Vortices in the presence of a nonmagnetic atom impurity in 2D XY ferromagnets

Using a model of nonmagnetic impurity potential, we have examined the behavior of planar vortex solutions in the classical two-dimensional XY ferromagnets in the presence of a spin vacancy localized out of the vortex core. Our results show that a spinless atom impurity gives rise to an effective potential that repels the vortex structure.Comment: 6 pages, 2 figures, RevTex

Exact edge singularities and dynamical correlations in spin-1/2 chains

Exact formulas for the singularities of the dynamical structure factor, S^{zz}(q,omega), of the S=1/2 xxz spin chain at all q and any anisotropy and magnetic field in the critical regime are derived, expressing the exponents in terms of the phase shifts which are known exactly from the Bethe ansatz solution. We also study the long time asymptotics of the self-correlation function . Utilizing these results to supplement very accurate time-dependent Density Matrix Renormalization Group (DMRG) for short to moderate times, we calculate S^{zz}(q,omega) to very high precision.Comment: 4 pages, 1 figure, 1 table, published versio

Orthogonality catastrophe and Kondo effect in graphene

Anderson's orthogonality catastrophe in graphene, at energies close to the Dirac point, is analyzed. It is shown that, in clean systems, the orthogonality catastrophe is suppressed, due to the vanishing density of states at the Dirac point. In the presence of preexisting localized states at the Dirac energy, the orthogonality catastrophe shows similar features to those found in normal metals with a finite density of states at the Fermi level. The implications for the Kondo effect induced by magnetic impurities, and for the Fermi edge singularities in tunneling processes are also discussed.Comment: 7 pages, 7 figure

Interfacial profiles of mismatched lamellae in thin diblock copolymer films

A number of recent experiments have allowed direct study of diblock copolymer morphology on patternedsurfaces. Here we examine, by computer simulation, the morphology of a diblock thin film in contact with a substrate having large stripes. The diblock aligns parallel to the surface but is frustrated at the point where two stripes join. We show here that at the joint one of the phases is continuous while the other is discontinuous. In the region of the join the lamellae form a kink with a length scale of the same size as the lamellar period. Within the kink the ordering is suppressed.G.G.P. and D.R.M.W. acknowledge support from an ARC Large Grant and D.R.M.W. is supported by an ARC QEII. AC acknowledges the Donors of the Petroleum Research Fund, administered by the American Chemical Society for support of this work. This work has also been supported by National Science Foundation Grant No. CDA- 9724289 which has funded the purchase of computational equipments ~including the Convex-Exemplar machine! at Kansas State University

Crecimiento in vitro de Lactarius deliciosus en medio de cultivo BAF y MNM

- Chávez, D.; Pereira, G. ; Machuca, A. Laboratorio de Biotecnología de Hongos. Departamento Forestal, Campus Los Ángeles, Universidad de Concepción. J. A. Coloma 0201, Casilla 341. Los Ángeles-Chile.Lactarius deliciosus (L. Gray) es un hongo ectomicorrícico que crece asociado a Pinus radiata, constituyendo sus cuerpos fructíferos un producto muy apetecido desde el punto de vista gastronómico en la alta cocina. Desde esta perspectiva es un hongo que puede entregar valor agregado al bosque, siendo necesario entonces, conocer y caracterizar su comportamiento en laboratorio, y posteriormente, en las inoculaciones en viveros. En el presente estudio se aisló Lactarius deliciosus a partir de carpóforos jóvenes, recolectados de plantaciones de Pinus radiata de la Comuna de Ninhue, Provincia de Ñuble, VIII Región. Dicha cepa se caracterizó in vitro, en dos medios de cultivo sólido, Melin-Norkrans-modificado (MNM) y Aneurina-Acido fólico- Agar (BAF), incubándose a 24 ºC en oscuridad, en donde se determinó velocidad de crecimiento radial (mm/día), y en medio de cultivo líquido BAF, se evaluó crecimiento miceliar, variación del pH y determinación del consumo de azúcares en el medio. Todos los medios de cultivos empleados (sólidos y líquidos) fueron ajustados a pH 5,8. Los resultados del estudio muestran un mayor incremento en velocidad media de crecimiento radial en el medio de cultivo BAF, mostrando diferencias significativas respecto al medio de cultivo MNM. La producción de biomasa miceliar en el medio líquido aumentó progresivamente a medida que avanzaban los días de incubación, induciendo ello una disminución moderada del pH del medio de cultivo, y un aumento en el consumo de azúcar producto del crecimiento del hongo

Quaternion-based deep belief networks fine-tuning

Deep learning techniques have been paramount in the last years, mainly due to their outstanding results in a number of applications. In this paper, we address the issue of fine-tuning parameters of Deep Belief Networks by means of meta-heuristics in which real-valued decision variables are described by quaternions. Such approaches essentially perform optimization in fitness landscapes that are mapped to a different representation based on hypercomplex numbers that may generate smoother surfaces. We therefore can map the optimization process onto a new space representation that is more suitable to learning parameters. Also, we proposed two approaches based on Harmony Search and quaternions that outperform the state-of-the-art results obtained so far in three public datasets for the reconstruction of binary images