A Mathematical Model of the Stability Control of Human Thorax and Pelvis Movements During Walking

A mathematical model is developed to study the human thorax and pelvis movements in the frontal plane during normal walking. The model comprises of two-link base-excited inverted pendulums with one-degree of rotational freedom for each link. Since the linear motion of the pelvis has a significant effect on the upper body stability, this effect is included in the model by having a base point moving in the frontal plane in a general way. Furthermore, because the postural stability is the primary requirement of normal human walking, the control law is developed based on Lyapunov's stability theory, which guarantees the stability of the pendulum system around the up-right position. To evaluate the model, the simulation results, including the angular displacement of each link and the torque applied on each link, are compared with those from gait measurements. It is shown that the simulation results match those from gait measurements closely. These results suggest that the proposed model can provide a useful framework for analysis of postural control mechanisms.     

Dynamic field testing of coating chemistry candidates by a rotating disk system

Quick and reliable testing is crucial for the development of new fouling release (FR) coatings. Exposure of these coatings to natural multispecies communities is essential in evaluating their efficacy. To this end, we present a rotating disk setup for dynamic field exposure. To achieve a well-defined flow on the surface of the disk, an easy to use sample mounting system was developed that provides a smooth and even surface. We related the angular velocity of the disk to the wall shear stress on the surface with a hydrodynamic model. The wall shear stress was adjusted to values previously found to be suitable to discriminate dynamic diatom attachment on different coating chemistries in the lab. The effect of the dynamic conditions was shown by comparing polystyrene slides under static and dynamic exposure. Using a set of self-assembled monolayers, the discrimination potential of the assay in a multispecies environment was demonstrated.     

Phenylacetylglycine, a putative biomarker of phospholipidosis: its origins and relevance to phospholipid accumulation using amiodarone treated rats as a model.

Amiodarone was given to male Sprague-Dawley rats at a dose of 150 mg kg(-1) day(-1) for 7 consecutive days to induce phospholipidosis in the lungs of treated rats. Amiodarone was given alone or concurrently with phenobarbitone. Animals given amiodarone had raised total phospholipid in serum, lung and lymphocytes, and elevated lyso(bis)phosphatidic acid (LBPA) in all tissues. Urinary and plasma phenylacetylglycine (PAG) and hepatic portal:aortal phenylacetate (PA) ratio were increased, whereas hepatic phenylalanine hydroxylase (PAH) activity and plasma phenylalanine:tyrosine ratio were not affected. Phenobarbitone treatment increased hepatic total P450 content and induced 7-pentoxyresorufin O-dealkylatian (PROD) activity, as expected, but had no effect on any other biochemical parameter. Plasma amiodarone concentration was reduced in rats co-administered both drugs and phospholipid accumulation in target tissues was attenuated compared with rats treated with amiodarone alone. However, phenobarbitone co-administration failed to alter the magnitude of response with regards to urinary PAG excretion and plasma concentration of its precursors after amiodarone treatment. Increased intestinal absorption of PAG precursors probably resulted in the raised urinary PAG after amiodarone treatment. Urinary PAG correlated weakly with serum, lymphocyte and lung phospholipids. However, urinary PAG excretion was similar in rats dosed solely with amiodarone or in combination with phenobarbitone, despite the fact that the degree of phospholipid accumulation was far less in rats given the combined treatment. Nevertheless, urinary PAG was raised only in animals exhibiting abnormal phospholipid accumulation in target tissues and may thus be useful as a surrogate biomarker for phospholipidosis.     

The responses of a lotic mayfly Nousia sp. (Ephemeroptera: Leptophlebiidae) to moving water and light of different wavelengths

1. Although laboratory studies of the behaviour of aquatic macroinvertebrates are common, there has been little critical evaluation of the importance of test conditions to them. We used a common Australian leptophlebiid mayfly, Nousia sp., to investigate responses to light, wavelength of light, presence or absence of cover and still or flowing water.
2. Nousia sp. showed substantial qualitative differences in behaviour, as measured by movement, when there was no refuge (in the form of a crevice beneath a tile) present in the experimental arena.
3. We found no evidence of diel periodicity in activity in Nousia sp.
4. Nousia sp. did not respond to infra-red, red or green light at a flux density of 18–19 μmol m^–2 s^–1.
5. Nymphs were three times more likely to remain stationary in flowing water (mean velocity 0.10 m s^–1) than in still water.
6. We conclude that generalized assumptions about test conditions for experiments designed to quantify laboratory behaviour in benthic macroinvertebrates are unjustified and that evaluation of the individual requirements of test species should be conducted routinely.