•Laser melting deposition of SiC dispersed 316L stainless steel MMCs was attempted.•Constituent phase of the MMCs evolved from single γ-Fe to γ-Fe + α-Fe + SiC phases.•The formation mechanism of α-Fe ...in the MMCs were explored with the addition of SiC.•The microhardness of MMCs increased from 362 HV to 974 HV with the SiC content.•The corrosion resistance and corrosion mechanism of the MMCs were investigated.
SiC dispersed (4, 8, 12 and 16 wt%) 316L stainless steel metal matrix composites (MMCs) have been prepared by laser melting deposition (LMD). The constituent phases, microstructure, microhardness and electrochemical properties of the MMCs were investigated as a function of SiC content. Experimental results showed that constituent phases of the MMCs evolved from single γ-(FeCrNi) phase with fcc structure for 4 wt% SiC dispersed MMC to γ-(FeCrNi) + α-(FeCrNi) + SiC phases for the 8, 12 and 16 wt% SiC dispersed MMCs. The presence of α-(FeCrNi) phase was due to the tensile stress resulting from the different coefficient of thermal expansion between SiC ceramic reinforcement and the γ-(FeCrNi) matrix in the MMCs. In addition, iron silicides (Fe3Si and FeSi) appeared in 16 wt% SiC dispersed MMC. The microstructure was dense, uniform and the addition of SiC obviously refined the solidification microstructure of the MMCs. In the 16 wt% SiC dispersed MMCs, a micro-crack can be clearly observed. The microhardness of MMCs increased obviously from 362 HV to 974 HV with the addition of SiC. Accompanying the increase in hardness, the corrosion current density increased and the charge transfer resistance decreased, and the corrosion resistance of 4 and 8 wt% SiC dispersed MMCs was superior compared to 12 and 16 wt% SiC dispersed MMCs in 3.5 wt% NaCl solution.
Abstract
A nanohertz-frequency stochastic gravitational-wave background can potentially be detected through the precise timing of an array of millisecond pulsars. This background produces ...low-frequency noise in the pulse arrival times that would have a characteristic spectrum common to all pulsars and a well-defined spatial correlation. Recently the North American Nanohertz Observatory for Gravitational Waves collaboration (NANOGrav) found evidence for the common-spectrum component in their 12.5 yr data set. Here we report on a search for the background using the second data release of the Parkes Pulsar Timing Array. If we are forced to choose between the two NANOGrav models—one with a common-spectrum process and one without—we find strong support for the common-spectrum process. However, in this paper, we consider the possibility that the analysis suffers from model misspecification. In particular, we present simulated data sets that contain noise with distinctive spectra but show strong evidence for a common-spectrum process under the standard assumptions. The Parkes data show no significant evidence for, or against, the spatially correlated Hellings–Downs signature of the gravitational-wave background. Assuming we did observe the process underlying the spatially uncorrelated component of the background, we infer its amplitude to be
A
=
2.2
−
0.3
+
0.4
×
10
−
15
in units of gravitational-wave strain at a frequency of 1 yr
−1
. Extensions and combinations of existing and new data sets will improve the prospects of identifying spatial correlations that are necessary to claim a detection of the gravitational-wave background.
White lupin (Lupinus albus) forms specialized cluster roots characterized by exudation of organic anions under phosphorus (P) deficiency. Here, the role of nitric oxide (NO) in P deficiency-induced ...cluster-root formation and citrate exudation was evaluated. White lupin plants were treated with the NO donor sodium nitroprusside (SNP) and scavenger or inhibitor of NO synthase under conditions of P deficiency (0 μM) or P sufficiency (50 μM). Phosphorus deficiency enhanced NO production in primary and lateral root tips, with a greater increase in cluster roots than in noncluster roots. NO concentrations decreased with cluster root development from the pre-emergent stage, through the juvenile stage, to the mature stage. The P deficiency-induced increase in NO production was inhibited by antagonists of NO synthase and xanthine oxidoreductase, suggesting the involvement of these enzymes in NO production. SNP markedly increased the number of cluster roots. Citrate exudation from different root segments in P-deficient roots was positively correlated with endogenous root NO concentrations. These findings demonstrate differential patterns of NO production in white lupin, depending on root zone, developmental stage and P nutritional status. NO appears to play a regulatory role in the formation of cluster roots and citrate exudation in white lupin under conditions of P deficiency.
Hypoglycaemia (low plasma glucose) is a serious and potentially fatal complication of insulin-treated diabetes. In healthy individuals, hypoglycaemia triggers glucagon secretion, which restores ...normal plasma glucose levels by stimulation of hepatic glucose production. This counterregulatory mechanism is impaired in diabetes. Here we show in mice that therapeutic concentrations of insulin inhibit glucagon secretion by an indirect (paracrine) mechanism mediated by stimulation of intra-islet somatostatin release. Insulin's capacity to inhibit glucagon secretion is lost following genetic ablation of insulin receptors in the somatostatin-secreting δ-cells, when insulin-induced somatostatin secretion is suppressed by dapagliflozin (an inhibitor of sodium-glucose co-tranporter-2; SGLT2) or when the action of secreted somatostatin is prevented by somatostatin receptor (SSTR) antagonists. Administration of these compounds in vivo antagonises insulin's hypoglycaemic effect. We extend these data to isolated human islets. We propose that SSTR or SGLT2 antagonists should be considered as adjuncts to insulin in diabetes therapy.
Divertor detachment offers a promising solution to the challenge of plasma-wall interactions for steady-state operation of fusion reactors. Here, we demonstrate the excellent compatibility of ...actively controlled full divertor detachment with a high-performance (β
~ 3, H
~ 1.5) core plasma, using high-β
(poloidal beta, β
> 2) scenario characterized by a sustained core internal transport barrier (ITB) and a modest edge transport barrier (ETB) in DIII-D tokamak. The high-β
high-confinement scenario facilitates divertor detachment which, in turn, promotes the development of an even stronger ITB at large radius with a weaker ETB. This self-organized synergy between ITB and ETB, leads to a net gain in energy confinement, in contrast to the net confinement loss caused by divertor detachment in standard H-modes. These results show the potential of integrating excellent core plasma performance with an efficient divertor solution, an essential step towards steady-state operation of reactor-grade plasmas.
Weyl fermions are a recently discovered ingredient for correlated states of electronic matter. A key difficulty has been that real materials also contain non-Weyl quasiparticles, and disentangling ...the experimental signatures has proven challenging. Here we use magnetic fields up to 95 T to drive the Weyl semimetal TaAs far into its quantum limit, where only the purely chiral 0th Landau levels of the Weyl fermions are occupied. We find the electrical resistivity to be nearly independent of magnetic field up to 50 T: unusual for conventional metals but consistent with the chiral anomaly for Weyl fermions. Above 50 T we observe a two-order-of-magnitude increase in resistivity, indicating that a gap opens in the chiral Landau levels. Above 80 T we observe strong ultrasonic attenuation below 2 K, suggesting a mesoscopically textured state of matter. These results point the way to inducing new correlated states of matter in the quantum limit of Weyl semimetals.
The Hippo pathway is a central regulator of tissue development and homeostasis, and has been reported to have a role during vascular development. Here we develop a bioluminescence-based biosensor ...that monitors the activity of the Hippo core component LATS kinase. Using this biosensor and a library of small molecule kinase inhibitors, we perform a screen for kinases modulating LATS activity and identify VEGFR as an upstream regulator of the Hippo pathway. We find that VEGFR activation by VEGF triggers PI3K/MAPK signaling, which subsequently inhibits LATS and activates the Hippo effectors YAP and TAZ. We further show that the Hippo pathway is a critical mediator of VEGF-induced angiogenesis and tumor vasculogenic mimicry. Thus, our work offers a biosensor tool for the study of the Hippo pathway and suggests a role for Hippo signaling in regulating blood vessel formation in physiological and pathological settings.
ABSTRACT
For the first time, we present an extensive study of stars with individual non-LTE (NLTE) abundances for 17 chemical elements from Li to Eu in a sample of stars uniformly distributed over ...the −2.62 ≤ Fe/H ≤ +0.24 metallicity range that is suitable for the Galactic chemical evolution research. The star sample has been kinematically selected to trace the Galactic thin and thick disks and halo. We find new results and improve earlier ones as follows: (i) the element-to-iron ratios for Mg, Si, Ca, and Ti form a metal-poor (MP) plateau at a similar height of 0.3 dex, and the knee occurs at common Fe/H ≃ −0.8. The knee at the same metallicity is observed for O/Fe, and the MP plateau is formed at O/Fe = 0.61. (ii) The upward trend of C/O with decreasing metallicity exists at Fe/H < −1.2, supporting the earlier finding of Akerman et al. (iii) An underabundance of Na relative to Mg in the Fe/H < −1 stars is nearly constant, with the mean Na/ Mg ≃ −0.5. (iv) The K/Sc, Ca/Sc, and Ti/Sc ratios form well-defined trends, suggesting a common site of the K–Ti production. (v) Sr follows the Fe abundance down to Fe/H ≃ −2.5, while Zr is enhanced in MP stars. (vi) The comparisons of our results with some widely used Galactic evolution models are given. The use of the NLTE element abundances gives increased credit to the interpretation of the data in the context of the chemical evolution of the Galaxy.
•Co-based composites coatings were fabricated on 35CrMo steel by laser cladding.•The addition of Ti3SiC2 led to reinforcement and lubrication of Co-based coatings.•Effect of Ti3SiC2 content on wear ...resistance of coatings was investigated.•The microhardness and wear mechanism of Co-based coatings were investigated.
Metal matrix composites (MMCs) self-lubricating coatings were fabricated on 35CrMo steel by laser cladding using Co-based alloy and Ti3SiC2 mixture, aiming at improving the wear resistance of 35CrMo steel. Phase constituents, microstructure, microhardness and wear property of the MMCs coatings with different Ti3SiC2 content were investigated using XRD, SEM, microhardness tester, and friction-wear tester, respectively. Experimental results showed that with appropriate laser processing parameters, crack and porosity-free coatings with good metallurgical bonding to the substrate could be obtained. The coatings were mainly composed of γ-Co, Ti3SiC2, Cr7C3 and TiC. During the cladding process, Ti3SiC2 partially dissolved to form TiC. The microhardness of the coatings was significantly enhanced, which was at least 2.3 times that of substrate. The wear resistance of the coatings was 3.6–6.2 times that of substrate and the coating with 10 wt% Ti3SiC2 addition possessed the highest wear resistance.
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