1,720,989 research outputs found
Early Stage Emission Spectroscopy Study of Metallic Titanium Plasma Induced in Air by fs- and ns- laser Pulses
No full textIn this work the laser induced plasma obtained in air at atmospheric pressure by the interaction of a fs (femtosecond) or a ns (nanosecond) laser pulse with a metallic titanium target has been investigated by optical emission spectroscopy. The temporal evolution of plasma parameters such as electron number density and excitation temperature has been determined in order to highlight the processes involved when the emission spectra are acquired at short time delays from the ablating laser pulse. A survey of elementary processes implicated during plasma formation and expansion of ns- and fs-Laser Induced Plasma has been performed. Departures from equilibrium conditions are even discussed. The dynamic aspects corresponding to ns- and fs-LIP have been investigated by optical time of flight (TOF) and by fast emission imaging. The overall results have been used for clarifying the basic mechanisms occurring during plasma expansion due to either ns or fs laser source when experimental conditions usually used for laser-induced breakdown spectroscopy (LIBS) applications are employed
pi-conjugated poly(monosubstituted) acetylenes containing Sn(II) and Sn(IV) species: investigation with laser ionization mass spectrometry
No full textPolyenes [HC=CR](n) (R = Ph, C13H9O), namely polyphenylacetylene (PPA) and polyethynylfluorenol (PEFI) containing Sn(II) and Sn(IV) in the polymer matrix, have been investigated using laser ionization mass spectrometry. The positive ion mass spectra show that carbon clusters linked to Sn, i.e. SnCnH+ (n = 1-25) are formed for PPA, while a higher degree of fragmentation occurs for PEFI which gives SnCnH+ (n = 1-8). The species SnCl3- is found in the negative ion patterns of the two polymers, regardless of whether the dopant was SnCl2 or SnCl4. This result suggests a lower stability of the tin complexes, formed by interaction with the polymer matrix, with respect to the iron chlorides or polyiodides species found in the LMS spectra of PPA/FeCl3 and PPA/I-2, respectively, previously studied
Calcium phosphate and fluorinated calcium phosphate coatings on titanium deposited by Nd : YAG laser at a high fluence
No full textCalcium phosphate coatings are known to enhance long-term fixation, reliability and promote osteointegration of cementless titanium-based implant devices. This study was aimed at the pulsed laser deposition of calcium phosphate coatings onto titanium using hydroxyapatite and hydroxyapatite-fluorapatite targets. The deposition was carried out at the high laser beam fluence conditions, about 12 J/cm2. The coatings were characterized with respect to their morphol., phase compn. and hardness. X-ray energy dispersive anal. revealed the coatings retain their elemental compn., and fluoride content within the film is the same as in the initial target. However, unlike sintered targets, the deposited films contain no apatite-like phases. The hardness of the films, about 18 GPa, is surprisingly high compared to that of hydroxyapatite and hydroxyapatite-fluorapatite ceramic targets. The deposited coatings of 2.7-2.9 μm thickness have uniform and dense microstructure, contg. the solidified droplets of the expulsed from the target phase. The uncommon structure and hardness of the films can be attributed to the melting and phase decompn. of the initial material in the laser plasma
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
Laser ionization mass spectrometry study of undoped and I2-doped polyphenylacetylene
No full textUndoped and I-2-doped polyphenylacetylene (PPA) have been investigated using laser ionization mass spectrometry. Both the positive and negative ion mass spectra show that carbon clusters C(n), C(n)H+, C(n)-, C(n)H- (n = 1-14) are formed. The negative ion fragment pattern of the doped PPA suggests a stabilizing effect of conjugated pi-electron carbon atoms on polyiodide species
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