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Exfoliated graphene nanosheets as high‑power anodes for lithium‑ion batteries
Duc‑Luong Vu,Yeon Ju Kwon,Soon Chang Lee,Jea Uk Lee,Jae‑Won Lee 한국탄소학회 2019 Carbon Letters Vol.29 No.1
High-quality and solution processable graphene sheets are produced by a simple electrochemical exfoliation method and employed as a high-power anode for lithium-ion batteries (LIBs). The electrochemically exfoliated graphene (EEG) composed of a few layers of graphene sheets, have low oxygen content and high C/O ratio (~ 14.9). The LIBs with EEG anode exhibit ultrafast lithium storage and excellent cycling stability, but low initial efficiency. The excellent rate capability and cycling stability are attributed to the favorable structural and chemical properties of the EEG, but the large irreversibility needs to be overcome for practical applications.
Predicting Financial Distress Distribution of Companies
Giang Huong VU(Giang Huong VU ),Chi Thi Kim NGUYEN(Chi Thi Kim NGUYEN ),Dang Van PHAM(Dang Van PHAM ),Diu Thi Phuong TRAN(Diu Thi Phuong TRAN ),Toan Duc VU(Toan Duc VU ) 한국유통과학회 2022 유통과학연구 Vol.20 No.10
Purpose: Predicting the financial distress distribution of an enterprise is important to warn enterprises about their future. Predicting the possibility of financial distress helps companies have action plans to avoid the possibility of bankruptcy. In this study, the author conducted a forecast of the financial distress distribution of enterprises. Research design, data and methodology: The forecasting method is based on Logit and Discriminant analysis models. The data was collected from companies listed on Vietnam Stock Exchange from 2012 to 2020. In which there are both companies suffer from financial distress and non-financial distress. Results: The forecast analysis results show that the Logistic model has better predictability than the Discriminant analysis model. At the same time, the results also indicate three main factors affecting the financial distress of enterprises at all three research stages: (1) Liquidity, (2) Interest payment, and (3) firm size. In addition, at each stage, the impact of factors on financial distress differs. Conclusions: From the results of this study, the author also made several recommendations to help companies better control company operations to avoid falling into financial distress. Adjustments to current assets, debt, and company expansion considerations are the most important factors for companies.
Minimizing Empty Trips of Yard Trucks in Container Terminals by Dual Cycle Operations
Vu Duc Nguyen,Kap Hwan Kim 대한산업공학회 2010 Industrial Engineeering & Management Systems Vol.9 No.1
One of the most important objectives of the schedules in a container terminal is to minimize the ship operation time, which consists of discharging and loading operation times. Recently, dual cycling techniques have been used for improving terminal operations, especially for reducing the total empty trips of handling equipment. The main focus of this study is to reduce the empty trip times of yard trucks with minimum delays for ship operations. A heuristic algorithm, modified from a previous algorithm, is proposed to solve this problem. A simulation study is conducted to evaluate the effect of different types of discharging and loading schedules and different locating methods for discharging containers in terms of the performance of the system, including the percentage of the dual cycle operations of yard trucks.
Vu Phuong Hoang,Tran Viet Duc,Duong Minh Cuong,Cong Quyet Thang,Nguyen Thu 대한중환자의학회 2020 Acute and Critical Care Vol.35 No.4
Background: Identifying when intubated patients are ready to be extubated remains challenging. The negative inspiratory force (NIF) is a recommended predictor of weaning success. However, little is known about the role of NIF in the weaning process for the Asian surgical intensive population, especially for the Vietnamese population. Here, we aimed to investigate the cutoff threshold and predictive value of the NIF index for predicting the success of ventilator weaning in Vietnamese surgical intensive care patients. Methods: A cross-sectional study was conducted at the Surgical Intensive Care Unit of Viet Duc Hospital from October 2016 to August 2017. A total of 64 patients aged 16–70 years undergoing ventilatory support through an orotracheal tube satisfied the criteria for readiness to begin weaning. The correlation between the NIF index with outcomes of the weaning process was analyzed. Specificity (Sp), sensitivity (Se), positive predictive value (PPV), negative predictive value (NPV), receiver operating characteristic (ROC) curve, and area under the curve (AUC) were calculated. Results: The success rate of the entire weaning process was 67.2% (43/64). The median NIF values were –26.0 cm H2O (interquartile range [IQR], –28.0 to –25.0) in the successful weaning group and –24.0 cm H2O (IQR, –25.0 to –23.0) in the weaning failure group (P<0.001). According to ROC analysis, an NIF value ≤–25 cm H2O predicted weaning success (AUC, 0.836) with 91% Se, 62% Sp, 83% PPV, and 77% NPV. Conclusions: An NIF cutoff threshold ≤–25 cm H2O can be used as predictor of weaning success in Vietnamese surgical intensive care patients.
Duc Thuan Vu,Pyung Hwang 한국트라이볼로지학회 2013 한국윤활학회지(윤활학회지) Vol.29 No.5
Overheating in electrical motors results in detrimental effects such as degradation of the insulation materials, demagnetization of magnets, increases in Joule losses, and decreases in motor efficiency and lifetime. Thus, it is important to find ways to dissipate heat from the motor and to keep the motor operating at its most efficient temperature. In this study, a new design to guide air flow through a given brushless direct current (BLDC) motor is developed and the design is analyzed, specifically by using computational fluid dynamics (CFD) simulations. The results showed that the temperature distribution in the three proposed models is lower than that in the original model, although the speed of the cooling fan in the original model reaches a very high value of 15 × 10³ rpm. The results also showed that CFD can be effectively used to simulate the heat transfer of BLDC motors.
Vu, Duc-Luong,Lee, Jae-Won The Korean Powder MetallurgyMaterials Institute 2018 한국분말재료학회지 (KPMI) Vol.25 No.6
The high theoretical energy density ($2600Wh\;kg^{-1}$) of Lithium-sulfur batteries and the high theoretical capacity of elemental sulfur ($1672mAh\;g^{-1}$) attract significant research attention. However, the poor electrical conductivity of sulfur and the polysulfide shuttle effect are chronic problems resulting in low sulfur utilization and poor cycling stability. In this study, we address these problems by coating a polyethylene separator with a layer of activated carbon powder. A lithium-sulfur cell containing the activated carbon powder-coated separator exhibits an initial specific discharge capacity of $1400mAh\;g^{-1}$ at 0.1 C, and retains 63% of the initial capacity after 100 cycles at 0.2 C, whereas the equivalent cell with a bare separator exhibits a $1200mAh\;g^{-1}$ initial specific discharge capacity, and 50% capacity retention under the same conditions. The activated carbon powder-coated separator also enhances the rate capability. These results indicate that the microstructure of the activated carbon powder layer provides space for the sulfur redox reaction and facilitates fast electron transport. Concurrently, the activated carbon powder layer traps and reutilizes any polysulfides dissolved in the electrolyte. The approach presented here provides insights for overcoming the problems associated with lithium-sulfur batteries and promoting their practical use.
Lumped Parameter Modeling and Analysis of Hybrid Magnet Engine Valve Actuator
Vu, Duc Thuan,Choi, Young,Kim, Jin-Ho 한국정밀공학회 2010 International Journal of Precision Engineering and Vol.11 No.6
The hybrid magnet engine valve actuator (HMEVA) composed of two types of magnets (permanent magnet and electromagnet) and two balanced springs is a promising tool for implementing innovative engine management strategies for variable valve timing. Finite Element Method (FEM), a favored actuator design tool due to its high accuracy, was utilized to analyze the electromagnetic actuator, but it consumes a lot of time especially in computation iterations jar optimization. Accordingly, the magnetic equivalent circuit analysis can be an alternative tool to FEM because of its computation iteration capability with fair accuracy. In this paper, an equivalent magnetic circuit model of an HMEVA is developed considering the reluctances, external magnetic forces and so on, and the simulation results are presented. In addition, the result of lumped parameter analysis (LA) is compared with those obtained from finite element ana£vsis for verification.