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 $\partial u/\partial t = \kappa\Delta u + \xi u$ in a space-time random medium $\xi$, where $\kappa$ is a positive diffusion constant, $\Delta$ is the lattice Laplacian on $\Z^d$, $d \geq 1$, and $\xi$ is a simple symmetric exclusion process on $\Z^d$ in Bernoulli equilibrium. This model describes the evolution of a \emph{reactant} $u$ under the influence of a \emph{catalyst} $\xi$. In G\"artner, den Hollander and Maillard (2007) we investigated the behavior of the annealed Lyapunov exponents, i.e., the exponential growth rates as $t\to\infty$ of the successive moments of the solution $u$. This led to an almost complete picture of intermittency as a function of $d$ and $\kappa$. In the present paper we finish our study by focussing on the asymptotics of the Lyaponov exponents as $\kappa\to\infty$ in the \emph{critical} dimension $d=3$, 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 $d\geq 4$, but also by a \emph{polaron} term. The presence of the latter implies intermittency of \emph{all} orders above a finite threshold for $\kappa$.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

Utilisation de modèles linéaires généralisés pour évaluer les stratégies de pêche thonière à la senne en présence d'espèces associées dans l'Atlantique ouest

Les stratégies de pêche, développées par les capitaines des thoniers senneurs vénézuéliens dans la mer des Caraïbes, reposent sur la recherche d'indices visuels indiquant la présence de thons à la surface de l'océan. Une fois que la détection est réalisée, le senneur peut choisir la tactique qui consiste à demander l'aide d'un thonier canneur (pêche à l'appât vivant) afin d'augmenter le taux de réussite d'un coup de senne. Pour prendre en compte la variabilité de différents facteurs, comme la saison, les indices de détection associés aux bancs, l'aide du thonier canneur, les espèces de thons et le poids moyen des poissons présents dans le banc, les probabilités de réalisation de certains événements sont estimées à l'aide de la modélisation Logit, issue de modèles Log-linéaires. Les probabilités de capturer des bancs de gros individus sont maximales lorsque l'albacore est l'espèce dominante et que la pêche a lieu sur banc libre ou sur requin-baleine ; cet effet est d'autant plus marqué en saison sèche. En revanche, si le listao est l'espèce dominante, la probabilité de capturer des gros individus est faible, en particulier lorsque la pêche est réalisée sur des baleines. Les résultats de cette modélisation sont intégrés dans un arbre de décision. Si on retient le critère de l'espérance mathématique des gains potentiels, l'aide du thonier canneur ne semble pas être la meilleure des tactiques possibles. Pourtant son impact est positif sur le taux de réussite d'un coup de senne, puisque le pourcentage de calées positives passe de 58% sans aide à 85% avec aide. L'efficacité de cette aide dépend du type d'association rencontré. Elle augmente lorsqu'il s'agit de bancs libres ou en association avec des baleines, mais diminue lorsque le banc est associé à un requin-baleine... (D'après résumé 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-Aminokaprons&#228;ure-L&#246;sung in Konzentrationen von 0, 02, 0.5, 2.5, 10, 20, 50 und 100 gamma, 0.1 ml CaCl&#178; L&#246;sung und 0.1 ml Michaelis' Puffer. Die erw&#228;hnten EACA-Konzentrationen hatten keinen charakteristischen Einfluss auf die Rekalzifikationszeit des frischen und des gel&#246;sten lyophilisierten Plasmas.</p

The Community Influence of Sponge and Coral Aquaculture in Zanzibar

Aquaculture has been presented as a means of income for coastal communities, particularly in the context of climate change and resource exploitation. The NGO Marine Cultures in Jambiani, Zanzibar has established a sponge cultivation program for women in response to declining feasibility of seaweed farming from warming ocean temperatures. In addition, the organization strives to restore a severely damaged reef while providing employment for coral farmers and tour boat operators. This study analyzed the influence of aquaculture on community stakeholders, primarily with respect to sponge cultivation and secondarily in regard to coral farms. Using Marine Cultures as a case study, the principal aim was to investigate the impacts of sponge farms on the lives of women, with supplementary examination of the coral project and potential for community benefit. Participant observation and interviews were employed to generate qualitative data about the farms themselves, Marine Cultures, and the individuals impacted, predominantly women sponge farmers. The results of the study were a holistic narrative of Marine Cultures, four biographical sketches (three sponge farmers and one coral farmer) and a clear representation of aquaculture’s benefits to individuals. Dhahania Kilimo bahari kilifanywa ikiwa ni njia ya kujipatia kipato kwa jamii ya watu wa mwambao wa Jambiani, Katika kukabiliana na hali ya tabia nchi na uvunaji wa maliasili. Taasisi isiyo ya kiserikali ya Kilimo bahari katika eneo la Jambiani, Zanzibar walianzisha upandaji wa spongi bahari (vinja bahari) kwa Wanawake kutoka na wasiwasi wa kushuka kwa uzalishaji wa mwani kutokana na kupanda kwa joto la bahari. Kwa kuongezeka, taasisi hii inaangalia uwezekano wa kurejesha matumbawe yaliyoathiriwa kwa kiwango kikubwa wakati huohuo wakitoa ajira kwa Wakulima wa Matumbawe pamoja waendesha boti. Utafiti huu ulichunguza pamoja na kuchambua ushawishi wa kilimo bahari kwa washika dau wa jamii ya Jambiani, kimsingi kwa kuzingatia kilimo cha Spongi na kilimo cha Matumbawe. Kwa kutumia jumuiya ya “Marine Culture” eneo la Kujifunzia, Madhumuni ya msingi yalikuwa ni utafiti kilimo cha mashamba ya spongi pamoja na maisha ya wakulima wa kike, utafiti wa ziada wa kilimo cha Matumbawe na faida kilimo kwa wanajamii. Uchunguzi kwa vitendo na mahojiano ulifanyika ili kuweza kupata data kuhusiana na mashamba yao, Kilimo bahari, na waathirika, Mara nyingi wakulima wa spongi ni wanawake. Matokeo ya utafiti huu ni kwa ujumla yanasimulia “Marine Cultures,” 4 michoro ya kibinadamu (3 wakulima wa spongi, 1 mkulima wa matumbawe) na uwakilishi mzuri wa faida kwa kilimo mmoja