1,721,127 research outputs found
Measuring spatial coherence by using a reversed-wavefront Young interferometer
No full textA very simple optical setup for the measurement of the modulus and the phase of the two-point correlation function of a partially coherent light field is presented. The system consists of a slightly modified version of a Young interferometer and requires a single Young mask in order to determine the correlation function at any pairs of points. Experimental results are presented for the case of a synthesized partially coherent secondary source
Ultra-High Q-Factor Silicon Resonator for High Frequency Oscillators
Full text linkThe thesis focuses on the investigation and characterisation of ultra-high Q-factor low loss Silicon resonators with transverse electric (TE)-like electromagnetic band-gap determined by two dimensional periodic structure made of a Silicon slab having a triangular lattice of air cylinders. A band-gap is observed where no energy is propagated through the slab, however engineering defects are created and optimised within the lattice producing resonant cavities and waveguides. The structure being excited with the fundamental TE10 mode can be coupled to external circuits via waveguides and its respective transitions in co-planar waveguide transmission line used to convey the millimetre-wave frequency signals.
The ultimate goal is to investigate and characterise the promising low loss and high frequency Silicon resonators suitable for millimetre-wave communications such as used in low phase noise oscillator application and band pass filters.
The results clearly show that electromagnetic band-gap structures or photonic crystals (PC) can be utilized for application in high frequency oscillators directly in fundamental mode with great benefits in obtaining ultra-high Q-factor and therefore low phase noise; and with better performance than alternative state-of-art technologies such as crystal oscillators in combination with frequency multiplication or frequency synthesis causing an increase in the overall phase noise by 20 log rule.
By successfully demonstrating the experiment of using electromagnetic band-gap structures with oscillators, it is a great contribution towards the solution of the problem of high phase noise affecting high frequency oscillators operating at millimetre-wave band
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
Maximizing Young’s fringe visibility through reversible optical transformations
No full textWhen a Young's interferometer is fed by an electromagnetic beam, fringes of low, or even zero, visibility do not necessarily indicate lack of correlation between two typical field components at the pinholes. The passage of light that emerges from one of the pinholes through a nonabsorbing anisotropic optical element may enhance the visibility. We inquire about the maximum visibility that can be attained through such a reversible transformation (polarizers being excluded). We find that such a quantity can be evaluated in closed form. Its value is directly related to the Ky Fan 1-norm of the correlation matrix of the illuminating beam
Phase and Amplitude Retrieval in Ghost Diffraction from Field-Correlation Measurements
No full textWe report the results of experiments about the inversion of ghost diffraction with pseudothermal light. A complete retrieval of the complex transmission function of planar transparencies, illuminated by spatially incoherent, quasimonochromatic light, is achieved. This is obtained by measuring the field (instead of the intensity) correlation function. In particular, the determination of the phase of the correlation function is made particularly easy and robust by the use of a suitably modified Young interferometer. The presented results r
Tourisme et Patrimoine Récent – Tourism and Recent Heritage
No full textThis publication represents one of the components
of Mutual Heritage, a project that is part of the
Euro-Mediterranean Euromed Heritage 4 programme
and which aims to extend the base of
proactive stakeholders on issues concerning heritage
in the Mediterranean area. One of the possible
strategies to reach this objective, is to facilitate the
involvement of players who have the impression
that they are less concerned in these issues and to
help them to become active agents of the new,
complex and modern dynamics around the enhancement
of architectural heritage.
This practical handbook provides information
as added value for existing buildings and
sites. It will help a
number of potential players in the domain of heritage
tourism to become proactive agents who will
rise to the challenge of enhancing heritage - a
sphere of activity that engenders cultural and economic
growth
Nonparaxial fields with maximum joint spatial-directional localization. II. Vectorial case
No full textThe monochromatic nonparaxial vector fields that achieve a minimum spatial spread for a given directional spread are found. The derivation of these fields is analogous to the one presented in part I of this series for the case of scalar fields. This derivation is based on a variational treatment and multipolar expansion. The resulting lower bounds for the spreads of vector fields turn out to be considerably more restrictive than for scalar fields
- …
