10 research outputs found
Anthropogenic disruption of the night sky darkness in urban and rural areas
The growing emissions of artificial light to the atmosphere
are producing, among other effects, a significant increase of
the night sky brightness (NSB) above its expected natural
values. A permanent sensor network has been deployed
in Galicia (northwest of Iberian peninsula) to monitor the
anthropogenic disruption of the night sky darkness in a
countrywide area. The network is composed of 14 detectors
integrated in automated weather stations of MeteoGalicia, the
Galician public meteorological agency. Zenithal NSB readings
are taken every minute and the results are openly available
in real time for researchers, interested stakeholders and the
public at large through a dedicated website. The measurements
allow one to assess the extent of the loss of the natural night
in urban, periurban, transition and dark rural sites, as well as
its daily and monthly time courses. Two metrics are introduced
here to characterize the disruption of the night darkness across
the year: the significant magnitude (m1/3) and the moonlight
modulation factor (Îł ). The significant magnitude shows that
in clear and moonless nights the zenithal night sky in the
analysed urban settings is typically 14–23 times brighter than
expected from a nominal natural dark sky. This factor lies in the
range 7–8 in periurban sites, 1.6–2.5 in transition regions and
0.8–1.6 in rural and mountain dark sky places. The presence
of clouds in urban areas strongly enhances the amount of
scattered light, easily reaching amplification factors in excess
of 25, in comparison with the light scattered in the same places
under clear sky conditions. The periodic NSB modulation due
to the Moon, still clearly visible in transition and rural places,
is barely notable at periurban locations and is practically lost at
urban sitesThis work was partially funded by the Xunta de Galicia, Programa de ConsolidaciĂłn e EstruturaciĂłn de
Unidades de InvestigaciĂłn Competitivas, grant CN 2012/156, and was partly developed within the framework of
the Spanish Network for Light Pollution Studies (Ministerio de EconomĂa y Competitividad, AYA2015-71542-REDTS
Sampling geometries for ocular aberrometry: A model for evaluation of performance
The purpose of this work is to outline a simple model to
assess the relative merits of different sampling grids for ocular aberrometry
and illustrate it with an example. While in traditional Hartmann-Shack
setups the sampling grid geometries have been somewhat restricted by the
geometries of the available microlens arrays, other techniques such as laser
ray tracing or spatially resolved refractometry allow for a greater freedom
of choice. For all available setups, including HS, it is worth studying
which of these choices perform better in terms of accuracy (closeness
of the obtained results to the actual ones) and precision (uncertainty
of the obtained results). Whilst the mathematical model presented in
this paper is quite general and it can be applied to optimise existing or
new aberrometers, the numerical results presented in the example are
only valid for the particular aberration sample used and centroiding algorithms studied, and should not be generalised outside of these boundariesS
Absolute Radiometric Calibration of TESS-W and SQM Night Sky Brightness Sensors
We develop a general optical model and describe the absolute radiometric calibration of the
readings provided by two widely-used night sky brightness sensors based on irradiance-to-frequency
conversion. The calibration involves the precise determination of the overall spectral sensitivity of the
devices and also the constant G relating the output frequency of the light-to-frequency converter chip
to the actual band-weighted and field-of-view averaged spectral radiance incident on the detector
(brightness). From these parameters, we show how to define a rigorous astronomical absolute
photometric system in which the sensor measurements can be reported in units of magnitudes per
square arcsecond with precise physical meaning.S
Equilateral hyperbolic moiré zone plates with variable focus obtained by rotations
We present equilateral hyperbolic zone plates with variable focal
length, which are formed as moiré patterns by a mutual rotation of two
identical basic grids. Among others, all principal zone plates, except of the
spherical one, can be used as these basic transmittances. Three most
important advantages of the proposed moiré zone plates are: a constant
aperture of the created element during the mutual movement of basic grids,
lack of aberrations due to their undesired mutual lateral displacements and
high diffraction efficiency of the binary phase version. To obtain clearer
moiré fringe pattern, a radial carrier frequency can be added additionally to
the transmittances of basic grids. The destructive interference between both
arms of the focal cross of the equilateral hyperbolic moiré zone plate can be
obtained by a constant phase shift introduced in the transmittances of the
basic grids. Potential applications of discussed elements are indicated,
including the most promising one in the three-point alignment techniqueThis work was supported by the Network of Excellence on Micro-Optics (NEMO) and the
programme CODI of the University of Antioquia, Medellin, ColombiaS
Imaging with extended focal depth by means of the refractive light sword optical element
The paper presents first experiments with a refractive light sword optical element (LSOE). A refractive version of the LSOE was prepared in photoresist by gray scale photolithography. Then we examined chromatic aberrations of the produced element and compared them with those corresponding to two different lenses. For this purpose we performed two experiments, the first one where white light illumination was used and the latter one by the help of monochromatic illumination with three different wavelengths. The obtained results lead to the conclusion that the refractive LSOE does not exhibit significant chromatic aberrations and can be successfully used for imaging with extended depth of focus in polychromatic illuminationThis work was supported by Warsaw University of Technology, by National Institute of
Telecommunications and by the Spanish Ministerio de EducaciĂłn y Ciencia, Plan Nacional de
InvestigaciĂłn CientĂfica, Desarrollo e InnovaciĂłn TecnolĂłgica (I+D+i), grant FIS2005-05020-
C03-02 and FEDERS
Strehl ratios characterizing optical elements designed for presbyopia compensation
We present results of numerical analysis of the Strehl ratio characteristics for the light sword optical element (LSOE). For comparison there were analyzed other optical imaging elements proposed for compensation of presbyopia such as the bifocal lens, the trifocal lens, the stenopeic contact lens, and elements with extended depth of focus (EDOF), such as the logarithmic and quartic axicons. The simulations were based on a human eye’s model being a simplified version of the Gullstrand model. The results obtained allow to state that the LSOE exhibits much more uniform characteristics of the Strehl ratio comparing with other known hitherto elements and therefore it could be a promising aid to compensate for the insufficient accommodation range of the human eye.This work was supported by the Polish Ministry of Science and Higher Education under
grants N N 514 149038 and N N 518 378237 as well as by the European Social Fund
implemented under the Human Capital Operational Programme (POKL), project:
“Preparation and Realization of Medical Physics Specialty” with complementary support
from the Spanish Ministerio de Ciencia e InnovaciĂłn (MICINN) grant FIS2008-03884S
Imaging properties of the light sword optical element used as a contact lens in a presbyopic eye model
The paper analyzes the imaging properties of the light sword optical element (LSOE) applied as a contact lens to the presbyopic human eye. We performed our studies with a human eye model based on the Gullstrand parameterization. In order to quantify the discussion concerning imaging with extended depth of focus, we introduced quantitative parameters characterizing output images of optotypes obtained in numerical simulations. The quality of the images formed by the LSOE were compared with those created by a presbyopic human eye, reading glasses and a quartic inverse axicon. Then we complemented the numerical results by an experiment where a 3D scene was imaged by means of the refractive LSOE correcting an artificial eye based on the Gullstrand model. According to performed simulations and experiments the LSOE exhibits abilities for presbyopia correction in a wide range of functional vision distances.This work was supported by the Polish Ministry of Science and Higher Education under grant
N N 514 149038 and by the Spanish Ministerio de Ciencia e InnovaciĂłn (MICINN), grant
FIS2008-03884 with complementary support from the European Social Fund implemented
under the Human Capital Programme (POKL), project, “Preparation and Realization of
Medical Physics Specialty.”S
Modulations of the visual N1 component of event-related potentials by central and peripheral cueing
Objective: The aim of this study is to investigate the effects of the central and peripheral cueing on N1 component of the event-related potentials (ERPs) and the time course of these effects. Methods: ERPs were recorded while participants performed a discrimination task on the height of target bars, which were presented after informative-central, informative-peripheral or uninformative-peripheral cues with stimulus onset asynchronies (SOAs) of 100, 300, 500 or 700 ms. Results: Peripheral cues (informative and uninformative) elicited stronger effects of cue validity on N1 300 ms after cue onset, whereas central cues led to a more sustained validity effect on N1, with later stronger effects, at 500 ms SOA. Conclusions: The present data showed that central and peripheral cues affected to the level of processing reflected by the N1 component, but there were differences in the time course of these effects. Attentional orienting in response to central cueing resulted in a sustained validity effect on N1, relative to the more transitory activation of the process reflected by the N1 validity effect in this peripheral cueing task. Significance: This study provides a detailed within-subject analysis of the time course of the effects of central and peripheral cueing on N1.This study was supported by Spain’s Ministerio de Ciencia y TecnologĂa (grant BSO2000-0041) and by the Galician SecretarĂa Xeral de I + D (PGIDT00PSI211102PR, PGIDT01PXI21101PN).S
The time course of the effects of central and peripheral cues on visual processing: an event-related potentials study
Objective: The varying results of visual event-related potential (ERP) studies of central and peripheral cueing suggest that these types of cue may modulate stimuli processing with different time courses. The aim of this study was to investigate differences in the time course of facilitatory effects on the visual processing induced by peripheral and central cues.
Methods: ERPs were recorded for visual target stimuli that were preceded by informative-central, informative-peripheral or uninformative-peripheral cues with stimulus onset asynchronies (SOAs) of 100, 300, 500 or 700 ms.
Results: Validly cued stimuli elicited an enhanced P1 component with peripheral cueing at 100 ms SOA. P1 amplitude in valid trials was reduced at 300, 500 and 700 ms SOAs with uninformative-peripheral cueing, but only at 500 ms SOA with informative-peripheral cueing. With informative-central cueing, there was no validity effect on P1.
Conclusions: These results suggest that the automatic attraction of attention by a peripheral cue results in improved sensory processing at the cued location. This facilitation is replaced by an inhibitory effect when SOA increases, although cue informativeness may modulate this effect. Central cueing does not affect sensory processing at the P1 levelThis study was supported by Spain’s Ministerio de Ciencia y TecnologĂa (grant BSO2000-0041) and by the Galician SecretarĂa Xeral de I+D (PGIDT00PSI211102PR, PGIDT01PXI21101PN)S