1,721,056 research outputs found
Viscous flows in ducts of arbitrary cross-section
No full textViene analizzata la possibilità di ottenere una soluzione quasi analitica per la distribuzione di velocità in un condotto a sezione costante di forma arbitraria, in condizioni di moto laminare. Il problema riveste una utilità pratica rilevante, in quanto la determinazione, con grado di accuratezza prefissato, della distribuzione di velocità consente la determinazione della distribuzione di temperatura e, conseguentemente, la corretta determinazione del coefficiente di scambio termico convettivo, determinante per la progettazione e verifica degli scambiatori di calore di tipo compatto. I condotti utilizzati per questo tipo di scambiatori sono solitamente caratterizzati da piccole sezioni, di forma assai variabile. Per questo motivo l'ipotesi di moto laminare non appare limitativa, mentre risulta determinante la capacità di
contemplare forme del contorno anche complesse. Il problema viene risolto mappando il contorno in un cerchio di raggio unitario, mediante una trasformazione conforme di Theodorsen-Moretti. Tale trasformazione è stata finora prevalentemente utilizzata in letteratura per generare griglie conformi all'esterno di profili alari; viene viceversa qui utilizzata qui per generare una griglia conforme all'interno della sezione reale. L'unica operazione di tipo numerico che deve essere utilizzata per generare il contorno reale a partire dal cerchio unitario è l'applicazione (iterativa) di un algoritmo FFT per la determinazione dei
coefficienti della trasformazione di Theodorsen-Moretti. Determinati tali coefficienti, la griglia interna viene ottenuta in maniera semplice, ed anche il campo di velocità può essere ottenuto analiticamente, a partire unicamente dalla funzione che descrive la trasformazione dal contorno del cerchio unitario al contorno reale. Il metodo è stato applicato a condotti di sezione ellittica, per i quali è disponibile la soluzione in forma chiusa della distribuzione di velocità. Le isotachie calcolate con la soluzione proposta sono indistinguibili da quelle esatte
A direct screening procedure for diuretics in human urine by liquid chromatography- tandem mass spectrometry with Information Dependent Acquisition
No full textBACKGROUND: Diuretics are a class of compounds largely used for either therapeutic (edemas, hypertension, etc.) or illegal (doping) purposes. Probably owing to the substantial variety of their chemical structures, which makes them hardly extractable from a biological matrix in a single procedure, a quite short list of screening methods can be retrieved in the literature.
METHODS: This work presents a screening procedure for 24 diuretics based on the direct injection of urine (after 50 folds dilution) in a LC-ESI-MS/MS system (Applied Biosytems 4000 QTrap). Two information dependent acquisitions (IDA), one in positive, one in negative ionization, allowed the acquisition of one selected reaction monitoring transition for each compound, which, when a significant peak was found, triggered the acquisition of the enhanced product ion (EPI) spectrum.
RESULTS AND CONCLUSIONS: EPI spectra were stored in a library and the procedure was able to recognize by library matching various diuretics in real positive samples. The limits of detection were comprised between 0.002 and 0.25 mg/l and ion suppression was not found to significantly influence the analysis
Numerical analysis of compact air condensers
No full textThe present work aims at analysing the thermal behaviour of the vapour flow inside the horizontal tube bundle of a cross-flow air condenser. It is pointed out that the steady-state air and watertemperature distribution cannot be determined by means of analytical solutions, due to the non-linearity of the problem. A model based on appropriate balance equations is introduced and a finite difference computer code is formulated. This code, which reports a large number of correlations found in the literature, is used to evaluate the different flow patterns that characterise the two-phase flow condensation. It is also employed to calculate the local heat transfer coefficient, for both air and water side, and thepressure drop on the water side. The main results, related to the evaluation of the condenser's thermal-hydraulic behaviour (pressure and temperature of the condensing fluid), are presented and discussed in detail
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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