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Now showing items 65 - 80 of 104

  • Modeling copper precipitation hardening and embrittlement in a dilute Fe-0.3at.%Cu alloy under neutron irradiation

    Bai, Xian-Ming   Ke, Huibin   Zhang, Yongfeng   Spencer, Benjamin W.  

    Neutron irradiation in light water reactors can induce precipitation of nanometer sized Cu clusters in reactor pressure vessel steels. The Cu precipitates impede dislocation gliding, leading to an increase in yield strength (hardening) and an upward shift of ductile-to-brittle transition temperature (embrittlement). In this work, cluster dynamics modeling is used to model the entire Cu precipitation process (nucleation, growth, and coarsening) in a Fe-0.3at.% Cu alloy under neutron irradiation at 300 degrees C based on the homogenous nucleation mechanism. The evolution of the Cu cluster number density and mean radius predicted by the modeling agrees well with experimental data reported in literature for the same alloy under the same irradiation conditions. The predicted precipitation kinetics is used as input for a dispersed barrier hardening model to correlate the microstructural evolution with the radiation hardening and embrittlement in this alloy. The predicted radiation hardening agrees well with the mechanical test results in the literature. Limitations of the model and areas for future improvement are also discussed in this work. (C) 2017 Elsevier B.V. All rights reserved.
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  • Built-in electric field promotes photoexcitation separation and depletion of most carriers in TiO2:C UV detectors

    Li, Kanzhe   Zhu, Yue   Zhang, Yongfeng   Zhang, Dezhong   Zhou, Jingran   Li, Xin   Ruan, Shengping  

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  • Energetics and diffusional properties of He in BCC Mo: An empirical potential for molecular dynamics simulations

    Zhang, Yongfeng   Millett, Paul C.   Tonks, Michael  

    This paper presents an interatomic potential for modeling He defects and bubbles in body-centered-cubic (BCC) Mo. We utilize three existing frameworks: the Finnis-Sinclair (FS) potential for Mo-Mo, the Effective-Medium-Theory (EMT) for He-Mo, and the Hartree-Fock-Dispersion (HFD) potential for He-He interactions. The energetics of He defects and the diffusivity of He interstitial given by this potential agree well with ab initio calculations and experimental measurements. Furthermore, in agreement with theoretical prediction, it is shown that the introduction of He gas suppresses the surface diffusivity of BCC Mo, which decays exponentially with increasing He pressure acting on the free surface. The decay constant, correlated with the characteristic interaction volume for He-Mo, is close to the atomic volume of BCC Mo. This suppression effect is important to understand the mobility of small He bubbles. (C) 2011 Elsevier B.V. All rights reserved.
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  • Phase-field modeling of fission gas bubble growth on grain boundaries and triple junctions in UO2 nuclear fuel

    Aagesen, Larry K.   Schwen, Daniel   Tonks, Michael R.   Zhang, Yongfeng  

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  • Pharmacological Basis for Use of Armillaria mellea Polysaccharides in Alzheimer's Disease:Antiapoptosis and Antioxidation

    An, Shengshu   Lu, Wenqian   Zhang, Yongfeng   Yuan, Qingxia   Wang, Di  

    Armillaria mellea, an edible fungus, exhibits various pharmacological activities, including antioxidant and antiapoptotic properties. However, the effects of A. mellea on Alzheimer's disease (AD) have not been systemically reported. The present study aimed to explore the protective effects of mycelium polysaccharides (AMPS) obtained from A. mellea, especially AMPSc via 70% ethanol precipitation in a L-glutamic acid-(L-Glu-) induced HT22 cell apoptosis model and an AlCl3 plus D-galactose-(D-gal-) induced AD mouse model. AMPSc significantly enhanced cell viability, suppressed nuclear apoptosis, inhibited intracellular reactive oxygen species accumulation, prevented caspase-3 activation, and restored mitochondrial membrane potential (MMP). In AD mice, AMPSc enhanced horizontal movements in an autonomic activity test, improved endurance times in a rotarod test, and decreased escape latency time in a water maze test. Furthermore, AMPSc reduced the apoptosis rate, amyloid beta (A beta) deposition, oxidative damage, and p-Tau aggregations in the AD mouse hippocampus. The central cholinergic system functions in AD mice improved after a 4-week course of AMPSc administration, as indicated by enhanced acetylcholine (Ach) and choline acetyltransferase (ChAT) concentrations, and reduced acetylcholine esterase (AchE) levels in serum and hypothalamus. Our findings provide experimental evidence suggesting A. mellea as a neuroprotective candidate for treating or preventing neurodegenerative diseases.
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  • Selective sensing of Fe3+ ions in aqueous solution by a biodegradable platform based lanthanide metal organic framework

    Jia, Peng   Wang, Zhonghao   Zhang, Yongfeng   Zhang, Dan   Gao, Weichen   Su, Yan   Li, Youbing   Yang, Chaolong  

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  • Analysis of Chlorophyll-a Correlation to Determine Nutrient Limitations in the Coastal Waters of the Bohai Sea,China

    Mao, Xiaodan   Kuang, Cuiping   Gu, Jie   Kolditz, Olaf   Chen, Kuo   Zhang, Jianle   Zhang, Wanlei   Zhang, Yongfeng  

    The coastal water of Qinhuangdao, a famous resort located in the NW of the Bohai Sea, China, suffered algal bloom for a consecutive 3 years by 2011, causing great economic loss. Based on measurements at 46 sampling points in the study's coastal area in May, August, and October 2011, the seasonal and spatial characteristics of the chemical indicators and chlorophyll-a (Chl-a) were analyzed. The chemical indicators for pH, chemical oxygen demand (COD), and reactive silicate (SiO3-Si) showed higher concentrations in the summer than in the spring and fall, whereas the nutrients of reactive phosphate (PO4-P) and dissolved inorganic nitrogen (DIN) presented complex seasonal characteristics under the combined influence of abundant nutrients from rivers and nutrient consumption by large algal bloom in August. Subsequently, two methods a fuzzy, integrated assessment and an organic pollution index were used to characterize the organic pollution. The trophic status of most coastal waters were oligotrophic and mesotrophic, and most coastal waters were clean in spring and summer, except in the vicinity of the harbor and estuaries, where the organic pollution index was generally high. Finally, Pearson correlation coefficients of various variables were analyzed, which demonstrated that, commonly, there was a significant positive correlation between COD and Chl-a. Because algal blooms in August changed the nutrients structure of the coastal waters, Chl-a, in a remarkably high concentration, had significant correlation with NO2-N, the atomic N/P ratio, and the atomic N/Si ratio. The algal bloom aggravated the current P limitation, and the atomic N/P ratio, the PO4-P concentration, and the COD can be selected as the three most-sensitive indicators of algal bloom in Qinhuangdao coastal water. These findings have provided scientific supports for local authorities who are taking measures to control pollution emissions and to prevent the recurrence of algal blooms.
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  • Homogeneous hydride formation path in α-Zr: Molecular dynamics simulations with the charge-optimized many-body potential

    Zhang, Yongfeng   Bai, Xian-Ming   Yu, Jianguo   Tonks, Michael R.   Noordhoek, Mark J.   Phillpot, Simon R.  

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  • Homogeneous hydride formation path in alpha-Zr:Molecular dynamics simulations with the charge-optimized many-body potential

    Zhang, Yongfeng   Bai, Xian-Ming   Yu, Jianguo   Tonks, Michael R.   Noordhoek, Mark J.   Phillpot, Simon R.  

    A path for homogeneous gamma hydride formation in hcp alpha-Zr, from solid solution to the zeta and then the gamma hydride, was demonstrated using molecular static calculations and molecular dynamic simulations with the charge-optimized many-body (COMB) potential. Hydrogen has limited solubility in alpha-Zr. Once the solubility limit is exceeded, the stability of solid solution gives way to that of coherent hydride phases such as the zeta hydride by planar precipitation of hydrogen. At finite temperatures, the zeta hydride goes through a partial hcp-fcc transformation via 1/3 < 1 (1) over bar 00 > slip on the basal plane, and transforms into a mixture of gamma hydride and alpha-Zr. In the zeta hydride, slip on the basal plane is favored thermodynamically with negligible barrier, and is therefore feasible at finite temperatures without mechanical loading. The transformation process involves slips of three equivalent shear partials, in contrast to that proposed in the literature where only a single shear partial was involved. The adoption of multiple slip partials minimizes the macroscopic shape change of embedded hydride clusters and the shear strain accumulation in the matrix, and thus reduces the overall barrier needed for homogeneous gamma hydride formation. This formation path requires finite temperatures for hydrogen diffusion without mechanical loading. Therefore, it should be effective at the cladding operating conditions. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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  • Intramolecular dynamics. III. Theoretical studies of the CH overtone spectra for benzene

    Zhang, Yongfeng   Marcus, R. A.  

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  • The Antiosteoporosis Effects of Yishen Bugu Ye Based on Its Regulation on the Differentiation of Osteoblast and Osteoclast

    Li, Yangyang   Zhang, Yongfeng   Meng, Weiqi   Li, Yutong   Huang, Tao   Wang, Di   Hu, Min  

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  • Modeling and energy-based sway reduction control for tower crane systems with double-pendulum and spherical-pendulum effects

    Zhang, Menghua   Zhang, Yongfeng   Ji, Bing   Ma, Changhui   Cheng, Xingong  

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  • Retrospective study of the clinical characteristics and risk factors of rheumatoid arthritis-associated interstitial lung disease

    Zhang, Yongfeng   Li, Hongbin   Wu, Nawei   Dong, Xin   Zheng, Yi  

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  • Titanium complexes bearing amine bis(phenolate) ligands:Synthesis,structure and catalysis in ring-opening polymerization of lactide

    Wang, Baolong   Zhang, Jianing   Zhao, Huanqin   Huang, He   Zheng, Junpei   Wang, Liying   Sun, Junmin   Zhang, Yongfeng   Cao, Zhenzhu  

    Monomeric bis(isopropoxy) titanium complexes LTi((OPr)-Pr-i)(2) (L=3DOC6H2-4-R-1-6-R-2-2-CH2N[(CH2)(2)N(R-3)(2)]CH2-4-R-4-6-R-5-C6H2O, R-1=3DR-2=3DBu-t, R-3=3DEt, R-4=3DR-5=3DCl, (L-1)Ti((OPr)-Pr-i)(2); R-1=3DR-2=3DMe, R-3=3DEt, R-4=3DR-5=3DMe, (L-2)Ti((OPr)-Pr-i)(2); R-1=3DR-2=3DBu-t, R-3=3DEt, R-4=3DOMe, R-5=3DBu-t, (L-3)Ti((OPr)-Pr-i)(2); R-1=3DR-4=3DOMe, R-3=3DEt, R-2=3DR-5=3DBu-t, (L-4)Ti((OPr)-Pr-i)(2); R-1=3DR-2=3DBu-t, R-3=3DMe, R-4=3DOMe, R-5=3DBu-t, (L-5)Ti((OPr)-Pr-i)(2)) supported by amine bis(phenolate) ligands were synthesized and characterized using NMR spectroscopy and elemental analysis. The solid-state structure of (L-3)Ti((OPr)-Pr-i)(2) was determined using single-crystal X-ray diffraction. (L1-5)Ti((OPr)-Pr-i)(2) were all found to initiate the ring-opening polymerization of l-lactide and rac-lactide in a controlled manner at 110-160 degrees C. As shown by kinetic studies, (L-1)Ti((OPr)-Pr-i)(2) polymerized l-lactide faster than did (L2-5)Ti((OPr)-Pr-i)(2). In addition, good number-average molecular weight and narrow polydispersity index (1.00-1.71) of polymers were also obtained. The microstructure of the polymers and a possible mechanism of coordination-insertion of polymerization were evidenced by MALDI-TOF and H-1 NMR spectra of the polylactides.
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  • Reticular nickel microwires with assembled nanostructures: Synthesis, magnetism and catalysis for the growth of carbon nanotubes

    Ni, Xiaomin   Zhao, Qingbiao   Zhang, Yongfeng   Zheng, Huagui  

    Reticular nickel microwires assembled from different-shaped building blocks are fabricated by a simple, one-pot method in the absence of any surfactants or external magnetic field. The synthetic process involves the chemical reduction of a nickel complex with hydrazine under controlled reaction conditions. Our strategy focuses on the modulation of the reaction rate to control the shape of the subunits and their spontaneous assembly behavior, which avoids the need for surfactants or an external force. The nickel wires can be reproducibly created with the assistance of various complexants, such as citrate, tartrate, lactate, ethylenediamine, triethanolamine and diethanolamine, which proves the generality of this method. These nickel wires show variable magnetic properties and catalysis for the growth of carbon nanotubes in pyrolyzing acetone due to the nature of their microstructures. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
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  • The vibrational force constant and transition stress for diatomic molecules

    Zhang, Yongfeng   Hanson, David M.  

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