• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.121-126
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• 1998

A numerical optimization procedure is developed to find the inlet velocity profile that yields the most uniform epitaxial layer in a vertical MOCVD reactor. It involves the solution of fully elliptic equations of motion, temperature, and concentration; the finite volume method based on SIMPLE algorithm has been adopted to solve the Navier-Stokes equations. The overall optimization process is highly nonlinear and has been efficiently treated by the sequential linear programming technique that breaks the non-linear problem into a series of linear ones. The optimal profile approximated by a 6th-degree Chebyshev polynomial is very successful in reducing the spatial non-uniformity of the growth rate. The optimization is particularly effective to the high Reynolds number flow. It is also found that a properly constructed inlet velocity profile can suppress the buoyancy driven secondary flow and improve the growth-rate uniformity.

• Journal of Korea Foundry Society
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• v.17 no.6
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• pp.545-551
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• 1997

14 cm length Al-15Cu-1Mg alloys have been directionally solidified in 3 mm diameter alumina tubes in a furnace moved with a constant velocity V=12 cm/hr under various furnace temperatures of 660, 710 and $760^{\circ}C$. By analysing the evolution of the temperature profiles along the alloy length during the solidification, the growth characteristics such as the position of the solid/liquid interface, the local growth velocity (R) and the temperature gradient at the solid/liquid interface (G) have been determined. The effects of the furnace temperature on the growth behavior have been investigated by the comparison of R and G values for each temperature. Under the furnace temperature of $760^{\circ}C$, steady state growth region was observed for the latter half of the growth period.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.10-23
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• 2008

The development of pre-set wavelength G$\ddot{o}$rtler vortices are studied in the boundary-layer flows on concave surfaces of 1.0 and 2.0 m radius of curvature. The wavelengths of the vortices were pre-set by thin wires of 0.2 mm diameter placed 10 mm upstream and perpendicular to the concave surface leading edge. Velocity contours were obtained from velocity measurements using a single hot-wire anemometer probe. The most amplified or dominant wavelength is found to be 15 mm for free-stream velocity of 2.1 m/s and 3.0 m/s on the concave surface of R = 1 m and 2 m, respectively. The velocity contours in the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices. Three different regions can be identified based on the growth rate of the vortices. The occurrence of a secondary instability mode is also shown in the form of mushroom-like structures as a consequence of the non-linear growth of the G$\ddot{o}$rtler vortices. By pre-setting the vortex wavelength to be much larger and much smaller than the most amplified one, the splitting and merging of G$\ddot{o}$rtler vortices can be respectively observed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.3
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• pp.771-783
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• 1995

A simplified model for the so-called ACRT(accelerated crucible rotation technique) Bridgman crystal growth was considered in order to investigate the principal effects of the periodic variation of angular velocity. Numerical solutions were obtained for Ro=0.5, Ra=4.236*10$_{6}$ and E=2.176*10$^{-3}$ . The effects of spin-up process combined with natural convection was investigated as a preliminary study. The spin-up time scale for the present problem was a little larger than that observed for homogeneous spin-up problems. Numerical results reveal that over a time scale of (H$^{2}$/.nu..omega.$_{f}$)$^{1}$2/ the forced convection due to the formation of Ekman layer predominates. When the state of rigid body rotation is attained, natural convection due to buoyancy emerges as the main driving force and them the steady-state is approached asymptotically. Based on our preliminary results with simple spin-up, several fundamental features associated with variation of rotation speed are successfully identified. When a periodic variation of angular velocity was imposed, the system response was also periodic. Due to effect of mixing, the heat transfer was enlarged. From the analysis of time-averaged Nusselt number along the bottom surface the effect of a periodic variation of angular velocity on the interface location could be indirectly identified.d.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.33-46
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• 2011

Concave surface boundary-layer flows are subjected to centrifugal instability which results in the formation of streamwise counter-rotating vortices. Such boundary layer flows have been experimentally investigated on concave surfaces of 1 m and 2 m radius of curvature. In the experiments, to obtain uniform vortex wavelengths, thin perturbation wires placed upstream and perpendicular to the concave surface leading edge, were used to pre-set the wavelengths. Velocity contours were obtained from hot-wire anemometer velocity measurements. The most amplified vortex wavelengths can be pre-set by the spanwise spacing of the thin wires and the free-stream velocity. The velocity contours on the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices. Three different vortex growth regions can be identified. The occurrence of a secondary instability mode is also shown as mushroom-like structures as a consequence of the non-linear growth of the streamwise vortices. Wall shear stress measurements on concave surface of 1 m radius of curvature reveal that the spanwise-averaged wall shear stress increases well beyond the flat plate boundary layer values. By pre-setting much larger or much smaller vortex wavelength than the most amplified one, the splitting or merging of the streamwise vortices will respectively occur.

• Journal of Mushroom
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• v.17 no.2
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• pp.41-46
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• 2019

This study was carried out to investigate optimum wind velocity for growth of Pleurotus ostreatus. In the chamber experiments, the divergence of pileus was $63^{\circ}$ in 0.3m/s, and it showed the tendency that the more the air velocity was increased, the more the divergence became small. And the ratio of commercial yields was 96% in the air velocity of 0.3m/s. In the cultivation room experiments, the divergence of pileus was $64^{\circ}$ in 0.3m/s, and it was the tendency that the more the air velocity was fast, the more the divergence became larger. And the commercial yields was similar to the trend of the chamber experiment as 94.8% in 0.3m/s, and the quality characteristics of the fruit-body showed the uniform quality in comparison with other treatment because the standard deviation of the size of the pileus, etc. was the lowest in 0.3m/s like the chamber experiment.

• Korean Journal of Health Education and Promotion
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• v.23 no.5
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• pp.13-27
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• 2006

This study was performed to formulate the most recent traits of physical growth of youth, and to identify the need of youth for health promotion planning in modern Korea. Study participants were 171 boys and 400 girls in two senior high schools in Seoul, Korea. Health records were collected from the individual students in May 2005. Longitudinal data on stature and body weight from 6 to 16 years old were analysed. Significance tests on some measures were performed by t-test and ANOVA. Major conclusions were as follows: 1. Girls were taller than boys during the specific time of adolescence. However, this phenomenon was not found in the growth process investigated by peak age and in over-all mean growth process of body weight. 2. Peak age came later in boys than in girls in both stature and body weight. This meant that boys matured later in stature and body weight than girls. However, boys were larger in peak velocity than girls. 3. Peak ages distributed more widely in girls than in boys both for stature and body weight. 4. Even in such short growth process from 6 through 16 years old, growth spurt tended to appear in several times. 5. Growth spurt tended to appear more often in boys than in girls.

• Korean Journal of Health Education and Promotion
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• v.24 no.5
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• pp.69-85
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• 2007

Purpose: The purpose of this study is to clarify the traits of differences supposed as secular differences in physical growth between samples of children and youth in 1999 and 2005, and to identify the need of children and youth for health promotion. Methods: Two samples of different cohort were selected. The first one was consisted of 231 boys and 346 girls in 1999. And the other was consisted of 171 boys and 400 girls in 2005. Then the longitudinal growth distance data were collected from their cumulative health examination records. Results: The 2005 were larger in growth distances of stature, body weight, sitting height, and chest girth a at all ages from 6 to 16 in both boys and girls, so it could be concluded that a certain positive shift in growth process appeared in such a short duration. The 2005 were larger in growth velocity before peak age and also after peak age in body weight, but only in the term after peak age significant secular differences were found in stature for both sexes. As far as the growth distance concerned, the 2005 boys were ahead of the 1999 boys from 0.28-1.02 years and the 2005 girls from 0.32 to 0.81 years. In growth distance. Only in peak velocity, significant secular change was recognized in both sexes, any positive evidences of appearance of secular change were not found in peal age. In such derived physical indices as BMI, body weight index, sitting height index, and chest girth index, obvious evidences of secular change appearance were found.

• Journal of Nutrition and Health
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• v.44 no.3
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• pp.212-221
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• 2011

This study was conducted to identify differences in growth based on the obesity index in sixth grade. Heights and weights of 141 students from first to sixth grades were collected from school records. Other information was gathered by survey, and the weight length index (WLI) was calculated. Subjects were classified into three groups: underweight (n = 57, UG), normal (n = 53, NG), and obese (n = 31, OG) using the WLI. Differences in weight, height, and growth velocity were compared among the three groups from the first to sixth grades. With regard to growth, the past physical status of the three groups was maintained. More than 50% of the OG was in the overweight range when they were in the third to fifth grades. Approximately 60% of NG was in the normal weight range between the first and fifth grades. More than 70% of UG was in the underweight range when they were in the first to fifth grades (p < 0.001). Growth velocity was faster in OG than that in NG and UG (p < 0.001). The annual growth rate of children was the highest when they moved from the third to the fourth grade (p < 0.001). The results indicate that general balanced diet education should be implemented in lower grades, because physical growth formed in lower grades tended to be maintained in senior grades. It would be better to educate students about diet to prevent obesity before the fifth grade when a major change in body structure has occurred.

• Clinical and Experimental Pediatrics
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• v.59 no.sup1
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• pp.121-124
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• 2016

Turner syndrome (TS) is a genetic disorder in phenotypic females that has characteristic physical features and presents as partial or complete absence of the second sex chromosome. Growth hormone deficiency (GHD) is a condition caused by insufficient release of growth hormone from the pituitary gland. The concomitant occurrence of TS and GHD is rare and has not yet been reported in Korea. Here we report 2 cases of TS and GHD. In case 1, GHD was initially diagnosed. Karyotyping was performed because of the presence of the typical phenotype and poor response to growth hormone therapy, which revealed 45,X/45,X+mar. The patient showed increased growth velocity after the growth hormone dose was increased. In case 2, a growth hormone provocation test and chromosomal analysis were performed simultaneously because of decreased growth velocity and the typical TS phenotype, which showed GHD and a mosaic karyotype of 45,X/46,XX. The patient showed spontaneous pubertal development. In female patients with short stature, it is important to perform a throughout physical examination and test for hormonal and chromosomal abnormalities because diagnostic accuracy is important for treatment and prognosis.