108 research outputs found
The design of transportation networks: a multi objective model combining equity, efficiency and efficacy
A network design problem consists in locating facilities (nodes and arcs) that enable the transfer of flows (passengers and/or goods) from given origin-destination pairs. The topic can have several applications within transportation and logistics contexts. In this work we propose a multi-objective model in which balancing or equity aspects, i.e. measures of the distribution of distances of users from the path, are considered. These kinds of models can be used when there is the need to balance risks or benefits among all the potential users deriving from the location of the path to be designed. The application of the proposed model to a benchmark problem used in the literature to test these kinds of models, shows that it is able to find solutions characterized by significant level of equity but also of efficiency and efficacy
Balancing the arrival times of users in a two-stage location problem
There has been a number of facility location problems dealing with the introduction of the equity issue in the travel distances distribution. In this paper we analyze a new aspect of equity concerning the distribution of the arrival times of customers. Given a depot and a set of demand points generating flow which also represent potential locations, we consider a discrete two-stage location problem whose aim is to locate a given number of facilities and to allocate the demand points to a facility. We assume as objective the maximization of the minimum difference between two consecutive arrival times of flows to the depot through the patronized facility. This particular equity measure is introduced in order to reduce risks of congestion in the dynamic of flow arrivals at the common destination. The problem is described through two Integer Programming formulations. Computational results for solution methods based on both formulations are then shown and analyzed
A general space-time model for combinatorial optimization problems (and not only)
We consider the problem of defining a strategy consisting of a set of facilities taking into account also the location where they have to be assigned and the time in which they have to be activated. The facilities are evaluated with respect to a set of criteria. The plan has to be devised respecting some constraints related to different aspects of the problem such as precedence restrictions due to the nature of the facilities. Among the constraints, there are some related to the available budget. We consider also the uncertainty related to the performances of the facilities with respect to considered criteria and plurality of stakeholders participating to the decision. The considered problem can be seen as the combination of some prototypical operations research problems: knapsack problem, location problem and project scheduling. Indeed, the basic brick of our model is a variable xilt which takes value 1 if facility i is activated in location l at time t, and 0 otherwise. Due to the conjoint consideration of a location and a time in the decision variables, what we propose can be seen as a general space-time model for operations research problems. We discuss how such a model permits to handle complex problems using several methodologies including multiple attribute value theory and multiobjective optimization. With respect to the latter point, without any loss of the generality, we consider the compromise programming and an interactive methodology based on the Dominance-based Rough Set Approach. We illustrate the application of our model with a simple didactic example
A multiple criteria methodology for prioritizing and selecting portfolios of urban projects
This paper presents an integrated methodology supporting decisions in urban
planning. In particular, it deals with the prioritization and the selection of
a portfolio of projects related to buildings of some values for the cultural
heritage in cities. More precisely, our methodology has been validated to the
historical center of Naples, Italy. Each project is assessed on the basis of a
set of both quantitative and qualitative criteria with the purpose to determine
their level of priority for further selection. This step was performed through
the application of the Electre Tri-nC method which is a multiple criteria
outranking based method for ordinal classification (or sorting) problems and
allows to assign a priority level to each project as an analytical
"recommendation" tool. To identify the efficient portfolios and to support the
selection of the most adequate set of projects to activate, a set of resources
(namely budgetary constraints) as well as some logical constraints related to
urban policy requirements have to be taken into consideration together with the
priority of projects in a portfolio analysis model. The process has been
conducted by means of the interaction between analysts, municipality
representative and experts. The proposed methodology is generic enough to be
applied to other territorial or urban planning problems. We strongly believe
that, given the increasing interest of historical cities to restore their
cultural heritage, the integrated multiple criteria decision aiding analytical
tool proposed in this paper has significant potential to be used in the future
Extending large-scale forest inventories to assess urban forests
Urban areas are continuously expanding
today, extending their influence on an increasingly
large proportion of woods and trees located
in or nearby urban and urbanizing areas, the socalled
urban forests. Although these forests have
the potential for significantly improving the quality
the urban environment and the well-being of
the urban population, data to quantify the extent
and characteristics of urban forests are still lacking
or fragmentary on a large scale. In this regard,
an expansion of the domain of multipurpose forest
inventories like National Forest Inventories
(NFIs) towards urban forests would be required.
To this end, it would be convenient to exploit the
same sampling scheme applied in NFIs to assess
the basic features of urban forests. This paper considers
approximately unbiased estimators of abundance
and coverage of urban forests, together with
estimators of the corresponding variances, which
can be achieved from the first phase of most largescale
forest inventories. A simulation study is carried
out in order to check the performance of the
considered estimators under various situations involving
the spatial distribution of the urban forests
over the study area. An application is worked out
on the data from the Italian NFI.L'articolo è disponibile sul sito dell'editore www.springer.co
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