• Journal of the Korean GEO-environmental Society
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• v.8 no.5
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• pp.57-65
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• 2007

Slope collapse occurs mostly at the rainy season or thawing season in Korea. From a engineer point of view, the design criterion in recent of soil slopes during the rainfall have a conservative tendency because a slope stability is evaluated in the condition that ground water level is located in the surface. However, for the rational design of soil slopes during rainfall, the raining conditions and the unsaturated soil characteristics of soil slopes have to be considered. For the unsaturated soil characteristics of soil slopes, the laboratory tests for unsaturated soils and the seepage analyses for the raining conditions have to be performed. Due to these difficulties, a conservative design of soil slopes in the current design criterion has been carried out. In this paper, therefore, a simple design method is proposed. The method is considered to the unsaturated soil characteristics and the results of seepage analysis without numerical analysis. To verify the suggested design method, it is compared with both analysis results by current design criterion and analysis results based on the seepage analysis. Through the comparative study, it was found that the current design criterion has been excessively conservative. Hence, simple design method in this study was evaluated as the rational design for the soil slopes during rainfall.

• Journal of the Korean Chemical Society
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• v.54 no.2
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• pp.248-256
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• 2010

This study investigated the effects of the level of enrichment for analogies upon students' mapping, conceptual understanding, and the types of mapping errors in concept learning about Boyle's Law. Analogical reasoning ability test was administered and the score was used as a blocking variable. Three types (simple, enriched, and extended analogies) of learning materials according to the level of enrichment for analogies were studied by randomly assigned middle school students, and a conceptions test and a mapping test were administered immediately. The retention tests of both were administered four weeks later. Analyses of the results revealed that there was no main effect in the level of enrichment for analogies, but there was interaction effect with analogical reasoning ability in the post test on mapping. And the score of enriched analogy group was significantly higher than those of simple analogy group, but the score differences among three groups were not significant in the retention test on conceptual understanding. The frequency of the total mapping errors in the simple analogy group was the highest, and the frequencies of most types of mapping errors in the enriched and the extended analogy groups were less than those in the simple analogy group. There were also some differences in the frequencies of mapping errors with respect to the level of analogical reasoning ability. Therefore, these results will help science teachers plan and practice instructions using analogy.

• Journal of the Korean GEO-environmental Society
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• v.8 no.4
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• pp.57-65
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• 2007

Earthquake is one of the factors to affect the stability of geotechnical structures. Numerous past earthquakes have shown that earthquakes have taught that damage of soil structures could occur on fine soils as well as coarse soils. For that reason, earthquake-induced decreasing tendency for strength on both coarse and fine soils has been investigated using direct simple shear (DSS) tests in laboratory. Based on the testing results the decreasing tendency for strength on coarse and fine soils is clearly identified in terms of the concept of volume decrease potential and plasticity index, respectively. Most of the soils except the weathered soil have shown similar reduction tendency of strength with the increasing number of cycles. Liquefaction strength of coarse and fine soils appears to decrease with the increment of volume decrease potential and the decrement of plasticity index, respectively. Reduction of strength on the weathered soil is particularly remarkable rather than others, which might be owing to the collapse phenomenon. From the DSS test results for soils, proposed is a simple method to evaluate strength decrement with the increasing number of cycles, and it can help estimate decrement of strength with the number of cycles easily.

• Computers and Concrete
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• v.22 no.3
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• pp.337-353
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• 2018

The present study focuses on examining the structural behaviour of steel-fibre-reinforced concrete (SFRC) beams under high rates of loading largely associated with impact problems. Fibres are added to the concrete mix to enhance ductility and energy absorption, which is important for impact-resistant design. A simple, yet practical non-linear finite-element analysis (NLFEA) model was used in the present study. Experimental static and impact tests were also carried out on beams spanning 1.3 meter with weights dropped from heights of 1.5 m and 2.5 m, respectively. The numerical model realistically describes the fully-brittle tensile behaviour of plain concrete as well as the contribution of steel fibres to the post-cracking response (the latter was allowed for by conveniently adjusting the constitutive relations for plain concrete, mainly in uniaxial tension). Suitable material relations (describing compression, tension and shear) were selected for SFRC and incorporated into ABAQUS software Brittle Cracking concrete model. A more complex model (i.e., the Damaged Plasticity concrete model in ABAQUS) was also considered and it was found that the seemingly simple (but fundamental) Brittle Cracking model yielded reliable results. Published data obtained from drop-weight experimental tests on RC and SFRC beams indicates that there is an increase in the maximum load recorded (compared to the corresponding static one) and a reduction in the portion of the beam span reacting to the impact load. However, there is considerable scatter and the specimens were often tested to complete destruction and thus yielding post-failure characteristics of little design value and making it difficult to pinpoint the actual load-carrying capacity and identify the associated true ultimate limit state (ULS). To address this, dynamic NLFEA was employed and the impact load applied was reduced gradually and applied in pulses to pinpoint the actual failure point. Different case studies were considered covering impact loading responses at both the material and structural levels as well as comparisons between RC and SFRC specimens. Steel fibres were found to increase the load-carrying capacity and deformability by offering better control over the cracking process concrete undergoes and allowing the impact energy to be absorbed more effectively compared to conventional RC members. This is useful for impact-resistant design of SFRC beams.

• Journal of the Korean Geotechnical Society
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• v.34 no.9
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• pp.5-17
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• 2018

A magnitude 5.4 earthquake struck the city of Pohang, North Gyeongsang Province, South Korea on November 15, 2017. Many sand volcanoes were observed on paddy fields, parks and roads. This phenomenon was the first to be observed as a sign of soil liquefaction in South Korea. In this study, two different kinds of ejected Pohang sands were collected from a liquefied paddy field. Those sands were reconstituted into loose and dense conditions and then a series of cyclic simple shear tests were conducted under confining stresses of 100 and 200 kPa. A real earthquake motion was also repetitively applied to the specimen. As a result of constant shear stress tests, the cyclic resistance ratio (CRR) of loose sand was 0.12-0.14, while the CRR value of dense sand was 0.17-0.21. It was shown that the relative density was more influencing factor on liquefaction resistance than the sand types and initial confining stress. When a real Pohang earthquake motion was repetitively applied to the specimen, a loose sand was liquefied at the second earthquake motion but the dense sand at the third earthquake motion.

• Journal of Preventive Medicine and Public Health
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• v.36 no.2
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• pp.101-107
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• 2003

Objectives : Dementia has emerged as a leading public health problem in elderly persons, and its early detection is important for the treatment of curable cases, and in the educational support for other family members. Although dementia screening tests are available, they have not gained widespread use in community or primary care settings. Our goal was to validate the Tine and Change (T&C) Test, -including its validity and reliability in patients, and to assess it as a simple, standardized method for the screening of dementia in the rural elderly. Methods : The participants in this study comprised of 59 patients from an urban hospital and 405 persons from a rural community aged 65 years or older. The time test evaluated the understanding of clock hands indicating 11:10, and the change test the ability to make 1,000 Won from a group of coins, consisting of one 500, seven 100, and seven 50 Won coins. The T&C ratings were validated against a reference standard based on the physician's diagnosis of the patients. The convergent validity in relation to other cognitive measure, test-retest agreement, and inter-observer reliability were assessed. To assess the relationship between the Korean Mini-Mental State Exam (K-MMSE) and the T&C Test, the mean K-MMSE scores were compared with the results of the T&C Test in the elderly from a rural community. Results The T&C Test had a sensitivity and specificity of 73.0, and 90.9%, and positive and negative predictive values of 93.1, and 66.7%, respectively. The test-retest and inter-observer agreement rates were both 95%. The K-MMSE scores and T&C Test were significantly related in the elderly from a rural community (p<0.01), The T&C Test was not influenced by the educational status. The Time and Change Tests took a mean of 6.3 and 12.7 seconds, respectively, to complete Conclusion : The T&C Test is a simple, accurate and reliable, performance-based tool in the screening for dementia. Because it is quick, and easy-to-use, it is hoped the T&C Test will be used for the widespread cognitive screening of aging populations.

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.466-472
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• 2013

The use of a concrete track is gradually growing in urban and high-speed railways in many part of the world. The resilient pad, which is essentially when concrete tracks are used, plays the important role of relieving the impact caused by train loads. The simple fatigue test[1] to estimate the variable stiffness of resilient pads is usually performed, but it differs depending on the practical conditions of different railways. In this study, the static stiffness levels of used resilient pads according to passing tonnages levels were measured in laboratory tests. Also, the simple fatigue test and the multi-stress accelerated degradation test for new resilient pads were performed in a laboratory. The static stiffness of the used pad was compared with the results of tests of usage times and cycles. The results of the comparison showed that the variable static stiffness levels of the used pad were similar to results of the multi-stress accelerated degradation test considering the fatigue and heat load. With a T-NT equation related to the degree of the multi-stress accelerated degradation, a model of multi-stress accelerated degradation for a resilient pad was devised. It was found through this effort that the total acceleration factor was approximately 2.62. Finally, this study proposes an equation for a multi-stress accelerated degradation model for polyurethane resilient pads.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.89-96
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• 2011

In this study, increasing the range of replacement rate of FA with concrete properties were analyzed to provide basic data of FA replacement 0-40 % and curing temperature $5-35^{\circ}C$ range. As a result of the increased fluidity in proportion to the increase in FA, but decreased air. Setting time delayed at replacement rate increases and low temperature, simple insulation temperature history of the FA up to 40 % replacement rate increases the maximum temperature was low $8^{\circ}C$, the highest temperature reaching time delay of 13 hours. FA replacement up stream of the curing temperature, compressive strength compared to the higher plane, it was found that improved strength development. In carbonation tests with increasing the replacement ratio of FA carbonation depth was increased. Therefore, continued research on carbonation measures was to be necessary.

• Asian-Australasian Journal of Animal Sciences
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• v.21 no.4
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• pp.494-498
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• 2008

MTT (3-(4, 5-dimethyl thiazol-2-yl)-2, 5-diphenyl tetrazolium bromide) reduction assay is a method that validates the viability of an active cell. Dehydrogenase in mitochondria converts yellow colored insoluble tetrazolium salt to purple colored water-soluble formazan. Sperm also have mitochondria in the midpiece, therefore sperm viability could be evaluated by MTT reduction assay. Several studies have already demonstrated the capability of application of the MTT reduction assay to sperm of several species in Hepes-BSA buffer. Because most liquid semen was diluted in extender like BTS (Beltsville Thawing Solution), Modena or Androhep when it is used or transferred, semen needed another dilution in Hepes-BSA buffer to assess sperm viability. In this study, we evaluated boar sperm viability especially in BTS extended semen and compared the efficiency of this test with eosin-nigrosin staining. We used the fresh BTS extended semen from a local A.I center. Semen sample was diluted to $3.0{\times}10^7$ sperms/ml in BTS. The rates of formazan production were measured in 96-well microtiter plates immediately and 1h after incubation at $17^{\circ}C$ using a spectrophotometer at wave length 560 nm. Simultaneously, split samples of the same semen were tested, using eosin-nigrosin staining to compare the efficiency of the MTT assay of sperm viability in BTS. The correlation between the results of these tests was calculated using Student-t test and ANOVA. The results revealed a strong correlation between the results of MTT reduction rate and the results that were simultaneously determined by eosin-nigrosin staining at 1 h. In conclusion, the MTT reduction test was an effective and simple method to validate sperm viability and it could be used as a simple tool to evaluate sperm viability in the local A.I center and laboratory.

• International Journal of Fluid Machinery and Systems
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• v.4 no.3
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• pp.317-323
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• 2011

Mini centrifugal pumps having a diameter smaller than 100mm are employed in many fields; automobile radiator pump, ventricular assist pump, cooling pump for electric devices and so on. Further, the needs for mini centrifugal pumps would become larger with the increase of the application of it for electrical machines. It is desirable that the mini centrifugal pump design be as simple as possible as precise manufacturing is required. But the design method for the mini centrifugal pump is not established because the internal flow condition for these small-sized fluid machines is not clarified and conventional theory is not suitable for small-sized pumps. Therefore, we started research on the mini centrifugal pump for the purpose of development of high performance mini centrifugal pumps with simple structure. Three types of rotors with different outlet angles are prepared for an experiment. The performance tests are conducted with these rotors in order to investigate the effect of the outlet angle on performance and internal flow condition of mini centrifugal pumps. In addition to that, the blade thickness is changed because blockage effect in the mini centrifugal pump becomes relatively larger than that of conventional pumps. On the other hand, a three dimensional steady numerical flow analysis is conducted with the commercial code (ANSYS-Fluent) to investigate the internal flow condition. It is clarified from the experimental results that head of the mini centrifugal pump increases according to the increase of the blade outlet angle and the decrease of the blade thickness. In the present paper, the performance of the mini centrifugal pump is shown and the internal flow condition is clarified with the results of the experiment and the numerical flow analysis. Furthermore, the effects of the blade outlet angle and the blade thickness on the performance are investigated and the internal flow of each type of rotor is clarified by the numerical analysis results.