• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1186-1192
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• 1990

It is well known that the fatigue crack growth retardation following overloads can be estimated reasonably well by the models of Wheeler and Willenborg. These models, however, can not explain the delayed-retardation revealed by every experimental result. This means that they necessarily have some qualitative defects in themselves despite of a fair approximation of quantity. In fact, they did not take into account the effects of the compressive portion of the overload cycle such as the change of reversed plastic zone size. The present study is focused on the acceleration effect in the reversed plastic zone in order to analyze qualitatively delayed-retardation phenomenon following single peak overload on the fatigue crack growth behavior using 2024-T3 aluminum alloy.

• Korea-Australia Rheology Journal
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• v.13 no.2
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• pp.89-95
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• 2001

Effects of particulate size and frictional characteristics were examined on the melting behavior of PP(polypropylene) in a twin screw extruder. Powder and pellet types of PP were used and each component was blended with PE(polyethylene) wax and clay, respectively. It was observed that small size particulates, 1.e. powder systems exhibit accelerated melting behavior; and it was also found that the abrasive auditive acts as an effective agent for fast melting of PP powder. Retardation of melting due to the reduced friction was observed in both types of PP, contrary to the result found in a batch mixer. The tendency observed in variation of torque and exit temperature was explained in terms of frictional effect and length of compacted region formed during evolution of melting.

• International Journal of Human Ecology
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• v.8 no.1
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• pp.1-8
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• 2007

Degradation of cellulose during prolonged exposure in atmospheric conditions has been recognized as one of main problems in preserving cellulose-made products. The purpose of this research was therefore to study effects of borohydride reduction in improving both the color and strength retention of cotton fabrics artificially aged at temperatures ranging from $100^{\circ}C$ to $150^{\circ}C$. Results indicated that the fabrics treated with either sodium or tetramethylammonium borohydrides (TMA) were degraded at rates about one-half that of water-washed cotton. These results were consistent over the temperature range. Calculation of the activation energy (Ea) by different methods showed $Ea\;=\;25.5{\pm}\;1.5\;Kcal$, in keeping with measurements made by others at lower temperatures. The TMA-treatment was effective in minimizing discoloration of the fabrics with pre-baking, but not of the un-prebaked fabrics.

• Journal of the Korean Ceramic Society
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• v.27 no.4
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• pp.560-566
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• 1990

The early hydration characteristics according to the C3A polymorphism and the presence of gypsum, in order to establish the hydration mechanism of the system C3S-C3A, have been studied. The hydration rate of C3A was changed according to the its crystal structure and influenced the hydration of C3S. That is, the hydration rate of C3S was accelerated in case of orthorhombic-C3A, but that was slightly retarded in case of melt-C3A than that of cubic-C3A. In the system C3S-C3A-gypsum, the retardation phenomenon of the reaction of monosulfate formation was observed in case of both orthorhombic and melt-C3A.

• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.115-123
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• 1994

Under variable amplitude loading conditions, retardation or accelerated condition of fatigue crack growth occurs with every cycle, Because fatigue crack growth behavior varied depend on load time history. The modeling of stress amplitude with storm loading acted to ships and offshore structures applied this paper. The crack closure behavior examine by recording the variation in load-strain relationship. By taking process mentioned above, fatigue crack growth rate, crack length, stress intensity factor, and crack closure stress intensity factor were obtained from the stress cycles of each type of storm ; A(6m), B(7m), C(8m), D(9m), E(11m) and F(15m) which was wave height. It showed that the good agreement with between the experiment results and simulation of storm loads. So this estimated method of crack propagtion rate gives a good criterion for the safe design of vessels and marine structure.

• Bulletin of the Korean Chemical Society
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• v.21 no.1
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• pp.61-64
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• 2000

FT-IR/ATR analysis shows that the oriental lacquer coating network degrades mostly in the unsaturated side chain. The rate of increase in carbonyl intensity (a measure of photodegradation) during the accelerated weathering test was substantially different for the unstabilized and stabilized samples; adding 2 wt% HALS into the oriental lacquer formulation enhanced photostabilization up to three times. Weight loss measurements, another indication of photodegradation, and SEM analysis support this conclusion. Despite the presence of the photo-stabilizer, the other properties of the lacquer were not significantly affected. In particular, the curing behavior of purified lacquer (PL) and HALS-stabilized samples is similar, although the in-situ DETA analysis showed that addition of HALS can slightly retard the cure reaction rate in oriental lacquer coating. It is hypothesized that this cure retardation may be related to the salt formation between HALS and acid of oriental lacquer.

• Journal of Adhesion and Interface
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• v.7 no.2
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• pp.19-25
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• 2006

Since the enzymatic degradation of microbial poly(hydroxylalkanoate)s (PHAs), such as poly[(R)-3-hydroxybutyrate] and poly[(R)-3-hydroxybutyrate-co-3-hydroxyvalerate] initially occurs by a surface erosion process, their degradation behaviors can be controlled by the change of surface property. In order to control the rate of enzymatic degradation, plasma modification technique was applied to change the surface property of microbial PHAs. The surface hydrophobic and hydrophilic properties of PHA films were introduced by $CF_3H$ and $O_2$ plasma exposures, respectively. The enzymatic degradation was carried out at $37^{\circ}C$ in 0.1 M potassium phosphate buffer (pH 7.4) in the presence of an extracellular PHB depolymerase purified from Alcaligenes facalis T1. The results showed that the significant retardation of initial enzymatic erosion of $CF_3H$ plasma-treated PHAs was observed due to the hydrophobicity and the enzyme inactivity of the fluorinated surface layers while the erosion rate of $O_2$ plasma-treated PHAs was not accelerated.

• The Korean Journal of Rheology
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• v.11 no.1
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• pp.44-49
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• 1999

Effects of particulate size and frictional characteristics were examined on the melting behavior of PP (polypropylene) in a batch mixer. Powder and pellet types of PP were used and each component was blended with PE (polyethylene) wax and clay, respectively. It was observed that small size particulates, i.e. powder systems exhibit accelerated melting behavior; and it was also found that the abrasive additive acts as an effective agent for fast melting of PP powder. Retardation of melting due to the reduced friction was observed in PP pellet/PE wax blends, while melting rate of PP powder was increased by addition of PE wax.

• Journal of the Korean Ceramic Society
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• v.21 no.4
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• pp.355-360
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• 1984

The effect of 2% of $P_2O_5$ substituted in gypsum(5 mol% as $HPO_3$) on the early hydration characteristics of $C_3A$ were investigated and then gypsum only and gypsum mixed with $Ca(H_2PO_4)_2$.$H_2O$(2% as $P_2O_5$) were studied separately for comparison. The early hydration reaction of $C_3A$ with each gypsum were examined by measuring the rate of heat libera-tion of hydration with calorimeter and by analysing the hydration products with X-ray diffractometer and differential thermal analyser. It was shown that phosphogypsum substituted with $P_2O_6$ in the crystal lattice accelerated exceedingly the formation of the ettrignite and following hydrated products. However the other gypsum especially gypsum without any phosphate delayed the formation of various hydration products, It was consequently suggested that when phosphogypsum are used as the retarder of cement setting its reta-rding effect for setting of cement is not ascribed to the retardation of ettringite formation.

• Clinical and Experimental Reproductive Medicine
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• v.41 no.3
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• pp.97-107
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• 2014

The placenta is a temporary fetomaternal organ capable of supporting fetal growth and development during pregnancy. In particular, abnormal development and dysfunction of the placenta due to cha nges in the proliferation, differentiation, cell death, and invasion of trophoblasts induce several gynecological diseases as well as abnormal fetal development. Autophagy is a catalytic process that maintains cellular structures by recycling building blocks derived from damaged microorganelles or proteins resulting from digestion in lysosomes. Additionally, autophagy is necessary to maintain homeostasis during cellular growth, development, and differentiation, and to protect cells from nutritional deficiencies or factors related to metabolism inhibition. Induced autophagy by various environmental factors has a dual role: it facilitates cellular survival in normal conditions, but the cascade of cellular death is accelerated by over-activated autophagy. Therefore, cellular death by autophagy has been known as programmed cell death type II. Autophagy causes or inhibits cellular death via the other mechanism, apoptosis, which is programmed cell death type I. Recently, it has been reported that autophagy increases in placenta-related obstetrical diseases such as preeclampsia and intrauterine growth retardation, although the mechanisms are still unclear. In particular, abnormal autophagic mechanisms prevent trophoblast invasion and inhibit trophoblast functions. Therefore, the objectives of this review are to examine the characteristics and functions of autophagy and to investigate the role of autophagy in the placenta and the trophoblast as a regulator of cell death.