• 대한기계학회논문집B
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• 제21권12호
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• pp.1710-1719
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• 1997

An approximate analytical solution for the initial transient process of close-contact melting occurring between a phase change material kept at its melting temperature and an isothermally heated flat surface is derived. The model is so developed that it can cover both rectangular and circular cross-sectional solid blocks. Normalization of simplified model equations in reference to the steady solution enables the solution to be expressed in a generalized form depending on the liquid-to-solid density ratio only. A selected result shows an excellent agreement with the previously reported numerical data, which justifies the present approach. The solution appears to be capable of describing all the fundamental characteristics of the transient process. In particular, dependence of the solid descending velocity oft the density ratio at the early stage of melting is successfully resolved. The effects of other parameters except the density ratio on the transient behaviors are efficiently represented via the steady solution implied in the normalized result. A simple approximate method for estimating the effect of convection on heat transfer across the liquid film is also proposed.

• 한국초등수학교육학회지
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• 제17권3호
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• pp.503-522
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• 2013

2009개정 교육과정부터 현장에서 창의성 교육에 대한 관심이 상당히 높아지고 있고, 평가에서도 '수학적 지식과 기능을 바탕으로 창의적으로 사고하는 능력'을 강조하고 있다. 이에 본 연구에서는 문제해결로서 수학창의성을 평가하는 비교적 간단한 방안을 제안한다. 수학적 창의성을 확산적 사고에 초점을 맞추어 유창성, 융통성 및 독창성 요인으로 측정하는 것은 수학이라는 본연의 특징을 반영하지 못한다는 비판도 있지만 지필고사로서는 창의적 산물의 두 가지 기준인 신기성(새로움)과 적절성(가치) 중에서 후자를 반영하기 힘들었다. 본 연구에서 수학적 문제해결에서 학생들이 제출한 해에 서로 다른 가중치를 부여하여 창의성의 적절성을 측정하는 방안에 대한 고려들을 연구하였다. 첫째, 학생과 교사가 생각하는 우수한 해의 특성은 무엇인가? 둘째, 두 집단 간 우수한 해의 판단은 일치하는가? 두 가지 의문에 대해 두 집단 모두 우수한 해는 '풀이과정이 간단하고 이해하기 쉽다.'로 요약되었으며, 반면 나쁜 풀이는 그 반대로 '풀이가 복잡하고 이해하기 힘었다.'로 약될 수 있었다. 그리고 본 연구에서 제시한 두 가지 문제해결에서 두 집단 모두 우수한 해의 순서는 일치하였다. 아울러 두 집단이 평가한 우수 해의 일치가 의미하는 바와 해의 차등화 방안에 대한 논의를 통해 수학창의성 평가 방안을 제안하였다.

• 한국염색가공학회지
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• 제35권4호
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• pp.239-245
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• 2023

Cellulose is an abundant biodegradable material in nature with excellent properties, but due to its poor processability, it has been widely studied for processing through modification. Cellulose acetate propionate (CAP) is a cellulose derivative in which the hydroxyl group of cellulose is replaced by acetyl and propionyl groups. CAP has several advantages, such as excellent solubility, structural stability, light and weather resistance, and good transparency. Porous nanofibers with excellent specific surface area, which can be applied in various fields, can be easily formed by the phase separation method using highly volatile solvents. High speed centrifugal spinning is a nano/micro fiber preparation method with advantages such as fast spinning and easy alignment control. In this study, a CAP/polybutylene succinate (PBS) spinning solution with chloroform as solvent was prepared to prepare porous microfibers and the fiber morphology was examined as a function of the disk rotation speed in an high speed centrifugal spinning device.

• 한국막학회:학술대회논문집
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• 한국막학회 2002년도 제10회 하계 Workshop
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• pp.59-101
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• 2002

PVDF is good material for a hollow fiber membrane with high porosity and excellent hydrophobicity. Asymmetric PVDF hollow fiber membranes were prepared by the Loeb-Sourirajan phase inversion method. Asymmetric PVDF hollow fiber membranes could be controlled in pore size and porosity using various additives(LiCl, ZnCl$_2$) and internal coagulants (water, EtOH/water, and DMAc/water mixture). $CO_2$removal efficiency of asymmetric PVDF hollow fiber membranes was 1.2 times high than that of commercialized PP hollow fiber membranes at MEA 5wt% solution. $CO_2$flux of asymmetric PVDF hollow fiber membranes was 2.5 times higher than that of commercialized PP hollow fiber membranes. $CO_2$removal efficiency and absorption rate of asymmetric PVDF hollow fiber membranes were 30 times higher than those of packed column at absorbent $H_2O$. $CO_2$flux of asymmetric PVDF hollow fiber membranes at MEA 5wt% solution was 48 times higher than that of pure water. In the case of MEA 5wt% solution used as an absorbent, the $CO_2$absorption rate and removal efficiency of PVDF hollow fiber membrane were 2.3 times higher than that of a packed column.

• Steel and Composite Structures
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• 제17권1호
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• pp.133-143
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• 2014

In this paper, we try to prepare an accurate analytical solution for solving nonlinear vibration of thin circular sector cylinder. A new approximate solution called variational approach is presented and correctly applied to the governing equation of thin circular sector cylinder. The effect of important parameters on the response of the problem is considered. Some comparisons have been presented between the numerical solution and the present approach. The results show an excellent agreement between these methods. It has been illustrated that the variational approach can be a useful method to solve nonlinear problems by considering the effects of important parameters.

• Steel and Composite Structures
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• 제17권1호
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• pp.123-131
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• 2014

In this paper we have considered the vibration of parametrically excited oscillator with strong cubic positive nonlinearity of complex variable in nonlinear dynamic systems with forcing based on Mathieu-Duffing equation. A new analytical approach called homotopy perturbation has been utilized to obtain the analytical solution for the problem. Runge-Kutta's algorithm is also presented as our numerical solution. Some comparisons between the results obtained by the homotopy perturbation method and Runge-Kutta algorithm are shown to show the accuracy of the proposed method. In has been indicated that the homotopy perturbation shows an excellent approximations comparing the numerical one.

• 한국환경보건학회지
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• 제17권2호
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• pp.95-101
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• 1991

Lead acetate solution were intraperitoneally injected to rats of average body weight 220g to cause lead poisoning. Antidotes were orally administered using catheter to the rats and the urine was collected after 24 hours. ALA in the urine were determined by U. V. spectrophotometer. Antidotes used in this experiment were the water extracts of scutellaria radix and D-penicillamine solution. ALA in the urine was determind by Wada method. It was found that ALA content in the urine was decreased after oral administration of water extracts of scutellaria radix and D-penicillamine solution. In this study it is believed that water extract of suctellaria radix could be used as an excellent antidate in lead poisoning.

• 한국염색가공학회지
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• 제22권2호
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• pp.163-172
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• 2010

In order to investigate the changes in mechanical properties of sanitary nonwoven fabrics actually used as a top sheet, the fabric was treated with a mixture of chitosan and nanosilver colloidal solution in accordance with the prescribed ratio. The former is a natural polymer with excellent biocompatibility and the latter can give an additional performance while compensating the weaknesses of chitosan of deteriorating adherence efficiency. It was shown that the bending and shearing characteristics of the chitosan/nanosilver treated fabrics decreased, which helped to make it softer, smoother and more flexible. The shape stability and drapability of the treated fabrics improved. As KES-FB system evaluation showed that Koshi was deduced, and both Numeri and Fukurami were increased. Thereby, the chitosan/nanosilver treated fabrics were smoother to provide elasticity. In the change of hand value compared to chitosan only treatment, a better THV was shown in the fabrics treated with chitosan/nanosilver mixed solution than the fabric treated with chitosan alone.

• 미생물학회지
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• 제12권1호
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• pp.25-30
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• 1974

It was convinced that with a relatively small capital investment and with a low operating cost, appreciable amounts of cement copper could be produced from low-grade minerals by the application of a bacterial leaching method. For the recovery of cement copper from the impure pregnant solution, direct precipitation of copper with tin plates by a bacterial leaching method was feasible. The results obtained were as follows: 1)In order to remove the cement copper from the reducing metal, aeration and agitation method were more effective and economic than shaking method. 2)The rate of copper recovery from the pregnant solution was accerelated according to increasing quantities of reducing metal. However, the excess of reducing metal reduced the grade of cement copper. 3)Among the comparative experiments of copper recovery at each reaction temperature of $10^{\circ}C$, $20^{\circ}C$, and $30^{\circ}C$, the recovery rate of copper at $30^{\circ}C$from the pregnant solution was highest. 4)Direct cementation method on iron-containing metal was an excellent method for the recovery of cement copper in bacterial leaching.

• 환경위생공학
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• 제11권2호
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• pp.33-41
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• 1996

This study was performed to examine the factors influencing on the degradation of TCE, Benzene and 2,4 DCP in aqueous solution using ultrasonic irradiation. The TCE,Benzene and 2,4 DCP, which are hazard compounds causing environmental pollution, were not decomposable pollutants by convientional treatment. The results shows that the generation of H$_{2}$O$_{2}$, H$^{+}$ and OH$^{-}$ radical was formed by the oxidation and reduction reaction of ultrasound, and then theses decomposed the refractory pollutants of TCE, Benzene & 2,4 DCP in aqueous solution. we conformed that the ultrasonic irradiation was excellent in removal efficiency of the refractory pollutants any other than Advanced Oxidation Processes(AOP), utilized the treatment of organic compounds in the industrial wastewater. Consequently, these results suggest that ultrasonic irradiation may be extremely useful for the treatment of wastewaters contaminated organic pollutants, which is difficult to treat economically by conventional process.