left ventricular assist device (LVAD) implant and at heart transplant plus tissue from 11 normal donors. They identified increased post-LVAD glycolytic metabolites without a coordinate increase in early, tricarboxylic acid (TCA) cycle intermediates. The increased pyruvate was not directed toward the mitochondria and the TCA cycle for complete oxidation, but instead, was mainly converted to cytosolic lactate. Increased nucleotide concentrations were present, potentially indicating increased flux through the pentose phosphate pathway. Evaluation of mitochondrial function and structure revealed a lack of post-LVAD improvement in mitochondrial oxidative functional capacity, mitochondrial volume density, and deoxyribonucleic acid content. Finally, post-LVAD unloading, amino acid levels were found to be increased and could represent a compensatory mechanism and an alternative energy source that could fuel the TCA cycle by anaplerosis. In summary, the authors report evidence that LVAD unloading induces glycolysis in concert with pyruvate mitochondrial oxidation mismatch, most likely as a result of persistent mitochondrial dysfunction. These findings suggest that interventions known to improve mitochondrial biogenesis, structure, and function, such as controlled cardiac reloading and conditioning, warrant further investigation to enhance unloading-induced reverse remodeling and cardiac recovery
Statement on the safety of EstroGâ100âą as a novel food pursuant to Regulation (EC) No 258/97
Following a request from the European Commission, the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to update its scientific opinion on the safety of EstroG-100 (TM) as a novel food (NF) in the light of additional information submitted by the applicant. In its previous scientific opinion of 2016, the Panel concluded that EstroG-100 (TM), which is a hot-water extract of a mixture of three herbal roots, is safe for the use in food supplements at the maximum intake level of 175 mg/day in post-menopausal women, which is lower than the maximum intake level proposed by the applicant (514 mg/day). The Panel reached its conclusions based on the effects of EstroG-100 (TM) on liver and haematology as observed in several oral toxicity studies, the lack of information on liver and haematological parameters in human studies and the absence of chronic toxicity data. In view of the Panel's conclusion on the safety of EstroG-100 (TM), the applicant has now provided additional information on haematological and liver parameters for the human intervention study with EstroG-100 (TM) and historical control data related to the subchronic 90-day oral toxicity study with EstroG-100 (TM). After assessing the additional information provided by the applicant, the Panel considers that the conclusion of the scientific opinion on the safety of EstroG-100 (TM) does not need to be revised, and thus, the Panel reconfirms that the NF is safe for the use in food supplements at the maximum intake level of 175 mg/day in post-menopausal women. (C) 2017 European Food Safety Authority. EFSA Journal published by John Wiley and Sons Ltd on behalf of European Food Safety Authority
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