1,723,104 research outputs found
Stability in GDSS under fuzzy production rules
No full textFedrizzi and Mich [6] have presented a new Group Decision Support System (GDSS) logic architecture in which linguistic variables and fuzzy production rules have been used for reaching consensus. We show that when all the fuzzy numbers representing the performance levels have continuous membership function, then the consensus degrees (defined by a certain similarity measure) relative to each alternative are stable under small changes of the experts' opinions. 1 Introduction Fedrizzi and Mich [6] have presented a new GDSS logic architecture in which linguistic variables and fuzzy production rules have been used to provide an approximate reasoning model [3] using which the group of experts arrives at consensus. In that model, (i) the experts' preferences are formalized in a matrix of linguistic variables (see also [4,5,8]); (ii) the ranking of the alternatives for each expert is performed by using one of the many algorithms proposed in the literature (see e.g. [2]); (iii) the knowledge r..
Hydrogen sulfide and its roles in Saccharomyces cerevisiae in a winemaking context
No full textThe rotten-egg odour of hydrogen sulfide (H₂S) produced by the yeast Saccharomyces cerevisiae has attracted considerable research interest due to its huge impact on the sensory quality of fermented foods and beverages. To date, the yeast genetic mechanisms of H₂S liberation during wine fermentation are well understood and yeast strains producing low levels of H₂S have been developed. Studies have also revealed that H₂S is not just a by-product in the biosynthesis of the sulfur-containing amino acids, but indeed a vital molecule involved in detoxification, population signalling and extending cellular life span. Moreover, polysulfides have recently emerged as key players in signalling and the sensory quality of wine because their degradation leads to the release of H₂S. This review will focus on the recent findings on the production of H₂S and polysulfides in S. cerevisiae and summarise their potential roles in yeast survival and winemaking. Recent advances in techniques for the detection of H₂S and polysulfides offer an exciting opportunity to uncover the novel genes and pathways involved in their formation from different sulfur sources. This knowledge will not only provide further insights into yeast sulfur metabolism, but could potentially improve the sensory quality of wine.Chien-Wei Huang, Michelle E. Walker, Bruno Fedrizzi, Richard C. Gardner and Vladimir Jirane
Stability in GDSS under fuzzy production rules
No full textFedrizzi and M#d h [6] have presented a new Group Decision Support System (GDSS) logic architecture in which linguistic variables and fuzzy production rules have been used for reaching consensus. We show that when all the fuzzy numbers representing the performance levels have continuous membership function, then the consensus degrees (defined by a certain similarity measure) relative to each alternative are stable under small changes of the experts' opinions.
Identification, quantitation and origin of sulfur compounds in grape products. An approach via hyphenated mass spectrometry techniques.
Full text linkThe contribute of the Analytical Chemistry in the study of complex matrices, as for instance foodstuff, is crucial. In particular the development of chromatographic methods allows to quantify important technological, microbiological and physiological markers. The ensemble of all these information furthers a deeper and higher knowledge.
This Ph.D. project was designed to define the tools and evaluate the contribution of an important class of molecule on wine aroma.
Grape products are really important in the cultural and dietary Italian traditions; moreover Italy is both the first producer and the first consumer around the world. Oenological products have been largely studied since the early ’70, even if the lack of biochemical and microbiological knowledge and the poor sensitivity of the analytical techniques did not allow to carry an deep study on sulfur compounds.
This project, planned to bid analytical and oenological chemistry, focussed its attention on the study of sulfur compounds.
Dealing with complex matrices, the first problem we had to face was the matrix effects. The overcoming of such issue or the attempts in reducing it, costs to chemical laboratory, wasting of time and money to prepare suitable internal standards.
In this thesis we proposed a statistical approach based on the variance component model able to handle matrix effects. The benefits obtained by this approach definitely outweigh both the slightly worse sensitivity and uncertainty.
Another topic discussed in the thesis is the definition of analytical methods to quantify sulfur compounds. This subject has been studied distinguishing sulfur compounds into two sub-groups:
o fermentative sulfur compounds: molecules produced by yeast metabolisms from amino acidic precursors.
o varietal sulfur compounds: molecules present in specific variety, as conjugated with cysteine and glutathione. The free forms, which are sensorially active, are released during fermentation by means of a specific enzymatic activity.
This further classification was kept in the development of the analytical methods because the two classes required different sensitivity as well as metabolomics study were separated.
Concerning fermentative sulfur compounds a HS-SPME/GC-MS method was optimised and validated. With this method a wide range of sulfur compounds were quantified. Such tool was applied to metabolomic studies, concerning the influence of variety, ageing, yeast strain and other technological practice on the level of 13 fermentative sulfur compounds.
The results obtained from the development of the analytical method permitted to highlight the potentiality of the HS-SPME technique in sampling volatile compounds in complex matrices. This approach allows an easier and safer lab conditions, avoiding the use of organic solvents. The metabolomic studies furnished important suggestion on the influence of important oenological variables on the level of important sulfur compounds.
The last topic discussed in this thesis concerns the study of varietal sulfur compounds. The lack of suitable analytical technique, sufficiently rapid and avoiding the use of mercuro-organic compounds stimulated our research in verifying the performance of headspace technique in extracting these analytes.
We optimised and validated HS-SPME and purge and trap methods and finally we defined a non-parametric robust approach to compare performances from different analytical methods.
Owing to the recent interest of the scientific research in trying to understand the formation and evolution of varietal sulfur compounds, we focussed our attention on their precursors.
The first step was the synthesis of the putative precursors, followed by the optimisation of LC-MS/MS methods to quantify them. It was possible to identify a new precursor by LC-MS/MS experiments.
Finally, by the isolation of the enzyme potentially responsible of the biosynthesis of the varietal thiols precursors, we gave a preliminary explanation of the formation of these glutathionylated precursors during grape ripening.
By this project it has been possible to study and apply the newest analytical techniques available and it has been possible to define statistical procedures to overcome the most common issues in studying complex matrices. Furthermore it was clarified the contribution of an important class of molecules, such as sullfur compounds, on oenological matrices.Il contributo della Chimica Analitica nello studio delle matrici complesse, quali ad esempio quelle alimentari, è cruciale. In particolare lo sviluppo di metodi cromatografici avanzati può permettere di dosare importanti marker tecnologici, microbiologici e fisiologici e quindi consentire un approfondimento delle attuali conoscenze.
Questo lavoro è stato concepito allo scopo di definire gli strumenti per valutare il contributo di un’importante classe di molecole all’aroma dei vini.
Il vino riveste un ruolo di primaria importanza nelle tradizioni culturali ed alimentari Italiane, inoltre l’Italia risulta primo produttore e primo consumatore mondiale di vino. I prodotti enologici sono stati largamente studiati fin dai primi anni ’70, anche se l’assenza di conoscenze biochimiche e microbiologiche e la mancanza di tecniche analitiche sufficientemente sensibili non ha consentito lo studio esaustivo della classe dei composti solforati.
Questa tesi, nata da esigenze legate alla chimica analitica e alla chimica enologica, ha avuto come punto centrale lo studio dei composti solforati nei vini.
Il primo problema che si è dovuto affrontare nello studio di matrici complesse come quelle enologiche è stato quello relativo agli effetti matrice. Il superamento o il contenimento di questo problema crea ogni giorno costi in termini di tempo e di preparazione di opportuni standard interni. In questa tesi si è proposto un metodo statistico basato sul modello a componente di varianza in grado di gestire questo problema. I vantaggi sono notevoli, a fronte di una incertezza leggermente maggiore e di una sensibilità di poco peggiorata.
Altro argomento trattato è stata la definizione dei metodi analitici in grado di quantificare e quindi di studiare i composti solforati. Questa materia è stata affrontata riconoscendo una prima distinzione all’interno del gruppo degli analiti indagati:
o composti solforati fermentativi: molecole derivanti dal metabolismo del lievito a partire da precursori amminoacidici
o composti solforati varietali: molecole presenti in specifiche varietà come coniugati della cisteina e del glutatione e rilasciati durante la fermentazione alcolica ad opera di specifiche attività enzimatiche.
Questa suddivisione è stata mantenuta anche nello sviluppo dei metodi analitici, in quanto sensibilità richieste e conseguenze metabolomiche erano anch’esse distinte.
Per quanto riguarda i composti solforati fermentativi, durante il dottorato di ricerca è stato ottimizzato e validato un metodo HS-SPME/GC-MS per l’analisi di un’ampia gamma di molecole tipicamente derivanti dal metabolismo del lievito. Tale approccio è poi stato la base per studi di natura più squisitamente metabolomica in cui è stato verificato come il cultivar (i.e. la varietà), l’invecchiamento, il ceppo di lievito e altre pratiche tecnologiche potessero influenze il livello e l’evoluzione degli analiti indagati.
I risultati ottenuti per quanto attiene lo sviluppo del metodo in spettrometria di massa hanno potuto confermare con la tecnica SPME con campionamento in spazio di testa sia una tecnica di elezione per l’analisi di molecole volatili. Inoltre questo approccio consente una gestione semplice ed enviromental friendly in confronto con i più obsoleti metodi di estrazione con solvente. Gli studi metabolomici hanno consentito di trarre importanti considerazioni su aspetti molto importanti nella definizione della qualità del prodotto finale. Tali risultati consentono anche una trasferibilità nei settori della ricerca applicata e dell’enologia.
Come ultima classe di analiti indagati si sono studiati i composti solforati varietali. L’assenza di metodi sensibili e sufficientemente rapidi da essere applicati per studi su un numero significativo di campioni ha spinto la nostra attenzione alla verifica delle potenzialità delle tecniche in spazio di testa nel dosare queste molecole. Si sono ottimizzati e validati metodi HS-SPME e purge and trap ed è stata definita una procedura non parametrica robusta per il confronto delle performance delle diverse procedure.
Visto il recente interesse della ricerca scientifica operante nel settore al controllo della formazione ed evoluzione di queste molecole, abbiamo focalizzato la nostra attenzione sui precursori dei composti solforati varietali.
Il primo stadio è stata la sintesi di queste molecole, seguito poi dall’ottimizzazione di metodi LC-MS/MS per il dosaggio di queste molecole. In questo contesto è stato possibile identificare per la prima volta un nuovo potenziale precursore di aroma, tramite esperimenti LC-MS/MS.
Da ultimo, attraverso l’isolamento dell’enzima responsabile della biosintesi dei precursori d’aroma è stato possibile proporre una preliminare spiegazione alla formazione di tali molecole durante la maturazione della materia prima.
In conclusione, grazie a questa tesi di dottorato, è stato possibile approfondire ed applicare alcune delle più moderne tecniche analitiche a disposizione, è stato possibile definire procedure statistiche per superare i più comuni ostacoli nello studio di matrici complesse, ed è stato possibile chiarire il contributo di una classe importante di molecole come i composti solforati nelle matrici enologiche
Pathwise uniqueness and continuous dependence of SDEs with non-regular drift
No full textA new proof of a pathwise uniqueness result of Krylov and Röckner is given. It concerns SDEs with drift having only certain integrability properties. In spite of the poor regularity of the drift, pathwise continuous dependence on initial conditions may be obtained, by means of this new proof. The proof is formulated in such a way to show that the only major tool is a good regularity theory for the heat equation forced by a function with the same regularity of the drift
Noise prevents singularities in linear transport equations
No full textA stochastic linear transport equation with multiplicative noise is considered and the question of no-blow-up is investigated. The drift is assumed only integrable to a certain power. Opposite to the deterministic case where smooth initial conditions may develop discontinuities, we prove that a certain Sobolev degree of regularity is maintained, which implies Hölder continuity of solutions. The proof is based on a careful analysis of the associated stochastic flow of characteristics
The dynamics of consensus in group decision making: investigating the pairwise interactions between fuzzy preferences.
Full text linkIn this paper we present an overview of the soft consensus model in group decision making and we investigate the dynamical patterns generated by the fundamental pairwise preference interactions on which the model is based. The dynamical mechanism of the soft consensus model is driven by the minimization of a cost function combining a collective measure of dissensus with an individual mechanism of opinion changing aversion. The dissensus measure plays a key role in the model and induces a network of pairwise interactions between the individual preferences. The structure of fuzzy relations is present at both the individual and the collective levels of description of the soft consensus model: pairwise preference intensities between alternatives at the individual level, and pairwise interaction coefficients between decision makers at the collective level. The collective measure of dissensus is based on non linear scaling functions of the linguistic quantifier type and expresses the degree to which most of the decision makers disagree with respect to their preferences regarding the most relevant alternatives. The graded notion of consensus underlying the dissensus measure is central to the dynamical unfolding of the model. The original formulation of the soft consensus model in terms of standard numerical preferences has been recently extended in order to allow decision makers to express their preferences by means of triangular fuzzy numbers. An appropriate notion of distance between triangular fuzzy numbers has been chosen for the construction of the collective dissensus measure. In the extended formulation of the soft consensus model the extra degrees of freedom associated with the triangular fuzzy preferences, combined with non linear nature of the pairwise preference interactions, generate various interesting and suggestive dynamical patterns. In the present paper we investigate these dynamical patterns which are illustrated by means of a number of computer simulations.
Competence-Based Coalition Choice, a Non-additive Approach
No full textThis contribution considers the choice of a coalition on the basis of its
competence, with a constraint on the cost of the coalition itself. First of all, we
consider a set C of competencies and assume that each expert is characterized by one
or more of them.We define a suitable set function in order to evaluate the competence
of each coalition. This set function turns out to be a non-additive measure, see [3, 5].
As a first proposal, competencies will be represented by Boolean quantities, meaning
that an expert can only have or not have a certain competence. The extension to a
degree of competence between zero and one is straightforward. Moreover, each
coalition is associated with a cost that depends on its size and the cost of each
expert. In this form, the optimization problem is that of maximizing the coalition
competence by respecting a cost constraint. We describe some examples in order to
clarify our contribution.We also propose a multi-objective approach where one will
try to maximize competence and minimize cost. We compute the Pareto front and
compare the results of the two approaches
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