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578 results on '"Vu, Tuan V."'

155. Oil-water interfaces with surfactants: A systematic approach to determine coarse-grained model parameters.

Author

Vu, Tuan V. and Papavassiliou, Dimitrios V.

Subjects
*OIL-water interfaces, *SURFACE active agents, *PARAMETER estimation, *COMPUTATIONAL chemistry, *INTERFACES (Physical sciences), *NONIONIC surfactants
Abstract

In order to investigate the interfacial region between oil and water with the presence of surfactants using coarse-grained computations, both the interaction between different components of the system and the number of surfactant molecules present at the interface play an important role. However, in many prior studies, the amount of surfactants used was chosen rather arbitrarily. In this work, a systematic approach to develop coarse-grained models for anionic surfactants (such as sodium dodecyl sulfate) and nonionic surfactants (such as octaethylene glycol monododecyl ether) in oil-water interfaces is presented. The key is to place the theoretically calculated number of surfactant molecules on the interface at the critical micelle concentration. Based on this approach, the molecular description of surfactants and the effects of various interaction parameters on the interfacial tension are investigated. The results indicate that the interfacial tension is affected mostly by the head-water and tail-oil interaction. Even though the procedure presented herein is used with dissipative particle dynamics models, it can be applied for other coarse-grained methods to obtain the appropriate set of parameters (or force fields) to describe the surfactant behavior on the oil-water interface. [ABSTRACT FROM AUTHOR]

Published
2018
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156. Atmospheric conditions and composition that influence PM2.5 oxidative potential in Beijing, China

Author

Campbell, Steven J., Wolfer, Kate, Utinger, Battist, Westwood, Joe, Zhang, Zhi Hui, Bukowiecki, Nicolas, Steimer, Sarah S., Vu, Tuan V., Xu, Jingsha, Straw, Nicholas, Thomson, Steven, Elzein, Atallah, Sun, Yele, Liu, Di, Li, Linjie, Fu, Pingqing, Lewis, Alastair C., Harrison, Roy M., Bloss, William J., Loh, Miranda, Miller, Mark R., Shi, Zongbo, and Kalberer, Markus

Subjects
complex mixtures
Abstract

Epidemiological studies have consistently linked exposure to PM2.5 with adverse health effects. The oxidative potential (OP) of aerosol particles has been widely suggested as a measure of their potential toxicity. Several acellular chemical assays are now readily employed to measure OP; however, uncertainty remains regarding the atmospheric conditions and specific chemical components of PM2.5 that drive OP. A limited number of studies have simultaneously utilised multiple OP assays with a wide range of concurrent measurements and investigated the seasonality of PM2.5 OP. In this work, filter samples were collected in winter 2016 and summer 2017 during the atmospheric pollution and human health in a Chinese megacity campaign (APHH-Beijing), and PM2.5 OP was analysed using four acellular methods: ascorbic acid (AA), dithiothreitol (DTT), 2,7-dichlorofluorescin/hydrogen peroxidase (DCFH) and electron paramagnetic resonance spectroscopy (EPR). Each assay reflects different oxidising properties of PM2.5, including particle-bound reactive oxygen species (DCFH), superoxide radical production (EPR) and catalytic redox chemistry (DTT/AA), and a combination of these four assays provided a detailed overall picture of the oxidising properties of PM2.5 at a central site in Beijing. Positive correlations of OP (normalised per volume of air) of all four assays with overall PM2.5 mass were observed, with stronger correlations in winter compared to summer. In contrast, when OP assay values were normalised for particle mass, days with higher PM2.5 mass concentrations (µg m−3) were found to have lower mass-normalised OP values as measured by AA and DTT. This finding supports that total PM2.5 mass concentrations alone may not always be the best indicator for particle toxicity. Univariate analysis of OP values and an extensive range of additional measurements, 107 in total, including PM2.5 composition, gas-phase composition and meteorological data, provided detailed insight into the chemical components and atmospheric processes that determine PM2.5 OP variability. Multivariate statistical analyses highlighted associations of OP assay responses with varying chemical components in PM2.5 for both mass- and volume-normalised data. AA and DTT assays were well predicted by a small set of measurements in multiple linear regression (MLR) models and indicated fossil fuel combustion, vehicle emissions and biogenic secondary organic aerosol (SOA) as influential particle sources in the assay response. Mass MLR models of OP associated with compositional source profiles predicted OP almost as well as volume MLR models, illustrating the influence of mass composition on both particle-level OP and total volume OP. Univariate and multivariate analysis showed that different assays cover different chemical spaces, and through comparison of mass- and volume-normalised data we demonstrate that mass-normalised OP provides a more nuanced picture of compositional drivers and sources of OP compared to volume-normalised analysis. This study constitutes one of the most extensive and comprehensive composition datasets currently available and provides a unique opportunity to explore chemical variations in PM2.5 and how they affect both PM2.5 OP and the concentrations of particle-bound reactive oxygen species.

Published
2021

157. Insight into PM2.5 Sources by Applying Positive Matrix Factorization (PMF) at an Urban and Rural Site of Beijing

Author

Srivastava, Deepchandra, Xu, Jingsha, Vu, Tuan V., Liu, Di, Li, Linjie, Fu, Pingqing, Hou, Siqi, Shi, Zongbo, and Harrison, Roy M.

Abstract

This study presents the source apportionment of PM2.5 performed by PMF on data collected at an urban (Institute of Atmospheric Physics – IAP) and a rural site (Pinggu-PG) in Beijing as part of the Atmospheric Pollution and Human Health in a Chinese megacity (APHH-Beijing) field campaigns. The campaigns were carried out from 9th November to 11th December 2016 and 22nd May to 24th June 2017. The PMF included both organic and inorganic species, and a seven-factor output provided the most reasonable solution for the PM2.5 source apportionment. These factors are interpreted to be traffic emissions, biomass burning, road dust, soil dust, coal combustion, oil combustion and secondary inorganics. Major contributors to PM2.5 mass were secondary inorganics (22–24 %), biomass burning (30–36 %), and coal combustion (20–21 %) sources during the winter period at both sites. Secondary inorganics (48 %), road dust (20 %) and coal combustion (17 %) showed the highest contribution during summer at PG, while PM2.5 particles were mainly composed of soil dust (35 %) and secondary inorganics (40 %) at IAP. Despite this, factors that were resolved based on metal signatures were not fully resolved and indicate a mixing of two or more sources. PMF results were also compared with sources resolved from another receptor model (i.e. CMB) and PMF performed on other measurements (i.e. online and offline aerosol mass spectrometry (AMS)) and showed a good agreement for some but not all sources. The biomass burning factor in PMF may contain aged aerosols as a good correlation was observed between biomass burning and oxygenated fractions (r2 = 0.6–0.7) from AMS. The PMF failed to resolve some sources identified by the CMB and AMS, and appears to overestimate the dust sources. A comparison with earlier PMF source apportionment studies from the Beijing area highlights the very divergent findings from application of this method.

Published
2021

158. Strain effects on electronic, optical properties and carriers mobility of Cs2SnI6 vacancy‐ordered double perovskite: A promising photovoltaic material.

Author

Rezini, Billel, Seddik, Taieb, Mouacher, Readh, Vu, Tuan V., Batouche, Mohammed, and Khyzhun, Oleg Y.

Subjects
CHARGE carrier mobility, POLAR effects (Chemistry), OPTICAL properties, ELECTRON mobility, CONDUCTION bands, CESIUM
Abstract

Perovskite halides have attracted substantial attention as materials for solar cell applications because of their fascinating optoelectronic and photovoltaic properties. We report the results of the first‐principles calculations of the strain effects on electronic and optical properties and carrier mobility of vacancy‐ordered Cs2SnI6 double perovskite. The calculated band gap energy of unstrained Cs2SnI6 is about 1.257 eV when using the Tran‐Blaha modified Becke Johnson (mBJ) exchange potential, which is in good agreement with experimental measurements. Under the applied strains, the energy band gap value increases up to 1.316 eV for −4% compressive strain and decreases to 1.211 eV for 4% tensile strain. This effect is mainly due to the fact that the conduction band minimum shifts under compressive and tensile strains. Based on carrier mobility calculations, we notice that under tensile strain the hole and electron carrier mobility diminish, whereas the carrier mobility increases by 16.3% for electrons and by 9.1% for holes under −4% compressive strain. Moreover, data of the calculated optical constants indicate that applied strains can affect the optical properties of Cs2SnI6 perovskite. [ABSTRACT FROM AUTHOR]

Published
2022
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163. Insight into PM2.5 sources by applying positive matrix factorization (PMF) at urban and rural sites of Beijing

Author

Moreno, Natalia [0000-0003-1488-2561], Srivastava, Deepchandra, Xu, Jingsha, Vu, Tuan V., Liu, Di, Li, Linjie, Fu, Pingqing, Hou, Siqi, Moreno, Natalia, Shi, Zongbo, Harrison, Roy M., Moreno, Natalia [0000-0003-1488-2561], Srivastava, Deepchandra, Xu, Jingsha, Vu, Tuan V., Liu, Di, Li, Linjie, Fu, Pingqing, Hou, Siqi, Moreno, Natalia, Shi, Zongbo, and Harrison, Roy M.

Abstract

This study presents the source apportionment of PM2.5 performed by positive matrix factorization (PMF) on data presented here which were collected at urban (Institute of Atmospheric Physics – IAP) and rural (Pinggu – PG) sites in Beijing as part of the Atmospheric Pollution and Human Health in a Chinese megacity (APHH-Beijing) field campaigns. The campaigns were carried out from 9 November to 11 December 2016 and from 22 May to 24 June 2017. The PMF analysis included both organic and inorganic species, and a seven-factor output provided the most reasonable solution for the PM2.5 source apportionment. These factors are interpreted as traffic emissions, biomass burning, road dust, soil dust, coal combustion, oil combustion, and secondary inorganics. Major contributors to PM2.5 mass were secondary inorganics (IAP: 22 %; PG: 24 %), biomass burning (IAP: 36 %; PG: 30 %), and coal combustion (IAP: 20 %; PG: 21 %) sources during the winter period at both sites. Secondary inorganics (48 %), road dust (20 %), and coal combustion (17 %) showed the highest contribution during summer at PG, while PM2.5 particles were mainly composed of soil dust (35 %) and secondary inorganics (40 %) at IAP. Despite this, factors that were resolved based on metal signatures were not fully resolved and indicate a mixing of two or more sources. PMF results were also compared with sources resolved from another receptor model (i.e. chemical mass balance – CMB) and PMF performed on other measurements (i.e. online and offline aerosol mass spectrometry, AMS) and showed good agreement for some but not all sources. The biomass burning factor in PMF may contain aged aerosols as a good correlation was observed between biomass burning and oxygenated fractions (r2= 0.6–0.7) from AMS. The PMF failed to resolve some sources identified by the CMB and AMS and appears to overestimate the dust sources. A comparison with earlier PMF source apportionment studies from the Beijing area highlights the very divergent f

Published
2021

164. Source apportionment of carbonaceous aerosols in Beijing with radiocarbon and organic tracers: insight into the differences between urban and rural sites

Author

Hou, Siqi, primary, Liu, Di, additional, Xu, Jingsha, additional, Vu, Tuan V., additional, Wu, Xuefang, additional, Srivastava, Deepchandra, additional, Fu, Pingqing, additional, Li, Linjie, additional, Sun, Yele, additional, Vlachou, Athanasia, additional, Moschos, Vaios, additional, Salazar, Gary, additional, Szidat, Sönke, additional, Prévôt, André S. H., additional, Harrison, Roy M., additional, and Shi, Zongbo, additional

Published
2021
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167. XSnS3 (X = Ga, In) monolayer semiconductors as photo-catalysts for water splitting: a first principles study.

Author

Naseri, Mosayeb, Salahub, Dennis R., Vu, Tuan V., and Zakaryae, Haman

Abstract

Considering the growth of global population, energy requirements and industrialization, and acceleration of the global warming issue, finding new clean energy resources is necessary for the sustainability of civilization. Pure hydrogen is considered as a new possible source of clean energy that promises to reduce carbon emissions. In this regard, photocatalytic water splitting is a promising approach that can be employed for the production of hydrogen. In this paper, using first principles calculations based on the density functional theory (DFT), two novel two-dimensional (2D) monolayer materials named 2D XSnS3 (X = Ga, In) monolayers with promise for water-splitting applications are predicted. After confirming their stability, their electrical and optical features were assessed. By using the hybrid functional level of theory, it was found that these two predicted materials are semiconductors showing moderate indirect band gaps of 1.38 and 1.68 eV for GaSnS3 and InSnS3, respectively. Our optical properties investigation shows that the proposed monolayers exhibit good absorption properties in the visible region. Moreover, it is found that both electrical and optical characteristics of these predicted 2D materials can be functionally adjusted by strain and, interestingly, an indirect–direct band gap transition occurs under compression strain. Considering their moderate band gaps and good absorption in the visible region, we further computed the absolute band edge positions and Gibb's free energy for hydrogen adsorption of the materials and it was found that the 2D InSnS3 monolayer is a promising material for water splitting applications. [ABSTRACT FROM AUTHOR]

Published
2022
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168. Ab initio calculations of Electronic, Magneto-Optical, and Transport Properties of the Ga1-2xSmxEuxN alloy (x = 0.0625) by GGA, GGA + U, and TB-mBj approximations.

Author

Maskar, E., Lamrani, A. Fakhim, Belaiche, M., Es-SMAIRI, A., Vu, Tuan V., and Rai, D. P.

Abstract

This article introduces and develop a new area of transparent conducting material by doping GaN with two rare earth (RE) impurities (Eu, Sm). Our theoretical calculations confirm that the co-doped compound exhibits half-metallic ferromagnet (HMF) with 100% spin polarization at the Fermi level using GGA and mBJ. To determine which magnetic configuration is the most stable one, we compared the energy of ferromagnetic and antiferromagnetic states. Our results suggest that the ferromagnetic state is the most stable ground state. The exchange splitting energy and exchange constants N 0 α and N 0 β are calculated. Additionally, we determined the electron specific heat 'c'. It has a high optical transmittance and conductivity. These properties make GaN doped with double rare-earth impurities a potential material in optoelectronic and solar cell applications. For the calculations of mechanical, optical, and transport properties, the generalized gradient approximation + Hubbard U (GGA + U) and the modified Becke–Johnson (GGA-TB-mBJ) approximations were used. [ABSTRACT FROM AUTHOR]

Published
2022
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169. Rashba-type spin splitting and transport properties of novel Janus XWGeN2 (X = O, S, Se, Te) monolayers.

Author

Vu, Tuan V., Phuc, Huynh V., Nguyen, Chuong V., Vi, Vo T. T., Kartamyshev, A. I., and Hieu, Nguyen N.

Abstract

We discuss and examine the stability, electronic properties, and transport characteristics of asymmetric monolayers XWGeN2 (X = O, S, Se, Te) using ab initio density functional theory. All four monolayers of quintuple-layer atomic Janus XWGeN2 are predicted to be stable and they are all indirect semiconductors in the ground state. When the spin–orbit coupling (SOC) is included, a large spin splitting at the K point is found in XWGeN2 monolayers, particularly, a giant Rashba-type spin splitting is observed around the Γ point in three structures SWGeN2, SeWGeN2, and TeWGeN2. The Rashba parameters in these structures are directionally isotropic along the high-symmetry directions Γ–K and Γ–M and the Rashba constant αR increases as the X element moves from S to Te. TeWGeN2 has the largest Rashba energy up to 37.4 meV (36.6 meV) in the Γ–K (Γ–M) direction. Via the deformation potential method, we calculate the carrier mobility of all four XWGeN2 monolayers. It is found that the electron mobilities of OWGeN2 and SWGeN2 monolayers exceed 200 cm2 V−1 s−1, which are suitable for applications in nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Published
2022
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173. Atmospheric conditions and composition that influence PM<sub>2.5</sub> oxidative potential in Beijing, China

Author

Campbell, Steven J., primary, Wolfer, Kate, additional, Utinger, Battist, additional, Westwood, Joe, additional, Zhang, Zhi-Hui, additional, Bukowiecki, Nicolas, additional, Steimer, Sarah S., additional, Vu, Tuan V., additional, Xu, Jingsha, additional, Straw, Nicholas, additional, Thomson, Steven, additional, Elzein, Atallah, additional, Sun, Yele, additional, Liu, Di, additional, Li, Linjie, additional, Fu, Pingqing, additional, Lewis, Alastair C., additional, Harrison, Roy M., additional, Bloss, William J., additional, Loh, Miranda, additional, Miller, Mark R., additional, Shi, Zongbo, additional, and Kalberer, Markus, additional

Published
2021
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176. Interfacial characteristics, Schottky contact, and optical performance of a graphene/Ga2SSe van der Waals heterostructure: Strain engineering and electric field tunability

Author

Nguyen, Hong T. T., Obeid, Mohammed M., Bafekry, Asadollah, Idrees, M., Vu, Tuan V., Phuc, Huynh, V, Hieu, Nguyen N., Le Hoa, T., Amin, Bin, and Nguyen, Chuong, V

Subjects
Condensed Matter::Materials Science, Physics, Physics::Atomic and Molecular Clusters, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect
Abstract

Two-dimensional graphene-based van der Waals heterostructures have received considerable interest because of their intriguing characteristics compared with the constituent single-layer two-dimensional materials. Here, we investigate the interfacial characteristics, Schottky contact, and optical performance of graphene/Ga2SSe van der Waals (vdW) heterostructure using first-principles calculations. The effects of stacking patterns, electric gating, and interlayer coupling on the interfacial properties of graphene/Ga2SSe heterostructures are also examined. Our results demonstrate that the Dirac cone of graphene is well preserved at the F point in all stacking patterns due to the weak vdW interactions, which keep the heterostructures feasible such that they can be obtained in further experiments. Moreover, depending on the stacking patterns, a small band gap of about 13-17 meV opens in graphene and has a high carrier mobility, indicating that the graphene/Ga2SSe heterostructures are potential candidates for future high-speed nanoelectronic applications. In the ground state, the graphene/Ga2SSe heterostructures form an n-type Schottky contact. The transformation from an n-type to a p-type Schottky contact or to an Ohmic contact can be forced by electric gating or by varying the interlayer coupling. Our findings could provide physical guidance for designing controllable Schottky nanodevices with high electronic and optical performances.

Published
2020

180. An evaluation of source apportionment of fine OC and PM2.5 by multiple methods: APHH-Beijing campaigns as a case study

Author

Xu, Jingsha, primary, Srivastava, Deepchandra, additional, Wu, Xuefang, additional, Hou, Siqi, additional, Vu, Tuan V., additional, Liu, Di, additional, Sun, Yele, additional, Vlachou, Athanasia, additional, Moschos, Vaios, additional, Salazar, Gary, additional, Szidat, Sönke, additional, Prévôt, André S. H., additional, Fu, Pingqing, additional, Harrison, Roy M., additional, and Shi, Zongbo, additional

Published
2021
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184. Assessing the Impact of Traffic Emissions on Fine Particulate Matter and Carbon Monoxide Levels in Hanoi through COVID-19 Social Distancing Periods

Author

Le, Nhung H., primary, Ly, Bich-Thuy, additional, Thai, Phong K., additional, Pham, Gia-Huy, additional, Ngo, Ich-Hung, additional, Do, Van-Nguyet, additional, Le, Thuy T., additional, Nhu, Luan V., additional, Son, Ha Dang, additional, Nguyen, Yen-Lien T., additional, Pham, Duong H., additional, and Vu, Tuan V., additional

Published
2021
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193. Source Apportionment of Carbonaceous Aerosols in Beijing with Radiocarbon and Organic Tracers: Insight into the Differences between Urban and Rural Sites

Author

Hou, Siqi, primary, Liu, Di, additional, Xu, Jingsha, additional, Vu, Tuan V., additional, Wu, Xuefang, additional, Srivastava, Deepchandra, additional, Fu, Pingqing, additional, Li, Linjie, additional, Sun, Yele, additional, Vlachou, Athanasia, additional, Moschos, Vaios, additional, Salazar, Gary, additional, Szidat, Sönke, additional, Prévôt, André S. H., additional, Harrison, Roy M., additional, and Shi, Zongbo, additional

Published
2020
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194. Supplementary material to "Source Apportionment of Carbonaceous Aerosols in Beijing with Radiocarbon and Organic Tracers: Insight into the Differences between Urban and Rural Sites"

Author

Hou, Siqi, primary, Liu, Di, additional, Xu, Jingsha, additional, Vu, Tuan V., additional, Wu, Xuefang, additional, Srivastava, Deepchandra, additional, Fu, Pingqing, additional, Li, Linjie, additional, Sun, Yele, additional, Vlachou, Athanasia, additional, Moschos, Vaios, additional, Salazar, Gary, additional, Szidat, Sönke, additional, Prévôt, André S. H., additional, Harrison, Roy M., additional, and Shi, Zongbo, additional

Published
2020
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197. Source apportionment of fine organic carbon (OC) using receptor modelling at a rural site of Beijing: Insight into seasonal and diurnal variation of source contributions

Author

Wu, Xuefang, primary, Chen, Chunrong, additional, Vu, Tuan V., additional, Liu, D., additional, Baldo, Clarissa, additional, Shen, Xiaobao, additional, Zhang, Qiang, additional, Cen, Kuang, additional, Zheng, Mei, additional, He, Kebin, additional, Shi, Zongbo, additional, and Harrison, Roy M., additional

Published
2020
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198. Atmospheric conditions and composition that influence PM2.5 oxidative potential in Beijing, China

Author

Campbell, Steven J., primary, Wolfer, Kate, additional, Utinger, Battist, additional, Westwood, Joe, additional, Zhang, Zhi-hui, additional, Bukiowiecki, Nicolas, additional, Steimer, Sarah S., additional, Vu, Tuan V., additional, Xu, Jingsha, additional, Straw, Nicholas, additional, Thomson, Steven, additional, Elzein, Atallah, additional, Sun, Yele, additional, Liu, Di, additional, Li, Linjie, additional, Fu, Pingqing, additional, Lewis, Alastair C., additional, Harrison, Roy M., additional, Bloss, William J., additional, Loh, Miranda, additional, Miller, Mark R., additional, Shi, Zongbo, additional, and Kalberer, Markus, additional

Published
2020
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199. Supplementary material to "Atmospheric conditions and composition that influence PM2.5 oxidative potential in Beijing, China"

Author

Campbell, Steven J., primary, Wolfer, Kate, additional, Utinger, Battist, additional, Westwood, Joe, additional, Zhang, Zhi-hui, additional, Bukiowiecki, Nicolas, additional, Steimer, Sarah S., additional, Vu, Tuan V., additional, Xu, Jingsha, additional, Straw, Nicholas, additional, Thomson, Steven, additional, Elzein, Atallah, additional, Sun, Yele, additional, Liu, Di, additional, Li, Linjie, additional, Fu, Pingqing, additional, Lewis, Alastair C., additional, Harrison, Roy M., additional, Bloss, William J., additional, Loh, Miranda, additional, Miller, Mark R., additional, Shi, Zongbo, additional, and Kalberer, Markus, additional

Published
2020
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