• International Journal of Control, Automation, and Systems
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• v.1 no.4
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• pp.520-526
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• 2003

In the case of a strapdown inertial navigation system (SDINS) with sizeable attitude errors, the uncertainty caused by linearization of the system degrades the performance of the filter. In this paper, a robust filter and various error models for the uncertainty are presented. The analytical characteristics of the proposed filter are also investigated. The results show that the filter does not require the statistical property of the system disturbance and that the region of the estimation error depends on a freedom parameter in the worst case. Then, the uncertainty of the SDINS is derived. Depending on the choice of the reference frame and the attitude error state, several error models are presented. Finally, various in-flight alignment methods are proposed by combining the robust filter with the error models. Simulation results demonstrate that the proposed filter effectively improves the performance.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.1167-1172
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• 1990

This paper discusses a force distribution scheme which minimizes the weighted norm of the forces/torques applied on weak points of cooperating multiple robot arms. The scheme is proposed to avoid the damage or unwanted motion of any weak point of robots or object stemming from excessive forces/torques. Since the proposed scheme can be used for either the joint torque minimization or the exerted force minimization on the object, it can be regarded as a unified force minimization method for multiple robot arms. The computational complexity in this scheme is analyzed using the properties of Jarcobian. Simulation of two identical PUMA robots held an object is carried out to illustrate the proposed scheme. By the proper choice of the weighting matrix in the performance index, we show that force minimization for a weak point can be achieved, and that the exerted force minimization on the object can be changed to the joint torque minimization.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.3
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• pp.231-235
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• 2008

Thyristor rectifiers are still the preferred choice for large magnet power supplies. However, large harmonic voltages, resulting in large current ripple, and slow dynamic response are major drawbacks of these converters. Joos presented a topology and a control technique for a hybrid large-power high-precision magnet power supply in 1996. The system consists of a phase controlled rectifier (PCR) connected in series with a high-frequency PWM converter. This paper improves the power circuit of the PWM converter using interphase transformer. Simulation result proves effect of the proposed system.

• Journal of Korean Institute of Industrial Engineers
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• v.34 no.3
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• pp.355-361
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• 2008

Technology developers in academia tend to be short of professional knowledge and recognition of technology transfer strategies. It is even severe in Korea where the concept of employee's invention has just started to effect in academia. Wasteful contract negotiation disputes cannot only be painful but also can hamper better invention. The main purpose of this paper is to design guidelines for an optimal contract strategy for technology transfer from the perspective of the technology developer in academia, the intermediary and the receiver. Applying conjoint analysis, this study shows not only the relative importance of the attributes related to the technology transfer contract but also the most important conditions of the contract. It is expected that this study may improve the efficiency of technology transfer activities in academia in Korea.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.254-258
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• 2014

This paper presents the performance analysis results of a short line fault interruption of a gas circuit breaker, particularly a self-blast type breaker. Hot gas flow analysis was carried out using a CFD calculation combined with the arc model and nozzle ablation model. To evaluate the interruption performance, the index function was defined using the pressure in the heating chamber and the density above the arc region. The simulation and test results showed that the gas flow field and suitable choice of an interruption performance index can be used to predict the interruption characteristics and provide guidelines for designing self-blast breakers with a higher interruption capability.

• Environmental and Resource Economics Review
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• v.10 no.4
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• pp.515-545
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• 2001

This paper introduces the least absolute deviations estimation of the contingent valuation model, which corresponds to the semi-parametric estimation of discrete choice models by Manski (1975, 1985) and Lee (1992). The least absolute deviations estimation is more robust to mis-specified distributional assumptions in the estimation of the contingent valuation model, compared to the maximum likelihood estimation. The full identification and strong consistency of the estimation are proved and its application to different formats of contingent valuation survey data is discussed. Simulation studies are designed to evaluate its operational characteristics including computational strategies, small sample properties and the efficiency gain of a follow-up question. The bias and efficiency of least absolute deviations and maximum likelihood estimation are compared in the presence of heteroskedasticity.

• Communications for Statistical Applications and Methods
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• v.21 no.2
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• pp.115-124
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• 2014

In this paper we derive a Berry-Esseen type bound for the kernel density estimator of a random left truncated model, in which each datum (Y) is randomly left truncated and is sampled if $Y{\geq}T$, where T is the truncation random variable with an unknown distribution. This unknown distribution is estimated with the Lynden-Bell estimator. In particular the normal approximation rate, by choice of the bandwidth, is shown to be close to $n^{-1/6}$ modulo logarithmic term. We have also investigated this normal approximation rate via a simulation study.

• Journal of the Korean Statistical Society
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• v.27 no.1
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• pp.25-55
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• 1998

Maximum likelihood estimates (MLEs) for recursive models of categorical variables are discussed under an EM framework. Since MLEs by EM often depend on the choice of the initial values for MLEs, we explore reasonable rules for selecting the initial values for EM. Simulation results strongly support the proposed rules.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.4
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• pp.989-1005
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• 2012

In this paper, throughput of IEEE 802.11 carrier-sense multiple access (CSMA) with collision-avoidance (CA) protocols in non-saturated traffic conditions is presented taking into account the impact of imperfect channel sensing. The imperfect channel sensing includes both missed-detection and false alarm and their impact on the utilization of IEEE 802.11 analyzed and expressed as a closed form. To include the imperfect channel sensing at the physical layer, we modified the state transition probabilities of well-known two state Markov process model. Simulation results closely match the theoretical expressions confirming the effectiveness of the proposed model. Based on both theoretical and simulated results, the choice of the best probability detection while maintaining probability of false alarm is less than 0.5 is a key factor for maximizing utilization of IEEE 802.11.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.6
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• pp.1901-1913
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• 2014

The IEEE 802.15.6 is a communication standard for Wireless Body Area Networks (WBANs). This standard includes a prioritized slotted Aloha as a choice for medium access control. This protocol is different from the traditional version as it has integral considerations for certain priorities of users. It attempts to resolve collision by halving the probability of retransmission, lower bounded by to a minimum, in the alternate slots to follow. In this paper, we present an analytical model to compute the non-saturated throughput of this protocol in the presence of finite number of nodes. The model is validated against simulation.