1,720,970 research outputs found
Radioactive Molecular Beams at CERN-ISOLDE
No full textThe present thesis addresses aspects of molecular beam developments for thick-target radioactive ion beam facilities such as CERN-ISOLDE. At these facilities, an intense and energetic driver beam impinges on a target. Radioisotopes are produced in a target matrix from which they require to diffuse into an ion source. On their way, numerous encounters with structural materials and the target material occur, which enable desired and undesired chemical interactions. The extracted ions are separated by their mass- to-charge ratio and supplied to various experiments for investigations e.g. in nuclear structure, reactions and applications. The motivation to extract radioisotopes as molecular beams is multifold. Firstly, the elements with the highest melting and boiling points (refractory elements) require em- bedding in a volatile carrier molecule to enable their transport to the ion source. Sec- ondly, a common issue are isobaric contaminations which come along with the isotope of interest after mass separation. They can render impossible the intended user experi- ments. A powerful tool to produce and purify these beams is the extraction as molecular sideband which synthesizes volatile compounds in-situ and shifts the mass as seen by the mass separator away from the contamination. Finally, a field of investigation on radioactive molecules themselves was recently arising. This thesis is based on four publications which cover different facets of molecular beam developments. The first publication concerns the redesign and implementation of the ISOLDE yield database which provides valuable information of available beams and demonstrates the need for molecular beam developments. This implementation also contains new data and models to predict ion beam yields based on measured data. The first extraction of radioactive boron beams at a thick-target ISOL-facility is discussed in the second publication. Boron is a reactive and refractory element which cannot be extracted in elemental form. Its release properties from multi-walled carbon nanotubes are described. The measured yield of 8B is presented along with predictions for yields of 12B and 13B, based on the derived release model. As an example for beam purification by molecule formation, the third publication provides investigations by online and offline measurements towards a reliable extraction of carbonyl selenide sidebands. The investigations towards extraction of transition metals as carbonyl complexes are a major contribution to this thesis. Most of the refractory transition metals are not avail- able as ISOL beam since no suitable carrier molecules to enable their transport have been identified yet. This is often due to the harsh conditions in the target an ion source unit that typically operates at high temperatures. It was studied by simulation, calcula- tion and exploratory experiments, if carbonyl compounds could be used within a cold target concept. To avoid slow diffusion processes, the recoil momentum in fission and spallation reactions is exploited. Transition metal carbonyl compounds (e.g. Mo(CO)6) form in-situ upon their thermalization in a carbon monoxide containing atmosphere already at ambient pressure and temperature. However, these are delicate compounds which easily decompose when exposed to heat, electron bombardment or plasma. The included publication presents first exploratory experiments with an electron beam in- duced arc discharge ion source operated at ambient pressure. In contrast to classical thermionic electron production, electrons are liberated by a laser from a cold ion source. The addendum of the thesis documents experimental results towards ionization of the fragile carrier molecule Mo(CO)6 with available ISOLDE ion sources. Their ionization efficiency turned out insufficient and underlines the need for development of a cold electron impact ion source, as proposed in the publication. Moreover, an experimen- tal setup has been built and tested to study the formation of neutral transition metal carbonyl complexes at ISOLDE. The included documents describe its purpose, mode of operation and management of involved risks
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
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
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
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
Extraction of Refractory Elements by Laser Induced Breakup and ionisation of Molybdenum Carbonyls
No full textAuthor-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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