• Korean Journal of Materials Research
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• v.11 no.7
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• pp.575-579
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• 2001

GaN buffer layer and epilayer have been grown on sapphire (0001) by metal organic chemical vapor deposition (MOCVD). GaN buffer layer ranging from 26 nm to 130 nm in thickness was grown at 55$0^{\circ}C$ prior to the 4 $\mu\textrm{m}$ thick GaN epitaxial deposition at 110$0^{\circ}C$. After GaN buffer layer growth, buffer layer surface was examined by atomic force microscopy (AFM). As the thickness of GaN buffer layer was increased, surface morphology of GaN epilayer was investigated by scanning electron microscopy (SEM). Double crystal X-ray diffraction (DCXRD) and Raman spectroscopy were employed to study crystallinity of GaN epilayers. Optical properties of GaN epilayers were measured by photoluminescence (PL). The epilayer grown with a thin buffer layer had rough surface, and the epilayer grown with a thick buffer layer had mirror-like surface of epilayer. Although the stress on the latter was larger than on the former, its crystallinity was much better. These results imply that the internal free energy is decreased in case of the thick buffer layer. Decrease in internal free energy promotes the lateral growth of the GaN film, which results in the smoother surface and better crystallinity.

• Korean Journal of Poultry Science
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• v.16 no.1
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• pp.9-15
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• 1989

This study was conducted to estimate genetic parameters for egg yolk cholesterol. Content of egg yok cholesterol was measured for a total of 473 hens of White Leghorn line. Cholesterol values were obtained from tee consecutively laid eggs when hens were 53 weeks of age. The yolk of each egg was weighted and freeze dried. Dried egg yolks were stored at -2$0^{\circ}C$ until analyzed. The results obtained from this study were as follows; 1. Yolk cholesterol content was measured in average $56.00\pm$0.194 mg/g dry yolk. 2. Heritability from the sire component of variance was $0.522\pm$0.215 and from the sire＋dam component of variance $0.33\pm$0.209. 3. Estimates of phenotypic correlation between your cholesterol and other factors such as body weight at 20 weeks of age, age at first egg, 40-week total egg number, egg Production rate: 53-week egg weight and 53-week yolk weight were -0.0208, -0.0321, -0.0378, -0.0834, 0.0790 and 0.1624, respectively. And genetic correlation coefficients for each item in the order were -0.5293, 0.7105, -0.4062, -0.0254, 0.2164 and 0.5027, respectively. 4. These results suggest the possibility that egg Yolk cholesterol should be reduced through selecting of sire families. To breed for low egg yolk cholesterol, it makes age at first egg earlier and enhances total egg number so that we can obtain the high rate of egg Production.

• Journal of Korean Ophthalmic Optics Society
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• v.6 no.2
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• pp.85-97
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• 2001

A mathematical model was proposed to analyze the damped motion of contact lens which is initially displaced from the equilibrium position. The model incorporates the differential equations and their numerical solution program, based on the formulations of restoring force arising from the capillary action in the tear-film layer between the lens and cornea. The model predicts the capillary action induced surface tension, time dependence of displacement of lens when it is released from the equilibrium position. It seems that the motion of lens is similar to the typical over-damped oscillation caused by the large viscous friction in the liquid layer between the cornea and lens. The effect of variables such as base curves, lens diameters and thickness of tear film layer were illustrated by the computer simulation of the derived program. The time required for the lens to return to the original position increases as the liquid layer thickness increases and it decreases as the diameter of lens increases. With the certain value of base curve the time interval is found to be minimum. The free vibrations of lenses were also simulated varying the parameters such as base curve, diameter, layer thickness. The resonant frequencies are inversely proportional to the liquid layer thickness and it increases as the lens diameter increases. The resonant frequency of lens has a maximum when the diameter is of certain value. If the external impulse or force of the same frequency as the natural frequency of contact lens acted on the cornea in vivo it may cause an excessive movement and thus it might cause the distortion 10 the lens or be pulled off the eye.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.1
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• pp.5-13
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• 2008

Purpose: This review article was written to investigate what kind of forces are acting on the contact lens fitted on the cornea and its subsequent motion. Methods: A capillary action-induced force develops in the tear layer between the lens and cornea, which leads to the restoring force due to difference in layer thickness according to lens rotation. The characteristics of the lens movement can be determined by the various factors such as friction between eyelid and lens, acceleration force based on blinking and the restoring force incorporated with the viscous damping force. A mathematical model which consists of the differential equations and their numerical solution was proposed to analyze the damped motion of lenses. The model predicts the time dependence of lenses during and after the blink varying the BC, blink period and eyelid pressure. Results: It was found that both the blink period and lid pressure increases the movement increases because of the enhanced lid friction. As the BC increases the viscous damping reduces due to the lacrimal layer's increase which resulted in the enhanced lens motion. After blink the lens illustrates the damped oscillation because of the restoring force by the increased lacrimal layer thickness and reduced viscous resistance. The time for the lens to return to the equilibrium shortens as the BC increase because of the resistance reduction. Conclusions: The movement of the contact lens is governed by the characteristics of the lacrimal layer between the lens and cornea as well as the lid blink.

• Journal of the Korean Wood Science and Technology
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• v.29 no.2
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• pp.84-90
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• 2001

To investigate morphological characteristics of zephyr produced from two bamboo species, Phyllostachys nigra var. henonis and Gigantochloa apus, basic anatomic properties were examined by scanning electron microscopy and image analysis. According to SEM observation, zephyr from Phyllostachys nigra var. henonis was not of uniform in shape and showed macro crack between vascular bundle sheaths. This may be attributes to the sclerenchymatous fibers connected closely, thus resulting in difficult separation of intercellular layer. Zephyr from Gigantochloa apus was of uniform in shape, which may be caused by easy separation of intercellular layer of sclerenchymatous fibers having thin cell wall and large cell lumen. By image analysis in cross section of two species, the ratio of vascular bundle sheaths and cell wall ratio of sclerenchymatous fibers were examined. The ratio of vascular bundle sheaths in Phyllostachys nigra var. henonis was lower than that in Gigantochloa apus. However, cell wall ratio of sclerenchymatous fibers in Phyllostachys nigra var. henonis was higher than that in Gigantochloa apus.

• Journal of the Korean Data and Information Science Society
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• v.25 no.4
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• pp.737-743
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• 2014

This experiment was conducted to compare heterogeneity for the variance in dairy cattle population and to induce homogeneity of variance using 502,228 performance test records of dairy cattle. The estimates of heritability for milk yields, fat yields and protein yields were 0.28, 0.26 and 0.24, respectively and the estimate of average breeding value by birth year was lower in HV (heterogenous variance) model than in animal model, collectively. The average breeding values of milk yields, fat yields and protein yields for 545 sire bulls applicable to the criteria of interbull MACE programme were 453.54kg, 10.75kg and 14.33kg, respectively and when the heterogeneity was adjusted they were 432.06kg, 10.15kg and 13.40kg, respectively, which were lower in all milk traits collectively. In animal model, coefficients of phenotypic correlation between dataset I and II were 0.839 in milk yields, 0.821 in fat yields, and 0.837 in protein yields, while in HV model, they were 0.841 in milk yields, 0.820 in fat yields, and 0.836 in protein yields, showing similar results in 2 models. When compared using animal model and HV model, the regression coefficient for ratio of number of daughters by calving year of milk yields increased from 15.157 to 16.105 and that of fat yields increased from =0.227 to =0.196, but that of protein yields decreased from 0.630 to 0.586.

• Journal of Korean Society of Forest Science
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• v.77 no.2
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• pp.186-192
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• 1988

This study was carried out to estimate the stand form factor that is necessary to estimate stand volume by STRAND method among plotless sampling methods. The data measured for this study were based on the 380 sample plots from Larix leptolepis and 358 sample plots from Pinus koraiensis which were distributed in the region of Kyeongi, Kangweon, Chungbuk, Chungnam, Chun-buk and Kyeongbuk. 1. Stand form factor was highly correlated with in the following order, stand form height, stand average height, average diameter, stand age, distance of stem, and basal area height. 2. The best fitted equation of stand form factor of above two tree species were presented in table 3. 3. Stand form factor tables using estimated equations on the table 3 were prepared and presented in table 4, 5(Larix leptolepis), 6, 7(Pinus karaiensis). 4. The relatioinships between estimated value and actual value were Y=bx, where b approached nearly 1.0, and there were not any significant differences between them. 5. The percentages of estimated error on stand form factor table were ranged from 2.39% to 4.15% in Larix leptolepis and from 1.73% to 2.50% in Pinus koraiensis. Therefore, the stand form factor could be exactly estimated by use of these tables.

• Journal of the Korea Concrete Institute
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• v.27 no.6
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• pp.651-659
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• 2015

Currently, social demands for long span building structures are increasing due to architectural planning purposes and economic efficiency. As a result, lighter board-type voiding materials were suggested. With the use of board-type voiding materials, a slab is able to become light weight and convenient. This process efficiently eliminates concrete where it is not required; considerably diminishing dead weight while maintaining the flexural strength of the slab. The reduction in concrete also allows for overall cost reductions and design flexibility. Also it can be ease with fixing the voided material that is composed of one body form. Although board-type voiding materials are ideal, the top and bottom concrete plates lack integrity. Because of this, test results show horizontal cracking towards the tops and bottoms of the concrete columns, or webs, connecting the slabs. The key to correcting this problem is to increase the shear strength. In order to increase the shear strength of the structure, horizontal shear area must increase. R70(100)-D-F has the largest horizontal shear area as it also shows stronger strength. As a result, shear strength ($V_{nh}$) is dependent on the horizontal shear area (N). $V_{nh}={\alpha}{\times}0.16{\sqrt{f_{ck}}}{\frac{{\pi}D^2}{4}}{\times}N({\alpha}=1.8125)$. The web columns have a shear span to depth ratio (a/d) that is less than 2; which classifies it as a deep beam. In this case, however, the shear strength of the deep beams may be as much as 2 to 3 times greater than that predicated conventional equations developed for members of normal proportions. As a result, ${\alpha}$ is suggested as an extra coefficient in the equation for shear strength ($V_{nh}$).

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.43-43
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• 2009

단련용 다결정 Ni기 초내열합금은 우수한 가공성, 내산화성, 고온특성 등으로 가스터빈 연소기, 디스크, 증기발생기 전열관 등 발전용 고온부품 소재에 널리 적용되고 있다. 최근 발전설비의 고효율화를 꾀하기 위해 작동 온도를 현격히 증가시키는 기술방향으로 발전하고 있고, 소재측면에서는 기존의 초내열합금 대비 고기능성을 확보할 수 있는 차세대 Ni기 초내열합금 개발이 유럽, 미국, 일본, 중국 등을 중심으로 활발히 이루어지고 있다. 이러한 소재의 고온강도 (온도수용성)를 향상시키기 위해서는 통상 규칙격자 금속간화합물인 $Ni_3(Al,Ti)-{\gamma}'$상의 분율을 증가시킬 수 있지만, ${\gamma}'$상분율이 증가할 경우 용접 및 후열처리 동안 용접열영향부 (HAZ)에서 액화균열이 발생할 가능성이 높아진다. 결정립계를 따라 발생하는 HAZ 액화균열은 입계특성에 의해 크게 영향을 받을 것으로 판단된다. 한편, 본 연구자들은 최근 입계 serration 현상을 단련용 합금에 도입시키는 특별한 열처리를 이론적 접근법을 통해 개발하였다. 형성된 파형입계는 결정학적인 관점에서 조밀 {111} 입계면을 갖도록 분해 (dissociation)되어 낮은 계면에너지를 갖게 됨을 확인하였으며, 입계형상 변화뿐만 아니라 탄화물 특성변화까지 유도하여 크리프 수명을 기존대비 약 40% 정도 향상시킴을 확인하였다. 이러한 직선형 입계 대비 'special boundary'로 간주되는 파형입계가 도입될 경우, HAZ 결정립크기 변화 및 액화거동에 미치는 영향을 고찰하고, 아울러 입계특성 제어가 용접성/용접부 품질 향상에 기여할 수 있는 가능성도 토의하고자 하였다. 본 연구에서는 재현 HAZ 열사이클 시험을 통해 미세구조를 정량적으로 비교하였다. 상대적으로 입계구조가 안정된 파형입계의 이동속도가 高계면 에너지를 갖는 직선형 입계보다 느려 HAZ 결정립 성장이 효과적으로 억제됨을 확인할 수 있었다. 입계 액화거동을 살펴보면, 두 시편 모두 $M_{23}C_6$, MC 등 입계탄화물 계면이 빠른 승온중 액화반응 (constitutional liquation)에 의해 입계가 액화되었으며, 이후 급냉에 의해 입계에 액상막이 존재한 흔적이 발견되었다. 최고온도별로 입계액화 폭/비율을 정량적으로 비교한 결과, 파형입계가 직선입계 대비 대체로 낮음을 확인할 수 있었으며, 때때로 액화되지 않고 잔존하는 입계 탄화물이 관찰되었다. 재현 HAZ 미세조직을 통해 Hot ductility 시험 결과를 유추하자면, 파형입계가 직선입계 보다 좁은 취성온도영역 (Brittle Temperature Range)을 나타낼 것으로 예상되어, 입계특성제어에 의해 Ni기 초내열합금의 용접성을 향상 가능성을 확인하였다.

• Journal of Animal Science and Technology
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• v.53 no.2
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• pp.99-106
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• 2011

This study estimated the genetic parameters of growth-related traits from 11-month-old olive flounder (Paralichthys olivaceus) base population in which wild and cultured broodstocks were introduced. The heritability of body weight, total length, body height, body shape, and condition factor of the base population was estimated to be 0.754, 0.753, 0.789, 0.438, and 0.369, respectively. Genetic correlations between body weight and total length, between body weight and body height, and between total length and body height were 0.969, 0.960, and 0.960, respectively, showing highly positive correlation. Genetic correlations between body weight and body shape, between total length and body shape, between body height and body shape were -0.403, -0.344, and -0593, respectively, showing low negative correlation. Overall, olive flounder might be an appropriate selective breeding species with the high heritability of the traits in an 11-month-old population.