1,721,188 research outputs found
Source Apportionment of Heavy Metal(loid)s in the Surface Soils of Cerrito Blanco, Mexico: A Comparative Study of Three Receptor Models (APCS-MLR, PMF and UNMIX Model)
No full textIt is essential for the monitoring and conservation of soil environments to have a comprehensive awareness of the source characteristics including that of heavy metal (loid)s. This study focuses on a semi-arid mining area in Mexico where heavy metal (loid)s originated from past mining and rapid industrialisation activities, which have degraded the soil environment as well as the security of agricultural products. In this study, Cerrito Blanco, which is part of an abandoned mining region in Matehuala, Mexico was identified as the principal source of contaminants. It was also observed that the contributions of the contaminants to the overall pollution could be calculated by using a combination of multivariate statistics and receptor models. The three receptor models such as APCS-MLR, PMF, and UNMIX were used and mutually compared to improve the accuracy and quantitative assessment of source contributions. A total of eleven heavy metal(loid)s were selected for this study, out of which the mean concentrations level of As, Fe, Mn, and Zn exceeded their reference limit values. The spatial distribution mapping revealed the distribution patterns and significant effects on concentrations of heavy metal(loid)s in surface soil. APCS-MLR identified three potential sources with contribution rates of 18.16% (groundwater source), 57.33% (past mining and industrialisation), and 24.51% (natural source) respectively. Two models, namely, PMF and UNMIX were employed to establish the contributions from common pollution sources. The contributions from four common sources (groundwater, past mining and industrialisation, natural source, and human activity) contributed 15.57, 42.86, 36.06, and 5.51% according to the PMF model, but 14.73%, 45%, 31.91%, and 8.36% respectively by the UNMIX model. The results of three receptor models showed that heavy metal(loid)s concentrations were mostly influenced by past mining and industrialisation activities. As a result, the identification of the potential sources of heavy metal(loid)s performed better using the APCS-MLR model than PMF and UNMIX model due to its higher R2 value (0.90–1) and lower P/M error (1–1.15). To achieve more reliable and objective conclusions of source apportionment, it was recommended that multiple receptor models be applied
Performance Evaluation of a Subterranean Arsenic Removal (SAR) Community Water Treatment Plant: A Sustainable Long-Term Approach to Removing Arsenic from Drinking Water
No full textSubterranean arsenic removal (SAR) is a low-cost, zero-waste, and ‘easy to operate’ process that can remove arsenic and iron from groundwater without using any adsorption bed. The SAR plant creates an aerobic high Eh bed in the aquifer by recharging oxygenated groundwater, thereby supporting the growth of arsenic and iron oxidizing aerobic bacteria. The arsenic and iron are immobilized in the aquifer sand in the forms of As (V) and Fe(III), respectively. This work reports the key performance data of a SAR plant installed at Ghetugachi village in West Bengal, India under an increased demand three times above the designed production volume. The naturally occurring water has an As concentration of 154 ppb, which was decreased to 13 ppb for 3000 L per day (LPD) water during the period of 2009 to 2015. However, with an increase in demand of up to 10,000 LPD, due to an increase in local consumer population, the As in the SAR treated water increased to 30 ppb. In order to control the As and Fe levels, a novel HAIX-nano Fe resin bead media filter (Lehigh University) was installed in line with the SAR plant thereby reducing the As and Fe in delivery water to 6 ppb and 240 ppb, respectively. This resulted in low filter cost, no filter clogging over the past 6 months, and a lower maintenance cost of both the SAR plant and HAIX media filter. The combined SAR-HAIX plant has been able to maintain a favourable Eh–pH value of the water in order to immobilize the arsenic and iron consistently over the last 6 months of the study. Locally, ~600 people and two schools depend upon the safe water supplied by this plant and the operating cost comes to about $30.00 US dollars a month to produce 10,000 L of safe water per day
The Contamination of Water and Soil from the Dissolution of As-Bearing Mineral Waste in Matehuala, Mexico
No full textExtremely high concentrations of arsenic (As) in groundwater have been reported in central Mexico related to leachates from metallurgical wastes from an abandoned smelter. At the site, contaminated groundwater has been extensively used for maize cultivation for a long time resulting in very high soil pollution. However, the As-containing minerals’ identity, concentration, and solubility remain unresolved. In the present work, highly contaminated soil samples from the area were studied to determine total As concentrations in shallow (0–5 cm) and deepsoils (5–30 cm) and to identify and characterize As-bearing minerals and their solubility behavior. Results showed that soil samples contained up to 4.2% As and the mineralogy consisted mainly of calcite, gypsum, and quartz. Identified arsenic minerals included pharmacosiderite, bukovskýite, scorodite, beudantite, clinoclase, sodium arsenate, adamite, arsenolite, arsenopyrite, orpiment, and a mixture of calcium arsenates (guerinite, haidingerite and pharmacolite). Additionally, As was adsorbed on ferrihydrite. Soil fractionation analysis showed that up to 74% of total As was present in the most mobile fractions, e.g., soluble, exchangeable, phosphate absorbable, and slightly reducible. Furthermore, As solubility in water accounted for up to 60 mg/L at pH 7, explaining the high pollution observed in groundwater and highlighting the risk to humans and ecosystems. According to saturation indices calculations, As may derive from the dissolution of adamite, arsenolite, pharmacolite, and haidingerite, while clinoclase and ferrihydrite may precipitate, counteracting As solubility and mobilization. The results of this study increase knowledge on the identification and solubility of As-bearing minerals in calcicxerosols and semi-arid climatic conditions where considerable contamination is observed in groundwater from As-containing waste disposal
Should routine eye examinations be included in treatment bundles for patients with candidemia?
No full text
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
- …
