• 대한치과기공학회지
• /
• 제31권2호
• /
• pp.39-44
• /
• 2009

In the orthopedic field which firstly used zirconia as artificial joints, researchers had studied the reasons for collapsing zirconia used as restorative material by accumulated inner cracks in several years and they found out Low Temperature Degradation is one of the reasons. In the dentistry field, it has not been too long since they used zirconia as the cores of all-ceramic restoration; however, the study is needed as prophylactic measure against Low Temperature Degradation which can be caused by saliva wetting the mouth all the time and frictional forces such as bite pressure and masticatory pressure. Artificial aging by autoclaving is used because there are difficulties of testing in the patient's mouth. To study the changes in the material properties, the flexural strength of dental zirconia ceramic is measured before and after the test. The following are the result of the test. 1) The zirconia blocks in the autoclaves at $130^{\circ}C$ and $200^{\circ}C$ are phase-shifted tetragonal to monoclinic by Low Temperature Degradation. 2)The non-autoclaved specimens have the average fractural strength of 1346.4MPa, the specimens autoclaved at $130^{\circ}C$ have 1226.4Mpa and the specimens autoclaved at $200^{\circ}C$ have 1024.1MPa. The tests show that as the temperature increases, the flexural strength tend to decrease and the differences are noticeable(p<0.001). 3)Through the Duncan's post-hoc test, the differences in flexural strength of the 3 groups were listed in order of strength like normal temperature>at $130^{\circ}C$ autoclave low temperature degradation> at $200^{\circ}C$ autoclave low temperature degradation.

• 생약학회지
• /
• 제46권3호
• /
• pp.234-242
• /
• 2015

Allium hookeri (Liliaceae), native to India is widely cultivated in Korea lately as a medicinal plant. This study was performed to evaluate the antioxidant and lifespan extending effects of the root of A. hookeri. Methanol extract from the root of A. hookeri was successively partitioned as methylene chloride, ethyl acetate, n-butanol and H₂O soluble fractions. Antioxidant effects of the fractions were measured by measuring the radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH), and superoxide quenching activities. Lifespan extending effects of the fractions were investigated using Caenorhabditis elegans model system. In addition, stress resistant, superoxide dismutase (SOD) and catalase activities, and intracellular reactive oxygen species (ROS) levels were also studied. Furthermore, we had investigated aging-related factors such as reproduction, food intake, growth and movement of C. elegans to find any sample-induced significant change. Our results revealed that ethyl acetate soluble fraction from the root of A. hookeri showed the most potent antioxidant and lifespan extending effects, and this fraction elevated the most potent SOD and catalase activities of worms, and reduce intracellular ROS accumulation.

• 펄프종이기술
• /
• 제42권1호
• /
• pp.54-63
• /
• 2010

Recently, as the function of largest supplier of biomass for "low carbon green growth", the necessity for systematic management of afforestation areas is emphasizing. The forestation of seedling, besides the afforestation cost itself, is required some additional follow-up management costs, like mowing and fertilizing of forestation area, and removal of bindweed. The mulching mat for afforestation seedlings is available for rooting of little seedlings as well as initial forestation expenses. Mulching technique is also used to control soil temperature and moisture by covering the surface of ground. In this study, the paper based-mulching film coated with biodegradable polymer and functional additive was specially produced using laboratory bar coater, and analyzed for its degradable behavior. Coating colors were prepared by dissolving PE (polyester) 80 % and PLA(polylactic acid) 20 % in chloroform and finally applied to handsheet prepared by preceding study conditions. Base paper and polymer-coated paper were artificially aged by 2 kinds of degradation methods, which are soil degradation by microorganism and light degradation by 257 nm UV wavelengths. Strength property, oxidation index and morphological property were evaluated by reduction rates of tensile strength, FTIR spectra ratio of carboxyl and carbonyl group and SEM micrograph. As these results, polymer coated-paper was superior to base paper in degradation behaviors, having results with lower reduction rate of strength properties.

• 한국재료학회지
• /
• 제28권6호
• /
• pp.317-323
• /
• 2018

Crystal structure of the $L1_2$ type $(Al,X)_3Ti$ alloy (X = Cr,Cu) is analyzed by X-ray diffractometry and the nonuniform strain behavior at high temperature is investigated. The lattice constants for the $L1_2$ type $(Al,X)_3Ti$ alloys decrease in the order of the atomic number of the substituted atom X, and the hardness tends to increase. In a compressive test at around 473K for $Al_{67.5}Ti_{25}Cr_{7.5}$, $Al_{65}Ti_{25}Cr_{10}$ and $Al_{62.5}Ti_{25}Cu_{12.5}$ alloys, it is found that the stress-strain curves showed serration, and deformation rate dependence appeared. It is assumed that the generation of serration is due to dynamic strain aging caused by the diffusion of solute atoms. As a result, activation energy of 60-95 kJ/mol is obtained. This process does not require direct involvement. In order to investigate the generation of serrations in detail, compression tests are carried out under various conditions. As a result, in the strain rate range of this experiment, serration is found to occur after 470K at a certain critical strain. The critical strain increases as the strain rate increases at constant temperature, and the critical strain tends to decrease as temperature rises under constant strain rate. This tendency is common to all alloys produced. In the case of this alloy system, the serration at around 473K corresponds to the case in which the dislocation velocity is faster than the diffusion rate of interstitial solute atoms at low temperature.

• 조명전기설비학회논문지
• /
• 제21권10호
• /
• pp.141-149
• /
• 2007

본 논문은 유도전동기 고정자권선의 절연물에 대하여 비파괴 및 파괴시험을 실시하여 절연물의 비파괴특성과 내전압강도와의 상호관계를 비교, 평가, 분석함으로써, 향후 전동기의 절연상태 평가시 수명 및 절연진단의 신뢰성을 도모하고자 제안하였다. 본 논문에서는 비파괴시험과 파괴시험과의 상관관계를 평가하기위하여 비파괴시험으로 절연저항시험, 성극지수시험, 유전정접시험, 부분방전시험을 실시하였으며, 파괴시험은 60[kV] AC 내전압를 이용하여 실시하였다. 또한 장기간 사용된 전동기 권선의 절연물에 대한 연구결과로부터 기존 선진국의 진단방법 및 판정기준이 국내에서 제작된 전동기에 대한 절연특성 평가 및 분석에도 타당함을 증명하였으며, 향후 본 논문에서 제시한 자료들은 유사조건의 산업현장에서 운용중인 유도전동기의 수명 및 상태 평가를 위한 기초자료로 유용하게 사용될 수 있으리라 기대된다.

• 대기
• /
• 제17권4호
• /
• pp.407-420
• /
• 2007

Optical characteristics of aerosols in Seoul are investigated from the measurements of sky radiance by Skyradiometer at Yonsei University from December 2005 to November 2006. Aerosol optical depth (AOD) shows a maximum in June due to weak ventilation and particle growth by aging process and hygroscopic effect. Single scattering albedo (SSA) and Angstrom Exponent (AE) show the lowest value in spring due to the Asian dust. It is clear that coarse mode is dominant in spring and fine mode is dominant in summer from the volume size distribution measured in this study. The explanations on the changes of aerosol loadings are provided through the correlation between AOD and AE, while the pattern of wavelength dependency related to particle size is shown through the correlation between SSA and AE. Backward trajectory analysis by HYSPLIT provides information about origin of aerosol, which allows us to classify the case according to the source region and the path distance. Although the direction of backward trajectory traces back mostly to west, coarse mode particle is dominant in the case of long pathway and fine mode particle is dominant in the case of short pathway. This discrepancy is caused by the regional difference of emitted particles.

• 한국의학물리학회지:의학물리
• /
• 제11권1호
• /
• pp.19-27
• /
• 2000

본 연구에서는 평탄한 지면 위의 도로 교통소음의 전파특성을 해석하고자 점음원과 쌍극자음원을 모델로 사용하였으며, 연속 지표면 음향임피던스에 대한 초과감쇠를 실험으로 조사하였다 연구결과 수음점이 지표면 가까이 있을 때, 도로 교통소음의 전파특성은 소음 전파경로 상의 지표면 음향임피던스에 크게 영향을 받는 것을 확인하였다. 또한 진행 차량으로부터 측정한 등가에너지레벨의 거리별 감쇠값을 이용하여 등음압곡선을 해석하였다 그리고 도로 교통소음이 인체에 미치는 영향을 조사하고자 초저주파 소음에 대한 응답특성, 깊은 수면율과 잠을 깨는 비율에 대한 연속적인 교통소음의 .효과, 연령과 소음폭로등 다양한 변수에 대하여 청력손실과 청감민감도 변화 등을 고찰하였다 해석결과 과도한 소음은 일시적 청력손실의 원인이며, 폭로가 길어지거나 강력하면 영구적 청력손실의 원인이 될 수 있음을 확인하였다.

• 한국의류학회지
• /
• 제33권12호
• /
• pp.1935-1940
• /
• 2009

본 연구는 기능성 등산복의 착용실태를 조사하여 등산복의 개발과 차별화에 기여하고자 하였다. 등산을 즐기는 107명의 응답자들이 본 설문조사에 응해주었고 문항은 개인정보, 구매습관, 등산복 선택시 가장 중요하게 여기는 기능, 본인이 소유한 등산복의 기능에 대한 만족도, 자유기술의 5개 항목으로 이루어져 있었다. 응답자들은 기능성 등산복을 선택할 때에 가장 중요하게 여기는 특성으로 흡습속건성, 보온성, 방수방풍성, 스트레치성 기능을 열거하였다. 이 기능들은 한 겹의 의복으로 착용하기보다는 여러 겹 겹쳐입을 경우 특히 그 효과가 증대한다 할 수 있다. 그리고 스트레치성의 경우 하체의 움직임이 많은 등산 활동 시 하의에 특히 필요한 기능이라 응답하였다. 그리고 응답자들은 기능성 등산복의 가격이 너무 비싸다고 응답하였으며 세탁이 불편하다고 답하였다. 이러한 설문결과로 보아 기능성 등산복의 개발 시 소비자들이 중요하게 여기는 기능을 고려해야 할 뿐만 아니라, 세탁성이나 가격과 같은 소비자들이 개선을 원하는 요소들에 대한 고려도 필요할 것이다.

• Asian Journal of Atmospheric Environment
• /
• 제4권3호
• /
• pp.189-197
• /
• 2010

An orchestrated attempt was made to analyze samples of bulk and individual particulate matters (PM) collected at the Gosan ground-based station on the west coast of Jeju, Korea. A two-stage filter pack sampler was operated to collect particles in both large (> $1.2\;{\mu}m$) and small size fractions (< $1.2\;{\mu}m$) between the Asian dust (hereafter called "AD") storm event and non-Asian dust period. Elemental components in bulk and individual particles were determined by PIXE and synchrotron XRF analysis systems, respectively. To assess the transport pathways of air parcels and to determine the spatial distribution of PM, the backward trajectories of the Meteorological Data Explorer (Center for Global Environmental Research, 2010) and the NOAA's HYSPLIT dispersion-trajectory models were applied. In line with general expectations, Si and other crustal elements in large size particles showed considerably higher mass loading on AD days in comparison with non-AD days. Computation of the crustal enrichment factors [(Z/Si)$_{particle}$/(Z/Si)$_{desert}$ sand] of elements in large size particles (> $1.2\;{\mu}m$) allowed us to estimate the source profile and chemical aging of AD particles as well as to classify the soil-origin elements. On the basis of a single particle analysis, individual AD particles are classified into three distinct groups (neutralized mineral particles, S-rich mineral particles, and imperfectly neutralized particles).

• The Korean Journal of Physiology and Pharmacology
• /
• 제16권5호
• /
• pp.321-326
• /
• 2012

Resveratrol, a natural compound, has been shown to possess anti-cancer, anti-aging, anti-inflammatory, anti-microbial, and neuroprotective activities. In this study, we examined the antiproliferative and cytotoxicity properties of resveratrol in Rat B103 neuroblastoma cells; although it's molecular mechanisms for the biological effects are not fully defined. Here, we examined the cellular cytotoxicity of resveratrol by cell viability assay, antiproliferation by BrdU assay, DNA fragmentation by DNA ladder assay, activation of caspases and Bcl-2 family proteins were detected by western blot analyses. The results of our investigation suggest that resveratrol increased cellular cytotoxicity of Rat B103 neuroblastoma cells in a dose-and time-dependent manner with $IC_{50}$ of 17.86 ${\mu}M$ at 48 h. On the other hand, incubation of neuroblastoma cells with resveratrol resulted in S-phase cell cycle arrests which dose-dependently and significantly reduced BrdU positive cells through the downregulation of cyclin D1 protein. In addition, resveratrol dose-dependently and significantly downregulated the expression of anti-apoptotic protein includes Bcl-2, Bcl-xL and Mcl-1 and also activates cleavage caspase-9 and-3 via the downregulation of procaspase-9 and -3 in a dose-dependent manner which indicates that involvement of intrinsic mitochondria-mediated apoptotic pathway. In conclusion, resveratrol increases cellular cytotoxicity and inhibits the proliferation of B103 neuroblastoma cells by inducing mitochondria-mediated intrinsic caspase dependent pathway which suggests this natural compound could be used as therapeutic purposes for neuroblastoma malignancies.