E. M. Gonzalez

Habitat selection patterns of common cranes Grus grus wintering in holm oak Quercus ilex dehesas of central Spain: Effects of human management

Abstract Most of the western European population of common cranes Grus grus spends the winter in Iberian wooded dehesas, a kind of wood-pasture composed of grasslands, cereal croplands and Mediterranean scrub, densely interspersed with holm oak trees Quercus ilex in a savanna-like landscape. Three main types of wooded dehesas can be distinguished according to management: grazed dehesas, shrubby dehesas with occasional grazing, and cultivated dehesas without livestock. Cranes depend largely on acorns during winter and mainly select dehesas cultivated with cereals where acorn abundance is not reduced by livestock. Apparent positive effects of livestock on earth-worm abundance, the main alternative food source for cranes, does not compensate for acorn depletion. Thus, any increase in livestock grazing pressure would have a strong impact on European crane populations during their wintering in Spain.

Control of the chirality and polarity of magnetic vortices in triangular nanodots

Magnetic vortex dynamics in lithographically prepared nanodots is currently a subject of intensive research, particularly after recent demonstration that the vortex polarity can be controlled by in-plane magnetic field. This has stimulated the proposals of nonvolatile vortex magnetic random access memories. In this work, we demonstrate that triangular nanodots offer a real alternative where vortex chirality, in addition to polarity, can be controlled. In the static regime, we show that vortex chirality can be tailored by applying in-plane magnetic field, which is experimentally imaged by means of variable-field magnetic force microscopy. In addition, the polarity can be also controlled by applying a suitable out-of-plane magnetic field component. The experiment and simulations show that to control the vortex polarity, the out- of-plane field component, in this particular case, should be higher than the in-plane nucleation field. Micromagnetic simulations in the dynamical regime show that the magnetic vortex polarity can be changed with short-duration magnetic field pulses, while longer pulses change the vortex chirality.

Experimental ratchet effect in superconducting films with periodic arrays of asymmetric potentials

A vortex lattice ratchet effect has been investigated in Nb films grown on arrays of nanometric Ni triangles, which induce periodic asymmetric pinning potentials. The vortex lattice motion yields a net dc voltage when an ac driving current is applied to the sample and the vortex lattice moves through the field of asymmetric potentials. This ratchet effect is studied taking into account the array geometry, the temperature, the number of vortices per unit cell of the array, and the applied ac currents.

Directional vortex motion guided by artificially induced mesoscopic potentials

Rectangular pinning arrays of Ni dots define a potential landscape for vortex motion in Nb films. Magnetotransport experiments in which two in-plane orthogonal electrical currents are injected simultaneously allow one to select the direction and magnitude of the Lorentz force on the vortex lattice, thus providing the angular dependence of the vortex motion. The background dissipation depends on the angle at low magnetic fields, which is progressively smeared out with increasing field. The periodic potential locks in the vortex motion along channeling directions. Because of this, the vortex-lattice direction of motion is up to 85degrees away from the applied Lorentz force direction.

Natural Antioxidants Protect Against Cadmium-Induced Damage during Pregnancy and Lactation in Rats' Pups

Free-radicals production is involved in the toxicity of cadmium. The aim of this study was to determine whether biochemical changes occurred in the liver and kidney of cadmium exposed pups during gestation and lactation, and additionally to investigate the potential beneficial role of the administration of certain antioxidants against cadmium exposure damage. Pregnant Wistar rats received the following treatments as drinking water: (1) Distilled water; (2) Cadmium (10 mg/L); (3) Cadmium + Zinc (20 mg/L) + vitamins A (50000 U/L), C (2 g/L), E (500 mg/L), and B(6) (500 mg/L); (4) Vitamins + Zinc solution. We found an increase in hemolysis and in the aminolevulinic acid dehydratase (delta-ALAD) activity in the erythrocytes among both cadmium-exposed groups. Cadmium exposure increased the production of thiobarbituric acid reactive substances (TBARS), catalase, and alkaline and acid phosphatase activity in both the organs studied. The effect on the enzymatic activity was reduced by the coadministration of vitamins and zinc. Our findings suggest that administration of antioxidants during gestation and lactation could prevent some of the negative effects of cadmium.

Transverse rectification in superconducting thin films with arrays of asymmetric defects

Superconducting Nb films have been grown on top of arrays of Cu nanotriangles. These asymmetric pinning centers strongly modify the vortex lattice dynamics. Two rectification effects have been observed: (i) longitudinal ratchet effect when the input currents are injected perpendicular to the triangle reflection symmetry axis and (ii) transverse rectification effect when the input currents are injected parallel to the triangle reflection symmetry axis and the output voltage drop occurs perpendicular to the triangle reflection symmetry axis. Increasing the applied magnetic field, the former shows a change of the output voltage polarity, the transverse output voltage does not show any polarity reversal.

Mixed-state properties of superconducting Nb/Ni superlattices

Superlattices of ðNb10 nm=NitÞ 8 (1 6 t 6 5 nm) have been grown on Si(1 0 0) by magnetron sputtering. Samples show textured growth of Nb(1 1 0) and Ni(1 1 1), with negligible interdiffusion and interface roughness below 0.3 nm. The critical superconducting temperature (Tcs) of these superlattices decreases as the Ni thickness (tNi) increases. Ferromagnetic order in Ni layers is suppressed for tNi < 2:2 nm. We have explored the behavior of these superlattices in the mixed state by measuring the upper critical fields. Critical fields in perpendicular (Hc2?) and parallel (Hc2k) configurations show moderate superlattice-induced anisotropy values, which increase as tNi increases. From Hc2ðT Þ measurements, we have found that superconducting superlattices behave like a three-dimensional system. This dimensional behavior is discussed in terms of coupling of Nb through Ni layers. 2001 Elsevier Science B.V. All rights reserved.

Anisotropic pinning enhancement in Nb films with arrays of submicrometric Ni lines

Arrays of submicrometric Ni lines have been fabricated in superconducting Nb films by electron beam lithography. In the mixed state, these arrays induce strong anisotropy in the dissipation behavior. The dissipation is reduced several orders of magnitude, in the whole applied magnetic field range, when the vortex motion is perpendicular to the Ni lines (applied current parallel to them) in comparison with dissipation of vortices moving parallel to the lines. In addition, for the samples studied in this work, a change in the slope of the ρ(B) curves is observed when the vortices move perpendicular to the lines and the vortex lattice parameter matches the width of the Ni lines.

Control of dissipation in superconducting films by magnetic stray fields

Hybrid superconducting/magnetic nanostructures on Si substrates have been built with identical physical dimensions but different magnetic configurations. By constructing arrays based on Co-dots with in-plane, out-of-plane, and vortex state magnetic configurations, the stray fields are systematically tuned. Dissipation in the mixed state of superconductors can be decreased (increased) by several orders of magnitude by decreasing (increasing) the stray magnetic fields. Furthermore, ordering of the stray fields over the entire array helps to suppress dissipation and enhance commensurability effects increasing the number of dissipation minima.

Transverse ratchet effect and superconducting vortices: simulation and experiment

A transverse ratchet effect has been measured in magnetic/ superconducting hybrid films fabricated by electron beam lithography and magnetron sputtering techniques. The samples are Nb films grown on top of an array of Ni nanotriangles. Injecting an ac current parallel to the triangle reflection symmetry axis yields an output dc voltage perpendicular to the current, due to a net motion of flux vortices in the superconductor. The effect is reproduced by numerical simulations of vortices as Langevin particles with realistic parameters. Simulations provide an intuitive picture of the ratchet mechanism, revealing the fundamental role played by the random intrinsic pinning of the superconductor.