1,721,377 research outputs found
Observation of charged few-particle states in the optical spectra of single semiconductor quantum dots
No full textA detailed discussion of the optical properties of single n-type modulation-doped semiconductor quantum dots is presented. We use the photo-depletion/back-hopping mechanism to optically control the number of surplus electrons in the dot. Comparison of the experimental data with calculated luminescence spectra, obtained within a direct-diagonalization approach for calculating electron-hole states, allows the identification of luminescence from the decay of up to fivefold charged excitons. Finally we study the influence of fluctuating local electric fields, produced by ionized impurities in the surrounding of the dots, on the optical selection rules and on the linewidth of the emission peaks
Semianalytical approach to the design of photonic crystal cavities
No full textMost current methods for the engineering of photonic crystal (PhC) cavities rely on cumbersome, computationally demanding trial-and-error procedures. In the present work, we take a different approach to the problem of cavity design, by seeking to establish a direct, semianalytic relationship between the target electromagnetic field distribution and the dielectric constant of the PhC structure supporting it. We find that such a relationship can be derived by expanding the modes of LN-type cavities as a linear combination of the one-dimensional (1D) Bloch eigenmodes of a PhC W1 waveguide. Thanks to this expansion, we can also ascertain the presence of a well-defined 1D character in the modes of relatively short cavities (e.g., L9–15), thus confirming recent theoretical predictions and experimental findings. Finally, we test our method through the successful design of a cavity supporting a mode with Gaussian envelope function and ultralow radiative losses (quality factor of 17.5×10^6)
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
Dense arrays of ordered pyramidal quantum dots with narrow linewidth photoluminescence spectra
No full textArrays of site-controlled, pyramidal InGaAs/GaAs quantum dots (QDs) grown by organo-metallic chemical vapour deposition with densities comparable to those of self-assembled QDs (5 × 109 cm−2) are demonstrated. The QDs exhibit high quality photoluminescence spectra with inhomogeneous broadening of only 6.5 meV. The QD dipole moment was estimated through the analysis of time-resolved photoluminescence measurements. Such ordered QD arrays should be useful for applications in active nanophotonic systems such as QD lasers, modulators and switches requiring high overlap of the optical modes with the QD active region
Few-particle effects in semiconductor quantum dots: Observation of multicharged excitons
No full textWe investigate experimentally and theoretically few-particle effects in the optical spectra of single quantum dots (QDs). Photodepletion of the QD together with the slow hopping transport of impurity-bound electrons back to the QD are employed to efficiently control the number of electrons present in the QD. By investigating structurally identical QDs, we show that the spectral evolutions observed can be attributed to intrinsic, multi-particle-related effects, as opposed to extrinsic QD-impurity environment-related interactions. From our theoretical calculations we identify the distinct transitions related to excitons and excitons charged with up to five additional electrons, as well as neutral and charged biexcitons
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
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