Effective slip lengths for flows over surfaces with nanobubbles: the effects of finite slip.

We consider effective slip lengths for flows of simple liquids over surfaces contaminated by gaseous nanobubbles. In particular, we examine whether the effects of finite slip over the liquid-bubble interface are important in limiting effective slip lengths over such surfaces. Using an expression that interpolates between the perfect slip and finite slip regimes for flow over bubbles, we conclude that for the bubble dimensions and coverages typically reported in the literature the effects of finite slip are secondary, reducing effective slip lengths by only 10%. Further, we find that nanobubbles do not significantly increase slip lengths beyond those reported for bare hydrophobic surfaces.

Effective slip boundary conditions for flows over nanoscale chemical heterogeneities.

We study slip boundary conditions for simple fluids at surfaces with nanoscale chemical heterogeneities. Using a perturbative approach, we examine the flow of a Newtonian fluid far from a surface described by a heterogeneous Navier slip boundary condition. In the far field, we obtain expressions for an effective slip boundary condition in certain limiting cases. These expressions are compared to numerical solutions which show they work well when applied in the appropriate limits. The implications for experimental measurements and for the design of surfaces that exhibit large slip lengths are discussed.

Assessment of language structure: from syntax to event-based analysis.

The last 70 years have seen much research and clinical attention devoted to the descriptions and assessment of children's developing language structures. From these efforts have evolved a number of ways to describe the kinds of structures children evidence at different stages of development, and thus the means to make comparisons across children or across time periods. This article reviews major trends that have emerged in syntactic descriptions and approaches to language habilitation, culminating in contemporary approaches that view syntactic structure in real life events rather than in artificial tasks or with arbitrary checklists. These new approaches allow us to determine the communication goals that are not being met rather than cataloging the syntactic structures that have not yet been mastered and provide us with the contexts for helping the children develop structures that will lead to clearer expression of meanings and fewer breakdowns in communication.

Sleep and the McCollough effect.

Orientation-contingent chromatic ("McCollough") aftereffects (OCCAs) were induced under carefully standardised conditions, in subjects suffering from varying degrees of sleep deprivation. The initial OCCA strength was found to vary systematically with the prior sleep pattern of the subject. In subjects whose sleep normally lasted 7-8 hr, loss of 3 or 4 hr of the previous night's sleep could reduce initial strength by as much as 50%; no further reduction was observed with still shorter sleep durations. Keeping the eye in darkness while awake had in this respect no comparable effects to those of sleep, and sleeping in a lighted room made no difference. The results suggest that the McCollough Effect depends on a form of neural plasticity which requires a normal sleep cycle for its maintenance.