1,720,964 research outputs found
Photoionization of an open-shell atom with open-shell final ionic state: A spin-resolved study of photoelectrons above the Tl+ (6s6p) P-3(1) limit
No full textKuntze R, Salzmann M, Bowering N, Heinzmann U, Cherepkov NA. Photoionization of an open-shell atom with open-shell final ionic state: A spin-resolved study of photoelectrons above the Tl+ (6s6p) P-3(1) limit. In: Journal of Electron Spectroscopy and Related Phenomena. JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. Vol 79. ELSEVIER SCIENCE BV; 1996: 335-338.Spin-resolved measurements of the dynamic photoionization parameters for photoelectrons from thallium atoms are presented for the Tl+ (5d(10)6s6p) P-3(1) final ionic state in the complex spectral region from 90 to 77 nm. For a complete description of this ionization process more than three transition matrix elements are needed since neither the initial nor the final state has closed-shell configuration. An approximate determination of matrix elements and phase shift differences is carried out. In addition, it is discussed how complete information may in principle be obtained
Resonance enhancement of non-dipole effects in spin polarization of atomic photoelectrons
No full textCherepkov NA, Semenov SK, Drescher M, Heinzmann U. Resonance enhancement of non-dipole effects in spin polarization of atomic photoelectrons. JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. 2003;36(14):3063-3078.Resonances in quadrupole channels corresponding to the np --> epsilonf transitions are investigated in atoms preceding Ce (Z = 59) and Pa (Z = 91), where the 4f and 5f shells, respectively, start to be filled. These resonances lead to a prominent enhancement of all non-dipole effects in the angular distribution and spin polarization of photoelectrons at low photon energies of the order of 100-200 eV. Since in atoms between Cd and Xe the 4p(1/2) photoline is absent from the photoelectron spectrum, we investigate these effects in more detail in Hg where both 5p(1/2) and 5p(3/2) lines are present. We demonstrate that near these resonances the non-dipole contribution to the degree of polarization of photoelectrons in Hg can be of the order of 5%. For the absorption of linearly polarized light the degree of polarization due to the non-dipole contribution tends towards 100%, but the photoelectron intensity in that case tends towards zero. Corrections to the photoelectron intensities in the angular distributions at some angles can exceed 10%. The similar resonance effects in Rn are expected to be substantially stronger
On the impossibility to perform a complete valence-shell photoionization experiment with closed-shell atoms
No full textSchmidtke B, Drescher M, Cherepkov NA, Heinzmann U. On the impossibility to perform a complete valence-shell photoionization experiment with closed-shell atoms. JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. 2000;33(13):2451-2465.A detailed investigation of the relation between five dynamical parameters (partial photoionization cross section sigma, angular asymmetry parameter beta and three spin polarization parameters A, alpha, xi) and five corresponding theoretical values (three dipole matrix elements and two phase shift differences) describing photoionization from p(3/2), d(3/2) and d(5/2) subshells of rare-gas atoms reveals a systematic ambiguity preventing the extraction of a unique set of five theoretical values from the experimental data which constitute a 'complete experiment'. Xe(5p(3/2))(-1) photoionization serves as an example to illustrate the problem using a numerical procedure as well as a mathematical analysis. A new equation is presented which connects four dynamical parameters. From these facts it follows that a complete experiment on closed-shell atoms with the extraction of five theoretical values is, in principle, impossible, if the photoelectron properties are measured exclusively
Spin polarization of zero kinetic energy electrons from HBr
No full textDrescher M, Irrgang R, Spieweck M, Heinzmann U, Cherepkov NA, Lefebvre-Brion H. Spin polarization of zero kinetic energy electrons from HBr. JOURNAL OF CHEMICAL PHYSICS. 1999;111(24):10883-10886.The range of observables in zero kinetic energy (ZEKE) electron spectroscopy of molecules, previously restricted to the total electron intensity, was extended by measuring the integral spin polarization of ZEKE electrons at the HBr Omega(+)=3/2 thresholds after single-photon excitation with narrow-band circularly polarized light. A comparison with calculated values from multichannel quantum defect theory underlines the importance of autoionization for the decay dynamics. (C) 1999 American Institute of Physics. [S0021-9606(99)00548-6]
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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