• Korea-Australia Rheology Journal
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• 제17권4호
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• pp.149-156
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• 2005

A simple constitutive model for viscoelastic suspensions is discussed in this paper. The model can be used to predict the rheological properties (relative viscosity and all stresses) for viscoelastic suspensions in shear and elongational flow, and the constitutive equations combine a 'viscoelastic' behaviour component and a 'Newtonian' behaviour component. As expected, the model gives a prediction of positive first normal stress difference and negative second normal stress difference; the dimensionless first normal stress difference strongly depends on the shear rate and decreases with the volume fraction of solid phase, but the dimensionless second normal stress difference (in magnitude) is nearly independent of the shear rate and increases with the volume fraction. The relative viscosities and all the stresses have been tested against available experimental measurements.

• Korea-Australia Rheology Journal
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• 제11권3호
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• pp.225-232
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• 1999

This study presents 1-dimensional simple model for sheet casting or rectangular fiber spinning process. In order to achieve this goal, we introduce the concept of force flux balance at the die exit, which assigns for the extensional flow outside the die the initial condition containing the information of shear flow history inside the die. With the Leonov constitutive equation that predicts non-vanishing second normal stress difference in shear flow, we are able to describe the anisotropic swelling behavior of the extrudate at least qualitatively. In other words, the negative value of the second normal stress difference causes thickness swelling much higher than width of extrudate. This result implies the importance of choosing the rheological model in the analysis of polymer processing operations, since the constitutive equation with the vanishing second normal stress difference is shown to exhibit the characteristic of isotropic swelling, that is, the thickness swell ratio always equal to the ratio in width direction.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 춘계 학술대회논문집
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• pp.192-198
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• 1999

The present study proposes modified temperature-dependent non-Newtonian viscosity model and investigates flow characters and heat transfer enhancement of the viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. The proposed modified temperature dependent viscosity model has non-zero value near the high temperature and high shear rate region while on the existing viscosity models have zero value. Two versions of thermal boundary conditions involving difference combination of heated walls and adiabatic walls are analyzed in this study. The combined effect of temperature dependent viscosity, buoyancy, and secondary flow caused by second normal stress difference are ail considered. The Reiner-Rivlin model is adopted as a viscoelastic fluid model to simulate the secondary flow caused by second normal stress difference. Calculated Nusselt numbers by the modified temperature-dependent viscosity model gives under prediction than the existing temperature-dependent viscosity model in the regions of thermally developed with same secondary normal stress difference coefficients with experimental results in the regions of thermally developed. The heat transfer enhancement of the viscoelastic fluid in a 2:1 rectangular duct is highly dependent on the secondary flow caused by the magnitude of second normal stress difference.

• Journal of Mechanical Science and Technology
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• 제20권3호
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• pp.382-390
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• 2006

The present study proposes a modified temperature-dependent non-Newtonian viscosity model and investigates the flow characteristics and heat transfer enhancement of the viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. The combined effects of temperature dependent viscosity, buoyancy, and secondary flow caused by the second normal stress difference are considered. Calculated Nusselt numbers by the modified temperature-dependent viscosity model give good agreement with the experimental results. The heat transfer enhancement of viscoelastic fluid in a rectangular duct is highly dependent on the secondary flow caused by the magnitude of second normal stress difference.

• Korea-Australia Rheology Journal
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• 제19권2호
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• pp.67-73
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• 2007

A finite volume method (FVM) base on the SIMPLE algorithm as the pressure correction strategy and the traditional staggered mesh is used to investigate steady, fully developed flow of Oldroyd-3-constant fluids through a duct with square cross-section. Both effects of the two viscoelastic material parameters, We and ${\mu}$, on pattern and strength of the secondary flow are investigated. An amusing sixteen vortices pattern of the secondary flow, which has never been reported, is shown in the present work. The reason for the changes of the pattern and strength of the secondary flow is discussed carefully. We found that it is variation of second normal stress difference that causes the changes of the pattern and strength of the secondary flow.

• 한국생활과학회지
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• 제21권6호
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• pp.1199-1210
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• 2012

This study investigated the influence of obesity on depression and stress by analyzing the results of the national survey on health and nutrition. Relationships between normal, obese, and severely obese groups were investigated. The results of the study are as follows. First, obesity caused by demographic variables showed a relationship to both gender and average monthly income. In the case of the seriously obese group, females had higher rates of depression than males, and the high obesity group had lower average monthly income than the normal and obese groups. Second, obesity caused by health-related variables found that high blood pressure, hyperlipidemia, and diabetes that was not angina-related displayed higher rates of depression in the serious obesity group than in the other groups. As for subjective evaluations of one's own health condition, the serious obesity group showed a high tendency to evaluate their own health conditions negatively. Third, the difference between depression and stress related to obesity level showed no difference between the normal weight group and the obesity group; however, the seriously obese group demonstrated relatively higher occurrences of depression and higher stress scores. Fourth, the result for depression and stress level caused by demographic variables, health-related variables, and obesity demonstrated a direct relationship to gender, subjective level of satisfaction with one's personal finances, average monthly income, subjective perception of one's own health and severely obesity status. More specifically, it was found that the ratio of depression and stress score was higher when the subject was female, among those whose subjective evaluation of their own finances and health condition was negative, and those who suffered from severe obesity.

• 한국감성과학회:학술대회논문집
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• 한국감성과학회 2001년도 추계학술대회 논문집
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• pp.169-172
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• 2001

There are many people who suffer from simulation sickness when immersing in virtual reality. In this study, we analyzed two photoplethysmogram(PPG) parameters - a second derivative parameter and power spectral density ratios - in order to relate PPG parameters with simulation sickness. 36 young, healthy subjects were participated in the experiment, and each subject was equipped with a PPG electrode during his or her immersion. Simulation sickness section was defined as a 7 - second section which starts from the point where a subject reported simulation sickness, and normal section as a same-length section where no physical stimuli was presented to him or her. We compared the PPG parameters of the simulation sickness sections with the normal sections, - d/a ratio is believed to have lower value during vasodilation and higher value during vasoconstriction, however, we could not find much difference in the parameter between normal and simulation sickness sections. We also compared 1 to 10Hz power spectral density ratios in normal sections with in simulation sickness section, and found that 6 density ratios among them have different value. Therefore, the density ratios might be utilized as parameters to detect simulation sickness of subjects.

• 재활치료과학
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• 제8권4호
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• pp.19-31
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• 2019

목적 : 본 연구에서는 자폐스펙트럼 장애(ASD) 영유아의 어머니를 대상으로 양육 스트레스 총점, 부모영역 및 아동영역 수준에 따라 MMPI-2를 통해 어머니가 경험할 수 있는 양육 스트레스 수준에 따른 다양한 심리적 증상의 차이를 검증하였다. 연구방법 : 서울 소재의 종합병원 소아정신과, 재활의학센터, 발달 장애 클리닉 등에서 2010년에서 2015년까지 ASD로 진단을 받은 만 1세에서 5세까지의 영유아 어머니 72명을 대상으로 실시되어 축적된 한국판 부모 양육 스트레스 척도(K-PSI)와 다면적 인성검사 II(MMPI-2) 자료를 최종분석에 사용하였다. 결과 : 양육 스트레스 총점과 부모영역은 MMPI-2의 여러 임상 척도들과 유의한 상관관계를 나타냈지만, 아동영역은 유의한 상관관계를 나타내지 않았다. 또한, 양육 스트레스 총점 수준에 따른 심리적 증상의 차이를 검증한 결과, 위험 수준 집단이 정상 범위 집단보다 MMPI-2의 임상 척도 중 건강염려증(Hs), 우울(D), 편집증(Pa), 강박증(Pt), 조현병(Sc)이 유의하게 높았다. 양육 스트레스 부모영역에서는 위험 수준 집단이 정상 범위 집단보다 MMPI-2의 임상 척도 중 건강염려증(Hs), 우울(D), 히스테리(Hy), 반사회성(Pd), 편집증(Pa), 강박증(Pt), 조현병(Sc), 경조증(Ma), 내향성(Si)이 유의하게 높았다. 반면에 양육 스트레스 아동영역에서 위험 수준 집단과 정상 범위 집단 간의 차이는 유의하지 않았다. 결론 : 양육 스트레스 총점과 부모영역에서 위험 수준 집단의 심리적 증상이 유의하게 높았다는 것을 확인하였다.

• 동의신경정신과학회지
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• 제30권4호
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• pp.357-369
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• 2019

Objectives: This study was designed to examine the effect of Hominis Placenta Pharmacopuncture on the change in behavior, sleep-related hormones, inflammatory cytokines, anti-oxidants, weight, blood, and serum on rats given chronic physical stress. Methods: Wistar rats older than age 10 weeks were used in this experiment. They were divided into six groups. The normal group was not given stress. The control group was given only chronic physical stress and no treatment. The positive control group was given chronic physical stress and treated with zolpidem. Three Hominis Placenta Pharmacopuncture (HPP) groups were given chronic physical stress, then treated with different concentrations of HPP; HPP-0.5× (0.5 times diluted), HPP-1× (undiluted) and HPP-2× (2 times condensed). The changes of values of Nestlet Shredding results, weight, Melatonin, Gamma-aminobutylic Acid (GABA), Tumor Necrosis Factor Alpha (TNF-α), Interleukin-6 (IL-6), Superoxide dismutase (SOD), glutathione peroxidase (GPx), AST, ALT, BUN, Creatinine, and leukocytes were observed during the experiment. Results: The changes in chronic physical stress of the rat model were as follow. The Nestlet Shredding result increased in the control group compared to the normal group (p<0.05), and decreased in the HPP-1× and HPP-2× compared to the control group (p<0.05). The amount of weight gain showed increasing tendency in the HPP-2× compared to the control group since the second week. The GABA increased (p<0.05) and Melatonin also showed certain increasing tendency in the HPP-1× and HPP-2× compared to the control group. The TNF-α and IL-6 increased in the control group compared to the normal group (p<0.01), and decreased in all the HPPs compared to the control group (p<0.05). The SOD level decreased in the control group compared to the normal group (p<0.01), and increased in all the HPPs compared to the control group (p<0.05). GPx, AST, ALT, Bun, Creatinine and leukocytes showed no noticeable difference among all groups. Conclusions: Hominis Placenta Pharmacopuncture was effective in increasing weight, GABA, Melatonin, SOD, and decreasing Nestlet Shredding and inflammatory cytokines, suggesting that it consequently facilitates in relieving physical stress.

• 한국보육지원학회지
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• 제12권6호
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• pp.19-39
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• 2016

The present study examined differences in children's behavior problems and peer interaction, and parental factors including self-esteem, depression and childrearing stress between atopic dermatitis(AD) and normal(non-AD) children in each gender, and analyzed the effects of the parental factors on the two variables of AD children. 165 AD and 1176 non-AD children of age 5 were selected from the 6th year data of the Panel Study on Korean Children. The results from t-test and multiple regression are as follows. First, only AD boys showed a higher level of behavior problems than non-AD boys, but peer interaction showed no difference between AD and non-AD groups. Compared with non-AD children's parents, mothers of AD children showed a higher stress level and mothers of AD boys had a higher depression level. But there were no differences in maternal self-esteem and paternal factors between the groups. Second, AD boys' behavior problems were related to maternal factors and paternal stress, and some characteristics of AD girls' behavior problems were related with some parental variables. But peer interaction of AD children had no relation with parental factors. Third, behavior problems were influenced by maternal stress in AD boys and influenced by maternal depression and parental self-esteem in AD girls.