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Yuxiang Li

Publications and source records attributed to Yuxiang Li.

71 records · Page 4Linked to original sources
arXiv2015

Global weak solutions for the three-dimensional chemotaxis-Navier-Stokes system with nonlinear diffusion

We consider an initial-boundary value problem for the incompressible chemotaxis-Navier-Stokes equations generalizing the porous-medium-type diffusion model $ \quad n_t+u\cdot\nabla n=Δn^m-\nabla\cdot(nχ(c)\nabla c), $ $ \quad c_t+u\cdot\nabla c=Δc-nf(c), $ $ \quad u_t+κ(u\cdot\nabla)u=Δu+\nabla P+n\nablaΦ, $ $ \quad \nabla\cdot u=0, $ in a bounded convex domain $Ω\subset\mathbb{R}^3$. It is proved that if $m\geq\frac{2}{3}$, $κ\in\mathbb{R}$, $0<χ\in C^2([0,\infty))$, $0\leq f\in C^1([0,\infty))$ with $f(0)=0$ and $Φ\in W^{1,\infty}(Ω)$, then for sufficiently smooth initial data $(n_0, c_0, u_0)$ the model possesses at least one global weak solution.

math.AP↗
arXiv2014

Radially Symmetric Solutions To The Graphic Willmore Surface Equation

We show that a smooth radially symmetric solution $u$ to the graphic Willmore surface equation is either a constant or the defining function of a half sphere in ${\mathbb R}^3$. In particular, radially symmetric entire Willmore graphs in ${\mathbb R}^3$ must be flat. When $u$ is a smooth radial solution over a punctured disk $D(ρ)\backslash\{0\}$ and is in $C^1(D(ρ))$, we show that there exist a constant $λ$ and a function $β$ in $C^0(D(ρ))$ such that $u''(r) =\fracλ{2}\log r+β(r)$; moreover, the graph of $u$ is contained in a graphical region of an inverted catenoid which is uniquely determined by $λ$ and $β(0)$. It is also shown that a radial solution on the punctured disk extends to a $C^1$ function on the disk when the mean curvature is square integrable.

math.DG↗
arXiv2013

Homotopy classes of harmonic maps of the stratified 2-spheres and applications to geometric flows

We show that the set of harmonic maps from the 2-dimensional stratified spheres with uniformly bounded energies contains only finitely many homotopy classes. We apply this result to construct infinitely many harmonic map flows and mean curvature flows of 2-sphere in the connected sum of two closed 3-dimensional manifolds $M_1\not=S^3$ and $M_2\not=S^3,\R¶^3$, which must develop finite time singularity.

math.DG↗
arXiv2011

Bubble tree of a class of conformal mappings and applications to Willmore functional

We develop a bubble tree construction and prove compactness results for $W^{2,2}$ branched conformal immersions of closed Riemann surfaces, with varying conformal structures whose limit may degenerate, in a compact Riemannian manifold with uniformly bounded areas and Willmore energies. The compactness property is applied to construct Willmore type surfaces in compact Riemannian manifolds. This includes (a) existence of a Willmore 2-sphere in ${\mathbb S}^n$ with at least 2 nonremovable singular points (b) existence of minimizers of the Willmore functional with prescribed area in a compact manifold $N$ provided (i) the area is small when genus is 0 and (ii) the area is close to that of the area minimizing surface of Schoen-Yau and Sacks-Uhlenbeck in the homotopy class of an incompressible map from a surface of positive genus to $N$ and $π_2(N)$ is trivial (c) existence of smooth minimizers of the Willmore functional if a Douglas type condition is satisfied.

math.DG↗
arXiv2011

Two-dimensional curvature functionals with superquadratic growth

For two-dimensional, immersed closed surfaces $f:Σ\to \R^n$, we study the curvature functionals $\mathcal{E}^p(f)$ and $\mathcal{W}^p(f)$ with integrands $(1+|A|^2)^{p/2}$ and $(1+|H|^2)^{p/2}$, respectively. Here $A$ is the second fundamental form, $H$ is the mean curvature and we assume $p > 2$. Our main result asserts that $W^{2,p}$ critical points are smooth in both cases. We also prove a compactness theorem for $\mathcal{W}^p$-bounded sequences. In the case of $\mathcal{E}^p$ this is just Langer's theorem \cite{langer85}, while for $\mathcal{W}^p$ we have to impose a bound for the Willmore energy strictly below $8π$ as an additional condition. Finally, we establish versions of the Palais-Smale condition for both functionals.

math.AP↗
arXiv2010

$W^{2,2}$-conformal immersions of a closed Riemann surface into $\R^n$

We study sequences $f_k:Σ_k \to \R^n$ of conformally immersed, compact Riemann surfaces with fixed genus and Willmore energy ${\cal W}(f) \leq Λ$. Assume that $Σ_k$ converges to $Σ$ in moduli space, i.e. $ϕ_k^\ast(Σ_k) \to Σ$ as complex structures for diffeomorphisms $ϕ_k$. Then we construct a branched conformal immersion $f:Σ\to \R^n$ and Möbius transformations $σ_k$, such that for a subsequence $σ_k \circ f_k \circ ϕ_k \to f$ weakly in $W^{2,2}_{loc}$ away from finitely many points. For $Λ< 8π$ the map $f$ is unbranched. If the $Σ_k$ diverge in moduli space, then we show $\liminf_{k \to \infty} {\cal W}(f_k) \geq \min(8π,ω^n_p)$. Our work generalizes results in \cite{K-S3} to arbitrary codimension.

math.DG↗
arXiv2006

A sharp Trudinger-Moser type inequality for unbounded domains in $\mathbb{R}^n$

The Trudinger-Moser inequality states that for functions $u \in H_0^{1,n}(Ω)$ ($Ω\subset \mathbb R^n$ a bounded domain) with $\int_Ω|\nabla u|^ndx \le 1$ one has $\int_Ω(e^{α_n|u|^{\frac n{n-1}}}-1)dx \le c |Ω|$, with $c$ independent of $u$. Recently, the second author has shown that for $n = 2$ the bound $c |Ω| $ may be replaced by a uniform constant $d$ independent of $Ω$ if the Dirichlet norm is replaced by the Sobolev norm, i.e. requiring $\int_Ω(|\nabla u|^n + |u|^n)dx \le 1$. We extend here this result to arbitrary dimensions $n > 2$. Also, we prove that for $Ω= \mathbb R^n$ the supremum of $\int_{\mathbb R^n} (e^{α_n|u|^{\frac n{n-1}}}-1)dx$ over all such functions is attained. The proof is based on a blow-up procedure.

math.FA↗
arXiv2005

Bubbling location for $F$-harmonic maps and Inhomogeneous Landau-Lifshitz equations

Let $f$ be a positive smooth function on a close Riemann surface (M,g). The $f-energy$ of a map $u$ from $M$ to a Riemannian manifold $(N,h)$ is defined as $$E_f(u)=\int_Mf|\nabla u|^2dV_g.$$ In this paper, we will study the blow-up properties of Palais-Smale sequences for $E_f$. We will show that, if a Palais-Smale sequence is not compact, then it must blows up at some critical points of $f$. As a sequence, if an inhomogeneous Landau-Lifshitz system, i.e. a solution of $$u_t=u\timesτ_f(u)+τ_f(u),\s u:M\to S^2$$ blows up at time $\infty$, then the blow-up points must be the critical points of $f$.

math.AP↗
arXiv2005

Remarks on the Extremal Functions for the Moser-Trudinger Inequalities

We will show in this paper that if $λ$ is very close to 1, then $$I(M,λ,m)= \sup_{u\in H^{1,n}_0(M) ,\int_M|\nabla u|^ndV=1}\int_Ω(e^{α_n |u|^\frac{n}{n-1}}-λ\sum\limits_{k=1}^m\frac{|α_nu^\frac{n}{n-1}|^k} {k!})dV,$$ can be attained, where $M$ is a compact manifold with boundary. This result gives a counter example to the conjecture of de Figueiredo, do ó, and Ruf in their paper titled "On a inequality by N.Trudinger and J.Moser and related elliptic equations" (Comm. Pure. Appl. Math.,{\bf 55}:135-152, 2002).

math.AP↗