25,914 research outputs found
The Penna model for biological ageing on a lattice: spatial consequences of child-care
We introduce a square lattice into the Penna bit-string model for biological
ageing and study the evolution of the spatial distribution of the population
considering different strategies of child-care. Two of the strategies are
related to the movements of a whole family on the lattice: in one case the
mother cannot move if she has any child younger than a given age, and in the
other case if she moves, she brings these young children with her. A stronger
condition has also been added to the second case, considering that young
children die with a higher probability if their mothers die, this probability
decreasing with age. We show that a highly non uniform occupation can be
obtained when child-care is considered, even for an uniform initial occupation
per site. We also compare the standard survival rate of the model with that
obtained when the spacial lattice is considered (without any kind of
child-care).Comment: 8 pages, 6 Postscript figure
Hybrid Quasicrystals, Transport and Localization in Products of Minimal Sets
We consider convex combinations of finite-valued almost periodic sequences
(mainly substitution sequences) and put them as potentials of one-dimensional
tight-binding models. We prove that these sequences are almost periodic. We
call such combinations {\em hybrid quasicrystals} and these studies are related
to the minimality, under the shift on both coordinates, of the product space of
the respective (minimal) hulls. We observe a rich variety of behaviors on the
quantum dynamical transport ranging from localization to transport.Comment: 3 figures. To appear in Journal of Stat. Physic
Generation of Superposition States and Charge-Qubit Relaxation Probing in a Circuit
We demonstrate how a superposition of coherent states can be generated for a
microwave field inside a coplanar transmission line coupled to a single
superconducting charge qubit, with the addition of a single classical magnetic
pulse for chirping of the qubit transition frequency. We show how the qubit
dephasing induces decoherence on the field superposition state, and how it can
be probed by the qubit charge detection. The character of the charge qubit
relaxation process itself is imprinted in the field state decoherence profile.Comment: 6 pages, 4 figure
Charge confinement and Klein tunneling from doping graphene
In the present work, we investigate how structural defects in graphene can
change its transport properties. In particular, we show that breaking of the
sublattice symmetry in a graphene monolayer overcomes the Klein effect, leading
to confined states of massless Dirac fermions. Experimentally, this corresponds
to chemical bonding of foreign atoms to carbon atoms, which attach themselves
to preferential positions on one of the two sublattices. In addition, we
consider the scattering off a tensor barrier, which describes the rotation of
the honeycomb cells of a given region around an axis perpendicular to the
graphene layer. We demonstrate that in this case the intervalley mixing between
the Dirac points emerges, and that Klein tunneling occurs.Comment: 11 pages, 5 figure
Applications and Sexual Version of a Simple Model for Biological Ageing
We use a simple model for biological ageing to study the mortality of the
population, obtaining a good agreement with the Gompertz law. We also simulate
the same model on a square lattice, considering different strategies of
parental care. The results are in agreement with those obtained earlier with
the more complicated Penna model for biological ageing. Finally, we present the
sexual version of this simple model.Comment: For Int.J.Mod.Phys.C Dec. 2001; 11 pages including 6 fig
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