American Institute of Mathematical Sciences

A chemotherapy model for cancer treatment is studied, where the chemotherapy agent and cells are assumed to follow a predator-prey type relation. The time delays from the instant that the chemotherapy agent is injected to the instant that the treatment is effective are taken into account and dynamics of systems with or without delays are compared. First basic properties of solutions including existence and uniqueness, boundedness and positiveness are discussed. Then conditions on model parameters are established for different outcomes of the treatment. Numerical simulations are provided to illustrate theoretical results.

We characterize when the classical first and second kind of periodic orbits of the planar circular restricted \begin{document}$ 3 $\end{document}–body problem obtained by Poincaré, can be extended to perturbed planar circular restricted \begin{document}$ 3 $\end{document}–body problems. We put special emphasis when the perturbed forces are due to zonal harmonic or to a solar sail.

The analytical approach for solution of pursuit differential-difference games with pure time-lag is considered. For the pursuit local problem with the fixed time the scheme of the method of resolving functions and Pontryagin's first direct method are developed. The integral presentation of game solution based on the time-delay exponential is proposed at first time. The guaranteed times of the game termination are found, and corresponding control laws are constructed. Comparison of the times of approach by the method of resolving functions and Pontryagin's first direct method for the initial problem are made.

We consider a simplified version of the Budyko diffusive energy balance climate model. We obtain the exact number of monotone stationary solutions of the associated discontinuous nonlinear elliptic with absorption. We show that the bifurcation curve, in terms of the solar constant parameter, is S-shaped. We prove the instability of the decreasing part and the stability of the increasing part of the bifurcation curve. In terms of the Budyko climate problem the above results lead to an important qualitative information which is far to be evident and which seems to be new in the mathematical literature on climate models. We prove that if the solar constant is represented by \begin{document}$ \lambda \in (\lambda _{1}, \lambda _{2}), $\end{document} for suitable \begin{document}$ \lambda _{1}<\lambda _{2}, $\end{document} then there are exactly two stationary solutions giving rise to a free boundary (i.e. generating two symmetric polar ice caps: North and South ones) and a third solution corresponding to a totally ice covered Earth. Moreover, we prove that the solution with smaller polar ice caps is stable and the one with bigger ice caps is unstable.

In this paper we study the robustness of dynamically gradient multivalued semiflows. As an application, we describe the dynamical properties of a family of Chafee-Infante problems approximating a differential inclusion studied in [3], proving that the weak solutions of these problems generate a dynamically gradient multivalued semiflow with respect to suitable Morse sets.

In this paper, we consider the environmental defensive expenditures model with delay proposed by Russu in [16] and obtain different results about stability of equilibria in the case of absence of delay. Moreover we provide a more detailed analysis of the stability for equilibria and Hopf bifurcation in the case with delay. Finally, we discuss possible modifications of the model in order to make it more accurate and realistic.

In this paper we study the problem of Levitan/Bohr almost periodicity of solutions for dissipative differential equations (Bronshtein's conjecture for Bohr almost periodic case). We give a positive answer to this conjecture for monotone Levitan/Bohr almost periodic systems of differential/difference equations.

The paper gives a comprehensive study of Inertial Manifolds for hyperbolic relaxations of an abstract semilinear parabolic equation in a Hilbert space. A new scheme of constructing Inertial Manifolds for such type of problems is suggested and optimal spectral gap conditions which guarantee their existence are established. Moreover, the dependence of the constructed manifolds on the relaxation parameter in the case of the parabolic singular limit is also studied.

Bibliography: 38 titles.

In [15], V. Jiménez López and J. Llibre characterized, up to homeomorphism, the \begin{document}$ \omega $\end{document}-limit sets of analytic vector fields on the sphere and the projective plane. The authors also studied the same problem for open subsets of these surfaces.

Unfortunately, an essential lemma in their programme for general surfaces has a gap. Although the proof of this lemma can be amended in the case of the sphere, the plane, the projective plane and the projective plane minus one point (and therefore the characterizations for these surfaces in [15] are correct), the lemma is not generally true, see [6].

Consequently, the topological characterization for analytic vector fields on open subsets of the sphere and the projective plane is still pending. In this paper, we close this problem in the case of open subsets of the sphere.

We consider the nonautonomous perturbation \begin{document}$ x_t+Ax = f(x)+\varepsilon h(t) $\end{document} of a gradient-like system \begin{document}$ x_t+Ax = f(x) $\end{document} in a Banach space \begin{document}$ X $\end{document}, where \begin{document}$ A $\end{document} is a sectorial operator with compact resolvent. Assume the non-perturbed system \begin{document}$ x_t+Ax = f(x) $\end{document} has an attractor \begin{document}$ {\mathscr A} $\end{document}. Then it can be shown that the perturbed one has a pullback attractor \begin{document}$ {\mathscr A} _\varepsilon $\end{document} near \begin{document}$ {\mathscr A} $\end{document}. If all the equilibria of the non-perturbed system in \begin{document}$ {\mathscr A} $\end{document} are hyperbolic, we also infer from [4,6] that \begin{document}$ {\mathscr A} _\varepsilon $\end{document} inherits the natural Morse structure of \begin{document}$ {\mathscr A} $\end{document}. In this present work, we introduce the notion of nonautonomous equilibria and give a more precise description on the Morse structure of \begin{document}$ {\mathscr A} _\varepsilon $\end{document} and the asymptotically synchronizing behavior of the perturbed system. Based on the above result we further prove that the sections of \begin{document}$ {\mathscr A} _\varepsilon $\end{document} depend on time symbol continuously in the sense of Hausdorff distance. Consequently, one concludes that \begin{document}$ {\mathscr A} _\varepsilon $\end{document} is a forward attractor of the perturbed nonautonomous system. It will also be shown that the perturbed system exhibits completely a global forward synchronizing behavior with the external force.

Sometimes it is not possible to prove the uniqueness of the weak solutions for problems of mathematical physics, but it is possible to bootstrap their regularity to the regularity of strong solutions which are unique. In this paper we formulate an abstract setting for such class of problems and we provide the conditions under which the global attractors for both strong and weak solutions coincide and the fractal dimension of the common attractor is finite. We present two problems belonging to this class: planar Rayleigh–Bénard flow of thermomicropolar fluid and surface quasigeostrophic equation on torus.

In this paper we study the dynamical system generated by the solutions of optimal control problems. We obtain suitable conditions under which such systems generate multivalued semiprocesses. We prove the existence of uniform attractors for the multivalued semiprocess generated by the solutions of controlled reaction-diffusion equations and study its properties.

In this work, we consider a dynamical system generated by a parabolic-hyperbolic equation with non-local boundary conditions. The optimal control problem for this system is studied using a notion of quasi-optimal solution. Existence and uniqueness of quasi-optimal control are proved.

Reaction-diffusion equations on time-variable domains are instrinsically nonautonomous even if the coefficients in the equation do not depend explicitly on time. Thus the appropriate asymptotic concepts, such as attractors, are nonautonomous. Forward attracting sets based on omega-limit sets are considered in this paper. These are related to the Vishik uniform attractor but are not as restrictive since they depend only on the dynamics in the distant future. They are usually not invariant. Here it is shown that they are asymptotically positively invariant, in general, and, if the future dynamics is appropriately uniform, also asymptotically negatively invariant as well as upper semi continuous dependence in a parameter will be established. These results also apply to reaction-diffusion equations on a fixed domain.

We study an optimal control problem for one class of non-linear elliptic equations with \begin{document}$p$\end{document}-Laplace operator and \begin{document}$L^1$\end{document}-nonlinearity. We deal with such case of nonlinearity when we cannot expect to have a solution of the state equation for any given control. After defining a suitable functional class in which we look for solutions, we reformulate the original problem and prove the existence of optimal pairs. In order to ensure the validity of such reformulation, we provide its substantiation using a special family of fictitious optimal control problems. The idea to involve the fictitious optimization problems was mainly inspired by the brilliant book of V.S. Mel'nik and V.I. Ivanenko "Variational Methods in Control Problems for the Systems with Distributed Parameters", Kyiv, 1998.

This paper is devoted to the existence of solutions for space-fractional parabolic hemivariational inequalities by means of the well-known surjectivity result for multivalued ($S_+$) type mappings.

The focus is on the existence of weak solutions to the quasilinear first-order partial differential inclusion

\begin{document}$\partial_t \; f \:\: ∈ \:\: - {\rm{div}}_{\mathbf{x}} \big( \mathcal{G}(t, f) \; f \big) + \mathcal{U}(t, f) · f + \mathcal{W}(t, f)$ \end{document}

with values in \begin{document}$L^p({{\mathbb{R}}^{N}})$\end{document} for \begin{document}$p ∈ (1, ∞)$\end{document}. The solution is to satisfy state constraints in addition, i.e., all its values belong to a given set \begin{document}$\mathcal{V} \subset L^p({{\mathbb{R}}^{N}})$\end{document} of constraints. We specify sufficient conditions such that every function in \begin{document}$\mathcal{V}$\end{document} initializes at least one weak solution with all its values in \begin{document}$\mathcal{V}$\end{document}(so-called weak invariance a.k.a. viability of \begin{document}$\mathcal{V}$\end{document}). Due to the regularity assumptions about the set-valued coefficient mappings, these solutions prove to be renormalized (in the sense of Di Perna and Lions).

Our aim in this article is to study generalizations of the nonconserved Caginalp phase-field system based on the Maxwell-Cattaneo law with two temperatures for heat conduction and with logarithmic nonlinear terms. We obtain well-posedness results and study the asymptotic behavior of the system. In particular, we prove the existence of the global attractor. Furthermore, we give some numerical simulations, obtained with the $\mathtt{FreeFem++}$ software [24], comparing the nonconserved Caginalp phase-field model with regular and logarithmic nonlinear terms.

This paper deals with the asymptotic behavior of the solutions of the non-autonomous one-dimensional stochastic Keller-Segel equations defined in a bounded interval with Neumann boundary conditions. We prove the existence and uniqueness of tempered pullback random attractors under certain conditions. We also establish the convergence of the solutions as well as the pullback random attractors of the stochastic equations as the intensity of noise approaches zero.

We study an optimal control problem associated to a Dirichlet boundary value problem of the type

\begin{document}$ \begin{equation*} \mbox{(BVP) }\,\,\,\,\,\,\,\, {\rm{div}}\; \left[ \beta(x)\nabla u (x) + \left( A\frac {x}{|x|^2 } +g(x) \right)u(x)\right] = {\rm{div}}\; \mathcal F,\quad u\in W^{1,p}_0( \Omega ) , \end{equation*} $\end{document}

\begin{document}$ 1<p\leqslant 2, $\end{document} where \begin{document}$ \Omega $\end{document} is a bounded regular domain of \begin{document}$ \mathbb{R}^N $\end{document}, \begin{document}$ 0\in \Omega , $\end{document} \begin{document}$ \beta: \Omega \rightarrow {\mathbb R} $\end{document} is an unbounded function satisfying \begin{document}$ \beta(x)\geqslant\lambda_0>0 $\end{document} a.e., \begin{document}$ A $\end{document} is a suitably small constant, and \begin{document}$ g\in L^\infty( \Omega ; \mathbb{R}^N ) $\end{document}.

We consider the vector field \begin{document}$ \mathcal F $\end{document} as the control and the corresponding weak solution \begin{document}$ u $\end{document} to (BVP) as the state. Our aim is to find the optimal vector field \begin{document}$ \mathcal F\in L^p( \Omega ) $\end{document} so that the corresponding state \begin{document}$ u\in W^{1,p}_0( \Omega ) $\end{document} is close to the desired profile in \begin{document}$ L^p( \Omega ) $\end{document} while the norm of \begin{document}$ u $\end{document} in \begin{document}$ W^{1,p}( \Omega ) $\end{document} is not too large.

We prove that, for every \begin{document}$ p $\end{document} less than \begin{document}$ 2 $\end{document} and suitably close to \begin{document}$ 2 $\end{document}, (BVP) admits an unique weak solution and for such values of \begin{document}$ p $\end{document}, we prove the existence of optimal pairs.