Drift- or Fluctuation-Induced Ordering and Self-Organization in Driven Many-Particle Systems

According to empirical observations, some pattern formation phenomena in driven many-particle systems are more pronounced in the presence of a certain noise level. We investigate this phenomenon of fluctuation-driven ordering with a cellular automaton model of interactive motion in space and find an optimal noise strength, while order breaks down at high(er) fluctuation levels. Additionally, we discuss the phenomenon of noise- and drift-induced self-organization in systems that would show disorder in the absence of fluctuations. In the future, related studies may have applications to the control of many-particle systems such as the efficient separation of particles. The rather general formulation of our model in the spirit of game theory may allow to shed some light on several different kinds of noise-induced ordering phenomena observed in physical, chemical, biological, and socio-economic systems (e.g., attractive and repulsive agglomeration, or segregation).Comment: For related work see http://www.helbing.or

Dynamical mechanism of atrial fibrillation: a topological approach

While spiral wave breakup has been implicated in the emergence of atrial fibrillation, its role in maintaining this complex type of cardiac arrhythmia is less clear. We used the Karma model of cardiac excitation to investigate the dynamical mechanisms that sustain atrial fibrillation once it has been established. The results of our numerical study show that spatiotemporally chaotic dynamics in this regime can be described as a dynamical equilibrium between topologically distinct types of transitions that increase or decrease the number of wavelets, in general agreement with the multiple wavelets hypothesis. Surprisingly, we found that the process of continuous excitation waves breaking up into discontinuous pieces plays no role whatsoever in maintaining spatiotemporal complexity. Instead this complexity is maintained as a dynamical balance between wave coalescence -- a unique, previously unidentified, topological process that increases the number of wavelets -- and wave collapse -- a different topological process that decreases their number.Comment: 15 pages, 14 figure

The Speed of Fronts of the Reaction Diffusion Equation

We study the speed of propagation of fronts for the scalar reaction-diffusion equation $u_t = u_{xx} + f(u)$\, with $f(0) = f(1) = 0$. We give a new integral variational principle for the speed of the fronts joining the state $u=1$ to $u=0$. No assumptions are made on the reaction term $f(u)$ other than those needed to guarantee the existence of the front. Therefore our results apply to the classical case $f > 0$ in $(0,1)$, to the bistable case and to cases in which $f$ has more than one internal zero in $(0,1)$.Comment: 7 pages Revtex, 1 figure not include

Finite to infinite steady state solutions, bifurcations of an integro-differential equation

We consider a bistable integral equation which governs the stationary solutions of a convolution model of solid--solid phase transitions on a circle. We study the bifurcations of the set of the stationary solutions as the diffusion coefficient is varied to examine the transition from an infinite number of steady states to three for the continuum limit of the semi--discretised system. We show how the symmetry of the problem is responsible for the generation and stabilisation of equilibria and comment on the puzzling connection between continuity and stability that exists in this problem

Practice Parameter: Therapies for Benign Paroxysmal Positional Vertigo (An Evidence-Based Review): Report of the Quality Standards Subcommittee of the American Academy of Neurologysymbol Symbol

American Academy of Neurology; BPPV = benign paroxysmal positional vertigo; CONSORT = Consolidated Standards of Reporting Trials; CRP = canalith repositioning procedure; NNT = number needed to treat

Avalanche of Bifurcations and Hysteresis in a Model of Cellular Differentiation

Cellular differentiation in a developping organism is studied via a discrete bistable reaction-diffusion model. A system of undifferentiated cells is allowed to receive an inductive signal emenating from its environment. Depending on the form of the nonlinear reaction kinetics, this signal can trigger a series of bifurcations in the system. Differentiation starts at the surface where the signal is received, and cells change type up to a given distance, or under other conditions, the differentiation process propagates through the whole domain. When the signal diminishes hysteresis is observed

Returning to an old question: What do television actors do when they act?

This article argues for acknowledging and exploring actors’ processes in critical considerations of television drama. Theatre Studies boasts a tradition of research privileging the actor, including a century’s worth of actor-training manuals, academic works observing rehearsals and performances, and actor accounts. However, such considerations within Television Studies are relatively nascent. Drawing upon continuing drama as a fertile case study for investigating the specificities of television acting, the article concludes that the only way to understand television acting is through the analysis of insights from actors themselves, in combination with the well-established practices of analysing the textual end-products of television acting

One-dimensional symmetry and Liouville type results for the fourth order Allen-Cahn equation in RN^N

In this paper, we prove an analogue of Gibbons' conjecture for the extended fourth order Allen-Cahn equation in R N , as well as Liouville type results for some solutions converging to the same value at infinity in a given direction. We also prove a priori bounds and further one-dimensional symmetry and rigidity results for semilinear fourth order elliptic equations with more general nonlinearities

Domain Walls in Non-Equilibrium Systems and the Emergence of Persistent Patterns

Domain walls in equilibrium phase transitions propagate in a preferred direction so as to minimize the free energy of the system. As a result, initial spatio-temporal patterns ultimately decay toward uniform states. The absence of a variational principle far from equilibrium allows the coexistence of domain walls propagating in any direction. As a consequence, *persistent* patterns may emerge. We study this mechanism of pattern formation using a non-variational extension of Landau's model for second order phase transitions. PACS numbers: 05.70.Fh, 42.65.Pc, 47.20.Ky, 82.20MjComment: 12 pages LaTeX, 5 postscript figures To appear in Phys. Rev.

A Decision Analysis Evaluating Screening for Kidney Cancer Using Focused Renal Ultrasound

Background Screening for renal cell carcinoma (RCC) has been identified as a key research priority; however, no randomised control trials have been performed. Value of information analysis can determine whether further research on this topic is of value. Objective To determine (1) whether current evidence suggests that screening is potentially cost effective and, if so, (2) in which age/sex groups, (3) identify evidence gaps, and (4) estimate the value of further research to close those gaps. Design, setting, and participants A decision model was developed evaluating screening in asymptomatic individuals in the UK. A National Health Service perspective was adopted. Intervention A single focused renal ultrasound scan compared with standard of care (no screening). Outcome measurements and statistical analysis Expected lifetime costs, quality-adjusted life years (QALYs), and incremental cost-effectiveness ratio (ICER), discounted at 3.5% per annum. Results and limitations Given a prevalence of RCC of 0.34% (0.18–0.54%), screening 60-yr-old men resulted in an ICER of £18 092/QALY (€22 843/QALY). Given a prevalence of RCC of 0.16% (0.08–0.25%), screening 60-yr-old women resulted in an ICER of £37 327/QALY (€47 129/QALY). In the one-way sensitivity analysis, the ICER was <£30 000/QALY as long as the prevalence of RCC was ≥0.25% for men and ≥0.2% for women at age 60 yr. Given the willingness to pay a threshold of £30 000/QALY (€37 878/QALY), the population-expected values of perfect information were £194 million (€244 million) and £97 million (€123 million) for 60-yr-old men and women, respectively. The expected value of perfect parameter information suggests that the prevalence of RCC and stage shift associated with screening are key research priorities. Conclusions Current evidence suggests that one-off screening of 60-yr-old men is potentially cost effective and that further research into this topic would be of value to society. Patient summary Economic modelling suggests that screening 60-yr-old men for kidney cancer using ultrasound may be a good use of resources and that further research on this topic should be performed