1,720,959 research outputs found
Transient electron energy distribution in supported Ag nanoparticles
Full text linkMerschdorf M, Kennerknecht C, Willig K, Pfeiffer W. Transient electron energy distribution in supported Ag nanoparticles. New Journal of Physics. 2002;4(1):95.The electron relaxation in Ag nanoparticles supported on graphite is investigated by time- resolved multiphoton photoemission spectroscopy. The photoemission spectra map the transient electron energy distribution in the nanoparticles and reveal the internal thermalization and cooling of the electron gas. The excess energy stored in the electron gas is calculated using the free-electron model. In contrast to the behaviour of isolated nanoparticles the energy loss rate from the electron gas increases with the pump fluence. This indicates that the electron gas equilibration in Ag nanoparticles on graphite is modified by excited electron transport
Surface plasmon assisted photoemission from Au nanoparticles on graphite
No full textKennerknecht C, Hövel H, Merschdorf M, Voll S, Pfeiffer W. Surface plasmon assisted photoemission from Au nanoparticles on graphite. Appl. Phys. B. 2001;73(4):425-429
Collective and single-particle dynamics in time-resolved two-photon photoemission
No full textMerschdorf M, Kennerknecht C, Pfeiffer W. Collective and single-particle dynamics in time-resolved two-photon photoemission. Physical Review B. 2004;70(19): 193401.A general model for time-resolved two-photon photoemission from solids is presented comprising both collective and single-electron dynamics. In combination with interferometric time-resolved two-photon photoemission, this allows one to determine the shape of the collective response function across the excitation spectrum and the single-particle lifetime of excited electrons. Ag nanoparticles supported on graphite exhibit a strong collective resonance and serve as model system to demonstrate experimentally this separation of collective and single-particle dynamics in two-photon photoemission
Electron dynamics in supported metal nanoparticles: relaxation and charge transfer studied by time-resolved photoemission
No full textPfeiffer W, Kennerknecht C, Merschdorf M. Electron dynamics in supported metal nanoparticles: relaxation and charge transfer studied by time-resolved photoemission. Applied Physics A. 2004;78(7):1011-1028.Resonant excitation of the plasmon polariton in supported nanoparticles leads to a strong enhancement of the multiphoton photoemission yield and consequently, the total yield is dominated by the emission from the nanoparticles although they cover only a minor fraction of the surface. This allows investigation of the electron dynamics in supported nanoparticles, directly in the time domain. Here, Ag nanoparticles grown on graphite are used to demonstrate that the transient shape of the photoemission spectrum in time-resolved two-color multiphoton photoemission spectroscopy, reveals the electron relaxation within the nanoparticle, and the dynamic charge transfer between substrate and nanoparticle. The photoemission spectra map the transient electron energy distribution and exhibit a transient shift that is attributed to a dynamic charging of the nanoparticle. The comparison with model calculations comprising the full relaxation cascade in the nanoparticle and substrate, shows that the dynamic charge transfer accounts for almost half of the total deposited energy in the nanoparticle
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
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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