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

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

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

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

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

Active Brownian Particles. From Individual to Collective Stochastic Dynamics

We review theoretical models of individual motility as well as collective dynamics and pattern formation of active particles. We focus on simple models of active dynamics with a particular emphasis on nonlinear and stochastic dynamics of such self-propelled entities in the framework of statistical mechanics. Examples of such active units in complex physico-chemical and biological systems are chemically powered nano-rods, localized patterns in reaction-diffusion system, motile cells or macroscopic animals. Based on the description of individual motion of point-like active particles by stochastic differential equations, we discuss different velocity-dependent friction functions, the impact of various types of fluctuations and calculate characteristic observables such as stationary velocity distributions or diffusion coefficients. Finally, we consider not only the free and confined individual active dynamics but also different types of interaction between active particles. The resulting collective dynamical behavior of large assemblies and aggregates of active units is discussed and an overview over some recent results on spatiotemporal pattern formation in such systems is given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte

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

Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory

Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influences the Moliere radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle Physic

Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropy in the arrival directions of cosmic rays above the Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{$6\times 10^{19}$eV}. The anisotropy was measured by the fraction of arrival directions that are less than $3.1^\circ$ from the position of an active galactic nucleus within 75 Mpc (using the V\'eron-Cetty and V\'eron $12^{\rm th}$ catalog). An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directions has increased from 27 to 69, allowing a more precise measurement. The correlating fraction is $(38^{+7}_{-6})$, compared with $21$ expected for isotropic cosmic rays. This is down from the early estimate of $(69^{+11}_{-13})$. The enlarged set of arrival directions is examined also in relation to other populations of nearby extragalactic objects: galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in hard X-rays by the Swift Burst Alert Telescope. A celestial region around the position of the radiogalaxy Cen A has the largest excess of arrival directions relative to isotropic expectations. The 2-point autocorrelation function is shown for the enlarged set of arrival directions and compared to the isotropic expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201

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