• Journal of Environmental Science International
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• v.18 no.4
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• pp.423-434
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• 2009

In recent years, the urban thermal environment has become worse, such as days on which the temperature goes above $30^{\circ}C$, sultry nights and heat stroke increase, due to the changes in terrestrial cover such as concrete and asphalt and increased anthropogenic heat emission accompanied by artificial structure. The land use type is an important determinant to near-surface air temperature. Due to these reasons we need to understand and improve the urban thermal environment. In this study, the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model(MMS) was applied to the metropolitan of Daegu area in order to investigate the influence of land cover changes and urban modifications increase of Albedo to the surface energy budget on the simulated near-surface air temperature and wind speed. The single urban category in existing 24-category U.S. Geological survey land cover classification used in MM5 was divided into 6 classes to account for heterogeneity of urban land cover. As a result of the numerical simulation intended for the metropolitan of Daegu assumed the increase of Albedo of roofs, buildings, or roads, the increase of Albedo (Cool scenario)can make decrease radiation effect of surface, so that it caused drops in ambient air temperature from 0.2 to 0.3 on the average during the daylight hours and smaller (or near-zero) decrease during the night. The Sensible heat flux and Wind velocity is decreased. Modeling studies suggest that increased surface albedo in urban area can reduce surface and air temperatures near the ground and affect related meteorological parameters such as winds, surface air temperature and sensible heat flux.

• Ocean and Polar Research
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• v.34 no.2
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• pp.239-251
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• 2012

The food web dynamics in a coastal ecosystem of Korea were predicted with Ecosim, a trophic flow model, under various scenarios of primary productivity due to ocean warming and ocean acidification. Changes in primary productivity were obtained from an earth system model 2.1 under A1B scenario of IPCC $CO_2$ emission and replaced for forcing functions on the phytoplankton group during the period between 2020 and 2100. Impacts of ocean acidification on species were represented in the model for gastropoda, bivalvia, echinodermata, crustacean and cephalopoda groups with effect sizes of conservative, medium and large. The model results show that the total biomass of invertebrate and fish groups decreases 5%, 11~28% and 14~27%, respectively, depending on primary productivity, ocean acidification and combined effects. In particular, the blenny group shows zero biomass at 2080. The zooplankton group shows a sudden increase at the same time, and finally reaches twice the baseline at 2100. On the other hand, the ecosystem attributes of the mean trophic level of the ecosystem, Shannon's H and Kempton's Q indexes show a similar reduction pattern to biomass change, indicating that total biomass, biodiversity and evenness shrink dynamically by impacts of climate change. It is expected from the model results that, after obtaining more information on climate change impacts on the species level, this study will be helpful for further investigation of the food web dynamics in the open seas around Korea.

• Journal of Korean Society for Atmospheric Environment
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• v.33 no.2
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• pp.139-158
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• 2017

CMAQ (Community Multiscale Air Quality Model) simulations were carried out to estimate the potential range of contributions on surface $PM_{2.5}$ concentrations over the Seoul Metropolitan Area (SMA) with the gaseous precursors and Primary Particulate Matters(PPM) available from a recent national emissions inventory. In detail, on top of a base simulation utilizing the 2013 Clean Air Policy Supporting System (CAPSS) emission inventory, a set of Brute Force Method (BFM) simulations after reducing anthropogenic $NO_x$, $SO_2$, $NH_3$, VOCs, and PPM emissions released from area, mobile, and point sources in SMA by 50% were performed in turn. Modeling results show that zero-out contributions(ZOC) of $NH_3$ and PPM emissions from SMA are as high as $4{\sim}5{\mu}g/m^3$ over the region during the modeling period. On the contrary, ZOC of local $NO_x$ and $SO_2$ emissions to SMA $PM_{2.5}$ are less than $1{\mu}g/m^3$. Moreover, model analyses indicate that a wintertime $NO_x$ reduction at least up to 50% increases SMA $PM_{2.5}$ concentrations, probably due to increased HNO3 formation and conversion to aerosols under more abundant ozone and radical conditions after the $NO_x$ reduction. However, a nation-wide $NO_x$ reduction decreased SMA $PM_{2.5}$ concentrations even during winter, which implies that nation-wide reductions would be more effective to curtail SMA $PM_{2.5}$ concentrations than localized efforts.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.10
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• pp.4308-4313
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• 2011

The objective of this study is to investigate the cooling performance of the roof mounted air-conditioning system using electric driven scroll compressor for zero emission vehicles. This air conditioner with air source was used R-134a as a refrigerant and tested under various operating conditions such as refrigerant charge amount and indoor temperature, and compressor frequencies. Experimental results revealed that at all tested compressor frequencies, heat transfer rate of the evaporator increased and the cooling COP increased with the indoor temperature. In addition, the heat transfer rate of the evaporator was over 25.0kW sufficient for the cooling loads of an electric bus.

• Resources Recycling
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• v.27 no.3
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• pp.86-92
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• 2018

The amount of construction waste generated is steadily increasing every year, and the Law for Promotion of Recycling is enacted. However, it is difficult to use it as a recycled aggregate for concrete, which is presented in the quality standard of recycled aggregate with high water uptake and low density due to low separation of aggregate between concrete and cement paste. Therefore, in this study, a multi-stage impact crusher was used to remove mortar, which is essential for improving the quality of recycled aggregate. In analyzing the characteristics of the equipment, the spectrum of energy generated in each part between the particle and the equipment was calculated by using DEM. In order to generate an effective separation phenomenon, it was confirmed that the operation condition of 900 RPM was appropriate based on the ratio of the number of collisions (L/H) of the low energy group (L) to the number of collisions of the high energy group (H).

• Environmental and Resource Economics Review
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• v.12 no.2
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• pp.347-382
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• 2003

The paper presents available options that Korea can adopt in an effort to promote eco-industrial development in a near future. What is missing and the reasons why Korea is behind the other countries in the area are: 1) Lack of holistic view and the integrated approach toward economy and environment in policy implementation, 2) Lack of understanding, among entrepreneurs, of the concept of productivity per input resource, and the fact that not only labor and capital productivity but also the total productivity enhancement is vital for industry's competitive edge; There has been no driving force in the market to develop economies of system integration to turn industrial wastes to valuable input resources, 3) Unsupportive regulatory system regarding the trade of by products, and 4) Lack of financing and incentive mechanism. 5) Lack of information forum. Regulatory reform should be taken for the direction that in effect increase the price of disposal and motivate firms to seek symbiotic relationship with other firms, and facilitate trade by-product between firms. Financing and incentive mechanism should be introduced in order for the industry to find easy access to the opportunities for organizing the network to transform wastes in negative value to the value added resources. Also information network should be established to provide a market for by-product exchange and public education to improve industry's environmental performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.9
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• pp.2073-2085
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• 2012

Recently, the International Telecommunication Union allocated the 470-862 MHz band to the digital broadcasting (DB) service. Moreover, the 790-862 MHz sub-band will be allocated to the next-generation mobile system, known as the International Mobile Telecommunication - Advanced (IMT-A), and to the DB on a co-primary basis in the year 2015. Currently, two candidate technologies are available to represent the IMT-A system; the Mobile WiMAX and Long Term Evolution - Advanced (LTE-A). One of the main criteria of the IMT-A candidate is to not cause additional interference to the primary service (i.e., DB). In this paper, we address the spectrum sharing issue between the IMT-A candidates and the DB service. More precisely, we investigate the interference effect between the DB service and the mobile network, which could be either LTE-A or WiMAX. Our study proposes a spectrum sharing model to take into account the impact of interference and evaluates the spectrum sharing requirements such as frequency separation and separation distance. This model considers three spectrum sharing scenarios: co-channel, zero guard band, and adjacent channel. A statistical analysis is performed, by considering the interferer spectrum emission mask and victim receiver blocking techniques. The interference-to-noise ratio is used as an essential spectrum sharing criterion between the systems. The model considers the random distribution of the users, antenna heights, and the bandwidth effect as well as the deployment environment in order to achieve spectrum sharing. The results show that LTE-A is preferable to WiMAX in terms of having less interference impact on DB; this can eventually allow the operation of both services without performance degradation and thus will lead to efficient utilization of the radio spectrum.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.2
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• pp.157-166
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• 2017

The Fuel Cell Electric Vehicle(FCEV) is recently evolving into a new trend in the automobile industry due to its relatively higher efficiency and zero greenhouse gas(GHG) emission in the tailpipe, as compared to that of the conventional internal combustion engine vehicles. However, it is important to analyze the whole process of the hydrogen's life cycle(from extraction of feedstock to vehicle operation) in order to evaluate the environmental impact of introducing FCEV upon recognizing that the hydrogen fuel, which is used in the fuel cell stack, is not directly available from nature, but instead, it should be produced from naturally available resources. Among the various hydrogen production methods, ${\sim}54.1%^{8)}$ of marketed hydrogen in Korea is produced from naphtha cracking process in the petrochemical industry. Therefore, in this study, we performed a well-to-wheels(WTW) analysis on the hydrogen fuel cycle for the FCEV application by using the GREET program from the US Argonne National Laboratory with Korean specific data. As a result, the well-to-tank and well-to-wheel GHG emissions of the FCEV are calculated as 45,638-51,472 g $CO_2eq/GJ$ and 65.0-73.4 g $CO_2eq/km$, respectively

• Advances in Energy Research
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• v.5 no.3
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• pp.227-237
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• 2017

The continuous increase of emission rates of green house gases and the effects on global warming added a new dimension to the problem of substituting the petroleum and its derivatives by environment friendly and sustainable energy sources for the world. Solar and wind energy appear at the top of the list of renewable of high potential, widely available, of dominated technology and well accepted. Brazil is one of the few countries in the world that receives number hours of sunshine exceeding 3,000 hours per year with a daily average of 4.5 to 6 kWh. However, this potential is largely unexplored and poorly tapped. The number of renewable systems implanted in Brazil has grown in recent years, but still insignificant when compared, for example, with Germany and Spain among others. This paper presents the results of an optical study on small concentration solar collector with evacuated tube enveloping the absorber and internal reflective surface fixed on the bottom part of the evacuated tube. The designed collector has a 2D geometrical concentration ratio between 2.455 and 4.91. The orientation of the solar collector, the ratio of the radius of the receiver to the radius of the absorber, the incidence angle for each period of the year, the collector inclination angle, the aperture angle of the reflective surface, concentration and optical efficiency were determined. The ray traces and flux distribution on the absorber of the evacuated tube solar collector were determined by using the program Ray Optics Simulation. The optical efficiency varies during the year according to the solar declination. For the periods were the solar declination is close to zero the efficiencies are maximum, and the variation during the day is around 25.88% and 99.9%. For the periods were the solar declination is maximum the efficiencies are minimum, and the variation during the day is around 23.78% and 91.79%.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.3B no.3
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• pp.147-154
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• 2003

This paper presents a high-frequency boost type ZVS-PWM chopper-fed DC-DC power converter with a single active auxiliary edge-resonant snubber at the load stage which can be designed for power conditioners such as solar photovoltaic generation, fuel cell generation, battery and super capacitor energy storages. Its principle operation in steady-state is described in addition to a prototype setup. The experimental results of boost type ZVS-PWM chopper proposed here, are evaluated and verified with a practical design model in terms of its switching voltage and current waveforms, the switching v-i trajectory and the temperature performance of IGBT module, the actual power conversion efficiency, and the EMI of radiated and conducted emissions, and then discussed and compared with the hard switching scheme from an experimental point of view. Finally, this paper proposes a practical method to suppress parasitic oscillation due to the active auxiliary resonant switch at ZCS turn-off mode transition with the aid of an additional lossless clamping diode loop, and can be reduced the EMI conducted emission.