25,980 research outputs found
Model inspired by population genetics to study fragmentation of brittle plates
We use a model whose rules were inspired by population genetics, the random
capability growth model, to describe the statistical details observed in
experiments of fragmentation of brittle platelike objects, and in particular
the existence of (i) composite scaling laws, (ii) small critical exponents \tau
associated with the power-law fragment-size distribution, and (iii) the typical
pattern of cracks. The proposed computer simulations do not require numerical
solutions of the Newton's equations of motion, nor several additional
assumptions normally used in discrete element models. The model is also able to
predict some physical aspects which could be tested in new experiments of
fragmentation of brittle systems.Comment: We have modified the text in order to make the description of the
model more clear. One Figure (Figure 1) was introduced showing the steps of
the dynamics of colonization. Twelve references were adde
Plastic Deformation of 2D Crumpled Wires
When a single long piece of elastic wire is injected trough channels into a
confining two-dimensional cavity, a complex structure of hierarchical loops is
formed. In the limit of maximum packing density, these structures are described
by several scaling laws. In this paper it is investigated this packing process
but using plastic wires which give origin to completely irreversible structures
of different morphology. In particular, it is studied experimentally the
plastic deformation from circular to oblate configurations of crumpled wires,
obtained by the application of an axial strain. Among other things, it is shown
that in spite of plasticity, irreversibility, and very large deformations,
scaling is still observed.Comment: 5 pages, 6 figure
Individual decision making in task-oriented groups
The strategies adopted by individuals to select relevant information to pass
on are central to understanding problem solving by groups. Here we use
agent-based simulations to revisit a cooperative problem-solving scenario where
the task is to find the common card in decks distributed to the group members.
The agents can display only a sample of their cards and we explore different
strategies to select those samples based on the confidences assigned to the
cards. An agent's confidence that a particular card is the correct one is given
by the number of times it observed that card in the decks of the other agents.
We use a Gibbs distribution to select the card samples with the temperature
measuring the strength of a noise that prevents the agents to correctly rank
the cards. The group is guaranteed to find the common card in all runs solely
in the infinite temperature limit, where the cards are sampled regardless of
their confidences. In this case, we obtain the scaling form of the time
constant that characterizes the asymptotic exponential decay of the failure
probability. For finite time, however, a finite temperature yields a
probability of failure that is several orders of magnitude lower than in the
infinite temperature limit. The available experimental results are consistent
with the decision-making model for finite temperature only
Policies for allocation of information in task-oriented groups: elitism and egalitarianism outperform welfarism
Communication or influence networks are probably the most controllable of all
factors that are known to impact on the problem-solving capability of
task-forces. In the case connections are costly, it is necessary to implement a
policy to allocate them to the individuals. Here we use an agent-based model to
study how distinct allocation policies affect the performance of a group of
agents whose task is to find the global maxima of NK fitness landscapes. Agents
cooperate by broadcasting messages informing on their fitness and use this
information to imitate the fittest agent in their influence neighborhoods. The
larger the influence neighborhood of an agent, the more links, and hence
information, the agent receives. We find that the elitist policy in which
agents with above-average fitness have their influence neighborhoods amplified,
whereas agents with below-average fitness have theirs deflated, is optimal for
smooth landscapes, provided the group size is not too small. For rugged
landscapes, however, the elitist policy can perform very poorly for certain
group sizes. In addition, we find that the egalitarian policy, in which the
size of the influence neighborhood is the same for all agents, is optimal for
both smooth and rugged landscapes in the case of small groups. The welfarist
policy, in which the actions of the elitist policy are reversed, is always
suboptimal, i.e., depending on the group size it is outperformed by either the
elitist or the egalitarian policies
Lorentz symmetry breaking in the noncommutative Wess-Zumino model: One loop corrections
In this paper we deal with the issue of Lorentz symmetry breaking in quantum
field theories formulated in a non-commutative space-time. We show that, unlike
in some recente analysis of quantum gravity effects, supersymmetry does not
protect the theory from the large Lorentz violating effects arising from the
loop corrections. We take advantage of the non-commutative Wess-Zumino model to
illustrate this point.Comment: 9 pages, revtex4. Corrected references. Version published in PR
Structural properties of crumpled cream layers
The cream layer is a complex heterogeneous material of biological origin
which forms spontaneously at the air-milk interface. Here, it is studied the
crumpling of a single cream layer packing under its own weight at room
temperature in three-dimensional space. The structure obtained in these
circumstances has low volume fraction and anomalous fractal dimensions. Direct
means and noninvasive NMR imaging technique are used to investigate the
internal and external structure of these systems.Comment: 9 pages, 4 figures, accepted in J. Phys. D: Appl. Phy
T-Duality in 2-D Integrable Models
The non-conformal analog of abelian T-duality transformations relating pairs
of axial and vector integrable models from the non abelian affine Toda family
is constructed and studied in detail.Comment: 14 pages, Latex, v.2 misprints corrected, reference added, to appear
in J. Phys.
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