Journal of Science and Technique
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KHẢO SÁT ẢNH HƯỞNG CỦA CHIỀU CAO VÀ ĐỘ CONG BỀ MẶT MẪU LÊN ĐẶC TÍNH KHỬ PHẢN XẠ CỦA LỚP MÀNG DLC PHỦ TRÊN ĐẾ Si BẰNG CÔNG NGHỆ PECVD
Get PDFTrong lĩnh vực an ninh, khí tài ảnh nhiệt ngày càng được sử dụng phổ biến trong các hệ thống giám sát và thường hoạt động trong điều kiện môi trường khắc nghiệt. Để bảo vệ khí tài ảnh nhiệt, người ta thường sử dụng lớp màng cacbon giả kim cương (DLC) mạ lên thấu kính ngoài cùng hoặc kính bảo vệ do màng DLC có khả năng chống mài mòn, độ cứng cao, chịu được môi trường khắc nghiệt và trong suốt trong vùng phổ hồng ngoại của ảnh nhiệt. Trong các thí nghiệm của chúng tôi, màng DLC được mạ phủ bởi phương pháp lắng đọng hơi hóa học tăng cường bằng plasma (PECVD) trên thiết bị Aegis DLC-PECVD của hãng Intlvac (Canada). Tuy nhiên, khi phủ các chi tiết quang học có kích thước lớn, sự thay đổi cấu hình plasma có thể gây ra hiện tượng không đồng nhất của lớp phủ. Bài báo trình bày các kết quả thực nghiệm mạ màng DLC khử phản xạ cho vật liệu Si trong vùng phổ từ 3-5 µm và thông qua phổ truyền qua, khảo sát sự đồng đều của lớp màng DLC trên các mẫu Si đặt ở các vị trí khác nhau trong buồng mạ. Kết quả thực nghiệm cho thấy, khi độ cao đặt mẫu thay đổi từ 0-40 mm so với điện cực của nguồn plasma, phổ truyền qua của các mẫu gần như không có sự thay đổi về hình dạng, cường độ phổ truyền qua thay đổi nhẹ trong khoảng 1,6% với các mẫu được phủ DLC lên một mặt. Với các mẫu đặt ở độ nghiêng khác nhau, vị trí đỉnh phổ có sự dịch chuyển về bước sóng dài từ 3,4-4 µm ứng với góc pháp tuyến từ 0-50 độ. Các kết quả thực nghiệm này giúp định hướng tối ưu hóa thiết kế bộ gá mẫu giúp cải thiện độ đồng đều của màng DLC trên thấu kính ảnh nhiệt kích thước lớn
HIGHLY EFFECTIVE SIMULATION MODELS IN ANALYZING AERODYNAMICS OF AIRFOILS AT LOW REYNOLDS NUMBER
Get PDFRecently, much work has been conducted for airfoils at low Reynolds and high velocity for further improving design airplanes those can fly on Mars and on stratosphere of the Earth. In this study, the aerodynamic characteristics of a typical airfoil shape named Ishii are studied by numerical approach for understanding the aerodynamic forces and flow fields at different angle of attack and Mach number. To reduce the numerical time, the Reynolds averaged Navier-Stokes equations are used for the simulation. The numerical results are compared with previous experimental data at the same flow conditions. This study found that the turbulent model should be changed from k-ω SST for angles of attack below 8° to k-ε model for higher angles of attack to obtain the accurate results. The maximum difference between simulation and experimental results is less than 9%. To extend the results, the aerodynamic characteristics were investigated for angles of attack from 0° to 20° and the Mach number between 0.2 and 0.8. The effect of serration at the leading edge on aerodynamic characteristics was also investigated. The results of the current study show that the angle of attack with maximum lift coefficient is around 8° at M = 0.2 and it increases for increasing Mach number. At high angle of attack, the lift decreases but large stall does not occur. The reason is from the generation of a separation bubble at leading edge of airfoil, which shows different characteristics from normal airfoil model. The serration at leading edge increases lift and aerodynamic performance for angles of attack above 8°. The results of the proper orthogonal decomposition indicates that the unsymmetric flow with a large wake structure is the most dominant flow at high angles of attack. The flow pattern of those modes, velocity and pressure distributions around the model are discussed
STABILITY MECHANISM OF MASONRY SEMI-CIRCULAR ARCHES
Get PDFMasonry arches are ancient structures, applied from tunnel works to complex constructions such as churches, temples, and castles, bearing the aesthetic and unique style of each civilization across various periods. A masonry arch consists of a series of blocks of a specific size stacked atop one another to create an upward curve that can maintain its shape and stability through the interaction of forces among the blocks within the structure. This research elucidates the principles and stability mechanisms of masonry arches in the case of support displacements. Focus on investigating the influence of structural thickness on the stability of masonry semi-circular arches. Simultaneously, it assesses the influence of the surrounding soil on the stability of the structural system. From there, determine the minimum structural thickness to ensure stability under different working conditions of masonry semi-circular arches
EVALUATION OF THE ABILITY TO TRANSFORM YPERITE BY GREEN DECONTAMINATION BASED ON TUNGSTEN
Get PDFThis article presents the research findings on the evaluation of the ability to transform yperite (HD - a blister agent) of green decontamination based on tungsten. Several key factors influencing the decontaminating potential are thoroughly investigated, including the decontaminant-to-contaminant ratio, reaction temperature, and solution stability. Additionally, the decontamination efficiency on various materials such as paint, alumium, and L1 rubber fabric is also assessed. The results show that at a reaction volume ratio of 1:10, temperature ranging from 10oC to 50oC, and solution stability maintained for 18 hours, the decontamination efficiency on the aluminum surfaces exhibits the highest rate of 99.5%, followed by L1 fabric with 96.2% and paint with 77.8%; the density of decontaminant is recommended to apply 0.2-0.3 L/m2. Moreover, the transformation mechanism of HD by the green decontamination agent is also proposed.
ĐỀ XUẤT MỘT PHƯƠNG PHÁP HUẤN LUYỆN KẾT HỢP CHO MẠNG NƠRON ĐỘT BIẾN ĐỂ CẢI THIỆN ĐỘ CHÍNH XÁC TRONG NHẬN DẠNG HỆ SỐ KHÍ ĐỘNG CỦA MÁY BAY
Get PDFBài báo đề xuất một phương pháp huấn luyện kết hợp cho mạng nơron đột biến để nhận dạng các hệ số khí động của máy bay trong kênh độ cao theo mô hình phi tuyến. Phương pháp huấn luyện đề xuất là sự kết hợp của thuật toán lan truyền ngược với thời gian phân rã thích nghi và thuật toán lan truyền ngược sai số đột biến chuẩn hóa. Sự kết hợp này tận dụng được ưu điểm của hai thuật toán trong việc cập nhật thời gian phân rã và trọng số khớp nối. Điều này sẽ rút ngắn được thời gian và tính ổn định trong quá trình suy giảm sai số khi huấn luyện mạng. Do đó, nó đảm bảo nâng cao độ chính xác và độ tin cậy của các tham số khí động cần nhận dạng. Các kết quả mô phỏng cho thấy các hệ số khí động trong kênh độ cao của máy bay được nhận dạng bằng phương pháp đề xuất có độ chính xác cao hơn các phương pháp truyền thống và tốc độ hội tụ của mạng nhanh hơn khi được huấn luyện với việc sử dụng riêng rẽ từng phương pháp. Ngoài ra, kỹ thuật bootstrapping được sử dụng để xác định khoảng tin cậy cho các tham số khí động. Dựa vào khoảng tin cậy cho thấy phương pháp đề xuất có kết quả tin cậy hơn so với thuật toán trước khi kết hợp
MACHINE LEARNING-BASED DOSE RECOMMENDATIONS FOR REMOVAL OF RESIDUAL THYROID TISSUE
Get PDFThyroid cancer, particularly differentiated types such as papillary and follicular carcinomas, presents a significant health challenge globally and in Vietnam, where surgical removal of the thyroid gland (thyroidectomy) is the primary treatment approach. However, residual thyroid tissue often remains post-surgery, necessitating effective ablation to prevent recurrence and complications. Radioactive iodine therapy using I-131 is the standard method for ablating this residual tissue. The accuracy of I-131 dose estimation plays a crucial role in ensuring therapeutic success and patient safety. Traditional methods rely on general guidelines and physician expertise but may lack the precision necessary for individual patients. While several previous studies have attempted to improve dose estimation using machine learning approaches, they have often overlooked the importance of data preprocessing techniques. This lack of attention to data quality has limited the performance of predictive models. To address this problem, our study expands upon prior work by placing a strong emphasis on data preprocessing, aiming to enhance model accuracy and reliability. We implement a multi-stage framework that processes medical records and identifies key features, using seven traditional machine learning models for prediction. Our results demonstrate that the Decision Tree model outperforms other models, achieving the highest True Positive Rate of 0.995, a low False Positive Rate of 0.001, and exceptional performance in Recall, Precision, and F1-score (0.995, 0.996, and 0.995, respectively). Moreover, we developed decision rules generated by the Decision Tree for dose prediction, which use a dataset of clinical information from Vietnamese patients. This model represents a promising tool for improving radiation therapy delivery, ensuring more accurate, data-driven decisions, and ultimately better patient outcomes
DEVELOPMENT OF AN AUTOMATIC PROGRAM FOR DYNAMICS ANALYSIS OF 3D CONCRETE PRINTER FRAME WITH FLEXIBLE LINKS
Get PDFThis article presents the development of an automated program for calculating the dynamics of a large-scale concrete 3D printer frame with flexible links. The calculation program was developed by integrating three modules: Ansys© Parametric Design Language (APDL) code, MSC Adams© code, and MATLAB© code. The Ansys APDL code is used to establish the model of flexible links. The MSC Adams code is utilized to analyze the dynamics of the printer frame. The MATLAB code connects the modules, enabling automatic modification of structural parameters and motion rules of the printer axis. The developed program allows for automated dynamic calculations of the system with flexible links across various design parameters conveniently. Based on this, the effects of some structural parameters of the flexible links (beam cross-sectional dimensions) and kinematic parameters (frequency of motion variation, velocity) on the positional error of the print nozzle trajectory have been calculated, analyzed, and compared to systems with rigid links. Particularly, the simulation time for each set of design parameters has been significantly shortened, from 30-40 minutes (in case manually) to just 3-4 minutes. The research results provide a foundation for optimizing the printer frame design according to structural and dynamic criteria
EVALUATION OF SOIL LOSS ACROSS LAND USE TYPES IN NORTHERN VIETNAM, A CASE STUDY OF TAY CON LINH MOUNTAIN
Get PDFDeforestation and farming offer two of the most serious risks to soil erosion (SER), water degradation, and desertification... Based on the Universal Soil Loss Equation (USLE) proposed by Wischmeier and Smith, the paper aims to use Geographic Information Systems (GIS) to evaluate the risk of SER in the Tay Con Linh mountain area in Vietnam. Maps of the environmental parameters and the resulting erosion risk were also proposed. The study has discovered that the kind of vegetation in the area was the primary factor in SER. It was concerned with farming methods relevant to steep topography. Studies have demonstrated that the vegetation type in this region is a key determinant of severe erosion. To validate the methodology, Google Earth images of locations identified as prone to erosion were analyzed based on strict criteria. The model demonstrated an efficiency rate of 88.5%. According to the Vietnamese standard TCVN 5299:2009, the levels of erosion in the study area are quite complex but classified as medium risk, with many regions exhibiting R-I level conditions (93.51% soil loss of 10 tons per hectare per year). The study established correlations between the degree of erosion and the amount of vegetation cover, emphasizing the impact of land use on soil erosion rates. This assessment of soil erosion not only aids land users in making informed decisions regarding land use and ecosystem conservation but also provides scientific criteria that complement traditional farmers' knowledge
DESIGNING INGREDIENTS OF BTX FLASH-REDUCED PROPELLANT WITH A HIGH PVC CONTENT
Get PDFBased on experiments, it was researched to determine the kind of pyroxylin and the effect of flash-reduced additives (PVC) on the quality of BTX propellant. Therefore, it designed ingredients for the research and manufacture of propellant of BTX with high PVC content. The results show that the kind of pyroxylin used type BA with a high nitrogen content (about 13.26% N). The flash-reduced additive is the PVC with chlorine content at 61-65% and the thermochemical coefficient of PVC is about -(2±0.5) [kcal/(kg ´ %)]. When using PVC with the above properties the chemical stability of the propellant is high. At that time, the ingredients of BTX flash-reduced propellant with a high PVC content are determined to be about 77% Pi-BA; 20% PVC; 1.38% DPA; 0.35% ethyl-alcohol; 0.15% ethyl-ether; 1.1% moisture and about 0.02% graphite (addition)
A PROPOSED DISTRIBUTED ARCHITECTURE FOR SEARCHING SEMANTICALLY ON A LARGE DATASET OF HACKING NEWS
Get PDFIn this paper, we propose a distributed architecture to support semantic search on largescale datasets of online technology news. The solution combines knowledge graph modeling, natural language processing techniques, and distributed processing on Apache Spark. The paper presents: (1) A distributed architecture that stores a large-scale semantic news dataset using resource description framework model; (2) A pipeline for extracting knowledge from text using natural language processing (NLP) tools such as dependency parsing and named entity recognition; (3) A distributed search engine that uses keyword expansion and graph reasoning to return semantically related results. The experimental results show that the proposed model improves the semantic search capabilities on large-scale data compared to traditional keywordbased search methods