• Tribology and Lubricants
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• 제25권2호
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• pp.81-85
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• 2009

Interests in micro/nano-particles have been greatly increasing due to their wide applications in various fields such as environmental and medical sciences as well as engineering. In order to obtain a fundamental understanding of the tribological characteristics at particle-surface contact interface, frictional behaviors according to load/pressure and materials were obtained by using atomic force microscope(AFM) cantilevers with different stiffnesses and tips. Lateral contact stiffnesses were observed in various tip-surface contact situations. Experimental results show that stick-slip friction behavior occurs even when the colloidal probes with a particle of a few micrometers in diameter, which have a relatively large contact area and lack a well-shaped apex, were used. This indicates that atomic stick-slip friction may be a more common phenomenon than it is currently thought to be. Also, experimental results were investigated by considering the competition between the stiffness of the interatomic potential across the interface and the elastic stiffnesses of the contacting materials and the force sensor itself.

• 한국식물학회:학술대회논문집
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• 한국식물학회 1993년도 제7회 식물생명공학 심포지움 식물 세포 분화의 분자적 접근 Seventh Symposium on Plant Biotechnology -Approach to Plant Cell Differentiation-
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• pp.1-36
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• 1993

It is possible to regenerate plants from calli, single cells and protoplasts of numerous species via organogenasis or embryogenesis in cell and tissue culture systems. Also such regeneration of plants can directly occur from cells of explants. However certain plant species has not been yet provided cultures suitable for plant regeneration from cells or tissues. For example, we have to confirm the regenerability of plant from cells before preparing transformed cells for application. Even more, it is very important to notice that regenerated plants in cell and tissue cultures often show structural abnormality. The mojority of those plants is functionally disordered and eventually cases degenerated. One of such examples is vitreous plants which are manifested mainly in the leaves and manifesteds to a lesser extent in the stems and roots. Regenerants in suspension cultures show more frequent vitrification than on gelled media so that relative humidity and water potential are the key factors involved in abnormal morphogenesis in vitro. The other is that somatic embryos formed in media containing BAP or high concentration of sucrose show frequently cotyledon aberrancy such as polycotyledon and born type cotyledon. The embryos with aberrant cotyledon of Codonopsis lanceolata could not germinate or regenerate into plants in many cases. In contrast, the polycotyledon embryos of Aralia cordata germinated in higher percentage than two cotyledonary embryos, but horn type cotyledonary embryos rarely germinated. The major cause of poor germination is the abnormal development of plumule apex meristem.

• 대한치과보철학회지
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• 제30권2호
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• pp.203-224
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• 1992

The purpose of this study was to evaluate the stress distribution developed in supporting structures by distal extension removable partial denture with 4-types of direct retainer. The direct retainers examined were Akers clasp, RPI clasp, RPA clasp and RPL clasp in bilateral & unilateral free end case. 3-dimensional photoelastic stress analysis was used to record the isochromatic fringe patterns and to calculate the compressive stress at measuring points. The results were as follows. 1. In bilateral free end case, RPI clasp exhibited the similar stress distribution on distal and mesial alveolar crest but Akers clasp exhibited higher stress concentration on distal alveolar crest than mesial alveolar crest. 2. In bilateral free end case, RPA clasp and RPL clasp exhibited the similar stress distribution on distal and mesial alveolar crest and RPL clasp exhibited higher stress concentration on buccal alveolar crest than lingual alveolar crest. 3. Akers clasp produced high stress concentration on residual alveolar ridge distally, but RPI clasp, RPA clasp and RPL clasp produced even stress distribution on residual alveolar ridge. 4. Removable partial denture in unilateral free end case exerted higher stress on abutment tooth root apex than bilateral distal extension removable partial denture.

• 대한치과보철학회지
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• 제32권3호
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• pp.396-410
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• 1994

Ten subjects who were going to wear conventional complete dentures were selected for this study. Theree subjects were women and seven were men. The average age was 63.1 years(range : 44 to 76 years). With the Height tracer (extraoral tracing device) in place the subject was instructed to go through the entire range of mandibular movements. The extreme lateral pathway of the incisor point, the so-called Gothic arch, was thereby inscribed by the stylus on the tracing plate. The mandibular movements in this study were peformed voluntarily by the subject(self guided technique) and guided by the dentist(chin-point technique and bimanual technique). The Gothic arch tracings were analysed and the Gothic arch angles and eccentric movement distances were measured. The results were as follows : 1. The apex position of the Gothic arch tracings of mandibular movements in edentulous patients varied both anterioposteriorly and mediolaterally. 2. The Gothic arch tracing had some lateral deviation during protrusion. 3. The average Gothic arch tracing angle was $136.7{\pm}12.0^{\circ}$ by subjects self guided technique, $135.7{\pm}5.9^{\circ}$ by chin-point technique, $136.6{\pm}6.5^{\circ}$ by bimanual technique. But there were no statistical differences in the reliability among the three techniques. 4. The average mandibular eccentric movements were irregular and the mandibular eccentric movement distances varied with a wide range.

• 대한기계학회논문집B
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• 제23권1호
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• pp.123-130
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• 1999

The objective of the current study is to understand steady 3-dimensional flow phenomena in a bifurcated duct experimentally. A bifurcation model is fabricated with transparent acrylic resin to visualize the whole flow field with the PIV system. The gray level cross-correlation method is applied to the image processing algorithm. The subpixel and the area interpolation methods are used to obtain the final velocity vectors. The finite volume predictions are used to analyze the flow patterns in the bifurcation model. The results of the computer simulation and the PIV experiment for three-dimensional flow show the recirculation zone and the formation of the paired secondary flow distal to the apex of the bifurcation model. The results obtained with the two methods also show that the branch flow strongly strikes the inner wall due to the inertial effect and accompanied helical motion as it flows toward the outer wall.

• 한국군사과학기술학회지
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• 제12권4호
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• pp.415-423
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• 2009

To investigate low frequency acoustic transmissions in the Sub-Polar Front(SPF) of the East Sea, numerical experiments are conducted with Range dependent Acoustic Model(RAM) using Circulation Research of the East Asian Marginal Seas(CREAMS) data and Autonomous Profiling Explorer(APEX)) data. Significant seasonal variations of sea water properties are existed across the Sub-Polar Front(SPF) region from the north and the south. The model results show that Transmission Loss(TL) decrease(about 20dB) with ideal front in the warm region whereas TL increase(about 25dB) with ideal front in the cold region. Regardless of season(both in summer and winter), when the sound source is located in the cold region of the SPF, the model results show weak TL, compared to the case of the source in the warm region(Maximum difference of TL reaches 28dB). This difference between the cases when the source is located in the cold region and the warm region, is accounted for from the different vertical profiles of sound speed in both regions.

• 한국환경과학회지
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• 제5권2호
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• pp.171-178
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• 1996

This experiment was performed with the purpose of finding out the effect of simulated acid rain at various pH levels on the morphology and enzyme of Perilla frutescens var. japonica hara. The pH levels of simulated acid rain ranged from pH 2.0 to pH 6.0. The experiment showed the anion concentrations in the order of $SO_4^{2-}$, Cl^-$, $NO_3^-$, and $F^-$, $SO_4^{-2}$ was found out to be the main factor which contributed to the rainwater acidification. A general decrease of growth in Perilla frutescens var. japonica hara growth was shown with the decreas of pH concentration. As acidity increases a definite reduction in the rates of germination, heigth of plant, malate dehydrogenase, and 6-phosphogluconate dehydrogenase was ovserved, but the density of spots on the leaf apex was increased.

• Imaging Science in Dentistry
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• 제41권1호
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• pp.17-21
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• 2011

Purpose : The purpose of this study was to examine the patient- and treatment-related etiologic factors of external root resorption. Materials and Methods : This study consisted of 163 patients who had completed orthodontic treatments and taken the pre- and post-treatment panoramic and lateral cephalometric radiographs. The length of tooth was measured from the tooth apex to the incisal edge or cusp tip on the panoramic radiograph. Overbite and overjet were measured from the pre- and post-treatment lateral cephalometric radiographs. The root resorption of each tooth and the factors of malocclusion were analyzed with an analysis of variance. A paired t test was performed to compare the mean amount of root resorption between male and female, between extraction and non-extraction cases, and between surgery and non-surgery groups. Correlation coefficients were measured to assess the relationship between the amount of root resorption and the age in which the orthodontic treatment started, the degree of changes in overbite and overjet, and the duration of treatment. Results : Maxillary central incisor was the most resorbed tooth, followed by the maxillary lateral incisor, the mandibular central incisor, and the mandibular lateral incisor. The history of tooth extraction was significantly associated with the root resorption. The duration of orthodontic treatment was positively correlated with the amount of root resorption. Conclusion : These findings show that orthodontic treatment should be carefully performed in patients who need the treatment for a long period and with a pre-treatment extraction of teeth.

• 대한기계학회논문집B
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• 제20권9호
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• pp.2991-3006
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• 1996

An experimental study of jet flow and heat transfer has been carried out for the jet impingement cooling on a semi-circular concave surface. For the jet impingement on the concave surface, three different regions-free jet region, stagnation region, and wall jet flow region-exist, and the distributions of mean velocity and fluctuating velocity for each region have been measured by Laser Doppler Velocimeter. Of particular interests are the effects of jet Reynolds number, the distance between the nozzle exit and cooling surface apex, and the distance from the stagnation point in the circumferential direction. The resulting characteristics of heat transfer at the stagnation point and the variation of heat transfer along the circumferential direction including the existence of secondary peak have been explained in conjunction with measured impinge jet flow.

• The Journal of the Acoustical Society of Korea
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• 제13권2E호
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• pp.83-91
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• 1994

쐐기형 영역에서 전파되는 음향파는 다음 3가지 성분으로 분류할 수 있다 : 직접 전달 경로에 의한 성분, 경계면으로 부터의 반사에 의한 상(image) 성분 그리고 정점에 의한 산란 성분, 2개의 평면으로 경계가 구성된 쐐기(또는 봉우리) 영역에서 점원에 의한 3차원적인 시간 조화 장(field)에 대한 Helmholtz 방정식의 새로운 해를 구하였으며, 그 해는 위의 3가지 성분을 모두 내포하고 있다. 이 해는 정상모우드 들의 무한 급수로 이루어졌으며 각 모우드 계수는 Gegenbauer polynomial을 포함하는 유한적분으로 주어진다. 위의 해석해를 사용하여 봉우리 영역에서 음파의 분포를 계산하였다.