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Phuc Nguyen Thien,Giang Nguyen Thi Huong,An Vu Nguyen Thien Truong,Nam Nguyen Thanh Hoai,Anh Ly Duc,Nguyen Huynh Cam,An Hoang,Phong Mai Thanh,Hieu Nguyen Huu 한국탄소학회 2023 Carbon Letters Vol.33 No.2
In this study, graphene oxide (GO) was synthesized by the improved Hummers’ method. The degree of oxidation from graphite (Gi) to GO was determined through interlayer spacing calculated from X–ray diffraction. Besides, the effect of KMnO4:Gi ratios (X1), H2SO4 volume (X2), oxidation temperature (X3), oxidation time of stage 1 (X4), and oxidation time of stage 2 (X5) was screened by the Plackett–Burman model. The simultaneous impact of three factors that influenced the degree of oxidation (X1, X2, and X3) was studied by the Box–Behnken experimental model of response surface methodology to achieve suitable conditions for the GO synthesis process. The characterization of GO product was investigated via the modern analytical methods: X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV–Vis spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. In addition, the study was also carried out on a pilot scale for orientation in industrial application with the yield of 14 g/batch.
Improving Utilization of GPS Data for Urban Traffic Applications
Nguyen Duc Hai,Nguyen Tan Phuc,Doan Khue,Ta Ho Thai Hai,Pham Tran Vu,Huynh Nam,Le Thanh Van 한국인터넷방송통신학회 2015 International Journal of Internet, Broadcasting an Vol.7 No.1
The use of Intelligent Transportation System (ITS) is promising to bring better solutions for managing and handling the city traffic. This system combines many fields in advanced technology such as Global Positioning System (GPS), Geographic Information System (GIS) and so on. The basement of applications in ITS is the effective collections and data integration tools. The purpose of our research is to propose solutions which involve the use of GPS time series data collected from GPS devices in order to improve the quality of output traffic data. In this study, GPS data is collected from devices attached to vehicles travelling on routes in Ho Chi Minh City (HCMC). Then, GPS data is stored in database system to serve in many transportation applications. The proposed method combines the data usage level and data coverage to improve the quality of traffic data.
Le-Phuc Nguyen,Yen Thi Hai Pham,Phuong Thuy Ngo,Tri Van Tran,Loc Vinh Tran,Nam Thi Hoai Le,Luong Huu Nguyen,Tung Thanh Dang,Duc Anh Nguyen,Marco Wenzel,David Hartmann,Karsten Gloe,Jan J. Weigand,Klaus 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.5
Acid leaching and a two-step solvent extraction procedure were developed to produce high purity mixture of La and Ce from iron-rich spent FCC catalyst discharged from Dzung Quat refinery (Vietnam). Acid leaching of the spent catalyst with 2M HNO3 and a solid-to-liquid ratio of 1/3 at 80 oC in 1 h dissolved almost 90% of La while 12% of Al and 25% of Fe were transferred to the leachate. The extraction of RE metals and main impurities such as Al and Fe by a mixture of di-2-ethylhexyl phosphoric acid (D2EHPA) and tributyl phosphate (TBP) was investigated. Experiments showed that it was necessary to remove Fe before extracting RE and the optimum extraction conditions for a high recovery of RE while 0% of Al extraction were pH1, contact time=10min, and D2EHPA/TBP volume ratio= 4 : 1. At these conditions, the extraction yields of La(III) and Ce(III) were 72% and 89%, respectively. A two-step solvent extraction was developed to achieve a high purity of RE mixture, which included (1) the removal of impurity Fe by 25% (v/v) diisooctyl phosphinic acid (DiOPA) in n-octane for 140 min, (2) the extraction of rare earths by a mixture of di-2-ethylhexyl phosphoric acid (D2EHPA) and tributyl phosphate (TBP) in n-octane for 10 min without the need for adjusting the pH of the leaching solution.
Port logistics service quality and customer satisfaction: Empirical evidence from Vietnam
Le Duc Nha,Nguyen Hong Thi,Hoang Truong Phuc 한국해운물류학회 2020 The Asian journal of shipping and Logistics Vol.36 No.2
This paper aims to validate five determinants of service quality and to examine the service qualitycustomer satisfaction link in the port logistics service industry of a developing and transitional economy. First,the research reviews literature pertinentto service quality and customer satisfaction. Second, it uses both qualitative and quantitative methods through focus group discussion and directinterviews with 212 respondents who are the employees of firms that have been using port logistics service provided by Cat Lai Port, Ho Chi Minh City, Vietnam. Finally, the multivariate analysis is subsequently employed to analyze data obtained from surveys by structural equation modeling (SEM) technique. Findings indicate that port logistics service quality is positively determined by five factors including responsiveness, assurance, reliability, tangibles and empathy. In addition, port logistics service quality exerts positive influence on customer satisfaction. Most noticeably, as embedded in the tangibles component, technological advancements appear to enhance service quality which ultimately satisfies customers in the port logistics service industry.
Position-Based Feature Selection for Body Sensors regarding Daily Living Activity Recognition
Nguyen, Nhan Duc,Bui, Duong Trong,Truong, Phuc Huu,Jeong, Gu-Min Hindawi Limited 2018 Journal of sensors Vol.2018 No.-
<P>This paper proposes a novel approach to recognize activities based on sensor-placement feature selection. The method is designed to address a problem of multisensor fusion information of wearable sensors which are located in different positions of a human body. Precisely, the approach can extract the best feature set that characterizes each activity regarding a body-sensor location to recognize daily living activities. We firstly preprocess the raw data by utilizing a low-pass filter. After extracting various features, feature selection algorithms are applied separately on feature sets of each sensor to obtain the best feature set for each body position. Then, we investigate the correlation of the features in each set to optimize the feature set. Finally, a classifier is applied to an optimized feature set, which contains features from four body positions to classify thirteen activities. In experimental results, we obtain an overall accuracy of 99.13% by applying the proposed method to the benchmark dataset. The results show that we can reduce the computation time for the feature selection step and achieve a high accuracy rate by performing feature selection for the placement of each sensor. In addition, our proposed method can be used for a multiple-sensor configuration to classify activities of daily living. The method is also expected to deploy to an activity classification system-based big data platform since each sensor node only sends essential information characterizing itself to a cloud server.</P>
Classification of Five Ambulatory Activities Regarding Stair and Incline Walking Using Smart Shoes
Nguyen, Nhan Duc,Bui, Duong Trong,Truong, Phuc Huu,Jeong, Gu-Min IEEE 2018 IEEE SENSORS JOURNAL Vol.18 No.13
<P>In this paper, we propose a novel method to classify five ambulatory activities, i.e., level ground, incline descent, incline ascent, stair descent, and stair ascent walking using smart shoes which contain eight plantar-pressure sensors on each shoe. Pressure data are collected using an insole-based monitoring system regarding the walking activities conducted by participants at their self-imposed “normal” speed. We present three new features based on an analysis of step patterns to characterize the ambulatory activities and utilize a k-nearest neighbor algorithm to classify the activities from the created features. In experimental results, we obtain walking activity-recognition error rates of 2.16% at the sixth walking step. Furthermore, a proposed method outperforms two reference methods in terms of F1-score and overall accuracy rate.</P>
Daily wrist activity classification using a smart band
Nguyen, Nhan Duc,Truong, Phuc Huu,Jeong, Gu-Min IOP PUBLISHING 2017 PHYSIOLOGICAL MEASUREMENT Vol. No.
<P> <I>Objective:</I> In this letter, we propose a novel method for classifying daily wrist activities by using a smart band. <I>Approach:</I> Triaxial acceleration data are collected by built-in sensors of the smart band during experiments regarding five activities, i.e. texting, calling, placing a hand in a pocket, carrying a suitcase, and swinging a hand. We analyze patterns in the sensor signals during these activities based on three types of features, i.e. norm, norm-variance, and frequency-domain features. After extracting the significant features, a multi-class support vector machine algorithm is applied to classify these activities. <I>Main results:</I> We obtained recognition error rates of approximately 2.7% by applying the proposed method to the experimental dataset.</P>
Capacity Maximization for an RF Energy-harvesting Cooperative Cognitive Radio Network
Khac-Khiem Nguyen,Duc-Phuc Vuong,Le Danh Khanh 대한전자공학회 2018 IEIE Transactions on Smart Processing & Computing Vol.7 No.5
This work considers a cooperative cognitive radio network including a primary system with a primary transmitter-receiver pair (PT-PR) and a secondary system with a secondary transmitter-receiver pair (ST-SR). In order to access the licensed band allocated to primary users, the ST plays the role of a decode-and-forward relay in order to forward primary signals to the PR. In particular, after receiving the primary signals, the ST first uses a power-splitting energyharvesting method to harvest energy and decode the primary signals. Then, the ST superimposes its information on the decoded primary signals, and use the harvested power to transmit the superimposed signal to the PR and the SR. We here devote our efforts to formulating and solving an optimization problem aimed at maximizing the capacity obtained by secondary users while also guaranteeing quality of service for the primary users. Simulation results clearly show that our solution significantly improves the achievable capacity of secondary users.