• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.422-429
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• 1997

Thermal stress induced by hydration heat may produce cracks in mass concrete structure, which can result in structural problems as well as bad appearance. To minimize crack occurrence in massive structural, thus, the study put an emphasis on the determination of optimized lift height and block size. In the parametric study different sizes and lift heights were used to measure the magnitudes of hydration heat and thermal stresses for 3 different types of concrete fabricated with 1 pure cement and 2 blended Portland cements. As a result of analysis. it was found that magnitude of hydration heat and the occurrence of thermal cracks depend on the restriction conditions and material characteristics, especially adiabatic material parameters. It was also found that optimized lift height and block size can be determined from an appropriate combination of the degree of inner and outer structural restrictions.

• Earthquakes and Structures
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• v.13 no.5
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• pp.465-471
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• 2017

This work derives a generalized time fractional differential equation governing wave propagation in a radially vibrating non-classical cylindrical medium. The cylinder is made of a transversely isotropic hyperelastic John's material which obeys frequency-dependent power law attenuation. Employing the definition of the conformable fractional derivative, the solution of the obtained generalized time fractional wave equation is expressed in terms of product of Bessel functions in spatial and temporal variables; and the resulting wave is characterized by the presence of peakons, the appearance of which fade in density as the order of fractional derivative approaches 2. It is obtained that the transversely isotropic structure of the material of the cylinder increases the wave speed and introduces an additional term in the wave equation. Further, it is observed that the law relating the non-zero components of the Cauchy stress tensor in the cylinder under consideration generalizes the hypothesis of plane strain in classical elasticity theory. This study reinforces the view that fractional derivative is suitable for modeling anomalous wave propagation in media.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1994.06b
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• pp.19-29
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• 1994

Since Winslow (1) has reported an electro - theological (ER) effect which features remarkable and reversible changes in the properties of the fluid due to an imposed external electric field, numerous applications of ER fluids in mechanical devices, such as clutches, control valves, active dampers, and etc. have been proposed to improye dramatical ly their performances (2,3). When the external electric field is imposed to the ER fluid, it behaves as a Bingham fluid, displaying a field dependent yield shear stress which is widely variable. Without the electric field, the ER fluid has a reversible and constant viscosity so that it flows as a Newtonian fluid. Another salient feature of the ER fluid is that the time required for the variation is very short (< 0.001 sec) (4-6). These attractive.characteristics of the ER fluid provide the possibility of the appearance of new engineering technology , for instance, an active vibration control system. Recently, the application of the ER fluid to rotor-bearing systems has been also initiated.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.6_1
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• pp.977-983
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• 2023

The tank uses a twin turbo diesel engine equipped with two turbocharger systems for high output. The main component of the turbocharger system is the turbine housing through which the exhaust flows. Turbine housing is manufactured through a sand casting process, taking into account the shape and material characteristics according to the environmental conditions in which it is used. Currently, turbine housing is imported, and local production is necessary. In this study, basic research was conducted to localize the turbine housing of a tank diesel turbo engine. Reverse engineering and finite element analysis of the imported turbine housing were performed. The prototype of the turbine housing was printed using FDM and PBF 3D printers. The prototype of the turbine housing printed with an FDM 3D printer has an overall appearance similar to 3D modeling, but the printed surface of the whorl part is rough. The prototype printed with the PBF 3D printer is completely identical to the 3D modeling, including the whorl part.

• Journal of Food Hygiene and Safety
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• v.6 no.1
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• pp.27-40
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• 1991

;ABSTRACT-The effects of gastric ulcer induced by restraint and water-immersion stress on gastric carcinogenesis in Wistar male rats treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were examined. Rats of group 1 were 2iven stress for 8 hours before they were received MNNG (100 mg/l) in drinking water for 20 weeks. Rats of group 2 were received MNNG first for 2 weeks and then were given stress once a week from 3rd to 12th weeks, with simultaneous MNNG adminitration and followed by MNNG only until 20th weeks. Rats of group 3 were received MNNG only as a positive control and rats of group 4 were not treated with carcinogen. All groups were sacrificed in 20 weeks. Sections of the pyloric mucosa were stained by avidin-biotin peroxidase complex (ABC) immuno-histochemical method. PAPG (pepsinogen isozyme 1 altered pyloric gland), body weight change, gross lesions and histopathological changes were examined. The results obtained from these studies were summarized as follows: 1. The mean body weight gains of the rats fed with carcinogens (group 1, 2, 3) were significantly lower than that of group 4 (control group, without carcinogen. p<0.05). However, the differences of the mean body weight of rats treated with carcinogen were not significant. 2. Stress treatment (group 1 and 2) increased the appearance of the numbers of PAPG (Pepsinogen 1 Altered Pyloric Gland) induced by carcinogen significantly compared with that of group 3 (carcinogen only, p<0.01). 3. The incidence rate of mucosal hyperplasia in pylorus was significantly increased in group 2 compared with group 3 (p<0.05).0.05).

• The Korean Journal of Cytopathology
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• v.9 no.1
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• pp.69-78
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• 1998

There is a lot of difficulty in the diagnosis of follicular lesions of the thyroid by fine needle aspiration cytology(FNAC). The main purpose of this report is offering more guidance regarding the cytologic appearance to distinguish follicular neoplasm from nodular golfer and laying stress on the presence of mixed group. The histologic and cytologic findings of 23 follicular neoplasms and 13 nodular (adenomatous) getters were reviewed. Histologic specimens were classified into the microfollicular(MIF), mixed(MIX), and nodular getter(NG) groups. The comparison of histologic patterns with histologic diagnosis revealed that all the lesions with predominantly microfollicular, trabecular, or solid pattern were follicular carcinoma and all the lesions with predominantly macrofollicular pattern were nodular goiter. The distinguishing cytologic features for the MIF group were irregular cell arrangement in cell groups(100%, p=0.00001), absence of atrophic follicular cells(100%, p=0.0007), abundant microfollicles(100%, 0=0.002), pleomorphic nuclei(100%, p=0.002), not predominant syncytial smear pattern(100%, p=0.002), heterochromatin(100%, p=0.032), absence of macrofollicles(100%, p=0.038), scant colloid(100%, 0=0.04), clear back-ground(83%, p=0.00006), and uniform sized follicles(83%, p=0.014). And regular cell arrangement(honeycomb appearance) in cell groups(85%, p=0.0000), atrophic change of follicular cells(69%, p=0.0002), syncytial smear pattern(54%, p=0.000), monomorphic nuclei(85%, p=0.008), and hemorrhagic background(100%, p=0.027) were characteristic features of the NG group. Seventeen out of 36 cases(47%) were the MIX group composed of combined cytologic features of the MIF and NG groups. Therefore the frequent presence of the MIX group is considered to be main cause of the difficulty in the diagnosis of follicular lesions by FNAC. The mixed morphologic feature may support the hypothesis of a biologic 'continuum' between nodular goiter and follicular neoplasm of thyroid gland.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.125-137
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• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.625-625
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• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.

• Journal of the Korean Dietetic Association
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• v.15 no.3
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• pp.232-252
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• 2009

This study investigated dieting behavior, awareness of body shapes, and eating disorders in female adolescents according to age and BMI. The Eating Attitude Test for Korean Adolescents (EAT-26KA) and sociocultural standards were used to measure eating disorders and sociocultural attitudes related to appearance, respectively. In addition, the BDI (Beck Depression Inventory) scale was used to measure the correlation between disordered eating and depression. The data were collected from 390 female adolescents living in Seoul and were analyzed using SPSS15.0. The results indicated that subjects wanted to be thinner despite having a normal body weight (BMI 19.35${\pm}$2.73). They also thought of themselves as fat and with desires to be slimmer, and viewed "diet and exercise" as the best way to lose weight. About 67.4% of the respondents had tried a diet and had experienced dizziness, anorexia, and general exhaustion while dieting. Also, 5.1% of the subjects were classified as eating disorder and suffered from stress to be thin. In addition, 85.0% of the subjects with eating disorder had tried a diet due to "appearance". They thought that "being underweight" was an ideal body image and considered themselves fat, although their BMIs were in the normal range (19.94${\pm}$2.02). In terms of symptoms during dieting, many of the subjects dealing with an eating disorder felt dizzy, had low energy, and were depressed. In conclusion, we must educate young females about healthy eating and positive body image to prevent the development of adolescent eating disorders.

• Journal of Korea Entertainment Industry Association
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• v.15 no.3
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• pp.171-182
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• 2021

This study analyzed the factors influencing the satisfaction of school students in Covid-19. The subjects of the study were surveyed in all 5th-6th grade of elementary school students, 1st-3rd grade of middle school, and 1st and 2nd grade of high school students in G metropolitan city. A total of 13,672 students participated in the survey, of which 13,613 were used for final data analysis. A hierarchical regression analysis of factors affecting students' life satisfaction showed that 22.2% of school life factors, 4.7% of home life factors, and 10.7% of daily stressors. The most influential factor in Covid-19 was home life satisfaction. Next was appearance stress for elementary school students and academic stress for middle and high school students. This can be seen as a result of Covid-19, which increased non-face-to-face classes and increased time for students to spend at home, which led to a greater impact on students' satisfaction in life. Nevertheless, middle and high school students can still see that academic stress has a significant impact on life satisfaction. Through this, it is necessary to support students to facilitate relationships, communication, studies, and leisure at home in the context of Corona 19. Especially, various educational policies must be accompanied so that the educational gap due to non-face-to-face classes does not deepen depending on the family environment.