• Structural Engineering and Mechanics
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• v.80 no.5
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• pp.563-583
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• 2021

Composite materials, composed of multiple constituent materials with dissimilar properties, are actively adopted in a wide range of industrial sectors due to their remarkable strength-to-weight and stiffness-to-weight ratio. Nevertheless, the failure mechanism of composite materials is highly complicated due to their sophisticated microstructure, making it much harder to predict their residual material lives in real life applications. A promising solution for this safety issue is structural damage detection. In the present paper, damage detection of composite material via electrical resistance-based technique and infrared thermography is reviewed. The operating principles of the two damage detection methodologies are introduced, and some research advances of each techniques are covered. The advancement of IR thermography-based non-destructive technique (NDT) including optical thermography, laser thermography and eddy current thermography will be reported, as well as the electrical impedance tomography (EIT) which is a technology increasingly drawing attentions in the field of electrical resistance-based damage detection. A brief comparison of the two methodologies based on each of their strengths and limitations is carried out, and a recent research update regarding the coupling of the two techniques for improved damage detection in composite materials will be discussed.

• International Journal of High-Rise Buildings
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• v.12 no.2
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• pp.145-152
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• 2023

Typical floor systems in contemporary tall buildings consist of reinforced concrete or composite metal deck over framing members and account for a majority of the structural weight of the building. The use of high-density materials, such as reinforced concrete and steel, increases the weight of floor systems, reducing the system's overall efficiency. With the introduction of high-performance materials, mainly mass timber products, and fiber-reinforced composites, in the construction industry, designers and engineers have multiple options to choose from when selecting structural materials. This paper discusses the application of mass timber and carbon fiber composites as structural materials in floor systems of tall buildings. The research focused on a comparative analysis of the structural system efficiency for five different design options for tall building floor systems. Finite Element Analysis (FEA) method was adopted to develop a simulation framework, and parametric structural models were simulated to evaluate the structural performance under specific loading conditions. Simulation results revealed the advantages of lightweight structural materials to improve system efficiency and reduce material consumption. The impact of mechanical properties of materials, loading conditions, and issues related to fire engineering and construction were briefly discussed, and future research topics were identified in conclusion.

• Restorative Dentistry and Endodontics
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• v.46 no.2
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• pp.18.1-18.13
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• 2021

Composite resins are the most commonly used dental restorative materials after minimally invasive dental procedures, and they offer an aesthetically pleasing appearance. An ideal composite restorative material should have wear properties similar to those of tooth tissues. Wear refers to the damaging, gradual loss or deformation of a material at solid surfaces. Depending on the mechanism of action, wear can be categorized as abrasive, adhesive, fatigue, or corrosive. Currently used composite resins cover a wide range of materials with diverse properties, offering dental clinicians multiple choices for anterior and posterior teeth. In order to improve the mechanical properties and the resistance to wear of composite materials, many types of monomers, silane coupling agents, and reinforcing fillers have been developed. Since resistance to wear is an important factor in determining the clinical success of composite resins, the purpose of this literature review was to define what constitutes wear. The discussion focuses on factors that contribute to the extent of wear as well as to the prevention of wear. Finally, the behavior of various types of existing composite materials such as nanohybrid, flowable, and computer-assisted design/computer-assisted manufacturing materials, was investigated, along with the factors that may cause or contribute to their wear.

• Journal of Gastric Cancer
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• v.1 no.3
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• pp.150-154
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• 2001

Purpose: Multiple early gastric cancers were found in $6.9\∼11.7\%$ of patients with early gastric cancer. The goal of this study was to clarify the clinicopathologic features of and to investigate treatment strategy for multiple early gastric cancer. Materials and Methods: Of 967 patients with an gastric adenocarcinoma who were treated by surgical resection during the period of $1993\∼1998$ at the Department of Surgery, Korea University College of Medicine, 267 patients had early gastric cancer. A retrospective analysis of the clinicopathologic differences between the main and the accessory lesions in multiple early gastric cancer was carried out. A comparative analysis was also conducted between solitary early gastric cancer and multiple early gastric cancer. Results: Of 267 patients with early gastric cancer, multiple early gastric cancers were found in 12 patients ($4.5\%$), including 10 men and 2 women. Eleven patients with multiple early gastric cancer had one accessory lesion and 1 patient had 2 accessory lesions. Of the 13 accessory lesions, 7 ($53.8\%$) were located in the same region as the main lesion. The most frequent combination of macroscopic types for the main lesion and the accessory lesion were depressed and depressed types (6 cases, $46.1\%$). The most frequent histologic type of main lesion was a well differentiated adenocarcinoma in 7 ($58.3\%$) of the 12 cases; the accessory lesion was also well differentiated in 4 of those 7 cases. Of the 13 accessory lesions, 4 ($30.8\%$) had been overlooked preoperatively; most of them were located in the lower third of the stomach and were IIb or IIc type and measured less than 1 cm in diameter. Lymph node metastasis was detected in 1 patient ($8.3\%$). The clinicopathologic features of multiple early gastric cancer were not different from those of solitary early gastric cancer. Conclusion: In multiple early gastric cancer, the main and the accessory lesions showed similar differentiation, and lymph node metastasis was less frequent than in solitary early gastric cancer. Therefore, limited procedures, including endoscopic mucosal resection, may be indicated if each lesion of the multiple early gastric cancer fits the criteria for treatment strategy.

• Journal of Korean Vacuum Science & Technology
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• v.4 no.2
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• pp.47-49
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• 2000

We report on the fabrication and characterization of InGaN/GaN multiple quantum well light emitting diode (LED) with a highly transparent Pt ohmic contact as a current spreading layer. The value of light transmittance of a Pt thin film with a thickness of 8 m on p-GaN was measured to be 85% at 450nm. The peak wavelength and the full-width at half-maximum (FWHM) of the emission spectrum of the LED at 20 mA were 453 m and 23 m, respectively. Pt-contacted LEDs show good electrical properties and high light-output efficiency compared to Ni/Au-contacted ones. These results suggest that a Pt thin film can be used as an effective current spreading layer with high light-transparency.

• Korean Institute of Interior Design Journal
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• v.21 no.3
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• pp.22-30
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• 2012

Nowadays the issue of environmental pollution and ecological destruction is not a simple issue but an important issue to be continuously considered. It is deemed that a study for recycled new materials is immediately required and this study is to analyze features and processing methods of new materials which can be used to interior space. We found the recycled new materials used for space through researching various web sits. And then we analyzed what the base materials are and classified that base materials are whether natural or artificial of the recycled materials. We classified processing methods of the recycled new materials after researching general processing methods. The result of this study would be an important material to the research and development of new finishing materials with consideration of environment and to the research for a guideline of applicable new materials. The results of this study are as follows : First, we could classify widely 2 categories into natural material and artificial material and then 10 subcategories into metal, glass, wood, rubber, stone, plastic, leather or fabric, ceramic, concrete and so on, and analyzed that which material is mostly used and whether it is single material or multiple material. In order to analyze the feature of processing method. Second, we could classify into 4 categories such as junction, surface process, molding, and insert, and found out which processing method is applied based on objects of research. Third, as an analysis result of the recycled new material feature, in order to develop various new materials, it is required to study on combination and application of 2 materials or more rather than single material. Four, as a analysis result of the processing method feature, I would like to suggest that development and application of various processing methods are required. Especially, it is necessary to grope for a way to develop new functional materials for interior space through a systemic research and analysis of processing method of other fields. Furthermore, a way to reuse recycled new materials should be considered in a stage of selection and application of processing method.

• Journal of Korean Vacuum Science & Technology
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• v.4 no.3
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• pp.78-80
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• 2000

We reprot on the fabrication and characterization of InGaN/GaN multiple quantum well light-emitting diode (LED) with a highly transparent Pt ohmic contact as a current spreading layer. The value of light transmittance of a Pt thin film with a thickness of 8 nm on-GaN was measured to be 85% at 450 nm. The peak wavelength and the full-width at half-maximum (FWHM) of the emission spectrum of the LED at 20 mA were 453 nm and 23 nm, respectively. Pt-contacted LEDs show good electrical properties and high light-output efficiency compared to Ni/Au-contacted ones. These results suggest that a Pt thin film can be used as an effective current spreading layer with high light-transparency.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2328-2339
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• 1992

The propagation of coherent time-harmonic elastic L-and SV-waves is studied in a medium with random distribution of cylindrical inclusions. The purpose of the research is to characterize the dynamic elastic moduli and the attenuation properties of fiber-reinforced composite materials. The cylindes representing the fibers are assumed to be distributed in parallel with each other and the direction of incident waves are normal to the cylinder axes. A multiple scattering formula using the single scattering coefficients in conjunction with the Lax's quasicrystalline approximation is derived from which the dispersion relation for such medium is obtained. In order to formulate the multiple scattering interaction between cylinders, the pair correlation functions are generated by the Monte Carlo simulation technique. From the numerically evaluated complex wavenumbers, the propagation speed of the average wave, the coherent attenuation and the effective elastic moduli are presented as functions of frequency and fiber volume fraction.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.5
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• pp.633-649
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• 2005

Statement of problem: In spite of the progress in techniques and materials in complete denture prosthodontics, patients still complain of discomfort after the insertion of complete dentures. For the last several decades many prosthodontists tried to find factors influencing patient complete denture satisfaction, however the reported results became a controversy. Purpose: The purpose of the present study was to verify the factors influencing patient satisfaction with complete dentures using multiple regression analysis. Materials and methods: 33 patients who visited the department of prosthodontics, dental hospital of Yonsei University, 4 to 6 weeks after the complete denture delivery, were asked to complete the questionnaires on complete denture satisfaction, social variables and psychological variables. The Prosthodontists who treated the patients with complete dentures were also asked to complete the questionnaires on evaluation of patients' oral condition and technical quality of dentures. The factors influencing patients' satisfaction with their complete dentures were analyzed using multiple regression analysis. Results: Among the patients' sociodemographic variables. the variables of relationship with children, economic status, housing condition, other people's opinions of dentures and gender were the influential factors on patients' satisfaction with complete dentures. Patients showing the symptoms of depression, one of the psychological variables, were dissatisfied with their complete dentures. In spite of the good oral condition, patients were dissatisfied with complete dentures, where-as the technical quality of dentures did not influence patients' complete denture satisfaction. Conclusion : According to the results above, patients' sociodemographic and psychological variables rather than clinical variables including oral condition and technical quality of dentures were the influential factors on complete denture satisfaction. The results of this study may not only enable prosthodontists to predict the success and failure of complete denture treatment, but also help both prosthodontists and patients be informed of the essentials of increasing satisfaction with complete dentures.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.917-920
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• 2008

ECC is a special kind of high performance cementititous composite which exhibits typically more than 2% tensile strain capacity by bridging microcracks at a crack section. Therefore, micromechanics should be adopted to obtain multiple cracking and strain hardening behavior. This paper propose a linear elastic analysis method to simulate the multiple cracking and strain hardening behavior of ECC. In an analysis, the stress-crack opening relation modified considering the orientation of fibers and the number of effective fibers is adopted. Furthermore, to account for uncertainty of materials and interface between materials, the randomness is assigned to the tensile strength(${\sigma}_{fci}$), elastic modulus($E_{ci}$), peak bridging stress(${\sigma}_{Bi}$) and crack opening at peak bridging stress(${\delta}_{Bi}$), initial stress at a crack section due to chemical bonding, (${\sigma}_{0i}$), and crack spacing(${\alpha}_cX_d$). Test results shows the number of cracking and stiffness of cracked section are important parameters and strain hardening behavior and maximum strain capacity can be simulated using the proposed method.