Deterministic ratchet from stationary light fields

Ratchets are dynamic systems where particle transport is induced by zero-average forces due to the interplay between nonlinearity and asymmetry. Generally, they rely on the effect of a strong external driving. We show that stationary optical lattices can be designed to generate particle flow in one direction while requiring neither noise nor driving. Such optical fields must be arranged to yield a combination of conservative (dipole) and nonconservative (radiation pressure) forces. Under strong friction all paths converge to a discrete set of limit periodic trajectories flowing in the same direction.Comment: 6 pages, 4 figure

Presentación de un levantamiento geomorfológico como documento básico para trazar mapas de peligrosidad natural

[Resumen] El siguiente trabajo describe una leyenda geomorfologica aplicativa donde van a señalarse los procesos naturales. Cada uno de ellos tiene una manifestación temporal y espacial. Por ello va a darse mucha relevancia a las recurrencias específicas de cada proceso y, a la vez, una representación cartográfica de los fenómenos descritos. Las inestabilidades de ladera tendrán un seguimiento particular. A partir de un trabajo de síntesis, pueden superponerse todos los caracteres sobre el mapa geomorfologico con la finalidad de trazar mapas de peligrosidad natural..[Abstract] The next work shows an applied legend on geomorphology where is possible to carry out natural processes in order to study spatial and temporal features. At both processes is being affected to specific recurrence, spatial behaviour and thereby is subjected to mapping. After that, the local smalllandslides was based on a specific study. Along a synthesis approach it is possible to cover up the first geomorphological survey for depicting natural hazard maps

Perspectivas pedagógicas en geomorfología.

[Resumen] Los nuevos planes que se están poniendo en práctica en educación primaria y secundaria como consecuencia de la aplicación de la LOGSE, así como la reorganización de los estudios universitarios, contemplan algunos aspectos de geomorfología aplicada en varias asignaturas. El presente trabajo va a tratar cuestiones concernientes al área de conocimiento de Ciencias de la Tierra y del Espacio, concretamente se aborda la problemática que suponen las inundaciones. Para hacerlo accesible a los estudiantes se proponen juegos de simulación territorial que forman parte de un proyecto curricular que con carácter experimental venimos desarrollando en centros de enseñanza de La Rioja.[Abstract] At the present, the national education authorities of Spain are involved in the arrangements of the Education Act named LOGSE for aH knowledge levels as primary, secondary and thereby university departments outside of LOGSE are implementing some subjects on applied geomorphology. So as, at the next work a little features into the province of Earth and Environment Sciences and particulary flood problems also are treated. AH of material is available for accessing the environmental issues to students using territory role - play games. At last, the results are covered from an educational project developed in secondary schools of La Rioja region

Effect of long range spatial correlations on the lifetime statistics of an emitter in a two-dimensional disordered lattice

The effect of spatial correlations on the Purcell effect in a bidimensional dispersion of resonant nanoparticles is analyzed. We perform extensive calculations on the fluorescence decay rate of a point emitter embedded in a system of nanoparticles statistically distributed according to a simple 2D lattice-gas model near the critical point. For short-range correlations (high temperature thermalization) the Purcell factors present a long-tailed statistic which evolves towards a bimodal distribution when approaching the critical point where the spatial correlation length diverges. Our results suggest long-range correlations as a possible origin of the large fluctuations of experimental decay rates in disordered metal films.Comment: 6 pages, 5 figure

Transition from Diffusive to Localized Regimes in Surface Corrugated Optical Waveguides

Exact calculations of the transmittance of surface corrugated optical waveguides are presented. The elastic scattering of diffuse light or other electromagnetic waves from a rough surface induces a diffusive transport along the waveguide axis. As the length of the corrugated part of the waveguide increases, a transition from the diffusive to the localized regime is observed. This involves an analogy with electron conduction in nanowires, and hence, a concept analogous to that of ``resistance'' can be introduced. We show an oscillatory behavior of both the elastic mean free path and the localization length versus the wavelength.Comment: 3 pages, REVTEX, 3 PS figure

Statistical Scattering of Waves in Disordered Waveguides: from Microscopic Potentials to Limiting Macroscopic Statistics

We study the statistical properties of wave scattering in a disordered waveguide. The statistical properties of a "building block" of length (delta)L are derived from a potential model and used to find the evolution with length of the expectation value of physical quantities. In the potential model the scattering units consist of thin potential slices, idealized as delta slices, perpendicular to the longitudinal direction of the waveguide; the variation of the potential in the transverse direction may be arbitrary. The sets of parameters defining a given slice are taken to be statistically independent from those of any other slice and identically distributed. In the dense-weak-scattering limit, in which the potential slices are very weak and their linear density is very large, so that the resulting mean free paths are fixed, the corresponding statistical properties of the full waveguide depend only on the mean free paths and on no other property of the slice distribution. The universality that arises demonstrates the existence of a generalized central-limit theorem. Our final result is a diffusion equation in the space of transfer matrices of our system, which describes the evolution with the length L of the disordered waveguide of the transport properties of interest. In contrast to earlier publications, in the present analysis the energy of the incident particle is fully taken into account.Comment: 75 pages, 10 figures, submitted to Phys. Rev

Semi-automatic detection of hepatic tumor in computed tomography images

In this work, the main purpose is develop a computational segmentation strategy for liver tumor semiautomatic detection. This strategy considers three-dimensional computed tomography images and it consists of techniques application that, on the one hand, diminish the noise and detect the edges of the objects present in those images and, on the other hand, generate the liver tumor morphology. For this, the sequence of techniques composed of gaussian smoothing, gradient magnitude, median filter, region growing and binary morphological dilation are used. The value obtained, for the metric called Dice score, show a good correlation between manual segmentation, performed by a hepatologist, and the tumor segmentation obtained using the proposed technique. This type of segmentation is the extreme utility for the characterization of hepatic tumors and the planning of the clinical behavior to be followed in the treatment of this human liver disease