• The Journal of Korean Academy of Prosthodontics
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• v.46 no.4
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• pp.325-334
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• 2008

Statement of problem & Purpose: The purpose of this study was to investigate the effect of a mouth guard material properties on the skull and brain when they were under impact loads on mandible. Material and methods: Two customized mouth protectors having different material propeerst ieach other were made for a female Korean who had no history of brain trauma, no cerebral diseases, nomal occlusion and natural dentition. The 3D finite element model of human skull and brain scanned by means of computed tomography was constructed. The FEM model of head was composed of 407,825 elements and 82,138 nodes, including skull, brain, maxilla, mandible, articular disc, teeth and mouth guard. The stress concentrations on maxillary teeth, maxilla and skull with two mouth guards were evaluated under oblique impact load of 800N onto mandibular 3 loading points for 0.1sec. And the brain relative displacement was compared in two different mouth guard materials under same condition. Result and Conclusion: The results were as follows; 1. In comparison of von Mises stress on maxillary teeth, a soft mouth guard material had significantly lower stress values on measuring point than a hard mouth protector materials (P < .05). 2. In comparison of von Mises stress on maxilla and skull, A soft mouth protector material had significantly lower stress values on measuring point than a hard mouth protector materials (P < .05). 3. For impact loads on mandible, there were more stress concentrated area on maxilla and skull with hard mouth guard than soft with mouth protector. 4. For impact loads on mandible, brain relative displacement had little relation with mouth guard material properties. In results of this study, soft mouth guard materials were superior to hard mouth guard materials for mandible impact loads for prevention of sports injuries. Although the results of this study were not enough to figure out the roles of needed mouth guard material properties for a human head, we got some knowledge of the pattern about stress concentration and distribution on maxilla and skull for impact loads with soft or hard mouth protector. More studies are needed to substantiate the relationship between the mouth guard materials and sports injuries.

• Journal of Soil and Groundwater Environment
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• v.13 no.1
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• pp.77-91
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• 2008

In this study, we developed a technique of applying DRASTIC, which is the most widely used tool for estimation of groundwater vulnerability to the aqueous phase contaminant infiltrated from the surface, and a groundwater flow model jointly to assess groundwater contamination potential. The developed technique is then applied to Buyeo-eup area in Buyeo-gun, Chungcheongnam-do, Korea. The input thematic data of a depth to water required in DRASTIC model is known to be the most sensitive to the output while only a few observations at a few time schedules are generally available. To overcome this practical shortcoming, both steady-state and transient groundwater level distributions are simulated using a finite difference numerical model, MODFLOW. In the application for the assessment of groundwater vulnerability, it is found that the vulnerability results from the numerical simulation of a groundwater level is much more practical compared to cokriging methods. Those advantages are, first, the results from the simulation enable a practitioner to see the temporally comprehensive vulnerabilities. The second merit of the technique is that the method considers wide variety of engaging data such as field-observed hydrogeologic parameters as well as geographic relief. The depth to water generated through geostatistical methods in the conventional method is unable to incorporate temporally variable data, that is, the seasonal variation of a recharge rate. As a result, we found that the vulnerability out of both the geostatistical method and the steady-state groundwater flow simulation are in similar patterns. By applying the transient simulation results to DRASTIC model, we also found that the vulnerability shows sharp seasonal variation due to the change of groundwater recharge. The change of the vulnerability is found to be most peculiar during summer with the highest recharge rate and winter with the lowest. Our research indicates that numerical modeling can be a useful tool for temporal as well as spatial interpolation of the depth to water when the number of the observed data is inadequate for the vulnerability assessments through the conventional techniques.

• The Korean Journal of Rheology
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• v.11 no.2
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• pp.143-152
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• 1999

Using a Rheometrics Fluids Spectrometer(RFS II), the steady shear flow and the small-amplitude dynamic viscoelastic properties of three kinds of semi-solid food materials(mayonnaise, tomato ketchup, and wasabi) have been measured over a wide range of shear rates and angular frequencies. The shear rate dependence of steady flow behavior and the angular frequency dependence of dynamic viscoelastic behavior were reported from the experimentally measured data. In addition, some viscoplastic flow models with a yield stress term were employed to make a quantitative evaluation of the steady flow behavior, and the applicability of these models was also examined in detail. Furthermore, the correlations between steady shear flow(nonlinear behavior) and dynamic viscoelastic(linear behavior)properties were discussed using the modified power-law flow equations. Main results obtained from this study can be summarized as follows : (1) Semi-solid food materials are regarded as viscoplastic fluids having a finite magnitude of yield stress, and their flow behavior shows shear-thinning characteristics, exhibiting a decrease in steady flow viscosity with increasing shear rate. (2) The Herschel-Bulkley, Mizrahi-Berk, and Heinz-Casson models are all applicable to describe the steady flow behavior of semi-solid food materials. Among these models, the Heinz-Casson model has the best validity. (3) Semi-solid food materials show a stronger shear-thinning behavior at shear rate region higher than a critical shear rate where a more progressive structure breakdown takes place. (4) Both the storage and loss moduli are increased with increasing angular frequency, but they have a slight dependence on angular frequency. The elastic behavior is dominant to the viscous behavior over a wide range of angular frequencies. (5) All of the steady flow, dynamic, and complex viscosities are well satisfied with the power-law model behavior. The relationships between steady shear flow and dynamic viscoelastic properties can well be described by the modified forms of the power-law flow equations.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.347-358
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• 2009

Recently, it is getting into a good situation for the flat-plate slab system to be applied. The flat-plate slab without beam, however, is often too weak to control deflection properly compared to other typical slab-beam structures, for which the post-tension method is generally regarded as one of best solutions. The post-tension (PT) method can effectively control deflection without increase of slab thickness. Despite this good advantage, however, the application of PT method has been very limited due to cost increase, technical problems, and lack of experiences. Therefore, in order to reduce difficulties on applying full PT method under the current domestic circumstances and to enhance constructability of PT system, this research proposed the partial PT method with top jacking anchorage applied in a part of span as need. For the top jacking anchorage system, the efficiency of deflection control shall be considered in detail because it can vary widely depending on the location of anchorage that can be placed anywhere as need, and tensile stresses induced at back of the anchorage zone also shall be examined. Therefore, in this study, analysis were performed on the efficiency of deflection control depending on the location of anchorage and on tensile stresses or forces using finite element method and strut and tie model in the proposed top jacking anchorage system. The proposed jacking system were also applied to the floor slabs at a construction site to investigate its applicability and the analysis results of slab behavior were compared to the measured values obtained from the PT slab constructed by the partial PT method. The result of this study indicates that the partial PT method can be very efficiently applied with little cost increase to control deflection and tensile stresses in the region as a need basis where problem exists.

• Geophysics and Geophysical Exploration
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• v.13 no.1
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• pp.1-8
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• 2010

Seismic reflection surveying is one of the most widely used and effective techniques for coal seam structure delineation and risk mitigation for underground longwall mining. However, the ability of the method can be compromised by the presence of volcanic cover. This problem arises within parts of the Bowen and Sydney Basins of Australia and seismic surveying can be unsuccessful. As a consequence, such areas are less attractive for coal mining. Techniques to improve the success of seismic surveying over basalt flows are needed. In this paper, we use elastic wave-equation-based forward modelling techniques to investigate the effects and characteristics of seismic wave propagation under different settings involving changes in basalt properties, its thickness, lateral extent, relative position to the shot position and various forms of inhomogeneity. The modelling results suggests that: 1) basalts with high impedance contrasts and multiple flows generate strong multiples and weak reflectors; 2) thin basalts have less effect than thick basalts; 3) partial basalt cover has less effect than full basalt cover; 4) low frequency seismic waves (especially at large offsets) have better penetration through the basalt than high frequency waves; and 5) the deeper the coal seams are below basalts of limited extent, the less influence the basalts will have on the wave propagation. In addition to providing insights into the issues that arise when seismic surveying under basalts, these observations suggest that careful management of seismic noise and the acquisition of long-offset seismic data with low-frequency geophones have the potential to improve the seismic results.

• International Journal of Highway Engineering
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• v.13 no.3
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• pp.21-30
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• 2011

As well known, dowel bars are used to transfer traffic load acting on one edge to another edge of concrete slab in concrete pavement system. The dowel bars widely used in South Korea are round shape steel bar and they shows satisfactory performance under bending stress which is developed by repetitive traffic loading and environment loading. However, they are not invulnerable to erosion that may be caused by moisture from masonry joint or bottom of the pavement system. Especially, the erosion could rapidly progress with saline to prevent frost of snow in winter time. The problem under this circumstance is that the erosion not only drops strength of the steel dower bar but also comes with volume expansion of the steel dowel bar which can reduce load transferring efficiency of the steel dowel bar. To avoid this erosion problem in reasonable expenses, dowers bars with various materials are being developed. Fiber reinforced plastic(FRP) dower that is presented in this paper is suggested as an alternative of the steel dowel bar and it shows competitive resistance against erosion and tensile stress. The FRP dowel bar is developed in tube shape and is filled with high strength no shrinkage. Several slab thickness designs with the FRP dowel bars are performed by evaluating bearing stress between the dowel bar and concrete slab. To calculated the bearing stresses, theoretical formulation and finite element method(FEM) are utilized with material properties measured from laboratory tests. The results show that both FRP tube dowel bars with diameters of 32mm and 40mm satisfy bearing stress requirement for dowel bars. Also, with consideration that lean concrete is typical material to support concrete slab in South Korea, which means low load transfer efficiency and, therefore, low bearing stress, the FRP tube dowel bar can be used as a replacement of round shape steel bar.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2255-2265
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• 2013

This study presents the width function-based Clark model. To this end, rescaled width function with distinction between hillslope and channel velocity is used as time-area curve and then it is routed through linear storage within the framework of not finite difference scheme used in original Clark model but analytical expression of linear storage routing. There are three parameters focused in this study: storage coefficient, hillslope velocity and channel velocity. SCE-UA, one of the popular global optimization methods, is applied to estimate them. The shapes of resulting IUHs from this study are evaluated in terms of the three statistical moments of hydrologic response functions: mean, variance and the third moment about the center of IUH. The correlation coefficients to the three statistical moments simulated in this study against these of observed hydrographs were estimated at 0.995 for the mean, 0.993 for the variance and 0.983 for the third moment about the center of IUH. The shape of resulting IUHs from this study give rise to satisfactory simulation results in terms of the mean and variance. But the third moment about the center of IUH tend to be overestimated. Clark model proposed in this study is superior to the one only taking into account mean and variance of IUH with respect to skewness, peak discharge and peak time of runoff hydrograph. From this result it is confirmed that the method suggested in this study is useful tool to reflect the heterogeneity of drainage path and hydrodynamic parameters. The variation of statistical moments of IUH are mainly influenced by storage coefficient and in turn the effect of channel velocity is greater than the one of hillslope velocity. Therefore storage coefficient and channel velocity are the crucial factors in shaping the form of IUH and should be considered carefully to apply Clark model proposed in this study.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.87-102
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• 1991

It has been reported that the failure of Carsington Dam in Eng1and occured due to the existence of a thin yellow clay layer which was not identified during the design work, and due to pre-existing shears of the clay layer. The slope stability analyses during the design work, which utilized traditional circular arc type failure method and neglected the existence of the clay layer, showed a safety factor of 1.4. However, the post-failure analyses which utilized translational failure mode considering the clay layer and the pre-existing shear deformation revealed the reduction of safety factor to unity. The post-failure analysis assumed 10。 inclination of the horizontal forces onto each slice based on the results of finite element analyses. In this paper, Bishop's simplified method, Janbu method, and Morgenstern-Price method were used for the comparison of both circular and translational failure analysis methods. The effects of the pre-existing shears and subsquent movement were also considered by varying the soil strength parameters and the pore pressure ratio according to the given soi1 parameters. The results showed factor of safefy 1.387 by Bishop's simplified method(STABL) which assumed circular arc failure surface and disregarding yellow clay layer and pre-failure material properties. Also the results showed factor of safety 1.093 by Janbu method(STABL) and 0.969 by Morgenstern-Price method(MALE) which assumed wedge failure surface and considerd yellow clay layer using post failure material properties. In addition, dam behavior was simulated by Cam-Clay model FEM program. The effects of pore pressure changes with loading and consolidation, and strength reduction near or at failure were also considered based on properly assumed stress-strain relationship and pore pressure characteristics. The results showed that the failure was initiated at the yellow clay layer and propagated through other zones by showing that stress and displacement were concentrated at the yel1ow clay layer.

• Korean journal of applied entomology
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• v.46 no.1 s.145
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• pp.37-42
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• 2007

To construct a life table and development model Schizaphis graminum (Rondani), its adult longevity and fecundity were studied at various constant temperatures ranging from 15 to $32.5^{\circ}C$, with $65{\pm}5%$ RH, and a photoperiod of 16L:8D. Adult longevity of the greenbug gradually increased with decreasing temperature below $32.5^{\circ}C$. Total fecundity was not significantly different at all temperatures except at $32.5^{\circ}C$. Daily fecundity gradually increased from $25.0^{\circ}C$. It was 3.6 at $27.5^{\circ}C$ and as temperatures either went down or up, it decreased to 1.4 at $15.0^{\circ}C$ and 0.4 at $32.5^{\circ}C$ Net reproduction rate (Ro) was highest with 47.6 at $25.0^{\circ}C$. The intrinsic rate of increase per day $(r_m)$ and the finite rate of increase per day $({\lambda})$ were highest with 0.4 and 1.5 at $30.0^{\circ}C$, respectively and the doubling time (Dt) was shortest with 0.98 at $32.5^{\circ}C$. The mean generation time (T) was 8.41 at $30.0^{\circ}C$.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.1
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• pp.10-20
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• 2012

Purpose: The purpose of this study was to investigate the stress distribution in mandibular implant-supported overdentures and tooth-supported overdentures with telescopic crowns. Materials and methods: The assumption of this study was that there were 2, 3, 4 natural teeth and implants which are located in the second premolar and canine regions in various distributed conditions. The mandible, teeth (or implants and abutments), and connectors are modeled, and analyzed with the commercial software, ANSYS Version 10.1. Stress distribution was evaluated under 150 N vertical load bilaterally on 3 experimental conditions - between canine areas, canine and $2^{nd}$ premolars, 10 mm posterior to $2^{nd}$ premolars. Results: Overall, the case of the implant group showed more stress than the case of the teeth group in stress distribution to bone. In stress distribution to superstructures of tooth and implants, there was no significant difference between TH group and IM group and the highest stress appeared in TH-IV and IM-IV. The stress caused from bar was much higher than those of implant and tooth. TH group showed less stress than IM group in stress distribution to abutment teeth and implant. Conclusion: The results shows that it is crucial to make sure that distance between impact loading point and abutment tooth does not get too far apart, and if it does, it is at best to set abutment tooth on premolar tooth region. It will be necessary to conduct more experiments on effects on implants, natural teeth and bone, in order to apply these results to a clinical treatment.