93 research outputs found
Giant enhanced diffusion of gold nanoparticles in optical vortex fields
We study the diffusion of a metal nanoparticle in the nonconservative force field of an optical vortex lattice. Radiation pressure in the vortex array is shown to induce a giant enhancement over the free thermal diffusion. Langevin dynamics simulations show that the diffusion coefficient of (50 nm radius) gold particles at room temperature is enhanced by 2 orders of magnitude at power densities of the order or smaller than those used to trap nanoparticles with optical tweezers
Controlling dispersion forces between small particles with artificially created random light fields
Appropriate combinations of laser beams can be used to trap and manipulate small particles with optical tweezers as well as to induce significant optical binding forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals and, in general, Casimir-Lifshitz interactions between neutral bodies arising from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations. Here we show, both theoretically and experimentally, that dispersion forces between small colloidal particles can also be induced and controlled using artificially created fluctuating light fields. Using optical tweezers as a gauge, we present experimental evidence for the predicted isotropic attractive interactions between dielectric microspheres induced by laser-generated, random light fields. These light-induced interactions open a path towards the control of translationally invariant interactions with tuneable strength and range in colloidal systemsThis work was supported by the Swiss National Science Foundation through project numbers 132736 and 149867, and through the National Centre of Competence in Research Bio-Inspired Materials. J.J.S. acknowledges financial support by the Spanish MEC (grant number FIS2012-36113), Comunidad de Madrid (grant number S2009/TIC-1476-Microseres Program-) and by an IKERBASQUE Visiting Fellowship (J.J.S.
Band gap formation and Anderson localization in disordered photonic materials with structural correlations
Disordered dielectric materials with structural correlations show unconventional optical behavior: They can be transparent to long-wavelength radiation, while at the same time have isotropic band gaps in another frequency range. This phenomenon raises fundamental questions concerning photon transport through disordered media. While optical transparency in these materials is robust against recurrent multiple scattering, little is known about other transport regimes like diffusive multiple scattering or Anderson localization. Here, we investigate band gaps, and we report Anderson localization in 2D disordered dielectric structures using numerical simulations of the density of states and optical transport statistics. The disordered structures are designed with different levels of positional correlation encoded by the degree of stealthiness χχ. To establish a unified view, we propose a correlation-frequency (χχ– νν) transport phase diagram. Our results show that, depending only on χχ, a dielectric material can transition from localization behavior to a band gap crossing an intermediate regime dominated by tunneling between weakly coupled states
Transport of light in amorphous photonic materials
Amorphous photonic materials based on dense assemblies of high refractive index spherical particles are presented. Light transmission through these photonic glasses shows a nontrivial wavelength dependence. The transmission spectra can be quantitatively reproduced by modeling the optical properties starting from their building blocks. Our results emphasize the relevance of including short range order correlations and an appropriate effective refractive index in the analysis of light transmission through amorphous photonic materials
Fluctuations of the electromagnetic local density of states as a probe for structural phase switching
We study the statistics of the fluorescence decay rates for single quantum emitters embedded in a scattering medium undergoing a phase transition. Under certain circumstances, the structural properties of the scattering medium explore a regime in which the system dynamically switches between two different phases. While in that regime the light-scattering properties of both phases are hardly distinguishable, we demonstrate that the lifetime statistics of single emitters with low diffusivity is clearly dependent on the dynamical state in which the medium evolves. Hence, lifetime statistics provides clear signatures of phase switching in systems where light scattering does not
Self-diffusion and structural properties of confined fluids in dynamic coexistence
Self-diffusion and radial distribution functions are studied in a strongly confined Lennard-Jones fluid. Surprisingly, in the solid–liquid phase transition region, where the system exhibits dynamic coexistence, the self-diffusion constants are shown to present up to three-fold variations from solid to liquid phases at fixed temperature, while the radial distribution function corresponding to both the liquid and the solid phases are essentially indistinguishable
Light in correlated disordered media
The optics of correlated disordered media is a fascinating research topic
emerging at the interface between the physics of waves in complex media and
nanophotonics. Inspired by photonic structures in nature and enabled by
advances in nanofabrication processes, recent investigations have unveiled how
the design of structural correlations down to the subwavelength scale could be
exploited to control the scattering, transport and localization of light in
matter. From optical transparency to superdiffusive light transport to photonic
gaps, the optics of correlated disordered media challenges our physical
intuition and offers new perspectives for applications. This article reviews
the theoretical foundations, state-of-the-art experimental techniques and major
achievements in the study of light interaction with correlated disorder,
covering a wide range of systems -- from short-range correlated photonic
liquids, to L\'evy glasses containing fractal heterogeneities, to hyperuniform
disordered photonic materials. The mechanisms underlying light scattering and
transport phenomena are elucidated on the basis of rigorous theoretical
arguments. We overview the exciting ongoing research on mesoscopic phenomena,
such as transport phase transitions and speckle statistics, and the current
development of disorder engineering for applications such as light-energy
management and visual appearance design. Special efforts are finally made to
identify the main theoretical and experimental challenges to address in the
near future.Comment: Submitted to Reviews of Modern Physics. Feedbacks are welcom
Caracterización de los determinantes sociales en salud relacionados con la educación en personas con discapacidad en el municipio los Patios, Colombia
INTRODUCCIÓN: caracterizar los determinantes sociales en salud relacionados con la educación desde la perspectiva de las personas con discapacidad del municipio de Los Patios, Norte de Santander, año 2018. MÉTODOS: a una muestra de 246 personas que presentaban algún tipo de discapacidad con residencia en el municipio Los patios, Norte de Santander, Colombia, bajo selección no probabilística intencionada, se administró el instrumento “Registro para la Localización y Caracterización de Personas con Discapacidad (RLCPD), para identificar los determinantes sociales de salud relacionados con la educación. RESULTADOS: los resultados muestran que las personas con discapacidad aún tienen limitaciones para su inclusión y consecución en el sistema escolar al percibir que no tienen la infraestructura y la formación necesaria para incorporarse al campo laboral. ANÁLISIS Y DISCUSIÓN: aunque se han desarrollado políticas gubernamentales para incorporar a la población con discapacidad al sistema escolar. CONCLUSIONES: pareciera que es necesario que estas transiten del enunciado a acciones concretas
Automatic segmentation of a meningioma using a computational technique in magnetic resonance imaging
Through this work we propose a computational techniquefor the segmentation of a brain tumor, identified as meningioma(MGT), which is present in magnetic resonance images(MRI). This technique consists of 3 stages developed inthe three-dimensional domain: pre-processing, segmentationand post-processing. The percent relative error (PrE) is consideredto compare the segmentations of the MGT, generatedby a neuro-oncologist manually, with the dilated segmentationsof the MGT, obtained automatically. The combination ofparameters linked to the lowest PrE, provides the optimal parametersof each computational algorithm that makes up theproposed computational technique. Results allow reporting aPrE of 1.44%, showing an excellent correlation between themanual segmentations and those produced by the computationaltechnique developed
Segmentación automática de un meningioma usando una técnica computacional en imágenes de resonancia magnética
Through this work we propose a computational technique
for the segmentation of a brain tumor, identified as meningioma
(MGT), which is present in magnetic resonance images
(MRI). This technique consists of 3 stages developed in
the three-dimensional domain: pre-processing, segmentation
and post-processing. The percent relative error (PrE) is considered
to compare the segmentations of the MGT, generated
by a neuro-oncologist manually, with the dilated segmentations
of the MGT, obtained automatically. The combination of
parameters linked to the lowest PrE, provides the optimal parameters
of each computational algorithm that makes up the
proposed computational technique. Results allow reporting a
PrE of 1.44%, showing an excellent correlation between the
manual segmentations and those produced by the computational
technique developed.Este trabajo propone una técnica computacional para la segmentación
de un tumor cerebral, identificado como meningioma
(MGT), que está presente en imágenes de resonancia
magnética (MRI). Esta técnica consta de 3 etapas desarrolladas
en el dominio tridimensional: preprocesamiento,
segmentación y postprocesamiento. El porcentaje de error
relativo (PrE) se considera para comparar las segmentaciones
de la MGT, generadas por un neurooncólogo de forma
manual, con las segmentaciones dilatadas de la MGT, obtenidas
automáticamente. La combinación de parámetros vinculados
al PrE más bajo proporciona los parámetros óptimos
de cada algoritmo computacional que conforma la técnica
de cálculo propuesta. Los resultados permiten informar un
PrE de 1.44%, mostrando una excelente correlación entre
las segmentaciones manuales y las producidas por la técnica
computacional desarrollada
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