Separation of isomeric xylenes by pervaporation through cellulose ester membranes

The interaction between the isomeric xylenes and different cellulose esters was investigated using solubility parameter considerations and through measurements of swelling values. p]Hansen's three-dimensional solubility parameters δd, δp, δh of all the components have been calculated. These values have been used to predict the interaction between polymer and penetrant. A measure for this interaction is given by Δ, which is the distance between polymer and penetrant in the δd, δr, δh space. As expected, the experimental swelling values varied in inverse proportion to the calculated Δ values. p]Pervaporation characteristics of different cellulose ester membranes were determined by measuring product rates and selectivity. The differences in membrane characteristics have been explained qualitatively in terms of the solubility parameter concept

Changes in Pilot Control Behaviour across Stewart Platform Motion Systems

Low-cost motion systems have been proposed for certain training tasks that would otherwise be performed on high-performance full flight simulators. These systems have shorter stroke actuators, lower bandwidth, and higher noise. The influence of these characteristics on pilot perception and control behaviour is unknown, and can be investigated by simulating a model of a simulator with limited capabilities on a high-end simulator. The platform limitations, such as a platform filter, time delay, and simulator noise characteristics, can then be removed one by one and their effect on control behaviour studied in isolation. By applying a cybernetic approach, human behaviour can be measured objectively in target-following disturbance-rejection control tasks. Experimental results show that small changes in time delay and simulator noise characteristics do not negatively affect human behaviour in these tasks. However, the motion system bandwidth has a significant effect on performance and control behaviour. Participants barely use motion cues when these have a low bandwidth, and instead rely on visual cues to generate lead to perform the control task. Therefore, simulator motion cues must be considered carefully in piloted control tasks in simulators and measured results depend on simulator characteristics as pilots adapt their control behaviour to the available cues

On the size and shape of excluded volume polymers confined between parallel plates

A number of recent experiments have provided detailed observations of the configurations of long DNA strands under nano-to-micrometer sized confinement. We therefore revisit the problem of an excluded volume polymer chain confined between two parallel plates with varying plate separation. We show that the non-monotonic behavior of the overall size of the chain as a function of plate-separation, seen in computer simulations and reproduced by earlier theories, can already be predicted on the basis of scaling arguments. However, the behavior of the size in a plane parallel to the plates, a quantity observed in recent experiments, is predicted to be monotonic, in contrast to the experimental findings. We analyze this problem in depth with a mean-field approach that maps the confined polymer onto an anisotropic Gaussian chain, which allows the size of the polymer to be determined separately in the confined and unconfined directions. The theory allows the analytical construction of a smooth cross-over between the small plate-separation de Gennes regime and the large plate-separation Flory regime. The results show good agreement with Langevin dynamics simulations, and confirm the scaling predictions.Comment: 15 pages, 3 figure

LTV O&M thema veiligheid: deelproject 1. Verbetering hydrodynamisch NEVLA model ten behoeve van scenario-analyse

In the framework of different projects, among which “LTV O&M thema Veiligheid - Deelproject 1” and “LTV O&M thema Toegankelijkheid - Ontwikkeling van een slibtransportmodel”, a calibration of the existing hydrodynamic NEVLA model of the Scheldt estuary is executed. This report gives a summary of all the steps which are undertaken to improve the model.The objective of the study “LTV O&M thema Veiligheid -- Deelproject 1” is to analyze the effect of different changes and their influence on the hydrodynamics of the estuary. Based on a literature review and data analysis some hypotheses concerning the change in tidal penetration in the estuary will be made. Afterwards these hypotheses will be verified with numerical models. In order to obtain reliable results, it is necessary that the numerical model performs well. Therefore a sensitivity analysis, a calibration and a validation of the NEVLA model, which will be used for 2D-3D hydrodynamic simulations, were carried out.The objective of the sensitivity analysis was to understand the impact of different model parameters on the tidal penetration. The results of this analysis are described in (Ides et al., 2008) and (Vanlede et al., 2008a). In (Vanlede et al., 2008b) the calibration was performed for the calculated water levels and discharges, based on the phase and magnitude of the most important harmonic tidal components of these parameters. In (Maximova et al., 2009) the calibration of the NEVLA model was extended. The resulting model parameters from (Vanlede et al., 2008b) were used as the reference simulation. The methodology was based on the comparison of phase and magnitude of the calculated and measured high and low water levels. This extended calibration was mainly focused on the Upper Sea Scheldt and the tributaries Zenne and Dijle because in these regions the differences between calculated and measured water levels were the largest. As a result of the calibration, the accuracy of the model for high water levels and low water levels was improved for most stations along the Scheldt estuary.The calibrated model was validated for a period with normal tide and for a period with an extreme high water. The calibrated model performs rather well for a period with normal tide. However, it does not simulate accurately a period with an extreme high water level. The reason for this and the possibilities to improve the model accuracy for such circumstances should be studied more in the future. The roughness field used for the calibrated model is strongly related to the bathymetry that was used during calibration of the model. If we use a different bathymetry for the scenario analysis the roughness field might change as well. Therefore, a simple roughness field without variation in the transversal direction was found, which gives rather similar results as the calibrated model with the space varying roughness field