1,720,961 research outputs found
Some analytical solutions for two-dimesional convection-dispersion equation in cylindrical geometry
No full textIn this paper some analytical solutions are given for a two-dimensional advection equation with anisotropic dispersion. Chemical
decay or adsorption-like reaction inside the liquid phase is considered. Bessel function expansion is used to solve the second order
PDE model with different initial conditions, corresponding to usual experimental practices. Cylindrical geometry is considered since
large columns could be adopted to investigate both anisotropic dispersion and adsorption/desorption kinetic mechanisms
Estimation of transport and kinetic parameters using analytical solutions of the 2D advection-dispersion-reaction model
No full textWe propose some analytical solutions of the advection-dispersion equation and adopt them to solve a non-linear parameter estimation problem. A solution with no reactive term and another one with a unique coefficient representing the kinetic mechanisms of the solute decay in groundwater are described in detail and are then considered in the estimation procedure. To test the robustness of these analytical solutions if adopted in inverse problems, the anisotropic dispersion and kinetics are estimated using sets of experimental data simulated by Monte Carlo techniques. Cylindrical geometry is considered since large columns are the most common devices adopted to study both
dispersion and kinetics mechanisms and, even if the solutions are expressed in terms of Bessel function expansion, they give very good results in terms of reliability and precision of our estimates. Discussion of results is based on the analysis of residuals, variance-covariance matrix and bias of parameters. The influence of location and time of sampling and of the number of samples on the estimates of dispersion and kinetic parameters is also analysed by means of Analysis of Variance and Fisher tests
A new method for laboratory estimation of the transverse dispersion coefficient
No full textWe introduce a method for identifying the transverse dispersion coefficient in laboratory experiments based on the analytical solution of pulse injection of a nonreactive solute in a soil column (cylindrical geometry) packed with a homogeneous porous medium. This method takes into account the effect of boundary conditions such as no flux on the column perimetr, and it does not need a priori knowledge of the longitudinal dispersion coefficient. Numerical applications of the method show that it is stable and robust and that the results are reasonably in accordance with those found using the classical maximum likelihood method
Integrated air stripping for remediation of soils contaminated by organic compounds
No full textThis paper presents the results of a laboratory scale investigation on the remediation of a soil contaminated by a mixture of organic compounds using a two-step process consisting of stripping and biofiltration. The biofilter was packed with the soil under examination in order to use autochthonous microorganisms. To assess the effects of both temperature and superficial velocity of the air stream on process performance different sets of experimental tests were carried out at two air temperatures (50 and 80 degrees C), and at two superficial air velocities (41.0 and 82.0 m h(-1)), corresponding to apparent air residence times in the biofilter column of 38 and 19s respectively. The stripping rate proves to be inversely correlated with the soil-water partitioning coefficient, while no evident correlation was found with the Henry coefficient. It can therefore be concluded that soil-water partitioning is limited by mass transfer while air-water partitioning reaches equilibrium. Temperature influences both stripping rate in the stripping column and degradation capacity in the biofilter. A stripping temperature of 80 degrees C combined with a biofiltration temperature of WC provides the best process performance. (c) 2007 Society of Chemical Industry
Metodi ottici per lo studio della dispersione di inquinanti in mezzi porosi: costruzione e messa a punto di un modello sperimentale bidimensionale
No full textNel presente articolo viene descritta la costruzione
e la messa a punto di un modello fisico bidimensionale
che è stato progettato per indagare i complessi
problemi connessi al trasporto di soluti in mezzi porosi. Il
modello sperimentale, sviluppato a scala di laboratorio, è
costituito da un mezzo poroso trasparente bidimensionale;
esso utilizza una tecnica ottica non invasiva associata ad un
tracciante fluorescente (fluoresceina sodica) per monitorare
il movimento del soluto stesso. Grazie ad un’illuminazione
ultravioletta, il tracciante emette luce nel visibile ed è
rilevato da una fotocamera digitale dotata di Charged
Coupled Device (CCD). L’immagine è analizzata per stimare
la distribuzione bidimensionale della concentrazione del
tracciante utilizzato. Le prime misure di concentrazione
mostrano che il modello fornisce una rappresentazione efficace
dell’evoluzione di un pennacchio di contaminante
all’interno di una matrice porosa omogenea costruita da
palline di vetro del diametro medio di 1 mm. Sviluppi futuri
riguarderanno l’utilizzo di una matrice non omogenea,
capace di simulare quanto riscontrabile a scala di campo,
nonché il confronto dei risultati sperimentali con modelli
numerici descriventi processi di trasporto di soluti in mezzi
porosi
SPATIAL MOMENTS ANALYSIS: AN APPLICATION TO QUANTITATIVE IMAGING OF CONTAMINANT DISTRIBUTION IN POROUS MEDIA
No full textWith the aim of characterizing complex solute transport problems in porous media, a two-dimensional physical model has been designed and constructed and is described in this paper along with some results relative to the estimation of the dispersive parameters and the pore water velocity. The experimental setup, simulating a fixed bed, uses a transmitted light imaging technique in conjunction with a fluorescent dye tracer (sodium fluorescein) to monitor solute movements
Assessment of Nitrate Hazards in Umbria Region (Italy) Using Field Datasets: Good Agriculture Practices and Farms Sustainability
No full textThe Nitrates Directive, EU 91/676/EEC, obliged all European Union member states to introduce laws that guarantee the use of proper agriculture and farm methods, with the aim to reduce pollution resulting from the excessive use of nitrates. In this work, we estimated the potential and effective nitrogen load from agriculture, farms, civil, and industrial sources in Umbria region, Italy, and assessed the previous (and actual) contamination by nitrates at different scales. The adopted methodology uses databases of the sources, such as the type of fertilizer (inorganic or manure), the type of industrial site, the census of livestock and field data at a local, basin, and regional scale. Hydrological and geological models are used to compute infiltration. The study shows that the contribution of farms to nitrate pollution is in the order of swine > cattle > sheep and goats; while the highest agricultural load is due to arable land, followed by olive and grape. The study also shows that municipalities that have values of nitrates over the threshold for both groundwater and surface water can rapidly change their status during consecutive years. This means that rules for farm sustainability, complying with the Nitrates Directive, EU 91/676/EEC, should be defined at a sub-basin scale, where the hydrogeological conditions strongly influence infiltration
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
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