8,470 research outputs found
Topological interactions in systems of mutually interlinked polymer rings
The topological interaction arising in interlinked polymeric rings such as
DNA catenanes is considered. More specifically, the free energy for a pair of
linked random walk rings is derived where the distance between two segments
each of which is part of a different ring is kept constant. The topology
conservation is imposed by the Gauss invariant. A previous approach (M.Otto,
T.A. Vilgis, Phys.Rev.Lett. {\bf 80}, 881 (1998)) to the problem is refined in
several ways. It is confirmed, that asymptotically, i.e. for large
where is average size of single random walk ring, the effective
topological interaction (free energy) scales .Comment: 16 pages, 3 figur
Analytical study of the effect of recombination on evolution via DNA shuffling
We investigate a multi-locus evolutionary model which is based on the DNA
shuffling protocol widely applied in \textit{in vitro} directed evolution. This
model incorporates selection, recombination and point mutations. The simplicity
of the model allows us to obtain a full analytical treatment of both its
dynamical and equilibrium properties, for the case of an infinite population.
We also briefly discuss finite population size corrections
Mutator Dynamics on a Smooth Evolutionary Landscape
We investigate a model of evolutionary dynamics on a smooth landscape which
features a ``mutator'' allele whose effect is to increase the mutation rate. We
show that the expected proportion of mutators far from equilibrium, when the
fitness is steadily increasing in time, is governed solely by the transition
rates into and out of the mutator state. This results is a much faster rate of
fitness increase than would be the case without the mutator allele. Near the
fitness equilibrium, however, the mutators are severely suppressed, due to the
detrimental effects of a large mutation rate near the fitness maximum. We
discuss the results of a recent experiment on natural selection of E. coli in
the light of our model.Comment: 4 pages, 3 figure
Passing to the Limit in a Wasserstein Gradient Flow: From Diffusion to Reaction
We study a singular-limit problem arising in the modelling of chemical
reactions. At finite {\epsilon} > 0, the system is described by a Fokker-Planck
convection-diffusion equation with a double-well convection potential. This
potential is scaled by 1/{\epsilon}, and in the limit {\epsilon} -> 0, the
solution concentrates onto the two wells, resulting into a limiting system that
is a pair of ordinary differential equations for the density at the two wells.
This convergence has been proved in Peletier, Savar\'e, and Veneroni, SIAM
Journal on Mathematical Analysis, 42(4):1805-1825, 2010, using the linear
structure of the equation. In this paper we re-prove the result by using solely
the Wasserstein gradient-flow structure of the system. In particular we make no
use of the linearity, nor of the fact that it is a second-order system. The
first key step in this approach is a reformulation of the equation as the
minimization of an action functional that captures the property of being a
curve of maximal slope in an integrated form. The second important step is a
rescaling of space. Using only the Wasserstein gradient-flow structure, we
prove that the sequence of rescaled solutions is pre-compact in an appropriate
topology. We then prove a Gamma-convergence result for the functional in this
topology, and we identify the limiting functional and the differential equation
that it represents. A consequence of these results is that solutions of the
{\epsilon}-problem converge to a solution of the limiting problem.Comment: Added two sections, corrected minor typos, updated reference
Behavior of Some Materials and Shapes in Supersonic Free Jets at Stagnation Temperatures up to 4,210 Degrees F, and Descriptions of the Jets
Inventories of extreme weather events and impacts: Implications for loss and damage from and adaptation to climate extremes
Extreme and impactful weather events of the recent past provide a vital but under-utilised data source for understanding present and future climate risks. Extreme event attribution (EEA) enables us to quantify the influence of anthropogenic climate change (ACC) on a given event in a way that can be tailored to stakeholder needs, thereby enhancing the potential utility of studying past events. Here we set out a framework for systematically recording key details of high-impact events on a national scale (using the UK and Puerto Rico as examples), combining recent advances in event attribution with the risk framework. These âinventoriesâ inherently provide useful information depending on a userâs interest. For example, as a compilation of the impacts of ACC, we find that in the UK since 2000, at least 1500 excess deaths are directly attributable to human-induced climate change, while in Puerto Rico the increased intensity of Hurricane Maria alone led to the deaths of up to 3670 people. We also explore how inventories form a foundation for further analysis, learning from past events. This involves identifying the most damaging hazards and crucially also vulnerabilities and exposure characteristics over time. To build a risk assessment for heat-related mortality in the UK we focus on a vulnerable group, elderly urban populations, and project changes in the hazard and exposure within the same framework. Without improved preparedness, the risk to this group is likely to increase by ~50% by 2028 and ~150% by 2043. In addition, the framework allows the exploration of the likelihood of otherwise unprecedented events, or 'Black Swansâ. Finally, not only does it aid disaster preparedness and adaptation at local and national scales, such inventories also provide a new source of evidence for global stocktakes on adaptation and loss and damage such as mandated by the Paris Climate Agreement
Elasticity of entangled polymer loops: Olympic gels
In this note we present a scaling theory for the elasticity of olympic gels,
i.e., gels where the elasticity is a consequence of topology only. It is shown
that two deformation regimes exist. The first is the non affine deformation
regime where the free energy scales linear with the deformation. In the large
(affine) deformation regime the free energy is shown to scale as where is the deformation ratio. Thus a highly non
Hookian stress - strain relation is predicted.Comment: latex, no figures, accepted in PRE Rapid Communicatio
Nitrogen recovery efficiency for corn intercropped with palisade grass.
Intercropping corn and palisade grass is a technique to increase straw production, soil C contents, nutrient cycling and crop yield. However, concerns arise from nitrogen (N) uptake by the intercropping crop causing reduction in the yield of the corn. Our objective was to evaluate N recovery efficiency (NRE), and the N dynamics in the soil-plant system in corn intercropped with palisade grass. A field trial was carried out in Bahia, Brazil, evaluating two cropping systems: corn (monoculture) and corn intercropped with palisade grass sowed between rows on the same day as the corn crop, with four replicates in a completely randomized block design. Nitrogen (150 kg∙ha?1of 15N-urea) was applied at sowing to determine NRE, which means the amounts of N-fertilizer uptake in corn and palisade grass, the amounts of N-fertilizer in soil and the 15N-fertilizer balance. Neither the NRE (63.3% in monoculture and 57.2% in intercropping) nor corn grain yield (9,800 kg∙ha?1 in monoculture and 9,671 kg∙ha?1 in intercropping) was affected by intercropping, which accumulated only 2.1 kg∙ha?1 of N-fertilizer or 1.4% N rate. In addition, palisade grass yielded 2,265 kg∙ha?1 of dry matter. The balance indicated that 82.4% of N-fertilizer was recovered in the monoculture and 86.9% in the intercropping. Intercropping palisade grass does not affect grain yield or N corn nutrition and has the potential to increase straw production contributing to maintenance of no-till
Particle approximation of the one dimensional Keller-Segel equation, stability and rigidity of the blow-up
We investigate a particle system which is a discrete and deterministic
approximation of the one-dimensional Keller-Segel equation with a logarithmic
potential. The particle system is derived from the gradient flow of the
homogeneous free energy written in Lagrangian coordinates. We focus on the
description of the blow-up of the particle system, namely: the number of
particles involved in the first aggregate, and the limiting profile of the
rescaled system. We exhibit basins of stability for which the number of
particles is critical, and we prove a weak rigidity result concerning the
rescaled dynamics. This work is complemented with a detailed analysis of the
case where only three particles interact
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