Lack of cerebellar tDCS effects on learning of a complex whole body dynamic balance task in middle-aged (50-65 years) adults.

BACKGROUND: Cerebellar transcranial direct current stimulation (tDCS) is widely considered as a promising non-invasive tool to foster motor performance and learning in health and disease. The results of previous studies, however, are inconsistent. Our group failed to provide evidence for an effect of cerebellar tDCS on learning of a complex whole body dynamic balance task in young and healthy participants. Ceiling effects in the young study population are one possible explanation for the negative findings. METHODS: In the present study, we therefore tested 40 middle-aged healthy participants between the ages of 50 to 65 years. Participants received either anodal or sham cerebellar tDCS using a double-blinded study design while performing a balance task on a Lafayette Instrument 16,030 stability platform®. Mean platform angle and mean balance time were assessed as outcome measures. RESULTS: Significant learning effects were found in all participants. Balancing performance and learning rate was significantly less in the group of middle-aged adults compared to our previous group of young adults. No significant effects of cerebellar tDCS were observed. CONCLUSIONS: Our findings are in line with other studies that have failed to prove robust effects of cerebellar tDCS on motor learning. The present findings, however, do not exclude cerebellar tDCS effects. tDCS effects may be more prominent after repeated stimulation, using other stimulus parameters, in patient populations, or in other motor learning tasks. TRIAL REGISTRATION: Not applicable.

Development and introduction of a ready-to-use pediatric pentavalent vaccine to meet and sustain the needs of developing countries--Quinvaxem®: the first 5 years.

Quinvaxem(®) injection (DTwP-HepB-Hib fully-liquid combined vaccine) is a ready-to-use, preservative-free, fully-liquid combined vaccine containing diphtheria and tetanus toxoids, Bordetella pertussis inactivated cellular suspension, hepatitis B surface antigen (HBsAg), and Haemophilus influenzae type b conjugated oligosaccharide. The vaccine was the first ready-to-use, fully-liquid pentavalent vaccine to gain WHO pre-qualification status in 2006. The immunogenicity and safety of Quinvaxem(®) was assessed in four clinical trials and a large post-marketing surveillance study. Quinvaxem(®) was found to be highly immunogenic in each of the primary vaccination studies and was also shown to be suitable as a booster with the advantage that it could be given concomitantly with measles vaccine. Quinvaxem(®) has become a cornerstone in EPI vaccination programs. To further support the needs of EPI vaccination processes and developing countries, a simple, all-in-one, compact, prefilled, auto-disabled Uniject(®) injection system has been chosen and optimized as a potential new presentation for Quinvaxem(®). Hopefully, Quinvaxem(®) in the Uniject(®) presentation will help vaccination programs in developing countries to achieve more.

Micro-rheology on (polymer-grafted) colloids using optical tweezers.

Optical tweezers are experimental tools with extraordinary resolution in positioning (± 1 nm) a micron-sized colloid and in the measurement of forces (± 50 fN) acting on it-without any mechanical contact. This enables one to carry out a multitude of novel experiments in nano- and microfluidics, of which the following will be presented in this review: (i) forces within single pairs of colloids in media of varying concentration and valency of the surrounding ionic solution, (ii) measurements of the electrophoretic mobility of single colloids in different solvents (concentration, valency of the ionic solution and pH), (iii) similar experiments as in (i) with DNA-grafted colloids, (iv) the nonlinear response of single DNA-grafted colloids in shear flow and (v) the drag force on single colloids pulled through a polymer solution. The experiments will be described in detail and their analysis discussed.

Dynamics of colloids in confined geometries.

We discuss the Brownian dynamics of colloids in confinement with special emphasis on the influence of the solvent dynamics. We review the derivation of a dynamic density functional theory (DDFT) including some aspects of hydrodynamic interactions and its application to the micro-rheology of suspensions. In particular we discuss the failure of Stokes' law in suspensions and non-equilibrium solvent structure mediated interactions. With regard to hydrodynamic chromatography we also discuss the stationary transport of particles in narrow channels, and the reasons for the failure of DDFT in this situation.

DDFT for Brownian particles and hydrodynamics.

Classical dynamic density functional theory (DDFT) has developed into a versatile tool for describing the dynamics of overdamped Brownian particles. The underlying equilibrium density functional is a quantitative model for colloidal suspensions. Non-equilibrium properties of these systems are strongly influenced by the solvent hydrodynamics. In this paper we discuss ways to introduce certain aspects of solvent hydrodynamics into the DDFT, in particular advection by a flowing solvent and hydrodynamic interactions among suspended particles as well as with container walls.

Nanoimprinting using self-assembled ceramic nanoislands.

We have combined self-assembled ceramic nanoislands with nanoimprinting to demonstrate a novel, simple, low-cost method for polymer surface patterning. The nanoislands are easy to make and inexpensive, and can produce different distinct island morphologies. With a similar stiffness to steel, the nanoislands have superior durability to silicon, glass, polydimethylsiloxane (PDMS), and other common nanoimprinting materials. The nanoislands are stable up to 1000 degrees C and resist acids, bases, and solvents. We have demonstrated nanoimprinting with PDMS, ethyleneglycol dimethacrylate, and polystyrene polymers. The combination of desirable properties, ease of making, and low cost suggests a useful nanopatterning platform for a wide array of research fields.

Dynamics of nanodroplets on topographically structured substrates.

Mesoscopic hydrodynamic equations are solved to investigate the dynamics of nanodroplets positioned near a topographic step of the supporting substrate. Our results show that the dynamics depends on the characteristic length scales of the system given by the height of the step and the size of the nanodroplets as well as on the constituting substances of both the nanodroplets and the substrate. The lateral motion of nanodroplets far from the step can be described well in terms of a power law of the distance from the step. In general the direction of motion depends on the details of the effective laterally varying intermolecular forces. But for nanodroplets positioned far from the step it is solely given by the sign of the Hamaker constant of the system. Moreover, our study reveals that the steps always act as a barrier for transporting liquid droplets from one side of the step to the other.

Size dependent motion of nanodroplets on chemical steps.

Nanodroplets on chemically structured substrates move under the action of disjoining pressure induced forces. A detailed analysis of them shows that, even in the absence of long-ranged lateral variations of the effective interface potential, already the fact that due to their small size nanodroplets do not sample the disjoining pressure at all distances from the substrate can lead to droplet motion toward the less wettable part of the substrate, i.e., in the direction opposite to the one expected on the basis of macroscopic wettability considerations.

Stability of liquid ridges on chemical micro- and nanostripes.

We analyze the stability of sessile filaments (ridges) of nonvolatile liquids versus pearling in the case of externally driven flow along a chemical stripe within the framework of the thin-film approximation. The ridges can be stable with respect to pearling even if the contact line is not completely pinned. A generalized stability criterion for moving contact lines is provided. For large wavelengths and no driving force, within perturbation theory, an analytical expression of the growth rate of pearling instabilities is derived. A numerical analysis shows that a body force along the ridge further stabilizes the ridge by reducing the growth rate of unstable perturbations, even though there is no complete stabilization. Hence the stability criteria established in the absence of driven flow ensure overall stability.

Motion of nanodroplets near chemical heterogeneities.

We investigate the dynamics of nanoscale droplets in the vicinity of chemical steps which separate parts of a substrate with different wettabilities. Due to long-ranged dispersion forces, nanodroplets positioned on one side of the step perceive the different character of the other side even at a finite distance from the step, leading to a dynamic response. The direction of the ensuing motion of such droplets depends not only on the difference between the equilibrium contact angles on these two parts but in particular on the difference between the corresponding Hamaker constants. Therefore, the motion is not necessarily directed toward the more wettable side and can also be different from that of droplets which span the step.

Thermal noise influences fluid flow in thin films during spinodal dewetting.

Experiments on dewetting thin polymer films confirm the theoretical prediction that thermal noise can strongly influence characteristic time scales of fluid flow and cause coarsening of typical length scales. Comparing the experiments with deterministic simulations, we show that the Navier-Stokes equation has to be extended by a conserved bulk noise term to accomplish the observed spectrum of capillary waves. Because of thermal fluctuations the spectrum changes from an exponential to a power law decay for large wave vectors. Also the time evolution of the typical wave vector of unstable perturbations exhibits noise-induced coarsening that is absent in deterministic hydrodynamic flow.

Quantifying hydrodynamic slip: a comprehensive analysis of dewetting profiles.

To characterize nontrivial boundary conditions of a liquid flowing past a solid, the slip length is commonly used as a measure. From the profile of a retracting liquid front (e.g., measured with atomic force microscopy), the slip length can be extracted with the help of a Stokes model for a thin liquid film dewetting from a solid substrate. Specifically, we use a lubrication model derived from the Stokes model for strong slippage and linearize the film profile around the flat, unperturbed film. For small slip lengths, we expand the linearized full Stokes model for small slopes up to third order. Using the respective model, we obtain, in addition to the slip length, the capillary number, from which we can estimate the viscosity of the fluid film. We compare numerical and experimental results, test the consistency and the validity of the models/approximations, and give an easy-to-follow guide of how they can be used to analyze experiments.

A thin-film model for corotational Jeffreys fluids under strong slip.

We derive a thin-film model for viscoelastic liquids under strong slip which obey the stress tensor dynamics of corotational Jeffreys fluids.

Slip vs. viscoelasticity in dewetting thin films.

Ultrathin polymer films on non-wettable substrates display dynamic features which have been attributed to either viscoelastic or slip effects. Here we show that in the weak- and strong-slip regime, effects of viscoelastic relaxation are either absent or essentially indistinguishable from slip effects. Strong slip modifies the fastest unstable mode in a rupturing thin film, which questions the standard approach to reconstruct the effective interface potential from dewetting experiments.

Motion of nanodroplets near edges and wedges.

Nanodroplets residing near wedges or edges of solid substrates exhibit a disjoining pressure induced dynamics. Our nanoscale hydrodynamic calculations reveal that nonvolatile droplets are attracted or repelled from edges or wedges depending on details of the corresponding laterally varying disjoining pressure generated, e.g., by a possible surface coating.

A thin-film equation for viscoelastic liquids of Jeffreys type.

We derive a novel thin-film equation for linear viscoelastic media describable by generalized Maxwell or Jeffreys models. As a first application of this equation we discuss the shape of a liquid rim near a dewetting front. Although the dynamics of the liquid is equivalent to that of a phenomenological model recently proposed by Herminghaus et al. (S. Herminghaus, R. Seemann, K. Jacobs, Phys. Rev. Lett. 89, 056101 (2002)), the liquid rim profile in our model always shows oscillatory behaviour, contrary to that obtained in the former. This difference in behaviour is attributed to a different treatment of slip in both models.

Fracture in mode I using a conserved phase-field model.

We present a continuum phase-field model of crack propagation. It includes a phase-field that is proportional to the mass density and a displacement field that is governed by linear elastic theory. Generic macroscopic crack growth laws emerge naturally from this model. In contrast to classical continuum fracture mechanics simulations, our model avoids numerical front tracking. The added phase-field smooths the sharp interface, enabling us to use equations of motion for the material (grounded in basic physical principles) rather than for the interface (which often are deduced from complicated theories or empirical observations). The interface dynamics thus emerges naturally. In this paper, we look at stationary solutions of the model, mode I fracture, and also discuss numerical issues. We find that the Griffith's threshold underestimates the critical value at which our system fractures due to long wavelength modes excited by the fracture process.

Porous silicon formation and electropolishing.

Electrochemical etching of silicon in hydrofluoride containing electrolytes leads to pore formation for low and to electropolishing for high applied current. The transition between pore formation and polishing is accompanied by a change of the valence of the electrochemical dissolution reaction. The local etching rate at the interface between the semiconductor and the electrolyte is determined by the local current density. We model the transport of reactants and reaction products and thus the current density in both, the semiconductor and the electrolyte. Basic features of the chemical reaction at the interface are summarized in the law of mass-action-type boundary conditions for the transport equations at the interface. We investigate the linear stability of a planar and flat interface. Upon increasing the current density the stability flips either through a change of the valence of the dissolution reaction or by a nonlinear boundary condition at the interface.

PR-1 protein inhibits the differentiation of rust infection hyphae in leaves of acquired resistant broad bean.

Treatment of broad bean leaves with salicylic acid (SA) or 2, 6-dichloro-isonicotinic acid (DCINA) induces resistance against the rust fungus Uromyces fabae resulting in reduced rust pustule density. Light-microscopy studies showed that in induced resistant plants the rust fungus is inhibited immediately after penetration through the stomatal pore. The differentiation of infection structures growing within the intercellular space of the leaf, i.e. infection hyphae and haustorial mother cells, is inhibited. Furthermore, low-temperature scanning electron microscopy studies of freeze fractures revealed protrusions at the tips of infection hyphae growing in induced resistant broad bean leaves. Treatment of in vitro-differentiating rust infection structures with intercellular fluids (IFs) from induced resistant plants confirmed that the fungus is sensitive towards an apoplastic anti-fungal activity only after having formed appressoria. Other legume rusts such as U. vignae and U. appendiculatus were likewise inhibited in the presence of IF from SA-treated broad bean leaves. Heterologous antibodies were used to study changes in the extracellular pathogenesis-related (PR) protein pattern after resistance induction. Western blots indicated that chitinases and beta-1,3-glucanases were present in both induced and control plants. In contrast, PR-1 proteins were newly synthesized in response to SA or DCINA application. The major induced PR-1 protein was purified and exhibited strong differentiation-inhibiting activity towards U. fabae infection structures. We conclude that the inhibition of rust infection hyphae in acquired resistant broad bean plants is mainly due to the anti-fungal activity of this induced basic PR-1 protein.