• Korean Journal of Environment and Ecology
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• v.29 no.4
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• pp.605-614
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• 2015

This study was carried out to maintain, manage and restore the trails by assessing the physical conditions, the patterns of deterioration and the impact rating class of the major trails of Juwangsan National Park. The major trails followed 4 routes including Jubong, Gamaebong, Janggunbong~Geumeungwangi and Woloe. The route length of Jubong was 4.6 km; it was 3.6 km for Gamaebong, 5.6 km for Janggunbong~Geumeungwangi and 5.9 km for Woloe. As for the physical conditions, Jubong was the widest and Janggunbong~Geumeungwangi was the narrowest in trail width. In terms of the bared trail width, Jubong was the widest and Janggunbong~Geumeungwangi was the narrowest. As for the depth of erosion, Gamaebong was the deepest and Woloe was the shallowest. Janggunbong~Geumeungwangi was the steepest and Gamaebong was the gentlest in the slope. Further, Gamaebong showed the highest soil hardness, and Woloe had the lowest hardness. In terms of the times of appearance of deterioration patterns, Jubong recorded 71 times, Gamaebong 62 times, Janggunbong~Geumeungwangi 63 times and Woloe 78 times. In case of the impact rating class, the trail erosion was similar to grades I and II grade; the rest were mostly I grade and hence considered to be in a generally good condition. For the ongoing management of trails, a comprehensive study needs to be conducted in the light of various environmental factors. Also, a restoration plan for damaged trails should be established with consideration for the surrounding environment and ecosystem.

• Macromolecular Research
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• v.17 no.8
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• pp.616-622
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• 2009

In-depth understanding of the influence of hot pressing and melt processing on the properties of thermoplastic polyurethane (TPU) is critical for effective mechanical recycling of TPU scraps. Therefore, this study focused on the effects of hot pressing and melt mixing on molecular weight (MW), polydispersity index (PDI), melt index (MI), characteristic IR peaks, hardness, thermal degradation and mechanical properties of TPU. The original TPU pellet (o-TPU) showed two broad peaks at lower and higher MW regions. However, four TPU film samples, TPU-0 prepared only by hot pressing of o-TPU pellet and TPU-1, TPU-2 and TPU-3 obtained by hot pressing of melt mixed TPUs (where the numbers indicate the run number of melt mixing), exhibited only a single peak at higher MW region. The TPU-0 film sample had the highest $M_n$ and the lowest PDI and hardness. The TPU-1 film sample had the highest $M_w$ and tensile modulus. As the run number of melt mixing increased, the peak-intensity of hydrogen bonded C=O stretching increased, however, the free C=O peak intensity, tensile strength/elongation at break and average MW decreased. All the samples showed two stage degradations. The degradation temperatures of TPU-0 sample (359 $^{\circ}C$ and 394 $^{\circ}C$)were higher than those of o-TPU (342 $^{\circ}C$ and 391 $^{\circ}C$). While all the melt mixed samples degraded at almost the same temperature (365 $^{\circ}C$ and 381 $^{\circ}C$). The first round of hot pressing and melt mixing was found to be the critical condition which led to the significant changes of $M_n$/$M_w$/PDI, MI, mechanical property and thermal degradation of TPU.

• Journal of Korean Society of Forest Science
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• v.110 no.1
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• pp.91-105
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• 2021

We conducted a study to identify the relationships between the investigated factors and provide a methodology and generate data by applying deterioration classes to the Seonjaryeong Forest Trail (4.3 km) in the Baekdudaegan Ridge. The average trail width (1.7 m) and bare width (1.4 m) were wider than those obtained in the previous studies. The frequency of trail deterioration was also high. Specific data on deterioration classes were obtained and evaluated using qualitative criteria. Specific data for heavy class stands at 20.1% in trail grade, 13.3 cm on average, and 16.1 cm in the center of erosion depth, 16.2 cm of CSA, 12.3 kg/cm (20.1 mm) on average and maximum 39.3 kg/cm (29.6 mm) of soil hardness. We observed a positive correlation between the deterioration class and trail grade, and the average and maximum soil erosion depths of the hill side were deeper than those of the ridge. The soil hardness data showed a statistically significant difference in terms of the transect site and calculation method (㎏/㎠, mm). Therefore, trail deterioration was observed at the sites having ≥20% trail grade; thus, continuous monitoring at fixed sites over time will be required for sustainability. Furthermore, the trail grade should be of the utmost priority in trail design and management.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.2
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• pp.190-201
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• 2004

The aim of this study was to evaluate the resistance to degradation and to compare the wear resistance characteristics of four esthetic restorative materials in an alkaline solution. The brands studied were Charmfil, Charmfil flow(composite resin), Compoglass F and PrimaFlow(compomer). The results were as follows: 1. The mass loss were not significantly different among the materials(p>0.05). 2. The sequence of the degree of degradation layer depth was in descending order by Compoglass F, PrimaFlow, Charmfil, and Charmfil flow. There were significant differences between Compoglass F and the others(p<0.05). 3. The sequence of the Si loss was in descending order by Charmfil flow, Charmfil, PrimaFlow, and Compoglass F. There were significant differences among these materials(p<0.05). 4. When observed with SEM, destruction of bonding between matrix and filler was observed and when observed with CLSM, the depth of degradation layer of specimen surface was observed. 5. The sequence of maximum wear depth was in descending order by Comfoglass, PrimaFlow Charmal, and Charmfil flow. There were significant differences among these materials(p<0.05). 6. The correlation coefficient between Si loss and degradation layer depth (r=0.602, p<0.05) Vicker's hardness number and maximum wear depth (r=0.501, p<0.05) were relatively high. These results indicate that wear and hydrolytic degradation may be considered to be evaluation factors of composite resins and compomers.

• Journal of the korean academy of Pediatric Dentistry
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• v.32 no.3
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• pp.557-568
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• 2005

The aim of this study was to evaluate the resistance to degradation and to compare the wear resistance characteristics of four esthetic restorative materials in an alkaline solution(0.1N NaOH). The brands studied were MetafilCX(Sun medical, Japan) Solitaire 2(Heraeus Kulzer, USA), Composan LCM(Promedica, Germany), DenFil(Vericom, Korea). The results were as follows: 1. The mass loss of each brand was 0.74~7.94% and highest value in Metafil($7.94{\pm}0.39%$). 2. The sequence of the degree of degradation layer depth was in descending order by Metafil, Solitaire 2, DenFil, Composan LCM. There were significant differences between Metafil and the others(p<0.05). 3. The sequence of the Si loss was in descending order by Metafil, Solitaire 2, Composan LCM, DenFil. There were significant differences among the materials(p<0.05). 4. On SEM, destruction of bonding between matrix and filler and on CLSM, the depth of degradation layer of specimen surface was observed. 5. The sequence of maximum wear depth was in descending order by Metafil, Solitaire 2, Composan LCM and DenFil. There were significant differences among the materials(p<0.05). 6. The correlation coefficient between Si loss and degradation layer depth (r=0.491, p<0.05) and Vicker's hardness number and maximum wear depth (r=-0.942, p<0.05) were relatively high. These results indicate that hydrolytic degradation and wear may consider as a evaluation factors of composite resins.

• Journal of The Korean Society of Grassland and Forage Science
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• v.39 no.2
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• pp.81-88
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• 2019

This study was carried out to investigate the growth characteristics, yield and feed value of Sorghum${\times}$Sudangrass hybrid for silage according to the drainage depths in the paddy field of lowland. The experimental design was arranged in a randomized block design with four treatments and three replication. The drainage depths of four treatments were 0cm, 20cm, 40cm and 60cm, respectively. Plant length, leaf length and leaf number were not significantly different, but leaf width increased as the higher the drainage depth(p<0.05). The number of dead leaf was higher in the order of $60cm>0cm{\geq}40cm{\geq}20cm$ treatment(p<0.05). Green degree was higher in the order of 20cm > 40cm > 0cm > 60cm treatment(p<0.05). Stem diameter and stem hardness increased significantly as drainage depth increased from 0cm to 60cm(p<0.05). Also, fresh yield, dry matter yield and TDN yield increased as the higher the drainage depth(p<0.05). Crude protein and TDN content were the highest in 40cm treatment(p<0.05). Crude ash was higher in the order of 20cm > 40cm > 0cm > 60cm treatment(p<0.05). ADF and NDF content were the highest in 0cm treatment(p<0.05). Total mineral content was higher in the order of 20cm > 0cm > 40cm > 60cm(p<0.05). Free sugar content(fructose, glucose and sucrose) was the highest in 0cm treatment(p<0.05). Total amino acid(EAA+NEAA) was higher in 40cm than the other treatments(p<0.05). There is a difference in the content of ingredients(crude protein, TDN, mineral, free sugar and amino acid) according to the treatments. But considering dry matter yield and TDN yield, Sorghum${\times}$Sudangrass hybrid cultivation is advantageous to set the drainage depth of about 60cm in the paddy field of lowland.

• Korean Journal of Environment and Ecology
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• v.16 no.1
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• pp.10-21
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• 2002

This study was intended to investigate injury rates of landscape trees planted in the reclaimed seaside areas and to analyse their causes in planting environment. The planting environment such as soil properties, reclaimed depth of soil, soil hardness, salt consistency of soil, and drainage system were surveyed in 8 reclaimed seaside areas in the middle and southern regions of the country. Injury rates of 42 species, 1,233 trees and growth of branches in 6 species. 130 trees were measured and analysed to fond out salt-resistant trees in the reclaimed lands. The results of the survey are as follows; the average injury rate of evergreen trees was 32%. which was much lower than that of deciduous trees as 52%. The lower injured trees in the 8 reclaimed lands were Pinus thunbergii, Pinus parvinora. Juniperus chinensis 'Kaizuka', Pinus koraiensis, Acer trifdum, Koelreuteria paniculata and Metasequoia glyptostroboides. The higher injured trees were Acer palmatum, Magnolia kobus. Lagerstroemia indica, Diospiros kaki, Cercidiphyllum japonicum, Sorbus commixta, Prunus yedoensis, Pinus desinora, Chaenomeles sinensis, Albizzia julibrissin and Zelkowa serrata. At least the mounding of 1.7m depth of soil is needed from the tidal saline soil to the roots of trees to protect trees from salt injury Roots of trees were found to have infiltrated to 0.77m under the soil of which solidity was over 4.5kg/㎥. And 22 of total 25 soils were acid from pH 3.72 to pH 5.85. Injury rate of trees was much higher when they were detached from the sea, and planted on the drainage.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.53-62
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• 1987

High power lasers provide a controllable and precise energy source in surface transformation hardening. A careful control of the process is needed in order that the surface layer of the material reaches the austenizing temperature, but that it does not melt. In order to achieve this the results of theoretical and experimental studies on the laser surface hardening of a medium carbon steel are described. A two-dimensional computer program, which can be used generally for the determination of transient temperature distributions in welding and heat treatment, was established on the basis of the finite element method. For the confirmation of the accuracy of the numerical analysis, a medium carbon steel (SM 45C) of 5mm thickness was heat-treated with a 1kW CW CO$_{2}$ laser machine, while the traverse speed and the distance from the focal point (defocused distance) were varied. Experimental and numerical results showed a similar tendency in correlations between the hardened zone shape and the process parameters. With increasing beam spot diameter the width and depth of the hardened zone increased for relatively small beam spot diameters, but decreased rapidly after reaching the maximum value, while with increasing traverse speed the width and depth of the hardened zone decreased monotonously. Too small beam spot diameters are to be avoided, since the surface melting would lower the surface hardness and produce an uneven surface which may be unacceptable because of the possible requirement for subsequent machining. It could be observed that for a given traverse speed and laser power input there exists a optimal range of the beam spot diameter, which produce a large width of the hardened zone but no melting on the surface.

• Journal of The Korean Society of Grassland and Forage Science
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• v.35 no.2
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• pp.137-144
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• 2015

This study was carried out to investigate the growth characteristics, yield, and chemical compositions of corn hybrids for silage according to the drainage depths in a lowland paddy field. The experimental design was arranged in a randomized block design with four treatments and three replications. The drainage depths of the four treatments were 0 cm, 20 cm, 30 cm and 50 cm. Tip-filling degree, ear length, and ear circle were higher in the 30 cm and 50 cm treatments compared with the other treatments (p < 0.05); but the plant length, leaf length, leaf width, ear height, stem diameter, and stem hardness were not significantly different (p < 0.05). The brix was higher in the order of 20 cm > 0 cm > 50 cm > 30 cm treatment. The fresh yield, dry matter yield, and TDN yield increased as the drainage depth increased (p < 0.05). The crude-protein and crude-ash content were highest in the 50 cm treatment (p < 0.05), but the crude-fat, NDF, ADF, and crude-fiber levels were not significantly different (p < 0.05). The total mineral content was higher in the order of 0 cm > 30 cm > 20 cm > 50 cm treatment (p < 0.05). Fructose, glucose, and sucrose were highest in the 20 cm treatment. The total amino-acid (EAA + NEAA) content was the highest in the 50 cm treatment. Based on these results, greater drainage depths increased the yield and feed value of silage corn.

• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.4
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• pp.662-670
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• 2008

The purpose of this in vitro study was to evaluate the effect of fluoride containing adhesive film on prevention of enamel demineralization. Eighty bovine enamel blocks were divided randomly into 4 groups of 25: (1) APF gel applied ; (2) CavityShield$^{TM}$ applied; (3) 3% fluoride film applied; (4) 5% fluoride film applied; Early caries lesions were produced by placing each specimen into demineralization solution at pH 4.0 for 72 hours. Then lesion of the surface microhardness were measured by the Vicke's hardness test and the lesions depth were measured by polarizing light microscope. The results of the present study are as follows: 1. Difference of microhardness value ($M{\pm}SD$) between control and experimental side was the highest in group II, followed by group IV, III, I but, no significant difference was between group II, III and IV. 2. Difference of mean lesion depth ($M{\pm}SD$) between control and experimental side was the highest in group II, followed by group III, IV and I but no significant difference was between group III and IV. The results of the present study indicate that the fluoride film application is more effective than APF gel and is similar to fluoride varnish application for prevention of dental caries.