A study on the effect of starting material phase on the production of trititanate nanotubes

Mixed phase TiO₂ powders of different composition and particle size were subjected to the hydrothermal reaction with 10 M NaOH. It was found that the anatase phase component of the starting material is easily converted to trititanate nanotubes at 140 °C. At this temperature the rutile phase remains unreacted, however at 170 °C it reacts to form trititanate plates and belts. When the reaction time is increased to 7 days, all the TiO₂ is converted to trititanate and the morphology is exclusively nanoplates and belts, with the tube phase destroyed. Many researchers have observed some heterogeneity in their reaction products, but have mainly focussed on the nanotubes. We observed that the tubes are only prepared from the anatase phase component of a TiO₂ precursor, whereas the rutile component produces trititanate plates and sheets, irrespective of the reaction length. The particle size affects the rate of reaction, resulting in the phase transition being more easily visible in the reactions starting with the larger TiO₂ particle size.     

Adaptive hierarchic transformations for dynamically p-enriched slope-limiting over discontinuous Galerkin systems of generalized equations

We study a family of generalized slope limiters in two dimensions for Runge–Kutta discontinuous Galerkin (RKDG) solutions of advection-diffusion systems. We analyze the numerical behavior of these limiters applied to a pair of model problems, comparing the error of the approximate solutions, and discuss each limiter’s advantages and disadvantages. We then introduce a series of coupled p-enrichment schemes that may be used as standalone dynamic p-enrichment strategies, or may be augmented via any in the family of variable-in-p slope limiters presented.     

Cascading of liquid crystal elastomer photomechanical optical devices

Photomechanical actuation is demonstrated in two coupled liquid crystal elastomer photomechanical optical devices (PODs) acting in series. The response function of an individual POD is characterized and used to predict the temporal response of the coupled system. The predicted coupled-system response agrees with the experiment for several waveforms and frequencies, suggesting that large-scale integration of photomechanical devices is possible.     

In vitro evaluation of cytotoxic and inflammatory properties of silica nanoparticles of different sizes in murine RAW 264.7 macrophages

The biological response to four well-characterized amorphous silica nanoparticles was investigated in RAW 264.7 macrophages in view of their potential application as drug carriers to sites of inflammation. All silica nanoparticles-induced cell membrane damage, reduced metabolic activity, generated ROS and released various cytokines, but to different extents. Two silica nanoparticles of 34 nm (A and B) with different zetapotentials were more cytotoxic than (aggregated) 11 and 248 nm nanoparticles, while cytokines were mostly induced by the (aggregated) 11 nm and only one of the 34 nm nanoparticles (34A). The results indicate that specific silica nanoparticles may have counterproductive effects, for example when used as carriers of anti-inflammatory drugs. The physicochemical properties determining the response of nanoparticles vary for different responses, implying that a screening approach for the safe development of nanoparticles needs to consider the role of combinations of (dynamic) physicochemical properties and needs to include multiple toxicity endpoints.     

InGaN micro-pixellated light-emitting diodes with nano-textured surfaces and modified emission profiles

We present the fabrication details and performance characteristics of InGaN light-emitting diodes (LEDs) consisting of arrays of interconnected micro-pixels where each micro-pixel is nano-textured via nano-imprinting. We have taken the further step of embodying the pixels in a rhomboidal geometry. It is found that the power output of these nano-textured micro-LEDs with rhomboidal geometries is 57% higher than that of conventional square-shaped broad-area reference LEDs. The series resistance of the textured LEDs is reduced, owing to the multi-finger electrodes introduced. Furthermore, these LEDs can sustain higher operation current of up to 500 mA without encapsulation, suggesting improved thermal dissipation capability. Finally, the combined effects of surface texturing, micro-LED configuration, and geometric shaping on the light extraction are analyzed. It is found that the power enhancement by surface texturing, micro-pixellating and the rhomboidal geometry are 32%, 16%, and 9%, respectively, implying that surface texturing is the most effective contribution to increasing the light extraction efficiency in our design. The angular dependent far-field beam profile is also remarkably changed, compared with the standard Lambertian emission pattern of the conventional square-shaped LEDs. Substantial increase in the EL intensity is evident from both the top surface and the sidewall.     

High sensitivity (1 ppm) hydrogen detection using an unconventional Pd/n-InP Schottky device

Hydrogen is detected using a Pd/n-InP Schottky diode in which the elongated, very thin Pd electrode is of greater resistance than the underlying semiconductor substrate. Four-probe measurements of the device resistance, as a function of hydrogen concentration, are made by contacting only the Pd electrode, with a sensitivity of 1 ppm being achieved. On hydrogen exposure the device resistance drops from an initial high value, characteristic of the Pd electrode alone, to a lower value due to a hydrogen-induced lowering of the Schottky barrier that opens up the InP substrate as a parallel current carrying channel.     

Tricritical point in heterogeneous k-core percolation

k-core percolation is an extension of the concept of classical percolation and is particularly relevant to understanding the resilience of complex networks under random damage. A new analytical formalism has been recently proposed to deal with heterogeneous k-cores, where each vertex is assigned a local threshold k(i). In this Letter we identify a binary mixture of heterogeneous k-cores which exhibits a tricritical point. We investigate the new scaling scenario and calculate the relevant critical exponents, by analytical and computational methods, for Erd?s-Rényi networks and 2D square lattices.     

The low temperature hyperfine structure of quartz under uniaxial pressure

The uniaxial pressure dependence of the muonium hyperfine tensor was measured at 80 K. Uniaxial pressures (0 and 0.2 GPa) were applied along the a‐axis of quartz, and the hyperfine tensor was measured by applying various transverse fields between 0 and 7 G. The structure appears to be the result of the three chemically equivalent sites in quartz. When pressure is applied perpendicular to the crystallographic c‐axis of quartz, the symmetry of these sites is broken such that two chemically inequivalent sites are observed. The resulting hyperfine structure is discussed and qualitative explanations are proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

High resolution upwind-mixed finite element methods for advection-diffusion equations with variable time-stepping

Numerical methods for advection-diffusion equations are discussed based on approximating advection using a high-resolution upwind finite difference method, and incorporating diffusion using a mixed finite element method. In this approach, advection is approximated explicitly and diffusion implicitly. We first describe the basic procedure where each advection time-step is followed by a diffusion step. Because the explicit nature of the advective scheme requires a CFL time-step constraint, the basic procedure may be expensive, especially if the CFL constraint is severe. Two alternative time-stepping approaches are presented for improving computational efficiency while preserving accuracy. In the first approach, several advective time-steps are computed before taking a diffusion step. In the second approach, the advective time-steps are also allowed to vary spatially. Numerical results for these three procedures for a model problem arising in flow through porous media are given. © 1995 John Wiley & Sons, Inc.