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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.

4 votes
0 answers
243 views

Dynamical obstruction for a vector field to have a Harmonic divergence

Let $(M,g)$ be an analytic Riemannian manifold and $X$ be an analytic vector field on $M$. Can we always have a volume form $\Omega$ such that $\operatorname{Div}_{\Omega} X$ is a harmonic …
Ali Taghavi's user avatar
3 votes
0 answers
89 views

Cycloid on manifolds

Inspired by differential equation $$y(1+y'^2)=c$$ which generates the cycloid we consider the following differential equation on a Riemannian manifold: $$f(1+|\nabla f|^2)=c$$ On the other hand th …
Ali Taghavi's user avatar
1 vote
0 answers
97 views

The module generated by kernel of an elliptic differential operator

Let $D$ be an elliptic differential operator defined on $\Gamma(E)$ where $\Gamma (E)$ is the space of smooth sections of vector bundle $E$ over a smooth manifold $M$. So $\Gamma (E)$ is a $C^\i …
Ali Taghavi's user avatar
3 votes
1 answer
272 views

Harmonic interpolation with analytic initial condition

Let $n>1$ and $M\subset \mathbb{R}^n$ be a (sufficiently low dimensional) compact analytic submanifold. Assume that $f:\mathbb{R}^n\to \mathbb{R}$ is an analytic function. Is there a Harmonic funct …
Ali Taghavi's user avatar
4 votes
1 answer
373 views

Differential inequalities under which a flat function must be identically zero

Let $f:\mathbb{R}\to \mathbb{R}$ be a smooth function which is flat at $0\in \mathbb{R}$. That is $f^{(k)}(0)=0,\; k=0,1,2,\ldots $. Assume that $|f''(x)|\leq M|f(x)|\quad \forall x\in \mathbb{R}$ …
Ali Taghavi's user avatar
4 votes
1 answer
825 views

Does $P_xP_y+Q_xQ_y=0 \implies$ "non-existence of limit cycle" for $P\partial_x+Q\partial_y$...

Let $X=P\partial_x+Q\partial_y$ be a vector field on the plane $\mathbb{R}^2$. Assume that we have :$$P_xP_y+Q_xQ_y=0$$ Does this imply that the vector field $X$ is a divergence-free vector field w …
Ali Taghavi's user avatar
2 votes
1 answer
235 views

Elliptic operators and Leibniz rule

Let $M$ be a manifold. Does it necessarily admit an elliptic operator on $C^{\infty}(M)$ which satisfy Leibniz rule? Let $M$ be a symplectic manifold with the standard Poisson structure on $C^{\inf …
Ali Taghavi's user avatar
0 votes
1 answer
147 views

Is it a sufficient condition for linearity?

Edit: According to the comment by LSpice we come back to the initial version of this question Let $f:\mathbb{R}^n\to \mathbb{R}^n$ be a smooth function such that for every $x\in \mathbb{R}^n$ the der …
Ali Taghavi's user avatar
6 votes
0 answers
266 views

Elliptic foliations of the plane

A $1$ dimensional foliation of the plane $\mathbb{R}^2$is called elliptic if it admits a non vanishing smooth tangent vector field $X$ with the following properties: The differential operator …
Ali Taghavi's user avatar
2 votes
0 answers
463 views

A Fourier elliptic vector field on a Riemannian manifold

Motivation for this question: Let $X$ be a vector field on a manifold $M$. Obviously the differential operator $D:C^{\infty}(M)\to C^{\infty}(M)$ with $D(f)=X.f$ is not an elliptic opetator when $\di …
Ali Taghavi's user avatar
6 votes
1 answer
340 views

Fredholm theory of non elliptic operators

In this question we search for a big list of non elliptic operators whose Fredholm index is finite or whose Fredholm theory is extensively discussed. The main motovation is the conference linked in th …
2 votes
1 answer
131 views

Global first integral for certain $3$ dimensional system

A physicist colleague asks me the following question. I have no idea to answer him. Your answer is very appreciated. Is there a global first integral on $\mathbb{R}^3$ for the following vector field? …
Ali Taghavi's user avatar
0 votes
0 answers
62 views

A uniform upper bound for Fredholm index of Laplace quasi-operators on a compact paralleliza...

Assume that $M$ is a compact parallelizable manifold. Is there an upper bound for the absolute value of Fredholm index of all operators in the form $D=\sum_{i=1}^n \partial^2/\partial{X_i^2} …
Ali Taghavi's user avatar
6 votes
2 answers
613 views

On equation $\Delta \circ \partial/\partial X=\partial/\partial X \circ \Delta$ on a Riemann...

Assume that $M$ is a compact Riemannian manifold whose Laplacian is denoted by $\Delta$. Assume that the Euler characteristic of $M$ is zero. Does $M$ admit a non vanishing vector field …
Ali Taghavi's user avatar
0 votes
0 answers
76 views

A kind of heat equation on a foliated 3D manifold whose leaves are invariant under the flow ...

Assume that $\mathcal{F}$ is a foliation of a $3$ dimensional compact Riemannian manifold $M$ which is invariant under flow of a transversal non vanishing vector field $X$. Let $\Delta_{\ …
Ali Taghavi's user avatar

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