• 대한금속재료학회지
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• 제49권6호
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• pp.474-487
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• 2011

Bars of OFHC Cu with the diameter of 45 mm were processed by equal channel angular pressing up to 16 passes via route $B_c$, and homogeneity of their microstructures and mechanical properties was examined at every four passes which develop the equiaxed ultrafine grains. In general, overall hardness, yield strength and tensile strength increased by 3, 7, and 2 times respectively compared with those of unECAPed sample. Cross-sectional hardness exhibited a concentric distribution. Hardness was the highest at the center of bar and it decreased gradually from center to surface. After 16 passes, overall hardness decreased due to recovery and partial recrystallization. Regardless of the number of passage, yield strength and tensile strength were quite uniform at all positions, but elongation showed some degree of scattering. At 4 passes, coarse and ultrafine grains coexisted at all positions. After 4 passes, uniform equiaxed ultrafine grains were obtained at the center, while uniform elongated ultrafine grains were manifested at the upper half position. At the lower half position, grains were equiaxed but its size were inhomogeneous. It was found that inhomogeneity of grain morphology and grain size distribution at different positions are to be attributed to scattering in elongation but they did not affect strength. The present results reveal the high potential of practical application of equal channel angular pressing on fabrication of large-sized ultrafine grained bars with quite homogeneous mechanical properties.

• Journal of Microbiology and Biotechnology
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• 제31권12호
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• pp.1684-1691
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• 2021

In this study, the physicochemical changes related to fishy smell were determined by storing high hydrostatic pressure (HHP)-treated mackerel (Scomber japonicus) meat in a refrigerator for 20 days. The inhibition of crude urease activity from Vibrio parahaemolyticus using HHP treatment was also investigated. The mackerel meat storage experiment demonstrated that production of trimethylamine (TMA) and volatile basic nitrogen (VBN), the main components of fishy smell, was significantly reduced on the 20th day of storage after the HHP treatment compared to the untreated mackerels. The results demonstrated that the increased ammonia nitrogen rates in the 2000, 3000, and 4000 bar, HHP-treated groups decreased by 23.8%, 23.8%, and 31.0%, respectively, compared to the untreated groups. The enzyme activity of crude urease was significantly reduced in the HHP-treated group compared to that in the untreated group. Measurement of the volatile organic compounds (VOCs) in mackerel meat during storage indicated that the content of ethanol, 2-butanone, 3-methylbutanal, and trans-2-pentenal, which are known to cause off-flavor due to spoilage, were significantly reduced by HHP treatment. Collectively, our results suggested that HHP treatment would be useful for inhibiting the activity of urease, thereby reducing the fishy smells from fish and shellfish.

• 대한치과기공학회지
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• 제46권3호
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• pp.73-83
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• 2024

Purpose: This study aimed to investigate whether the accuracy and internal porosity of removable partial denture frameworks differ depending on the build direction in the selective laser melting method. Methods: A partially edentulous maxillary study model was scanned, and the anterior-posterior palatal bar was then digitally designed. The angles formed between the z-axis and the path of the insertion and removal were divided into five groups: -60°, -30°, 0°, 30°, and 60°. For each group, three removable partial denture metal frameworks were fabricated and used as specimens. The inner surface of each sample was scanned and superimposed on the design file to obtain the root mean square (RMS) value, and the average RMS value of each group was measured. One sample was randomly selected from each group, and the equivalent diameter and sphericity of the pores were analyzed using industrial X-ray three-dimensional computed tomography. To compare statistical differences between groups, the Kruskal-Wallis test of SPSS Statistics ver. 27.0 (IBM) was used (α=0.05). Results: The average RMS values of the whole inner surface accuracy of the specimens were in the order of -60°<0°<-30°<30°<60° (p<0.05). The equivalent diameter and sphericity of internal pores were significantly different among groups (p<0.001). Conclusion: The build orientation of the selective laser melting method influences the accuracy and internal porosity of removable partial denture frameworks.

• 한국전문물리치료학회지
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• 제18권1호
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• pp.57-63
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• 2011

The purpose of this study was to identify the effects of manual facilitation and a stick on lumbar and hip joint flexion angles in subject with lumbar flexion syndrome during forward bending from a sitting position. Fifteen subjects with lumbar flexion syndrome were recruited for this study. As a pretest, all subjects performed three repetitions of bending the trunk forward until the tips of their fingers touched the target bar. After this pretest, the subjects practiced the forward bending of the trunk 10 times, using either manual facilitation or a stick. Then, as a posttest, all subjects repeated the pretest procedure. The flexion angles of lumbar spine and hip joint during forward bending in a sitting position were measured using a three-dimensional motion analysis system. A paired t-test was used to determine the statistical differences between pre-test and post-test flexion angles and pre- and post-test flexion angle differences between forward bending with manual facilitation and forward bending with a stick. The level of statistical significance was set at p=.05. The results of the study showed that the angle of the lumbar flexion decreased significantly and the bilateral hip flexion angle increased significantly when performing forward bending with stick and manual facilitation. Furthermore, the angle of lumbar flexion decreased significantly and the angle of bilateral hip flexion increased significantly in forward bending with a stick compared to forward bending with manual facilitation. The findings of this study indicate that both forward bending with manual facilitation and sticks could be used to prevent excessive lumbar flexion and increase hip flexion, and that forward bending with a stick is more effective than forward bending with manual facilitation for inducing lumbar spine and hip joint angle changes.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1516-1522
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• 2014

A series of 20 wt % $(NH_4)_2SO_4$ and 3 wt % $Al_2O_3$ surface treatments were applied to $Li[Li_{0.2}Mn_{0.54}Co_{0.13}Ni_{0.13}]O_2$ substrates. The $Li[Li_{0.2}Mn_{0.54}Co_{0.13}Ni_{0.13}]O_2$ substrates were synthesized using a co-precipitation method. Sample (a) was left pristine and variations of the 20 wt % $(NH_4)_2SO_4$ and 3 wt % $Al_2O_3$ were applied to samples (b), (c) and (d). XRD was used to verify the space group of the samples as R$\bar{3}$m. Additional morphology and particle size data were obtained using SEM imagery. The $Al_2O_3$ coating layers of sample (b) and (d) were confirmed by TEM images and EDS mapping of the SEM images. 2032-type coin cells were fabricated in a glove box in order to investigate their electrochemical properties. The cells were charged and discharged at room temperature ($25^{\circ}C$) between 2.0V and 4.8V during the first cycle. The cells were then charged and discharged between 2.0V and 4.6V in subsequent cycles. Sample (d) exhibited lower irreversible capacity loss (ICL) in the first charge-discharge cycle as compared to sample (c). Sample (d) also had a higher discharge capacity of ~250 mAh/g during the first and second charge-discharge cycles when compared with sample (c). The rate capability of the $Al_2O_3$-coated sample (b) and (d) was lower when compared with sample (a) and (c). Sample (d), coated with $Al_2O_3$ after the surface treatment with $(NH_4)_2SO_4$, showed an improvement in cycle performance as well as an enhancement of discharge capacity. The thermal stability of sample (d) was higher than that of the sample (c) as the result of DSC.

• 설비공학논문집
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• 제29권11호
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• pp.559-569
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• 2017

Various studies examining how to conserve building energy have been conducted recently. From such studies it has been determined that insulation performance of an aircap is viable and therefore aircaps are used as material for improving insulation performance of windows. However, the aircap for improving insulation performance of a window is attached on the front, causing infringement of the prospect right. Therefore, the purpose of this study is to develop an aircap module attached to the window through rolling, conducting performance verification throughfull-scale testbed and verifying its effectiveness. Findings of this study are as follow : 1) The module suggested in this study enables setting of an area wherein the aircap is attached through rolling so that the aircap rolls up using Velcro tape, and an insulation bar is suggested to block the gap between the aircap and window glass. 2) When the aircap is applied to the window, consumption of lighting energy increased during summer and winter by 2.8%~16.4% and 0%~76.2% respectively in comparison to no aircap application, indicating that it is unsuitable for conserving lighting energy. 3) In terms of conserving cooling and heating energy, an advantageous or effective aircap attachment method is the method whereby an aircap is attached to the front surface of a window. However, the method whereby an aircap is attached to a part of a window and where no aircap is attached increases consumption of cooling and heating energy during summer and winter by 6.0%~35.7% and 2.7%~41.6% respectively in comparison to the method wherein an aircap is attached to the front surface of a window. 4) In consideration of conserving cooling, heating and lighting energy, the attachment of an aircap to the front surface of window is the most appropriate method, and it is appropriate to attach the aircap at a position that is 1,500 mm or higher from the floor to secure the prospect right and minimize energy loss.

• 정보보호학회논문지
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• 제18권6A호
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• pp.63-73
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• 2008

RFID(Radio Frequency IDentification) 시스템은 일정한 라디오 주파수 대역을 이용해 무선 방식으로 각종 데이터를 주고받을 수 있는 시스템으로 기본적으로 태그(Tag)와 리더(Reader) 그리고 백-엔드-데이터베이스(Back-End-Database)로 구성된다. 태그에 쓰기(Re-Write)가 가능하고 무선공간에서 다수의 태그를 동시에 인식 가능하다는 장점으로 인해 기존의 바코드 시스템을 대체하여 물류관리, 유통관리, 재고관리 분야에서 널리 사용되고 있다. 그러나 태그와 리더가 무선 주파수를 이용하여 통신하기 때문에 시스템 보안과 개인 프라이버시 침해 문제가 발생한다. 현재까지 RFID 시스템의 이러한 문제를 해결하기 위해 많은 연구가 있었으며 그 결과 다양한 보안 기법들이 제안되었다. 하지만 제안된 많은 보안 기법들은 UHF대역의 국제 표준인 Class-1 Generation-2 태그에는 적용하기 어렵다. 최근에 Chien과 Chen은 Class-1 Generation-2 태그에 적합한 상호 인증 프로토콜을 제안하였지만 이 또한 취약성이 존재하며 데이터베이스에서의 효율성이 떨어지는 문제점이 있다. 따라서 본 논문에서 Chien과 Chen이 제안한 기법을 분석하고 안전성과 효율성을 향상된 새로운 상호 인증 기법을 제안한다.

• 콘크리트학회논문집
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• 제26권4호
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• pp.491-497
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• 2014

철근의 부식은 철근콘크리트 교량 바닥판의 성능 저하에 큰 요인으로 작용한다. FRP는 비부식성 재료이기 때문에 이를 활용하여 보강근을 개발하려는 노력이 이루어지고 있다. 여러 종류의 FRP 보강근이 개발되었으나 아직 활용 실적은 많지 않은 상황이다. 그 이유로는 FRP 보강 콘크리트 구조물에 대한 단/장기 검증 데이터가 부족하기 때문이다. 이 연구에서는 GFRP 보강 바닥판에 대한 피로성능을 관찰하기 위해서 길이 4000 mm, 폭이 3000 mm, 높이 240 mm인 실제 크기의 교량 바닥판을 도로교설계기준을 준용하여 제작한 후 실험을 실시하였다. 하부 보강비를 변수로 설정하였으며 DB-24 하중이 바닥판 중앙에 집중 작용하는 것으로 실험을 실시하였다. 사용하중의 3.5, 4.5, 5.0배에 해당하는 다양한 하중을 2백 만회 이상 반복 재하하여 GFRP 보강 바닥판의 피로성능을 관찰하였다. 실험 결과 거더가 횡구속된 GFRP 보강 바닥판의 최대성능은 보강근비에는 민감하지 않았고, 피로성능은 보강비보다는 적용하중의 크기에 민감하며, 바닥판이 200만회 이상 반복재하에 저항하기 위해서는 재하되는 집중하중의 크기는 최대하중의 58% 수준 이하이어야 하며, 이 연구의 실험 대상 GFRP 보강 바닥판의 피로수명은 철근 콘크리트 바닥판의 수명 예측값보다는 다소 낮은 값을 나타내었고 FRP 보강 콘크리트 바닥판의 기존 예측값보다는 높은 값을 나타내었다.

• 해양환경안전학회지
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• 제24권7호
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• pp.939-944
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• 2018

청정소화약제는 지구오존층 보호를 위해 발효된 몬트리올 의정서에 따라 할론 1211 및 할론 1310을 대체할 수 있는 약제를 말한다. 국 내외적으로는 청정소화약의 시스템 표준화와 성능평가가 수행되고 있다. 본 논문은 일반적인 청정소화약제 시스템을 바탕으로 다양한 노즐의 형상에 대한 모델링 및 수치해석을 수행하여 최적의 노즐 형상을 제안하였다. Type A와 B의 2가지 형상에 대한 노즐의 3차원 모델링을 통해 노즐의 분출속도가 개선될 수 있도록 하였다. 2가지 형상의 노즐에 대하여 유동해석을 실시하였으며 노즐의 홀 직경을 다르게 하여 가스속도 및 압력분포를 측정하였다. 측정결과 노즐 홀 수 및 직경에 따라 노즐출구에서 분출속도가 달라지는 것을 확인 할 수 있었으며 노즐 홀 직경에 관계없이 유량은 압력이 증가함에 따라 증가하는 경향을 나타내었다. 실험을 통해 얻어진 결과를 바탕으로 노즐 직경이 5 mm인 경우의 K-factor값이 $101.8l/min{\cdot}bar^{-0.5}$임을 확인하였으며, 최종적으로 노즐 홀 5 mm인 12개의 홀이 2층 구조로 되어 있는 형상의 노즐을 제안하였다.

• 한국결정성장학회지
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• 제34권4호
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• pp.109-116
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• 2024

β-Ga₂O₃는 4.9 eV의 넓은 밴드갭과 8 MV/cm의 높은 항복전압으로 전력 소자 응용 분야에서 많은 관심을 받고 있는 대표적인 UWBG(Ultra-wide Band-gap) 반도체이다. 또한 용액 성장이 가능하기 때문에 SiC, GaN에 비해 성장 속도가 빠르고 생산 비용이 저렴하다는 장점이 있다[1,2]. 본 연구에서는 EFG(Edge-defined Film-fed Growth) 법을 통해 Si 도핑 된 β-Ga₂O₃ 단결정을 성장시키는 데에 성공하였다. 성장 방향과 성장 주 면은 각각 [010] / (001)로 설정하였으며 성장속도는 7~20 mm/h이다. 성장시킨 β-Ga₂O₃ 단결정은 다양한 결정 면 방향(001, 100, ${\bar{2}}01$)과 off-angle(1^o, 3^o, 4^o)에 따라 절단하여 표면 가공을 진행하였고, 가공 후 HVPE(Halide vapor phase epitaxy) 법을 이용해 epi-ready 기판 위에 homoepitaxial 층을 성장시켰다. 가공 후의 샘플과 epi-layer를 성장시킨 샘플을 XRD, AFM, OM, Etching 등의 분석을 통해 결정면과 off-angle에 따른 표면 특성을 비교하였다.