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1,030 results on '"Rao Feng"'

1. Ultrahigh-temperature ferromagnetism in ultrathin insulating films with ripple-infinite-layer structure

Author

Yi, Yazhuo, Huang, Haoliang, Shao, Ruiwen, Liu, Yukuai, Chen, Guangzheng, Ou, Jiahui, Zhang, Xi, Hua, Ze, Chen, Lang, Leung, Chi Wah, Zeng, Xie-Rong, Rao, Feng, Liu, Nan, Wang, Heng, Si, Liang, An, Hongyu, Chen, Zhuoyu, and Huang, Chuanwei

Subjects
Condensed Matter - Materials Science
Abstract

Ferromagnetism and electrical insulation are often at odds, signifying an inherent trade off. The simultaneous optimization of both in one material, essential for advancing spintronics and topological electronics, necessitates the individual manipulation over various degrees of freedom of strongly correlated electrons. Here, by selective control of the spin exchange and Coulomb interactions, we report the achievement of SrFeO2 thin films with resistivity above 106 Ohm.cm and strong magnetization with Curie temperature extrapolated to be 1200 K. Robust ferromagnetism is obtained down to 1.0 nm thickness on substrate and 2.0 nm for freestanding films. Featuring an out of plane oriented ripple infinite layer structure, this ferromagnetic insulating phase is obtained through extensive reduction of as grown brownmillerite SrFeO2.5 films at high compressive strains. Pronounced spin Hall magnetoresistance signals up to 0.0026 is further demonstrated with a Pt Hall bar device. Our findings promise emerging spintronic and topological electronic functionalities harnessing spin dynamics with minimized power dissipations.

Published
2024

22. Nutritional Regulation Influencing Colony Dynamics and Task Allocations in Social Insect Colonies

Author

Rao, Feng, Messan, Marisabel Rodriguez, Marquez, Angelica, Smith, Nathan, and Kang, Yun

Subjects
Quantitative Biology - Populations and Evolution
Abstract

In this paper, we use an adaptive modeling framework to model and study how nutritional status (measured by the protein to carbohydrate ratio) may regulate population dynamics and foraging task allocation of social insect colonies. Mathematical analysis of our model shows that both investment to brood rearing and brood nutrition are important for colony survival and dynamics. When division of labor and/or nutrition are in an intermediate value range, the model undergoes a backward bifurcation and creates multiple attractors due to bistability. This bistability implies that there is a threshold population size required for colony survival. When the investment in brood is large enough or nutritional requirements are less strict the colony tends to survive, otherwise the colony faces collapse. Our model suggests that the needs of colony survival are shaped by the brood survival probability, which requires good nutritional status. As a consequence, better nutritional status can lead to a better survival rate of larvae, and thus a larger worker population., Comment: 27 pages, 7 figures

Published
2020

32. Progressive amorphization of GeSbTe phase-change material under electron beam irradiation

Author

Jiang, Ting-Ting, Wang, Jiang-Jing, Lu, Lu, Ma, Chuan-Sheng, Zhang, Dan-Li, Rao, Feng, Jia, Chun-Lin, and Zhang, Wei

Subjects
Condensed Matter - Materials Science
Abstract

Fast and reversible phase transitions in chalcogenide phase-change materials (PCMs), in particular, Ge-Sb-Te compounds, are not only of fundamental interests, but also make PCMs based random access memory (PRAM) a leading candidate for non-volatile memory and neuromorphic computing devices. To RESET the memory cell, crystalline Ge-Sb-Te has to undergo phase transitions firstly to a liquid state and then to an amorphous state, corresponding to an abrupt change in electrical resistance. In this work, we demonstrate a progressive amorphization process in GeSb2Te4 thin films under electron beam irradiation on transmission electron microscope (TEM). Melting is shown to be completely absent by the in situ TEM experiments. The progressive amorphization process resembles closely the cumulative crystallization process that accompanies a continuous change in electrical resistance. Our work suggests that if displacement forces can be implemented properly, it should be possible to emulate symmetric neuronal dynamics by using PCMs.

Published
2019
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40. Influence of Wastes and Synthesis Conditions on the Compressive Strength, Setting Time and Gels of Waste-Based Geopolymers.

Author

Wang, Tianyu, Rao, Feng, Yang, Lang, Jiang, Kaixi, Lin, Nanan, and Mo, Liwei

Subjects
HEAT of hydration, HEAT conduction, SCANNING electron microscopy, IRON ores, MICROENCAPSULATION
Abstract

In civil engineering, both rapid setting and delayed setting are needed for various application scenarios. In order to regulate the setting time of concrete, the iron ore tailings-blast furnace slag (IOT-BFS)-based geopolymers were synthesized with a broad range of setting time and a high compressive strength in this study. The factors of iron ore tailings content, alkali content, liquid–solid ratio, and modulus of alkali activator on setting time of the geopolymers were analyzed. The setting times of geopolymers are tested by a manual Vicat apparatus, and their microstructure is characterized by scanning electron microscopy (SEM), as well as that the hydration heat flow is characterized by an isothermal heat conduction calorimeter (TAM Air). It is found that setting time of the geopolymers was mostly affected by the modulus of alkaline activators due to the reasons that changes in modulus lead to the accelerated hydration reaction, formation of low-polymeric silicates, generation of gels, and encapsulation of precursor particles caused by high viscosity. Adjusting the modulus of the alkaline activator to 0.8 can control the initial setting time of the geopolymers to around 3 min. When the modulus ranges from 1–1.8, the initial setting time fell in the range of 15–45 min. For an alkaline activator modulus of 2, the initial setting time increased to 108 min. This study gives a clue for the preparation of geopolymers with adjustable setting times for multi-scenario applications in construction materials. [ABSTRACT FROM AUTHOR]

Published
2024
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41. Tuning the 5d State of Pr3+ in Oxyhalides for Efficient Deep Ultraviolet Upconversion.

Author

Du, Yangyang, Jin, Zhengyuan, Li, Ziyu, Sun, Tianying, Meng, Haotian, Jiang, Xiaojuan, Wang, Yu, Peng, Dengfeng, Li, Jianwei, Wang, Aiwu, Zou, Hua, Rao, Feng, Wang, Feng, and Chen, Xian

Subjects
VISIBLE spectra, LIGHT absorption, XENON, PRASEODYMIUM, LAMPS, PHOTON upconversion
Abstract

Visible‐to‐ultraviolet (UV) upconversion provides a fascinating strategy to achieve deep UV emission through readily accessible visible light. However, the intensity of deep UV emission obtained through visible‐to‐UV upconversion progress is still far from satisfactory, severely constraining its practical applications. Herein, a novel class of praseodymium ion (Pr3+)‐doped rare‐earth oxyhalides (YOCl, YOBr, and LuOBr) to achieve efficient upconverted deep UV emission in the spectral range of 250–350 nm is developed. The upconverted UV emission intensity of LuOBr:Pr3+ is determined to be 56.7 times stronger than that of the well‐established Lu7O6F9:Pr3+. When employed as a photon‐converter to activate photocatalytic water splitting reactions, upconverted deep UV emission enables H2 generation under visible light (λ > 420 nm) excitation from a xenon lamp. The efficient deep UV upconversion stems from tuning 4f15d1 state of Pr3+ by oxyhalide constituent which both facilitates the absorption of excitation photons in long‐lived intermediate 4f2 states and suppress the probability of nonradiative relaxation from 4f15d1 state. These findings not only provide new insights into a mechanistic understanding of the host effect on upconversion process but also make a breakthrough in developing efficient deep upconversion materials that will expand their further applications. [ABSTRACT FROM AUTHOR]

Published
2024
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