• ETRI Journal
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• v.40 no.5
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• pp.570-581
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• 2018

This work analyzes the performance of implementable detectors for the multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) technique under specific and realistic operation system conditions, including antenna correlation and array configuration. A time-domain channel model was used to evaluate the system performance under realistic communication channel and system scenarios, including different channel correlation, modulation order, and antenna array configurations. Several MIMO-OFDM detectors were analyzed for the purpose of achieving high performance combined with high capacity systems and manageable computational complexity. Numerical Monte Carlo simulations demonstrate the channel selectivity effect, while the impact of the number of antennas, adoption of linear against heuristic-based detection schemes, and the spatial correlation effect under linear and planar antenna arrays are analyzed in the MIMO-OFDM context.

• Structural Engineering and Mechanics
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• v.38 no.5
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• pp.651-674
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• 2011

This paper presents a novel method for predicting the failure probability of structural or mechanical systems subjected to random loads and material properties involving multiple design points. The method involves Multicut High Dimensional Model Representation (Multicut-HDMR) technique in conjunction with moving least squares to approximate the original implicit limit state/performance function with an explicit function. Depending on the order chosen sometimes truncated Cut-HDMR expansion is unable to approximate the original implicit limit state/performance function when multiple design points exist on the limit state/performance function or when the problem domain is large. Multicut-HDMR addresses this problem by using multiple reference points to improve accuracy of the approximate limit state/performance function. Numerical examples show the accuracy and efficiency of the proposed approach in estimating the failure probability.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.5
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• pp.511-520
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• 1999

An anti-reset windup (ARW) based compensation method for state constrained control systems is studied. First, a linear controller is constructed to give a desirable nominal performance ignoring state-constraints of a plant. Then, an additional compensator is introduced to provide smooth performance degradation under state-constraints of the plant. This paper focuses on the effective design method of the additional compensator. By minimizing a reasonable performance index, the proposed compensator is expressed in terms of theplant and ocntroller parameters. The resulting dynamics of the compensated controller exhibits the dominant part of the linear closed-loop system which can be seen from the singular perturbation model reducton theory. THe proposed method guarantees total stability of overall resulting systems if linear controllers were constructed to meet certain condition.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.269-269
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• 2000

This paper presents a predictive control with H$_{\infty}$ suboptimal performance which is robust to disturbances and has a guaranteed stability. In order to derive the control law conveniently, state-space based approach, where the state variable is involved explicitly in the controller design and implementation is allowed. So an input-output model is converted to an equivalent observable canonical state-space form. The suggested control guarantees the norm bounded system output values from disturbances. A systematic way using the LMI method is presented to obtain appropriate parameters for Quadratic stability condition and optimization problem.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.705-707
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• 2004

In this paper, we propose a robust control technique against parameter uncertainties as well as external disturbances. It is robust control scheme using discrete-time state space disturbance observer. It does not require disturbance modeling, plant inverse modeling and/or Q filter. In frequency domain, its performance is evaluated in terms of sensitivity and complementary sensitivity as well as gain and phase margin. Finally we discuss design criterion of state space disturbance observer considering its performance in frequency domain.

• 제어로봇시스템학회:학술대회논문집
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• 1986.10a
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• pp.321-325
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• 1986

A new control scheme for the state space model of the robot system using the theory of optimal multi-variable structure is presented in this paper. It is proposed to optimize multi-dimensional variable structure systems for obtaining the required stabilizing signal by minimizing a performance index with respect to the state vector in the sliding mode. It is concluded the proposed variable structure controller yields better system dynamic performance than that obtained by using the only linear optimal controller inthat responses for a step disturbance have a shorter setting time, no matter what overshoot values and rising time.

• Transactions of the Society of Information Storage Systems
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• v.5 no.1
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• pp.47-52
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• 2009

Most hard disk drives that apply the ramp load/unload technology unload the heads at the outer edge of the disk while the disk is rotating. The load/unload includes the benefits as like an increased areal density, a reduced power consumption and an improved shock resistance. A lot of papers investigating the effects of the various load/unload parameters such as a suspension tab, a limiter, a ramp and air-bearing surface designs have been published. However, in previous researches, an effect of the suspension is not considered at each load/unload step. In this paper, we focus that a variation of the state matrix affects the load/unload performance on based on a state matrix that is a stiffness matrix of the suspension. Because the state matrix is related to the suspension at each load/unload step, to change the state matrix means the structural change of the suspension. Therefore, we investigated a range of a pitch static attitude(PSA) and a roll static attitude(RSA) for load/unload performance. We also analyzed an effect of the variation of the state matrix a range of load/unload velocity occurred a slider-disk contact. We determined the variation of the state matrix to improve the load/unload performance through comparison of each factor of state matrix.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.6
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• pp.409-416
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• 2020

The research has been conducted to explore the combination of three intangible resources, including social capital, entrepreneurship, and resilience capability on the performance of State Capital Enterprises (SCEs) in Vietnam. Both qualitative and quantitative approaches are applied in the study. An in-depth interview of ten CEOs at SCEs in Vietnam was made to explore new indicators for the contextual latent variables in the research models. By employing the data from the authors' survey of 568 SCEs in Vietnam in 2019, using Cronbach's alpha, confirmatory factor analysis (CFA) and path analysis (SEM), the mechanism that social capital impacts on SCE performance has been analyzed. In addition to the direct role, social capital indirectly affects corporate performance through entrepreneurship and resilience capability. It was found that social capital has a larger impact on entrepreneurship than resilience capacity. However, the contribution of resilience capacity to the firm performance is much more than the entrepreneurship's in Vietnamese context. This study enriches the theory by proposing a measurement scale of the contextual latent variables as a result of in-depth interviews with experts using a qualitative analysis technique. In addition, the path analysis findings suggest practical implications for managers to effectively use their resources in SCEs.

• The Journal of Industrial Distribution & Business
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• v.10 no.7
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• pp.7-16
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• 2019

Purpose - Economic globalization provides firms with a new channel to gain benefits from foreign countries. Therefore, using the real MNEs, this paper set China's firms as an example to explore the relationship between multinationality and performance. Research design, data, and methodology - Panel data from 2008 to 2017 was used and 390 multinational firms listed in China's A-share market was selected. Additionally, related econometric methods were employed to analyze the relationship between multinationality and performance in this study. The return on assets was treated as a dependent variable, and the sales of a firm, the firm age, the debt asset ratio of a firm, the ratio of foreign sales to total sales and the enterprise properties were treated as independent variables. All of these factors were used to conduct an empirical analysis. Results - The empirical findings in this study revealed that there is a linear relationship between multinationality and performance, as well as that non state-owned enterprises (non-SOEs) have a greater effect on the relationship between multinationality and performance than that of the state-owned enterprises (SOEs). Conclusions - On the basis of evidences this paper provided, China's government should take measures in the future to help China's firms when they fulfil international economic activities.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.11
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• pp.195-204
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• 2020

The aim of this study is to estimate the impact of ownership structure on the performance of listed firms in transition economy. Buiding upon agency theory, hypotheses on such relationship are proposed. A detailed panel data of 502 non-financial companies listed on Ho Chi Minh Stock Exchange and Hanoi Stock Exchange over the period from 2013 to 2018, and the system generalized method of moment estimation are employed to test the proposed hypotheses. To ensure the reliability of data, this study excludes companies that violate information disclosure regulations or that are subject to special supervision by the State Securities Commission of Vietnam. Some firms with inadequate information, firms that lack the financial data required for creating variable or firms that have inconsistent construction are also re-screened. We only collect the data of enterprises that have ownership structure of two or more components. Estimation results reveal that state ownership has an U-shaped relationship with the performance of Vietnamese listed firms, while foreign ownership and the degree of ownership concentration have an inverted U-shaped relationship with listed firms' performance. The article provides governance implications that Vietnamese listed firms should decrease state ownership and foreign ownership to improve firm performance in order to boost investors' confidence.