Browsing by Autor "Jaime Cisternas"

Now showing 1 - 4 of 4

Lurching waves in thalamic neuronal networks
(2010) Jaime Cisternas; Thomas M. Wasylenko; Ioannis G. Kevrekidis
Regularization of diffusion tensor images
(2008) Jaime Cisternas; Takeshi Asahi; Marcelo Gálvez; Gonzalo Rojas
We present a regularization scheme for diffusion tensor images, that respects the geometrical structure of diffusion ellipsoids and does not introduce artifacts such as anisotropy drops. The method can be stated as a variational problem and solved by means of a gradient flow. The main ingredient is the notion of a distance between two ellipsoids that considers differences in shape as well as differences in orientation. The method is specialized to the case of cylindrically-symmetric ellipsoids and implemented in terms of ordinary vector manipulations such as cross and dot products. The regularization algorithm is tested using a synthetic tensor field and a dataset acquired from a diffusion phantom. In both cases the algorithm was able to reduce the noise from the tensor field.
Selection of OAM signal constellations for atmospheric channels using optimal transport theory
(Optica Publishing Group, 2024) Jaime Cisternas; Jaime A. Anguita
We describe a method for determining optimal selections of orbital angular momentum (OAM) superpositions for OAM signal modulation in free-space optical communications using a measure of distance in the context of the Optimal Transport theory. Within the range of topological charges ℓ = −20 to ℓ = 20 we design OAM constellations using 16 to 128 symbols consisting of solos, duets, trios, and quartets of OAM modes. We propose a classification strategy requiring relatively low complexity to evaluate the performance of these constellations, achieving a classification error smaller than 1/1000 in weak to strong turbulence conditions for the 16-OAM constellation. We have found that the optimal set shows some dependence on the receiver’s architecture, so we offer results for optical detectors based on the conjugate projection, the mode sorter, and the Shack-Hartmann sensor.
The transition to explosive solitons and the destruction of invariant tori
(De Gruyter Open, 2012) Jaime Cisternas; Orazio Descalzi; Carlos Cartes
Abstract We investigate the transition to explosive dissipative solitons and the destruction of invariant tori in the complex cubic-quintic Ginzburg-Landau equation in the regime of anomalous linear dispersion as a function of the distance from linear onset. Using Poncaré sections, we sequentially find fixed points, quasiperiodicity (two incommesurate frequencies), frequency locking, two torus-doubling bifurcations (from a torus to a 2-fold torus and from a 2-fold torus to a 4-fold torus), the destruction of a 4-fold torus leading to non-explosive chaos, and finally explosive solitons. A narrow window, in which a 3-fold torus appears, is also observed inside the chaotic region.