• The Korean Journal of Rheology
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• v.11 no.2
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• pp.82-90
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• 1999

Electrorheological(ER) fluid is a material that shows the dramatic change of rheological properties under an electric field and responds reversibly in a few milliseconds. ER fluid's response to an electric field along with its fast switching capability allows ER devices to be precisely controlled. The real application with ER fluid, however, has many limitations to be overcome; temperature fluctuation, moisture, dust, aggregation, precipitation, and low yield stress, for example. The magnitude and the characteristics of yield stress of ER fluid plays an important role in practical applications. In this research, a dynamic simulation on the squeezing flow of the ER fluid was carried out. Numerical simulation on isolated chains was performed to find out the effect of hydrodynamic and electrostatic force depending on the chain location, the squeezing rate, and the chain structure. Suspension model that is composed of a large number of particles was also investigated. The increase of normal stresses as well as the existence of a yield stress at an earlier stage could be observed, and the effective control of the normal stresses could be achieved at an optimal condition of the hydrodynamic force and the electrostatic force.

• The Journal of the Acoustical Society of Korea
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• v.35 no.3
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• pp.175-182
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• 2016

For application to several MHz photoacoustic imaging systems, a needle hydrophone was designed and fabricated by using PMN-PZT piezoelectric single crystal, and its characteristics were evaluated through comparison with a commercial PVDF(Polybinylidene Fluoride) hydrophone of which receiving sensitivity is known. The simulation using the KLM model results show that the peak receiving impulse response for $50{\Omega}$ terminating impedance of the fabricated hydrophone is -261.6 dB re $1V/{\mu}Pa$ and the frequency response is relatively flat over 2 ~ 12 MHz with fluctuation less than 5 dB. The measurement results using tone burst signals also show that it has higher (ave. 10.9 dB) sensitivity than the commercial hydrophone in 2 ~ 8 MHz, and the receiving sensitivity of $-255.8{\pm}2.8$ dB re $1V/{\mu}Pa$ was measured for the fabricated hydrophone. In addition, it is known that the photoacoustic signals and the image of a hair obtained by a mechanical scanned photoacoustic imaging system with the fabricated hydrophone were bigger and better than those obtained with the commercial hydrophone.

• Environmental and Resource Economics Review
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• v.13 no.4
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• pp.593-619
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• 2004

This study analyzes the interfuel substitution of energy demand in Korean manufacturing sector using static and dynamic linear logit models. For the period of 1981~2002, this study uses petroleum, electricity, natural gas and coal as energy sources. According to the empirical results, firstly, the own-price elasticity of coal has been increased steadily even though its elasticity is smallest compared with those of other energy sources. On the other hand, price elasticity of natural gas is largest, but its value has been decreased after 1997. Price elasticities of petroleum and electricity are very stable over the sample period. One of the main features in trends of interfuel substitution is as follows. Substitution effect of a change in price of natural gas on both petroleum and coal has been increased especially after 1997. The implication of the empirical results is summarized as follows: First, the fact of inelastic own-price elasticity of petroleum implies that the dependency of Korean manufacturing sector on petroleum and coal will be persistent even in a sharp fluctuation of petroleum price. Second, the effects of price increase in natural gas on demand for petroleum and coal are very significant. Thus, price decline of natural gas rather than price declines of coal and petroleum could be more effective as an energy price policy for the reduction of $CO_2$ emission. The assessment on this implication will remain for future researches.

• Journal of the Korean GEO-environmental Society
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• v.13 no.1
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• pp.53-61
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• 2012

In this study, the research on MC anchor has been developed as composite type has done. MC anchor exerts bearing pressure on pre-bored hole where the end fixing device is expanded. Therefore, the uplift capacity is to be increased and it has the characteristics that the anchor body is not eliminated from the ground even if the grouting is not carried out properly. Furthermore, it reduces the loss of tension and raises the construction availability by inserting the reinforced bar as well as the anchor cable, while it can improve the long-term stability because the nail is expected to play the role when the loss of the anchor cable is occurred in a long-term. However, because the resistance mechanism of the compound anchor such as MC anchor is different from friction anchor, the estimation method of the uplift capacity by the frictional force of the ground and the grout is not proper. Particularly, in domestic cases, the problem to overestimate or underestimate the uplift capacity is expected because the design method considering the soil characteristics about the compound anchor has not been developed. Therefore, in this study, in order to evaluate the characteristics of MC anchor and a kind of compound anchor, we measured the uplift, the tension and the creep by nine anchors tests in shale ground that the fluctuation of the strength is great. In addition, we analyzed the test result comparing to the result of the general friction anchor and evaluated the characteristics of MC anchor movement to gather the results. As a result of the test, we found the effect that the uplift capacity is increased in shale ground comparing to the general friction anchor.

• The Journal of Engineering Geology
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• v.23 no.2
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• pp.105-115
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• 2013

Increasing the river cross-section by barrage construction causes rises in the average river water levels and discharge rates in the rainy season. The time series patterns for groundwater levels measured at 23 riverside monitoring wells along the lower Nakdong River are compared for two cases: before and after water-filling at the Changnyeong-Haman Barrage. Monthly average groundwater levels indicate a distinct increase in groundwater levels in the upstream riverside close to the barrage. River-water level management by barrage gate control in August, during the rainy season, resulted in a 0.1 m decrease in groundwater levels, while water-filling at the barrage in December caused a 1.3 m increase in groundwater levels. The results of hierarchical cluster analysis indicate that seven groundwater monitoring wells and river water levels were in the same group before barrage construction, but that this number increased to 14 after barrage construction. Principal component analysis revealed that the explanation power of two principal components corresponding to river fluctuation, PC1 and PC2, was approximately 82% before barrage construction but decreased to 45% after construction. This finding indicates that the effect of the river level component that contributes to change in groundwater level, decreases after barrage construction; consequently, other factors, including groundwater pumping, become more important. Continuous surveying and monitoring is essential for understanding change in the hydrological environment. Water policy that takes groundwater-surface water interaction into consideration should be established for riverside areas.

• Economic and Environmental Geology
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• v.51 no.5
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• pp.463-471
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• 2018

In this paper, we review previous studies on the relative sea-level changes in the Yellow Sea during the Holocene to comprehensive understand the various research results. Currently, it is reported two theories : 1) the Holocene sea-level has never been higher than the present-day level; and 2) sea-level have reached highstand during mid-Holocene, followed by slow lowering to that of the present. The first theory yields a curve that is similar to a climate-change-related eustatic sea-level curve. However, in reality, most of the relative sea-level fluctuation resulted from land uplift or subsidence. The second theory yields a curve that is fairly coincident with a relative sea-level curve indicative of continental margins being located away from the ice sheets(i.e., far-field), and is considered as an effect of GIA(Glacio Isostatic Adjustment) and gravitational attraction. Based on detailed review of previous researches, we realized that they sourced the same papers, but obtained different results because they selectively chose and added the data. The data used to derive the second theory pertain to the northern Gunsan region, which is located within the western area of the Chugaryeong fault. Thus, we believe that the sea-level curve for the second theory is only representative of the area north of Gunsan, which is subject to GIA and tectonic deformation. Although the relative sea-level curve for the west coastal area is comparable to that for the far-field continental margin region, it is necessary to evaluate local tectonic activities as suggested by active seismicity in the west coastal area and the more than 400 faults currently existing in on the Korean Peninsula.

• The Korean Journal of Mycology
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• v.13 no.4
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• pp.195-201
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• 1985

Numbers of total bacteria and fungal propagules were highly populated in the soil of diseased plot in Gumsan, whereas numbers of actinomycetes were high in the soil of healthy plot in Goesan. In microbial fluctuation of different soil conditions four weeks after amended with various plant materials, bacteria were decreased in the soil amended with various plant materials as compared with non-amended soil except for Goesan. On the contrary, numbers of fungal propagules were increased amended with onion and potato stalk in two soils at different conditions, and also the propagules were enhanced in the soil amended with various plant materials in general. Higher numbers of bacteria and fungal propagules were observed in the diseased replanted plot in general, but germination rate of fungal spores relatively reversed against the microbial population. Alternaria panax was not affected much in their germination by natural soil condition, while Fusarium spp. were affected in their germination by natural soil. Natural soil showed a fungistatic effect against four fungal spores.

• Journal of the Korean Academy of Child and Adolescent Psychiatry
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• v.6 no.1
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• pp.3-17
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• 1995

The so-called borderline children are characterised by disturbances in the sense of reality and interpersonal relationships, lack of control, fluctuation of functioning, uneven development and excessive anxiety. But the concept of borderline disorder of childhood is very difficult to define and diagnose in current classification system. The present study adapted the consensus symptoms in borderline children by Bemporad and Vera eight cases aged 7-11 were examined in 37 variables. Results are as follows 1) All subjects are boys and girl hardly be diagnosis n current diagnostic system and have many concurrent diagnoses. Common chief complaints in the sense of reality. 2) In KEDI-WISC test, the borderline children showed average intelligence, but performance IQ tends to be higher than verbal IQ. In Rorscharch test, they showed high thought disorder index, emotional instabilities and aggressive impulses. The results of TOVA suggested attentional deficit in half of the subjects. The organicity is not prominent. 3) Many of the borderline children were unwanted baby. Although primary care takers of all the subjects were their mothers there were moderate problems in caring attitude of their children and marital relationship with their husband. Sccioeconomic status was generally below middle class. Most of all subjects have delayed language development, but have overcome subsequently. Many subjects were rejected by peers because of their aggression. 4) The first visit of the subjects was about 6 years of age. Average duration of treatment was 2 years. All of them were treated in the outpatient basis except one. The effect of pharmacotherapy was doubtful and the necessity of long term play therapy was suggested. Although there were many limitations of method in present study, it was suggested that further research is needed for diagnostic criteria, epidemiology and treatment.

• The Korean Journal of Soil Zoology
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• v.5 no.2
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• pp.47-62
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• 2000

This study investigated the effect of soil animals at forest fire area, and it carried out the mountain located at Jundae Ri, Houeng-chen Myen, Ha-dong Gun, Kyoung-Nam Province, southern part of Korea, where burned out about 50 hectars on April 11, 1997. Vegetation of the examined area absolutely dominated with the pines of 7-14 cm in diameter and 20 to 30 years old and the rest were covered with mixed forest with a shrub such as the oak (Quereus mongolia Fisch, Quereus variabilis BI, Quereus dentana Thunb), snowbell(Styrax japonica, S, et, z), lacquer tree (Rhus trichocarpa Mig), azalea (Rhododendron mucronulatum Turcz), etc. And there were simple area organized as a herbaceous plant, and the burnt area was poor experimental sites, where litter layer and herbaceous plant disappeard due to fire, and the unburnt area was rich in surface plant, dead leaves, twigs, etc. But the ground cover vegetations were poor in the unburnt area. The distribution of each animal groups, the seasonal fluctuation in population density, the biomass of meso$.$macroarthropods and the relationship between soil animal and some environmental factors were investigated and analyzed at each experimental area. The result are summarized as follow: 1. Identificated 257,087 individuals of soil microarthropods were classified into 7 classes and 24 orders of Arachinida, Insecta, Chilopoda, Symphyla, Diplopoda, Isopoda and Oligochaeta., and identified 8,006 individuals of the total meso$.$macroarthropods were classified into 7 classes and 20 orders of Arachinida, Insecta, Chilopoda, Symphyla, Diplopoda, Isopoda and Oligochaeta. 2. Among the total soil microarthropods, Arachinida formed 70.9%, followed by Insecta for 28.4% and among the total meso$.$macroarthropod , Insecta formed 57.6%, followed by Chilopoda for 23.8%.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.5
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• pp.288-302
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• 2017

Accurate measurement of benthic nutrient fluxes (BNF) is a prerequisite for evaluating the effect of sediments on nutrient cycle in the surface water. The intact sediment cores were collected in July 2015 at the midstream of Nakdong River. We identified pre-incubation time (6, 12, 24 hr), dissolved oxygen concentration (90, 70, 50% saturation), diffusive boundary layer thickness (0, 0.6-0.8, 1.2-1.4 mm), and incubation temperature (10, 17, 20, $25^{\circ}C$) as the most important control factors, and measured the BNF fluctuation with the variation of these factors using the laboratory sediment core incubation method. Since the chemical composition, redox condition, hydrodynamic regimes and microbial activities at the sediment-water interface were changed as a result of the alteration of control factors, sediment core incubation should be conducted under as close to the natural conditions of study site as possible, in order to produce the results similar to actual values. Relative percentage differences between two replicates were below 20% in most control factors, which showed satisfactory precision for strict compliance with the experimental conditions and procedures. In the further studies, we will compare the results of core incubation with those of in situ measurements to confirm the accuracy of the sediment core incubation method.