531 research outputs found
Advertising, consensus, and ageing in multilayer Sznajd model
In the Sznajd consensus model on the square lattice, two people who agree in
their opinions convince their neighbours of this opinion. We generalize it to
many layers representing many age levels, and check if still a consensus among
all layers is possible. Advertising sometimes but not always produces a
consensus on the advertised opinion.Comment: 6 pages including 4 figures, for Int. J. Mod. Phys.
Superconducting junctions from non-superconducting doped CuO layers
The theoretical approach proposed recently for description of redistribution
of electronic charge in multilayered selectively doped systems is modified for
a system with finite number of layers. A special attention is payed to the case
of a finite heterostructure made of copper-oxide layers which are all
non-superconducting (including non-conducting) because of doping levels being
beyond the well-known characteristic interval for superconductivity. Specific
finite structures and doping configurations are proposed to obtain atomically
thin superconducting heterojunctions of different compositions.Comment: 4 pages, 3 figures, two bibliography references were update
Effects of noise and confidence thresholds in nominal and metric Axelrod dynamics of social influence
We study the effects of bounded confidence thresholds and of interaction and
external noise on Axelrod's model of social influence. Our study is based on a
combination of numerical simulations and an integration of the mean-field
Master equation describing the system in the thermodynamic limit. We find that
interaction thresholds affect the system only quantitatively, but that they do
not alter the basic phase structure. The known crossover between an ordered and
a disordered state in finite systems subject to external noise persists in
models with general confidence threshold. Interaction noise here facilitates
the dynamics and reduces relaxation times. We also study Axelrod systems with
metric features, and point out similarities and differences compared to models
with nominal features. Metric features are used to demonstrate that a small
group of extremists can have a significant impact on the opinion dynamics of a
population of Axelrod agents.Comment: 15 pages, 12 figure
Diffusing opinions in bounded confidence processes
We study the effects of diffusing opinions on the Deffuant et al. model for
continuous opinion dynamics. Individuals are given the opportunity to change
their opinion, with a given probability, to a randomly selected opinion inside
an interval centered around the present opinion. We show that diffusion induces
an order-disorder transition. In the disordered state the opinion distribution
tends to be uniform, while for the ordered state a set of well defined opinion
clusters are formed, although with some opinion spread inside them. If the
diffusion jumps are not large, clusters coalesce, so that weak diffusion favors
opinion consensus. A master equation for the process described above is
presented. We find that the master equation and the Monte-Carlo simulations do
not always agree due to finite-size induced fluctuations. Using a linear
stability analysis we can derive approximate conditions for the transition
between opinion clusters and the disordered state. The linear stability
analysis is compared with Monte Carlo simulations. Novel interesting phenomena
are analyzed
Remarks on supersymmetry of quantum systems with position-dependent effective masses
We apply the supersymmetry approach to one-dimensional quantum systems with
spatially-dependent mass, by including their ordering ambiguities dependence.
In this way we extend the results recently reported in the literature.
Furthermore, we point out a connection between these systems and others with
constant masses. This is done through convenient transformations in the
coordinates and wavefunctions.Comment: 8 pages, 1 figur
Analytical solution to position dependent mass Schr\"odinger equation
Using a recently developed technique to solve Schr\"odinger equation for
constant mass, we studied the regime in which mass varies with position i.e
position dependent mass Schr\"odinger equation(PDMSE). We obtained an
analytical solution for the PDMSE and applied our approach to study a position
dependent mass particle scattered by a potential . We
also studied the structural analogy between PDMSE and two-level atomic system
interacting with a classical field.Comment: 5 pages, 4 figure
Evolution and extinction dynamics in rugged fitness landscapes
Macroevolution is considered as a problem of stochastic dynamics in a system
with many competing agents. Evolutionary events (speciations and extinctions)
are triggered by fitness records found by random exploration of the agents'
fitness landscapes. As a consequence, the average fitness in the system
increases logarithmically with time, while the rate of extinction steadily
decreases. This dynamics is studied by numerical simulations and, in a simpler
mean field version, analytically. We also study the effect of externally added
`mass' extinctions. The predictions for various quantities of paleontological
interest (life-time distributions, distribution of event sizes and behavior of
the rate of extinction) are robust and in good agreement with available data.
Brief version of parts of this work have been published as Letters. (PRL 75,
2055, (1995) and PRL, 79, 1413, (1997))Comment: 30 pages 9 figures LaTe
Local Manipulation of Nuclear Spin in a Semiconductor Quantum Well
The shaping of nuclear spin polarization profiles and the induction of
nuclear resonances are demonstrated within a parabolic quantum well using an
externally applied gate voltage. Voltage control of the electron and hole wave
functions results in nanometer-scale sheets of polarized nuclei positioned
along the growth direction of the well. RF voltages across the gates induce
resonant spin transitions of selected isotopes. This depolarizing effect
depends strongly on the separation of electrons and holes, suggesting that a
highly localized mechanism accounts for the observed behavior.Comment: 18 pages, 4 figure
Love kills: Simulations in Penna Ageing Model
The standard Penna ageing model with sexual reproduction is enlarged by
adding additional bit-strings for love: Marriage happens only if the male love
strings are sufficiently different from the female ones. We simulate at what
level of required difference the population dies out.Comment: 14 pages, including numerous figure
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