• Steel and Composite Structures
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• v.46 no.5
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• pp.709-718
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• 2023

The absence of an important portion of the web plate in steel beams with multiple circular perforations, cellular beams, causes the web plate to undergo distortions prior to and during lateral torsional buckling (LTB). The conventional LTB equations in the codes and literature underestimate the buckling moments of cellular beams due to web distortions. The present study is an attempt to develop analytical methods for estimating the elastic buckling moments of cellular beams. The proposed methods rely on the reductions in the torsional and warping rigidities of the beams due to web distortions and the reductions in the weak-axis bending and torsional rigidities due to the presence of web openings. To test the accuracy of the analytical estimates from proposed solutions, a total of 114 finite element analyses were conducted for six different standard IPEO sections and varying unbraced lengths within the elastic limits. These analyses clearly indicated that the LTB solutions in the AISC 360-16 and AS4100:2020 codes overestimate the buckling loads of cellular beams within elastic limits, particularly at shorter span lengths. The LDB solutions in the literature and the Eurocode 3 LTB solution, on the other hand, provided conservative buckling moment estimates along the entire range of elastic buckling.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.4_1
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• pp.517-527
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• 2023

Many techniques have been proposed and investigated for microlens array manufacturing in three-dimensional (3D) structures. We present fabricating a microlens array using selective laser etching and a CO₂ laser. The femtosecond laser was employed to produce multiple micro-cracks that comprise the predesigned 3D structure. Subsequently, the wet etching process with a KOH solution was used to produce the primary microlens array structures. To polish the nonoptical surface to the optical surface, we performed reflow postprocessing using a CO₂ laser. We confirmed that the micro lens array can be manufactured in three primary shapes (cone, pyramid and hemisphere). Compared to our previous study, the processing time required for laser processing was reduced from approximately 1 hour to less than 30 seconds using the proposed processing method. Therefore, micro lens arrays can be manufactured using our processing method and can be applied to mass productionon large surface areas.

• Wind and Structures
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• v.37 no.3
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• pp.179-189
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• 2023

Multiple studies conducted in the past evaluated the conductor response under one tornado wind field, while the performance of transmission lines under different tornado wind fields still remains unknown. Thus, the objective of this paper is to estimate the variation in the conductor's critical longitudinal and transverse reactions under different tornado wind fields, as well as providing the corresponding critical tornado configurations. The considered full-scale tornadoes are the Spencer, South Dakota, 1998, the Stockton, Kansas, 2005 and the Goshen County, Wyoming, 2009. Computational Fluid Dynamics (CFD) simulations were previously conducted to develop these wind fields. All tornadoes have been rescaled to have a common velocity matching the upper limit of the F2 Fujita scale. Eight conductor systems, each including six spans, are considered in this paper. For each conductor, parametric studies are conducted by varying the location of the three tornado wind fields relative to the tower of interest, therefore the peak reactions associated with each tornado are determined. A semi-analytical closed-form solution, previously developed and validated, is used to calculate the reactions. The study conducted in this paper can be divided into two parts: In the first part, a parametric study considering a wide range of tornado locations is conducted. In the second part, the parametric study focuses on the tornado location leading to the critical tangential velocity on the tower. Based on this extensive parametric study, a critical tornado defined as the Design Tornado and its critical locations, tornado distance R = 125 m, tornado angle 𝜃 = 15° and 30°, are recommended for design purposes.

• Electronics and Telecommunications Trends
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• v.38 no.5
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• pp.34-50
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• 2023

Quantum error correction is a key technology for achieving fault-tolerant quantum computation. Finding the best decoding solution to a single error syndrome pattern counteracting multiple errors is an NP-hard problem. Consequently, error decoding is one of the most expensive processes to protect the information in a logical qubit. Recent research on quantum error decoding has been focused on developing conventional and neural-network-based decoding algorithms to satisfy accuracy, speed, and scalability requirements. Although conventional decoding methods have notably improved accuracy in short codes, they face many challenges regarding speed and scalability in long codes. To overcome such problems, machine learning has been extensively applied to neural-network-based error decoding with meaningful results. Nevertheless, when using neural-network-based decoders alone, the learning cost grows exponentially with the code size. To prevent this problem, hierarchical error decoding has been devised by combining conventional and neural-network-based decoders. In addition, research on quantum error decoding is aimed at reducing the spacetime decoding cost and solving the backlog problem caused by decoding delays when using hardware-implemented decoders in cryogenic environments. We review the latest research trends in decoders for quantum error correction with high accuracy, neural-network-based quantum error decoders with high speed and scalability, and hardware-based quantum error decoders implemented in real qubit operating environments.

• Journal of Platform Technology
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• v.11 no.1
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• pp.3-10
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• 2023

Unmanned Aerial Vehicles (UAVs) have gained significant attention in 5G and 6G wireless networks due to their high flexibility and low hardware costs. However, UAV communication is still challenged by blockage and energy consumption issues. Reconfigurable Intelligent Surfaces (RISs) have emerged as a promising solution to these challenges, enabling improved spectral efficiency and reduced energy consumption by transmitting signals to users who cannot receive signals because of the obstacles. Many previous studies have focused on minimizing power consumption and data transmission delay through phase shift and power optimization. This paper proposes an algorithm that maximizes the sum rate by including bandwidth optimization. Simulation results demonstrate the effectiveness of the proposed algorithm.

• Progress in Superconductivity and Cryogenics
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• v.11 no.4
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• pp.20-24
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• 2009

YBCO coated conductors (CC) on the $CeO_2$-buffered IBAD-MgO template were fabricated by metal-organic deposition (MOD) Process with Ba-trifluoroacetate and fluorine-free Y and Cu precursor materials. The precursor solution was coated on $CeO_2$-buffered IBAD MgO templates using the multiple dip-coating method, decomposed into inorganic precursors by pyrolysis up to $400^{\circ}C$ within 3 h, and finally fired at $740{\sim}800^{\circ}C$ in a reduced oxygen atmosphere. Microstructure, texture, and superconducting properties of YBCO films were found highly sensitive to both the firing temperature and time. The high critical current density ($J_C$) of $1.15\;MA/cm^2$ at 77.3K in the self-field could be obtained from $1\;{\mu}m$ thick YBCO CC, fired at $740^{\circ}C$ for 3.5 h, implying that high performance YBCO CC is producible on IBAD MgO template. Further enhancement of $J_C$ values is expected by improving the in-plane texture of $CeO_2$-buffer layer and avoiding the metal substrate contamination.

• Proceedings of the Korean Society of Computer Information Conference
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• 2021.07a
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• pp.313-315
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• 2021

Timely and accurate diagnosis of lung diseases using Chest X-ray images has been gained much attention from the computer vision and medical imaging communities. Although previous studies have presented the capability of deep convolutional neural networks by achieving competitive binary classification results, their models were seemingly unreliable to effectively distinguish multiple disease groups using a large number of x-ray images. In this paper, we aim to build an advanced approach, so-called Ensemble Knowledge Distillation (EKD), to significantly boost the classification accuracies, compared to traditional KD methods by distilling knowledge from a cumbersome teacher model into an ensemble of lightweight student models with parallel branches trained with ground truth labels. Therefore, learning features at different branches of the student models could enable the network to learn diverse patterns and improve the qualify of final predictions through an ensemble learning solution. Although we observed that experiments on the well-established ChestX-ray14 dataset showed the classification improvements of traditional KD compared to the base transfer learning approach, the EKD performance would be expected to potentially enhance classification accuracy and model generalization, especially in situations of the imbalanced dataset and the interdependency of 14 weakly annotated thorax diseases.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.151-151
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• 2021

The alarming climate change impacts are demanding the use of renewable energy sources like never before. Hydropower is one of the most cost-effective and environmental friendly energy technology recognized in the world. Big hydropower projects come up with the requirements of huge investment costs along with environmental impacts, whereas small hydropower(SHP) are considered a best solution for the economical source of energy. SHP, basically Run-of-River (RoR) type plants can be sustainable renewable energy sources and given the nature of perennial rivers flowing from steep gradient and rugged topography, feasibility of such plants is equally high in Nepal. The objective of this study is to determine the primary potential sites for the development of RoR type SHP sites using Geo-spatial Information System(GSIS). The use of GSIS enables precise survey of large area within a short period of time. This study has focused on the determination of locations by establishing defined criterions and methodologies and hence have located multiple locations rather than selecting one best location. The approach is applicable for the rapid initial screening of potential locations and results can facilitate detail feasibility study for the technical and economic analysis of SHP in the basin.

• Advances in concrete construction
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• v.15 no.1
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• pp.63-74
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• 2023

All production and consumption activities produce wastes, which often cause damage to our environment and multiple risks to the human health. The valorization of these wastes in concrete technology is a future solution that will allow finding other construction materials sources, optimizing energy consumption and protecting the environment. Among these wastes, there is the marble waste. Every year, huge amount of marble waste is discarded as dust or aggregates form, in open-air storage areas causing serious problems for the environment and public health. In this context, the incorporation of marble waste as a replacement of ordinary aggregates or cement in concrete composition is actively investigated by researchers. This paper presents a comprehensive review of published studies over the last 20 years, dealing the effect of marble waste on fresh and hardened properties of concrete. Most of the studies carried out have used marble waste as dust with substitution rates between 5 and 20%. Besides the economic and ecological benefits, this review showed that marble waste can improve the physical, mechanical and durability properties of concrete. This improvement depends on the form (dust, fine aggregate or coarse aggregate), substitution method (as cement or aggregates replacement) and substitution rate of marble waste. Additionally, the review results showed that the use of 10-15% of marble waste dust as cement substitution can lead to increase the compressive strength.

• The Journal of the Korea Contents Association
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• v.22 no.2
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• pp.71-79
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• 2022

Currently, even if control and mock hacking are performed for the security of web servers, vulnerabilities continue to occur and be hacked. To solve this problem, we have developed a secure web server that can control all web communication using sockets between L4 and L5. And when giving HTTP responses, we proposed a method of combining files and headers in advance. As a result, both security and speed could be improved. Therefore, in this paper, we proposed the reason why vulnerabilities occur even if control and mock hacking occur, a solution to it, and a security web server development method that can maintain security up to DB.