140 research outputs found
Nonparaxial shape-preserving Airy beams with Bessel signature
Spatially accelerating beams that are solutions to the Maxwell equations may
propagate along incomplete circular trajectories, after which diffraction
broadening takes over and the beams spread out. Taking these truncated Bessel
wave fields to the paraxial limit, some authors sustained that it is recovered
the known Airy beams (AiBs). Based on the angular spectrum representation of
optical fields, we demonstrated that the paraxial approximation rigorously
leads to off-axis focused beams instead of finite-energy AiBs. The latter will
arise under the umbrella of a nonparaxial approach following elliptical
trajectories in place of parabolas. Deviations from full-wave simulations
appear more severely in beam positioning rather than its local profile
Light capsules shaped by curvilinear meta-surfaces
We propose a simple yet efficient method for generating in-plane hollow beams
with a nearly-full circular light shell without the contribution of backward
propagating waves. The method relies on modulating the phase in the near field
of a centro-symmetric optical wavefront, such as that from a
high-numericalaperture focused wave field. We illustrate how beam acceleration
may be carried out by using an ultranarrow non-flat meta-surface formed by
engineered plasmonic nanoslits. A mirrorsymmetric, with respect to the optical
axis, circular caustic surface is numerically demonstrated that can be used as
an optical bottle
Oblique surface waves at an interface of metal-dielectric superlattice and isotropic dielectric
We investigate the existence and the dispersion characteristics of surface
waves that propagate at an interface between metal-dielectric superlattice and
isotropic dielectric. Within the long wavelength limit, when the
effective-medium approximation is valid, the superlattice behaves like a
uniaxial plasmonic crystal with the main optical axes perpendicular to the
metal-dielectric interfaces. We demonstrate that if such a semi-infinite
plasmonic crystal is cut normally to the layer interfaces and brought into the
contact with semi-infinite dielectric, a new type of surface modes can appear.
The propagation of such modes obliquely to the optical axes occurs under
favorable conditions that regard thicknesses of the layers, as well as the
proper choice of dielectric permittivity of the constituent materials. We show
that losses within the metallic layers can be substantially reduced by making
the layers sufficiently thin. At the same time, a dramatic enlargement of the
range of angles for oblique propagation of the new surface modes is observed.
This can lead, however, to the field non-locality and consequently to the
failure of the effective-medium approximation.Comment: 4 pages, 3 figure
Apunts de teoria de FĂsica II. Ă’ptica geomètrica
El document forma part dels materials docents programats mitjançant l'ajut del Servei de PolĂtica LingĂĽĂstica de la Universitat de València.Aquest material docent son apunts de teoria que hem preparat per a l'assignatura obligatòria "FĂsica II. Ă’ptica Geomètrica", impartida en el Grau d'Ă’ptica i Optometria.This theory notes have been prepared for the subject "Physics II. Geometrical Optics," included in the Degree in Optics and Optometry
Variations of OCT measurements corrected for the magnification effect according to axial length and refractive error in children
The aim of this paper was to examine the distribution of macular, retinal nerve fiber layer (RNFL) thickness and optic disc parameters of myopic and hyperopic eyes in comparison with emmetropic control eyes and to investigate their variation according to axial length (AL) and spherical equivalent (SE) in healthy children. Methods: This study included 293 pairs of eyes of 293 children (145 boys and 148 girls), ranging in age from 6 to 17 years. Subjects were divided according to SE in control (emmetropia, 99 children), myopia (100 children) and hyperopia (94 children) groups and according to axial AL in 68 short ((Formula presented.)22.00(Formula presented.)mm, 68), medium (from (Formula presented.)22.00(Formula presented.)mm to 25.00(Formula presented.)mm, 189) and long eyes ((Formula presented.)25.00(Formula presented.)mm, 36). Macular parameters, RNFL thickness and optic disc morphology were assessed by the CirrusTM HD-OCT. AL was measured using the IOL-Master system. Littmann’s formula was used for calculating the corrected AL-related ocular magnification. Results: Mean age ((Formula presented.)(Formula presented.)SD) was 10.84(Formula presented.)(Formula presented.)(Formula presented.)3.05 years; mean ((Formula presented.)(Formula presented.)SD) SE was (Formula presented.)0.14(Formula presented.)(Formula presented.)(Formula presented.)0.51 D (range from (Formula presented.)8.75 to (Formula presented.)8.25 D) and mean AL ((Formula presented.)(Formula presented.)SD) was 23.12(Formula presented.)(Formula presented.)(Formula presented.)1.49. Average RNFL thickness, average macular thickness and macular volume decreased as AL and myopia increased. No correlations between AL/SE and optic disc parameters were found after correcting for magnification effect. Conclusions: AL and refractive error affect measurements of macular and RNFL thickness in healthy children. To make a correct interpretation of OCT measurements, ocular magnification effect should be taken into account by clinicians or OCT manufacturers.Postprint (published version
Consumption of Herbal Supplements or Homeopathic Remedies to Prevent COVID-19 and Intention of Vaccination for COVID-19 in Latin America and the Caribbean
Users of complementary and alternative medicine (CAM) have a lower intention to receive vaccines. Furthermore, Latin America and the Caribbean (LAC) region are among the most affected areas by the COVID-19 pandemics and present a high proportion of CAM users. Therefore, this study evaluates the association between the consumption of herbal supplements or homeopathic remedies to prevent COVID-19 and the intention to vaccinate against COVID-19 in the LAC region. We conducted a secondary data analysis of a Massachusetts Institute of Technology (MIT) survey with Facebook to assess COVID-19 beliefs, behaviours, and norms. Crude and adjusted prevalence ratios (aPR) with their respective 95% confidence intervals (95% CI) were calculated using generalized linear models of the Poisson family with the log link function. The prevalence of the use of products to prevent COVID-19 was the following: consumption of herbal supplements (7.2%), use of homeopathic remedies (4.8%), and consumption of garlic, ginger, and lemon (11.8%). An association was found between using herbal supplements (19.0% vs. 12.8%; aPR = 1.44; 95% CI: 1.30–1.58), the use of homeopathic remedies (20.3% vs. 12.3%; aPR = 1.58; 95% CI: 1.25–1.98), and the consumption of garlic, ginger, and lemon (18.9% vs. 11.9%; aPR = 1.55; 95% CI: 1.50–1.61) and non-intention to vaccinate against COVID-19. In the LAC population, there is an association between using herbal supplements, using homeopathic remedies and consuming garlic, ginger, and lemon to prevent infection by COVID-19 and non-intention to vaccinate against this disease. Therefore, it is necessary to design targeted strategies for groups that consume these products as preventive measures against COVID-19 to increase vaccination coverage and expand the information regarding transmission and prevention strategies for SARS-CoV-2.Revisión por pare
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