10,986 research outputs found
Caloric curve for finite nuclei in relativistic models
In this work we calculate the caloric curve (excitation energy per particle
as a function of temperature) for finite nuclei within the non--linear Walecka
model for different proton fractions. It is shown that the caloric curve is
sensitive to the proton fraction. Freeze-out volume effects in the caloric
curve are also studied.Comment: 11 pages, 1 figure, 4 table
Chern-Simons theory and atypical Hall conductivity in the Varma phase
In this letter, we analyze the topological response of a fermionic model
defined on the Lieb lattice in presence of an electromagnetic field. The
tight-binding model is built in terms of three species of spinless fermions and
supports a topological Varma phase due to the spontaneous breaking of
time-reversal symmetry. In the low-energy regime, the emergent effective
Hamiltonian coincides with the so-called Duffin-Kemmer-Petiau (DKP)
Hamiltonian, which describes relativistic pseudospin-0 quasiparticles. By
considering a minimal coupling between the DKP quasiparticles and an external
Abelian gauge field, we calculate both the Landau-level spectrum and the
emergent Chern-Simons theory. The corresponding Hall conductivity reveals an
atypical quantum Hall effect, which can be simulated in an artificial Lieb
lattice.Comment: 5 pages, 3 figures; New version with an improved discussion about our
finding
Conformal QED in two-dimensional topological insulators
It has been shown recently that local four-fermion interactions on the edges
of two-dimensional time-reversal-invariant topological insulators give rise to
a new non-Fermi-liquid phase, called helical Luttinger liquid (HLL). In this
work, we provide a first-principle derivation of this non-Fermi-liquid phase
based on the gauge-theory approach. Firstly, we derive a gauge theory for the
edge states by simply assuming that the interactions between the Dirac fermions
at the edge are mediated by a quantum dynamical electromagnetic field. Here,
the massless Dirac fermions are confined to live on the one-dimensional
boundary, while the (virtual) photons of the U(1) gauge field are free to
propagate in all the three spatial dimensions that represent the physical space
where the topological insulator is embedded. We then determine the effective
1+1-dimensional conformal field theory (CFT) given by the conformal quantum
electrodynamics (CQED). By integrating out the gauge field in the corresponding
partition function, we show that the CQED gives rise to a 1+1-dimensional
Thirring model. The bosonized Thirring Hamiltonian describes exactly a HLL with
a parameter K and a renormalized Fermi velocity that depend on the value of the
fine-structure constant .Comment: (5+4) pages, 2 figure
Risk aversion and bidding theory
Theory of bidding behavior and formation of bidding model with risk aversio
Brazilian social bee must cultivate fungus to survive.
Resumo: The nests of social insects provide suitable micro-environments for many microorganisms as they offer stable environmental conditions and a rich source of food. Microorganisms in turn may provide several benefits to their hosts, such as nutrients and protection against pathogens. Several examples of symbiosis between social insects and microorganisms have been found in ants and termites. These symbioses have driven the evolution of complex behaviors and nest structures associated with the culturing of the symbiotic microorganisms. However, while much is known about these relationships in many species of ants and termites, symbiotic relationships between microorganisms and social bees have been poorly explored. Here we report the first case of an obligatory relationship between the Brazilian stingless bee Scaptotrigona depilis and a fungus of the genus Monascus (Ascomycotina). Fungal mycelia growing on the provisioned food inside the brood cell are eaten by the larva. Larvae reared in vitro on sterilized larval food supplemented with fungal mycelia had a much higher survival rate (76%) compared to larvae reared under identical conditions but without fungal mycelia (8% survival). The fungus was found to originate from the material from which the brood cells are made. Since the bees recycle and transport this material between nests, fungus would be transferred to newly built cells, and also to newly founded nests. This is the first report of a fungus cultivation mutualism in a social bee
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