• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.871-874
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• 1998

It is most important in small signal stability analysis of large scale power systems to compute only the dominant eigenvalues selectively with numerical stability and efficiency. Hessenberg process is numerically very stable and identifies the largest eigenvalues in magnitude. Hence, transformed system matrix must be used with the process. Inverse transformation with complex shift provides high selectivity centered on the shift, but does not possess the desired property of computing the dominant mode first. Thus, advantage of high selectivity of the transformation can be fully utilized only when the complex shift is given close to the dominant eigenvalues. In this paper, complex shift is determined by Fourier transforming the results of dynamic simulation with PTI's PSS/E transient simulation program. The convergence in Hessenberg process is accelerated using the iterative scheme. Overall, a numerically stable and very efficient small signal stability program is obtained. The stability and efficiency of the program has been validated against New England 10-machines 39-bus system and KEPCO system.

• Journal of the Korean Society of Industry Convergence
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• v.27 no.1
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• pp.161-172
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• 2024

Approximately 89% of all capsizing accidents involve small vessels, and despite their relatively high accident rates, small vessels are not subject to ship stability regulations. Small vessels, where the provision of essential basic design documents for stability calculations is omitted, face challenges in directly calculating their stability. In this study, considering that the majority of domestic coastal small vessels are of the Chine-type design, the goal is to establish the major hull form characteristic data of vessels, which can be identified from design documents such as the general arrangement drawing, as input data. Through the application of a deep learning approach, specifically a multilayer neural network structure, we aim to infer hydrostatic curves, operational draft ranges, and more. The ultimate goal is to confirm the possibility of directly calculating the initial stability of small vessels.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.73-73
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• 2010

Various organic- and bio-conjugated nanoparticles have been studied extensively for biological applications in medical diagnoses and drug delivery systems. Gold nanoparticles (AuNP) and poly(ethylene glycol) (PEG) are known biocompatible materials to be used in vivo and are becoming increasingly important in biomedical applications. In this work, we investigated the stability of PEG-conjugated AuNPs, dialysis and centrifuge effects after synthesis or pegylation of AuNPs as a function of elapsed time by using ToF-SIMS imaging technique along with dynamic light scattering (DLS), UV-visible absorption spectroscopic and statistical analyses. Roughly 15-nm-sized AuNPs were synthesized in a citrate-conjugated form, and then converted into the thiol-terminated PEG (O-[2-(3-Mercaptopropionylamino)ethyl]-O'-methylpolyethyleneglycol, M.W.=5 kDa) form. Based on our data, we will show that ToF-SIMS imaging analysis along with DLS, UV-visible absorption and statistical analyses would be a useful method to evaluate stability of PEG-conjugated AuNPs in various environmental conditions.

• Journal of Institute of Convergence Technology
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• v.3 no.2
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• pp.23-29
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• 2013

When a human operator interacts with a virtual wall that is modeled as a virtual spring model, the lager the stiffness of the virtual spring is, the more realistic the operator feels that the virtual wall is. In the previous studies, it is shown that the maximum available stiffness of a virtual spring to guarantee the stability can be increased when the first-order-hold method is applied, however the effects of a human impedance on the stability are not considered. This paper presents the effects of a human impedance on stability of haptic system with a virtual spring and a first-order-hold (FOH) method. The human impedance model is modeled as a linear second-order system model. The relations between the maximum available stiffness of a virtual spring and the human impedance such as a mass, a damping and a stiffness are analyzed through the MATLAB simulation. It is shown that the maximum available stiffness is proportional to the square root of the human mass or damping respectively.

• The Journal of Korea Robotics Society
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• v.19 no.1
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• pp.31-38
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• 2024

A mobile manipulator is capable of handling a wide range of workspaces by overcoming the limitations of mobility inherent in existing fixed-base manipulators. To simulate the mobile manipulator, two contact operations should be considered in the physics engines. One of these operations is the grasp stability between the gripper and the object, while the other involves the contact between the wheels of the mobile robot and the ground during driving. However, it is still difficult to choose an appropriate physics engine for simulating these contact operations of the mobile manipulator. In this paper, the performance of physics engines for simulating the mobile manipulator is evaluated. Firstly, the grasp stability of the physics engine is quantitatively evaluated based on the contact force discontinuity. Secondly, when the mobile robot is controlled by open or closed-loop control methods, differences in the path taken by the mobile robot depending on the physics engine are analyzed. To assess the performance of robot simulation, three dynamic simulators-MuJoCo, CoppeliaSim, and IsaacSim-are used along with five physics engines: MuJoCo, Newton, ODE, Bullet, and PhysX.

• The Pure and Applied Mathematics
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• v.11 no.4
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• pp.293-308
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• 2004

Let K be a nonempty convex subset of an arbitrary Banach space X and $T\;:\;K\;{\rightarrow}\;K$ be a uniformly continuous strictly hemi-contractive operator with bounded range. We prove that certain Ishikawa iteration scheme with errors both converges strongly to a unique fixed point of T and is almost T-stable on K. We also establish similar convergence and almost stability results for strictly hemi-contractive operator $T\;:\;K\;{\rightarrow}\;K$, where K is a nonempty convex subset of arbitrary uniformly smooth Banach space X. The convergence results presented in this paper extend, improve and unify the corresponding results in Chang [1], Chang, Cho, Lee & Kang [2], Chidume [3, 4, 5, 6, 7, 8], Chidume & Osilike [9, 10, 11, 12], Liu [19], Schu [25], Tan & Xu [26], Xu [28], Zhou [29], Zhou & Jia [30] and others.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.30B no.3
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• pp.10-21
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• 1993

Bilinear models are attractive for adaptive filtering applications because they can approximate a large class of nonlinear systems adequately, and usually with considerable parsimony in the number of coefficients compared with Volterra models. But bilinear filters have stability problem because they involve nonlinear feedback. Adaptive algorithms for bilinear filters may be diverge and have poor convergence characteristics when input signal is large In this paper, necessary and sufficient condition for mean square stability of bilinear filters for given input signal statistics is briefly described, and the method obtaining the input bound to guarantee the stability of bilinear filters is presented. New RPEM algorithm, which does not diverge and has the superior convergence characteristics compared with the conventional RPEM algorithm when input signal is large, is derived by applying the time-varying Kalman filtering concept to the conventional RPEM algorithm.

• Journal of Microbiology and Biotechnology
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• v.29 no.7
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• pp.1078-1082
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• 2019

Poly-${\gamma}$-glutamate (${\gamma}$-PGA) has various applications due to its desirable characteristics in terms of safety and biodegradability. Previous studies have been conducted on ${\gamma}$-PGA hydrogels produced by ${\gamma}$-ray irradiation, but these hydrogels have proved unstable in solutions. This study was conducted to enable the ${\gamma}$-PGA hydrogel to maintain a stable form in solutions. The ${\gamma}$-PGA mixture for UV-irradiation was prepared with a cross-linker (N,N,N-trimethyl-3-[(2-methylacryloyl)amino]propan-1-aminium). Both ${\gamma}$-PGA hydrogels' characteristics, including stability in solutions, were examined. The UV-irradiated ${\gamma}$-PGA hydrogel maintained a stable form during the nine weeks of the study, but the ${\gamma}$-ray irradiated hydrogel dissolved after one week.

• Journal of Ocean Engineering and Technology
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• v.34 no.2
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• pp.55-65
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• 2020

A review of the 2nd generation of intact stability by the International Maritime Organization is performed. The main issues with the new stability criteria are reviewed. In particular, the physical background and related mathematical formulations of the pure loss of stability and parametric roll are summarized. Based on a literature review, benchmark calculation results for 17 different types of ships are discussed, and the final results are in excellent agreement with our physical expectations. Some relatively serious design problems are found in the application of the new stability criteria to sample ships built in Korea, and possible technical solutions are proposed, which have to be improved in the coming years.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1122-1133
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• 2003

Numerical characteristics of implicit upwind schemes, such as upwind ADI, line Gauss-Seidel (LGS) and point Gauss-Seidel (LU) algorithms, for Navier-Stokes equations have been investigated. Time-derivative preconditioning method was applied for efficient convergence at low Mach/Reynolds number regime as well as at large grid aspect ratios. All the algorithms were expressed in approximate factorization form and von Neumann stability analysis was performed to identify stability characteristics of the above algorithms in the presence of high grid aspect ratios. Stability analysis showed that for high aspect ratio computations, the ADI and LGS algorithms showed efficient damping effect up to moderate aspect ratio if we adopt viscous preconditioning based on min-CFL/max-VNN time-step definition. The LU algorithm, on the other hand, showed serious deterioration in stability characteristics as the grid aspect ratio increases. Computations for several practical applications also verified these results.