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Spiking neural networks are usually limited in their applications due to their complex mathematical models and the lack of intuitive learning algorithms. In this paper, a simpler, novel neural network derived from a leaky integrate and fire neuron model, the ‘cavalcade’ neuron, is presented. A simulation for the neural network has been developed and two basic learning algorithms implemented within the environment. These algorithms successfully learn some basic temporal and instantaneous problems. Inspiration for neural network structures from these experiments are then taken and applied to process sensor information so as to successfully control a mobile robot.

Hepatitis C virus is a genetically heterogeneous RNA virus that is a major cause of liver disease worldwide. Here, we show that, despite its extensive heterogeneity, the evolution of hepatitis C virus is primarily shaped by negative selection and that numerous coordinated substitutions in the polyprotein can be organized into a scale-free network whose degree of connections between sites follows a power-law distribution. This network shares all major properties with many complex biological and technological networks. The topological structure and hierarchical organization of this network suggest that a small number of amino acid sites exert extensive impact on hepatitis C virus evolution. Nonstructural proteins are enriched for negatively selected sites of high centrality, whereas structural proteins are enriched for positively selected sites located in the periphery of the network. The complex network of coordinated substitutions is an emergent property of genetic systems with implications for evolution, vaccine research, and drug development. In addition to such properties as polymorphism or strength of selection, the epistatic connectivity mapped in the network is important for typing individual sites, proteins, or entire genetic systems. The network topology may help devise molecular intervention strategies for disrupting viral functions or impeding compensatory changes for vaccine escape or drug resistance mutations. Also, it may be used to find new therapeutic targets, as suggested in this study for the NS4A protein, which plays an important role in the network. complex systems | scale-free network | covariation | natural selection | epistasis

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2007.01227.x Byline: R.J. MITCHELL, C. D. CAMPBELL (*), S. J. CHAPMAN (*), G. H. R. OSLER (*), A. J. VANBERGEN, L. C. ROSS, C. M. CAMERON (*), L. COLE Keywords: Betula; Calluna moorland; cascades; collembola; decomposition; ecosystem engineer; mites; soil; succession Abstract: Summary Single species can have a disproportionate effect on ecosystem function and diversity, yet our understanding of the importance of single species in driving terrestrial ecosystems during succession remains poor. Utilizing a long-term experiment, where birch was planted on heather moorland 20 years ago, the cascading effects of a single tree species (Betula pubescens) on ecosystem characteristics (plant species richness, soil chemistry, soil fauna and decomposition rates) were tested. Under the birch, plant species richness decreased and the vegetation composition changed, with lower cover of grasses and Vaccinium myrtillus. The depth of the soil organic horizon, its moisture content and percentage carbon were all smaller under the birch than under the heather. Concentrations of available phosphorus and mineralizable-N were significantly greater in the soil under birch than under the heather plots. Decomposition was faster in the birch than in the heather plots. The abundance and species richness of collembola and oribatid, mesostigmatid and prostigmatid mites were all significantly greater under the birch than under the heather. The durability of the engineering effects of the birch was studied in a second experiment. Plots were established in first generation birch woodland that had developed on Calluna-dominanted moorland. The plots were cleared of birch and planted with heather. After 20 years soil chemical properties, microarthropod communities and decomposition rates were not significantly different between plots with and without the birch. However, the mass of the soil O-horizon was significantly greater in the felled birch plots than in the control birch plots, providing the first indication of a change towards soil properties more typical of a Calluna moorland. Thus for most of the birch engineering effects measured here their durability in the absence of the engineering species is at least 20 years. This work has provided experimental evidence that birch acts as a top-down engineer, driving cascading effects on both above- and below-ground communities, soil chemical and physical properties and ecosystem processes. The work also shows that the role of birch in driving changes in the ecosystem is durable 20 years after the removal of the birch. Author Affiliation: (*)The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK Article History: Received 4 July 2006; revision accepted 26 January 2007 Handling Editor: Robert Jones Article note: Correspondence: R.J. Mitchell (tel. +44 01330 826316; fax +44 01330 823303; e-mail rujm@ceh.ac.uk).

Abstract: The longleaf pine (Pinus palustris Mill.) forest ecosystems of the US southeastern Coastal Plain, among the most biologically diverse ecosystems in North America, originally covered over 24 x 106 [...]

Gut 2004;53:291-295. doi: 10.1136/gut.2003.027896 Background and aims: Family history is used extensively to estimate the risk of colorectal cancer but there is considerable potential for recall bias and inaccuracy. Hence [...]

1 Many areas of lowland heaths are being lost due to invasion by Betula spp., Pinus sylvestris, Pteridium aquilinum, Rhododendron ponticum and Ulex europaeus. One of the factors influencing the success of restoration of heathland on such sites will be the content of their viable seedbanks. 2 Ten heathland areas in the Poole Basin area of Dorset, where succession to one or more of the above species had occurred were studied. The viable seedbanks of the successional sites were compared with those of nearby heathland using Canonical Discriminant Analysis. 3 The seedbanks of all the successional stages were significantly different from the seedbank of the heath. 4 The seedbanks from the Pinus sylvestris and Pteridium aquilinum successional stages contained significantly lower numbers of heathland species than did the heathland seedbank, although few non heathland species were present. 5 The seedbanks from the Betula spp., Rhododendron ponticum and Ulex europaeus successional sites contained both significantly lower numbers of heathland species and significantly higher numbers of non heathland species than the heathland seedbank. 6 The results are discussed in relation to the restoration of heathland on successional sites and the use of the seedbank as a source of propagales for the establishment of heathland species. Keywords: Canonical Discriminant Analysis, heaths, restoration, seeds, succession

Variation on the Y chromosome may permit our understanding the evolution of the human paternal lineage and male gene flow. This study reports upon the distribution and non random association of alleles at four Y-chromosome specific loci in four populations, three Caucasoid (Italian, Greek and Slav) and one Asian. The markers include insertion/deletion (p12f), point mutation (92R7 and pY[Alpha]I), and repeat sequence (p21A1) polymorphisms. Our data confirm that the p12f/TaqI 8 kb allele is a Caucasoid marker and that Asians are monomorphic at three of the loci (p12f, 92R7, and pY[Alpha]I). The alleles at 92R7 and pY[Alpha]I were found to be in complete disequilibrium in Europeans. Y-haplotype diversity was highly significant between Asians and all three European groups (P < 0.001), but the Greeks and Italians were also significantly different with respect to some alleles and haplotypes (P < 0.02). We find strong evidence that the p12f/TaqI 8 kb allele may have arisen only once, as a deletion event, and, additionally, that the present-day frequency distribution of Y chromosomes carrying the p12f/8 kb allele suggests that it may have been spread by colonising sea-faring peoples from the Near East, possibly the Phoenicians, rather than by expansion of Neolithic farmers into continental Europe. The p12f deletion is the key marker of a unique Y chromosome, found only in Caucasians to date, labelled 'Mediterranean' and this further increases the level of Y-chromosome diversity seen among Caucasoids when compared to the other major population groups. KEY WORDS Y chromosome; RFLPs; haplotypes; 92R7; pY[Alpha]I; p12f; p21A1; migration; Italians; Greeks; Slavs; Asians

We examined variation on the nonrecombining portion of the human Y chromosome to investigate human evolution during the last 200,000 years. The Y-specific polymorphic sites included the Y Alu insertional polymorphism or 'YAP' element (DYS287), the poly(A) tail associated with the YAP element, three point mutations in close association with the YAP insertion site, an A-G polymorphic transition (DYS271), and a tetranucleotide microsatellite (DYS19). Global variation at the five bi-allelic sites (DYS271, DYS287, and the three point mutations) gave rise to five 'YAP haplotypes' in 60 populations from Africa, Europe, Asia, Australasia, and the New World (n = 1500). Combining the multi-allelic variation at the microsatellite loci (poly(A) tail and DYS19) with the YAP haplotypes resulted in a total of 27 'combination haplotypes'. All five of the YAP haplotypes and 21 of the 27 combination haplotypes were found in African populations, which had greater haplotype diversity than did populations from other geographical locations. Only subsets of the five YAP haplotypes were found outside of Africa. Patterns of observed variation were compatible with a variety of hypotheses, including multiple human migrations and range expansions.

Lipoprotein lipase (LPL) plays a critical role in the metabolism of lipoproteins because this enzyme hydrolyzes the triacylglycerides in chylomicrons and very low density lipoproteins. This process influences the production of high-density lipoprotein (HDL), which takes up tissue cholesterol for transport to the liver for excretion. Accordingly, LPL qualifies as a candidate gene for understanding lipid metabolic disorders and atherosclerosis. Studies on the relationship between genetic variation at the LPL locus and lipid phenotypes have produced equivocal results to date. To help clarify this issue, we investigated 144 outwardly healthy male Mediterranean migrants (from Italy and Greece), age between 40 and 70 years and resident in Australia, for associations between two common LPL restriction site polymorphisms and the following lipid and lipoprotein phenotypes: total plasma cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), and triacylglycerides. A series of analysis of variance tests, controlling for age, body mass index, and ethnicity, showed that the HindIII polymorphism at the LPL locus is significantly associated with both triacylglyceride and HDL cholesterol concentrations in this sample. The PvuII polymorphism, however, showed no association with any lipid. Kruskal-Wallis tests confirmed the significance of the associations between the HindIII RFLP and both HDL (p = 0.008) and triacylglycerides (p = 0.03). When the sample was subdivided into subjects who exhibited primary hypertriacylglyceridemia and normolipidemics, a significant difference was observed in the frequency of HindIII (p |is less than~ 0.05) but not PvuII genotypes. HindIII heterozygotes (H1,H2) were least and H2,H2 individuals were most at risk for triacylglyceridemia. Examination of the normolipidemic sample revealed some evidence for an independent effect of the PvuII polymorphism on both LDL cholesterol and total cholesterol levels., Lipoprotein lipase (LPL; EC 3.1.1.34) is a critical enzyme in the metabolism and transport of lipids. Its primary function is the hydrolysis of core triacylglycerides of circulating chylomicrons and very [...]