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.

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

Structural, magnetic, electric, dielectric, and thermodynamic properties of multiferroic GeV4S8

The lacunar spinel GeV4S8 undergoes orbital and ferroelectric ordering at the Jahn-Teller transition around 30 K and exhibits antiferromagnetic order below about 14 K. In addition to this orbitally driven ferroelectricity, lacunar spinels are an interesting material class, as the vanadium ions form V4 clusters representing stable molecular entities with a common electron distribution and a well-defined level scheme of molecular states resulting in a unique spin state per V4 molecule. Here we report detailed x-ray, magnetic susceptibility, electrical resistivity, heat capacity, thermal expansion, and dielectric results to characterize the structural, electric, dielectric, magnetic, and thermodynamic properties of this interesting material, which also exhibits strong electronic correlations. From the magnetic susceptibility, we determine a negative Curie-Weiss temperature, indicative for antiferromagnetic exchange and a paramagnetic moment close to a spin S = 1 of the V4 molecular clusters. The low-temperature heat capacity provides experimental evidence for gapped magnon excitations. From the entropy release, we conclude about strong correlations between magnetic order and lattice distortions. In addition, the observed anomalies at the phase transitions also indicate strong coupling between structural and electronic degrees of freedom. Utilizing dielectric spectroscopy, we find the onset of significant dispersion effects at the polar Jahn-Teller transition. The dispersion becomes fully suppressed again with the onset of spin order. In addition, the temperature dependencies of dielectric constant and specific heat possibly indicate a sequential appearance of orbital and polar order.Comment: 15 pages, 9 figure

Dynamics of a Heisenberg spin chain in the quantum critical regime: NMR experiment versus effective field theory

A comprehensive comparison between the magnetic field- and temperature-dependent low frequency spin dynamics in the antiferromagnetic spin-1/2 Heisenberg chain (AFHC) system copper pyrazine dinitrate, probed via the 13C-nuclear magnetic resonance (NMR) relaxation rate 1/T1, and the field theoretical approach in the Luttinger liquid (LL) regime has been performed. We have found a very good agreement between the experiment and theory in the investigated temperature and field range. Our results demonstrate how strongly the quantum critical point affects the spin dynamics of Heisenberg spin chain compounds.Comment: 5 pages, 3 figure

Dynamic properties of silicon-integrated short-wavelength hybrid-cavity VCSEL

We present a vertical-cavity surface-emitting laser (VCSEL) where a GaAs-based "half-VCSEL" is attached to a dielectric distributed Bragg reflector on silicon using ultra-thin divinylsiloxane-bis-benzocyclobutene (DVS-BCB) adhesive bonding, creating a hybrid cavity where the optical field extends over both the GaAs- and the Si-based parts of the cavity. A VCSEL with an oxide aperture diameter of 5 mu m and a threshold current of 0.4 mA provides 0.6 mW output power at 845 nm. The VCSEL exhibits a modulation bandwidth of 11 GHz and can transmit data up to 20 Gbps

Stabilization of internal spaces in multidimensional cosmology

Effective 4-dimensional theories are investigated which were obtained under dimensional reduction of multidimensional cosmological models with a minimal coupled scalar field as matter source. Conditions for the internal space stabilization are considered and the possibility for inflation in the external space is discussed. The electroweak as well as the Planck fundamental scale approaches are investigated and compared with each other. It is shown that there exists a rescaling for the effective cosmological constant as well as for gravitational exciton masses in the different approaches.Comment: 12 pages, LaTeX2e, to appear in Phys.Rev.D, note adde

Magnetic ground state and 2D behavior in pseudo-Kagome layered system Cu3Bi(SeO3)2O2Br

Anisotropic magnetic properties of a layered kagome-like system Cu3Bi(SeO3)2O2Br have been studied by bulk magnetization and magnetic susceptibility measurements as well as powder and single-crystal neutron diffraction. At T_N = 27.4 K the system develops an alternating antiferromagnetic order of (ab) layers, which individually exhibit canted ferrimagnetic moment arrangement, resulting from the competing ferro- and antiferro-magnetic intralayer exchange interactions. A magnetic field B_C ~ 0.8 T applied along the c axis (perpendicular to the layers) triggers a metamagnetic transition, when every second layer flips, i.e., resulting in a ferrimagnetic structure. Significantly higher fields are required to rotate the ferromagnetic component towards the b axis (~7 T) or towards the a axis (~15 T). The estimates of the exchange coupling constants and features indicative of an XY character of this quasi-2D system are presented.Comment: 7 pages, 6 figures, final versio

AdS and stabilized extra dimensions in multidimensional gravitational models with nonlinear scalar curvature terms 1/R and R^4

We study multidimensional gravitational models with scalar curvature nonlinearities of the type 1/R and R^4. It is assumed that the corresponding higher dimensional spacetime manifolds undergo a spontaneous compactification to manifolds with warped product structure. Special attention is paid to the stability of the extra-dimensional factor spaces. It is shown that for certain parameter regions the systems allow for a freezing stabilization of these spaces. In particular, we find for the 1/R model that configurations with stabilized extra dimensions do not provide a late-time acceleration (they are AdS), whereas the solution branch which allows for accelerated expansion (the dS branch) is incompatible with stabilized factor spaces. In the case of the R^4 model, we obtain that the stability region in parameter space depends on the total dimension D=dim(M) of the higher dimensional spacetime M. For D>8 the stability region consists of a single (absolutely stable) sector which is shielded from a conformal singularity (and an antigravity sector beyond it) by a potential barrier of infinite height and width. This sector is smoothly connected with the stability region of a curvature-linear model. For D<8 an additional (metastable) sector exists which is separated from the conformal singularity by a potential barrier of finite height and width so that systems in this sector are prone to collapse into the conformal singularity. This second sector is not smoothly connected with the first (absolutely stable) one. Several limiting cases and the possibility for inflation are discussed for the R^4 model.Comment: 28 pages, minor cosmetic improvements, Refs. added; to appear in Class. Quantum Gra