A Geometric Monte Carlo Algorithm for the Antiferromagnetic Ising model with "Topological" Term at θ=π\theta=\pi

In this work we study the two and three-dimensional antiferromagnetic Ising model with an imaginary magnetic field $i\theta$ at $\theta=\pi$. In order to perform numerical simulations of the system we introduce a new geometric algorithm not affected by the sign problem. Our results for the $2D$ model are in agreement with the analytical solutions. We also present new results for the $3D$ model which are qualitatively in agreement with mean-field predictions

A New Perspective on Clustered Planarity as a Combinatorial Embedding Problem

The clustered planarity problem (c-planarity) asks whether a hierarchically clustered graph admits a planar drawing such that the clusters can be nicely represented by regions. We introduce the cd-tree data structure and give a new characterization of c-planarity. It leads to efficient algorithms for c-planarity testing in the following cases. (i) Every cluster and every co-cluster (complement of a cluster) has at most two connected components. (ii) Every cluster has at most five outgoing edges. Moreover, the cd-tree reveals interesting connections between c-planarity and planarity with constraints on the order of edges around vertices. On one hand, this gives rise to a bunch of new open problems related to c-planarity, on the other hand it provides a new perspective on previous results.Comment: 17 pages, 2 figure

Advances on Testing C-Planarity of Embedded Flat Clustered Graphs

We show a polynomial-time algorithm for testing c-planarity of embedded flat clustered graphs with at most two vertices per cluster on each face.Comment: Accepted at GD '1

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS). II. Constraints on star formation in ram-pressure stripped gas

Context: Several galaxies in the Virgo cluster are known to have large HI gas tails related to a recent ram-pressure stripping event. The Virgo cluster has been extensively observed at 1539 A in the far-ultraviolet for the GALEX Ultraviolet Virgo Cluster Survey (GUViCS), and in the optical for the Next Generation Virgo Survey (NGVS), allowing a study of the stellar emission potentially associated with the gas tails of 8 cluster members. On the theoretical side, models of ram-pressure stripping events have started to include the physics of star formation. Aim: We aim to provide quantitative constraints on the amount of star formation taking place in the ram-pressure stripped gas, mainly on the basis of the far-UV emission found in the GUViCS images in relation with the gas content of the tails. Methods: We have performed three comparisons of the young stars emission with the gas column density: visual, pixel-by-pixel and global. We have compared our results to other observational and theoretical studies. Results: We find that the level of star formation taking place in the gas stripped from galaxies by ram-pressure is low with respect to the available amount of gas. Star formation is lower by at least a factor 10 compared to the predictions of the Schmidt Law as determined in regular spiral galaxy disks. It is also lower than measured in dwarfs galaxies and the outer regions of spirals, and than predicted by some numerical simulations. We provide constraints on the star formation efficiency in the ram-pressure stripped gas tails, and compare these with current models.Comment: Accepted in A&A, 17 pages (including the appendix and "on-line" figures of the paper

CoPIRIDE : new technical expertise relating to the anionic polymerisation of 1,3-Butadiene

Abstract onl

Splitting Clusters To Get C-Planarity

In this paper we introduce a generalization of the c-planarity testing problem for clustered graphs. Namely, given a clustered graph, the goal of the S PLIT-C-P LANARITY problem is to split as few clusters as possible in order to make the graph c-planar. Determining whether zero splits are enough coincides with testing c-planarity. We show that S PLIT-C-P LANARITY is NP-complete for c-connected clustered triangulations and for non-c-connected clustered paths and cycles. On the other hand, we present a polynomial-time algorithm for flat c-connected clustered graphs whose underlying graph is a biconnected seriesparallel graph, both in the fixed and in the variable embedding setting, when the splits are assumed to maintain the c-connectivity of the clusters

On the Nature of Star Formation at Large Galactic Radii

We have compared far-ultraviolet (FUV), near-ultraviolet (NUV), and Halpha measurements for star forming regions in 21 galaxies, in order to characterise the properties of their discs at radii beyond the main optical radius (R25). In our representative sample of extended and non-extended UV discs we find that half of the extended UV discs also exhibit extended Halpha emission. We find that extended UV discs fall into two categories, those with a sharp truncation in the Halpha disc close to the optical edge (R25), and those with extended emission in Halpha as well as in the ultraviolet. Although most galaxies with strong Halpha truncations near R25 show a significant corresponding falloff in UV emission (factor 10--100), the transition tends to be much smoother than in Halpha, and significant UV emission often extends well beyond this radius, confirming earlier results by Thilker et al. (2007) and others. After correcting for dust attenuation the median fraction of total FUV emission from regions outside of R25 is 1.7%, but it can be as high as 35% in the most extreme cases. The corresponding fractions of Halpha emission are approximately half as large on average. This difference reflects both a slightly lower ratio of Halpha to UV emission in the HII regions in the outer discs, as well as a lower fraction of star clusters showing HII regions. Most HII regions in the extended disc have fluxes consistent with small numbers of ionising O-type stars, and this poor sampling of the upper initial mass function in small clusters can probably account for the differences in the emission properties, consistent with earlier conclusions by Zaritsky & Christlein (2007), without needing to invoke a significant change in the stellar IMF itself. Consistent Ha/FUV ratios and brightest HII region to total Halpha fluxes in the inner and extended discs across our whole galaxy sample demonstrate no evidence for a change in the cluster luminosity function or the IMF in the low gas density outer disc.Comment: Accepted for publication in MNRAS. 21 Pages, 13 Figures, 2 Table

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS): genetic and clinical aspects

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) typically presents in middle life with a combination of neuropathy, ataxia and vestibular disease, with patients reporting progressive imbalance, oscillopsia, sensory disturbance and a dry cough. Examination identifies a sensory neuropathy or neuronopathy and bilaterally impaired vestibulo-ocular reflex. The underlying genetic basis is of biallelic AAGGG expansions in the second intron of replication factor complex subunit 1 (RFC1). The frequency and phenotype spectrum of RFC1 disease is expanding, ranging from typical CANVAS to site-restricted variants affecting the sensory nerves, cerebellum and/or the vestibular system. Given the wide phenotype spectrum of RFC1, the differential diagnosis is broad. RFC1 disease due to biallelic AAGGG expansions is probably the most common cause of recessive ataxia. The key to suspecting the disease (and prompt genetic testing) is a thorough clinical examination assessing the three affected systems and noting the presence of chronic cough