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Tan Long,Li Songyang,Zhao Liangyin,Wang Lulu,Zhao Xiuxiu 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.11
This study employs the microshear test method to examine the local mechanical properties of narrow-gap welded joints, revealing the mechanical inhomogeneity by evaluating the microshear strength, stress‒strain curves, and failure strain. On this basis, the influence of weld joints micromechanical inhomogeneity on the crack tip opening displacement (CTOD) fracture toughness is investigated. From the root weld layer to the cover weld layer, the fracture toughness at the center of the weld seam demonstrates an increasing trend, with the experimental and calculated CTOD values showing a good correspondence. The microproperties of the welded joints significantly impact the load-bearing capacity and fracture toughness. During the deformation process of the “low-matching” microregions, the plastic zone expansion is hindered by the surrounding microregion strength constraints, thus reducing the fracture toughness. In contrast, during the deformation of the “high-matching” microregions, the surrounding microregions absorb some of the loading energy, partially releasing the concentrated stress at the crack tip, which in turn increases the fracture toughness.
Effect of welding residual stress on operating stress of nuclear turbine low pressure rotor
Tan Long,Zhao Liangyin,Zhao Pengcheng,Wang Lulu,Pan Jiajing,Zhao Xiuxiu 한국원자력학회 2020 Nuclear Engineering and Technology Vol.52 No.8
The purpose of this study is to investigate the effect of welding residual stress on operating stress in designing a nuclear turbine welded rotor. A two-dimensional axisymmetric finite element model is employed to calculate the residual stress before and after post weld heat treatment (PWHT), and then the superposition of residual stress after PWHT and operating stress at normal speed and overspeed were discussed. The investigated results show that operating stress can be affected significantly by welding residual stress, and the distribution trend of superposition stress at the weld area is mainly determined by welding residual stress. The superposition of residual stress and operating stress is linear superposition, and the hoop stress distribution of superposition stress is similar with the distribution of residual stress. With the increasing overspeed, the distribution pattern of the hoop superimposed stress remains almost unchanged, while the stress level increases
A superelement formulation for efficient structural analysis in progressive collapse
Long, Xu,Yuan, Weifeng,Tan, Kang Hai,Lee, Chi King Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.3
An integrated superelement concept is proposed to improve the computational efficiency when analyzing structural responses during progressive collapses of large-scale structures, such as multi-storey reinforced concrete buildings. While the proposed methodology is straightforward and can be implemented into an existing finite element program with little effort, it is able to significantly reduce the computational cost without the loss of any critical information of the structural responses. Compared with the models without superelement, significant saving in computational cost and satisfactory prediction accuracy can be obtained with the proposed approach.
Tan, Guo-Jin,Cheng, Yong-Chun,Liu, Han-Bing,Wang, Long-Lin Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.38 No.3
Input excitation and output response of structure are needed in conventional modal analysis methods. However, input excitation is often difficult to be obtained in the dynamic load test of bridge structures. Therefore, what attracts engineers' attention is how to get dynamic parameters from the output response. In this paper, a structural experimental modal analysis method is introduced, which can be used to conveniently obtain dynamic parameters of the structure from the free decay response. With known damping coefficients, this analysis method can be used to identify the natural frequencies and the mode shapes of MDOF structures. Based on the modal analysis theory, the mathematical relationship of damping ratio and frequency is obtained. By using this mathematical relationship to improve the previous method, an improved experimental modal analysis method is proposed in this paper. This improved method can overcome the deficiencies of the previous method, which can not identify damping ratios and requires damping coefficients in advance. Additionally, this improved method can also identify the natural frequencies, mode shapes and damping ratios of the bridge only from the free decay response, and ensure the stability of identification process by using modern mathematical means. Finally, the feasibility and effectiveness of this method are demonstrated by a numerical example of a simply supported reinforced concrete beam.
A 3D co-rotational beam element for steel and RC framed structures
Long, Xu,Tan, Kang Hai,Lee, Chi King Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.5
A 3-node 3D co-rotational beam element using vectorial rotational variables is employed to consider the geometric nonlinearity in 3D space. To account for shape versatility and reinforced concrete cross-sections, fibre model has been derived and conducted. Numerical integration over the cross-section is performed, considering both normal and shear stresses. In addition, the derivations associated with material nonlinearity are given in terms of elasto-plastic incremental stress-strain relationship for both steel and concrete. Steel reinforcement is treated as elasto-plastic material with Von Mises yield criterion. Compressive concrete behaviour is described by Modified Kent and Park model, while tensile stiffening effect is taken into account as well. Through several numerical examples, it is shown that the proposed 3D co-rotational beam element with fibre model can be used to simulate steel and reinforced concrete framed structures with satisfactory accuracy and efficiency.
Tan, Xue Fei,Kim, Dae Wook,Song, Yeong Hun,Kim, Jeong Yoon,Yuk, Heung Joo,Wang, Yan,Curtis-Long, Marcus J.,Park, Ki Hun Informa UK (Informa Healthcare) 2016 Journal of enzyme inhibition and medicinal chemist Vol.31 No.-
<P>Campylotropis hirtella is used as a food supplement in the subtropical region of China. In an intensive hunt for human neutrophil elastase inhibitors, we isolated eight flavonoids from C. hirtella three of which (1-3) emerged to be elastase inhibitors. Geranylated flavonoids (1-3) displayed significant inhibitory activity with IC(50)s between 8.5 and 30.8 mu M. The most striking example was geranylated isofavanone 3 that inhibited elastase significantly (IC50 = 30.8 mu M) but its parent compound (dalbergioidin) and isoflavone analog (5) were inactive (IC50 > 200 mu M). Compounds (1-3) displayed different kinetic mechanisms (noncompetitive, competitive, and mixed type, respectively) that were dependent upon the parent skeleton. The competitive inhibitor, isoflavan-3-ol-4-one 2 manifested an inhibition of isomerization profile for elastase with kinetic parameters K-5 = 0.0386 M-1 S-1, K-6 = 0.0244 mu M-1 S-1 and K-i(app) = 16.3427 mu M. The specific identification of metabolites was accomplished by LC-DAD-ESI/MS that was also used to analyze abundance of active components (1-3) within the plant.</P>
Long, Le Ngoc,Thi, Pham Tan,Trung Kien, Pham,Trung, Pham Thanh,Ohtani, Masataka,Kumabe, Yoshitaka,Tanaka, Hirofumi,Ueda, Shigenori,Lee, Hyoyoung,Thang, Phan Bach,Khai, Tran Van Elsevier 2020 APPLIED SURFACE SCIENCE - Vol.504 No.-
<P><B>Abstract</B></P> <P>In this study, a novel hydrothermal route has been developed for the synthesis of MoS<SUB>2</SUB>/graphene composite with controllable structures, in which ammonium molybdatetetrahydrate, as-prepared graphene oxide (GO), and thioacetamide were used as staring materials. Effects of Mo<SUP>4+</SUP>-to-C precursor ratios and crystalline time on the structures, components and morphologies of MoS<SUB>2</SUB>/graphene were investigated. MoS<SUB>2</SUB>/graphene samples were characterized using XRD, FESEM, HRTEM, FTIR, Raman spectroscopy, HAADF-STEM/EDS, HXPES and electrical measurements. The results show that petal-like MoS<SUB>2</SUB> nanostructures with ultrathin petals (~1–10 layers) and coexistence of 1T- and 2H-MoS<SUB>2</SUB> phases can be synthesized on graphene surface in a short time (~2 h). Comparison of crystallization conditions, we found that the crystallization time had a significant effect on the size of the MoS<SUB>2</SUB> nanopetals. The shorter the reaction time is, the thinner the petal-like MoS<SUB>2</SUB> nanoscale is. On the other hand, by adjusting the ratios of Mo<SUP>4+</SUP>to C (denoted as: MoS<SUB>2</SUB>/C (1:2), MoS<SUB>2</SUB>/C (3:2), MoS<SUB>2</SUB>/C (2.5:1) and MoS<SUB>2</SUB>/C (3:1)), different MoS<SUB>2</SUB>/graphene architectures including “sandwich-liked”, “layer–by–layer” and “anchored” can be obtained. On the basis of these results, a possible growth mechanism of MoS<SUB>2</SUB>nanopetals on GO was proposed. Interestingly, the as-synthesized material depicts its memristive behavior through the Volt-Ampere characteristics, suggesting a potential application in logic memory devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel hydrothermal route has been developed for the synthesis of MoS<SUB>2</SUB>/graphene composite with controllable structures. </LI> <LI> The effects of Mo<SUP>4+</SUP>-to-C precursor ratios and crystalline time on properties of MoS<SUB>2</SUB>/graphene were investigated by FESEM, HRTEM, XRD, FTIR, Raman spectroscopy, HAADF-STEM/EDS and HXPES. </LI> <LI> The memristive properties of the MoS<SUB>2</SUB>/graphenenanocomposite were presented. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Tan, Xuefei,Song, Yeong Hun,Park, Chanin,Lee, Ki-Won,Kim, Jeong Yoon,Kim, Dae Wook,Kim, Kwang Dong,Lee, Keun Woo,Curtis-Long, Marcus J.,Park, Ki Hun Pergamon 2016 Bioorganic & medicinal chemistry Vol.24 No.2
<P>Tyrosinase inhibition may be a means to alleviate not only skin hyperpigmentation but also neurodegeneration associated with Parkinson's disease. In the course of metabolite analysis from tyrosinase inhibitory methanol extract (80% inhibition at 20 mu g/ml) of Campylotropis hirtella, we isolated fourteen phenolic compounds, among which neorauflavane 3 emerged as a lead structure for tyrosinase inhibition. Neorauflavane 3 inhibited tyrosinase monophenolase activity with an IC50 of 30 nM. Thus this compound is 400-fold more active than kojic acid. It also inhibited diphenolase (IC50 = 500 nM), significantly. Another potent inhibitor 1 (IC50 = 2.9 mu M) was found to be the most abundant metabolite in C. hirtella. In kinetic studies, compounds 3 showed competitive inhibitory behavior against both monophenolase and diphenolase. It manifested simple reversible slow-binding inhibition against monophenolase with the following kinetic parameters: K-i(app) = 1.48 nM, k(3) = 0.0033 nM (1) min (1) and k(4) = 0.0049 min (1). Neorauflavane 3 efficiently reduced melanin content in B16 melanoma cells with 12.95 mu M of IC50. To develop a pharmacophore model, we explored the binding mode of neuroflavane 3 in the active site of tyrosinase. Docking results show that resorcinol motif of B-ring and methoxy group in A-ring play crucial roles in the binding the enzyme. (C) 2015 Elsevier Ltd. All rights reserved.</P>