Julián Candia | National Institutes of Health (original) (raw)

Papers by Julián Candia

Brazilian Journal of Physics, 2012

In every country, public and private agencies allocate extensive funding to collect large-scale s... more In every country, public and private agencies allocate extensive funding to collect large-scale statistical data, which in turn are studied and analyzed in order to determine local, regional, national, and international policies regarding all aspects relevant to the welfare of society. One important aspect of that process is the visualization of statistical data with embedded geographical information, which most often relies on archaic methods such as maps colored according to graded scales. In this work, we apply non-standard visualization techniques based on physical principles. We illustrate the method with recent statistics on homicide rates in Brazil and their correlation to other publicly available data. This physics-based approach provides a novel tool that can be used by interdisciplinary teams investigating statistics and model projections in a variety of fields such as economics and gross domestic product research, public health and epidemiology, socio-demographics, political science, business and marketing, and many others.

Journal of Statistical Mechanics-theory and Experiment, 2008

We study an extension of Axelrod's model for social influence, in which cultural drift is represe... more We study an extension of Axelrod's model for social influence, in which cultural drift is represented as random perturbations, while mass media are introduced by means of an external field. In this scenario, we investigate how the modular structure of social networks affects the propagation of mass media messages across the society. The community structure of social networks is represented by coupled random networks, in which two random graphs are connected by intercommunity links. Considering inhomogeneous mass media fields, we study the conditions for successful message spreading and find a novel phase diagram in the multidimensional parameter space. These findings show that social modularity effects are of paramount importance in order to design successful, cost-effective advertising campaigns.

International Journal of Modern Physics C, 2007

In the context of an extension of Axelrod's model for social influence, we study the interplay an... more In the context of an extension of Axelrod's model for social influence, we study the interplay and competition between the cultural drift, represented as random perturbations, and mass media, introduced by means of an external homogeneous field. Unlike previous studies [J. C. González-Avella et al, Phys.

Complex phenotypic differences among different acute leukemias cannot be fully captured by analyz... more Complex phenotypic differences among different acute leukemias cannot be fully captured
by analyzing the expression levels of one single molecule, such as a miR, at a time, but requires systematic analysis of large sets of miRs. While a popular approach for analysis of such datasets is principal component analysis (PCA), this method is not designed to optimally discriminate different phenotypes. Moreover, PCA and other low-dimensional representation methods yield linear or non- linear combinations of all measured miRs. Global human miR expression was measured in AML, B-ALL, and T-ALL cell lines and patient RNA samples. By systematically applying support vector machines to all measured miRs taken in dyad and triad groups, we built miR networks using cell
line data and validated our findings with primary patient samples. All the coordinately transcribed members of the miR-23a cluster (which includes also miR-24 and miR-27a), known to function as tumor suppressors of acute leukemias, appeared in the AML, B-ALL and T-ALL centric networks. Subsequent qRT-PCR analysis showed that the most connected miR in the B-ALL-centric network, miR-708, is highly and specifically expressed in B-ALLs, suggesting that miR-708 might serve as a biomarker for B-ALL. This approach is systematic, quantitative, scalable, and unbiased. Rather than a single signature, our approach yields a network of signatures reflecting the redundant nature of intracellular pathways. The network representation allows for visual analysis of all signatures by an expert and for future integration of additional information. Furthermore, each signature involves only small sets of miRs, such as dyads and triads, which are well suited for in depth validation through laboratory experiments. In particular, loss- and gain-of-function assays designed to drive changes in leukemia cell survival, proliferation and differentiation will benefit from the identification of multi- miR signatures that characterize leukemia subtypes and their normal counterpart cells of origin.

International Journal of Modern Physics C, 2009

Irreversible opinion spreading phenomena are studied on smallworld and scale-free networks by mea... more Irreversible opinion spreading phenomena are studied on smallworld and scale-free networks by means of the magnetic Eden model, a nonequilibrium kinetic model for the growth of binary mixtures in contact with a thermal bath. In this model, the opinion of an individual is affected by those of their acquaintances, but opinion changes (analogous to spin flips in an Ising-like model) are not allowed. We focus on the influence of advertising, which is represented by external magnetic fields. The interplay and competition between temperature and fields lead to order-disorder transitions, which are found to also depend on the link density and the topology of the complex network substrate. The effects of advertising campaigns with variable duration, as well as the best cost-effective strategies to achieve consensus within different scenarios, are also discussed.

Physical Review E, 2007

We study the dynamical and critical behavior of a model for irreversible opinion spreading on Bar... more We study the dynamical and critical behavior of a model for irreversible opinion spreading on Barabási-Albert (BA) scale-free networks by performing extensive Monte Carlo simulations. The opinion spreading within an inhomogeneous society is investigated by means of the magnetic Eden model, a nonequilibrium kinetic model for the growth of binary mixtures in contact with a thermal bath. The deposition dynamics, which is studied as a function of the degree of the occupied sites, shows evidence for the leading role played by hubs in the growth process. Systems of finite size grow either ordered or disordered, depending on the temperature. By means of standard finite-size scaling procedures, the effective order-disorder phase transitions are found to persist in the thermodynamic limit. This critical behavior, however, is absent in related equilibrium spin systems such as the Ising model on BA scale-free networks, which in the thermodynamic limit only displays a ferromagnetic phase. The dependence of these results on the degree exponent is also discussed for the case of uncorrelated scale-free networks.

Journal of Statistical Mechanics: Theory and Experiment, 2007

Irreversible opinion spreading phenomena are studied on small-world networks generated from 2D re... more Irreversible opinion spreading phenomena are studied on small-world networks generated from 2D regular lattices by means of the magnetic Eden model, a nonequilibrium kinetic model for the growth of binary mixtures in contact with a thermal bath. In this model, the opinion or decision of an individual is affected by those of their acquaintances, but opinion changes (analogous to spin flips in an Ising-like model) are not allowed. Particularly, we focus on aspects inherent to the underlying 2D nature of the substrate, such as domain growth and cluster size distributions. Larger shortcut fractions are observed to favor long-range ordering connections between distant clusters across the network, while the temperature is shown to drive the system across an order-disorder transition, in agreement with previous investigations on related equilibrium spin systems. Furthermore, the extrapolated phase diagram, as well as the correlation length critical exponent, are determined by means of standard finite-size scaling procedures.

Journal of Cosmology and Astroparticle Physics, 2004

At high energies, the very steep decrease of the conventional atmospheric component of the neutri... more At high energies, the very steep decrease of the conventional atmospheric component of the neutrino spectrum should allow the emergence of even small and isotropic components of the total spectrum, indicative of new physics, provided that they are less steeply decreasing, as generically expected. One candidate is the prompt atmospheric neutrino flux, a probe of cosmic ray composition in the region of the knee as well as small-x QCD, below the reach of collider experiments. A second is the diffuse extragalactic background due to distant and unresolved AGNs and GRBs, a key test of the nature of the highest-energy sources in the universe. Separating these new physics components from the conventional atmospheric neutrino flux, as well as from each other, will be very challenging. We show that the charged-current electron neutrino "shower" channel should be particularly effective for isolating the prompt atmospheric neutrino flux, and that it is more generally an important complement to the usuallyconsidered charged-current muon neutrino "track" channel. These conclusions remain true even for the low prompt atmospheric neutrino flux predicted in a realistic cosmic ray scenario with heavy and varying composition across the knee (Candia and Roulet, 2003 JCAP 0309, 005). We also improve the corresponding calculation of the neutrino flux induced by cosmic ray collisions with the interstellar medium.

The growth of confined magnetic films with ferromagnetic interactions between nearest-neighbor sp... more The growth of confined magnetic films with ferromagnetic interactions between nearest-neighbor spins is studied in a stripped (1+1)−(1+1)-(1+1)−dimensional rectangular geometry. Magnetic films are grown irreversibly by adding spins at the boundaries of the growing interface. A competing situation with two opposite short range surface magnetic fields of the same magnitude is analyzed. Due to the antisymmetric condition considered, an interface

Physical review. E, Statistical, nonlinear, and soft matter physics, 2015

We investigate the irreversible growth of (2+1)-dimensional magnetic thin films. The spin variabl... more We investigate the irreversible growth of (2+1)-dimensional magnetic thin films. The spin variable can adopt three states (s(I)=±1,0), and the system is in contact with a thermal bath of temperature T. The deposition process depends on the change of the configuration energy, which, by analogy to the Blume-Capel Hamiltonian in equilibrium systems, depends on Ising-like couplings between neighboring spins (J) and has a crystal field (D) term that controls the density of nonmagnetic impurities (s(I)=0). Once deposited, particles are not allowed to flip, diffuse, or detach. By means of extensive Monte Carlo simulations, we obtain the phase diagram in the crystal field vs temperature parameter space. We show clear evidence of the existence of a tricritical point located at D(t)/J=1.145(10) and k(B)T(t)/J=0.425(10), which separates a first-order transition curve at lower temperatures from a critical second-order transition curve at higher temperatures, in analogy with the previously studi...

International Journal of Modern Physics C, 2008

In the magnetic Eden model (MEM), particles have a spin and grow in contact with a thermal bath. ... more In the magnetic Eden model (MEM), particles have a spin and grow in contact with a thermal bath. Although Ising-like interactions affect the growth dynamics, deposited spins are frozen and not allowed to flip. This review article focuses on recent developments and future prospects, such as spontaneous switching phenomena, critical behavior associated with fractal, wetting, and order-disorder phase transitions, the equilibrium/nonequilibrium correspondence conjecture, as well as dynamical and critical features of the MEM defined on complex network substrates.

Physical review letters, Jan 7, 2002

The irreversible growth of a binary mixture under far-from-equilibrium conditions is studied in t... more The irreversible growth of a binary mixture under far-from-equilibrium conditions is studied in three-dimensional confined geometries of size L(x) x L(y) x L(z), where L(z)>Lx = L(y) is the growing direction. A competing situation where two opposite surfaces prefer different species of the mixture is analyzed. Because of this antisymmetric condition, an interface between the different species develops along the growing direction. Such interface undergoes a localization-delocalization transition that is the precursor of a wetting transition in the thermodynamic limit. Furthermore, the growing interface also undergoes a concave-convex transition in the growth mode. So, the system exhibits a multicritical wetting point.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2001

The magnetic Eden model (MEM) [N. Vandewalle and M. Ausloos, Phys. Rev. E 50, R635 (1994)] with f... more The magnetic Eden model (MEM) [N. Vandewalle and M. Ausloos, Phys. Rev. E 50, R635 (1994)] with ferromagnetic interactions between nearest-neighbor spins is studied in (d+1)-dimensional rectangular geometries for d=1,2. In the MEM, magnetic clusters are grown by adding spins at the boundaries of the clusters. The orientation of the added spins depends on both the energetic interaction with already deposited spins and the temperature, through a Boltzmann factor. A numerical Monte Carlo investigation of the MEM has been performed and the results of the simulations have been analyzed using finite-size scaling arguments. As in the case of the Ising model, the MEM in d=1 is noncritical (only exhibits an ordered phase at T=0). In d=2 the MEM exhibits an order-disorder transition of second order at a finite temperature. Such transition has been characterized in detail and the relevant critical exponents have been determined. These exponents are in agreement (within error bars) with those o...

In this chapter we consider a cell phone network as a set of automatically deployed sensors that ... more In this chapter we consider a cell phone network as a set of automatically deployed sensors that records movement and interaction patterns of the population. We discuss methods for detecting anomalies in the streaming data produced by the cell phone network. We motivate this discussion by describing the Wireless Phone Based Emergency Response (WIPER) system, a proof-of-concept decision support system for emergency response managers. We also discuss some of the scientific work enabled by this type of sensor data and the related privacy issues. We describe scientific studies that use the cell phone data set and steps we have taken to ensure the security of the data. We describe the overall decision support system and discuss three methods of anomaly detection that we have applied to the data.

International Journal of Modern Physics C, 2007

In the context of an extension of Axelrod's model for social influence, we study the interplay an... more In the context of an extension of Axelrod's model for social influence, we study the interplay and competition between the cultural drift, represented as random perturbations, and mass media, introduced by means of an external homogeneous field. Unlike previous studies [J. C. González-Avella et al, Phys.

We show that the second knee in the cosmic ray spectrum (i.e. the steep- ening occurring at E ≃ 4... more We show that the second knee in the cosmic ray spectrum (i.e. the steep- ening occurring at E ≃ 4 ×1017 eV) could be related to drift effects affecting the heaviest nuclear component, the iron group nuclei, in a scenario in which the knee at 3 ×1015 eV indicates the onset of drift effects in the lighter proton component. We

Journal of High Energy Physics, 2002

We show that the second knee in the cosmic ray spectrum (i.e. the steepening occurring at E simeq... more We show that the second knee in the cosmic ray spectrum (i.e. the steepening occurring at E simeq 4 × 1017 eV) could be related to drift effects affecting the heaviest nuclear component, the iron group nuclei, in a scenario in which the knee at 3 × 1015 eV indicates the onset of drift effects in the lighter proton component.

Physical Review E, 2008

An analytic effective medium theory is constructed to study the mean access times for random walk... more An analytic effective medium theory is constructed to study the mean access times for random walks on hybrid disordered structures formed by embedding complex networks into regular lattices, considering transition rates F that are different for steps across lattice bonds from the rates f across network shortcuts. The theory is developed for structures with arbitrary shortcut distributions and applied to a class of partially-disordered traversal enhanced networks in which shortcuts of fixed length are distributed randomly with finite probability. Numerical simulations are found to be in excellent agreement with predictions of the effective medium theory on all aspects addressed by the latter. Access times for random walks on these partially disordered structures are compared to those on small-world networks, which on average appear to provide the most effective means of decreasing access times uniformly across the network.

Physical Review E, 2011

The irreversible growth of thin films under far-from-equilibrium conditions is studied in (2+1)-d... more The irreversible growth of thin films under far-from-equilibrium conditions is studied in (2+1)-dimensional strip geometries. Across one of the transverse directions, a temperature gradient is applied by thermal baths at fixed temperatures between T(1) and T(2), where T(1)<T(c)(hom)<T(2) and T(c})(hom)=0.69(1) is the critical temperature of the system in contact with an homogeneous thermal bath. By using standard finite-size scaling methods, we characterized a continuous order-disorder phase transition driven by the thermal bath gradient with critical temperature T(c)=0.84(2) and critical exponents ν=1.53(6), γ=2.54(11), and β=0.26(8), which belong to a different universality class from that of films grown in an homogeneous bath. Furthermore, the effects of the temperature gradient are analyzed by means of a bond model that captures the growth dynamics. The interplay of geometry and thermal bath asymmetries leads to growth bond flux asymmetries and the onset of transverse ordering effects that explain qualitatively the shift in the critical temperature.

Physical Review E, 2006

Binary mixtures growing on small-world networks under far-from-equilibrium conditions are studied... more Binary mixtures growing on small-world networks under far-from-equilibrium conditions are studied by means of extensive Monte Carlo simulations. For any positive value of the shortcut fraction of the network (p > 0), the system undergoes a continuous order-disorder phase transition, while it is noncritical in the regular lattice limit (p = 0). Using finite-size scaling relations, the phase diagram is obtained in the thermodynamic limit and the critical exponents are evaluated. The small-world networks are thus shown to trigger criticality, a phenomenon analogous to similar observations reported recently in the investigation of equilibrium systems.

Brazilian Journal of Physics, 2012

In every country, public and private agencies allocate extensive funding to collect large-scale s... more In every country, public and private agencies allocate extensive funding to collect large-scale statistical data, which in turn are studied and analyzed in order to determine local, regional, national, and international policies regarding all aspects relevant to the welfare of society. One important aspect of that process is the visualization of statistical data with embedded geographical information, which most often relies on archaic methods such as maps colored according to graded scales. In this work, we apply non-standard visualization techniques based on physical principles. We illustrate the method with recent statistics on homicide rates in Brazil and their correlation to other publicly available data. This physics-based approach provides a novel tool that can be used by interdisciplinary teams investigating statistics and model projections in a variety of fields such as economics and gross domestic product research, public health and epidemiology, socio-demographics, political science, business and marketing, and many others.

Journal of Statistical Mechanics-theory and Experiment, 2008

We study an extension of Axelrod's model for social influence, in which cultural drift is represe... more We study an extension of Axelrod's model for social influence, in which cultural drift is represented as random perturbations, while mass media are introduced by means of an external field. In this scenario, we investigate how the modular structure of social networks affects the propagation of mass media messages across the society. The community structure of social networks is represented by coupled random networks, in which two random graphs are connected by intercommunity links. Considering inhomogeneous mass media fields, we study the conditions for successful message spreading and find a novel phase diagram in the multidimensional parameter space. These findings show that social modularity effects are of paramount importance in order to design successful, cost-effective advertising campaigns.

International Journal of Modern Physics C, 2007

In the context of an extension of Axelrod's model for social influence, we study the interplay an... more In the context of an extension of Axelrod's model for social influence, we study the interplay and competition between the cultural drift, represented as random perturbations, and mass media, introduced by means of an external homogeneous field. Unlike previous studies [J. C. González-Avella et al, Phys.

Complex phenotypic differences among different acute leukemias cannot be fully captured by analyz... more Complex phenotypic differences among different acute leukemias cannot be fully captured
by analyzing the expression levels of one single molecule, such as a miR, at a time, but requires systematic analysis of large sets of miRs. While a popular approach for analysis of such datasets is principal component analysis (PCA), this method is not designed to optimally discriminate different phenotypes. Moreover, PCA and other low-dimensional representation methods yield linear or non- linear combinations of all measured miRs. Global human miR expression was measured in AML, B-ALL, and T-ALL cell lines and patient RNA samples. By systematically applying support vector machines to all measured miRs taken in dyad and triad groups, we built miR networks using cell
line data and validated our findings with primary patient samples. All the coordinately transcribed members of the miR-23a cluster (which includes also miR-24 and miR-27a), known to function as tumor suppressors of acute leukemias, appeared in the AML, B-ALL and T-ALL centric networks. Subsequent qRT-PCR analysis showed that the most connected miR in the B-ALL-centric network, miR-708, is highly and specifically expressed in B-ALLs, suggesting that miR-708 might serve as a biomarker for B-ALL. This approach is systematic, quantitative, scalable, and unbiased. Rather than a single signature, our approach yields a network of signatures reflecting the redundant nature of intracellular pathways. The network representation allows for visual analysis of all signatures by an expert and for future integration of additional information. Furthermore, each signature involves only small sets of miRs, such as dyads and triads, which are well suited for in depth validation through laboratory experiments. In particular, loss- and gain-of-function assays designed to drive changes in leukemia cell survival, proliferation and differentiation will benefit from the identification of multi- miR signatures that characterize leukemia subtypes and their normal counterpart cells of origin.

International Journal of Modern Physics C, 2009

Irreversible opinion spreading phenomena are studied on smallworld and scale-free networks by mea... more Irreversible opinion spreading phenomena are studied on smallworld and scale-free networks by means of the magnetic Eden model, a nonequilibrium kinetic model for the growth of binary mixtures in contact with a thermal bath. In this model, the opinion of an individual is affected by those of their acquaintances, but opinion changes (analogous to spin flips in an Ising-like model) are not allowed. We focus on the influence of advertising, which is represented by external magnetic fields. The interplay and competition between temperature and fields lead to order-disorder transitions, which are found to also depend on the link density and the topology of the complex network substrate. The effects of advertising campaigns with variable duration, as well as the best cost-effective strategies to achieve consensus within different scenarios, are also discussed.

Physical Review E, 2007

We study the dynamical and critical behavior of a model for irreversible opinion spreading on Bar... more We study the dynamical and critical behavior of a model for irreversible opinion spreading on Barabási-Albert (BA) scale-free networks by performing extensive Monte Carlo simulations. The opinion spreading within an inhomogeneous society is investigated by means of the magnetic Eden model, a nonequilibrium kinetic model for the growth of binary mixtures in contact with a thermal bath. The deposition dynamics, which is studied as a function of the degree of the occupied sites, shows evidence for the leading role played by hubs in the growth process. Systems of finite size grow either ordered or disordered, depending on the temperature. By means of standard finite-size scaling procedures, the effective order-disorder phase transitions are found to persist in the thermodynamic limit. This critical behavior, however, is absent in related equilibrium spin systems such as the Ising model on BA scale-free networks, which in the thermodynamic limit only displays a ferromagnetic phase. The dependence of these results on the degree exponent is also discussed for the case of uncorrelated scale-free networks.

Journal of Statistical Mechanics: Theory and Experiment, 2007

Irreversible opinion spreading phenomena are studied on small-world networks generated from 2D re... more Irreversible opinion spreading phenomena are studied on small-world networks generated from 2D regular lattices by means of the magnetic Eden model, a nonequilibrium kinetic model for the growth of binary mixtures in contact with a thermal bath. In this model, the opinion or decision of an individual is affected by those of their acquaintances, but opinion changes (analogous to spin flips in an Ising-like model) are not allowed. Particularly, we focus on aspects inherent to the underlying 2D nature of the substrate, such as domain growth and cluster size distributions. Larger shortcut fractions are observed to favor long-range ordering connections between distant clusters across the network, while the temperature is shown to drive the system across an order-disorder transition, in agreement with previous investigations on related equilibrium spin systems. Furthermore, the extrapolated phase diagram, as well as the correlation length critical exponent, are determined by means of standard finite-size scaling procedures.

Journal of Cosmology and Astroparticle Physics, 2004

At high energies, the very steep decrease of the conventional atmospheric component of the neutri... more At high energies, the very steep decrease of the conventional atmospheric component of the neutrino spectrum should allow the emergence of even small and isotropic components of the total spectrum, indicative of new physics, provided that they are less steeply decreasing, as generically expected. One candidate is the prompt atmospheric neutrino flux, a probe of cosmic ray composition in the region of the knee as well as small-x QCD, below the reach of collider experiments. A second is the diffuse extragalactic background due to distant and unresolved AGNs and GRBs, a key test of the nature of the highest-energy sources in the universe. Separating these new physics components from the conventional atmospheric neutrino flux, as well as from each other, will be very challenging. We show that the charged-current electron neutrino "shower" channel should be particularly effective for isolating the prompt atmospheric neutrino flux, and that it is more generally an important complement to the usuallyconsidered charged-current muon neutrino "track" channel. These conclusions remain true even for the low prompt atmospheric neutrino flux predicted in a realistic cosmic ray scenario with heavy and varying composition across the knee (Candia and Roulet, 2003 JCAP 0309, 005). We also improve the corresponding calculation of the neutrino flux induced by cosmic ray collisions with the interstellar medium.

The growth of confined magnetic films with ferromagnetic interactions between nearest-neighbor sp... more The growth of confined magnetic films with ferromagnetic interactions between nearest-neighbor spins is studied in a stripped (1+1)−(1+1)-(1+1)−dimensional rectangular geometry. Magnetic films are grown irreversibly by adding spins at the boundaries of the growing interface. A competing situation with two opposite short range surface magnetic fields of the same magnitude is analyzed. Due to the antisymmetric condition considered, an interface

Physical review. E, Statistical, nonlinear, and soft matter physics, 2015

We investigate the irreversible growth of (2+1)-dimensional magnetic thin films. The spin variabl... more We investigate the irreversible growth of (2+1)-dimensional magnetic thin films. The spin variable can adopt three states (s(I)=±1,0), and the system is in contact with a thermal bath of temperature T. The deposition process depends on the change of the configuration energy, which, by analogy to the Blume-Capel Hamiltonian in equilibrium systems, depends on Ising-like couplings between neighboring spins (J) and has a crystal field (D) term that controls the density of nonmagnetic impurities (s(I)=0). Once deposited, particles are not allowed to flip, diffuse, or detach. By means of extensive Monte Carlo simulations, we obtain the phase diagram in the crystal field vs temperature parameter space. We show clear evidence of the existence of a tricritical point located at D(t)/J=1.145(10) and k(B)T(t)/J=0.425(10), which separates a first-order transition curve at lower temperatures from a critical second-order transition curve at higher temperatures, in analogy with the previously studi...

International Journal of Modern Physics C, 2008

In the magnetic Eden model (MEM), particles have a spin and grow in contact with a thermal bath. ... more In the magnetic Eden model (MEM), particles have a spin and grow in contact with a thermal bath. Although Ising-like interactions affect the growth dynamics, deposited spins are frozen and not allowed to flip. This review article focuses on recent developments and future prospects, such as spontaneous switching phenomena, critical behavior associated with fractal, wetting, and order-disorder phase transitions, the equilibrium/nonequilibrium correspondence conjecture, as well as dynamical and critical features of the MEM defined on complex network substrates.

Physical review letters, Jan 7, 2002

The irreversible growth of a binary mixture under far-from-equilibrium conditions is studied in t... more The irreversible growth of a binary mixture under far-from-equilibrium conditions is studied in three-dimensional confined geometries of size L(x) x L(y) x L(z), where L(z)>Lx = L(y) is the growing direction. A competing situation where two opposite surfaces prefer different species of the mixture is analyzed. Because of this antisymmetric condition, an interface between the different species develops along the growing direction. Such interface undergoes a localization-delocalization transition that is the precursor of a wetting transition in the thermodynamic limit. Furthermore, the growing interface also undergoes a concave-convex transition in the growth mode. So, the system exhibits a multicritical wetting point.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2001

The magnetic Eden model (MEM) [N. Vandewalle and M. Ausloos, Phys. Rev. E 50, R635 (1994)] with f... more The magnetic Eden model (MEM) [N. Vandewalle and M. Ausloos, Phys. Rev. E 50, R635 (1994)] with ferromagnetic interactions between nearest-neighbor spins is studied in (d+1)-dimensional rectangular geometries for d=1,2. In the MEM, magnetic clusters are grown by adding spins at the boundaries of the clusters. The orientation of the added spins depends on both the energetic interaction with already deposited spins and the temperature, through a Boltzmann factor. A numerical Monte Carlo investigation of the MEM has been performed and the results of the simulations have been analyzed using finite-size scaling arguments. As in the case of the Ising model, the MEM in d=1 is noncritical (only exhibits an ordered phase at T=0). In d=2 the MEM exhibits an order-disorder transition of second order at a finite temperature. Such transition has been characterized in detail and the relevant critical exponents have been determined. These exponents are in agreement (within error bars) with those o...

In this chapter we consider a cell phone network as a set of automatically deployed sensors that ... more In this chapter we consider a cell phone network as a set of automatically deployed sensors that records movement and interaction patterns of the population. We discuss methods for detecting anomalies in the streaming data produced by the cell phone network. We motivate this discussion by describing the Wireless Phone Based Emergency Response (WIPER) system, a proof-of-concept decision support system for emergency response managers. We also discuss some of the scientific work enabled by this type of sensor data and the related privacy issues. We describe scientific studies that use the cell phone data set and steps we have taken to ensure the security of the data. We describe the overall decision support system and discuss three methods of anomaly detection that we have applied to the data.

International Journal of Modern Physics C, 2007

In the context of an extension of Axelrod's model for social influence, we study the interplay an... more In the context of an extension of Axelrod's model for social influence, we study the interplay and competition between the cultural drift, represented as random perturbations, and mass media, introduced by means of an external homogeneous field. Unlike previous studies [J. C. González-Avella et al, Phys.

We show that the second knee in the cosmic ray spectrum (i.e. the steep- ening occurring at E ≃ 4... more We show that the second knee in the cosmic ray spectrum (i.e. the steep- ening occurring at E ≃ 4 ×1017 eV) could be related to drift effects affecting the heaviest nuclear component, the iron group nuclei, in a scenario in which the knee at 3 ×1015 eV indicates the onset of drift effects in the lighter proton component. We

Journal of High Energy Physics, 2002

We show that the second knee in the cosmic ray spectrum (i.e. the steepening occurring at E simeq... more We show that the second knee in the cosmic ray spectrum (i.e. the steepening occurring at E simeq 4 × 1017 eV) could be related to drift effects affecting the heaviest nuclear component, the iron group nuclei, in a scenario in which the knee at 3 × 1015 eV indicates the onset of drift effects in the lighter proton component.

Physical Review E, 2008

An analytic effective medium theory is constructed to study the mean access times for random walk... more An analytic effective medium theory is constructed to study the mean access times for random walks on hybrid disordered structures formed by embedding complex networks into regular lattices, considering transition rates F that are different for steps across lattice bonds from the rates f across network shortcuts. The theory is developed for structures with arbitrary shortcut distributions and applied to a class of partially-disordered traversal enhanced networks in which shortcuts of fixed length are distributed randomly with finite probability. Numerical simulations are found to be in excellent agreement with predictions of the effective medium theory on all aspects addressed by the latter. Access times for random walks on these partially disordered structures are compared to those on small-world networks, which on average appear to provide the most effective means of decreasing access times uniformly across the network.

Physical Review E, 2011

The irreversible growth of thin films under far-from-equilibrium conditions is studied in (2+1)-d... more The irreversible growth of thin films under far-from-equilibrium conditions is studied in (2+1)-dimensional strip geometries. Across one of the transverse directions, a temperature gradient is applied by thermal baths at fixed temperatures between T(1) and T(2), where T(1)<T(c)(hom)<T(2) and T(c})(hom)=0.69(1) is the critical temperature of the system in contact with an homogeneous thermal bath. By using standard finite-size scaling methods, we characterized a continuous order-disorder phase transition driven by the thermal bath gradient with critical temperature T(c)=0.84(2) and critical exponents ν=1.53(6), γ=2.54(11), and β=0.26(8), which belong to a different universality class from that of films grown in an homogeneous bath. Furthermore, the effects of the temperature gradient are analyzed by means of a bond model that captures the growth dynamics. The interplay of geometry and thermal bath asymmetries leads to growth bond flux asymmetries and the onset of transverse ordering effects that explain qualitatively the shift in the critical temperature.

Physical Review E, 2006

Binary mixtures growing on small-world networks under far-from-equilibrium conditions are studied... more Binary mixtures growing on small-world networks under far-from-equilibrium conditions are studied by means of extensive Monte Carlo simulations. For any positive value of the shortcut fraction of the network (p > 0), the system undergoes a continuous order-disorder phase transition, while it is noncritical in the regular lattice limit (p = 0). Using finite-size scaling relations, the phase diagram is obtained in the thermodynamic limit and the critical exponents are evaluated. The small-world networks are thus shown to trigger criticality, a phenomenon analogous to similar observations reported recently in the investigation of equilibrium systems.