Ising model on two connected Barabasi-Albert networks

We investigate analytically the behavior of Ising model on two connected Barabasi-Albert networks. Depending on relative ordering of both networks there are two possible phases corresponding to parallel or antiparallel alingment of spins in both networks. A difference between critical temperatures of both phases disappears in the limit of vanishing inter-network coupling for identical networks. The analytic predictions are confirmed by numerical simulations.Comment: 6 pages including 6 figure

Are consumers willing to pay more for biofortified foods?: Evidence from a field experiment in Uganda

Vitamin A deficiency is a major health problem in Africa and in many other developing countries. Biofortified staple crops that are high in beta-carotene and adapted to local growing environments have the potential to significantly reduce the prevalence of vitamin A deficiency. One such example is the orange sweet potato (OSP). Because of its distinctive orange color, which is in contrast to the white varieties that are typically consumed in Africa, it is important to assess whether consumers will accept it. This paper attempts to address this question by using a choice experiment with the real product to quantify the magnitude of the premium or discount in consumers' willingness to pay that may be associated with it. It also considers the extent to which the provision of nutrition information affects valuations. Finally, the paper addresses whether the use of hypothetical scenarios is justified in a developing country context, and quantifies the magnitude of hypothetical bias that results as a consequence. We examine whether a “cheap talk” script, which as elaborated in the paper, reminds respondents that hypothetical scenarios are to be treated as if they are real, is effective in mitigating hypothetical bias. The experiment was conducted in Uganda, a key target country for the dissemination of orange sweet potato. Our results suggest that in the absence of nutrition information, there is no difference between white and orange varieties in consumers' willingness to pay, but there is a discount for yellow sweet potato (which does not have any beta-carotene). The provision of nutrition information does translate into substantial premia for the orange varieties, indicating that an information campaign may be key to driving market acceptance of the new product. Finally, there is a substantial hypothetical bias in both the willingness to pay (WTP), and the marginal WTP, for the new varieties; while “cheap talk” may mitigate this bias, it does not eliminate it.Cheap talk, Field experiments, Hypothetical bias, conjoint analysis, Universal logit,

Collective traffic-like movement of ants on a trail: dynamical phases and phase transitions

The traffic-like collective movement of ants on a trail can be described by a stochastic cellular automaton model. We have earlier investigated its unusual flow-density relation by using various mean field approximations and computer simulations. In this paper, we study the model following an alternative approach based on the analogy with the zero range process, which is one of the few known exactly solvable stochastic dynamical models. We show that our theory can quantitatively account for the unusual non-monotonic dependence of the average speed of the ants on their density for finite lattices with periodic boundary conditions. Moreover, we argue that the model exhibits a continuous phase transition at the critial density only in a limiting case. Furthermore, we investigate the phase diagram of the model by replacing the periodic boundary conditions by open boundary conditions.Comment: 8 pages, 6 figure

A new cellular automata model for city traffic

We present a new cellular automata model of vehicular traffic in cities by combining ideas borrowed from the Biham-Middleton-Levine (BML) model of city traffic and the Nagel-Schreckenberg (NaSch) model of highway traffic. The model exhibits a dynamical phase transition to a completely jammed phase at a critical density which depends on the time periods of the synchronized signals.Comment: 6 pages, 5 figures, uses Springer Macros 'lncse', to appear in "Traffic and Granular Flow '99: Social, Traffic, and Granular Dynamics" edited by D. Helbing, H. J. Herrmann, M. Schreckenberg, and D. E. Wolf (Springer, Berlin