1,720,983 research outputs found
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
Exploitation of gold in an historic sewage sludge stockpile, Werribee, Australia: resource evaluation, chemical extraction and subsequent utilisation sludge
No full textSewage sludges are potential targets for economic extraction of Au because of the documented Au content of sewage sludges worldwide, which are of the order of some ore deposits currently mined for Au. The sewage of Melbourne, Australia, was stockpiled in large, closed, lagoonal tanks from 1898 until 1980. Reeves, Plimer and Foster, 1999, have conducted, and published, an extensive and exhaustive study of the Werribee sewage reserves utilising RNAA, INAA, GFAAS, ICPMS, and FLAAS to determine 31 elements, including Au, Ag, Sb, As, Cd, Hg, Zn, Cu, and Pb. The study was initiated to determine Au, Ag and other metal variations in both space and time and to investigate the economics of chemical extraction of the precious metals. A total of 149 samples from over 50 hand-auger drillholes to a depth up to 4m were analysed from the stockpiles, with Au assays yielding remarkably consistent results. Average grades of 0.77 g/t Au and 18.8 g/t Ag have been documented for a measured resource of 770,000 m3. Laboratory-based extractive metallurgy of the Werribee sludges has demonstrated that Au, Ag, and Zn can be removed with relative ease by heap-leaching using modified conventional technology, albeit with prohibitive reagent consumption. The extraction of the precious metals also results in the variable removal of contaminant metals such as Cd, As, Sb, Hg and Cr which may render the sludges fit for sale as agricultural fertiliser, provided organic pollutants and pathogenic organisms are below governmental environmental protection limits
Mobilisation of metals and metalloids from historical smelting slag dumps, Rio Tinto, Spain
Get PDFWhile the chemistry and mineralogy of sulfidic, AMD
producing wastes have been studied in great detail, few
studies have focused on smelting residues commonly present
at historic mine sites. This is despite the fact that historical base metal smelting slags contain elevated levels of heavy metals and metalloids and are subject to contemporaneous weathering processes thereby releasing elements to ground and surface waters. This work reports the chemistry and mineralogy of slag deposits (3 Mt) at the historic Rio Tinto smelter site, southwest Spain.
The microcrystalline slags contain primary slag phases, relict flux, ore and furnace materials and secondary weathering related minerals. Common primary slag phases are glass, Zn-rich fayalite and Zn-rich hedenbergite/augite. The slag materials contain wt% concentrations of Zn, major (ie. 1000 - 10000 ppm) Cu and Pb, minor (ie. 100 - 1000 ppm) Co, Sb and Sn, and traces (ie. <100 ppm) of Ag, As, Bi, Cd, Mo, Ni, TI and W. The slags have been subject to weathering since dumping in the 19th and 20th century, and a series of mineral efflorescences has been observed. They most commonly occur as powdery or cemented salt precipitates at seepage points and as solid aggregates in protected overhangs facing the Rio Tinto river. Mineral salts include gypsum, epsomite and copiapite as well as a series of minor phases such as roemerite, bloedite and hexahydrite. The mineral mixtures contain variable metal concentrations, including major Cu and Zn, minor As and Co, and traces of Cd, Ni and Pb.
Rio Tinto slags have high concentrations of metals and
metalloids in the order of Zn>Cu>Pb>Sb>Co>As>Ni. In contrast, the mineral salt mixtures have metal concentrations in the order of Zn>Cu>As>Co>Ni>Sb. Such distinctly different relative concentrations of elements in the two sample media collected from the weathered slag dumps can be related to the different mobility of elements in surface environments. For example, Sb displays a reduced mobility possibly due to the formation of insoluble precipitates, coprecipitation and adsorption in the slag dump. Thus, weathering of siliceous smelting slags is accompanied by the preferential mobilisation of some trace elements (ie. As, Co) into pore and seepage waters. Evaporation of the saline, metalliferous seepage waters emanating from the siliceous slag dumps causes the precipitation of secondary minerals. These minerals
temporarily store metals, metalloids and sulfate until
redissolution during the next rainfall. The Rio Tinto slag
dumps represent long-term sources of metals and metalloid
pollutants to local ground and surface waters
Mobilization of heavy metals from historical smelting slag dumps, north Queensland, Australia
No full textSlag dumps occur at several historical smelting sites in north Queensland, Australia. The microcrystalline slags contain primary slag phases, relict flux, ore and furnace materials and secondary weathering related minerals. Common primary slag phases are glass, Zn-rich fayalite (± Zn-rich kirschsteinite) and Zn-rich hedenbergite. Other minor minerals include wollastonite, Zn-rich melilite, Zn-rich iscorite (Fe7SiO10), magnetite as well as a number of sulphides (pyrrhotite, galena, bornite, sphalerite, wurtzite), metallic phases (Ag, Cu, Pb, Sb), alloys (Cu3Sn), and unknown metal compounds. The slag materials contain wt.% concentrations of Zn and elevated levels of Ag, As, Cd, Cu, Ni, Pb, Sb and W. Glass, hedenbergite and fayalite/kirschsteinite are the main repositories of Zn, whereas much of the Cu and Pb is hosted by glass, sulphides, Cu3Sn alloys, metallic Cu and Pb, and unknown CuSb, AsSnPb and FeAsCu compounds. The slags are undergoing contemporaneous reaction with air and rainwater. The weathering results in the release of metals and metalloids from primary slag phases, particularly from glass, and the partial immobilization of these metals in secondary soluble and insoluble minerals in the slag heaps. Zinc exhibits pronounced chemical mobility and reports together with elevated Ca and sulphate into surface seepages (up to 10.2 mg 1-1 Zn at pH 6.97). The slag dumps represent long-term sources of metal pollutants, particularly of Zn, to local ground and surface waters
Evaporative mineral precipitates from a historical smelting slag dump, Río Tinto, Spain
No full textThis work reports the chemistry and mineralogy of mineral efflorescences associated with slag deposits at the historical Río Tinto smelter site, southwest Spain. The slags have been subject to weathering since dumping in the 19 th and 20 th century, and a series of evaporative mineral efflorescences has been observed. The efflorescences commonly occur as powdery or cemented salt precipitates at seepage points at the base of the slag dump and as solid aggregates in protected overhangs facing the Tinto river. The mineral salt types include Ca and Mg sulfates (gypsum, epsomite, hexahydrite, bloedite) as well as mixed Fe2+ – Fe3+ hydrated sulfates (copiapite, roemerite). The salt mixtures have variable metal concentrations, including major (> 1 wt %) concentrations of Zn, minor Cu (> 1000 ppm), sub-minor (100–1000 ppm) to traces (< 100 ppm) of As and Co as well as traces (< 100 ppm) of Ag, Bi, Cd, Mo, Ni, Pb, Sb, Sn, Tl and W. Copiapite-rich samples exhibit the highest As, Cd and Cu, epsomite–hexahydrite rich samples have the highest Zn, and the gypsum-rich samples show the lowest metal and metalloid concentrations. Dissolution experiments show that all salt mixtures are acid generating due to Fe and Al hydrolysis and resultant pH decrease in the solution. Thus, weathering and leaching of metalliferous smelting slags are accompanied by the mobilisation of metals, metalloids, alkali earth elements and sulfate into pore and seepage waters. Evaporation of seepage waters emanating from the slag dump causes the precipitation of mobilised elements and compounds and leads to their temporary fixation in secondary soluble minerals. Dissolution of the efflorescences during the next rainfall and flushing event and associated Al3+ and Fe3+ hydrolysis contribute to the acidification and metal and sulfate contamination of Río Tinto waters
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
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
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
- …
