1,721,050 research outputs found
Experimental verification of anomalous spectral features of SKALA4.1 antenna
No full textIn this communication, we present a detailed measurement process of the SKALA4.1 antenna frequency response as the S_21 of its coupling with a reference antenna in an anechoic chamber environment. This is the first experimental evidence of anomalous spectral features of SKALA4.1 antenna. We validate the consistency of the results by examining the error between measurement and a corresponding FEKO simulation. Finally, we pinpoint all the spectral features inherent in SKALA4.1 antenna and examine their occurrence in measurement and simulation
Ricostruzione olografica di grandi antenne a riflettore mediante metodo iterativo-perturbativo basato sulla SVD
No full text
Investigation of a new approach to reflector profile retrieval
No full textThe retrieval of the surface profile of a reflector antenna is an important issue,
especially for radioastronomical applications. Microwave holography retrieves the reflector
profile starting from a set of measured far-field data. The main step of this technique is
the computation of the induced currents on the reflector surface. This requires the solution
of a linear inversion problem which is strongly ill-conditioned. The aim of this work is to
investigate a new solution technique for this linear inversion problem based on the SVD.
This new technique supplies a flexible regularization scheme, able to take into account also
the noise level of the data. Some numerical results are obtained, starting from a simulated
far-field
Reflective Toraldo pupil for high-resolution millimeter-wave astronomy
Full text linkA novel, to the best of our knowledge, beam-shaping reflective surface for high-resolution millimeter/ submillimeter-wave astronomy instruments is presented. The reflector design is based on Toraldo’s superresolution principle and implemented with annulated binary-phase coronae structure inspired by the achromatic magnetic mirror approach. A thin, less than half a free-space wavelength, reflective Toraldo pupil device operated in the W-band has been fabricated using mesh-filter technology developed at Cardiff University. The device has been characterized on a quasi-optical test bench and demonstrated expected reduction of the beam width upon reflection at oblique incidence, while featuring a sidelobe level lower than −10 dB. The proposed reflective Toraldo pupil structure can be easily scaled for upper millimeter and infrared frequency bands as well as designed to transform a Gaussian beam into a flat-top beam with extremely low sidelobe level
An Alternative Solution for the Reflector Surface Retrieval Problem
No full textThe retrieval of the surface profile of a reflector antenna
is an important task, mainly for radio-astronomical applications. The
microwave holography retrieves the reflector profile starting from a set
of measured far-field data. The main stepof this technique is the
computation of the induced currents on the reflector surface. This
requires the solution of a linear inverse problem which is strongly illconditioned.
We propose a new technique, based on the Singular Value
Decomposition, for the solution of this linear inversion problem. This
technique supplies a flexible regularization scheme, able to take into
account also the noise level of the data. The proposed procedure has
been tested on a number of different cases, with field data generated
by a commercial software
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
An atmosphere monitoring system for the Sardinia radio telescope
Full text linkThe Sardinia radio telescope (SRT) is a new facility managed by the Italian National Institute for Astrophysics (INAF). SRT will detect the extremely faint radio wave signals emitted by astronomical objects in a wide frequency range from decimeter to millimeter wavelengths. Especially at high frequencies (>10 GHz), specific weather conditions and interactions between signal and atmospheric constituents (mainly water and oxygen molecules) affect the radio astronomic observation reducing the antenna performances. Thus, modern ground-based telescopes are usually equipped with systems able to examine in real-time several atmospheric parameters (opacity, integrated water vapor, etc.), and in some cases to forecast the weather conditions (wind, rain, snow, etc.), in order to ensure the antenna safety and support the schedule of the telescope observations. Here, we describe the atmosphere monitoring system (AMS) realized with the aim to improve the SRT operative efficiency. It consists of a network of different sensors such as radiometers, radiosondes, weather stations, GPS and some well-established weather models. After a validation of the scheme, we successfully tested the AMS in two real practical scenarios, comparing the AMS outcomes with those of independent techniques. In the first one we were able to detect an incoming storm front applying different techniques (GPS, radiometer and the weather forecast model), while in the last one we modeled the SRT antenna system temperature at 22 GHz processing the AMS data set
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