3,594 research outputs found
A Characterization of Uniquely Representable Graphs
The betweenness structure of a finite metric space is a pair
where is the so-called betweenness
relation of that consists of point triplets such that . The underlying graph of a betweenness structure
is the simple graph where
the edges are pairs of distinct points with no third point between them. A
connected graph is uniquely representable if there exists a unique metric
betweenness structure with underlying graph . It was implied by previous
works that trees are uniquely representable. In this paper, we give a
characterization of uniquely representable graphs by showing that they are
exactly the block graphs. Further, we prove that two related classes of graphs
coincide with the class of block graphs and the class of distance-hereditary
graphs, respectively. We show that our results hold not only for metric but
also for almost-metric betweenness structures.Comment: 16 pages (without references); 3 figures; major changes: simplified
proofs, improved notations and namings, short overview of metric graph theor
On the concept of Bell's local causality in local classical and quantum theory
The aim of this paper is to give a sharp definition of Bell's notion of local
causality. To this end, first we unfold a framework, called local physical
theory, integrating probabilistic and spatiotemporal concepts. Formulating
local causality within this framework and classifying local physical theories
by whether they obey local primitive causality --- a property rendering the
dynamics of the theory causal, we then investigate what is needed for a local
physical theory, with or without local primitive causality, to be locally
causal. Finally, comparing Bell's local causality with the Common Cause
Principles and relating both to the Bell inequalities we find a nice
parallelism: Bell inequalities cannot be derived neither from local causality
nor from a common cause unless the local physical theory is classical or the
common cause is commuting, respectively.Comment: 24 pages, 5 figure
Winning strategies in congested traffic
One-directional traffic on two-lanes is modeled in the framework of a
spring-block type model. A fraction of the cars are allowed to change
lanes, following simple dynamical rules, while the other cars keep their
initial lane. The advance of cars, starting from equivalent positions and
following the two driving strategies is studied and compared. As a function of
the parameter the winning probability and the average gain in the
advancement for the lane-changing strategy is computed. An interesting
phase-transition like behavior is revealed and conclusions are drawn regarding
the conditions when the lane changing strategy is the better option for the
drivers.Comment: 5 pages, 5 figure
Generalized mean-field study of a driven lattice gas
Generalized mean-field analysis has been performed to study the ordering
process in a half-filled square lattice-gas model with repulsive nearest
neighbor interaction under the influence of a uniform electric field. We have
determined the configuration probabilities on 2-, 4-, 5-, and 6-point clusters
excluding the possibility of sublattice ordering. The agreement between the
results of 6-point approximations and Monte Carlo simulations confirms the
absence of phase transition for sufficiently strong fields.Comment: 4 pages (REVTEX) with 4 PS figures (uuencoded
Phase transitions for rock-scissors-paper game on different networks
Monte Carlo simulations and dynamical mean-field approximations are performed
to study the phase transitions in rock-scissors-paper game on different host
networks. These graphs are originated from lattices by introducing quenched and
annealed randomness simultaneously. In the resulting phase diagrams three
different stationary states are identified for all structures. The comparison
of results on different networks suggests that the value of clustering
coefficient plays an irrelevant role in the emergence of a global oscillating
phase. The critical behavior of phase transitions seems to be universal and can
be described by the same exponents.Comment: 4 pages, 4 figures, to be published in PR
Evolutionary prisoner's dilemma games with optional participation
Competition among cooperators, defectors, and loners is studied in an
evolutionary prisoner's dilemma game with optional participation. Loners are
risk averse i.e. unwilling to participate and rather rely on small but fixed
earnings. This results in a rock-scissors-paper type cyclic dominance of the
three strategies. The players are located either on square lattices or random
regular graphs with the same connectivity. Occasionally, every player
reassesses its strategy by sampling the payoffs in its neighborhood. The loner
strategy efficiently prevents successful spreading of selfish, defective
behavior and avoids deadlocks in states of mutual defection. On square
lattices, Monte Carlo simulations reveal self-organizing patterns driven by the
cyclic dominance, whereas on random regular graphs different types of
oscillatory behavior are observed: the temptation to defect determines whether
damped, periodic or increasing oscillations occur. These results are compared
to predictions by pair approximation. Although pair approximation is incapable
of distinguishing the two scenarios because of the equal connectivity, the
average frequencies as well as the oscillations on random regular graphs are
well reproduced.Comment: 6 pages, 7 figure
Benefits of a marketing cooperative in transition agriculture: MĂłrakert purchasing and service co-operative
The paper analyses the potential benefits of marketing cooperatives in Hungary, employing a transaction cost economics framework. We found that the purchased quantity, the existence of contracts, flexibility and trust are the most important factors farmers consider when selling their products via a cooperative. The most striking result is that diversification has positive influences on the share of cooperatives in farmersâ sale. Furthermore, farmers with larger bargaining power have less willingness to sell their product to the cooperative. Surprisingly, asset specificity has rather negative effects on the share of cooperatives in membersâ sales
Causation, Measurement Relevance and No-conspiracy in EPR
In this paper I assess the adequacy of no-conspiracy conditions employed in
the usual derivations of the Bell inequality in the context of EPR
correlations. First, I look at the EPR correlations from a purely
phenomenological point of view and claim that common cause explanations of
these cannot be ruled out. I argue that an appropriate common cause explanation
requires that no-conspiracy conditions are re-interpreted as mere common
cause-measurement independence conditions. In the right circumstances then,
violations of measurement independence need not entail any kind of conspiracy
(nor backwards in time causation). To the contrary, if measurement operations
in the EPR context are taken to be causally relevant in a specific way to the
experiment outcomes, their explicit causal role provides the grounds for a
common cause explanation of the corresponding correlations.Comment: 20 pages, 1 figur
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