Pseudo-T2 mapping for normalization of T2-weighted prostate MRI

Magnetic Resonance Materials in Physics, Biology and Medicine - Signal intensity normalization is necessary to reduce heterogeneity in T2-weighted (T2W) magnetic resonance imaging (MRI) for...     

Transmission electron microscopy study of a dental gallium alloy

Analytical transmission electron microscopy (TEM) studies of a dental gallium alloy have been carried out. This commercial Ga alloy was made by triturating a Ag-Sn-Cu-rich alloy powder with a liquid Ga alloy containing Ga, In and Sn. Ga alloys are of increasing interest as an alternative to amalgam. The dental material studied in the present work was found to be a composite consisting of remaining, undissolved particles from the Ag-based alloy powder in a matrix of reaction products with the liquid Ga alloy. The phases in the matrix and the remaining Ag-based alloy particles have been identified by electron diffraction, high resolution electron microscopy and energy dispersive X-ray spectroscopy. the following phases were identified: orthorhombic Ag₃Sn, cubic -Cu₉Ga₄, cubic Ag₉In₄, tetragonal -Sn and hexagonal Ag₂Ga. In addition to these well-known phases Ga-rich regions of Cu-Ga were observed consisting of an intergrowth of the tetragonal CuGa₂ and one of the cubic -Cu₉Ga₄ phases.     

Learning short synfire chains by self-organization

A model of cortical neurons capable of sustaining a low level of spontaneous activity is investigated. Without learning the activity of the network is chaotic. We report on attempts to learn synfire chains in this type of network by introducing a Hebbian learning mechanism and exciting a small set of neurons at random intervals. We discuss the types of instabilities that can arise and prevent the formation of long synfire chains and also discuss various biologically plausible mechanisms which to some extent cure these instabilities.     

Monte Carlo simulations of systems with complex energy landscapes

Non-traditional Monte Carlo simulations are a powerful approach to the study of systems with complex energy landscapes. After reviewing several of these specialized algorithms we shall describe the behavior of typical systems including spin glasses, lattice proteins, and models for “real” proteins. In the Edwards-Anderson spin glass it is now possible to produce probability distributions in the canonical ensemble and thermodynamic results of high numerical quality. In the hydrophobic-polar (HP) lattice protein model Wang-Landau sampling with an improved move set (pull-moves) produces results of very high quality. These can be compared with the results of other methods of statistical physics. A more realistic membrane protein model for Glycophorin A is also examined. Wang-Landau sampling allows the study of the dimerization process including an elucidation of the nature of the process.     

Monte Carlo simulations of the HP model (the "Ising model" of protein folding)

Using Wang–Landau sampling with suitable Monte Carlo trial moves (pull moves and bond-rebridging moves combined) we have determined the density of states and thermodynamic properties for a short sequence of the HP protein model. For free chains these proteins are known to first undergo a collapse “transition” to a globule state followed by a second “transition” into a native state. When placed in the proximity of an attractive surface, there is a competition between surface adsorption and folding that leads to an intriguing sequence of “transitions”. These transitions depend upon the relative interaction strengths and are largely inaccessible to “standard” Monte Carlo methods.     

An Industrial Case Study on Distributed Prioritisation in Market-Driven Requirements Engineering for Packaged Software

When developing packaged software, which is sold ‘off-the-shelf’ on a worldwide marketplace, it is essential to collect needs and opportunities from different market segments and use this information in the prioritisation of requirements for the next software release. This paper presents an industrial case study where a distributed prioritisation process is proposed, observed and evaluated. The stakeholders in the requirements prioritisation process include marketing offices distributed around the world. A major objective of the distributed prioritisation is to gather and highlight the differences and similarities in the requirement priorities of the different market segments. The evaluation through questionnaires shows that the stakeholders found the process useful. The paper also presents novel approaches to visualise the priority distribution among stakeholders, together with measures on disagreement and satisfaction. Product management found the proposed charts valuable as decision support when selecting requirements for the next release, as they revealed unforeseen differences among stakeholder priorities. Conclusions on stakeholder tactics are provided and issues of further research are identified, including ways of addressing identified challenges.