• Bulletin of the Korean Chemical Society
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• v.35 no.9
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• pp.2851-2854
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• 2014

• Korea-Australia Rheology Journal
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• v.20 no.2
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• pp.51-58
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• 2008

This paper describes a two-step Tikhonov regularization procedure for converting the steady shear data generated by parallel-disk viscometers, in the presence of wall slip, into a shear stress-shear rate function and a wall shear stress-slip velocity functions. If the material under test has a yield stress or a critical wall shear stress below which no slip is observed the method will also provide an estimate of these stresses. Amplification of measurement noise is kept under control by the introduction of two separate regularization parameters and Generalized Cross Validation is used to guide the selection of these parameters. The performance of this procedure is demonstrated by applying it to the parallel disk data of an oil-in-water emulsion, of a foam and of a mayonnaise.

• Korea-Australia Rheology Journal
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• v.21 no.2
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• pp.135-141
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• 2009

Effect of activation energy and crystallization kinetics of polyethylenes (PEs) on the dynamics and stability has been investigated by changing rheological properties and crystallization rate in film casting process. The effect of changes of these properties has been shown using a typical example of short-chain branching (SCB) in linear polyethylenes. SCBs in linear polymers generally lead to the increase of the flow activation energy, and to the decrease of the crystallization rate, making polymer viscosity lower in the case of equivalent molecular weight. In general, the increment of the crystallinity of polymers under partially crystallized state helps to enhance the process stability by increasing tension, and lower fluid viscoelasticity possesses the stabilizing effect for linear polymers. It has been found that the fluid viscoelasticity plays a key role in the control of process stability than crystallization kinetics which critically depends on the cooling to stabilize the film casting process of short-chain branched polymers operated under the low aspect ratio condition.

• Journal of the Korean Applied Science and Technology
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• v.30 no.3
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• pp.411-422
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• 2013

Polymers in cosmetics are used to deliver desired attributes to skin and hair. Precisely constructed block and graft copolymers widen the range of available mechanical properties and compatibilities. Stimuli responsive hydrophobic polymers can be triggered to become hydrophilic by changes in their environment and this can confer waterproof properties at low temperature and easy water removal at higher temperatures. Transfer-resistant cosmetics can be possible due to silicone resins. The control of rheology properties in cosmetics gradually continue to be easy with copolymers. Durability of colors and fragrances for rinse-off products can be enhanced by delivery systems from complex coacervates. Polymeric anti-microbials promise product preservation while minimizing the concern of skin permeation. This article reviews recent trends in the use of polymers in cosmetics.

• The Korean Journal of Rheology
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• v.5 no.1
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• pp.34-48
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• 1993

최근 CAD/CAM의 발전과 더불어 사출성형공정은 여러분야에 폭넓게 응용되고 있 다. 사출성형공정은 크게 충전과정(filling stage), 냉각과정(cooling stage), 보압과정(packing stage)로 나누어 지는데 이중 충전과정은냉각과정과 보압과정에서 나타날 물리적인 현상과 최종 성형품의 기계적 성질에 중요한 영향을 끼치게 된다. 충전과정의 수치 해석 방법은 대 표적으로 control volume method, branching flow method, transient moving boun-dary method로 구분된다. 본 연구에서는 격자의 형태를 양호하게 형성시키고 유동선단의 형태를 개선하기위한 기법인 Spline 곡선을 이용한 선단격자 재구성(frontal remeshing using spline curve)과 수치해석에 소요되는 시간을 줄이기 위하여 벽면경계조건 처리를 위한 선단 유동 장생성(frontal flow field construction for wall boun-dary condition treatment)기법을 개발 하고 transient moving voundary method에 적용시켜 원형 평판과 인장 및 굽힘시편 그리고 두께가 변하는 사각 형상을 가진 캐비터에서의 충전과정을 수치해석하였다. 그결과 압력 분 포, 온도분포, 속도장, 유동선단의 진전형태 등이 기존에 제출된 해석결과와 비교하여 볼 때 만족스러운 수치해석결과를 보였다.

• The Korean Journal of Rheology
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• v.6 no.1
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• pp.20-29
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• 1994

본 논문에서는 실리콘 오일을 용매로 사용하여 조성된 전기유동유체의 전기장 부하 변화에 따른 역학적 특성을 고찰하였으며 그응용성에 대하여 연구하였다. 유체에 가해지는 전기장은 0~0.25kV/mm까지 변화시켰고 외부에서 가해지는 회전력은 0∼500rpm까지의 범위로 설정하였으며 용매의 점성계수 및 각각의 용매에 대한 입자 중량비를 달리하여 자체 조성한 4종류의 전기유동유체에 대하여 특성을 고찰하였고, 전기유동유체의 항복응력도 부 하되는 전기장의 함수로 증가함을 알수 있었다. 또한 부하되는 전기장의 크기 뿐만이 아니 라 입자의 중량비 용매의 점성계수도 전기유동유체의 거동에 많은 영향을 미침을 알수 있었 다. 또한, 전기유동유체를 이용한 응용예로서 지능구조물을 제작하여 전기장에 따른 진동특 성변화를 고찰하였다. 실험결과 부하되는 전기장의 강도가 증가함에 따라 구조물의 고유진 동수가 점차적으로 증가하였으며 입자의 중량비가 증가할수록 증가폭이 커 넓은 범위의 제 어영역을 가짐을 알수 있었다. 전기유동유체의 진동제어 이용가능성을 입증하기 위하여 시 간영역에서 구조물의 전기장에 대한 과도 진동제어 응답과 강제진동제어 응답을 실험하였다.

• Korea-Australia Rheology Journal
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• v.20 no.3
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• pp.153-164
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• 2008

Modeling and experiments of three electrospinning systems have been presented and they are i) axisymmetric instabilities in electrospinning of various polymeric solutions, ii) non-isothermal modeling of polymer melt electrospinning, and iii) control of nanoparticle distribution and location via confined self-assembly of block copolymers during electrospinning. It has been demonstrated that predicted simulations are in good agreement with corresponding electro spinning experiments, and theoretical analysis provides fundamental understanding of phenomena that take place during electrospinning of various polymeric liquids.

• Korea-Australia Rheology Journal
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• v.13 no.2
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• pp.97-106
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• 2001

Three-dimensional flow analysis was performed by using the control volume finite-element method for design of a profile extrusion die. Because polymer melt behavior is complicated and cross-sectional shape of the profile extrusion die is changing continuously, the fluid flow within the die must be analyzed three-dimensionally. A commercially available polypropylene is used for theoretical and experimental investigations. Material properties are assumed to be constant except for the viscosity. The 5-constant modified Cross model is used for the numerical analysis. A test problem is examined in order to verify the accuracy of the numerical method. Simulations are performed for conditions of three different screw speeds and three different die temperatures. Predicted pressure distribution is compared with the experimental measurements and the results of the previous two-dimensional study. The computational results obtained by using three dimensional CVFEM agree with the experimental measurements and are more accurate than those obtained by using the two-dimensional cross-sectional method. The velocity profiles and the temperature distributions within several cross-sections of the die are given as contour plots.

• Computers and Concrete
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• v.25 no.5
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• pp.401-409
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• 2020

Artificial neural networks are used as a useful tool in distinct fields of civil engineering these days. In order to control long-term quality of Self-Compacting Semi-Lightweight Concrete (SCSLC), the 90 days compressive strength is considered as a key issue in this paper. In fact, combined artificial neural networks are used to predict the compressive strength of SCSLC at 28 and 90 days. These networks are able to re-establish non-linear and complex relationships straightforwardly. In this study, two types of neural networks, including Radial Basis and Multilayer Perceptron, were used. Four groups of concrete mix designs also were made with two water to cement ratios (W/C) of 0.35 and 0.4, as well as 10% of cement weight was replaced with silica fume in half of the mixes, and different amounts of superplasticizer were used. With the help of rheology test and compressive strength results at 7 and 14 days as inputs, the neural networks were used to estimate the 28 and 90 days compressive strengths of above-mentioned mixes. It was necessary to add the 14 days compressive strength in the input layer to gain acceptable results for 90 days compressive strength. Then proper neural networks were prepared for each mix, following which four existing networks were combined, and the combinatorial neural network model properly predicted the compressive strength of different mix designs.

• Korea-Australia Rheology Journal
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• v.12 no.1
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• pp.83-92
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• 2000

In resin transfer molding (RTM) process, preplaced fiber mat is set up in a mold and thermoset resin is injected into the mold. An important interest in RTM process is to minimize cycle time without sacrificing part quality or increasing cost. In this study, the numerical simulation and optimization process in filling stage were conducted in order to determine the optimum gate locations. Control volume finite element method (CVFEM) was used in this numerical analysis with the coordinate transformation method to analyze the complex 3-dimensional structure. Experiments were performed to monitor the flow front to validate simulation results. The results of numerical simulation predicted well the experimental results with every single, simultaneous and sequential injection procedure. We performed the optimization analysis for the sequential injection procedure to minimize fill time. The complex geometry of an automobile bumper core was chosen. Genetic algorithm was used in order to determine the optimum gate locations with regard to 3-step sequential injection case. These results could provide the information of the optimum gate locations in each injection step and could predict fill time and flow front.