• Journal of Korean Society on Water Environment
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• v.23 no.5
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• pp.636-641
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• 2007

A pilot-scale biofilm nitiritation reactor was operated with the reject water from a large wastewater treatment plant. The effects of various operating parameters including pH, temperature, dissolved oxygen, solids and organic concentrations were examined. A stable nitritation was achieved at operating pH range of 7.3 to 8.8 with an alkalinity addition. Higher operating temperature of $35{\pm}0.7^{\circ}C$ achieved more stable nitritation compared to $30{\pm}0.2^{\circ}C$. It has been noticed that nitrite accumulation maintained with DO, solids and organic concentrations range of 0.8 to 3.9 mg/L, 3,400 to 11,000 mg/L, and 86 to 572 mg/L, respectively. It seems that the accumulation of nitrite was caused by both the inhibition of $NO_2{^-}$ oxidizers due to free ammonia and the maintenance of the high operating temperature of $35^{\circ}C$ which promote to accumulate the $NH_4{^+}$ oxidizers in the reactor. According to microbial community analysis of fluorescence in situ hybridization and INT-Dehydrogenase measurements, more nitrifiers were presented in attached form compared to suspended growth.

• Management & Information Systems Review
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• v.5
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• pp.33-59
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• 2000

Problem definition is as important as problem solving in decision making. Decision makers, however, tend to see problem partly or to define it unclearly. The researchers on decision making tend to lay a focus only on the Process of solving the given problem. This dissertation empirically studied the Problem diagnosis and definition in the decision making process. This study developed three kinds of DSS(Decision Support System) for the research and analyzed the effectiveness of the problem diagnosis and definition using DSS developed in this study. The three kinds of DSS are K-T(Kennel and Tregoe) DSS which is a method of table-styled information Presentation, and F-N(Fact-Net) DSS and C-E(Cause and Effect) DSS which are methods of graphic-styled information presentation. The empirical study was conducted twice; the pilot test and the main test. The samples of experiment are 218 students for the pilot test and 259 students for the main test. The author used K-T DSS and F-N DSS for the pilot test, and the revised K-T DSS and C-E DSS for the main test. A questionnaire survey method was included in the main test process The result of the study shows that the group using DSS in problem diagnosis and definition is more effective than the group not using DSS. A table-styled information presentation DSS, K-T, turns out more effective than a graphic-styled information presentation DSS, F-N, K-T DSS and C-E DSS showed no significant differences in the effectiveness in the main test. These results indicate that the use of DSS in the stage of problem diagnosis and definition is very effective and the methods and types of system design are a significant factors for DSS development.

• Membrane and Water Treatment
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• v.9 no.1
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• pp.43-51
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• 2018

Hollow fiber (HF) membranes are gaining wide interest over flat membranes due to their compaction and high area to surface volume ratio. This work addresses the fabrication of HF from polysulfone (PS) and polyethersulfone (PES) using N-methylpyrrolidone (NMP) as solvent in addition to other additives to achieve desired characteristics. The semi-pilot spinning system includes jacketed vessel, four spinneret block, coagulation and washing baths in addition to dryer and winder. Different parameters affecting dry-wet spinning phase inversion process were investigated. Dope compositions of PES, NMP and polyvinyl pyrrolidone (PVP) of varying molecular weights as additive were addressed. Some critical parameters of importance were also investigated. Those include dope flow rate, air gap, coagulation & washing baths and drying temperatures. The measured dope viscosity was in the range from 1.7 to 36.5 Pa.s. Air gap distance was adjusted from 20 to 45 cm and coagulation bath temperature from 20 to $46^{\circ}C$. The HF membranes were characterized by scanning electron microscope (SEM), atomic force microscope (AFM) and mechanical properties. Results indicated prevalence of finger like structure and average surface roughness from about 29 to 78.3 nm. Profile of stress strain characteristics revealed suitability of the fibers for downstream interventions for fabrication of thin film composite membrane. Different empirical correlations were formulated which enable deeper understanding of the interaction of the above mentioned variables. Data of pure water permeability (PWP) confirmed that the fabricated samples fall within the microfiltration (MF)-ultrafiltration (UF) range of membrane separation.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.3
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• pp.146-153
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• 2011

American NREL (National Renewable Energy Laboratory) reported that BDF20 could reduce PM, CO, SOx, and cancerogenic matters by 13.6%, 9.3%, 17.6%, and 13% respectively, compared to diesel fuel. BDF20 has been being tested on garbage trucks and official vehicles at Seoul City, which is positive on air environment, but negative on combustion by higher viscosity in winter season. This study investigated the combustion characteristics by applying pilot injection for improving the deterioration of combustibility caused by the higher viscosity of the BDF20 with the combustion flames taken by a high-speed camera and the cylinder pressure diagram. A 4-cycle single-cylinder diesel engine was remodeled to a visible 2-cycle engine taking the flame photographs, which has a common-rail injection system. The test was done laboratory temperature at $5{\sim}6^{\circ}C$. The results obtained are summarized as follows, (1) In the case of without pilot injection, the flame propagation speed was slowed and the maximum combustion pressure became lower. The phenomena became further aggravated as the fuel viscosity gets higher. (2) In the case of with pilot injection, early stage of combustion such as rapid ignition timing and flame propagation was activated since intermediate products formed by pilot injection act as a catalyst for combustion of main fuel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.554-561
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• 2010

This paper proposes an integer frequency offset estimation scheme robust to timing offset for the orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems. The proposed scheme exploits a feature that a sample distance between a continual pilot and a scattered pilot nearest to it in an OFDM symbol belongs to one of predetermined distances. First after calculating a correlation value of every continual pilot and its nearest scattered pilot. Then, it is divided into several groups according to the sample distances. Since correlation values with the same sample distance undergo the same effect of the timing offset, the effect of the timing offset can be removed by re-correlating these correlation values. From the simulation results we can confirm that the proposed algorithm estimates the integer frequency offset with the robustness to the timing offset when compared to a conventional scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.5C
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• pp.351-360
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• 2008

In cellular mobile radio systems with frequency reuse, the interference signals degrade the channel estimation and signal detection performance due to the low signal-to-interference ratio near coverage boundaries. When the preamble pilot sequences from different cells are orthogonal or located in disjointed positions, they can be used for multi-cell channel estimation and interference cancellation. In time-varying channels caused by Doppler spread, data pilot symbols are needed for channel estimations. However, data pilot symbols are usually located in identical positions for the overhead reduction, which degrades the channel estimation performance. In this paper, we demonstrate a significant amount of performance improvement is achieved by multiplying different pseudonoise(PN) sequences to the data pilot symbols from adjacent interference cells. In particular, for detection scheme using maximal ratio combining(MRC) and inter-cell spatial demultiplexing(ISD), quantitative performance gain of spectral efficiency for different values of Doppler frequency and interference power is presented.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.2
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• pp.249-258
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• 1998

In land mobile communication, very extensive studies on pilot symbol assisted modulation (PSAM) have been made on fading compensation. This paper analyzes the effect of power amplifier nonlinearity on PSA-QAM with maximal ratio combining space diversity. In practical PSAM, information on fading is obtained through interpolation of the pilot symbols. We employed the interpolation filter which could minimize the average power of error and analyzed effects on the system performance of the number of filter taps, period of the pilot symbol frame, and the Doppler frequency. Nonlinear power amplifiers of class AB, B, and C were incorporated in the system models and their AM/AM and AM/PM characteristics were taken into account in the performance analysis. We showed the performance variations according to the types of the nonlinear power amplifiers in the AWGN and Rayleigh fading channels using nonlinear compensation technique, Cartesian Feedback Loop (CFB).

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.422-425
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• 2009

A sea water source cascade heat pump was designed and tested in this study. The system was designed to perform a single stage operation in summer, as well as a cascade operation in winter to ensure the high temperature lift. A steady-state simulation model was developed to analyze and optimize its performance. The simulation results show that the R717 exhibits best performance among combinations considered in this study. A R410A also exhibits the highest performance among HFCs with the smallest compressor displacement. A 15-RT R410A-R134a pilot system was installed in the 5-story commercial building at Samcheok City by the East Sea. A scroll type R410A compressor, a reciprocating type R134a compressor, plate type condenser/evaporator/ cascade heat exchanger and two electronic expansion valves were used to build a pilot. A titanium plate type heat exchanger is also used for the heat exchanging with a sea water. The heat source/sink water is supplied from the well below the seashore in the depth of 5 m. In the initial test of the system, supply water temperature was rising up to $67^{\circ}C$ using a sea water heat source of $9^{\circ}C$, while an ambient temperature was $4.5^{\circ}C$.

• Journal of Soil and Groundwater Environment
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• v.16 no.2
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• pp.6-11
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• 2011

In this report, we provide experimental evidence that heavy metal ions could be removed using Pachymeniopsis sp., particularly soluble arsenic in leachate from soil contaminated by arsenic. We performed pilot scale of soil washing process based on our results. The adsorption of arsenic by Pachymeniopsis sp. indicated that it could be described with the Langmuir Model and the maximum adsorption capacity increased with decreasing pH (pH 3: 102.48 mg/g, pH 5: 98.32 mg/g, pH 7: 57.70 mg/g, pH 9: 43.34 mg/g) and increasing temperature (10$^{\circ}C$ : 60.38 mg/g, 20$^{\circ}C$ : 76.39 mg/g, 30$^{\circ}C$ : 112.12 mg/g). Our results revealed that soluble arsenic in leachate was removed from 24.03 mg/L to 0.6 ${\pm}$ 0.1 mg/L by Pachymeniopsis sp. for 48hours on pilot scale of soil washing process.

• Journal of Animal Environmental Science
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• v.4 no.2
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• pp.149-160
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• 1998

Hog manure slurry amended with sawdust was composted in pilot-scale reactor vessels using continuous aeration nuder different C/N ratios and pH conditions during composting high rate (decomposition) process. For each material two replicated piles were built and monitored over a period of three weeks. The compost piles had an initial volume of 0.18 ㎥. In this study we evaluated the temperature in compost O2 and CO2 evolution, aeration rate, NH3 concentration etc. and investigated the stability of compost during composting high rate process. According to measured results, while the maximum NH3 concentration during composting high rate process. According to measured results, while the maximum NH3 concentration during composting high rate was in the range of 213 to 412 ppm on 5th day which was near the optimum C/N(22∼24) and pH(7.5∼7.9). And then, the NH3 concentration reduced to between 22∼26 ppm by 13th day. The maximum NH3 concentration for the lower C/N(18∼19) and pH value of 6 reached 574∼1,063 ppm by the 16th through 11th days and the NH3 concentration during continuous aerated composting high rate process, it was more important to manage NH3 gas so that compost odor is reduced.