Herschel-PACS Measurements of Nitrogen Enrichment in Nebulae around Wolf-Rayet Stars

For three nebulae that have early-WN Wolf-Rayet exciting stars, NGC 6888, WR 8 and Abell 48, we have obtained Herschel-PACS line scans of the [N III] 57 um and [O III] 88 micron lines, along with the 122 and 205 micron lines of [N II]. From the former two lines we have derived N$^{2+}$/O$^{2+}$ abundance ratios, equal to the overall N/O ratio under a wide range of nebular conditions. We find that all of the nebulae observed possess significant nitrogen enrichment, with derived N/O ratios greater than solar. The two nebulae with massive Wolf-Rayet exciting stars, NGC 6888 and WR8 are found to have N/O ratios that are enhanced by factors of 7 - 10 relative to the solar N/O ratio, consistent with an origin as material ejected just before the onset of the Wolf-Rayet phase. The other nebula, Abell 48, has recently been reclassified as a member of the rare class of three planetary nebulae that have early-WN central stars and are not of Peimbert Type I. We derive a nebular N/O ratio for it that is a factor of 4 enhanced relative to solar and slightly above the range of N/O values that have been measured for the other three members of its [WN] planetary nebula class.Comment: 11 pages, 5 figures, MNRAS accepte

Hadronization conditions in relativistic nuclear collisions and the QCD pseudo-critical line

We compare the reconstructed hadronization conditions in relativistic nuclear collisions in the nucleon-nucleon centre-of-mass energy range 4.7-2760 GeV in terms of temperature and baryon-chemical potential with lattice QCD calculations, by using hadronic multiplicities. We obtain hadronization temperatures and baryon chemical potentials with a fit to measured multiplicities by correcting for the effect of post-hadronization rescattering. The post-hadronization modification factors are calculated by means of a coupled hydrodynamical-transport model simulation under the same conditions of approximate isothermal and isochemical decoupling as assumed in the statistical hadronization model fits to the data. The fit quality is considerably better than without rescattering corrections, as already found in previous work. The curvature of the obtained "true" hadronization pseudo-critical line kappa is found to be 0.0048 +- 0.0026, in agreement with lattice QCD estimates; the pseudo-critical temperature at vanishing mu_B is found to be 164.3+-1.8 MeV.Comment: 9 pages, 2 figures. Minor corrections, version published in PL

Adaptive Ising Model and Bacterial Chemotactic Receptor Network

We present a so-called adaptive Ising model (AIM) to provide a unifying explanation for sensitivity and perfect adaptation in bacterial chemotactic signalling, based on coupling among receptor dimers. In an AIM, an external field, representing ligand binding, is randomly applied to a fraction of spins, representing the states of the receptor dimers, and there is a delayed negative feedback from the spin value on the local field. This model is solved in an adiabatic approach. If the feedback is slow and weak enough, as indeed in chemotactic signalling, the system evolves through quasi-equilibrium states and the ``magnetization'', representing the signal, always attenuates towards zero and is always sensitive to a subsequent stimulus.Comment: revtex, final version to appear in Europhysics Letter

Cenozoic evolution of Neotethys and implications for the causes of plate motions

Africa-North America-Eurasia plate circuit rotations, combined with Red Sea rotations and new estimates of crustal shortening in Iran define the Cenozoic history of the Neotethyan ocean between Arabia and Eurasia. The new constraints indicate that Arabia-Eurasia convergence has been fairly constant at 2 to 3 cm/yr since 56 Ma with slowing of Africa-Eurasia motion to <1 cm/yr near 25 Ma, coeval with the opening of the Red Sea. Ocean closure occurred no later than 10 Ma, and could have occurred prior to this time only if a large amount of continental lithosphere was subducted, suggesting that slowing of Africa significantly predated the Arabia-Eurasia collision. These kinematics imply that Africa's disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern Eurasia slowed its motion. The slow, steady rate of northward subduction since 56 Ma contrasts with strongly variable rates of magma production in the Urumieh-Dokhtar arc, implying magma production rate in continental arcs is not linked to subduction rate