1,721,045 research outputs found
A new semi-empirical correlation for the evaluation of the dynamic viscosity of nanofluids
Full text linkThanks to their excellent heat transfer coefficient, nanofluids can be considered as ideal heat transfer fluids for a large number of relevant engineering and scientific applications. Precise assessments of their thermophysical properties are thus essential for reliable calculations. In this work, a new semi-empirical scaled correlation based on 8 parameters (volume fraction, temperature, base fluid critical temperature, base fluid density, base fluid critical density, nanoparticle diameter, base fluid molar mass, nanoparticle density) is introduced to evaluate the dynamic viscosity of nanofluids. The correlation is regressed and evaluated using a dynamic viscosity dataset for 32 nanofluids, including a total of 737 experimental points: 10 nanofluids have water as base fluid (Ag, Al2O3, Al2O3/CuO, C, CuO, diamond, Fe/Si, MWCNT, ND-Ni, TiO2), 6 nanofluids have ethylene glycol (Ag, Al2O3, CeO2, Co3O4, SiC, TiO2/CuO), 11 nanofluids comprise different mixtures of water and ethylene glycol (Al2O3, MWCNT/WO3, CB, fGnP, G/Dp, G/Dr, nD87, nD97, TiO2), 1 nanofluid has propylene glycol (SiC) and 4 nanofluids comprise different mixtures of water and propylene glycol (TiB2, TiB2/B4C, fGnP). The dynamic viscosity dataset was derived from experimental measurements documented in the scientific literature and conducted with samples that were prepared using consistent and reliable methods. The study evaluates the dynamic viscosity of nanofluids using 14 literature equations to verify their accuracy against the proposed correlation. Results show that the correlation has an average absolute relative deviation of 8.16%, which is significantly lower than that of the literature equations. A 4-fold cross-validation also shows that the correlation is resilient and accurate with different regression dataset
Documentazione statistica sul sistema pensionistico
No full textLa nota descrive le fonti statistiche e i modi per utilizzarle al fine di trarvi informazioni statistiche sul sistema pensionistico italiano
Twenty-four hour ambulatory antroduodenal manometry in normal subjects (co-operative study)
No full textCircadian antroduodenal motor activity was studied in 40 normal subjects by means of a portable recording system consisting of a computerized data logger and a probe with microtransducers. The quantitative and qualitative characteristics of contraction events during the interdigestive and digestive periods, as well as during the awake and asleep periods, were analysed. The composition and timing of meals and night recumbence were standardized. In spite of the high interindividual variability in motor parameters, significant differences in the characteristics of interdigestive and digestive periods between waking and sleep states were found. This paper confirms the existence of a circadian variation in antroduodenal motor activity and provides reference values from a large series of normal subjects that can be used for statistical comparisons with those obtained from patients recorded with the same method
Thermal conductivity of nanofluids: A review of the existing correlations and a scaled semi-empirical equation
No full textEfficiency of energy systems can be improved in different ways. One of these consists in adopting heat transfer fluids with better thermo-physical properties, e.g. thermal conductivity and dynamic viscosity, which can improve convective heat transfer coefficient. Being mixtures of high-conductive nanoparticles and common base fluids, nanofluids have the potential to increase the efficiency of a large number of energy systems. Thus, great importance should be dedicated to a correct and reliable estimation of the thermophysical properties of these fluids. In this work, the thermal conductivity of 11 nanofluids, for a total of 239 experimental points, was analyzed in detail: 7 nanofluids have water as base fluid (Ag, Al2O3, CuO, Fe2O3, SiO2, TiO2, ZnO), while 4 nanofluids have ethylene glycol (Al2O3, CuO, SiC and SnO2). All nanofluids’ thermal conductivity data derive from experimental measurements available in literature, carried out with samples characterized by stable preparation methods. The thermal conductivity of the nanofluids was estimated with 13 well-known correlations, in order to verify their accuracy. A new semi-empirical, scaled equation for predicting the thermal conductivity of nanofluids was also proposed. The equation requires the use of six parameters (volume fraction, temperature, base fluid critical temperature, nanoparticle diameter, nanoparticle thermal conductivity, base fluid thermal conductivity) and shows small deviations respect to the experimental data, having an average absolute relative deviation of 2.60%. This value was found to be the lowest among the other studied correlations. The study also highlights some issues and limitations that the research field related to nanofluids should overcome
microstructural and mechanical behaviour of high speed steels by activated sintering method
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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
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