• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.677-680
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• 2005

In numerical analysis on the thermal performance of the heat exchanger with phase change fluids, the numerical values of thermodynamic properties are needed. But the steam table should be modeled properly as the direct use of thermodynamic properties of the steam table is impossible. In this study the function approximation characteristics of neural networks was used in modeling the saturated vapor region of refrigerant R12. The neural network consists of one input layer with one node, two hidden layers with 10 and 20 nodes each and one output layer with 7 nodes. Input can be both saturation temperature and saturation pressure and two cases were examined. The proposed model gives percentage error of ${\pm}$0.005% for enthalpy and entropy, ${\pm}$0.02% for specific volume and ${\pm}$0.02% for saturation pressure and saturation temperature except several points. From this results neural network could be a powerful method in function approximation of saturated vapor region of R12.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.395-400
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• 2006

Among the various error sources in positioning and navigation, the paper focuses on the modeling and prediction of receiver clock bias and then tries to achieve positioning based on simulated and predicted clock bias. With the SA off, it is possible to model receiver clock bias more accurately. We selected several types of GNSS receivers for test using ARMA model. To facilitate prediction with short and limited sample pseudorange observations, AR and ARMA are compared, and the improved AR model is presented to model and predict receiver clock bias based on previous solutions. Our work extends to clock bias prediction and positioning based on predicted clock bias using only 3 satellites that is usually the case under urban canyon situation. In contrast to previous experiences, we find that a receiver clock bias can be well modeled using adopted ARMA model. Test has been done on various types of GNSS receivers to show the validation of developed model. To further develop this work, we compare solution conditions in terms of DOP values when point positioning is conducted using 3 satellites to simulate urban positioning environment. When condition allows, height component is derived from other ways and can be set as known values. Given this condition, location is possible using less than 2 GNSS satellites with fixed height. Solution condition is also discussed for this background using mode of constrained positioning. We finally suggest an effective predictive time span based on our test exploration under varied conditions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.5
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• pp.352-365
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• 2012

A primary study on the rapid modeling of storm surge, which is one of typical coastal disasters, for immediate forecasting in conjunction with typhoon advisories is done and tested for the typhoons Bolaven, Tembin and Sanba which attacked to Korean Peninsula on August and September in this year 2012. Semi automatic rapid computations according to JTWC typhoon advisories were performed and uploaded to the web by models SLOSH in PC and ADCIRC in parallel clusters with 64 cores having 57k nodes encompassing the North-Western Pacific region. It only takes 1 and 2 hours from taking advisory to web uploading, respectively. By comparison with observed water surface elevations for the major tidal stations after Bolaven attack it shows within RMS error of 0.17~0.19 m for surge heights and only deviates 1 hour of peak surge time in ADCIRC model. Thus it is concluded that this approach provides a frame of near real-time immediate forecasting of storm surges with satisfactions.

• Journal of Biosystems Engineering
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• v.41 no.4
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• pp.342-356
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• 2016

Purpose: The drying of a thin layer of native cassava starch in a tray dryer was modeled to establish an equation for predicting the drying behavior under given conditions. Methods: Drying tests were performed using samples of native cassava starch over a temperature range of $40-60^{\circ}C$. We investigated the variation in the drying time, dynamic equilibrium moisture content, drying rate period, critical moisture content, and effective diffusivity of the starch with temperature. The starch diffusion coefficient and drying activation energy were determined. A modification of the model developed by Hii et al. was devised and tested alongside fourteen other models. Results: For starch with an initial moisture content of 82% (db), the drying time and dynamic equilibrium moisture content decreased as the temperature increased. The constant drying rate phase preceded the falling rate phase between $40-55^{\circ}C$. Drying at $60^{\circ}C$ occurred only in the falling rate phase. The critical moisture content was observed in the $40-55^{\circ}C$ range and increased with the temperature. The effective diffusivity of the starch increased as the drying temperature increased from 40 to $60^{\circ}C$. The modified Hii et al. model produced randomized residual plots, the highest $R^2$, and the lowest standard error of estimates. Conclusions: Drying time decreased linearly with an increase in the temperature, while the decrease in the moisture content was linear between $40-55^{\circ}C$. The constant drying rate phase occurred without any period of induction over a temperature range of $40-55^{\circ}C$ prior to the falling rate period, while drying at $60^{\circ}C$ took place only in the falling rate phase. The effective diffusivity had an Arrhenius relationship with the temperature. The modified Hii et al. model proved to be optimum for predicting the drying behavior of the starch in the tray dryer.

• Journal of KIISE:Software and Applications
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• v.30 no.12
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• pp.1158-1171
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• 2003

The UML is a widely accepted standard in object-oriented modeling. As the UML is semantically rich, we can describe in detail the system that will be developed, but we cannot guarantee the correctness and consistency of the designed model. Therefore, it is important to minimize the error by verifying user models in an early stage. In this paper, we propose a method for verifying the consistency of UML structural diagrams and behavioral diagrams using OCL verification rules and meta-metamodel. The consistency is a nature for checking whether the structural diagrams and behavioral diagrams are coherently designed according to a specific requirement. First we build meta-metamodels of the structural diagram and behavioral diagram that are described with the UML diagrams and the related elements, we derive rules for verifying the consistency from each meta-metamodels, and then formally specify with the language such as OCL for automatic verification. Finally, we verify the usefulness of the rule through a case study.

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.4
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• pp.168-176
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• 2005

We propose a method for 3-dimensionally reconstructing an object using a line that includes the midpoint information from a single image. A pre-defined polygon is used as the primitive and the recovery is processed from a single image. The 3D reconstruction is processed by mapping the correspondence point of the primitive model onto the photo. In the recent work, the reconstructions of camera parameters or error minimizing methods through iterations were used for model-based 3D reconstruction. However, we proposed a method for the 3D reconstruction of primitive that consists of the segments and the center points of the segments for the reconstruction process. This method enables the reconstruction of the primitive model to be processed using only the focal length of various camera parameters during the segment reconstruction process.

• The KIPS Transactions:PartA
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• v.10A no.3
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• pp.189-198
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• 2003

In this paper, we propose a method of analysis to show the heavy-tailed statistical distribution of file sizes in web servers, using TTT plot technique. TTT plot technique, a well-known method in the area of reliability engineering, determines that a distribution of samples fellows a heavy tailed one when their TTT statistical plots are lied on a straight line. We performed an intensive simulation using data gathered from real web servers. The simulation indicates that the proposed method is superior to Hill estimation technique or LLCD plot method in efficiency of data analysis. Moreover, the proposed method eliminates the possible decision error, which Pareto distribution or traditional method might cause.

• Smart Structures and Systems
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• v.25 no.3
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• pp.369-384
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• 2020

A wavefield sparse reconstruction technique based on compressed sensing is developed in this work to dramatically reduce the number of measurements. Firstly, a severely underdetermined representation of guided wavefield at a snapshot is established in the spatial domain. Secondly, an optimal compressed sensing model of guided wavefield sparse reconstruction is established based on l₁-norm penalty, where a suite of discrete cosine functions is selected as the dictionary to promote the sparsity. The regular, random and jittered undersampling schemes are compared and selected as the undersampling matrix of compressed sensing. Thirdly, a gradient projection method is employed to solve the compressed sensing model of wavefield sparse reconstruction from highly incomplete measurements. Finally, experiments with different excitation frequencies are conducted on an aluminum plate to verify the effectiveness of the proposed sparse reconstruction method, where a scanning laser Doppler vibrometer as the true benchmark is used to measure the original wavefield in a given inspection region. Experiments demonstrate that the missing wavefield data can be accurately reconstructed from less than 12% of the original measurements; The reconstruction accuracy of the jittered undersampling scheme is slightly higher than that of the random undersampling scheme in high probability, but the regular undersampling scheme fails to reconstruct the wavefield image; A quantified mapping relationship between the sparsity ratio and the recovery error over a special interval is established with respect to statistical modeling and analysis.

• Journal of the Korea Society for Simulation
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• v.25 no.4
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• pp.137-144
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• 2016

This paper proposes characteristics of management system for defense system development. This research shows how effectiveness of SBA (simulation-based acquisition) can be represented even necessity of SBA is recognized by researchers. To achieve this goal there are two key information, (1)the cost for modeling and simulation and (2) number of trial and error of a certain step in a phase. This paper presents user interface of gathering those two key information and a way of showing the effectiveness of SBA using those two information. In this work, all the data gathering for calculation of effectiveness should be considered as a saving logs. The contribution of this research is in presenting quantitative value representing effectiveness of SBA and proposing a system architecture for deriving the quantitative effectiveness.

• Journal of Information Technology Services
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• v.20 no.4
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• pp.95-111
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• 2021

Recently, many organizations are actively adopting VDI (Virtual Desktop Infrastructure), an IT-based business system, to build a non-face-to-face business environment for smart-work. However, most of the existing research on VDI has focused on the satisfaction of system service quality or the use of IT resources and investment for VDI introduction. However, research on effective management and utilization of factors according to the characteristics of VDI technology is urgently required. This study is an empirical research study on how VDI technology characteristics affect interactions and work performance by identifying differences in utilization factors between general organization members and IT managers, presenting standards for business utilization and management. This study proposed a model and hypothesis that the system technology characteristics for VDI use are mediated by interactions in which users respond to functions appropriate to their work. In order to verify the hypothesis, a questionnaire survey was conducted on 188 people of companies and institutions that have adopted and used VDI through a questionnaire survey. Data analysis was performed with partial least squares (PLS), a structural equation modeling (SEM) technique that uses a component-based approach to estimation. As a result of the empirical analysis, the same environmental function for performing work, N-th security, and remote access function factors for non-face-to-face work have a significant effect on interactivity, and IT managers have an additional significant effect on the management technology characteristics of resource reallocation. Has been shown to affect. The results of this study aim to minimize trial and error due to new introduction by presenting considerations for future VDI introduction through case analysis.