1,720,975 research outputs found
Performance Investigation of Fountaine Codes on a Simulated Terrestrial Free Space Optical Channel
No full textPerformance analysis and preliminary experimental verification of a coherent optical receiver for PPM signals in the presence of atmospheric turbulence
Full text linkWe present the performance analysis and experimental verification of a coherent free-space optical communications system in the presence of simulated atmospheric turbulence. Bit Error Rate (BER) performance is analyzed, and laboratory equipment and experimental setup used to carry out these experiments at the Jet Propulsion Laboratory are described. The key components include two lasers operating at 1064 nm wavelength for use with coherent detection, a 16 element (4X4) focal plane detector array, and data acquisition and signal processing assembly needed to sample and collect the data and analyze the results. The detected signals are combined using the least-mean-square (LMS) algorithm. Convergence of the algorithm for experimentally obtained signal tones in the presence of atmospheric turbulence is demonstrated
Design and evaluation of ALMA band 9 quasioptical system
Full text linkThe Atacama Large Millimeter Array (ALMA) project requires the development of reliable quasi-optical systems with requirements similar to the ones in space. The operating condition for optical elements of higher frequency channels are similar to the conditions in spacecraft, since these elements are contained within the ALMA cryostat in high vacuum and at cryogenic temperatures. The remote terrain of the Atacama Desert and the scale of project suggest that a significant effort should be made to ensure high reliability of the system. Therefore the techniques, common to a space mission are applied with this development. In this report we would like to present the design of the quasi-optical system for ALMA band 9 (600-702 GHz) containing elements typical to a space system. A design assumptions and details will be presented for a frequency independent system. A measurement of near field antenna beam pattern (phase and amplitude) will be presented and comparison with theoretical predictions will be made.</p
The space-Time explorer and quantum test of the equivalence principle mission (STE-QUEST)
Full text linkThe Space-Time Explorer and Quantum Test of the Equivalence Principle mission (STEQUEST) is devoted to a precise measurement of the effect of gravity on time and matter using an atomic clock and an atom interferometer. The mission was selected by ESA as one of four candidates for the M3 mission within the Cosmic Vision Program (launch in 2022)
The space-time explorer and quantum test of the equivalence principle mission (STE-QUEST)
No full text
Dynamic diffraction gratings and a spectrometer demonstrator
No full textThis paper describes the outcome of the ESA contract 20532/06/NL/Sfe entitled "Instrument concepts using dynamic diffraction gratings". The goal of the project was to study the optical performance of state of the art dynamic diffraction grating technology and identify potential applications for space missions. A dynamic diffraction grating sample was obtained for characterisation and a demonstrator for a compact spectrometer architecture was implemented and tested
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
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