We develop a detailed regularity theory of $-Δ+b\cdot\nabla$ in $L^p(\mathbb R^d)$, for a wide class of vector fields. The $L^p$-theory allows us to construct associated strong Feller process in $C_\infty(\mathbb R^d)$. Our starting object is an operator-valued function, which, we prove, coincides with the resolvent of an operator realization of $-Δ+ b\cdot \nabla$, the generator of a holomorphic $C_0$-semigroup on $L^p(\mathbb R^d)$. Then the very form of the operator-valued function yields crucial information about smoothness of the domain of the generator.
In $\mathbb R^d$, $d \geq 3$, consider the divergence and the non-divergence form operators \begin{equation} \tag{$i$} - \nabla \cdot a \cdot \nabla + b \cdot \nabla, \end{equation} \begin{equation} \tag{$ii$} - a \cdot \nabla^2 + b \cdot \nabla, \end{equation} where $a=I+c \mathsf{f} \otimes \mathsf{f}$, the vector fields $\nabla_i \mathsf{f}$ ($i=1,2,\dots,d$) and $b$ are form-bounded (this includes the sub-critical class $[L^d + L^\infty]^d$ as well as vector fields having critical-order singularities). We characterize quantitative dependence on $c$ and the values of the form-bounds of the …
We construct a strong Feller process associated with $-Δ+ σ\cdot \nabla$, with drift $σ$ in a wide class of measures (weakly form-bounded measures, e.g. combining weak $L^d$ and Kato class measure singularities), by exploiting a quantitative dependence of the smoothness of the domain of an operator realization of $-Δ+ σ\cdot \nabla$ generating a holomorphic $C_0$-semigroup on $L^p(\mathbb R^d)$, $p>d-1$, on the value of the form-bound of $σ$. Our method admits extension to other types of perturbations of $-Δ$ or $(-Δ)^{\fracα{2}}$, e.g. to yield new $L^p$-regularity results for Schrödinger ope…
We consider the operator $-Δ+b \cdot \nabla$ with $b:\mathbb R^d \rightarrow \mathbb R^d$ ($d \geq 3$) in the class of form-bounded vector fields (containing vector fields having critical-order singularities), and characterize quantitative dependence of the $\mathcal W^{1+\frac{2}{q},p}$ ($2 \leq p < q$) and the $C^{0,γ}$ regularity of solutions to the corresponding elliptic equation in $L^p$ on the value of the form-bound of $b$.
We obtain the basic results concerning the problem of constructing operator realizations of the formal differential expression $\nabla \cdot a \cdot \nabla - b \cdot \nabla$ with measurable matrix $a$ and vector field $b$ having critical-order singularities as the generators of Markov semigroups in $L^p$ and $C_\infty$.
In $\mathbb R^d$, $d \geq 3$, consider the divergence and the non-divergence form operators \begin{equation} \tag{$i$} -Δ- \nabla \cdot (a-I) \cdot \nabla + b \cdot \nabla, \end{equation} \begin{equation} \tag{$ii$} - Δ- (a-I) \cdot \nabla^2 + b \cdot \nabla, \end{equation} where the second order perturbations are given by the matrix $$a-I=c|x|^{-2}x \otimes x, \quad c>-1.$$ The vector field $b:\mathbb R^d \rightarrow \mathbb R^d$ is form-bounded with the form-bound $δ>0$ (this includes a sub-critical class $[L^d + L^\infty]^d$, as well as vector fields having critical-order singularities). We…
Remarks on the paper: Ikehata, M., Extraction formulae for an inverse boundary value problem for the equation $\nabla\cdot(σ-iωε)\nabla u=0$, Inverse Problems, 18(2002), 1281-1290
We show that for an $L^2$ drift $b$ in two dimensions, if the Hardy norm of $\text{div }b$ is small, then the weak solutions to $Δu+b\cdot\nabla u=0$ have the same optimal Hölder regularity as in the case of divergence-free drift, that is, $u\in C^α_{\text{loc}}$ for all $α\in (0, 1)$.
This paper deals with a boundary-value problem in three-dimensional smooth bounded convex domains for the coupled chemotaxis-Stokes system with slow $p$-Laplacian diffusion \begin{equation}\nonumber \left\{ \begin{aligned} &n_t+u\cdot\nabla n=\nabla\cdot\left(|\nabla n|^{p-2}\nabla n\right)-\nabla\cdot(n\nabla c), &x\inΩ,\ t>0,\ \ &c_t+u\cdot\nabla c=Δc-nc,&x\inΩ,\ t>0,\ \ &u_t=Δu+\nabla P+n\nablaϕ,&x\inΩ,\ t>0,\ \ &\nabla\cdot u=0, &x\inΩ,\ t>0,\ \ \end{aligned} \right. \end{equation} where $ϕ\in W^{2,\infty}(Ω)$ is the gravitational potential. It is proved that global bounded weak solutions …
We establish a result which provides the criteria for a divergence operator dependent both on the gradient and the function itself, to satisfy the S+ property. The result is complemented by several examples and an application.
In bounded smooth domains $Ω\subset\mathbb{R}^N$, $N\in\{2,3\}$, we consider the Keller-Segel-Stokes system \begin{align*} n_t + u\cdot \nabla n &= Δn - χ\nabla \cdot(\frac{n}{c}\nabla c),\\ c_t + u\cdot \nabla c &= Δc - c + n,\\ u_t &= Δu + \nabla P + n\nabla ϕ, \qquad \nabla \cdot u=0, \end{align*} and prove global existence of generalized solutions if \[ χ<\begin{cases} \infty,&N=2,\\ \frac{5}{3},&N=3. \end{cases} \] These solutions are such that blow-up into a persistent Dirac-type singularity is excluded.
This paper investigates an incompressible chemotaxis-Navier-Stokes system with slow $p$-Laplacian diffusion \begin{eqnarray} \left\{\begin{array}{lll} n_t+u\cdot\nabla n=\nabla\cdot(|\nabla n|^{p-2}\nabla n)-\nabla\cdot(nχ(c)\nabla c),& x\inΩ,\ t>0, c_t+u\cdot\nabla c=Δc-nf(c),& x\inΩ,\ t>0, u_t+(u\cdot\nabla) u=Δu+\nabla P+n\nablaΦ,& x\inΩ,\ t>0, \nabla\cdot u=0,& x\inΩ,\ t>0 \end{array}\right. \end{eqnarray} under homogeneous boundary conditions of Neumann type for $n$ and $c$, and of Dirichlet type for $u$ in a bounded convex domain $Ω\subset \mathbb{R}^3$ with smooth boundary. Here, $Φ\in …
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_…
We consider the coupled chemotaxis Navier-Stokes model with logistic source terms \[ n_t + u\cdot \nabla n = Δn - χ\nabla \cdot (n \nabla c) + κn - μn^2\] \[ c_t + u\cdot \nabla c = Δc - nc\] \[ u_t + (u\cdot \nabla)u = Δu +\nabla P + n\nabla Φ+ f, \quad\qquad \nabla \cdot u=0 \] in a bounded, smooth domain $Ω\subset \mathbb{R}^3$ under homogeneous Neumann boundary conditions for $n$ and $c$ and homogeneous Dirichlet boundary conditions for $u$ and with given functions $f\in L^\infty(Ω\times(0,\infty))$ satisfying certain decay conditions and $Φ\in C^{1+β}(\barΩ)$ for some $β\in(0,1)$. We cons…
We consider an inverse boundary value problem for the equation $\nabla\cdot(σ-iωε)\nabla u=0$ in a given bounded domain $Ω$ at a fixed $ω>0$. $σ$ and $ε$ denote the conductivity and permittivity of the material forming $Ω$, respectively. We give some formulae for extracting information about the location of the discontinuity surface of $(σ,ε)$ from the Dirichlet-to-Neumann map. In order to obtain results we make use of two methods. The first is the enclosure method which is based on a new role of the exponentially growing solutions of the equation for the background material. The second is a g…
In bounded smooth domains $Ω\subset\mathbb{R}^N$, $N\in\{2,3\}$, considering the chemotaxis--fluid system \[ \begin{cases} \begin{split} & n_t + u\cdot \nabla n &= Δn - χ\nabla \cdot(\frac{n}{c}\nabla c) &\\ & c_t + u\cdot \nabla c &= Δc - c + n &\\ & u_t + κ(u\cdot \nabla) u &= Δu + \nabla P + n\nabla Φ& \end{split}\end{cases} \] with singular sensitivity, we prove global existence of classical solutions for given $Φ\in C^2(\barΩ)$, for $κ=0$ (Stokes-fluid) if $N=3$ and $κ\in\{0,1\}$ (Stokes- or Navier--Stokes fluid) if $N=2$ and under the condition that \[ 0<χ<\sqrt{\frac{2}{N}}. \]
In this paper, we consider the following system $$\left\{\begin{array}{ll} n_t+u\cdot\nabla n&=Δn-\nabla\cdot(n\mathcal{S}(|\nabla c|^2)\nabla c)-nm,\\ c_t+u\cdot\nabla c&=Δc-c+m,\\ m_t+u\cdot\nabla m&=Δm-mn,\\ u_t&=Δu+\nabla P+(n+m)\nablaΦ,\qquad \nabla\cdot u=0 \end{array}\right.$$ which models the process of coral fertilization, in a smoothly three-dimensional bounded domain, where $\mathcal{S}$ is a given function fulfilling $$|\mathcal{S}(σ)|\leq K_{\mathcal{S}}(1+σ)^{-\fracθ{2}},\qquad σ\geq 0$$ with some $K_{\mathcal{S}}>0.$ Based on conditional estimates of the quantity $c$ and the gra…
We consider the system \begin{align*} \begin{cases} n_t + u \cdot \nabla n = Δn - χ\nabla \cdot (\frac{n}{c} \nabla c), \\ c_t + u \cdot \nabla c = Δc - nf(c), \\ u_t + (u \cdot \nabla) u = Δu + \nabla P + n \nabla ϕ, \quad \nabla \cdot u = 0, \end{cases} \end{align*} in smooth bounded domains $Ω\subset \mathbb R^N$, $N \in \mathbb N$, for given $f \ge 0$, $ϕ$ and complemented with initial and homogeneous Neumann--Neumann--Dirichlet boundary conditions, which models aerobic bacteria in a fluid drop. We assume $f(0) = 0$ and $f'(0) = 0$, that is, that $f$ decays slower than linearly near $0$, a…
We prove that for an open domain $D \subset \mathbb{R}^d $ with $d \geq 2 $ , for every (measurable) uniformly elliptic tensor field $a$ and for almost every point $y \in D$ , there exists a unique Green's function centred in $ y $ associated to the vectorial operator $ -\nabla \cdot a\nabla $ in D. In particular, when $d > 2$ this result also implies the existence of the fundamental solution for elliptic systems, i.e. the Green function for $ -\nabla \cdot a\nabla $ in $ \mathbb{R}^d $. Moreover, introducing an ensemble $\langle\cdot \rangle$ over the set of uniformly elliptic tensor fields, …
A class of chemotaxis-Stokes systems generalizing the prototype \[\left\{ \begin{array}{rcl} n_t + u\cdot\nabla n &=& \nabla \cdot \big(n^{m-1}\nabla n\big) - \nabla \cdot \big(n\nabla c\big), c_t + u\cdot\nabla c &=& Δc-nc, u_t +\nabla P &=& Δu + n \nabla ϕ, \qquad \nabla\cdot u =0, \end{array} \right. \] is considered in bounded convex three-dimensional domains, where $ϕ\in W^{2,\infty}(Ω)$ 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…
In this paper we study the global regularity of the following 2D (two-dimensional) generalized magnetohydrodynamic equations \begin{eqnarray*} \left\{\begin{array}{llll} u_t + u \cdot \nabla u & = & - \nabla p + b \cdot \nabla b - ν(-\triangle)^α u b_t + u \cdot \nabla b & = & b \cdot \nabla u - κ(-\triangle)^β b \end{array}\right. \end{eqnarray*} and get global regular solutions when $ 0\leqslantα< 1 / 2,\,\, β\geqslant 1, \,\,3α+ 2β>3 $, which improves the results in \cite{TYZ2013}. In particular, we obtain the global regularity of the 2D generalized MHD when $α=0$ and $β>\frac 32$.
This paper considers the degenerate and singular chemotaxis-Navier--Stokes system with logistic term $n_t + u\cdot\nabla n =Δn^m - χ\nabla\cdot(n\nabla c) + κn -μn^2$, $x \in Ω,\ t>0$, $c_t + u\cdot\nabla c = Δc - nc$, $x \in Ω,\ t>0$, $u_t + (u\cdot\nabla)u = Δu + \nabla P + n\nablaΦ, \quad \nabla\cdot u = 0$, $x \in Ω,\ t>0$, where $Ω\subset \mathbb{R}^3$ is a bounded domain and $χ,κ\ge 0$ and $m, μ>0$. In the above system without fluid environment Jin (J. Differential Equations, 2017) showed existence and boundedness of global weak solutions. On the other hand, in the above system with $m=1…
In this work, we consider the one dimensional very singular fourth-order equation for solid-on-solid model in attachment-detachment-limit regime with exponential nonlinearity $$h_t = \nabla \cdot (\frac{1}{|\nabla h|} \nabla e^{\frac{δE}{δh}}) =\nabla \cdot (\frac{1}{|\nabla h|}\nabla e^{- \nabla \cdot (\frac{\nabla h}{|\nabla h|})})$$ where total energy $E=\int |\nabla h|$ is the total variation of $h$. Using a logarithmic correction $E=\int |\nabla h|\ln|\nabla h| d x$ and gradient flow structure with a suitable defined functional, we prove the evolution variational inequality solution prese…
In this paper, we investigate a chemotaxis-fluid system involving both the effect of potential force on cells and the effect of chemotactic force on fluid: \begin{equation*} \left\{ \begin{split} \partial_t n + \mathbf{u}\cdot\nabla n & = Δn - \nabla\cdot\left(χ(c)n\nabla c\right) + \nabla\cdot(n\nablaϕ), \\ \partial_t c + \mathbf{u}\cdot\nabla c &= Δc - nf(c), \\ \partial_t\mathbf{u} + κ(\mathbf{u}\cdot\nabla)\mathbf{u} + \nabla P & = Δ\mathbf{u} - n\nablaϕ+ χ(c)n\nabla c, \\ \nabla\cdot\mathbf{u} &= 0 \end{split} \right. \end{equation*} in $\mathbb{R}^d\times(0,T)\, (d=2,3)$. One of the nove…
We study a chemotaxis-Stokes system with signal consumption and logistic source terms of the form \noindent \begin{align*} \left\{ \begin{array}{r@{\ }l@{\quad}l@{\quad}l@{\,}c} n_{t}+u\cdot\!\nabla n&=Δn-\nabla\!\cdot(n\nabla c)+κn-μn^{2},\ &x\inΩ,& t>0,\\ c_{t}+u\cdot\!\nabla c&=Δc-nc,\ &x\inΩ,& t>0,\\ u_{t}&=Δu+\nabla P+n\nablaϕ,\ &x\inΩ,& t>0,\\ \nabla\cdot u&=0,\ &x\inΩ,& t>0,\\ \big(\nabla n-n\nabla c\big)\cdotν&=0,\quad c=c_{\star}(x),\quad u=0, &x\in\partialΩ,& t>0, \end{array}\right. \end{align*} where $κ\geq0$, $μ>0$ and, in contrast to the commonly investigated variants of chemotaxi…
This paper considers the chemotaxis-Navier--Stokes system with nonlinear diffusion and logistic-type degradation term \begin{align*} \begin{cases} n_t + u\cdot\nabla n = \nabla \cdot(D(n)\nabla n) - \nabla\cdot(n χ(c) \nabla c) + κn - μn^α, & x\in Ω,\ t>0, \\ c_t + u\cdot\nabla c = Δc - nf(c), & x \in Ω,\ t>0, \\ u_t + (u\cdot\nabla)u = Δu + \nabla P + n\nablaΦ+ g, \ \nabla\cdot u = 0, & x \in Ω,\ t>0, \end{cases} \end{align*} where $Ω\subset \mathbb{R}^3$ is a bounded smooth domain; $D \ge 0$ is a given smooth function such that $D_1 s^{m-1} \le D(s) \le D_2 s^{m-1}$ for all $s\ge 0$ with som…
We study the chemotaxis-fluid system \begin{align*} \left\{\begin{array}{r@{\,}l@{\quad}l@{\,}c} n_{t}&=Δn-\nabla\!\cdot(n\nabla c)-u\cdot\!\nabla n,\ &x\inΩ,& t>0,\\ c_{t}&=Δc-c+f(n)-u\cdot\!\nabla c,\ &x\inΩ,& t>0,\\ u_{t}&=Δu+\nabla P+n\cdot\!\nablaϕ,\ &x\inΩ,& t>0,\\ \nabla\cdot u&=0,\ &x\inΩ,& t>0, \end{array}\right. \end{align*} where $Ω\subset\mathbb{R}^2$ is a bounded and convex domain with smooth boundary, $ϕ\in W^{1,\infty}\left(Ω\right)$ and $f\in C^1([0,\infty))$ satisfies $0\leq f(s)\leq K_0 s^α$ for all $s\in[0,\infty)$, with $K_0>0$ and $α\in(0,1]$. This system models the chemot…
We prove two new functional inequalities of the forms\[ \int_G φ(ψ- \overlineψ) \leq \frac{1}{a}\int_G ψ\ln \left(\frac{\;ψ\;}{ \overlineψ}\right) + \frac{a}{4β_0} \left\{ \int_G ψ\right\}\int_G|\nabla φ|^2 \] and \[ \int_G ψ\ln \left(\frac{\;ψ\;}{ \overlineψ}\right) \leq \frac{1}{β_0}\left\{ \int_G ψ\right\}\int_G |\nabla \ln(ψ)|^2 \] for any finitely connected, bounded $C^2$-domain $G \subseteq \mathbb{R}^2$, a constant $β_0 > 0$, any $a > 0$ and sufficiently regular functions $φ$, $ψ$. We then illustrate their usefulness by proving long time stabilization and eventual smoothness properties …
The coupled chemotaxis fluid system \begin{equation} \left\{ \begin{array}{llc} \displaystyle n_t=Δn-\nabla\cdot(nS(x,n,c)\cdot\nabla c)-u\cdot\nabla n, &(x,t)\in Ω\times (0,T),\\ c_t=Δc-nc-u\cdot\nabla c , &(x,t)\inΩ\times (0,T),\\ u_t=Δu-κ(u\cdot\nabla)u+\nabla P+n\nablaϕ, &(x,t)\inΩ\times (0,T),\\ \nabla\cdot u=0,&(x,t)\inΩ\times (0,T), \end{array} \right.(\star) \end{equation} is considered under the no-flux boundary conditions for $n,c$ and the Dirichlet boundary condition for $u$ on a bounded smooth domain $Ω\subset\mathbb{R}^N$ ($N=2,3$), $κ=0,1$. We assume that $S(x,n,c)$ is a matrix-v…
This paper is concerned with the following quasilinear chemotaxis--Navier--Stokes system with nonlinear diffusion and rotation $$ \left\{ \begin{array}{l} n_t+u\cdot\nabla n=Δn^m-\nabla\cdot(nS(x,n,c)\cdot\nabla c),\quad x\in Ω, t>0, c_t+u\cdot\nabla c=Δc-nc,\quad x\in Ω, t>0,\\ u_t+κ(u \cdot \nabla)u+\nabla P=Δu+n\nabla ϕ,\quad x\in Ω, t>0,\\ \nabla\cdot u=0,\quad x\in Ω, t>0 \end{array}\right.\eqno(CNF) $$ is considered under the no-flux boundary conditions for $n, c$ and the Dirichlet boundary condition for $u$ in a three-dimensional convex domain $Ω\subseteq \mathbb{R}^3$ with smooth bound…
We consider an initial-boundary value problem for the incompressible four-component Keller-Segel-Navier-Stokes system with rotational flux $$\left\{\begin{array}{l} n_t+u\cdot\nabla n=Δn-\nabla\cdot(nS(x,n,c)\nabla c)-nm,\quad x\in Ω, t>0,\\ c_t+u\cdot\nabla c=Δc-c+m,\quad x\in Ω, t>0,\\ m_t+u\cdot\nabla m=Δm-nm,\quad x\in Ω, t>0,\\ u_t+κ(u \cdot \nabla)u+\nabla P=Δu+(n+m)\nabla ϕ,\quad x\in Ω, t>0,\\ \nabla\cdot u=0,\quad x\in Ω, t>0 \end{array}\right.$$ in a bounded domain $Ω\subset \mathbb{R}^3$ with smooth boundary, where $κ\in \mathbb{R}$ is given constant, $S$ is a matrix-valued sensitiv…
Systems of the type $$\begin{cases} u_t = \nabla \cdot (D_1(u) \nabla u - S_1(u) \nabla v) + f_1(u, v),\\ v_t = \nabla \cdot (D_2(v) \nabla v + S_2(v) \nabla u) + f_2(u, v) \end{cases} \qquad (\star)$$ can be used to model pursuit-evasion relationships between predators and prey. Apart from local kinetics given by $f_1$ and $f_2$, the key components in this system are the taxis terms $-\nabla \cdot (S_1(u) \nabla v)$ and $+\nabla \cdot (S_2(v) \nabla u)$; that is, the species are not only assumed to move around randomly in space but are also able to partially direct their movement depending on…
This paper deals with convergence of solutions to a class of parabolic Keller-Segel systems, possibly coupled to the (Navier-)Stokes equations in the framework of the full model \begin{eqnarray*} \left\{ \begin{array}{lcl} \, \, \partial_t n_ε + u_ε \cdot \nabla n_ε &=& Δn_ε - \nabla \cdot \Big( n_ε S(x, n_ε, c_ε)\cdot\nabla c_ε\Big) + f(x, n_ε, c_ε), \\[1mm] ε\partial_t c_ε + u_ε\cdot\nabla c_ε &=& Δc_ε - c_ε + n_ε , \\[1mm] \,\,\partial_t u_ε + κ(u_ε\cdot\nabla) u_ε &=& Δu_ε + \nabla P_ε + n_ε \nablaϕ, \qquad \nabla\cdot u_ε=0 \end{array} \right. \end{eqnarray*} to solutions of the parabolic…
The chemotaxis--Navier--Stokes system \begin{equation*}\label{0.1} \left\{\begin{array}{ll} n_t+u\cdot \nabla n=\triangle n-χ\nabla\cdotp \left(\displaystyle\frac n {c}\nabla c\right)+n(r-μn), c_t+u\cdot \nabla c=\triangle c-nc, u_t+ (u\cdot \nabla) u=Δu+\nabla P+n\nablaϕ, \nabla\cdot u=0, \end{array}\right. \end{equation*} is considered in a bounded smooth domain $Ω\subset \mathbb{R}^2$, where $ϕ\in W^{1,\infty}(Ω)$, $χ>0$, $r\in \mathbb{R}$ and $μ> 0$ are given parameters. It is shown that there exists a value $μ_*(Ω,χ, r)\geq 0$ such that whenever $ μ>μ_*(Ω,χ, r)$, the global-in-time classi…
This paper deals with the two-species Keller--Segel-Stokes system with competitive kinetics $(n_1)_t + u\cdot\nabla n_1 =Δn_1 - χ_1\nabla\cdot(n_1\nabla c)+ μ_1n_1(1- n_1 - a_1n_2)$, $(n_2)_t + u\cdot\nabla n_2 =Δn_2 - χ_2\nabla\cdot(n_2\nabla c) + μ_2n_2(1- a_2n_1 - n_2), c_t + u\cdot\nabla c =Δc - c + αn_1 +βn_2$, $u_t= Δu + \nabla P+ (γn_1 + δn_2)\nablaϕ$, $ \nabla\cdot u = 0$ under homogeneous Neumann boundary conditions in a bounded domain $Ω\subset \mathbb{R}^3$ with smooth boundary. Many mathematicians study chemotaxis-fluid systems and two-species chemotaxis systems with competitive ki…
In this note we comment on the homogenization of a random elliptic operator in divergence form $-\nabla \cdot a\nabla$, where the coefficient field $a$ is distributed according to a stationary, but not necessarily ergodic, probability measure $P$. We generalize the well-known case for $P$ stationary and ergodic by showing that the operator $-\nabla \cdot a(\frac{\cdot}{\varepsilon})\nabla$ almost surely homogenizes to a constant-coefficient, random operator $-\nabla \cdot A_h\nabla$. Furthermore, we use a disintegration formula for $P$ with respect to a family of ergodic and stationary probabi…
We consider initial-boundary value problems for the $κ$-dependent family of chemotaxis-(Navier--)Stokes systems \begin{align*} \left\{ \begin{array}{r@{\,}c@{\,}c@{\ }l@{\quad}l@{\quad}l@{\,}c} n_{t}&+&u\cdot\!\nabla n&=Δn-\nabla\!\cdot(n\nabla c),\ &x\inΩ,& t>0,\\ c_{t}&+&u\cdot\!\nabla c&=Δc-cn,\ &x\inΩ,& t>0,\\ u_{t}&+&κ(u\cdot\nabla)u&=Δu+\nabla P+n\nablaϕ,\ &x\inΩ,& t>0,\\ &&\nabla\cdot u&=0,\ &x\inΩ,& t>0, \end{array}\right. \end{align*} in a bounded domain $Ω\subset\mathbb{R}^3$ with smooth boundary and given potential function $ϕ\in C^{1+β}(\overlineΩ)$ for some $β>0$. It is known that…
In this work, we study a chemotaxis-Navier-Stokes model in a two-dimensional setting as below, \begin{eqnarray} \left\{ \begin{array}{llll} \displaystyle n_{t}+\mathbf{u}\cdot\nabla n=Δn-\nabla \cdot(n\nabla c)+f(n), &&x\inΩ,\,t>0,\\ \displaystyle c_{t}+\mathbf{u}\cdot\nabla c=Δc - c+ n, &&x\inΩ,\,t>0,\\ \displaystyle \mathbf{u}_{t}+κ(\mathbf{u}\cdot\nabla)\mathbf{u}=Δ\mathbf{u} +\nabla P+ n\nablaϕ, &&x\inΩ,\,t>0,\\ \displaystyle \nabla\cdot\mathbf{u}=0,&&x\inΩ,\,t>0.\\ \end{array} \right. \end{eqnarray} Motivated by a recent work due to Winkler, we aim at investigating generalized solvability…
We study the problem of maximizing the expected lifetime of drift diffusion in a bounded domain. More formally, we consider the PDE \[ - Δu + b(x) \cdot \nabla u = 1 \qquad \mbox{in}~Ω\] subject to Dirichlet boundary conditions for $\|b\|_{L^{\infty}}$ fixed. We show that, in any given $C^2-$domain $Ω$, the vector field maximizing the expected lifetime is (nonlinearly) coupled to the solution and satisfies $b = -\|b\|_{L^{\infty}} \nabla u/ |\nabla u|$ which reduces the problem to the study of the nonlinear PDE \[ -Δu - b \cdot \left| \nabla u \right| = 1,\] where $b = \|b\|_{L^{\infty}}$ is a…
This paper investigates the following quasilinear Keller-Segel-Navier-Stokes system $$\left\{ \begin{array}{l} n_t+u\cdot\nabla n=Δn^m-\nabla\cdot(n\nabla c),\quad x\in Ω, t>0, \\ c_t+u\cdot\nabla c=Δc-c+n,\quad x\in Ω, t>0,\\ u_t+\nabla P=Δu+n\nabla ϕ,\quad x\in Ω, t>0,\\ \nabla\cdot u=0, \quad x\in Ω, t>0 \end{array}\right.$$ under homogeneous boundary conditions of Neumann type for $n$ and $c$, and of Dirichlet type for $u$ in a three-dimensional bounded domains $Ω\subseteq \mathbb{R}^3$ with smooth boundary, where $ϕ\in W^{1,\infty}(Ω),m>0$. It is proved that if $m>\frac{4}{3}$, then for a…
In this paper, the three-dimensional chemotaxis-stokes system \begin{eqnarray*} \left\{\begin{array}{lll} \medskip n_{t}+u\cdot\nabla n=Δn^m-\nabla\cdot(n S(x,n,c)\cdot\nabla c),&x\inΩ,\ \ t>0, \medskip c_t+u\cdot\nabla c=Δc-nf(c),&x\inΩ,\ \ t>0, \medskip u_t+\nabla P=Δu +n\nablaϕ,&x\inΩ,\ \ t>0, \nabla\cdot u=0, &x\inΩ,\ \ t>0,, \end{array}\right. \end{eqnarray*} posed in a bounded domain $Ω\subset\mathbb{R}^3$ with smooth boundary is considered under the no-flux boundary condition for $n$, $c$ and the Dirichlect boundary condition for $u$ under the assumption that the Frobenius norm of the t…
The chemotaxis-Navier-Stokes system linking the chemotaxis equations \[ n_t + u\cdot\nabla n = Δn - \nabla \cdot (nχ(c)\nabla c) \] and \[ c_t + u\cdot\nabla c = Δc-nf(c) \] to the incompressible Navier-Stokes equations, \[ u_t + (u\cdot\nabla)u = Δu +\nabla P + n \nabla Φ, \qquad \nabla \cdot u = 0, \] is considered under homogeneous boundary conditions of Neumann type for $n$ and $c$, and of Dirichlet type for $u$, in a bounded convex domain $Ω\subset R^3$ with smooth boundary, where $Φ\in W^{1,\infty}(Ω)$, and where $f\in C^1([0,\infty))$ and $χ\in C^2([0,\infty))$ are nonnegative with $f(0…
A class of Keller-Segel-Stokes systems generalizing the prototype \[ \left\{ \begin{array}{rcl} n_t + u\cdot\nabla n &=& Δn - \nabla \cdot \Big(n(n+1)^{-α}\nabla c\Big), c_t + u\cdot\nabla c &=& Δc-c+n, u_t +\nabla P &=& Δu + n \nabla ϕ+ f(x,t), \qquad \nabla\cdot u =0, \end{array} \right. \qquad \qquad (\star) \] is considered in a bounded domain $Ω\subset R^3$, where $ϕ$ and $f$ are given sufficiently smooth functions such that $f$ is bounded in $Ω\times (0,\infty)$. It is shown that under the condition that \[ α>\frac{1}{3}, \] for all sufficiently regular initial data a corresponding Neuma…
This paper investigates the following Keller-Segel-Navier-Stokes system with nonlinear diffusion and rotational flux $$\begin{align}\begin{cases} &n_t+u\cdot\nabla n=Δn^m-\nabla\cdot(nS(x, n, c)\nabla c),\quad &x\in Ω, t>0, \\ &c_t+u\cdot\nabla c=Δc-c+n,\quad &x\in Ω, t>0, \\ &u_t+κ(u\cdot\nabla)u+\nabla P=Δu+n\nabla ϕ,\quad &x\in Ω, t>0, \\ &\nabla\cdot u=0,\quad &x\in Ω, t>0, \end{cases}\end{align}$$ where $κ\in \mathbb{R},ϕ\in W^{2,\infty}(Ω)$ and $S$ is a given function with values in $\mathbb{R}^{2\times2}$ which fulfills $$ |S(x,n,c)| \leq C_S $$ with some $C _S > 0$. Systems of this typ…
In this work we extend a recent result to chemotaxis fluid systems which include matrix-valued sensitivity functions $S(x,n,c):Ω\times[0,\infty)^2\to\mathbb{R}^{3\times3}$ in addition to the porous medium type diffusion, which were discussed in the previous work. Namely, we will consider the system \begin{align*} \left\{ \begin{array}{r@{\,}c@{\,}c@{\ }l@{\quad}l@{\quad}l@{\,}c} n_{t}&+&u\cdot\!\nabla n&=Δn^m-\nabla\!\cdot(nS(x,n,c)\nabla c),\ &x\inΩ,& t>0,\\ c_{t}&+&u\cdot\!\nabla c&=Δc-c+n,\ &x\inΩ,& t>0,\\ u_{t}&+&(u\cdot\nabla)u&=Δu+\nabla P+n\nablaϕ,\ &x\inΩ,& t>0,\\ &&\nabla\cdot u&=0,\ …
We show the existence of locally bounded global solutions to the chemotaxis system \[ u_t = \nabla\cdot(D(u)\nabla u) - \nabla\cdot(\frac{u}{v} \nabla v) \] \[ v_t = Δv - uv \] with homogeneous Neumann boundary conditions and suitably regular positive initial data in smooth bounded domains $Ω\subset \mathbb{R}^N$, $N\geq2$, for $D(u)\geq δu^{m-1}$ with some $δ>0$, provided that $m>1+\frac N4$.
Suppose that ${\cal L}$ is a divergence form differential operator of the form ${\cal L}f:=(1/2) e^{U}\nabla_x\cdot\big[e^{-U}(I+H)\nabla_x f\big]$, where $U$ is scalar valued, $I$ identity matrix and $H$ an anti-symmetric matrix valued function. The coefficients are not assumed to be bounded, but are $C^2$ regular. We show that if $Z=\int_{\mathbb{R}^d}e^{-U(x) }dx<+\infty$ and the supremum of the numerical range of matrix $-\frac12\nabla^2_x U+\frac12\nabla_x\left\{\nabla_x\cdot H-[\nabla_x U]^TH\right\}$ satisfies some exponential integrability condition with respect to measure $dμ=Z^{-1}e^…
Consider the following Kolmogorov type hypoelliptic operator $$ \mathscr L_t:=\mbox{$\sum_{j=2}^n$}x_j\cdot\nabla_{x_{j-1}}+{\rm Tr} (a_t \cdot\nabla^2_{x_n}), $$ where $n\geq 2$, $x=(x_1,\cdots,x_n)\in(\mathbb R^d)^n =\mathbb R^{nd}$ and $a_t$ is a time-dependent constant symmetric $d\times d$-matrix that is uniformly elliptic and bounded.. Let $\{\mathcal T_{s,t}; t\geq s\}$ be the time-dependent semigroup associated with $\mathscr L_t$; that is, $\partial_s {\mathcal T}_{s, t} f = - {\mathscr L}_s {\mathcal T}_{s, t}f$. For any $p\in(1,\infty)$, we show that there is a constant $C=C(p,n,d)>…
This paper deals with the following quasilinear Keller-Segel-Navier-Stokes system modeling coral fertilization $(*)$: $$\left\{ \begin{array}{l} n_t+u\cdot\nabla n=Δn-\nabla\cdot(nS(x,n,c)\nabla c)-nm,\quad x\in Ω, t>0, c_t+u\cdot\nabla c=Δc-c+m,\quad x\in Ω, t>0, m_t+u\cdot\nabla m=Δm-nm,\quad x\in Ω, t>0,\\ u_t+κ(u \cdot \nabla)u+\nabla P=Δu+(n+m)\nabla ϕ,\quad x\in Ω, t>0,\\ \nabla\cdot u=0,\quad x\in Ω, t>0 \end{array}\right.$$ under no-flux boundary conditions in a bounded domain $Ω\subset \mathbb{R}^3$ with smooth boundary, where $ϕ\in W^{2,\infty} (Ω)$. Here the matrix-valued function $…
We shall establish the interior Hölder continuity for locally bounded weak solutions to a class of parabolic singular equations whose prototypes are \begin{equation} u_t= \nabla \cdot \bigg( |\nabla u|^{p-2} \nabla u \bigg), \quad \text{ for } \quad 1<p<2, \end{equation} and \begin{equation} u_{t}- \nabla \cdot ( u^{m-1} | \nabla u |^{p-2} \nabla u ) =0 , \quad \text{for} \quad m+p>3-\frac{p}{N}, \end{equation} via a new and simplified proof using recent techniques on expansion of positivity and $L^{1}$-Harnack estimates.
This article deals with an initial-boundary value problem for the coupled chemotaxis-haptotaxis system with nonlinear diffusion \begin{align*} u_t=&\nabla\cdot(D(u)\nabla u)-χ\nabla\cdot(u\nabla v)-ξ\nabla\cdot(u\nabla w)+μu(1-u-w),\\ v_t=&Δv-v+u,\\ w_t=&-vw\end{align*} under homogeneous Neumann boundary conditions in a bounded smooth domain $Ω\subset\mathbb{R}^n$, $n=2, 3, 4$, where $χ, ξ$ and $μ$ are given nonnegative parameters. The diffusivity $D(u)$ is assumed to satisfy $D(u)\geqδu^{m-1}$ for all $u>0$ with some $δ>0$. It is proved that for sufficiently regular initial data global bounde…
This paper establishes existence of solutions for a partial differential equation in which a differential operator involving variable exponent growth conditions is present. This operator represents a generalization of the $p(\cdot)$-Laplace operator, i.e. $Δ_{p(\cdot)}u={\rm div}(|\nabla u|^{p(\cdot)-2}\nabla u)$, where $p(\cdot)$ is a continuous function. The proof of the main result is based on Schauder's fixed point theorem combined with adequate variational arguments. The function space setting used here makes appeal to the variable exponent Lebesgue and Sobolev spaces.
It is shown that for each finite number of Dirac measures supported at points $s_n$ in three-dimensional Euclidean space, with given amplitudes $a_n$, there exists a unique real-valued Lipschitz function $u$, vanishing at infinity, which distributionally solves the quasi-linear elliptic partial differential equation of divergence form $-\nabla\cdot(\nabla{u}/\sqrt{1-|\nabla{u}|^2})=4π\sum_{n=1}^N a_n δ_{s_n}$. Moreover, $u$ is real analytic away from the $s_n$. The result can be interpreted in at least two ways: (a) for any number of point charges of arbitrary magnitude and sign at prescribed …
