15 research outputs found
Scaling in Numerical Simulations of Domain Walls
We study the evolution of domain wall networks appearing after phase
transitions in the early Universe. They exhibit interesting dynamical scaling
behaviour which is not yet well understood, and are also simple models for the
more phenomenologically acceptable string networks. We have run numerical
simulations in two- and three-dimensional lattices of sizes up to 4096^3. The
theoretically predicted scaling solution for the wall area density A ~ 1/t is
supported by the simulation results, while no evidence of a logarithmic
correction reported in previous studies could be found. The energy loss
mechanism appears to be direct radiation, rather than the formation and
collapse of closed loops or spheres. We discuss the implications for the
evolution of string networks.Comment: 7pp RevTeX, 9 eps files (including six 220kB ones
The Shapes of Dirichlet Defects
If the vacuum manifold of a field theory has the appropriate topological
structure, the theory admits topological structures analogous to the D-branes
of string theory, in which defects of one dimension terminate on other defects
of higher dimension. The shapes of such defects are analyzed numerically, with
special attention paid to the intersection regions. Walls (co-dimension 1
branes) terminating on other walls, global strings (co-dimension 2 branes) and
local strings (including gauge fields) terminating on walls are all considered.
Connections to supersymmetric field theories, string theory and condensed
matter systems are pointed out.Comment: 24 pages, RevTeX, 21 eps figure
Level Set Method for the Evolution of Defect and Brane Networks
A theory for studying the dynamic scaling properties of branes and
relativistic topological defect networks is presented. The theory, based on a
relativistic version of the level set method, well-known in other contexts,
possesses self-similar ``scaling'' solutions, for which one can calculate many
quantities of interest. Here, the length and area densities of cosmic strings
and domain walls are calculated in Minkowski space, and radiation, matter, and
curvature-dominated FRW cosmologies with 2 and 3 space dimensions. The scaling
exponents agree the naive ones based on dimensional analysis, except for cosmic
strings in 3-dimensional Minkowski space, which are predicted to have a
logarithmic correction to the naive scaling form. The scaling amplitudes of the
length and area densities are a factor of approximately 2 lower than results
from numerical simulations of classical field theories. An expression for the
length density of strings in the condensed matter literature is corrected.Comment: 46pp LaTeX, revtex4(preprint), 1 eps figure, revised for publication.
Note title chang
Sorção de fósforo em função do teor inicial e de sistemas de manejo de solos
A relação entre o P sorvido/P solução do solo pode ser influenciada pelo teor de P previamente sorvido e pelos sistemas de manejo. Este trabalho teve o objetivo de avaliar as modificações na capacidade de sorção máxima (Pmax) e na constante relacionada com a energia de ligação de P com os colóides (k) da isoterma de Langmuir, provocadas (a) pela inclusão do teor de P previamente sorvido (Ppre) e (b) por sistemas de manejo de solos. Coletaram-se, em maio de 1997, amostras de solo (Latossolo Vermelho distroférrico típico, Latossolo Vermelho distrófico típico e Argissolo Vermelho distrófico típico), em três camadas (0-2,5, 2,5-7,5 e 7,5-17,5 cm), de três experimentos instalados a partir de 1979, envolvendo os sistemas plantio direto e cultivo convencional com diferentes sucessões de cultura. O solo foi equilibrado com oito concentrações de P em solução de CaCl2 0,001 mol L-1. Após a agitação por 16 h, avaliou-se a concentração de P no sobrenadante. Os dados de P-sorvido e P-solução foram ajustados à equação de Langmuir, obtendo-se a Pmax e a k, considerando ou não o Ppre. A inclusão do Ppre no modelo de Langmuir aumenta, em média, 2,9 vezes o valor da k e não afeta a Pmax, no LVdf, e aumenta em todas as camadas, no LVd, e na camada superficial, no PVd. A Pmax é pouco influenciada pelos métodos de preparo do solo, sucessões de culturas e camadas amostradas