• Environmental and Resource Economics Review
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• v.19 no.4
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• pp.733-752
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• 2010

This study applies the Luenberger indicator approach to estimate productivity of the Korean fossil-fueled power plants. A panel data set of 25 power plants was used. The method incorporates $CO_2$ emission as an undesirable output and shows that ignoring $CO_2$ emission overestimates the productivity change. There are two sources of overestimation. First, the usual method estimates productivity change ignoring the increase in $CO_2$ emission that occurred during the study period. Second, the productivity change estimated by the usual method that does not incorporate $CO_2$ emission is very sensitively affected by the change in operation rate. The paper decomposes the productivity change into the efficiency change and the technical change. The results show that the two sources contribute to the productivity change almost equally. It is also shown that the size and the pattern of productivity change are dependent on the plants' fuel types. Non-LNG power plants which saved their energy consumption and thereby reduced their $CO_2$ emission have achieved relatively high rate of productivity improvement.

• Applied Biological Chemistry
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• v.41 no.2
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• pp.181-186
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• 1998

The effects of sewage treatment on characteristics of sludge as a composting material were investigated for a year during the initial operation at the full-scale Chunan sewage treatment plant. Due to the shortage of design capacity of belt press, a sludge dewatering unit, non-volatile solids were recirculating and concentrating in the treatment plant, resulting in an increase of MLSS and a decrease in F/M ratio at the activated sludge system. Special attention is required for long term operations since the increase of non-volatile solids in the plant would deteriorates the treatment efficiency. The sewage sludge of the Chunan sewage treatment plant showed 79.5% of water content, 11.6% of organic content, and C/N ratio of 6.1, and contained As 1.8 mg/kg, Cd 27 mg/kg, Hg <0.1 mg/kg, Pb 54 mg/kg, T-Cr 370 mg/kg, and Cu 1,100mg/kg of heavy metals. In order to be used as raw material for optimum composting, the sewage sludge requires bulking agents for moistrure/porosity control and a carbon source for adjusting C/N ratio. However, the sewage sludge is not adequate as a soil conditioner after composing due to a high content of heavy metals. If the sewage sludge has to he used as a soil conditioner after composting, it as required to identify and remove tire industrial wastewater portions in tire influent of the plant since heavy metals in the influent were mostly concentrated in dewatered sludge.

• Convergence Security Journal
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• v.13 no.2
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• pp.33-43
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• 2013

The Private Security Industry of Korea began after served security service for the United States army of 8 division. The industry grew up after establish private security regulation on December 31th of 1976. Early 1980's the industry was accelerated from bringing technical knowledge of developed nations rapidly. Also, private security was gotten into the spotlight by one of futurity industry instead public security after companies performed 86 Asian game and 88 Seoul Olympic successfully. Therefore, the industry became to increase qualitatively and quantitatively. From late 1990's the private security regulations were revised fifteen times and created about education system, bodyguard, and leader of security. 3,836 private companies and 150,030 private guards had operated until 2012. However, some of companies received administrative measure, because of the companies ran immorally. The minor companies are continuously closed down from the leader's inefficient operation. Approval standard of establishment has imperfect law. Solutions of problems are to provide high quality service, to expand company affairs, to attract specific customers through efficiency expert, to change standard of leader of security guards, to establish security education institution through the government and to intensify requirements to establish the company.

• Korean Chemical Engineering Research
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• v.48 no.6
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• pp.791-794
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• 2010

This study presents channel design of a CDI stack to achieve high removal efficiency in a large scale by applying parallel flow structure with a concentrated stream. The flow pattern in the stack was simulated by COMSOL Multiphysics program. To prove the salt removal performance, a unit cell and 20 cell stacks were tested at a flow rate condition of 18 ml/min and 360 ml/min, respectively. The removal efficiencies of the unit cell and the 20 cell stacks were obtained as 70.8 % and 75.6 %, respectively, with 100 mg/L sodium chloride solution. During the operation of cell test, water pressures of unit cell and 20 cell pair stack maintained in the ranges of 1.1 psi and 1.3~1.5 psi, respectively. It was demonstrated that the parallel cell structure with two concentrated streams can be employed in a large scale CDI for salt removal.

• Clean Technology
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• v.24 no.2
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• pp.87-98
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• 2018

Phosphorus (P) is an essential and irreplaceable element for all living organisms, and it is widely used as a fertilizer. Unfortunately, it is estimated that phosphate reservoir is depleted within about 100 years. Sewage sludge ash (SSA) is an alternative resource for P recovery because of its high P content. However, SSA cannot be directly used as a fertilizer due to heavy metals in it and low P bioavailability. Thermochemical treatment with Cl donor is known to reduce heavy metal contents and increase P bioavailability of SSA. Literature review on thermochemical technologies of SSA for the reduction of heavy metals and bioavailability enhancement has been carried out to estimate the status of current P recovery technology and to develop strategic future research plan for P recovery. The review showed that $CaCl_2$ and $MgCl_2$ were the most effective Cl donors and reaction temperature (< $1000^{\circ}C$) was the critical operation condition for the reduction. The removal efficiency depends on the species of heavy metals. Thermochemical technology of SSA for P recovery showed the possibility of commercial application in the near future to overcome the coming crisis of human sustainability by P depletion, but it needs cost effectiveness and more ecofriendly process to reduce energy consumption.

• Membrane Journal
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• v.22 no.3
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• pp.171-177
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• 2012

Effect of humic acid (HA), photo-oxidation and adsorption with periodic $N_2$ back-flushing was investigated in hybrid process of ceramic ultrafiltration and photocatalyst for drinking water treatment. It was compared and investigated with the previous result at water back-flushing in viewpoints of membrane fouling resistance ($R_f$), permeate flux (J), and total permeate volume ($V_T$). As decreasing HA, $R_f$ decreased dramatically and J increased, and finally $V_T$ was the highest at HA 2 mg/L. As HA concentration increased from 2 to 10 mg/L, the membrane fouling resistance after 180 mins' operation ($R_{f,180}$) improved 0.8 times more than that of water back-flushing. Therefore, HA concentration should affect on the membrane fouling at $N_2$ back-flushing than water back-flushing. Turbidity treatment efficiencies were almost constant independent of HA concentration, but HA treatment efficiency was the maximum at HA 2 mg/L. This means that adsorption and photo-oxidation of photocatalyst beads could removed HA at HA 2 mg/L, but it was not enough at 4 mg/L. Beyond HA 6 mg/L, UF could effectively treat HA by thick cake layer on membrane surface and severe inner membrane fouling.

• Journal of KIISE:Computing Practices and Letters
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• v.11 no.3
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• pp.224-234
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• 2005

As the network-related technology develops the number of both Internet users and the usage are explosively increasing. The networking traffic is increasing in the campus as the networking system inside universities, following the trend, adds more nodes and various networking services. Nonetheless, the quality of services for users has been degraded. Accordingly, core problems, which can cause troubles for network management, design and expansion of the network, and the cost policy, has appeared. To effectively cope with the problems with analyses a great number of technicians, tools, and budget are needed. However, it is not possible for mid and small-sized colleges to spend such a high expenditure for professional consulting. To reduce the cost and investment creating the optimized environment, the analyses on the replacement of the tools, changing the network structure, and performance analysis about capacity planning of networking is necessary. For this reason, in this paper, framework-based performance management tools are used for all steps that are related to the subject of the analysis for the network management. As the major research method, the current data in detailed categories are collected, processed, and analyzed to provide the solution for the problems. As a result we could manage the network, server, and application more systematically and react efficiently to errors and degrading of performance that affect the networking tasks. Also, with the scientific and organized analyses the overall efficiency is upgraded by optimizing the cost for managing the operation of entire system.

• Clean Technology
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• v.20 no.4
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• pp.449-456
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• 2014

There has been increasing concerns for the problems of water security in countries, caused by the frequent occurrence of localized drought due to the climate change and uncertainty of water balance. The importance of fresh water is emphasized as considerable amount of usable fresh water is utilized for power generation sector producing electricity. PV power system, the source of renewable energy, consumes water for the every steps of life cycle: manufacturing, installation, and operation. However, it uses relatively less water than the traditional energy sources such as thermal power and nuclear power sources. In this study, to find out the use of water for the entire process of PV power system from extracting raw materials to operating the system, the footprint of water in the whole process is measured to be analyzed. Measuring the result, the PV water footprint of value chain was $0.989m^3/MWh$ and the water footprint appeared higher specially in poly-Si and solar cell process. The following two reasons explain it: poly-Si process is energy-intensive process and it consumes lots of cooling water. In solar cell process, deionized water is used considerably for washing a high-efficiency crystalline silicon. It is identified that PV system is the source using less water than traditional ones, which has a critical value in saving water. In discussing the future energy policy, it is vital to introduce the concept of water footprint as a supplementary value of renewable energy.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.9
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• pp.71-80
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• 2007

This paper presents a new push-push VCO technique that extracts a second harmonic output signal from a capacitive commonnode in a negativegm oscillator topology. The generation of the $2^{nd}$ harmonics is accounted for by the nonlinear current-voltage characteristic of the emitter-base junction diode causing; 1) significant voltage clipping and 2) different rising and falling time during the switching operation of core transistors. Comparative investigations show the technique is more power efficient in the high-frequency region that a conventional push-push technique using an emitter common node. Prototype 12GHz and 17GHz MMIC VCO were realized in GaInP/GaAs HBT technology. They have shown nominal output power of -4.3dBm and -5dBm, phase noise of -108 dBc/Hz and -110.4 dBc/Hz at 1MHz offset, respectively. The phase noise results are also equivalent to a VCO figure-of-merit of -175.8 dBc/Hz and -184.3 dBc/Hz, while dissipate 25.68mW(10.7mA/2.4V) and 13.14mW(4.38mA/3.0V), respectively.

• Korean Journal of Food Science and Technology
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• v.21 no.5
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• pp.676-685
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• 1989

Optimal operating conditions of on-farm red pepper dryer were searched by using the simulation-optimization algorithm combining the drying and quality deterioration models of red pepper with Box's complex method. Determination of control variables such as air temperature, air recycle ratio and air flow rate was based on a criterion of minimizing energy consumption under the constrainst conditions that satisfied the specified color retention of carotenoids. As quality constraint was stricter, energy consumption increased and total drying time decreased with lower recycle ratio and higher air flow rate Product mixing during drying was found to be able to improve the energy efficiency and product quality. Currently used air flow rate was assessed to be increased for the optimal operation. Two stage drying at the fixed optimal air flow rate was proven to be useful means for further saying of energy consumption. In the optimal bistaged drying, the second stage began at about one third of the total drying time and low air temperature in the first stage Increased to a high value and air recycle ratio increased slightly in the second stage. Optimal control variable scheme could be explained by the dryer performance and the carotenoids destruction kinetics in red pepper drying.