1,721,107 research outputs found
The VST Telescope Control Software in the ESO VLT Environment
Full text linkThe VST (VLT Survey Telescope) is a 2.6 m Alt-Az telescope to be installed at Mount Paranal in Chile, in the European Southern Observatory (ESO) site. The VST is a wide-field imaging facility planned to supply databases for the ESO Very Large Telescope (VLT) science and carry out stand-alone observations in the UV to I spectral range. This paper will focus mainly on control software aspects, describing the VST software architecture in the context of the whole ESO VLT control concept. The general architecture and the main components of the control software will be described...
Integration of the VIMOS Control System
Full text linkThe VIRMOS consortium of French and Italian Institutes (PI: O. Le Fevre, co-PI: G. Vettolani) is manufacturing two wide field imaging multi-object spectrographs for the European Southern Observatory Very Large Telescope (VLT), with emphasis on the ability to carry over spectroscopic surveys of large numbers of sources: the VIsible Multi-Object Spectrograph, VIMOS, and the Near InfraRed Multi-Object Spectrograph, NIRMOS. There are 52 motors to be controlled in parallel in the spectrograph, making VIMOS a complex machine to be handled. This paper will focus on the description of the control system, designed in the ESO VLT standard control concepts, and on some integration issues and problem solving strategies...
Model predictive star tracking control for ground-based telescopes: the Telescopio Nazionale Galileo case
Full text linkWith the aim of improving the star tracking performance of ground-based telescopes, we deal with the design of model predictive control architecture so as to properly lead their axes while mitigating possible external disturbances affecting the control task. The proposed architecture is composed of two layers, namely, (i) a trajectory generator that determines, based on the astronomic computation, the telescope position and speed references to be tracked while ensuring that all the telescope physical constraints, in terms of speed and acceleration, are never violated; (ii) an model predictive control (MPC) controller that guarantees the optimal tracking of the desired reference behavior by providing the torque inputs for telescope axes for the achievement of star observation task. The control architecture is tailored for the tracking control problem of Telescopio Nazionale Galileo (TNG), located at La Palma (Spain). To this end, by leveraging real data measurements in specific operative scenarios, a 12-order linear system describing the TNG dynamics is identified, via the non-iterative subspace method, for the design of the second layer. Validation results confirm the goodness of the dynamical model in predicting the TNG behavior within the operative range of (80 and 90 deg) altitude position. The effectiveness of the proposed MPC-based control architecture is proven via an ad-hoc virtual testing simulation platform implemented in MATLAB and Simulink and tailored for the identified TNG model. Virtual testing results, involving the real scientific target TYC 1731-916-1, confirm the capability of the proposed solution in ensuring optimal star tracking while mitigating the wind external disturbances forces. Finally, a comparison analysis w.r.t. the state-of-the-art control approaches, i.e., Linear-Quadratic-Gaussian and Proportional-Integrator-Derivative controller, and a robustness analysis w.r.t. the model mismatch between the MPC prediction model and the simulated TNG dynamics are provided to disclose the improved tracking performance achievable via the proposed MPC-based control architecture
Singular values behaviour optimization in the diagnosis of feed misalignments in radioastronomical reflectors
Full text linkThe communication presents an innovative method for the diagnosis of reflector antennas in radio astronomical applications. The approach is based on the optimization of the number and the distribution of the far field sampling points exploited to retrieve the antenna status in terms of feed misalignments, this to drastically reduce the time length of the measurement process and minimize the effects of variable environmental conditions and simplifying the tracking process of the source. The feed misplacement is modeled in terms of an aberration function of the aperture field. The relationship between the unknowns and the far field pattern samples is linearized thanks to a Principal Component Analysis. The number and the position of the field samples are then determined by optimizing the Singular Values behaviour of the relevant operator. © 2016 SPIE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Efficient diagnosis of radiotelescopes misalignments
Full text linkAn innovative method for the diagnosis of large reflector antennas from far field data in radio astronomical application is presented, which is based on the optimization of the number and the location of the far field sampling points required to retrieve the antenna status in terms of feed misalignments. In these applications a continuous monitoring of the Antenna Under Test (AUT), and its subsequent reassessment, is necessary to guarantee the optimal performances of the radiotelescope. The goal of the method is to reduce the measurement time length to minimize the effects of the time variations of both the measurement setup and of the environmental conditions, as well as the issues raised by the complex tracking of the source determined by a prolonged acquisition process. Furthermore, a short measurement process helps to shorten the idle time forced by the maintenance activity. The field radiated by the AUT is described by the aperture field method. The effects of the feed misalignments are modeled in terms of an aberration function, and the relationship between this function and the Far Field Pattern is recast in the linear map by expanding on a proper set of basis functions the perturbation function of the Aperture Field. These basis functions are determined using the Principal Component Analysis. Accordingly, from the Far Field Pattern, assumed measured in amplitude and phase, the unknown parameters defining the antenna status can be retrieved. The number and the position of the samples is then found by a Singular Values Optimization (SVO). © 2016 AMTA
Active Optics Control of the VST Telescope with the CAN Field-Bus
Full text linkThe VST (VLT Survey Telescope) is a 2.6 m class Alt-Az telescope to be installed at Mount Paranal in the Atacama desert, Chile, in the European Southern Observatory (ESO) site. The VST is a wide-field imaging facility planned to supply databases for the ESO Very Large Telescope (VLT) science and carry out stand-alone observations in the UV to I spectral range. This paper will focus on the distributed control system of active optics based on CAN bus and PIC microcontrollers. Both axial and radial pads of the primary mirror will be equipped by astatic lever supports controlled by microcontroller units. The same CAN bus + microcontroller boards approach will be used for the temperature acquisition modules...
Optimized diagnosis of reflectors misalignements in radioastronomical applications
No full textThe paper presents an innovative method for the diagnosis of reflector antennas for radio astronomical applications in terms of feed misalignment. The method optimizes the number and the location of the far field sampling points exploited to retrieve the antenna status in order to reduce the time required for the measurement. The goal is achieved by introducing a relevant linear operator connecting the unknowns describing the status of the antenna and its far field pattern thanks to a proper representation of the unknowns, and by optimizing its singular values behavior. A numerical result is provided in the simple case of a phase aperture affected by tilt only, even if the approach is suited for higher order aberrations too. It show that the approach is capable to significantly reduce the number of required samples compared to a standard grid defined according to the Nyquist criterion without affecting the performance of the diagnosis
Variations on the Author
Full text link“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
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