• Journal of Korean Society of Environmental Engineers
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• v.34 no.2
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• pp.91-96
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• 2012

In this study we investigated the effects of operational parameters of a multi-layered soil filtration (filter depth, filtration velocity, and continuous/intermittent operation) on removal of pollutants in river water. As filter depth increased removal of all the pollutants (COD, TP, TN, and $NH_4$-N) was increased because the increase in filter depth increased in contact time between media and pollutants. The removal of TP and $NH_4$-N more increased with the increase in filter depth, comparing to the biological COD removal which was performed only in the top layer, since the removal mechanism of TP and $NH_4$-N was physicochemical process occurring throughout the whole layers. However, the reduction in filtration velocity resulted in decrease of removal all the pollutants removal due to shorter retention time. Biological COD removal was more influenced with the reduction in filtration velocity (longer retention time), than the removal of TP and $NH_4$-N. Because biological process was occurred only in the top layer which has relatively shorter retention time, comparing with physicochemical process occurred throughout whole media. Therefore, it is desirable that the operation parameters be controlled toward increasing retention time, in order to achieve efficient pollutants removal. The change in operation mode (continuos vs. intermittent operations) did not provide significant effects on the pollutant treatment efficiency by the multi-layered soil filtration system. Our findings suggest that for stable long-term operation it should be considered keeping conditions for biological activity and accelerating clogging.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.12
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• pp.2450-2460
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• 2015

Recently, as interest in IoT (Internet of Things) increase, research and standardization of a new protocol which reflects the characteristics of IoT has progressed. Among them, RPL(IPv6 for Low-Power Lossy Network) is a standardized routing protocol for IoT. RPL utilizes DIO (DODAG Information Object) messages which is flooded from the sink node to the whole network for path establish and maintenance. However, in large scale networks, not only a long time is required to propagate the DIO message to the whole networks but also a bottleneck effect around the sink node is occurred. Multi-sink based approaches which take advantage of reducing routing overhead and bottleneck effect are widely used to solve these problems. In this paper, we define 'unnecessary path update problems' that may arise when applying the RPL protocol to the multi sink based IoT networks and propose two methods namely Routing Metric based Path Update Decision method and Immediate Successor based Path Update Decision method for selective routing update.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1B
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• pp.15-30
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• 2000

The important considerations in the design of fiber-optic networks are reliability and survivability preparing against a failure. The SDH(Synchronous Digital Hierarchy), the international standard of optical transmission, offers several network reconfiguration methods that enable network to be automatically restored from failure. One of the methods is the SHR(Self Healing Ring), which is a ring topology system. Most network providers have constructed their backbone networks with SHR architecture since it can provide survivability economically. The network architecture has eventually evolved into a multi-ring network comprised of interconnected rings. This paper addresses multi-ring network design problems is to minimize ring-construction cost. This problem can be formulated with MIP(mixed integer programming) model. However, it is difficult to solve the model within reasonable computing time on a large scale network because the model is NP-complete. Furthermore, in practice we should consider the problem of routing demands on rings to minimize total cost. This routing problem involves multiplex bundling at the intermediate nodes. A family of heuristic algorithms is presented for this problem. These algorithms include gateway selection and routing of inter-ring demands as well as load balancing on single rings. The developed heuristic algorithms are applied to some network provider's regional and long-distance transmission networks. We show an example of ring design and compare it with another ring topology design. Finally, we analysis the effect bundling.

• Journal of the Korean Vacuum Society
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• v.19 no.2
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• pp.114-120
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• 2010

Conventional surface texturing in crystalline silicon solar cell have been use wet texturing by Alkali or Acid solution. But conventional wet texturing has the serious issue of wafer breakage by large consumption of wafer in wet solution and can not obtain the reflectance below 10% in multi crystalline silicon. Therefore it is focusing on RIE texturing, one method of dry etching. We developed large scale plasma RIE (Reactive Ion Etching) equipment which can accommodate 144 wafers (125 mm) in tray in order to provide surface texturing on the silicon wafer surface. Reflectance was controllable from 3% to 20% in crystalline silicon depending on the texture shape and height. We have achieved excellent reflectance below 4% on the weighted average (300~1,100 nm) in multi crystalline silicon using plasma texturing with gas mixture ratio such as $SF_6$, $Cl_2$, and $O_2$. The texture shape and height on the silicon wafer surface have an effect on gas chemistry, etching time, RF frequency, and so on. Excellent conversion efficiency of 16.1% is obtained in multi crystalline silicon by RIE process. In order to know the influence of RF frequency with 2 MHz and 13.56 MHz, texturing shape and conversion efficiency are compared and discussed mutually using RIE technology.

• Journal of Mechanical Science and Technology
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• v.20 no.1
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• pp.133-146
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• 2006

Collaborative optimization (CO) is a multi-level decomposed methodology for a large-scale multidisciplinary design optimization (MDO). CO is known to have computational and organizational advantages. Its decomposed architecture removes a necessity of direct communication among disciplines, guaranteeing their autonomy. However, CO has several problems at convergence characteristics and computation time. In this study, such features are discussed and some suggestions are made to improve the performance of CO. Only for the system level optimization, genetic algorithm is used and gradient-based method is used for subspace optimizers. Moreover, response surface models are replaced as analyses in subspaces. In this manner, CO is applied to aero-structural design problems of the aircraft wing and its results are compared with the multidisciplinary feasible (MDF) method and the original CO. Through these results, it is verified that the suggested approach improves convergence characteristics and offers a proper solution.

• Journal of computational fluids engineering
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• v.16 no.2
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• pp.17-23
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• 2011

The turbulent flow and vortex shedding phenomena around pantograph panhead of high speed train were investigated and compared with available experimental data and other simulations. The pantograph head was simplified to be a square-cross-section pillar and assumed to be no interference with other bodies. The Reynolds number (Re) was 22,000. The LES(large eddy simulation) of FDS code was applied to solve the momentum equations and the Wener-Wengle wall model was employed to solve the near wall turbulent flow. Smagorinsky model($C_s$=0.2) was used as SGS(subgrid scale) model. The total grid numbers were about 9 millions and the analyzed domain was divided into 12 multi blocks which were communicated with each other by MPI. The time-averaged mainstream flows were calculated and well compared with experimental data. The phased-averaged quantities had also a good agreement with experimental data. The near-wall turbulence should be carefully treated by wall function or direct resolution to get successful application of LES methods.

• Journal of Navigation and Port Research
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• v.35 no.9
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• pp.755-763
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• 2011

Recently, extreme tsunami waves generated by submarine earthquake have caused tremendous damages to the coastal cities and ports. Strong seiche oscillations and runups are observed in specific sea areas around the world. Although no frequent impacts to the coast of Korean peninsula, there exist some important events in the east of Korea in the past. This study focuses on two historical events and recalculate with different fault and rupture mechanism for prediction considering the recent trend of submarine earthquake. The present study of the 1983 Akita tsunamis demonstrates the multi-scale resonance along continental coasts. Together with the Nankai tsunami for inland sea, we have confirmed the inland sea resonance surrounded by islands in defining the impact along the coast. Coherence and wavelet analyses for deducing a predominant period and time frequency are useful in reasoning the inundation. The resonance modes, which are largely independent of the tsunami source, allow identification of at-risk communities and infrastructure for mitigation of tsunami hazards. Furthermore, understanding of the resonance and the predicted runups for the site of power plant and industrial complex in the east coast of Korea would allow better preparation for the future disasters.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.11
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• pp.5427-5433
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• 2012

In this paper a ultrasonic level meter for accurately and simply measuring oil levels of vehicle transmission is developed and its effectiveness is shown by experiments. By using a FPGA, all digital signal processes for the oil level calculation is fulfilled, and the programming on a FPGA project IDE enables very short developing time. And besides, analog circuits including a transmit/receive switch, multi-stage active filters and an envelope detect circuit are designed to process low-level ultrasonic echo signal. Under experiments, the designed level meter has proven to have the accuracy of about within 1[mm] scale.

• International Journal of Control, Automation, and Systems
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• v.6 no.5
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• pp.639-650
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• 2008

Electricity price forecasting has become an integral part of power system operation and control. In this paper, a wavelet transform (WT) based neural network (NN) model to forecast price profile in a deregulated electricity market has been presented. The historical price data has been decomposed into wavelet domain constitutive sub series using WT and then combined with the other time domain variables to form the set of input variables for the proposed forecasting model. The behavior of the wavelet domain constitutive series has been studied based on statistical analysis. It has been observed that forecasting accuracy can be improved by the use of WT in a forecasting model. Multi-scale analysis from one to seven levels of decomposition has been performed and the empirical evidence suggests that accuracy improvement is highest at third level of decomposition. Forecasting performance of the proposed model has been compared with (i) a heuristic technique, (ii) a simulation model used by Ontario's Independent Electricity System Operator (IESO), (iii) a Multiple Linear Regression (MLR) model, (iv) NN model, (v) Auto Regressive Integrated Moving Average (ARIMA) model, (vi) Dynamic Regression (DR) model, and (vii) Transfer Function (TF) model. Forecasting results show that the performance of the proposed WT based NN model is satisfactory and it can be used by the participants to respond properly as it predicts price before closing of window for submission of initial bids.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.115.1-115.1
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• 2016

Electrochemical anodization has been interested due to its useful way for the nano-scale architecture of metal oxides obtained from a metal substrate. By using this method, it is easy to control the morphology of the oxide materials by controlling electrochemical conditions. Among oxide materials obtained from the transition metals such as Ti, V, W, etc., in this paper, the morphological study of anodized $TiO_2$ was employed at various voltage conditions in fluoric based electrolyte, and the effects of applied voltage (sweep rate and retention time) on the tube morphologies were investigated. Furthermore, by using anodization of tungsten substrate (W), we fabricated the porous structure of $WO_3$ and provided merits of tailored structure for the hybridization of inorganic and organic materials as electrochromic (EC) applications. The hybrid porous $WO_3$ shows multi-chromic properties during the EC reactions at specific voltage conditions. From these results, the anodization process with tailoring nano-structure is one of the promising methods for EC applications.