• Steel and Composite Structures
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• v.39 no.3
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• pp.229-241
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• 2021

This work focused on aluminum foam sandwich (AFS) with different foam core densities and different face-sheet thicknesses subjected to constant amplitude three-point bending cyclic loading to study its fatigue performance. The experiments were conducted out by a high frequency fatigue test machine named GPS-100. The experimental results showed that the fatigue life of AFS decreased with the increasing loading level and the structure was sensitive to cyclic loading, especially when the loading level was under 20%. S-N curves of nine groups of AFS specimens were obtained and the fatigue life of AFS followed three-parameter lognormal distribution well. AFS under low cyclic loading showed pronounced cyclic hardening and the static strength after fatigue test increased. For the same loading level, effects of foam core density and face-sheet thickness on the fatigue life of AFS structure were trade-off and for the same loading value, the fatigue life of AFS increased with aluminum foam core density or face-sheet thickness monotonously. Core shear was the main failure mode in the present study.

• Smart Structures and Systems
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• v.23 no.2
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• pp.107-122
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• 2019

As one of the most important parameters in structural health monitoring, structural frequency has many advantages, such as convenient to be measured, high precision, and insensitive to noise. In addition, frequency-change-ratio based method had been validated to have the ability to identify the damage occurrence and location. However, building a precise enough finite elemental model (FEM) for the test structure is still a huge challenge for this frequency-change-ratio based damage detection technique. In order to overcome this disadvantage and extend the application for frequencies in structural health monitoring area, a novel method was developed in this paper by combining the cross-model cross-mode (CMCM) model updating algorithm with the frequency-change-ratio based method. At first, assuming the physical parameters, including the element mass and stiffness, of the test structure had been known with a certain value, then an initial to-be-updated model with these assumed parameters was constructed according to the typical mass and stiffness distribution characteristic of shear buildings. After that, this to-be-updated model was updated using CMCM algorithm by combining with the measured frequencies of the actual structure when no damage was introduced. Thus, this updated model was regarded as a representation of the FEM model of actual structure, because their modal information were almost the same. Finally, based on this updated model, the frequency-change-ratio based method can be further proceed to realize the damage detection and localization. In order to verify the effectiveness of the developed method, a four-level shear building was numerically simulated and two actual shear structures, including a three-level shear model and an eight-story frame, were experimentally test in laboratory, and all the test results demonstrate that the developed method can identify the structural damage occurrence and location effectively, even only very limited modal frequencies of the test structure were provided.

• Journal of Distribution Science
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• v.16 no.10
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• pp.5-21
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• 2018

Purpose - This case study reviews the development history of Lotte Shopping, which has played a key role in modernizing Korea's retail industry. Research design, data, and methodology - Lotte Shopping's expansion to various channel types has been reviewed from the perspective of the resource-based view of strategy. The opening of Lotte Department Store in 1979 signaled the beginning of the modernized distribution system in Korea. Lotte Shopping expanded its business domains to various types of retail channels, such as discount stores, online shopping malls, TV home shopping, convenience stores, supermarkets, home appliances specialty stores and health & beauty stores. Results - Lotte Shopping has been able to maintain high level of customer satisfaction with leading merchandising skills. It has developed mutually beneficial relationship with the partner firms. It has also been a leading firm in implementing corporate social responsibility activities and environment-friendly management. Lotte Shopping has applied advanced information and communication technology to provide customized goods/services. Conclusions - This study summarizes the business environment and new challenges Lotte Shopping faces currently. Lotte Shopping is trying to reinforce the omni-channel strategy, which can create synergy among various distribution channels based on its core competences.

• ETRI Journal
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• v.45 no.2
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• pp.267-276
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• 2023

R&D strategies of companies with low and high technological levels are discussed based on the concept of technology convergence and divergence. However, empirically detecting enterprise technology convergence in the distribution of enterprise technology (total productivity increase) over time and identifying key change factors are challenging. This study used a novel statistical indicator that captures the internal technology distribution change with a single number to clearly measure the technology distribution peak as a change in critical bandwidth for enterprise technology convergence and presented it as evidence of each technology convergence or divergence. Furthermore, this study applied the quantitative technology convergence identification method. Technology convergence appeared from the separation of total corporate productivity distribution of 69 IT companies in Korea in 2019-2020 rather than in 2015-2016. Results indicated that when the total technological level was separated from the technology leading and technology catch-up, IT companies were found to be pursuing R&D strategies for technology catch-up.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.4
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• pp.447-461
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• 2016

Recently, the Renewable Fuel Standard(RFS) has been commenced from July 31, 2015 in the New and Renewable Energy Act for expanding the supply of renewable energy and reduction of national GHG target in Korea. The biodiesel is only a means of implementation for the RFS, therefore the biodiesel supply expansion is important for fulfilling the RFS obligation policy. The major key points of the biodiesl supply are expanding domestic feedstocks due to the over 60% dependence on foreign feedstock and reducing the price of feedstock because of the over 70% occupation of feed stock price in the biodiesl production cost. Therefore, we estimated actual amount of potential feedstocks which are possible to use for biodiesl production in Korea and investigated technical and political improvements for expanding biodiesl. For estimating a potential feedstocks, first selected the potential biodiesl feedstocks by investigating the status of global biodiesl feedstocks and then analyzed the possible potential amount of each feedstock by surveying the generation situations, the distribution structures and the technical level.

• Progress in Superconductivity and Cryogenics
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• v.12 no.2
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• pp.17-20
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• 2010

A considerable amount of research material discussing designs and properties of High Temperature Superconducting Fault Current Limiter (HTS FCL) is available. However, a shortage of research concerning positioning of HTS FCL in power grid is felt. In this paper a feasibility study of HTS FCL positioning in Smart Grid through simulation analysis is carried out. A complete power network (including generation, transmission and distribution) is modeled in Simulink / SimPowerSystems. A generalized HTS FCL is also designed by integrating Simulink and SimPowerSystem blocks. The distribution network of the model has a wind turbine attached to it forming a micro grid. Three phase fault have been simulated along with placing FCL models at key points of the distribution grid. It is observed that distribution grid, having distributed generation sources attached to it, must not have a single FCL located at the substation level. Optimized HTS FCL location regarding the best fault current contribution from wind turbine has been determined through simulation analysis.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2022.09a
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• pp.57-57
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• 2022

A taxonomic revision of Deutzia in Korea was conducted based on critical observations of wild populations and herbarium specimens. Species delimitations were re-evaluated on the basis of morphological characters and distributions resulting in the recognition of five taxa. The texture of leaf, flower disk and capsules, the shape of leaf, inflorescence and capsules are useful diagnostic traits at the specific level. The five taxa are well distinguished from each other. Deutzia grandiflora var. baroniana can be distinguished by its distribution and calyx from Deutzia uniflora, which are morphologically similar. Deutzia paniculata Nakai, a rare and endemic plant, is characterized by having panicle in inflorescences. On the other hand, Deutzia glabrata Kom. is occasionally confused with Deutzia parviflora, but the most distinctive characters include the surface of leaves, the surface and size of capsules. Photographs and a key to five species of Deutzia were provided in addition to distribution.

• Journal of the Korea Society of Computer and Information
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• v.6 no.2
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• pp.90-96
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• 2001

The development of network and the other communication-network can generate serious social problems. So. it is highly required to control security of network. These problems related security will be developed and keep up to confront with anti-security part such as hacking. cracking. In this paper. the proposed multiple nonlinear S-box function which is capable to cipher regardless of key distribution or key-length for these definite problem is proposed and designed in hardware. The proposed multiple nonlinear S-box function increase secret level from using a nonlinear function in multiply for key data utilized in cryptography that generates MDP and MLP in maximum is proposed to prevent cryptography analysis. The designed the multiple nonlinear S-box function in this paper performed synthesization and simulation using Synopsys Ver. 1999.10 and VHDL

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.4C
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• pp.356-364
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• 2003

Presently, etwork is being in the existence as an influence can not be neglected. This rapid progress of network has gone with development of mobile network and information communication. But the development of network can generate serous social problems. So, it is highly required to control security of network. These problems related security will be developed and keep up to confront with anti-security part such as hacking, cracking. There's no way to preserve security from hacker or cracker without delvelopping new cryptographic algorithm or keeping the state of anti-cryptanalysis in a prescribed time by means of extendig key-length. Worldwidely, many researchers for network security are trying to handle these problems. In this paper, we proposed a new block cryptosystem. The Block cipher-Secure Electronic Xenogenesis Algorithm(B-SEXA) which is capable to cipher regardless of key distribution or key-length for these definite problem is proposed and designed in hardware. B-SEXA increase secret level from using a MDP and MLP in maximum is proposed to prevent cryptograpy analysis. The designed B-SEXA in this paper performed synthesization and simulation using Synopsys Vwe. 1999.10 and VHDL.

• International Journal of Internet, Broadcasting and Communication
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• v.13 no.2
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• pp.60-66
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• 2021

Blockchain is a technology that enables trust-based consensus and verification based on a decentralized network. Distributed ID (DID) is based on a decentralized structure, and users have the right to manage their own ID. Recently, interest in self-sovereign identity authentication is increasing. In this paper, as a method for transparent and safe sovereignty management of data, among data pseudonymization techniques for blockchain use, various methods for data encryption processing are examined. The public key technique (homomorphic encryption) has high flexibility and security because different algorithms are applied to the entire sentence for encryption and decryption. As a result, the computational efficiency decreases. The hash function method (MD5) can maintain flexibility and is higher than the security-related two-way encryption method, but there is a threat of collision. Zero-knowledge proof is based on public key encryption based on a mutual proof method, and complex formulas are applied to processes such as personal identification, key distribution, and digital signature. It requires consensus and verification process, so the operation efficiency is lowered to the level of O (log_eN) ~ O(N²). In this paper, data encryption processing for blockchain DID, based on zero-knowledge proof, was proposed and a one-way encryption method considering data use range and frequency of use was proposed. Based on the content presented in the thesis, it is possible to process corrected zero-knowledge proof and to process data efficiently.