On the relationship between drag and vertical velocity fluctuations in flow over riblets and liquid infused surfaces

Direct numerical simulations (DNS) of flow over triangular and rectangular riblets in a wide range of size and Reynolds number have been carried out. The flow within the grooves is directly resolved by exploiting the immersed-boundary method. It is found that the drag reduction property is primarily associated with the capability of inhibiting vertical velocity fluctuations at the plane of the crests, as in liquid-infused surfaces (LIS) devices. This is mimicked in DNS through artificial suppression of the vertical velocity component, which yields large drag decrease, proportionate to the riblets size. A parametrization of the drag reduction effect in terms of the vertical velocity variance is found to be quite successful in accounting for variation of the controlling parameters. A Moody-like friction diagram is thus introduced which incorporates the effect of slip velocity and a single, geometry-dependent parameter. Reduced drag-reduction efficiency of LIS-like riblets is found as compared to cases with artificially imposed slip velocity. Last, we find that simple wall models of riblets and LIS-like devices are unlikely to provide accurate prediction of the flow phenomenon, and direct resolution of flow within the grooves in necessary.     

Lanthanide induced shifts of sterically hindered aromatic carbonyl compounds oxomethylene-bridged,acetyl-, and formyl-2,2′-spirobiindanes

The lanthanide induced shift (LIS) data of 10 polysubstituted 2,2-spirobiindanes with a carbonyl group in conjugation to an aromatic ring were simulated using theMcConnell-Robertson equation. In the case of oxomethylene-bridged derivates (with CO incorporated in a more or less rigid ring) the classical one site or two site models gave reasonable results. For sterically hindered acetyl or formyl derivates (bothortho positions alkyl-substituted) a new model was developed: the carbonyl group was found to be 30° out of the aromatic plane and the possible 4 positions (±30° and ±150°) turned out to be populated differently depending on theortho substituents. The LIS programme had to be modified to account for this situation.Dedicated to Prof. Dr.A. Neckel on the occasion of his 60th birthday.     

Lanthanide induced 1H and 13C NMR shifts and their use for geometry analysis with alicyclic compounds

Based on computations with conformationally rigid substrates the ambiguities involved in the geometrical analysis of pseudocontact shifts are demonstrated. The minimal agreement factors R and the corresponding lanthanide positions (usually more than one) are extremely dependent upon the chosen structural data for the model substrate and on the errors of the experimental shift values. It is observed, that a difference or improvement of R factors of less than 3% is not significant in most cases. This is so, even on the basis of Ytterbium induced ¹³C shifts, which are found to be more accurate than ¹H shifts and free from contact contributions within the experimental error. Using lanthanide induced shifts some ¹³C signal assignment problems are discussed. The computed minima for five substituted norbornanols indicate a lanthanide position with an L . . . O distance of d = 2·5 Å for the secondary alcohols and an orientation avoiding gauche interactions with the two neighbouring CC bonds. Similar computed results are obtained with five bicyclic ketones, except for an L . . . O distance from 3 to 4 Å increasing with steric hindrance. The particular problems with the analysis of symmetrical compounds like cyclohexyl derivatives are pointed out.     

Specific boundary conditions for the simulation of extraction for ECRIS,LIS, and H−-sources

The necessity of a three-dimensional simulation of the extraction has been accepted for electron cyclotron resonance ion sources (ECRIS) as well as for negative ion sources. For an ECRIS, the magnetic hexapole together with the solenoidal mirror field defines a minimum B structure which confines the plasma. Depending on the magnetic flux density distribution, the plasma density in front of the extraction electrode might be non-homogeneous. In H^?-sources, magnetic filter fields are used to separate electrons with different energies or to separate electrons from negative ions. These magnetic filters influence the ions as well. Besides these asymmetry effects other quantities have to be considered, namely the correct formulation of initial conditions of all present charged particles. For ECRIS the initial conditions for ions are assumed to be in the electronvolt range, whereas it can be in the kilo electronvolt range for laser ion sources. Another quantity of interest is the electron energy and the distribution of electrons in real space and their movability if magnetic fields are present.     

Droplet manipulation with bioinspired liquid-infused surfaces: A review of recent progress and potential for integrated detection

Point-of-need (PON) diagnostics offer promising methods to gather information relevant to health and safety on-site without the requirement for a fully equipped laboratory. In this review, we discuss how liquid-infused surfaces offer a promising platform to expand the capabilities of PON devices in the areas of biological sample preparation and system integration, providing new methods of controlling the movement of droplets and facilitating detection of biological and chemical compounds contained therein. Modifications to the underlying surface structure can be used to passively control the direction of droplet movement, and the careful selection of responsive solid substrates and/or overlying liquids can allow active control through induced temperature gradients, electrical stimulation, and exposure to magnetic fields. Recent work leveraging other advantages of liquid-infused systems such as ultra-low friction, noncoalescence of droplets, and liquid–liquid patterning has demonstrated the unique ways in which this approach can be used to both enhance current detection methods as well as enable new ones. Together, these recent developments in the manipulation of droplets on liquid-infused surfaces point to their significant potential for furthering the capacity of PON devices for both biological and environmental samples.