1,720,972 research outputs found
Determinazione di bromo- e cloro-anisoli in campioni di vino mediante microestrazione in fase solida (SPME-HS) e gas-cromatografia con spettrometria di massa ad alta risoluzione (GC-HRMS)
No full textComunicazione ORALE
“Characterization of the acyl chains of sulfoquinovosyldiacylglycerols (SQDGs) by LC-ESI - tandem mass spectrometry”
No full textTandem mass spectrometry of sulphur-containing glycolipids: a step forward towards the regiochemical assignment of fatty acid acyl chains
No full textCollision induced dissociation tandem mass spectrometry (CID-MS/MS) of
glycolipids with special interest to sulfoquinovosyldiacylglycerols (SQDGs)
(1,2) was employed for a detailed study of their fragmentation, clarifying
some controversial aspects of previous investigations on these compounds.
Losses of neutral fatty acids from the acyl side chains (i.e.
[M−H−RxCOOH]−, x =1,2) were found to prevail over ketene losses or
generation of long-chain fatty acid (FA) anions [RxCOO]−, x =1,2). The
chain length, degree of unsaturation and positional distribution of the FAs
attached to the primary (sn1) and secondary (sn2) hydroxyl groups of the
glycerol moiety were established for all SQDG species identified in a
sample extract of spinach leaves. The systematically observed preferential
loss of FAs from the sn1 position of the glycerol backbone was exploited for
the regiochemical assignment of the investigated species (3). The prevailing
presence of a 16:0 (i.e., palmitic) acyl chain on the glycerol sn2 position of
SQDGs suggests a prokaryotic path as the main route for their biosynthesis
in spinach leaves (4). We envision that the versatility of this CID MS/MS
approach, with ability to establish the regiochemistry of the acyl chains of
SQDGs, will enable the systematic investigation of photosynthetic plants,
algae, cyanobacteria, purple sulfur and non-sulfur bacteria with broad
implications within and beyond the realm of sulfolipids and their
involvement in membrane structures and cell communication
HS-SPME optimization by RSM and discrimination analysis for volatile profile of X-ray irradiated mozzarella cheese
No full textHeadspace Solid-Phase MicroExtraction (HS-SPME) and subsequent analysis by gas chromatography coupled to mass spectrometry (GC-MS), provided a detailed volatolomic profile of X-ray irradiated mozzarella cheese. Response Surface Methodology (RMS), obtained from a Central Composite Design (CCD) was employed to define the optimized combination of extraction temperature (°C), extraction time (min) and sample amount (g). From the analysis of the response surfaces it can be stated that all three parameters equally influenced the extraction efficiency. The optimal HS-SPME conditions were the highest level for all the factors, i.e., at 50 °C for extraction temperature, 75 min for extraction time and 5 g for sample amount. The optimised HS-SPME were used to analyse a rapresentive number of non-irradiated and irradiated samples at three dose levels, i.e., 1.0, 2.0, 3.0 kGy. Principal Component Analysis (PCA), Partial Least Squares-Discriminant Analysis (PLS-DA) and Linear Discriminant Analysis (LDA) were applied to explore the variation of volatile profile with respect to the X-ray irradiation treatment
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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