Various Rejuvenation Behaviors of Zr-Based Metallic Glass by Cryogenic Cycling Treatment with Different Casting Temperatures

Abstract The rejuvenation behavior of an Zr50Cu40Al10 (at.%) metallic glass upon cryogenic cycling treatment has been investigated. At a high casting temperature, the microstructure of the glass is quite homogenous and thus, internal stress cannot be generated during cycling. Therefore, the glass cannot be rejuvenated by cryogenic cycling treatment. In the contrary, by lowering the casting temperature, nano-sized heterogeneity can be induced and subsequently generates the internal stress and rejuvenates the glass. Once the glass is rejuvenated, the more induced free volume can plasticize the glass with a higher plastic strain. These findings point out that the synthesis conditions can tailor the heterogeneity of the glass and subsequently affect the following rejuvenation behavior upon thermal treatment. It can also help understand the mechanisms of rejuvenation of metallic glass upon cryogenic cycling treatment

Sources and formation of carbonaceous aerosols in Xi'an, China:Primary emissions and secondary formation constrained by radiocarbon

To investigate the sources and formation mechanisms of carbonaceous aerosols, a major contributor to severe particulate air pollution, radiocarbon (C-14) measurements were conducted on aerosols sampled from November 2015 to November 2016 in Xi'an, China. Based on the C-14 content in elemental carbon (EC), organic carbon (OC) and water-insoluble OC (WIOC), contributions of major sources to carbonaceous aerosols are estimated over a whole seasonal cycle: primary and secondary fossil sources, primary biomass burning, and other non-fossil carbon formed mainly from secondary processes. Primary fossil sources of EC were further sub-divided into coal and liquid fossil fuel combustion by complementing C-14 data with stable carbon isotopic signatures. The dominant EC source was liquid fossil fuel combustion (i.e., vehicle emissions), accounting for 64 % (median; 45 %-74 %, interquartile range) of EC in autumn, 60 % (41 %-72 %) in summer, 53 % (33 %-69 %) in spring and 46 % (29 %-59 %) in winter. An increased contribution from biomass burning to EC was observed in winter (similar to 28 %) compared to other seasons (warm period; similar to 15 %). In winter, coal combustion (similar to 25 %) and biomass burning equally contributed to EC, whereas in the warm period, coal combustion accounted for a larger fraction of EC than biomass burning. The relative contribution of fossil sources to OC was consistently lower than that to EC, with an annual average of 47 +/- 4 %. Non-fossil OC of secondary origin was an important contributor to total OC (35 +/- 4 %) and accounted for more than half of non-fossil OC (67 +/- 6 %) throughout the year. Secondary fossil OC (SOCfossil) concentrations were higher than primary fossil OC (POCfossil) concentrations in winter but lower than POCfossil in the warm period. Fossil WIOC and water-soluble OC (WSOC) have been widely used as proxies for POCfossil and SOCfossil, respectively. This assumption was evaluated by (1) comparing their mass concentrations with POCfossil and SOCfossil and (2) comparing ratios of fossil WIOC to fossil EC to typical primary OC-to-EC ratios from fossil sources including both coal combustion and vehicle emissions. The results suggest that fossil WIOC and fossil WSOC are probably a better approximation for primary and secondary fossil OC, respectively, than POCfossil and SOCfossil estimated using the EC tracer method

Measurement report:Dual-carbon isotopic characterization of carbonaceous aerosol reveals different primary and secondary sources in Beijing and Xi'an during severe haze events

To mitigate haze pollution in China, a better understanding of the sources of carbonaceous aerosols is required due to the complexity in multiple emissions and atmospheric processes. Here we combined the analysis of radiocarbon and the stable isotope 13C to investigate the sources and formation of carbonaceous aerosols collected in two Chinese megacities (Beijing and Xi'an) during severe haze events of a "red alarm"level from December 2016 to January 2017. The haze periods with daily PM2:5 concentrations as high as ∼400 μgm-3 were compared to subsequent clean periods (i.e., PM2:5 less than median concentrations during the winter 2016/2017) with PM2:5 concentrations below 100 μgm-3 in Xi'an and below 20 μgm-3 in Beijing. In Xi'an, liquid fossil fuel combustion was the dominant source of elemental carbon (EC; 44 %-57 %), followed by biomass burning (25 %-29 %) and coal combustion (17 %-29 %). In Beijing, coal combustion contributed 45 %-61% of EC, and biomass burning (17 %-24 %) and liquid fossil fuel combustion (22 %-33 %) contributed less. Non-fossil sources contributed 51 %-56% of organic carbon (OC) in Xi'an, and fossil sources contributed 63 %-69% of OC in Beijing. Secondary OC (SOC) was largely contributed by non-fossil sources in Xi'an (56∼6 %) and by fossil sources in Beijing (75∼10 %), especially during haze periods. The fossil vs. non-fossil contributions to OC and EC did not change drastically during haze events in both Xi'an and Beijing. However, compared to clean periods, the contribution of coal combustion to EC during haze periods increased in Xi'an and decreased in Beijing. During clean periods, primary OC from biomass burning and fossil sources constituted ∼70% of OC in Xi'an and ∼53% of OC in Beijing. From clean to haze periods, the contribution of SOC to total OC increased in Xi'an but decreased in Beijing, suggesting that the contribution of secondary organic aerosol formation to increased OC during haze periods was more efficient in Xi'an than in Beijing. In Beijing, the high SOC fraction in total OC during clean periods was mainly due to an elevated contribution from non-fossil SOC. In Xi'an, a slight day-night difference was observed during the clean period with enhanced fossil contributions to OC and EC during the day. This day-night difference was negligible during severe haze periods, likely due to the enhanced accumulation of pollutants under stagnant weather conditions

Differential responses of carbon-degrading enzyme activities to warming: implications for soil respiration

Extracellular enzymes catalyze rate‐limiting steps in soil organic matter decomposi-tion, and their activities (EEAs) play a key role in determining soil respiration (SR).Both EEAs and SR are highly sensitive to temperature, but their responses to cli-mate warming remain poorly understood. Here, we present a meta‐analysis on theresponse of soil cellulase and ligninase activities and SR to warming, synthesizingdata from 56 studies. We found that warming significantly enhanced ligninase activ-ity by 21.4% but had no effect on cellulase activity. Increases in ligninase activitywere positively correlated with changes in SR, while no such relationship was foundfor cellulase. The warming response of ligninase activity was more closely related tothe responses of SR than a wide range of environmental and experimental method-ological factors. Furthermore, warming effects on ligninase activity increased withexperiment duration. These results suggest that soil microorganisms sustain long‐term increases in SR with warming by gradually increasing the degradation of therecalcitrant carbon pool

A computerized scheme for lung nodule detection in multiprojection chest radiography: Lung nodule detection in multiprojection chest radiography

Purpose: Our previous study indicated that multiprojection chest radiography could significantly improve radiologists’ performance for lung nodule detection in clinical practice. In this study, the authors further verify that multiprojection chest radiography can greatly improve the performance of a computer-aided diagnostic (CAD) scheme