• Tribology and Lubricants
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• v.11 no.5
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• pp.128-135
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• 1995

Atomic force microscopy/friction force microscopy (AFM/FFM) techniques are increasingly used for tribological studies of engineering surfaces at scales, ranging from atomic and molecular to microscales. These techniques have been used to study surface roughness, adhesion, friction, scratching/wear, indentation, detection of material transfer, and boundary lubrication and for nanofabrication/nanomachining purposes. Micro/nanotribological studies of single-crystal silicon, natural diamond, magnetic media (magnetic tapes and disks) and magnetic heads have been conducted. Commonly measured roughness parameters are found to be scale dependent, requiring the need of scale-independent fractal parameters to characterize surface roughness. Measurements of atomic-scale friction of a freshly-cleaved highly-oriented pyrolytic graphite exhibited the same periodicity as that of corresponding topography. However, the peaks in friction and those in corresponding topography were displaced relative to each other. Variations in atomic-scale friction and the observed displacement has been explained by the variations in interatomic forces in the normal and lateral directions. Local variation in microscale friction is found to correspond to the local slope suggesting that a ratchet mechanism is responsible for this variation. Directionality in the friction is observed on both micro- and macro scales which results from the surface preparation and anisotropy in surface roughness. Microscale friction is generally found to be smaller than the macrofriction as there is less ploughing contribution in microscale measurements. Microscale friction is load dependent and friction values increase with an increase in the normal load approaching to the macrofriction at contact stresses higher than the hardness of the softer material. Wear rate for single-crystal silicon is approximately constant for various loads and test durations. However, for magnetic disks with a multilayered thin-film structure, the wear of the diamond like carbon overcoat is catastrophic. Breakdown of thin films can be detected with AFM. Evolution of the wear has also been studied using AFM. Wear is found to be initiated at nono scratches. AFM has been modified to obtain load-displacement curves and for nanoindentation hardness measurements with depth of indentation as low as 1 mm. Scratching and indentation on nanoscales are the powerful ways to screen for adhesion and resistance to deformation of ultrathin fdms. Detection of material transfer on a nanoscale is possible with AFM. Boundary lubrication studies and measurement of lubricant-film thichness with a lateral resolution on a nanoscale have been conducted using AFM. Self-assembled monolyers and chemically-bonded lubricant films with a mobile fraction are superior in wear resistance. Finally, AFM has also shown to be useful for nanofabrication/nanomachining. Friction and wear on micro-and nanoscales have been found to be generally smaller compared to that at macroscales. Therefore, micro/nanotribological studies may help def'me the regimes for ultra-low friction and near zero wear.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.4
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• pp.421-428
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• 2009

In Korea, the change of river flux due to seasons change is so considerable because of the mountainous terrain with the sharp slope and leaned rainfall. This unfavorable natural condition and the difficulties in precise grasping of the river status made the water resource management difficult so that the necessity of the precise river management has been continuously increased. In this study, a precise river-region DEM using the latest equipments of ALS and MBES is constructed. After acquiring DEM from each senor on the river region, a single DEM was generated by combining them. Also, the field inspection was carried out in the overlapped region of ALS and MBES in order to verify the quality of DEM. The verification of DEM was carried out by comparison between TINs obtained from the combined result of ALS and MBES and the surveying result from total station at more than 10 points in the selected two test areas. As a result, NO.1-area's RMSE of 0.322m and 0.113m are obtained for NO. 1 and NO. 2 areas, respectively. The result of this study shows the feasibility of DEM construction for river region using ALS and MBES as seen in the case of NO. 2 area. At the same time, it was appeared that a better method on the data fusion should be developed as seen in the result of NO. 1 area.

• Economic and Environmental Geology
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• v.35 no.5
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• pp.465-478
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• 2002

We measured subsidences occurred in a coastal reclaimed land, Noksan industrial complex, from May 2, 1996 to February 21, 1998, using 5 interferograms of JERS-1 L-band SAR. SAR with a spatial resolution of about 16 m can detect the two-dimensional distribution of subsidence that is difficult to be estimated from in situ measurements. Accuracy of the subsidences estimated by 2-pass DInSAR was evaluated using the measurements of Magnetic Probe Extensometer (accuracy of :${\pm}$1 mm) installed at 42 stations. DInSAR measurements were well correlated with the field measurements showing an average correlation coefficient of 0.77. The correlation coefficient was further improved to be 0.87 (with RMSE of 1.44 cm) when only highly coherenced (>0.5) pixels were used. The slope of regression line was 1.04, very close to the unit value. In short, DInSAR measurements have a good linear relation with field measurements so that we can effectively detect a subsidence in the coastal reclaimed area especially using pixels of high coherence (>0.5). The maximum accumulated subsidence was about 60 cm in the study area, while the subsidence in the northern and south western areas were less than 20 cm. The resuts show that DInSAR is extremely useful for geotechnical applications as well as observation of natural deformation.

• Journal of Korean Society for Geospatial Information Science
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• v.17 no.4
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• pp.13-22
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• 2009

Urban expansion has caused environmental problems, traffic jam and real estate. Trend analysis of Urban expansion is needed for analysis and prediction of the existing problem-solving, urban planning and land use. In this study, We constructed database based on MOE(Minister of environment)'s landcover(1980's, 2000's), 1: 25,000 digital topographical map using of DEM and data of the National Statistical Office for urban and build up expand analysis of South Korea. As a result, The rate of increase in population of Gyeonggi-do, Incheon and Ulsan are high but Jeollanam-do is low. Area of development zone was 2.15 fold increase in comparison with before it. Slope aspect is south or east and urban expansion was increase in district such as Chungcheongnam-do, Gyeonggi-do, Jeollanam-do. Existing road of accessibility was high than development zone. Metropolitan city developre it. In conclusion, we found that South Korea urban expansion was developed from metropolitan city. In natural topographical conditions, the development was progress advantageous zone to disadvantageous zone. Also, we found that population was rapidly increase with new development as the center zone in urban expansion zone.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.14 no.5
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• pp.53-67
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• 2011

The major objective of this study was to quantify the effects of substrate depth and substrate composition on the development of sedum etc., in a sloped rooftop (6 : 12 pitch) environment during a 4-year period. The experiment was conducted from 2006 October to 2010 December under several conditions without soil erosion control : two substrate depth (5cm, 10cm), four substrate composition (A5N3C2, A3N3C4, A6C4, G5L3C2: A: artificial lightweight soil, N : natural soil, G : granite decomposed soil, C : leave composite, L : loess), four sloped roof direction ($E40^{\circ}W$, $W40^{\circ}N$, $S40^{\circ}W$, $N40^{\circ}E$). In this experiment 4 sedum etc., were used: Sedum sarmentosum, Sedum kamtschaticum, Sedum rupestre, Sedum telephium, flowering herbs (mixed seed : Taraxacum platycarpum, Lotus corniculatus, Aster yomena, Aster koraiensis), western grasses (mixed seed : Tall fescue, Creeping redfescue, Bermuda grass, Perennial ryegrass). The establishment factor had two levels : succulent shoot establishment (sedum), seeding (flowering herbs, western grasses). 1. Enkamat, as it bring about top soil exfoliation, was unsuitable material for soil erosion control. 2. Sedum species exhibited greater growth at a substrate depth of 10cm relative to 5cm. All flowering herbs and western grasses established only at a substrate depth of 5cm were died. A substrate depth of 5cm was not suited in sloped rooftop greening without maintenance. If additional soil erosion control will be supplemented, a substrate depth of 10cm in sloped rooftop greening without maintenance was considered suitable. 3. For all substrate depth and composition, the most abundant species was Sedum kamtschaticum. The percentage of surviving Sedum kamtschaticum was 73.4% at a substrate depth of 10cm in autumn 2007 one year after the roof vegetation had been established. But the percentage of surviving other sedum were 33.3%~51.9%, therefor mulching for soil erosion control was essential after rooftop establishment in extensive sloped roof greening was proved. To raise the ratio of plant survival, complete establishment of plant root at substrate was considered essential before rooftop establishment. 4. There was a significant interaction between biomass and substrate moisture content. There were also a significant difference of substrate moisture and erosion among substrate composition. The moisture content of A6C4 was highest, the resistance to erosion of A5N3C2 was highest among substrate composition. The biomass of plants were not significantly higher in A5N3C2 and A6C4 relative to A3N3C4 and G5L3C2, For substrate moisture and erosion resistance, A5N3C2 and A6C4 were considered suitable in sloped rooftop greening without maintenance. 5. There were significant difference among roof slope direction on the substrate moisture. Especially, the substrate moisture content of $S40^{\circ}W$ was lower relative to that of $N40^{\circ}E$, that guessed by solar radiation and erosion.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.11 no.3
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• pp.94-106
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• 2008

As populations inhabiting in natural ecosystem are fragmented by artificial barriers and habitats are destructed by development, extinction possibility of species is getting higher. It is necessary to design and to manage conservation areas and corridors considering animals' movement and migration for sustainable species diversity in present circumstances. 'Least-cost modeling' is one commonly employed approach in which dispersal costs are assigned to distinct habitat types and the last-costly dispersal paths among habitat patches are calculated using a geographical information system (GIS). This study aims to design ecological corridor using least-cost path method and to apply it to a regional ecological network considering movability of medium-large size mammals. This study was carried out over the metropolitan area, which has been deforested by rapid urbanization. Nevertheless there is connected with Gangwon province, Baekdudaegan mountain range and DMZ, considered where many forest species can migrate to this region. This study employs such an approach to develop least-cost path models for medium-large size mammals, have inhabited for this entire region. Considering those species, two forest areas as a source of species supply and forest areas more than 1,000ha are selected as focal forest areas. Movement and migration paths from species supply sources to focal forest areas are calculated by applying landscape permeability theory using land cover map, road density map and land slope map. Results showed least-cost paths from species supply sources to focal forest areas on two species. Wildcat and roe deer are different in some least-cost paths caused by their landscape permeability but paths show generally same specifics. The result of considering regional distribution of expected movement and migration paths to regional ecological network, low altitude mountains of western metropolitan area are evaluated important area for species connectivity. In national or regional levels ecological connectivity is essential to promote species diversity and to preserve integrated ecosystem. This study concludes that developing least-cost models from similar empirical data could significantly improve the utility of these tools.

• Journal of the Korean Geosynthetics Society
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• v.9 no.1
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• pp.39-46
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• 2010

Recently, the effective use of closed waste landfill nearby urban areas has been demanded, because of the lack of the usable land. However, the reuse of closed landfill is needed an adequate stabilization of liner system. But most of these places are consisted of steep slope and hence it is necessary to use the geosynthetics liners in there. Liner system of waste landfills is an important facility which prevents leachate outgoing from the landfills and also groundwater infiltrating from surroundings into the landfills. During the waste disposal stage, differential settlement and tensile stress of the geosynthetic materials could occur due to impact load of trucks and dozers, waste loads and weak foundation soils. In this study, the tensile strength and tracer test were performed to evaluate the stability of geomembrane liner systems. Based on the tensile strength test result of in-situ geomembrane sample, the yield tensile strength maintain the suitable strength by specification and current law. However, according to the tracer test, the damage of geomembrane liner was detected on sanitary landfill section.

• Korean Journal of Optics and Photonics
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• v.15 no.5
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• pp.455-460
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• 2004

We have developed a mode-locked ultra-short pulse C $r^{4+}$:YAG laser, as well as a continuous wave C $r^{4+}$:YAG laser. The laser was pumped by a Nd:YAG laser and its characteristics were investigated. In continuous wave mode, we obtained as much as 600 mW at 1.436 ${\mu}{\textrm}{m}$ with pumping power of 6 W, by using an output coupler with a reflectivity of 98%. The power slope efficiency was 10%, when the gain medium was cooled to 19$^{\circ}C$. The tuning range was varied from 1.39 ${\mu}{\textrm}{m}$ to 1.55 ${\mu}{\textrm}{m}$ and the maximum power was 400 mW at 1.492 ${\mu}{\textrm}{m}$ with a 3-plate birefringent filter. The C $r^{4+}$:YAG laser was mode-locked by a Kerr lens mode locking method. Mode locking at 1.436 ${\mu}{\textrm}{m}$was initiated by slightly rocking a mirror mount. But the pulses were very unstable because of the strong water absorption at this region. So we shifted the lasing wavelength to 1.492 ${\mu}{\textrm}{m}$ by using a 3-plate birefringent filter. Then we obtained stable state mode-locking with the maximum average power of 280 mW for a pumping power of 6 W. The pulse width of 43 fs was measured using an autocorrelator and the repetition rate was 104.5 MHz.

• Korean Journal of Environment and Ecology
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• v.18 no.1
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• pp.92-102
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• 2004

In this study, landscape changes were examined by periods through the analysis of visual quantity on the landscape components of national road including the mountains, the sky, road pavements, street trees, paddy fields and dry fields, billboard, telegraph pole, building, structure, slope, guard fence, soundproof wall, and median strip etc. For this, subject national road in suburb arreas was selected to grasp its landscape characteristics, and divisional criteria of landscape type of the national road were suggested to look into the trend of landscape changes by periods. Findings of this study are as follows：1.Divisional criteria of landscape type of the national road include location and geometry, structure, land use, perspective, and surrounding buildings of the national road. 2.The highest visual quantity was found in road pavements by periods among landscape components of the national road. It was found that this result has a thread of connection with previous study emphasizing the importance of road geometry as one of landscape components, and road geometry shall be regarded as a visually significant component in analyzing and evaluating landscape of the national road. 3.Most distinguished factors of landscape changes of the national road by periods were median strip(F＝33.296) and street tree(F＝32.881), and then the sky(F＝24.735) and mountain(F＝23.477) showed similar level of statistically significant difference. However, statistically significance difference was not found in buildings and structures. 4.It was shown that natural elements decreased gradually but structural landscape made of artificial elements became the main in construction of the national road. This result implies that although the scenic and ecological soundness is recognized in construction of the national road, it is not out of the limitation of functionalities that is, access and mobility.

• Korean Journal of Environment and Ecology
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• v.30 no.2
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• pp.214-227
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• 2016

This study was conducted to classify the vegetation structure of the Geumsan in Namhae-gun. Using the phytosociological method and DCCA ordination, the vegetation was classified into 10 communities of natural forests (Quercus serrata, Carpinus tschonoskii, Q.mongolica, Pinus densiflora, P.thunbergii, C. turczaninowii, Q. variablis, Zelkova serrata, C.laxifora and Corylopsis gotoana var. coreana) and 2 communities of plantation forests (Chamaecyparis obtusa and Cryptomeria japonica). Among the communities other than the plantation forests, the importance value of Q. serrata (45.7) was found to be the highest. According to the results of DBH analysis among the species with high importance values, Q. serrata, Q. mongolica and C. tschonoskii showed normal patterns in the size-frequency distribution, suggesting that these species will continue to hold their current dominance. The average soil pH in the communities ranged from 4.28 to 4.76. The results of DCCA ordination analysis showed that Q. serrata was evenly distributed in the high and low elevation habitats. P. thunbergii and P. densiflora communities were mainly distributed in the lowest elevation habitats on the southern slope.