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Matchstick and coin shaped specimens are used to determine the material strength consistency and mean fracture strength under five different stress rations, using Weibull statistics.Many practical loading modes of these simple shapes are assessed. For the best, the necessary experimental work and results of the analyses are presented and illustrated for as-fired reaction-bonded silicon nitride (RBSN) tested at room-temperature.

Static axial push-on and lift-off, and push-on and twist-off experiments were designed and performed to measure the effective, room-temperature coefficient of friction μ for different design femoral prosthesis cone taper joints comprising a universal head on a stem spigot. Alumina and metal heads were tested on metal spigots using either distilled water, Ringer's solution, blood or no lubricant. Complementary push-on and lift-off friction tests of Araldite model joints for subsequent frozen-stress, photoelastic stress analysis were performed at 130°C.It was found that lubricant caused little decrease in the values of the coeficient of friction in prosthesis tapers. The values measured were typically μ =0.2 for an alumina head on a Co-Cr-Mo or Ti-6Al-4V spigot, μ = 0.15 for a Co-Cr-Mo head on a Co-Cr-Mo or Ti-6Al-4V spigot and μ =0.13 for a stainless steel head on a stainless steel spigot. For Araldite photoelastic models of an alumina head on a Vitallium spigot, as-cast taper surfaces lubricated with silicone grease gave consistent friction of typically μ = 0.14. The axial displacements of model heads on their spigots were compared with predicted values and previously measured values for prosthesis heads.

Three-dimensional, frozen-stress photoelasticity was used to study the best shape for a proposed alumina universal head loaded on to a Vitallium cone taper spigot with a 30° inclined force, as in vivo. Typical cone taper friction values were reproduced in the photoelastic models.The location of the highest tensile stresses in the Mark I shape with a flat crown was found to be on the inner surface of the crown. Changing to a torispherical surface in the Mark II shape reduced this magnitude. However, the Mark III shape with a hemispherical inner crown surface gave even lower stress there, equal to the maximum value of the hoop stress at the taper, which was measured to be fairly uniform both around and along the taper except at the ends where contact pressure concentrations were found to occur and it became reduced.Lamé axisymmetric cylinder stress predictions were found to be useful approximations to measured values and were generally overestimates of the tensile hoop stress at the head taper surface.

1The patterns of discharge of spontaneous GABAA‐mediated inhibitory postsynaptic currents (sIPSCs), originating from the nucleus reticularis thalami (NRT), and their modulation by GABAg autoreceptors, were studied in rat thalamocortical (TO) neurones using whole‐cell voltage‐clamp recordings in brain slices.2sIPSCs were recorded in all ventro‐basal (VB) and dorsal lateral geniculate (LGN) neurones. In VB neurones, in the presence of tetraethylammonium (TEA, 5 mm), these sIPSCs can occur in bursts at frequencies of either 0.1 or 1–2 Hz. In the presence of tetrodotoxin (TTX), these bursting activities are replaced by the continuous discharge of miniature IPSCs (mIPSCs), recorded in the absence of TEA, at a frequency of 4 Hz. The kinetic properties of mIPSCs were similar in VB and LGN TC neurones.3In VB TC neurones the GABABreceptor agonist (±)‐baclofen, at a concentration of 0.05 μm, decreased the mIPSC frequency by 22% without affecting their amplitude distribution. Increasing the (±)‐baclofen concentration to 1 and 10 μmcaused similar reductions (41 and 47%, respectively) in the mIPSCs frequency: these values were significantly different from the one observed with 0.05 μm(±)‐baclofen. In LGN TC neurones, where mIPSCs originate from both NRT and local interneurone terminals, 1 μm(±)‐baclofen produced a 66% reduction in the mIPSC frequency.4The GABABreceptor antagonist CGP55845A (50 nm) not only blocked the baclofen‐mediated decrease in mIPSC frequency, but also produced a 52% increase in the mIPSC frequency compared with control in three out of seven neurones. Application of CGP55845A (50–500 nm) alone produced a 77 % increase in the mIPSC frequency in three out of nine VB neurones, and in the LGN, CGP55845A (100 nm) produced a 53% increase in four out of nine neurones. CGP55845A (100 nm) also reversibly increased the amplitude of evoked GABAAIPSCs by 74 and 57 % in three out of three VB and three out of five LGN neurones, respectively.5Application of GABA (1.5–5 μm) decreased the mIPSC frequency in VB TC neurones by a similar extent (48%) as 1–10 μm(±)‐baclofen.6In the presence of 100 μmCd2+, (±)‐baclofen still decreased the mIPSC frequency by about 40%, indicating that the effect of presynaptic GABABreceptor activation on spontaneous GABA release did not occur through a reduction of voltage‐dependent Ca2+currents.7Cd2+(100 μm) decreased the amplitude of both mIPSCs and isoguvacine‐induced current by 30 and 19%, respectively, indicating an effect of this divalent cation on postsynaptic GABAAreceptors.8We conclude that GABABautoreceptors are present on the GABAergic terminals within the thalamic sensory nuclei and that these receptors can be tonically activated by the ambient GABA.