1,720,981 research outputs found
Indagine sull'utilizzo del biochar derivante da processi ad alta temperatura per una maggiore sostenibilità ambientale dei contesti agro-industriali
No full textIl biochar è un materiale carbonioso avente un contenuto di carbonio fino all'80% e prodotto a temperature di 600-1000°C attraverso processi di gassificazione o la pirolisi, rimane stabile per decenni nel terreno motivo per cui è riconosciuto come un metodo di stoccaggio di carbonio. Tradizionalmente considerato un sottoprodotto della gassificazione, il biochar sta diventando sempre più importante perché considerato strategia efficace per la decarbonizzazione. Le caratteristiche del biochar dipendono da diversi fattori: biomassa, processi utilizzati, temperature e tempi di permanenza. A prescindere dal metodo di produzione, il biochar presenta elevate area superficiale e porosità, elevate capacità di scambio cationico e conducibilità elettrica e un alto potenziale di ritenzione idrica. Grazie a queste proprietà, il biochar può apportare miglioramenti in vari settori: in agricoltura, per la concezione di nuovi materiali, nella gestione dei rifiuti, nei sistemi geotermici, ecc. In questa tesi, innanzitutto, il biochar è stato caratterizzato “tal quale”. La valutazione della qualità del biochar è fondamentale per identificare il biochar più adatto alle specifiche applicazioni. Un'attenzione particolare è stata rivolta alla conduttività elettrica del biochar, ovvero la capacità di trasferimento di elettroni attraverso la struttura carboniosa. La conducibilità elettrica è una delle proprietà fondamentali ed influisce sul modo in cui il biochar interagisce con i microrganismi del suolo. Ad oggi, però, la misurazione di questa grandezza non è standardizzata e per questo si sono indagati i parametri che influenzano la misura attraverso una campagna di test su diversi campioni di biochar. A partire dai risultati si è ipotizzato che nessuno dei valori ottenuti rappresenti realmente la conducibilità percepita dai microrganismi del suolo. Una seconda parte della tesi è poi incentrata sulle indagini sperimentali di applicazioni innovative del biochar. Sono stati indagati gli effetti dell'applicazione del biochar sul comportamento termico dei processi di compostaggio della frazione organica dei rifiuti urbani. Il biochar è stato aggiunto al materiale organico e le temperature di processo sono state registrate per due mesi. I dati sono stati utilizzati come input per un modello per il calcolo dell’energia termica che ha rivelato come l’aggiunta di biochar ha incrementato la produzione di energia termica. I risultati sono un punto di partenza per ulteriori considerazioni in termini di miglioramento dei metodi di compostaggio e di nuovi prodotti a impronta di carbonio negativa. Contemporaneamente, sono state eseguite misure dei gas serra emessi. I risultati hanno mostrato che il biochar riduce fino al 45% le emissioni di CO2eq. La tesi presenta poi un'indagine sugli impatti tecnologici, economici e ambientali dell'applicazione del biochar in un impianto di compostaggio esistente. Lo studio presenta vari scenari combinando gassificatori SynCraft e l’acquisto di biochar. La fattibilità viene valutata calcolando il tempo di ritorno dell'investimento, stimando il fabbisogno di biomassa e valutando l'energia elettrica e il biochar prodotti. Lo stoccaggio di carbonio è stato quantificato in crediti di carbonio. L’aggiunta del biochar nel compostaggio emerge come modalità promettente per ottimizzare la gestione dei rifiuti, bilanciando redditività economica e sostenibilità ambientale. Infine è stato condotto uno studio sul miglioramento dell'efficienza delle pompe di calore geotermiche. La conduttività termica del suolo è un fattore chiave per il funzionamento di questi sistemi e il biochar come materiale di riempimento rappresenta una soluzione migliorativa. Il biochar assorbe acqua, ne facilita la risalita capillare e la trattiene a lungo, determinando un aumento dell’umidità del suolo. I risultati dimostrano che il biochar migliora lo scambio termico tra sonde geotermiche e il terreno.Biochar is charcoal material like activated carbons, with a carbon content up to 80%, produced at temperatures of 600-1000°C through gasification or pyrolysis. Thanks to the high recalcitrance it remains stable for decades in the soil, when buried, and for this reason it is recognize by the scientific community as a long-term storage method. Traditionally considered only a byproduct of gasification, in the last decade biochar is becoming more and more important as it is considered an effective strategy for decarbonize our world. The characteristics of biochar depend on various factors, such as the feedstock, the thermochemical process, the temperatures and the time of residence. However, despite the way it is produced, all biochars have high surface area and porosity, high cation exchange capacity and electrical conductivity, and high water-retention potential. Thanks to all these proprieties, biochar brings significant improvements in various areas: in agriculture, for new materials conception, in the waste managements, in geothermal systems, ... In this thesis, biochar "as it is" was first investigated. Evaluating the quality of biochar is a key factor for identifying the best biochar suitable for specific applications. A special focus has been turned toward the electrical conductivity of biochar: the capacity of electron transfer through the carbonaceous structure. The electrical conductivity is one of biochar’s fundamental properties that affects the way it interacts with microorganisms in soil applications. However, to date, the measurement of this quantity is not univocal. A testing campaign is carried out on different samples of biochar to understand the parameters that affect the conductivity measurement. The final point of this discussion hypothesizes that neither one of the obtained conductivities truly represents the conductivity perceived by the soil microorganism that interacts with the biochar. A second part is then focused on experimental investigations of innovative applications of biochar. The effects of biochar application on the thermal behavior of organic municipal waste composting are investigated. Biochar was mixed with the organic fraction of municipal waste in nine bins and compost temperatures were logged for 2 months. Experimental data were used as a basis for thermal energy modeling that reveals the addition of biochar to composting processes increases the thermal energy production. Results are a starting point for further considerations in terms of improved composting method and new carbon sequestration product. At the same time, measures of greenhouse gases and ammonia emitted from the bins were performed. The results showed that biochar reduces up to 45% of CO2eq emissions. The thesis presents a investigation of technological, economic, and environmental feasibility of biochar application to a composting facility. The study hybridizes an existing facility creating various scenarios mixing SynCraft gasifier model and biochar trading. The feasibility is assessed by calculating payback time, estimating annual biomass needs and prioritizing electrical energy and biochar production. Carbon storage is also considered and quantified in Carbon Credits. Results show that aiding biochar into composting emerges as a promising way for waste management optimization, balancing economic viability and environmental sustainability. Thirdly, since low-enthalpy geothermal systems are increasingly important, a study on the efficiency improve of ground source heat pump is investigated. Since the soil thermal conductivity is a crucial factor for the heat exchange of geothermal probes, biochar as additive/filler material represents a sustainable solution. Biochar facilitates capillary absorption of water and retains it over time, resulting in increased soil moisture content and elevation of the groundwater level. Results demonstrate biochar can enable better thermal exchange between geothermal probes and the soil
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Gasification of agricultural residues to support the decarbonization of the transport sector via electricity generation: a case study
No full textThe gradual electrification of transport, particularly private cars, requires widespread electricity availability and potential peak demand in rural or underdeveloped regions could strain the existing electricity network. Therefore, exploring distributed electricity generation is crucial to reduce grid demand and can be an opportunity to promote low-carbon technologies. In this research work we analyze the potential contribution of a biomass gasifier, fueled by vine prunings, in supplying electricity to a local site for electric vehicles charging. The performance of the system is assessed from a technical, economic and environmental point of view. In particular, the specific equivalent CO2 emissions of the system are compared to the alternative emissions of the national power grid, considering the estimated charging profiles based on available patterns from real case studies that incorporate different users' behaviours and preferences. The electricity produced by the gasifier has a calculated supply chain carbon intensity of 134 gCO2e/kWh, which can be sharply reduced to -34 gCO2e/kWh, indicating a carbon-negative process, when the carbon sequestration of the co-produced biochar is considered. These figures should be evaluated against a weighted average carbon intensity of the national electricity mix equal to 384 gCO2e/kWh in 2018, while the same figure for 2030 ranges from 141 gCO2e/kWh to 226 gCO2e/kWh depending on the future scenario that is considered. The economic assessment estimates payback times between 6 and 8 years with an average utilization factor of the charging station equal to 14% and a charging price equal to 0.62 €/kWh. In addition to the emission savings that are obtained, this approach could generate further positive effects on the territory: a) the production of electricity allows rural areas to establish their sustainable electric transportation network, reducing their marginalization; b) the production portfolio of farms or agricultural consortia is diversified; c) create a carbon-negative recovery chain for lignocellulosic waste and offers a sustainable solution for their disposal. The results of this analysis can be of use for other researchers dealing with similar topics, and for policymakers that aim to compare available solutions for the decarbonization of the transport sector
Variations on the Author
Get PDF“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
High temperature properties of nichrome resistant heaters – A systematic comparison of APS, suspension and filament HVOF sprayed coatings
Get PDFThis study investigates the performance of Nichrome coatings, a nickel‐chromium alloy containing 20 wt.-% chromium, applied using three thermal spray techniques: powder plasma spray, suspension HVOF, and filament HVOF. Thin, homogeneous coatings approximately 35 μm thick were deposited onto steel substrates pre-coated with an insulating Al2O3 layer. The oxide content in the coatings varied based on the spraying technique and parameters, ranging from 57 to 64 vol.-% for plasma spraying, 42 to 54 vol.-% for filament HVOF, and 9 to 43 vol.-% for suspension HVOF. The coating's heating performance was evaluated over a temperature range of room temperature (RT) to 700 °C. Analytical techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) were employed to investigate the mechanisms affecting temperature-dependent resistivity in relation to the coating microstructure. The results indicate that increased oxidation leads to a decrease in specific resistivity at RT (ρ0). In example, plasma sprayed coatings exhibited lower specific resistivity ρ0 of 0.80 Ωmm2/m. In contrast, suspension HVOF reaches values up to 2.75 Ωmm2/m. At the same time coatings with higher oxidation levels demonstrate an elevated dependence of resistivity as compared to less oxidized coatings. Both can be attributed to changes in the phase composition of the conductive phase as the dominating factor, primarily driven by the preferential oxidation of chromium during the spraying process. Notably, the results provide valuable information for adjusting the coating properties to suit specific needs, such as self-regulating or high-temperature heating applications
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
The conductivity dilemma: How biochar grain’s chemical composition and morphology hinder the direct measurement of its electrical conductivity
No full textAlthough electrical conductivity is one of biochar's fundamental properties that affects the way it interacts with microorganisms in soil applications, however its measurement is not univocal. This work starts from the results of a testing campaign on gasification biochar as the basis for a larger discussion on the parameters that affect the conductivity measurement and, therefore, the limits of the most widely used compression measuring approach. Different samples were obtained by combining sifting and grinding on a single batch of biochar. The samples were tested in a PTFE cylinder with conductive plunger and cap in a range of pressures up to 25 bar. The same biochar prepared in different ways showed different conductivity behaviors, with variation up to 85%, proving that the testing condition can strongly affect the measurement. These findings encourage the scientific community to further investigate the meaning of the results obtained with a further recommendation to properly describe the sample preparation and the testing conditions when a compression method is used. The final point of this discussion hypothesizes that neither one of the obtained conductivities truly represents the conductivity perceived by the microorganism that interacts with the char in soil applications
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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