• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.40-51
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• 1991

A Propeller design method using the newly developed blade section(KH18), which behaves better cavitation characteristics, is presented. Experimental results for two-dimensional foil sections show that the lift-drag curve and the cavitation-free bucket diagram of the new blade section are wider comparing to those of the existion NACA sections. This characteristic of the new section is particularly important for marine propeller applications since angle of attack variation of the propeller blade operating behind a non-uniform ship's wake is relatively large. A lifting surface theory is used for the design of a propeller with the developed section for a 2700 TEU container ship. Since the most suitable chordwise loading shape is not known a priori, chordwise loading shape is chosen as a design parameter. Five propellers with different chordwise loading shapes and different foil sections are designed and tested in the towing tank and cavitation tunnel at KRISO. It is observed by a series of extensive model tsets that the propeller(KP197) having the chordwise loading shape, which has less leading edge loading at the inner radii and more leading edge loading at the outer radii of 0.7 radius, has higher propulsive efficiency and better cavitation characteristics. The KP197 propeller shows 1% higher efficiency, 30% cavitation volume reduction and 9% reduction of fluctuating pressure level comparing to the propeller with an NACA section. More appreciable efficiency gain for the new blade section propeller would be expected by reduction of expanded blade area considering the better cavitation characteristics of the new blade section.

• Elastomers and Composites
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• v.39 no.2
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• pp.131-141
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• 2004

The recycling of waste XLPE(crosslinked polyethylene), which is a major source of scraps from high voltage power transmission cables, has been discussed. The waste XLPE scraps were ground into fine powder with various sizes from less than $100{\mu}m$ up to about $1000{\mu}m$ using two types of tailor-made pulverizers. The compounds were prepared in a modular intermeshing co-rotating twin screw extruder at various conditions such as different compositions, types and powder sizes of waste XLPE, screw configurations and various polymer matrices (LDPE, HDPE, PP, PS). The mechanical and rheological properties and the fracture surface or the compounds were investigated. It was found that an improved impact strength was obtained from the compound with white XLPE powder pulverized from the scraps without outer/inner semi-conductive layers. Generally, the impact strength increases with the content of XLPE but decreases with the size of XLPE. Especially for LDPE, the extrusion was possible up to 80 wt% loading of XLPE. Also, the impact strength increases with the number of kneading disc blocks in the given screw configurations. The melt viscosity of the compounds increases with increasing XLPE loading. However, the higher shear thinning behavior of the compounds at common shear rates implies proper processibility of the compounds. In addition, the impact strength for other polymer matrices used increases with XLPE and it is noticeable that the impact strength of PS/XLPE (80/20 wt%) compound was improved twice that of pure PS.

• Corrosion Science and Technology
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• v.13 no.1
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• pp.20-27
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• 2014

The structures of reinforced concrete has been extensively increased with rapid development of industrial society. Futhermore, these reinforced concretes are easy to expose to severe corrosive environments such as sea water, contaminated water, acid rain and seashore etc.. Thus, corrosion problem of inner steel bar embedded in concrete is very important in terms of safety and economical point of view. In this study, multiple mortar test specimen(W/C:0.4) with six types having different cover thickness each other was prepared and was immerged in seawater solution for five years to evaluate the effect of cover thickness and immersion years to corrosion property of embedded steel bar. And the polarization characteristics of these embedded steel bars was investigated using electrochemical methods such as measuring corrosion potential, cathodic polarization curve, and cyclic voltammogram. At the beginning of immersion, the corrosion potentials exhibited increasingly nobler values with increasing cover thickness. However, after immersed for 5 years, the thicker cover of thickness, the corrosion potentials shifted in the negative direction, and the relationship between corrosion potential and cover thickness was not in good agreement with each other. Therefore, it is considered that the thinner cover of thickness, corrosive products deposited on the surface of the embedded steel bar plays the role as a resistance polarization which is resulted in decreasing the corrosion rate as well as shifting the corrosion potential in the positive direction. As a result, it seemed that the evaluation which corrosion possibility of the reinforced steel would be estimated by only measuring the corrosion potential may not be a completely desirable method. Therefore, it is suggested that we should take into account various parameters, including cover thickness, passed aged years as well as corrosion potential for more accurate assessment of corrosion possibility of reinforced steel which is exposed to partially or fully in marine environment for long years.

• Korean Journal of Social Welfare
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• v.69 no.2
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• pp.191-218
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• 2017

The purpose of this study was to examine the effect of the possibility of job-related risk, emotional labor, and emotional leadership on the job turnover intention of caregivers working at the long-term care facilities in Korea. For the study, survey data of 434 caregivers at senior nursing homes were collected and analyzed using hierarchical multiple regression method. The results showed that high level of caregivers'perception of both the possibility of management risk and employee risk led to increased turnover intention. On the other hand, perception of the possibility of social-disaster risk did not give significant impact on turnover intention. Although the perception of the possibility of service user risk gave statistically significant effect on the turnover intention, the direction was the opposite to the one set at the research hypothesis. Frequent camouflage behavior("surface acting") of caregivers, which is the kind of emotional labor led to increased turnover intention. However, caregivers'behavior consistent with their inner warm heart("deep acting") did not lead to a statistically significant result. Lastly, the more caregivers perceive their superiors'emotionally supportive leadership, the lower possibility of turnover intention. Based on the above result, the researchers suggested several intervention methods in order to prevent turnover of caregivers and improve service quality of long-term care institutions.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.3
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• pp.64-73
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• 2000

The joint parts was composed of inner AL(aluminum) ring, FRP wedge and motor case which was manufactured by filament wound method. Where the motor case consists of helical and hoop layer. The finite element analysis was performed for the design variable of joint parts to improve the performance of motor case. Where the adhesive layer was modeled to elasto-perfect plastic material and the contact condition of AL ring and wedge was modeled by using the contact surface element of ABAQUS. And the sliding distance of AL ring and the hoop strain of composite case were compared to hydro-static test results to verify the accuracy of analysis results. When wedge and AL ring was perfect bonding, though the hoop strain of joint part was reduced, the maximum shear stress was occurred at the adhesive layer. Thus the adhesive layer had failed due to the high shear stress before the failure was occurred at the case. And as another design method, when wedge and AL ring was contact condition, the shear stress on adhesive layer was decreased. But the hoop stress of joint part increased due to the sliding behavior of AL ring. Finally, the fail was occurred at the composite case of joint part. The improved joint method reinforced by hoop layer to the joint parts under contact condition for wedge and Al. ring reduced the joint part's hoop strain by constraint the sliding behavior of AL ring.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.825-831
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• 2017

In this study, we perform the design of dome geometry for the composite pressure vessel with applying the equation of Fulton and Vasiliev considering external load(thrusts). Variables of the dome geometry are opening radius ratio(${\rho}_0$) from 0.1 to 0.5 and thrust level from 40kN to 200kN. We conduct Finite Element Analysis(FEA) by using ABAQUS. As a result, the strain of the composite pressure vessel has shown strain gradient from inner to outer of dome surface. And the strain gradient may cause crack of resin inside the composite laminate. Strain gradient of Fulton dome is monotonously decreased as the ${\rho}_0$ increases, but the strain gradient of Vasiliev dome bas shown some different trend. when ${\rho}_0{\leq}0.1$, strain gradient of Fulton's is higher than Vasiliev's. But when 0.1<${\rho}_0$<0.35, strain gradient of Vasiliev's becomes higher than Fulton's. And in the case of $0.35{\leq}{\rho}_0$, strain gradient of Vasiliev's is higher than Fulton's. So the Vasiliev dome is more effective in ${\rho}_0{\leq}0.1$ condition and Fulton dome is more effective in $0.35{\leq}{\rho}_0$ condition. So, it's important for dome design to consider the crack of resin cause of the strain gradient.

• Polymer(Korea)
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• v.36 no.2
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• pp.124-130
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• 2012

The uniform nanofibers of poly(L-lactide-$co$-${\varepsilon}$-caprolactone) (PLCL) with different contents of marine collagen (MC) were successfully prepared by electrospinning method. The effects of the major parameters in electrospinning process such as tip to target distance (TTD), voltage, nozzle size and flow rate on the average diameter of the electrospun nanofiber were investigated in generating composite nanofiber. The diameter and morphology of the nanofibers were confirmed by a scanning electron microscopy (SEM). Also, we measured a water contact angle to determine the surface wettability of the nanofibers. The average diameter of the nanofibers decreased as the value of TTD, MC contents, and voltages increased in comparison with that of pristine PLCL nanofiber. In contrast, the diameter of the nanofibers increased as the flow rate and inner diameter of nozzle increased in comparison with that of pristine PLCL. In addition, the hydrophilicity of the nanofiber and attachment of MG-63 cells on the sheets increased as incorporated collagen contents increased. Therefore, the marine collagen would be a potential material to enhance cellular interactivity of synthetic materials by mimicking the natural tissue.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7754-7760
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• 2015

The outer tie rod is one of the part of steering system, the optimization process was executed to find the lightweight design. The inner tie rod was considered in the optimum design of an outer tie rod. it could be closer to the test condition than in the case of considering outer tie rod only. The aluminum forging material was considered as a weight reduction proposal. The target of optimization was the shape of the minimum weight to resist at the load of buckling. RSM and Kriging interpolation method were applied as a optimization method to consider the nonlinear shape optimization problem. Then, 16.3%, 16.6% of weight reduction was obtained from the result comparing with that of the initial model. The results of meta model optimization was compared with that of finite element method. The error values of buckling load estimation were 2.6%, 2.04%. and those of weight estimation were 0.17%, 0.13%. Therefore, it seemed that the result of Kriging model could be obtained closer to optimum value than that of RSM model.

• Applied Microscopy
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• v.29 no.2
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• pp.177-187
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• 1999

Ultrastructure of gametes in the three-spine stickleback, Gasterosteus aculeatus aculeatus was observed, utilizing light, scanning and transmission electron microscopes. The egg of three-spine stickleback is spherical and demersal type. The eggs are highly adhesived to each other but not to substrates. There are many oil droplets in vitelline membrane. The outer surface of egg envelope is arranged by mushroom-like structures and pore canals. The egg have a micropyle, sperm entry site, in the area of the animal pole. The egg envelope consists of three layers, an outer layer with high electron density, a middle layer consisting two layers and an inner layer consisting of 16 to 20 layers. In the fertilized egg envelope, the molecular weights of these components ranged from 14 kDa to 205 kDa. The molecular weights of nam protein bands are 19.4 kDa, 36.7 KDa, 39.4 kDa, 42.9 kDa, 46.1 kDa and 53.0 kDa. The head of spermatozoa is spherical shape and the acrosome is absent. The mitochondria in midpiece are arranged from one to three layers and separated from the axoneme by the cytoplasmic canal. The tail has two lateral fins and the axoneme is of the 9+2 structure.

• Applied Microscopy
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• v.34 no.2
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• pp.145-157
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• 2004

The aim of the present study was to examine in detail, both at light and electron microscopical levels, the morphological variations in ameloblast of the fetal rat incisor enamel organ. Rats were started on distilled water at the beginning of pregnancy. The pups were sacrificed 11 days after delivery and animals were perfused intravascularly with glutaraldehyde and the incisors were removed. To examine on the ultrastructure of the ameloblast, the study employed primary light microscopy but electron microscopy was used to clarify some of the light microscopic finding. Longitudinal sections through the incisors of the rat show a continuous layer of ameloblasts on the labial surface of the tooth. This layer contains the entire sequence of developmental stages in enamel production. The ameloblast layer was divided into three main zones: 1) Presecretory zone, region of ameloblasts facing pulp. 2) Secretory zone, region of inner and outer enamel secretion. 3) Maturation zone, region of reduced ameloblasts. In particularly, the present study has shown that two distinctively different types of ameloblasts appear in the enamel organ during enamel maturation in the rat incisor. These two types have been designated ruffle-ended ameloblasts (rAB) and smooth-ended ameloblasts (sAB). The fluoride produces marked alteration in the fine structure of ameloblast from teeth of young rats, such as large confluent distensions of the endoplasmic reticulum and swelling of isolated mitochondria. This experimental data suggested that exposure prolonged of animal to high level of fluoride appears to induce a few dramatic changes in the normal appositional growth and initial mineralization of enamel created during amelogenesis.