A demonstration of the resolution of NMR imaging in biological systems

Summary A proton NMR imaging study of several fruit specimens demonstrates the integrity and resolution of this new imaging method.Acknowledgment. We thank Professor E. R. Andrew, Dr W. S. Moore and Miss C. Simaroj for their contributions. The work was supported by MRC grant G975-102.     

The effect of Nicotinamide Adenine Dinucleotide on lipolysis in adipose tissue in vitro

Zusammenfassung Es wird gezeigt, dass Nikotinamid Adenin Dinukleotid (NAD) eine starke Hemmung auf die Lipolyse der Fettgewebe in vitro ausübt. Untersuchung der antilipolytischen Wirkung verschiedener Bestandteile des NAD ergab, dass für die Hemmungswirkung die Gegenwart des Adenosins, nicht aber die der Nikotinsäure notwendig ist.     

Strong effect of dispersal network structure on ecological dynamics

A central question in ecology with great importance for management, conservation and biological control is how changing connectivity affects the persistence and dynamics of interacting species. Researchers in many disciplines have used large systems of coupled oscillators to model the behaviour of a diverse array of fluctuating systems in nature. In the well-studied regime of weak coupling, synchronization is favoured by increases in coupling strength and large-scale network structures (for example 'small worlds') that produce short cuts and clustering. Here we show that, by contrast, randomizing the structure of dispersal networks in a model of predators and prey tends to favour asynchrony and prolonged transient dynamics, with resulting effects on the amplitudes of population fluctuations. Our results focus on synchronization and dynamics of clusters in models, and on timescales, more appropriate for ecology, namely smaller systems with strong interactions outside the weak-coupling regime, rather than the better-studied cases of large, weakly coupled systems. In these smaller systems, the dynamics of transients and the effects of changes in connectivity can be well understood using a set of methods including numerical reconstructions of phase dynamics, examinations of cluster formation and the consideration of important aspects of cyclic dynamics, such as amplitude.     

STUDYING COMPLEX ADAPTIVE SYSTEMS

Complex adaptive systems(cas)-systems that involve many components that adapt orlearn as they interact - are at the heart of important contemporary problems.The study of cas posesunique challenges:Some of our most powerful mathematical tools,particularly methods involving fixedpoints,attractors,and the like.are of limited help in understanding the development of cas.This papersuggests ways to modify research methods and tools,with an emphasis on the role of computer-basedmodels.to increase our understanding of cas.     

A central role for denervated tissues in causing nerve sprouting

One of the oldest known forms of neuronal plasticity is the ability of peripheral nerves to grow and form functional connections after damage to neighbouring axons. Yet the source of the signal which elicits this "sprouting" remains unknown. In mammalian muscles, paralysis-which gives rise to many of the changes which occur in denervated muscles-causes motor nerve terminals to sprout. Could the inactive muscle fibres (rather than nerve degeneration products, another likely source) be responsible for some of the sprouting found in partial denervation? We confirm in this paper that direct stimulation of a partially denervated muscle inhibits sprouting and show that stimulation does so by activating the denervated fibres. Consequently after partial denervation the same signal as that which causes terminal sprouting in a paralysed muscle is able to spread from the denervated muscle fibres to the nerves on the innervated fibres and initiate terminal sprouting.     

Long-term sensitivity of soil carbon turnover to warming

The sensitivity of soil carbon to warming is a major uncertainty in projections of carbon dioxide concentration and climate. Experimental studies overwhelmingly indicate increased soil organic carbon (SOC) decomposition at higher temperatures, resulting in increased carbon dioxide emissions from soils. However, recent findings have been cited as evidence against increased soil carbon emissions in a warmer world. In soil warming experiments, the initially increased carbon dioxide efflux returns to pre-warming rates within one to three years, and apparent carbon pool turnover times are insensitive to temperature. It has already been suggested that the apparent lack of temperature dependence could be an artefact due to neglecting the extreme heterogeneity of soil carbon, but no explicit model has yet been presented that can reconcile all the above findings. Here we present a simple three-pool model that partitions SOC into components with different intrinsic turnover rates. Using this model, we show that the results of all the soil-warming experiments are compatible with long-term temperature sensitivity of SOC turnover: they can be explained by rapid depletion of labile SOC combined with the negligible response of non-labile SOC on experimental timescales. Furthermore, we present evidence that non-labile SOC is more sensitive to temperature than labile SOC, implying that the long-term positive feedback of soil decomposition in a warming world may be even stronger than predicted by global models.