Griffiths phase, metal-insulator transition, and magnetoresistance of doped manganites

A phenomenological model is developed for systematic study of the universal features in metal-insulator transition and magnetoresistivity of mixed-phase manganites. The approach is based on utilization of some hypothesis appropriate to the Preisach picture of the magnetization process for half-metallic ferromagnets and an assumption that in doped manganites a Griffiths-type phase exists just above the magnetic-ordering temperature. Within the model, the system is considered as a random three-dimensional resistor network where a self-consistent formation of paths with metal and polaron types of conductivity is not only due to magnetic field variation but also due to temperature changes, as well. Both mechanisms of intrinsic percolation transition are considered on one basis. The theory is able to replicate the basic regularities found experimentally for doped manganites resistivity dependence on temperature and magnetic field without the need for empirical input from the magnetoresistive data. Within the approach a natural basis has arisen for a qualitative classification of magnetoresistive materials into those, such as La0.7Sr0.3MnO3, showing modest magnetoresistivity, and those, such as La0.7Ca0.3MnO3, showing large magnetoresistivity

Vascular Editor: From Angiographic Images to 3D Vascular Models

Modern imaging techniques are able to generate high-resolution multimodal angiographic scans. The analysis of vasculature using numerous 2D tomographic images is time consuming and tedious, while 3D modeling and visualization enable presentation of the vasculature in a more convenient and intuitive way. This calls for development of interactive tools facilitating processing of angiographic scans and enabling creation, editing, and manipulation of 3D vascular models. Our objective is to develop a vascular editor (VE) which provides a suitable environment for experts to create and manipulate 3D vascular models correlated with surrounding anatomy. The architecture, functionality, and user interface of the VE are presented. The VE includes numerous interactive tools for building a vascular model from multimodal angiographic scans, editing, labeling, and manipulation of the resulting 3D model. It also provides comprehensive tools for vessel visualization, correlation of 2D and 3D representations, and tracing of small vessels of subpixel size. Education, research, and clinical applications of the VE are discussed, including the atlas of cerebral vasculature. To our best knowledge, there are no other systems offering similar functionality as the VE does