• Korean Journal of Materials Research
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• v.21 no.11
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• pp.592-595
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• 2011

It is well known that modified 9Cr-1Mo steel has a low thermal expansion and high thermal conductivity with excellent high temperature properties compared to austenitic stainless steel. For these advantages, the steel is very popular for the boiler tube of thermal power plants. Normalizing is commonly utilized to obtain martensite in this steel, which shows an unusual toughness for martensite. However, some accidents related to this steel have been reported recently, opening the necessity for further study. As a particular behavior of the steel, an abrupt drop of the impact value has been identified upon tempering at 750$^{\circ}C$ for about 1 hour. It is well known that $Fe_3C$ forms during autotempering and turns to $Cr_2C$ at an early stage and then transforms to $Cr_{23}C_6$. In this study, the cause of the abrupt drop of the impact value was investigated with an impact test, microstructural observation, nanodiffraction and phase analyses using instruments such as optical and transmission electron microscopes (TEM) with an extraction carbon replica of the carbides. The analyses revealed that the $M_2C$ that formed when retained for about 1 hour at 750$^{\circ}C$ causes a drastic decrease in the mechanical properties. The sharp drop in mechanical properties, however, disappeared as the $M_2C$ transformed into $M_{23}C_6$ with longer retention.

• Journal of the Korea Computer Industry Society
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• v.2 no.7
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• pp.945-952
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• 2001

In consequence of expansion of internet users, electronic commerce is becoming a new prototype for marketing and sales, arid most of electronic commerce sites or internet shopping malls provide a rich source of information and convenient user interfaces about the organizations customers to maintain their patrons. One of the convenient interfaces for users is service to recommend products. To do this, they must exploit methods to extract and analysis specific patterns from purchasing information, behavior and market basket about customers. The methods are association rules and sequential patterns, which are widely used to extract correlation among products, and in most of on-line electronic commerce sites are executed with users information and purchased history by category-oriented. But these can't represent the diverse correlation among products and also hardly reflect users' buying patterns precisely, since the results are simple set of relations for single purchased pattern. In this paper, we propose an efficient mining technique, which allows for multiple purchased patterns that are category-independent and have relationship among items in the linked structure of single pattern items.

• Bulletin of the Korean Chemical Society
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• v.2 no.2
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• pp.60-66
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• 1981

The hypothesis that three classes of water exist in hydrogels, namely X water (free water-like), Z-water (bound water-like), and Y water (interfacial water-like), has been verified and generally accepted. To further check the validity of this hypothesis and to study the nature of X, Y, and Z water as conformation changes, several experiments have been done using Tactic Poly(2-hydroxyethyl methacrylate) (P-HEMA) gels. Thermal expansively data for tactic P-HEMA gel was obtained. In each case of isotactic and syndiotactic P-HEMA, the higher water content gels showed an extremely sharp volume change at $0^{\circ}C$, indicating the presence of normal free water-like. Lower water content gels showed no anomalous change in thermal expansion, indicating that the water is bound water-like. The medium water content gels exhibited intermediate behavior. These results were also confirmed by bulk gel conductivity measurments. The differential scanning calorimeter(DSC) experiment was simply introduced to further verify the bound water-like quantities which was obtained by the method of dilatometry and specific conductivity. Observing the amounts of X, Y, and Z water with the change of tacticity, the similar content of bound water-like may be due to the same primary structure of isotactic and syndiotactic polymer and the difference in free and interfacial water-like content may be due to the difference in secondary and tertiary structure of tactic polymer. Therefore, as the polymer conformation varies, the free and interfacial water-like content will be varied. In order to demonstrate these concepts, Russel et al.'s CPK space-filling molecular models of isotactic and syndiotactic P-HEMA was utilized.

• Hwankyungkyoyuk
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• v.15 no.1
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• pp.137-147
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• 2002

The progress of environmental science and technology in the developed countries has been rapid in recent years. Particularly remarkable has been the advancement of various pollutant control measures, which have brought the pollution of inorganic factors such as air and water under control. In contrast, diversity of the ecosphere, of which man is a part, is being steadily Impoverished and the biological community is getting unvaryingly uniform. These phenomena were brought about by the expansion of artificial environment such as new industrial complexes, transportation facilities and urban development. Man has constructed uniform and artificial environment, believing in the premise of confrontation with nature, to such a scale that the natural environment and biological community have lost their balance. This will increasingly endanger the soundness of the biotic environment of nature, which constitutes the potential foundation both for the survival environment of man as biological entity and for the development of human civilization. In order to guarantee the soundness of man's body, intelligence and sensitivity as wholesome gene Pool on the earth and for the future of man, primarily important environmental education is the understanding of how man can everlasting exist in and with the survival environment. In view of this reality, it is vitally important to create ecologically diverse and well-balanced environment with living materials, i.e., vegetation in order to secure lasting survival environment for man. This task is urgently required in highly artificial environment where non-biological materials have forced the impoverishment of the biological community. Therefore, environmental education for the future should not be totally oriented to technology as that in the past nor it is limited to the medical aspect where well-being of human is the sole object of concern. That is to say, environmental education for the future should be one that provides knowledge that human can understand his place based on the ecological concept and thereby make him to have ethical consciousness that he can control his behavior within the reasonable level for ecological niche who he is located.

• Archives of Plastic Surgery
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• v.46 no.4
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• pp.365-370
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• 2019

The syndrome of the trephined is a neurologic phenomenon that manifests as sudden decline in cognition, behavior, and sensorimotor function due to loss of intracranial domain. This scenario typically occurs in the setting of large craniectomy defects, resulting from trauma, infection, and/or oncologic extirpation. Cranioplasty has been shown to reverse these symptoms by normalizing cerebral hemodynamics and metabolism. However, successful reconstruction may be difficult in patients with complex and/or hostile calvarial defects. We present the case of a 48-year-old male with a large cranial bone defect, who failed autologous cranioplasty secondary to infection, and developed rapid neurologic deterioration leading to a near-vegetative state. Following debridement and antibiotic therapy, delayed cranioplasty was accomplished using a polyetheretherketone (PEEK) implant with free chimeric latissimus dorsi/serratus anterior myocutaneous flap transfer for vascularized resurfacing. Significant improvements in cognition and motor skill were noted in the early postoperative period. At 6-month follow-up, the patient had regained the ability to speak, ambulate and self-feed-correlating with evidence of cerebral/ventricular re-expansion on computed tomography. Based on our findings, we advocate delayed alloplastic implantation with total vascularized soft tissue coverage as a viable alternative for reconstructing extensive, hostile calvarial defects in patients with the syndrome of the trephined.

• Journal of the Korean Physical Society
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• v.73 no.10
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• pp.1495-1501
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• 2018

We have developed an extended three-dimensional free-electron laser (3D FEL) code with source-dependent expansion to calculate the intensity of the radiation field and the spot size in a free-electron laser oscillator. The effect of the wiggler field errors was evaluated for the case of a planar wiggler generated by a magnet stack with parabolic shaped pole faces by using the extended three-dimensional equations in a free-electron laser oscillator based on the proposed FEL facility which is to be operated in the far-infrared and the infrared regions. The radiation spot size due to the wiggler field errors also have been analyzed for wiggler errors of ${\Delta}B/B=0.0$, 0.03, 0.06 and 0.09% at z = 1 m and z = 2 m. The effect of the diffraction of radiation field due to the wiggler field errors of ${\Delta}B/B=0.0$ and ${\Delta}B/B=0.09%$ at 200 passes was evaluated by using the extended 3D code that we developed. The variation of the curvature of the phase front and the effect of the radiation field intensity due to the wiggler field errors were also evaluated for B = 0.5 T and B = 0.7 T with the wiggler error of ${\Delta}B/B=0.09%$ at 200 passes and the results were compared to those of without errors. The intensity of the radiation, behavior of the radiation spot size and the variation of the curvature of the phase were highly sensitive to the wiggler error of ${\Delta}B/B$ > 0.09%, but were less sensitive to the wiggler errors for ${\Delta}B/B$ < 0.09% in a free-electron laser (FEL) oscillator based on the proposed FEL facility.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.8
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• pp.1238-1247
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• 2022

The e-commerce market is growing faster as demand for non-face-to-face shopping increases due to COVID-19. These changes lead to the expansion of various opportunities for consumers, but companies are required to understand consumer characteristics and reflect them in their sales strategies so that they can be competitive in the market. This study examined how the perceived ease and utility of consumers affect the intention to use the platform according to the technology acceptance model (TAM). As a result, it was confirmed that the price competitiveness, awareness, and ease of use of the platform had a significant effect on the utility. In addition, it was confirmed that there was no moderating effect of user characteristics on the effect of ease of use on the platform intention. These results present important implications for a company's sales strategy, and in future studies, it is necessary to expand the study in consideration of more diverse variables.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.1
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• pp.1-9
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• 2022

Semi-integral abutment bridges are a type of integral abutment bridges. These bridges eliminate expansion joints on the structure and can be used in situations not suitable for full-integral abutment bridge. Moreover, Semi-integral bridges have excellent maintenance and can be economically constructed. This study is about precast wall-type blocks at each end which provide lateral support for PSC girder, as well as acting as retaining walls to resist longitudinal movement of semi-integral abutment bridge. The end-diaphragm connection between ended blocks of PSC girders can be achieved by in-suit nonshrinkage concrete. The results show that 3-point experiment of end-diaphragm beam have an acceptable performance which is so better than results of structural design. Moreover, the effects of backfill soil on semi-integral abutment bridge constructed are analyzed the behavior according to the temperature changes.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.3
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• pp.43-48
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• 2022

In this study, simulation method was developed to improve the accuracy of the warpage simulation based on the equivalent anisotropic viscoelastic model. First, a package with copper traces and bumps was modeled to implement anisotropic viscoelastic behavior. Then, equivalent anisotropic viscoelastic properties and thermal expansion coefficient for the bump region were derived through the representative volume element model. A thermal cycle of 0 to 125 degrees was applied to the package based on the derived mechanical properties, and the warpage according to the thermal cycle was simulated. To verify the simulation results, the actual package was manufactured, and the warpage with respect to the thermal cycle was measured through shadow moiré interferometer. As a result, by applying the equivalent anisotropic viscoelastic model, it was possible to calculate the warpage of the package within 5 ㎛ error and predict the shape of the warpage.

• Geomechanics and Engineering
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• v.29 no.3
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• pp.291-300
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• 2022

Tunnel boring machines combined with the earth pressure balanced shield method (EPB shield TBMs) have been adopted in urban areas as they allow excavation of tunnels with limited ground deformation through continuous and repetitive excavation and support. Nevertheless, the expansion of TBM construction requires much more minor and exquisitely controlled surface settlement to prevent economic loss. Several parametric studies controlling the tunnel's geometry, ground properties, and TBM operational factors assuming ordinary conditions for EPB shield TBM excavation have been conducted, but the impact of excessive excavation on the induced settlement has not been adequately studied. This study conducted a numerical evaluation of surface settlement induced by the ground loss from face imbalance, excessive excavation, and tail void grouting. The numerical model was constructed using FLAC3D and validated by comparing its result with the field data from literature. Then, parametric studies were conducted by controlling the ground stiffness, face pressure, tail void grouting pressure, and additional volume of muck discharge. As a result, the contribution of these operational factors to the surface settlement appeared differently depending on the ground stiffness. Except for the ground stiffness as the dominant factor, the order of variation of surface settlement was investigated, and the volume of additional muck discharge was found to be the largest, followed by the face pressure and tail void grouting pressure. The results from this study are expected to contribute to the development of settlement prediction models and understanding the surface settlement behavior induced by TBM excavation.