• KOREAN JOURNAL OF CROP SCIENCE
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• v.40 no.1
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• pp.103-112
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• 1995

Six African rice varieties, two each from three types having the characteristics of partially, irregularly, and completely developed abscission layers, were selected and grown 1） to investi-gate the histological differences during the formation and development of the abscission layers and 2） to evaluate the changes in the breaking tensile strength required to detach a grain from its pedicel dur-ing ripening period in relation with developmental stage of the abscission layers. In African rice, the panicle and spikelet grew rapidly from 15 days before heading and almost completely grown in length at five days before heading. The abscission regions were recognized at 15 days before heading. However, any apparently developed abscission layers were not recognized in the lemma side for partially developed abscission layers. A group of parenchymatous cells could be observed sporadically in the abscission layers of the lemma side for irregularly developed ab-scission layers. At ten days before heading, abscission layers consisting of one or two layers of parenchymatous cells were clearly distinguished from neighboring cells due to thickened and lignified cell walls. There were a number of individual parenchymatous cells scattered sporadically in the lemma side of partially developed abscission layers, and a number of grouped parenchymatous cells scattered randomly in the lemma side of irregularly developed abscission layers. At two weeks after heading, the grains became almost fully filled. The cracking of abscission layers between rachilla and pedicel was observed, and the breaking tensile strength required to detach a grain from its pedicel was as low as that at harvest time.

• Polymer(Korea)
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• v.27 no.3
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• pp.210-216
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• 2003

4-Vinyl-1-cyclohexene diepoxide (VCE)/diglycidyl ether of bisphenol-A (DGEBA) epoxy blends with benzylquinoxalinium hexafluoroanti-monate were cured using an electron-beam technique. The effect of DGEBA content to VCE on cure behavior, thermal stabilities, and mechanical properties was investigated. The composition of VCE/DGEBA blend system vaned within 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100 wt%. The cure behavior and thermal stability of the cured specimens was monited by near-infrared spectroscopy and thermogravimetric analysis, respectively. Also, the critical stress intensity factor ($_{4}$) test of the cured specimens was performed to study the mechanical interfacial properties. As a result, the decreases of short side-chain structure and chain scission were observed in NIR measurements as the DGEBA content increases, resulting in varying the hydroxyl and carbonyl groups. And, the initial decomposition temperature (IDT), temperature of maximum weight loss (T$\_$max/), and decomposition activation energy (E$\_$d/) as thermal stability factors were increased with increasing the DGEBA content. These results could be explained by mean of decreasing viscosity, stable aromatic ring structure, and grafted interpenetrating polymer network with increasing of DGEBA content. Also, the maximum $_{4}$ value showed at mixing ratio of 40:60 wt% in this blend system. in this blend system.

• Polymer(Korea)
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• v.33 no.5
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• pp.446-451
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• 2009

Reliability evaluations of linear low density polyethylene (LLDPE) pipe with respect of thermal exposure time have been investigated in accordance with RS M 0042, which is a reliability standard for polymer pipe. As the thermal exposure time is prolonged, a progressive increase, until 250 days, in tensile strength and a slight increase in hardness are observed, while a proportional decrease in elongation at break is showed. These results can be explained by the increase of crystallinity, followed by the increase of crosslinking density, chain scission and the decrease in chain mobility, due to thermal oxidation as the exposure time increases. Long term hydrostatic pressure test result implies the existence of transition point from ductile to brittle fracture. Oxidation induction time (OIT) test is employed to monitor the thermo-oxidative degradation of LLDPE pipe. This result shows that after the exposure time is 250 days, the depletion of antioxidants added in LLDPE pipe occurs. An empirical equation as function of exposure time, under $100^{\circ}C$ thermal-degradation condition, is proposed to assess the remaining amount of antioxidants owing to thermo-oxidative degradation. Fourier transform infrared spectroscopy results show the increase of carbonyl (-C=O) and hydroxyl (O-H) function groups on the surface of thermally exposed LLDPE pipe. This result suggests that the hydrocarbon groups locally undergo the oxidation on the LLDPE surface due to thermal-degradation.

• Journal of the Korean Society for Precision Engineering
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• v.3 no.1
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• pp.40-49
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• 1986

Crack, craze and void are common defects which may be found in the bulk of polymeric materials such as either themoplastics or thermosets. The healing phenomena, autohesion, of these defects are known to be a intrinsic material property of various polymeric materials. However, only a few experimental and theoretical investigations on crack, void and craze healing phenomena for various polymeric materials have been reported up to date [1, 2, 3]. This may be partly due to the complications of healing processes and lacking of appropriate theoretical developments. Recently, some investigators have been urged to study the healing phenomena of various polymenic materials since the significance of the use of polymer based alloys or composites has been raised in terms of specific strength and energy saving. In the earlier published reports [1, 2, 3, 4], the crack and void healing velocity, healing toughness and some other healing mechanical and physical properties were measured experimentally and compared with predicted values by utilizing a simple model such as the reptation model under some resonable assumptions. It seems, however, that the general acceptance of the proposed modeling analyses is yet open question. The crack healing processes seem to be complicate and highly dependent on the state of virgin material in terms of mechanical and physical properties. Furthermore, it is also strongly dependent on the histories of crack, craze and void development including fracture suface morphology, the shape of void and the degree of disentanglement of fibril in the craze. The rate of crack healing may be a function of environmental factors such as healing temperature, time and pressure which gives different contact configurations between two separated surfaces. It seems to be reasonable to assume that the crack healing processes may be divided in several distinguished steps like stress relaxation with molecular chain arrangement, surface contact (wetting), inter- diffusion process and com;oete healing (to obtain the original strength). In this context, it is likely that we no longer have to accept the limitation of cumulative damage theories and fatigue life if it is probable to remove the defects such as crack, craze and void and to restore the original strength of polymers or polymer based compowites by suitable choice of healing histories and methods. In this paper, we wish to present a very simple and intuitive theoretical model for the prediction of healed fracture toughness of cracked or defective polymeric components. The central idea of this investigation, thus, may be the modeling of behavior of chain molecules under healing conditions including the effects of chain scission on the healing processes. The validity of this proposed model will be studied by making comparisons between theoretically predicted values and experimentally determined results in near future and will be reported elsewhere.

• Toxicological Research
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• v.17 no.3
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• pp.187-194
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• 2001

The oxidative stress causes the cell damage and death and thereby, stimulates membrane lipid peroxidation. In this study, the correlation between the lipid peroxidation product and the parameter of liver fibrosis (cirrhosis) was investigated in cholestasis induced rats. The Sprague-Dawley rats were divided into 3 groups (sham: sham operation, BDL/S-I and BDL/S-II : bile duct ligation/scission) and were observed for 2 or 4 weeks. After observation period, the organs were weighed and the ratio of organ weight/body weight was calculated. Sera and liver tissue were used for the measurement of malondealdehyde (MDA), parameter of clinical biochemistry, total collagen content and the staining. The ratio of organ weight/body weight in BDL/S-I and BDL/S-II was significantly increased compared to sham operated group. Serological parameters (Alanine transaminase, Aspartate transaminase, Alkaline phosphatase and Total bilirubin) in BDL/S-I and BDL/S-II group were significantly higher than those in sham operated group. Concentration of MDA in BDL/S-I (261%) and BDL/S-II(790%) was significantly increased compared to MDA in sham operated group. And the content of hydroxyproline (hyp) in BDL/S-I and BDL/S-II group was significantly increased 2~4 times than in sham operated group. The good correlations between hyp in liver tissue and MDA in sera of sham operated group and all operated group were found (r=0.825). The significantly higher value of MDA, hyp and serological parameters in BDL/S-I and BDL/S-II group suggests the stimulation of lipid peroxidation and chronic liver damage. Especially the activation of lipid peroxidation and the stimulation of liver fibrosis was stronger in BDL/S-II group than in BDL/S-I group. The stronger fibrosis, portal-portal septum formation, the more massive bile duct proliferation in portal triads and stroma, and hepatocytes swelling were observed in liver tissue of and BDL/S-II group compared to BDL/S-I group. Conclusively, a good correlation between MDA as a lipid peroxidation marker and hyp as a liver fibrotic parameter could be connected with the process of liver fibrosis. Moreover, cholestasis condition may cause jaundice, activation of lipid peroxidation, and collagen accumulation in liver. Additionally, optimal observation period of bile duct obstruction for the screening of antioxidant and antifibrotic effect in rats would be four weeks.

• YAKHAK HOEJI
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• v.46 no.2
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• pp.129-136
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• 2002

The pathogenesis of cholestatic liver injury as well as the modulation of hepatic fibrogenesis is causally associated with involvement of reactive oxygen species (ROS) and free radical reactions. In this study, we investigated whether dried extracts of oriental medicine (LH) have antioxidant and antifibrotic effect under the biliary liver fibrosis (cirrhosis) c ondition. The female Sprague-Dawley rats were divided in six groups (Normal, N-LH, op-2, op-4, opLH-2, opLH-4) and were observed in 2 weeks or 4 weeks. For this purpose the rats were operated by bile duct ligation/scission (BDL/S), which induced to liver fibrosis and cirrhosis. After surgery, the prepared LH was administered p.o. 2 mι/day/rat in 2 weeks or 4 weeks for opLH groups. During the observation period, jaundices appeared in eyes, ears and tail of all BDL/S operated rats. And at the time of sacrifice, cholestasis was observed in proximal bile duct, especially the color of bile juice and urine in opLH-4 group showed more clear than op-2, op-4 and opLH-2 group. The value of clinical parameters and product of lipid peroxidation (MDA) in sera and the hydroxyproline (hyp) content in liver tissue were significantly increased in all liver fibrosis (cirrhosis) developed rats (p＜0.001~0.05). Among the clinical parameters of sera, value of BUN, ALP in opLH-4 group showed significantly lower than in op-4 group (p＜0.05, p＜0.001). The content of hyp in opLH-2, opLH-4 group (478.0 $\pm$ 134.3 $\mu\textrm{g}$/g 897.5 $\pm$ 118.2 $\mu\textrm{g}$/g) showed lower than in op-2, op-4 group (528.9 $\pm$ 220.7 $\mu\textrm{g}$/g, 1023.8 $\pm$ 277.1 $\mu\textrm{g}$/g) and then the value of MDA in opLH-4 was also significantly reduced to 59.4% of that in op-4 group (p＜0.001). The histological change (bile duct proliferation, fibrosis, collagen bundle) was similarly observed in op-2 group and in opLH-2 group, but the weak fibrosis and bile duct proliferation were observed in opLH-4 group compared with in op-4 group. Our data indicate that the 4 weeks treatment with LH extract suppressed lipid peroxidation and inhibited fibrotic (cirrhosis) process, and experimental cholestatic liver disease is associated with increased lipid peroxidation in BDL/S operated rats. Hence we concluded that the measurement of MDA and hyp can be useful monitor for the screening of antioxidant and antifibrotic effect in experimental liver fibrosis (cirrhosis), and LH has been shown to have hepatoprotective effect, antifibrotic effect and antioxidant effect.

• Progress in Medical Physics
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• v.25 no.4
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• pp.205-209
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• 2014

Medical polymers require sterilization and must be able to maintain material properties for a specified shelf life. Sterilization can be achieved by using gamma or e-beam exposure. In this study, accelerated aging tests of poly(ether-block-amide) (PEBA) copolymer samples is presented. PEBA copolymer samples with different polyether content that result in Shore hardness of 35D to 72D, were sterilized using e-beam radiation followed by accelerated aging at $55^{\circ}C$. E-beam sterilization effect on molecular weight and mechanical property has performed and analyzed. The average molecular weight significantly reduced as a result of ageing. The enlarged proportion of low molecular weight chains in the aged samples is consistent with the generation of degradation products produced by oxidative chain scission. Also E-beam materials have shown decreased tensile strength and elongation. Overall, this study demonstrated that the medical grade PEBA was significantly affected by radiation exposure over aging time, particularly at high irradiation doses. For medical use in case of radiation sterilization required, it is recommended to avoid Pebax material. If Pebax material must be in use for medical device, recommend to use alternate sterilization method such as Ethylene Oxide sterilization.

• YAKHAK HOEJI
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• v.40 no.5
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• pp.550-557
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• 1996

One of therapeutics in liver disease (morbus wilson) is D-penicillamin (D-pen: D-3-mercapto-valin). Especially the cross-linking of collagen molecules could be inhibited by D-pe n in extracellular space. In this study we investigated the antifibrotic effects of D-pen in rats that were induced the liver fibrosis by bile duct ligation and scission (BDL/S). Rats were treated for 4 weeks with D-pen after BDL/S operation or sham operation. The balance between fibrogenesis-marker (PNIIIP) and the fibrolysis-maker (PNIVP) were observed in sera by RIA (radioimmunoassay), and the parameter of collagen deposition in liver tissue (hydroxyproline: HYP) was measured by colorimetry. The weight of liver in BDL/S operated group was increased significantly in compared with sham operation group (15.2g${\pm}$1.1, vs 11.9g${\pm}$3.9: p<0.005, p<0.05). The rats group treated by D-pen showed the lower level of PNIIIP (6.7ng/ml${\pm}$1.5, vs 9.5ng/ml${\pm}$2.8) and the higher value of PIVCP (14.0ng/ml${\pm}$1.9, vs 7.9ng/ml${\pm}$1.5) in sera that compared to untreated rats. The content of HYP was decreased by 141% in BDL/S with D-pen treated group than that of it in BDL/S group. No correlation was revealed between collagen parameters in sera and HYP in liver tissue of BDL/S operated and D-pen treated rats. The group treated with D-pen showed the lower value of clinical biochemistry parameters (GOT: glutamate oxalacetate transaminase, Total-Bilirubin) in compared with only BDL/S operated rats, but the value of GPT (glutamate pyruvate transaminase) and Alkaline phosphatase in two BDL/S groups was nearly same. In the histological finding, we observed mild bile duct proliferation, weak inflammation and fibrosis in BDL/S with D-pen treated group, but BDL/S operated group showed the formation of septum (island of hepatocytes), massive bile duct proliferation. This result represents that the BDL/S operation induces liver fibrosis (cirrhosis) in 4 weeks, and D-pen inhibits the synthesis of collagen weakly and stimulates the degradation of collagen in the extracellular space. We conclude that the monitoring of PNIIIP, PIVCP in sera is useful parameter for screening of antifibrotic effect, and D-pen delay the liver fibrosis.

• Journal of the Korean Vacuum Society
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• v.18 no.1
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• pp.15-23
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• 2009

Saturation-coverage silyl, $-SiH_3(a)$, overlayers were prepared from $Si_2H_6$ adsorption on three comparative surfaces: clean unmodified; D-precovered; and atomically roughened Si(100). Together with its precursor-mediated adsorption behavior, the surface reactivity of $Si_2H_6$ was found to be the highest on the unmodified Si(100)-$2{\times}1$ surface. This was correlated with its dissociative adsorption mechanism, in which both the $H_3Si-SiH_3$ bond scission and the dual surface $Si-SiH_3(a)$ bond formation require a surface dangling bond 'pair'. The unusually high thermal stability of $-SiH_3(a)$ on the unmodified surface was ascribed to a nearly close-packed $-SiH_3(a)$ coverage of ${\sim}0.9$ monolayer and the consequent lack of dangling bonds on the silyl-packed surface.

• YAKHAK HOEJI
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• v.45 no.5
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• pp.513-521
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• 2001

The chronic cholestasis induce to biliary liver fibrosis (cirrhosis) and the increased products of ROS(reactive oxygen species) cause to the liver damage. In this study ; the antioxidant and antifibrotic effect of dried extracts of oriental medicine (DW) was investigated under the liver fibrotic (cirrhotic) condition. The female Sprague-Dawley rats were divided in 5 groups (Normal, Op-2, Op-4, OpDW-2, OpDW-4). Except for normal group, the rats were induced to biliary liver fibrosis (cirrhosis) by the operation of bile duct ligation/scission (BDU/S) and were observed in 2 weeks or 4 weeks. And the prepared DW was treated p.o.2 ml/day/rats in 2 weeks or 4 weeks for OpDW groups. At the time of sacrifice, the liver, kidney, spleen were weighed and the ratio of organ weight/body weight was calculated. The MDA, the hyp and biochemical parameters (GOT GTP, ALP, t-bili) were measured in sera and liver tissue of rats. The biochemical change was observed on liver tissue. In the result, the hepatomegaly and spleenomegaly appeared in all BDL/S operated rats, and significantly lower liver weight was observed in OpDW-4 group compared with in Op-4 group (p<0.05). The level of clinical parameters in sera of all liver fibrosis (cirrhosis) developed rats was higher than in normal group. Especial1y, the value of GOT in OpDW-2 group and ALP in OpDW-4 group showed significantly lower than in Op-2 group and Op-4 group (p<0.01, p<0.005). The content of hyp in all operation groups was significantly higher than in normal group (p<0.05∼<0.005), and showed significantly lower value in the OpDW-4 group than in Op-4 group (p<0.05). The product of lipid peroxidationUDA) increased significantly under the fibrotic(cirrhotic) condition (p<0.05∼ <0.005), and the MDA value in OpDW-4 group decreased significantly in Op-4 group (p<0.005). The histological change (bile duct proliferation, fibrosis, collagen bundle) was similarly observed in Op-2 group and in OpDW-2 group, but the weak fibrosis and bile duct proliferation were observed in OpDW-4 group compared with in Op-4 group. In conclusion, lipid peroxidation and severe liver damage were activated by bile duct obstruction, and the measurement of MDA and hap can be useful monitor for the screening of antioxidant and antifibrotic effect in experimental liver fibrosis (cirrhosis). The 4 weeks treatment with DW extracts suppressed lipid peroxidation and inhibited fibrotic (cirrhotic) process in BDL/S operated rats.