4,861 research outputs found

    CMB anisotropies in the presence of a stochastic magnetic field

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    Primordial magnetic fields present since before the epoch of matter-radiation equality have an effect on the anisotropies of the cosmic microwave background. The CMB anisotropies due to scalar perturbations are calculated in the gauge invariant formalism for magnetized adiabatic initial conditions. Furthermore the linear matter power spectrum is calculated. Numerical solutions are complemented by a qualitative analysis.Comment: 26 pages, 21 figures; sections 2 and 4 expanded; matches version published in PR

    Geostatistical mapping and spatial variability of surficial sediment types on the Beaufort Sea shelf based on grain size data

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    The nearshore Beaufort Sea is a sensitive marine environment that is also the focus of oil and gas exploration. Offshore, the Beaufort Sea contains large potential reserves of hydrocarbons. Any future exploitation of these resources will present unique engineering challenges and will require an understanding of the processes that govern stability, nearshore morphology and sediment properties in the extensive shallow coastal zone of the Beaufort Sea shelf. Knowledge of the surficial sediment distribution is, therefore, necessary to provide a framework for understanding sediment stability, sediment transport, platform foundation conditions and to balance engineering challenges with environmental concerns, resource development and precautionary sustainable management. We describe an approach for a quality controlled mapping of grain sizes and sediment textures for the Beaufort Sea shelf in the Canadian Arctic. The approach is based on grain size data sampled during the period 1969-2008. A replenishment of grain size data since the 1980’s, as well as the consideration of correlating parameters (bathymetry, slope and sediment input) to a cokriging algorithm, amends the former way of mapping the surficial sediments of the Beaufort Sea shelf. Subsequent to data processing and applying autocorrelation, four single grids (clay, silt, sand and gravel) were generated from grain size data by ordinary kriging and cokriging. Cokriging also considered parameters that influence sediment texture such as bathymetry, slope, cost distance from the Mackenzie River and data anisotropy (directional dependency). The cokriging algorithm expressed as a variogram was quality controlled by cross-validation and predicted standard errors (PSEs). PSE values express a maximum deviation of modeled from the real values and therefore help to estimate the quality in these regions regarding the interpolation results for each grain size range. A sediment type classification scheme applied to the set of clay, silt, sand and gravel content maps resulted in a sediment type map of the Beaufort Sea shelf. The PSEs of ordinary kriging and cokriging have been compared and showed that the cokriging technique provided superior interpolation results for silt and slightly improved results for clay and sand. Cokriging was able to capture most of the small variations in the sediment texture distribution. Furthermore, reduced nugget effects confirmed that the cost distance grid was a better indicator for sediment texture when compared to bathymetry and slope. For gravel, ordinary kriging achieved better prediction probabilities and was, therefore, used for generation of the distribution map for this grain size class. The use of cokriging and ordinary kriging greatly enhanced interpolation estimates without additional sampling. Especially in nearshore regions, like the Beaufort Sea shelf, geostatistical interpolation techniques are very useful for evaluating seabed sediment texture because sampling is often difficult or impossible due to ice conditions or even prohibited near oil platforms. The described methodology along with the inclusion of recent data, provided an improved mapping of the surficial sediments of the Beaufort Sea shelf

    Origins of Bulk Viscosity at RHIC

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    A variety of physical phenomena can lead to viscous effects. Several sources of shear and bulk viscosity are reviewed with an emphasis on the bulk viscosity associated with chiral restoration and with chemical non-equilibrium. We show that in a mean-field treatment of the limiting case of a second order phase transition, the bulk viscosity peaks in a singularity at the critical point.Comment: submitted to PR

    Spatial scales of interactions among bacteria and between bacteria and the leaf surface.

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    Microbial life on plant leaves is characterized by a multitude of interactions between leaf colonizers and their environment. While the existence of many of these interactions has been confirmed, their spatial scale or reach often remained unknown. In this study, we applied spatial point pattern analysis to 244 distribution patterns of Pantoea agglomerans and Pseudomonas syringae on bean leaves. The results showed that bacterial colonizers of leaves interact with their environment at different spatial scales. Interactions among bacteria were often confined to small spatial scales up to 5-20 ÎŒm, compared to interactions between bacteria and leaf surface structures such as trichomes which could be observed in excess of 100 ÎŒm. Spatial point-pattern analyses prove a comprehensive tool to determine the different spatial scales of bacterial interactions on plant leaves and will help microbiologists to better understand the interplay between these interactions

    Can models of agents be transferred between different areas?

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    One of the main reasons for the sustained activity and interest in the field of agent-based systems, apart from the obvious recognition of its value as a natural and intuitive way of understanding the world, is its reach into very many different and distinct fields of investigation. Indeed, the notions of agents and multi-agent systems are relevant to fields ranging from economics to robotics, in contributing to the foundations of the field, being influenced by ongoing research, and in providing many domains of application. While these various disciplines constitute a rich and diverse environment for agent research, the way in which they may have been linked by it is a much less considered issue. The purpose of this panel was to examine just this concern, in the relationships between different areas that have resulted from agent research. Informed by the experience of the participants in the areas of robotics, social simulation, economics, computer science and artificial intelligence, the discussion was lively and sometimes heated

    The mucormycete-host interface

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    Mucormycosis is a fungal infection with fulminant angioinvasion leading to high morbidity and mortality in susceptible individuals. The major predisposing conditions are uncontrolled diabetes, neutropenia, malignancies, receipt of a transplant and traumatic injury [1]. Over the past decade, mucormycosis has become an emerging fungal infection due to the increase in patient groups presenting with these pre-disposing conditions and our medical advances in diagnosing the infection [2-4]. Yet, we currently lack clinical interventions to treat mucormycosis effectively. This in turn is due to a lack of understanding of mucormycosis pathogenesis. Here, we discuss our current understanding of selected aspects of interactions at the mucormycete-host interface. We will highlight open questions that might guide future research directions for investigations into the pathogenesis of mucormycosis and potential innovative therapeutic approaches

    Exact f(R)f(R)-cosmological model coming from the request of the existence of a Noether symmetry

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    We present an f(R)f(R)-cosmological model with an exact analytic solution, coming from the request of the existence of a Noether symmetry, which is able to describe a dust-dominated decelerated phase before the current accelerated phase of the universe.Comment: 4 pages, 2 figures, Contribution to the proceedings of Spanish Relativity Meeting 2008, Salamanca, Sapin, 15-19 September 200

    Studien zu Genotyp-Umwelt-Interaktionen beim Deutschen Schwarzbunten Niederungsrind

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    The aims of the present study were i) to analyse the genetic structure of the local black and white cattle breed (DSN), and ii) to analyse genotype by environment interactions based on defined herd parameter groups (geographic, environmental, phenotypic descriptors). The study considered 3688 DSN and 3599 HF cows from 46 herds keeping both breeds. Farms mostly reflected pasture based low input production systems. A multiple trait approach, i.e. defining same traits in different clusters as two different traits, was applied to prove genotype by environment interactions based on genetic correlation estimates. Genetic correlations between low heritability functional traits were lower than for production traits. Especially for functional traits such as somatic cell score (SCS) and fat to protein ratio genetic correlations remained below rg= 0.80 and showed possible genotype by environment interactions
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