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1,535 results on '"Oh, Min-A"'

12. A delay-product-type Lyapunov functional approach for enhanced synchronization of chaotic Lur'e systems using a quantized controller

Author

Boomipalagan Kaviarasan, Ramasamy Kavikumar, Oh-Min Kwon, and Rathinasamy Sakthivel

Subjects
chaotic lur'e systems, synchronization, delay-product-type lyapunov functional, quantization, time-varying delay, Mathematics, QA1-939
Abstract

The asymptotic synchronization problem of chaotic Lur'e systems in the master-slave framework was explored in this paper. A time-varying delay feedback controller with quantization considerations and a delay-product-type Lyapunov-Krasovskii functional technique were employed to tackle this problem. Consider an error system based on master and slave systems, for which sufficient asymptotic stability requirements are developed to assure that the addressed system achieves proper synchronization. Following that, the desired control gain was determined by finding a feasible solution to these stability requirements. The results of this paper were validated using a numerical example with simulations, which revealed that they were superior to previously published ones.

Published
2024
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14. Special Education Representation Trends Vary by Language Status: Evidence of Underrepresentation in Tennessee

Author

Mancilla-Martinez, Jeannette, Oh, Min Hyun, Luk, Gigi, and Rollins, Adam

Abstract

Using state-level data, we report unadjusted and adjusted odds ratio of special education (SPED) trends in Tennessee from 2009-2019 for students in grades 3-8 by 3 language groups: native English speakers (NES), English-proficient bilinguals (EPB) and Current English learners (Current EL). We report trends across all SPED disability categories and across five prevalent disability categories (specific learning disability, specific language impairment, intellectual disability, other health impairments, and autism). The cross-sectional analytic sample included 812,783 students from 28 districts that met the SPED risk-ratio threshold set by the state. Results revealed that, compared to NES students, both EPB and Current EL students were generally less likely to receive SPED services, suggesting evidence of language status disparities in SPED representation. Furthermore, findings varied depending on whether adjustments were made to generate odds ratios, especially for higher-incidence disabilities (specific, learning disability, specific language impairment, and intellectual disability). Finally, the most severe evidence of underrepresentation was in lower-incidence disabilities (other health impairments and autism). Our results underscore the need for further examination into low rates of SPED identification among learners whose first language is not English (EPB and Current EL). We discuss the contextualized research, practice, and policy implications of our findings. [This paper will be published in "Journal of Learning Disabilities."]

Published
2023

21. Robust memory control design for semi-Markovian jump systems with cyber attacks

Author

Ramalingam Sakthivel, Palanisamy Selvaraj, Oh-Min Kwon, Seong-Gon Choi, and Rathinasamy Sakthivel

Subjects
memory control, semi-markovian jump systems, input delays, cyber attacks, Mathematics, QA1-939, Applied mathematics. Quantitative methods, T57-57.97
Abstract

This paper addressed the problem of observer-based memory state feedback control design for semi-Markovian jump systems subject to input delays and external disturbances, where the measurement output was vulnerable to randomly occurring cyber attacks. To facilitate analysis, the cyber attacks were described by a nonlinear function that meets Lipschitz continuity and the possible attack scenarios were represented by a stochastic parameter that follows the Bernoulli distribution. Based on the information from the considered system and state observer, an augmented closed loop system was constructed. Then, by using the Lyapunov stability theory, an extended Wirtinger's integral inequality and stochastic analysis, the required stability criterion was proposed in the form of linear matrix inequalities. As a result, the control and observer gain matrices were efficiently derived, ensuring the stochastic stability of closed-loop systems with $ H_\infty $ performance, regardless of cyber attacks. To demonstrate the effectiveness and theoretical value of the proposed robust memory state feedback control design, simulation results were presented.

Published
2023
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24. Revisiting the Traditional Conceptualizations of Vocabulary Knowledge as Predictors of Dual Language Learners' English Reading Achievement in a New Destination State

Author

Oh, Min Hyun, Mancilla-Martinez, Jeannette, and Hwang, Jin Kyoung

Abstract

The unprecedented growth of Spanish-English dual language learners (DLLs) in new destination states (e.g., Georgia, Indiana, South Carolina, Tennessee) calls for better understanding of the relation between their bilingual vocabulary skills and English reading achievement. The current study focused on school-age Spanish-English DLLs (N = 60) in Tennessee and explored how various vocabulary knowledge conceptualizations predict English reading comprehension achievement, controlling for English word reading skills and grade level. Vocabulary knowledge was assessed using monolingual (English-only and Spanish-only) and bilingual (conceptual and total) scoring methods. Results showed that, while DLLs performed below the national mean for English-only and Spanish-only vocabulary, they performed within the average to above-average range for bilingually scored conceptual vocabulary. More uniquely, the expressive vocabulary knowledge emerged as a robust predictor of English reading comprehension above and beyond the influence of English word reading skills. Findings suggest practical and theoretical value of bilingually driven vocabulary assessment approaches. As expected, bilingually scored vocabulary provided a more comprehensive understanding of DLLs' vocabulary knowledge by accounting for vocabulary knowledge in both Spanish and English, compared to monolingually scored vocabulary. We discuss theoretical and instructional implications, with a focus on asset-driven and scientific assessment understandings for supporting DLLs' vocabulary and reading achievement in new destination states.

Published
2023
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45. Enhancing Stability Criteria for Linear Systems with Interval Time-Varying Delays via an Augmented Lyapunov–Krasovskii Functional

Author

Dong-Hoon Lee, Yeong-Jae Kim, Seung-Hoon Lee, and Oh-Min Kwon

Subjects
augmented approaches, linear system, Lyapunov–Krasovskii functional, stability analysis, time delay, Mathematics, QA1-939
Abstract

This work investigates the stability conditions for linear systems with time-varying delays via an augmented Lyapunov–Krasovskii functional (LKF). Two types of augmented LKFs with cross terms in integrals are suggested to improve the stability conditions for interval time-varying linear systems. In this work, the compositions of the LKFs are considered to enhance the feasible region of the stability criterion for linear systems. Mathematical tools such as Wirtinger-based integral inequality (WBII), zero equalities, reciprocally convex approach, and Finsler’s lemma are utilized to solve the problem of stability criteria. Two sufficient conditions are derived to guarantee the asymptotic stability of the systems using linear matrix inequality (LMI). First, asymptotic stability criteria are induced by constructing the new augmented LKFs in Theorem 1. Then, simplified LKFs in Corollary 1 are proposed to show the effectiveness of Theorem 1. Second, asymmetric LKFs are shown to reduce the conservatism and the number of decision variables in Theorem 2. Finally, the advantages of the proposed criteria are verified by comparing maximum delay bounds in four examples. Four numerical examples show that the proposed Theorems 1 and 2 obtain less conservative results than existing outcomes. Particularly, Example 2 shows that the asymmetric LKF methods of Theorem 2 can provide larger delay bounds and fewer decision variables than Theorem 1 in some specific systems.

Published
2024
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