1,720,971 research outputs found
Sulla validità del principio di identità degli indiscernibili in meccanica quantistica: verso una nuova discernibilità debole
Get PDFLo scopo di questa tesi di dottorato è quello di discutere la controversa questione sulla validità del principio di identità degli indiscernibili di Leibniz in meccanica quantistica. In particolare, si esporrà un anuova relazone di discernibilità debole (WD) per particelle quantistiche, con l'obiettivo di risolvere le critiche sollevate dal Bigaj (2015). Il pioniere della WD è certamente Simon Saunders (2003, 2006) che ha dimostrato come sia possibile distinguere le particelle in meccanica quantistica con metodi basati sull'utilizzo di predicati qualitativi. Egli ha dimostrato che la WD, può essere applicata a fermioni. Il secondo sostenitore della WD è stato F. A. Muller che ha risolto le critiche sollevate contro Saunders (2008). Muller e Saunders (2008) hanno messo a punto la tecnica della distinguibilità dei fermioni con l'uso delle proprietà categoriali (cioè non probabilistici). Muller e Seevinck (2009) hanno esteso la discernibilità debole per tutte le particelle quantistiche. Bigaj (2015) ha sollevato il problema che la proposta di WD di Muller, Saunders, Seevinck è affetta da circolarità, poiché la scelta dell'operatore, su cui si applica la WD, cambia se le particelle sono o meno la stessa. Se si accettano le critiche di Bigaj, sembra opportuno cercare una nuova discernibilità debole, conciliando le posizioni di Muller, Saunders e Seevinck con quella di Bigaj. Secondo Bigaj (2015), quello che sarebbe giusto dire è che, se la relazione R, su cui si basa la WD, contiene l'identità numerica come una componente essenziale, allora la discernibilità diventa banale e l'intera struttura è circolare. Sarebbe desiderabile, invece, avere lo stesso operatore o almeno la stessa operazione sia nel caso in cui le particelle, a e b, sono a priori diverse sia quando sono uguali. Ad esempio una corretta relazione con un unico operatore O sarebbe tale da potersi scrivere: dove xy. Una nuova relazione di discernibilità debole deriva dall' uso della matrice di Gram, seguendo il formalismo della seconda quantizzazione. Se due particelle sono uguali allora la matrice di Gram ha determinante diverso da zero, altrimenti la matrice di Gram ha determinante pari a zero.
Indicando con l'operatore G, l’operazione “determinante della matrice di Gram” è possibile definire la relazione R in questo modo: . Questa relazione soddisfa i requisiti di Bigaj (2015). Inoltre, soddisfa anche il requisito di Muller e Saunders (2008) circa l'invarianza per permutazione (dimostrazione banale). L’unico svantaggio è rappresentato dal significativo fisico non particolarmente incisivo di questo particolare operatore. Questa relazione è valida non solo per fermioni, ma anche per qualsiasi tipo di particella quantistica, come i bosoni.The purpose of this PhD thesis is to show the contentious issue of the validity of Leibniz’s Principle of Identity of Indiscernibles in quantum mechanics. In particular, a new weak discernibility relation (WD) for quantum particles which aims to resolve the criticism raised by Bigaj (2015). Simon Saunders (2003, 2006) is certainly a pioneer in WD who has shown how it is possible to discern the particles in quantum mechanics without primitive facts but using a method based on the use of qualitative predicates. He showed that WD, can be applied to fermions. The second supporter of WD was F. A. Muller who resolved the criticisms raised versus Saunders (2008). Muller and Saunders (2008) have developed the technique of distinctness of fermions by the use of the categorical property (no probabilistic properties). Muller and Seevinck (2009) have extended weak discernibility to all quantum particles. Bigaj (2015) raised the issue that the proposal of WD by Muller, Saunders, Seevinck are affected by circularity, since the choice of the operator, which can be applied in the WD, changes if the particles are or are not the same. If we accept the criticisms of Bigaj, it seems appropriate to look for a new weak discerniblity, reconciling the positions of Muller, Saunders and Seevinck with that of Bigaj. According to Bigaj (2015), it would be fair to say that if the relation R, which the WD is constructed on, contains numerical identity as an essential component, then the discernibility becomes trivial and the whole structure is circular. It would be desirable, rather, to have the same operator, or at least the same operation in the case that particles, a and b, are a priori either different or the same. For example, a correct operator O would be such that where xy. A new relation of weak discernibility follows from the use of the Gram’s matrix, according to the formalism of the second quantization. If two particles are the same, then Gram’s matrix has a determinant different from zero, otherwise Gram’s matrix has a determinant equal to zero.
Then, if G indicates the Gram operator, it is possible to define the relation R such that: . This relation satisfies the requirements of Bigaj (2015), in particular, it is valid for fermions. Furthermore, it also satisfies the requirements of Muller and Saunders (2008) about the permutation invariance (trivial demonstration). It is not clear whether it has a physical meaning
A simple problem for simulating demographic noise in biological differential equation models: a discrepancy effect
No full textDynamical systems described by deterministic differential equations represent idealized situations where random implications are ignored. In the context of biomathematical modeling, the introduction of random noise must be distinguished between environmental (or extrinsic) noise and demographic (or intrinsic) noise. In this last context it is assumed that the variation over time is due to demographic variation of two or more interacting populations, and not to fluctuations in the environment. The modeling and simulation of demographic noise as a stochastic process affecting single units of the populations involved in the model are well known in the literature and they result in discrete stochastic systems. When the population sizes are large, these discrete stochastic processes converge to continuous stochastic processes, giving rise to stochastic differential equations. If noise is ignored, these stochastic differential equations turn to ordinary differential equations. The inverse process, i.e., inferring the effects of demographic noise on a natural system described by a set of ordinary differential equations, is an issue addressed in a recent paper by Carletti M, Banerjee M, A backward technique for demographic noise in biological ordinary differential equation models, Mathematics 7:1204, 2019. In this paper we show an example of how the technique to model and simulate demographic noise going backward from a deterministic continuous differential system to its underlying discrete stochastic process can provide a discrepancy effect, modifying the dynamics of the deterministic model
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Determination of the most reliable method for the evaluation of formaldehyde emissions from wood-based panels produced by an Italian leading company in the furniture sector
No full textFor wood-based panels, is possible to apply two different testing methodologies for formaldehyde emissions (gas analysis (GA) method and chamber method), respectively, regulated by UNI EN717-2:1996 and UNI EN717-1:2004; the analysis procedures have many differences, with regard to the equipment, the dimensions of samples and the testing environment parameters (temperature and relative humidity). The aim was to identify the most reliable method, by evaluating the technical results obtained, as well as by making a supporting statistical analysis aimed at the definition of the agreement degree between the two methodologies. In detail, we individuated the nine most used wood-based panels by a kitchens producer and we performed two different types of analysis: the GA method and chamber method. As properly described in this paper, the chamber method has a higher reliability due to the more realistic environmental testing conditions; moreover, we have demonstrated a low correlation between the two methodologies
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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