Metallic Continuum Quantum Ferromagnets at Finite Temperature

We study via renormalization group (RG) and large N methods the problem of continuum SU(N) quantum Heisenberg ferromagnets (QHF) coupled to gapless electrons. We establish the phase diagram of the dissipative problem and investigate the changes in the Curie temperature, magnetization, and magnetic correlation length due to dissipation and both thermal and quantum fluctuations. We show that the interplay between the topological term (Berry's phase) and dissipation leads to non-trivial effects for the finite temperature critical behavior.Comment: Corrected typos, new discussion of T=0 results, to appear in Europhys. Let

Spin-orbit mode transfer via a classical analog of quantum teleportation

We translate the quantum teleportation protocol into a sequence of coherent operations involving three degrees of freedom of a classical laser beam. The protocol, which we demonstrate experimentally, transfers the polarisation state of the input beam to the transverse mode of the output beam. The role of quantum entanglement is played by a non-separable mode describing the path and transverse degrees of freedom. Our protocol illustrates the possibility of new optical applications based on this intriguing classical analogue of quantum entanglement.Comment: 5 pages, 7 figure

Uso do fogo no controle de pragas das pastagens.

bitstream/item/59277/1/CPATU-ComTec50.pd

Extraordinary magnetoresistance in graphite: experimental evidence for the time-reversal symmetry breaking

The ordinary magnetoresistance (MR) of doped semiconductors is positive and quadratic in a low magnetic field, B, as it should be in the framework of the Boltzmann kinetic theory or in the conventional hopping regime. We observe an unusual highly-anisotropic in-plane MR in graphite, which is neither quadratic nor always positive. In a certain current direction MR is negative and linear in B in fields below a few tens of mT with a crossover to a positive MR at higher fields, while in a perpendicular current direction we observe a giant super-linear and positive MR. These extraordinary MRs are respectively explained by a hopping magneto-conductance via non-zero angular momentum orbitals, and by the magneto-conductance of inhomogeneous media. The linear orbital NMR is a unique signature of the broken time-reversal symmetry (TRS) in graphite. While some local paramagnetic centers could be responsible for the broken TRS, the observed large diamagnetism suggests a more intriguing mechanism of this breaking, involving superconducting clusters with unconventional (chiral) order parameters and spontaneously generated normal-state current loops in graphite.Comment: 4 pages, 5 figure

Chemical abundances and kinematics of barium stars

In this paper we present an homogeneous analysis of photospheric abundances based on high-resolution spectroscopy of a sample of 182 barium stars and candidates. We determined atmospheric parameters, spectroscopic distances, stellar masses, ages, luminosities and scale height, radial velocities, abundances of the Na, Al, $alpha$-elements, iron-peak elements, and s-process elements Y, Zr, La, Ce, and Nd. We employed the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code {\sc moog}. We found that the metallicities, the temperatures and the surface gravities for barium stars can not be represented by a single gaussian distribution. The abundances of $alpha$-elements and iron peak elements are similar to those of field giants with the same metallicity. Sodium presents some degree of enrichment in more evolved stars that could be attributed to the NeNa cycle. As expected, the barium stars show overabundance of the elements created by the s-process. By measuring the mean heavy-element abundance pattern as given by the ratio [s/Fe], we found that the barium stars present several degrees of enrichment. We also obtained the [hs/ls] ratio by measuring the photospheric abundances of the Ba-peak and the Zr-peak elements. Our results indicated that the [s/Fe] and the [hs/ls] ratios are strongly anti-correlated with the metallicity. Our kinematical analysis showed that 90% of the barium stars belong to the thin disk population. Based on their luminosities, none of the barium stars are luminous enough to be an AGB star, nor to become self-enriched in the s-process elements. Finally, we determined that the barium stars also follow an age-metallicity relation.Comment: 30 pages, 26 figures, 18 tables, accepted for publication in MNRA

Bloques de hormigón ligero con áridos reciclados de EVA: una contribución a la eficiencia térmica de paredes exteriores de edificios

The regions with lots of shoe production suffer environmental impacts from waste generation during manufacturing of insoles and outsoles. Research conducted in Brazil has demonstrated the technical feasibility to recycle these wastes, especially Ethylene Vinyl Acetate (EVA), as lightweight aggregate, in the production of non-structural cement blocks. This article presents an evaluation of thermal performance with measurements of temperature variation in mini walls (1 m2) built with different materials, including various kinds of EVA block and ceramic bricks. Tests have shown efficient thermal performance for masonry blocks with EVA. These results and supplementary estimates contribute to add value to the EVA block, considering that there are good expectations that the component, with the new geometry proposed, can contribute to the energy efficiency of buildings, highlighting its suitability to most Brazilian bioclimatic regions.Las regiones con una gran producción de calzado sufren impactos ambientales derivados de la generación de residuos durante la producción de plantillas y suelas. Investigaciones realizadas en Brasil han demostrado la viabilidad técnica para el reciclaje de estos residuos, especialmente el Etileno Vinil Acetato (EVA), como agregado ligero en la fabricación de bloques de hormigón no estructurales. Este trabajo presenta una evaluación del rendimiento térmico, con mediciones de la variación de la temperatura en pequeñas paredes (1 m2) construidas con diversos materiales, incluyendo algunos tipos de bloques EVA y ladrillos de cerámica. Las pruebas demostraron actuaciones térmicas eficientes para las muestras con bloques EVA. Estos resultados y cálculos adicionales contribuyen con un aporte de valor añadido al bloque EVA, considerando que existen buenas expectativas del componente, con una nueva propuesta de geometría, pudiendo contribuir a la eficiencia energética de edificios, especialmente por su adecuación a la mayoría de las regiones bioclimáticas brasileñas