• The Journal of Korean Academy of Prosthodontics
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• v.39 no.6
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• pp.682-697
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• 2001

This investigation evaluated the fracture toughness($K_{IC}$) of eight currently available core materials, and relate the fracture toughness value to fractography analysis and surface characteristics using a atomic force microscope (AFM). Single-edge notched (SEN) test specimens (n=10) and compact tension (CT) test specimens (n=10) were prepared conforming to the ASTM Standard E-399 for a high copper amalgam, three composite core materials (Core-Max II, Core Paste, Bisfil Core), two reinforced composite core materials (Ti-Core, Ti-Core Natural), a resin-modified glass ionomer core material (Vitremer), and a conventional glass ionomer core material (Ketac-Molar). The specimens were tested with an Instron Universal Testing Machine. The maximum loads were measured to calculate the fracture toughness ($K_{IC}$). Thereafter, fracture surfaces of SEN specimens of each material were investigated for fractography analysis using scanning electron microscope. And, disc-shaped specimens with 1mm thickness were fabricated for each material and were investigated under AFM for surface morphology analysis. The results were as follows: 1. Bisfil Core showed the highest mean fracture toughness regardless of test methods. 2. For the tooth-colored materials, Ti-Core Natural exhibited the highest fracture toughness. 3. Ketac Molar showed a significantly low fracture toughness when compared with the amalgam and the composite resin core materials(p<0.05). 4. The fracture toughness values obtained with the single-edge notched test, except Ketac Molar, were higher than those obtained in the compact tension test. 5. SEM revealed that the fracture surface of high fracture toughness material was rougher than that of low fracture toughness material. 6. AFM revealed that the surface particles of the composite resins were smaller in size, with a lower surface roughness than the glass ionomer core materials.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.21-26
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• 2016

This study evaluates the magnitudes and distributions of contact tangential forces with the swaging depth of punch acting at the contact surfaces between a rotor core slot and a Cu bar during a sequential rotor core swaging process. The effects of the core slot shape on the magnitudes and distributions of the total contact forces were investigated to improve the productivity of the rotor core swaging process. Parametric elastic-plastic numerical analyses were performed using simplified two-dimensional cyclic symmetric plane strain models to evaluate the contact force distributions at the contact surfaces. The numerical analysis results show that the total contact tangential forces increased by about 55% with the adjacent Cu bar swaging process. The length of the core slot is a dominant factor in the core slot design as result of the increased total contact tangential forces during the swaging process of the rotor core.

• Journal of Power Electronics
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• v.13 no.1
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• pp.113-121
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• 2013

This paper introduces a simple core loss calculation method for output filter inductor in pulse width modulation (PWM) DC-AC inverter. Amorphous C-core (AMCC-320) is used to analyze the core loss. In order to measure core loss of the output filter inductor and validate the proposed method, a single-phase half-bridge inverter and a calorimeter are used. By changing switching frequency and modulation index (MI) of the inverter, core loss of the AMCC-320 is measured with the lab-made calorimeter and the results are compared with calculated core loss. The proposed method can be easily extended to other core loss calculation of various converters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.8
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• pp.816-822
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• 1992

In this paper, propagation characteristics of trapezoidal-shaped segmented core single mode fibers is investigated theoretically as a function of relative Index difference ratio( =p) under the condition of zero dispersion at i=1.,isrm, and bending loss of trape zoidalshaped segmented core single mode fiber is greatly decreased less than that of conventional single mode fibers ( triangular Index, dual shape core). And mode field distribution In core Is confined 2H% stronger than that of a tapezoidal Index fiber In addition, the advantages of trapezoldal-shaped segmented core fibers are compared with t hose of conventional triangular -shaped segmented core fibers.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.3
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• pp.110-116
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• 2020

Grains in the BaTiO₃, which is used for a dielectric layer in MLCC(Multi-Layer Ceramic Capacitor) are necessary to form core/shell structure for a stable TCC(Temperature Coefficient of Capacitance) behavior. The shell property has been deduced from the whole TCC behavior of core/shell structure due to its tiny size, ~ few ㎛. This study demonstrates the individual TCC behavior of the shell phase measured by micro-contact measurement in a temperature range between 35 and 135℃. Pt electrode pairs deposited on an enlarged core/shell structure in a diffusion couple sample made the measurement possible. As a result, the DPT (Diffusion Phase Transition) behavior of the shell phase was revealed as a different TCC behavior from that of the core: a broad peak with T_m at 65℃. This would be also useful experimental data for a modelling that depicts dielectric-temperature behavior of core/shell structure.

• Journal of dental hygiene science
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• v.19 no.3
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• pp.170-180
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• 2019

Background: Recently, competency-based education has been reorganized in the dental hygiene curriculum. In education, non-cognitive factors are emphasized. Grit, the non-cognitive ability to persevere to achieve an individual's long-term goals, is emerging. This study aims to identify the degree of grit and core competencies in students and to investigate the relationship between them and the factors that affect these core competencies. Methods: This study was conducted using 350 dental hygiene students who were randomly assigned a structured questionnaire to complete. The final analysis included 321 students. The survey contents evaluated grit, core competencies, and general characteristics. The difference in the degree of grit and core competencies in conjunction with the general characteristics of the subjects was analyzed using the t-test/Mann Whitney U-test and the ANOVA/Kruskal-Wallis H test. Multiple regression analysis was then conducted to determine the factors affecting the core competencies of the subjects. Results: The difference of 'grit' according to general characteristics was statistically significant in 'major satisfaction', 'relationship', 'perceived academic achievement', 'grade point average (GPA)'. The difference in 'core competency' according to general characteristics was statistically significant in 'grade', 'department selection', 'major satisfaction', 'relationship', 'perceived academic achievement', 'GPA'. Among the sub-areas of 'grit', 'perseverance of effort' showed a high correlation with 'core competency' and was statistically significant. As a result of regression analysis, 'major satisfaction', 'perceived academic achievement' and 'grit' of dental hygiene students had a statistically significant influence on 'core competency'. Meanwhile, 'GPA' was not seen to be statistically significant in 'core competency'. Conclusion: Grit, a non-cognitive factor, had a statistically significant effect on core competency, while the effects on GPA, a cognitive factor, were not statistically significant. Among the sub-factors of grit, 'perseverance of effort' had a statistically significant effect on 'problem-solving competency' and 'academic competency', which are 'core competency' sub factors.

• Nuclear Engineering and Technology
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• v.53 no.11
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• pp.3528-3542
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• 2021

A detailed geometrical model of a Krško reactor core was developed using a Monte Carlo neutron transport code MCNP. The main goal of developing an MCNP core model is for it to be used in future research focused on ex-core calculations. A script called McCord was developed to generate MCNP input for an arbitrary fuel cycle configuration from the diffusion based core design package CORD-2, taking advantage of already available material and temperature data obtained in the nuclear core design process. The core model was used to calculate 3D power density profile inside the core. The applicability of the calculated power density distributions was tested by comparison to the CORD-2 calculations, which is regularly used for the nuclear core design calculation verification of the Krško core. For the hot zero power and hot full power states differences between MCNP and CORD-2 in the radial power density profile were <3%. When studying axial power density profiles the differences in axial offset were less than 2.3% for hot full power condition. To further confirm the applicability of the developed model, the measurements with in-core neutron detectors were compared to the calculations, where differences of 5% were observed.

• Journal of Engineering Education Research
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• v.21 no.6
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• pp.63-73
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• 2018

This research aims to analyze core competencies of engineering students in Korea as well as to explore the application plans of extracurricular activities(hereafter, ECA) and programs in order to enhance their core competencies. Participation in ECA has long been recognized as having positive benefits and impacts upon students. To achieve the purpose of this study, first, we investigated whether there were differences between core competencies in undergraduates according to majors, gender and grades. 'Core competencies', first introduced in management theory as 'core competency' can be defined as personal attributes or underlining characteristics, capable of delivering a role or job. 'Core competencies' has received particular attention in recent years and there has been much related research (domestic and foreign) combined with diverse factors. However, few studies have addressed the question on engineering student's core competencies as well as the ways of their enhancement. This study was conducted with a total of 286 students, and core competencies have been measured online, through K-CESA. Our findings show that firstly, there were significant differences in undergraduate students' core competencies by majors. Engineering students scored significantly lower in core competencies overall. Second, there was no significant difference in students' core competencies by gender and grade. Third, there was a significant correlation among components of core competencies. Finally, there was a significant correlation between core competencies and grades(GPA, grades in major subject & liberal arts subject), rather levels in the correlation were low. Furthermore, the study suggested that the appropriate application of extracurricular activities would enhance core competencies of students.

• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.35-39
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• 2016

In recent years, high-temperature superconductor (HTS) Quadruple Triplets are being developed for heavy ion accelerators, because the HTS magnets are suitable to withstand radiation and high heat loads in the hot cell of accelerators. Generally, an iron yoke, which costs a mass of material, was employed to enhance the magnetic field when a quadrupole magnet was designed. The type of the magnet is called iron-dominated magnet, because the total magnetic field was mainly induced by the iron. However, in the HTS superconductor iron-dominated magnets, the coil-induced field also can have a certain proportion. Therefore, the air-core HTS quadrupole magnets can be considered instead of the iron-core HTS quadrupole magnet to be employed to save the iron material. This study presents the design of an air-core HTS quadruple triplet which consists three by air-core HTS quadruple magnet and compare the design result with that of an iron-core HTS quadruple triplet. First, the characteristics of an air-core HTS quadrupole magnet were analyzed to select the magnet system for the magnetic field uniformity impairment. Then, the field uniformity was improved(< 0.1%) exactly using evolution strategy (ES) method for each iron-core HTS quadrupole magnet and the air-core HTS quadruple triplet was established. Finally, the designed air-core triplet was compared with the iron-core HTS quadruple triplet, and the results of beam trajectories were presented with both the HTS quadruple triplet systems to show that the air-core triplet can be employed instead of the iron-core HTS triplet. The design of the air-core quadruple triplet was suggested for a heavy ion accelerator.

• Journal of information and communication convergence engineering
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• v.18 no.4
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• pp.222-229
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• 2020

Recent multi-core processors for smart devices use per-core dynamic voltage and frequency scaling (DVFS) that enables independent voltage and frequency control of cores. However, because the conventional task scheduler was originally designed for per-core DVFS disabled processors, it cannot effectively utilize the per-core DVFS and simply allocates tasks evenly across all cores to core utilization with the same CPU frequency. Hence, we propose a novel task scheduler to effectively utilize percore DVFS, which enables each core to have the appropriate frequency, thereby improving performance and decreasing energy consumption. The proposed scheduler classifies applications into two types, based on performance-sensitivity and allows a performance-sensitive application to have a dedicated core, which maximizes core utilization. The experimental evaluations with a real off-the-shelf smart device showed that the proposed task scheduler reduced 13.6% of CPU energy (up to 28.3%) and 3.4% of execution time (up to 24.5%) on average, as compared to the conventional task scheduler.