• The Journal of the Korean dental association
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• v.47 no.7
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• pp.444-454
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• 2009

The purpose of this study was to compare the shaping abilities of LightSpeed, ProTaper-Universal, and hybrid technique using S-series of ProTaper-Universal and LigthSpeed. The 72 simulated root canals of J-shape were used and classified as flowing 3 groups according to the instrumentation methods; Group P of 24 canal blocks were prepared with ProTaper-Universal, Group L was prepared with LightSpeed, and Group H was prepared with hybrid technique (initial shaping with ProTaper-Universal SI and S2 and apical shaping with LightSpeed from #25 to #50). A second-year resident of Endodontic department prepared the resin block canals to apical size #50 (F5 in Group P). The time lapses for instrumentation and the reduction of root canal curvature after shaping were measured. The pre- and post-instrumented root canals were scanned and superimposed to evaluate and calculate the increased canal width and apical centering ratio. The results were as followings: Group Land H showed significant less instrumentation time than Group P (p < 0.05). The ProTaper system showed greater reduction of root canal curvature and working length diminishment than other methods (p < 0.05). LightSpeed system showed best canal curvature preserving characteristics. The Group P had greater instrumented widths at all levels examined (p < 0.05). Group L and Group H showed lower centering ratio (ability to preserve the canal center; the lower ratio means the better canal center preservation) than Group P (p < 0.05). Group H had the lowest centering ratio at the 1 mm level.

• Journal of the Korean Mathematical Society
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• v.50 no.6
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• pp.1311-1332
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• 2013

This paper concerns the evolution of a closed hypersurface of the hyperbolic space, convex by horospheres, in direction of its inner unit normal vector, where the speed equals a positive power ${\beta}$ of the positive mean curvature. It is shown that the flow exists on a finite maximal interval, convexity by horospheres is preserved and the hypersurfaces shrink down to a single point as the final time is approached.

• International Journal of Automotive Technology
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• v.8 no.3
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• pp.337-342
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• 2007

A multi-objective optimization technique was implemented to obtain optimal topologies of the inner reinforcement for a vehicle's hood simultaneously considering the static stiffness of bending and torsion and natural frequency. In addition, a smoothing scheme was used to suppress the checkerboard patterns in the ESO method. Two models with different curvature were chosen in order to investigate the effect of curvature on the static stiffness and natural frequency of the inner reinforcement. A scale factor was employed to properly reflect the effect of each objective function. From several combinations of weighting factors, a Pareto-optimal topology solution was obtained. As the weighting factor for the elastic strain efficiency went from 1 to 0, the optimal topologies transmitted from the optimal topology of a static stiffness problem to that of a natural frequency problem. It was also found that the higher curvature model had a larger static stiffness and natural frequency than the lower curvature model. From the results, it is concluded that the ESO method with a smoothing scheme was effectively applied to topology optimization of the inner reinforcement of a vehicle's hood.

• Steel and Composite Structures
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• v.4 no.3
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• pp.227-246
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• 2004

This paper presents a moment-curvature method that accounts for the strength deterioration of steel at elevated temperature in estimating the response of steel beams exposed to fire. A modification to the EC4 method is proposed for a better estimation of the temperature distribution in the steel beam supporting a concrete slab. The accuracy of the proposed method is verified by comparing the results with established test results and the nonlinear finite element analysis results. The beam failure criterion based on a maximum strain of 0.02 is proposed to assess the limiting temperature as compared to the traditional criteria that rely on deflection limit or deflection rate. Extensive studies carried out on steel beams with various span lengths, load ratios, beam sizes and loading types show that the proposed failure criterion gives consistent results when compared to nonlinear finite element results.

• Proceedings of the Korean Nuclear Society Conference
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• 2003.05a
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• pp.143.1-143.1
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• 2003

• Transactions of Materials Processing
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• v.16 no.7
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• pp.555-560
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• 2007

This paper shows some achievements at bending of extruded aluminum profiles during the extrusion process. The conventional process for the production of bent profiles involves a successive extrusion, stretching, and bending of the profiles. Conventional bending methods can not meet demands far precision and cost-effective production in some cases, due to cross sectional deformation, irregular decrease of tube wall thickness and a complication of the process design. An estimation of spring-back required for precision of the bending radius can not always be achieved by the over bending of the profile. Since the profile is hot during the bending process, the spring-back phenomenon can be avoided. This means that an additional bending process is not necessary. Consequently, flexible bending can be achieved with cost reduction and quality improvement. Experimental tests were completed to study the relationship between curvature radius of profile and position of guide on the extrusion for vehicle bumper. A7108 is applied as a billet material in order to increase strength. The overall correlation between the experimental and numerical results is good. It is therefore concluded that the present method provides an efficient means for the constant curvature extrusion process.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3223-3226
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• 2013

Spherical phospholipid-bilayers, vesicles, were prepared using the layer-by-layer double emulsion technique, which allows the bilayer to be formed asymmetrically. On the outer layer of the vesicles, the phospholipase D (PLD) reacted to convert phosphatidylcholine (PC) to phosphatidic acid (PA). The reaction induced the curvature change of the vesicles, which eventually led to rupture. The response time from the time of PLD injection to the time of rupture was measured against different vesicle curvatures and the outer layer phase, using the fluorescence intensity change of a pH-sensitive dye encapsulated within the vesicles. The effect of the vesicle curvature on the response was observed to be more significantly dramatic at the solid phase, compared to the liquid phase. Furthermore, in the solid phase, the response time was faster for 80 and 155 nm vesicles and, slower for 605 nm vesicles than similarly sized vesicles in the liquid phase vesicles. This difference in the response time was thought to result from the configuration determined by the phase difference and the PLD behavior.

• Bulletin of the Korean Mathematical Society
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• v.36 no.2
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• pp.217-224
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• 1999

In this paper the properties of the Finsler metrics compatible with an f-structure are investigated.

• Journal of the Korean Mathematical Society
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• v.48 no.2
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• pp.329-340
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• 2011

We shall give some curvature conditions for the unit tangent sphere bundle of an n($\geq$ 4)-dimensional Riemannian manifold to be H-contact. Furthermore, we provide an example illustrating Main Theorem.

• Communications of the Korean Mathematical Society
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• v.24 no.2
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• pp.265-275
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• 2009

The object of the present paper is to study 3-dimensional normal almost contact metric manifolds satisfying certain curvature conditions. Among others it is proved that a parallel symmetric (0, 2) tensor field in a 3-dimensional non-cosympletic normal almost contact metric manifold is a constant multiple of the associated metric tensor and there does not exist a non-zero parallel 2-form. Also we obtain some equivalent conditions on a 3-dimensional normal almost contact metric manifold and we prove that if a 3-dimensional normal almost contact metric manifold which is not a ${\beta}$-Sasakian manifold satisfies cyclic parallel Ricci tensor, then the manifold is a manifold of constant curvature. Finally we prove the existence of such a manifold by a concrete example.