arXiv subjects

Carlos E. Laciana

Publications and source records attributed to Carlos E. Laciana.

11 recordsLinked to original sources

arXiv2017

Size invariance sector for an agent-based innovation diffusion model

It is shown that under certain conditions it is possible to model a complex system in a way that leads to results that do not depend on system size. As an example of complex system an innovation diffusion model is considered. In that model a set of individuals (the agents), which are interconnected, must decide if adopt or not an innovation. The agents are connected in a member of the networks family known as small worlds networks (SWN). It is found that for a subfamily of the SWN the saturation time and the form of the adoption curve are invariants respect to the change in the size of the system.

physics.soc-ph↗

arXiv2017

A causal viscous cosmology without singularities

An isotropic and homogeneous cosmological model with a source of dark energy is studied. That source is simulated with a viscous relativistic fluid with minimal causal correction. In this model the restrictions on the parameters coming from the following conditions are analized: a) energy density without singularities along time, b) scale factor increasing with time, c) universe accelerated at present time, d) state equation for dark energy with "w" bounded and close to -1. It is found that those conditions are satified for the following two cases. i) When the transport coefficient (τ_{Π}), associated to the causal correction, is negative, with the aditional restriction ζ|τ_{Π}|>2/3, where ζ is the relativistic bulk viscosity coefficient. The state equation is in the "phantom" energy sector. ii) For τ_{Π} positive, in the "k-essence" sector. It is performed an exact calculation for the case where the equation of state is constant, finding that option (ii) is favored in relation to (i), because in (ii) the entropy is always increasing, while this does no happen in (i).

gr-qc↗

arXiv2013

An agent based multi-optional model for the diffusion of innovations

We propose a model for the diffusion of several products competing in a common market based on the generalization of the Ising model of statiscal mechanics (Potts model). Using an agent based implementation, we analyze two problems: (i) a three options case, i.e. to adopt a product A, a product B, or non-adoption and (ii) a four options case, i.e. the adoption of product A, product B, both, or none. In the first case we analyze a launching strategy for one of the two products, which delays its launching with the objective of competing with improvements. Market shares reached by each product are then estimated at market saturation. Finally, simulations are carried out with varying degrees of social network topology, uncertainty, and population homogeneity.

stat.AP↗

arXiv2013

Ising-like agent-based technology diffusion model: adoption patterns vs. seeding strategies

The well-known Ising model used in statistical physics was adapted to a social dynamics context to simulate the adoption of a technological innovation. The model explicitly combines (a) an individual's perception of the advantages of an innovation and (b) social influence from members of the decision-maker's social network. The micro-level adoption dynamics are embedded into an agent-based model that allows exploration of macro-level patterns of technology diffusion throughout systems with different configurations (number and distributions of early adopters, social network topologies). In the present work we carry out many numerical simulations. We find that when the gap between the individual's perception of the options is high, the adoption speed increases if the dispersion of early adopters grows. Another test was based on changing the network topology by means of stochastic connections to a common opinion reference (hub), which resulted in an increment in the adoption speed. Finally, we performed a simulation of competition between options for both regular and small world networks.

physics.soc-ph↗

arXiv2013

Exploring associations between micro-level models of innovation diffusion and emerging macro-level adoption patterns

A micro-level agent-based model of innovation diffusion was developed that explicitly combines (a) an individual's perception of the advantages or relative utility derived from adoption, and (b) social influence from members of the individual's social network. The micro-model was used to simulate macro-level diffusion patterns emerging from different configurations of micro-model parameters. Micro-level simulation results matched very closely the adoption patterns predicted by the widely-used Bass macro-level model (Bass, 1969). For a portion of the domain, results from micro-simulations were consistent with aggregate-level adoption patterns reported in the literature. Induced Bass macro-level parameters and responded to changes in micro-parameters: (1) increased with the number of innovators and with the rate at which innovators are introduced; (2) increased with the probability of rewiring in small-world networks, as the characteristic path length decreases; and (3) an increase in the overall perceived utility of an innovation caused a corresponding increase in induced and values. Understanding micro to macro linkages can inform the design and assessment of marketing interventions on micro-variables - or processes related to them - to enhance adoption of future products or technologies.

cs.SI↗

arXiv2011

Can the conformal factor of the gravitational field be a physical degree of freedom?

The role of the conformal factor was analysed in two gauge-invariant perturbative formulations. Using the classical and quantum linearized perturbation approach given by Mukhanov et al \cite{Mukhanov:1990me}, the non-physical behaviour of the conformal perturbation as an isolated degree of freedom is shown. In the quantum gravity context, the restriction to conformal perturbations gives us an incompatibility with the dynamical equations.

gr-qc↗

arXiv1996

Temperature Notion in a Curved Spacetime

Scalar radiation, represented by a massless scalar field in a Robertson-Walker metric, is taken into account. By using a weak non minimum vacuum definition, the radiation temperature as a time dependent function is obtained. When the universe evolution is nearly but non equal to $t^{1/2}$, it is possible to fit the temperature of the microwave background. A particular massive case is compared with the massless one. When the mass of the matter field is next to the Planck one and the time is going to infinite, a similar result to the Hawking radiation of the blackhole is obtained.

hep-th↗

arXiv1996

Rotation Operator vs Particle Creation in a Curved Space Time

Taking into account a neutral massive scalar field minimally coupled to gravity, in a Robertson-Walker metric, it is shown that when the final state is connected with the initial one by means of a Bogoliubov transformation, which does not include the single-mode rotation operator, the mean value of created particles is conserved. When the rotation operator is considered, it is still possible to use the approach of single-mode squeezed operators and get the entropy as the logarithm of the created particles.

hep-th↗

arXiv1996

Thermal and Dynamical Particle Creation in a Curved Geometry

A generalization of ``Termo Field Dynamics'' to a curved geometry is proposed. In particular a neutral scalar field minimally coupled to gravity is considered as matter content in a Robertson-Walker metric. A non linear amplification in the particle creation is obtained, due to the altogether action of thermal and geometric effects. As a consequence the frequencies in the system look like red shifted with respect to the case where the thermal creation is not taken into account.

hep-th↗

arXiv1996

Thermal Conditions for Scalar Bosons in a Curved Space Time

The conditions that allow us to consider the vacuum expectation value of the energy-momentum tensor as a statistical average, at some particular temperature, are given. When the mean value of created particles is stationary, a planckian distribution for the field modes is obtained. In the massless approximation, the temperature dependence is as that corresponding to a radiation dominated Friedmann-like model.

hep-th↗

arXiv1995

Particle Creation Amplification in Curved Space due to Thermal Effects

A physical system composed by a scalar field minimally coupled to gravity and a thermal reservoir, as in thermo field dynamics, all of them in curved space time, is considered. When the formalism of thermo field dynamics is generalized to the above mentioned case, an amplification in the number of created particles is predicted.

hep-th↗