Validating clusterings of gene expression data

We propose a measure for the validation of clusterings of gene expression data. This measure also useful to estimate missing gene expression levels, based the similarity information contained in a given clustering. It is shown that this measure is an improvement over the figure of merit, an existing validation measure especially developed for clusterings of gene expression data

Evolutionary Theorising on Technological Change and Sustainable Development

This paper examines the significance of evolutionary theorising on technological change for (technology) policies aiming to move society into a more ecologically sustainable direction. It is argued that fundamental changes in production processes and consumption patterns underpinned by alternative technological trajectories are required for achieving environmental sustainability. Such changes, which go beyond the control of particular pollutants and eco-efficiency improvements, are referred to as technological regime shifts. Technological regime shift changes do not refer so much to the diffusion of environmental technologies but rather to system changes producing environmental benefits because the new regimes or trajectories are inherently more environmentally benign. An example of such a shift is found in the use of gas turbine for (co)generating electricity and heat. An important question is: how do technological regime shifts occur, and how can environmentally beneficial regime shifts be stimulated? Evolutionary theory, which emphasises the non-linear, branched nature of sociotechnical change, offers a useful framework for understanding and managing regime shifts. It draws attention to the lock-in phenomenon and also suggests a way in which it can be escaped: through the development of niches for new technologies. It appears that evolutionary perspectives have something to offer here, but they need to be further developed to be of practical use

Modeling a Cortical Auxin Maximum for Nodulation: Different Signatures of Potential Strategies

Lateral organ formation from plant roots typically requires the de novo creation of a meristem, initiated at the location of a localized auxin maximum. Legume roots can form both root nodules and lateral roots. From the basic principles of auxin transport and metabolism only a few mechanisms can be inferred for increasing the local auxin concentration: increased influx, decreased efflux, and (increased) local production. Using computer simulations we investigate the different spatio-temporal patterns resulting from each of these mechanisms in the context of a root model of a generalized legume. We apply all mechanisms to the same group of preselected cells, dubbed the controlled area. We find that each mechanism leaves its own characteristic signature. Local production by itself can not create a strong auxin maximum. An increase of influx, as is observed in lateral root formation, can result in an auxin maximum that is spatially more confined than the controlled area. A decrease of efflux on the other hand leads to a broad maximum, which is more similar to what is observed for nodule primordia. With our prime interest in nodulation, we further investigate the dynamics following a decrease of efflux. We find that with a homogeneous change in the whole cortex, the first auxin accumulation is observed in the inner cortex. The steady state lateral location of this efflux reduced auxin maximum can be shifted by slight changes in the ratio of central to peripheral efflux carriers. We discuss the implications of this finding in the context of determinate and indeterminate nodules, which originate from different cortical positions. The patterns we have found are robust under disruption of the (artificial) tissue layout. The same patterns are therefore likely to occur in many other contexts

Solution Space-Based Complexity Analysis of ATC Aircraft Merging Tasks

Air traffic controller workload is considered to be a limiting factor in the growth of air traffic. In this paper a new method of assessing controller task demand load will be developed and tested. Based on the hypothesis that workload is primarily caused by the complexity of the task to be conducted, the concept of the “solution space” is described. For any particular air traffic control problem, the solution space describes the constraints in the environment that limit (and therefore, guide) air traffic controller decisions and actions. The complexity of that particular control problem can then be analyzed by considering the properties of the solution space. The task of merging an aircraft into a stream of other aircraft that fly along a fixed route is considered. An experiment has been conducted in which subjects were instructed to solve merging problem scenarios of varying complexity. After completing each scenario, subjects were asked to rate the task complexity. High correlations are found between several solution space properties and reported complexity