RESUMEN
This study focuses on developing a comprehensive model of a rigid overhead system, which includes essential components such as the suspension structure, positioning clamp, and expansion joint. The modelling approach utilizes finite element theory and beam elements to accurately represent the displacement, stiffness, and mass characteristics of the system. The models also incorporate the suspension structure and positioning line clamp, which play crucial roles in suspending and positioning the busbar. Various suspension structures and positioning line clamps are evaluated based on their dynamic characteristics. The expansion joint, responsible for connecting different anchor sections of the rigid overhead system, undergoes a detailed analysis. Different assembly scenarios, including ideal and deflected assembly conditions, are considered. To simulate the dynamic behaviour of the expansion joint, additional beams are introduced into the system model. The primary finding of the analysis is that the maximum stresses observed in the constructed expansion joint model, under different temperature conditions and normal/deflected assembly conditions, remain within the permissible stress limits of the material. This indicates a high level of safety. However, certain areas exhibit stress concentration, particularly at the sliding block B and sliding rod A positions. This stress concentration is primarily attributed to the unique assembly form of the expansion joint. To improve stress distribution and enhance service reliability, the analysis suggests optimizing the installation deflection angle and geometric design of the expansion joint. Furthermore, the concentrated mass at the expansion joint significantly impacts the current collection quality of the pantograph-overhead system. Mitigating this negative impact can be achieved by reducing the mass of the expansion joint.
RESUMEN
The effect of a recombinant RGD (arginine-glycine-aspartic acid)-containing fusion protein, cellulose-binding domain (CBD)-RGD, on the cellular adhesion to a biomedical polyurethane (PU) was evaluated. A series of different cell lines, as well as freshly harvested animal cells, were grown on the PU surfaces with or without CBD-RGD, in serum or serum-free media. The results showed that the enhancement of cellular attachment by CBD-RGD varied with cell types. This is believed to be a result of the unique integrin receptors on each type of cell surface. The existence of certain divalent ions (Mg2+ and Mn2+) may increase the efficacy of the CBD-RGD, in a cell type-dependent manner. The fusion protein was also found to inhibit the platelet activation. The effect of CBD-RGD was further examined in two other substrate materials, poly(L-lactide) (PLLA) and poly(lactide-co-glycolide) (PLGA). The effect on cellular adhesion correlated with the amount of CBD-RGD physically adsorbed on the material surface.