• Korean Journal of Environment and Ecology
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• v.27 no.4
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• pp.462-472
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• 2013

This study was carried out to provide a basic data for preservation of Pinus desiflora forest as cultural landscape forest by analyzing characteristics of plant community of P. desiflora forest in Geumjeongsan(mountatin) in Busan city. In order to analyze plant community of P. densiflora in Geumjeongsan, we set up 10 study plots inside and 8 plots outside of Geumjeongsansung(mountain fortress, hereinafter 'Sansung')(unit area: $400m^2$), a total of 18 plots. TWINSPAN analysis divided these 18 study plots into 6 communities which are Querqus serrata-P. desiflora community, P. desiflora community, P. desiflora-Q. serrata community, P. thunbergii-P. densiflora community, P. densiflora-P. thubergii-Q. acutissima community, and P. densiflora-Platycarya strobilacea community. Importance Percentage (I.P.) of each area and DBH class distribution of main species showed that P. densiflora community would succeed to Q. serrata community or C. tschonoskii community. Analysis on tree age found out that communities in the Sansung were 32~37 years old and those outside the Sansung were 44~57 years old. Shannon's species diversity index ranged from 0.4826 to 1.2499. Regarding correlation between species, P. densiflora had negative correlation with Styrax japonica. Based on abovementioned result we expected ecological succession from P. densiflora community to Q. serrata community inside of the Sansung. Outside the Sansung, succession from P. densiflora-P. thunbergii community to C. tschonoskii-Q. serrata community was expected. In order to manage P. densiflora forest as cultural landscape forest, Q. spp in the understory and shrub layer and deciduous broad-leaved arboreal trees should be managed. Tree crown management of deciduous broad-leaved trees in competition with P. desiflora, is also required.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.2
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• pp.157-164
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• 2007

In this paper, a novel sensorless drive for brushless DC (BLDC) motor using the fuzzy back-EMF observer is proposed to improve the performance of conventional sensorless drive methods. Existing sensorless drive methods of the BLDC motor have low performance at transients or low speed range and occasionally require additional circuits. To cope with these problems, the back-EMF of the BLDC motor must be precisely estimated by a fuzzy logic, which is suitable to estimate the back-EMF which has a trapezoidal shape. The proposed algorithm using fuzzy back-EMF observer can achieve robust control for the change of an external condition and continuously estimate position of the rotor at transients as well as at steady state. The superiority of the proposed algorithm is proved through the simulation compared with other sensorless drive methods.

• Spatial Information Research
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• v.18 no.4
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• pp.1-11
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• 2010

Unlike the previous studies which have focused on 2-dimensional urban characteristics, this paper presents statistical models explaining urban heat island(UHI) effect by 3-dimensional urban morphologic information and addresses its policy implications. 3~dimensional informations of Columbus, Ohio arc captured from LiDAR data and building boundary informations are extracted from a building digital map, Finally NDV[ and temperature data are calculated by manipulating band 3, band 4, and thermal hand of LandSat images. Through complicated data processing, 6 independent variables(building surface area, building volume, height to width ratio, porosity, plan surface area) are introduced in simple and multiple linear regression models. The regression models are specified by Box-Tidwell method, finding the power to which the independent variable needs to raised to be in a linearity. Porosity, NDVI, and building surface area are carefully chosen as explanatory variables in the final multiple regression model, which explaining about 57% of the variability in temperatures. On reducing UHI, various implications of the results give guidelines to policy-making in open space, roof garden, and vertical garden management.

• Korean Journal of Plant Resources
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• v.19 no.1
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• pp.97-104
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• 2006

This study was conducted to investigate effect of temperature and NaCl on the seed germination and water absorption of Thuja orientalis. Seeds were treated with 0, 500, 1,000, 2,000 and 4,000ppm of NaCl and placed in different chambers at 15, 20, 25 and $30^{\circ}C$, respectively. And seed properties and relative water absorptions were analyzed. Germination decreased with the increase of both temperature and NaCl concentration, and especially the difference was obvious at $30^{\circ}C$. Dormancy and mortality increased with the increase of temperature in non-NaCl treatment. Two-way analysis of variance showed significant effects of temperature, NaCl concentration and interaction between temperature and NaCl concentration (p<0.001). Mean germination time increased with the increase of NaCl concentration at 15, 20 and $25^{\circ}C$ but decreased at $30^{\circ}C$ because the seeds were mortal by NaCl high concentration, Germination speed and germination performance index decreased with the increase of NaCl concentration. Those represented decreasing tendency with NaCl concentration but high positive correlation with germination. Relative water absorption decreased with the increase of NaCl concentration and represented high values at $15^{\circ}C$, and showed high positive correlations with germination, germination speed and germination performance index. It was reported that the high temperature and salinity were inhibitive factors of seed germination of Thuja orientalis.

• Korean Journal of Environment and Ecology
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• v.36 no.5
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• pp.525-534
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• 2022

In this study, we investigated the psychological and physiological effects of experiences in real natural forests and virtual forests using artificially controllable VR. The experiment tested 60 adult college students in a natural forest and a graduate seminar room where external light was blocked. It evaluated the effects of the natural and the VR forest environments by comparing the psychological and physiological recovery of the subjects. Psychometric testing using the PANAS psychological index showed increased positive emotions and decreased negative emotions after experiencing forest scenery in the natural and VR forest environments. And a stress index, based on measuring cortisol in saliva, decreased significantly in the subjects in both environments. The experiment results can be used to support the creation of a psychological and physiological recovery environment with VR for those who cannot go to the natural forest due to certain restrictions such as physical distance, mobility difficulties, etc. It is expected that the results will be the basis for further research into the visual effects of forest healing and also for widening the use of VR, a technology of the fourth industry, in the field of forestry.

• Tunnel and Underground Space
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• v.23 no.4
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• pp.308-318
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• 2013

Thermal stratification in heat stores is essential to improve the efficiency of energy storage systems and deliver more useful energy on demand. It is generally well known that the degree of thermal stratification in heat stores varies depending on the aspect ratio (the height-to-width ratio) and size of the stores. The present study aims to investigate the effect of the aspect ratio and storage volume of rock caverns for storing hot water on thermal stratification in the caverns and heat loss to the surroundings. Heat transfer simulations using a computational fluid dynamics code, FLUENT were performed at different aspect ratios and storage volumes of rock caverns. The variation of thermal stratification with respect to time was examined using an index to quantify the degree of stratification, and the heat loss to the surroundings was evaluated. The results of the numerical simulations demonstrated that the thermal stratification in rock caverns was improved by increasing the aspect ratio, but this effect was not remarkable beyond an aspect ratio of 3-4. When the storage volume of rock caverns was large, a higher thermal stratification was maintained for a relatively longer time compared to caverns with a small storage volume, but the difference in thermal stratification between the two cases tended to decrease as the aspect ratio became larger. In addition, the numerical results showed that the heat loss to the surrounding rock tended to increase with an increase in aspect ratio because the surface area of rock caverns increased as the aspect ratio became larger. The total heat loss from multiple small caverns with a reduced storage volume per cavern was larger compared to a single cavern with the same total storage volume as that of the multiple caverns.

• Journal of Korea Port Economic Association
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• v.39 no.1
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• pp.115-129
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• 2023

This study analyzed the risk spillover of BDI on shipping company stock prices through the Copula-CoVaR method based on daily data from January 4, 2010, to October 31, 2022. The main empirical analysis results and policy implications are as follows. First, copula results showed that there was a weak dependence between BDI and shipping company stock prices, and PAN, KOR, and YEN were selected as the most fitting model for dynamic Student-t copula, HMM was selected as the rotated Gumbel copula, and KSS was selected as the best model. Second, in the results of CoVaR, it was confirmed that the upside (downside) CoVaR was significantly different from the upside (downside) VaR in all shipping companies. This means that BDI has a significant risk spillover on shipping companies. In addition, as for the risk spillover, the downside risk is generally lower than the upside risk, so the downside and upside risk spillover were found to be asymmetrical. Therefore, policymakers should strengthen external risk supervision and establish differentiated policies suitable for domestic conditions to prevent systematic risks from BDI shocks. And investors should reflect external risks from BDI fluctuations in their investment decisions and construct optimal investment portfolios to avoid risks. On the other hand, investors propose that the investment portfolio should be adjusted in consideration of the asymmetric characteristics of up and down risks when making investment decisions.

• Journal of the Korean Association of Geographic Information Studies
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• v.8 no.2
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• pp.175-185
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• 2005

Governmental authorities have been trying to develop our city in respect to the growth of economy and it is true that their developmental policies have negative effects on ecosystem without doubt. To estimate these negative effects, this study is mainly focused on analysing the usage of the land according to the urban growth, and the temporal and spatial patterns between the elements which consist of the landscape of Daegu Metropolitan Sphere, by using the GIS method and the landscape indices. The results of the this study are as follow; the urban areas widened for $193.4km^2$ due to the shift of the urban function, and the forest areas were encroached for $455.6km^2$ into other landcover patterns. It was the shift of the agriculture areas that are given the most influence in those procedures since those developmental conditions are relatively satisfactory. Moreover the forest areas are structurally fragmented into the complicated form, and also the patterns of adjacent patches are become complex. These transitions are regarded as causes of increased external interventions to the forest areas, and these could possibly deteriorate the soundness of forest areas by reducing the core areas which are habitats of species. In conclusion, the results of this study evaluate the influence of much broader urban development on environment structure around urban and mutual relationship between them. In addition, it can provide methods and basic informations for the establishment of metropolitan urban plan after due considerations of the landscape ecological principle.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.5
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• pp.574-583
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• 2021

Predicting shipping markets is an important issue. Such predictions form the basis for decisions on investment methods, fleet formation methods, freight rates, etc., which greatly affect the profits and survival of a company. To this end, in this study, we propose a shipping freight rate prediction model for container ships using gated recurrent units (GRUs) and long short-term memory structure. The target of our freight rate prediction is the China Container Freight Index (CCFI), and CCFI data from March 2003 to May 2020 were used for training. The CCFI after June 2020 was first predicted according to each model and then compared and analyzed with the actual CCFI. For the experimental model, a total of six models were designed according to the hyperparameter settings. Additionally, the ARIMA model was included in the experiment for performance comparison with the traditional analysis method. The optimal model was selected based on two evaluation methods. The first evaluation method selects the model with the smallest average value of the root mean square error (RMSE) obtained by repeating each model 10 times. The second method selects the model with the lowest RMSE in all experiments. The experimental results revealed not only the improved accuracy of the deep learning model compared to the traditional time series prediction model, ARIMA, but also the contribution in enhancing the risk management ability of freight fluctuations through deep learning models. On the contrary, in the event of sudden changes in freight owing to the effects of external factors such as the Covid-19 pandemic, the accuracy of the forecasting model reduced. The GRU1 model recorded the lowest RMSE (69.55, 49.35) in both evaluation methods, and it was selected as the optimal model.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.7
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• pp.550-559
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• 2017

In order to maintain communication while the vehicle is moving, satellite azimuth angle and elevation angle correction are needed in real time. The elevation angle correction affects the system G/T according to the variation of the external noise temperature flowing into the antenna. G/T is expressed as a ratio of power gain G to noise temperature T and is an important performance function required for antenna gain design. This paper aims to G/T analysis considering elevation angle change and the establishment of an antenna design procedure. For this purpose, the relationship between elevation angle and brightness temperature including rain attenuation was analyzed according to recommendation ITU-R P.372 radio noise. Next, an antenna was designed based on the analysis results and design procedure was verified by G/T measurement. Through this experiment, G/T according to elevation angle was confirmed, and the minimum antenna gain analysis and design procedure required in the system could be established.