Photosynthetically active radiation (PAR) is a vital parameter for various applications such as the study of plant physiology or greenhouse lighting. Since instruments for direct PAR measuring are very specific and have less accessibility compared to radiometric or photometric instruments, PAR is often estimated through empirical models that use meteorological parameters that describe the sky conditions as input data. Although it can be estimated through empirical models, these estimations are carried out only in a few areas of interest, for example, some areas of China and the Mediterranean basin, while in some agricultural areas of interest of North America the estimation of such radiation is scarce, being an example of this the Mexican Northern Plateau, which is a region with large agricultural production. In this work, the information obtained in different meteorological stations distributed within the Mexican Northern Plateau is used to assess several empirical models reported in the literature in order to know the behavior of PAR in this area. The performance validation of the models is done using statistical analysis of the Qp/Rsratios at noon and the monthly mean values of Qp obtained from each of the meteorological stations. The models used for its implementation were developed in various geographic areas along the planet, and based on the results obtained they are classified according to their performance to predict PAR within the study area.
We present a method to measure spherical power in ophthalmic lenses based on the measurement of moiré patterns, using the technique called infinite fringe moiré deflectometry. We develop a theoretical model using a geometrical analysis that was validated by a computer simulation using the LabVIEW software; also we build an experimental setup in which we get experimental data. As results, we obtain a measurement of the spherical power of a set of ophthalmic test lenses in the range of ± 0.50 to ± 3.00 diopters. This power is obtained by measuring the separation between each fringe of moiré pattern, from the obtained data we analyze the theoretical model and we make the necessary corrections, using polynomial regression by the method of least squares, to comply with standard ISO8598. At the same time, some components of the experimental setup were being improved to facilitate its implementation and obtain better experimental data.
Nowadays refractive errors in the human eye affect approximately 10% of world’s population, decreasing vision acuity and life quality. However a simple common solution is the use of an adequate ophthalmic lens. Due to the importance of ophthalmic lenses, the best measurement equipment is required for testing, these days experimental and commercial apparatus are available but with the possibility of improvement. We present a method to measure spherical and cylindrical power in ophthalmic lenses. The system uses an equation obtained from lateral amplification concept and Gauss formula to make calculations. Also an experimental setup is presented for the measurement of ophthalmic lens from -20 diopters to 20 diopters in the case of spherical lenses, and from -6 diopters to 6 diopters in the case of cylindrical lenses. The setup contains a reference object, the lens to be tested and a digital camera connected to a computer with software designed in LabVIEW for the data processing. Satisfactory preliminary results were obtained according to ISO 8598.
KEYWORDS: Signal to noise ratio, Interference (communication), Cameras, Sensors, Polarizers, Electronic filtering, Linear filtering, Optical filters, Signal detection, Photoplethysmography
In this work we report the improvement of signal-to-noise ratio in photoplethysmographic images by using a linear
polarized filtered light source and the capture of the corresponding scene through a linear polarized analyzer; we also
discuss the impact of its use in non-contact reflection photoplethysmographic setups. In all regions in which we acquire
useful signals, we observe a reduction in the intensity of the images when the angle between the axes of the polarizer and
the analyzer goes from parallel to perpendicular. Despite this, we obtain an increased ratio between the expected
pulsatile signal and the background noise. As a consequence, the extinction of the specular component of the image
should be considered for any experimental setup intended to detect the backscattered component.
In this work, we obtain backscattered signals from human forehead for wavelengths from 380 to 980 nm. The results
reveal bands with strong pulsatile signals that carry useful information. We describe those bands as the most suitable
wavelengths in the visible and NIR regions from which heart and respiratory rate parameters can be derived using long
distance non-contact reflection photoplethysmography analysis. The latter results show the feasibility of a novel
technique for remotely detection of vital signs in humans. This technique, which may include morphological analysis or
maps of tissue oxygenation, is a further step to real non-invasive remote monitoring of patients.
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