• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.4
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• pp.317-326
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• 2022

This research performed single fiber pull-out test to evaluate the effect between fineness modulus of cement composites and the fiber bond performance (bond strength and pull-out energy). A synthetic fiber (polypropylene) and a steel fiber (hooked ends type) were inserted in the middle of dog bone shape specimens which were designed with fine aggregates of F. M. 1.96, 2.69, 3.43. The experiment results showed bond strength and pullout energy of synthetic fiber are improved as fineness modulus of cement composites increases. It is considered that the frictional resistance between synthetic fiber and cement composite increases as fineness modulus of cement composite increases and consume more energy while pull out the fiber from cement composite. However bond performance of steel fiber which resist pull out by mechanical behavior is less effected on fineness modulus of cement composite. It is considered that the mechanical fixedness of hooked ends exerts a greater effect on the pullout resistance than the frictional resistance between the cement composite and the steel fiber so F. M. of fine aggregate has a relatively small effect on the pullout resistance with the steel fiber.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.10
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• pp.4717-4724
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• 2012

This study is to examine the relation between Korean fermented food and discoloration on teeth, which have undergone profession tooth whitening. The color change of natural tooth, which has undergone professional tooth whitening, is objectively measured by dental colorimeter after being immersed in Korean fermented food for certain period. The tooth specimens used in this study are 30 pieces and measured 30 times per one tooth, 900 times totally by dental colorimeter ShadeEye NCC$^{(R)}$ Dental Chroma Meter. As a result of analyzing the collected data by using PASW(statistical package) 18.0, the significant difference is found (p<0.001) in lightness and yellowness before and after of professional tooth whitening. The lightness and yellowness after immersion is changed (p<0.001) according to time. As a result of examining the degree of discoloration based on type of fluids, the similar difference is indicated (p=0.001, p<0.001 1,2 and 3 weeks after getting professional tooth whitening. As a result, Korean traditional fermented food influences on discoloration on bleached tooth depended on the duration of immersion and the type of fluids. However, this study failed to represent internal oral condition accurately therefore the results of this study could be altered by the internal oral condition, frequency of consumption of food, and the management oral hygiene.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.389-398
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• 2013

Studies of the thermal properties of various rock types obtained from several locations in Korea have revealed significant differences in thermal conductivities in the thermal response test (TRT), which has been applied to the design of a ground-source heat pump system. In the present study, we aimed to compare the thermal conductivities of the samples with those obtained by TRT. The thermal conductivities of soil and rock samples were 1.32W/m-K and 2.88 W/m-K, respectively. In comparison, the measured TRT value for thermal conductivity was 3.13W/m-K, which is 10% higher than that of the rock samples. We consider that this difference may be due to groundwater flow because abundant groundwater is present in the study area and has a hydraulic conductivity of 0.01. It is natural to consider that the object of TRT is to calculate the original thermal conductivity of the ground, following the line source theory. Therefore, we conclude that the TRT applied to a domestic standing column type well is not suitable for a line source theory. To solve these problems, values of thermal conductivity measured directly from samples should be used in the design of ground-source heat pump systems.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.803-809
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• 2005

The purpose of this study is to investigate the mechanical characteristics of plain and steel fiber high strength concrete under uniaxial and biaxial loading condition. A number of plain and steel fiber high strength concrete cubes having 28 days compression strength of 82.7MPa(12,000 psi) were made and tested. Four principal compression stress ratios ($\sigma_2/\sigma_1$=0.00, 050, 0.75 and 1.00), and four fiber concentrations($V_f$ =0.0, 0.5, 1.0 and $1.5\%$) were selected as major test variables. From test results, it is shown that confinement stress in minor stress direction has pronounced effect on the strength and deformational behavior. Both of the stiffness and ultimate strength of the plain and fiber high strength concrete Increased. The maximum increase of ultimate strength occurred at biaxial stress ratio of 0.5($\sigma_2/\sigma_1=0.5$) in the plain high strength concrete and the value were recorded $30\%$ over than the strength under uniaxial condition. The failure modes of plain high strength concrete under uniaxial compression were shown as splitting type of failure but steel fiber concrete specimens under biaxial condition showed shear type failure. The values of elastic modulus were also examined higher than that from ACI and CEB expression under biaxial compression condition.

• Pediatric Infection and Vaccine
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• v.7 no.1
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• pp.108-112
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• 2000

Purpose : Acute diarrhea in one of the most important diseases in children with high morbidity and mortality worldwide. Most of acute diarrhea is induced by viruses. Rotavirus and adenovirus are leading causes of severe gastroenteritis among infants and young children worldwide. Studies for adenovirus gastroenteritis in Korea are limited. We studied the prevalence of rotavirus and adenovirus gastroenteritis from March 1998 to June 1999 in Chungju area. Methods : Stool samples were collected from 143 children with acute diarrhea. Specimens were tested for group A rotavirus antigen and for adenovirus type 40 and 41 by using available commercial kits. Results : Among 143 samples, 37% were positive for rotavirus and 16% were positive for adenovirus. Rotavirus was most prevalent from January to March, 1999 and adenovirus was prevalent during September 1999. The greatest number of rotavirus infections occurred under 24 months of age, followed by 2~4 years of age. Adenovirus was most common in 2~24 months of age. Conclusion : Rotavirus was most prevalent in winter and early spring. In our study, rotavirus was prevalent in early spring and adenovirus was in autumn.

• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.721-728
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• 2006

Earthquakes are reported thai building structures have been colossal damaged, but before 1988 designed structures which were not applicate seismic design code have no seismic performance. Especially, for the apartment structures were indicated that it have no resist wall element of earthquake before 1988 designed structures. We have to evaluate for seismic performance this structures, therefore it will be retrofitted for seismic index sufficient structures. We performed seismic performance evaluation for model structures by MIDAS which is general structure analysis software. In this study, it was performed shaking table test to evaluate model structure which is reinforcement concrete and 5 floors for seismic performance index. We made specimens by similar's law and tested shaking table test. In the shaking table test it is not performed prototype model test because of space and equipment condition. So we had made scale-down model for 1/5 by similar's law. That's why it needs for the evaluation of performance. However, it is not possible to do an experiment of prototype owing to the shortage of space and the limit of an experimental instrument in the shaking table test. Then, modeling and reducing the part of prototype do the experiment. In this experiment a shaking table test is done and seismic performance of model structures is evaluated by using similitude laws for scale down specimen. As a result it is proved that non-seismic design structures need to retrofit since seismic performance shows life safe grade in 0.12g of an earthquake.

• Journal of Korean Society of Steel Construction
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• v.29 no.5
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• pp.389-400
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• 2017

Based on U-shaped composite beam, the new form of AU-composite beam were developed to create economical and efficient components reducing the cost and shortening the length of construction work. Because the U-shaped sections are open and needs to be fixed by topping concrete securely. Therefore, it is required to maintain the U-shaped sections in a structure and to work in the safe condition through construction. It also requires accessories that resist the horizontal shear force for synthesis between the top and bottom of the U-shaped section. To reinforce these shortcomings, a shear connector has been developed with various purposes of steel plate anchors. In this study, the steel plate anchors were directly tested and the shear force was evaluated by the horizontal shear force. The experiment was divided into two types, depending on the applicable deck plates. As a result of the experiment, the continuous type specimens showed greater resistance in both strength and displacement than the ones of stud anchor specimen. In discontinuous type case, due to shear simulations and simple element analysis, the less increase the ratio of width to height and the more shear strength decreased. Thus, the shear strength equation of the stud anchor was modified to suggest the new shear strength based on the testing results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.129-136
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• 2012

Temperature of fresh concrete can be effectively used to predict the strength of concrete being cured and make an informed decision for stripping the molds. A hygrothermograph and thermo-couple sensors that require an extensive wiring have been applied to measure a temperature of concrete at the early stage of the curing process on site. However, these methods have limits to provide the temperature data in real time due to harsh working environment including frequent cutting of wires. Therefore, this study is aiming at developing a device based on wireless sensor network to measure the temperature of concrete being cured in formwork. The result showed that the wireless sensor with probe type thermistor which is developed had the same temperature data compared to the existed wire type thermistor, and we confirmed the temperature history of concrete in real time for 28 days throughout the gateway by wireless network that collects the temperature data measured from specimens in laboratory. Also, the network device for transmission can be easily separated from the probe sensor part and reused consistently. If the wireless sensor network device developed uses in the field, the temperature management of concrete will be systematically conducted from at the early stage of the curing, and especially be effective for cold weather concrete construction. In addition, it will contribute to the establishment of advanced quality control system for concrete and productivity of supervisors on site will be increased in the future.

• Proceedings of the KOR-BRONCHOESO Conference
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• 1983.05a
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• pp.19.2-19
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• 1983

A Clinical and bacteriologcal observation was performed 128 cases of chronic otitis media who had taken middle ear surgery at Dept. of otolaryngology of St. Benedict Hospital during the period of Feb. 1981 to Feb. 1983. The following results were obtained. 1) Among total 128 cases, male were 60 cases (46.9%) and female were 68 cases (53.1 %) and age distribution showed 48 cases (37.5 %) in 3rd decade, 37 cases (28.9 %) in 2nd decade and 27 cases (21.1 %) in 4th decade. 2) Site distribution were 71 cases (55.5%) in right, 57 cases (44.5 %) in left. 3) Degree of preoperative hearing loss were 64 cases (50%) in moderate, 32 cases (25% ) in mild, 27 cases (21.1 %) in severe and 5 cases (3.9%) were normal. 4) Central perforation were observed in 65 cases (50.8 %), total perforation in 44 cases (34.4 %), attic perforation in 12 cases (9.4 %) and marginal perforation in 7 cases (5.4 %). 5) Pathologic changes of middle ear and mastoid antrum showed granulation in 81 cases (63.3 %), cholesteatoma in 47 cases (36.7%). 6) The route of approach were 123 cases (96.1%) in postauricular, 3 cases (2.3%) in transmeatal and 2 cases (1.6 %) in endaural. 7) Type of operation were 53 cases (41.4 %) in intact canal wall tympanoplasty with mastoidectomy, 42 cases (32.8 %) in tympanoplasty without mastoidectomy, 23 cases (18%) in modified radical mastoidectomy and 10 cases (7.8%) in radical mastoidectomy. 8) Type of anesthesia were 95 cases (74.2 %) by local anesthesia, 33 cases (25.8 %) were by general anesthesia. 9) Among 93 specimens of culture, proteus (31.2%), staphylococcus (28.7%), pseudomonas (23.7 %), streptococcus (7.5 %) and etc. (8.7%) in order of frequency.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.28-36
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• 2021

It is known that buried rebars inside concrete structures are protected from corrosion due to passive layer. It is very important to delay the timing of corrosion or evaluate a detection of corrosion initiation for the purpose of cost-beneficiary service life of a structure. In this study, corrosion monitoring was performed on concrete specimens considering 3 levels of cover depth(60 mm, 45 mm, and 30 mm), W/C(water to cement) ratio(40.0%, 50.0%, and 60.0%) and chloride concentration(0.0%, 3.5%, and 7.0%). OCP(Open Circuit Potential) was measured using agar-based socket type sensors. The OCP measurement showed the consistent behavior where the potential was reduced in wet conditions and it was partially recovered in dry conditions. In the case of 30 mm of cover depth for most W/C ratio cases, the lowest OCP value was measured and rapid OCP recovery was evaluated in increasing cover depth from 30 mm to 45 mm, since cover depth was an effective protection against chloride ion ingress. As the chloride concentration increased, the effect on the cover depth tended to be more dominant than the that of W/C ratio. After additional monitoring and physical evaluation of chloride concentration after specimen dismantling, the proposed system can be improved with increasing reliability of the corrosion monitoring.