An electrokinetic sensor for studying immersed surfaces, using focused ultrasound

A novel method for obtaining information on the charge density of an immersed surface is presented. The technique uses focused ultrasound to excite oscillatory fluid motion in the plane of the solid-liquid interface, over a localised area. The displacement current (resulting from the motion of fluid-borne ions in the outer double-layer) is detected by electrodes in the liquid. The method is demonstrated as a means for monitoring protein adsorption, and for monitoring interactions between two different proteins. A second electrokinetic effect at the interface is identified, isolated from the first, and shown to provide additional information on the compressibility and charge density of the double-layer. © 2001 Elsevier Science B.V. All rights reserved.

Viscous state effect on the activity of Fe nanocatalysts.

Many applications of nanotubes and nanowires require controlled bottom-up engineering of these nanostructures. In catalytic chemical vapor deposition, the thermo-kinetic state of the nanocatalysts near the melting point is one of the factors ruling the morphology of the grown structures. We present theoretical and experimental evidence of a viscous state for nanoparticles near their melting point. The state exists over a temperature range scaling inversely with the catalyst size, resulting in enhanced self-diffusion and fluidity across the solid-liquid transformation. The overall effect of this phenomenon on the growth of nanotubes is that, for a given temperature, smaller nanoparticles have a larger reaction rate than larger catalysts.

First-principles energetics of water: a many-body analysis

Standard forms of density-functional theory (DFT) have good predictive power for many materials, but are not yet fully satisfactory for solid, liquid and cluster forms of water. We use a many-body separation of the total energy into its 1-body, 2-body (2B) and beyond-2-body (B2B) components to analyze the deficiencies of two popular DFT approximations. We show how machine-learning methods make this analysis possible for ice structures as well as for water clusters. We find that the crucial energy balance between compact and extended geometries can be distorted by 2B and B2B errors, and that both types of first-principles error are important.

A solid-state dye-sensitized solar cell based on a novel ionic liquid gel and ZnO nanoparticles on a flexible polymer substrate.

This paper describes a new strategy to make a full solid-state, flexible, dye-sensitized solar cell (DSSC) based on novel ionic liquid gel, organic dye, ZnO nanoparticles and carbon nanotube (CNT) thin film stamped onto a polyethylene terephthalate (PET) substrate. The CNTs serve both as the charge collector and as scaffolds for the growth of ZnO nanoparticles, where the black dye molecules are anchored. It opens up the possibility of developing a continuous roll to roll processing for THE mass production of DSSCs.

Failure and formation of axial nanowire heterostructures in vapor-liquid-solid growth

To observe the axial growth behavior of InAs on GaAs nanowires, InAs was grown for different growth durations on GaAs nanowires using Au nanoparticles. Through transmission electron microscopy, we have observed the following evolution steps for the InAs growth. (1) In the initial stages of the InAs growth, InAs clusters into a wedge shape preferentially at an edge of the Au/GaAs interface by minimizing Au/InAs interfacial area; (2) with further growth of InAs, the Au particle moves sidewards and then downwards by preserving an interface with GaAs nanowire sidewalls. The lower interfacial energy of Au/GaAs than that of Au/In As is attributed to be the reason for such Au movement. This downward movement of the Au nanoparticle later terminates when the nanoparticle encounters InAs growing radially on the GaAs nanowire sidewalls, and with further supply of In and As vapor reactants, the Au nanoparticle assists the formation of InAs branches. These observations give some insights into vapor-liquid-solid growth and the formation of kinks in nanowire heterostructures. © 2008 Materials Research Society.

Microfabrication and application of reservoir pins for liquid transfer in biotechnology

Microarraying involves laying down genetic elements onto a solid substrate for DNA analysis on a massively parallel scale. Microarrays are prepared using a pin-based robotic platform to transfer liquid samples from microtitre plates to an array pattern of dots of different liquids on the surface of glass slides where they dry to form spots diameter < 200 μm. This paper presents the design, materials selection, micromachining technology and performance of reservoir pins for microarraying. A conical pin is produced by (i) conventional machining of stainless steel or wet etching of tungsten wire, followed by (ii) micromachining with a focused laser to produce a microreservoir and a capillary channel structure leading from the tip. The pin has a flat end diameter < 100 μm from which a 500 μm long capillary channel < 15 μm wide leads up the pin to a reservoir. Scanning electron micrographs of the metal surface show roughness on the scale of 10 μm, but the pins nevertheless give consistent and reproducible spotting performance. The pin capacity is 80 nanolitres of fluid containing DNA, and at least 50 spots can be printed before replenishing the reservoir. A typical robot holds can hold up to 64 pins. This paper discusses the fabrication technology, the performance and spotting uniformity for reservoir pins, the possible limits to miniaturization of pins using this approach, and the future prospects for contact and non-contact arraying technology.

Numerical simulations of unsteady wet steam flows with non-equilibrium condensation in the nozzle and the steam turbine

Numerical techniques for non-equilibrium condensing flows are presented. Conservation equations for homogeneous gas-liquid two-phase compressible flows are solved by using a finite volume method based on an approximate Riemann solver. The phase change consists of the homogeneous nucleation and growth of existing droplets. Nucleation is computed with the classical Volmer-Frenkel model, corrected for the influence of the droplet temperature being higher than the steam temperature due to latent heat release. For droplet growth, two types of heat transfer model between droplets and the surrounding steam are used: a free molecular flow model and a semi-empirical two-layer model which is deemed to be valid over a wide range of Knudsen number. The computed pressure distribution and Sauter mean droplet diameters in a convergent-divergent (Laval) nozzle are compared with experimental data. Both droplet growth models capture qualitatively the pressure increases due to sudden heat release by the non-equilibrium condensation. However the agreement between computed and experimental pressure distributions is better for the two-layer model. The droplet diameter calculated by this model also agrees well with the experimental value, whereas that predicted by the free molecular model is too small. Condensing flows in a steam turbine cascade are calculated at different Mach numbers and inlet superheat conditions and are compared with experiments. Static pressure traverses downstream from the blade and pressure distributions on the blade surface agree well with experimental results in all cases. Once again, droplet diameters computed with the two-layer model give best agreement with the experiments. Droplet sizes are found to vary across the blade pitch due to the significant variation in expansion rate. Flow patterns including oblique shock waves and condensation-induced pressure increases are also presented and are similar to those shown in the experimental Schlieren photographs. Finally, calculations are presented for periodically unsteady condensing flows in a low expansion rate, convergent-divergent (Laval) nozzle. Depending on the inlet stagnation subcooling, two types of self-excited oscillations appear: a symmetric mode at lower inlet subcooling and an asymmetric mode at higher subcooling. Plots of oscillation frequency versus inlet sub-cooling exhibit a hysteresis loop, in accord with observations made by other researchers for moist air flow. Copyright © 2006 by ASME.

The limits of flexoelectricity in liquid crystals

The flexoelectric conversion of mechanical to electrical energy in nematic liquid crystals is investigated using continuum theory. Since the electrical energy produced cannot exceed the mechanical energy supplied, and vice-versa, upper bounds are imposed on the magnitudes of the flexoelectric coefficients in terms of the elastic and dielectric coefficients. For conventional values of the elastic and dielectric coefficients, it is shown that the flexoelectric coefficients may not be larger than a few tens of pC/m. This has important consequences for the future use of such flexoelectric materials in devices and the related energetics of distorted equilibrium structures. © 2011 Author(s).