Chain minors are FPT

Given two finite posets P and Q, P is a chain minor of Q if there exists a partial function f from the elements of Q to the elements of P such that for every chain in P there is a chain C_Q in Q with the property that f restricted to C_Q is an isomorphism of chains. We give an algorithm to decide whether a poset P is a chain minor of o poset Q that runs in time O(|Q| log |Q|) for every fixed poset P. This solves an open problem from the monograph by Downey and Fellows [Parameterized Complexity, 1999] who asked whether the problem was fixed parameter tractable

Max-Cut and Max-Bisection are NP-hard on unit disk graphs

We prove that the Max-Cut and Max-Bisection problems are NP-hard on unit disk graphs. We also show that $\lambda$-precision graphs are planar for $\lambda$ > 1 / \sqrt{2}$

Shortest paths between shortest paths and independent sets

We study problems of reconfiguration of shortest paths in graphs. We prove that the shortest reconfiguration sequence can be exponential in the size of the graph and that it is NP-hard to compute the shortest reconfiguration sequence even when we know that the sequence has polynomial length. Moreover, we also study reconfiguration of independent sets in three different models and analyze relationships between these models, observing that shortest path reconfiguration is a special case of independent set reconfiguration in perfect graphs, under any of the three models. Finally, we give polynomial results for restricted classes of graphs (even-hole-free and $P_4$-free graphs)

Nuclear ashes and outflow in the eruptive star Nova Vul 1670

CK Vulpeculae was observed in outburst in 1670-16721, but no counterpart was seen until 1982, when a bipolar nebula was found at its location. Historically, CK Vul has been considered to be a nova (Nova Vul 1670), but a similarity to 'red transients', which are more luminous than classical nova and thought to be the result of stellar collisions, has re-opened the question of CK Vul's status. Red transients cool to resemble late M-type stars, surrounded by circumstellar material rich in molecules and dust. No stellar source has been seen in CK Vul, though a radio continuum source was identified at the expansion centre of the nebula. Here we report CK Vul is surrounded by chemically rich molecular gas with peculiar isotopic ratios, as well as dust. The chemical composition cannot be reconciled with a nova or indeed any other known explosion. In addition, the mass of the surrounding gas is too high for a nova, though the conversion from observations of CO to a total mass is uncertain. We conclude that CK Vul is best explained as the remnant of a merger of two stars.Comment: an older version of an article that appeared in Nature; published in Nature, online version, 23 March 201

Online Piracy, Anonymity and Social Change – Deviance Through Innovation

This article analyses current trends in the use of anonymity services among younger Swedes (15-25) and focuses on individuals engaging in illegal file sharing in order to better understand the rationale behind both file sharing as well as online anonymity, especially in relation to enforcement of copyright. By comparing the findings of a survey conducted on three different occasions (early 2009, late 2009 and early 2012), we measure the fluctuations in the use of anonymity services among approximately 1,000 15-25-year olds in Sweden, compare them to file sharing frequencies and, to some extent, trends within legal enforcement. The article also suggests that the key to understanding any relationship between copyright enforcement and fluctuations in online anonymity can be found in the law’s relationship to social norms in terms of legitimacy by showing a correlation between file sharing frequency and the use of anonymity services. The findings indicate that larger proportions of frequent file sharers (downloaders) also use anonymity services more often than those who file share less. However, in comparison to the earlier surveys, the strongest increase in the use of anonymity services is found in the groups where file sharing is less frequent, suggesting that reasons for actively making oneself less traceable online other than avoiding copyright enforcement have emerged since the initial two surveys in 2009. Further, the overall increase (from 8.6% to 14.9%) in using anonymity services found for the whole group of respondents suggests both that high file sharing frequency is a driver for less traceability as well as a larger trend for online anonymity relating to other factors than mere file sharing of copyright infringing content – for example, increased governmental identification, data retention and surveillance in the online environment. The results are analysed in Merton’s terminology as file sharers and protocol architects adapting in terms of both innovation and rebellion in the sense that institutional means for achieving specific cultural goals are rejected. This means, to some extent, participating in or contributing to the construction of other means for reaching cultural goals

Professionalizzazione, Gender, e Animato nelle Comunità di File Sharing Globale

Abstract in Italian Nell’aprile 2011, al famoso logo della community di file sharing globale The Pirate Bay fu aggiunta l’immagine di una lente di ingrandimento e il nome del sito cambiò in The Research Bay. Gli utenti che cliccarono sul nuovo logo furono reindirizzati su un sondaggio online; durante le 72 ore di svolgimento dello studio, 75.000 file-sharer compilarono il questionario preparato dal gruppo di ricerca Cybernorms. Il sondaggio, in lingua inglese, conteneva domande a risposta multipla e domande aperte: lo scopo era migliorare la comprensione dei comportamenti, delle motivazione e delle dinamiche alla base del fenomeno del file sharing. Per tale motivo, le norme sociali interne alla comunità di file sharing, in netto contrasto con la legge, sono state il focus principale dello studio. Il proposito alla base di questo studio è stato il tentativo di descrivere dall’interno una community di file sharing e fare luce sui profili demografici e sulle strutture sociali sottese al fenomeno diventato una delle più grandi sfide per la Proprietà Intellettuale. Analizzando i dati del sondaggio abbiamo riscontrato due temi vitali al fine di comprender le community di file sharing come The Pirate Bay: 1) Il gender: una comunità composta da giovani uomini; 2) La “professionalizzazione” o specializzazione: la suddivisione del lavoro tra gli utenti. Si potrebbe parlare di professionalizzazione o di specializzazione dei ruoli all’interno dell’“ecosistema” del file sharing. Gli utenti che hanno risposto ai nostri quesiti rappresentano un legame con una catena più ampia, una componente vitale di un ecosistema di condivisione più esteso. Tale professionalizzazione suggerisce la presenza di una organizzazione strutturata all’interno della comunità di cui BitTorrent gioca un ruolo importante ma non omnicomprensivo. Non si tratta di una struttura costruita ad hoc piuttosto di un’organizzazione per la disseminazione di contenuti dove il gender svolge un ruolo significativo. Un gruppo piuttosto ristretto e specializzato di giovani uomini, con buone competenze tecniche e legali, scarica contenuti attraverso il protocollo BitTorrent e a sua volta lo passa su network locali dove viene distribuito attraverso differenti strumenti come il passa mano di supporti digitali. Ciò fa si che l’intera catena di scambi sia protetta da eventuali forme di controllo. Gli scambi offline, infatti, sono decisamente più complessi da monitorare e controllare