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Nguyen Huu Nghia,Nguyen Thi Nguyen,Phan Trong Binh,Le Thi May,Tong Tran Huy,Pham Thai Giang,Sophie St-Hilaire,Phan Thi Van 한국수산과학회 2022 Fisheries and Aquatic Sciences Vol.25 No.8
This study assessed the effects of oxygen and ozone nanobubbles on gill morphology, weight gain, and mortality of Pacific white shrimp (Penaeus vannamei), as well as the level of Vibrio parahaemolyticus and water quality of shrimp culture tanks under lab conditions. Two experiments were carried out with oxygen macrobubble, ozone macrobubble, oxygen nanobubble, ozone nanobubble, and control treatments (air-stone macrobubble). Experiments were done in triplicate in 100 L tanks with 15‰ saline water, and 20 shrimp per tank. Tanks in Experiment 1 were not inoculated with bacteria; tanks in Experiment 2 were inoculated with V. parahaemolyticus at a concentration of 106 CFU/mL. The results revealed that short treatments with ozone nanobubbles had minimal impact on shrimp gills, mortality, and growth rates, reduced V. parahaemolyticus concentration in water compared to the other groups, and improve water quality. These laboratory results indicate that ozone nanobubble treatment may be useful for controlling V. parahaemolyticus. More work is needed to find the best protocol to apply the technology on a commercial scale.
Bending analysis of a single leaf flexure using higher-order beam theory
Nghia Huu Nguyen,이동연 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.4
We apply higher-order beam theory to analyze the deflections and stresses of a cantileveredsingle leaf flexure in bending. Our equations include shear deformation and the warping effect in bending. The results are compared with Euler-Bernoulli and Timoshenko beam theory, and are verified by finiteelement analysis (FEA). The results show that the higher-order beam theory is in a good agreement with theFEA results, with errors of less than 10%. These results indicate that the analysis of the deflections andstresses of a single leaf flexure should consider the shear and warping effects in bending to ensure highprecision mechanism design.
Warping stresses of a rectangular single leaf flexure under torsion
Nghia Huu Nguyen,Ji-Soo Kim,이동연 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.59 No.3
We describe a stress analysis of a single leaf flexure under torsion in which the warping effect is considered. The theoretical equations for the warping normal stress (xx) and shear stresses (xz and xy) are derived by applying the warping function of a rectangular cross-sectional beam and the twist angle equation that includes the warping torsion. The results are compared with those of the non-warping case and are verified using finite element analysis (FEA). A sensitivity analysis over the length, width, and thickness is performed and verified via FEA. The results show that the errors between the theory of warping stress results and the FEA results are lower than 4%. This indicates that the proposed theoretical stress analysis with warping is accurate in the torsion analysis of a single leaf flexure.
Peer Effects on Corporate Cash Holdings: Evidence from Vietnam
Nghia Huu Nguyen,Wei-Hsien Li 한국재무학회 2022 財務硏究 Vol.35 No.2
This research examines corporate cash holdings in Vietnam, an emerging market, and finds reverse peer effects on them - that is, a firm’s level of cash holdings negatively relates to those of its peers. We also note the reverse peer effects are stronger for firms facing less competition and with low intangibility. Because the Vietnam market has noticeably lower competition and investment in innovation than in developed economics like the U.S., our evidence supports the role of competition and innovation investment in driving cash holdings’ peer effects and complements the literature that mostly focuses on developed economies. Our findings are consistent with the notion that some firms strategically accumulate cash to drive their competitors’ cash level lower when they are in less competitive industries or when they have lower innovation investments. Thus, the existing competition or innovation environment is crucial when modeling the cash holding behavior among industry peers. However, our tests on the preemptive motive for peer effects on cash holdings are inconclusive. Lastly, our results also support heterogeneity across countries in peer mimicking behavior and contributes to the cash holdings literature for the Vietnam market.
Displacement Analysis of a Single-Bent Leaf Flexure under Transverse Load
Nghia Huu Nguyen,임병덕,이동연 한국정밀공학회 2015 International Journal of Precision Engineering and Vol. No.
We report a displacement analysis of a single-bent leaf flexure under transverse loading. Euler-Bernoulli, Timoshenko, and third-orderbeam theories, and the partially restrained warping effect, are considered. Castigliano’s theorem is used to derive theoreticalexpressions of deflection under transverse loading. A sensitivity analysis is performed, and all of the results are verified using finiteelement analysis (FEA). The results show that the theoretical equations with third-order beam theory and a warping restraint factorof K=0.5 are in a good agreement with the FEA results, within a maximum 4% error. These results indicate that the accuracy of thedisplacement analysis of the single-bent flexure under transverse loading depends on both the transverse shear deformation and thepartially restrained warping effect.
Torsional analysis of a single-bent leaf flexure
Nguyen, Nghia Huu,Lim, Byoung-Duk,Lee, Dong-Yeon Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.1
We present a torsion analysis of single-bent leaf flexure that is partially restrained, subject to a torsional load. The theoretical equations for the torsional angle are derived using Castigliano's theorem. These equations consider the partially restrained warping, and are verified using finite element analysis (FEA). A sensitivity analysis over the length, width, and thickness is performed and verified via FEA. The results show that the errors between the theory result and the FEA result are lower than 6%. This indicates that the proposed theoretical torsional analysis with partially restrained warping is sufficiently accurate.
Bending analysis of a single leaf flexure using higher-order beam theory
Nguyen, Nghia Huu,Lee, Dong-Yeon Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.4
We apply higher-order beam theory to analyze the deflections and stresses of a cantilevered single leaf flexure in bending. Our equations include shear deformation and the warping effect in bending. The results are compared with Euler-Bernoulli and Timoshenko beam theory, and are verified by finite element analysis (FEA). The results show that the higher-order beam theory is in a good agreement with the FEA results, with errors of less than 10%. These results indicate that the analysis of the deflections and stresses of a single leaf flexure should consider the shear and warping effects in bending to ensure high precision mechanism design.
Torsional analysis of a single-bent leaf flexure
Nghia Huu Nguyen,임병덕,이동연 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.1
We present a torsion analysis of single-bent leaf flexure that is partially restrained, subject to a torsional load. The theoretical equations for the torsional angle are derived using Castigliano’s theorem. These equations consider the partially restrained warping, and are verified using finite element analysis (FEA). A sensitivity analysis over the length, width, and thickness is performed and verified via FEA. The results show that the errors between the theory result and the FEA result are lower than 6%. This indicates that the proposed theoretical torsional analysis with partially restrained warping is sufficiently accurate.