Visuo-motor performance in children visually impaired due to fetal alcohol syndrome (FAS)

Purpose: To investigate the ophthalmological characteristics and to evaluate the magnocellular function in Russian orphanage children with fetal alcohol syndrome (FAS). Methods: In the study 100 children aged 10-16 from Russian (St Petersburg) orphanages were examined: 50 with FAS and 50 control children. In the first study all 100 children were tested with distant visual acuity with subjective optimal correction (VA; Sivtsev chart), skiascopy, visual inspection for FAS external ocular features, biomicroscopy, eye alignment using cover test and indirect ophthalmoscopy.In the second study 89 children from above groups (49 with FAS and 40 controls) were included in the study. A coherent motion perception test was used. The test consisted of 150 white moving dots on a black background presented in different signal-to-noise ratio conditions. The task was direction detection of the coherently moving dots whose percentage decreased at each step of the test. Results: All analyzed parameters were worse in children with FAS compared with controls. FAS children showed a higher incidence of amblyopia, hyperopia, astigmatism and anisometropia. In FAS children the incidence of blepharophimosis was 34% (8% in controls), epicantus 14% (2% in controls), telecantus 32% (compared to 4% in controls), eye-lid ptosis 9% (none in controls) and strabismus 26% (10% in controls). Ophthalmoscopy revealed a tilted optic disc in five FAS-children (7%) compared with none in controls. In the Motion perception test a significant difference between the two groups was found (p = 0.018). Children with FAS had lower coherent motion perception ability in all the signal-to-noise ratio conditions. A significant difference between difficulty levels (p < 0.001) was found for all subjects in both groups – decreasing the stimulus signal-to-noise level decreased the motion perception score. In both groups, the motion perception score differed for vertical and horizontal stimuli (p = 0.003) with better performance for vertical stimuli. Conclusion: Russian FAS children show a higher incidence of structural and functional visual problems that needs to be taken into account and demands participation of the ophthalmologist in monitoring of those patients. Impaired motion perception in FAS children could be indicative of a magnocellular pathway developmental dysfunction resulting from alcohol brain damage

Influence of Charge Carrier Mobility on the Performance of Organic Solar Cells

The power conversion efficiency of organic solar cells based on donor--acceptor blends is governed by an interplay of polaron pair dissociation and bimolecular polaron recombination. Both processes are strongly dependent on the charge carrier mobility, the dissociation increasing with faster charge transport, with raised recombination losses at the same time. Using a macroscopic effective medium simulation, we calculate the optimum charge carrier mobility for the highest power conversion efficiency, for the first time accounting for injection barriers and a reduced Langevin-type recombination. An enhancement of the charge carrier mobility from $10^{-8}$m$^2$/Vs for state of the art polymer:fullerene solar cells to about $10^{-6}$m$^2$/Vs, which yields the maximum efficiency, corresponds to an improvement of only about 20% for the given parameter set.Comment: 3 pages, 4 figure

Modulating self-assembly of a nanotape-forming peptide amphiphile with an oppositely charged surfactant

A peptide amphiphile (PA) C16-KTTKS, containing a pentapeptide headgroup based on a sequence from procollagen I attached to a hexadecyl lipid chain, self-assembles into extended nanotapes in aqueous solution. The tapes are based on bilayer structures, with a 5.2 nm spacing. Here, we investigate the effect of addition of the oppositely charged anionic surfactant sodium dodecyl sulfate (SDS) via AFM, electron microscopic methods, small-angle X-ray scattering and X-ray diffraction among other methods. We show that addition of SDS leads to a transition from tapes to fibrils, via intermediate states that include twisted ribbons. Addition of SDS is also shown to enhance the development of remarkable lateral ‘‘stripes’’ on the nanostructures, which have a 4 nm periodicity. This is ascribed to counterion condensation. The transition in the nanostructure leads to changes in macroscopic properties, in particular a transition from sol to gel is noted on increasing SDS (with a further reentrant transition to sol on further increase of SDS concentration). Formation of a gel may be useful in applications of this PA in skincare applications and we show that this can be controlled via development of a network of fine stranded fibrils

Structure Transition in PSS/Lysozyme Complexes: A Chain-Conformation-Driven Process, as Directly Seen by Small Angle Neutron Scattering

Measurements of chain conformation in proteins/polyelectrolytes complexes (lysozyme and PSSNa) show that the crossover observed between an open structure -a chain network crosslinked by the proteins, and a globular one - dense globules of ~ 10 nm aggregated in a fractal way, results from a conformation modification prior to the transition. Before showing this, we have widened the parameters range for the observation of the transition. We had shown before that the two structures can be formed depending on chain length (for a given [PSS]/[lysozyme] ratio): gel for large chains, globules for short chains. We show here that the crossover between these two regimes can also be reached as a function of chains concentration or salinity of the buffer. Since all these crossover parameters act on chains overlapping concentration c*, we reinforce the idea of a transition from the dilute to the semi-dilute regime, but c* is shifted compared to pure PSS solutions. In order to understand this, we have measured by SANS the conformation of a single chain of PSS in presence of proteins within the complexes. This is achieved by a specific labeling trick where we take advantage of the fact that lysozyme and hydrogenated PSS chains have the same neutron scattering length density. In the gel structure, the PSS chains keep a wormlike structure as in pure solutions, but their persistence length is strongly reduced, from 50 {\AA} without proteins to 20 {\AA} in average with lysozyme. With this value of 20 {\AA}, we calculate new overlapping thresholds (concentration, mass, ionic strength) in agreement with observed ones. In a second stage, after the globular structure is formed, the PSS chains get a third conformation, no longer wormlike, but more collapsed, within the globules

Concentration dependent pathways in spontaneous self-assembly of unilamellar vesicles

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.We report on the structural dynamics underlying the formation of unilamellar vesicles upon mixing dilute solutions of anionic and zwitterionic surfactant solutions. The spontaneous self-assembly was initiated by rapid mixing of the surfactant solutions using a stopped-flow device and the transient intermediate structures were probed by time-resolved small-angle X-ray scattering. The initial surfactant solutions comprised of anionic lithium perfluorooctanoate and zwitterionic tetradecyldimethylamine oxide, where the mixtures form unilamellar vesicles over a wide range of concentrations and mixing ratios. We found that disk-like transient intermediate structures are formed at higher concentrations while more elongated forms such as cylinder-like and torus-like micelles are involved at lower concentrations. These differences are attributed to monomer addition mechanism dominating the self-assembly process when the initial concentration is well below the critical micellar concentration of the anionic surfactant, while at higher concentrations the process is governed by fusion of disk-like mixed micelles. This means that the pathway of vesicle formation is determined by the proximity to the critical micellar concentration of the more soluble component

Multiple Scale Reorganization of Electrostatic Complexes of PolyStyrene Sulfonate and Lysozyme

We report on a SANS investigation into the potential for these structural reorganization of complexes composed of lysozyme and small PSS chains of opposite charge if the physicochemical conditions of the solutions are changed after their formation. Mixtures of solutions of lysozyme and PSS with high matter content and with an introduced charge ratio [-]/[+]intro close to the electrostatic stoichiometry, lead to suspensions that are macroscopically stable. They are composed at local scale of dense globular primary complexes of radius ~ 100 {\AA}; at a higher scale they are organized fractally with a dimension 2.1. We first show that the dilution of the solution of complexes, all other physicochemical parameters remaining constant, induces a macroscopic destabilization of the solutions but does not modify the structure of the complexes at submicronic scales. This suggests that the colloidal stability of the complexes can be explained by the interlocking of the fractal aggregates in a network at high concentration: dilution does not break the local aggregate structure but it does destroy the network. We show, secondly, that the addition of salt does not change the almost frozen inner structure of the cores of the primary complexes, although it does encourage growth of the complexes; these coalesce into larger complexes as salt has partially screened the electrostatic repulsions between two primary complexes. These larger primary complexes remain aggregated with a fractal dimension of 2.1. Thirdly, we show that the addition of PSS chains up to [-]/[+]intro ~ 20, after the formation of the primary complex with a [-]/[+]intro close to 1, only slightly changes the inner structure of the primary complexes. Moreover, in contrast to the synthesis achieved in the one-step mixing procedure where the proteins are unfolded for a range of [-]/[+]intro, the native conformation of the proteins is preserved inside the frozen core

Filtration of precipitated silica aggregates: Length scales, percolation threshold and yielding behaviour

Reinforcing precipitated silica systems have a complex hierarchical structure consisting of a branched network made of connected clusters composed of small silica beads welded together into larger dense aggregates. Here, we study the evolution of such structural features during a filtration process. The typical behaviour is that the cakes formed at constant pressure do not reorganize at local scale during a filtration experiment. Accordingly, the creep resistance of a precipitated silica network is high. Overall, there is a percolation threshold, which appears when the branches are pushed into each other. Once this percolation path is reached, the cake withstands compression over more than a decade of applied pressure. Beyond, it seemed useful to make predictions of the filtration properties knowing the typical length scales – small silica beads, dense aggregates, and consolidation behaviour of the cake. A simple approach introducing the concept of an effective medium approximation into Darcy’s law was tested. This approach treats the network as a pseudo-continuum of porous medium built at two main length scales: the size of dense aggregates and a length scale representing the typical distance between the aggregates. The quality of the fit of experimental filtration rates by this simple model indicates that a description based on a continuous network made of two material phases is accurate

Drying dip-coated colloidal films

We present the results from a small-angle X-ray scattering (SAXS) study of lateral drying in thin films. The films, initially 10 μm thick, are cast by dip-coating a mica sheet in an aqueous silica dispersion (particle radius 8 nm, volume fraction ϕs = 0.14). During evaporation, a drying front sweeps across the film. An X-ray beam is focused on a selected spot of the film, and SAXS patterns are recorded at regular time intervals. As the film evaporates, SAXS spectra measure the ordering of particles, their volume fraction, the film thickness, and the water content, and a video camera images the solid regions of the film, recognized through their scattering of light. We find that the colloidal dispersion is first concentrated to ϕs = 0.3, where the silica particles begin to jam under the effect of their repulsive interactions. Then the particles aggregate until they form a cohesive wet solid at ϕs = 0.68 ± 0.02. Further evaporation from the wet solid leads to evacuation of water from pores of the film but leaves a residual water fraction ϕw = 0.16. The whole drying process is completed within 3 min. An important finding is that, in any spot (away from boundaries), the number of particles is conserved throughout this drying process, leading to the formation of a homogeneous deposit. This implies that no flow of particles occurs in our films during drying, a behavior distinct to that encountered in the iconic coffee-stain drying. It is argued that this type of evolution is associated with the formation of a transition region that propagates ahead of the drying front. In this region the gradient of osmotic pressure balances the drag force exerted on the particles by capillary flow toward the liquid–solid front