• The Journal of Korean Academy of Prosthodontics
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• v.46 no.1
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• pp.22-30
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• 2008

Purpose: The purpose of this study is to compare three different CAD/CAM systems through the fracture strength of zirconia core and to evaluate the clinical availability of each system. Material and methods: The following three groups of 30 maxillary mesial incisor core for all-ceramics(each group 10) were fabricated as follows: group 1. $Adens^{(R)}$ CAD/CAM system, group 2. $Cerasys^{(R)}$ CAD/CAM system, group 3. 3M $Lava^{(R)}$ CAD/CAM system. All specimens were manufactured consistently thickness 0.5mm and relief $40{\mu}m$. Specimens were subjected to compressive loading on the lingual area by Z250/$SN5S^{(R)}$. Each group's mean and standard deviation were calculated and Kruskal Waillis test, Wilcoxon Rank Sum test were utilized to find out the relationship among the groups. Results: The results were as follows: 1. The mean fracture strength of $Adens^{(R)}$ system was $615.89{\pm}156.1N$, the $Cerasys^{(R)}$ system was $863.98{\pm}151.5N$, and the 3M $Lava^{(R)}$ system was $1143.1{\pm}286.6N$. 2. The fracture strength of the systems showed the significant statistical differences in order of 3M $Lava^{(R)}$ system, $Cerasys^{(R)}$ system, $Adens^{(R)}$ system. Conclusion: In this study, in spite of the differences among the groups, every group showed clinically useful results. It is necessary to study further clinical experiments on a long term basis.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.279-288
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• 1999

The creep of concrete structures caused by variable stresses is generally calculated by step-by-step method based on the superposition of creep function. Although most practical application is carried out by this linear assumption. significant deviations between predictions and experiments have been observed when unloading takes place, that is. stress is reduced. This shows that the superposition of creep function does not describe accurately the effect of sustained compressive preload. The main purpose of this study is to propose a creep analysis model which is expressed with both creep function and creep recovery function where increase or decrease of stress is repeated. In these two function method, the creep behavior is modelled by using linear creep law for loading and creep recovery law for unloading. To apply two function method to time analysis of concrete structures, the calculation method of creep strain increment under varying stress is proposed. The calculation results based on the present method correlates very well with test data, but the conventional superposition method exhibits large deviation from test results. This paper provides a more accurate method for the time dependent analysis of concrete structures subjected to varying stress, i.e. increasing or decreasing stress. The present method may be efficiently employed in the revision of future concrete codes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.2
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• pp.21-29
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• 2014

This paper evaluates the shear strength, behavior and failure mode of reinforced concrete beams with deformed GFRP reinforcing bar. Four concrete beam specimens were constructed and tested. It was carried out to observe failure behavior and load-deflection of simply supported concrete beams subjected to four-point monotonic loading. In order to eliminate of the uncertainty by the shear reinforcements, any stirrups were not used. Variables of the specimens were shear span-depth ratio, effective reinforcement ratio. The dimensions of specimen is 3,300 or $1,950mm{\times}200mm{\times}240mm$. Clear span and shear span were 2,900mm, 1,000mm respectively. Shear span-depth ratios were 6.5 and 2.5. Effective ratios of Longitudinal GFRP reinforcing bar were $1.126{\rho}_{fb}$, $2.250{\rho}_{fb}$, $3.375{\rho}_{fb}$ and $0.634{\rho}_{fb}$. All beam specimens were broken by diagonal-tension shear and the ACI 440.1R, CSA S806 and ISIS, which was used to design test beams, showed considerable deviation between prediction and test results of shear strengths.

• Korean Journal of Environmental Agriculture
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• v.20 no.3
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• pp.192-200
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• 2001

The event-based agricultural non-point source(AGNPS) pollution model was applied to estimate the loads of nitrogen and phosphorus in a stream draining small agricultural watersheds. Calibration and verification of the model were performed using observed data collected from rainfall events in the Imgo watersheds during 1997-1998. Parameter calibrations were made for the runoff curve number. The peak flow volumes in the watersheds were well reproduced by the modified model. Average deviation between observed and simulated values was 10%, and this match was confirmed by the coefficient of efficiency value of 0.97. The deviations tended to increase as the peak flows increased. The simulated total N concentrations in the stream water were fairly close to the measured values, and the coefficient of efficiency in the estimation was 0.93. However, there were relatively large variations between calculated and observed values of total P concentration, and the coefficient of efficiency in the estimation was 0.74. Any inaccuracies that arise in estimating runoff flow and nutrient loading can not be explained exactly and further adjustment and refinements may be needed for application of AGNPS in agricultural watersheds. With this restrictions in mind, it can be concluded that AGNPS can provide realistic estimates of nonpoint source nutrient yields.

• Korean Journal of Medicinal Crop Science
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• v.16 no.6
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• pp.446-454
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• 2008

An advanced extraction method by ultrasonic extraction with applied solid phase extraction (SPE) has been developed for the determination of simultaneous eight major ginsenosides, namely ginsenosides Rg1, Re, Rf, Rb1, Rg2, Rc, Rb2, and Rd in the root of Panax ginseng. Four extraction methods including n-BuOH reflux extraction (Method A), 70% EtOH reflux extraction (Method B), 50% MeOH reflux extraction with SPE (Method C), and 50% MeOH ultrasonication with SPE clean-up process (Method D) were investigated for the determination of eight major ginsenosides. Total contents of ginsenosides were highest by extraction of Method C as $2.408{\pm}0.011%$. However, Method D was evaluated as relatively simpler and more efficient method due to short extraction time, small solvent consumption and less expensive, compared to conservative reflux method. Ginsenosides were also satisfactorily separated with good resolution and the accuracy range was between 1.05 and 4.06% as relative standard deviation (RSD) by Method D. SPE condition and HPLC condition were further optimized for determination of eight major ginsenosides by the ultrasonic extraction method. Conclusively, ultrasonic extraction of 2 g sample of ginseng using ultrasonic bath and 1 loading for SPE was evaluated as proper condition for extraction of ginseng.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.205-214
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• 2012

Crack widths play an important role in the serviceability limit state. When crack widths are controlled sufficiently, the reinforcement corrosion can be reduced using only existing concrete cover thickness due to low permeability in the region of finely distributed hair-cracks. Thus, the knowledge about the tensile crack opening is essential in designing more durable concrete structures. Therefore, numerous researches related to the topic have been performed. Nevertheless accurate measurement of a crack width is not a simple task due to several reasons such as unknown potential crack formation location and crack opening damaging strain gages. In order to overcome these difficulties and measure precise crack widths, a displacement measurement system was developed using digital image correlation. Accuracy calibration tests gave an average measurement error of 0.069 pixels and a standard deviation of 0.050 pixels. Direct tensile test was performed using ultra high performance concrete specimens. Crack widths at both notched and unnotched locations were measured and compared with clip-in gages at various loading steps to obtain crack opening profile. Tensile deformation characteristics of concrete were well visualized using displacement vectors and full-field displacement contour maps. The proposed technique made it possible to measure crack widths at arbitrary locations, which is difficult with conventional gages such as clip-in gages or displacement transducers.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.6
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• pp.780-786
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• 2007

Statement of problem. The performance and maintenance of implant-supported prostheses are primarily dependent upon load transmission both at the bone-to-implant interface and within the implant-abutment-prosthesis complex. The design of the interface between components has been shown to have a profound influence on the stability of screw joints. Purpose. The Purpose of this study was to compare the strength and the fatigue resistance of 1-piece and 2-piece abutment connected to oral implant, utilizing an internal conical interface. Material and methods. Twenty $Implatium^{(R)}$ tapered implants were embedded to the top of the fixture in acrylic resin blocks. Ten $Combi^{(R)}$(1-piece) and $Dual^{(R)}$(2-piece) abutments of the same dimension were assembled to the implant, respectively. The assembled units were mounted in a testing machine. A load was applied perpendicular to the long axis of the assemblies and the loading points was at the distance of 7mm from the block surface. Half of 1-piece and 2-piece abutment-implant units were tested for the evaluation of the bending strength, and the others were cyclically loaded for the evaluation of the fatigue resistance until plastic deformation occurred. Nonparametric statistical analysis was performed for the results. Results. Mean plastic and maximum bending moment were $1,900{\pm}18Nmm,\;3,609{\pm}106Nmm$ for the 1-piece abutment, and $1,250{\pm}31Nmm,\;2,688{\pm}166Nmm$ for the 2-piece abutment, respectively. Mean cycles and standard deviation when implant-abutment joint showed a first plastic deformation were $238,610{\pm}44,891$. cycles for the 1-piece abutment and $9,476{\pm}3,541$ cycles for the 2-piece abutment. A 1-piece abutment showed significantly higher value than a 2-piece abutment in the first plastic bending moment (p<.05), maximum bending moment (p<.05) and fatigue strength (p<.05). Conclusion. Both 1-piece and 2-piece conical abutment had high strength and fatigue resistance and this suggests long-term durability without mechanical complication. However, the 1-piece conical abutment was more stable than the 2-piece conical abutment in the strength and the fatigue resistance.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.143-159
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• 2017

A probabilistic fragility assessment procedure is developed in this paper to predict risks of damage arising from seismic loading to the two-cell RC box tunnel. Especially, the paper focuses on establishing a simplified methodology to derive fragility curves which are an indispensable ingredient of seismic fragility assessment. In consideration of soil-structure interaction (SSI) effect, the ground response acceleration method for buried structure (GRAMBS) is used in the proposed approach to estimate the dynamic response behavior of the structures. In addition, the damage states of tunnels are identified by conducting the pushover analyses and Latin Hypercube sampling (LHS) technique is employed to consider the uncertainties associated with design variables. To illustrate the concepts described, a numerical analysis is conducted and fragility curves are developed for a large set of artificially generated ground motions satisfying a design spectrum. The seismic fragility curves are represented by two-parameter lognormal distribution function and its two parameters, namely the median and log-standard deviation, are estimated using the maximum likelihood estimates (MLE) method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.3
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• pp.866-872
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• 2010

In this paper, we developed a digital soldering station based on PID controller, which supply stable power by controlling the current of heater of soldering iron. The proposed system designed PID controller to converge quickly to the set up temperature by user, and regain the lost of heat by external factors quickly. PID controller, designed by Ziegler-Nichols' tuning method, decides triac's trigger timing using setting temperature and present temperature to control the phase of AC 24V power that supply to the heater. Also, we give the function that shows present temperature and setting temperature of iron, and working time by graphic LCD. And during the rest time, we decided the power saving and extension of iron tip by dropping to the optimal temperature. Two experiments had implemented in $25^{\circ}C$ laboratory to confirm the performance of proposed method. The first experiment took 12sec, 13sec, 16sec, 18sec, reaching to $200^{\circ}C$, $300^{\circ}C$, $400^{\circ}C$, $480^{\circ}C$ respectively which result showed shorten of rising time than previous method. In the loading experiment of $300^{\circ}C$, $400^{\circ}C$, $480^{\circ}C$ steady state showed temperature drop of $3.8^{\circ}C$, $4.1^{\circ}C$, $4.5^{\circ}C$ which result showed the low temperature deviation than previous method.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.2
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• pp.191-198
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• 2009

Statement of problem: Ceramics have been important materials for the restoration of teeth. The demands of patients for tooth-colored restorations and the availability of various dental ceramics has driven the increased use of new types of dental ceramic materials. Improved physical properties of theses materials have expanded its use even in posterior crowns and fixed partial dentures. However, ceramic still has limitation such as low loading capability. This is critical for long-span bridge, because bridge is more subject to tensile force. Purpose: The wire reinforced ceramic was designed to increase the fracture resistance of ceramic restoration. The purpose of this study was to evaluate the fracture resistance of wire reinforced ceramic. Material and methods: Heat pressed ceramic(ingot No.200 : IPS Empress 2, Ivoclar Vivadent, Liechtenstein) and Ni-Cr wire(Alfa Aesar, Johnson Matthey Company, USA) of 0.41 mm diameter were used in this study. Five groups of twelve uniform sized ceramic specimens(width 4 mm, thickness 2 mm, length 15 mm) were fabricated. Each group had different wire arrangement. Wireless ceramic was used as control group. The experimental groups were divided according to wire number and position. One, two and three strands of wires were positioned on the longitudinal axis of specimen. In another experimental group, three strands of wires positioned on the longitudinal axis and five strands of wires positioned on the transverse axis. Three-point bending test was done with universal testing machine(Z020, Zwick, Germany) to compare the flexural modulus, flexural strength, strain at fracture and fracture toughness of each group. Fractured ceramic specimens were cross-sectioned with caborundum disc and grinded with sandpaper to observe interface between ceramic and Ni-Cr wire. The interface between ceramic and Ni-Cr wire was analyzed with scanning electron microscope(JSM-6360, JEOL, Japan) under platinum coating. Results: The results obtained were as follows: 1. The average and standard deviation in flexural modulus, flexural strength and fracture toughness showed no statistical differences between control and experimental groups. However, strain was significantly increased in wire inserted ceramics(P<.001). 2. Control group showed wedge fracture aspects across specimen, while experimental groups showed cracks across specimen. 3. Scanning electron microscopic image of cross-sectioned and longitudinally-sectioned specimens showed no gap at the interface between ceramic and Ni-Cr wire. Conclusion: The results of this study showed that wire inserted ceramics have a high strain characteristic. However, wire inserted ceramics was not enough to use at posterior area of mouth in relation to flexural modulus and flexural strength. Therefore, we need further studies.