Growth limiting conditions and denitrification govern extent and frequency of volume detachment of biofilms

This study aims at evaluating the mechanisms of biofilm detachment with regard of the physical properties of the biofilm. Biofilms were developed in Couette–Taylor reactor under controlled hydrodynamic conditions and under different environmental growth conditions. Five different conditions were tested and lead to the formation of two aerobic heterotrophic biofilms (aeHB1 and aeHB2), a mixed autotrophic and heterotrophic biofilm (MAHB) and two anoxic heterotrophic biofilms (anHB1 and anHB2). Biofilm detachment was evaluated by monitoring the size of the detached particles (using light-scattering) as well as the biofilm physical properties (using CCD camera and image analysis). Results indicate that volume erosion of large biofilm particles with size ranging from 50 to 500 lm dominated the biomass loss for all biofilms. Surface erosion of small particles with size lower than 20 lm dominates biofilm detachment in number. The extent of the volume detachment events was governed by the size of the biofilm surface heterogeneities (i.e., the absolute biofilm roughness) but never impacted more than 80% of the mean biofilm thickness due to the highly cohesive basal layer. Anoxic biofilms were smoother and thinner than aerobic biofilms and thus associated with the detachment of smaller particles. Our results contradict the simplifying assumption of surface detachment that is considered in many biofilm models and suggest that discrete volume events should be considered

RESOUDRE UN PROBLEME D’ASYMETRIE D’INFORMATION EN S’ABSTENANT DE FAIRE DU PROFIT : LES ORGANISATIONS SANS BUT LUCRATIF REPONDENT-ELLES A UNE DEMANDE DE BIENS DE CONFIANCE ?

Contract Failure Theory (CFT) argues that the Non Distribution Constraint prototypical of Non Profit Organizations (NPOs) plays the role of a safeguard given to buyers of “trust goods”, the latter of which involving dramatic asymmetrical information. Although stimulating, such a paradigm stumbles over the coexistence of firms and commercial NPOs on markets for nursing, medical services and education. Thus, it calls for further discussion in order to study its premises and prescriptions more closely. Existing literature obviously helps to achieve such an analytical project although it does not always specify the type of good –nor the type of consumer- CFT should the more rigorously be applied to. Therefore, our paper is willing to (a) identify the contractual problems specifically attached to trust goods, (b) sketch conditions making for profit provision of trust goods viable and (c) figure out devices complementary to non profit status that could emphasise the competitive advantage of commercial NPOs. It concludes that non profit status signals a specific ability to deal with the distorted rationality of some consumers rather than resolving an overall “contract failure” rooted in a general problem of asymmetrical information.La théorie de l'échec du contrat (CFT) pare le statut sans but lucratif d'une fonction discriminante de garantie apportée aux agents privés demandeurs de « biens de confiance », ces derniers donnant prise à d'insurmontables asymétries informationnelles. Quoique stimulante, la CFT peine cependant à expliquer la coexistence entre firmes et organisations sans but lucratif sur leurs secteurs d offre communs : services de prise en charge, soins et éducation. Elle appelle donc une discussion théorique visant à délimiter son périmètre d'application. L'examen des travaux théoriques et empiriques inspirés de la CFT fournit à ce travail d'analyse, d'indispensables jalons ; cependant, la littérature pèche par un défaut de spécification des types de biens –et de consommateurs-auxquels le périmètre de l'échec du contrat s'applique le plus sûrement. Ce papier tente donc (a) d'identifier les problèmes de contractualisation spécifiquement posés par les biens de confiance, (b) d'esquisser les conditions de viabilité de l'offre des firmes et (c) de dégager les conditions auxquelles les NPOs commerciales peuvent se prévaloir d'un avantage concurrentiel discriminant. Ce faisant, nous suggérons la conclusion suivante : plutôt qu'à un problème générique d'asymétrie informationnelle, les NPOs peuvent être conçues en tant que réponse institutionnelle à l'introuvable rationalité de certains consommateurs

CAN MARKET ECONOMY BE ECOLOGY-FRIENDLY ? THE CASE OF WASTE RECYCLING IN THE NINETEENTH CENTURY

International audienceSustainable development theorists frequently stress various ways by which market economies could be reformed in order to preserve the natural environment. Regulatory interventionism or ethical activism are frequently stressed a normative way in order to fulfil such an institutional task. European industrial history, however, suggests that the creation of valuable by-products from polluting industrial waste and emissions was “business as usual”, resting on economic behaviors brought about a free market economy. This case suggests that market incentives might have been more compatible with "environmental responsibility" than is usually believed

Parameter and State Estimation of an Anaerobic Digestion of Organic Wastes Model with Addition of Stimulating Substances

New control inputs are introduced in the 5th order mass-balance non-linear model of the anaerobic digestion, which reflects the addition of stimulating substances (acetate and glucose). Laboratory experiments have been done with step-wise and pulse changes of these new inputs. On the basis of the step responses of the measured variables (biogas flow rate and acetate concentration in the bioreactor) and iterative methodology, involving non-linear optimisation and simulations, the model coefficients have been estimated. The model validity has been proved by another set of experiments. The observation part is built on a two-step structure. One estimator and two observers are designed on the basis of this process model. Their stability has been proved and their performances have been investigated with experimental data and simulations

La croissance économique des grandes ONG françaises : facteurs-clés et principaux enjeux institutionnels

National audienceDepuis une trentaine d’années, les ONG ont connu une croissance importante de leurs ressources financières. Il s’agit d’une tendance internationale à laquelle la France ne fait pas exception, les « associations de solidarité internationale » (qu’on assimilera aux ONG) ayant substantiellement augmenté leur collecte de dons privés et de financements publics, depuis les années 1980. Surtout, cet âge d’or a permis à certaines associations d’atteindre une dimension économique considérable, porteuse d’enjeux de structure importants et de questionnements identitaires concomitants. Cette communication s’efforcera de faire un point général sur la situation économique des grandes ONG françaises : on analysera, à partir de leurs comptes annuels, la structure de leurs ressources ainsi que les contraintes de gestion qui s’y attachent. On s’interrogera également sur les conséquences de cette prospérité sur leur image et leur identité institutionnelles

ENTREPRENEURIAL DISCOVERY AS A BLIND SPOT OF ENVIRONMENTAL ECONOMICS

Cette communication devrait prochainement donner lieu à publication d'un chapitre d'ouvrage.International audienceSustainable development theorists and environmental economists almost invariably promote greater fiscal, regulatory and ethical activism as desirable means to reconcile economic development and environmental protection. Closer examination of industrial behaviour during the nineteenth and early twentieth century, however, suggests that market economies might be more self-correcting in this respect than generally acknowledged. A case in point is the long-standing, spontaneous and widespread creation of valuable by-products out of once polluting waste and emissions. By documenting how market incentives and institutions played the key roles in this respect, this paper challenges the foundations of the now dominant environmental market failure paradigm

VLBI observations of jupiter with the initial test station of LOFAR and the nancay decametric array

AIMS: To demonstrate and test the capability of the next generation of low-frequency radio telescopes to perform high resolution observations across intra-continental baselines. Jupiter's strong burst emission is used to perform broadband full signal cross-correlations on time intervals of up to hundreds of milliseconds. METHODS: Broadband VLBI observations at about 20 MHz on a baseline of ~50000 wavelengths were performed to achieve arcsecond angular resolution. LOFAR's Initial Test Station (LOFAR/ITS, The Netherlands) and the Nancay Decametric Array (NDA, France) digitize the measured electric field with 12 bit and 14 bit in a 40 MHz baseband. The fine structure in Jupiter's signal was used for data synchronization prior to correlation on the time-series data. RESULTS: Strong emission from Jupiter was detected during snapshots of a few seconds and detailed features down to microsecond time-scales were identified in dynamic spectra. Correlations of Jupiter's burst emission returned strong fringes on 1 ms time-scales over channels as narrow as a hundred kilohertz bandwidth. CONCLUSIONS: Long baseline interferometry is confirmed at low frequencies, in spite of phase shifts introduced by variations in ionospheric propagation characteristics. Phase coherence was preserved over tens to hundreds of milliseconds with a baseline of ~700 km. No significant variation with time was found in the correlations and an estimate for the fringe visibility of 1, suggested that the source was not resolved. The upper limit on the source region size of Jupiter Io-B S-bursts corresponds to an angular resolution of ~3 arcsec. Adding remote stations to the LOFAR network at baselines up to thousand kilometers will provide 10 times higher resolution down to an arcsecond.Comment: 6 pages, 4 figures. Nigl, A., Zarka, P., Kuijpers, J., Falcke, H., Baehren, L., VLBI observations of Jupiter with the Initial Test Station of LOFAR and the Nancay Decametric Array, A&A, 471, 1099-1104, accepted on 31/05/200

Characterization and Derivation of Heard-Of Predicates for Asynchronous Message-Passing Models

In distributed computing, multiple processes interact to solve a problem together. The main model of interaction is the message-passing model, where processes communicate by exchanging messages. Nevertheless, there are several models varying along important dimensions: degree of synchrony, kinds of faults, number of faults... This variety is compounded by the lack of a general formalism in which to abstract these models. One way to bring order is to constrain these models to communicate in rounds. This is the setting of the Heard-Of model, which captures many models through predicates on the messages sent in a round and received on time. Yet, it is not easy to define the predicate that captures a given operational model. The question is even harder for the asynchronous case, as unbounded message delay means the implementation of rounds must depend on details of the model. This paper shows that characterising asynchronous models by heard-of predicates is indeed meaningful. This characterization relies on delivered predicates, an intermediate abstraction between the informal operational model and the heard-of predicates. Our approach splits the problem into two steps: first extract the delivered model capturing the informal model, and then characterize the heard-of predicates that are generated by this delivered model. For the first part, we provide examples of delivered predicates, and an approach to derive more. It uses the intuition that complex models are a composition of simpler models. We define operations like union, succession or repetition that make it easier to derive complex delivered predicates from simple ones while retaining expressivity. For the second part, we formalize and study strategies for when to change rounds. Intuitively, the characterizing predicate of a model is the one generated by a strategy that waits for as much messages as possible, without blocking forever