3,370 research outputs found
Let my people go (home) to Spain: a genealogical model of Jewish identities since 1492
The Spanish government recently announced an official fast-track path to
citizenship for any individual who is Jewish and whose ancestors were expelled
from Spain during the inquisition-related dislocation of Spanish Jews in 1492.
It would seem that this policy targets a small subset of the global Jewish
population, i.e., restricted to individuals who retain cultural practices
associated with ancestral origins in Spain. However, the central contribution
of this manuscript is to demonstrate how and why the policy is far more likely
to apply to a very large fraction (i.e., the vast majority) of Jews. This claim
is supported using a series of genealogical models that include transmissable
"identities" and preferential intra-group mating. Model analysis reveals that
even when intra-group mating is strong and even if only a small subset of a
present-day population retains cultural practices typically associated with
that of an ancestral group, it is highly likely that nearly all members of that
population have direct geneaological links to that ancestral group, given
sufficient number of generations have elapsed. The basis for this conclusion is
that not having a link to an ancestral group must be a property of all of an
individual's ancestors, the probability of which declines (nearly)
superexponentially with each successive generation. These findings highlight
unexpected incongruities induced by genealogical dynamics between present-day
and ancestral identities.Comment: 6 page, 4 figure
Packing-Limited Growth
We consider growing spheres seeded by random injection in time and space.
Growth stops when two spheres meet leading eventually to a jammed state. We
study the statistics of growth limited by packing theoretically in d dimensions
and via simulation in d=2, 3, and 4. We show how a broad class of such models
exhibit distributions of sphere radii with a universal exponent. We construct a
scaling theory that relates the fractal structure of these models to the decay
of their pore space, a theory that we confirm via numerical simulations. The
scaling theory also predicts an upper bound for the universal exponent and is
in exact agreement with numerical results for d=4.Comment: 6 pages, 5 figures, 4 tables, revtex4 to appear in Phys. Rev. E, May
200
Drainage in a model stratified porous medium
We show that when a non-wetting fluid drains a stratified porous medium at
sufficiently small capillary numbers Ca, it flows only through the coarsest
stratum of the medium; by contrast, above a threshold Ca, the non-wetting fluid
is also forced laterally, into part of the adjacent, finer strata. The spatial
extent of this partial invasion increases with Ca. We quantitatively understand
this behavior by balancing the stratum-scale viscous pressure driving the flow
with the capillary pressure required to invade individual pores. Because
geological formations are frequently stratified, we anticipate that our results
will be relevant to a number of important applications, including understanding
oil migration, preventing groundwater contamination, and sub-surface CO
storage
An Objective Definition of Damage Spreading - Application to Directed Percolation
We present a general definition of damage spreading in a pair of models.
Using this general framework, one can define damage spreading in an objective
manner, that does not depend on the particular dynamic procedure that is being
used. The formalism is applied to the Domany-Kinzel cellular automaton in one
dimension; the active phase of this model is shown to consist of three
sub-phases, characterized by different damage-spreading properties.Comment: 10 pages, RevTex, 2 ps figure
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