Characterization of the growth of 2D protein crystals on a lipid monolayer by ellipsometry and rigidity measurements coupled to electron microscopy

We present here some sensitive optical and mechanical experiments for monitoring the process of formation and growth of two-dimensional (2D) crystals of proteins on a lipid monolayer at an air-water interface. The adsorption of proteins on the lipid monolayer was monitored by ellipsometry measurements. An instrument was developed to measure the shear elastic constant (in plane rigidity) of the monolayer. These experiments have been done using cholera toxin B subunit (CTB) and annexin V as model proteins interacting with a monosialoganglioside (GM1) and dioleoylphosphatidylserine (DOPS), respectively. Electron microscopy observations of the protein-lipid layer transferred to grids were systematically used as a control. We found a good correlation between the measured in-plane rigidity of the monolayer and the presence of large crystalline domains observed by electron microscopy grids. Our interpretation of these data is that the crystallization process of proteins on a lipid monolayer passes through at least three successive stages: 1) molecular recognition between protein and lipid-ligand, i.e., adsorption of the protein on the lipid layer; 2) nucleation and growth of crystalline patches whose percolation is detected by the appearance of a non-zero in-plane rigidity; and 3) annealing of the layer producing a slower increase of the lateral or in-plane rigidity.     

Traitement anodique de suspensions de poudre de graphite sur des électrodes de métal déployé

Résumé L'article présente une étude expérimentale de l'oxydation anodique de suspensions de particules de graphite dans un réacteur fermé agité puis dans un réacteur ouvert dont l'amenée de courant anodique est un empilement de grilles de métal déployé traversé par la suspension. L'influence de plusieurs paramètres est examinée.

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This paper reports an experimental study of the anodic oxidation of suspensions of graphite particles in two types of cell, a closed stirred cell and a flow-through cell. In the latter case the anodic current feeder is a grid or a stack of grids of expanded metal; the suspension flows through this current feeder. The influence of various parameters is investigated.

     

The effects of vibrations on the rheological behaviour of bentonite muds. Comparison with cement pastes

The bentonite muds, widely used in civil engineering and in the oil industry, have a binghamian and thixotropic behaviour, that impedes their flow (pumping, displacement by a slurry, etc). A mechanical vibration able to reduce this rheological character, as it does with fresh cement pastes, would improve the flow. Unfortunately vibrations, whatever their frequency may be (from 0 to 3000 Hz) and acceleration (from 1 to 55 times the gravity one) reduce neither the yield-value nor the thixotropic activity of the muds. This results from the structure of the solid phase which is not very resistant but particularly deformable, contrary to the fresh cement pastes: vibration amplitude is not enough to break the bonds between bentonite particles.     

A trilogy on surfaces. II. On Gibb's adsorption equation and Antonow's law

The Gibb's adsorption equations for a multicomponent multiphase system are used to discuss the relationship between the surface tensions and interfacial tension. It is shown for binary systems that when the terms involving the surface excesses vanish, Antonow's rule is obtained.     

Contribution à l'étude de la rhéologie du béton frais

Résumé Cette étude comprend trois parties, intitulées respectivement: ?Les mesures en rhéologie des mortiers?, ?Les comportements rhéologiques des mortiers?, et ?L'influence de la composition des mortiers sur leur viscosité?. Elle a fait l'objet d'une thèse de Doctorat ès-Sciences Physiques présentée à l'Université Paul Sabatier de Toulouse et soutenue le 27 avril 1971. Etant donné son importance, nous ne publions dans ce numéro que les deux premières parties; la publication de la troisième partie est prévue dans notre prochain numéro.     

Demonstration projects and sustainable housing

Because of the complicated structure of the built environment, it is frequently difficult to obtain good results on sustainable development projects. In The Netherlands, the Dutch government have used a range of new steering instruments which have cleverly enabled innovation to take place within a market economy. This imaginative governmental process uses covenants, network management and above all, demonstration projects to assess the feasibility of innovation. The authors describe the process and consider examples from energy efficient and sustainable housing, highlighting the importance of clear targets.     

Les comportements rheologiques du mortier frais

There are two critical values of the concentration C of the dispersed solid in fresh mortars called C_i and C_d such that, for angular granulates, when C ? C_i, the behaviour is binghamian at rest and pseudoplastic when the mortar is vibrated; when C ? C_d, it is dilatant in the two cases and when C_i < C < C_d, it is unstable. For spherical granulates, these behaviours are unchanged, except under vibration when C ? C_i : in this case, the behaviour is newtonian. These changes of behaviour are explained by structural modifications in the packing of particles : dilatancy comes out with close-packing while instability appears with maximum loose-packing.