1,720,987 research outputs found
Frequency domain electromagnetic induction imaging: an effective method to see inside a capped landfill
No full textThe frequency-domain electromagnetic (FDEM) methods are a powerful tool for evaluating the impact caused on natural environments by anthropic facilities such as landfills. Noninvasive FDEM rapidly investigates large areas with no impact on the system. This is essential in case of capped landfills, as the impermeable liner represents a strong limitation for the use of all others direct and indirect investigation methods. This technique allows the propagation of the EM fields and collection of subsurface response below the liner thus representing the only effective solution both for static imaging and time-lapse monitoring of the processes that take place into the waste deposits. Traditionally, electromagnetic data are visualized as apparent electrical conductivity (ECa) maps that give practically no information about the variation of the conductivity with depth because ECa is only the equivalent conductivity of a homogeneous soil that would give the same measured response along depth. More recent approaches allow for an inversion of data thus providing clear information on the thickness of the investigated subsurface layers. The need for building a 3D electromagnetic model is crucial in the context of the urban waste landfill characterization, where leachate induces strong anomalies in electrical conductivity, which in turn causes a nonlinear model of the EMI response. A rigorous EMI inversion approach has been tested at a closed landfill in Southern Italy. The inverted model provided detailed information unattainable with other methods, by corroborating the assumption that electromagnetic measurements represent the best technique to characterize closed systems such as capped landfills
FDEMtools: a MATLAB package for FDEM data inversion
No full textElectromagnetic induction surveys are among the most popular techniques for non-destructive investigation of soil properties, in order to detect the presence of both ground inhomogeneities and particular substances. This paper introduces a MATLAB package, called FDEMtools, for the inversion of frequency-domain electromagnetic data collected by a ground conductivity meter, which includes a graphical user interface to interactively modify the parameters of the computation and visualize the results. Based on a non-linear forward model used to describe the interaction between an electromagnetic field and the soil, the software reconstructs the distribution of either the electrical conductivity or the magnetic permeability with respect to depth, by a regularized damped Gauss-Newton method. The regularization part of the algorithm is based on a low-rank approximation of the Jacobian of the non-linear model. The package allows the user to experiment with synthetic and experimental data sets, and different regularization strategies, in order to compare them and draw conclusions
Integrated modeling of geological, hydro-chemical and geophysical data as a support for a combined chemical-physical and biological groundwater remediation intervention: the contaminated site of the new high speed railway station of Bologna
No full textInversion of multiconfiguration complex EMI data with minimum gradient support regularization: a case study
No full textFrequency-domain electromagnetic instruments allow the collection of data in different configurations, that is, varying the intercoil spacing, the frequency, and the height above the ground. Their handy size makes these tools very practical for near-surface characterization in many fields of applications, for example, precision agriculture, pollution assessments, and shallow geological investigations. To this end, the inversion of either the real (in-phase) or the imaginary (quadrature) component of the signal has already been studied. Furthermore, in many situations, a regularization scheme retrieving smooth solutions is blindly applied, without taking into account the prior available knowledge. The present work discusses an algorithm for the inversion of the complex signal in its entirety, as well as a regularization method that promotes the sparsity of the reconstructed electrical conductivity distribution. This regularization strategy incorporates a minimum gradient support stabilizer into a truncated generalized singular value decomposition scheme. The results of the implementation of this sparsity-enhancing regularization at each step of a damped Gauss--Newton inversion algorithm (based on a nonlinear forward model) are compared with the solutions obtained via a standard smooth stabilizer. An approach to estimate the depth of investigation (DOI), that is, the maximum depth that can be investigated by a chosen instrument configuration in a particular experimental setting, is also
discussed. The effectiveness and limitations of the whole inversion algorithm are demonstrated on synthetic and real datasets
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
Integrated approach in the management of a jet fuel contaminated site. The Decimomannu air base (CA, Sardinia)
No full textUsually, the design of remediation interventions in polluted sites is carried out based on the characterization data, which are aimed
at acquiring the necessary parameters for the Risk Assessment, often utilized for the defiition of the remediation targets. These
data are often, unfortunately, insuffient to identify the best remediation strategy. In particular, the remediation strategy/plan is
usually defied based on characterization data collected (many) years before and that do not take into account the natural “aging”
of potential secondary sources of contamination. This aspect is particularly relevant in the case of fuel contamination, complex
mixtures of hydrocarbons that contain categories of substances with signifiantly diffrent chemical / physical and biodegradability
properties. In the initial phase of the spill, or however when the primary source is active, the most soluble components (i.e. BTEX)
are mobilizable in the groundwater flw and aerobic biodegradation processes are active on the more readily degradable fractions
(linear hydrocarbons with shorter chain). The progressive aging of the contamination source corresponds to a depletion of the more
mobile and degradable fractions, with the accumulation of high molecular weight fractions, less transferable to both aqueous and
soil gaseous phase. Therefore, the accurate characterization of the residual phase’s real characteristics allows the defiition of the best
remediation strategy. An illustrative case history is here presented concerning the Military Airport of Decimomannu (CA), affcted by various aviation fuel (JP8) spills in 2007 (40000 l), in 2009 (5000 l) and in 2010 (5000 l). The creation of a “4D” geographical database (which also considers the timing factor) allows the integrated management, representation and analysis of diffrent data (geological, hydrogeological, hydrogeochemical and geophysical). The data used for the construction of a georeferenced database, have been enriched by fild hydraulic tests and detailed speciation, through GC-MS, of supernatant that has been occasionally detected over the years in the piezometric monitoring network. A campaign has been conducted on the site with the UVOST-LIF (Laser Induced Fluorescence) technology, the fist performed in our country, which allowed to delimit the volumes of subsoil previously impacted by the primary spills. The laboratory and fild investigations carried out have made it possible to identify the presence of contaminants in the residual phase. Based on the results, an in situ enhanced chemical desorption strategy was implemented to increase the desorption of hydrocarbons adsorbed to saturated soils or at the capillary fringe and to increase the product recoverability in a separate phase. The hydrocarbons are made available in the dissolved phase or in a separate phase with lower viscosity, allowing a subsequent rapid and effctive physical recovery. The integration of the large amount of information has allowed to outline a conceptual model of the site more representative of the current situation and essential for defiing the correct intervention strategy
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
- …
