Casting Light on the Hidden Bilevel Combinatorial Structure of the Capacitated Vertex Separator Problem

Given an undirected graph, we study the capacitated vertex separator problem that asks to find a subset of vertices of minimum cardinality, the removal of which induces a graph having a bounded number of pairwise disconnected shores (subsets of vertices) of limited cardinality. The problem is of great importance in the analysis and protection of communication or social networks against possible viral attacks and for matrix decomposition algorithms. In this article, we provide a new bilevel interpretation of the problem and model it as a two-player Stackelberg game in which the leader interdicts the vertices (i.e., decides on the subset of vertices to remove), and the follower solves a combinatorial optimization problem on the resulting graph. This approach allows us to develop a computational framework based on an integer programming formulation in the natural space of the variables. Thanks to this bilevel interpretation, we derive three different families of strengthening inequalities and show that they can be separated in polynomial time. We also show how to extend these results to a min-max version of the problem. Our extensive computational study conducted on available benchmark instances from the literature reveals that our new exact method is competitive against the state-of-the-art algorithms for the capacitated vertex separator problem and is able to improve the best-known results for several difficult classes of instances. The ideas exploited in our framework can also be extended to other vertex/edge deletion/ insertion problems or graph partitioning problems by modeling them as two-player Stackel- berg games and solving them through bilevel optimization

accuracy of cultural heritage 3d models by rpas and terrestrial photogrammetry

The combined use of high-resolution digital images taken from ground as well as from RPAS (Remotely Piloted Aircraft Systems) have significantly increased the potential of close range digital photogrammetry applications in Cultural Heritage surveying and modeling. It is in fact possible, thanks to SfM (Structure from Motion), to simultaneously process great numbers of aerial and terrestrial images for the production of a dense point cloud of an object. In order to analyze the accuracy of results, we started numerous tests based on the comparison between 3D digital models of a monumental complex realized by the integration of aerial and terrestrial photogrammetry and an accurate TLS (Terrestrial Laser Scanner) reference model of the same object. A lot of digital images of a renaissance castle, assumed as test site, have been taken both by ground level and by RPAS at different distances and flight altitudes and with different flight patterns. As first step of the experimentation, the images were previously processed with Agisoft PhotoScan, one of the most popular photogrammetric software. The comparison between the photogrammetric DSM of the monument and a TLS reference one was carried out by evaluating the average deviation between the points belonging to the two entities, both globally and locally, on individual façades and architectural elements (sections and particular). In this paper the results of the first test are presented. A good agreement between photogrammetric and TLS digital models of the castle is pointed out

VSCAN: An Enhanced Video Summarization using Density-based Spatial Clustering

In this paper, we present VSCAN, a novel approach for generating static video summaries. This approach is based on a modified DBSCAN clustering algorithm to summarize the video content utilizing both color and texture features of the video frames. The paper also introduces an enhanced evaluation method that depends on color and texture features. Video Summaries generated by VSCAN are compared with summaries generated by other approaches found in the literature and those created by users. Experimental results indicate that the video summaries generated by VSCAN have a higher quality than those generated by other approaches.Comment: arXiv admin note: substantial text overlap with arXiv:1401.3590 by other authors without attributio

Características agronômicas dos acessos do Banco Ativo de Germoplasma de Uva.

Este trabalho teve por objetivo caracterizar agronomicamente 19 acessos do Banco Ativo de Germoplasma de Uva (BAGUva), por um período compreendido entre sete e 11 anos. Os materiais são cultivados a campo, em condições padronizadas, sob porta-enxerto '101-14?, com sistema de sustentação em espaldeira e poda em Guyot. Foram avaliadas características relacionadas ao cacho, à baga, à produtividade e à incidência das principais doenças da videira no país

Caracterização da qualidade do mosto de acessos do Banco Ativo de Germoplasma de Uva.

O objetivo deste trabalho foi avaliar a qualidade do mosto, com relação ao pH, conteúdo de sólidos solúveis totais (SS) e acidez total titulável (ATT) de 19 acessos do Banco Ativo de Germoplasma de Uva

Características agronômicas dos acessos do Banco Ativo de Germoplasma de Uva da Embrapa Uva e Vinho.

A caracterização de acessos de uva mantidos em coleção é uma etapa importante, que contribui para o melhoramento genético. Este trabalho teve como objetivo caracterizar agronomicamente 43 acessos do Banco Ativo de Germoplasma de Uva (BAG-Uva), mantido pela Embrapa Uva e Vinho, localizada em Bento Gonçalves-RS

Avaliação físico-química de acessos do Banco Ativo de Germoplasma de Uva (BAG-Uva).

O objetivo deste trabalho é caracterizar 43 acessos do BAG-Uva, com relação à qualidade do mosto [pH, Sólidos Solúveis Totais (SS) e Acidez Total Titulável (ATT)], por um período que variou entre sete e 10 anos. Trinta e oito acessos também foram avaliados com relação ao Índice de Polifenóis Totais (IPT) e conteúdo de antocianinas (ANT), por um período que variou de dois e três anos

Análise fenológica de acessos mantidos pelo Banco Ativo de Germoplasma de Uva.

O objetivo deste trabalho foi avaliar o ciclo fenológico de 19 acessos mantidos no Banco Ativo de Germoplasma de Uva

Can an aversive, extinction-resistant memory trigger impairments in walking adaptability? An experimental study using adult rats

Cognitive demands can influence the adaptation of walking, a crucial skill to maintain body stability and prevent falls. Whilst previous research has shown emotional load tunes goal-directed movements, little attention has been given to this finding. This study sought to assess the effects of suffering an extinction-resistant memory on skilled walking performance in adult rats, as an indicator of walking adaptability. Thus, 36 Wistar rats were divided in a two-part experiment. In the first part (n = 16), the aversive, extinction-resistance memory paradigm was established using a fear-conditioning chamber. In the second, rats (n = 20) were assessed in a neutral room using the ladder rung walking test before and tree days after inducing an extinction-resistance memory. In addition, the elevated plus-maze test was used to control the influence of the anxiety-like status on gait adaptability. Our results revealed the shock group exhibited worse walking adaptability (lower skilled walking score), when compared to the sham group. Moreover, the immobility time in the ladder rung walking test was similar to the controls, suggesting that gait adaptability performance was not a consequence of the fear generalization. No anxiety-like behavior was observed in the plus maze test. Finally, correlation coefficients also showed the skilled walking performance score was positively correlated with the number of gait cycles and trial time in the ladder rung walking test and the total crossings in the plus maze. Overall, these preliminary findings provide evidence to hypothesize an aversive, extinction-resistant experience might change the emotional load, affecting the ability to adapt walking

Fenologia de acessos mantidos pelo Banco Ativo de Germoplasma de Uva (BAG-Uva).

Cultivares de videira com ciclos produtivos diferenciados são importantes para a viticultura praticada em clima tropical e temperado. O objetivo deste trabalho foi avaliar o ciclo fenológico de 43 acessos mantidos no BAG-Uva. Os acessos foram avaliados em condições padronizadas no campo por um período que variou entre 7 e 10 anos em clima temperado (29º09?S, 51º31'W, 680m de altitude)