1,720,960 research outputs found
Transport Processes and Optimization Strategies in Wetland Design
Get PDFTransitional areas, between inland and coastal environments, represent an important habitat for their environmental and natural value. They act as a natural buffer for all those chemicals which are produced by diffused sources of pollutants (run-off rain water from agriculture) or from hidden sources (sewers not connected to a wastewater treatment plant). Pollutants produced by this type of sources can lead, if not conveniently treated, to eutrophication and to other water quality problems along coastal areas. Traditional wastewater treatment methods appear to be not effective in these conditions because of the big volumes of water and the relatively low concentration of dissolved pollutants to be treated. Since traditional wastewater treatment plants can not be used, it becomes important to better understand transport phenomena in transitional environments (rivers and wetlands) and all the removal processes in such zones in order to manage them to treat all the chemicals before they arrive to the coastal areas. Particular attention must be therefore stressed on retention processes and on the formulation of predictive models which allow scientists and engineers to better manage and design these buffer areas.
In Chapter 1, the role of different transport processes is analyzed focusing the attention on different spatial and temporal scales. Principal modeling approaches are discussed underlining the role of each term on the mass balance equation and the most classical model closures are described in this chapter.
In Chapter 2, retention characteristics of three different rivers are analyzed, relating different model closures with planimetric features of the rivers, their vegetational cover and bottom permeability. The analysis is carried on using STIR (Solute Transport In Rivers) model, a one-dimensional solute transport model that describes concentration breakthrough curves implementing a wide set of retention phenomena characterized by different time scales, represented by a specific residence time distribution in each retention domain. Comparison of modeling results and experimental data shows the capability of the model to characterize, with an inverse analysis, retention processes that occur in a river.
In Chapter 3 a two-dimensional schematic wetland is studied with a numerical model that solves, with a shallow water approach, hydrodynamic and mass transport equations. A specific processing of the numerical results is used to determine numerical residence time distributions of the wetland as a function of a particular vegetation distribution that reproduces a central channel delimited by two lateral, more densely vegetated, banks. To each different density ratio it corresponds a specific shape of the residence time distribution, that present a clear bimodality below a critical value. To model this specific phenomenon, typical in natural environments, a simple and a more easy to use one-dimensional model approach is implemented in the former STIR model. The new version is called STIR-DTD.
In Chapter 4 a new innovative optimization approach to wetland design is defined. Numerical solution of a two-dimensional shallow water model using the open-source suite TELEMAC2D, is integrated with an evolutionary optimization algorithm. At the initial stage of the evolution strategy, the removal efficiency of a random population of individuals (each individual represents a specific distribution of vegetated patches over the wetland domain) is evaluated numerically solving a shallow water hydrodynamic model coupled with a solute transport model. Once the removal efficiency is known, the evolutionary algorithm, using a wide range of selection operators that mimic natural evolution, evolve the initial population to an individual that maximizes the pollutant mass removal. Performed tests show how the optimized distribution tends to cover the maximum wetland available area or, if a maximum vegetated area is kept fixed, how the distribution tends to lengthen the flow paths between the inlet and the outlet section of the wetland.
Chapter 5 shows results of a preliminary analysis on the removal efficiency of randomly distributed vegetation characterized by a Gaussian spatial probability density function. Vegetation density is treated as a random variable characterized by a mean, a variance and an homogeneous correlation length. The effect of each distribution on the removal efficiency is numerically evaluated by a coupled hydrodynamic and solute transport that accounts for the pollutant decay. Results show how removal efficiency is correlated with the statistical parameters of the space probability density function used to generate the random filed
LIFE VIMINE - an integrated approach to the sustainable conservation of intertidal salt marshes in the lagoon of Venice
No full textEvidence of distinct contaminant transport patterns in rivers using tracer tests and a multiple domain retention model
No full textSolute transport in rivers is controlled by surface hydrodynamics and by mass exchanges with distinct retention zones. Surface and hyporheic retention processes can be accounted for separately in solute transport models with multiple storage compartments. In the simplest two component model, short term storage can be associated to in-channel transient retention, e.g. produced by riparian vegetation or surface dead zones, and the long-term storage can be associated to hyporheic exchange. The STIR (Solute Transport In Rivers) multiple domain transport model is applied here to tracer test data from three very different Mediterranean streams with distinctive characteristics in terms of flow discharge, vegetation and substrate material. The model is used with an exponential residence time distribution (RTD) to represent surface storage processes and two distinct modeling closures are tested to simulate hyporheic retention: a second exponential RTD and a power-law distribution approximating a known solution for bedform-induced hyporheic exchange. Each stream shows distinct retention patterns characterized by different timescales of the storage time distribution. Both modeling closures lead to very good approximations of the observed breakthrough curves in the two rivers with permeable bed exposed to the flow, where hyporheic flows are expected to occur. In the one case where the occurrence of hyporheic flows is inhibited by bottom vegetation, only the two exponential RTD model is acceptable and the time scales of the two components are of the same magnitude. The significant finding of this work is the recognition of a strong signature of the river properties on tracer data and the evidence of the ability of multiple-component models to describe individual stream responses. This evidence may open a new perspective in river contamination studies, where rivers could possibly be classified based on their ability to trap and release pollutants
AN INTEGRATED APPROACH TO PREVENT THE EROSION OF SALT MARSHES IN THE LAGOON OF VENICE
Get PDFThe loss of coastal habitats is a widespread problem in Europe. To
protect the intertidal salt marshes of the lagoon of Venice from the
erosion due to natural and human causes which is diffusely and intensely
impacting them, the European Commission has funded the demonstrative
project LIFE VIMINE. LIFE VIMINE aims to protect the most interior,
hard-to-access salt marshes in the northern lagoon of Venice through an
integrated approach, whose core is the prevention of erosion through
numerous, small but spatially-diffuse soil-bioengineering protections
works, mainly placed through semi-manual labour and with low impact on
the environment and the landscape. The effectiveness of protection works
in the long term is ensured through routine, temporally-continuous and
spatially-diffuse actions of monitoring and maintenance. This method
contrasts the common approach to managing hydraulic risk and erosion in
Italy which is based on large, one-off and irreversible protection
actions. The sustainability of the LIFE VIMINE approach is ensured by
the participatory involvement of stakeholders and the recognition that
protecting salt marshes means defending the benefits they provide to
society through their ecological functions, as well as protecting the
jobs linked to the existence or conservation of this habitat
The influence of vegetation distribution on wetland efficiency
Get PDFThis research work aims to find a relationship between the statistics of the vegetation distribution and the removal efficiency, in terms of mass and concentration. It has been made also an attempt to define a couple of dimensionless parameters for correlating the statics with the efficiencyopenEmbargo per motivi di priorità nella ricerca previo accordo con terze part
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
- …
