Pulsating tension tests with constant amplitude (CA) and variable amplitude (VA) were conducted to investigate the interior failure mechanisms of a carburized Cr steel, and a cumulative damage model ...with the fine granular area (FGA) formation process was proposed in this study. Such a steel represents the continuously descending S‐N (stress‐number of cycles) curve characteristics associated with inclusion‐FGA‐fisheye induced failure even under variable amplitude. Due to crack growth retardations and accelerations resulted from the interaction effect between stepwise resets of the applied stress, the crack morphology under variable amplitude loading is much rougher. The interior failure mechanism was elucidated in combination with the determination of stress intensity factor values at different crack tips. Based on proposed damage model, the agreement between the predicted and experimental results is fairly good within the factor‐of‐two range.
The fatigue crack growth (FCG) behaviour in a Ni-based turbine disc alloy with two grain sized variants, in a low solvus high refractory (LSHR) superalloy has been investigated under a range of ...temperatures (650–725°C) and environments (air and vacuum) with trapezoidal waveforms of 1:1:1:1 and 1:20:1:1 durations at an R=0.1. The results indicate that a coarse grained structure possesses better FCG resistance due to the enhanced slip reversibility promoted by planar slip as well as the reduction in grain boundary area. The fatigue performance of the LSHR superalloy is significantly degraded by the synergistic oxidation effect brought about by high temperature, oxidising environment and dwell at the peak load, associated with increasingly intergranular fracture features and secondary grain boundary cracking. Secondary cracks are observed to be blocked or deflected around primary γ′, carbides and borides, and their occurrence closely relates to the roughness of the fracture surface, FCG rate and grain boundary oxidation. The apparent activation energy technique provides a further insight into the underlying mechanism of the FCG under oxidation–creep–fatigue testing conditions, and confirms that oxidation fatigue is the dominant process contributing to the intergranular failure process. At high enough crack growth rates, at lower temperatures, cycle dependent crack growth processes can outstrip crack-tip oxidation processes.
The multi-principal-element alloys (MPEAs), also referred to as high-entropy alloys (HEAs), have attracted extensive attention during the last decade and a half due to their unique and excellent ...properties. However, many MPEAs show coarse and anisotropic columnar grains in the as-cast state. While constitutional supercooling (CS)-driven parameters have been widely used to evaluate and predict the effect of solutes on columnar-to-equiaxed transition (CET) and grain refinement of diluted binary alloys, similar studies are lacking on MPEAs. Due to the multiple solute elements (solutes) and their high concentrations, the CS-driven parameters for MPEAs are different from those proposed for diluted binary alloys. Here, we derived the CS-driven parameters, including undercooling parameter and growth restriction factor, for MPEAs based on their physical significances, with the help of calculated phase diagrams. The calculated CS-driven parameters were then used to predict the effect of a solute on CET and grain refinement in NiCoFeCr MPEAs. Additional alloying solutes Nb, Ti, and V in the NiCoFeCr MPEA were also evaluated for their different CS-driven characteristics. The grain size of the as-solidified microstructures of NiCoFeCr with and without Nb, Ti, and V were compared and interpreted with the predicted tendency of the CS-driven parameters.
Several case clusters occurred in high-rise residential buildings in Hong Kong in the 2003 SARS (the severe acute respiratory syndrome) epidemic, which motivated a series of engineering ...investigations into the possible airborne transport routes. It is suspected that, driven by buoyancy force, the polluted air that exits the window of the lower floor may re-enter the immediate upper floor through the window on the same side. This cascade effect has been quantified and reported in a previous paper, and it is found that, by tracer gas concentration analysis, the room in the adjacent upstairs may contain up to 7% of the air directly from the downstairs room. In this study, after validation against the experimental data from literatures, Eulerian and Lagrangian approaches are both adopted to numerically investigate the dispersion of expiratory aerosols between two vertically adjacent flats. It is found that the particle concentration in the upper floor is two to three orders of magnitude lower than in the source floor. 1.0
μm particles disperse like gaseous pollutants. For coarse particles larger than 20.0
μm, strong deposition on solid surfaces and gravitational settling effect greatly limit their upward transport.
Atomic simulations are used to investigate the interaction between nanoscale interstitial dislocation loops and grain boundaries (GBs), the subsequent evolution of the GBs' structures, and the ...resulting impact on mechanical properties, in BCC iron. The interaction between loops and GBs — Σ3{111} and Σ3{112} — is affected by the angle (θ) between the Burgers vector and the normal to the GB plane, as well as by the distribution of free volume (FV) and stress. Loops can be totally absorbed by Σ3{111} boundaries, while the interaction with Σ3{112} boundaries is found to change the Burgers vector and habit plane after absorption, but to otherwise leave the loop intact, resulting in selective absorption. When θ=90o, no absorption occurs in Σ3{112}. The stress accumulation induced by the absorption affects the local mechanical properties of GBs. In nanocrystalline iron sample, a similar phenomenon is also observed, resulting in rearrangement of GBs and grain growth.
Quinone molecules are intracellular electron-transport carriers, as well as critical intra- and extracellular signals. However, transcriptional regulation of quinone signaling and its molecular basis ...are poorly understood. Here, we identify a thiol-stress-sensing regulator YodB family transcriptional regulator as a central component of quinone stress response of Staphylococcus aureus , which we have termed the quinone-sensing and response repressor (QsrR). We also identify and confirm an unprecedented quinone-sensing mechanism based on the S-quinonization of the essential residue Cys-5. Structural characterizations of the QsrR–DNA and QsrR–menadione complexes further reveal that the covalent association of menadione directly leads to the release of QsrR from operator DNA following a 10° rigid-body rotation as well as a 9-Å elongation between the dimeric subunits. The molecular level characterization of this quinone-sensing transcriptional regulator provides critical insights into quinone-mediated gene regulation in human pathogens.
•Only M23C6 carbides precipitate in a low-carbon NiFeCoCr HEA during aging.•Rhombic and needle-like carbides formed on (111) and (100) plane, respectively.•(100)M23C6//(100)matrix and ...013M23C6∥013matrix relationship is kept.
Previous studies have reported dramatical strengthening of carbides in NiCoFeCr high-entropy alloy. The feature of carbides, especially species, morphology and distribution, plays an important role in its properties. Hence, their precipitation behavior in the compositionally complex NiCoFeCr HEA deserves to explore. Here, the carbide precipitation behavior in a (NiFeCoCr)99.75C0.25 alloy at 800 °C was studied. Intergranular and intragranular M23C6 carbides form with quite different morphologies and change gradually with the prolonging time. Intragranular carbides with needle-like and rhombus morphologies have a parallel OR of (100)M23C6//(100)matrix and 013M23C6∥013matrix with matrix, which were formed on (111) plane and (100) plane respectively.
Evidence between air pollution and COPD admissions is inconsistent and limited in China. In this study, we aimed to explore the effects of air pollutants on COPD admissions in Beijing, China.
Daily ...COPD hospital admission visits derived from tertiary and secondary hospitals in Beijing were retrieved from January 2013 to February 2017. Air pollutant levels and meteorological data over the same periods were also achieved. Generalized additive model was applied to estimate the percentage changes with 95% CIs in daily admissions corresponding to 10 µg/m
increases in pollutants levels 1 mg/m
in carbon monoxide (CO), stratified by age, gender, and season.
Seventy-three thousand seventy-six COPD hospital admission visits were included with mean daily visits of 48 (21). Cumulative lag effect with per 10 µg/m
increase in air pollutant levels was largest for nitrogen dioxide (NO
) with 3.03% (95% CI: 1.82%-4.26%) at lag 06, for sulfur dioxide (SO
) with 2.07% (95% CI: 1.00%-3.15%) at lag 01, for particulate matter ≤10 µm in aerodynamic diameter (PM
) with 0.92% (95% CI: 0.55%-1.30%) at lag 07, and for particulate matter ≤2.5 µm in aerodynamic diameter (PM
) with 0.82% (95% CI: 0.38%-1.26%) at lag 06, respectively. Percentage increase for each 1 mg/m
increase in CO was 5.99% (95% CI: 2.74%-9.34%) at lag 06. Further, stronger effects on COPD admissions were found in warm seasons than in cold seasons.
Short-term exposures to PM
, PM
, NO
, SO
, and CO had adverse effects on COPD hospitalizations in Beijing with different magnitudes and lag days.
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Theoretical and numerical investigations are carried out for the instability of the dust–acoustic waves (DAWs) under the transverse perturbation in a magnetized dusty plasma with two-temperature ...nonthermal ions. By the reductive perturbation technique, the Zakharov–Kuznetsov (ZK) equation and modified ZK equation of the DAWs are derived. Under the higher-order transverse perturbations, the instability growth rate of the soliton solutions of the ZK equations is studied. It is found that the most unstable wave mode exists in system. It is also noted that solitary waves are unstable when the ratio of the perturbation wave length to solitary wave width in the experimental coordinate is larger than a certain critical value.
The formation and evolution of radiation defects and their effects on bending property of a single graphite under low energy helium atom implantation have been studied at atomic scale through ...molecular dynamics simulations. Various simple interstitial and vacancy defects are observed during the implantation process, which is a function of incident energy and cross section of helium-carbon interaction. Large defects are observed after continuous helium atom implantations. The effects of incident energy on the density, size and distribution of defects are analyzed in detail. Furthermore, the kinetic evolution process of radiation defects at different annealing temperatures have also been simulated, including the migration, aggregation, transformation, coalescence, and self-healing. The large defect clusters, crossing several carbon layers, have been confirmed to be the primary reasons that affect the bending property of graphite. All these results provide a new understanding for further applications of graphite in nuclear reactors.
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