
An optimal control problem from the differential geometric viewpoint consists of finding integral curves of vector fields depending on parameters, called controls, satisfying endpoint conditions and minimizing a particular functional. High order Maximum Principle (Krener, 1977) provides necessary conditions for finding optimal solutions. These conditions include the first order necessary conditions in Pontryagin's Maximum Principle.
Here, we state high order Maximum Principle for controlaffine systems in a weaker way by means of a presymplectic equation. This equation starts a presymplectic constraint algorithm in the sense of GotayNesterHinds. We establish the connections between the presymplectic constraint algorithm and the candidates to be optimal curves obtained from the necessary conditions in high order Maximum Principle. These connections are obtained by means of the high order perturbation cones that contain the vectors that approximate conveniently all the perturbations of a reference trajectory.
An optimal control problem has different kinds of solutions: the normal and the abnormal ones. As application of the above results, we characterize the abnormal extremals, i.e., curves candidates to be optimal, for control mechanical systems described by affine connections. The peculiarity of abnormality is that, in a first approach, does not depend on the cost function whose functional needs to be minimized.
The concept of graph energy was defined by Ivan Gutman in 1978 and originates from theoretical chemistry. To determine the energy of a graph, we essentially add up the eigenvalues (in absolute value) of the adjacency matrix of a graph. Recently, a few analogous quantities of energy have been defined, including the Laplacian energy and distance energy. In this talk, we analyze the normalized Laplacian energy of a graph, called Lenergy, defined as

In the course of their work on Salem numbers and uniform distribution modulo 1 (see Publ. Math. Debrecen 64(2004), 329341), A. Akiyama and Y. Tanigawa proved some inequalities concerning the values of the Bessel function J_{0} at multiples of p, i.e., at the zeros of J_{1/2}. This raises the question of inequalities and monotonicity properties for the sequences of values of one cylinder function at the zeros of another such function. Here we derive such results by differential equations methods. Some related results are considered.
This is joint work with Lee Lorch.
We analyze a model for dynamic adhesive contact between a stretched viscoelastic membrane and a reactive obstacle that lies beneath it. The model consists of a hyperbolic equation for the vibrations of the membrane coupled with a nonlinear ordinary differential equation for the evolution of the bonding function.
The new feature in the model is the choice of the adhesion rate exponent which allows for complete debonding of the membrane from the support in finite time.
The existence of the unique weak solution for the model with viscosity is established using a sequence of approximate and truncated problems, a priori estimates on their solutions, and a fixed point argument. The solutions are found to be quite regular. We also use these estimates to pass to the limit of vanishing viscosity and obtain a weak solution of the inviscid problem.
The Schiffer problem is an overdetermined problem for the Laplace operator: find connected, bounded domains on which some nonconstant eigenfunction under homogeneous Neumann boundary conditions, is also constant on the boundary. The conjecture due to M. M. Schiffer is that the only simplyconnected domains possessing solutions are nballs. Such domains are said to fail the Schiffer property. We derive a purely geometric condition, necessarily satisfied by the boundary curve of any twodimensional domain failing the Schiffer property. Schiffer's problem then becomes a problem of differential geometry in the large.