7,456 research outputs found
Soil carbon sequestration in Switzerland - the DOK trial
Organic systems, by closing nutrient cycles and making more efficient use of local (on-farm) resources, can contribute to mitigating climate change1. This is due to the fact that certain farming practices result in storage of carbon (C) in the soil (sequestration), thereby effectively reducing the amount of CO2 in the atmosphere. The DOK trial, a research project on the mitigation potential of Organic Agriculture has demonstrated this
Multicolor chromosome bar codes
Chromosome bar codes are multicolor banding patterns produced by fluorescence in situ hybridization (FISH) with differentially labeled and pooled sub-regional DNA probes. These molecular cytogenetic tools facilitate chromosome identification and the delineation of both inter- and intra-chromosomal rearrangements. We present an overview of the various conceptual approaches which can be largely divided into two classes: Simple bar codes designed for chromosome identification and complex bar codes for high resolution aberration screening of entire karyotypes. We address the issue of color redundancy and how to overcome this limitation by complementation of bar codes with whole chromosome painting probes. Copyright (c) 2006 S. Karger AG, Base
Don't Fall for Tuning Parameters: Tuning-Free Variable Selection in High Dimensions With the TREX
Lasso is a seminal contribution to high-dimensional statistics, but it hinges
on a tuning parameter that is difficult to calibrate in practice. A partial
remedy for this problem is Square-Root Lasso, because it inherently calibrates
to the noise variance. However, Square-Root Lasso still requires the
calibration of a tuning parameter to all other aspects of the model. In this
study, we introduce TREX, an alternative to Lasso with an inherent calibration
to all aspects of the model. This adaptation to the entire model renders TREX
an estimator that does not require any calibration of tuning parameters. We
show that TREX can outperform cross-validated Lasso in terms of variable
selection and computational efficiency. We also introduce a bootstrapped
version of TREX that can further improve variable selection. We illustrate the
promising performance of TREX both on synthetic data and on a recent
high-dimensional biological data set that considers riboflavin production in B.
subtilis
Cellular Probabilistic Automata - A Novel Method for Uncertainty Propagation
We propose a novel density based numerical method for uncertainty propagation
under certain partial differential equation dynamics. The main idea is to
translate them into objects that we call cellular probabilistic automata and to
evolve the latter. The translation is achieved by state discretization as in
set oriented numerics and the use of the locality concept from cellular
automata theory. We develop the method at the example of initial value
uncertainties under deterministic dynamics and prove a consistency result. As
an application we discuss arsenate transportation and adsorption in drinking
water pipes and compare our results to Monte Carlo computations
Speeding up SOR Solvers for Constraint-based GUIs with a Warm-Start Strategy
Many computer programs have graphical user interfaces (GUIs), which need good
layout to make efficient use of the available screen real estate. Most GUIs do
not have a fixed layout, but are resizable and able to adapt themselves.
Constraints are a powerful tool for specifying adaptable GUI layouts: they are
used to specify a layout in a general form, and a constraint solver is used to
find a satisfying concrete layout, e.g.\ for a specific GUI size. The
constraint solver has to calculate a new layout every time a GUI is resized or
changed, so it needs to be efficient to ensure a good user experience. One
approach for constraint solvers is based on the Gauss-Seidel algorithm and
successive over-relaxation (SOR).
Our observation is that a solution after resizing or changing is similar in
structure to a previous solution. Thus, our hypothesis is that we can increase
the computational performance of an SOR-based constraint solver if we reuse the
solution of a previous layout to warm-start the solving of a new layout. In
this paper we report on experiments to test this hypothesis experimentally for
three common use cases: big-step resizing, small-step resizing and constraint
change. In our experiments, we measured the solving time for randomly generated
GUI layout specifications of various sizes. For all three cases we found that
the performance is improved if an existing solution is used as a starting
solution for a new layout
Fisher-Wright model with deterministic seed bank and selection
Seed banks are a common characteristics to many plant species, which allow
storage of genetic diversity in the soil as dormant seeds for various periods
of time. We investigate an above-ground population following a Fisher-Wright
model with selection coupled with a deterministic seed bank assuming the length
of the seed bank is kept constant and the number of seeds is large. To assess
the combined impact of seed banks and selection on genetic diversity, we derive
a general diffusion model. The applied techniques outline a path of
approximating a stochastic delay differential equation by an appropriately
rescaled stochastic differential equation, which is a common issue in
statistical physics. We compute the equilibrium solution of the site-frequency
spectrum and derive the times to fixation of an allele with and without
selection. Finally, it is demonstrated that seed banks enhance the effect of
selection onto the site-frequency spectrum while slowing down the time until
the mutation-selection equilibrium is reached
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