33 research outputs found
Majority versus minority dynamics: Phase transition in an interacting two-state spin system
We introduce a simple model of opinion dynamics in which binary-state agents
evolve due to the influence of agents in a local neighborhood. In a single
update step, a fixed-size group is defined and all agents in the group adopt
the state of the local majority with probability p or that of the local
minority with probability 1-p. For group size G=3, there is a phase transition
at p_c=2/3 in all spatial dimensions. For p>p_c, the global majority quickly
predominates, while for p<p_c, the system is driven to a mixed state in which
the densities of agents in each state are equal. For p=p_c, the average
magnetization (the difference in the density of agents in the two states) is
conserved and the system obeys classical voter model dynamics. In one dimension
and within a Kirkwood decoupling scheme, the final magnetization in a
finite-length system has a non-trivial dependence on the initial magnetization
for all p.ne.p_c, in agreement with numerical results. At p_c, the exact 2-spin
correlation functions decay algebraically toward the value 1 and the system
coarsens as in the classical voter model.Comment: 11 pages, 3 figures, revtex4 2-column format; minor revisions for
publication in PR
Influence of auto-organization and fluctuation effects on the kinetics of a monomer-monomer catalytic scheme
We study analytically kinetics of an elementary bimolecular reaction scheme
of the Langmuir-Hinshelwood type taking place on a d-dimensional catalytic
substrate. We propose a general approach which takes into account explicitly
the influence of spatial correlations on the time evolution of particles mean
densities and allows for the analytical analysis. In terms of this approach we
recover some of known results concerning the time evolution of particles mean
densities and establish several new ones.Comment: Latex, 25 pages, one figure, submitted to J. Chem. Phy
Co-limitation towards lower latitudes shapes global forest diversity gradients
The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025°âĂâ0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers
Minnesota Farm Business Notes No. 207
Democracy in Land Use Planning in Minnesota; Farm real estate taxes in Minnesota; Change in size of Minnesota farms since purchase of a tractor; Minnesota farm prices for February 194
Minnesota Farm Business Notes No. 208
Operating Results of Minnesota Cooperative Oil Associations; Earnings of diary farmers in southeastern Minnesota; Meat consumed by locker patrons; Minnesota farm prices for March 194
Minnesota Farm Business Notes No. 210
Methods of Handling Minnesota Eggs; AAA payments in Southeastern Minnesota; Budgeting alternative soil conservation programs; Minnesota farm prices for May 194