Micro-behaviors and structural properties of knowledge networks: toward a 'one size fits one'cluster policy

The economic returns of cluster policies have been recently called into question. Based on a “one size fits all” approach consisting in boosting R&D collaborations and reinforcing network density, cluster policies are suspected to have failed in reaching their objectives. The paper proposes to go back to the micro foundations of clusters in order to disentangle the links between the long run performance of clusters and their structural properties. We use a simple agent-based model to shed light on how individual motives to build knowledge relationships can give rise to emerging structures with different properties, which imply different innovation and renewal capacities. The simulation results are discussed in a micro-macro perspective, and motivate suggestions to reorient cluster policy guidelines towards more targeted public-funded incentives for R&D collaboration

Etude écologique des biotopes du criquet pèlerin Schistocerca gregaria (Forskal, 1775) en Afrique Nord-Occidentale : mise en évidence et description des unités territoriales écologiquement homogènes.

Les biotopes du criquet pèlerin, Schistocerca gregaria, en Afrique nord-occidentale sont décrits de façon standardisée, homogène et hiérarchisée. Vingt-six classes de biotopes sont finalement mises en évidence dans les trois zones éco-climatiques saharo-méditerranéennes, sahariennes et saharo-sahéliennes où évoluent les populations de solitaires. Les biotopes des zones méditerranéennes et sahéliennes, colonisés essentiellement en période d'invasion par les populations grégaires, font l'objet d'une description plus rapide. Les informations de base, dans leur intégralité, sont mises à la disposition du lecteur par le biais de nombreux tableaux et de quatre annexes. Ces informations peuvent être exploitées pour l'organisation des prospections dans le cadre de la lutte préventive contre les invasions du criquet pèlerin, ou à toute autre fin. Dépassant le cadre de la seule lutte antiacridienne, le présent ouvrage peut être perçu comme une contribution à la description des milieux sahariens

Conformational change in elastase following complexation with alpha1-proteinase inhibitor: a CD investigation.

The CD spectrum of porcine pancreatic elastase in complex with alpha1-proteinase inhibitor (alpha1-PI) was calculated by subtracting the CD spectrum of the proteolytically cleaved inhibitor from that of the elastase-alpha1-PI complex. Elastase undergoes a moderate secondary structure change: its beta-structure is partially disordered while its alpha-helix content is poorly affected. In contrast, its tertiary structure undergoes a significant structural loosening upon complexation. These alterations have been compared with those following chemical and thermal unfolding of free elastase. Inhibitor-bound elastase and the denaturation intermediate of free elastase share secondary but not tertiary structural features. On the other hand, both free and complexed elastases undergo a single-step transition in tertiary structure upon thermal unfolding. These data are discussed in terms of the inhibition and structural modification of elastase induced by alpha1-PI observed by previous investigators

Inhibition of Neutrophil Serine Proteinases by Suramin

International audienceSuramin, a hexasulfonated naphtylurea recently used as an anti-tumor drug, is a potent inhibitor of human neutrophil elastase, cathepsin G, and proteinase 3. The complexes it forms with these enzymes are partially active on synthetic substrates, but full inhibition takes place when elastase activity is measured with fibrous elastin or when cathepsin G activity is measured using platelet aggregation. One molecule of elastase binds four molecules of suramin with a Ki of 2 x 10(-7) M as determined by enzyme inhibition or intrinsic fluorescence enhancement of suramin. The binding curves show no sign of cooperativity or anticooperativity. The Ki for the complexes with cathepsin G and proteinase 3 are 8 x 10(-8) and 5 x 10(-7) M, respectively. Ionic strength increases the Ki of the elastase-suramin complex in a way that suggests that four of the six sulfonate groups of suramin form ionic interactions with basic residues of the enzyme and that at saturation almost all arginines of elastase form salt bridges with suramin. The neutrophil proteinase-inhibitory activity of suramin might be used to prevent tissue destruction and thrombus formation in diseases where massive infiltration and activation of neutrophils take place

THE NA (+)/H+ EXCHANGER NHE-1, A CRUCIAL CELLULAR INTEGRATOR CONTROLLED BY ITS MEMBRANE ENVIRONMENT

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