scholarly journals The hot spots conjecture can be false: some numerical examples

2021 ◽  
Vol 47 (6) ◽  
Author(s):  
Andreas Kleefeld
Keyword(s):  
Eigenvalue Problem ◽  
Hot Spots ◽  
Neumann Boundary Condition ◽  
Boundary Integral Equations ◽  
Neumann Boundary ◽  
Boundary Integral ◽  
Zero Eigenvalue ◽  
Numerical Examples ◽  
Linear Eigenvalue Problem ◽  
Hot Spots Conjecture

AbstractThe hot spots conjecture is only known to be true for special geometries. This paper shows numerically that the hot spots conjecture can fail to be true for easy to construct bounded domains with one hole. The underlying eigenvalue problem for the Laplace equation with Neumann boundary condition is solved with boundary integral equations yielding a non-linear eigenvalue problem. Its discretization via the boundary element collocation method in combination with the algorithm by Beyn yields highly accurate results both for the first non-zero eigenvalue and its corresponding eigenfunction which is due to superconvergence. Additionally, it can be shown numerically that the ratio between the maximal/minimal value inside the domain and its maximal/minimal value on the boundary can be larger than 1 + 10− 3. Finally, numerical examples for easy to construct domains with up to five holes are provided which fail the hot spots conjecture as well.

Novel Boundary Integral Equations for Two-Dimensional Isotropic Elasticity: An Application to Evaluation of the In-Boundary Stress

2003 ◽  
Vol 70 (6) ◽  
pp. 817-824 ◽  
Author(s):  
V. Manticˇ ◽  
F. J. Calzado ◽  
F. Pari´s
Keyword(s):  
Integral Equations ◽  
Boundary Integral Equations ◽  
Anisotropic Elasticity ◽  
Boundary Integral ◽  
Two Dimensional ◽  
Numerical Examples ◽  
Tangential Derivative ◽  
Boundary Stress ◽  
Isotropic Elasticity ◽  
Boundary Integral Representation

A new nonsingular system of boundary integral equations (BIEs) of the second kind for two-dimensional isotropic elasticity is deduced following a recently introduced procedure by Wu (J. Appl. Mech., 67, pp. 618–621, 2000) originally applied for anisotropic elasticity. The physical interpretation of the new integral kernels appearing in these BIEs is studied. An advantageous application of one of these BIEs as a boundary integral representation (BIR) of tangential derivative of boundary displacements on smooth parts of the boundary, and subsequently as a BIR of the in-boundary stress, is presented and analyzed in numerical examples. An equivalent BIR obtained by an integration by parts of the integral including tangential derivative of displacements in the former BIR is presented and analyzed as well. The resulting integral is only apparently hypersingular, being in fact a regular integral on smooth parts of the boundary.

scholarly journals On the solution of the Helmholtz equation on regions with corners

2016 ◽  
Vol 113 (33) ◽  
pp. 9171-9176 ◽  
Author(s):  
Kirill Serkh ◽  
Vladimir Rokhlin
Keyword(s):  
Helmholtz Equation ◽  
Boundary Value Problems ◽  
Integral Equations ◽  
Potential Theory ◽  
Bessel Functions ◽  
Boundary Integral Equations ◽  
Numerical Algorithms ◽  
Boundary Integral ◽  
Numerical Examples ◽  
Polygonal Domains

In this paper we solve several boundary value problems for the Helmholtz equation on polygonal domains. We observe that when the problems are formulated as the boundary integral equations of potential theory, the solutions are representable by series of appropriately chosen Bessel functions. In addition to being analytically perspicuous, the resulting expressions lend themselves to the construction of accurate and efficient numerical algorithms. The results are illustrated by a number of numerical examples.

Eigenvalues of −Δp − Δq Under Neumann Boundary Condition

2016 ◽  
Vol 59 (3) ◽  
pp. 606-616 ◽  
Author(s):  
Mihai Mihăilescu ◽  
Gheorghe Moroşanu
Keyword(s):  
Boundary Condition ◽  
Eigenvalue Problem ◽  
Neumann Boundary Condition ◽  
Smooth Boundary ◽  
Neumann Boundary ◽  
Careful Analysis ◽  
Full Description ◽  
Open Set ◽  
Homogeneous Neumann Boundary Condition ◽  
Isolated Point

AbstractThe eigenvalue problem −Δpu − Δqu = λ|u|q−2u with p ∊ (1,∞), q ∊ (2,∞), p ≠ q subject to the corresponding homogeneous Neumann boundary condition is investigated on a bounded open set with smooth boundary from ℝN with N ≥ 2. A careful analysis of this problem leads us to a complete description of the set of eigenvalues as being a precise interval (λ1, ∞) plus an isolated point λ = 0. This comprehensive result is strongly related to our framework, which is complementary to the well-known case p = q ≠ 2 for which a full description of the set of eigenvalues is still unavailable.

scholarly journals Mathematical and Numerical Modeling of On-Threshold Modes of 2-D Microcavity Lasers with Piercing Holes

Axioms ◽  
2019 ◽  
Vol 8 (3) ◽  
pp. 101 ◽  
Author(s):  
Spiridonov ◽  
Karchevskii ◽  
Nosich
Keyword(s):  
Eigenvalue Problem ◽  
Light Emission ◽  
Boundary Integral Equations ◽  
Active Regions ◽  
Boundary Integral ◽  
Complex Frequency ◽  
Microcavity Lasers ◽  
Gain Material ◽  
Real Emission ◽  
Mathematical And Numerical Modeling

This study considers the mathematical analysis framework aimed at the adequate description of the modes of lasers on the threshold of non-attenuated in time light emission. The lasers are viewed as open dielectric resonators equipped with active regions, filled in with gain material. We introduce a generalized complex-frequency eigenvalue problem for such cavities and prove important properties of the spectrum of its eigensolutions. This involves reduction of the problem to the set of the Muller boundary integral equations and their discretization with the Nystrom technique. Embedded into this general framework is the application-oriented lasing eigenvalue problem, where the real emission frequencies and the threshold gain values together form two-component eigenvalues. As an example of on-threshold mode study, we present numerical results related to the two-dimensional laser shaped as an active equilateral triangle with a round piercing hole. It is demonstrated that the threshold of lasing and the directivity of light emission, for each mode, can be efficiently manipulated with the aid of the size and, especially, the placement of the piercing hole, while the frequency of emission remains largely intact.

scholarly journals Exponentially Convergent Galerkin Method for Numerical Modeling of Lasing in Microcavities with Piercing Holes

Axioms ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 184
Author(s):  
Alexander O. Spiridonov ◽  
Anna I. Repina ◽  
Ilya V. Ketov ◽  
Sergey I. Solov’ev ◽  
Evgenii M. Karchevskii
Keyword(s):  
Eigenvalue Problem ◽  
Galerkin Method ◽  
Numerical Solution ◽  
Original Problem ◽  
Boundary Integral Equations ◽  
Nonlinear Eigenvalue Problem ◽  
Boundary Integral ◽  
Generalized Eigenfunctions ◽  
Eigenvalue And Eigenfunction ◽  
Lasing Modes

The paper investigates an algorithm for the numerical solution of a parametric eigenvalue problem for the Helmholtz equation on the plane specially tailored for the accurate mathematical modeling of lasing modes of microring lasers. The original problem is reduced to a nonlinear eigenvalue problem for a system of Muller boundary integral equations. For the numerical solution of the obtained problem, we use a trigonometric Galerkin method, prove its convergence, and derive error estimates in the eigenvalue and eigenfunction approximation. Previous numerical experiments have shown that the method converges exponentially. In the current paper, we prove that if the generalized eigenfunctions are analytic, then the approximate eigenvalues and eigenfunctions exponentially converge to the exact ones as the number of basis functions increases. To demonstrate the practical effectiveness of the algorithm, we find geometrical characteristics of microring lasers that provide a significant increase in the directivity of lasing emission, while maintaining low lasing thresholds.

scholarly journals On a Steklov eigenvalue problem associated with the (p,q)-Laplacian

2021 ◽  
Vol 37 (2) ◽  
pp. 161-171
Author(s):  
LUMINIŢA BARBU ◽  
GHEORGHE MOROŞANU
Keyword(s):  
Boundary Condition ◽  
Eigenvalue Problem ◽  
Neumann Boundary Condition ◽  
Neumann Boundary ◽  
Full Description ◽  
Continuous Family ◽  
Edinburgh Math ◽  
Nonlinear Anal ◽  
Homogeneous Neumann Boundary Condition ◽  
Steklov Eigenvalue

"Consider in a bounded domain \Omega \subset \mathbb{R}^N, N\ge 2, with smooth boundary \partial \Omega, the following eigenvalue problem (1) \begin{eqnarray*} &~&\mathcal{A} u:=-\Delta_p u-\Delta_q u=\lambda a(x) \mid u\mid ^{r-2}u\ \ \mbox{ in} ~ \Omega, \nonumber \\ &~&\big(\mid \nabla u\mid ^{p-2}+\mid \nabla u\mid ^{q-2}\big)\frac{\partial u}{\partial\nu}=\lambda b(x) \mid u\mid ^ {r-2}u ~ \mbox{ on} ~ \partial \Omega, \nonumber \end{eqnarray*} where 1<r<q<p<\infty or 1<q<p<r<\infty; r\in \Big(1, \frac{p(N-1)}{N-p}\Big) if p<N and r\in (1, \infty) if p\ge N; a\in L^{\infty}(\Omega),~ b\in L^{\infty}(\partial\Omega) are given nonnegative functions satisfying \[ \int_\Omega a~dx+\int_{\partial\Omega} b~d\sigma >0. \] Under these assumptions we prove that the set of all eigenvalues of the above problem is the interval [0, \infty). Our result complements those previously obtained by Abreu, J. and Madeira, G., [Generalized eigenvalues of the (p, 2)-Laplacian under a parametric boundary condition, Proc. Edinburgh Math. Soc., 63 (2020), No. 1, 287–303], Barbu, L. and Moroşanu, G., [Full description of the eigenvalue set of the (p,q)-Laplacian with a Steklov-like boundary condition, J. Differential Equations, in press], Barbu, L. and Moroşanu, G., [Eigenvalues of the negative (p,q)– Laplacian under a Steklov-like boundary condition, Complex Var. Elliptic Equations, 64 (2019), No. 4, 685–700], Fărcăşeanu, M., Mihăilescu, M. and Stancu-Dumitru, D., [On the set of eigen-values of some PDEs with homogeneous Neumann boundary condition, Nonlinear Anal. Theory Methods Appl., 116 (2015), 19–25], Mihăilescu, M., [An eigenvalue problem possesing a continuous family of eigenvalues plus an isolated eigenvale, Commun. Pure Appl. Anal., 10 (2011), 701–708], Mihăilescu, M. and Moroşanu, G., [Eigenvalues of -\triangle_p-\triangle_q under Neumann boundary condition, Canadian Math. Bull., 59 (2016), No. 3, 606–616]."

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