• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.609-616
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• 2005

While the SIMPLE algorithm is most widely used for the simulations of flow phenomena that take place in the industrial equipments or the manufacturing processes, it is less adopted for the simulations of the free surface flow. Though the SIMPLE algorithm is free from the limitation of time step, the free surface behavior imposes the restriction on the time step. As a result, the explicit schemes are faster than the implicit scheme in terms of computation time when the same time step is applied to, since the implicit scheme includes the numerical method to solve the simultaneous equations in its procedure. If the computation time of SIMPLE algorithm can be reduced when it is applied to the unsteady free surface flow problems, the calculation can be carried out in the more stable way and, in the design process, the process variables can be controlled based on the more accurate data base. In this study, a modified SIMPLE algorithm is presented fur the free surface flow. The broken water column problem is adopted for the validation of the modified algorithm (MoSIMPLE) and for comparison to the conventional SIMPLE algorithm.

• Journal of Korea Game Society
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• v.1 no.1
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• pp.17-23
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• 2001

In this paper, we refer to positive effect and negative effect of game. And we inquire the recent trend of edutainment that emphasizes charm of game and educational effect at the same time. Because the simulation game and the role-playing game have strong toxication, the limitation of computer use is essential. Therefore, we present dynamic computer using-time control system for prevention of game toxicaton and for activity of educational contents. The method considered in this paper increases computer using-time n proportion to using of educational contents. So it lead user of computer to use educational contents voluntarily.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.2
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• pp.83-89
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• 2017

Numerical simulations of ship resistance have been performed to compare spatial characteristics of Courant number when using structured and unstructured meshes. When Euler scheme was used for time integration, the structured mesh provided a more efficient calculation because the calculation time interval was larger than that of unstructured mesh. The automatic generation of very small meshes in the unstructured mesh was mainly responsible for the limitation of calculation time interval. When local time stepping Euler scheme was applied, however, the ship resistance of unstructured mesh showed a rapid convergence while a slow convergence of ship resistance in structured mesh was caused by the small time interval in bulbous bow.

• The KIPS Transactions:PartD
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• v.14D no.7
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• pp.727-732
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• 2007

Most of previous work on indexing and searching time series focused on the similarity matching and retrieval of one-attribute time series. However, multimedia databases such as music, video need to handle the similarity search in multi-attribute time series. The limitation of the current similarity models for multi-attribute sequences is that there is no consideration for attributes' sequences. The multi-attribute sequences are composed of several attributes' sequences. Since the users may want to find the similar patterns considering attributes's sequences, it is more appropriate to consider the similarity between two multi-attribute sequences in the viewpoint of attributes' sequences. In this paper, we propose the similarity search method based on attributes's sequences in multi-attribute time series databases. The proposed method can efficiently reduce the search space and guarantees no false dismissals. In addition, we give preliminary experimental results to show the effectiveness of the proposed method.

• Journal of Korean Neurosurgical Society
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• v.50 no.4
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• pp.363-369
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• 2011

Objective : We investigated the clinical and radiological advantages of unilateral laminectomy in posterior lumbar interbody fusion (PLIF) procedure comparing with bilateral laminectomy, under the same procedural condition including bilateral instrumentation and insertion of two cages, in patients with degenerative lumbar disease with unilateral leg symptoms. Methods : We retrospectively reviewed 124 consecutive cases of PLIF via unilateral or bilateral approach between January 2006 and April 2010. In 80 cases (bilateral group), two cages were inserted via bilateral laminectomy, and in 44 cases (unilateral group), via unilateral laminectomy. The average follow-up duration was 29.5 months. The clinical outcomes were evaluated with the Visual Analogue Scale (VAS) and the Oswestry disability index (ODI). The fusion rates and disc space heights were determined by dynamic standing radiographs and/or computed tomography. Operative times, intra-operative and post-operative blood losses and hospitalization periods were also evaluated. Results : In clinical evaluation, the VAS and ODI scores showed excellent outcomes in both groups. There were no significant differences in term of fusion rate, but the perioperative blood loss and the operative time of the unilateral group were lower than that of the bilateral group. Conclusion : Unilateral laminectomy can minimize the operative time and perioperative blood loss in PLIF procedure. However, the different preoperative disc height between two groups is a limitation of this study. Despite this limitation, solid fusion and satisfactory symptomatic improvement could be achieved uniquely by our surgical method. This surgical method can be an alternative surgical technique in patients with unilateral leg pain.

• 한국생물공학회:학술대회논문집
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• 2000.11a
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• pp.241-244
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• 2000

Continuous $H_2$ production from CO and water was studied in a trickle bed reactor(TBR) using Rhodopspedomonas palustris P4. To achieve high cell density, R. palustris P4 were cultivated by a fed-batch culture mode under chemoheterotrophic and aerobic condition, and final cell concentration was 13 g/L. TBR could provide sufficient residence time for CO to contact with cell suspension circulating TBR. The maximum CO uptake rate was found to be 16 mmol/L/hr at gas retention time of 50 min and CO partial pressure of 0.4 atm. In our correlation of the experimental data with mathematical model of TBR, the TBR operation with P4 was found to be lie in an intermediate state between mass transfer limitation and kinetic limitation. Due to the high cell density as well as hydrogen production activity in this study, TBR operation showed a superior performance to other previous reports on microbial hydrogen production.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.41 no.2
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• pp.1-8
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• 2018

K-means algorithm is one of the most popular and widely used clustering method because it is easy to implement and very efficient. However, this method has the limitation to be used with fixed number of clusters because of only considering the intra-cluster distance to evaluate the data clustering solutions. Silhouette is useful and stable valid index to decide the data clustering solution with number of clusters to consider the intra and inter cluster distance for unsupervised data. However, this valid index has high computational burden because of considering quality measure for each data object. The objective of this paper is to propose the fast and simple speed-up method to overcome this limitation to use silhouette for the effective large-scale data clustering. In the first step, the proposed method calculates and saves the distance for each data once. In the second step, this distance matrix is used to calculate the relative distance rate ($V_j$) of each data j and this rate is used to choose the suitable number of clusters without much computation time. In the third step, the proposed efficient heuristic algorithm (Group search optimization, GSO, in this paper) can search the global optimum with saving computational capacity with good initial solutions using $V_j$ probabilistically for the data clustering. The performance of our proposed method is validated to save significantly computation time against the original silhouette only using Ruspini, Iris, Wine and Breast cancer in UCI machine learning repository datasets by experiment and analysis. Especially, the performance of our proposed method is much better than previous method for the larger size of data.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.4
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• pp.831-840
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• 2010

While Wireless Internet services were activated, many users got possible to use various Internet services without limitation in location. In particular, the demands to Wireless Internet Services are getting expanded because mobile devices that support high mobility are getting smarter. However, if a user uses various wireless networks, much limitation occurs in network setting when they move to another network. This is because there are few appropriate Handover Mechanisms to support Heterogeneous Network. So, this paper propose that Fast-Handover for Vertical Network Handover with MIH in PMIPv6 to support heterogeneous network and to reduce the handover latency time. Analysis result presented in this paper shows that by carefully selecting suitable system configuration model and parameters, suggestion has reduced latency time of 26% and packet losses of 90% (Avg.) at the maximum in comparison with original PMIPv6 handover.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.9
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• pp.4183-4191
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• 2011

Considering the characteristics of a data stream whose data elements are continuously generated and may change over time, there have been many techniques to differentiate the importance of data elements in a data stream by their generation time. The conventional techniques are efficient to get an analysis result focusing on the recent information in a data stream, but they have a limitation to differentiate the importance of information in various ways more flexible. An information differentiation technique based on the term of a fuzzy set can be an alternative way to compensate the limitation. A term of a fuzzy set has been widely used in various data mining fields, which can overcome the sharp boundary problem and give an analysis result reflecting the requirements in real world applications more. In this paper, a fuzzy window mechanism is proposed, which is adapting a term of a fuzzy set and is efficiently used to differentiate the importance of information in mining data streams. Basic concepts including fuzzy calendars are described first, and subsequently details on data stream mining of weighted patterns using a fuzzy window technique are described.

• Korean Journal of Heritage: History & Science
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• v.48 no.1
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• pp.132-147
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• 2015

In this article, the research trends regarding the analysis and restoration of the pigments applied on colored cultural properties during past 25 years are reviewed and the future research direction in this field of study is proposed. There are over 100 different pieces of the colored cultural property samples that have been analyzed in Korea during the time and are increasing numbers of studies on comparative investigations as well. In addition, new analysis techniques have been introduced to surpass the limitation of the current analysis techniques and the database construction has been developed tremendously, which will enhance the analysis reliability, indicating fast growth in the related research areas. There are also studies on finding new materials to replace the traditional ingredients for producing color pigments and related other materials to overcome the limitation of the traditional ingredients on top of the steady number of studies on reproduction and restoration of the traditional pigments. These various research efforts will bring much development in this area of research. One suggestion to be made is that there need to be long term planned research works for certain type of studies. For instance, the effect to the colored cultural properties due to the environmental change is one of important research topics that should be carefully studied, which requires longer time period and also more patience than the research works in the current and past trends.