Diffusive logistic equation with a non-Lipschitz nonlinear boundary condition arising from coastal fishery harvesting: the resonant case
Kenichiro Umezu, For bifurcation analysis, we study the positive solution set for a semilinear elliptic equation of the logistic type, equipped with a sublinear boundary condition modeling coastal fishery harvesting., Springer
Zeitschrift für angewandte Mathematik und Physik, 2025年01月, ［査読有り］

Logistic elliptic equation with a nonlinear boundary condition arising from coastal fishery harvesting II
Kenichiro Umezu, Elsevier
Journal of Mathematical Analysis and Applications, 2024年06月, ［査読有り］

Logistic elliptic equation with a nonlinear boundary condition arising from coastal fishery harvesting
Kenichiro Umezu, Elsevier
Nonlinear Analysis: Real World Applications, 2023年04月, ［査読有り］

Uniqueness of a positive solution for the Laplace equation with indefinite superlinear boundary condition
Kenichiro Umezu, Elsevier
Journal of Differential Equations, 2023年03月, ［査読有り］

Nonnegative solutions of an indefinite sublinear Robin problem II: local and global exactness results
Uriel Kaufmann; Humberto Ramos Quoirin; Kenichiro Umezu, Springer
Israel Journal of Mathematics, 2022年04月, ［査読有り］

Uniqueness and positivity issues in a quasilinear indefinite problem
Uriel Kaufmann; Humberto Ramos Quoirin; Kenichiro Umezu, Springer
Calculus of Variations and Partial Differential Equations, 2021年08月, ［査読有り］

Uniqueness and sign properties of minimizers in a quasilinear indefinite problem
Uriel Kaufmann; Humberto Ramos Quoirin; Kenichiro Umezu, American Institute of Mathematical Sciences
Communications on Pure and Applied Analysis, 2021年06月, ［査読有り］

Nonnegative solutions of an indefinite sublinear Robin problem I: positivity, exact multiplicity, and existence of a subcontinuum
Uriel Kaufmann; Humberto Ramos Quoirin; Kenichiro Umezu, Springer
Annali di Matematica Pura ed Applicata(1923-), 2020年10月, ［査読有り］

A curve of positive solutions for an indefinite sublinear Dirichlet problem
Uriel Kaufmann; Humberto Ramos Quoirin; Kenichiro Umezu, American Institute of Mathematical Sciences
Discrete and Continuous Dynamical Systems-A, 2020年02月, ［査読有り］

Loop type subcontinua of positive solutions for indefinite concave-convex problems
Uriel Kaufmann; Humberto Ramos Quoirin; Kenichiro Umezu, De Gruyter
Advanced Nonlinear Studies, 2019年05月, ［査読有り］

An elliptic equation with an indefinite sublinear boundary condition
Humberto Ramos Quoirin; Kenichiro Umezu, De Gruyter
Advances in Nonlinear Analysis, 2019年01月, ［査読有り］

A loop type component in the non-negative solutions set of an indefinite elliptic problem
Humberto Ramos Quoirin; Kenichiro Umezu, We prove the existence of a loop type component of non-negative solutions for an indefinite elliptic equation with a homogeneous Neumann boundary condition. This result complements our previous results obtained in [12], where the existence of another loop type component was established in a different situation. Our proof combines local and global bifurcation theory, rescaling and regularizing arguments, a priori bounds, and Whyburn's topological method. A further investigation of the loop type component established in [12] is also provided., American Institute of Mathematical Sciences
Communications on Pure and Applied Analysis, 2018年05月01日, ［査読有り］

Positive solutions of an elliptic Neumann problem with a sublinear indefinite nonlinearity
Uriel Kaufmann; Humberto Ramos Quoirin; Kenichiro Umezu, Let Ω ⊂ RN (N≥ 1) be a bounded and smooth domain and a: Ω → R be a sign-changing weight satisfying ∫ ΩaOpenSPiltSPi 0. We prove the existence of a positive solution uq for the problem [Equation not available: see fulltext.]if q0OpenSPiltSPi qOpenSPiltSPi 1 , for some q0= q0(a) CloseSPigtSPi 0. In doing so, we improve the existence result previously established in Kaufmann et al. (J Differ Equ 263:4481–4502, 2017). In addition, we provide the asymptotic behavior of uq as q→ 1 -. When Ω is a ball and a is radial, we give some explicit conditions on q and a ensuring the existence of a positive solution of (Pa , q). We also obtain some properties of the set of q’s such that (Pa , q) admits a solution which is positive on Ω ¯. Finally, we present some results on nonnegative solutions having dead cores. Our approach combines bifurcation techniques, a priori bounds and the sub-supersolution method., Birkhauser Verlag AG
Nonlinear Differential Equations and Applications, 2018年04月01日, ［査読有り］

Positivity results for indefinite sublinear elliptic problems via a continuity argument
U. Kaufmann; H. Ramos Quoirin; K. Umezu, We establish a positivity property for a class of semilinear elliptic problems involving indefinite sublinear nonlinearities. Namely, we show that any nontrivial nonnegative solution is positive for a class of problems the strong maximum principle does not apply to. Our approach is based on a continuity argument combined with variational techniques, the sub and supersolutions method and some a priori bounds. Both Dirichlet and Neumann homogeneous boundary conditions are considered. As a byproduct, we deduce some existence and uniqueness results. Finally, as an application, we derive some positivity results for indefinite concave-convex type problems. (C) 2017 Elsevier Inc. All rights reserved., ACADEMIC PRESS INC ELSEVIER SCIENCE
Journal of Differential Equations, 2017年10月, ［査読有り］

An indefinite concave-convex equation under a Neumann boundary condition I
Humberto Ramos Quoirin; Kenichiro Umezu, We investigate the problem (P (lambda)) -Delta u = lambda b(x)|u| (q-2) u + a(x)|u| (p-2) u in Omega, a,u/a,n = 0 on a,Omega, where Omega is a bounded smooth domain in R (N) (N ae<yen> 2), 1 < q < 2 < p, lambda a R, and a, b a with 0 < alpha < 1. Under certain indefinite type conditions on a and b, we prove the existence of two nontrivial nonnegative solutions for small |lambda|. We then characterize the asymptotic profiles of these solutions as lambda -> 0, which in some cases implies the positivity and ordering of these solutions. In addition, this asymptotic analysis suggests the existence of a loop type component in the non-negative solutions set. We prove the existence of such a component in certain cases, via a bifurcation and a topological analysis of a regularized version of (P (lambda))., HEBREW UNIV MAGNES PRESS
Israel Journal of Mathematics, 2017年06月, ［査読有り］

An Indefinite concave-convex equation under a Neumann boundary condition II
Humberto Ramos Quoirin; Kenichiro Umezu, We proceed with the investigation of the problem
(P-lambda) -Delta u = lambda b(x)vertical bar u vertical bar(q-2)u + a(x)vertical bar u vertical bar(p-2)u in Omega, a partial derivative/partial derivative n = 0 on partial derivative Omega,
where Omega is a bounded smooth domain in R-N (N >= 2), 1 < q < 2 < p, lambda is an element of R, and a, b is an element of C-alpha(<(Omega)over bar>) with 0 < alpha < 1. Dealing now with the case b >= 0, b 0, we show the existence (and several properties) of an unbounded subcontinuum of nontrivial nonnegative solutions of (P-lambda). Our approach is based on a priori bounds, a regularisation procedure, and Whyburn's topological method., JULIUSZ SCHAUDER CTR NONLINEAR STUDIES
Topological Methods in Nonlinear Analysis, 2017年06月, ［査読有り］

On a concave-convex elliptic problem with a nonlinear boundary condition
Humberto Ramos Quoirin; Kenichiro Umezu, We investigate an indefinite superlinear elliptic equation coupled with a sublinear Neumann boundary condition (depending on a positive parameter ), which provides a concave-convex nature to the problem. We establish a global multiplicity result for positive solutions in the spirit of Ambrosetti-Brezis-Cerami and obtain their asymptotic profiles as . Furthermore, we also analyse the case where the nonlinearity is concave. Our arguments are based on a bifurcation analysis, a comparison principle, and variational techniques., SPRINGER HEIDELBERG
Annali di Matematica Pura ed Applicata (1923 -), 2016年12月, ［査読有り］

Positive steady states of an indefinite equation with a nonlinear boundary condition: existence, multiplicity, stability and asymptotic profiles
Humberto Ramos Quoirin; Kenichiro Umezu, We investigate positive steady states of an indefinite superlinear reaction-diffusion equation arising from population dynamics, coupled with a nonlinear boundary condition. Both the equation and the boundary condition depend upon a positive parameter lambda, which is inversely proportional to the diffusion rate. We establish several multiplicity results when the diffusion rate is large and analyze the asymptotic profiles and the stability properties of these steady states as the diffusion rate grows to infinity. In particular, our results show that in some cases bifurcation from zero and from infinity occur at lambda = 0. Our approach combines variational and bifurcation techniques., SPRINGER HEIDELBERG
Calculus of Variations and Partial Differential Equations, 2016年08月, ［査読有り］

Bifurcation for a logistic elliptic equation with nonlinear boundary conditions: A limiting case
Humberto Ramos Quoirin; Kenichiro Umezu, We investigate bifurcation from the zero solution for a logistic elliptic equation with a sign-definite nonlinear boundary condition. In view of the lack of regularity of the term on the boundary, the abstract theory on bifurcation from simple eigenvalues due to Crandall and Rabinowitz does not apply. A regularization procedure and a topological method due to Whyburn are used to prove the existence and the global behavior at infinity of a subcontinuum of nontrivial non-negative weak solutions. The direction of the bifurcation component at zero is also investigated. This paper treats a limiting case of our previous work [19], where the case of sign-changing nonlinear boundary conditions is considered. (C) 2015 Elsevier Inc. All rights reserved., ACADEMIC PRESS INC ELSEVIER SCIENCE
Journal of Mathematical Analysis and Applications, 2015年08月, ［査読有り］

The effects of indefinite nonlinear boundary conditions on the structure of the positive solutions set of a logistic equation
Humberto Ramos Quoirin; Kenichiro Umezu, We investigate a semilinear elliptic equation with a logistic nonlinearity and an indefinite nonlinear boundary condition, both depending on a parameter A. Overall, we analyze the effect of the indefinite nonlinear boundary condition on the structure of the positive solutions set. Based on variational and bifurcation techniques, our main results establish the existence of three nontrivial non-negative solutions for some values of A., as well as their asymptotic behavior. These results suggest that the positive solutions set contains an S-shaped component in some case, as well as a combination of a C-shaped and an S-shaped components in another case. (C) 2014 Elsevier Inc. All rights reserved., ACADEMIC PRESS INC ELSEVIER SCIENCE
Journal of Differential Equations, 2014年12月, ［査読有り］

Global structure of supercritical bifurcation with turning points for the logistic elliptic equation with nonlinear boundary conditions
Kenichiro Umezu, In this paper, we give rather complete descriptions of the global bifurcation diagrams of positive solutions for the logistic elliptic equation with nonlinear boundary conditions in three cases of an included weight function. Besides the abstract theory of local and global bifurcation, careful observation of the reduced bifurcation equation in finite dimensional space and blow up arguments for the corresponding initial boundary value problem play an important role in characterizing the global behavior of the bifurcating positive solutions for values of a parameter. The critical case is dealt with by using a topological technique proposed by Whyburn. © 2013 Elsevier Ltd. All rights reserved.
Nonlinear Analysis, Theory, Methods and Applications, 2013年, ［査読有り］

Bifurcation approach to a logistic elliptic equation with a homogeneous incoming flux boundary condition
Kenichiro Umezu, In this paper, we consider a semilinear elliptic boundary value problem in a smooth bounded domain, having the so-called logistic nonlinearity that originates from population dynamics, with a nonlinear boundary condition. Although the logistic nonlinearity has an absorption effect in the problem, the nonlinear boundary condition is induced by the homogeneous incoming flux on the boundary. The objective of our study is to analyze the existence of a bifurcation component of positive solutions from trivial solutions and its asymptotic behavior and stability. We perform this analysis using the method developed by Lyapunov and Schmidt, based on a scaling argument. (C) 2011 Elsevier Inc. All rights reserved., ACADEMIC PRESS INC ELSEVIER SCIENCE
Journal of Differential Equations, 2012年01月, ［査読有り］

Global bifurcation results for semilinear elliptic boundary value problems with indefinite weights and nonlinear boundary conditions
Kenichiro Umezu, We investigate the global nature of bifurcation components of positive solutions of a general class of semilinear elliptic boundary value problems with nonlinear boundary conditions and having linear terms with sign-changing coefficients. We first show that there exists a subcontinuum, i.e., a maximal closed and connected component, emanating from the line of trivial solutions at a simple principal eigenvalue of a linearized eigenvalue problem. We next consider sufficient conditions such that the subcontinuum is unbounded in some space for a semilinear elliptic problem arising from population dynamics. Our approach to establishing the existence of the subcontinuum is based on the global bifurcation theory proposed by Lpez-Gmez. We also discuss an a priori bound of solutions and deduce from it some results on the multiplicity of positive solutions., BIRKHAUSER VERLAG AG
NoDEA Nonlinear Differential Equations and Applications, 2010年06月, ［査読有り］

Blowing-up properties of the positive principal eigenvalue for indefinite Robin-type boundary conditions
Kenichiro Umezu, In this paper, we consider the positive principal eigenvalue for some linear elliptic eigenvalue problem with Robin-type boundary conditions having indefinite coefficients, where its asymptotic behavior for indefinite varying weights is investigated. The aim of this paper is to study necessary and sufficient conditions for the positive principal eigenvalue to blow up to infinity. The analysis is based on variational characterization of the positive principal eigenvalue., ROCKY MT MATH CONSORTIUM
Rocky Mountain Journal of Mathematics, 2010年, ［査読有り］

Positive solutions of semilinear elliptic eigenvalue problems with concave nonlinearities
Kenichiro Umezu, Khayyam Publishing, Inc.
Advances in Differential Equations, 2007年12月, ［査読有り］

Blowing-up of principal eigenvalues for Neumann boundary conditions
Kenichiro Umezu, This paper studies blowing-up properties of a unique positive principal eigenvalue for a linear elliptic eigenvalue problem with an indefinite weight function and Neumann boundary condition. Necessary and sufficient conditions for the blowing-up property are discussed, based on the variational characterization of the unique positive principal eigenvalue. A counterexample is constructed, which shows that a known necessary and sufficient condition for the blowing-up property in the Dirichlet boundary condition case no longer remains true in the Neumann case., The Royal Society of Edinburgh
Proceedings of the Royal Society of Edinburgh Section A: Mathematics, 2007年06月, ［査読有り］

On eigenvalue problems with Robin type boundary conditions having indefinite coefficients
Kenichiro Umezu, Taylor & Francis
Applicable Analysis, 2006年11月, ［査読有り］

Non-existence of positive solutions for diffusive logistic equations with nonlinear boundary conditions
Kenichiro Umezu, In this paper a diffusive logistic equation with large diffusion is considered under nonlinear boundary conditions. Non-existence of the corresponding stationary positive solutions is discussed by use of variational techniques., Birkhauser
Progress in Nonlinear Differential Equations and Their Applications, 64, 2005年10月, ［査読有り］

One parameter-dependent nonlinear elliptic boundary value problems arising in population dynamics
Kenichiro Umezu, World Scientific
Advances in Analysis, 2005年07月, ［査読有り］

Local bifurcation analysis and stability of steady-state solutions of diffusive logistic equations with nonlinear boundary conditions
Kenichiro Umezu, Academic Publications
Communications in Applied Analysis, 2004年12月, ［査読有り］

Multiplicity of positive solutions under nonlinear boundary conditions for diffusive logistic equations
K Umezu, In this paper we consider the existence and multiplicity of positive solutions of a nonlinear elliptic boundary-value problem with nonlinear boundary conditions which arises in population dynamics. While bifurcation problems from lines of trivial solutions are studied, the existence of bifurcation positive solutions from infinity is discussed. The former will be caught by the reduction to a bifurcation equation following the Lyapunov and Schmidt procedure. The latter will be based on a variational argument depending on the corresponding constrained minimization problem., CAMBRIDGE UNIV PRESS
Proceedings of the Edinburgh Mathematical Society, 2004年06月, ［査読有り］

Bifurcation analysis in diffusive logistic equations with nonlinear boundary conditions
Kenichiro Umezu, Local bifurcation of positive solutions from the line of trivial solutions is considered for a nonlinear elliptic boundary value problem arising in population dynamics, having nonlinear boundary conditions. The bifurcation theory based on the Lyapunov and Schmidt procedure and the super-sub-solution method are used., World Sci. Publishing
Progress in Analysis, Vol. I, II (Berlin, 2001), 2003年08月, ［査読有り］

Bifurcation in population dynamics
Kenichiro Umezu, World Sci. Publishing
Elliptic and parabolic problems (Rolduc/Gaeta, 2001), 2002年08月, ［査読有り］

Behavior and stability of positive solutions of nonlinear elliptic boundary value problems arising in population dynamics
Kenichiro Umezu, Elsevier
Nonlinear Analysis: Theory, Methods & Applications, 2002年06月, ［査読有り］

Bifurcation from infinity for asymptotically linear elliptic eigenvalue problems
K Umezu, In this paper we are going to discuss bifurcation from infinity for asymptotically linear elliptic eigenvalue problems having nonlinear boundary conditions. Behavior of the bifurcation components is also studied. (C) 2002 Elsevier Science (USA)., ACADEMIC PRESS INC ELSEVIER SCIENCE
Journal of Mathematical Analysis and Applications, 2002年03月, ［査読有り］

Stability in chemical reactor theory
K Taira; K Umezu, MARCEL DEKKER
Evolution Equations and Their Applications in Physical and Life Sciences, 2001年, ［査読有り］

Bifurcation and stability for diffusive logistic equations with nonlinear boundary conditions
Kenichiro Umezu, IAMM of NAS of Ukraine
Nonlinear Boundary-Value Problems 10, 2000年12月, ［査読有り］

Nonlinear elliptic boundary value problems suggested by fermentation
Kenichiro Umezu, This paper is devoted to the study of a class of elliptic equations with nonlinear boundary conditions of one parameter dependence, including models in fermentation industries. The author proves the existence of positive solutions growing-up to infinity as the parameter goes to infinity and considers their asymptotic behavior. Our method is based mainly on super- and sub-solutions., Springer
Nonlinear Differential Equations and Applications NoDEA, 2000年08月, ［査読有り］

Global positive solution branches of positone problems with nonlinear boundary conditions
Kenichiro Umezu, Khayyam Publishing, Inc.
Differential and Integral Equations, 2000年04月, ［査読有り］

Positive solutions of semilinear elliptic boundary value problems in chemical reactor theory
K Umezu; K Taira, This paper is devoted to the study of semilinear elliptic boundary value problems arising in chemical reactor theory which obey the simple Arrhenius rate law and Newtonian cooling. We prove that ignition and extinction phenomena occur in the stable steady temperature profile at some critical values of a dimensionless heat evolution rate. Moreover the asymptotic behavior of the stable steady temperature is also studied., SPRINGER
Direct and Inverse Problems of Mathematical Physics, 2000年, ［査読有り］

Multiplicity of positive solutions to semilinear elliptic boundary value problems
Kenichiro Umezu, Hindawi Publishing
Abstract and Applied Analysis, 1999年12月, ［査読有り］

Positive solutions of a forced nonlinear elliptic boundary value problem
Kenichiro Umezu, This paper is a continuation of the previous paper Taira and Umezu [12] where we studied the existence and uniqueness of positive solutions of a class of sublinear elliptic problems with degenerate boundary conditions. We intend here to give a further investigation of the set of positive solutions in the forced case., The Mathematical Society of Japan
Journal of the Mathematical Society of Japan, 1999年10月, ［査読有り］

Growing-up positive solutions of semilinear elliptic boundary value problems
Kenichiro Umezu; Kazuaki Taira, This paper is devoted to the study of the existence, uniqueness, and asymptotic behavior of positive solutions of a class of degenerate boundary value problems for semilinear second-order elliptic differential operators which originates from the so-called Yamabe problem in Riemannian geometry. Our approach is based on the super-sub-solution method adapted to the degenerate case. (C) 1999 Academic Press., Elsevier
Journal of Mathematical Analysis and Applications, 1999年10月, ［査読有り］

Semilinear Elliptic Boundary Value Problems in Chemical Reactor Theory
Kazuaki Taira; Kenichiro Umezu, Elsevier
Journal of Differential Equations, 1998年01月, ［査読有り］

Positive solutions of sublinear elliptic boundary value problems
Kazuaki Taira; Kenichiro Umezu, Elsevier
Nonlinear Analysis: Theory, Methods & Applications, 1997年10月, ［査読有り］

Bifurcation for nonlinear elliptic boundary value problems. III.
Kazuaki Taira; Kenichiro Umezu, Khayyam Publishing, Inc
Advances in Differential Equations, 1996年07月, ［査読有り］

Bifurcation for Nonlinear Elliptic Boundary Value Problems II
Kazuaki Taira; Kenichiro Umezu, This paper is a continuation of the previous paper [Ta] where we studied local static bifurcation theory for a class of degenerate boundary value problems for semilinear second-order elliptic differential operators which includes as particular cases the Dirichlet and Neumann problems. This paper is devoted to global static bifurcation theory. © 1996 by the University of Notre Dame. All rights reserved.
Tokyo Journal of Mathematics, 1996年, ［査読有り］

Lp-approach to mixed boundary value problems for second-order elliptic operators
Kenichiro Umezu
Tokyo Journal of Mathematics, 1994年, ［査読有り］

On the Cauchy problem for analytic semigroups with weak singularity
Kenichiro Umezu, Institute of Mathematics, University of Tsukuba
Tsukuba Journal of Mathematics, 1991年12月, ［査読有り］

Past and recent contributions to indefinite sublinear elliptic problems
Uriel Kaufmann; Humberto Ramos Quoirin; Kenichiro Umezu
Rendiconti dell'Istituto di Matematica dell'Università di Trieste, 2020年10月, ［査読有り］, ［招待有り］

An indefinite superlinear elliptic equation with a nonlinear boundary condition of sublinear type
Humberto Ramos Quoirin; Kenichiro Umezu
京都大学数理解析研究所講究録, 2016年11月, ［招待有り］

Semilinear elliptic boundary value problems in chemical reactor theory (Japanese)
Kenichiro Umezu
京都大学数理解析研究所講究録, 1998年02月, ［招待有り］

Positive solutions of a diffusive logistic equation with a non Lipschitz boundary condition arising in coastal fishery harvesting　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2025年年会函数方程式論分科会, 2025年03月18日, 日本数学会
20250318, 20250321

Positive solutions for logistic type elliptic equation with a non Lipschitz boundary condition arising in coastal fishery harvesting　　　　　　　　　　　　　　　
Kenichiro Umezu
Equadiff2024 in Karlstad, 2024年06月13日
20240610, 20240614

Positive solutions for some sublinear Robin problem with an indefinite weight　　　　　　　　　　　　　　　
梅津健一郎
茨城大学金曜セミナー, 2023年07月07日, ［招待有り］
20230707, 20230707

An exact multiplicity result for some sublinear Robin problem with an indefinite weight　　　　　　　　　　　　　　　
Kenichiro Umezu
The 13th AIMS Conference on Dynamical Systems, Differential Equations and Applications in Wilmington NC, 2023年06月01日, AIMS(American Institute of Mathematical Sciences), ［招待有り］
20230531, 20230604

Logistic elliptic equations with the nonlinear boundary condition arising in coast fishery harvesting　　　　　　　　　　　　　　　
梅津健一郎
東北大学応用数理解析セミナー, 2022年06月09日, 東北大学大学院理学研究科数学教室, ［招待有り］

Uniqueness of a positive solution for the Laplace equation with indefinite superlinear boundary conditions: near a critical case　　　　　　　　　　　　　　　
梅津健一郎
南大阪応用数学セミナー, 2021年12月11日, 大阪市立大学理学研究科, ［招待有り］

Global exact multiplicity of positive solutions for an indenite sublinear Robin problem　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2020年年会函数方程式論分科会, 2020年03月16日, 日本数学会

Existence of a loop of positive solutions for concave-convex problems with indefinite weights　　　　　　　　　　　　　　　
Kenichiro Umezu
Equadiff 2019 in Leiden, 2019年07月11日

Exact multiplicity of positive solutions for an indefinite concave Robin bvp　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2019年年会函数方程式論分科会, 2019年03月17日, 日本数学会

Positivity of bifurcating nontrivial nonnegative solutions of indefinite concave problems　　　　　　　　　　　　　　　
Kenichiro Umezu
The 12th AIMS Conference on Dynamical Systems, Differential Equations and Applications in Taipei, 2018年07月06日, American Institute of Mathematical Sciences, ［招待有り］

Loop components of nontrivial nonnegative solutions for indefinite concave-convex problems　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2018年年会函数方程式論分科会, 2018年03月18日, 日本数学会

concave-convex タイプの非線形楕円型境界値問題に対するループ型有界連続体解集合の存在について　　　　　　　　　　　　　　　
梅津健一郎
変分問題セミナー（首都大学東京）, 2017年12月14日, 首都大学東京理工学研究科数理情報科学専攻, ［招待有り］

Positivity for nontrivial nonnegative solutions of an indefinite sublinear problem　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2017年年会函数方程式論分科会, 2017年03月24日, 日本数学会

On the existence of a loop component of nontrivial non-negative solutions for some concave-convex problem　　　　　　　　　　　　　　　
Kenichiro Umezu
Workshop on reaction diffusion equations and numerical analysis (Kyoto Sangyo University), 2016年10月08日, ［招待有り］

A loop type component of positive solutions of an indefinite concave-convex problem with the Neumann boundary condition　　　　　　　　　　　　　　　
Kenichiro Umezu
The 11th AIMS Conference on Dynamical Systems, Differential Equations and Applications in Orlando, 2016年07月04日, American Institute of Mathematical Sciences (AIMS), ［招待有り］

An indefinite superlinear elliptic equation with a nonlinear boundary condition of sublinear type　　　　　　　　　　　　　　　
Kenichiro Umezu
RIMS Workshop `Shapes and other properties of solutions of PDEs' (RIMS, Kyoto University), 2015年11月13日, ［招待有り］

Bifurcation analysis for a logistic elliptic equation having nonlinear boundary conditions with sign-definite weights　　　　　　　　　　　　　　　
Kenichiro Umezu
Seminar of Department of Mathematics, Universidad de Santiago de Chile, 2015年09月01日, Department of Mathematics, Universidad de Santiago de Chile, ［招待有り］

convex-concave 混合型境界値問題の解構造における不定符号係数の役割について　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2015年年会函数方程式論分科会, 2015年03月21日, 日本数学会

The effect of a nonlinear boundary condition with an indefinite weight on the positive solution set of the logistic elliptic equation　　　　　　　　　　　　　　　
Kenichiro Umezu
The 10th AIMS Conference on Dynamical Systems, Differential Equations and Applications in Madrid, 2014年07月08日, AIMS(American Institute of Mathematical Sciences), ［招待有り］

On S-shaped and CS-shaped bifurcation diagrams in population dynamics　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2014年年会函数方程式論分科会, 2014年03月17日, 日本数学会

On the effect of spatial heterogeneity in logistic type elliptic equations with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
The 9th AIMS Conference on Dynamical Systems, Differential Equations and Applications in Orlando, 2012年07月04日, American Institute of Mathematical Sciences, ［招待有り］

ロジスティックタイプの非線形楕円型境界値問題に対する正値解の大域的分岐構造について　　　　　　　　　　　　　　　
梅津健一郎
変分問題セミナー（首都大学東京）, 2012年03月09日, 首都大学東京理工学研究科数理情報科学専攻, ［招待有り］

Global bifurcation of positive solutions for some elliptic problems with nonlinear boundary conditions　　　　　　　　　　　　　　　
梅津健一郎
洞爺解析セミナー, 2010年09月28日, ［招待有り］

Global bifurcation analysis of indefinite nonlinear boundary value problems with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
The 8th AIMS Conference on Dynamical Systems, Differential Equations and Applications in Dresden, 2010年05月27日, American Institute of Mathematical Sciences, ［招待有り］

Global bifurcation for indefinite weighted elliptic problems with nonlinear boundary conditions　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2010年年会函数方程式論分科会, 2010年03月25日, 日本数学会

A super and subsolution method for sublinear problems with low regularity coefficients　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2008年総合分科会函数方程式論分科会, 2008年09月25日, 日本数学会

Blowing-up properties of the positive principal eigenvalue for indefinite Robin-type boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
The Second China-Japan Colloquium of Mathematical Biology in Okayama, 2008年08月06日

Nehari manifolds, fibering maps and semilinear elliptic boundary value problems　　　　　　　　　　　　　　　
梅津健一郎
数理科学セミナー, 2007年09月10日

Multiplicity of positive solutions to nonlinear elliptic boundary value problems arising in population dynamics　　　　　　　　　　　　　　　
Kenichiro Umezu
Workshop "Direct, Inverse And Control Problems For PDE's" in Rome, 2007年06月27日

Principal eigenvalues of Neumann and Robin type eigenvalue problems with indefinite weights　　　　　　　　　　　　　　　
Kenichiro Umezu
The 4th International Conference on Mathematical Biology in Wuyishan, 2007年06月01日, ［招待有り］

主固有値の爆発と人口動態　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2007年年会函数方程式論分科会, 2007年03月28日, 日本数学会

Blowing-up principal eigenvalues of Neumann eigenvalue problems with indefinite weights　　　　　　　　　　　　　　　
梅津健一郎
解析セミナー, 2006年12月20日, 筑波大学数学系

ノイマン条件下における主固有値の爆発問題　　　　　　　　　　　　　　　
梅津健一郎
応用解析研究会, 2006年12月02日, 早稲田大学理工学部数学科

ノイマン条件のもとでの主固有値の爆発問題　　　　　　　　　　　　　　　
梅津健一郎
数理科学セミナー, 2006年09月10日

Blowing-up behavior of principal eigenvalues for Neumann boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
The first China-Japan Colloquium of Mathematical Biology (CJCMB) in Chongqing, 2006年04月25日

符号不定な重み係数をもつロバン型境界条件に対する主固有値の特徴付け　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2006年年会函数方程式論分科会, 2006年03月27日, 日本数学会

Elliptic eigenvalue problems with indefinite Robin boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
ISAAC05, the 5th Congress in Catania, 2005年07月29日, ［招待有り］

An estimate for turning points in sublinear elliptic boundary value problems　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2005年年会函数方程式論分科会, 2005年03月28日, 日本数学会

Stationary solutions of diffusive logistic equations with large diffusion and nonlinear boundary conditions　　　　　　　　　　　　　　　
梅津健一郎
数理科学セミナー, 2004年07月18日

Existence and nonexistence of positive solutions for a semilinear elliptic problem arising in population dynamics　　　　　　　　　　　　　　　
Kenichiro Umezu
Nonlinear Elliptic and Parabolic Problems: A Special Tribute to the Work of Herbert Amann in Zurich, 2004年06月30日

Existence and limiting behavior of positive solutions for diffusive logistic equations with nonlinear flux on the boundary　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2003年総合分科会函数方程式論分科会, 2003年09月27日, 日本数学会

人口動態論に現れる非線形楕円型方程式の正値解の多重性と挙動　　　　　　　　　　　　　　　
梅津健一郎
筑波大学数学系談話会, 2003年09月04日, 筑波大学数学系

On diffusive logistic equations having nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
ISAAC03, the 4th Congress in Toronto, 2003年08月, ISAAC, ［招待有り］

Multiplicity of positive solutions to a nonlinear elliptic boundary value problem arising in population dynamics　　　　　　　　　　　　　　　
梅津健一郎
都立大変分問題セミナー, 2003年02月, 東京都立大学理学部数学教室, ［招待有り］

Bifurcation analysis of a semilinear elliptic problem arising in population dynamics and having nonlinear boundary conditions　　　　　　　　　　　　　　　
梅津健一郎
自己相互作用粒子系の数学解析と数理, 2002年11月, 大阪大学基礎工学部, ［招待有り］

Bifurcation problem for a semilinear elliptic equation arising in population dynamics, having nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
International Conference on Nonlinear Partial Differential Equations Theory and Approximation in Hong Kong, 2002年08月

Local and global bifurcation analysis on a nonlinear problem from population　　　　　　　　　　　　　　　
梅津健一郎
数理科学セミナー, 2002年06月

Global subcontinua arising in population dynamics　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2002年年会函数方程式論分科会, 2002年03月, 日本数学会

Bifurcation in population dynamics　　　　　　　　　　　　　　　
Kenichiro Umezu
The 4th European Conference on Elliptic and Parabolic Problems in Gaeta, 2001年09月

Bifurcation analysis in diffusive logistic equations with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
ISAAC01, the 3rd Congress in Berlin, 2001年08月, ISAAC, ［招待有り］

Bifurcation on nonlinear eigenvalue problems in population dynamics　　　　　　　　　　　　　　　
梅津健一郎
解析セミナー, 2001年05月, 筑波大学数学系

Bifurcation in Population Genetics　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2001年年会函数方程式論分科会, 2001年03月, 日本数学会

人口動態モデルに現れる分岐現象　　　　　　　　　　　　　　　
梅津健一郎
生物現象と非線形微分方程式, 2000年09月

Diffusive logistic equations with indefinite weights and nonlinear boundary ,conditions　　　　　　　　　　　　　　　
梅津健一郎
数理科学セミナー, 2000年05月

非線形境界条件における人口動態モデルの正値解の挙動　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2000年年会函数方程式論分科会, 2000年03月, 日本数学会

Bifurcation from infinity and uniqueness of positive solutions to semilinear elliptic equations with nonlinear boundary conditions　　　　　　　　　　　　　　　
梅津健一郎
日本数学会2000年年会函数方程式論分科会, 2000年03月, 日本数学会

非線形境界条件に対する人口動態モデルの正値解の挙動　　　　　　　　　　　　　　　
梅津健一郎
生物現象と非線形微分方程式, 1999年11月

Bifurcation and stability for diffusive logistic equations with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
International Conference on Nonlinear Partial Differential Equations 99 in Lviv, 1999年08月

Elliptic boundary value problems with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
ICIAM 99, the 4th Congress in Edinburgh, 1999年07月, ICIAM, ［招待有り］

Diffusive logistic equations with nonlinear boundary conditions　　　　　　　　　　　　　　　
梅津健一郎
数理科学セミナー, 1999年06月

化学反応論における漸近安定性　　　　　　　　　　　　　　　
梅津健一郎
日本数学会1999年年会函数方程式論分科会, 1999年03月, 日本数学会

酵素反応に現われる非線型楕円型境界値問題　　　　　　　　　　　　　　　
梅津健一郎
解析セミナー, 1999年01月, 筑波大学数学系

Positive solutions of semilinear elliptic boundary value problems　　　　　　　　　　　　　　　
梅津健一郎
日本数学会1998年秋季総合分科会函数方程式論分科会, 1998年10月, 日本数学会

発酵作用に現われる非線型楕円型境界値問題　　　　　　　　　　　　　　　
梅津健一郎
生物現象と非線形微分方程式, 1998年09月

Positive solutions of semilinear elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
偏微分方程式長野シンポジウム, 1998年07月

化学反応論における安定性　　　　　　　　　　　　　　　
梅津健一郎
日本数学会1998年年会函数方程式論分科会, 1998年03月, 日本数学会

半線型楕円型境界値問題とその応用　　　　　　　　　　　　　　　
梅津健一郎
偏微分セミナー, 1997年10月, 東京都立大学理学部数学教室, ［招待有り］

Semilinear elliptic boundary value problems in chemical reactor theory　　　　　　　　　　　　　　　
Kenichiro Umezu
変分問題とその周辺, 1997年06月, 京都大学数理解析研究所, ［招待有り］

Semilinear elliptic boundary value problems in chemical reactor theory　　　　　　　　　　　　　　　
Kenichiro Umezu
ISAAC1997, the 1st Congress in Delaware, 1997年06月, International Society for Analysis, its Applications and Computation, ［招待有り］

化学反応論における半線型楕円型境界値問題　　　　　　　　　　　　　　　
梅津健一郎
日本数学会1997年年会函数方程式論分科会, 1997年04月, 日本数学会

化学反応論における半線型楕円型境界値問題　　　　　　　　　　　　　　　
梅津健一郎
応用解析研究会, 1996年12月, 早稲田大学理工学部数学科

Fourier multipliers in weighted Lp spaces　　　　　　　　　　　　　　　
梅津健一郎
実解析シンポジウム96大分応用解析研究会, 1996年11月

半線形楕円型境界値問題の正値解の一意存在定理　　　　　　　　　　　　　　　
梅津健一郎
日本数学会1996年年会函数方程式論分科会, 1996年04月, 日本数学会

非線形楕円型境界値問題の正値解の一意存在定理　　　　　　　　　　　　　　　
梅津健一郎
微分方程式研究会, 1995年12月, 早稲田大学理工学部数学科, ［招待有り］

非線形楕円型境界値問題の正値解の一意存在定理　　　　　　　　　　　　　　　
梅津健一郎
日本数学会1995年秋季総合分科会函数方程式論分科会, 1995年09月, 日本数学会

Positive solutions of semi linear elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
偏微分方程式賢島シンポジウム, 1995年09月

非線形楕円型境界値問題の解の分岐定理　　　　　　　　　　　　　　　
梅津健一郎
日本数学会1995年年会函数方程式論分科会, 1995年03月, 日本数学会

Orderが変化するBesov空間について　　　　　　　　　　　　　　　
梅津健一郎
函数空間論とその応用, 1994年01月, 筑波大学数学系

２階楕円型作用素に対する混合型境界値問題の L^p アプローチ　　　　　　　　　　　　　　　
梅津健一郎
日本数学会1993年秋季総合分科会函数方程式論分科会, 1993年09月, 日本数学会

2001年01月 - 現在, 日本応用数理学会

1993年06月 - 現在, 日本数学会