1,720,960 research outputs found
Spontaneous photonic lattices and nonlinear waves in nanodisordered ferroelectrics
Full text linkIn this Thesis we deal with nanodisordered ferroelectric perovskite crystals. These material have been demonstrated to be a good test-bed to study nonlinear optical phenomena due to their strong optical properties. In fact, their embedded disorder enhances their response at the phase transition and makes these materials suitable to sustain solitons and rogue waves also with low optical power.
We first use self-focusing at the paraelectric phase to study nonlinear wave propagation. Our experiments are conceived to investigate the evolution of structured waves in time and in space. We make three beams to interfere to optically observe the Fermi-Pasta-Ulam-Tsingou recurrence. We experimentally verify its analytic solution provided by Grinevich-Santini that allows us to predict the exact position of each recurrence. Moreover, we demonstrate that the periodic behavior is lost if the system ceases to be integrable. We study the appropriate interference pattern in the form of nondiffractive Bessel beams to investigate what happens to such waves in a self-focusing medium. We identify two regimes: a Bessel beam selftrapping and a breathing soliton. Furthermore, we demonstrate the feasibility of Bessel beam writing to build a scalable and rewritable network of waveguides inside the bulk ferroelectric medium.
We also studied the unique properties of the ferroelectric phase. The most evident outcome is the so-called super-crystal that is a spontaneous photonic 3D lattice that emerges from the interplay between material order and disorder. We study the super-crystal in different ways and we recover the periodic behavior for linear and nonlinear propagation. In detail we report a periodic pattern for birefringence and second harmonic generation. The main result is that we have observed the highest value of the refractive index reported in literature for visible light and we have connected the effect to the super-crystal. This material allows, in theory, to transmit light without any information loss, that is without diffraction and chromatic dispersion.
The physics of diffraction is also investigated with the introduction of an innovative method to achieve super-resolution. We exploit a confocal microscope and a remote knifeedge technique. This allows us to directly study the role of evanescent waves in superresolution imaging forming, i.e. they are filtered out as the super-resolved image approaches to the diffraction-limited one. Experiments here are performed with a terahertz frequency, λ ∼ 1.00 mm, to easily accede the near field and capture the information carried by the evanescent wave
Using Bessel Beams to Induce Optical Waveguides
No full textOptical fabrication of waveguides in a volume is limited by diffraction in the writing beams. We
demonstrate the use of nondiffracting waves in the form of Bessel beams to fabricate scalable optical wiring through direct writing in a photosensitive volume. Experiments are performed in paraelectric
potassium-lithium-tantalate-niobate (KLTN), where writing occurs through photogenerated space charge
while guiding and electro-optic functionality are supported by the quadratic electro-optic effect. The
method allows components to be integrated sequentially without interfering with each other during fabrication, an intrinsic superposition property that is used to realize single, double, and multiple waveguides,
and 1 × 2, 1 × 3, and 1 × 4 splitters, and electrically controlled optical switching
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
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
Continuous Solitons in a Lattice Nonlinearity
No full textWe study theoretically and experimentally the propagation of optical solitons in a lattice nonlinearity, a periodic pattern that both affects and is strongly affected by the wave. Observations are carried out using spatial photorefractive solitons in a volume microstructured crystal with a built-in oscillating low-frequency dielectric constant. The pattern causes an oscillating electro-optic response that induces a periodic optical nonlinearity. On-axis results in potassium-lithium-tantalate-niobate indicate the appearance of effective continuous saturated-Kerr solitons, where all spatial traces of the lattice vanish, independently of the ratio between beam width and lattice constant. Decoupling the lattice nonlinearity allows the detection of discrete delocalized and localized light distributions, demonstrating that the continuous solitons form out of the combined compensation of diffraction and of the underlying periodic volume pattern
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
