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Van Bon Nguyen(Van Bon Nguyen ) 서울대학교 경제연구소 2022 Seoul journal of economics Vol.35 No.4
Public spending is a crucial instrument of fiscal policy in running the economy. Most governments use public spending actively to overcome the cyclicality of the economy. However, the increase in government spending financed by public debt can negatively contribute to the private sector investment. This study raises two research questions: (i) Does public debt in developing countries crowd out private investment? (ii) What is the role of governance in public debt–private investment relationship in these countries? For the answers, we apply the two-step difference generalized method of moments Arellano–Bond estimator to empirically investigate the effects of public debt, governance, and their interactions on private investment for a sample of 98 developing countries from 2002 to 2019. We then employs the pooled mean group estimator to check the robustness of estimates. Results show that public debt crowds out private investment, whereas governance stimulates it. Notably, the crowding-out effect of interaction on private investment seems counterintuitive. Furthermore, economic growth and trade openness enhance private investment. These findings suggest policy implications for governments in developing countries for controlling and managing public debt to promote the private sector investment.
Numerical Study of Flow Characteristics over Square Cylinders with an Attached Splitter Plate
Nguyen, Van Minh,Koo, Bon-Guk Korean Society of Ocean Engineers 2018 Journal of advanced research in ocean engineering Vol.4 No.2
The fluid flow over structures has been widely investigated by many researchers because its extensive application in offshore structures, skyscrapers, chimneys and cooling towers, brides. In the viewpoint of reducing the drag for offshore structure, it becomes challenging problem in the field of hydrodynamic of offshore structure. The purpose of this study is to investigate a flow over a square cylinder with an attached splitter plate using RANS method. First, RANS turbulent models such as a standard $k-{\omega}$ model, SST $k-{\omega}$ model, RNG $k-{\varepsilon}$ model, realizable $k-{\varepsilon}$ model, standard $k-{\varepsilon}$ model were used for choosing suitable turbulent model which has the best agreement with available experimental result. Drag of single cylinder estimated by using standard $k-{\omega}$ has a good agreement with published experimental result. Therefore, the stand $k-{\omega}$ was selected for simulation for flow over a square cylinder with an attached plate. Second, the numerical results of drag of square cylinder with an attached splitter plate in various length of an attached plate were performed using RANS method in ANSYS Fluent. In this paper, the numerical simulations were conducted at a Reynolds number of 485 and the thickness of the splitter plate is chosen as a constant value about 10% of cylinder width. The numerical results of drag coefficient of square cylinder are compared with experimental result published by other researchers. Finally, the effect of the splitter plate attached to the rear side of the square cylinder has been investigated numerically with a focus on the drag coefficient and flow characteristic. As a result, the drag coefficient decreases with an increase in splitter plate length.
Synthesis and Characterization of Silver Vanadium Oxide as a Cathode for Lithium Ion Batteries
Nguyen, Van Hiep,Gu, Hal-Bon The Korean Institute of Electrical and Electronic 2016 Transactions on Electrical and Electronic Material Vol.17 No.3
β-AgVO<sub>3</sub> nanorods have been successfully synthesized using a soft chemistry route followed by heat treatment. They were characterized by X-ray diffraction and field emission scanning electron microscopy, and their electrochemical properties were investigated using cyclic voltammetry, impedance spectra, and charge-discharge tests. The results showed that the smooth-surfaced nanorods are very uniform and well dispersed, with diameters of ~100-200 nm and lengths of the order of several macrometers. The nanorods deliver a maximum specific discharge capacity of 275 mAh g<sup>-1</sup> at 30 mA g<sup>-1</sup>. They also demonstrated good rate capability with a discharge capacity at the 100<sup>th</sup> cycle of 51 mAh g<sup>-1</sup>.
Nguyen, Hiep Van,Jin, En Mei,Gu, Hal-Bon The Korean Institute of Electrical and Electronic 2012 Transactions on Electrical and Electronic Material Vol.13 No.4
In this study, we prepared $LiFePO_4$- poly (sodium 4-styrenesulfonate) (PSS) composite by the hydrothermal method and ball-milling process. Different wt% PSS were added to $LiFePO_4$. The cathode electrodes were made from mixtures of $LiFePO_4$-PSS: SP-270: PVDF in a weighting ratio of 70%: 25%: 5%. $LiFePO_4$-PSS powders were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM). The electrochemical properties of $LiFePO_4$-PSS/Li batteries were analyzed by cyclic voltammetry, charge/discharge tests, and AC impedance spectroscopy. A Li/$LiFePO_4$-PSS battery with 4.75 wt% PSS shows the best electrochemical properties, with a discharge capacity of 128 mAh/g.
Nguyen, Van Hiep,Lee, Dong-Hee,Baek, Sae-Yane,Gu, Hal-Bon,Kim, Young Ho Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.11
<P><B>Abstract</B></P> <P>In this study, silicon and its effect on the properties of Li<SUB>3</SUB>V<SUB>2</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> were studied for lithium-ion battery applications. The composite material was synthesized and found to show enhanced capacity and cyclability. The presence of silicon in the composites was confirmed. Furthermore, large particles with rough, corroded-like structures formed, and these were distributed well with the silicon particles. The Li<SUB>3</SUB>V<SUB>2</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>-Si battery had good properties showing improved cyclability, an improved high performance rate, smaller impedance values and improved lithium-ion diffusion coefficients, as determined by cyclic voltammetry. Furthermore, the optimization of the silicon content led to a Li<SUB>3</SUB>V<SUB>2</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>-Si battery with a 2 wt% silicon loading that had a discharge capacity of 181 mA h g<SUP>−1</SUP>. At 2 C, Li<SUB>3</SUB>V<SUB>2</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>-Si (2 wt%) still demonstrated a capacity of 111.8 mA h g<SUP>−1</SUP>, which was 83.8% of its original capacity (compared with 70.3 mA h g<SUP>−1</SUP> and 63.8% for Li<SUB>3</SUB>V<SUB>2</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>) after 400 cycles.</P>
Improving Electrochemical Properties of LiFePO4 by Doping with Gallium
Van Hiep Nguyen,Hal-Bon Gu,박주영 한국전기전자재료학회 2014 Transactions on Electrical and Electronic Material Vol.15 No.6
Ga-doped LiFePO4 cathode materials were synthesized using a hydrothermal method. The microstructuralcharacteristics and electrochemical performances were systematically investigated using field emission scanningelectron microscopy, high-resolution X-ray diffraction, energy dispersive X-ray spectroscopy, charge-dischargecycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Among the as-prepared samples,LiFe0.96Ga0.04PO4 demonstrates the best electrochemical properties in terms of discharge capacity, electrochemicalreversibility, and cycling performance with an initial discharge capacity of 125 mAh g-1 and high lithium ion diffusioncoefficient of 1.38 × 10-14 cm2 s-1 (whereas for LiFePO4, these were 113 mAh g-1 and 8.09 × 10-15 cm2 s-1, respectively). Theimproved electrochemical performance can be attributed to the facilitation of Li+ ion effective diffusion induced byGa3+ substitution.
Improving Electrochemical Properties of LiFePO<sub>4</sub> by Doping with Gallium
Nguyen, Van Hiep,Park, Ju-Young,Gu, Hal-Bon The Korean Institute of Electrical and Electronic 2014 Transactions on Electrical and Electronic Material Vol.15 No.6
Ga-doped $LiFePO_4$ cathode materials were synthesized using a hydrothermal method. The microstructural characteristics and electrochemical performances were systematically investigated using field emission scanning electron microscopy, high-resolution X-ray diffraction, energy dispersive X-ray spectroscopy, charge-discharge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Among the as-prepared samples, $LiFe_{0.96}Ga_{0.04}PO_4$ demonstrates the best electrochemical properties in terms of discharge capacity, electrochemical reversibility, and cycling performance with an initial discharge capacity of $125mAh\;g^{-1}$ and high lithium ion diffusion coefficient of $1.38{\times}10^{-14}cm^2s^{-1}$ (whereas for $LiFePO_4$, these were $113mAh\;g^{-1}$ and $8.09{\times}10^{-15}cm^2\;s^{-1}$, respectively). The improved electrochemical performance can be attributed to the facilitation of Li+ ion effective diffusion induced by $Ga^{3+}$ substitution.
Synthesis and Characterization of Silver Vanadium Oxide as a Cathode for Lithium Ion Batteries
Hal-Bon Gu,Van Hiep Nguyen 한국전기전자재료학회 2016 Transactions on Electrical and Electronic Material Vol.17 No.3
β-AgVO3 nanorods have been successfully synthesized using a soft chemistry route followed by heat treatment. Theywere characterized by X-ray diffraction and field emission scanning electron microscopy, and their electrochemicalproperties were investigated using cyclic voltammetry, impedance spectra, and charge-discharge tests. The resultsshowed that the smooth-surfaced nanorods are very uniform and well dispersed, with diameters of ~100-200 nmand lengths of the order of several macrometers. The nanorods deliver a maximum specific discharge capacity of 275mAh g-1 at 30 mA g-1. They also demonstrated good rate capability with a discharge capacity at the 100th cycle of 51mAh g-1.