• Journal of information and communication convergence engineering
• /
• v.9 no.1
• /
• pp.74-77
• /
• 2011

PSPICE modeling of a commercial LED driver IC (TOP245P) and PC817A optocoupler is proposed for the switch-mode power supply (SMPS) (applicable to LED driver) design and simulation. An analog behavioral model of the TOP245P IC including the shunt regulator, under-voltage(UV) detection, over-voltage(OV) shut-down and SR flip-flop is developed by using PSPICE. The empirical equation of PC817A current transfer ratio (CTR) is fitted from the datasheet of PC817A. Two types of SMPSs are simulated with the averaged-model and switching-model. The simulation results by the proposed PSPICE models are in good agreement with those in the data sheet and an experimental data.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.733-738
• /
• 2004

This paper deals with feedback control of a hydraulic unit for direct yaw moment control, a method used to actively maintain the dynamic stability of an automobile. The uncertain parameters and complex structure naturally call for empirical modeling of the hydraulic unit, which readily results in a control-oriented model with high fidelity. The identified model is cross-validated against experimental data under various conditions, which helps to establish model uncertainty. Then, the $H_{\infty}$ optimization technique is employed to synthesize a controller with guaranteed robust stability and performance against the model uncertainty. The performance of the synthesized controller is verified using experimental results, which shows the viability of the proposed approach in a real-world application.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.49 no.8
• /
• pp.545-550
• /
• 2000

This paper presents design and analysis of an HID lamp ballast for a fast turn on characteristics and stable operation. It produces a high open circuit voltage for the ignition and it is controlled to supply effectively the power required to shorten the warm-up period after the breakdown. The lamp modeling by empirical data is presented. It is very effective in the designing of the control loop in the steady-state operating region. A stable operation of the lamp power regulation in the steady state is achieved, which is crucial for the long life time and constant light output. Stability analysis of the system is performed and the results are verified through various simulation results and the hardware experiments.

• Journal of Power Electronics
• /
• v.11 no.3
• /
• pp.381-388
• /
• 2011

This article presents the development of a model for SiC power diodes based on the physics of the semiconductor. The model is able to simulate the behavior of the dynamics of the charges in the N- region based on the stored charge inside the SiC power diode, depending on the working regime of the device (turn-on, on-state, and turn-off). The optimal individual calculation of the ambipolar diffusion length for every phase of commutation allows for solving the ambipolar diffusion equation (ADE) using a very simple approach. By means of this methodology development a set of differential equations that models the main physical phenomena associated with the semiconductor power device are obtained. The model is developed in Pspice with acceptable simulation times and without convergence problems during its implementation.

• Wind and Structures
• /
• v.1 no.1
• /
• pp.77-109
• /
• 1998

An evaluation and comparison of seven of the world's major building codes and standards is conducted in this study, with specific discussion of their estimations of the alongwind, acrosswind, and torsional response, where applicable, for a given building. The codes and standards highlighted by this study are those of the United States, Japan, Australia, the United Kingdom, Canada, China and Europe. In addition, the responses predicted by using the measured power spectra of the alongwind, acrosswind and torsional responses for several building shapes tested in a wind tunnel are presented and a comparison between the response predicted by wind tunnel data and that estimated by some of the standards is conducted. This study serves not only as a comparison of the response estimates by international codes and standards, but also introduces a new set of wind tunnel data for validation of wind tunnel-based empirical expressions.

• East Asian mathematical journal
• /
• v.35 no.3
• /
• pp.305-318
• /
• 2019

Over the past decades, the Lee-Carter model [1] has attracted much attention from various demography-related fields in order to project the future mortality rates. In the Lee-Carter model, the speed of mortality improvement is stochastically modeled by the so-called mortality index and is used to forecast the future mortality rates based on the time series analysis. However, the modeling is applied to long time series and thus an important structural change might exist, leading to potentially large long-term forecasting errors. Therefore, in this paper, we are interested in detecting the structural change of the Lee-Carter model and investigating the actuarial implications. For the purpose, we employ the tests proposed by Coelho and Nunes [2] and analyze the mortality data for six countries including Korea since 1970. Also, we calculate life expectancies and whole life insurance premiums by taking into account the structural change found in the Korean male mortality rates. Our empirical result shows that more caution needs to be paid to the Lee-Carter modeling and its actuarial applications.

• Journal of Conservation Science
• /
• v.37 no.1
• /
• pp.25-33
• /
• 2021

To extend the application of digital technology to the replication of artifacts, meticulous details of the process and the diversity of three-dimensional (3D) printing output materials need to be supplemented. Thus, in this study, a bronze mirror with Hwangbichangcheon inscription was digitalized by 3D scanning, converted into a voxel model, and virtual conservation treatment was performed using a haptic device. Furthermore, the digital mold of the bronze mirror completed by Boolean modeling was printed using a 3D sand-printer. Such contactless replication based on digital technology reflects the stability, precision, expressivity, collectivity, durability, and economic feasibility of artifacts. Its application can be further extended to cultural products as well as such areas as education, exhibition, and research. It is expected to be in high demand for metal artifacts that require casting. If empirical studies through experimental research on casting are supplemented in the future, it could extend the application of digital technology-based contactless replication methods.

• Journal of Information Processing Systems
• /
• v.17 no.3
• /
• pp.586-598
• /
• 2021

Nowadays, users' reviews and feedback on e-commerce sites stored in text create a huge source of information for analyzing customers' experience with goods and services provided by a business. In other words, collecting and analyzing this information is necessary to better understand customer needs. In this study, we first collected a corpus with 99,322 customers' comments and opinions in English. From this corpus we chose the best number of topics (K) using Perplexity and Coherence Score measurements as the input parameters for the model. Finally, we conducted an experiment using the latent Dirichlet allocation (LDA) topic model with K coefficients to explore the topic. The model results found hidden topics and keyword sets with high probability that are interesting to users. The application of empirical results from the model will support decision-making to help businesses improve products and services as well as business management and development in the field of hotel services.

• Journal of Smart Tourism
• /
• v.2 no.3
• /
• pp.5-15
• /
• 2022

As the utilization of technology in the tourism field becomes familiar, it greatly impacts people's tourism activities. These changes could also affect the behavior of tourists during the pandemic. To investigate consumers' adaptation to the self-service technology (SST) environment during the coronavirus disease of 2019 (COVID-19) pandemic, we adopted a model of absorptive capacity as the main framework for empirical research. To track the social effects of COVID-19, consumers' behavioral intentions for four different points in time are collected. The analysis was conducted using latent growth and structural equation modeling. We set the organizational and environmental characteristics as the first step of the model, with assimilation and trust as a middle step. Intention to use a kiosk is placed at the final step as an exploit. Findings indicate that organizational characteristics and environmental characteristics positively influenced assimilation and trust, except for environmental characteristics. Consumers' assimilation in SST encourages immediate intention to use a kiosk. Consumers' trust in kiosks positively impacts both immediate and continuance intention to use a kiosk during COVID-19.

• International Journal of Korean Welding Society
• /
• v.2 no.1
• /
• pp.11-14
• /
• 2002

A metallurgical model for bainite transformation kinetics in the coarse-grained heat affected zone(CGHAZ) on the basis of an Avrami-type equation was studied. Isothermal transformation tests were carried out to obtain the empirical equations for incubation time and Avrami kinetic constants for C-Mn-Mo-Ni steel. The effect of prior austenite grain size(PAGS) on the reaction rate of bainite was also investigated. Compared with experimental transformation behavior of bainite, the predicted behavior was in good agreement. It was also found that a smaller grain size retard the bainite reaction rate, contrary to the classical grain size effect and this is considered to be caused by constraint of grain size to bainite growth.