Coupled NASTRAN/boundary element formulation for acoustic scattering

A coupled finite element/boundary element capability is described for calculating the sound pressure field scattered by an arbitrary submerged 3-D elastic structure. Structural and fluid impedances are calculated with no approximation other than discretization. The surface fluid pressures and normal velocities are first calculated by coupling a NASTRAN finite element model of the structure with a discretized form of the Helmholtz surface integral equation for the exterior field. Far field pressures are then evaluated from the surface solution using the Helmholtz exterior integral equation. The overall approach is illustrated and validated using a known analytic solution for scattering from submerged spherical shells

CCAFS Theory of Change facilitation guide

The CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) has in total produced two facilitation guides to support the development of Impact Pathways and project Monitoring and Evaluation (M&E) for result-based management. The "CCAFS Theory of Change facilitation guide" is the original, and more comprehensive guide, and was developed in June 2014. The updated version is more easy-to-use and stripped down version of the original facilitation guide, called "Revised CCAFS Theory of Change Facilitation Guide", from late 2014. The Annex belongs to the original version. The updated version can be found here: http://hdl.handle.net/10568/5687

CCAFS Theory of Change facilitation guide

The CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) has in total produced two facilitation guides to support the development of Impact Pathways and project Monitoring and Evaluation (M&E) for result-based management. The "CCAFS Theory of Change facilitation guide" is the original, and more comprehensive guide, and was developed in June 2014. The updated version is more easy-to-use and stripped down version of the original facilitation guide, called "Revised CCAFS Theory of Change Facilitation Guide", from late 2014. The Annex belongs to the original version. The updated version can be found here: http://hdl.handle.net/10568/5687

The exceptional Herbig Ae star HD101412: The first detection of resolved magnetically split lines and the presence of chemical spots in a Herbig star

We obtained high-resolution, high signal-to-noise UVES and a few lower quality HARPS spectra revealing the presence of resolved magnetically split lines. HD101412 is the first Herbig Ae star for which the rotational Doppler effect was found to be small in comparison to the magnetic splitting. The measured mean magnetic field modulus varies from 2.5 to 3.5kG, while the mean quadratic field was found to vary in the range of 3.5 to 4.8kG. To determine the period of variations, we used radial velocity, equivalent width, line width, and line asymmetry measurements of variable spectral lines of several elements, as well as magnetic field measurements. The most pronounced variability was detected for spectral lines of He I and the iron peak elements, whereas the spectral lines of CNO elements are only slightly variable. From spectral variations and magnetic field measurements we derived a potential rotation period P_rot=13.86d, which has to be proven in future studies with a larger number of observations. It is the first time that the presence of element spots is detected on the surface of a Herbig Ae/Be star. Our previous study of Herbig Ae stars revealed a trend towards stronger magnetic fields for younger Herbig Ae stars, confirmed by statistical tests. This is in contrast to a few other (non-statistical) studies claiming that magnetic Herbig Ae stars are progenitors of the magnetic Ap stars. New developments in MHD theory show that the measured magnetic field strengths are compatible with a current-driven instability of toroidal fields generated by differential rotation in the stellar interior. This explanation for magnetic intermediate-mass stars could be an alternative to a frozen-in fossil field.Comment: 7 pages, 6 figures, 1 table, to appear in Astronomische Nachrichte

Expansion velocity of a one-dimensional, two-component Fermi gas during the sudden expansion in the ballistic regime

We show that in the sudden expansion of a spin-balanced two-component Fermi gas into an empty optical lattice induced by releasing particles from a trap, over a wide parameter regime, the radius $R_n$ of the particle cloud grows linearly in time. This allow us to define the expansion velocity $V_{ex}$ from $R_n=V_{ex}t$. The goal of this work is to clarify the dependence of the expansion velocity on the initial conditions which we establish from time-dependent density matrix renormalization group simulations, both for a box trap and a harmonic trap. As a prominent result, the presence of a Mott-insulating region leaves clear fingerprints in the expansion velocity. Our predictions can be verified in experiments with ultra-cold atoms.Comment: 8 pages 10 figures, version as published with minor stylistic change

SIMBA's view of the epsilon Eri disk

We present the first observational confirmation for an extended circumstellar dust disk around epsilon Eri. The observations were obtained with the bolometer array SIMBA at the 15 m radio telescope SEST in Chile and measure the dust continuum at 1.2 mm. The emission, with a total flux of 21.4 mJy and a rms of 2.2 mJy/beam, is resolved to a deconvolved size of 27.4 arcsec which corresponds to 88 AU. No clear indication for a ring-like disk structure is seen, possibly also due to the telescope's large beam width of 24 arcsec. Models of the object's spectral energy distribution from IR to mm-wavelengths show that the emission can also be explained by a simple disk model. We further demonstrate the strong influence of noise and propose to be cautious with interpretations of the ring substructure.Comment: To appear in A&A Letters, in pres

Measuring the Impact of Agglomeration on Productivity: Evidence from Chilean Retailers

This research extends the agglomeration literature to a country that has not been studied and a market sector that has received little attention. The majority of research that examines how density affects productivity has indirectly measured productivity through worker wages or property prices. The research uses individual supermarkets’ store productivity, proxied by 10 years of annual sales per square foot. Studying supermarkets permits the examination of the effect consumers might have on productivity. Agglomerations (density) could increase or decrease productivity depending on the relative extent of increased competition versus productivity gains, as consumers choose where to shop based on their interests in reducing shopping time (transport costs) and comparison shopping (product quality and pricing). Stores are described by who operates the store, the brand of the store and the size of the store. Results indicate that density has a differential impact depending on the store itself and the mix of stores nearby