724 research outputs found
On Bruen chains
It is known that a Bruen chain of the three-dimensional projective space
exists for every odd prime power at most , except
for . It was shown by Cardinali et. al (2005) that Bruen chains do not
exist for . We develop a model, based on finite fields, which
allows us to extend this result to , thereby adding
more evidence to the conjecture that Bruen chains do not exist for .
Furthermore, we show that Bruen chains can be realised precisely as the
-cliques of a two related, yet distinct, undirected simple graphs
Some sporadic translation planes of order
In \cite{PK}, the authors constructed a translation plane of order arising from replacement of a sporadic chain of reguli in a regular spread of . They also showed that two more non isomorphic translation planes, called and , arise respectively by derivation and double derivation in 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 contains a subgroup isomorphic to \SL(2,5). Here, the full collineation group of each of the planes , and is determined
Phylogenomics and analysis of shared genes suggest a single transition to mutualism in Wolbachia of nematodes
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
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
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
We study -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
Postprint (published version
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