17,438 research outputs found
Reduced branching processes with very heavy tails
The reduced Markov branching process is a stochastic model for the genealogy
of an unstructured biological population. Its limit behavior in the critical
case is well studied for the Zolotarev-Slack regularity parameter
. We turn to the case of very heavy tailed reproduction
distribution assuming Zubkov's regularity condition with parameter
. Our main result gives a new asymptotic pattern for the
reduced branching process conditioned on non-extinction during a long time
interval.Comment: 15 pages, 1 figur
ranger: A Fast Implementation of Random Forests for High Dimensional Data in C++ and R
We introduce the C++ application and R package ranger. The software is a fast
implementation of random forests for high dimensional data. Ensembles of
classification, regression and survival trees are supported. We describe the
implementation, provide examples, validate the package with a reference
implementation, and compare runtime and memory usage with other
implementations. The new software proves to scale best with the number of
features, samples, trees, and features tried for splitting. Finally, we show
that ranger is the fastest and most memory efficient implementation of random
forests to analyze data on the scale of a genome-wide association study
Computation of and with Lattice QCD
We pursue a new method, based on lattice QCD, for determining the quantities
, , and of heavy-quark effective theory.
We combine Monte Carlo data for the meson mass spectrum with perturbative
calculations of the short-distance behavior, to extract and
from a formula from HQET. Taking into account uncertainties from
fitting the mass dependence and from taking the continuum limit, we find
and in the quenched approximation.Comment: 7 pp, 4 figs (in v2 Fig. 4 now shows Ref. 13, as advertised); in v3
error in BLM scale is correcte
Using Realistic MHD Simulations for Modeling and Interpretation of Quiet-Sun Observations with the Solar Dynamics Observatory Helioseismic and Magnetic Imager
The solar atmosphere is extremely dynamic, and many important phenomena
develop on small scales that are unresolved in observations with the
Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics
Observatory (SDO). For correct calibration and interpretation of the
observations, it is very important to investigate the effects of small-scale
structures and dynamics on the HMI observables, such as Doppler shift,
continuum intensity, spectral line depth, and width. We use 3D radiative
hydrodynamics simulations of the upper turbulent convective layer and the
atmosphere of the Sun, and a spectro-polarimetric radiative transfer code to
study observational characteristics of the Fe I 6173A line observed by HMI in
quiet-Sun regions. We use the modeling results to investigate the sensitivity
of the line Doppler shift to plasma velocity, and also sensitivities of the
line parameters to plasma temperature and density, and determine effective line
formation heights for observations of solar regions located at different
distances from the disc center. These estimates are important for the
interpretation of helioseismology measurements. In addition, we consider
various center-to-limb effects, such as convective blue-shift, variations of
helioseismic travel-times, and the 'concave' Sun effect, and show that the
simulations can qualitatively reproduce the observed phenomena, indicating that
these effects are related to a complex interaction of the solar dynamics and
radiative transfer.Comment: 21 pages, 10 figures, accepted for publication in Ap
On the coefficients of differentiated expansions of ultraspherical polynomials
A formula expressing the coefficients of an expression of ultraspherical polynomials which has been differentiated an arbitrary number of times in terms of the coefficients of the original expansion is proved. The particular examples of Chebyshev and Legendre polynomials are considered
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