Lithium nitrate salt-assisted CO2 absorption for the formation of corrosion barrier layer on AZ91D magnesium alloy.

Mg alloy corrosion susceptibility is a major issue that limits its wide industrial application in transport, energy and medical sectors. A corrosion-resistant layer containing crystalline MgCO3 was formed on the surface of AZ91D Mg alloy by Li salt loading and thermal CO2 treatment. Compared to the uncoated AZ91D surface, the surface layer exhibited up to a ∼15-fold increase in corrosion resistance according to the electrochemical results in 3.5 wt% NaCl solution and ∼32% decrease in wear rate compared to untreated AZ91D. The improved corrosion resistance is attributed to the formation of a <10 µm thick dense layer containing Mg, O, C and Li with crystalline MgCO3 phases. The initial step was to form a porous MgO layer on the surface of AZ91D Mg alloy, followed by loading an alkali metal salt (i.e., LiNO3) onto the MgO surface. The porous MgO surface was then reconstructed into a dense insulation layer containing Mg carbonate through CO2 absorption facilitated by molten Li salt during thermal CO2 treatment at 350 °C. As a potential method to utilize excessive CO2 for beneficial outcomes, the formation of the carbonate-containing film introduced in this study opens a new pathway for protecting various existing Mg alloys for diverse industrial applications.

[Yishen Tonglong Decoction inhibits the epithelial-mesenchymal transition and Ras/ERK signaling pathway in human prostate cancer DU-145 cells].

Objective: To observe the effect of Yishen Tonglong Decoction (YTD) on the epithelial-mesenchymal transition (EMT) and Ras/ERK signaling pathway in human PCa DU-145 cells and explore its action mechanism. METHODS: We treated human PCa DU-145 cells with normal plasma (the blank control) or plasma containing 5% (low-dose), 10% (medium-dose) and 15% (high-dose) YTD. After intervention, we examined the proliferation of the DU-145 cells in different groups with CCK-8 and their apoptosis by Annexin V/PI double staining. We detected the cell cycle by PI assay, the invasion and migration of the cells using the Transwell chamber and scratch test, and the expressions of the proteins and genes related to the EMT and Ras/ERK signaling pathways in the cells by Western blot and RT-PCR. RESULTS: Compared with the blank control group, high-, medium- and low-dose YTD significantly inhibited the proliferation of the PCa DU-145 cells, decreased their adherence and growth (P < 0.05, P < 0.01), promoted their apoptosis (P < 0.01), regulated their cell cycles (P < 0.05, P < 0.01), and reduced their in vitro invasion and migration abilities (P < 0.05), all in a dose-dependent manner. The results of Western blot and RT-PCR revealed down-regulated protein and mRNA expressions of N-cadherin, zinc finger transcription factor (Snail), Ras, p-ERK1/2 and ERK1/2, but up-regulated protein and mRNA expressions of E-cadherin in the PCa DU-145 cells treated with YTD (P < 0.05, P < 0.01). CONCLUSIONS: Yishen Tonglong Decoction can effectively inhibit the proliferation, promote the apoptosis, regulate the cell cycle and suppress the invasion and migration abilities and EMT process of human PCa DU-145 cells. The mechanism of Yishen Tonglong Decoction acting on PCa may be associated with its inhibitory effect on the EMT process and expression of the Ras/ERK signaling pathway in PCa cells./.

Origin of the enhanced Nb3Sn performance by combined Hf and Ta doping.

In recent years there has been an increasing effort in improving the performance of Nb3Sn for high-field applications, in particular for the fabrication of conductors suitable for the realization of the Future Circular Collider (FCC) at CERN. This challenging task has led to the investigation of new routes to advance the high-field pinning properties, the irreversibility and the upper critical fields (HIrr and Hc2, respectively). The effect of hafnium addition to the standard Nb-4Ta alloy has been recently demonstrated to be particularly promising and, in this paper, we investigate the origins of the observed improvements of the superconducting properties. Electron microscopy, Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) and Atom Probe Tomography (APT) characterization clearly show that, in presence of oxygen, both fine Nb3Sn grains and HfO2 nanoparticles form. Although EXAFS is unable to detect significant amounts of Hf in the A15 structure, APT does indeed reveal some residual intragrain metallic Hf. To investigate the layer properties in more detail, we created a microbridge from a thin lamella extracted by Focused Ion Beam (FIB) and measured the transport properties of Ta-Hf-doped Nb3Sn. Hc2(0) is enhanced to 30.8 T by the introduction of Hf, ~ 1 T higher than those of only Ta-doped Nb3Sn, and, even more importantly the position of the pinning force maximum exceeds 6 T, against the typical ~ 4.5-4.7 T of the only Ta-doped material. These results show that the improvements generated by Hf addition can significantly enhance the high-field performance, bringing Nb3Sn closer to the requirements necessary for FCC realization.

Development and characterization of Nb3Sn/Al2O3 superconducting multilayers for particle accelerators.

Superconducting radio-frequency (SRF) resonator cavities provide extremely high quality factors > 1010 at 1-2 GHz and 2 K in large linear accelerators of high-energy particles. The maximum accelerating field of SRF cavities is limited by penetration of vortices into the superconductor. Present state-of-the-art Nb cavities can withstand up to 50 MV/m accelerating gradients and magnetic fields of 200-240 mT which destroy the low-dissipative Meissner state. Achieving higher accelerating gradients requires superconductors with higher thermodynamic critical fields, of which Nb3Sn has emerged as a leading material for the next generation accelerators. To overcome the problem of low vortex penetration field in Nb3Sn, it has been proposed to coat Nb cavities with thin film Nb3Sn multilayers with dielectric interlayers. Here, we report the growth and multi-technique characterization of stoichiometric Nb3Sn/Al2O3 multilayers with good superconducting and RF properties. We developed an adsorption-controlled growth process by co-sputtering Nb and Sn at high temperatures with a high overpressure of Sn. The cross-sectional scanning electron transmission microscope images show no interdiffusion between Al2O3 and Nb3Sn. Low-field RF measurements suggest that our multilayers have quality factor comparable with cavity-grade Nb at 4.2 K. These results provide a materials platform for the development and optimization of high-performance SIS multilayers which could overcome the intrinsic limits of the Nb cavity technology.

Direct evidence of microstructure dependence of magnetic flux trapping in niobium.

Elemental type-II superconducting niobium is the material of choice for superconducting radiofrequency cavities used in modern particle accelerators, light sources, detectors, sensors, and quantum computing architecture. An essential challenge to increasing energy efficiency in rf applications is the power dissipation due to residual magnetic field that is trapped during the cool down process due to incomplete magnetic field expulsion. New SRF cavity processing recipes that use surface doping techniques have significantly increased their cryogenic efficiency. However, the performance of SRF Nb accelerators still shows vulnerability to a trapped magnetic field. In this manuscript, we report the observation of a direct link between flux trapping and incomplete flux expulsion with spatial variations in microstructure within the niobium. Fine-grain recrystallized microstructure with an average grain size of 10-50 µm leads to flux trapping even with a lack of dislocation structures in grain interiors. Larger grain sizes beyond 100-400 µm do not lead to preferential flux trapping, as observed directly by magneto-optical imaging. While local magnetic flux variations imaged by magneto-optics provide clarity on a microstructure level, bulk variations are also indicated by variations in pinning force curves with sequential heat treatment studies. The key results indicate that complete control of the niobium microstructure will help produce higher performance superconducting resonators with reduced rf losses1 related to the magnetic flux trapping.

Effect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As2.

Fe-based superconductors and in particular K-doped BaFe2As2 (K-Ba122) are materials of interest for possible future high-field applications. However the critical current density (Jc) in polycrystalline Ba122 is still quite low and connectivity issues are suspected to be responsible. In this work we investigated the properties of high-purity, carefully processed, K-Ba122 samples synthesized with two separate heat treatments at various temperatures between 600 and 825 °C. We performed specific heat characterization and Tc-distribution analysis up to 16 T and we compared them with magnetic Tc and Jc characterizations, and transmission-electron-microscopy (TEM) microstructures. We found no direct correlation between the magnetic Tc and Jc, whereas the specific heat Tc-distributions did provide valuable insights. In fact the best Jc-performing sample, heat treated first at 750 °C and then at 600 °C, has the peak of the Tc-distributions at the highest temperatures and the least field sensitivity, thus maximizing Hc2. We also observed that the magnetic Tc onset was always significantly lower than the specific heat Tc: although we partially ascribe the lower magnetization Tc to the small grain size (< λ, the penetration depth) of the K-Ba122 phase, this behaviour also implies the presence of some grain-boundary barriers to current flow. Comparing the Tc-distribution with Jc, our systematic synthesis study reveals that increasing the first heat treatment above 750 °C or the second one above 600 °C significantly compromises the connectivity and suppresses the vortex pinning properties. We conclude that high-purity precursors and clean processing are not yet enough to overcome all Jc limitations. However, our study suggests that a higher temperature Tc-distribution, a larger Hc2 and a better connectivity could be achieved by lowering the second heat treatment temperature below 600 °C thus enhancing, as a consequence, Jc.

Hollow metal halide perovskite nanocrystals with efficient blue emissions.

Metal halide perovskite nanocrystals (NCs) have emerged as new-generation light-emitting materials with narrow emissions and high photoluminescence quantum efficiencies (PLQEs). Various types of perovskite NCs, e.g., platelets, wires, and cubes, have been discovered to exhibit tunable emissions across the whole visible spectrum. Despite remarkable advances in the field of perovskite NCs, many nanostructures in inorganic NCs have not yet been realized in metal halide perovskites, and producing highly efficient blue-emitting perovskite NCs remains challenging and of great interest. Here, we report the discovery of highly efficient blue-emitting cesium lead bromide (CsPbBr3) perovskite hollow NCs. By facile solution processing of CsPbBr3 precursor solution containing ethylenediammonium bromide and sodium bromide, in situ formation of hollow CsPbBr3 NCs with controlled particle and pore sizes is realized. Synthetic control of hollow nanostructures with quantum confinement effect results in color tuning of CsPbBr3 NCs from green to blue, with high PLQEs of up to 81%.

Optimization of metallic nanoapertures at short-wave infrared wavelengths for self-induced back-action trapping.

This paper presents simulation results for double nanohole and inverted bowtie nanoapertures optimized to resonate in the short-wave infrared regime (1050 nm and 1550 nm). These geometries have shown great promise for trapping nanoparticles with applications in optical engineering, physics, and biology. Using a finite element analysis tool, we found that the outline length for inverted bowtie nanoapertures in a 100 nm thick gold film with a 20 nm gap dimension having an optimized transmission resonance for 1050 nm and 1550 nm optical wavelengths is 106.5 nm and 188.5 nm, respectively. With the same gap size, the radii of the circles for the double nanohole nanoapertures are 72 nm and 128 nm. The near-field enhancements of the two structures are almost the same, while the double nanohole geometries have a 20% larger full width at half-maximum than the inverted bowtie. Next, by studying the effect of changing the inner radii of the inverted bowtie corners, we found that the difference between 2 nm and 6 nm corner radii can blue-shift the optical resonance by up to 45 nm. As a result of not having any inner corners, the double nanohole structure requires less precise fabrication and therefore could potentially have a higher successful yield of nanoapertures during the manufacturing process. Lastly, we will show experimental results that confirm the optical resonance of the nanoapertures at 1550 nm. These results will enable better performance and signal-to-noise ratio in nanoaperture trapping for the short-wave infrared wavelength regime.

Public Health Emergency Response in Taiwan.

In recent years, growth of international travel and trade, as well as climate change, has resulted in the frequent emergence and reemergence of infectious diseases such as Ebola, Zika, and MERS. In 2016, Taiwan used the Joint External Evaluation (JEE) tool to evaluate its public health emergency response capacities and understand important areas for improvement. This article presents Taiwan's disaster and public health emergency response organizational structure, real-time integrated information, response processes, and command center structure. After reviewing the results of the JEE tool and drawing lessons from emergency response efforts in the United States, we provide 3 recommendations that may enhance Taiwan's public health emergency response capacities: establish common principles for disaster response regardless of which agency is in charge, standardize operation procedures, and perform regular training that includes nongovernmental organizations and a range of government departments.

Influence of grain boundary characteristics on thermal stability in nanotwinned copper.

High density grain boundaries provide high strength, but may introduce undesirable features, such as high Fermi levels and instability. We investigated the kinetics of recovery and recrystallization of Cu that was manufactured to include both nanotwins (NT) and high-angle columnar boundaries. We used the isothermal Johnson-Mehl-Avrami-Kolmogorov (JMAK) model to estimate activation energy values for recovery and recrystallization and compared those to values derived using the non-isothermal Kissinger equation. The JMAK model hinges on an exponent that expresses the growth mechanism of a material. The exponent for this Cu was close to 0.5, indicating low-dimensional microstructure evolution, which is associated with anisotropic twin coarsening, heterogeneous recrystallization, and high stability. Since this Cu was of high purity, there was a negligible impurity-drag-effect on boundaries. The twin coarsening and heterogeneous recrystallization resulted from migration of high-angle columnar boundaries with their triple junctions in one direction, assisted by the presence of high concentration vacancies at boundaries. Analyses performed by electron energy loss spectroscopy of atomic columns at twin boundaries (TBs) and in the interior showed similar plasma peak shapes and L3 edge positions. This implies that values for conductivity and Fermi level are equal for atoms at TBs and in the interior.

Characterization at Atomic Resolution of Carbon Nanotube/Resin Interface in Nanocomposites by Mapping sp 2-Bonding States Using Electron Energy-Loss Spectroscopy.

Functionalization is critical for improving mechanical properties of carbon nanotubes (CNTs)/polymer nanocomposites. A fundamental understanding of the role of the CNT/polymer interface and bonding structure is key to improving functionalization procedures for higher mechanical performance. In this study, we investigated the effects of chemical functionalization on the nanocomposite interface at atomic resolution to provide direct and quantifiable information of the interactions and interface formation between CNT surfaces and adjacent resin molecules. We observed and compared electronic structures and their changes at the interfaces of nonfunctionalized and functionalized CNT/polymer nanocomposite samples via scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) spectrum imaging techniques. The results show that the state of sp 2 bonding and its distribution at the CNT/resin interface can be clearly visualized through EELS mapping. We found that the functionalized CNT/polymer samples exhibited a lower fraction of sp 2 bonding and a lower π*/σ* ratio compared with the nonfunctionalized cases. A good correlation between near-edge fine structures and low-loss plasmon energies was observed.

Facility implementation and comparative performance evaluation of probe-corrected TEM/STEM with Schottky and cold field emission illumination.

We report the installation and performance evaluation of a probe aberration-corrected high-resolution JEOL JEM-ARM200F transmission electron microscope (TEM). We provide details on construction of the room that enables us to obtain scanning transmission electron microscope (STEM) data without any evident distortions/noise from the external environment. The microscope routinely delivers expected performance. We show that the highest STEM spatial resolution and energy resolution achieved with this microscope are 0.078 nm and 0.34 eV, respectively. We report a direct comparative evaluation of the performance of this microscope with a Schottky thermal field-emission gun versus a cold field-emission gun. Cold field-emission illumination improves spatial resolution of the high current probe for analytical spectroscopy, the TEM information limit, and the electron energy resolution compared to the Schottky thermal field-emission source.