1,720,988 research outputs found
Numerical Optimization of Combined Heat and Power Organic Rankine Cycles - Part B: simultaneous design & part-load optimization
Full text linkTowards an efficient management of livestock slurries in intensive agro-ecosystems: insights on N loss pathways, trade-offs, and mitigation strategies
No full textI liquami zootecnici rappresentano una preziosa fonte di fertilità per l'agricoltura. Tuttavia, con l’aumento della popolazione mondiale, il settore zootecnico ha un impatto sempre maggiore sull'agroecosistema, e una corretta gestione dei reflui rappresenta un punto chiave da affrontare, dallo stoccaggio all'applicazione al suolo, per evitare perdite di nutrienti indesiderati e effetti collaterali sull'ambiente.
L'azoto (N) è allo stesso tempo il più importante fattore di limitazione della resa delle colture (insieme all'acqua) e il macronutriente vegetale più abusato, specialmente sotto forma di fertilizzanti chimici. Questi possono essere parzialmente, o totalmente, come per l'agricoltura biologica, sostituiti con letami e liquami. Tuttavia, una gestione sostenibile dei reflui zootecnici dovrebbe necessariamente comportare una riduzione delle perdite azotate attraverso forme reattive (Nr), come le volatilizzazioni di ammoniaca (NH3), lisciviazioni di nitrato (NO3-) ed emissioni di ossido nitroso (N2O) che rappresentano non solo una perdita di valore nutritivo, ma anche una minaccia per la salute umana e ambientale.
Gli obiettivi specifici di questa tesi sono: (i) identificare strategie di distribuzione del liquame bovino che minimizzino le perdite di Nr, migliorando nel contempo l'efficienza dell'uso dell'azoto (NUE), attraverso vari ecosistemi, compresi i prati permanenti e le coltivazioni di mais nella pianura padana; (ii) testare strategie di mitigazione delle perdite basate su pratiche agricole sostenibili, comprese le colture di copertura, e strategie innovative di trattamento e distribuzione dei liquami (fertirrigazione); (iii) valutare l'impatto di queste strategie su tre principali vie di perdita di Nr, vale a dire NH3, NO3 e N2O.Slurries represent a valuable source of fertility for Agriculture. However, with growing population, animal husbandry has become increasingly impacting on the agroecosystem, with correct slurries management as a key point to address, from storage to land application, to avoid undesirable nutrients losses and side effects on the environment.
Nitrogen (N) is at the same time the most important crop yield-limiting factor (together with water) and the most overused plant macronutrient, especially in the form of chemical fertilizers. Those can be partially, or totally, as for Organic Farming, replaced with manures and slurries. However, the adoption of sustainable management strategies for slurries that can improve their fertilizing value, should necessarily come with a reduction in the leakage on N through reactive forms (Nr), like ammonia (NH3) volatilizations, nitrate (NO3-) leaching and nitrous oxide (N2O) emissions that represent not only a loss of nutrient value, but also a threaten to human and environmental health.
Specific objectives of this thesis are: (i) to identify distribution strategies of livestock slurry that minimize Nr losses, while enhancing nitrogen use efficiency (NUE), across various intensive agro-ecosystems, including the permanent grasslands and the maize cultivations in the Italian Po valley; (ii) to test Nr losses mitigation strategies based on sustainable agriculture practices, including cover crops, and innovative slurry treatment and distribution strategies (i.e., fertigation); (iii) to assess the impact of these strategies on three main Nr loss pathways, namely NH3, NO3- and N2O
Numerical Optimization of Combined Heat and Power Organic Rankine Cycles - Part A: Design Optimization
No full text
Process selection, modelling and optimization of a water scrubbing process for energy-self-sufficient biogas upgrading plants
No full textThis study focuses on the techno-economic optimization of an energy-self-sufficient biomethane production plant based on anaerobic digestion of agricultural residues and maize silage and an optimized water scrubbing process. The biomethane production plant features a biogas production system, a water scrubbing upgrading section and an internal combustion engine fed with a fraction of the produced biogas. The engine is properly sized to provide both the electric and thermal power required to operate the whole plant. A thorough literature review is performed to select the most promising water scrubbing layout, which features a scrubber, a flash and a stripping column. Accurate process and preliminary cost models of the main equipment units are developed and validated against literature and industrial data. A techno-economic bi-objective optimization of the upgrading process is then performed in order to determine the set of Pareto optimal solutions with maximum net biomethane recovery efficiency and minimum capital cost. Process optimization is performed with a black-box strategy using the PGS-COM single-objective algorithm and the NSGA-II multi-objective algorithm. The resulting Pareto front achieves net biomethane recovery figures in the range 88.1–89.7% and specific Total Equipment Costs between 0.95 and 1.03 k€/(Nm3BM/h). Compared to the conventional plant configuration, the proposed integration allows to avoid 188 g CO2/Nm3BM emissions and to save between 6.8 and 8.5% of primary energy, with an estimated increase of Total Equipment Cost of approximately 11–13.5% (anaerobic digestion section included)
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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