Distribution and reproduction of Bursaphelenchus xylophilus populations in wood and bark of western north american conifers

La croissance de population de #Bursaphelenchus xylophilus a été étudiée dans le bois et l'écorce d'#Abies grandis, #Pinus contorta, #Pseudotsuga menziesii, #Tsuga heterophylla et #Thuja plicata. Le nématode a été inoculé dans des tronçons de tige (6 cm de diamètre et 25 cm de longueur) de chaque essence, puis mis en incubation dans des sacs de plastique, à la température ambiante (22 plus ou moins 4°C). Les populations de nématodes ont été échantillonnées séparément dans le bois et l'écorce de chaque essence 4, 8 et 16 semaines après l'inoculation. Dans le bois, pour l'ensemble des dates d'échantillonnage, la densité moyenne était de 233, 13, 12, 2 et 0,03 nématodes par gramme de bois sec pour #P. contorta, #P. menziesii, #A. grandis, #T. heterophylla et #T. plicata respectivement. Dans l'écorce, pour les mêmes essences, la densité était de 70, 267, 88, 113 et 21 nématodes par gramme d'écorce sèche. La croissance des populations de nématodes a été également étudiée dans les bois et l'écorce de chacune des essences finement hachés, stérilisés ou non à l'autoclave et sur du papier filtre imbibé d'un extrait à l'éthanol d'aubier de #P. contorta et de #P. menziesii. Que le bois soit stérilisé ou non, la plus forte densité de nématodes est observée chez #P. contorta. Après 6 semaines, dans le bois non chauffé, la densité était de 137, 46, 5, 23 et 1 nématodes par gramme de bois sec pour #P. contorta, #P. menziesii, #A. grandis, #T. heterophylla et #T. plicata, respectivement. Par ailleurs, les populations de nématodes croissaient plus rapidement dans le papier filtre imbibé d'extrait de #P. contorta que dans celui imbibé d'extrait de #P. menziesii$. (Résumé d'auteur

Population dynamics of the pine wood nematode, Bursaphelenchus xylophilus, in excised branch segments of western north american conifers

La dynamique des populations de deux souches de nématode des pins (#Bursaphelenchus xylophilus) a été étudiée dans des segments de branche excisés d'#Abies grandis, #Pinus contorta, #Pseudotsuga menziesii, #Tsuga heterophylla et #Thuja plicata dans lesquels on a inoculé le champignon responsable du bleuissement (#Ophiostoma piceae). Des nématodes ont été inoculés avec le champignon dans de petits trous percés au centre des segments de branche. La taille et la structure par âge des populations de nématode ont été déterminées à intervalles de temps réguliers après l'inoculation. La population de nématode s'est développée dans les segments de branche de toutes les essences analysées. Toutefois, les densités de population étaient beaucoup plus importantes chez #P. contorta que chez les autres essences. Dans une des expériences, les nombres respectifs de nématodes dans les segments de branche de #P. contorta, #A. grandis, #P. menziesii, #T. heterophylla et #T. plicata, qui étaient de 2,0 ; 0,02 ; 0,1 ; 0,04 et 0,05 nématodes par gramme de bois sec 2 semaines après l'inoculation, sont passés à 57, 15, 11, 13 et 6 nématodes par gramme de bois sec après 16 semaines. L'abondance relative des juvéniles persistants du troisième stade (J3P) a augmenté avec le temps chez toutes les essences et elle était supérieure chez #P. contorta à la plupart des dates d'échantillonnage. L'abondance relative des J3P était significativement plus importante chez #P. contorta$ que chez les autres essences dans une des deux expériences seulement. (Résumé d'auteur

Evaluation of the BCS Approximation for the Attractive Hubbard Model in One Dimension

The ground state energy and energy gap to the first excited state are calculated for the attractive Hubbard model in one dimension using both the Bethe Ansatz equations and the variational BCS wavefunction. Comparisons are provided as a function of coupling strength and electron density. While the ground state energies are always in very good agreement, the BCS energy gap is sometimes incorrect by an order of magnitude, particularly at half-filling. Finite size effects are also briefly discussed for cases where an exact solution in the thermodynamic limit is not possible. In general, the BCS result for the energy gap is poor compared to the exact result.Comment: 25 pages, 5 Postscript figure

Forest tree seed health for germplasm conservation

The conservation and use of forest genetic resources worldwide poses several challenges to scientists, policy-makers and, in particular, to local stakeholders interested in long-term strategies to manage these biological resources in a sustainable manner. The vast diversity of tree species, many of which are still unknown, the high level of threats and the increased demand for forest products require prioritization of actions, clear indications for research and development, and strategies to mitigate the current trends in the depletion of forest resources. The strategy of conservation 'through-use' of forest genetic resources is a very important alternative to an in situ approach and, as such, is to be promoted and developed. However, basic knowledge and understanding of species' reproductive biology, seed production, seed quality and health aspects, limit the use of a larger number of species in important activities such as restoration, rehabilitation, agroforestry and on-farm conservation practices. Increasingly, the use of forest genetic diversity in research and breeding requires a greater movement of germplasm. This technical bulletin, prepared by Drs J. R. Sutherland, M. Diekmann and P. Berjak, all well-known scientists in their respective areas of specialization, aims to breach some of the knowledge gaps in forest seed biology and technology and, more importantly, to contribute to future research on priority forest seed health aspects. In addition, this it aims to increase awareness amongst technical staff involved in conservation and use activities. To this end it presents state-of-the-art tools for the identification of the most important tree seed pathogens and provides clear and ready-touse molecular-based tools for the screening of fungi and virus in seeds

Coherent states for exactly solvable potentials

A general algebraic procedure for constructing coherent states of a wide class of exactly solvable potentials e.g., Morse and P{\"o}schl-Teller, is given. The method, {\it a priori}, is potential independent and connects with earlier developed ones, including the oscillator based approaches for coherent states and their generalizations. This approach can be straightforwardly extended to construct more general coherent states for the quantum mechanical potential problems, like the nonlinear coherent states for the oscillators. The time evolution properties of some of these coherent states, show revival and fractional revival, as manifested in the autocorrelation functions, as well as, in the quantum carpet structures.Comment: 11 pages, 4 eps figures, uses graphicx packag

The 3D Structure of N132D in the LMC: A Late-Stage Young Supernova Remnant

We have used the Wide Field Spectrograph (WiFeS) on the 2.3m telescope at Siding Spring Observatory to map the [O III] 5007{\AA} dynamics of the young oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. From the resultant data cube, we have been able to reconstruct the full 3D structure of the system of [O III] filaments. The majority of the ejecta form a ring of ~12pc in diameter inclined at an angle of 25 degrees to the line of sight. We conclude that SNR N132D is approaching the end of the reverse shock phase before entering the fully thermalized Sedov phase of evolution. We speculate that the ring of oxygen-rich material comes from ejecta in the equatorial plane of a bipolar explosion, and that the overall shape of the SNR is strongly influenced by the pre-supernova mass loss from the progenitor star. We find tantalizing evidence of a polar jet associated with a very fast oxygen-rich knot, and clear evidence that the central star has interacted with one or more dense clouds in the surrounding ISM.Comment: Accepted for Publication in Astrophysics & Space Science, 18pp, 8 figure

Electromagnetic corrections in eta --> 3 pi decays

We re-evaluate the electromagnetic corrections to eta --> 3 pi decays at next-to-leading order in the chiral expansion, arguing that effects of order e^2(m_u-m_d) disregarded so far are not negligible compared to other contributions of order e^2 times a light quark mass. Despite the appearance of the Coulomb pole in eta --> pi+ pi- pi0 and cusps in eta --> 3 pi0, the overall corrections remain small.Comment: 21 pages, 11 figures; references updated, version published in EPJ

Constraining the Power Spectrum using Clusters

(Shortened Abstract). We analyze a redshift sample of Abell/ACO clusters and compare them with numerical simulations based on the truncated Zel'dovich approximation (TZA), for a list of eleven dark matter (DM) models. For each model we run several realizations, on which we estimate cosmic variance effects. We analyse correlation statistics, the probability density function, and supercluster properties from percolation analysis. As a general result, we find that the distribution of galaxy clusters provides a constraint only on the shape of the power spectrum, but not on its amplitude: a shape parameter 0.18 < \Gamma < 0.25 and an effective spectral index at 20Mpc/h in the range [-1.1,-0.9] are required by the Abell/ACO data. In order to obtain complementary constraints on the spectrum amplitude, we consider the cluster abundance as estimated using the Press--Schechter approach, whose reliability is explicitly tested against N--body simulations. We conclude that, of the cosmological models considered here, the only viable models are either Cold+Hot DM ones with \Omega_\nu = [0.2-0.3], better if shared between two massive neutrinos, and flat low-density CDM models with \Omega_0 = [0.3-0.5].Comment: 37 pages, Latex file, 9 figures; New Astronomy, in pres

The chemical enrichment of the ICM from hydrodynamical simulations

The study of the metal enrichment of the intra-cluster and inter-galactic media (ICM and IGM) represents a direct means to reconstruct the past history of star formation, the role of feedback processes and the gas-dynamical processes which determine the evolution of the cosmic baryons. In this paper we review the approaches that have been followed so far to model the enrichment of the ICM in a cosmological context. While our presentation will be focused on the role played by hydrodynamical simulations, we will also discuss other approaches based on semi-analytical models of galaxy formation, also critically discussing pros and cons of the different methods. We will first review the concept of the model of chemical evolution to be implemented in any chemo-dynamical description. We will emphasise how the predictions of this model critically depend on the choice of the stellar initial mass function, on the stellar life-times and on the stellar yields. We will then overview the comparisons presented so far between X-ray observations of the ICM enrichment and model predictions. We will show how the most recent chemo-dynamical models are able to capture the basic features of the observed metal content of the ICM and its evolution. We will conclude by highlighting the open questions in this study and the direction of improvements for cosmological chemo-dynamical models of the next generation.Comment: 25 pages, 11 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 18; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

X-ray Spectroscopy of Cooling Clusters

We review the X-ray spectra of the cores of clusters of galaxies. Recent high resolution X-ray spectroscopic observations have demonstrated a severe deficit of emission at the lowest X-ray temperatures as compared to that expected from simple radiative cooling models. The same observations have provided compelling evidence that the gas in the cores is cooling below half the maximum temperature. We review these results, discuss physical models of cooling clusters, and describe the X-ray instrumentation and analysis techniques used to make these observations. We discuss several viable mechanisms designed to cancel or distort the expected process of X-ray cluster cooling.Comment: To appear in Physics Reports, 71 pages, 20 figure