70,071 research outputs found
The Spine of the Cosmic Web
We present the SpineWeb framework for the topological analysis of the Cosmic
Web and the identification of its walls, filaments and cluster nodes. Based on
the watershed segmentation of the cosmic density field, the SpineWeb method
invokes the local adjacency properties of the boundaries between the watershed
basins to trace the critical points in the density field and the separatrices
defined by them. The separatrices are classified into walls and the spine, the
network of filaments and nodes in the matter distribution. Testing the method
with a heuristic Voronoi model yields outstanding results. Following the
discussion of the test results, we apply the SpineWeb method to a set of
cosmological N-body simulations. The latter illustrates the potential for
studying the structure and dynamics of the Cosmic Web.Comment: Accepted for publication HIGH-RES version:
http://skysrv.pha.jhu.edu/~miguel/SpineWeb
Boosting Functional Response Models for Location, Scale and Shape with an Application to Bacterial Competition
We extend Generalized Additive Models for Location, Scale, and Shape (GAMLSS)
to regression with functional response. This allows us to simultaneously model
point-wise mean curves, variances and other distributional parameters of the
response in dependence of various scalar and functional covariate effects. In
addition, the scope of distributions is extended beyond exponential families.
The model is fitted via gradient boosting, which offers inherent model
selection and is shown to be suitable for both complex model structures and
highly auto-correlated response curves. This enables us to analyze bacterial
growth in \textit{Escherichia coli} in a complex interaction scenario,
fruitfully extending usual growth models.Comment: bootstrap confidence interval type uncertainty bounds added; minor
changes in formulation
Systematic Microcanonical Analyses of Polymer Adsorption Transitions
In detailed microcanonical analyses of densities of states obtained by
extensive multicanonical Monte Carlo computer simulations, we investigate the
caloric properties of conformational transitions adsorbing polymers experience
near attractive substrates. For short chains and strong surface attraction, the
microcanonical entropy turns out to be a convex function of energy in the
transition regime, indicating that surface-entropic effects are relevant.
Albeit known to be a continuous transition in the thermodynamic limit of
infinitely long chains, the adsorption transition of nongrafted finite-length
polymers thus exhibits a clear signature of a first-order-like transition, with
coexisting phases of adsorbed and desorbed conformations. Another remarkable
consequence of the convexity of the microcanonical entropy is that the
transition is accompanied by a decrease of the microcanonical temperature with
increasing energy. Since this is a characteristic physical effect it might not
be ignored in analyses of cooperative macrostate transitions in finite systems.Comment: 8 pages, 6 figure
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