• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.99-106
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• 2001

The main objective of this study is to develop a continuity of double tee slab with two modified dap-ends to solve the problems of excessive moment, slab depth, deflection, and joint cracking in the original simply supported double tee slab systems. The modified joint is produced in a combination with two slabs with modified dap and one rectangular beam. The modified joint can be justified as following different merits. The span capacity for a design load is increased, while the deflection of the slab is decreased due to the decrease of positive moment at the center span of the slab. The joint cracking between slab and beam, which occur frequently in the original slab systems of double tee will be reduced. No more additional form work is needed to cast topping concrete for continuity. Three point loading tests are performed on the specimens with a variable of an amount of main longitudinal reinforcement to evaluate flexural and shear behavior. Following conclusions are obtained from the experimental investigation. The continuity of double tee slab effectively is provided by placing longitudinal steel reinforcement in the topping concrete over the connection, and generally leads to an increase in span capacity of double tee slabs with reduced deflection. It is more effective to control the initial cracking at the connection than that of some simply supported double tee slab systems.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.1
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• pp.29-39
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• 2006

Statements of problem: Zirconia core is used for posterior fixed partial dentures because it's good mechanical properties. Stress is concentrated on connectors in fixed partial dentures, so the proper design of connector areas is needed for adequate mechanical long-term properties of any prosthesis. The area of connector is critical, but tooth size and surrounding soft tissue limit the connector design. Purpose: The purpose of this study is to compare fracture strengths between different connector designs of zirconia core for posterior fixed partial dentures manufactured with CAD/CAM system and determining the optimal connector design satisfying strength and hygiene. Material and method: The following four groups of 40 posterior fixed partial denture specimens(each group 10) were fabricated as followed; group 1 vertical height of connector is 3mm (control group, all groups have the same condition); group 2, lingual vertical 1mm reinforcement on connector; group 3, lingual vertical 2mm reinforcing on connector and group 4, lingual vertical 3mm reinforcing on connector. Specimens were subjected to compressive loading on the central fossa of pontic by instron. SEM was used to identify the initial crack and characterize the fracture mode. Results: The results were as follows: 1. The mean fracture load of the non-lingual reinforcing group was 1212N and the lingual vertical 1mm reinforcing group was 1510N, the lingual vertical 2mm reinforcing group was 1882N, the lingual vertical 3mm reinforcing group was 1980N. 2. The reinforcing groups were statistically significant compared to non-reinforcing groups(P<0.001). 3. There were 2, 3mm reinforcing groups that were statistically significant compared to 1mm reinforcing groups(P<0.001), and the 3mm reinforcing group was not statistically significant compared to 2mm reinforcing groups(P>0.05) 4. Fractures were initiated in gingival embrasures of connectors and processed to the loading site. Conclusion: In this study, lingual reinforcement of connector for improved strength of zirconia based fixed partial denture is nessasary. And long-term study for clinical application is required

• Applied Microscopy
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• v.29 no.2
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• pp.189-193
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• 1999

The response of ameloblast to long term (3 weeks) exposure to fluoride was examined in continuously erupting mandibular incisors of pregnancy rats as compared to control rats receiving a similar diet (Teklad L-356) but no sodium fluoride in there drinking water. Rats were started on water containing 0 ppm, 100 ppm, 200 ppm, and 300 ppm NaF at the beginning of pregnancy. To examine on the ultrastructural changes of the ameloblast, electron microscopy was used. The results indicated that rat incisors expressed two major changes in normal amelogenesis that could be attributed to chronic fluoride treatment. 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, in particular on the morphology of the rough-surfaced endoplasmic reticulum. A graded series of alterations to these organelles were produced, and the severity of the changes would seem to be dependent on dose and time. This experimental data suggested that exposure prolonged of animal to high level of fluoride appears to induce morphological changes in the normal appositional growth and initial mineralization of enamel created during amelogenesis.

• Korean Journal of Community Nutrition
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• v.2 no.5
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• pp.687-694
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• 1997

This study investigated the effects of vitamin C supplementation on the nutritional iron status of 31 adolescent girls, aged 12-15 years, with low hemoglobin levels. They were randomly divided into four groups, and for two groups daily150mg or 900mg of L-ascorbic acid(AsA) was given in three equal doses at three meals during 9 weeks. To another group daily 60mg iron as ferrous sulfate was given in the same way as AsA. The control group was given sugar placebo. Body iron status was monitored through the determination of Hb, Hct, MCHC, and serum ferritin concentrations. Dietary AsA and iron intakes were measured from food consumption surveys performed by 3-day 24-hour recalls. The amount of absorbed iron was estimated from the model of Monsen et al. The average amounts of food iron for four groups were 12.3- 15.0mg and 11.1 - 18.9mg at initial and at final period of the supplementation trial, respectively. The tentatively estimated amount of absorbed iron was significantly increased in the 900mg AsA and iron supplementing groups, but not in the 150mg AsA and placebo groups. Both Hb and MCHC were improved to above normal levels in all groups except the placebo group. Hct was elevated only in the AsA 900mg group whose Hct was relatively lower than the other groups. Serum ferritin concentrations of the four groups, which were as low as 8.50 - 14.39ng/mL on average at the intial periods, augmented significantly to 20.18ng/mL and 26.63ng/mL in the 900mg AsA and iron groups, respectively. Serum ferritin was not elevated in either the AsA 300mg group or the placebo group. The above data indicated that the daily supplementaion of 150mg AsA to the meals containing 12-15mg iron per day promoted Hb levels of adolescent girls with low Hb, and the 900mg AsA supplementing improved not only Hb level but also body iron store. A supplementation of 60mg iron per day appeared to be slightly more effective in improving the iron status in comparison to the 900mg AsA supplement. (Korean J Community Nutrition 2(5) : 687-694, 1997)

• KOREAN JOURNAL OF CROP SCIENCE
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• v.53 no.4
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• pp.427-433
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• 2008

Barley Yellow Mosaic Virus (BaYMV) caused significant reduction in barley yield and is difficult to control due to alive parasitic soil-borne fungus, Palmyra gamines that transmits the, virus. Previous studies have indicated that a virus-free soil could be infested by using virus-contaminated farming machineneries and implements. For the further confirmation of this finding, different proportions of BaYMV-infested soil were mixed into virus free soil. Three barley varieties (Hordum vulgarae, cv "Olbori", "Baegdong" and "Sacheon 6") were sown in pots treated with different rate of P. graminis-infested soil ranging from 0% to 100% in October 20, 2001. Results showed that BaYMV infection increased as the rate of infested soil increased. Initial symptoms were observed in a pots treated with 10% infested soil in all the 3 varieties of barley. "Olbori" had about 5% infection in 20% infested soil and about 10% infection in 40% or 50% infested soil and about 20% infection in 60% infested soil. In "Baegdong", the trend of BYMV occurrence was similar with "Olbori" but the time of severe infection was earlier than "Olbori". BaYMV infection in "Sacheon 6" was even earlier than "Baegdong" with much more severe symptoms than "Baegdong". The growth rate of barley was affected by about 19-22% when grown in 20% infested soil. As the rate of BaYMV infested soil increased the heading date was delayed but the maturing date was early in "Olbori" and "Sacheon 6". Also, reduction rate of culm length in 3 varieties increased with increase of infested soil content. However, "Olbori" showed the highest reduction. "Sacheon 6", have been characterized with long spike length, however was significantly reduced as the infested soil increased. On the other hand, spike length of "Olbori" was not significantly affected despite of increased of infested soil. The reduction rate of 1000 kernel weight was higher in large kernel size cultivar "Sacheon 6" and "Olbori" than small kernel size "Baegdong" as increase of BaYMV-infested soil content.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.62 no.4
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• pp.325-332
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• 2017

This research was conducted to evaluate methods of enhancing the waterlogging resistance of soybean plant. Thus, we applied seven types of plant growth regulators (PGRs) to soybean plants and exposed them to waterlogged conditions for a total of 14 days. To evaluate stress resistance, we monitored plant growth characteristics data such as height, chlorophyll content, and chlorophyll fluorescence for 28 days after the initial waterlogging (14 days under waterlogging conditions and 14 days after waterlogging). According to the results, plant height was significantly increased by gibberellin A4 ($GA_4$) treatment compared to the control treatment and waterlogging-only treatment. However, we could not detect plant height owing to plant death when we applied abscisic acid (ABA). Except for $GA_4$ and ABA treatments, plant heights slightly decreased in all treatments compared to the waterlogging-only treatment. The chlorophyll content and chlorophyll fluorescence showed a similar tendency among PGR treatments. The chlorophyll content and chlorophyll fluorescence were significantly increased by ethephon and kinetin treatments 28 days after waterlogging compared to the waterlogging-only treatment. Consequently, kinetin and ethephon treatments induced more resistant phenotypes in soybean plants during or after exposure to waterlogging conditions.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.6
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• pp.323-328
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• 2016

Pressurized membrane used for side-stream MBR process requires fouling control strategy both for normal and abnormal operation conditions for stable operation of the facilities. In this study, $85m^3/day$ of pilot-scale side-stream MBR process was constructed for the evaluation of fouling mitigation by air bubble injection into the membrane module. In addition, fouling phenomena at abnormal operation conditions of low influent and/or loading rate were also investigated. Injection of air bubble was found to be effective in delaying transmembrane pressure (TMP) increase mainly due to scouring effect on the membrane surface, resulting in expanded filtration cycle at a high flux of $40L/m^2{\cdot}h$ (LMH). At abnormal operation condition, injection of PACl (53 mg/L as Al) into the bioreactor showed 19% reduction of TMP increase. However, inhibition of nitrifying bacteria by continuous PACl injection was observed from batch experiments. In contrast, injection of powdered activated carbon (PAC, 0.6 g/L) was able to maintain the initial TMP of $0.2kg/cm^2$ for 5 days at the abnormal conditions. It may have been caused from the adsorption of extracellular polymeric substances (EPS), which was known to be excessively released during growth inhibition condition and act as the major foulants in MBR operations.

• Journal of Animal Science and Technology
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• v.52 no.6
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• pp.505-511
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• 2010

Thirty six Hanwoo steers (average BW, $564.5\;{\pm}\;25.7\;kg$; average age, approximately 23 months) were used to evaluate the effects of a mixture of eugenol (14%), thymol (1%) and malate (85%) on growth performance, beef quality and liver function in Hanwoo finishing steers fed a high-concentrate diet. A feeding trial was conducted for 7 months in National Agricultural Cooperative Federation farm located in Anseong, Korea. Steers were assigned randomly to one of three treatments: control (without additive supplementation), treatment 1 (0.05% additive of concentrate), treatment 2 (0.1% additive of concentrate). The results of this study showed that initial and final BW averaged 564 and 755 kg, respectively, and BW gain was significantly higher (P<0.05) for steers fed the additive mixture than for those fed no mixture (0.78 and 0.79 vs. 0.69 kg/d, respectively). Serum aspartate aminotransferase in the T2 treatment was decreased during the 24 to 31 months of age. Although supplementation of additives resulted in no substantial effect on carcass characteristics, it had a potential effect to improve feed efficiency and AST concentration in Hanwoo finishing steers fed a high-concentrate diet. In conclusion, a mixture of eugenol, thymol and malate has shown promise in improving feed efficiency and liver function in the finishing phase of Hanwoo steers.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.44-50
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• 2016

A study to apply phase change material(PCM) to rapid hardening cement paste forming semi-rigid pavement was carried out. The characteristics fresh and hardened paste were evaluated through the experiment for a total of 6 mixtures according to the cement type and the substitution of phase change material for acrylate. The fluidity by substituting phase change material for acrylate satisfied the target flow time of 10 to 13 seconds. In case of setting time, it was possible to secure the performance of rapid hardening cement by substituting phase change material, and if the substitution ratio over 60%, the initial set occurred 1 to 2 minutes faster than other mixtures. In case of compressive strength and bond strength, it showed similar strength characteristics with the plain mixture, and it satisfied both the target compressive and bonding strength of 36MPa and 2MPa. The mixture substituting phase change material showed higher resistance to chloride ion penetration than the mixture only using acrylate and the OPC level was insufficient. From the results of physical and mechanical performances of semi-rigid pavement cement paste, the phase change material substitution rate of 20% was effective in the range of this study.

• Restorative Dentistry and Endodontics
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• v.32 no.4
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• pp.365-376
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• 2007

The purpose of this study was to evaluate the effect of different etching times on microtensile bond strength (${\mu}TBS$) to dentin both initial and after thermocycling with 3 different types of total-etching adhesives. Fifty four teeth were divided into 18 groups by etching times (5, 15, 25 sec), adhesives types (Scotchbond Multipurpose (SM), Single Bond (SB), One-Step (OS)) and number of thermocycling (0, 2,000 cycles). Flat dentin surfaces were prepared on mid-coronal dentin of extracted third molars. After exposed fresh dentin surfaces were polished with 600-grit SiC papers, each specimen was acid-etched with 35% phosphoric acid (5, 15, 25 sec) and bonded with 3 different types of total etching adhesives respectively. Then, hybrid composite Z-250 was built up. Half of them were not thermocycled (control group) and the ethers were subjected to 2,000 thermocycle (experimental group). They were sectioned occluso-gingivally into $1.0\;{\times}\;1.0\;mm^2$ composite-dentin beams and tested with universal testing machine at a crosshead speed of 1.0 mm/min. Within limited data of this study, the results were as follows 1. There was no statistically significant difference in ${\mu}TBS$ between the thermocycled and non-thermocycled groups, except for both SM and SB etched for 25 sec. 2. In thermocycled SM and SB groups, bond strength decreased by extended etching time. In total etching systems, adhesive durability for dentin could be affected by type of solvents in adhesive and etching time. Especially, extended etching time may cause deteriorate effects on bond strength when ethanol-based adhesive was used.