1,721,078 research outputs found
Replication Data for: Networks of Grievances: Social Capital and Mainstream Party Decline
No full textReplication material. See readm
Zeoliti per il recupero delle terre rare: lo scambio cationico a sostegno dell'economia circolare
No full textDal 2011, per la loro elevata importanza economica e per il rischio legato al loro approvvigionamento, gli elementi del gruppo delle terre rare (REE) sono classificati come Materie Prime Critiche (CRMs) per l'UE. I REE si dividono in Elementi delle Terre Rare Pesanti (HREE), utilizzati per le loro proprietà ottiche, ed Elementi delle Terre Rare Leggere (LREE), utilizzati in catalisi, metallurgia, lucidatura del vetro e magneti. L'85% dei LREE e la totalità degli HREE sono importati dalla Cina, il che comporta una catena di approvvigionamento molto vulnerabile. Una recente regolamentazione europea sottolinea la necessità di programmi nazionali per aumentare la raccolta, la selezione e il trattamento dei rifiuti con potenziale di recupero di CRMs, al fine ultimo di incrementare l'uso di materie prime critiche secondarie. I REE possono essere recuperati da vari rifiuti, in particolare dai RAEE (rifiuti da apparecchiature elettriche ed elettroniche), ma tale potenziale è ancora poco sfruttato. Un passaggio cruciale nella fase di recupero è la separazione dei REE da altri elementi e tra di loro, argomento che è stato il focus di questo progetto, in cui si è andata a valutare la capacità di selezione e di scambio cationico di una zeolite 13X sintetica commerciale e di una zeolite sintetizzata a partire da cenerei volanti (CFA). Questi materiali sono stati utilizzati per test di scambio con quattro REE a concentrazioni simili a quelle ottenute dalla lisciviazione di lampade a fluorescenza esauste. In un primo esperimento, una zeolite 13X in forma di ammonio è stata messa a contatto con soluzioni mono-elementari con concentrazioni di Ce 0,03 M, La 0,04 M, Eu 0,006 M e Y 0,17 M, utilizzando tre diversi rapporti solido/liquido. Ulteriori scambi con NH4 sono stati poi condotti per recuperare i REE dalle zeoliti. Le polveri sono state analizzate tramite SEM-EDS, TG ed EA, mentre le soluzioni sono state analizzate tramite ICP-OES. Campioni rappresentativi per ciascun REE, prima e dopo il recupero, sono stati analizzati tramite XRPD ad alta risoluzione (ID22 – ESRF) per ottenere informazioni strutturali. Ad integrazione dei risultati dei test mono-elementari, è stata eseguita una seconda serie di prove su soluzioni contenenti coppie di REE (Ce + La, Eu + Y), sia con la zeolite commerciale scambiata con NH4 sia con una zeolite sintetizzata da CFA. Anche in questo caso, sono stati testati tre diversi rapporti solido/liquido per ciascuna soluzione, seguiti da scambi con NH4 per recuperare i REE. Sia le polveri ottenute che le soluzioni sono stati analizzati come descritto in precedenza. I risultati degli scambi mono-elementari hanno rivelato che i diversi REE mostrano comportamenti di scambio differenti. Nonostante la sua concentrazione maggiore, l’Y ha raggiunto valori di scambio inferiori rispetto a Ce e La, che hanno mostrato invece risultati simili tra loro. La concentrazione iniziale di Eu si è rivelata essere troppo bassa per trarre conclusioni certe. L'analisi strutturale delle zeoliti scambiate con Ce e La ha confermato che questi elementi occupano gli stessi siti di scambio con occupanze simili. Mentre Eu, seppur in basse concentrazioni, è risultato comportarsi similmente a Ce e La, Y ha mostrato un comportamento distinto, occupando un sito di scambio diverso, interagendo con l'acqua a discapito del framework della zeolite, il che spiega la sua maggiore solubilità e il minore scambio complessivo. Gli scambi bi-elementari hanno confermato i risultati dei test mono-elementari: Ce e La hanno mostrato comportamenti quasi identici, mentre gli scambi di Eu e Y sono risultati essere fortemente condizionati dalle concentrazioni di partenza dei due elementi, con Y scambiato selettivamente a discapito di Eu in ogni rapporto solido/liquido testato.Since 2011, Rare Earth Elements (REEs) have been classified as Critical Raw Materials (CRMs) for the EU due to their high Economic Importance and Supply Risk. This reflects their irreplaceable role in key applications. REEs are divided into Heavy Rare Earth Elements (HREEs), valued for their optical properties, and Light Rare Earth Elements (LREEs), used in catalysis, metallurgy, glass polishing, and magnets. A major concern is that 85% of LREEs and all HREEs are imported from China, creating a vulnerable supply chain. A recent European regulation emphasizes the need for national programs to increase the collection, sorting, and processing of wastes with CRM recovery potential, aiming to boost secondary raw material use. REEs can be recovered from waste, notably WEEE (waste from electrical and electronic equipment), but this potential remains underexploited. A critical step is the separation of REEs from other elements and from each other’s, which was the focus of this project, assessing the cation exchange capacity of a synthetic, commercial 13X zeolite and a zeolite derived from coal fly ash. These materials were tested against four REEs at concentrations similar to those found in leached spent fluorescent lamps. In the first experiment, NH4-exchanged 13X zeolite was exchanged with mono-elemental solutions with concentration of Ce 0.03 M, La 0.04 M, Eu 0.006 M, and Y 0.17 M, using three different solid/liquid ratios. Further NH4 exchanges were conducted to recover the REEs from the zeolites. The powders were analysed by SEM-EDS, TG, and EA, while the solutions after the first exchange were analysed by ICP-OES. Representative samples for each REE before and after the recovery were analyse by XRPD (ID22 – ESRF) to obtain structural information. Encouraged by the mono-elemental results, a second set of tests was done using solutions containing paired REEs (Ce + La, Eu + Y), with both commercial NH4-exchanged 13X zeolite and the zeolite synthesized from coal fly ash. Again, three different solid/liquid ratios were tested for each solution, followed by NH4 exchanges to recover the REEs. Both solids and solutions were analysed as previously described. The mono-elemental exchange results revealed that different REEs exhibit different exchange behaviours. Despite being the most concentrated, Y had lower exchange values than Ce and La, which showed similar performance. Eu’s concentration was too low to draw conclusions about its exchange behaviour. Structural analysis of the Ce- and La-exchanged zeolites confirmed that these elements occupy the same exchange sites with similar occupancy rates. While Eu behaved similarly, Y showed distinct behaviour, occupying a different site in the zeolite where it interacted with water rather than the framework, explaining its greater solubility and lower overall exchange. The bi-elemental exchanges supported the mono-elemental findings: Ce and La exhibited nearly identical behaviours, while Eu and Y's exchanges were controlled by their concentrations, with Y consistently exchanged over Eu at every tested solid/liquid ratio
Universae Gothorum gentes Romano sese imperio dediderunt. Profili dei rapporti romano-gotici nel IV sec. d.C.
No full textThe paper analyzes the particularly problematic political, juridical-legislative and cultural situation of the period between 350 A.D. and 410 AD about, coinciding with the great migrations of the barbarian populations (especially the Gothic ones) within the borders of the Roman Empire and placing as a thematic and temporal center of gravity, the Foedus Gothicum of 382 A.D. In this context, the scientific target pursued is to identify and distinguish, if it’s possible, which legislative provisions and which literary works, produced in conjunction with the aforementioned migrations of peoples, were in causal, direct or indirect relationship, with the same relocations; which imperial constitutions were the expression of the legislative, pro-barbaric or anti-barbaric, policy of the imperial chancelleries (especially under Valente, Theodosius and his direct successors) and which coeval philosophical-literary works, on the other hand, showed the social and cultural perception of this situation and of the consequent imperial Gothic politics
New Insights Into Upper Messinian Microbial Carbonates: A Dendrolite‐Thrombolite Build‐Up From the Salento Peninsula, Central Mediterranean
Full text linkUpper Messinian carbonates recently recorded in the Salento Peninsula (southern Italy, central Mediterranean) contain microbial facies, including textures never previously described in the Late Miocene of the Mediterranean. This study focuses on the geometry and internal fabrics of a 3 × 28 m build-up of coalescent dendrolite and thrombolite, to examine its formation and the possible microbes involved, and to reconstruct its growth dynamics and related palaeoenvironmental conditions. Salento dendrolites have centimetric dendritic growth forms with a microlaminated, originally aragonitic, microstructure. The thrombolites, in contrast, are characterized by larger mesoclots with arborescent, anastomose growth patterns and a distinctive microfabric of small, originally calcitic, spheroids with a sparry nucleus surrounded by acicular crystals. Bio-geochemical analyses (UV epifluorescence, micro-Raman spectroscopy and SEM-EDS) reveal the presence of organic matter intimately associated with both dendrolite and thrombolite textures, supporting a biotic origin. The sedimentary context and microfabrics suggest that cyanobacteria may have played a major role in the formation of these structures, together with heterotrophic microbes, mainly sulfate-reducing bacteria, in the dendrolite. Build-up geometries, stratigraphic setting, and analysis of the associated sediment suggest that the dendrolite-thrombolite framework developed in a small, shallow-water lagoon, under moderate to high energy, variable salinity, and possibly high sedimentation rate. Salento dendrolite-thrombolite build-up appears to be the only known example of large microbial bioconstruction made by microlaminated dendrolites
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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