1,721,002 research outputs found
Fast photodetectors and their role in measuring star diameters with the MAGIC intensity interferometer
No full textA few years ago MAGIC Stellar Intensity Interferometer (MAGIC-SII) was implemented by applying adjustments to the existing MAGIC IACT array. One of the key parts of the instrument are the photodetectors. Improved photodetector properties as a higher PDE or a better SPTR could increase the sensitivity of the interferometer. This could be achieved, for instance, if the PMTs were replaced by SiPMs thanks to their excellent SPTR. Probably the main drawback of SiPMs is their limited area. I worked on two approaches that aimed at overcoming this limitation: LASiP and Photo-Trap. The first one sums the current of several SiPMs into a single output. We built and characterized a LASiP prototype that used an ASIC called MUSIC to sum the output of 8 SiPMs of 6 mm 6 mm. I explored the feasibility of using LASiPs in SPECT, which is an application in which one needs to cover a large area (50 40 cm) with a limited amount of readout channels (typically 100). I showed that it was possible to reconstruct simple images with an energy resolution of 11.6 \% and an intrinsic spatial resolution of 2 mm (comparable to standard SPECT cameras). Using SiPMs would allow reducing by at least 50 \% the volume of a SPECT camera which would result in a compact and lighter camera. A few LASiPs are also present in one of the MAGIC cameras. These pixels could be a good starting point for testing the feasibility of using SiPMs in intensity interferometry.\\
Photo-Trap provides a different solution to build large SiPM pixels, combining a WLS plastic and a dichroic filter with a commercial SiPM. We built four prototypes using WLS plastics of 20~~20~mm or 40~~40~mm and SiPMs of 3~~3 mm or 3~~12~mm. One of those prototypes is, as far as I know, the largest existing SiPM pixel with single-phe resolution at room temperature. One of the main advantages of Photo-Trap is that it is easily scalable to larger sizes. The prototypes achieved a trapping efficiency of (which corresponds to a peak PDE of ) with a time resolution of ~ns (FWHM).
My main contribution to the MAGIC-SII was the development of the analysis chain which was used to analyze the data of multiple calibration campaigns. The calibration results of the MAGIC-SII showed that the current MAGIC-SII is a working and reliable instrument. MAGIC-SII has so far measured the diameter of over 25 stars. The diameters of several of them were measured for the first time by MAGIC-SII, at least in its wavelength band (412-438 nm). Since some of them are variable stars, they appear as interesting targets to study their oblateness and might be candidates for asteroseismology studies. Observations of these types of targets may contribute to improving our knowledge of stellar structure and evolution
Evaluation of temperature influence on ultrasound velocity in concrete by coda wave interferometry
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Investigating the accuracy achievable in reconstructing the angular sizes of stars through stellar intensity interferometry observations
Get PDFContext. In recent years, stellar intensity interferometry has seen renewed interest from the astronomical community because it can be efficiently applied to Cherenkov telescope arrays.
Aims. We have investigated the accuracy that can be achieved in reconstructing stellar sizes by fitting the visibility curve measured on the ground. The large number of expected available astronomical targets, the limited number of nights in a year, and the likely presence of multiple baselines will require careful planning of the observational strategy to maximise the scientific output.
Methods. We studied the trend of the error on the estimated angular size, considering the uniform disk model, by varying several parameters related to the observations, such as the total number of measurements, the integration time, the signal-to-noise ratio, and different positions along the baseline.
Results. We found that measuring the value of the zero-baseline correlation is essential to obtain the best possible results. Systems that can measure this value directly or for which it is known in advance will have better sensitivity. We also found that to minimise the integration time, it is sufficient to obtain a second measurement at a baseline half-way between 0 and that corresponding to the first zero of the visibility function. This function does not have to be measured at multiple positions. Finally, we obtained some analytical expressions that can be used under specific conditions to determine the accuracy that can be achieved in reconstructing the angular size of a star in advance. This is useful to optimise the observation schedule
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