Archive for November, 2007
Deposition and meniscus alignment of DNA-CNT on a substrate
We present a study of deposition and meniscus alignment of DNA-carbon nanotube (DNA-CNT) hybrids on a silicon wafer coated with an alkyl-silane monolayer. We show that this process occurs in two stages: adsorption of DNA-CNT onto the hydrophobic surface and subsequent alignment by a passing meniscus. In our work we study how the pH, ionic strength, and time affect the density of nanotubes deposited on the surface. We also study how surface density of nanotubes and the speed of the meniscus motion affect alignment of nanotubes. Experimental results are interpreted using models for the kinetics of deposition and for forces that affect alignment by the meniscus. We show that this deposition and alignment process can be used to generate spatially varying surface patterns that may be useful for applications that require targeted placement of nanotubes on a surface.
Mechanical Limitations of Materials for Steel Foil Based Flexible Electronics
This work investigates mechanical limitations of thin film materials on steel foil substrates for flexible electronic applications. A three layer structure consisting of 100 μm thick stainless steel foil as the substrate, followed by 1 μm thick spin-on-glass passivation layer and 0.3 μm thick patterned aluminum interconnect layer on top with varying widths between 10- 35 μm. A collapsing radius test method was adopted for the bending experiment and an elliptical curve fit was used to facilitate the strain measurement. The failure strain of aluminum interconnect layer was detected by monitoring the continuity of the test circuit during the experiment. The corresponding results reveal that the passivation layer cracked at a tensile strain of 0.46% and delaminated at a compressive strain of 0.68%. The metal interconnect layer ruptured at a tensile strain of 1.26% and delaminated from the substrate at a compressive strain of 1.22% due to the delamination of the passivation layer underneath. The steel foil substrate was plastically deformed at the relative small strain of 0.13%. The flexibility of steel foil based electronics can be effectively improved by using thinner foil substrates.
Effect of Pitch Rate on Time Evolution of Surface Topology on a Delta Wing
A basic delta wing of moderate sweep angle, representative of Unmanned Combat Air Vehicles (UCAVs) and Micro Air Vehicles (MAVs), undergoes a pitching maneuver. Near-surface flow patterns are visualized by a technique of high-image-density particle image velocimetry for a wide range of pitch rates. Five different universal states are defined during the relaxation process following cessation of the pitching motion. These states involve distinct patterns that can be defined in terms of topological features such as negative (separation) and positive (reattachment) bifurcation lines, saddle points, foci, and nodes. Such universal states can be identified for all pitch rates, extending over an eightfold range. Irrespective of the severity of the flow distortion at the end of the pitching maneuver, the relaxation of the flow involves the same sequence of universal states. The time delay to occurrence of the first universal state is very sensitive to the pitch rate. The delay between subsequent states is, however, nearly independent of pitch rate. Due to the highly three-dimensional nature of the flow, the flow patterns and topological states will also be visualized by stereoscopic particle image velocimetry.
Power Consumption And Granular Flow In A Vibro-Fluidized Stirred Granular Bed
This work examines the behavior of a deep granular bed subject to simultaneous vertical vibration and stirring. The power necessary to stir a 5.6 cm diameter and 20 cm deep granular bed of 150 micron glass beads using a 4-blade vane impeller was measured over a wide range of forcing conditions. Impeller rotation rates from 0 – 1000 rpms and vibration accelerations in the range 0 ≤ Γ = ω2a/g ≤ 4.0 were explored. Both the power required for stirring and vibration were recorded. Sharp changes in vane power draw indicate flow transitions from dense granular flow to vibro-fluidized flow at a critical acceleration (Γc ). The total power profile (vane plus vibration power) demonstrates a minimum just above the critical acceleration. Progressive increases or decreases n both vane speed and Γ independently show hysteresis as the flow bifurcates between two primary states of dense granular flow and loose-packed, vibrofluidized behavior. These observations are compared to those found in fluidized systems and flows generated in high-shear granulators. Finally, preliminary results of direct density measurements using a localized capacity probe will be discussed. These observations are compared to those found in fluidized systems and flows generated in high-shear granulators.
Using LIBS Measurements for Coal Quality Monitoring and Upgraded Power Plant Control
Laser-induced breakdown spectroscopy (LIBS) has been developed and applied to measure key inorganic components in coal ash such as Si, Al, Fe, Na, Ca, Mg, and K – , which contribute to the slagging and fouling behavior of pulverized coal. A coal inventory was assembled from fuels used at utility boilers with a range of slagging/fouling characteristics. These coals included Eastern US bituminous and sub-bituminous coals and some foreign fuels. These coals were tested in a custom-built LIBS analyzer for ash metal composition and major element concentration (i.e. O, S, N). Detection limits are on the order of 0.01 percent, with variations depending on the particular element and type of coal. Measurement repeatability and accuracy are typically within 10 percent (relative). The elemental analyses were used in concert with a neural network algorithm to calculate a slagging and fouling index for the prediction of deposition behavior. The values of the predicted indices are very similar to the resulting indices from standard coal analysis procedure. A future on-line version of the LIBS system will be installed at a 650 MW coal-fired unit and equipped with expert system-based software to demonstrate the real-time capabilities of this technology to monitor coal ash composition, slagging/fouling prediction and recommend actions to the operators for boiler operation modifications for slagging/fouling mitigation.