• Ecology and Resilient Infrastructure
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• v.1 no.2
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• pp.49-60
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• 2014

Fish assemblages play an integral role in stream ecosystem and are influenced by stream environmental conditions and habitat disturbances. Fish community structures and habitat parameters of U.S. EPA rapid bio-assessment protocol were surveyed to investigate the effect of stream environment and habitat disturbance on fish communities at 13 study sites in the Gapyeong Stream, a typical gravel-bed stream. Principal component analysis (PCA) based on data from habitat assessment at each study site indicated that the study sites were differentiated by habitat parameters such as embeddedness, velocity/depth regime and sediment deposition, which were related with bed slope. A total of 46 species belonging to 12 families were collected in the Gapyeong Stream. A dominant species was Zacco koreanus, subdominant species was Z. platypus. Hierarchical cluster analysis based on species abundance classified fish communities into the three main groups along the stream longitudinal change. Non-metric multidimensional scaling (NMDS) portrayed that fish community structures were related to major habitat parameters, i.e., epifaunal substrate/available cover, embeddedness, velocity/depth regime, sediment deposition, channel alternation and frequency of riffles. These results suggested that fish community structures were primary affected by the longitudinal environmental changes, and those were modified by habitat disturbance in the Gapyeong Stream, a gravel-bed stream.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.79-87
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• 2002

Acoustic responses to pressure oscillations in axisymmetric combustion chamber are numerically investigated to examine the qualitative trend of acoustic instability in liquid rocket engine. Chamber operating condition and excitation frequency of oscillating pressure are selected as exciting parameters of acoustic instability. Artificial perturbation is simulated by total-pressure oscillation with sine wave at chamber inlet. Many approximations and simplifications are introduced without losing the essence of acoustic pressure response. First, steady-state solution for each operating condition is obtained and next, transient analysis is conducted. Depending on operating condition and excitation frequency, the distinct response characteristics are brought. Weak-strength flames and high-frequency excitation tend to cause sensitive acoustic pressure response leading to unstable pressure field. These results are analyzed based on the correlation with acoustic pressure responses from the previous works adopting laminar flamelet model.

• Journal of Korea Water Resources Association
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• v.51 no.8
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• pp.713-727
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• 2018

This study is to develop an assessment system for stream physical environments by considering stream characteristics. Comprehensively, the descriptions of and steam classification, assessing reach selection, contents of assessment categories and indexes are summarized. Since the physical structure of stream is results of reaction by stream power, streams were classified into three types (as high gradient stream, mid gradient stream and low gradient stream) according to the slope of channel, the grain size of bed material and the characteristics of channel topography. The scale of assessment reach was selected based on 10 or 25 times of channel width according to typical characteristics such as interval of step or riffle and sinuosity in each stream type. The assessment indexes were organized into common indicators such as channel stability, flow status, cross-section shape, bank stability, channel alteration and stream crossing structure, and characteristic indicators by stream type such as effective habitats, bed embeddedness, diversity of flow and frequency of step or riffle. To evaluate the applicability, the assessment system was applied to 9 streams and the results were analyzed and presented.

• Korean Journal of Environment and Ecology
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• v.27 no.3
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• pp.381-395
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• 2013

In this study, we surveyed 6 times for the actual vegetation type and flora of Amgok wetland (Intermediate moor area, Alnus japonica community area) and it's watershed area in Tohamsan district, Gyeongju National Park from Apr. to Nov. in 2011. As a result of the actual vegetation type, most vegetation of watershed area was disturbed by human activity except wetland area. Even though the wetland is relatively broad compared with it's watershed, the wetland: watershed is around 1:10. The flora was surveyed 65 family, 184 species, 1 subspecies, 39 variety, 8 forma and totally 233 taxonomic group in the watershed. The wetland type was looked intermediate moor. Naturalized plants was surveyed 2taxonomic in the wetland area and total was17 taxonomic. This area has relatively broad wetland and soundly conserved. But several Salix koreensis and Acer ginnala are growing so needed the interest and monitoring.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.28-30
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• 2012

A mechanical pulsator is manufactured for study of combustion instabilities in a model chamber with impinging-jet injectors. Artificial disturbance is generated by the device and thereby, artificial instability can be examined experimentally. A sample F(fuel)-O(dxidizer)-O-F impinging-jet injector is adopted for the test. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions. Pressure fluctuation data, which is obtained from the dynamic pressure transducers installed in combustion chamber, is analyzed.

• Korean Journal of Ecology and Environment
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• v.50 no.2
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• pp.195-206
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• 2017

We described a spatial distribution pattern and floral diversity on the Paspalum distichum community occurring at the ecological parks of Hwamyeong, Daejeo, Samnak, and Maekdo in the Nakdong river estuary. A total distribution area of P. distichum community was $303,462.6m^2$. Its largest area was found in Samnak eco-park ($185,910.1m^2$). The most richness of knotgrass patches in each ecological park was determined Maekdo eco-park (87). Cover class level-5 shows the largest area ($260,663.2m^2$). A total of 73 taxa (34 families, 55 genus, 65 species, and 8 varieties) were listed up on the P. distichum community. A welldeveloped population of knotgrass was found predominantly at sites linked into human impacts at the riverine floodplain, the stream courses flowing through the parks, and the man-made channels and wetlands. Finally we proposed an ecological management strategy for knotgrass population in the study area.

• Korean Journal of Heritage: History & Science
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• v.46 no.3
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• pp.114-133
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• 2013

This study aims to identify the natural damage of the Samcheonsaji Temple Site in Bukhansan National Park and to suggest the plans to minimize damage for the remains. The types of natural damage are classified into direct vegetation damage, indirect topographical damage, and artificial damage. The most popular causes of damage to temple sites include the roots of trees as direct vegetation damage and the soil erosion by rain or stream as topographical damage. Direct vegetation damage includes burial remains damaged by the root of trees and vines, but it is often observed that some trees have contributed to protection against collapse. Indirect topographical changes have damaged the ruins by soil erosion caused by floods or typhoons. Vegetation changes due to topographical reasons have also caused damage. Artificial reasons of damage include forestry operations and compaction by hikers. Based on the analysis of the findings, the following could be suggested as plans to resolve these problems: 1. Natural damage occurs slowly due to negligence. Therefore, it could be reduced by forestry improvement, including forest density control through thinning, planting to prevent landslides, maintaining grasslands nearby. 2. Deciduous broadleaf trees can be planted to reduce soil erosion by rainfall. It is necessary to maintain the density of forests at around $0.02{\sim}0.18trees/m^2$. 3. It would be good to grow Quercus spp and Carpinus spp or weaken the community of Robinia pseudoacacia and Pueraria lobata which disturb the ecosystem. Samcheonsaji Temple Site is located in Mt. Bukhan National Park that is a publicly owned property. Therefore, it is constantly maintained for natural preservation and vegetation management could be considered for the preservation of historical remains.

• Korean Journal of Environment and Ecology
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• v.27 no.6
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• pp.733-744
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• 2013

This study was launched in order to collect basic data such as emergent species, a succession trend based on the actual vegetation at the ridge from Haneoryoung to Daetjae, thereby designating 46 quadrats($10m{\times}10m:100m^2$). As a result of classification by TWINSPAN, the plant community was categorized into eight different communities, such as Pinus densiflora-Quercus mongolica-Fraxinus rhynchophylla, P. densiflora-Q. mongolica, Ulmus davidiana var. japonica, Q. mongolica-Deciduous Broad-leaved, Q. mongolica, Q. mongolica-Betula davurica, Q. mongolica-F. sieboldiana, and Larix kaempferi. An analyzation of each communities indicated that P. densiflora dominant community will change into a Q. mongolica dominant community if there are no outside artificial disturbances. U. davidiana var. japonica community maintains its present condition, because it doesn't appear to be a competitive species. In the case of Q. mongolica dominant community, if nothing comes in a competitive species against Q. monglica, it is possible to succeed to a muture stand. These communities with competitive species such as F. rhynchophylla, B. davurica that do not emerge at a canopy layer will gradually progress to the Deciduous Broad-leaved community. With regard to the species diversity index per unit ($400m^2$), succession processing communities (P. densiflora: 1.0477~1.1283) tend to be higher than succession-processed communities (Q. mongolica dominant: 0.6446~0.9424).

• Korean Journal of Environment and Ecology
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• v.30 no.4
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• pp.783-792
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• 2016

The purpose of this study is to investigate the characteristics of the vegetation structure and the location environment of Albizzia kalkora (AK) growing in Mt. Yudal located in Mokpo city and in the nearby islands. The AK community in Mt. Yudal in Mokpo city (Community I) is located in a region which is relatively high above the sea level. The average age of the major kinds of trees found in the region is about 30 years. The vegetation structure in the community shows an early stage of vegetation development due to continued disturbance. In Community IV, on the sandy soil in the flatland near the seashores, the average age of the major kinds of trees is about 9 years. In this community, a pure forest is presumed to have been formed in a poor environment which is artificially disturbed in relatively recent times even as AK with its strong adoptability was introduced into the region. In other communities (II, III), the vegetation state shows a competition between AK and deciduous oak trees, and the average age of the major kinds of trees is about 13 to 30 years. AK communities with a better developed vegetation structure are located on the higher steep slopes near the seashore. In the early stage of vegetation development, the forest floor received more effective light for photosynthesis, and thus more seedlings of AK emerged and grew. The probability of AK appearing in the damaged or sterile soil near the seashore was high because of its strong adaptability. However, as the vegetation structure developed further and the soil fertility increased, the domination of AK in the vegetation structure decreased as deciduous oak trees won the competition with AK.

• Korean Journal of Soil Science and Fertilizer
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• v.14 no.2
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• pp.64-69
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• 1981

A field and laboratory experiments were conducted to evaluate the effect of visible biopores (larger than 0.2 mm in diameter) on the saturated hydraulic conductivity of Bonryang sandy loam (Coarse loamy over sandy, mixed, mesic family of Typic Udifluvents) developed on alluvial plains. The saturated hydraulic conductivity was significantly correlated with the equivalent permeble surface area (EPSA) which was calculated from the number of various sized biopores in the soil observed by naked eye, and negatively correlated with the bulk density. The effect of biopores on the saturated hydraulic conductivity was remarkable in subsoil al though it was not pronounced in plowed layer and sandy substrata. The bulk density was found to be correlated with the number and the EPSA of the visible biopores. A remarkable spatial variability was observed in the number of biopore and the bulk density.