1,720,968 research outputs found
Disorder-induced single-mode transmission
Full text linkLocalized states trap waves propagating in a disordered potential and play a crucial role in
Anderson localization, which is the absence of diffusion due to disorder. Some localized states
are barely coupled with neighbours because of differences in wavelength or small spatial
overlap, thus preventing energy leakage to the surroundings. This is the same degree of
isolation found in the homogeneous core of a single-mode optical fibre. Here we show that
localized states of a disordered optical fibre are single mode: the transmission channels
possess a high degree of resilience to perturbation and invariance with respect to the launch
conditions. Our experimental approach allows identification and characterization of the
single-mode transmission channels in a disordered matrix, demonstrating low losses and
densely packed single modes. These disordered and wavelength-sensitive channels may be
exploited to de-multiplex different colours at different locations
What is the right theory for anderson localization of light? An experimental test
Full text linkAnderson localization of light is traditionally described in analogy to electrons in a random potential. Within this description, the random potential depends on the wavelength of the incident light. For transverse Anderson localization, this leads to the prediction that the distribution of localization lengths — and, hence, its average — strongly depends on the wavelength. In an alternative description, in terms of a spatially fluctuating electric modulus, this is not the case. Here, we report on an experimentum crucis in order to investigate the validity of the two conflicting theories using optical samples exhibiting transverse Anderson localization. We do not find any dependence of the observed average localization radii on the light wavelength. We conclude that the modulus-type description is the correct one and not the potentialtype one. We corroborate this by showing that in the derivation of the traditional potential-type theory, a
term in the wave equation has been tacitly neglected. In our new modulus-type theory, the wave equation is exact. We check the consistency of the new theory with our data using the nonlinear sigma model. We comment on the consequences for the general case of three-dimensional disorde
Secure information transport by transverse localization of light
Full text linkA single-photon beating with itself can produce even the most elaborate optical fringe pattern. However, the large amount of information enclosed in such a pattern is typically inaccessible, since the complete distribution can be visualized only after many detections. In fact this limitation is only true for delocalized patterns. Here we demonstrate how reconfigurable localized optical patterns allow to encode up to 6 bits of information in disorder-induced high transmission channels, even using a small number of photon counts. We developed a quantum key distribution scheme for fiber communication in which high information capacity is achieved through position and momentum complementarity
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
Anderson localization in a partially random Bragg grating and a conserved area theorem
Full text linkWe investigate the gradual emergence of the disorder-related phenomena in
intermediate regimes between a deterministic periodic Bragg grating and a fully
random grating and highlight two critical properties of partially disordered
Bragg gratings. First, the integral of the logarithm of the transmittance over
the reciprocal wavevector space is a conserved quantity. Therefore, adding
disorder merely redistributes the transmittance over the reciprocal space.
Second, for any amount of disorder, the average transmittance decays
exponentially with the number of grating layers in the simple form of
for sufficiently large , where is a constant and
is the number of layers. Conversely, the simple exponential decay form does not
hold for small except for a highly disordered system. Implications of these
findings are demonstrated
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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