Survival rate of Suid herpesvirus (SuHV-1, Aujeszky's disease virus, ADV) in composted sewage sludge.

Sewage sludge constitutes a source of valuable biogenic raw materials, but it is a carrier of many pathogenic microorganisms and viruses. Subjected to an effective sanitization by means of the process of composting, it is suitable to use in agriculture as fertilizers. The aim of this study was to observe the survival rate of Suid Herpesvirus under the influence of the temperature alone (water bath) as well as in sewage sludge subjected to the process of composting (pile). The samples were taken at different time intervals, and the virus titres were determined. The viruses survived considerably longer under laboratory conditions: at 30 degrees C as long as 21 days, at 40 degrees C - 93 hours, and at 50 degrees C - less than an hour. In the compost pile, in spite of the lack of the thermophylic phase, the total survival time of the viruses ranged from 34 to 44.5 hours, which indicates the vast importance of other physicochemical factors, apart from the temperature, contributing to virus inactivation.

Crystallization of hard disks induced by a temperature gradient.

While uniform temperature has no effect on equilibrium properties of hard-core systems, its gradient might substantially change their behavior. In particular, in hard-disk system subject to temperature difference ΔT disks are repelled from the hot boundary of the system and accumulate at the cold one. Using event-driven molecular dynamics simulations we show that for sufficiently large ΔT or coverage ratio ρ∗, crystal forms at the cold boundary. In this spatially inhomogeneous system a significant decrease of diffusivity of disks clearly marks the stationary interface between liquid and crystal. Such a behavior is also supported through calculation of the radial distribution function and the bond order parameter. Simulations show that for this nonequilibrium system the equipartition of energy holds and velocity obeys the Boltzmann distribution.

Survival of BPV and Aujeszky's disease viruses in meat wastes subjected to different sanitization processes.

The effect of composting and anaerobic fermentations under meso- and thermophylic conditions (37 degrees and 55 degrees C) on the survival of bovine parvovirus (BPV) and Aujeszky's disease viruse (ADV) in meat wastes has been examined in this study. Viruses were adsorbed on filters and introduced into carriers which were made of meat fragments of different sizes and bones or in the form of suspension they were introduced into the biomass in the course of processes of waste treatment. Carriers were removed at appropriate time intervals and virus titres were determined. The thermoresistant parvovirus survived for the longest time during mesophylic fermentation (almost 70 days), slightly shorter during composting (7-9.5 days depending on the type of carrier) and for the shortest time--at 55 degrees C (46-76 hours). Its inactivation rate was the fastest in a suspension, slower in meat and bone carriers. ADV inactivation proceeded considerably faster, as compared with BPV. Its active particles were not detected as early as in the 30th minute of thermophylic fermentation, the 6th hour of mesophylic fermentation and at the first sampling time during composting (at the 72nd hour). Total survival time ranged from 50 min to 13 hours. All the tested technologies enabled the effective elimination of ADV and on average twofold decrease in BPV titre. From the study conducted it follows that of both viruses, the BPV should be applied for validation processes of methods used in meat waste processing, particularly if this refers to methods where higher temperature is the factor inactivating pathogens.

Evaluation of efficacy and safety of Aujeszky's disease vaccines.

Since Aujeszky's disease have become an economic problem in pig farms in late 1960's and early 1970's many different vaccines, either inactivated or live - attenuated were developed. Soon it became evident that they differ in their efficacy. In this article a panel of tests used for evaluation of safety and efficacy of inactivated as well as live Aujeszky's disease vaccines is described.

Extinction dynamics of Lotka-Volterra ecosystems on evolving networks.

We study a model of a multispecies ecosystem described by Lotka-Volterra-like equations. Interactions among species form a network whose evolution is determined by the dynamics of the model. Numerical simulations show power-law distribution of intervals between extinctions, but only for ecosystems with sufficient variability of species and with networks of connectivity above certain threshold that is very close to the percolation threshold of the network. The effect of slow environmental changes on extinction dynamics, degree distribution of the network of interspecies interactions, and some emergent properties of our model are also examined.

Yang-Lee zeros for an urn model for the separation of sand.

We apply the Yang-Lee theory of phase transitions to an urn model for the separation of sand. The effective partition function of this nonequilibrium system can be expressed as a polynomial of the size-dependent effective fugacity z. Numerical calculations show that in the thermodynamic limit the zeros of the effective partition function are located on the unit circle in the complex z plane. In the complex plane of the actual control parameter, certain roots converge to the transition point of the model. Thus, the Yang-Lee theory can be applied to a wider class of nonequilibrium systems than those considered previously.

Tensionless structure of a glassy phase.

We study a class of homogeneous finite-dimensional Ising models which were recently shown to exhibit glassy properties. Monte Carlo simulations of a particular three-dimensional model in this class show that the glassy phase obtained under slow cooling is dominated by large-scale excitations whose energy E(l) scales with their size l as E(l) approximately l(Theta) with Theta approximately 1.33(20). Simulations suggest that in another model of this class, namely the four-spin model, energy is concentrated mainly in linear defects, making the domain walls tensionless in this case also. Two-dimensional variants of these models are trivial and most likely the energy of excitations scales with the exponent Theta=1.

Crystallization of a supercooled liquid and of a glass: Ising model approach.

Using Monte Carlo simulations we study crystallization in the three-dimensional Ising model with four-spin interaction. We monitor the morphology of crystals which grow after placing crystallization seeds in a supercooled liquid. Defects in such crystals constitute an intricate and very stable network that separates various domains by tensionless domain walls. We also show that the crystallization which occurs during the continuous heating of the glassy phase takes place at a heating-rate-dependent temperature.

Criticality of natural absorbing states.

We study a recently introduced ladder model that undergoes a transition between an active and an infinitely degenerate absorbing phase. In some cases the critical behavior of the model is the same as that of the branching-annihilating random walk with N>/=2 species both with and without hard-core interaction. We show that certain static characteristics of the so-called natural absorbing states develop power-law singularities that signal the approach of the critical point. These results are also explained using random-walk arguments. In addition to that we show that when dynamics of our model is considered as a minimum-finding procedure, it has the best efficiency very close to the critical point.

Critical behavior of a lattice prey-predator model.

The critical properties of a simple prey-predator model are revisited. For some values of the control parameters, the model exhibits a line of directed percolationlike transitions to a single absorbing state. For other values of the control parameters one finds a second line of continuous transitions toward an infinite number of absorbing states, and the corresponding steady-state exponents are mean-field-like. The critical behavior of the special point T (bicritical point), where the two transition lines meet, belongs to a different universality class. A particular strategy for preparing the initial states used for the dynamical Monte Carlo method is devised to correctly describe the physics of the system near the second transition line. Relationships with a forest fire model with immunization are also discussed.

Criticality in a model with absorbing states.

We study a one-dimensional model that undergoes a transition between an active and an absorbing phase. Monte Carlo simulations supported by some additional arguments prompted us to predict the exact location of the critical point and critical exponents in this model. The exponents delta=0.5 and z=2 follows from random-walk-type arguments. The exponents beta=nu( perpendicular) are found to be nonuniversal and encoded in the singular part of reactivation probability, as recently discussed by H. Hinrichsen (cond-mat/0008179). A related model with quenched randomness is also studied.

Cooling-rate effects in a model of glasses

Using Monte Carlo simulations we study cooling-rate effects in a three-dimensional Ising model with four-spin interactions. During coarsening, this model develops growing energy barriers, which at low temperature lead to very slow dynamics. We show that the characteristic zero-temperature length increases very slowly with the inverse cooling rate, similarly to the behavior of ordinary glasses. For computationally accessible cooling rates the model undergoes an ideal glassy transition, i.e., the glassy transition for a very small cooling rate coincides with a thermodynamic singularity. We also study the cooling of this model with a certain fraction of spins fixed. Due to such heterogeneous crystallization seeds, the final state strongly depends on the cooling rate. Only for a sufficiently fast cooling rate does the system end up in a glassy state, while slow cooling inevitably leads to a crystal phase.

Generic criticality in a model of evolution

Using Monte Carlo simulations, we show that for a certain model of biological evolution, which is driven by nonextremal dynamics, active and absorbing phases are separated by a critical phase. In this phase both the density of active sites rho(t) and the survival probability of spreading P(t) decay as t(-delta), where delta approximately 0.5. At the critical point that separates the active and critical phases delta approximately 0.29, which suggests that this point belongs to the so-called parity-conserving universality class. Such a classification is also supported by finite-size analysis. The model has infinitely many absorbing states and, except for a single point, has no apparent conservation law.

Slow dynamics of ising models with energy barriers

Using Monte Carlo simulations we study the dynamics of three-dimensional Ising models with nearest-, next-nearest-, and four-spin (plaquette) interactions. During coarsening, such models develop growing energy barriers, which leads to very slow dynamics at low temperature. As already reported, the model with only the plaquette interaction exhibits some of the features characteristic of ordinary glasses: strong metastability of the supercooled liquid, a weak increase of the characteristic length under cooling, stretched-exponential relaxation, and aging. The addition of two-spin interactions, in general, destroys such behavior: the liquid phase loses metastability and the slow-dynamics regime terminates well below the melting transition, which is presumably related with a certain corner-rounding transition. However, for a particular choice of interaction constants, when the ground state is strongly degenerate, our simulations suggest that the slow-dynamics regime extends up to the melting transition. The analysis of these models leads us to the conjecture that in the four-spin Ising model domain walls lose their tension at the glassy transition and that they are basically tensionless in the glassy phase.

First-order transition with power-law singularity in models with absorbing states

We study one- and two-dimensional models which undergo a transition between active and absorbing phases. The transition point in these models is of a novel type: jump of the order parameter coincides with its power-law singularity. Some arguments supported by Monte Carlo simulations prompted us to predict the exact location of the transition point. Both models possess gaugelike symmetry.

Safety and efficacy of a classical swine fever subunit vaccine in pregnant sows and their offspring.

In the study three groups with five pregnant sows each were used. The animals were vaccinated twice, 2 weeks apart, in different stages of gestation, i.e. +/-4, +/-8 and +/-12 weeks after insemination and then 14 days later, respectively. From each group of sows three litters were randomly selected and vaccinated twice, 4 weeks apart, at 5 and 9, 7 and 11, and 9 and 13 weeks of life, respectively. Blood for serological investigations by virus neutralisation test and ELISA tests (for E(rns) antibodies and for E2 antibodies, separately) was taken before immunisation, at each vaccination and 2 weeks thereafter. Clinical observations shown that no local nor systemic reactions as well as no adverse effect on gestation occurred after vaccinations in any of the sows. Serological tests detected a low level of antibodies after the first vaccination and a typical booster effect after the second one. In piglets no adverse effect of the vaccination on the body weight gain was found. The presence of maternally derived antibodies (MDA) in non-vaccinated control piglets was observed up to the age of 5-13 weeks of life. The most evident immunological reaction was obtained in piglets vaccinated at the age of 5 or 7 weeks of life and revaccinated 4 weeks later. The CSFV-E2 subunit marker vaccine tested proved to be safe for pregnant sows and immunogenic for MDA positive piglets.

Multiplicity of species in some replicative systems.

In an attempt to explain the uniqueness of the coding mechanism of living cells as contrasted with the multispecies structure of ecosystems we examine two models of individuals with some replicative properties. In the first model the system generically remains in a multispecies state. Even though for some of these species the replicative probability is very high, they are unable to invade the system. In the second model, in which the death rate depends on the type of the species, the system relatively quickly reaches a single-species state and fluctuations might at most bring it to yet another single-species state.

Classical swine fever: the global situation.

A historical and current perspective is given of classical swine fever and its impact on pig production in different regions of the world. Data were obtained from a variety of sources including returns to the Office International des Epizooties, official government reports, other published material and local information through personal contacts. The disease has been recognized for about 170 years and efforts to control it by official intervention began in the nineteenth century. Despite this it remains a lingering problem in many parts of the world where it has both, an economic impact on swine production and a constraining effect on trade due to the measures necessary to prevent spread.

Model of biological evolution with threshold dynamics and infinitely many absorbing states.

We study a model of biological evolution where the survival of a given species depends on its interactions with neighboring species. In the steady state the model has an active phase and an absorbing phase, which are separated by the critical point of the directed percolation universality class. The absorbing phase is infinitely degenerate and the dynamical behavior of our model is found to be nonuniversal.

Oscillatory behavior in a lattice prey-predator system.

Using Monte Carlo simulations we study a lattice model of a prey-predator system. We show that in the three-dimensional model populations of preys and predators exhibit coherent periodic oscillations but such a behavior is absent in lower-dimensional models. Finite-size analysis indicate that amplitude of these oscillations is finite even in the thermodynamic limit. This is an example of a microscopic model with stochastic dynamics which exhibits oscillatory behavior without any external driving force. We suggest that oscillations in our model are induced by some kind of stochastic resonance.