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Son Tung Ha,Thi Hong Hanh Pham,Thi Nguyet Anh Nguyen 세종대학교 경제통합연구소 2021 Journal of Economic Integration Vol.36 No.3
We examine the stock market performance of Vietnam’s listed firms in response to the country’s approval of the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP). Employing an event study methodology, we first calculate the abnormal returns of all listed Vietnamese firms around the CPTPP’s approval date. Then, we attempt to link these abnormal returns to firms’ characteristics. We find evidence that the announcement of the CPTPP’s approval is associated with positive abnormal returns for Vietnam’s listed firms. We also find considerable heterogeneity in the magnitude and pace of the impacts of the CPTPP’s approval on market returns across Vietnam’s two stock exchanges. However, we fail to reject the null hypothesis that the market did not react to the CPTPP’s approval at the sectoral level.
Size Control of Highly Monodisperse Polystyrene Particles by Modified Dispersion Polymerization
Son Tung Ha,박오옥,임상혁 한국고분자학회 2010 Macromolecular Research Vol.18 No.10
Highly monodisperse polystyrene (PS) particles have been synthesized by modified dispersion polymerization in which aqueous alcohols, polyvinylpyrrolidone (PVP), and ammonium persulfate (APS) are used as a medium, steric stabilizer, and initiator, respectively. An ionic initiator, APS, in typical dispersion polymerization would help stabilize the growing PS particles by electrical repulsion, resulting in a monodisperse particle size distribution. Moreover, the dual functions of APS as an initiator and electric stabilizer compete to determine the final size of the PS particles and lead the size of PS particles to be less sensitive to the APS concentration. Therefore, it was possible to control precisely the size of highly monodisperse PS particles in the diameter range, 800 to 2,000nm. In addition, the highly monodisperse PS particles below 800 nm in size could be obtained just by quenching the reactant with time. Therefore, these PS particles can be used readily to fabricate colloidal crystals owing to their high monodispersity.
HA, Son Tung,TRAN, Manh Linh,HOANG, Huy Viet,TRAN, Van Hung Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.6
This paper investigates the potential impact of external factors on bid/no-bid decision for supervision consultant service on construction project in Hanoi, the capital of Vietnam. The data used in this study are secondary data taken from annual reports and sourced from the Department of Public Procurement, Ministry of Planning and Investment in Hanoi. Besides, to identify the impact of external factors on bid/no-bid decision for supervision consultant service on construction project in Hanoi, the study collected data from 272 qualified questionnaires from bidders doing business in Hanoi. Cronbach's Alpha, EFA and regression model are used to explore the impact of each independent variable on bid/no-bid decision for supervision consultant service on construction project. The results show that three external determinants, including Project characteristic (PC), Legal codes (LC) and Competition (C) are affecting bid/no-bid decision for supervision consultant service on construction project in Hanoi. Among them, Project characteristic (PC) and Legal codes (LC) have positive relationships with bid/no-bid decision for supervision consultant service on construction project, whereas Competition (C) negatively affects bid/no-bid decision for supervision consultant service on construction project. It means the more contractors actually participate in a bid, the less bid/ no-bid decisions are made.
Ultra-broadband and flexible metamaterial absorber based on MoS2 cuboids with Mie resonances
Ha Duong Thi,Nam Man Hoai,Tung Bui Son,Khuyen Bui Xuan,Lam Vu Dinh,Le-Van Quynh 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.11
In this work, we present a type of fexible and broadband metamaterial absorber operating in the GHz range. The proposed structure consists of three layers: a periodic square-shaped array made of molybdenum disulfde (MoS2) on the top, a continuous polyimide layer in the middle and a continuous copper layer at the bottom. For fat model, the proposed absorber exhibits a broadband absorption in the frequency range of 10.1–17.6 GHz with an absorption of more than 90% under normal incidence. Due to the symmetry of structure, the absorption feature is polarization-insensitive. The absorption remains above 80% in the frequency range of 11.1–15.6 GHz when the incident angle is up to 60° for TE-polarized wave, while the absorption is higher than 90% in the frequency range of 13.5–18 GHz for incident angles up to 60° for TM-polarized wave. For bending model, the absorption is signifcantly expanded when the bending radius decreases to under 100 mm. The physical mechanism of the absorption properties is explained in detail by the electric feld distribution, the magnetic feld distribution following the Mie resonance theory and infuence of the loss of MoS2. Obtained results in the work might contribute to the development of potential applications based on metamaterials in the microwave region such as imaging, protecting and light emitting devices.
Numerical Study of Free Surface Effect on Supercavitating Flows
Son-Tung Dang,Cong-Tu Ha,Van-Tu Nguyen,Warn-Gyu Park(박원규),Dong-Hyun Kim(김동현) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
In this paper, we focus on applying the volume of fluid (VOF) method coupled with an interface reconstruction technique to capture the free surface between liquid and gas. The governing equation is the compressible Navier-Stokes equations based on the homogeneous mixture model. A preconditioned method is applied for enhancing efficient and accurate computations over a wide range of Mach numbers. For evaluation, the present results have been compared with experiments and other numerical results. A fairly good agreement with the experimental data and other numerical results has been obtained. Finally, the simulation of natural supercavitating flows over a plate hydrofoil was conducted to show the effect of free surface on characteristic length of supercavitation.
An efficient shock-capturing scheme for simulating compressible homogeneous mixture flow
Son-Tung Dang,Cong-Tu Ha,Warn-GyuPark,Chul-Min Jung 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.9
This work is devoted to the development of a procedure for the numerical solution of Navier-Stokes equations for cavitating flows with and without ventilation based on a compressible, multiphase, homogeneous mixture model. The governing equations are discretized on a general structured grid using a high-resolution shock-capturing scheme in conjunction with appropriate limiters to prevent the generation of spurious solutions near shock waves or discontinuities. Two well-known limiters are examined, and a new limiter is proposed to enhance the accuracy and stability of the numerical scheme. A sensitivity analysis is first conducted to determine the relative influences of various model parameters on the solution. These parameters are adopted for the computation of water flows over a hemispherical body, conical body and a divergent/convergent nozzle. Finally, numerical calculations of ventilated supercavitating flows over a hemispherical cylinder body with a hot propulsive jet are conducted to verify the capabilities of the numerical scheme.