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The impact of chemical reactions on the thermal boundary conductance (TBC) of Au/metal contact/β-Ga2O3 layered samples as a function of contact thickness is investigated using high-throughput thermoreflectance measurements. A maximum in TBC of 530 ± 40 (260 ± 25) MW/m2 K is discovered for a Cr (Ti) contact at a thickness of 2.5 (5) nm. There is no local maximum for a Ni contact, for which the TBC saturates at 410 ± 35 MW/m2 K for thicknesses greater than 3 nm. Relative to the Au/β-Ga2O3 interface, which has a TBC of 45 ± 7 MW/m2 K, these nanoscale contacts enhance TBC by factors of 6 to 12. The TBC maximum only exists for metals capable of forming oxides that are enthalpically favorable compared to β-Ga2O3. The formation of Cr2O3, via oxygen removal from the β-Ga2O3 substrate, is confirmed by TEM analysis. The reaction-formed oxide layer reduces the potential TBC and leads to the maximum, which is followed by a plateau at a lower value, as its thickness saturates due to passivation. Many advanced materials are prone to similar chemical reactions, impacting contact engineering and thermal management for a variety of applications.

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A benign, but aggressive, giant cell tumor of tendon sheath developed over a period of 20 years into a metasasizing, histologiclly malignant giant cell tumor. Ultrastructure of the malignant tumor showed the same five cell types as described in giant cell tumors of tendon sheath. Even the same crystals were identified in the osteoblast-like and osteoclast-like cells. It therefore appears reasonable to assume that giant cell tumors of tendon sheath indeed are neoplasms with a malignant potential and not an inflammatory with partial osseous differentiation. No ultrastructural similarities with fibrous histiocytoma were apparent.

A postal survey of 160 members of the Neurosurgical Anaesthetists' Travelling Club was conducted in 1991 to investigate the current use of the sitting position in neurosurgery. There was a 78% response rate; at least one reply was received from every neurosurgical centre in the UK. Patients were placed normally in the sitting position for posterior fossa surgery in eight (20%) of the centres, compared with 19 (53%) in 1981. For posterior cervical spinal surgery, only three (7%) centres routinely used the sitting position, compared with 11 (31%) in 1981. Thus in the period 1981-1991, the number of neurosurgical centres using the sitting position routinely, decreased by more than 50%. Current techniques of ventilation and monitoring for the sitting position are discussed briefly.

Low resistance, high dynamic range reconfigurable phase change switch for radio frequency applications

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