• Journal of Korea Foundry Society
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• v.14 no.3
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• pp.240-247
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• 1994

TiC particulate reinforced magnesium matrix composites were fabricated by melt stirring method. The effect of alloying elements on TiC particulate dispersion into molten magnesium and mechanical properties were investigated. The incorporation time is defined as the time required for dispersion of solid particles into molten metal. The incorporation time of TiC particles into molten pure magnesium was remarkably shorter and the particulated dispersion was more uniform than that of pure aluminum which was reported previously. The incorporation time was, prolonged by the addition of Al, Bi, Ca, Ce, Pb, Sn or Zn. The tensile strength increased and elongation decreased by the addition of Cu or Sn into the matrices and composites. Although, the tensile strength of the matrices and composites increased by alloying with Ca or Ce, the maximum elongation was observed at a content of about 1% for the matrices. By alloying with Zn, the tensile strength increased for the matrices and composites, but the elongation of the matrices increased. The pure magnesium and its alloy matrix composites reinforced with 20vol% TiC have the tensile strength of about 400MPa. This value is compared with the tensile strength of SiC whisker reinforced magnesium matrix composites fabricated by liquid infiltration method at the same volume fraction. There fore, the melt strirring method which has the advantages of simple process is considered to be efficient in fabricating magnesium matrix composites.

• Journal of Soil and Groundwater Environment
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• v.25 no.3
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• pp.43-51
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• 2020

About 90% of groundwater wells in Jeju Island are reported to be under the threat of contamination by infiltration of the surface pollutants. Most of those wells have improperly grouted annulus which is an empty space between the well and the inner casing. As a remedy to this problem, some of the wells were re-grouted by filling the annulus with cement without lifting an inner casing. In order to evaluate whether this method is appropriate for the geological structure of Jeju Island, two wells (W1 and W2) were selected and this method was applied. The water holding capacity did not decrease while the nitrate levels decreased from 16.8 and 20.2 to 6.8 and 13.8 mg/L in W1 and W2, respectively. The higher nitrate level in W2 is deemed to be influenced by the livestock farms located in the upper area of the well. In addition, transmissivity of the vedose zone was higher in W2 than W1, potentially facilitating the transport of nitrate to the groundwater. The overall result of this study suggests re-grouting of wells for the purpose of protecting water quality of goundwater should take into account geological structure of vadose zone as well as appropriate source control of the contaminants.

• Journal of Korean Society on Water Environment
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• v.26 no.3
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• pp.432-438
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• 2010

LIDMOD2 was developed for evaluation of low impact development (LID) and best management practice (BMP) by modification of Site Evaluation Tool (SET). The modification includes employment of SCS-CN method for annual runoff simulation, unit load method for annual pollutant loads simulation, and the method proposed by Korean TMDL for calculating pollutant reduction by BMPs. The CN values were updated with regionalized parameters within Nack-Dong River basin because these are important parameters for simulating hydrology. LIDMOD2 was tested by applying to Andong Bus terminal. As a simulation results, pollutant loads and surface runoff will be significantly increased by post-development without LID compared with those from pre-development. LID technique was simulated to efficiently reduce surface runoff and pollutant load and increase infiltration. LIDMOD2 is screening level tool and easy to use because LIDMOD2 is based on spread sheet and most of parameters are regionalized. LIDMOD2 was illustrate that it could evaluate LID well by summarizing and graphing annual hydrology, annual pollutant loading, and hydrograph for event storm. The calculation methods related with pollutant loads are employed from the guideline of Korean TMDL and it can be useful tool for Korean TMDL to evaluate the effect of LID/BMP on developing area.

• Journal of Korea Water Resources Association
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• v.41 no.12
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• pp.1199-1210
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• 2008

The mean residence time is the time scale for intermediate status between infiltration and runoff and one of the critical factors for understanding runoff response, erosion, and eco-hydrological processes. This research explored a direct method to estimate the mean residence time over existing indirect, isotope tracer method. Spatial and temporal distributions of soil moisture have been monitored for a year with 2-hours monitoring interval. Mean residence time for soil moisture showed apparent increasing tendency to deeper depth and decreasing trend during summer periods, which had intensive rainfall events. The mean residence times obtained from this research showed similar trend to those obtained from other isotope methods, which means the direct method can be an efficient approach to obtain the mean residence time.

• Journal of Wetlands Research
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• v.7 no.3
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• pp.57-66
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• 2005

This paper is to present the determination of the optimal loss rate parameters and unit hydrographs from the observed single rainfall-runoff event using optimization model. The linear program models has been formulated to derive the optimal unit hydrographs and loss rate parameters for the site of the Su-Jik Bridge in the HwangGuJichen River; one minimizes the summation of the absolute residual between predicted and observed runoff ordinates. In the perturbation stage of parameters the trial and error method has been adopted to determine the loss rate parameters for Kostiakov's, Philip's, Horton's, and Green-Ampt's equation. The unique unit hydrograph ordinates for a given rainfall-runoff event is exclusively obtained with ${\Phi}$ index, but unit hydrograph ordinates depend upon the parameters for each loss rate equations. In this paper the single rainfall-runoff event observed from the sample watershed is considered to test the proposed method. The optimal unit hydrograph obtained by the optimization model has smaller deviations than the ones by the conventional method.

• Korean Journal of Metals and Materials
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• v.46 no.8
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• pp.538-544
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• 2008

MMCs were manufactured in two different forms. One was two-layered non FGM composite and the other was four-layered FGM composite. The matrix used in this study was AZ31 magnesium alloy and the reinforcement was $Al_{18}B_4O_{33}$. The composite materials contained reinforcement fibers with a volume fraction of 0, 15, 25 and 40%. Squeeze infiltration method was used for the fabrication of each block. The thermal properties of the FGM alloy and composite joints were studied by conducting thermal cycling tests. The numerical calculation (the finite elements method-FEM) results exhibited a good agreement with the experimental results. Thermal stresses induced by thermal cycling test were clearly reduced in the functionally graded materials.

• Journal of Dental Anesthesia and Pain Medicine
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• v.23 no.1
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• pp.1-8
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• 2023

Backgrounds: Pain management is one of the most important factors affecting the success of pediatric dentistry. Therefore, new needle- and pain-free local anesthesia techniques have been developed in parallel with technological advancements. The purpose of this study is to compare the pain perception and dental anxiety levels associated with a needle-free injection system (Comfort-in^TM) and the classic needle method during treatment-required infiltration anesthesia in children. Methods: This randomized controlled crossover split-mouth clinical study included 94 children who required dental treatment with local anesthesia using a dental needle or needle-free injection system for the bilateral primary molars. The Wong-Baker Scale (WBS) was used to measure pain perception at different times, and the Modified Child Dental Anxiety Scale (MCDAS) was used to measure the anxiety level of the child. A statistical software package was used to process the data. Statistical significance was set at P < 0.05. Results: There was no significant difference between the needle-free injection system and dental needle method during the induction stage for filling and pulpotomy (P > 0.05). "Pain on postoperative 1st day" was similar in both types of anesthesia (P = 0.750). Conclusions: The needle-free injection system was as effective as the dental needle method. The Comfort-in^TM system was an acceptable alternative for patients during the postoperative period. Understanding how pain management may be provided during local anesthesia administration and a child's fear and anxiety regarding the dentist may lead to better dental compliance.

• Journal of the Korean Geotechnical Society
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• v.23 no.6
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• pp.77-84
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• 2007

One of the most sensitive design specifications to be considered is infiltration and external pore-water pressures on underground structure construction. Development of pore-water pressure may accelerate leakage and consequently cause deterioration of the lining. In this paper, the development of pore-water pressure due to malfunctioning of drainage system and its potential effect on the linings are investigated using physical model tests. The deterioration procedure was simulated by controlling both permeability and flow rate. Development of pore-water pressure was monitored on the lining using pore pressure measurement cells. Test results identified the mechanism of pore-water pressure development on the tunnel lining. In addition, they showed that controlling flow rate is more effective method fur simulating deterioration procedure than permeability control. The laboratory model tests were reproduced using coupled numerical method, and showed that the effect of deterioration of drainage system can be theoretically expected using coupled numerical modeling method.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.22 no.1
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• pp.137-144
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• 1992

This study was performed to observe the effects of arthrography on the tissues of temporomandibular joint histopathologically. Among 17 rabbits (34 joints), 2 (4 joints) were used as normal control group, others (30 joints) were experimentally arthrographed using 0.03㎖ diatrizoate meglumine (Hypaque meglumine 60, Wintrop, U.S.A). The rabbits were sacrificed at 2-hour, 1-, 2-, 4- and 7-day after experiment and the tissues of temporomandibular joint were prepared according to the usual method for light microscopic examination. The results were as follows: 1. There were no changes of the fibrous connective tissues of the condylar fossa, the fibrous connective tissues and hyaline cartilages of the condyle, and the articular dislc 2. In 2-hour experimental group, the proliferation of the surface synovial membrane cells, the congestion and hemorrage of the vessels were observed. 3. In 1 and 2-day experimental group, minimal lymphocytes infiltration was observed with the proliferation of the surface synovial membrane cells, the congestion and hemorrage of the vessels. 4. In 4-day experimental group, the diminution of the proliferation of the surface synovial membrane cells was seen, but there was no vascular changes. 5. In 7-day experimental group, the tissues showed similar appearance to the normal control group.

• The Journal of Korean Medicine
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• v.23 no.3
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• pp.104-118
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• 2002

Objectives : To study the effects of Kumsooyukkun-jeon on asthma. Methods : Asthma was induced to Balb/c mice with ovalbumin using the method of Hatfield et al. We measured the histological profiles of lung and trachea, numbers of cellular compartments in the bronchoalveolar lavage fluid (BALF), numbers and morphology of the mast cells in the trachea, numbers of mucous-secretory cells in the bronchus, morphology of the bronchus, ultramicroscopical appearance of surface of trachea and number of cilia and mucous-secretory cells by scanning electron microscope. Results : 1. Hypertrophy of mucous membrane of trachea and bronchus and bronchioles in the lung, peritracheal, peribronchus and peribronchiolar inflammatory cell infiltration, and mucoid exudate deposition the lumen were observed in control groups but these phenomena were recovered in the Kumsooyukkun-jeon groups. 2. Cellular compartments including neutrophil and eosinophil were increased in the BALF of control groups but these phenomena were recovered in the Kumsooyukkun-jeon groups. 3. Degranulation and decrease of the numbers of mast cells were detected in the trachea of control groups. However, these phenomena were recovered in the Kumsooyukkun-jeon groups. 4. Shedding, decrease of cilia cell and increase of mucous-secretory cells in the surface of the trachea were measured in control groups but these phenomena were recovered in the Kumsooyukkun-jeon groups. Conclusions : It is considered that Kumsooyukkun-jeon has somewhat favorable effects on asthma.