1,720,959 research outputs found
Multivariate statistical and geostatistical techniques for redox zonation assessment in a tropical alluvial aquifer
No full textWhen high concentrations of Mn and Fe are detected in groundwater, the redox processes are likely occurring in the aquifer. They are due to organic matter oxidation, which can be naturally present in the solid matrix or released in the aquifer by anthropic activities. Thus, the definition of redox zonation within an aquifer can be an effective tool for the conceptual model refinement in remediation strategies planning. In developing countries, either the incorrect management of wastewaters or the land use distribution can affect the environmental quality of surface-water, creating eutrophication conditions in the main streams. In hydrogeological contexts where a multilayer alluvial aquifer is connected with surface-water, also the groundwater quality degrades and redox processes can occur. This issue complicates the groundwater study, its exploitation for drinking purpose
and its management. The objectives of the study are to investigate the effect of the surface-water/groundwater interactions of San Pedro Sula alluvial aquifer, located in north-western Honduras, on the redox zonation, performing a partition of the aquifer in homogeneous areas.
The datasets available refer to 2 monitoring rounds performed in 2002 (wet and in the dry season) consisting of 94 groundwater samplings. In each sample, chemico-physical parameters (pH, EC, Temp, Turb) and analytes (Na, K, Ca, Mg, HCO3, Cl, SO4, NO3, NH4, PO4, Fe, Mn) have been assessed. To assess hydrogeochemical spatial relationships among the variables involved in the redox processes, a multivariate geostatistical approach was performed, called Factorial cokriging, consisting in three main steps: 1) Gaussian anamorphosis to transform raw variables into Gaussian transformed variables; 2) fitting a Linear Model of Coregionalization, including the variogram models of both direct and cross-variograms; 3) extraction and interpolation of the sets of scale-dependent regionalized factors. The first results show a strong relation of Mn concentration with redox processes, which may be ascribed to the organic matter transfer from heavy polluted surface-water to the aquifer. For Fe, its relation to turbidity can be due to a fine colloidal phase developed when different groundwaters, characterized by distinct redox conditions, mix up in the wells
New insights on advanced redox zonation of aquifers using multivariate geostatistics: the San Pedro Sula case study
No full textThe incorrect land use and wastewater management represent anthropogenic pressures on the environment,
which can create heavy euthrophication conditions in surface-water. When surface-water/groundwater
relationships exist, the organic matter produced in the euthrophicated streams can be transferred into the aquifer,
triggering redox processes (i.e. Terminal Electron Accepting Processes, TEAPs). These hydrogeochemical
processes provoke severe groundwater quality modifications (e.g. Mn and Fe solubilization), that complicate
its exploitation and management. The definition of the redox zonation of aquifers represents an effective tool
for the identification of the pollution sources and for the conceptual model refinement, when remediation
strategies and groundwater management plans need to be implemented.
The study area is the San Pedro Sula aquifer (north-western Honduras), which is a multi-layer alluvial
aquifer characterized by well-known surface-water/groundwater interactions and by heavy euthrophicated
streams. Here, high concentrations of Mn and Fe have been found in the aquifer (Di Curzio et al., 2016).
Although the redox processes are dynamic reactions, the redox zonation is generally aimed to identify
homogenous zones within an aquifer characterized by a predominant TEAP (McMahon & Chapelle, 2008).
To overcome this methodological approach, the Multi-Collocated Factorial Kriging (MCFK) (Sollitto et
al., 2010) has been applied to chemico-physical parameters and analytes, diagnostic of the redox processes
(i.e. temperature, pH, turbidity, Mn, Fe, NO3, NH4, PO4). These parameters have been measured in 93 wells,
both in the wet and dry season. In addition, the distance from the surface-water has been selected as an auxiliary
variable, essential to perform the MCFK, because the eutrophicated streams have been considered one of the
pollution sources.
The MCFK results show a short range variability, highlighting a strong relation between Mn concentrations
and redox processes, due to the organic matter transfer from heavy polluted surface-water to the aquifer.
Simultaneously, the relation between Fe and turbidity can be due to a fine colloidal phase, developed when
different redox conditions of groundwater mix up in the wells. At a wider range, Fe seems to be related with
redox processes, near the other pollution source detected in the northern San Pedro Sula alluvial plain
The application of multivariate geostatistical techniques for the study of natural attenuation processes of chlorinated compounds
No full textThe application of multivariate geostatistical techniques for the study of natural attenuation processes of chlorinated compounds
No full textModeling spatial variability of environmental parameters through the application of modem techniques of geostatistics has permitted to acquire elements apt to evaluate the possibility of using natural attenuation as a remediation technique for groundwater contaminated by chlorinated compounds. Moreover, a precise delineation of hazardous areas in a polluted site is strongly based on accurate predictions of contaminant concentrations, a task that is complicated by the presence of censored data and highly positively skewed distributions.
The present work proposes a geostatistical approach that includes different methods for the study and the control of the ongoing activity of natural attenuation in an abandoned industrial area. The considered variables in this application are the values of concentration in groundwater of some aliphatic chlorinated carcinogenic compounds (PCE and TCE), measured in numerous piezometers, which show highly skewed distributions, characterized by a considerable number of values below the detection limit of the instrument.
Indicator Kriging has been applied and the areas with 90% probability of exceeding the detection limit have been considered, inside which the variables were transformed through gaussian anamorphosis. The application of geostatistics has put into evidence the existence of a correlation between them not only from the chemical point of view, but also from the point of view of their spatial distribution: the shared presence of "hot spot" areas might be imputed to the existence of localized hazard sources. In those areas it is possible to detect coherence between the concentrations of the contaminants in study and of the parameters that control the phenomenon, which might be considered a clue that the degrading chemical activity is in progress.
In the areas characterized by higher uncertainty for both variables (PCE and TCE), it is possible to presume that the phenomenon of attenuation is in progress, because it is in those areas that the transformations from PCE to TCE may happen in function of the parameters that control the phenomenon
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
Delineation of site-specific management zones using geostatistics and fuzzy clustering analysis
No full textThe application of site-specific techniques and technologies in precision agriculture requires the identification of contiguous homogenous zones within a field, often referred as management zones (MZ). The delineation of MZ involves some sort of clustering, however there is not a widely accepted method. The application of fuzzy set theory to clustering algorithm has allowed researchers to better account for the continuous variability in natural phenomena. Moreover, the methods based on nonparametric density estimation can detect clusters of unequal size and dispersion. The objective of this paper is to compare different procedures of clustering in order to assist researchers and producers in delineating within- field management zones. One hundred georeferenced measurements of soil, radiometric and crop attributes were collected on a 12-ha durum wheat field in two seasons in south-east Italy. All variables were interpolated on a 1×1 m grid using geostatistical techniques of kriging and cokriging. We compared the following techniques: (1) iterative Self-Organising Data Analysis Technique (ISODATA); (2) fuzzy c-means method; (3) non-parametric density algorithm. All the methods produced consistent results, creating the subdivision of the field into 2 or 3 distinct classes of suitable size for site-specific management. The clusters differed mainly in soil textural properties and crop response. Fuzzy c-means algorithm provides the user with two performance indices to choose the most appropriate number of clustering for creating MZ. Nonparametric density algorithm allows to assess the local variation within each cluster
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
- …
