• The Journal of Advanced Prosthodontics
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• v.1 no.3
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• pp.113-117
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• 2009

STATEMENT OF PROBLEM. Recently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported. PURPOSE. The objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM). MATERIAL AND METHODS. Y-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad $S\ddot{a}ckingen$, Germany) were prepared in 40 mm (length) $\times$ 4 mm (width) $\times$ 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and $225^{\circ}C$ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences ($\alpha$= .05). RESULTS. The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below $125^{\circ}C$ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above $150^{\circ}C$, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa. CONCLUSION. The monoclinic phase started to appear after aging treatment above $100^{\circ}C$. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above $175^{\circ}C$. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.1
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• pp.10-16
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• 2007

In this paper, we propose a technique for retrieving images using spatial color correlation and texture characteristics based on local fourier transform. In order to retrieve images, two new descriptors are proposed. One is a color descriptor which represents spatial color correlation. The other is a descriptor combining the proposed color descriptor with texture descriptor. Since most of existing color descriptors including color correlogram which represent spatial color correlation considered just color distribution between neighborhood pixels, the structural information of neighborhood pixels is not considered. Therefore, a novel color descriptor which simultaneously represents spatial color distribution and structural information is proposed. The proposed color descriptor represents color distribution of Min-Max color pairs calculating color distance between center pixel and neighborhood pixels in a block with 3x3 size. Also, the structural information which indicates directional difference between minimum color and maximum color is simultaneously considered. Then new color descriptor(min-max color correlation descriptor, MMCCD) containing mean and variance values of each directional difference is generated. While the proposed color descriptor includes by far smaller feature vector over color correlogram, the proposed color descriptor improves 2.5 % ${\sim}$ 13.21% precision rate, compared with color correlogram. In addition, we propose a another descriptor which combines the proposed color descriptor and texture characteristics based on local fourier transform. The combined method reduces size of feature vector as well as shows improved results over existing methods.

• The Journal of the Acoustical Society of Korea
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• v.22 no.1
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• pp.1-6
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• 2003

This paper analyses the performance of either the minimum variance distortionless response (MVDR) or the recursive least square (RLS) beamformer structured on the systolic array. Provided that the snapshot vector including the desired user's signal and the interferences with the noise is received at the array antenna. In order to improve the quality of received signal, MVDR or RLS algorithm can be utilized to update the beamformer weights recursively. Furthermore to increase the channel capacity, by the usage of the above schemes, the effect of the spatial filtering can be obtained which constructively combining multipath components corresponding to the desired user whereas the multiple access interferences (MAI) is nulled out on spatial domain. This paper introduces the MVDR and RLS beamformer structured on systolic array conducting the spatial filtering, and its performance under the multipath fading channel in the presence of multiple access interferences will be analyzed. To show the superior spatial filtering performances of the proposed scheme employing the systolic way structured beamformer, the computer simulations are carried out. And the validity of practical deployment of the proposed scheme will be confirmed throughout showing the BER behaviors and the beampatterns.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.5
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• pp.891-903
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• 2017

In recent days, school violence has been rising as a significant social problem. The occurrence of school violence can be fueled by a wide range of social and environmental contexts, thus it is very difficult to come up with the ultimate solution. Community CPTED program is one of the more comprehensive set of efforts that has been developed to prevent crime in general, and the primary focus of the study is to investigate suitable components of CPTED to prevent school violence based on the physical conditions of communities as well as the perception of residents outside of school grounds, in the vicinity of schools. Three sets of analyses in series were employed in the research. First, Ward's minimum-variance cluster analysis was used to classify the places where school violence can occur outside of school grounds based on the physical conditions recognized by local residents. Next, Importance-Performance Analysis was performed to analyze the perception of local residents about the importance and the effectiveness of CPTED components in preventing school violence. Subsequently, Ordered Logit Model was used to analyze the local residents' awareness on safety regarding school violence in their community space. Combining the results of the analyses, the priority of the community CPTED applications to prevent school violence outside of school was derived. Reflecting the local residents' perception on safety of students in their community, the sense of security in communities against school violence can be reinforced by the communities' sensible efforts in creating safer environment for their students.

• Analytical Science and Technology
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• v.14 no.3
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• pp.221-229
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• 2001

The bioequivalence study of two tiropramide products was evaluated in 16 health male volunteers following intra-muscular injection. Test product was Tiram$^{(R)}$ injection (S Pharm. Co, Ltd.) and reference product was Tiropa$^{(R)}$ injection(D Pharm. Co., Ltd.). The drug concentration in plasma was determined by GC/MS for over a period of 8 hours after injection. Analysis of variance reveal that there are no differences in AUC (area under the plasma concentration-time curve from time zero to infinity), Cmax (maximum plasma concentration) and Tmax (time to reach Cmax). The differences of mean AUC, Cmax and Tmax between two products were 0.73, -1.385 and -12.994%, respectively. Minimum detectable differences (%) at ${\alpha}=0.05$ were all less than 20% given as a guideline (10.05, 17.90 and 19.01% for AUC, Cmax and Tmax, respectively). From these results, the two formulations of tiropramide are bioequivalent and thus, may be prescribed interchangeably.

• Journal of Pharmaceutical Investigation
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• v.28 no.4
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• pp.283-288
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• 1998

Lovastatin, one of the potent cholesterol-lowering agents, is an inactive lactone prodrug which is metabolized to its active open acid, lovastatin acid (LVA). Bioequivalence study of two lovastatin preparations, the test drug ($Mevacor^{\circledR}$: Chungwae Pharmaceutical Co., Ltd.) and the reference drug ($Lovaload^{\circledR}$: Chong Kun Dang Pharmaceutical Co., Ltd.), was conducted according to the guidelines of Korea Food and Drug Administration (KFDA). Fourteen healthy male volunteers, $23.9{\pm}3.9$ years old and $67.6{\pm}8.0$ kg of body weight in average, were divided randomly into two groups and administered the drug orally at the dose of 160 mg as lovastatin in a $2{\times}2$ crossover study. Plasma concentrations of lovastatin acid were analysed by HPLC method for 12 hr after administration. The extent of bioavailability was obtained from the plasma concentration-time profiles of total lovastatin acid after alkaline hydrolysis of the plasma samples. By alkaline hydrolysis, trace amounts of unmetabolized lovastatin were converted to lovastatin acid. The $AUC_{0-12hr}$ was calculated by the linear trapezoidal rule method. The $C_{max}$ and $T_{max}$ were compiled directly from the plasma drug concentration-time data. Student's t-test indicated no significant differences between the formulations in these parameters. Analysis of variance (ANOVA) revealed that there were no differences in AUC, $C_{max}$, and $T_{max}$ between the formulations. The apparent differences between the formulations were far less than 20% (e.g., 7.07, 5.77 and 1.18% for AUC, $C_{max}$, and $T_{max}$, respectively). Minimum detectable differences(%) between the formulations at ${\alpha}=0.05$ and $1-{\beta}=0.8$ were less than 20% (e.g., 17.2, 15.1, and 15.9% for AUC, Cmax, and Tmax, respectively). The 90% confidence intervals for these parameters were also within ${\pm}20%$ (e.g.. $-5.20{\sim}19.3$, $-5.00{\sim}16.5$, and $-10.2{\sim}12.5%$ for AUC, $C_{max}$, and $T_{max}$, respectively). These results satisfied the bioequivalence criteria of KFDA guidelines, indicating that the two formulations of lovastatin were bioequivalent.

• Journal of Broadcast Engineering
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• v.21 no.2
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• pp.169-179
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• 2016

Recently, MPEG-H has been standardizing for a multimedia coder in UHDTV (Ultra-High-Definition TV). Thus, the demand for not only channel-based audio contents but also object-based audio contents is more increasing, which results in developing a new technique of converting channel-based audio contents to object-based ones. In this paper, a non-uniform linear microphone array based source separation method is proposed for realizing such conversion. The proposed method first analyzes the arrival time differences of input audio sources to each of the microphones, and the spectral magnitudes of each sound source are estimated at the horizontal directions based on the analyzed time differences. In order to demonstrate the effectiveness of the proposed method, objective performance measures of the proposed method are compared with those of conventional methods such as an MVDR (Minimum Variance Distortionless Response) beamformer and an ICA (Independent Component Analysis) method. As a result, it is shown that the proposed separation method has better separation performance than the conventional separation methods.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.786-791
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• 2007

Korean high speed train(HSR-350x) has adopted a combined electrical and mechanical(friction) braking system. Brake blending control unit(BBCU) controls each brake system to fulfill the required brake performances such as braking distance, deceleration and jerk. Also the braking system should be designed considering the economical management, such as effective use of generated braking energy and the minimum wear of friction materials(a pad and a brake shoe). In this paper, we establish the disc braking force pattern that reduces the wear of pad in the disc braking system by minimizing the variance of the instantaneous disk baking energy during braking time, and compare the wear mass of pad between the conventional disc braking force pattern and the established results.

• Geotechnical Engineering
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• v.3 no.4
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• pp.41-54
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• 1987

A stochastic numerical analysis for predicting the groundswater fluctuations in hillside slopes is performed in this paper to account for the uncertainties associated with the rainfall and site characteristics. The effect of spatial variabilities of aquifer parameters and the effect of temporal variability of recharge on the groundwater fluctuations are studied in depth. The Kriging is used to account for the spatial tariabilities of aquifer parameters. This technique prolevides the best linear unbiased estimator of a parameter and its minimum variance from a litsitem number of measured data. A stochastic one-dimensional numerical model is delreloped b) combining the groundwater flow model, the Kriging, and the first-order second-moment analysis. In addition, a two dimensional detelministic groundwater model is developed to study the change of ground water surfas in the transverse direction as well as in the downslope direction. It is revealed that the undulations of the impervious bedrock in addition to the permeability and the specific yield have an important influence on the fluctuations of the groundwater surface. It is also found that th'e groundwater changes significantly in the transverse direction as well as in the downslope direction. The results obtained in this analysis may be used for evaluation of landslide risks due to high porewater pressure.

• Progress in Medical Physics
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• v.13 no.1
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• pp.21-26
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• 2002

A practical calculation algorithm which calculates the relative output factor(ROF) for irregular shaped electron field has been developed and evaluated the accuracy of the algorithm. The algorithm adapted two-source model, which assumes that the electron dose can be express as sum of the primary source component and the scattered component from the shielding block. Original two-source model has been modified in order to make the algorithm simpler and to reduce the number of parameters needed in the calculation, while the calculation error remains within clinical tolerance range. The primary source is assumed to have Gaussian distribution, while the scattered component follows the inverse square law. Depth and angular dependency of the primary and the scattered are ignored ROF can be calculated with three parameters such as, the effective source distance, the variance of primary source, and the scattering power of the block. The coefficients are obtained from the square shaped-block measurements and the algorithm is confirmed from the rectangular or irregular shaped-fields used in the clinic. The results showed less than 1.0 ％ difference between the calculation and measurements for most cases. None of cases which have bigger than 2.1 ％ have been found. By improving the algorithm for the aperture region which shows the largest error, the algorithm could be practically used in the clinic, since one can acquire the 1011 parameter's with minimum measurements(5∼6 measurements per cones) and generates accurate results within the clinically acceptable range.