1,720,999 research outputs found
Load levelling through Storage System for Hybrid Diesel Electric Ship Propulsion in Irregular Wave Conditions
No full textThis paper concerns the identification of the most suitable electrical energy storage system, devoted to propulsion power leveling of ship sailing in irregular wave conditions. Power irregularity originates from different flow conditions at the propeller disk that, in a quite complex way, causes torque and shaft speed variations. In this paper, the more adequate storage system is identified by relating storage performances with the period of the sea waves that suggests the employment of a threshold frequency, which allows choosing between two electrical energy storage technologies, namely supercapacitor and battery.This study is carried out for a Ro-Pax ferry powered by an electrical motor. Numerical simulations of ship dynamics in irregular seas, combined with propeller behaviour in waves, allow the estimation of the power propulsion spectra. The analysis of these numerical outcomes discloses that the power fluctuations due to irregular sea are characterized by frequencies higher than the threshold frequency. Therefore, these results indicate the suitability of supercapacitor in minimizing the irregularity of electrical power requested to the electrical power system
Design of an electrical energy storage system for hybrid diesel electric ship propulsion aimed at load levelling in irregular wave conditions
No full textThis paper focuses on the design stage of an electrical energy storage system which is intended to be used to level
the power required by ships for propulsion when sailing in irregular seas. Particularly, a preliminary analysis has
been carried out aimed at choosing, between two storage technologies namely battery and ultracapacitor, the
more adequate storage system for the levelling action with respect to the period of the sea waves. A sizing
procedure based upon a Hilbert transform decomposition of load demand is used. More specifically, a specified
threshold frequency has been identified such that, power fluctuations related to irregular seas which are char-
acterized by frequencies higher than the specified threshold, indicate the ultracapacitor as the more appropriate
device for load levelling. For sizing the storage device, the load demand has been decomposed into two signals
without overlapping frequencies. An optimal control strategy is proposed, by exploiting the decomposition of the
load power, which allows simulating ultracapacitor real-time operation within the previously determined size
constraints. Numerical results have been carried out referring to a Ro-Pax ferry powered by an electrical moto
Unravelling the luminescence spectrum of garnet grossular var. tsavorite: The role of chromium (III), manganese (II) and misattribution of vanadium (II)
Full text linkGem quality garnet var. tsavorite from Tanzania is investigated by means of SEM-EDS, XPS and fluorescence spectroscopy to decipher its luminescence spectrum. The EDS analysis confirms that the main constituents of the tsavorite samples from Tanzania are those of grossularia (i.e. Ca, Al, Si, O), with V, Mn, Cr, Ti and Mg as minor but characteristic elements (particularly V, Mn and Cr) of the tsavorite variety. The XPS analysis shows that the oxidation state of Mn is +2 and that of V is +3. The luminescence of tsavorite in the yellow region (591 nm) is originated by Mn 2+ in dodecahedral coordination (D 2 point symmetry) while the luminescence in the red region
(690–750 nm) is originated by Cr 3+ in octahedral coordination (O h point symmetry) in a strong crystal field. Contrary to what is often reported in the literature, this study demonstrates that V 2+ (or other 3d transition metal ions as well) is not responsible for the red emissions of tsavorite
Surface modification of food-grade PVC monitored by angle-resolved XPS
Full text linkIn this work the covalent functionalization of polyvinyl chloride (PVC) with (3-mercaptopropyl)trimethoxysilane (MPTMS) by nucleophilic substitution was investigated by X-ray photoelectron spectroscopy (XPS). The surface of food-grade PVC was characterized before and after treatment with ethanol and with 5% and 10% MPTMS solutions in ethanol. Special attention was paid to the determination of the chemistry, composition and thickness of the functionalized polymer surface by angle-resolved XPS (ARXPS). XPS analysis in standard mode and ARXPS spectra showed the presence of sulphur, silicon and oxygen from the MPTMS molecule. The quantitative analysis was in good agreement with the stoichiometry of the molecule. A small amount of chlorine, detected also at grazing angles, supported the formation of a layer, which resulted to be 2.2(0.2) nm thick including the hydrocarbon contamination usually detected by XPS on samples in contact with solutions. It is here demonstrated that XPS and ARXPS allow monitoring the surface functionalization and tune the conditions for achieving a good reproducibility during the functionalization of food-grade PVC by MPTMS. This is the starting point for further functionalization to obtain active food packaging with antimicrobial properties
Ferry ships: A cost/environmental comparison of innovative solutions for the electric power generation in port
No full textIn order to cope with continuously increasing environmental demands, the maritime sector is
investigating alternative solutions for the power generation on board. These solutions include both alternative
fuel, such as Liquefied Natural Gas (LNG) and hydrogen, and green technologies, such as fuel cells (FC) and
batteries. Although in-port emissions are responsible of a small percentage of the overall emissions, ports constitute sources of concentrated ship harmful emissions, potentially very dangerous for the human health. Moreover,the environmental regulations suggest switching present marine fuels as soon as possible. In this frame, this work investigates innovative solutions for the electric power generation in port for passenger ships in terms of cost and environmental benefits. These can be shore power solutions (such as cold ironing) and on-board solutions (such as dual fuel, fuel cell and others). The results show that some solutions could be more competitive than others according to specific operating conditions. The aim of the study is to identify the most eco-friendly and promising solutions. The cost analysis methodology takes into account the efficiency, fuel costs, operating and maintenance costs and the initial investment costs. The environmental comparison considers the emissions of nitrogen and sulphur oxides, carbon monoxide and dioxide, particulate matter and hydrocarbon
Optimal sizing of distributed energy resources in smart microgrids: A mixed integer linear programming formulation
No full text
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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