Enhancing the description of multi-time-scale geophysical phenomena: Incorporating finite time Scale separation and feedback, illustrated with the case of a 1D variable of interest.

Stochastic approaches play a vital role in weather, climate, and, more in general, geophysics systems, addressing processes and scales beyond the resolution of deterministic models. Similar to equilibrium/non-equilibrium thermodynamics, intricate fast and local dynamics may not always be the primary focus. Practical applications often prioritize observables capturing phenomena at dominant temporal and spatial scales.

Personalized modeling of Alzheimer's disease progression estimates neurodegeneration severity from EEG recordings.

Introduction: Early identification of Alzheimer's disease (AD) is necessary for a timely onset of therapeutic care. However, cortical structural alterations associated with AD are difficult to discern.

Methods: We developed a cortical model of AD-related neurodegeneration accounting for slowing of local dynamics and global connectivity degradation.

Dopamine depletion leads to pathological synchronization of distinct basal ganglia loops in the beta band.

Motor symptoms of Parkinson's Disease (PD) are associated with dopamine deficits and pathological oscillation of basal ganglia (BG) neurons in the β range ([12-30] Hz). However, how dopamine depletion affects the oscillation dynamics of BG nuclei is still unclear. With a spiking neurons model, we here capture the features of BG nuclei interactions leading to oscillations in dopamine-depleted condition.

On the determination of the optimal parameters in the CAM model.

In the field of complex systems, it is often possible to arrive at some simple stochastic or chaotic Low Order Models (LOMs) exploiting the time scale separation between leading modes of interest and fast fluctuations. These LOMs, although approximate, might provide interesting qualitative insights regarding some important aspects like the average time between two extreme events. Recently, the simplest example of a LOM with multiplicative noise, namely, a linear system with a linearly state dependent noise [also called correlated additive and multiplicative (CAM) model], has been considered as archetypal for numerous phenomena that present markedly non-Gaussian statistics.

Frequency stabilization and noise-induced spectral narrowing in resonators with zero dispersion.

Mechanical resonators are widely used as precision clocks and sensitive detectors that rely on the stability of their eigenfrequencies. The phase noise is determined by different factors including thermal noise, frequency noise of the resonator and noise in the feedback circuitry. Increasing the vibration amplitude can mitigate some of these effects but the improvements are limited by nonlinearities that are particularly strong for miniaturized micro- and nano-mechanical systems.

Estimate of the average timing for strong El Niño events using the recharge oscillator model with a multiplicative perturbation.

El Niño Southern Oscillation (ENSO) is the leading mode of tropical Pacific variability at interannual timescales. Through atmospheric teleconnections, ENSO exerts large influences worldwide, so that improved understanding of this phenomenon can be of critical societal relevance. Extreme ENSO events, in particular, have been associated with devastating weather events in many parts of the world, so that the ability to assess their frequency and probability of occurrence is extremely important.

Encephalitozoon cuniculi in rabbits: Serological screening and histopathological findings.

Serological prevalence of E. cuniculi infection was assessed in 183 rabbits from central Italy. In seropositive deceased rabbits, histopathological lesions were also evaluated.

Intestinal and lung parasites in owned dogs and cats from central Italy.

Prevalence and risk factors of intestinal and lung parasites were investigated in 239 owned dogs and 81 owned cats from central Italy. In 36 dogs and 20 cats found infected by nematodes, pre and post-treatment faecal egg count (FEC) was also evaluated. About 31% of dogs and about 35% of cats resulted positive for at least one intestinal or lung parasitic species.

The Italian veterinary medicine admission test: analysis of student intake in the years 2007, 2008, and 2009, and of the test's relationship with students' academic careers.

The present paper analyzes the admission test administered to candidates to the veterinary medicine program in Italy for the academic years 2007-2008, 2008-2009, and 2009-2010 nationwide as well as the University of Pisa student intake from 2001-2002 through 2009-2010, comparing the relationship between the admission test and students' academic careers at Pisa. This paper finds that the Italian system of a locally enforced fixed intake number does not select the best possible candidates for admission because (1) there are significant variations in the candidates' preparation among the different locations where the test is held, (2) the subjects tested are not equally selective in identifying the best candidates, and (3) there is a very strong relationship between candidates' performance on the admission test and the subsequent academic career of the admitted candidates. In its findings, this study in part contradicts what is commonly believed by the Italian veterinary medicine community, and, as a result, it is extremely important that care is taken in the decision-making process-in the process, that is, of identifying a fixed intake number and of selecting the subjects to be tested on the admission test.

Gastrointestinal parasites in mammals of two Italian zoological gardens.

The prevalence of gastrointestinal parasites was investigated in mammals housed in two of the main Italian zoological gardens: the Zoo Safari of Fasano (province of Bindisi, Apulia, Italy) and the Giardino Zoologico of Pistoia (Tuscany, Italy). In November 2007, fecal samples were collected at the Zoo Safari of Fasano (n = 96) and at the Giardino Zoologico of Pistoia (n = 60), from primates, carnivores, perissodactyls, artiodactyls and proboscideans. In most of the cases, the same animal species or genera were considered in both the zoos.

Maximal width of the separatrix chaotic layer.

The main goal of the paper is to find the absolute maximum of the width of the separatrix chaotic layer as function of the frequency of the time-periodic perturbation of a one-dimensional Hamiltonian system possessing a separatrix, which is one of the major unsolved problems in the theory of separatrix chaos. For a given small amplitude of the perturbation, the width is shown to possess sharp peaks in the range from logarithmically small to moderate frequencies. These peaks are universal, being the consequence of the involvement of the nonlinear resonance dynamics into the separatrix chaotic motion.

Time-resolved measurement of Landau-Zener tunneling in periodic potentials.

We report time-resolved measurements of Landau-Zener tunneling of Bose-Einstein condensates in accelerated optical lattices, clearly resolving the steplike time dependence of the band populations. Using different experimental protocols we were able to measure the tunneling probability both in the adiabatic and in the diabatic bases of the system. We also experimentally determine the contribution of the momentum width of the Bose condensates to the temporal width of the tunneling steps and discuss the implications for measuring the jump time in the Landau-Zener problem.

Matching of separatrix map and resonant dynamics, with application to global chaos onset between separatrices.

We have developed a general method for the description of separatrix chaos, based on the analysis of the separatrix map dynamics. Matching it with the resonant Hamiltonian analysis, we show that, for a given amplitude of perturbation, the maximum width of the chaotic layer in energy may be much larger than it was assumed before. We use the above method to explain the drastic facilitation of global chaos onset in time-periodically perturbed Hamiltonian systems possessing two or more separatrices, previously discovered [S.

Many-body interband tunneling as a witness of complex dynamics in the Bose-Hubbard model.

A perturbative model is studied for the tunneling of many-particle states from the ground band to the first excited energy band, mimicking Landau-Zener decay for ultracold, spinless atoms in quasi-one-dimensional optical lattices subjected to a tunable tilting force. The distributions of the computed tunneling rates provide an independent and experimentally accessible signature of the regular-chaotic transition in the strongly correlated many-body dynamics of the ground band.

Langevin stabilization of molecular-dynamics simulations of polymers by means of quasisymplectic algorithms.

Algorithms for the numerical integration of Langevin equations are compared in detail from the point of view of their accuracy, numerical efficiency, and stability to assess them as potential candidates for molecular-dynamics simulations of polymeric systems. Some algorithms are symplectic in the deterministic frictionless limit and prove to stabilize long time-step integrators. They are tested against other popular algorithms.

Divergence of the chaotic layer width and strong acceleration of the spatial chaotic transport in periodic systems driven by an adiabatic ac force.

We show for the first time that a weak perturbation in a Hamiltonian system may lead to an arbitrarily wide chaotic layer and fast chaotic transport. This generic effect occurs in any spatially periodic Hamiltonian system subject to a sufficiently slow ac force. We explain it and develop an explicit theory for the layer width, verified in simulations.

Solution of the boundary value problem for optimal escape in continuous stochastic systems and maps.

Topologies of invariant manifolds and optimal trajectories are investigated in stochastic continuous systems and maps. A topological method is introduced that simplifies the solution of boundary value problems: The activation energy is calculated as a function of a set of parameters characterizing the initial conditions of the escape path. The method is applied explicitly to compute the optimal escape path and the activation energy for a variety of dynamical systems and maps.

Resonant nonlinear quantum transport for a periodically kicked bose condensate.

Our realistic numerical results show that the fundamental and higher-order quantum resonances of the delta-kicked rotor are observable in state-of-the-art experiments with a Bose condensate in a shallow harmonic trap, kicked by a spatially periodic optical lattice. For stronger confinement, interaction-induced destruction of the resonant motion of the kicked harmonic oscillator is predicted.

Quasisymplectic integrators for stochastic differential equations.

Two specialized algorithms for the numerical integration of the equations of motion of a Brownian walker obeying detailed balance are introduced. The algorithms become symplectic in the appropriate limits and reproduce the equilibrium distributions to some higher order in the integration time step. Comparisons with other existing integration schemes are carried out both for static and dynamical quantities.

Dynamic importance sampling for the escape problem in nonequilibrium systems: observation of shifts in optimal paths.

The activation problem is investigated in two-dimensional nonequilibrium systems. A numerical approach based on dynamic importance sampling (DIMS) is introduced. DIMS accelerates the simulations and allows the investigation to access noise intensities that were previously forbidden.

Fast monte carlo simulations and singularities in the probability distributions of nonequilibrium systems.

A numerical technique is introduced that reduces exponentially the time required for Monte Carlo simulations of nonequilibrium systems. Results for the quasistationary probability distribution in two model systems are compared with the asymptotically exact theory in the limit of extremely small noise intensity. Singularities of the nonequilibrium distributions are revealed by the simulations.

Drastic facilitation of the onset of global chaos.

We show that the onset of global chaos in a time periodically perturbed Hamiltonian system may occur at unusually small magnitudes of perturbation if the unperturbed system possesses more than one separatrix. The relevant scenario is the combination of the overlap in the phase space between resonances of the same order and their overlap in energy with chaotic layers associated with separatrices of the unperturbed system. We develop the asymptotic theory and verify it in simulations.

Noise-induced escape on time scales preceding quasistationarity: New developments in the Kramers problem.

Noise-induced escape from the metastable part of a potential is considered on time scales preceding the formation of quasiequilibrium within that part of the potential. It is shown that, counterintuitively, the escape flux may then depend exponentially strongly, and in a complicated manner, on time and friction. (c) 2001 American Institute of Physics.

Activated escape of periodically driven systems.

We discuss activated escape from a metastable state of a system driven by a time-periodic force. We show that the escape probabilities can be changed very strongly even by a comparatively weak force. In a broad parameter range, the activation energy of escape depends linearly on the force amplitude.