Charge instabilities and topological phases in the extended Hubbard model on the honeycomb lattice with enlarged unit cell

We study spontaneous symmetry breaking in a system of spinless fermions in the Honeycomb lattice paying special emphasis to the role of an enlarged unit cell on time reversal symmetry broken phases. We use a tight binding model with nearest neighbor hopping t and Hubbard interaction V1 and V2 and extract the phase diagram as a function of electron density and interaction within a mean field variational approach. The analysis completes the previous work done in Phys. Rev. Lett. 107, 106402 (2011) where phases with non--trivial topological properties were found with only a nearest neighbor interaction V1 in the absence of charge decouplings. We see that the topological phases are suppressed by the presence of metallic charge density fluctuations. The addition of next to nearest neighbor interaction V2 restores the topological non-trivial phases

Topological Fermi liquids from Coulomb interactions in the doped Honeycomb lattice

We get an anomalous Hall metallic state in the Honeycomb lattice with nearest neighbors only arising as a spontaneously broken symmetry state from a local nearest neighbor Coulomb interaction V . The key ingredient is to enlarge the unit cell to host six atoms that permits Kekul\'e distortions and supports self-consistent currents creating non trivial magnetic configurations with total zero flux. We find within a variational mean field approach a metallic phase with broken time reversal symmetry (T) very close in parameter space to a Pomeranchuk instability. Within the T broken region the predominant configuration is an anomalous Hall phase with non zero Hall conductivity, a realization of a topological Fermi liquid. A T broken phase with zero Hall conductivity is stable in a small region of the parameter space for lower values of V

The earliest spectroscopy of the GRB 030329 afterglow with 6-m telescope

The earliest BTA (SAO RAS 6-m telescope) spectroscopic observations of the GRB 030329 optical transient (OT) are presented, which almost coincide in time with the "first break" ($t\sim 0.5$ day after the GRB) of the OT light curve. The beginning of spectral changes are seen as early as $\sim 10-12$ hours after the GRB. So, the onset of the spectral changes for $t<1$ day indicates that the contribution from Type Ic supernova (SN) into the OT optical flux can be detected earlier. The properties of early spectra of GRB 030329/SN 2003dh can be consistent with a shock moving into a stellar wind formed from the pre-SN. Such a behavior (similar to that near the UV shock breakout in SNe) can be explained by the existence of a dense matter in the immediate surroundings of massive stellar GRB/SN progenitor). The urgency is emphasized of observation of early GRB/SN spectra for solving a question that is essential for understanding GRB physical mechanism: {\it Do all} long-duration gamma-ray bursts are caused by (or physically connected to) {\it ordinary} core-collapse supernovae? If clear association of normal/ordinary core-collapse SNe (SN Ib/c, and others SN types) and GRBs would be revealed in numbers of cases, we may have strong observational limits for gamma-ray beaming and for real energetics of the GRB sources.Comment: 4 pages, 5 figures. Proceedings of the 4th Workshop "Gamma-Ray Bursts in the Afterglow Era", Roma, 2004 October 18-22, eds. L. Piro, L. Amati, S. Covino, and B. Gendre. Il Nuovo Cimento, in pres

AE Aurigae: first detection of non-thermal X-ray emission from a bow shock produced by a runaway star

Runaway stars produce shocks when passing through interstellar medium at supersonic velocities. Bow shocks have been detected in the mid-infrared for several high-mass runaway stars and in radio waves for one star. Theoretical models predict the production of high-energy photons by non-thermal radiative processes in a number sufficiently large to be detected in X-rays. To date, no stellar bow shock has been detected at such energies. We present the first detection of X-ray emission from a bow shock produced by a runaway star. The star is AE Aur, which was likely expelled from its birthplace by the encounter of two massive binary systems and now is passing through the dense nebula IC 405. The X-ray emission from the bow shock is detected at 30" to the northeast of the star, coinciding with an enhancement in the density of the nebula. From the analysis of the observed X-ray spectrum of the source and our theoretical emission model, we confirm that the X-ray emission is produced mainly by inverse Compton upscattering of infrared photons from dust in the shock front.Comment: Accepted for publication in the Astrophysical Journal with number ApJ, 757, L6. Four figure

Monitoramento de resíduos de carbofuran no plantio de banana 'prata anã' utilizando diferentes tratamentos químicos.

bitstream/CTAA-2009-09/8946/1/ct79-2005.pd

Theoretical Aspects of the Fractional Quantum Hall Effect in Graphene

We review the theoretical basis and understanding of electronic interactions in graphene Landau levels, in the limit of strong correlations. This limit occurs when inter-Landau-level excitations may be omitted because they belong to a high-energy sector, whereas the low-energy excitations only involve the same level, such that the kinetic energy (of the Landau level) is an unimportant constant. Two prominent effects emerge in this limit of strong electronic correlations: generalised quantum Hall ferromagnetic states that profit from the approximate four-fold spin-valley degeneracy of graphene's Landau levels and the fractional quantum Hall effect. Here, we discuss these effects in the framework of an SU(4)-symmetric theory, in comparison with available experimental observations.Comment: 12 pages, 3 figures; review for the proceedings of the Nobel Symposium on Graphene and Quantum Matte

Influência de boro no rendimento do girassol.

O objetivos do trabalho foram estudar o efeito de doses de boro nos componentes de rendimento de girassol na movimentação do nutriente no perfil de um Latossolo vermelho eutroférrico emlondrina, PR, Brasil

Avaliação da estratificação do conteúdo ruminal de bubalinos suplementados com farelo de amêndoa de dendê.

Avaliou-se o efeito da suplementação do farelo de amêndoa de dendê, correlacionando com a cinética ruminal, através da estratificação do rúmen e quantificação do volume ocupado pelo conteúdo sólido, líquido e gasoso. O experimento foi conduzido na Unidade de Pesquisa Animal Senador Álvaro Adolpho da Embrapa Amazônia Oriental em Belém, Pará. Foram utilizados quatro bubalinos fistulados no rúmen mantidos em pastagem cultivada com capim Panicum maximum Jacq cv Mombaça em sistema silvipastoril. Os tratamentos experimentais foram a suplementação com um quilograma de farelo de amêndoa de dendê comparado à dieta controle sem suplementação. O conteúdo ruminal foi quantificado em porções sólidas e líquidas e amostrado para determinação de matéria seca. O espaço vazio ruminal foi mensurado com o Método das Bolas. As áreas ocupadas pelas porções sólida, líquida e vazia do rúmen não foram afetada pela suplementação. A porção vazia do rúmen ocupou a menor parte do conteúdo, variando entre 0,007 e 0,017 m3. A porção sólida e líquida do conteúdo ruminal em matéria seca variou entre 6,71 e 9,63 kg nos diversos tratamentos. A conclusão foi que o tempo de esvaziamento não influenciou a estratificação do conteúdo ruminal nas porções líquidas, sólidas e gasosas