504 research outputs found
Cluster Percolation and Explicit Symmetry Breaking in Spin Models
Many features of spin models can be interpreted in geometrical terms by means
of the properties of well defined clusters of spins. In case of spontaneous
symmetry breaking, the phase transition of models like the q-state Potts model,
O(n), etc., can be equivalently described as a percolation transition of
clusters. We study here the behaviour of such clusters when the presence of an
external field H breaks explicitly the global symmetry of the Hamiltonian of
the theory. We find that these clusters have still some interesting
relationships with thermal features of the model.Comment: Proceedings of Lattice 2001 (Berlin), 3 pages, 3 figure
Key Success Factors of Innovation in Multinational Agrifood Prospector Companies
The Wageningen Innovation Assessment Tool (WIAT) assesses a companyâs drivers and barriers to innovation and benchmarks the critical success and failure factors of its innovation projects with data of agrifood prospector companies around the world. The present paper discusses its application in 12 multinational agrifood prospector companies in the Netherlands and France. It is concluded that WIAT by uncovering the tacit knowledge of the innovation project team creates opportunities for substantial improvement of the innovation process, and that agrifood companies should specifically pay attention to market and product related up-front activities.innovation, assessment tool, agrifood prospector companies, Agribusiness, Agricultural and Food Policy, International Relations/Trade,
Extended Defects in the Potts-Percolation Model of a Solid: Renormalization Group and Monte Carlo Analysis
We extend the model of a 2 solid to include a line of defects. Neighboring
atoms on the defect line are connected by ?springs? of different strength and
different cohesive energy with respect to the rest of the system. Using the
Migdal-Kadanoff renormalization group we show that the elastic energy is an
irrelevant field at the bulk critical point. For zero elastic energy this model
reduces to the Potts model. By using Monte Carlo simulations of the 3- and
4-state Potts model on a square lattice with a line of defects, we confirm the
renormalization-group prediction that for a defect interaction larger than the
bulk interaction the order parameter of the defect line changes discontinuously
while the defect energy varies continuously as a function of temperature at the
bulk critical temperature.Comment: 13 figures, 17 page
Oriented Percolation in One-Dimensional 1/|x-y|^2 Percolation Models
We consider independent edge percolation models on Z, with edge occupation
probabilities p_ = p if |x-y| = 1, 1 - exp{- beta / |x-y|^2} otherwise. We
prove that oriented percolation occurs when beta > 1 provided p is chosen
sufficiently close to 1, answering a question posed in [Commun. Math. Phys.
104, 547 (1986)]. The proof is based on multi-scale analysis.Comment: 19 pages, 2 figures. See also Commentary on J. Stat. Phys. 150,
804-805 (2013), DOI 10.1007/s10955-013-0702-
Exact sampling from non-attractive distributions using summary states
Propp and Wilson's method of coupling from the past allows one to efficiently
generate exact samples from attractive statistical distributions (e.g., the
ferromagnetic Ising model). This method may be generalized to non-attractive
distributions by the use of summary states, as first described by Huber. Using
this method, we present exact samples from a frustrated antiferromagnetic
triangular Ising model and the antiferromagnetic q=3 Potts model. We discuss
the advantages and limitations of the method of summary states for practical
sampling, paying particular attention to the slowing down of the algorithm at
low temperature. In particular, we show that such a slowing down can occur in
the absence of a physical phase transition.Comment: 5 pages, 6 EPS figures, REVTeX; additional information at
http://wol.ra.phy.cam.ac.uk/mackay/exac
Potts-Percolation-Gauss Model of a Solid
We study a statistical mechanics model of a solid. Neighboring atoms are
connected by Hookian springs. If the energy is larger than a threshold the
"spring" is more likely to fail, while if the energy is lower than the
threshold the spring is more likely to be alive. The phase diagram and
thermodynamic quantities, such as free energy, numbers of bonds and clusters,
and their fluctuations, are determined using renormalization-group and
Monte-Carlo techniques.Comment: 10 pages, 12 figure
A necklace of Wulff shapes
In a probabilistic model of a film over a disordered substrate, Monte-Carlo
simulations show that the film hangs from peaks of the substrate. The film
profile is well approximated by a necklace of Wulff shapes. Such a necklace can
be obtained as the infimum of a collection of Wulff shapes resting on the
substrate. When the random substrate is given by iid heights with exponential
distribution, we prove estimates on the probability density of the resulting
peaks, at small density
Conformal Invariance in Percolation, Self-Avoiding Walks and Related Problems
Over the years, problems like percolation and self-avoiding walks have
provided important testing grounds for our understanding of the nature of the
critical state. I describe some very recent ideas, as well as some older ones,
which cast light both on these problems themselves and on the quantum field
theories to which they correspond. These ideas come from conformal field
theory, Coulomb gas mappings, and stochastic Loewner evolution.Comment: Plenary talk given at TH-2002, Paris. 21 pages, 9 figure
Critical slowing down in polynomial time algorithms
Combinatorial optimization algorithms which compute exact ground state
configurations in disordered magnets are seen to exhibit critical slowing down
at zero temperature phase transitions. Using arguments based on the physical
picture of the model, including vanishing stiffness on scales beyond the
correlation length and the ground state degeneracy, the number of operations
carried out by one such algorithm, the push-relabel algorithm for the random
field Ising model, can be estimated. Some scaling can also be predicted for the
2D spin glass.Comment: 4 pp., 3 fig
Team boosting behaviours:Development and validation of a new concept and scale
In teams, some people are truly noticed when present, and sorely missed when absent. Often they are described as the âlife of the partyâ, but in a formal team context, we refer to their behaviors as âteam boosting behaviorâ. These behaviors have the potential to affect the teamâs processes. In three consecutive studies, we conceptualized these behaviors and developed and validated a questionnaire to measure them. In Study 1, we defined team boosting behaviors as the extent to which team members exhibit mood-enhancing, energizing, and uniting behaviors, directed towards team members. In Study 2, we developed and validated an instrument to measure team boosting behaviors using a sample of team members in work and sports teams (N = 385). Results supported a three-factor structure and indicated positive relationships with conceptually similar constructs. In Study 3, we cross-validated the three-factor structure among the members of 120 work teams and offer evidence for convergent and criterion validity of the Team Boosting behavior scale. The behaviors related positively to a positive team climate, team work engagement, and leader-rated team performance. The scale provides a useful tool for future empirical research to study the role of individual team boosting behaviors in shaping team processes and outcomes
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