• 동력기계공학회지
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• 제2권1호
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• pp.25-30
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• 1998

In order to investigate the droplet size distribution and Sauter Mean Diameter in a ultra high pressure diesel spray, fuel was injected with ultra high pressure into the environments of high pressure and room temperature by an Electronic Hydraulic Fuel Injection System. Droplet size was measured with the immersion liquid sampling technique. The immersion liquid was used a mixture of water-methycellulose solution and ethanol. The Sauter Mean Diameter decreased with increasing injection pressure, with a decrease environmental pressure (back pressure) and nozzle diameter. Increasing the injection pressure makes the fuel density distribution of the spray more homogeneous. An empirical correlation was developed among injection pressure, air density, nozzle diameter and the Sauter Mean Diameter of spray droplets.

• 한국표면공학회지
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• 제54권5호
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• pp.238-247
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• 2021

PEO (plasma electrolytic oxidation) was applied to modify the surface of AZ31 magnesium alloy in this study. The mixed solution of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) was used as the electrolyte, and 0 - 0.05 g/L of Ca-GP (Glycerol Phosphate Calcium salt) was added in the electrolyte as an additive. PEO treatment was conducted at a current density of 30mA/cm² for 5 minutes using a DC power supply. The surface properties were identified by SEM, XRD and surface roughness analyses, and the corrosion resistance was evaluated by potentiodynamic polarization and immersion tests. In addition, the biocompatibility was evaluated by immersion test in SBF solution. As the concentration of Ca-GP was increased, the surface morphology was denser and more uniform, and the amount of Ca and the thickness of oxide layer increased. Only Mg peak was observed in XRD analysis due to very thin oxide layer. The corrosion resistance of PEO-treated samples increased with the concentration of Ca-GP in comparision with the untreated sample. In particular, the highest corrosion resistance was identified at the group of 0.04g Ca-GP through potentiodynamic polarization and immersion tests in saline solution (0.9 wt.%NaCl). During the immersion in saline solution, pH rapidly increased at the beginning of immersion period due to rapid corrosion, and then increase rate of pH decreased. However, the pH value in the SBF temporarily increased from 7.4 to 8.5 during the day, then decreased due to the inhibition of corrosion with HA(hydroxyapatite) formation.

• Corrosion Science and Technology
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• 제22권6호
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• pp.419-428
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• 2023

Seawater has been used to cool devices in nuclear power plants. However, the pipes used to transport seawater are vulnerable to corrosion; hence, the inner side of pipelines is coated with an epoxy layer as prevention. Upon coating damage, the pipe becomes exposed, and corrosion progresses. The major cause is widely known as cavitation corrosion, causing the degradation of mechanical properties. In this study, corroded specimens were prepared using cavitation and immersion methods to clarify the degradation trend of mechanical properties with corrosion. Three different types of epoxy coatings were used, and accelerated cavitation procedures were composed of amplitudes of 15 ㎛, 50 ㎛, and 85 ㎛ for 2 h, 4 h, and 6 h. The immersion periods were 3 and 6 weeks. We conducted instrumented indentation tests on all degradation samples to measure mechanical properties. The results showed that higher cavitation amplitudes and longer cavitation or immersion times led to more degradation in the samples, which, in turn, decreased the yield strength. Of the three samples, the C coating had the highest resistance to cavitation and immersion degradation.

• 동아시아식생활학회지
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• 제24권1호
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• pp.101-108
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• 2014

본 연구에서는 최근 건강 관리를 위해 다양하게 상용되고 있는 당침액의 오 남용을 막기 위해 과학적으로 물 추출물과 당침액의 특성을 규명하고자 하였다. 그 결과, 일반 물 추출물과 비교하였을 때 당침액의 총 폴리페놀 및 플라보노이드 함량이 크게 감소하는 것을 확인하였으며, 그에 따라 항산화 활성 또한 감소한 것을 확인할 수 있었다. 이는 물 추출물과 비교하여 당침액의 건조 분말에는 설탕 또는 그 분해물들이 많은 부분을 차지하기 때문이라 판단된다. 그러나 혈당강하 효능의 target 효소로 연구되고 있는 ${\alpha}$-amylase 및 ${\alpha}$-glucosidase의 활성을 측정한 결과, 청고추, 쇠비름, 표고버섯의 물 추출물과 당침액은 ${\alpha}$-amylase 억제 활성을 나타내지 않았지만, ${\alpha}$-glucosidase 억제 활성은 의약품인 acarbose에는 미치지 못하였으나, 물 추출물에 비해 당침액이 농도 의존적으로 높은 억제 활성을 나타내었다. 또한 세포 독성을 HepG2 cell에서 확인한 결과, 물 추출물과 비교하여 당침액의 독성이 약 1/10 감소한 것을 확인할 수 있었다. 이와 같은 결과는 민간에서의 믿음처럼 당침액이 물 추출물과 비교하였을 때 모든 부분에서 우수한 기능을 가진다고 할 수 없으며, 활용할 용도에 따라 소재를 물 추출하거나 당침액을 제조하는 등의 가공 과정을 거치는 것이 목표한 기능을 효과적으로 확보하는 방법임을 의미한다. 따라서 민간에서 맹목적으로 믿는 당침액의 효능에 대한 과학적인 연구 접근법은 당침액의 적절한 사용 목적과 방법을 설정하는 기초 자료로 활용이 가능할 것이다.

• Corrosion Science and Technology
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• 제13권5호
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• pp.163-169
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• 2014

The corrosion resistance of epoxy-coated carbon steel was evaluated. The carbon steel surface was subjected to different treatment methods such as steel grit blasting and power tool treatment as well as contamination of water soluble salt. To study the effect of the surface treatments and contamination, the topology of the treated surface was observed by confocal microscopy and a pull-off adhesion test was conducted. The corrosion resistance of the epoxy-coated carbon steel was further examined by electrochemical impedance spectroscopy (EIS) combined with immersion test of 3.5 wt% of NaCl solution. Consequently, the surface contamination by sodium chloride with $16mg/m^2$, $48mg/m^2$ and $96mg/m^2$ didn't affect the adhesion strength for current epoxy coated carbon steel and blister and rust were not observed on the surface of epoxy coating contaminated by various concentration of sodium chloride after 20 weeks of immersion in 3.5 wt% NaCl aqueous solutions. In addition, the results of EIS test showed that the epoxy-coated carbon steel treated with steel grit blasting and power tool showed similar corrosion protection performance and surface cleanness such as Sa 3 and Sa 2.5 didn't affect the corrosion protectiveness of epoxy coated carbon steel.

• 동력기계공학회지
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• 제8권3호
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• pp.44-51
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• 2004

Effect of corrosion characteristics in relation to loaded stress in the welded zone of A5083-H116 aluminum alloy, in the seawater was studied. The corrosion experiment was performed for 120 hours on the specimens in the natural seawater tank with four steps of the loaded stress. The corrosion crack, corrosion rate, electrode potential, current, and corrosion pattern, etc. were examined for the specimens with the elapse of the immersion time. The main result derived from this study is the crack growth length is increased with the increasing loaded stress. The electrode potential and the corrosion current are decreased rapidly in the early stage of the corrosion, and then decreased gradually and stabilized eventually with the elapse of the immersion time. The test condition of the longer crack growth tends to show the higher corrosion rate. Corrosion pattern of the welded zone indicates that the depth and width of the pitting become increasing with the increasing loaded stress.

• Corrosion Science and Technology
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• 제10권5호
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• pp.167-174
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• 2011

Due to commercialization of nuclear power, most countries have taken interest in decontamination process of nuclear power plant and tried to develop a optimum process. Because open literature of the decontamination process are rare, it is hard to obtain skills on decontamination of foreign country and it is necessarily to develop proper chemical decontamination process system in Korea. In this study, applicable possibility in chemical decontamination for reactor coolant pump (RCP) was investigated for the various stainless steels. The stainless steel (STS) 304 showed the best electrochemical properties for corrosion resistance and the lowest weight loss ratio in chemical decontamination process with immersion type than other materials. However, the pitting corrosion was generated in both STS 415 and STS 431 with the increasing numbers of cycle. The intergranular corrosion in STS 431 was sporadically observed. The sizes of their pitting corrosion also increased with increasing cycle numbers.

• 동력기계공학회지
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• 제10권4호
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• pp.5-10
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• 2006

The purpose of this study is to measure the droplet distribution and Sauter mean diameter(SMD) of biodiesel fuel, using the immersion sampling method. This method involves using an optical microscope and a CCD camera, to take an image of the droplets. These images are then measured by using a 'Sigma Scan' processing program. The results of the above experiment are summarized as followed ; (1) There can be as much as a 10% error rate when measuring the diameter of these droplets, using the image processing method and the naked eye. (2) The result of droplet size distribution test, TVO(transesterified vegetable oil) big size droplet distribution were increased at ambient pressure $6kg/cm^2$. (3) When ambient pressure increased $6kg/cm^2$ above, SMD variation of TVO and UVO(used vegetable oil) 30 are small. (4) On Rosin-Rammler analysis, droplets size distribution of UVO(used vegetable oil) 30 uniform more than TVO 20 on ambient pressure $1kg/cm^2$.

• 마이크로전자및패키징학회지
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• 제25권4호
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• pp.35-40
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• 2018

다양한 디바이스 응용분야에 블록공중합체가 사용되기 위해, 블록공중합체의 형상을 제어하기 위한 간단하면서도 실용적인 합성방법이 필요하다. 하지만 콜로이드성의 형판을 사용하는 기존의 방식은 공정이 복합하고 비용이 많이 발생하여, 고순도의 코어-쉘 나노입자를 대량생산하기에 적합하지 않다. 본 논문에서 PS-b-PDMS 블록공중합체를 담금어닐링하여, 20 nm 이하크기를 가지는 PS가 봉입된 코어-쉘 구조의 $SiO_x$나노입자를 합성하였다. 또한, 어닐링 공정에 사용되는 헵테인과 에탄올의 혼합비율이 자기조립된 PS-b-PDMS 블록공중합체 나노입자의 형상에 어떠한 영향을 미치는지 분석하였으며, 최적의 담금어닐링 조건에서 나노입자가 worm-like구조로 변화하는 것을 확인하였다. 이러한 파우더 합성법은 다른 용매기반의 블록공중합체 합성방법에 응용이 가능할 것으로 생각되며, 새로운 가이드라인을 제공할 것으로 예상된다.

• 문화기술의 융합
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• 제10권1호
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• pp.35-50
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• 2024

본 연구는 여대생의 월경전 증후군, 월경에 대한 태도, 수면의 질, 통증이 학습 몰입도에 미치는 영향을 파악하고자 시도되었다. 연구대상자는 경상남도 C 대학교 여대생 166명이며, 자료수집은 구글 설문지를 이용하여 2023년 7월 01부터 8월 31일까지 진행하였다. 수집된 자료는 상관관계, 다중회귀분석으로 분석하였다. 월경전 증후군은 월경에 대한 태도(r=.40, p<.001)와 월경통(r=.33, p<.001)과 유의한 정적 상관관계가 있었다. 그리고 수면의 질은 월경통(r=.31, p<.001), 학습몰입도(r=.24, p=.002)와 유의한 정적 상관관계가 있었다. 학습몰입도에 유의한 영향을 미치는 변인은 식사 '불규칙적'(β=.20, p=.007), 월경통 완화 '복무마사지'(β=.27, p=.003), 수면의 질(β=.16, p=.038)이었다. 월경통 완화 '복무마사지'가 학습몰입도를 가장 잘 예측하는 요인으로 나타났고, 그 다음 식사 '불규칙적', 수면의 질 순이었다. 총 설명력은 13.9%이었다. 이상의 결과를 토대로 월경전 증후군을 완화를 통한 학습몰입도 증가를 위해서는 다양한 치료법과 이에 대한 관심을 증대시켜 적극적인 대처 방안을 모색하고, 올바른 식사 습관을 갖추어 월경에 대한 긍정적인 태도를 갖도록 교육이 필요하다.