102,857 research outputs found
Vincenzo Cerulli
No full textNel presente articolo viene fornita una breve biografia di Vincenzo Cerulli, con particolare riguardo all'Osservatorio da lui fondato a Teramo
Vincenzo Cerulli e l’Osservatorio
No full textNel presente lavoro ci si propone di illustrare la biografia di uno dei più illustri personaggi del territorio teramano, precisamente Vincenzo Cerulli, il fondatore dell'Osservatorio Astronomico "Vincenzo Cerulli" di Collurania - Teramo
Linear degenerations of flag varieties: partial flags, defining equations, and group actions
No full textWe continue, generalize and expand our study of linear degenerations of flag varieties from Cerulli Irelli et al. (Math Z 287(1–2):615–654, 2017). We realize partial flag varieties as quiver Grassmannians for equi-oriented type A quivers and construct linear degenerations by varying the corresponding quiver representation. We prove that there exists the deepest flat degeneration and the deepest flat irreducible degeneration: the former is the partial analogue of the mf-degenerate flag variety and the latter coincides with the partial PBW-degenerate flag variety. We compute the generating function of the number of orbits in the flat irreducible locus and study the natural family of line bundles on the degenerations from the flat irreducible locus. We also describe explicitly the reduced scheme structure on these degenerations and conjecture that similar results hold for the whole flat locus. Finally, we prove an analogue of the Borel–Weil theorem for the flat irreducible locus
A tabu search heuristic based on k-diamonds for the weighted feedback vertex set problem
No full textGiven an undirected and vertex weighted graph G = (V,E,w), the Weighted Feedback Vertex Problem (WFVP) consists of finding a subset F ⊆ V of vertices of minimum weight such that each cycle in G contains at least one vertex in F. The WFVP on general graphs is known to be NP-hard and to be polynomially solvable on some special classes of graphs (e.g., interval graphs, co-comparability graphs, diamond graphs). In this paper we introduce an extension of diamond graphs, namely the k-diamond graphs, and give a dynamic programming algorithm to solve WFVP in linear time on this class of graphs. Other than solving an open question, this algorithm allows an efficient exploration of a neighborhood structure that can be defined by using such a class of graphs. We used this neighborhood structure inside our Iterated Tabu Search heuristic. Our extensive experimental show the effectiveness of this heuristic in improving the solution provided by a 2-approximate algorithm for the WFVPon general graphs
A homological interpretation of transverse quiver Grassmannians
No full textIn recent articles, the investigation of atomic bases in cluster algebras associated to affine quivers led the second–named author to introduce a variety called transverse quiver Grassmannian and the first–named and third–named authors to consider the smooth loci of quiver Grassmannians. In this paper, we prove that, for any affine quiver Q, the transverse quiver Grassmannian of an indecomposable representation M is the set of points N in the quiver Grassmannian of M such that Ext1(N, M/N) = 0. As a corollary we prove that the transverse quiver Grassmannian coincides with the smooth locus of the irreducible components of minimal dimension in the quiver Grassmannian
Link prediction and feature relevance in knowledge networks: A machine learning approach
No full textWe propose a supervised machine learning approach to predict partnership formation between universities. We focus on successful joint R&D projects funded by the Horizon 2020 programme in three research domains: Social Sciences and Humanities, Physical and Engineering Sciences, and Life Sciences. We perform two related analyses: link formation prediction, and feature importance detection. In predicting link formation, we consider two settings: one including all features, both exogenous (pertaining to the node) and endogenous (pertaining to the network); and one including only exogenous features (thus removing the network attributes of the nodes). Using out-of-sample cross-validated accuracy, we obtain 91% prediction accuracy when both types of attributes are used, and around 67% when using only the exogenous ones. This proves that partnership predictive power is on average 24% larger for universities already incumbent in the programme than for newcomers (for which network attributes are clearly unknown). As for feature importance, by computing super-learner average partial effects and elasticities, we find that the endogenous attributes are the most relevant in affecting the probability to generate a link, and observe a largely negative elasticity of the link probability to feature changes, fairly uniform across attributes and domains
Datanet: A Stata routine for organising a dataset for network analysis purposes
No full textThis paper presents and applies a new user-written Stata program, datanet, which facilitates the dataset organisation for network analysis purposes. Given a fixed number of units (or nodes) belonging to the same group (there will be a variable denoting group membership), possibly connected one each other or possibly not, this routine creates a new dataset containing all their possible couplings to then be easily exploited using Stata network analysis commands. So far, to our knowledge, no routine has been developed in Stata which executes this type of procedure
Ignazio Guidi, Martino Mario Moreno, Enico Cerulli, studiosi dell'Etiopia
No full textIgnazio Guidi, Martino Mario Moreno and Enrico Cerulli marked in a permanent way the studies on institutions and languages of the ‘Ethiopian’ region. As academics they left a unique legacy, still traceable in their publications, and they gave an indelible imprint to the subsequent generations of researchers, until today. As civil servants in different admnistrative offices they contributed to familiarize their country, then still narrow-minded, with the traditional East African cultures. Nevertheless they had to come to terms with the ideological context of the contemporary Euope, marked by racist and colonial ideas, and they took part actively in that political mood. A sincere tribute to their scientific talent cannot be separated from asking ourselves about the reasons and the outcomes of their cultural and political militancy. This paper has been delivered on the occasion of the workshop “Cinque Grandi Italiani tra Africa e Oriente”, held at the Circolo del Ministero degli Affari Esteri in Rome, 10 November 201
Surgical Treatment of a Rare Isolated Bilateral Agenesis of Anterior and Posterior Cruciate Ligaments
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