1,721,031 research outputs found
Centrifugal and Asymmetrical Field-Flow Fractionation for the analysis of ZnO particles in cosmetic products
No full textZinc oxide (ZnO) is a versatile material used in many productive sectors, of which the rubber application accounted for the largest market share, followed by ceramics, chemicals, pharmaceuticals, cosmetics, personal care and agricultural products. In the cosmetic sector, ZnO is used as a colorant or bulking agent, but mainly as UV-blocker, soothing and protective coating against skin irritation and abrasion, analogously to its use in the pharmaceutical products, mostly as ointments and creams, where it carries out antibacterial, antimicrobial, disinfecting and drying actions.
The recent increase of nano-materials to enhance the quality of many products has determined the revision of many existing international regulations, either in the cosmetic and food sectors. The European Union (EU) Commission’s Working Group on Cosmetics, in 2016, for example, stated that ZnO-NPs cannot be used in spray products, or if it used in dermal application, ZnO-NPs must have a median diameter of the particle number size distribution D50 (50 % of the number below this diameter) > 30 nm and D1 (1 % below this size) > 20 nm (1).
The size analysis of ZnO particles dispersed in cosmetic or pharmaceutical formulations is consequently now an important task that analytical methods should face (2), since they could be used to discriminate the presence of particles in the nano or/and micro form. This implies that the analytical methods should be able possibly to determine the particle size distribution or at least to contribute, for example through a separation, to its determination.
There are a number of analytical methods that might be used to size the particles (3,4). In many cases, the determination of the average particle sizes and the size distribution of particles incorporated in cosmetic products, requires a preliminary extraction step. This work has consequently two main aims, to study whether and how the extraction procedures should differ depending on the cosmetic matrices and to compare the separation performances of two FFF techniques, Centrifugal FFF (CF3) and Asymmetrical Flow FFF (AF4), both used for the particle size characterization.
The separation performances of CF3 and AF4 are evaluated by analysing (i) two different types of pristine ZnO powdered particles, bare and superficially modified with triethoxycaprylyl silane, available on the market to formulate cosmetic products, (ii) four cosmetic creams formulated in-house, and (iii) three cosmetic commercial products, sold in Italy and Germany for the baby skin care
Investigation of zinc oxide particles in cosmetic products by means of centrifugal and asymmetrical flow field-flow fractionation
No full textThe dimensional characterization of insoluble, inorganic particles, such as zinc oxide ZnO, dispersed in cosmetic or pharmaceutical formulations, is of great interest considering the current need of declaring the possible presence of nanomaterials on the label of commercial products.This work compares the separation abilities of Centrifugal- and Asymmetrical Flow Field-Flow Fractionation techniques (CF3 and AF4, respectively), equipped with UV-vis, MALS and DLS detectors, in size sorting ZnO particles, both as pristine powders and after their extraction from cosmetic matrices.ZnO particles, bare and superficially modified with triethoxycaprylyl silane, were used as test materials. To identify the most suitable procedure necessary to isolate the ZnO particles from the cosmetic matrix, two O/W and two W/O emulsions were formulated on purpose. The suspensions, containing the extracted particles ZnO, were separated by both Field-Flow Fractionation (FFF) techniques to establish a common analysis protocol, applicable for the analysis of ZnO particles extracted from three commercial products, sold in Europe for the baby skin care.Key aspects of this study were the selection of an appropriate dispersing agent enabling the particles to stay in stable suspensions (>24. h)and the use of multiple detectors (UV-vis, MALS and DLS) coupled on-line with the FFF channels, to determine the particle dimensions without using the retention parameters. Between the two FFF techniques, CF3 revealed to be the most robust one, able to sort all suspensions created in this work
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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