• The Journal of Korean Academy of Prosthodontics
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• v.43 no.1
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• pp.61-77
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• 2005

Statement of problem. The implant prosthesis has been utilized in various clinical cases thanks to its increase in scientific effective application. The relevant implant therapy should have the high success rate in osseointegration, and the implant prosthesis should last for a long period of time without failure. Resorption of the peri-implant alveolar bone is the most frequent and serious problem in implant prosthesis. Excessive concentration of stress from the occlusal force and biopressure around the implant has been known to be the main cause of the bone destruction. Therefore, to decide the location and angulation of the implant is one of the major considering factors for the stress around the implant fixture to be dispersed in the limit of bio-capacity of load support for the successful and long-lasting clinical result. Yet, the detailed mechanism of this phenomenon is not well understood. To some extent, this is related to the paucity of basic science research. Purpose. The purpose of this study is to perform the stress analysis of the implant prosthesis in the partially edentulous mandible according to the different nature locations and angulations using three dimensional finite element method. Material and methods, Three 3.75mm standard implants were placed in the area of first and second bicuspids, and first molar in the mandible Thereafter, implant prostheses were fabricated using UCLA abutments. Five experimental groups were designed as follows : 1) straight placement of three implants, 2) 5$^{\circ}$ buccal and lingual angulation of straightly aligned three implants, 3) 10$^{\circ}$ buccal and lingual angulation of straightly aligned three implants. 4) lingual offset placement of three implants, and 5) buccal offset placement of three implants. Average occlusal force with a variation of perpendicular and 30$^{\circ}$ angulation was applied on the buccal cusp of each implant prosthesis, followed by the measurement of alteration and amount of stress on each configurational implant part and peri-implant bio-structures. The results of this study are extracted from the comparison between the distribution of Von mises stress and the maximum Von mises stress using three dimensional finite element stress analysis for each experimental group. Conclusion. The conclusions were as follows : 1. Providing angulations of the fixture did not help in stress dispersion in the restoration of partially edentulous mandible. 2. It is beneficial to place the fixture in a straight vertical direction, since bio-pressure in the peri-implant bone increases when the fixture is implanted in an angle. 3. It is important to select an appropriate prosthodontic material that prevents fractures, since the bio-pressure is concentrated on the prosthodontic structures when the fixture is implanted in an angle. 4. Offset placement of the fixtures is effective in stress dispersion in the restoration of partially edentulous mandible.

• Journal of Dental Rehabilitation and Applied Science
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• v.29 no.3
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• pp.259-271
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• 2013

The purpose of this study was to make the stress distribution produced by simulated different load under two types of internal connection implant system (stepped and tapered type) by means of 3D finite element analysis, The finite element model was designed with the parallel placement of the one fixtures ($4.0mm{\times}11.5mm$) with reverse buttress thread on the mandibular 1st molar. Two models were loaded with 200 N magnitude in the vertical direction on the central position of the crown, the 1.5 mm and 3 mm buccal offset point from the central position of the fixture. The oblique load was applied at the angle of $30^{\circ}$ on the crown surface. Von Mises stress value was recorded and compared in the fixture-bone interface in the bucco-lingual dimension. The results were as follows; 1. The loading conditions of two internal connection implant systems (stepped and tapered type) were the main factor affecting the equivalent bone strain, followed by the type of internal connections. 2. The stepped model had more mechanical stability with the reduced max. stress compared to $11^{\circ}$ tapered models under the distributed oblique loading. 3. The more the contact of implant-abutment interface to the inner wall of implant fixture, the less stress concentration was reduced.

• Geophysics and Geophysical Exploration
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• v.20 no.2
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• pp.88-95
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• 2017

Chogye basin, which is surrounded by country rock, has a closed-basin form. In such a basin, incident seismic energy can form multiply reflected waves, thus causing energy concentration to occur at this closed-basin area. Microtremor measurement survey was performed at the Chogye basin, which is located in Chogye-myeon and Jeokjungmyeon, Hapcheon-gun, Gyeongsangnam-do, Republic of Korea. Microtremor data were transformed into the frequency domain, and then the horizontal-to-vertical spectral ratios (HVSR) were calculated. Fundamental resonance frequencies were estimated from the HVSR results for every observation point. Using the empirical relationship between site period and thickness for sediment sites in Korea known from the previous study, the distribution of sediment thickness of the Chogye basin was estimated from the fundamental resonance frequencies. Being compared with the mountainous rim with steep slope, the measurement points inside the basin have low values of the fundamental resonance frequency with the minimum of 1.03 Hz, which corresponds to the thickness of sedimentary layer with the maximum depth of about 100 m. A three-dimensional basin model was constructed for bedrock topography of the Chogye basin by an interpolation of basin depths estimated at each measurement site.

• Journal of the Korean Solar Energy Society
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• v.34 no.1
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• pp.72-80
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• 2014

This study proposed a wind power generation system utilizing outdoor air on the rooftop and indoor ventilation, which would increase according to the building height, as a way to help to save energy consumption in a building by using wind power energy of the new renewable energy sources. The study measured the distribution of air currents and power generation according to the usage factor of exhaust pipes in the kitchen and bathroom and identified the elements to consider when applying a wind power generation system to buildings in order to use outdoor air on the rooftop increasing according to the height and the indoor ventilation produced in the facility vertical shafts inside the buildings by installing a wind power generation system on the rooftop. (1) The study measured the ventilation velocity of the kitchen hood and bathroom ventilation fan by changing the zone areas by the households according to the usage factor of [${\alpha}$]=33~100%. As a result, the kitchen ventilation pipe generated the ventilation wind of 3.0m/s or more at the usage factor of [${\alpha}$] 66% or higher, and the bathroom ventilation pipe generated ventilation velocity lower than 3.0m/s, the blade velocity of the wind power generator, even after the usage factor rose to [${\alpha}$]=100%. (2) As the old bathroom ventilation pipe generated the ventilation velocity of 3.0m/s, the blade velocity of the wind power generator, even with the rising usage factor [${\alpha}$], the application of an outdoor air induction module increased the ventilation velocity by 2.9m/s at the usage factor of [${\alpha}$]=33%, 3.8m/s at the usage factor of [${\alpha}$]=66%, and 3.6m/s at the usage factor of [${\alpha}$]=100%. Thus the ventilation velocity of 3.0m/s, the blade velocity of the wind power generator, or higher was secured. (3) The findings prove that the applicability of a wind power generation system using outdoor air on the rooftop and indoor ventilation is excellent, which raises a need for various efforts to increase the possibility of its commercialization such as securing its structural stability according to momentary gusts on the rooftop and typhoons in summer and making the structure light to react to the wind directions of outdoor air on the rooftop according to the seasons.

• Journal of Korea Water Resources Association
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• v.41 no.12
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• pp.1187-1198
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• 2008

Many reservoirs in Korea and their downstream environments are under increased pressure for water utilization and ecosystem management from longer discharge of turbid flood runoff compared to a natural river system. Turbidity($C_T$) is an indirect measurement of water 'cloudiness' and has been widely used as an important indicator of water quality and environmental "health". However, $C_T$ modeling studies have been rare due to lack of experimental data that are necessary for model validation. The objective of this study is to validate a coupled three-dimensional(3D) hydrodynamic and particle dynamics model (ELCOM-CAEDYM) for the simulation of turbid density flows in stratified Daecheong Reservoir using extensive field data. Three different groups of suspended solids (SS) classified by the particle size were used as model state variables, and their site-specific SS-$C_T$ relationships were used for the conversion between field measurements ($C_T$) and state variables (SS). The simulation results were validated by comparing vertical profiles of temperature and turbidity measured at monitoring stations of Haenam(R3) and Dam(R4) in 2004. The model showed good performance in reproducing the reservoir thermal structure and propagation of stream density flow, and the magnitude and distribution of turbidity in the reservoir were consistent with the field data. The 3D model and turbidity modeling framework suggested in this study can be used as a supportive tool for the best management of turbidity flow in other reservoirs that have similar turbidity problems.

• Korean Journal of Microbiology
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• v.30 no.5
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• pp.383-390
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• 1992

In the periods of July 31 to August 10. 1988 and March 9 to 13. 1989. sediment samples were collected from the South Sea stations (010] to 092]) located in the area from $N 32^{\circ}$/30' to $34^{\circ}$/30', of latitude and from E $123^{\circ}$ 30' to $128^{\circ}$30' of longitude. These samples were analyzed for the number of total heterotrophic bacteria and extracellular digesting enzyme activities. In the 1989 spring period the number of heterotrophic bacteria in the sediment surface layer was increased more than 100 times at the maximum compared to that in the 1988 summer period. The proportion of fresh water bacteria to total heterotrophic bacteria was also higher in the spring period than the summer period. The extracellular digesting enzyme activities were higher in spring season than summer. Although the water content of sediment in the spring period was lower than that the summer period. the ash weight indicating organic material content was higher. These results means that the diameters of sediment particles were larger in spring than summer but the input of organic material into the sediment was greater. Based on these results bacterial distributions in the sediment layer of South Sea depend greatly on the season due to the effect of fresh water. During the spring season plankton could grow extensively owing to the inorganic nutrients input by the vertical mixing in the water column, then be precipitated into the sediment. Organic nutrients supplied from enzymatic degradation of polymeric particle from plankton can increase the bacterial number, too.

• Geophysics and Geophysical Exploration
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• v.4 no.2
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• pp.25-33
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• 2001

Loop-loop electromagnetic (EM) survey in frequency domain has been carried out in order to provide basic solution to geotechnical applications. Source and receiver configuration may be horizontal co-planar (HCP) and/or vertical co-planar (VCP). Three quadrature components of mutual impedance ratio for each configuration are used to construct the subsurface image. For the purpose of obtaining the model response and validating the reasonable performance of the inversion, we obtained each responses of two-layered and three-layered earth models and two-dimensional (2-D) isolated anomalous body. The response of 2-D isolated anomalous body has been calculated using extended Born approximation for the solution of 2.5-D integral equation describing EM scattering problem. As a result of the least-squares inversion with variable Lagrangian multiplier, we could construct more resolvable image from HCP data than VCP data. Furthermore, joint inversion of HCP and VCP data made better stability and resolution of the inversion. Resistivity values, however, did not exactly match the true ones. Loop-loop EM field data was obtained with EM34-3XL system manufactured by Geonics Ltd. (Canada). Electrical resistivity survey was conducted on the same line for the comparison in advance. Since the constructed image from loop-loop EM data by 2-D inversion algorithm showed almost similar resistivity distribution to that from electrical resistivity one, we expect the developed 2.5-D loop-loop EM inversion program can be applied for the reconnaissance site survey.

• Geophysics and Geophysical Exploration
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• v.12 no.3
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• pp.239-245
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• 2009

To verify the reinforcing effect of grouting materials composed of colloid cement and ordinary portland cement on the water leakage region in a small scale dike, we performed a tubecasing method and applied surface electrical resistivity survey including electrical resistivity tomography (ERT) to find resistivity variation before and after grouting. Hydraulic conductivities after grouting show 10 times lower than those of before grouting. These variation indicates that the cement grout blocks the leakage pathway effectively. As the results of dipole-dipole resistivity survey along the dike, resistivity distribution after grouting did not represent noticeable spatial variation in time. Resistivity monitoring results at the dike with vertical electrical sounding (VES) showed that the region of decreasing apparent resistivity was occupied by the grout after grouting. Predicted resistivities from the inversion of ERT data well matched with results of VES at the same regions. From the ERT using check holes to inspect the effect of grouting, we could find that the ERT is quite effective to identify spatially the grout region in a dike.

• Korean Journal of Plant Taxonomy
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• v.46 no.1
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• pp.83-116
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• 2016

This study was carried out to investigate the flora and vegetation of Yokjido Island in Tongyeong-si, Korea. Vascular plants collected six times (from March of 2015 to January of 2016) were identified as 547 taxa in total, including 113 families, 354 genera, 487 species, four subspecies, 50 varieties, four forms and two hybrids. The first records from this region contained 314 taxa. In the flora of this area, endemic Korean species numbered eight taxa, and the red list of vascular plants according to the IUCN valuation basis numbered six taxa. In addition, 86 taxa of floristic regional indicator plants specially designated by the Ministry of Environment are included. Among the species investigated in this survey, 99 taxa were identified as specific species bio-geographically as compared floras of other terrestrial regions; 97 taxa of plants in southern areas and two taxa of limited distribution plants on the Korean Peninsula. In all, 74 naturalized plants were recorded in the investigated area. Samples of the forest vegetation of Yokjido Island were mainly classified as Pinus thunbergii community and the Alus firma community. Vertical structures of the communities were stable, and a DBH-class analysis showed that the dominant tree species would be maintained. If disturbance factors such as thinning could be halted, the composition of woody species and herbaceous species would change.

• Journal of Korea Water Resources Association
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• v.46 no.11
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• pp.1115-1128
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• 2013

The purpose of this study is to evaluate the suspended solids and eutrophication processes relationships in Chungju lake using CE-QUAL-W2, two-dimensional (2D) longitudinal/vertical hydrodynamic and water quality model. For water quality modeling, the lake segmentation was configured as 7 branches system according to their shape and tributary distribution. The model was calibrated (2010) and validated (2008) using 2 years of field data of water temperature, suspended solids (SS), total nitrogen (TN), total phosphorus (TP) and algae (Chl-a). The water temperature began to increase in depth from April and the stratification occurred at about 10 m early July heavy rain. The high SS concentration of the interflow density currents entering from the watershed was well simulated especially for July 2008 heavy rainfall event. The simulated concentration range of TN and TP was acceptable, but the errors might occur form the poor reflection for sedimentation velocity of nitrogen component and adsorption-sediment of phosphorus in model. The concentration of Chl-a was simulated well with the algal growth patterns in summer of 2010 and 2008, but the error of under estimation may come from the use of width-averaged velocity and concentration, not considering the actual to one side inclination by wind effect.