Clique-Based Separators for Geometric Intersection Graphs

Let F be a set of n objects in the plane and let G^x(F) be its intersection graph. A balanced clique-based separator of G^x(F) is a set S consisting of cliques whose removal partitions G^x(F) into components of size at most δn, for some fixed constant δ < 1. The weight of a clique-based separator is defined as ∑_{C ∈ S} log (|C|+1). Recently De Berg et al. (SICOMP 2020) proved that if S consists of convex fat objects, then G^x(F) admits a balanced clique-based separator of weight O(√n). We extend this result in several directions, obtaining the following results. - Map graphs admit a balanced clique-based separator of weight O(√n), which is tight in the worst case. - Intersection graphs of pseudo-disks admit a balanced clique-based separator of weight O(n^{2/3} log n). If the pseudo-disks are polygonal and of total complexity O(n) then the weight of the separator improves to O(√n log n). - Intersection graphs of geodesic disks inside a simple polygon admit a balanced clique-based separator of weight O(n^{2/3} log n). - Visibility-restricted unit-disk graphs in a polygonal domain with r reflex vertices admit a balanced clique-based separator of weight O(√n + r log(n/r)), which is tight in the worst case. These results immediately imply sub-exponential algorithms for MAXIMUM INDEPENDENT SET (and, hence, VERTEX COVER), for FEEDBACK VERTEX SET, and for q-Coloring for constant q in these graph classes.ISSN:1868-896

TSP in a Simple Polygon

We study the Traveling Salesman Problem inside a simple polygon. In this problem, which we call tsp in a simple polygon, we wish to compute a shortest tour that visits a given set S of n sites inside a simple polygon P with m edges while staying inside the polygon. This natural problem has, to the best of our knowledge, not been studied so far from a theoretical perspective. It can be solved exactly in poly(n,m) + 2^O(?nlog n) time, using an algorithm by Marx, Pilipczuk, and Pilipczuk (FOCS 2018) for subset tsp as a subroutine. We present a much simpler algorithm that solves tsp in a simple polygon directly and that has the same running time

Mapping and measuring the phenomenon of precariousness in Cyprus: challenges and implications

This research study utilises a mixed design model to empirically measure and address the phenomenon of precarious work and precariousness in Cyprus. For the purposes of this study precariousness is perceived as a condition in which people face specific dangers, risk of disease or accident, material deprivation and poverty. Furthermore, as a result of precarious employment, insufficient income and lack of property, these individuals are not able to cope or be exposed to prolonged periods of unemployment and its subsequent social risks and dangers. By analysing data from the EU-SILC (2020) for Cyprus, the characteristics of precarious employees were identified, along with the factors contributing to precariousness. The majority of precarious workers in Cyprus were women, immigrants and young people. Following this, precarity was examined as a condition in which precariousness and economic vulnerability intersect and interact. Precarious workers accounted for 9,5% of all employees in 2019, whereas those in precarity (i.e., precarious and economically vulnerable) amounted for 4,4% of all employees. The present research and its empirics contribute to the discussion of the phenomenon of precarious work and precariousness by introducing new variables and introducing new empirical approaches to the examination of precarious employment and precariousness. The results of this study are intended to provide stakeholders with an enhanced understanding of the phenomenon which will ultimately lead to new theoretical and policy avenues towards its reduction and elimination

Clique-Based Separators for Geometric Intersection Graphs

Funding Information: The work in this paper is supported by the Dutch Research Council (NWO) through Gravitation-grant NETWORKS-024.002.003. Publisher Copyright: © 2022, The Author(s).Let F be a set of n objects in the plane and let G×(F) be its intersection graph. A balanced clique-based separator of G×(F) is a set S consisting of cliques whose removal partitions G×(F) into components of size at most δn, for some fixed constant δ< 1. The weight of a clique-based separator is defined as ∑ C∈Slog (| C| + 1). Recently De Berg et al. (SIAM J. Comput. 49: 1291-1331. 2020) proved that if S consists of convex fat objects, then G×(F) admits a balanced clique-based separator of weight O(n). We extend this result in several directions, obtaining the following results. (i) Map graphs admit a balanced clique-based separator of weight O(n), which is tight in the worst case. (ii) Intersection graphs of pseudo-disks admit a balanced clique-based separator of weight O(n2 / 3log n). If the pseudo-disks are polygonal and of total complexity O(n) then the weight of the separator improves to O(nlogn). (iii) Intersection graphs of geodesic disks inside a simple polygon admit a balanced clique-based separator of weight O(n2 / 3log n). (iv) Visibility-restricted unit-disk graphs in a polygonal domain with r reflex vertices admit a balanced clique-based separator of weight O(n+rlog(n/r)), which is tight in the worst case. These results immediately imply sub-exponential algorithms for Maximum Independent Set (and, hence, Vertex Cover), for Feedback Vertex Set, and for q-Coloring for constant q in these graph classes.Peer reviewe

Reconstruire l'été grec : le rôle de la presse pour relancer le voyage et le tourisme à l'époque de la pandémie de Covid-19

La présente recherche s'attache à explorer le rôle que joue la presse dans la procédure de reprise du secteur touristique en période de crise pandémique. Pour atteindre cet objectif, des sources sélectionnées de la presse grecque ont été analysées en profondeur afin d'évaluer la gestion par le gouvernement grec de la reprise du tourisme grec après la première vague de la pandémie de COVID-19 au cours de l'été 2020. Une analyse de contenu a été appliquée aux colonnes éditoriales de quatre quotidiens grecs afin d'examiner si, et dans quelle mesure, l'affiliation politique de ces journaux a influencé leur perception du processus décisionnel et de la gestion concernant la reprise du tourisme par le gouvernement grec. La recherche explore en outre les façons dont ces journaux tentent de remodeler le récit du gouvernement vers le redémarrage du tourisme grec

Ανακατασκευάζοντας το Ελληνικό Καλοκαίρι: ο ρόλος του Τύπου στην επανεκκίνηση του Τουρισμού στην εποχή της Πανδημίας Covid-19

Μύκονος 2020. Η φωτογραφία αφορά τα μέτρα προετοιμασίας για την επανεκκίνηση του Τουρισμού τον Μάιο του 2020. Πηγή: Η ΚΑΘΗΜΕΡΙΝΗ (31/08/2020). © Getty Images/Ideal Image Εισαγωγή & βιβλιογραφική ανασκόπηση Η επιστημονική μελέτη και έρευνα της διαχείρισης κρίσεων σε χώρες με υπερβολική εξάρτηση από τον τουρισμό κρίνεται αναγκαία και επιτακτική (Novelli et al, 2018; Ritchie, 2009; De Sausmarez, 2004; Mansfield and Pizam, 2006). Είναι καταγεγραμμένο ότι οι κρίσεις -όπως οι πανδημίες- έχουν κατα..

Reconstructing the Greek Summer: the role of the Press for restarting travel and tourism in the Covid-19 pandemic era

The present research focused on exploring the role that the press plays in the recovery procedure of the tourism sector in times of pandemic crisis. Towards achieving this goal, selected sources of the Greek press were in-depth analysed to evaluate Greek Government’s management of the resumption of Greek tourism following the first wave of the COVID-19 pandemic in the summer of year 2020. Content Analysis was applied to the editorial columns of four Greek daily newspapers to examine whether and to what extent the political affiliation of these newspapers influenced their perception of the decision-making process and the management concerning the resumption of tourism by the Greek government. Τhe research further explores the ways these newspapers attempt to reshape government’s narrative towards the restarting of Greek tourism

Mapping and measuring the phenomenon of precariousness in Cyprus: challenges and implications

This research study utilises a mixed design model to empirically measure and address the phenomenon of precarious work and precariousness. For the purposes of this study precariousness is perceived as a condition in which people face specific dangers, risk of disease or accident, material deprivation and poverty. Furthermore, as a result of precarious employment, insufficient income and lack of property, these individuals are not able to cope or be exposed to prolonged periods of unemployment and its subsequent social risks and dangers. By analysing data from the EU-SILC (2020) for Cyprus, the characteristics of precarious employees were identified, along with the factors contributing to precariousness. The majority of precarious workers in Cyprus were women, immigrants and young people. Following this, precarity was examined as a condition in which precariousness and economic vulnerability intersect and interact. Precarious workers accounted for 9,5% of all employees in 2019, whereas those in precarity (i.e., precarious and economically vulnerable) amounted for 4,4% of all employees. The present research attempts to contribute to the discussion of class theory by bringing new variables and introducing new empirical approaches to the examination of precarious employment and precariousness. The results of this study are intended to provide stakeholders with an enhanced understanding of the phenomenon which will ultimately lead to new theoretical and policy avenues towards its reduction and elimination