Co-contraction of ankle muscle activity during quiet standing in individuals with incomplete spinal cord injury is associated with postural instability

Previous findings indicate that co-contractions of plantarflexors and dorsiflexors during quiet standing increase the ankle mechanical joint stiffness, resulting in increased postural sway. Balance impairments in individuals with incomplete spinal cord injury (iSCI) may be due to co-contractions like in other individuals with reduced balance ability. Here we investigated the effect of co-contraction between plantar- and dorsiflexors on postural balance in individuals with iSCI (iSCI-group) and able-bodied individuals (AB-group). Thirteen able-bodied individuals and 13 individuals with iSCI were asked to perform quiet standing with their eyes open (EO) and eyes closed (EC). Kinetics and electromyograms from the tibialis anterior (TA), soleus and medial gastrocnemius were collected bilaterally. The iSCI-group exhibited more co-contractions than the AB-group (EO: 0.208% vs. 75.163%, p = 0.004; EC: 1.767% vs. 92.373%, p = 0.016). Furthermore, postural sway was larger during co-contractions than during no co-contraction in the iSCI-group (EO: 1.405 cm/s2 vs. 0.867 cm/s2, p = 0.023; EC: 1.831 cm/s2 vs. 1.179 cm/s2, p = 0.030), but no differences were found for the AB-group (EO: 0.393 cm/s2 vs. 0.499 cm/s2, p = 1.00; EC: 0.686 cm/s2 vs. 0.654 cm/s2, p = 1.00). To investigate the mechanism, we performed a computational simulation study using an inverted pendulum model and linear controllers. An increase of mechanical stiffness in the simulated iSCI-group resulted in increased postural sway (EO: 2.520 cm/s2 vs. 1.174 cm/s2, p < 0.001; EC: 4.226 cm/s2 vs. 1.836 cm/s2, p < 0.001), but not for the simulated AB-group (EO: 0.658 cm/s2 vs. 0.658 cm/s2, p = 1.00; EC: 0.943 cm/s2 vs. 0.926 cm/s2, p = 0.190). Thus, we demonstrated that co-contractions may be a compensatory strategy for individuals with iSCI to accommodate for decreased motor function, but co-contractions may result in increased ankle mechanical joint stiffness and consequently postural sway.

Applicability of Concrete–Steel Composite Piles for Offshore Wind Foundations

Offshore wind-turbine support structures are largely made of steel since steel monopiles have accounted for the majority of installations in the last decade. As turbines become bigger, steel structures have led to an exponential increase in material and installation costs. From this point of view, the use of concrete for future support structures has been initiated. In this study, concrete–steel composite piles have been investigated. A pre-tensioned high strength concrete pile was placed in the lower part, mainly to support the axial load, and a steel pile in the upper part to resist the lateral load. A mechanical joint was adapted to connect the two different types of piles. Static axial, dynamic axial, and lateral load tests were performed to evaluate the load-displacement response of the composite pile, verify the integrity of the mechanical joint, and investigate its potential application to offshore wind foundations. This paper focused on the load-displacement response and the connection integrity; in particular, it investigated the lateral load-displacement response by comparing it to the results of beam-spring analysis. Based on the results from the field tests, a site-specific lateral load-displacement curve was suggested, and the connection integrity was verified.

Inverted Honeycomb Cell as a Reinforcement Structure for Building Soft Pneumatic Linear Actuators

In this article, the inverted honeycomb cell, known to exhibit an auxetic behavior, is considered to design two pneumatic linear actuators. The actuators are built using a combination of soft and rigid structures. They present complementary performances in terms of displacement, force, and stiffness. Experimental evaluations are conducted using prototypes produced using multimaterial additive manufacturing to combine soft and rigid materials with freedom of shape. The first actuator is inspired by origami structures. The possibility to obtain large deformations under low pressure is observed. The second actuator is based on a cylindrical auxetic structure based on the inverted honeycomb cell. Smaller deformation is reached but the design favors the off-axis stiffness, so the component can be integrated without any additional mechanical joint for translation. A discussion on the relative performances of these two actuators and their possible uses conclude the paper.

Complex evaluation of quality of glued-mechanical joints

The component tree of the complex index of the glued-mechanical joint quality is presented. Its main branches are purpose and processability indices, and economy indices. The change of quality indices when replacing the traditional mechanical joints (welded, riveted) by the glued-mechanical ones (glued-welded, glued-riveted) was examined. The classification of factors that have influence on fracture processes of glued-mechanical joints is given. Based on analysis of fracture characters of glued-mechanical joints, possible causes of fractures are demonstrated.