• Journal of the Korean Society of Systems Engineering
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• v.18 no.2
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• pp.94-107
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• 2022

Accidents prevention and mitigation is the highest priority of nuclear power plant (NPP) operation, particularly in the aftermath of the Fukushima Daiichi accident, which has reignited public anxieties and skepticism regarding nuclear energy usage. To deal with accident scenarios more effectively, operators must have ample and precise information about key safety parameters as well as their future trajectories. This work investigates the potential of machine learning in forecasting NPP response in real-time to provide an additional validation method and help reduce human error, especially in accident situations where operators are under a lot of stress. First, a base-case SGTR simulation is carried out by the best-estimate code RELAP5/MOD3.4 to confirm the validity of the model against results reported in the APR1400 Design Control Document (DCD). Then, uncertainty quantification is performed by coupling RELAP5/MOD3.4 and the statistical tool DAKOTA to generate a large enough dataset for the construction and training of neural-based machine learning (ML) models, namely LSTM, GRU, and hybrid CNN-LSTM. Finally, the accuracy and reliability of these models in forecasting system response are tested by their performance on fresh data. To facilitate and oversee the process of developing the ML models, a Systems Engineering (SE) methodology is used to ensure that the work is consistently in line with the originating mission statement and that the findings obtained at each subsequent phase are valid.

• Journal of Environmental Impact Assessment
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• v.4 no.3
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• pp.9-13
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• 1995

In July 1993 a new prescription of the EC was finished, concerning the voluntary participation of enterprises in a common auditing system. By this in the EC-member countries there must be founded centers of environmental auditing where experienced experts of environmental auditing should be accredited. These accredited experts are controllers for evaluating and certification of carried out environmental-auditings. An environmental-auditing practically represents an environmental assessment for an already existing enterprise with establishing corresponding programmes and strategies for the internal management to improve the environmental relations. Much experiences, which could be collected in the field of EIA during the last years may be transfered to this new task immediately. Only an essential difference there should not be overseen because of national legislation EIA in the defined cases must be carried out. By the EC-prescription carrying out an environmental-auditing for an enterprise is optional, it is recommended only. It was not introduced as a must. In spite of this fact because of the hard competition on the market there will be developed a pressure for the enterprises, to carry out such environmental-auditings. At present already a number of first projects in this direction can be seen, in the first line above all enterprises with the necessary economic power want to use this possibility, to gain better positions on the market. We have already gathered the first experiences in this field. We arranged corresponding contacts to several enterprises within the surroundings of Dresden. Within an opening discussion, where the project is explained and discussed with the management of the enterprise very detailed, the understanding, the readiness and the cooperation for the project are generated necessary prerequesits for the success of the whole work. By means of careful detail-work in collaboration with all departments and on all levels of the enterprise the total mass and energy-balances of the factory established and analysed. There are included also such ranges like material delivery, personal policy, public relations and sale as well as waste management. It is important that all people working in the factory have the feeling to be our partners, and not to have the impression to be checked or controled by an outside organization. This one of the most important factors of environmental auditing, in order to wake up and to develop a common interest on all sides. At the end of the environmental auditing there will be according to the prescription of the EC a catalogue of measures to do immediately, short time, mean time and long time for improvement of the environmental situation of the enterprise. All proposals are made in connection with a corresponding economic evaluation. These measures and programmes are declared as the environmental manual and are the basis for the work of the environmental management of the enterprise for the next three years. According to the EC-prescription, the enterprise with this environmental manual can get a corresponding certificate, which may be used for public relation purposes.

• Journal of the Korean Wood Science and Technology
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• v.44 no.5
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• pp.776-784
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• 2016

In this study, green Larix kaempferi lumber was heat-treated by using superheated steam (SHS) at a pilot scale and then various physico-mechanical properties of the heat-treated wood were evaluated and compared with the properties of conventional hot air (HA) heat-treated wood. Decay resistance of brown rot fungi and compressive strength parallel to the grain of the SHS heat-treated wood without occurrence of drying check from green lumber were increased. On the other hand, density, equilibrium moisture content, shrinkage, and bending strength of the SHS heat-treated wood were lower than those of the conventional HA heat-treated wood. Because heat transfer and thermal hydrolysis of SHS heat treatment was accelerated by a large amount of water, the effect of SHS heat treatment on the physico-mechanical properties was higher than that of HA heat treatment at the similar conditions of temperature and time. From the results of this study, because green lumber can be heat-treated without occurrence of cracks or checks by using SHS and similar heat treatment effect on the physico-mechanical properties of wood can be produced despite a low temperature or short time of heat treatment, it is expected that heat time and energy consumption could be reduced by using SHS.

• Polymer(Korea)
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• v.30 no.6
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• pp.525-531
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• 2006

In this study, Sulfonated PONF-g-styrene ion exchange fibers were synthesized by radiation induced graft copolymerization. And also, hybride ion exchange fibers, which was combined sulfonated PONF-g-styrene fibers and cationic ion exchange resin, were fabricated by hot melt adhesion method and then their adsorption properties were investigated. ion exchange capacity and water content of hybrid ion exchange fibers increased as compared with those of bead and ion exchange fiber. Their maximum values were 4.76 meq/g and 23.5%, respectively. Adsorption breakthrough time for mercury of hybrid ion exchange fiber was slower than those of bead resin and fibrous ion exchanger. It's value was 130 minutes. Their breakthrough time become short as increasing of pH, and concentration. The initial breakthrough time was observed before and after 10 minutes as increasing of concentration. The adsorption of hybrid ion exchange fibers for $Hg^{2+}\;Pb^{2+},\;Cd^{2+}$ among heavy metals in the mixed solution was observed before 20 min. And also, The adsorption for $Hg^{2+}$ among the heavy metals by hybride ion exchange fibers was observed.

• Journal of Biomedical Engineering Research
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• v.34 no.1
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• pp.8-13
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• 2013

Persons with sensorineural hearing impairment have troubles in hearing at noisy environments because of their deteriorated hearing levels and low-spectral resolution of the auditory system and therefore, they use hearing aids to compensate weakened hearing abilities. Various algorithms for hearing loss compensation and environmental noise reduction have been implemented in the hearing aid; however, the performance of these algorithms vary in accordance with external sound situations and therefore, it is important to tune the operation of the hearing aid appropriately in accordance with a wide variety of sound situations. In this study, a sound classification algorithm that can be applied to the hearing aid was suggested. The proposed algorithm can classify the different types of speech situations into four categories: 1) speech-only, 2) noise-only, 3) speech-in-noise, and 4) music-only. The proposed classification algorithm consists of two sub-parts: a feature extractor and a speech situation classifier. The former extracts seven characteristic features - short time energy and zero crossing rate in the time domain; spectral centroid, spectral flux and spectral roll-off in the frequency domain; mel frequency cepstral coefficients and power values of mel bands - from the recent input signals of two microphones, and the latter classifies the current speech situation. The experimental results showed that the proposed algorithm could classify the kinds of speech situations with an accuracy of over 94.4%. Based on these results, we believe that the proposed algorithm can be applied to the hearing aid to improve speech intelligibility in noisy environments.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.1
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• pp.153-160
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• 2021

Nitrous oxide is a global warming substance and is known as the main cause of the destruction of the ozone layer because its global warming effect is 310 times stronger than carbon dioxide, and it takes 120 years to decompose. Therefore, in this study, we investigated the characteristics of NOx emission from N2O reduction by thermal decomposition of N2O. Bunsen premixed flames were adopted as a heat source to form a high-temperature flow field, and the experimental variables were nozzle exit velocity, co-axial velocity, and N2O dilution rate. NO production rates increased with increasing N2O dilution rates, regardless of nozzle exit velocities and co-axial flow rates. For N2O, large quantities were emitted from a stable premixed flame with suppressed combustion instability (Kelvin Helmholtz instability) because the thermal decomposition time is not sufficient with the relatively short residence time of N2O near the flame surface. Thus, to improve the reduction efficiency of N2O, it is considered effective to increase the residence time of N2O by selecting the nozzle exit velocities, where K-H instability is generated and formed a flow structure of toroidal vortex near the flame surface.

• Membrane Journal
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• v.28 no.1
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• pp.67-74
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• 2018

In the molecular dynamics study of polymeric membranes, it is very important to select the proper length of the polymer main chain because it requires a large number of constituent atoms and a long time to simulate the permeation behavior. In this study, we tried to investigate how the correlation between polymer main chain length and permeation behavior appears in actual molecular dynamics simulation results. Molecular dynamics were performed using the widely known commercial polymer Kapton(R) polyimide structure and the gas permeation behavior was simulated. The movement of the polymer main chain was not related to its length and the short main chain length did not act more actively. In addition, unlike the prediction that the end group of the polymer main chain is relatively easy to move, there are many cases where the atoms located at the middle of the polymer main chains have a higher movement than the atoms located at the end groups. Finally, permeabilities of the gas molecules was not affected by the length of the main chain and the end groups of the polymer, which indicates that the end effect should be carefully mentioned and followed by the verification process.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.500-504
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• 2008

The objective of this paper is to evaluate the feasibility of using an optimization model as a effective way to search conjunctive operation scheme to meet two conditions; one is to minimize the electric cost for pumping and another is to meet the water demand for satisfying customers. The feasibility is confirmed as comparing the best combinations of pumps between multi-regional water supply networks from multiple sources which are obtained through an optimization modeling and EPAnet modeling. KModsim model, a network optimization model, was used to determine conjunctive operation scheme in the pipe system. KModsim, based on Lagrangian Relaxation algorithm, is useful for modeling network system and obtaining simultaneously pump combination and water allocation with given input option such as energy unit cost supplying from a source into a consumer, operating pumping combination. This study develops the procedure of determining optimal conjunctive operation scheme with using KModsim model. As a study region, the water supplying systems of the Geojae-city in the Geongsang Namdo Province was selected and investigated. The EPAnet hydraulic simulation result(Ryu et al, 2007, KSWW) gave input data for optimization model; energy unit price(won/$m^3$), water service available area etc.. It was assured that the combination of pump operation through optimum conjunctive operation is to be optimum scheme to obtain the best economic water allocation with comparison to the hydraulic simulation result such as electric cost and pump combination cases. The results obtained through the study are as follows. First, It was found that a well-allocated water supply scheme, the best combination of pump operation through optimum joint operation, promises to save the electric cost and satisfy all operational goals such as stability and revenues during the period. Second, an application of KModSim, a network model, gave the amount of water allocation from each source to a consumer with consideration of economic supply. Finally, in a service area available to supply through conjunctive operation of existing inter-regional water supply networks within short distance, a conjunctive operation is useful for determining each transmission pipeline's service area and maximizing the effectiveness of optimizations in pumping operation time.

• Korean Journal of Microbiology
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• v.48 no.2
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• pp.125-133
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• 2012

Anaerobic digestion is an alternative method to digest food wastes and to produce methane that can be used as a renewable energy source. We investigated bacterial and archaeal community structures in a three-stage methane production process using food wastes with concomitant wastewater treatment. The three-stage methane process is composed of semianaerobic hydrolysis/acidogenic, anaerobic acidogenic, and strictly anaerobic methane production steps in which food wastes are converted methane and carbon dioxide. The microbial diversity was determined by the nucleotide sequences of 16S rRNA gene library and quantitative real-time PCR. The major eubacterial population of the three-stage methane process was belonging to VFA-oxidizing bacteria. The archaeal community consisted mainly of two species of hydrogenotrophic methanogen (Methanoculleus). Family Picrophilaceae (Order Thermoplasmatales) was also observed as a minor population. The predominance of hydrogenotrophic methanogen suggests that the main degradation pathway of this process is different from the classical methane production systems that have the pathway based on acetogenesis. The domination of hydrogenotrophic methanogen (Methanoculleus) may be caused by mesophilic digestion, neutral pH, high concentration of ammonia, short HRT, and interaction with VFA-oxidizing bacteria (Tepidanaerobacter etc.).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.9
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• pp.1248-1256
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• 1993

The propagation and delay properties in opical fiber are particularly attractive because digital signal processing and conventional analog signal processing techniques such as those using surface acoustic wave devices are limited In their usefulness for signal bandwidth exceeding one or two GHz, although they are very effective at lower frequencies. Since an accurate, low loss and short time delay elements can be obtained by using such an optical fiber, optical signal precessing has attracted much attention for high speed and broad-band signal precessing in particular channel separation filtering for optical FDM signals. In this paper, we consider a coherent optical lattice filter, which uses coherent light sources and consists of directional couplers and optical fiber delay elemnts. The optical fiber fitters are more restricted than the usual digital filters. The reasons are as follows. 1) the coupling coefficients of directional couplers are restricted to the number between 0 and 1. 2) optical signal E(complex amplitude) is divided into J If-$\boxUl$ and J L/7$\div$$\boxUl$ at the directional coupler. Considering these restrictions and in this case all the coupling coefficients of summing and branching elements are set to be equal, we have given design formulae for optical lattice filter, which make the best use of optical signal energy.