1,720,985 research outputs found
Experimental single photon exchange along a space link of 7000 km
Get PDFExtending the single photon transmission distance is a basic requirement for the implementation of quantum communication on a global scale. In this work we report the single photon exchange from a medium Earth orbit satellite (MEO) at more than 7000 km of slanted distance to the ground station at the Matera Laser Ranging Observatory. The single photon transmitter was realized by exploiting the corner cube retro-reflectors mounted on the LAGEOS-2 satellite. Long duration of data collection is possible with such altitude, up to 43 minutes in a single passage. The mean number of photons per pulse (µsat) has been limited to 1 for 200 seconds, resulting in an average detection rate of 3.0 cps and a signal to noise ratio of 1.5. The feasibility of single photon exchange from MEO satellites paves the way to tests of Quantum Mechanics in moving frames and to global Quantum Information
Experimental Satellite Quantum Communications
Get PDFQuantum communication (QC), namely, the faithful transmission of generic quantum states, is a key ingredient of quantum information science. Here we demonstrate QC with polarization encoding from space to ground by exploiting satellite corner cube retroreflectors as quantum transmitters in orbit and the Matera Laser Ranging Observatory of the Italian Space Agency in Matera, Italy, as a quantum receiver. The quantum bit error ratio (QBER) has been kept steadily low to a level suitable for several quantum information protocols, as the violation of Bell inequalities or quantum key distribution (QKD). Indeed, by taking data from different satellites, we demonstrate an average value of QBER = 4.6% for a total link duration of 85 s. The mean photon number per pulse μsat leaving the satellites was estimated to be of the order of one. In addition, we propose a fully operational satellite QKD system by exploiting our communication scheme with orbiting retroreflectors equipped with a modulator, a very compact payload. Our scheme paves the way toward the implementation of a QC worldwide network leveraging existing receivers
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
Dual-Polarization NFDM Transmission with Continuous and Discrete Spectral Modulation
Get PDFNonlinear distortion experienced by signals during their propagation through optical fibers strongly limits the throughput of optical communication systems. Recently, a strong research focus has been dedicated to nonlinearity mitigation and compensation techniques. At the same time, a more disruptive approach, the nonlinear Fourier transform, aims at designing signaling schemes more suited to the nonlinear fiber channel. In a short period, impressive results have been reported by modulating either the continuous spectrum or the discrete spectrum. Additionally, very recent works further introduced the opportunity to modulate both spectra for single polarization transmission. Here, we extend the joint modulation scheme to dual-polarization transmission by introducing the framework to construct a dual-polarization optical signal with the desired continuous and discrete spectra. After a brief analysis of the numerical algorithms used to implement the proposed scheme, the first experimental demonstration of dual-polarization joint nonlinear frequency division multiplexing modulation is reported for up to 3200 km of low-loss transmission fiber. The proposed dual-polarization joint modulation schemes enables to exploit all the degrees of freedom for modulation (both polarizations and both spectra) provided by a single-mode fiber
Nonlinear Fourier transform for dual-polarization optical communication system
Get PDFNew services and applications are causing an exponential increase in the internet traffic. In a few years, the current fiber-optic communication system infrastructure will not be able to meet this demand because fiber nonlinearity dramatically limits the information transmission rate. Eigenvalue communication is considered an emerging paradigm in fiber-optic communications that could potentially overcome these limitations. It relies on a mathematical technique called “inverse scattering transform” or “nonlinear Fourier transform (NFT)” to exploit the “hidden” linearity of the nonlinear Schrödinger equation as the master model for signal propagation in an optical fiber. One of the rapidly evolving NFT-based communication techniques is called nonlinear frequency division multiplexing (NFDM). Being still in its infancy, NFDM systems still have some practical limitations. One of these limitations is the lack of polarization division multiplexing. This thesis addresses this problem by introducing the novel concept of dual-polarization NFDM. First, the structure of a single polarization NFDM system using the discrete nonlinear spectrum is described. The particular design aspects of this system are then discussed in details. Afterwards, the theoretical tools that define the NFT for the Manakov system,which describes the evolution of a dual polarization signal in a single-mode fiber, are presented. Using these tools the discrete NFDM system is extended to the dual polarization case. Finally, the results of the first experimental transmission of a dual polarization NFDM system are presented. A transmission of up to 373.5km with bit error rate smaller than the hard-decision forward error correction threshold has been achieved. The results presented demonstrate that dual-polarization NFT can work in practice and that it enables an increased spectral efficiency in NFT-based communication systems, which are currently based on single polarization channel
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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Tecnologie di relay per sistemi mobili LTE-advanced e WiMax
Get PDFIn questa tesi vengono presentate alcune tecnologie di relay che potrebbero essere incluse negli standard di telefonia cellulare di prossima generazione LTE-Advanced e Wimax. Inizialmente vengono illustrare alcune caratteristiche tecniche dei due standard menzionati. Nel capitolo successivo vengono presentati i diversi tipi di relay previsti dai due standard, tre tecniche di trasmissione utilizzabili, vautando pro e contro di ognuna, e alcune modifiche necessarie agli standard per poter supportare il relay; in particolare ci si sffermerà sulla struttura del frame.
Successivamente vengono illustrati uno schema di pairing centralizzato e uno distribuito per la selezione delle stazioni partner nella fase di relay; inoltre viene descritto uno schema di pairing per la selezione dei relay ottimi per effettuare trasmissioni cooperative. Infine vengono valutate le prestazioni delle tre differenti tecniche di trasmissione in termini di efficienza di trasmissione e vengono anche valutate le
prestazioni degli schemi di pairing proposti in termini di throughput raggiungibile e probabilità di accoppiament
Signal Handling for Space Quantum Key Distribution
Get PDFIn this work of thesis we will present an experiment, which aims to realize a fully working quantum key distribution system for satellite communications, in order to prove the feasibility of a global quantum cryptography network. In particular we will deal with the implementation issues that arise when such system is realized using the already existing satellite laser ranging facilitiesopenEmbargo per motivi di segretezza e/o di proprietà dei risultati e/o informazioni sensibil
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