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, Jan. 2025, [Reviewed]

Logistic elliptic equation with a nonlinear boundary condition arising from coastal fishery harvesting II
Kenichiro Umezu, Elsevier
Journal of Mathematical Analysis and Applications, Jun. 2024, [Reviewed]

Logistic elliptic equation with a nonlinear boundary condition arising from coastal fishery harvesting
Kenichiro Umezu, Elsevier
Nonlinear Analysis: Real World Applications, Apr. 2023, [Reviewed]

Uniqueness of a positive solution for the Laplace equation with indefinite superlinear boundary condition
Kenichiro Umezu, Elsevier
Journal of Differential Equations, Mar. 2023, [Reviewed]

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, Apr. 2022, [Reviewed]

Uniqueness and positivity issues in a quasilinear indefinite problem
Uriel Kaufmann; Humberto Ramos Quoirin; Kenichiro Umezu, Springer
Calculus of Variations and Partial Differential Equations, Aug. 2021, [Reviewed]

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, Jun. 2021, [Reviewed]

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-), Oct. 2020, [Reviewed]

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, Feb. 2020, [Reviewed]

Loop type subcontinua of positive solutions for indefinite concave-convex problems
Uriel Kaufmann; Humberto Ramos Quoirin; Kenichiro Umezu, De Gruyter
Advanced Nonlinear Studies, May 2019, [Reviewed]

An elliptic equation with an indefinite sublinear boundary condition
Humberto Ramos Quoirin; Kenichiro Umezu, De Gruyter
Advances in Nonlinear Analysis, Jan. 2019, [Reviewed]

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, 01 May 2018, [Reviewed]

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, 01 Apr. 2018, [Reviewed]

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, Oct. 2017, [Reviewed]

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, Jun. 2017, [Reviewed]

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, Jun. 2017, [Reviewed]

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 -), Dec. 2016, [Reviewed]

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, Aug. 2016, [Reviewed]

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, Aug. 2015, [Reviewed]

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, Dec. 2014, [Reviewed]

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, [Reviewed]

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, Jan. 2012, [Reviewed]

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, Jun. 2010, [Reviewed]

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, [Reviewed]

Positive solutions of semilinear elliptic eigenvalue problems with concave nonlinearities
Kenichiro Umezu, Khayyam Publishing, Inc.
Advances in Differential Equations, Dec. 2007, [Reviewed]

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, Jun. 2007, [Reviewed]

On eigenvalue problems with Robin type boundary conditions having indefinite coefficients
Kenichiro Umezu, Taylor & Francis
Applicable Analysis, Nov. 2006, [Reviewed]

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, Oct. 2005, [Reviewed]

One parameter-dependent nonlinear elliptic boundary value problems arising in population dynamics
Kenichiro Umezu, World Scientific
Advances in Analysis, Jul. 2005, [Reviewed]

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, Dec. 2004, [Reviewed]

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, Jun. 2004, [Reviewed]

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), Aug. 2003, [Reviewed]

Bifurcation in population dynamics
Kenichiro Umezu, World Sci. Publishing
Elliptic and parabolic problems (Rolduc/Gaeta, 2001), Aug. 2002, [Reviewed]

Behavior and stability of positive solutions of nonlinear elliptic boundary value problems arising in population dynamics
Kenichiro Umezu, Elsevier
Nonlinear Analysis: Theory, Methods & Applications, Jun. 2002, [Reviewed]

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, Mar. 2002, [Reviewed]

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

Bifurcation and stability for diffusive logistic equations with nonlinear boundary conditions
Kenichiro Umezu, IAMM of NAS of Ukraine
Nonlinear Boundary-Value Problems 10, Dec. 2000, [Reviewed]

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, Aug. 2000, [Reviewed]

Global positive solution branches of positone problems with nonlinear boundary conditions
Kenichiro Umezu, Khayyam Publishing, Inc.
Differential and Integral Equations, Apr. 2000, [Reviewed]

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, [Reviewed]

Multiplicity of positive solutions to semilinear elliptic boundary value problems
Kenichiro Umezu, Hindawi Publishing
Abstract and Applied Analysis, Dec. 1999, [Reviewed]

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, Oct. 1999, [Reviewed]

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, Oct. 1999, [Reviewed]

Semilinear Elliptic Boundary Value Problems in Chemical Reactor Theory
Kazuaki Taira; Kenichiro Umezu, Elsevier
Journal of Differential Equations, Jan. 1998, [Reviewed]

Positive solutions of sublinear elliptic boundary value problems
Kazuaki Taira; Kenichiro Umezu, Elsevier
Nonlinear Analysis: Theory, Methods & Applications, Oct. 1997, [Reviewed]

Bifurcation for nonlinear elliptic boundary value problems. III.
Kazuaki Taira; Kenichiro Umezu, Khayyam Publishing, Inc
Advances in Differential Equations, Jul. 1996, [Reviewed]

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, [Reviewed]

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

On the Cauchy problem for analytic semigroups with weak singularity
Kenichiro Umezu, Institute of Mathematics, University of Tsukuba
Tsukuba Journal of Mathematics, Dec. 1991, [Reviewed]

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, Oct. 2020, [Reviewed], [Invited]

An indefinite superlinear elliptic equation with a nonlinear boundary condition of sublinear type
Humberto Ramos Quoirin; Kenichiro Umezu
Sūrikaisekikenkyūsho Kōkyūroku, Nov. 2016, [Invited]

Semilinear elliptic boundary value problems in chemical reactor theory (Japanese)
Kenichiro Umezu
Sūrikaisekikenkyūsho Kōkyūroku, Feb. 1998, [Invited]

Positive solutions of a diffusive logistic equation with a non Lipschitz boundary condition arising in coastal fishery harvesting　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2020 Annual Meeting of MSJ, 18 Mar. 2025, MSJ
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, 13 Jun. 2024
20240610, 20240614

Positive solutions for some sublinear Robin problem with an indefinite weight　　　　　　　　　　　　　　　
Kenichiro Umezu
The Friday Seminar of Ibaraki University, 07 Jul. 2023, [Invited]
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, 01 Jun. 2023, AIMS(American Institute of Mathematical Sciences), [Invited]
20230531, 20230604

Logistic elliptic equations with the nonlinear boundary condition arising in coast fishery harvesting　　　　　　　　　　　　　　　
Kenichiro Umezu
The Applied Mathematical Analysis Seminar of Tohoku University, 09 Jun. 2022, 東北大学大学院理学研究科数学教室, [Invited]

Uniqueness of a positive solution for the Laplace equation with indefinite superlinear boundary conditions: near a critical case　　　　　　　　　　　　　　　
Kenichiro Umezu
The South Osaka Applied Mathematics Seminar, 11 Dec. 2021, 大阪市立大学理学研究科, [Invited]

Global exact multiplicity of positive solutions for an indenite sublinear Robin problem　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2020 Annual Meeting of MSJ, 16 Mar. 2020, 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, 11 Jul. 2019

Exact multiplicity of positive solutions for an indefinite concave Robin bvp　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2019 Annual Meeting of MSJ, 17 Mar. 2019, 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, 06 Jul. 2018, American Institute of Mathematical Sciences, [Invited]

Loop components of nontrivial nonnegative solutions for indefinite concave-convex problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2018 Annual Meeting of MSJ, 18 Mar. 2018, 日本数学会

Subcontinua of loop for positive solutions to concave-convex elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Variation Problem Seminar of Tokyo Metropolitan University, 14 Dec. 2017, 首都大学東京理工学研究科数理情報科学専攻, [Invited]

Positivity for nontrivial nonnegative solutions of an indefinite sublinear problem　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2017 Annual Meeting of MSJ, 24 Mar. 2017, 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), 08 Oct. 2016, [Invited]

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, 04 Jul. 2016, American Institute of Mathematical Sciences (AIMS), [Invited]

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), 13 Nov. 2015, [Invited]

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, 01 Sep. 2015, Department of Mathematics, Universidad de Santiago de Chile, [Invited]

Role of indefinite weights for the structure of the solution set of concave-convex mixed boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2015 Annual Meeting of MSJ, 21 Mar. 2015, 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, 08 Jul. 2014, AIMS(American Institute of Mathematical Sciences), [Invited]

On S-shaped and CS-shaped bifurcation diagrams in population dynamics　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2014 Annual Meeting of MSJ, 17 Mar. 2014, 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, 04 Jul. 2012, American Institute of Mathematical Sciences, [Invited]

Global structure of bifurcation for positive solutions to nonlinear elliptic boundary value problems of logistic type　　　　　　　　　　　　　　　
Kenichiro Umezu
Variation Problem Seminar of Tokyo Metropolitan University, 09 Mar. 2012, 首都大学東京理工学研究科数理情報科学専攻, [Invited]

Global bifurcation of positive solutions for some elliptic problems with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
Toya Analysis Seminar, 28 Sep. 2010, [Invited]

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, 27 May 2010, American Institute of Mathematical Sciences, [Invited]

Global bifurcation for indefinite weighted elliptic problems with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2010 Annual Meeting of MSJ, 25 Mar. 2010, 日本数学会

A super and subsolution method for sublinear problems with low regularity coefficients　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2008 Annual Meeting of MSJ in Autumn, 25 Sep. 2008, 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, 06 Aug. 2008

Nehari manifolds, fibering maps and semilinear elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Mathematical Science Seminar, 10 Sep. 2007

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, 27 Jun. 2007

Principal eigenvalues of Neumann and Robin type eigenvalue problems with indefinite weights　　　　　　　　　　　　　　　
Kenichiro Umezu
The 4th International Conference on Mathematical Biology in Wuyishan, 01 Jun. 2007, [Invited]

Principal eigenvalues and population dynamics　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2007 Annual Meeting of MSJ, 28 Mar. 2007, 日本数学会

Blowing-up principal eigenvalues of Neumann eigenvalue problems with indefinite weights　　　　　　　　　　　　　　　
Kenichiro Umezu
Analysis Seminar (Institute of Math., University of Tsukuba), 20 Dec. 2006, 筑波大学数学系

Principal eigenvalues for Neumann boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
Applied Analysis Seminar (Waseda University), 02 Dec. 2006, 早稲田大学理工学部数学科

Principal eigenvalues for Neumann boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
Mathematical Science Seminar, 10 Sep. 2006

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

Principal eigenvalues for Robin boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2006 Annual Meeting of MSJ, 27 Mar. 2006, 日本数学会

Elliptic eigenvalue problems with indefinite Robin boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
ISAAC05, the 5th Congress in Catania, 29 Jul. 2005, [Invited]

An estimate for turning points in sublinear elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2005 Annual Meeting of MSJ, 28 Mar. 2005, 日本数学会

Stationary solutions of diffusive logistic equations with large diffusion and nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
Mathematical Science Seminar, 18 Jul. 2004

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, 30 Jun. 2004

Existence and limiting behavior of positive solutions for diffusive logistic equations with nonlinear flux on the boundary　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2003 Annual Meeting of MSJ in Autumn, 27 Sep. 2003, 日本数学会

Multiplicity and behavior of positive solutions to nonlinear elliptic equations arising in population dynamics　　　　　　　　　　　　　　　
Kenichiro Umezu
Colloquium of Institute of Mathematics, University of Tsukuba, 04 Sep. 2003, 筑波大学数学系

On diffusive logistic equations having nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
ISAAC03, the 4th Congress in Toronto, Aug. 2003, ISAAC, [Invited]

Multiplicity of positive solutions to a nonlinear elliptic boundary value problem arising in population dynamics　　　　　　　　　　　　　　　
Kenichiro Umezu
Variation Problem Seminar of Tokyo Metropolitan University, Feb. 2003, 東京都立大学理学部数学教室, [Invited]

Bifurcation analysis of a semilinear elliptic problem arising in population dynamics and having nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
Mathematical Analysis for Self-Interacting Particle System, Nov. 2002, 大阪大学基礎工学部, [Invited]

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, Aug. 2002

Local and global bifurcation analysis on a nonlinear problem from population　　　　　　　　　　　　　　　
Kenichiro Umezu
Mathematical Science Seminar, Jun. 2002

Global subcontinua arising in population dynamics　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2002 Annual Meeting of MSJ, Mar. 2002, 日本数学会

Bifurcation in population dynamics　　　　　　　　　　　　　　　
Kenichiro Umezu
The 4th European Conference on Elliptic and Parabolic Problems in Gaeta, Sep. 2001

Bifurcation analysis in diffusive logistic equations with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
ISAAC01, the 3rd Congress in Berlin, Aug. 2001, ISAAC, [Invited]

Bifurcation on nonlinear eigenvalue problems in population dynamics　　　　　　　　　　　　　　　
Kenichiro Umezu
Analysis Seminar (Institute of Math., University of Tsukuba), May 2001, 筑波大学数学系

Bifurcation in Population Genetics　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2001 Annual Meeting of MSJ, Mar. 2001, 日本数学会

Bifurcation in population models　　　　　　　　　　　　　　　
Kenichiro Umezu
Biological phenomena and nonlinear differential equations (Hiroshima University), Sep. 2000

Diffusive logistic equations with indefinite weights and nonlinear boundary ,conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
Mathematical Science Seminar, May 2000

Positive solutions for population model under a nonlinear boundary condition　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2000 Annual Meeting of MSJ, Mar. 2000, 日本数学会

Bifurcation from infinity and uniqueness of positive solutions to semilinear elliptic equations with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 2000 Annual Meeting of MSJ, Mar. 2000, 日本数学会

Positive solutions for population model under a nonlinear boundary condition　　　　　　　　　　　　　　　
Kenichiro Umezu
Biological phenomena and nonlinear differential equations (Hiroshima University), Nov. 1999

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

Elliptic boundary value problems with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
ICIAM 99, the 4th Congress in Edinburgh, Jul. 1999, ICIAM, [Invited]

Diffusive logistic equations with nonlinear boundary conditions　　　　　　　　　　　　　　　
Kenichiro Umezu
Mathematical Science Seminar, Jun. 1999

Asymptotical stability in chemical reactor theory　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 1999 Annual Meeting of MSJ, Mar. 1999, 日本数学会

Nonlinear elliptic boundary value problem arising in fermentation industry　　　　　　　　　　　　　　　
Kenichiro Umezu
Analysis Seminar (Institute of Math., University of Tsukuba), Jan. 1999, 筑波大学数学系

Positive solutions of semilinear elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 1998 Annual Meeting of MSJ in Autumn, Oct. 1998, 日本数学会

Nonlinear elliptic boundary value problem arising in fermentation industry　　　　　　　　　　　　　　　
Kenichiro Umezu
Biological phenomena and nonlinear differential equations (Hiroshima University), Sep. 1998

Positive solutions of semilinear elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Nagano Symposium on partial differential equations, Jul. 1998

Stability in chemical reactor theory　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 1998 Annual Meeting of MSJ, Mar. 1998, 日本数学会

Semilinear elliptic boundary value problem and its application　　　　　　　　　　　　　　　
Kenichiro Umezu
Seminar on partial differential equations, Oct. 1997, 東京都立大学理学部数学教室, [Invited]

Semilinear elliptic boundary value problems in chemical reactor theory　　　　　　　　　　　　　　　
Kenichiro Umezu
Variational problems and related topics (RIMS, Kyoto University), Jun. 1997, RIMS, Kyoto Univ., [Invited]

Semilinear elliptic boundary value problems in chemical reactor theory　　　　　　　　　　　　　　　
Kenichiro Umezu
ISAAC1997, the 1st Congress in Delaware, Jun. 1997, International Society for Analysis, its Applications and Computation, [Invited]

Semilinear elliptic boundary value problem arising in chemical reactor theory　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 1997 Annual Meeting of MSJ, Apr. 1997, 日本数学会

Semilinear elliptic boundary value problem arising in chemical reactor theory　　　　　　　　　　　　　　　
Kenichiro Umezu
Applied Analysis Seminar (Waseda University), Dec. 1996, 早稲田大学理工学部数学科

Fourier multipliers in weighted Lp spaces　　　　　　　　　　　　　　　
Kenichiro Umezu
Real Analysis Symposium in Oita, Nov. 1996

Existence and uniqueness of positive solutions for semilinear elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 1996 Annual Meeting of MSJ, Apr. 1996, 日本数学会

Existence and uniqueness of positive solutions for semilinear elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Seminar on differential equations, Dec. 1995, 早稲田大学理工学部数学科, [Invited]

Existence and uniqueness of positive solutions for semilinear elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 1995 Annual Meeting of MSJ in Autumn, Sep. 1995, 日本数学会

Positive solutions of semi linear elliptic boundary value problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Kashikojima symposium on partial differential equations, Sep. 1995

Bifurcation for nonlinear elliptic boundary valuer problems　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 1995 Annual Meeting of MSJ, Mar. 1995, 日本数学会

Besov spaces with variable order　　　　　　　　　　　　　　　
Kenichiro Umezu
Function space and its application, Jan. 1994, 筑波大学数学系

L^p approach to mixed boudary value problems of second order　　　　　　　　　　　　　　　
Kenichiro Umezu
Division of Functional Equations, The 1993 Annual Meeting of MSJ in Autumn, Sep. 1993, 日本数学会

Jan. 2001 - Present, 日本応用数理学会

Jun. 1993 - Present, 日本数学会