Morphology and rheology of an immiscible polymer blend subjected to a step electric field under shear flow.

We have investigated the structural change of an immiscible polymer blend in shear flow when subjected to a step electric field. During the process three-dimensional images were successfully constructed with a confocal scanning laser microscope and at the same time the transient shear stress was also measured. The interface tensor was calculated from the images. Several factors are incorporated into the shear stress, such as the bulk viscosity, the interfacial tension and the Maxwell stress. We performed an experiment to separate the Maxwell stress from the total shear stress. The results are discussed in terms of the interface tensor.

A Monte Carlo study of lung counting efficiency for female workers of different breast sizes using deformable phantoms.

There are currently no physical phantoms available for calibrating in vivo counting devices that represent women with different breast sizes because such phantoms are difficult, time consuming and expensive to fabricate. In this work, a feasible alternative involving computational phantoms was explored. A series of new female voxel phantoms with different breast sizes were developed and ported into a Monte Carlo radiation transport code for performing virtual lung counting efficiency calibrations. The phantoms are based on the RPI adult female phantom, a boundary representation (BREP) model. They were created with novel deformation techniques and then voxelized for the Monte Carlo simulations. Eight models have been selected with cup sizes ranging from AA to G according to brassiere industry standards. Monte Carlo simulations of a lung counting system were performed with these phantoms to study the effect of breast size on lung counting efficiencies, which are needed to determine the activity of a radionuclide deposited in the lung and hence to estimate the resulting dose to the worker. Contamination scenarios involving three different radionuclides, namely Am-241, Cs-137 and Co-60, were considered. The results show that detector efficiencies considerably decrease with increasing breast size, especially for low energy photon emitting radionuclides. When the counting efficiencies of models with cup size AA were compared to those with cup size G, a difference of up to 50% was observed. The detector efficiencies for each radionuclide can be approximated by curve fitting in the total breast mass (polynomial of second order) or the cup size (power).