Multiple ionization cross sections of neon (Ne-Nen+, with n=1-5) by electron impact have been measured with energies ranging from threshold up to 3000 eV, by a time-of-flight technique. A comparison with other experimental data is presented. The integrated oscillator strengths (Mn+2) for the processes have been determined showing a good agreement with previous reported data.

Modifications of the electromagnetic Maxwell Lagrangian in four dimensions have been considered by some authors. One may include an explicit massive ͑Proca͒ term and a topological but not Lorentz-invariant term within certain observational limits. We find the dual-corresponding gauge-invariant version of this theory by using the recently suggested gauge embedding method. We enforce this dualization procedure by showing that, in many cases, this is actually a constructive method to find a sort of parent action, which manifestly establishes duality. We also use the gauge-invariant version of this theory to formulate a Batalin-Vilkovisky quantization and present a detailed discussion of the excitation spectrum.

Boundary conditions play a non trivial role in string theory. For instance the rich structure of D-branes is generated by choosing appropriate combinations of Dirichlet and Neumann boundary conditions. Furthermore, when an antisymmetric background is present at the string end-points (corresponding to mixed boundary conditions) space time becomes non-commutative there.We show here how to build up normal ordered products for bosonic string position operators that satisfy both equations of motion and open string boundary conditions at quantum level. We also calculate the equal time commutator of these normal ordered products in the presence of antisymmetric tensor background.

We show how to translate boundary conditions into constraints in the symplectic quantization method by an appropriate choice of generalized variables. This way the symplectic quantization of an open string attached to a brane in the presence of an antisymmetric background field reproduces the non commutativity of the brane coordinates.

So far, it is not well known how to deal with dissipative systems. There are many paths of investigation in the literature and none of them present a systematic and general procedure to tackle the problem. On the other hand, it is well known that the fractional formalism is a powerful alternative when treating dissipative problems. In this paper we propose a detailed way of attacking the issue using the fractional calculus to construct an extension for the Dirac brackets in order to furnish the quantization of nonconservative theories through the standard canonical way. We believe that it can be the first step to construct gauge theories from second-class nonlinear systems using these extended Dirac brackets.