Dirac mass dynamics in multidimensional nonlocal parabolic equations

Nonlocal Lotka-Volterra models have the property that solutions concentrate as Dirac masses in the limit of small diffusion. Is it possible to describe the dynamics of the limiting concentration points and of the weights of the Dirac masses? What is the long time asymptotics of these Dirac masses? Can several Dirac masses co-exist? We will explain how these questions relate to the so-called "constrained Hamilton-Jacobi equation" and how a form of canonical equation can be established. This equation has been established assuming smoothness. Here we build a framework where smooth solutions exist and thus the full theory can be developed rigorously. We also show that our form of canonical equation comes with a structure of gradient flow. Numerical simulations show that the trajectories can exhibit unexpected dynamics well explained by this equation. Our motivation comes from population adaptive evolution a branch of mathematical ecology which models darwinian evolution

On a Boltzmann mean field model for knowledge growth

In this paper we analyze a Boltzmann type mean field game model for knowledge growth, which was proposed by Lucas and Moll. We discuss the underlying mathematical model, which consists of a coupled system of a Boltzmann type equation for the agent density and a Hamilton-Jacobi-Bellman equation for the optimal strategy. We study the analytic features of each equation separately and show local in time existence and uniqueness for the fully coupled system. Furthermore we focus on the construction and existence of special solutions, which relate to exponential growth in time - so called balanced growth path solutions. Finally we illustrate the behavior of solutions for the full system and the balanced growth path equations with numerical simulations.Comment: 6 figure

Balanced growth path solutions of a Boltzmann mean field game model for knowledge growth

In this paper we study balanced growth path solutions of a Boltzmann mean field game model proposed by Lucas et al [13] to model knowledge growth in an economy. Agents can either increase their knowledge level by exchanging ideas in learning events or by producing goods with the knowledge they already have. The existence of balanced growth path solutions implies exponential growth of the overall production in time. We proof existence of balanced growth path solutions if the initial distribution of individuals with respect to their knowledge level satisfies a Pareto-tail condition. Furthermore we give first insights into the existence of such solutions if in addition to production and knowledge exchange the knowledge level evolves by geometric Brownian motion

Germany, the Transatlantic Trade and Investment Partnership and investment-dispute settlement: Observations on a paradox

The use of subsidies to attract investment costs government billions of dollars annually, making regulation urgent. While comprehensive limitations such as the EU’s are not likely soon, we should improve transparency, have major stakeholders promote incentive rules within preferential trade areas, strengthen WTO notifications, and ban relocation subsidies where possibl

Long-term analysis of phenotypically structured models

Phenotypically structured equations arise in population biology to describe the interaction of species with their environment that brings the nutrients. This interaction usually leads to selection of the fittest individuals. Models used in this area are highly nonlinear, and the question of long term behaviour is usually not solved. However, there is a particular class of models for which convergence to an Evolutionary Stable Distribution is proved, namely when the quasi-static assumption is made. This means that the environment, and thus the nutrient supply, reacts immediately to the population dynamics. One possible proof is based on a Total Variation bound for the appropriate quantity. We extend this proof to several cases where the nutrient is regenerated with delay. A simple example is the chemostat with a rendering factor, then our result does not use any smallness assumption. For a more general setting, we can treat the case with a fast reaction of nutrient supply to the population dynamics

Populational adaptive evolution, chemotherapeutic resistance and multiple anti-cancer therapies

Resistance to chemotherapies, particularly to anticancer treatments, is an increasing medical concern. Among the many mechanisms at work in cancers, one of the most important is the selection of tumor cells expressing resistance genes or phenotypes. Motivated by the theory of mutation-selection in adaptive evolution, we propose a model based on a continuous variable that represents the expression level of a resistance gene (or genes, yielding a phenotype) influencing in healthy and tumor cells birth/death rates, effects of chemotherapies (both cytotoxic and cytostatic) and mutations. We extend previous work by demonstrating how qualitatively different actions of chemotherapeutic and cytostatic treatments may induce different levels of resistance. The mathematical interest of our study is in the formalism of constrained Hamilton-Jacobi equations in the framework of viscosity solutions. We derive the long-term temporal dynamics of the fittest traits in the regime of small mutations. In the context of adaptive cancer management, we also analyse whether an optimal drug level is better than the maximal tolerated dose

On interfaces between cell populations with different mobilities

Partial differential equations describing the dynamics of cell population densities from a fluid mechanical perspective can model the growth of avascular tumours. In this framework, we consider a system of equations that describes the interaction between a population of dividing cells and a population of non-dividing cells. The two cell populations are characterised by different mobilities. We present the results of numerical simulations displaying two-dimensional spherical waves with sharp interfaces between dividing and non-dividing cells. Furthermore, we numerically observe how different ratios between the mobilities change the morphology of the interfaces, and lead to the emergence of finger-like patterns of invasion above a threshold. Motivated by these simulations, we study the existence of one-dimensional travelling wave solutions.PostprintPeer reviewe

Eine Rahmenanwendung für die informelle Teamarbeit in Dokumentenbeständen

Die Zusammenarbeit an gemeinsam genutzten Dokumenten ist ein zentraler Aspekt virtueller Gemeinschaften und verteilt arbeitenden Teams. In diesem Beitrag werden die Konzepte und der Prototyp einer Rahmenanwendung vorgestellt, welche die informelle Zusammenarbeit in den Dokumentenbeständen virtueller Gemeinschaften unterstützt. Die Kernidee der vorgestellten Lösung liegt in der Einführung einer Dokumenten-Metapher in Verbindung mit einem feingranularen Rechtesystem, einem Konzept zur Strukturierung des Dokumentenraums und einer Strategie zur Verteilung von Dokumenten zwischen mehreren Speicherorten und zur Gewährleistung der Verfügbarkeit von Dokumenten bei nicht-permanenter Netzwerkanbindung. Auf der Grundlage dieser Konzepte werden Workflows auf spezielle Dokumente abgebildet, die durch die gleichen Mechanismen wie die eigentlichen Inhalte und Dokumente gespeichert, verwaltet und zwischen den einzelnen Nutzern verteilt werden