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Khoa Dang Truong 아시아영어교육학회 2021 The Journal of Asia TEFL Vol.18 No.2
This mixed-method study investigated teacher and student perceptions of the importance of taskrelated motivational strategies (TRMS) in English as a foreign language (EFL) classroom instruction. A 48-item Likert scale questionnaire covering seven domains of TRMS were electronically delivered to teachers (N = 96) at different institutions in a large city in southern Vietnam and their students (N = 220). Concurrently, thirty-four written reflections were obtained from the teachers (N = 17) and the students (N = 17) to shed further light on their perceptions. Examining the participants’ central tendencies showed that they agreed on the motivational value of task nature, task relevance, task materials, task-related feedback, and during-task teacher behavior, but not on task presentation and task level. Item analyses further revealed statistically significant differences in the participants’ perceptions of as much as 23 percent of the TRMS. Recursive content analysis of the journal data corroborated a substantial part of the quantitative results and offered explanations for why each specific difference occurred. These perceptual mismatches provide important pedagogical implications for how teachers can design and implement tasks in the way that is motivating to students whose English learning is entirely confined within classroom walls.
Khoa-Dang Pham,Nho-Van Nguyen 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.3
This paper presents a pulse-width modulation strategy to eliminate the common mode voltage (CMV) with reduced CMV spikes in multilevel inverters since a high CMV magnitude and its fast variations dv/dt result in bearing failure of motors, overvoltage at motor terminals, and electromagnetic interference (EMI). The proposed method only utilizes the zero CMV states in a space vector diagram and it is implemented by a carrier-based pulse-width modulation (CBPWM) method. This method is generalized for odd number levels of inverters including neutral-point-clamped (NPC) and cascaded H-bridge inverters. Then it is extended to the over-modulation mode. The over-modulation mode is implemented by using the two-limit trajectory principle to maintain linear control and to avoid look-up tables. Even though the CMV is eliminated, CMV spikes that can cause EMI and bearing current problems still exist due to the deadtime effect. As a result, the deadtime effect is analyzed. By taking the deadtime effect into consideration, the proposed method is capable of reducing CMV spikes. Simulation and experimental results verify the effectiveness of the proposed strategy.
Required Base Station Density for Communication-Efficient Federated Learning in Small-Cell Networks
Khoa Anh Nguyen,Quan Anh Nguyen,Jun-Pyo Hong 한국통신학회 2021 한국통신학회 학술대회논문집 Vol.2021 No.6
Federated Learning (FL) generates massive benefits of shared machine learning models without violating security and privacy requirements, making this setting relevant for many wireless applications. In this paper, we comprehensively investigate the effects of geographic node deployment on the model aggregation in federated learning on the basis of stochastic geometry-based analysis. Based on the coverage probability expression derived with stochastic geometry framework, we derive and discuss the minimum required base station density for achieving a target model aggregation rate in small-cell networks with algorithms for optimizing the target transmission rate and the base station density.
Text Segmentation from Images with Various Light Conditions Based on Gaussian Mixture Model
Khoa Anh Tran,Gueesang Lee 한국콘텐츠학회 2013 International Journal of Contents Vol.9 No.1
Standard Gaussian Mixture Model (GMM) is a well-known method for image segmentation. However, one of its problems is that we consider the pixel as independent to each other, which can cause the segmentation results sensitive to noise. It explains why some of existing algorithms still cannot segment texts from the background clearly. Therefore, we present a new method in which we incorporate the spatial relationship between a pixel and its neighbors inside 3x3 windows to segment the text. Our approach works well with images containing texts, which has different sizes, shapes or colors in case of light changes or complex background. Experimental results demonstrate the robustness, accuracy and effectiveness of the proposed model in image segmentation compared to other methods.
Autoencoder-based Anomaly Detection
Khoa Anh Ngo(노안콰),Junhan Kim(김준한),Jiseob Kim(김지섭),Jaseong Koo(구자성),Seungjae Baeck(백승재),Byonghyo Shim(심병효) 한국통신학회 2021 한국통신학회 학술대회논문집 Vol.2021 No.2
Recently, much research has been devoted to developing deep learning-based anomaly detection techniques. If there is a huge amount of data samples, then deep learning models can be trained to provide an end-to-end solution for anomaly detection. However, in many realistic scenarios, the number of anomalies that can be used for training deep learning models is very limited. In this case, deep learning models trained in the manner of supervised learning performs poor, especially when detecting anomalies in the test phase. In this paper, to overcome this limitation, we put forth an autoencoder-based anomaly detection technique. Through the simulations based on the dataset provided by Samsung display, we show that the proposed technique can detect anomalies well.
Khoa D. Nguyen,Son H. Doan,Anh N.V. Ngo,Tung T. Nguyen,Nam T.S. Phan 한국공업화학회 2016 Journal of Industrial and Engineering Chemistry Vol.44 No.-
A metal–organic framework Fe3O(BPDC)3 was synthesized, and used as a productive heterogeneouscatalyst for the direct C–N coupling of azoles with ethers via oxidative C–H activation to produce azolederivatives. The MOF-based catalyst displayed higher catalytic efficiency than many homogeneouscatalysts as well as several MOFs in the transformation. The MOF-based catalyst could be reused manytimes for the synthesis of azole derivatives by the direct C–N coupling of azoles with ethers without anoteworthy deterioration in catalytic efficiency. To the best of our knowledge, this direct C–N couplingreaction was not previously performed in the presence of heterogeneous catalysts.