Microgripper using a diamond like carbon/metal bilayer

A novel normally closed microcage has been fabricated and characterized. This device was made from a highly compressively stressed diamond like carbon (DLC) and electroplated Ni bimorph structure. The large stress in the DLC causes the bimorph layer to curve once it is released from the substrate. The radius of curvature is in the range of 18 - 50μm, and can be controlled by varying the DLC and the Ni thicknesses. The devices can be operated in a pulsed mode current with low operation temperature, and can be opened by ∼60μm laterally with a power consumption of only ∼16mW. © 2004 IEEE.

Osteoblast and monocyte responses to 444 ferritic stainless steel intended for a Magneto-Mechanically Actuated Fibrous Scaffold

The rationale behind this work is to design an implant device, based on a ferromagnetic material, with the potential to deform in vivo promoting osseointegration through the growth of a healthy periprosthetic bone structure. One of the primary requirements for such a device is that the material should be non-inflammatory and non-cytotoxic. In the study described here, we assessed the short-term cellular response to 444 ferritic stainless steel; a steel, with a very low interstitial content and a small amount of strong carbide-forming elements to enhance intergranular corrosion resistance. Two different human cell types were used: (i) foetal osteoblasts and (ii) monocytes. Austenitic stainless steel 316L, currently utilised in many commercially available implant designs, and tissue culture plastic were used as the control surfaces. Cell viability, proliferation and alkaline phosphatase activity were measured. In addition, cells were stained with alizarin red and fluorescently-labelled phalloidin and examined using light, fluorescence and scanning electron microscopy. Results showed that the osteoblast cells exhibited a very similar degree of attachment, growth and osteogenic differentiation on all surfaces. Measurement of lactate dehydrogenase activity and tumour necrosis factor alpha protein released from human monocytes indicated that 444 stainless steel did not cause cytotoxic effects or any significant inflammatory response. Collectively, the results suggest that 444 ferritic stainless steel has the potential to be used in advanced bone implant designs. © 2011 Elsevier Ltd.

DLC/TiNi microcage for biopsy applications

A TiNi/diamond-like-carbon (DLC) microcage for biological application has been designed, fabricated and characterized. A compressively stressed DLC film with TiNi pattern on top lifts the fingers upwards once they are released from the substrate, and the microcage can be closed through shape memory effect of top TiNi film with temperature below 80°C. Further heating above 100°C, the gradual opening of the microcage can be obtained due to thermal bimorph effect. The biocompatibility of both the TiNi and DLC films has been proved using a cell-culture method.

Performance of CMOS Devices in Silicon-on-Sapphire Films After Solid-Phase Epitaxial Growth With Rapid Electron-Beam Heating

The crystal quality of 0.3-μm-thick as-grown epitaxial silicon-on-sapphire (SOS) was improved using solid-phase epitaxy (SPE) by implantation with silicon to 1015 ions/cm2 at 175 keV and rapid annealing using electron-beam heating, n-channel and p-channel transistormobilities increased by 31 and 19 percent, respectively, and a reduction in ring-oscillator stage delay confirmed that crystal defects near the upper silicon surface had been removed. Leakage in n-channel transistors was not significantly affected by the regrowth process but for p-channel transistors back-channel leakage was considerably greater than for the control devices. This is attributed to aluminum released by damage to the sapphire during silicon implantation. © 1985 IEEE

Laser micromachining of sputtered DLC films

DLC films with different thicknesses (from 100 nm to 1.9 μm) were deposited using sputtering of graphite target in pure argon atmosphere without substrate heating. Film microstructures (sp2/sp3 ratio) and mechanical properties (modulus, hardness, stress) were characterized as a function of film thickness. A thin layer of aluminum about 60 nm was deposited on the DLC film surface. Laser micromachining of Al/DLC layer was performed to form microcantilever structures, which were released using a reactive ion etching system with SF6 plasma. Due to the intrinsic stress in DLC films and bimorph Al/DLC structure, the microcantilevers bent up with different curvatures. For DLC film of 100 nm thick, the cantilever even formed microtubes. The relationship between the bimorph beam bending and DLC film properties (such as stress, modulus, etc.) were discussed in details. © 2005 Elsevier B.V. All rights reserved.

X-ray observation of micro-failures in granular piles approaching an avalanche

An X-ray imaging technique is used to probe the stability of 3-dimensional granular packs in a slowly rotating drum. Well before the surface reaches the avalanche angle, we observe intermittent plastic events associated with collective rearrangements of the grains located in the vicinity of the free surface. The energy released by these discrete events grows as the system approaches the avalanche threshold. By testing various preparation methods, we show that the pre-avalanche dynamics is not solely controlled by the difference between the free surface inclination and the avalanche angle. As a consequence, the measure of the pre-avalanche dynamics is unlikely to serve as a tool for predicting macroscopic avalanches.

The flow of steel into the construction sector

Half of the world's annual production of steel is used in constructing buildings and infrastructure. Producing this steel causes significant amounts of carbon dioxide to be released into the atmosphere. Climate change experts recommend this amount be halved by 2050; however steel demand is predicted to have doubled by this date. As process efficiency improvements will not reach the required 75% reduction in emissions per unit steel output, new methods must be examined to deliver service using less steel production. To apply such methods successfully to construction, it must first be known where steel is used currently within the industry. This information is not available so a methodology is proposed to estimate it from known data. Results are presented for steel flows by product for ten construction sectors for both the UK and the world in 2006. An estimate for steel use within a 'typical' building is also published for the first time. Industrial buildings and utility infrastructure are identified as the largest end-uses of steel, while superstructure is confirmed as the main use of steel in a building. The results highlight discrepancies in previous steel estimates and life-cycle assessments, and will inform future research on lowering demand for steel, hence reducing carbon emissions. © 2012 Elsevier B.V. All rights reserved.

End-of-range defects in germanium and their role in boron deactivation

We investigated the thermal evolution of end-of-range (EOR) defects in germanium and their impact on junction thermal stability. After solid-phase epitaxial regrowth of a preamorphized germanium layer, EOR defects exhibiting dislocation loop-like contrast behavior are present. These defects disappear during thermal annealing at 400 °C, while boron electrical deactivation occurs. After the whole defect population vanishes, boron reactivation is observed. These results indicate that germanium self-interstitials, released by EOR defects, are the cause of B deactivation. Unlike in Si, the whole deactivation/reactivation cycle in Ge is found to take place while the maximum active B concentration exceeds its solubility limit. © 2010 American Institute of Physics.

Detailed design of242mAm breeding in pressurized water reactors

There is growing interest in the use of 242mAm as a nuclear fuel. Because of its very high thermal fission cross section and its large number of neutrons released per fission, it can be used for various unique applications, such as space propulsion, medical applications, and compact energy sources. Since the thermal absorption cross section of 242mAm is very high, the best way to obtain 242mAm is by the capture of fast or epithermal neutrons in 241Am. However, fast spectrum reactors are not readily available. In this paper, we explore the possibility of producing 242mAm in existing pressurized water reactors (PWRs) with minimal interference in reactor performance. As suggested in previous studies on the subject, the 242mAm breeding targets are shielded with strong thermal absorbers in order to suppress the thermal neutron flux that causes 242mAm destruction. Since 242mAm enrichment within the Am target mainly depends on the neutron energy distribution, which in turn depends on the Am target thickness and on the neutron filter cutoff energy (thermal absorber type), this unique Am target design was developed. In our study, Cd, Sm, and Gd were considered as thermal neutron filters, as suggested by Cesana et al. The most favorable results were obtained by irradiating Am targets covered either with Gd or Cd. In these cases, up to 8.65% enrichment of 242mAm is obtained after 4.5 yr (three successive PWR fuel cycles) of irradiation. It was also found that significant quantities [up to 1.3 kg/GW (electric)-yr] of 242mAm can be obtained in PWR reactors without notable interference with reactor performance. However, in order to maintain the original fuel cycle length, the enrichment of the driver (UO2) fuel must be increased by ∼1%, raised from the conventional 4.5 to 5.5%, depending on the thermal neutron filter used. The most important reactivity feedback coefficients for fuel assemblies containing the 242mAm breeding targets were evaluated and found to be close to those of a standard PWR. Another product of neutron capture in the 241Am reaction is 238Pu. It was found that in a typical 1000 MW (electric) PWR core with one-third of the fuel assemblies containing 241Am targets, up to 15.1 kg of 238Pu enriched to 80% can be produced per year.

Non-equilibirum condensation effects on the flow field and the performance of a low pressure steam turbine

The influence of non-equilibrium condensation on the flow field and performance of a three stage low pressure model steam turbine is examined using modern three dimensional CFD techniques. An equilibrium steam model and a non-equilibrium steam model, which accounts for both subcooling and condensation effects, are used, and have been verified by comparison with test data in an earlier publication [1]. The differences in the calculated flow field and turbine performance with these models show that the latent heat released during condensation influences both the thermodynamic and the aerodynamic performance of the turbine, leading to a change in inlet flow angles of about 5°. The calculated three dimensional flowfield is used to investigate the magnitude and distribution of the additional thermo-dynamic wetness loss arising from steam condensation under non-equilibrium flow conditions. Three simple methods are described to calculate this, and all show that this amounts to around 6.5% of the total losses at the design condition. At other load conditions the wetness losses change in magnitude and axial distribution in the turbine. © 2010 by ASME.