335 research outputs found
An efficient PSF construction method
Image computation is a fundamental tool for performance assessment of
astronomical instrumentation, usually implemented by Fourier transform
techniques. We review the numerical implementation, evaluating a direct
implementation of the discrete Fourier transform (DFT) algorithm, compared with
fast Fourier transform (FFT) tools. Simulations show that the precision is
quite comparable, but in the case investigated the computing performance is
considerably higher for DFT than FFT. The application to image simulation for
the mission Gaia and for Extremely Large Telescopes is discussed.Comment: The paper contains 7 figures and 1 tabl
Astrometric signal profile fitting for Gaia
A tool for representation of the one-dimensional astrometric signal of Gaia
is described and investigated in terms of fit discrepancy and astrometric
performance with respect to number of parameters required. The proposed basis
function is based on the aberration free response of the ideal telescope and
its derivatives, weighted by the source spectral distribution. The influence of
relative position of the detector pixel array with respect to the optical image
is analysed, as well as the variation induced by the source spectral emission.
The number of parameters required for micro-arcsec level consistency of the
reconstructed function with the detected signal is found to be 11. Some
considerations are devoted to the issue of calibration of the instrument
response representation, taking into account the relevant aspects of source
spectrum and focal plane sampling. Additional investigations and other
applications are also suggested.Comment: 13 pages, 21 figures, Accepted by MNRAS 2010 January 29. Received
2010 January 28; in original form 2009 September 3
Neural network correction of astrometric chromaticity
In this paper we deal with the problem of chromaticity, i.e. apparent
position variation of stellar images with their spectral distribution, using
neural networks to analyse and process astronomical images. The goal is to
remove this relevant source of systematic error in the data reduction of high
precision astrometric experiments, like Gaia. This task can be accomplished
thanks to the capability of neural networks to solve a nonlinear approximation
problem, i.e. to construct an hypersurface that approximates a given set of
scattered data couples. Images are encoded associating each of them with
conveniently chosen moments, evaluated along the y axis. The technique
proposed, in the current framework, reduces the initial chromaticity of few
milliarcseconds to values of few microarcseconds.Comment: 9 pages, 8 figures Accepted by Monthly Notices of the Royal
Astronomical Societ
Determination of folic acid using biosensors: a short review of recent progress
Folic acid (FA) is the synthetic surrogate of the essential B vitamin folate, alternatively named folacin, pteroylglutamic acid or vitamin B-9. FA is an electroactive compound that helps our body to create and keep our cells healthy: it acts as the main character in a variety of synthetic biological reactions such as the synthesis of purines, pyrimidine (thus being indirectly implied in DNA synthesis), fixing and methylation of DNA. Therefore, physiological folate deficiency may be responsible for severe degenerative conditions, including neural tube defects in developing embryos and megaloblastic anaemia at any age. Moreover, being a water-soluble molecule, it is constantly lost and has to be reintegrated daily; for this reason, FA supplements and food fortification are, nowadays, extremely diffused and well-established practices. Consequently, accurate, reliable and precise analytical techniques are needed to exactly determine FA concentration in various media. Thus, the aim of this review is to report on research papers of the past 5 years (2016-2020) dealing with rapid and low-cost electrochemical determination of FA in food or biological fluid samples
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