Effects of Oxidation Reduction Potential and Organic Compounds on Anammox Reaction in Batch Cultures

Truong Nguyen Viet,Shishir Kumar Behera,Ji Won Kim,Hung Suck Park 대한환경공학회 2008 Environmental Engineering Research Vol.13 No.4

The present study investigates the effect of oxidation-reduction potential (ORP) and organic compounds on specific anaerobic ammonium oxidation activity (SAA) using batch experiments. The batch tests were based on the measurement of nitrogen gas production. The relationship between ORP and dissolved oxygen (DO) concentration was found to be ORP (mV) = 160.38 + 68 log [O₂], where [O₂] is the DO concentration in mg/L. The linear relationship obtained between ORP and SAA (R2 = 0.99) clearly demonstrated that ORP can be employed as an operational parameter in the Anammox process. At ORP value of -110 mV, the SAA was 0.272 ± 0.03 g N2-N (g VSS)-1 d-1. The investigation also revealed inhibitory effect of glucose on the SAA while acetate concentration up to 640 mg COD/L (corresponding to 10 mM) had stimulating effect on the SAA. However, acetate concentration beyond 640 mg COD/L had inhibitory effect on the Anammox activity. The results indicated that nitrogen rich wastewaters containing low level organic matter could be better treated by Anammox microorganisms in real-world conditions after some acidification process.

An efficient method of system reliability analysis of steel cable-stayed bridges

Truong, Viet-Hung,Kim, Seung-Eock Elsevier 2017 Advances in engineering software Vol.114 No.-

<P><B>Abstract</B></P> <P>The IHS-EIS method is developed for reliability analysis of steel cable-stayed bridges by integrating the improved Latin Hypercube (IHS) and a proposed effective importance sampling (EIS). All nonlinearity sources of bridges are directly captured by the proposed practical advanced analysis (PAA) using catenary elements for cables and beam-column elements for pylons, girders, and cross beams. The innovation of the proposed method comes from both PAA for performing structural analysis and IHS-EIS for solving reliability analysis. Compared to commercial software ABAQUS, the computational cost of structural analysis is significantly reduced by using the proposed PAA method. IHS-EIS can accurately capture the failure probability of structure and considerably decrease the number of samples in comparison with Monte Carlo simulation, importance sampling, Latin hypercube, and subset simulation methods. Three mathematical examples and two steel frames are first presented to demonstrate the accuracy and efficiency of IHS-EIS. This method is then applied for the semi-harp type of a steel cable-stayed bridge. The reliability sensitivity of the bridge is also investigated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This paper proposes the IHS-EIS method for reliability analysis of steel cable-stayed bridges by integrating the improved Latin Hypercube (IHS) and an effective importance sampling (EIS) proposed in current work. </LI> <LI> The practical advanced analysis (PAA) using catenary elements for cables and beam-column elements for pylons, girders, and cross beams is proposed for directly capturing all nonlinearity sources of bridges. </LI> <LI> The computational cost of structural analysis by using PAA is significantly reduced in comparison with by using ABAQUS. </LI> <LI> IHS-EIS accurately captures the mean value and significantly reduces the COV value of structural failure probability compared Monte Carlo simulation, importance sampling, Latin Hypercube, and Subset simulation methods. </LI> <LI> Three mathematical examples and two steel frames are firstly considered to demonstrate the accuracy and efficiency of the proposed method, and then the semi-harp type of the steel cable-stayed bridge is studied. The reliability sensitivity of the bridge is also investigated. </LI> </UL> </P>

Reliability-based design optimization of nonlinear inelastic trusses using improved differential evolution algorithm

Truong, Viet-Hung,Kim, Seung-Eock Elsevier 2018 Advances in engineering software Vol.121 No.-

<P><B>Abstract</B></P> <P>A robust method for sizing reliability-based design optimization (RBDO) of truss structures is developed by integrating nonlinear inelastic analysis, a structural reliability analysis method, and a proposed optimization method based on differential evolution (DE) algorithm. Both discrete and continuous optimizations are considered. Compared to conventional DE, three main improvements are introduced in the proposed optimization method such as: (1) a new mutation scheme based on p-best strategy to balance between local and global searches; (2) modifications of the scale factor and crossover rate parameters; (3) a multi-comparison technique to reduce the useless objective function evaluations. 20 test functions and 4 real-world examples are first considered to demonstrate the performance of the proposed optimization method for deterministic optimization problems. 3 nonlinear inelastic truss structures are then carried out to investigate the robustness of proposed RBDO method.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An efficient improvement of Different Evolution algorithm has been developed. </LI> <LI> A robust method for sizing reliability-based design optimization (RBDO) of nonlinear inelastic truss structures has been developed. </LI> <LI> 20 test functions and 4 real-world optimization problems have been considered to demonstrate the performance of the improved Different Evolution algorithm for deterministic optimization problems. </LI> <LI> 3 nonlinear inelastic truss structures have been carried out to investigate the robustness of the proposed RBDO method. </LI> </UL> </P>

Failure load analysis of C-shaped composite beams using a cohesive zone model

Truong, Viet-Hoai,Nguyen, Khanh-Hung,Park, Sang-Seon,Kweon, Jin-Hwe Elsevier 2018 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.184 No.-

<P><B>Abstract</B></P> <P>Delamination-based failure is commonly observed in curved composite structures owing to the significant curvature-induced through-thickness stresses present therein. To gain further insights on this failure mode, we investigated the initiation/propagation of delamination in C-shaped composite beams under an opening load and determined their failure load utilizing a three-dimensional finite element simulation based on a cohesive zone model (CZM). Several cohesive parameters (e.g., initial interface stiffness, cohesive zone length, and interface strength) were examined to construct an optimal CZM for the chosen loading conditions, with all parameters except for mode II fracture toughness (directly obtained from end-notched flexure test results) determined by an extensive literature survey. The predicted beam failure loads were compared with experimental results, with the obtained maximum prediction error of 8.4% indicating good agreement. Finally, the predicted position of delamination initiation was found to be heavily dependent on the ratio of the shear strength to the normal strength of the interlayer.</P>

A robust method for optimization of semi-rigid steel frames subject to seismic loading

Truong, Viet-Hung,Kim, Seung-Eock Elsevier 2018 Journal of constructional steel research Vol.145 No.-

<P><B>Abstract</B></P> <P>In this study, we develop a seismic optimization method to minimize the semi-rigid steel frame cost. In the proposed method, cross-sections of columns and beams and types of beam-to-column and base restraint semi-rigid joints are considered as the design variables of the optimization. The nonlinear seismic behaviors of the structure are carried out by using plastic-hinge beam-column elements for beams and columns, zero-length elements for semi-rigid connections, and time-history dynamic analysis. An effective implementation of harmony search technique (HS) is presented to find the global optimal solution of the optimization. In order to improve HS, a multi-comparison technique (MCT) is proposed that significantly reduces the useless time-consuming evaluations in the optimization. The robustness and efficiency of the proposed method are demonstrated through three optimization problems of semi-rigid steel frames. Compared with particle swarm optimization (PSO), micro-genetic algorithm (micro-GA), and genetic algorithm (GA), the proposed method is found to significantly reduce the number of structural analyses required and yield the better optimum frame designs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A method for optimizing semi-rigid steel frames under earthquake is proposed using advanced analysis and harmony search. </LI> <LI> Structural nonlinear seismic behaviors are carried out by using a time-history dynamic analysis. </LI> <LI> Cross-sections of beams and columns and connection types of beam-to-column and base restraint joints are design variables. </LI> <LI> Some numerical examples of semi-rigid steel frames under seismic loading are considered. </LI> </UL> </P>

Structural reliability analysis using temporal deep learning-based model and importance sampling

Truong-Thang Nguyen,Viet-Hung Dang 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.84 No.3

The main idea of the framework is to seamlessly combine a reasonably accurate and fast surrogate model with the importance sampling strategy. Developing a surrogate model for predicting structures’ dynamic responses is challenging because it involves high-dimensional inputs and outputs. For this purpose, a novel surrogate model based on cutting-edge deep learning architectures specialized for capturing temporal relationships within time-series data, namely Long-Short term memory layer and Transformer layer, is designed. After being properly trained, the surrogate model could be utilized in place of the finite element method to evaluate structures’ responses without requiring any specialized software. On the other hand, the importance sampling is adopted to reduce the number of calculations required when computing the failure probability by drawing more relevant samples near critical areas. Thanks to the portability of the trained surrogate model, one can integrate the latter with the Importance sampling in a straightforward fashion, forming an efficient framework called TTIS, which represents double advantages: less number of calculations is needed, and the computational time of each calculation is significantly reduced. The proposed approach’s applicability and efficiency are demonstrated through three examples with increasing complexity, involving a 1D beam, a 2D frame, and a 3D building structure. The results show that compared to the conventional Monte Carlo simulation, the proposed method can provide highly similar reliability results with a reduction of up to four orders of magnitudes in time complexity.

Synthesis of highly concentrated suspension of chemically converted graphene in organic solvents: Effect of temperature on the extent of reduction and dispersibility

Viet Hung Pham,정진석,Thanh Truong Dang,Tran Viet Cuong,Seung Hyun Hur,Byung-Seon Kong,김의정 한국화학공학회 2012 Korean Journal of Chemical Engineering Vol.29 No.5

We report the effect of temperature on the extent of graphene oxide reduction by hydrazine and the dispersibility of the resulting chemically converted graphene (CCG) in polar organic solvents. The extent of graphene oxide reduction at high temperatures was only slightly higher than at low temperatures (30-50 oC), while the dispersibility of the resulting CCG in organic solvents decreased markedly with increasing temperature. The low dispersibility of CCGs prepared at high temperatures was greatly affected by reduction and influenced by the formation of an irreversible agglomerate of CCG at high temperatures. The reduction of graphene oxide at low temperatures is necessary to prepare highly dispersible CCG in organic solvents. CCG prepared at 30 oC is dispersible in N-methyl-2-pyrrolidone concentrations as high as 0.71 mg/mL. The free-standing paper made of this CCG possessed an electrical conductivity of more than 22,000 S/m, one of the highest values ever reported.

Highly Conductive Poly(methyl methacrylate) (PMMA)-Reduced Graphene Oxide Composite Prepared by Self-Assembly of PMMA Latex and Graphene Oxide through Electrostatic Interaction

Pham, Viet Hung,Dang, Thanh Truong,Hur, Seung Hyun,Kim, Eui Jung,Chung, Jin Suk American Chemical Society 2012 ACS APPLIED MATERIALS & INTERFACES Vol.4 No.5

<P>We report a simple, environmentally friendly approach for preparing highly conductive poly(methyl methacrylate)–reduced graphene oxide (PMMA-RGO) composites by self-assembly of positively charged PMMA latex particles and negatively charged graphene oxide sheets through electrostatic interactions, followed by hydrazine reduction. The PMMA latex was prepared by surfactant-free emulsion polymerization using a cationic free radical initiator, which created the positive charges on the surface of the PMMA particle. By mixing PMMA latex with a graphene oxide dispersion, positively charged PMMA particles easily assembled with negatively charged graphene oxide sheets through electrostatic interaction. The obtained PMMA-RGO exhibited excellent electrical properties with a percolation threshold as low as 0.16 vol % and an electrical conductivity of 64 S/m at only 2.7 vol %. Moreover, the thermomechanical properties of PMMA-RGO were also significantly improved. The storage modulus of PMMA-RGO increased by about 30% at 4.0 wt % RGO at room temperature while the glass transition temperature of PMMA-RGO increased 15 °C at only 0.5 wt % RGO.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2012/aamick.2012.4.issue-5/am300297j/production/images/medium/am-2012-00297j_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am300297j'>ACS Electronic Supporting Info</A></P>

Effects of Oxidation Reduction Potential and Organic Compounds on Anammox Process in Batch Cultures

Nguyen Viet Truong,Ji Won Kim,Hung Suck Park 대한환경공학회 2008 대한환경공학회 학술발표논문집 Vol.2008 No.12

AN EFFECTIVE SEGMENT PRE-FETCHING FOR SHORT-FORM VIDEO STREAMING

Nguyen Viet Hung,Truong Thu Huong International Journal of Computer ScienceNetwork S 2023 International journal of computer science and netw Vol.23 No.3

The popularity of short-form video platforms like TikTok has increased recently. Short-form videos are significantly shorter than traditional videos, and viewers regularly switch between different types of content to watch. Therefore, a successful prefetching strategy is essential for this novel type of video. This study provides a resource-effective prefetching technique for streaming short-form videos. The suggested solution dynamically adjusts the quantity of prefetched video data based on user viewing habits and network traffic conditions. The results of the experiments demonstrate that, in comparison to baseline approaches, our method may reduce data waste by 21% to 83%, start-up latency by 50% to 99%, and the total time of Re-buffering by 90% to 99%.