• 한국재료학회지
• /
• 제33권12호
• /
• pp.558-564
• /
• 2023

In this study, we designed and manufactured a large angular contact ball bearing (LACBB) with low deformation using JIS-SUJ2 steel and analyzed changes in its structural characteristics and chemical composition upon heat treatment. The bearing was produced by hot forging and heat treatment including a quenching and tempering (Q/T) process, and its properties were analyzed using 4 mm thick specimens. A difference in the size distribution of the carbide in the outer and inner parts of the bearing was observed and it was confirmed that large and non-uniform carbide was distributed in the inner part of the bearing. After heat treatment, the hardness value of the outer part increased from 13.4 HRC to 61 HRC and the inner part increased from 8.0 HRC to 59.7 HRC. As a result of X-ray diffraction (XRD) measurements, the volume fraction of the retained austenite contained in the outer part was calculated to be 3.5~4.8 % and the inner part was calculated to be 3.6~5.0 %. The surface chemical composition and the content of chemical bonds were quantified through X-ray photoelectron spectroscopy (XPS), and a decrease in C=C bonds and an increase in Fe-C bonds were confirmed.

• 대기
• /
• 제26권3호
• /
• pp.401-412
• /
• 2016

A 3D sonic anemometer has been installed at Yongpyong alpine slope since Oct. 23th 2014 to observe the slope winds and to analyze turbulent characteristics with the change in surface cover (grass and snow) and the synoptic wind strength. Eddy covariance method has been applied to calculate the turbulent quantity after coordinate transformation of a planar-fit rotation. We have carefully selected 3 good episodes in the winter season (23 October 2014 to 28 February 2015) for each category (9 days in total), such as grass and snow covers in case of weak synoptic wind condition, and grass cover of strong synoptic wind. The diurnal variations of the slope winds were well developed like the upslope wind in the daytime and downslope wind in the nighttime for both surface covers (grass and snow) in the weak synoptic forcing, when accordingly both heat and momentum fluxes significantly increased in the daytime and decreased in the nighttime. Meanwhile, diurnal variation of heat flux was not present on the snow cover probably in associated with significant fraction of sunlight reflection due to high albedo especially during the daytime in comparison to those on the grass cover. In the strong synoptic regime, the most dominant feature at Yongpyong, only the southeasterly downslope winds were steadily generated irrespective of day and night with significant increases in momentum flux and turbulent kinetic energy as well, which could suggest that local circulations are suppressed by the synoptic scale forcing. In spite of only one season analysis applied to the limited domain, this kind of an observation-based study will provide the basis for understanding of the local wind circulation in the complex mountain domain such as Gangwon in Korea.

• Journal of Welding and Joining
• /
• 제31권1호
• /
• pp.58-64
• /
• 2013

The following results were obtained, microstructures and tensile properties in arc brazed joints of DP(dual phase) steel using Cu-5.3wt%Sn insert metal was investigated as function of brazing current. 1) The Fusion Zone was composed of ${\alpha}Fe+{\gamma}Cu$ and Cu23Sn2. The reason for the formation of these solid solutions. Despite, Fe & Cu were impossible to solid solution at room temperature. It's melting & reaction to something of insert metal & Base Metal (DP Steel) by Arc. Brazing Process has faster cooling rate then Cast Process, Supersaturated solid solution at room temperature. 2) The increase Hardness of Fusion Zone was directly proportional to the rise of welding current. Because, ${\alpha}Fe+{\gamma}Cu$ phase (higher hardness than the Cu23Sn2.(104.1Hv < 271.9Hv)) Volume fraction was Growth, due to increasing the amount of base metal melting by High current. 3) The results of tensile shear test by Brazing, All specimens happen to fracture in Fusion Zone. On the other hand, when Brazing Current increasing tend to rise tensile load. but it was very small, about 26-30% of the base metal. 4) The result of fracture analysis, The crack initiate at Triple Point for meet to Upper B.M/Under B.M/Fusion Zone. This Crack propagated to Fusion zone. So ruptured by tensile strength. The Reason to in the fusion zone fracture, Fusion zone by Brazing of hardness (strength) was very lower then the base metal (DP steel). In addition the Fusion Zone's thickness in triple point was thin than the base metal's thickness in triple point.

• Journal of Applied Biological Chemistry
• /
• 제50권4호
• /
• pp.275-280
• /
• 2007

Dried unripe fruits of Rubus coreanus Miq. were extracted with 80% aqueous MeOH and the concentrated extract was partitioned with EtOAc and $H_2O$. From the EtOAc fraction, four triterpenoids were isolated through repeated silica gel, ODS and Sephadex LH-20 column chromatographies. From the result of physico-chemical data including NMR, MS aud IR, the chemical structures of the compounds were determined as tormentic acid (1), myrianthic acid (2), hovenic acid (3) and 2${\alpha}$,3${\beta}$,19${\beta}$,23-tetrahydroxylolean-12-en-28-oic acid (4). Compounds 3 and 4 were isolated for the first time from this plant. All isolated compounds were evaluated for cytotoxic activity against human colon carcinoma cells using in vitro three-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, compound 3 showed a higher cytotoxicity ($IC_{50}$ = 7.8 ${\mu}M$) than doxorubicin ($IC_{50}$= 50 ${\mu}M$).

• 한국분말재료학회지
• /
• 제21권3호
• /
• pp.196-201
• /
• 2014

In this study, nanocrystalline Cu-Ni bulk materials with various compositions were cold compacted by a shock compaction method using a single-stage gas gun system. Since the oxide layers on powder surface disturbs bonding between powder particles during the shock compaction process, each nanopowder was hydrogen-reduced to remove the oxide layers. X-ray peak analysis shows that hydrogen reduction successfully removed the oxide layers from the nano powders. For the shock compaction process, mixed powder samples with various compositions were prepared using a roller mixer. After the shock compaction process, the density of specimens increased up to 95% of the relative density. Longitudinal cross-sections of the shock compacted specimen demonstrates that a boundary between two powders are clearly distinguished and agglomerated powder particles remained in the compacted bulk. Internal crack tended to decrease with an increase in volumetric ratio of nano Cu powders in compacted bulk, showing that nano Cu powders has a higher coherency than nano Ni powders. On the other hand, hardness results are dominated by volume fraction of the nano Ni powder. The crystalline size of the shock compacted bulk materials was greatly reduced from the initial powder crystalline size since the shock wave severely deformed the powders.

• ALGAE
• /
• 제32권4호
• /
• pp.379-388
• /
• 2017

In the present study, we enhanced the phenolic content of 70% ethanol extracts of Spirogyra sp. (SPE, $260.47{\pm}5.21$ gallic acid equivalent $[GAE]mg\;g^{-1}$), 2.97 times to $774.24{\pm}2.61GAE\;mg\;g^{-1}$ in the ethyl acetate fraction of SPE (SPEE). SPEE was evaluated for its antiradical activity in online high-performance liquid chromatography-ABTS analysis, and the peaks with the highest antiradical activities were identified as gallic acid derivatives containing gallic acid, methyl gallate, and ethyl gallate. Isolation of ethyl gallate from Spirogyra sp. was performed for the first time in this study. In ultraviolet B (UVB)-irradiated keratinocytes (HaCaT cells), SPEE improved cell viability by 8.22%, and 23.33% and reduced accumulation of cells in the sub-$G_1$ phase by 20.53%, and 32.11% at the concentrations of 50 and $100{\mu}g\;mL^{-1}$, respectively. Furthermore, SPEE (50 and $100{\mu}g\;mL^{-1}$) reduced reactive oxygen species generation in UVB-irradiated zebrafish by 66.67% and 77.78%. This study suggests a protective activity of gallic acid and its derivatives from Spirogyra sp. against UVB-induced stress responses in both in vitro and in vivo models, suggesting a potential use of SPEE in photoprotection.

• 미생물학회지
• /
• 제50권1호
• /
• pp.15-21
• /
• 2014

Pseudomonas sp. P7014 박테리아를 통한 큰느타리버섯 균사체의 생육촉진에 관한 연구가 수행되었다. 박테리아 배양액으로 부터 분리한 ethyl acetate 분획물(F5)에는 성장촉진물질(GPC)이 함유되어 있음을 확인하였다. TLC, HPLC, NMR 및 MS/MS분석법으로 확인한 바, indole acetic acid (IAA)로 확인되었다. 큰느타리버섯 균사체는 성장촉진물질(GPC)이 첨가된 PDA와 PDB 배지에서 빠른 성장을 보였다. 성장촉진물질(GPC)의 농도는 1.0 nM로 매우 낮았지만, 확인된 tryptophan은 IAA의 전구체로써 IAA가 아민화된 형태였다. 이들 결과는 박테리아에서 분비된 성장촉진물질(GPC)은 IAA이었고 큰느타리버섯 균사체의 생육촉진에 중요한 역할을 하는 것으로 확인되었다.

• Composites Research
• /
• 제33권3호
• /
• pp.169-175
• /
• 2020

콘형 복합재 격자 구조체의 강성 평가를 위한 두 종류의 시편 단위 압축 및 인장 시험을 수행하였으며 유한요소해석 결과와 비교하였다. 구조체는 높이별로 반경이 변화하는 콘형이므로 단순 압축 및 인장 시험이 어려우므로 시험 수행이 가능한 형태의 시편 및 지그를 제작하여 시험을 수행하였다. 압축 시험이 가능하도록 단위 격자 구조체를 Subelement 형태로 가공하였으며, 압축 시험을 수행하여 측정된 섬유방향 압축 변형률을 유한요소해석 결과와 비교하여 헬리컬 리브의 강성을 확인하였다. 후프 리브의 강성 평가를 위해서는 구조체에서 후프 링 시편을 가공하여 인장 시험을 수행하였다. 후프 링에 인장 하중을 가하여 굽힘 변형이 크게 발생하도록 하였으며, 두께 방향 섬유체적비를 고려한 유한요소해석 결과와 비교하여 후프 리브의 강성을 확인하였다.

• 자원환경지질
• /
• 제43권6호
• /
• pp.543-553
• /
• 2010

이 연구는 부여 정동리 꿩바윗골 유적에서 출토된 백제시대 경작토양의 광물학적 및 지구화학적 특정을 조사하고, 이를 사용하여 제작한 것으로 추정되는 무령왕릉 및 송산리 전(벽돌)과 토양을 비교하여 태토로서의 가능성을 검토하였다. 연구대상 토양시료들은 모두 미사질 양토로 가장 하부층을 제외하고는 모두 유사한 토양입도를 가지고 있다. 토양은 산성으로 일부 시료에서 유기물, P, S 등의 집적현상이 나타났다. 또한 지구화학적 원소 분포경향이 유사하며 석영, 사장석, 정장석, 질석, 운모, 고령석 등으로 구성되어 동일한 광물조성을 보인다. 부분적으로 붉은 철산화물의 농집이 관찰되는데, 강의 범람과 배수에 따른 산화와 환원환경이 반복되었던 환경이 토양 내 철산화물의 농집을 일으킨것으로 보인다. 이는 자연현상과 인간의 경작활동에 의한 풍화양상으로 볼 수 있다. 특히 무령왕릉과 송산리고분군 출토 전에서 발견되는 철산화물의 농집현상은 연구지역 토양이 전의 태도로 추정될 수 있는 추가적인 증거로 판단된다.

• Nuclear Engineering and Technology
• /
• 제51권5호
• /
• pp.1406-1416
• /
• 2019

In this research, a multi-slit prompt-gamma camera was developed to locate the distal dose falloff of the proton beam spots in spot scanning proton therapy. To see the performance of the developed camera, therapeutic proton beams were delivered to a solid plate phantom and then the prompt gammas from the phantom were measured using the camera. Our results show that the camera locates the 90% distal dose falloff (= d90%), within about 2-3 mm of error for the spots which are composed $3.8{\times}10^8$ protons or more. The measured location of d90% is not very sensitive to the irradiation depth of the proton beam (i.e., the depth of proton beam from the phantom surface toward which the camera is located). Considering the number of protons per spot for the most distal spots in typical treatment cases (i.e., 2 Gy dose divided in 2 fields), the camera can locate d90% only for a fraction of the spots depending on the treatment cases. However, the information of those spots is still valuable in that, in the multi-slit prompt-gamma camera, the distal dose falloff of the spots is located solely based on prompt gamma measurement, i.e., not referring to Monte Carlo simulation.