1,720,976 research outputs found
Tecniche idrogeofisiche per la caratterizzazione di un acquifero eterogeneo
No full textTecniche idrogeofisiche per la caratterizzazione di un acquifero eterogene
LABORATORIO HYDROGEOSITE: PRIMI ESPERIMENTI IDROGEOFISICI
No full textLaboratorio hydrogeosite: primi esperimenti idrogeofisic
Estimating of the transmissivities of a real aquifer using a Self Potential signals associated with a pumping test
No full textIn this article, experimental hydraulic heads and electrical (self-potential) signals associated with a pumping test were used in an inverse model to estimate the transmissivity distribution of a real aquifer. Several works reported in the literature show that there is a relatively good linear relationship between the hydraulic heads in the aquifer and electrical signals measured at the ground surface. In this experimental test field, first, the current coupling coefficient was determined by the best fit between experimental and modeled self-potential signals at the end of the pumping phase. Soon afterward, with the hydraulic heads obtained from the self-potential signals, the transmissivity distribution of the aquifer was conditioned by means an inverse model based on the successive linear estimator (SLE). To further substantiate the estimated T field from the SLE analysis, we analyzed the drawdown rate, the derivative of the drawdown with respect to the ln(t), because the drawdown rate is highly sensitive to the variability in the transmissivity field. In our opinion, these results show that self-potential signals allow the monitoring of subsurface flow in the course of pumping experiments, and that electrical potentials serve as a good complement to piezometric observations to condition and characterize the transmissivity distribution of an aquifer
Assessment of natural background levels in potentially contaminated coastal aquifers
Full text linkThe estimation of natural background levels (NBLs) of dissolved concentrations of target chemical species in subsurface reservoirs relies on a proper assessment of the effects of forcing terms driving flow and transport processes taking place within the system and whose dynamics drive background concentration values. We propose coupling methodologies based on (a) global statistical analyses and (b) numerical modeling of system dynamics to distinguish between the impacts of different types of external forcing components influencing background concentration values. We focus on the joint application of a statistical methodology based on Component Separation and experimental/numerical modeling studies of groundwater flow and transport for the NBL estimation of selected chemical species in potentially contaminated coastal aquifers. We consider a site which is located in Calabria, Italy, and constitutes a typical example of a Mediterranean coastal aquifer which has been subject to intense industrial development. Our study is keyed to the characterization of NBLs of manganese and sulfate and is geared to the proper identification of the importance of a natural external forcing (i.e., seawater intrusion) on NBL assessment. Results from the Component Separation statistical approach are complemented by numerical simulations of the advective-dispersive processes that could influence the distribution of chemical species (i.e., sulfate) within the system. Estimated NELs for manganese are consistent with the geochemical composition of soil samples. While Component Separation ascribes the largest detected sulfate concentrations to anthropogenic sources, our numerical modeling analysis suggests that they are mainly related to the natural process of seawater intrusion. Our results indicate that the use of statistical methodologies in complex groundwater systems should be assisted by a detailed characterization of the dynamics of natural (and/or induced) processes to distinguish effective anthropogenic contamination from natural conditions and to define realistic environmental clean-up goals
Stochastic characterization of the Montalto Uffugo reasearch site (Italy) by geostatistical inversion of moment equations of groundwater flow.
No full textWe assess the applicability and performance of a methodology of inverting stochastic mean groundwater flow equations to characterize the spatial variability of (natural) log-transmissivity (Y) of a heterogeneous aquifer. The methodology, originally proposed by Hernandez et al. (2003, 2006), relies on a nonlinear geostatistical inverse algorithm for recursive approximations of steady-state (ensemble) mean groundwater flow that allows estimating jointly the spatial variability of Y, the underlying variogram parameters, and the variance-covariance of the estimates. Estimates of prediction errors of hydraulic heads and fluxes are then calculated a posteriori, upon solving equations satisfied by the corresponding co-variances. Here, we extend the methodology to quasi-steady state flow conditions and present its first field application by using information collected during a pumping test performed at the Montalto Uffugo research site (Italy). Log-transmissivity is parameterized geostatistically on the basis of an available measured value and a set of unknown values at discrete pilot points. Best estimates of Y at the measurement location and at the pilot points are obtained by a maximum likelihood fit of computed and measured heads. These posterior estimates are then projected onto the computational grid by kriging. Information on head drawdowns is provided through self-potential signals recorded by 47 surface electrodes during the test. The maximum likelihood-based objective function includes a regularization term reflecting prior information about Y. The relative weight assigned to this term is evaluated separately from other model parameters to avoid bias and instability. We explore the effectiveness of both a zero- and a second-order closure of the mean flow equation at providing a proper geostatistical characterization of the log-transmissivity field. The parameters of the variogram of Y are estimated a posteriori using formal model selection criteria. The adoption of a second-order mean flow model renders the sharpest definition of the regularization term and of the Y variogram parameters
Caratterizzazione di un sito sperimentale sedimentario sulla base di informazioni sedimentologiche e geofisiche
No full textSi presenta la caratterizzazione di un acquifero sedimentario eterogeneo mediante l’uso congiunto di osservazioni sedimentologiche, idrauliche e geofisiche. L’acquifero è concettualizzato con modello a continui multipli. La ricostruzione dell’architettura interna del sistema è effettuata a partire da informazioni sedimentologiche (porosità) ottenute mediante una sonda a neutroni ed attraverso una applicazione di Kriging ad indicatori multipli. La struttura variografica degli indicatori che individuano i diversi litotipi è analizzata mediante criteri formali di identificazione di modelli. La distribuzione spaziale della conducibilità idraulica è condizionata su misure piezometriche e di potenziale spontaneo, ottenute durante una lunga campagna sperimentale, svolta al Boise Hydrogeophysical Research Site, Idaho, in cui sono stati effettuati una serie di test di emungimento/iniezione con una configurazione a dipolo. I dati di carico idraulico sono ottenuti da usuali letture piezometriche e rappresentano un valore integrato sulla profondità. I segnali di potenziale spontaneo restituiscono la stima della posizione della superficie freatica. La procedura adottata consente la ricostruzione tridimensionale dell’eterogeneità del sito con un livello di dettaglio che non è stato possibile ottenere negli studi precedenti e con modesti sforzi computazionali. La robustezza dei risultati è stata analizzata utilizzando il modello calibrato per la riproduzione di risultati di test con dipolo non utilizzati nella procedura di inversione
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
Guidelines for validation and verification of groundwater mathematical studies (GULLIVER): a case study
No full textThe goal of this work is to define a set of guidelines for “validating" mathematical models that are to be used in real-world problems of subsurface flow and contaminant transport. Groundwater models today are being used to study increasingly complex problems involving large temporal and spatial scales and with many uncertainties inherent in the data and in the
models themselves. It becomes important therefore to establish procedures
and benchmark tests with which to assess a given model's adequacy for
simulating a specific groundwater problem. In the GULLIVER project we
propose to create a public library of phenomenological schemes (PS), each
one satisfactorily solved by an established model. A user with a specific
application and model at hand can select the PS that most closely corresponds to his application, and corroborate his model against the established solution. The user's model is considered validated when the two numerical solutions match according to specified criteria. In this paper we describe this methodology and present its application to a 2D saturated flow and transport test case based on data from a field study site in Calabria, Italy.281-29
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
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