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Nguyen, Van-Toan,Tran, Quoc Chinh,Quang, Nguyen Duc,Nguyen, Ngoc-Anh,Bui, Van-Tien,Dao, Van-Duong,Choi, Ho-Suk Elsevier 2018 Journal of alloys and compounds Vol.766 No.-
<P><B>Abstract</B></P> <P>The improvement of the catalytic performance for methanol and formic acid oxidation reactions remains a key issue for the development of a new generation of direct methanol and formic acid fuel cells. This study reports a simple approach, using selective chemical etching for the synthesis of unique nitrogen-doped carbon dot/Pt<SUB>84</SUB>Pd<SUB>16</SUB> (N-Cdot/Pt<SUB>84</SUB>Pd<SUB>16</SUB>) nano-network structure at room temperature with excellent electrocatalytic properties. The obtained nano-network hybrid material exhibits significant enhancement of the electrocatalytic activity for the electro-oxidation reaction of both methanol and formic acid with current densities of 999.0 and 1919.5 mA/mg<SUB>metal</SUB>, respectively, compared with the commercial ones of 751.32 and 806.02 mA/mg<SUB>metal</SUB>, respectively. Furthermore, the N-Cdot/Pt<SUB>84</SUB>Pd<SUB>16</SUB> nano-network hybrid materials exhibit excellent stability and hydrophilic dispersibility at room temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> N-Cdot/PtPd nanonetwork hybrid material is synthesized at room temperature. </LI> <LI> A simple coreduction and a selective chemical etching are applied to the synthesis. </LI> <LI> It generates a nano-network structure with excellent electrocatalytic properties. </LI> <LI> N-Cdot functions as a uniform interconnection between the nanohybrid materials. </LI> <LI> The hybrid exhibits significant enhancement of the activity for both MOR and FAOR. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Van Toan Nguyen,Hyochan Kim,Byoung Jae Kim Korean Nuclear Society 2023 Nuclear Engineering and Technology Vol.55 No.7
Film boiling may lead to burnout of the heating element. Even though burnout does not occur, the heating element is subject to deformation because it is not sufficiently strong to withstand external loads. In particular, the ballooning and rupture of a tube under film boiling are important phenomena in the field of nuclear reactor safety. If the tube-type cladding of nuclear fuel ruptures owing to high internal pressure and thermal load, radioactive materials inside the cladding are released to the coolant. Therefore, predicting the ballooning and rupture is important. This study presents numerical simulations to predict the ballooning behavior and rupture time of a horizontal tube at high internal pressure under saturated film boiling. To do so, a multi-step coupled simulation of conjugated film boiling heat transfer and ballooning using creep model is adopted. The numerical methods and models are validated against experimental values. Two different nonuniform heat flux distributions and four different internal pressures are considered. The three-step simulation is enough to obtain a convergent result. However, the single-step simulation also successfully predicts the rupture time. This is because the film boiling heat transfer characteristics are slightly affected by the tube geometry related to creep ballooning.
Toan Van Pham,Vinh Mai Phuoc,Dung Van Nguyen,Jiro Koyama 대한환경공학회 2021 Environmental Engineering Research Vol.26 No.6
Pesticide containing wastewater is concerned due to their toxicity to human health and the environment, and therefore, is attracted much attention by public communities and scientists. This type of wastewater can be treated by conventional treatment methods including physical, chemical, biological methods and so on. Unfortunately, the efficiency of these methods are mostly undesired as expectation because they cannot completely remove toxic organic pollutants from wastewater. In this study, an experiment on laboratory scale model of cold plasma technology, a well-known water treatment method in recent decades, was performed to assess its efficiency on removing pesticide fenobucarb from the wastewater. Furthermore, another experiment on laboratory scale model of the cold plasma combined with coagulation/flocculation and ion exchange process was implemented to assess the efficiency of these combination and each process as well on treatment of pesticide containing wastewater. Experimental results demonstrated that the model of technologies combined was high effective in removing organic pollutants from wastewater. However, the specific efficiency of cold plasma technology in treating wastewater was low. Treatment time, energy supply and wastewater characteristics are the factors which are necessary to be further studied for cold plasma technology application.
Fabrication and evaluation of capacitive silicon resonators with piezoresistive heat engines
Van Toan, N.,Van Nha, N.,Song, Y.,Ono, T. Elsevier Sequoia 2017 Sensors and actuators. A, Physical Vol.262 No.-
<P>This work reports the design, fabrication and evaluation of capacitive silicon resonators with piezoresistive heat engines. A combination of capacitive transduction and piezoresistive actuation based on a piezoresistive heat engine in the single micromechanical resonator is proposed to achieve a low insertion loss and small motional resistance. Capacitive silicon resonators with single and multiple piezoresistive beams have been demonstrated. In these structures, resonant bodies are divided into many parts that are connected to each other by using small piezoresistive beams to enhance electromechanical transductions by the piezoresistive heat engines. When a bias voltage V-b = 7 V is applied to the piezoresistive beams, the insertion loss and motional resistance of the capacitive silicon resonator with multiple piezoresistive beams are improved by 20 dB (enhanced from -68 dB to -48 dB) and 90% (reduced from 125.5 k Omega to 12.5 k Omega), respectively, in comparison to the case without a bias voltage. In addition, the tuning frequency characteristic with the piezoresistive effect is increased by 165 times over that of the structure with only the capacitive effect. (C) 2017 Elsevier B.V. All rights reserved.</P>
The Impact of Debt on Corporate Profitability: Evidence from Vietnam
Van Toan NGO,Thị Xuan Huong TRAM,Ba Thanh VU 한국유통과학회 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.11
The study aims to investigate the impact of debt on corporate profitability in the context of Vietnam. The paper investigates the impact of debt on corporate profitability in non-finance listed companies on the Vietnam stock market. The panel data of the research sample includes 118 non-financial listed companies on the Vietnam stock market for a period of nine years, from 2009 to 2017. The Generalized Method of Moments (GMM) is employed to address econometric issues and to improve the accuracy of the regression coefficients. In this research, corporate profitability is measured as the return of EBIT on total assets. The debt ratio is a ratio that indicates the proportion of a company’s debt to its total assets. Firm sizes, tangible assets, growth rate, and taxes are control variables in the study. The empirical results show that debt has a statistically significant negative effect on corporate profitability. The result also shows this effect is stronger in a non-linear (concave) way, we show that the debt ratio has nonlinear effects on corporate profitability. From this, experimental evidence shows that the optimal debt ratio is 38.87%. This evidence provides a new insight to managers of the non-finance companies on how to improve the firm’s profitability with debt.
Toan Van Pham,Vinh Mai Phuoc,Dung Van Nguyen,Jiro Koyama 대한환경공학회 2021 Environmental Engineering Research Vol.26 No.6
Pesticide containing wastewater is concerned due to their toxicity to human health and the environment, and therefore, is attracted much attention by public communities and scientists. This type of wastewater can be treated by conventional treatment methods including physical, chemical, biological methods and so on. Unfortunately, the efficiency of these methods are mostly undesired as expectation because they cannot completely remove toxic organic pollutants from wastewater. In this study, an experiment on laboratory scale model of cold plasma technology, a well-known water treatment method in recent decades, was performed to assess its efficiency on removing pesticide fenobucarb from the wastewater. Furthermore, another experiment on laboratory scale model of the cold plasma combined with coagulation/flocculation and ion exchange process was implemented to assess the efficiency of these combination and each process as well on treatment of pesticide containing wastewater. Experimental results demonstrated that the model of technologies combined was high effective in removing organic pollutants from wastewater. However, the specific efficiency of cold plasma technology in treating wastewater was low. Treatment time, energy supply and wastewater characteristics are the factors which are necessary to be further studied for cold plasma technology application.
Van Toan Nguyen,Sun Rock Choi,Yohan Jung,Sunghyuk Im,김병재 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.8
In the steam generator of a sodium-cooled fast reactor, heat transfer occurs from the primary sodium flow side at high temperature to the secondary water flow side at low temperature. Preventing the interaction between sodium and water in the heat exchanger is important to avoid a reactive explosion. To do so, the concept of the copper bonded steam generator, which consists of heat-exchanger modules with cross-flow-type arrangement, was recently proposed. In this cross-type arrangement, the sodium flow should be as uniform as possible throughout the horizontal channels in terms of the heat transfer efficiency between the sodium and water sides. This study aims to design a perforated plate leading to uniform sodium flow distribution throughout the 66×33 channels. The geometrical design and location of the perforated plate are optimized using numerical simulation. The designed plate improves the flow distribution uniformity at a slight cost of pressure loss.