733 research outputs found
Corpus ItaIst
No full textCorpus ItaIst
The corpus containing 198 texts was collected by the research unit of the University of Molise including linguists (Giuliana Fiorentino, Vittorio Ganfi), jurists (Alessandro Cioffi, Maria Assunta Simonelli, Ludovico Di Benedetto) and computer scientists (Rocco Oliveto, Marco Russodivito).
The corpus is diatopically balanced (it contains texts from the PAs of 8 Italian regions) and includes different types of administrative acts with which the PAs address citizens
Candia: ricordi di escursione (illustrati con fotografie e disegni dell'autore)
No full textPreface.Appendix.Dedication:Content description: TitleIllustration: (Maps ,Views ,portraits ,)Pagination: PP10+180PVolumes: 1Text Genre:Prose / JournalIllustration: (χάρτες ,τοπία ,πορτραίτα ,
A practically tractable expression of the covariances of the Cross-Nested Logit model
No full textThis paper proposes a practically tractable mathematical procedure for the calculation of the covariances underlying whatever given Cross-Nested Logit (CNL) model, based on the variance of a one-dimensional random variable, whose cumulative distribution function and density probability function are given in closed form. This allows expressing the CNL covariances as a function of just a one-dimensional integral, which can be evaluated easily and effectively by means of standard numerical techniques, implementable also in basic computer spreadsheets. Firstly, a formal theoretical proof of the procedure is illustrated. Then, a comparison with the calculations performed by Marzano and Papola [Marzano, V., Papola, ., 2008. On the covariance structure of the Cross-Nested Logit model. Transportation Research B 42(2), 83-98] is proposed, and details about the practical implementation of the procedure are discussed. Finally, estimation of the CNL model in contexts with prior expectations on covariances/correlations is addressed practically, thanks to the simplification achieved in the calculation of the CNL covariances
Empirical comparison of parametric and nonparametric trade gravity models
No full textA systematic comparison is made of parametric (i.e., ordinary leastsquares regressions and related generalizations) and nonparametric (i.e., kernel regressions and regression trees) log-linear gravity models for reproducing international trade. Experiments were conducted to estimate a log-linear gravity model reproducing import and export trade fows in quantity between Italy and 13 world economic zones, based on a panel estimation data set. The best parametric regression model was estimated to defne a baseline reference model. Some spec-ifcations of nonparametric models, belonging to the categories of kernel regressions and regression trees, were also estimated. The performance of parametric and nonparametric models is contrasted through a comparison of goodness-of-ft measures (R2, mean absolute percentage error) both in estimation and in hold-out sample validation. To assess the differences in model elasticity and forecasts, both parametric and nonparametric models are applied to future scenarios and the corresponding results compared
A network sensor location procedure accounting for o-d matrix estimate variability
No full textThe paper illustrates an innovative and theoretically founded methodology for solving the network sensor location problem (NSLP), explicitly accounting for the variability of the o-d matrix estimate. The proposed approach is based on a specific measure, termed synthetic dispersion measure (SDM), related to the trace of the covariance matrix of the posterior demand estimate conditional upon a set of sensor locations. Under the mild assumption of multivariate normal distribution for the prior demand estimate, the proposed SDM does not depend on the specific values of the counted flows – unknown in the planning stage – but just on the locations of such sensors. From a practical standpoint, a stepwise algorithm is implemented for calculating the proposed measure given a set of link counts, which avoids matrix inversion. In addition, a sequential heuristic algorithm is presented for the application of the proposed NSLP to real contexts. The methodology also allows a formal budget allocation problem to be set between surveys and counts in the planning stage, in order to maximize the overall quality of the demand estimation process
Methodology for Locating Link Count Sensors That Accounts for Reliability of Prior Estimates from Origin–Destination Matrices
No full textThe paper proposes an innovative methodology for addressing the issue of the optimal link count sections location, based on the proposition of a reliability measure in which the prior accuracy of the o-d matrix estimate, that is its statistical distribution rather its prior punctual estimate, is explicitly considered, together with its posterior distribution conditioned on a given subset of link count
locations. Notably, the proposed measure, under the mild assumptions of prior normal distribution and through appropriate algebraic rotations of the reference system, is proved not to depend on the unknown values of the counted flows, and this is actually the key point allowing for effective implementation of a fast and operational procedure based on this mathematical framework, in the sense stated in the introduction. As an example, toy network and real network applications are
presented, in order to show how a heterogeneous level of knowledge across o-d pairs may lead to the choice of counting sections different from those resulting from the commonly adopted procedures.
The proposed methodology allows for a more effective theoretical interpretation of the phenomenon and leads to a very efficient computational procedure - suitable also in real size networks - whose results outperform those obtained with the methods to date available in the literature
A modelling framework for the design of sustainable integrated regional transit systems: the case study of Campania region (Italy)
No full textLimits and perspectives of effective O-D matrix correction using traffic counts
No full textCorrection of the O–D matrix from traffic counts is a classical procedure usually adopted in transport engineering by practitioners for improving the overall reliability of transport models. Recently, Papola and Marzano showed through laboratory experiments that this procedure is generally unable to provide for effective correction of the O–D matrix. From a theoretical standpoint, this result can be justified by the lower number of (stochastic) equations (independent observed link flows) with respect to the unknowns (O–D flows). This paper first confirms that this represents the main reason for the failure of this procedure, showing that satisfactory correction is generally obtained when the number of equations is greater than the number of unknowns. Then, since this circumstance does not occur in practice, where the number of O–D pairs usually far exceeds the number of link counts, we explore alternative assumptions and contexts, allowing for a proper balance between unknowns and equations. This can be achieved by moving to within-day dynamic contexts, where a much larger number of equations are generally available. In order to bound the corresponding increase in the number of unknowns, specific reasonable hypotheses on O–D flow variation across time slices must be introduced. In this respect, we analyze the effectiveness of the O–D matrix correction procedure in the usually adopted linear hypothesis on the dynamic process evolution of O–D flows and under the assumption of constant distribution shares. In the second case it is shown that satisfactory corrections can be performed using a small number of time slices of up to 3 min in length, leading to a time horizon in which the hypothesis of constant distribution shares can be regarded as trustworthy and realistic
- …
