15,347 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
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
Site-dependent hydrogenation on graphdiyne
Graphene is one of the most important materials in science today due to its
unique and remarkable electronic, thermal and mechanical properties. However in
its pristine state, graphene is a gapless semiconductor, what limits its use in
transistor electronics. In part due to the revolution created by graphene in
materials science, there is a renewed interest in other possible graphene-like
two-dimensional structures. Examples of these structures are graphynes and
graphdiynes, which are two-dimensional structures, composed of carbon atoms in
sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two
acetylenic groups) were recently synthesized and some of them are intrinsically
nonzero gap systems. These systems can be easily hydrogenated and the relative
level of hydrogenation can be used to tune the band gap values. We have
investigated, using fully reactive molecular dynamics (ReaxFF), the structural
and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes.
Our results showed that the hydrogen bindings have different atom incorporation
rates and that the hydrogenation patterns change in time in a very complex way.
The formation of correlated domains reported to hydrogenated graphene is no
longer observed in graphdiyne cases.Comment: Submitted to Carbo
Sistemas agroflorestais: experiência local na validação de princípios agroecológicos.
A Agroecologia não é um modelo e nem uma forma ou estilo particular de agricultura. A Agroecologia propõe um conjunto de princípios e de metodologias participativas que apóiam o processo de transição dos modelos de agricultura convencional para um estilo de agriculturas e de desenvolvimento rural sustentáveis
Evaluation of noni (Morinda citrifolia) volatile profile by dynamic headspace and gas chromatography-mass spectrometry.
Manuseio do pólen de Ocotea porosa (Nees & C. Mart.) para conservação genética: estágio ideal para a coleta.
EVINCI. Resumo 027
Enraizamento de estaca de Tococa formicaria (Melastomataceae Juss), uma alternativa para acelerar o processo de restauração em matas ripárias.
Quantum theory of spectral diffusion induced electron spin decoherence
A quantum cluster expansion method is developed for the problem of localized
electron spin decoherence due to dipolar fluctuations of lattice nuclear spins.
At the lowest order it provides a microscopic explanation for the Lorentzian
diffusion of Hahn echoes without resorting to any phenomenological Markovian
assumption. Our numerical results show remarkable agreement with recent
electron spin echo experiments in phosphorus doped silicon.Comment: 5 pages, 1 figur
- …