• Journal of Technologic Dentistry
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• 제34권4호
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• pp.353-359
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• 2012

Purpose: The aim of this study measured and compared the marginal and internal fit of metal cores with two base metal alloy (Ni-Cr alloy(non-beryllium), Co-Cr alloy). Methods: Maxillary right first molar abutment fabricated by titanium was prepared for this study. Impressions(10ea) were made from titanium model, and study models were poured with improved dental stone. Wax cores of twenty were prepared for burn-out and casting. Ten wax cores cast Ni-Cr alloy(non-Be), and finally ten cast Co-Cr alloy. Marginal and internal fit of cores was evaluated using silicone replica technique and digital microscope(x160). The data were statistically analyzed with the independent samples t-test (${\alpha}$ <.05). Results: Mean(standard deviation, SD) marginal and internal fit total size of Ni-Cr alloy(non-Be) group was $73.3(14.4){\mu}m$ and of Co-Cr alloy group $65.6(17.4){\mu}m$. The marginal and internal fit total size of Ni-Cr alloy group(non-Be) was statistically significantly greater than that of Co-Cr alloy group (P=.004). Conclusion: Co-Cr alloy cores in this study had a better marginal fit than Ni-Cr alloy(non-Be) cores.

• Journal of the Korean Mathematical Society
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• 제51권2호
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• pp.225-238
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• 2014

We apply modular function theory to find the relation among t-core partitions. By using the generators of function field corresponding to a certain modular group, we reprove the identities in [1] because their relations are linear for t = 3 or 5.

• Journal of the Korean Magnetics Society
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• 제14권5호
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• pp.186-191
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• 2004

The variation of magnetic properties with insulating materials(glass frits, talc and polyamide) in compressed powder cores composed of Fe$\sub$73.5/Cu$_1$Nb$_3$Si$\sub$15.5/B$\sub$7/ nanocrystalline alloy powders(size: 250～850 $\mu\textrm{m}$) and 3 wt% insulators has been investigated. Larger permeability was obtained at the frequency lower than 300～400 kHz for the powder cores including ceramic insulators(glass frits and talc) as compared to the cores with polyamide, while at higher frequency than 1 MHz the permeability of the former cores decreased rapidly. Further the cores with ceramic insulators showed larger core loss and smaller peak quality factor attained at lower frequency. On the contrary, the powder cores with polyamide exhibited high stability of permeabilities up to several MHz and superior core-loss and quality-factor properties. Moreover the dc bias property was better in the wide field range for the cores having polyamide. The enhanced magnetic properties of polyamide-added cores were attributed to the more sufficient electrical insulation between magnetic particles, where the higher insulation state was considered to be obtained from the larger volume fraction of polyamide in the powder cores.

• ETRI Journal
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• 제30권3호
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• pp.451-460
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• 2008

Recently, the power consumption of integrated circuits has been attracting increasing attention. Many techniques have been studied to improve the power efficiency of digital signal processing units such as fast Fourier transform (FFT) processors, which are popularly employed in both traditional research fields, such as satellite communications, and thriving consumer electronics, such as wireless communications. This paper presents solutions based on parallel architectures for high throughput and power efficient FFT cores. Different combinations of hybrid low-power techniques are exploited to reduce power consumption, such as multiplierless units which replace the complex multipliers in FFTs, low-power commutators based on an advanced interconnection, and parallel-pipelined architectures. A number of FFT cores are implemented and evaluated for their power/area performance. The results show that up to 38% and 55% power savings can be achieved by the proposed pipelined FFTs and parallel-pipelined FFTs respectively, compared to the conventional pipelined FFT processor architectures.

• Proceedings of the Korean Magnestics Society Conference
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• 한국자기학회 2002년도 동계연구발표회 논문개요집
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• pp.202-203
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• 2002

Ribbon type nanocrystalline alloy cores have shown excellent soft magnetic properties in the high frequency range because of small crystalline anisotropy and nearly zero magnetostriction[1]. In present, however ribbon alloys gives some limit in applications such as a large inductor and reactors of PFC circuit, which are required good DC bias property and low loss in the high frequency. Powder alloys with ultra fine grain structure can be an important way to overcome this kind of disadvantage, and to improve the high frequency soft magnetic properties in conventional metallic powder cores[2]. (omitted)

• Proceedings of the KIEE Conference
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1666-1669
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• 1996

To produce low loss amorphous molding cores which are used as choke cores in high efficiency electronic ballast for Metal Halide Lamp, the magnetic properties of amorphous molding cores were investigated with the various fabrication methods. The results are as follows : (1) The total weight of molding core gradually increased as molding time increases. (2) The magnetic properties($B_{10}$, $B_r$, $B_t/B_s$, $H_c$, $W_c$) of molding core drastically deteriorated. This is presumably due to the compressive stress imposed on amorphous core occurred during epoxy curing treatment. (3) Two step annealing process(curing+field annealing) was more or less effective to recover the damaged properties.

• Journal of Magnetics
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• 제11권3호
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• pp.126-129
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• 2006

The phosphate coating on the $(Fe_{0.97}Cr_{0.03})_{76}(Si_{0.5}B_{0.5})_{22}C_2$ amorphous powders with an average size of 10 ${\mu}m$ in diameter has been carried out in aqueous 1.0-2.0 wt% $H_3PO_4$ solutions, and the consolidation behavior and magnetic properties of their compressed powder cores has been investigated. The phosphate coating could provide efficient electrical insulation between amorphous powders and improved consolidation ability at room temperature. Especially when the powders were treated in more concentrated phosphoric acid solution, enhanced phosphate covering and higher frequency/dc-bias stability were achieved. The powder cores phosphate-coated in 2.0 wt% $H_3PO_4$ solution exhibited constant permeability of 21 up to 10 MHz, 110 of the quality factor at 0.9 MHz, 610 mW/cm3 core loss at 100 kHz/0.1 T and 89 of percent permeability at 100 kHz.

• Journal of the Korean Magnetics Society
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• 제15권3호
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• pp.191-197
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• 2005

In the fabrication process of Fe-based amorphous alloy powder cores by pulverization of the melt-spun ribbons and cold compaction, the effects of powder preparation method on the magnetic & electric properties, powder shapes and microstructure of cores have been investigated. The powder cores made by using rotor mill showed low effective permeability as compared to the cores prepared by ball milling. However the frequency dependence and quality factor properties were superior in the case of rotor-milling. Further the powders prepared by rotor mill had homogeneous and round shapes through strong shearing in the sieve ring, while the ball milled powders were inhomogeneous and relatively small. The lower permeability of the powder cores fabricated with rotor mill was considered to be due to the high internal stress occurred by very intensive shearing. Moreover the powder cores produced by rotor-milling showed lower core loss and good frequency dependence of effective permeability possibly due to the higher electrical insulation between magnetic particles. The dc bias property of the powder cores made by rotor-milling was better than the one by ball-milling.

• Carbon letters
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• 제18권
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• pp.18-23
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• 2016

Polyacrylonitrile (PAN)-based carbon fibers have high specific strength, elastic modulus, thermal resistance, and thermal conductivity. Due to these properties, they have been increasingly widely used in various spheres including leisure, aviation, aerospace, military, and energy applications. However, if exposed to air at high temperatures, they are oxidized, thus weakening the properties of carbon fibers and carbon composite materials. As such, it is important to understand the oxidation reactions of carbon fibers, which are often used as a reinforcement for composite materials. PAN-based carbon fibers T300 and T700 were isothermally oxidized in air, and microstructural changes caused by oxidation reactions were examined. The results showed a decrease in the rate of oxidation with increasing burn-off for both T300 and T700 fibers. The rate of oxidation of T300 fibers was two times faster than that of T700 fibers. The diameter of T700 fibers decreased linearly with increasing burn-off. The diameter of T300 also decreased with increasing burn-off but at slower rates over time. Cross-sectional observations after oxidation reactions revealed hollow cores in the longitudinal direction for both T300 and T700 fibers. The formation of hollow cores after oxidation can be traced to differences in the fabrication process such as the starting material and final heat treatment temperature.

• Journal of the Korean Institute of Educational Facilities
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• 제16권6호
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• pp.13-20
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• 2009

The purpose of this study is to analyze the configuration and properties of university campus cores for systematic approach and planning through space syntax based on master plans of 55 universities in Korea. The results of this study showed that: first, the campus cores were classified into 10 types through axial map analysis. They were '一 type', '二 type', 'ㄱ type', 'T type', '+ type', 'radiation type', 'grid type', 'polygon type', 'tree structure type' and 'combination type'.(table 7) The frequency of '一 type' was the highest by 27.2%, and 'radiation type' was the next by 14.5%; second, the integration value was 2.03(+ type), te90(grid type), te75(ㄱ type), te74(一 type), te67(二 type), te63(T type), te46(polygon type), te347(tree structure type) and te343(radiation type).(table 9) We could categorize the 'radiation type' and the 'tree structure type' as the first group, the 'polygon type' as the second group, the 'T type', the '二 type', the '一 type', and the 'ㄱ type' as the third group, the 'grid type' as the fourth group, the '+ type' as the fifth group; third, cases that the integration value of access road was very low(58.2%) was much more frequent than that of very high(32.7%); fourth, the most important space in the campus core were as follows: library and media center(18.1%), administration buildings and headquarters(15.7%), student center(15.7%), lecturing building(13.9%), streets and squares(13.3%).