1,721,048 research outputs found
Measurement on spatial coherence in hard x-ray free electron laser apart from the intensity noise and its dependance on the focusing process
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Current status of the CXI beamline at the PAL-XFEL
No full textThe Pohang Accelerator Laboratory's X-ray free electron laser (PAL-XFEL) is a research facility currently under construction. It will provide ultra-bright (1 x 10(12) photons/pulse at 12.4 keV) and ultra-short (10 - 60 femtosecond) X-ray pulses. The CXI (coherent X-ray imaging) hard X-ray experimental station is designed to deliver brilliant hard X-rays (2 - 20.4 keV) and to measure diffraction signals with a forward scattering geometry. It will not only offer imaging studies of biological, chemical and physical samples with the "diffraction-before-destruction" scheme, but also be helpful in high-field hard X-ray physics and material science. The scientific programs are currently aimed at serial femtosecond crystallography (SFX) and coherent diffraction imaging (CDI) for bio specimens, nano materials, etc. In this paper, we describe the beamline layout, beam diagnostics, X-ray focusing optics, sample environments and detector system at the CXI experimental hutch.11Nsciescopuskc
Characterization of XFEL single pulses using single particle imaging: application to PAL-XFEL
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Visualization of a mammalian mitochondrion by coherent x-ray diffractive imaging
Full text linkWe report a three dimensional (3D) quantitative visualization of a mammalian mitochondrion by coherent x-ray diffractive imaging (CXDI) using synchrotron radiation. The internal structures of a mitochondrion from a mouse embryonic fibroblast cell line (NIH3T3) were visualized by tomographic imaging at approximately 60 nm resolution without the need for sectioning or staining. The overall structure consisted of a high electron density region, composed of the outer and inner membranes and the cristae cluster, which enclosed the lower density mitochondrial matrix. The average mass density of the mitochondrion was about 1.36 g/cm3. Sectioned images of the cristae reveal that they have neither a baffle nor septa shape but were instead irregular. In addition, a high resolution, about 14 nm, 2D projection image was captured of a similar mitochondrion with the aid of strongly scattering Au reference objects. Obtaining 3D images at this improved resolution will allow CXDI to be an effective and nondestructive method for investigating the innate structure of mitochondria and other important life supporting organelles. ? 2017 The Author(s).11Ysciescopu
Comparing the spatial coherence of the natural and focused X-rays from a free electron laser
No full textThe degree of spatial coherence, as basic characteristics of the radiation, becomes an important guide to evaluate the performance of X-rays from newly introduced advanced light sources including the X-ray free electron laser (XFEL). Often the modification of the Xray wavefronts to fulfill various applications is necessary, but also there is the need to preserve its coherence property. However, experimental investigation directly comparing the coherence property of focused X-ray radiations with the unmodified ones has not been available. We have performed Young's double-slit experiments by recording diffraction patterns both from slit apertures for unfocused XFEL radiation and from pairs of Au nanoparticles for one-micron focused XFEL radiations. The results confirm that the degree of spatial coherence is preserved for well-built K-B focusing mirrors. (c) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement11Nsciescopu
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
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
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