1,720,961 research outputs found
Approcci Multiset e Multi-way nell'Autenticazione Alimentare
No full textI progressi nella progettazione della strumentazione analitica, in special modo per le tecniche ifenate, hanno portato a una crescente necessità di analizzare dati con una struttura multi-way, dove ciascun campione è rappresentato da un landscape a due dimensioni (es. cromatografia/spettrometria di massa, eccitazione/ emissione in fluorescenza). Da qui nasce il bisogno di strumenti di analisi dati, in grado di trattare queste strutture complesse. La questione diventa poi di fondamentale importanza nell’analisi alimentare, dove le certificazioni di qualità e autenticità oggi sono un obbligo sia dal punto di vista del consumatore che del produttore. Diventa chiaramente necessario migliorare le metodiche analitiche in termini di efficienza robustezza e rapidità, ed accoppiarle all’analisi multivariata dei dati per selezionare l’effettiva informazione. Il mio progetto di tesi esplora due strumenti chemiometrici che operano sui dati multi-way: Multivariate Curve Resolution (MCR) e i metodi di classificazione per array a tre dimensioni (o superiori). Inoltre vengono studiati due campi di applicazione: la risoluzione e quantificazione dei costituenti alimentari, attraverso il così detto ‘approccio matematico alla cromatografia’, dove i picchi sono risolti a posteriori utilizzando MCR, il che permette di risolvere problemi di coeluzione; e la costruzione di modelli di autenticazione per riconoscere prodotti identificati dalla denominazione di origine protetta (DOP). Per questo scopo metodi discriminanti multi-way (NPLS-DA) e multiset (MCR discriminante), così come modellamento di classe multi-way (N-SIMCA) sono applicati confrontandoli rispetto all’attuale stato dell’arte. I casi studiati derivano da applicazioni per tecniche ifenate, qui utilizzate come metodo di fingerprinting, in particolare, tre diverse denominazioni di vino Lambrusco DOP sono state per la prima volta caratterizzate rispetto alla frazione di composti fenolici (HPLC-DAD). Altri dataset di precedenti lavori del nostro gruppo o della letteratura riguardano Olio Extra Vergine di Oliva Ligure DOP e vini di differente provenienza geografica (entrambi caratterizzati tramite HS-SPME/GC-MS). Gli aspetti salienti delle applicazioni MCR, del lavoro di ricerca, sono stati l’uso di alcuni vincoli come il rango locale o la selettività, fondamentali per la corretta risoluzione e quantificazione dei composti d’interesse. Per la classificazione, lo studio si è concentrato sulla versione a n dimensioni del metodo SIMCA (Soft Independent Modeling of Class Analogies), di recente sviluppo, N-SIMCA. L’obiettivo era di dimostrare quali sono i vantaggi e svantaggi di una tecnica di modellamento di classe rispetto a un approccio discriminante e della classificazione multi-way rispetto a quella 2-way sugli stessi dati srotolati o sugli scores ottenuti da un metodo di decomposizione come PARAFAC o Tucker3.
Si è dimostrato che l’analisi multi-way rappresenta una valida strategia per i casi di autenticazione e classificazione, fornendo alti valori di sensibilità e specificità per tutti i modelli calcolati; le tecniche di modellamento di classe rispetto agli approcci discriminanti sono meno performanti nel caso in cui ci sia una forte eterogeneità all’interno della classe. Inoltre è descritto e proposto un nuovo metodo di classificazione discriminante, basato su una regressione attraverso MCR. Il metodo è basato sul fornire l’informazione riguardante la classe attraverso un vincolo di selettività. I principali vantaggi riguardano i profili di concentrazioni risultanti (matrice degli spettri) che forniscono un’interessante interpretazione delle caratteristiche del modello.The progress in design of analytical instrumentations, especially hyphenated techniques, has rapidly increased the need to analyze data, which have a multi-way structure, i.e. each sample is characterized by a 2D landscape (e.g. chromatography/mass spectrometry, excitation/emission fluorescence). Hence the need of data analysis tools capable of handling this complex data structure. This issue is topical in food analysis, dealing with quality and authentication assessment, nowadays mandatory both from producers and consumers points of view. From here the necessity of improving analytical methods, in terms of efficiency, robustness and rapidity, and coupling them with multivariate data analysis to effectively extract information. My thesis project explored two chemometrics tools handling multi-way data: Multivariate Curve Resolution (MCR) and Multi-way classification methods. As well as two application fields are investigated: resolution and quantification of food constituents, by the so called Mathematical chromatography approach, where peaks are resolved ‘a posteriori’ (using MCR), which allows handling strong co-elution issues; and building authenticity models to recognize typical products label by protected denomination of origin (PDO). To this aim multi-way (NPLS-DA) and multiset (discriminant-MCR) discriminant methods as well as multi-way class modeling (N-SIMCA) were comparatively applied and discussed with respect to the current state of art methodology. Case studied derived from hyphenated techniques, here used as fingerprinting methods, in particular PDO Lambrusco wine of three different denomination were for the first time characterized (HPLC-DAD) with respect to the phenolic fraction. Additional data sets, from previous work of our group or from literature regards PDO Ligurian Extra Virgin Olive Oil and wines of different geographical for the identification of provenience characterized by (HS-SPME/GC-MS).
In the MCR application salient aspects dealt within the research work have been the use of local rank and selectivity constraints, that had been crucial for the correct resolution and quantification of target compound.
Regarding classification, the study focuses on the n-dimensional version of the SIMCA (Soft Independent Modeling of Class Analogies) methodology, recently developed, N-SIMCA. Here focus was on demonstrating advantages/disadvantages of class modeling with respect to discriminant approaches and of multi-way classification with respect to classical 2-way classification performed on unfolded data or on scores from decomposition methods, such us PARAFAC or Tucker3.
This part demonstrates that multi-way data analysis can represent a powerful strategy in authentication and classification tasks giving high values of sensitivity and specificity for all the model calculated; class modeling techniques respect to discriminant one results suboptimal in case of strong intra-class heterogeneity.
Furthermore, a new classification approach based on extension of MCR based regression to discrimination task is also proposed. Basically, it works including class information as an additional selectivity constraint. Main advantages is that, the while resulting MCR concentration profiles can be interpreted as classical samples scores, the recovered component profiles (spectral matrix) provides a very interesting interpretation of the characteristic of the modeled classes in terms of spectral signature which are class specific
Application of CZE Method in Routine Analysis for Determination of B-Complex Vitamins in Pharmaceutical and Veterinary Preparations.
No full textA competitive CZE method for quality control analysis of multivitamin preparations and veterinary products containing B-group vitamins was developed. Vitamins of interest are thiamine hydrochloride (B(1)), thiamine monophosphate chloride (B(1a)), riboflavine (B(2)), riboflavine-5'monophosphate (B(2a)), nicotinamide (B(3)), d-pantothenic acid calcium salt (B(5)), pyridoxine hydrochloride (B(6)), folic acid (B(9)), and 4-aminobenzoic acid (B(10)). These analytes were separated optimizing the experimental conditions in 20 mM tetraborate buffer pH = 9.2 as a BGE (background electrolyte), on a Beckman P/ACE System MDQ instrument, using uncoated fused silica capillary. The effective capillary length was of 49.5 cm, I.D. = 50 μm, the applied voltage 20 kV and the temperature 25°C. Detection was performed by a diode array detector at 214 nm for all vitamins except B(5) (190 nm) and B(2a) (260 nm). Separation time was about 9 min. After experimental conditions optimization, the proposed method was validated. Precision of migration time and corrected peak area, linearity range, LOD and LOQ, accuracy (recovery), robustness, and ruggedness were evaluated for each analyte demonstrating the good reliability of the method. Analyses of the pharmaceutical real samples were performed and confirmed the versatility of this method
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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