• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.321-322
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• 2006

In many manufacturing processes such as web formation, manufacturing of paper and nonwoven, fabric weaving, etc., planar sheets are transported and at the same time appropriate tension is imposed. The input material rolled up on beams is fed by unwinding the beam and the processed is then taken up on beams by winding it. While processed, the planar sheets are thrown under the processing load of impulse form, which causes irregular thickness of the processed sheet. To improve the quality of the product, a dynamic model is needed and the dynamic characteristics is to be analyzed by simulation. This study shows that density variation dynamics of the in-process-sheet in the machine direction can be described at each moment of disturbing impacts in forms of difference equations, while the impacts and tension, the time-dependency of the material properties were taken into account. Simulation showed the most serious variation of the density occurred in the process starting phase. The starting velocity curve with step form showed the least variation of the density. As the time order of the function of the starting velocity cure becomes higher, the density variation gets greater.

• Journal of Photoscience
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• v.7 no.2
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• pp.67-71
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• 2000

A quantum-chemical investigation on the conformations and electronic properties of trans(diphenyl-diheterocyclic) ethenes(t-PHEs) as building block for fully $\pi$-conjuated polymer are performed in order to display the effects of heterocyclic ring substitution. Structures for the molecules, t-PHEs were fully optimized by using semiempirical AM1, PM3 methods, and ab initio HF methods, with 6-31G basic set. The potential energy curves with respect to the change of single are obtained by using ab initio HF/6-31G basic set. The curves are not similar shapes in the molecules with respect to heterocyclic rings. It is shown that the steric repulsion interactions between phenyl ring and heterocyclic ring are subjected to different type with the respect to each heterocyclic ring. Electronic properties of the molecules were molecules were obtained by applying the optimized structures and selected geometries to the extended Huckel method. To investigate the change of HOMO-LUMO gap with respedt to the torsion angle, we select the optimized structures. By using the results, the dependency of conjugation for the energy gaps is analyzed. For t-PHE the energy gap increase up to 0.52 eV compared with its planar structure. In the cases of t-PHE and t-PHE, the energy gap increase by 1.29 and 1.15 eV, respectively, compared with its planar structure.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.1
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• pp.14-28
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• 1992

For a planar curve-sided paned with constant or linear density distributions of source or doublet in the singularity methods, Cantaloube and Rehbach(1986) show that the surface integral can be transformed into contour integral by using Stokes' formulas. As an extension of their formulations, this paper deals with a planar polygonal panel for which we derive the closed-forms of the potentials and the velocities induced by the singularity distributions. Test calculations show that the analytical evaluation of the closed-forms is superior to numerical integration(suggested by Cantaloube and Rehbach) of the contour integral. The compact and explicit expressions may produce accurate values of matrix elements of simultaneous linear equations in the singularity methods with much reduced computer tiome.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.97-97
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• 2013

We present a comprehensive study on the integration of h-BN with silicon MOSFET. Temperature dependent mobility modeling is used to discern the effects of top-gate dielectric on carrier transport and identify limiting factors of the system. The result indicates that coulomb scattering and surface roughness scattering are the dominant scattering mechanisms for silicon MOSFETs at relatively low temperature. Interposing a layer of h-BN between $SiO_2$ and Si effectively weakens coulomb scattering by separating carriers in the silicon inversion layer from the charged centers as 2-dimensional h-BN is relatively inert and is expected to be free of dangling bonds or surface charge traps owing to the strong, in-plane, ionic bonding of the planar hexagonal lattice structure, thus leading to a significant improvement in mobility relative to undecorated system. Furthermore, the atomically planar surface of h-BN also suppresses surface roughness scattering in this Si MOSFET system, resulting in a monotonously increasing mobility curve along with gate voltage, which is different from the traditional one with a extremum in a certain voltage. Alternatively, high-k dielectrics can lead to enhanced transport properties through dielectric screening. Modeling indicates that we can achieve even higher mobility by using h-BN decorated $HfO_2$ as gate dielectric in silicon MOSFETs instead of h-BN decorated $SiO_2$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.8 s.227
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• pp.895-901
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• 2004

Single-phase convection and nucleate boiling heat transfer were locally investigated for confined planar water jets. The detailed distributions of the wall temperature and the convection coefficient as well as the typical boiling curves were discussed. The curve for the single-phase convection indicated the developing laminar boundary layer, accompanied by monotonic increase of the wall temperature in the stream direction. Boiling was initiated from the furthest downstream as heat flux increased. Heat transfer variation according to the streamwise location was reduced as heat flux increased enough to create the vigorous nucleate boiling. Velocity effects were considered for the confined free-surface jet. Higher velocity of the jet caused the boiling incipient to be delayed more. The transition to turbulence precipitated by the bubble-induced disturbance was obvious only for the highest velocity, which enabled the boiling incipient to start in the middle of the heated surface, rather than the furthest downstream as was the case of the moderate and low velocities. The temperature at offset line were somewhat tower than those at the centerline for single-phase convection and partial boiling, and these differences were reduced as the nucleate boiling developed. For the region prior to transition, the convection coefficient distributions were similar in both cases while the temperatures were somewhat lower in the submerged jet. For single-phase convection, transition was initiated at $x/W{\cong}2.5$ and completed soon for the submerged jet, but the onset of transition was retarded to the distance at $x/W{\cong}6$ for the fee-surface jet.

• Journal of radiological science and technology
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• v.20 no.2
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• pp.73-78
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• 1997

The goal of this paper is that we know the usefulness of echo-planar imaging(EPI) for discriminate between hepatocellular carcinoma(HCC) and hemangioma. We get a time signal intensity curve for liver diseases from the dynamic contrast enhancement images and compared and analyze both the contrast ratio(CR) and the contrast to noise ratio(CNR) using echo planar imaging. The obtained results are follows : 1. Hepatocellular carcinoma was shown the best contrast after about 20 seconds when Is the earlist time in the main artery, and then reduced. The center where is disease was shown the characteristic that the best contrast is appeared after about 35-45 seconds and then slowly reduced. Liver parenchyma was shown the best contrast and reduced after 60 seconds. 2. The peripheral nodular of hemangioma was shown the better contrast soon. On the other hend, the contrast of center where is disease started to increase after 60 seconds and was equal to that of liver parenchyma. Increasing of the contrast continued after. 3. Turbo SE technic was used, the average of CR for hepatocellular carcinoma was $36.7{\pm}1.2$ and the average of CNR was $2.4{\pm}3.2$, while the average of CNR for hemangioma was $54.9{\pm}1.0$ and the average of CNR was $9.7{\pm}1.3$. 4. EPI technic was used, the average of CR for hepatocellular carcinoma was $47.8{\pm}1.2$ and the average of CNR was $3.4{\pm}2.1$, while the average of CNR for hemangioma was $75.7{\pm}2.2$ and the average of CNR was $9.5{\pm}1.1$. According to above we can find that hemangioma is more bright than hepatocellular carcinoma and the difference of brightness between hepatocellular carcinoma and hemangioma is useful sequence.

• Korean Journal of Radiology
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• v.23 no.2
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• pp.180-188
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• 2022

Objective: To validate the performance of 3T spin-echo echo-planar imaging (SE-EPI) magnetic resonance elastography (MRE) for staging hepatic fibrosis in a large population, using surgical specimens as the reference standard. Materials and Methods: This retrospective study initially included 310 adults (155 undergoing hepatic resection and 155 undergoing donor hepatectomy) with histopathologic results from surgical liver specimens. They underwent 3T SE-EPI MRE ≤ 3 months prior to surgery. Demographic findings, underlying liver disease, and hepatic fibrosis pathologic stage according to METAVIR were recorded. Liver stiffness (LS) was measured by two radiologists, and inter-reader reproducibility was evaluated using the intraclass correlation coefficient (ICC). The mean LS of each fibrosis stage (F0-F4) was calculated in total and for each etiologic subgroup. Comparisons among subgroups were performed using the Kruskal-Wallis test and Conover post-hoc test. The cutoff values for fibrosis staging were estimated using receiver operating characteristic (ROC) curve analysis. Results: Inter-reader reproducibility was excellent (ICC, 0.98; 95% confidence interval, 0.97-0.99). The mean LS values were 1.91, 2.41, 3.24, and 5.41 kPa in F0-F1 (n = 171), F2 (n = 26), F3 (n = 38), and F4 (n = 72), respectively. The discriminating cutoff values for diagnosing ≥ F2, ≥ F3, and F4 were 2.18, 2.71, and 3.15 kPa, respectively, with the ROC curve areas of 0.97-0.98 (sensitivity 91.2%-95.9%, specificity 90.7%-99.0%). The mean LS was significantly higher in patients with cirrhosis (F4) of nonviral causes, such as primary biliary cirrhosis (9.56 kPa) and alcoholic liver disease (7.17 kPa) than in those with hepatitis B or C cirrhosis (4.28 and 4.92 kPa, respectively). There were no statistically significant differences in LS among the different etiologic subgroups in the F0-F3 stages. Conclusion: The 3T SE-EPI MRE demonstrated high interobserver reproducibility, and our criteria for staging hepatic fibrosis showed high diagnostic performance. LS was significantly higher in patients with non-viral cirrhosis than in those with viral cirrhosis.

• Journal of the Korea Computer Graphics Society
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• v.22 no.5
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• pp.1-16
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• 2016

In this paper, we propose and efficient curve reconstruction method based on the classical least-square fitting scheme. Specifically, given planar sample points equipped with normals, we reconstruct the objective curve as the zero set of a hierarchical implicit ZP(Zwart-Powell)-spline that can recover large holes of dataset without loosing the fine details. As regularizers, we adopted two: a Tikhonov regularizer to reduce the singularity of the linear system and a discrete Laplacian operator to smooth out the isocurves. Benchmark tests with quantitative measurements are done and our method shows much better quality than polynomial methods. Compared with the hierarchical bi-quadratic spline for datasets with holes, our method results in compatible quality but with less than 90% computational overhead.

• Journal of KIISE:Computer Systems and Theory
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• v.29 no.8
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• pp.440-444
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• 2002

This paper presents an efficient and robust algorithm to compute the isophote of a surface of revolution. A surface of revolution can be decomposed to a set of cross-sectional circles. The surface normals along each cross-sectional circle form a cone. Using the characteristics of the normal vectors and the symmetric property of the surface of revolution, we propose a method to find the connected components of an isophote, which requires intersecting a planar curve(and its reflection) with two rays. Moreover, we propose a closed-form representation of an isophote as a parametric curve.

• Journal of the Korean Vacuum Society
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• v.10 no.4
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• pp.440-448
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• 2001

The operation properties of DBD plasma reactors were observed by using 20 kV square pulse at the cylindrical and planar type of reactors in the condition of air pressure. The optimum operation frequency $f_0$ which optimizes the efficiency of operation was found as such $f_0\proptoexp(-C)$ when the current-voltage curve and charge-voltage curve were observed. Using these properties the dissipated power was evaluated. The dissipated power at the optimum frequency of operation was varied as the value of capacitance which is dependent on the structure and the dielectric material of the reactor, and had the maximum value at the specific value of capacitance. With these value of capacitance, DBD reactors which has a high level of efficiency can be formed.