72 research outputs found
Vortex and gap generation in gauge models of graphene
Effective quantum field theoretical continuum models for graphene are
investigated. The models include a complex scalar field and a vector gauge
field. Different gauge theories are considered and their gap patterns for the
scalar, vector, and fermion excitations are investigated. Different gauge
groups lead to different relations between the gaps, which can be used to
experimentally distinguish the gauge theories. In this class of models the
fermionic gap is a dynamic quantity. The finite-energy vortex solutions of the
gauge models have the flux of the "magnetic field" quantized, making the
Bohm-Aharonov effect active even when external electromagnetic fields are
absent. The flux comes proportional to the scalar field angular momentum
quantum number. The zero modes of the Dirac equation show that the gauge models
considered here are compatible with fractionalization
Moment Approach for the 2D Attractive Hubbard Model
We constructed the one-particle spectral functions (diagonal and
off-diagonal) which reproduce BCS for weak coupling and which take into account
the effect of correlations on superconductivity in the attractive Hubbard
model. The diagonal spectral function is composed of three peaks and the
off-diagonal one is composed of two peaks. This ansatz satisfies the sum rules
for the first six moments. Our solutions are valid for intermediate coupling,
i.e., for . Our set of analytical equations for the unknown
variables is self-consistent and has been solved numerically in lowest order of
the order parameter. As a result, we obtain that the presence of the third
band, or {\it upper Hubbard band}, strongly renormalizes the two lower bands,
making that the energy gap be -dependent while the order parameter is
pure s-wave. This shows that the order parameter and the gap are two different
quantities.Comment: 8 pages, 3 figures (2 ps files for Fig. 2) To appear in Physica
Quantum field theory approach to the optical conductivity of strained and deformed graphene
The computation of the optical conductivity of strained and deformed graphene is discussed within the framework of quantum field theory in curved spaces. The analytical solutions of the Dirac equation in an arbitrary static background geometry for one dimensional periodic deformations are computed, together with the corresponding Dirac propagator. Analytical expressions are given for the optical conductivity of strained and deformed graphene associated with both intra and interbrand transitions. The special case of small deformations is discussed and the result compared to the prediction of the tight-binding model.The authors acknowledge financial supportfrom the Brazilian agencies FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico)
Chirality and Symmetry Breaking in a discrete internal Space
In previous papers the permutation group S_4 has been suggested as an
ordering scheme for elementary particles, and the appearance of this finite
symmetry group was taken as indication for the existence of a discrete inner
symmetry space underlying elementary particle interactions. Here it is pointed
out that a more suitable choice than the tetrahedral group S_4 is the
pyritohedral group A_4 x Z_2 because its vibrational spectrum exhibits exactly
the mass multiplet structure of the 3 fermion generations. Furthermore it is
noted that the same structure can also be obtained from a primordial symmetry
breaking S_4 --> A_4. Since A_4 is a chiral group, while S_4 is achiral, an
argument can be given why the chirality of the inner pyritohedral symmetry
leads to parity violation of the weak interactions.Comment: 42 pages, 3 table
Frequência alimentar e taxa de arraçoamento durante o condicionamento alimentar de juvenis de pacamã
ARIA 2016: Care pathways implementing emerging technologies for predictive medicine in rhinitis and asthma across the life cycle
The Allergic Rhinitis and its Impact on Asthma (ARIA) initiative commenced during a World Health Organization workshop in 1999. The initial goals were (1) to propose a new allergic rhinitis classification, (2) to promote the concept of multi-morbidity in asthma a
NEOTROPICAL XENARTHRANS: a data set of occurrence of xenarthran species in the Neotropics
Xenarthrans – anteaters, sloths, and armadillos – have essential functions for ecosystem maintenance, such as insect control and nutrient cycling, playing key roles as ecosystem engineers. Because of habitat loss and fragmentation, hunting pressure, and conflicts with 24 domestic dogs, these species have been threatened locally, regionally, or even across their full distribution ranges. The Neotropics harbor 21 species of armadillos, ten anteaters, and six sloths. Our dataset includes the families Chlamyphoridae (13), Dasypodidae (7), Myrmecophagidae (3), Bradypodidae (4), and Megalonychidae (2). We have no occurrence data on Dasypus pilosus (Dasypodidae). Regarding Cyclopedidae, until recently, only one species was recognized, but new genetic studies have revealed that the group is represented by seven species. In this data-paper, we compiled a total of 42,528 records of 31 species, represented by occurrence and quantitative data, totaling 24,847 unique georeferenced records. The geographic range is from the south of the USA, Mexico, and Caribbean countries at the northern portion of the Neotropics, to its austral distribution in Argentina, Paraguay, Chile, and Uruguay. Regarding anteaters, Myrmecophaga tridactyla has the most records (n=5,941), and Cyclopes sp. has the fewest (n=240). The armadillo species with the most data is Dasypus novemcinctus (n=11,588), and the least recorded for Calyptophractus retusus (n=33). With regards to sloth species, Bradypus variegatus has the most records (n=962), and Bradypus pygmaeus has the fewest (n=12). Our main objective with Neotropical Xenarthrans is to make occurrence and quantitative data available to facilitate more ecological research, particularly if we integrate the xenarthran data with other datasets of Neotropical Series which will become available very soon (i.e. Neotropical Carnivores, Neotropical Invasive Mammals, and Neotropical Hunters and Dogs). Therefore, studies on trophic cascades, hunting pressure, habitat loss, fragmentation effects, species invasion, and climate change effects will be possible with the Neotropical Xenarthrans dataset
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