Electrochromic nanostructures grown on a silicon nanowire template

Vertically grown Si nanowires were prepared as a nanotemplate for conducting polymers. Electrochromic (EC) PEDOT (poly(3,4-ethylenedioxythiophene)) layer was successfully grown on Si nanowires by electrochemical polymerization method to form PEDOT nanowires having average wall thickness of approximately 60nm. As-prepared conductive nanowire electrode was applied to a low voltage working EC device by fabricating an all solid state EC device. The EC properties of the device were enhanced in the nanowire structure, showing reversible fast optical transition by applying +/-2V. The response time (t(R)) of the EC device from the PEDOT grown on Si nanowires was approximately 0.7s, which was much faster than that from PEDOT film coated on ITO glass electrochemically (t(R)=1.9s).     

Multi sensor data fusion for improving performance and reliability of fully automatic welding system

This paper presents a new generation of system for pressure vessel and shipbuilding. Typical pressure vessel and ship building weld joint preparations are either traditional V, butt, fillet grooves or have narrow or semi narrow gap profiles. The fillet and U groove are prevalently used in heavy industries and shipbuilding to melt and join the parts. Since the wall thickness can be up to 6 in. or greater, welds must be made in many layers, each layer containing several passes. However, the welding time for the conventional processes such as submerged arc welding (SAW) and flux cored arc welding (FCAW) can be many hours. Although SAW and FCAW are normally mechanized processes, pressure vessel and ship structures welding up to now have usually been controlled by a full time operator. The operator has typically been responsible for positioning each individual weld run, for setting weld process parameters, for maintaining flux and wire levels, for removing slag and so on. The aim of the system is to develop a high speed welding system with multi-torch for increasing the production speed on the line and to remove the need for the operator so that the system can run automatically for the complete multi-torch multi-layer weld. To achieve this, a laser vision sensor and a special image processing algorithm have been made. Also, the multi-torch welding system can be applicable for fine grained steel because of the high welding speed and lower heat input compared to a conventional welding process.     

Mechanical characterization of micro/nanoscale structures for MEMS/NEMS applications using nanoindentation techniques

Mechanical properties of micro/nanoscale structures are needed to design reliable micro/nanoelectromechanical systems (MEMS/NEMS). Micro/nanomechanical characterization of bulk materials of undoped single-crystal silicon and thin films of undoped polysilicon, SiO(2), SiC, Ni-P, and Au have been carried out. Hardness, elastic modulus and scratch resistance of these materials were measured by nanoindentation and microscratching using a nanoindenter. Fracture toughness was measured by indentation using a Vickers indenter. Bending tests were performed on the nanoscale silicon beams, microscale Ni-P and Au beams using a depth-sensing nanoindenter. It is found that the SiC film exhibits higher hardness, elastic modulus and scratch resistance as compared to other materials. In the bending tests, the nanoscale Si beams failed in a brittle manner with a flat fracture surface. The notched Ni-P beam showed linear deformation behavior followed by abrupt failure. The Au beam showed elastic-plastic deformation behavior. FEM simulation can well predict the stress distribution in the beams studied. The nanoindentation, scratch and bending tests used in this study can be satisfactorily used to evaluate the mechanical properties of micro/nanoscale structures for use in MEMS/NEMS.     

Improvement of the hydrogen-storage kinetics of Mg by reactive mechanical grinding with 10 wt.% Fe2O3 and 5 wt.% Ni

The addition of Fe₂O₃ to Mg is believed to be able to increase the hydriding rate of Mg, and the addition of Ni is thought to be able to increase the hydriding and dehydriding rates of Mg. A sample Mg-(10wt.%Fe₂O₃, 5 wt.%Ni) was prepared by mechanical grinding under H₂ (reactive mechanical grinding). The as-milled sample absorbed 4.61 wt.% of hydrogen at 593 K under 12 bar H₂ for 60 min. Its activation was accomplished after two hydriding-dehydriding cycles. The activated sample absorbed 4.59 wt.% of hydrogen at 593 K under 12 bar H₂ for 60 min, and desorbed 3.83 wt.% hydrogen at 593 K under 1.0 bar H₂ for 60 min. The activated Mg-(10wt.%Fe₂O₃, 5 wt.%Ni) had a slightly higher hydriding rate at the beginning of the hydriding reaction but a much higher dehydriding rate compared with the activated Mg-10 wt.%Fe₂O₃. prepared via spray conversion. After hydriding-dehydriding cycling, Fe₂O₃ was reduced, Mg₂Ni was formed by the reaction of Mg with Ni, and a small fraction of Mg was oxidized.     

Forced air cooling by using manifold microchannel heat sinks

A study of manifold microchannel (MMC) heat sinks for forced air cooling was performed experimentally. The manifold microchannel heat sink differs from a traditional microchannel (TMC) heat sink in that the flow length is greatly reduced to a small fraction of the total length of the heat sink. In other words, the MMC heat sink features many inlet and outlet channels, alternating at a periodic distance along the length of the microchannels while the TMC heat sink features one inlet and one outlet channels. The present study primarily focused to investigate the effects of geometrical parameters on the thermal performance of the manifold microchannel heat sinks for optimal design. Also, the thermal resistances of the MMC heat sinks were compared with those of the TMC heat sinks. Experimental results showed the thermal resistances of MMC heat sinks were affected strongly by the pumping power, the microchannel width and the manifold inlet/outlet channel width, but weakly by the microchannel thickness-width ratio and the microchannel depth coorporated with the manifold inlet/outlet channel width. However, it was found that there existed the optimum values of the latter parameters. Under the optimum condition of geometrical parameters in the present study, the thermal resistance of the MMC heat sink was approximately 35% lower than that of a TMC heat sink, which clearly demonstrated the effectiveness of using a manifold.     

Impact collapse characteristics of CF/Epoxy composite tubes for light-weights

This paper investigates the collapse characteristics of CF/Epoxy composite tubes subjected to axial loads as changing interlaminar number and outer ply orientation angle. The tubes are aften used for automobiles, aerospace vehicles, trains, ships, and elevators. We have performed static and dynamic impact collapse tests by a way of building impact test machine with vertical air-compression. It is fanad that CF/Epoxy tube of the 6 interlaminar number (C-type) with 90° outer orientation angle and trigger absorbed more energy than the other tubes (A, B and D types). Also collapse mode depended upon outer orientation angle of CF/Epoxy tubes and loading type as well ; typical collapse modes of CF/Epoxy tubes are wedged, splayed and fragmentcl.     

Supersonic flow of hydrogen and air in a duct with variable area

A chemically nonequilibrium supersonic flow of hydrogen and air has been investigated in a duct with conically divergent or convergent walls. Elementary reaction schemes of radicals involved in reaction of hydrogen-air have been considered and solved through the CHEMKIN code. The aim was to promote an understanding of characteristics of chemically nonequilibrium supersonic flow by introducing a simple mathematical formulation. The temperature, pressure, and density all were found to decrease for divergent ducts as the flow was accelerated, whereas they increased for a slightly convergent duct or a constant cross-sectional area duct. For the divergent nozzle with a greater degree the flow became chemically frozen. But it was quite necessary to take account of the effect of chemical nonequilibrium in a moderately expanded or all convergent conical ducts. As was expected, it was found that the temperature, pressure and Mach number were reduced for a fuel-lean mixture.     

Magnetically suspended contact-free linear actuator for precision stage

With the development of precision manufacturing technologies, the importance of precision positioning devices is increasing. Conventional actuators, dual stage or mechanically contacting type, have limitation in coping with performance demands. As a possible solution, magnetic suspension technology was studied. Such a contact-free system has advantages in terms of high accuracy, low production cost and easy adaptability to high precision manufacturing processes. This paper deals with magnetically suspended multi-degrees of freedom actuator which can realize large linear motion. In this paper, the operating principle is explained with the magnetic force analysis, and the equations of motion are derived. Experimental results of the implemented system are also given.     

A single dof magnetic levitation system using time delay control and reduced-order observer

Magnetic levitation systems are required to have a large operating range in many applications. As one method to solve this problem, Time Delay Control (TDC) is applied to a single-axis magnetic levitation system in this paper. A reduced-order observer is utilized to estimate states excluding measurable states in the control law. The system consists of a square air-core solenoid and a circular permanent magnet attached on a plastic ball. Theoretical magnetic forces of the system are obtained on the basis of the location of the magnet around the solenoid. The magnetic levitation force is obtained by the experiment, and then compared with the theoretical one. As the results of the control experiments, the nonlinear controller (TDC : 1–2 mm) has a larger operating range than the linear controller (PD control: 1–1.4 mm), and is superior to linear control in the robustness to the modeling uncertainty and the performance of the disturbance rejection.     

Effect of acid treatment of Fe-BEA zeolite on catalytic N<Subscript>2</Subscript>O conversion

The effect of acid treatment on the physical and chemical characteristics of BEA zeolite, as well as the catalytic activity of the Fe-BEA catalyst for N₂O reduction under NH₃-selective catalytic reduction (NH₃-SCR) conditions, was examined. The acid treatment caused dealumination of BEA and enrichment of the silanol groups on vacant T-sites and the Brønsted acid sites. As the acid treatment time increased, the silanol groups and the weak acid sites in BEA also increased. Because the weak acid sites behave as anchoring sites for Fe ions, the catalytic activity also increased as the treatment time increased. However, extended exposure of BEA to acid decreased the catalytic activity of the Fe-BEA catalyst somewhat, and decreased the silanol groups and weak acid sites. The catalytic activity and the amount of weak acid sites were well correlated with the BEA acid treatment time.