1,720,963 research outputs found
X-ray waveguides with multiple guiding layers
No full textWe have generalized the principle of resonant x-ray beam coupling to waveguides containing multiple guiding layers and characterized their x-ray optical properties. In such a device, several coherent beams of a width on the order of 10-100 nm can be extracted at the end of the waveguide. By measuring the farfield pattern formed by the interference of the beams, we demonstrate the possibility of using these devices as new tools to tailor the field distribution in the near- and far-field region for specific applications: Besides coherent diffraction and imaging, interferometry with two or more nanometer sized beams can be envisioned
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No full textPlanar x-ray waveguide structures can be used as resonant beam coupling devices to produce a coherent and divergent x-ray line source with cross-sections in the sub-micrometer range. This article reviews the basic x-ray optical properties of such devices and generalizes the principle of resonant x-ray beam coupling to waveguides containing multiple guiding layers. In such a device, several coherent beams of a width on the order of 100 angstrom to 1000 angstrom can be extracted at the end of the waveguide. Besides coherent diffraction and imaging, interferometry with two or more nanometer sized beams can be envisioned. Furthermore this article presents measurements of the internal reflection of an excited x-ray waveguide mode in a synthetic nanostructure defined by e-beam lithography. In this device the x-ray beam is first coupled into a conventional vertical thin film waveguide structure and then reflected laterally at the quasi one-dimensional edge of the waveguiding layer. The reflectivity of the quasi one- dimensional interface has been recorded under simultaneous excitation of the (vertical) waveguide mode. This experiment constitutes an important step towards the production of a coherent, nanometer sized x-ray point source by two- dimensionally defined waveguide structures
Observation of the Huygens-principle growth mechanism in sputtered W/Si multilayers
No full textWe have investigated the interfacial roughness of a W/Si multilayer sputtered at high Ar gas pressure. The roughness exponents as determined from diffuse X-ray scattering agree well with the Huygens-principle growth model proposed by Tang, Alexander and Bruinsma (TAB). Simple microscopic explanations are given to account for the finding of Edwards-Wilkinson (EW) type growth at low Ar pressure and the TAB growth mechanism at high pressures, as well as for the absence of any scaling according to the Kardar-Parisi-Zhang (KPZ) equation
Interfacial roughness and related growth mechanisms in sputtered W/Si multilayers
No full textWe have studied interfacial roughness in amorphous W/Si multilayers grown by rf sputtering at different deposition parameters by cross-sectional transmission electron microscopy, x-ray reflectivity, and diffuse x-ray scattering. The diffuse scattering intensity has been recorded in an unprecedented wide range of parallel momentum transfer, 5x10(-4) Angstrom(-1)less than or equal to q(parallel to)less than or equal to 1 Angstrom(-1), giving access to the height-height self- and cross-correlation functions on lateral length scales between a few Angstrom and 1 mu m. The results are compared for the different samples and discussed in view of the deposition parameters
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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