A graph-theoretic method for organizing overlapping clusters into trees,multiple trees,or extended trees

A clustering that consists of a nested set of clusters may be represented graphically by a tree. In contrast, a clustering that includes non-nested overlapping clusters (sometimes termed a “nonhierarchical” clustering) cannot be represented by a tree. Graphical representations of such non-nested overlapping clusterings are usually complex and difficult to interpret. Carroll and Pruzansky (1975, 1980) suggested representing non-nested clusterings with multiple ultrametric or additive trees. Corter and Tversky (1986) introduced the extended tree (EXTREE) model, which represents a non-nested structure as a tree plus overlapping clusters that are represented by marked segments in the tree. We show here that the problem of finding a nested (i.e., tree-structured) set of clusters in an overlapping clustering can be reformulated as the problem of finding a clique in a graph. Thus, clique-finding algorithms can be used to identify sets of clusters in the solution that can be represented by trees. This formulation provides a means of automatically constructing a multiple tree or extended tree representation of any non-nested clustering. The method, called “clustrees”, is applied to several non-nested overlapping clusterings derived using the MAPCLUS program (Arabie and Carroll 1980).     

CLUSCALE ("CLUstering and multidimensional SCAL[E]ing"): A Three-Way Hybrid Model Incorporating Overlapping Clustering and Multidimensional Scaling Structure

Traditional techniques of perceptual mapping hypothesize that stimuli are differentiated in a common perceptual space of quantitative attributes. This paper enhances traditional perceptual mapping techniques such as multidimensional scaling (MDS) which assume only continuously valued dimensions by presenting a model and methodology called CLUSCALE for capturing stimulus differentiation due to perceptions that are qualitative, in addition to quantitative or continuously varying perceptual attributes or dimensions. It provides models and OLS parameter estimation procedures for both a two-way and a three-way version of this general model. Since the two-way version of the model and method has already been discussed by Chaturvedi and Carroll (2000), and a stochastic variant discussed by Navarro and Lee (2003), we shall deal in this paper almost entirely with the three-way version of this model. We recommend the use of the three-way approach over the two-way approach, since the three-way approach both accounts for and takes advantage of the heterogeneity in subjects’ perceptions of stimuli to provide maximal information; i.e., it explicitly deals with individual differences among subjects.     

The use of tetracycline fluorescence to identify necrosis of renal tubules and to assess renal blood flow

Zusammenfassung Tetracyclin wird in mit vorübergehender Ischämie oder mit verschiedenen Nephrotoxinen geschädigten Tubulusepithelzellen intensiver gespeichert. Diese zunehmende Speicherung ist bereits nachweisbar, wenn histologische Veränderungen noch unausgeprägt sind.Die Untersuchung der tubulären Tetracyclinaufnahme ist auch für die Beurteilung renaler Blutverteilungsänderungen wertvoll.     

Chance and necessity: the evolution of morphological complexity and diversity

The primary foundation for contemplating the possible forms of life elsewhere in the Universe is the evolutionary trends that have marked life on Earth. For its first three billion years, life on Earth was a world of microscopic forms, rarely achieving a size greater than a millimetre or a complexity beyond two or three cell types. But in the past 600 million years, the evolution of much larger and more complex organisms has transformed the biosphere. Despite their disparate forms and physiologies, the evolution and diversification of plants, animals, fungi and other macroforms has followed similar global trends. One of the most important features underlying evolutionary increases in animal and plant size, complexity and diversity has been their modular construction from reiterated parts. Although simple filamentous and spherical forms may evolve wherever cellular life exists, the evolution of motile, modular mega-organisms might not be a universal pattern.     

Ciliary neurotrophic factor prevents degeneration of motor neurons in mouse mutant progressive motor neuronopathy.

Ciliary neurotrophic factor (CNTF) supports the survival of embryonic motor neurons in vitro and in vivo, and prevents lesion-mediated degeneration of rat motor neurons during early post-natal stages. Here we report that CNTF greatly reduces all the functional and morphological changes in pmn/pmn mice, an autosomal recessive mutant leading to progressive caudo-cranial motor neuron degeneration. The first manifestations of progressive motor neuronopathy in homozygous pmn/pmn mice become apparent in the hind limbs at the end of the third post-natal week, and all the mice die up to 6 or 7 weeks after birth from respiratory paralysis. Treatment with CNTF prolongs survival and greatly improves motor function of these mice. Moreover, morphological manifestations, such as loss of motor axons in the phrenic nerve and degeneration of facial motor neurons, were greatly reduced by CNTF, although the treatment did not start until the first symptoms of the disease had already become apparent and substantial degenerative changes were already present. The protective and restorative effects of CNTF in this mouse mutant give new perspectives for the treatment of human degenerative motor neuron diseases with CNTF.