Finiteness results for subgroups of finite extensions

We discuss in the context of finite extensions two classical theorems of Takahasi and Howson on subgroups of free groups. We provide bounds for the rank of the intersection of subgroups within classes of groups such as virtually free groups, virtually nilpotent groups or fundamental groups of finite graphs of groups with virtually polycyclic vertex groups and finite edge groups. As an application of our generalization of Takahasi's Theorem, we provide an uniform bound for the rank of the periodic subgroup of any endomorphism of the fundamental group of a given finite graph of groups with finitely generated virtually nilpotent vertex groups and finite edge groups.Comment: 20 pages; no figures. Keywords: finite extensions, Howson's Theorem, Hanna Neumann Conjecture, Takahasi's Theorem, periodic subgroup

Single spin-torque vortex oscillator using combined bottom-up approach and e-beam lithography

A combined bottom-up assembly of electrodeposited nanowires and electron beam lithography technique has been developed to investigate the spin transfer torque and microwave emission on specially designed nanowires containing a single Co/Cu/Co pseudo spin valve. Microwave signals have been obtained even at zero magnetic field. Interestingly, high frequency vs. magnetic field tunability was demonstrated, in the range 0.4 - 2 MHz/Oe, depending on the orientation of the applied magnetic field relative to the magnetic layers of the pseudo spin valve. The frequency values and the emitted signal frequency as a function of the external magnetic field are in good quantitative agreement with the analytical vortex model as well as with micromagnetic simulations.Comment: 9 pages, 4 figure

Efficient Yield Curve Estimation and Forecasting in Brazil

Term Structure of the Interest Rate, Yield Curve, State-Space Model, Kalman Filter.

Universal R-C crossover in current-voltage characteristics for unshunted array of overdamped Nb-AlO_x-Nb Josephson junctions

We report on some unusual behavior of the measured current-voltage characteristics (CVC) in artificially prepared two-dimensional unshunted array of overdamped Nb-AlO_x-Nb Josephson junctions. The obtained nonlinear CVC are found to exhibit a pronounced (and practically temperature independent) crossover at some current I_{cr}=\left(\frac{1}{2\beta_C}-1\right)I_C from a resistance R dominated state with V_R=R\sqrt{I^2-I_C^2} below I_{cr} to a capacitance C dominated state with V_C=\sqrt{\frac{\hbar}{4eC}} \sqrt{I-I_C} above I_{cr}. The origin of the observed behavior is discussed within a single-plaquette approximation assuming the conventional RSJ model with a finite capacitance and the Ambegaokar-Baratoff relation for the critical current of the single junction

Manifestation of geometric resonance in current dependence of AC susceptibility for unshunted array of Nb-AlOx-Nb Josephson junctions

A pronounced resonance-like structure has been observed in the current dependence of AC susceptibility for two-dimensional array of unshunted Nb-AlOx-Nb Josephson junctions. Using a single-plaquette approximation, we were able to successfully fit our data assuming that resonance structure is related to the geometric (inductive) properties of the array.Comment: to appear in Physica C (in press

Contribuição ao conhecimento sobre os Miobantia Giglio-Tos (Mantodea, Thespidae, Miopteryginae), com associação molecular de sexos dimórficos e estágios imaturos, e descrição de quatro espécies novas

O gênero neotropical de louva-a-deus Miobantia Giglio-Tos inclui seis espécies com uma história taxonômica complexa. Embora freqüentemente encontradas na Mata Atlântica, pouco se sabe sobre elas e alguns obstáculos tornam difícil identificá-las, como o dimorfismo sexual elevado e o conhecimento de ambos os sexos para apenas uma das seis espécies. Este trabalho investiga os limites taxonômicos das espécies de Miobantia através de uma análise cladística, utilizando 99 caracteres morfológicos, além de seqüenciamento de 700 pb do gene mitocondrial COI para a associação de sexos dimórficos e ninfas. A variação intra-específica é também investigada a partir de um grande número de espécimes de M. fuscata (Giglio-Tos) para escolher características mais relevantes para a separação das espécies a serem utilizados nos comentários taxonómicos e nas chaves de identificação. O macho de M. aptera Giglio-Tos, e as fêmeas de M. ciliata (Stål) e M. fuscata são descritos pela primeira vez, e são fornecidas redescrições dos machos destas e da fêmea de M. aptera com base em numerosos dados complementares. Miobantia nebulosa (Giglio-Tos) é proposta como sinônimo júnior de M. rustica (Fabr.), com base na comparação entre seus tipos, incluindo a investigação de genitália masculina, e a espécie é redescrita. Adicionalmente, quatro novas espécies são aqui descritas: M. sp. nov. 1 sp. nov., M. sp. nov. 2 sp. nov., M. sp. nov. 3 sp. nov., e M. sp. nov. 4 sp. nov.; ambos os sexos são descritos, com exceção apenas para o macho de M. sp. nov. 2. Chaves de identificação são fornecidas para machos e fêmeas das espécies válidas, e figuras das características diagnósticas são fornecidas para todos eles. A distribuição das espécies é mapeada de acordo com dados da literatura e 50 novos registros

Antisymmetric tensor propagator with spontaneous Lorentz violation

In this work, we study the spontaneous Lorentz symmetry breaking due to an antisymmetric 2-tensor field in Minkowski spacetime. For a smooth quadratic potential, the spectrum of the theory exhibits massless and massive excitations. We show that the equations of motion for the free field obey some constraints which lead to the massive mode be non-propagating at leading order. Besides, there exists a massless mode in the theory which can be identified with the usual Kalb-Ramond field, carrying only one on-shell degree of freedom. The same conclusion holds when one analyses the pole structure of its Feynman propagator. A new complete set of spin-type operators is found, which was the requirement to evaluate the propagator of the Kalb-Ramond field modified by the presence of a nonzero vacuum expectation value responsible for the Lorentz violation.Comment: 13 pages. Some modifications to match published version in EuroPhysics Letter