Pattern forming pulled fronts: bounds and universal convergence

We analyze the dynamics of pattern forming fronts which propagate into an unstable state, and whose dynamics is of the pulled type, so that their asymptotic speed is equal to the linear spreading speed v^*. We discuss a method that allows to derive bounds on the front velocity, and which hence can be used to prove for, among others, the Swift-Hohenberg equation, the Extended Fisher-Kolmogorov equation and the cubic Complex Ginzburg-Landau equation, that the dynamically relevant fronts are of the pulled type. In addition, we generalize the derivation of the universal power law convergence of the dynamics of uniformly translating pulled fronts to both coherent and incoherent pattern forming fronts. The analysis is based on a matching analysis of the dynamics in the leading edge of the front, to the behavior imposed by the nonlinear region behind it. Numerical simulations of fronts in the Swift-Hohenberg equation are in full accord with our analytical predictions.Comment: 27 pages, 9 figure

Universal Algebraic Relaxation of Velocity and Phase in Pulled Fronts generating Periodic or Chaotic States

We investigate the asymptotic relaxation of so-called pulled fronts propagating into an unstable state. The ``leading edge representation'' of the equation of motion reveals the universal nature of their propagation mechanism and allows us to generalize the universal algebraic velocity relaxation of uniformly translating fronts to fronts, that generate periodic or even chaotic states. Such fronts in addition exhibit a universal algebraic phase relaxation. We numerically verify our analytical predictions for the Swift-Hohenberg and the Complex Ginzburg Landau equation.Comment: 4 pages Revtex, 2 figures, submitted to Phys. Rev. Let

Pattern forming pulled fronts: bounds and universal convergence Abstract

We analyze the dynamics of pattern forming fronts which propagate into an unstable state, and whose dynamics is of the pulled type, so that their asymptotic speed is equal to the linear spreading speed v ∗. We discuss a method that allows to derive bounds on the front velocity, and which, hence, can be used to prove for, among others, the Swift–Hohenberg equation, the extended Fisher–Kolmogorov equation and the cubic complex Ginzburg–Landau equation, that the dynamically relevant fronts are of the pulled type. In addition, we generalize the derivation of the universal power law convergence of the dynamics of uniformly translating pulled fronts to both coherent and incoherent pattern forming fronts. The analysis is based on a matching analysis of the dynamics in the leading edge of the front, to the behavior imposed by the nonlinear region behind it. Numerical simulations of fronts in the Swift–Hohenberg equation are in full accord with our analytical predictions

Failure-mode transition in transient polymer networks with particle-based simulations

Transient polymer networks are known to undergo a wide variety of viscoelastic flow instabilities. In this paper we investigate two of these flow failure modes: shear banding and melt fracture. Using particle-based simulations we reveal a transition from gradient banding to fracture in transient polymer networks with reversible associative nodes. We discuss the failure-mode transition on the basis of an energetic and a kinetic approach to fracturing in soft material

Undeclared doping substances are highly prevalent in commercial sports nutrition supplements

Sports nutrition supplements have previously been reported to contain undeclared doping substances. The use of such supplements can lead to general health risks and may give rise to unintentional doping violations in elite sports. To assess the prevalence of doping substances in a range of high-risk sports nutrition supplements available from Dutch web shops. A total of 66 sports nutrition supplements - identified as potentially high-risk products claiming to modulate hormone regulation, stimulate muscle mass gain, increase fat loss, and/or boost energy - were selected from 21 different brands and purchased from 17 web shops. All products were analyzed for doping substances by the UK life sciences testing company LGC, formerly known as the Laboratory of the Government Chemist, using an extended version of their ISO17025 accredited nutritional supplement screen. A total of 25 out of the 66 products (38%) contained undeclared doping substances, which included high levels of the stimulants oxilofrine, β-methylphenethylamine (BMPEA) and N,β-dimethylphenethylamine (NBDMPEA), the stimulant 4-methylhexan-2-amine (methylhexaneamine, 1,3-dimethylamylamine, DMAA), the anabolic steroids boldione (1,4-androstadiene-3,17-dione) and 5-androstene-3β,17α-diol (17α-AED), the beta-2 agonist higenamine and the beta-blocker bisoprolol. Based upon the recommended dose and the potential variability of analyte concentration, the ingestion of some products identified within this study could pose a significant risk of unintentional doping violations. In addition to inadvertent doping risks, the prescribed use of 3 products (4.5%) could likely impose general health risks

Effectieve bestrijding van Phytophthora infestans bij minimaal fungicidengebruik met behulp van waarschuwingssystemen

Fungiciden zijn onmisbaar voor de beheersing van P. infestans, maar intensief gebruik staat onder druk. Ineen effectieve beheersingsstrategie wordt een maximaal resultaat behaald met een minimale inzet vanmiddelen. Hiervoor is de timing van de bespuitingen van essentieel belang. Bij het bepalen van het juistespuittijdstip spelen de weersomstandigheden een belangrijke rol. Telers en adviseurs kunnen voor hetbepalen van het spuittijdstip gebruik maken van de adviezen van de beslissingsondersteunende systemenProphy of PlantAPlus. Bij de keuze van het middel en de dosering staat vooral de effectiviteit voorop, waarbijrekening wordt gehouden met de gewasontwikkeling (nieuwe groei / knolbescherming). Onderzoek heeftdaarnaast aangetoond dat er mogelijkheden zijn om afhankelijk van het resistentieniveau van het ras en deweersomstandigheden de dosering van Shirlan (en na evaluatie van proeven 2007A2009 ook anderemiddelen) te verlagen. In 2009 is op vijf proeflocaties onderzocht of er nog factoren aan debeslissingsondersteunende systemen kunnen worden toegevoegd zoals verspreidingscapaciteit van deatmosfeer van PhytophthoraAsporen (ziektedruk) en de dosering aanpassen aan de lengte van de kritiekeperiode. In 2010 is het onderzoek op drie proeflocaties voortgezet om met een zo laag mogelijke inzet vanfungiciden de Phytophthora onder controle te houden. Behalve proefboerderijen zijn in 2010 ookpraktijkbedrijven met waarschuwingssystemen met verlaagde doseringen aan de slag gegaan. Zes bedrijvenmet veel hectares aardappels, verspreid over de verschillende teeltregio’s (consumptieA, pootA enzetmeelaardappelen), zijn hierbij intensief begeleid door adviseurs van het Telen met Toekomst netwerk.In dit rapport worden de onderzoeksresultaten van 2010 op de proefboerderijen en de praktijkervaringenbij de zes telers behandeld.Het onderzoek in 2010 is gefinancierd door het Masterplan Phytophthora (PA) en Telen met Toekomst(LNV)