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Hoang Anh Nguyen,Thi Nam Pham,Le Thanh Nguyen Huynh,Tran Ha Trang Nguyen,Viet Hai Le,Nguyen Thai Hoang,Thi Thom Nguyen,Thi Thu Trang Nguyen,Dai Lam Tran,Thi Mai Thanh Dinh The Korean Electrochemical Society 2024 Journal of electrochemical science and technology Vol.15 No.2
Due to its high theoretical capacity, Silicon (Si) has shown great potential as an anode material for lithium-ion batteries (LIBs). However, the large volume change of Si during cycling leads to poor cycling stability and low Coulombic efficiency. In this study, we synthesized Si/Carbon C45:Graphene composites using a ball-milling method with a fixed Si content (20%) and investigated the influence of the C45/Gr ratio on the electrochemical performance of the composites. The results showed that carbon C45 networks can provide good conductivity, but tend to break at Si locations, resulting in poor conductivity. However, the addition of graphene helps to reconnect the broken C45 networks, improving the conductivity of the composite. Moreover, the C45 can also act as a protective coating around Si particles, reducing the volume expansion of Si during charging/discharging cycles. The Si/C45:Gr (70:10 wt%) composite exhibits improved electrochemical performance with high capacity (~1660 mAh g<sup>-1</sup> at 0.1 C) and cycling stability (~1370 mAh g<sup>-1</sup> after 100 cycles). This work highlights the effective role of carbon C45 and graphene in Si/C composites for enhancing the performance of Si-based anode materials for LIBs.
Evaluation of axial strength in circular STCC columns using UHPC and UHPFRC
Le Hoang, An,Fehling, Ekkehard,Thai, Duc-Kien,Van Nguyen, Chau Elsevier 2019 Journal of constructional steel research Vol.153 No.-
<P><B>Abstract</B></P> <P>This study investigates the axial strength of circular steel tube confined concrete (STCC) columns with the employment of plain ultra high performance concrete (UHPC) and ultra high performance fiber reinforced concrete (UHPFRC) having compressive strengths of cylinders varying from 178.9 MPa and 198 MPa. UHPFRC used in this study had 1% and 2% volume fraction of steel fibers in the mixture. Eighteen specimens including both short and intermediate columns were cast and tested under concentric loading on the concrete core to generate the maximal confinement effect. Experimental results showed that the effect of steel fibers on the axial load versus axial strain responses, and on the enhancement of strength and ductility was insignificant, while the parameters of the steel tube and the concrete core length were found to play a major role. The ultimate loads of the tests presented herein were compared with those obtained from the predictions by seven analytical models and five existing design codes. The design expressions from these analytical models and codes were assessed. For the prediction of the ultimate loads of both short and intermediate column, the model by De Oliveira et al. [] was the most suitable approach among seven selected models, whereas the ACI provision [] was the best among five existing design codes. Furthermore, the experimental ultimate loads obtained from this study were combined with those from previous studies to examine the influence of different concrete strength ranges on the strength enhancement. Finally, unified formulae to predict the ultimate strength with a wide range of concrete strength up to 200 MPa were also proposed for both short and intermediate columns.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Tests on 18 circular STCC columns using UHPC and UHPFRC with compressive strength up to 200 MPa were conducted to evaluate the axial strength. </LI> <LI> The accuracy of seven analytical models and five existing design codes in prediction of the ultimate strength was assessed. </LI> <LI> The effect of concrete strength ranges including NSC, HSC, UHPC and UHPFRC on the strength enhancement of circular STCC columns was identified. </LI> <LI> The unified formulae for predicting the confined peak stress (<I>f</I> <SUB> <I>cc</I> </SUB>) and the ultimate load (<I>N</I> <SUB> <I>u</I> </SUB>) of circular STCC columns were proposed. </LI> </UL> </P>
Competency Gap in the Labor Market: Evidence from Vietnam
LE, Quan Thai Thuong,DOAN, Tam Ho Dan,NGUYEN, Quyen Le Hoang Thuy To,NGUYEN, Doang Thi Phuc Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.9
The relationship between education and work is of the greatest concern to individuals and society because they are the key drivers of growth and development. In the context of Industry 4.0, labor and educators are facing the challenges of big changes in the workplace. How to prepare undergraduate students for the world of employment has become the most important mission of higher education providers. This paper explored the competency gap in the labor market in Vietnam from the perspective of employees who have been dissatisfied with the current status. First, a qualitative method with the Delphi technique was applied to confirm this consensus in an employees' competency model. Then, the satisfaction level for each competency criterion was explored by applying the advance quantitative method, namely, best non-fuzzy performance approach. Lifelong learning was ranked first, followed by creativity and innovation, foreign languages, expertise and digitalization, adaptability, and finally, organizing and managing ability. Critical thinking and problem-solving were perceived to have the biggest gap. The order of competency satisfaction is useful in explaining the mismatch between education quality and labor market demand. The findings provide valuable guidelines for education managers who seek to bridge the competency gap and improve education quality.
Hydroxyapatite Nano-Rods/Chitosan Modified Glassy Carbon Electrode for Cu(II) Ions Determination
Hoang V. Tran,Chinh D. Huynh,Thu D. Le,Hong S. Hoang 대한금속·재료학회 2020 ELECTRONIC MATERIALS LETTERS Vol.16 No.4
In this work, we propose a simple approach for fabrication of an electrochemical sensor for copper (II) ion determination in aqueous solution based on using a hydroxyapatite nano-rods/chitosan (HA/CS) nanocomposite coated on glassy carbon electrode (GCE) surface. Firstly, hydroxyapatite (HA) nano-rods has been synthesized by a simple precipitation reactions using Ca(OH)2 slurry and orthophosphoric acid (H3PO4) as precursors. After that, as-synthesized HA was dispersed into chitosan (CS) matrix to HA/CS-modify GCE by a drop casting technique. Characteristic of HA and HA/CS coating on GCE have been analysed by Transmission/Scanning Electron Microscope (TEM/SEM), X-ray Diffraction (XRD) and Fourier-Transform infrared spectroscopy (FT-IR) techniques. Electrochemical activities of neat GCE, CS-modified GCEs (GCE/CS) and HA/CS-modified GCE (GCE/HA/CS) have been evaluated in sodium acetate (NaAc-HAc) buffer with presence/absence of Ni2+, Co2+ or Cu2+ ions to test whether sensitive and selective of these developed Cu2+ sensors. Evaluated results demonstrated that GCE/HA/CS sensor has a sensitivity to Cu2+ ion of 7.688 ± 0.5324 µA mM− 1, it is the most sensitive to Cu2+ ions compared with GCE or GCE/CS. In additional, proposed Cu2+ electrochemical sensor has been applied to determine Cu2+ ions concentration in tap water with a high recoveries was found.
Hoang Vinh Tran,Hai Van Nguyen,Doanh Viet Vu,Thu Dieu Le,Binh Thanh Nguyen,Dang Hai Le 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.2
We report here a simple approach for synthesis of carbon coated magnetite (C@MFe2O4, M=Co, Ni, Fe) with shell@core nanostructured composites that we used as magnetic-nanosorbents for direct yellow (DYG) and moderacid red (RS) as pollutant textile dyes removal via an adsorption process. The synthesized C@MFe2O4 was characterized by TEM, SEM, EDX, XRD, FT-IR and VSM techniques. TEM results indicated that C@MFe2O4 nanocomposites have 20-30 nm of MFe2O4 nanoparticle core and 2-3 nm in thickness of the amorphous carbon shell. The synthesized C@MFe2O4 nanocomposites have the zero point charge (pHZPC) at 5.5, which suggests that DYG and RS, anionic dyes can be adsorbed onto the C@MFe2O4 nanosorbents in the acidic medium. Adsorption of DYG and RS onto magnetic nanosorbents was optimized and adsorption thermodynamic parameters were evaluated, clearly indicating that the adsorption of RS onto synthesized magnetic-nanosorbents was facile more than that DYG. The adsorption isotherm data showed that the adsorption processes of DYG and RS onto Fe3O4 or C@MFe2O4 nanosorbents are more suitable for the Langmuir model than Freundlich model. The maximum adsorption capacity (qmax) of DYG dye onto Fe3O4, C@Fe3O4 and C@CoFe2O4 adsorbents was 14.641, 36.232 and 7.85mg g1, respectively; meanwhile, these values were 41.152, 61.728 and 39.683mg g1 for RS dye. These obtained data indicate that the developed Fe3O4, C@Fe3O4 and C@CoFe2O4 nanoparticles can be used as recoverable and recyclable adsorbents for not only organic pigments adsorption but also for heavy metal ion removal or protein extraction as well.
Diluents and Cryoprotectants for Cryopreservation of Filefish Thamnaconus modestus Sperm
Le, Minh-Hoang,Lim, Han-Kyu,Min, Byung-Hwa,Son, Maeng-Hyun,Lee, Jung-Uie,Chang, Young-Jin The Korean Society of Fisheries and Aquatic Scienc 2008 韓國養殖學會誌 Vol.21 No.1
The present study aimed to find the best diluent and cryoprotectant for sperm cryopreservation of filefish Thamnaconus modestus. Two kinds of artificial seminal plasma(ASP1, ASP2), 0.3 M glucose and marine fish Ringer's solution(MFRS) were employed as diluent. Dimethyl sulfoxide(DMSO) and methanol as cryoprotectant were selected for sperm cryopreservation. Sperm was diluted at the ratio of 1:3 with diluents containing cryoprotectants and adjusted for final concentration at 5%, 10%, 15% and 20%. Mixed milt was frozen at liquid nitrogen vapor after equilibration for 5 min. The highest motility($40.5{\pm}2.8%$) and swimming speed($81.5{\pm}4.1{\mu}m/s$) of frozen/thawed sperm were observed in ASP1 diluent containing 10% DMSO and in ASP2 containing 15% DMSO, respectively. Results showed that cryopreservation with ASP as diluent and DMSO as cryoprotectant could be adopted for long term storage of filefish sperm.
Le, Thi Thanh,Ha, Manh Tuan,Hoang, Le Minh,Vu, Ngoc Khanh,Kim, Jeong Ah,Min, Byung Sun The Korean Society of Pharmacognosy 2022 Natural Product Sciences Vol.28 No.3
In our study, sixteen known phenolic compounds, including quercetin (1), methyl gallate (2), caesalpiniaphenol C (3), 8S,8'S,7'R-(-)-lyoniresinol (4), 7,3',5'-trihydroxyflavanone (5), sappanchalcone (6), sappanone A (7), taxifolin (8), fisetin (9), fustin (10), (+)-catechin (11), brazilin (12), 3,4,5-trimethoxyphenyl β-ᴅ-glucopyranoside (13), 1-(2-methylbutyryl)phloroglucinol-glucopyranoside (14), (+)-epi-catechin (15), and astragalin (16) and one mixture of two conformers of protosappanin B (17/18) were isolated from the stems of Caesalpinia decapetala var. japonica. Their structures were elucidated based on a comparison of their physicochemical and spectral data with those of literature. To the best of our knowledge, this represents the first isolation of compounds 3, 4, 8, 9, and 10 from C. decapetala and compounds 13 and 14 from the Caesalpinia genus. All the isolated compounds were evaluated for their inhibitory effect against the α-glucosidase enzyme. Among them, two flavonols (1 and 9), one chalcone (6), and one homoisoflavanone (7) exhibited an inhibitory effect on α-glucosidase action with an IC<sub>50</sub> range value of 5.08-15.01 μM, stronger than that of the positive control (acarbose, IC<sub>50</sub> = 152.22 μM). Kinetic analysis revealed that compounds 1 and 9 showed non-competitive α-glucosidase inhibition, while the inhibition type was mixed for compounds 6 and 7.