Spin inversion devices with Fano anti-resonances

Analyzing spin transport of quasi-2D electrons gas moving through a semiconductor wave guide subject to a sectionally homogeneous tilted magnetic field, we found well-defined selection rules for resonant and antiresonant spin carrier transmission. Based on these selection rules and the band shift induced by the magnetic field strength and the tilting angles, we propose an efficient spin inversion device. For a polarized incoming electron beam, we can determine from our theoretical approach, physical conditions for spin-inversion efficiency up to 80%. We visualize this mechanism in terms of conductance and the spacial behavior of the wave function amplitude along the superlattice.Comment: 3 pages, 3 figures, regular pape

New gravitational solutions via a Riemann-Hilbert approach

We consider the Riemann-Hilbert factorization approach to solving the field equations of dimensionally reduced gravity theories. First we prove that functions belonging to a certain class possess a canonical factorization due to properties of the underlying spectral curve. Then we use this result, together with appropriate matricial decompositions, to study the canonical factorization of non-meromorphic monodromy matrices that describe deformations of seed monodromy matrices associated with known solutions. This results in new solutions, with unusual features, to the field equations.Comment: 29 pages, 2 figures; v2: reference added, matches published versio

On Quantum Special Kaehler Geometry

We compute the effective black hole potential V of the most general N=2, d=4 (local) special Kaehler geometry with quantum perturbative corrections, consistent with axion-shift Peccei-Quinn symmetry and with cubic leading order behavior. We determine the charge configurations supporting axion-free attractors, and explain the differences among various configurations in relations to the presence of ``flat'' directions of V at its critical points. Furthermore, we elucidate the role of the sectional curvature at the non-supersymmetric critical points of V, and compute the Riemann tensor (and related quantities), as well as the so-called E-tensor. The latter expresses the non-symmetricity of the considered quantum perturbative special Kaehler geometry.Comment: 1+43 pages; v2: typo corrected in the curvature of Jordan symmetric sequence at page 2

Spin-dependent Fano resonance induced by conducting chiral helimagnet contained in a quasi-one-dimensional electron waveguide

Fano resonance appears for conduction through an electron waveguide containing donor impurities. In this work, we consider the thin-film conducting chiral helimagnet (CCH) as the donor impurity in a one-dimensional waveguide model. Due to the spin spiral coupling, interference between the direct and intersubband transmission channels gives rise to spin-dependent Fano resonance effect. The spin-dependent Fano resonance is sensitively dependent on the helicity of the spiral. By tuning the CCH potential well depth and the incident energy, this provides a potential way to detect the spin structure in the CCH.Comment: 14 pages, 6 figure

Cooperative Spectrum Sensing Using Random Matrix Theory

In this paper, using tools from asymptotic random matrix theory, a new cooperative scheme for frequency band sensing is introduced for both AWGN and fading channels. Unlike previous works in the field, the new scheme does not require the knowledge of the noise statistics or its variance and is related to the behavior of the largest and smallest eigenvalue of random matrices. Remarkably, simulations show that the asymptotic claims hold even for a small number of observations (which makes it convenient for time-varying topologies), outperforming classical energy detection techniques.Comment: Submitted to International Symposium on Wireless Pervasive Computing 200

Caves of the Hesperic basement from Portugal with Pleistocene large-size mammals. A review

[Abstract] This study presents a review of the large-sized mammals from the Upper Pleistocene of portuguese caves situated at the Hesperic basement. At the moment, only two caves are known: the Lorga de Dine cave (Vinhais, Braganc.;a) and Escoural cave (Montemor-o-Novo, Ivora). Both were excavated at the sixteens and no stratigraphic or horizontal records are published. The presence ofCrocuta crocuta intermedia at Lorga de Dine allows us to suppose an occupation ofthe cave during the Mindel-Riss; in that case, it will be the oldest cavity with palaeontological interest known in Portugal. Nevertheless, we must admit the role ofthe Iberian Peninsula as a refuge-territory, that couldjustify the presence of several species, later than is known elsewere in Europe. Escoural cave - the most occidental cave with parietal pleistocene art - gave the only Cuon alpinus europaeus remains known at present in Portugal. Considering the large majority or even the totality ofthe remains relate to the Late Wurm, the ungulates associations ofLorga de Dine and Escoural suggest the existence oflarge open spaces, with aurochs and horses, with spaced arboreal areas, with red deers