1,720,964 research outputs found
Heterodyne speckle velocimetry
No full textWe present a simple method for fluid velocimetry based on the velocity of the heterodyne speckles
generated by tracking particles illuminated with coherent light. It works in real time and provides
instantaneous two-dimensional velocity mappings in the direction orthogonal to the optical axis,
independently of the particle concentration and size, also for subwavelength particles. It also
provides the velocity distribution of the fluid over the entire sample thickness. The method has been
quantitatively tested by using the motions of rigid diffusers and applied for mapping the flow of a
confined fluid
Probing the transverse coherence of an undulator X-ray beam using Brownian particles
No full textWe present a novel method to map the two-dimensional transverse coherence of an x-ray beam using
the dynamical near-field speckles formed by scattering from colloidal particles. Owing to the statistical
nature of the method, the coherence properties of synchrotron radiation from an undulator source is
obtained with high accuracy. The two-dimensional complex coherence function is determined at the
sample position and the imaging optical scheme further allowed us to evaluate the coherence factor at the
undulator output despite the aberrations introduced by the focusing optics
How to measure the optical thickness of scattering particles from the phase delay of scatterred waves : application to turbid samples
No full textWe present a method based on the optical theorem that yields absolute, calibration free estimates of the optical thickness of scattering particles. The thickness is determined from the phase delay of the zero angle scattered wave. It uses a heterodyne scattering scheme operating in the Raman-Nath approximation. The phase is determined by the position of Talbot-like modulations in the two dimensional power spectrum S(q(x), q(y)) of the transmitted beam intensity distribution. The method is quite insensitive to multiple scattering. It is successfully tested to provide quantitative verification of the optical theorem. Exploratory tests on soft matter samples are reported to suggest its wide applicability to turbid samples
Heterodyne speckle velocimetryof Poiseuille flow
No full textWe review the technique named heterodyne speckle velocimetry and present two applications for
testing the method with a fluid moving under the conditions of Poiseuille flow. The fluid was seeded
with small tracking particles diameter 300 nm and fluxed between the two parallel planes of a cell
with constant or variable cross section. In the first case the velocity distribution was constant along
the direction parallel to the planes and was in excellent agreement with the expected Poiseuille
profile along the orthogonal direction. In the second case, where velocity gradients were present also
along the planes, the technique was able to reconstruct both the orthogonal Poiseuille profile and the
in-plane two dimensional mapping of the velocity vectors, with the possibility of measuring the fluid
flux within an accuracy of 1%
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
Dynamic heterodyne near field scattering
No full textThe technique heterodyne near field scattering (HNFS), originally developed for low-angle static light scattering, has also been implemented for carrying out dynamic light scattering. While the classical dynamic light scattering method measures the intensity-intensity correlation function, dynamic HNFS gives directly the field-field correlation function, without any assumption on the statistical properties of the sample, as the ones required by the Siegert relation. The technique has been tested with calibrated Brownian particles and its performances compared to those of the classical dynamic light scattering method.The technique heterodyne near field scattering (HNFS), originally developed for low-angle static light scattering, has also been implemented for carrying out dynamic light scattering. While the classical dynamic light scattering method measures the intensity-intensity correlation function, dynamic HNFS gives directly the field-field correlation function, without any assumption on the statistical properties of the sample, as the ones required by the Siegert relation. The technique has been tested with calibrated Brownian particles and its performances compared to those of the classical dynamic light scattering method. © 2008 American Institute of Physics
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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