• Tribology and Lubricants
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• v.40 no.1
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• pp.8-16
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• 2024

This study conducts numerical modeling and eigen-analysis of a rod-fastened rotor, which is mainly used in aircraft gas turbine engines in which multiple disks are in contact through curvic coupling. Nayak's theory is adopted to calculate surface parameters measured from the tooth profile of the curvic coupling gear. Surface parameters are important design parameters for predicting the stiffness between contact surfaces. Based on the calculated surface parameters, elastoplastic contact analysis is performed according to the interference between two surfaces based on the Greenwood-Williamson model. The equivalent bending stiffness is predicted based on the shape and elastoplastic contact stiffness of the curvic coupling. An equation of motion of the rod-fastened rotor, including the bending stiffness of the curvic coupling, is developed. Methods for applying the bending stiffness of a curvic coupling to the equation of motion and for modeling the equation of motion of a rotor that includes both inner and outer rotors are introduced. Rotordynamic analysis is performed through one-dimensional finite element analysis, and each element is modeled based on Timoshenko beam theory. Changes in bending stiffness and the resultant critical speed change in accordance with the rod fastening force are predicted, and the corresponding mode shapes are analyzed.

• The Korean Journal of Applied Statistics
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• v.1 no.2
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• pp.34-44
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• 1987

In order to estimate the optimum fertilizer level for rice, a major food crop, the experimental results obtained from the fertilizer trials conducted at 642 experimental sites(farmers' fields) throughout the country for the period from 1976 to 1979 were examined. Since non-significant interactions among fertilizers have been ovserved from the past experiences, only thirteen treatments(combinations of fertilizer levels) for the experiments as given in the Table 1 were chosen such that simple response curves can be fitted with independent variables being N, $P_2O_5, and K_2O$. Weighted combining analysis of variance was also carried out for each type of paddy fields to test the significance of Treatments $\times$ Experimental sites interaction, and highly significant variability in response to treatments among experimental sites in the same type of paddy fields was observed in most types of fields. For the types of paddy fields where the treatments $\times$ experimental sites interaction was not significant, separate response curves for N, $P_2O_5, and K_2O$ were estimated on the basis of the mean yields of rice, and common values of the optimum levels of fertilizers were extimated thereform. When the interaction is significant, response curves were fitted for each experimental sites. The average fertilizer doses estimated for the types of paddy fields based on the individual sites are given in Tables 7-1 and 7-2.

• Journal of the Korean Institute of Landscape Architecture
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• v.18 no.4
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• pp.73-85
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• 1991

Rhododendron mucronulatum for. albiflorum, native species is a shrub that has white flowers on May to June, and rare species endangered by people's rash digging or cutting. But its physiological ecological characteristics and propagation method are not being known at all. Therefore, this study was executed to utilize this species as the planting material for landscaping by analysing its habitat environment and growth form, and also experimenting its seed and vegetative propagation, and it field culture and utilization. The results are as follows; 1. The elevation, gradient and direction of this species were 295-1,350m, 10-36$^{\circ}$, northwest respectively. It was found that the species is shade-liking plant that grows under forest cover of average 51.33%. 2. The soil pH and water content of its habitat were 5.4, 25.41% respectively. The organic matter content was 6.29% that was higher than 3.2%, the average organic matter content of forest soil in Korea. 3. Representative plant community within which this species was living was Quercus mongolica community, and its main neighboring species were Lindea obtusiloba, Fraxinus sieboldiana, Rhus trichocarpa, Rhododendron Schlippenbachii, Rododendron mucronulatum. 4. The leaf length and width of this species were 39.18mm, 12.60mm respectively. This result showed that generally its leaf size was larger than that of R. micranthum, R. yedoense var. poukhanense and R. mucronulatum var. ciliatum and smaller than that of R. mucronulatum and R. schlippenbachii. 5. The whole size of its pollen was, as 59${\times}$61$\mu\textrm{m}$, the largest of plants of Rhododendron family including R. mucronulatum and R. mucronulatum var. ciliatum. 6. The result of seed germination experiment at intervals of 5$^{\circ}C$ from 15$^{\circ}C$ to 30$^{\circ}C$ presented the highest germination rate of 94.7% at 20$^{\circ}C$ numerically, but high percent germination at all temperature levels without significant difference. And the seed of this plant proved to be sun-liking seed at requiring dormancy in germination. 7. Through seed germination experiment by treatment of growth regulators such as GA. Thiourea and Kinetin under dark condition, it was found that the effect of GA treatment on germination increase and acceleration was the highest. 8. In greenwood cutting, rooted rate by treatment of various concentration of IBA and NAA on clay and vermiculite bed was not wholly high, but 100ppm plots of both IBA and NAA of clay bed showed relatively good rooted rate. 9. As result of field culture experiment for finding out optimum growth temperature and light intensity, growth conditions such as height, number of leaves, fresh weight and chlorophyll contents were the best at night/day temperature of 20/25$^{\circ}C$ and under 1/2sun. Also, the photosynthetic rate was the highest at 25$^{\circ}C$. Accordingly, it was found that optimum temperature and light intensity for growth of this plant are 25$^{\circ}C$ (day temperature), 50% of natural light respectively.

• Journal of Korean Society of Forest Science
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• v.83 no.2
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• pp.205-210
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• 1994

This study was conducted to develop a method of mass production by cutting of superior genotypes of Larix leptolepis and to examine the effects of ortet age, clone, crown position, and an applied plant growth substance upon the rooting of cuttings. Four different ortet ages, 2, 8, 16 and 30 years and three levels of root-promoting substances, indole butyric acid(IBA), at 1000, 2000, and 5000ppm were employed. Greenwood cuttings were taken from mother trees in late July and rooted for three months in rooting medium containing peatmoss : vermiculite : perlite(1 : 1 : 1 by volume). with temperature controlled at $20-25^{\circ}C$, humidity by intermittent misting and light by partial shading in the greenhouse. Cuttings treated with 1000ppm IBA showed highest rooting, with 80%, 71%, 52%, 25% for 2-, 8-, 16-. 30-year-old ortet, respectively. Untreated cuttings showed rooting of 52%, 48%, 36%, 20% for the ortet age of 2, 8, 16, 30 years, respectively. The average number of adventitious roots decreased with increasing ortet age from 2 to 30 years, whereas IBA treatment increased the number of roots in all ages. A variation in rooting among 20 clones tested was observed. The 4 clones, Chungnam 6, and 7 and Chonbuk 1, and 9 showed good rooting of about 67%, while Kangwon 49 showed boor rooting of 40% at 1000ppm IBA treatment. When crown position was compared, cuttings taken from middle crown showed highest rooting of 60%, while cuttings from upper crown showed lowest rooting of 53%.

• Current Optics and Photonics
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• v.2 no.3
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• pp.269-279
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• 2018

We are currently investigating the feasibility of a 1.6 m telescope with a laser-guide star adaptive optics (AO) system. The telescope, if successfully commissioned, would be the first dedicated adaptive optics observatory in South Korea. The 1.6 m telescope is an f/13.6 Cassegrain telescope with a focal length of 21.7 m. This paper first reviews atmospheric seeing conditions measured over a year in 2014~2015 at the Bohyun Observatory, South Korea, which corresponds to an area from 11.6 to 21.6 cm within 95% probability with regard to the Fried parameter of 880 nm at a telescope pupil plane. We then derive principal seeing conditions such as the Fried parameter and Greenwood frequency for eight astronomical spectral bands (V/R/I/J/H/K/L/M centered at 0.55, 0.64, 0.79, 1.22, 1.65, 2.20, 3.55, and $4.77{\mu}m$). Then we propose an AO system with a laser guide star for the 1.6 m telescope based on the seeing conditions. The proposed AO system consists of a fast tip/tilt secondary mirror, a $17{\times}17$ deformable mirror, a $16{\times}16$ Shack-Hartmann sensor, and a sodium laser guide star (589.2 nm). The high order AO system is close-looped with 2 KHz sampling frequency while the tip/tilt mirror is independently close-looped with 63 Hz sampling frequency. The AO system has three operational concepts: 1) bright target observation with its own wavefront sensing, 2) less bright star observation with wavefront sensing from another bright natural guide star (NGS), and 3) faint target observation with tip/tilt sensing from a bright natural guide star and wavefront sensing from a laser guide star. We name these three concepts 'None', 'NGS only', and 'LGS + NGS', respectively. Following a thorough investigation into the error sources of the AO system, we predict the root mean square (RMS) wavefront error of the system and its corresponding Strehl ratio over nine analysis cases over the worst ($2{\sigma}$) seeing conditions. From the analysis, we expect Strehl ratio >0.3 in most seeing conditions with guide stars.

• Korean Journal of Medicinal Crop Science
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• v.11 no.1
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• pp.46-52
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• 2003

This experiment was conducted to investigate the propagation for mass production of Acanthopanax koreanum NAKAI utilized for health food and medicine material. Germination rate of A. koreanum seeds were 64% when seeds were stored at 15 for 60 days and then were treated with 50 ppm of kinetin and dormancy were broken at 5 for 60 days. Rooting rates of green-wood cuttings treated with IBA 100 ppm, NAA 50 ppm, and IAA 100 ppm were 61.7, 56.7, and 60.0%, respectively. Rooting rates of greenwood cuttings treated with Rooton in scoria + horticulture media and volcanic ash were 76.7 and 66.7%, respectively. Survival rate of seedlings planted on Aug. 10 was highest (96%) under 75% shading net while shoot growth was best under 55% shading net. Survival rate of seedlings planted on May 2 was highest (91%) 55% shading net, and shoot growth was also best 55% under shading net.

• Journal of the Korean Wood Science and Technology
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• v.42 no.3
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• pp.327-338
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• 2014

Relationship between growth rate and wood quality was investigated by physical and mechanical properties with Quercus rubra (24 years old) from five different origin of apricot. In greenwood moisture content, sapwood had higher moisture content than heartwood, and there was difference among different origin of apricot. There were different specific gravity of wood among different origin of apricot. Compared with higher growth rate with higher specific gravity in sapwood, opposite trend was observed in heartwood. There were difference in shrinkage based on origin of apricot, and higher growth rate wood had higher shrinkage and T/R ratio. Compression Young's modulus, bending strength, bending Young's modulus, and compact strength was difference among different origin of apricot. Higher growth rate wood had higher tensile strength, and also there was difference amont different origin of apricot. In hardness, 3 different directions had all difference among different origin of apricot, and higher growth rate wood showed higher hardness than others. Based on overall physical and/or mechanical properties and growth rate, apricot from Bancroft was best quality in current.

• Communications of Mathematical Education
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• v.23 no.4
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• pp.977-998
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• 2009

In this article, we give a comparative study on the last 300 years of USA and Korean tertiary mathematics. The first mathematics classes in United States were offered before July, 1638, but the real founding of tertiary mathematics courses was in 1640 when Henry Dunster assumed the duties of the presidency at Harvard. President Dunster read arithmetics and geometry on Mondays and Tuesdays to the third year students during the first three quarters, and astronomy in the last quarter. So tertiary mathematics education in United States began at Harvard which is the oldest college in USA. After 230 years since then, Benjamin Peirce in 1870 made a major and first American contribution to mathematics and got an attention from European mathematicians. Major change on the role of Harvard mathematics from teaching to research made by G.D. Birkhoff when he joined as an assistant professor in 1912. Tertiary mathematics education in Korea started long before Chosun Dynasty. But it was given to only small number of government actuarial officers. Modern mathematics education of tertiary level in Korea was given at Sungkyunkwan, Ewha, Paichai, and Soongsil. But all college level education opportunity, particularly in mathematics, was taken over by colonial government after 1920. And some technical and normal schools offered some tertiary mathematics courses. There was no college mathematics department in Korea until 1945. After the World War II, the first college mathematics department was established, and Rimhak Ree in 1949 made a major and first Korean contribution to modern mathematics, and later found Ree group. He got an attention from western mathematicians for the first time as a Korean. It can be compared with Benjamin Peirce's contribution for USA.

• Journal of Korean Society of Forest Science
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• v.78 no.2
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• pp.103-118
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• 1989

The occurrence of witches' broom in Ligustrum ovalifolium was first noticed in Korea by author in 1984. The present study was carried out with particular emphasis on the symptomatology, etiology, transmission of the disease and antibiotic treatments. The infected tissue was observed by the fluorescence and electron microscopy and its biochemical characteristics were compared with healthy one by electrophoresis. The results are summarized as follows : 1. symptoms of the infected trees were characterized by the dwarfing of the organs, yellowing and brooming of the foliage. 2. The observation by the trans electron microscopy on the witches' broom of L. ovalifolium revealed the occurrence of numerous mycoplasma-like organisms(MLOs) in the phloem tissue cells of the midribs of infected leaves. 3. The MLOs were surrounded by a single unit membrane, and they appeared to be multiplied by binary fission. 4. The presence of crystals unidentified in the phloem parenchyma cells was noticed by electron rnicroscopy, 5. The disease was able to be transmitted by budding, crown, and greenwood graftings to L. ovalifolium, L. obtusifolium, L, japonicum and also transmitted, even when the stocks and scions were not completely grafted. 6. Insect transmission on L. ovalifolium and L, obtzrsifolium was carried by Hishimonus sellatus. 7. The infected roots dipped in the 1,000 ppm of teracyclin solution was only temporarily effective in controlling the disease. 8. Infected plant with MLOs showed specific fluorescent reactions in phloems with DAPI stain. 9. The protein and peroxidase separated by electrophoresis showed strikingly distinctive difference between the healthy and diseased leaves.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.10 no.2
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• pp.97-114
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• 1977

The fresh water prawn, Macrobrachium rosenbergi(de Man) is a very common species in Indopacific region, which inhaits both fresh and brackish water in low land area, most of rivers and especially aboundant in the lower reaches which are influenced by sea water. It is one of the largest and commercial species of genus Macrobrachium, which is commonly larger than $18\~21cm$ in body length, from the basis of eye-stalked to the distal of telson. As a part of the researches in order to investigate the possibilities on transplantation and propagation of this species, this work dealt with the problems on the effects of chlorinities upon zoeal larvae and post-larvae 1). metamorphosis rate and optimum chlorinity for metamorphosis to post-larve, 2). tolerance and comparative survival rate on various chlorinties, from fresh water to sea water $(19.38\%_{\circ}\;Cl)$, which reared for six days upon each stage of zoeal larvae, 3). accomodation rate on chlonities which reared for twelve days after transmigration into variant chlorinities of the range from $3.68\%_{\circ}$ Cl to $1.53\%_{\circ}$ Cl in the way of rearing of the range from $3.82\%_{\circ}$ Cl to $11.05\%_{\circ}$ upon each stage of zoea, 4). tolerance on both of fresh and sea water upon zoeal larva and post-larva under the condition of $28^{\circ}C{\pm}1$ in temperature and feeding on Artenia salina nauplii, 5). relationship between various chlorinities and grwth of post-larvae under the condition of $28^{\circ}C$ in tmperature and feeding on meat of clam. Thus these investigations were performed in order to grope for a comfortable method on seedmass production. Up to the present, the study on the effects of chlorinity upon earlier zoeal larvae and post-larvae of Macrobrachium species has been scarcely performed by workers with the exception of Lewis(1961) and Ling (1962,, 1967), even so their works were not so detailed. On the other hand, larvae of several species of this genus were reared at the water which mixed sea water so as to carry out complete metamorphosis to post-larva by workers in order to investigate on earlier 1 arval and earlier post-larval development, such as Macrobrachium lamerrei (Rajyalakshmi, 1961), M. rosenbergi and M. nipponense (Uno and Kwoa, 1969; Kwon and Uno, 1969), M. acanthurs (Choudhury, 1970; Dobkin, 1971), M. carcinus(Choudhury, 1970), M. formosense(Shokita, 1970), M. olfersii (Duggei et al., 1975), M. novaehallandiae (Greenwood et al., 1976), M. japonicum (Kwon, 1974) and M. lar (Shokita, personal communication), and there fore it is regarded that chlorinity is, generally, one of absolute factors to rear zoeal larvae of brackish species of Macrobrachium genus. Synthetic results on this work is summarized as the follwings: 1) Zoeal larvae required different chlorinities to grow according to each stage, and generally, it is regarded that optimum range of living and growing is from $7.63\%_{\circ}Cl\to\;7.63\%_{\circ}Cl$, and while differences of metamorphsis rate, from first zoea to post-larva, is rarely found in this range, and however it occurs apparently in both of situation at $7.63\%_{\circ}Cl$ below and $16.63\%_{\circ}Cl$ above and moreover, metamorphosis rate is delayed somewhat in case of lower chlorinity as compared with high chlorinity in these situations. 2) Accomodation in each chlorinity on the range, from fresh water to sea water, is different according to larval stages and while the best of it is, generally, on the range from $14.24\%_{\circ}Cl$ to $8.28\%_{\circ}Cl$ and favorite chlorinity of zoea have a tendency to remove from high chlorinity to lower chlorinity in order to advance larval age throughout all zoeal stages, setting a conversional stage for eighta zoea stage. 3) Optimum chlorinity of living and growth upon postlarvae is on the range of $4.25\%_{\circ}Cl$ below, and in proportion as approach to fresh water, growth rate is increased. 4) Post-large are able to live better in fresh water in comparison with zoeal larvae, which are only able to live within fifteen hours, and by contraries, post-larvae are merely able to live for one day as compared with ?미 larvar, which are able to live for six days more in sea water $19.38\%_{\circ}Cl\;above$. 5) Also, in case of transmigration into higher and lower chlorinities in the way of rearing in the initial chlorinities $ 3.82\%_{\circ}Cl,\;7.14%_{\circ}Cl\;and\;11.05%_{\circ}Cl$, accoodation rate is a follow: accomodation capacity in ease of removing into higher chlorinities from lower chlorinities is increased in proportion as earlier stages, setting a conversional stage for eighth zoea stage, and by contraries, in case of advanced stages from eighth zoea it is incraesed in proportion as approach to post-larva stage in the case of transmigration into lower chlorinity from higher chlorinity. On the other hand, it is interesting that in case of reciprocal transmigration between two different chlorinitiess, each survival rate is different, and in this case, also, its accomodation in each zoea stage has a tendency to vary according to larval stages as described above, setting a conversional stage for eighth zoea stage. 6) It is likely that expension of radish pigments on body surface is directly proportional to chlorinity during the period of zoea rearing, and therefore it seems like all body surfacts of zoea larvae be radish coloured in case of higher chlorinity. 7) By the differences that each zoeal larvae, postlarvae, juvaniles and adult prawn are required different chlorinity for inhabiting in each, it is regarded that this species migrats from up steam to near the estuary of the river which the prawns inhabits commonly in natural field for spawning and growth migration. 8) It had better maintainning chlorinities according to zoeal stage for a comfortable method on seed-mass production that earlier larva stages than eighth zoea are maintained on the range from $8\%_{\circ}Cl\;to\;12\%_{\circ}Cl$ to rear, and later larva stages than eighth zoea, by contraries, are gradually regula ted-to love chlorininity of the range from $7\%_{\circ}Cl\;to\;4\%_{\circ}Cl$ according to advance for post-larva stage.