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Local edge detectors using a sigmoidal transformation for piecewise smooth data
Yun, B.I.,Rim, K.S. Pergamon Press ; Elsevier Science Ltd 2013 APPLIED MATHEMATICS LETTERS Vol.26 No.2
For piecewise smooth data, edges can be recognized by jump discontinuities in the data. Successful edge detection is essential in digital signal processing as the most relevant information is often observed near the edges in each segmented region. In this paper, using the concentration property of existing local edge detectors and the clustering property of sigmoidal transformations, we provide enhanced edge detectors which diminish the oscillations of the local detector near jump discontinuities as well as highly improve rate of convergence away from the discontinuities. Numerical results of some examples illustrate efficiency of the presented method.
Iterative methods for solving nonlinear equations with finitely many roots in an interval
Koninklijke Vlaamse Ingenieursvereniging ; Elsevie 2012 Journal of computational and applied mathematics Vol.236 No.13
In this paper we consider a nonlinear equation f(x)=0 having finitely many roots in a bounded interval. Based on the so-called numerical integration method [B.I. Yun, A non-iterative method for solving non-linear equations, Appl. Math. Comput. 198 (2008) 691-699] without any initial guess, we propose iterative methods to obtain all the roots of the nonlinear equation. In the result, an algorithm to find all of the simple roots and multiple ones as well as the extrema of f(x) is developed. Moreover, criteria for distinguishing zeros and extrema are included in the algorithm. Availability of the proposed method is demonstrated by some numerical examples.
On a general transformation of multipoint root-solvers
Yun, B.I.,Petkovic, M.,Dzunic, J. Koninklijke Vlaamse Ingenieursvereniging ; Elsevie 2016 Journal of computational and applied mathematics Vol.292 No.-
<P>Optimal multipoint methods for solving nonlinear equations of arbitrary order of convergence are investigated. A low cost transformation that converts Newton-preconditioned methods into a derivative free variant is presented. This transforming procedure preserves both algorithm body structure and order of convergence of the original scheme. Another useful application of the proposed transformation is the acceleration of convergence order of non-optimal methods. (C) 2015 Elsevier B.V. All rights reserved.</P>
New higher order methods for solving nonlinear equations with multiple roots
Koninklijke Vlaamse Ingenieursvereniging ; Elsevie 2011 Journal of computational and applied mathematics Vol.235 No.5
For a nonlinear equation f(x)=0 having a multiple root we consider Steffensen's transformation, T. Using the transformation, say, F<SUB>q</SUB>(x)=T<SUP>q</SUP>f(x) for integer q>=2, repeatedly, we develop higher order iterative methods which require neither derivatives of f(x) nor the multiplicity of the root. It is proved that the convergence order of the proposed iterative method is 1+2<SUP>q-2</SUP> for any equation having a multiple root of multiplicity m>=2. The efficiency of the new method is shown by the results for some numerical examples.
Investor Sentiment and Stock Price Crash Risk: Evidence from China
Yunbi An 연세대학교 동서문제연구원 2021 Global economic review Vol.50 No.4
We study the cross-sectional effects of investor sentiment on stock price crash risk from the perspective of investor behavioural biases. We develop a firm-specific investor sentiment measure, and find that stocks with stronger investor sentiment are more prone to a future price crash. The positive relation is more pronounced for stocks eligible for margin trading, as higher investor sentiment induces greater margin buy/cover by optimistic investors. Short interest moderates the impact of optimistic sentiment on crash risk. The positive relation is also particularly prominent for stocks with a more speculative appeal, especially for those with lower institutional ownership.
Yunbi An 연세대학교 동서문제연구원 2020 Global economic review Vol.49 No.3
This paper presents a three-period dynamic model establishing the expropriation-investment relation for firms with financing constraints. Focusing on Chinese listed companies, we find that firms with less tight financing constraints overinvest before expropriation if the intended expropriation level is below a threshold, and underinvest if otherwise, while expropriation in these firms does not impact inefficient investment during and after expropriation even after relevant sanctions are imposed. We also find that expropriation in firms with tight financing constraints has no significant impacts on inefficient investment before expropriation, but further tightens firms’ financing constraints during and after expropriation, leading to underinvestment.
Fangzhao Zhou,Yajing Fu,Yunbi An,Jun Yang 연세대학교 동서문제연구원 2019 Global economic review Vol.48 No.1
This paper investigates the impacts of nongovernmental stake, ownership balance, and nonexecutive directors on bank performance and risk taking in city commercial banks (CCBs) in China. We find that ownership balance can improve CCBs’ financial performance and reduce their bankruptcy risk as well as nonperforming loan level. Nonexecutive directors can help reduce bankruptcy risk, but have no significant effect on performance or nonperforming loans. The impacts of ownership balance and nonexecutive directors become more prominent when the nongovernmental stake is relatively high, suggesting that mixed ownership reform can promote bank performance and risk control via these two avenues.
Kwon Dohyun,Kim Dongwon,Bae Yunbi,Choi Hyoju,Kim Bongsu,최명철,An Sangmin,Lee Manhee 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.5
A quartz tuning fork is an electromechanical resonator with self-actuating and self-sensing capabilities and is widely used as a force sensor in atomic force microscopy and spectroscopy. While the electrical response of a tuning fork is affected by the two prongs’ mechanical motion and stray capacitive current, a purely mechanical motion signal of the tuning fork is required for a quantitative analysis. Here, we demonstrate the extraction of a mechanical motion signal from the electrical signal of an electrically driven quartz tuning fork in various environments, including vacuum, air, and liquid. We show that the extraction formalism is well implemented in vacuum and air, but it does not work in liquid due to the largely enhanced damping and ions present in liquids. Furthermore, using the mechanical signal extracted from the electrical signal, we determine the interaction force exerted on the tip of the tuning fork in ambient air. The present extraction method enables versatile use of electrically driven tuning forks for force, mass, and environmental sensing, in which true mechanical motion signals should be used for accurate and quantitative analysis.