1,720,959 research outputs found
Photon Bose-Einstein condensate in and out of steady state: theory and experiment
No full textThe Bose-Einstein condensate is a thermal equilibrium state characterized by a macroscopicoccupation of the ground state. Such a state exhibits spontaneous coherence at the critical temperature or particle density. In this thesis, we focus on in- and out-of steady-state properties of recently observed photon Bose-Einstein condensates. The condensed state is achieved at room temperature in a microcavity due to the small effective mass of the photon. Unlike in atom condensates, where atoms thermalize spontaneously, photons must interact with a reservoir to reach thermal equilibrium. For large reservoir sizes, the photon condensate can be regarded as an open quantum system. The photon condensate is also subjected to photon losses through the cavity. As such, condensates of light are of fundamental interest and are a promising platform for studying optical quantum gases in complex structures. In this thesis, we develop a nonequilibrium theory of photonic Bose-Einstein condensation from first principles combining the frameworks of open quantum systems and macroscopic quantum electrodynamics. This approach allows us to model the condensate in various cavity geometries and precisely evaluate the system’s influence on the condensate rates. Subsequently, we theoretically investigate the photonic condensation in a two-dimensional planar cavity at the crossover towards small mode spacing. Alongside the conventional threshold required for the transition into the condensed state, we find a second threshold emerging for smaller mode spacings, governed by system losses. Consistent with the literature, we find that the photon condensation does not occur in the limit of a free photon gas, since the critical particle number diverges. Finally, we report on the experimental measurements of the out-of-steady-state dynamics of the photon Bose-Einstein condensate in the presence of single-frequency periodic perturbation. For weak perturbations, we observe that the condensate response dynamics resembles that of a classical harmonic oscillator, in agreement with the theory. The monochromatic driving establishes an experimental platform to probe optical quantum gases and extract the system’s parameters, such as cavity decay rate and total molecule number. In addition, it allows for phase-sensitive measurements, paving the way for the demonstration of the frequency-dependent fluctuation-dissipation theorem
Bose-Einstein Condensation of Light in Disordered Nano Cavities at Room Temperature
No full textBose-Einstein Condensation is a macroscopic occupation of bosons in the lowest energy state. For atoms, extremely low temperatures are required to observe this phenomenon. For photons, condensation has been demonstrated at room temperature, requiring a large number of particles (N ∼ 77000) and very complicated setup. Here we study the possibility of observing BEC of light at room temperature with a much lower number of particles by leveraging disorder in a dielectric material. There is no constraint in the number of photons in the system like in the previous research. We investigate what happens to photons once they are put inside a cavity with a disorder. The analysis is carried out by using time-dependent quantum Langevin equations, complemented by a thermodynamic analysis on quantum photons. Both approaches give the same expression for the critical temperature of condensation. We demonstrate that photons in a disordered cavity with arbitrary initial statistical distribution reach thermal equilibrium and undergo a Bose-Einstein Condensation if the temperature is sufficiently reduced. In our model we demonstrate that the temperature is related to the losses of the system. At this state, photons follow Boltzmann distribution. It is demonstrated that by only varying the strength of disorder, it is possible to change the critical temperature of the phase transition, thus making condensation possible at room temperature. This work opens up the possibility to create new types of light condensate by using disorder
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
