Ion beam, focused ion beam, and plasma discharge machining

Non-conventional methods of machining are used for many engineering applications where the traditional processes fail to be cost-effective. Such processes include Ion Beam Machining (IBM), focused ion beam (FIB) machining and plasma discharge machining. The mechanisms of material removal and associated hardware and software developed for industrial applications of these fascinating electro-physical and chemical machining processes are reviewed together with the latest research findings. © 2009 CIRP.

Boundary effects on the vibration statistics of a random plate

This paper considers the estimation of statistics of displacement of a vibrating rectangular plate with random wave scatterers. The influence of uncertainty is investigated using point impedance theory. Coherent boundary effects are seen, which decrease when the number of scatterers increases. The boundary effect is investigated using images and the first side and corner reflections are found to be a minimum requirement to estimate the spatial correlation. Statistics for point driven response are investigated under the assumption that the statistics of the natural frequencies follow those of the Gaussian Orthogonal Ensemble (GOE). The estimates are compared with Monte Carlo simulation results, and they show good agreement. © 2012 Elsevier Ltd. All rights reserved.

Intrinsic state lifetimes in Pd103 and Cd106,107

The mean-lifetimes, τ, of various medium-spin excited states in Pd103 and Cd106,107 have been deduced using the Recoil Distance Doppler Shift technique and the Differential Decay Curve Method. In Cd106, the mean-lifetimes of the Iπ=12+ state at Ex=5418 keV and the Iπ=11- state at Ex=4324 keV have been deduced as 11.4(17)ps and 8.2(7)ps, respectively. The associated β2 deformation within the axially-symmetric deformed rotor model for these states are 0.14(1) and 0.14(1), respectively. The β2 deformation of 0.14(1) for the Iπ=12+ state in Cd106 compares with a predicted β2 value from total Routhian surface (TRS) calculations of 0.17. In addition, the mean-lifetimes of the yrast Iπ=152- states in Pd103 (at Ex=1262 keV) and Cd107 (at Ex=1360 keV) have been deduced to be 31.2(44)ps and 31.4(17)ps, respectively, corresponding to β2 values of 0.16(1) and 0.12(1) assuming axial symmetry. Agreement with TRS calculations are good for Pd103 but deviate for that predicted for Cd107. © 2007 The American Physical Society.

Interaction between Fe-based oxygen carriers and n-heptane during chemical looping combustion

Chemical looping combustion (CLC) uses a metal oxide (the oxygen carrier) to provide oxygen for the combustion of a fuel and gives an inherent separation of pure CO2 with minimal energy penalty. In solid-fuel CLC, volatile matter will interact with oxygen carriers. Here, the interaction between iron-based oxygen carriers and a volatile hydrocarbon (n-heptane) was investigated in both a laboratory-scale fluidised bed and a thermogravimetric analyser (TGA). Experiments were undertaken to characterise the thermal decomposition of the n-heptane occurring in the presence and in the absence of the oxygen carrier. In a bed of inert particles, carbon deposition increased with temperature and acetylene appeared as a possible precursor. For a bed of carrier consisting of pure Fe2O3, carbon deposition occurred once the Fe2O3 was fully reduced to Fe. When the Fe2O3 was doped with 10 mol % Al2O3 (Fe90Al), deposition started when the carrier was reduced to a mixture of Fe and FeAl2O4, the latter being very unreactive. Furthermore, when pure Fe2O3 was fully reduced to Fe, agglomeration of the fluidised bed occurred. However, Fe90Al did not give agglomeration even after extended reduction. The results suggest that Fe90Al is promising for the CLC of solid fuels. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Control and operation of a high temperature superconducting synchronous motor

We have built a four-pole high temperature superconducting (HTS) permanent magnet synchronous motor (PMSM) in our lab. At this stage, the HTS PMSM uses two 2G HTS racetrack coils, which are YBCO wires, type 344 from AMSC, and four conventional copper coils as stator windings. 75 YBCO bulks are mounted on the surface of the rotor. After the pulsed field magnetization system had been developed and tested in our lab in 2011, the rotor can trap a four-pole magnetic field. This makes HTS bulks possible for motor application, other than HTS coils. The HTS PMSM can successfully run at a low speed of around 150 rpm for an initial test. This paper states theoretical and practical works on the HTS PMSM's operation including HTS motor drive development and its application. © 2002-2011 IEEE.

Nanowire and graphene architectures for room temperature THz detection

Antenna-coupled field effect transistors have been developed as plasma-wave THz detectors in both InAs nanowire and graphene channel material. Room temperature operation has been achieved up to frequencies of 1.5 THz, with noise equivalent powers as low as a few 10-11 W/Hz1/2, and high-speed response. © 2012 IEEE.

Theoretical and experimental magnetization loss comparison between IBAD coils and RABiTS coils

This paper presents a comparative study of ac magnetization losses in two types of 2 G HTS racetrack coils. The magnetic substrate made by RABiTS is the main difference between the two types, because ferromagnetic loss caused by magnetic substrate is accounted into the total ac losses. IBAD and RABiTS tapes were successfully wound into racetrack shape with identical geometry. The measurements were carried out by using electromagnetic method with pick-up coils under a sinusoidally varying external magnetic field, with amplitudes up to 27 mT, ranging from 10 Hz to 100 Hz at a temperature of 77 K. The field was oriented perpendicularly to the surface of the tapes. Experimental measurements were validated by applying theoretical models and the results showed that the magnetization loss in the MAG RABiTS coil is always higher than that in the NON MAG coil due to the presence of the magnetic substrate, which increases the magnetic field penetration into the coil and causes higher magnetic flux density within the penetrated region. © 2002-2011 IEEE.

π-Conjugated molecules with fused rings for organic field-effect transistors: design, synthesis and applications

π-Conjugated molecular materials with fused rings are the focus of considerable interest in the emerging area of organic electronics, since the combination of excellent charge carrier mobility and high stability may lead to their practical applications. This tutorial review discusses the synthesis, properties and applications of π-conjugated organic semiconducting materials, especially those with fused rings. The achievements to date, the remaining problems and challenges, and the key research that needs to be done in the near future are all discussed.