• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.3
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• pp.179-184
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• 2019

In many countries, such as developing countries where electricity is scarce, small wind turbines in the form of Off Grid are an effective solution to solve power supply problems. In some countries, the expansion of power systems and the decline of electricity-intensive areas have led to the use of small wind power in urban road lighting, mobile communications base stations, aquaculture and seawater desalination. With this change, the size of the small wind power industry is expected to have greater potential than large-scale wind power. In the case of small wind power generators, the generator is controlled at a variable speed, and the voltage and current generated by the generator have many harmonic components. To solve this problem, the AC to DC converter to be studied in this paper is a three-phase step-up type converter with a single switch. The inductor current is controlled in discontinuous mode, and has a characteristic of having a unit power factor by eliminating the harmonic of the input current. The proposed converter is composed of LCL filter and three phase rectification boost converter at the input stage and a single phase full bridge for grid connection. It is a control system with energy storage system(ESS) that the system stabilization can be pursued against the electric power.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.4
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• pp.2060-2077
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• 2019

Recently, mobile healthcare services have attracted significant attention because of the emerging development and supply of diverse wearable devices. Smartwatches and health bands are the most common type of mobile-based wearable devices and their market size is increasing considerably. However, simple value comparisons based on accumulated data have revealed certain problems, such as the standardized nature of health management and the lack of personalized health management service models. The convergence of information technology (IT) and biotechnology (BT) has shifted the medical paradigm from continuous health management and disease prevention to the development of a system that can be used to provide ground-based medical services regardless of the user's location. Moreover, the IT-BT convergence has necessitated the development of lifestyle improvement models and services that utilize big data analysis and machine learning to provide mobile healthcare-based personal health management and disease prevention information. Users' health data, which are specific as they change over time, are collected by different means according to the users' lifestyle and surrounding circumstances. In this paper, we propose a prediction model of user physical activity that uses data characteristics-based long short-term memory (DC-LSTM) recurrent neural networks (RNNs). To provide personalized services, the characteristics and surrounding circumstances of data collectable from mobile host devices were considered in the selection of variables for the model. The data characteristics considered were ease of collection, which represents whether or not variables are collectable, and frequency of occurrence, which represents whether or not changes made to input values constitute significant variables in terms of activity. The variables selected for providing personalized services were activity, weather, temperature, mean daily temperature, humidity, UV, fine dust, asthma and lung disease probability index, skin disease probability index, cadence, travel distance, mean heart rate, and sleep hours. The selected variables were classified according to the data characteristics. To predict activity, an LSTM RNN was built that uses the classified variables as input data and learns the dynamic characteristics of time series data. LSTM RNNs resolve the vanishing gradient problem that occurs in existing RNNs. They are classified into three different types according to data characteristics and constructed through connections among the LSTMs. The constructed neural network learns training data and predicts user activity. To evaluate the proposed model, the root mean square error (RMSE) was used in the performance evaluation of the user physical activity prediction method for which an autoregressive integrated moving average (ARIMA) model, a convolutional neural network (CNN), and an RNN were used. The results show that the proposed DC-LSTM RNN method yields an excellent mean RMSE value of 0.616. The proposed method is used for predicting significant activity considering the surrounding circumstances and user status utilizing the existing standardized activity prediction services. It can also be used to predict user physical activity and provide personalized healthcare based on the data collectable from mobile host devices.

• The Journal of the Korea Contents Association
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• v.19 no.1
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• pp.141-151
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• 2019

A network of graph data structure is used in many applications to represent interactions between entities. Recently, as the size of the network to be processed due to the development of the big data technology is getting larger, it becomes more difficult to handle it in one server, and thus the necessity of distributed processing is also increasing. In this paper, we propose a distributed processing system for efficiently performing subgraph and stores. To reduce unnecessary searches, we use statistical information of the data to determine the search order through probabilistic scoring. Since the relationship between the vertex and the degree of the graph network may show different characteristics depending on the type of data, the search order is determined by calculating a score to reduce unnecessary search through a different scoring method for a graph having various distribution characteristics. The graph is sequentially searched in the distributed servers according to the determined order. In order to demonstrate the superiority of the proposed method, performance comparison with the existing method was performed. As a result, the search time is improved by about 3 ~ 10% compared with the existing method.

• Korean Journal of Construction Engineering and Management
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• v.20 no.1
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• pp.96-104
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• 2019

Recently, projects are being actively promoted to develop a new residential district centered around the metropolitan area, or to redevelop the residential area that was established long ago as unplanned land development. In this residential area, the owner can directly construct the building, and the way the building owner builds the residential house is called the direct construction of the owner. If the owner has the construction management (CM) capability while conducting direct management of the owner, the direct construction can be carried out by the CM method. This type of construction is called Owner-CM delivery method. However, it is very rare for small-scale construction in Korea to be implemented by the Owner-CM method. This may be due to the lack of knowledge and experience about the CM of the owner. In this study, we investigated the actual cases of the scheduling for the residential houses of similar size which were built at the same time in the residential housing complex developed near the metropolitan area. The purpose of this study is to derive the success factors of the scheduling in the small-scale construction from the cases carried out by the Owner-CM method. These success factors of the scheduling can be used as meaningful reference for the owners who want to build their own house in the future.

• Clean Technology
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• v.25 no.1
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• pp.7-13
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• 2019

Recently, attention has been paid to obtaining bio-polyols from renewable resources. Successful use of these natural ingredients successfully produced in the industry for the synthesis of various polyurethanes is a very important task. In this study, a series of dimethylformamide (DMF) based polyurethanes were synthesized from methylene diphenyl diisocyanate (MDI)/1, 4-butanediol and bio-polyol (polytrimethylene ether glycol based on 1, 3-propanediol : B-POL)/polyester polyol (polyadipate diol based on 1,4-butandiol : H-PET). The effect of different ratio of bio-polyol (B-POL)/polyester polyol (H-PET) on the physical properties of polyurethane was investigated. As the B-POL content in B-POL/H-PET mixture increased, the glass transition of soft segment (Tgs) and tensile strength of polyurethane decreased, however, the elongation at break and tear strength increased. On the other hand, artificial leather was produced by wet process using synthesized DMF-based polyurethanes. It was found that there was almost no difference in the effect of the B-POL/H-PET composition on the average size and density (the number of cells per unit volume) of the porous cells formed in artificial leather. These results show that there is no problem in using bio-polyol (B-POL) based polyurethane for artificial leather produced by wet process.

• Earthquakes and Structures
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• v.15 no.6
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• pp.667-685
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• 2018

In eccentrically braced steel frames (EBFs), the links are fuse members which enter inelastic phase before other structure members and dissipate the seismic energy. Based on the force-based seismic design method, damages and plastic deformations are limited to the links, and the main structure members are required tremendous sizes to ensure elastic with limited or no damage. Force-based seismic design method is very common and is found in most design codes, it is unable to determine the inelastic response of the structure and the damages of the members. Nowadays, methods of seismic design are emphasizing more on performance-based seismic design concept to have a more realistic assessment of the inelastic response of the structure. Links use ordinary steel Q345 (the nominal yielding strength $f_y{\geq}345MPa$) while other members use high strength steel (Q460 $f_y{\geq}460MPa$ or Q690 $f_y{\geq}690MPa$) in eccentrically braced frames with high strength steel combination (HSS-EBFs). The application of high strength steels brings out many advantages, including higher safety ensured by higher strength in elastic state, better economy which results from the smaller member size and structural weight as well as the corresponding welding work, and most importantly, the application of high strength steel in seismic fortification zone, which is helpful to popularize the extensive use of high strength steel. In order to comparison seismic behavior between HSS-EBFs and ordinary EBFs, on the basis of experimental study, four structures with 5, 10, 15 and 20 stories were designed by PBSD method for HSS-EBFs and ordinary EBFs. Nonlinear static and dynamic analysis is applied to all designs. The loading capacity, lateral stiffness, ductility and story drifts and failure mode under rare earthquake of the designs are compared. Analyses results indicated that HSS-EBFs have similar loading capacity with ordinary EBFs while the lateral stiffness and ductility of HSS-EBFs is lower than that of EBFs. HSS-EBFs and ordinary EBFs designed by PBSD method have the similar failure mode and story drift distribution under rare earthquake, the steel weight of HSS-EBFs is 10%-15% lower than ordinary EBFs resulting in good economic efficiency.

• Fire Science and Engineering
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• v.32 no.6
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• pp.108-116
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• 2018

A melted bead microstructure can be divided into a deformed and undeformed layer. Measurement errors occur in the presence of a deformed layer, which should be removed through grinding/polishing whilst preserving the original structure. This paper proposes a grinding/polishing process to analyze the microstructure of copper melted beads. For the removal of the deformed layer, the correlation between the abrasive type/size, the polishing time and polishing rate was analyzed and the thickness of the deformed layer was less than $1{\mu}m$. The results suggest a new grinding/polishing procedure: silicon carbide abrasive $15{\mu}m$ (SiC P1200) 2 min, and $10{\mu}m$ (SiC P2400) 1 min; and diamond abrasive $6{\mu}m$ 8 min, $3{\mu}m$ 6 min, $1{\mu}m$ 10 min, and $0.25{\mu}m$ 8 min. In addition, a method of increasing the sharpness of the microstructure by chemical polishing with $0.04{\mu}m$ colloidal silica for 3 min at the final stage is also proposed. The overall grinding/polishing time is 38 min, which is shorter than that of the conventional procedure.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.6
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• pp.133-137
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• 2018

Arduino is a small microcomputer that is used in a variety of industry fields and especially is widely used as an open source hardware IoT device. The multi-tasking method of Arduino is divided into super loop timing and RTOS thread method. The super loop timing method is simple and easy to understand. However, when one task is long, it affects the execution of the next task. In addition, RTOS threading has the advantage of being able to run without being influenced by other work time. However, Arduino, a small microcomputer, has a disadvantage in that, when the number of threads increases, the context switching time of the thread causes additional time not included in the super loop timing method have. In this paper, we use Arduino Uno R3 and FreeRTOS to analyze these different features, and the task for the experiment is to send 8000 digital signals to the built-in LED port. If two tasks of the same size are executed, the super loop method executes 3 ms faster than FreeRTOS multitasking. If multiple tasks are executed simultaneously, superloop type task is sequential execution and difference in execution time between first task and last task is large. FreeRTOS method can be executed concurrently, but execution time delay of about 30 ms occurs in context switching time.

• Journal of the Korean earth science society
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• v.40 no.2
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• pp.177-187
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• 2019

Several volcanic activities have continued in Mt. Baekdu since the Millennium eruption, and these phenomena have increased the need for volcanic activity surveillance. Various geophysical approaches are needed to obtain the depth and size of magma chamber that lie several kilometers below the surface. We examined the applicability of direct-current resistivity survey in this study. In order to explore the deep magma chamber of Mt. Baekdu, which has a spatial limitation due to the borderline, a large-scale survey with a length of tens of kilometers should be conducted. This type of survey requires a distributed measurement system and optimized exploration designs. Therefore, we propose survey designs taking advantage of our developed distributed acquisition system and analyze the applicability using numerical simulation. We confirmed that our designs that use single survey line with offline transmitting points show comparable results to the conventional 3D survey. It is expected that our research result can contribute to the deep geophysical exploration in Mt. Baekdu.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.1
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• pp.18-26
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• 2019

The Maritime Labour Convention, 2006, (MLC) aimed to ensure decent working conditions for seafarers and entered into force on August 20, 2013. It was considered as the fourth pillar in the maritime sector. This paper evaluates how the MLC has been implemented in the field and what issues were addressed in the shipping industry. To achieve this, statistical analysis was conducted using inspection data of Port State Control (PSC) carried out by the Paris MOU and the Tokyo MOU during 2010-2012 and 2014-2016 for deficiencies under the MLC and International Labour Organization (ILO) No. 147 Convention. This study compared pre-2013 and post-2013 deficiency data according to ship's age, size (gross tonnage) and type. The results showed that, although the deficiencies reported by the Tokyo MOU during 2014-2016 were nearly double those from 2010-2012, the deficiency share against total deficiencies for the Tokyo MOU remained two thirds of those for the Paris MOU. This study suggests that the Tokyo MOU should strengthen its inspection efforts on MLC and ILO should provide clear references, such as guidelines and a unified interpretation for national discretions under the MLC for the purpose of harmonized PSC inspections. Additionally, it would be desirable to consolidate the deficiency coding system for the MLC by deleting the codes for the ILO No. 147 Convention, which was incorporated into the MLC. It would also be beneficial to add new deficiency codes for social security, including seafarers' leave and repatriation.