Statistics of Lead Changes in Popularity-Driven Systems

We study statistical properties of the highest degree, or most popular, nodes in growing networks. We show that the number of lead changes increases logarithmically with network size N, independent of the details of the growth mechanism. The probability that the first node retains the lead approaches a finite constant for popularity-driven growth, and decays as N^{-phi}(ln N)^{-1/2}, with phi=0.08607..., for growth with no popularity bias.Comment: 4 pages, 4 figures, 2 column revtex format. Minor changes in response to referee comments. For publication in PR

Investigations of Forage Fish and Lake Trout Salvelinus Namaycush Interactions in Flaming Gorge Reservoir, Wyoming-Utah

I investigated the interaction of lake trout (Salvelinus namaycush) and their dominant forage fish populations, Utah chub (Gila atraria) and kokanee salmon (Oncorhynchus nerka), in Flaming Gorge Reservoir, Wyoming-Utah. Through bioenergetics modeling, I quantified the consumption dynamics of the lake trout population. From hydroacoustics analyses, I quantified the density and biomass of the two dominant forage fish populations. In Chapter II, I report the results of the energetics analysis. The objective of this chapter was to understand the role of lake trout predation in recent changes in fish assemblage structure of the reservoir. Through lake trout diet analysis and exploration of forage fish growth rates, I quantified the duration of time that chubs and kokanee are vulnerable to lake trout predation. Faster growth rates of kokanee greatly reduce the duration of time that this species is vulnerable to predation relative to Utah chubs. Although chubs are more fecund than kokanee, this advantage in reproductive potential may not make up for differences in duration of vulnerability. I predict that kokanee will make up an even larger proportion of the total fish assemblage of the reservoir in future years. In Chapter III, I compare annual estimates of lake trout consumption demand to biomass estimates of forage fish. I used vertical gill net sampling, beach seine surveys, and hydroaocustics to assess the distributions and biomasses of the Utah chub and kokanee populations. Biomasses of pelagic Utah chubs and kokanee were calculated to be 83 300 and 209 000 kg, respectively. Energetics analyses indicated that between 1985 and 1989 the lake trout population consumed 79 000 kg of chub and 196 000 kg of kokanee per year. These results suggest \u27 that forage fish populations should decline in future years. Annual consumption demand of lake trout between 400 and 600 mm (137 000 kg) exceeded biomass estimates of forage fish of useable size (22 000 kg), suggesting that this size-class of predator is currently food-limited. High occurrence of invertebrate prey taxa in the diet of small predators supports this food-limitation hypothesis. The lack of small pelagic forage fishes may reduce the ability of lake trout to recruit to sizes that are accessible to anglers and of value to the fishery

Effect of cylinder wall parameters on the final packing density of mono-disperse spheres subject to three-dimensional vibrations

Achieving densely packed particles is desirable within the industries of ceramics, pharmaceuticals, defence and additive manufacturing. In this work, we use the discrete element method (DEM) to determine the effect of wall parameters on the final packing density of mono-disperse spheres subject to 4 varying three-dimensional vibration and fill conditions. We focus specifically on the impact of the container wall parameters on the particles' final packing density. Following on from the validation of the DEM simulation the particle-wall coefficient of restitution, the particle-wall coefficient of rolling friction and the particle-wall coefficient of sliding friction were varied individually and the effect on the final packing density analysed. For relatively low particle-particle friction glass beads, the effect of these wall properties had no discernible effect on the final packing density achieved. Following on from these findings the particle-wall properties were varied at the extreme values of particle-particle coefficient of rolling friction and particle-particle coefficient of sliding friction. For a particle-particle coefficient of sliding friction = 1, increases in particle-wall coefficient of restitution resulted in a minor increase in the final packing density of particles though this was not statistically significant. For a particle-particle coefficient of sliding friction = 1, increases in particle-wall coefficient of rolling friction resulted in a minor decrease in the final packing density of the particles though again not to a degree where the trend can, with complete certainty, be distinguished from the random error across the repeats. Finally, when the particle-particle coefficient of sliding friction = 1, increases in particle-wall coefficient of sliding friction resulted in a significant decrease in the final packing density of particles. This decrease was attributed to the propagation of force chains throughout the packing. The significant decrease in final packing density with particle-wall coefficient of sliding friction highlights the need to choose appropriate vessel materials to optimise packing of particles with a high particle-particle coefficient sliding friction. Conversely, for particles with minimal particle-particle friction, the particle-wall friction coefficient has no effect on the final packing density of particles - a potentially valuable finding for certain industrial applications. All simulations were run using the open-source DEM package LIGGGHTS on the University of Birmingham's high-performance computer: BlueBEAR. All the code files used within this paper can be found on Github: https://github.com/Jack-Grogan/DEM-Vibropacking-Wall-Effects

In situ tropical peatland ire emission factors and their variability, as determined by field measurements in peninsula Malaysia

Fires in tropical peatlands account for >25% of estimated total greenhouse gas emissions from deforestation and degradation. Despite significant global and regional impacts, our understanding of specific gaseous fire emission factors (EFs) from tropical peat burning is limited to a handful of studies. Furthermore, there is substantial variability in EFs between sampled fires and/or studies. For example, methane EFs vary by 91% between studies. Here we present new fire EFs for the tropical peatland ecosystem; the first EFs measured for Malaysian peatlands, and only the second comprehensive study of EFs in this crucial environment. During August 2015 (under El Niño conditions) and July 2016, we embarked on field campaigns to measure gaseous emissions at multiple peatland fires burning on deforested land in Southeast Pahang (2015) and oil palm plantations in North Selangor (2016), Peninsula Malaysia. Gaseous emissions were measured using open-path Fourier transform infrared spectroscopy. The IR spectra were used to retrieve mole fractions of 12 different gases present within the smoke (including carbon dioxide and methane), and these measurements used to calculate EFs. Peat samples were taken at each burn site for physicochemical analysis and to explore possible relationships between specific physicochemical properties and fire EFs. Here we present the first evidence to indicate that substrate bulk density affects methane fire EFs reported here. This novel explanation of interplume, within-biome variability, should be considered by those undertaking greenhouse gas accounting and haze forecasting in this region and is of importance to peatland management, particularly with respect to artificial compaction

A Group-Based Yule Model for Bipartite Author-Paper Networks

This paper presents a novel model for author-paper networks, which is based on the assumption that authors are organized into groups and that, for each research topic, the number of papers published by a group is based on a success-breeds-success model. Collaboration between groups is modeled as random invitations from a group to an outside member. To analyze the model, a number of different metrics that can be obtained in author-paper networks were extracted. A simulation example shows that this model can effectively mimic the behavior of a real-world author-paper network, extracted from a collection of 900 journal papers in the field of complex networks.Comment: 13 pages (preprint format), 7 figure

Agonist-Specific Calcium Signaling and Phosphoinositide Hydrolysis in Human SK-N-MCIXC Neuroepithelioma Cells

Fura-2 digital imaging microfluorimetry was used to evaluate the Ca 2+ signals generated in single clonal human neuroepithelioma cells (SK-N-MCIXC) in response to agonists that stimulate phosphoinositide hydrolysis. Addition of optimal concentrations of either endothelin-1 (ET-1), ATP, oxotremorine-M (Oxo-M), or norepinephrine (NE) all resulted in an increase in the concentration of cytosolic calcium (Ca 2+ i ) but of different magnitudes (ET-1 = ATP> NE). The Ca 2+ signals elicited by the individual agonists also differed from each other in terms of their latency of onset, rate of rise and decay, and prevalence of a sustained phase of Ca 2+ influx. The Ca 2+ signals that occurred in response to ATP had a shorter latency and more rapid rates of rise and decay than those observed for the other three agonists. Furthermore, a sustained plateau phase of the Ca 2+ signal, which was characteristic of the response to Oxo-M, was observed in 94% of cells responded to ET-1 or ATP, whereas corresponding values for Oxo-M and NE were ∼74 and ∼48%. Sequential addition of agonists to cells maintained in a Ca 2+ -free buffer indicated that each ligand mobilized Ca 2+ from a common intracellular pool. When monitored as a release of a total inositol phosphate fraction, all four agonists elicited similar (four- to sixfold) increases in phosphoinositide hydrolysis. However, the addition of ET-1 or ATP resulted in larger increases in the net formation of inositol 1,4,5-trisphosphate than did either Oxo-M or NE. These results indicate that, in SK-N-MCIXC cells, the characteristics of both Ca 2+ signaling and inositol phosphate production are agonist specific.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66414/1/j.1471-4159.1994.63062099.x.pd

Managing bereavement in the classroom: a conspiracy of silence?

The ways in which teachers in British schools manage bereaved children are under-reported. This article reports the impact of students' bereavement and their subsequent management in primary and secondary school classrooms in Southeast London. Thirteen school staff working in inner-city schools took part in in-depth interviews that focused on the impact of bereaved children on the school and how teachers responded to these children. All respondents had previously had contact with a local child bereavement service that aims to provide support, advice, and consultancy to children, their parents, and teachers. Interviews were audiotaped, transcribed verbatim, and analyzed using ATLAS-ti. Three main themes were identified from analysis of interview data. Firstly, British society, culture, local communities, and the family were significant influences in these teachers' involvement with bereaved students. Secondly, school staff managed bereaved students through contact with other adults and using practical classroom measures such as "time out" cards and contact books. Lastly, teachers felt they had to be strong, even when they were distressed. Surprise was expressed at the mature reaction of secondary school students to deaths of others. The article recommends that future research needs to concentrate on finding the most effective way of supporting routinely bereaved children, their families, and teachers

A Yule-Simon process with memory

The Yule-Simon model has been used as a tool to describe the growth of diverse systems, acquiring a paradigmatic character in many fields of research. Here we study a modified Yule-Simon model that takes into account the full history of the system by means of an hyperbolic memory kernel. We show how the memory kernel changes the properties of preferential attachment and provide an approximate analytical solution for the frequency distribution density as well as for the frequency-rank distribution.Comment: 7 pages, 5 figures; accepted for publication in Europhysics Letter