Topological dragging of solitons

We put forward properties of solitons supported by optical lattices featuring topological dislocations, and show that solitons experience attractive and repulsive forces around the dislocations. Suitable arrangements of dislocations are even found to form soliton traps, and the properties of such solitons are shown to crucially depend on the trap topology. The uncovered phenomenon opens a new concept for soliton control and manipulation, e.g., in disk-shaped Bose-Einstein condensates.Comment: 15 pages, 5 figures, to appear in Physical Review Letter

Multicolor vortex solitons in two-dimensional photonic lattices

We report on the existence and stability of multicolor lattice vortex solitons constituted by coupled fundamental frequency and second-harmonic waves in optical lattices in quadratic nonlinear media. It is shown that the solitons are stable almost in the entire domain of their existence, and that the instability domain decreases with the increase of the lattice depth. We also show the generation of the solitons, and the feasibility of the concept of lattice soliton algebra.Comment: 18 pages,6 figures. To appear in Physical Review

Nonlinear switching of low-index defect modes in photonic lattices

We address nonlinear signal switching between two low-index defect channels induced in periodic optical lattices. In contrast to conventional directional couplers, where the guiding mechanism is total internal reflection or refraction, in such Bragg-type coupler, the guidance is of a photonic-bandgap origin. The coupling length in the low-index coupler is controlled by the lattice parameters and by the channel spacing. In the nonlinear regime the Bragg-type coupler behaves as an all-optical switch, exhibiting a remarkable difference of switching power for focusing versus defocusing nonlinearity.Comment: 13 pages, 4 figures, to appear in Physical Review

Solitary-wave Vortices in Quadratic Nonlinear Media

We find families of vortex solitary waves in bulk quadratic nonlinear media under conditions for second-harmonic generation. We show that the vortex solitary waves are azimuthally unstable and that they decay into sets of stable spatial solitons. We calculate the growth rates of the azimuthal perturbations and show how those affect the pattern of output light. © 1998 Optical Society of AmericaThis work has been partially supported by the Spanish Government under grant PB95-0768.Peer Reviewe

Soliton topology versus discrete symmetry in optical lattices

We address the existence of vortex solitons supported by azimuthally modulated lattices and reveal how the global lattice discrete symmetry has fundamental implications on the possible topological charges of solitons. We set a general ``charge rule'' using group-theory techniques, which holds for all lattices belonging to a given symmetry group. Focusing in the case of Bessel lattices allows us to derive also a overall stability rule for the allowed vortex solitons.Comment: 4 pages, 3 figures. To appear in Phys. Rev. Let

Introducción a la Geografía Física de Menorca

Abstract not availabl

Structural instability of vortices in Bose-Einstein condensates

In this paper we study a gaseous Bose-Einstein condensate (BEC) and show that: (i) A minimum value of the interaction is needed for the existence of stable persistent currents. (ii) Vorticity is not a fundamental invariant of the system, as there exists a conservative mechanism which can destroy a vortex and change its sign. (iii) This mechanism is suppressed by strong interactions.Comment: 4 pages with 3 figures. Submitted to Phys. Rev. Let

Intron splice acceptor site polymorphism in the hMSH2 gene in sporadic and familial colorectal cancer

A polymorphism in hMSH2 gene has been associated with an increased susceptibility to develop colorectal cancer (CRC). Here we show that it is a genetic risk factor for CRC in the Spanish population. However, its presence does not apparently affect hMSH2 function. © 2000 Cancer Research Campaig