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.     

Stability analysis of inclined stratified two-phase gas-liquid flow

The present investigation involves the modeling of gas-liquid interface in a two-phase stratified flow through a horizontal or nearly-horizontal circular duct. The most complete and fundamental model used for these calculations is known as the one-dimensional two-fluid model. It is the most accurate of the two-phase models since it considers each phase independently and links both phases with six conservation equations. The mass and momentum balance equations are written in dimensionless form. The dimensionless mass and momentum balance equations are combined with the method of characteristics and an explicit method to simulate the flow. At first, the linear stability of the flow is investigated by disturbing the liquid flow with a small perturbation. An improved version of the one-dimensional two-fluid model for horizontal flows is developed as a set of non-linear hyperbolic governing equations. The importance of this research lies in obtaining a model that accounts for the effects of flow and geometrical conditions (such as liquid viscosity, surface tension). It is shown that, for positive values of the slope angle (upward inclination), the slug flow becomes more probable, whereas negative values of the slope angle (downward inclination) induce a more stable stratified flow.     

Locating eating pathology within an empirical diagnostic taxonomy: Evidence from a community-based sample.

Existing structural models of psychopathology need to be expanded to include additional diagnostic constructs beyond mood, anxiety, substance use, and antisocial behavior disorders. The goal of this study was to locate eating disorders within a hierarchical structural model of psychopathology that is anchored by broad Internalizing and Externalizing factors. Participants were female adolescent twins (N = 1,434) from the Minnesota Twin Family Study. The authors compared the fit of 4 models in which eating disorders (a) defined their own diagnostic class, (b) represented a subclass within Internalizing, (c) formed a subclass within Externalizing, and (d) were allowed to cross-load on both Internalizing and Externalizing. In the best fitting model, eating disorders formed a subfactor within Internalizing. These findings underscore the value of developing more comprehensive empirically based models of psychopathology to increase researchers' understanding of diverse mental disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparing the growth of a molecular semiconductor on amorphous and semi-crystalline polycarbonate substrates

Polymeric substrates are of importance in plastic electronics. However, polymeric surfaces can exhibit different morphologies depending on whether they are amorphous or semi-crystalline. This work focuses on the impact of the surface structure of bisphenol A polycarbonate substrates on the nucleation and growth of a p-type semi-conductor, namely zinc phthalocyanine (ZnPc). ZnPc films were deposited under high vacuum at different substrate temperatures on oriented semi-crystalline as well as amorphous substrates of PC. The oriented substrates of PC were prepared by a method combining mechanical rubbing and solvent induced crystallization: the substrates show a periodic and regular alternation of oriented crystalline lamellae. Grazing incidence X-ray diffraction shows that the crystalline lamellae of PC have a preferential (a, c) contact plane. Moreover, the substrates show a bilayer structure made of a 60 nm-thick semi-crystalline overlayer atop an amorphous underlayer. UV–vis spectroscopy shows that the polymorphism of the ZnPc films is not modified by the surface structure of the PC substrate (amorphous versus semi-crystalline). However, the statistical analysis of domain size and density versus substrate temperature T_s evidences different apparent activation energies of the growth mechanism. High Resolution Transmission Electron Microscopy suggests that twinning along a (2 ?1 0) plane accounts for the bifurcations of the in-plane b-axis direction of the ZnPc nanocrystals. On oriented substrates of PC, such bifurcations are partly suppressed by the nanocorrugation of the surface, resulting in larger apparent domain sizes and unidirectional in-plane orientation.     

Mise en évidence expérimentale des interactions entre pâte interstitielle et granulats dans l’écoulement du béton frais vibré

L’étude du comportement mécanique du béton frais est abordée en considérant ce matériau très hétérogène comme un milieu diphasique, pate interstitielle-granulats. La caractérisation propre de chaque phase ne suffit pas pour décrire le comportement global du matériau. Les interactions entre granulats et pate interstitielle doivent être impérativement prises en considération; elles sont analysées à travers l’étude expérimentale d’un écoulement sous charge constante et sous vibrations dans un ajutage à axe vertical. Les granulats interviennent dans l’écoulement du béton frais vibré par des actions d’encombrement qui tendent à gêner l’écoulement mais aussi par des effets liés à leur masse volumique qui peuvent, en fonction de la différence de masse volumique pate-granulats, favoriser l’écoulement. Summary The study of the mechanical behaviour of fresh concrete is approached considering this very heterogeneous material as a diphasic medium (interstitial paste-aggregates). The specific characterization of each phase is not sufficient to describe the complete behaviour of the mix. The mutual actions of aggregates and interstitial paste must be imperatively taken into account; they are analysed with the aid of an experimental study of the flow through a vertical nozzle under constant load and vibrations. Aggregates appear in the fresh concrete flow through actions of hindrance reactions which impede the flow, but also through effects of gravity which can aid the flow in function of the difference of density between aggregates and interstitial paste.      

Study of Nicalon-based ceramic fibres and powders by EXAFS spectrometry,X-ray diffractometry and some additional methods

The Nicalon SiC-based ceramic fibres and their precursors have been investigated by complementary techniques: EXAFS, WAXS, ESCA and NMR. For SiC-Nicalon fibres, an alternative model is proposed based on a microcrystalline structure where pureβ-SiC is embedded in a continuum of tetrahedral SiC_xO_y(x+y=4). We have found that the inorganic material skeleton is already contained in the carbon and silicon structure of the polymer precursor.     

Characterization of hydrogen production by Platymonas Subcordiformis in torus photobioreactor

Platymonas subcordiformis, a marine green alga, was demonstrated to photo-biologically produce hydrogen when regulated by a kind of proton uncoupler CCCP (Carbonyl Cyanide m-Chlorophenylhydrazone). In this paper, hydrogen production experiments by P. subcordiformis were carried out in a torus photobioreactor equipped with a mass spectrometer and other necessary sensors so that instantaneous gas components could be measured and other successive physiological states could be well recorded.