• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.27-30
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• 2005

In a microfluidic chips pressure driven flow or electro-osmotic flow has been usually employed to deliver bio-samples. Flow in the chips is usually slow and the mixing performance is poor. A micro-mixer with a rapid mixing is important for practical applications. In this study a newly designed and electro-osmotic driven micro-mixer is proposed. This design is comprised of a channel and a series of metal electrodes periodically attached on the side surface. In this configuration electro-osmotic flows and the stirring effects are simulated three-dimensionally using a commercial code, CFD-ACE. Focus is given the effect on the electro-osmotic flow characteristics under the local variation of the electric field.

• Journal of Korean Institute of Industrial Engineers
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• v.21 no.1
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• pp.33-49
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• 1995

Simulated annealing(SA) has been admitted as a general purpose optimization technique which can be utilized for almost all kinds of combinatorial optimization problems without much difficulty. But there are still some weak points to be resolved, one of which is the slow speed of convergence. In this study, we carefully review various previous efforts to improve SA and propose some variations of SA which can enhance the speed of convergence to the optimum solution. Then, we apply the revised SA algorithms to the scheduling and hardware allocation problems occurring in high-level synthesis(HLS) of VLSI design. We confirm the efficiency of the proposed methods through several HLS examples.

• Tribology and Lubricants
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• v.14 no.3
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• pp.87-93
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• 1998

Crank pin bearing in two-stroke marine diesel engine is operated under quite severe conditions since the elements are big and heavy and the sliding speed is very slow. Therefore it is very difficult to form oil film. In this paper, two types of bearings with different groove shape are compared. One has circumferential oil groove at lower position and the other has lengthwise oil groove at upper position. Bearing clearance, oil inlet pressure and length to diameter ratio are selected as design parameters. Locus of journal center and minimum oil film thickness are investigated to compare two cases.

• Proceedings of the KIPE Conference
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• 2004.07b
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• pp.479-483
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• 2004

Fuel Cell (FC) has slow response characteristic for load variation. During a load step, the inverter cannot pull more power from the fuel cell than is currently available so supplemental power must be provide by some sort of energy storage elements. In this paper, hi-directional do-dc converter for FC generation system is proposed to improve load response characteristic. The hi-directional converter interfaces the low voltage battery to the inverter dc link of FC generation system. The converter is based on a active full bridge in the primary side and on a half bridge in the secondary of a high frequency isolation transformer. The complete operating principles and simulation results in presented.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.865-871
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• 2004

The safety evaluations of railway wheel sets make use of the static fracture toughness obtained in ingot materials. The static fracture toughness of wheelset materials has been extensively studied by experiments, but the dynamic fracture toughness with respect to wheel set materials has not been studied enough yet. It is necessary to evaluate the characteristics of the fracture mechanics depending on each location for a full-scale wheel set for high-speed trains, because the load state for each location of the wheel set while running is different the contact load between the wheel and rail, cyclic stress in the wheel plate, etc. This paper deals with the fracture toughness depend on load rates. The fracture toughness depending on load rate data shows that once the downward curve from quasi-static values was reached, subsequent values showed a slow increase with respect to the impact velocity. This means that dynamic fracture toughness should be considered in the design code of the wheelset material.

• Journal of Fisheries and Marine Sciences Education
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• v.17 no.1
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• pp.67-75
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• 2005

Mobile devices compared with personal computers on the desktop have low bandwidths, small screens, and relatively slow speeds. These systems have practical problems with information searches in a web environment. Information searching of various web contents on the small size screen has especially severe limitations. We propose a filtering technique of web contents which can overcome the limitations of small size screens and meet the user requirements in a PDA environment. For these constructions, we first divide the screen into segment blocks and then extract content blocks according to the user requirements, so that only filtered web contents will be shown. The performance evaluation of the proposed technique saves an average time of about 30% by displaying only the extracted information instead of the whole web page.

• Journal of the Ergonomics Society of Korea
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• v.18 no.3
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• pp.105-125
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• 1999

As speech is the human being's most natural communication medium, using it gives many advantages. Currently, most user interfaces of a computer are using a mouse/keyboard type but the interface using speech recognition is expected to replace them or at least be used as a tool for supporting it. Despite the advantages, the speech recognition interface is not that popular because of technical difficulties such as recognition accuracy and slow response time to name a few. Nevertheless, it is important to optimize the human-computer system performance by improving the usability. This paper presents a set of guidelines for designing speech recognition interfaces and provides a method for evaluating the usability. A total of 113 guidelines are suggested to improve the usability of speech-recognition interfaces. The evaluation method consists of four major procedures: user interface evaluation; function evaluation; vocabulary estimation; and recognition speed/accuracy evaluation. Each procedure is described along with proper techniques for efficient evaluation.

• 제어로봇시스템학회:학술대회논문집
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• 1994.10a
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• pp.152-155
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• 1994

The presence of joint elasticity or the arm flexibility causes low damped oscillatory position error along a desired trajectory. We utilize a stochastic model for describing the fast dynamics and the approximation error. A second order shaping filter is synthesized such that its spectrum matches that of the fast dynamics. Augmenting the state vector of slow part with that of shaping filter, we obtain a nonlinear dynamics to which a Gaussian white noise is injected. This modeling approach leads us to the design of an extended Kalman filter(KEF) and a linear quadratic Gaussian(LQG) control scheme. We present the simulation results of this control method. The simulation results show us that our Kalman filtering approach is one of prospective methods in controlling the flexible arms.

• International Journal of Control, Automation, and Systems
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• v.5 no.5
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• pp.501-507
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• 2007

This paper presents a new algorithm for the closed-loop $H_{\infty}$ control of a class of singularly perturbed nonlinear systems with an exogenous disturbance, using the successive Galerkin approximation (SGA). The singularly perturbed nonlinear system is decomposed into two subsystems of a slow-time scale and a fast-time scale in the spirit of the general theory of singular perturbation. Two $H_{\infty}$ control laws are obtained to each subsystem by using the SGA method. The composite control law that consists of two $H_{\infty}$ control laws of each subsystem is designed. One of the purposes of this paper is to design the closed-loop $H_{\infty}$ composite control law for the singularly perturbed nonlinear systems via the SGA method. The other is to reduce the computational complexity when the SGA method is applied to the high order systems.

• Journal of electromagnetic engineering and science
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• v.7 no.3
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• pp.109-115
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• 2007

The performances of M-ary PSK(MPSK) systems using L-branch maximum ratio combining(MRC) diversity reception in frequency-nonselective slow Rician fading channels are derived theoretically. Especially we investigate the effect of number of symbols on the difference between the approximation to bit error probability and the exact bit error rate(BER) in evaluating the performance of MPSK signals through numerical analyses. On the other hand, when M-ary DPSK(MDPSK) signals experience the Rician fading channels, the general formula for evaluating BER of MDPSK signals in the independent branch diversity system is presented using the integral-form expressions.