Some results on rational surfaces and Fano varieties

The goal of this article is to study the equations and syzygies of embeddings of rational surfaces and certain Fano varieties. Given a rational surface X and an ample and base-point-free line bundle L on X, we give an optimal numerical criterion for L to satisfy property Np. This criterion turns out to be a characterization of property Np if X is anticanonical. We also prove syzygy results for adjunction bundles and a Reider type theorem for higher syzygies. For certain Fano varieties we also prove results on very ampleness and higher syzygies.Comment: 26 pages, AMSTe

Effect of spin-orbit interaction on a magnetic impurity in the vicinity of a surface

We propose a new mechanism for surface-induced magnetic anisotropy to explain the thickness-dependence of the Kondo resistivity of thin films of dilute magnetic alloys. The surface anisotropy energy, generated by spin-orbit coupling on the magnetic impurity itself, is an oscillating function of the distance d from the surface and decays as 1/d^2. Numerical estimates based on simple models suggest that this mechanism, unlike its alternatives, gives rise to an effect of the desired order of magnitude.Comment: 4 pages, 4 figure

Mapping the star formation history of Mrk86: I. Data and models

We have obtained optical (BVR, [OIII]5007 and Halpha), near infrared (JHK) imaging and long-slit optical spectroscopy for the Blue Compact Dwarf galaxy Mrk86 (NGC2537). In this paper, the first of two, we present optical-near- infrared colors and emission-line fluxes for the currently star-forming regions, intemediate aged starburst and underlying stellar population. We also describe the evolutionary synthesis models used in Paper II. The R and Halpha luminosity distributions of the galaxy star-forming regions show maxima at M_R=-9.5 and L_Halpha=10^37.3 erg s^-1. The underlying stellar population shows an exponential surface brigthness profile with central value, mu_E,0=21.5 mag arcsec^-2, and scale, alpha=0.88 kpc, both measured in the R-band image. In the galaxy outer regions, dominated by this component, no significant color gradients are observed. Finally, a set of evolutionary synthesis models have been developed, covering a wide range in metallicity and burst strength.Comment: 21 pages, 14 figures, 2 landscape tables, accepted for publication in Astronomy & Astrophysics Supplement Series, for higher resolution images see ftp://cutrex.fis.ucm.es/pub/OUT/gil/PAPERS/aa00_I.ps.g

Tipificació de dos noms Cavanillesians, Galium Fruticescens (Rubiaceae) i Scorzonera pumila (Compositae)

The Cavanillesian names Galium fruticescens and Scorzonera pumila, basionym of Launaea pumila, are lectotypified from original specimens preserved in the Cavanilles herbarium in the Royal Botanic Garden of Madrid (MA).Els noms cavanillesians Galium fruticescens i Scorzonera pumila, basiònim de Launaea pumila, són lectotipificats a partir d’espècimens que pertanyen al material original de l’autor conservat a l’herbari del Reial Jardí Botànic de Madrid (MA)

Restricted dog leucocyte antigen (DLA) class II haplotypes and genotypes in Beagles

AbstractBeagles are commonly used in vaccine trials as part of the regulatory approval process. Genetic restriction within this breed and the impact this might have on vaccine responses are rarely considered. This study was designed to characterise diversity of dog leucocyte antigen (DLA) class II genes in a breeding colony of laboratory Beagles, whose offspring are used in vaccine studies. DLA haplotypes were determined by PCR and sequence-based typing from genomic DNA extracted from blood. Breeding colony Beagles had significantly different DLA haplotype frequencies in comparison with pet Beagles and both groups showed limited DLA diversity. Restricted DLA class II genetic variability within Beagles might result in selective antigen presentation and vaccine responses that are not necessarily representative of those seen in other dog breeds

Simulating Turbulence Using the Astrophysical Discontinuous Galerkin Code TENET

In astrophysics, the two main methods traditionally in use for solving the Euler equations of ideal fluid dynamics are smoothed particle hydrodynamics and finite volume discretization on a stationary mesh. However, the goal to efficiently make use of future exascale machines with their ever higher degree of parallel concurrency motivates the search for more efficient and more accurate techniques for computing hydrodynamics. Discontinuous Galerkin (DG) methods represent a promising class of methods in this regard, as they can be straightforwardly extended to arbitrarily high order while requiring only small stencils. Especially for applications involving comparatively smooth problems, higher-order approaches promise significant gains in computational speed for reaching a desired target accuracy. Here, we introduce our new astrophysical DG code TENET designed for applications in cosmology, and discuss our first results for 3D simulations of subsonic turbulence. We show that our new DG implementation provides accurate results for subsonic turbulence, at considerably reduced computational cost compared with traditional finite volume methods. In particular, we find that DG needs about 1.8 times fewer degrees of freedom to achieve the same accuracy and at the same time is more than 1.5 times faster, confirming its substantial promise for astrophysical applications.Comment: 21 pages, 7 figures, to appear in Proceedings of the SPPEXA symposium, Lecture Notes in Computational Science and Engineering (LNCSE), Springe

Friedel oscillations induced surface magnetic anisotropy

We present detailed numerical studies of the magnetic anisotropy energy of a magnetic impurity near the surface of metallic hosts (Au and Cu), that we describe in terms of a realistic tight-binding surface Green's function technique. We study the case when spin-orbit coupling originates from the d-band of the host material and we also investigate the case of a strong local spin-orbit coupling on the impurity itself. The splitting of the impurity's spin-states is calculated to leading order in the exchange interaction between the impurity and the host atoms using a diagrammatic Green's function technique. The magnetic anisotropy constant is an oscillating function of the separation d from the surface: it asymptotically decays as 1/d2 and its oscillation period is determined by the extremal vectors of the host's Fermi Surface. Our results clearly show that the host-induced magnetic anisotropy energy is by several orders of magnitude smaller than the anisotropy induced by the local mechanism, which provides sufficiently large anisotropy values to explain the size dependence of the Kondo resistance observed experimentally.Comment: 11 pages, 7 figures, submitted to PR