• Investigative Magnetic Resonance Imaging
• /
• v.11 no.2
• /
• pp.103-109
• /
• 2007

To develop an advanced non-linear curve fitting (NLCF) algorithm for performing dynamic susceptibility contrast study of the brain. The first pass effects give rise to spuriously high estimates of $K^{trans}$ for the voxels that represent the large vascular components. An explicit threshold value was used to reject voxels. The blood perfusion and volume estimation were accurately evaluated in the $T2^*$-weighted dynamic contrast enhanced (DCE)-MR images. From each of the recalculated parameters, a perfusion weighted image was outlined by using the modified non-linear curve fitting algorithm. The present study demonstrated an improvement of an estimation of the kinetic parameters from the DCE $T2^*$-weighted magnetic resonance imaging data with using contrast agents.

• Proceedings of the Korean Magnestics Society Conference
• /
• 1998.05a
• /
• pp.134-135
• /
• 1998

• 한국정보디스플레이학회:학술대회논문집
• /
• 2009.10a
• /
• pp.1092-1094
• /
• 2009

The purpose of the research was to figure out the optimal binocular parallax inducing the least 3D visual fatigue. Subjective 3D visual fatigue was measured while the revolution depth and the average depth of an object were manipulated. The optimal binocular parallax was figured out by using data fitting method.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.9
• /
• pp.41-48
• /
• 2008

The aim of this study is to present a graphical method in order to evaluate stages in shrinkage cracking. Firstly, the distribution of crack openings is established by sorting the openings of individual cracks in the soil cracking system. Secondly, it is normalized in a range of 0 to 1 to obtain the normalized crack opening distribution. Thirdly, three S-shape curve models introduced by Brooks and Corey(1964), Fredlund and Xing(1994) and van Genuchten(1980) are chosen to fit the normalized crack opening distribution using a curve fitting method. The accuracy of fitting which is described through fitting parameters by the van Genuchten equation is much higher than that by the Brooks and Corey equation and slightly higher than that by the Fredlund and Xing equation; thus the van Genuchten model is used. Finally, the stages of shrinkage cracking are graphically evaluated by drawing three separate straight lines corresponding to three linear parts of the fitted normalized crack opening distribution. The proposed method is tested with different sample thicknesses. The measured data are fitted by the selected model with the fairly high regression coefficient and small root mean square error. The results show graphically that shrinkage cracking comprises three stages; namely, primary, secondary and residual stages. Subsequently, the ranges of evaluated crack opening for each of these stages are presented.

• Smart Structures and Systems
• /
• v.29 no.4
• /
• pp.549-560
• /
• 2022

The optimum damping and tuning frequency ratio of the tuned mass damper-inerter (TMDI) for the base-isolated structure is obtained using the numerical searching technique under stationary white-noise and filtered white-noise earthquake excitation. The minimization of the isolated structure's mean-square relative displacement and absolute acceleration, as well as the maximization of the energy dissipation index, were chosen as the criteria for optimality. Using a curve-fitting technique, explicit formulae for TMDI damping and tuning frequency for white-noise excitation are then derived. The proposed empirical expressions for TMDI parameters are found to have a negligible error, making them useful for the effective design of base-isolated structures. The effectiveness of TMDI and its optimum parameters are influenced by the soil condition and isolation frequency, according to the comparison made of the optimized parameters and response with different soil profiles. The effectiveness of an optimally designed TMDI in controlling the displacement and acceleration response of the flexible isolated structure under real and pulse-type earthquakes is also observed and found to be increased as the inertance mass ratio increases.

• Journal of Soil and Groundwater Environment
• /
• v.7 no.3
• /
• pp.103-114
• /
• 2002

Knowledge of soil water retention characteristic is essential for many problems involving water flow and organic solute transport in unsaturated soils. A physico-empirical approach based on the translation of the particle-size distribution (PSD) into a corresponding water retention curve has been accomplished by others using the concept that the pore-size distribution is directly related to PSD. This approach implies that details of a PSD curve may affect the estimation of water retention characteristic (WRC). To determine whether the WRC estimation using the Arya-Paris model could be affected by the selection of a PSD model, four PSD models with one to four fitting parameters were used. The Jaky model with only one fitting parameter had greater WRC estimation ability than other models with greater number of fitting parameters. The better performance of the Jaky model may be explained by the effect of soil structure in field soils.

• Journal of KIISE:Computing Practices and Letters
• /
• v.14 no.5
• /
• pp.527-531
• /
• 2008

For statistical modeling, the model parameters are usually estimated by maximizing a probability measure, such as the likelihood or the posterior. In contrast, a variational Bayesian method treats the parameters of a model as probability distributions and computes optimal distributions for them rather than values. It has been shown that this approach effectively avoids the overfitting problem, which is common with other parameter optimization methods. This paper applies a variational Bayesian technique to surface fitting for height field data. Then, we propose point cloud denoising based on the basic surface fitting technique. Validation experiments and further tests with scan data verify the robustness of the proposed method.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.5 no.4
• /
• pp.57-64
• /
• 1985

An optimization model is presented that can be used in the determination of a loss rate function and conceptual runoff models using observed rainfall and runoff data. In order to estimate the lumped parameters and to control inputs of the model, the differential equations, linear for underground flow and non-linear for overland flow, are transformed into state equations. Parameters of a loss rate function and runoff model under stationary assumption can be determined by the following procedures: optimization technique, linear control and non-linear curve fitting theory using several multiperiod storms simultaneously or using individual multiperiod storms. An infiltration equation that includes rainful intensity is used to dtermine the effective rainfall for a given rain of varying. The optimization model is applied to storms in Hyong Song watershed of Wonju area. The results of the new model are compared with earlier one.

• Composites Research
• /
• v.27 no.4
• /
• pp.135-140
• /
• 2014

A constitutive equation, which was suggested for describing the compressive deformation behaviour of the expanded polyurethane, was applied to the expanded polypropylene under dynamic loading. This equation consists of seven parameters, five of which are obtained by fitting the stress strain curve obtained from the quasi-static compression test at the lowest base strain rate. The remaining two parameters are able to be determined by fitting the curve from the compression test at different two stage strain rates. In order to check the eligibility of the equation at high strain rate, the impact test was performed and the results were compared to the analytical constitutive equation results for the expanded polypropylene with expansion ratios of 30 and 40 times, respectively.

• Journal of radiological science and technology
• /
• v.21 no.2
• /
• pp.53-56
• /
• 1998

Highly sensitive $CaSO_4:Tm$ TLD is fabricated and their trap parameters are determined. The glow curve of $CaSO_4:Tm$ consists of three glow peaks and these peaks are isolated by the thermal bleaching method. The isolated glow peaks are fitted by a least squares method. The activation energies are 0.68, 0.82 and 1.03 eV. The frequency factors are $8.09{\times}10^8,\;9.14{\times}10^8$ and $1.03{\times}10^9/s$, and the kinetic orders are 1.37, 1.54 and 1.68, respectively. The optimum temperature range of the main peak for radiation dosimetry is between 220 and $290^{\circ}C$.