• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.33-41
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• 2008

This paper is an extension of previous study[9] on a development of a divergence-free element method using a hermite interpolated stream function. Divergence-free velocity bases defined on rectangles derived herein produce pointwise divergence-free flow fields. Hence the explicit imposition of continuity constraint is not necessary and the Galerkin finite element formulation for velocities does not involve the pressure. The divergence-free element of the previous study employed hermite serendipity cubic for interpolation of stream function, and it has been noted a possible discontinuity in variables along element interfaces. This deficiency can be removed by use of a hermite bicubic interpolated stream function, which requires at each element corners four degrees-of-freedom such as the unknown variable, its x- and y-derivatives and its cross derivative. Detailed derivations are presented for both solenoidal and irrotational bases from the hermite bicubic interpolated stream function. Numerical tests are performed on the lid-driven cavity flow, and results are compared with those from hermite serendipity cubics and a stabilized finite element method by Illinca et al[7].

• Journal of Drive and Control
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• v.19 no.1
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• pp.51-61
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• 2022

This paper presents a model-free system based on a framework of a backstepping sliding mode control (BSMC) with a radial basis function neural network (RBFNN) and adaptive mechanism for electro-hydraulic systems (EHSs). First, an EHS mathematical model was dedicatedly derived to understand the system behavior. Based on the system structure, BSMC was employed to satisfy the output performance. Due to the highly nonlinear characteristics and the presence of parametric uncertainties, a model-free approximator based on an RBFNN was developed to compensate for the EHS dynamics, thus addressing the difficulty in the requirement of system information. Adaptive laws based on the actor-critic neural network (ACNN) were implemented to suppress the existing error in the approximation and satisfy system qualification. The stability of the closed-loop system was theoretically proven by the Lyapunov function. To evaluate the effectiveness of the proposed algorithm, proportional-integrated-derivative (PID) and improved PID with ACNN (ACPID), which are considered two complete model-free methods, and adaptive backstepping sliding mode control, considered an ideal model-based method with the same adaptive laws, were used as two benchmark control strategies in a comparative simulation. The simulated results validated the superiority of the proposed algorithm in achieving nearly the same performance as the ideal adaptive BSMC.

• Journal of Photoscience
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• v.9 no.2
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• pp.174-177
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• 2002

Sugar-linked porphyrin and chlorin compounds have been synthesized. Phototoxicity of these compounds against the HeLa cell line was also examined. For the porphyrin derivatives, the higher activity was observed for a derivative having four OH-protected sugar moieties. For the chlorin derivatives, OH-unprotected free-base derivatives were generally effective. Singlet oxygen producing ability were examined to evaluate the activity on photodynamic therapy of the compounds.

• Environmental Analysis Health and Toxicology
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• v.5 no.1_2
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• pp.45-50
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• 1990

In order to investigate the phototoxicity of five phenothiazine derivatives and one thioxanthen derivative were examined by using in vitro method based on growth inhibition of Candida albicans and red blood cell hemolysis. Effects of the test compounds on RBCs were monitored with a spectrophotometer and a drug PI in the Candida albicans was calculated on the basis of the lowest concentration giving a yeast-free zone. All phenothiazines phototoxic in the red blood cell hemolysis method were positive in the yeast test except promethazine. It was also observed that toxic photo-products were formed by perphenazine and chlorpromazine in the red blood cell hemolysis.

• Journal of applied mathematics & informatics
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• v.16 no.1_2
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• pp.125-142
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• 2004

We analyze the convergence properties of Powell's UOBYQA method. A distinguished feature of the method is its use of two trust region radii. We first study the convergence of the method when the objective function is quadratic. We then prove that it is globally convergent for general objective functions when the second trust region radius p converges to zero. This gives a justification for the use of p as a stopping criterion. Finally, we show that a variant of this method is superlinearly convergent when the objective function is strictly convex at the solution.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2001.10a
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• pp.241-242
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• 2001

Chitosan, a deacetylated derivative of chitin, is one of the abundant resources, and its biological properties such as antibactierial activity, hypocholesterolemic activity, and hypertensive action are remarked. However, increasing attention has recently been yen to converting chitosan to its oligosaccharides because they possess various functional properties like antitumor activity, immune-enhancing effects, enhancing protective effects against infection with some pathogens in mice, antifungal activity, and antimicrobial activity (Jeon et al., 2001). (omitted)

• YAKHAK HOEJI
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• v.43 no.4
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• pp.442-446
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• 1999

The synthesis and antimicrobial activity of N-substituted glycyl derivatives of Norfloxacin were described. Norfloxacin was treated with chloroacetyl chloride to yield chloroacetyl norfloxacin (1). This compounds was treated with alkylamines to obtain quinolone carboxylic acids (2-6), which were reacted with pivaloyloxymethyl chloride to get pivaloyloxymethyl quinolone carboxylates (7-11). Free carboxylic quinolones (2-6) showed little stronger activities to their pivaloyloxymethyl esters (7-11). In quinolone analogues, longer alkyl chain compounds showed stronger activities than shorter one.

• Journal of Ocean Engineering and Technology
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• v.14 no.1
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• pp.1-5
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• 2000

A numerical analysis for wave motion in the shallow water is presented. The method is based on potential theory. The fully nonlinear free surface boundary condition is assumed in an inner domain and this solution is matched along an assumed common boundary to a linear solution in outer domain. In two-dimensional problem Cauchy's integral theorem is applied to calculate the complex potential and its time derivative along boundary.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.341-344
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• 1999

We reported compositional separation(CS) into Co-enriched and Cri-enriched components inside the grains of Co-Cr based thin films prepared by rf sputtering. CS strongly depends on the sputtering conditions of substrate temperature and target composition. Tuning the microstructure of the Co-Cr films is important in order to employ the CS for high-density magnetic recording. We investigated the origin of CS from thermodynamic viewpoint. We employ a spinodal decomposition-like model to describe the origin of the CS in Co-Cr films. We consider the total free energy of the Co-Cr films as the sum of several free energies of; 1) thermodynamic mixing entropy of a binary solid solution, 2) magnetic ordering interaction(MOI) energy below the Curie temperature, and 3) excess interaction energy(XS) caused by the sputtering process as a function of temperature and composition. Those energies distorted the total free energy like the spinodal decomposition and caused the compositionally separated fine microstructure inside the grains. If the second derivative of the total free energy with respect to Cr composition becomes negative at a given substrate temperature, we may observe a metastable compositional separation inside the Co-Cr alloy films. We expect to exploit the microstructure of CS for ultra-high density magnetic recording.

• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1094-1097
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• 1999

This paper presents a new PID control scheme based on the feedback of averaged derivatives to realize a noise-free differential control. The PID(Proportional, Integral and Differential) control is still one of the control methods in most wide use. In the paper, the conventional PID control adopting filtering technique is analyzed with new interpretation of filtering function. In order to overcome the drawbacks of the conventional PID control, this paper introduces the feedback of averaged derivatives in the noisy environment, and suggests a new PID control scheme using delay components to realize a noise-free differential control. The proposed PID control yields good performance much similar to the original system response in case of no noises. The proposed control scheme has been tested for the load frequency control of power systems.