312,755 research outputs found
Catchment classification based on characterisation of streamflow and precipitation time series
No full textThe formulation of objective procedures for the delineation of homogeneous groups of catchments is a fundamental issue in both operational and research hydrology. For assessing catchment similarity, a variety of hydrological information may be considered; in this paper, gauged sites are characterised by a set of streamflow signatures that include a representation, albeit simplified, of the properties of fine time-scale flow series and in particular of the dynamic components of the data, in order to keep into account the sequential order and the stochastic nature of the streamflow process. The streamflow signatures are provided in input to a clustering algorithm based on unsupervised SOM neural networks, obtaining groups of catchments with a clear hydrological distinctiveness, as highlighted by the identification of the main patterns of the input variables in the different classes and the interpretation of their interrelations. In addition, even if no geographical, morphological nor climatological information is provided in input to the SOM network, the clusters exhibit an overall consistency as far as location, altitude and precipitation regime are concerned. In order to assign ungauged sites to such groups, the catchments are represented through a parsimonious set of morphometric and pluviometric variables, including also indexes that attempt to synthesise the variability and correlation properties of the precipitation time series, thus providing information on the type of weather forcing that is specific to each basin. Following a principal components analysis, needed for synthesizing and better understanding the morpho-pluviometric catchment properties, a discriminant analysis finally assigns the ungauged catchments, through a leave-one-out cross validation, to one of the above identified hydrologic response classes. The approach delivers a quite satisfactory identification of the membership of ungauged catchments to the streamflow-based classes, since the comparison of the two cluster sets shows a misclassification rate of around 20%. Overall results indicate that the inclusion of information on the properties of the fine time-scale streamflow and rainfall time series may be a promising way for better representing the hydrologic and climatic character of the study catchments
Guest Editorial to the Feature Cluster “New Trends in Applied Combinatorial Optimization” (EURO/ALIO 2018)
No full textApplied Combinatorial Optimization has always received large interest in the scientific community. Thanks to the development of new solution methods and innovative techniques, hard real-world problems can now be tackled more effectively, and new challenges arise, such as considering uncertain conditions, combining hard problems together, solving problems in real-time. Given the strong scientific interest on this topic, the Joint EURO/ALIO International Conference 2018 focused on Applied Combinatorial Optimization. This conference was jointly promoted by the Association of European Operational Research Societies (EURO) and the Association of Latin–Iberoamerican Operational Research Societies (ALIO), both within the International Federation of Operational Research Societies (IFORS). The main purpose of this event was to bring together European and Latin American researchers and to stimulate activities and discussions about methods and applications in the field of Combinatorial Optimization.
The Joint EURO/ALIO International Conference 2018 was held in Bologna, Italy, between June 25 and 27, 2018. The conference had about 250 registered participants from all over the world, who delivered talks on the most advanced methodologies for Applied Combinatorial Optimization problems. This Feature Cluster collects high-quality contributions, authored by participants to the conference or by researchers in the large scientific community of Combinatorial Optimization, which propose effective formulations and algorithms that allow solving relevant problems
Estimation of flood warning runoff thresholds in ungauged basins with asymmetric error functions
No full textIn many real-world flood forecasting systems, the runoff thresholds for
activating warnings or mitigation measures correspond to the flow peaks with
a given return period (often 2 years, which may be associated with the
bankfull discharge). At locations where the historical streamflow records
are absent or very limited, the threshold can be estimated with
regionally derived empirical relationships between catchment descriptors and
the desired flood quantile. Whatever the function form, such models are
generally parameterised by minimising the mean square error, which assigns
equal importance to overprediction or underprediction errors.
Considering that the consequences of an overestimated warning threshold
(leading to the risk of missing alarms) generally have a much lower level of
acceptance than those of an underestimated threshold (leading to the
issuance of false alarms), the present work proposes to parameterise the
regression model through an asymmetric error function, which penalises the overpredictions more.
The estimates by models (feedforward neural networks) with increasing degree
of asymmetry are compared with those of a traditional, symmetrically trained
network, in a rigorous cross-validation experiment referred to a database of
catchments covering the country of Italy. The analysis shows that the use of
the asymmetric error function can substantially reduce the number and extent
of overestimation errors, if compared to the use of the traditional square
errors. Of course such reduction is at the expense of increasing
underestimation errors, but the overall accurateness is still acceptable and
the results illustrate the potential value of choosing an asymmetric error
function when the consequences of missed alarms are more severe than those
of false alarms
Classificazione dei bacini in base alle caratteristiche delle serie idrometriche e pluviometriche per l’applicazione a sezioni non strumentate
No full textSi presenta dapprima la classificazione di un insieme di bacini idrografici emilianoromagnoli in funzione di indici che sintetizzano le proprietà delle serie temporali di misure idrometriche. In tal modo è possibile caratterizzare la risposta idrologica a scala temporale fine e, in particolare, rappresentarne la componente dinamica attraverso una descrizione, seppure approssimata, della struttura di autocorrelazione.
Obiettivo dello studio è l’attribuzione a tali classi di bacini privi di osservazioni di portata, in funzione di attributi di natura morfologica e pluviometrica. In particolare, sono identificati anche parametri caratterizzanti le serie storiche delle precipitazioni sui bacini, in analogia con gli indici selezionati per le serie idrometriche. Viene svolta prima l’analisi delle componenti principali delle variabili disponibili, sintetizzando e interpretando l’informazione che caratterizza il regime pluviometrico. Viene poi effettuata un’analisi discriminante per associare ogni bacino - a turno considerato come non strumentato - ad una delle classi di similarità idrometrica, fornendo in ingresso solo le prime componenti principali delle variabili morfo-pluviometriche. La classificazione dei bacini non strumentati, seppur basata su un insieme di parametri piuttosto ridotto per la rappresentazione dei fenomeni, risulta essere in soddisfacente accordo con quella basata sugli attributi idrometrici, indicando le buone potenzialità della metodologia proposta
Toth e il pensiero trans-euclideo in Aristotele (Toth and trans-euclidean thought in Aristotle)
No full textAbstract For about 2000 years the postulate of parallels, enunciated by Euclid, was a source of doubts (postulate or theorem?) clarified with the birth of non-Euclidean geometry.In the light of this new knowledge of geometry, Toth, a Greek scholar and historian of mathematics, glimpses typical properties of geometry today defined as non-Euclidean in some writings of Aristotle. To clearly highlight free will, the Stagirite uses geometric examples partly taken from the geometry known at the time, partly uses its negation, that is, he shows, involuntarily, the presuppositions of the geometry that we know today as non-Euclidean, without delving into the possible logical coexistence of antithetical statements.This short note is an invitation to read Aristotle in a re-interpretative way.Keywords: Toth, Aristotle, free will, non-euclidean geometry.SuntoPer cica 2000 anni il postulato delle parallele, enunciato da Euclide, è stato fucina di dubbi (postulato o teorema?) chiariti con la nascita dela Geometria Non-Euclidea. Alla luce d queste nuove conoscenze di geometria, Toth, grecista e storico della matematica, in alcuni scritti di Aristotele intravede proprietà tipiche di geometria non euclidea. Lo Stagirita, per descrivere con rigore il libero arbitrio, usa esempi geometrici, in parte prelevati dalla geometria all’epoca nota, in parte ponendo la sua negazione, ovvero mostra, involontariamente, i presupposti della geometria, oggi definita non euclidea, senza approfondire la possibile coesistenza logica di affermazioni antitetiche. Questa breve nota è un invito alla lettura d’Aristotele in chiave re-interpretativa.Parole chiave: Toth, Aristotele, libero arbitrio, geometria non-euclidea
Algorithm 750: CDT A Subroutinefor the Exact Solution ofLarge-Scale, Asymmetric Traveling Salesman Problems
No full textThe FORTRAN code CDT, implementing the algorithm of Carpaneto, Dell'Amico and Toth 1995afor the Asymmetric Travelling Salesman Problem, is presented. The method is based on the Assignment Problem relaxation and on a subtour elimination branching scheme. The effectiveness of the implementation derives from reduction procedures and parametric solution of the relaxed problems associated with the nodes of the branch-decision tree
Il dibattito sulla sostenibilità del SSN
No full textIl progressivo invecchiamento della popolazione e i recenti tagli al fondo sanitario nazionale mettono in dubbio la sostenibilità futura del Servizio sanitario nazionale. L'adozione di nuovi modelli organizzativi e l'utilizzo delle tecnologie informatiche possono costituire una risposta a tali problemi
Classification of hydro-meteorological conditions and multiple artificial neural networks for streamflow forecasting
No full textThis paper presents the application of a modular approach for real-time streamflow forecasting that uses different system-theoretic rainfall-runoff models according to the situation characterising the forecast instant. For each forecast instant, a specific model is applied, parameterised on the basis of the data of the similar hydrological and meteorological conditions observed in the past. In particular, the hydro-meteorological conditions are here classified with a clustering technique based on Self-Organising Maps (SOM) and, in correspondence of each specific case, different feed-forward artificial neural networks issue the streamflow forecasts one to six hours ahead, for a mid-sized case study watershed. The SOM method allows a consistent identification of the different parts of the hydrograph, representing current and near-future hydrological conditions, on the basis of the most relevant information available in the forecast instant, that is, the last values of streamflow and areal-averaged rainfall. The results show that an adequate distinction of the hydro-meteorological conditions characterising the basin, hence including additional knowledge on the forthcoming dominant hydrological processes, may considerably improve the rainfall-runoff modelling performance
Hermenêutica e Geometria Não Euclidiana: Imre Toth e os instrumentos específicos de uma filologia matemática
No full textEste artigo tem como objetivo destacar alguns dos elementos hermenêuticos e metodológicos empregados por Imre Toth em sua pesquisa. O foco deste estudo encontra-se em sua obra Aristotele e i fondamenti assiomatici della geometria, onde são apontados e examinados os trechos das obras de Aristóteles que segundo Toth discutem a existência de uma geometria heterodoxa na Academia de Platão. Dispondo diferentes autores e momentos da história da geometria não euclidiana em um mesmo plano, e confrontando sempre a história e a filosofia da matemática moderna com a antiga, Toth traça uma via alternativa para compreender o desenvolvimento da matemática em período anterior a Euclides
The Summer School ‘Sustainability in communication and education. Spreading the word, creating awareness’. An introduction
No full textIntroduction to the book of abstracts of the summer school 'Sustainability in communication and education. Spreading the word, creating awareness
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