2,193 research outputs found
Segregation process and phase transition in cyclic predator-prey models with even number of species
We study a spatial cyclic predator-prey model with an even number of species
(for n=4, 6, and 8) that allows the formation of two defective alliances
consisting of the even and odd label species. The species are distributed on
the sites of a square lattice. The evolution of spatial distribution is
governed by iteration of two elementary processes on neighboring sites chosen
randomly: if the sites are occupied by a predator-prey pair then the predator
invades the prey's site; otherwise the species exchange their site with a
probability . For low values a self-organizing pattern is maintained by
cyclic invasions. If exceeds a threshold value then two types of domains
grow up that formed by the odd and even label species, respectively. Monte
Carlo simulations indicate the blocking of this segregation process within a
range of X for n=8.Comment: 5 pages, 5 figures, to be appear in Phys. Rev.
Research on coherences between the residual stresses and tool rake angle by hard turning
A broad base of researchers are concerned in studying chip removal by hard turning. The reason for that is the most of the accurate selection of the cutting conditions to be able to exploit the advantages of hard turning. Among the parameters influencing the material removal, the geometry and edge formation of the cutting tool play a decisive role too. The efficient chip removal from hardened surfaces of about 60 HRC hardness can be ensured by edge formation that can be called special. In this paper the effect of the tool rake angle on the chip removal process is investigated, within this more detailed is the effect on the residual stress formation. The main method of the investigation is the FEM simulation, with which investigations were done in a wide interval of rake angle values
Sources of variability in essential oil composition of Ocimum americanum and Ocimum tenuiflorum
Basil has traditionally been used for a long time in medicine and gastronomy. Essential oil is the most important active substance of the drug, which influences the aroma and the effect of the plant. Although the compositions of essential oils vary in different basil cultivars, the main components are oxygenated monoterpenes and phenylpropane derivates. The high chemical variation is most likely caused by interspecific hybridization. Various factors, like genetic background, ontogenesis, morphogenesis, abiotic factors, essential oil extraction method, drying, and storage, are responsible for the variant essential oil composition
Vortex dynamics in a three-state model under cyclic dominance
The evolution of domain structure is investigated in a two-dimensional voter
model with three states under cyclic dominance. The study focus on the dynamics
of vortices, defined by the points where three states (domains) meet. We can
distinguish vortices and antivortices which walk randomly and annihilate each
other. The domain wall motion can create vortex-antivortex pairs at a rate
which is increased by the spiral formation due to the cyclic dominance. This
mechanism is contrasted with a branching annihilating random walk (BARW) in a
particle antiparticle system with density dependent pair creation rate.
Numerical estimates for the critical indices of the vortex density
() and of its fluctuation () improve an earlier
Monte Carlo study [Tainaka and Itoh, Europhys. Lett. 15, 399 (1991)] of the
three-state cyclic voter model in two dimensions.Comment: 5 pages, 6 figures, to appear in PR
Phase transition and selection in a four-species cyclic Lotka-Volterra model
We study a four species ecological system with cyclic dominance whose
individuals are distributed on a square lattice. Randomly chosen individuals
migrate to one of the neighboring sites if it is empty or invade this site if
occupied by their prey. The cyclic dominance maintains the coexistence of all
the four species if the concentration of vacant sites is lower than a threshold
value. Above the treshold, a symmetry breaking ordering occurs via growing
domains containing only two neutral species inside. These two neutral species
can protect each other from the external invaders (predators) and extend their
common territory. According to our Monte Carlo simulations the observed phase
transition is equivalent to those found in spreading models with two equivalent
absorbing states although the present model has continuous sets of absorbing
states with different portions of the two neutral species. The selection
mechanism yielding symmetric phases is related to the domain growth process
whith wide boundaries where the four species coexist.Comment: 4 pages, 5 figure
Phase transition in a spatial Lotka-Volterra model
Spatial evolution is investigated in a simulated system of nine competing and
mutating bacterium strains, which mimics the biochemical war among bacteria
capable of producing two different bacteriocins (toxins) at most. Random
sequential dynamics on a square lattice is governed by very symmetrical
transition rules for neighborhood invasion of sensitive strains by killers,
killers by resistants, and resistants by by sensitives. The community of the
nine possible toxicity/resistance types undergoes a critical phase transition
as the uniform transmutation rates between the types decreases below a critical
value above which all the nine types of strain coexist with equal
frequencies. Passing the critical mutation rate from above, the system
collapses into one of the three topologically identical states, each consisting
of three strain types. Of the three final states each accrues with equal
probability and all three maintain themselves in a self-organizing polydomain
structure via cyclic invasions. Our Monte Carlo simulations support that this
symmetry breaking transition belongs to the universality class of the
three-state Potts model.Comment: 4 page
Vertex dynamics during domain growth in three-state models
Topological aspects of interfaces are studied by comparing quantitatively the
evolving three-color patterns in three different models, such as the
three-state voter, Potts and extended voter models. The statistical analysis of
some geometrical features allows to explore the role of different elementary
processes during distinct coarsening phenomena in the above models.Comment: 4 pages, 5 figures, to be published in PR
Flow properties of driven-diffusive lattice gases: theory and computer simulation
We develop n-cluster mean-field theories (0 < n < 5) for calculating the flow
properties of the non-equilibrium steady-states of the Katz-Lebowitz-Spohn
model of the driven diffusive lattice gas, with attractive and repulsive
inter-particle interactions, in both one and two dimensions for arbitrary
particle densities, temperature as well as the driving field. We compare our
theoretical results with the corresponding numerical data we have obtained from
the computer simulations to demonstrate the level of accuracy of our
theoretical predictions. We also compare our results with those for some other
prototype models, notably particle-hopping models of vehicular traffic, to
demonstrate the novel qualitative features we have observed in the
Katz-Lebowitz-Spohn model, emphasizing, in particular, the consequences of
repulsive inter-particle interactions.Comment: 12 RevTex page
- …