Detecting degree symmetries in networks

The surrounding of a vertex in a network can be more or less symmetric. We derive measures of a specific kind of symmetry of a vertex which we call degree symmetry -- the property that many paths going out from a vertex have overlapping degree sequences. These measures are evaluated on artificial and real networks. Specifically we consider vertices in the human metabolic network. We also measure the average degree-symmetry coefficient for different classes of real-world network. We find that most studied examples are weakly positively degree-symmetric. The exceptions are an airport network (having a negative degree-symmetry coefficient) and one-mode projections of social affiliation networks that are rather strongly degree-symmetric

Network Evolution Based on Centrality

We study the evolution of networks when the creation and decay of links are based on the position of nodes in the network measured by their centrality. We show that the same network dynamics arises under various centrality measures, and solve analytically the network evolution. During the complete evolution, the network is characterized by nestedness: the neighbourhood of a node is contained in the neighbourhood of the nodes with larger degree. We find a discontinuous transition in the network density between hierarchical and homogeneous networks, depending on the rate of link decay. We also show that this evolution mechanism leads to double power-law degree distributions, with interrelated exponents.Comment: 6 pages, 3 figure

Habitat relationships and gene flow of Martes americana in northern Idaho

Forest fragmentation can have a dramatic effect on landscape connectivity and dispersal of animals, potentially reducing gene flow within and among populations. American marten populations (Martes americana) are sensitive to forest fragmentation and the spatial configuration of patches of remnant mature forest has an important impact on habitat quality. This study represents an extensive multiple scale habitat relationships analysis conducted for American marten. In conjunction with Idaho Department of Fish and Game (IDFG) and the U.S. Forest Service, genetic data on marten populations across the Idaho Panhandle National Forest was used to build habitat relationships models. Over 3 years of winter fieldwork during 2004, 2005, and 2006, I detected martens at 569 individual hair snare stations distributed across a 3,000 square kilometer study area covering the Selkirk, Purcell, and Cabinet Mountain ranges. I investigated habitat relationships of this population of Martes americana in the Idaho Panhandle National Forest (IPNF) at three spatial scales: Plot, Home Range, and Multiple-Scale. I used bivariate scaling to measure each environmental variable across a broad range of radii ranging from 90m-1080m around each sample station. I used an information-theoretic approach to rank 45 a priori candidate models that described hypothesized habitat relationships at each spatial scale. At the plot scale, marten presence was positively predicted by the Percentage of Landscape (PLand) comprised of large sawtimber, and negatively predicted by PLand of seedling/sapling timber type. At the home range scale, the probability of detecting a marten decreased with increasing amounts of fragmentation and highly contrasted edges between patches of large sawtimber and patches of seedling/sapling and non-stocked patches. In the multiple-scale analysis, I used a variable screening step to find variables that were universal and consistent throughout all models in order to build candidate models. PLand comprised of large homogeneous patches of large sawtimber was a positive predictor of marten presence, while highly contrasted edges and fragmentation were strong negative predictors of marten presence. The scale at which martens selected habitats varied greatly across variables. Martens actively selected for high quality habitat at the fine scale (plot level) and strongly avoided areas comprised of seedling/sapling and non-stocked timber areas. Martens negatively responded to high contrast edges and strongly avoided them. Juxtaposition and configuration of patches of large sawtimber was important to marten habitat selection. This study demonstrates the importance of investigating marten habitat at multiple spatial scales and provides insights to linkages among scales and how martens respond to forest fragmentation. Genetic information was used to model genetic relationships of this marten population with respect to environmental and spatial variables within my study landscape. Over three field seasons 70 individual marten were detected across the study area. The genetic similarities were based on the pair-wise percentage dissimilarity among all individuals based on 7 microsatellite loci. I compared their genetic similarities with several landscape resistance hypotheses. The landscape resistance hypotheses describe a range of potential relationships between movement cost and landcover, elevation, roads, Euclidean distance and valleys between mountain ranges as barriers. The degree of support for each model was tested with causal modeling on resemblance matrices using partial Mantel tests. Hypotheses of Isolation by Distance and Isolation by Barrier were not supported, and Isolation by Landscape Resistance proved to be the best model describing genetic patterns of Martes americana in the IPNF. Elevation 1600m with a standard deviation of 600m was the most highly supported landscape resistance model correlated to genetic structure of marten in this landscape. Correlating genetic similarity of individuals across large landscapes with hypothetical movement cost models can give reliable inferences about population connectivity. By linking cost modeling to the actual patterns of genetic similarity among individuals it is possible to obtain rigorous, empirical models describing the relationship between landscape structure and gene flow, and to produce speciesspecific maps of landscape connectivity, and can provide managers with critical information to better administer our forests for meso-carnivores and other species of concern

Profiles of Neuropsychological Functioning in Children and Adolescents with Spina Bifida: Associations with Biopsychosocial Predictors and Functional Outcomes

The current study examined neuropsychological performance among children with spina bifida (SB) to determine biological and functional correlates of distinct “profiles” of cognitive functioning. Methods: A total of 95 children with SB myelomeningocele (ages, 8–15 years) completed a neuropsychological assessment battery. Hierarchical and non-hierarchical cluster analyses were used to identify and confirm a cluster solution. Hypothesized predictors of cluster membership included lesion level, number of shunt surgeries, history of seizures, age, ethnicity, socio-economic status, and family stress. Outcomes included independence, academic success, expectations for the future, and quality of life. Results: Ward’s cluster method indicated a three-cluster solution, and was replicated with two other cluster analytic methods. The following labels were applied to the clusters: “average to low average” (n=39), “extremely low to borderline” (n=27), and “broadly average with verbal strength” (n=29). Socio-econimc status, lesion level, and seizure history significantly predicted group membership. Cluster membership significantly predicted independence, academic success, parent expectations for the future, and child reported physical quality of life. Conclusions: Findings from this study suggest qualitatively different cognitive profiles exist among children with SB, and the relevance of neuropsychological functioning for day-to-day adaptive functioning and quality of life. Clinical implications and future research are discussed. (JINS, 2016, 22, 804–815

Continuum states from time-dependent density functional theory

Linear response time-dependent density functional theory is used to study low-lying electronic continuum states of targets that can bind an extra electron. Exact formulas to extract scattering amplitudes from the susceptibility are derived in one dimension. A single-pole approximation for scattering phase shifts in three dimensions is shown to be more accurate than static exchange for singlet electron-He$^+$ scattering.Comment: 5 pages, 2 figures, J. Chem. Phys. accepte

Realising context-sensitive mobile messaging

Mobile technologies aim to assist people as they move from place to place going about their daily work and social routines. Established and very popular mobile technologies include short-text messages and multimedia messages with newer growing technologies including Bluetooth mobile data transfer protocols and mobile web access.Here we present new work which combines all of the above technologies to fulfil some of the predictions for future context aware messaging. We present a context sensitive mobile messaging system which derives context in the form of physical locations through location sensing and the co-location of people through Bluetooth familiarity