For a system of ODEs defined on an open, convex domain U containing a positively invariant set Γ, we prove that under appropriate hypotheses, Γ is the graph of a Cr function and thus a Cr manifold. Because the hypotheses can be easily verified by inspecting the vector field of the system, this invariant manifold theory can be used to study the existence of invariant manifolds in systems involvi...

We consider a cardinal invariant closely related to Hindman’s theorem. We prove that this cardinal invariant is small in the iterated Sacks perfect set forcing model, and that its corresponding parametrized diamond principle implies the existence of union ultrafilters. As a corollary, this establishes the existence of union ultrafilters in the iterated Sacks model of Set Theory.

In this paper, we use Conley index theory to examine the Poincaré index of an isolated invariant set. We obtain some limiting conditions on a critical point of a planar vector field to be an isolated invariant set. As a result we show the existence of infinitely many homoclinic orbits for a critical point with the Poincaré index greater than one.

The theory of relativistic strings is considered in frames of Hamiltonian formalism and Dirac’s quantization procedure. A special gauge fixing condition is formulated, related with the world sheet of the string in Lorentz-invariant way. As a result, a new set of Lorentz-invariant canonical variables is constructed, in which a consistent quantization of bosonic open string theory could be done i...

In this work, we define a fuzzy soft set theory and its related properties. We then define fuzzy soft aggregation operator that allows constructing more efficient decision making method. Finally, we give an example which shows that the method can be successfully applied to many problems that contain uncertainties.

We use Heegaard decompositions and the theta divisor on a Riemann-ian surface to define a three-manifold invariant for rational homology three-spheres. This invariant is defined on the set of Spin c structures θ : Spin c (Y) −→ Q. In the first part of the paper, we give the definition of the invariant (which builds on the theory developed in [18]). In the second part, we establish a relationshi...