W01,1 solutions in some borderline cases of Calderon–Zygmund theory

In this paper we study the existence of $W_0^{1,1}(\Omega )$ distributional solutions of Dirichlet problems whose simplest example is$\{\begin{array}{cc}?\mathrm{div}\left({|\mathrm{?}u|}^{p?2}\mathrm{?}u\right)=f(x),\hfill & \text{in}\Omega ;\hfill \\ u=0,\hfill & \text{on}?\Omega .\hfill \end{array}$     

A proof of the Tn conjecture: Centralizers,Jacobians and spectrally arbitrary sign patterns

We prove the so-called $T_n$ conjecture: for every real-monic polynomial $p(x)$ of degree $n?2$ there exists an n by n matrix with sign pattern$T_n=\left[\begin{array}{ccccc}\hfill -\hfill & \hfill +\hfill & \hfill 0\hfill & \hfill ?\hfill & \hfill 0\hfill \\ \hfill -\hfill & \hfill 0\hfill & \hfill ?\hfill & \hfill \hfill & \hfill ?\hfill \\ \hfill 0\hfill & \hfill ?\hfill & \hfill ?\hfill & \hfill ?\hfill & \hfill 0\hfill \\ \hfill ?\hfill & \hfill \hfill & \hfill ?\hfill & \hfill 0\hfill & \hfill +\hfill \\ \hfill 0\hfill & \hfill ?\hfill & \hfill 0\hfill & \hfill -\hfill & \hfill +\hfill \end{array}\right]\text{,}$whose characteristic polynomial is $p(x)$. The proof converts the problem of determining the nonsingularity of a certain Jacobi matrix to the problem of proving the non-existence of a nonzero matrix B that commutes with a nilpotent matrix with sign pattern $T_n$ and has zeros in positions $(1\text{,}1)$, and $(j+1\text{,}j)$ for $j=2\text{,}\dots \text{,}n-1$.     

Essential dimension of finite groups in prime characteristic

Let F be a field of characteristic $p>0$ and G be a smooth finite algebraic group over F. We compute the essential dimension ${\mathrm{ed}}_F(G;p)$ of G at p. That is, we show that

${\mathrm{ed}}_F(G;p)=\{\begin{array}{cc}1,\hfill & \text{if}p\text{divides}|G|,\text{and}\hfill \\ 0,\hfill & \text{otherwise.}\hfill \end{array}$

     

Boundedness in a three-dimensional chemotaxis–haptotaxis model with nonlinear diffusion

The quasilinear chemotaxis–haptotaxis system

$\{\begin{array}{cc}{u}_t=\mathrm{?}?(D(u)\mathrm{?}u)?\chi \mathrm{?}?(u\mathrm{?}v)?\xi \mathrm{?}?(u\mathrm{?}w)\hfill & \hfill \\ \phantom{u_t=}+\mu u(1?u?w),\hfill & x\in \mathrm{\Omega },t>0,\hfill \\ v_t=\mathrm{\Delta }v?v+u,\hfill & x\in \mathrm{\Omega },t>0,\hfill \\ w_t=?vw,\hfill & x\in \mathrm{\Omega },t>0,\hfill \end{array}$

is considered under homogeneous Neumann boundary conditions in a bounded and smooth domain $\mathrm{\Omega }?{\mathbb{R}}^3$. Here $\chi >0$, $\xi >0$ and $\mu >0$, $D(u)\ge c_D{u}^{m?1}$ for all $u>0$ with some $c_D>0$ and $D(u)>0$ for all $u\ge 0$. It is shown that if the ratio $\frac{\chi }{\mu }$ is sufficiently small, then the system possesses a unique global classical solution that is uniformly bounded. Our result is independent of m.     

Global existence and stabilization in a degenerate chemotaxis-Stokes system with mildly strong diffusion enhancement

A class of chemotaxis-Stokes systems generalizing the prototype

$\{\begin{array}{ccc}\hfill n_t+u?\mathrm{?}n& \hfill =\hfill & \mathrm{?}?\left(n^{m?1}\mathrm{?}n\right)?\mathrm{?}?\left(n\mathrm{?}c\right),\hfill \\ \hfill c_t+u?\mathrm{?}c& \hfill =\hfill & \mathrm{\Delta }c?nc,\hfill \\ \hfill u_t+\mathrm{?}P& \hfill =\hfill & \mathrm{\Delta }u+n\mathrm{?}?,\mathrm{?}?u=0,\hfill \end{array}$

is considered in bounded convex three-dimensional domains, where $?\in W^{2,\infty }(\mathrm{\Omega })$ is given.The paper develops an analytical approach which consists in a combination of energy-based arguments and maximal Sobolev regularity theory, and which allows for the construction of global bounded weak solutions to an associated initial-boundary value problem under the assumption that

(0.1)$m>\frac{9}{8}.$

Moreover, the obtained solutions are shown to approach the spatially homogeneous steady state $(\frac{1}{|\mathrm{\Omega }|}{\int }_{\mathrm{\Omega }}{n}_0,0,0)$ in the large time limit.This extends previous results which either relied on different and apparently less significant energy-type structures, or on completely alternative approaches, and thereby exclusively achieved comparable results under hypotheses stronger than (0.1).     

Complex variable approach to the analysis of a fractional differential equation in the real line

The first aim of this work is to establish a Peano-type existence theorem for an initial value problem involving a complex fractional derivative, and then, as a consequence of this theorem, to give a partial answer for the local existence of the continuous solution to the initial value problem:

$\{\begin{array}{cc}\hfill & D_x^{q}u(x)=f(x,u(x)),\hfill \\ \hfill & u(0)=b,(b\ne 0).\hfill \end{array}$

Moreover, for some special cases of the problem, we investigate the corresponding geometric properties of the solutions.