1,720,974 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Mode structure of the radiation emitted through high-gain parametric down-conversion
Get PDFQuantumness and brightness of light are not usually found together in today’s optical quantum information, communication or measurement technologies. Yet, the last two decades saw an increased interest in the study of bright sources of nonclassical light where lossless control of their spatio-temporal spectrum promises to improve the capabilities of existing applications or to create novel ones. One of the most popular light sources for quantum optics is parametric down-conversion (PDC), a nonlinear process that occurs inside certain dielectrics where non-classical radiation originates from the parametric amplification of vacuum fluctuations. Even though
the PDC process is known for almost six decades, the quantum aspects of PDC have mostly been studied at low pump power regimes. In this case, much less than one photon per mode is spontaneously produced. At strong pump power regimes, where several photons per mode
are produced, PDC becomes a source of a multiphoton non-classical state of light known as bright squeezed vacuum (BSV). BSV is recognized as a good candidate for efficient light-light and light-matter interactions, multichannel quantum communications, parallel information
processing, high-resolution metrology and imaging, among other applications.
This thesis addresses one out of several unexplored questions regarding BSV, namely, what is its spatial modal structure? To answer this question, orthonormal modes dictated by the spatial
coherence of the radiation (or so-called Schmidt modes) which also account for photon number
correlations, have been considered. The Schmidt-mode formalism has been successfully used in
the description of the radiation generated by low-gain PDC but their usage in the BSV case was challenging. This thesis presents several experiments that validated the results of an analytical
theory for BSV based on Schmidt modes. According to the theory, the modes describing BSV, to a good approximation, are invariant to the pump power used in the process, while the photon
population of each mode is not. The observed changes in the spatial intensity spectrum, spatial photon number correlations and the effects of the spatial anisotropy on the spectrum shape corroborated this prediction.
Additionally, different methods for engineering the spatial spectrum of BSV were proposed and implemented by using unseeded and strongly pumped traveling-wave optical parametric amplifiers (OPAs) made of bulk nonlinear crystals, where the radiation produced is highly multimode in several degrees of freedom. For instance, spatial walk-off was exploited to obtain
tunable, bright, narrowband and diffraction-limited twin beams through the amplification of the
radiation in the direction of the pump Poynting vector. Alternatively, tailoring of the BSV state was achieved through the amplification of the radiation produced in one unseeded traveling-wave
OPA by the presence of a second OPA, up to the generation of a single spatial mode. The modal content of the output light was further studied in terms of radial and orbital angular momentum
modes. Finally, as an alternative to generation, lossless projective filtering of a single spatial BSV mode by means of a single-mode fiber was performed. The examples given in this thesis
on the lossless control of the BSV spatial spectrum are extensible to the temporal domain, as proved in subsequent works. Since the elucidation of the mode structure of BSV radiation is
a requirement for further development of reliable light tailoring strategies that preserve BSV nonclassical properties, this thesis is a direct contribution to the know-how that will allow full
involvement of BSV in quantum technologies in the near future
Variations on the Author
Get PDF“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
Get PDFWe 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
Nonlinear interferometry with high-gain parametric down-conversion
Get PDFInterferometers have become essential devices within research and industry because they can measure phase shifts, often very small ones. Increasing the number of probing photons enhances the accuracy of this measurement, but with a bounded scaling called the shot-noise limit. The field of nonlinear interferometry studies how to surpass this limit using nonclassical properties produced with nonlinear effects. The advantage offered -- often referred to as super-sensitivity -- becomes relevant when the precision cannot be pushed further, for instance, by an arbitrary increase of the number of photons. Therefore, this field pioneers the technological advance of interferometers and, in the last decades, it had a substantial impact on applications in quantum information, metrology and imaging.
This thesis aims to demonstrate robust and versatile nonlinear interferometers that encompass the process of parametric down-conversion in nonlinear crystals as the source of nonclassical radiation. The squeezed vacuum state produced in this process can yield a macroscopic number of photons per mode in the strongly-pumped regime while still possessing quantum features. This state is injected together with a laser in a classical interferometer for the first experiment of this work. The super-sensitivity to a scalar phase shift results from the reduced noise in one electric field quadrature, a nonclassical feature. However, the output state can be fragile if the detection is lossy or inefficient; this work proves that noiseless optical amplification before detection leads to robustness and that a stronger amplification pre-compensates for a higher loss or inefficiency. This proof-of-principle scheme is suitable for many applications employing squeezed states, especially in those challenging wavelength ranges for detection like mid-infrared.
The noiseless amplification is obtained here with the external stimulation of the down-conversion process in similar nonlinear crystals to the ones used to produce the squeezed vacuum. The measurement of a scalar phase shift does not fully exploit the potential of the squeezed vacuum and the amplification process: the broad multimode spatial structure would enable two-dimensional phase super-sensitivity. However, since the amplification in nonlinear crystals is not necessarily noiseless, as a preliminary step, this thesis addresses the unexplored conditions on the input signal to achieve this regime for the spatially-multimode case. The examples given here for the spatial degree are extensible also to the temporal domain, which is of great interest for quantum spectroscopy.
This thesis proposes another scheme, usually referred to as the SU(1,1) interferometer, to pave the way towards two-dimensional super-sensitivity. In this scheme, the beam splitter, which is a passive building block of interferometers, is substituted with the nonlinear crystal, a pumped active element, and no other source than the squeezed vacuum may be required. Previous experiments achieved super-sensitive detection of scalar phase shifts, but the novel configuration presented here works with multiple spatial modes and in two dimensions. The operation in the quantum regime is ensured by the measured reduction in the quadrature noise for the plane-wave modes of the state that probes the phase shift. As the phase changes, this configuration is also stable in the output spatial mode content, both in the radial and azimuthal degree of freedom. The full mode structure for this interferometer is not analytically known; this thesis proposes a method to experimentally reconstruct the modes with the acquisition of only intensity distributions. The knowledge of this structure is fundamental for applications in remote sensing and sub-shot-noise imaging because it helps developing schemes that preserve the nonclassical properties, nontrivial for multiple modes
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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