Abstract
The dynamic properties of a modified nonlinear noisy voter model on a square lattice are studied in the paper. The introduced modifications are as follows. First, the changes of the binary ...variable (opinion) at the voters (agents) are caused by avalanche-like perturbations of the system. Secondly, the structure of inter-agent links is not static. Its temporal evolution is due to a new characteristic of the agent called ‘activity’. It determines the probability for the agent to be linked with its nearest neighbors at a given time moment. In addition we introduce a binary variable that changes randomly in time (an ‘external opinion’). According to the proposed rules for opinion changes, an agent that unlinked to neighbors changes its opinion to a current value of the external opinion, regardless of the opinions of other agents. A linked agent can copy the opinion of its neighbor during an avalanche process. Analytically and numerically, we show that the agents’ ‘activity’ distribution and the time-averaged value of the external opinion completely determines the mode of opinion dynamics. The phase diagram for the model under consideration is obtained. In the case of large values of averaged agents’ ‘activity’ the system switches between two consensus states spending the most of time in the consensus with shared opinion corresponding to the prevailing value of the external opinion. For small value of averaged ‘activity’ the system tends to the state where the opposite opinions coexist, but agents predominate with opinion corresponding to sign of the time-averaged value of the external opinion. We demonstrate that the resulting model reflects the main features of the behavior of real multi-agent systems where the external information inflows into the system and, spreading among agents, drives opinion dynamics.
A model of opinion dynamics in a multiagent system is proposed that represents a change in agent’s opinion as a result of two processes. The first is an avalanche-like distribution of information ...between agents through the links existing in the system, during which the agents participating in the distribution can copy the opinions of neighbors under the information pressure from them. The second is an independent change of opinion by agents who do not participate in the information avalanche but are under excessive information pressure. The probabilities of the agent’s participation in a particular process are determined by the main parameters of the model: the activity
a
of agents, which determines the probability for the agent to establish links with his neighbors, and the probability
p
of an independent change in the agent’s opinion under the pressure of the information obtained. It is shown that, depending on the relationship between these parameters, one of three dynamical regimes (phases) can be realized in the system. The first is a state close to dynamic parity that is characterized by a unimodal probability density function for the system-averaged opinion
m
with a maximum
m
0
= 0. In the second regime, the system spends most of its time in states close to consensus. This regime is described by a bimodal probability density function for the system-averaged opinion with maxima
m
1, 2
= ±1. The third dynamical phase is transient, all values of the system-averaged opinion in this phase are almost equiprobable, and the probability density function of this quantity is close to that for a uniform distribution. It is also shown that the proposed model makes it possible to study the opinion formation process in multiagent systems under conditions that could not be considered in previously developed models. As an example, the effect of the lifetime of the links established in the system on the implementation of various dynamical regimes in it is considered. It is shown that, as this time decreases, the range of parameter values at which the bimodal regime is realized narrows; i.e., it becomes difficult to achieve consensus in the system.
We consider a model of the dynamics of opinions in a multiagent system in which the structure of connections between agents changes over time. Within the framework of the model, agents change their ...minds as a result of changes in the information pressure on them. These changes occur both due to the receipt of information by agents from the outside and during the avalanche-like exchange of information between them through the connections existing in the system. At the same time, agents that have established connections with their neighbors at the moment and participate in the process of information exchange can copy the opinion of the neighbor from whom they receive information. Agents not connected with neighbors, but experiencing excessive information pressure, can change their minds regardless of the environment. To describe this type of dynamics, each agent in our model, in addition to the binary variable denoting his opinion, is assigned two additional characteristics: “activity,” which determines the probability for the agent to be currently connected with its nearest neighbors, and a threshold dynamic variable, denoting the magnitude of information pressure. Using computer simulations and analytically, we have shown that, with a change in the average activity of agents in the system, a second-order phase transition is realized between the mode in which the system spends most of the time in the states of consensus and dynamic parity.
Anisotropic Magnetization of an NbN Film Gokhfeld, D. M.; Savitskaya, N. E.; Popkov, S. I. ...
Journal of experimental and theoretical physics,
06/2022, Letnik:
134, Številka:
6
Journal Article
Recenzirano
The structural and magnetic properties of a niobium nitride (NbN) film prepared by reactive sputtering onto a quartz substrate are investigated. It is shown using scanning electron microscopy that ...the film has a columnar structure with a diameter of crystallite columns of about 50 nm. The film magnetization loops are measured for the field orientation parallel and perpendicular to its surface. Based on the experimental data, the critical current densities of the film are estimated in both cases. For the field parallel to the film surface, the estimate is 6.5 × 10
4
A/cm
2
at the liquid helium temperature. For the field perpendicular to the surface, the critical current density is close to the depairing current density (10
7
A/cm
2
). Analysis of the results based on different models of magnetic vortex pinning in superconductors shows that in the former case, pinning occurs at the boundaries of columns in the bulk of the sample, while in the latter case, it is determined by the influence of the surface barrier.
The properties of the avalanche processes that develop on a dynamical lattice, the structure of links in which changes due to a specific characteristic of each lattice node, namely, its “activity,” ...which determines the probability of connection of a certain node with neighboring nodes in one step of lattice evolution. The statistics of the sizes of the avalanches appearing in the lattice system is studied as a function of the node activity and the link lifetime (the lifetime of the links formed in the system). It is analytically and numerically shows that the type of avalanche dynamics in the system changes as a function of these parameters. The following three regimes can take place in the system: (1) avalanches of any sizes, from small to catastrophic, can appear, which is reflected in the power-law behavior of the probability density function of the appearance of avalanches of certain sizes; (2) avalanches of a certain average size mainly appear in the system, and the probability density is close to that of a normal distribution; and (3) transient regime, where the probability density function of the appearance of avalanches of certain sizes is close to an exponential function. These results open up the possibilities of controlling the behavior of a complex system; in particular, they can be used to prevent catastrophic avalanches by changing the link lifetime and the average node activity.
Three-dimensional periodic tin structures were synthesized by filling pores in silicon opals with a sphere diameter of 194 nm (Sn190) and 310 nm (Sn300). The samples were examined by the ...ultra-small-angle x-ray diffraction method, energy dispersive x-ray microanalysis and scanning electron microscopy. It was found that the inverse opal structure consists of tin nanoparticles inscribed in octahedral and tetrahedral pores with diameters of 128 nm and 70 nm for the sample Sn300, and 80 nm and 42 nm for the sample Sn190. The study of the magnetic properties of the samples by SQUID magnetometry showed that magnetization reversal curves exhibit hysteretic behavior. The mechanisms of magnetic flux pinning in the samples depend on the size of the tin nanoparticles. Tin nanoparticles in Sn300 behave like a classical type-I superconductor. The hysteretic behavior of the magnetization reversal curves at low magnetic fields is due to the formation of a network of superconducting contours in Sn300. These superconducting contours effectively trap the magnetic flux. The octahedral tin nanoparticles in Sn190 remain type-I superconductors, but smaller tetrahedral particles behave like type-II superconductors. Type-I and II superconducting particles in Sn190 lead to the coexistence of different mechanisms of flux pinning. These are flux trapping by superconducting contours at low magnetic fields and flux pinning by tetrahedral particles due to the surface barrier at high magnetic fields.
The stabilization of avalanches on dynamical networks has been studied. Dynamical networks are networks where the structure of links varies in time owing to the presence of the individual “activity” ...of each site, which determines the probability of establishing links with other sites per unit time. An interesting case where the times of existence of links in a network are equal to the avalanche development times has been examined. A new mathematical model of a system with the avalanche dynamics has been constructed including changes in the network on which avalanches are developed. A square lattice with a variable structure of links has been considered as a dynamical network within this model. Avalanche processes on it have been simulated using the modified Abelian sandpile model and fixed-energy sandpile model. It has been shown that avalanche processes on the dynamical lattice under study are more stable than a static lattice with respect to the appearance of catastrophic events. In particular, this is manifested in a decrease in the maximum size of an avalanche in the Abelian sandpile model on the dynamical lattice as compared to that on the static lattice. For the fixed-energy sandpile model, it has been shown that, in contrast to the static lattice, where an avalanche process becomes infinite in time, the existence of avalanches finite in time is always possible.
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A passive neutron dosemeter (PND) for high-energy accelerators is described. The slide of the DVGN-01 personal dosemeter, which is placed at the center of a polyethylene moderator, is used as a ...thermal-neutron detector. The moderator includes a lead insert, which increases the sensitivity of the dosemeter to high-energy neutrons, and a cadmium filter. Optimization calculations of the dosemeter design parameters have been performed with respect to the energy dependence of the response in the range from the thermal energy to 1 GeV. The results of the calculations are in good agreement with the experimental data obtained in low-energy neutron reference fields. Comparative measurements using the PND and a low-energy passive dosemeter have been performed in the neutron fields outside the shield of the 70-GeV U-70 proton accelerator at the Institute for High Energy Physics.
It is shown that there exists an optimal thickness of a rubidium target, dependent on the proton energy at its ingress, for reaching a compromise between the maximum yield of
82
Sr and a minimum ...relative yield of the impurities
83
Sr and
85
Sr. The optimal irradiation regime and holding time are determined for a target to chemical separation of strontium from it during operation with no accelerator downtime. Recommendations are made for operating with partial loads.
239Pu–Be-Source Based Neutron Reference Fields Peleshko, V. N.; Savitskaya, E. N.; Sannikov, A. V. ...
Atomic energy (New York, N.Y.),
09/2019, Letnik:
126, Številka:
5
Journal Article
Recenzirano
New neutron reference fields, based on a
239
Pu–Be source, intended for increasing the accuracy of measurements of neutron dosimeters and radiometers in the IHEP accelerator complex are described. A ...Bonner SB-RSU-01 spectrometer was used to measure the spectra of the neutron reference fields. The BON95 code was used to reconstruct the spectra; the initial spectra for the iteration procedure were determined by parameterization or by a calculation using the FAN15 code. Good agreement was obtained between the neutron spectra and the integral characteristics of the reference fields reconstructed by the two methods.
