1,721,034 research outputs found
The beam position monitor of the BEAR beamline
No full textThis article describes the photon beam position monitor installed at the BEAR beamline at Elettra, Trieste. The device, based on four Mo photoemitting plates, is installed upstream of the beamline optics. Two modes of operation are possible, including single-plate operation (integral mode) and two-plate operation (differential mode). The integral mode allows beam height determination in the laboratory frame of reference with an overall accuracy of about 0.1 mm, while the differential mode features a sensitivity of the order of about 1 mu m. A quantitative model connecting the device output with beam height was deduced. A satisfactory agreement was found between model predictions and experimental results. The quantitative performance opens the possibility to implement a feedback procedure to stabilize or automatically numerically correct the delivered photon energy
Polarization and higher-order content measurement of a soft-x-ray monochromatized beam with Mo-Si multilayers
No full textA Mo-Si multilayer mirror has been used for determination of the ellipticity and higher-order content of a synchrotron beam. The method is based on the angular measure of multilayer reflectivity in the region of Bragg first- and second-order reflections. Beam parameters were derived by a fitting procedure
Coordination of boron and phosphorous in Borophosphosilicate glasses
No full textWe report boron K-edge x-ray absorption near-edge structure measurements on borophosphosilicate glasses and density functional theory calculations aimed at determining the most stable local geometries for boron and phosphorous. We demonstrate that phosphorous induces a modification in the local structure of boron, from a trigonal to a tetrahedral geometry. The microscopic mechanisms involved are discussed
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
Electronic properties and orbital-filling mechanism in Rb-intercalated copper phthalocyanine
No full textThe evolution of the electronic properties of a thin film of copper phthalocyanine deposited on Al(100) and progressively intercalated with rubidium atoms was followed by photoemission and X-ray absorption spectroscopies. Electron donation from the Rb atoms to the C32H16N8Cu molecules results in the lifting of the degeneracy in the e(g) ligand-derived molecular orbital and the lowering of the molecular symmetry. For Rb similar to 2C32H16N8Cu, spectral evidence indicates that both donated electrons reside in the first split-off e(g)-derived level, thus creating an electronic inequivalence between the C atoms in the benzene rings. For higher Rb concentrations, a reduction of the Cu oxidation state is observed, together with a new Cu-derived state in valence-band photoemission spectra, testifying to the filling of the b(1g) orbital. Thus, even though b(1g) is the lowest unoccupied orbital of the neutral molecule, in the film, the Cu-derived b(1g)-derived states are occupied only after a partial filling of the e.-derived band has taken place. Despite the fact that the eg-derived spectral weight becomes larger as the rubidium content in the RbxC32H16N8Cu compound increases, no spectral density was observed at the Fermi level, showing that the film remains insulating for all of the investigated stoichiometries
EUV Polarimetry with single multilayer optical element
No full textA polarimetric measurement technique based on the analysis of the reflection data given by a single mirror rotated around the incidence beam axis is presented. In the extreme ultraviolet spectral region, a multilayer coated mirror must be used. The multilayer mirror must be fully characterized before the experiment. Theory demonstrates how this method allows complete determination of Stoke's parameters in case of a totally polarized beam. A simulation code has been developed in order to model the experiment in case of synchrotron radiation propagating in a bending magnet beamline and impinging a multilayer mirror. The simulation is useful to verify each time the effectiveness of the method in the different experimental conditions considered. Finally an experimental application is presented
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
Photon Reflectivity Distributions from the LHC Beam Screen and their Implications on the Arc Beam Vacuum System
No full textIn particle accelerators with intense positively charged bunched beams, an electron cloud may induce beam instabilities and the related beam induced electron multipacting (BIEM), result in an undesired pressure rise and, in a cryogenic machine such as the Large Hadron Collider (LHC), introduce addition heat loads. When present, synchrotron radiation (SR) may generate a significant number of photoelectrons, that may play a role in determining the onset and the detailed properties of the electron-cloud related instability. Since electrons are constrained to move along field lines, those created on the accelerator equator in a strong vertical (dipole) field cannot participate in the ecloud build-up. Therefore, for the LHC there has been a continuous effort to find solutions to absorb the photons on the equator. The solution adopted for the LHC dipole beam screens is a saw-tooth structure on the illuminated equator. SR from a bending magnet beamline at ELETTRA, Italy (BEAR) has been used to measure the reflectivities (forward, backscattered and diffuse), for a flat and a saw-tooth structured Cu co-laminated surface using both white light SR, similar to the one emitted by LHC, and monochromatic light. Our data show that the saw-tooth structure does reduce the total reflectivity and modifies the photon energy distribution of the reflected photons. The implications of these results on the LHC arc vacuum system are discussed
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