• Journal of Ecology and Environment
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• v.41 no.10
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• pp.290-301
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• 2017

Background: Forest edges create distinctive ecological space as adjacent constituents, which distinguish between different ecosystems or land use types. These edges are made by anthropogenic or natural disturbance and affects both abiotic and biotic factors gradually. This study was carried out to assess edge effects on disturbed landscape at the pine-dominated clear-cut area in a genetic resources reserve in Uljin-gun, eastern Korea. This study aims to estimate the distance of edge influence by analyzing changes of abiotic and biotic factors along the distance from forest edge. Further, we recommend forest management strategy for sustaining healthy forest landscapes by reducing effects of deforestation. Results: Distance of edge effect based on the abiotic factors varied from 8.2 to 33.0 m. The distances were the longest in $Mg^{2+}$ content and total nitrogen, $K^+$, $Ca^{2+}$ contents, canopy openness, light intensity, air humidity, $Na^+$ content, and soil temperature followed. The result based on biotic factors varied from 6.8 to 29.5 m, coverage of tree species in the herb layer showed the longest distance and coverage of shrub plant in the herb layer, evenness, species diversity, total coverage of herb layer, and species richness followed. As the result of calculation of edge effect by synthesizing 26 factors measured in this study, the effect was shown from 11.0 m of the forest interior to 22.4 m of the open space. In the result of stand ordination, Rhododendron mucronulatum, R. schlippenbachii, and Fraxinus sieboldiana dominated arrangement of forest interior sites and Quercus mongolica, Vitis amurensis, and Rubus crataegifolius dominated spatial distribution of the open area plots. Conclusions: Forest interior habitat lies within the influence of both abiotic and biotic edge effects. Therefore, we need a forest management strategy to sustain the stability of the plant and further animal communities that depend on its stable conditions. For protecting forest interior, we recommend selective logging as a harvesting method for minimizing edge effects by anthropogenic disturbance. In fact, it was known that selective logging contributes to control light availability and wind regime, which are key factors affecting microclimate. In addition, ecological restoration applying protective planting for the remaining forest in the clear-cut area could contribute to prevent continuous disturbance in forest interior.

• Journal of Ecology and Environment
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• v.29 no.2
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• pp.113-124
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• 2006

Landscape structure, habitat types, vegetation structure and biodiversity in the Bokha stream chosen as a reference stream were investigated to get ecological information necessary for restoration of urban stream degraded by excessive artificial interference. Landscape structure showed a slight change between before and after flooding. Habitat types of nine sorts were identified based on ecological information obtained from field survey such as micro-topography, hydrological characteristics, disturbance regime, and so on. Each habitat holds specific organisms to each site. Consequently, the number of plant communities, and species of benthos and fish increased as the kinds of habitat type increase. Ordination of habitat types based on vegetation, benthos, and fish data reorganized them into three groups of pool types of two kinds depending on whether they are connected to the water course or not and riffle one. Vegetation showed different stratification and species composition depending on topographical position in relation to disturbance cycle. Based on the results from this study, relationship between environmental heterogeneity and biodiversity was discussed and a restoration plan was suggested in a viewpoint of vegetation.

• Journal of Environmental Impact Assessment
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• v.20 no.1
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• pp.1-11
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• 2011

This study was carried out to suggest the baseline data necessary for vegetation restoration at riverine wetland within stream corridor. We used the prevalence index for wetland assessment by applying the method of weighted averages with index values based on five hydrophyte indicator status as defined by estimated probability occurred in wetland. We selected near nature and urbanized reach of Gap and Yanghwa streams as experimental site. Although two sites have some different disturbance and characteristics of watershed, they showed that similarity of vegetation community including three dominant species - Salix koreensis, Phragmites communis, Miscanthus sacchariflorus - was very high. But in case of Yanghwa stream, various kinds of emergent plants along wetted condition were distinctly occurred, resulted from difference of hydrological regime and substrate, etc. Degree of naturalness of vegetation at the sampled areas indicated that near nature area of Gap stream and all area of Yanghwa stream were fitted as riverine wetland, while urbanized area of Gap stream has changed into upland condition. In conclusion assessment system using prevalence index would be considered an effective method for evaluating of natural states of riverine wetland, but further integrated consideration of physical, hydrological, and biological factors of stream process, and also with considering the difference between those qualitative data of vegetation community.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.317-322
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• 2012

The low speed aerodynamic characteristics for a modified sonic arc airfoil which is designed by using the nose shape function of sonic arc, the shape function of NACA four-digit wing sections, and Maple are experimentally investigated. The small rotor blades of a modified sonic arc and NACA0012 airfoil are precisely fabricated with a commercially available light aluminum(Al 6061-T6) and are spin tested over a low speed range (3000rpm-5000rpm). In a consuming power comparison, the consuming powers of NACA0012 are higher than that of modified sonic arcs at each pitch angle. The measured rotor thrust for each pitch angle is used to estimate the rotor thrust coefficient according to momentum theory in the hover state. The value of thrust coefficients for both two airfoils at each pitch angle show almost constant values over the low Mach number range. However, the rotor thrust coefficient of NACA0012 is higher than that of the modified sonic arc at each pitch angle. In conclusion, the aerodynamic performance of NACA0012 is better than that of modified sonic arcs in the low speed regime. This test model will provide a convenient platform for improving the aerodynamic performance of small scale airfoils and for performing design optimization studies.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.2
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• pp.96-103
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• 2020

The new geometric disturbance is proposed to control the flow around the bluff body. The new geometry is characterized by the variable pitch which is applied on the Helically Elliptic Twisted (HET) cylinder. The performance of the HTE geometry as a biomimetic passive flow control was confirmed by Jung and Yoon (2014). The Large Eddy Simulation (LES) is used for the evaluation of the flow control performance of the Variable Pitch HTE (VPHTE) cylinder at Reynolds number (Re) of 3000 corresponding to the subcritical regime. The circular and HTE cylinders are also considered to compare the performance of the VPHTE cylinder at the same Re. The VPHTE cylinder gives the smallest values of the force coefficients than the circular and HTE cylinders. The drag and lift coefficients of the VPHTE cylinder are about 15.2% and 94.0% lower than those of the circular cylinder, respectively. Especially, the VPHTE cylinder achieves about 2.3% and 30.0% reduction of the drag coefficient and the root mean square of the lift coefficient than the HTE cylinder, respectively. Furthermore, The VPHTE cylinder forms more elongated and stabilized separated shear layer than the circular cylinder, which supports the reduction of the force coefficients.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.119.1-119.1
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• 2012

It is well known that the FLRs are excited by compressional waves via mode conversion, but there has been no apparent criterion on the maximum amplitude in the regime of linear approximations. Such limited range of amplitude should be understood by including nonlinear saturation of FLRs, which has not been examined until now. In this study, using a three-dimensional magnetohydrodynamic (MHD) simulation code, we examine the evolution of nonlinear field line resonances (FLRs) in the cold plasmas. The MHD code used in this study allows a full nonlinear description and enables us to study the maximum amplitude of FLRs. When the disturbance is sufficiently small, it is shown that linear properties of MHD wave coupling are well reproduced. In order to examine a nonlinear excitation of FLRs, it is shown how these FLRs become saturated as the initial magnitude of disturbances is assumed to increase. Our results suggest that the maximum amplitude of FLRs become saturated at the level of the same order of dB/B as in observations roughly satisfies the order of ~0.01. In addition, we extended this study for the plasma sheet boundary layer (PSBL) region. We can discuss the maximum disturbances of the Alfven via mode conversion becomes differently saturated through each region.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.39.2-39.2
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• 2010

Field line resonances (FLRs) observed in the magnetosphere often have the amplitude of a few nT, which indicates that dB/B roughly satisfies ~0.01. It is well known that the FLRs are excited by compressional waves via mode conversion, but there has been no apparent criterion on the maximum amplitude in the regime of linear approximations. Such limited range of amplitude should be understood by including nonlinear saturation of FLRs, which has not been examined until now. In this study, using a three-dimensional magnetohydrodynamic (MHD) simulation code, we examine the evolution of nonlinear field line resonances (FLRs) in the cold plasmas. The MHD code used in this study allows a full nonlinear description and enables us to study the maximum amplitude of FLRs. When the disturbance is sufficiently small, it is shown that linear properties of MHD wave coupling are well reproduced. In order to examine a nonlinear excitation of FLRs, it is shown how these FLRs become saturated as the initial magnitude of disturbances is assumed to increase. Our results suggest that the maximum amplitude of FLRs become saturated at the level of the same order of dB/B as in observations. In addition, we discuss the role of both linear terms and nonlinear terms in the MHD wave equations.

• Journal of Korean Society of Forest Science
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• v.112 no.1
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• pp.11-22
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• 2023

This study was established to provide basic information necessary for ecological management to restore the naturalness of black locust (Robinia pseudoacacia L.) plantations located in the mountains of Gyeongbuk, Korea. Using vegetation data collected from 200 black locust stands, vegetation types were classified using the TWINSPAN method, the spatial arrangement status according to the environmental gradient was identified through DCA analysis, and a synoptic table of communities was prepared based on the diagnostic species determined by determining community fidelity (Φ) for each vegetation type. The vegetation types were classified into seven types, namely, Quercus mongolica-Polygonatum odoratum var. pluriflorum type, Castanea crenata-Smilax china type, Clematis apiifolia-Lonicera japonica type, Rosa multiflora-Artemisia indica type, Quercus variabilis-Lindera glauca type, Ulmus parvifolia-Celtis sinensis type, and Prunus padus-Celastrus flagellaris type. These types usually reflected differences in complex factors such as altitude, moisture regime, successional stage, and disturbance regime. The mean relative importance value of the constituent species was highest for black locust(39.7), but oaks such as Quercus variabilis, Q. serrata, Q. mongolica, Q. acutissima, and Q. aliena were also identified as important constituent species with high relative importance values, indicating their potential for successional trends. In addition, the total percent cover of constituent species by vegetation type, life form composition, species diversity index, and indicator species were compared.

• Korean Journal of Ecology and Environment
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• v.40 no.4
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• pp.503-510
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• 2007

The purposes of the study were to analyze the seasonal effects on the fish fauna and compositions including trophic guilds and tolerance guilds. For the study, we collected fish samples twice in June as premonsoon period and early September 2007 as monsoon periods in five sampling sites of the Gap Stream, and then biological oxygen demand (BOD), nutrients (TN, TP) and suspended solids (SS) were compared with the guild data along the gradient of upstream-to-downstream. Chemical water quality, based on BOD, TP, and TN degraded gradually from the upstream to downstream reach and there were about 3 fold difference between S1 and S5. Water quality was worse in the premonsoon than the monsoon, and the heavy monsoon resulted in a dilution of the polluted river by rain water, especially, in the downstream reach. Total number of fish species, based on the catch per unit effort (CPUE), showed a distinct difference between the two seasons; 30 species were sampled in premonsoon, but 23 species were sampled in the monsoon, indicating a seasonal difference in the fish fauna. Tolerant species dominated the fish community (48.3%) in the stream, and the proportions prior to physical disturbance by the monsoon rain were evidently greater in the downstream reach than the upstream. This reflected the characteristics of urban stream polluted by nutrient enrichment as shown in the BOD and TP values. Sensitive species in the premonsoon decreased from the gradient of upstream-to-downstream reach. Such seasonal modifications in the trophic and tolerance guilds were evident. In the analysis of trophic guild and habitat guild, during the premonsoon the proportion of insectivore and riffle-benthic species were largely greater in the upstream reach than the downstream, whereas the proportions were opposite along the gradient of the stream in monsoon. Thus, the patterns of chemical water quality along the longitudinal gradients reflected the premonsoon conditions of insectivores and tolerant species, indicating that summer monsoon data of fish may not match with water quality due to large physical disturbance by flow regime. Seasonal monsoon in this region as well as the chemical pollution may act as a key role influencing the fish compositions of trophic and tolerance guilds and fauna. The data collected during the premonsoon rather than the monsoon, thus, may be better predictor for a diagnosis of stream health conditions.

• Journal of Korean Society of Forest Science
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• v.85 no.2
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• pp.260-270
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• 1996

Structure and dynamics of Pinus densiflora community in Mt. Kaya were studied to provide the information needed for management of Pinus densiflora forest in the southern inland of Korea. Stratification structure of Pinus densiflora community in the lower and middle slope consisted of tree layer(10~15m), subtree layer(4~10m), shrub layer(1~4m), and herb layer(below 1m), while in the rock zone of ridge and top area consisted of tree layer(7~10m), subtree layer(2~7m), shrub layer(1~2m), and herb layer(below 1m). According to the diameter distribution of tree species in Pinus densiflora community, secondary Pinus densiflora forest will gradually decline. Its forest may be replaced by Quercus mongolica, Quercus serrata, Carpinus laxiflora, C. cordata, and Fraxinus rhychophylla in the lower slope, and by Quercus mongolica in the middle slope. Pinus densiflora forest has its seedlings and saplings in ridge and top area, so it may be sustained. By taking cores from Pinus densiflora trees in research area, it could be obtained that in the lower and middle slope, age of Pinus densiflora forest was about 80~90 years old. When the age of its trees was about 72~80 years old, withering trees of standing dead occurred. Disturbance regime of Pinus densiflora community in Mt. Kaya consisted of standing dead, uprooting and limbfall, these were 70.6%, 17.6% and 11.8% respectively. It takes about 100~110 years for advance growth of Pinus densiflora in ridge and top area to reach tree layer. During the period, it has twice chances of disturbance in standing dead. Annual diameter growth of Pinus densiflora was 2.45~2.9mm in the lower and middle slope, while it was 1.75mm in ridge and top region, by measuring cores.