• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.11
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• pp.1104-1111
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• 2009

In the low altitude, mission of the aircraft is restricted by a variety of threats such as anti-air missiles and terrain obstacles. Especially, aircraft have always a risk of ground collision near terrain. In this study, to effectively solve this problem, we developed the flight path generation algorithm that is considered the terrain avoidance. In this flight path generation algorithm, waypoints that should be passed by the UAV are selected first. The waypoints are located in the middle of the terrain obstacles. Then, physically meaningful waypoints sets are classified by Dijkstra algorithm. The optimal waypoint guidance law based on the optimal control theory is applied to produce trajectory candidates. And finally the minimum control energy trajectory is determined.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.2
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• pp.161-170
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• 2014

It is essential to decrease energy consumption and excess sludge to economically operate sewage treatment plant. This becomes more important along with a ban on sea dumping and exhaustion of resource. Therefore, many researchers have been study on energy consumption reduction and strategies for minimization of excess sludge production from the activated sludge process. The aeration cost account for a high proportion of maintenance cost because sufficient air is necessary to keep nitrifying bacteria activity of which the oxygen affinity is inferior to that of heterotrophic bacteria. Also, additional costs are incurred to stabilize excess sludge and decrease the volume of sludge. There were anoxic, aerobic, membrane, deairation and concentration zone in this MBR process. Continuous aeration was provided to prevent membrane fouling in membrane zone and intermittent aeration was provided in aerobic zone through ammonia sensor. So, there was the minimum oxygen to remove $NH_4-N$ below limited quantity that could be eliminated in membrane zone. As the result of this control, energy consumption of aeration system declined by between 10.4 % and 19.1 %. Besides, we could maintain high MLSS concentration in concentration zone and this induced the microorganisms to be in starved condition. Consequentially, the amount of excess sludge decrease by about 15 %.

• Journal of radiological science and technology
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• v.41 no.5
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• pp.405-411
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• 2018

We will provide basic data on the evaluation of patient dose in terms of DECT quality control by comparing the equipment-provided dose with the measured dose according to the configuration method of the X-ray generator by the manufacturer of the dual-energy CT unit. For computed tomography (CT) equipment, Discovery 750HD, Aquilion ONE GENESIS Edition, and Somatom Definition Flash were used. The $CTDI_{vol}$ value was measured by inserting the Unfors Xi ion chamber into a 32 cm PMMA acryl Phantom. The results of estimated $CTDI_{vol}$ DECT and measured $CTDI_{vol}$ showed that the dose difference between DECT 80 + 140 kVp of G company was at least 0.51% and -1.90% max, and measured $CTDI_{vol}$ was slightly lower (p<0.05). The difference of 80 + 140 kVp of S company was the minimum of 5.84% and the maximum of 7.52% (p<0.05). The measured $CTDI_{vol}$ was less than estimated $CTDI_{vol}$. The C company's 80 + 135 kVp showed a difference of at least 7.58% and a maximum of 13.58% (P<0.05), and all of measured $CTDI_{vol}$ was less. The linearity of exposure dose for all DECT equipment was very linearly reflected with $R^2$ being 0.97 or above, and the measured dose of the ionization chamber was less than the predicted dose of the monitor.

• Membrane and Water Treatment
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• v.11 no.4
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• pp.257-274
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• 2020

There are many previous review articles are available to summarize either the characterization methods of effluent organic matter (EfOM) or the individual control treatment options. However, there has been no attempt made to compare in parallel the physicochemical treatment options that target the removal of EfOM from biological treatments. This review deals with the recent progress on the characterization of EfOM and the novel technologies developed for EfOM treatment. Based on the publications after 2010, the advantages and the limitations of several popularly used analytical tools are discussed for EfOM characterization, which include UV-visible and fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), size exclusion chromatography (SEC), and Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS). It is a recent trend to combine an SEC system with various types of detectors, because it can successfully track the chemical/functional composition of EfOM, which varies across a continuum of different molecular sizes. FT-ICR-MS is the most powerful tool to detect EfOM at molecular levels. However, it is noted that this method has rarely been utilized to understand the changes of EfOM in pre-treatment or post-treatment systems. Although membrane filtration is still the preferred method to treat EfOM before its discharge due to its high separation selectivity, the minimum requirements for additional chemicals, the ease of scaling up, and the continuous operation, recent advances in ion exchange and advanced oxidation processes are greatly noteworthy. Recent progress in the non-membrane technologies, which are based on novel materials, are expected to enhance the removal efficiency of EfOM and even make it feasible to selectively remove undesirable fractions/compounds from bulk EfOM.

• KIPS Transactions on Computer and Communication Systems
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• v.4 no.11
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• pp.369-382
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• 2015

Energy aware server clusters aim to reduce power consumption at maximum while keeping QoS(quality of service) compared to energy non-aware server clusters. They adjust the power mode of each server in a fixed or variable time interval to activate only the minimum number of servers needed to handle current user requests. Previous studies on energy aware server cluster put efforts to reduce power consumption or heat dissipation, but they do not consider energy efficiency well. In this paper, we propose an energy efficient cluster management method to improve not only performance per watt but also QoS of the existing server power mode control method based on autonomous learning. Our proposed method is to adjust server power mode based on a hybrid approach of autonomous learning method with multi level thresholds and power consumption prediction method. Autonomous learning method with multi level thresholds is applied under normal load situation whereas power consumption prediction method is applied under abnormal load situation. The decision on whether current load is normal or abnormal depends on the ratio of the number of current user requests over the average number of user requests during recent past few minutes. Also, a dynamic shutdown method is additionally applied to shorten the time delay to make servers off. We performed experiments with a cluster of 16 servers using three different kinds of load patterns. The multi-threshold based learning method with prediction and dynamic shutdown shows the best result in terms of normalized QoS and performance per watt (valid responses). For banking load pattern, real load pattern, and virtual load pattern, the numbers of good response per watt in the proposed method increase by 1.66%, 2.9% and 3.84%, respectively, whereas QoS in the proposed method increase by 0.45%, 1.33% and 8.82%, respectively, compared to those in the existing autonomous learning method with single level threshold.

• Journal of Bio-Environment Control
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• v.23 no.3
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• pp.192-198
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• 2014

To establish the design criteria for seasonal heating load calculation in greenhouses, standard weather data are required. However, they are being provided only at seven regions in Korea. So, instead of using standard weather data, in order to find the method to build design weather data for seasonal heating load calculation, heating degree-hour and heating degree-day were analyzed and compared by methods of fundamental equation, Mihara's equation and modified Mihara's equation using normal and thirty years from 1981 to 2010 hourly weather data provided by KMA and standard weather data provided by KSES. Average heating degree-hours calculated by fundamental equation using thirty years hourly weather data showed a good agreement with them using standard weather data. The 24 times of heating degree-day showed relatively big differences with heating degree-hour at the low setting temperature. Therefore, the heating degree-hour was considered more appropriate method to estimate the seasonal heating load. And to conclude, in regions which are not available standard weather data, we suggest that design weather data should be analyzed using thirty years hourly weather data. Average of heating degree-hours derived from every year hourly weather data during the whole period can be established as environmental design standards, and also minimum and maximum of them can be used as reference data for energy estimation.

• Journal of the Korean Vacuum Society
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• v.8 no.1
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• pp.75-82
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• 1999

Ion energy is one of the crucial property in thin film deposition by internal ICP assisted I-PVD. As ion energy is determined by the difference between the plasma potential and the substrate bias potential, ICP excitation frequency was tested with medium frequency of 4 MHz and two types of tuning circuits, alternate and floating LC network with a biasing resistor, were tested. The results showed that plasma potential was less than 5 V in a range of Ar pressures, 5mTorr to 30 mTorr, at 4 MHz RF 600 W and 60 V of maximum RF antenna voltage was maintained either at RF input or output terminal. By proper control of RLC circuit installed after after RF antenna, 50V of RF induced voltage on RF antenna was obtained at 500W input power. The total impedance of RF antenna and plasma was around 10$\Omega$, and minimum RF voltage was obtained with a condition of lowest reactance at most 0.05$\Omega$.

• Environmental Engineering Research
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• v.25 no.3
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• pp.335-344
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• 2020

This work describes highly efficient recovery and selective leaching of Zn from electric arc furnace dust (EAFD) with different physicochemical properties, induced by acid leaching at ambient conditions. The chemical compositions, mineralogical phases, and particle sizes of the EAFDs were analyzed and compared. The effects of leaching time, liquid/solid ratio, acid type, and acid concentration on the selective leaching of Zn were also studied. The EAFD with high Fe/Zn ratio (> 1, EAFD₃) was richer in ZnFe₂O₄ and exhibited larger particle size than samples with low Fe/Zn ratio (< 1, EAFD_1,2). ANOVA analysis revealed that the Fe/Zn ratios of the EAFDs also have a significant effect on Zn extraction (p < 0.005). Selective leaching of Zn with minimum Fe dissolution was obtained at pH > 4.5, regardless of other parameters or sample properties. The maximum Zn extraction rate obtained by the pH control was over 97% for EAFD₁ and EAFD₂, 76% for EAFD₃, and 80% for EAFD₄. The present results confirm that the Fe/Zn ratio can be used to identify EAFDs that permits facile and high-yield Zn recovery, and pH can be used as a process control factor for selective leaching of Zn regardless of any differences in the properties of the EAFD sample.

• Journal of the Korean Institute of Gas
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• v.19 no.6
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• pp.34-39
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• 2015

Recently, most of the energy consumed in vehicle is derived from fossil fuels. For this reason, the demand for clean, renewable and affordable alternative energy is forcing the automotive industry to look beyond the conventional fossil fuels. Natural gas represents today a promising alternative to conventional fuels for vehicles propulsion, because it is characterized by a relatively low cost, better geopolitical distribution than oil, lower environmental impact, higher octane number and a higher self ignition temperature. Above all, CNG is an environmentally clean alternative to the existing spark ignition engines with the advantages of minimum change. In this study was installed bi-fuel system that a conventional 2 liters gasoline engine was modified to run on natural gas by a gas injection system. Experiments were mainly carried on the optimization of an ECU control strategy affecting the emission characteristics of CNG/Gasoline bi-fule vehicle. The test results shown that CO2 emission in bi-fuel mode was reduced 16% compared to gasoline fuel in the NEDC mode. Also the amount of CO and HC emissions in bi-fuel and gasoline modes were found to equality. But Compared to gasoline, the bi-fuel mode resulted in higher NOx emissions.

• Journal of Bio-Environment Control
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• v.27 no.1
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• pp.64-70
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• 2018

In this study, eleven major coastal areas were selected and the climate environment and the greenhouse direction were analyzed. This research investigates the greenhouse heat loss according to the wind environment at target areas. The target areas were selected based on heated greenhouse cultivation area and wind environment standard. Temperature, wind speed, and wind direction among weather data for 30 years were collected and analyzed. The data were divided into the minimum, average, and maximum temperatures and the Meteorological Agency criteria applied to the weather and wind direction criteria. Data were collected in the range of $0{\sim}180^{\circ}$ considering the symmetry of the shape of the greenhouse. In addition, the wind direction is different for each region and the applied wind direction can be different when referring to the longitudinal direction of the greenhouse and the data are collected in the range of $0{\sim}90^{\circ}$. The results of this study are expected to be used to calculate the heating load of greenhouse installed in places wind speed high.