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Improved Stability criterion for Delay Neural Networks: High-order Matrix-valued Polynomial Approach
Yongbeom Park,Chan Park,Hyeon-Woo Na,PooGyeon Park 제어로봇시스템학회 2022 제어로봇시스템학회 국제학술대회 논문집 Vol.2022 No.11
This paper presents a stability criterion for delayed neural networks system through a high-order matrix-valued polynomial approach. The augmented generalized Lyapunov-Krasovskii functionals (LKFs) are adopted to consider cross information about the delay state of the neural networks system. To approximate the upper bound of the quadratic integral terms in derivate of LKFs, the integral inequality based on free matrices is applied. In addition, zero equation which is obtained from the time delay assumption is added to LKF to reflect more information on the delay neural networks system. Two numerical examples showed that the proposed stability criterion guarantees the larger maximum admissible time delay bounds.
Lithium-excess olivine electrode for lithium rechargeable batteries
Park, Kyu-Young,Park, Inchul,Kim, Hyungsub,Yoon, Gabin,Gwon, Hyeokjo,Cho, Yongbeom,Yun, Young Soo,Kim, Jung-Joon,Lee, Seongsu,Ahn, Docheon,Kim, Yunok,Kim, Haegyeom,Hwang, Insang,Yoon, Won-Sub,Kang, Ki The Royal Society of Chemistry 2016 ENERGY AND ENVIRONMENTAL SCIENCE Vol.9 No.9
<P>Lithium iron phosphate (LFP) has attracted tremendous attention as an electrode material for next-generation lithium-rechargeable battery systems due to the use of low-cost iron and its electrochemical stability. While the lithium diffusion in LFP, the essential property in battery operation, is relatively fast due to the one-dimensional tunnel present in the olivine crystal, the tunnel is inherently vulnerable to the presence of Fe-Li anti-site defects (Fe ions in Li ion sites), if any, that block the lithium diffusion and lead to inferior performance. Herein, we demonstrate that the kinetic issue arising from the Fe-Li defects in LFP can be completely eliminated in lithium-excess olivine LFP. The presence of an excess amount of lithium in the Fe ion sites (Li-Fe) energetically destabilizes the Fe-Li-related defects, resulting in reducing the amount of Fe defects in the tunnel. Moreover, we observe that the spinodal decomposition barrier is notably reduced in lithium-excess olivine LFP. The presence of Li-Fe and the absence of Fe-Li in lithium-excess olivine LFP additionally induce faster kinetics, resulting in an enhanced rate capability and a significantly reduced memory effect. The lithium-excess concept in the electrode crystal brings up unexpected properties for the pristine crystal and offers a novel and interesting approach to enhance the diffusivity and open up additional diffusion paths in solid-state ionic conductors.</P>
2차 적분항을 포함하는 적분 부등식을 활용한 시변 지연을 갖는 신경망의 안정성 분석
박용범(Yongbeom Park),이준희(Jun Hui Lee),류승현(Seung Hyun Ryu),박부견(PooGyeon Park) 대한전기학회 2021 대한전기학회 학술대회 논문집 Vol.2021 No.10
본 논문은 시변 지연을 가지는 신경망의 안정성에 대해 분석하였다. 2차 적분항을 포함하는 적분 부등식을 활용하여 경계 기술을 통해 안정성 기준의 보수성을 줄일 수 있음을 보였다. 적절한 Lyanpunov-Krasovskii 함수를 설정하고, zero equation들을 활용하여 덜 보수적인 안정성 영역을 얻을 수 있다. 수치적 예제를 통해 최대 지연 상한을 구하고 제안된 안정성 기준이 효과적임을 보였다.
Yongbeom Cho,Seongjae Cho,Byung-Gook Park,James S. Harris 대한전자공학회 2017 Journal of semiconductor technology and science Vol.17 No.5
Ge is on increasing demand in the advanced Si-compatible high-speed integrated circuits due to its high carrier mobilities. In particular, its hole mobility is much higher than those of other group-IV and III-V compound semiconductor materials. At the same time, Ge has the local minimum at the Γ valley, which enables the utilization for optical applications. The fact that Ge becomes a direct-bandgap semiconductor material by applying tensile strain can be a good merit in obtaining higher spontaneous radiation probability. However, engineering the electronic structure of Ge by external mechanical stress through stressors with different thermal expansion coefficients might require a complicated set of processes. Efforts were made to turn it into a direct-bandgap one by incorporating Sn. Carrier mobilities are further enhanced when Sn is substitutionally incorporated into the Ge matrix. Thus, advantageous features are expected in improving both optical and electrical performances. Furthermore, the small bandgap energy and bandgap tunability make Ge1-xSnx alloy a promising material for components making up the optical interconnect on Si platform including optical source of near-infrared wavelength. In this work, we study the electrical and optical characteristics of Ge1-xSnx alloy as a function of Sn content. To achieve this goal, ab initio calculations of energy-band structures of Ge1-xSnx with different Sn fractions have been carried out based on linearized augmented plane wave (LAPW) method with modified Becke-Johnson potential model for more accurate bandgap energy. Then, a novel coding method has been adopted for more reliable overall band structures. The minimum Sn content required for direct- and indirect-bandgap material transition of Ge1-xSnx, electrical and optical energy bandgaps to investigate the bandgap tunability, as well as effective masses, have been extracted as a function of Sn content. The transition point was found to be 6.9% and succinct reductions of effective masses of electron and hole have been confirmed.
Park Tae Sung,Tak Young Jin,Ra Youngjin,Kim Jinmi,Han Sang Hun,Kim Sang Hun,Shin YongBeom,Shin Myung-Jun,Kang Jong Ho 대한의학회 2023 Journal of Korean medical science Vol.38 No.40
Background: In Korea, tests for evaluating respiratory muscle strength are based on other countries’ clinical experience or standards, which can lead to subjective evaluations. When evaluating respiratory function based on the standards of other countries, several variables, such as the race and cultures of different countries, make it difficult to apply these standards. The purpose of this study was to propose objective respiratory muscle strength standards and predicted values for healthy Korean adults based on age, height, weight, and muscle strength, by measuring maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), and peak cough flow (PCF). Methods: This cross-sectional study analyzed MIP, MEP, and PCF in 360 people, each group comprising 30 adult men and women aged 20–70, diagnosed as healthy after undergoing medical check-ups at a general hospital. Hand grip strength (HGS) and the five times sitto-stand test (FTSST) results were also recorded. Correlations among respiratory muscle strength, participant demographics, and overall muscle strength were evaluated using Pearson’s correlation analysis. The predicted values of respiratory muscle strength were calculated using multiple regression analysis. Results: Respiratory muscle strength differed from the values reported in studies from other countries. In the entire samples, both MIP and MEP had the highest correlations with peak HGS (r = 0.643, r = 0.693; P < 0.05), while PCF had the highest correlation with forced expiratory volume in 1 s (r = 0.753; P < 0.05). Age, body mass index, peak HGS, and FTSST results were independent variables affecting respiratory muscle strength. A predictive equation for respiratory muscle strength was developed using the multiple regression equation developed in this study. Conclusion: Respiratory muscle strength index may differ by country. For more accurate diagnoses, standard values for each country are required. This study presents reference values for Korea, and a formula for estimation is proposed when no respiratory muscle strength measurement equipment is available.