Kinematics of locomotion by cats with a single hindlimb deafferented

1. Cinematographic measurements were made of stepping by cats on a motor-driven treadmill, both normally and 2-3 wk after deafferentation of the LH (left hind) limb. 2. After surgery, rhythmic cycling of the LH limb was blurred whether the leg was dragged, as by some cats, or if it was lifted from the surface, as by others. 3. Interlimb coordination was also blurred with respect to normal, although distinct rhythms were still seen. The RH (right hind) limb descended prematurely and, in the walk, had a prolonged stance phase. The interval between touchdowns of hind- and forelimb on the left side no longer equaled that interval on the right side. 4. As is true for a normal cat, if the LH-deafferented animal stumbled, relatively normal single and interlimb cyclings were regained after several strides. 5. By kinematic analysis, force deficits were found in the deafferented LH limb both during the stance, when extensors should be most active, and the swing, when the limb failed to attain a normal position above the surface of the belt. Weight bearing by the LF (left fore) limb was altered in some animals. 6. At high speed, mean LH stance duration failed to decrease in the normal fashion. Inter-limb timings were reset to greater extent than in low-speed walking, as if the LH limb was being used only minimally. 7. It was concluded that both rhythm and force were impaired in the deafferented limb and also in the three intact limbs, whose weight bearing had to compensate for LH weakness. The changed mechanical demands after surgery were probably met by interactions between the remaining afferent input and central pattern generators so as to secure fairly effective and expedient locomotion.     

Scratch test model for the determination of fracture toughness

We revisit the scratch test within the framework of linear elastic fracture mechanics. In the analysis, we employ an Airy stress function approach to determine stresses and displacement in the vicinity of the scratch-blade–material interface, which serve as input for the evaluation of the energy release rate by means of the J-Integral. In contrast to previous models, the energy release rate thus found scales with the sum of the applied forces squared. This entails a linear relation between the applied forces and , where w is the scratch width and d the scratch depth. This analytical scaling is validated using experimental scratch data on cement paste and sandstone, which shows that the proposed approach provides a convenient way to determine the fracture toughness from scratch tests carried out with different scratch widths and depths.     

Positive Effect of Periodic Micropatterns on Compression Ring Friction

Internal combustion engines are increasingly regulated in regard to efficiency and environmental impact, which requires advanced optimization strategies of engine components. The contact between the top ring and the cylinder liner is critical to the efficiency of an internal combustion engine. As shown in a previous study, an amorphous carbon coating can greatly improve the friction properties of piston rings. This work expands on these results by fabricating laser-interference-induced microchannels on the coating perpendicular to the direction of movement with a mean depth of 0.97 and 3.13 μm spatial period to further optimize the tribology. Fired single-cylinder engine measurements of the microtextured rings show a significant reduction in mean piston assembly friction of 5% for operation points that are relevant for urban transportation and up to 10% for specific operation points. Subsequent multibody elastohydrodynamic simulations prove that measured friction changes result from the compression ring microtexture. In particular, the microtexture increases the hydrodynamic pressure, reduces hydrodynamic losses, and leads to 20% lowered compression ring losses for an entire combustion cycle of the investigated operation point. In the future, such tribological concepts can be deployed in internal combustion engines that are powered by sustainable hydrogen or methanol.