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Partial differential equations (PDEs): Existence and uniqueness, regularity, boundary conditions, linear and non-linear operators, stability, soliton theory, integrable PDEs, conservation laws, qualitative dynamics.

7 votes
2 answers
2k views

Eigenvalues of Laplace-Beltrami on half sphere

Let $ \Delta_\theta$ denote the Laplace-Beltrami operator on $S^{N-1}$. The eigenvalues of this are well known. I assume the same is the case of this operator on the upperhalf sphere; say $ S^{N …
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6 votes
1 answer
321 views

finding subharmonic function on the ball with both Dirichlet and Neumann boundaries prescribed

I have a question which looks like some sort of inverse problem. Let $B$ denote the unit ball centered at the origin in $R^N$ (take $N \ge 2$). Given any $h:\partial B \rightarrow (0,\infty)$ (smooth) …
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  • 1,385
6 votes
0 answers
189 views

behaviour of first eigenfunction near the boundary

Consider $\Omega$ a smooth bounded domain in $R^N$ and suppose $ \phi_1(x)>0$ is the first eigenfunction of $ -\Delta$ in $H_0^1(\Omega)$ normalized however one chooses. My interest is in how $ \nab …
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  • 1,385
5 votes
1 answer
439 views

improved Sobolev embedding

This is probably not a research level question but I am struggling with the geometry. My question is related to whether some monotonicity can increase the range of exponents in the Sobolev embedding. …
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4 votes
1 answer
178 views

Elliptic regularity for two dimensional domains

Suppose $ \Omega$ is a smooth bounded domain in $ R^2$. I am interested in the regularity of solutions to $$-\Delta u(x) = f(x) \mbox{ in } \Omega$$ with $ u=0$ on $ \partial \Omega$. If $ f \in …
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4 votes
0 answers
137 views

Smooth dependence of solution to elliptic pde depending on parameter

I have a question in mind but let me generalize it slightly. Suppose I am looking at some pde like $$-\Delta u + t u = f(u)$$ in $B_1$ (here $u=u(x)$) with $u=0$ on $ \partial B_1$ where $B_1$ is t …
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  • 1,385
4 votes
0 answers
95 views

Biharmonic operator and maximum principle (PPP)

I have a question related to the Positivity Preserving Principle (PPP) for $ \Delta^2$ and related topics. Recall if $u$ solves $$\Delta^2 u = f(x) \mbox{ in } \Omega, \quad u=\partial_\nu u =0 \m …
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4 votes
1 answer
163 views

Smoothness of critical elliptic problem

I am convinced I have seen results along the lines of: if $ u \ge 0$ is an $H_0^1(\Omega)$ solution of $$-\Delta u = u^{q-1}$$ in $\Omega$ with $ u=0$ on $ \partial \Omega$ (here $\Omega$ is a smooth …
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  • 1,385
4 votes
0 answers
105 views

Gradient bounds on a solution of a linear elliptic problem

Take $\Omega$ to be a bounded domain in $N$ dimensional Euclidean space with smooth boundary and we assume $\Omega$ contains the origin. I am interested is the following equation $$ \Delta \phi(x) …
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  • 1,385
4 votes
1 answer
330 views

Fundamental gap for Schrödinger operator

Consider $ \Omega$ a smooth bounded domain in $ \mathbb R^N$. I am interested in the gap between the first and second eigenvalues of the operator $ -\Delta + V(x)$. Let $ \phi_1>0$ and $ \phi_2$ be …
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3 votes
1 answer
335 views

elliptic regularity of Neumann problem on Square

I asked a similar question the other day, but I will be more precise now. Consider $ \Omega:=(0,1 ) \times (0,1)$ and consider $$ - u_{xx}(x,y) - u_{yy}(x,y) + a(x) u_x + b(y) u_y + u = f(x,y) \mbox …
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3 votes
1 answer
133 views

Maximum principle for an elliptic like operator

I am trying to prove some monotonicity of a solution of a given pde; after considering a quantity like $ \phi(x) = x \cdot \nabla v(x)$ ($v$ is the solution of a given pde) I arrive at something alo …
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  • 1,385
3 votes
0 answers
55 views

system of Euler like ode's

I am interested in solving some linear elliptic system like $$ -\Delta \phi(x) + \frac{C_1 \psi(x)}{|x|^\beta} =f(x)$$ $$ -\Delta \psi(x) + \frac{C_2 \phi(x)}{|x|^\alpha} =g(x)$$ in $B_1$ (the u …
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3 votes
0 answers
75 views

solutions of a pde smooth with respect to a parameter

I have a generic type question, but I will pose it with a specific example. Suppose $1<p<\frac{N+2}{N-2}$ and $B_1$ is the unit ball in $ R^N$ for $N \ge 3$. Consider the pde $$-\Delta u(x) = t …
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  • 1,385
3 votes
1 answer
133 views

Positive first eigenvalue; operator satisfies maximum principle

I am attempting to understand a paper. They have $u$ is a stable smooth solution of $ -\Delta u = f(u)$ in $ \Omega$ with $ u=0$ on $ \partial \Omega$ where $\Omega$ is a bounded domain in Euclidean …
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