2,286 research outputs found
Intermittency on catalysts
The present paper provides an overview of results obtained in four recent
papers by the authors. These papers address the problem of intermittency for
the Parabolic Anderson Model in a \emph{time-dependent random medium},
describing the evolution of a ``reactant'' in the presence of a ``catalyst''.
Three examples of catalysts are considered: (1) independent simple random
walks; (2) symmetric exclusion process; (3) symmetric voter model. The focus is
on the annealed Lyapunov exponents, i.e., the exponential growth rates of the
successive moments of the reactant. It turns out that these exponents exhibit
an interesting dependence on the dimension and on the diffusion constant.Comment: 11 pages, invited paper to appear in a Festschrift in honour of
Heinrich von Weizs\"acker, on the occasion of his 60th birthday, to be
published by Cambridge University Pres
Intermittency on catalysts: three-dimensional simple symmetric exclusion
We continue our study of intermittency for the parabolic Anderson model
in a space-time random medium
, where is a positive diffusion constant, is the lattice
Laplacian on , , and is a simple symmetric exclusion
process on in Bernoulli equilibrium. This model describes the evolution
of a \emph{reactant} under the influence of a \emph{catalyst} .
In G\"artner, den Hollander and Maillard (2007) we investigated the behavior
of the annealed Lyapunov exponents, i.e., the exponential growth rates as
of the successive moments of the solution . This led to an
almost complete picture of intermittency as a function of and . In
the present paper we finish our study by focussing on the asymptotics of the
Lyaponov exponents as in the \emph{critical} dimension ,
which was left open in G\"artner, den Hollander and Maillard (2007) and which
is the most challenging. We show that, interestingly, this asymptotics is
characterized not only by a \emph{Green} term, as in , but also by a
\emph{polaron} term. The presence of the latter implies intermittency of
\emph{all} orders above a finite threshold for .Comment: 38 page
Insights into invasion and restoration ecology : time to collaborate towards a holistic approach to tackle biological invasions
The aim of our study is to provide an integrated framework for the management of alien plant invasions, combining insights and experiences from the fields of invasion and restoration ecology to enable more effective management of invasive species. To determine linkages between the scientific outputs of the two disciplines we used an existing data base on restoration studies between 2000 and 2008 and did a bibliometric analysis. We identified the type of restoration applied, determined by the aim of the study, and conducted a content analysis on 208 selected studies with a link to biological invasions (invasion-restoration studies). We found a total of 1075 articles on ecosystem restoration, with only eight percent of the studies having the main objective to control alien invasions. The content analysis of 208 invasion-restoration studies showed that the majority of the studies focused on causes of degradation other than alien invasions. If invaders were referred to as the main driver of degradation, the prevalent cause for degradation was invaders outcompeting and replacing native species. Mechanical control of alien plant invasions was by far the most common control method used. Measures that went beyond the removal of alien plants were implemented in sixty-five percent of the studies. Although invasion control was not as common as other types of restoration, a closer look at the sub-group of invasion-restoration studies shows a clear link between restoration and invasion ecology. Concerns, as identified in the literature review, are firstly that restoration activities mostly focus on controlling the invader while other underlying causes for degradation are neglected, and secondly that the current approach of dealing with alien invasions lacks a combination of theoretical and practical aspects. We suggest that closer collaboration between invasion and restoration ecologists can help to improve the management of alien plant invasions. We conclude with a framework and a case study from Perth Western Australia integrating the two disciplines, with the aim of informing restoration practice
Common Ingroup Identity Model
This entry introduces the Common Ingroup Identity Model. In intergroup interactions, it is possible for ingroup members to make biased judgments toward both ingroup and outgroup members. People tend to evaluate ingroup members positively and outgroup members negatively. The Common Ingroup Identity Model proposes that intergroup bias can be reduced by transforming the group boundaries from âusâ versus âthemâ into a more general âweâ that include all the original in- and outgroup members
Utilisation de modĂšles linĂ©aires gĂ©nĂ©ralisĂ©s pour Ă©valuer les stratĂ©gies de pĂȘche thoniĂšre Ă la senne en prĂ©sence d'espĂšces associĂ©es dans l'Atlantique ouest
Les stratĂ©gies de pĂȘche, dĂ©veloppĂ©es par les capitaines des thoniers senneurs vĂ©nĂ©zuĂ©liens dans la mer des CaraĂŻbes, reposent sur la recherche d'indices visuels indiquant la prĂ©sence de thons Ă la surface de l'ocĂ©an. Une fois que la dĂ©tection est rĂ©alisĂ©e, le senneur peut choisir la tactique qui consiste Ă demander l'aide d'un thonier canneur (pĂȘche Ă l'appĂąt vivant) afin d'augmenter le taux de rĂ©ussite d'un coup de senne. Pour prendre en compte la variabilitĂ© de diffĂ©rents facteurs, comme la saison, les indices de dĂ©tection associĂ©s aux bancs, l'aide du thonier canneur, les espĂšces de thons et le poids moyen des poissons prĂ©sents dans le banc, les probabilitĂ©s de rĂ©alisation de certains Ă©vĂ©nements sont estimĂ©es Ă l'aide de la modĂ©lisation Logit, issue de modĂšles Log-linĂ©aires. Les probabilitĂ©s de capturer des bancs de gros individus sont maximales lorsque l'albacore est l'espĂšce dominante et que la pĂȘche a lieu sur banc libre ou sur requin-baleine ; cet effet est d'autant plus marquĂ© en saison sĂšche. En revanche, si le listao est l'espĂšce dominante, la probabilitĂ© de capturer des gros individus est faible, en particulier lorsque la pĂȘche est rĂ©alisĂ©e sur des baleines. Les rĂ©sultats de cette modĂ©lisation sont intĂ©grĂ©s dans un arbre de dĂ©cision. Si on retient le critĂšre de l'espĂ©rance mathĂ©matique des gains potentiels, l'aide du thonier canneur ne semble pas ĂȘtre la meilleure des tactiques possibles. Pourtant son impact est positif sur le taux de rĂ©ussite d'un coup de senne, puisque le pourcentage de calĂ©es positives passe de 58% sans aide Ă 85% avec aide. L'efficacitĂ© de cette aide dĂ©pend du type d'association rencontrĂ©. Elle augmente lorsqu'il s'agit de bancs libres ou en association avec des baleines, mais diminue lorsque le banc est associĂ© Ă un requin-baleine... (D'aprĂšs rĂ©sumĂ© d'auteur
Managing for change: March 6, 1989
Bi-weekly newsletter of University Hospital's Change Project, provided to managers at the hospital
Der einfluss von epsilon-aminokapronsaure (eaca) auf die plasma-gerinnungszeit
Man bestimmte die Gerinnungszeit einer Mischung von 0.1 ml des frischen Zitratplasmas, 0.1 ml einer Epsilon-Aminokapronsäure-Lösung in Konzentrationen
von 0, 02, 0.5, 2.5, 10, 20, 50 und 100 gamma, 0.1 ml CaCl² Lösung und 0.1 ml Michaelis' Puffer. Die erwähnten EACA-Konzentrationen hatten keinen charakteristischen Einfluss auf die Rekalzifikationszeit des frischen und des gelösten lyophilisierten Plasmas.</p
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