1,721,099 research outputs found
Emerging Ta4C3 and Mo2Ti2C3 MXene Nanosheets for Ultrafast Photonics
No full textUltrafast nonlinear optical (NLO) response, fast carrier recovery, broadband absorption, and resistance to radiation and heat make 2D materials promising for photonic technologies. However, low electronic conductivity and carrier concentration limit the performance of semiconducting or semimetallic materials. This work investigates the ultrafast NLO properties and carrier dynamics of Ta4C3Tx and out-of-plane ordered Mo2Ti2C3Tx MXenes using Z-scan and pump-probe optical Kerr effect techniques under visible and infrared femtosecond laser pulses. Their NLO response surpasses all previously studied MXenes and most other 2D nanomaterials, attaining exceptionally high third-order susceptibility (χ(3)) values on the order of 10−13 esu. Mo2Ti2C3Tx exhibits the strongest NLO response under both excitation regimes, attributed to charge transfer between Mo and Ti layers in the MXene structure. Under visible excitation, the studied MXenes display pronounced saturable absorption, while under infrared excitation, they exhibit strong reverse saturable absorption, resulting in efficient optical limiting. Additionally, pump-probe experiments identify two distinct relaxation processes: a fast one on the sub-picosecond timescale and a slower one a few picoseconds after photoexcitation. The results indicate that these MXenes are among the strongest NLO materials. They show their great potential for advanced photonic and optoelectronic applications in laser technologies, optical protection, telecommunications, and optical/quantum computing
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
Carbide-derived-carbons with hierarchical porosity from a preceramic polymer
No full textSynthesis of carbon by extraction of metals from carbides has been successfully used to
produce a variety of micro-porous carbide-derived carbons (CDCs) with narrow pore size
distributions and tunable sorption properties. This approach is of limited use when larger
mesopores are targeted, however, because the relevant synthesis conditions yield broad
pore size distributions. Here we demonstrate the porosity control in the 3–10 nm range
by employing preceramic polymer-derived silicon carbonitride (SiCN) precursors. Polymer
pyrolysis in the temperature range 600–1400 C prior to chlorine etching yields disordered
or graphitic CDC materials with surface area in the range 800–2400 m2 g1. In the hierarchical
pore structure formed by etching SiCN ceramics, the mesopores originate from etching
silicon nitride (Si3N4) nano-sized crystals or amorphous Si–N domains, while the micropores
come from SiC domains. The etching of polymer-derived ceramics allows synthesis
of porous materials with a very high specific surface area and a large volume of mesopores
with well controlled size, which are suitable for applications as sorbents for proteins or
large drug molecules, and supports for metal catalyst nanoparticles
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
Ultrafast Nonlinear Optical Properties and Carrier Dynamics of Ta4C3Tx and Mo2Ti2C3Tx MXene Nanosheets
No full textMaterials exhibiting strong nonlinear optical (NLO) properties along with fast carrier recovery have fostered significant advancements in photonic devices, enabling the development of ultrafast lasers, optical limiters, optical switches, modulators, photodetectors, and more. Among these materials, transition metal carbides, nitrides, and carbonitrides (MXenes), characterized by the general formula Mn+1XnTx (where M is a transition metal, X is C or N, and Tx represents surface terminated groups such as -OH, -O, or -F), are particularly attractive for such applications due to their exceptional NLO response, broadband absorption, ultrafast carrier relaxation, and resistance to radiation and heat
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
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