724 research outputs found

    On Bruen chains

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    It is known that a Bruen chain of the three-dimensional projective space PG(3,q)\mathrm{PG}(3,q) exists for every odd prime power qq at most 3737, except for q=29q=29. It was shown by Cardinali et. al (2005) that Bruen chains do not exist for 41q4941\le q\leq 49. We develop a model, based on finite fields, which allows us to extend this result to 41q9741\leqslant q \leqslant 97, thereby adding more evidence to the conjecture that Bruen chains do not exist for q>37q>37. Furthermore, we show that Bruen chains can be realised precisely as the (q+1)/2(q+1)/2-cliques of a two related, yet distinct, undirected simple graphs

    Some sporadic translation planes of order 11211^2

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    In \cite{PK}, the authors constructed a translation plane Π\Pi of order 11211^2 arising from replacement of a sporadic chain FF' of reguli in a regular spread FF of PG(3,11)PG(3,11). They also showed that two more non isomorphic translation planes, called  Π1\Pi_1 and Π13\Pi_{13}, arise respectively by derivation and double derivation in FFF\setminus F' which correspond to a further replacement of a regulus with its opposite regulus and a pair of reguli with their opposite reguli, respectively.  In \cite{AL}, the authors proved that the translation complement of Π\Pi contains a subgroup isomorphic to \SL(2,5). Here, the full collineation group of each of the planes Π\Pi, Π1\Pi_1 and Π13\Pi_{13} is determined

    Phylogenomics and analysis of shared genes suggest a single transition to mutualism in Wolbachia of nematodes

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    Wolbachia, endosymbiotic bacteria of the order Rickettsiales, are widespread in arthropods but also present in nematodes. In arthropods, A and B supergroup Wolbachia are generally associated with distortion of host reproduction. In filarial nematodes, including some human parasites, multiple lines of experimental evidence indicate that C and D supergroup Wolbachia are essential for the survival of the host, and here the symbiotic relationship is considered mutualistic. The origin of this mutualistic endosymbiosis is of interest for both basic and applied reasons: How does a parasite become a mutualist? Could intervention in the mutualism aid in treatment of human disease? Correct rooting and high-quality resolution of Wolbachia relationships are required to resolve this question. However, because of the large genetic distance between Wolbachia and the nearest outgroups, and the limited number of genomes so far available for large-scale analyses, current phylogenies do not provide robust answers. We therefore sequenced the genome of the D supergroup Wolbachia endosymbiont of Litomosoides sigmodontis, revisited the selection of loci for phylogenomic analyses, and performed a phylogenomic analysis including available complete genomes (from isolates in supergroups A, B, C, and D). Using 90 orthologous genes with reliable phylogenetic signals, we obtained a robust phylogenetic reconstruction, including a highly supported root to the Wolbachia phylogeny between a (A + B) clade and a (C + D) clade. Although we currently lack data from several Wolbachia supergroups, notably F, our analysis supports a model wherein the putatively mutualist endosymbiotic relationship between Wolbachia and nematodes originated from a single transition event

    Uncertainty propagation for flood forecasting in the Alps: different views and impacts from MAP D-PHASE

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    D-PHASE was a Forecast Demonstration Project of theWorldWeather Research Programme (WWRP) related to the Mesoscale Alpine Programme (MAP). Its goal was to demonstrate the reliability and quality of operational forecasting of orographically influenced (determined) precipitation in the Alps and its consequences on the distribution of run-off characteristics. A special focus was, of course, on heavy-precipitation events. The D-PHASE Operations Period (DOP) ran from June to November 2007, during which an end-to-end forecasting system was operated covering many individual catchments in the Alps, with their water authorities, civil protection organizations or other end users. The forecasting system’s core piece was a Visualization Platform where precipitation and flood warnings from some 30 atmospheric and 7 hydrological models (both deterministic and probabilistic) and corresponding model fields were displayed in uniform and comparable formats. Also, meteograms, nowcasting information and end user communication was made available to all the forecasters, users and end users. D-PHASE information was assessed and used by some 50 different groups ranging from atmospheric forecasters to civil protection authorities or water management bodies. In the present contribution, D-PHASE is briefly presented along with its outstanding scientific results and, in particular, the lessons learnt with respect to uncertainty propagation. A focus is thereby on the transfer of ensemble prediction information into the hydrological community and its use with respect to other aspects of societal impact. Objective verification of forecast quality is contrasted to subjective quality assessments during the project (end user workshops, questionnaires) and some general conclusions concerning forecast demonstration projects are drawn

    Ebola respons-ibility: moving from shared to multiple responsibilities

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    Combating threats of infectious diseases has been increasingly framed as a global shared responsibility for a multi-actor framework, of states, international organisations and non-governmental actors. However, the outbreak of Ebola Virus Disease (EVD) has shown that this governance framework has not been able to limit the spread of this virus, despite the normative and legislative changes to global disease control. By unbundling the concept of responsibility, this article will assess how global shared responsibility may have failed due to the fact that accountability does not fall on any one state or stakeholder, highlighting an inherent weakness with the global disease governance regime. As such, this paper concludes that a move towards multiple responsibilities may prove a more effective mechanism for ensuring global health security

    Near MDS poset codes and distributions

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    We study qq-ary codes with distance defined by a partial order of the coordinates of the codewords. Maximum Distance Separable (MDS) codes in the poset metric have been studied in a number of earlier works. We consider codes that are close to MDS codes by the value of their minimum distance. For such codes, we determine their weight distribution, and in the particular case of the "ordered metric" characterize distributions of points in the unit cube defined by the codes. We also give some constructions of codes in the ordered Hamming space.Comment: 13 pages, 1 figur

    Polynomials in finite geometry

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