• 대한치과교정학회지
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• 제21권3호
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• pp.635-656
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• 1991

It was the aim of this investigation to evaluate some histologic aspect of rat pulp tissue after it had been compromised by an experimental orthodontic force. Experimental animals of thirty five Spraque-Dawley rats were employed. The first upper molars had been successively mesial moved (initial load 100 gr.) with a closed coil spring during 21 days. The experimental periods were set on immediate, 1 day, 1 week, 2 weeks, 3 weeks, 4 weeks following retention time. On each experimental period, the rats were killed and prepared for the light microscopy. After prepared with H/E stain and Gomori's one-step trichrome stain, the specimens were analyzed with evaluation criteria which were adopted in this study. The result may be summarized as follows; 1. The main pulp changes due to experimental orthodontic force included vacuolization of odontoblastic layer, circulation disturbance, root resorption, reduced pulp collagenous fiber density and mean cell count of pulp fibroblast in the immediate group. 2. The pulp tissue changes were revealed reversible because the relieved pulp tissues from experimental orthodontic force were recovered rapidly in each evaluation criteria during retention periods. 3. Compared with normal control group, pulp collagenous fiber density were decreased in immediated group (p < 0.01), but increased in each retention groups. These seem to suggest that the pulp tissues were aged after experimental orthodontic force conditions. 4. Compared with normal control group, mean cell counts of pulp fibroblasts were decreased in immediate group (p < 0.05), but increased continuous in each retention groups. These seem to indicate that the pulp tissues were highly regenerative after experimental orthodontic force conditions. 5. Compared with normal control group, root resorptions occurred in all immediate specimens (p < 0.01) and they were healed in each retention periods, but often observed in 4 weeks retention group. These seem to indicate that root resorptions were recovered slowly after experimental orthodontic force conditions.

• 한국정밀공학회지
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• 제25권6호
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• pp.159-167
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• 2008

Cooling lubricants are used in machining operations in order to reduce friction at the tool-chip and tool-workpiece interfaces, cool both chip and tool, and remove chip. Furthermore, they influence a strong effect on the shearing mechanisms and, consequently, on the machined surface quality and tool wear. However, several researchers state that the costs related to cutting fluids is frequently higher than those related to cutting tools. Moreover, the cooling lubricants cause an increase in both worker's health and social problems related to their use and correct disposal. Therefore, many researchers have focused on the environmentally conscious machining technologies. One of the technologies is known as MQL(Minimum Quantity Lubrication) machining. In this paper, an experimental model to obtain the optimal cutting conditions in MQL turning was suggested, and the effects of cutting conditions on surface roughness and cutting force were analyzed. For these purposes, FFD (Fractional Factorial Design) and RSM (Response Surface Methods) were used for the experiment. Cutting force and surface roughness with different cutting conditions were measured through the external cylindrical turning of Al 6061 based on the experiment plan. The measured data were analyzed by regression analysis and verification experiments with random conditions were conducted to confirm the suggested experimental model.

• Integrative Medicine Research
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• 제6권4호
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• pp.388-394
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• 2017

Background: The present study optimized ultrasound-assisted extraction conditions to maximize extraction yields of glycyrrhizic acid from licorice. Methods: The optimal extraction temperature ($X_1$), extraction time ($X_2$), and methanol concentration ($X_3$) were identified using response surface methodology (RSM). A central composite design (CCD) was used for experimental design and analysis of the results to obtain the optimal processing parameters. Results: Statistical analyses revealed that three variables and the quadratic of $X_1$, $X_2$, and $X_3$ had significant effects on the yields and were followed by significant interaction effects between the variables of $X_2$ and $X_3$ (p<0.01). A 3D response surface plot and contour plots derived from the mathematical models were applied to determine the optimal conditions. The optimum ultrasound-assisted extraction conditions were as follows: extraction temperature, $69^{\circ}C$; extraction time, 34?min; and methanol concentration, 57%. Under these conditions, the experimental yield of glycyrrhizic acid was 3.414%, which agreed closely with the predicted value (3.406%). Conclusion: The experimental values agreed with those predicted by RSM models, thus indicating the suitability of the model employed and the success of RSM in optimizing the extraction conditions.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.125.2-125.2
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• 2010

In this paper, both theoretical and experimental investigations have been performed to examine the effects of key operating parameters on the cell performance of a DMFCs (i.e., methanol feed concentration and operating temperature). For experiment, the membrane electrode assemblies (MEAs) were prepared using a conventional MEA fabrication method based on a catalyst coated electrode (CCE) and tested under various cell temperatures and methanol feed concentrations. The polarization curve measurements were conducted using in-house-made $25cm^2$ MEAs. The voltage-current density data were collected under three different cell temperatures ($50^{\circ}C$, $60^{\circ}C$, and $70^{\circ}C$) and four different methanol feed concentrations (1 M, 2 M, 3 M, and 4 M). The experimental data indicate that the measured I-V curves are significantly altered, depending on these conditions. On the other hand, previously developed one-dimensional, two-phase DMFC model is simulated under the same operating conditions used in the experiments. The model predictions compare well with the experimental data over a wide range of these operating conditions, which demonstrates the validity and accuracy of the present DMFC model. Furthermore, both simulation and experimental results exhibit the strong influences of methanol and water crossover rates through the membrane on DMFC performance and I-V curve characteristics.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.233-243
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• 2019

In this paper, numerical and experimental studies are performed to investigate the liquid impact on a free falling wedge. In the numerical simulation, the structure is assumed to be rigid and the elastic response is ignored. The fully nonlinear coupling between wedge and water is considered by an auxiliary function method based on the Boundary Element Method (BEM). At the intersection of the wedge surface and liquid surface, two coincident nodes are used to decouple the boundary conditions. The Eulerian free surface conditions in the local coordinate system are adopted to update the deformed free surface. In the experiments, five pressure sensors are fixed on each side of the wedge which is released from an experimental installation. Steel and aluminum wedges that have different structural elasticity are used in the experiments to investigate the influence of structural elasticity on the impact force. Numerical results are compared with experimental data and they agree very well. The influence of fluid gravity, body mass, initial entry speed and deadrise angle on the impact pressure are further investigated.

• Journal of the Korean Data and Information Science Society
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• 제21권5호
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• pp.853-861
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• 2010

선박운항 안정성 평가를 위한 시뮬레이션 설계 시 선박운항에 영향을 미치는 요인들을 고려하여 실험조건을 설정한다. 배속 시뮬레이션에서는 이론적으로 수많은 실험조건도 수행 가능하나, 동일 실험조건 하에서는 동일 항해위험 관련 측정치를 얻으므로 확률모형이 아니다. 실시간 시뮬레이션은 실험에 참여하는 선박운항 전문가로 인한 변동이 발생하여 확률모형 분석이 가능하나 소요되는 실험시간으로 인하여 실험회수의 제한이 있다. 그리하여 배속 시뮬레이션을 활용하여 항해 위험도가 높은 실험조건을 선택하고, 선택된 실험조건에서만 실시간 시뮬레이션을 실시하여 항만 항해 위험도를 산정하고 있다. 이전 연구에서는 전문가의 주관적 판단이나 확률분포함수 개념을 활용하여 항해 위험도가 높은 실험조건을 선택하는 방법이 제안되었다. 그러나 이 방법들은 최종 횡단 데이터를 활용하여 시뮬레이션 과정에서 발생하게 되는 위험도를 측정하는 방법으로는 적절하지 못하다. 본 연구에서는 시뮬레이션의 항적 데이터로부터 얻는 주성분 점수를 활용하여 이상 실험조건을 진단하고 항해 위험도 높은 지점을 판단하는 방법을 제안하고 실증분석 결과도 제시하였다.

• Design & Manufacturing
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• 제14권1호
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• pp.30-35
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• 2020

Plastic pulleys used for the purpose of power transmission have to very high roundness characteristics. The roundness of plastic pulleys is influenced by many factors. In this study, the effect of molding conditions on the roundness of pulleys was analyzed using a numerical analysis program. To improve the roundness, molding conditions that minimize the amount of deformation of the pulley were studied through an experimental design method. Among the experimental design methods, the Taguchi method was used, and the main molding conditions affecting the deformation of the pulley were the resin temperature and the holding pressure. It was found that the amount of deformation is reduced by about 2.86% when molding with the optimum molding conditions compared to when the optimum molding conditions are not applied.

• Journal of Advanced Marine Engineering and Technology
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• 제35권7호
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• pp.881-890
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• 2011

Analyses of performance and behavior of the individual PEM fuel cells (PEMFC) under different operating conditions are of importance optimally to design and efficiently to operate the stack. The paper focuses on experimental analyses of a two-cell stack under different operating conditions, which performance and behavior are measured by the voltage of a cell as well as the stack. Experimental parameters include stoichiometric ratio, temperature of the air supplied under different working stack temperatures and loads. Results showed that the cell voltages are dominantly influenced by the temperature of the air supplied among others. In addition, an inherent difference between the first and the second cell voltage exists because of the tolerances of the cell components and the resulting different over-potentials at different equilibrium states. Furthermore, it is shown that the proton conductivity in the membranes conditioned by the humidity in the cathode channel highly affects the voltage differences of the two cells.

• International Journal of Air-Conditioning and Refrigeration
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• 제14권1호
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• pp.28-39
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• 2006

Two-phase flow through a T-junction has been studied by numerous researchers so far. The dividing characteristics of the gas and liquid phases at the T-junction are very complicated due to a lot of related variables. The prediction models have been suggested by using experimental data for a specific condition or working fluid. But, they showed the application limitation for the most of the other conditions or fluids. Since most of them are applicable for their own experimental range, the generalized model for the wide range of conditions and fluids is needed. Even though it's not available now, some of the models developed for air-water flow at a T-junction might be applicable for the part of refrigerants with some modifications. Especially, for the two-phase flow of refrigerants at the T-junction, very few studies have been performed. Further experimental study is required to be performed for the wide range of test conditions and fluids to predict properly the two-phase flow distribution and phase separation through the T-junction.

• 한국기계가공학회지
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• 제11권2호
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• pp.73-78
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• 2012

Recently, the laser processing method has used as micro-machining technologies in industries of aerospace, electronics and automotive. The laser processing newly focused could be alternative to existing machining method. However, there are few practical results of research about the proper setting of the laser machining conditions and the laser machining characteristics for mechanical materials. The purposes of this study was to choose optimum machining conditions and to estimate the laser machining characteristics using taguchi experimental method for various mechanical materials that is S45C, Stainless steel, Aluminum, Copper, Titanium and Tungsten carbide. From obtained results, it was confirmed that optimum machining conditions could be found and laser machinability depends on thermal conductivity and hardness of workpiece.