• Korean Journal of Materials Research
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• v.20 no.11
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• pp.586-591
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• 2010

Solar cells have been more intensely studied as part of the effort to find alternatives to fossil fuels as power sources. The progression of the first two generations of solar cells has seen a sacrifice of higher efficiency for more economic use of materials. The use of a single junction makes both these types of cells lose power in two major ways: by the non-absorption of incident light of energy below the band gap; and by the dissipation by heat loss of light energy in excess of the band gap. Therefore, multi junction solar cells have been proposed as a solution to this problem. However, the $1^{st}$ and $2^{nd}$ generation solar cells have efficiency limits because a photon makes just one electron-hole pair. Fabrication of all-silicon tandem cells using an Si quantum dot superlattice structure (QD SLS) is one possible suggestion. In this study, an $SiO_x$ matrix system was investigated and analyzed for potential use as an all-silicon multi-junction solar cell. Si quantum dots with a super lattice structure (Si QD SLS) were prepared by alternating deposition of Si rich oxide (SRO; $SiO_x$ (x = 0.8, 1.12)) and $SiO_2$ layers using RF magnetron co-sputtering and subsequent annealing at temperatures between 800 and $1,100^{\circ}C$ under nitrogen ambient. Annealing temperatures and times affected the formation of Si QDs in the SRO film. Fourier transform infrared spectroscopy (FTIR) spectra and x-ray photoelectron spectroscopy (XPS) revealed that nanocrystalline Si QDs started to precipitate after annealing at $1,100^{\circ}C$ for one hour. Transmission electron microscopy (TEM) images clearly showed SRO/$SiO_2$ SLS and Si QDs formation in each 4, 6, and 8 nm SRO layer after annealing at $1,100^{\circ}C$ for two hours. The systematic investigation of precipitation behavior of Si QDs in $SiO_2$ matrices is presented.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.3
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• pp.230-237
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• 2007

Titania nanotube(TiNT) and CdS sol were synthesized by hydrothermal reaction under strongly basic condition and by precipitation reaction of $Cd(N0_3)_2$ and $Na_2S$ aqueous solutions, respectively. After preparing a series of CdS-TiNT composite films on $F:SnO_2$ conducting glass with variation of the mole ratio (r) of TiNT/(CdS+TiNT), their visible light absorption, photocatalytic activities for hydrogen production, and the photocurrent generation were examined. In general, this CdS-TiNT series showed lower photocatalytic activities and photocurrent generation under Xe light irradiation compared to their counterparts, i.e., CdS-$TiO_2$ particulate series. It appeared that TiNTs are not so effective photocatalyic material in spite of their larger specific surface areas compared to $TiO_2$ nanoparticles, because they indicate a poor crystallinity and less intimate interaction or contact with CdS particles owing to the tubular morphology and an easy agglomeration among themselves.

• Applied Chemistry for Engineering
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• v.28 no.6
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• pp.655-662
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• 2017

Sulfide photocatalysts, CdS and CdZnS, were synthesized using a simple precipitation method and their photocatalytic activities were evaluated by the degradation of rhodamine B under visible light irradiation. The effects of four inorganic salt additives, KCl, NaCl, $K_3PO_4$, and $Na_3PO_4$, on the photocatalytic reaction were examined and the role of $K^+$, $Na^+$, $Cl^-$ and $PO_4{^{3-}}$ ions during photocatalytic reaction was discussed. The added inorganic salts were shown to have a remarkable effect on the photocatalytic reaction. It was also found that the anions in inorganic salts have a much more profound effect on the reaction rate, as compared to the cations. Under the present experimental conditions, $PO_4{^{3-}}$ revealed a significant inhibitory effect on the degradation rate whereas $Cl^-$ enhanced the rate slightly. This work pointed out that the consideration of additive effects is needed in the photocatalytic reaction for wastewater treatment.

• The Journal of Information Systems
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• v.31 no.3
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• pp.177-195
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• 2022

Purpose This paper aims to prepare a full operational readiness by establishing an optimal flight plan considering the weather conditions in order to effectively perform the mission and operation of military aircraft. This paper suggests a flight prediction model and rules by analyzing the correlation between flight implementation and cancellation according to weather conditions by using big data collected from historical flight information of military aircraft supplied by Korean manufacturers and meteorological information from the Korea Meteorological Administration. In addition, by deriving flight rules according to weather information, it was possible to discover an efficient flight schedule establishment method in consideration of weather information. Design/methodology/approach This study is an analytic study using data mining techniques based on flight historical data of 44,558 flights of military aircraft accumulated by the Republic of Korea Air Force for a total of 36 months from January 2013 to December 2015 and meteorological information provided by the Korea Meteorological Administration. Four steps were taken to develop optimal flight prediction models and to derive rules for flight implementation and cancellation. First, a total of 10 independent variables and one dependent variable were used to develop the optimal model for flight implementation according to weather condition. Second, optimal flight prediction models were derived using algorithms such as logistics regression, Adaboost, KNN, Random forest and LightGBM, which are data mining techniques. Third, we collected the opinions of military aircraft pilots who have more than 25 years experience and evaluated importance level about independent variables using Python heatmap to develop flight implementation and cancellation rules according to weather conditions. Finally, the decision tree model was constructed, and the flight rules were derived to see how the weather conditions at each airport affect the implementation and cancellation of the flight. Findings Based on historical flight information of military aircraft and weather information of flight zone. We developed flight prediction model using data mining techniques. As a result of optimal flight prediction model development for each airbase, it was confirmed that the LightGBM algorithm had the best prediction rate in terms of recall rate. Each flight rules were checked according to the weather condition, and it was confirmed that precipitation, humidity, and the total cloud had a significant effect on flight cancellation. Whereas, the effect of visibility was found to be relatively insignificant. When a flight schedule was established, the rules will provide some insight to decide flight training more systematically and effectively.

• Korean journal of applied entomology
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• v.21 no.1 s.50
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• pp.38-48
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• 1982

This study was conducted to investigate the changes in moth occurrence of striped rice barer, Chilo suppressalis (Walker), in relation to climatic factors, rice varieties, and cultural practices. The light trap data from 41 forecasting stations for 14 years from 1966 to 1979 were analyzed by means of the changes in the time and amount of borer occurrence in connection with the introduction of new rice varieties, the accumulated effective day-degree and its variation for completing one generation, and the climatic factors affecting the moth occurrence. The total number of moths caught by light traps in both spring and summer generations were considerably decreased with the wide cultivation of new rice varieties. In fact, the spring moths were remarkably decreased since the new varieties were introduced in 1972. The occurrence ratio of summer moths against the preceeding spring moths was higher in the middle region and middle southern mountainous area than the other regions. Its high ratio of regions was annually expanded from the middle region to the southern region. The $50\%$ emergence dates of both generations were later in the southeastern region than in the middle region. The ecological characteristics were clearly shown between the northern and southern region of Chupungryeong in terms of the occurrence of summer moths, the ratio of occurrence of summer moths to the preceeding spring moths, and $50\%$ emergence dates of the summer moths during the years of $1977\~1979$. The ratio of the summer moth occurrence to the preceeding generation was negatively correlated with the average temperature in lune and July, respectively, and the average precipitation in late June. The ratio of spring moth occurrence over the preceeding generation was positively correlated with the average temperature in September, October, November, and March, respectively, whereas it was negatively correlated with the average precipitation in early September and March, and the average humidity in early May. The effective day-degree for one generation was in the range from 600 to 900 DD at upper threshold $30^{\circ}C$ and lower threshold $10^{\circ}C$.

• Korean Journal of Environment and Ecology
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• v.33 no.5
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• pp.605-619
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• 2019

The objective of this study was to analyze eutrophication characteristics, empirical model analysis, and variation of water quality according to monsoon intensity in Hapcheon Reservoir for 16 years from 2002 to 2017. Long-term annual water quality analysis showed that Hapcheon Reservoir was in a meso-nutrition to eutrophic condition, and the eutrophic state intensified after the summer monsoon. Annual rainfall volume (high vs. low rainfall) and the seasonal intensity in each year were the key factors that regulate the long-term water quality variation provided that there is no significant change of the point- and non-point source in the watershed. Dry years and wet years showed significant differences in the concentrations of TP, TN, BOD, and conductivity, indicating that precipitation had the most direct influence on nutrients and organic matter dynamics. Nutrient indicators (TP, TN), organic pollution indicators (BOD, COD), total suspended solids, and chlorophyll-a (Chl-a), which was an estimator of primary productivity, had significant positive relations (p<0.05) with precipitation. The Chl-a concentration, which is an indicator of green algae, was highly correlated with TP, TN, and BOD, which differed from other lakes that showed the lower Chl-a concentration when nutrients increased excessively. Empirical model analysis of log-transformed TN, TP, and Chl-a indicated that the Chl-a concentration was linearly regulated by phosphorus concentration, but not by nitrogen concentration. Spatial regression analysis of the riverine, transition, and lacustrine zones of $log_{10}TN$, $log_{10}TP$, and $log_{10}CHL$ showed that TN and Chl-a had significant relations (p<0.005) while TN and Chl-a had p > 0.05, indicating that phosphorus had a key role in the algal growth. Moreover, the higher correlation of both $log_{10}TP$ and $log_{10}TN$ to $log_{10}CHL$ in the riverine zone than the lacustrine zone indicated that there was little impact of inorganic suspended solids on the light limitation in the riverine zone.

• Clean Technology
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• v.27 no.1
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• pp.9-16
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• 2021

Since the active matrix organic light-emitting diode (AMOLED) encapsulation process is very vulnerable to moisture and oxygen, high-purity nitrogen with minimal moisture and oxygen must be used. In this study, a copper-based catalyst used to remove oxygen from nitrogen in the AMOLED encapsulation process was optimized. Two-component and three-component catalysts composed of CuO, Al2O3, or ZnO were prepared through a co-precipitation method. The prepared catalysts were characterized by using BET, XRD, TPR, and XRF analysis. In order to verify the oxygen removal performance of the catalyst, several catalytic reactions were conducted in a fixed bed reactor, and the corresponding oxygen contents were measured through an oxygen analyzer. In addition, reusability of the catalysts was proven through repetitive regeneration. The properties and oxygen removal capacity of the catalysts prepared with CuO and Al2O3 ratios of 6 : 4, 7 : 3, and 8 : 2 were compared. The number of active sites of the catalyst with a ratio of CuO and Al2O3 of 8 : 2 was the highest among the 2-component catalysts. Moreover, the reducibility of the catalyst with a ratio of CuO and Al2O3 of 8 : 2 was the best as it had the highest CuO dispersion. As a result, the oxygen removal ability of the catalyst with a ratio of CuO and Al2O3 of 8 : 2 was the best among the 2-component catalysts. The best oxygen removal capacity was obtained when 2wt% of ZnO was added to the sub-optimized catalyst (i.e., CuO : Al2O3 = 8 : 2) probably due to its outstanding reducibility. Furthermore, the optimized catalyst kept its performance during a couple of regeneration tests.

• Korean Journal of Ecology and Environment
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• v.52 no.4
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• pp.293-305
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• 2019

In this study we investigated the effect of a floating photovoltaic (FPV) system in Cheongpung Lake on water quality. The FPV with a tilt angle of 33° covered ca. 0.04% of surface area (97 ㎢) of Chungju Lake. The water qualities of the whole lake before and after installation of FPV were first compared. DO, BOD, TOC, and Chl-a of the whole lake were increased, while conductivity decreased after installation period at the significance level of 0.05. This change was probably due to the increased influx of nutrients by 40% resulting from increased precipitation during the same period. We also measured water quality parameters on May and Nov. 2017 at the FPV center (FPVC) and nearby control sites, and compared water quality. The result showed that the FPVC and nearby sites were not significantly different (p>0.05), demonstrating that the FPV does not cause a decline of water quality. The water temperature, light intensity, and phytoplankton community were also measured. The water temperature was not different between the sites, while the light intensity decreased to 27~50%. Despite reduced light intensity at FPVC, the phytoplankton standing crops and the number of species were not significantly different (p>0.05). However, in the early November samples, standing crops was significantly higher in FPVC than control with periphytic diatoms belonging to Aulacoseira genus being dominant. This may be due to the temporal water body behavior or local retention of current by FPV system. This study may provide a measure of future installation of a FPV system.

• Korean Journal of Environment and Ecology
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• v.30 no.4
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• pp.724-729
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• 2016

Environmental factors that affect the singing of cicadas have not been studied extensively, especially those affecting the cicadas' singing during the nighttime. Therefore, the objective of this study is to identify the effects of tropical night and light pollution on the cicadas' singing in a downtown area. The study sites were an apartment complex in Seocho-gu, Seoul, and the Chiaksan National Park in Wonju-si. The study subjects were Hyalessa fuscata and Cryptotympana atrata, which are the dominant species in Korea during summer. Cicada songs were recorded 24 hours a day, every day. The recording period was between July and August, lasting 25 days at the Seoul site and 14 days at the Chiaksan National Park. Temperature, precipitation, humidity, and amount of sunshine were selected as the environmental factors that potentially affect the cicadas' singing. Statistical analyses included correlations of meteorological factors with the cicadas' singing per hour, per 24 hours, and at nighttime (21:00~04:00). The results showed that: 1) H. fuscata began singing during the dawn hours, and the singing increased in intensity early in the morning. C. atrata's singing reached its peak in the morning and afternoon, ceased during sunset hours, thereby exhibiting a difference in the singing pattern of the two species. 2) The frequency of singing by H. fuscata decreased when C. atrata began to sing intensively in numbers, thereby exhibiting interspecific influence. 3) The results of the correlation analysis between meteorological factors and the singing of H. fuscata and C. atrata showed that both species tended to sing more when the temperature was higher and sang less on rainy days. 4) When limited to nighttime only, C. atrata showed a tendency of singing when the nighttime temperature was high ($24-30^{\circ}C$, average $27^{\circ}C$), whereas H. fuscata did not show a correlation with meteorological factors. However, since H. fuscata sang during the night in areas with artificial lighting, it was concluded that its singing was due to light pollution.

• Clean Technology
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• v.25 no.1
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• pp.46-55
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• 2019

CdS and CdZnS/ZnO materials were prepared using precipitation method and used as photocatalysts for the photocatalytic degradation of rhodamine B (RhB) under visible light irradiation. The prepared photocatalysts were also characterized by XRD and UV-vis DRS. The results indicated that the photocatalysts with intended crystalline structures were successfully obtained and both the CdS and CdZnS/ZnO can absorb visible light as well as UV. The photocatalytic activities were examined with the addition of scavenger for various active chemical species and the difference of reaction mechanisms over the catalysts were discussed. The $CH_3OH$, KI and p-benzoquinone were used as scavengers for ${\cdot}OH$ radical, photogenerated positive hole and ${\cdot}O_2{^-}$ radical, respectively. The CdS and CdZnS/ZnO showed different photocatalytic degradation mechanisms of RhB. It can be postulated that ${\cdot}O_2{^-}$ radical is the main active species for the reaction over CdS photocatalyst, while the photogenerated positive hole for CdZnS/ZnO photocatalyst. As a result, the predominant reaction pathways over CdS and CdZnS/ZnO photocatalysts were found to be the dealkylation of chromophore skeleton and the cleavage of the conjugated chromophore structure, respectively. The above results may be mainly ascribed to the difference of band edge potential of conduction and valence bands in CdS, CdZnS and ZnO semiconductors and the redox potentials for formation of active chemical species.