Magnetization pinning in modulated nanowires: from topological protection to the "corkscrew" mechanism

Diameter-modulated nanowires offer an important paradigm to design the magnetization response of 3D magnetic nanostructures by engineering the domain wall pinning. With the aim to understand its nature and to control the process, we analyze the magnetization response in FeCo modulated polycrystalline two-segment nanowires varying the minor diameter. Our modelling indicates a very complex behavior with a strong dependence on the disorder distribution and an important role of topologically non-trivial magnetization structures. We demonstrate that modulated nanowires with a small diameter difference are characterized by an increased coercive field in comparison to the straight ones which is explained by a formation of topologically protected walls formed by two 3D skyrmions with opposite chiralities. For a large diameter difference we report the occurrence of a novel pinning type called here the "corkscrew": the magnetization of the large diameter segment forms a skyrmion tube with a core position in a helical modulation along the nanowire. This structure is pinned at the constriction and in order to penetrate the narrow segments the vortex/skyrmion core size should be reduced

Long-term Occupancy (1900–2015) of an Egyptian Vulture Nest

Peer reviewe

Reducing Down(stream)time: Pretraining Molecular GNNs using Heterogeneous AI Accelerators

The demonstrated success of transfer learning has popularized approaches that involve pretraining models from massive data sources and subsequent finetuning towards a specific task. While such approaches have become the norm in fields such as natural language processing, implementation and evaluation of transfer learning approaches for chemistry are in the early stages. In this work, we demonstrate finetuning for downstream tasks on a graph neural network (GNN) trained over a molecular database containing 2.7 million water clusters. The use of Graphcore IPUs as an AI accelerator for training molecular GNNs reduces training time from a reported 2.7 days on 0.5M clusters to 1.2 hours on 2.7M clusters. Finetuning the pretrained model for downstream tasks of molecular dynamics and transfer to a different potential energy surface took only 8.3 hours and 28 minutes, respectively, on a single GPU.Comment: Machine Learning and the Physical Sciences Workshop at the 36th conference on Neural Information Processing Systems (NeurIPS

Tunability of exchange bias in Ni@NiO core-shell nanoparticles obtained by sequential layer deposition

Films of magnetic Ni@NiO core-shell nanoparticles (NPs, core diameter d\ua0 45\ua012 nm, nominal shell thickness variable between 0 and 6.5 nm) obtained with sequential layer deposition were investigated, to gain insight into the relationships between shell thickness/morphology, core-shell interface, and magnetic properties. Different values of NiO shell thickness ts could be obtained while keeping the Ni core size fixed, at variance with conventional oxidation procedures where the oxide shell is grown at the expense of the core. Chemical composition, morphology of the as-produced samples and structural features of the Ni/NiO interface were investigated with x-ray photoelectron spectroscopy and microscopy (scanning electron microscopy, transmission electron microscopy) techniques, and related with results from magnetic measurements obtained with a superconducting quantum interference device. The effect of the shell thickness on the magnetic properties could be studied. The exchange bias (EB) field Hbias is small and almost constant for ts up to 1.6 nm; then it rapidly grows, with no sign of saturation. This behavior is clearly related to the morphology of the top NiO layer, and is mostly due to the thickness dependence of the NiO anisotropy constant. The ability to tune the EB effect by varying the thickness of the last NiO layer represents a step towards the rational design and synthesis of core-shell NPs with desired magnetic properties

An in vitro and in situ evaluation of a diet for cattle added with organic oils

Objective: To perform in vitro and in situ evaluation of a diet for dairy cattle with fish oil and soybean oil at different proportions. Design /methodology /approach: Four treatments with different proportions of fish oil (FO) and soybean oil (SO) were evaluated (Control: no added oil, diet 1: 2% FO, diet 2: 2% FO and 1.5% SO, diet 3: 2% FO and 3% SO). In vitro digestibility and in situ degradability were evaluated. Ammonia nitrogen, lactic acid, volatile fatty acids (VFAs), and microbial protein were determined. For the in situ evaluation, a protein degradability kinetic was carried out. The means were compared by Tukey's test at a 5% confidence level. Results: The proposed diets increased gas production in in vitro kinetics as the addition of oils increased (p <0.001) and the kinetic latency time decreased (p <0.001). All diets decreased the production of short chain fatty acids (p <0.001), the production of ammonia nitrogen and lactic acid did not differ compared to the control (p <0.05). Diet 3 presented a higher production of propionic acid in comparison to diet 1 and 2. In the in situ kinetic, the "kd" rate increased as the addition of the oils increased. Study limitations /implications: Although the production in milliliters of  and  increased in all treatments, it is an upsurge proportional to the gas production given by a better use of the diets. Findings /conclusions: The addition of oils produced changes in the fermentation patterns and in the degradation of the protein at the ruminal level, increasing the bypass protein. Which offers an opportunity to improve performance in certain production situations.Objective: To perform in vitro and in situ evaluation of a diet for dairy cattle at different rates of fish oil and soybean oil. Design /methodology /approach: Four treatments with different rates of fish oil (FO) and soybean oil (SO) were evaluated (Control: no added oil; diet 1: 2% FO; diet 2: 2% FO and 1.5% SO; diet 3: 2% FO and 3% SO). In vitro digestibility and in situ degradability were evaluated. Ammonia nitrogen, lactic acid, volatile fatty acids (VFAs), and microbial protein were determined. For the in situ evaluation, a protein degradability kinetic was carried out. The means were compared using a Tukey test at a 5% confidence level. Results: The proposed diets increased gas production in in vitro kinetics, as the addition of oils increased (p<0.001) and the kinetic latency time decreased (p<0.001). All diets decreased the production of short-chain fatty acids (p<0.001). The production of ammonia nitrogen and lactic acid did not differ compared to the control (p<0.05). Diet 3 had a higher production of propionic acid in comparison to diet 1 and 2. In the in situ kinetic, the "kd" rate increased as more oils were added. Study limitations/implications: Although all treatments increased the production (milliliters) of  and , the gas production had a proportional increase, as a result of a better use of the diets. Findings/conclusions: The addition of oils produced changes in the fermentation patterns and in the degradation of the protein at the ruminal level, increasing bypass protein. This offers an opportunity to improve performance in certain production situation

Validación de un instrumento para medir el nivel de satisfacción de mujeres embarazadas durante el parto

Objetivos: Evaluar la validez y fabilidad de un instrumento adaptado a partir de la escala SERVPERF para medir el nivel de satisfacción en gestantes durante el parto en una Institución de Salud en Lima, Perú. Métodos: Estudio transversal, descriptivo con componentes analíticos de validación del cuestionario SERVPERF adaptado para mujeres gestantes peruanas (GP) durante el parto. Se realizó una prueba piloto con posterior análisis de propiedades psicométricas de validez y fabilidad mediante análisis factorial exploratorio de componentes principales y cálculo de alfa de Cronbach. Resultados: Se reporta una muestra de 345 mujeres, atendidas en la Clínica Good Hope, en el período de febrero a abril del año 2016. La prueba de adecuación de Kaiser-Meyer Olkin fue de 0.919 y la prueba de esfericidad de Barlett de 4008.9 (p<0.000). La varianza acumulada explicada por los 5 factores fue de 65.039%,. La fabilidad mostró un alfa de Cronbach de 0.92. Se clasifcaron 5 factores con 22 items, redefniendose un factor como “calidad clinica”. Conclusión: El instrumento adaptado y validado SERVPERF-GP posee sufcientes propiedades psicométricas para ser considerado una herramienta útil y fable para medir la satisfacción de gestantes durante su experiencia de parto en instituciones privadas de salud y con potencial aplicación a gestantes en los diversos sectores de salud del Perú.   DOI:https://doi.org/10.25176/RFMH.v16.n3.65

Generated carrier dynamics in V-pit enhanced InGaN/GaN light emitting diode

We investigate the effects of V-pits on the optical properties of a state-of-the art highly efficient, blue InGaN/GaN multi-quantum-well (MQW) light emitting diode (LED) with high internal quantum efficiency (IQE) of > 80%. The LED is structurally enhanced by incorporating pre-MQW InGaN strain relief layer with low InN content and patterned sapphire substrate. For comparison, a conventional (unenhanced) InGaN/GaN MQW LED (with IQE of 46%) grown under similar conditions was subjected to the same measurements. Scanning transmission electron microscopy (STEM) reveals the absence of V-pits in the unenhanced LED, whereas in the enhanced LED, V-pits with {10-11} facets, emerging from threading dislocations (TDs) were prominent. Cathodoluminescence mapping reveals the luminescence properties near the V-pits, showing that the formation of V-pit defects can encourage the growth of defect-neutralizing barriers around TD defect states. The diminished contribution of TDs in the MQWs allows indium-rich localization sites to act as efficient recombination centers. Photoluminescence and time-resolved spectroscopy measurements suggest that the V-pits play a significant role in the generated carrier rate and droop mechanism, showing that the quantum confined Stark effect is suppressed at low generated carrier density, after which the carrier dynamics and droop are governed by the carrier overflow effect