• Journal of Communications and Networks
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• v.5 no.1
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• pp.65-72
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• 2003

Internet roundtrip delay/time (RTT) prediction plays an important role in detecting packet losses in reliable transport protocols for traditional web applications and determining proper transmission rates in many rate-based TCP-friendly protocols for Internet-based real-time applications. The widely adopted autoregressive and moving average (ARMA) model with fixed-parameters is shown to be insufficient for all scenarios due to its intrinsic limitation that it filters out all high-frequency components of RTT dynamics. In this paper, we introduce a novel parameter-varying RTT model for Internet roundtrip time prediction based on the information theory and the maximum entropy principle (MEP). Since the coefficients of the proposed RTT model are updated dynamically, the model is adaptive and it tracks RTT dynamics rapidly. The results of our experiments show that the MEP algorithm works better than the ARMA method in both RTT prediction and RTO estimation.

• Proceedings of the KIEE Conference
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• 2003.07d
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• pp.2492-2494
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• 2003

Urine analysis is one of the most important medical examination in the hospital. Not only the data for the ingredients of urine through chemical analysis, but also the data related to fluid dynamics, e.g., peak flow rate, average flow rate, may provide some useful information about patient's state of health. Therefore, we develop the portable system to measure and analyse fluid volume/flow rate in this study. This system can store and print the measured data during the pre-specified time interval, and provide some meaningful data related with fluid dynamics. We explain the method and the technical stuff to implement the system, and show the result.

• Bulletin of the Korean Chemical Society
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• v.18 no.5
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• pp.501-509
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• 1997

In recent papers[Bull. Kor. Chem. Soc. 1996, 17, 735; ibid 1997, 18, 478] we reported results of molecular dynamics (MD) simulations for the thermodynamic, structural, and dynamic properties of liquid normal alkanes, from n-butane to n-heptadecane, using three different models. Two of the three classes of models are collapsed atomic models while the third class is an atomistically detailed model. In the present paper we present results of MD simulations for the corresponding properties of liquid branched-chain alkanes using the same models. The thermodynamic property reflects that the intermolecular interactions become weaker as the shape of the molecule tends to approach that of a sphere and the surface area decreases with branching. Not like observed in the straight-chain alkanes, the structural properties of model Ⅲ from the site-site radial distribution function, the distribution functions of the average end-to-end distance and the root-mean-squared radii of gyration are not much different from those of models Ⅰ and Ⅱ. The branching effect on the self diffusion of liquid alkanes is well predicted from our MD simulation results but not on the viscosity and thermal conductivity.

• Ocean Systems Engineering
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• v.9 no.1
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• pp.97-109
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• 2019

Accurate calculation of the mean drift forces and moments is necessary when studying the higher order excitations on the floater in waves. When taking the time average of the second order forces and moments, the second order potential and motion diminish with only the first order terms remained. However, in the results of the first order forces or motions, the irregular frequency effects are often observed in higher frequencies, which will affect the accuracy of the calculation of the second order forces and moments. Therefore, we need to pay close attention to the irregular frequency effects in the mean drift forces. This paper will discuss about the irregular frequency effects in the calculations of the mean drift forces and validate our in-house program MDL Multi DYN using some examples which are known to have irregular frequency effects. Finally, we prove that it is necessary to remove the effects and demonstrate that the effectiveness of the formula and methods adopted in the development of our program.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.2
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• pp.159-165
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• 2017

Small-signal modeling and controller design methodology are proposed to improve the dynamics and stability of a DC-DC dual active bridge (DAB) converter. The state-space average method has a limitation when applied to the DAB converter because its state variables are nonlinear and have zero average values in a switching period. Therefore, the small-signal model and the frequency response of the DAB converter are derived and analyzed using a generalized average method instead of conventional modeling methods. The design methodology of a lead-lag controller instead of the conventional proportional-integral controller is also proposed using the derived small-signal model. The accuracy and performance of the proposed small-signal model and controller are verified by simulation and experimental results with a 500 W prototype DAB converter.

• Structural Engineering and Mechanics
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• v.43 no.6
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• pp.823-833
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• 2012

An experimental method was suggested for obtaining fracture toughness ($K_{Ic}$) and the tensile strength (${\sigma}_t$) of chopped strand glass fiber reinforced polymer concretes (PC). Semi-circular bend (SCB) specimens subjected to three-point bending were used for conducting the experiments on the PC material. While the edge cracked SCB specimen could be used to evaluate fracture toughness, the tensile strength was obtained from the un-cracked SCB specimen. The experiments showed the practical applicability of both cracked and un-cracked SCB specimens for using as suitable techniques for measuring $K_{Ic}$ and ${\sigma}_t$ in polymer concretes. In comparison with the conventional rectangular bend beam specimen, the suggested SCB samples need significantly less material due to its smaller size. Furthermore, the average values of ${\sigma}_t$ and $K_{Ic}$ of tested PC were approximately 3.5 to 4.5 times the corresponding values obtained for conventional concrete showing the improved strength properties of PC relative to the conventional concretes.

• Korea-Australia Rheology Journal
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• v.14 no.3
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• pp.129-138
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• 2002

A cationic surfactant, cetyltrimethylammonium $\rho$-toluenesufonate (CTA$\rho$TS), forms long threadlike micelles in aqueous solution. The threadlike micelles make concentrated entanglement networks, so that the solution shows pronounced viscoelastic behavior as concentrated polymer systems do. However, a mechanism for a process responsible for the longest relaxation time of the threadlike micellar system is different from that of semi-dilute to concentrated polymer systems. The threadlike micellar system exhibits unique viscoelasticity described by a Maxwell model. The longest relaxation time of the threadlike micellar system is not a function of the concentration of CTA$\rho$TS, but changes with that of $\rho$-toluenesufonate ($\rho$$TS^{-}$) ions in the bulk aqueous phase supplied by adding sodium $\rho$-toluenesulfonate (NapTS). The rates of molecular motions in the threadlike micelles are not influenced by the concentration of $\rho$$TS^{-}$ anions, therefore, molecular motions in the threadlike micelles (micro-dynamics) are independent of the longest relaxation mechanism (macro-dynamics). A nonionic surfactant, oleyldimethylamineoxide (ODAO), forms long threadlike micelles in aqueous solution without any additives. The aqueous threadlike micellar system of ODAO also shows Maxwell type viscoelastic behavior. However, the relaxation mechanism for the longest relaxation process in the system should be different from that in the threadlike micellar systems of CTA$\rho$TS, since the system of ODAO does not contain additive anions. Because increase in the average degree of protonation of head groups of ODAO molecules in micelles due to adding hydrogen bromide causes the relaxation time remarkably longer, changes in micro-structure and micro-dynamics in the threadlike micelle are closely related to macro-dynamics in contrast with the threadlike micellar system of CTA$\rho$TS.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.38 no.1
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• pp.57-67
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• 2020

Recently, smart cities are attracting attention as a solution for a plethora of urban problems, including transportation, environment, safety, and energy. However, despite a substantial body of research dealt with the concept, trends, policy, and legal institutions of smart cities, few researchers have examined how the smart city services influence the cities from the dynamic perspective that considers the entire cycle of a city, including its growth, stagnation, and decline. Thus, it is vital to understand how the city changes with time from the view that a city is a system of sub-elements-population, industry, transportation, environment, housing, and land-closely interacting together. Within this context, this study explores how the urban dynamics of Anyang-city develop for the long term using the System Dynamics method and analyzes the effect of smart city project investment on the dynamics of Anyang-city. According to the result, Anyang-city is a "mature and stable" type, and its population is expected to decrease slowly by 2040. Specifically, the Anyang-city population will be reduced to 553,000 by 2030. It was analyzed that the number will decrease to 543,000 by 2040. It was also found that the investment in smart city projects in Anyang, based on the Plan for Anyang Smart City, would have the following effects: easing population decline, increasing number of businesses, improving urban safety index, and increasing average driving speed. The population will grow by 4,000 and the number of businesses will increase by 761 than before budget investment. The result of this paper is expected to contribute to identifying and predicting the effect of smart city policies from a long-term perspective.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.126-129
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• 1999

This paper presents a new averaged model for controlled on time boost power factor correction (PFC) circuit. The proposed model accurately predicts the average behavior of the PFC circuit, and offers a good alternative in studying the large signal dynamics of the circuit. The accuracy of the model is verified through both computer simulation and experiments.

• Journal of Electrical Engineering and information Science
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• v.2 no.3
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• pp.61-65
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• 1997

This paper proposes an intelligent controller for brushless DC motor and load with unknown nonlinear dynamics. The proposed intelligent control system consists of a plant identifier and PID controller with varying gains. The identifier is constructed using an Auto Regressive Moving Average (ARMA) model. In order to tune the parameters of the identifier and the gains of the PID controller efficiently, e also propose a modified Evolution Strategy. Experimental results show that the proposed intelligent controller for brushless DC motor has good control performance under unknown disturbance.