Journal of Science and Technique
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AN APPLICATION OF ANALYTICAL METHOD FOR EVALUATING THE STRESS-STRAIN STATE OF DEEP LINED CIRCULAR TUNNELS IN DRY ANISOTROPIC ROCK CONSIDERING ROCK-LINING INTERACTION AND CONSTRUCTION STAGES
Get PDFIn the context of Vietnam's strategic orientation toward developing nuclear energy, the disposal of high-level radioactive waste (HLW) from nuclear power plants is a pressing issue that must be addressed. The long-term storage of HLW in deep geological repositories is a solution being researched and applied in many developed countries, wherein deep tunnels constitute a fundamental component of this system. Circular cross-section tunnels at depth are also widely used for road and high-speed railway tunnels through mountains. Currently, studies on deep tunnels, where the rock strata often exhibit anisotropic properties, are rarely mentioned and investigated in Vietnam. This article aims to present an analytical method for evaluating the stress-strain state of a deep, lined circular tunnel in a dry, anisotropic rock mass, considering the rock-liner interaction under two conditions: perfect bonding and relative slip. Additionally, the influence of the tunnel face advance on the stress-strain state of the tunnel is taken into account based on the well-known convergence-confinement method. The analytical solution for the interaction problem is developed using the complex potential approach with the conformal mapping technique and the theory of thin elastic cylindrical shells. The derived analytical solution is verified against available solutions for several special cases. Based on the obtained solution, parametric studies of the anisotropic rock mass are conducted to assess their influence on the liner's response. This analytical solution can serve as a rapid analysis tool for the preliminary design of deep tunnels in anisotropic rock
BALANCING COMPOSITE MOTION OPTIMIZATION FOR CONSTRUCTION SITE FACILITY LAYOUT PROBLEMS
Get PDFThe arrangement of construction facilities on the construction site is one of the important problems of construction organization, but at the same time it represents a complex combinatorial optimization problem. Metaheuristic methods are recognized as powerful and effective tools in solving such problems. The Balancing Composite Motion Optimization (BCMO) algorithm is a recently proposed metaheuristic algorithm. This article introduces the results of establishing a problem model and applying the BCMO algorithm with discrete variables receiving integer values to solve the problem of arranging service facilities on the construction site based on a static model. A numerical experiment with three static problem cases selected from the sample problems is conducted. The obtained layout options are compared with the results from other algorithms, thereby demonstrating the proposed algorithm's advantages: its ease of implementation, capability to search for and identify multiple good solutions, and fast convergence speed. The numerical experiment also shows the need for further experimentation and exploration to enhance the algorithm
ENHANCING ADVERSARIAL ROBUSTNESS IN MACHINE LEARNING-BASED MALWARE DETECTION VIA ACTIVATION FUNCTION DESIGN
Get PDFIn recent years, machine learning (ML) has significantly enhanced the efficiency of malware detection systems. Despite achieving high performance, these models now face a growing threat from adversarial attacks. Adversarial malware samples can be intricately crafted to deceive detection models, resulting in misclassifications of malicious programs, thereby allowing them to bypass security systems. Various techniques have been developed to generate adversarial malware specifically designed to evade different ML-based detection systems. This threat underscores the urgent need for solutions that enhance the resilience of malware detection models against adversarial attacks. The paper evaluates and proposes an empirical cost-efficient adversarial defense strategy recommendation via activation function design, that does not require computationally intensive methods such as adversarial training, while boosting the inherent resilience of ML-based malware detection models against black-box attacks. Results show that specific combinations, in particular Rectified Linear Unit (ReLU) and Tanh, can significantly boost robustness without additional training or inference setup. This work provides an empirical design aspect for building intrinsically robust ML-based malware detection systems
MỞ RỘNG THUẬT TOÁN CBSL CHO BÀI TOÁN ĐỊNH HƯỚNG VỚI MẢNG ĂNG TEN LỒNG GHÉP TRONG SÔ NA THỤ ĐỘNG
Get PDFBài báo nghiên cứu việc áp dụng thuật toán CBSL (Combine Filter - Broadband - Simultaneous Orthogonal Matching Pursuit - Least Squares) cho bài toán định hướng tín hiệu (DOA) trong sô na thụ động sử dụng mảng ăng ten lồng ghép (Nested). Thuật toán này kết hợp biểu diễn thưa và lọc răng lược thích nghi, được nhóm tác giả đề xuất trước đó. Bài báo tập trung phân tích mô hình tín hiệu cho mảng Nested và đánh giá hiệu suất của phương pháp đề xuất thông qua mô phỏng. Kết quả chỉ ra rằng phương pháp này cải thiện độ phân giải phổ, giảm số lượng đỉnh phụ và nâng cao độ chính xác định hướng, đồng thời phương pháp ước lượng DOA sử dụng thuật toán CBSL cho mảng Nested ưu điểm hơn so với phương pháp truyền thống sử dụng mảng ULA về số lượng nguồn tín hiệu khi có cùng số lượng cảm biến vật lý với mảng thẳng cách đều (ULA)
IMPACTS OF TEXTILE MATERIALS ON THE MAIN PROPERTIES OF WEFT KNITTING FABRIC MADE FROM BAMBOO AND POLYAMIDE YARNS
Get PDFThis article represents the evaluation of the influence of textile materials on some physical and mechanical properties of knit fabrics concerning break load, elongation at break, determination of capillarity, air permeability, stretch properties, and elasticity. The evaluations are performed on 3 fabric samples with composition ratio: 70% bamboo/ 20% polyamide/ 10% spandex, 100% polyamide, 80% bamboo/ 20% polyamide, provied by local manufacturers for testing. The research uses the standard test methods of determination of breaking load and elongation at break to TCVN 5795:1994, capillarity to TCVN 5073:1990, air permeability of textile fabrics to TCVN 5092:2009 (ASTM D 73:2004), stretch properties of knitted fabrics having low power to (ASTM D2594), textiles - stretchability of fabrics and ribbons to NF G07-196. Experimental results are synthesized and calculated to compare and analyze the data obtained for each sample of test cloth and the results showed that textile materials and some structural parameters affect some physical and mechanical properties of knit fabrics
GREEN SYNTHESIS OF NANO-ZERO-VALENT IRON USING CLEISTOCALYX OPERCULATUS EXTRACT FOR EFFICIENT RHODAMINE B DEGRADATION
Get PDFIn this study, nano-zero-valent iron (nZVI) was successfully synthesized via a green method using Cleistocalyx operculatus leaf extract as a natural reducing and capping agent. The synthesized nZVI was characterized by XRD, SEM-EDS, FT-IR, and BET. The XRD pattern confirmed the formation of crystalline α-Fe⁰, while SEM images revealed spherical aggregates in the 50-100 nm size range. FT-IR analysis identified organic functional groups from the plant extract on the nanoparticle surface, indicating bio-capping. BET analysis showed a specific surface area of 67.484 m2/g with a mixed micro-mesoporous structure. Batch experiments revealed that while nZVI alone primarily adsorbed Rhodamine B (RhB) and H₂O₂ alone exhibited limited oxidation, the combined nZVI/H₂O₂ system achieved nearly complete decolorization within 50 min. The enhanced efficiency was attributed to a heterogeneous Fenton-like process generating highly reactive ·OH radicals. These findings demonstrate that Cleistocalyx operculatus-mediated nZVI offers a sustainable and effective approach for the removal of organic dyes from wastewater, highlighting its potential in advanced water treatment applications
EFFECT OF COMPRESSION FORCE IN THE FABRICATION OF MEMBRANE ELECTRODE ASSEMBLY BY DECAL METHOD FOR PROTON EXCHANGE MEMBRANE WATER ELECTROLYZER
Get PDFProton exchange membrane water electrolysis (PEMWE) is a promising technique for producing high-purity hydrogen without using fossil fuels. The outstanding advantage of PEMWE is that it is combined with renewable energy sources such as solar, wind, etc. to produce green hydrogen. The most important part in a proton exchange membrane water electrolyzer is the membrane electrode assembly (MEA). The performance of PEMWE is mainly determined by the properties of the MEA. In this paper, the authors studied the preparation of the anode catalyst layer by ink spray technique on a teflon substrate in the fabrication of MEA by decal method. This is the most advanced method that allows the fabrication of MEAs that are both of good quality and easy to perform. The pressing conditions were studied, tested and evaluated, thereby providing the optimal pressing parameters for the fabrication of MEA and then applying MEA to the proton exchange membrane water electrolyzer, running tests at different current densities and achieving the minimum potential value of 1.708 V at a current density of 1 A/cm2
EFFECT OF SILICON ADDITION ON DEZINCIFICATION OF L72 BRASS IN CHLORIDE MEDIA
Get PDFBrass alloys (Cu-Zn) are susceptible to dezincification, especially in chloride-rich environments. This study investigates the effect of adding 0.5% silicon to L72 brass on its corrosion behavior and resistance to localized corrosion induced by microcracks. Samples with and without silicon were immersed in a 3.5% NaCl solution and analyzed using electrochemical testing, EDX techniques, and dezincification coefficient (z) measurements. The results show that silicon addition improves corrosion resistance by increasing the corrosion potential, reducing current density, and minimizing zinc loss. OM and EDX analyses confirmed that the silicon-containing alloy exhibited a smoother surface and higher copper content. However, microstructural observations revealed that silicon can alter grain boundaries and promote microcrack formation, which may initiate localized corrosion. These findings suggest that while silicon enhances overall dezincification resistance, it may also introduce structural vulnerabilities, highlighting the need to optimize silicon-alloyed brass compositions to improve corrosion resistance while minimizing microcrack-induced degradation in aggressive environments
INVESTIGATION OF ELECTROCHEMICAL CHARACTERISTICS of α-NaxMnO2 CATHODES FOR SODIUM-ION BATTERIES
Get PDFP2 and O3 layered structure materials have large potential for application as cathodes for sodium-ion batteries. This article presents the research results on the electrochemical properties of layered structure α-NaxMnO2 (x = 0.7-1.0) cathode materials synthesized via the sol-gel method. The α-NaxMnO2 cathode materials were characterized by X-ray diffraction (XRD) to determine their crystal structure, scanning electron microscopy (SEM) to analyze their morphology, and energy-dispersive X-ray spectroscopy (EDX) to assess their elemental composition. The electrochemical properties of α-NaxMnO2 materials were investigated using CR2032 coin cells, in which the cathodes were fabricated from the synthesized α-NaxMnO2 materials. The α-NaxMnO2 cathode material exhibited the highest initial charge-discharge capacity at a rate of 0.1 C when x = 1.0, with values of 168.43 mAh.g-1 and 165.18 mAh.g-1 in the first cycle, respectively. However, the capacity declined significantly after 10 cycles and reached only about 50.02% of its initial value after 50 cycles. The composition with the highest cycling stability was Na0.8MnO2 (x = 0.8), maintaining 63.37% of its initial capacity after 50 cycles. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were conducted using an Ivium potentiostat to evaluate the electrochemical properties of the synthesized materials. The α-NaxMnO2 material demonstrates strong potential as a cathode candidate for sodium-ion batteries
A NEW TYPE OF POST-QUANTUM DIGITAL SIGNATURE SCHEME
Get PDFIn this paper, the authors propose a new type of post–quantum digital signature scheme based on hard problems, which belongs to the group of unsolvable problems that currently have no solution. Therefore, this type of digital signature scheme can be resistant to quantum attacks based on the quantum algorithm proposed by P. Shor. In addition to quantum resistance, the type of signature scheme proposed here can also be used as pre–quantum digital signature schemes that are widely used in current practical applications