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The objective of this study was to measure the wear response of immature bovine articular cartilage tested against glass or alloys used in hemiarthroplasties. Two cobalt chromium alloys and a stainless steel alloy were selected for these investigations. The surface roughness of one of the cobalt chromium alloys was also varied within the range considered acceptable by regulatory agencies. Cartilage disks were tested in a configuration that promoted loss of interstitial fluid pressurization to accelerate conditions believed to occur in hemiarthroplasties. Results showed that considerably more damage occurred in cartilage samples tested against stainless steel (10 nm roughness) and low carbon cobalt chromium alloy (27 nm roughness) compared to glass (10 nm) and smoother low or high carbon cobalt chromium (10 nm). The two materials producing the greatest damage also exhibited higher equilibrium friction coefficients. Cartilage damage occurred primarily in the form of delamination at the interface between the superficial tangential zone and the transitional middle zone, with much less evidence of abrasive wear at the articular surface. These results suggest that cartilage damage from frictional loading occurs as a result of subsurface fatigue failure leading to the delamination. Surface chemistry and surface roughness of implant materials can have a significant influence on tissue damage, even when using materials and roughness values that satisfy regulatory requirements.

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Two sets of silicon detectors were irradiated with 1 MeV neutrons to different fluences and then characterized. The first batch were ordinary p - i - n photodiodes fabricated from high-resistivity silicon, while the second batch were gold-doped power diodes fabricated from silicon material initially of low resistivity . The increase in reverse leakage current after irradiation was found to be more in the former case than in the latter. The fluence dependence of the capacitance was much more pronounced in the p - i - n diodes than in the gold-doped diodes. Furthermore, photo current generation by optical means was less in the gold doped devices. All these results suggest that gold doping in silicon somewhat suppresses the effects of neutron irradiation.

Low-frequency noise (1/f noise) has been measured in light emitting diodes (LEDs) which have been subjected to an accelerated life test by means of large forward bias current pulses. Over a large range of stress pulses the electrical and functional LED properties remain unaltered but an increase in the 1/f noise level was seen and this was correlated with the device reliability. The product 'initial noise × initial rate of noise increase' correlated best with the LED lifetime.

Low-frequency electrical noise is well accepted as a very sensitive measure of the quality and reliability of electrical components and electronic devices. It shows changes in magnitude very much greater than in the static electrical properties. The excess noise is due to defects and nonideality in the device. Although the excess noise is a general indicator of quality there can be many physical processes that could be involved. These noise contributions are additive and therefore not easy to distinguish so that the noise is not so valuable as a diagnostic tool. Also, there is not a detailed understanding of some noise sources, such as in some semiconductor devices. Recently devices have continued to become smaller in size so that the noise signal has become more significant compared to the real signal and the number of individual defects involved has become fewer. This has resulted in a growing trend to the study of the time varying signal rather than the noise spectral density. A review is given of the developments in the subject over the last few years.

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A simple electronic circuit is described which can be used in the student laboratory to demonstrate and study nonlinear effects and chaos. The circuit shows the changes to the dynamical properties of the system with respect to three control parameters: the applied voltage amplitude and frequency and the circuit damping. The response voltage and its derivative can be displayed to give the phase space plot and the bifurcation diagram against any control parameter. The circuit is sufficiently ideal and stable to allow comparison of its analog output with the output obtained from standard digital computer simulations. As examples, the routes to chaos with respect to the control parameters and the bifurcation route to chaos, which follows the Feigenbaum scenario, are shown.