• Journal of Korea Foundry Society
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• v.23 no.2
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• pp.63-68
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• 2003

Al-Ti-C grain refiner form a relatively new alternative to the existing class of Al-Ti-B type grain refiners for achieving fine equiaxed structures in aluminum alloys during casting and solidification. The present study was carried out to investigate the influence of Al-Ti-C master alloys on the grain structure of Al-7Si alloys. The present study also investigates the relationship between grain refining efficiency and concentrations of Fe and Si in hypo-eutectic Al-Si alloys using Al-3Ti-0.13C master alloys. It is found that several parameters affect significantly the grain refining performance in silumin alloys. The present study reports the influence of various parameters such as alloy content, master alloy addition level, melt holding time and superheat on the grain refining efficiency in Al-7Si alloys.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.62.2-62.2
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• 2007

• Korean Journal of Materials Research
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• v.25 no.2
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• pp.90-94
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• 2015

We prepared 8 samples of non-silver and silver-added master alloys containing silicon to confirm the existence of nickel-silicides. We then prepared products made of 14K and 18K white gold by using the prepared master alloys containing 0.25, 0.35, and 0.50 wt% silicon to check for nickel release. We then employed the EN 1811 testing standard to investigate the nickel release of the white gold products, and we also confirmed the color of the white gold products with an UV-VIS-NIR-color meter. We observed $NiSi_x$ residue in all master alloys containing more than 0.50 wt% Si with EDS-nitric acid etching. For the white gold products, we could not confirm the existence of $NiSi_x$ through XRD after aqua-regia etching. In the EN 1811 test, only the white gold products with 0.25 wt% silicon master alloys successfully passed the nickel release regulations. Moreover, we confirmed that our white gold products showed excellent Lab indices as compared to those of commercial white gold ones, and the silver-added master alloys offered a larger L index. Our results indicate that employing 0.25 wt% silicon master alloys might be suitable for white gold products without nickel-silicide defects and nickel release problems.

• Journal of the Korean Operations Research and Management Science Society
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• v.31 no.4
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• pp.157-179
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• 2006

Recently, as business becomes more dependent on information technology for their operations, SI project managers are under increasing pressure to implement SI projects on time and within budget, and to satisfy customer requirements. For the success of SI projects and customer satisfaction, SI project managers should master the critical shills and knowledge requirements and consider the proper leadership style to lead the team members and to manage SI projects. The leadership style includes four categories, such as directive leadership, supportive leadership, participative leadership, and achievement-oriented leadership. This study has examined the project managers' competency and suggests the three competency factors, which are technical, human, and conceptual shills, for the success of SI projects and customer satisfaction. The study suggests that SI project managers should master the three critical skills and knowledge requirements, and consider the proper leadership style for the successful implementation of SI projects. Also SI project managers should consider contingency factors such as project size and duration and outcome variables such as protect performance and customer satisfaction so as to enhance the leadership effectiveness.

• Journal of the Korean Vacuum Society
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• v.19 no.2
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• pp.96-104
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• 2010

We suggest here a cost-effective replica fabrication method for transparent and hard molds for imprinting lithography such as NIL and S-FIL. The process starts with the use of a replica hard mold from a master, using a polymer copy as a carrier. The polymer copy as a carrier was treated by soluble process for forming anti-adhesion layer. Duplicated hard molds can eliminate direct contact between a hard master and a patterned polymer on a substrate and the generated contamination of a master during the imprinting process. The replica hard mold exhibits the glass-like properties introduced here, such as transparency and hardness, make it appropriate for nanoimprint lithography and step-and-flash imprint lithography.

• Journal of Information Technology Applications and Management
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• v.20 no.1
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• pp.1-17
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• 2013

It has been found that users' characteristics are important variables that explain information systems adoption. These user groups, which are called COIs (Community Of Interests), might show different behaviors to each other to the same information system. We study differences in MDM (master data management) system adoption between military users and SI developers using TAM (Technology Acceptance Model). In case of military users, the perceived usefulness of an MDM system does not have impacts on intention to use an MDM system. Only the ease of use of an MDM system has impacts on intention to use an MDM system. However, in case of SI developers, both the perceived usefulness and the ease of use of an MDM system have impacts on intention to use an MDM system, which are similar to findings in previous studies. These results might be interpreted that users do not pay much attention to the usefulness in adopting a new information system in a centralized organization. They are obligated to use an information system whether it is useful or not. Thus the ease of use has more impacts on users than the usefulness.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.16 no.6
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• pp.17-29
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• 2013

Recently, the importance of forest landscape as a visual resource has been increased, so it is emphasized that the necessity of forest landscape management through 'Forest landscape management master plan' and 'National Forest landscape belt'. As such, this study aims to suggest a method for forest landscape management plan considering visual landscape analysis and regional landscape resources in case of Sangju-si, Gyeongsangbuk-do. Accordingly, this study has investigated regional landscape resources and surveyed existing forest conditions of target area. In order to analyze the characteristics of visual landscape, landscape control points are selected through viewshed analysis. And, Forest landscape plan is suggested 3 areas considering comprehensive analysis of forest landscape resources survey and characteristics of visual landscape:the landscape resource management area, the landscape resource restoration area and the landscape resources exploit area.

• The Journal of Advanced Prosthodontics
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• v.2 no.4
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• pp.128-133
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• 2010

PURPOSE. The purpose of this study was to compare the accuracy of the implant master cast according to the type (pick-up, transfer) and the length (long, short) of the impression copings. MATERIALS AND METHODS. The metal master cast was fabricated with three internal connection type implant analogs (Osstem GS III analog), embedded parallel and with $10^{\circ}$ of mesial angulation to the center analog. Four types of impression coping were prepared with different combinations of types (transfer, pick-up) and lengths (long, short) of the coping. The impressions were made using vinyl polysiloxane (one step, heavy + light body) with an individual tray, and 10 impressions were made for each group. Eventually, 40 experimental casts were produced. Then, the difference in the distance between the master cast and the experimental cast were measured, and the error rate was determined. The analysis of variance was performed using the SPSS (v 12.0) program (${\alpha}$= .05), and the statistical significance was set at P < .05. RESULTS. The ANOVA showed that the pick-up type impression coping exhibited a significantly lower error rate than the transfer type. However, no significant difference was observed with respect to the length of the impression coping. Additionally, no significant difference was observed between the parallel and mesial angulated groups. CONCLUSION. Within the limitations of this study, the pick-up type impression coping exhibited a more accurate implant master cast than the transfer type in parallel group. The accuracy of the implant master cast did not differ for different lengths of impression coping of at least 11 mm. Additionally, the accuracy of the implant cast was not different for the parallel and $10^{\circ}$ mesial angulated groups.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.4
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• pp.134-139
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• 2008

A spirally arrayed nano-pattern is designed as a model pattern for the next generation optical storage media. The pattern consists off types of embossed rectangular dot, which are 50nm, 100nm, 150nm and 200nm in length and 50nm in width. The height of the dot is designed to be 50nm. The pitch of the spiral track of the pattern is 100nm. A ER(Electron resist) master for this pattern is fabricated by e-beam lithography process. The ER is first spin-coated to be 50nm thick on a Si wafer and then the model pattern is written on the coated ER layer by e-beam. After developing this pattern written wafer in the solution, a ER pattern master is fabricated. The most conventional e-beam machine can write patterns in orthogonal way, so we made our own pattern generator which can write the pattern in circular or spiral way. This program generates the patterns to be compatible with the e-beam machine from Raith(Raith 150). To fabricate 50nm pattern master precisely, a series of experiments were done including the design compensation for the pattern size, optimization of the dose, acceleration voltage, aperture size and developing. Through these experiments, we conclude that the higher accelerating voltages and smaller aperture size are better for mastering the nano pattern which is in order of 50nm. With the optimized e-beam lithography process, a spiral arrayed 50nm pattern master adopting PMMA resist was fabricated to have dimensional accuracy over 95% compared to the designed. Using this pattern master, a metal pattern stamp will be fabricated by Ni electro plating for injection molding of the patterned plastic substrate.

• Journal of Ocean Engineering and Technology
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• v.10 no.4
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• pp.84-91
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• 1996

A fractal analysis on fracture surface of aluminium-particulate SiC composites was attempted. As the volume fraction of SiC in composites increases, the fractal dimension tends to increase. However, no correlation between the fractal dimension and the fracture toughness in terms of critical energy release rate was observed. Since the fractal dimension represents the roughness of fracture surface, the fracture toughness would be a function of not only fracture surface roughness but also additional parameters. Thus the applicability of fractal analysis to the estimation of fracture toughness must depend on the proper choice and interpretation of additioal paramerters. In this paper, the size of characteristic strctural unit for fracture was considered as an additional parameter. As a result, the size appeared to be a function of only volume fraction of SiC. Finally, a master curve for fracture toughness of aluminium-particulate SiC composites was proposed as a function of fractal dimension and volume fraction of SiC.