• Journal of the Chungcheong Mathematical Society
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• v.25 no.2
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• pp.201-215
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• 2012

In this paper, we prove the stability in random normed spaces via fixed point method for the functional equation $f(x+y+z+w)\;+\;2f(x)\;+\;2f(y)\;+\;2f(z)\;+\;2f(w)\;-\;f(x+y)\;-\;f(x+z)\;-\;f(x+w)\;-\;f(y+z)\;-\;f(y+w)\;-\;f(z+w)=0$.

• Journal of the Chungcheong Mathematical Society
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• v.25 no.1
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• pp.51-63
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• 2012

In this paper, we prove the stability in random normed spaces via fixed point method for the functional equation $$f(2x+y)+f(2x-y)+2f(x)-f(x+y)-f(x-y)-2f(2x)=0$$.

• Journal of the Korean Mathematical Society
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• v.49 no.4
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• pp.843-854
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• 2012

In this paper, the iterative Uzawa method with a modified Lagrangian functional is investigated to seek a saddle point for the semicoercive variational Signorini inequality.

• The Pure and Applied Mathematics
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• v.26 no.1
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• pp.49-58
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• 2019

In this paper, I prove the stability problem for a quadratic-cubic functional equation $$f(x+ky)-k^2f(x+y)-k^2f(x-y)+f(x-ky)+f(kx)-{\frac{k^3-3k^2+4}{2}}f(x)+{\frac{k^3-k^2}{2}}f(-x)=0$$ in modular spaces by applying the direct method.

• Honam Mathematical Journal
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• v.41 no.2
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• pp.391-402
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• 2019

In this paper, I prove the stability of the following set-valued functional equation $$f(x+2y){\oplus}f(x-2y){\oplus}3f(2x){\oplus}f(-2x)\\{\hspace{100}}=4f(x+y){\oplus}4f(x-y){\oplus}10f(x)$$ by employing the direct method in the sense of Hyers and Ulam.

• Nonlinear Functional Analysis and Applications
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• v.28 no.1
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• pp.95-105
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• 2023

In the present paper, we introduce a new system of functional equations, known as orthogonal Pexider hom-derivation and Pexider hom-Pexider derivation (briefly, (Pexider) hom-derivation). Using the fixed point method, we investigate the stability of Pexider hom-derivations and (Pexider) hom-derivations on Banach algebras.

• Journal of Food Hygiene and Safety
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• v.30 no.2
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• pp.173-177
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• 2015

Rosa canina L. is health functional food materials that can help to temporarily relieve symptoms of arthritis. This study has been conducted to develop and validate analytical methods for hyperoside of Rosa canina L.. Methods based on HPLC with ultraviolet detection (UVD) were established through instrumental analytical conditions, and the examination of data, such as domestic and foreign reliable methods and journals. HPLC UVD analysis using Capcell Pak $C_{18}$ MG II column at 353 nm was determined on test through the column, mobile phase. The validation has been performed on the method to determine linearity, accuracy, limits of quantification (LOQ) and repeatability for hyperoside. The method showed high linearity in the calibration curve at a coefficient of correlation ($R^2$) of 0.999, and the LOQ was $0.393{\mu}g/mL$. Relative standard deviation (RSD) values of data from repeatability precision was between 0.6 and 2.6%. Recovery rate test at hyperoside scored between 98 and 99%. These results indicate that the established HPLC method is very useful for the determination of hyperoside in Rosa canina L. to develop a health functional material.

• Proceedings of the Korean Vacuum Society Conference
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• 2009.08a
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• pp.123-123
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• 2009

• Korean Journal of Mathematics
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• v.20 no.1
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• pp.77-89
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• 2012

Using fixed point method, we prove the Hyers-Ulam stability of the orthogonally additive functional equation (0.1) $f(2x+y)=2f(x)+f(y)$ and of the orthogonally quadratic functional equation (0.2) $2f(\frac{x}{2}+y)+2f(\frac{x}{2}-y)=f(x)+4f(y)$ for all $x$, $y$ with $x{\perp}y$ in orthogonality spaces.

• Korean Journal of Mathematics
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• v.30 no.2
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• pp.403-412
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• 2022

In this paper, we introduce the following cubic-quartic functional equation of the form $$f(x+4y)+f(x-4y)=16[f(x+y)+f(x-y)]{\pm}30f(-x)+\frac{5}{2}[f(4y)-64f(y)]$$. Further, we investigate the general solution and the Ulam stability for the above functional equation in non-Archimedean spaces by using the direct method.