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Li, Yang

Publications and source records attributed to Li, Yang.

At least 181 records · Page 10
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DOE OSTI2018

Ce-Substituted M-Type SrFe{sub 12}O{sub 19} Ferrites: Phase Formation and Magnetic Properties

Ce-substituted hexagonal M-type SrCe{sub x}Fe{sub 12−x} O{sub 19} ferrites were prepared via a ceramic method, and their structural and magnetic properties were studied. It is found that in order to prepare the single-phase SrM ferrite, the atomic ratio of Sr/(Fe + Ce) should be 1:9.5 and the substituted amount (x) should be less than 0.04. The Ce substitution can improve the saturation magnetization to a certain degree, and both the impurities and the lattice distortion that resulted from the Ce substitution can enhance the coercivity markedly.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Experimental Investigation and Finite Element Analysis on Fatigue Behavior of Aluminum Alloy 7050 Single-Lap Joints

The fatigue behavior of single-lap four-riveted aluminum alloy 7050 joints was investigated by using high-frequency fatigue test and scanning electron microscope (SEM). Stress distributions obtained by finite element (FE) analysis help explain the fatigue performance. The fatigue test results showed that the fatigue lives of the joints depend on cold expansion and applied cyclic loads. FE analysis and fractography indicated that the improved fatigue lives can be attributed to the reduction in maximum stress and evolution of fatigue damage at the critical location. The beneficial effects of strengthening techniques result in tearing ridges or lamellar structure on fracture surface, decrease in fatigue striations spacing, delay of fatigue crack initiation, crack deflection in fatigue crack propagation and plasticity-induced crack closure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Plasma Nitriding of AISI 304 Stainless Steel in Cathodic and Floating Electric Potential: Influence on Morphology, Chemical Characteristics and Tribological Behavior

In direct current plasma nitriding (DCPN), the treated components are subjected to a high cathodic potential, which brings several inherent shortcomings, e.g., damage by arcing and the edging effect. In active screen plasma nitriding (ASPN) processes, the cathodic potential is applied to a metal screen that surrounds the workload, and the component to be treated is placed in a floating potential. Such an electrical configuration allows plasma to be formed on the metal screen surface rather than on the component surface; thus, the shortcomings of the DCPN are eliminated. In this work, the nitrided experiments were performed using a plasma nitriding unit. Two groups of samples were placed on the table in the cathodic and the floating potential, corresponding to the DCPN and ASPN, respectively. The floating samples and table were surrounded by a steel screen. The DCPN and ASPN of the AISI 304 stainless steels are investigated as a function of the electric potential. The samples were characterized using scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffraction, atomic force microscopy and transmission electron microscope. Dry sliding ball-on-disk wear tests were conducted on the untreated substrate, DCPN and ASPN samples. The results reveal that all nitrided samples successfully produced similar nitrogen-supersaturated S phase layers on their surfaces. This finding also shows the strong impact of the electric potential of the nitriding process on the morphology, chemical characteristics, hardness and tribological behavior of the DCPN and ASPN samples.

36 MATERIALS SCIENCE↗
DOE OSTI2018

High glucose up-regulates microRNA-34a-5p to aggravate fibrosis by targeting SIRT1 in HK-2 cells

Highlights: • The expression of SIRT1 is declined and the level of miR-34a-5p is up-regulated in the kidneys of DN mice. • SIRT1 prevents TGF-β1-induced pro-fibrotic gene expression. • SIRT1 expression was declined time-dependently under high glucose in HK-2 cells. • MiR-34a-5p aggravate fibrosis through directly suppressing SIRT1. • MiR-34a-5p inhibitor reverse the expressions of downstream genes through SIRT1 in HK-2 cells. Tubulointerstitial fibrosis (TIF) is crucial in the development of renal fibrosis in diabetic nephropathy(DN). Previous data shows that SIRT1 plays an important role on fibrosis, but the effect on TIF in DN and underlying mechanisms remains uncertain. In this study, we evaluated the vital role of SIRT1 and identified SIRT1 as a downstream target gene of microRNA-34a-5p (miR-34a-5p) in TIF of DN. The result revealed that expression of miR-34a-5p, fibronectin(FN),collagen type I (COL1) and transforming growth factor β1 (TGF-β1) were up-regulated accompanied by the corresponding down-regulation of SIRT1 in renal tissues of high fat diet and streptozotocin(HFD/STZ)induced diabetic mice with DN, and that the SIRT1 mRNA level was negatively correlated with miR-34a-5p expression in high glucose stimulated human proximal tubule cell line(HK-2) cells. We then demonstrated that overexpression of SIRT1 reduced, whereas small interfering RNA targeting SIRT1 enhanced the expressions of TGF-β1 and fibrosis-related genes including FN and COL1 in HK-2 cells. Furthermore, we identified that miR-34a-5p directly suppressed SIRT1 to increase the profibrogenic effects of TGFβ1 through targeting the 3'untranslated region of SIRT1. The functional correlation of miR-34a-5p induced SIRT1 decrease was supported by overexpression and inhibition of miR-34a-5p in HK-2 cells. All the results reveal that SIRT1 which is vital in the evolution of renal TIF in DN can be directly suppressed by miR-34a-5p, and suggest that miR-34a-5p is a new target for DN treatment.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Multiscale finite element modeling of sheet molding compound (SMC) composite structure based on stochastic mesostructure reconstruction

Predicting the mechanical behavior of the chopped carbon fiber Sheet Molding Compound (SMC) due to spatial variations in local material properties is critical for the structural performance analysis but is computationally challenging. Such spatial variations are induced by the material flow in the compression molding process. In this work, a new multiscale SMC modeling framework and the associated computational techniques are developed to provide accurate and efficient predictions of SMC mechanical performance. The proposed multiscale modeling framework contains three modules. First, a stochastic algorithm for 3D chip-packing reconstruction is developed to efficiently generate the SMC mesoscale Representative Volume Element (RVE) model for Finite Element Analysis (FEA). A new fiber orientation tensor recovery function is embedded in the reconstruction algorithm to match reconstructions with the target characteristics of fiber orientation distribution. Second, a metamodeling module is established to improve the computational efficiency by creating the surrogates of mesoscale analyses. Third, the macroscale behaviors are predicted by an efficient multiscale model, in which the spatially varying material properties are obtained based on the local fiber orientation tensors. Our approach is further validated through experiments at both meso- and macro-scales, such as tensile tests assisted by Digital Image Correlation (DIC) and mesostructure imaging.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure-Property Correlations in Fiber Laser Welded Nb-Ti Microalloyed C-Mn Steel

Mechanical Performance of traditional gas-shielded arc welded joints of 700 MPa grade microalloyed C-Mn steel cannot meet service requirements. Laser welding, with its characteristic high energy density, is known to improve the welding performance of experimental steels. In the present study, Nb-Ti microalloyed steel with a thickness of 4.5 mm was welded using a 4 kW fiber laser. The microstructure, precipitation, and mechanical properties of the welded joints were studied. The hardness and tensile strength of the welded joints were higher than those of the base metal (BM). The microstructure of the fusion zone (FZ) and coarse grain heat affected zone (CGHAZ) was lath martensite (LM), while the microstructure of the fine grain HAZ and mixed grain HAZ consisted of ferrite and martensite/austenite islands. Although LM was observed in both the FZ and CGHAZ, the hardness and calculated tensile strength of the FZ were lower than those of the CGHAZ, due to a reduction in solid solution strengthening by element loss and the dissolution of high-hardness precipitates in FZ. Most precipitates such as [(Nb,Ti)C and (Nb,Ti)(C,N)] that were present in the BM were dissolved, which led to an increase in C and N in solid solution in the FZ. Thus, the elastic modulus of the FZ was higher than that of the BM. Similarly, the elastic modulus of the CGHAZ was higher than that of the BM due to the segregation of C and N atoms during the welding process. The toughness of the FZ was superior to that of the BM, and the toughness of the HAZ approached 91% of that of the BM. The change in toughness primarily depended on the microstructural refinement, the increase in the fraction of grains with high misorientation, the residual austenite in the FZ and CGHAZ, and the dissolution of coarse precipitates.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Correlation between failure and local material property in chopped carbon fiber chip-reinforced sheet molding compound composites under tensile load

To develop further understanding towards the role of a heterogeneous microstructure on tensile crack initiation and failure behavior in chopped carbon fiber chip-reinforced composites, uni-axial tensile tests are performed on coupons cut from compression molded plaque with varying directions. Our experimental results indicate that failure initiation is relevant to the strain localization, and a new criterion with the nominal modulus to predict the failure location is proposed based on the strain analysis. Furthermore, optical microscopic images show that the nominal modulus is determined by the chip orientation distribution. At the area with low nominal modulus, it is found that chips are mostly aligning along directions transverse to loading direction and/or less concentrated, while at the area with high nominal modulus, more chips are aligning to tensile direction. On the basis of failure mechanism analysis, it is concluded that transversely-oriented chips or resin-rich regions are easier for damage initiation, while longitudinally-oriented chips postpone the fracture. Good agreement is found among failure mechanism, strain localization and chip orientation distribution.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ultrasensitive tunability of the direct bandgap of 2D [Twp-dimensional] InSe flakes via strain engineering

InSe, a member of the layered materials family, is a superior electronic and optical material which retains a direct bandgap feature from the bulk to atomically thin few-layers and high electronic mobility down to a single layer limit. We, for the first time, exploit strain to drastically modify the bandgap of two-dimensional (2D) InSe nanoflakes. We demonstrated that we could decrease the bandgap of a few-layer InSe flake by 160 meV through applying an in-plane uniaxial tensile strain to 1.06% and increase the bandgap by 79 meV through applying an in-plane uniaxial compressive strain to 0.62%, as evidenced by photoluminescence (PL) spectroscopy. The large reversible bandgap change of ~239 meV arises from a large bandgap change rate (bandgap strain coefficient) of few-layer InSe in response to strain, ~154 meV/% for uniaxial tensile strain and ~140 meV/% for uniaxial compressive strain, representing the most pronounced uniaxial strain-induced bandgap strain coefficient experimentally reported in 2D materials. We developed a theoretical understanding of the strain-induced bandgap change through first-principles DFT and GW calculations. We also confirmed the bandgap change by photoconductivity measurements using excitation light with different photon energies. In conclusion, the highly tunable bandgap of InSe in the infrared regime should enable a wide range of applications, including electro-mechanical, piezoelectric and optoelectronic devices.

2D materials↗
DOE OSTI2018

Cancer stem cell-like population is preferentially suppressed by EGFR-TKIs in EGFR-mutated PC-9 tumor models

Highlights: • EGFR-TKIs strongly inhibited the β-catenin signal and decreased CSCs sorted out by SP cells. • The reduction of CSCs significantly reduced the migration capability. • Targeting β-catenin could be a potential strategy for EGFR-mutated NSCLC. Although the epidermal growth factor receptor (EGFR) and Wnt/β-catenin signaling systems synergistically regulate many essential developmental and regenerative processes in lung cancer, the mechanisms of their crosstalk remain poorly defined. Our study aimed to investigate an interaction between EGFR and the β-catenin signal.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Improvement of mechanical behaviors of a superlight Mg-Li base alloy by duplex phases and fine precipitates

Limitations of strength and formability are the major obstacles to the industrial application of magnesium alloys. Here, we demonstrate, by producing the duplex phases and fine intermetallic particles in composition-optimized superlight Mg-Li-Al alloys, a unique approach to simultaneously improve the comprehensive mechanical properties (a strength-ductility balance). In conclusion, the phase components and microstructures, including the size, morphology, and distribution of precipitated-intermetallic particles can be optimized by tuning the Li content, which strongly influences the work-hardening behavior and tension-compression yield asymmetry.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Anomalous Kondo resonance mediated by semiconducting graphene nanoribbons in a molecular heterostructure

An unusually large spin-coupling of almost 100% is found in vertically stacked molecular hetrostructures composed of cobalt-porphyrin based magnetic molecules adsorbed on semiconducting armchair graphene nanoribbon on a Au(111) surface. Although the graphene nanoribbons are electronically decoupled from the gold substrate due to their band gaps and weak adsorption, they enable spin coupling between the magnetic moment of the molecule and the electrons from the substrate exhibiting a Kondo resonance. Surprisingly, the Kondo temperatures corresponding to three adsorption sites of the molecules on Au(111) surface are reproduced on the molecules adsorb on the graphene nanoribbons although the molecules are located 7.5 Å away from the surface. This finding suggests that the molecules on graphene nanoribbons experience almost the same environment for spin-electron interactions as the ones directly adsorb on Au(111). This puzzling effect is further confirmed by density functional theory calculations that reveal no spin electron interactions if the molecule is left at the same height from the Au(111) surface without the graphene nanoribbon in between.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Theoretical Kinetics Analysis for $\dot{H}$ Atom Addition to 1,3-Butadiene and Related Reactions on the $\dot{C}$ 4 H 7 Potential Energy Surface

The oxidation chemistry of the simplest conjugated hydrocarbon, 1,3-butadiene, can provide a first step in understanding the role of poly-unsaturated hydrocarbons in combustion and, in particular, an understanding of their contribution towards soot formation. Based on our previous work on propene and the butene isomers (1-, 2- and isobutene), it was found that the reaction kinetics of H-atom addition to the C=C double bond plays a significant role in fuel consumption kinetics and influences the predictions of high-temperature ignition delay times, product species concentrations and flame speed measurements. In this study, the rate constants and thermodynamic properties for $\dot{H}$-atom addition to 1,3-butadiene and related reactions on the $\dot{C}$ 4 H 7 potential energy surface have been calculated using two different series of quantum chemical methods and two different kinetic codes. Excellent agreement is obtained between the two different kinetics codes. The calculated results including zero point energies, single point energies, rate constants, barrier heights and thermochemistry are systematically compared among the two quantum chemical methods. 1-methylallyl ($\dot{C}$ 4 H 7 1-3) and 3-buten-1- yl ($\dot{C}$ 4 H 7 1-4) radicals and C 2 H 4 + $\dot{C}$2H3 are found to be the most important channels and reactivity promoting products, respectively. We calculated that terminal addition is dominant (> 80%) compared to internal $\dot{H}$-atom addition at all temperatures in the range 298 – 2000 K. However, this dominance decreases with increasing temperature. The calculated rate constants for the bimolecular reaction C 4 H 6 + $\dot{H}$ → products and C 2 H 4 + $\dot{C}$ 2 H 3 → products are in excellent agreement with both experimental and theoretical results from the literature. For selected C 4 species the calculated thermochemical values are also in good agreement with literature data. In addition, the rate constants for H-atom abstraction by $\dot{H}$ atoms have also been calculated, and it is found that abstraction from the central carbon atoms is the dominant channel (> 70%) at temperatures in the range 298 – 2000 K. Lastly, by incorporating our calculated rate constants for both H-atom addition and abstraction into our recently developed 1,3-butadiene model, we show that laminar flame speed predictions are significantly improved, emphasizing the value of this study.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Tb{sup 3+} induced orange persistent luminescence in Cs{sub 2}CaP{sub 2}O{sub 7}:Eu{sup 2+}: The role of the auxiliary codopant

Highlights: • The orange persistent luminescence of Cs{sub 2}CaP{sub 2}O{sub 7}:Eu{sup 2+},Tb{sup 3+} was first reported. • The role of Tb{sup 3+} was discussed. • The TL curve reveals there are two traps responsible for the persistent luminescence. - Abstract: This study reports an orange emitting persistent phosphor Cs{sub 2}CaP{sub 2}O{sub 7}:Eu{sup 2+},Tb{sup 3+}. The material was synthesized by solid state reaction method in a reducing atmosphere. The persistent phosphor was characterized in detail by X-ray powder diffraction, photoluminescence, persistent luminescence and thermoluminescence spectra. After UV irradiation, Cs{sub 2}CaP{sub 2}O{sub 7}:Eu{sup 2+},Tb{sup 3+} phosphor shows an orange persistent luminescence (∼590 nm) at room temperature, whereas only photoluminescence is observed in Eu{sup 2+} singly doped samples. Both of the photoluminescence and persistent luminescence is due to the 4f{sup 6}5d{sup 1} → 4f{sup 7} transition of Eu{sup 2+} and the emission lines of Tb{sup 3+} are totally absent. The deconvolution of the thermoluminescence curve reveals there are two kinds of traps responsible for the persistent luminescence. The depth of the dominating trap is 0.61 eV. Based on experimental results, the role of Tb{sup 3+} and the trapping/detrapping processes of charge carriers were discussed. An energy level scheme was proposed to explain the mechanisms of persistent luminescence as well as photoluminescence.

36 MATERIALS SCIENCE↗