1,720,973 research outputs found
Design of a cooperative voltage harmonic compensation strategy for islanded microgrids combining virtual admittance and repetitive controller
No full textNon-linear loads (NLLs) in three-phase systems are known to produce current harmonics at -5, 7, -11, 13... times the fundamental frequency; harmonics of the same frequencies are induced in microgrid voltage, reducing therefore the power quality. Dedicated equipment like active power filters can be used to compensate the microgrid harmonics; alternatively, each distributed generation (DG) unit present in the microgrid can be potentially used to compensate for those harmonics. The use of the virtual admittance concept combined with a PI-RES control structure has been recently proposed as a harmonic compensation sharing strategy when multiple DGs operate in parallel. The drawback of this methodology is that a large number of RES controllers might be required to compensate for all harmonic components induced by NLLs. This paper proposes the combined use of virtual admittance control loop and repetitive controller (RC) for harmonic compensation. The main advantage of the proposed method is that only one RC is required to compensate for all the harmonic components, significantly reducing the computational burden and the design complexity. © 2016 IEEE
Effetto di stabilizzanti su alcuni parametri biochimici di mele lavorate in IV gamma
No full textThe aim of this research was the evaluation of preservative substances on biochemical (PAL and PPO activities) and nutraceutical (phenol content and antioxidant capacity) characteristics of apple fruits cv Granny Smith stored as fresh-cut products at 4°C for 7 days. The results evidenced as the used preservatives influenced the visual aspect of the fruits. In fact, whereas control showed evident visible symptoms attributable to browning immediately after the cut, fruits treated with ascorbic acid did not show any colour alterations until the end of storage. Treatment with citric acid alone or combined with CaCl2 did not reduce the browning. In the report is underlined as browning phenomenon is quite complex as evidenced by biochemical analysis. In fact, in apple fruits treated with AA is not evident a reduction in PPO activity and a similar response was observed in presence of citric acid. The presence of CaCl2 did not modify the response
Design of a cooperative voltage harmonic compensation strategy for islanded microgrids combining virtual admittance and repetitive controller
No full textNonlinear loads (NLLs) in three-phase systems are known to produce current harmonics at -5, 7, -11, 13,... times the fundamental frequency. However, harmonics of the same frequencies are induced in microgrid voltage thereby reducing the power quality. Dedicated equipment, such as active power filters, can be used to compensate the microgrid harmonics. Alternatively, each distributed generation (DG) unit present in the microgrid can also be used for the same. The use of the virtual admittance concept combined with a proportional integral with resonant controller (PI-RES) control structure has previously been proposed as a harmonic compensation sharing strategy when multiple DGs operate in parallel. The drawback of this methodology is that a large number of RES controllers might be required to compensate for all the harmonic components induced by NLLs, increasing the tuning complexity as well as the execution time. This paper proposes the combined use of virtual admittance control loop and repetitive controller (RC) for harmonic compensation. The main advantage of the proposed method is that only one RC is required to compensate for all the harmonic components, significantly reducing the computational burden and the design complexity. The dynamic performance of the whole system is tested under variable NLL. © 1972-2012 IEEE
A Unidirectional Flying Chain-link Modular Multilevel Rectifier (FCL-MMR) with Reduced Energy Storage for Offshore Wind Integration
No full textIn recent years, the Modular Multilevel Converter (MMC) has been widely recognised as the state-of-art for AC/DC conversion stages in the integration of offshore wind energy through HVDC links. The MMC guarantees high power quality, efficiency, reliability and flexibility. However, in applications where the power flow is mostly unidirectional, the capabilities of the MMC are not fully exploited, resulting in a converter whose weight and volume are not optimised. This aspect is particularly challenging in offshore applications where the platform cost is a key factor. A more traditional solution could be the use of an AC/DC converter based on diode rectifiers, providing minimum size and complexity at the cost of poor AC power quality, requiring large active/passive filters. This paper proposes a new unidirectional AC/DC converter, named Flying Chain-link Modular Multilevel Rectifier (FCL-MMR), that combines a three-phase diode rectifier with modular chain-links of submodules (SMs) that enable the control of sinusoidal AC currents and, if needed, the exchange of reactive power with the offshore AC grid. This is achieved with a limited number of submodules characterized by low energy storage requirements. The conversion concept and the theoretical analysis are presented and SM selection criteria is discussed. The proposed converter has been validate in Plecs simulation. © 2018 IEEE
Do Sun- versus Shade-Grown Kiwifruits Perform Differently upon Storage? An Overview of Fruit Maturity and Nutraceutical Properties of Whole and Fresh-Cut Produce
No full textFresh-cut produce represents a good method to save about 25% of the kiwifruit not useful to meet the fresh fruit-marketing standard due to improper size and shape. For that reason, fresh-cut kiwifruit has been extensively studied. However, the comprehension of the influence of some aspects of cultivation might further increase the shelf life as well as the nutritional values of that fruit. This study explored the hypothesis that kiwifruits grown fully exposed to sunlight or partially shaded differently perform upon storage as whole fruit and as minimally processed produce. Flesh firmness (FF), total solids soluble (SSC), ascorbate (AAT), flavonoids (TFO), and phenols (TF) contents were evaluated in sliced and whole fruit upon 3 days of storage at 4 °C after 75 days of cold chamber storage at 0 °C. The activities of two enzymes related to the softening process, polygalacturonase (PG) and pectinmethylesterase (PME), were evaluated as well. FF and SSC were constitutively higher in sun-exposed fruit, and those characteristics remained higher during the storage as whole fruit. Greater constitutive content of AAT, TFO, and TP was found in sun-exposed whole fruit, although after cutting the reduction in their content was significantly lower in shaded fruits. PME and PG activities were higher only in whole shaded fruits, whereas no relevant differences occurred after cutting. In summary, sun-exposed fruits were more suitable for the fresh-fruit market, whereas the shaded counterpart displayed a good predisposition for use as fresh-cut produce, maintaining similar fruit maturity properties but higher nutraceutical values when sliced than fruit grown under full sun
Effects of 1-methylcyclopropene and post-controlled atmosphere air storage treatments on fresh-cut Ambrosia apple slices
No full textBACKGROUND: The effect of 1-methylcyclopropene (1-MCP) treatment and two different post-controlled atmosphere air storage (PCAAS) durations on the quality and chemistry of fresh-cut Ambrosia apple slices was studied. RESULTS: PCAAS for 1 or 2 weeks prior to slicing had an overall positive effect on the resultant quality of fresh-cut apple slices. The most significant responses to PCAAS were the suppression of both phenolic and o-quinone accumulation in slices, and this was related to the significantly lower browning potential values obtained for slices from PCAAS-treated apples. Polyphenol oxidase (PPO), peroxidase (POX) and ascorbate peroxidase (APOX) activities were not affected by 1-MCP or PCAAS treatments. PPO and POX activities were almost completely inhibited by a 50 g L-1 calcium ascorbate anti-browning dip of apple slices from all treatments. CONCLUSION: The most dramatic effect of the PCAAS treatments was to reduce the accumulation of soluble phenolics, which is likely the reason that o-quinone accumulation was also inhibited in treated fruits. The consequent reduction in browning potential may be the explanation as to why PCAAS treatment has been shown to reduce fresh apple slice browning in previous work
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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