1,720,974 research outputs found
Investigations on the behaviuor of Tellurium (IV) and Selenium (IV) in ion-exchange chromatography
No full textFor the development of an on-column chromatographic method for the simultaneous separation and detection of selenium(IV) and tellurium(IV), their chromatographic behaviours on cation and anion exchangers as well as on multiphase cation- and anion-exchange/reversed-phase columns, have been investigated. The eluent medium consisted of diluted hydrochloric acid at different concentrations and flow-rates. The detection of selenium(IV) and tellurium(IV) was based on post-column derivatization, of the eluted species, with 1,1,3,3-tetramethylthiourea (TMTU). The TMTU concentration, pH and flow-rate was optimized in order to obtain the best sensitivity for both the analytes. The capacity factor value, k', as well as the charge of the species eluted on the different columns tested, have been obtained for all experimental conditions. It has been demonstrated that the on-column chromatographic separation between selenium(IV) and tellurium(IV) is achievable by exploiting their different elution patterns on ion exchangers. On the basis of peak symmetry and analyte resolution at different concentration ratios, the cation-exchange mode was chosen. Injecting 50 ul of samples, detection limits of 78 and 83 ug/1 for tellurium and selenium, respectively were obtained. Concentrations lower than 10 txg/1 could be determined by increasing the injection volume or by means of on-line preconcentration
Chemical Vapor Generation AAS using borane complexes. A contribution to the comprehension of reaction mechanisms in the generation of volatile hydrides
No full textThe effect of seasonal pack ice melting on the sea water polychlorobiphenyl contents at Gerlache Inlet and Wood Bay (Ross Sea – Antarctica)
No full textThe effect of seasonal formation/melting process of pack ice on the PCB level of sea water at Gerlache Inlet and Wood Bay (Ross Sea, Antarctica) was investigated during four Italian expeditions, i.e. !988-89, 1990-91, 1991-92 and 1993-94. Surface sea water samples from Gerlache Inlet and Wood Bay before pack ice melting showed a typical total PCB concentration of 133 pg/l and 120 pg/l, respectively, which increased by a factor of about 1.3 in both sampling sites during pack ice melting. This effect was attributed to the transfer of PCBs contained in the pack ice to sea water, and salinity was used as a tracer to verify this hypothesis. In this respect, pack ice and sea water samples were collected during the 1993-94 Italian expedition, and both salinity (S) and PCB content were measured. A fairly good agreement was observed between the experimental PCB concentration and the value calculated by the dilution model which was applied to the mixing process between sea and pack ice melting waters. Although this effect seems to be limited in time and space it is nevertheless significant because it happens during summer when biological species have their highest activity
Chemical vapour generation for atomic spectrometry. A contribution to the comprehension of reaction mechanisms in the generation of volatile hydrides using borane complexes
No full textChemical vapor generation atomic spectrometry using amine-boranes and cyanotrihydroborate(III) reagents
No full text
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
- …
