The relation of conducting polymer actuator material properties to performance

Materials used in many branches of engineering are of low molecular weight and not flexible. As we develop more sophisticated engineering devices one can look to nature for inspiration and advocate the use of high molecular weight flexible materials. Conducting polymer actuators will soon be used in applications where traditional low molecular weight actuator systems are incapable of mimicking the functionality provided by nature's muscle. To incorporate conducting polymer actuators into engineering systems it is of high importance to not only model and predict the behavior of these actuators but also understand the connection of material properties to performance. In this paper, the importance of fundamental actuation mechanisms and the fundamental material properties of conducting polymer muscles such as ionic diffusion rate, electrochemical operating window, strain to charge ratio, ratio of charge carried by positive versus negative ions, and salt draining are discussed and their effect on performance is demonstrated. The relevance of engineered geometry to the performance of conducting polymer muscles is also shown. Our understanding of what limits the performance of existing conducting polymers actuators provides directions for the improvement of the next generation of conducting polymer actuators.     

Synrift to syntransform deformation along the Côte d’Ivoire–Ghana transform margin: evidence from deep-sea dives

Fourteen deep dives were conducted along the southern slope of the Côte d’Ivoire–Ghana marginal ridge. Detrital rock samples reveal Early Cretaceous synrift sediments. In situ observations and microtectonic analysis identify the nature and the timing of three successive episodes of deformation. Clay layers are affected by early diagenetic deformational structures such as slump microfolds and normal microfaults. Most of the clastic deposits display a second deformational episode. These structures result from a layer-parallel extension and are related to extensional synrift tectonics. The last stage of deformation is identified by right lateral wrench folds associated with brittle joints and slaty cleavage. It is attributed to the syntransform evolution of the Côte d’Ivoire–Ghana marginal ridge.     

Oceanic methane layers: the hydrocarbon seep bubble deposition hypothesis

ABSTRACT Bubble plumes from hydrocarbon seeps drive upwelling flows in the water column that can disappear if the bubbles dissolve. This may lead to formation of a layer enriched in gases and substances transported by the bubbles, a process we term bubble deposition. A review of observed dissolved methane layers in the North Sea showed their existence in an area of active seeping pockmarks at a height of ∼ 20–30 m above the sea bed, well below the thermocline. To test the bubble deposition hypothesis, rising seep bubbles were simulated numerically. The model predicted a dissolution depth consistent with the observed methane layer for ∼ 2700-µm-radius bubbles. The model also predicted that bubbles smaller than 3400 µm dissolved subsurface, decreasing to 2000 µm for a 10-cm s⁻¹ upwelling flow. We speculate that this layer may be attractive to marine organisms. Although North Sea seeps are not oily, this mechanism also applies to oily bubbles from hydrocarbon seeps or a leaking undersea gas/oil pipeline. Thus bubble deposition can create a subsurface oil layer which rises far slower than either the bubble stream or droplets entrained in the stream.     

Mathematical modelling of sea water intrusion,Nauru Island

A two-dimensional finite element model for density dependent groundwater flow was calibrated to simulate sea water intrusion in Nauru Island in the Central Pacific Ocean. Nauru Island occupies an area of 22 km² and supports a population of 8500. The island has been mined for its phosphate deposits and current reserves indicate that the mine has about eight years life remaining. The water supply of the island is about one third dependent on imported water which is also used as ballast on the phosphate ships. Imported water will not be available in the future, and a hydrogeological investigation shows that the island is underlain by a fresh water layer, less than 5 m thick. The freshwater layer overlies a thick transition zone of brackish water which in turn overlies sea water. Simulation of several management options shows that it is possible to substitute current importation of fresh water by careful extraction from the groundwater resources of the island.