1,721,023 research outputs found
Optical design and performance simulations for the 1.49 keV beamline of the BEaTriX X-ray facility
Get PDFThe BEaTriX (Beam Expander Testing X-ray) facility, now operational at INAF-Brera Astronomical Observatory, will represent a cornerstone in the acceptance roadmap of Silicon Pore Optics (SPO) mirror modules, and will so contribute to the final angular resolution of the ATHENA X-ray telescope. By expansion and collimation of a microfocus X-ray source via a paraboloidal mirror, a monochromation stage, and an asymmetric crystal, BEaTriX enables the full-aperture illumination of an SPO mirror module with a parallel, monochromatic, and broad (140 mm × 60 mm) X-ray beam. The beam then propagates in a 12 m vacuum range to image the point spread function of the mirror module, directly on a focal plane camera. Currently the 4.51 keV beamline, based on silicon crystals, is operational in BEaTriX. A second beamline at 1.49 keV, which requires a separate paraboloidal mirror and organic crystals (ADP) for beam expansion, is being realized. As for monochromators, the current design is based on asymmetric quartz crystals. In this paper, we show the current optical design of the 1.49 keV beamline and the optical simulations carried out to predict the achievable performances in terms of beam collimation, intensity, and uniformity. In the next future, the simulation activity will allow us to determine manufacturing and alignment tolerances for the optical components
Improved low dark current MWIR/LWIR MCT detectors: first results of ROIC and MCT tests
Get PDFWithin the TRP program “Development of Low Dark Current MWIR/LWIR Detectors” ne MCT material was tested with reduced dark current for low photon flux applications. A specific ROIC design was set up within this program to allow a proper characterization of the material and act as a demonstrator for further ROIC derivates. Demonstrator assemblies were prepared and tested.
The poster will highlight the specific design approaches for the ROIC and the MCT. Four different topologies for the input stage on the ROIC were implemented to allow direct assessment of the impact of the design approach. A part of these input stages were designed using radiation hardened cell library. The ROIC doesn’t contain any internal state machine but id fully controlled via a high speed SPI interface driven by an external sequencer.
A test setup will be highlighted. A liquid helium cryostat was prepared to allow dark current measurements in an environment which does not suffer from parasitic radiation sources. The same setup is capable for operation with external illumination and optical filers, which can be moved into the beam.
The detector assemblies are presented. A two-step approach is shown which is initially scanning the performance of the different input topologies. A final detector assembly is selected upon the best performance; final assemblies are shown, the test results will be given on the poster
Latency-Constrained Fading Mitigation for Coherent Optical Feeder Links based on Space-Time-Frequency Coding
Get PDFOptical feeder links (OFLs) benefit from the vast amount of bandwidth available in the THz-regime of the electromagnetic spectrum, and can be considered as enablers for future terabit-per-second satellite systems. A particular challenge for OFLs is to mitigate the effects of fading, caused by a combination of turbulence-induced scintillation, beam wander and pointing errors. The conventional solution is to exploit temporal diversity by a combination of interleaving and forward error correction (FEC). In this study we present an overview of fading mitigation techniques for latency-constrained coherent ground-to-satellite OFL and contribute a generic model which combines various diversity schemes including temporal, spatial, frequency and site diversity. To unlock spatial diversity, multi-beam space-time block coding and multi-beam, multi-λ are proposed and simulated. Though space-time block coding (STBC) provides more diversity gain, it requires accurate timing synchronization at the transmitter and channel state information at the receiver. Temporal, frequency and site diversity all rely on some form of interleaving and the potential diversity, pros and cons of each of these diversity techniques are covered in the presented study. In general, with a strict latency constraint and a tight link budget, frequency diversity, spatial diversity - either by STBC or multi-beam multi-λ - and site diversity can be effective methods to mitigate the effects of fading and close the link budget.</p
A compressive sensing with photonic crystals enabled spectrometer for trace gas observation
No full textRecently a spectrometer concept has been invented which uses compressive sensing in combination with photonic crystal filters. Here we present an adaption of this concept in push-broom configuration for earth observation. This implementation allows for a compact design, while maintaining a high spatial resolution and high signal-to-noise ratio compared to other traditional implementations. The photonic crystals have a unique transmission profile and act as a spectral filter, which allows for the computational reconstruction of the input spectrum with a limited number of filters. We show, using simulations, that our approach is able to reconstruct input radiance spectra with high accuracy and assess the performance for different number of filter sets. We furthermore show proof-of-principle measurements of the transmission profile of a manufactured photonic crystal. Future research will focus on the effect of noise on the reconstruction algorithm as well as further filter set optimization by combining the filter selection process with trace gas concentration retrieval.ImPhys/Adam grou
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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