677 research outputs found
Diffractive Contribution to the Elasticity and the Nucleonic Flux in the Atmosphere
We calculate the average elasticity considering non-diffractive and single
diffractive interactions and perform an analysis of the cosmic-ray flux by
means of an analytical solution for the nucleonic diffusion equation. We show
that the diffractive contribution is important for the adequate description of
the nucleonic and hadronic fluxes in the atmosphere.Comment: 10 pages, latex, 2 figures (uuencoded PostScript
Flat-Band Ferromagnetism in Organic Polymers Designed by a Computer Simulation
By coupling a first-principles, spin-density functional calculation with an
exact diagonalization study of the Hubbard model, we have searched over various
functional groups for the best case for the flat-band ferromagnetism proposed
by R. Arita et al. [Phys. Rev. Lett. {\bf 88}, 127202 (2002)] in organic
polymers of five-membered rings. The original proposal (poly-aminotriazole) has
turned out to be the best case among the materials examined, where the reason
why this is so is identified here. We have also found that the ferromagnetism,
originally proposed for the half-filled flat band, is stable even when the band
filling is varied away from the half-filling. All these make the ferromagnetism
proposed here more experimentally inviting.Comment: 11 pages, 13figure
On the chiral anomaly in non-Riemannian spacetimes
The translational Chern-Simons type three-form coframe torsion on a
Riemann-Cartan spacetime is related (by differentiation) to the Nieh-Yan
four-form. Following Chandia and Zanelli, two spaces with non-trivial
translational Chern-Simons forms are discussed. We then demonstrate, firstly
within the classical Einstein-Cartan-Dirac theory and secondly in the quantum
heat kernel approach to the Dirac operator, how the Nieh-Yan form surfaces in
both contexts, in contrast to what has been assumed previously.Comment: 18 pages, RevTe
Gapless Excitation above a Domain Wall Ground State in a Flat Band Hubbard Model
We construct a set of exact ground states with a localized ferromagnetic
domain wall and with an extended spiral structure in a deformed flat-band
Hubbard model in arbitrary dimensions. We show the uniqueness of the ground
state for the half-filled lowest band in a fixed magnetization subspace. The
ground states with these structures are degenerate with all-spin-up or
all-spin-down states under the open boundary condition. We represent a spin
one-point function in terms of local electron number density, and find the
domain wall structure in our model. We show the existence of gapless
excitations above a domain wall ground state in dimensions higher than one. On
the other hand, under the periodic boundary condition, the ground state is the
all-spin-up or all-spin-down state. We show that the spin-wave excitation above
the all-spin-up or -down state has an energy gap because of the anisotropy.Comment: 26 pages, 1 figure. Typos are fixe
A New Genus And Species Of Euptychiina (lepidoptera: Nymphalidae: Satyrinae) From Southern Brazil.
This paper describes a new genus and a new species of Euptychiina from open grassland habitats (campos de cima da serra) in southern Brazil. The systematic position of this new taxon is discussed based on morphological and molecular data, and it is considered sister to Taydebis Freitas. Since the campos vegetation is considered endangered due to anthropogenic activities, this butterfly species deserves attention and should be included in future conservation plans for this biome.40231-
Uncovered diversity of a predominantly Andean butterfly clade in the Brazilian Atlantic Forest : a revision of the genus Praepedaliodes Forster (Lepidoptera : Nymphalidae, Satyrinae, Satyrini)
A new and rare actinote hübner (Lepidoptera : Nymphalidae: Heliconiinae : Acraeini) from southeastern Brazil
The present paper describes a new species of Actinote (Nymphalidae, Heliconiinae, Acraeini), Actinote keithbrowni Freitas, Francini & Mielke sp. nov., from southeastern Brazil, based on morphological and molecular data. The new species is very similar in wing pattern to Actinote eberti, within what we term the “light-gray mimicry complex.” The host plants and immature stages of the new species are unknown. Actinote keithbrowni sp. nov. is one of the rarest species of Actinote from Brazil: in total, only eight individuals of this species are known from a narrow region of the Itatiaia massif despite years of collecting effort in that region since the 1940s495696703CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP303834/2015-3; 304639/2014-20012011/50225-3; 2013/50297-0; 2015/24663-4AVLF acknowledges support from Fundação de Amparo à Pesquisa do Estado de São Paulo – (FAPESP) (Biota-Fapesp grants 2011/50225-3, 2013/50297-0) and from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (303834/2015-3). LMM acknowledges FAPESP (PhD scholarship - 2015/24663-4). AHBR thanks Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brazil (CAPES) - Finance Code 001. OHHM acknowledges support from the – CNPq (304639/2014-2
Stochastic Energetics of Quantum Transport
We examine the stochastic energetics of directed quantum transport due to
rectification of non-equilibrium thermal fluctuations. We calculate the quantum
efficiency of a ratchet device both in presence and absence of an external load
to characterize two quantifiers of efficiency. It has been shown that the
quantum current as well as efficiency in absence of load (Stokes efficiency) is
higher as compared to classical current and efficiency, respectively, at low
temperature. The conventional efficiency of the device in presence of load on
the other hand is higher for a classical system in contrast to its classical
counterpart. The maximum conventional efficiency being independent of the
nature of the bath and the potential remains the same for classical and quantum
systems.Comment: To be published in Phys. Rev.
Ferromagnetism in multi--band Hubbard models: From weak to strong Coulomb repulsion
We propose a new mechanism which can lead to ferromagnetism in Hubbard models
containing triangles with different on-site energies. It is based on an
effective Hamiltonian that we derive in the strong coupling limit. Considering
a one-dimensional realization of the model, we show that in the quarter-filled,
insulating case the ground-state is actually ferromagnetic in a very large
parameter range going from Tasaki's flat-band limit to the strong coupling
limit of the effective Hamiltonian. This result has been obtained using a
variety of analytical and numerical techniques. Finally, the same results are
shown to apply away from quarter-filling, in the metallic case.Comment: 12 pages, revtex, 12 figures,needs epsf and multicol style file
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