• Restorative Dentistry and Endodontics
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• v.32 no.1
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• pp.28-36
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• 2007

The purpose of this study was to compare the effect of exponential curing method with conventional curing and soft start curing method on polymerization shrinkage of composite resins. Three brands of composite resins (Synergy Duo Shade, Z250, Filtek Supreme) and three brands of light curing units (Spectrum 800, Elipar Highlight, Elipar Trilight) were used. 40 seconds curing time was given. The shrinkage was measured using linometer for 90 seconds. The effect of time on polymerization shrinkage was analysed by one-way ANOVA and the effect of curing modes and materials on polymerization shrinkage at the time of 90s were analysed by two-way ANOVA. The shrinkage ratios at the time of 20s to 90s were taken and analysed the same way. The results were as follows : 1. All the groups except Supreme shrank almost within 20s Supreme cured by soft start and exponential curing had no further shrinkage after 30s (p < 0.05). 2. Statistical analysis revealed that polymerization shrinkage varied among materials (p = 0.000) and curing modes (p = 0.003). There was no significant interaction between material and curing mode. 3. The groups cured by exponential curing showed the statistically lower polymerization shrinkage at 90s than the groups cured by conventional curing and soft start curing (p < 0.05). 4. The initial shrinkage ratios of soft start and exponential curing were statistically lower than conventional curing (p < 0.05). From this study, the use of low initial light intensities may reduce the polymerization rate and, as a result, reduce the stress of polymerization shrinkage.

• Progress in Medical Physics
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• v.20 no.4
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• pp.308-316
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• 2009

To achieve the accurate evaluation of given absorbed dose from output dose of linear accelerator photon beam through investigate the characteristics of LiF:Mg,Cu,P TLD powder. This experimental TL phosphor is performed with a commercial LiF:Mg,Cu,P powder (Supplied by PTW) and TL reader (LTM, France). The TLD was exposed to 6 MV X rays of linear accelerator photon beam with range 15 to 800 cGy in blind dose at two hospitals. The dose evaluation of TLD was through the experimental algorithms which were dose dependency, dose rate dependency, fading and powder weight dependency. The glow curve has shown the three peaks which are 110, 183 and 232 degrees of heating temperature and the main dosimetric peak showed highest TL response at 232 high temperature. In this experiments, the LiF:Mg,Cu,P phosphor has shown the 2.5 eV of electron trap energy with a second order. This experiments guided the dose evaluation accuracy is within 1% +2.58% of discrepancy. The TLD powder of LiF:Mg,Cu,P was analyzed to dosimetric characterists of electron captured energy and order by glow shape, and dose-TL response curve guided the accuracy within 1.0+2.58% of output dose discrepancy.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.555-566
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• 2007

In general, RMR classification system is used for the support design of a tunnel. Face mapping during excavation and RMR-based rock classifications are conducted in order to provide information for complementary changes to preliminary survey plans and for continuous geological estimations in direction of tunnel route. Although they are ever so important, there are not enough time for survey in general and sometimes even face mapping is not available. Linear regression analysis for the estimation of mediating RQD and condition of discontinuities, which require longer time and more detailed observation in RMR, was performed and optimum regression equations are suggest as the result. The geological data collected from tunnels were analyzed in accordance with three rock types as sedimentary rock, phyllite and granite to see geological effects, generally not been considered in previous researches. Parameters for the regression analysis were set another RMR factor.

• Korean Journal of Materials Research
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• v.6 no.3
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• pp.253-263
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• 1996

고온.고압하에서 장시간 사용되는 고온부재용 구조물은 경년열화현상을 나타낸다 그러므로 구조물의 안정성 측면에서 재질열화의 정도를 정량적으로 평가하는 것이 중요하다. 그러나 실기 구조물에서 채취할 시험편의 크기와 수는 제한이 되기 때문에 새로운 비파괴적인 평가법이 요구되고 있다. 따라서 본 연구에서는 화력발전설비에 이용되는 탄소강과 페라이트강에 대한 열화도의 평가를 위해 입계부식법의 적용 가능성을 조사한다. 시험결과, 재질열화의 정도는 사용시간보다 사용온도에 더 큰 영향을 받았으며, Larson-Miller인자와 열화도([$\Delta$DBTT]SP)사이의 관계는 선형적이었으나, 강종에 따라 다른 기울기를 보였다. 반면, 연성-취성천이온도 ([$\Delta$DBTT]SP)와 격자절단비(Ni/No)와 관계는 강종에 무관하게 선형적인 비례관계를 나타내었다. 또한, [$\Delta$DBTT]SP와 Ni/No 의 관계로부터 입계부식법은 페라이트계 강뿐만아니라 탄소강에 대해서도 유용한 재질열화 평가 방법임을 알 수 있었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.1
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• pp.57-65
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• 2023

A vibration response-based detection system was used to investigate the adhesive areas of single-lap joints using a nonlinear transformation approach for deep learning. In industry or engineering fields, it is difficult to know the condition of an invisible part within a structure that cannot easily be disassembled and the conditions of adhesive areas of adhesively bonded structures. To address these issues, a detection method was devised that uses nonlinear transformation to determine the adhesive areas of various single-lap-jointed specimens from the vibration response of the reference specimen. In this study, a frequency response function with nonlinear transformation was employed to identify the vibration characteristics, and a virtual spectrogram was used for classification in convolutional neural network based deep learning. Moreover, a vibration experiment, an analytical solution, and a finite-element analysis were performed to verify the developed method with aluminum, carbon fiber composite, and ultra-high-molecular-weight polyethylene specimens.

• Proceedings of the Korean Association for Survey Research Conference
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• 2001.04a
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• pp.59-71
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• 2001

We investigate design-based variance estimation methods of homogeneous linear estimator for population total under stratified multi-stage sampling. One method is unbiasedly estimating the first stage variance and the second stage variance separately in each stratum. And another is sub-sampling method that estimating the first stage variance only by using sub-sample selected from the second stage sample so that resulting estimator is unbiased for the total variance. The first is useful when the second stage unbiased estimator is available and the second is when the second stage variance is not estimable. For each case, we proposed a form of non-negative unbiased variance estimator. We expect the proposed variance estimation methods can be effectively used for many practical surveys.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3D
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• pp.435-444
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• 2006

This paper investigates the effect of 3-dimensional FE models to evaluation results of jointed concrete pavements which is back-calculated by AREA method. Sensitivity of 3-dimensional FE models developed to simulate the behavior of real jointed concrete pavement are analyzed after compared with 2-dimensional FE models using ILLISLAB. In comparison with 2-dimensional models, influence of concrete contraction under loading plate and base layer on surface deflections is more than that of loading configuration. Deflections at 3-dimensional model between linear and nonlinear temperature distribution under same temperature difference are similar, but noticeable differences are investigated in low elastic modulus of foundations. Dynamic deflections under loading plate are larger than static deflections in high elastic modulus of foundation, but smaller in low elastic modulus. Lower dynamic modulus of subgrade reactions are backcalculated by dynamic deflections than by static deflections. But reverse trend is investigated in the backcalculated elastic modulus of concrete which describes trends of the field backcalculation values calculated from AREA method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.54-59
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• 2005

Nonlinear aeroelastic analyses of a missile control fin are performed considering backlash and dynamic stiffness of actuator. Doublet-Hybrid method is used for the calculation of subsonic unsteady aerodynamic forces, and aerodynamic forces are approximated by the minimum-state approximation. For nonlinear flutter analysis backlash is represented by a free-play and is linearized by using the describing function method. Also, dynamic stiffness is function of frequency and is calculated by solving equation of motion for actuator. The linear and nonlinear flutter analyses show that the aeroelastic characteristics are significantly dependent on the backlash and dynamic stiffness. From the nonlinear flutter analysis, various types of limit cycle oscillations are observed in a range of air speeds below the linear divergent flutter boundary. The nonlinear flutter characteristics and the nonlinear aeroelastic responses are also investigated in the time domain.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.407-415
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• 1999

There are two kinds of instability phenomena for shell-type structures which are snap-through and bifurcation buckling. These are very sensitive according to the shape characteristics including rise-span ratio and especially shape initial imperfection. In this study, the equilibrium path of shallow sinusoidal arches supported by hinges at both ends is investigated to grasp the instability behavior of shell-type structures with initial imperfection. The Galerkin method is used to get the nonlinear discretized equation of governing differential equation considering geometric nonlinearity of arches and the perturbation method is also used to transform the nonlinear equation to incremental form.

• Journal of the Korean Data and Information Science Society
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• v.11 no.2
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• pp.235-245
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• 2000

In this paper, we consider the Regression Quantiles Estimators in nonlinear regression models. This paper provides the sufficient conditions for strong consistency and asymptotic normality of proposed estimation and drives asymptotic relative efficiency of proposed estimatiors with least square estimation. We give some examples and results of Monte Carlo simulation to compare least square and regression quantile estimators.