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Multilayer Metal-Dielectric Stack Ultraviolet Filter
No full textWe present an ultraviolet (UV) filter composed of a multilayer metal-dielectric stack that functions as a coupled set of nanoscale Fabry-Pérot etalons having resonant transmission in the UV
Nanophotonics for dark materials, filters, and optical magnetism
Get PDFResearch on nanophotonic structures for three application areas is described, a near perfect optical absorber based on a graphene/dielectric stack, an ultraviolet bandpass filter formed with an aluminum/dielectric stack, and structures exhibiting homogenizable magnetic properties at infrared frequencies. The graphene stack can be treated as a effective, homogenized medium that can be designed to reflect little light and absorb an astoundingly high amount per unit thickness, making it an ideal dark material and providing a new avenue for photonic devices based on two-dimensional materials. Another material stack arrangement with thin layers of metal and insulator forms a multi-cavity filter that can effectively act as an ultraviolet filter without the usual sensitivity of the incident angle of the light. This is important in sensing applications where the visible part of the spectrum is to be removed, allowing detection of ultraviolet signals. Finally, achieving a magnetic material that functions at optical frequencies would be of enormous scientific and technological impact, including for imaging, sensing and optical storage applications. The challenge has been to find a guiding principle and a suitable arrangement of constituent materials. A lattice of dielectric spheres is shown to provide a legitimately homogenized material with a magnetic response. This should pave the way for experimental studies. More specifically, a graphene stack is designed, fabricated and characterized. The structure shows strong absorption of light. Spectroscopic ellipsometry is used to obtain the complex sheet conductivity of graphene. Further modeling results establish the graphene stack as the darkest optical material, with lower reflectivity and higher per-unit-length absorption than alternative light-absorbing materials. An optical bandpass filter based on a metal/dielectric structure is modeled, showing performance that is largely independent of the angle of incidence. Parametric evaluations of the reflection phase shift at the metal-dielectric interface provide insight and design information. Filter passbands in the ultraviolet (UV) through visible or longer wavelengths can be achieved by engineering the dielectric thickness and selecting a metal with an appropriate plasma frequency, as demonstrated in simulations. A lattice of suitable dielectric particles is shown to fulfill the requirements for a magnetic optical material. Using Mie theory, the microscopic origin of the magnetic response is explicitly identified as being due to the magnetic dipole resonance of an isolated sphere. This provides a design basis, and dielectric and lattice requirements with candidate dielectrics that will allow magnetic materials to be designed and fabricated for optical applications are presented
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
Simulation of multilayer metamaterials
No full textA new class of non-magnetic optical metamaterials capable of achieving negative refraction for all incident angles is thoroughly analyzed in this thesis. This new design consists solely of periodically stratified planar media, as first proposed by Hoffman et al., which obviates the fabrication difficulty and high intrinsic losses associated with conventional metamaterial designs involving resonant structures, and is less susceptible to fabrication inaccuracies. In this non-magnetic multilayer design, negative refraction is achieved via anisotropy in permittivity tensor, rather than simultaneously negative electric permittivity and magnetic permeability. The overall composite forms a macroscopically homogeneous uniaxial medium, and is capable of achieving negative refraction of Poynting vector for TM-polarized light incident from isotropic medium. In this thesis, multilayer metamaterials are analyzed from two perspectives, both as homogeneous effective medium and as stratified media. The analyses are in terms of transmission and reflection spectra calculated with transfer matrix method, as well as full-wave simulation with Finite-Element Method (FEM) using COMSOL Multiphysics. It is demonstrated that negative refraction can be achieved with many material combinations including InGaAs/AlInAs and Ag/Al2O3 which are arranged in a pattern of alternating layers of intrinsic and heavily doped semiconductors or metal and dielectric. By using metals or extrinsic semiconductors with different plasma frequencies and loss characteristics, the regime of negative refraction can be shifted over a wide range of spectrum, from mid-infrared with semiconductors to visible spectrum with metals, which spans the entire spectrum of interest to applications in optical imaging and communications. The new multilayer metamaterial design proves to be customizable, of low loss at optical frequencies and easy to fabricate. It is hoped that this work will influence future metamaterials designs and their incorporation into semiconductor photonic devices.Bachelor of Engineerin
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
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
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