• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.2
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• pp.84-89
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• 2006

A laser ultrasonic inspection system is a non-contact inspection device which generates and measures ultrasounds by using laser beams. A laser ultrasonic inspection system provides a high measurement resolution because the ultrasonic signal generated by a pulse laser beam has a wide-band spectrum and the ultrasonic signal is measured from a small focused spot of a measuring laser beam. In this paper, we have investigated the detection techniques of a surface-breaking crack by using the laser ultrasonic surface waves. A crack acts as a low pass filter whose cut-off frequency is lowered in proportion to the depth of a crack. And, the center frequency value of a spectrum is decreased in proportion to the depth of a crack. In this paper, we extracted the crack information by using the frequency attenuation from the normalized transfer function spectrum of a surface-breaking crack. Also, we effectively measured the crack depth by using the decreasing value of the center frequency from a crack passed ultrasonic signal. The proposed measuring techniques of crack depths provided more precise information than the amplitude measuring technique.

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.419-426
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• 1999

In this study, the reaction rate constant, activation energy, total crosslinking density, elastic constant, cure properties ($t_5,\;t_{90}$), modulus, and abrasion resistance of rubber compounds were investigated as a function of cure temperatures, cure systems and reinforcing filler loadings. Reaction rate constants showed strong dependence on thc carbon black loading, cure temperature and cure system, and increased sharply with increasing the reaction temperatures. The lowest activation energy was obtained in the efficient cure (EC) system which corresponds to the high level of sulfur to accelerator ratio, and the activation energy was decreased with decreasing the carbon black loadings. The change of carbon black loadings directly affects the modulus and abrasion resistance, but the change of cure system showed various effects on the rubber compounds. Increased carbon black loadings showed the high modulus, improved abrasion resistance and short scorch time but decrease in crosslinking density and elastic constant. Higher crosslinking density and elastic constant were shown in the EC cure system regardless of carbon black loadings, but scorch timc ($t_5$) was not affected by the change of the ratio of sulfur to accelerator. Rapid optimum cure time ($t_{90}$) were showen in the EC cure system. Also, the equivalent cure curve coefficient of rubber compound was 0.96 for conventional cure (CC) system, and 0.94 for semi-efficient cure (SEC) and EC system regardless carbon black loadings. As regarding the abrasion resistance, wear volume showed the logarithmic increase for the loaded weight.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.4
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• pp.439-446
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• 2009

This study was performed to evaluate SND(simultaneous nitrification and denitrification)efficiency, nitrogen removal efficiency and filtration function of non-woven fabric by using submerging MBR packed with granular sulfur covered with non-woven fabric filter. Synthetic wastewater was used as influent wastewater. Concentration of $NH_4{^+}-N$ in influent was maintained about 40 mg/L and the experiment was performed in four phases according to the flow rate. Nitrogen loading rate divided four phases ranging from $0.04 kg\;NH_4{^+}-N/m^3-day$ to $0.16 kg\;NH_4{^+}-N/m^3-day$. As a result, the maximum $NH_4{^+}-N$ removal rate was accomplished at $0.142 kg\;NH_4{^+}-N/m^3-day$ in nitrogen loading of $0.147 kg\;NH_4{^+}-N/m^3-day$. Nitrification efficiency was higher than 95% in all phases. $NO_3{^-}-N$ loading rate was adjusted ranging from $0.22 kg\;NO_3{^-}-N/m^3-day$ to $0.89 kg\;NO_3{^-}-N/m^3-day$. The maximum $NO_3{^-}-N$ removal rate was accomplished up to $0.71 kg\;NO_3{^-}-N/m^3-day$ in $NO_3{^-}-N$ loading of $0.89 kg\;NO_3{^-}-N/m^3-day$. The maximum $NO_3{^-}-N$ removal efficiency was 95% in $NO_3{^-}-N$ loading of $0.22 kg\;NO_3{^-}-N/m^3-day$. T-N removal rate was 90% and concentration of T-N in effluent was 3.7 mg/L in T-N loading rate of $0.039 kg\;NO_3{^-}-N/m^3-day$. In this study, TMP in reactor with and without non-woven fabric filter were observed to define fouling of hollow-fiber membrane module. Reaching time to standard washing pressure(22 cm Hg) of two reactors were 29 days with non-woven fabric But the reactor without non-woven fabric reached standard washing pressure only after 4 days. Accordingly, non-woven fabric was demonstrated the superiority as a filtration ability. With high nitrogen removal rate and decreasing of fouling of membrane, MBR packed with granular sulfur covered with non-woven fabric filter submerging in activated sludge aeration tank can be used as an advanced treatment process.

• Korean Journal of Animal Reproduction
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• v.4 no.1
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• pp.47-74
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• 1980

The present experiments were carried out to elucidate the effects of hypophysectomy and subsequent administration of sex hormone on thyroid, adrenal gland, gonads and blood plasma components in the rat. The jresults obtained were summarized as follows: The weight of the thyroid gland of both male and female hypophysectiomzed rats decreased markedly from 7 days up to 56 days after the hypophysectomy as compared to the control group. The administration of sex hormone (6 mg of testosterone propionate to male and 6 mg of hexestrol to female) to the hypophysectomized rat gave on effect on the change in the weight of the thyroid gland. The hopophysectomy decreased the uptake of radioactive iodine in the thyroid gland in both male and female rats with time. Subsequent administration of the sex hormone caused no effect. With regard to the histological changes of the thyroid gland, the hypophysectomy caused significant changes in the gland showing a remarkable degeneration. The function of the gland seemed to disa, pp.ar almost completely on 56th day after the hypophysectomy. Upon the administration of sex hormone after the hypophysectomy, however. the epithelia of the follicle which has changed to flat from has partly returned to its functional cubicfrom and nuclei recovered as nearly as normal. These recovery were more remarkable in the female than in the male. The hypophysectomy kept causing a significant decrease in the weight of the adrenal gland in male and female rats during the period of observation (up to 56 days) as in the case of thyroid gland. The administration of sex hormone has on effect in this respect either. The hypophysectomy also caused a marked morphological change in the gland: zona fasciculata and zona reticularis were dicreased in size quichly after the hypophysectomy. The administraton of the sex hormone to the hypophysectomized rat resulted in clear distinction among the three layers of the adrenal cortex which otherwise very diffused. In the male, this phenomenum was more remarkable than in the female and the pattern of the cell arrangements and the thickening of each layer became similar to those of normal rats. The gonads of both sexes have also kept decreasing in the weight and degenerated in morpohology after the hypophysectomy. However, the degenerate follicle became enlarged after the administration of hexestrol in the female. Furthermore, the vacuoles found in interstitial cells of hypophysectomized rat disa, pp.ared after the administration of testosterone in the male and the formation of spermatocytes seemed to be recovered. Hypophysectomy also caused a gradual increase in the contents of total protein, non-protein nitrogen, total lipid, cholesterol and calcium in the blood plasma with time. The concentrations of sodium, potassium and chloride in the blood did not change after the hypophysectomy. Sex hormone caused practically no change in above tendency.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.50 no.1
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• pp.11-15
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• 2005

This experiment was conducted to investigate the changes of growth and maturity and to clarify the function of supernodulating characters, excessive nodules and high biological nitrogen fixation rate (BNF), on maturity in response to different planting time in supernodulating soybean mutants. Two supernodulating soybean mutants, Sakukei4 and SS2-2, and their parent cultivars, Enrei and Shinpaldalkong2, were planted on May 24 and June 15, 2004. The degrees of the shortening of growth days by the planting time delay were 18 to 22 days in four cultivar, and there were no significant differences among the cultivars. However, four cultivars showed the different maturity properties. Sakukei4, mutated from Enrei, showed later maturity than that of Enrei, and 882-2, mutated from Shinpaldalkong2, showed earlier maturity than that of Shinpaldalkong2. The plant and nodule dry weights at R6 stage of Sakukei4 showed the smallest decrement and those of SS2-2 was showed the largest decrement by the delay of planting time. The photosynthetic rates of Sakukei4 during the late reproductive growth period were slowly decreased, however those of SS2-2 were steeply decreased in two planting time treatments. Overall, the growth of Sakukei4 was decreased slowly, however the growth of SS2-2 was decreased sharply according to the delay of planting time. The percentage of seed yield of Sakukei4 in June planting plot compared with May planting plot at R8 stage was $92\%$, which was the lowest decreasing rate of yield among the cultivars, and in the case of SS2-2, it was in $76\%$, the highest one. These results indicated that the responses of supernodulating mutants by the delay of planting time were very similar to the wild types. This means supernodulating characters in supernodulating soybean mutants might not affect to the maturity property. Additionally, the maturity property could be considered as an important characteristics to decide or to select on the developments of supernodulating soybean mutants, which have a low productivity by an excessive nodules, especially.

• Korean Journal of Environmental Biology
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• v.17 no.3
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• pp.285-292
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• 1999

Di-(2-ethylhexyl) phthalate (DEHP) is a plasticizer known as one of endocrine disruptors. The present study was carried out to investigate the alterations of function and ultrastructure in rat testes after oral intubation of DEHP in dosages of 1g/kg/day, 2 g/kg/day or 3 g/kg/day in 0.5 ml of corn oil for 15 days. DEHP reduced the growth of body and testes, inhibited apermatogenesis and induced structural changes on various cell types of the rat testis. Leydig cells, Sertoli cells and the developing germ cells seemed to be impaired their differentiations in terms of the structural changes of cell organelles. The increase of heterochromatin in amount were common features in all 3 cell types. In addition, the Leydig cells were characterized by the swelling of smooth endoplasmic reticulum and perinuclear space, the increases in number and size of Iysosomes. The Sertoli cells became irregular in nuclear envelope and the number of Iysosomes and vacuoles seemed to be increased. There were some indications of necrosis of the germ cells, such as vacuolized nucleus and segregated nucleolus. And also, DEHP lowered the level of testosterone in experimental rat serum. DEHP suppressed apermatogenesis decreasing developing germ cells and these effects of DEHP on the rat testis were dose dependent. The detrimental effect of DEHP on apermatogenesis and ultrastructure of rat testes seems to be derived from the decreased level of testosterone by Leydig cells, followed by the abnomalities of Sertoli cells and the germ cells.

• Journal of the Korean Geotechnical Society
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• v.34 no.7
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• pp.5-15
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• 2018

The unconfined compressive strength (UCS) test through coring is widely used to determine the reinforcement effect of the ground with grouting. However, the UCS test through coring can disturb the ground, is expensive and takes a lot of time to prepare the specimen. In this study, the factors affecting UCS of microfine cement grouted sand are evaluated and an empirical equation of UCS of microfine grouted sand is suggested. It is observed that UCS increases linearly until 28 days, however, the increasing rate of strength decreases sharply after that 28 days. The W/C ratio is dominant factor influencing UCS and UCS increases exponentially with the decrease of water/cement (W/C) ratio. Also, UCS increases linearly with increasing the relative density ranging from 30% to 70% and with decreasing median particle size. However, in case of W/C ratio=1 and K6 ($D_{50}=0.47mm$), UCS is lower than that of K4 ($D_{50}=1.08mm$) and K5 ($D_{50}=0.80mm$) due to filtration effect. Based on the experimental results, the empirical equation of UCS of microfine cement grouted sand can be expressed as the function of median particle size ($D_{50}$), porosity (n) and W/C ratio.

• Journal of Dental Rehabilitation and Applied Science
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• v.28 no.2
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• pp.213-221
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• 2012

The purpose of this study was to evaluate the stability of external stain that long term attrition caused by tooth brushing affected the color variation of external stain of IPS e.max Press Porcelain. The specimen was made by IPS e.max Press LT ingots, and treated the shade of external staning as Orange, A, B, C, D After conducting horizontal toothbrush strokes about 11,000 / 22,000 / 44,000 / 66,000 / 88,000, Color changers of the external stained layer was measured with SpectroShade$^{tm}$ MICRO(MHT, Italy). The result of this study was obtained as follows: 1. After 11,000 strokes, the color changes of shade were greater in Orange shade than the other 4 shade groups. And even though toothbrush strokes were increased until 88,000, there were no statistical significant color changes about the external stain shade variation. 2. The amount of color variation about increasing of toothbrushing strokes was irregular(no consistent increasing, or decreasing), and it was no statistical significant changes According to these results, the long term tooth-brushing doesn't affect the changes of external stain about IPS e.max press porcelain. And it doesn't reduce the stability of external stain clinically. Later, it will be needed to study other factors affecting the external stain.

• Journal of Dental Rehabilitation and Applied Science
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• v.28 no.2
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• pp.109-118
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• 2012

This experimental study was undertaken to evaluate the efficacy of polyvinylpyrrolidone-sodium hyaluronate(Aloclair$^{TM}$) in decreasing pain in orthodontic procedures. A total of 60 patients who were use Aloclair$^{TM}$ ordered to were included. These patients were categorized by 3 cases; 1. Patients who were bonded with their first brackets. 2. Patients who were in pain with additional appliance such as anchorage devices. 3. Patients who got ulcer caused by appliances. We collected information about pain and assessed it using visual analogue scale. According to questionnaire, it took 3.5 min. for pain to subside and pair relief durated for 2.7 hours. Most patients in the study reported rapid pain relief and found Aloclair$^{TM}$ easy and pleasant to use than wax. Accordingly Aloclair$^{TM}$ provided raid relief of resting and provoked ulcer pain.

• Journal of Dental Rehabilitation and Applied Science
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• v.25 no.1
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• pp.31-40
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• 2009

The rheologic properties of elastic impression materials is a very important role as taking high accuracy impression. But, the studies that are focused on the rheologic properties of Korean elastic impression materials are not sufficient. The purpose of this study is to help clinical high accuracy impression taking by testing rheologic properties of elastic impression material that is made by Korea and other countries. Six type III elastic impression materials are tested. Subjects are 2 Korean polyvinylsiloxane(PVS), 2 imported PVS, 1 polyether, and 1 polysulfide. HAAKE RheoStress $1^{(R)}$(Thermo Electron Co. Germany)is used in measuring. HAAKE RheoStress $1^{(R)}$ is plate to plate type rheometer. All subjects is tested 3 times and measuring time is 900 seconds. We measured G′ and loss tangent after mixing. All elastic impression materials had a sigmoid shape on increasing G′ by time and decreasing loss tangent after setting, maximum G' is appeared highest in polyether, and lowest in polysulfide. Initial loss tangent is highest in polyether, and is lowest in Koreans PVS. Significant difference is showed in initial loss tangent between Korean PVS and imported PVS.