Transport by molecular motors in the presence of static defects

The transport by molecular motors along cytoskeletal filaments is studied theoretically in the presence of static defects. The movements of single motors are described as biased random walks along the filament as well as binding to and unbinding from the filament. Three basic types of defects are distinguished, which differ from normal filament sites only in one of the motors' transition probabilities. Both stepping defects with a reduced probability for forward steps and unbinding defects with an increased probability for motor unbinding strongly reduce the velocities and the run lengths of the motors with increasing defect density. For transport by single motors, binding defects with a reduced probability for motor binding have a relatively small effect on the transport properties. For cargo transport by motors teams, binding defects also change the effective unbinding rate of the cargo particles and are expected to have a stronger effect.Comment: 20 pages, latex, 7 figures, 1 tabl

A model for the run out table cooling in a compact rolling mill

A fundamental part of hot rolling of steel strip processing takes place in the run out table of industrial mills. It is in this place that most of the material transforms from austenite to ferrite. Cooling of the steel strip is promoted by high and low pressure water jets coming from different types of headers. The efficiency of such headers depends on the type of header, their flow and position, as well as the speed at which the strip is delivered from the rolling mill. Computer simulation is carried out by means of a two-dimensional finite difference model that takes into account the number, flow, position and type of headers used along the run out table. It is found that the cooling capacity of the headers is affected by the velocity of the hot rolled steel strip

Modelling descaling during hot rolling of steel

A computer model was developed to study the stresses that develop within the oxide formed on the surface of reheated steel slabs. The model considers that the crust grows during reheating following temperature dependent parabolic rates, and, as result of its thickness and growth rate, it will be stressed. Removal of this crust takes place by the impingement of water from high pressure jets installed in descaling units, which are located prior to deformation to avoid oxide imprint on the steel surface. Removal of the oxide layer depends on the velocity and amount of the water, as well as the force of the impact. A criterion based on these parameters can be established to determine the feasibility for oxide removal

CFD simulation of airborne pathogen transport due to human activities

Computational Fluid Dynamics (CFD) is an increasingly popular tool for studying the impact of design interventions on the transport of infectious microorganisms. While much of the focus is on respiratory infections, there is substantial evidence that certain pathogens, such as those which colonise the skin, can be released into, and transported through the air through routine activities. In these situations the bacteria is released over a volume of space, with different intensities and locations varying in time rather than being released at a single point. This paper considers the application of CFD modelling to the evaluation of risk from this type of bioaerosol generation. An experimental validation study provides a direct comparison between CFD simulations and bioaerosol distribution, showing that passive scalar and particle tracking approaches are both appropriate for small particle bioaerosols. The study introduces a zonal source, which aims to represent the time averaged release of bacteria from an activity within a zone around the entire location the release takes place. This approach is shown to perform well when validated numerically though comparison with the time averaged dispersion patterns from a transient source. However, the ability of a point source to represent such dispersion is dependent on airflow regime. The applicability of the model is demonstrated using a simulation of an isolation room representing the release of bacteria from bedmaking