• Journal of Korean Society of Environmental Engineers
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• v.29 no.3
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• pp.289-296
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• 2007

Porous media for sewage treatment were developed through a pyrolysis process of food wastes with loess in the study. This work was carried out in two consecutive stages; in the first stage, new porous media were prepared through a high temperature pyrolysis process, and then the resultant media were applied to a simple lab-scale sewage treatment process in the second stage. To determine the optimum operating conditions of pyrolysis and mixing ratio of materials, physical properties such as specific surface area, porosity and compressive strength of final products were analyzed. The removal efficiencies of TOC and COD were measured to evaluate the effectiveness of resultant porous media. As a result of the experiment, we found that the best mixing ratio of food wastes to loess was 1 : 1 at $1,100^{\circ}C$. Average porosity of the developed media was 37.0%, in which pore size ranged from 1 to $20{\mu}m$, showing quite vigorous microbial activation. After immersing the media into a reactor for sewage treatment for eight days, removal efficiencies of TOC and COD were 87.3% and 85.0%, respectively.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.771-776
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• 1997

The various shape of calcium carbonate were prepared. For the preparation of the PP/$CaCO_3$ composite, these synthetic calcium carbonate(cubic, spheric and neddle type) and PP were mixed on a two roll mill and the mixture were pressed into plate. The effect of particle shape in the prepared composite on the crystallization temperature, heat of fusion, size of spherulite and mechanical properities were investigated. It was found that the former four were strongly influenced by that. When, especially, vaterite was mixed with PP, the size of spherulite was smaller and the degree of crystallinity was higher than others. Therefore, the tensile strength and Young's modulus were higher.

• Journal of the Korean Institute of Gas
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• v.10 no.1 s.30
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• pp.19-25
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• 2006

Explosion limit is one of the major physical properties used to determine the fire and explosion hazards of the flammable substances. Explosion limits are used to classify flammable materials according to their relative flammability. Such a classification is important for the safe handling, storage, transportation of flammable substances. In this study, the lower explosion limits(LEL) of the flammable mixtures predicted with the appropriate use of the vapor composition and the heat of combustion of the individual components which constitute mixture. The values calculated by the proposed equations were a good agreement with literature data within a few percent. From a given results, It is to be hoped that this methodology will contribute to the estimation of the explosive properties of flammable mixtures with improved accuracy and the broader application for other flammable substances.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1994.11a
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• pp.90-96
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• 1994

본 연구는 에너지를 집중적으로 사용하는 발전소와 대규모 공장 단지에서 발생하는 배기가스 중에 포함된 황산화물의 제거 방법에 관한 것으로서, 활성탄의 적절한 전처리를 통해 이산화황 흡착능을 향상시켜 머지 않은 장래에 엄격히 적용될 대기오염 기준을 만족시킴과 동시에, 오염 물질의 제거 효율이 높고 폐기물 매립의 부담이 없는 건식 탈황 공정의 효율향상에 기여하는 것을 목적으로 하고 있다. Activated Char나 활성탄을 이용하여 황산화물과 질소산화물을 동시에 제거하기 위해서는 Carbon 표면을 적절하게 처리함으로써 활성탄의 촉매활성을 향상시키는 것이 필요하다. 따라서 본 연구에서는 활성탄을 열 및 $O_2$-NH$_3$ 혼합가스로 전처리하여 표면의 특성 변화와 SO$_2$ 흡착능에 미치는 영향을 살펴보았다. Coconut Shell로부터 제조한 활성탄을 NH$_3$의 농도를 변화시켜가며 $O_2$와의 혼합가스로 973~1173K에서 열처리하는 방법에 의해 전처리하여, 이률 고정층 반응기에서 SO$_2$흡착 및 반응실험을 수행하였고, 이 과정 중의 활성탄 표면의 특성변화를 원소분석, TPD(Temperature Programmed Desorption), FTIR(Fourier Transform Infrared Spectroscopy), Acid-Base Titration, SEM(Scanning Electrolic Microscopy)등의 분석 방법을 통해서 알아보았다. 그 결과, 활성탄을 열 및 $O_2$-NH$_3$혼합가스로 처리하여 환원성 분위기 하에서 표면 활성점을 증가시킴으로써 황산화물 흡착제거율이 향상됨을 얻었다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.1
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• pp.30-38
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• 1993

In this study, the combustion characteristics in a pre-combustion chamber diesel engine was investigated with experimental conditions of marine engine load. The heat release analysis used was a single-zone single-chamber thermodynamic analysis based on pre-combustion chamber pressure-time data. Based on the results of this investigation, the following conclusions were reached: 1) Increasing the load, peak pressure was increased and position of P sub(max) was retarded in crank angle degrees. 2) Ignition delay time was almost constant without relating to the load and the heat values to form a combusitible mixture were decreased apparently with increasing the load. 3) In premixed-combustion mode, the pattern of heat release rate was resembled without relating to the load and premixed-combustion time was shortened with increasing the load. 4) Increasing the load, mass of premixed-burned fuel was increased slightly, but was invariable beyond a certain fuel-air ratio. 5) Increasing the load, premixed-burned fraction was decreased.

• Nuclear Engineering and Technology
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• v.26 no.1
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• pp.63-77
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• 1994

The objective of this work is to investigate fluid mixing phenomena related to pressurized thermal shock(PTS) in a pressurized water reactor(PWR) vessel downcomer during transient cooldown with direct vessel injection(DVI) using test models. The test model designs were based on ABB Combustion Engineering(C-E) System 80＋ reactor geometry. A cold leg small break loss-of-coolant accident(LOCA) md a main steam line teak were selected as the potential PTS events for the C-E System 80＋. This work consist of two parts. The first part provides the visualization tests of the fluid mixing between DVI fluid and existing coolant in the downcomer region, and the second part is to compare the results of thermal mixing tests with DVI in the other test model. Row visualization tests with DVI have clarified the physical interaction between DVI fluid and primary coolant during transient cooldown. A significant temperature drop was observed in the downcomer during the tests of a small break LOCA Measured transient temperature profiles agree well with the predictions by the REMIX code for a small break LOCA and with the calculations by the COMMIX-1B code for a steam line break event.

• The Korean Journal of Applied Statistics
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• v.29 no.3
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• pp.525-537
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• 2016

The paper considers a hybrid model to analyze and forecast time series data based on an empirical mode decomposition (EMD) that accommodates complex characteristics of time series such as nonstationarity and nonlinearity. We aggregate IMFs using the concept of cumulative energy to improve the interpretability of intrinsic mode functions (IMFs) from EMD. We forecast aggregated IMFs and residue with a hybrid model that combines the ARIMA model and an exponential smoothing method (ETS). The proposed method is applied to forecast KOSPI time series and is compared to traditional forecast models. Aggregated IMFs and residue provide a convenience to interpret the short, medium and long term dynamics of the KOSPI. It is also observed that the hybrid model with ARIMA and ETS is superior to traditional and other types of hybrid models.

• Journal of computational fluids engineering
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• v.20 no.1
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• pp.84-91
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• 2015

SMART adopts, very unique facility, an FMHA to enhance the thermal and flow mixing capability in abnormal conditions of some steam generators or reactor coolant pumps. The FMHA is important for enhancing thermal mixing of the core inlet flow during a transient and even during accidents, and thus it is essential that the thermal mixing characteristics of flow of the FMHA be understood. Investigations for the mixing characteristics of the FMHA had been performed by using experimental and CFD methods in KAERI. In this study, the temperature distribution at the core inlet region is investigated for several abnormal conditions of steam generators using the commercial code, FLUENT 12. Simulations are carried out with two kinds of FMHA shapes, different mesh resolutions, turbulence models, and steam generator conditions. The CFD results show that the temperature deviation at the core inlet reduces greatly for all turbulence models and steam generator conditions tested here, and the effect of mesh refinement on the temperature distribution at the core inlet is negligible. Even though the uniformity of FMHA outlet hole flow increases the thermal mixing, the temperature deviation at the core inlet is within an acceptable range. We numerically confirmed that the FMHA applied in SMART has an excellent mixing capability and all simulation cases tested here satisfies the design requirement for FMHA thermal mixing capability.

• Journal of the Korean Chemical Society
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• v.40 no.6
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• pp.420-426
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• 1996

The critical micelle concentration(CMC) and the counterion binding $constant(\beta)$ at the CMC of the mixtures of Sodium dodecylsulfate(SDS) with Sodium dodecylbenzenesulfonate(DBS) in aqueous solutions have been determined from the concentration dependence of electrical conductance at several temperatures from $15^{\circ}C$ to $35^{\circ}C.$ Thermodynamic parameters(${\Delta}C_p,\;{\Delta}G_m^{\circ},\;{\Delta}H_m^{\circ}$ 및 ${\Delta}S_m^{\circ}$ and ${\Delta}C_p$), associated with the micelle formation of SDS/DBS mixtures, have been estimated from the temperature dependence of CMC and $\beta$ values. The measured values of ${\Delta}G_m^{\circ}\;and\;{\Delta}C_p$ are negative but the values of ${\Delta}S_m/^{\circ}$ are positive in the whole measured temperature region. The significance of these thermodynamic parameters and their relation to the theory of the micelle formation of SDS/DBS mixtures have been also considered.

• The Journal of the Acoustical Society of Korea
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• v.40 no.2
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• pp.148-154
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• 2021

Text-Independent speaker verification needs to extract text-independent speaker embedding to improve generalization performance. However, deep neural networks that depend on training data have the potential to overfit text information instead of learning the speaker information when repeatedly learning from the identical time series. In this paper, to prevent the overfitting, we propose a segment unit shuffling layer that divides and rearranges the input layer or a hidden layer along the time axis, thus mixes the time series information. Since the segment unit shuffling layer can be applied not only to the input layer but also to the hidden layers, it can be used as generalization technique in the hidden layer, which is known to be effective compared to the generalization technique in the input layer, and can be applied simultaneously with data augmentation. In addition, the degree of distortion can be adjusted by adjusting the unit size of the segment. We observe that the performance of text-independent speaker verification is improved compared to the baseline when the proposed segment unit shuffling layer is applied.