• 대한수학회보
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• 제53권6호
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• pp.1741-1751
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• 2016

We prove the boundary Harnack principle and the Carleson type estimate for ratios of solutions u/v of non-divergence second order elliptic equations $Lu=a_{ij}D_{ij}+b_iD_iu=0$ in a bounded domain ${\Omega}{\subset}R_n$. We assume that $b_i{\in}L^n({\Omega})$ and ${\Omega}$ is a $H{\ddot{o}}lder$ domain of order ${\alpha}{\in}$ (0, 1) satisfying a strong regularity condition.

• 대한수학회지
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• 제57권2호
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• pp.313-329
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• 2020

In this paper, we derive various differential Harnack estimates for positive solutions to the nonlinear backward heat type equations on closed manifolds coupled with the Ricci-Bourguignon flow, which was done for the Ricci flow by J.-Y. Wu [30]. The proof follows exactly the one given by X.-D. Cao [4] for the linear backward heat type equations coupled with the Ricci flow.

• Kyungpook Mathematical Journal
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• 제61권3호
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• pp.631-644
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• 2021

In the present paper, we obtain gradient estimates for positive solutions to the following nonlinear parabolic equation under general geometric flow on complete noncompact manifolds $$\frac{{\partial}u}{{\partial}t}={\Delta}u+a(x,t)u^p+b(x,t)u^q$$ where, 0 < p, q < 1 are real constants and a(x, t) and b(x, t) are functions which are C² in the x-variable and C¹ in the t-variable. We shall get an interesting Harnack inequality as an application.

• 대한수학회보
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• 제58권4호
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• pp.909-914
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• 2021

In this short note we prove new differential Harnack inequalities interpolating those for the static surface and for the Ricci flow. In particular, for 0 ≤ 𝜀 ≤ 1, α ≥ 0, 𝛽 ≥ 0, 𝛾 ≤ 1 and u being a positive solution to $${\frac{{\partial}u}{{\partial}t}}={\Delta}u-{\alpha}u\;{\log}\;u+{\varepsilon}Ru+{\beta}u^{\gamma}$$ on closed surfaces under the flow ${\frac{\partial}{{\partial}t}}g_{ij}=-{\varepsilon}Rg_{ij}$ with R > 0, we prove that $${\frac{\partial}{{\partial}t}}{\log}\;u-{\mid}{\nabla}\;{\log}\;u{\mid}^2+{\alpha}\;{\log}\;u-{\beta}u^{{\gamma}-1}+\frac{1}{t}={\Delta}\;{\log}\;u+{\varepsilon}R+{\frac{1}{t}{}\geq}0$$.