Giant Resonances based on Unitarily Transformed Two-Nucleon plus Phenomenological Three-Nucleon Interactions

We investigate giant resonances of spherical nuclei on the basis of the Argonne V18 potential after unitary transformation within the Similarity Renormalization Group or the Unitary Correlation Operator Method supplemented by a phenomenological three-body contact interaction. Such Hamiltonians can provide a good description of ground-state energies and radii within Hartree-Fock plus low-order many-body perturbation theory. The standard Random Phase Approximation is applied here to calculate the isoscalar monopole, isovector dipole, and isoscalar quadrupole excitation modes of the 40Ca, 90Zr, and 208Pb nuclei. Thanks to the inclusion of the three-nucleon interaction and despite the minimal optimization effort, a reasonable agreement with experimental centroid energies of all three modes has been achieved. The role and scope of the Hartree-Fock reference state in RPA methods are discussed.Comment: v2: 11 pages, incl. 3 figures; extended discussion and outlook; to appear in J.Phys.

The evolution of the jet from Herbig Ae star HD 163296 from 1999 to 2011

Young A and B stars, the so-called Herbig Ae/Be stars (HAeBe), are surrounded by an active accretion disk and drive outflows. We study the jet HH 409, which is launched from the HAeBe star HD 163296, using new and archival observations from Chandra and HST/STIS. In X-rays we can show that the central source is not significantly extended. The approaching jet, but not the counter-jet, is detected in Ly alpha. In addition, there is red-shifted Ly alpha emission extended in the same direction as the jet, that is also absent in the counter-jet. We can rule out an accretion or disk-wind origin for this feature. In the optical we find the knots B and B2 in the counter-jet. Knot B has been observed previously, so we can derive its proper motion of 0.37+-0.01 arcsec/yr. Its electron density is 3000/cm^3, thus the cooling time scale is a few months only, so the knot needs to be reheated continuously. The shock speed derived from models of H alpha and forbidden emission lines (FELs) decreased from 50 km/s in 1999 to 30 km/s in 2011 because the shock front loses energy as it travels along the jet. Knot B2 is observed at a similar position in 2011 as knot B was in 1999, but shows a lower ionization fraction and higher mass loss rate, proving variations in the jet launching conditions.Comment: 14 pages, 8 figures, accepted by A&

Non-axisymmetric Magnetorotational Instabilities in Cylindrical Taylor-Couette Flow

We study the stability of cylindrical Taylor-Couette flow in the presence of azimuthal magnetic fields, and show that one obtains non-axisymmetric magnetorotational instabilities, having azimuthal wavenumber m=1. For Omega_o/Omega_i only slightly greater than the Rayleigh value (r_i/r_o)^2, the critical Reynolds and Hartmann numbers are Re_c ~ 10^3 and Ha_c ~ 10^2, independent of the magnetic Prandtl number Pm. These values are sufficiently small that it should be possible to obtain these instabilities in the PROMISE experimental facility.Comment: final version as accepted by Phys Rev Let

Preface "Methods and strategies to evaluate landslide hazard and risk"

Federal Institute for Geosciences and Natural Resources, Hannover, GermanyThe special issue of Natural Hazards and Earth SystemSciences entitled "Methods and strategies to evaluatelandslide hazard and risk", which we had the fortune to edit,contains a selected set of contributions originally presentedat the General Assembly of the European GeosciencesUnion, in Vienna, Austria, on 13–18 April 2008. Themeeting proved to be a valuable opportunity to discussand compare methods, techniques and tools for discovering,evaluating, avoiding and mitigating landslide hazards andthe related risk. Novel approaches and case studies ofheuristic, statistical, and physically based models to evaluatelandslide hazards and risk at different geographical scalesand in different physiographic environments were presented.During the meeting, Theo van Asch, 2008 Sergey Solovievmedallist, gave an inspiring presentation on "Some issues andchallenges in landslide hazard modelling". This presentationsummarized the state-of-the-art, physically based landslidemodelling, and set the path for future research on thischallenging topic.The special issue contains six of the 29 oral and postercontributions originally presented and discussed by morethan 50authors at the meeting. The six papers cover alarge spectrum of topics, from site-specific investigationsto global-scale landslide hazard assessments. van Aschand Malet (2009) focused on the potential transition ofsliding blocks (slumps) into flow-like processes due tothe generation of excess pore water pressure in undrainedconditions. The generation of excess pore water pressuremay be the consequence of the deformation of the landslidebody during motion. The authors propose and discuss twomodel concepts that are tested on two slumps that havedeveloped in secondary scarps of the Super-Sauze mudslidein the Barcelonnette area, Southern Alps, France.Correspondence to: P. Reichenbach([email protected])Gunther and Thiel (2009) evaluated structurally-controlled¨failure susceptibility of fractured Cretaceous chalk rocks andtopographically-controlled shallow landslide susceptibilityof overlying glacial sediments in the Jasmund cliff area,Rugen Island, Germany. These authors adopted a combined¨methodology that involved spatially distributed kinematicalrock slope failure testing with tectonic fabric data, andphysically-based and inventory-based shallow landslidesusceptibility analyses. Romstad et al. (2009) presentedan innovative approach for regional hazard assessment ofNorwegian lakes exposed to tsunamis that can generatecatastrophic rockslides. The method successfully distin-guished between lakes with high and low rockslide potential.For each lake, the rockfall potential was determined basedon the topographical setting. For this reason, the rockfallpotential does not measure the probability of rockslides in thelakes. Van Den Eeckhaut et al. (2009) discussed a combinedlandslide inventory and susceptibility assessment based ondifferent mapping units carried out in the Flemish Ardennes,Belgium. The landslide susceptibility zonation was preparedthrough heuristic combination of, (i) a regional landslideinventory, (ii) a grid-cell-based map showing susceptibilityto landslide initiation, and (iii) a topographic-unit-based mapshowing the susceptibility to landslide spatial occurrence.Garc´ia-Rodr ´iguez and Malpica (2010) presented an approachfor assessing earthquake-triggered landslide susceptibilityusing artificial neural networks (ANN) in El Salvador.Modelling results were checked using independent landslideinformation, and revealed a good agreement between thelandslide inventory and the high susceptibility zoning. Thenew susceptibility zonation was compared critically to anexisting susceptibility zonation obtained through logisticregression analysis. Kirschbaum et al. (2009) presented apreliminary global landslide hazard algorithm developed toestimate areas of potential landslide occurrence in near real-time by combining a calculation of landslide susceptibilitywith satellite-derived rainfall estimates to forecast areas withPublished by Copernicus Publications on behalf of the European Geosciences Union

The Ekman-Hartmann layer in MHD Taylor-Couette flow

We study magnetic effects induced by rigidly rotating plates enclosing a cylindrical MHD Taylor-Couette flow at the finite aspect ratio $H/D=10$. The fluid confined between the cylinders is assumed to be liquid metal characterized by small magnetic Prandtl number, the cylinders are perfectly conducting, an axial magnetic field is imposed \Ha \approx 10, the rotation rates correspond to \Rey of order $10^2-10^3$. We show that the end-plates introduce, besides the well known Ekman circulation, similar magnetic effects which arise for infinite, rotating plates, horizontally unbounded by any walls. In particular there exists the Hartmann current which penetrates the fluid, turns into the radial direction and together with the applied magnetic field gives rise to a force. Consequently the flow can be compared with a Taylor-Dean flow driven by an azimuthal pressure gradient. We analyze stability of such flows and show that the currents induced by the plates can give rise to instability for the considered parameters. When designing an MHD Taylor-Couette experiment, a special care must be taken concerning the vertical magnetic boundaries so they do not significantly alter the rotational profile.Comment: 9 pages, 6 figures; accepted to PR