Revealing the Young Starburst in Haro 3 with Radio and Infrared Imaging

The Wolf-Rayet galaxy Haro 3 (Mrk 35, NGC 3353) was observed at the near-IR and radio wavelengths as part of ongoing program to study the earliest stages of starbursts. These observations confirm that the current episode of star formation is dominated by a single region (region A). While there are knots of recent (~10 Myr) star formation outside of region A, the sources of ionizing radiation as observed in both radio and Br-gamma observations are almost exclusively associated with region A. The derived ionizing flux implies a star formation rate of ~0.6 solar masses per year localized within a radius of ~0.1 kpc. A comparison with observations from HST indicates that one or more of the star clusters in region A are optically obscured. The star clusters in region A have ages at least as young as ~5 Myr, and possibly as young as ~0.1 Myr. The star cluster that appears to be the youngest also exhibits a near-IR excess in its colors, possibly indicating natal dust in very close proximity to the ionizing stars. The difference between optical- and radio-determined ionizing fluxes as well as the near-IR colors indicate an average extinction value of A_V ~2.5 in region A. The total stellar mass associated with the current starburst in region A is inferred from both the near-IR and radio observations to be ~10^6 solar masses. The other main stellar concentrations observed in the near-IR (Regions B1 and B2) are somewhat older than region A, with ages ~8-10 Myr, and the near-IR observations indicate they have stellar masses of ~8x10^4 and ~2x10^4 solar masses, respectively.Comment: 17 pages, 3 figures, to appear in AJ August 200

Geometry of entangled states, Bloch spheres and Hopf fibrations

We discuss a generalization to 2 qubits of the standard Bloch sphere representation for a single qubit, in the framework of Hopf fibrations of high dimensional spheres by lower dimensional spheres. The single qubit Hilbert space is the 3-dimensional sphere S3. The S2 base space of a suitably oriented S3 Hopf fibration is nothing but the Bloch sphere, while the circular fibres represent the qubit overall phase degree of freedom. For the two qubits case, the Hilbert space is a 7-dimensional sphere S7, which also allows for a Hopf fibration, with S3 fibres and a S4 base. A main striking result is that suitably oriented S7 Hopf fibrations are entanglement sensitive. The relation with the standard Schmidt decomposition is also discussedComment: submitted to J. Phys.

Presentations: from Kac-Moody groups to profinite and back

We go back and forth between, on the one hand, presentations of arithmetic and Kac-Moody groups and, on the other hand, presentations of profinite groups, deducing along the way new results on both

On the distortion of twin building lattices

We show that twin building lattices are undistorted in their ambient group; equivalently, the orbit map of the lattice to the product of the associated twin buildings is a quasi-isometric embedding. As a consequence, we provide an estimate of the quasi-flat rank of these lattices, which implies that there are infinitely many quasi-isometry classes of finitely presented simple groups. In an appendix, we describe how non-distortion of lattices is related to the integrability of the structural cocycle

Plant traits correlated with generation time directly affect inbreeding depression and mating system and indirectly genetic structure

<p>Abstract</p> <p>Background</p> <p>Understanding the mechanisms that control species genetic structure has always been a major objective in evolutionary studies. The association between genetic structure and species attributes has received special attention. As species attributes are highly taxonomically constrained, phylogenetically controlled methods are necessary to infer causal relationships. In plants, a previous study controlling for phylogenetic signal has demonstrated that Wright's <it>F</it>_ST, a measure of genetic differentiation among populations, is best predicted by the mating system (outcrossing, mixed-mating or selfing) and that plant traits such as perenniality and growth form have only an indirect influence on <it>F</it>_STvia their association with the mating system. The objective of this study is to further outline the determinants of plant genetic structure by distinguishing the effects of mating system on gene flow and on genetic drift. The association of biparental inbreeding and inbreeding depression with population genetic structure, mating system and plant traits are also investigated.</p> <p>Results</p> <p>Based on data from 263 plant species for which estimates of <it>F</it>_ST, inbreeding (<it>F</it>_IS) and outcrossing rate (<it>t</it>_m) are available, we confirm that mating system is the main influencing factor of <it>F</it>_ST. Moreover, using an alternative measure of <it>F</it>_STunaffected by the impact of inbreeding on effective population size, we show that the influence of <it>t</it>_mon <it>F</it>_STis due to its impact on gene flow (reduced pollen flow under selfing) and on genetic drift (higher drift under selfing due to inbreeding). Plant traits, in particular perenniality, influence <it>F</it>_STmostly via their effect on the mating system but also via their association with the magnitude of selection against inbred individuals: the mean inbreeding depression increases from short-lived herbaceous to long-lived herbaceous and then to woody species. The influence of perenniality on mating system does not seem to be related to differences in stature, as proposed earlier, but rather to differences in generation time.</p> <p>Conclusion</p> <p>Plant traits correlated with generation time affect both inbreeding depression and mating system. These in turn modify genetic drift and gene flow and ultimately genetic structure.</p

Sex-biased dispersal promotes adaptive parental effects

<p>Abstract</p> <p>Background</p> <p>In heterogeneous environments, sex-biased dispersal could lead to environmental adaptive parental effects, with offspring selected to perform in the same way as the parent dispersing least, because this parent is more likely to be locally adapted. We investigate this hypothesis by simulating varying levels of sex-biased dispersal in a patchy environment. The relative advantage of a strategy involving pure maternal (or paternal) inheritance is then compared with a strategy involving classical biparental inheritance in plants and in animals.</p> <p>Results</p> <p>We find that the advantage of the uniparental strategy over the biparental strategy is maximal when dispersal is more strongly sex-biased and when dispersal distances of the least mobile sex are much lower than the size of the environmental patches. In plants, only maternal effects can be selected for, in contrast to animals where the evolution of either paternal or maternal effects can be favoured. Moreover, the conditions for environmental adaptive maternal effects to be selected for are more easily fulfilled in plants than in animals.</p> <p>Conclusions</p> <p>The study suggests that sex-biased dispersal can help predict the direction and magnitude of environmental adaptive parental effects. However, this depends on the scale of dispersal relative to that of the environment and on the existence of appropriate mechanisms of transmission of environmentally induced traits.</p

Spectrométrie neutronique pratique et approche à l'aide de détecteurs ionographiques visuels

A l'aide de détecteurs solides visuels, on fait une spectrométrie neutronique entre 0 et 20 MeV. On utilise : i) entre 0 et 10 MeV, les réactions de fission sur diverses cibles : uranium naturel et enrichi avec et sans écran de cadmium, neptunium et thorium ; ii) entre 3 et 20 MeV, les réactions (n, α) sur cibles de béryllium, carbone et oxygène. Les détecteurs utilisés sont le Makrofol pour les réactions de fission et la nitrocellulose pour les réactions (n, α)