1,720,977 research outputs found
Mechanical anti-reflection Structure for optical devices in the mm band
No full textA major challenge in the implementation of optical element in the millimetre band is to minimize the radiation loss caused by reflection. The widely
used method is based on the realization of an Anti-Reflection Coating (ARC), which exploits the behaviour of interference the radiation generated by the deposition of one or more layers of polymeric material on the optical element, so as to obtain a unique surface having refractive index conveniently selected.
The major limitations that affect the ARC, reside in the complexity of manufacturing, with consequent increase of costs, and possible bonding process issues after several cooling cycles; an essential feature to achieve measurements at these wavelengths.
Here we report about an alternative and innovative technique based on the realization of a mechanical Anti-Reflection Structures (ARS), possibly a more simple and economic manufacture, based on the mechanical processing of the surface of a dielectric material. The antireflective behaviour is linked to the geometrical textureof the surface.
The simulations of these ARS provide us a detailed analysis of the optical properties for dierent geometrical realizations. The results will be compared with those of the ARC and further experimentally validated.
Particular attention is put on to the analysis of the possible presence of spurious polarization effects, because this type of technology could find employment in the realization of cold optical elements for telescopes devoted CMB observations
Site-testing and continuous atmospheric monitoring at mm wavelength band with CASPER 2
No full textGround-based cosmological observations need a detailed knowledge about atmospheric transmission. A continuous monitoring of the transmission in the FIR/mm wavelength range is needed mainly due to H2O high frequency variations along the line of sight of a telescope. CASPER 2 (Concordia Atmospheric Spectroscopy of Emitted Radiation) is a spectrometer devoted to measurements of atmospheric emission in the millimetric region (4-12 cm -1, 120-360 GHz) with a spectral resolution of 0.2 cm-1. The instrument allows a continuous monitoring of the atmospheric transmission of the same sky region explored with MITO (Millimeter and Infrared Testagrigia Observatory, 3480 m asl, Italy) telescope, during cosmological observations. © 2010 EAS, EDP Sciences
Atmospheric monitoring in the millimetre and submillimetre bands for cosmological observations: CASPER2
No full textCosmological observations from ground at millimetre and submillimetre wavelengths are affected by atmospheric absorption and consequent emission. The low- and high-frequency (sky-noise) fluctuations of atmospheric performance necessitate careful observational strategies and/or instrumental technical solutions. Measurements of atmospheric emission spectra are necessary for accurate calibration procedures as well as for site-testing statistics. CASPER2, an instrument designed to explore the 90-450 GHz (3-15 cm-1) spectral region, was developed and had its operation verified in the Alps. A Martin-Puplett interferometer (MPI) operates by comparing sky radiation, coming from a field of view (FOV) of 28 arcmin (full width at half-maximum) and collected by a 62-cm-diameter Pressman-Camichel telescope, with a reference source. The signals at the two output ports of the interferometer are detected by two bolometers cooled to 300 mK inside a wet cryostat. Three different but complementary interferometric techniques can be performed with CASPER2: amplitude modulation (AM), fast-scan (FS) and phase modulation (PM). An altazimuthal mount allows sky pointing, possibly co-aligned with the optical axis of the 2.6-m-diameter telescope of MITO (Millimetre and Infrared Testagrigia Observatory, Italy). The optimal time-scale to average acquired spectra is inferred by Allan variance analysis at five fiducial frequencies. We present the motivation for and design of the atmospheric spectrometer CASPER2. The procedure adopted to calibrate the instrument and the preliminary performance of it are described. Instrument capabilities were checked during the summer observational campaign at MITO in 2010 July by measuring atmospheric emission spectra with the three procedures
S-Z constraints on the dependence of the CMB temperature on redshift
No full textPrecise measurements of the Sunyaev–Zel’dovich (S–Z) effect on clusters of galaxies can be used to constrain anomalous scalings of the CMB temperature as a function of redshift, providing an unbiased test of the current cosmological paradigms. This is possible through a precise characterization of the S–Z spectrum as a function of frequency and all the higher order effects which determine small corrections to the amplitude of the effect. Combined with excellent systematic modeling and high quality, routine observations of the S–Z effect on a moderate-to-high redshift sample of galaxy clusters at millimeter and submillimeter wavelengths, this method can constrain deviations from standard scalings of the CMB temperature based on zero-redshift precisions comparable with that of COBE/FIRAS. We describe here the analysis procedure and a pioneering approach to the problem using existing multifrequency S–Z observations
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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