1,720,958 research outputs found
Planning and concession management under port co-operation schemes: A multiple case study of Italian port mergers
No full textRecent governance reforms have driven many ports to introduce innovative co-operation schemes, including the merger of Port Authorities (PAs). Port merger is generally characterized by a certain level of complexity due to the challenges that ports must face within the most critical management processes affected by port amalgamation.
This paper aims to identify and analyse the main challenges that might emerge within two of these critical processes: port planning and concession management. This study undertakes a multiple case study analysis of two newly merged PAs: Genoa-Savona, as the major multi-site gateway port in Italy, and Naples-Salerno, which was renamed as the PA of the Central Tyrrhenian Sea.
The main findings of both case studies emphasize the existence of challenging areas that may result in either opportunities or threats, which can also depend on the managerial skills of PA organizations
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
Quasi-dynamic estimation of o-d flows from traffic counts: formulation, statistical validation and performance analysis on real data
No full textThe paper proposes a “quasi-dynamic” framework for estimation of origin-destination (o-d) flow from traffic counts, under the assumption that o-d shares are constant across a reference period, whilst total flows leaving each origin vary for each sub-period within the reference period. The advantage of this approach over conventional within-day dynamic estimators is that of reducing drastically the number of unknowns given the same set of observed time-varying traffic counts. Obviously, the gain in accuracy depends on how realistic is the underlying assumption that total demand levels vary more rapidly over time than o-d shares. Firstly, the paper proposes a theoretical specification of the quasi-dynamic estimator. Subsequently, it proposes empirical and statistical tests to check the quasi-dynamic assumption and then compares the performances of the quasi-dynamic estimator of o-d flows with both classical off-line simultaneous dynamic estimators and on-line recursive Kalman filter-based estimators. Experiments are carried out on the real test site of A4-A23 motorways in North-Eastern Italy. Results confirm the acceptability of the assumption of quasi-dynamic o-d flows, even under the hypothesis of constant distribution shares for the whole day and show that the quasi-dynamic estimator outperforms significantly the simultaneous estimator. Data also suggest that using the quasi-dynamic estimates instead of the simultaneous estimates as historical o-d flows improves significantly the performances of the Kalman filter, which strongly depends of the quality of the seed o-d flows. In addition, it is shown that the aggregation of quasi-dynamic o-d estimates across subsequent time slices represents also the most effective way to obtain o-d estimates for larger time horizons (e.g. hourly estimates). Finally, a validation based on an hold-out sample of link flows (i.e. counts not used as inputs in the o-d estimation/updating process) revealed the quasi-dynamic estimator to be overall more robust and effective with respect to the other tested estimators
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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