arXiv subjects
Publications and source records attributed to Constantin Udriste.
This paper investigates the multitime linear normal PDE systems. We study especially the controllability of such systems, obtaining complementary results to those in our recent papers. Here the multitime controllability original results are formulated using the $γ$ - gramian matrix, the Im - gramian space and a controllability functional. There are given also some original examples which illustrate and round the theoretical results.
In this paper we address again the problem of the connection between multitime Brownian sheet and heat type PDEs. The main results include: the volumetric character of the solutions of the forward (backward) diffusion-like PDEs; the forward mean value of a Brownian process as the solution of the forward heat PDE; the backward mean value of a Brownian process as the solution of the backward heat PDE; the multitime stochastic processes with volumetric dependence; the stochastic partial derivative of a stochastic process with respect to a multitime Wiener process; Hermite polynomials stochastic processes; union of Tzitzeica hypersurfaces (constant level sets of multitime stochastic processes with volumetric dependence). The original results permit to extend the complete integrability theory to multitime stochastic differential systems, using path independent curvilinear integrals and volumetric dependence.
Based on stochastic curvilinear integrals in the Cairoli-Walsh sense and in the Itô-Udrişte sense, we develop an original theory regarding the multitime stochastic differential systems. The first group of the original results refer to the complete integrable stochastic differential systems, the path independent stochastic curvilinear integral, the Itô-Udrişte stochastic calculus rules, examples of path independent processes, and volumetric processes. The second group of original results include the multitime Itô-Udrişte product formula, first stochastic integrals and adjoint multitime stochastic Pfaff systems. Thirdly, we formulate and we prove a multitime maximum principle for optimal control problems based on stochastic curvilinear integral actions subject to multitime Itô-Udrişte process constraints. Our theory requires the Lagrangian and the Hamiltonian as stochastic 1-forms.
Some optimization problems coming from the Differential Geometry, as for example, the minimal submanifolds problem and the harmonic maps problem are solved here via interior solutions of appropriate multitime optimal control problems. Section 1 underlines some science domains where appear multitime optimal control problems. Section 2 (Section 3) recalls the multitime maximum principle for optimal control problems with multiple (curvilinear) integral cost functionals and $m$-flow type constraint evolution. Section 4 shows that there exists a multitime maximum principle approach of multitime variational calculus. Section 5 (Section 6) proves that the minimal submanifolds (harmonic maps) are optimal solutions of multitime evolution PDEs in an appropriate multitime optimal control problem. Section 7 uses the multitime maximum principle to show that of all solids having a given surface area, the sphere is the one having the greatest volume. Section 8 studies the minimal area of a multitime linear flow as optimal control problem. Section 9 contains commentaries.
The aim of this paper is fourfold. Firstly, we introduce and study the f-ultra-harmonic maps. Secondly, we recall the geometric dynamics generated by a first order normal PDE system and we give original results regarding the geometric dynamics generated by other first order PDE systems. Thirdly, we determine the Gauss PDEs and the fundamental forms associated to integral manifolds of first order PDE systems. Fourthly, we change the Gauss PDEs into a geometric dynamics on the jet bundle of order one, showing that there exist an infinity of Riemannian metrics such that the lift of a submanifold map into the first order jet bundle to be an ultra-potential map.
In this paper we construct the differential equations of the stream lines that characterize plasma regarded as a non-isotropic medium geometrized by a jet rheonomic time-invariant Berwald-Moor metric. Section 1 contains historical notes regarding the Plasma Physics and its geometrical description. Section 2 analyzes the generalized Lagrange geometrical approach of the non-isotropic plasma on 1-jet spaces. Section 3 studies the non-isotropic plasma as a medium geometrized by the jet rheonomic Berwald-Moor metric.
Having in mind the well known model of Euclidean convex hypersurfaces [4], [5], and the ideas in [1] many authors defined and investigate convex hypersurfaces of a Riemannian manifold. As it was proved by the first author in [7], there follows the interdependence between convexity and Gauss curvature of the hypersurface. In this paper we define $H$-convexity of a Riemannian submanifold of arbitrary codimension, replacing the normal versor of a hypersurface with the mean curvature vector $H$. A characterization, used by B.Y. Chen [2], [3] as the definition of strictly $H$-convexity, it is obtained.
To our knowledge, there are two main references [9], [12] regarding the periodical solutions of multi-time Euler-Lagrange systems, even if the multi-time equations appeared in 1935, being introduced by de Donder. That is why, the central objective of this paper is to solve an open problem raised in [12]: what we can say about periodical solutions of multi-time Hamilton systems when the Hamiltonian is convex? Section 1 recall well-known facts regarding the equivalence between Euler-Lagrange equations and Hamilton equations. Section 2 analyzes the action that produces multi-time Hamilton equations, and introduces the Legendre transform of a Hamiltonian together a new dual action. Section 3 proves the existence of periodical solutions of multi-time Hamilton equations via periodical extremals of the dual action, when the Hamiltonian is convex.
The objective of this paper is to find some inequalities satisfied by periodical solutions of multi-time Hamilton systems, when the Hamiltonian is convex. To our knowledge, this subject of first-order field theory is still open. Section 1 recall well-known facts regarding the equivalence between Euler-Lagrange equations and Hamilton equations and analyses the action that produces multi-time Hamilton equations, emphasizing the role of the polysymplectic structure. Section 2 extends two inequalities of [21] from a cube to parallelipiped and proves two inequalityes concerning multiple periodical solutions of multi-time Hamilton equations.
The main purpose of this paper is the study of the action that produces Poisson-gradient systems and their multiple periodical solutions. The Section 1 establishes the basic tools. The section 2 underlines conditions in which the action $ϕ(u) = \displaystyle\displaystyle\int_{T_{0}}[ \displaystyle% \displaystyle{1/2}| \displaystyle\displaystyle\frac{\partial u}{% \partial t}| ^{2}+F(t,u(t)) ] dt^{1}\wedge >...\wedge dt^{p}$, that produces the Poisson-gradient systems, is continuous, and some conditions in which the general action $ϕ(u) = \displaystyle\displaystyle\int_{T_{0}}L(t,u(t), \displaystyle\displaystyle\frac{\partial u}{\partial t}(t)) dt^{1}\wedge >...\wedge dt^{p}$ is continuously differentiable. The Section 3 studies the multiple periodical solutions of a Poisson-gradient system in the case when the potential function $F$ has a spatial periodicity.
The basic aim is to extend some results and concepts of non-autonomous second order differential systems with convex potentials to the new context of multi-time Poisson-gradient PDE systems with convex potential. In this sense, we prove that minimizers of a suitable action functional are multiple periodical solutions of a Dirichlet problem associated to the Euler-Lagrange equations. Automatically, these are solutions of the associated multi-time Hamiltonian equations.
We study the periodical solutions of a Poisson-gradient PDEs system with bounded nonlinearity. Section 1 introduces the basic spaces and functionals. Section 2 studies the weak differential of a function and establishes an inequality. Section 3 formulates some conditions under which the action functional is continuously differentiable. Section 4 analyzes the Poisson-gradient systems and some conditions that ensure periodical solutions.
The paper proved that every $C^2$-solution of a given first order PDEs system, regarded on the jet fibre bundle of order one $J^1(T,M)$, may be viewed as a "generalized harmonic map", via the least squares variational method. Our ideas are structured in the following way: 1) we find a suitable geometrical structure on $J^1(T,M)$ that convert the solutions of the given PDEs system into "generalized harmonic maps"; 2) we build a natural geometry induced by a such PDEs system; 3) we construct a field theory, in a general setting, naturally attached to this PDEs system.
In this paper are constructed a series of geometrical objects on the 1-jet fibre bundle $J^1(T,M)$, which is a basic object in the study of classical and quantum field.
The paper introduces the notion of Γ-linear connection \nabla on the 1-jet fibre bundle J^1(T,M), and presents its local components. We also describe the local Ricci and Bianchi identities of $\nabla$.
A geometrization of a Kronecker $h$-regular multi-time Lagrangian function with partial derivatives of order one is described, in the sense of d-connections, d-torsions and d-curvatures.
The paper analyses the extrema of p-energy functional on a Finsler space with constant curvature.
We proved that the solutions of $C^2$ class of certain ODEs or PDEs belong to a class of harmonic maps between two convenient generalized Lagrange spaces.