Kinematic modeling for the assessment of wheelchair user'sstability

A computer kinematic model was developed to simulate the lateral and transverse stabilities of wheelchair users in order to compare the effect of different backrests. This model is composed of ellipsoids and parallelepipeds representing the main components of the human body, the seating devices and the wheelchair. A fifteen-segment three-dimensional (3-D) model linked by spherical and revolute joints was created using the ADAMS software (Mechanical Dynamics, Inc.). Torsional springs and dampers are used at the joints to represent four sets of articulation stiffness. Seating devices are represented with 45 rectangular surface patches. The interface between human body and seating devices is modeled by contact elements, which included the specification of stiffness, damping, and deformation of cushions and buttocks. Simulations of a user and his wheelchair moving at 1.4 m/s on a tilted pathway were performed. Different indexes [trunk lateral tilt (TLT) and trunk transverse rotation (TTR)] were measured and compared to those of a similar experimental study on four subjects. The effect of joint stiffness was quantified and a sensitivity study showed the importance of the hip, neck, lumbar, and thoracic joint stiffness on model response (between 16% and 68%). Two backrests (standard and highly contoured) were tested with the kinematic model and their stability compared. Overall, the coherence between the simulations and the experiments shows that this approach is appropriate to compare various seating devices (maximal difference of 1.3° between the simulated and experimental curves for the intermediate joint stiffness sets). The smallest rotations of the highly contoured backrest (6.3° versus 8.9° for TLT and 3.9° versus 6.7° for TTR) suggest that the contouring of the mid torso is more efficient than the lower torso to provide stability to the wheelchair user. This model is an adequate tool to test and improve the design of seating aids     

Variability of wheat and other cereal water extract viscosity. 1 – Improvements in measuring viscosity

Experiments were carried out to improve the measurement of the viscosity of cereal water extracts. Water extract viscosity (WEV) appeared to be related to the particle size of the meals obtained after grinding. With ball‐mills, viscosity was higher than with rotating‐mills and also depended on grinding conditions such as quantity of grains, volume of the pot, number of balls and time of grinding. With rotating‐mills fitted with a 0.5 mm screen, viscosity was quite constant whatever the type of mill was used. It also appeared that WEV decreased with time after filtration and temperature of storing extracts, but temperature during extraction had no effect on wheat WEV. These results allowed a standard protocol for measuring wheat WEV to be defined. © 1999 Society of Chemical Industry