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  • 51.
    Wu, Zhi-Xi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Holme, Petter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Local interaction scale controls the existence of a non-trivial optimal critical mass in opinion spreading2010Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 82, nr 2, s. 022102-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study a model of opinion formation where the collective decision of a group is said to happen if the fraction of agents having the most common opinion exceeds a threshold value, a critical mass. We find that there exists a unique nontrivial critical mass giving the most efficient convergence to consensus. In addition, we observe that for small critical masses, the characteristic time scale for the relaxation to consensus splits into two. The shorter time scale corresponds to a direct relaxation and the longer one can be explained by the existence of intermediate metastable states similar to those found in [P. Chen and S. Redner, Phys. Rev. E 71, 036101 (2005)]. This longer time scale is dependent on the precise condition for consensus—with a modification of the condition it can go away.

  • 52.
    Wu, Zhi-Xi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Holme, Petter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Sungkyunkwan Univ, Dept Energy Sci, Suwon 440746, South Korea.
    Majority-vote model on hyperbolic lattices2010Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 81, nr 1, artikkel-id 011133Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the critical properties of a nonequilibrium statistical model, the majority-vote model, on heptagonal and dual heptagonal lattices. Such lattices have the special feature that they only can be embedded in negatively curved surfaces. We find, by using Monte Carlo simulations and finite-size analysis, that the critical exponents 1/ν, β/ν, and γ/ν are different from those of the majority-vote model on regular lattices with periodic boundary condition, which belongs to the same universality class as the equilibrium Ising model. The exponents are also from those of the Ising model on a hyperbolic lattice. We argue that the disagreement is caused by the effective dimensionality of the hyperbolic lattices. By comparative studies, we find that the critical exponents of the majority-vote model on hyperbolic lattices satisfy the hyperscaling relation 2β/ν+γ/ν=Deff, where Deff is an effective dimension of the lattice. We also investigate the effect of boundary nodes on the ordering process of the model.

  • 53.
    Wu, Zhi-Xi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Rong, Zhihai
    Donghua University.
    Holme, Petter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Diversity of reproduction time scale promotes cooperation in spatial prisoner's dilemma games2009Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 80, nr 3, s. 036106-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Westudy an evolutionary spatial prisoner's dilemma game where the fitnessof the players is determined by both the payoffs fromthe current interaction and their history. We consider the situationwhere the selection time scale is slower than the interactiontime scale. This is done by implementing probabilistic reproduction onan individual level. We observe that both too fast andtoo slow reproduction rates hamper the emergence of cooperation. Inother words, there exists an intermediate selection time scale thatmaximizes cooperation. Another factor we find to promote cooperation isa diversity of reproduction time scales.

  • 54.
    Yang, Han-Xin
    et al.
    Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.
    Wang, Wen-Xu
    Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287, USA.
    Wu, Zhi-Xi
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Lai, Ying-Cheng
    Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287, USA.
    Wang, Bing-Hong
    Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.
    Diversity-optimized cooperation on complex networks2009Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 79, nr 5, s. 056107-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a strategy for achieving maximum cooperation in evolutionary games on complex networks. Each individual is assigned a weight that is proportional to the power of its degree, where the exponent α is an adjustable parameter that controls the level of diversity among individuals in the network. During the evolution, every individual chooses one of its neighbors as a reference with a probability proportional to the weight of the neighbor, and updates its strategy depending on their payoff difference. It is found that there exists an optimal value of α, for which the level of cooperation reaches maximum. This phenomenon indicates that, although high-degree individuals play a prominent role in maintaining the cooperation, too strong influences from the hubs may counterintuitively inhibit the diffusion of cooperation. Other pertinent quantities such as the payoff, the cooperator density as a function of the degree, and the payoff distribution are also investigated computationally and theoretically. Our results suggest that in order to achieve strong cooperation on a complex network, individuals should learn more frequently from neighbors with higher degrees, but only to a certain extent.

  • 55.
    Yang, Han-Xin
    et al.
    Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.
    Wu, Zhi-Xi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wang, Bing-Hong
    Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.
    Role of aspiration-induced migration in cooperation2010Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 81, nr 6, s. 065101-065104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Both cooperation and migration are ubiquitous in human society and animal world. In this Rapid Communication, we propose an aspiration-induced migration in which individuals will migrate to new sites provided that their payoffs are below some aspiration level. It is found that moderate aspiration level can best favor cooperative behavior. In particular, moderate aspiration level enables cooperator clusters to maintain and expand whereas induces defector clusters to disintegrate, thus promoting the diffusion of cooperation among population. Our results provide insights into understanding the role played by migration in the emergence of cooperative behavior.

  • 56.
    Yang, Han-Xin
    et al.
    Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.
    Wu, Zhi-Xi
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Zhou, Changsong
    2Department of Physics, Hong Kong Baptist University, Kowloon Tong, Hong Kong.
    Zhou, Tao
    Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.
    Wang, Bing-Hong
    Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China.
    Effects of social diversity on the emergence of global consensus in opinion dynamics2009Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 80, nr 4, s. 046108-046112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a variant of the voter model by introducing the social diversity in the evolution process. Each individual is assigned a weight that is proportional to the power of its degree, where the power exponent α is an adjustable parameter that controls the level of diversity among individuals in the network. At each time step, a pair of connected individuals, say i and j, are randomly selected to update their opinions. The probability pi of choosing is opinion as their common opinion is proportional to is weight. We consider the scale-free topology and concentrate on the efficiency of reaching the final consensus, which is significant in characterizing the self-organized systems. Interestingly, it is found that there exists an optimal value of α, leading to the shortest consensus time. This phenomenon indicates that, although a strong influence of high-degree individuals is helpful for quick consensus achievement, over strong influence inhibits the convergence process. Other quantities, such as the probability of an individual’s initial opinion becomes the final opinion as a function of degree, the evolution of the number of opinion clusters, as well as the relationship between average consensus time and the network size, are also studied. Our results are helpful for better understanding the role of degree heterogeneity of the individuals in the opinion dynamics.

  • 57.
    Zelan, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hagman, Henning
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Karlsson, Kristoffer
    Luleå University of Technology, EISLAB, 971 87 Luleå, Sweden..
    Dion, Claude
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kastberg, Anders
    Laboratoire de Physique de la Matière Condensée, CNRS UMR 6622, Université de Nice-Sophia Antipolis, Parc Valrose, 06108 Nice Cedex 2, France.
    Fluctuation-induced drift in a gravitationally tilted optical lattice2010Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 82, nr 3, s. 031136-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experimental and theoretical studies are made of Brownian particles trapped in a periodic potential, which is very slightly tilted due to gravity. In the presence of fluctuations, these will trigger a measurable average drift along the direction of the tilt. The magnitude of the drift varies with the ratio between the bias force and the trapping potential. This can be closely compared to a theoretical model system, based on a Fokker-Planck equation formalism. We show that the level of control and measurement precision we have in our system, which is based on cold atoms trapped in a three-dimensional dissipative optical lattice, makes the experimental setup suitable as a testbed for fundamental statistical physics. We simulate the system with a very simplified and general classical model, as well as with an elaborate semiclassical Monte Carlo simulation. In both cases, we achieve good qualitative agreement with experimental data.

  • 58.
    Zelan, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hagman, Henning
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Labaigt, Gabriel
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Jonsell, Svante
    Stockholms universitet.
    Dion, Claude M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Experimental measurement of the efficiency and the transport coherence of a cold-atom Brownian motor realized with cold atoms in optical lattices2011Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 83, nr 2, artikkel-id 020102Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rectification of noise into directed movement or useful energy is utilized by many different systems. The peculiar nature of the energy source and conceptual differences between such Brownian motor systems makes a characterization of the performance far from straightforward. In this work, where the Brownian motor consists of atoms interacting with dissipative optical lattices, we adopt existing theory and present experimental measurements for both the efficiency and the transport coherence. We achieve up to 0.3% for the efficiency and 0.01 for the Péclet number.

12 51 - 58 of 58
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