1,720,964 research outputs found
Low-energy physics in strongly correlated materials via nonlinear spectroscopies
No full textIn this thesis, I studied low-energy phenomena in condensed matter out of its equilibrium state via various approaches linked to non-equilibrium spectroscopies.
In the first part, I studied an out-of-equilibrium phase transition in magnetite. Magnetite is an iron oxide and displays an insulating low-temperature phase and a metallic high-temperature phase. Ultrashort light pulses in the near-infrared range are able to photo-induce the phase transition between these two phases on the timescale of the picosecond. When this process happens close to the threshold for its triggering, the sample displays out-of-equilibrium phase separation between the insulating and metallic phases. In this work, we show what signatures this out-of-equilibrium phase transition has on the reflectivity of the sample.
The near-infrared pulses produced by commercial lasers are not always well suited to study condensed matter, especially when one wants to study low-energy degrees of freedom. For the second work presented in this thesis, I built an optical set-up for the production of ultrashort mid-infrared pulses, with the goal of studying the out-of-equilibrium dynamics of low-energy degrees of freedom in a hight-critical-temperature superconductor, the yttrium-doped Bi2Sr2CaCu2O8. In this work, we show that the response of the material is markedly different in different directions. In particular, at room temperature, the B2g-symmetry response of the material is coupled to a charge density wave.
In the third and fourth part of the thesis, I tackled some questions from a theoretical point of view.
What is the thermalization dynamics in condensed matter out-of-equilibrium? Can we study them via the measurement of the fluctuations of the optical properties of the system? To answer this questions, we performed numerical calculations of the out-of-equilibrium behaviour of the Holstein model, in non-equilibrium dynamical mean field theory. We show that the thermalization dynamics of the system after an excitation is non-trivial and that it strongly depends on the coherent oscillations which are photoinduced in the system. Moreover, the thermalization dynamics of the system can be studied through the fluctuations of the optical properties of the system.
The last part of the thesis describes a proposal for an enhancement of the standard set-up for time-resolved photoemission experiments. The Heisenberg uncertainty principle is at the core of quantum mechanics. The uncertainty relation between energy and time is often erroneously considered to be stemming from the uncertainty principle, and its consequences on the temporal and energetic resolutions in time-resolved photoemission experiments have always been taken as fundamental. In this part of my thesis, we show that the tradeoff between the two resolutions can be, instead, overcome in a particular experimental scheme, analogously to what is done in optical multidimensional spectroscopy
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
Bypassing the energy-time uncertainty in time-resolved photoemission
Full text linkThe energy-time uncertainty is an intrinsic limit for time-resolved experiments imposing a tradeoff between the duration of the light pulses used in experiments and their frequency content. In standard time-resolved photoemission, this limitation maps directly onto a tradeoff between the time resolution of the experiment and the energy resolution that can be achieved on the electronic spectral function. Here we propose a protocol to disentangle the energy and time resolutions in photoemission. We demonstrate that dynamical information on all time scales can be retrieved from time-resolved photoemission experiments using suitably shaped light pulses of quantum or classical nature. As a paradigmatic example, we study the dynamical buildup of the Kondo peak, a narrow feature in the electronic response function arising from the screening of a magnetic impurity by the conduction electrons. After a quench, the electronic screening builds up on timescales shorter than the inverse width of the Kondo peak and we demonstrate that the proposed experimental scheme could be used to measure the intrinsic time scales of such electronic screening. The proposed approach provides an experimental framework to access the nonequilibrium response of collective electronic properties beyond the spectral uncertainty limit and will enable the direct measurement of phenomena such as excited Higgs modes and, possibly, the retarded interactions in superconducting systems
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
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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