Stationary axisymmetric exteriors for perturbations of isolated bodies in general relativity, to second order

Perturbed stationary axisymmetric isolated bodies, e.g. stars, represented by a matter-filled interior and an asymptotically flat vacuum exterior joined at a surface where the Darmois matching conditions are satisfied, are considered. The initial state is assumed to be static. The perturbations of the matching conditions are derived and used as boundary conditions for the perturbed Ernst equations in the exterior region. The perturbations are calculated to second order. The boundary conditions are overdetermined: necessary and sufficient conditions for their compatibility are derived. The special case of perturbations of spherical bodies is given in detail.Comment: RevTeX; 32 pp. Accepted by Phys. Rev. D. Added references and extra comments in introductio

Abundant Z-cyanomethanimine in the interstellar medium: paving the way to the synthesis of adenine

We report the first detection in the interstellar medium of the Z-isomer of cyanomethanimine (HNCHCN), an HCN dimer proposed as precursor of adenine. We identified six transitions of Z-cyanomethanimine, along with five transitions of E-cyanomethanimine, using IRAM 30m observations towards the Galactic Center quiescent molecular cloud G+0.693. The Z-isomer has a column density of (2.0$\pm$0.6)$\times$10$^{14}$ cm$^{-2}$ and an abundance of 1.5$\times$10$^{-9}$. The relative abundance ratio between the isomers is [Z/E]$\sim$6. This value cannot be explained by the two chemical formation routes previously proposed (gas-phase and grain surface), which predicts abundances ratios between 0.9 and 1.5. The observed [Z/E] ratio is in good agreement with thermodynamic equilibrium at the gas kinetic temperature (130$-$210 K). Since isomerization is not possible in the ISM, the two species may be formed at high temperature. New chemical models, including surface chemistry on dust grains and gas-phase reactions, should be explored to explain our findings. Whatever the formation mechanism, the high abundance of Z-HNCHCN shows that precursors of adenine are efficiently formed in the ISM.Comment: Accepted in Monthly Notices of the Royal Astronomical Society Letter

El pas de la decoració naturalista a la decoració geomètrica en els teixits andalusins

A la primera meitat del segle xii la tècnica del lampàs apareix a Alandalus, sempre unida a la del taqueté, amb una decoració de cercles amb animals o personatges al seu interior, de tradició persa. La decoració, amb la mateixa tècnica, va passar a formes més geometritzades durant la segona meitat del segle, a causa de la invasió d’Alandalus pels almohades i la formació de l’Imperi almohade. Aquesta decoració va arribar al total geometrisme a la fi del segle xii i l’inici del xiii, qeometrisme i alhora riquesa de colors, mentre que la tècnica va evolucionar cap a una major simplificació del treball, però mantenint el teixit fet alhora amb tècnica de lampàs i taqueté en un teler no preparat per a teixir lampàs. En aquest article hem volgut posar al dia les nostres recerques i l’estat de la qüestió sobre els lampàs andalusins del segle xii i del primer quart i la segona meitat del segle xiii, tot fent menció a teixits específics que ens van mostrant aquesta evolució i, especialment, als que es conserven al Museu Episcopal de Vic. In the first half of the 12th century the Persian technique of lampas appears in Alandalus –always together with the taqueté technique–, with a decoration of circles with animals or people in their interior. During the second half of the century and using the same technique, the decorations started to become more geometric in form owing to the invasions of Alandalus by the Almohads and the formation of the Almohad Empire. These decorations become totally geometric in form and rich in colour by the end of the 12th century and through into the beginning of the 13th. The technique moved towards a greater simplification of the work, although the fabric continued to be made using lampas and taquete with a loom not prepared for weaving lampas. In this article we have tried to update our research and shed light on the technique of Andalusian lampas of the 12th century and the first quarter and second half of the 13th century, while presenting fabrics that show these evolutions –in particular, the fabrics kept in the Museu Episcopal de Vic

Complex organic molecules in the Galactic Centre: the N-bearing family

We present an unbiased spectral line survey toward the Galactic Centre (GC) quiescent giant molecular cloud (QGMC), G+0.693 using the GBT and IRAM 30$\,$ telescopes. Our study highlights an extremely rich organic inventory of abundant amounts of nitrogen (N)-bearing species in a source without signatures of star formation. We report the detection of 17 N-bearing species in this source, of which 8 are complex organic molecules (COMs). A comparison of the derived abundances relative to H$_2$ is made across various galactic and extragalactic environments. We conclude that the unique chemistry in this source is likely to be dominated by low-velocity shocks with X-rays/cosmic rays also playing an important role in the chemistry. Like previous findings obtained for O-bearing molecules, our results for N-bearing species suggest a more efficient hydrogenation of these species on dust grains in G+0.693 than in hot cores in the Galactic disk, as a consequence of the low dust temperatures coupled with energetic processing by X-ray/cosmic ray radiation in the GC.Comment: 24 pages, 23 figures, 7 tables, accepted for publication in MNRA

L'Humeral de Sant Eudald

L'Humeral de Sant Eudald va ser trobat durant l'obertura del reliquiari del sant monestir de Santa Maria de Ripoll el desembre de 1979. Va ser restaurat i estudiat al Museu Tèxtil i d'Indumentària de Barcelona i actualment es conserva al Museu Etnogràfic de Ripoll. És una peça d'indumentària andalusina del tipus almaizar, utilitzada a Rupoll com a humeral, fet del qual li ve el nom. Tècnicament, està format per dos teixits: la part central és una baiadera que alterna tafetà i sarja, mentre que els dos extrems són d'un teixit que combina tafetà, espiga i tapisseria. És d'ordit de seda i trames de seda i or. Pertany a un grup de tapisseries andalusines del segle XIII amb decoració de llaceries, ataurics i inscripcions de caràcter nasj

Order in driven vortex lattices in superconducting Nb films with nanostructured pinning potentials

Driven vortex lattices have been studied in a material with strong pinning, such as Nb films. Samples in which natural random pinning coexists with artificial ordered arrays of defects (submicrometric Ni dots) have been fabricated with different geometries (square, triangular and rectangular). Three different dynamic regimes are found: for low vortex velocities, there is a plastic regime in which random defects frustrate the effect of the ordered array; then, for vortex velocities in the range 1-100 m/s, there is a sudden increase in the interaction between the vortex lattice and the ordered dot array, independent on the geometry. This effect is associated to the onset of quasi long range order in the vortex lattice leading to an increase in the overlap between the vortex lattice and the magnetic dots array. Finally, at larger velocities the ordered array-vortex lattice interaction is suppresed again, in agreement with the behavior found in numerical simulations.Comment: 8 text pages + 4 figure

On The spectrum of a Noncommutative Formulation of the D=11 Supermembrane with Winding

A regularized model of the double compactified D=11 supermembrane with nontrivial winding in terms of SU(N) valued maps is obtained. The condition of nontrivial winding is described in terms of a nontrivial line bundle introduced in the formulation of the compactified supermembrane. The multivalued geometrical objects of the model related to the nontrivial wrapping are described in terms of a SU(N) geometrical object which in the $N\to \infty$ limit, converges to the symplectic connection related to the area preserving diffeomorphisms of the recently obtained non-commutative description of the compactified D=11 supermembrane.(I. Martin, J.Ovalle, A. Restuccia. 2000,2001) The SU(N) regularized canonical lagrangian is explicitly obtained. In the $N\to \infty$ limit it converges to the lagrangian in (I.Martin, J.Ovalle, A.Restuccia. 2000,2001) subject to the nontrivial winding condition. The spectrum of the hamiltonian of the double compactified D=11 supermembrane is discussed. Generically, it contains local string like spikes with zero energy. However the sector of the theory corresponding to a principle bundle characterized by the winding number $n \neq 0$, described by the SU(N) model we propose, is shown to have no local string-like spikes and hence the spectrum of this sector should be discrete.Comment: 16 pages.Latex2