• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.397-401
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• 2000

The corrosion-fatigue characteristics of the 12Cr steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the Rayleigh surface wave. In this study, the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the aged specimens, and then compared to the corrosion-fatigue characteristics. The width of the backward radiation profile decreases as the increase of the aging temperature, which seems to result from the increase of the effective degrading layer thickness. This parameter also shows an inversely proportionality to the exponent, m, in the Paris law which predicts the crack size increasement due to fatigue. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion-fatigue characteristics of the aged materials.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.3
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• pp.29-40
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• 1989

A new blade section of propeller is developed to obtain higher propeller efficiency and better cavitation performance. Eleven foil sections are carefully designed and manufactured to compare the lift-drag characteristics and cavitation performances. It is expected that the developed section behaves better in the vicinity of the ship's wake, where the angle of attack variation is large, because of its wider width in lift-drag and cavitation-free bucket diagrams. A propeller design method using the selected foil section is presented. Three chordwise loading shapes are selected to investigate the influence of the lift-drag ratios on the propeller efficiencies and cavitation performances. Three propellers are designed, which correspond to the selected chordwise loading shapes. Two more propellers which use existing foil sections are designed to compare the section performance.

• Weed & Turfgrass Science
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• v.7 no.3
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• pp.231-238
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• 2018

This study was carried out to develope new zoysiagrass cultivars 'JangsungChorok' (Application No. :2013-3) and 'JangsungSaetbyeol' (Application No. :2013-4). One hundred and one genetic resources were collected at Jangsung Gun area from 2010 to 2011. Among the collected lines, CY6097 (JangsungChorok) and CY6069 (JangsungSaetbyeol) showed superior performance in spring green up and growth rate. 'JangsungChorok' showed genetically light green leaf color, with medium leaf width (4.4 mm), height from ground to first leaf blade of 3.2 cm and average plant height of 18 cm. Fast recovery rate and early spring green up rate will make this cultivar (JangsungChorok) for efficient sod producer. 'JangsungSaetbyeol' showed genetically dark green leaf color, with fine to medium leaf width of 3.5 mm, height from ground to first leaf blade of 4.3 cm and average plant height of 22.6 cm. Fast recovery rate and early spring green up rate with relatively narrow leaf will make this cultivar (JangsungSaetbyeol) for high sod quality.

• Asian Journal of Turfgrass Science
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• v.26 no.1
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• pp.1-7
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• 2012

Field experiments were conducted to evaluate the morphological characteristics and growth rates of 101 medium-leaf type zoysiagrasses (Zoysia spp.) collected at the major sod production area (Jang Seong Gun) in South Korea. Collected lines with distinctive morphology and visual growth rate were planted in plastic pots and measured morphological characteristics under the plastic house conditions. Variation of leaf width, plant height, leaf angle, length of leaf sheath, trichome, stolon length, and color were measured. Six lines were selected by evaluating growth rates from one hundred one collected lines. Eight standard cultivars and three other superior lines previously collected were compared to 7 selected lines form Jang seong area by checking growth rates and morphological characteristics. Average leaf blade width was 3.4 mm, leaf angle was 45.8 degree, plant height was 21.6 cm, height of lowest leaf was 5.0 cm, and length of leaf blade was 14.1 cm. Ground cover rates of selected lines 'CY6097' and 'CY6069' were 70% and 68.3%, respectively. These are believed to be faster than 60% ground cover rate of zoysiagrass 'Anyang', and also, twice as faster than the 31.7% ground cover rate of Z. matrella. Selected line 'CY6069' showed fast growth rate with shorter internode length (5.1 cm) compared to zoysiagrass 'Anyang'. Based on the results of this study, we could select useful fast growing zoysiagrass breeding lines from the major sod production area (Jang Seong Gun) in Korea.

• Journal of agriculture & life science
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• v.45 no.3
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• pp.25-33
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• 2011

This study was conducted to examine genetic variation on leaf characteristics of Machilus thunbergii populations. Ten populations were subjected to multivariate analysis for 9 characteristics of leaf morphology. Average length of leaf blade, leaf width, petiole length, vein number were 9.8cm, 4.0cm, 1.8cm, 8.4 respectively, while angle of leaf base and leaf apex were $67.9^{\circ}$ and $78^{\circ}$ respectively. The coefficient of variation (C.V.) on leaf characteristics was 20% which indicate similar features among the populations. Nested analysis showed statistically signigicant differences among populations as well as among individuals within populations. Genetic relationship between populations using complete linkage method showed four groups to Euclidean distance 1.2 and did not show a tendency to cluster into the same group. There were three principal components that had a meaningful eigenvalue over 1.0 among the 9 components. The explanatory power of the top three main components on the total variation was 92.8%. The first principal component (PC) was explained about 40.3% which is mainly correlated with maximum leaf width and the second PC was explained about 28.7% which is correlated with leaf blade length. The third PC was explained about 23.8% which is correlated with petiole length ($X_3$). These characters were important factors for analysis of the relationship among natural populations of M. thunbergii.

• Korean Journal of Agricultural Science
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• v.13 no.1
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• pp.103-112
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• 1986

This study was carried out to prevent the entwining of rice straw on rotary shaft and blade where rice straw was spreaded on paddy field as an organic source before rotary tilling. The rotary tillage was conducted in the paddy field having the soil moisture contents of 30%, 39%, 59% in dry basis and spreaded rice straw (450kg/10a) of 30cm, 45cm, 90cm length with the edged curve angles of rotary blade of $30^{\circ}$, $40^{\circ}$, $50^{\circ}$, $55^{\circ}$ at Yuseung area. And the test were performed on the plot which has width of 30cm and 5cm length and the quantity of entwined rice straw was analized. The test results were summarized as the followings. 1. Entwining phenomenon of rice straw was decreased as the blade edged curve angle increased. The edged curve angle of rotary blade must be determind by considering the characteristics of soil cutting resistance, tilling torque and entwining phenomenon of rice straw. But according to the entwining phenomenon of rice straw only, the edged curve angle of rotary blade should be bigger than $55^{\circ}$ for design. 2. Amount of entwining rice straw was minimized when soil moisture contents was 30 percent (d. b.). It would be better that rotary tillage is performed when soil moisture contents is lower than 30 percent in dry basis. 3. Amount of entwining rice straw was minimized when the length of rice straw was 30cm with $55^{\circ}$ edged curve angle. Therefore, it would be better to chop rice straw as 30cm. 4. Entwining phenomenon of rice straw was decreased as the forward speed decreased. To decrease the entwining rice straw, rotary tillage should be done with forward fist gear (0.35m/s).

• Korean Journal of Organic Agriculture
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• v.10 no.3
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• pp.41-55
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• 2002

In order to evaluate the effects of functional composts which include elvan, jade and loess, the growth and the yield of Chinese Cabbage and its content of sugar, nitrate and vitamin C were analysed. This study was conducted in lysimeter which was installed in the Experimental Farm of Dankook University. Total fresh weights of Chinese Cabbage were higher in the treatments of compost with mixture of elvan, jade and loess, while numbers of leaf was not increased in those treatments compared to control plot. Leaf length increased more than leaf width, specially in the evlan treatment. Fresh weight of leaf blade and midrib in outer leaf was highest in the plot of elvan treatment among the 6 treatments. Sugar content in the Chinese Cabbage showed lower in the treatment of compost with mixture of elvan, jade and loess compared to control plot. Vitamin content was high in leaf blade compare to those in midrib, and it showed highest value in the treatment of compost with mixture of jade. Nitrate concentration of leaf blade and midrib in the treatment of compost with mixture of loess was lowest at 2,021ppm and 2,235ppm respectively. It shows the effective function of mixture compost with jade, loess and elvan to decrease nitrate content in the Chinese Cabbage.

• Korean Journal of Materials Research
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• v.21 no.6
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• pp.320-326
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• 2011

Flat rolling of wire is an industrial process used to manufacture electrical flat wire, medical catheters, springs, piston segments and automobile parts, among other products. In a multi-step wire flat rolling process, a wire with a circular crosssection is rolled at room temperature between two flat rolls in several passes to achieve the desired thickness to width ratio. To manufacture a flat wire with a homogeneous microstructure, mechanical and metallurgical properties with an appropriate pass schedule, this study investigated the effect of each pass schedule (1stand ~ 4stand) on the microstructures, mechanical properties and widths of cold rolled high carbon steel wires using four-pass flat rolling process. The evolutions of the microstructures and mechanical properties of the widths of cold rolled wires during three different pass schedules of the flat rolling process of high carbon wires were investigated, and the results were compared with those for a conventional eight-pass schedule. In the width of cold rolled wires, three different pass schedules are clearly distinguished and discussed. The experimental conditions were the same rolling speed, rolling force, roll size, tensile strength of the material and friction coefficient. The experimental results showed that the four-pass flat cold rolling process was feasible for production of designed wire without cracks when appropriate pass schedules were applied.

• Korean Journal of Environmental Biology
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• v.42 no.1
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• pp.80-94
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• 2024

This study aimed to examine the morphological characteristics and variation in main traits by comparing the growth of individuals of Ecklonia cava Kjellman(Laminariales, Phaeophyceae) under an aquaculture environment. This survey was conducted from April 2018 to November 2019 at the aquafarm in Jindo-gun, Jeollanam-do(South coast of Korea). To classify the morphology of individuals in the aquaculture farm of E. cava, we investigated fourteen morphological characteristics and calculated four ratios between the measured values. Juvenile individuals showed a simple or oblong lanceolate, and at 3-4 months, a short stipe and holdfast developed, along with a bladelet that developed into the secondary blade form. At 5-7 months, secondary blades were found to develop irregularly on the primary blade. At 8-10 months, the primary blade expanded and secondary blades elongated. At 11-12 months, the secondary blades became oblong. At 13-14 months, the thallus area expanded. At 15-16 months, tertiary blades were formed, the thallus became more complex, the stipe thickened, and the holdfast widened. At 17-18 months, secondary blades clearly developed along with lobes. At 19-20 months, tertiary blades developed and became similar to mature natural blades. In the principal component analysis (PCA), the monthly population of the first year(Q1) and that of the second year(Q2) of the cultured population were divided along PC1, which is related to secondary blade morphological characteristics and the holdfast width. Q2 and natural populations are distributed in descending order of volume in Jeju(J), East Coast(E), and South Coast(S) along PC2, which is related to primary blade and stipe morphological characteristics. The results of this study were judged to offer important criteria for the development of different varieties of E. cava.

• The KSFM Journal of Fluid Machinery
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• v.7 no.3 s.24
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• pp.32-38
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• 2004

Shape of a multi-blades centrifugal fan is optimized by response surface method based on three-dimensional Navier-Stokes analysis. For numerical analysis, Reynolds-averaged Navier-Stokes equations with standard $k-{epsilon}$ turbulence model are transformed into non-orthogonal curvilinear coordinate system, and are discretized with finite volume approximations. Due to the large number of blades in this centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models for economic calculations. Optimizations with and without constraints are carried out. Design variables, location of cur off, radius of cut off, expansion angle of scroll and width of impeller were selected to optimize the shapes of scroll and blades. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, the efficiency was successfully improved. The correlation of efficiency with relative size of inactive zone at the exit of impeller is discussed as well as with average momentum fluxes in the scroll.