Critical behavior of a non-equilibrium interacting particle system driven by an oscillatory field

First- and second-order temperature driven transitions are studied, in a lattice gas driven by an oscillatory field. The short time dynamics study provides upper and lower bounds for the first-order transition points obtained using standard simulations. The difference between upper and lower bounds is a measure for the strength of the first-order transition and becomes negligible small for densities close to one half. In addition, we give strong evidence on the existence of multicritical points and a critical temperature gap, the latter induced by the anisotropy introduced by the driving field.Comment: 12 pages, 4 figures; to appear in Europhys. Let

Digital Dilemma 2018

In October 2018 a one-day conference was held at the UCL Institute of Archaeology focussing on the ‘Digital Dilemma’ in biological archaeology —specifically human remains research where the use of digitisation methods have increased exponentially over the last decade while comparatively little discussion of the ethical and legal considerations of these data has taken place. Papers presented at Digital Dilemma 2018 explored the use of digital data in human remains research, discussing both the benefits provided by these data, areas of ethical or methodological concern and suggestions for future research. This paper and the following conference proceedings will discuss this research demonstrating the importance that this Digital Dilemma in archaeology continues to be discussed and considered in future research

Numerical study of a first-order irreversible phase transition in a CO+NO catalyzed reaction model

The first-order irreversible phase transitions (IPT) of the Yaldran-Khan model (Yaldran-Khan, J. Catal. 131, 369, 1991) for the CO+NO reaction is studied using the constant coverage (CC) ensemble and performing epidemic simulations. The CC method allows the study of hysteretic effects close to coexistence as well as the location of both the upper spinodal point and the coexistence point. Epidemic studies show that at coexistence the number of active sites decreases according to a (short-time) power law followed by a (long-time) exponential decay. It is concluded that first-order IPT's share many characteristic of their reversible counterparts, such as the development of short ranged correlations, hysteretic effects, metastabilities, etc.Comment: 17 pages, 10 figure

Maximal height statistics for 1/f^alpha signals

Numerical and analytical results are presented for the maximal relative height distribution of stationary periodic Gaussian signals (one dimensional interfaces) displaying a 1/f^alpha power spectrum. For 0<alpha<1 (regime of decaying correlations), we observe that the mathematically established limiting distribution (Fisher-Tippett-Gumbel distribution) is approached extremely slowly as the sample size increases. The convergence is rapid for alpha>1 (regime of strong correlations) and a highly accurate picture gallery of distribution functions can be constructed numerically. Analytical results can be obtained in the limit alpha -> infinity and, for large alpha, by perturbation expansion. Furthermore, using path integral techniques we derive a trace formula for the distribution function, valid for alpha=2n even integer. From the latter we extract the small argument asymptote of the distribution function whose analytic continuation to arbitrary alpha > 1 is found to be in agreement with simulations. Comparison of the extreme and roughness statistics of the interfaces reveals similarities in both the small and large argument asymptotes of the distribution functions.Comment: 17 pages, 8 figures, RevTex

Application of a renormalization group algorithm to nonequilibrium cellular automata with one absorbing state

We improve a recently proposed dynamically driven renormalization group algorithm for cellular automata systems with one absorbing state, introducing spatial correlations in the expression for the transition probabilities. We implement the renormalization group scheme considering three different approximations which take into account correlations in the stationary probability distribution. The improved scheme is applied to a probabilistic cellular automaton already introduced in the literature.Comment: 7 pages, 4 figures, to be published in Phys. Rev.

An algorithm to calculate the transport exponent in strip geometries

An algorithm for solving the random resistor problem by means of the transfer-matrix approach is presented. Preconditioning by spanning clusters extraction both reduces the size of the conductivity matrix and speed up the calculations.Comment: 17 pages, RevTeX2.1, HLRZ - 97/9

Fixed Versus Free Combinations of Antihypertensive Drugs: Analyses Of Real-World Data Of Persistence With Therapy In Italy

Purpose: To analyse the pattern of use and cost of antihypertensive drugs in new users in an Italian population, and explore the patient/treatment factors associated with the risk of therapy discontinuation. Patients and methods: In this retrospective study, information was collected from a population-based electronic primary-care database. Persistence with medication use 1 year from therapy initiation was evaluated for each user using the gap method. Each new user was classified according to his/her pattern of use as: \u201ccontinuer\u201d, \u201cdiscontinuer\u201d \u201cswitching\u201d or \u201cadd-on\u201d. A Cox regression model was used to analyse the factors influencing therapy discontinuation. Primary-care costs comprised specialists\u2019 visits, diagnostic procedures and pharmacologic therapies. Results: Among 14,999 subjects included in persistence analyses, 55.1% of cases initially started on monotherapy were classified as discontinuers vs 36.5% of cases taking combination therapy (42.3% vs 32.7%, respectively, for free and fixed combinations, P &lt; 0.01). Old age, high cardiovascular risk and being in receipt of fixed-combination therapy were associated with greater persistence. Overall, the primary-care cost/person/year of hypertension management was 3c\u20ac95.3 (IQR, 144.9). The monotherapy cost was \u20ac88 per patient (IQR, 132.9), and that for combination therapy was \u20ac151\ub1148.3. The median cost/patient with a fixed combination was lower than that for a free combination (\u20ac98.4 (IQR, 155.3) and \u20ac154.9 (IQR, 182.6), respectively). Conclusion: The initial type of therapy prescribed influences persistence. Prescribing fixed combinations might be a good choice as initial therapy

Dynamic behavior of anisotropic non-equilibrium driving lattice gases

It is shown that intrinsically anisotropic non-equilibrium systems relaxing by a dynamic process exhibit universal critical behavior during their evolution toward non-equilibrium stationary states. An anisotropic scaling anzats for the dynamics is proposed and tested numerically. Relevant critical exponents can be evaluated self-consistently using both the short- and long-time dynamics frameworks. The obtained results allow us to clarify a long-standing controversy about the theoretical description, the universality and the origin of the anisotropy of driven diffusive systems, showing that the standard field theory does not hold and supporting a recently proposed alternative theory.Comment: 4 pages, 2 figure

Phase Transitions and Oscillations in a Lattice Prey-Predator Model

A coarse grained description of a two-dimensional prey-predator system is given in terms of a 3-state lattice model containing two control parameters: the spreading rates of preys and predators. The properties of the model are investigated by dynamical mean-field approximations and extensive numerical simulations. It is shown that the stationary state phase diagram is divided into two phases: a pure prey phase and a coexistence phase of preys and predators in which temporal and spatial oscillations can be present. The different type of phase transitions occuring at the boundary of the prey absorbing phase, as well as the crossover phenomena occuring between the oscillatory and non-oscillatory domains of the coexistence phase are studied. The importance of finite size effects are discussed and scaling relations between different quantities are established. Finally, physical arguments, based on the spatial structure of the model, are given to explain the underlying mechanism leading to oscillations.Comment: 11 pages, 13 figure

Critical behavior of a one-dimensional monomer-dimer reaction model with lateral interactions

A monomer-dimer reaction lattice model with lateral repulsion among the same species is studied using a mean-field analysis and Monte Carlo simulations. For weak repulsions, the model exhibits a first-order irreversible phase transition between two absorbing states saturated by each different species. Increasing the repulsion, a reactive stationary state appears in addition to the saturated states. The irreversible phase transitions from the reactive phase to any of the saturated states are continuous and belong to the directed percolation universality class. However, a different critical behavior is found at the point where the directed percolation phase boundaries meet. The values of the critical exponents calculated at the bicritical point are in good agreement with the exponents corresponding to the parity-conserving universality class. Since the adsorption-reaction processes does not lead to a non-trivial local parity-conserving dynamics, this result confirms that the twofold symmetry between absorbing states plays a relevant role in determining the universality class. The value of the exponent $\delta_2$, which characterizes the fluctuations of an interface at the bicritical point, supports the Bassler-Brown's conjecture which states that this is a new exponent in the parity-conserving universality class.Comment: 19 pages, 22 figures, to be published in Phys. Rev