Vietnam Academy of Science and Technology: Journals Online
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MULTI-BAND PERFECT ABSORPTION INDUCED BY BREAKING THE SYMMETRY OF METAMATERIAL STRUCTURE
Get PDFIn this work, a multi-band metamaterial perfect absorber is demonstrated numerically and experimentally in the microwave region based on the breaking symmetry of geometrical structure. Initially, when the structure, which is designed in the X shape, is in the symmetric geometry, only one absorption peak is observed. By breaking the symmetry of structure, new absorption peaks emerge, leading to the multi-band perfect absorption. In addition, the separations of absorption peaks are proportional to the degree of geometrical asymmetry. Our work presents a simple and efficient approach to create multi-band metamaterial perfect absorbers
GLYCOSIDES ISOLATED FROM THE AERIAL PARTS OF Premna integrifolia L. GROWING IN THAI BINH
Get PDFFrom the aerial parts of Premna integrifolia L., three glycosides acteoside (1), premnaodoroside A (2), and premnaodoroside B (3) were isolated. Their chemical structures were elucidated by means of ESI-MS, 1H-NMR, 13C-NMR, HSQC, HMBC spectra and in comparison with the previous literature. To our best knowledge, this is the first report of 1 and 3 from P. integrifolia
PREPARATION AND CHARACTERIZATION OF GO/ZnO ELECTRODE FOR SUPERCAPACITORS
Get PDFIn this paper, zinc oxide (ZnO) nanoparticles were prepared by solvothermal method. A mixture of ZnO nanoparticles and GO, surfactants, binders are dispersed in aqueous solvent. This suspension was then used as the ink for the modified 3d printer to coat on the graphite substrate to form electrodes. The GO/ZnO film has a specific capacitance of 119.9 F/g at a scan rate of 5 mV/s of CV test. The specific discharge capacitance was 153.9 F/g and retained 94.5% after 3000 cycles of galvanostatic charge-discharge (GCD) measurement with a current density of 15 mA/cm2
PHÂN TÍCH CÁC CHỈ SỐ NƯỚC TỪ ẢNH VỆ TINH LANDSAT 8 OLI ĐỂ CHIẾT TÁCH ĐƯỜNG BỜ BIỂN KHU VỰC TÂY NAM VIỆT NAM
No full textThe paper presents results of analysis of water indices using remote sensing data to extract an instantaneous shoreline at the time of image acquisition on the southwest coast of Vietnam. The water indices as NDWI (Normalized Difference Water Index), MNDWI (Modified Normalized Difference Water Index), and AWEI (Automated Water Extraction Index) were calculated from Landsat 8 OLI imagery. Then, an extracted distribution histogram of water indices’ values in the study area was used to separate the land from the sea. The position having abnormal frequency of pixels on the histogram is the threshold value to determine the boundary of land and water, and it is considered the shoreline. The study showed the threshold values of NDWI, MNDWI and AWEI which were defined at 0.12, 0.17 and 0.18 respectively. The precision of shoreline extraction from each respective water index was verified by field survey data using Mean Absolute Error (MAE) and Root Mean Square Error (RMSE) methods. The verified results showed that MAE and MSE of the shorelines extracted from all three water indices were lower than an allowed limit of 30 m (equivalent to spatial resolution of the Landsat 8 image). However, the shoreline extracted from AWEI had the highest accuracy and it was considered the most appropriate shoreline at the acquisition time of image.Bài báo giới thiệu kết quả phân tích các chỉ số nước từ tư liệu ảnh viễn thám để chiết tách đường bờ biển khu vực Tây Nam Việt Nam. Các chỉ số nước NDWI, MNDWI và AWEI được tính toán từ các kênh ảnh của ảnh vệ tinh Landsat 8 OLI. Sau đó, dựa vào biểu đồ phân phối giá trị của các chỉ số nước ở khu vực nghiên cứu để phân tích ranh giới đất và nước. Giá trị đột biến về tần suất các điểm ảnh trên biểu đồ phân phối của các chỉ số nước là giá trị ngưỡng để xác định ranh giới đất và nước, và được coi là đường bờ biển. Kết quả nghiên cứu đã cho thấy, giá trị ngưỡng của chỉ số NDWI được xác định là 0.12, tương ứng các giá trị ngưỡng là 0.17 đối với chỉ số MNDWI và 0.18 đối với chỉ số AWEI. Sau khi chiết tách các đường bờ tương ứng từ các chỉ số nước, việc kiểm chứng độ chính xác được thực hiện bằng các dữ liệu khảo sát thực địa theo hai phương pháp đánh giá sai số tuyệt đối trung bình và sai số trung phương. Kết quả kiểm chứng đã cho thấy, đường bờ được chiết tách từ cả ba chỉ số nước có sai số tuyệt đối trung bình và sai số trung phương đều nằm trong giới hạn cho phép là nhỏ hơn 30m (tương đương với độ phân giải không gian của ảnh Landsat 8). Tuy nhiên, đường bờ được chiết tách từ chỉ số AWEI là có độ chính xác cao nhất và được coi là đường bờ phù hợp nhất tại thời điểm thu nhận ảnh
TRACKING CONTROL FOR ELECTRO-OPTICAL SYSTEM IN VIBRATION ENVIROMENT BASED ON SELF-TUNING FUZZY SLIDING MODE CONTROL
Get PDFThe paper presents a new method for tracking control of EOTS (Electro-Optical Tracking System) operating in mobile environment such as ship, air plane, tank and so on. This makes the base body of the EOTS has angular motion. The control alogorithm used in this paper is adaptive fuzzy sliding mode. The overall control is built and simulated in Matlab and compared with a sliding mode controller and a conventional PID controller. The simulation result illustrated the effectiveness of the proposed controlle
Real-Time Smile Detection using Deep Learning
Get PDFReal-time smile detection from facial images is useful in many real world applications such as automatic photo capturing in mobile phone cameras or interactive distance learning. In this paper, we study different architectures of object detection deep networks for solving real-time smile detection problem. We then propose a combination of a lightweight convolutional neural network architecture (BKNet) with an efficient object detection framework (RetinaNet). The evaluation on the two datasets (GENKI-4K, UCF Selfie) with a mid-range hardware device (GTX TITAN Black) show that our proposed method helps in improving both accuracy and inference time of the original RetinaNet to reach real-time performance. In comparison with the state-of-the-art object detection framework (YOLO), our method has higher inference time, but still reaches real-time performance and obtains higher accuracy of smile detection on both experimented datasets
VLSP Shared Task: Named Entity Recognition
Get PDFNamed entities (NE) are phrases that contain the names of persons, organizations, locations, times and quantities, monetary values, percentages, etc. Named Entity Recognition (NER) is the task of recognizing named entities in documents. NER is an important subtask of Information Extraction, which has attracted researchers all over the world since 1990s. For Vietnamese language, although there exists some research projects and publications on NER task before 2016, no systematic comparison of the performance of NER systems has been done. In 2016, the organizing committee of the VLSP workshop decided to launch the first NER shared task, in order to get an objective evaluation of Vietnamese NER systems and to promote the development of high quality systems. As a result, the first dataset with morpho-syntactic and NE annotations has been released for benchmarking NER systems. At VLSP 2018, the NER shared task has been organized for the second time, providing a bigger dataset containing texts from various domains, but without morpho-syntactic annotation. These resources are available for research purpose via the VLSP website vlsp.org.vn/resources. In this paper, we describe the datasets as well as the evaluation results obtained from these two campaigns
An improved space domain algorithm for determining the 3-D structure of the magnetic basement
No full textThe paper presents an improved algorithm based on Bhaskara Rao and Ramesh Babu’s algorithm to invert magnetic anomalies of three-dimensional basement structures. The magnetic basement is approximated by an ensemble of juxtaposed vertical prisms whose bottom surface coincides with Curie surface with the known depth. The computer program operating with the proposed algorithm is built in Matlab environment. Test applications show that the proposed method can perform computations with fast and stable convergence rate where the results also coincide well with the actual model structure. The effectiveness of the method is demonstrated by inverting magnetic anomalies of the southeast part of Vietnam continental shelf. The calculated magnetic basement relief of the study area provides useful additional information for studies in the aim of dealing with the geological structure of the area.References Beiki M., 2010. 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Spatial distribution of submerged aquatic vegetation in An Chan coastal waters, Phu Yen province using the PlanetScope satellite image
No full textSeaweed and seagrass form marine submerged aquatic vegetation (SAV), which plays an essential role in economic development and ecological protection in coastal areas. In this study, PlanetScope (PS )imaging data was combined with in situ samplings to demonstrate their ability to map SAV distribution in An Chan commune, Tuy An district, Phu Yen province, Central Vietnam. Thanks to data pre-processing by Lyzenga’s algorithm and the masking in PS image allow us to remove partly the signals of spectral noises from sun glint effect as well as other random noises. The analysis and accuracy assessment of SAV classification by four different techniques: DII, enhanced DII, BRI and enhanced BRI were alternately performed. The overall accuracy in the accuracy assessment of SAV classification by the above techniques were alternately 83.33%, 88.58%, 86.17%, and 92.52% respectively. Kappa coefficients in the accuracy assessment of SAV classification by the above techniques were alternately 0.77, 0.84, 0.81 and 0.90 respectively. The results of SAV classification by enhanced BRI technique provided the best accuracies and will be chosen for assessing the distribution of Submerge Aquatic Vegetation (SAV) canopies in An Chan coastal waters from PS satellite image. The seagrass beds in An Chan is spread along the coast as well as lie close to the coast of islets. Whereas, the seaweed meadows lie in deeper waters and in the foot of the reefs in 3–4m deep. The total seagrass area in An Chan region was approximately 12.22 ha, with 10.93 ha seagrasses in My Quang, 1.18 ha in Hon Chua and 0.11 ha in Hon Dua. The total seaweed area in An Chan region was approximately 50.32 ha, with 20.20 ha seaweed meadows in My Quang, 22.8 ha in Hon Chua, 5.72 ha in Hon Dua and a small part of 1.60 ha in underwater small reefs
