42 research outputs found
Nucleation dynamics in 2d cylindrical Ising models and chemotaxis
The aim of our work is to study the effect of geometry variation on
nucleation times and to address its role in the context of eukaryotic
chemotaxis (i.e. the process which allows cells to identify and follow a
gradient of chemical attractant). As a first step in this direction we study
the nucleation dynamics of the 2d Ising model defined on a cylindrical lattice
whose radius changes as a function of time. Geometry variation is obtained by
changing the relative value of the couplings between spins in the compactified
(vertical) direction with respect to the horizontal one. This allows us to keep
the lattice size unchanged and study in a single simulation the values of the
compactification radius which change in time. We show, both with theoretical
arguments and numerical simulations that squeezing the geometry allows the
system to speed up nucleation times even in presence of a very small energy gap
between the stable and the metastable states. We then address the implications
of our analysis for directional chemotaxis. The initial steps of chemotaxis can
be modelled as a nucleation process occurring on the cell membrane as a
consequence of the external chemical gradient (which plays the role of energy
gap between the stable and metastable phases). In nature most of the cells
modify their geometry by extending quasi-onedimensional protrusions (filopodia)
so as to enhance their sensitivity to chemoattractant. Our results show that
this geometry variation has indeed the effect of greatly decreasing the
timescale of the nucleation process even in presence of very small amounts of
chemoattractants.Comment: 27 pages, 6 figures and 2 table
Desenvolvimento de métodos para a quantificação de potássio em amostras de solo sob aplicação de subprodutos do processamento de cana-de-açúcar utilizando LIBS.
Pressure induced metallization of Cu3N
We employed accurate full potential density-functional theory and linearized
augmented plane wave method to investigate the electronic properties and
possible phase transitions of Cu3N under high pressure. The anti perovskite
structure Cu3N is a semiconductor with a small indirect band gap at ambient
pressure. The band gap becomes narrower with increasing pressure, and the
semi-conducting anti ReO3 structure undergoes a semiconductor to semimetal
transition at pressure around 8.0 GPa. At higher pressure, a subsequent
semimetal to metal transition could take place above 15GPa with a structural
transition from anti ReO3 to Cu3Au structure