On the application of the light-attenuation technique as a tool for non-intrusive buoyancy measurements

This article describes the application of the light-attenuation technique as a tool for measuring dilution occurring in buoyancy-driven flows. Whilst this technique offers the experimental fluid dynamicist the ability to make rapid synoptic buoyancy measurements non-intrusively, its successful application requires careful selection of chemical dye, dye concentration, illumination and optics. After establishing the advantages offered by methylene blue as a dyeing agent, we assess the accuracy of buoyancy measurements made using this technique compared with direct measurements made with density meters. Density measurements obtained using light-attenuation differ from those obtained using the density meter by typically less than 3%. It is hoped that this article will provide useful advice with regards to its implementation in the field of buoyancy-driven flows. © 2011 Elsevier Inc.

Boundary integral technique for the numerical modelling of the air flow for the Aaberg exhaust system

A boundary integral technique has been developed for the numerical simulation of the air flow for the Aaberg exhaust system. For the steady, ideal, irrotational air flow induced by a jet, the air velocity is an analytical function. The solution of the problem is formulated in the form of a boundary integral equation by seeking the solution of a mixed boundary-value problem of an analytical function based on the Riemann-Hilbert technique. The boundary integral equation is numerically solved by converting it into a system of linear algebraic equations, which are solved by the process of the Gaussian elimination. The air velocity vector at any point in the solution domain is then computed from the air velocity on the boundary of the solution domains.

Series-connected IGBTs using active voltage control technique

With series insulated-gate bipolar transistor (IGBT) operation, well-matched gate drives will not ensure balanced dynamic voltage sharing between the switching devices. Rather, it is IGBT parasitic capacitances, mainly gate-to-collector capacitance Cgc, that dominate transient voltage sharing. As Cgc is collector voltage dependant and is significantly larger during the initial turn-off transition, it dominates IGBT dynamic voltage sharing. This paper presents an active control technique for series-connected IGBTs that allows their dynamic voltage transition dV\ce/dt to adaptively vary. Both switch ON and OFF transitions are controlled to follow a predefined dVce/dt. Switching losses associated with this technique are minimized by the adaptive dv /dt control technique incorporated into the design. A detailed description of the control circuits is presented in this paper. Experimental results with up to three series devices in a single-ended dc chopper circuit, operating at various low voltage and current levels, are used to illustrate the performance of the proposed technique. © 2012 IEEE.

Electrical transport and magnetic properties of Mn3O4-La0.7Ca0.3MnO3 ceramic composites prepared by a one-step spray-drying technique

La0.7Ca0.3MnO3/Mn3O4 composites can be synthesized in one step by thermal treatment of a spray-dried precursor, instead of mixing pre-synthesized powders. Another advantage of this composite system is that a long sintering step can be used without leading to significant modification of the manganite composition. The percolation threshold is reached at ∼20 vol% of manganite phase. The 77 K low field magnetoresistance is enhanced to ∼11% at 0.15 T when the composition is close to the percolation threshold. © 2007 Elsevier Ltd. All rights reserved.

YBa 2Cu 3O 7-δ thick films on Ag prepared by the Electrophoretic Deposition technique

YBa 2Cu 3O 7-δ thick films have been deposited onto Ag substrates by the Electrophoretic Deposition (EPD) technique. Different microstructures and electrical behaviours were observed depending on the starting powder. Coatings prepared from commercial powder displayed significant porosity and the superconducting transition width was found to be magnetic-field dependent. Films produced from home-made coprecipitated powder are denser but contain some secondary phases. No dependence of the resistive transition as a function of magnetic field (H 20 Oe) was observed in that case. © 2006 IOP Publishing Ltd.

Investigation of DyBa2Cu3O7-d superconducting domains grown by the infiltration technique starting with small size Dy-211 particles

An infiltration and growth process is here used as an alternative to the classical top-seeded melt-textured growth process for the production of Dy-123 single-domains with finely dispersed small size Dy-211 particles. The starting materials are the 211-particles and a barium and copper rich liquid phase precursor. The infiltration and growth process allows for controlling both the spatial and size distribution of the 211-particles in the final superconducting 123-single-domain. The main parameters (set-ups, maximum processing temperature with respect to the peritectic temperature, nature of reactant, porosity of the 211-preform) of the infiltration and growth process are discussed. Moreover, different processes of chimie douce are shown in order to produce Dy-211 particles with controlled shape and size, particles that can be used as precursors for the infiltration and growth process. © 2005 IOP Publishing Ltd.

Low-field magnetoresistance in La0.7Ca0.3MnO 3 manganite compounds prepared by the spray drying technique

Calcium-substituted lanthanum manganite compounds were synthesized by the spray drying technique. This method - whose main advantages are versatility, high reproducibility and scalability - yields small grain materials of high homogeneity and displaying low-field magnetoresistance effects. We report about the physical and chemical characterizations of these samples in order to investigate the potential interest of spray drying for the production of materials for low-field magnetoresistance applications. We have studied the dependence of the low-field magnetoresistance on the temperature and duration of the thermal treatment applied to the pelletized powders. The issue of the shape anisotropy (demagnetisation effects) influence on the magnetoresistance properties has also been dealt with. © 2005 Springer Science + Business Media, Inc.

Generating Options for Active Risk Control (GO-ARC): introducing a novel technique.

BACKGROUND: After investing significant amounts of time and money in conducting formal risk assessments, such as root cause analysis (RCA) or failure mode and effects analysis (FMEA), healthcare workers are left to their own devices in generating high-quality risk control options. They often experience difficulty in doing so, and tend toward an overreliance on administrative controls (the weakest category in the hierarchy of risk controls). This has important implications for patient safety and the cost effectiveness of risk management operations. This paper describes a before and after pilot study of the Generating Options for Active Risk Control (GO-ARC) technique, a novel tool to improve the quality of the risk control options generation process. OUTCOME MEASURES: The quantity, quality (using the three-tiered hierarchy of risk controls), variety, and novelty of risk controls generated. RESULTS: Use of the GO-ARC technique was associated with improvement on all measures. CONCLUSIONS: While this pilot study has some notable limitations, it appears that the GO-ARC technique improved the risk control options generation process. Further research is needed to confirm this finding. It is also important to note that improved risk control options are a necessary, but not sufficient, step toward the implementation of more robust risk controls.

A fixed-grid b-spline finite element technique for fluid-structure interaction

We present a fixed-grid finite element technique for fluid-structure interaction problems involving incompressible viscous flows and thin structures. The flow equations are discretised with isoparametric b-spline basis functions defined on a logically Cartesian grid. In addition, the previously proposed subdivision-stabilisation technique is used to ensure inf-sup stability. The beam equations are discretised with b-splines and the shell equations with subdivision basis functions, both leading to a rotation-free formulation. The interface conditions between the fluid and the structure are enforced with the Nitsche technique. The resulting coupled system of equations is solved with a Dirichlet-Robin partitioning scheme, and the fluid equations are solved with a pressure-correction method. Auxiliary techniques employed for improving numerical robustness include the level-set based implicit representation of the structure interface on the fluid grid, a cut-cell integration algorithm based on marching tetrahedra and the conservative data transfer between the fluid and structure discretisations. A number of verification and validation examples, primarily motivated by animal locomotion in air or water, demonstrate the robustness and efficiency of our approach. © 2013 John Wiley & Sons, Ltd.

Inhibition of no tail (ntl) gene expression in zebrafish by external guide sequence (EGS) technique

External guide sequence (EGS) technique, a branch of ribozyme strategy, can be enticed to cleave the target mRNA by forming a tRNA-like structure. In the present study, no tail gene (ntl), a key gene participating in the formation of normal tail, was used as a target for ribonuclease (RNase) P-mediated gene disruption in zebrafish in vivo. Transient expression of pH1-m3/4 ntl-EGS or pH1-3/4 ntl-EGS produced the full no tail phenotype at long-pec stage in proportion as 24 or 35%, respectively. As is expected that the full-length ntl mRNA of embryos at 50% epiboly stage decreased relative to control when injected the embryos with 3/4 EGS or m3/4 EGS RNA. Interestingly, ntl RNA transcripts, including the cleaved by EGS and the untouched, increased. Taken together, these results indicate that EGS strategy can work in zebrafish in vivo and becomes a potential tool for degradation of targeted mRNAs.

Comparison of acoustic velocity perturbation measurements using PIV vs. two-microphone technique

Understanding combustion instabilities requires accurate measurements of the acoustic velocity perturbation into injectors. This is often accomplished via the use of the two microphone technique, as this only requires two pressure transducers. However, measurements of the actual velocities emerging from the injectors are not often taken, leaving questions regarding the assumptions about the acoustic velocity. A comparison of velocity measured at downstream of the injector with that of two-microphone technique can show the accuracy and limitations of two-microphone technique. In this paper, velocity measurements are taken using both particle image velocimetry (PIV) and the two-microphone technique in a high pressure facility designed for aeroengine injector measurements. The flow is excited using an area modulation device installed on the choked end of the combustion chamber, with PIV measurements enabled by optical access downstream of the injector through a quartz tube and windows. Acoustic velocity perturbations at the injector are determined by considering the Fourier transformed pressure fluctuations for two microphones installed at a known distance upstream of the injector. PIV measurements are realized by seeding the air flow with micrometric water particles under 2.5 bar pressure at ambient temperature. Phase locked velocity fields are realized by synchronizing the acquisition of PIV images with the revolution of the acoustic modulator using the pressure signal measured at the face of injector. The mean velocity fluctuation is calculated as the difference between maximum and minimum velocities, normalized by the mean velocity of the unforced case. Those values are compared with the peak-to-peak velocity fluctuation amplitude calculated by the two-microphone technique. Although the ranges of velocity fluctuations for both techniques are similar, the variation of fluctuation with forcing frequencies diverges significantly with frequency. The differences can be attributed to several limitations associated with of both techniques, such as the quality of the signal, the signal/noise ratio, the accuracy of PIV measurements and the assumption of isentropic flow of the particle velocity from the plenum through the injector. We conclude that two-microphone methods can be used as a reference value for the velocity fluctuation in low order applications such as flame transfer functions, but not for drawing conclusions regarding the absolute velocity fluctuations in the injector. Copyright © 2013 by ASME.

Electrical control of nanoscale functionalization in graphene by the scanning probe technique

Functionalized graphene is a versatile material that has well-known physical and chemical properties depending on functional groups and their coverage. However, selective control of functional groups on the nanoscale is hardly achievable by conventional methods utilizing chemical modifications. We demonstrate electrical control of nanoscale functionalization of graphene with the desired chemical coverage of a selective functional group by atomic force microscopy (AFM) lithography and their full recovery through moderate thermal treatments. Surprisingly, our controlled coverage of functional groups can reach 94.9% for oxygen and 49.0% for hydrogen, respectively, well beyond those achieved by conventional methods. This coverage is almost at the theoretical maximum, which is verified through scanning photoelectron microscope measurements as well as first-principles calculations. We believe that the present method is now ready to realize 'chemical pencil drawing' of atomically defined circuit devices on top of a monolayer of graphene. © 2014 Nature Publishing Group All rights reserved.