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12,922 results on '"Zheng Hui"'

103. Multi-scale Investigation of Chemical Short-Range Order and Dislocation Glide in the MoNbTi and TaNbTi Refractory Multi-Principal Element Alloys

Author

Zheng, Hui, Fey, Lauren T. W., Li, Xiang-Guo, Hu, Yong-Jie, Qi, Liang, Chen, Chi, Xu, Shuozhi, Beyerlein, Irene J., and Ong, Shyue Ping

Subjects
Condensed Matter - Materials Science
Abstract

Refractory multi-principal element alloys (RMPEAs) are promising materials for high-temperature structural applications. Here, we investigate the role of chemical short-range ordering (CSRO) on dislocation glide in two model RMPEAs - TaNbTi and MoNbTi - using a multi-scale modeling approach. A highly accurate machine learning interatomic potential was developed for the Mo-Ta-Nb-Ti system and used to demonstrate that MoNbTi exhibits a much greater degree of SRO than TaNbTi and the local composition has a direct effect on the unstable stacking fault energies (USFE). From mesoscale phase-field dislocation dynamics simulations, we find that increasing SRO leads to higher mean USFEs, thereby increasing the stress required for dislocation glide. The gliding dislocations experience significant hardening due to pinning and depinning caused by random compositional fluctuations, with higher SRO decreasing the degree of USFE dispersion and hence, amount of hardening. Finally, we show how the morphology of an expanding dislocation loop is affected by the applied stress, with higher SRO requiring higher applied stresses to achieve smooth screw dislocation glide.

Published
2022
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105. Diminished Advantage or Persistent Protection? A New Approach to Assess Immigrants Mortality Advantages Over Time.

Author

Zheng, Hui and Yu, Wei-Hsin

Subjects
Duration of residence, Gender, Immigrant health advantage, Mortality disparities by nativity, Race/ethnicity, Cross-Sectional Studies, Emigrants and Immigrants, Emigration and Immigration, Ethnicity, Health Status, Humans
Abstract

Much research has debated whether immigrants health advantages over natives decline with their duration at destination. Most such research has relied on (pooled) cross-sectional data and used years since immigration as a proxy for the duration of residence, leading to the challenge of distilling the duration effect from the confounding cohort-of-arrival and age-of-arrival effects. Because longitudinal studies tend to use self-rated health as the outcome, the changes they observed may reflect shifts in immigrants awareness of health problems. We illuminate the debate by examining how immigrants mortality risk-a relatively unambiguous measure tied to poor health-changes over time compared to natives mortality risk. Our analysis uses the National Health Interview Survey (1992-2009) with linked mortality data through 2011 (n = 875,306). We find a survival advantage for U.S. immigrants over the native-born that persisted or amplified during the 20-year period. Moreover, this advantage persisted for all immigrants, regardless of their race/ethnicity and gender or when they began their U.S. residence. This study provides unequivocal evidence that immigrant status health protection as reflected in mortality is stable and long-lasting.

Published
2022

106. Do Immigrants Health Advantages Remain After Unemployment? Variations by Race-Ethnicity and Gender.

Author

Zheng, Hui and Yu, Wei-hsin

Subjects
Gender, Immigration, Mortality, Nativity, Race/Ethnicity, Unemployment
Abstract

Immigrants tend to display more favorable health outcomes than native-born co-ethnics. At the same time, they face considerable employment instability. It is unclear whether immigrants job conditions may compromise their health advantage. Using U.S. National Health Interview Survey data, this study shows that the experience of unemployment reduces immigrants health advantage, but unemployed foreign-born Blacks, White women, and Asian women still have lower mortality rates than their native-born employed counterparts. Overall, unemployment is less detrimental to immigrants than to natives, and immigrants survival advantage after unemployment persists as their duration of residence extends. We further find substantial heterogeneity in the unemployment effect within immigrants. Asian immigrants display a much sharper gender difference in the mortality consequence of unemployment than other immigrants. Asian mens worse general health and substantially higher smoking rate, especially among the unemployed, lead them to fare much worse than Asian women following unemployment.

Published
2022

135. A Universal Machine Learning Model for Elemental Grain Boundary Energies

Author

Ye, Weike, Zheng, Hui, Chen, Chi, and Ong, Shyue Ping

Subjects
Condensed Matter - Materials Science, Physics - Computational Physics
Abstract

The grain boundary (GB) energy has a profound influence on the grain growth and properties of polycrystalline metals. Here, we show that the energy of a GB, normalized by the bulk cohesive energy, can be described purely by four geometric features. By machine learning on a large computed database of 361 small $\Sigma$ ($\Sigma < 10$) GBs of more than 50 metals, we develop a model that can predict the grain boundary energies to within a mean absolute error of 0.13 J m$^{-2}$. More importantly, this universal GB energy model can be extrapolated to the energies of high $\Sigma$ GBs without loss in accuracy. These results highlight the importance of capturing fundamental scaling physics and domain knowledge in the design of interpretable, extrapolatable machine learning models for materials science., Comment: 12 pages, 4 figures

Published
2022

146. Subsynchronous Oscillation Problem Research in the UHVDC System of a Regional Power Grid in China

Author

Qu Ying, Zhang Chao, Zheng Hui Ping, Xue Min, and Zhang Ying

Subjects
UHVDC, subsynchronous oscillation (SSO), PSCAD/EMTDC simulation, Engineering (General). Civil engineering (General), TA1-2040
Abstract

Along with the grid structure being more and more complex and the rapid development of the HVDC system, studying the subsynchronous oscillation (SSO) problem on HVDC system has more engineering practice significance. The paper studies subsynchronous oscillations problem of generators near the ±800kV UHVDC converter station, and analyzes the subsynchronous oscillation possibilities through PSCAD/EMTDC simulation. At last, though the researched UHVDC thermal plants have none SSO risk but it needs other measures to make the relevant generators return on normal operation.

Published
2016
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