• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.6
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• pp.53-62
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• 2009

The EFDC (Environmental Fluid Dynamics Code), a numerical model for simulating three-dimensional (3D) flow, transport, and biogeochemical processes in surface water systems including rivers, reservoirs, and estuaries, was applied to assess the effect of sea water and fresh water exchange rates ($Q_e$) on the mixing characteristics of a conservative pollutant (tracer) induced from upstreams and salinity in Saemangeum Lake, Korea. The lake has been closed by a 33 km estuary embankment since last April of 2006, and now seawater enters the lake partially through two sluice gates (Sinsi and Garyuk), which is driving the changes of hydrodynamic and water quality properties of the lake. The EFDC was constructed and calibrated with surveyed bathymetry data and field data including water level, temperature, and salinity in 2008. The model showed good agreement with the field data and adequately replicated the spatial and temporal variations of the variables. The validated model was applied to simulated the tracer and salinity with two different gate operation scenarios: RUN-1 and RUN-2. RUN-1 is the case of real operation condition ($Q_e=25,000,000\;m^3$) of 2008, while RUN-2 assumed full open of Sinsi gate to increase $Q_e$ by $120,000,000\;m^3$. Statistical analysis of the simulation results indicate that mixing characteristics of pollutants from upstream can be significantly affected by the amount of $Q_e$.

• Journal of Korean Society for Atmospheric Environment
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• v.16 no.1
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• pp.49-60
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• 2000

The concentration of atmospheric mercury(Hg0 and relevent environmental parameters that include both meteorological and criteria pollutant data were dtermined at hourly intervals during two field campaigns covering the periods of September 1997 and May/June 1998. The mean concentrations of Hg for the two study periods were computed as 3.94 and 3.43ngm-3, respectively. Through a separation of these data into both daytime and nighttime periods, we further analyzed diurnal variation patterns for Hg between two different seasons. Using our Hg data sets, we were able to recognize two contrasting diurnal variation patterns of Hg between two diffeerent seasons that can be characterized as: (1) the occurrences of peak Hg concentration during daytime(fall0 and (2) slight reductions in daytime Hg concentration relative to nighttiime Hg data(summer). To study the systematic differences in diurnal patterns between two different seasons, we analyzed Hg data in terms of different statistical approaches such as correlation(and linear regression0 and factor analysis. Results of these analyses consistently indicated that different mechanisms were responsible for controlling the daytime distribution patterns of Hg. The variation of boundary layer conditions betwen day/night periods may have been important in introducing the relative reduction in daytime Hg levels during summer. However, when the relationship between Hg and concurrently determined O3 is concerned, these differences are unlikely to be an effective sink mechanism within the ranges of ozone concentrations determined concurrently during this study, regardless of season. To further provide the general account for short-term variations in Hg distribution data, we should be able to describe the various factors underlying its sink mechanism.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.46 no.6
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• pp.868-877
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• 2013

To understand the effects of marine environmental and meteorological parameters on laver Porphyra yezoensis production at Nakdong River Estuary, we analyzed marine environmental (water temperature, salinity, nutrients, etc.) and meteorological properties (air temperature, wind speed, precipitation, sunshine hours) with yearly and monthly variations in laver production over 10 years (2003-2013). Air and water temperature, wind speed, sunshine hours and precipitation were major factors affecting yearly variability in laver production at the Nakdong River Estuary. Lower air and water temperatures together with higher levels of nutrients and sunshine and stronger wind speeds resulted in higher laver harvests. Salinity and nitrogen did not show clear correlations with laver production, mainly due to the plentiful supply of nitrogen from river discharge and the low frequency of environmental measurements, which resulted in low statistical confidence. However, environmental factors affecting monthly laver production were related to the life cycle (culturing stage) of Porphyra yezoensis and were somewhat different from factors affecting annual laver production. In November, a young laver needs lower water temperatures for rapid growth, while a mature laver needs much stronger winds and more sunshine, as well as lower temperatures for massive production and effective photosynthesis, mostly in December and January. However, in spring (March), more stable environments with fewer fluctuations in air temperature are needed to sustain the production of newly deployed culture-nets ($2^{nd}$ time culture). These results indicate that rapid changes in weather and marine environments caused by global climate change will negatively affect laver production and, thus, to sustain the yield of and predict future variability in laver production at the Nakdong River estuary, environmental variation around laver culturing farms needs to be monitored with high resolution in space and time.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.3
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• pp.51-58
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• 2010

According to dramatic increase of wireless communication demand, more spectrum resources are needed to support considerable and various wireless services, so cognitive radio(CR) was proposed to reuse unused frequency efficiently. Also, FCC revises its policies regarding the usage of the TV white spaces by unlicensed users. CR is an intelligent wireless communication system that is aware of the radio environment and is capable of adapting its operation to the statistical variations. Spectrum sensing is the key task of the CR systems. However, since spectrum sensing performance changes according to the received signal that is received various geography environment, regional characteristics are considered to estimate the path-loss. Therefore, for more accurate analysis and simulation, we demonstrate the spectrum sensing performance of CR system by various method applying Okumura-hata propagation model.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.11
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• pp.7-13
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• 2004

Experimental results are presented for the degradation of 3 nm-thick gate oxide under -2.5V $\leq$ V$_{g}$ $\leq$-4.0V stress and 10$0^{\circ}C$ conditions using P and NMOSFETs that are annealed with hydrogen or deuterium gas at high-pressure (5 atm). The degradation mechanisms are highly dependent on stress conditions. For low gate voltage, hole-trapping is found to dominate the reliability of gate oxide both in P and NMOSFETs. With increasing gate voltage to V$_{g}$ =-4.0V, the degradation becomes dominated by electron-trapping in NMOSFETs, however, the generation rate of "hot" hole was very low, because most of tunneling electrons experienced the phonon scattering before impact ionization at the Si interface. Statistical parameter variations as well as the gate leakage current depend on and are improved by high-pressure deuterium annealing, compared to corresponding hydrogen annealing. We therefore suggest that deuterium is effective in suppressing the generation of traps within the gate oxide. Our results therefore prove that hydrogen related processes are at the origin of the investigated oxide degradation.gradation.

• Journal of Environmental Science International
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• v.24 no.11
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• pp.1513-1523
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• 2015

In order to clarify the characteristics of PM10 in coastal and inland cities and their variation statistical analysis were carried out using environmental and meteorological data observed at Busan and Daegu metropolitans during 4 year from 2010. Averaged PM10 concentration was higher in industrial area than any other land-use sites, and its maximum value reach on over $50{\mu}g/m^3$ at Jangrim site in Busan. Temporal and spatial variations of PM10 concentration in Busan were more sharply, since topograph and mesoscale wind pattern in Busan is more complicated than those in Daegu. Correlation of PM10 concentrations between sites within Daegu appeared strongly and maximum values $R^2$ is about 0.8. This indicate that because wind pattern induced by mesoscale forcing in Daegu are well unified, the variation of PM10 concentration tends to be similar in all sites within Daegu. However, due to complicate wind pattern induced by topography and coastal line, PM10 correlation of sites within Busan was weaker in comparison with in Daegu. And correlation of PM10 at same lane-use in Busan and Daegu tend to be related to the intensity of meteorological forcing, which can decide the intensity of wind pattern.

• Journal of the Korean earth science society
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• v.26 no.7
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• pp.706-713
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• 2005

Subsurface oceanic data (Z20; Depth of $20^{\circ}C$ isotherm and WWV; Warm Water Volume) from the tropical Pacific Ocean from 1980 to 2004 were utilized to examine upper ocean variations in relation to E1 Nino. Time series analysis using EOF, composite, and cross-correlation methods indicated that there are significant time delays between subsurface oceanic parameters and the Nino3.4 SST. It implied that Z20 and WWV would be more reliable predictors of El Nino events. Based on analyzed results, we also constructed neural network model to predict the Nino3.4 SST from 1996 to 2004. The forecasting skills for the model using WWV were statistically higher than that using the trade wind except for short range forecasting less than 3 months. This model greatly predicted SST than any other previous statistical model, especially at lead times of 5 to 8 months.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.59-59
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• 2012

Self-consistent mathematical model of the exotic object OTJ 071126+440405= CSS 081231:071126+440405 is discussed. The system was discovered as a polar at the New year night 31.12.2008/01.01.2009 by D.Denisenko (VSNET Circ), and we have initiated an international campaign of photometric and polarimetric observations of this object (totally -80 runs in Ukraine, Korea, Slovakia, Finland, USA) as a part of the "Inter-Longitude Astronomy" (ILA) project on monitoring of variable stars of different classes (Andronov et al., 2003). Here we present the geometrical and physical model of the system in the low luminosity state and in the intermediate luminosity state as well as in the high luminosity state. As the system is of -20 mag at minimum, no spectral observations were made to determine parameters of the red dwarf. From the statistical relationship, the mass of the red dwarf is estimated to be -0.165 solar masses, for the white dwarf (from eclipse duration) - from 0.5 to 1.76 solar masses. As the system resembles ER UMa in some characteristics, the lower value may be assumed. The inclination of the system and other physical parameters are estimated. The object is an excellent laboratory to study multiple physical processes in the magnetic systems.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.9
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• pp.1931-1942
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• 2002

In this paper a formulation of robust optimization is presented and illustrated by a design example of vibratory micro gyroscopes in order to reduce the effect of variations due to uncertainties in MEMS fabrication processes. For the vibratory micro gyroscope considered it is important to match the resonance frequencies of the vertical (sensing) and lateral (driving) modes as close as possible to attain a high sensing sensitivity. A deterministic optimization in which the difference of both the sensing and driving natural frequencies is minimized as an objective function results in highly enhanced performance but apt to be very sensitive to fabrication errors. The formulation proposed is to attain robustness of the performance by including the sensitivity of the response with respect to uncertain variables as a term of objective function to be minimized. This formulation is simple and practically applicable since no detail statistical information on fabrication errors is required. The geometric variables, beam width, length and thickness of vibratory micro gyroscopes are adopted as design variables and at the same time considered as uncertain variables because here occur the fabrication errors. A robustness test in terms of a percentage yield by using the Monte Carlo simulation has shown that the robust optimum produces twice more acceptable designs than the deterministic optimum. Improvement of robustness becomes bigger as the amount of fabrication errors is assumed larger. Considering that the magnitude of fabrication errors and uncertainties in a MEMS structure are comparatively large, the present method is illustrated to be a viable approach for a robust MEMS design.

• Journal of the korean society of oceanography
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• v.34 no.4
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• pp.220-230
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• 1999

Four tidal flats, covering two dissipative type beaches and two other tidal mud flats, around Yonaiong-Yongyu Islands, Inchon, Korea were studied in May 1991 to analyze the spatial distribution patterns of benthic communities on macrotidal flats. From the statistical test on spatial patterns of species number, density, and biomass, significant trends were found in species number and biomass. Although quantitative analysis was not performed, the interpretation showed that the variations were ruled out by environmental gradients such as sediment grain size and tidal elevation. The eight communities revealed in this study are as follows: Moerella-Mactra(Group 1), llyoplax-Glycera -Magelona japonica-Magelona sp.-Pe riserrula ( Group 2), Amphiura-Nephtys californiensis-Bullacta-Eohaustorius (Group 3), Leonnates-Heteromastus-Pretankyra-Nephtys polybranchia (Group4), Nephtys chemulpoensis-Macrophthalmus (Group 5), Ceratonereis-Scopimera (Group 6), Haustorioides-Urothoe (Group 7) and Cycladicama-Armandia-Minuspio community (Group 8). Some of these communities were classified into substratum-specific (Group 1 to 3) and tidal elevation-specific communities (Group 4). It was difficult to identify the predominant governing agent in Groups 5,6,7 and 8 because of their presence at extreme types of sediment and at uppermost elevations. Mixed effects seemed to act upon the latter four communities (Group 5 to 8). Based on the number of samples, 60% of the target samples were influenced by substratum properties, 20% by tidal elevation effect and 20% by mixed effect of the two factors. From this, it was concluded that substratum properties serve as the most important factors on soft bottom inhabitants in the area studied.