Piotr Michał Bies
We study parabolic equations in variable Hölder spaces on domains of Euclidean spaces. The existence and uniqueness of solutions is proved.
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H{ö}lder regularity of parabolic equations with Dirichlet boundary conditions and application to reaction-diffusion and reaction-cross-diffusion systems
本文研究了具有狄利克雷边界条件的抛物方程的Hölder正则性，并将其应用于证明反应扩散和反应交叉扩散系统的全局强解存在性及解的估计。
We show that local weak solutions to parabolic systems of p-Laplace type are H{ö}lder continuous in time with values in a spatial Lebesgue space and H{ö}lder continuous on almost every time line. We provide an elementary and self-contained proof building on the local higher integrability result of Kinnunen and Lewis.
This work studies the regularity and the geometric significance of solution of the Cauchy problem for a degenerate parabolic equation $u_{t}=Δu^{m}$. Our main objective is to improve the H$\ddot{o}$lder estimate obtained by pioneers and then, to show the geometric characteristic of free boundary of degenerate parabolic equation. To be exact, the present work will show that: (1) the weak solution $u(x,t)\in{}C^{α,\fracα{2}}(\mathbb{R}^{n}\times\mathbb{R}^{+})$, where $α\in(0,1)$ when $m\geq2$ and $α=1$ when $m\in(1,2)$; (2) the surface $ϕ=(u(x,t))^β$ is a complete Riemannian manifold, which is …
In this paper we study a rather wide class of quasilinear parabolic problems with nonlinear boundary condition and nonstandard growth terms. It includes the important case of equations with a $p(t,x)$-Laplacian. By means of the localization method and De Giorgi's iteration technique we derive global a priori bounds for weak solutions of such problems. Our results seem to be new even in the constant exponent case.
In this article we derive a priori error estimates for the $hp$-version of the mortar finite element method for parabolic initial-boundary value problems. Both semidiscrete and fully discrete methods are analysed in $L^2$- and $H^1$-norms. The superconvergence results for the solution of the semidiscrete problem are studied in an eqivalent negative norm, with an extra regularity assumption. Numerical experiments are conducted to validate the theoretical findings.
We prove a priori gradient bounds for classical solutions of the fully nonlinear parabolic equation $$u_{t}=F(D^2u,D u,u,x,t).$$ The domain is the torus {\mathbb{T}}^{d} of dimension $d\ge1$. Up to the price of technicalities, our work can be extended to the case of bounded domains or the case of the whole space ${\mathbb{R}}^d$. Several applications are given, including the standard porous medium equation.
We investigate some smoothness properties for a transport-diffusion equation involving a class of non-degerate L{é}vy type operators with singular drift. Our main argument is based on a duality method using the molecular decomposition of Hardy spaces through which we derive some H{ö}lder continuity for the associated parabolic PDE. This property will be fulfilled as far as the singular drift belongs to a suitable Morrey-Campanato space for which the regularizing properties of the L{é}vy operator suffice to obtain global H{ö}lder continuity.
A priori estimates of solutions to local and nonlocal superlinear parabolic problems
本文研究超线性抛物型问题变号解的先验估计，涵盖局部与非局部情形，应用包括爆破速率等，方法基于能量、插值及Pohozaev恒等式。
A'priori estimates and precise regularity for parabolic systems with discontinuous data
本文研究了具有不连续主系数的抛物系统，通过势分析和奇异积分算子的有界性，证明了Sobolev和Sobolev-Morrey空间中的先验估计，并给出了解及其导数的精确正则性刻画。
We prove boundedness of gradients of solutions to quasilinear parabolic system, the main part of which is a generalization to p-Laplacian and its right hand side's growth depending on gradient is not slower (and generally strictly faster) than p - 1. This result may be seen as a generalization to the classical notion of a controllable growth of right hand side, introduced by Campanato, over gradients of p-Laplacian-like systems. Energy estimates and nonlinear iteration procedure of a Moser type are cornerstones of the used method.
A source identification problem in a bi-parabolic equation: convergence rates and some optimal results
针对双抛物方程空间源函数终值观测识别的不适定问题，本文首次采用拟可逆性方法，得到更优的Hölder阶先验/后验误差估计，部分达最优阶，还首次允许源的时间分量变号，拓展了问题适用范围。
A priori estimates for general elliptic and parabolic boundary value problems over irregular domains
本文提出了一种统一方法，用于处理一般椭圆和抛物边值问题在不规则区域上的先验估计，涵盖多种边界条件和应用领域。
A priori estimates for parabolic Monge-Ampère type equations
本文研究抛物型 Monge–Ampère 方程在一致凸区域上的第一初边值问题，通过先验估计建立凸解的存在性与正则性，并将方法推广至 $0<\gamma\le 1$ 的 $\gamma$-Gauss 曲率流。
A priori estimates and Liouville-type theorems for the semilinear parabolic equations involving the nonlinear gradient source
本文研究含非线性梯度源的半线性热方程，通过逐点梯度估计、Gidas-Spruck 积分法和 doubling lemma 证明 Liouville 型定理并导出普适先验估计。
In this paper, we derive a priori estimates for the gradient and second order derivatives of solutions to a class of Hessian type fully nonlinear parabolic equations with the first initial-boundary value problem on Riemannian manifolds. These a priori estimates are derived under conditions which are nearly optimal. Especially, there are no geometric restrictions on the boundary of the Riemannian manifolds. And as an application, the existence of smooth solutions to the first initial-boundary value problem even for infinity time is obtained.
In this paper, we prove existence of \emph{very weak solutions} to nonhomogeneous quasilinear parabolic equations beyond the duality pairing. The main ingredients are a priori esitmates in suitable weighted spaces combined with the compactness argument developed in \cite{bulicek2018well}. In order to obtain the a priori estimates, we make use of the full Calderón-Zygmund machinery developed in the past few years and combine it with some sharp bounds for the subclass of Muckenhoupt weights considered in this paper.
We prove a self-improving property for reverse H{ö}lder inequalities with non-local right hand side. We attempt to cover all the most important situations that one encounters when studying elliptic and parabolic partial differential equations as well as certain fractional equations. We also consider non-local extensions of A$\infty$ weights. We write our results in spaces of homogeneous type.
We deal with the problem of determining a time varying inclusion within a thermal conductor. In particular we study the continuous dependance of the inclusion from the Dirichlet-to-Neumann map. Under a priori regularity assumptions on the unknown defect we establish logarithmic stability estimates.
In this paper, we are concerned with the first initial boundary value problem for a class of fully nonlinear parabolic equations on Riemannian manifolds. As usual, the establishment of the a priori C^2 estimates is our main part. Based on these estimates, the existence of classical solutions is proved under conditions which are nearly optimal.
A priori bounds for the generalized parabolic Anderson model in the full subcritical regime
该研究利用正则性结构框架，证明了有限体积下广义抛物Anderson模型在全次临界区域内的先验界，为该模型的分析提供了关键的理论支撑。
Boundedness of single layer potentials associated to divergence form parabolic equations with complex coefficients
研究了具复系数散度形式抛物型算子的单层位势有界性，证明其可归结为两个关键估计，并通过建立局部抛物型Tb定理和逆向Hölder不等式在实对称算子下完成验证，为经典边值问题的可解性奠定基础。
We consider the situation when an elliptic problem in a subdomain $Ω_1$ of an $n$-dimensional bounded domain $Ω$ is coupled via inhomogeneous canonical transmission conditions to a parabolic problem in $Ω\setminusΩ_1$. In particular, we can treat elliptic-parabolic equations in bounded domains with discontinuous coefficients. Using Fourier multiplier techniques, we prove an a priori estimate for strong solutions to the equations in $L^p$-Sobolev spaces.
We consider the Hardy-Hénon parabolic equation $u_t-Δu =|x|^a |u|^{p-1}u$ with $p>1$ and $a\in {\mathbb R}$. We establish the space-time singularity and decay estimates, and Liouville-type theorems for radial and nonradial solutions. As applications, we study universal and a priori bound of global solutions as well as the blow-up estimates for the corresponding initial boundary value problem.
We prove $L^p$-parabolic a-priori estimates for $\partial_t u + \sum_{i,j=1}^d c_{ij}(t)\partial_{x_i x_j}^2 u = f $ on $R^{d+1}$ when the coefficients $c_{ij}$ are locally bounded functions on $R$. We slightly generalize the usual parabolicity assumption and show that still $L^p$-estimates hold for the second spatial derivatives of $u$. We also investigate the dependence of the constant appearing in such estimates from the parabolicity constant. Finally we extend our estimates to parabolic equations involving non-degenerate Ornstein-Uhlenbeck type operators.
Global well-posedness for the nonlinear generalized parabolic Anderson model equation
本文基于仿射控制分布和重正化方法，将非线性抛物Anderson模型方程拆分为两个简单方程，通过先验估计、光滑逼近及经典能量估计，证明了该方程在二维环面上的整体适定性与解的唯一性。
We present a new, short proof of the increased regularity obtained by solutions to uniformly parabolic partial differential equations. Though this setting is fairly introductory, our new method of proof, which uses a priori estimates, can be extended to prove analogous results for problems with time-dependent coefficients, transport equations, and nonlinear equations even when other tools, such as semigroup methods or the use of explicit fundamental solutions, are unavailable.
Boundary value problems for some quasilinear parabolic equations under minimal conditions on the coefficients
研究拟线性抛物边值问题，给出保证Sobolev类解存在唯一性的尖锐条件，包括数据的光滑性、相容性及确保极值原理的不等式，证明基于先验估计和参数延拓法。
We study the existence of segregated solutions to a class of reaction-diffusion systems with strong interactions, arising in many physical applications. These special solutions are obtained as weak limits of minimizers of a family of perturbed functionals. We prove some a priori estimates through a minimization procedure which is nonstandard in the parabolic theory: our approach is purely variational and all the information is encoded in the family of functionals we consider.
In this paper, we consider the following type of non-local (pseudo-differential) operators $\LL $ on $\R^d$: $$ \LL u(x) =\frac12 \sum_{i, j=1}^d \frac{\partial}{\partial x_i} (a_{ij}(x) \frac{\partial}{\partial x_j}) + \lim_{\eps \downarrow 0} \int_{\{y\in \R^d: |y-x|>\eps\}} (u(y)-u(x)) J(x, y) dy, $$ where $A(x)=(a_{ij}(x))_{1\leq i, j\leq d}$ is a measurable $d\times d$ matrix-valued function on $\R^d$ that is uniform elliptic and bounded and $J$ is a symmetric measurable non-trivial non-negative kernel on $\R^d\times \R^d$ satisfying certain conditions. Corresponding to $\LL$ is a symmetr…
In this paper we will review the main results concerning the issue of stability for the determination unknown boundary portion of a thermic conducting body from Cauchy data for parabolic equations. We give detailed and selfcontained proofs. We prove that such problems are severely ill-posed in the sense that under a priori regularity assumptions on the unknown boundaries, up to any finite order of differentiability, the continuous dependence of unknown boundary from the measured data is, at best, of logarithmic type.
In this paper we study the following parabolic system \begin{equation*} Δ\u -\partial_t \u =|\u|^{q-1}\u\,χ_{\{ |\u|>0 \}}, \qquad \u = (u^1, \cdots , u^m) \ , \end{equation*} with free boundary $\partial \{|\u | >0\}$. For $0\leq q<1$, we prove optimal growth rate for solutions $\u $ to the above system near free boundary points, and show that in a uniform neighbourhood of any a priori well-behaved free boundary point the free boundary is $C^{1, α}$ in space directions and half-Lipschitz in the time direction.
In this paper, we study a class of nonlinear evolution equations with damping arising in fluid dynamics and rheology. The nonlinear term is monotone and possesses a convex potential but exhibits non-standard growth. The appropriate functional framework for such equations is the modular Museilak-Spaces. We prove the existence and uniqueness of a weak solution using an approximation approach by combining an internal approximation with the backward Euler scheme, also a priori error estimate for the temporal semi-discretization is given.
On some Elliptic and Parabolic Problems Involving the Anisotropic $p(u)$-Laplacian
研究由各向异性$p(u)$-拉普拉斯算子驱动的椭圆和抛物方程，利用变指数Sobolev空间、伪单调算子、时间离散及Schauder不动点定理，证明了弱解的存在性。
We study fractional parabolic equations with indefinite nonlinearities $$ \frac{\partial u} {\partial t}(x,t) +(-Δ)^s u(x,t)= x_1 u^p(x, t),\,\, (x, t) \in \mathbb{R}^n \times \mathbb{R}, $$ where $0<s<1$ and $1<p<\infty$. We first prove that all positive bounded solutions are monotone increasing along the $x_1$ direction. Based on this we derive a contradiction and hence obtain non-existence of solutions. These monotonicity and nonexistence results are crucial tools in a priori estimates and complete blow-up for fractional parabolic equations in bounded domains. To this end, we introduce seve…
The Cauchy-Dirichlet Problem for Complex Hessian Flows: From A Priori Estimates to Pluripotential Theory
研究Hermitian流形和有界严格m-伪凸域上抛物复Hessian方程的Cauchy-Dirichlet问题，通过先验估计建立光滑解的存在唯一性，并发展退化右端项的势理论框架。
In this paper, we study the numerical approximation of a coupled system of elliptic-parabolic equations posed on two separated spatial scales. The model equations describe the interplay between macroscopic and microscopic pressures in an unsaturated heterogeneous medium with distributed microstructures as they often arise in modeling reactive flow in cementitious-based materials. Besides ensuring the well-posedness of our two-scale model, we design two-scale convergent numerical approximations and prove a priori error estimates for the semidiscrete case. We complement our analysis with simulat…
We show the existence of solution in the maximal $L_p-L_q$ regularity framework to a class of symmetric parabolic problems on a uniformly $C^2$ domain in ${\mathcal R}$. Our approach consist in showing ${\mathcal R}$ - boundedness of families of solution operators to corresponding resolvent problems first in the whole space, then in half-space, perturbed half-space and finally, using localization arguments, on the domain. Assuming additionally boudedness of the domain we also show exponential decay of the solution. In particular, our approach does not require assuming a priori the uniform Lopa…
We study the parabolic flow for generalized complex Monge-Ampère type equations on closed Hermitian manifolds. We derive {\em a priori} $C^\infty$ estimates for normalized solutions, and then prove the $C^\infty$ convergence.
For a class of quasilinear parabolic systems with nonlinear Robin boundary conditions we construct a compact local solution semiflow in a nonlinear phase space of high regularity. We further show that a priori estimates in lower norms are sufficient for the existence of a global attractor in this phase space. The approach relies on maximal $L_p$-regularity with temporal weights for the linearized problem. An inherent smoothing effect due to the weights is employed for gradient estimates. In several applications we can improve the convergence to an attractor by one regularity level.
Hölder Continuity for Fully Fractional Parabolic Equations with Space-time Nonlocal Operators
本文研究含空间分数阶扩散与Marchaud型分数阶时间导数的全分数阶抛物型方程，在不假设解和非齐次项有界的条件下，引入时间依赖非局部尾项，利用非局部De Giorgi迭代技术证明弱解的局部有界性与局部Hölder连续性。
Let Omega be a non-empty open proper and connected subset of R^n. Consider p elliptic Schrödinger type operator L_{E}u=A_{E}u+V in Omega, and the linear parabolic operator L_{P}u=A_{P}u+Vu in Omega x (0,T), where the coefficients of A_{E} and A_{P} are in VMO and the potential V satisfies a reverse-Hölder condition. The aim of this paper is to obtain a priori estimates for the operators L_{E} and L_{P} in weighted Sobolev spaces involving the distance to the boundary and weights in a local-A class.
Neumann Problems for Elliptic and Parabolic Sum Hessian Equations
本文研究与 Hessian 方程的 Neumann 边值问题，在几乎凸且一致 $(k-1)$-凸区域中建立 $(k-1)$-容许解的先验 $C^2$ 估计与存在性，并推广至一致凸区域及抛物型情形。
We study the boundary regularity properties and derive a priori pointwise supremum estimates of weak solutions and their derivatives in terms of suitable weighted $L^2$-norms for a class of degenerate parabolic equations that satisfy homogeneous Dirichlet boundary conditions on certain portions of the boundary. Such equations arise in population genetics in the study of models for the evolution of gene frequencies. Among the applications of our results is the description of the structure of the transition probabilities and of the hitting distributions of the underlying gene frequencies process…
A nonlinear parabolic equation of the fourth order is analyzed. The equation is characterized by a mobility coefficient that degenerates at 0. Existence of at least one weak solution is proved by using a regularization procedure and deducing suitable a-priori estimates. If a viscosity term is added and additional conditions on the nonlinear terms are assumed, then it is proved that any weak solution becomes instantaneously strictly positive. This in particular implies uniqueness for strictly positive times and further time-regularization properties. The long-time behavior of the problem is als…
A degenerate fourth-order parabolic equation modeling condensation phenomena related to Bose-Einstein particles is analyzed. The model is a Fokker-Planck-type approximation of the Boltzmann-Nordheim equation, only keeping the leading order term. It maintains some of the main features of the kinetic model, namely mass and energy conservation and condensation at zero energy. The existence of a local-in-time nonnegative continuous weak solution is proven. If the solution is not global, it blows up with respect to the $L^\infty$ norm in finite time. The proof is based on approximation arguments, i…
Well-Posedness of Quasilinear Parabolic Equations in Time-Weighted Spaces
本文研究定义域严格包含的拟线性抛物方程，借助抛物正则化效应证明其在时间加权空间的适定性与中间空间半流生成，可通过更弱先验估计得全局存在性，以趋化系统为例验证。
Well--posedness for the continuum Calogero--Moser equations by parabolic regularization
通过抛物正则化、一致先验估计和 Bona--Smith 逼近，证明了聚焦和散焦连续 Calogero--Moser 方程在 $H^s_+$ 中全局适定，聚焦情形需质量条件。
Inverse source problem for the space-time fractional parabolic equation on a metric star graph with an integral overdetermination condition
本文研究度量星图上分数阶抛物型方程初边值问题，基于先验估计证明强解存在唯一性，并首次通过算子方程转化研究带积分超定条件的时空分数阶逆源问题，证明预解算子适定。
We consider a one-dimensional system arising from a chemotaxis model in tumour angiogenesis, which is described by a Keller-Segel equation with singular sensitivity. This hyperbolic-parabolic system is known to allow viscous shocks (so-called traveling waves), and in literature, their nonlinear stabilities have been considered in the class of certain mean-zero small perturbations. We show the global existence of the solution without assuming the mean-zero condition for any initial data as arbitrarily large perturbations around traveling waves in the Sobolev space $H^1$ while the shock strength…
We study the parabolic complex Monge-Ampère type equations on closed Hermitian manfolds. We derive uniform $C^\infty$ {\em a priori} estimates for normalized solutions, and then prove the $C^\infty$ convergence. The result also yields a way to carry out method of continuity for elliptic Monge-Ampére type equations.
We obtain new $L^1$ contraction results for bounded entropy solutions of Cauchy problems for degenerate parabolic equations. The equations we consider have possibly strongly degenerate local or non-local diffusion terms. As opposed to previous results, our results apply without any integrability assumption on the %(the positive part of the difference of) solutions. They take the form of partial Duhamel formulas and can be seen as quantitative extensions of finite speed of propagation local $L^1$ contraction results for scalar conservation laws. A key ingredient in the proofs is a new and non-t…
A priori bounds for 2-d generalised Parabolic Anderson Model
本文在Hairer正则结构框架下，针对二维广义抛物型安德森模型给出先验界，保证解非爆炸且多项式增长，还证明环面相关模型全局适定及测度存在，估计适用于Itô SPDE并表明迹类区域外随机流存在。
We present some new ideas to derive {\em a priori} second order estiamtes for a wide class of fully nonlinear parabolic equations. Our methods, which produce new existence results for the initial-boundary value problems in $\bfR^n$, are powerful enough to work in general Riemannian manifolds.
A priori estimates for solutions to Landau equation under Prodi-Serrin like criteria
该研究引入Prodi-Serrin型准则，给出了所有经典软势、$d\geq3$维空间齐次Landau方程解的先验估计，涵盖三维库仑相互作用物理情形，推广了已有工作，且方法为定量，无需复杂非线性抛物方程工具。
This work focuses on drift-diffusion equations with fractional dissipation $(-Δ)^α$ in the regime $α\in (1/2,1)$. Our main result is an a priori Hölder estimate on smooth solutions to the Cauchy problem, starting from initial data with finite energy. We prove that for some $β\in (0,1)$, the $C^β$ norm of the solution depends only on the size of the drift in critical spaces of the form $L^{q}_{t}(BMO^{-γ}_{x})$ with $q>2$ and $γ\in (0,2α-1]$, along with the $L^{2}_{x}$ norm of the initial datum. The proof uses the Caffarelli/Vasseur variant of De Giorgi's method for non-local equations.
Parabolic De Giorgi classes with doubly nonlinear, nonstandard growth: local boundedness under exact integrability assumptions
该研究定义了含非平衡能量估计的抛物型De Giorgi函数类$\mathcal{PDG}$，证明其在奇异抛物算子的三类增长条件下局部有界，次临界情形的结果为全新成果，无需额外可积性条件。
A priori Bound of Solutions to a Class of Elliptic/Parabolic Cross Diffusion Systems of $m$ Equations on Two/Three Dimensional Domains. Existence on thin domains
该研究针对二维/三维区域上含$m$个方程的椭圆/抛物交叉扩散系统，建立了解的先验界，解决了对应情形的存在性与全局存在性问题，给出一般维数的新反例，还证明了$m=N=3$时区域薄性的充要性，拓展了非线性交叉扩散系统的全局存在性结果。
In this paper, we obtain $C^{1,α}$ estimates for weak solutions of certain quasilinear parabolic equations satisfying nonstandard growth conditions, the prototype examples being $$u_t - \text{div} (|\nabla u|^{p-2} \nabla u + a(t)|\nabla u|^{q-2} \nabla u) = 0,$$ $$u_t - \text{div} (|\nabla u|^{p(t)-2} \nabla u) = 0.$$ under the assumption that the solutions a priori have bounded gradient. We build on the recently developed scaling and covering argument which allows us to consider the singular and degenerate cases in a uniform manner and with minimal regularity requirements on the phase switch…
This paper is concerned with the existence and stability of phase transition steady states to a quasi-linear hyperbolic-parabolic system of chemotactic aggregation, which was proposed in \cite{ambrosi2005review, gamba2003percolation} to describe the coherent vascular network formation observed {\it in vitro} experiment. Considering the system in the half line $ \mathbb{R}_{+}=(0,\infty)$ with Dirichlet boundary conditions, we first prove the existence \textcolor{black}{and uniqueness of non-constant phase transition steady states} under some structure conditions on the pressure function. Then …
In the theory of second-order, nonlinear elliptic and parabolic equations, obtaining local or global gradient bounds is often a key step for proving the existence of solutions but it may be even more useful in many applications, for example to singular perturbations problems. The classical Bernstein's method is a well-known tool to obtain these bounds but, in most cases, it has the defect of providing only a priori estimates. The "weak Bernstein's method", based on viscosity solutions' theory, is an alternative way to prove the global Lipschitz regularity of solutions together with some estima…
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